Patent Publication Number: US-10308054-B2

Title: Fluid ejection module mounting

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation application of and claims then benefit of priority to U.S. application Ser. No. 15/174,138, filed on Jun. 6, 2016, which is a divisional of U.S. application Ser. No. 13/828,608, filed on Mar. 14, 2013, now U.S. Pat. No. 9,358,818, issued on Jun. 7, 2016, the contents of which are hereby incorporated by reference. 
    
    
     TECHNICAL FIELD 
     The following description relates to mounting a fluid ejection module to a mounting apparatus. 
     BACKGROUND 
     An ink jet printer typically includes an ink path from an ink supply to an ink nozzle assembly that includes nozzles from which ink drops are ejected. Ink drop ejection can be controlled by pressurizing ink in the ink path with an actuator, for example, a piezoelectric deflector, a thermal bubble jet generator, or an electrostatically deflected element. A typical printhead has a line or an array of nozzles with a corresponding array of ink paths and associated actuators, and drop ejection from each nozzle can be independently controlled. In a so-called “drop-on-demand” printhead, each actuator is fired to selectively eject a drop at a specific location on a medium. The printhead and the medium can be moving relative one another during a printing operation. 
     As one example, a printhead can include a semiconductor printhead body and a piezoelectric actuator. The printhead body can be made of silicon etched to define pumping chambers. Nozzles can be defined by a separate layer that is attached to the printhead body. The piezoelectric actuator can have a layer of piezoelectric material that changes geometry, or flexes, in response to an applied voltage. Flexing of the piezoelectric layer pressurizes ink in a pumping chamber located along the ink path. 
     Printing accuracy can be influenced by a number of factors. Precisely positioning the nozzles relative to the medium can be necessary for precision printing. If multiple printheads are used to print contemporaneously, then precise alignment of the nozzles included in the printheads relative to one another also can be critical for precision printing. Maintaining alignment of the printheads during and after alignment and mounting can be important. 
     SUMMARY 
     In one aspect, the systems, apparatus, and methods disclosed herein feature a fluid ejection module mounting apparatus, including a module mount having a horizontal portion and a vertical portion, a fluid ejection module mounted to the module mount, and a clamp assembly including a recessed portion, a clamp along a wall of the recessed portion, and a lever coupled to the clamp and configured to move the clamp from an open position to a closed position. The horizontal portion has an opening configured to receive a fluid ejection module and the vertical portion has a protruding portion. The protruding portion of the module mount is configured to mate with the recessed portion of the clamp assembly. 
     Within the mounting apparatus, the module mount can further include precision surfaces in the x, y, and z direction that contact corresponding alignment contact points in the x, y and z direction on the clamp assembly. 
     Within the mounting apparatus, the clamp assembly can further include a θz adjustment mechanism configured to move the fluid ejection module in the θz direction relative to the clamp assembly. The θz adjustment mechanism can include a differential screw being configured to move 50 microns or less per revolution. The θz adjustment mechanism can be accessible from more than one surface of the clamp assembly. 
     Within the mounting apparatus, the clamp assembly can further include a x adjustment mechanism configured to move the fluid ejection module in the x direction relative to the clamp assembly. The x adjustment mechanism can include a cam assembly including a cam that is sloped to an angle, α. The cam is sloped to an angle, α, such that one rotation of the cam translates into moving the fluid ejection module over one pixel in the x-direction. The x adjustment mechanism can be accessible from more than one surface of the clamp assembly. 
     In various implementations, one or more of the following features may also be included. The clamp can include a spring. The clamp assembly can further include a cam plate coupled to the lever and the clamp. The cam plate can be coupled to a spring. The clamp assembly can include a plurality of clamps. The clamp assembly can mount to the frame. 
     In various implementations, the mounting apparatus can further include a plurality of fluid ejection modules, a plurality of module mounts, and a plurality of clamp assemblies, wherein each fluid ejection module is mounted to a module mount, and each module mount is mounted to a clamp assembly. The mounting apparatus can also include a frame, wherein the clamp assemblies are mounted to the frame. 
