Abstract:
A segmented platen for heat-sealing a film material to a non-planar surface of an ink jet printer cartridge includes a heat-transferring housing having sidewalls defining an internal cavity and a first aperture. Heat-transferring segments, which partially protrude through the first aperture of the housing, are operable to independently move in relation to the housing and each other in a direction substantially parallel to the sidewalls of the housing. Biasing devices, corresponding in number to the segments, independently urge the segments through the first aperture of the housing, thereby urging the segments to follow any curvature in the non-planar surface of the ink jet printer cartridge. The platen further includes a heating element for generating and transferring heat into the housing. The segments receive the heat from the housing, and transfer the heat into the underlying film. Each of the segments of the platen has high thermal conductivity, thereby transferring heat into the film material at a rate much higher than may be attained using compliant rubber platens. The independent movement and downward pressure of the segments upon the film provides efficient heat transfer into the film without deforming high spots in the non-planar surface of the ink jet cartridge.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention is generally directed to an apparatus for heat-sealing film materials. More particularly, the invention is directed to a platen having a segmented heating surface for heat-sealing a polymer film to an ink jet cartridge.  
         BACKGROUND OF THE INVENTION  
         [0002]    Various configurations of ink-containment vessels, tanks, and print heads for use in ink jet printers incorporate a pressure-regulating device for maintaining optimum ink pressure during operation of the printer. Many of these pressure-regulating devices typically comprise a polymer film covering a precision stainless steel ball disposed in an asymmetrical hole. The film is typically heat-sealed to a surface of the ink tank in order to hold the ball precisely in the hole, thereby forming narrow channels between the ball and the inside of the hole. The film may also cover a vent path in the tank. The ball typically protrudes slightly above the top edge of the hole so that the process of sealing the film over the ball applies a slight normal force to the ball, thereby holding it in a precise location within the hole. The surface to which the film is sealed is typically molded polypropylene or other polymer, or metal.  
           [0003]    Due to the geometry and tolerances of the molded or formed tank material, and the geometry of the pressure-regulating device, the surface to which the film is to be sealed is usually not essentially planar. The planarity of the surface may vary by up to 0.2 mm. In the past, rigid platens, such as heated blocks of copper, have been used to heat-seal the film to the non-planar surfaces. Such rigid platens typically cause deformations in high spots of the sealing surface on the tank. This deformation can adversely affect the performance of the vent paths and narrow air channels in the pressure-regulating device.  
           [0004]    The use of flexible or elastomeric material having a thickness sufficient to compensate for the non-planarity of the surface to be heated have not proved to be to be completely satisfactory.  
           [0005]    Therefore, an improved heat-sealing platen is needed having a compliant heating surface that can accommodate the variations in height of the ink vessel and the pressure-regulating device.  
         SUMMARY OF THE INVENTION  
         [0006]    The foregoing and other needs are met by a segmented platen for transferring heat into a film for heat-sealing the film to a non-planar surface of an ink jet printer cartridge. The platen includes a heat-transferring housing having sidewalls defining an internal cavity and a first aperture. A plurality of heat-transferring segments are disposed substantially within the housing and contacting the sidewalls of the housing. The segments partially protrude through the first aperture of the housing, and each segment has a heating surface disposed outside the cavity. Each of the segments is operable to independently move in relation to the housing and each other in a direction substantially parallel to the sidewalls of the housing. The platen includes a plurality of biasing devices disposed within the housing and corresponding in number to the plurality of heat-transferring segments. Each of the biasing devices independently urges a corresponding one of the segments through the first aperture, such that the heating surface of each segment is thereby urged to follow any curvature in the non-planar surface to which the film is applied when the platen engages the film. A heating element is disposed within the cavity and in contact with the housing. The heating element generates and transfers heat to the housing and the segments.  
