Printing apparatus and printing method

Abstract

A printing apparatus (10) for printing on to a substrate, including a printhead (24) and a monitoring device (40) operable to detect movement of a target surface (T) relative to the printhead (24); wherein the target surface (T) is intended to move substantially parallel to a first axis (x), and the monitoring device (40) is operable to detect movement of the target surface (T) along a second axis (y), the second axis (y) being substantially perpendicular to the first axis (x), and a method of operating such a printing apparatus (10).

Description

[0001] PRINTING APPARATUS AND PRINTING METHOD

[0002] FIELD

[0003] The invention relates to a printing apparatus, in particular, but not exclusively, to a transfer printing apparatus, and a method of monitoring one or more parameters of the printing apparatus.

[0004] BACKGROUND

[0005] Transfer printing is well known in the art of commercial printing. An ink carrying tape or ribbon is transferred along a ribbon path from a supply spool, to a take up spool, past a printhead which is operable to transfer ink from the ribbon to a substrate. A printing apparatus may be installed in a production line, for example, adjacent a substrate.

[0006] The printhead may include thermally energisable printing elements or pixels, which are operable to warm the ink on the ribbon such that it can be removed from the ribbon and transferred to the substrate to form an image, for example data, a pattern, a bar code, QR code, etc.. One or both of the supply spool and the take up spool are typically driven in order to transfer the ribbon between the spools.

[0007] The ribbon can typically be moved in two directions between the spools, i.e., in a forward direction and reverse direction. The substrate on to which ink is to be transferred during a printing operation is typically moveable relative to the printhead. There are two principal operating modes 0 intermittent printing and continuous printing. In intermittent printing, the substrate is advanced to a printing position near to the printhead and then stops, the printhead is then moved relative to the substrate, for example by movement of a printhead carriage, to transfer ink from the ribbon to the substrate to create an image. The substrate then advances to a next printing position. This printing operation process is typically repeated until all required printing operations have been completed, and / or the inked ribbon is depleted and / or the substrate is depleted. In continuous printing, the substrate moves substantially continuously relative to the printhead, whilst the printhead remains in a substantially fixed lateral position relative to a substrate support. In this instance, □lateral!] movement of the printhead (or the absence thereof) is intended to mean movement substantially parallel with the direction of movement of the substrate. In both intermittent and continuous printing modes, the printhead typically moves in a longitudinal direction, towards and away from the ribbon and the substrate, between a non-printing position, in which the printhead is not in contact with the ribbon (or at least not sufficiently close to be able to transfer ink from the ribbon) and a printing position, in which the printhead is in contact with the ribbon (or at least is close enough to transfer ink from the ribbon). The non-printing position may include a plurality of positions, including a Dready to print position^ and a retracted position, which may be required, for example, for maintenance purposes. It is important to be able to control the speed of the ribbon accurately relative to the speed of the substrate, so as to optimise print quality. In some circumstances, it is beneficial to control the ribbon speed accurately to correspond with the speed of the substrate, for example to prevent smearing of ink, and / or to ensure that ink is present on the portion of ribbon adjacent the printhead, to avoid failed or poor quality prints. The ribbon speed may be different from the speed of the substrate, but may be linked to the substrate speed. The ribbon speed may be slower than the speed of the substrate. Therefore, monitoring the speed of the ribbon and / or the substrate is desirable.

[0008] It is desirable to be able to determine the position of the printhead, for example relative to the ribbon and / or the substrate, accurately. This is such that a printhead drive apparatus which is responsible for positioning the printhead relative to the ribbon and / or the substrate does not cause too much or too little pressure to be applied during a printing operation, for example, and may also ensure that the printhead does not contact other parts of the printing apparatus and / or contact the ribbon and / or the substrate and / or a substrate support in the wrong place. If the printhead moves out of alignment, for example in a lateral direction along the ribbon path, or in a direction perpendicular to the ribbon path, but in approximately the same plane as the ribbon path, the image produced may be incorrectly positioned on the substrate or may be incomplete. Inaccurate positioning of the printhead may lead to damage to the printhead, and / or damage to other parts of the printing apparatus and / or inadequate print quality, for example. It is known to determine the pressure applied by the printhead on the ribbon / substrate by the use of a load cell. The load cell determines that the printhead has contacted the ribbon / substrate when the load cell detects that a predetermined pressure has been reached or exceeded.

[0009] If a printing apparatus is installed incorrectly (for example, the substrate support and substrate travel path are non-parallel) or the ribbon in a cassette has not been properly wound on (i.e., when coning or telescoping occurs) the ribbon can track across the printhead (as opposed to being positioned consistently underneath it). By tracking, we mean moving perpendicular to the general direction of travel of the substrate, in the plane of the substrate. With reference to Figures 3 and 5 of the drawings, for example, this is movement in the axial direction y.

[0010] For example, a 32mm printhead is usually paired with a 33mm ribbon, so, if the ribbon tracks (along axis y) by more than 0.5mm, the printhead may be exposed directly to the substrate causing additional wear, early failure, and poor print quality.

[0011] DTrackingD or misalignment of the substrate relative to the printing apparatus, e.g. the printhead and / or the ribbon can also cause problems with incomplete or insufficient quality prints, and / or can cause damage to the printing apparatus, the ribbon, the substrate and / or parts of a production line in which the apparatus is installed. If the printing apparatus is not installed to align well with direction of substrate travel, during a printing operation, when the head traps the ribbon against the substrate, the substrate can pull the ribbon significantly off the printhead, causing wear to the printhead especially at the extremes. The printing apparatus and method described herein seek to minimize tracking of the substrate and / or ribbon.

[0012] If the ribbon has been hand-wound, or the cassette has been dropped, for example causing nonparallelism of the rollers / guides / spindle, some tracking can occur when ribbon is transferred from the supply to take-up spool or vice versa.

[0013] Embodiments relating to the present disclosure seek to alleviate one or more of the problems associated with known systems.

[0014] There is provided a printing apparatus for printing on to a substrate, including a printhead and a monitoring device operable to detect movement of a target surface relative to the printhead; wherein the target surface is intended to move substantially parallel to a first axis, and the monitoring device is operable to detect movement of the target surface along a second axis, the second axis being substantially perpendicular to the first axis.

[0015] The monitoring device may be operable to detect movement of the target surface along the first axis and the second axis.

