Printhead containing a micro pneumatic control unit

Abstract

To provide a micro-pneumatic control unit having improved functions, service life and performances while reducing manufacturing costs.SOLUTION: A micro-pneumatic control unit (3) generates control pressures (pC) in a pneumatically actuated multi-channel coating head for coating components with a coating agent. A control channel comprises the followings: a valve element comprising a valve bore (12) in a valve plate (10) and a diaphragm layer (20) which is a diaphragm closing element (21); a micro-actuator (25) having a plunger (26) which actuates the diaphragm closing element through the valve bore; a second micro-pneumatic element (15) which is connected in series with the valve element, and generates the control pressures; and pneumatic pressurization of the micro-pneumatic control unit, which is directed toward the valve element.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The invention relates to the field of printheads for coating agents, which are intended to print, coat or dispense liquid substances on the surface of an object, i.e. to apply liquid substances. In particular, the invention relates to application by means of printheads, dosing heads, dispensers or other liquid applicators, which will hereinafter be generally referred to as printheads 1. The printheads 1 comprise a number of channels arranged in a geometrically regular arrangement, preferably in rows. The invention relates in particular to the field of drop-on-demand application, including fluid jet application, in which the fluid volume is of the order of picolitres, nanolitres, microlitres or more per liquid ejection, the fluid viscosity is of the order of 1 mPas [milli-pascal second] to 1 Pas [pascal second], the fluid can contain particles (with sizes of up to 0.3 mm [millimeter]) in a concentration of up to 90%, the ejection frequency is in the range of up to kilohertz and the channel spacing is well below a millimeter. [Background technology]

[0002] The printhead according to the invention has possible applications in the following fields: painting, sealing and gluing of all kinds of mobile vehicles, including cars, aircraft and ships, in particular adhesive bonding of parts of such mobile vehicles, mainly using industrial robots, in particular multi-axis articulated arm robots, which move the printhead, or coating of any kind of parts, including products of the consumer goods industry, with liquid coating agents using industrial or Cartesian robots or such robots integrated into single-pass printing or coating systems, and all coatings required in connection with construction. The invention also relates to printing using mobile devices.

[0003] The invention is based on a printhead or dispensing head that relies on a micro-pneumatic actuation principle, as described in US Pat. No. 5,399,633.

[0004] Furthermore, US Pat. No. 5,399,633 discloses a micropilot valve for use in a printhead or in a dosing head. Such a pilot valve comprises an individual closing element in a chamber connected to a control pressure output. The individual closing element alternately closes an upper opening, which is under ambient pressure, or a lower opening, which is connected to a pressure supply. The individual closing element is driven by a plunger protruding through the first opening and is externally actuated by a piezo bending transducer. In this way, the dead volume of the chamber of the micropilot valve can be kept low and high pressure gradients can be achieved in the switching process. However, a disadvantage in this case is that the violent closing process leads to considerable wear of the lower valve seat and the plunger, which results in an increased stroke of the diaphragm-type closing element. The violent closing process also leads to a shortened service life of the piezo bending transducer due to the periodic occurrence of high mechanical stress peaks. In this respect, it would be desirable to prevent the plunger and the valve seat from acting violently against each other. Furthermore, the individual closing elements of US Pat. No. 5,399,633, which have sufficient hardness and durability, have a large mass. When the upper opening is closed, this mass must be moved from the lower opening by air pressure, but the closing time cannot be rapid and must be assisted by another micro-spring element. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] German Patent Application Publication No. 102009029946 [Patent Document 2] International Publication No. 2013 / 139326 Summary of the Invention [Problem to be solved by the invention]

[0006] The problem addressed by the present invention is to at least partially overcome the drawbacks known from the prior art, in particular to improve the functionality, service life and performance of the micro pneumatic control unit of Patent Document 1 and the pilot valve of Patent Document 2, while reducing their manufacturing costs. [Means for solving the problem]

[0007] This problem is solved by the features of the independent claims. The dependent claims provide advantageous developments.

[0008] The micro-pneumatic control unit according to the invention is used for generating a control pressure pC in a micro-pneumatically actuated multi-channel printhead for coating parts with a coating agent, the micro-pneumatic control unit comprising a plurality of control channels, each of which is characterized in that: a) a valve element comprising a valve hole in a valve plate and a diaphragm layer, which is located below the valve plate and is designed as a diaphragm-type closure element in the region of the valve hole, the shape of which is determined by a recess located next to the valve hole, b) a microactuator having a plunger, the plunger actuating a diaphragm-type closure element through a valve hole to open the valve element; c) a second micro-pneumatic element, connected in series with the valve element, at a connection node between the second micro-pneumatic element and the valve element, a control pressure is generated and a cavity is located, the cavity being connected to at least one pneumatically operated coating agent outlet; e) Finally, pneumatic pressurization of the valve element in a series circuit oriented such that there is a pressure gradient from the diaphragm side to the valve hole.

[0009] The valve plate and the diaphragm layer extend over all the channels of the micro-pneumatic control unit and can each be manufactured cost-effectively as a continuous part. The diaphragm layer forms a diaphragm-type closure element below the valve hole, which is formed by one or more recesses in the diaphragm layer. In this case, the term "below" shall be understood to refer to the first longitudinal side of the valve plate. In comparison with a separate diaphragm-type closure element (e.g. a sphere) as proposed in the patent document 2, this diaphragm-type closure element has almost no mass. Furthermore, by suitable diaphragm material, diaphragm thickness, shape and size of the diaphragm recess etc., a restoring force can be generated indirectly. This restoring force assists the closing of the valve hole driven by the pressure gradient. The low mass of the diaphragm-type closure element leads to a low shock load on the piezo bending transducer and a short closing time.

[0010] In principle, all pneumatic circuits or networks in the field are based on a series connection of two or more pneumatic elements between two pressure levels or in a pressure gradient (for example between a high pressure level pH and a low pressure level pL). A pneumatic element is also called a pneumatic impedance Z. In this case, each impedance may consist of further impedances or a network of impedances. Depending on the ratio of the impedances involved, a corresponding pressure level is established at the connection node. The height of that pressure level is between the two pressure levels. The individual pneumatic elements can be linear or non-linear throttle or valve elements. In terms of system theory, it is also possible to consider a valve element as a non-linear throttle.