           [0007]    Thus, the present invention provides a segmented platen having heating surfaces that may move up and down independently of each other to accommodate any non-planarity in the surface to which the film is to be sealed. Each of the segments of the platen have high thermal conductivity, thereby transferring heat into the film material at a rate much higher than may be attained using existing compliant heated rubber platens. The independent movement and downward pressure of the segments upon the film provides efficient heat transfer into the film without deforming the high spots in the non-planar surface.  
           [0008]    Preferred embodiments of the platen include a compliant metal shim disposed between the film and the lower heating surfaces of the segments. The shim prevents the edges of the segments from imprinting a grid-like pattern in the film.  
           [0009]    In a preferred embodiment, the biasing devices provide differing levels of compressive force to the individual segments depending on the position of the segments within the platen, thereby providing different amounts of pressure to different locations on the film. This position-dependent variation in downward pressure is useful in sealing film over certain types of surface defects or irregularities in an ink jet cartridge, such as sink marks.  
           [0010]    In another aspect, the invention provides a platen for heat-sealing a film to a non-planar surface. The platen includes a heating body containing a heating element. The platen also includes a plurality of independently-urgeable elements having non-elastomeric heating surfaces pending from the heating body and contacting the non-planar surface. The platen further includes urging devices corresponding to each of the independently-urgeable elements for urging the independently-urgeable elements toward the non-planar surface. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]    Further advantages of the invention will become apparent by reference to the detailed description of preferred embodiments when considered in conjunction with the drawings, which are not to scale, wherein like reference characters designate like or similar elements throughout the several drawings as follows:  
         [0012]    [0012]FIG. 1 is an exploded view of the segmented platen according to a preferred embodiment of the invention;  
         [0013]    [0013]FIG. 2 is a length-wise cross-sectional view of the segmented platen according to a preferred embodiment of the invention;  
         [0014]    [0014]FIG. 3 is a width-wise cross-sectional view of the segmented platen according to a preferred embodiment of the invention; and  
         [0015]    [0015]FIG. 4 is perspective view of the segmented platen according to a preferred embodiment of the invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0016]    Shown in FIGS.  1 - 4  is a segmented platen  10  for heat-sealing thermoplastic film materials to non-planar surfaces. The preferred embodiment of the platen  10  includes a rigid heat-transferring housing  12  for enclosing heat-transferring segments  14 , biasing devices  16 , a heat-transferring block  18 , and at least one heater cartridge  20 . Each of these components of the platen  10  and their function is described in further detail below.  
         [0017]    In typical use, the platen  10  is attached to a positioning device, such as a pneumatic cylinder, that moves the platen  10  into position to seal the film to the sealing surface, and that retracts the platen  10  after the film is sealed. This positioning device provides the normal force that compresses the biasing devices  16 , thereby creating the compressive force against the film. The positioning device could also be a spring, a series or combination of springs, or other linear indexing devices.  
         [0018]    The housing  12  is preferably constructed from a substantially rigid material having a high thermal conductivity, such as brass or copper. The housing  12  is preferably rectangular in cross-section, having four rectangular sidewalls  12   a ,  12   b ,  12   c , and  12   d . The four sidewalls  12   a - d  have inner surfaces connected together to form a cavity  13  of rectangular cross-section within the housing  12 , the cavity  13  opening into upper and first apertures  12   e  and  12   f . As shown in FIGS. 1 and 3A-B, the sidewalls  12   b  and  12   d  preferably have projections that form shelves  12   g  and  12   h  near the first aperture  12   e.    
         [0019]    Disposed within the cavity  13  of the housing  12  are a set of heat-transferring segments  14 . In the preferred embodiment, the platen  10  includes eighteen adjacently-disposed segments  14 , arranged in two parallel rows of nine each. Other numbers of segments  14  could be used, depending upon the size and unevenness of the surface to which the film is to be sealed. Each of the segments  14  is formed from heat-transferring material, such as brass or copper. Each of the segments  14  has a lower heating surface  14   a  and an opposing top surface  14   b . In planes parallel to the lower heating surface  14   a , the segments  14  are substantially rectangular in cross-section.  