[0016] The monitoring device may be operable to detect movement along the first axis and the second axis simultaneously.

[0017] The printing apparatus may include a processor operable to determine one of linear or angular displacement of a part of the printing apparatus relative to the target surface.

[0018] The printing apparatus may include a processor operable to determine one of linear or angular displacement of a part of the printhead relative to the target surface.

[0019] The printing apparatus may include a processor operable to process data indicative of movement of the target surface along the first axis and the second axis to determine an angular displacement of the printhead relative to target surface.

[0020] The monitoring device may be operable to observe an interference pattern created by radiation reflected by the target surface. The target surface may be one of a substrate on to which the printing apparatus is arranged to print, and an inked ribbon associated with the printing apparatus and operable to transfer ink to the substrate.

[0021] The target surface may be a component whose movement is indicative of movement of at least one of a substrate on to which the printing apparatus is arranged to print, and an inked ribbon associated with the printing apparatus arranged to transfer ink to the substrate to be printed.

[0022] The component whose movement is indicative of movement of the substrate and / or ribbon may be one of a substrate support and a ribbon guide.

[0023] The printing apparatus may be operable to respond to an indication of movement of the target surface along the second axis, and / or an indication of displacement of a part of the printing apparatus relative to the target surface wherein the response may include at least one of: a. providing an indication to a user that movement along the second axis is occurring or has occurred; b. providing an indication to another device that movement along the second axis is occurring or has occurred; c. carrying out automatic adjustment of the position of the printing apparatus relative to the target surface, by causing movement of at least one of:

[0024] I. a part of the printing apparatus,

[0025] II. the whole printing apparatus, ill. the target surface; d. adjusting printing operation instructions to take the movement or displacement into account; e. stopping or pausing printing operations.

[0026] The printing apparatus may include a plurality of monitoring devices.

[0027] The printing apparatus may be a thermal transfer printer.

[0028] There is provided a method of operating a printing apparatus printing apparatus for printing on to a substrate, including a printhead and a monitoring device operable to detect movement of a target surface relative to the printhead; wherein the target surface is intended to move substantially parallel to a first axis, and the monitoring device is operable to detect movement of the target surface along a second axis, the second axis being substantially perpendicular to the first axis, the method including using the monitoring device to detect movement of the target surface along the second axis. The method of operating a printing apparatus may include: using the monitoring device to monitor at least one of: o movement of the target surface along the second axis, o displacement of a part of the printing apparatus relative to the target surface; providing an indication of movement of the target surface along the second axis, and / or an indication of displacement of a part of the printing apparatus relative to the target surface, to a processor of the printing apparatus; responding to indication of movement or displacement, the wherein the response includes at least one of: o providing an indication to a user that movement along the second axis or displacement of a part of the printing apparatus is occurring or has occurred; o providing an indication to another device that movement along the second axis is occurring or has occurred; o carrying out automatic adjustment of the position of the printing apparatus relative to the target surface, by causing movement of at least one of:

[0029] D a part of the printing apparatus,

[0030] D the whole printing apparatus,

[0031] D the target surface; o adjusting printing operation instructions to take the movement or displacement into account; o stopping or pausing printing operations.

[0032] The method may include taking into account known or intentional movement or displacement of at least a part of the printing apparatus relative to the target surface, along the first and / or second axis.

[0033] The target surface may be the substrate to be printed, and the method may include using an indication that the substrate has moved and / or is moving and / or is displaced relative to the printhead along the second axis to indicate that a ribbon associated with the printing apparatus for transferring ink to the substrate has moved, and / or is moving and / or is displaced relative to the printhead.

[0034] BRIEF DESCRIPTION OF THE FIGURES

[0035] In order that the present disclosure may be more readily understood, preferable embodiments thereof will now be described, by way of example only, with reference to the accompanying drawings, in which: FIGURE 1 is an illustrative cut away view of a printing apparatus;

[0036] FIGURE 2 is an enlarged, illustrative view of a monitoring device of the printing apparatus of Figure 1 and a target surface;

[0037] FIGURE 3 is an illustrative perspective view of a printhead adjacent a substrate to be printed, to illustrate possible directions of displacement of the printhead and / or a target surface;

[0038] FIGURE 4 is a perspective view of a part of the printing apparatus of Figure 1 ;

[0039] FIGURE 5 is a perspective view of parts of a printing apparatus according to embodiments of the technology; and

[0040] FIGURE 6 is an illustration showing angular displacement of a printhead relative to the target surface.

[0041] DETAILED DESCRIPTION OF THE DISCLOSURE

[0042] Referring to the figures, there is shown a printing apparatus 10, having a body 11 housing a first spool 12, and a second spool 14 of inked ribbon or tape 16. Each of the spools 12, 14 is mounted on a respective spindle 18, 20. Each of the first spindle 18 and the second spindle 20 may be driven by a ribbon drive apparatus 22, which may include one or more motors. Rotation of each spindle 18, 20 causes rotation of the respective spool 12, 14, and may be controlled so as to transfer ribbon 16 from one of the first spool 12 and the second spool 14, to the other of the first spool 12 and the second spool 14. Ribbon 16 may be transferred in two directions, i.e. a forward direction and a reverse direction, between the spools 12, 14. The rotation of the or each spindle 18, 20 and / or spool 12, 14 may be controlled and / or monitored in any appropriate way, for example in accordance with known methods, for example by a single motor, or a respective motor for each spindle 18, 20, etc.. The printing apparatus 10 may be a print and apply printing apparatus, e.g. operable to print labels for application to another object, or may be operable to print directly on to product packaging, e.g., DoverprintingD.

[0043] The ribbon drive apparatus 22 is operable to transfer ribbon 16 between one of the first and second spools 12, 14 and the other of the first and second spools 12, 14, past a printhead 24. A ribbon support 17, e.g. a ribbon roller may support the ribbon 16 near the printhead 24. The printhead 24 may include a plurality of energisable printing elements, for example thermally energisable printing elements, which may be selectively operable to transfer ink from the ribbon 16 to a substrate 26. The substrate 26 may be a roll of material, for example paper, film, e.g., biaxially oriented polypropylene, labels, etc.. The substrate 26 may be provided as discrete items to be printed, e.g., labels, as in Dprint and applyD applications.