[0011] The valve hole, in cooperation with a diaphragm-type closure element, forms a valve element and is preferably associated with a first micro-pneumatic (non-linear) impedance Z1. The second micro-pneumatic element may have any micro-pneumatic impedance or a combination thereof and is preferably associated with a second micro-pneumatic impedance Z2.

[0012] The second micro-pneumatic element is preferably a linear throttle or the like, for example if it is a simple hole (called the second hole) opening into the cavity, this second hole can also be a multi-hole or sieve type structure, opening into the cavity and connected in parallel.

[0013] In this case, the second hole has a smaller diameter than the valve hole. Depending on the application, the diameter of the valve hole is, for example, 1.5 to 3 times the diameter of the second hole. Expressed more generally, the preferred series connection of the valve element and the second micro-pneumatic element is designed so that there is as large a pressure drop as possible across the second micro-pneumatic element when the valve element is open. Depending on the application, the flow resistance of the second pneumatic element is at least 2, 3, 5, 10 or 20 times greater than the flow resistance of the valve element in the open state.

[0014] Conversely, when the valve orifice is closed by the diaphragm-type closure element, the total available pressure difference across the valve element between the high pressure level pH and the low pressure level pL is constantly decreasing.

[0015] If it is ensured that there is a pressure gradient from the diaphragm-type closure element to the valve orifice over the entire valve element, the positions of the valve element and the second micro-pneumatic element can be interchanged in the series connection in order to enable the diaphragm-type closure element to close the valve orifice in a pressure-assisted manner. In principle, the force of the plunger acts on the diaphragm-type closure element in the opposite direction, i.e. against the pressure gradient, in order to lift the diaphragm-type closure element out of the valve orifice and allow air to pass. Depending on the position of the valve element and the second pneumatic element in the pneumatic series connection, various embodiments of the micro-pneumatic control unit are possible. These embodiments are described below with reference to the drawings.

[0016] A specific example is given in which the valve hole is in a low pressure or pressure level pL (L=LOW) environment, such as ambient pressure, and the second hole is in a higher operating pressure or high pressure level pH (H=HIGH) environment, and the second hole is located at a short distance (e.g., 20 μm [micrometers] to 100 μm) below the valve hole, so that the second hole is within the operating range of the diaphragm-type closure element. For example, the valve hole and the second hole can be arranged concentrically, or their central axes can be offset by a short distance. When the vertical distance in the cavity between the valve hole and the second hole is short, the diaphragm-type closure element is located at its lower position close to the second hole. At this position, the horizontal gap flow at the lower surface of the diaphragm-type closure element, which flows radially with respect to the second hole, is important for the flow resistance of the second micro-pneumatic element, and its nonlinearity is greatly increased. In the case of perfect sealing, i.e. when the diaphragm-type closure element is in contact with the opening area of ​​the second hole in the cavity, the flow resistance of the second micro-pneumatic impedance Z2 is infinite, in which case the control pressure pC has the value of the low pressure level pL.

[0017] A drawback of this configuration is that a stronger force must be applied to the actuator, such as the piezo bending transducer, to completely seal the lower micro-aperture against the operating pressure (high pressure level), but in the lower position, the piezo bending transducer is already highly deflected within its operating range and has less force to close the second aperture against the operating pressure. Another drawback is that the plunger permanently impacts the lower micro-aperture through the diaphragm, causing high wear and shock loads, which shortens the service life of the piezo bending transducer.

[0018] These drawbacks can be partially alleviated: the plunger and its associated piezo bending transducer are configured and controlled depending on the application, such that the technically possible unloaded operating range of the actuator is between 20 μm, 40 μm, 60 μm or 100 μm above the sealing surface of the valve bore and 40 μm, 60 μm, 100 μm or 150 μm below said sealing surface (measured on the contact surface of the plunger). In the upper position, the contact surface of the plunger is thus located above the sealing surface of the upper micro-aperture so as not to touch the diaphragm-type closure element. Alternatively, the central or zero position in the working range of the contact surface of the plunger can be used as a reference for the reference alignment of the piezo bending transducer. The central or zero position can be simply defined as the center of the working range when using a bimorph piezo bending transducer, for example when this transducer is electrically and mechanically stress-free, or in the case of a monomorph piezo bending transducer.

[0019] The working range of the microactuator is preferably set so that the central or zero position of the working range of the microactuator is located as far as possible below the sealing surface of the valve hole, for example at a distance of 20 μm, 40 μm, 60 μm, 100 μm or 150 μm. However, the central position can be virtually located below the mouth of the second microhole, because the lower the central position, the higher the actuation force F available to obtain a good sealing effect at the mouth of the second microhole. However, in this case the piezo bending transducer must be operated with a large total deflection overall, i.e. it must have a wide working range, which will adversely affect the forces and lower its natural frequency. In order to keep the closing force at the mouth of the second microhole small, the diameter of the lower micro-opening must be selected to be sufficiently small, for example 50 μm to 300 μm. However, in this case the flow resistance of the second hole becomes relatively large, the (non-linear) throttle has a large pressure drop, and the time constant of the pressure rise in the cavity is impaired.

[0020] The operating range is preferably selected such that the upper position of the operating range is located slightly above the position of the sealing surface of the valve element. The force profile of the piezoelectric bending transducer proceeding upwards within the operating range results in a large actuation force F open is available to open the valve element when in this position of the sealing surface. In a preferred design for the actuated state, this actuating force F open is the maximum available actuation force F at the upper position of the operating range. max It should be noted in this respect that in the case of a bimorph piezoelectric bending transducer, for example, a voltage is applied to the upper lamina, resulting in a deflection (contraction) to the upper position of the working range, at which the piezoelectric bending transducer is under a maximum mechanical preload. If the upper piezoelectric lamina subsequently discharges and a voltage is simultaneously applied to the lower lamina, the mechanically induced preload resulting from the current deflection is combined with the piezoelectrically induced preload. Thus, the maximum actuation force F available for the actuation task at the upper position of the working range is max is twice the clamping force that characterizes the piezo bending transducer in the zero position.

