System and method for detecting and correcting split inkjet in an inkjet printer during printing.

Abstract

To identify split inkjet in an inkjet printer and correct them during printing operation.SOLUTION: A method analyzes image data of a test pattern printed on an image receiving member by a printer to identify split inkjet in printheads of the printer. The test pattern is formed by operating each inkjet of a printhead to form a dash, and the areas of the dashes are compared to an average dash area to identify split inkjet. Firing signal parameters for the split inkjet are adjusted and firing signals are generated using the adjusted parameters. Image data formed by the split inkjet is analyzed after the split inkjet have been operated using the adjusted firing signal parameters. If the pixel size for a split inkjet indicates that the split inkjet has been corrected, then the firing signal parameters are returned to their nominal values.SELECTED DRAWING: Figure 1

Description

【Technical Field】 【0001】 The present disclosure generally relates to the identification of split inkjets in an inkjet printer having one or more printheads, and more particularly to the correction of those inkjets during a printing operation. 【Background Art】 【0002】 An inkjet printer has a printhead that operates a plurality of inkjets that eject liquid ink onto an image receiving member. The ink can be an aqueous ink, an ink emulsion, a gel ink, or an ink filled in a solid form and then melted to produce a liquid ink. A typical inkjet printer uses one or more printheads. Each printhead typically includes an array of individual nozzles for ejecting drops of ink onto an image receiving member across an open gap to form an ink image. The image receiving member can be a continuous web of recording media, a series of media sheets, or a rotating surface such as a printing drum or an endless belt. The image printed on the rotating surface is then transferred to the recording media by mechanical force in a transfer nip formed by the rotating surface and a transfer roller. In an inkjet printhead, individual piezoelectric, thermal, or acoustic actuators generate a mechanical force that causes ink to be ejected from an ink-filled chamber through an orifice in response to an electrical voltage signal, sometimes called a firing signal. The magnitude or voltage level of the signal affects the amount of ink ejected with each drop. The firing signal is generated by a printhead controller according to image data. An inkjet printer forms a printed image using image data by printing a pattern of individual ink drops at specific locations on an image receiving member. The location where an ink drop adheres is sometimes referred to as an "ink drop location", "ink drop position", or "pixel". Thus, the printing operation can be viewed as placing ink drops on an image receiving member using image data to generate an ink image corresponding to the image data. 【0003】 One problem arising from the operation of inkjet in the print head to form an ink image is called "split inkjet." When the term is used in the context of documents, split inkjet refers to an inkjet that, when operated to eject ink droplets, produces a group of ink droplet fragments rather than a single ink droplet. These ink fragments, sometimes called satellites, tend to spread out and produce speckled pixels rather than well-defined circles. These defective pixels can result in streaks, which are detrimental to the final image quality perceived by the customer. 【0004】 The procedure called "purging" is an effective way to overcome the degradation of inkjet performance. To purge the printhead, pressurized air is applied to the ink reservoir within the printhead, pushing the ink through the inkjet. The pushed-out ink collects on the faceplate of the printhead and is typically wiped into a waste ink reservoir. While this procedure restores many inkjet printers to their working state, it comes at a significant cost, as it requires a complete halt to printing to purge the printhead, resulting in a loss of productivity and potentially high costs for the ink pushed out, especially if purging is performed frequently. As a result, purging is generally limited to once every two hours of printer operation. 【0005】 Unfortunately, inkjet degradation can occur on a timescale significantly shorter than the typical 2 hours required for a printer's purge operation. Depending on the area coverage of the print being produced, defects can appear as quickly as 10 minutes after a purge operation, corresponding to approximately 2500 sheets. Techniques have been developed to camouflage missing or weak inkjet prints. Missing inkjet prints practically do not eject any ink, while weak inkjet prints eject small portions of full-sized ink droplets. The effect of missing or weak inkjet prints can be reduced to some extent by increasing the amount of ink in the ink droplet ejected by other inkjet prints near a missing or weak inkjet print. However, these inkjet prints are not effective in addressing split inkjet prints because they spread the amount of ink droplets over a larger area than where the droplets should adhere. Adding more ink to that area can cause image defects to the point of curing them. It would be beneficial to be able to detect split inkjet prints during a print operation and correct them to some extent without stopping the print operation. [Overview of the project] 【0006】 A method for operating a printer involves analyzing image data corresponding to a test pattern generated by the printer on an image-receiving member to identify segmented inkjet inks, and then generating a modified firing signal for the identified segmented inkjet inks for a limited time. This method includes operating at least one print head to form a test pattern on an image-receiving member, generating image data of the test pattern on the image-receiving member, and analyzing the generated image data to identify segmented inkjet inks in at least one print head. 【0007】 The new printer analyzes image data corresponding to a test pattern generated on an image-receiving member by the printer to identify segmented inkjet, and then generates a modified firing signal for the identified segmented inkjet for a limited time. The printer includes at least one print head and a controller configured to operate at least one print head to form a test pattern on an image-receiving member in an inkjet printer, generate image data of the test pattern on the image-receiving member, and analyze the generated image data to identify segmented inkjet in at least one print head. [Brief explanation of the drawing] 【0008】 The aforementioned aspects and other features of the printer, as well as its operation for detecting and correcting split inkjet during printing, are described in the following description in conjunction with the attached drawings. 