     In another aspect, the systems, apparatus, and methods disclosed herein feature loosely securing a plurality of clamp assemblies to a frame, securing an alignment jig to the plurality of clamp assemblies, firmly securing the plurality of clamp assemblies to the frame, removing the alignment jig from the plurality of clamp assemblies, and securing a plurality of module mount assemblies to the plurality of clamp assemblies. Securing an alignment jig to the plurality of clamp assemblies includes placing the alignment jig in the plurality of clamp assemblies, and moving a lever on each clamp assembly from an open position to a closed position such that a clamp on each clamp assembly secures the alignment jig to the clamp assembly. Each module mount assembly comprises a fluid ejection module mounted to a module mount. 
     Some implementations can include one or more of the following features: aligning a plurality of fluid ejection modules to a plurality of module mounts, and bonding the plurality of fluid ejection modules to the plurality of module mounts to form the plurality of module mount assemblies. Aligning the plurality of fluid ejection modules to the plurality of module mounts can set the x, y, and θz direction for each fluid ejection module relative to the corresponding clamp assembly. At least one module mount assembly can be adjusted relative to a corresponding clamp assembly in the x direction using an x adjustment mechanism. At least one module mount assembly can be adjusted relative to a corresponding clamp assembly in the θz direction using a θz adjustment mechanism. 
     In another aspect, the systems, apparatus, and methods disclosed herein feature a mounting apparatus including an alignment jig having a plurality of protruding portions, and a plurality of clamp assemblies. Each clamp assembly includes a recessed portion, wherein a corresponding protruding portion of the alignment jig is configured to mate with the recessed portion, a clamp along a wall of the recessed portion, and a lever coupled to the clamp and configured to move the clamp from an open position to a closed position. 
     Within the mounting apparatus, each protruding portion can slidably connect with a recessed portion of each clamp assembly. The mounting apparatus can further include a frame, wherein the plurality of clamp assemblies mount to the frame. 
     Implementations of the invention(s) can realize one or more of the following advantages. A mounting apparatus is provided to achieve precise alignment of a fluid ejection module relative to a supporting print frame. The mounting apparatus can facilitate easy installation and removal of a single fluid ejection module from the print frame, for example, to replace or repair the device. The alignment process can use an alignment jig to accurately align a plurality of clamp assemblies to a print frame. Without using an alignment jig, the individual clamp assemblies must be individually aligned one at a time. The alignment jig facilitates aligning the plurality of clamp assemblies simultaneously. In addition, the alignment jig can be precisely machined within millionths of an inch. By using the same jig, the alignment can be repeatable from print bar to print bar. Using a jig can also remove alignment errors encountered when aligning a single fluid ejection module at a time. The clamp assemblies can include clamps that are spring-loaded, so that the clamps provide a constant clamping force. Unlike spring-loaded clamps, other securing means (e.g., screws) can have variable forces. The clamping force of the spring-loaded clamps can also be repeatable from clamp assembly to clamp assembly. 
     The details of one or more implementations of the subject matter described in this specification are set forth in the accompanying drawings and the description below. Other features, aspects, and advantages of the subject matter will become apparent from the description, the drawings, and the claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of an assembled print bar. 
         FIGS. 2A and 2B  are perspective views of a mounting apparatus including a module mount and clamp assembly. 
         FIG. 3  is a flowchart of an example process for mounting a fluid ejection module to a print frame. 
         FIG. 4  is a perspective view of a module mount assembly including a module mount and a fluid ejection module. 
         FIGS. 5A and 5B  are perspective views of the module mount. 
         FIG. 6  is a perspective view of a clamp assembly (rendered in a partially transparent mode for visibility of components). 
         FIG. 7A  is a perspective view of an alignment apparatus. 
         FIG. 7B  is a close-up view of a portion of the alignment apparatus. 
         FIG. 7C  is a schematic representation of an alignment mask. 
         FIG. 7D  is a schematic representation of a fiducial. 
         FIG. 7E  is a schematic representation of a calibration mask. 
         FIG. 7F  is a schematic representation of an alignment mask and a substrate of a fluid ejection module. 
         FIG. 8  is a perspective view of an alignment jig (in transparent mode) in a print bar. 
         FIGS. 9A and 9B  are perspective view of a clamp assembly and print frame (in transparent mode). 
         FIG. 10  is a perspective view of an aligned print bar. 
         FIGS. 11A and 11B  are perspective views of a populated print bar. 
         FIG. 12  is a perspective view of a clamp assembly. 
         FIGS. 13A and 13B  are perspective views of a mounting apparatus including a module mount in clamp assembly. 
         FIGS. 14A and 14B  are perspective views of an alignment tool. 
     
