Ink drop catcher assembly

Abstract: A screen mesh ink drop catcher assembly (28), which is adapted to catch non-printed ink drops (58) while not catching printed ink drops (46), includes a housing (30) having a fluid return channel (32), and a screen (60) extending from the housing shaped to collect unwanted ink drops. The housing of the ink drop catcher assembly may include at least one surface, at least a portion of which is grooved and operatively associated with the screen such that ink drops flow from the screen to the fluid return channel. The housing of the ink drop catcher assembly may include a screen support (70) with the screen being at least partially positioned about the screen support. The screen support of the ink drop catcher assembly may include at least one surface, at least a portion of which is grooved and operatively associated with the screen such that ink drops flow from the screen to the fluid return channel.

Description: This invention relates generally to the field of digitally controlled printing devices, and in particular to continuous ink jet printers in which a liquid ink stream breaks into droplets, some of which are selectively collected by a catcher and prevented from reaching a receiver while other droplets are permitted to reach a recording surface. Ink jet printing has become recognized as a prominent contender in the digitally controlled, electronic printing arena because, e.g., of its non-impact, low-noise characteristics, its use of plain paper and its avoidance of toner transfers and fixing. Ink jet printing mechanisms can be categorized as either continuous ink jet or drop on demand ink jet. Conventional continuous inkjet utilizes electrostatic charging tunnels that are placed close to the point where the drops are formed in a stream. In this manner individual drops may be charged. The charged drops may be deflected downstream by the presence of deflector plates that have a large potential difference between them. A catcher (sometimes referred to as a "gutter", an "interceptor", or a "collector") may be used to intercept either the charged or the uncharged drops, while the non-intercepted drops are free to strike a receiver or recording medium. U.S. Patent No. 3,878,519, which issued to Eaton on April 15, 1975, discloses a method and apparatus for synchronizing droplet formation in a liquid stream using electrostatic deflection by a charging tunnel and deflection plates. The function of a deflection charge plate and its associated catcher in a continuous jet printer is well known, being described in U.S. Patent No. 4,107,699 which issued to Kenworthy on August 15, 1977. The catcher may be an integral part of systems which serve multiple functions, including: blocking unwanted ink droplets, collecting and removing unwanted ink droplets, measuring drop charge levels, recycling ink, and solving start-up and shut-down problems. Individual ink droplets receive an electrical charge. An opposite electrical charge is applied to the surface of a catcher parallel to the normal trajectory of the ink stream. The opposite polarities create an attraction force that deflects the droplets toward and onto the surface of the catcher. The droplets accumulate on the surface of the catcher until they are overcome by gravitational forces that cause the accumulated droplets to travel toward a collection area. U.S. Patent No. 5,105,205, issued to Fagerquist on April 14, 1992, and U.S. Patent No. 5,469,202, issued to Stephens on November 21, 1995, both disclose ink jet catcher assemblies of this type. However, the disadvantage of this type of catcher is that when ink strikes the surface of the catcher the force of the drop impact causes the ink to splatter and/or mist. Ink splatter and mist creates unwanted artifacts on the printed media that reduces image quality and the splatter and mist contaminate other components in the printer. U.S. Patent No. 4,757,328, which issued to Braun et al. on July 12, 1988, illustrates an assembly of a catcher that minimizes splattering and misting. However, this type of catcher affects print quality in other ways. The need to create an electric charge on the catcher surface complicates the construction of the catchers and it requires more components. This complicated catcher structure requires large spatial volumes between the printhead and the media, increasing the ink drop trajectory distance. Increasing the distance of the drop trajectory decreases drop placement accuracy and affects the print image quality. There is a need to minimize the distance the drop must travel before striking the print media in order to insure high quality images. U.S. Patent No. 4,460,903, which issued to Guenther et al. on