[0021] It should be noted that these considerations regarding the design of the working range and the location of the central position of the microactuator are also valid, preferably, if there is no direct pneumatic interaction of the second hole with the diaphragm-type closure element and the second hole opens into the cavity at another point. In this case, the smaller of the specific working ranges is sufficient here, since it is not necessary to apply significant reserve forces to seal the valve hole against the working pressure at some distance below the valve element. This has a positive effect on the service life, forces and natural frequency of the microactuator. It should be noted that in this case the second hole can in principle open into any other point of the total dead volume, for example into the cavity, the pneumatic working chamber of the ejector and the connections between them.

[0022] The valve hole has a diameter of 0.3 mm [millimeter], 0.4 mm, 0.5 mm, or 0.8 mm, depending on the application, and the second hole has a diameter of 0.1 mm, 0.15 mm, 0.2 mm, or 0.3 mm, depending on the application. Furthermore, the valve hole and the second hole must be dimensioned to achieve an air pressure switching time of 0.05 ms [millisecond] to 1 ms, or 0.5 ms to 5 ms, depending on the application. Depending on the application, the cavity, the fluid outlet, and the intermediate connection are dimensioned such that the combined air pressure dead volume is in the range of 1 μL [microliter], 2 μL, 4 μL, or 10 μL. The connection between the cavity and the fluid outlet is, for example, between 0.2 mm and 0.5 mm and has a length between 2 mm and 8 mm.

[0023] It should be noted that the stop is used to initialize the position of the actuator (including the plunger) (e.g., zero position or another reference position), e.g., during assembly, and can be located in the area below the valve element. During assembly, the piezo thin layer of the piezo bending transducer is first in a predefined charge state or has a defined voltage applied to it. The actuator, including the plunger, is then positioned against the stop by means of an adjustment screw or the like.

[0024] The stop can be placed in the working range of the actuator relative to the contact surface of the plunger. In this case, the stop also acts as a stop or stroke limiter for the lower diaphragm position of the diaphragm-type closure element during operation. This is the case, for example, when the second hole interacts with the diaphragm-type closure element as a valve seat. For example, in this case, in the case of a bimorph piezoelectric bending transducer, the lower diaphragm position can be defined as coinciding with the zero position or the center position of the working range of the bimorph piezoelectric bending transducer. In this case, the full one-sided deflection of the bimorph piezoelectric bending transducer from the zero position to the upper position of the working range is available to seal the second hole against the working pressure (high pressure level) pH at the level of the lower diaphragm position, and the full compression force of the piezoelectric bending transducer at the zero position is available. Note that this also applies to monomorph piezoelectric bending transducers, but in this case only half of the maximum compression force Fmax, i.e. Fmax / 2, is available for sealing with respect to the stress-free zero position of the transducer. It should be noted that the location and position of the operating range must take into account a maximum error of 20% to 30%, and the inventive teachings are not limited to cases where exact location and position are maintained.

[0025] The stop can also be outside the actuator's working range (below or above) with respect to the contact surface of the plunger. In this case, the stop is not touched by the diaphragm-type closure element while the micro-pneumatic control unit is in operation. In order to use the stop outside the actuator's working range, the actuator is operated in an initial alignment step outside its electrical working range used during operation. For example, if the stop is below the actuator's working range, in a piezo bending transducer, the lower piezo lamina is operated using an overvoltage Ve higher than the working voltage U, or the upper piezo lamina is also operated with the opposite polarity, or both.

[0026] As explained above, the design of the micro-pneumatic control unit described herein and its mode of operation not only already provides optimal utilization of the force profile of the piezoelectric bending transducer, but at the same time keeps the pulse load for opening the valve element low. However, further precautions can still be taken to keep the shock load of the piezoelectric bending transducer low. These precautions include the use of elastomeric materials at various points of the actuation line. These precautions are described below with reference to the figures.

[0027] For the avoidance of doubt, ordinal numbers ("first," "second," ...) used herein primarily and only serve to distinguish between multiple similar objects, values, or steps, i.e., do not necessarily dictate any dependency or ordering of those objects, values, or steps relative to one another. If a dependency or ordering is necessary, this will be set forth herein or will be apparent to those skilled in the art from a review of the embodiments actually described.

[0028] The present invention and technical environment will be described in more detail below with reference to the drawings. It should be noted that the present invention should not be limited by the illustrated embodiments. Unless otherwise specified, it is possible to extract partial features of the technical contents described in the drawings and combine them with other components and knowledge from the present specification and drawings. In particular, the drawings and the dimensional ratios shown in the drawings are merely approximate. The same reference numerals represent the same objects, and any explanations from the explanations of other drawings can be used as supplements as necessary. [Brief description of the drawings]

[0029] [Figure 1] The functioning principle of a micro pneumatically driven printhead 1 of the type considered is shown by means of a pneumatic circuit diagram. [Diagram 2] FIG. 1 is a plan view of a pneumatic network having n (n=2) channels 2. The valve plate 10 and the diaphragm layer 20 are shown in perspective. [Diagram 3] FIG. 2 shows a cross-sectional view of an embodiment of a micro pneumatic control unit 3 for generating a control pressure pC in a ventilated state. [Figure 4] 1 shows a cross-sectional view of an embodiment of a micro pneumatic control unit 3 for generating a control pressure pC in a vented state. [Diagram 5] 2 is a cross-sectional view of a microactuator 25 in the form of a bimorph piezoelectric bending transducer 25, showing a plunger 26 and its fastener for actuating a valve element. [Figure 6] The relationships involved in actuating the micro pneumatic control unit 3 with the bimorph piezo bending transducer 25 are illustrated in the enlarged view. [Figure 7] A cross-section of the channel 2 in a special variant of the micro-pneumatic control unit 3 is shown, where the second hole 16 is provided at a short distance below the first valve element 11, thereby interacting with a diaphragm-type closure element to form the second valve element 36. The concept of a screw connection is also shown. [Figure 8] A cross-sectional view of the channel 2 in a further special variant of the micro-pneumatic control unit 3 is shown. Here, the second hole 16 is provided above the first valve element 11. On the diaphragm side, the valve element 11 is directly connected to a common pressure supply 35 for the operating pressure (high pressure level) pH. The plunger 26 for actuating the valve element 11 also protrudes through the second plate 14. [Figure 9] 1 shows a possible diaphragm structure consisting of multiple layers and a plunger with a molded resilient contact element. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0030] Various terms within this specification may be used in a manner that differs from their general definition. Herein, the following definitions apply:

