Patent Grant
9573382
This disclosure relates generally to printers that eject ink from inkjets onto an image receiving surface and, more particularly, to printers that emit multiple ink drop sizes and that compensate for inoperable inkjets.
Drop on demand inkjet technology for producing printed media has been employed in commercial products such as printers, plotters, and facsimile machines. Generally, an inkjet image is formed by selectively ejecting ink drops from a plurality of inkjets, which are arranged in one or more printheads, onto an image receiving surface. In a direct inkjet printer, the printheads eject ink drops directly onto the surface of a print medium such as a paper sheet or a continuous paper web. In an indirect inkjet printer, the printheads eject ink drops onto the surface of an intermediate image receiving member such as a rotating imaging drum or belt. During printing, the printheads and the image receiving surface move relative to one other and the inkjets eject ink drops at appropriate times to form an ink image on the image receiving surface. A controller in the printer generates electrical signals, also known as firing signals, at predetermined times to activate individual inkjets in the printer. The ink ejected from the inkjets can be liquid ink, such as aqueous, solvent, oil based, UV curable ink or the like, which is stored in containers installed in the printer. Alternatively, some inkjet printers use phase change inks that are loaded in a solid form and delivered to a melting device. The melting device heats and melts the solid phase change ink to a liquid form that is supplied to a printhead for printing as liquid drops onto the image receiving surface.
During operation, some inkjets in one or more printheads fail to operate due to contaminants that clog nozzles or due to other malfunctions in the printhead. As used herein, the term “inoperable inkjet” refers to an inkjet that fails to eject ink drops onto the predetermined locations of an image receiving surface in a reliable manner during a printing operation. Inoperable inkjets may fail to eject ink drops entirely, eject drops only intermittently, or eject drops onto incorrect locations on the image receiving surface.
Existing compensation methods for inoperable inkjets identify pixel locations in binary halftoned image data that correspond to inoperable inkjets and redistribute the “orphan” pixels from the inoperable inkjet to neighboring inkjets to reduce the perceptible impact of the inoperable inkjet. However, the hardware and software implementations of prior art printers are not suited for use in printers that eject ink drops of different sizes from two or more arrays of inkjets in a print zone. As used herein, the term “multi-level” as used to apply to a printer or to image data for a printed image refers to configurations in which a combination of multiple drop sizes form printed images. For example, in a printer that forms images using two different drop sizes, each halftoned pixel has a total of four potential values or “levels” (e.g. no drops, one small drop, one large drop, or both a small and large drop) instead of the traditional binary image data that only includes two values for drop/no drop. Consequently, improvements systems and methods for inoperable inkjet compensation methods in multi-level printers would be beneficial.
In one embodiment, a method for printing pixels in an image to compensate for an inoperable inkjet in a multi-level printer has been developed. The method includes identifying, with a controller, a first pixel in multi-bit halftoned image data stored in a memory to be printed by an inoperable inkjet in a plurality of inkjets, identifying, with the controller, at least one neighboring pixel in a predetermined region of pixels around the first pixel to compensate for the first pixel with reference to a search of the predetermined region of pixels, generating, with the controller a modified multi-bit halftoned value for the at least one neighboring pixel to control operation of a neighboring inkjet of the inoperable inkjet to eject an ink drop based on the modified at least one neighboring pixel, and storing with the controller the at least one modified neighboring pixel in the memory to control operation of the plurality of inkjets to produce a printed image with the plurality of inkjets other than the inoperable inkjet to compensate for the inoperable inkjet.
