Charging electrode assembly and method of aligning printhead components

Abstract

A charging electrode assembly for a continuous inkjet printer. The charging electrode is a charging electrode defining a channel for charging ink droplets, the channel extending from an inlet aperture to an outlet aperture along an ink travel axis along which an ink jet travels from a nozzle during printing, the electrode being configured to induce charge on a selected ink droplet by capacitive coupling. The charging electrode further includes a mounting device configured to couple the charging electrode to the nozzle body, the mounting device configured to allow the charging electrode to move relative to the nozzle to compensate for inkjet misalignment.

Description

Technical Field

[0001] The present invention relates to a charging electrode for a printhead of a continuous inkjet (CIJ) printer, a printhead for a continuous inkjet printer, a continuous inkjet printer, and related methods. Background Art

[0002] In an inkjet printing system, printing is constituted by individual ink droplets generated at a nozzle and propelled towards a substrate. There are two main systems: drop-on-demand, where ink droplets for printing are generated as needed and when needed; and continuous inkjet (CIJ) printing, where droplets are continuously generated and only selected droplets are directed towards the substrate, with other droplets being recycled to the ink system.

[0003] A CIJ printer supplies pressurized ink to a printhead droplet generator where a continuous stream of ink issuing from a nozzle is broken up into individual regular droplets by, for example, an oscillating piezoelectric element. The droplets are directed through a charging electrode where they are selectively and individually given a predetermined charge and then through a transverse electric field provided across a pair of deflection plates, the pair of deflection plates including a high voltage (or extra-high tension (EHT)) plate and a zero or negative voltage plate ("ground" plate). Each charged droplet is deflected by the field by an amount depending on its charge amount before hitting the substrate, while uncharged droplets proceed without deflection and are collected at a gutter from where they are recycled to the ink system. The charged droplets bypass the gutter and hit the substrate at a position determined by the charge on the droplet and the position of the substrate relative to the printhead. Typically, the substrate moves relative to the printhead in one direction and the droplets are deflected in a direction substantially perpendicular thereto, although the deflection plates can be oriented obliquely with respect to the vertical to compensate for the speed of the substrate (the movement of the substrate relative to the printhead between droplet arrivals means that a row of droplets would otherwise not extend exactly perpendicular to the direction of movement of the substrate). Various components of the printhead are typically contained within a cover tube or a printhead housing.

[0004] In continuous inkjet (CIJ) printing, characters are printed by a dot matrix consisting of regularly arranged potential ink droplet positions. Each dot matrix contains a plurality of columns (i.e., strokes), each column being constituted by a row of a plurality of potential ink droplet positions (e.g., 7) which are determined by the charge applied to the ink droplets. Thus, each actually used ink droplet is charged according to its target position in the stroke. If a particular ink droplet is not used, the droplet is not charged and is captured by a recovery gutter for recycling. This process is cyclically repeated for all strokes of the dot matrix, and then the next character dot matrix is processed.

[0005] Ink is delivered to the print head under pressure through an ink system, which is typically housed in a sealed compartment of a cabinet that includes separate compartments for control circuitry and a user interface panel. The ink system includes a main pump that draws ink from a reservoir or tank (commonly referred to as a mixing tank) via a filter and delivers it to the print head under pressure. When the ink is consumed, the reservoir is refilled as needed from a replaceable ink cartridge that is releasably connected to the reservoir via a supply conduit. The ink is supplied from the reservoir to the print head via a flexible delivery conduit. Unused ink droplets captured by a gutter are recycled to the reservoir via a pump and a return conduit. The flow of ink in each conduit is typically controlled by solenoid valves and / or other similar components.

[0006] As the ink circulates through the system, there is a tendency for the ink to thicken due to solvent evaporation, particularly in relation to the recycled ink that has been exposed to air in the channels between the nozzles and the gutter. To compensate for this, "make-up" solvent is added to the ink as needed from a replaceable solvent cartridge to maintain the ink viscosity within a desired limit. The ink cartridge and the solvent cartridge are filled with a predetermined amount of fluid and are typically releasably connected to the reservoir or mixing tank of the ink supply system so that the reservoir can be intermittently topped up by drawing ink and / or solvent from the cartridges as needed.

[0007] CIJ printers typically operate in high-throughput environments for which the printer and the ink need to be able to keep up with high production line speeds, fast drying time requirements, and near-constant production.

[0008] One problem faced by existing continuous inkjet (CIJ) printer operators is the formation of harmful deposits inside and around the print head. Such deposits include "ink fluff", which is formed by pigments in the ink remaining after the evaporation of the liquid components of the ink (and solvent mixture). These deposits not only endanger print accuracy and print head operation, but in extreme cases can cause blockages in the inkjet holes of the print head (for example rendering the print head inoperable for at least some period of time). Currently, these deposits must be removed by manually cleaning the print head (sometimes even partially disassembling it). This approach has many drawbacks due to factors such as the complexity of the cleaning process, the need for operator intervention, print head downtime, and the difficulty of ensuring cleaning quality.

[0009] Continuous inkjet printheads typically cause a charge to be induced on ink droplets by providing a charged conductive element, known as a charging electrode, at the point of jet breakup. The charging electrode can comprise a flat plate, a slotted bar, or a hole with a window. It is desirable to inspect the jet for diagnostic purposes. Inspection typically involves observing jet breakup and determining the velocity and phase of the droplet stream. Determination of the velocity and phase of the droplet stream is typically carried out by means of one or more phase detectors and one or more velocity detectors downstream of the charging electrode. Observation of jet breakup is facilitated by LED stroboscopic backlighting and associated optics adjacent to or integrated with the charging electrode. The phase detectors and velocity detectors must be in close and even proximity to the jet (i.e., the jet and the charging electrode assembly are coaxially aligned) in order to ensure sufficient and consistent signal strength, respectively.

[0010] In use, the undeflected jet trajectory is adjusted so as to fall into a slot, however the alignment of the charging electrode and the jet are typically independent of each other. As a result, such adjustment disturbs the axial alignment between the charging electrode and the jet. In cases where the jet trajectory is substantially adjusted, the charging electrode may interfere with the jet trajectory - a phenomenon known as "shearing" which substantially prevents any printing.

[0011] Non-coaxial alignment of the electrode and the jet can also cause lateral forces to be applied to the droplet stream. The lateral forces are caused by unequal lateral distances between the electrode surface and the droplets and thus electrostatic force imbalance. As a result, there is a reduction in print quality and / or collisions with the slot.

[0012] There is a need to provide an alternative charging electrode and printhead for a continuous inkjet (CIJ) printer which overcomes one or more of the disadvantages of known systems, whether mentioned in this document or otherwise. SUMMARY OF THE INVENTION

[0013] According to a first aspect of the present invention, there is provided a charging electrode assembly for a continuous inkjet printer. The charging electrode comprises a charging electrode defining a channel for charging ink droplets, the channel extending along an ink travel axis from an inlet hole to an outlet hole, during printing, inkjet travels along the ink travel axis from a nozzle, the electrode being configured to induce a charge on selected ink droplets by capacitive coupling. The charging electrode further comprises mounting means configured to couple the charging electrode to a nozzle body, the mounting means being configured to allow the charging electrode to move relative to the nozzle to compensate for inkjet misalignment.

[0014] Manufacturing tolerances in an inkjet nozzle can result in misalignment of the inkjet. This can be accommodated by adjusting the relative position between a slot configured to capture non-printed ink droplets and the nozzle. However, any jet misalignment can result in incomplete alignment between the inkjet (and the ink droplet, once separated from the inkjet) and the charging electrode. This can have various adverse effects on print quality, including, for example, distortion of the amount of charge induced on the ink droplet, interference with the direction of the ink droplet, and even in severe cases, a collision between the ink droplet and the charging electrode.

[0015] The effects of any jet misalignment can be mitigated by providing a mounting arrangement that couples the variable electrode to the nozzle while also allowing adjustment of the charging electrode position. That is, by mounting the charging electrode to the nozzle (rather than, for example, to the printhead platform), any movement or adjustment of the nozzle (e.g., to ensure alignment of the inkjet with the slot) will also cause a corresponding movement of the charging electrode.

[0016] The mounting arrangement can include an adjustment configuration and a fixation configuration, in the adjustment configuration, allowing the charging electrode to move relative to the nozzle to compensate for inkjet misalignment, and in the fixation configuration, not allowing the charging electrode to move relative to the nozzle.

[0017] In this way, adjustment can be made during manufacturing, assembly, repair, or calibration operations and then the adjusted charging electrode configuration can be fixed for subsequent use during print operations.

[0018] The channel can have a first dimension in a first direction perpendicular to the nominal ink travel axis and a second dimension different from the first dimension in a second direction perpendicular to the first direction and the nominal ink travel axis.

[0019] By providing a channel that does not have circular symmetry with respect to the nominal ink travel axis (i.e., having different dimensions in directions perpendicular to the nominal ink travel axis), a convenient mechanism can be achieved for providing precise positioning between the charging electrode and the inkjet. For example, the charging electrode can be rotated such that the jet is centered between opposing channel walls.

[0020] The nominal ink travel axis can also be referred to as the central printhead axis and refers to the expected direction in which ink travels from the nozzle. However, it should be understood that manufacturing tolerances can result in a (small) misalignment (e.g., up to 1.5 degrees) between the inkjet direction (i.e., the ink travel axis) and the central printhead axis. Components of the printhead (e.g., the nozzle body, the slot, etc.) will be designed based on the central printhead axis or the nominal travel axis. However, the actual ink travel axis can vary between printheads and may not be determined until the components of the printhead have been assembled.

[0021] The mounting arrangement can be configured to allow the charging electrode to rotate relative to the nozzle.

[0022] By rotating the charging electrode relative to the nozzle, the relative position of the channel wall and the ink jet can be adjusted. For example, in the case where the channel does not have circular symmetry, the charging electrode can be rotated to center the jet between the opposing channel walls.

[0023] The mounting device can be configured to allow the charging electrode to rotate relative to the nozzle about a rotational axis that is substantially coaxial with the nominal ink travel axis.

[0024] The mounting device can be configured to allow the charging electrode to rotate relative to the nozzle through an angular range of at least 45 degrees, and optionally, wherein the mounting device is configured to allow the charging electrode to rotate relative to the nozzle through an angular range up to about 90 degrees.

[0025] By providing a 90-degree range of rotation in either direction, jet misalignment in any direction can be compensated for.

[0026] The mounting device can be configured to allow the charging electrode to rotate relative to the nozzle through an angular range up to about 180 degrees. By providing a 180-degree range of rotation, in combination with a channel having an elongated cross-section (i.e., different first and second dimensions), jet misalignment in any direction can be compensated for, since the longer dimension of the two dimensions can be aligned with the direction of jet misalignment.

[0027] The mounting device can be configured to allow the charging electrode to rotate relative to the nozzle to an infinite extent.

[0028] The mounting device can be configured to allow relative movement between the charging electrode and the nozzle in a plane of movement perpendicular to the nominal ink travel axis.

[0029] That is, the allowed relative movement may not include relative movement along the nominal ink travel axis, but may allow the components to move relative to each other in the plane of movement (e.g., rotate) (e.g., by sliding past each other).

[0030] The mounting device can include a guiding surface and a guiding element configured to be guided by the guiding surface. The allowed range of movement between the charging electrode and the nozzle can be determined at least in part by the configuration of the guiding surface and the guiding element.

[0031] Thus, the interaction of the guiding surface and the guiding element can provide a limited degree of allowed movement. The guiding surface can include a guiding slot within which the guiding element moves. The guiding slot can extend in the direction of movement. The charging electrode assembly can include two guiding slots disposed on opposite sides of the central axis.

[0032] One of the guiding surface and the guiding element may have a fixed configuration relative to the charging electrode in the moving plane. The other of the guiding surface and the guiding element may have a fixed configuration relative to the nozzle in the moving plane.

[0033] In this way, the movement of the guiding element along the guiding surface (e.g., within a guiding slot, socket, and / or hole) allows the charging electrode to move relative to the nozzle in the moving plane, where the extent of the movement is determined by the configurations of the guiding surface and the guiding element.

[0034] The guiding element may include a fixing element. The charging electrode assembly may include an adjustment configuration and a fixing configuration. In the adjustment configuration, the fixing element is configured to guide the movement of the charging electrode relative to the nozzle. In the fixing configuration, the fixing element is configured to fix the position of the charging electrode relative to the nozzle.

[0035] It should be understood that when the electrode assembly “includes” an adjustment and / or fixing configuration, this should be taken to mean that the charging electrode assembly defines the adjustment and fixing configurations between which the charging electrode assembly can operate.

[0036] The guiding element may also be a fixing element (e.g., a screw or a bolt or a clamping nut). When tightened, relative movement can be prevented, but when loosened, the charging electrode can rotate relative to the nozzle.

[0037] The guiding surface may include a substantially cylindrical socket, and the guiding element may include a cylindrical protrusion.

[0038] The mounting device may include a charging electrode coupler. The charging electrode coupler can be coupled to each of the charging electrode and the nozzle body in use.

[0039] By providing an intermediate member (i.e., the charging electrode coupler) between the charging electrode and the nozzle, electrical isolation can be provided between the charging electrode and the nozzle while allowing them to be mechanically coupled together.

[0040] The charging electrode coupler may define a guiding surface (e.g., a slot or a socket), and may be rigidly coupled to one of the charging electrode and the nozzle, and slidably coupled to the other of the charging electrode and the nozzle. The guiding surface may be integrally formed within the charging electrode coupler. The guiding surface may be integrally formed with one of the nozzle body and the charging electrode.

[0041] In the adjustment configuration, the slidable coupler may allow a rotational sliding motion.

[0042] The charging electrode coupler may include an annular member configured to surround a central printhead axis (e.g., and centered about the central printhead axis), thereby defining a central aperture for receiving a portion of the nozzle and / or a portion of the charging electrode. In this way, precise alignment between the nozzle and the charging electrode can be provided.

[0043] The charging electrode coupler may include an electrical insulator configured to electrically insulate the charging electrode from the nozzle body.

[0044] A seal may be provided between the charging electrode and the nozzle.

[0045] In this way, a sealable cavity can be provided extending from the nozzle orifice to the inkjet orifice, thereby allowing the cavity to be cleaned.

[0046] The charging electrode assembly may include a first seal between the guide and the charging electrode, and a second seal between the guide and the nozzle. An O-ring or gasket may be provided at or at each of the first and second seals.

[0047] The guiding surface may include a substantially cylindrical socket defined by the nozzle body, and the guiding element may include a cylindrical protrusion defined by the charging electrode coupler.

[0048] The guiding element and the guiding surface form a concentric cylindrical interface between the charging electrode coupler and the nozzle body, thereby allowing relative rotation therebetween.

[0049] In an alternative, the guiding surface may include a substantially cylindrical socket defined by the charging electrode coupler, and the guiding element may include a cylindrical protrusion defined by the nozzle body.

[0050] The mounting means may include another guiding element defined by the nozzle body, the nozzle body including a cylindrical protrusion and a charging electrode, and the charging electrode may define another guiding surface including a socket.

[0051] The mounting means may include a clamping nut, wherein the clamping nut includes a threaded portion and a shoulder, the threaded portion being configured to be screwed onto the nozzle body, and the shoulder being configured to hold the charging electrode coupler against the nozzle body. In use, the clamping nut may be operated by rotation between an adjustment configuration in which the charging electrode coupler is held loosely, and a fixed configuration in which the charging electrode coupler is pressed against the nozzle body by the shoulder, thereby restricting axial and rotational movement of the charging electrode relative to the nozzle.

[0052] Advantageously, the clamping nut arrangement does not restrict rotation of the charging electrode coupler about its axis.

[0053] The charging electrode assembly may further include a support member that at least partially defines a spherical surface, the support member being coupled to the charging electrode. The support member may be configured to be pivotally coupled to the charging electrode mount to form a ball-and-socket joint, thereby allowing the charging electrode to rotate about a center of rotation in two different planes.

[0054] The first dimension may be at least 0.5 mm. The first dimension may be less than 1 mm. The second dimension may be at least 1 mm. The second dimension may be less than 5 mm.

[0055] By providing a charging electrode channel having a slot-like shape, a close spacing between the channel wall and the ink jet can be provided at the ink splitting point (due to the smaller dimension), and a certain degree of insensitivity to jet misalignment can be provided (due to the larger dimension). Rotation of the charging electrode allows the smaller dimension separation to be oriented such that the wall is substantially the same distance from the ink jet on each side, thereby promoting uniform charging and avoiding unnecessary droplet deformation and deflection. On the other hand, the larger dimension can be aligned with the plane defined by the ink travel axis and the nominal ink travel axis.

[0056] The first dimension may be between about 0.6 mm and about 0.7 mm. The second dimension may be between about 1.2 mm and about 1.5 mm.

[0057] The charging electrode may include first and second axially disposed regions. The first region may be configured to induce a charge on a selected ink droplet by capacitive coupling. The second region may be configured to shield charged ink droplets by surrounding at least a portion of the travel axis.

[0058] That is, the first region may surround the channel from the inlet hole to the jet splitting position. The second region may surround the channel from the jet splitting position to the outlet hole. In this way, charged droplets can be shielded from external electromagnetic interference (e.g., the HT field for deflecting droplets).

[0059] The first axially disposed region and the second axially disposed region may be located on either side of the viewing hole.

[0060] The channel may have a first dimension and a second dimension in at least a portion of the first axially disposed region. In at least a portion of the second axially disposed region, the channel may have a third dimension in a first direction and a fourth dimension in a second direction. The third dimension may be greater than the first dimension. The fourth dimension may be greater than the second dimension.

[0061] That is, the first region may have a relatively small dimension between the inlet hole and the jet splitting point in order to provide a reliable coupling between the charging electrode and the ink jet (and the droplets as they form) without the need to apply an overly high charging electrode voltage.

[0062] The second region surrounding the channel from the droplet splitting position to the outlet orifice can primarily shield the droplets and thus may not require such small dimensions. By providing larger dimensions, an increased tolerance for jet misalignment can be allowed.

[0063] The channel can be referred to as a closed channel. The channel can be partially closed.

[0064] The channel can be fully closed. That is, the inlet orifice and the outlet orifice can define the only openings through which fluid can pass into the closed channel. In this way, the charging electrode can be sealed to the nozzle and the printhead housing, facilitating the provision of a closed cleaning chamber.

[0065] At least a portion of the charging electrode can be transparent such that the charging electrode is configured to allow monitoring of the formation of ink droplets within the channel.

[0066] The charging electrode can include a transparent body. It should be understood that 100% transparency is not required, but sufficient transparency is needed to allow observation of the jet splitting position.

[0067] The charging electrode can include a transparent and conductive charging electrode body. The charging electrode can include a transparent and non-conductive charging electrode body having a transparent conductive coating (such as an ITO sputtered transparent plastic component).

[0068] The charging electrode can include an observation orifice for monitoring the formation of ink droplets within the channel.

[0069] By providing the observation orifice, the jet splitting position within the charging electrode can be observed. The observation orifice can be closed by a transparent window, allowing the channel to remain sealed from the region external to the charging electrode while still allowing observation of the internal channel.

[0070] The charging electrode can further include a light source or a second observation orifice disposed on the side of the travel axis opposite to the observation orifice.

[0071] By providing a pair of opposing observation orifices or a single observation orifice and an opposing light source, the jet splitting position can be observed through the charging electrode while providing (e.g., stroboscopic) backlighting to enhance the clarity of imaging.

[0072] The observation orifice can have an elongated shape extending in the direction of the travel axis.

[0073] There is also provided an assembly for a printhead of a continuous inkjet printer, the assembly including a charging electrode assembly and a nozzle having one or more of the above-described features.

[0074] There is also provided a printhead for a continuous inkjet printer, which includes a charging electrode assembly according to the first aspect of the present invention.

[0075] The printhead may also include nozzles for generating and ejecting ink, which ink then undergoes jet splitting into a stream of ink droplets for printing.

[0076] The printhead may also include deflection electrodes configured to deflect the ink droplets after they have been charged by the charging electrodes.

[0077] The printhead may also include a gutter for receiving ink droplets not used for printing.

[0078] The printhead may also include a printhead housing configured to encapsulate the deflection electrodes within a cleaning chamber, with the printhead defining a seal between the charging electrodes and the cleaning chamber. The printhead housing may also be referred to as a chamber housing.

[0079] In this way, the internal volume (i.e., the cleaning chamber) defined within the printhead housing can be filled with a solvent to remove any ink deposits, thereby allowing effective cleaning of the internal channels of the charging electrodes and the surfaces of the deflection electrodes.

[0080] The printhead may also include a flexible member disposed between the charging electrodes and the printhead housing, the flexible member being configured to provide a seal and being configured to allow movement between the printhead housing and the charging electrodes.

[0081] In this way, the charging electrodes (and possibly the attached nozzles) can be adjusted without the need to also move the printhead housing. The flexible member may be referred to as a boot. The flexible member can ensure that a fluid seal is maintained while accommodating some movement.

[0082] The printhead may further define ink holes configured to allow the droplets to leave the printhead for printing. The printhead may include a sealing mechanism configured to selectively close the ink holes.

[0083] The sealing mechanism can include any convenient device (e.g., a rotary shutter, a pneumatic or hydraulic shutter, a sliding cover, etc.).

[0084] When the ink holes are closed by the sealing mechanism, a closed fluid volume can be defined between the nozzles and the ink holes, with a portion of the closed fluid volume being defined by the charging electrode channels.

[0085] The printhead may also include a nozzle adjustment mechanism. The nozzle adjustment mechanism may be configured to allow adjustment of the nozzles relative to the gutter to compensate for inkjet misalignment.

[0086] The nozzle adjustment mechanism can include a first adjustment screw and a second adjustment screw, each adjustment screw being configured to provide adjustment along mutually orthogonal axes, the mutually orthogonal axes being perpendicular to the ink travel axis.

[0087] There is also provided a continuous inkjet printer including a print head as described above. The continuous inkjet printer may also include an ink system for storing ink and supplying ink to the print head.

