WO2009141355A2

WO2009141355A2 - Printer head alignment apparatus & method

Info

Publication number: WO2009141355A2
Application number: PCT/EP2009/056087
Authority: WO
Inventors: Robert Haslett
Original assignee: Klg Maschinen Gmbh & Co. Kg
Priority date: 2008-05-19
Filing date: 2009-05-19
Publication date: 2009-11-26
Also published as: GB0808966D0

Abstract

An embodiment of the present invention relates to apparatus (75) for aligning a print head, the apparatus comprising: an alignment jig (77) that is configured to securely hold a print head assembly that comprises a carrier (41) and a print head (35), said jig (77) including means for adjusting the position of said print head (31) relative to said carrier (41); and means (81) for providing an indication of the position of said print head (31) relative to said carrier (41).

Description

PRINTER HEAD ALIGNMENT APPARATUS & METHOD

Field of the Invention

In general terms, this invention relates to apparatus for aligning a printer head, in particular for aligning a printer head for a drop-on-demand printing apparatus. A method for aligning a printer head, a carrier for a print head and a drop-on-demand printer are also disclosed.

Background to the Invention Drop-on-demand printers comprise a platen on which a substrate that is to be printed upon is mounted, a print head assembly, and a controller (such as a personal computer) that is operable to control the print heads of the head assembly to eject droplets of print fluid "on demand".

In operation the print head assembly and platen are moved relative to one another (either by moving the print head assembly over a fixed platen or by moving the platen relative to a fixed head assembly) whilst the controller controls the print heads to deposit droplets of printer fluid onto the substrate in a predetermined pattern.

Such printers are used for a variety of different purposes including, for example, the printing of legends or identification marks onto printed circuit boards (PCBs), the printing of electronic components (such as solar cells, resistors, capacitors or transistors) on a PCB, and the printing of conductive tracks onto a substrate to form a PCB. The printer fluid may be a printer's ink, a conductive fluid (that forms a conductive track or electronic component, at least when cured) or any other fluid suitable for the particular task in hand. As PCBs get smaller and circuits more complex, space on a PCB is increasingly at a premium and as a result it is important to be able to accurately print the conductive tracks of the circuit on the substrate, and to be able to accurately print legends and other marks so that they do not impinge on any conductive tracks that are to be or have been printed on the substrate. It is also important for any pattern printed onto the substrate to be continuous (i.e. without holes or other discontinuities and imperfections), in the first instance so that the circuit is continuous and without shorts or other imperfections, in the second instance so that legends and ID marks (which are in some instances less than a millimetre in height) can reliably be read by automated equipment, and in the third instance so that the resulting printed board has a high quality appearance. For accurate printing onto a substrate such as a PCB it is important for the print heads of the printing assembly to be carefully aligned with respect to one another, with respect to a frame in which the print head assembly is provided and hence to the platen on which the substrate is mounted. To date this has been accomplished by installing the print heads in a given configuration, printing a number of test prints, inspecting those prints (either by eye or by automated equipment), adjusting the relative orientation of the print heads as necessary following inspection of the test prints, and then repeating the process until the prints are deemed to be acceptable at which point the heads are deemed to be properly aligned.

This iterative process necessarily takes quite a long time to accomplish and as the printer cannot be used whist the heads are being aligned, there is a financial cost associated with this delay. Another factor which complicates matters is that as the distance between the centres of adjacent print heads is in the order of less than a hundred microns and droplets are typically deposited on the substrate to an accuracy of 10 microns or less, the adjustments that need to be made to correct the alignment of the print heads are typically very small and hence difficult to accurately achieve. Other factors that further complicate the situation are that any two print heads are typically not identical in size (because they are not manufactured to a particularly low tolerance), and also tend to vary in size with ambient temperature.

The aforementioned problems arise not only when print head assemblies are inserted in a printer for the first time, but also when print head assemblies are replaced through the life of the printer.

It is apparent from the foregoing that correctly aligning print heads is not a trivial matter, and as such it would be advantageous if steps could be taken to facilitate the alignment process.

Summary of the Invention

To this end, a presently preferred embodiment of the present invention provides apparatus for aligning a print head, the apparatus comprising: an alignment jig that is configured to securely hold a print head assembly that comprises a carrier and a print head, said jig including means for adjusting the position of said print head relative to said carrier; and means for providing an indication of the position of said print head relative to said carrier.

