Abstract:
An apparatus for a laser transmission welding process for attaching a synthetic filter material to a filter tower frame in an ink jet printer cartridge. The apparatus includes a laser beam source and a filter clamping fixture containing a base, slide rods attached on first ends thereof to the base, an optics support plate attached to second ends of the slide rods, a movable platform for holding an ink cartridge slidably disposed on the slide rods between the base and the optics support plate, a platform moving device for translating the platform to and from a laser welding position, a laser beam transparent plate suspended by support legs from the optics support plate to a position between the movable platform and the optics support plate. The apparatus greatly improves synthetic filter attachment to a filter tower frame in an ink cartridge.

Description:
FIELD OF THE INVENTION 
     The invention relates to methods for attaching ink jet filters to an ink cartridge for an ink jet printer, and in particular to apparatus for reliable filter attachment to the cartridge. 
     BACKGROUND 
     Ink jet printers have achieved wide acceptance in the field of printing and continue to make great strides towards high speed, high quality printing. In order to improve the quality and speed of printing, nozzle plates having a larger number of smaller orifices are provided. As the size of the orifices continue to decrease, components of the ink cartridge assembly become increasingly more important. A component of the ink cartridge that is particularly important for proper operation of an ink jet printhead attached to the cartridge is a filter disposed between an ink reservoir and a flow path for ink to the printhead. The filter is the first and most important line of protection for large or foreign particles entering ink flow features of the printheads. Particles larger than the flow features of the printhead can adversely affect the operation of the printhead thus dramatically decreasing the quality and operation of the printhead. 
     The most widely used filter material for application in an ink cartridge is a Dutch weave stainless steel material. Metal filters are typically attached to a filter assembly in the ink cartridge by hot stamping the metal filter onto a plastic frame using a hot block or hot die. Melted plastic from the frame is squeezed into the filter mesh to create a mechanical interlock between the frame and the filter. However, the cost of such stainless steel material is relatively high. 
     In order to reduce the cost of the filter and to provide better wetting of the filter during the melting process, synthetic fiber filter materials have been selected for providing filters. Such synthetic fiber materials include acrylics, nylon, polyester, polyethylene, polypropylene, and polyvinylchloride. However, the replacement of metal filter material with synthetic filter materials, makes attachment of the filter to the frame much more difficult. In a hot stamping process, heat must be transferred from the hot block to the filter material and then to the filter frame. If the melting temperature of the frame is lower than that of the filter material, the frame material will be squeezed into the pores of the filter and create a mechanical lock as before. On the other hand, if the melting temperature of the frame is higher than that of the filter material, the filter will be melted and thinned under pressure, and in some cases the stitches around the perimeter of the filter may be damaged thereby weakening the filter. 
     Ultrasonics may also be used to attach plastic materials to one another. However, when ultrasonics are applied to synthetic filter materials, the high frequency mechanical vibration may cause loose stitches, broken stitches, and particle generation. Loose stitches and broken stitches may cause the filter to fail prematurely. Particle generation may inhibit the flow of ink to and in the ink jet printheads thereby reducing print quality. Another disadvantage of plastic filter materials is that these materials are generally less stiff than metal filter materials and are thus prone to bending, stretching, and wrinkling during the attachment process. 
     Thus, there continues to be a need for improved low cost filter materials and improved methods for attaching the filter materials to a frame in an ink cartridge for an ink jet printhead. 
     SUMMARY OF THE INVENTION 
     With regard to the foregoing and other objects and advantages, the invention provides an apparatus for a laser transmission welding process for attaching a synthetic filter material to a filter tower frame in an ink jet printer cartridge. The apparatus includes a filter clamping fixture having a base, slide rods attached on first ends thereof to the base, an optics support plate attached to second ends of the slide rods, a movable platform for holding an ink cartridge slidably disposed on the slide rods between the base and the optics support plate, a platform moving device for translating the platform to and from a laser welding position, a laser beam transparent plate suspended by support legs from the optics support plate to a position between the movable platform and the optics support plate, and a laser beam source for heating an interface between the synthetic filter material and the filter tower frame to weld the filter material to the frame. 
