Image formation apparatus

Abstract

To provide an image formation apparatus which stabilizes image adjustment accuracy by determining the use possibility of a recording medium for adjustment of an image formation condition.SOLUTION: An image formation apparatus comprises: an engine unit 1011 which forms an image on a recording medium on the basis of an image formation condition; a colorimetric unit 138 which detects an image formed on the recording medium; and a printer controller 300 which determines whether or not the recording medium can be used for adjustment of an image formation condition on the basis of the characteristic of the recording medium, causes the engine unit 1011 to form the test image for adjustment of the image formation condition on the recording medium when the recording medium can be used, adjusts the image formation condition on the basis of the detection result of the test image by the colorimetric unit 138 and does not adjust the image formation condition using the recording medium when the recording medium cannot be used.SELECTED DRAWING: Figure 4

Description

Technical Field

[0001] The present invention relates to an image forming apparatus such as a copying machine, a multifunction peripheral, a printer, and the like.

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, inkjet image forming apparatuses, which have succeeded in extensive market development for reasons such as large format, low initial cost, and ultra-high speed, are also expanding their market in on-demand image forming apparatuses. However, market expansion is not easy, and it is necessary to maintain the image quality (hereinafter referred to as "image quality") of the preceding image forming apparatuses that have been responsible for that market. In order to maintain the image quality, the image forming conditions when the image forming apparatus forms an image on a recording medium are appropriately corrected.

[0003] For example, when performing gradation correction of an image forming apparatus, the image forming conditions are corrected so that the gradation characteristics of the image forming apparatus match the target gradation characteristics. For correction of gradation characteristics, a gradation correction table that associates the gradation characteristics of the image forming apparatus with the target gradation characteristics is used. The gradation characteristics of the image forming apparatus vary due to environmental conditions such as temperature and humidity, and changes over time in the components and members used for image formation. Therefore, the image forming apparatus needs to periodically adjust (calibrate) the gradation characteristics and optimize the gradation correction table.

[0004] Calibration may be performed using the reading result of a test image formed on a recording medium, or using the reading result of a test image on an image carrier before transferring it to the recording medium. In either case, it is a process of updating the gradation correction table according to the error between the gradation characteristics obtained from the measurement result of the test image and the target gradation characteristics. In order to form a test image on a recording medium or an image carrier, calibration can be performed in real time even during a printing job. Therefore, it is possible to prevent a decrease in productivity while maintaining appropriate gradation characteristics.

[0005] The image forming apparatus disclosed in Patent Document 1 performs calibration by forming a test image in a margin area on a recording medium on which an image (user image) according to an instruction from a user is formed. Thereby, calibration is performed in real time. The margin area where the test image is formed is an area to be cut off at the outer edge of the recording medium. Therefore, the test image is not included in the product.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0007] In an electrophotographic image forming apparatus, an image of a product or a test image is formed by electrostatically transferring a developer such as toner (hereinafter simply referred to as "toner") from an image carrier to a recording medium (transfer step), and the transferred toner is fixed to the recording medium by a fixing step. When the surface property of the recording medium is not uniform, the toner may not adhere to the recording medium uniformly during the transfer step, resulting in image unevenness. Further, even when the transfer step is properly performed, image unevenness may occur due to non-uniform pressure during pressurization in the fixing step. When image unevenness occurs, the variation in the measurement results of the test image increases, and the image adjustment accuracy decreases.

[0008] Further, even when there is no image unevenness in the test image, the image adjustment accuracy may decrease. The test image is generally detected by an optical sensor such as an image density sensor or a chromaticity sensor. For an on-demand image forming apparatus, the requirement for the detection accuracy of the optical sensor is high. In order to achieve the required accuracy for the optical sensor, it is necessary to keep the distance from the optical sensor to the recording medium constant due to its characteristics. However, for example, when the stiffness of the recording medium is low, the behavior of the recording medium becomes unstable (wavy), and the optical sensor cannot properly detect the test image.

[0009] In view of the above problems, an object of the present invention is to provide an image forming apparatus that determines whether a recording medium can be used for adjusting image forming conditions and stabilizes image adjustment accuracy.

Means for Solving the Problems

[0010] The image forming apparatus of the present invention includes: an image forming unit that forms an image on a recording medium based on image forming conditions; a detection unit that detects the image formed on the recording medium; and a control unit that determines whether the recording medium can be used for adjusting the image forming conditions based on the characteristics of the recording medium, and if it can be used, causes the image forming unit to form a test image for adjusting the image forming conditions on the recording medium, adjusts the image forming conditions based on the detection result of the test image by the detection unit, and does not perform the adjustment of the image forming conditions using the recording medium if it cannot be used.

Effects of the Invention

[0011] According to the present invention, it is possible to determine whether a recording medium can be used for adjusting image forming conditions and stabilize image adjustment accuracy.

Brief Description of the Drawings

[0012]

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Mode for Carrying Out the Invention

[0013] Hereinafter, embodiments of the present invention will be described with reference to the drawings. However, although various technically preferable limitations are imposed on the embodiments described below for carrying out the present invention, the scope of the invention is not limited to the following embodiments and illustrated examples.

