EP1728642A1

EP1728642A1 - Ink-jet printer with a print-head mounting assembly

Info

Publication number: EP1728642A1
Application number: EP05405365A
Authority: EP
Inventors: Peter Frei
Original assignee: Glaxo Group Ltd
Current assignee: Glaxo Group Ltd
Priority date: 2005-06-02
Filing date: 2005-06-02
Publication date: 2006-12-06

Abstract

An ink-jet printer with a print-head mounting assembly comprises at least one print-head (80) and a printer base plate having at least one slot to permit the positioning of the nozzles of said print-head within such a slot to enable ink ejected by said nozzles to be deposited on a printing surface. Such a base plate comprises, for each slot, three or more base plate bearing surfaces arranged around each slot. Each print-head (50,80) comprises a corresponding number of bearing surfaces in a position, that the print-head (50,80) can be positioned on the base plate so that the corresponding bearing surfaces come in releasable predefined contact. Locking means (46) are provided to lock each print-head (50,80) in said releasable predefined contact on the base plate (20). Balls (25) enable accurate pre-defined positioning. This enables a quick exchange of the print-head (50,80) without conducting any adjustment work.

Description

Technical field of the invention

The invention relates to an ink-jet printer with a print-head mounting assembly. It further relates to an adapter element for a print-unit of a print-head and to a print-head.

Prior Art

Ink-jet printers are droplet deposition apparatuses having often more than one print-head. More than one print-head can be needed for a wider print surface; then two or more print-heads are mounted one beside the other, wherein the e.g. leftmost printable pixels of one print-head are adjacent to the rightmost printable pixels of said adjacent print-head or the print-heads are so arranged that there is a overlapping printing area. More than one print-head is also needed, if there the printer is a colour printer; then the print-heads for the different colours are usually arranged one behind the other in such a way that the print areas, subsequently addressed by the various print-heads, are identical.
When there is a need to change a print-head for whatever reason, because he is defective, an attached colour reservoir is empty, etc. the new print-head must be placed at accurately at the same position
It is known from prior art to machine datum surfaces on a print cartridge body as shown in US 2002/0 148 091 A1 .
A droplet deposition apparatus is known from US 6,796,630 B2 showing an ink-jet printer with a print-head mounting assembly according to the preamble of present claim 1. The printer comprises a printer base plate having a plurality of slots to permit the positioning of the nozzles of the different print-heads within these slots to enable ink ejected by said nozzles to be deposited on a printing surface. Each print-head is adjustably mounted on said base plate by means of two tapered adjustment screws, engaging alignment surfaces of the print-head. Said aligning surfaces are tapered, the taper conforming to that of the respective adjustment screw. There is one thrust pin, acting against a further surface of the print-head, being the flexible pin for urging against the surfaces opposite to the tapered surfaces engaged by the adjustment screws. When a print-head is replaced, it is therefore necessary to adjust manually the two adjustment screws after insertion of the print-head to obtain the same printed impression. Although this is an easier solution than the machining of every print-head as mentioned above, this adjustment is still time consuming, iterative and asks for a qualified user.

Summary of the invention

It is therefore an object of the invention to provide an ink-jet printer with a print-head allowing a faster replacement of print-heads.
It is a further object of the invention to provide an assembly, which can be used without the necessity of any adjustment steps within the printer.
Said object can be reached for an apparatus through the features of claim 1.
The use of the mentioned symmetrical bearings in connection with well defined datum, it is possible to snap-in or click-in the print-head in the ink-jet printer. Of course, this approach necessitates the antecedent calibration of each of the print-heads against the defined position. However, this calibration step can be performed with a calibration printer base plate and therefore in absence of the production printer. It is even possible to outsource this calibration from the actual printer usage site to a printer cartridge assemble site, so that readily usable print-heads can be delivered which only need to replace a former print-head without any adjustment step.
The invention is based on the insight that the print-heads genuine positioning datum's are not precise enough for the printing application. Therefore, the print-head (together with a print-head clamping element) is mounted onto an adapter interface. This interface provides precise datum, which are used to position the head on the head mount plate or base plate.
The head clamping element holding the clamped head is positioned towards the datum of the adapter element by two conical screws, which move vertical towards tilted planes of the clamping element, thus moving the clamping element towards a spring pin. Only the x-direction and the orientation are mechanically adjusted. The height offset is measured in the production process, stored in the calibration data and used by the controller to adjust the print position.

