Inkjet printer and method for operating the same

Abstract

The present invention is entitled "System and method for detecting and remediating a split jet in an inkjet printer during printing operations." A method that analyzes image data of a test pattern printed on an image receiving member by a printer to identify a split jet in a print head of the printer. A test pattern is formed by operating each ink jet of the print head to form a short line, and the area of ​​the short line is compared with an average short line area to identify the split jet. The firing signal parameters of the split jet are adjusted, and subsequent firing signals are generated using the adjusted parameters. After the split jet has been operated using the adjusted firing signal parameters, the image data of the pixels formed by the split jet is analyzed. If the pixel size of the split jet indicates that the split jet has been remedied, the firing signal parameters are restored to their nominal values.

Description

Technical Field

[0001] The present disclosure relates generally to identifying stray inkjets in an inkjet printer having one or more printheads, and more particularly to remediating those inkjets during printing operations. Background Art

[0002] An inkjet printer has a printhead that operates multiple jets of ink that eject liquid ink onto an image receiving member. The ink may be an aqueous ink, an ink emulsion, a gel ink, or an ink that is loaded in solid form and then melted to produce a liquid ink. A typical inkjet printer uses one or more printheads. Each printhead typically contains a separate nozzle array for ejecting droplets of ink onto an image receiving member across an open gap to form an ink image. The image receiving member may be a continuous web of recording medium, a series of media sheets, or a rotating surface such as a print drum or endless belt. The image printed on the rotating surface is then transferred to the recording medium by mechanical forces in a moving nip formed by the rotating surface and a moving roller. In an inkjet printhead, a separate piezoelectric, thermal, or acoustic actuator generates a mechanical force that expels ink from an ink-filled chamber through an orifice in response to a voltage signal (sometimes referred to as a firing signal). The magnitude or voltage level of the signal affects the amount of ink ejected in each droplet. The firing signal is generated by a printhead controller based on image data. An inkjet printer uses image data to form a printed image by printing a pattern of individual ink droplets at specific locations on an image receiving member. The locations where ink droplets land are sometimes referred to as "drop locations," "drop locations," or "pixels." Thus, the printing operation can be viewed as placing ink droplets on an image receiving member using image data to produce an ink image corresponding to the image data.

[0003] One problem resulting from operating an inkjet in a printhead to form an ink image is known as "split jet inkjet". The term split jet inkjet as used in this document refers to an inkjet that produces a group of droplet fragments rather than a single droplet when the inkjet is operated to eject an ink drop. These ink fragments (sometimes referred to as satellites) tend to spread and produce spotty pixels rather than sharply defined circles. These defective pixels can result in streaks that are detrimental to the final image quality perceived by the customer.

[0004] A procedure known as "purging" is an effective procedure to overcome any degradation in inkjet performance. To purge the printhead, pressurized air is applied to the ink reservoir in the printhead to expel ink through the inkjet. The expelled ink collects on the faceplate of the printhead and is typically wiped into a waste ink reservoir. While this procedure restores many inkjets to their operating condition, it causes significant losses due to lost productivity, because of the need to bring the printing operation to a complete stop in order to purge the printhead, and because the cost of expelling ink can be high, especially when the purge is performed frequently. Therefore, purging is typically limited to once every two hours of printer operation.

[0005] Unfortunately, inkjet degradation may occur in a time scale significantly shorter than the two hours of purge operations that are usually separated for printers. Depending on the area coverage of the print being manufactured, defects may appear as fast as ten minutes after the purge operation, which corresponds to about 2500 sheets being printed. Technologies for masking missing or weak inkjets have been developed. Missing inkjets actually do not eject ink, and weak inkjets eject a small portion of full-size ink drops. By increasing the amount of ink in the ink drops ejected by other inkjets near the missing or weak inkjets, the impact of missing or weak inkjets can be reduced to a certain extent. However, these technologies are not effective for solving shunt inkjets because these inkjets spread the amount of ink drops in an area larger than the area where the droplets should land. Adding more ink to the area may also cause image defects while repairing them. It would be beneficial to be able to detect shunt inkjets during printing operations and to remedy them to a certain extent without stopping the printing operation. Summary of the invention

[0006] A method of operating a printer that analyzes image data corresponding to a test pattern generated by the printer on an image receiving member to identify a split inkjet, and then generates a remedial firing signal for the identified split inkjet within a limited time. The method includes operating at least one printhead to form a test pattern on the image receiving member, generating image data of the test pattern on the image receiving member, and analyzing the generated image data to identify a split inkjet in the at least one printhead.

[0007] A novel printer analyzes image data corresponding to a test pattern generated by the printer on an image receiving member to identify a split inkjet, and then generates a remedial firing signal for the identified split inkjet within a limited time. The printer includes at least one printhead and a controller configured to operate the at least one printhead 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 a split inkjet in the at least one printhead. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] The foregoing aspects and other features of a printer and method of operation thereof for detecting and remediating stray inkjet during printing operations are explained in the following description in conjunction with the accompanying drawings.