     In another embodiment, the invention provides a method for attaching a synthetic filter material to a filter tower frame in an ink jet printer cartridge. The method includes providing a laser beam source and a filter clamping fixture for laser beam transmission welding of the filter material to the filter tower frame. The clamping fixture includes a base, slide rods attached on first ends thereof to the base, an optics support plate attached to second ends of the slide rods, a movable platform for holding an ink cartridge slidably disposed on the slide rods between the base and the optics support plate, a platform moving device for translating the platform to and from a laser welding position, and a laser beam transparent plate suspended by support legs from the optics support plate to a position between the movable platform and the optics support plate. The ink cartridge having a filter tower frame therein is placed onto the movable platform. The synthetic filter material is positioned onto the filter tower frame in the ink cartridge. The movable platform is moved toward the laser beam transparent plate so that the synthetic filter material is disposed between the transparent plate and the filter tower frame and is in intimate contact with a perimeter of the filter tower frame. The synthetic filter material is then laser welded to the filter tower frame by heating the perimeter of the filter tower frame with a laser beam from the laser beam source having sufficient power to melt a portion of the filter tower frame for melt flow of the portion of the frame through pores in the synthetic filter material. 
     In yet another embodiment, the invention provides an ink cartridge for an ink jet printer, the cartridge containing a filter tower frame and a polyester filter material attached to perimeter of the filter tower frame using a laser beam transmission welding process. The polyester filter material attached to the frame has a laser beam transmission rate of at least 50% or more for laser beam wavelengths ranging from about 750 to about 1200 nanometers. The filter tower frame has a laser beam absorption rate of greater than about 50% for laser beam wavelengths ranging from about 750 to about 1200 nanometers. At least a portion of the perimeter of the filter tower frame is melt-flowed into pores of the filter material by the laser welding process. 
     The invention provides a number of advantages over conventional apparatus and methods for attaching filter materials in ink jet cartridges. In particular, the process and apparatus enables use of a synthetic filter material which is less costly than a metal filter material. The apparatus also enables welding of synthetic filter materials to a filter tower structure while maintaining the filter material in a desired shape. For example, contoured or tented filters may be attached to filter towers using the apparatus according to the invention. Another advantage of the invention is that the process of laser welding is substantially a non-contact process thereby avoiding abrasion of the filter material. As compared to ultrasonic welding, the laser welding process according to the invention does not cause vibrations during the welding process which can generate particles or otherwise damage the filter. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other aspects and advantages of the invention will become further apparent by reference to the following detailed description of preferred embodiments when considered in conjunction with the accompanying drawings in which: 
         FIG. 1  is schematic representation of a laser transmission welding process according to the invention; 
         FIG. 2  is side elevational view, not to scale, of an ink cartridge containing a filter welded to a filter tower according to the process of the invention; 
         FIG. 3  is a side elevational view, not to scale, of a laser transmission welding fixture for use in the process of laser transmission welding according to the invention; 
         FIG. 4  is a partial perspective view, not to scale, of an upper portion of a laser transmission welding fixture according to the invention; 
         FIG. 5  is a detailed view, not to scale, of a transparent plate and support legs for a laser transmission welding fixture according to the invention; 
         FIGS. 6A and 6B  are side elevational view of a fixture according to the invention during a laser transmission welding process; 
         FIG. 7  is a detailed side view of an alternate filter shape and an alternate transparent plate for use with a laser transmission welding fixture according to the invention; 
         FIG. 8  is a detailed side view of another alternate filter shape and another alternate transparent plate for use with a laser transmission welding fixture according to the invention; 
         FIG. 9  is a detailed side view, not to scale, of a transparent plate for use in welding a filter to a filter tower frame according to another embodiment of the invention; 
         FIG. 10  is a plan view, not to scale, of the transparent plate of  FIG. 9 ; and 
         FIGS. 11 and 12  are plan views, not to scale, of transparent plates and support legs for laser welding a filter to an angled filter tower frame according to the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     With reference to  FIG. 1 , a schematic representation of a laser transmission welding process  10  for attaching a synthetic filter to a filter tower structure is shown. According to the process, a laser beam  12  is focused through a lens  14  onto an interface  16  between a first material  18  to be welded to a second material  20 . For this process, it is important that at least one of the two materials being joined together be substantially transparent to the laser beam  12 . 