The apparatus may further comprise an alignment screen.

The means for providing an indication of the position of said print head relative to said carrier may further be operable to provide an indication of the position of said print head relative to said screen.

The means for providing an indication of the position of said print head relative to said carrier may be operable to provide a visual indication of the relative position of the print head and carrier.

The means for providing an indication of the position of said print head relative to said carrier may comprise a camera. The camera may be arranged to provide a view of at least part of the print head through said screen.

The screen may comprise an aperture, the camera being arranged to image one or more nozzles of said print head through said aperture.

The apparatus may comprise means for supporting the alignment jig, alignment screen and indication providing means in a fixed spatial relationship.

The alignment jig may comprise means for retaining the carrier in a fixed position with respect to said jig.

The carrier and said jig may comprise complementary formations that may be engaged to retain the carrier in a fixed position on said jig. The complementary formations may comprise a plurality of accurately positioned pegs projecting from the jig, which pegs can mate with complementary holes in the carrier.

The means for adjusting the position of the print head may comprise a plurality of rods that can be moved to bear on the print head and so move the print head relative to the carrier.

The means for adjusting may further comprise means operable to move the rods to bear on the print head.

Each rod may be associated with a means for moving that rod, and said means for moving the rod may comprise a pivot arm having a first end coupled to the rods and a second end.

The pivot arm may be pivoted about a pivot point that is closer to said first end than said second end.

The means for moving each rod comprises a thumbwheel that can be rotated to withdraw or extend a pin that is coupled to said pivot arm in the vicinity of said second end.

The means for moving the rods may comprise a motor.

Each said rod may be associated with a motor for moving that rod.

The apparatus may comprise a processor that is configured to energise the as required to effect a movement of the rod that urges said print head towards an aligned position where the print head is aligned with said carrier.

The jig may comprise a spacer block on which the carrier is supported, the spacer block defining a void in which a part of said print head is received.

The spacer block may include a plurality of apertures through each of which a said rod may be received.

Another aspect of the invention relates to a carrier for a print head assembly, the carrier comprising a body that defines an internal cavity into which a print head may be inserted, a plurality of formations that are configured to engage with complementary formations provided on an alignment jig of an alignment apparatus, and means to enable the carrier to be fixedly coupled to a print head inserted into said cavity.

The formations may comprise a plurality of holes that fit onto complementary pegs provided on said jig.

The means enabling the carrier to be fixed to the print head may comprise a plurality of through-holes that align with corresponding through holes in the print head, and through which fixings may be inserted to couple the print head to the carrier.

The formations that are configured to engage with complementary formations on the jig may also engage with complementary formations provided on a print head assembly frame of a drop-on-demand printer.

Another aspect of the present invention relates to a drop on demand printer comprising a platen, a mount for a print head assembly frame, a print head assembly frame mounted on the mount so as to be spaced from the platen, and means for moving the print head assembly frame and platen relative to one another, wherein said print head assembly frame includes a plurality of formations that are configured to engage with complementary formations of a carrier of a print head assembly to accurately mount the print head assembly in the frame.

The plurality of formations provided on the frame may be configured to engage with complementary formations of a plurality of print head assembly carriers so as to accurately mount said print head assemblies in the frame.

The printer may comprise an irradiation source.

The irradiation source may comprise a UV lamp.

The printer may comprise a controller configured to energise said source to irradiate print fluid ejected from said print head assembly.

The controller may be operable to energise said source to irradiate print fluid inflight between said print head assembly and a substrate received on said platen.

The controller may be operable to control the source to irradiate a substrate received on said platen. In a preferred arrangement the print head assembly frame is fixed and said moving means is configured to move the platen relative to said fixed print head assembly frame.

Another aspect of the present invention relates to a print-head assembly frame that is configured to fit on a mount of a drop-on-demand printer, the print head assembly frame including a plurality of formations that are configured to engage with complementary formations of a carrier of a print head assembly to accurately mount the print head assembly in the frame.

Another aspect of the present invention relates to a print head that is configured to mate with and be coupled to a carrier as described herein.