[0088] According to a second aspect of the present invention, there is provided a method of configuring a print head for a continuous inkjet printer. The method includes adjusting the nozzles of the print head such that the ink jets ejected from the nozzles are aligned with a gutter for receiving ink droplets not used for printing. The method further includes fixing the nozzles to the body of the print head in the aligned configuration, adjusting the position of the charging electrode relative to the nozzles to compensate for misalignment of the ink jets, and fixing the charging electrode to the nozzles in the adjusted configuration.

[0089] Adjusting the position of the charging electrode relative to the nozzles to compensate for misalignment of the ink jets may include rotating the charging electrode relative to the nozzles.

[0090] Compensating for misalignment of the ink jets may include positioning the charging electrode relative to the jet such that the charging electrode channel is substantially centered relative to the jet in at least one direction.

[0091] The method of the second aspect may also include one or more of the above optional features in combination with the charging electrode, print head, and continuous inkjet printer of the first aspect.

[0092] According to a third aspect of the present invention, there is provided a charging electrode assembly for a continuous inkjet printer. The charging electrode assembly includes: a charging electrode defining a channel for charging ink droplets, the channel extending from an inlet hole to an outlet hole along an ink travel axis, during printing, an ink jet travels along the ink travel axis from a nozzle, the electrode being configured to induce a charge on selected ink droplets by capacitive coupling; and a support member at least partially defining a spherical surface, coupled to the charging electrode. The support member is configured to be pivotally coupled to a charging electrode mount, forming a ball-and-socket joint, thereby allowing the charging electrode to rotate about a center of rotation in two different planes.

[0093] Advantageously, the spherical joint allows for easy adjustment of the ink jets to compensate for misalignment of the ink jets and the gutter, while hydraulically sealing the clean room of the print head.

[0094] The support member may include an annular flange disposed coaxially about the charging electrode channel.

[0095] The annular flange may define a truncated spherical surface circumferentially disposed about the charging electrode channel.

[0096] The charging electrode assembly may further include mounting means configured to couple the charging electrode to a nozzle body, the mounting means being configured to allow rotational movement of the charging electrode relative to the nozzle.

[0097] Advantageously, the rotational movement of the charging electrode relative to the nozzle enables compensation for misalignment of the ink jets.

[0098] The mounting device may include: a charging electrode coupler configured to couple a charging electrode and a nozzle body; and a clamping nut. The clamping nut may include a threaded portion configured to be screwed onto the nozzle body; and a shoulder configured to hold the charging electrode coupler against the nozzle body. In use, the clamping nut may be operated by rotation between an adjustment configuration and a fixed configuration, in which the charging electrode coupler is loosely held and in which the charging electrode coupler is pressed against the nozzle body by the shoulder, thereby restricting axial and rotational movement of the charging electrode relative to the nozzle.

[0099] Advantageously, the clamping nut arrangement does not restrict rotation of the charging electrode coupler about its axis.

[0100] The socket and the support member may be configured to form a hydraulic seal in a plurality of relative orientations.

[0101] According to a fourth aspect of the present invention, there is provided a print head for a continuous inkjet printer, which includes a charging electrode assembly according to the third aspect of the present invention. The charging electrode assembly may include any one of the above optional features. The print head further includes: the nozzle for generating and ejecting an ink jet, which is then subjected to jet splitting into a stream of ink droplets for printing; a deflection electrode configured to deflect the ink droplets after the ink droplets have been charged by the charging electrode; and a gutter for receiving the ink droplets not used for printing; and a charging electrode mount configured to be pivotally coupled to the support member to form a ball and socket joint, thereby allowing the charging electrode to rotate about a center of rotation in two different planes.

[0102] The charging electrode mount may define a socket configured to receive the support member.

[0103] The socket may be annular.

[0104] Advantageously, the annular shape of the socket allows the ink jet to pass through the socket and thus through the ball and socket joint.

[0105] The socket may be a truncated spherical surface.

[0106] The socket may be integrally formed with the chamber housing.

[0107] The print head may be configured to allow the charging electrode to rotate about the center of rotation up to 10 degrees away from the nominal ink travel axis.

[0108] The nozzle and the charging electrode may be axially coupled.

[0109] The gutter may be rigidly coupled to the charging electrode mount by a single component.

[0110] The chamber housing can include a single component.

[0111] According to a fifth aspect of the present invention, there is provided a modular printhead for a continuous inkjet printer. The modular printhead includes: a sealing mechanism releasably coupled to a housing assembly at an interface. The sealing mechanism includes: a rotatable body rotatable about a rotation axis between a first configuration and a second configuration; and a housing defining an ink hole, the housing holding the rotatable body. The housing assembly includes: a chamber selectively sealable by the rotatable body, the rotatable body rotatable about a rotation axis between a first configuration with an open ink hole and a second configuration with a closed ink hole; a nozzle for generating and ejecting a stream of ink droplets for printing; at least one electrode for guiding the stream of ink droplets; and a gutter for receiving ink droplets not used for printing. The at least one electrode is disposed in the chamber; and at least one fluid path and at least one mechanical coupling extend through the interface.

[0112] Advantageously, the releasable coupling of the housing assembly and the sealing mechanism of the modular printhead facilitates easy disassembly and maintenance of the modular printhead.

[0113] The fluid path extending through the interface may include a connection block configured to provide a detachable fluid connection through the interface.

[0114] The gutter may be configured to remain in place relative to the chamber when the sealing mechanism is separated from the housing assembly.

[0115] According to a sixth aspect of the present invention, there is provided a method of disassembling the modular printhead of the fifth aspect. The modular printhead may include any of the above optional features. The method includes: decoupling the sealing mechanism from the housing assembly at the interface, separating the at least one fluid path extending through the interface, and disengaging the mechanical coupling extending through the interface.

[0116] According to a seventh aspect of the present invention, there is provided a method of aligning components of a printhead for a continuous inkjet printer, the method including: adjusting the position of a charging electrode relative to a nozzle to compensate for inkjet misalignment; fixing the charging electrode to the nozzle in the adjusted configuration; fitting the charging electrode into a charging electrode mount to form a ball joint mount; adjusting the orientation of the charging electrode by rotating the charging electrode about the ball joint mount relative to the body of the printhead to align the inkjet ejected from the nozzle with the gutter for receiving ink droplets not used for printing; and fixing the nozzle to the body of the printhead in the aligned configuration.

[0117] Adjusting the position of the charging electrode relative to the nozzle can be performed before assembling the charging electrode into the charging electrode mount, thereby forming a ball-and-socket joint mount.

[0118] Adjusting the charging electrode before assembling it into the charging electrode mount is advantageous because, for example, approaching the charging electrode for adjustment is not hindered by the charging electrode mount.

[0119] The nozzle and the charging electrode can be fixed together to form a single assembly. Advantageously, fixing the nozzle and the charging electrode to each other in an aligned configuration allows the orientation of the charging electrode and the nozzle relative to the printhead body to be adjusted in series as a single assembly while maintaining the alignment between the nozzle and the charging electrode.

[0120] The method can further include attaching a sealing mechanism.

[0121] For some or all of the method, the printhead can be attached to a test fixture.

[0122] The orientation of the charging electrode can be adjusted by an external alignment tool.

[0123] Advantageously, using an external alignment tool eliminates the need to build alignment components into each printhead, thereby saving costs.

[0124] The charging electrode can be snap-fitted into the charging electrode mount.

[0125] The method can further include detaching the sealing mechanism from the printhead to expose the groove.

[0126] The sealing mechanism is configured to be releasably coupled to the housing assembly at the interface, and the sealing mechanism includes:

[0127] A rotatable body that can rotate between a first configuration and a second configuration about a rotation axis; and

[0128] A housing that defines an ink hole and holds the rotatable body;

[0129] Wherein, the housing assembly includes a chamber that can be selectively sealed by the rotatable body, and the rotatable body can rotate about the rotation axis between a first configuration with an open ink hole and a second configuration with a closed ink hole; and further, wherein at least one fluid path and at least one mechanical coupling extend through the interface.

[0130] The housing assembly can further include a nozzle for generating and ejecting a stream of ink droplets for printing; at least one electrode for guiding the stream of ink droplets; and a groove for receiving ink droplets not used for printing.

[0131] The method can be part of a method of manufacturing a printhead.

[0132] According to an eighth aspect of the present invention, there is provided a print head for a continuous inkjet printer. The print head includes: a nozzle for generating and ejecting an ink jet, which subsequently undergoes jet breakup into a stream of ink droplets for printing; a charging electrode defining a closed channel for charging the ink droplets, the closed channel extending from an inlet hole to an outlet hole along an ink travel axis, during printing, the ink jet travels along the ink travel axis from the nozzle, and the electrode is configured to induce a charge on selected ink droplets by capacitive coupling; a deflection electrode configured to deflect the ink droplets after they have been charged by the charging electrode; a gutter for receiving ink droplets not used for printing; and an ink port configured to allow droplets to leave the print head for printing. The print head has a printing configuration and a cleaning configuration, in the printing configuration the ink port is open, and in the cleaning configuration the ink port is closed. In the cleaning configuration, the print head defines a closed cleaning chamber, and the closed cleaning chamber is at least partially defined by the closed channel.

[0133] That is, by partially defining the cleaning chamber by the charging electrode channel, the minimum cleaning volume required for cleaning can be defined, because only the inner surface of the charging electrode (i.e., the closed channel) will need to be cleaned. That is, the outer surface of the charging electrode can thus be excluded from the cleaning chamber, thereby reducing the volume to be cleaned, and thus reducing the volume of cleaning fluid required for cleaning.

[0134] The ink droplets received by the gutter can be uncharged and / or undeflected; and the ink port can be configured to specifically allow selected ink droplets for printing to leave the print head.

[0135] The selected ink droplets should be considered to mean those ink droplets that have been charged by the charging electrode and deflected by the deflection electrode, and only the selected ink droplets are directed towards the substrate for printing.

[0136] The ink port can be spaced from the nozzle by the closed cleaning chamber. That is, when traveling from the nozzle to the ink port during printing, the droplets can pass through the cleaning chamber (which is not completely closed during printing).

[0137] The closed cleaning chamber can have a variable geometry.

[0138] The print head can further include a print head housing. The closed cleaning chamber can be at least partially defined by the print head housing. The print head can define a seal between the print head housing and the charging electrode.

[0139] The enclosed passage can be completely enclosed. That is, the inlet hole and the outlet hole can define the only openings leading to the enclosed passage through which fluid can pass. In this way, the charging electrode can be sealed to the nozzle and the print head housing, facilitating the provision of an enclosed cleaning chamber.

[0140] The print head can include a flexible member disposed between the charging electrode and the print head housing, and the flexible member is configured to provide a seal. The flexible member can be configured to allow adjustment between the print head housing and the charging electrode.

[0141] In this way, the charging electrode (and possibly the attached nozzle) can be adjusted without the need to also move the housing. The flexible member can be referred to as a sheath. The flexible member can ensure the maintenance of a fluid seal while accommodating some movement.

[0142] The charging electrode and the print head housing can be movably coupled to allow relative movement between the print head housing and the charging electrode.

[0143] The charging electrode and the print head housing can be pivotally coupled to allow adjustment between the print head housing and the charging electrode.

[0144] The print head can include a ball joint, and the ball joint includes: a support member that at least partially defines a spherical surface and is coupled to the charging electrode; and a charging electrode mount that is coupled to the print head housing and defines a socket for holding the support member. The support member and the charging electrode mount can form a ball joint, thereby allowing the charging electrode to rotate about a center of rotation in two different planes.

[0145] The socket and the support member provide a movable hydraulic seal interface.

[0146] The print head can define a seal between the nozzle and the charging electrode. The cleaning chamber can be at least partially defined by the nozzle.

[0147] The charging electrode can move relative to the print head housing and the nozzle.

[0148] The print head can include one or more conduits in communication with the enclosed cleaning chamber via one or more corresponding ports.

[0149] The conduits and ports can be used to supply cleaning fluid to the chamber and drain the cleaning fluid from the sump. The conduits and ports can be used to supply gas (such as air) to the chamber and / or drain gas (such as air) from the chamber.

[0150] At least one of the one or more ports can be provided in the nozzle. In this way, residual cleaning fluid can be drained from within the charging electrode.

[0151] At least one of the one or more ports may be disposed near the charging electrode. In this way, residual cleaning fluid can be discharged from within the charging electrode.

[0152] At least one of the one or more ports may be arranged to be close to the slot. In this way, residual cleaning fluid can be discharged from the end of the printhead remote from the nozzle. The slot may provide at least one of the one or more ports.

[0153] One or more ports may be configured to fill, supply or discharge a closed chamber with cleaning fluid.

[0154] The one or more ports may be configured to discharge air from the closed chamber.

[0155] Thus, the cleaning chamber may extend from the nozzle to the ink hole, thereby allowing all parts along the ink travel axis to be cleaned in a single volume while also minimizing the volume of the cleaning chamber.

[0156] The printhead may further include mounting means configured to couple the charging electrode to the nozzle. The mounting means may be configured to allow the charging electrode to move relative to the nozzle to compensate for inkjet misalignment during adjustment operations. The mounting means may be configured to rigidly fix the charging electrode to the nozzle during printing.

[0157] The mounting means may be the mounting means provided by the charging electrode assembly of the first aspect. The mounting means may include one or more optional features described above in the context of the charging electrode assembly of the first aspect.

[0158] The charging electrode closed channel may be a rotational volume about an axis. The rotational volume may include a first narrow parallel section adjacent to a second divergent section. The first narrow parallel section may be configured to be adjacent to the nozzle and receive inkjet from the nozzle.

[0159] Advantageously, due to the relatively large divergent section provided by the jet intersecting the hole axis at the first narrow section, this geometry can tolerate large angular misalignments without adjustment. Due to its small size and the resulting close proximity to the inkjet, the first section may be configured to provide a reliable coupling between the charging electrode and the nascent droplet.

[0160] The ink hole may be disposed downstream of the deflection electrode.

[0161] The ink hole may be arranged to be close to the slot.

[0162] According to a ninth aspect of the present invention, there is provided a method of cleaning a print head for a continuous inkjet printer. The method includes closing the ink holes of the print head to define a closed cleaning chamber, the closed cleaning chamber being at least partially defined by a charging electrode of the print head. The method further includes directing a cleaning fluid into the cleaning chamber to clean the chamber. Directing the cleaning fluid into the chamber includes directing the cleaning fluid into the closed channel of the charging electrode, the closed channel extending from an inlet hole to an outlet hole along an ink travel axis, during printing, ink jets travel along the ink travel axis from a nozzle, and the electrode is configured to induce a charge on selected ink droplets by capacitive coupling.

[0163] The method may include one or more optional features described above with reference to the first and / or third aspects of the present invention.

[0164] It should be understood that by at least partially enclosing the closed chamber, the closed channel of the charging electrode can define the closed chamber.

[0165] According to a tenth aspect of the present invention, there is provided a charging electrode for a continuous inkjet printer. The charging electrode defines a closed channel for charging ink droplets. The closed channel is a rotational volume around an axis, the rotational volume including a first narrow parallel section. The first narrow parallel section is adjacent to a second diverging section. The first narrow parallel section is configured to receive ink jets from a nozzle and induce a charge on selected ink droplets by capacitive coupling.

[0166] Advantageously, due to the relatively large diverging section provided by the jet intersecting the hole axis at the first narrow section, this geometry can tolerate large angular misalignments without adjustment. Due to its small size and the resulting close proximity to the ink jets, the first part can be configured to provide a reliable coupling between the charging electrode and the nascent droplets.

[0167] The second diverging section may have a radius around the axis that increases substantially monotonically along the axis.

[0168] The second diverging section may be generally conical.

[0169] The second diverging section may have a radius around the axis that increases non-monotonically along the axis.

[0170] The first narrow parallel section may be configured to be in a sealing relationship with the nozzle.

[0171] The second diverging section may be configured to be in a sealing relationship with the print head housing.

[0172] The charging electrode may be at least partially made of a conductive material.

[0173] The charging electrode may be substantially composed of a transparent conductive plastic.

[0174] Advantageously, the construction of the charge electrode facilitates charge induction on the nascent droplet by capacitive coupling and also facilitates visual observation of the jet.

[0175] The first narrow parallel section may be constituted by a narrow metal tube having an observation hole that is press-fitted into a wider plastic body.

[0176] The charging electrode of the tenth aspect can be used in combination with the print head of the eighth aspect and / or the method of the ninth aspect.

[0177] More generally, it will be further understood that the charging electrode or charging electrode assembly of any one of the first, third or tenth aspects can be used in combination with the print head of any one of the fourth, fifth and eighth aspects and / or the methods of the second, sixth, seventh and ninth aspects. Description of the Drawings

[0178] Specific embodiments of the present invention will now be described by way of example only with reference to the accompanying drawings, in which:

[0179] Figure 1 is a schematic diagram of a continuous inkjet (CIJ) printer according to an embodiment of the present invention;

[0180] Figure 2 is Figure 1 a separate perspective view of the print head of the printer shown;

[0181] Figure 3 is Figure 2 an alternative perspective view of the print head of, with the outer housing omitted;

[0182] Figure 4 is Figure 3 an alternative perspective view of the print head of;

[0183] Figure 5 is Figure 4 and Figure 5 an enlarged view of a part of the print head shown in, with the chamber outer housing omitted;

[0184] Figure 6 is Figures 2 to 5 a perspective view of a sub-assembly of the print head of;

[0185] Figure 7 is Figure 6 a cross-sectional side view of the sub-assembly of;

[0186] Figure 8 is Figure 6 and Figure 7 an alternative cross-sectional view of the sub-assembly of;

[0187] Figure 9is a simplified schematic diagram of a fluid system for a printer Figure 1 ; combined with Figures 2 to 7 the print head shown in

[0188] Figure 10 is a cross-sectional view of adjacent parts of a charging electrode assembly and a nozzle body;

[0189] Figure 11 is Figure 10 a perspective view of adjacent parts of a charging electrode assembly and a nozzle body of

[0190] Figure 12 is Figure 10 and Figure 11 a perspective view of an insulating coupling and adjacent parts of a nozzle body of

[0191] Figure 13A is a plan view of a nozzle adjustment mechanism, also showing Figure 10 , 11 and the attached charging electrode assembly and nozzle body of 12;

[0192] Figure 13B is Figure 13A another view of a nozzle adjustment mechanism and a connected charging electrode assembly and nozzle body of

[0193] Figure 13C is Figure 13B a view of a nozzle adjustment mechanism and an attached charging electrode assembly and nozzle body, with the nozzle carriage omitted;

[0194] Figure 14A is a view of a Figures 10 - 13C transverse cross-section of a closed channel of a charging electrode used in an ideal configuration;

[0195] Figure 14B is a view of a Figure 14A transverse cross-section of a closed channel of a charging electrode in use in a non-ideal configuration;

[0196] Figure 14C is Figure 14B a view of a Figure 14A and 14B transverse cross-section of a closed channel of a charging electrode in use after adjustment in a non-ideal configuration; and

[0197] Figure 15 schematically shows an alternative embodiment of a charging electrode.

[0198] Figure 16 is a cross-sectional view of a part of a charging electrode assembly and a print head, showing the electrical contact arrangement of the charging electrode.

[0199] Figure 17 is Figure 10 、 Figure 11 and Figure 12 a perspective view of a portion of an insulating coupling member and a nozzle body.

[0200] Figure 18A Schematically shows an alternative insulating coupling arrangement.

[0201] Figure 18B Schematically shows the Figure 18A alternative insulating coupling arrangement in another orientation.

[0202] Figure 19 is a separate perspective view of a print head according to another embodiment.

[0203] Figure 20 is Figure 19 a perspective view of a print head of

[0204] Figure 21 is Figure 19 and Figure 20 a cross-sectional side view of a print head of

[0205] Figure 22 is Figures 19 - 21 a cross-sectional side view of a charging electrode assembly and surrounding components of a print head of

[0206] Figure 23A is Figure 22 a separate perspective view of the charging electrode mount shown in

[0207] Figure 23B is Figure 22 and 23A a separate alternative perspective view of the charging electrode mount shown in

[0208] Figure 24 is Figure 22 a separate perspective view of the charging electrode coupling shown in

[0209] Figure 25 is Figure 22 a separate perspective view of the charging electrode shown in

[0210] Figure 26 is Figures 19 - 21 a perspective view of a selected portion of a print head of

[0211] Figure 27 is Figure 26 a separate alternative perspective view of a selected portion of the print head shown in

[0212] Figure 28 Shows separatelyFigure 21 and Figure 27 a portion of the shaft shown in

[0213] Figure 29 shows a Figures 19 - 21 perspective view of another part of the printhead of , where the sealing mechanism is removed.

[0214] Figure 30 shows a Figures 19 - 21 selected cross-sectional view of the printhead of .

[0215] Figure 31 schematically shows a method of adjusting Figures 19 - 21 the printhead of . DETAILED DESCRIPTION

[0216] Figure 1 Schematically shown is a continuous inkjet (CIJ) printer 1 according to an embodiment of the present invention. Printer 1 includes a printer body 2 (which may be referred to as a cabinet) connected to a printhead 3 by an umbilical cable 4. Printer body 2 houses an ink system 5 and a printer controller 6. Printer body 2 also has an interface 7 (e.g., a display, a keypad, and / or a touchscreen) for use by an operator.

[0217] Printhead 3 is arranged to print on a substrate disposed adjacent to printhead 3. Printer 1 typically includes two cartridge connectors for engaging respective fluid cartridges. In particular, printer 1 includes a cartridge connector for engaging a ink cartridge 8 and a (separate) solvent cartridge connector for engaging a solvent cartridge 10. The cartridge connectors each typically include a fluid port that is arranged to connect to a fluid passage within printer 1 to allow fluid to flow (via umbilical cable 4) between cartridges 8, 10 and other parts of inkjet printer 1 such as ink system 5 and printhead 3.

[0218] In operation, ink from ink cartridge 8 and solvent from solvent cartridge 10 can be mixed within ink system 5 to produce print ink having a desired viscosity suitable for printing. The ink is supplied to printhead 3, and unused ink returns from printhead 3 to ink system 5 (via umbilical cable 4). When unused ink returns from printhead 3 to ink system 5, air can be drawn in with the ink from the slots of printhead 3. Then, the air may be saturated with solvent in the slot lines.