[0044] The substrate 26 may be supported adjacent the printhead 24 by a substrate support 28. The substrate support 28 may be a platen roller, or a substantially planar platen, for example. The substrate support 28 may be driven by a substrate drive apparatus 29, for example a motor, to advance the substrate 26. It will be appreciated that the substrate drive apparatus 29 need not be positioned in the substrate support 28 and / or need not drive the substrate support 28 directly. The substrate support 28 may be rotated to move the substrate 26 relative to other parts of the printing apparatus 10, for example the printhead 24. The substrate drive apparatus 29 may be operable to advance the substrate 26 into a printing position adjacent the printhead 24. Whilst the substrate drive apparatus 29 is primarily provided to move the substrate in a lateral direction x, the substrate drive apparatus 29 (and / or additional / alternative substrate drive apparatus, not shown) may be operable to move the substrate 26 in one or more directions and / or along each of the axes x, y, z shown in Figure 3.

[0045] The printing apparatus 10 may include a controller 30. The controller 30 may be operable to control one or more functions of the printing apparatus 10. For example, the controller 30 may be operable to control the movement of the ribbon 16, for example by controlling the ribbon drive apparatus 22, movement of the printhead 24, and / or the energization of printing elements of the printhead 24. The controller 30 may be operable to monitor parameters and / or functions of the printing apparatus 10. For example, the controller 30 may be operable to receive signals which are indicative of functions and / or parameters of the printing apparatus 10. For example, the controller 30 may be operable to determine and / or monitor the diameters of each spool 12, 14, and / or to determine and / or monitor tension in the ribbon 16 for example. It will be understood that these examples are not intended to be limiting, and any combination of functions of the controller 30 to enable the printing apparatus 10 to carry out printing operations, may be possible.

[0046] The printing apparatus 10 may include a monitoring device 40. The monitoring device 40 is shown in illustrative form in Figure 2.

[0047] The monitoring device 40 may be operable to monitor one or more parameters or characteristics of one or more parts of the printing apparatus 10, for example the printhead 24 and / or the ribbon 16, and / or an item co-operating with the printing apparatus 10, for example the substrate 26.

[0048] The monitoring device 40 may include a non-contact sensor. The monitoring device 40 may include an emitter 42 and a receiver 44. The monitoring device 40 may include a processor 46, for example a microprocessor. The emitter 42, receiver 44 and the processor 46 may be integrated in a single device, for example a single integrated circuit or chip.

[0049] The emitter 42 may be operable to emit an output signal So. The output So may be or include electromagnetic radiation. The output So of the emitter 42 may include coherent light, e.g. the emitter 42 may be or include a laser. The output of the emitter 42 may be in the infra-red range of the electromagnetic spectrum. The monitoring device 40 may include a vertical-cavity surface-emitting laser (VCSEL). A series of output signals may be emitted. The output signal So may be a pulsed signal. There may be a time interval t between each output signal So being emitted. The output signal So may be emitted at a substantially constant frequency, with the interval t between each output being substantially the same. The time interval t between successive output signals So may be nominally substantially constant, but it will be appreciated that it may be necessary to identify and account for jitter.

[0050] The output signal So of the emitter 42 may be directed towards a target surface T, a parameter of which is to be determined and / or monitored.

[0051] The target surface T may be a part of the printing apparatus 10, an item which co-operates with the printing apparatus 10 or an item separate from the printing apparatus 10.

[0052] The receiver 44 of the monitoring device 40 may be configured to receive all or part of the output signal So from the emitter 42. The receiver 44 may be configured to receive a reflected portion SR of the signal output So from the emitter 42. The receiver 44 may be a CCD or CMOS device, for example. The emitter 42 may be positioned adjacent the receiver 44. The receiver 44 may partially or completely surround the emitter 42.

[0053] The monitoring device 40 may be a miniature chip. The monitoring device 40 may include integrated digital image process circuits. The monitoring device 40 may be a surface mountable component. The monitoring device 40 may be motion detector. The monitoring device 40 may be a laser scatter motion detector. The monitoring device 40 may be of a kind which does not require a lens. The monitoring device 40 may be selected to have a depth of field (DOF) appropriate for positioning the monitoring device 40 inside a printing apparatus. The depth of field of the monitoring device 40 may be selected to be in the range 5mm to 60mm, for example.

[0054] A plurality of monitoring devices 40 may be associated with the printing apparatus 10. Each monitoring device 40 may be provided to monitor a particular characteristic or parameter. A plurality of parameters and / or characteristics may be monitored by one or more monitoring devices 40. Each parameter or characteristic to be monitored may be monitored by one monitoring device 40 or a plurality of monitoring devices 40. The number of monitoring devices 40 required to monitor a particular parameter / characteristic may depend on the parameter / characteristic to be monitored and / or the target surface(s) T, and may be selected accordingly. The monitoring device 40 may be positioned in or near the printhead 24. The or each monitoring device 40 may be communicable with the controller 30. A single monitoring device 40 is generally referred to herein, for the sake of simplicity, but it is intended that such references may encompass the use of a plurality of monitoring devices 40, where appropriate.

[0055] The monitoring device 40 may be operable to measure changes in the position of the target surface T relative to the monitoring device 40, i.e., the monitoring device 40 may be operable to monitor displacement of the target surface T. For example, the monitoring device 40 may be operable to monitor displacement of the substrate 26 and / or the ribbon 16, relative to the monitoring apparatus 40, and / or relative to another part of the printing apparatus 10. The monitoring device 40 may be operable to determine the speed of the target surface T. The speed of the target surface T may be an absolute speed, or may be a speed relative to another part of the printing apparatus 10, for example the printhead 24 and / or the monitoring device 40.

[0056] The monitoring device 40 may be operable to determine changes in position of the target surface T. The target surface T has a reflectivity RT. The reflectivity T may not be constant, in other words different areas of the target surface may have different reflectivity values. The reflectivity of the surface may also vary with time, for example, the reflectivity of the ribbon 16 may depend on the quantity of ink on the ribbon, and therefore the reflectivity T of a portion of the ribbon may have one value before ink has been removed during a printing operation, and a different reflectivity T after ink has been removed. The texture or roughness of the target surface T may affect the reflectivity T and / or the signal or pattern reflected by the target surface T.

