Image forming apparatus

Abstract

To provide an image forming apparatus that allows stable colorimetry performed by a reading device regardless of the type of sheets.SOLUTION: An image forming apparatus comprises: an engine control unit 312 that prints an image on a sheet; a color sensor 200 that reads patch images from the sheet having thereon the image printed by the engine control unit 312 and conveyed through a conveyance path; and a printer controller 103 that performs image adjustment for the image printed by the engine control unit 312 on the basis of a result of reading of the patch images performed by the color sensor 200. The printer controller 103 causes the engine control unit 312 to print a patch image that is determined to be any one of a first patch image and a second patch image on the basis of the type of the sheet.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to an image forming apparatus, such as a copying machine, a multifunction machine, or a printer, that incorporates a reading device for reading an image formed on a sheet of paper. [Background technology]

[0002] In commercial printing, color management is considered important. For this reason, image forming devices used in commercial printing are required to not only stabilize the color reproducibility of the output, but also to have diversity in color measurement, such as color certification of the image forming device. Color certification of the image forming device requires reading and measuring a predetermined number of patch images determined by the certification organization of each country (FOGRA, JapanColor, etc.). The predetermined number is, for example, 1000 or more. Hereinafter, the paper on which the patch images are printed is referred to as "chart paper."

[0003] It is required to perform color measurement of patch images in-line to save labor. In other words, it is preferable that a sensor that performs color measurement of patch images is provided inside the image forming apparatus. For highly accurate color measurement, it is necessary to detect multi-colors as spectral reflectance waveforms, and a configuration that performs color measurement in-line using a spectral color sensor has been proposed (Patent Document 1). For highly accurate color measurement, an image forming apparatus has been proposed that has a built-in spectral color sensor that detects multi-colors as spectral reflectance waveforms (Patent Document 1). This image forming apparatus is capable of in-line color measurement using the built-in spectral color sensor.

[0004] Inline colorimetry is also performed to increase the added value of the final product. One example of added value is information about the color stability during printing, which indicates the state of the final product delivered in commercial printing during printing. Information about the color stability during printing is obtained, for example, from the results of inline colorimetry. Color is not determined by color materials alone, but is also influenced by paper characteristics such as the texture and whiteness of the paper. For this reason, inline colorimetry must be performed not only on a reference paper, but also on various types of paper.

[0005] Inline colorimetry is performed immediately before or during the execution of a print job, and it is required to reduce the time required for colorimetry as much as possible so as not to impede printing productivity. Furthermore, from the viewpoint of reducing paper waste, it is required that many patch images are printed on one sheet of chart paper that is the subject of inline colorimetry, so the size of the patch images printed on the paper must be minimized. The size of the patch image is determined by the responsiveness of the sensor used for colorimetry and the exposure time of the sensor required to perform stable colorimetry from the chart paper being transported. Since the size of the patch image is determined in this way, there is a limit to the number of patch images that can be printed on the paper. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2013-54324 A Summary of the Invention [Problem to be solved by the invention]

[0007] When thick paper (generally paper with a basis weight of 300 gsm or more) is transported by rollers, slight slippage occurs even on a nearly horizontal transport path where the transport resistance of the paper is low. This causes the transport speed of the thick paper to decrease, and slight transport delays may occur compared to plain paper (generally paper with a basis weight of less than 300 gsm).

[0008] When measuring the color of a plurality of patch images while conveying the paper, it is efficient in terms of maximizing the number of patch images that can be arranged on one sheet of chart paper to continuously perform color measurement a predetermined number of times upon detection of a trigger patch image that serves as a trigger for color measurement. After the first trigger patch image is detected, the color measurement operation is repeated continuously at a predetermined timing. Therefore, when measuring the color of chart paper made of thick paper, errors in the color measurement position accumulate due to a decrease in the conveyance speed of the paper.

[0009] When the accumulated error in the color measurement position becomes large, there is a possibility that a patch image adjacent to the patch image that should be measured is measured. In this case, a false detection occurs. To prevent such a false detection, a margin is provided in the size of the patch image by the amount of the speed error that is usually assumed. However, if the size of the patch image is set taking into consideration the transport delay of the thick paper compared to the plain paper as the reference paper of the image forming device, the number of patch images that can be arranged on one sheet of chart paper decreases and paper waste increases. Since the size of the patch image printed on the thick chart paper cannot be made larger than the size of the patch image printed on the plain chart paper, stable inline color measurement on the thick paper becomes difficult.

[0010] The present invention has been made in consideration of the above problems, and has as its main object to provide an image forming apparatus that enables stable color measurement by a reading device even when different types of paper are used. [Means for solving the problem]

[0011] The image forming apparatus of the present invention is characterized by comprising an image forming means for printing an image on paper, a reading means for reading an image adjustment image from the paper on which an image has been printed by the image forming means and which is transported along a transport path, an adjustment means for performing image adjustment of the image printed by the image forming means based on the reading result of the image adjustment image by the reading means, and a control means for causing the image forming means to print the image adjustment image, which has been determined to be either a first image adjustment image or a second image adjustment image based on the type of paper. Effect of the Invention

[0012] According to the present invention, stable color measurement can be performed even when different types of paper are used. [Brief description of the drawings]

