Abstract:
A microdeposition system includes a stage, a printhead carriage, and a controller. The stage holds a substrate. The printhead carriage includes N printhead modules, where N is an integer greater than one. Each of the N printhead modules includes a printhead and an alignment mechanism. The printhead includes a plurality of nozzles that deposit droplets of fluid manufacturing material onto the substrate while relative movement between the substrate and the printhead is along a first axis. The alignment mechanism adjusts the printhead with respect to the printhead module. The controller controls the alignment mechanisms of the N printhead modules to set effective nozzle spacing for the pluralities of nozzles to a uniform value. The effective nozzle spacing is defined as spacing between adjacent ones of the plurality of nozzles as projected onto a second axis perpendicular to the first axis.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. Provisional Application No. 61/289,702, filed on Dec. 23, 2009. The disclosure of the above application is incorporated herein by reference in its entirety. 
     
    
     FIELD 
       [0002]    The present disclosure relates to inkjet printing and more particularly to method and apparatus for adjusting nozzle alignment of an inkjet printhead module. 
       BACKGROUND 
       [0003]    The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure. 
         [0004]    Manufacturers have developed various techniques for fabricating microstructures that have small feature sizes. The microstructures may form one of more layers of an electronic circuit. Examples of these structures include light-emitting diode (LED) display devices, polymer LED (PLED) display devices, organic LED (OLED) devices, liquid crystal display (LCD) devices, and printed circuit boards. Many of these manufacturing techniques are relatively expensive to implement and require high production quantities to amortize the cost of the fabrication equipment. 
         [0005]    One technique for forming microstructures on a substrate is screen printing. During screen printing, a fine mesh screen is positioned on the substrate. Fluid material is deposited through the screen and onto the substrate in a pattern defined by the screen. Screen printing therefore causes contact between the screen and the substrate. Contact also occurs between the screen and the fluid material, which contaminates both the substrate and the fluid material. 
         [0006]    While screen printing is suitable for forming some microstructures, many manufacturing processes do not allow contamination of the substrate by the screen. Therefore, screen printing is not a viable option for the manufacture of certain microstructures. For example, polymer light-emitting diode (PLED) display devices may require a contamination-free manufacturing process. 
         [0007]    Certain polymeric substances can be used to manufacture diodes that generate visible light of different wavelengths. Using these polymers, display devices having pixels with sub-components of red, green, and blue can be created. PLED fluid materials enable full-spectrum color displays and require very little power to emit a substantial amount of light. PLED displays can be used in various applications, including televisions, computer monitors, PDAs, other handheld computing devices, cellular phones, etc. PLED technology may also be used for manufacturing light-emitting panels that provide ambient lighting for office, storage, and living spaces. One obstacle to the widespread use of PLED display devices is the difficulty and expense of manufacturing PLED display devices. 
         [0008]    Photolithography is another manufacturing technique that is used to manufacture microstructures on substrates. Photolithography may also be incompatible with PLED display devices. Manufacturing processes using photolithography generally involve the deposition of a photoresist material onto a substrate. The photoresist material is cured by exposure to light. A patterned mask is therefore used to selectively apply light to the photoresist material. Photoresist that is exposed to the light is cured and unexposed portions are not cured. The uncured portions can be removed from the substrate while the cured portions remain. 
         [0009]    An underlying surface of the substrate is exposed through the removed photoresist layer. Another material is then deposited onto the substrate through the opened pattern on the photoresist layer, followed by the removal of the cured portion of the photoresist layer. 
         [0010]    Photolithography has been used successfully to manufacture many microstructures, such as traces on circuit boards. However, photolithography contaminates the substrate and the material formed on the substrate. Photolithography may not be compatible with the manufacture of PLED displays because the photoresist contaminates the PLED polymers. In addition, photolithography involves multiple steps for applying and processing the photoresist material. The cost of the photolithography process can be prohibitive when relatively small quantities are to be fabricated. Further, expensive PLED material may be lost when it is deposited on cured photoresist that is later removed. 
         [0011]    Spin coating has also been used to form microstructures. Spin coating involves rotating a substrate while depositing fluid material at the center of the substrate. The rotational motion of the substrate causes the fluid material to spread evenly across the surface of the substrate. Spin coating is also an expensive process because a majority of the fluid material does not remain on the substrate. In addition, the size of the substrate is limited by the spin coating process to less than approximately 12″, which makes spin coating unsuitable for larger devices such as PLED televisions. 
       SUMMARY 
       [0012]    A microdeposition system includes a printhead carriage, a stage, and a controller. The printhead carriage includes N printhead modules and moves along an x axis. N is an integer greater than one. The stage holds a substrate beneath the printhead carriage and moves the substrate along a y axis perpendicular to the x axis. Each of the N printhead modules includes a fixed bracket a rotating bracket, first, second, and third actuators, a printhead bracket, and a printhead. The fixed bracket is rigidly mounted to the printhead carriage. The rotating bracket is rotatably and slidably coupled to the fixed bracket. 