July 17, 1994, also illustrates a catcher assembly that minimizes splattering and misting. However, as the ink drops first strike and collect on a hard surface of the catcher, the potential for splattering and misting still exists. Additionally, ink drops have built up on the surface of the catcher could be "flung" onto the receiving media by the movement of the printhead. Continuous inkjet printheads, such as those shown in the Fagerquist patent and the Stephens patent, may incorporate a screen into the catcher to assist with ink fluid removal. Additionally, the Stephens patent includes a thick mesh insert that prevents the fine mesh screen from collapsing during assembly of the catcher. However, the thick mesh insert does not improve fluid removal. Additionally, these printheads experience the misting and splattering disadvantage discussed above. Scanning type ink jet printheads, such as those shown in the Stephens patent, the Fagerquist patent, and the Braun et al. patent, experience acceleration forces that "fling" onto the media ink that has built up on the catcher. In order to minimize the amount of ink flung onto the media, a vacuum is commonly applied at one end of an ink removal channel to assist in removing the ink build up. However, air turbulence created by the vacuum decreases drop placement accuracy and adversely affects the print quality image. Additionally, ink that has built up on catcher surfaces can become contaminated with paper dust, dirt, debris, etc., due to the operating environment of the catcher. Contaminated ink must be cleaned before the ink can be reused, adding to the overall cost and expense of an ink jet system. As the catcher is positioned in close proximity to the media, portions of the catcher are exposed to paper dust, dirt, debris, etc., that is easily collected on portions of the catcher, especially portions having ink buildup, causing the catcher to become clogged. When this happens, the catcher must be thoroughly cleaned prior to operating the ink jet system. It can be seen that there is a need to provide a simply constructed catcher that reduces ink splattering and misting, increases fluid removal without affecting ink drop trajectory, and minimizes clogging of the catcher due to exposure to environmental debris such as paper dust. It is an object of the present invention to provide an ink drop catcher assembly for collecting non-printed ink drops. This object is achieved by the invention as defined in the appended claims. The invention, and its objects and advantages, will become more apparent in the detailed description of the preferred embodiments presented below. In the detailed description of the preferred embodiments of the invention presented below, reference is made to the accompanying drawings, in which: FIG. 1 is a schematic diagram of an inkjet printing apparatus; FIG. 2 is a partial cross sectional view of a nozzle bore with asymmetric heating deflection; FIG. 3 is a top view of a circular nozzle bore with asymmetric heating deflection, shown with a heater having two opposing sections; FIG. 4 is a perspective view of an inkjet catcher made in accordance with the presenting invention; FIG. 5 is an exploded view of the catcher shown in Figure 4; FIG. 6 is a partial side view of the catcher as shown in Figure 4 with a side cover removed; FIGS. 7 and 8 are perspective views of a portion of the catcher made in accordance with the present invention; FIG. 9 is a perspective view of an alternative embodiment of a feature made in accordance with the present invention; FIGS. 10A-10E are top views of alternative embodiments of a feature made in accordance with the present invention; FIG. 11 is a perspective view of an alternative embodiment of a feature made in accordance with the present invention; FIG. 12 is a partial side cross sectional view of an altemative embodiment of a feature made in accordance with the present invention. The present description will be directed in particular to elements forming part of, or cooperating more directly with, apparatus in accordance with the present invention. It is to be understood that elements not specifically shown or described may take various forms well known to those skilled in the art. Referring to FIG. 1, a printhead 20 receives ink from an ink supply reservoir 22 under pressure. As a pressurized ink stream exits from a nozzle opening of printhead 20, the stream breaks into droplets 24. Droplets 24 are selectively subjected to a force that can be turned on and off to determine whether each individual droplet strikes a recording media 26 such as a moving paper or falls into a catcher assembly 28. Typically attached to printhead 20, catcher assembly 28 includes a