【0009】 [Figure 1] This is a flowchart illustrating a method for identifying and correcting segmented inkjet prints in an inkjet printer. 【0010】 [Figure 2] This sample test pattern is suitable for use with the method shown in Figure 1. 【0011】 [Figure 3] These are images of dashes generated by segmented inkjet and dashes generated by operational inkjet. 【0012】 [Figure 4] This shows a histogram correlating the number of inkjet prints in the printer with the size of the area of ​​the dashes formed by the inkjet prints. 【0013】 [Figure 5] These are images of a dash produced by split inkjet and another image of a dash produced by a movable inkjet. 【0014】 [Figure 6] This image shows a correction of split inkjet printing using an elevated peak-to-peak emission signal voltage. 【0015】 [Figure 7] This is a schematic diagram of a prior art inkjet imaging system in which ink is discharged onto a continuous web of media as the media passes through the print head in the system. 【0016】 [Figure 8] This is a schematic diagram of the print head configuration of prior art. [Modes for carrying out the invention] 【0017】 Figure 1 shows a process 120 for detecting split inkjet prints and correcting them to an operational state. Process 120 uses an optical sensor to analyze image data obtained from the surface of an image-receiving member in the printing system. This analysis allows for a more accurate determination of the position and area of ​​the dashes, and the position and area information of the dashes can be used to determine which inkjet prints in the print head are split inkjet prints. In one embodiment, the optical sensor includes an array of optical detectors mounted on a bar or other longitudinal structure extending across the width of the imaging area on the image-receiving member. In one embodiment, where the imaging area is approximately 20 inches wide in the cross-processing direction and the print head prints at a resolution of 600 dpi in the cross-processing direction, more than 12,000 optical detectors are arranged in a row along the bar to generate a single scan line across the imaging member. The optical detectors are configured in relation to one or more light sources that direct light toward the surface of the image-receiving member. The optical detectors receive the light generated by the light sources after the light has been reflected from the image-receiving member. The magnitude of the electrical signal generated by the optical detector in response to light reflected by the exposed surface of an image-receiving member is higher than the magnitude of the signal generated in response to light reflected from an ink droplet on the image-receiving member. The difference in the magnitude of the generated signals is used to identify ink droplets on an image-receiving member such as a paper sheet, media web, or printing drum. However, readers should note that the optical detector generates a lower contrast signal with respect to the uncoated portion of the image-receiving member for brighter colored inks such as yellow than for darker inks such as black. Therefore, the difference in contrast signals is used to distinguish dashes of different colors. The magnitude of the electrical signal generated by the optical detector is converted into a digital value by a suitable analog-to-digital converter. These digital values ​​are represented as image data in this document, and this data is analyzed to identify the positional information of the dashes on the image-receiving member and the inkjet that produced the dashes. 【0018】 Where used in this document, the terms “analyze” or “analyze” mean using a controller to process image data and determine whether the ink bucket, which is operated to eject the inkjet, has actually ejected ink, whether ejected ink has adhered, and the area of ​​an image-receiving surface that has not received ink. In some printing systems, the image of a printed image is produced by printing the printed image onto a medium, or by transferring the printed image onto a medium, ejecting the medium from the system, and then scanning the image with a flatbed scanner or other known offline imaging device. This method of producing a photograph of a printed image does not allow for in-situ analysis of the printed image and introduces the inaccuracies imposed by external scanners. In some printers, the scanner is integrated into the printer and positioned within the printer to enable the generation of an image of the ink image while the image is on a medium within the printer, or while the ink image is on a rotating image member. These integrated scanners typically include one or more illuminators and multiple optical detectors that receive radiation from the illuminators reflected from the image-receiving surface. The radiation from the illuminators is usually visible light, but the radiation may be at or beyond any end of the visible light spectrum. When light is reflected by a white surface, the reflected light has the same spectrum as the illuminating light. In some systems, ink on the imaging surface may absorb some of the incident light, resulting in reflected light having a different spectrum. Furthermore, some inks may emit radiation at wavelengths different from the illuminating radiation, such as when the ink fluoresces in response to stimulating radiation. Each optical sensor generates an electrical signal corresponding to the intensity of the reflected light received by the detector. The electrical signal from the optical detector can be converted into a digital signal by an analog-to-digital converter and provided to an image processor as digital image data. Analysis of the printed image is performed with reference to two directions: the "process direction" refers to the direction in which the image receiving member moves as the imaging surface receives ink ejected from the print head, and the "cross-process direction" refers to the direction across the width of the image receiving member. 