[0013] [Figure 1] FIG. 1 is a diagram illustrating the configuration of an image forming apparatus. [Diagram 2] FIG. [Diagram 3] FIG. [Figure 4] An illustration of an ICC profile. [Diagram 5] FIG. 1 is an explanatory diagram of color management. [Figure 6] 4 is a flowchart showing a color measurement process. [Figure 7] 6 is a diagram illustrating the variation in conveying speed for each type of paper. [Figure 8] FIG. 13 is an example of a first patch image. [Figure 9] 6 is an explanatory diagram of the color measurement process of the first patch image. [Figure 10] FIG. 13 is an example of a second patch image. [Figure 11] 6 is an explanatory diagram of the color measurement process of a second patch image. [Figure 12] FIG. 11 is a diagram showing a modified example of the second patch image. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0015] (Image forming device) 1 is a configuration diagram of an image forming apparatus according to the present embodiment. Image forming apparatus 100 according to the present embodiment is a printer that prints an image on paper 110 by electrophotography. Note that image forming apparatus 100 according to the present embodiment may also be an inkjet printer or a dye-sublimation printer.

[0016] Image forming apparatus 100 includes, within housing 101, mechanisms constituting an engine section for image formation and a controller (described below) for controlling the operation of each mechanism. An operation panel 180 is provided on the top of housing 101. Operation panel 180 is a user interface, and includes an input interface for receiving instructions from a user and an output interface for displaying a screen such as an operation screen. The input interface is various key buttons, a touch panel, or the like. The output interface is a display and a speaker. The mechanisms constituting the engine section include a mechanism for forming an image (image forming mechanism), a mechanism for transferring an image to paper 110 (transfer mechanism), a mechanism for feeding paper 110 (feed mechanism), and a mechanism for fixing an image to paper 110 (fixing mechanism).

[0017] The image forming mechanism includes four image forming units 120, 121, 122, and 123 corresponding to the colors of yellow (Y), magenta (M), cyan (C), and black (K). Each image forming unit 120, 121, 122, and 123 forms an image of the corresponding color. The image forming units 120, 121, 122, and 123 have the same configuration, except that the colors of the images they form are different. Here, the configuration of the image forming unit 120 will be described, and descriptions of the configurations of the other image forming units 121, 122, and 123 will be omitted.

[0018] The image forming unit 120 includes a photosensitive drum 105, a charger 111, a laser scanner 107, and a developing unit 112. The photosensitive drum 105 is a drum-shaped photosensitive body having a photosensitive layer on its surface, and rotates around a drum axis. The charger 111 uniformly charges the photosensitive layer on the surface of the rotating photosensitive drum 105. The laser scanner 107 scans the surface of the photosensitive drum 105 with a laser beam modulated based on image data representing an image to be formed. The laser scanner 107 includes a light emitting unit 108 that scans the laser beam emitted from a semiconductor laser in one direction, and a reflecting mirror 109 that reflects the laser beam from the light emitting unit 108 toward the photosensitive drum 105. The direction in which the laser scanner 107 scans the photosensitive drum 105 (the depth direction in the figure) is the main scanning direction.

[0019] The photosensitive drum 105 is charged and then scanned with a laser beam, so that an electrostatic latent image corresponding to the image data is formed on the surface. The developing device 112 develops the electrostatic latent image formed on the photosensitive drum 105 with a developer of a corresponding color. As a result, an image (developer image) in which the electrostatic latent image is visualized is formed on the surface of the photosensitive drum 105. A yellow image (developer image) is formed on the photosensitive drum 105 of the image forming unit 120. A magenta image (developer image) is formed on the photosensitive drum 105 of the image forming unit 121. A cyan image (developer image) is formed on the photosensitive drum 105 of the image forming unit 122. A black image (developer image) is formed on the photosensitive drum 105 of the image forming unit 123. The photosensitive drum 105 and the developing device 112 are detachable from the housing 101.

[0020] The transfer mechanism includes an intermediate transfer body 106 and a transfer roller 114. Images are transferred from the photosensitive drums 105 of the image forming units 120, 121, 122, and 123 in a sequentially superimposed manner onto the intermediate transfer body 106. In this embodiment, the intermediate transfer body 106 rotates clockwise in the figure, and images are transferred in the order of the image forming unit 120 (yellow), the image forming unit 121 (magenta), the image forming unit 122 (cyan), and the image forming unit 123 (black). An image density detection sensor 117 is provided downstream of the image forming unit 123 in the rotation direction of the intermediate transfer body 106 for detecting image density from an image for image density detection formed on the intermediate transfer body 106.

[0021] The image transferred to the intermediate transfer body 106 is transported to a transfer roller 114 by the rotation of the intermediate transfer body 106. An image formation start position detection sensor 115 for determining the transfer position onto the paper 110 is provided upstream of the transfer roller 114 in the rotation direction of the intermediate transfer body 106. The image formation start position detection sensor 115 detects the image on the intermediate transfer body 106. The transfer roller 114 presses the paper 110 onto the intermediate transfer body 106 and at the same time applies a bias with reverse characteristics to the image, thereby transferring the image from the intermediate transfer body 106 to the paper 110.

[0022] The feeding mechanism includes a paper feed cassette 113 that stores paper 110, a transport path along which the paper 110 is fed, and various rollers for transporting the paper 110 to the transport path. The paper 110 is fed from the paper feed cassette 113, and while being transported along the transport path, an image is transferred and fixed onto the paper 110 to form an image. The paper 110 is then discharged to a discharge tray 700 outside the housing 101.

