Abstract:
A printhead including a body; an actuator attached to the body, and an enclosed space between the actuator and the body forms a chamber; an opening defined by the body for releasing pressure in the chamber; and a seal attached to the opening to seal the chamber while permitting pressure to be released.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a divisional application of U.S. patent application Ser. No. 11/741,325 filed on Apr. 27, 2007, now U.S. Pat. No. 8,403,460, which claims the benefit under 35 USC §119(e) to U.S. Patent Application Ser. No. 60/796,154, filed on Apr. 28, 2006. The contents of both of which are hereby incorporated by reference in their entirety. 
    
    
     BACKGROUND 
     Droplet ejection devices are used for depositing droplets on a substrate. Ink jet printers are a type of droplet ejection device. Ink jet printers typically include an ink supply to a nozzle path. The nozzle path terminates in a nozzle opening from which ink drops are ejected. Ink drop ejection is controlled by pressurizing ink in the ink path with an actuator, which may be, for example, a piezoelectric deflector, a thermal bubble jet generator, or an electro statically deflected element. A typical printhead has an array of ink paths with corresponding nozzle openings and associated actuators, such that drop ejection from each nozzle opening can be independently controlled. In a drop-on-demand printhead, each actuator is fired to selectively eject a drop at a specific pixel location of an image as the printhead and a printing substrate are moved relative to one another. In high performance printheads, the nozzle openings typically have a diameter of 50 microns or less, e.g. around 35 microns, are separated at a pitch of 100-300 nozzle/inch, have a resolution of 100 to 3000 dpi or more, and provide drop sizes of about 1 to 70 picoliters or less. Drop ejection frequency can be 10 kHz or more. 
     Printing accuracy is influenced by a number of factors, including the size and velocity uniformity of drops ejected by the nozzles in the head and among multiple heads in a printer. The drop size and drop velocity uniformity are in turn influenced by factors such as the dimensional uniformity of the ink paths, acoustic interference effects, contamination in the ink flow paths, and the actuation uniformity of the actuators. 
     SUMMARY 
     In general, in an aspect, a printhead includes a body; an actuator attached to the body, and an enclosed space between the actuator and the body forms a chamber; an opening defined by the body for releasing pressure in the chamber; and a seal attached to the opening to seal the chamber while permitting pressure to be released. 
     Implementation can include one or more of the following features. The actuator can include a piezoelectric material, and the seal can be made of plastic (e.g., polyimide). The printhead can include a laminate subassembly, the actuator can be attached to the laminate subassembly, and the laminate subassembly can include a flex print, cavity plate, descender plate, acoustic dampener, spacer, and an orifice plate. Openings can be formed in the acoustic dampener, and channels can be formed in the descender plate. The printhead can include an ink manifold defined by the body. The seal can be attached to the opening using a detachable adhesive. 
     In another aspect, a flexible circuit includes a body made of a flexible material, electrical traces formed on the body, and openings defined by the body for fluid to pass through. 
     Implementations can include one or more of the following features. The body can be made of a polyimide, or can include two layers of a flexible material (e.g., polyimide) that are bonded together (e.g., with an adhesive that can include polyimide). The body can include a base layer (e.g., polyimide material), the electrical traces being formed on the base layer, and a coverlay (e.g., printable polyimide) covering the electrical traces. 
     In yet another aspect, a laminate subassembly includes a plurality of laminates, including an actuator, cavity plate, descender plate, and orifice plate, each laminate having openings, the openings in each laminate align with the openings in the other laminates, and inspection of the openings ensures alignment and placement of the laminates. 
     Implementations can include one or more of the following features. The laminate subassembly can further include a fiducial mark on the actuator, such that the fiducial mark is visible when the laminates are aligned. The plurality of laminates can also include an acoustic dampener, flexible circuit, and a spacer. 
     In an aspect, a method of aligning laminates includes providing a plurality of laminates with openings, including an actuator, cavity plate, descender plate, and orifice plate, one of the laminates includes a fiducial mark; aligning the laminates using the openings in the laminates and the fiducial mark on one of the laminates; attaching the laminates together; and inspecting the openings to determine alignment of the laminates. Inspecting the openings can include using a camera to look through the openings in the laminates to verify that the fiducial mark is aligned with the openings. 
     Further aspects, features, and advantages will become apparent from the following detailed description, the drawings, and the claims. 
    
    
     
       DESCRIPTION OF DRAWINGS 
         FIG. 1A  is a perspective view of a printhead. 
         FIG. 1B  is an exploded view of a printhead. 
         FIG. 2A  is a perspective view of a body and laminate subassembly of a printhead. 
         FIG. 2B  is a cross-sectional view of the printhead. 
         FIG. 2C  is a perspective view of the bottom side of the body. 
         FIG. 3  is an exploded view of the laminate subassembly. 
         FIG. 4A  is a perspective view of the flex print. 
         FIG. 4B  is a cross-sectional view of the flex print. 
     