housing 30 defining at least one fluid return channel 32 for returning non-printed droplets to ink supply reservoir 22 via an ink recovery system 34. Typically, ink recovery system 34 includes a vacuum-generating mechanism that is used to apply a vacuum to fluid return channel 32 to assist with and improve ink fluid flow away from catcher assembly 28 and to ink recovery system 34. As illustrated, non-deflected droplets fall into catcher assembly 28 and deflected droplets reach recording media 26. However, printheads are known wherein the opposite is true, and the present invention can be used in conjunction with either type of printhead. Referring to FIG. 2, a cross-sectional view of one nozzle of an array of such nozzles formed on printhead 20 of FIG. 1, an ink delivery channel 36, along with a plurality of nozzle bores 38 are etched in a substrate 40, which is silicon in this example. Delivery channel 36 and nozzle bores 38 may be formed by anisotropic wet etching of silicon, using a p + etch stop layer to form nozzle bores 38. Ink 42 in delivery channel 36 is pressurized above atmospheric pressure, and forms a stream 44. At a distance away from nozzle bore 38, stream 44 breaks into a plurality of drops 46 due to a periodic heat pulse supplied by a heater 48. Heater 48 is separated from substrate 40 by thermal and insulating layers 50 to minimize heat loss to substrate. Nozzle bore 38 may be etched allowing the nozzle exit orifice to be defined by insulating layers 50. Referring to FIG. 3, heater 48 has two sections 52a and 52b, each covering approximately one-half of the perimeter of nozzle bore 38. The power connections 54a and 54b and the ground connections 56a and 56b from the drive circuitry of the heater (not shown) to heater 48 are also shown. Stream 44 may be deflected by an asymmetric application of heat by supplying electrical current to one, but not both, of heater sections 52a and 52b. This technology is distinct from other prior systems of electrostatic continuous-stream deflection printers, which rely upon deflection of charged drops previously separated from their respective streams. With stream 44 being undeflected, drops 46, shown in FIG. 2, may be blocked from reaching recording media 26 by catcher assembly 28 according to the present invention. In an alternate printing scheme, ink catcher assembly 28 may be placed to block deflected drops 46 so that undeflected drops 58 will be allowed to reach recording media 26. Referring to FIGS. 4 and 5, catcher assembly 28 includes housing 30 and a screen 60 with screen 60 extending beyond housing 30. Housing 30 includes a top cover 62, a bottom cover 64, a right side cover 66, and a left side cover 68 positioned substantially about a screen support 70. Screen support 70 may also extend beyond housing 30. Housing 30 also includes a vacuum manifold 72 to which vacuum is applied to by a vacuum generating mechanism of ink recovery system 34 in order to improve and assist flow of non-printed ink droplets from catcher assembly 28 to ink recovery system 34. Referring to FIG. 6, in a preferred embodiment of the present invention, screen 60 may be positioned at least partially about screen support 70 with screen ends 74 being inserted into a pair of fluid return channels 76 defined by housing 30. In this embodiment, two fluid return channels 76 are created when screen support 70 is positioned substantially within housing 30, approximately centered between top cover 62 and bottom cover 64. However, it is contemplated and, therefore, within the scope of this disclosure that screen support 70 may be positioned substantially within housing 30 such that only one fluid return channel is created. As non-printed ink droplets 58 contact screen 60, ink droplets 58 are transformed in shape, shown generally at 78, from a generally spherical shape to substantially a path or layer of fluid 80. Surface tension between fluid 80 and screen 60 cause fluid 80 to wet screen 60. The wetting of screen 60 creates a fluid layer or path 80, for the collected, non-printed ink droplets 58, away from screen 36 and towards fluid return channels 76. In a preferred embodiment, a woven metal wire mesh material is used to manufacture screen 60. Woven in a manner very similar to that of textiles, the wire diameter of the screen 60 in a preferred embodiment of the present invention is approximately 1.0 to 1.5 mils, and woven in what is commonly called a twilled-dutch weave pattern yielding a spacing of approximately 8 microns. This type of wire mesh is commercially available from, for example, Ron-Vik, Inc., Minneapolis, Minnesota. Woven wire mesh having these characteristics has excellent shape retaining qualities, while the geometry and