Patent Application
20150022588
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. For example, seven printheads may be arranged in two rows with one row having three printheads and one row having four printheads. The printheads in the first row are separated by gaps having a distance approximately equivalent to the width of a printhead. The printheads in the second row are positioned to align with the gaps between the printheads in the first row. This arrangement is called a staggered full width array (SFWA) printhead assembly and an exemplary 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 up to three degrees of positional freedom. 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.
The possible degrees of movement for a printhead are now discussed with reference to
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 arise when the printhead shifts in the process (Y) direction or the cross-process (X) direction. These errors result in misalignment of drops from one printhead with the drops of another printhead.
In the case of Y-direction stitch errors, the drops in the rows of one printhead are shifted up or down from the drops in the rows of a neighboring printhead. In the case of X-direction stitch errors, the first and last drops in the rows printed by the shifted printhead are too close or too far from the last and first drops, respectively, in the rows printed by the neighboring printheads. 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.
To adjust the printhead position to correct for printhead misalignments, one previously known printhead assembly uses a right-angle lever arm that pivots to push a plate to which a printhead is mounted. The movement of the printhead in this assembly is limited by the length of the lever arm. Additionally, movement of the lever arm may produce backlash and compensation for this backlash must be incorporated in the movement of the arm to properly adjust the position of the printhead. Printhead adjustment systems that operate with little or no backlash and that possess an increased range of movement are desirable.
An apparatus enables the position of a printhead to be independently aligned in an ink printing system. The apparatus includes a first member, a second member, a first rotational member, and a first driver. The first member is configured for selective mounting of the printhead. The first member is operatively connected to the second member. The first rotational member is operatively connected to the second member and is positioned to extend from the second member to the first member to frictionally engage the first member. The first driver is operatively connected to the first rotational member to rotate the first rotational member either to translate the first member laterally or to rotate the first member about an axis of the first rotational member.
A method enables independently aligning printhead position in an ink printing system. The method includes selectively mounting a printhead to a first member. The method also includes operatively connecting the first member to a second member. The method also includes operatively connecting a first rotational member to the second member and positioning the first rotational member to extend from the second member to the first member to frictionally engage the first member. The method also includes operatively connecting at least one driver to the first rotational member and rotating the first rotational member with the at least one driver either to translate the first member laterally or to rotate the first member about an axis of the first rotational member.
The foregoing aspects and other features of an apparatus that enables the position of a printhead to be independently aligned in an ink printing system 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 and 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 words “printer” and “imaging apparatus”, which may be used interchangeably, 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, etc. Furthermore, a printer is an apparatus that forms images with marking material on media and fixes and/or cures the images before the media exits the printer for collection or further printing by a subsequent printer.
The imaging apparatus 5 shown in
The imaging apparatus 5 includes a print engine to process the image data before generating the control signals for the inkjet ejectors for ejecting colorants. Colorants may be ink, or any suitable substance that includes one or more dyes or pigments and that may be applied to the selected media. The colorant may be black, or any other desired color, and a given imaging apparatus may be capable of applying a plurality of distinct colorants to the media. The media may include any of a variety of substrates, including plain paper, coated paper, glossy paper, or transparencies, among others, and the media may be available in sheets, rolls, or another physical formats.
The direct-to-sheet, continuous-media, phase-change inkjet imaging apparatus 5 includes a media supply and handling system configured to supply a long (i.e., substantially continuous) web of media W of “substrate” (paper, plastic, or other printable material) from a media source, such as spool of media 10 mounted on a web roller 8. For simplex printing, the printer is comprised of feed roller 8, media conditioner 16, printing station 20, printed web conditioner 80, coating station 95, and rewind unit 90. For duplex operations, the web inverter 84 is used to flip the web over to present a second side of the media to the printing station 20, printed web conditioner 80, and coating station 95 before being taken up by the rewind unit 90.
The media 10 may be unwound from the source as needed and propelled by a variety of motors, not shown, that rotate one or more rollers. The media conditioner includes rollers 12 and a pre-heater 18. The rollers 12 control the tension of the unwinding media as the media moves along a path through the printer. In alternative embodiments, the media may be transported along the path in cut sheet form in which case the media supply and handling system may include any suitable device or structure that enables the transport of cut media sheets along a desired path through the imaging apparatus. The pre-heater 18 brings the web to an initial predetermined temperature that is selected for desired image characteristics corresponding to the type of media being printed as well as the type, colors, and number of inks being used. The pre-heater 18 may use contact, radiant, conductive, or convective heat to bring the media to a target preheat temperature, which in one practical embodiment, is in a range of about 30° C. to about 70° C.