[0031] When relating to micro-pneumatic elements, the attribute "micro" is intended to indicate that one or more dimensions that substantially determine the function of the component lie primarily between 1 μm and 999 μm.

[0032] When referring to actuators, the attribute "micro" describes the property of an actuator that produces actuation motion in the sub-millimeter range, for example, 0-300 μm.

[0033] The term "ambient pressure" refers here to a lower or low pressure level pL, as opposed to a higher operating pressure (high pressure level) pL. The term ambient pressure also encompasses pressures higher or lower than ambient pressure. For example, instead of ambient pressure, negative pressure can in principle also be used, which can increase the efficiency of the printhead.

[0034] "Channel" 2 refers to the smallest individually electrically controllable unit of the coating head or print head 1.

[0035] 1 shows the functional principle of a printhead 1 operating according to the electro-pneumatic principle and consisting of several channels 2. Each channel comprises one or several fluid ejectors 5, which essentially comprise a fluidic diaphragm valve 7, whose fluidic diaphragm is actuated by a pneumatic control pressure pC via an actuation chamber 6. Under normal conditions, an overpressure prevails in the actuation chamber 6 with respect to the fluid pressure in the fluid supply 45, and therefore the fluidic diaphragm valve 7 is closed. The fluidic pressure vents the actuation chamber 6, which opens the fluidic diaphragm valve 7, and the fluid leaves through one or several fluid outlets 8. In the case of short venting times, for example in the range of less than 1 ms or less than 2 ms or less than 5 ms, the ejection of a droplet is performed. In the case of longer venting times, a fluid jet is ejected. For a more detailed description, see US Pat. No. 5,399,343.

[0036] The required control pressure pC is generated in the micro-pneumatic control unit 3 from two available pressure levels for every channel 2: one is a low pressure level 17 (pL), such as ambient pressure (referred to below), and the other is a higher (higher) pressure level, the operating pressure 18 (pH). In some embodiments, these pressure levels can be reversed (values ​​in brackets in FIG. 1).

[0037] The following description relates to any individual channel of the micro-pneumatic control unit 3. A micro-pneumatic network 4 in the form of a series circuit consisting essentially of two micro-pneumatic impedances Z1, Z2 is clamped between the operating pressure pH and the ambient pressure pL. Each of these micro-pneumatic impedances may consist of a network of further impedances. At the connection node between the aforementioned impedances there is a cavity 9 which is connected to the working chamber 6 of the fluid delivery 5 via a connection 19 which is as short as possible. In the cavity 9, a control pressure pC is determined in proportion to the magnitude of the impedances Z1 and Z2, similar to the pressure divider rule. The micro-pneumatic impedance Z1 has a valve element 11 which is actuated via a microactuator 25. The micro-pneumatic impedance Z2 has a second micro-pneumatic element 15. In the second micro-pneumatic element, a pressure drop occurs when the valve element 11 (of Z1) is open.

[0038] Figures 2 and 3 show a first embodiment, and a slight variation of it in figure 4. Figure 3 shows a cross-section through the channel 2 of the micro pneumatic control unit 3. The word vertical in this case refers to the vertical direction as shown in figure 3.

[0039] The top of the cavity 9 is determined by a diaphragm layer 20, which is located below the valve plate 10, which has a valve hole 12 in the region of the cavity 9. The diaphragm layer 20 covers the valve hole 12 and has recesses 22, which allow air to pass through the diaphragm layer 20 with little resistance and determine the shape of a movable diaphragm-type closure element 21, which finally cooperates with the valve hole 12 to form the valve element 11. The valve hole 12 can be designed as a circular hole or can have any other shape, such as an elliptical or elongated shape or can have a corresponding cross section. The recess or recesses 22 are shaped such that a tongue-shaped diaphragm-type closure element 21 is obtained, for example as shown in the upper part of FIG. 2, which is connected on one side to the remaining diaphragm layer 20 and determines its position.

[0040] 4, it can be seen that such a tongue-shaped diaphragm-type closure element 21, when deflected by the plunger 26, has one side (the left side in the figure) separated from the valve plate 10 in the deflected state. In this case, if the valve hole has an elongated shape, it is also possible to arrange the plunger 26 eccentrically in the valve hole 12 or at one end of the valve hole 12. This has the advantage that the diaphragm-type closure element 21 can be first opened on one side while the plunger 26 is moving, thereby reducing the required operating force F.

[0041] In the lower part of FIG. 2, two semicircular or semicircular annular recesses 22 are shown as a further embodiment. These recesses allow for a different shape of the diaphragm-type closure element. Furthermore, more recesses 22 may be arranged in a circle at a certain distance from the valve hole 12 or in other ways. However, a certain minimum distance from the edge of the valve hole (for example 20 μm to 100 μm) must never be reached. To support the closing process of the diaphragm-type closure element 21, it is possible to realize a restoring force by a certain shape of the diaphragm-type closure element 21 and, for example, a defined diaphragm bending strength. Otherwise, this is only realized by overpressure in the cavity 9. The closing process of the diaphragm-type closure element 21 can be supported by an indirect restoring force of said closure element, which shortens the closing time. However, this presupposes that the diaphragm-type closure element 21 is designed such that its fundamental natural frequency ωo is significantly greater than 1 / Ts (Ts=closing time).