         [0013]    The rotating bracket rotates about a z axis perpendicular to a horizontal plane parallel to the x and y axes, and slides along the z axis. The first actuator rotates the rotating bracket with respect to the fixed bracket. The second actuator slides the rotating bracket relative to the fixed bracket. The printhead bracket is slidably coupled to the rotating bracket. The printhead bracket slides along the x axis when the rotating bracket is parallel to the x axis. The third actuator slides the printhead bracket relative to the rotating bracket. The printhead is rigidly attached to the printhead bracket. The printhead includes a plurality of nozzles separated from each other by a physical nozzle spacing and arranged along a line parallel to the horizontal plane. The plurality of nozzles deposit droplets of fluid material onto the substrate. 
         [0014]    The controller controls the first actuator of each of the N printhead modules to set an effective nozzle spacing of the N printhead modules to a common spacing value. The effective nozzle spacing is defined by spacing between positions of the plurality of nozzles as projected onto the x axis. The controller selectively adjusts the third actuator of first and second printhead modules of the N printhead modules such that an effective spacing between a last nozzle of the first printhead module and a first nozzle of the second printhead module, with respect to the x axis, is equal to the common spacing value. The common spacing value is determined based on a minimum one of the physical nozzle spacings of the N printhead modules. The controller controls the second actuator of each of the N printhead modules to set a vertical position of each of the N printhead modules to a common vertical value. The printhead carriage includes a turntable that holds the N printhead modules. The turntable rotates with respect to the printhead carriage about the z axis. 
         [0015]    A microdeposition system includes a stage, a printhead carriage, and a controller. The stage holds a substrate. The printhead carriage includes N printhead modules. N is an integer greater than one. Each of the N printhead modules includes a printhead and an alignment mechanism. The printhead includes a plurality of nozzles that deposit droplets of fluid manufacturing material onto the substrate while relative movement between the substrate and the printhead is along a first axis. The alignment mechanism adjusts the printhead with respect to the printhead module. The controller controls the alignment mechanisms of the N printhead modules to set effective nozzle spacing for the pluralities of nozzles to a uniform value. The effective nozzle spacing is defined as spacing between adjacent ones of the plurality of nozzles as projected onto a second axis perpendicular to the first axis. 
         [0016]    In other features, the stage moves the substrate along the first axis during deposition of the droplets of fluid manufacturing material. The printhead carriage translates to new positions along the second axis between passes of the substrate. For each of the N printhead modules, the plurality of nozzles are separated by a physical nozzle spacing. The controller determines the uniform value based on the physical nozzle spacings of the N printhead modules. The controller determines the uniform value based on a smallest one of the physical nozzle spacings of the N printhead modules. 
         [0017]    In further features, the microdeposition system further includes a camera facing toward the printhead carriage along a third axis perpendicular to the first and second axes. The controller determines the physical nozzle spacing of each of the N printhead modules based on information from the camera. The controller controls the alignment mechanism of one of the N printhead modules to set the effective nozzle spacing for the plurality of nozzles of the one of the N printhead modules to the uniform value. 
         [0018]    In other features, the alignment mechanism of the one of the N printhead modules includes a fixed bracket mounted to the printhead carriage, a rotating bracket rotatably coupled to the fixed bracket, and an actuator. The printhead is coupled to the rotating bracket. Based on control from the controller, the actuator rotates the rotating bracket about a third axis perpendicular to the first and second axes. The controller controls the alignment mechanisms of first and second adjacent printhead modules of the N printhead modules to set the effective nozzle spacing between a last nozzle of the first adjacent printhead module and a first nozzle of the second adjacent printhead module to the uniform value. 
         [0019]    In further features, the N printhead modules are arranged in a plurality of rows that are parallel to the second axis. The first adjacent printhead module is in a first one of the plurality of rows. The second adjacent printhead module is in a second one of the plurality of rows. The alignment mechanism of the second adjacent one of the N printhead modules includes a bracket coupled to the printhead carriage, a printhead assembly slidably coupled to the bracket, and an actuator. The printhead is mounted to the printhead assembly. The printhead assembly slides along the second axis when the bracket is parallel to the second axis. Based on control from the controller, the actuator slides the printhead assembly with respect to the bracket. 
         [0020]    In other features, for each of the N printhead modules, the alignment mechanism adjusts the printhead along a third axis perpendicular to the first and second axes. The controller sets a spacing between the printhead and the stage to a common height for each of the N printhead modules. The microdeposition system includes a camera facing toward the printhead carriage along the third axis. The controller controls the alignment mechanism of the N printhead modules based on a focal length measurement of the respective one of the N printhead modules by the camera. 
