Abstract:
A mechanism for aligning the jetting module in a continuous inkjet printhead and for making fluid and electrical connections to the jetting module without compromising the alignment is disclosed. A mechanism to aid in installing the jetting module is also disclosed.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates generally to ink jet printing, and more specifically, to aligning and installing components of a continuous ink jet printhead. 
       BACKGROUND OF THE INVENTION 
       [0002]    Ink jet printing systems are known in which a printhead includes a jetting module that defines one or more rows of nozzles in a nozzle plate which receive a recording fluid, such as a water-based ink, from a pressurized fluid supply manifold and eject the ink in rows of parallel streams. Such printing systems achieve image production by allowing drops which are to be printed to contact the recording medium and deflecting drops that are not to be printed to a drop catcher device. 
         [0003]    Conventional methods for assembling the components of a printhead include locating the jetting module or drop generator with the aid of an assembly fixture, then using an adhesive such as epoxy to fasten it in place. A charge plate/catcher assembly is then aligned to the drop generator using external adjustment fixtures. Once a proper alignment is achieved, the charge plate/catcher assembly is fastened with screws or adhesive to the common frame holding the drop generator. 
         [0004]    Traditional systems allow replacement of a printhead by creating field replaceable units which includes a jetting module, a charge plate, and a catcher. Some field replaceable units also include fluid system components such as valves and pressure and temperature sensors, and support electronics for the inkjet module. As the number of jets to be controlled increased, it became impractical to connect each charge electrode in the field replaceable printhead to the controlling charge driver electronics that were not part of the field replaceable printhead. In such printheads, it became preferable to include charge driver electronics in the field replaceable unit. As the charge plate was also subject to failure, such field replaceable units were preferable because, in addition to the jetting module, the charge plate was also field replaceable. 
         [0005]    Unfortunately, existing assembly and alignment methods have several drawbacks. For example, using an adhesive increases assembly time because it takes several hours for the adhesive to cure and using epoxy is problematic because epoxy is sensitive to heat and humidity. Additionally, the final fastening of the charge plate/catcher assembly alters the alignment, usually requiring realignment. 
         [0006]    High costs of shipping make it advantageous to replace only the jetting module rather then the entire printhead. Additionally, jetting modules providing higher resolution require high precision alignment. Accordingly, there is a need for a jetting module to be a field replaceable unit that an be properly aligned during installation. 
       SUMMARY OF THE INVENTION 
       [0007]    According to a feature of the present invention, an apparatus for installing a jetting module in a printhead includes a drop deflection mechanism, a catcher, a printhead frame including a first set of mounting features, a jetting module including a second set of mounting features that correspond to the first set of mounting features of the printhead frame, and a coupling frame including a second set of fluid and electrical connections that correspond to a first set of fluid and electrical connections of the jetting module. The coupling frame provides a force to maintain contact between the first and second sets of mounting features after the first and second sets of mounting contact each other. The coupling frame also provides the force to maintain contact between the first and second sets of fluid and electrical connections after the first and second sets of fluid and electrical connections contact each other. 
         [0008]    According to another feature of the present invention, a method for mounting a jetting module in a printhead including a drop deflection mechanism and a catcher includes providing a printhead frame including a first set of mounting features, providing a jetting module including a second set of mounting features that correspond to the first set of mounting features of the printhead frame, providing a coupling frame including a second set of fluid and electrical connections that correspond to a first set of fluid and electrical connections of the jetting module, causing the first and second sets of mounting features to contact each other, causing the first and second sets of fluid and electrical connections to contact each other, and providing a force to maintain contact between the first and second sets of mounting features, and between the first and second sets of fluid and electrical connections. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    In the detailed description of the preferred embodiments of the invention presented below, reference is made to the accompanying drawings, in which: 
           [0010]      FIGS. 1A and 1B  are schematic side views of a printhead including a jetting module, drop deflection mechanism and catcher in a printhead frame; 
           [0011]      FIG. 2  is an inverted isometric view of a jetting module and first and second mounting features; 
           [0012]      FIG. 3  is an isometric view of the printhead showing the carriages and actuators for installing the jetting module and making fluid and electrical connections to it; 
           [0013]      FIG. 4  is a side view of the printhead with the jetting module lowered into an aligned position without fluid and electrical connections having been made; 
           [0014]      FIG. 5  is an exploded view of portions of the printhead showing fluid and electrical connections; and 
           [0015]      FIG. 6  is a front view of a coupling frame showing electrical connections. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0016]    The present description will be directed in particular to elements forming part of, or cooperating more directly with, apparatus in accordance with the present invention. It is to be understood that elements not specifically shown or described may take various forms well known to those skilled in the art. 