         [0020]    In the preferred embodiment, the lower heating surfaces  14   a  are substantially flat. In alternative embodiments, the lower heating surfaces  14   a  are slightly convex or crowned to more closely match the shape of concave or dimpled features in the surface to which the film is to be sealed. In some embodiments of the invention, a thin metal shim, described in more detail hereinafter, is disposed between the surfaces  14   a  and the sealing surface. In the embodiments including the shim, the convex-shaped lower heating surfaces  14   a  tend to increase the compliance of the shim which increases the contact area of the lower surface of the shim against the film. This is especially advantageous when there are abrupt discontinuities in the surface to which the film is to be sealed. However, it will be appreciated that the use of convex-shaped heating surfaces  14   a  would decrease the overall contact area, and would therefore require more heat to seal the film against a relatively flat surface. Therefore, the heating surfaces  14   a  could be custom-shaped depending on the degree of non-planarity in the surface to which the film is to be sealed.  
         [0021]    The size of the segments is determined based upon the size of the film to be sealed. In the preferred embodiment, the lower heating surface  14   a  of each segment  14  is approximately 5×5 millimeters (25 mm 2 ). A platen  10  having two parallel rows of nine such segments  14  provides for sealing a surface of about 45×10 millimeters (450 mm 2 ).  
         [0022]    In the preferred embodiment, the segments  14  each have a shoulder  14   c , such that the lower heating surface  14   a  of each segment  14  is narrower than the top surface  14   b . Preferably, the geometry of the shoulders  14   c  mates with the geometry of the shelves  12   g  and  12   h  in the sidewalls  12   b  and  12   d . As shown in FIGS.  3 A-B, shelves  12   g  and  12   h  contact the shoulders  14   c  to provide a lower limit of travel of the segments  14  relative to the housing  12 . In the top surface  14   b  of each segment  14  is a bore  14   d  for receiving and retaining one of the biasing devices  16 , such as a spring.  
         [0023]    Although the segments  14  contact each other and the sidewalls  12   a - d , the dimensions, tolerances, and smoothness of the segments  14  and the housing  12  allow the segments  14  to substantially slide relative to each other and relative to the sidewalls  12   a - d  in a direction perpendicular to the plane of the first aperture  12   e . Thus, the segments  14  may rise and fall with little interaction or undue friction with each other or with the sidewalls  12   a - d.    
         [0024]    In the preferred embodiment of the invention, the housing  12 , the segments  14 , and the block  18  are all formed from the same material, or from different materials having substantially the same coefficient of thermal expansion. This preferred design criteria eliminates the possibility that the segments  14  could become either too loose in the housing  12  at elevated temperatures, thereby decreasing the amount of heat transfer from the housing  12  to the segments  14 , or that the segments  14  could bind in the housing  12 , thereby preventing the desired relative movement between the segments  14  and the housing  12 .  
         [0025]    The biasing devices  16  are preferably coil springs, although other types of springs, such as wave springs, bevel springs, or leaf springs may also be used. The preferred material for the biasing devices  16  is stainless steel due to its high ratio of modulus to wire diameter. However, it is contemplated that other compliant materials and configurations could be used to form the biasing devices  16 , such cylinders or blocks of high-temperature foam.  
         [0026]    In the preferred embodiment, the platen  10  includes eighteen biasing devices  16  corresponding to the eighteen segments  14 . As shown in FIGS.  2 A-B and  3 A-B, one end of each biasing device  16  is retained within the bore  14   d  in the top surface  14   b  of the associated segment  14 . The other end of each biasing device  16  engages the heat-transferring block  18 . As the platen  10  is lowered to engage the film  24 , each segment  14  provides a downward normal force to the film  24 , where the level of downward force corresponds to the compressive force of the biasing device  16  associated with the segment  14 .  