Short description of the drawings

The invention is now described by a description of an advantageous embodiment in connection with the drawings, showing:

Fig. 1: shows a schematic perspective view of print-head mounting assembly for an ink-jet printer, according to the invention,
Fig. 2: shows a schematic explosive view of the print-head mounting assembly without the base plate, according to Fig. 1,
Fig. 3: shows a schematic detail view from above on the base plate of Fig. 1,
Fig. 4: shows a schematic view from below on the adapter element of the print-head mounting assembly according to the invention, and
Fig. 5: shows a schematic view from above on the adapter element according to Fig. 4.

Detailed description of an embodiment of the invention

Fig. 1 shows a schematic perspective view of print-head mounting assembly 10 for an ink-jet printer, according to the invention. The assembly 10 comprises a base plate 20 having a plurality of slots 21. Said slots 21 are arranged in two parallel rows comprising an overlapping portion 22. Beside each slot 21 are arranged two-time two, i.e. four bearing surfaces 23. It will be seen in connection with Fig. 3 that each of these bearing surfaces 23 may be constituted by a precisely machined hole 24, especially a blind hole, wherein in each of these holes a ball 25 is inserted in a press fit. The base plate 20 is very accurately machined to provide four datum points for each slot 21, i.e. for each print-head 30.
Said base plate 10 is mounted in a printer, e.g. with the help of screws used in connection with four mounting holes 11, one in each corner. There are ten slots 21 in one row, with two rows of parallel slots 21, but every other combination of number or rows and slots within a row can be used. The invention is even applicable for a printer having only one single slot 21. This base plate 10 can be mounted fix within a printer or can be part of a movable printer carriage. Each print-head is in advance adjusted and can be mounted directly on said base plate 10 with two fixation screws 46, engaging the print-head 30 through bores 36 in the head assembly, and ending in threaded bores 26 in the base plate 10. Said threaded bores 26 are directly placed between two adjacent bearing surfaces 23.
Four print-heads 30 are shown in the first rows and columns of the base plate 10. The Fig. 2 shows now in greater detail a schematic explosive view of a print-head 30 of the mounting assembly without the base plate 10. The print-head 30 comprises the printing unit 80, which can be a conventional printing unit with a nozzle surface 81, some electronics to control the nozzle spray action and an ink reservoir. The printing unit 80 is held with a clamping element 40, comprising on both sides a fixation slot 41 and horizontally oriented fixation screws 42 intended to engage the printing unit 80. In order to urge the printing unit 80 in a well defined position, the inner backside surface of the clamp comprises two grooves 43, especially in the form of dovetails 43, to accommodate leaf springs 43, bringing the printing unit 80 in a well defined position.
Said clamping element 40, attached to the printing unit 80, is mounted together with the adapter element 50. Therefore two bushings 51 having an internal thread and extending through bores 53 in the adapter element 50 are used together with corresponding screws 52 having a conical head, the connection being obtained through corresponding abutment surfaces 54, 55 of the clamping element 40. The abutment surface 55 allows a relative translation between elements 40 and 50 in the longitudinal direction of these elements, whereas abutment surface 54 allows the adjustment of the angle between the elements 40 and 50. In fact they are alignment surfaces of the print unit 80. A corresponding spring pin 58 is inserted in a press fit into a recess 56. Said spring pin 58 comprises a head which is in contact with the arcuate back surface 57 of the clamping element 40, so that a three point adjustment system is created, using the flexible pin 58 for urging against the surfaces opposite to the tapered surfaces 54 and 55 towards the adjustment screws 52.
Within other embodiments, it is possible to use different adjustment systems. It is important, that the print unit 80 of the print-head 30 can be and is adjusted in relationship to the adapter element 50. It will be noted below that such an adjustment can be effected without the ink-jet printer and without inserting the print-head assembly 30 on the base plate 20.
It is possible to replace the system of tapered screws 52 and a spring element 58 by micrometer screws integrated within the adapter element or clamping element, having driven actuators being controlled on a trial printing platform by the trial printer station. It is thus possible to pre-adjust the print-head automatically against the position of the bearing surface 71.
Within other embodiments it is possible to mount the print-unit 80 directly on the adapter element 50 without an intervening clamping element 40.
Fig. 3 shows a schematic detail view from above on the base plate 20 of Fig. 1. Same reference numerals designate same or similar features throughout the drawings. The detail view shows one full slot 21 having a mounting recess 27 extending on both sides of the through going slot bore 21. This enables a pre-arrangement of the print head assembly 30 with the print unit 80 at the intended space. The definitive and precise position is found as follows and can be explained in connection with Fig. 4 showing a schematic view from below on the adapter element 50 of the print-head mounting assembly 10 according to the invention.