[0009] Figure 1 is a flow chart of a method for identifying and remedying a spilt inkjet in an inkjet printer.

[0010] Figure 2 Is suitable for Figure 1 The method is used together with a sample test pattern.

[0011] Figure 3 It is an image of short lines produced by split-flow inkjet and short lines produced by operating inkjet.

[0012] Figure 4 A histogram is depicted regarding multiple inkjets in a printer and the area sizes of short lines formed by the inkjets.

[0013] Figure 5 It is another image of the short lines produced by split-flow inkjet and the short lines produced by operating inkjet.

[0014] Figure 6 is an image showing the use of an elevated peak-to-peak firing signal voltage to remediate a shunted inkjet.

[0015] Figure 7 is a schematic diagram of a prior art inkjet imaging system that ejects ink onto a continuous web of media as the media moves past printheads in the system.

[0016] Figure 8 is a schematic diagram of a prior art print head configuration. DETAILED DESCRIPTION

[0017] Figure 11 is a process 120 for detecting split jets and remediating them to an operational state. Process 120 employs an optical sensor to analyze image data obtained from the surface of an image receiving member in a printing system. This analysis enables the location and area of ​​a short line to be determined more accurately, and the location and area information of the short line is used to determine which jet in the print head is a split jet. In one embodiment, the optical sensor includes an optical detector array mounted to a rod or other longitudinal structure extending across the width of an imaging area on the image receiving member. In one embodiment, where the imaging area is approximately 20 inches wide in the cross-process direction and the print head prints at a resolution of 600 dpi in the cross-process direction, more than 12,000 optical detectors are arranged in a single row along the rod to generate a single scan line on the imaging member. The optical detectors are configured in conjunction with one or more light sources that direct light to the surface of the image receiving member. The optical detectors receive light generated by the light source after the light is reflected from the image receiving member. The magnitude of the electrical signal generated by the optical detector in response to light reflected from the exposed surface of the image receiving member is higher than the magnitude of the signal generated in response to light reflected from ink droplets on the image receiving member. The difference in the magnitude of the generated signal is used to identify ink droplets on an image receiving member (such as a sheet of paper, a media web, or a print drum). However, the reader should note that lighter colored inks, such as yellow, cause the contrast signal generated by the optical detector relative to the uncovered portion of the image receiving member to be lower than the contrast signal generated by darker inks (such as black) relative to the uncovered portion of the image receiving member. Therefore, the contrast signal difference is used to distinguish between short lines of different colors. The magnitude of the electrical signal generated by the optical detector is converted into digital values ​​by an appropriate analog-to-digital converter. These digital values ​​are represented as image data in this document, and these data are analyzed to identify positional information about the short line on the image receiving member and the inkjet that produced the short line.

[0018] As used in this document, the term "profiling" or "analysis" refers to processing image data using a controller to determine whether an inkjet operating to eject ink actually ejected ink, where the ejected ink landed, and the area of ​​the image receiving surface that did not receive ink. In some printing systems, an image of a printed image is generated 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 off-line imaging device. This method of generating a picture of a printed image has the problem of not being able to analyze the printed image in situ and the inaccuracies imposed by an external scanner. In some printers, the scanner is integrated into the printer and positioned at a position in the printer that enables imaging of the ink image to be generated when the image is on the medium within the printer or when the ink image is on a rotating image member. These integrated scanners typically include one or more illumination sources and multiple optical detectors that receive radiation reflected from the image receiving surface from the illumination source. The radiation from the illumination source is typically visible light, but the radiation may be at or beyond either end of the visible light spectrum. If the light is reflected by a white surface, the reflected light has the same spectrum as the illumination light. In some systems, the ink on the imaging surface may absorb a portion of the incident light, which causes the reflected light to have a different spectrum. In addition, some inks may emit radiation of a different wavelength than the illuminating radiation, such as when the ink fluoresces in response to the 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 to 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 respect to two directions. "Process direction" refers to the direction in which the image receiving member moves as the imaging surface passes the print head to receive the ejected ink, and "lateral process direction" refers to the direction across the width of the image receiving member.

[0019] The environment in which the image data is generated is not pristine. Several sources of noise exist and need to be addressed in the analysis of the image data. For example, the image receiving member may contribute noise to the image data. Specifically, structures in the image receiving surface and colored contaminants in the image receiving surface may be confused with ink droplets in the image data, and light-colored inks and weaker-performing inkjets provide ink droplets that have less obvious contrast with the image receiving member than dark-colored inks or ink droplets formed with appropriate droplet mass. Analysis of the image data of the printed image can be used to detect droplets ejected by a split-flow inkjet and to identify which ink jet in the printhead is a split-flow inkjet.

