Continuous ink jet printer having an alignment apparatus for the components of the print head

Abstract: An apparatus and method provides a means for mounting and aligning the charge plate/catcher assembly (10) and the droplet generator (14) has six degrees of freedom of adjustment, including three degrees of freedom of translation and three degrees of freedom of rotation. A first degree of freedom of translation comprises a height adjustment of the resonator (26) relative to the charge plate; a second degree of freedom of translation comprises an alignment adjustment for aligning the plurality of jets with respect to the plurality of charge leads; and a third degree of freedom of translation comprises a reciprocal adjustment for moving the plurality of jets relative to the charge plate. Additionally, a first degree of freedom of rotation comprises a first parallel adjustment for aligning the plurality of jets parallel to the charge plate face; a second degree of freedom of rotation comprises a second parallel adjustment for aligning the array of orifices parallel to the charge plate face; and a third degree of freedom of rotation comprises a third parallel adjustment for aligning the orifice plate parallel to the top of the charge leads. The present invention also provides for a strain relief which provides a mechanical means to insure an electrical contact to control leads associated with charge leads.

Description: Technical Field The present invention relates to continuous ink jet printers and, more particularly, to mounting and aligning a drop generator and catcher assembly in an ink-jet print head. Background Art Ink jet printing systems are known in which a print head defines one or more rows of orifices which receive an electrically conductive recording fluid, such as for instance a water base ink, from a pressurized fluid supply manifold and eject the fluid in rows of parallel streams, see for example US-A-4080607, US-A-4238805, US-A-4538157 and US-A-4672390. Printers using such print heads accomplish graphic reproduction by selectively charging and deflecting the drops in each of the streams and depositing at least some of the drops on a print receiving medium, while others of the drops strike a drop catcher device. The charge plate/catcher and droplet generator elements must be precisely positioned relative to each other in order to ensure ink-jet imaging. The preciseness of this alignment is beyond acceptable machining tolerances that would permit mechanically fastening two elements in a frame with no further adjustment. An existing assembly method for assembling the components of an ink jet print head includes locating the droplet generator with the aid of an assembly fixture, then using an epoxy or other adhesive to fasten it into place. The charge plate/catcher assembly was then aligned to the droplet generator through the use of external adjustment fixtures. Once a proper alignment was achieved, the charge plate/catcher assembly was fastened with screws to the common frame holding the droplet generator. Unfortunately, use of epoxy in existing assembly and alignment methods has had some drawbacks. For instance, the use of adhesive increases assembly cycle time, since it takes several hours for the adhesive to cure. The use of epoxy is also problematic in that epoxy is temperature and humidity sensitive. Finally, the sensitivity of the alignment is such that the final fastening of charge plate/catcher assembly once alignment is achieved can and does alter the alignment, requiring a realignment. In order to overcome the problems associated with using an epoxy, a mechanical structure for mounting and aligning components of an ink jet printer is disclosed in US-A-5477254 published after this application was filed. US-A-5477254 provides a means for mounting and aligning the charge plate/catcher assembly and the droplet generator of an ink jet print head, within a frame structure for holding the two components. The precise positioning of the alignment is achieved by incorporating three degrees of freedom of adjustment into the frame which are self-locking. Unfortunately, the location of screws for in/out adjustment is located behind the resonator, which is extremely difficult for the operator during the adjustment operation. Since the z height adjustment controls the filament length breakoff location relative to the charging leads, lack of assembly consistency in the location of the charge plate relative to the catcher mounting surface requires matching resonators to charge plates, instead of having a universal setting. Finally, scaling up from the flex assembly would create a print head of excessive size. US-A-4277790 discloses an ink jet head assembly having modular subassemblies with predetermined relationships between the subassemblies to minimize realignment of the ink stream when a subassembly is replaced in the field. The head assembly is modularized into nozzle, charge electrode, deflection electrode and gutter subassemblies. The charge electrode module is mounted on the nozzle module in a manner such that no field adjustment is necessary to center the charge electrode horizontally to the ink stream. The deflection electrode module is mounted on the gutter module in a manner such that no field adjustment is necessary to center the deflection electrode horizontally to the ink stream. The nozzle and charge electrode subassembly have a preset adjustment, and the gutter and deflection electrode assembly have a preset adjustment such that no field adjustment between these two subassemblies is necessary to maintain a constant flight distance for the ink drops. Finally, the nozzle module is adjustable to reposition the ink stream about the pitch axis (vertical adjustment) and the yaw axis (horizontal adjustment). The yaw axis adjustment may be preset. The pitch axis adjustment is the only mechanical adjustment necessary in the field when replacing the nozzle module. US-A-4356499 discloses an ink jet recording device in which the pressurized ink is supplied from a single source of pressurized ink to an ink manifold with one inlet port and a plurality of outlet ports each of which is connected to one end of a flexible pipe the other end of which is connected to an ink emission