Another aspect of the invention relates to a print head assembly that comprises a print head as described herein and a carrier as described herein, wherein the print head and carrier have been aligned and are fixed one to the other.

Another embodiment of the present invention relates to a drop on demand printer comprising a platen, a mount for a print head assembly frame, a print head assembly frame mounted on the mount so as to be spaced from the platen, and means for moving the platen relative to the print head assembly frame, wherein said print head assembly frame includes a plurality of formations that are configured to engage with complementary formations of a carrier of a print head assembly to accurately mount the print head assembly in the frame, said carrier comprising a body that defines an internal cavity into which a print head may be inserted, a plurality of formations that are configured to engage with complementary formations provided on an alignment jig of an alignment apparatus, and means to enable the carrier to be fixedly coupled to a print head inserted into said cavity.

Yet another aspect of the present invention relates to a method for aligning a print head, the method comprising assembling the print head with a carrier to form a print head assembly, mounting the print head assembly on an alignment jig, obtaining an indication of the position of the print head relative to said carrier, and adjusting the position of the print head relative to the carrier to align the print head therewith.

Other features, aspects and advantages of embodiments of the invention will be apparent from the following detailed description.

Brief Description of the Drawings

Various aspects of the teachings of the present invention, and arrangements embodying those teachings, will hereafter be described by way of illustrative example with reference to the accompanying drawings, in which: Fig. 1 is a diagrammatic representation of a drop-on-demand printing apparatus;

Fig. 2 is a photograph of part of an illustrative drop-on-demand printing apparatus;

Fig. 3 is a photograph of another part of an illustrative drop-on-demand printing apparatus;

Fig. 4 is a schematic perspective view of a print cartridge for use with printers of the type depicted in Figs. 1 to 3;

Fig. 5 is a schematic perspective view of a carrier for a print head of the type depicted in Fig. 4;

Fig. 6 is an exploded perspective view of a print head assembly comprising a print head as depicted in Fig. 4 and a carrier as depicted in Fig. 5; Fig. 7 is a plan view of the underneath of a print head of the type depicted in Fig.

4;

Fig. 8 is an enlarged view of a portion of the underside of the print head depicted in Fig. 8;

Fig. 9 is a perspective view of illustrative apparatus for aligning a print head; Fig. 10 is an exploded perspective view of the apparatus shown in Fig. 10;

Fig. 11 is a perspective view of the underside of part of the apparatus shown in Figs. 9 and 10;

Fig. 12 is a perspective view of part of the apparatus shown in Fig. 9;

Fig. 13 is a schematic representation of an image of a print head and alignment screen;

Fig. 14 is a schematic plan view of an alignment jig;

Fig. 15 is an enlarged plan view of part of the jig depicted in Fig. 14;

Fig. 16 is a schematic perspective view of an alignment jig with a carrier and print head installed thereon; Figs. 17 and 18 are enlarged schematic representations of parts of the arrangement depicted in Fig. 16;

Fig. 19 is a schematic perspective view of the inside of a frame for the print head assembly;

Fig. 20 is an enlarged view of part of the inside of the frame depicted in Fig. 19; and

Fig. 21 is a schematic illustration of an arrangement for automatically adjusting the position of a print head relative to a carrier.

Detailed Description of Preferred Embodiments Referring now to Fig. 1 of the drawings, there is shown an diagrammatic representation of the core components of a drop-on-demand printer 1. In this illustrative arrangement the printer 1 comprises a control computer 3 that is capable of interfacing with other computers in a local area network via an Ethernet interface (for example for the receipt of image data). The control computer 3 is coupled to a motor controller 5 that is operable to accurately control three motors (one for movement in an X plane, one for movement in a Y plane, and one for movement in a Z plane) that are configured to move a platen 7 on which a substrate to be printed upon may be mounted.

The control computer 3 is coupled to an operator interface 9, i.e. some means (for example a computer controlled touch-screen interface) by which an operator can control the printer 1 , and to a printer control interface 1 1 that is coupled to a temperature control unit 13, a print fluid supply system 15, a power supply unit 17 for an irradiation source (such as one or more ultraviolet lamps), and a sensor assembly 19.

The printer components are provided within a housing (not shown) and the temperature control unit 13 is configured to maintain the interior of the housing at an optimum printing temperature for the printing fluid and substrate that is being printed upon.