[0023] For this purpose, the paper 110 is first fed along a transport path from a paper feed cassette 113 to a transfer roller 114. A paper feed timing sensor 116 for adjusting the transport timing of the paper 110 is provided midway along the transport path from the paper feed cassette 113 to the transfer roller 114. The timing at which the paper 110 is transported to the transfer roller 114 is adjusted based on the timing at which the image formation start position detection sensor 115 detects the image on the intermediate transfer body 106 and the timing at which the paper feed timing sensor 116 detects the paper 110. As a result, the image is transferred from the intermediate transfer body 106 to a predetermined position on the paper 110.

[0024] The paper 110 onto which the image has been transferred is transported to a fixing mechanism. The fixing mechanism of this embodiment includes a fixing device 150 and a cooling unit 160. The fixing device 150 includes a fixing roller 151 for heating the paper 110 in order to thermally pressurize the image onto the paper 110, a pressure belt 152 for pressing the paper 110 against the fixing roller 151, and a post-fixing sensor 153 for detecting completion of fixing. The fixing roller 151 is a hollow roller having an internal heater and configured to transport the paper 110 by rotating. The pressure belt 152 presses the paper 110 against the fixing roller 151 and is driven by the rotation of the fixing roller 151. The post-fixing sensor 153 detects the paper 110 after the image has been fixed.

[0025] The cooling unit 160 is disposed downstream of the fixing device 150 in the conveying direction of the paper 110, and is used to cool the paper 110 heated during the fixing process by the fixing device 150. The cooling unit 160 cools the paper 110, thereby reducing the heat supply from the paper 110 to the transfer mechanism during double-sided printing, and reducing the amount of curl in the resultant product. The cooling unit 160 has a roller 161, a roller 162, and a post-cooling sensor 163. The cooling unit 160 transfers the heat of the paper 110 to the rollers 161 and 162 by nipping and conveying the paper 110 at a nip portion formed by the rollers 161 and 162. The rollers 161 and 162 are configured to dissipate the heat transferred from the paper 110 by a cooling fan (not shown). The post-cooling sensor 163 detects the paper 110 after cooling.

[0026] The paper 110 cooled by the cooling unit 160 may be discharged as it is, or may be conveyed to a conveying path 133. For this reason, a flapper 132 is provided after the cooling unit 160. The flapper 132 guides the paper 110 to either the conveying path 133 or a discharge path 139 for the paper 110. The paper 110 guided to the discharge path 139 is discharged to a discharge tray 700 as it is.

[0027] The conveying path 133 is a path for conveying the paper 110 to an inversion path 138 used for inverting the front and back sides of the paper 110. The inversion path 138 is provided with an inversion sensor 137 for detecting the paper 110. When the inversion sensor 137 detects the rear end of the paper 110, the conveying direction of the paper 110 is inverted at the inversion path 138. The paper 110 whose conveying direction has been inverted is conveyed to either the rear conveying path 135 or the inversion path 140. For this purpose, flappers 134 and 136 are provided for branching the rear conveying path 135 and the inversion path 140. When conveyed to the rear conveying path 135, the paper 110 is guided to the rear conveying path 135 by the flappers 134 and 136, and is inverted and discharged to the discharge tray 700 via the discharge path 139. When conveyed to the inversion path 140, the paper 110 is inverted and conveyed to the transfer roller 114 again. This allows the paper 110 to have an image formed on the back side.

[0028] (Color measurement unit) The image forming apparatus 100 incorporates a color measurement unit 500 having a color sensor 200 for measuring the spectral reflectance of an image printed on the paper 110. The color measurement unit 500 is a reading device that reads a patch image, which is an image for image adjustment printed on the paper 110, and is provided on the post-conveying path 135. Based on the result of reading the image for image adjustment by the color measurement unit 500, image adjustment of the image to be printed next is performed. Image quality such as color tone is kept constant by the image adjustment. Note that the color measurement unit 500 may be provided on a conveying path other than the post-conveying path 135 as long as it is at a position where color measurement can be performed after the fixing process and before the paper is discharged. For example, the color measurement unit 500 may be provided on the discharge path 139. FIG. 2 is a configuration explanatory diagram of the color measurement unit 500.

[0029] The color sensor 200 is a spectral color sensor for detecting the spectral reflectance of a patch image 170 formed on the paper 110 and performing color measurement. The patch image 170 is an image for maintaining the image quality of the image to be printed. The color sensor 200 includes a white LED (Light Emitting Diode) 201, a diffraction grating 202, a line sensor 203, a calculation unit 204, a memory 205, and a lens 206. The color sensor 200 reads the image formed on the paper 110 being conveyed.

[0030] The white LED 201 is a light emitting unit that irradiates white light onto the paper 110 transported along the rear transport path 135. The lens 206 focuses the white light emitted from the white LED 201 onto the patch image 170, and diffuses the reflected light 207 from the patch image 170 toward the diffraction grating 202. The diffraction grating 202 separates the reflected light 207 from the patch image 170 into wavelengths. The line sensor 203 receives the reflected light 207 separated by the diffraction grating 202.