[0219] In operation, ink is conveyed from the ink system 5 to the print head 3 under pressure and recirculated via a flexible tube back into the umbilical cable 4, with the flexible tube bundled together with other fluid tubes and electrical wires (not shown). To maintain the correct consistency of the ink, the ink system 5 is operable to mix the ink removed from the cartridge 8 with the solvent removed from the cartridge 10 and blend them together to obtain an ink having the correct viscosity and / or density for a particular printing application.

[0220] Of particular relevance to the present application, the print head 3 is a self-cleaning print head. Without operator intervention, the print head 3 can be sealed and a cleaning fluid flushed through at least a portion of the print head 3 in order to clean the print head 3. As will be set forth in the following description and drawings, this is achieved by incorporating a sealing mechanism including a rotatable body within the print head 3.

[0221] Turning to Figure 2 , a separate perspective view of the print head 3 is provided.

[0222] The print head 3 includes a first end 100 through which the print head 3 can be connected to the umbilical cable 4, as Figure 1 shown. Accordingly, the first end 100 may include a connector (e.g., a threaded connector in the illustrated embodiment). At the opposite end, the print head 3 includes a second end 102. An end cap 104 is provided at the second end 102. The end cap 104 defines the outermost portion of the print head 3. The end cap 104 includes an ink hole 106, which may be referred to as an ink well. In operation, deflected ink is ejected from the print head 3 through the ink hole 106 onto a substrate (e.g., a moving substrate passing external to the print head 3). Extending generally between the first end 100 and the second end 102 is a housing 108. In the illustrated embodiment, the housing 108 is generally cylindrical and provides a protective cover for the components making up the print head 3. The housing 108 is removable in order to expose components, e.g., for maintenance. The combination of the end cap 104 and the housing 108 can be described as an outer cover 110 of the print head 3.

[0223] When the print head 3 is to be cleaned (e.g., via the self-cleaning ability of the print head 3), the ink hole 106 can be effectively closed and sealed by a sealing mechanism within the print head 3. That is, when the cleaning fluid is flushed through the chamber of the print head 3 (which will be described below), the cleaning fluid cannot escape from the print head 3 through the ink hole 106. For the purposes of the present application, the closing of the ink hole 106 may not imply a change in the geometry of the ink hole 106 itself. That is, the ink hole 106 remains as Figure 2 shown, regardless of whether it is open or closed (by the operation of the sealing mechanism). However, at least in the illustrated embodiment, the ink hole 106 can be occluded (e.g., internally covered) by an upstream rotatable body to define a sealed chamber. This will be described in more detail later in this document.

[0224] Go to Figure 3 , a perspective view of the printhead 3 is provided, with the housing 108 omitted. Thus, the various components that make up the printhead 3 are visible, and a number of components are also shown in partial cross-section to improve visibility.

[0225] Figure 3 The connector 112 is shown. The printhead 3 can be connected via the connector 112 to an umbilical cable provided at the first end 100 of the printhead. The connector 112 is integral with the chassis 114. The chassis 114 defines various platforms to which various other components are mounted. For example, in the illustrated embodiment, the motor 116 and the high-voltage resistor 118 are mounted to the chassis 114. The high-voltage resistor 118 limits the current and spark energy available to the electrodes (described below). In other embodiments, the high-voltage resistor 118 can be mounted closer to the deflection electrode 168 to reduce the cable length therebetween. Thus, the high-voltage resistor 118 can be mounted to, for example, the chamber housing 162 or the PCB 167. The solenoid valve 120 is also mounted on the chassis 114. In the illustrated embodiment, the solenoid valve 120 is mounted to the chassis 114 via a valve manifold. In the illustrated embodiment, the motor 116 is a stepper motor, but other types of motors can be used in other ways.

[0226] The shaft of the motor 116 rotates about a rotational axis 117, which can be referred to as the motor axis. The motor 116 is arranged to be in power communication with a rotatable body 122 that forms part of a sealing mechanism 124. The sealing mechanism 124 is located at the second end 102 of the printhead 3 and, as described above, is a particular focus of the present application. Briefly, the rotatable body 122 can rotate about a rotational axis 126. The rotatable body 122 can rotate between a first configuration and a second configuration (as Figure 3 shown), in the first configuration, an ink path is defined as spanning the rotatable body 122 and passing through the ink holes 106, and in the second configuration, the rotatable body 122 closes the ink holes 106. In the second configuration, the sealing mechanism 124 (specifically its rotatable body 122) seals a portion (i.e., the chamber) of the printhead 3 to allow that portion to be flushed with a cleaning fluid to clean the printhead 3.

[0227] As previously described, the motor 116 is in power communication with the rotatable body 122 to drive the rotation of the rotatable body 122. The motor 116 is in power communication with the rotatable body 122 via a shaft 128. The shaft 128 is provided outside the chamber selectively sealed by the rotatable body 122 (for example, see Figure 7the chamber 164). The shaft 128 extends along the extent of the chamber. The shaft 128 is in power communication with the rotatable body 122 via a worm gear 130 that includes a worm 132 and a gear 134. The worm 132 is coupled to an end of the shaft 128 (e.g., its second end 102 proximate the printhead 3). The gear 134 is rotatably coupled to the rotatable body 122. The worm gear 130 changes the direction of rotation of the shaft 128 from the axis of rotation 129 to the axis of rotation 126. Although not visible in Figure 3 , another worm gear is used to change the direction of rotation of the motor 116 at the shielded end of the shaft 128 (e.g., positioned toward the first end 100 of the printhead 3). As described above, the shaft 128 rotates about the axis of rotation 129. The axis of rotation 129 extends longitudinally along the printhead 3, and the printhead 3 can be described as extending generally in the same longitudinal direction.

[0228] For a variety of reasons, it is advantageous to use the drive assembly that includes the shaft 128 and the worm gear 130. First, the incorporation of the shaft 128 means that the motor 116 can be disposed in a different portion of the printhead 3 than the remainder of the sealing mechanism 124. This is desirable because the longitudinal length of the printhead 3 at the second end 102 does not increase beyond the length required (e.g., to accommodate the volume of the motor). Increasing the longitudinal length of the printhead 3 at the second end 102 risks reducing the projection distance by which the printhead 3 must be offset from the substrate to be printed. The use of the worm gear 130 is also advantageous, at least because the gearing can effectively increase the torque output transmitted by the motor 116 to the rotatable body 122. This is particularly desirable in situations where the rotatable body 122 may become partially stuck in place (e.g., static friction) after the cleaning process and subsequent drying process. In other words, the use of the worm gear 130 reduces the risk that the rotatable body 122 becomes stuck in place such that the drive assembly cannot rotate the rotatable body 122 about the axis of rotation 126.

[0229] Returning to describe other components of the printhead 3, the manifold 136 is coupled to the chassis 114. Various fluid and electrical connections extend through the manifold 136.

[0230] The nozzle housing 138 (shown in a partial cross-sectional view in Figure 3 ) is coupled to the manifold 136 and houses the nozzle assembly 140. The nozzle housing 138 can alternatively be described as a body that forms part of the housing. The nozzle assembly 140 includes a nozzle carriage 142 and a nozzle body 143 among other components. The nozzle body 143 defines nozzles ( Figure 3 not visible in ) for generating and ejecting a stream of ink droplets for printing.

[0231] The charging electrode assembly 146 is coupled to the nozzle assembly 140. The charging electrode assembly 146 includes a charging electrode 148 and an insulating coupler 150 coupled to the charging electrode 148. When the ink droplet stream is guided past the charging electrode 148 in use, they are selectively and individually given a predetermined level of charge by the charging electrode 148. To assist in aligning the charging electrode 148 relative to the droplet stream emitted from the nozzle of the nozzle body 143, the charging electrode 148 can be rotationally adjusted about an axis. The adjustment mechanism is described in more detail below with reference to Figure 12 As can be seen, the sheath 151 is sandwiched between the charging electrode 148 and the chamber outer shell 162. The sheath 151 allows the charging electrode 148 to remain in sealed engagement or sealed connection with the chamber outer shell 162 when the charging electrode 148 is adjusted (see also Figure 3 / 8). Figure 7 / 8).

[0232] Returning to Figure 3 , the chamber outer shell 162 (also shown in partial section in Figure 3 ) is coupled to the nozzle housing 138. The chamber outer shell 162 defines a chamber 164. The chamber 164 can alternatively be described as a wash chamber. Although further information related to the chamber 164 will be provided in the following figures (specifically, the chamber 164 is visible in Figure 7 and Figure 8 ), when the rotatable body 122 is in the second configuration with the ink hole 106 closed, the chamber 164 is sealed for cleaning. Thus, when sealed, a cleaning fluid is directed or flushed into and through the chamber 164, cleaning the chamber 164 and the associated components of the print head 3 disposed in the chamber 164. Directing the cleaning fluid into the chamber 164 can include pumping the cleaning fluid (e.g., by the action of an upstream pump and at positive pressure) and / or sucking the cleaning fluid (e.g., by the action of a downstream pump and at negative pressure).

[0233] A low voltage (e.g., grounded or negative potential) electrode 166 and a deflection (e.g., high voltage) electrode 168 are coupled to the chamber outer shell 162 and mounted within the chamber 164. The electrodes 166, 168 can be collectively referred to as a pair of deflection electrodes. The low voltage electrode 166 can also include a phase detector that detects the phase of the charged particles during operation. The low voltage electrode 166 can be coupled to the chamber outer shell 162 by an adhesive. In other embodiments, the low voltage electrode 166 can be coupled to the chamber outer shell 162 by a gasket. The deflection electrode 168 is used to direct the ink droplet stream ejected by the nozzle and charged by the charging electrode 148 away from the gutter and towards the ink hole 106 for printing onto a substrate in use. The deflection electrode 168 is disposed within the chamber 164 and can thus be cleaned when the chamber 164 is sealed and the cleaning process is performed.

[0234] The printhead 3 further includes a housing 170. The housing 170 forms part of the sealing mechanism 124. The housing 170 is coupled to the chamber outer housing 162. The housing 170 is sealingly engaged with the chamber outer housing 162 through a gasket 173 interposed between the chamber outer housing 162 and the housing 170. The housing 170 may alternatively be described as a rotatable body mount or housing. As will be described in detail herein later, the rotatable body 122 is rotatably mounted within the housing 170 to selectively open and close the ink holes 106. The housing 170 further includes a cover 172, which can be selectively detached from the remainder of the housing 170 to facilitate the installation and maintenance of the moving parts (e.g., the rotatable body 122) of the sealing mechanism 124. The housing 170 further includes an end cap 104 that defines the ink holes 106. Thus, the housing 170 may be said to define the ink holes 106. Although in the illustrated embodiment the ink holes 106 are specifically defined by the end cap 104, in other embodiments, the end cap 104 may be omitted. Thus, even in the absence of an end cap, the housing 170 can define the ink holes. It is also worth noting that in the illustrated embodiment, the ink holes 106 are downstream of the rotatable body 122. That is, the ink droplets flow first through the rotatable body 122 and then through the ink holes 106. In other embodiments, the rotatable body may define the most downstream point of the ink path such that no end cap is positioned downstream of the rotatable body. In such an embodiment, the surrounding housing may be considered to define the ink holes passing through the rotatable body.

[0235] To avoid ambiguity, in the illustrated embodiment, the end cap 104 is coupled to the chamber outer housing 162 and does not move during operation. That is, the end cap 104 is fixed in place. However, in other embodiments, the end cap may define at least a portion of the rotatable body of the sealing mechanism. For example, the end cap may rotate about an axis generally parallel to the axis 129. The rotational position of the end cap can determine the degree to which the ink holes of the end cap overlap with the ink holes of the adjacent housing to "open" the ink holes of the adjacent housing. In the case where the ink holes at least partially or fully overlap, the rotatable body (e.g., the end cap) may be said to be in a first configuration, in which the ink path is defined to pass through the end cap. In the case where the ink holes of the end cap do not overlap with the ink holes of the adjacent housing, it can be said that the rotatable body (e.g., the end cap) is in a second configuration, in which the ink holes of the housing are closed.

[0236] Although shown in Figure 3 For the sake of brevity, various fasteners used to couple the chassis 114, the manifold 136, the nozzle housing 138, the chamber outer housing 162, and the housing 170 together are not detailed or described herein.

[0237] As will be apparent from Figure 7It is understood that chamber 164 is defined by the combination of chamber outer housing 162 and housing 170. Chamber 164 has a lower surface defined by the combination of low voltage electrode 166 (e.g., by surface 166a) and the surrounding chamber outer housing 162 (e.g., surface 162a), and an upper surface that extends above deflection electrode 168 (i.e., such that deflection electrode 168 is disposed within chamber 164) and is at least wide enough to accommodate deflection electrode 168. The third surface 164c and fourth surface 164d of chamber 164 (which may be referred to as side surfaces) extend between the first surface 164a and the second surface 164b to define the perimeter of chamber 164. The fourth surface 164d is not visible in Figure 7 as shown.

[0238] Referring Figure 3 to, printhead 3 also includes a PCB 167 that is mounted within chamber outer housing 162. However, as Figure 7 shown, the PCB is not disposed within chamber 164.

[0239] Turning Figure 4 to, an alternative perspective view of printhead 3 is provided. Due to the different viewing angles, a number of components that are not visible or are only partially visible in Figure 3 are visible in Figure 4 as shown.

[0240] Starting from the first end 100 of printhead 3, connector 112 and integral chassis 114 are shown. Solenoid valve 120 is shown mounted to chassis 114 together with valve block 174. Also visible in Figure 4 is worm gear 176 including worm 178 and gear 180. Worm 178 is rotatably coupled to motor 116, which is only visible on the opposite side of chassis 114, as Figure 4 shown (and more clearly visible in Figure 3 ). Worm 178 is driven to rotate about axis of rotation 117. Worm 178 is arranged in driving communication with gear 180, which is rotatably coupled to shaft 128. Gear 180 and shaft 128 are thus driven to rotate about axis of rotation 129, which may be referred to as the axis center line. It should be understood that by using worm gear 176, the direction of rotation driven by motor 116 is effectively translated by 90°, which is advantageous due to space limitations within printhead 3. Shaft 128 is shown extending across the entire extent of each of manifold 136, nozzle housing 138, chamber outer housing 162 and partially through housing 170.

[0241] As described in connection with Figure 3 , manifold 136, nozzle housing 138, chamber outer housing 162 and housing 170 are also coupled to chassis 114. PCB 167 is within Figure 4Also visible. The nozzle assembly 140 and the charging electrode assembly 146 coupled to the nozzle housing 138 are also visible in Figure 4 the middle part.

[0242] Temporarily turning to the sealing mechanism 124 at the second end 102 of the print head 3, as previously described, the sealing mechanism 124 includes a housing 170 (which includes a cover 172 and an end cap 104) and a rotatable body 122. The ink hole 106 defined by the housing 170 is also visible.

[0243] It should be noted that the components not described in detail in connection with the print head 3 are the components of the slot. The print head 3 does include a slot, which in the illustrated embodiment is a fixed slot coupled to the housing 170. The details of the slot will be described in connection with Figure 6 providing the details of the slot.

[0244] Turning to Figure 5 , an enlarged perspective view of a part of the print head 3 is provided. As will be understood from Figure 5 , the motor 116 is partially visible, as is the chassis 114, but any components further towards the first / connector end of the print head 3 are not visible. Similarly, as Figure 3 and Figure 4 shown, the chamber housing 162 is not shown in Figure 5 to facilitate the visibility of the components contained therein.

[0245] Figure 5 The geometry of the deflection electrode 168 is shown, which is used to direct the stream of ink droplets towards the substrate to be printed.

[0246] Figure 6 is a perspective view of a sub-assembly of the print head 3. Figure 6 The chamber housing 162 is shown, to which the nozzle assembly 140 and the sealing mechanism 124 are coupled.

[0247] As previously described, various components of the sealing mechanism 124 are visible, including the rotatable body 122, the housing 170 (including the cap 172), and the worm 132 and gear 134. The slot block 182 can also be seen in Figure 6 . The slot block 182 will be described in more detail in connection with the following figures, but briefly, the slot block 182 includes a slot hole ( Figure 6 not visible in Figure 9 ), through which the ink droplets not used for printing are received and then recycled back to the mixing tank of the ink system (as will be described in detail in connection with Figure 17 , 18). In the illustrated embodiment, the slot block 182 is a component separate from the surrounding housing 170 and other components. However, in some embodiments, the slot can be integral with the rotatable body (for example, see

[0248] The slot block 182 further includes a recess 200 defined in the effective lower side of the slot block 182. The recess 200 leads to a port 202. The port 202 in turn defines a second conduit (e.g., 214 as shown in Figure 9 ). Due to the presence of the recess 200, even when the rotatable body 122 is in the second closed configuration as shown in Figure 6 , the second conduit is still arranged to be in fluid communication with the chamber. Thus, the cleaning fluid can be pumped or suctioned into the chamber via the second conduit, or the used (e.g., dirty) cleaning fluid can be pumped or suctioned out of the chamber via the second conduit. Further details in this regard will be provided below.

[0249] Figure 6 The first and second cross-sectional markers 184, 186 are also schematically shown in. 184 is a vertical cross-section, and 186 is a horizontal cross-section. The markers 184, 186 respectively correspond to Figure 7 and 8 the cross-sectional views provided in.

[0250] Turning to Figure 7 , a cross-sectional side view of the subassembly shown in Figure 6 is provided, as shown by the marker 184 in Figure 6 . Figure 7 A chamber 164 that can be selectively sealed by a sealing mechanism 124 is shown.

[0251] Starting from the right-hand end of Figure 7 , only a portion of the nozzle body 143 of the nozzle assembly 140 is visible. The nozzle body 143 holds a nozzle 144 that generates and ejects a stream of ink droplets 188 for printing. Downstream of the nozzle 144 is a charging electrode 148. The charging electrode 148 is coupled to an insulating coupler 150. In the illustrated embodiment, the charging electrode 148 is rotatably coupled to the insulating coupler 150 by fasteners 147, 149. The insulating coupler 150 (and the charging electrode 148) is rotatably adjustable relative to the nozzle body 143. The insulating coupler 150 is an insulator (which can be plastic) that separates the charging electrode 148 from the nozzle body 143 (which is grounded). The charging electrode 148 abuts a sheath 151 such that the sheath 151 is sandwiched between the charging electrode 148 and the chamber outer shell 162. The sheath 151 also facilitates the adjustment of the charging electrode 148 relative to the chamber outer shell 162 by allowing a certain degree of movement of the charging electrode 148 relative to the chamber outer shell 162.

[0252] The charging electrode 148 is arranged to communicate with the chamber 164 through a channel 189. In use, as shown in Figure 7As shown, the flow of ink droplets 188 is generated and ejected by nozzle 144 and travels through chamber 164 via charging electrode 148 and first channel 189. After passing through charging electrode 148, the flow of ink droplets 188 has a charge applied thereto. The selectively charged flow of ink droplets 188 can be selectively deflected by deflection electrode 168 for printing. The flow of ink droplets that has been deflected by deflection electrode 168 for printing is labeled 190 in Figure 7 . The flow of ink droplets that is not used for printing and is thus not deflected by deflection electrode 168 is labeled 194. The flow of ink droplets 194 that is not used for printing is received by slot 183 of slot block 182. A portion of slot conduit 196 defined by slot 183 is also visible in Figure 7 . This is the conduit through which ink droplets 194 that are not used for printing and are received by slot 183 travel.

[0253] For completeness, in Figure 7 , rotatable body 122 of sealing mechanism 124 is shown in a second closed configuration. Thus, when sealing mechanism 124 is in the Figure 7 shown configuration, there will be no flow of ink droplets 188, 190, 194. Figure 7 It is shown that slot block 182 is at least partially received by housing 170. Although not visible in Figure 7 , chamber 164 also extends behind slot block 182, as Figure 7 shown (e.g., extending into the page). However, this is visible in Figure 8 and will be described in connection with Figure 8 .

[0254] Returning to Figure 7 , sealing mechanism 124 including rotatable body 122 rotatably coupled to gear 134 is also shown. Shaft 198 of rotatable body 122 is also visible. In use, rotatable body 122 rotates about axis of rotation 126 of shaft 198. Shaft 198 is received by recess 199 of cap 172 to constrain and position rotatable body 122.

[0255] Ink hole 171 defined by housing 170 is also visible in Figure 7 . In the Figure 7 shown configuration, rotatable body 122 effectively closes ink hole 171. In a first open configuration, in which rotatable body 122 rotates relative to the Figure 7 shown position, ink hole 171 is effectively opened such that the flow of ink droplets 190 can pass through rotatable body 122 via ink path 190 and through ink hole 171. When the flow of ink droplets 188 passes through chamber 164, a phase detector that is part of low voltage electrode 166 also operates to detect the phase of the ink particles. It is noted that, as Figure 2 shown, end cap 104 defines ink hole 106.Figure 7 The ink hole 171 shown therein overlaps with the ink hole 106 defined by the end cap 104, and the ink hole 106 can thus also be considered to be opened / closed by the rotatable body 104 (at least due to being downstream of the ink hole 171).

[0256] Finally, Figure 7 A recess 200 defined in the slot block 182 is also shown therein. As combined with Figure 6 described, the recess 200 partially defines a port 202 for cleaning and draining.

[0257] Moving on to Figure 8 , an alternative cross-sectional view as shown in Figure 7 is provided. In Figure 8 , a cross-sectional view as indicated by the annotation 186 in Figure 6 shows the sub-assemblies of Figure 6 and Figure 7 . Thus, Figure 8 can be described as a cross-sectional plan view of the sub-assembly.