[0014] (First Embodiment) 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 is composed of a printer 101, a reader 400, and a processing device 600. The image forming apparatus 100 (printer 101) forms an image on a sheet-like recording medium 110 by an electrophotographic method. Note that the printer 101 according to the present embodiment may be an inkjet printer or a sublimation printer.

[0015] The image forming apparatus 100 includes each mechanism that constitutes an engine unit for image formation within the printer 101, an engine control unit 102 that controls the operation of each mechanism, and a control board housing unit 104 that houses the printer controller 300. An operation panel 180 is provided on the upper part of the printer 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. The input device includes various key buttons and a touch panel, etc. The output device includes a display and a speaker. The reader 400 is an image reading device that reads an image from a recording medium (original document) on which an image has been formed.

[0016] Each mechanism that constitutes the engine unit includes a charging and exposure mechanism, a developing mechanism, a transfer mechanism, a fixing mechanism, a paper feeding mechanism for the recording medium 110, and a transport mechanism for the recording medium 110. The charging and exposure mechanism forms an electrostatic latent image by scanning with laser light. The developing mechanism visualizes the electrostatic latent image. The transfer mechanism transfers the toner image generated by visualization to the recording medium 110. The fixing mechanism fixes the toner image transferred to the recording medium 110. These mechanisms are constituted by the image forming units 120, 121, 122, 123 within the printer 101, an intermediate transfer belt 106, a fuser 150, a paper feed cassette 113, etc.

[0017] The image forming units 120, 121, 122, 123 only differ in the color of the image to be formed and perform the same operations with the same configuration. The image forming unit 120 forms a yellow (Y) image. The image forming unit 121 forms a magenta (M) image. The image forming unit 122 forms a cyan (C) image. The image forming unit 123 forms a black (K) image. The image forming units 120, 121, 122, 123 each include a photosensitive drum 105, a charger 111, a laser scanner 107, and a developer 112.

[0018] The charging and exposure mechanism uniformly charges the surface of the photosensitive drum 105 with a charger 111, and forms an electrostatic latent image on the surface of the photosensitive drum 105 with a laser scanner 107. The photosensitive drum 105 is a drum-shaped photoreceptor having a photosensitive layer on its surface, and rotates about a drum axis. The charger 111 uniformly charges the photosensitive layer on the surface of the rotating photosensitive drum 105.

[0019] 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. The laser scanner 107 is provided with a laser driver that drives the laser light emitted from the light emitting unit 108 according to the image data supplied from the printer controller 300. The laser light emitted from the semiconductor laser is deflected in one direction according to the rotation of a rotating polygon mirror in the light emitting unit 108. The laser light deflected in one direction irradiates the photosensitive drum 105 via the reflection mirror 109. As a result, the laser light scans the surface of the photosensitive drum 105 in one direction (the drum axis direction) to form an electrostatic latent image. The one direction (the depth direction in the figure) in which the laser scanner 107 scans the photosensitive drum 105 is the main scanning direction.

[0020] The developing mechanism visualizes the electrostatic latent image with toner supplied from a developing device 112 to form a toner image on the photosensitive drum 105. The toner image on the photosensitive drum 105 is transferred onto an intermediate transfer member 106 which is an image carrier to which a voltage of the opposite polarity to that of the toner image is applied. When forming a color image, toner images of respective colors are sequentially transferred onto the intermediate transfer member 106 from the respective photosensitive drums 105 of the image forming units 120, 121, 122, and 123 so as to be superimposed. In the present embodiment, the intermediate transfer member 106 rotates clockwise in the figure, and toner 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). As a result, a full-color toner image (visible image) is formed on the intermediate transfer member 106. Note that the photosensitive drum 105 and the developing device 112 are detachable from the housing of the printer 101.

[0021] The transfer processing mechanism transfers the visible image (toner image) formed on the intermediate transfer member 106 to the recording medium 110 fed from the paper feed cassette 113. The transfer processing mechanism includes a transfer roller 114 for transferring the toner image from the intermediate transfer member 106 to the recording medium 110. The toner images transferred from each image forming unit 120, 121, 122, 123 to the intermediate transfer member 106 are conveyed to the transfer roller 114 as the intermediate transfer member 106 rotates clockwise in the figure. The recording medium 110 is conveyed to the transfer roller 114 in accordance with the timing when the toner image is conveyed to the transfer roller 114. The transfer roller 114 transfers the toner image to the recording medium 110 by pressing the recording medium 110 against the intermediate transfer member 106 and applying a bias of the opposite polarity to the toner image.

[0022] An image formation start position detection sensor 115 and an image density sensor 117 are arranged around the intermediate transfer member 106. The image formation start position detection sensor 115 is used to determine the transfer start position of the toner image to the recording medium 110. The image formation start position detection sensor 115 is provided upstream of the transfer roller 114 in the rotation direction of the intermediate transfer member 106. The image density sensor 117 is used to detect a test image for gradation correction formed on the intermediate transfer member 106 during image density control. The image density sensor 117 is provided downstream of the image forming unit 123 in the rotation direction of the intermediate transfer member 106.

