The present disclosure relates to imaging devices that utilize printheads to form images on media, and, in particular, to the alignment of such print heads in the imaging device.
Ink jet printing involves ejecting ink droplets from orifices in a print head onto a receiving substrate to form an image. Ink-jet printing systems commonly utilize either direct printing or offset printing architecture. In a typical direct printing system, ink is ejected from jets in the print head directly onto the final receiving substrate. In an offset printing system, the print head jets the ink onto an intermediate transfer surface, such as a liquid layer on a drum. The final receiving substrate is then brought into contact with the intermediate transfer surface and the ink image is transferred and fused or fixed to the substrate.
Alignment of the print head within an ink jet printing system including a single print head may be expressed as the position of the print head relative to the image receiving surface. Alignment of multiple print heads in ink jet printing systems including multiple print heads may be expressed as the position of one print head relative to the image receiving surface, such as a media substrate or intermediate transfer surface, or another print head within a coordinate system of multiple axes. For purposes of discussion, the terms “cross-process direction” and “X-axis direction” refer to a direction or axis perpendicular to the direction of travel of an image receiving surface past a print head, the terms “process direction” and “Y-axis direction” refer to a direction or axis parallel to the direction of an the image receiving surface, the term “Z-axis” refers to an axis perpendicular to the X-Y axis plane.
One particular type of alignment parameter is print head roll. As used herein, print head roll refers to clockwise or counterclockwise rotation of a print head about an axis normal to the image receiving surface, i.e., Z-axis. Print head roll misalignment may result from factors such as mechanical vibrations, and other sources of disturbances on the machine components, that may alter print head positions and/or angles with respect to an image receiving surface. As a result of roll misalignment, the rows of nozzles may be arranged diagonally with respect to the process direction movement of the image receiving surface as a result of the roll of the print head, which may cause horizontal lines, image edges, and the like to be skewed relative to the image receiving surface.
One method that may be used to detect print head roll is printing a horizontal line using one or more rows of nozzles of a print head and measuring the angle of the one or more lines with respect to the horizontal using a flatbed scanner or inline linear array sensor. The angle measurements may then be used to detect print head roll. Measuring angles of printed lines, however, requires precise alignment of the scanner or sensor with respect to the image receiving surface. If the measurement system uses a printed sheet on a flatbed scanner, rotation of the paper with respect to the scanner may produce inaccurate measurements. Similarly, if the measurement system utilizes an inline linear array sensor, misalignment of the sensor with respect to the image receiving surface may produce inaccurate measurements.
A method of detecting print head roll has been developed that is insensitive to misalignment or skew of an image sensor relative an image receiving surface or of misalignment of the image receiving surface relative to the image sensor. In particular, the method of detecting print head roll begins with the formation of a test pattern on an image receiving surface. The test pattern includes a plurality of marks arrayed across the image receiving surface in a cross-process direction with each mark in the plurality being formed by a different nozzle of a print head. The cross-process direction positions of each mark in the plurality of marks are then detected; and the detected cross-process direction positions are correlated to a print head roll value for the print head.
In another embodiment, a method of detecting print head roll includes the formation of a test pattern on an image receiving surface. The test pattern includes a plurality of marks arrayed across the image receiving surface in a cross-process direction with each mark in the plurality being formed by a different nozzle of a print head. The test pattern is then scanned to determine cross-process direction spacings between each mark in the plurality of marks. The determined cross-process direction spacings are then correlated to a print head roll value for the print head.
In another embodiment, a system for detecting print head roll is provided. The system includes a test pattern comprising a plurality of marks arrayed across an image receiving surface in a cross-process direction, each mark in the plurality being formed by a different nozzle of a print head. The system includes an image sensor configured to generate signals indicative of a cross-process direction position of each mark in the test pattern. A controller is configured to receive the signals from the image sensor and to correlate the cross-process direction positions of the marks to a print head roll value for the print head.
a and 9b depict an alternative embodiment of a test pattern for print head roll measurement that utilizes a jet interlacing technique.
For a general understanding of the present embodiments, reference is made to the drawings. In the drawings, like reference numerals have been used throughout to designate like elements.
Aspects of the exemplary embodiment relate to an imaging device and to a registration system for an imaging device. The imaging device includes an extensible image receiving member, such as a web or drum, which defines an image receiving surface that is driven in a process direction between marking stations. As used herein, the process direction is the direction in which the substrate onto which the image is transferred moves through the imaging device. The cross-process direction, along the same plane as the substrate, is substantially perpendicular to the process direction.