[0258] As combined with Figure 7 described, Figure 8 the nozzle body 143, the insulating coupler 150, the charging electrode 148, and the sheath 151 are also shown. Figure 8 The low-voltage electrode 166 located within the chamber 164 is also shown. In Figure 8 the phase detector electrode 166b (which can be referred to as a phase pick-up electrode) and the velocity detector electrode 166c are also visible. The electrodes 166b, 166c (and the low-voltage electrode 166) are etched into the PCB that defines the low-voltage electrode 166 (e.g., the rear of the PCB in the shown embodiment). The combination of the electrodes 166, 166b, 166c can be referred to as a phase detector assembly. The phase detector electrode 166b is configured to determine the magnitude of the charge applied to the ink droplet when the ink droplet moves past the phase detector electrode 166b. The measurement from the phase detector electrode 166b is used to determine when to apply a voltage to the charging electrode 148. The velocity detector electrode 166c is configured to determine the velocity of the ink droplet as it moves past the electrode 166b. The velocity is determined by measuring the time between the charge "pulses" detected by the phase detector electrode 166b and subsequently by the velocity detector electrode 166c, and dividing the distance between the electrodes 166b, 166c by this time. In the shown embodiment, the low-voltage electrode 166 takes the form of an electroless nickel immersion gold (ENIG)-coated copper ground plane. The low-voltage electrode 166 serves as the 0V plate of a deflection electrode that establishes an EHT field that deflects the ink droplet stream in use. The phase detector electrode 166b and the velocity detector electrode 166c are covered by an insulator (e.g., solder mask in the shown embodiment). This prevents the ink and / or solvent from shorting the electrodes 166b, 166c to the low-voltage electrode 166.

[0259] Since each of the phase detector electrode 166b, the velocity detector electrode 166c, the low voltage electrode 166, and the deflection electrode 168 ( Figure 8 not shown) is disposed in the chamber 164, all of these components can be cleaned during the cleaning cycle. Similarly, although the charging electrode 148 is located outside the chamber 164, it can also be cleaned during the cleaning cycle by means of a third port or a charging electrode drain port ( Figure 8 not visible in the figure but will be described in detail below).

[0260] Figure 8 It is shown that in the illustrated embodiment, the chamber 164 includes a first chamber portion 164g and a second chamber portion 164h. The first chamber portion 164g is defined by the chamber outer shell 162. The second chamber portion 164h is defined by the housing 170. Thus, in the illustrated embodiment, the chamber 164 can be said to be at least partially defined by the housing 170. In other embodiments, it should be understood that the chamber outer shell 162 can be integrally formed with the housing 170 such that the chamber 164 is completely defined by the housing 170.

[0261] Figure 8 It is also shown that the chamber outer shell 162 includes a (first) conduit 204 that extends partially through the chamber outer shell 162 and communicates with the chamber 164 via a port 206. Thus, it can be said that the port 206 at least partially defines the chamber 164. The conduit 204 is multi-purpose because it can be used to supply a cleaning fluid to the chamber 164 or to drain the used cleaning fluid from the chamber 164. Thus, the conduit 204 can be described as a chamber cleaning and drain channel. The conduit 204 can be specifically described as an upstream chamber cleaning / drain channel because of its proximity to the channel 190 through which the ink droplets are ejected into the chamber 164.

[0262] Figure 8 More features of the slot block 182 are also shown. As combined with Figure 7As described above, the slot block 182 includes a slot hole 183, and ink droplets not used for printing are received / collected in the slot hole 183. The slot hole 183 defines an upstream end of a slot conduit 196 that extends through the slot block 182. At a downstream point, the slot conduit 196 appears to branch into a recess 210. The recess 210 is sealed during use and only facilitates the formation of the slot conduit 196 through the slot block 182. Further downstream of the slot conduit 196 is a return conduit 212 that is at least partially defined by the chamber housing 162. The return conduit 212 is arranged to be in fluid communication with the slot conduit 196 and thus with the slot hole 183. Accordingly, ink droplets not used for printing are received by the slot hole 183 and are suctioned through the slot conduit 196 and the return conduit 212 by suction. The unused ink droplets then return to the mixing tank. For completeness, the slot block 182 is sealed to the chamber housing 162 by a seal 213.

[0263] In the illustrated embodiment, the slot block 182 forms a separate component fixedly coupled to the chamber housing 162. In other embodiments (e.g., Figure 17 , FIG. 18), at least a portion of the slot may be rotatably coupled to a rotatable body 122 and may be integral with the rotatable body 122. Figure 8 The recess 123 of the rotatable body 122 is partially shown in

[0264] When the rotatable body 122 is in the second configuration as shown in Figure 8 wherein the rotatable body 122 closes the ink hole 171, the slot block 182 is partially received by the recess 123 of the rotatable body 122. When the rotatable body 122 is in the first configuration, wherein the ink path is defined to span across the rotatable body 122 and through the ink hole 171, the rotatable body 122 effectively rotates counterclockwise by approximately 90°, such that the slot block 182 is still partially received by the recess 123 but in a different orientation. This will be described in more detail in conjunction with Figure 10 and Figure 11 .

[0265] Now referring to Figure 9 , a schematic diagram of a fluid system for a Figure 1 printer is shown, the fluid system including a print head 3. The inkjet printer 1 includes an ink system 5 housed within the printer body 2. The ink system 5 includes at least components that form part of the main ink block 11. The ink system may also include a cartridge module 12 and a cleaning module 13. The components of the print head are schematically represented as 3.

[0266] Starting from the main ink block 11, the main ink block 11 includes a mixing tank 17 (which may also be referred to as an ink supply tank or an ink feeding tank), which is configured to supply ink along the main supply line 19. The ink is drawn out of the mixing tank 17 by an ink pump 21. The ink also passes through a first filter 23 disposed downstream of the ink pump 21 along the main supply line 19. The first filter 23 removes any particles (e.g., deposits) contained within the mixing tank 17. In the illustrated embodiment, the first filter 23 is a 100-micron filter, but it should be understood that filters of other sizes may be used in other ways. A Venturi line 24 is connected to the main supply line 19 downstream of the first filter 23. Disposed along the Venturi line 24 is a Venturi tube 24a (e.g., a restriction). In operation, a fluid (e.g., an ink mixture) continuously circulates from the mixing tank 17 through the main supply line 19, through the Venturi line 24, and thus through the Venturi tube 24a before returning to the mixing tank 17. This continuous circulation, in combination with the Venturi tube 24a, creates a suction force to draw the fluid into the mixing tank 17 via a refill line 25 that extends between the cartridge module 12 and the Venturi tube 24a. The fluid is drawn into the mixing tank 17 through the Venturi tube 24a and a downstream portion 24b of the Venturi line 24.

[0267] The ink pump 21 can be operated as a pressure control pump, which means that the ink flow rate through the pump 21 will be adapted as needed to maintain a target pressure downstream of the ink pump 21 (e.g., as monitored by a pressure sensor 33). The ink pump 21 can be configured to supply ink to the print head 3 at a predetermined system operating pressure, which can be determined based on the printer configuration (e.g., nozzle geometry). For example, a nozzle with a diameter of 75 μm may require a lower operating pressure than a nozzle with a diameter of 62 μm to achieve similar jetting performance (e.g., ink droplet breakup point, or breakup flight time). The system operating pressure can also vary according to other system parameters (e.g., ink type, viscosity).

[0268] A second filter 26 with a filtration size of 5 microns is provided downstream of the first filter 23 along the main supply line 19. A damper 27 is provided downstream of the ink pump 21 and downstream of the second filter 26 to reduce fluctuations in the ink pressure within the ink source. Downstream of the damper 27, a load line 28 branches off from the main supply line 19. The load line 28 includes a restriction 29. The load line 28 is configured to maintain a nearly constant load on the main supply line 19, thereby avoiding pressure spikes in the print head 3 due to load spikes of the ink pump 21 (e.g., due to activation of the ink pump 21). A viscometer valve 30 is provided along the load line 28. The viscometer valve 30 can selectively place the load line 28 in fluid communication with the mixing tank 17 or the viscometer 32 via a tank line 31. The default configuration of the viscometer valve 30 is to place the load line 28 in fluid communication with the mixing tank 17. This creates a circular fluid flow path. When it is desired to determine the viscosity of the ink mixture in the main supply line 19 and thus in the load line 28, the viscometer valve 30 is energized to direct the flow into the viscometer 32. Initially, the viscometer 32 is empty. By monitoring the time taken to fill and / or empty the viscometer 32 and based on the known volume of the fluid in the viscometer 32, the viscosity of the ink mixture can be determined.

[0269] Downstream of the damper 27 and the load line 28, a pressure sensor 33 is connected to the main supply line 19 and is configured to monitor the pressure downstream of the ink pump 21. The ink pump 21 can be operated as a constant pressure pump (i.e., the pump is controlled to maintain a constant output pressure). A third filter 34 with a filtration size of 15 microns is provided downstream of the pressure sensor 33.

[0270] The main supply line 19 is configured to deliver ink from the ink mixing tank 17 along the umbilical cable 4 to the print head 3. The main supply line 19 is connected to the print head 3 via a feed valve 35. The feed valve 35 is configured to control the ink supply to the print head 3. A heater 36 is provided downstream of the feed valve 35. The heater 36 is used to control the temperature of the ink mixture. Controlling the temperature of the ink mixture reduces the effect of temperature fluctuations on the viscosity of the ink mixture. For example, activation of the heater 36 provides a heating effect that reduces the viscosity of the ink mixture. A temperature sensor 37 is provided downstream of the heater 36. The heater 36 is arranged to be in fluid communication with the nozzle body 143 via a nozzle line 38 and thus with the nozzle 144. The heater 36 preferably maintains the ink mixture at a temperature of at least about 308°K (e.g., ~35°C).

[0271] As described above, ink is fed along the main supply line 19 to the print head 3 via the umbilical cable 4. Inside the print head 3, the ink is supplied to the nozzles 144. The ink is supplied to the nozzles 144 under pressure (under the influence of the ink pump 21) and forms an ink jet. The ink jet starts as a constant stream of ink and, under the influence of the surface tension and vibration (e.g., by a piezoelectric oscillator) applied in the nozzle body 143, gradually separates into a series of ink droplets 188, which continue to travel in the direction of the ink jet 57.

[0272] Shortly after emerging from the nozzles 144 of the nozzle body 143, the ink jet passes through a charging electrode ( Figure 9 not shown in Figure 3 but labeled 148 in Figure 9 not shown in Figure 3 but labeled 148 in

[0273] Thereafter, the stream of ink droplets 188 continues from the charging electrode through between additional electrodes ( Figure 9 not shown in Figure 3 but labeled 166, 168 in

[0274] The ink droplets that pass through the deflection field and are deflected by the electrodes are not shown in Figure 9 but labeled 190 in Figure 7 The stream of ink droplets 190 is used for printing. The stream of ink droplets 190 can be described as defining an ink path that passes through a rotatable body (of a sealing mechanism) and through an ink hole.

[0275] Return to Figure 9 Droplets of ink that pass through the deflection field without being deflected (i.e., droplets not used for printing) travel to trough 40 (e.g., trough block 182 of the previous figures). Trough 40 includes an orifice 183 (e.g., trough orifice 183 of the previous figures) through which the ink droplets enter. Trough 40 is connected to trough pipeline 42, which extends from trough 40 back to main ink block 11 (e.g., trough pipeline 42 extends between at least trough 40 and trough pump 46). Trough valve 44 is optionally provided within trough pipeline 42 such that trough pipeline 42 can be opened and closed. Suction is applied to trough pipeline 42 by trough pump 46 to suck ink back along the pipeline from trough 40 towards main ink block 11. In other embodiments, the suction can be provided by a venturi tube in communication with ink pump 21.

[0276] Tank valve 48 is provided downstream of trough pump 46. Tank valve 48 selectively places trough pump 46 in fluid communication with mixing tank 17 or solvent tank 50 (which can be described as a “used” solvent reservoir). In the illustrated embodiment, solvent tank 50 is provided adjacent to mixing tank 17. In the illustrated embodiment, solvent tank 40 and mixing tank 17 are shown as different compartments within an overall tank, but in other embodiments, mixing tank 17 and solvent tank 40 can be physically separate tanks. During a printing operation, tank valve 48 places trough pump 46 in fluid communication with mixing tank 17. The ink mixture received by trough 40 (e.g., a stream of ink droplets 188) thus returns to mixing tank 17 and can be recycled / reused at a later time. During non-printing operations (e.g., such as filling, cleaning operations, etc.), tank valve 48 can place trough pump 46 in fluid communication with solvent tank 50. This is to avoid undesired contamination of the ink mixture in mixing tank 17 by cleaning fluids (such as “used” solvent) (e.g., changing the viscosity of the ink mixture).

[0277] In addition to the unprinted ink droplets being recycled via the sump 40, any air that is drawn into the sump 40 will also be conveyed to the mixing tank 17 or the solvent tank 50. The mixing tank 17 and the solvent tank 50 communicate with each other via a condenser 52 (which also acts as a vent). The solvent in the ink mixture in the mixing tank 17 tends to evaporate as solvent vapor in the mixing tank 17. Saturated solvent vapor is thus present in the mixing tank 17 during use. When the vapor passes through the condenser 52, the relatively cold surface of the condenser 52 causes the solvent contained in the vapor to condense. Thus, the solvent vapor returns to the liquid and deposits back into the solvent tank 50. This advantageously avoids excessive loss of solvent from within the system (which would otherwise occur if both tanks were directly vented to the atmosphere). Additionally, the mixing tank 17 is effectively vented by the condenser 52, thereby preventing the build-up of excessive pressure within the mixing tank 17. The gas discharged from the mixing tank 17 thus travels into the solvent tank 50. In turn, the solvent tank 50 is vented by a solvent tank exhaust line 54 that is arranged to be in fluid communication with the solvent tank 50. Through the solvent tank exhaust line 54, the gas can be discharged, preferably to the outside of the printer cabinet (where the ink system is housed).

[0278] The ink system, particularly its cartridge module 12, includes a cartridge connector 56 that can be connected to an associated ink cartridge 8 and a solvent cartridge connector 58 that can be connected to an associated solvent cartridge 10. The cartridge connector 56 and the solvent cartridge connector 58 are connected to a refill line 25, thereby allowing ink or solvent to be suctioned into the mixing tank 17 through a Venturi line 24. In other embodiments, a dedicated transfer pump may be used instead of the Venturi line 24.

[0279] By using the Venturi tube in this way (i.e., as a jet pump), a system can be designed in which the main system ink pump 21 can generate both a positive pressure (e.g., to supply ink to the print head 3) and a negative vacuum pressure (e.g., to suction ink or solvent into the mixing tank 17 via the refill line 25).

[0280] A feed valve 27 arranged along the main supply line 19 is configured to prevent the main supply line 19 from remaining open continuously. However, since the feed valve 27 is arranged downstream of the Venturi line 24, even when the feed valve 27 is closed, when the ink pump 21 is operating, ink flow will pass through the Venturi tube 24a along the Venturi line 24, thereby causing suction to be applied to the refill line 25. In this way, suction can be applied even when ink is not being supplied to the print head 3. Of course, a second valve 61 can also be operated to block the refill line 25, which means that the refill line suction can be controlled independently of the Venturi tube 24a.

[0281] It should be understood that by selectively activating one or more of the four cartridge valves 60, 61, 62, 63, the ink cartridge 56 can be placed in fluid communication with the refill line 25. For example, only opening the first valve 60 and the second valve 61 (and closing the third valve 62 and the fourth valve 63) places the ink cartridge 8 in fluid communication with the refill line 25 via the ink refill line 59. Ink can thus be drawn into the mixing tank 17 via the ink refill line 59 and the refill line 25 to add ink to the mixing tank 17.

[0282] The solvent can be directed directly from the solvent cartridge 58 to the solvent tank 50 through the solvent refill line 64 and the solvent tank line 65. Closing the first valve 60 and the second valve 61 and opening the third valve 62 and the fourth valve 63 places the solvent cartridge 10 in fluid communication with the solvent tank 50 via the solvent tank line 65 and the solvent refill line 64. The solvent can also be withdrawn from the solvent tank 50, through the solvent tank line 65 and into the cleaning module inlet line 72 (which will be described below). A solvent tank refill line filter 66 is provided along the solvent tank refill line 64. A solvent pump 67 is provided along the solvent refill line 64 downstream of the solvent cartridge 10. Activation of the solvent pump 67 can be used to pump the solvent from the solvent cartridge 10 into the solvent tank 50. Advantageously, the amount of solvent added to the solvent tank 50 can be measured by determining the fluid level within the solvent tank 50. This volume can then be subtracted from the remaining solvent cartridge volume on the smart chip maintained on the solvent cartridge 10. Thus, the remaining volume of solvent in the solvent cartridge 10 can be determined. This has been found to be more accurate than measuring the volume of solvent withdrawn from the solvent cartridge 10 under negative pressure (since the vacuum level within the cartridge typically changes as the cartridge empties of fluid). In the illustrated embodiment, the solvent is pumped out of the solvent cartridge 10 by the action of the solvent pump 67.

[0283] When it is desired to add solvent to the mixing tank 17, the second valve 61 and the fourth valve 63 are opened, and the first valve 60 and the third valve 62 are closed. The solvent is then drawn from the solvent tank 50 into the mixing tank 17 through the venturi tube 24a via the solvent tank line 65 and the refill line 25.

[0284] Activation of the solvent pump 67 can also be used to pump solvent from the solvent cassette 10 along the solvent refill line 64 for some non-print operations, such as priming the fluid circuit. This will be described below. In the illustrated embodiment, the solvent pump 67 is not used to actively pump pressurized cleaning fluid (such as solvent) into the chamber 164 via the cleaning module inlet line 72 for cleaning. Instead, the cleaning fluid is preferably drawn into the chamber 164 under vacuum for cleaning. This provides fail-safe operation in the event that the sealing mechanism fails, as the cleaning fluid will not be drawn into the chamber 164. If the cleaning fluid is pumped into the chamber 164 under pressure (e.g., by an upstream pump), a failure of the sealing mechanism has the risk of the cleaning fluid being ejected from the printhead 3 (e.g., via the ink holes) onto the print line. This has the risk of unwanted contamination. That is, in some embodiments, the cleaning fluid can also be pumped into the chamber.

[0285] A check valve 68 is provided along the solvent refill line 64 downstream of the solvent pump 66 to prevent fluid from traveling past the check valve 68 towards the solvent pump 66. An additional check valve 69 is provided in a branch line that extends around the solvent pump 67. The check valve 69 is an overpressure valve for the solvent pump 67. The check valve 69 is a pressure relief valve that determines the maximum solvent pressure from the solvent pump 67. For completeness, the cassette valves 60-63 can also be selectively activated to provide other configurations for, e.g., priming of the fluid system and for discharging the mixing tank 17 and / or the solvent tank 50 (e.g., during maintenance).

[0286] A flush line 70 is connected between the third valve 62 and the check valve 68. The flush line 70 directly connects the cassette module 12 to the printhead 3 via the umbilical cable 4. A flush filter 71 is provided along the flush line 70 upstream of the cleaning module inlet line 72, which branches from the flush line 70. The flush line 70 extends to the printhead 3 via a flush valve 73 provided along the flush line 70. The flush line 70 is used to direct solvent from the solvent cassette 58 into the nozzle body 143. Solvent can thus be forced through the nozzle 144 to clean the nozzle. This is accomplished by activating the solvent pump 67, which supplies pressurized solvent to the nozzle 144 for nozzle cleaning. The flush valve 73 is normally closed (e.g., during print operations) and is only opened during non-print operations (e.g., priming). By selectively activating the valves in the cleaning module 13, solvent can be prevented from being pumped into the chamber 164 via the cleaning module inlet line 72. In other words, the cleaning module inlet line 72 can be effectively closed by selectively activating the valves in the cleaning module 13, such that the solvent flows through the flush line 70 to the flush valve 73.

[0287] The purge line 74 is connected to the nozzle body 143. The purge line 74 is connected to the purge port 74a of the nozzle body 143. The nozzle body 143 may be provided as part of a nozzle assembly that includes the nozzle body 143 and a piezoelectric oscillator having known acoustic properties. The purge port may be provided by the body or by a separate component connected to the body. The purge line 74 allows ink (and / or air and / or debris) to flow out (or pass through) the nozzle body 143 via the purge orifice 74a (e.g., the purge port) without passing through the nozzle 144 and allows the nozzle body 143 to be cleaned. The purge line 74 extends from the nozzle body 143 along the umbilical cable 4 and returns ink (or solvent) to the mixing tank 17 depending on the operating phase. The purge line 74 is arranged to be selectively in fluid communication with the sump pump 46 via the purge valve 75. Fluid is drawn through the purge line 74 by the suction of the downstream sump pump 46. The purge valve 75 is arranged along the purge line 74. It should be understood that the purge line is not essential and may be omitted in some printers. Incorporating the purge line 74 is advantageous for a variety of reasons. The purge line 74 can be used to remove air from the nozzle body 143 (e.g., from within the chamber of the nozzle body 143). Removing air from the nozzle body 143 is desirable because the presence of air can have a negative impact on the acoustic performance of the nozzle body 143. The purge line 74 can also be used to remove debris that may be trapped in the nozzle chamber when performing a backflush. A backflush is a process in which a solvent is applied to the front surface of the nozzle 144 while creating a vacuum in the nozzle body. The purge line 74 also allows ink to be removed / drained from the interior of the nozzle body 144 and more effectively purifies the interior of the nozzle body 144.

[0288] Accordingly, the main supply line 19, the purge line 74, the sump line 42, and the flushing line 70 connect the ink system (e.g., the main ink block 11 and the cartridge block 12) to the printhead 3. Additional fluid connections housed within the umbilical cable 4 may connect the ink system 5 to the printhead 3. For example, an air recirculation line may be provided to supply solvent-saturated air to the sump line 42 near the sump inlet.