[0023] The paper feed processing mechanism includes a paper feed cassette 113 for storing the recording medium 110, a conveyance path through which the recording medium 110 is conveyed, and various rollers for conveying the recording medium 110. The recording medium 110 is fed from the paper feed cassette 113, and an image is formed by transferring and fixing the toner image while being conveyed through the conveyance path, and then discharged to the outside of the printer 101. The conveyance direction of the recording medium 110 is the sub-scanning direction orthogonal to the main scanning direction.

[0024] The recording medium 110 is fed from the paper feed cassette 113 and conveyed through the conveyance path to the transfer roller 114. A paper feed timing sensor 116 for adjusting the conveyance timing of the recording medium 110 is provided midway in the conveyance path from the paper feed cassette 113 to the transfer roller 114. 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 recording medium 110 are used to adjust the timing at which the recording medium 110 is conveyed to the transfer roller 114. Thereby, the toner image is transferred from the intermediate transfer member 106 to a predetermined position on the recording medium 110.

[0025] The recording medium 110 onto which the toner image has been transferred is conveyed to the fixing mechanism. The fixing mechanism of the present embodiment includes a fuser 150. The fuser 150 includes a fixing roller 151 for heating the recording medium 110 in order to thermally press the toner image onto the recording medium 110, a pressure belt 152 for pressing the recording medium 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 having a heater inside and is configured to convey the recording medium 110 by rotating. The pressure belt 152 presses the recording medium 110 against the fixing roller 151. The post-fixing sensor 153 detects the recording medium 110 after the image has been fixed.

[0026] The recording medium 110 on which the image has been fixed by the fuser 150 may be discharged as it is or conveyed to the conveyance path 135. For this purpose, a flapper 132 is provided after the fuser 150. The flapper 132 guides the recording medium 110 to either the conveyance path 135 or the conveyance path 201. The conveyance path 201 includes conveyance rollers 140 and 141. The recording medium 110 guided to the conveyance path 201 is conveyed by the conveyance rollers 140 and 141 and discharged from the printer 101 to the processing device 600 with the surface on which the image has been formed facing upward. A colorimetric unit 138 is provided at a position where the image of the recording medium 110 can be detected between the conveyance roller 140 and the conveyance roller 141 in the conveyance path 201.

[0027] The color measurement unit 138 is an optical sensor such as a CMOS line sensor or a CCD line sensor. The color measurement unit 138 reads an image formed on the recording medium 110 that is conveyed through the conveyance path 201 by the conveyance rollers 140 and 141. The color measurement unit 138 outputs a reading signal including the luminance values of each color of red (R), green (G), and blue (B) as a reading result. The luminance values of these reading signals are converted into density values of each color of cyan (C), magenta (M), yellow (Y), and black (K) and used. Generally, cyan is calculated from the luminance value of the red sensor, magenta is calculated from the luminance value of the green sensor, yellow is calculated from the luminance value of the blue sensor, and black is calculated from the luminance value of the green sensor. At that time, the conversion from each luminance value to each color density value is performed using a LUT (Look Up Table) that is generated by previously obtaining the relationship between each luminance value of RGB and each density value of CMYK. Such a LUT is stored in advance in the image forming apparatus 100.

[0028] The conveyance path 135 is a path for conveying the recording medium 110 to the inversion path 136 used for inverting the front and back surfaces of the recording medium 110. An inversion sensor 137 for detecting the recording medium 110 is provided in the inversion path 136. When the inversion sensor 137 detects the rear end of the recording medium 110, the conveyance direction of the recording medium 110 is inverted in the inversion path 136. The recording medium 110 with the inverted conveyance direction is conveyed to either the conveyance path 135 or the inversion path 139. For this purpose, a flapper 133 is provided at the branch point between the conveyance path 135 and the inversion path 139. When conveyed to the conveyance path 135, the recording medium 110 is guided to the conveyance path 135 by the flapper 133 and further guided to the conveyance path 201 by the flapper 134. As a result, the recording medium 110 is discharged from the printer 101 to the processing device 600 with the front and back surfaces inverted (with the surface on which the image is formed facing down). When conveyed to the inversion path 139, the recording medium 110 is guided to the inversion path 139 by the flapper 133. The recording medium 110 guided to the inversion path 139 has its front and back surfaces inverted and is conveyed to the transfer roller 114 again. As a result, image formation on the back surface of the recording medium 110 is performed.

[0029] The processing device 600 acquires the recording medium 110 (product) on which an image is formed from the printer 101. The processing device 600 performs post-processing such as stapling and bookbinding on the acquired product, and discharges it to a tray.

