Abstract:
A compliant chamber for use in a fluidic ink jetting system having a jetting device, such as a printhead, and a fluid reservoir, the compliant chamber comprising a chamber body having an inlet for a fluid and an outlet for the fluid, the body defining an open region therein, a cover for closing the body and for further defining the open region, and a resilient material disposed in the open region, the resilient material being an energy absorbing material, wherein fluidic pressure fluctuations are absorbed by the resilient material in the open region. A method of using such is also disclosed.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The present invention relates to impulse fluid ink jets which eject a droplet of fluid such as ink in response to the energization of a transducer. 
         [0002]    Impulse fluid or ink jets are designed and driven so as to eject a droplet of fluid such as ink on demand from a chamber through an orifice in the chamber. Ink jets are utilized in many applications including industrial applications. In these applications, it is important that the ink jets operate reliably. Reliability can be reduced when there are pressure disturbances in the ink jet system. Such disturbances can occur during ink jet head shuttling, or due to external forces, for example, a shock to the printer apparatus. 
         [0003]    An impulse fluid jet apparatus with depriming protection is disclosed in Duong et al., U.S. Pat. No. 6,209,997, which patent is commonly owned with the present application and is incorporated herein by reference. The device disclosed in the patent to Duong uses a diaphragm to form a compliant chamber that is vented to atmosphere. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         [0004]    The benefits and advantages of the present invention will become more readily apparent to those of ordinary skill in the relevant art after reviewing the following detailed description and accompanying drawings, wherein: 
           [0005]      FIG. 1  is a schematic illustration of a fluid delivery system having a compliant chamber embodying the principles of the present invention; 
           [0006]      FIGS. 2A and 2B  are side views showing the compliant chamber and various alternate orientations for the chamber relative to the environment and the fluid jet (print engine); 
           [0007]      FIG. 3  is a perspective view of a first embodiment of the compliant chamber; 
           [0008]      FIG. 4  is a plan view of the first embodiment compliant chamber; 
           [0009]      FIGS. 5 and 6  are perspective views an embodiment of the chamber, shown with the chamber open for viewing the inside of the body and the cover, and with the foam insert in the open chamber area; 
           [0010]      FIG. 7  is a perspective view of the base of the first embodiment of the compliant chamber assembly; 
           [0011]      FIG. 8  is a perspective view of a second embodiment of the compliant chamber in a tubular or cylindrical form, showing the foam in a helical shape; 
           [0012]      FIG. 9  is a perspective view of a third embodiment of a partially cut away tubular compliant chamber. 
           [0013]      FIG. 10  is a perspective view of a fourth embodiment of the chamber, showing the chamber in an exploded view. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0014]    While the present invention is susceptible of embodiment in various forms, there is shown in the figures and will hereinafter be described a presently preferred embodiment with the understanding that the present disclosure is to be considered an exemplification of the invention and is not intended to limit the invention to the specific embodiment illustrated. 
         [0015]    Referring to the figures and in particular to  FIGS. 1 and 2  there is shown an impulse or ink jet printing system  10 . Generally, the system  10  includes a jetting device or engine  12 , such as an ink jet printhead, and a fluid reservoir or ink supply  14 . A compliant chamber assembly  16  is disposed between the reservoir  14  and the printhead  12  and in a preferred arrangement, an external filter  18  is positioned in the system  10  between the compliant chamber assembly  16  and the printhead  12  (that is, downstream of the chamber assembly  16  and upstream of the printhead  12 ). The compliant chamber  16  can be positioned at any angle α between the engine  12  and the ink reservoir  14 , and shuttles with the engine (printhead)  12 . 
         [0016]    The chamber  16  is designed to attenuate pressure disturbances created, for example, during shuttling motion, as shown by the arrows at  FIGS. 1 and 2A , of the printhead  12  on a device such as a plotter or printer  20 . The compliant chamber  16  design permits mounting the chamber  16  externally or separated from the printhead  12 . Accordingly, the chamber  16  can shuttle with the printhead  12 , or can be stationary relative to the printhead  12 . 