[0031] The line sensor 203 is a light receiving unit having n (n pixels) light receiving elements 203-1 to 203-n. Each of the light receiving elements 203-1 to 203-n of the line sensor 203 receives reflected light separated into wavelengths by the diffraction grating 202. Each of the light receiving elements 203-1 to 203-n receives reflected light of a wavelength assigned to it. The light receiving elements 203-1 to 203-n are, for example, CMOS (Complementary Metal Oxide Semiconductor) sensors.

[0032] The light receiving results (detection results) by each of the light receiving elements 203-1 to 203-n relate to the spectral wavelength. The number of the light receiving elements 203-1 to 203-n is preferably 41 (n=41) or more in order to obtain detection results with a resolution of 10 nm from 380 nm to 780 nm. In order to align the relationship between the wavelength and the number of the light receiving element, 48 or 64 light receiving elements are appropriate based on the adjustment range, etc. Also, the number of light receiving elements may be reduced, and the detection results of the missing wavelengths may be interpolated.

[0033] Each of the light receiving elements 203-1 to 203-n outputs a light intensity value representing the intensity of the received reflected light as a detection result. The calculation unit 204 performs a predetermined calculation on the light intensity value of each wavelength output from each of the light receiving elements 203-1 to 203-n. For example, the calculation unit 204 calculates a spectroscopic calculation or Lab value on the light intensity value. The calculation unit 204 has an A / D conversion function and converts the detection results by each of the light receiving elements 203-1 to 203-n into digital signals to perform various calculations. The memory 205 stores color measurement results such as calculation results.

[0034] (controller) 3 is an explanatory diagram of a controller that controls the operation of the image forming apparatus 100 configured as above. The image forming apparatus 100 is provided with a printer controller 103 that controls the overall operation of the image forming apparatus 100 and an engine control unit 312 that controls the operation of the engine unit as controllers.

[0035] The engine control unit 312 is connected to the post-fixing sensor 153, the post-cooling sensor 163, the reversing sensor 137, the drive motor 311 that drives various rollers that transport the paper 110, and the flappers 132, 134, and 136. The engine control unit 312 controls the drive motor 311 and the flappers 132, 134, and 136 included in the feeding mechanism based on the detection results of each sensor, thereby causing the engine unit to transport the paper 110. Although not shown in the figure, the engine control unit 312 also controls the operations of the image forming mechanism, the transfer mechanism, and the fixing mechanism to form an image on the paper 110. The operation of the engine control unit 312 is controlled by the printer controller 103.

[0036] The printer controller 103 is connected to a color sensor 200, an operation panel 180, and an external I / F 308. The external I / F 308 is a communication interface that communicates with a host computer 300, which is an external device, via a predetermined network. The printer controller 103 can receive print jobs and the like from the host computer 300 via the external I / F 308.

[0037] Printer controller 103 controls the operation of image forming apparatus 100 to print an image on paper 110. Printer controller 103 is configured by combining semiconductor devices and various electronic components. Examples of the semiconductor devices include a CPU (Central Processing Unit), an ASIC (Application Specific Integrated Circuit), and an MPU (Micro Processing Unit). Printer controller 103 may also be configured by a SOC (System-On-a-Chip).

[0038] The printer controller 103 processes the print job acquired from the host computer 300 via the external I / F 308 by each functional block stored in the ROM 320. The ROM 320 stores a RIP (Raster Image Processor) unit 314, a color processing unit 315, a tone correction table generating unit 316, a multi-color table generating unit 317, and a maximum density condition determining unit 318. The RIP unit 314 develops various image objects generated from data included in the print job received from the host computer 300 into a bitmap image. The maximum density condition determining unit 318, the tone correction table generating unit 316, and the multi-color table generating unit 317 reflecting the multi-color correction results manage and update the ICC profile, γLUT, and Vcont information used during image formation. The color processing unit 315 performs color conversion processing of the multi-color of the image to be printed based on this information.

[0039] The printer controller transmits image data generated from a print job by processing each functional block of the ROM 320 to the engine control unit 312. The engine control unit 312 prints an image on the paper 110 based on this image data.

[0040] In addition to ROM 320, printer controller 103 includes a profile creation unit 301, a color sensor control unit 302, a Lab calculation unit 303, and a color sensor input ICC profile storage unit 304. Printer controller 103 also includes an output ICC profile storage unit 305, a CMM (Color Management Module) 306, and an input ICC profile storage unit 307.

[0041] The color sensor control unit 302 controls the operation of the color sensor 200 under instructions from the engine control unit 312. The color sensor 200 performs color measurement processing under the control of the color sensor control unit 302. The engine control unit 312 instructs the color sensor control unit 302 to control the color sensor 200 according to, for example, the timing when the chart paper reaches the color measurement position of the color sensor 200. The timing when the chart paper reaches the color measurement position of the color sensor 200 is determined according to, for example, the timing when the inversion sensor 137 detects the chart paper.

[0042] When a customer engineer replaces a part, before a job that requires color matching accuracy is started, or when the user wants to know the color of the final output at the design concept stage, the user instructs the profile creation process through the operation panel 180. The printer controller 103 creates a profile in response to the instruction from the operation panel 180.