size of the weave spacing has superior fluid retention properties. However, a plastic, polymer, or cloth material could be woven and used for screen 60 with substantially similar results. Additionally, a paper filter media, a synthetic material, either woven or unwoven, or a sintered metal could also be used as the material for screen 60 with substantially similar results. Alternatively, an open cell foam could be used with substantially similar results, provided that a foam having a pore size sufficiently small enough to create a fluid layer was used. The combination of the shape of the wire, the small apertures formed by the weaving process, and the ink droplets themselves creates the thin fluid layer 80 on the surface of screen mesh 60. The fluid layer 80 intercepts and absorbs the non-printed ink droplets preventing them from reaching the media. Additionally, as surface tension exists between the fluid layer 80 and screen mesh 60, collected ink droplets are prevented from being "flung" onto the recording media as the printhead moves and accelerates, thereby eliminating unwanted artifacts on the recording media and improving overall print quality. The screen mesh also acts as a filter, prohibiting environmental contaminants from entering the ink stream, thereby increasing ink recycling efficiency. The catcher assembly of the present invention is operable to intercept and absorb non-printed droplets directly through the fluid layer 80 preventing the non-printed ink droplets from reaching recording media 26. As such, there is no need to deflect the non-printed ink droplets onto a surface of the catcher assembly prior to collecting the ink drops, thereby reducing or eliminating misting and splattering. This reduces printhead maintenance and cleaning. Additionally, the catcher assembly of the present invention does not require a large geometry to accommodate an electrostatic electrode deflector to steer the ink droplets, or a large flat surface to collect the ink droplets after the ink droplets are deflected; therefore, the overall size of the catcher assembly is reduced. Although the ink drops must still be deflected by a heater, for example, in order to reach the printing media or be intercepted by the catcher assembly, the configuration of the catcher assembly allows the catcher assembly to be positioned closer to the ink jet printhead reducing ink drop trajectory distance. Reducing ink drop trajectory distance reduces printed drop placement error, thereby increasing print image quality. Again referring to FIG. 5, and to FIGS. 7 and 8, portions of screen support 70, bottom cover 64, and top cover 62 can be contoured or grooved such that at least one channel 82 is formed on one or more of these surfaces. FIGS. 7 and 8 show channels 82 in more detail using the screen support 70 as an example. However, it is to be understood, and therefore within the scope of this disclosure, that channels 82, as shown in FIGS. 7 and 8 may also be placed on surfaces of the bottom cover 64 and the top cover 62. Channels 82 are positioned longitudinally along front and back surfaces 84 and 86, respectively, of screen support 70. Typically, channels 82 are cut, milled, etched, molded, or integrally formed in surfaces 84 and 86 at the desired location of the placement. Channels 82 improve ink fluid flow from screen 60 to fluid return channels 76. As ink fluid flow is increased, the amount of vacuum typically required to remove ink fluid is significantly decreased. As such, the overall ink fluid removal capability of the catcher assembly is increased without the adverse effects on ink drop trajectory typically associated with applying vacuum to the fluid return channels. Again referring to FIG. 6, as the operating environment of the printhead 20 is relatively confined and the angle of ink drop deflection is relatively small, tolerance issues are present. In this respect, screen support 70, acts to form and retain screen 60 in a precise shape. This allows precise placement of the screen in close proximity to the printed ink drop path such that the screen is operable to intercept non-printed ink drops directly. Positioning screen 60 substantially about screen support 70 in this manner also helps to eliminate ink fluid buildup on the backside of catcher assembly 28 because the ink may be removed through fluid return channel 76 positioned in a lower portion of the housing 30. In a preferred embodiment, bottom cover 64, top cover 62, right side cover 66, left side cover 68, and screen support 70 are made from a plastic or other suitable polymer material. Alternatively, the components of housing 30 could be made from other materials such as stainless steel or ceramic, for example, with