[0289] The chamber 164 is also Figure 9 shown schematically. As Figure 9 shown, in the illustrated embodiment, the sump 40 is provided in the chamber 164. In the illustrated embodiment, the nozzle body 143 is external to the chamber 164. Two conduits 204, 214 are shown connected to the chamber 164. The first conduit 204 is also Figure 8is shown. The first conduit 204 is in fluid communication with the chamber 164 via the first port 206. The first port 206 is disposed near the charging electrode and the nozzle body 144 (e.g., at an upstream position within the chamber 164). The second conduit 214 is in fluid communication with the chamber 164 via the second port 202. The second port 202 is disposed near the groove 40 (e.g., Figure 6 the groove block 183 in). The second port 202 is disposed at a downstream position within the chamber 164. The first conduit 204 and the second conduit 214 and thus the first port 206 and the second port 202 can be used to supply cleaning fluid to the chamber 164 or to discharge the used cleaning fluid from the chamber 164. Each of the first conduit 204 and the second conduit 214 can be selectively opened / closed by the actuation of a corresponding valve of the cleaning module 13.

[0290] Figure 9 Also shown is a third conduit 216 that extends from the second conduit 214 to the nozzle body 143 and partially through the nozzle body 143. Thus, the third conduit 216 can be described as a branch of the second conduit 214. The third conduit 216 terminates at a third port 217. The third port 217 is defined in the front of the nozzle body 143. The third conduit 216 and the third port 217 are optional features of the illustrated embodiment and may be omitted in other embodiments. The third conduit 216 and the corresponding third port 217 are used to supply cleaning fluid to at least a portion of the charging electrode and the downstream chamber, or to discharge the used cleaning fluid from at least a portion of the charging electrode and the chamber 164. Since it is a branch of the second conduit 214, in the illustrated embodiment, the third conduit 216 is not controllable independently of the second conduit 214. In other words, in the illustrated embodiment, when the cleaning fluid is supplied through the second conduit 214, the cleaning fluid is ejected from the first port 206 (into the chamber 164) and the third port 217 (into at least a portion of the charging electrode). Similarly, in the case where the used cleaning fluid is discharged through the second conduit 214, the cleaning fluid is discharged from the chamber 164 (through the first port 206) and from at least a portion of the charging electrode (via the third port 217). In some orientations of the printhead 3 and the chamber 164 (e.g., vertically upward), the used cleaning fluid can be discharged through both the first port 206 and the third port 217. Advantageously, the first port 206 discharges fluid from the chamber 164, while the third port 217 discharges fluid from the charging electrode. Thus, the incorporation of the third port 217 avoids the accumulation of used cleaning fluid outside the chamber 164, which could otherwise undesirably increase the drying time of the printhead 3 after cleaning. However, in other embodiments, one or more valves can be incorporated along the second conduit 204 and / or the third conduit 216 to provide independent control.

[0291] The third port 217 can also be referred to as a charging electrode discharge port.

[0292] The components of the cleaning module 13 are now described, providing first to fourth control valves 80, 81, 82, 83. An air line 84 also extends at least partially through the cleaning module 13, where an air pump 85 is disposed along the air line 84. A pressure relief valve 86 is also disposed downstream of the air pump 85. The air line 84 is connected to the atmosphere and can be used to selectively supply air to the chamber 164. This can be used for positive pressure drying of the chamber 164 (e.g., after cleaning) or to provide an air supply into the chamber 164 during printing. This is to avoid creating an excessive negative pressure within the chamber 164 due to the suction of the sump pump 46 via the sump 40, otherwise the excessive negative pressure may cause debris to be drawn into the print head 3 from the print line. Advantageously, a single air pump 85 provides two functions.

[0293] Also shown is a downstream portion of the cleaning module inlet line 72, which for simplicity may be referred to as the inlet line 72. The break in the inlet line 72 between the left hand side of the figure (i.e., above the filter 71) and the right hand side of the figure (i.e., above the air pump 85) is simply included to improve the clarity of the figure and to avoid the line extending through the various other components of the fluid circuit. Also shown is the suction line 87. The suction line 87 extends via a portion of the sump line 42 to the sump pump 46. Thus, fluid can be drawn through the suction line 87 by the operation of the sump pump 46. For completeness, in the illustrated embodiment, the sump valve 87 also forms part of the cleaning module 13. However, in other embodiments, the sump valve 87 can form part of the main ink block 11.

[0294] The first control valve 80 can selectively place the first conduit 204 (via the second control valve 81) in fluid communication with the inlet line 72 or the air line 84. The other of the inlet line 72 and the air line 84 can be selectively closed by the first control valve 80.

[0295] The second control valve 81 can selectively place the first conduit 204 in fluid communication with the suction line 87 or the inlet line 72 (via the first control valve 80) or the air line 84 (via the first control valve 80). In Figure 9 the illustrated configuration, the second control valve 81 places the first conduit 204 in fluid communication with the suction line 87. Thus, activation of the sump pump 46 applies suction through the suction line 87 and through the first conduit 204. In this configuration, fluid will be drawn from the chamber 164 through the first conduit 204 and the suction line 84. In Figure 9 the illustrated configuration, the first conduit 204 is not arranged to be in fluid communication with either the inlet line 72 or the air line 84.

[0296] The third control valve 82 can selectively place the second conduit 214 in fluid communication with the suction line 87 or the inlet line 72 (via the fourth control valve 83) or the air line 84 (via the fourth control valve 83). In Figure 9 the configuration shown, the third control valve 82 places the second conduit 214 in fluid communication with the suction line 84. Accordingly, activation of the sump pump 46 applies suction through the suction line 87 and through the second conduit 214. In this configuration, fluid will be suctioned from the chamber 164 through the second conduit 214 and the suction line 87. In Figure 9 the configuration shown, the second conduit 214 is not arranged to be in fluid communication with either the inlet line 72 or the air line 84.

[0297] The fourth control valve 83 can selectively place the second conduit 214 (via the third control valve 82) in fluid communication with the inlet line 72 or the air line 84. The other of the inlet line 72 and the air line 84 can be selectively closed by the fourth control valve 83.

[0298] By the selective operation of the control valves 80 - 83, different conduits / ports can be placed in fluid communication with the inlet line 72, the air line 84, and the suction line 87. When connected to the inlet line 72, the cleaning fluid can be directed through the conduit / port into the chamber 164. When connected to the air line 84, air can be pumped by the air pump 85 through the conduit / port into the chamber 164. When connected to the suction line 87, fluid (e.g., used cleaning fluid) can be suctioned from the chamber 164 through the sump pump 46 through the conduit / port, through the suction line 87. The air line 84 can be used to pump air into the chamber 164 to dry the chamber 164 after the cleaning fluid has been drawn into and withdrawn from the chamber 164. The air line 84 can also be used to pump air into the print head 3 (e.g., into the chamber 164) to replenish the air removed from the chamber 164 under the action of the sump 40 (e.g., during a printing operation). This advantageously reduces the risk of the pressure inside the print head 3 dropping to a level where debris is drawn into the print head 3 from outside the print head 3.

[0299] In a preferred embodiment, one of the first conduit 204 and the second conduit 214 is placed in fluid communication with the inlet line 72, and the other of the first conduit 204 and the second conduit 214 is placed in fluid communication with the suction line 87. Activation of the sump pump 46 then draws the cleaning fluid through the inlet line 72 and into the chamber 164 via the conduit connected to the inlet line 72. Then, under the suction of the sump pump 46 via the suction line 87, the cleaning fluid is drawn back from the chamber 164 via the other conduit (e.g., the conduit of the first conduit 204 or the second conduit 214 that is not connected to the inlet line 72). Which port is the fill port and which port is the discharge port can be selected based on the orientation of the printhead 3 and the chamber 164.

[0300] In a preferred embodiment, the cleaning fluid remains / resides in the chamber 164 for a dwell time before being subsequently withdrawn / discharged. Air can be bubbled through the chamber 164 while the chamber 164 is at least partially filled with the cleaning fluid to agitate the cleaning fluid and remove debris within the chamber 164. The chamber 164 can be only partially filled with the cleaning fluid (e.g., about half full). The chamber 164 can be mostly filled with the cleaning fluid (e.g., at least about 80% of the volume of the chamber 164 is filled with the cleaning fluid).

[0301] Now refer to Figure 10 , which shows in detail an axial cross-section of adjacent portions of the charging electrode assembly 146 and the attached nozzle body 143. The charging electrode assembly 146 and the nozzle body 143 are coupled in a fixable manner.

[0302] Figure 10 A set of axes is provided in. The z-axis is substantially parallel to the direction 310 in which the jet and the droplets travel, also referred to as the ink travel axis. The z-axis is parallel to the central axis 301 of the charging electrode assembly 146, about which the charging electrode assembly 146 has a substantially circular symmetry. The x-axis and the y-axis are perpendicular to each other and are also both perpendicular to the z-axis.

[0303] The charging electrode assembly 146 includes a charging electrode 148 and an insulating coupler 150 (also referred to as the charging electrode coupler 150). In the illustrated embodiment, the charging electrode 148 and the insulating coupler 150 are rigidly coupled by threaded fasteners 147 and 149, but other arrangements are possible. The charging electrode 148 and the insulating coupler 150 squeeze a first washer or O-ring 318 against each other, which hydraulically seals their interface.

[0304] It should be understood that any material that is both conductive and resistant to ink contact (i.e., relatively chemically inert) is suitable for the construction of the charging electrode 148. For example, suitable materials include stainless steel, conductive plastics, aluminum alloys, or titanium. Notably, stainless steel is conductive and corrosion-resistant - moreover, manufacturing components from it (e.g., by injection molding) is simple and economical.

[0305] The charging electrode 148 includes a pair of rectangular planar glass windows 320 and a charging electrode body 322 that defines a closed channel 328 bounded by an internal channel surface 330. The closed channel 328 extends coaxially with the central axis 301 from an inlet hole 324 at a first end 323 of the charging electrode body 322 to a second, opposite end of the charging electrode body or a plug 329 that forms an outlet hole 325. The first end of the charging electrode body 323 abuts against the insulating coupler 150 via a first gasket 318.

[0306] The insulating coupler 150 abuts against the nozzle body 143 via flat mating surfaces on the two components. The nozzle body 143 and the insulating coupler 150 squeeze a second gasket 319 therebetween. The insulating coupler 150 is annular and defines an internal central channel 316 to receive a protruding portion 306 of the nozzle body 143 and to allow a jet of fluid from a nozzle 144 (also referred to as a jewel) that is rigidly coupled to the nozzle body 143 to pass through in one direction or along a trajectory into the closed channel 328. The nozzle 144 is held in a mating recess 308 of the nozzle body 143 by a retaining ring 334.

[0307] The second gasket 319 circumferentially contacts the protruding portion 306 of the nozzle body 143. In an alternative, the second gasket can be configured to circumferentially contact the insulating coupler 150 (i.e., by enlarging the second gasket), and this alternative is shown as 319a in Figure 10 which is shown as 319a.

[0308] It should also be understood that the insulating coupler 150 and / or the charging electrode body 322 may also include grooves or other features adapted to hold the alignment of the gaskets 318 or 319.

[0309] The plug 329 is disposed within and seals against a flexible charging electrode shroud 151. The nozzle 144 and the charging electrode assembly 146 can thus move relative to the chamber of a wider printhead (referred to as 164 in Figure 4 ).

[0310] The nozzle 144 is a planar element having a central orifice 332 that is in fluid communication with an upstream reservoir 333, which is a volume formed as an integral part of the nozzle body 143. In use, the ink in the volume is held at a pressure above ambient in order to eject ink from the orifice 332. Typically, the nozzle orifice 332 is centered on the central axis 301.

[0311] In use, the insulating coupler 150 insulates the (charged) charging electrode 148 from the nozzle body 143, which is normally held at ground potential. The charging electrode 148 is subject to a varying voltage (more details of which are provided below in connection with Figure 16 providing the electrical connection). Since the jet is split near the charged closed-channel surface 330, the charging electrode 148 can selectively induce a variable charge on the ink droplets by capacitive coupling, which is common in the operation of an electrostatic deflection continuous inkjet printer. The closed channel 328 has a first dimension in a first direction (x-axis) perpendicular to the travel axis and a second dimension different from the first dimension in a second direction (y-axis), the second direction being perpendicular to the first direction and the central axis 301. The second direction is parallel to the plane normal of the window 320. These first and second dimensions vary along the length of the closed channel 328, and thus the axial cross-section of the closed channel 328 varies along its z-axis direction.

[0312] Regarding the presently described embodiment, the cross-section of the charging electrode closed channel 328 is indicated by cross-sections A, B, C, and D in Figure 10 Cross-section D is substantially circular - its first and second dimensions being substantially similar. At cross-sections A and B, the first dimension of the closed channel is much larger than the second dimension (especially at cross-section B). Cross-section C is substantially a combination of cross-sections B and D.

[0313] Thus, the variable cross-section defines two regions of predominantly axial settings. A first region 327, substantially bounded by the inlet hole 324 and cross-section B, is configured to induce charge on the selected ink droplets by capacitive coupling at the jet splitting point 311. It should be noted that the actual point of the jet splitting point 311 can vary depending on environmental conditions and the inherent characteristics of the ink and the printer, among other factors. A second region 331, substantially bounded by cross-section B and the outlet hole 325, is configured to shield the charged ink droplets from external electromagnetic interference by enclosing the channel 328 for at least a portion of the travel axis 310. The first region 327 and the second region 331 are located on either side of the viewing hole 321 (although both also span at least a portion of the length of the viewing hole 321 in the direction of inkjet travel).

[0314] The first region 327 has a relatively small dimension between the adjacent closed-channel surface 330 and the (nominal) jet splitting point 311 to provide a reliable coupling between the charging electrode 148 and the inkjet without the need to apply an unduly high charging electrode voltage.

[0315] The second region 331, by virtue of its enclosed structure, blocks the high-voltage deflection electrode 168 (in Figure 5The direct line of sight to the jet splitting point 311 (best seen in [reference]) and other sources of electromagnetic interference. Therefore, the second region 331 does not need to be as small in size as the first region 327 in order to mitigate the adverse effects of electromagnetic interference on droplet formation and flight. By providing a larger size, an increased tolerance for jet misalignment can be allowed.

[0316] Additionally, by providing a closed channel 328 that does not have circular symmetry with respect to the central axis 301 (i.e., different dimensions in a direction perpendicular to the ink travel axis), a convenient mechanism for providing precise positioning between the charging electrode and the inkjet can be achieved. For example, the charging electrode can be rotated such that the inkjet is centered between the opposing channel walls - this will be described in detail with reference Figure 13A , Figure 13B and Figure 13C of this mechanism.

[0317] The nominal ink travel axis can also be referred to as the central printhead axis and refers to the expected direction in which the ink travels from the nozzle. However, manufacturing tolerances can result in a (small) misalignment (e.g., up to 1.5 degrees) between the inkjet direction 310 (i.e., the ink travel axis) and the central printhead axis. The components of the printhead (e.g., Figure 8 the nozzle body 143, the slot block 182, etc.) will be designed based on the central printhead axis or the nominal ink travel axis. However, the actual ink travel axis 310 can vary between printheads and may not be determined until the components of the printhead have been fully assembled.

[0318] The second region 331 that surrounds the channel 328 from the jet splitting point 311 to the exit hole 325 can primarily shield the droplets and, therefore, may not need to be so small in size. By providing a larger size, an increased tolerance for inkjet misalignment can be allowed.

[0319] In an example, the length of the first region 327 can be about 4 - 6 mm, and the length of the second region 331 can be about 5 - 7 mm (i.e., the dimension parallel to the central axis 301).

[0320] Figure 11 A perspective view showing the charging electrode assembly 146 and the nozzle body 143 from the side. The pair of windows 320 are arranged around the closed channel, which is disposed adjacent to the corresponding viewing holes 321. The pair of viewing holes 321 are defined by openings in the charging electrode body 322.

[0321] By providing the viewing holes 321, the jet splitting point 311 within the charging electrode 148 can be observed. The viewing holes 321 are closed by a pair of transparent windows 320, thereby allowing the closed channel 328 to remain sealed from the region outside the charging electrode while still allowing observation of the closed channel 328. In some alternative variations, the viewing holes 321 can remain unsealed.

[0322] Window 320 and viewing aperture 321 are substantially opposite each other to provide a direct optical path 340 that is substantially perpendicular to and passes through the central axis 301 of the enclosed passage 328. The pair of windows 320 is substantially rectangular.

[0323] By providing a pair of opposing viewing apertures 321, the jet breakup location can be observed through the charging electrode while providing (e.g., gated) external backlighting 388 (best seen in Figure 16 ) to enhance the clarity of imaging. The optical path 340 allows the jet breakup point 311 to be observed or inspected through an optical device, such as a camera (not shown).

[0324] Alternatively, backlighting can be provided directly in-situ by providing a light source, such as an LED, instead of the light source in window 320.

[0325] In one example, jet breakup can be more easily observed with a strobing LED backlight. The backlighting is highly advantageous because the composite image formed by the jet is contoured and thus easy to inspect. In the case where the LED strobing frequency closely matches an integer divisor of the jet breakup frequency, the resulting image has the effect of a distinct static image showing the jet breakup (see stroboscopic imaging). This makes the inspection of the jet breakup geometry much easier. For example, this technique can be used to accurately determine the exact location where the jet breaks up into droplets.

[0326] Preferably, the backlighting will be provided by one or more red LEDs because the CCD sensors of many cameras used for imaging are more sensitive to red visible light.

[0327] Figure 12 The insulating coupler 150 and nozzle body 143 are shown from different angles. For clarity, the wider charging electrode assembly 146 has been omitted, but its connection to the insulating coupler 150 is readily understood by reference Figure 10 is easily understood.

[0328] The insulating coupler 150 has a substantially annular geometry; the annular cross-section is substantially similar to a "step", defining a hole with a radially protruding flange 342. The flange 342 integrally defines three enclosed axially concentric guiding surfaces 346 through a rotationally symmetrically arranged semi-annular slot 347. Note that the term semi-annular here can denote any annular profile facing an angle less than 360°.

[0329] The central channel 320 of the insulating coupler 150 receives a complementary nozzle body protrusion 306 (in Figure 10is best shown). Due to the complementary circular symmetric geometries of the central channel 316 and the nozzle protrusion 306, which are similar to a journal (guiding surface) and a bearing (guiding element), only a rotational relative movement about the central axis 301 can occur.

[0330] The charging electrode assembly 146 is coupled to the nozzle body 143 by a pair of bolts (or more generally, guiding elements) 344 that pass through two of three closed semi-circular slots 347 in the insulating coupling 150 and are received in corresponding threaded holes in the nozzle body 143. The pair of bolts 344 are 180 degrees apart from each other such that their axes lie on a common line. In the presently described embodiment, the axially concentric guiding surfaces 346 and / or the semi-circular slots 347 face an angle of approximately 90 degrees but less than 120 degrees.

[0331] The above-described coupling arrangement between the charging electrode assembly 146 and the nozzle body 143 facilitates two coupling configurations: an adjustment configuration and a fixed configuration.

[0332] In the adjustment configuration, the bolts 344 are loosened. In this way, the insulating coupling 150 and, by extension, the wider charging electrode assembly 146 can be rotated coaxially to perform the adjustment. The sliding contact of the guiding surfaces 346 with their corresponding bolts 344 (and the central channel 316 and the nozzle body protrusion 306, as Figure 10 best shown therein) facilitates rotation but interferes with any translational movement.

[0333] After adjusting the rotational position of the charging electrode assembly 146 as needed, the adjustment can be made permanent by changing the mounting means to the fixed configuration. In the fixed configuration, the bolts 344 are tightened so as to apply a clamping force between the charging electrode assembly 146 and the nozzle body 143. The above-described clamping force prevents any relative movement between the charging electrode assembly 146 and the nozzle 144. The lack of such relative movement means that the adjustment of the orientation of the nozzle 144 and the charging electrode 148 (and thus the ejection direction 310) occurs in a coordinated manner.

[0334] In this way, the adjustment can be made during manufacturing, assembly, repair, or calibration operations and then the adjusted charging electrode configuration can be fixed for subsequent use during printing operations.

[0335] As described above, manufacturing tolerances in an inkjet nozzle such as nozzle 144 can result in misalignment of the inkjet. This can be accommodated by adjusting the relative position between the slot configured to capture the unprinted ink droplets and the nozzle. However, any jet misalignment can result in imperfect alignment between the inkjet (and the ink droplet, once separated from the inkjet) and the charging electrode. This can have various adverse effects on print quality, including, for example, distortion of the amount of charge induced on the droplet, interference with the droplet direction, and even in severe cases, a collision between the droplet and the charging electrode, which is also referred to as "shearing".

[0336] By providing mounting means (e.g., the arrangement described with reference to Figure 12 which couple the charging electrode to the nozzle, while also allowing adjustment of the charging electrode position, the effects of any jet misalignment can be mitigated. That is, by mounting the charging electrode 148 to the nozzle 144 via the nozzle body 143 (rather than, for example, to the printhead platform), any movement or adjustment of the nozzle 144 (e.g., to ensure alignment of the inkjet with the slot) will also cause a corresponding movement of the charging electrode 148.

[0337] The geometry of the concentric guiding surfaces 346 through which the bolts 344 pass allows the insulating coupling 150 (and by extension, the wider charging electrode assembly 146) to rotate relative to the nozzle body 143 through any rotational alignment angle and be fixed by tightening the bolts 344 while maintaining their coaxial alignment. It should be understood that in order to achieve the full range of rotational alignment, it may be necessary to completely remove the bolts 344 and rotate the charging electrode assembly 146 by 180 degrees so that the bolts 344 can be aligned with different slots 347.

[0338] By providing three guiding surfaces 346 each allowing a 90-degree range of rotation, jet misalignment in many directions can be compensated for.

[0339] By providing a degree of rotation of 180 degrees or greater, the charging electrode 148 can be aligned with all possible jet misalignments due to the second-order rotational symmetry of the closed channel 328 about the central axis 301.

[0340] In an alternative embodiment, a degree of rotation of 180 degrees or greater can be provided by varying the number and / or the geometry of the slots, bolts.

[0341] In Figure 18AA variant arrangement is schematically shown in FIG. 0, which includes a main (semicircular) slot 512, a secondary (semicircular) slot 514, two bolts (omitted for clarity), and three threaded holes 516a, 516b, 516c. The slots have unequal extents, with the larger main slot 512 subtending an angle of at least 180 degrees. Two of the threaded holes 516a and 516b are disposed substantially opposite the third threaded hole 516c so that the two bolts can be fixed in any rotational orientation even when one of the threaded holes is blocked by the insulating coupling 150 ( Figure 18B as shown).