【0019】 The environment in which image data is generated is not pure. Several noise sources exist and need to be addressed in the analysis of the image data. For example, image-receiving materials can contribute to noise in the image data. Specifically, structures on the image-receiving surface and colored contaminants on the image-receiving surface can be confused with ink droplets in the image data. Lightly colored inks and weakly running inkjet printers produce ink droplets that form less contrast with the image-receiving material than darkly colored inks or ink droplets formed with appropriate droplet mass. Analysis of image data of printed images is useful for detecting droplets ejected by split inkjet printers and for identifying which inkjet printers in the print head are split inkjet printers. 【0020】 An exemplary test pattern suitable for use in an image analysis process such as process 120 is shown in FIG. 2. Test pattern 300 includes a plurality of dashes, each dash being formed from ink ejected from a single inkjet ejector within a print head. Dash 302 is formed in the print process direction 332, and multiple columns of dashes are arranged along the cross-process axis 336. Test pattern 300 is configured to be used with a printer that uses cyan, magenta, yellow, and black (CMYK) color stations. Test pattern 300 is further configured to be used with an ink coloring station configured for interlaced printing using two print head arrays for each of the CMYK colors. As seen in cyan dash 304, magenta dash 308, yellow dash 312, and black dash 316, one dash of the same color from each of the aligned print heads in each coloring station is spaced adjacent to each other in each column of test pattern 300. In FIG. 2, the dashes in each column of test pattern 300 are arranged in a ladder-like fashion including seven inkjet ejectors, whereby one inkjet ejector in the inkjet print head forms one dash and the next dash in that column results from an inkjet ejector offset by six positions along the cross-process axis 336. The space 320 between consecutive dashes in a column of test pattern 300 is the width of six non-printing inkjet ejectors. Alternative test patterns may use ladders having a greater or lesser number of inkjet ejectors within each group that produce similar test patterns having multiple columns of dashes. 【0021】 The length of the dash 302 corresponds to the number of droplets used to form the dash. The number of droplets is selected to produce a dash whose length is sufficiently greater than the resolution of the optical detector in the process direction. The distance imaged by the optical detector depends on the velocity of the image member passing through the detector and the line velocity of the optical detector. A single line of optical detectors extending across the width of the imaging area on the image receiving member is referred to in this document as a scan line. The dash is generated with a length greater than a single scan in the process direction, and therefore the dash image can be resolved in image processing. Thus, multiple scan lines are required to image the entire length of the dash in the process direction. 【0022】 In the test pattern 300, the columns are grouped according to the waffle formation so as to leave spaces 302 for dashes, as seen by groups 324A to 324D. Each column in one of groups 324A to 324D is offset from the previous column by one ink jet ejector at the cross process axis 336. Each group has seven columns, enabling each ink jet ejector in the seven ink jet ejector series to form one dash. The number of groups is determined by the number of unique colors produced by the printing system, and the test pattern 300 shows an example of a CMYK printing system providing four groups 324A, 324B, 324C, and 324D. The four groups 324A to 324D enable each ink jet ejector within the print head for each color (CMYK) to print a dash in the test pattern 300. Thus, the lines 340 parallel to the process direction 332 are aligned to pass through the centers of the dashes of each color at the same cross process position. The line 340 passes through the center of the black dash 344A and through the edge of the black dash 344B. In relative terms, the black dash 344A is formed by the ink jet ejector in the first black print head at the first position of a group of seven consecutive ink jet ejectors within the first print head. The dash 344B corresponds to the seventh and final ink jet ejector of the previous group from the second black print head, and the second black print head is offset at the cross process axis 336 by half the width separating the ejectors within each print head. This offset enables the two black print heads to interlace the dashes for complete coverage of all locations under the print heads within the print zone. 【0023】 Line 340 passes through the yellow dashes 344C and 344D, the magenta dashes 344E and 344F, and the cyan dashes 344G and 344H in a similar manner to the black dashes 344A and 344B. When aligned in the cross-process direction, droplets of various colored inks are placed in the same location for color printing, where secondary colors are produced by mixing inks from CMYK colors. Furthermore, the interlaced arrangement of the print heads allows for parallel printing of ink droplets, producing colors that expand the color gamut and hue available to the printer. The test pattern 300 in Figure 2 can be repeated along the cross-process axis to include some or all of the inkjet ejectors from each print head in the print zone used to form an image on an image receiving member passing through the print zone. 【0024】 The process in Figure 120 begins by printing the test pattern discussed above and determining which dashes were printed by the split inkjet (block 124). The analysis for identifying the split inkjet is discussed in more detail below. Once the split inkjet is identified, the firing signal parameters are adjusted in a manner that modifies the inkjet. The firing signal parameters include the peak voltage of the signal, the frequency of the signal, and others known in the art. In one embodiment, the peak voltage of the firing signal of the split inkjet is increased. Eight dashes are formed using eight different inkjet, as shown in the upper image of Figure 6. The size of the dash area of ​​dashes 604 and 608 indicates that the inkjet that formed these dashes is the split inkjet. All injet that formed the dashes in this figure were operated with a firing signal having a peak voltage of 1.5V. The inkjet that formed dashes 604 and 608 was then operated with a peak voltage of 4.5V. As shown in the lower part of Figure 6, a dash formed by the same inkjet has approximately the same area as another dash formed by operating another inkjet with a firing signal having a peak voltage of 1.5V. 