The media is transported through a printing station 20 that includes a series of color units or modules 21A, 21B, 21C, and 21D, each color module effectively extends across the width of the media and is able to eject ink directly (i.e., without use of an intermediate or offset member) onto the moving media. The arrangement of printheads in the print zone of the system 5 is discussed in more detail with reference to
The imaging apparatus may use “phase-change ink,” by which is meant that the ink is substantially solid at room temperature and substantially liquid when heated to a phase change ink melting temperature for jetting onto the imaging receiving surface. The phase change ink melting temperature may be any temperature that is capable of melting solid phase change ink into liquid or molten form. In one embodiment, the phase change ink melting temperature is approximately 70° C. to 140° C. In alternative embodiments, the ink utilized in the imaging device may comprise UV curable gel ink. Gel ink may also be heated before being ejected by the inkjet ejectors of the printhead. As used herein, liquid ink refers to melted solid ink, heated gel ink, or other known forms of ink, such as aqueous inks, ink emulsions, ink suspensions, ink solutions, or the like.
Associated with each color module is a backing member 24A-24D, typically in the form of a bar or roll, which is arranged substantially opposite the printheads on the back side of the media. Each backing member is used to position the media at a predetermined distance from the printheads opposite the backing member. Each backing member may be configured to emit thermal energy to heat the media to a predetermined temperature which, in one practical embodiment, is in a range of about 40° C. to about 60° C. The various backing members may be controlled individually or collectively. The pre-heater 18, the printheads, backing members 24 (if heated), as well as the surrounding air combine to maintain the media along the portion of the path opposite the printing station 20 in a predetermined temperature range of about 40° C. to 70° C.
Following the printing station 20 along the media path are one or more “mid-heaters” 30. A mid-heater 30 may use contact, radiant, conductive, and/or convective heat to control a temperature of the media. The mid-heater 30 brings the ink placed on the media to a temperature suitable for desired properties when the ink on the media is sent through the spreader 40. Following the mid-heaters 30, a fixing assembly 40 is configured to apply heat and/or pressure to the media to fix the images to the media. The term “fixing” may refer to the stabilization of ink on media through components operating on the ink and/or the media, including, but not limited to, fixing rollers and the like. In the embodiment of the
The spreader 40 may also include a cleaning/oiling station 48 associated with image-side roller 42. The station 48 cleans and/or applies a layer of some release agent or other material to the roller surface. The release agent material may be an amino silicone oil having viscosity of about 10-200 centipoises. Only small amounts of oil are required and the oil carried by the media is only about 1-10 mg per A4 size page.
The coating station 95 applies a clear ink to the printed media. This clear ink helps protect the printed media from smearing or other environmental degradation following removal from the printer. The overlay of clear ink acts as a sacrificial layer of ink that may be smeared and/or offset during handling without affecting the appearance of the image underneath. The coating station 95 may apply the clear ink with either a roller or a printhead 98 ejecting the clear ink in a pattern. Clear ink for the purposes of this disclosure is functionally defined as a substantially clear overcoat ink that has minimal impact on the final printed color, regardless of whether or not the ink is devoid of all colorant.
Following passage through the spreader 40, the printed media may be wound onto a roller for removal from the system (simplex printing) or directed to the web inverter 84 for inversion and displacement to another section of the rollers for a second pass by the printheads, mid-heaters, spreader, and coating station. The duplex printed material may then be wound onto a roller for removal from the system by rewind unit 90. Alternatively, the media may be directed to other processing stations that perform tasks such as cutting, binding, collating, and/or stapling the media or the like.
Operation and control of the various subsystems, components and functions of the device 5 are performed with the aid of the controller 50. The controller 50 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 and/or print engine to perform the functions, such as the electrical motor calibration function, described below. 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. Controller 50 may be operatively connected to the printheads of color modules 21A-21D in order to operate the printheads to form the test patterns with indicia described below to enable visual detection of defective inkjets.
The imaging apparatus 5 may also include an optical imaging system 54 that is configured for the imaging of the printed web. The optical imaging system is configured to detect, for example, the presence, intensity, and/or location of ink drops jetted onto the receiving member by the inkjets of the printhead assembly. The optical imaging system may include an array of optical detectors/sensors mounted to a bar or other longitudinal structure that extends across the width of an imaging area on the image receiving member. In one embodiment in which the imaging area is approximately twenty inches wide in the cross process direction and the printheads print at a resolution of 600 dpi in the cross process direction, over 12,000 optical detectors are arrayed in a single row along the bar to generate a single scanline across the imaging member. The optical detectors are configured in association in one or more light sources that direct light towards the surface of the image receiving member. The optical detectors receive the light generated by the light sources after the light is reflected from the image receiving member. The magnitude of the electrical signal generated by an optical detector in response to light being reflected by the bare surface of the image receiving member is larger than the magnitude of a signal generated in response to light reflected from a drop of ink on the image receiving member. This difference in the magnitude of the generated signal may be used to identify the positions of ink drops on an image receiving member, such as a paper sheet, media web, or print drum. The reader should note, however, that lighter colored inks, such as yellow, cause optical detectors to generate lower contrast signals with respect to the signals received from uninked portions than darker colored inks, such as black. Thus, the contrast may be used to differentiate between dashes of different colors. The magnitudes of the electrical signals generated by the optical detectors may be converted to digital values by an appropriate analog/digital converter. These digital values are denoted as image data in this document and these data are analyzed to identify positional information about the dashes on the image receiving member as described below.