    
    
     Many of the levels, sections and features are exaggerated to better show the features, process steps, and results. Like reference numbers and designations in the various drawings indicate like elements. 
     DETAILED DESCRIPTION 
     A method, apparatus, and system are described for mounting a fluid ejection module to a frame (which may be referred to herein as a “print frame”) of a printer system. A typical printer system may include one or several fluid ejection modules. When combining two or more fluid ejection modules in a printing system, each module can be aligned relative to the print frame, and relative to one another, to achieve printing accuracy. 
     In the case of a print bar having a plurality of fluid ejection modules, if a single module fails, it is desirable to replace the single module rather than the entire print bar. To make the modules replaceable, each module can be releasably secured to the print bar. 
       FIG. 1  shows an assembled print bar  100  including a plurality of fluid ejection modules  102 , each module  102  being secured to a module mount  104 . Each module mount  104  is secured to a corresponding clamp assembly  106 , and the clamp assemblies  106  are secured to a frame  108 . Alternatively, a single clamp assembly could hold a plurality of fluid ejection modules with the clamp assembly being mounted to a frame. In another configuration, the frame and the clamp assembly could be a single part, and the modules could be mounted to the frame/clamp assembly. To prevent misalignment caused by thermal expansion, the frame and the clamp assembly can be made of a material having a low coefficient of thermal expansion (CTE), such as invar, kovar, or silicon carbide. The module mount can be made of stainless steel, kovar, or silicon carbide. 
       FIGS. 2A and 2B  show a module mount assembly  200  secured to a clamp assembly  106  including a module  102  attached to a module mount  104 . The fluid ejection module  102  can include a semiconductor substrate  202  (e.g., silicon) fabricated using semiconductor processing techniques. Each fluid ejection module  102  can also include a housing  204  to support the substrate  202 , along with other components such as a flexible circuit (not shown) to receive data from an external processor and to provide drive signals to the module. A plurality of fluid flow paths can be formed in the semiconductor substrate  202  for ejection of droplets of a fluid. The fluid can be, for example, a chemical compound, a biological substance, or ink. 
     The semiconductor substrate can also include a plurality of actuators to cause fluid to be selectively ejected from the flow paths. Thus, each flow path with its associated actuator provides an individually controllable micro-electromechanical system (MEMS) fluid ejector. The substrate can include a flow-path body, a nozzle layer and a membrane layer. The flow-path body, nozzle layer and membrane layer can each be silicon, e.g., single crystal silicon. The fluid flow path can include an inlet, an ascender, a pumping chamber adjacent the membrane layer, and a descender that terminates in a nozzle formed through the nozzle layer. Activation of the actuator causes the membrane to deflect into the pumping chamber, forcing fluid out of the nozzle. 
     A fluid inlet  212  and a fluid outlet  214  can be formed in the housing  204 . In other implementations, the fluid ejection module does not include a fluid outlet (which optionally can provide for a recirculation scheme for the printing fluid). 
       FIG. 2B  shows an example fluid ejection module  102  including a mounting component  206  having a mounting surface  208 . The mounting surface  208  of the module is bonded (e.g., using an adhesive, such as room temperature epoxy) to a mounting surface  210  of the module mount  104 . A protruding portion  216  (e.g., dovetail) of the module mount can be mated with the clamp assembly  106 . For example, the protruding portion  216  can slidably connect with the recessed portion  218 . By having the protruding portion vertically slidable (i.e., perpendicular to the face of semiconductor substrate  202 ), this can help with lining up the nozzle surfaces of adjacent fluid ejection modules  102 . In addition, the vertically slidable mount can help with clearing and not disturbing adjacent modules  102 . 
       FIG. 3  is a flowchart showing an example process  300  for mounting a fluid ejection module to a print frame. For illustrative purposes, the process  300  shall be described in the context of mounting the example fluid ejection module  102  to the example print frame  108 . However, it should be understood the process  300  can be implemented to mount a differently configured fluid ejection module to the same or a differently configured print frame. 
     The fluid ejection module  102  is positioned adjacent to the module mount  104  with the mounting surface  208  facing the module mount  104 . An alignment apparatus aligns the module  102  to the module mount  104  using fiducial marks on an alignment mask and the nozzle layer (step  310 ), as discussed in more detail below. A first adhesive is applied to the mounting surface  210  of the module mount, to the mounting surface  208  (see  FIGS. 2A and 2B ) of the fluid ejection module, or both. The first adhesive can be formed from a material that allows for relative movement between the fluid ejection module and the module mount to facilitate the alignment process. For example, the first adhesive can be an epoxy, e.g. room temperature curing epoxy (such as Araldite® 5863-A/B, 2011/A, 2013/A), thermal curing epoxy, or UV curing epoxy. Once alignment is achieved, a second adhesive that is fast curing but not necessarily a robust adhesive (e.g., cyanoacrylate) can be applied to the sides of the module mount assembly to secure the fluid ejection module to the module mount while the first adhesive finishes curing (step  320 ). Once the first adhesive is cured, no significant relative movement of the fluid ejection module and the module mount is possible. 