One or more print heads 21 are coupled to the print fluid supply system 13 for the receipt of print fluid (e.g. ink), and one or more irradiation sources (for example ultraviolet lamps) 23 are coupled to the source power supply 17. The irradiation sources can be energised for example to irradiate and cure print fluid deposited onto the substrate.

The print heads 21 and irradiation sources 23 are controlled by a drop placement controller 25 that is coupled to the control computer 3 by a fast image data link (i.e. a link that has a high data throughput). The drop placement controller controls the print heads 21 to deposit print fluid on the substrate in a pattern dictated by the image data received from the control computer 3 via the fast image data link. The drop placement controller also controls the irradiation sources and synchronises operation of those sources with the deposition of drops from the print heads 21. In one arrangement the irradiation sources may be controlled to irradiate drops in flight, i.e. drops that are in flight between the print heads and the substrate. In another arrangement the irradiation sources may be configured to irradiate drops after they have been deposited, and in yet another arrangement the irradiation sources may be configured to irradiate the substrate before drops of printer fluid are deposited onto it. In a preferred arrangement the irradiation sources are ultraviolet lamps that can be illuminated to cure the deposited print fluid, but it will be apparent that the nature of the source can be varied (or indeed dispensed with) in dependence upon the particular properties of the fluid being printed or the substrate being printed upon.

Fig. 2 of the accompanying drawings is a photograph of part of an illustrative drop-on-demand printer that has been stripped down so that its internal components can more easily be seen. As illustrated the printer comprises a platen 7 on which a substrate that is to be printed upon can be mounted, and a mount 27 on which a print head assembly frame (not shown in Fig. 2) is supported. As aforementioned, the platen 7 is moveable in three dimensions (i.e. along X, Y and Z axes) relative to a print head assembly frame (not shown) supported on the mount 27.

Fig. 3 is a photograph of part of an assembled drop-on-demand printer where a print head assembly frame 29 (further details of which are later provided) is supported on the mount 27. As shown, the print head assembly frame 29 is supported above the platen 7 and the platen can be moved in three-dimensions relative to the frame 29 to allow one or more print head assemblies (not shown) that are carried within the frame to deposit print fluid in a predetermined pattern on a substrate that is mounted on the platen 7. In an alternative arrangement the print head assembly could be moved relative to the platen, but as the print heads are very carefully aligned within the print head assembly it is preferred to avoid moving the assembly lest that movement should cause the print heads to go out of alignment.

Fig. 4 is a schematic perspective view of a print head 31 that forms part of a print head assembly and is carried within the frame 29. The print head comprises a main body 33, a lower part of which includes a pair of projecting flanges 35 that each include a through-hole 36 (both of which are shown in Fig. 7). The main body 33 includes within it the known components of a typical print head and includes a fluid port 37 in a wall thereof (in this instance in an upper wall of the main body) by means of which print fluid can be supplied to the head, and a control port 39 in another wall (in this instance a sidewall of the main body) by means of which the print head can receive instructions from the drop placement controller 25.

Fig. 5 is a schematic perspective view of a carrier 41 that assembles with the print head 31 of Fig 4 (in the manner later described with reference to Fig. 6) to provide a print head assembly for use with the printer depicted in Figs. 1 to 3.

The carrier comprises a generally rectangular portion 43 that defines an aperture 45 that is sized to accommodate the main body 33 of the print head 31. One long wall 47 of the rectangular portion 43 is laterally extended at one end to form a finger 49, and the finger 49 includes a first through-hole 51. The long wall is extended towards its other end to form a projection 53 and a peripheral lip 55. The projection 53 includes a second locating through-hole 57, and the lip 55 includes a third locating through-hole 59 (best shown in Figs. 17 or 20). The other long wall 61 of the rectangular portion 43 is extended at the end closest to the finger to form a second projection 63 that includes a third through-hole 65. Two further through holes 67 are provided at opposite locations in vertical aspects of the long walls 61 , 47 of the rectangular portion 43 and are each sized to accommodate a grub screw 69. The carriers used for the print heads are all accurately machined within a small tolerance (e.g. +/- 1 to 5 microns) to be of substantially the same size.