         [0017]    The compliant chamber assembly  16  is a closed chamber (that is having an inlet  22  and an outlet  24 ) and is not vented to the atmosphere. An open area  26 , hence the chamber, is between the inlet  22  and the outlet  24 . In a preferred configuration, a check valve  28  is present at the inlet  22  to prevent backflow from the chamber  26  to the ink reservoir  14 . 
         [0018]    Known compliant devices use a deflecting membrane which is exposed to the atmosphere to dampen fluidic motion due to tube shock and head motion. 
         [0019]    Turning to  FIGS. 5-7 , in the present compliant chamber  16 , an energy absorbing or dampening element  30  is present in the chamber  26 . A present element  30  is formed from an internal, closed cell foam. The foam  30  is compressed by the fluid (e.g., during movement of the printhead  12 ) and returns to its original state by releasing the stored energy and creating an offsetting positive pressure at the meniscus of the jetting device  12  orifice more slowly than would otherwise occur without a dampening device. It has been found that the use of a foam energy absorbing element  30  smoothes the fluidic motion and minimizes abrupt changes in orifice meniscus pressure which could otherwise cause channel drop out and deprime as the acceleration and velocity are increased during shuttling. The present compliant chamber device  16  has been found to help maintain a more constant pressure at the orifice meniscus. 
         [0020]    It is contemplated that the energy absorbing element  30  can be made from differing densities and materials, changing the amount of compliance within the energy absorbing element  30 . The absorbing element  30  may be of one density for differing performance requirements. It is also contemplated that the absorbing element  30  have differing densities within the same element  30 , improving the response to differing pulses. 
         [0021]    The check valve  28  at the inlet  22  to the chamber  16  has an upstream side that faces the fluid supply  14  and a downstream side that faces the open chamber  26 . A present valve  28  is a normally closed, spring-loaded valve configured to open to allow forward fluid flow to the printhead  12  from the ink supply  14  when the pressure exceeds both the spring force and the pressure in the downstream side of the check valve  28 . 
         [0022]    The check valve  28  closes to prevent reverse fluid flow from the orifice back to the ink supply  14  when the pressure on the upstream side is less than or equal to the fluid pressure on the downstream side. This further prevents a pressure wave that could otherwise deprime the orifice. 
         [0023]    In a present embodiment, the compliant chamber assembly  16  is configured as an external chamber having a sealed cover  32  (that is not open to atmospheric pressure) and a low density cross-linked foam  30  insert in the chamber  26 . 
         [0024]    Alternate configurations are shown in  FIGS. 8 through 10 .  FIG. 8  illustrates an embodiment in which the compliant chamber assembly  116  is constructed as a tubular element with a check valve  128  at an inlet end  122  and a twisted corkscrew or helical element  130  as the energy absorbing element. 
         [0025]      FIG. 9  illustrates an embodiment of the compliant chamber  216  in which a plain barb fitting  225  is on the outlet end  224  and a check valve  228  is at the inlet  222 . The inside foam element is configured as a hollow tube  230 . 
         [0026]      FIG. 10  illustrates another embodiment of the compliant chamber  316  in which a flat rectangular element  330  is provided for energy absorption within a tubular chamber  316 . A check valve  328  is located at the inlet  322  and the outlet is located at  324 . As is illustrated, various embodiments and configurations and permutations thereof are contemplated and within the scope and spirit of this invention. 
         [0027]    Tests were conducted to determine the effectiveness of the present chamber. A standard Trident 768Jet inkjet printhead (commercially available from ITW Trident of Brookfield, Conn.) was the baseline for comparison of the present chamber design. The standard 768Jet could shuttle without channel loss at 28 inches per second (ips), 40 ips and 60 ips at up to 2 g acceleration. The test image was run at 180 dpi with 60% random fill for the 28 and 40 ips testing and 100 dpi with 60% random fill. The velocity and acceleration needed to meet requirements of 20 cm distance to reach the desired velocity are shown below: 
       Plotter Requirements: 
       [0028]      
         [0000]    
       