[0042] The cavity 9 is bounded at its bottom by a second plate 14, which has a second micro-pneumatic element 15 in the form of a hole, called second hole 16, and further has a pneumatic connection 19 to the working chamber 6 of the fluid outlet 5. In this case, the valve hole 12 is connected to the ambient pressure pL, and the second hole 16 is connected to the operating pressure pH via a pressure supply 35 (FIG. 7) in the substrate 34. The pressure supply is shared by all channels 2. When the valve element 11 is in the closed state, the operating pressure pH is present in the cavity. In the open state, air flows in a steady manner from the pressure supply 35 to the ambient pressure end of the valve hole 12 through the second hole 16 in FIGS. 3 and 4 and through the valve element 11. The control pressure pC that arises in the cavity 9 then corresponds to the ratio of its flow resistances.

[0043] The open valve element 11 and the second hole 16 are dimensioned with respect to their flow resistance such that (taking into account the diaphragm deflection and the associated design of the microactuator) the control pressure pC has a value between 5% and 20% of the operating pressure pC. Guidance values ​​for suitable hole sizes are found earlier in this document. In order to ensure that the opening clearance of the valve element 11 is always large, a stop 32 as shown in FIG. 3 can be used. In the illustrated case, said stop is mounted, for example, at a distance of 30 μm to 100 μm below the height of the diaphragm layer 20 and is, for example, located within the working range 28 of the microactuator 25. On the other hand, in FIG. 4, instead of the stop 32, a reference position 33 is shown diagrammatically, which is located at a distance further away from the diaphragm layer. It is also shown that the diaphragm-type closure element 21 of the valve element 11 is in the lower position 31 or lower diaphragm position 24 of the working range 28 of the microactuator 25. The reference position 33 is located further below the lower position 31 of the operating range 28, such that during operation the diaphragm-type closure element 21 does not come into contact with the reference position 33. Thus, there are also no load peaks in the piezo bending transducer 25 due to periodic shock loads.

[0044] Figures 3 and 4 also each show spacer plates 39 of different thicknesses that define the cavity 9 in its lateral portions. The use of spacer plates sets the vertical boundary conditions that determine the actuation path and range of motion.

[0045] 3 and 4 further show a microactuator 25 in the form of a bimorph piezoelectric bending transducer. A plunger 26 protrudes through the valve plate 10 and acts on the diaphragm-type closure element 21 with a contact surface 27 formed at the bottom of the plunger 26. The plunger 26 is rigidly connected to the movable end of the piezoelectric bending transducer 25. In FIG. 3, the microactuator 25 is shown in an upper position 30 of its working range 28. This upper position is located, for example, at a distance of 20 μm, 40 μm, 60 μm or 100 μm above the sealing surface 13 of the valve element 11. This distance is necessary so that the plunger 26 does not come into contact with the diaphragm-type closure element 21 when the valve element 11 is closed, and therefore there is no leakage.

[0046] In Fig. 4 the microactuator 25 is shown in the lower position 31 of its working range 28, where the diaphragm-type closure element 21 is also simultaneously located in its lower diaphragm position 24. The distance between the contact surface 27 of the plunger 26 and the sealing surface 13 of the valve element 11 is then, for example, 40 μm, 60 μm, 100 μm or 150 μm.

[0047] With reference to FIG. 2, it should be noted that typical widths of channel 2 are between 0.7 mm and 1.5 mm for high resolution coating applications, e.g. for low to medium viscosity paint applications, 1.5 mm to 3 mm for construction wall paints, and over 2 mm for higher viscosity adhesive and sealant applications.

[0048] FIG. 5 shows the microactuator 25. It consists of a bimorph piezoelectric bending transducer with a central electrode 43 and a plunger 26 connected to the transducer at its movable end. The plunger 26 is connected to the piezoelectric bending transducer via a resilient element 42 made of an elastomeric material, which reduces the transmission of high mechanical stress peaks, which occur, for example, when the contact surface of the plunger 26 hits a stop. The use of this resilient element improves the service life of the piezoelectric bending transducer 25. As shown, the piezoelectric bending transducer 25 is firmly pressed or glued to the screw connection plate 41, to the substrate 34 and to the housing 38 of the printhead 1. The piezoelectric bending transducer 25 is activated, for example, by applying a fixed voltage V1=+VDD to the upper piezoelectric lamina 37 and a ground voltage V0=GND to the lower piezoelectric lamina 44. Normally, the voltage and polarity of the piezoelectric lamina 37, 44 are always rectified. The voltage U of the electrode 43 is switched between +VDD and GND. With voltage U=GND at the central electrode 43, a voltage difference of +VDD is generated across the upper piezo lamina 37, which contracts laterally and deflects the piezo actuator upwards to the upper position 30 of its working range 28 (see also FIG. 6). Conversely, with voltage U=+VDD at the central electrode 43 of the piezo bending transducer 25, a voltage difference of +VDD is generated across the lower piezo lamina 44, which deflects the piezo actuator downwards to the lower position 31 of its working range 28. The deflection x of the unloaded piezo bending transducer 25 thus moves within the working range 28 of the piezo bending transducer 25. This deflection x is measured symmetrically around the zero position (electrically and mechanically stress-free position of the piezo bending transducer 25).

[0049] Considering the actuation force F available for actuating the diaphragm-type closure element 21 (force pointing in the negative z direction for U=+VDD) as a function of the deflection x, above the zero position 29, the force resulting from the mechanical stress caused by the pre-deflection of the piezo bending transducer 25 is added to the constant piezoelectrically generated force. The force resulting from the mechanical stress is highest when the microactuator 25 is in the upper position 30 of the working range 28. This force corresponds to twice the compression force of the piezo actuator, which parameter represents the maximum actuation force when the deflection of the piezo bending transducer 25 is suppressed by the compression, i.e. when the deflection becomes zero. This force is available in the negative z direction for actuation when a voltage +VDD is applied to the central electrode 43 in the upper position 30 of the working range 28.

