Image forming apparatus

Abstract

To measure a test chart on a sheet passing through a bent path with high accuracy regardless of the kind of the sheet.SOLUTION: An image forming device comprises: a color measurement sensor 200 that reads out a test chart for adjusting an image formation condition from a sheet having the test chart printed thereon; a conveying roller 141 arranged on the upstream side of the color measurement sensor 200 in a conveying direction of the sheet; a conveying roller 142 arranged on the downstream side of the color measurement sensor 200 in the conveying direction of the sheet; a first driving motor 145 that rotationally drives the conveying roller 141; a second driving motor 146 that rotationally drives the conveying roller 142; and a printer controller 103 that controls the first driving motor 145 and the second driving motor 146 on the basis of a speed set value of a conveying speed of the sheet set in accordance with the characteristics of the sheet, thereby adjusting a conveying speed at the time when the sheet passes through a reading position for the color measurement sensor 200 to be within a predetermined allowable range.SELECTED DRAWING: Figure 6

Description

Technical Field

[0001] The present invention relates to image forming apparatuses such as copiers, multifunction peripherals, and printers.

Background Art

[0002] In recent years, the market for on-demand image forming apparatuses has been expanding. For example, in the offset printing market, electrophotographic image forming apparatuses are spreading. Also, there are inkjet image forming apparatuses that have succeeded in extensive market development for reasons such as large format, low initial cost, and ultra-high speed. However, market expansion is not easy, and the image quality (hereinafter referred to as "image quality") of the preceding image forming apparatuses that have borne this market must be maintained. In order to maintain the image quality, the image forming conditions when the image forming apparatus forms an image on a sheet are appropriately corrected.

[0003] Image quality includes gradation, granularity, in-plane uniformity, character quality, color reproducibility (including color stability), etc. It is said that color reproducibility is the most important among these. Humans have memories of expected colors (especially human skin, sky, metal, etc.) based on experience, and may feel a sense of discomfort about colors that exceed the allowable range of this memory. Such memorized colors are called "memory colors". Memory colors are important for their reproducibility when outputting to photographs, etc. In addition, office user layers that feel a sense of discomfort about the color difference between printed business documents and monitors, graphic arts user layers that handle computer graphics, etc. have a high degree of demand for color reproducibility including stability for on-demand image forming apparatuses.

[0004] Regarding color reproducibility, not only between the same models but also between different models, differences in color with other types of image forming devices or image display devices such as displays become an issue. To perform color matching between these devices, there is software for creating a multi-dimensional LUT (Look Up Table) called an ICC (International Color Consortium) profile and a colorimeter. For professional users, ICC profiles for printers and offset printing presses are created, and a color management environment is constructed. As a result, it becomes possible to match the colors output by the printer to the colors printed by the offset printing press, so the printer can be used for color calibration of the offset printing press and for printing small quantities.

[0005] The contents of the ICC profiles for the offset printing press and the printer are calibrated in association with a color space that is independent of the printing press and the printer based on the color measurement results of a test chart using a colorimeter. The test chart is composed of a combination of a plurality of test images. The color space is, for example, the CIE L*a*b* color space (CIE is the Commission Internationale d'Eclairage). As a result, it is possible to match the colors printed by the printing press and the colors printed by the printer. The color management module (CMM) can create print data by performing color conversion using these ICC profiles.

[0006] As described above, a color management environment such as a colorimeter, an application, and profile creation software is in place. However, off-line colorimeters take time for color measurement. Also, this environment has issues such as the creation of ICC profiles, the upload of ICC profiles to printers, etc., and the effective use of the uploaded ICC profiles, and has not spread to general users. To perform color measurement faster, easily create ICC profiles, and automate the setting work, an image forming device is provided with an in-line colorimeter mounted near the sheet discharge section of the printer.

[0007] Patent Documents 1 and 2 disclose an image forming apparatus including a reading unit (measurement unit) that reads an image printed on a sheet during conveyance. The image forming apparatus needs to suppress as much as possible the variation in the conveyance speed of the sheet to be read, and accurately read a test chart printed within a limited range on the sheet by the reading unit. Based on the reading result of the test chart, image forming conditions such as image density and geometric characteristics of the image are corrected.

Prior Art Documents

Patent Documents

[0008]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0009] The types of sheets used by users vary widely. To meet different color standards in each country, color measurement results of many test images are required. To reduce the number of sheets consumed by forming test images on the sheet, it is necessary to reduce the size of the test images and print more test images on one sheet. However, to reduce the size of the test images, the conveyance speed when conveying the sheet must be stabilized.

[0010] When the conveyance path for conveying the sheet to the reading unit is bent (bent path), the conveyance speed becomes unstable. For example, the conveyance speed of cardboard passing through the bent path is slower than that of plain paper passing through the same bent path. This is because the cardboard has a greater thickness and higher stiffness than plain paper, resulting in an increase in conveyance resistance. As a result, cardboard or sheets with high stiffness may have a delayed passing time at the reading position of the reading unit compared to plain paper. Also, when the leading edge side of the sheet on which the test image is formed enters the bent path while the reading unit is reading the test image, similarly, the passing time of the sheet on which the test image is formed varies depending on the paper type of the sheet. Therefore, when the reading unit reads the test chart on the sheet passing through the bent path, color measurement is performed at a position different from the planned test image. This causes poor reading of the test chart.

[0011] The present invention has been made in view of the above problems, and an object thereof is to accurately measure a test chart on a sheet passing through a bent path regardless of the paper type.

Means for Solving the Problems

[0012] The image forming apparatus of the present invention Image forming means for forming a test chart on a sheet, conveying means for conveying the sheet along a conveyance path from the image forming means, and control means for controlling the conveying means while the sheet is being conveyed along the conveyance path by the conveying means. The conveying means has means for reading the test chart from the sheet reading and, the control means for controlling the conveying means. The conveying path has a bent portion that bends downstream in the sheet conveyance direction from the position of the first conveying roller. The control means controls the rotational speed of the first driving means and the rotational speed of the second driving means based on the basis weight of the sheet so that the conveyance speed of the sheet becomes the target speed when the test chart on the sheet passes through the reading position of the reading means while the leading end of the sheet passes through the bent portion. a first conveyance roller disposed upstream of the reading means in the conveyance direction of the sheet, a second conveyance roller disposed downstream of the reading means in the conveyance direction of the sheet, a first driving means for rotationally driving the first conveyance roller, and a second driving means for rotationally driving the second conveyance roller, has, and the conveyance path has a bent portion that bends downstream in the sheet conveyance direction from the position of the first conveying roller. The control means controls the rotational speed of the first driving means and the rotational speed of the second driving means based on the basis weight of the sheet so that the conveyance speed of the sheet becomes the target speed when the test chart on the sheet passes through the reading position of the reading means while the leading end of the sheet passes through the bent portion. characterized by the above.

