Patent Application
20100245415
This disclosure relates generally to imaging devices having multiple printhead assemblies, and more particularly, to the alignment of printheads in such imaging devices.
Some ink printing devices use a single printhead, but many use a plurality of printheads to increase the rate of printing. For example, four printheads may be arranged in two rows with each row having two printheads. The two printheads in the first row are separated by a distance corresponding to the width of a printhead. The first printhead in the second row is positioned at a location corresponding to the gap between the two printheads in the first row and the last printhead in the second row is separated from the first printhead in the second row by a distance corresponding to the width of a printhead. This arrangement is called a staggered full width array (SFWA) printhead assembly and an embodiment of a SFWA assembly is shown in
Synchronizing the passage of an image receiving member with the firing of the inkjets in the printheads enables a continuous ink image to be formed across the member in the direction perpendicular to the direction of member passage. Alignment of the ink drops ejected by the printheads, however, may not be as expected. Each printhead in the printhead assembly has six degrees of positional freedom, three of which are translational and three of which are rotational. The printheads need to be precisely aligned to provide a smooth transition from the ink drops ejected by one printhead to the ink drops printed by the other printheads in the assembly. Misalignment of printheads may occur from, for example, printheads failing to meet manufacturing tolerances, thermal expansion of the printhead and associated parts of the printer, vibration of the printhead, or the like.
Misalignments between printheads in three of the six degrees of freedom may be categorized as roll or stitch errors. Roll errors can occur when a printhead rotates about an axis normal to the imaging member. Roll error causes a skew in the rows of ink drops ejected by the printhead relative to the imaging member. This skew may be noticeable at the interface between two printheads and may cause an objectionable streak. Stitch errors occur from shifts in one printhead compared to another printhead. Y-axis stitch errors arise from shifts that cause ink drop rows from the shifted printhead to land above or below the ink drop rows ejected by preceding or following printhead. X-axis stitch errors arise from shifts that cause the first and last drops in the rows printed by the shifted printhead to be too close or too far from the last and first drops, respectively, in the rows printed by the preceding and following printheads, respectively. Of course, if the shifted printhead is the first or last printhead in the assembly, shifting of the first drop or the last drop in the rows, respectively, does not occur at an intersection with another printhead. Thus, aligning printheads in a printhead assembly with sufficient accuracy to allow high image quality is desired.
One previously known printhead assembly included printheads that were attached to a mounting of a translation carriage. The printheads have flanges extending from them that are acted on by cams to move the printhead for alignment. This type of alignment system requires the printheads to be formed with extensions. Additionally, one printhead in the assembly was deemed the reference printhead and alignment of the other printheads was conducted with reference to the ink drops ejected by the reference printhead. Moreover, if a printhead was replaced in a printhead assembly, the printhead required alignment as manufacturing tolerances for the printhead extensions may position the printhead on the translation carriage differently than the extensions on the replaced printhead. Because printheads may be replaced during service calls once a printer is put into operation, easier and faster printhead replacement with minimal impact on printhead alignment is desirable.
A system enables a printhead to be replaced easily and aligned independently of other printheads in a printhead assembly. The system includes a printhead configured to eject ink onto an image receiving member, a plate to which the printhead can be rigidly mounted and selectively removed, and a translation carriage to which the plate is rigidly mounted and locked into position with reference to a distance between the plate and the image receiving member (Z position), a pitch position, and a yaw position, the translation carriage being coupled to an actuator for movement of the translation carriage, plate, and printhead in a cross-process direction across the image receiving member.
The system may be implemented in a printer to enable replacement of printheads in the printer without disrupting the Z position, pitch position, and yaw position of the plate. The printer includes an image receiving member, two printheads configured to eject ink onto the image receiving member, two plates, each plate having one printhead rigidly mounted to the plate, and a translation carriage to which the two plates are rigidly mounted and each plate being locked into position with reference to a distance between the plate and the image receiving member (Z position), a pitch position, and a yaw position, the translation carriage being coupled to an actuator for movement of the translation carriage, plate, and printhead in a cross-process direction across the image receiving member and the plates being configured to enable the printheads to be removed from the plates without disturbing the Z position, pitch position, and yaw position of the plates.
A method enables a printhead to be replaced and aligned independently of other printheads in a printhead assembly. The method includes rigidly mounting a plate to a translation carriage that is coupled to an actuator for movement of the translation carriage and plate in a cross-process direction across an image receiving member in a printer, fixing a distance between the plate and the imaging member, a yaw orientation of the plate, and a pitch orientation of the plate, rigidly mounting a printhead to the plate, and controlling at least one actuator coupled to at least one movable member that engages the plate to adjust one of a X stitch position and a roll angle of the plate with reference to the image receiving member.