     The material facing the laser source, the first material, may preferably be clear or colored provided the coloring material or pigment does not significantly affect the transmission of the laser beam through the material. The second material is placed on a side of the first material opposite the laser beam side of the first material. The second material must be able to absorb the laser beam  12  so that it heats up and melts during the welding process. 
     It is also important that the two materials be in intimate contact with each other during the welding process. As the second material absorbs the laser energy and heats up it also heats up the first material in contact with it thereby also melting a portion of the first material in contact with the second material. Hence, the laser beam transmission rate of the first material is an important factor in use of the laser transmission welding process. If the transmission rate is too low, the energy absorbed by the material facing the laser beam  12  may overheat and degrade before the laser energy is transmitted to the second material. 
     In this case, the first material  18  is preferably a synthetic filter material having a laser beam transmission rate of greater than about 50% at laser beam wavelengths in the near infrared (NIR) spectrum. The second material  20  preferably has a laser beam absorption rate of greater than about 50% at laser beam wavelengths in the NIR spectrum. Particularly preferred wavelengths range from about 750 to about 1200 nanometers. It is also preferred that the melting point of the first material  18  be higher than the melting point of the second material and that the melting point of the first and second materials be no more than 30° C. apart. It is also preferred that the first and second materials  18  and  20  be compatible with each other so that there is intimate mixing of the first and second materials at the interface  16  thereof. 
     With reference to  FIG. 2 , a simplified drawing of an ink cartridge  22  for an ink jet printer is illustrated. The ink cartridge  22  includes a cartridge body  24  for providing an ink reservoir  26  therein. Disposed in the ink reservoir is an ink filter  28  attached to a filter tower frame  30 . A particularly preferred ink cartridge  22  includes a body  24  molded from a material selected from the group consisting of thermoplastic materials including but not limited to polyphenylene oxide/polystyrene alloys, polypropylene, acrylonitrile/buta-diene/styrene terpolymers, polystyrene/butadiene alloys or copolymers, polyetherimide, polysulfone, polyesters and the like, having a melting point or softening point above about 120° C. A particularly preferred material for the ink cartridge body is a polyphenylene ether/polystyrene resin from GE Plastics of Pittsfield, Mass. under the trade name NORYL SE1701. 
     The filter tower frame  30  is preferably made of a material that is chemically compatible with the synthetic filter material and is able to absorb a substantial amount of radiation from a laser source. Particularly preferred materials for providing the filter tower frame  30  include thermoplastic polyester materials such as a glass reinforced polyethylene terephthalate material available E. I. DuPont Company of Wilmington, Del. under the trade name RYNITE FR515. Other preferred materials that may be used for providing the filter tower frame  30  include, but are not limited to, polybutylene terephthalate materials available from GE Plastics of Pittsfield, Mass. under the trade names VALOX 357 and VALOX 855. A laser absorption dye or a pigment such as carbon black is preferably included in the resin for making the filter tower frame  30  in order to increase the absorption of the laser beam radiation so as to melt a portion of the filter tower frame  30  around a perimeter thereof during the welding process. The percentage of pigment dispersed in the material for the filter tower frame  30  may range from about 0.2% to about 2% by weight. 
     In order to effectively weld the filter  28  to the filter tower frame  30 , the filter  28  is preferably made of a woven synthetic thermoplastic material having a substantial laser beam radiation transmission rate at the near infrared spectrum (NIR). Accordingly, it is preferred that the filter material be selected from a polyester material such as a woven polyester available from Saati SpA Corporation of Milano, Italy under the trade name SAATIFIL. It is particularly preferred that the filter material be chemically compatible with the filter tower frame material so that upon melting of a portion of the filter tower frame material, the molten filter tower frame material will wet and the filter material and form a bond with the filter material fibers. The laser beam transmission rate of the filter material is preferably greater than about 50% in at near the NIR spectrum. 
     Another important aspect of the invention is that there is preferably intimate contact between the filter  28  and the filter tower frame  30  during the laser welding process. Intimate contact between the filter  28  and frame  30  insures that there a solid perimeter around the filter is provided so that ink in the ink reservoir  26  cannot bypass the filter and get into minute flow features in a printhead attached to the ink cartridge  22 . Intimate contact is preferably obtained by use of a laser transmission welding fixture  32  generally as shown in  FIG. 3 . 