Effects of the Invention

[0013] According to the present invention, it is possible to accurately measure a test chart on a sheet passing through a bent path regardless of the paper type.

Brief Description of the Drawings

[0014]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Mode for Carrying Out the Invention

[0015] Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[0016] (Image Forming Apparatus) FIG. 1 is a configuration diagram of the image forming apparatus according to the present embodiment. The image forming apparatus 100 according to the present embodiment forms an image on a sheet 110 by an electrophotographic method. Note that the image forming apparatus 100 according to the present embodiment may be an inkjet printer or a sublimation printer.

[0017] The image forming apparatus 100 includes each mechanism that constitutes an engine unit for image formation within the housing 101 and a controller (described later) that controls the operations of each mechanism. An operation panel 180 is provided on the upper part of the housing 101. The operation panel 180 is a user interface and includes an input device that receives instructions from the user and an output device that displays a screen such as an operation screen. Each mechanism that constitutes the engine unit includes a mechanism for forming an image (image forming mechanism), a mechanism for transferring the image to the sheet 110 (transfer mechanism), a mechanism for feeding the sheet 110 (feeding mechanism), and a mechanism for fixing the image to the sheet 110 (fixing mechanism).

[0018] The image forming mechanism includes four image forming units 120, 121, 122, and 123 corresponding to each color of yellow (Y), magenta (M), cyan (C), and black (K). The image forming units 120, 121, 122, and 123 form images of the corresponding colors. The image forming units 120, 121, 122, and 123 have the same configuration except that the colors of the formed images are different. Here, the configuration of the image forming unit 120 will be described, and the descriptions of the configurations of the other image forming units 121, 122, and 123 are omitted.

[0019] The image forming unit 120 includes a photosensitive drum 105, a charger 111, a laser scanner 107, and a developing device 112. The photosensitive drum 105 is a drum-shaped photoreceptor and rotates about a drum axis. The charger 111 uniformly charges the surface of the rotating photosensitive drum 105. The laser scanner 107 scans the photosensitive drum 105 with laser light modulated based on image data representing the image to be formed. The laser scanner 107 includes a light emitting unit 108 that scans the laser light emitted from a semiconductor laser in one direction and a reflection mirror 109 that reflects the laser light from the light emitting unit 108 toward the photosensitive drum 105. Note that the direction in which the laser scanner 107 scans the photosensitive drum 105 (the depth direction in the figure) is the main scanning direction.

[0020] The photosensitive drum 105 is scanned by a laser beam after being charged, 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. As a result, an image in which the electrostatic latent image on the photosensitive drum 105 is visualized is formed. A yellow image is formed on the photosensitive drum 105 of the image forming unit 120. A magenta image is formed on the photosensitive drum 105 of the image forming unit 121. A cyan image is formed on the photosensitive drum 105 of the image forming unit 122. A black image is formed on the photosensitive drum 105 of the image forming unit 123. Note that the photosensitive drum 105 and the developing device 112 are detachable from the housing 101.

[0021] The transfer mechanism includes an intermediate transfer member 106 and a transfer roller 114. The intermediate transfer member 106 sequentially superimposes and transfers images from the photosensitive drums 105 of the image forming units 120, 121, 122, and 123. In the present embodiment, the intermediate transfer member 106 rotates clockwise in the figure, and the 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 for detecting the image density from the image for detecting the image density formed on the intermediate transfer member 106 is provided on the downstream side of the image forming unit 123 in the rotation direction of the intermediate transfer member 106.

[0022] The image transferred to the intermediate transfer member 106 is conveyed to the transfer roller 114 as the intermediate transfer member 106 rotates. An image formation start position detection sensor 115 for determining the transfer position to the sheet 110 is provided on the upstream side of the transfer roller 114 in the rotation direction of the intermediate transfer member 106. The transfer roller 114 presses the sheet 110 against the intermediate transfer member 106 and at the same time applies a bias having a reverse characteristic to the image on the intermediate transfer member 106, thereby transferring the image from the intermediate transfer member 106 to the sheet 110.

[0023] The feeding mechanism includes a paper feed cassette 113 for storing the sheet 110, a conveyance path through which the sheet 110 is fed, and various rollers for conveying the sheet 110 to the conveyance path. The sheet 110 is fed from the paper feed cassette 113, and an image is formed by transferring and fixing the image while being conveyed through the conveyance path, and is discharged to the outside of the housing 101 as a product.

[0024] For this purpose, the sheet 110 is first fed from the paper feed cassette 113 and conveyed to the transfer roller 114 through the conveyance path. A paper feed timing sensor 116 for adjusting the conveyance timing of the sheet 110 is provided in the middle of the conveyance path from the paper feed cassette 113 to the transfer roller 114. The timing at which the sheet 110 is conveyed 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 member 106 and the timing at which the paper feed timing sensor 116 detects the sheet 110. Thereby, the image is transferred from the intermediate transfer member 106 to a predetermined position of the sheet 110.

[0025] The sheet 110 onto which the image has been transferred is conveyed to the fixing mechanism. The fixing mechanism of the present embodiment includes a first fuser 150 and a second fuser 160. The first fuser 150 includes a fixing roller 151 for heating the sheet 110 in order to thermally bond the image to the sheet 110, a pressure belt 152 for pressing the sheet 110 against the fixing roller 151, and a post-fixing sensor 153 for detecting the completion of fixing. The fixing roller 151 is a hollow roller, has a heater inside, and is configured to convey the sheet 110 by rotating. The post-fixing sensor 153 detects the sheet 110 after the image has been fixed.

[0026] The second fuser 160 is disposed downstream of the first fuser 150 in the conveyance direction of the sheet 110, and is used to add gloss to the image on the sheet 110 fixed by the first fuser 150 and to ensure fixability. The second fuser 160 includes a fixing roller 161, a pressure roller 162, and a post-fixing sensor 163. The fixing roller 161 has the same configuration as the fixing roller 151 and functions in the same manner. The pressure roller 162 functions in the same manner as the pressure belt 152. The post-fixing sensor 163 functions in the same manner as the post-fixing sensor 153. The second fuser 160 performs a fixing process on the sheet 110 in the same manner as the first fuser 150.