In another embodiment, a multi-level inkjet printer that is configured to compensate for inoperable inkjets has been developed. The printer includes a plurality of inkjets and a controller operatively connected to the plurality of inkjets and a memory. The controller is configured to identify a first pixel in multi-bit halftoned image data stored in the memory to be printed by an inoperable inkjet in a plurality of inkjets, identify at least one neighboring pixel in a predetermined region of pixels around the first pixel to compensate for the first pixel with reference to a search of the predetermined region of pixels, generate a modified multi-bit halftoned value for the at least one neighboring pixel to control operation of a neighboring inkjet of the inoperable inkjet to eject an ink drop based on the modified at least one neighboring pixel, and store the at least one modified neighboring pixel in a memory to control operation of the plurality of inkjets to produce a printed image with the plurality of inkjets other than the inoperable inkjet to compensate for the inoperable inkjet.
The foregoing aspects and other features of a printer that enable compensation for inoperable inkjets in an inkjet printer that forms printed images using multiple ink drop sizes 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 produces images with colorants on media, such as digital copiers, bookmaking machines, facsimile machines, multi-function machines, etc.
As used herein, the term “inoperable inkjet” refers to a malfunctioning inkjet in a printer that does not eject ink drops, ejects ink drops only on an intermittent basis, or ejects ink drops onto an incorrect location of an image receiving member when the inkjet receives an electrical firing signal. A typical inkjet printer includes a plurality of inkjets in one or more printheads, and operational inkjets that are located near the inoperable inkjet can compensate for the inoperable inkjet to preserve the quality of printed images when an inkjet becomes inoperable.
As used herein, the term “pixel” refers to a single value in a two-dimensional arrangement of image data corresponding to an ink image that an inkjet printer forms on an image receiving surface. The locations of pixels in the image data correspond to locations of ink drops on the image receiving surface that form the ink image when multiple inkjets in the printer eject ink drops with reference to the image data. An “activated pixel” refers to a pixel in the image data that causes the printer to eject at least one drop of ink onto an image receiving surface location corresponding to the activated pixel. As described in more detail below, in a multi-bit printer embodiment, the printer is further configured to eject ink drops with varying sizes and combinations of different ink drops to deposit varying amounts of ink onto a single location in a printed image corresponding to each pixel. A “deactivated pixel” refers to a pixel in the image data having a value that does not cause the printer to eject a drop of ink onto an image receiving surface location corresponding to the deactivated pixel.
The term “multi-bit halftoned image data” refers to image data formed as a two-dimensional arrangement of pixels that are each encoded with more than two values that correspond to a plurality of different ink drop sizes that may be placed in each pixel location. A multi-level inkjet printer uses multi-bit halftoned image data to encode the different drop sizes that the printer uses to form printed images. For example, a two-bit multi-bit halftoned image data printer configuration provides four distinct levels of ink that can be ejected onto a single pixel including a deactivated pixel with no ink (e.g. 00), a “small” sized ink drop (e.g. 01), a “medium” sized ink drop (e.g. 10), and a “large” ink drop (e.g. 11). Of course, printers that operate using multi-bit halftoned image data may encode halftoned image data using additional bits that enable a larger number of levels (e.g. three bits for eight levels, four bits for sixteen levels, etc.). In many printers, the “medium” or “large” sized ink drops may be a composite drop that is formed by two or more ink drops having smaller sizes. As used herein, the term “composite ink drop” refers to an ink pattern formed on a location of an image receiving surface that corresponds to a single pixel, but that is actually formed by separate drops that are ejected from either a single inkjet that performs two or more ejection operations or from two or more different inkjets in a printer. Using the example above, in one embodiment of a printer, a first inkjet ejects “small” drops and a second inkjet that is aligned with the first inkjet in a cross-process direction ejects the “medium” sized drops, while a composite operation of both inkjets generates the “large” sized drop.
Halftoned image data are often arranged in a two-dimensional array with dimensions that correspond to the process direction and cross-process direction during a print job. As used herein, the term “pixel column” refers to an arrangement of pixels in image data that extend in the process direction P. Since the image receiving surface moves past the inkjets in a print zone in the process direction P, if an inkjet is inoperable, then the inkjet cannot eject the ink drops corresponding to activated pixels in a pixel column that is aligned with the inoperable inkjet in the print zone. As described below, the printer activates additional pixels in the image data for inkjets that are proximate to the inoperable inkjet in the cross-process direction to reduce or eliminate defects in the printed images that are formed with the inoperable inkjet.