     One or more clamp assemblies  106  are aligned and attached to the print frame  108 , for example, using an alignment jig, which is discussed in more detail below. (step  330 ) The clamp assemblies can be attached to the print frame, for example, by screws received within threaded openings  902  (see  FIG. 9 ) formed within the print frame. Alternatively, the clamp assemblies can be bonded to the frame with an adhesive. The module mount assemblies  200  can then be loaded into the clamp assemblies to form a populated print bar. (step  340 ) As previously mentioned, preferably the module mount is detachably secured to the print frame to allow for relatively easy removal at a later time without damaging the print frame. 
       FIG. 4  shows a module mount  104  including precision surfaces to align the fluid ejection module to the print frame. The precision machining of the module mount can set three degrees of freedom (e.g., θx, θy, and z) between the module and the print frame. For example, the x precision surfaces set the θy direction, the y precision surfaces set the θx direction, and the z precision surface sets the z direction (e.g., height). 
     A precision surface can be an entire surface of the module mount or only a portion of a surface, such as an alignment datum that is a raised or recessed feature. The precision surface can be machined using precision grinding. On the module mount, the x and y precision surfaces are machined perpendicular to the z precision surface, for example, within ±10 microns. The precision surfaces can have a surface profile within ±10 microns or less, such as ±3 microns. The nozzle surface  422  to the x and y precision surface can have a perpendicularity within ±25 microns. The distance from a nozzle surface  422  to a mounting surface  208  of the mounting component  206  can be within ±50 microns. 
       FIG. 4  shows a module mount  106  having alignment datums, including two x datums  416 , three y datums  418 , and one z datum  420 . For example, the x alignment datums  416  are raised features on a surface of the protruding portion  216 . The y alignment datums  418  are raised features on a back surface of the module mount  104  that contact the clamp assembly. The z alignment datum  420  is a surface of the module mount that is perpendicular to the x and y alignment datums. 
       FIG. 6  shows a clamp assembly  600 , having corresponding x, y, and z contact points,  602 ,  604 ,  606 . For example, the x contact points  602  are located on an interior surface of the recessed portion  218 . They contact points  604  are located on an exterior surface of the clamp assembly facing the module mount. The z contact point is located near an end of the recessed portion  218 . The contact points can be set to a nominal position that is adjustable. For example, the x and y contact points can adjust the module relative to the clamp assembly in the x and Oz direction, respectively, as discussed below in more detail. The contact points can include magnets. For example, the z contact point can include a magnet. The magnet can hold the module mount in place prior to clamping the module mount to the clamp assembly. When the module mount is clamped to the clamp assembly, the alignment datums and contact points align the module to the print frame in θx, θy, and z direction. The remaining degrees of freedom (i.e., x, y, and Oz direction) are set when the module is mounted in the module mount. Adjusting the position of the one or more of the contact points of a clamp assembly brings the plurality of nozzles of the ejection module attached to the clamp assembly via a module mount into a desired alignment with the frame. 
     The module is mounted to the module mount using an aligning apparatus to form a module mount assembly.  FIGS. 5A and 5B  shows a module mount  104  having an L-shape including a horizontal portion  502  and a vertical portion  504 . The horizontal portion  502  can have an opening  506  for receiving a fluid ejection module while the vertical portion  504  can have a protruding portion  216  (e.g., dovetail) that mates with a clamp assembly. The fluid ejection module can be inserted through the opening  506  from the bottom surface  510  of module mount. The mounting surface  208  of the module can be attached to the mounting surface  210  of the module mount, such as with an adhesive (e.g., BCB) or screws.  FIG. 5B  shows the mounting surface of the module mount having grooves  512  for receiving adhesive. 
       FIG. 7A  shows an example alignment apparatus  700  that can be used to align the fluid ejection module to the module mount. The alignment apparatus  700  is one example of a device that can be used to achieve the alignment step  310  described above. However, it should be understood that other configurations of the alignment apparatus  700  can be used, and the apparatus described is but one example. For illustrative purposes, the alignment apparatus  700  is described in the context of aligning the fluid ejection module to the module mount, although it should be understood that the alignment apparatus  700  can be used to align a differently configured fluid ejection module to the same or a differently configured module mount. 
     In this implementation, the alignment apparatus  700  includes a base  702 . A camera support rail  704  is mounted on the base  702 , and a camera support  706  is mounted on, and configured to move along, the camera support rail  704 . The camera support  706  supports a camera assembly  708 . A print frame support  710  is also mounted on the base  702 . The print frame support  710  supports the print frame  712  and a mask holder  714 . The mask holder  714  supports an alignment mask  716 . The alignment mask  716  can be used together with the camera assembly  708  to align the fluid ejection module to the module mount. A manipulator assembly  718  is mounted to the base  702  by a manipulator base  720  and a manipulator rail  722 . The manipulator assembly  718  is configured to move the fluid ejection module relative to the module mount. The manipulator base  720  is configured to move along the manipulator rail  722 . 
       FIG. 7B  is a close-up view of a portion of the alignment apparatus  700 . The fluid ejection module  102  is placed in the module mount  104 . Before placing the module  102  in the module mount, an adhesive can be applied to the module mount, module, or both. The module mount is positioned between the fluid ejection module and the print frame. The mask holder  714  supports the alignment mask  716 , and the alignment mask  716  includes fiducials  724 , which are discussed in more detail below. The manipulator assembly  718  includes a manipulator plate  726  configured such that movement of the manipulator plate  726  effects movement of the fluid ejection module  102  relative to the module mount, e.g. x, y, and θz direction. 
