Abstract:
A tank for a micro-fluid ejection device and a method for making the tank containing a liquid level lens. The tank includes a tank body made of a first material defining a lens aperture. A lens made of a second material that is different from the first material is disposed within the lens aperture.

Description:
FIELD 10011 The disclosure relates to fluid supply tanks for micro-fluid ejection heads, and in particular, to methods for fabricating fluid supply tanks for micro-fluid ejection heads.  
     BACKGROUND AND SUMMARY  
       [0001]     Micro-fluid ejection heads, such as inkjet print cartridges, may include a disposable ink supply tank for supplying ink to permanent or semi-permanent printheads. Such tanks may include a transparent lens in the tank that is used to reflect light to a sensor for optically sensing the presence or absence of ink in the tank. When an absence of ink is detected, a command signal is generated to limit operation of the printhead so that damage to the printhead is avoided. Fabrication of tanks having suitable lenses is challenging and improvement is needed.  
         [0002]     Accordingly, the disclosure relates to a tank for a micro-fluid ejection device and methods for making the tank containing a liquid level lens. In some embodiments, the tank includes a tank body made of a first material defining a lens aperture, and a lens made of a second material that is different from the first material is disposed within the lens aperture.  
         [0003]     In other embodiments, there is provided a method for making a tank containing a fluid level lens therein. The method includes providing a lens made of a lens material having a first melting point. The lens is placed within a mold configured to provide a tank body having a lens aperture therein. A tank material is introduced into the mold containing the lens to yield a tank having the lens bonded within the lens aperture of the tank body. The tank material used for making the tank body has a second melting point less than the first melting point of the lens material.  
         [0004]     An advantage of exemplary embodiments described herein is the provision of a tank/lens assembly having improved lens and tank properties as compared to conventional structures.  
         [0005]     Further advantages of the exemplary embodiments will become apparent by reference to the detailed description when considered in conjunction with the figures, which are not to scale, wherein like reference numbers indicate like elements through the several views, and wherein:  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0006]      FIG. 1  is a sectional perspective view of a tank/lens assembly of a micro-fluid ejection head according to the disclosure.  
         [0007]      FIG. 2  is a perspective view of a lens component of the ejection head of  FIG. 1 .  
         [0008]      FIG. 3  is a sectional perspective view of a tank component of the ejection head of  FIG. 1 .  
         [0009]      FIG. 4  is a cross-sectional side view of a tank/lens assembly showing its relationship to a printhead and an optical sensor of a micro-fluid ejection device.  
         [0010]      FIG. 5  is a top perspective view of a tank/lens assembly according to the disclosure.  
         [0011]      FIG. 6  is a bottom perspective view of a tank/lens assembly according to the disclosure.  
         [0012]      FIG. 7  is a perspective view of a plurality of tank/lens assemblies according to the disclosure installed in a carriage for supplying fluid to a plurality of micro-fluid ejection heads of a micro-fluid ejection device. 
     