【0025】 The inkjet is operated using adjusted firing signal parameters during image printing (block 132), and the image is analyzed in the area corresponding to the segmented inkjet (block 136). If the pixels produced by the inkjet operating with the adjusted firing signal parameters are approximately the same size as pixels formed by a normal inkjet (block 140), the adjusted firing signal parameters are returned to their nominal value (block 144). As used in this document, the term "normal inkjet" means an inkjet that is not operational, weak, or segmented. Also, as used in this document, the term "nominal value" means the default value used for the firing signal parameters. If the size of the pixels is not within the acceptable range for pixels printed by a normal inkjet, the number of checks made on this inkjet is incremented by 1, and the number of checks is compared to the maximum threshold (block 148). If the maximum number of checks for the inkjet has not been reached, the inkjet continues to operate with the adjusted firing signal parameters, and additional checks are made until the inkjet is corrected or the maximum number of checks is made. Where used in this document, the term “correction” means a split inkjet that has been returned to a normal inkjet state by the operation of the split inkjet using a firing signal generated with adjusted firing signal parameters. If the check for the maximum number of inkjet is reached, the identifier of the split inkjet is stored in a list of non-functioning inkjets (block 152). The number of non-functioning inkjets in the list is then compared to the maximum number of inkjets allowed in the print head (block 156). If the number is equal to the maximum number of inkjets, the printing operation is stopped, thereby allowing purging (block 160). If the maximum number of non-functioning inkjets has not been reached, the firing signal parameters of the non-functioning inkjet are further adjusted (block 128), and the process continues. In this example, the peak voltage can be further increased to see if a higher peak voltage can correct the split inkjet. 【0026】 Figure 3 shows eight dashes formed by inkjet printing within the print head. The dashes in the top row are formed by normal inkjet printing, and the dashes in the bottom row are formed by split inkjet printing. Figure 5 is a magnified view of the dashes formed by inkjet printing within the print head. The top three rows of dashes are formed by split inkjet printing, and the dashes in the bottom row are formed by normal inkjet printing. As can be clearly observed from the figure, split inkjet printing produces dashes with a larger area than normal inkjet printing. Figure 4 shows a histogram of the dash area sizes of 5,544 inkjet prints within the print head. Approximately 4,500 inkjet prints are 55 mm². 2 The following area is produced: approximately 800 inkjet prints, 55mm 2 ~60mm 2 A dash with an area of ​​the range is formed, and approximately 100 inkjet prints are used, 60mm 2 It forms dashes with an area exceeding a certain value. Analysis of this histogram reveals that dashes with an area 1.5 times the standard deviation of the average dash area indicate that the inkjet print is a segmented inkjet print. Therefore, the distribution of dash areas can be determined empirically and used to identify the standard deviation and thus identify segmented inkjet prints. 【0027】 Referring to Figure 7, a prior art inkjet imaging system 110 is shown. The controller 50 of this system can be reconfigured with programmed instructions stored in a non-temporary computer-readable medium operably connected to the controller, thereby the controller executes the process of Figure 1 when executing the programmed instructions and operating the components of the printing system 110. For the purposes of this disclosure, the imaging apparatus is in the form of an inkjet printer using one or more inkjet print heads and associated ink supply. However, the systems and methods described herein are applicable to any of the various other imaging apparatuses that use inkjet to eject one or more colorants onto one or more media. The imaging apparatus includes a printing engine for processing image data before generating control signals for the inkjet ejector. The colorants can be any suitable substance, including ink or one or more dyes or pigments, to be applied to a selected medium. The colorants can be black or any other desired color, and a given imaging apparatus can apply multiple different colorants to a medium. The medium includes any of the various substrates, in particular plain paper, coated paper, glossy paper, or transparent film, and the medium can be provided as a sheet, roll, or another physical form. 【0028】 Figure 7 is a simplified schematic diagram of a direct-to-sheet, continuous-media, phase-change inkjet imaging system 110, which can be modified as described above to generate a test pattern and adjust the firing signal parameters for segmented inkjet using the method discussed above. The media supply and handling system is 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 a spool of media 10 mounted on a web roller 8. For single-sided printing, the printer consists of a feed roller 8, a media conditioner 16, a printing station 20, a printed web conditioner 80, a coating station 100, and a rewind unit 90. For double-sided operation, the web is inverted using a web inverter 84 before being taken up by the rewind unit 90, and the second side of the media is provided to the printing station 20, the printed web conditioner 80, and the coating station 100. In single-sided operation, the media source 10 has a width that substantially covers the width of the roller over which the media travels through the printer. In double-sided operation, the web travels over half of the rollers in the printing station 20, printed web conditioner 80, and coating station 100, and is then reversed by the inverter 84 and displaced laterally by a distance that allows the web to travel over the other half of the rollers opposite to the printing station 20, printed web conditioner 80, and coating station 100 for printing, conditioning, and coating on the back side of the web, so the medium source is approximately half the width of the rollers. The rewinding unit 90 is configured to wind the web onto the rollers for removal from the printer and subsequent processing. 