[0030] (Color measurement unit) FIG. 2 is an explanatory diagram of the color measurement unit 138. The color measurement unit 138 includes two line sensors 138a and 138b that are arranged so as to partially overlap in the main scanning direction orthogonal to the conveyance direction of the recording medium 110. Line sensors generally have little demand for a size capable of reading a recording medium 110 of A3 size or more and are expensive. By using two line sensors of a size capable of reading an inexpensive recording medium 110 of A3 size or less, even when reading a recording medium 110 of A3 size or more, it is possible to suppress costs and perform reading.

[0031] FIG. 3 is a configuration explanatory diagram of the line sensor 138a. The line sensor 138b has the same configuration. The line sensor 138a is an optical sensor that performs color measurement by detecting the spectral reflectance of the test image 520 formed on the recording medium 110. The line sensor 138a includes a white LED (Light Emitting Diode) 501, a diffraction grating 502, a light receiving element array 503, an arithmetic unit 504, a memory 505, and a lens 506.

[0032] The white LED 501 is a light emitting unit that irradiates light onto the recording medium 110 conveyed through the conveyance path 201. The diffraction grating 502 disperses the reflected light by the test image 520 for each wavelength. The lens 506 condenses the light irradiated from the white LED 501 onto the test image 520, and condenses the reflected light by the test image 520 onto the diffraction grating 502. The light receiving element array 503 is a light receiving unit having light receiving elements 503-1 to 503-n for n pixels. Each light receiving element 503-1 to 503-n of the light receiving element array 503 receives the reflected light dispersed for each wavelength by the diffraction grating 502. Each light receiving element 503-1 to 503-n outputs, as a detection result, a voltage (electrical signal) correlated with, for example, the intensity of the received reflected light.

[0033] The calculation unit 504 converts the voltage values output from each of the light receiving elements 503-1 to 503-n into digital signals (light intensity values). The correspondence between each of the light receiving elements 503-1 to 503-n and the wavelength is determined in advance. Therefore, the light intensity values of each of the light receiving elements 503-1 to 503-n correspond to the reflected light intensity (spectral data) for each wavelength. The calculation unit 504 performs spectral calculations of the light intensity values, calculations of Lab values, and the like. As a result, the calculation unit 504 generates a reading signal including the luminance values of each of the colors red (R), green (G), and blue (B). The memory 505 stores various data such as the light intensity for each wavelength when each of the light receiving elements 503-1 to 503-n receives the reflected light from a reference member (not shown).

[0034] The color measurement unit 138 of the present embodiment forcibly emits light from the light source (white LED 501) before color measurement. Since the output values of the light receiving element array 503 are stabilized by the forced light emission, the color measurement unit 138 has a configuration that is less affected by temperature characteristics.

[0035] (Printer Controller) FIG. 4 is an explanatory diagram of the printer controller 300 of the present embodiment. The printer controller 300 is communicably connected to a host computer 301, which is a device provided outside the image forming apparatus 100. The host computer 301 and the image forming apparatus 100 are communicably connected by a communication line such as USB2.0 High-Speed, 1000Base-T / 100Base-TX / 10Base-T (compliant with IEEE 802.3) or wirelessly.

[0036] The printer controller 300 controls the operation of the entire printer 101. For this purpose, the printer controller 300 is connected to the operation panel 180, the reader 400, and the engine unit 1011. The engine unit 1011 controls the operation of each mechanism in the printer 101 in response to an instruction from the printer controller 300, and performs image forming processing on the recording medium 110. The engine unit 1011 includes an engine control unit 102. The engine control unit 102 controls the operation of each mechanism of the engine unit 1011. The engine control unit 102 also controls the detection operation of the test image by the image density sensor 117 and the color measurement unit 138. The engine control unit 102 is constituted by, for example, a CPU (Central Processing Unit).

[0037] The printer controller 300 includes a host interface (I / F) 302, a panel interface (I / F) 312, a reader interface (I / F) 313, an engine interface (I / F) 319, and an input / output buffer 303. The host I / F 302 is a communication interface with the host computer 301. The panel I / F 302 is a communication interface with the operation panel 180. The reader I / F 313 is a communication interface with the reader 400. The engine I / F 319 is a communication interface with the engine unit 1011. The input / output buffer 303 is a temporary storage area for transmitting and receiving control codes and data via each interface.

[0038] The printer controller 300 includes a CPU 314, a program ROM (Read Only Memory) 304, and a RAM (Random Access Memory) 310. The CPU 314 controls the operation of the printer controller 300 by executing a computer program stored in the program ROM 304. The RAM 310 provides a work area when the printer controller 300 executes processing.

[0039] The program ROM 304, as a module, includes an image information generation unit 305, a main scanning unevenness correction table generation unit 306, an automatic gradation correction generation unit 307, a multi-color table generation unit 308, and an image defect detection unit 309. The image information generation unit 305 generates various image objects according to the settings of the data acquired from the host computer 301. The main scanning unevenness correction table generation unit 306 generates a main scanning unevenness correction table for suppressing the image density unevenness in the main scanning direction by correcting the laser emission intensity. The automatic gradation correction generation unit 307 generates a gradation correction table (γLUT) for performing monochromatic density gradation correction. The multi-color table generation unit 308 generates an ICC profile, which is a multi-dimensional LUT, for correcting the variation of multi-colors. The image defect detection unit 309 detects image defects in the image read by the colorimetric unit 138.