    
    
     DETAILED DESCRIPTION 
     Referring to  FIGS. 1A and 1B , a printhead  10  includes a body  12  bonded to a laminate subassembly  14 . The parts can be bonded together with an adhesive, such as an epoxy. Ink is first introduced to the printhead  10  through the filter  16  and tube  18  and into the body  12  via an ink barb  20  formed in the body  12 . An opening  22  is formed in the body  12  to release air pressure between the body  12  and subassembly  14 ; a seal  24  is placed over the opening  22 . A cover  26  is attached to the top of the body  12 . 
       FIGS. 2A and 2B  show the body  12  and the subassembly  14  of the printhead  10 . The first layer in the subassembly  14  is a piezoelectric element  28 , which is bonded to a flex print  30 . When the body  12  is bonded to the subassembly  14 , a chamber  32  is formed to protect the piezoelectric element  28  from the environment and to seal it from the ink flow path. 
     Referring to  FIG. 3 , the subassembly  14  includes the following parts bonded together, a piezoelectric element  28 , a flex print  30 , cavity plate  34 , descender plate  36 , acoustic dampener  38 , spacer  40 , and orifice plate  42 . The parts can be bonded together with an adhesive, such as an epoxy. 
     Referring to  FIG. 2A , the ink travels down the ink barb  20  to the bottom side of the body  12  and into a fluid manifold  44  formed in the body  12  as shown in  FIG. 2C . The ink fills the fluid manifold  44  and then travels through openings  46  in the flex print  30  and into the pumping chambers  48  formed in the cavity plate  34  as shown in  FIG. 3 . 
     Referring to  FIG. 3 , when the piezoelectric element  28  is actuated, the ink in the pumping chambers is pumped through openings  50  in the pumping chambers through openings  52  in the descender plate  36  through openings (not shown) in the acoustic dampener  38  through the spacer openings  54  and out the orifices  56  in the orifice plate  42 . 
       FIG. 2B  shows a cross-sectional view of the chamber  32  formed when the body  12  is bonded to the subassembly  14  with the piezoelectric element  28  as the first layer in the subassembly  14 . The chamber  32  protects the piezoelectric element  28  from the external environment. An opening  22  is formed in the body  12  to release air pressure in the chamber  32 , and a seal  24  is bonded to the opening  22  with adhesive (i.e., epoxy). The seal  24  can be made of a compliant material (i.e., polyimide) that changes shape under pressure. 
     When the air pressure inside the chamber  32  rises, a force is applied around the perimeter of the opening  22 , where the seal  24  contacts the opening  22 . The amount of force applied to the seal  24  is a function of the radius of the opening  22 . At a certain pressure, the adhesive that bonds the seal  24  to the opening  22  can detach from the surface of the opening  22  to release air pressure, and subsequently reattach. The radius of the opening  22  and strength of the adhesive can be designed for specified air pressures, such that the adhesive detaches and reattaches at specified air pressures. 
       FIG. 2A  shows the opening  22  in the body  12  raised above the surface of the body  12 . By raising the opening  22 , the piezoelectric element  28  is protected from ink leaks, and the seal  24  further protects the piezoelectric element  28  from ink or other environmental factors. 
     Referring to  FIG. 3 , the openings in the flex print  30  provide an ink flow path from the manifold  44  to the pumping chambers.  FIG. 4A  shows a flex print  30  with electrical traces  58  running through the spaces between the openings to avoid contact with the fluid as it travels through the openings  46 . The electrical traces  58  run from electrodes near the center of the flex print  30  (next to the piezoelectric element) to the connectors  60  at the ends of the flex print  30 . Tabs  62  extend on either side of the connectors  60 , which snap into the cover  26  as shown in  FIG. 1A . 
       FIG. 4B  shows a flex print  30  with a first layer  64  and second layer  66  bonded together with an adhesive. Over time ink can separate the adhesive from the two layers and leak inside the flex print  30  and contact the electrical traces  58 . In an implementation, the two layers of the flex print  30  are made of a polyimide and the adhesive also contains polyimide. The ink is less likely to separate the adhesive from the two layers when the layers of the flex print  30  and adhesive are made of the same material. The openings in the flex print  30  can be cut with a die, laser, or other similar methods. Coatings or other materials can be used to protect the edges of the openings in the flex print  30  from degradation by fluids passing through them. 
     Referring to  FIG. 3 , while the openings in the flex print  30  provide an ink flow path to the pumping chambers, only some of the openings actually line up with the pumping chambers in the cavity plate  34 . The remaining pumping chambers are blocked by the spaces between the openings. For ink to reach the blocked pumping chambers, the ink travels through the openings in the flex print  30  through the unblocked pumping chambers and into channels  68  in the descender plate  36 . The ink in these channels  68  then travels back up into the cavity plate  34  into the blocked pumping chambers. 