         [0017]    Referring to  FIG. 1A , a printhead  10  according to the present invention includes a jetting module  18 , a drop deflection mechanism  12 , a catcher  14 , and a frame  20 . The drop deflection mechanism can be a gas flow deflection mechanism, such as is described in U.S. Pat. No. 6,588,888, an electrostatic deflection mechanism, such as is described in U.S. Pat. No. 4,636,808, or other drop deflection mechanisms known in the art. In  FIG. 1 , the invention the drop deflection mechanism is a gas flow deflection mechanism, including of a positive gas flow duct  15  and a negative gas flow duct  17 . Positive gas flow duct  15  is connected to a fan or blower that produces a positive pressure in the gas flow duct from which a flow of gas is directed across the trajectories of drops  19  formed by the jetting module. Negative gas flow duct  17  is connected of a vacuum source, producing a vacuum or negative pressure in the gas flow duct. The suction of gas into duct  17  produces a flow of gas across the drop trajectories  19 . Typically, the placement of the blower, vacuum source, and the gas flow duct extensions that connect the positive and negative gas flow ducts to the blower and vacuum source relative to the jetting module is controlled by the amount of available space around printhead  10 . Catcher  14  is positioned under the negative gas flow duct  17 , but can alternatively be located under the positive gas flow duct. 
         [0018]    Operation of the printhead  10  depends critically on the alignment of catcher  14  and drop deflection mechanism  12  relative to jetting module  18 . The printhead frame  20  includes a first set of mounting features  22 , and at least one of the drop deflection mechanism  12  and the catcher  14  is affixed to the printhead frame  20 . In a preferred embodiment, the catcher  14  and at least a portion of the drop deflection mechanism  12  are assembled together, and this catcher-drop deflector assembly is affixed to the printhead frame  20 . The jetting module  18  includes a second set of mounting features  30  that correspond to the first set of mounting features  22  of the printhead frame  20 . The second set of mounting features  30  can be integrally formed in the jetting module  18 . The jetting module  18  also includes a first set of fluid and electrical connections  50 . 
         [0019]    Referring to  FIG. 1B , the printhead frame  20  includes a first set of mounting features  22 , a carriage  24  for installing a jetting module  18 , and a coupling frame  26  supported by a second carriage  28  to enable making fluid and electrical connections to the jetting module  18 . The mounting features  22  are preferably kinematic alignment features. These kinematic alignment features allow the jetting module  18  to be precisely positioned in the printhead  10 . 
         [0020]    One type of kinematic alignment feature, known as a “2-2-2 mount” or a “three-groove mount” is shown in  FIG. 2 .  FIG. 2  shows a jetting module, in an inverted position, to show the three V-groove alignment features  30 . Spherical mounting features  22  are shown in each of the V-grooves. When the spacing of the three spherical mounting features  22  is fixed by some structure (which has been hidden in  FIG. 2  to better show the engagement of the mounting features), the three V-groove mounting features  30  in the jetting module  18  can engage the three spherical mounting features (each groove contacting a sphere at two points) in only one position. When the jetting module  18  is separated from the spherical mounting features  22 , the jetting module can be returned to the original position to high precision by again having the mounting features  30  engage the mounting features  22 . 
         [0021]    While the 2-2-2 mount is shown in the illustrated embodiments, other kinematic mount configurations, such as a “3-2-1 mount” can be employed. In a 3-2-1 mount, also known as a “cone, groove, and flat” mount, one set of alignment features is a system which includes three balls, and the second set of alignment features includes a cone shape, which constrains 3 degrees of freedom, a v-groove, which constrains 2 degrees of freedom, and a flat, which constrains one degree of freedom. In this way all six degrees of freedom can be defined. 