【0029】 The medium is unwound from the supply source 10 as needed and propelled by various motors (not shown) to rotate one or more rollers. The medium conditioner includes rollers 12 and a preheater 18. Rollers 12 control the tension of the unwound medium as it moves along the path through the printer. In an alternative embodiment, the medium is transported along the path in the form of cut sheets, in which case the medium supply and handling system includes any suitable device or structure that enables the transport of the cut medium sheets along the expected path through the imaging device. The preheater 18 brings the web to an initial predetermined temperature selected for desired image characteristics corresponding to the type of medium being printed, as well as the type, color, and number of inks used. The preheater 18 can use contact heat, radiant heat, conductive heat, or convective heat to bring the medium to a target preheat temperature in one practical embodiment, ranging from about 30°C to about 70°C. 【0030】 The medium is transported through a printing station 20 which includes a series of printhead modules 21A, 21B, 21C, and 21D, each printhead module extending effectively across the width of the medium and capable of directly (i.e., without the use of intermediate or offset members) placing ink onto the moving medium. As is commonly known, each printhead can eject one color of ink, i.e., one of each of the colors commonly used in color printing, namely cyan, magenta, yellow, and black (CMYK). The printer's controller 50 receives speed data from encoders mounted in close proximity to rollers positioned on both sides of a portion of the opposite path of the four printheads to calculate the position of the web as it passes through the printheads. The controller 50 uses this data to generate timing signals to activate the inkjet ejectors within the printheads, enabling the ejection of four colors with reliable accuracy for the alignment of different color patterns to form four primary color images on the medium. The inkjet ejectors, activated by the ejection signals, correspond to the image data processed by the controller 50. Image data can be sent to a printer and generated by a scanner (not shown), which is a component of the printer, or generated by other means and provided to the printer. In various possible embodiments, a printhead module for each primary color may include one or more printheads, and the multiple printheads within the module may be formed in one or more rows of arrays, and the printheads in the multiple-row array may be staggered, and the printheads may print two or more colors, or the printheads or parts thereof may be mounted to be movable in a direction across the process direction P for spot color applications, etc. 【0031】 A printer may use “phase-change ink,” meaning that the ink is substantially solid at room temperature and becomes substantially liquid when heated to the phase-change ink melting temperature for spraying onto an imaging-receiving surface. The phase-change ink melting temperature can be any temperature at which a solid phase-change ink can be melted into a liquid or molten form. In one embodiment, the phase-change ink melting temperature is about 70°C to 140°C. In an alternative embodiment, the ink used in the imaging device may include UV-curable gel ink. Gel ink can also be heated before being ejected by the inkjet ejector of the print head. As used herein, liquid ink refers to molten solid ink, heated gel ink, or other known forms of ink such as aqueous ink, ink emulsion, ink suspension, or ink solution. 【0032】 Each printhead module is associated with backing members 24A–24D, typically in the form of bars or rolls, which are positioned substantially opposite the printhead on the back of the medium. Each backing member is used to position the medium at a predetermined distance from the printhead on the opposite side of the backing member. Each backing member can be configured to release thermal energy to heat the medium to a predetermined temperature, which in one practical embodiment is in the range of about 40°C to about 60°C. The various backing members can be controlled individually or collectively. The preheater 18, printhead, backing members 24 (if heated), and ambient air work together to maintain the medium within a predetermined temperature range of about 40°C to 70°C along the opposite side of the path of the printing station 20. 【0033】 As a partially imaged medium moves to receive various colored inks from the print head of the printing station 20, the temperature of the medium is maintained within a given range. The ink is typically discharged from the print head at a significantly higher temperature than the receiving medium temperature. As a result, the ink heats the medium. Therefore, the medium temperature can be maintained within a given range using other temperature control devices. For example, the air temperature and airflow behind and in front of the medium also affect the medium temperature. Therefore, an air blower or fan can be used to facilitate control of the medium temperature. Thus, the medium temperature is kept substantially uniform throughout all ink ejection from the print head of the printing station 20. To enable control of the medium temperature, temperature sensors (not shown) can be positioned along this portion of the medium path. These temperature data can also be used by a system to measure or estimate (e.g., from image data) how much of a given primary color ink is being applied to the medium at a given time from the print head. 【0034】 Following the printing zone 20 along the media path are one or more “intermediate heaters” 30. The intermediate heaters 30 can use contact, radiation, conductivity, or convection heating, or a combination of these different heaters, to control the temperature of the media. The intermediate heaters 30 bring the ink placed on the media to a temperature suitable for desired properties as the ink on the media is delivered through the spreader 40. In one embodiment, the useful range for the target temperature of the intermediate heater is about 35°C to about 80°C. The intermediate heaters 30 have the effect of equalizing the ink and substrate temperatures within about 15°C of each other. Lower ink temperatures result in less line diffusion, while higher ink temperatures result in transparency (visibility of the image from the other side of the print). The intermediate heaters 30 adjust the substrate and ink temperatures to be 0°C to 20°C higher than the spread temperature. 