[0043] An instruction to create a profile is input to the profile creation unit 301 from the operation panel 180. In response to the instruction, the profile creation unit 301 sends a signal to the engine control unit 312 to form CMYK (cyan, magenta, yellow, black) color signals (patch images) of the ISO12642 test form without using a profile. At the same time, the printer controller 103 sends a color measurement instruction from the color sensor control unit 302 to the color sensor 200. The engine control unit 312 controls the operation of the image forming apparatus 100 to print the ISO12642 test form (patch images) on the paper 110. The paper 110 (chart paper) on which the test form (patch images) is printed is colorimetrically measured by the color sensor 200. Spectral reflectance data, which is the colorimetric result of the 928 patch images that have been measured, is input to the printer controller 103. The spectral reflectance data is converted to L*a*b* data by a Lab calculation unit 303 and temporarily stored in a color sensor input ICC profile storage unit 304, and then input to a profile creation unit 301. Note that the spectral reflectance data may be converted to the CIE1931XYZ color system, which is a device-independent color space signal rather than L*a*b*.

[0044] The profile creation unit 301 creates an output ICC profile based on the relationship between the CMYK color signals of the test form and the input L*a*b* data. The profile creation unit 301 replaces the output ICC profile already stored in the output ICC profile storage unit 305 with the created output ICC profile, updating it.

[0045] The ISO12642 test form includes patch images of CMYK color signals that cover the color reproduction range that a general copier can output. The profile creation unit 301 creates a color conversion table based on the relationship between each color signal value and the measured L*a*b* data. In other words, a conversion table (A2Bx tag) from CMYK to Lab is created. Based on this conversion table, a reverse conversion table (B2Ax tag) is created.

[0046] Figure 4 is an explanatory diagram of an ICC profile. An ICC profile consists of a header, tags, and data. In addition to a color conversion table, the tags also include a white point (Wtpt) and a tag (gamt) that describes whether a color expressed by the L*a*b values ​​defined in the profile is inside or outside the reproducible reproduction range of a hard copy.

[0047] The printer controller 103 may also receive an instruction to create a profile from the host computer 300 via the external I / F 308. In this case, the printer controller 103 obtains the output ICC profile created by the host computer 300, and performs color conversion using an application compatible with the ICC profile.

[0048] In color conversion in normal color image formation, image data inputted assuming RGB signal values ​​inputted via an external I / F 308 or standard printing CMYK signal values ​​such as JapanColor is stored in an input ICC profile storage unit 307 for external input. In this case, a scanner or the like is connected to the external I / F 308 as the host computer 300. The image data stored in the input ICC profile storage unit 307 is converted from RGB to L*a*b* or CMYK to L*a*b*. The input ICC profile is composed of a one-dimensional LUT that controls the gamma value of the input signal, a multi-color LUT called direct mapping, and a one-dimensional LUT that controls the gamma value of the generated conversion data. Using these tables, the image data stored in the input ICC profile storage unit 307 is converted from a device-dependent color space to device-independent L*a*b* data.

[0049] The image data converted into the L*a*b* chromaticity coordinates is input to the CMM 306. FIG. 5 is an explanatory diagram of color management by the CMM 306. The CMM 306 performs GUMAT conversion to map mismatches between the read color space of the scanner or the like, which is the host computer 300, and the output color reproduction range of the image forming apparatus 100, which is the output device. The CMM 306 also performs color conversion to adjust the mismatch between the light source type at the time of input and the light source type when observing the output (also called the mismatch of the color temperature setting), and performs black character determination, etc. As a result, the L*a*b* data is converted into L*'a*'b*' data and stored in the output ICC profile storage unit 305. As described above, the created profile is stored in the output ICC profile storage unit 305, and the data is color converted by the newly created ICC profile, converted into a CMYK signal dependent on the output device, and output. As shown in FIG. 5, the CMM 306 is a module that performs color management. The CMM 306 is a module that performs color conversion using the input profile and the output profile.

[0050] (Color measurement processing) 6 is a flowchart showing color measurement processing using the color measurement unit 500. This processing is started, for example, when a user designates a color measurement print job, such as creating a color profile for image adjustment, from the operation panel 180, and designates the paper type (name, basis weight, surface property, etc.) to be used in the color measurement print job.

[0051] The printer controller 103 controls the engine control unit 312 to start feeding the paper 110 from the paper feed cassette 113 (S601). The printer controller 103 controls the engine control unit 312 to transfer a patch image for creating a color profile onto the paper 110 (S602). After that, the printer controller 103 controls the engine control unit 312 to fix and cool the patch image onto the paper 110 by the fixing unit 150 and the cooling unit 160 (S603). In this manner, a chart paper on which a patch image for creating a color profile is printed is generated.

[0052] The printer controller 103 controls the engine control unit 312 to transport the chart paper to the transport path 133, and when the reversal sensor 137 detects the leading edge of the chart paper in the transport direction, a timer counts up to the length of the chart paper in the transport direction (S604). The printer controller 103 controls the engine control unit 312 to transport the chart paper to the reversal path 138 by at least the length in the transport direction, and then stops transporting (S605). As a result, the entire chart paper is transported to the reversal path 138.

[0053] The printer controller 103 controls the engine control unit 312 to reverse the conveying direction and resume conveying of the chart paper that was stopped on the reversing path 138 (S606). This causes the chart paper to be conveyed to the rear conveying path 135. The printer controller 103 controls the engine control unit 312 to increase the conveying speed of the chart paper (S607).