         [0027]    In the preferred embodiment of the invention, the biasing devices  16  are identical, such that each biasing device  16  provides substantially the same downward force on its associated segment  14  as every other biasing device  16 . In an alternative embodiment, biasing devices  16  of differing sizes are used to provide different amounts of downward force on different ones of the segments  14 . For example, in one embodiment, biasing devices  16  located toward the center of the platen  10  are designed to provide a greater downward force than biasing devices  16  located toward the ends of the platen  10 . Such an embodiment is useful in sealing film over certain types of surface defects, such as sink marks which may result from the injection molding of the ink jet cartridge.  
         [0028]    The heat-transferring block  18  is preferably constructed from a rigid material having high thermal conductivity, such as brass or copper. The block  18  is dimensioned to fit snugly within the cavity  13  formed by the sidewalls  12   a - d  of the housing  12  to maximize heat transfer between the block  18  and the housing  12 . Preferably, the block  18  is held securely in the housing  12  by fasteners, such as set screws. The block  18  includes a cavity  22  for receiving one or more heater cartridges  20 . As shown in the preferred embodiment of FIG. 1, the cavity  22  is cylindrical. As will be appreciated by one skilled in the art, the cavity  22  could also be rectangular for receiving a rectangular heater cartridge.  
         [0029]    As shown in FIG. 1, the preferred heater cartridge  20  is an electrical resistance type cartridge, such as model number TCH0002 manufactured by D-M-E Company of Madison Heights, Mich. The cavity  22  is dimensioned such that the cartridge  20  fits snugly therein, thereby maximizing heat transfer between the cartridge  20  and the block  18 .  
         [0030]    As the cartridge  20  generates heat, the heat is transferred into the block  18  and then into the housing  12 . Contact between the housing  12  and the segments  14  provides for conduction of heat into the segments  14 , which then conduct heat into the film  26  for sealing the film  26  to the ink jet cartridge  28 . Some heat is also conducted through the biasing devices  16  into the segments  14 . The selection of materials having high thermal conductivities for the housing  12 , the segments  14 , and the block  18 , provides for rapid heat transfer from the heater cartridge  20  to the lower surfaces  14   a  of the segments  14 . As mentioned above, the preferred materials for these components are brass or copper. However, one skilled in the art will appreciate that other materials could be used, such as materials having thermal conductivities of no less than about 10 Btu/hr-ft-° F.  
         [0031]    As depicted in the Figures, the preferred embodiment of the invention includes a shim  24  for transferring heat from the segments  14  into the film material  26  that is to be heat-sealed to the ink jet cartridge  28 . As shown in FIGS.  2 A-B and  3 A-B, the shim  24  is disposed between the film material  26  and the lower surfaces  14   a  of the segments  14 . The shim  24 , which is preferably made from brass, prevents the edges of the lower surfaces  14   a  of the segments  14  from forming an imprinted pattern in the film  26  or in the surface of the underlying ink jet cartridge material  28 . The thickness of the shim  24  is selected so that the shim  24  is able to move in compliance with the motion of the segments  14 , but is also being self-supporting in a horizontal position when attached to the housing  12 . The preferred thickness of the brass shim  24  that meets these criteria ranges from about 0.05 mm to about 0.15 mm, and is most preferably about 0.10 mm. A preferred embodiment of the invention wherein the shim  24  snaps onto the housing  12  is described in more detail hereinafter.  
         [0032]    FIGS.  2 A-B and  3 A-B depict width-wise and length-wise cross-sectional views, respectively, of the platen  10 , and use of the platen  10  to seal a film  26  to a cartridge  28 . The cross-sections of FIGS.  2 A-B are taken at section line I-I and the cross-sections of FIGS.  3 A-B are taken at section line II-II, as shown in FIG. 1. FIGS. 2A and 3A depict the positions of the segments  14  prior to the platen  10  engaging the film  26 . Thus, FIGS. 2A and 3A depict the segments  14  in a fully extended position. In this fully extended position, the biasing devices  16  urge the segments  14  downward such that the shoulders  14   c  of the segments  14  contact the shelves  12   g  and  12   h  in the sidewalls  12   b  and  12   d.    