[0057] In use, the monitoring device 40 may be operable to acquire sequential surface images (frames) of the target surface T, and by comparing (by auto-correlation, cross-correlation or convolution, or using Fourier analysis in the detector plane, for example) two or more frames with one another, determining one or more of the speed, direction and magnitude of motion of the target surface T relative to the monitoring device 40. This method will be described in more detail below.

[0058] The monitoring device 40 may be operable to carry out a series of monitoring operations to generate displacement data. During a first monitoring operation, the emitter 42 is configured to emit a first output signal So towards the target surface T, and the receiver 44 is configured to receive the reflected portion SR of the output signal So which is reflected by the target surface T. Data representative of the reflected portion SR, for example a pattern, e.g. a speckle pattern, created by the reflected portion SR of the output may be stored by the processor 46. A series of monitoring operations may be carried out. A monitoring operation may be carried out multiple times per second, for example several thousand times per second. In each monitoring operation, the emitter 42 is configured to emit an output signal So towards the target surface T and the receiver 44 is configured to receive a respective reflected portion SR corresponding with each output signal So. The reflected portion SR is reflected by the target surface T, and is characteristic of the portion of the target T surface that the output was directed towards and reflected from. Each reflected portion SR may be an interference pattern, e.g. a speckle pattern. Comparing the interference patterns enables a parameter of the target surface T to be determined and / or monitored. The pattern created by each reflected portion SR, or data which is characteristic of each reflected portion SR may be stored, for example as an image or DframeD, or in any appropriate manner.

[0059] The monitoring device 40 is operable to report the movement of the target surface T during a monitoring period, as a change in position, or displacement, in one or more dimensions x, y, z since a previous monitoring operation / reading. The monitoring period may be one or more time intervals t, in other words the monitoring period may include a plurality of monitoring operations. Change in position data, i.e., displacement, of the target surface T relative to the monitoring device 40 may be provided to a controller, e.g., the controller 30. Change in position data determined by the monitoring device 40 and passed to the controller 30 may be read by the controller 30. The monitoring device 40 may pass data to the controller 30 automatically, for example in accordance with a duty cycle and / or in response to a trigger event. Additionally or alternatively, the controller 30 may interrogate the monitoring device 40 for data relating to a change in parameter. Interrogation of the monitoring device 40 by the controller 30 may be automatic, for example in accordance with a duty cycle and / or in response to a trigger event. The term DreadingD is intended to mean the receipt of data by the controller 30 from the monitoring device 40, regardless of whether the controller 30 has interrogated the monitoring device 40, or whether the monitoring device 40 has passed the data automatically, for example in accordance with a predetermined schedule, or in response to a trigger event.

[0060] The monitoring device 40 may be operable to determine that a change in parameter has been zero since the previous monitoring operation or during a monitoring period. The monitoring device 40 may be operable to indicate to the controller 30 that the change in parameter has been zero since the previous monitoring operation or during a monitoring period. No change in a parameter since the previous monitoring operation or during a monitoring period may be a trigger event. A change in parameter following a period of no change in parameter may be a trigger event. Therefore, monitoring periods may be approximately the same duration, or may be of varying duration. The controller 30 and / or the monitoring device 40 may determine or set the duration of each monitoring period.

[0061] Change in parameter data, e.g., displacement, of the target surface T relative to the monitoring device 40, may be summed by the processor 46, and the summed values may be passed to the controller 30. Change in position data in two dimensions may be provided. The change in one dimension may be zero, whilst the change in position in another dimension may be non-zero during the same monitoring period or time interval t. The monitoring device 40 may be operable to indicate that it has detected a change in parameter, e.g. when it has detected movement (displacement) of the target surface T in at least one dimension. If, for example, the target surface T is stationary for a period of time, the monitoring device 40 may carry out a number of monitoring operations during that period of time, and no displacement will be detected. The monitoring device 40 may not pass the data relating to the time during which the target surface is stationary to the controller 30. If at the end of the period of time during which the target surface was stationary, the monitoring device 40 detects that the target surface has moved in at least one dimension, this change may trigger the monitoring device 40 to pass the data relating to the change in position (displacement) to the controller 30. The controller 30 may be operable to use a single datum indicative of a change, for example a datum which indicates that the target surface T has moved by a distance d in at least one of the dimensions x, y, z during the most recent time interval. The time interval may be set by the monitoring device 40. By carrying out monitoring operations and / or readings at regular intervals, the speed of the target surface T can be calculated, since the frequency of the monitoring operations and / or the frequency at which the data provided by the monitoring device 40 is sampled (read) by the controller 30 is known. The controller 30 receiving the change in position data may process the data and use the change in parameter (e.g., position) data to control aspects of the printing process, and the operation of the printing apparatus. The time interval between each monitoring operation by the monitoring device and / or between each sample (reading) by the controller 30 may or may not be the same. A clock of the controller 30 may be synchronized with a clock of the monitoring device 40, in order to be able to carry out accurate calculations, for example to determine the rotational and / or translational displacement, or its derivatives, e.g., speed, acceleration and jerk in multiple dimensions, of the target surface T relative to the monitoring device 40.

[0062] Displacement data obtained by the monitoring device 40 may be sent to the controller 30, and used by the controller 30 in calculations of other parameters / characteristics of the printing apparatus 10 and / or an associated item, e.g. the substrate 26, and / or may be used to determine control functions of the printing apparatus 10, to enable printing operations to be carried out.

[0063] As explained briefly above, a parameter or characteristic may be monitored by a plurality of monitoring devices 40. A monitoring array may include a plurality of monitoring devices 40. Each monitoring device 40 in the monitoring array may be spaced from one or more adjacent monitoring devices 40 by a distance less than 10mm, for example 6mm. The plurality of monitoring devices 40 may be arranged in any appropriate manner. The arrangement of the plurality of monitoring devices 40 may be a line, a rectangular array, a substantially circular array, etc.. The arrangement and / or type of the monitoring devices 40 in the monitoring array may depend upon the target surfacesurface T being monitored and / or the parameter of the target surfacesurface T being monitored.

[0064] A plurality of monitoring arrays may be provided. The plurality of monitoring arrays may be operable to monitor a plurality of target surfaces and / or a plurality of parameters, and / or to provide data indicative which may be used to determine one or more further parameters. Where a monitoring device 40 is referred to herein, the skilled person will understand that a single monitoring device 40 may be used or a monitoring array may be used. The most appropriate arrangement of monitoring devices 40 may be selected dependent upon the space available, and / or the parameter / characteristic to be monitored, and / or the accuracy of the monitoring required, and / or the target surface(s) T to be monitored. For example, a matte target surface may be optimally monitored using a monitoring array, to provide sufficiently accurate data indicating a parameter of the surface (it will be understood that this simply a suggestion of a possibility, rather than an indication of an essential feature).