     In this implementation, the camera assembly  708  includes two low magnification cameras  728  and four high magnification cameras  730 , although more or fewer cameras can be used. The high magnification cameras  730  can be calibrated using a calibration mask  732  (see  FIG. 7E ), as discussed in more detail below. 
       FIG. 7C  is a schematic representation of an implementation of the alignment mask  732 . The alignment mask includes one row of fiducials  724 . The fiducials  724  can be used as reference marks for aligning the fluid ejection modules. For example, the fiducials  724  can be arranged in a line in the x-direction that is parallel to an edge of the print frame  712  (shown in  FIG. 7B ).  FIG. 7D  is a schematic representation of an implementation of the fiducial  724 . In this implementation, the fiducial  724  includes conspicuity features  734  arranged around a fiducial point  736 . The conspicuity features  734  facilitate locating of the fiducial point  736  with the high magnification cameras  730 . References in this disclosure to alignment with a fiducial can refer to alignment with a fiducial point. That is, for example, aligning a high magnification camera  730  with a fiducial  724  can include aligning the high magnification camera  730  with a fiducial point  736 . The conspicuity features can be sized to be conspicuous to a low magnification camera, to a camera with no magnification, or to a human eye. 
       FIG. 7E  is a schematic representation of an implementation of the calibration mask  732 . The calibration mask  732  includes fiducials  724  arranged in a first row  738  and a second row  740 . The fiducials  724  are configured such that the four high magnification cameras  730  are properly positioned when each of the four high magnification cameras  730  is aligned with a certain fiducial. A high magnification camera  730  is aligned with a fiducial  724  when the center of the field of view of the high magnification camera, or some other reference point within the field of view of the high magnification camera, is aligned with a fiducial. For example, the high magnification cameras  730  can be calibrated by alignment with the four fiducials  724  shown within a broken circle in  FIG. 7E . In this implementation, the spacing S between the fiducials in the first row  738  is equal to the spacing S between the fiducials in the second row  740 . The first row  738  and the second row  740  are parallel to each other and separated by a distance D. In some implementations, once calibrated, the four high magnification cameras  730  are maintained in a fixed relation with respect to each other after alignment, unless and until calibration is performed again. 
       FIG. 7F  is a schematic representation of an implementation of the alignment mask  716  and the substrate  202 . The substrate  202  has a nozzle face  752  that can include two or more fiducials  724  (two fiducials in this example). The fiducials  724  on the nozzle face  752  are positioned such that a line defined by such fiducials is parallel to a line defined by the fiducials on the alignment mask when the nozzle face is properly aligned. Because the substrate is attached to the fluid ejection module, proper alignment of the nozzle face of the substrate indicates proper alignment of the fluid ejection module. 
     The fields of view of the four high magnification cameras  730  are shown as broken circles in  FIG. 7F . The fields of view each have a center represented by a crosshair in  FIG. 7F  for illustrative purposes. The centers of the fields of view of a first pair  748  of high magnification cameras  730  define a first line  744 . The centers of the fields of view of a second pair  750  of high magnification cameras  730  define a second line  746 . The high magnification cameras  730  are shown having been calibrated by the calibration mask  732 , as described above, so the first line  744  and the second line  746  are parallel to each other and separated by a distance D. The first pair  748  of high magnification cameras can be aligned to two of the fiducials  724  on the alignment mask  716 . The second pair  750  of high magnification cameras can be positioned over the nozzle face  752  of the fluid ejection module. Because the first line  744  and the second line  746  are parallel, a line defined by the fiducials  724  on the nozzle face  752  is parallel to a line defined by the fiducials on the alignment mask  716  if the nozzle face is properly aligned. Aligning the nozzle face to the second pair of high magnification cameras thus achieves the desired alignment of the remaining degrees of freedom, i.e. x, y, and θz direction. After the module is aligned, a second adhesive can be applied to the sides between the module and module mount to hold the parts together while the first adhesive cures (step  320 ). 
     Before securing a module mount to the print frame, the clamp assemblies are aligned to a frame (step  330 ). For example,  FIG. 8  shows an alignment jig  800 , such as a dovetail jig, that can be used to align clamp assemblies  106  to each other. An alignment jig  800  is a precision mold that represents the shape of the module mounts. The alignment jig can be made of a material with a low CTE, such as invar, kovar, or silicon carbide. The jig can be precision machined using, for example, jig grinding or wire EDM, to an accuracy of 50 microns or less, such as 1 micron or less (e.g., millionths of an inch). An alignment jig  800  aligns the clamp assemblies to the frame  108  and to each other. 