As shown in Fig. 6, when the print head and carrier are assembled together to form a print head assembly, the main body 33 of the print head 31 passes through the aperture 45 of the carrier until the flanges 35 bear against the underside of the rectangular portion 43. When the flange through holes 36 are aligned with the second through-hole 57 and the third through-hole 65, respectively, bolts 71 (or other fixings) can be passed through the aligned through-holes to couple the carrier and print head together. As illustrated the second and third through-holes 57, 65 have a slightly larger diameter than that of the flange through-holes so that the relative position of the print head and carrier can be adjusted (once the two components have been aligned and coupled one to the other by bolts). Once the alignment of the print head and carrier has been adjusted, nuts 72 can be screwed onto the bolts and the grub screws 69 can be tightened to bear upon the print head in the carrier so that movement of the print head with respect to the carrier is resisted.

Fig. 7 is a plan view of the underneath of the print head 31 (i.e. the part of the print head that will be closest to the substrate in use) and Fig. 8 is an enlargement of part of the underneath of the print head within the circle that is labelled "A". As shown in Figs 7 and 8, the underneath of the print head includes, in this particular example, two parallel rows 73 of print head nozzles through which print fluid is ejected by the print head in use. In a particularly preferred arrangement the nozzles are arranged in a zigzag on the underneath of the print head.

As aforementioned it is important to ensure that the print heads in a printer are properly aligned, and to this end an illustrative embodiment of the present invention provides an alignment apparatus 75 as depicted in Figs. 9 and 10 (Fig. 10 being an exploded view of the apparatus depicted in Fig. 9.

The alignment apparatus comprises a jig 77 on which a print head 31 and carrier 43 that are to be aligned are provided. The jig 77 rests on a support frame 79 that functions to space the jig 77 a known distance from a device 81 that provides an indication of the relative position of the print head and carrier.

In the preferred implementation alignment of a print head and carrier on the jig is accomplished in environmental conditions that match (to an acceptable degree of accuracy) the environmental conditions within the printer during its operation. This arrangement is advantageous because any misalignment that might occur due to thermal expansion or contraction of the print head assembly can be avoided. For example, in an arrangement where the jig is operated in a relatively hot ambient environment and the printer is air conditioned to operate at a lower temperature, the dimensions of the print head assembly could change to such an extent that if the print head were to be aligned with the carrier in the hot environment it could go out of alignment when placed in the air conditioned environment of the printer. Referring now to Figs, 1 1 and 12, in the preferred embodiment the aforementioned device 81 comprises one or more, preferably two, CCD cameras 81 that are configured (when the alignment apparatus is assembled as shown in Fig. 9) to capture an image of the underside of the print head through an alignment screen 83 that locates within a depression formed in the underside of the jig 7. The CCD cameras 81 generate an image for viewing on a display (not shown) by an operator.

The alignment screen 83 is in the region of 1 micron thick and is accurately machined (for example by laser cutting) to include a number of apertures 85 through which, as shown in Fig. 13, the nozzles on the underside of the print head can be imaged. The alignment screen functions to provide a reference in relation to which the position of the print head relative to the carrier can be adjudged.

Referring now to Figs. 14 and 15 (Fig. 15 being an enlarged view of part of the jig 77 that is within the circle labelled "B"), the alignment jig 77 comprises a plate 87 with an internal aperture 89. A spacer block 90 that is similar in shape to the carrier 43, but somewhat larger, is provided over the aperture 89 and fixedly attached to the plate 87. The walls of the spacer block define a main aperture 92 and are further provided with a plurality of transverse apertures through each of which one end of a rod 91 is inserted so that the rods 91 project into the internal aperture 89. The other ends of the rods are configured to slide within brackets 92 mounted to the plate 87 and couple to a pivot arm 93 that is coupled to an adjustment mechanism 95. As shown the adjustment mechanism comprises a thumbwheel and is configured so that rotation of the thumbwheel extends or withdraws a pin that is coupled to the pivot arm 93. As the thumbwheel is moved, the pin moves to draw the pivot arm towards or to push the pivot arm away from the adjustment mechanism 95, and hence move the rod 91 associated with that mechanism. An advantageous feature of this arrangement is that as the pivot arm is arranged to pivot about a pivot point 97 that is much closer to the rod than to the adjustment mechanism, it is the case that a relatively large movement of the adjustment wheel causes a relatively small movement of the rod 91. This means that the adjustment mechanism can be used to make relatively small changes to the position of the rod, and anything in side the aperture that bears against the rod.