[0020] Figure 2An example test pattern suitable for use with an image analysis process, such as process 120, is depicted in . Test pattern 300 includes a plurality of short lines, each of which is formed by ink ejected from a single inkjet ejector in a printhead. Short lines 302 are formed in a printing process direction 332, with multiple rows of short lines arranged along a transverse process axis 336. Test pattern 300 is configured for use with a printer using cyan, magenta, yellow, and black (CMYK) coloring stations. Test pattern 300 is further configured for use with an ink coloring station configured for interlaced printing of each of the CMYK colors using two printhead arrays. In each row of test pattern 300, short lines of the same color from each of the aligned printheads in each coloring station are spaced adjacent to each other, as shown by cyan short line 304, magenta short line 308, yellow short line 312, and black short line 316. In Figure 2 3, the dashes in each row of the test pattern 300 are arranged in a ladder comprising seven (7) inkjet ejectors such that one inkjet ejector in the inkjet printhead forms the dash and the next dash in the row is from an inkjet ejector that is offset six (6) positions on the transverse process axis 336. The space 320 between consecutive dashes in a row of the test pattern 300 is the width of six non-printing inkjet ejectors. Alternative test patterns may employ ladders having a greater or lesser number of inkjet ejectors in each group, thereby producing a similar test pattern with multiple rows of dashes.

[0021] The length of the short line 302 corresponds to the number of droplets used to form the short line. The number of droplets is selected to produce a short line of sufficient length to be greater than the resolution of the optical detector in the process direction. The distance imaged by the optical detector depends on the speed of the image member moving past the detector and the line rate of the optical detector. A single row of optical detectors extending across the width of the imaging area on the image receiving member is referred to as a scan line in this document. The short line is generated in the process direction with a length greater than a single scan line, so that the short line image can be resolved in image processing. Therefore, multiple scan lines are required to image the entire length of the short line in the process direction.

[0022] The rows in the test pattern 300 are grouped according to the ladder formation for the space short lines 302, as seen by the groups 324A-324D. Each row in one of the groups 324A-324D is offset by one inkjet ejector on the transverse process axis 336 from the previous row. Each group has seven rows, allowing each inkjet ejector in the series of seven inkjet ejectors to form a short line. The number of groups is determined by the number of unique colors generated by the printing system, where the test pattern 300 shows an example of a CMYK printing system that provides four groups: 324A, 324B, 324C and 324D. The four groups 324A-324D allow each inkjet ejector in the print head for each color (CMYK) to print a short line in the test pattern 300. Therefore, the line 340 parallel to the process direction 332 is aligned to pass through the center of the short line of each color at the same transverse process position. Line 340 passes through the center of the black short line 344A and passes through the edge of the black short line 344B. In relative terms, black dash 344A is formed by an inkjet ejector in a first black printhead at a first position of a group of seven consecutive inkjet ejectors in the first printhead. Dash 344B corresponds to the seventh and final inkjet ejector from the previous group of a second black printhead, where the second black printhead is offset on the transverse process axis 336 by half the width separating the ejectors in each printhead. This offset allows the two black printheads to stagger dashes for complete coverage of all positions under the printheads in the print zone.

[0023] Line 340 passes through yellow short lines 344C and 344D, magenta short lines 344E and 344F, and cyan short lines 344G and 344H in a similar manner to black short lines 344A and 344B. When aligned in the cross-process direction, droplets of various color inks are placed in the same position for color printing, which produces a second color by mixing the ink with the CMYK color. In addition, the staggered arrangement of the printheads enables the ink droplets to be printed side by side to produce colors with an extended color gamut and hues available in the printer. Figure 2 The test pattern 300 may be repeated along the cross-process axis to include some or all of the inkjet ejectors from each printhead in the print zone used to form an image on an image receiving member passing through the print zone.

[0024] Figure 1 The process of 120 begins by printing the test pattern discussed above and determining which short lines are printed by a shunt inkjet (box 124). The analysis used to identify the shunt inkjet is discussed in more detail below. Once the shunt inkjet is identified, the firing signal parameters are adjusted in a manner that remediates 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 for the shunt inkjet is increased. Figure 6 As shown in the upper image of , eight different inkjets have been used to form eight short lines. The size of the short line area of ​​short lines 604 and 608 indicates that the inkjets forming such short lines are split-flow inkjets. All of the inkjets forming the short lines in this figure were operated with a firing signal having a peak voltage of 1.5V. The inkjets forming short lines 604 and 608 were subsequently operated with a peak voltage of 4.5V. Figure 6 As shown in the lower figure, the short line formed by the same inkjet now has approximately the same area as other short lines formed by operating other inkjets with a firing signal having a peak voltage of 1.5V.