       FIG. 9A  shows the back side of the clamp assembly  106  that can be secured to a frame  108 , for example, with screws  908 . The clamp assembly  106  includes two retractable clamps  907 .  FIG. 9A  shows precision mounting surfaces  904  (e.g., raised surfaces) that contact the print frame  108 . In this case, there are six mounting surfaces. The clamp assemblies can be loosely secured to a frame, for example, by only partly securing the screws.  FIG. 9B  shows the back side of the frame  108 , where the screws  908  can be inserted into threaded openings  902 . Other securing means can be used. Next, the alignment jig  800  can be inserted into the clamp assemblies, as shown in  FIG. 8 . The protruding portions  806  of the alignment jig  800  can mate with the recessed portions  808  of the clamp assemblies  106 . After inserting the jig into the clamp assemblies, the clamp levers  810  are moved from an open position to a closed position. The clamp assemblies  106  are then firmly secured to the frame  108 , for example, by tightening the screws  908 . After firmly securing the clamp assemblies, the clamp levers  810  are opened and the alignment jig  800  is removed, leaving an aligned print bar  1000 , as shown in  FIG. 10 . The individual module mount assemblies can then be loaded in each clamp assembly  106  to form a populated print bar  1100  (step  340 ), as shown in  FIGS. 11A and 11B . 
     To load an individual module mount assembly into the clamp assembly  106 , shown in  FIG. 12 , a lever  1206  is moved to an open position. After loading the module, the lever  1206  is moved from an open position to a closed position. The clamp assembly  106  can include a clamp  1202  along a wall of the recessed portion  1204 . In an open position, the lever  1206  can move the clamp  1202  away from a center  1208  of the recessed portion  1204 . In a closed position, the lever  1206  can move the clamp  1202  toward a center  1208  of the recessed portion, such that the clamp secures the protruding portion of the module mount to the clamp assembly. To release the module mount, the clamp is moved to the open position. 
     In an implementation, the clamp assembly  106  can include at least one clamp  1202  (e.g., two clamps are shown in  FIG. 12 ) that is spring-loaded against a retractable cam plate  1210 . The retractable cam plate  1210  can be spring-loaded against the lever  1206 . In an implementation, in an open position, the lever  1206  is lifted up such that the cam plate  1210  pushes down on the cam plate spring  1212 . The cam plate  1210  pushes the clamps  1202  away from the center  1208  of the recessed portion  1204  in the open position. In a closed position, the lever  1206  is pushed down releasing the cam plate  1210  so that the clamp springs  1214  pull the clamps  1202  toward the center  1208  of the recessed portion. In the closed position, the clamps  1202  push against the protruding portion  216  (e.g. dovetail) to firmly hold the module mount  104  in the clamp assembly  106 , as shown in  FIG. 2A . When the clamps  1202  are closed, the only surfaces that contact are the x, y, and z precision surfaces and corresponding contact points. 
       FIGS. 11A and 11B  show a populated print bar including a plurality of module mount assemblies fastened to the plurality of clamp assemblies. The alignment process  300  can form a populated print bar with a positional accuracy of ±30 microns in the x-direction and ±10 microns in the θz-direction. The alignment of the modules can be checked using an alignment apparatus similar (or identical) to the alignment apparatus shown in  FIG. 7A . If necessary, micro-adjustments can be made to the module mounts using the x and θz adjustments, as discussed below in more detail. 
     To replace an individual module, the clamp lever is moved to an open position so that the clamps release the module mount. A new module can slide into the clamp assembly, and the clamp lever is moved to a closed position to secure the new module. Any micro-adjustments can be made in the x and θz direction, as described below. 
       FIG. 12  shows micro-adjustments, e.g., x and θz adjustments  1216 ,  1228 , that can move the x and y contact points  1230 ,  1232 , respectively. To provide more flexibility in integrating the fluid ejection modules in a printer, the adjustments can be accessible from one or more surfaces. For example, the x adjustment mechanism  1216  can be accessible from either the top or bottom surface  1218 ,  1220  of the clamp assembly  106 . The x adjustment mechanism  1216  can include a cam assembly that engages one or more ball bearings mounted in counter bores (e.g. two are shown in  FIG. 12 ). The ball bearings can be the x contact points  1230 . The cam assembly can include one or more cams, for example, an upper cam  1224  and a lower cam  1225 . The cams are locked together, such that they move together when the cam assembly is adjusted from either the top or bottom  1218 ,  1220 . The cam assembly can fit inside a counter bore in the clamp assembly. The cam assembly can have a threaded section (not shown) between the two cams  1224 ,  1225  that mates with a threaded section in the counter bore or a threaded nut so that the cam assembly can move up and down within the counter bore. The upper and lower cams are sloped to an angle, α, from the z-axis. The slope can vary depending on the amount of translation in the x-direction specified. When the sloped cams  1224 , 1225  are rotated, the cam assembly moves the ball bearings in a linear direction, e.g., either right or left. The slope of the cams and the pitch of the threaded section can be designed so that one rotation of the cam assembly translates into moving the module over one pixel in the x-direction. 
     For example, if the print resolution is 1200 dpi, then the distance between pixels is 1/1200 inch (about 21 microns). If the threaded section has a pitch of 450 microns (Δy) and the desired x travel is 21 microns (Δx), then the angle, α, of the cams  1224 ,  1225  would be arctan (Δx/Δy), arctan (21 microns/450 microns), about 2.67° from the z-axis. Thus, one rotation of the cam assembly translates into the ball bearing moving 21 microns in the x-direction, e.g. one pixel. 
     Table 1 summarizes the x adjustment of a module mount relative to the clamp assembly. Table 1 shows the rotation of a cam assembly (degrees), the number of revolutions, the vertical distance that the cam assembly travels (mm), and the x-direction travel of the ball bearings (microns). For example, the maximum number of degrees that the cam assembly can rotate is 1896°, which is equal to 5.267 revolutions of the cam assembly. This translates into a maximum vertical travel of the cam assembly of 2.37 millimeters and a maximum horizontal travel of the ball bearings of 111.478 microns. For a single revolution, which is 360°, the cam assembly travels vertically 0.45 millimeters and the ball bearings move 21.167 microns (e.g., about one pixel for 1200 dpi). 
     