     With reference to  FIG. 3 , the laser transmission welding fixture  32  includes a base plate  34 , a moving plate  36 , and a top plate  38 . The top plate  36  and base plate  32  are connected to one another by slide rods  40  so that the base plate  32  is attached on a first end  42  of the slide rods  40  and the top plate  36  is attached on a second end  44  of the slide rods  40 . The movable plate  36  is movably positionable between the top plate  38  and the base plate  34  by, for example, an electric or hydraulic cylinder  48  and push rod  50 . Accordingly, the movable plate  36  is freely slidable in the direction of arrow  46  along a portion of the length of the slide rods  40 . 
     The upper plate  38  includes an opening  52  therein ( FIG. 4 ) for transmission of a laser beam  54  from a laser source  56  to a workpiece placed on movable plate  36 . A preferred laser beam source  56  is a diode laser having a wavelength ranging from about 750 to about 1200 nanometers. An Nd:YAG laser may also be used to provide the laser beam source  56 . A laser beam transparent plate  60  is attached to support legs  62  which are attached to the top plate  38  so that the transparent plate  60  is fixedly suspended between the top plate  38  and the movable plate  36 . The support legs  62  enable the transparent plate  60  to resiliently contact a surface of the workpiece as described in more detail below. 
     A more detailed view of the transparent plate  60  and support legs  62  is shown in  FIG. 5 . The transparent plate  60  may be provided by glass, clear polycarbonate, clear polymethyl methacrylate cyclic olefin polymer, or quartz. A particularly preferred material for the transparent plate is glass. The transparent plate  60  preferably has a thickness ranging from about 8 to about 12 millimeters for glass and from about 18 to about 25 millimeters for polymeric or plastic materials. 
     The transparent plate  60  is attached to the support legs  62  with a resilient pad  64  interposed between an end  66  of legs  62  and the transparent plate  60 . The resilient pad  64  may be made of natural or synthetic rubbers such as neoprene rubber or a thermoplastic elastomer available from Advanced Elastomer Systems of Akron, Ohio under the trade name SANTOPRENE. 
     Use of a resilient pad  64  between the legs  62  and transparent plate  60  is important to maintain the plate  60  in intimate contact with the workpiece such as filter  28  on filter tower frame  30  as pressure is applied to the filter  28  and filter tower frame  30  during the welding process. As with all molded plastic parts, there is some variation in the height or planarity of the perimeter of the filter tower frame  30 . The resilient pad  64  enables full surface contact between the filter  28  and the transparent plate  60  regardless of variations in the height or planarity of the filter tower frame  30 . During the welding process, the transparent plate  60  is pressed against the filter  28  and filter tower frame  30  with a pressure ranging from about 1500 to about 3000 mm Hg. 
     An opposite surface of the transparent plate  60  is preferably coated with a release coating material  70  such as silicone, siloxane, parylene, or fluoropolymer coating materials. A particularly preferred coating material is a fluoropolymer coating material available from the E. I. DuPont Company under the trade name TEFLON. The release coating material  70  is preferably substantially transparent to laser beam radiation in the near infrared spectrum, most preferably having a laser beam transmission rate of at least about 80% at wavelengths ranging from about 750 to about 1200 nanometers. 
     During the laser transmission welding process, the perimeter  72  of the filter tower frame  30  is heated to the melting point of the frame material. As a portion of the frame  30  melts, it flows through pores in the filter  28  and adheres to the coating material  70  on the transparent plate  60 . If the filter tower material is not removed from the transparent plate  60 , it will absorb laser energy from the laser beam  54  and may burn or crack the transparent plate  60 . Filter tower material stuck to the transparent plate  60  may also stick to and cause separation between a filter  28  and filter tower  30  on the next welding cycle. Accordingly, the coating material  70  serves to protect the integrity of the welded structures and to prevent damage to the welding fixture  32 . 
     The entire fixture  32  is preferably positioned atop an XY translation table  74  for moving the fixture  32  under the laser beam  54  during the welding process. By moving the fixture  32  and workpiece on the fixture  32 , a stationary laser beam source  56  may be used to perform the welding operation. 