The adapter element 50 comprises a longitudinal web 61 to accommodate the place for the print unit 80 in the free space between the U-shaped adapter element 50. On the underside of the adapter unit, there are provided four bearing surfaces 71, 72, 73 and 74, to be associated with the bearing surfaces 23.
One bearing surface 71 is a hollow cone, adapted to accommodate a portion of one ball 25. This fixes the x/y position of the print-head 30 and thus the position of the nozzles in relation to the base plate 10 having a well defined position.
A second bearing surface 72 is a hollow, preferably semispherical groove, wherein the longitudinal direction is aligned with the centre of the first bearing surface 71 to provide the correct angle orientation of the print-head 30.
A third bearing surface 73 is a plane machined in a way to give the third bearing point. It has to be noted that, if said bearing surface 73 would be arranged in the longitudinal web 61, the system would be well defined. Since the third bearing surface 73 is located in a corner of the adapter element 50 to enable a print-head 30 with a small width, it is preferable but not necessary to provide a fourth bearing surface 74 in the fourth corner of the adapter element 50. The planes 73 and 74 are machined to enable to obtain, operational connected with the balls 25, a horizontal nozzle surface 81 when the printer-head 30 is mounted on the base plate 20. In order to fix the obtained position of the print-head 30 in relation to the base plate 20, said screws 46 are entered into the base plate 20. In other embodiments, it is also possible to provide a snap-in assembly or to lock the print-head 30 with the bearing surfaces 71, 72, 73 and 74 on the corresponding ball points 25 in another releasable way. It is due to the precise predefinition of the well defined ball points 25 being engaged by the corresponding four bearing surfaces 71, 72, 73 and 74, that it is possible to replace print-heads 30 without any further adjustment steps. It has to be noted that the surfaces 71, 72, 73 and 74 do not need to be machined precisely, since the correct orientation of the print unit 80 within print-head 30 is achieved through the precisely provided balls 25, since any distance surface 71 from the intended position of surface 71 and any misalignment surface 72 from the intended angle of surface 72 will be corrected in advance within the pre-adjustment step, preferably before the print-head is shipped to the production site of the printer.
It is noted that the balls 25 have the advantage that they can easily be entered in a press fit in a precisely machined recess in the base-plate 20. However, such balls 25 can be replaced, intended to connect with the bearing surfaces 73 and 74, by different bearing surfaces, if they provide a point contact without damaging the corresponding planes. The ball 25, intended to connect with the bearing surface 72, can be replaced by a bearing surface allowing a line contact, e.g. with a cylindrical shaped body for the groove 72.
When a print-head 30 is to be replaced, it is therefore only necessary to place a new pre-adjusted print-head 30 onto the device and to fix it, such reducing the down-time of the printer considerably. This replacement is no longer time consuming, iterative and does not ask for a qualified user because the pre-adjusted adapter element 50 provides for a stable position on a base plate 20 of an ink-jet printer relative to a datum. The adjustment steps can be performed outside the production site on an adjustment base plate 20 by different personnel, so that the replacement of a print-head 30 only necessitates to unlock the old print-head 30, lifting up said print-head, positioning the new print-head 30 on the bearing surfaces and locking the new print-head 30 on the base plate 20.
The personnel adjusting the print-heads 30 mounts every print-unit 80 on the corresponding adapter element 50, possibly by using a clamping element 40. Then the adapter element 50 is mounted on the base plate 20 and the trial prints are conducted. It is of course possible to adjust a number of print-heads on one single base plate 20. The base plate 20 is accurately machined as is the base plate 20 of the production printers and comprises the same or at least similar bearing surfaces 25. The fixation of the print-head 30 or the adapter element 50 can be different and adapted to the trial site. Within the iterative approach of adjustment via turning the adjustment means, here the screws 52 with conical heads, these screws are adjusted to position the print-unit 80, i.e. the nozzles of said print-unit 80, in a predefined relative position to the conical bearing surface 71 and the groove bearing surface 72. The inclination is usually predefined in a sufficient manner by the machining of the adapter element 50 and the production of the print-unit (planar orientation of the nozzles). When the adjustment for the pre-adjusted print-head is concluded, it is possible to cover the adjustment screws 52 with glue or a different agent to avoid later change of their position. Then such a print-head can be packaged, shipped and later on directly used in a production printer. When positioned, the clamping element 40 and the adapter element 50 can also be locked with two additional screws, inserted in from the bottom. Preferably, the screw heads are sealed. As mentioned above, it is also possible to use optical test systems without such conical screws.
Pre-adjusted print-heads according to the invention have shown, that it is possible to obtain a reproducibility of the intended position of far less than 1/100 millimetre.