         
               
               
               
             
           
               
                   
               
               
                   
                   
                 Acceleration 
               
               
                 Distance to reach velocity 
                 Velocity 
                 required 
               
               
                   
               
             
             
               
                 7.77 in (20 cm) 
                 28 ips (.71 m/s) 
                 .13 g 
               
               
                 7.77 in (20 cm) 
                 40 ips (1 m/s)   
                 .27 g 
               
               
                 7.77 in (20 cm) 
                 60 ips (1.5 m/s) 
                  .6 g 
               
               
                   
               
             
          
         
       
     
         [0029]    The design goal was to meet the 768Jet baseline performance which greatly exceeds these minimums requirements and would result in a very robust product that could also meet future demands. 
         [0030]    Configurations were tested which included: (1) the standard 768Jet design (having a diaphragm-type chamber, check valve and filter); (2) a modified 768Jet design (modified to remove the diaphragm from the compliant chamber, the check valve and the filter); and (3) a 768Jet design (again modified to remove the diaphragm from the chamber, the check valve and the filter), used in series with the present compliant chamber with an internal check valve and an external filter. In the chamber of the present design, a closed cell cross linked polyethylene foam (Valora 2 pcf) was inserted to the open chamber area. The chamber  16  was mounted to shuttle with the printhead  12 . It was found that the foam-containing compliant chamber provided the same level of performance as the flexible membrane approach. 
         [0031]    In a current compliant chamber  16 , as seen in  FIGS. 6 and 7 , the foam element  30  is about 4 inches long and about ½ inch wide (extending over almost the entire length of the interior area of the chamber and across the entire width of the chamber) and is about ⅛ inch thick (the height of the chamber was ⅜ to ½ inches). The foam is affixed in place by an adhesive to prevent shifting. It will appreciated that other dimensions and methods to affix the foam may also be used. 
         [0032]    As set forth above, the chamber  16  is not vented to atmosphere; accordingly, the entire chamber  16  is sealed. The chamber  16  can be formed with a gasket or seal  34  between the body  36  of the chamber  16  and the cover  32 , or the cover  32  can be affixed (by a compatible adhesive, welding or the like) directly to the body  36 . 
         [0033]    Consideration is to be given to the orientation of the check valve  28  present in the system  10 . A typical check valve uses a spring actuated plug or disk to isolate or permit flow. When the flow is in the “correct” direction, the pressure of the fluid overcomes the (often minimal) spring force, which moves the plug or disk off of a seat to allow fluid flow. When flow stops or is in a reverse direction, the spring force seats the plug or disk on the valve seat. There is thus a direction in which the valve “moves” that is the same direction as fluid flow through the valve. 
         [0034]    It has been found that the check valve  28  should be mounted in the system in a direction other than the direction of travel dt 12  of the fluid jet  12  (the print head). This prevents pressure fluctuations due to print head shuttling from opening and closing (e.g., cycling) the check valve  28 . It has also been found that the chamber  16  can in most cases be mounted in any orientation (e.g., horizontal, vertical, askew) preferably to shuttle with the printhead  12 , and will function properly. Consideration here should be given to the overall operation of the fluid (ink) supply system  10 , such as to prevent air bubbles and the like. It will also be appreciated that the present chamber  16  can be retrofitted into existing print systems. 
         [0035]    All patents referred to herein, are hereby incorporated herein by reference, whether or not specifically done so within the text of this disclosure. 
         [0036]    In the present disclosure, the words “a” or “an” are to be taken to include both the singular and the plural. Conversely, any reference to plural items shall, where appropriate, include the singular. 
         [0037]    From the foregoing it will be observed that numerous modifications and variations can be effectuated without departing from the true spirit and scope of the novel concepts of the present invention. It is to be understood that no limitation with respect to the specific embodiments illustrated is intended or should be inferred. The disclosure is intended to cover all such modifications as fall within the scope of the claims.