[0342] Another variant arrangement includes three identical slots spaced 120 degrees apart around an insulating coupling flange, three threaded holes spaced 120 degrees apart in the nozzle body, and three corresponding bolts. To allow for an effective 180-degree rotation range, the slots must subtend at least 60 degrees. The structural integrity of the insulating coupling means that the slots must subtend less than 120 degrees. In the adjusted configuration, the interaction of the bolts and slots limits rotation, but removal of the bolts allows the slots to be aligned with different threaded holes, thereby allowing another set of rotational positions, for a total of three.

[0343] The nozzle body 143 also includes a nozzle adjustment mechanism, as shown in two different views in Figure 13A , 13B and 13C, which is configured to allow adjustment of the orientation of the nozzle 144 (not visible in Figure 13A , 13B and 13C) relative to the slot to compensate for misalignment of the inkjet with the slot (i.e., alignment of the ejection travel direction 310 with the central printhead / nominal ink travel axis).

[0344] The nozzle body 143 can be tilted or rotated about first and second mutually orthogonal tilt axes (designated 357 and 369, respectively) that are parallel to the x-axis and y-axis, respectively, i.e., they are perpendicular to the central axis 301 and the z-axis. This tilting or rotation is achieved by a first tilt axis mechanism and a second tilt axis mechanism.

[0345] The first tilt axis 357 adjustment mechanism (best shown in Figure 13A and 13B ) includes a first adjustment screw 348 rigidly coupled to an eccentric circular first cam 350, a first nozzle bracket 352 that defines a first cam surface 354, a first pivot axis or first pivot 356, and a first locking screw 358. The first nozzle bracket 352 can be the same component as the nozzle bracket labeled 142 with respect to Figure 3 above.

[0346] The first pivot 356 pivotally couples the first nozzle carriage 352 to the wider printhead. The first cam 350 abuts against the corresponding first cam surface 354. The first adjustment screw 348 and the locking screw 358 are also pivotally coupled to the wider printhead. The first adjustment screw 348, the first locking screw 358, and the first pivot 356 are mounted in alignment with the central axis 301 and have parallel axes of rotation.

[0347] The first cam surface 354 includes a recess in the first nozzle carriage 352 sized such that the circular first cam 350 can be seated therein with its circumference making partial contact with the edge of the recess 355.

[0348] The first tilt axis 357 (best shown in Figure 13B ) is defined by the pivot 356 and is coaxial with the pivot 356.

[0349] The first cam 350 causes rotation about the first tilt axis 357: due to the eccentric geometry of the first cam 350, rotating the first cam 350 causes displacement of the first adjustment screw 348 relative to the first nozzle carriage 352. The displacement of the first nozzle carriage 352 relative to the wider printhead under the constraint of the first pivot 356 results in rotation of the first nozzle carriage 352 about the first tilt axis 357. The degree of the aforementioned rotation or tilt is determined by the degree of rotation of the first adjustment screw 348 and by the extent of the first cam 350.

[0350] Referring to Figure 13B and Figure 13C the second tilt axis adjustment mechanism will be described. Figure 13C From the same perspective as Figure 13B the aforementioned adjustment mechanism is shown (as indicated by the provided axes). However, the first nozzle carriage 352 is omitted for a better view of the second tilt axis adjustment mechanism.

[0351] The second tilt axis adjustment mechanism includes a second adjustment screw 360 rigidly connected to an eccentric circular second cam 362, a second nozzle carriage 364 defining a second cam surface 366, a second pivot shaft or second pivot 356, and a second locking screw 370.

[0352] The second nozzle carriage is rigidly coupled to the nozzle body 143, with the first nozzle carriage 352 adjacent to and wrapped around it.

[0353] The second pivot 368 pivotally couples the second nozzle carriage 364 to the first nozzle carriage 352. The second cam 350 abuts against a corresponding second cam surface 366. The second adjustment screw 360 and the locking screw 370 are pivotally coupled to the second nozzle carriage 364: they are partially restricted in corresponding holes 371 in the first nozzle carriage 352. The second adjustment screw 360, the second locking screw 370, and the second pivot shaft 368 are mounted in alignment with the central axis 301 and have parallel axes of rotation.

[0354] The second cam surface 366 includes a recess in the second nozzle carriage 364 sized such that the circular eccentric second cam 362 can be seated in the recess.

[0355] The second tilt axis 369 (best shown in Figure 13A ) is defined by the second pivot shaft 368 and is coaxial with the second pivot shaft 368.

[0356] As closely mechanically analogous to the first tilt axis adjustment mechanism, the rotational displacement is also achieved by a very similar device - rotation of the second adjustment screw 360 causes the second nozzle carriage 364 to tilt under cam pressure from the second cam 362 and, via the extension nozzle body 143, about the second tilt axis 369. Since the second nozzle carriage 364 itself undergoes tilting about the first tilt axis 357, the nozzle body 143 itself can undergo tilting about both the tilt axes 357 and 369 to allow for full adjustment of the nozzle 144 orientation.

[0357] Any adjustment obtained in the above manner can be fixed by tightening the first locking screw 348 and the second locking screw 370, which apply clamping forces on the first nozzle carriage 352 and the second nozzle carriage 364 respectively by means of their threads.

[0358] Now briefly referring to Figure 16 , Figure 16 shows a cross-section of a print head to which nozzle adjustment has been applied. To maintain electrical connection, the charging electrode 148 is electrically connected by a spring-loaded pin 382, also known as a spring pin, which is mechanically coupled to the wider print head and electrically connected to the printer controller 6 as Figure 1as shown) and a charging electrode 148. The spring-loaded pin 382 includes a follower contact 384 that is held captive within a cylindrical bore body 386 under expanding spring pressure from an internal spring (not shown). Thus, the spring-loaded contact can axially contract and expand against the outside of the charging electrode 148, thereby complying during adjustment while remaining conductive. Accordingly, during the entire adjustment of the charging electrode orientation, the follower contact 382 maintains a constant mechanical pressure on the charging electrode 148 and thus maintains electrical contact with the charging electrode 148.

[0359] In an alternative embodiment, the charging electrode 148 can also be connected (as Figure 1 shown) to the printer controller 6 by direct bonding (e.g., welding) or a clamped compliant connection (e.g., via a flexible wire).

[0360] Figure 14A shows a transverse cross-section 372 of the charging electrode channel near point B of the embodiment described with reference to Figure 10 Here, the cross-section represents a plane perpendicular to the central axis 301, as described with reference to Figure 10 , 11 and 12.

[0361] The enclosed channel 328 has a "slot-like" cross-section, i.e., there is a minor (x) dimension 374 and a major (y) dimension 376. There is a plane of central symmetry parallel to the YZ plane 378. The smaller dimension allows for a close proximity between the incoming jet 380 and the charged enclosed channel surface 330, thereby enhancing the capacitive coupling between the enclosed channel surface 330 and any nascent droplets formed at the jet splitting point 311 (best shown in Figure 10 ).

[0362] Under ideal operating conditions, the direction of the enclosed channel 328 and the jet 380 produced by the nozzle are perfectly coaxial, as Figure 14A shown. Thus, the jet direction 380 traverses the plane of central symmetry 378. Briefly returning to reference Figure 10 , this perfect coaxial alignment would mean that the central axis 301 would be aligned with the direction of jet and droplet travel 310.

[0363] In practice, due to manufacturing tolerances or imperfect assembly, the jet direction 310 (shown in Figure 10 ) is typically not coaxial with the central axis 301. The jet can exhibit a trajectory that is significantly skewed with respect to the central axis 301. This misalignment can be due to the adjustment of the nozzle body 143. The misalignment of the jet can result in undesirable lateral forces and, in extreme cases, jamming.

[0364] This situation is shown in Figure 14B .Figure 14B A front view and a top view of a misaligned jet 380 within a closed channel 328 are shown. Due to the misalignment, the jet 380 is not coplanar with and / or does not cross the central symmetry plane 378.

[0365] The relatively large range of the major dimension 376 of the closed channel 328 means that a jet having a large y-component in its trajectory can pass through the charging electrode 148 without pinching the closed channel surface 330. However, due to the restricted minor dimension 374 of the closed channel 328, a jet having a significant x-component will pinch the closed channel surface 330.

[0366] By providing a charging electrode channel having a slot-like shape, a tight separation can be provided between the channel surface 330 and the ink jet at the ink splitting point (due to the smaller minor dimension 374), and a certain degree of insensitivity to jet misalignment can be provided (due to the larger major dimension 376). Rotation of the charging electrode assembly 146 allows the smaller dimension separation to be oriented such that the distance between the closed channel surface 330 and the ink jets on each side is substantially the same (i.e., the jet 380 crosses the central symmetry plane 378), thereby facilitating uniform charging and avoiding unnecessary droplet deformation and deflection. On the other hand, the larger dimension can be aligned with the central symmetry plane 378 and the central axis 301 by means of rotation of the charging electrode assembly 146, as shown by the comparison in Figure 14B and 14C . Figure 14C The result of such adjustment is shown.

[0367] The presently described embodiments can be implemented in various sizes. For example, the first (minor) dimension of the closed channel 328 can be between 0.5 - 1 mm; and the second (major) dimension of the closed channel 328 can be about 1 - 5 mm. The first dimension can be between about 0.7 mm and 0.8 mm. The second dimension can be between about 1.2 mm and about 1.5 mm.

[0368] Returning to Figure 10 , the charging electrode cover 151, the first gasket 318, and the second gasket 319 define a substantially hydraulically sealed volume including the closed channel 328.

[0369] The above-mentioned hydraulically sealed volume is in fluid communication with the chamber of the wider print head (referred to as 164 in Figure 4 ). The first and second gaskets (318, 319) seal the conduit between the nozzle 314 and the closed channel 328 through which ink is ejected during print head operation and on which unwanted ink deposits may form.

[0370] The sheath 151 is a compliant sealing element that seals the outer surface of the charging electrode 326 and the chamber 164 of the wider printhead from each other, while allowing a degree of relative movement between the charging electrode assembly 146, the nozzle body 143, and the printhead chamber. In one example, the sheath 151 can be an O-ring or a corrugated elastomeric gasket. In this way, the charging electrode 148 (and possibly the attached nozzle 144) can be adjusted without also moving the wider printhead 3 (as seen in Figure 1 , Figure 2 and elsewhere) and maintaining the required hydraulic seal.

[0371] As described with reference to Figures 2 - 9 , the presently described printhead has a printing configuration and a cleaning configuration, in which the ink holes 106 are open (best shown in Figure 2 ), and in the cleaning configuration, the ink holes 106 are closed. In the cleaning configuration, the printhead defines a closed cleaning chamber that is defined by the closed channel 328, the nozzle 144, and the chamber 164.

[0372] In this way, the closed cleaning chamber defined within the printhead 3 is configured such that a cleaning fluid can be pumped therein to flood the closed cleaning chamber. Any ink deposits are then dissolved, and the cleaning fluid is drained to remove any ink deposits, thereby allowing the closed channels of the charging electrode 328 and the surfaces of the deflection electrodes 168 (best shown in Figure 5 ) to be cleaned. These operations are described in more detail above with reference to Figure 9 .

[0373] Advantageously, defining a closed cleaning chamber within the printhead 3 that includes the hydraulic seals of the nozzle 144, the closed channel 328, and the chamber 164 can minimize the volume flooded during cleaning. Since the components outside the cleaning chamber are not exposed to ink during the printing operation, excessive cleaning fluid is not required to clean them.

[0374] In addition, the hydraulic sealing nature of the aforementioned closed cleaning chamber prevents the leakage of hazardous cleaning fluids from the printhead 3, thereby making self-cleaning a safer, more convenient, and more inclusive process than previous methods.

[0375] The charging electrode discharge port 217 facilitates the entry or exit of fluid (i.e., discharge and filling) into the aforementioned internal volume, as best shown in Figure 17 , which makes the insulating coupling 150 translucent to better show the discharge port 217. The charging electrode discharge port 217 is located in the nozzle body 143 and leads to a recess for the second gasket 319, as shown in Figure 10As best shown. The charging electrode discharge port 217 can also supply air to assist in the discharge or drying of the printhead. The discharge port 217 is in fluid communication with the above internal volume via a set of six bypass channels 343, which are radially arranged around the insulating coupling member central channel 316. It should be understood that the bypass channels can be completely or partially blocked by the second gasket 319, and thus the alternative gasket configuration 319a described with respect to Figure 10 can be used.

[0376] Depending on the cleaning configuration selected by the user, the charging electrode discharge port 217 can be a discharge port or a filling port.

[0377] It should be understood that the present invention has been described by way of example only. Those skilled in the art will understand that various modifications are possible, such as changes in construction, scale, and / or geometric configuration without materially changing the function of such a device.

[0378] In the embodiment described above with reference to Figures 10 - 14B the window 320 is a discrete glass component fixed to the conductive charge electrode body. A possible alternative is to form them as a transparent plastic overmolded on the underlying conductive metal structure.

[0379] The charging electrode can include a transparent body. It should be understood that 100% transparency is not required, but sufficient transparency to allow observation of the jet breakup point.

[0380] It should be understood that the transparency requirements (or lack thereof) detailed above can refer to either or both of the properties of light transmission and / or scattering and the coverage area of the transparent material.

[0381] The charging electrode can include a transparent and conductive charging electrode body. The charging electrode can include a transparent and conductive charging electrode body or a transparent and non-conductive charging electrode body with a transparent conductive coating. For example, a single-piece non-conductive transparent plastic molded part with a sputtered indium tin oxide (ITO) conductive coating on the channel surface. Such a structure will allow 360° visibility of the internal enclosed channel while still being conductive to allow selective charging of the droplets.

[0382] Alternative embodiments can be limited not only to material or manufacturing variations, but also to the configuration of the charging electrode itself.

[0383] For example, in some embodiments, the mounting device described herein can be applied to a charging electrode assembly, where the enclosed channel is not completely enclosed. A gap, orifice, or opening can be provided in addition to the inlet and outlet holes. Thus, "enclosing" is not intended to mean enclosing completely or thoroughly. Instead, the channel is enclosed or surrounded to some extent to allow charging of the ink droplets by capacitive coupling. In such an arrangement, alternative cleaning arrangements to those described in detail above can be provided. For example, the printhead housing can define a cleaning chamber within which the charging electrode is fully accommodated for cleaning. Alternatively, any additional openings can be sealed by a suitably configured sealing mechanism for cleaning. In another alternative, such a printhead can be inserted into a separate cleaning device for cleaning. Thus, it should be understood that the charging electrode assembly and mounting device described herein are not limited to a fully sealed assembly where a fluid seal is formed on the one hand between the charging electrode and the nozzle and on the other hand between the charging electrode and the printhead body.

[0384] As Figure 15 shown, in another alternative charging electrode embodiment 500, there is an enclosed channel 501. The geometry of the charging electrode enclosed channel 501 can be a rotational volume with a central hole axis 504. The rotational volume includes a first small and narrow parallel section 506. The narrow parallel section 506 can be joined to a diverging second conical section 508, which is oriented such that a jet enters through the first section 506 and exits from the second section along the hole axis. If the jet intersects the hole axis at the first narrow section, this geometry can tolerate a large angular misalignment due to the relatively large conical section 508 (see jet 510). Due to the small size of the first part 506 and the resulting proximity to the ink jet 510, the first part 506 is configured to provide a reliable coupling between the charging electrode 500 and the nascent droplet.

[0385] It should be understood that various diverging geometries can also provide an equivalent function to the second conical part 506. The radius of the second section can have any monotonic or non-monotonic increasing relationship with the central hole axis.

[0386] The charging electrode embodiment 500 can advantageously be made at least partially of a conductive material. In one example, it can consist essentially of a transparent conductive plastic, thus facilitating charge induction on the nascent droplet by capacitive coupling as well as visual observation of the jet. Alternatively, the narrow parallel section 506 can be formed of a narrow conductive tube with an observation hole (e.g., stainless steel or any other metal), which can be press-fitted into a wider plastic body.

[0387] Generally, although Figures 10 - 14BThe embodiments specify the use of the semi-circular slot 347 and the bolt 318 to serve as the guiding surface and element respectively. However, alternative arrangements to achieve equivalent effects are also possible. For example, the guiding pin can be an alternative guiding element instead of the above-mentioned bolt. In another example, a system of mechanical mating lugs on the nozzle body and recessed tracks on the insulating coupler will respectively achieve the functions of the guiding element and the surface.

[0388] It should be noted that alternative example guiding surface and guiding element arrangements will require separate mechanisms (e.g., additional threaded fasteners) to fix the arrangement after adjustment.

[0389] In Figures 10 - 14B the embodiment, the semi-circular slot 347 is defined by the flange 342 of the insulating coupler 150. Alternatively, an equivalent semi-circular slot can also be provided in the flange on the charging electrode itself, and then the corresponding bolt can pass through the slot into the corresponding threaded hole in the nozzle body, thus bypassing the insulating coupling. It should be understood that in order to maintain the electrical isolation between the charging electrode and the nozzle body, the bolt and / or the groove will need to be insulated.

[0390] In another alternative guiding surface and element arrangement, the charging electrode can be captured in an annular "ferrule" coupled to the nozzle body. The ferrule shoulder is configured to clamp the charging electrode as needed, for example, by mating with the external threads on the nozzle body. Hereinafter, such an embodiment will be described.

[0391] Turning to Figure 19 , a perspective view of a print head 800 according to another embodiment is provided. For completeness, the print head 800 shares various common features with the print head 3 shown in Figures 2 to 8 and only the differences relative to the print head 3 will be described in detail. The print head 800 can also be used in the printer 1 of Figure 1 and the fluid system shown in Figure 9 . Similarly, the description provided in conjunction with Figures 10 to 1 8 is also applicable to the print head 800 where appropriate. The print head 800 is thus also a self-cleaning print head.

[0392] At a first end 802, the printhead 800 includes a connector 804 through which the printhead 800 can be connected to an umbilical cable. At a second end 806 of the printhead 800, an end cap 808 is provided. There are many differences between the end cap 808 of the printhead 800 and the previous embodiments, which will be described in detail below. The printhead 800 includes a single ink orifice 810, however, the ink orifice 810 through which the ink deflected during operation is ejected is still defined as passing through the end cap 808. The housing 812 is generally cylindrical and extends along most of the printhead 800. A seal cap 814 extends adjacent to the housing 812, near the second end 806 of the printhead, and extends around and slightly beyond the end cap 808. The combination of the housing 812 and the seal cap 814 defines an outer cover of the printhead 800, which is removable for maintenance.

[0393] Go to Figure 20 , a perspective view of the printhead 800 is provided, in which the housing 812 is omitted. By comparing Figure 20 with Figure 3 , it can be understood that there are various similarities between the printhead 800 and the printhead 3. Again, only the differences will be described in detail.

[0394] Briefly, the printhead 800 includes a chassis 816 to which various other components are mounted. A motor 817 (a brushless DC motor in this embodiment) is also mounted to the chassis 816. A solenoid valve 818 and a valve block 820 are also mounted to the chassis 816. A chamber housing 822 is connected to the chassis 816 and is coupled to a sealing mechanism 824 at the other end, and the sealing mechanism 824 is actuated by the motor 817. The sealing mechanism 824 can be described as an example of a cover assembly. Other examples of cover assemblies may not be sealing mechanisms. For example, a non-self-cleaning printhead may include a cover assembly but does not use a sealing mechanism.

[0395] By comparing Figure 20 with Figure 5 , one difference between the printhead 800 and the printhead 3 can be observed. Different from the printhead 3, in the printhead 800, the chamber housing 822 is connected to the chassis 816 and the sealing mechanism 824. That is, by using a single chamber housing 822, multiple housing components are eliminated. In addition, by removing four fasteners (two of which are visible in Figure 20 and are respectively labeled 826, 828), the chamber housing 822 can be separated from the chassis 816 and removed from the chassis 816. This is advantageous for at least the following reasons: various components that may be of concern for maintenance are mounted to the chamber housing 822. These components can also be easily disassembled from the chassis 816 for easy maintenance.

[0396] In Figure 21 , there is provided Figure 20Axial cross-section of the printhead 800 in the shown configuration (i.e., where the outer housing is received). This cross-section is taken with respect to Figure 20 the plane 859 schematically indicated in

[0397] As in the previous embodiment, the deflection electrodes 840, 842 are disposed in the chamber 856. By sealing the chamber 856 and at least partially filling the chamber 856 with a cleaning fluid, these components can be cleaned. Other components that can be cleaned as part of a cleaning cycle include the groove 844 and the rotatable body 868.

[0398] A first portion 856a of the chamber 856 is defined by the chamber outer housing 822. A second portion 856b of the chamber 856 is defined by the housing 870. The housing 870 forms part of the sealing mechanism 824. Relative to the housing 870, the rotatable body 864 can rotate to selectively seal the chamber 856 (e.g., by closing the ink hole defined by the housing 870). The end cap 808 is shown disposed above the housing 870. This will be described in detail in connection with the following figures. The rotatable body 868 is actuated by the shaft 846 via the socket 850 and the transmission generally labeled 872.

[0399] The groove 844 is visible in Figure 21 and is disposed downstream of the pair of deflection electrodes. Notably, the groove 844 is not connected to the sealing mechanism 824. Thus, the sealing mechanism 824 can be removed while leaving the groove 844 in place. In other words, the groove 844 has a fixed spatial relationship with the chamber outer housing 822.

[0400] The printhead 800 also includes a nozzle assembly 834 and a charging electrode assembly 848. The charging electrode assembly 848 includes a charging electrode 860 and a mounting device. The nozzle assembly 834 includes a single nozzle 858 and a single nozzle body 832. The charging electrode assembly 838 and the nozzle assembly 834 are axially coupled together by the mounting device. The nozzle assembly 834 also includes a nozzle carriage 830 to which the nozzle body 832 is coupled.