head, whereby the pressurized ink is supplied from the ink manifold to the ink emission head. The ink manifold is hollow and the inlet and outlet ports are communicated with each other through the hollow space. Alternatively, inserted into the ink manifold is an ink distributor having a plurality of branches which are in alignment with said outlet ports and are spaced apart from each other. An ink flow control means is disposed in each branch. The ink manifold is provided with a common ink passage or chamber which is communicated with an air vent means so that air bubbles trapped in the ink passage or chamber may be vented. Three degrees of freedom of rotation are provided for the ink distributor having a plurality of branches for the purpose of alignment. It is seen then that there is a need for an apparatus for mounting and alignment components of an ink jet print head which overcomes the problems associated with existing techniques. Summary of the Invention According to one aspect of the present invention, there is provided a continuous ink jet printer having a jet array including a plurality of jets, a plurality of charge leads associated with a charge plate forming part of a charge plate/catcher assembly, a drop generator, an orifice plate with an array of orifices, and mounting and alignment apparatus for the charge plate/catcher assembly and the drop generator, the mounting and alignment apparatus comprising: a. a first degree of freedom of translation; b. a second degree of freedom of translation; c. a third degree of freedom of translation; d. a first degree of freedom of rotation; e. a second degree of freedom of rotation; and f. a third degree of freedom of rotation. Preferably, the first degree of freedom of translation comprises a height adjustment of the drop generator relative to the charge plate, the second degree of freedom of translation comprises an alignment adjustment for aligning each of the plurality of jets with respect to each of the plurality of charge leads, and the third degree of freedom of translation comprises a reciprocal adjustment for moving the plurality of jets relative to the plurality of charge leads. Preferably, the first degree of freedom of rotation comprises a first parallel adjustment for aligning the plurality of jets parallel to the charge plate face, the second degree of freedom of rottaion comprises a second parallel adjustment for aligning the array of orifices parallel to the charge plate face, and the third degree of freedom of rotation comprises a third parallel adjustment for aligning the orifice plate parallel to the top of the charge leads. Preferably, the mounting and alignment apparatus comprises: a. a first frame for allowing physical adjustments; b. a second frame for providing a spring bias for the physical adjustments, and further for providing a clamp force; and c. a drop generator assembly which includes the drop generator and is situated between the first frame and the second frame. Preferably, the clamp force comprises a strain relief for providing a mechanical means to insure an electrical contact to a plurality of control leads associated with the plurality of charge leads. According to another aspect of the present invention, there is provided a method of mounting and aligning a charge plate/catcher assembly and a drop generator of an ink jet printer, within a frame, the printer having a jet array including a plurality of jets, and a plurality of charge leads, the method comprising the steps of: a. adjusting a height of the drop generator; b. tilting the drop generator outward to improve help charging; c. securing the drop generator to the charge plate/catcher assembly; and d. performing secondary adjustments to complete alignment of the charge plate/catcher assembly and the drop generator. An embodiment of the invention will now be described with refernce to the accompanying drawings. Brief Description of the Drawings Fig. 1 is an assembled isometric view of the principal assemblies which are aligned and the removable alignment frame; Fig. 2 is an assembled top view of the alignment of the droplet generator and charge plate/catcher assemblies in the aligned and locked positions; Fig. 3 is an isometric view of the resonator assembly showing adjustments used to fix two rotations and one translation; and Fig. 4 is a section view through the charge plate/catcher assembly showing the flex cables, strain relief, and alignment spring load. Detailed Description of the Preferred Embodiment The embodiment of the present invention provides a means for mounting and aligning two components, including (1) the charge plate/catcher assembly and (2) the droplet generator of an ink jet print head. The precise positioning of the alignment is achieved using a mechanical holding means. The mounting and alignment apparatus comprises six degrees of freedom of adjustment, which will be described in more detail below, The degrees of freedom include first, second, and third degrees of freedom of translation; and first, second, and third degrees of freedom of rotation. The first degree of freedom of translation comprises a height adjustment of resonator relative to a charge plate. The second degree of freedom of translation comprises an alignment adjustment for aligning each of the plurality of jets with respect to each of the plurality of charge leads. The third degree of freedom of translation comprises a reciprocal adjustment for moving the plurality of jets relative to the plurality of charge leads. With respect to the degrees of freedom of rotation, the first degree of freedom of rotation comprises a first parallel adjustment for aligning the plurality of jets parallel to the charge plate face; the second degree of freedom of rotation comprises a second parallel adjustment for aligning the array of orifices parallel to the charge plate face; and the third degree of freedom of rotation comprises a third parallel adjustment for aligning the orifice plate parallel to the top of the charge leads. Referring now to the drawings, in Fig. 1 an isometric view of the principal components for the six-degrees-of-freedom adjustment assembly used in an ink jet printer is illustrated. A charge plate/catcher assembly 10 is fixed in an alignment stand by a