         [0021]    The alignment mechanism of one of the N printhead modules includes a fixed bracket mounted to the printhead carriage, a second bracket slidably coupled to the fixed bracket along the third axis, and an actuator. The printhead is coupled to the second bracket. Based on control from the controller, the actuator slides the second bracket with respect to the fixed bracket. 
         [0022]    In further features, the alignment mechanism for one of the N printhead modules includes a fixed bracket mounted to the printhead carriage, a rotating bracket rotatably coupled to the fixed bracket, and a first actuator that rotates the rotating bracket relative to the fixed bracket. The rotating bracket rotates about a third axis perpendicular to the first and second axes. The printhead is coupled to the rotating bracket. 
         [0023]    In other features, the printhead is slidably coupled to the rotating bracket. The printhead slides along the second axis when the rotating bracket is parallel to the second axis. The alignment mechanism for one of the N printhead modules further includes a second actuator that slides the printhead with respect to the rotating bracket. The rotating bracket is slidably coupled to the fixed bracket. The alignment mechanism for one of the N printhead modules further includes a third actuator that slides the rotating bracket along the third axis with respect to the fixed bracket. 
         [0024]    In further features, the printhead carriage includes a turntable that holds the N printhead modules. The turntable rotates with respect to the printhead carriage about a third axis perpendicular to the first and second axes. The controller performs a calibration routine to set the effective nozzle spacing for the pluralities of nozzles to the uniform value before depositing the droplets of fluid manufacturing material onto the substrate has begun. 
         [0025]    A printhead module includes a printhead including a plurality of nozzles that deposit droplets of fluid manufacturing material onto a substrate, a head manifold that distributes the fluid manufacturing material to the plurality of nozzles and that includes a supply port and a return port, and a fluid distribution system that connects to the supply port and the return port. The fluid distribution system includes a pressure port that receives one of a pressure and a vacuum and a reservoir having a cylindrical shape with a tapered bottom portion, wherein the pressure port applies the one of the pressure and the vacuum to a top of the reservoir. The fluid distribution system also includes an ink port that receives one of the fluid manufacturing material and a solvent, a refill valve that selectively connects the ink port to the reservoir, fluid sensors that measure levels of fluid in the reservoir, and a control module that controls the refill valve based on the measured levels of fluid. 
         [0026]    The fluid distribution system also includes a recirculation port that returns unused amounts of the fluid manufacturing material to an external fluid supply, a bypass valve that alternately connects the reservoir to a common fluid node and to the recirculation port, a solvent port that receives the solvent, and a solvent valve that selectively connects the solvent port to the common fluid node. The fluid distribution system also includes an ink valve that selectively connects the common fluid node to the supply port, a removable filter assembly interposed between the ink valve and the supply port, a waste port, and a return valve that selectively connects the return port to the waste port. 
         [0027]    Further areas of applicability of the present disclosure will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the disclosure. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0028]    The present disclosure will become more fully understood from the detailed description and the accompanying drawings, wherein: 
           [0029]      FIG. 1  is an isometric view of an example microdeposition system; 
           [0030]      FIG. 2  is a simplified top view of an example microdeposition system; 
           [0031]      FIG. 3A  is a simplified side view of an example printhead module; 
           [0032]      FIG. 3B  depicts nozzle plate rotation to achieve a desired uniform pitch; 
           [0033]      FIG. 3C  depicts alignment between head packs along the x axis; 
           [0034]      FIGS. 4-6  are isometric views of an example printhead module; 
           [0035]      FIG. 7  is an exploded view of alignment components of the printhead module; 
           [0036]      FIG. 8  is another isometric view of the printhead module; 
           [0037]      FIG. 9  is a functional block diagram of example fluid routing in the printhead module; 
           [0038]      FIG. 10  is a partial cutaway view of the printhead module to show fluid components; 
           [0039]      FIG. 11  is an exploded view of the printhead module; 
           [0040]      FIG. 12  is a side view of the printhead module; 
           [0041]      FIG. 13  is a front view of the printhead module; and 
           [0042]      FIG. 14  is a rear view of the printhead module. 
       
    
    
     DETAILED DESCRIPTION 
       [0043]    The following description is merely illustrative in nature and is in no way intended to limit the disclosure, its application, or uses. For purposes of clarity, the same reference numbers will be used in the drawings to identify similar elements. As used herein, the phrase at least one of A, B, and C should be construed to mean a logical (A or B or C), using a non-exclusive logical or. It should be understood that steps within a method may be executed in different order without altering the principles of the present disclosure. 