[0054] When the transport speed of the chart paper reaches the transport speed for color measurement (S608), the printer controller 103 puts the color sensor 200 into a trigger waiting state (S609) at the timing when the leading edge of the chart paper in the transport direction reaches the color measurement position of the color measurement unit 500. The trigger is the reading by the color measurement unit 500 of a trigger patch image printed on the chart paper. The trigger patch image will be described later.

[0055] The printer controller 103 monitors the reading of the trigger patch image by the color measurement unit 500 (S610: N). When the color measurement unit 500 reads the trigger patch image (S610: Y), the printer controller 103 starts a timer count based on the timing of reading the trigger patch image (S611). The printer controller 103 continues the timer count until the color measurement timing arrives (S612: N). The color measurement timing is the timing at which the count value reaches a value corresponding to a predetermined time. The predetermined time is the time from the reading of the trigger patch image to the time when the patch image reaches the color measurement position of the color sensor 200.

[0056] When the count value reaches the colorimetry timing (S612: Y), printer controller 103 causes white LED 201 to emit light and performs colorimetry on one patch image (S613). Printer controller 103 detects the color of the patch image based on the colorimetry result (S614). Printer controller 103 repeats the processes of S611 to S614 until colorimetry of all patch images printed on one sheet of chart paper is completed (S615: N).

[0057] When colorimetry of all patch images printed on one sheet of chart paper is completed (S615: Y), the printer controller 103 controls the engine control unit 312 to discharge the chart paper to the discharge tray 700 (S616). The printer controller 103 obtains the colorimetry results as spectral reflectance data, and performs the above-mentioned processing to generate and store various tables and color profiles (S617). The printer controller 103 repeats the processing of S601 to S617 for a predetermined number of sheets of chart paper (S618: N). When colorimetry for the predetermined number of sheets of chart paper is completed (S618: Y), the printer controller 103 ends the colorimetry processing.

[0058] 7 is an explanatory diagram of the variation in conveying speed for each type of paper 110. Using the conveying speed of plain paper with a basis weight of 81 [gsm] as a reference, the conveying speed variations of thin paper (basis weight 52 [gsm]), plain paper (basis weight 128 [gsm]), and thick paper (basis weights 300 [gsm], 400 gsm [gsm]) are illustrated. As is clear from FIG. 7, there is a tendency for the conveying speed of thick paper to vary more. Such conveying speed variations affect the color measurement process (reading process) of each patch image by the color measurement unit 500.

[0059] Fig. 8 is an example diagram of a patch image (first patch image) used for color measurement. Fig. 9 is an explanatory diagram of the color measurement process of the first patch image of Fig. 8. Fig. 10 is an example diagram of a patch image (second patch image) used for color measurement. Fig. 11 is an explanatory diagram of the color measurement process of the second patch image of Fig. 8.

[0060] When the type of paper 110 used for the chart paper is plain paper (here, the basis weight is less than 300 [gsm]), a chart paper is generated on which the first patch image is printed as shown in Fig. 8. In this embodiment, an example is described in which the first patch image is printed on A3 size paper 110, but the same effect can be obtained when using paper 110 of other sizes.

[0061] Plain paper generally has a basis weight of 50 [gsm] to 128 [gsm], and is widely distributed and therefore used as a standard paper for representing the color of images printed by image forming apparatus 100. However, because plain paper has low stiffness, it is prone to "uneven depth of focus due to undulation and waviness of the paper surface," which has the greatest impact on ensuring stable reading by color sensor 200 during color measurement.

[0062] Therefore, margins 8T and 8B are provided at the leading edge and trailing edge of the chart paper in the transport direction, so that the colorimetry of the trigger patch image 800 and the patch images 801 to 822 can be performed after the paper posture is stabilized. In this embodiment, the trigger patch image 800 is provided at a position spaced apart from the leading edge of the paper by a distance of the margin 8T in order to perform colorimetry while the chart paper is transported in the transport direction F. Then, a plurality of patch images 801 to 822 (total of 22 patches) are subjected to colorimetry for one sheet of chart paper. The patch images 801 to 822 each have a different image density. In this embodiment, the image density of the patch images 801 to 822 is set to be higher toward the leading edge. The patch image 822 provided at the rear end is provided at a position spaced apart from the trailing edge of the paper by a distance of the margin 8B. A blank space is provided between the trigger patch image 800 and the patch image 801, so that the colorimetry unit 500 can recognize the trigger patch image 800.

[0063] 9 shows the light emission timing of white LED 201 when reading the first patch image. White LED 201 is controlled to emit light at timings T1 to T22, based on detection timing T0 of trigger patch image 800.

[0064] In chronological order of the color measurement process, the color sensor 200 is first in a trigger waiting state (S609 in FIG. 6). The color sensor 200 starts counting with the timer 310 based on the detection timing T0 at which the trigger patch image 800 is read, and emits the white LED 201 to measure the color of the patch image 801 at timing T1.

[0065] Timing T1 is set by providing a paper transport delay margin M901 from the leading edge of patch image 810. After timing T1, color sensor 200 emits light multiple times during exposure time 91, and continuously receives reflected light from patch image 801 to obtain a spectral reflectance waveform. After measuring the color of patch image 801 by multiple light emission operations, color sensor 200 repeats the same operation at timings T2 to T22 to continuously measure the color of patch images 802 to 822 and obtain a spectral reflectance waveform. This completes the color measurement of one sheet of chart paper.