[0025] The inkjet is operated during image printing using the adjusted firing signal parameters (box 132), and the image in the area corresponding to the shunted inkjet is analyzed (box 136). If the inkjet operating under the adjusted firing signal parameters produces pixels that are approximately the same size as the pixels formed by normal inkjet (box 140), the adjusted firing signal parameters are restored to their nominal values ​​(box 144). As used in this document, the term "normal inkjet" refers to an inkjet that is not an inoperable, weak, or shunted inkjet. In addition, as used in this document, the term "nominal value" refers to the default value of the firing signal parameter. If the size of the pixel is not within the allowable range around the pixel size printed by the normal inkjet, the number of checks performed on the inkjet is incremented by one, and the number of checks is compared to a maximum threshold value (box 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 perform additional checks until the inkjet is remedied or the maximum number of checks has been performed. As used in this document, the term "remediate" refers to a shunt inkjet that has been restored to a normal inkjet state by operation of the shunt inkjet using a firing signal generated using adjusted firing signal parameters. If the maximum inspection number of the inkjet is reached, the identifier of the shunt inkjet is stored in a list of inoperable inkjets (box 152). The number of inoperable inkjets in the list is then compared to the maximum number of inkjets allowed in the printhead (box 156). If the number is equal to the maximum number of inkjets, the printing operation is stopped so that a purge can be performed (box 160). If the maximum number of inoperable inkjets has not been reached, the firing signal parameters of the inoperable inkjets are further adjusted (box 128), and processing continues. In this example, the peak voltage can be further increased to investigate whether a higher peak voltage can remedy the shunt inkjet.

[0026] Figure 3 Eight short lines formed by ink jetting in a print head are shown. The upper row of short lines is formed by normal ink jetting, and the short lines in the lower row are formed by split-flow ink jetting. Figure 5is an enlarged view of the short lines formed by the inkjet in the print head. The top three rows of short lines are formed with split-flow inkjet, and the short lines in the bottom row are formed with normal inkjet. As can be clearly observed from the figure, the split-flow inkjet produces short lines with a larger area than the normal inkjet. Figure 4 A histogram of the size of the dashed area for 5,544 inkjets in the printhead is plotted. Approximately 4,500 of the inkjets produce a 55 mm 2 or less area, and about 800 inkjet shots form a 55mm 2 Up to 60mm 2 The short line within the area of ​​​​the range and about 100 times of inkjet formation have a size greater than 60mm 2 Analysis of the histogram reveals that short lines with an area of ​​1.5 times the standard deviation of the mean short line area indicate that the inkjet is a split-flow inkjet. Therefore, the distribution of the short line area is determined empirically, so the standard deviation can be identified and used to identify the split-flow inkjet.

[0027] refer to Figure 7 , shows a prior art inkjet imaging system 110. The controller 50 of this system can be reconfigured with programming instructions stored in a non-transitory computer readable medium operably connected to the controller, so that when the controller executes the programmed instructions and operates the components of the printing system 110, it performs Figure 1 For purposes of this disclosure, the imaging device is in the form of an inkjet printer that employs one or more inkjet printheads and an associated ink supply. However, the systems and methods described herein are applicable to any of a variety of other imaging devices that use inkjet to eject one or more colorants onto a medium or media. The imaging device includes a print engine to process image data before generating control signals for the inkjet ejectors. The colorant may be ink or any suitable substance containing one or more dyes or pigments, and the colorant is applied to the selected medium. The colorant may be black or any other desired color, and a given imaging device may be capable of applying a variety of different colorants to the medium. The medium includes any of a variety of substrates, including plain paper, coated paper, glossy paper, or transparent film, and the medium may be provided as a sheet, a roll, or another physical format.

[0028] Figure 7is a simplified schematic diagram of a phase change inkjet imaging system 110 for direct-to-paper continuous media, which can be modified as previously described to generate test patterns and adjust firing signal parameters for split-stream inkjet using the methods 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 reel of media 10 mounted on a web roll 8). For pure printing, the printer consists of a feed roll 8, a media conditioner 16, a print station 20, a print web conditioner 80, a coating station 100, and a rewind unit 90. For duplex operation, a web inverter 84 is used to flip the web before being wound up by the rewind unit 90 to present the second side of the media to the print station 20, the print web conditioner 80, and the coating station 100. In pure operation, the media source 10 has a width that substantially covers the width of the roll, and the media travels through the printer over the width of the roll. In duplex operation, the media source is approximately half the width of the roll before being flipped by the inverter 84 and laterally displaced a distance, as the web travels on one half of the roll in the print station 20, print web conditioner 80, and coating station 100, a distance that enables the web to travel on the other half of the roll opposite the print station 20, print web conditioner 80, and coating station 100 for printing, conditioning, or coating the opposite side of the web, if necessary. The rewind unit 90 is configured to wind the web onto the roll for removal from the printer and subsequent processing.