[0065] Where a monitoring array is provided, the controller 30 may be operable to distinguish between data provided by each monitoring device 40 of the monitoring array. The controller 30 may be operable to combine data from some or all of the monitoring devices 40 of the monitoring array to determine further parameters of the target surface and / or determine control functions of the printing apparatus 10, to enable printing operations to be carried out.

[0066] The target surface T towards which the signal of the monitoring device 40 is directed may be the substrate 26. The monitoring device 40 may be operable to determine the displacement and / or the speed and / or the acceleration of the substrate 26 and / or the orientation of the substrate 26 relative to a part of the printing apparatus 10, e.g. the printhead 24. In this case, the monitoring device 40 may be positioned inside the body 11 of the printing apparatus 10. Alternatively, the monitoring device 40 may be positioned externally of the body 11 of the printing apparatus 10. The monitoring device 40 may be spaced between approximately 10mm and approximately 40mm from the substrate 26. The monitoring device 40 may be positioned such that the angle of incidence 0i of the output signal So emitted by the monitoring device 40 at the substrate 26 is approximately 90°. The monitoring device 40 may be mounted on or in the printhead 24. The monitoring device 40 may be positioned at or near a centre line of the printhead 24. The monitoring device 40 may be positioned such that the or each output signal So of the monitoring device 40 is incident on the substrate 26 at a position which is substantially aligned with one or more printing elements of the printhead 24. The monitoring device 40 may be positioned such that the output signal So is directed towards a crown or top dead centre position of the substrate support 28. The method of determining a characteristic, e.g displacement, speed, acceleration, of the substrate 16 is as described above. The monitoring device 40 may be positioned on the printhead carriage 25.

[0067] The target surface T may be the ribbon 16. The monitoring device 40 may determine and / or monitor the displacement and / or speed of the ribbon 16 directly. The monitoring device 40 may be mounted inside the body 11 of the printing apparatus 10. The monitoring device 40 may be positioned such that the angle of incidence ©i of the output signal So emitted by the monitoring device 40 at the ribbon 16 is approximately 90°. The monitoring device 40 may be positioned near a centre line of the ribbon 16. The monitoring device 40 may be positioned such that the output signal So is directed towards the centre line of the ribbon 16, The printing apparatus 10 may be configured to be operable with different types, e.g. different widths of ribbon 16. The monitoring device 40 may be positioned such that the output signal So is directed towards a centre line of the narrowest ribbon 16 that the printing apparatus 10 is configured to use. The monitoring device 40 may be mounted on or near the printhead 24, to determine a parameter of the ribbon 16 at or near the printhead 24. The method of determining a characteristic, e.g displacement, orientation, speed and / or acceleration of the ribbon 16 may be as described above generally, and in relation to the substrate 26.

[0068] The monitoring device 40 may be positioned adjacent one of the first and second spools 12, 14. A monitoring device 40 may be associated with each of the first and second spools 12, 14. The or each monitoring device 40 may provide an indication of displacement (i.e. rotation) of the associated spool 12, 14, and / or the speed of rotation of its associated spool 12, 14. This may include determining the displacement and / or speed of rotation of an outer surface of the ribbon 16. A linear displacement of ribbon 16 near to the or each spool 12, 14 may be monitored. Such linear displacement may be indicative of the amount of ribbon 16 wound on to or off the associated spool 12, 14. The angle of rotation of the spool 12, 14 may be known, therefore the diameter of the spools may be calculated from the monitored linear displacement of ribbon 16 near the spool. The monitoring device 40 may be operable to determine a rotational displacement of the outer surface of one or both spools 12, 14 in order to determine the circumference of the or each spool 12, 14. The determination of the speed of rotation and / or the diameter of the or each spool 12, 14 may be carried out as a calibration step. Determination of the speed of rotation and / or the diameter of the or each spool 12, 14 may take place in a very short space of time, which may be the time taken for a few millimeters, for example less than 10mm, of ribbon 16 to be wound on to and / or unwound from one of the spools 12, 14. This enables virtually instantaneous determination of the diameters of the spools 12, 14. This reduces the time spent carrying out the calibration process, and removes the need to transfer the ribbon 16 in both directions. The ability of the monitoring device 40 to directly monitor characteristics / parameters such as displacement, means that determination of a characteristic of the or each spool 12, 14 may take place during operation of the printing apparatus 10, rather than during a calibration step. Monitoring of characteristics may take place continually (i.e. repeatedly) or substantially continuously during use of the printing apparatus 10. Such monitoring during use of the printing apparatus 10 may be instead of or in addition to a calibration step or steps.

[0069] The ability of the or each monitoring device 40 to directly determine characteristics / parameters of the or each spool 12, 14 means that ancillary parts, for example a monitoring roller and / or a Hall effect sensor are not required to determine the relative speeds of the spools 12, 14, for example. Further, these implementations do not require a cassette insertion / removal switch it is possible to track lateral (axial) movement of the spool / ribbon instead. The speed of one of or each of the spools 12, 14 (and / or the relative speed of the spools 12, 14, and / or a signal indicative of the speed of each spool 12, 14) may be communicated to the controller 30. The controller 30 may use this information relating to the speed of the or each spool 12, 14 to determine control of the ribbon drive, for example to determine the control of a motor drive circuit of the ribbon drive apparatus 22.

[0070] The monitoring device 40 may be operable to determine a characteristic, e.g. the position, displacement and / or speed of the printhead 24. The monitoring device 40 may be operable to determine displacement of the printhead 24 relative to another part of the printing apparatus 10, for example. In this case, the monitoring device 40 may be in a fixed position relative to the printhead 24, e.g. attached to the printhead 24 or the carriage 25, and the target surface T may be another part of the printing apparatus 10, for example a part of the body 11 . Alternatively, the monitoring device 40 may be mounted on a (preferably stationary) part of the printing apparatus 10, for example the body 11 , and the target surface T may be a part of the printhead 24. This is useful in determining whether the printhead 24 is in the correct position relative to the ribbon 16, and / or the substrate 26, and / or one or more other parts of the printing apparatus 10, e.g. the substrate support 28. With reference to Figures 5 and 6, we now look at the case in which the monitoring device 40 determines that a deviation, for example an angular deviation, has occurred in the relative positioning of the printing apparatus 10 (for example the printhead 24 and / or the ribbon 16) and the substrate 26, and / or that a cumulative distance error has occurred in the position of the substrate 26 in a direction substantially perpendicular to the substrate path, i.e. along the y axis.