         [0044]    The terms “fluid manufacturing material” and “fluid material,” as defined herein, are broadly construed to include any material that can assume a low viscosity form and that is suitable for being deposited, for example, from a microdeposition head onto a substrate for forming a microstructure. Fluid manufacturing materials may include, but are not limited to, light-emitting polymers (LEPs), which can be used to form polymer light-emitting diode display devices (PLEDs and PolyLEDs). Fluid manufacturing materials may also include plastics, metals, waxes, solders, solder pastes, biomedical products, acids, photoresists, solvents, adhesives, and epoxies. The term “fluid manufacturing material” is interchangeably referred to herein as “fluid material.” 
         [0045]    The term “deposition,” as defined herein, generally refers to the process of depositing individual droplets of fluid materials on substrates. The terms “let,” “discharge,” “pattern,” and “deposit” are used interchangeably herein with specific reference to the deposition of the fluid material from a microdeposition head, for example. The terms “droplet” and “drop” are also used interchangeably. 
         [0046]    The term “substrate,” as defined herein, is broadly construed to include any material having a surface that is suitable for receiving a fluid material during a manufacturing process such as microdeposition. Substrates include, but are not limited to, glass plate, pipettes, silicon wafers, ceramic tiles, FR- 4  and other printed circuit board materials, rigid and flexible plastic, and metal sheets and rolls. In certain embodiments, a deposited fluid material itself may form a substrate, as the fluid material itself also includes surfaces suitable for receiving a fluid material during manufacturing, such as, for example, when forming three-dimensional microstructures. 
         [0047]    The term “microstructures,” as defined herein, generally refers to structures formed with a high degree of precision, and that are sized to fit on a substrate. Because the sizes of different substrates may vary, the term “microstructures” should not be construed to be limited to any particular size and can be used interchangeably with the term “structure.” Microstructures may include a single droplet of a fluid material, any combination of droplets, or any structure formed by depositing the droplet(s) on a substrate, such as a two-dimensional layer, a three-dimensional architecture, and any other desired structure. 
         [0048]    The microdeposition systems referenced herein perform processes by depositing fluid materials onto substrates according to user-defined computer-executable instructions. The term “computer-executable instructions,” which is also referred to herein as “program modules” or “modules,” generally includes routines, programs, objects, components, data structures, or the like that implement particular abstract data types or perform particular tasks such as, but not limited to, executing computer numerical controls for implementing microdeposition processes. 
         [0049]    Program modules may be stored on any non-transitory, tangible computer-readable media, including, but not limited to RAM, ROM, EEPROM, CD-ROM or other optical disk storage, magnetic disk storage or other magnetic storage devices, or any other medium capable of storing instructions or data structures and capable of being accessed by a general purpose or special purpose computer. 
         [0050]    Referring now to  FIG. 1 , a microdeposition system  100  includes a printhead carriage  104  that slides along beams  108 . For example only, the beams  108  may be constructed from granite. The direction of travel of the printhead carriage  104  is referred to as the x axis. The printhead carriage  104  includes one or more rows of nozzles that deposit a fluid manufacturing material on a substrate  112 . For example only, the substrate  112  may be a sheet of glass and may be a component of a PLED video monitor or television. 
         [0051]    The substrate  112  may be secured by a chuck, which may hold the substrate  112  using a vacuum. The substrate  112  may translate back and forth along the y axis, which is perpendicular to the x axis. For example only, the printhead carriage  104  may align the rows of nozzles to be parallel to the x axis. As the substrate  112  moves along the y axis, the rows of nozzles selectively deposit fluid manufacturing material onto the substrate  112 . The rows of nozzles may be unable to cover the entire substrate  112  in one pass. The printhead carriage  104  may therefore translate to another position along the x axis. The substrate  112  will then move back along the y axis to print the next pass. 
         [0052]    Alternatively, the printhead carriage  104  may print while moving along the x axis, with the substrate  112  remaining stationary. The substrate  112  would then translate to a new position along the y axis after each pass is completed. The nozzles in the printhead carriage  104  may be periodically maintained to ensure uniform dispensing of droplets. In various implementations, nozzle maintenance may be performed when the substrate  112  is being loaded into the system  100  and/or when the substrate  112  is being unloaded from the system  100 . 
         [0053]    Referring now to  FIG. 2 , the printhead carriage  104  is depicted as having four rows of white rectangles, where each white rectangle graphically represents a printhead module. Each printhead module may include multiple nozzles, such as 128 nozzles. Therefore, the example of  FIG. 2  includes four rows of six printhead modules each having 128 nozzles, for a total of 3072 nozzles. 
         [0054]    Each row of printhead modules may be connected to a common pack mounting block and referred to as a pack. The nozzles of each pack may be generally colinear. In various implementations, the nozzles selectively eject droplets of fluid manufacturing material as the substrate  112  translates along the y axis. After printing one pass, the printhead carriage  104  translates into the next position along the x axis, and the substrate  112  traverses the printhead carriage  104  in the other direction along the y axis. 