[0027] The second fuser 160 may not be used depending on the type of the sheet 110 and the content of the image forming process. The conveyance path 130 is provided to convey the sheet 110 fixed by the first fuser 150 without passing through the second fuser 160. For this purpose, a flapper 131 is provided downstream of the first fuser 150 in the conveyance direction of the sheet 110 to guide the sheet 110 to either the second fuser 160 or the conveyance path 130.

[0028] The sheet 110 that has passed through either the second fuser 160 or the conveyance path 130 may be discharged as it is or conveyed to the conveyance path 135. For this purpose, a flapper 132 is provided after the conveyance path after the second fuser 160 and the conveyance path 130 merge. The flapper 132 guides the sheet 110 to either the conveyance path 135 or the discharge path of the sheet 110. The sheet 110 guided to the discharge path is discharged to the outside of the housing 101 with the surface on which the image is formed facing upward. A downstream sensor 144 is disposed in the discharge path. The downstream sensor 144 detects the sheet 110 conveyed through the discharge path.

[0029] The conveyance path 135 is a path for conveying the sheet 110 to the inversion path 136 used for inverting the front and back surfaces of the sheet 110. An inversion sensor 137 for detecting the sheet 110 is provided on the inversion path 136. When the inversion sensor 137 detects the trailing edge of the sheet 110, the conveyance direction of the sheet 110 is inverted on the inversion path 136. The sheet 110 with the inverted conveyance direction is conveyed to either the conveyance path 135 or the inversion path 138. For this purpose, a flapper 133 is provided at the branch between the conveyance path 135 and the inversion path 138. When conveyed to the conveyance path 135, the sheet 110 is guided to the conveyance path 135 by the flapper 133, the front and back surfaces are inverted (with the surface on which the image is formed facing downward), and discharged to the outside of the housing 101. When the sheet 110 is conveyed to the conveyance path 135, the conveyance of the sheet 110 is controlled so that the conveyance speed of the sheet 110 becomes the target conveyance speed regardless of the paper type of the sheet 110. When conveyed to the inversion path 138, the sheet 110 is guided to the inversion path 138 by the flapper 133. The sheet 110 guided to the inversion path 138 has its front and back surfaces inverted and is conveyed to the transfer roller 114 again. Thereby, image formation on the back surface of the sheet 110 is performed.

[0030] On the conveyance path 135, conveyance rollers 141 and 142 are provided to convey the sheet 110. The conveyance rollers 141 and 142 are rotatable in both directions. Between the conveyance roller 141 and the conveyance roller 142, a colorimeter 200 which is a colorimetric sensor for reading a test chart for adjusting image forming conditions formed on the sheet 110, and an upstream sensor 143 are provided. The reading result of the test chart by the colorimetric sensor 200 is used for adjusting image forming conditions such as image density adjustment, gradation correction, color mixing adjustment, and geometric characteristics of the image of the image to be printed. The upstream sensor 143 detects the sheet 110 conveyed on the conveyance path 135. When the colorimetric sensor 200 reads the test chart, the sheet 110 on which the test chart is printed passes through the reading position of the colorimetric sensor 200 after passing through the detection position of the upstream sensor 143, and passes through the detection position of the downstream sensor 144 via the conveyance path 139. The conveyance path 139 is a bent path and is provided near the colorimetric sensor 200. As described above, the conveyance speed of the sheet 110 conveyed on the conveyance path 135 is controlled to be a target conveyance speed regardless of the paper type of the sheet 110. When the conveyance speed at the time of reading the test chart varies depending on the paper type of the sheet 110, it is necessary to change the layout of the test chart for each paper type of the sheet 110 or define the sampling timing for each paper type of the sheet 110. By controlling the conveyance speed at the time of reading the test chart to be the target conveyance speed regardless of the paper type, it is not necessary to prepare image data for the test chart for each paper type, and it is possible to suppress the compression of the memory capacity by the image data for the test chart. Also, by controlling the conveyance speed at the time of reading the test chart to be the target conveyance speed regardless of the paper type, it is not necessary to perform different sampling controls corresponding to the conveyance speed for each paper type, and it is possible to suppress the compression of the memory capacity by a complicated program.

[0031] (Colorimetric Sensor) FIG. 2 is a configuration explanatory diagram of the colorimetric sensor 200. The colorimetric sensor 200 measures the reflected light from the test chart 220 formed on the sheet 110. The colorimetric sensor 200 includes a white LED (Light Emitting Diode) 201, a diffraction grating 202, a line sensor 203, an arithmetic unit 204, a memory 205, and a lens 206. The white LED 201 is a light emitting unit that irradiates light onto the sheet 110 conveyed through the conveyance path 135. The diffraction grating 202 disperses the reflected light from the test chart 220 for each wavelength. The lens 206 condenses the light irradiated from the white LED 201 onto the test chart 220, and also condenses the reflected light from the test chart 220 onto the diffraction grating 202.

[0032] The line sensor 203 is a light receiving unit having light receiving elements 203-1 to 203-n for n pixels. Each of the light receiving elements 203-1 to 203-n of the line sensor 203 receives the reflected light dispersed for each wavelength by the diffraction grating 202. Each of the light receiving elements 203-1 to 203-n outputs, as a detection result, for example, a voltage (electrical signal) correlated with the intensity of the received reflected light. The correspondence between each of the light receiving elements 203-1 to 203-n and the wavelength of the received reflected light is determined in advance. Therefore, the light intensity values of each of the light receiving elements 203-1 to 203-n correspond to the reflected light intensity (spectral data) for each wavelength.

[0033] The arithmetic unit 204 converts the voltage values output from each of the light receiving elements 203-1 to 203-n into digital signals (light intensity values). The arithmetic unit 204 further has a spectral arithmetic unit that calculates the spectral reflectance from the spectral data converted into digital signals. The spectral data converted into digital signals by the arithmetic unit 204, or the spectral reflectance calculated by the spectral arithmetic unit, is output to the printer controller 103 (FIG. 3) described later. The memory 205 stores various data used for the operation of the line sensor 203 by each of the light receiving elements 203-1 to 203-n.