[0029] The media is unwound from a source 10 as needed and advanced by a variety of motors that rotate one or more rollers, not shown. The media conditioner includes a roller 12 and a preheater 18. The roller 12 controls the tension of the unwound media as the media moves along a path through the printer. In an alternative embodiment, the media is conveyed along a path in the form of a cut sheet, in which case the media supply and handling system includes any suitable device or structure that enables conveyance through the imaging device along the intended path. The preheater 18 brings the web to an initial predetermined temperature, which is selected for the desired image characteristics corresponding to the type of media being printed and the type, color and amount of ink being used. The preheater 18 can use contact, radiation, conduction or convection heating to bring the media to a target preheat temperature, which in one practical embodiment is in the range of about 30°C to about 70°C.

[0030] The media is conveyed through a print station 20, which includes a series of printhead modules 21A, 21B, 21C and 21D, each of which effectively extends across the width of the media and is capable of directly placing ink (i.e., without the use of intermediate or offset members) onto the moving media. As is well known, each of the printheads is capable of ejecting a single color of ink, one for each of the colors commonly used in color printing, namely cyan, magenta, yellow and black (CMYK). The controller 50 of the printer receives speed data from encoders mounted to the near side of the rollers positioned on either side of the portion of the path opposite the four printheads to calculate the position of the web as it moves past the printheads. The controller 50 uses this data to generate timing signals for actuating the inkjet ejectors in the printheads so that the four colors can be ejected with a reliable degree of accuracy for registration of different color patterns, thereby forming four original color images on the media. The inkjet ejectors actuated by the firing signals correspond to the image data processed by the controller 50. The image data may be transmitted to the printer, generated by a scanner (not shown) as a component of the printer, or otherwise generated and delivered to the printer. In various possible embodiments, the printhead module for each original color may include one or more printheads; the multiple printheads in the module may be formed in a single row or a multi-row array; the printheads in the multi-row array may be staggered; the printheads may print more than one color; or the printheads or portions thereof may be movably mounted in a direction transverse to the process direction P, such as for spot color applications, etc.

[0031] The printer may use "phase change inks," which refers to inks that are substantially solid at room temperature and substantially liquid when heated to a phase change ink melting temperature for ejection onto an imaging receiving surface. The phase change ink melting temperature may be any temperature that is capable of melting a solid phase change ink into a liquid or molten form. In one embodiment, the phase change ink melting temperature is approximately 70°C to 140°C. In an alternative embodiment, the ink utilized in the imaging device may include UV curable gel ink. The gel ink may also be heated prior to being ejected by the inkjet head inkjet ejector of the printhead. As used herein, liquid ink refers to melted solid ink, heated gel ink, or other known forms of ink, such as aqueous ink, ink emulsion, ink suspension, ink solution, etc.

[0032] Associated with each printhead module is a backing member 24A-24D, typically in the form of a rod or roller, arranged substantially opposite the printhead on the back side of the media. Each backing member is used to position the media at a predetermined distance from the printhead opposite the backing member. Each backing member can be configured to emit thermal energy to heat the media to a predetermined temperature, which in a 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, the printhead, the backing member 24 (if heated), and the surrounding air combine to maintain the media along the portion of the path opposite the print station 20 within a predetermined temperature range of about 40°C to 70°C.

[0033] When the partially imaged medium moves to receive inks of various colors from the printhead of the print station 20, the temperature of the medium is maintained within a given range. The ink is ejected from the printhead at a temperature that is usually significantly higher than the temperature of the receiving medium. Therefore, the ink heats the medium. Therefore, other temperature regulating devices can be used to maintain the medium temperature within a predetermined range. For example, the air temperature and air flow rate behind and in front of the medium also affect the medium temperature. Therefore, a blower or fan can be used to promote the control of the medium temperature. Therefore, for the ejection of all inks from the printhead of the print station 20, the medium temperature remains substantially uniform. A temperature sensor (not shown) can be positioned along this portion of the medium path to enable the medium temperature to be adjusted. These temperature data can also be used by the system to measure or infer (e.g., from image data) how much ink of a given original color from the printhead is applied to the medium at a given time.

[0034] Following the print zone 20 along the media path are one or more "intermediate heaters" 30. The intermediate heater 30 may use contact, radiation, conduction or convection heating, or a combination of these different heaters, to control the temperature of the media. As the ink on the media is sent through the spreader 40, the intermediate heater 30 brings the ink placed on the media to a temperature suitable for the desired properties. In one embodiment, the useful range of the target temperature of the intermediate heater is from about 35°C to about 80°C. The intermediate heater 30 has the effect of equalizing the ink and substrate temperatures to within about 15° of each other. Lower ink temperatures give less line spreading, while higher ink temperatures result in show-through (the image is visible from the other side of the print). The intermediate heater 30 adjusts the substrate and ink temperatures to 0°C to 20°C above the temperature of the spreader.