         [0022]    The use of kinematic mount features can provide not only reproducible alignment of printhead components, such as the alignment of the jetting module  18  to the drop deflection mechanism  12 , but they can be employed to enable interchangeability of parts. In the jetting module production process, fixtures that engage the mounting features  30  of the jetting module can be used to align the nozzle array  32  of nozzle plate  34  with high precision to the alignment features  30  of the jetting module  18 . The nozzle plate  34  can then be secured in that aligned position using an epoxy or other adhesive bonding process. Similarly, fixtures that engage the mounting features  22  of the printhead frame  20  can be used to align the catcher-drop deflector assembly of the printhead  10  with high precision relative to the first set of mounting features  22 . In this manner, the nozzle array  32  of the nozzle plate  34  attached to the jetting module  18  and the catcher-drop deflector assembly are each precisely aligned relative to the respective kinematic mounting features, so engagement of the kinematic features of the jetting modules  18  with the kinematic features of the printhead frame  20  produces consistent alignment of the nozzle array  32  to the gas flow ducts  15 ,  17  and the catcher  14 . 
         [0023]    The consistency of alignment of the critical printhead components, for example, nozzle array  32 , drop deflection mechanism  12 , and catcher  14 , depend on the consistency of the mounting features  22 ,  30 . The spherical mounting features  22  are therefore preferably fabricated from a material, for example, a ceramic or hardened metallic material, that won&#39;t be elastically deformed by the contact forces. It is also desirable to harden the contact surfaces of V-groove mounting features  30  that are machined into the jetting module. Alternatively, the contact surfaces of the grooves can comprise inserts of a material, such as a hardened metal or ceramic, that won&#39;t be elastically deformed by the contact forces. 
         [0024]    In some embodiments, the mounting features  22  are located in three holes of printhead frame  20  that are machined precisely by jig grinding. Three spheres are then press fit into these holes. Alternatively, the mounting features  22  can be truncated spheres or hemispheres rather than complete spheres that are secured in the three holes of the printhead frame  20 . As the mounting features  22  that are used to align the jetting module  18  are also used to align deflection mechanism  12  and catcher  14  to the printhead frame  22 , small variations in the placement of the mounting features  22  from one printhead frame  20  to another don&#39;t produce alignment errors between the nozzle array  32  of the jetting module  18  and the deflection mechanism  12  and catcher  14  secured to the printhead frame  20 . Similarly, small variations in the mounting features  30  of the jetting module  18  don&#39;t produce alignment errors of the between the nozzle array  32  of the jetting module  18  and the catcher-drop deflector assembly as the same mounting features  30  are used both for the locating the nozzle array  32  on the jetting module  18  and locating the jetting module  18  in the printhead frame  20 . 
         [0025]    Referring back to  FIG. 1B , in some embodiments, the printhead frame  20  includes a third set of mounting features  35  that are precisely aligned to the mounting features  22 . This third set of mounting features  35  enables the printhead  10 , and more significantly the nozzle array  32 , to be aligned with precision to other printer components, such as paper guides or other printheads. 
         [0026]    While the mounting features  22 ,  30  of the jetting module  18  and the printhead frame  20  enable the jetting module  18  to be aligned with precision to the deflection mechanism  12  and catcher  14 , alignment integrity can be compromised if the jetting module  18  isn&#39;t allowed to settle into proper engagement with the alignment features  22  of the printhead frame  20 . The printhead  20  therefore includes an carriage  24  to enable the jetting module  18  to properly engage the alignment features  22  of the printhead frame  20 . 
         [0027]    Referring back to  FIG. 1B , carriage  24  of the printhead frame  20  is located on guide posts  36  that allow the carriage  24  to move vertically, substantially perpendicular to the plane defined by the mounting features  22 . The carriage includes a pocket  38  into which the jetting module  18  can be inserted when the carriage is in the up position as shown in  FIG. 1B . The pocket  38  is shaped to receive the jetting module  18 , and supports the jetting module  18  before lowering the jetting module  18  into position to engage the first set of mounting features  22  of the printhead frame  20 . The pocket  38  serves to establish the location of the jetting module  18  sufficiently to enable the second set of mounting features  30  to contact the first set of mounting features  22 , while providing sufficient clearance to allow the jetting module  18  to shift laterally as needed to properly engage the first set of mounting features  22  of printhead frame  20 . 