[0034] (Controller) FIG. 3 is an explanatory diagram of a controller that controls the operation of the image forming apparatus 100 configured as described above. The image forming apparatus 100 includes, as a controller, a printer controller 103 that controls the operation of the entire image forming apparatus 100 and an engine control unit 312 that controls the operation of the above-described engine unit for image formation. The printer controller 103 and the engine control unit 312 may be realized by different processors, or may be realized by one processor.

[0035] The engine control unit 312 is connected to the fixing sensors 153 and 163, the reverse sensor 137, a drive motor 311 that drives each roller for transporting the sheet 110, and the flappers 131 and 132. The engine control unit 312 controls the drive motor 311 and the flappers 131 and 132 based on the detection results of the respective sensors, thereby transporting the sheet 110 by the engine unit. Although not shown, the engine control unit 312 controls the operations of the image forming mechanism, the transfer mechanism, the feeding mechanism, and the fixing mechanism to form an image on the sheet 110. The operation of the engine control unit 312 is controlled by the printer controller 103.

[0036] The printer controller 103 is connected to an operation panel 180, an external I / F 308, and a colorimetric sensor 200. The external I / F 308 is a communication interface that communicates with an external device via a predetermined network. The printer controller 103 can receive a job or the like from an external device via the external I / F 308. Details of the operation of the printer controller 103 will be described later.

[0037] (Adjustment Basic Process) In order to maintain the image quality on the sheet 110, the image forming apparatus 100 of the present embodiment forms a test chart 220 (see FIG. 2) including a combination of a plurality of test images. The image forming apparatus 100 conveys the sheet 110 on which the test chart 220 is formed in the direction from the conveyance roller 141 to the conveyance roller 142 in the conveyance path 135. The colorimetric sensor 200 provided in the conveyance path 135 reads the test chart 220 formed on the sheet 110. The image forming apparatus 100 performs feedback control based on the detection result (reading result) by the colorimetric sensor 200 to maintain the image quality such as color reproducibility.

[0038] The image forming apparatus 100 of the present embodiment creates a profile and performs image formation using the created profile. In the present embodiment, an ICC profile is used as a profile for realizing excellent color reproducibility. Note that, as the profile, a CRD (Color Rendering Dictionary), a color separation table, a ColorWise internal CMYK simulation, etc. can also be used.

[0039] The image forming apparatus 100 creates an ICC profile as a color conversion profile based on the spectral reflectance of the test chart 220 output from the colorimetric sensor 200. The color management module (CMM) 306 of the printer controller 103, which will be described later, performs color conversion processing using the created ICC profile so that the color of the image formed based on the image data becomes the target color.

[0040] The calculation formulas for L*, a*, and b* will be described. The colorimetric sensor 200 splits the reflected light of the light irradiated from the white LED 201 by the measurement object with the diffraction grating 202, and detects it with the light receiving elements 203-1 to 203-n arranged in each wavelength range of 380 [nm] to 720 [nm]. In the present embodiment, in order to improve the detection calculation accuracy, as stipulated by the CIE, the spectral reflectance is converted into the coordinate information (L*, a*, b*) in the CIE L*a*b* color space by the metameric function. An ICC profile, which is a color conversion profile, is created based on the relationship between the data of L*, a*, b* and the signal values (image data) of the test chart 220.

[0041] (L*a*b* Calculation) The following is a method for calculating the coordinate information (L*, a*, b*) in the CIE L*a*b* color space from the spectral reflectance (stipulated in ISO13655). a. Obtain the spectral reflectance R(λ) of the sample (380 [nm] to 780 [nm]) b. Prepare the metameric functions x(λ), y(λ), z(λ) and the standard light spectral distribution SD50(λ) Note that the metameric functions are stipulated in JIS Z8701, and SD50(λ) is stipulated in JIS Z8720, and is also called the auxiliary standard illuminant D50. c. R(λ)×SD50(λ)×x(λ), R(λ)×SD50(λ)×y(λ), R(λ)×SD50(λ)×z(λ) d. Integrate each wavelength Σ{R(λ)×SD50(λ)×x(λ)} Σ{R(λ)×SD50(λ)×y(λ)} Σ{R(λ)×SD50(λ)×z(λ)} e. Integrate the product of the metameric function y(λ) and the standard light spectral distribution SD50(λ) at each wavelength Σ{SD50(λ)×y(λ)} f. XYZ calculation X = 100×Σ{SD50(λ)×y(λ)} / Σ{R(λ)×SD50(λ)×x(λ)} Y = 100×Σ{SD50(λ)×y(λ)} / Σ{R(λ)×SD50(λ)×y(λ)} Z = 100×Σ{SD50(λ)×y(λ)} / Σ{R(λ)×SD50(λ)×z(λ)} Calculation of g.L*, a*, b* L* = 116×(Y / Yn)^(1 / 3) - 16 a* = 500{(X / Xn)^(1 / 3) - (Y / Yn)^(1 / 3)} b* = 200{(Y / Yn)^(1 / 3) - (Z / Zn)^(1 / 3)} when Y / Yn > 0.008856 When Y / Yn > 0.008856: Xn, Yn, Zn are the standard colorimetric tristimulus values (X / Xn)^(1 / 3) = 7.78(X / Xn)^(1 / 3) + 16 / 116 (Y / Yn)^(1 / 3) = 7.78(Y / Yn)^(1 / 3) + 16 / 116 (Z / Zn)^(1 / 3) = 7.78(Z / Zn)^(1 / 3) + 16 / 116

[0042] (Profile creation) When a custom engineer replaces parts, before a job that requires color matching accuracy, and further when the user wants to know the color tone of the final output during the design concept stage, etc., the user instructs the operation panel 180 to perform the profile creation process. The printer controller 103 creates a profile according to the instruction from the operation panel 180. As shown in Figure 3, the printer controller 103 includes a profile creation unit 301, a colorimetric sensor control unit 302, a Lab calculation unit 303, and an input ICC profile storage unit 304 for the colorimetric sensor. Also, the printer controller 103 includes an output ICC profile storage unit 305, a CMM 306, and an input ICC profile storage unit 307.