The foregoing aspects and other features of a system that facilitates printhead replacement with minimal impact on printhead alignment and enables independent alignment of the printhead in at least two degrees of freedom of movement are explained in the following description, taken in connection with the accompanying drawings.
For a general understanding of the environment for the system and method disclosed herein as well as the details for the system and method, reference is made to the drawings. In the drawings, like reference numerals have been used throughout to designate like elements. As used herein, the word “printer” encompasses any apparatus that performs a print outputting function for any purpose, such as a digital copier, bookmaking machine, facsimile machine, a multi-function machine, or the like. Also, the description presented below is directed to a system that enables positional correction for a printhead in two degrees of freedom of movement that is independent of any adjustments made to any other printhead in a printhead assembly.
Referring now to
The high-speed phase change ink image producing machine or printer 10 also includes a phase change ink delivery subsystem 20 that has at least one source 22 of one color phase change ink in solid form. Since the phase change ink image producing machine or printer 10 is a multicolor image producing machine, the ink delivery system 20 includes four (4) sources 22, 24, 26, 28, representing four (4) different colors CYMK (cyan, yellow, magenta, black) of phase change inks. The phase change ink delivery system also includes a melting and control apparatus (not shown) for melting or phase changing the solid form of the phase change ink into a liquid form. The phase change ink delivery system is suitable for supplying the liquid form to a printhead system 30 including at least one printhead assembly 32. Since the phase change ink image producing machine or printer 10 is a high-speed, or high throughput, multicolor image producing machine, the printhead system 30 includes multicolor ink printhead assemblies and a plural number (e.g., two (2)) of separate printhead assemblies 32 and 34 as shown.
As further shown, the phase change ink image producing machine or printer 10 includes a substrate supply and handling system 40. The substrate supply and handling system 40, for example, may include sheet or substrate supply sources 42, 44, 48, of which supply source 48, for example, is a high capacity paper supply or feeder for storing and supplying image receiving substrates in the form of cut sheets 49, for example. The substrate supply and handling system 40 also includes a substrate handling and treatment system 50 that has a substrate heater or pre-heater assembly 52. The phase change ink image producing machine or printer 10 as shown may also include an original document feeder 70 that has a document holding tray 72, document sheet feeding and retrieval devices 74, and a document exposure and scanning system 76.
Operation and control of the various subsystems, components and functions of the machine or printer 10 are performed with the aid of a controller or electronic subsystem (ESS) 80. The ESS or controller 80, for example, is a self-contained, dedicated mini-computer having a central processor unit (CPU) 82 with electronic storage 84, and a display or user interface (UI) 86. The ESS or controller 80, for example, includes a sensor input and control circuit 88 as well as a pixel placement and control circuit 89. In addition, the CPU 82 reads, captures, prepares and manages the image data flow between image input sources, such as the scanning system 76, or an online or a work station connection 90, and the printhead assemblies 32 and 34. As such, the ESS or controller 80 is the main multi-tasking processor for operating and controlling all of the other machine subsystems and functions, including the printhead cleaning apparatus and method discussed below.
The controller 80 may be implemented with general or specialized programmable processors that execute programmed instructions. The instructions and data required to perform the programmed functions may be stored in memory associated with the processors or controllers. The processors, their memories, and interface circuitry configure the controllers to perform the processes that enable the generation and analysis of printed test strips for the generation of firing signal waveform adjustments and digital image adjustments. The processes implemented by one or more controllers also enable actuators to be controlled selectively to align one or more of the printheads. These components may be provided on a printed circuit card or provided as a circuit in an application specific integrated circuit (ASIC). Each of the circuits may be implemented with a separate processor or multiple circuits may be implemented on the same processor. Alternatively, the circuits may be implemented with discrete components or circuits provided in VLSI circuits. Also, the circuits described herein may be implemented with a combination of processors, ASICs, discrete components, or VLSI circuits.
In operation, image data for an image to be produced are sent to the controller 80 from either the scanning system 76 or via the online or work station connection 90 for processing and output to the printhead assemblies 32 and 34. Additionally, the controller determines and/or accepts related subsystem and component controls, for example, from operator inputs via the user interface 86, and accordingly executes such controls. As a result, appropriate color solid forms of phase change ink are melted and delivered to the printhead assemblies. Additionally, pixel placement control is exercised relative to the imaging surface 14 thus forming desired images per such image data, and receiving substrates are supplied by any one of the sources 42, 44, 48 and handled by substrate system 50 in timed registration with image formation on the surface 14. Finally, the image is transferred from the surface 14 and fixedly fused to the image substrate within the transfix nip 18.