[0040] The RAM 310 temporarily stores the processing results by the image information generation unit 305, the main scanning unevenness correction table generation unit 306, the automatic gradation correction generation unit 307, and the multi-color table generation unit 308. The RAM 310 has a table storage unit 311. The table storage unit 311 stores the main scanning unevenness correction table, the γLUT, and the ICC profile.

[0041] The printer controller 300 includes a RIP (Raster Image Processor) unit 315, a color processing unit 316, a gradation correction unit 317, and a pseudo halftone processing unit 318. The RIP unit 315 expands an image object (image data) into a bitmap image. The color processing unit 316 performs color conversion processing for multi-color using an ICC profile on the image data expanded into a bitmap image by the RIP unit 315. The gradation correction unit 317 executes single-color gradation correction processing on the image data color-converted by the color processing unit 316 using a γLUT. The pseudo halftone processing unit 318 executes pseudo halftone processing such as a dither matrix or an error diffusion method on the image data gradation-corrected by the gradation correction unit 317. The image data pseudo halftone-processed by the pseudo halftone processing unit 318 is transmitted to the engine unit 1011 via the engine I / F 319. The engine control unit 102 of the engine unit 1011 performs image formation processing based on the image data acquired from the engine I / F 319.

[0042] Each unit of the printer controller 300 as described above is connected to the system bus 320 and can communicate via the system bus 320. The CPU 314 manages and updates the ICC profile, γLUT, and main scanning unevenness correction table used during image formation via the system bus 320. The CPU 314 enables the output of an image of a desired color by reflecting the latest tables in the color processing unit 316, gradation correction unit 317, etc.

[0043] (Test image for gradation correction formed on the recording medium 110) FIG. 5 is an exemplary diagram of a test image for gradation correction formed on the recording medium 110 together with a user image in response to an instruction from the user. The recording medium 110 is conveyed in the direction of the arrow shown in FIG. 5 (conveying direction). The test image for gradation correction (gradation correction pattern 1104) formed on the recording medium 110 is formed in the end region (non-image region 1102) of the recording medium 110 excluding the image region 1101 where the user image is formed. The gradation correction pattern 1104 of the present embodiment is formed in the end region (non-image region 1102) of the recording medium 110 in the conveying direction. The image region 1101 is the region indicated by dots in FIG. 5. The cutting marks 1103 are previously provided on the recording medium 110. The cutting marks 1103 are configured by combining two L-shaped marks and are provided at the four corners of the image region 1101. The recording medium 110 is cut by the cutting marks 1103. Note that the dots in the image region 1101 are shown for explanation purposes and are not actually printed on the recording medium 110.

[0044] The gradation correction pattern 1104 is formed for each color on one surface of the recording medium 110. The gradation correction pattern 1104 is usually formed in the outer non-image region 1102 so as not to overlap the image region 1101. However, when the CPU 314 determines that it is to be formed overlapping the image region 1101, the gradation correction pattern 1104 may be formed overlapping the image region 1101. In the present embodiment, overlapping the image region 1101 includes not only the case of being formed overlapping only the image region 1101 but also the case of being formed straddling the image region 1101 and the non-image region 1102.

[0045] The gradation correction pattern 1104 may be formed at any position on the periphery of the recording medium 110. In the present embodiment, the gradation correction pattern 1104 is formed at both ends of the recording medium 110 in a direction (the short side direction of the recording medium 110) orthogonal to the conveyance direction (the longitudinal direction of the recording medium 110) of the recording medium 110. That is, two-color gradation correction patterns 1104 are formed at one end of the recording medium 110 in the short side direction, and the remaining two-color gradation correction patterns 1104 are formed at the other end of the recording medium 110 in the short side direction. In the present embodiment, the cyan and magenta gradation correction patterns 1104 are formed at one end of the recording medium 110 in the short side direction, and the yellow and black gradation correction patterns 1104 are formed at the other end of the recording medium 110 in the short side direction. Thereby, the gradation correction pattern 1104 is not formed at the leading end of the recording medium 110 in the conveyance direction, and the occurrence of winding of the recording medium 110 during the fixing process can be more reliably suppressed.

[0046] The gradation correction pattern 1104 is composed of a plurality of gradation patches (11 gradations in FIG. 5) with different gradation values for each color stepwise. Each of the plurality of gradation patches is, for example, a square shape with a side length of about 8 [mm], and is arranged in a row in the conveyance direction.

[0047] For each color gradation patch, gradation patches for detecting the condition of the recording medium 110 (that is, gradation patches with a gradation value of 0) are arranged at both ends of the recording medium 110 in the conveyance direction. Nine gradation patches with evenly allocated gradation values are arranged between the gradation patches with a gradation value of 0. When the gradation value is represented by 0 to 255, the gradation correction pattern 1104 is composed of gradation patches of each color with gradation values of 0, 16, 32, 64, 86, 104, 128, 176, 224, 255, 0. Note that the gradation correction pattern 1104 is not limited to yellow, magenta, cyan, and black, and may be composed of each color of red, green, blue, or process black. Also, the size and gradation order are not limited.