[0050] Advantageously, during the operation of the printhead 1, it is possible to vary and displace the entire operating range 28 for operation in the z-direction within certain limits, by setting the voltage V1 different from +VDD, by setting the voltage V0 different from GND, by switching the voltage U alternately between values ​​different from +VDD and GND. In this case, it can be stated that: An increase in the operating range can be achieved only by increasing the voltage amplitude ΔU of the two switching positions of the central electrode 43. For example, a displacement of the operating range 28 can be achieved by changing at least one of the voltages V1 and V0 relative to the voltage profile of the voltage U of the central electrode. For example, a negative displacement of the position of the operating range 28 in the z-direction can be achieved only by reducing the voltage V1. See the deflection ξ1 (dashed line). It should be noted that in this case, when the central electrode 43 is operated with +VDD, the upper piezo lamina 37 operates with a negative difference (V1-VDD) and the microactuator 25 is located in the lower position of the (new) operating range 28. However, due to the risk of depolarization of the piezo material, such measures can only be implemented to a very limited extent. However, it is preferable to use these measures to fine-tune the position of the working range 28 of the bimorph piezo bending transducer 25 to the position of the stop 32 or to the reference position 33 or to the valve seat or to the sealing surface 13 of the valve element 11. Thus, for example, small changes occurring during long-term operation can be compensated during operation. However, the same effect can also be achieved by changing the voltage V0 or U on the same basis. The distinctions and combinations of possible cases are not analyzed in more detail here, but can be performed at any time by a person skilled in the art of electrical engineering to derive sufficient solutions specific to the case.

[0051] FIG. 6 shows the above mentioned relationships in several diagrams for a freely movable (unclamped) piezo bending transducer 25 under static conditions. On the right side, the voltage U of the central electrode 43 and the resulting z position are shown. The z position is measured at the contact surface 27 of the plunger 26. The central diagram shows the available actuation force F, which is available in the negative z direction, which causes the opening of the valve element 11. At the lower position 31 of the operating range 28, the actuation force is zero (0), i.e. no actuation force F is available. At the upper position 30 of the operating range 28, the actuation force Fmax is shown. The actuation force F thus increases from bottom to top, with the maximum actuation force F in the negative z direction being available near the upper position 30. On the left side, the deflection x of the stress-free piezo bending transducer 25 around the zero or central position is also shown.

[0052] Advantageously, for the actuation of the diaphragm-type closure element 21, the microactuator is oriented such that the position of the sealing surface 13 of the valve element 11, i.e. the upper diaphragm position 23, is below and as close as possible to the upper position 30 of the working range 28 of the bimorph piezo bending transducer 25, so that at least two thirds (2 / 3) of the maximum actuation force Fmax is available to open the diaphragm-type closure element 21. This design is shown on the left side of FIG. 6, which shows the position of the valve element 11, the contact surface 27 of the plunger 26 and various positions of the diaphragm-type closure element 21. The plunger is shown in the upper position 30 of the working range 28. In this preferred position, the distance between the plunger 26 and the sealing surface 13 of the valve element 11 is at most one third (1 / 3) of the (unloaded) working range 28. However, depending on the application, it is at least 20 μm or 40 μm. It is also evident that in a corresponding design, the central position 29 (for a monomorph piezoelectric bending transducer 25) or the zero position 29 (for a bimorph piezoelectric bending transducer 25, to which the right diagram in FIG. 6 relates) is below the sealing surface 13 of the valve element 11, for example at a distance of 20 μm, 40 μm, 60 μm, 100 μm or 150 μm as mentioned above. Furthermore, the case according to FIG. 4 is shown, i.e. the lower position 31 of the operating range 28 coincides with the lower diaphragm position 24, i.e. without contacting the lower stop during operation.

[0053] This design is particularly suitable for ensuring a long service life of the piezo bending transducer, since in this case shock loads occur only at the moment of contact with the diaphragm-type closure element 21, but these are small since the contact takes place near the stationary upper position 23, where the momentum of the movement of the plunger 26 is also low.

[0054] FIG. 6 also shows how the reference alignment of the (bimorph) piezo bending transducer 25 can be performed at a reference position 33 located below the lower position 31 of the working range 28 of the (bimorph) piezo bending transducer 25. As already described, in the initial alignment step, the transducer is operated outside its electrical working range used during operation. In the example given, for the bimorph piezo bending transducer 25, the transducer is operated with an excess voltage Ve>+VDD. Alternatively or additionally, the upper piezo lamina 37 can be operated with the opposite polarity by reducing the voltage V1 applied to the upper piezo lamina 37, for example by 30%. This extends along the bending transducer and further increases the deflection in the negative z-direction.

[0055] Figure 7 shows a variant of Figure 3, where the second hole 16 is located immediately below the valve hole 12 within the working range of the diaphragm-type closure element 21. As a result, this combination of the diaphragm-type closure element 21 and the second hole 16 creates a second valve element, which is actuated by the same microactuator 25 and the same diaphragm-type closure element 21 as the valve element 11.

[0056] The stroke of the diaphragm-type closure element 21 is the distance between the upper diaphragm position 23 and the lower diaphragm position 24; in this way, it proves advantageous to use a spacer plate 39 of a defined thickness, as in the embodiment according to Fig. 3. From a pneumatic point of view, it has proven expedient to adjust the stroke to 50 μm (30 μm - 80 μm) by using a spacer plate 39 of a suitable thickness.

[0057] In order to achieve a sufficient sealing effect of the second hole 16 against the operating pressure 18 at the lower diaphragm position 24, the microactuator 25 must not operate near the lower position 31 of its operating range 28, in which the operating force F approaches zero, at this lower diaphragm position 24. Rather, in order to obtain a high closing force, the operating range of the microactuator 25 must be set such that the zero or central position 29 of the microactuator 25 is as low as possible, relative to the one described in FIG. 6. In this case, it proves advantageous if the zero or central position 29 lies within a (lower) tolerance of + / - 20 μm (maximum + / - 50 μm) around the lower diaphragm position 24. This tolerance results from the stop 32. Similarly, the upper position 30 of the working range 28 of the microactuator 25 must be positioned at least 20 μm (maximum 50 μm) (upper tolerance) above the position of the sealing surface 13 of the valve element 11, so that when the valve element 11 is closed, the contact surface 27 of the plunger 26 does not touch the diaphragm-type closure element 21. Thus, checking the minimum tolerance of the working range 28 of the microactuator 25 gives a value of 2×(stroke+lower tolerance+upper tolerance)=2×90 μm (2×70 μm to 2×155 μm)=180 μm (to 300 μm).