A schematic view of a prior art print zone 900 that may be used in the imaging apparatus 5 is depicted in
Referring now to
The ejecting face, also known as the aperture plate, of each printhead 220A-220G includes a plurality of nozzles 232A-232G, respectively, that may be arranged in rows that extend in the cross-process direction (X axis) across the aperture plate. 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 aperture plate. To enable the printing of drops onto media 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 aperture plate 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 contain only one color of ink so the jets of the printhead eject the same color of ink. In this embodiment, an assembly of printheads may include fourteen printheads dedicated to each of cyan, magenta, yellow and black for a total of fifty-six printheads. In one embodiment, the plurality of nozzles within a printhead enables the printhead assembly to print an image that is approximately 17.5 inches wide in the cross-process direction.
As discussed above, misalignment of a printhead with respect to the receiving substrate and with respect to other printheads in the imaging device may present image quality issues. To facilitate independent alignment of printheads in a printhead assembly and enable more efficient replacement of printheads in the assembly, a tracking mechanism 320 has been incorporated in an intermediate plate 308 to which a printhead carriage plate 312 is mounted. A schematic illustration of the intermediate plate 308 and the carriage plate 312 is now discussed with reference to
Turning to
Turning now to
The tracking mechanism 320 within the intermediate plate 308 interacts with the tracking member, also referred to herein as a track ball 344, which engages the carriage plate 312 to enable independent alignment adjustment of the printhead 316 in two of the six degrees of freedom of movement. In particular, the intermediate plate 308 and the tracking mechanism 320 provide a plurality of contact points with the carriage plate 312 to constrain the carriage plate 312 in the Y, Z, pitch, and yaw directions relative to the intermediate plate 308 (see
More specifically, the tracking mechanism 320 includes two extension springs 326 (shown in
The extension springs 324 extend from the carriage plate 312 to the intermediate plate 308 and bias the carriage plate 312 and intermediate plate 308 toward one another. Tips 368 (shown in
The track ball 344 is spherically shaped and extends from the carriage plate 312 to the intermediate plate 308 and partially into the tracking mechanism opening 350 such that the track ball 344 contacts the track ball receiving area 348, formed in the carriage plate 312, and contacts the first driven rotational member 352, the second driven rotational member 356, and the idle rotational member 360, which are mounted to extend from the intermediate plate 308 in a direction substantially parallel with the intermediate plate 308 and the carriage plate 312. The first driven rotational member 352, the second driven rotational member 356, and the idle rotational member 360 are substantially cylindrically shaped and the round circumference of each rotational member 352, 356, 360 is in contact with the track ball 344. The contact between the track ball 344 and features of the tracking mechanism 320 retains the track ball 344 between the carriage plate 312 and the intermediate plate 308. More specifically, the idle rotational member 360 urges the track ball 344 into contact with the first driven rotational member 352 and the second driven rotational member 356. Additionally, the contact of the track ball 344 with features of the tracking mechanism 320 is frictional such that movement of the first driven rotational member 352 and/or the second driven rotational member 356 relative to the intermediate plate 308 results in corresponding movement of the track ball 344 relative to the intermediate plate 308, in turn resulting in corresponding movement of the carriage plate 312 relative to the intermediate plate 308.
The tracking mechanism 320 further includes a controller 372 operatively connected to an output shaft of a first driver 376 and an output shaft of a second driver 380 to selectively operate the first driver 376 and the second driver 380. In at least one embodiment, the controller 372 is integrated with the controller 118 (shown in
The pivot 364 extends from the intermediate plate 308 to the carriage plate 312 and is received through a slot 392 (shown in
The arrangement of the tracking mechanism 320 is such that contact between the rotational members 352, 356, 360, the track ball 344, and the track ball receiving area 348 assists the extension spring 324, 326, the screws 328, 332, and the receiving surfaces 336, 340 in constraining the carriage plate 312 in the Z, pitch, and yaw directions. Additionally, contact between the pivot 362 and the slot 392 in the carriage plate 312 constrains the carriage plate 312 in the Y direction relative to the intermediate plate 308 because the pivot 364 only slides along the lateral dimension 404 of the slot 392. Accordingly, the arrangement of the tracking mechanism 320 allows movement of the carriage plate 312 in the roll and X directions only.
In operation, the controller of a printing system is configured with programmed instructions for implementing the roll and X direction 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 X direction positional correction data. These data are used to generate control signals for the first driver 376 and second driver 380 that are coupled to the first driven rotational member 352 and the second driven rotational member 356, respectively.
The output shaft of the first driver 376 rotates the first driven rotational member 352 about the first axis 384. The first driven rotational member 352 is configured to rotate about the first axis 384 in both clockwise and counter-clockwise directions. Due to frictional contact with the track ball 344, rotation of the first driven rotational member 352 in the clockwise direction (when viewed from the perspective shown in
Similarly, the output shaft of the second driver 380 is configured to rotate the second driven rotational member 356 about the second axis 388 in both clockwise and counter-clockwise directions. Rotation of the second driven rotational member 356 in the clockwise direction (when viewed from the perspective shown in
It will be appreciated that variations of the above-disclosed and other features, and functions, or alternatives thereof, may be desirably combined into many other different systems or applications. 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.