【0035】 Following the intermediate heater 30, the fixing assembly 40 is configured to fix the image to the medium by applying heat, pressure, or both. The fixing assembly may include any suitable device or apparatus for fixing the image to the medium, including heated or unheated pressure rollers, radiant heaters, heat lamps, etc. In the embodiment of Figure 7, the fixing assembly includes a “spreader” 40 that applies a predetermined pressure, and in some embodiments, heat, to the medium. The function of the spreader 40 is to take essentially droplets, strings of droplets, or lines of ink on the web W and rub them together by pressure, thereby filling the spaces between adjacent droplets and making the image solid uniform in some systems. In addition to spreading the ink, the spreader 40 also improves image permanence by increasing the aggregation of the ink layer and increasing ink-web adhesion. The spreader 40 includes rollers, such as an image-side roller 42 and a pressure roller 44, for applying heat and pressure to the medium. Either roll may include a heating element, such as a heating element 46, to bring the web W to a temperature in the range of about 35°C to about 80°C. In an alternative embodiment, the fixed assembly may be configured to spread the ink using non-contact heating (without pressure) of the medium after the printing zone. Such a non-contact fixed assembly can use any suitable type of heater for heating the medium to the desired temperature, such as a radiant heater or a UV heating lamp. 【0036】 In one practical embodiment, the roller temperature within the spreader 40 is maintained at an optimal temperature, such as 55°C, depending on the properties of the ink. Generally, lower roller temperatures result in less line spread, while higher temperatures cause gloss defects. Roller temperatures that are too high can cause the ink to be offset on the roll. In one practical embodiment, the nip pressure is set in the range of approximately 500 to approximately 2000 psi lbs / side. Lower nip pressure results in less line spread, while higher pressure can reduce the lifespan of the pressure roller. 【0037】 The spreader 40 may also include a cleaning / oiling station 48 associated with the image-side roller 42. The station 48 cleans the roller surface and applies a layer of several release agents or other materials to the roller surface. The release agent material can be an aminosilicone oil having a viscosity of about 10-200 centipoise. Only a small amount of oil is required, and the amount of oil carried by the medium is only about 1-10 mg per A4-sized page. In one possible embodiment, the intermediate heater 30 and the spreader 40 can be combined into a single unit, and their respective functions occur simultaneously for the same portion of the medium. In another embodiment, the medium is kept at a high temperature when printed to allow for ink spreading. 【0038】 The coating station 100 applies a transparent ink to the printed medium. This transparent ink helps protect the printed medium from rubbing or other environmental degradation after removal from the printer. The transparent ink overlay acts as a sacrificial layer of ink that can be rubbed or offset during handling without affecting the appearance of the image beneath it. The coating station 100 applies the transparent ink by either a roller or a print head 104 that ejects the transparent ink in a pattern. For the purposes of this disclosure, transparent ink is functionally defined as a substantially transparent overcoat ink that has minimal impact on the final printed color, regardless of whether the ink lacks all colorants. In one embodiment, the transparent ink used for the coating ink comprises a phase-change ink formulation that does not contain colorants. Alternatively, the transparent ink coating can be formed using a reduced set of typical solid ink components, or a single solid ink component such as polyethylene wax or polywax. As used herein, polywax refers to a family of relatively low molecular weight linear polyethylene or polymethylene waxes. Similar to colored phase-change inks, transparent phase-change inks are substantially solid at room temperature and are substantially liquid or melted when first sprayed onto a medium. Transparent phase-change inks can be heated to approximately 100°C to 140°C, thereby melting the solid ink for spraying onto a medium. 【0039】 After passing through the spreader 40, the printing medium is either wound onto rollers for removal from the system (single-sided printing) or directed to the web inverter 84 for reversal and displacement to another part of the rollers for a second pass by the print head, intermediate heater, spreader, and coating station. The double-sided printed material is then wound onto rollers by the rewind unit 90 for removal from the system. Alternatively, the medium can be directed to other processing stations that perform tasks such as cutting, binding, collating, and stapling. 【0040】 The operation and control of various subsystems, components, and functions of device 110 are performed using a controller 50. The controller 50 is implemented using a general-purpose or dedicated programmable processor that executes programmed instructions. Instructions and data required to perform programmed functions may be stored in a non-temporary computer-readable medium associated with the processor or controller. The processor, their memory, and interface circuits constitute the controller and print engine for performing the functions described above. These components may be provided on a printed circuit card or as circuits within an application-specific integrated circuit (ASIC). Each circuit may be implemented on a separate processor, or multiple circuits may be implemented on the same processor. Alternatively, the circuit may be implemented with separate components or circuits provided for a VLSI circuit. Furthermore, the circuits described herein may be implemented in combination with processors, ASICs, individual components, or VLSI circuits. 【0041】 The imaging system 110 includes an optical sensor 54. The drum sensor is configured to detect, for example, the presence, intensity, and location of ink droplets ejected onto a receiving member by an inkjet of a print head assembly. In one embodiment, the optical sensor includes a light source and a photodetector. The light source may be a single light-emitting diode (LED) coupled to a light pipe, which transmits the light generated by the LED to one or more apertures in the light pipe that direct the light toward an image substrate. In one embodiment, three LEDs, namely an LED that generates green light, an LED that generates red light, and an LED that generates blue light, are selectively activated so that only one light is emitted at a time, directing the light through the light pipe toward 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 the light toward the image substrate. The light source in this embodiment includes three linear arrays, namely one linear array for each of 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 LED light source can be coupled to a controller 50 or some other control circuit to operate the LED for image illumination. 