As used herein, the term “process direction” (P) refers to a relative direction of motion between inkjets in a printhead and an image receiving surface, such as a print medium or an indirect image receiving member such as a rotating drum or belt. As described in more detail below, a single inoperable inkjet produces an artifact in a printed image corresponding to a linear streak arranged along the process direction corresponding to locations where the inoperable inkjet is unable to print ink drops. The term “cross-process direction” (CP) refers to an axis that extends across the image receiving surface perpendicular to the process direction. An array of inkjets includes neighboring inkjets that are located proximate to the inoperable inkjet along the cross-process direction axis. As described in more detail below, one or more neighboring inkjets eject additional ink drops to compensate for an inoperable inkjet in the printer.
As used herein, the term “image density” refers to a number of pixels in either image data or an ink image that receive ink drops. In a high density region, a comparatively large portion of the pixels are activated and the corresponding region of the image receiving surface receives a correspondingly large number of ink drops and, in a multi-bit halftoned printer, larger drop sizes. In a low density region, fewer pixels are activated and the corresponding region of the image receiving surface receives fewer ink drops.
The phase change ink printer 10 also includes a phase change ink delivery subsystem 20 that has multiple sources of different color phase change inks in solid form. Since the phase change ink printer 10 is a multicolor printer, the ink delivery subsystem 20 includes four (4) sources 22, 24, 26, 28, representing four (4) different colors CMYK (cyan, magenta, yellow, and black) of phase change inks. The phase change ink delivery subsystem 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. Each of the ink sources 22, 24, 26, and 28 includes a reservoir used to supply the melted ink to the printhead assemblies 32 and 34.
In the example of
The phase change ink printer 10 includes a substrate supply and handling subsystem 40. The substrate supply and handling subsystem 40, for example, includes 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 a cut sheet print medium 49. The phase change ink printer 10 as shown also includes 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 subsystem 76. A media transport path 50 extracts print media, such as individually cut media sheets, from the substrate supply and handling system 40 and moves the print media in a process direction P. The media transport path 50 passes the print medium 49 through a substrate heater or pre-heater assembly 52, which heats the print medium 49 prior to transfixing an ink image to the print medium 49 in the transfix nip 18.
Media sources 42, 44, 48 provide image receiving substrates that pass through media transport path 50 to arrive at transfix nip 18 formed between the image receiving member surface 14 and transfix roller 19 in timed registration with the ink image formed on the image receiving surface 14. As the ink image and media travel through the nip, the ink image is transferred from the surface 14 and fixedly fused to the print medium 49 within the transfix nip 18. In a duplexed configuration, the media transport path 50 passes the print medium 49 through the transfix nip 18 a second time for transfixing of a second ink image to a second side of the print medium 49.
Operation and control of the various subsystems, components and functions of the 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 a digital memory 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 an ink drop placement and control circuit 89. In one embodiment, the ink drop placement control circuit 89 is implemented as a field programmable gate array (FPGA). In addition, the CPU 82 reads, captures, prepares and manages the image data flow associated with print jobs received from image input sources, such as the scanning system 76, or an online or a work station connection 90. As such, the ESS or controller 80 is the main multi-tasking processor for operating and controlling all of the other printer subsystems and functions.
The controller 80 can be implemented with general or specialized programmable processors that execute programmed instructions, for example, printhead operation. The instructions and data required to perform the programmed functions are stored in the memory 84 that is associated with the processors or controllers. The processors, their memories, and interface circuitry configure the printer 10 to form ink images, and, more particularly, to control the operation of inkjets in the printhead assemblies 32 and 34 to compensate for inoperable inkjets. These components are provided on a printed circuit card or provided as a circuit in an application specific integrated circuit (ASIC). Each of the circuits can be implemented with a separate processor or multiple circuits are implemented on the same processor. In alternative configurations, the circuits are implemented with discrete components or circuits provided in very large scale integration (VLSI) circuits. Also, the circuits described herein can be implemented with a combination of processors, FPGAs, ASICs, or discrete components.