substantially similar results. Referring to FIGS. 9 and 10A-10E, various shapes of channel 82 are shown. These shapes include channels 82 having a generally triangular cross section, as shown in FIGS. 9 and 10A; a generally square cross section, as shown in FIG. 10B; a generally elliptical or curved cross section, as shown in FIGS. 10C (illustrating a single channel) and 10D (illustrating a plurality of channels); and a generally rectangular cross section, as shown in FIG. 10E. Surprisingly, test results have shown that channels 82 having an elliptical or curved cross section, as shown in FIG. 10D, work unusually well for improving and assisting with ink fluid flow from screen 60 to fluid return channels 76. Again, it is to be understood that the channel shapes disclosed in FIGS. 9 and 10A-10E may be positioned on any surface of screen support 70, top cover 62, and bottom cover 64 that contacts screen 60 and fluid return channel 76. Also, channels 82 may extend over the entire length of screen support 70, top cover 62, and bottom cover 64, or any portion thereof. Additionally, it is contemplated that channels 82 may be positioned on right and left side covers 66 and 68, respectively, also resulting in improved ink fluid flow. Again referring to FIGS. 7 and 8, in a preferred embodiment, screen support 70 includes two legs 88 and 90 joined at an elbow 92 in a substantially "L" shape. Leg 90 extends in a direction that is substantially towards the direction of non-printed ink drop flow such that non-printed ink drops contact leg 90, either directly or directly through screen 60. The substantially "L" shape decreases the distance non-printed ink drops must travel before reaching their destination, thereby reducing the overall size of the catcher assembly and printhead assembly. As screen 60 is positioned substantially about screen support 70, in a preferred embodiment, screen 60 also has a substantially "L" shape. Referring to FIGS. 11 and 12, an alternative embodiment for screen support 70 is shown. In this embodiment, screen support 70 is substantially straight having at least one channel 82 extending longitudinally over generally the entire length of screen support 70. Screen 60 is positioned substantially about screen support 70 with at least a portion of screen 60 and screen support 70 extending beyond top cover 62 and bottom cover 64 of housing 30. Screen 60 is operable to receive non-printed ink drops 58 directly, thereby creating an ink fluid layer as described above, resulting in at least the same advantages also described above.

Claims: An ink drop catcher assembly (28) comprising: a housing (30) defining a fluid return channel (32) and including a screen (60); characterized by said fluid return channel having a surface, at least a portion of said surface having a groove (82) substantially parallel to said fluid return channel; and said screen extending from said housing shaped to directly collect non-printed ink drops (58), said screen being in fluid communication with said groove such that ink flows from said screen to said fluid return channel (32). The ink drop catcher assembly as defined in Claim 1, wherein said housing includes a screen support (70) and said screen is at least partially positioned about said screen support. The ink drop catcher assembly as defined in Claim 2, wherein a portion of said screen support is angled toward a direction of ink drop flow. The ink drop catcher assembly as defined in Claim 2, wherein said screen support includes a surface, at least a portion of said surface having a groove (82) substantially parallel to said fluid return channel, said groove of said screen support being in fluid communication with said screen such that ink flows from said screen to said fluid return channel. The ink drop catcher assembly as defined in Claim 4, wherein said groove of said screen support has a cross section and at least a portion of said cross section is elliptical. The ink drop catcher assembly as defined in Claim 1, wherein said groove of said fluid return channel has a cross section and at least a portion of said cross section is elliptical. The ink drop catcher assembly as defined in Claim 1, wherein a portion of said screen is angled toward a direction of ink drop flow. The ink drop catcher assembly as defined in Claim 1, wherein said screen is made from a woven wire mesh material. The ink drop catcher assembly as defined in Claim 1, wherein a fluid layer is created on said screen by the non-printed ink drops.

Inventors: FAISST CHARLES F, WOJCIK TIMOTHY J, FAISST, CHARLES F., WOJCIK, TIMOTHY J.
Applicants: EASTMAN KODAK CO, EASTMAN KODAK COMPANY
Application year: 2001
Main classification: B41J2
IPC codes: B41J2