The spacer block 91 further comprises first and second accurately (to within +/- 1-5 microns) positioned upstanding pegs 99, 101 onto which the first through-hole 51 and the third through hole 59, respectively, of the carrier 41 fit to accurately locate the carrier 41 with respect to the space block. When, as shown in Figs. 16, 17 and 18, a print head assembly consisting of a print head 31 and carrier 41 that are at this stage loosely coupled together by bolts 71 is mounted on the jig 77 the carrier locates on the upstanding pegs 99, 101 so that the lower end of the print head 31 is provided within the main aperture 92 of the spacer block 91. As shown in Fig. 17, when the carrier is properly located on the spacer block the second upstanding peg 101 projects through the third through-hole 59 in the carrier 41 , and as shown in Fig. 18 the first upstanding peg 99 projects through the first through-hole 51 in the carrier 41. Once the print head assembly has been located on the jig, the rods 91 can be brought to bear against the print head 31 (by operation of the adjustment mechanisms) and the relative position of the print head to the carrier can be adjusted (by further operation of each (if necessary) of the adjustment mechanisms) until the nozzles on the underside of the print head 31 are properly located, in the image of the underside of the print head that is captured by the cameras 81 , within the apertures 85 in the alignment screen 83 (see Fig. 13).

When the nozzles are properly located within the apertures 85, as viewed by an operator looking at an image of the underside of the print head captured by the cameras, the user knows that the carrier is properly located with respect to the spacer block (because of the engagement of the pegs and the through-holes), and further that the print head is properly positioned with respect to the carrier. At this point the nuts 72 can be screwed down onto the bolts 71 and the grub screws 69 tightened to fix the position of the print head with respect to the carrier.

The print head assembly (i.e. the assembled carrier and print head) can then be removed from the jig and mounted in the print head carrier frame 29.

As the print head carrier frame will typically carry a number of print head assemblies, it is important to ensure that each of these assemblies is properly located with to the other assemblies within the frame, and indeed to the frame itself.

To accomplish this, the frame 29 comprises, as illustrated in Figs. 19 and 20 (from which the print heads have been removed for clarity), a plurality of first pegs 103 onto which the first though-holes 51 of the carriers 41 locate, and a plurality of second pegs 105 (see Fig. 20 which comprises an enlarged view of the region of Fig. 19 within circle E) onto which the third-through holes 59 of the carriers 41 locate. The pegs 103, 105 are accurately positioned within the frame 29 (to within +/- 1 to 5 microns), and as the carriers are machined to be substantially the same size (again to within +/- 1 to 5 microns) the user knows that when the carriers are located on the pegs within the frame the print heads carried by the carriers 41 are properly located with respect to one another and with respect to printing ports 107 through which droplets of printing fluid are ejected during use.

The advantage of the arrangement herein described is that the carriers and print heads are carefully aligned before they are inserted into the frame, and as such it is no longer necessary to undertake the sort of iterative printing and inspection process of the type that has hitherto been employed. As a result, print heads can more quickly be aligned and printers rendered operational, thereby avoiding the significant financial penaltities associated with machine down-time. The embodiments hitherto described employ a manual adjustment process, and it will be appreciated by persons skilled in the art that at least part of the adjustment process could optionally be automated.

A schematic representation of such an arrangement is depicted in Fig. 21. As shown the jig 77 of this embodiment comprises six adjustment mechanisms 95 (as before), but in this instance the adjustment mechanisms are coupled to a servo assembly 109 that comprises a plurality of motors (such as highly accurate worm drives for example) for driving each of the adjustment mechanisms 95. The servo assembly 109 is controlled by a processor 1 11 that receives data from the position indication device 81 and controls the servos 109 to operate the adjustment mechanisms until the data from the position indication device 81 indicates that the print head is properly aligned with respect to the carrier.