         [0055]    In order to achieve finer resolution, the packs can be rotated as a group by the printhead carriage  104 . By rotating the packs, the nozzles are more closely spaced in terms of their x coordinates. For example, if two adjacent nozzles were to continuously disperse droplets, two parallel lines would be created on the substrate  112 . These lines are closer together as the head packs are rotated away from an orientation parallel to the x axis. 
         [0056]    In various implementations, the packs may be slid in the x-y plane with respect to each other while keeping the rows of nozzles of each pack parallel. This may allow for more consistent coverage of the substrate  112  when the printhead carriage  104  rotates the packs. 
         [0057]    When the packs are rotated, printing a line parallel to the x axis on the substrate  112  requires staggering the firing of the angled nozzles. Nozzle firing times may therefore be based on the angle of the packs. 
         [0058]    Referring now to  FIG. 3A , an example printhead module  202  includes an electronics assembly  206 , an ink/air system  210 , an alignment assembly  214 , and a printhead assembly  218 . In various implementations, the printhead assembly may include  128  nozzles. The nozzles receive fluid manufacturing material, solvent, air pressure, and vacuum from the ink/air system  210 . 
         [0059]    The electronics assembly  206  controls which of these inputs is applied to the printhead assembly  218 . For example, the electronics assembly  206  may actuate valves of the ink/air system  210  to allow solvent to reach the printhead assembly. 
         [0060]    The electronics assembly  206  may also control the alignment assembly  214 . The electronics assembly  206  may communicate with an alignment module. For example only, this communication may occur over a controller area network (CAN) bus. The alignment module may determine whether alignment of the nozzles in the printhead assembly  218  matches a desired alignment. 
         [0061]    For example only, the alignment module may include a camera facing up at the printhead assembly  218 . The alignment module may use the camera to determine whether adjustments need to be made by the alignment assembly  214 . These adjustments are communicated to the electronics assembly  206 , which drives actuators of the alignment assembly  214  to adjust the printhead assembly  218 . 
         [0062]    For example, the camera may determine the height of the printhead assembly  218  relative to the substrate. The alignment module may determine height based on a lens position that brings the nozzle into focus. The alignment module may instruct the electronics assembly  206  to drive the alignment assembly  214  to achieve a desired height of the printhead assembly  218 . For example only, a uniform height may be set for all of the printhead modules in the microdeposition system. 
         [0063]    The alignment module may also determine the spacing between the nozzles of the printhead assembly  218 . For example only, while spacing between each of the nozzles in the printhead assembly  218  may be uniform, that spacing may vary between different printhead assemblies.  FIG. 3B  depicts a mechanism for realizing a standard nozzle spacing by rotating the printhead assembly  218  around the z axis. Further, the alignment module may align the printhead assembly  218  with printhead assemblies of other printhead modules in the pack with respect to the x axis. The reason for this is shown in  FIG. 3C . 
         [0064]    Referring now to  FIG. 3B , a top view of the nozzles of a printhead assembly  250  is shown. For purposes of illustration, four nozzles are depicted. The distance between the first and last nozzle is d 0  and the spacing between each nozzle is therefore d 0  divided by three. If the spacing between the nozzles is too great, the printhead assembly can be rotated, such as is shown at  254 . With respect to the x axis (i.e., with nozzle positions projected onto the x axis), the distance between the first and last nozzles is now d 1 , which is less than d 0 . The effective nozzle spacing is now d 1  divided by three. 
         [0065]    As seen in  FIG. 3B , rotating the printhead assembly  250  can decrease the nozzle spacing, but cannot increase the nozzle spacing. Therefore, the nozzle spacing of all of the printhead assemblies of a microdeposition system may be set equal to the smallest spacing of any one of the printhead assemblies. While the printhead assembly  254  is shown rotated at a 45 degree angle for purposes of illustration, actual rotation angles may be much smaller. 
         [0066]    Rotation of the printhead assembly for a printhead module is performed by the respective alignment assembly for that printhead module while the printhead module itself remains stationary. This is performed in order to achieve a nozzle spacing that is uniform for all of the printhead modules, which may be done as part of an initial calibration process, such as whenever a printhead module is added or removed from a pack. By contrast, the procedure described with respect to  FIG. 2  rotates all of the packs of printhead modules as a group using the printhead carriage  104 . This rotation may be performed once the printhead modules are adjusted individually, and the rotation may be based on the feature pattern to be printed. 
         [0067]    Referring now to  FIG. 3C , an example of two packs, each including two printhead modules having four nozzles each, is shown for purposes of illustration. Gaps may be present between the printhead modules of a pack because of the space requirements of mechanical, electrical, and fluidic components of the printhead module. The distance between the nozzle plates of the two printhead modules may be designed to be approximately equal to the length of one of the nozzle plates. 