[0071] In embodiments, non-parallelism between a plane of the printing apparatus (a primary plane) and the path of travel of the substrate 26 is detectable using the y axis data from the monitoring device(s) 40. Note the position of the arrow denoted 1 in Figure 5, marking a position at which a monitoring device 40a may interact with the substrate 26, in line with the method and configuration set out above. It will be appreciated that other positions of the monitoring device 40a may be appropriate. Any non-zero data on the y axis, received from the monitoring device 40, may be an indicator of non-parallelism. In other words, if the monitoring device 40 determines a change in position of the substrate 26 in the direction y, i.e. in a direction substantially perpendicular to the substrate path, the monitoring device 40, e.g. monitoring device 40 may provide an output to the controller 30, or other processor, to indicate that the printing apparatus 10 and the substrate 26 are no longer in alignment. The deviation or misalignment may be indicated as a linear misalignment, an angular deviation, or an amount of deviation predicted in a given time period, length, number of printing operations, etc. There may be a tolerance associated with the alignment of the substrate 26 and the printing apparatus 10, such that a certain amount of misalignment or deviation may be acceptable. The tolerance may be dependent upon the application in which the printing apparatus 10 is used. The controller 30 may be operable to provide a signal to a user that the printing apparatus 10 and the substrate 26 are misaligned or are about to become misaligned. An indication may additionally or alternatively be provided to another device, for example a controller or actuator configured to adjust the position of the printing apparatus in relation to other devices, for example a production line. The indication of misalignment may be provided whilst the misalignment is within the acceptable tolerance, for example to enable remedial steps to be carried out prior to misalignment falling outside the tolerance. The indication may be provided such that remedial steps may be carried out before misalignment is too great for printing operations to continue.

[0072] During the installation process, a setup interface may prompt an installation engineer to start the substrate 26 rolling, i.e. moving past the printing apparatus 10 (in particular past the printhead 24). The x, y outputs of the monitoring device 40 may be used to detect significant non-zero y data. Such data is an indicator of non-parallelism between the printing apparatus 10, and the ideal substrate travel path, e.g. an indication of a deviation between an ideal substrate path and the actual substrate path y. The angular deviation 0 can be derived almost trivially by using the following relationship:

[0073] 0 = tan-1- (1) or

[0074] 0 = tan1- y (2)

[0075] With the sub-millimetric resolution achievable from the monitoring device 40, this should be able to read sub-degree accuracy, in other words, deviation 0 of less than 1 ° may be detected by the monitoring device 40.

[0076] A visualization may be provided to the engineer instructing them to adjust the position, e.g. turn the printing apparatus / bracket or platen mount, for example, to correct the angle between the printing apparatus 10 and the substrate 26 until it is correct 0 determined when the y data averages zero for an expected typical print cycle. Additionally or alternatively, printing operations may be interrupted if the deviation or misalignment exceeds a predetermined limit.

[0077] During normal use, a monitoring process can run in the background, informing / warning the maintenance engineer (or a remote service team) that some tracking error has occurred, denoting non-alignment (misalignment or deviation) from the originally installed position, or falls outside a predetermined tolerance, for example. This can then be remedied if perceived to be a problem by the customer. The data from the monitoring device 40 can be interrogated and used to diagnose print quality, printhead dot death or reported ribbon tracking issues e.g., by studying the average y- axis values of data observed over a recent period. Where the printhead 24 is installed at a nonsquare angle 0 to the substrate, the angle of installation can be determined.

[0078] In embodiments, ribbon mount issues can be tracked using a monitoring device 40b, for example located at the position denoted by arrow D2D in Figure 5. Even if a printing apparatus 10 is perfectly installed such that the printhead 24 is perfectly orthogonal to the path of the substrate 26, problems with ribbon 16 being incorrectly installed in a cassette or wound onto the core incorrectly, can cause tracking issues. If the cassette has been dropped there may also be issues with perpendicularity of the guide rollers around which the ribbon 16 extends in the tape path between the spools 12, 14, to the cassette or baseplate which can force the ribbon 16 off its desired path.

[0079] To detect these issues, the monitoring device 40 may observe the ribbon 16, and the y data can be used to ensure that y data averages zero. This can be reviewed per print cycle i.e. to determine whether the user installed the ribbon 16 correctly, and that it hasnt tracked across the printhead 24 since the last print. It can also be reviewed across multiple print cycles, e.g., to detect whether the ribbon 16 has shifted left or right across the printhead 24 (i.e. along the y-axis) in the last 1 m of ribbon transferred, for example, which may be continuously tracked. This is particularly useful immediately after the cassette has been reinserted in the printing apparatus 10. The or each monitoring device 40 may provide 16bit data (i.e. potentially 1 / 65k resolution) for each dimension (x, y, z).

[0080] The user can be informed the ribbon 16 is poorly wound, that they need to change the cassette, and / or that they can acknowledge the tracking occurring and simply ignore the warning, via an interface of the printing apparatus 10.

[0081] In some installations the printing apparatus 10 may be moved orthogonally (e.g. along the y-axis) between print cycles to allow optimisation of ribbon usage. This is termed DtranslationD. If the substrate 26 is moving whilst the printing apparatus 10 is translated, any non-orthogonal movement of the substrate 26 cannot be differentiated from the translation. For example, if the printing apparatus is moving left 10mm in 10milliseconds between prints, and the substrate 26 moves net relative 1 mm left in the same time, the sensor will measure only 9mm movement. This gives the advantage that the printing apparatus 10 can command an additional 1 mm movement to ensure that the net relative movement is the required 10mm. A separate sensor is not necessary to differentiate substrate drift from printing apparatus translation as the integrated encoder (monitoring device 40) will accumulate the relative motion.