【0042】 The reflected light is measured by a photodetector in the optical sensor 54. In one embodiment, the light sensor is a linear array of photosensitive devices, such as a charge-coupled device (CCD). The photosensitive devices generate an electrical signal corresponding to the intensity or amount of light received by the photosensitive devices. The linear array extends substantially across the width of the image-receiving member. Alternatively, a shorter linear array can be configured to translate across the image substrate. For example, the linear array can be mounted on a movable carriage that translates across the image-receiving member. Other devices for moving the light sensor can also be used. 【0043】 The reflectance is detected by a photodetector in an optical sensor 54 corresponding to each inkjet and each pixel position on the receiving member. The photodetector is configured to generate electrical signals corresponding to the reflected light, and these signals are provided to the controller 50. These electrical signals are used by the controller 50 to determine information related to the ink droplets ejected onto the receiving member as described above. Using this information, the controller 50 adjusts the firing signal parameters to modify the generation of the firing signal to correct the split inkjet as described above. 【0044】 Figure 8 shows a schematic diagram of a prior art printing zone 1000 that can be used in system 110. The printing zone 1000 includes four color units 1012, 1016, 1020, and 1024 arranged along a process direction 1004. Each color unit discharges ink of a different color from the other color units. In one embodiment, color unit 1012 discharges cyan ink, color unit 1016 discharges magenta ink, color unit 1020 discharges yellow ink, and color unit 1024 discharges black ink. The process direction is the direction in which the image receiving member moves as it travels under the color units from color unit 1012 to color unit 1024. Each color unit includes two printing arrays, each containing two print bars, each having multiple print heads. For example, the print head array 1032 of the magenta color unit 1016 includes two print bars 1036 and 1040. Each print bar has multiple print heads, as exemplified by print head 1008. Print bar 1036 has three print heads, and print bar 1040 has four print heads, although alternative print bars may use more or fewer print heads. Print heads on print bars within print arrays, such as the print heads on print bars 1036 and 1040, are staggered to provide printing across image-receiving members at a first resolution. Print heads on print bars having print array 1034 within color unit 1016 are interlaced with the print heads in print array 1032, enabling printing in colored inks across image-receiving members in the cross-process direction at a second resolution. The print bars and print arrays of each color unit are arranged in this manner. One print head array within each color unit is aligned with one of the respective print head arrays of the other color units. The other print head arrays within color units are similarly aligned with each other. Thus, the aligned print head arrays enable drop-on-drop printing of different primary colors to produce secondary colors.Interlaced printheads also allow for parallel ink droplets of different colors, expanding the color gamut and hue available in the printer. 【0045】 It will be understood that various variations of the above-disclosed features and functions, or substitutes thereof, may be desirablely combined with many other different systems or applications. Various currently unforeseen substitutes, modifications, variations, or improvements, which are also intended to be covered by the following "Claims," ​​may be subsequently made by those skilled in the art.

Claims

[Claim 1] A method for operating an inkjet printer, Operating at least one print head to form a test pattern having a plurality of dashes on an image receiving member, wherein the at least one print head operates such that each inkjet in the at least one print head forms one of the plurality of dashes, each dash in the plurality of dashes is formed by a plurality of ink droplets ejected from each inkjet in the at least one print head, each dash extends in the process direction such that it is longer than the length of a single scan line in the process direction in which the image receiving member moves, generated by a plurality of optical detectors extending in a cross-process direction across the image receiving member, and each dash is formed by only a single inkjet in the at least one print head. To generate image data of the test pattern on the image receiving member, A method comprising: identifying the area of ​​each of the plurality of dashes; and analyzing the generated image data by identifying the inkjet as a segmented inkjet if the identified area of ​​the dash formed by the inkjet is larger than the identified area of ​​the dash formed by a normal inkjet. [Claim 2] The method according to claim 1, further comprising adjusting at least one firing signal parameter for each segmented inkjet identified in the at least one print head. [Claim 3] The method according to claim 2, wherein the adjusted at least one launch signal parameter is a peak voltage. [Claim 4] The method according to claim 3, wherein the peak voltage is increased. [Claim 5] The identification of the divided inkjet is The method of claim 2, further comprising detecting that the difference between the identified area of ​​the dash formed by the segmented inkjet and the average area of ​​the dash among the plurality of dashes formed by the normal inkjet in the at least one print head is 1.5 times the standard deviation of the average area. [Claim 6] The method of claim 5, further comprising generating a firing signal for operating the split inkjet using the at least one firing signal parameter adjusted for each split inkjet. [Claim 7] The image data of the ink droplets ejected onto the image receiving