The present invention relates generally to ink jet printing, and more specifically, to aligning and installing components of a continuous ink jet printhead.
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.
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.
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.
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.
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.
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.
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.
In the detailed description of the preferred embodiments of the invention presented below, reference is made to the accompanying drawings, in which:
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.
Referring to
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.
Referring to
One type of kinematic alignment feature, known as a “2-2-2 mount” or a “three-groove mount” is shown in
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.
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.
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'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't be elastically deformed by the contact forces.
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'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'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.
Referring back to
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'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.
Referring back to
Referring to
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.
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.
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.
Referring to
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
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.
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Number | Date | Country | |
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20090295878 A1 | Dec 2009 | US |