[0082] It is possible for the monitoring device(s) 40 to provide ^distance movedD information, removing the need for an external encoder to be attached to the translation mechanism. This provides a solution wherein the printing apparatus 10 can provide the distance information for the control system that manages the printing apparatus translation, and the printing apparatus 10 can drive the actuator, e.g. robot arm electronics, managing more of the translated radial ribbon saving process. Note that in this case, even for continuous printing applications where a curved surface (i.e. the platen roller) is observed, because the motion is along the rollerfe flat y-axis, the sensed speed is true / real speed independent of the placement of the monitoring device 40 relative the platen roller.

[0083] As mentioned, between print cycles of a thermal transfer overprinting apparatus (TTO), the entire TTO printing apparatus 10 may be translated by an equivalent width of the printed image (i.e., the printhead is moved relative to the substrate and ribbon). In other words, the whole printing apparatus 10 may be shifted in a direction substantially perpendicular to the substrate path (lateral to the substrate direction of travel) by a distance which may be equivalent of the printed image size to ensure that whilst a different part of the ribbon 16 and printhead 24 are being exercised, the printed image is in the same place on the substate 26, e.g. packaging film. This is known as radial ribbon saving (RRS). An observation is that the substrate 26 may touch the ribbon 16 when the ribbon is slack, just after the printhead 24 is lifted. This may cause the ribbon 16 to track, i.e. move substantially perpendicular to the intended ribbon path. This may occur when the printing apparatus 10 has indicated it has finished the printing cycle, but the ribbon tension has not been reset.

[0084] Where a printing apparatus uses a mechanical tension adjustment mechanism, this typically provides a fast response time in picking up the slack when the printhead is lifted. However, others are more prone to ribbon tracking where for example software is responsible for maintaining tension control via the motors, which typically has an inherently slower response time.

[0085] Observing the substrate 26 using one or more monitoring devices 40 may enable misalignment between the printing apparatus 10, e.g. the printhead 24, and the substrate 26 to be detected.

[0086] In this way, we address the problem that the printing apparatus 10 does not know when it is being translated so cannot inform its controller (especially in high speed RRS applications) that ribbon tracking may potentially occur.

[0087] A related issue is misalignment between the ribbon roller 17 / substrate 26 and the printing apparatus 20. This case is particularly important for continuous applications printing long images. In this case even a small misalignment shows up as significant pull-across, i.e., we may find that a 0.5 degree visually imperceptible misalignment between printhead and the substrate / roller results in 1 mm of drag, i.e. displacement / distortion with a 100mm image.

[0088] This invention solves the problem of detecting this misalignment so that ribbon tracking and its effect of cropped prints is avoided.

[0089] In embodiments providing continuous / combined printing apparatus one or more monitoring devices 40, the optical sensor (a laser scatter sensor) as described above may be positioned on or near the printhead carriage 25. Positioning the monitoring device 40 at this physical location is advantageous so that the interaction with i.e. observation of the substrate support 28 / substrate 26 is as close as possible to the printhead 24. In embodiments providing intermittent printing apparatus, or each monitoring device 40 may be placed further away from the printhead 24, with the main requirement being that it is able to monitor the substrate 26.

[0090] The monitoring device 40 is operable to monitor the substrate 26. This may use the information relating to displacement to detect the movement in distance units, or using the angle 6 between substrate 26 and a part of the printing apparatus 10, e.g. the printhead 24 in degree units simply as arctan (x / y), where x and y are the distances moved within a given timeframe (see Figure 6) It will be appreciated that this relationship may be used to determine an angle 0 between any target surface T and the printing apparatus 10, e.g. the printhead 24.

[0091] An indication of the substrate 26 having a component of its movement along the y-axis and / or being misaligned relative to the printhead 24 may be indicative that the ribbon 16 is also moving / has moved and / or is misaligned relative to the printhead by a corresponding angle or distance.

[0092] In some cases, the substrate 26 is not necessarily misaligned, but because the monitoring device 40 can detect movement, substantially perpendicular to the substrate 26 and / or ribbon 16 path this information can be cross-correlated with the state of ribbon tension (and or printhead lift) to determine probability of ribbon tracking. For example, in an RRS application, and lateral (y-axis) substrate movement component is detected whilst we have not re-tensioned the ribbon, this may be indicative of ribbon tracking.

[0093] In this case the monitoring device 40 may indicate the occurrence and the potential causes of the potential ribbon tracking, e.g. via an interface, since the controller 30 (for example) would determine that insufficient time had elapsed between print-cycle end and the y-axis shift for RRS to be responsible for the movement. An appropriate response may be carried out. The printing apparatus 10 can subsequently be reconfigured to take that into account. Reconfiguration may include manual adjustment and / or automatic adjustment and / or calibration.

[0094] Where there is misalignment, the monitoring device 40 can monitor any y-axis motion of the substrate 26 in relation to the printing apparatus 10 and correlate it with the print cycle state. In other words, if the substrate moved sideways during printing operation it may have dragged the ribbon 16 across the printhead 24.

[0095] This feature may then be used to: a. inform the operator of the misalignment, e.g. via a user interface: i. For example in mm / print units e.g. Beach print has 1 mm lateral ribbon shear because of the substrate, possibly causing a 0.5mm crop ;

[0096] II. for example in degrees (e.g.1 degree deviation), so that the installation engineer (or user) can correct the deviation, e.g. by adjusting positioning of the printing apparatus 10, and / or adjusting the ribbon 16; b. stop the printing apparatus c. provide a warning to the user; d. adjust printing instructions, for example by adding an offset to the print position and / or orientation to avoid image cropping 0 the operator / image designer may be required to agree to such automatic adjustment, for example during set up / power up; and / or e. provide an indication to another device, for example an actuator configured to adjust the position or orientation of the printing apparatus (or a part of the printing apparatus) to enable correction of the movement / displacement.

[0097] For intermittent printing apparatus, because the printhead 24 could move (return to its ready to print position) whilst the substrate 26 is being driven forward, the control system, e.g. the controller 30 needs to account for the movement of the printhead carriage 25 as well.

[0098] The monitoring or observation of the target surface T may involve monitoring data that is not visible to the human eye, for example monitoring an interference pattern created by reflected radiation, rather than a pattern marked on the target surface T itself. No special markings, header portions or trailer portions of the target surface are required 0 the monitored data may be that acquired from any portion of the target surface T, including usable portions of a target surface, e.g. a printable or printed area of a substrate, an inked portion of a ribbon or a portion of ribbon from which ink has been removed . It is not necessary for reference data to be stored in a look up table or the like in order to determine movement of the target surface T; a comparison between readings is necessary, but this is different from comparing with Dexpected dataD, for example.