     Referring to  FIG. 3 , if the acoustic dampener  38  is made of a plastic material, such as Upilex® polyimide, the material may not bond evenly, which could leave an area of the material unbonded. For a better bond, openings  70  can be cut out of the acoustic dampener  38 . 
     The body  12  can be made of a plastic material, such as polyphenylene sulfide (PPS), or metal, such as aluminum. The cover  26  can be made of metal or a plastic material, such as Delrin® acetal. The flex print  30  and acoustic dampener  38  can be made of Upilex® polyimide, while the descender plate  36  and cavity plate  34  can be made of a metal, such as Kovar® metal alloy. The spacer  40  can be made of material with a low modulus, such as carbon (about 7 MPa) or polyimide (about 3 MPa). The orifice plate  42  can be made of stainless steel. 
     The spacer  40  can be used to bond the orifice plate  42  and acoustic dampener  38  within the laminate subassembly  14 . Rather than directly apply adhesive to the orifice plate  42  or acoustic dampener  38 , adhesive can be directly applied on both sides of the spacer and the orifice plate  42  and acoustic dampener  38  can then be bonded to the spacer. The spacer can also distribute the strain between laminates with different thermal coefficients of expansion. For example, laminates with different thermal coefficients of expansion bonded together at a bonding temperature of about 150° C. can bow as the laminates cool to room temperature (about 22° C.). The spacer can reduce bowing in the laminate subassembly by distributing the bond strain. The thickness of the spacer and its modulus can affect its ability to distribute strain within the subassembly. The percent strain of the spacer is a function of the strain divided by the thickness of the spacer. 
       FIG. 2C  depicts the body  12  with three holes  72 , two on one side of the body  12  and one on the other side, for receiving three eccentric screws to secure the printhead  10  to a rack assembly. 
     Referring to  FIG. 3 , openings  74  on the ends of each part are used to check for missing parts and alignment of the parts. An inspection camera looks into the openings  74  to visually inspect the alignment of the parts. A fiducial mark is placed on the piezoelectric element  28  and can be seen when all the parts are properly aligned. Additionally, after production or during maintenance of a printhead  10 , a visual inspection through the openings  74  ensures that all the parts are present and that the parts are in the correct order. 
     In other implementations, the body and laminate subassembly can be attached by other securing devices, such as adhesives, screws, and clasps. The parts of the subassembly can be secured by other materials or adhesives. The seal  24  can be attached to the opening in the body by other adhesives. Referring to  FIGS. 2A and 2B , rather than forming a chamber between the subassembly and the body to protect the piezoelectric element, the piezoelectric element could be protected by a coating. While  FIG. 1A  shows the tabs  62  snapping into the cover  26  of the printhead  10 , the tabs could be secured to a printhead by screws, clasps, adhesive, or other fasteners. The flex print  30  in  FIG. 3  shows several openings on both sides of the flex print  30 , however, the flex print  30  can have only one opening for an ink passage or openings on just one side. Similarly, the cavity plate in  FIG. 3  shows several pumping chambers on both sides of the cavity plate, but the cavity plate can have only one pumping chamber or pumping chambers on only one side. 
     The connectors  60  in  FIG. 1A  can be directly secured to the cover  26  without using the tabs  62 . For example, the connectors  60  could be glued to the cover  26  using an adhesive. 
     Referring to  FIG. 4A , the electrical traces  58  on flex print  30  can be sealed to prevent fluid flowing through openings  46  from contacting the traces. For example, a first layer  64  in  FIG. 4B  can be a polyimide material (i.e., Upilex® polyimide), the electrical traces can be formed on the first layer  64 , and a second layer  66  can be a coverlay that covers the electrical traces. The coverlay can be a printable polyimide, such as Espanex® SPI screen printable polyimide coverlay available from Nippon Steel Chemical, Japan. The polyimide can be deposited using a silk screen printing method or other deposition methods. 
     Referring to  FIG. 1A , the dimensions of the printhead  10  can include a height of about 29.15 mm, a length of about 115.9 mm, and a width of about 30.6 mm. Referring to  FIG. 3 , the laminate subassembly  14  can also include a ground plate  41  that can include a tab  43 . When the laminates are stacked together, the tab  43  extends from the subassembly  14  as seen in  FIG. 2A  and can be folded over the housing  12 . The ground wire  13  in  FIG. 1  connects to the tab  43  of ground plate  41 . 
     Referring to  FIG. 3 , the laminate subassembly  14  can also include a ground plate  41  that can include a tab  43 . When the laminates are stacked together, the tab  43  extends from the subassembly  14  as seen in  FIG. 2A  and can be folded over the housing  12 . The ground wire  13  in  FIG. 1  connects to the tab  43  of ground plate  41 . 
     Referring again to  FIG. 3 , the fluid flowing through the laminate subassembly  14  can pass through openings  54  in the ground plate  41  and out the orifices  56  in the orifice plate  42 . The ground plate  41  can also have openings  74  that align with the openings  74  of the other laminates in subassembly  14 . 
     Other implementations are within the scope of the following claims.