     A process for laser transmission welding of the filter  28  to the filter tower frame  30  is illustrated schematically in  FIGS. 6A and 6B . After completion of a welding procedure, the movable plate  36  is lowered by cylinder  48  and piston  50  to a first position indicated by arrow  76 . An ink cartridge  22  is placed in the welding position on movable plate  36  so that the filter tower  30  and filter  28  align generally with the position of the transparent plate  60 . During this step, the laser beam from the laser source  56  is not turned on. 
     Next, cylinder  48  is activated to extend piston  50  therefrom and move movable plate  36  to a second position indicated by arrow  78  wherein the transparent plate  60  is in intimate contact with the filter  28  inside the ink cartridge  22 . The laser source  56  is activated to provide laser beam  54  for welding the filter  28  to the filter tower frame  30  while the XY table moves the entire fixture  32  in the X and Y directions so that a weld can be provided around the perimeter of the filter tower frame  30 . Upon completion of the welding process, the movable plate  36  is again lowered to the first position indicated by arrow  76  ( FIG. 6A ) for removal of the ink cartridge  22  from the fixture  22 . 
     The invention is also adaptable to contoured or shaped filter elements  80  as shown in  FIGS. 7–9 . With reference to  FIG. 7 , the filter  80  has a concave shape extending down into the filter tower  30 . In order to weld the filter  80  to the filter tower frame  30 , a transparent plate  82  having a convex portion  84  is used in the fixture  32  of the invention. 
     In  FIG. 8 , filter  86  has a convex shape. Accordingly, transparent plate  88 , in this case, has a concave shape  90  as shown. Supports  92  may be provided in the filter tower  30  to support the shape of the filters  80  and  86 . 
     The invention is also adaptable to filters  94  having a complex shape by providing a transparent plate  96  as shown in  FIGS. 9 and 10  having an opening  98  therein. A round opening  98  is shown in  FIG. 10 , however any shape opening may be provided in the plate  96  provided there is a portion of the plate such as portion  100  that may be used to apply pressure to the filter  94  and filter tower frame  30  around the periphery of the frame  30 . 
       FIGS. 11 and 12  illustrate variations on the transparent plate and support legs that enable attaching a filter on an angle to an angled filter tower frame  110 . In  FIG. 11 , the support legs  62  have substantially the same length. However, a transparent plate  112  thereof is thicker on end  114  compared to end  116  thereof. This enables the transparent plate  112  to apply substantially the same pressure around the entire periphery of the filter  28  and the filter tower frame  110  around the entire periphery of the filter tower frame during the welding process. 
     In  FIG. 12 , a transparent plate  118  has the same thickness from end  120  to end  122 . However, support leg  124  is made longer than support leg  126  to enable the transparent plate to apply substantially the same pressure to the filter  28  and to the filter tower frame  110  around the entire periphery of the filter tower frame  110  during the welding process. 
     The apparatus of the invention as described above may also be adaptable to other laser welding techniques. Such techniques include, but are not limited to, contour laser welding, mask laser welding, quasi-simultaneous laser welding and the like. 
     Contour laser welding uses a laser light source and moves the part under the laser beam or moves the laser beam over the part, typically using an X,Y table. The laser beam typically travels around the weld area once or only a few times to complete the welding process. 
     Mask laser welding uses a laser light source that irradiates a linear section at a time. The mask is placed between the laser light source and the part to be welded. Then the laser beam or the part and mask combination are moved to sweep the laser beam across the mask and through the mask to the part being welded. Quasi-simultaneous laser welding uses a laser beam reflected off of movable mirrors such as those on a galvanometer head. The mirrors typically move very fast causing the laser beam to scan around the surface of the part to be welded at a rate of about 1 to about 10 meters/sec. This method heats the welding surface by quickly scanning an intense laser beam around the area to be welded. Accordingly, the laser beam scans around the part many times, from a few to thousands of passes, during the welding process. In yet another embodiment, simultaneous welding may also be used with the apparatus of the present invention. Simultaneous laser welding irradiates all of the weld area at the same time. Diode laser stacks can be placed directly above the weld area. Alternatively a diode laser, Nd:YAG laser, or some other laser can be used with optical fibers or some other light transmission media to direct the laser beam to the weld area. 
     The foregoing description of certain exemplary embodiments of the present invention has been provided for purposes of illustration only, and it is understood that numerous modifications, alterations, substitutions, or changes may be made in and to the illustrated embodiments without departing from the spirit and scope of the invention.