V-groove 12 in the charge plate/catcher assembly 10. This assembly 10 provides charging and collecting means for controlling droplet streams generated by a droplet generator assembly 14. The charge plate/catcher assembly 10 incorporates a fixed rear frame 16 which provides a spring bias at location 18 against a removable first adjustment frame 20, which allows for physical adjustments. The rear frame 16, also designated the second frame, provides a spring bias for the physical adjustments, and further provides a clamp force. The drop generator assembly 14, then, is situated between the first frame 20 and the second frame 16. Referring now to Fig. 2 and continuing with Fig. 1, a top view which demonstrates the principle adjustments between the charge plate/catcher assembly 10 and the droplet generator assembly 14 is shown. The spring bias at location 18 provides compressive force on the droplet generator assembly 14 against precision adjustment screws 22, preferably 120 tpi. This coupling provides a method for moving the droplet array generated by the droplet generator assembly 14 toward and away from the charge lead array, thereby providing the third degree of freedom of translation for the mounting and alignment apparatus. The third degree of freedom of translation comprises a reciprocal adjustment for moving the plurality of jets relative to the plurality of charge leads. This coupling also allows an operator to rotate the droplet generator assembly 14 array until it is parallel to the face of the charge plate/catcher assembly 10 lead array, thereby providing for the second degree of freedom of rotation, which comprises a second parallel adjustment for aligning the array of orifices parallel to the charge plate face. Continuing with Fig. 2, a similar spring bias and screw combination is accomplished with the spring 23 and the screw 24. This causes the components of Figs. 1 and 2 to be loaded against a barrier which is permanently attached to the droplet generator assembly 14. This portion of the assembly provides a translation means for positioning each of the plurality of droplets relative to the plurality of charge leads. This portion of the assembly, along with a member 25 for translation, provide the second degree of freedom of translation. The second degree of freedom of translation comprises an alignment adjustment for aligning each of the plurality of jets with respect to each of the plurality of charge leads. The remaining first and second degrees of freedom of rotation and the first degree of freedom of translation of the droplet generator assembly 14 will now be described. These remaining degrees of freedom of adjustment are accomplished by a preliminary setup of the droplet generator assembly 14, which is best illustrated in Fig. 3. The droplet generator assembly 14 comprises a drop generator 26 in the form of a resonator with dowel pins 28 used to mount into a lower frame 30. Clamp bars 32 are used to fix the drop generator 26 to the lower frame 30. The lower frame 30 couples to a first base support 34 and a second base support 36. The bottom surfaces of the base supports 34 and 36 rest directly on the charge plate/catcher assembly 10 of Figs. 1 and 2. The height of the drop generator 26, the parallelism for aligning the plurality of jets relative to the charge plate face, the parallelism for aligning the orifice plate parallel to the top of the charge leads, and the rotation of the plurality of jets about the x-axis indicated by rotation arrow 38, are obtained by adjusting precision screws 40, best illustrated in Fig. 2. The height adjustment of the drop generator 26 relative to the charge plate of assembly 10 provides the first degree of freedom of translation. The first parallel adjustment for aligning the plurality of jets parallel to the charge plate face provides the first degree of freedom of rotation. The third parallel adjustment for aligning the orifice plate parallel to the top of the charge leads provides the third degree of freedom of rotation. Once the nominal positions for the drop generator 26 are achieved using a fixture or a coordinate measuring system, the drop generator 26 is locked into place using set screws 42, and corresponding screws (not shown) on the opposing side of the frame 30. Referring now to Fig. 4, there is illustrated a section view through the charge plate/catcher assembly 10. As shown in Fig. 4, the second frame 16 is a second permanent frame and provides the spring bias for critical alignment parameters. The second frame 16 also constrains a compression member 44 acting as strain relief, which is attached to a low durometer compressive material 45 which provides a clamping force on cables 49 from charge driver boards 47. The cables provide charging signals to the plurality of charge leads fixed to the charge plate/catcher assembly 10. The compression member 44 is constrained from motion by affixing the compression member 44 to the charge plate/catcher assembly 10 at location 46, and fixing the second frame 16 to the charge plate/catcher assembly 10 at location 48. Although the preferred mode of practicing the invention has been described with reference to an ink jet print head for a continuous ink jet printer, the principle of the present invention can also be applied to a wide variety of ink jet printers. Industrial Applicability and Advantages The mounting and alignment apparatus according to the present invention is useful in continuous ink jet printers. The mounting and alignment apparatus of the present invention provides for adjustment by height and tilt of the resonator structure to precisely control the tilt of the resonator relative to the charge plate, thereby providing consistent print windows. The present invention provides the further advantage of allowing height changes to accommodate a wider range of charge plate flatness co-planarity. Finally, the present invention provides the advantage of easily compensating for changes in ink which may have difficult filament break-off centers. Having described the invention in detail and by reference to the preferred embodiment thereof, it will be apparent that modifications and variations are possible without departing from the scope of the invention defined in the appended claims.