[0066] 7, when plain paper is used as the chart paper, the variation in transport speed is less than 0.2%. Therefore, even if there is a deviation in the transport distance due to the variation in transport speed, the delay margin M922 of the timing T22 is maintained. Because the delay margin M922 is maintained, erroneous detection of the patch image is prevented, and the color measurement unit 500 can measure the color of the 22 patch images 801 to 822 one by one in order.

[0067] However, when the type of chart paper is thick paper, there is a possibility that the transport speed may vary significantly by approximately 0.7%, which may result in a small delay margin M922. As a result, at the colorimetry timing T22 of patch image 822, patch image 821 may still be present at the colorimetry position by color sensor 200, which may result in erroneous detection of the patch image. Therefore, when thick paper is used as the type of chart paper, the second patch image in FIG. 10 is printed on paper 110 to prevent erroneous detection of the patch image.

[0068] Since thick paper is stiff, the above-mentioned "uneven depth of focus due to undulation and waviness of the paper surface" is unlikely to occur. Therefore, margins 10T and 10B provided at the leading and trailing ends of the chart paper in the transport direction can be set shorter than margins 8T and 8B of plain paper. In the second patch image, in addition to trigger patch image 10a, trigger patch image 10b can be provided between patch image 1011 and patch image 1012 in the space thus obtained. Margin 10C is provided between patch image 1011 and trigger patch image 10b.

[0069] Trigger patch image 10b is provided to reset delays caused by variations in conveying speed that increase when thick paper is used. Between trigger patch image 10a and patch image 1001, and between trigger patch image 10b and patch image 1012, blank spaces are provided, respectively, so that color measurement unit 500 can recognize trigger patch images 10a and 10b.

[0070] Since the trigger patch images 10a and 10b are also read while the chart paper is being conveyed, the trigger patch images 10a and 10b have the same size as the trigger patch image 800 in FIG. 8. The sizes of the patch images 1001-1011 arranged behind the trigger patch image 10a and the patch images 1012-1022 arranged behind the trigger patch image 10b are the same as the patch images 801-822 in FIG. 8, respectively. This makes it possible to perform colorimetry of thick chart paper with the same accuracy as that of plain paper under the same colorimetry conditions (exposure time 91, number of colorimetry measurements) as those for plain paper. The patch images 1001-1022 have different image densities. In this embodiment, the image densities of the patch images 1001-1022 are set to be higher toward the leading edge.

[0071] 11 shows the light emission timing of white LED 201 when reading the second patch image. White LED 201 is controlled to emit light at timings T1 to T11 based on detection timing T0a of trigger patch image 10a, and to emit light at timings T12 to T22 based on detection timing T0b of trigger patch image 10b.

[0072] In chronological order of the color measurement process, color sensor 200 is first in a trigger wait state (S609 in FIG. 6). Color sensor 200 starts counting with timer 310 based on detection timing T0a when trigger patch image 10a is read, and measures patch images 1001-1011. As shown in FIG. 7, the variation in conveying speed when thick paper is used as the chart paper is large at about 0.7%. However, because the number of patch images to be measured based on the reading of trigger patch image 10a is reduced by half compared to plain paper, the delay margin M1111 of timing T11 is maintained.

[0073] After measuring the color of patch image 1011, color sensor 200 again enters a trigger wait state and waits to read trigger patch image 10b. Color sensor 200 starts counting with timer 310 based on detection timing T0a when trigger patch image 10b is read, and measures patch images 1012 to 1022. Because the number of patch images to be measured based on the reading of trigger patch image 10b is halved compared to plain paper, the delay margin M1122 of timing T22 is maintained.

[0074] In this way, since the delay margins M1111 and M1122 are maintained even in the case of thick paper, erroneous detection of patch images is prevented. The colorimetric unit 500 first measures the colors of the eleven patch images 1101-1111 one by one in sequence, with timing based on the detection timing T0a. Then, the colorimetric unit 500 can measure the colors of the eleven patch images 1112-1122 one by one in sequence, with timing based on the detection timing T0b.

[0075] Here, trigger patch image 10b is provided so that the number of patch images 1001-1011 following trigger patch image 10a is the same as the number of patch images 1012-1022 following trigger patch image 10b. The number of patch images following the trigger patch image may be any number that can prevent erroneous detection of patch images due to variations in conveying speed, and therefore trigger patch image 10b does not necessarily need to be placed in the center of patch images 1001-1022.

[0076] The type of paper used for the chart paper is specified by the operation panel 180. As described above, when the user instructs the colorimetry process of FIG. 6, for example, the user specifies a colorimetry print job and a paper type (name, basis weight, surface property, etc.) by the operation panel 180. Before printing the patch image on the paper in the processes of S602 and S603, the printer controller 103 determines whether to print the first patch image or the second patch image according to the specified paper type. Specifically, the first patch image is printed on paper whose basis weight is smaller than a predetermined value, and the second patch image is printed on paper whose basis weight is larger than the predetermined value. In the above description, the type of patch image to be printed is determined based on the basis weight, but it may be determined based on the name of the paper. In any case, the second patch image is printed on paper whose transport speed varies greatly.

[0077] The image forming apparatus 100 may also include a detection device for detecting the type of paper. The detection device detects the basis weight of the paper, for example, and determines the type of paper based on the detected basis weight. The printer controller 103 detects the type of paper based on the result of the determination of the type of paper, and determines the patch image to be printed.