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS  
       [0013]     With reference to  FIGS. 1-6 , there is shown a tank/lens assembly  10 , according to the disclosure for providing fluid to a micro-fluid ejection device. The tank/lens assembly  10  includes a tank body  12  and a lens  14  mounted within a lens aperture  16  of the tank body. A lid  18  ( FIG. 5 ) is installed on the tank body  12  so that the tank body  12  may be filled with a fluid, such as ink.  
         [0014]     The tank/lens assembly  10  is particularly suitable for use as a disposable fluid supply to supply fluid, such as ink, to a micro-fluid ejection device, such as a permanent or a semi-permanent printhead utilized by an inkjet printer, as described in more detail below in connection with  FIG. 7 .  
         [0015]     The assembly  10  is made by providing the lens  14  and the tank body  12  in separate forming steps. The tank  12  and the lens  14  being made of different but chemically compatible materials, with the pre-formed lens  14  being integrated into the tank body  12 . The lens  14  may be integrated into the tank body  12  during formation of the tank body  12  or after formation of the tank body  12 . Separate formation of the lens  14  enables both the tank body  12  and the lens  14  to each be made of a material suitable for their purpose. Conventional constructions provide a tank body and a lens in a single molding step, with the tank body and the lens being simultaneously formed of the same material that is a compromise to the desired performance of at least the lens. That is, materials that facilitate the molding of the tank body typically have disadvantages for use as lens materials, such as low scratch resistance or a high shrinkage rate, poor transparency, and the like which compromises the formation of the desired lens shape for fluid level sensing or detection applications. Likewise, materials suitable for forming the transparent lens may be more costly to use for the entire tank material and may have poorer compatibility with the fluid contained in the tank body.  
         [0016]     With continuing reference to  FIG. 3 , and with additional reference to  FIG. 4 , the tank body  12  is desirably of one-piece molded plastic construction, and made of a first material that is selected to be economical and have a high chemical resistance to the fluid to be contained by the tank body  12 . Suitable materials which may be used in manufacture of the tank body  12  for holding fluids such as inks of the type commonly used in inkjet printing include polypropylene and high density polyethylene (HDPE). Other suitable materials may include a polymeric material selected from the group consisting of amorphous thermoplastic polyetherimide available from G.E. Plastics of Huntersville, N.C. under the trade name ULTEM 1010, glass filled thermoplastic polyethylene terephthalate resin available from E. I. du Pont de Nemours and Company of Wilmington, Del. under the trade name RYNITE, syndiotactic polystyrene containing glass fiber available from Dow Chemical Company of Midland, Mich. under the trade name QUESTRA, polyphenylene oxide/high impact polystyrene resin blend available from G.E. Plastics under the trade names NORYL SEI and polyamide/polyphenylene ether resin available from G.E. Plastics under the trade name NORYL GTX. Still other materials that may be used for the tank body  12  include, but are not limited to, polypropylene (PP), polymethylmethacrylate (PMMA), polycarbonate (PC), styrene-acrylonitrile (SAN), polypropylene/ethylene-propylene-diene monomer (PP/EPDM), polyvinylchloride with plasticizer (PVC-W), polybutyleneterephthalate (PBT), polysulfone (PSU), and thermoplastic polyurethane (TPU).  
         [0017]     With reference to  FIG. 4 , the tank body  12  may include a pair of chambers  20  and  22  interconnected by a passage  24  formed through a lower portion of a partition  26  between the chambers  20  and  22 . The chamber  20  contains a supply of fluid, such as ink. The chamber  22  may be substantially filled with permeable solid material, such as one or more porous absorbent members  28  and  30 , such as felted foam blocks, for inducing a negative pressure and enabling a uniform supply of fluid to a micro-fluid ejection head  31 . The fluid travels from the chamber  20  through the passage  24  and accumulates in the chamber  22  so that the fluid level is substantially equalized between the chambers  20  and  22 . During operation of the micro-fluid ejection head  31 , fluid flows from the chamber  22  to the ejection head  31  via a supply port  32  located in a side wall  33  of the tank body  12  adjacent to the chamber  22 .  
         [0018]     The lens aperture  16  is defined on the side wall  33 , so that the lens  14  may be located in the aperture  16  adjacent to the chamber  20 . As depicted in  FIG. 4 , a sensor  34  associated with the micro-fluid ejection device, such as a printer, is located for cooperation with the lens  14 . For example, the sensor  34  may be located on a printer so as to be immediately below the chamber  20  at least periodically during printing operations.  
         [0019]     The sensor  34  may include a source of light  36 , such as a light emitting diode, positioned so as to direct light angularly toward the lens  14 . If the chamber  20  contains sufficient ink to cover the lens  14 , then a low to medium amount of light will be reflected for detection by a detector  38 . If the chamber  20  is empty or otherwise does not contain sufficient ink to cover the lens  14 , then a medium to high amount of light will be reflected back to the detector  38 , as depicted in  FIG. 4  by arrows Li and Lr, representing the incident light (Li) and the reflected light (Lr). The presence or absence of reflected light may be used to provide a signal to a controller to limit operation of the micro-fluid ejection device so that damage to the micro-fluid ejection head  31  is avoided.  
         [0020]     To enable the desired light reflection function, the lens  14  may include a stepped configuration as seen in  FIG. 2  having a serrated surface  40  and a relatively smooth surface  42  opposite the serrated surface  40 . Suitable lens geometry is described in co-pending application Ser. No. 11/206,610, filed Aug. 17, 2005, entitled “System, Methods, and Apparatuses for Sensing Ink Container and In Presence,” and incorporated herein by reference in its entirety.  
         [0021]     It has been observed that lens structures made using materials such as clear polypropylene or HDPE have disadvantages such as poor optical properties and low scratch resistance. Accordingly, the lens  14  is suitably made using a material having desirable optical and mechanical properties. For there to be sufficient internal reflection when no fluid is present above the lens, the refiactive index may be selected so that the light incident on the lens/air interface is at an angle greater than the critical angle associated with the two mediums. To achieve this, with the given sensor configuration where light is incident on the lens surface at a 45 degree angle, the material is selected to have a refractive index greater than about 1.445. The lens material must also be chemically compatible with the tank material. Accordingly, suitable lens materials may be selected from polypropylene (PP), polymethylmethacrylate (PMMA), polycarbonate (PC), and styrene-acrylonitrile. The following Table 1 provides the melting points of the lens and tank materials that may be used. Table 2 provides a selection chart for selecting suitable lens materials for the tank materials and vice versa.  
                       TABLE 1                           Mean Melt   Melt           Temperature   Temperature       Material   (° C.)   Range (° C.)                   Polypropylene (PP)   230   200-280       Styrene-acrylonitrile (SAN)   230   200-270       Polycarbonate (PC)   293   282-304       Polymethylmethacrylate (PMMA)   250   240-280       Polypropylene/ethylene-propylene diene   240   220-260       monomer (PP/EPDM)       Polyvinylchloride with plasticizer   180   160-200       (PVC-W)       Polybutyleneterephthalate (PBT)   260   250-270       Thermoplastic Polyurethane (TPU)   230   223-240       Polysulfone (PSU)   189   188-190                  
 