[0058] In Fig. 8 a further embodiment of the micro-pneumatic control unit 3 is shown in cross section. This further embodiment is characterized by a valve element 11 consisting of the aforementioned valve plate 10 with the valve hole 12 and a diaphragm layer 20 with a diaphragm-type closure element 21 and stretched under the valve plate 10. However, in this embodiment, the operating pressure (high pressure level) pH acts directly on the valve element 11 on the side of the diaphragm layer 20 and is available via a pressure supply 35. For the lower diaphragm position or for the reference position 33 to which the microactuator 35 is aligned in the reference alignment step, a stop 32 can be placed below the valve element 11 as described above in order to improve the defined position. In this embodiment, the cavity 9 together with the connection 19 to the fluid outlet 5 is located above the valve element 11, i.e. above the valve plate 10. The second plate 14 defines the top of the cavity 9 and is therefore located above the valve plate 10. In this case, the plunger 26 of the microactuator 25 protrudes through the valve hole 12 in the valve plate 10 and further through a second hole 16 in the second plate 14. The second hole is arranged concentrically with the valve hole 12 and forms (at least partially) the second micro-pneumatic element 15 together with the plunger shaft. It should be noted in this respect that in a special embodiment the second hole 16 and the plunger shaft can be designed as a tight clearance fit that just allows the movement of the plunger. The micro-pneumatic element 15 can have a further second hole 16 (shown by a dashed line) connected in parallel, which opens into the cavity 9 at another point and is designed to have a lower flow resistance than the clearance of the clearance fit.

[0059] With regard to the individual components and assemblies of the micro-pneumatic control unit 3, the following should be added: the plates listed below, which also have in their structure or microstructure the numerous channels 2 of the micro-pneumatic control unit 3; the valve plate 10 with the valve holes 12; the second plate 14 with the second holes 16, the optional stop 32 or reference position 33 and the optional second valve seat; the diaphragm layer 20 with the recess 22 defining the diaphragm-type closure element 21; the spacer plate 39 with the recess determining the lateral shape of the cavity and also with the optional sealing layer. Furthermore, the following peripheral plates can be added to the list: for example the screw connection plate 41 with all the threaded holes and the necessary holes, and the substrate 34 with the pressure supply channels 35 and the optional stop 32 and the connections 19 to the individual fluid outlets 5.

[0060] The plates 10, 14, 20, 39, 41, 34 can be assembled by threaded connections 40 at regular close intervals of a few millimeters in line with the channel 2 to form a single micro pneumatic control unit 3 while maintaining tight tolerances.

[0061] The choice of material and manufacture of the individual plates 10, 14, 20, 39, 41, 34 is preferably determined by the number of parts desired. The plates 10, 14, 20, 39, 41, 34 (plate 34 or screw connection 40, etc.) which have a mainly three-dimensional extent are preferably made of any solid material such as metal (e.g. aluminum, brass, steel, stainless steel, nickel) or plastic material (solid thermoplastics, thermosetting plastics) which are manufactured in the usual manner. For mass production, the thinner plates 10, 14, 20, 39, 41, 34 (plates 10, 14, 39, etc.) are preferably made of metal such as copper, brass or stainless steel which are etched, for example, by wet chemical etching. In this case, the step shown in the figure (plate 14 in Figs. 3 and 7) can be implemented on both sides, for example by time-controlled etching. Alternatively, plastic material can be used for the thinner plates or embossing or molding methods can be used.

[0062] The diaphragm layer 20 is preferably made of a single material in a single layer, for example of a metal (for example stainless steel, titanium, bronze, nickel) with a thickness in the range of 10 μm to 100 μm. In this case, the fabrication can be carried out by an etching process or an additive (galvanic) process. Alternatively, the diaphragm layer 20 is preferably made of high performance polymers (for example PEEK, PI, PTFE, PEI, PVDF) or elastomers (PU, TPE, TPU, silicone and many others) in different fabrication methods (for example embossing, casting, punching, laser structuring, dry etching).

[0063] During operation, if the plunger 26 permanently impacts the diaphragm-type closure element 21 on the lower stop 32, the diaphragm and the stop 32 are subjected to mechanical wear and the piezo bending transducer 25 is subjected to high-frequency shock loads. These disadvantages are e.g. Elastic element 42The impact contact can be damped and somewhat reduced by using elastic materials such as the plunger tip (FIG. 9) with a thickness of 0.1 mm. The diaphragm layer can be constructed from a thin layer of several individual layers performing different functions. For example, if the middle layer is made of one of the metals mentioned above, it can have a certain mechanical stiffness. Furthermore, if at least one of the lower and upper layers is made of one of the elastomers, it can reduce the stress peaks that occur when the plunger 26 hits the diaphragm or when the diaphragm hits the stop 32 and are transmitted to the piezo bending transducer 25. Conversely, if the diaphragm consists of a layered structure with two outer metal layers and an intermediate polymeric, elastomeric or viscoelastic layer, it can also achieve the damping of the movement of the diaphragm and the stress peaks.