       
         
           
               
            
               
                   
               
               
                 X Adjustment 
               
            
           
           
               
               
               
               
               
            
               
                   
                 cam assembly 
                 revolutions 
                 vertical 
                   
               
               
                   
                 rotation 
                 of cam 
                 distance of 
                 X travel 
               
               
                   
                 (degrees) 
                 assembly 
                 cam assembly 
                 (microns) 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
            
               
                 Travel from 
                 1896 
                 5.267 
                 2.37000 
                 111.478 
               
               
                 C/L = 
               
               
                 one 1200 
                 360 
                 1.000 
                 0.45000 
                 21.167 
               
               
                 dpi-pixel = 
               
               
                   
                 180 
                 0.500 
                 0.22500 
                 10.583 
               
               
                   
                 170 
                 0.472 
                 0.21260 
                 10 
               
               
                   
                 90 
                 0.250 
                 0.11250 
                 5.292 
               
               
                   
                 45 
                 0.125 
                 0.05625 
                 2.646 
               
               
                   
                 22.5 
                 0.063 
                 0.02813 
                 1.323 
               
               
                   
                 11.25 
                 0.031 
                 0.01406 
                 0.661 
               
               
                   
                 10 
                 0.028 
                 0.01250 
                 0.588 
               
               
                   
                 5 
                 0.014 
                 0.00625 
                 0.294 
               
               
                   
                 1 
                 0.003 
                 0.00125 
                 0.059 
               
               
                   
               
            
           
         
       
     