member by the segmented inkjet is generated after analyzing the generated image of the ink droplets ejected by the segmented inkjet in order to form an additional dash on the image receiving member, and then used to form the additional dash on the image receiving member. The method of claim 6, further comprising identifying the modified segmented inkjet in response that the difference between the area of ​​at least one of the additional dashes and the average area of ​​the dashes among the plurality of dashes formed by the normal inkjet in the at least one print head is less than 1.5 times the standard deviation. [Claim 8] The method of claim 7, further comprising returning the at least one adjusted firing signal parameter for the split inkjet, which is identified as being modified to a nominal value. [Claim 9] It is an inkjet printer, A print head having multiple inkjet inks, A plurality of optical detectors extending in a cross-process direction across the surface of an image receiving member moving through at least one print head, wherein the plurality of optical detectors are configured to generate scan lines of data on the surface of the image receiving member, A controller operationally connected to the at least one print head and the plurality of optical detectors, wherein the controller Each inkjet in at least one print head is operated to discharge a plurality of ink droplets onto the image receiving member as the image receiving member moves in the process direction, forming a single dash in a test pattern having a plurality of dashes on the image receiving member in the inkjet printer, and each of the plurality of dashes extending in the process direction by a distance greater than the length in the process direction of the scan line generated by the plurality of optical detectors. The image data generated by the plurality of optical detectors of the plurality of dashes in the test pattern on the image receiving member is received, Identify the area of ​​each dash in the image data of the plurality of dashes. A controller is configured to identify an inkjet as a segmented inkjet when the identified area of ​​the dash formed by the inkjet is larger than the identified area of ​​the dash formed by a normal inkjet in at least one print head, The aforementioned controller Adjusting at least one firing signal parameter for each segmented inkjet identified in the at least one print head, The peak voltage is adjusted as at least one of the adjusted firing signal parameters. An inkjet printer further configured to increase the aforementioned peak voltage. [Claim 10] The aforementioned controller The inkjet printer according to claim 9, further configured to detect that the difference between the identified area of ​​the dash formed by the segmented inkjet and the average area of ​​the dashes formed among the plurality of dashes by the normal inkjet in at least one print head is 1.5 times the standard deviation of the average area. [Claim 11] The inkjet printer according to claim 10, further comprising generating a firing signal for operating the segmented inkjet using the at least one firing signal parameter adjusted for each segmented inkjet. [Claim 12] The aforementioned controller After the segmented inkjet operates with the generated firing signal, the image data generated by the plurality of optical detectors of the ink droplets ejected onto the image receiving member by the segmented inkjet to form additional dashes on the image receiving member is received. Analyzing the generated image of the ink ejected by the split inkjet, The inkjet printer according to claim 11, further configured to identify the modified segmented inkjet in response that the difference between the area of ​​at least one of the additional dashes and the average area of ​​the dashes among the plurality of dashes formed by the normal inkjet in the at least one print head is less than 1.5 times the standard deviation. [Claim 13] The aforementioned controller The inkjet printer according to claim 12, further configured to return the at least one adjusted firing signal parameter for the segmented inkjet identified as being modified to a nominal value. [Claim 14] A method for operating an inkjet printer, Operating at least one print head to form a test pattern having a plurality of dashes on an image receiving member, wherein each inkjet in the at least one print head operates to form one of the plurality of dashes, and each of the plurality of dashes has a length in the process direction that is longer than the length of the scan line in the process direction in which the image receiving member moves, generated by a plurality of optical detectors extending in a cross-process direction across the image receiving member. The plurality of optical detectors generate image data of the test pattern on the image receiving member, The process includes identifying the area of ​​each of the plurality of dashes, and identifying the inkjet as a segmented inkjet if the identified area of ​​the dash formed by the inkjet is larger than the identified area of ​​the dash formed by a normal inkjet. The identification of the divided inkjet is A method further comprising detecting that the difference between the identified area of ​​the dash formed by the segmented inkjet and the average area of ​​the dashes formed among the plurality of dashes by the normal inkjet in at least one print head is 1.5 times the standard deviation of the average area. [Claim 15] The image data of the ink droplets ejected onto the image receiving member by the segmented inkjet is generated after operating the segmented inkjet with a firing signal having at least one firing signal parameter adjusted from a nominal value, thereby forming additional dashes on the image receiving member. Analyzing the generated image data of the additional dashes formed by the segmented inkjet using the firing signal having at least one adjusted firing signal parameter, The method of claim 14, further comprising identifying the modified segmented inkjet in response that the difference between the area of ​​at least one of the additional dashes and the average area of ​​the dashes among the plurality of dashes formed by the normal inkjet in the at least one print head is less than 1.5 times the standard deviation. [Claim 16] The method of claim 15, further comprising returning the at least one adjusted firing signal parameter for the split inkjet, which has been identified as being modified to the nominal value.

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