[0048] (Judgment process for available recording media) Due to reasons such as surface properties, there may be significant variations in the measurement results of test images by the color measurement unit 138 for the recording medium 110. This causes a decrease in the image adjustment accuracy. Therefore, the types of recording media 110 used for adjusting image formation conditions such as tone correction are selected. FIG. 6 is a flowchart showing a process for determining whether the recording medium 110 can be used for adjusting image formation conditions. When accommodating a different type of recording medium in the paper feed cassette 113 than before, the user registers the recording medium 110 via the operation panel 180.

[0049] The CPU 314 receives the brand information of the recording medium 110 accommodated in the paper feed cassette 113 from the operation panel 180 (S1). The CPU 314 determines whether the received brand is a registered brand (S2). If it is not registered (S2: N), the CPU 314 performs a registration information acquisition process. The registration information is characteristic information such as the basis weight and surface properties of the recording medium 110. The CPU 314 displays a basis weight setting screen illustrated in FIG. 7 on the operation panel 180 to prompt the user to input the basis weight. The user inputs the corresponding basis weight from the setting screen displayed on the operation panel 180. The CPU 314 acquires the basis weight information input from the operation panel 180 (S3).

[0050] In addition to determining the use of the recording medium 110 for image adjustment, the basis weight is used to optimize various control values (for example, high voltage setting during transfer and temperature setting during fixing) in the image forming apparatus 100. In the present embodiment, when the recording medium 110 is coated paper, the range of the basis weight that can be used for image adjustment is limited to 56 "g / m^2" or more.

[0051] FIG. 8 is an explanatory diagram of the relationship between the basis weight of coated paper and the amount of noise components of the reflected light amount of the white background portion (portion where no image is formed) detected by the color measurement unit 138. As is clear from FIG. 8, the lower the basis weight, the larger the amount of noise components in the white background portion. This is because the stiffness of the recording medium 110 is low, and the behavior of the recording medium 110 becomes unstable at the detection position of the color measurement unit 138, resulting in instability of the amount of reflected light from the recording medium 110.

[0052] In this embodiment, the target value of the variation in the detection accuracy of the blank area is set to 3% or less. This is the threshold for achieving the target accuracy of image adjustment such as image density correction with ΔE≦1. This threshold (target value) is not limited to 3%, and may vary depending on the characteristics of the sensor to be detected and the correction processing accuracy.

[0053] The CPU 314 that has acquired the basis weight information displays the surface property setting screen of the recording medium 110 illustrated in FIG. 9 on the operation panel 180, and prompts the user to input the surface property. The user inputs the corresponding surface property from the setting screen displayed on the operation panel 180. The CPU 314 acquires the surface property information input from the operation panel 180 (S4).

[0054] FIG. 10 is an exemplary diagram of the average reflected light quantity rate for each type of surface property of the recording medium 110 and the variation amount of the reflected light quantity of the blank area. The average reflected light quantity rate is calculated based on the reflected light quantity when a high-quality paper satisfying a predetermined standard is detected by the color measurement unit 138. As is clear from FIG. 10, the variation amount becomes large in some of the embossed paper and recycled paper. This is due to the scattering of reflected light due to the unevenness of the surface of the recording medium 110 and the non-uniformity of the paper fibers forming the recording medium 110.

[0055] In this embodiment, as a necessary condition (threshold) for the recording medium 110 used for adjusting the image forming conditions, the average reflected light quantity rate is set to 85% or more. This is because if it is lower than this value, the signal value difference (dynamic range) between the blank area and the test image becomes small and the correction accuracy cannot meet the target. Also, the signal value variation is set to 3% or less. In this embodiment, high-quality paper, single-sided coated paper, and double-sided coated paper can be used.

[0056] The CPU 314 stores, as registered information, the acquired basis weight and surface property in association with the brand of the recording medium 110 in the non-volatile storage area of the program ROM 304 or the RAM 310. The registration information of the brands that have already been registered is also stored in this storage area. In the process of S2, this storage area is referred to and the presence or absence of registration is determined.

[0057] When the received brand is already registered (S2: Y), or after registering new registration information, the CPU 314 refers to the registration information (basis weight, surface property) of the brand (S5). The CPU 314 determines whether the recording medium 110 of the brand can be used for adjusting the image forming conditions based on the referred registration information (S6). The CPU 314 compares the basis weight and the surface property with their respective threshold values, and determines usability based on the comparison results. For example, if the basis weight is such that the variation in the detection accuracy of the white background portion is equal to or less than the target value, and the surface property is such that the reflected light quantity ratio is equal to or more than a predetermined value and the variation in the detection accuracy of the white background portion is equal to or less than the target value, the CPU 314 determines that the recording medium 110 of the brand can be used.