As used herein, the terms “printer” or “imaging device” generally refer to a device for applying an image to print media and may encompass any apparatus, such as a digital copier, bookmaking machine, facsimile machine, multi-function machine, etc. which performs a print outputting function for any purpose. “Print media” can be a physical sheet of paper, plastic, or other suitable physical print media substrate for images, whether precut or web fed. The imaging device may include a variety of other components, such as finishers, paper feeders, and the like, and may be embodied as a copier, printer, or a multifunction machine. A “print job” or “document” is normally a set of related sheets, usually one or more collated copy sets copied from a set of original print job sheets or electronic document page images, from a particular user, or otherwise related. An image generally may include information in electronic form which is to be rendered on the print media by the marking engine and may include text, graphics, pictures, and the like.
Referring now to
The imaging device 10 also includes an ink delivery subsystem 20 that has at least one source 22 of one color of ink. Since the imaging device 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 ink. In one embodiment, the ink utilized in the imaging device 10 is a “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 an imaging receiving surface. Accordingly, the ink delivery system includes a phase change ink 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 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 temperate is approximately 100° C. to 140° C. In alternative embodiments, however, any suitable marking material or ink may be used including, for example, aqueous ink, oil-based ink, UV curable ink, or the like.
The ink delivery system is configured to supply ink in liquid form to a print head system 30 including at least one print head assembly 32. Since the imaging device 10 is a high-speed, or high throughput, multicolor device, the print head system 30 includes multicolor ink print head assemblies and a plural number (e.g. four (4)) of separate print head assemblies (32, 34 shown in
As further shown, the imaging device 10 includes a media supply and handling system 40. The media 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 or sheet heater or pre-heater assembly 52. The imaging device 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, electronic storage 84, and a display or user interface (UI) 86. The ESS or controller 80 for example includes a sensor input and control system 88 as well as a pixel placement and control system 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 print head assemblies 32, 34, 36, 38. 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 print head cleaning apparatus and method discussed below.
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 print head assemblies 32, 34, 36, 38. 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 print head 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 along supply path 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 copy sheet within the transfix nip 18.
The imaging device may include an inline image sensor 54. The inline image sensor 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 print head assembly. In one embodiment, the image sensor includes a light source (not shown) and a light sensor (not shown). The light source may be a single light emitting diode (LED) that is coupled to a light pipe that conveys light generated by the LED to one or more openings in the light pipe that direct light towards the image substrate. In one embodiment, three LEDs, one that generates green light, one that generates red light, and one that generates blue light are selectively activated so only one light shines at a time to direct light through the light pipe and be directed towards the image substrate. In another embodiment, the light source is a plurality of LEDs arranged in a linear array. The LEDs in this embodiment direct light towards the image substrate. The light source in this embodiment may include three linear arrays, one for each of the colors red, green, and blue. Alternatively, all of the LEDS may be arranged in a single linear array in a repeating sequence of the three colors. The LEDs of the light source are coupled to the controller 80, which selectively activates the LEDs. The controller 80 may generate signals indicating which LED or LEDs to activate in the light source.
The reflected light is measured by the light sensor. The light sensor, in one embodiment, is a linear array of photosensitive devices, such as charge coupled devices (CCDs). The photosensitive devices generate an electrical signal corresponding to the intensity or amount of light received by the photosensitive devices. The linear array that extends substantially across the width of the image receiving member. Alternatively, a shorter linear array may be configured to translate across the image substrate. For example, the linear array may be mounted to a movable carriage that translates across image receiving member. Other devices for moving the light sensor may also be used.
The controller is configured to provide control signals to the image sensor 54 that, for example, selectively activate the LEDS to direct light onto the web and/or activate the light sensors to detect reflected light from the image receiving surface. The activation of the light sources and light sensors of the image sensor may be synchronized to the movement of the image receiving surface so that the surface is scanned only in targeted areas where images from one or more of the print heads are formed.
Referring now to
The ejecting face of each print head includes a plurality of nozzles that are arranged in rows and columns in the ejecting face at positions that correspond to ink jet positions in the print head. Nozzle rows extend linearly in the cross-process direction of the ejecting face. Nozzles may also be arranged linearly in the process direction of the ejecting face. The spacing between each nozzle in a row, however, is limited by the number of ink jets that can be placed in a given area in the print head. In order to increase the printing resolution, the nozzles in the rows may be offset or staggered from the nozzles in at least some of the other rows extending in the cross-process direction (along the X axis). Staggering or offsetting the nozzles in the rows increases the number of columns of ink that may be formed per unit of distance in the cross-process direction of an image receiving surface, and thus increases the resolution of images that may be formed by the imaging device.