[0078] The number of types of patch images may be more than the above two. A type of patch image may be prepared for each type of paper that can be printed by image forming apparatus 100. However, the number of patch images printed on one sheet of paper must be the same for each type.

[0079] As described above, the image forming apparatus 100 of the present embodiment prepares multiple arrangement patterns of patch images used for inline colorimetry according to the type of paper used. This makes it possible to perform inline colorimetry even on thick paper such as paperboard while maintaining highly accurate colorimetry performance. This expands the range of inline colorimetry that can be handled, and makes it possible to achieve labor savings for a wider variety of colorimetry needs, such as guaranteeing the outcome by attaching a colorimetry result report.

[0080] 12 is a diagram showing a modified example of the second patch image. In the patch image of FIG. 12, the size in the transport direction of each of the patch images 1201-1222 is set to be larger than the size in the transport direction of each of the patch images 1001-1022 of FIG. 10. The trigger patch image 1200a is disposed closer to the leading edge of the paper than the trigger patch image 10a of FIG. 10. In other words, the margins 12T and 12B are set to be shorter than the margins 10T and 10B of FIG. 10. Between the trigger patch image 1200a and the patch image 1201, and between the trigger patch image 1200b and the patch image 1212, there is a blank space, so that the color measurement unit 500 can recognize the trigger patch images 1200a and 1200b.

[0081] In this way, by making the size of each patch image 1201-1222 larger when thick paper is used as the chart paper than when plain paper is used, it is possible to provide a larger margin for variation in the conveying speed. Note that the patch images 1201-1222 each have a different image density. In this embodiment, the image density of the patch images 1201-1222 is set to be higher toward the leading edge.

[0082] As described above, in the case of image adjustment using a type of paper with large variation in transport speed, the number of patch images taken in response to one trigger detection (reading of trigger patch images) is made smaller than in the case of image adjustment using a type of paper with small variation in transport speed. For example, the number of patch images taken in response to one trigger detection when performing image adjustment using thick paper is made smaller than the number of patch images taken in response to one trigger detection when performing image adjustment using plain paper. In the examples of Figures 10 and 12, the number of patch images read in response to one trigger detection when performing image adjustment using thick paper is half the number of patch images read in response to one trigger detection when performing image adjustment using plain paper.

[0083] By adjusting the images using chart paper on which such trigger patch images and patch images are printed, the risk of erroneous detection caused by reading patch images adjacent in the transport direction can be reduced even when the variation in the transport speed of the paper is greater than a predetermined value, and therefore, even when thick paper is used as the chart paper, it is possible to improve the stability of color measurement.

Claims

1. Image forming means for printing an image on paper, A reading means reads an image adjustment image from the paper on which an image has been printed by the image forming means and which is being transported along a transport path, Based on the reading result of the image adjustment image by the reading means, an adjustment means performs image adjustment of the image to be printed by the image forming means, The image forming means includes a control means that causes a first image adjustment image, including a trigger patch image, to be printed on a first type of paper, and a second image adjustment image, including the trigger patch image, to be printed on a second type of paper having a larger basis weight than the first type of paper. The number of trigger patch images included in the second image adjustment image is greater than the number of trigger patch images included in the first image adjustment image. Image forming apparatus.

2. The first image adjustment image and the second image adjustment image each have the trigger patch image provided on the leading side in the paper transport direction, and a plurality of patch images provided on the rear side of the trigger patch image in the transport direction. The control means is characterized by causing the reading means to read the plurality of patch images in succession at a predetermined timing, based on the timing of the reading of the trigger patch image by the reading means. The image forming apparatus according to claim 1.

3. A blank space is provided between the trigger patch image and the leading patch image in the transport direction of the plurality of patch images, characterized in that The image forming apparatus according to claim 2.

4. The first image adjustment image includes the plurality of patch images behind one of the trigger patch images in the transport direction, The second image adjustment image is characterized in that a portion of the plurality of patch images is provided behind the first trigger patch image in the transport direction, a second trigger patch image is provided behind the portion of the plurality of patch images in the transport direction, and the remaining portion of the plurality of patch images is provided behind the second trigger patch image in the transport direction. The image forming apparatus according to claim 3.

5. The second image adjustment image is characterized in that the second trigger patch image is provided such that the number of patch images provided on the rear side of the first trigger patch image in the transport direction is the same as the number of patch images provided on the rear side of the second trigger patch image in the transport direction. The image forming apparatus according to claim 4.

6. The distance from the leading edge of the paper of the second image adjustment image to the first trigger patch image is shorter than the distance from the leading edge of the paper of the first image adjustment image to the trigger patch image. The image forming apparatus according to claim 5.

7. The number of patch images in the first image adjustment image and the number of patch images in the second image adjustment image are the same, The image forming apparatus according to claim 6.

8. The first image adjustment image is characterized in that the size of each patch image in the transport direction of the plurality of patch images is the same as the size of each patch image in the transport direction of the plurality of patch images of the second image adjustment image. The image forming apparatus according to claim 7.

9. The size of each patch image in the transport direction of the plurality of patch images of the second image adjustment image is larger than the size of each patch image in the transport direction of the plurality of patch images of the first image adjustment image. The image forming apparatus according to claim 7.

Images