In the context of a position indicating device that is a camera, the processor 1 11 may be configured to implement a pattern matching algorithm and actuate the servos to move the adjustment mechanisms 95 until the image data generated by the camera matches (to an acceptable level of accuracy) a stored image held in memory 1 13. The processor could accomplish this by implementing an iterative process whereby an image from the camera is compared to a stored image, the processor determines an adjustment for one or more of the servos, the servos are actuated to move the print head, a new image is captured and compared to the stored image, and so on until the image captured by the camera is determined to match the stored image. In this scenario to avoid oscillating around a "perfect" match, it would be preferred if the processor were configured to implement an iterative process that determines adjustments for the servos that are within +/- 1 to 5% of an adjustment that would perfectly match the current image to the stored image.

The processor 111 is coupled to a user interface 115 by means of which a user can start the alignment process, and by means of which the processor can advise the user when the process has been completed.

It will be appreciated that whilst various aspects and embodiments of the present invention have heretofore been described, the scope of the present invention is not limited to the particular arrangements set out herein and instead extends to encompass all arrangements, and modifications and alterations thereto, which fall within the scope of the appended claims. For example, in the particular arrangement depicted in Fig. 20, adjacent pairs of carriers are oppositely orientated to reduce the distance between adjacent print heads, but it will be appreciated that the frame could be configured so that the carriers all have the same orientation. In another modification, the servos depicted in Fig. 21 could bear directly on the rods 91 or the pivot arms instead of acting to control the adjustment mechanism. it should also be noted that whilst the accompanying claims set out particular combinations of features described herein, the scope of the present invention is not limited to the particular combinations hereafter claimed, but instead extends to encompass any combination of features herein disclosed.

Claims

1. Apparatus for aligning a print head, the apparatus comprising: an alignment jig that is configured to securely hold a print head assembly that comprises a carrier and a print head, said jig including means for adjusting the position of said print head relative to said carrier; and means for providing an indication of the position of said print head relative to said carrier.

2. Apparatus according to Claim 1 , further comprising an alignment screen.

3. Apparatus according to Claim 2, wherein said means for providing an indication of the position of said print head relative to said carrier is further operable to provide an indication of the position of said print head relative to said screen.

4. Apparatus according to any preceding claim, wherein said means for providing an indication of the position of said print head relative to said carrier is operable to provide a visual indication of the relative position of the print head and carrier.

5. Apparatus according to Claim 4, wherein said means for providing an indication of the position of said print head relative to said carrier comprises a camera.

6. Apparatus according to Claim 5, wherein said camera is arranged to provide a view of at least part of the print head through said screen.

7. Apparatus according to Claim 6, wherein said screen comprises an aperture, the camera being arranged to image one or more nozzles of said print head through said aperture.

8. Apparatus according to any of Claims 3 to 7 when dependent on Claim 2, further comprising means for supporting the alignment jig, alignment screen and indication providing means in a fixed spatial relationship.

9. Apparatus according to any preceding claim, wherein said alignment jig comprises means for retaining the carrier in a fixed position with respect to said jig.

10. Apparatus according to Claim 9, wherein said carrier and said jig comprise complementary formations that may be engaged to retain the carrier in a fixed position on said jig.

11. Apparatus according to Claim 10, wherein said complementary formations comprise a plurality of accurately positioned pegs projecting from the jig, which pegs can mate with complementary holes in the carrier.

12. Apparatus according to any preceding claim, wherein said means for adjusting the position of the print head comprises a plurality of rods that can be moved to bear on the print head and so move the print head relative to the carrier.

13. Apparatus according to Claim 12, wherein said means for adjusting further comprises means operable to move the rods to bear on the print head.

14. Apparatus according to Claim 13, wherein each rod is associated with a means for moving that rod, and said means for moving the rod comprises a pivot arm having a first end coupled to the rods and a second end.

15. Apparatus according to Claim 14, wherein said pivot arm can be pivoted about a pivot point that is closer to said first end than said second end.

16. Apparatus according to Claim 14 or 15, wherein said means for moving each rod comprises a thumbwheel that can be rotated to withdraw or extend a pin that is coupled to said pivot arm in the vicinity of said second end.

17. Apparatus according to Claim 13, wherein said means for moving the rods comprises a motor.

18. Apparatus according to Claim 17, wherein each said rod is associated with a motor for moving that rod.

19. Apparatus according to Claim 17 or 18, comprising a processor that is configured to energise the as required to effect a movement of the rod that urges said print head towards an aligned position where the print head is aligned with said carrier.