[0043] Instructions for profile creation are input from the operation panel 180 to the profile creation unit 301. In response to the instruction, the profile creation unit 301 transmits CMYK (cyan, magenta, yellow, black) color signals of an ISO 12642 test form (test chart) to the engine control unit 312 so as to be formed without going through the profile. At the same time, the printer controller 103 transmits a color measurement instruction to the color measurement sensor 200 by the color measurement sensor control unit 302. The engine control unit 312 controls the operation of the engine unit to print the ISO 12642 test form (test chart) on the sheet 110. For the sheet 110 on which the test form (test chart) is printed, each test image included in the test chart is color-measured by the color measurement sensor 200. The spectral reflectance of the color-measured test image is input to the printer controller 103. The spectral reflectance is converted into L*, a*, b* data by the Lab calculation unit 303. The L*, a*, b* data is input to the profile creation unit 301 via the input ICC profile storage unit 304 for the color measurement sensor. Note that the spectral reflectance may be converted into coordinate information (X, Y, Z) in the CIE 1931 XYZ color system, which is a device-independent color space and not the CIE L*a*b* color space.

[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 created output ICC profile with the output ICC profile already stored in the output ICC profile storage unit 305.

[0045] The ISO12642 test form (test chart) includes test 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 from the relationship between each color signal value and the measured L*, a*, b* data. That is, a conversion table (A2Bx tag) from CMYK to L*, a*, b* data is created. The profile creation unit 301 generates a conversion table that converts L*’, a*’, b*’ data into CMYK data based on this conversion table. The color mixing adjustment is a process in which the profile creation unit 301 generates a conversion table that inversely converts L*’, a*’, b*’ data into CMYK data based on the measurement results of the test chart. Note that the L*’, a*’, b*’ data is generated from the L*, a*, b* data in the CMM306.

[0046] Figure 4 is an explanatory diagram of the ICC profile. The ICC profile consists of a header, tags, and data. The tags include, of course, the color conversion table, as well as tags such as the white point (Wtpt) and the gamt tag that describes whether the color represented by the Lab values defined inside the profile is inside or outside the reproducible range of hard copy reproduction.

[0047] The printer controller 103 may receive an instruction for profile creation from an external device via the external I / F 308. In this case, the printer controller 103 acquires the output ICC profile created by the external device and performs color conversion using an application corresponding to the ICC profile.

[0048] (Color conversion process) In color conversion in normal color image formation, for the image data input assuming RGB signal values or standard printing CMYK signal values such as JapanColor from the external I / F 308, it is stored in the 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 an external device. The image data stored in the input ICC profile storage unit 307 undergoes RGB→L*a*b* or CMYK→L*a*b* conversion. The input ICC profile storage unit 307 includes a one-dimensional LUT that controls the gamma characteristics of the image data, a multi-color LUT called direct mapping, and a one-dimensional LUT that controls the gamma of the generated conversion data. 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 by these tables.

[0049] The image data converted to L*,a*,b* data is input to the CMM 306. FIG. 5 is an explanatory diagram of color management by the CMM 306. The CMM 306 performs GAMUT conversion that maps the mismatch between the reading color space of an external device such as a scanner and the output color reproduction range of the image forming apparatus 100 as an output device. Also, the CMM 306 performs color conversion that adjusts the mismatch between the light source type at the time of input and the light source type when observing the output (also referred to as the mismatch in color temperature setting), black character determination, etc. As a result, the L*,a*,b* data is converted to 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, color-converted by the newly created ICC profile, and converted to a CMYK signal dependent on the output device and output.

[0050] The input ICC profile storage unit 307 and the output ICC profile storage unit 305 have been described separately. As shown in FIG. 5, the CMM 306 is a module that controls color management and performs color conversion using the input profile and the output profile.

[0051] (Adjustment of Conveyor Speed 1) FIG. 6 is a control configuration diagram near the colorimetric sensor 200 which is the control target of this embodiment. As described above, the operation of the colorimetric sensor 200 is controlled by the printer controller 103 (colorimetric sensor control unit 302). The detection results of the upstream sensor 143 and the downstream sensor 144 are transmitted to the printer controller 103. The printer controller 103 controls the operations of two conveyor rollers 141 and 142 adjacent to the colorimetric sensor 200. For this purpose, the printer controller 103 is connected to the first motor driver 147 and the second motor driver 148. The first motor driver 147 drives and controls the first drive motor 145 which is the drive source of the conveyor roller 141. The second motor driver 148 drives and controls the second drive motor 146 which is the drive source of the conveyor roller 142.

[0052] The printer controller 103 sets the type of the sheet on which the test chart is formed in the colorimetric mode by the user selecting the type of the sheet for colorimetry using the operation panel 180. When set to the colorimetric mode, the printer controller 103 causes the engine control unit 312 to control each part of the image forming apparatus 100 to print a test chart on the sheet 110 of the set type and convey the sheet 110 to the reading position of the colorimetric sensor 200.

[0053] The test chart can contain up to several thousand test images. For example, 10 test images of each color for maximum density confirmation are printed on the first sheet, 100 test images of each color for gradation confirmation are printed on the second sheet, and about 200 test images of each color for color tone confirmation are printed on the third and subsequent sheets as the test chart. The larger the number of test images required for color tone confirmation, the finer the adjustment can be, and the color difference ΔE can be reduced. However, as the number of test images increases, the number of sheets (coated paper) used for color measurement also increases. In order to minimize the coated paper and confirm the color tone with a small number of sheets, it is necessary to print about 200 test images on at least one sheet 110. As a result, when the test images are printed on a sheet 110 of A3 size (420 [mm] × 297 [mm]) with about 200 test images, the area of the test images read during color measurement is approximately 30 [mm] in width and 15 [mm] in length at the smallest.

[0054] In a spectroscopic colorimeter such as the color measurement sensor 200, the spot diameter for receiving reflected light is about 2 [mm]. The color measurement sensor 200 of the present embodiment performs sampling about 20 times for one test image and averages the values of the reading results as the color measurement result. The sampling period is about 1 millisecond. The conveyance speed of the sheet 110 during color measurement is near the image formation speed so that it can be used in many models. In the present embodiment, the case of performing color measurement while conveying the sheet 110 with a target conveyance speed of 400 [mm / s] will be described.

[0055] In order to correctly read a test image with a length of about 15 [mm] in the conveyance direction, when the conveyance speed is 400 [mm / s], considering the outer diameter tolerance of ±0.5% of the conveyance rollers 141 and 142, the faster side has an allowable range of +0.5%. The slower side has an allowable range of -1.0 to +0.5% considering the outer diameter tolerance of ±0.5% of the conveyance rollers 141 and 142 and the outer diameter friction of ±0.5% due to the durability of the conveyance rollers 141 and 142. That is, the conveyance speed of the sheet 110 needs to be within the range of "a speed 1.0% slower than the target conveyance speed" to "a speed 0.5% faster than the target conveyance speed".