         [0033]    [0033]FIGS. 2B and 3B depict the lower surfaces  14   a  of the segments  14  in contact with the shim  24  while pressing the shim  24  against the film material  26 . As shown in FIGS. 2B and 3B, the independent motion of each segment  14  relative to the housing  12 , and the independent urging of each biasing device  16  against its associated segment  14 , allows the lower surfaces  14   a  of the segments  14  to move in correspondence to the curvature of the surface of the cartridge  28 . In this manner, the amount of surface area of the segments  14  contacting the film  26  is maximized, thereby transferring the maximum amount of heat from the segments  14  into the film  26 , while not exerting an excessive amount of force on the high spots in the surface of the cartridge  28 . Since the segmented platen  10  does not apply excessive amounts of force on the high spots, the cartridge  28  is not substantially deformed by the platen  10 . Thus, the invention offers a significant improvement over rigid platens that may cause significant deformations in a non-planar sealing surface.  
         [0034]    The platen  10  also offers significant advantages over existing platens that use rubber to contact and transfer heat into the film material. The higher thermal conductivity of the brass or copper segments  14  and shim  24  allow sealing time to be significantly shorter at a given temperature than would be the case using a rubber platen. For example, experiments have shown that, for the same platen temperatures, the sealing time is approximately 3.5 seconds using the platen  10  compared to about 6.5 seconds for a platen having an elastomeric surface, such as a rubber platen. Alternatively, the sealing time using the platen  10  could be the same as the sealing time using an elastomeric platen, but with the platen  10  operated at a significantly lower temperature. The platen  10  is also more durable than an elastomeric platen, thus requiring less frequent replacement. Because rubber or other elastomeric materials are not used with the platen  10  of the present invention, the platen  10  is less likely to produce volatile compounds that could contaminate the surface of the film  26  being sealed. Due to the relatively large range of movement of the segments  14 , leveling of the platen  10  is less critical than with a rubber platen. Due to the lower thermal conductivity of rubber and other such elastomeric materials, a platen containing rubber or another elastomeric material of a thickness sufficient to provide a range of compliance approaching that of the platen  10  would require a heating time for sealing a film to a surface which is substantially greater than the time required using the platen  10 .  
         [0035]    As depicted in FIGS. 5 and 6, in a most-preferred embodiment of the platen  10 , the surface area of the shim  24  approximately matches the combined areas of the heating surfaces of the segments  14 . In this embodiment, the shim  24  includes six tabs  24   a  distributed about the periphery thereof, each having an inward projection. Preferably, as shown in FIGS. 5 and 6, the segments  14  each have a notch  14   e  for capturing the projections on the tabs  24   a  of the shim  24  when the shim  24  is pushed into position over the segments  14 .  
         [0036]    As indicated in FIG. 6, the tabs  24   a  are preferably positioned so that each tab  24   a  is substantially centered on a corresponding one of the segments  14  when the shim  24  is snapped into place. This prevents the tabs  24   a  from interfering with the movement of segments  14  adjacent the segments  14  to which the tabs  24   a  are attached.  
         [0037]    With the embodiment shown in FIGS. 5 and 6, the shim  24  may be removed and replaced, even while the platen  10  is mounted in a production environment. Typically, the shim replacement process may be accomplished in under ten seconds.  
         [0038]    It is contemplated, and will be apparent to those skilled in the art from the preceding description and the accompanying drawings that modifications and/or changes may be made in the embodiments of the invention. Accordingly, it is expressly intended that the foregoing description and the accompanying drawings are illustrative of preferred embodiments only, not limiting thereto, and that the true spirit and scope of the present invention be determined by reference to the appended claims.