         [0022]    
       
         
               
               
               
               
               
               
               
             
           
               
                 TABLE 2 
               
               
                   
               
               
                   
               
               
                 Lens 
                 Tank 
                 Tank 
                 Tank 
                 Tank 
                 Tank 
                 Tank 
               
               
                 Material 
                 Material 
                 Material 
                 Material 
                 Material 
                 Material 
                 Material 
               
               
                   
               
             
             
               
                 PP 
                 PP 
                 PP/EPDM 
                 — 
                 — 
                 — 
                 — 
               
               
                 PMMA 
                 PMMA 
                 PVC-W 
                 — 
                 — 
                 — 
                 — 
               
               
                 PC 
                 PC 
                 PBT 
                 PSU 
                 TPU 
                 PP/EPDM 
                 — 
               
               
                 SAN 
                 SAN 
                 PBT 
                 — 
                 PMMA 
                 PVC-W 
                 TPU 
               
               
                   
               
             
          
         
       
     
         [0023]     As seen by table 2, materials that are compatible with a PP lens material, for example, include PP and PP/EPDM. In another example, a lens material made of SAN may be compatible with a tank material selected from SAN, PBT, PMMA, PVC-W, and TPU.  
         [0024]     Various methods may be used to fixedly attach the lens  14  in the aperture  16  of the tank  10 . In one manner of attachment, the lens  14  may be mechanically secured within the aperture  16  of the tank body  12  as by a friction fit and a suitable adhesive or the like to provide a hermetic seal at an interface between the lens  14  and the body  12  so that air does not enter chambers  20  or  22  and fluid does not escape therefrom. Other means for securing the lens  14  in the aperture  16  include, but are not limited to, ultrasonic welding, laser welding, and the like.  
         [0025]     In another method of manufacture, the lens  14  may be provided, as by conventional injection molding techniques, and the lens subsequently incorporated into the tank body  12  during manufacture of the tank body  12 . For example, the formed lens  14  may be installed in a mold configured to provide the tank body  12  depicted in  FIG. 3  having the tank aperture  16 . Tank material is injected into the mold containing the lens to yield the tank/lens assembly  10  having the lens  14  bonded within the lens aperture  16  of the tank body  12 .  
         [0026]     During the foregoing tank molding procedure, it is desirable that the lens material have a melting point that is sufficiently greater than the melting point of the tank material so that the lens  14  does not deform under the thermal conditions associated with molding the tank body  12  so that the lens  14  substantially retains its shape and optical properties. For example, a suitable tank material, such as PP/EPDM has a lower melting point of 220° C., and a suitable lens material for the tank material is a lens material such as polypropylene having an upper melting point 280° C.  
         [0027]     Use of a lens  14  made of one of the foregoing lens materials in the above described integrated molding step desirably results in the formation of a chemical and mechanical bond between the lens material and the tank material that creates a hermetic seal between the tank body  12  and the lens  14 , while the lens  14  substantially retains its shape and optical properties. Without being bound by theory, it is believed that during the body molding step for integrating the lens  14  in the body  12 , some of the boundary regions of the lens  14  soften under frictional and thermal forces associated with the molding process to promote bonding between the lens  14  and body  12  without altering the optical properties of the relevant surfaces of the lens  14 .  
         [0028]     With reference to  FIG. 7 , a plurality of the tank/lens assemblies  10  are shown installed on a carrier  52  containing micro-fluid ejection heads for a micro-fluid ejection device such as a printer. The micro-fluid ejection heads may be semi-permanent or permanent ejection heads associated with an ink jet printer and the tank/lens assemblies  10  may each contain different color inks. Periodic movement of the carrier  52  in a printer carriage across the sensor  34  provides periodic indication of the status of fluid in each of the tank/lens assemblies  10 .  
         [0029]     Having described various aspects and exemplary embodiments and several advantages thereof, it will be recognized by those of ordinary skills that the disclosed embodiments is susceptible to various modifications, substitutions and revisions within the spirit and scope of the appended claims.