[0056] FIG. 7 is an explanatory diagram of the conveyance speed for each type of sheet. This conveyance speed is the speed when the sheet 110 passes through the reading position of the color measurement sensor 200. The conveyance speed is calculated by dividing the length of the sheet 110 in the conveyance direction by the time required for the sheet 110 to pass through the reading position of the color measurement sensor 200. The time required for the sheet to pass through the reading position of the color measurement sensor 200 is, for example, the time T (e.g., the time from when the detection result changes from off to on until it changes from on to off) during which a laser displacement meter (not shown) installed in the color measurement sensor 200 detects the sheet. FIG. 7 shows the average value (circles in the figure) and the variation of the conveyance speed of the sheet calculated in this way. Note that the conveyance speed includes the measurement results in both states: when the friction coefficient μ on the surfaces of the conveyance rollers 141 and 142 is reduced by attaching paper dust, and when the friction coefficient μ is in the initial state.

[0057] For sheets (plain paper, cardboard) with a basis weight of 300 [gsm] or less, the difference between the target conveyance speed and the actual conveyance speed during color measurement is within the allowable range (within the range from the upper reading limit to the lower reading limit). For sheets (extremely thick paper) with a basis weight greater than 300 [gsm], the difference between the target conveyance speed and the actual conveyance speed during color measurement is outside the allowable range. The conveyance speed is uniformly about 0.2 - 0.3% slower than the target conveyance speed.

[0058] Note that the stiffness of plain paper and cardboard is, for example, about 30 [mN]. On the other hand, the stiffness of extremely thick paper with a basis weight exceeding 300 [gsm] is much greater than 30 [mN]. Therefore, the conveyance resistance when conveying the sheet 110 in the bending path increases, and the conveyance speed of the sheet 110 becomes slower than the lower limit of the allowable range.

[0059] As described above, when the basis weight of the sheet 110 exceeds 300 [gsm], the conveyance speed rapidly decreases. This is because when the highly rigid (hard) sheet 110 passes through the bent conveyance path 139, it strongly receives a reaction force from the conveyance path 139, increasing the conveyance resistance. As a result, the conveyance rollers 141 and 142 convey the sheet 110 while slightly slipping. The slipping ratio depends on the stiffness of the sheet 110 rather than the presence or absence of paper dust. It is well known that the stiffness of the sheet 110 is correlated with the basis weight. Therefore, in the image forming apparatus 100, as the stiffness of the sheet 110 increases, the conveyance speed set value increases, and the conveyance speed is adjusted to be faster.

[0060] To enable the mounting of multiple models of the color measurement sensor 200, the conveyance speed of the sheet 110 is fixed to the conveyance speed of the product that adopts the slowest image forming speed. If there is a delay in the passing time of the sheet 110 at the reading position of the color measurement sensor 200, the color measurement sensor 200 will read a position different from the original reading position on the sheet 110. This causes a reading defect. When a reading defect occurs, appropriate image forming conditions cannot be adjusted. Note that the deviation of the conveyance speed increases towards the rear end of the sheet 110 in the conveyance direction.

[0061] In the present embodiment, the rotational speeds of the conveyance rollers 141 and 142 are adjusted so that the conveyance speed of the sheet 110 passing through the reading position of the color measurement sensor 200 falls within the allowable range of the target conveyance speed. FIG. 8 is an explanatory diagram of the adjustment value (conveyance speed set value) of the conveyance speed for each type of sheet. The conveyance speed set value for each type of sheet is set so that the conveyance speed during color measurement falls within the allowable range. The conveyance speed table in FIG. 8 is stored, for example, in a memory (not shown) provided in the printer controller 103.

[0062] The information on the type of sheet 110 (information regarding the basis weight of sheet 110) set by manual input of the user is input from the printer controller 103 to the engine control unit 315. When the sheet 110 is plain paper (for example, with a basis weight of 64 [gsm] to 120 [gsm]), the engine control unit 315 sets the conveyance speed set value to 0%. Then, the engine control unit 315 controls the rotational drive of the first drive motor 145 and the second drive motor 146 so that the rotational speeds of the first drive motor 145 and the second drive motor 146 at the time of chart reading become the standard rotational speed. Thereby, the conveyance speed of the sheet 110 conveyed by the conveyance rollers 141 and 142 becomes the target conveyance speed.

[0063] When the sheet is thick paper (for example, with a basis weight of 120 [gsm] to 300 [gsm]), the engine control unit 315 sets the conveyance speed set value to +0.5%. According to the experimental results in FIG. 7, the average of the actual conveyance speeds of thick paper is slightly slower than the average of the actual conveyance speeds of plain paper. Therefore, the image forming apparatus 100 increases the rotational speed for thick paper to be faster than the rotational speed for plain paper within the range where the actual conveyance speed is controlled within the allowable range of the target conveyance speed. The engine control unit 315 controls the rotational drive of the first drive motor 145 and the second drive motor 146 so that the rotational speeds of the first drive motor 145 and the second drive motor 146 at the time of chart reading become the first rotational speed that is faster than the standard rotational speed. When the type of the sheet is thick paper, the first drive motor 145 and the second drive motor 146 rotate about 0.5% faster than when it is plain paper according to the conveyance speed set value. Thereby, the conveyance speed of the sheet 110 conveyed by the conveyance rollers 141 and 142 becomes the target conveyance speed.

[0064] When the sheet is thick paper (for example, basis weight is 300 [gsm] to 450 [gsm]), the engine control unit 315 sets the conveyance speed set value to +0.9%. Then, the engine control unit 315 controls the rotational drive of the first drive motor 145 and the second drive motor 146 so that the rotational speeds of the first drive motor 145 and the second drive motor 146 at the time of chart reading become a second rotational speed faster than the first rotational speed. When the type of the sheet is thick paper, according to the conveyance speed set value, the first drive motor 145 and the second drive motor 146 rotate about 0.9% faster than when it is plain paper. Thereby, the conveyance speed of the sheet 110 conveyed by the conveyance rollers 141 and 142 becomes the target conveyance speed.