In one embodiment, the controller 80 includes a reconfigurable digital processing device such as an FPGA that is reconfigurable based on a synthesized logic description, such as the hardware configuration data 116 that are stored in the memory 84. In a multi-bit halftoned printer, the controller 80 optionally includes a pipelined hardware configuration that is depicted in
As depicted above, the configuration of
Each of the MJC modules 312A-312D includes a data buffer that stores a portion of the region of the image data around the inoperable inkjet, such as a seven pixel wide by three pixel long (7×3) set of image data or another suitable size for performing the compensation process. At any one time, each of the MJC modules 312A-312D in the pipeline only processes a comparatively small window of the multi-bit halftoned image data along the entire column of the image data, and the pipeline processes the entire column in progression using a “sliding window” technique to process successive rows of the image data. For example, the region 347 depicts the 7×3 pixel sliding window region around the pixel 346 in the image data 344. The data buffers within each MJC are quite small in comparison to the total size of the full image data stored in the external memory and accessed via the DMA unit 302, and these memory buffers can be implemented as memory registers or other suitable logic structures in an FPGA or other digital logic device in a practical manner. Thus, only the first MJC module 312A needs to access the external memory to receive input image data and only the final MJC module 312D needs to write fully processed output image data to the external memory. After each MJC module completes processing of the image data within the buffer, the module passes the buffer to the next MJC module in the pipeline for additional processing as described above.
The pipeline depicted in
Referring again to
While
During operation, the printer 10 ejects a plurality of ink drops from inkjets in the printhead assemblies 32 and 34 onto the surface 14 of the image receiving member 12. The controller 80 generates electrical firing signals to operate individual inkjets in one or both of the printhead assemblies 32 and 34. In the multi-color printer 10, the controller 80 processes digital image data corresponding to one or more printed pages in a print job, and the controller 80 generates multi-bit halftoned image data for each of the CMYK color separations. Each bit map includes a two dimensional arrangement of pixels corresponding to locations on the image receiving member 12. Each pixel has three or more potential values that indicate if the pixel is activated, and which size of ink drop or combination of ink drops should be printed, or deactivated in which case the pixel receives no ink drops. The controller 80 generates a firing signal to activate an inkjet and eject a drop of ink onto the image receiving member 12 for the activated pixels, but does not generate a firing signal for the deactivated pixels. The combined bit maps for each of the colors of ink in the printer 10 generate multicolor or monochrome images that are subsequently transfixed to the print medium 49. The controller 80 generates the bit maps with selected activated pixel locations to enable the printer 10 to produce multi-color images, half-toned images, dithered images, and the like.
During a printing operation, one or more of the inkjets in the printhead assemblies 32 and 34 may become inoperable. An inoperable inkjet may eject ink drops on an intermittent basis, eject ink drops onto an incorrect location on the image receiving surface 14, or entirely fail to eject ink drops. In the printer 10, an optical sensor 98 generates image data corresponding to the ink drops that are printed on the image receiving surface 14 after formation of the ink images and prior to the imaging drum 12 rotating through the nip 18 to transfix the ink images. In one embodiment, the optical sensor 98 includes a linear array of individual optical detectors that detect light reflected from the image receiving surface. The individual optical detectors each detect an area of the image receiving member corresponding to one pixel on the surface of the image receiving member in a cross-process direction, which is perpendicular to the process direction P. The optical sensor 98 generates digital data, referred to as reflectance data, corresponding to the light reflected from the image receiving surface. The controller 80 is configured to identify inoperable inkjets in the printhead assemblies 32 and 34 with reference to the reflectance values detected on the imaging receiving surface 14 and the predetermined image data of the printed ink images. In an alternative embodiment, an optical sensor detects defects in ink images after the ink images have been formed on the print medium 49. In another alternative embodiment, the inoperable inkjets are identified with sensors located in the printhead assemblies. In response to identifying an inoperable inkjet, the controller 80 ceases generation of firing signals for the inoperable inkjet, and generates firing signals for other inkjets that are proximate the inoperable inkjet in the printer to compensate for the inoperable inkjet.