     Referring to  FIGS. 13A and 13B , the module mount  104  can also be adjusted in the θz direction relative to the clamp assembly  106  using a θz adjustment mechanism. For example, the θz adjustment mechanism can include a y contact point  1308  on the clamp assembly that is adjustable. The other y contact points  1309  (only one shown in  FIG. 13B ) can be stationary. The y contact point  1308  contacts the y alignment datum  1302  on the vertical portion  1304  of the module mount  104 . As the y contact point  1308  moves in a linear direction, the module mount  104  moves in a radial direction relative to the clamp assembly. For example, the y contact point  1308  can be a screw that is movable back and forth in the y-direction causing the module mount to rotate about the z-axis, i.e. θz direction. 
       FIG. 14A  shows a θz adjustment tool  1400  that mates with the y-direction screw  1402  to make micro-adjustments.  FIG. 14B  shows the θz tool  1400  adjusting the y-direction screw  1402  from a front surface  1404 . To provide more flexibility in integrating the fluid ejection modules in a printer, the y-direction screw  1402  can be accessible from more than one surface, such as a front surface  1404  ( FIG. 14B ) and a back surface  1102  ( FIG. 11B ).  FIG. 11B  shows openings  1104  in the frame  108  for accessing the y-direction screw. 
     For example, the y-direction screw  1402  can be designed to travel 50 microns or less (e.g., 25 microns or less, 10 microns or less) along the y-axis per revolution of the screw. This can be done by using a screw having a pitch of 50 microns or less, such as 25 microns or less, 10 microns or less. However, this would require making a custom screw, which can be expensive. Alternatively, a differential screw can be used to achieve the same micro-adjustments using screws with standard pitches. A differential screw can include an outer screw with a first pitch and an inner screw with a second pitch, such that the net movement of the differential screw is the difference between the pitch of the outer and the inner screw. For example, to achieve a net movement of 50 microns, the outer screw and inner screw can have a pitch of 0.50 millimeters and 0.45 millimeters, respectively, so that the difference between the two is 50 microns. Thus, one revolution of the differential screw equals 50 microns of travel along the y-axis. As the differential screw moves the y contact point, the module rotates about the z-axis. For example, a movement of 50 microns in the y-direction with a pivot distance of about 38 mm translates into a rotation in the θz-direction of about 1.32 milliradians (mr) (i.e., arctan (y travel/pivot distance)). 
     Table 2 summarizes the θz adjustment of a module mount  104  relative to the clamp assembly  106 . Table 2 shows the rotation of a differential screw (degrees), the number of revolutions of the outer screw, the travel of the outer screw in the y direction (mm), the travel of the differential screw in the y direction (microns), and the rotation of the module mount in the θz direction (mr). For example, the maximum number of degrees that the differential screw can rotate is 1800°, which is equal to 5 revolutions of the outer screw. This translates into a travel of about 2.5 mm for the outer screw and 250 microns of travel for the differential screw. This results in about 6.58 mr of movement of the module mount in the θz direction. In another example, for a single revolution, which is 360°, the outer screw can travel 0.5 mm while the differential screw moves 50 microns, which results in about 1.32 mr of movement of the module mount in the θz direction. Table 2 provides additional calculations for 180°, 152.4°, 90°, 76.2°, 45°, 22.5°, 11.25°, 10°, 5°, and 1°, where 152.4° and 76.2° represent a pixel and a half a pixel, respectively, for a 1200 dpi print resolution. Other configurations for the differential screw as well as other combinations for the pitches of the screws are possible. 
     
       
         
           
               
            
               
                   
               
               
                 θz adjustment 
               
               
                 Using differential screw having: 
               
               
                 0.50 mm pitch outer screw thread 
               
               
                 0.45 mm pitch inner screw thread 
               
               
                 difference of 0.05 mm travel/revolution 
               
            
           
           
               
               
               
               
               
               
            
               
                 screw 
                 revolutions 
                 Y travel 
                 Y travel of 
                   
                   
               
               
                 rotation 
                 of outer 
                 of outer 
                 differential 
                 Z rotation 
               
               
                 (degrees) 
                 screw 
                 screw (mm) 
                 screw (microns) 
                 (milliradians) 
               
               
                   
               
            
           
           
               
               
               
               
               
               
            
               
                   
                   
                   
                   
                 38 
                 =pivot distance in mm 
               
               
                 1800 
                 5.000 
                 2.50000 
                 250.0 
                 6.5789 
                 =Travel from C/L 
               
               
                 360 
                 1.000 
                 0.50000 
                 50.0 
                 1.3158 
               
               
                 180 
                 0.500 
                 0.25000 
                 25.0 
                 0.6579 
               
               
                 152.4 
                 0.423 
                 0.21167 
                 21.1667 
                 0.5570 
                 =One pixel 
               
               
                   
                   
                   
                   
                   
                 (1200 dpi) Y travel 
               
               
                 90 
                 0.250 
                 0.12500 
                 12.5 
                 0.3289 
               
               
                 76.2 
                 0.212 
                 0.10583 
                 10.6 
                 0.2785 
                 =½ pixel 
               
               
                   
                   
                   
                   
                   
                 (1200 dpi) Y travel 
               
               
                 45 
                 0.125 
                 0.06250 
                 6.250 
                 0.1645 
               
               
                 22.5 
                 0.063 
                 0.03125 
                 3.125 
                 0.0822 
               
               
                 11.25 
                 0.031 
                 0.01563 
                 1.563 
                 0.0411 
               
               
                 10 
                 0.028 
                 0.01389 
                 1.389 
                 0.0365 
               
               
                 5 
                 0.014 
                 0.00694 
                 0.694 
                 0.0183 
               
               
                 1 
                 0.003 
                 0.00139 
                 0.139 
                 0.0037 
               
               
                   
               
            
           
         
       
     
     The use of terminology such as “front,” “back,” “top,” “bottom,” “over,” “above,” and “below” throughout the specification and claims is for describing the relative positions of various components of the system, printhead, and other elements described herein. Similarly, the use of any horizontal or vertical terms to describe elements is for describing relative orientations of the various components of the system, printhead, and other elements described herein. Unless otherwise stated explicitly, the use of such terminology does not imply a particular position or orientation of the printhead or any other components relative to the direction of the Earth gravitational force, or the Earth ground surface, or other particular position or orientation that the system, printhead, and other elements may be placed in during operation, manufacturing, and transportation. 
     A number of embodiments of the invention have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the inventions.