[0065] When the sheet is coated paper (for example, basis weight is 85 [gsm] to 220 [gsm]), the engine control unit 315 sets the conveyance speed set value to -0.2%. This is because the inventors conducted an experiment to measure the conveyance speeds of plain paper and coated paper of the same basis weight with a part entering the bending path, and the conveyance speed of the coated paper became faster than that of the plain paper. The engine control unit 315 controls the rotational drive of the first drive motor 145 and the second drive motor 146 so that the rotational speeds of the first drive motor 145 and the second drive motor 146 at the time of chart reading become a third rotational speed slower than the standard rotational speed. When the type of the sheet is coated paper, according to the conveyance speed set value, the first drive motor 145 and the second drive motor 146 rotate about 0.2% slower than when it is plain paper. When the sheet is thick coated paper (for example, basis weight is 220 [gsm] to 350 [gsm]), the conveyance speed set value is +0.1%. According to the conveyance speed set value, the first drive motor 145 and the second drive motor 146 rotate about 0.1% faster than when it is plain paper.

[0066] In this way, the image forming apparatus 100 controls the rotational speeds of the first drive motor 145 and the second drive motor according to the type of sheet, and performs speed adjustment so that the conveyance speed of the sheet falls within the allowable range of the target conveyance speed. Therefore, even when in-line color measurement is performed using the color measurement sensor 200, the conveyance speed of the sheet passing through the reading position of the color measurement sensor 200 remains within the allowable range. As a result, the test chart on the sheet passing through the bending path can be measured with high accuracy regardless of the paper type.

[0067] Note that due to the pressure, hardness, resistance value, etc. of the conveyance rollers 141 and 142, even if the conveyance rollers 141 and 142 have the same rotational speed, the conveyance speed varies depending on the type of sheet. Therefore, the conveyance speed setting value is derived experimentally. By making the conveyance speed variable according to the type of sheet, the types of sheets compatible with in-line color measurement increase. As a result, the types of sheets for which color measurement is possible with a test image of the same length increase, improving the compatibility of the color measurement sensor 200 with the sheet.

[0068] (Adjustment of Conveyance Speed 2) By using the image forming apparatus 100 for a long period of time, the outer diameters of the conveyance rollers 141 and 142 become smaller. This is because the rubber on the surfaces of the conveyance rollers 141 and 142 wears due to the passage of the sheet 110. As a result, even if the rotational speed of the drive motor is the same, the conveyance speed of the sheet 110 after durability becomes slower.

[0069] In the color measurement mode, adjustments of different types of image forming conditions (for example, image density adjustment, gradation correction, color mixing adjustment) may be continuously executed. In this case, at least three or more sheets are passed. The number of test images printed on one sheet in color mixing adjustment is larger than the number of test images printed on one sheet in image density adjustment or gradation correction. Therefore, the size of the test image used for color mixing adjustment is smaller than the size of the test image used for image density adjustment and smaller than the size of the test image used for gradation correction. Thus, the color mixing adjustment of thick paper when durability has advanced is most likely to cause reading failures in in-line color measurement.

[0070] Therefore, according to the detection timings of the upstream sensor 143 arranged on the upstream side in the sheet conveyance direction and the downstream sensor 144 arranged on the downstream side with respect to the color measurement sensor 200, the conveyance speed table at the time of color measurement is changed. By changing the conveyance speed table, the rotational speeds of the first drive motor 145 and the second drive motor 146 are adjusted.

[0071] FIG. 9 is an explanatory diagram of the timings for each type of sheet 110 passing through the reading position of the color measurement sensor 200 after the durability of the image forming apparatus 100. FIG. 9(a) represents the timing before durability, and FIG. 9(b) represents the timing after durability. Let the distance from the upstream sensor 143 to the downstream sensor 144 be L [mm]. The target time for the plain paper S to pass from the detection position of the upstream sensor 143 to the reading position of the color measurement sensor 200 is Ts1 (FIG. 9(a)). The target time for the plain paper S to pass from the detection position of the upstream sensor 143 to the detection position of the downstream sensor 144 is T1.

[0072] The time for the first plain paper S1 to pass from the detection position of the upstream sensor 143 to the detection position of the downstream sensor 144 after durability is T1'. The difference ΔT (= T1' - T1) from the target time T1 is reflected in the conveyance speed table at the time of color measurement of the second plain paper. The conveyance speed setting value in the conveyance speed table is corrected by L / ΔT.

[0073] For example, in the case of the apparent speed change ΔV (= L / T1' - L / T1) of the conveyance speed when L = 200 [mm], T1 = 2000 milliseconds, and T1' = 2020 milliseconds after durability, the target conveyance speed V” of the plain paper at the time of color measurement for the second and subsequent sheets is expressed by the following formula. V” = V + αV / 100 = V(1 + α / 100) “α” is the amount [%] for correcting the speed reduction due to durability and is expressed by the following formula. α / 100 = ΔV / V =(L / T1' - L / T1) / L / T1 =(T1' - T1) / T1 =(20) / 2000 = 0.001 α = 0.1 [%]

[0074] In this case, the conveyance speed setting value for plain paper in the conveyance speed table is adjusted by only 0.1%. With such adjustment, even if there is a slight delay in the conveyance speed when measuring the color of the test chart with the highest density of the test image, when reading the test chart of the second and subsequent sheets, the delay in the conveyance speed is reflected in the conveyance speed table. Therefore, accurate reading can be performed even for small test images printed on the second and subsequent sheets.

[0075] Even when performing in-line color measurement using the color measurement sensor 200 by correcting the conveyance speed setting value according to durability, the conveyance speed of the sheet 110 passing through the reading position of the color measurement sensor 200 remains within the allowable range. As a result, the influence of the durability of the conveyance rollers that convey the sheet 110 is suppressed, and accurate reading of the test chart (test image) printed on the sheet 110 is performed. By making the conveyance speed variable according to the type of the sheet 110 and the durability of the conveyance rollers 141 and 142, the types of sheets compatible with in-line color measurement increase. As a result, since the types of sheets for which color measurement can be performed with a test image of the same length increase, the compatibility of the color measurement sensor 200 with the sheet is improved.

[0076] (Adjustment of Conveyance Speed 3) The amount of wear on the outer diameters of the conveyance rollers 141 and 142 can be predicted to a certain extent by the paper passing durability test. The change amount of the wear on the outer diameters of the conveyance rollers 141 and 142 according to the number of sheets passed is consistent with the change amount of the conveyance speed of the sheet 110 by the conveyance rollers 141 and 142. Therefore, the drive frequencies of the first drive motor 145 / the second drive motor 146 that drive the conveyance roller 141 / the conveyance roller 142 adjacent to the color measurement sensor 200 are changed according to the number of sheets passed.