[0099] The setup process of installing the printing apparatus may be eased due to the simplicity of checking that it is configured correctly for the ribbon to travel along the correct path without tracking occurring. Further, complexity may be reduced in applications where the printing apparatus is translated (physically moved sideways) to optimize the print position in radial ribbon saving mode, which has an inherent complexity between components external to the printing apparatus, e.g. an actuator, a robot arm or linear motor, the printing apparatus, and a encoder (or other monitoring device) of the actuator which determines how much the printing apparatus needs to be translated between prints.

[0100] Correction of deviations during use of the printer may be notified to the user, directly or indirectly and / or may be corrected in response to an indication of the movement, deviation, misalignment, and / or in response to an indication of movement, misalignment, deviation being likely to fall outside a threshold.

[0101] Printing operations may be adjusted to take into account likely or actual tracking of the substrate and / or the ribbon and / or incorrect positioning of a part or the whole of the printing apparatus , e.g. misalignment, deviation, in addition or as an alternative to correction of the error(s).

[0102] When used in this specification and claims, the terms "comprises" and "comprising" and variations thereof mean that the specified features, steps or integers are included. The terms are not to be interpreted to exclude the presence of other features, steps or components. The invention may also broadly consist in the parts, elements, steps, examples and / or features referred to or indicated in the specification individually or collectively in any and all combinations of two or more said parts, elements, steps, examples and / or features. In particular, one or more features in any of the embodiments described herein may be combined with one or more features from any other embodiment(s) described herein.

[0103] Protection may be sought for any features disclosed in any one or more published documents referenced herein in combination with the present disclosure.

[0104] Although certain example embodiments of the invention have been described, the scope of the appended claims is not intended to be limited solely to these embodiments. The claims are to be construed literally, purposively, and / or to encompass equivalents.

Claims

CLAIMS1. A printing apparatus for printing on to a substrate, including a printhead and a monitoring device operable to detect movement of a target surface relative to the printhead; wherein the target surface is intended to move substantially parallel to a first axis, and the monitoring device is operable to detect movement of the target surface along a second axis, the second axis being substantially perpendicular to the first axis.

2. A printing apparatus according to claim 1 wherein the monitoring device is operable to detect movement of the target surface along the first axis and the second axis.

3. A printing apparatus according to claim 2, wherein the monitoring device is operable to detect movement along the first axis and the second axis simultaneously.

4. A printing apparatus according to any of the preceding claims including a processor operable to determine one of linear or angular displacement of a part of the printing apparatus relative to the target surface.

5. A printing apparatus according to claim 4 wherein the part of the printing apparatus is the printhead.

6. A printing apparatus according to claims any of the preceding claims including a processor operable to process data indicative of movement of the target surface along the first axis and the second axis to determine an angular displacement of the printhead relative to target surface.

7. A printing apparatus according to any of the preceding claims wherein the monitoring device is operable to observe an interference pattern created by radiation reflected by the target surface.

8. A printing apparatus according to any preceding claim wherein the target surface is one of a substrate on to which the printing apparatus is arranged to print, and an inked ribbon associated with the printing apparatus and operable to transfer ink to the substrate.

9. A printing apparatus according to any of the preceding claims wherein the target surface is a component whose movement is indicative of movement of at least one of a substrate on to which the printing apparatus is arranged to print, and an inked ribbon associated with the printing apparatus arranged to transfer ink to the substrate to be printed.

10. A printing apparatus according to claim 9 wherein the component is one of a substrate support and a ribbon guide.

11. A printing apparatus according to any of the preceding claims that is operable to respond to an indication of movement of the target surface along the second axis, and / or an indication of displacement of a part of the printing apparatus relative to the target surface wherein the response includes at least one of: a. providing an indication to a user that movement along the second axis is occurring or has occurred; b. providing an indication to another device that movement along the second axis is occurring or has occurred; c. carrying out automatic adjustment of the position of the printing apparatus relative to the target surface, by causing movement of at least one of:I. a part of the printing apparatus,II. the whole printing apparatus, ill. the target surface; d. adjusting printing operation instructions to take the movement or displacement into account; e. stopping or pausing printing operations.

12. A printing apparatus according to any of the preceding claims including a plurality of monitoring devices.

13. A printing apparatus according to any of the preceding claims wherein the printing apparatus is a thermal transfer printer.

14. A method of operating a printing apparatus printing apparatus for printing on to a substrate, including a printhead and a monitoring device operable to detect movement of a target surface relative to the printhead; wherein the target surface is intended to move substantially parallel to a first axis, and the monitoring device is operable to detect movement of the target surface along a second axis, the second axis being substantially perpendicular to the first axis, the method including using the monitoring device to detect movement of the target surface along the second axis.

15. A method according to claim 14 of operating a printing apparatus as defined in claim 11 , wherein the method includes: a. using the monitoring device to monitor at least one of:I. movement of the target surface along the second axis,ii. displacement of a part of the printing apparatus relative to the target surface; b. providing an indication of movement of the target surface along the second axis, and / or an indication of displacement of a part of the printing apparatus relative to the target surface, to a processor of the printing apparatus; c. responding to indication of movement or displacement, the wherein the response includes at least one of: i. providing an indication to a user that movement along the second axis or displacement of a part of the printing apparatus is occurring or has occurred; ii. providing an indication to another device that movement along the second axis is occurring or has occurred; ill. carrying out automatic adjustment of the position of the printing apparatus relative to the target surface, by causing movement of at least one of: D a part of the printing apparatus,D the whole printing apparatus,D the target surface; iv. adjusting printing operation instructions to take the movement or displacement into account; v. stopping or pausing printing operations. A method according to claim 15 including taking into account known or intentional movement or displacement of at least a part of the printing apparatus relative to the target surface, along the first and / or second axis. A method according to any of claims 14 to 16 wherein the target surface is the substrate to be printed, and the method includes using an indication that the substrate has moved and / or is moving and / or is displaced relative to the printhead along the second axis to indicate that a ribbon associated with the printing apparatus for transferring ink to the substrate has moved, and / or is moving and / or is displaced relative to the printhead.

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