         [0068]    The second pack may therefore be staggered with respect to the first pack so that the nozzles of the second pack line up with the gaps between the printhead modules of the first pack. Each of the printhead modules may be individually translated with respect to the x axis to accurately align the modules of each pack with each other. With respect to the x axis, the combined nozzles of the first and second packs then have a uniform spacing. Similar to the spacing adjustment described in  FIG. 3B , the x axis alignment may be performed as part of a calibration process. 
         [0069]    Referring now to  FIG. 4 , an example implementation of a printhead module  300  includes a rear cover  304  and a datum mounting block  308 . The datum mounting block  308  includes openings  312  that fit into projections of a pack mounting block (not shown). The datum mounting block  308  seats against the pack mounting block, which establishes a position in the z axis of the printhead module  300 . Because the datum mounting block  308  seats firmly against a flat surface of the pack mounting block, rotation of the printhead module  300  about the y axis is limited. 
         [0070]    The openings  312  in the datum mounting block  308  are closely matched to the sizes of projections of the pack mounting block to prevent movement of the printhead module  300  along the y axis. In addition, this matching limits rotation of the printhead module  300  around the z axis. Further, a flat-faced datum bracket  316  may sit against a corresponding face of the pack mounting block, further establishing the y axis position of the printhead module  300 . 
         [0071]    A projection  320  of the datum bracket  316  may insert into a corresponding opening of the pack mounting block. Combined with the mechanical connections at the openings  312 , the projection  320  prevents rotation of the printhead module  300  around the x axis. A locking rod  324 , which may be turned using a handle  328 , engages a threaded tip  332  into the pack mounting block. This secures the printhead module  300  and forces the datum mounting block  308  against the pack mounting block. In various implementations, the opening of the pack mounting block that receives the projection  320  and the projections of the pack mounting block that are received by the openings  312  may include spring-loaded bearings or bearing surfaces to ensure a tight fit. 
         [0072]    Pins  314  may extend down from the datum mounting block  308 . The pins may fit into corresponding voids in the pack mounting block. The voids in the pack mounting block may be oval channels that each have an x axis dimension approximately equal to the diameter of the pins  314  and have a y axis dimension greater than the diameter of the pins  314 . The voids in the pack mounting block therefore do not constrain the pins  314  in the y axis direction, but do establish the x axis location of the datum mounting block  308 . The pins  314  therefore allow the x axis tolerances of the openings  312  and the projection  312  to be relaxed. 
         [0073]    An inkjet printhead assembly  340  is mounted to an alignment bracket  344 . The alignment bracket  344  is adjusted using an alignment mechanism  348  described in more detail below. The printhead assembly  340  may include piezoelectric transducers to selectively fire droplets of a fluid manufacturing material. Fluid lines are connected to the printhead module  300  via a fluid port  360 , which may allow rapid connection of multiple fluid lines. 
         [0074]    Referring now to  FIG. 5 , removal of the rear cover  304  reveals a printed circuit board  364  (individual traces and components not shown), which may include communication circuitry, motor drive circuitry, sensor circuitry, and fluid valve control circuitry. Power and communication signals may be received at an input connector  368 . The communication signals may include networking signals, which for example may comply with the IEEE 802.3 standard. A sensor input connector  372  may receive signals from one or more fluid sensors, which may monitor fluid levels of a reservoir. A motor connector  376  may control one or more actuators of the alignment mechanism  348 . A solenoid connector  380  provides control signals to fluid control valves. 
         [0075]    Referring now to  FIG. 6 , an input connector  384  receives drive signals for the nozzles of the printhead assembly  340 . These signals are communicated to the printhead assembly  340  by a flexible circuit  388 . An adapter  392  may interface between the flexible circuit  388  and the input connector  384 . In various implementations, the flexible circuit  388  may be provided by the manufacturer of the printhead assembly  340 . 
         [0076]    In various implementations, the input connector  384  may include a signal pin for each of the nozzles of the printhead assembly  340 . Firing waveforms are received at the input connector  384  from an outside drive control module. The input connector  384  may also include a signal return pin for each of the nozzles of the printhead assembly  340 . 
         [0077]    Referring now to  FIG. 7 , the datum mounting block  308  serves as a reference point when secured to the pack mounting block (not shown). A datum bracket  404  is rigidly secured to the datum mounting block  308 . The datum bracket  404  may include datum pads  408 ,  408 , and  410 , which seat against a flat surface of the pack mounting block. The datum pads  408 ,  409 , and  410  may therefore establish the y axis position of the datum bracket  404 . 
         [0078]    The datum bracket  404  is formed from a rigid material and includes a first portion  412  and a second portion  416  that is perpendicular to the first portion  412 . The outside corner formed by the portions  412  and  416  is visible in  FIG. 7 . On the inside corner, datum pads are mounted on both the first and second portions  412  and  416 . Spherical pivots  420  and  424  are pressed against these datum pads by a rotating bracket  440 . 