[0035] After the intermediate heater 30, the fixing assembly 40 is configured to apply heat or pressure or both to the media to fix the image to the media. The fixing assembly may include any suitable device or apparatus for fixing the image to the media, including heated or unheated pressure rollers, radiant heaters, heat lamps, etc. Figure 7In an embodiment of the present invention, the fixing assembly includes a "spreader" 40, which applies a predetermined pressure and, in some specific implementations, applies heat to the medium. The function of the spreader 40 is to take the ink on the web W, which is essentially a droplet, a string of droplets, or a line, and spread them by pressure, and in some systems, heat, so that the space between adjacent droplets is filled and the image entity becomes uniform. In addition to spreading the ink, the spreader 40 also improves the image persistence by increasing the cohesion of the ink layer and increasing the ink-web adhesion. The spreader 40 includes rollers, such as an image side roller 42 and a pressure roller 44, to apply heat and pressure to the medium. Either roller 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 fixing assembly can be configured to spread the ink using non-contact heating (no pressure) of the medium after the printing zone. Such a non-contact fixing assembly can use any suitable type of heater to heat the medium to the desired temperature, such as a radiant heater, a UV heating lamp, etc.

[0036] In a practical embodiment, the roller temperature in the spreader 40 is maintained at a certain temperature to a certain optimal temperature, which depends on the properties of the ink, such as 55°C; generally, a lower roller temperature gives less line spreading, while a higher temperature causes gloss defects. Too high a roller temperature may cause the ink to shift to the roller. In a practical embodiment, the roller nip pressure is set in the range of about 500 to about 2000 psi lbs / side. A lower roller nip pressure gives less line spreading, while a higher pressure may reduce the pressure roller life.

[0037] The spreader 40 may also include a cleaning / oiling station 48 associated with the image side roller 42. The station 48 cleans and applies a layer of some stripper or other material to the roller surface. The stripper material may be an amino silicone oil having a viscosity of about 10-200 centipoise. Only a small amount of oil is required, and the oil carried by the medium is only about 1-10 mg per A4 size page. In one possible embodiment, the intermediate heater 30 and the spreader 40 may be combined into a single unit, wherein their respective functions occur simultaneously relative to the same portion of the medium. In another embodiment, the medium is maintained at an elevated temperature while it is printed to achieve spreading of the ink.

[0038] The coating station 100 applies a transparent ink to the print medium. This transparent ink helps prevent tailing or other environmental degradation after the print medium is removed from the printer. The superposition of transparent ink serves as a sacrificial layer of ink that can be smeared or offset during processing without affecting the appearance of the image below. The coating station 100 applies the transparent ink in a pattern using a roller or a print head 104 that sprays the transparent ink. For the purposes of this disclosure, the 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 without colorants. Alternatively, the transparent ink coating can be formed using a set of reduced typical solid ink components or a single solid ink component (such as polyethylene wax or poly wax). As used herein, poly wax 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 molten when initially sprayed onto the medium. The transparent phase change ink may be heated to about 100° C. to 140° C. to melt the solid ink for jetting onto media.

[0039] After passing through the spreader 40, the printed media is wound onto rollers for removal from the system (print-only) or directed to a web inverter 84 for inversion and shifting to another section of rollers for a second pass through the printhead, interheater, spreader, and coating stations. The duplex printed material is then wound onto rollers for removal from the system by a rewind unit 90. Alternatively, the media may be directed to other processing stations that perform tasks such as cutting, gluing, collating, and stitching the media.

[0040] The operation and control of the various subsystems, components and functions of the device 110 are performed by means of a controller 50. The controller 50 is implemented with a general or special programmable processor that executes programming instructions. The instructions and data required to perform the programming functions are stored in a non-transitory computer-readable medium associated with the processor or controller. The processor, the memory of the processor and the interface circuit configure the controller and the print engine to perform the functions described above. These components can be arranged on a printed circuit card, or arranged as a circuit in an application-specific integrated circuit (ASIC). Each circuit can be implemented by a separate processor, or multiple circuits can be implemented on the same processor. Alternatively, the circuit can be implemented by discrete components or circuits arranged in a VLSI circuit. In addition, the circuit described herein can be implemented with a combination of a processor, an ASIC, discrete components or a VLSI circuit.

[0041] The imaging system 110 includes an optical sensor 54. The drum sensor is configured to detect the presence, intensity and position of ink drops ejected onto the receiving member, for example, by the inkjet of the printhead assembly. In one embodiment, the optical sensor includes a light source and a light detector. The light source can be a single light emitting diode (LED) coupled to a light pipe, and the light pipe transmits the light generated by the LED to one or more openings in the light pipe, and the one or more openings direct the light to the imaging substrate. In one embodiment, three LEDs are selectively activated, one LED generates green light, one LED generates red light, and one LED generates blue light, so only one light is irradiated at a time to guide the light through the light pipe and be directed to the imaging 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 to the imaging substrate. The light source in this embodiment includes three linear arrays, one linear array for each of red, green and blue. Alternatively, all LEDs can be arranged in a single linear array in a repeating sequence of three colors. The LEDs of the light source can be coupled to a controller 50 or some other control circuit to activate the LEDs for image illumination.