Reference numerals

10: print-head mounting assembly
11: mounting hole
20: base plate
21: slots
22: overlapping portion
23: bearing surface
24: hole
25: ball
26: threaded bore
27: mounting recess
30: print-head
36: through-bore in the head assembly
40: clamping element
41: fixation slot
42: fixation screw
43: dovetail groove
44: leaf spring
46: fixation screw
50: adapter element
51: bushing
52: screw
53: bore
54: abutment surface
55: abutment surface
56: recess
57: back surface
58: spring pin
61: longitudinal web
80: print unit
81: nozzle surface

Claims

Ink-jet printer with a print-head mounting assembly (10) comprising at least one print-head (30, 80) and a printer base plate (20) having at least one slot (21) to permit the positioning of the nozzles of said print-head (30, 80) within such a slot (21) to enable ink ejected by said nozzles to be deposited on a printing surface, characterized in that the base plate (20) comprises, for each slot (21), three or more base plate bearing surfaces (25) arranged around each slot (21), that each print-head (30, 50, 80) comprises a corresponding number of bearing surfaces (71, 72, 73, 74) in a position, that the print-head (30, 50, 80) can be positioned on the base plate (20) so that the corresponding bearing surfaces (25 to 71, 72, 73, 73) come in releasable predefined contact, and that locking means (46) are provided to lock each print-head (30, 50, 80) in said releasable predefined contact on the base plate (20).
Ink-jet printer according to claim 1, wherein the position of the print-head (30, 50, 80) in relation to the base plate (20) is fixed through a first pair of corresponding bearing surfaces (25 to 71), wherein the angle orientation of the print-head (30, 50, 80) within the plane of the base plate (20) is fixed through a second pair of corresponding bearing surfaces (25 to 72), wherein the inclination of the print-head (30, 50, 80) in relation to the base plate (20) is fixed through a third pair of corresponding bearing surfaces (25 to 73 or 74).
Ink-jet printer according to claim 1 or 2, wherein the locking means are at least two screws (46) to be inserted in corresponding bores (26) within the base plate (20) or wherein the locking means (46) are snap-in hooks attached at the base plate (20) to engage the print-head (30).
Ink-jet printer according to one of claims 1 to 3, wherein the base plate bearing surfaces (25) comprise four surfaces being arranged symmetrical around each slot (21).
Ink-jet printer according to one of claims 1 to 4, wherein the base plate bearing surfaces (25) are spherical portions extending beyond the surface of the base plate (20).
Ink-jet printer according to one of claims 1 to 5, wherein the first bearing surface (71) of each print-head (30, 80) is a hollow conical portion to accommodate a spherical portion of the bearing surface of the base plate (20), wherein the second bearing surface (72) of each print-head (30, 80) is a groove, and wherein the third and a possible fourth bearing surface (73, 74) of the each print-head (30, 80) are aligned planes.
Ink-jet printer according to one of claims 1 to 6, wherein each print-head (30, 80) comprises an adapter element (50) having said bearing surfaces (71, 72, 73, 74).
Adapter element (50) for a print-unit (80) to be used with an ink-jet printer having a base plate (20), comprising three or four bearing surfaces (71, 72, 73, 74) on the underside to engage corresponding base plate bearing surfaces (25), comprising adjustment means (51, 52, 54, 55, 58) to predefine a precise position relationship between at least the first, second and third bearing surfaces and the nozzles of the print-unit (80) and further comprising locking means (36, 46) to lock the print-unit (80) in a releasable predefined contact on the base plate (20).
Print-head (30, 50, 80) comprising a print-unit (80) attached at and pre-adjusted with a adapter element (50) according to claim 8 to be positioned on a base plate (20) of an ink-jet printer relative to a datum.