[0058] When it is not usable (S6: N), the CPU 314 adjusts the image forming conditions using the intermediate transfer member 106 (S8). FIG. 11 is an exemplary view of a test image for gradation correction formed on the intermediate transfer member 106 of the present embodiment. Four image density sensors 117 are arranged in a direction perpendicular to the rotation direction of the intermediate transfer member 106, and the respective measured colors are determined. The test image (gradation correction pattern) is composed of 10 gradation patches with different gradation values for each color. The gradation correction pattern is read by the image density sensor 117. By correcting the image forming conditions according to the difference between the gradation characteristics obtained from the reading result of the image density sensor 117 and the target gradation characteristics, the image density is stably maintained. In the present embodiment, every time 200 sheets of the recording medium 110 are passed, the space between the sheets is widened and the image forming conditions using the intermediate transfer member 106 are adjusted, thereby stabilizing the image quality.

[0059] The arrangement of the image density sensors 117 and the gradation patches is of course not limited to this, and may be outside the range in the direction perpendicular to the rotation direction of the intermediate transfer member 106 than the range where the image is formed on the intermediate transfer member 106. In that case, it is possible to adjust the image forming conditions using the intermediate transfer member 106 while performing normal image formation. Therefore, productivity can be maintained.

[0060] When it is possible to use (S6: Y), the CPU 314 displays a selection screen illustrated in FIG. 12 on the operation panel 180 (S7). On the selection screen, it is possible to select either adjustment of image formation conditions (on-paper adjustment) using the recording medium 110 of the type determined to be usable or adjustment of image formation conditions (in-engine adjustment) using the intermediate transfer body 106 by the image density sensor 117. When the user selects either one using the operation panel 180, the image formation conditions are adjusted by the selected method. The CPU 314 determines which adjustment method has been selected from the selection screen (S9). When in-engine adjustment is selected (S9: in-engine adjustment), the CPU 314 performs the process of S8. When on-paper adjustment is selected (S9: on-paper adjustment), the CPU 314 forms a test image (tone correction pattern) on the recording medium 110. The CPU 314 adjusts the image formation conditions based on the measurement results by the color measurement unit 138 of the test image on the recording medium 110 (S10).

[0061] In this way, based on the characteristics of the recording medium 110, it is determined whether or not the recording medium 110 can be used for adjusting the image formation conditions. If it cannot be used, adjustment of the image formation conditions using the recording medium 110 is not performed. Thereby, it is possible to prevent the variation in the measurement results of the test image from increasing due to the type of the recording medium 110 and the image adjustment accuracy from decreasing. In addition to the basis weight and surface properties, the color of the recording medium 110 may be added to the characteristics of the recording medium 110. FIG. 13 is an exemplary view of a color setting screen of the recording medium 110. When the color of the recording medium 110 is dark, the dynamic range of the measurement result of the image density of the tone patch of the test image of a specific color becomes small, and the adjustment accuracy may decrease. Therefore, the recording medium 110 with a dark color is determined to be unusable for adjusting the image formation conditions.

[0062] (Second Embodiment) In recent years, recording media 110 with various characteristics have been used for image formation in order to meet user needs. In this case, in addition to registering the characteristics of the recording media 110, the characteristics of the recording media 110 may be detected based on the detection results of the colorimetric unit 138. FIG. 14 is a flowchart showing a process of determining whether the recording media 110 can be used for adjusting image formation conditions based on the detection results of the colorimetric unit 138. Note that since the configurations of the image forming apparatus 100 and the printer controller 300 in the second embodiment are the same as those in the first embodiment, the description thereof is omitted.

[0063] When accommodating the recording media 110 in the paper feed cassette 113, the user registers the recording media 110 via the operation panel 180. The CPU 314 receives the brand information of the recording media 110 accommodated in the paper feed cassette 113 from the operation panel 180 (S11). The CPU 314 determines whether the received brand is already a registered brand (S12). If it is registered (S12: Y), the CPU 314 has already determined whether the recording media 110 can be used for image adjustment, and the determination result is also registered. If it is not usable (S16: N), the CPU 314 performs adjustment of image formation conditions using the intermediate transfer body 106 in the same manner as the process of S8 in FIG. 6 (S18). If it is usable (S16: Y), the CPU 314 displays a selection screen illustrated in FIG. 12 on the operation panel 180 (S17). The CPU 314 determines which adjustment method has been selected from the selection screen (S19). If in-engine adjustment is selected (S19: in-engine adjustment), the CPU 314 performs the process of S18. If on-paper adjustment is selected (S9: on-paper adjustment), the CPU 314 performs adjustment of image formation conditions using the recording media 110 in the same manner as the process of S20 in FIG. 6 (S20).

[0064] If not registered (S12: N), the CPU 314 determines whether the recording medium 110 can be passed through and used for adjusting the image forming conditions. For this purpose, the CPU 314 first controls the engine unit 1011 to form a test image on the recording medium 110 to determine whether it can be used for adjusting the image forming conditions (S13). FIG. 15 is an exemplary diagram of the test image. The position of the tone correction pattern 1105 in the test image of FIG. 15 is the same as the position of the tone correction pattern 1104 in the test image of FIG. 5. No user image is formed in the image area 1101. The color of the tone patches in the tone correction pattern 1105 is different from the color of the tone patches in the tone correction pattern 1104.