[0401] The charging electrode assembly 848 is pivotally connected to the wider printhead, particularly the chamber outer housing 822, by a ball-and-socket (or ball joint) arrangement that will be discussed in more detail below. The nozzle carriage 830 is engaged by two screws 896, one of which is visible in Figure 21 Advancing each screw 896 causes the nozzle body 832 to pivot in one direction, and selectively adjusting each screw 896 helps to precisely control the orientation of the nozzle body 832.

[0402] It should be understood that the slot is rigidly coupled to the charging electrode mount by a single component (the chamber outer shell 822). By reducing the number of connections between the slot 844 and the nozzle 858, the likelihood that the nozzle 858 becomes misaligned with the slot 844 (e.g., during the service life of the printhead 800) is reduced. In an alternative, the chamber outer shell may include multiple component parts, but the slot may be rigidly coupled to the charging electrode mount by a single component part.

[0403] In Figure 22 is an axial cross-sectional view of the charging electrode assembly 848 and surrounding components (such as the chamber outer shell 822). Figure 22 Combined structural details of adjacent portions of the charging electrode assembly 848 and the nozzle assembly 834 in situ within the printhead 800 are shown. The charging electrode assembly 848 includes a charging electrode 860 and a charging electrode coupler 862.

[0404] The charging electrode 860 (shown in detail in Figure 25 ) defines a channel 861 for charging the ink droplets. The charging electrode 860 has a geometry and function comparable to that of the charging electrode 148 of the printhead 3 described with reference to Figure 10 and Figure 11 In other words, the charging electrode channel 861 has a narrow non-circular cross-section, and in particular, its cross-section may correspond to some or all of the cross-sections A - D of the charging electrode 148 of Figure 10 . In contrast to its outer geometry which is substantially a rotational volume. The charging electrode also includes a pair of viewing holes 898 for visually inspecting the jet splitting of the inkjet.

[0405] The charging electrode may be formed of any conductive material, such as stainless steel.

[0406] The mounting means includes a charging electrode coupler (or couplers) 862 and a clamping nut 864. The charging electrode coupler (or couplers) 862 is configured to couple the charging electrode 860, and the clamping nut 864 is configured to hold the charging electrode coupler against the nozzle body 832.

[0407] The coupler 862 is an axially symmetric component (the features of which are best shown in Figure 24 , Figure 24is a cutaway perspective view of the coupler), which has a first cylindrical socket 875a at its first end to receive the charging electrode 860 via a press fit, and a second cylindrical socket 875b at its second end to receive the cylindrical protrusion 877 of the nozzle body 832 (which supports the nozzle 858 and is held by the retaining ring 839), thus forming a cylindrical interface. The outer surface 876 of the second end (which itself forms a cylindrical protrusion) is received by the cylindrical nozzle body socket 878 concentrically disposed around the protrusion 877, forming another cylindrical interface. The concentric cylindrical interface between the coupler 862 and the nozzle body 832 allows the coupler to rotate, and by extension, allows the charging electrode 860 and the nozzle body 832 to rotate relative to each other about the nominal axis of ink travel 801. The mounting means is configured to allow the charging electrode 860 to rotate relative to the nozzle 858 to an infinite extent. This allows the charging electrode 860 to be misaligned with any ink jet and aligned in a manner similar to the way described in Figure 14A -C. The coupler 862 also includes a flange 880 disposed between the first end and the second end.

[0408] To electrically isolate the charging electrode 860 and the nozzle assembly 834 (best shown in Figure 21 ), the coupler 862 can be substantially made of an electrically insulating material. Additionally, to allow visual inspection of ink jet breakup via a pair of viewing holes 898, the coupler 862 can also be transparent. In an example, the coupler 862 can be substantially formed of transparent plastic and / or glass.

[0409] In some embodiments, the viewing holes can be covered by a transparent glass or sapphire tube fitted over at least a portion of the charging electrode, thus providing a transparent window for viewing ink jet breakup. The combined charging electrode and transparent tube can be assembled into the coupler mechanically or adhesively. In such embodiments, the coupler does not need to be transparent, but can define an opening that exposes the transparent window. Glass and sapphire can be particularly suitable materials for the tube due to their chemical inertness and resistance to solvent attack.

[0410] In the printhead 800, the charging electrode 860 and the coupler 862 are separate components. In an alternative, the charging electrode and the coupler can be integrally formed with each other. For example, the coupler can be formed from a single transparent plastic / glass component having holes or channels coated with indium tin oxide (ITO), and the conductive ITO serves as the integral charging electrode. In an alternative, the channel can have a stainless steel lining instead of an ITO coating, and the stainless steel lining has viewing holes to allow visual inspection of ink jet breakup.

[0411] The clamping nut 864 includes a body and a shoulder 866. The body defines an outer surface 865 and a bore 867 having an internal threaded portion 863. The shoulder 866 is circumferentially disposed about the bore 867. The threaded portion 863 is coupled to the nozzle body 832 through a threaded interface with the nozzle body socket 878, which has a complementary external thread.

[0412] The shoulder 866 is configured to hold the charging electrode coupler 862 against the nozzle body 832 by contacting the flange 880 of the coupler, thereby forcing the flange against the nozzle body socket 878. Rotating the clamping nut 864 causes a change in the axial position of the clamping nut 864 relative to the nozzle body socket 878. By changing the axial position of the clamping nut 864, an axial clamping force can be applied through the shoulder 866 to press the coupling flange 880 against the nozzle body socket 878. By changing the axial position of the clamping nut (i.e., by changing the torque applied to the clamping nut), the axial clamping force can be changed. Thus, the clamping nut 864 can be operated by rotating between an adjustment configuration and a fixed configuration. In the adjustment configuration, the charging electrode coupler 862 is loosely held to allow relative rotation between the charging electrode 860 and the nozzle body 832. In the fixed configuration, the charging electrode coupler 832 is pressed against the nozzle body socket 878 by the shoulder 866, restricting the axial and rotational movement of the charging electrode 860 and ensuring its alignment. In the fixed configuration, the nozzle body 832 (which is also extended to the nozzle assembly 834) and the charging electrode assembly 848 are coaxially coupled and can be considered as a single assembly, referred to as the charging electrode-nozzle body assembly.

[0413] In use, the clamping nut 864 can be rotated by means of an external tool engaging the outer surface 865, which may include a flat surface or other engagement features for external tool engagement and torque transmission.

[0414] The charging electrode 860 includes a support member 882. As Figure 25 shown, the support member 882 is an annular flange coaxially disposed at the end of the charging electrode 860 opposite the nozzle 858 (such that it surrounds the charging electrode channel 861) (see Figure 22 ), and defines an outer surface 884 having a frustoconical spherical geometry. The charging electrode 860 and the support member 882 are integrally formed as a single component, but in an alternative, they may also be separate rigidly coupled components.

[0415] Although the charging electrode 860 includes a support member 882, in other embodiments, the ball joint mount can include other components. For example, the charging electrode coupler can include a support member configured to be received in a socket to form a ball and socket joint mount (see support member 882). For example, the charging electrode coupler (which can be transparent) can include a support member and define a stainless steel lined channel to form an integrated charging electrode.

[0416] The charging electrode 860 is press fit into the coupler 862. In an alternative, the charging electrode and the coupler can be coupled by means of an adhesive, and a transparent UV curable adhesive is particularly suitable for embodiments where the coupler 862 is glass. The glass coupler can also be bonded to the charging electrode by glass microbonding or glass wafer bonding. In another alternative, the coupler 862 can be overmolded onto the charging electrode, thereby reducing stress relative to a press fit.

[0417] Although in the printhead 800, the nozzle body 832 and the charging electrode assembly 848 are coaxially coupled, and the support member 882 is coaxially disposed at the end of the charging electrode 860, alternative arrangements are possible. In an alternative, the nozzle body 832 and the charging electrode assembly 848 can be paraxially coupled or angled. Additionally or alternatively, the support member 882 can be paraxial or angled relative to the charging electrode 860.

[0418] Figure 23A and 23B The charging electrode mount 836 is shown from front and back perspective views. The charging electrode mount 836 includes a mounting plate 986 and an annular cup 988. The annular cup 988 and the mounting plate 986 are integrally formed, but in an alternative, they can also be separate rigidly coupled components.

[0419] The annular cup 988 has an inner surface having a frustoconical spherical surface that is the socket 992. The spherical surface is truncated such that there is a hole through the annular cup 988 facing the axial direction (as shown by axis 801).

[0420] The support member 882 is held in the complementary socket 992 of the charging electrode mount 836 in the ball joint mount. The ball joint mount seals the charging electrode and the chamber housing while also allowing rotation about a center of rotation 894 defined by the common center of the spherical surfaces of the support member 882 and the charging electrode mount 836 (see Figure 22)。In other words, the ball joint allows the charging electrode to rotate in two different (i.e., non-parallel) planes that are arranged such that they intersect the center of rotation 894. It should be understood that the combination of rotations in the two different planes can define a conical envelope of the movement of the charging electrode 860, where the axis of the cone coincides with the nominal ink travel axis 801. The truncated spherical surfaces of the support member 884 and the charging electrode mount 836 have substantially the same radius, thereby forming a hydraulic seal interface. The charging electrode support member 882 can snap-fit into the socket 992 of the charging electrode mount 836. It should be understood that in order for the charging electrode 860 to snap-fit into the charging electrode mount 836, at least a portion of the ball joint mount must be elastic. For example, either or both of the support member 882 and the annular cup 988 can be made of an elastic material (e.g., a solvent-resistant engineering plastic) to allow sufficient deflection to permit the support member 882 to be seated in the socket 992 without excessive insertion force, while maintaining sufficient interference between the seated support member 882 and the socket 992 to maintain the hydraulic seal and mechanical rigidity of the ball joint mount.

[0421] As Figure 21 shown, the mounting plate 986 allows the charging electrode mount 836 to be rigidly coupled to the chamber outer shell 822 with the aid of the O-ring 894 and to be hydraulically sealed against the chamber outer shell 822. The hydraulic seal between the chamber outer shell 822 and the charging electrode mount 836 and the hydraulic seal between the charging electrode mount 836 and the support member 882 define a barrier to fluid communication between the chamber 856 and the remainder of the printhead (i.e., the region of the printhead outside the chamber 856). Advantageously, the above-described ball joint mount allows the orientation of the nozzle 858 and the charging electrode 860 to be adjusted (by relative movement between the printhead housing and the charging electrode), while maintaining the hydraulic seal around the chamber 856.

[0422] It should be understood that the charging electrode is sealingly and movably coupled to the printhead housing, and thus the enclosed cleaning chamber 856 has a variable geometry.

[0423] It should be understood that the enclosed passage 861 of the charging electrode 860 and the nozzle 858 remain in fluid communication with the chamber to enable those areas to be cleaned.

[0424] In some embodiments, the charging electrode assembly 848 and / or the printhead 800 may be configured to allow the charging electrode 860 to rotate up to 10 degrees about a center of rotation 894 away from a nominal ink travel axis 801 such that the range of motion of the charging electrode-nozzle body assembly defines a cone having a 10-degree half angle. The range of motion of the charging electrode-nozzle body assembly may be physically limited by mechanical interference between the charging electrode 860 and / or the nozzle body 832 and surrounding components (such as the charging electrode mount 836).

[0425] In some embodiments, the ball joint mount may further include an O-ring retained in a groove defined by the support member 882 or socket 992.

[0426] Although the printhead 800 includes a separate charging electrode mount 836, in some embodiments, the charging electrode mount (including the socket) may be integrally formed (e.g., by molding) with another part (and a portion thereof) of the printhead (such as the chamber outer shell 822). Alternatively, the charging electrode mount may be melted or ultrasonically welded into the chamber outer shell 822.

[0427] In an alternative, the support member and / or coupling of the charging electrode may alternatively define a socket-shaped surface configured to pivotally couple to a charging electrode mount that defines a convex spherical surface fixed to another part of the printhead (such as the chamber outer shell 822).

[0428] Turning to Figure 26 , a perspective view of a portion of the printhead 800 is provided. Referring to Figure 19[[END , in FIG. 40, the outer shell 812 and the seal cover 814 are omitted.

[0429] From ​ 's perspective, two fasteners 932, 934 are visible. The fasteners 932, 934, along with two corresponding fasteners on the other side of the chamber outer shell 822, extend through holes in the chamber outer shell 822 to releasably couple the sealing mechanism 824 to the chamber outer shell 822. In other words, the fasteners 932, 934 extend through holes in the chamber outer shell 822 and the housing 870 and are received by threaded holes in the end cap 808. Securing the fasteners 932, 934 engages the sealing mechanism 824 with the chamber outer shell 822 and compresses a washer 940 therebetween. An interface is defined between the sealing mechanism 824 and the chamber outer shell 822 (e.g., at a face 942 as shown in ​ ). The interface is generally labeled 941 in ​ . The chamber outer shell 822 and components coupled thereto (optionally including the chassis 816) may be referred to as the outer shell assembly.

[0430] Turning to​ , provides a perspective view of the printhead 800 from a different perspective than that shown in ​ . Accordingly, ​ shows two additional fasteners 936, 938, which are used in combination with the fasteners 932, 934 shown in ​ to releasably couple the sealing mechanism 824 to the chamber outer shell 822. ​ Also shown is a shaft 846 that extends through a portion of the chamber outer shell 822 to drive a rotatable body. The combination of the shaft 846 and the socket 850 can be described as providing a mechanical coupling that extends through the interface 941.

[0431] ​ Also shown is a slot connector block 1022. The slot connector block 1022 is coupled to the chamber outer shell 822. The slot connector block 1022 defines a detachable fluid connection. The slot connector block 1022 facilitates the removal of the sealing mechanism 824 even when coupled to the chamber outer shell 822 (since the slot connector block 1022 only sealingly engages with the sealing mechanism 824). In other words, when (only) the fasteners 932, 934, 936, 938 are removed, the sealing mechanism 824 can be pushed away from the chamber outer shell 822. The slot connector block 1022 defines a fluid path that extends through the interface 941. When the sealing mechanism 824 is separated from the chamber outer shell 822, the fluid path is separated, and the mechanical coupling is also separated across the interface.

[0432] ​ A portion of the shaft 846 is shown separately. The shaft 846 includes a dome-shaped tip 847 at one end. Advantageously, if the sealing mechanism 824 is removed and then reattached (e.g., after maintenance), the dome-shaped tip 847 provides greater alignment tolerance when rotationally coupling the shaft 846 and the socket 850 (see ​ ). In other words, the incorporation of the dome-shaped tip 847 provides some axial clearance between the rotational axis of the shaft 846 and the socket 850 that receives the shaft 846. The rotational coupling features, in the form of a hexagonal pattern in the illustrated embodiment, are labeled 849 and surround the dome-shaped tip 847. Through the rotational coupling features 849, the shaft 846 is rotationally coupled to the socket 850 (e.g., the socket 850 includes an inner profile corresponding to the outer profile of the shaft 846). Similarly, the same rotational coupling features extend along the extent of the shaft 846 and provide a rotational coupling between the shaft 846 and the drive motor (optionally via a gearbox). A narrow neck 851 is also defined near the dome-shaped tip 848. Similar to the dome-shaped tip 847, the neck 851 provides greater (axial) alignment tolerance between the shaft 846 and the socket 850.

[0433] Turning to ​, a perspective view of the printhead 800 is provided, in which the sealing mechanism 824 is removed.

[0434] From ​ 's perspective, the end face 942 of the chamber housing 822 is visible. The gasket 940 is shown as being disposed on the chamber housing 822. The gasket 944 is also shown as being disposed in the end face 942. The gasket 944 extends around the chamber 856, specifically around the first portion 856a defined by the chamber housing 822. A portion of the high-voltage deflection electrode 840 is also visible in ​ (although within the chamber 856). The groove 844 can also be seen in ​ . The groove 844 includes a slot hole defined at the end of the groove line 946. As will be understood from ​ , the groove 844 remains in place, positioned relative to the chamber housing 822, even when the sealing mechanism has been removed. Advantageously, this means that even when the sealing mechanism 824 is removed for maintenance, the alignment of the nozzle and the charging electrode assembly relative to the groove 844 is maintained.

[0435] ​ Also shown is the dome-shaped tip 847 of the shaft 846 exposed through the hole 948 defined in the end face 942. The recess 950 is also defined in the end face 942 and is configured to receive the transmission 872.

[0436] Turning to ​ , a cross-sectional view of the printhead 800 is provided around the plane 837 schematically marked on ​ . Thus, ​ is a cross-sectional view taken just outside the charging electrode mount 836.

[0437] ​ is taken facing the groove 844. Thus, ​ From the position where the charging electrode-nozzle body assembly is installed (the hole of the socket 992, best shown in ​ and 23B ), a line of sight of the groove 844 passing through the chamber 856 is shown. Advantageously, by providing a line of sight through the chamber 856 such that the groove 844, particularly its slot hole, is visible, the charging electrode-nozzle body assembly can be easily aligned with the groove 844 regardless of whether the chamber 856 has a closed or semi-closed geometry. Thus, the ink jet produced by the nozzle 858 can be aligned such that the undeflected ink is received by the groove 844.

[0438] ​ A method of aligning or adjusting the printhead 800 is schematically shown, which can form part of a factory setup procedure during manufacturing.

[0439] In step S1, align the charging electrode. In the case where the mounting device is in the adjustment configuration, the charging electrode 860 can be rotated into alignment with the inkjet (see ​ -C and the associated description). Once aligned, the charging electrode can be fixed relative to the nozzle 858 by turning the clamping nut 864, thereby placing the mounting device in the fixed configuration. The nozzle body 832 and the charging electrode 860 are (adjustably) coupled to each other via the charging electrode coupler 862.

[0440] In step S2, snap-fit the charging electrode 860 into the charging electrode mount 836, thereby forming a ball joint mount.

[0441] In step S3, adjust the orientation of the charging electrode-nozzle body assembly by rotating the charging electrode-nozzle body assembly about the rotation center 894 in two different planes to align the inkjet and the slot 844. The correct alignment of the inkjet and the slot 844 (i.e., the slot 844 receives the ink droplets not used for printing) can be visually verified (thus requiring the sealing mechanism 824 to be omitted or removed from the print head 800, as ​ shown). Advantageously, in step S3, the adjustment can correct any misalignment or skew of the inkjet due to the manufacturing tolerances of the nozzle 858 that affects the slot-inkjet alignment.

[0442] In step S4, attach the sealing mechanism 824 to the chamber housing 822 as described with reference to ​ to produce the adjusted print head 800.

[0443] In some embodiments of the method, the sealing mechanism 824 can be attached to the print head 800 before step S3, as described with reference to ​ In such embodiments, the sealing mechanism 824 can be disassembled before step S4 to allow visual inspection of the slot 844.

[0444] Generally, the charging electrode 860 is aligned in step S1 before being snap-fit into the charging electrode mount 836. Performing the actions in this order allows easier access to the clamping nut 864 and the charging electrode 860 when the nozzle assemblies 834 and 848 are separated from the print head, for adjustment and alignment. By first snap-fitting the charging electrode 860 into the charging electrode mount 836, access to the clamping nut 864 and the charging electrode 860 may be severely restricted by the surrounding components (such as the chamber housing 822 or the charging electrode mount 836), potentially hindering the easy adjustment and alignment of the charging electrode 860, whether by external tools or otherwise.

[0445] It should be understood that some further assembly of the printhead may be performed before step S1. That is, the charging electrode 860 can be press-fitted into the coupling 862, and then the coupling 862 can be mounted to the nozzle body 832 of the nozzle assembly 834 using the clamping nut 864.

[0446] The printhead 800 can be connected to a test fixture for some or all of the above steps, where the test fixture provides the necessary connections to enable all or part of the operation of the printhead. For example, the test fixture can be configured to supply a fluid (such as ink) to the nozzle 858 and provide suction to the gutter 844. Additionally, the fixture can further be configured to supply power to the printhead 800, such as supplying power to the nozzle assembly 834 for droplet generation.

[0447] In the printhead 800, the orientation of the charging electrode - nozzle body assembly is adjusted by the nozzle carriage 830 and the screw 896 as described above. However, in some embodiments, the charging electrode - nozzle body assembly can be adjusted by means of an external alignment tool, which can be used to perform ​ step S4. Such an external alignment tool can be removably coupled to the nozzle body 832 and is used to precisely adjust the orientation / alignment of the charging electrode - nozzle body assembly, for example, by a screw mechanism. When the correct alignment of the inkjet and the gutter 844 is achieved, the alignment tool can be removed, and the alignment can be permanently or semi-permanently fixed or fastened, for example, by potting the nozzle body.

[0448] It should be noted that the nozzle 858 does not coincide with the rotation center 894 (see ​ ). Thus, the point from which the (misaligned) inkjet originates is offset from the rotation center 894. Therefore, the angular adjustment of the charging electrode - nozzle body assembly at S3 does not necessarily precisely correspond to the inkjet misalignment angle or skew.

[0449] Generally, the guiding surface and the guiding element are configured to cooperate so as to limit the relative movement of the nozzle and the charging electrode to a desired envelope. For example, the desired envelope can include a partial rotation about an axis. By relative movement, the charging electrode and the nozzle can be adjusted so that they are optimally oriented relative to each other. After adjustment, the guiding surface and the guiding element can also cooperate to fix the adjusted configuration. The restricted envelope of relative movement can facilitate easy adjustment. However, as described above, several different mechanical arrangements are possible.

[0450] Maintaining a coaxial relationship between the jet and the charging electrode results in symmetric forces on the jet and thus consistent print quality. A parallel but offset spatial relationship between the jet and the charging electrode results in reduced print quality. Thus, the relationship between the jet and the charging electrode defined by the interaction of the guiding surface and the guiding element is preferably as coaxial as possible, but small offsets are also acceptable, such as up to about 30% off-center or less.

[0451] In addition, ​ embodiments of also specify the use of threaded bolts / screws 318 to provide a fixed configuration of the adjustment mechanism. Alternative mechanisms such as lever cams (see bicycle quick release) can also provide the necessary clamping pressure.

[0452] Guiding surfaces and elements can also be provided to allow the manufacturer to make adjustments and then permanently fix them in the adjusted configuration. Methods of permanent fixation can include various types of adhesives or blocking of components of the adjustment mechanism (such as bolt 318). In such embodiments, the charging electrode assembly will not be adjustable by the end user.