20. Apparatus according to any preceding claim, wherein the jig comprises a spacer block on which the carrier is supported, the spacer block defining a void in which a part of said print head is received.

21. Apparatus according to Claim 17 when dependent on any of Claims 12 to 16, wherein said spacer block includes a plurality of apertures through each of which a said rod may be received.

22. A carrier for a print head assembly, the carrier comprising a body that defines an internal cavity into which a print head may be inserted, a plurality of formations that are configured to engage with complementary formations provided on an alignment jig of an alignment apparatus, and means to enable the carrier to be fixedly coupled to a print head inserted into said cavity.

23. A carrier according to Claim 22, wherein said formations comprise a plurality of holes that fit onto complementary pegs provided on said jig.

24. A carrier according to Claim 22 or 23, wherein said means enabling the carrier to be fixed to the print head comprises a plurality of through-holes that align with corresponding through holes in the print head, and through which fixings may be inserted to couple the print head to the carrier.

25. A carrier according to any of Claims 22 to 24, wherein the formations that are configured to engage with complementary formations on the jig also engage with complementary formations provided on a print head assembly frame of a drop-on- demand printer.

26. A drop on demand printer comprising a platen, a mount for a print head assembly frame, a print head assembly frame mounted on the mount so as to be spaced from the platen, and means for moving the print head assembly frame and platen relative to one another, wherein said print head assembly frame includes a plurality of formations that are configured to engage with complementary formations of a carrier of a print head assembly to accurately mount the print head assembly in the frame.

27. A printer according to Claim 26, wherein the plurality of formations provided on the frame are configured to engage with complementary formations of a plurality of print head assembly carriers so as to accurately mount said print head assemblies in the frame.

28. A printer according to Claim 26 or 27, further comprising an irradiation source.

29. A printer according to Claim 28, wherein said source comprises a UV lamp.

30. A printer according to Claim 28 or 29, comprising a controller configured to energise said source to irradiate print fluid ejected from said print head assembly.

31. A printer according to Claim 30 wherein said controller is operable to energise said source to irradiate print fluid in-flight between said print head assembly and a substrate received on said platen.

32. A printer according to Claim 30 or 31 , wherein said controller is further operable to control the source to irradiate a substrate received on said platen.

33. A printer according to any of Claims 26 to 32, wherein said print head assembly frame is fixed and said moving means is configured to move the platen relative to said fixed print head assembly frame.

34. A print-head assembly frame that is configured to fit on a mount of a drop-on- demand printer, the print head assembly frame including a plurality of formations that are configured to engage with complementary formations of a carrier of a print head assembly to accurately mount the print head assembly in the frame.

35. A print head that is configured to mate with and be coupled to the carrier of any of claims 22 to 25.

36. A print head assembly comprising a print head according to Claim 35 and a carrier according to any of Claims 22 to 25, wherein the print head and carrier have been aligned and are fixed one to the other.

37. A drop on demand printer comprising a platen, a mount for a print head assembly frame, a print head assembly frame mounted on the mount so as to be spaced from the platen, and means for moving the platen relative to the print head assembly frame, wherein said print head assembly frame includes a plurality of formations that are configured to engage with complementary formations of a carrier of a print head assembly to accurately mount the print head assembly in the frame, said carrier comprising a body that defines an internal cavity into which a print head may be inserted, a plurality of formations that are configured to engage with complementary formations provided on an alignment jig of an alignment apparatus, and means to enable the carrier to be fixedly coupled to a print head inserted into said cavity.

38. A method for aligning a print head, the method comprising assembling the print head with a carrier to form a print head assembly, mounting the print head assembly on an alignment jig, obtaining an indication of the position of the print head relative to said carrier, and adjusting the position of the print head relative to the carrier to align the print head therewith.

39. Apparatus for aligning a print head substantially as hereinbefore described with reference to the accompanying drawings.

40. A carrier for a print head assembly, the carrier being substantially as hereinbefore described with reference to the accompanying drawings.

41. A print head assembly, a drop-on-demand printer, or a print head, each of which is substantially as hereinbefore described with reference to the accompanying drawings.