[0042] The reflected light is measured by a light detector in the optical sensor 54. In one embodiment, the light sensor is a linear array of light-sensitive devices, such as charge coupled devices (CCDs). The light-sensitive devices generate an electrical signal corresponding to the intensity or amount of light received by the light-sensitive 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 imaging substrate. For example, the linear array can be mounted to a movable carriage that translates across the image receiving member. Other devices for moving the light sensor can also be used.

[0043] The reflectivity is detected by a light detector in the optical sensor 54, which corresponds to each ink jet and to each pixel location on the receiving member. The light sensor 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 about the ink droplets ejected onto the receiving member as previously described. Using this information, the controller 50 makes adjustments to the firing signal parameters to change the generation of the firing signal to remedy the split-flow inkjet as previously described.

[0044] Figure 81000. A schematic diagram of a prior art print zone 1000 that can be used in system 110 is shown in FIG. Print zone 1000 includes four color units 1012, 1016, 1020, and 1024 arranged along a process direction 1004. Each color unit ejects ink of a color different from that of the other color units. In one embodiment, color unit 1012 ejects cyan ink, color unit 1016 ejects magenta ink, color unit 1020 ejects yellow ink, and color unit 1024 ejects black ink. The process direction is the direction in which the image receiving member moves when it travels from color unit 1012 to color unit 1024 under the color unit. Each color unit includes two print arrays, each of which includes two print bars carrying a plurality of print heads. For example, print head array 1032 of magenta unit 1016 includes two print bars 1036 and 1040. Each print bar carries a plurality of print heads, as illustrated by print head 1008. Print bar 1036 has three print heads, while print bar 1040 has four print heads, but alternative print bars may employ a greater or lesser number of print heads. The print heads on the print bars within the print array, such as the print heads on print bars 1036 and 1040, are staggered to provide printing at a first resolution across the image receiving member. The print heads on the print bars where print array 1034 is located within color unit 1016 are staggered relative to the print heads in print array 1032 to enable printing with color ink across the image receiving member 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 in each color unit is aligned with one of the print head arrays in each color unit in the other color units. The other print head arrays in the color units are similarly aligned with each other. Thus, the aligned print head arrays enable drop-by-drop printing of different original colors to produce a second color. Staggered print heads also enable side-by-side ink drops of different colors to expand the color gamut and hue available in the printer.

[0045] It should be understood that variations of the above disclosed and other features and functions or their alternatives may be desirably combined into many other different systems or applications. Those skilled in the art may subsequently make various currently unforeseen or unanticipated replacements, modifications, changes or improvements, which are also intended to be covered by the appended claims.

Claims

1. A method of operating an inkjet printer, comprising: operating at least one printhead to form a test pattern having a plurality of short lines on an image receiving member, the at least one printhead being operated to form a single short line of the plurality of short lines with each ink jet from the at least one printhead, each short line of the plurality of short lines being formed by a plurality of ink droplets ejected from each ink jet from the at least one printhead, such that each short line extends a distance in a process direction that is greater than a length of a single scan line in the process direction, the single scan line being generated by a plurality of optical detectors extending in a cross-process direction across the image receiving member, and each short line being formed with only one ink jet from the at least one printhead; generating image data of the test pattern on the image receiving member; as well as analyzing the generated image data by identifying an area of ​​each of the plurality of short lines; as well as When the identified area of ​​the short lines formed by the inkjet in the plurality of short lines is larger than the identified area of ​​the short lines produced by normal inkjet in the at least one print head in the plurality of short lines, the inkjet is identified as a split-flow inkjet.

2. The method according to claim 1, further comprising: At least one firing signal parameter is adjusted for each split jet identified in the at least one printhead.

3. The method of claim 2, wherein the at least one firing signal parameter adjusted is a peak voltage. The method of claim 3 , wherein the peak voltage is increased.

5. The method according to claim 2, wherein the identifying of the split-flow inkjet further comprises: The identified area of ​​the short line formed by the split-flow inkjet is detected to be 1.5 times the standard deviation of the average area of ​​the short lines among the plurality of short lines formed by the normal inkjet in the at least one print head.

6. The method according to claim 5, further comprising: The at least one firing signal parameter adjusted for each split-flow inkjet is used to generate a firing signal for operating the split-flow inkjet.

7. The method according to claim 6, further comprising: generating image data that the ink drops ejected by the split-flow inkjet onto the image receiving member form additional short lines on the image receiving member; analyzing image data generated by the ink droplets ejected by the split-flow inkjet to form the additional short lines on the image receiving member, and The diverted inkjet that has been remedied is identified in response to an area of ​​at least one of the additional stubs being less than 1.5 times a standard deviation of an average area of ​​the stubs in the plurality of stubs formed by the normal inkjet in the at least one printhead.