[0077] FIG. 10 is an exemplary diagram of the conveyance speed table in this case. FIG. 10(a) is a table showing the relationship between the conveyance speed setting value for each type of sheet and the drive frequency. FIG. 10(b) is a table showing the relationship between the adjustment values for each number of sheets passed. The printer controller 103 counts the number of sheets passed through the conveyance roller 141 and the conveyance roller 142.

[0078] For example, for a thick paper with a basis weight of 300 [gsm], the conveyance speed setting value is S2 = +0.5%. When the number of sheets passed is about 5000 sheets, the adjustment value Ni is 0% (see FIG. 10(b)). The drive frequency F2 of the drive motor during color measurement is F2 = F0 × (100 + 0.5 + 0) / 100 = 1.005. F0 is the drive frequency of the initial drive motor. In this case, the first drive motor 145 / second drive motor 146 is rotationally driven at a rotational speed 1.005 times the initial motor rotation speed.

[0079] Also, for example, for an extra-thick paper with a basis weight of 350 [gsm], the conveyance speed setting value is S3 = +0.9%. When the number of sheets passed is about 5 million sheets, the adjustment value Ni is +1.5%. The drive frequency F3 of the drive motor during color measurement is F3 = F0 × (100 + 0.9 + 1.5) / 100 = 1.024. In this case, the first drive motor 145 / second drive motor 146 is rotationally driven at a rotational speed 1.024 times the initial motor rotation speed.

[0080] In this way, even when the durability of the image forming apparatus 100 progresses, by adjusting the drive frequency of the drive motor, the conveyance speeds of various types of sheets 110 can be adjusted to fall within the allowable range. As a result, the influence of the durability of the conveyance rollers 141 and 142 that convey the sheet 110 is suppressed, and the test chart (test image) printed on the sheet 110 is accurately read. By making the conveyance speed variable according to the type of sheet 110, the number of types of sheets that can support in-line color measurement increases. As a result, the number of types of sheets for which color measurement can be performed with a test image of the same length increases, improving the compatibility of the color measurement sensor 200 with the sheet.

[0081] Note that the conveyance rollers 141 and 142 are replaced when an accidental failure occurs or periodically. When they are replaced, the printer controller 103 resets the count value of the number of sheets passed. The image forming apparatus 100 counts the number of sheets passed through the conveyance rollers 141 and 142 separately from the durability number of sheets of the main body.

[0082] As described above, the color measurement sensor 200 can accurately read the test chart by being able to adjust the conveyance speed of the sheet 110 even in the vicinity of the bent conveyance path 139. Thereby, it becomes possible to read the test chart from a large number of types of sheets 110 and correct the image forming conditions for each type of sheet 110. Further, since the color measurement sensor 200 can be arranged in the vicinity of the bent conveyance path 139, the main body of the image forming apparatus 100 can be miniaturized. Note that even when the bent conveyance path 139 is on the upstream side of the color measurement sensor 200 in the conveyance direction of the sheet 110, the adjustment of the conveyance speed of the sheet 110 as in the present embodiment is effective for reading an image by the color measurement sensor 200.

[0083] The image forming apparatus 100 has described the color mixing adjustment in which a conversion table is generated based on the measurement results of a test chart as an adjustment of image forming conditions. However, the adjustment of image forming conditions is not limited to color mixing adjustment. As the adjustment of image forming conditions, for example, there is image density adjustment in which the intensity (laser power) of the laser beam emitted from the light emitting unit 108 of the laser scanner 107 is controlled based on the reading result of a test chart for laser power adjustment by the colorimetric sensor 200. Further, as the adjustment of image forming conditions, for example, there is gradation correction in which a one-dimensional LUT is generated based on the reading result of a gradation test image by the colorimetric sensor 200. Further, as the adjustment of image forming conditions, for example, there is correction of geometric characteristics in which correction data for correcting the geometric characteristics of the image formed on the sheet is generated based on the reading result of a test chart for geometric correction by a CIS (or a CCD sensor) instead of the colorimetric sensor 200. Note that the test chart for geometric correction is a test chart in which marks are formed in four corner regions of the sheet. The correction data is data used for affine transformation of the image formed on the sheet, for example, in the printer controller 103. By forming an image based on the image data that has been image-processed by the image forming apparatus 100 based on the correction data, the rectangularity of the image formed on the sheet, the position of the image with respect to the sheet, etc. are adjusted to target values.

Claims

1. Image forming means for forming a test chart on a sheet, conveying means for conveying the sheet along a conveyance path from the image forming means, reading means for reading the test chart from the sheet being conveyed along the conveyance path by the conveying means, control means for controlling the conveying means, and having, the conveying means, a first conveying roller disposed upstream of the reading means in the conveying direction of the sheet, a second conveying roller disposed downstream of the reading means in the conveying direction of the sheet, first driving means for rotationally driving the first conveying roller, second driving means for rotationally driving the second conveying roller, and having, the conveyance path has a bent portion bent downstream in the conveying direction of the sheet from the position of the first conveying roller, the control means controls the rotational speed of the first driving means and the rotational speed of the second driving means based on the basis weight of the sheet such that the conveyance speed of the sheet becomes a target speed when the test chart on the sheet passes through the reading position of the reading means while the leading end of the sheet passes through the bent portion. Characterized in that, Image forming apparatus.

2. The control means is characterized in that it controls such that the rotational speeds of the first driving means and the second driving means increase as the stiffness of the sheet increases. The image forming apparatus according to claim 1.

3. Further comprising storage means for storing a table representing the target speed for each type of sheet. Characterized in that, The image forming apparatus according to claim 1 or 2.

4. Further comprising correction means for correcting image forming conditions for adjusting the image quality of an image to be formed by the image forming means based on the reading result of the test chart read by the reading means. Characterized in that, The image forming apparatus according to any one of claims 1 to 3.

5. The image forming conditions are color conversion profiles used for image processing. Characterized in that, The image forming apparatus according to claim 4.

6. The image forming conditions are control parameters for adjusting the density of an image to be formed by the image forming means. Characterized in that, The image forming apparatus according to claim 4.

7. The image forming conditions are correction data for correcting geometric characteristics of an image to be formed on a sheet by the image forming means. Characterized in that, The image forming apparatus according to claim 4.

Images