         [0079]    In various implementations, the datum pads  408 ,  409 , and  410 , extend through the first portion  412  to serve as datum pads on the other side of the datum bracket  404 . The datum pads  409  and  410  therefore have one side that seats against the pack mounting block while the other side supports the pivots  420  and  424 . In this way, the y axis orientation of the rotating bracket  440  is determined directly from the pack mounting block. 
         [0080]    Datum pads  426  and  428  support the pivots  420  and  424 , and are visible in  FIG. 7  because the datum pads  426  and  428  extend through the second portion  416 . The datum pads  409 ,  410 ,  426 , and  428  may have a contact surface large enough to allow the z position of the pivots  420  and  424  to change, as described in more detail below. 
         [0081]    The rotating bracket  440  rotates about the pivots  420  and  424 . Washers, such as a spherical pivot washer  450 , may be located between the pivots  420  and  424  and the rotating bracket  440 . The washers may retain the pivots  420  and  424  and prevent them from rolling out of position. The rotating bracket  440  is held in place against the datum bracket  404  by springs  452 ,  453 ,  454 ,  455 , and  456 . 
         [0082]    In order to rotate the rotating bracket  440 , a force can be applied to the rotating bracket  440  on a side opposite from the pivots  420  and  424 . For example, applying force against a projection  458  rotates the rotating bracket  440  about the z axis. The force applied to the projection  458  may be applied by an actuator  462 , which may be a linear actuator. In various implementations, linear actuators having an accuracy of 0.5 microns may be used. 
         [0083]    The actuator  462  may be mounted to the datum mounting block  308  in a vertical orientation. Vertical operation of the actuator  462  may be translated into horizontal force against the projection  458  by a rocker arm  464 . A tip of the actuator  462  may press on the rocker arm  464  at a contact point  466 . The rocker arm  464  may rotate about a rod inserted through a hole  468  and apply pressure to the projection  458  with an engagement point  470 . 
         [0084]    Another actuator  480  may be mounted to the datum mounting block  308  in a vertical orientation. The actuator  480  may apply a force along the z axis to the rotating bracket  440 . The pressure may be applied to the rotating bracket  440  at a contact point  482 . The actuator  480  therefore translates the rotating bracket  440  along the z axis. Because pressure is applied in line with the pivots  420  and  424 , movement along the z axis should not change the angle about the z axis of the rotating bracket  440 . The pivots  420  and  424  are able to roll along the datum pads  409 ,  410 ,  426 , and  428  to the new position along the z axis. 
         [0085]    The alignment bracket  344  rigidly retains the printhead assembly  340 . The alignment bracket  344  attaches to the rotating bracket  440  via linear slides  490 . The alignment bracket  344  can therefore slide along the rotating bracket  440  in the x axis direction. The alignment bracket  344  is forced to one end of its x axis travel by a spring  492 . One end of the spring  492  attaches to the alignment bracket  344  and an opposite end of the spring  492  attaches to the rotating bracket  440 , such as at projection  493  (see  FIG. 13 ). An actuator  494  oriented in the x axis direction moves the alignment bracket  344  against the force of the spring  492 . The printhead assembly  340  can therefore be adjusted in the theta z, z, and x directions by the actuators  462 ,  480 , and  494 , respectively. 
         [0086]    Referring now to  FIG. 8 , a protective front cover  504  may have an opening to allow access to a removable filter assembly  508 . The filter assembly  508  may filter out contaminants before they have an opportunity to cause flow problems with the nozzles in the printhead assembly  340 . 
         [0087]    Referring now to  FIG. 9 , a functional block diagram of a fluid system  600  of the printhead module  300  is presented. An ink/solvent port  604  receives either ink or solvent from an external fluid supply module (not shown). A solvent port  608  receives solvent from the external fluid supply module. A waste port  610  provides waste material to an external waste station. A recirculation port  612  provides returns ink back to the fluid supply module. 
         [0088]    A pressure or a vacuum can be applied at a pressure/vacuum port  616 . Ink or solvent is supplied to a reservoir  620  from the ink/solvent port via an optional shutoff valve  624 . The reservoir  620  may include a low sensor  622 , a full sensor  624 , and an overflow sensor  626 . These sensors sense the level of fluid within the reservoir  620 . 
         [0089]    When the level of the fluid decreases below the full sensor  624 , fluid may be provided to the reservoir  620  until the overflow sensor  626  is reached. At this point, supply of the fluid from the external fluid supply module is stopped. The shutoff valve  624  may be actuated to prevent the reservoir  620  from overfilling while the external fluid supply module is shutting off. If the level of fluid drops below the low sensor  622 , printing may be stopped. 