8. The method according to claim 7, further comprising: The at least one firing signal parameter of the adjustment identified as being remedied for the split jet is restored to a nominal value.

9. An inkjet printer, comprising: at least one print head having multiple ink jets; a plurality of optical detectors extending across a surface of an image receiving member in a cross-process direction, the image receiving member moving past the at least one print head, the plurality of optical detectors configured to: generate a data scan line of the surface of the image receiving member; as well as a controller operably connected to the at least one printhead and the plurality of optical detectors, the controller being configured to: operating each ink jet in the at least one print head to eject a plurality of ink droplets onto the image receiving member as the image receiving member moves in a process direction to form a single short line in a test pattern having a plurality of short lines on the image receiving member in the inkjet printer, whereby each short line in the plurality of short lines extends a distance in the process direction that is greater than a length of the scan lines generated by the plurality of optical detectors in the process direction; receiving image data generated by the plurality of optical detectors for the plurality of dashes in the test pattern on the image receiving member; identifying an area of ​​each short line in the image data of the plurality of short lines; as well as When the identified area of ​​the short line formed by the inkjet is larger than the identified area of ​​the short line formed by normal inkjet in the at least one printhead, the inkjet is identified as a split-flow inkjet.

10. The inkjet printer according to claim 9, wherein the controller is further configured to: At least one firing signal parameter is adjusted for each split jet identified in the at least one printhead.

11. The inkjet printer according to claim 10, wherein the controller is further configured to: The peak voltage is adjusted according to the at least one firing signal parameter that is adjusted.

12. The inkjet printer according to claim 11, wherein the controller is further configured to: Increase the peak voltage.

13. The inkjet printer according to claim 10, wherein the controller is further configured to: The identified area of ​​the short line formed by the split-flow inkjet is detected to be 1.5 times the standard deviation of the average area of ​​the short line formed by the normal inkjet in the at least one print head among the plurality of short lines.

14. The inkjet printer according to claim 13, further comprising: The at least one firing signal parameter adjusted for each split-flow inkjet is used to generate a firing signal for operating the split-flow inkjet.

15. The inkjet printer according to claim 14, wherein the controller is further configured to: receiving image data generated by the plurality of optical detectors of ink drops ejected by the split-flow inkjet onto the image receiving member forming additional dashes on the image receiving member after the split-flow inkjet has been operated with the generated firing signal; analyzing image data generated by ejecting the ink drops from the split-flow inkjet to form the additional short lines on the image receiving member; as well as The diverted inkjet that has been remedied is identified in response to at least one of the additional stubs having an area that is less than 1.5 times a standard deviation of an average area of ​​the stubs in the plurality of stubs formed by the normal inkjet in the at least one printhead.

16. The inkjet printer according to claim 15, wherein the controller is further configured to: The at least one adjusted firing signal parameter of the split jet identified as being remedied is restored to a nominal value.

17. A method of operating an inkjet printer, comprising: operating at least one print head to form a test pattern having a plurality of short lines on an image receiving member, the at least one print head being operated to form a single short line of the plurality of short lines with each ink ejection in the at least one print head, each short line of the plurality of short lines having a length in a process direction greater than a length in the process direction of a scan line generated by a plurality of optical detectors extending in a cross-process direction across the image receiving member; generating image data of the test pattern on the image receiving member using the plurality of optical detectors; as well as identifying an area of ​​each of the plurality of short lines; as well as When the identified area of ​​the short lines formed by the inkjet in the plurality of short lines is larger than the identified area of ​​the short lines formed by normal inkjet in the at least one print head in the plurality of short lines, the inkjet is identified as a split-flow inkjet.

18. The method of claim 17, wherein the identifying of the split-flow inkjet further comprises: The identified area of ​​the short line formed by the split-flow inkjet is detected to be 1.5 times the standard deviation of the average area of ​​the short line formed by the normal inkjet in the at least one print head among the plurality of short lines.

19. The method according to claim 18, further comprising: generating image data of ink drops ejected by the split-flow inkjet to form an additional short line on the image receiving member after the split-flow inkjet has been operated using a firing signal having at least one firing signal parameter adjusted from a nominal value; analyzing image data generated by the additional dash formed by the split-stream inkjet using the firing signal having the at least one firing signal parameter adjusted; as well as The diverted inkjet that has been remedied is identified in response to at least one of the additional stubs having an area that is less than 1.5 times a standard deviation of an average area of ​​the stubs in the plurality of stubs formed by the normal inkjet in the at least one printhead.

20. The method according to claim 19, further comprising: The at least one firing signal parameter of the adjustment of the split jet identified as being remedied is restored to the nominal value.

Images