[0064] We propose a micro-pneumatic control unit (3) for generating a control pressure (pC) in a pneumatically actuated multi-channel coating head (1) for coating components with a coating agent, the control channels (2) being characterized in that: a valve element (11) with a valve hole (12) in a valve plate (10) and with a diaphragm layer (20) which is located below said valve plate (10) and in the region of the valve hole (12) is designed as a diaphragm-type closure element (21), the shape of which is determined by a recess located next to the valve hole (12). A microactuator (25) having a plunger (26) which actuates a diaphragm-type closure element (21) via said valve hole (12) so as to open the valve element (11). A second micro-pneumatic element (15) connected in series with the valve element (11), at a connection node between the second micro-pneumatic element (15) and the valve element (11) a control pressure (pC) is generated and a cavity (9) is located, the cavity (9) being connected to at least one pneumatically operated coating agent outlet (5). A pneumatic pressure application of the micro-pneumatic control unit (3) directed to the valve element (11) such that there is a pressure gradient from the diaphragm-type closure element (21) to the valve hole (12) in the valve plate (10). [Explanation of symbols]

[0065] 1 Print head 2 Channel 3. Micro pneumatic control unit with multiple channels 4 Pneumatic Circuit Network 5 Fluid discharge section 6 Working chamber 7 Fluid Diaphragm Valve 8 Fluid outlet 9 hollow 10 Valve plate 11 Valve elements 12 Valve hole 13 Valve element sealing surface 14 2nd board 15 Second micro pneumatic element 16 2nd hole 17 First (low) pressure level, ambient pressure 18 Second (high) pressure level, operating pressure 19 Connection to fluid outlet 20 Diaphragm layer 21 Diaphragm-type closure element 22 Recess 23 Upper diaphragm position 24 Lower diaphragm position 25 Microactuators including plungers, in particular monomorph or bimorph piezo bending transducers 26 Plunger 27 Plunger contact surface 28 No-load operating range 29 Zero position of the operating range 30 Upper position of the operating range 31 Lower position of the operating range 32 Fastener 33 Reference position 34 Substrate 35 Pressure supply line 36 Second valve element 37 Upper Piezo Thin Layer 38 Housing 39 Spacer plate 40 Threaded Connection 41 Screw connection plate 42 Elastic Elements 43 Central electrode 44 Lower Piezoelectric Layer 45 Fluid supply section pC Control Pressure pH High pressure level, operating pressure pL Low pressure level, ambient pressure U Voltage V0 Voltage V1 Voltage Ve Excess voltage ξ Bias ξ1 Bias

Claims

1. A micro pneumatic control unit (3), The micro pneumatic control unit (3) comprises a number of control channels (2), said micro pneumatic control unit (3) for generating a control pressure (pC) to a pneumatically actuated multi-channel coating head (1) for coating a part with a coating agent; The control channel (2) a) a valve element (11), The valve element (11) comprises a valve hole (12) in a valve plate (10) and a diaphragm layer (20); the diaphragm layer (20) is designed as a diaphragm-type closing element (21) below the valve plate (10) and in the region of the valve hole (12), a valve element (11), the shape of the diaphragm-type closure element (21) being determined by a recess located next to the valve hole (12); b) a microactuator (25) having a plunger (26), a microactuator (25) for actuating the diaphragm-type closure element (21) through the valve hole (12) so as to open the valve element (11); c) a second micro-pneumatic element (15), connected in series with said valve element (11); At the connection node between the second micro-pneumatic element (15) and the valve element (11), the control pressure (pC) occurs and a cavity (9) is located, said cavity (9) being connected to at least one pneumatically operated coating agent outlet (5) by a second micro-pneumatic element (15); e) pneumatic pressure application of the micro pneumatic control unit (3), pneumatic pressure applied to the valve element (11) such that there is a pressure gradient from the diaphragm-type closure element (21) to the valve hole (12) in the valve plate (10); A micro pneumatic control unit (3) characterized by:

2. 2. The micro air pressure control unit according to claim 1, The flow resistance of the second micro-pneumatic element (15) is at least twice as large as the flow resistance of the valve element (11) in the open state. A micro air pressure control unit.

3. 3. The micro air pressure control unit according to claim 1 or 2, the no-load operating range (28) of the plunger (26) relative to the plunger contact surface (27) is between 60 μm and 300 μm; an upper position (30) of said operating range (28) is located 20 μm to 100 μm above the sealing surface (13) of said valve hole (12); The lower position (31) of the operating range (28) is between 40 μm and 150 μm below the sealing surface A micro air pressure control unit.

4. 4. The micro air pressure control unit according to claim 3, The central position (29) of the operating range (28) is between 20 μm and 100 μm below the sealing surface (13) of the valve hole (12). A micro air pressure control unit.

5. The micro air pressure control unit according to any one of claims 1 to 4, A second hole (16) is located in the second plate (14) below the valve hole (12); The diaphragm-type closure element (21) covers the second hole (16) at a lower diaphragm position (24) and seals the cavity (9) against the operating pressure (pH) at the second hole (16). A micro air pressure control unit.

6. 6. The micro air pressure control unit according to claim 5, The distance between an upper diaphragm position (23), where the diaphragm-type closure element (21) closes the valve hole (12), and a lower diaphragm position (24), where the diaphragm-type closure element (21) closes the second hole (16), is 30 μm to 80 μm. A micro air pressure control unit.

7. The micro air pressure control unit according to any one of claims 1 to 6, The microactuator (25) comprises a piezoelectric bending transducer; The elastic element (42) for damping the shock load comprises: between the piezoelectric bending transducer and the plunger (26), or Located on the contact surface (27) which is the tip of the plunger (26) A micro air pressure control unit.

8. The micro air pressure control unit according to any one of claims 1 to 7, The diaphragm-type closure element (21) is connected on one side to the diaphragm layer (20) and is designed as a valve tongue. A micro air pressure control unit.

9. The micro air pressure control unit according to any one of claims 1 to 8, A microactuator (25) having a bimorph piezo bending transducer, The operating range of the bimorph piezoelectric bending transducer is such that the piezoelectric thin layer (37) of the bimorph piezoelectric bending transducer is displaced in a direction perpendicular to the position of the sealing surface (13) of the valve hole (12) by moving in the opposite polarity direction. A micro pneumatic control unit characterized by:

10. 10. The micro air pressure control unit according to claim 9, The voltage on the upper piezo thin layer (37) can be varied during operation. A micro air pressure control unit.

Images