To evaluate the position and alignment of the printheads in a printhead assembly, the controller 80 may execute programmed instructions that enable the printer to implement a plurality of processes for generating positional correction data to address the roll and/or stitch errors, and evaluate the application of the correction data and the need to continue further error processing. In general, these processes receive captured image data of a test pattern printed on an image receiving member. The controller may implement an image evaluator that processes captured image data and enables the controller to generate positional correction data for alignment of the printheads. In order to enable one printhead in the printhead assembly to be adjusted in more than one degree of freedom without reference to alignment of another printhead in the assembly, a carrier plate has been developed that enables simplification of the printhead configuration and facilitates selective replacement of a printhead in the assembly. An implementation of the carrier plate and its use in an alignment method is discussed below.
Referring now to
As described in more detail below, each printhead is rigidly mounted to a carrier plate that is rigidly mounted to a translation carriage. The carrier plate is coupled to an actuator 220 for selective movement of the carrier plate and the printhead carried by the plate. The actuator is coupled to the carrier plate through gear trains, translational, or rotational linkages to move the plates and the printheads mounted to them. The actuator 220 responds to signals from the controller 80. A portion of the instructions executed by the controller 80 implement an image evaluator 210 that processes captured image data of test patterns to generate positional correction data for roll and stitch errors. Other processes implemented by the controller 80 convert the positional correction data to stepper motor pulses or other control signals for manipulating the actuator 220 and the printheads 232, 234, 236, and 238.
The ejecting face of each printhead 232, 234, 236, and 238 includes a plurality of nozzles 243, 247, 245, 249, respectively, that may be arranged in rows that extend in the cross-process direction (X axis) across the ejecting face. The spacing between each nozzle in a row is limited by the number of ink jets that can be placed in a given area in the printhead. To enable the printing of drops onto a receiving substrate at distances that are closer in the cross-process direction than the distance between adjacent nozzles in a row, the nozzles in one row of a printhead are offset in the cross-process direction (along the X axis) from the nozzles in at least some of the other rows in the printhead. The offset between nozzles in adjacent rows enables the number of ink drops in a printed row to be increased by actuating the inkjets in a subsequent row to eject ink as the drops ejected by a previous row arrive. Of course, other arrangements of nozzles are possible. For example, instead of having offset rows of nozzles, the nozzles may be arranged in a grid in the ejecting face with linear rows and columns of nozzles. Each printhead in an assembly may be configured to emit ink drops of each color utilized in the imaging device. In such a configuration, each printhead may include one or more rows of nozzles for each color of ink used in the imaging device. In another embodiment, each printhead may be configured to utilize one color of ink so the jets of the printhead eject the same color of ink.
As discussed above, alignment of a printhead with respect to the receiving substrate and with respect to other printheads in the imaging device may present image quality issues. The possible degrees of movement for a printhead are now discussed with reference to
To facilitate independent alignment of printheads in a printhead assembly and enable more efficient replacement of printheads in the assembly, a carrier plate has been developed. The arrangement of the carrier plate and other components of a printer are now discussed with reference to
The features of the carrier plate that enable independent alignment adjustment in some of the six degrees of freedom of movement are shown in
With further reference to
As shown in the rear view of the carrier plate 312 depicted in
Again with reference to
The calibration procedure is now discussed with further reference to
The factory calibrated carrier plate 312 has a high level of accuracy that enables any printhead manufactured to independent specifications to be installed on any carrier plate. Because the carrier plate is installed with such accuracy, printheads may be replaced in the field during the life of the printer without requiring any adjustments in the Z, pitch, or yaw directions. The actuated adjustments of the X stitch and roll angle positions that can be accomplished as described above enable a replacement printhead to integrate seamlessly into a multiple printhead array without requiring operator intervention.
In operation, the controller of a printing system is configured with programmed instructions for implementing the roll and stitch positional displacement correction data adjustment processes. During the life of the imaging system, the controller selects and operates the processes in accordance with a schedule or as they are activated manually. The processes generate test patterns, capture images of the test patterns, and evaluate the captured image data of the test patterns, to generate roll and stitch positional correction data. These data may be used to generate control signals for one or more actuators that are coupled to lead screws that contact the carrier plates as described above. The actuator turns the lead screws to adjust the roll and the position of the printhead in the cross-process direction. Adjustments in the Y axis position are adjusted by measuring an error in the Y position of ejected ink drops and compensating for these errors by either adjusting the timing of the firing signals to eject ink drops from ink jets as the image receiving member passes by the printhead.
It will be appreciated that various of the above-disclosed and other features, and functions, or alternatives thereof, may be desirably combined into many other different systems or applications. For example, cams may be used as displaceable members to contact the carrier plate and move the carrier plate in two directions with the actuator rotating in a single direction. Various presently unforeseen or unanticipated alternatives, modifications, variations, or improvements therein may be subsequently made by those skilled in the art, which are also intended to be encompassed by the following claims.