The printer 10 is an illustrative embodiment of a printer that compensates for inoperable inkjets using the processes described herein, but the processes described herein can compensate for inoperable inkjets in alternative inkjet printer configurations. For example, while the printer 10 depicted in
Process 200 begins as the controller 80 identifies an inoperable inkjet in the printer (block 204). In the printer 10, the optical sensor 98 generates scanned image data of printed ink test patterns on the surface 14 of the imaging drum 12. The controller 80 analyzes the scanned image data to identify one or more inkjets in the printhead assemblies 32 and 34 that are inoperable. Existing techniques for the identification of inoperable inkjets are known to the art and are not presented in further detail herein.
After identification of an inoperable inkjet, the printer 10 identifies an activated pixel in a column of the halftoned multi-bit image data that corresponds to the inoperable inkjet (block 208). Since the halftoned image data are arranged in a two-dimensional array that corresponds to the predetermined physical arrangement of inkjets, the controller 10 identifies the column of image data that extends in the process direction corresponding to the inoperable inkjet via a LUT or other similar operation. For example, in
Process 200 continues as the controller 80 performs an ordered search process in a predetermined region of pixels that surround the identified pixel to identify at least one neighboring pixel that serves as an “adoption site” for a first pixel that corresponds to the inoperable inkjet (block 212).
The controller 80 searches for deactivated pixels in the region 508 based on a predetermined search order. In
In some embodiments, the controller 80 does not perform the search using every potential neighbor pixel in the region of pixels that surrounds the inoperable inkjet. Instead, the controller 80 applies a predetermined bit mask to the region and omits any pixels that correspond to a mask 112 during the search. The masks include selected pixels that are not included in the search based on various factors including specific characteristics of different printer models, and in some instances pixels are masked if the pixels are reserved for compensation of other nearby pixels in the column of image data corresponding to the inoperable inkjet. Other mask types are based on the different sizes of ink drops in activated pixels in the predetermined region.
In some embodiments, the search process continues until the controller 80 either identifies a predetermined number of suitable neighboring pixels that can receive all or a part of the ink for the first pixel of the inoperable inkjet or the controller 80 searches all of the available neighboring pixels without identifying one or more suitable neighboring pixels. For example, in the printer 10 that employs a two-bit halftoned process, the controller 80 identifies up to three neighboring pixel locations that can serve as adoption sites for a large ink drop that is distributed to a single neighboring pixel (large ink drop moved to a single neighboring pixel), two neighboring pixels (one small ink drop and one medium ink drop), or three neighboring pixels (three small ink drops). Other configurations of the printer 10 search for a different number of pixel locations. In some high density regions of a printed image, the search process may fail to identify one or more deactivated neighboring pixels in the region that may serve as adoption sites. As described in more detail below in
Process 200 continues as the controller 80 generates modified multi-bit halftoned image data in the identified neighboring pixels in the region around the first pixel of the inoperable inkjet (block 216). During process 200, the controller 80 stores the modified multi-bit halftoned image data in the memory 84 to control the operation of the inkjets in the printhead assemblies 32 and 34 during a printing operation.