[0453] Other embodiments can allow relative movement between the charging electrode and the nozzle in a plane of motion perpendicular to the nominal ink travel axis.

[0454] In ​ embodiments, the hydraulic seal at the interface between components is provided by additional sealing members: sheath 151 or washers 318 or 319. Mechanically, these components are positioned and fixed to each other by threaded fasteners and mating recesses (e.g., rotary bolt 344 and semi-circular slot 347). Alternatively, some or all of the interfaces between the various component parts can be provided with press-fit interfaces, such as male and female Luer tapers. The Luer taper provides a combination of mechanical positioning and connection and hydraulic sealing through the interaction of the mating (tapered) portions by press-fit. Such interfaces can also be provided with threaded collars to increase the security of the connection (see hypodermic syringe). It should be understood that there are many other press-fit interfaces that will also provide mechanical positioning and connection in combination with hydraulic sealing.

[0455] In ​ embodiments, the charging electrode discharge port 217 is located in the nozzle body 143. In another alternative embodiment, radial ducts can also be provided in the insulation pair so as to be exposed through discharge ports substantially adjacent to and upstream of the nozzle. The radial ducts are configured to directly discharge, fill, or discharge into a closed cleaning chamber via the discharge ports at the nozzle face.

[0456] The sheath and ball-and-socket joint have both been described above as devices for hydraulically sealing the enclosed chamber defined by the charging electrode and the chamber housing while facilitating their relative movement such that the geometry of the enclosed cleaning chamber is variable and adjustable. It should be understood that a cleaning chamber of variable geometry may be provided by other means. For example, the charging electrode and the chamber housing may be sealingly and movably coupled by a flexible conduit or an elastic membrane.

[0457] While embodiments of the present disclosure have been described above, it should be understood that these embodiments are provided by way of example only and are not intended to be limiting in nature. Indeed, various alternatives and variations of the specific embodiments described herein will be understood to be possible without departing from the scope of the present disclosure. The scope of the invention is defined by the appended claims.

Claims

1. A charging electrode assembly for a continuous inkjet printer, comprising: A charging electrode that defines a channel for charging ink droplets, the channel extending from an inlet hole to an outlet hole along an ink travel axis, during printing, inkjet travels along the ink travel axis from a nozzle, and the electrode is configured to induce charge on selected ink droplets through capacitive coupling; Mounting means configured to couple the charging electrode to a nozzle body, the mounting means being configured to allow the charging electrode to move relative to the nozzle to compensate for inkjet misalignment.

2. The charging electrode assembly according to claim 1, wherein, The mounting means includes: An adjustment structure that allows the charging electrode to move relative to the nozzle to compensate for inkjet misalignment; and A fixing structure configured not to allow the charging electrode to move relative to the nozzle.

3. The charging electrode assembly according to any one of the preceding claims, wherein, The channel has a first dimension in a first direction perpendicular to the nominal ink travel axis and a second dimension different from the first dimension in a second direction perpendicular to the first direction and the nominal ink travel axis.

4. The charging electrode assembly according to any one of the preceding claims, wherein, A seal is provided between the charging electrode and the nozzle.

5. The charging electrode assembly according to any one of the preceding claims, wherein, The mounting means is configured to allow the charging electrode to rotate relative to the nozzle.

6. The charging electrode assembly according to claim 5, wherein, The mounting means is configured to allow the charging electrode to rotate relative to the nozzle about a rotation axis substantially coaxial with the nominal ink travel axis.

7. The charging electrode assembly according to claim 5 or 6, wherein The mounting means is configured to allow the charging electrode to rotate relative to the nozzle within an angular range of at least 45 degrees, and optionally, wherein the mounting means is configured to allow the charging electrode to rotate relative to the nozzle within an angular range of up to about 90 degrees.

8. The charging electrode assembly according to claim 5 or 6, wherein, The mounting means is configured to allow the charging electrode to rotate relative to the nozzle to an infinite extent.

9. The charging electrode assembly according to any one of the preceding claims, wherein, The mounting means is configured to allow relative movement between the charging electrode and the nozzle in a movement plane perpendicular to the nominal ink travel axis.

10. The charging electrode assembly according to any one of the preceding claims, wherein, The mounting means includes a guiding surface and a guiding element, the guiding element being configured to be guided by the guiding surface, wherein the allowable movement range between the charging electrode and the nozzle is at least partially determined by the configuration of the guiding surface and the guiding element.

11. The charging electrode assembly according to claim 9 and claim 10, wherein, One of the guiding surface and the guiding element has a fixed structure relative to the charging electrode in the movement plane, and the other of the guiding surface and the guiding element has a fixed structure relative to the nozzle in the movement plane.

12. The charging electrode assembly according to claim 10 or 11, wherein The guiding surface includes a substantially cylindrical socket, and the guiding element includes a cylindrical protrusion.

13. The charging electrode assembly according to any one of the preceding claims, wherein, The mounting means includes a charging electrode coupler that can be coupled to each of the charging electrode and the nozzle body in use.

14. The charging electrode assembly according to claim 13, wherein, The charging electrode coupler includes an electrical insulator configured to electrically insulate the charging electrode from the nozzle body.

15. The charging electrode assembly according to claim 13 or 14 when dependent on claim 12, wherein, The guiding surface includes a substantially cylindrical socket defined by the nozzle body, and the guiding element includes a cylindrical protrusion defined by the charging electrode coupler.

16. The charging electrode assembly according to claim 15, wherein, The mounting device includes another guiding element defined by the nozzle body including a cylindrical protruding portion and the charging electrode defining another guiding surface, the charging electrode including a socket.

17. The charging electrode assembly according to any one of claims 12 to 16, wherein, The mounting device includes: a clamping nut, wherein the clamping nut includes: a threaded portion configured to be screwed onto the nozzle body; and; a shoulder configured to hold the charging electrode coupler against the nozzle body, wherein, in use, the clamping nut can be operated by rotating between an adjustment configuration and a fixed configuration, in the adjustment configuration, the charging electrode coupler is held loosely, and in the fixed configuration, the charging electrode coupler is pressed against the nozzle body by the shoulder, thereby restricting the axial and rotational movement of the charging electrode relative to the nozzle.

18. The charging electrode assembly according to claim 9, 13 or 14, wherein, The guiding element includes a fixing element, and the charging electrode assembly includes an adjustment configuration and a fixed configuration, in the adjustment configuration, the fixing element is configured to guide the movement of the charging electrode relative to the nozzle, and in the fixed configuration, the fixing element is configured to fix the position of the charging electrode relative to the nozzle.

19. The charging electrode assembly according to any one of the preceding claims, wherein, The charging electrode assembly further includes: a support member that at least partially defines a spherical surface, the support member being coupled to the charging electrode; wherein the support member is configured to be pivotally coupled to the charging electrode mount to form a ball-and-socket joint, thereby allowing the charging electrode to rotate about a center of rotation in two different planes.

20. The charging electrode assembly according to claim 3 or any one of the preceding claims dependent thereon, wherein: the first dimension is at least 0.5 mm; and / or the first dimension is less than 1 mm; and / or the second dimension is at least 1 mm; and / or the second dimension is less than 5 mm.

21. The charging electrode assembly according to any one of the preceding claims, wherein, The charging electrode includes an axially disposed first region and a second region, wherein the first region is configured to induce charge on selected ink droplets by capacitive coupling, and the second region is configured to shield charged ink droplets by at least one section around the travel axis.

22. The charging electrode assembly according to claim 21 and claim 3, wherein: the channel has the first dimension and the second dimension in at least a portion of the axially disposed first region, the channel has a third dimension in a first direction and a fourth dimension in a second direction in at least a portion of the axially disposed second region, and the third dimension is greater than the first dimension, and / or the fourth dimension is greater than the second dimension.

23. The charging electrode assembly according to any one of the preceding claims, wherein, At least a portion of the charging electrode is transparent such that the charging electrode is configured to allow monitoring of the formation of ink droplets within the channel.

24. The charging electrode assembly according to claim 23, wherein, The charging electrode includes an observation hole for monitoring the formation of ink droplets within the channel.

25. The charging electrode assembly according to claim 24, wherein, The charging electrode further includes a light source or a second observation hole disposed on a side of the travel axis opposite to the observation hole.

26. A printhead for a continuous inkjet printer, including the charging electrode assembly according to any one of the preceding claims, the printhead further including: The nozzle, for generating and ejecting an ink jet, which ink jet subsequently undergoes jet breakup into a stream of ink droplets for printing; A deflection electrode, which is configured to deflect the ink droplets after the ink droplets have been charged by the charging electrode; and A gutter for receiving ink droplets not used for printing.

27. The printhead according to claim 26, further comprising a printhead housing configured to enclose the deflection electrode within a cleaning chamber, the printhead defining a seal between the charging electrode and the cleaning chamber.

28. The printhead according to claim 27, further comprising a flexible member disposed between the charging electrode and the printhead housing, the flexible member configured to provide the seal, the flexible member configured to permit movement between the printhead housing and the charging electrode.

29. The printhead according to any one of claims 26 to 28, further defining an ink orifice configured to permit droplets to leave the printhead for printing, the printhead including a sealing mechanism configured to selectively close the ink orifice.

30. The printhead according to any one of claims 26 to 29, further comprising a nozzle adjustment mechanism configured to permit adjustment of the nozzle relative to the gutter to compensate for ink jet misalignment.

31. A continuous ink jet printer, comprising: A printhead according to any one of claims 27 to 30; and An ink system for storing ink and supplying ink to the printhead.

32. A method of configuring a printhead for a continuous ink jet printer, the method comprising: Adjusting a nozzle of the printhead to align an ink jet ejected from the nozzle with a gutter for receiving ink droplets not used for printing; Fixing the nozzle in an aligned configuration to a body of the printhead; Adjusting a position of a charging electrode relative to the nozzle to compensate for ink jet misalignment; and Fixing the charging electrode in the adjusted configuration to the nozzle.

33. A charging electrode assembly for a continuous ink jet printer, comprising: A charging electrode defining a channel for charging ink droplets, the channel extending along an ink travel axis from an inlet orifice to an outlet orifice, during printing an ink jet travels along the ink travel axis from a nozzle, the electrode configured to induce a charge on selected ink droplets by capacitive coupling; and A support member at least partially defining a spherical surface, the support member coupled to the charging electrode; Wherein the support member is configured to be pivotally coupled to a charging electrode mount to form a ball and socket joint, thereby permitting the charging electrode to rotate about a center of rotation in two different planes.

34. The charging electrode assembly according to claim 33, wherein, The support member includes an annular flange coaxially disposed about the charging electrode channel.

35. The charging electrode assembly according to claim 34, wherein, The annular flange defines a truncated spherical surface circumferentially disposed about the charging electrode channel.

36. The charging electrode assembly according to any one of claims 33 to 35, wherein, The charging electrode assembly further includes mounting means configured to couple the charging electrode to a nozzle body, the mounting means configured to permit rotational movement of the charging electrode relative to the nozzle.

37. The charging electrode assembly according to any one of claims 33 to 36, wherein, The mounting means includes: A charging electrode coupler configured to couple the charging electrode and the nozzle body; and A clamping nut, wherein the clamping nut comprises: A threaded portion configured to be screwed onto the nozzle body; and A shoulder configured to hold the charging electrode coupler against the nozzle body, wherein, in use, the clamping nut can be operated by rotation between an adjustment configuration and a fixed configuration, in the adjustment configuration, the charging electrode coupler is loosely held, and in the fixed configuration, the charging electrode coupler is pressed against the nozzle body by the shoulder, thereby restricting the axial and rotational movement of the charging electrode relative to the nozzle.

38. The charging electrode assembly according to any one of claims 33 to 37, wherein, The socket and the support member are configured to form a hydraulic seal in a plurality of relative orientations.

39. A print head for a continuous inkjet printer, comprising a charging electrode assembly according to any one of claims 33 to 38, the print head further comprising: The nozzle for generating and ejecting an ink jet, which is subsequently subjected to jet splitting into a stream of ink droplets for printing; A deflection electrode configured to deflect the ink droplets after the ink droplets have been charged by the charging electrode; and A gutter for receiving ink droplets not used for printing; and A charging electrode mount configured to be pivotally coupled to the support member, forming a ball and socket joint, thereby allowing the charging electrode to rotate about a center of rotation in two different planes.

40. The print head according to claim 39, wherein, The charging electrode mount defines a socket configured to receive the support member.

41. The print head according to claim 39 or 40, wherein, The socket is annular.

42. The print head according to any one of claims 39 to 41, wherein, The socket is a truncated spherical surface.

43. The print head according to any one of claims 39 to 42, wherein, The socket is integrally formed with the chamber housing.

44. The print head according to any one of claims 39 to 43, wherein, The print head is configured to allow the charging electrode to rotate about the center of rotation away from the nominal ink travel axis by up to 10 degrees.

45. The print head according to any one of claims 39 to 44, wherein, The nozzle and the charging electrode are axially coupled.

46. The print head according to any one of claims 39 to 45, wherein, The gutter is rigidly coupled to the charging electrode mount by a single component.

47. The print head according to claim 46, wherein, The chamber housing includes the single component.

48. A modular print head for a continuous inkjet printer, comprising: A sealing mechanism releasably coupled to a housing assembly at an interface, the sealing mechanism comprising: A rotatable body capable of rotating between a first configuration and a second configuration about a rotation axis; and A housing defining an ink hole and holding the rotatable body; The housing assembly includes: A chamber selectively sealable by the rotatable body, the rotatable body being capable of rotating about the rotation axis between a first configuration with an open ink hole and a second configuration with a closed ink hole; A nozzle for generating and ejecting a stream of ink droplets for printing; At least one electrode for guiding the stream of ink droplets; and A gutter for receiving ink droplets not used for printing; wherein the at least one electrode is disposed in the chamber; and wherein at least one fluid path and at least one mechanical coupler extend through the interface.

49. The modular printhead according to claim 48, wherein, The fluid path extending through the interface includes a connection block configured to provide a detachable fluid connection through the interface.

50. The modular printhead according to claim 48 or 49, wherein, The slot is configured to remain in place relative to the chamber when the sealing mechanism is separated from the housing assembly.

51. A method of disassembling a modular printhead according to any one of claims 48 to 50, comprising: Disconnecting the sealing mechanism from the housing assembly at the interface, separating at least one fluid path passing through the interface, and disengaging the mechanical coupling passing through the interface.

52. A method of aligning components of a printhead for a continuous inkjet printer, the method comprising: Adjusting the position of a charging electrode relative to a nozzle to compensate for inkjet misalignment; Fixing the charging electrode to the nozzle in an adjusted configuration; Fitting the charging electrode into a charging electrode mount to form a ball joint mount; Adjusting the orientation of the charging electrode by rotating the charging electrode about the ball joint mount relative to the body of the printhead to align inkjet ejected from the nozzle with the slot for receiving ink droplets not used for printing; and Fixing the nozzle to the body of the printhead in an aligned configuration.

53. The method according to claim 52, wherein, The method further comprises attaching a sealing mechanism.

54. The method according to any one of claims 52 or 53, wherein For some or all of the method, attaching the printhead to a test fixture.

55. The method according to any one of claims 52 to 54, wherein, Adjusting the orientation of the charging electrode by means of an external alignment tool.

56. The method according to any one of claims 52 to 55, wherein The charging electrode snap-fits into the charging electrode mount.

57. The method according to any one of claims 52 to 56, wherein The method includes disassembling the sealing mechanism from the printhead to expose the slot.

58. The method according to claim 53 or 57, wherein, The sealing mechanism is configured to be releasably coupled to a housing assembly at an interface, the sealing mechanism comprising: A rotatable body that can rotate between a first configuration and a second configuration about a rotation axis; and A housing that defines an ink hole and holds the rotatable body; Wherein the housing assembly includes a chamber that can be selectively sealed by the rotatable body, the rotatable body being able to rotate about a rotation axis between a first configuration with an open ink hole and a second configuration with a closed ink hole; and further, wherein at least one fluid path and at least one mechanical coupling extend through the interface.

59. The method according to claim 58, wherein, The housing assembly further includes: A nozzle for generating and ejecting a stream of ink droplets for printing; At least one electrode for guiding the stream of ink droplets; and A slot for receiving ink droplets not used for printing.

60. The method according to any one of claims 52 to 59, wherein, The method is part of a method of manufacturing a printhead.

61. A printhead for a continuous inkjet printer, comprising: A nozzle for generating and ejecting an inkjet that subsequently undergoes jet splitting into a stream of ink droplets for printing; A charging electrode that defines a closed channel for charging ink droplets, the closed channel extending from an inlet hole to an outlet hole along an ink travel axis, during printing, the inkjet travels along the ink travel axis from the nozzle, the electrode being configured to induce a charge on selected ink droplets by capacitive coupling; A deflection electrode configured to deflect the ink droplets after they have been charged by the charging electrode; A slot for receiving ink droplets not used for printing; and An ink hole configured to allow droplets to leave the printhead for printing; Wherein: The printhead has a printing configuration and a cleaning configuration, in the printing configuration, the ink holes are open, and in the cleaning configuration, the ink holes are closed; and In the cleaning configuration, the printhead defines a closed cleaning chamber, and the closed cleaning chamber is at least partially defined by a closed channel.

62. The print head according to claim 61, wherein, The closed cleaning chamber has a variable geometry.

63. The print head according to claim 61 or 62 further includes a print head housing, wherein, The closed cleaning chamber is at least partially defined by the printhead housing, and the printhead defines a seal between the printhead housing and the charging electrode.

64. The print head according to claim 63, wherein, The printhead includes a flexible member disposed between the charging electrode and the printhead housing, the flexible member being configured to provide the seal, and the flexible member being configured to allow adjustment between the printhead housing and the charging electrode.

65. The print head according to claim 63, wherein, The charging electrode and the printhead housing are movably coupled to allow relative movement between the printhead housing and the charging electrode.

66. The print head according to claim 65, wherein, The charging electrode and the printhead housing are pivotally coupled to allow adjustment between the printhead housing and the charging electrode.

67. The print head according to claim 66, wherein, The printhead includes a ball joint, the ball joint including: A support member that at least partially defines a spherical surface, the support member being coupled to the charging electrode; and A charging electrode mount that is coupled to the printhead housing and defines a socket for holding the support member; Wherein the support member and the charging electrode mount form a ball joint, thereby allowing the charging electrode to rotate about a center of rotation in two different planes.

68. The print head according to any one of claims 61 to 67, wherein, The printhead defines a seal between the nozzle and the charging electrode, and the cleaning chamber is at least partially defined by the nozzle.

69. The print head according to claim 68, wherein, The charging electrode is movable relative to both the printhead housing and the nozzle.

70. The print head according to any one of claims 61 to 69, wherein, The printhead includes one or more conduits in communication with the closed cleaning chamber via one or more respective ports.

71. The print head according to claim 70, wherein, At least one of the one or more ports is disposed in the nozzle.

72. The print head according to claim 70 or 71, wherein, At least one of the one or more ports is arranged to be close to the charging electrode.

73. The print head according to any one of claims 70 to 72, wherein, At least one of the one or more ports is arranged adjacent to the groove.

74. The print head according to any one of claims 70 to 73, wherein, The one or more ports are capable of filling, supplying, or discharging the closed chamber with a cleaning fluid.

75. The print head according to any one of claims 70 to 74, wherein, The one or more ports are capable of discharging air from the closed chamber.

76. The printhead according to any one of claims 61 to 75, further comprising mounting means configured to couple the charging electrode to the nozzle, wherein: The mounting means is configured to allow the charging electrode to move relative to the nozzle to compensate for inkjet misalignment during an adjustment operation; And The mounting means is configured to rigidly fix the charging electrode to the nozzle during printing.

77. The print head according to any one of claims 61 to 75, wherein, The charging electrode closed channel is a rotational volume about an axis, the rotational volume including: A first narrow parallel section; adjacent to A second diverging section; Wherein the first narrow parallel section is configured to be adjacent to the nozzle and receive the inkjet from the nozzle.

78. The print head according to any one of claims 61 to 77, wherein, The ink holes are disposed downstream of the deflection electrode.

79. A method of cleaning a printhead for a continuous inkjet printer, the method comprising: Close the ink holes of the print head to define a closed cleaning chamber, the closed cleaning chamber being at least partially defined by the charging electrode of the print head; Direct a cleaning fluid into the cleaning chamber to clean the chamber; wherein directing the cleaning fluid into the chamber includes directing the cleaning fluid into the closed channel of the charging electrode, the closed channel extending from an inlet hole to an outlet hole along an ink travel axis, during printing, ink jets travel along the ink travel axis from a nozzle, and the electrode is configured to induce a charge on selected ink droplets by capacitive coupling.

80. A charging electrode for a continuous inkjet printer, the charging electrode defining a closed channel for charging ink droplets, the closed channel being a rotational volume around an axis, the rotational volume including: A first narrow parallel section; Adjacent A second divergent section; Wherein the first narrow parallel section is configured to receive an ink jet from a nozzle and induce a charge on selected ink droplets by capacitive coupling.

81. The charging electrode according to claim 80, wherein, The second divergent section has a radius around the axis, the radius increasing monotonically along the axis.

82. The charging electrode according to claim 80 or 81, wherein, The second divergent section is substantially conical.

83. The charging electrode according to claim 80, wherein, The second divergent section has a radius around the axis, the radius increasing non-monotonically along the axis.

84. The charging electrode according to any one of claims 80 to 83, wherein, The first narrow parallel section is configured to be in a sealing relationship with the nozzle.

85. The charging electrode according to any one of claims 80 to 84, wherein, The second divergent section is configured to be in a sealing relationship with the print head housing.

86. The charging electrode according to any one of claims 80 to 85, wherein, The charging electrode is at least partially made of a conductive material.

87. The charging electrode according to claim 86, wherein, The charging electrode is substantially composed of a transparent conductive plastic.

88. The charging electrode according to claim 86, wherein, The first narrow parallel section is composed of a narrow metal tube having an observation hole, the observation hole being press-fitted into a wider plastic body.

Images