         [0028]    Referring to  FIGS. 1B ,  3  and  4 , the carriage  24  is moved up and down on the guide posts  36  by an actuator  40 . Actuator  40  may be a stepper motor, a solenoid, or any other actuator known to those in the art, so long as it operates to cause relative movement of the jetting module  18  to bring the first set of mounting features  22  of the printhead frame  20  and second set of mounting features  30  of the jetting module  18  into contact with each other. Actuator  40  causes the carriage  24  to be lowered and the second set of mounting features  30  of jetting module  18  are brought into contact the first set of mounting features  22  of the printhead frame  20  (shown in  FIG. 4 ). The actuator  40  continues to lower the carriage  24 , and the jetting module  18  lifts off from the pocket  38  allowing the jetting module  18  to shift laterally so that first set of mounting features  22  fully engages the second set of mounting features  30 . As the carriage  24  continues to be lowered, load management features  42  begin to apply a load to the jetting module  18  to maintain secure alignment of the jetting module  18  with the printhead frame  20 . In some embodiments, load management features  42  include spring plungers, though other load management features can be used, provided they do not produce an over-constraint to the system. The forces applied by each of the load management features  42  to the jetting module  18  are substantially perpendicular to the plane defined by the mounting features  22  to maintain the integrity of the alignment. The forces applied by the load management features  42  are applied at locations between the locations of the three mounting features  22  or  30  so as not to produce a torque on the jetting module  18  that could cause one of the three mounting features  22  or  30  to fail to fully engage the mating features  30  or  22  and thereby compromise the integrity of the alignment. 
         [0029]    A second carriage  28  is also located on the guide posts  36 . This second carriage  28  is moved up and down on the guide posts  36  by second actuator  44 . A coupling frame  26  is attached to the second carriage  28  through a biasing mechanism  46 . 
         [0030]      FIG. 5  provides an exploded view of portions of the printhead  10 . The carriage  24  for locating the jetting module  18  has been omitted to enable the jetting module  18  and the fluid and electrical connects  50  to be seen more clearly. As shown in  FIG. 5 , the coupling frame  26  includes a second set of fluid and electrical connections  48  that are designed to mate with a first set of fluid and electrical connections  50  that are a part of the jetting module  18 . After the carriage  24  has lowered the jetting module  18  into place so that the first and second set of mounting features  22 ,  30  are fully engaged, second actuator  44  is employed to lower the second carriage  28 and the attached coupling frame  26 . Alignment pins  52  on the coupling frame  26  engage alignment holes  52  in the jetting module  18  to guide the coupling frame so that the appropriate fluid and electrical connections are made between the first and second sets of fluid and electrical connections  48  and  32 . 
         [0031]    As a result of the force on the coupling frame  26  provided by the biasing mechanism  46 , the coupling frame  26  provides a force to maintain contact between the second set of mounting features  30  of the jetting module and the first set of mounting features  22  of the printhead frame after the second set of mounting features  30  of the jetting module  18  and the first set of mounting features  22  of the printhead frame  20  contact each other. The force provided by the coupling frame  26  also serves to maintain contact between the second set of fluid and electrical connections  48  of the coupling frame  26  and the first set of fluid and electrical connections  50  of the jetting module  18  after the second set of fluid and electrical connections  48  of the coupling frame  26  and the first set of fluid and electrical connections  50  of the jetting module  18  contact each other. 