While
Process 200 continues as described above with reference to the processing of blocks 208-216 for any additional pixels in the column of multi-bit halftoned image data corresponding to the inoperable inkjet (block 220). Once the controller has modified all of the pixels in the column of image data corresponding to the inoperable inkjet and stored the modified multi-bit halftoned image data in the memory 84, the controller 80 performs a printing operation using the multi-bit halftoned image data including the modified neighboring pixels to form a printed pattern of ink drops on an image receiving surface (block 224). In the printer 10, the controller 80 uses the modified multi-bit halftoned image data to generate electrical firing signals for the operable inkjets in the printhead assemblies 32 and 34, and the printer 10 transfixes the ink image from the image receiving drum 12 to a print medium to produce the printed image. The operable inkjets eject ink drops of the predetermined sizes for the printer 10 to form a printed image that corresponds to the modified multi-bit halftoned image data. The controller 80 deactivates any identified inoperable inkjets to ensure that the printed image is formed using only the operable inkjets in the printhead assemblies 32 and 34. The controller 80 operates the neighboring inkjets of the inoperable inkjet to eject the additional ink drops based on the modified multi-bit halftoned image data to compensate for the inoperable inkjet and reduce or eliminate streaks or other artifacts that would otherwise be caused by the inoperable inkjet in the printed image.
While process 200 is described for processing of individual pixels that correspond to an inoperable inkjet, in some embodiments the controller 80 performs parallel processing of the multi-bit halftoned image data to generate the modified multi-bit halftoned image data for multiple pixels concurrently. Additionally, the printer 10 optionally performs the process 200 for multiple inoperable inkjets in situations where more than one inkjet in the printhead assemblies 32 and 34 fails to operate properly.
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. 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.
| Number | Name | Date | Kind |
|---|---|---|---|
| 5635967 | Klassen | Jun 1997 | A |
| 6215557 | Owens | Apr 2001 | B1 |
| 6575549 | Silverbrook | Jun 2003 | B1 |
| 6695435 | Cheng et al. | Feb 2004 | B1 |
| 6863361 | Barr et al. | Mar 2005 | B2 |
| 6880907 | Tsai | Apr 2005 | B2 |
| 7021739 | Burke et al. | Apr 2006 | B2 |
| 7075677 | Silverbrook | Jul 2006 | B1 |
| 7095531 | Mizes et al. | Aug 2006 | B2 |
| 7318637 | Ishimoto et al. | Jan 2008 | B2 |
| 7484830 | Kim et al. | Feb 2009 | B2 |
| 7639402 | Vestjens et al. | Dec 2009 | B2 |
| 7731342 | Mantell | Jun 2010 | B2 |
| 7815274 | De Waal | Oct 2010 | B2 |
| 7854490 | Snyder | Dec 2010 | B2 |
| 7866778 | Silverbrook et al. | Jan 2011 | B2 |
| 7903290 | Faken et al. | Mar 2011 | B2 |
| 8001893 | McCoy et al. | Aug 2011 | B2 |
| 8042899 | Folkins et al. | Oct 2011 | B2 |
| 8714692 | Metcalfe et al. | May 2014 | B1 |
| 8894179 | Metcalfe et al. | Nov 2014 | B1 |
| 8955937 | Metcalfe et al. | Feb 2015 | B2 |
| 8985723 | Metcalfe et al. | Mar 2015 | B2 |
| 20040196320 | Walmsley et al. | Oct 2004 | A1 |
| 20050110817 | Burke et al. | May 2005 | A1 |
| 20050146543 | Smith et al. | Jul 2005 | A1 |
| 20050285897 | Temple | Dec 2005 | A1 |
| 20060082848 | Takakura | Apr 2006 | A1 |
| 20060125850 | Kim et al. | Jun 2006 | A1 |
| 20060279591 | Lee | Dec 2006 | A1 |
| 20060285131 | Mantell et al. | Dec 2006 | A1 |
| 20090231375 | Folkins et al. | Sep 2009 | A1 |
| 20090315939 | Mantell et al. | Dec 2009 | A1 |
| 20100245454 | Ramakrishnan et al. | Sep 2010 | A1 |