         [0090]    In various implementations, the reservoir  620  may be formed from tubing, such as 18 millimeter diameter polytetrafluoroethylene tubing. A bottom surface of the reservoir  620  may be tapered to prevent solid material from collecting in corners of the tubing, such as when spacer molecules suspended in solvent are being printed. 
         [0091]    A head manifold  630  may supply fluid to each of the nozzles of the printhead module  300 . The head manifold  630  may include a supply port  634  and a return port  638 . An output of reservoir  620  is connected to a recirculation valve  642 . The recirculation valve  642  directs fluid from the reservoir either to the recirculation port  612  or to an ink valve  646 . 
         [0092]    When the recirculation valve  642  directs ink to the recirculation port  612 , ink can continuously flow into the reservoir  620  and out of the recirculation port  612 . This prevents molecules held in suspension from settling when the printhead module  300  is not printing. For example, recirculation may be used while substrates are loaded and unloaded. 
         [0093]    The ink valve  646  selectively allows ink to reach the supply port  634 . In various implementations, the ink valve  646  may be absent. The ink valve  646  may also receive solvent from a solvent valve  650 . The solvent valve  650  selectively allows solvent from the solvent port  608  to reach the ink valve  646 . Solvent from the solvent port  608  may be used to clean the nozzles to correct printing problems, while solvent from the ink/solvent port  604  may be used to flush the reservoir  620  in preparation for printing with new ink. A return valve  654  selectively allows fluid from the return port  638  to leave the waste port  610 . The return valve  654  may also open to allow air to quickly escape from the head manifold  630 . 
         [0094]    The pressure/vacuum port  616  is connected to the reservoir  620 . Pressure may be applied to force solvent and/or ink through the supply port  634  into the head manifold  630 , such as when cleaning the head manifold  630 , cleaning the nozzles, and/or replacing one fluid with another. For example only, a pressure of 5 psi may be applied for one second to produce a puff of ink from the nozzles. Pressure may also be used to eject ink onto a blotting material. The blotting material may be wiped across the face of the nozzle to remove contamination and/or dried ink. For example only, 1.5 milliliters of ink may be deposited on the blotting material. 
         [0095]    When filling the head manifold  630 , the nozzles may be pulsed at 5 kHz to agitate the ink and allow small channels in the head manifold  630  and the nozzles to fill with ink faster. A small amount of vacuum may be applied to the reservoir  620  to counteract the static head of the fluid, which may be provided from a location above the reservoir  620 . For example, a vacuum may be pulled to counteract approximately 8 inches of static head. 
         [0096]    In addition, a negative miniscus may be formed at the nozzles by applying further negative pressure to the reservoir  620 . This negative pressure may be two inches of vacuum, for example. A negative miniscus may allow droplets to be formed more evenly and at a more deterministic time. A filter assembly  660  may remove contaminants from the fluid prior to the fluid reaching the head manifold  630 . For example only, the filter assembly  660  may be located between the ink valve  646  and the supply port  634 . 
         [0097]    In various implementations, ink may be recirculated through the head manifold  630 . In such a case, the recirculation valve  642  may be located between the return port  638  and the return valve  654 . During recirculation, the recirculation valve  642  would route fluid from the return port  638  to the recirculation port  612 . Otherwise, the recirculation valve  642  would route fluid from the return port  638  to the waste port  610 . In such an implementation, the solvent valve  650  may be located between the solvent port  608  and the supply port  634 . Outputs of the ink valve  646  and the solvent valve  650  would therefore join at the supply port  634 . 
         [0098]    Referring now to  FIG. 10 , a perspective view of the printhead module  300  is shown. The filter assembly  660  may be removable so that the filter can be cleaned and/or replaced. The filter assembly  660  may be part of a lower manifold  664 . The lower manifold  664  may serve as a mounting surface for three valves, such as the ink valve  646 , the solvent valve  650 , and the recirculation valve  642 . 
         [0099]    The lower manifold  664  may provide channels to route fluid between the connected valves. For example, the lower manifold  664  may implement some of the fluid routes shown in  FIG. 9 . An upper manifold  670  may provide a similar function. The upper manifold  670  may serve as a mounting surface for the shutoff valve  624  and the return valve  654 . In addition, the upper manifold  670  may receive fluid lines from the fluid port  360 , which may be a quick disconnect port. The reservoir  620  may be connected between the upper manifold  670  and the lower manifold  664 . The level sensors  622 ,  624 , and  626  may wrap partially or fully around the reservoir  620 . 
         [0100]    The broad teachings of the disclosure can be implemented in a variety of forms. Therefore, while this disclosure includes particular examples, the true scope of the disclosure should not be so limited since other modifications will become apparent to the skilled practitioner upon a study of the drawings, the specification, and the following claims.