A simplified illustration of an ejecting face, such as ejecting face 33 of print head 32, is depicted in
As mentioned above, one factor that affects imaging operations is alignment of a print head with respect to the receiving substrate and with respect to other print heads in the imaging device. One particular type of alignment parameter is print head roll. As used herein, print head roll refers to clockwise or counterclockwise rotation of a print head about an axis normal to the image receiving surface. Print head roll may result from factors such as mechanical vibrations, head mounting, periodic head maintenance, and other sources of disturbances on the machine components, that may alter print head positions and/or angles with respect to an image receiving surface.
Another consequence of print head roll misalignment is a change in the spacing between jets in the cross-process direction (X axis) of the ejecting face. Depending on the arrangement of nozzles in the ejecting face and the direction or roll (e.g., clockwise or counterclockwise), X axis spacing between nozzles may be increased or decreased, and in some cases, may result in unequal spacing, or gaps, in coverage along the X axis of the ejecting face. For example, as depicted in
Print head roll may be detected by measuring or detecting the difference in cross-process direction (X axis) spacing between marks, such as dashes, dots, and the like, formed using at least two different nozzles of a print head from an expected spacing between the marks. For example, referring to
In one embodiment, in order to detect print head roll, the controller is configured to actuate at least one print head of the imaging device to form a test pattern onto the image receiving surface. A test pattern comprises a plurality of marks formed on an image receiving surface that are spaced from each other extending in the cross-process direction (X axis) of the image receiving surface. Each mark in a test pattern is formed using a different nozzle of a print head. Any suitable number of nozzles and positioning of nozzles in the ejecting face of a print head may be utilized to form a test pattern. For example, test patterns may be printed using as few as two nozzles or all of the nozzles of a print head. The marks in a test pattern may be any suitable type of mark, such as dashes, dots, or the like, that enable detection of the cross-process direction distances between the marks.
Test patterns comprise data, such as, for example, a bitmap, for the controller indicating from which ink jets/nozzles to eject drops and timings for the actuations. Test patterns may be created and stored in the memory during system design or manufacture. Alternatively, the controller may include software, hardware and/or firmware that are configured to generate test patterns “on the fly.” The controller is operable to generate drop ejecting signals for driving the ink jets to eject drops through the corresponding nozzles in accordance with the test patterns.
A test pattern may be printed using nozzles from at least two different rows of nozzles in the print head.
One issue faced in the measurement of the distances between marks of a test pattern is drop misdirection resulting in position deviations of marks from intended positions. Drop misdirection is uncorrelated from jet to jet and may occur, for instance, due to fabrication non-uniformity from nozzle to nozzle or due to dirt, debris, deposits, or the like in or around a nozzle. In the embodiment of
With knowledge of the measured spacings and/or average measured spacings, and the expected spacings between the marks of the pattern, a determination may be made by the controller as to whether the print head is exhibiting roll as well as the degree or magnitude of the roll. Print head roll may be determined based on the test pattern of
Similar to the discussion above in regards to
Another factor that influences the measurement of print head roll is lateral motion of a print head relative to an image receiving surface. In the imaging device of
For an imaging device configured to form images on a continuous web of media, a factor that may influence measurement of print head roll is lateral motion of web of media with respect to the print heads. Using the test pattern of
A flowchart of an embodiment of a method for detecting and measuring roll of a print head is shown in
A print head roll value for the print head is then determined based on the detected cross-process direction positions of the marks in the pattern (block 810). The print head roll value may be determined from the detected cross-process direction positions of the marks in any suitable manner in the manner described above. At block 814, a decision is made as to whether or not the determined print head roll value should be adjusted or corrected for lateral motion such as print head lateral motion relative to the media or media lateral motion relative to the print head. If no further adjustments of the print head roll are deemed to be necessary, control passes to block 824 at which point the physical position of the print head in the imaging device is adjusted to change the roll from its measured value to its desired value. If further adjustment is required, then the relative motion between the media and the print head may be calculated using the slope of the graph that plots expected average mark position in the cross-process direction versus the process direction position of the row of the nozzle used to form the marks. Lateral motion may be inferred for row to row changes in mark position (block 818). The determined print head roll may then be corrected for media/head lateral motion (block 820). Control then passes to block 824 at which point the physical position of the print head in the imaging device is adjusted to change the roll from its measured value to its desired value. Adjusting the physical positions of print heads within an imaging device to correct roll is known in the art. Therefore, the exact method of adjusting the physical position of the print head to correct print head roll is not critical to this disclosure.
a and 9b show an alternative embodiment of a test pattern for measuring print head roll that uses a jet interlacing technique. As used herein, the term “jet interlacing” refers to printing marks from jets that are in the same X axis position in a print head, such as the left most jet (1) from row A and the left most jet (1) from row C of
Using the print head configuration described above in relation to
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, applications or methods. 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.
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Number | Date | Country | |
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20100245455 A1 | Sep 2010 | US |