         [0032]    The first set of fluid and electrical connections  50  on the jetting module  18  can include one or more fluid ports  56  and an electrical contact board  58 . The second set of fluid and electrical connectors  30  on the coupling frame  26  can include corresponding fluid ports  60  and an electrical contact board  62  having electrical contacts  64 . Preferably, the fluid ports  55 ,  60  of the jetting module  18  and the coupling frame  26  are of a drip resistant type, preventing any fluid from dripping from the fluid ports  56 ,  60  while a jetting module  18  is being replaced. To prevent the fluid port connection from applying any lateral loads to the jetting module  18 , o-ring face seals are used on at the fluid port  56  on the jetting module  18  as well as on the fluid port  56  mating port in the second set of fluid and electrical connections  48  on the coupling frame  26 . Additionally, the mating fluid port in the second set of fluid and electrical connections  48  can be float mounted to the coupling frame  26  to ensure that proper sealing is achieved without providing any lateral forces. Likewise, the electrical contact board  58  in the first set of fluid and electrical connections  50  can be float mounted to the jetting module  18 . 
         [0033]    Referring to  FIG. 6  and back to  FIG. 5 , in some embodiments, electrical contacts  64  can be spring pin contacts that are attached to electrical contact board  62 . This type of electrical contact  64  is commercially available from Interconnect Devices, Inc., Kansas City, Kans. Such electrical contacts  64  can vary in length as shown so electrical contacts  64  can make and break electrical contact with the corresponding contacts on the electrical contact board in a prescribed order so that the contacts to first make contact while establishing electrical connection are the last ones to break contact when such a connection is to be broken. Through the use of such first make-last break electrical connections, the printhead  10  can be made to safely replace a jetting module while electrical power is still supplied to the electrical contact board  62 . Other types of first make-last break connections can be used, as can other types of electrical contacts in general, provided that they do not over constrain the system and therefore compromise the integrity of the jetting module alignment. 
         [0034]    Coupling frame  26  is attached to the second carriage  44  by a biasing mechanism  46 . Biasing mechanism  46  can be a spring, though other types of biasing mechanisms can be used, provided they are capable of providing a force to the jetting module  18  after the second set of mounting features  30  of the jetting module  18  and the first set of mounting features  22  of the printhead frame  20 . The force provided by the biasing mechanism  46  through the coupling frame  26  is substantially perpendicular to the plane defined by the first set of mounting features  22 . The biasing mechanism  46  provides sufficient compliance to the enable the coupling frame to rotate and shift laterally to enable all the fluid and electrical connections to be made without producing significant torques or lateral forces that would compromise the integrity of the alignment. To reduce the risk of the jetting module  18  shifting as the fluid and electrical connections are made it is preferable that load managing features  36  provide a force to the jetting module  18  before the coupling frame  26  begins to contact the jetting module  18 . The second carriage  28  with the attached coupling frame  26  are lowered into position by an second actuator  44 . This actuator can be a stepper motor, a solenoid, or any other actuator known to those in the art. Additionally, this actuator can be the same actuator as actuator  40 , or it can be a second actuator as is shown in  FIG. 3 . Other embodiments can include limit switches and stall-sensing circuitry to enable the actuator to be stopped when the jetting module  18  is bearing the entire load, though other methods of controlling change in position can be used. The use of limit switches and stall-sensing circuitry allows the mechanism to recalibrate itself in the event of an unforeseen power failure during printhead installation. 
         [0035]    The invention has been described in detail with particular reference to certain preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the scope of the invention. 
       Parts List  
       [0000]    
       
           10  Printhead 
           12  Drop deflection mechanism 
           14  Catcher 
           15  Positive gas flow duct 
           17  Negative gas flow duct 
           19  Drop trajectories 
           18  Jetting module 
           20  Printhead frame 
           22  First set of mounting features 
           24  Carriage 
           26  Coupling frame 
           28  Second carriage 
           30  Second set of mounting features 
           32  Nozzle array 
           34  Nozzle plate 
           35  Third set of mounting features 
           36  Guide posts 
           38  Pocket 
           40  Actuator 
           42  Load management features 
           44  Second actuator 
           46  Biasing mechanism 
           48  Second set of fluid and electrical connections 
           50  First set of fluid and electrical connections 
           52  Alignment pin 
           54  Alignment hole 
           56  Fluid ports 
           58  Electrical contact board 
           60  Fluid ports 
           62  Electrical contact board 
           64  Electrical contacts