Claims: A continuous ink jet printer having a jet array including a plurality of jets, a plurality of charge leads associated with a charge plate forming part of a charge plate/catcher assembly (10), a drop generator (26), an orifice plate with an array of orifices, and mounting and alignment apparatus for the charge plate/catcher assembly (10) and the drop generator (26), the mounting and alignment apparatus comprising: a. a first degree of freedom of translation; b. a second degree of freedom of translation; c. a third degree of freedom of translation; d. a first degree of freedom of rotation; e. a second degree of freedom of rotation; and f. a third degree of freedom of rotation. A continuous ink jet printer according to claim 1, characterised in that the first degree of freedom of translation comprises a height adjustment of the drop generator (26) relative to the charge plate, the second degree of freedom of translation comprises an alignment adjustment for aligning each of the plurality of jets with respect to each of the plurality of charge leads, and the third degree of freedom of translation comprises a reciprocal adjustment for moving the plurality of jets relative to the plurality of charge leads. A continuous ink jet printer according to claim 1, characterised in that the first degree of freedom of rotation comprises a first parallel adjustment for aligning the plurality of jets parallel to the charge plate face, the second degree of freedom of rotation comprises a second parallel adjustment for aligning the array of orifices parallel to the charge plate face, and the third degree of freedom of rotation comprises a third parallel adjustment for aligning the orifice plate parallel to the top of the charge leads. A continuous ink jet printer according to claim 1, characterised in that the mounting and alignment apparatus comprises: a. a first frame (20) for allowing physical adjustments; b. a second frame (16) for providing a spring bias for the physical adjustments, and further for providing a clamp force; and c. a drop generator assembly (14) which includes the drop generator (26) and is situated between the first frame and the second frame. A continuous ink jet printer according to claim 4, characterised in that the clamp force comprises a strain relief for providing a mechanical means to insure an electrical contact to a plurality of control leads associated with the plurality of charge leads. A continuous ink jet printer according to claim 5, characterised in that the mechanical means comprises: a. the charge plate/catcher assembly (10); b. clamp means (44) wherein a first end of the clamp means is attached to the charge plate/catcher assembly (10) and a second end of the clamp means (44) is restrained in a vertical plane by the second frame (16); and c. a compressible layer (45) situated between the charge plate/catcher assembly (10) and the clamp means to hold the cable connections in a desired position. A method of mounting and aligning a charge plate/catcher assembly (10) and a drop generator (26) of an ink jet printer, within a frame, the printer having a jet array including a plurality of jets, and a plurality of charge leads, the method comprising the steps of: a. adjusting a height of the drop generator (26); b. tilting the drop generator (26) outward to improve help charging; c. securing the drop generator (26) to the charge plate/catcher assembly (10); and d. performing secondary adjustments to complete alignment of the charge plate/catcher assembly (10) and the drop generator (26). A method according to claim 7 which includes the step of securing the charge plate/catcher assembly (10) in a fixed position. A method according to claim 8 wherein the drop generator (26) has six degrees of freedom of adjustment relative to the charge plate/catcher assembly (10), the six degrees of freedom of adjustment comprising: a. a first degree of freedom of translation; b. a second degree of freedom of translation; c. a third degree of freedom of translation; d. a first degree of freedom of rotation; e. a second degree of freedom of rotation; f. a third degree of freedom of rotation.

Inventors: SIMON ROBERT JAMES, STRAIN GARY LEE, SIMON, ROBERT JAMES, STRAIN, GARY LEE, Simon, Robert James, c/o Eastman Kodak Company, Strain, Gary Lee, c/o Eastman Kodak Company
Applicants: SCITEX DIGITAL PRINTING INC, SCITEX DIGITAL PRINTING, INC.
Application year: 1993
Main classification: B41J2
IPC codes: B41J2