[0065] Specifically, the tone patches contain many white background parts (non-image forming parts). In order to detect the image density with high precision, the stability of the level of the white background part in the reflected light amount is important. Therefore, the tone correction pattern 1105 is configured to have a wide white background range with 6 patches out of all 11 tone patches being white background parts. Also, many high image density tone patches with the same tone value are arranged for the colored tone patches. In the example of FIG. 15, 5 patches out of all 11 tone patches have a tone value of 255 levels. With such a tone correction pattern 1105, it becomes possible to determine whether the transferability depending on the resistance of the recording medium 110 and the fixing property depending on the heat capacity are stable.

[0066] The test image formed on the recording medium 110 is conveyed through the normal conveyance path. The CPU 314 detects the test image by the color measurement unit 138 (S14). The CPU 314 calculates the detection accuracy based on the detection result by the color measurement unit 138 (S15). The CPU 314 determines whether the recording medium 110 can be used for adjusting the on-paper image based on the detection accuracy (S16).

[0067] In this embodiment, the detection accuracy is represented by two items: the variation in the blank areas of the detection results and the dynamic range. When both items meet the conditions, the CPU 314 determines that the recording medium 110 can be used for image adjustment. The respective judgment criteria (threshold values) are that the detection error ΔE ≦ 1. The variation in the blank areas is determined using the detection results of a predetermined number (here, 5) of blank areas for each color. The CPU 314 determines the variation in the blank areas based on whether the variation in each detection result is within a predetermined range (for example, 2[%] or less). Also, the CPU 314 detects the image density from the detection results of the blank areas and determines the variation in the dynamic range based on whether the difference in the image density from the solid areas (dynamic range) is smaller than a predetermined value. When the dynamic range is smaller than the predetermined value, the sensitivity for reading the change amount of the image density decreases, and the correction accuracy decreases. In this embodiment, based on whether 90[%] or more of the dynamic range of high-quality paper that meets a predetermined standard can be ensured as a reference value, the variation in the dynamic range is determined.

[0068] If it is not usable (S16: N), the CPU 314 performs the process of S18. If it is usable (S16: Y), the CPU 314 performs the processes of S17 to S20.

[0069] Even when the characteristics of the recording medium 110 are not input in this way, based on the detection results by the color measurement unit 138, it is possible to appropriately determine whether the recording medium 110 can be used for image adjustment. If it is not usable, the adjustment of the image formation conditions using the recording medium 110 is not performed. Note that the judgment criteria for usability are an example. For example, in order to more accurately judge the behavior of the recording medium 110 at the reading position of the color measurement unit 138, the gradation correction pattern 1104 may be all white. Also, in order to use the transferability and fixability of the recording medium 110 as judgment criteria, the entire recording medium 110 may be a solid image. Furthermore, the number of sheets of the recording medium 110 passed through may be increased to add judgments in other gradation ranges.

Claims

1. Image forming means for forming an image on a recording medium based on image forming conditions, Detection means for detecting the image formed on the recording medium, Based on the characteristics of the recording medium, it is determined whether the recording medium can be used for adjusting the image forming conditions. If it is usable, a test image for adjusting the image forming conditions is formed on the recording medium by the image forming means, and the image forming conditions are adjusted based on the detection result of the test image by the detection means. If it is not usable, control means for not performing the adjustment of the image forming conditions using the recording medium, characterized by comprising, An image forming apparatus.

2. The control means is characterized in that it determines whether the recording medium can be used for adjusting the image forming conditions based on the basis weight and surface property of the recording medium. The image forming apparatus according to claim 1.

3. The control means is characterized in that it compares the basis weight and the surface property of the recording medium with respective threshold values, and determines whether the recording medium can be used for adjusting the image forming conditions based on the comparison result. The image forming apparatus according to claim 2.

4. The control means is characterized in that it determines whether the recording medium can be used for adjusting the image forming conditions based on the color of the recording medium. The image forming apparatus according to claim 2 or 3.

5. Further comprising input means for inputting the basis weight and the surface property of the recording medium, characterized by. The image forming apparatus according to any one of claims 2 to 4.

6. Further comprising registration means for registering the characteristics of the recording medium, The control means is characterized in that it determines whether the recording medium can be used for adjusting the image forming conditions based on the characteristics registered in the registration means. The image forming apparatus according to any one of claims 1 to 5.

7. The control means is characterized in that it determines whether the recording medium can be used for adjusting the image forming conditions based on the detection result of the recording medium by the detection means. The image forming apparatus according to claim 1.

8. The control means is characterized in that it causes the image forming means to form a second test image on the recording medium, and determines whether the recording medium can be used for adjusting the image forming conditions based on the detection result of the second test image by the detection means. The image forming apparatus according to claim 7.

9. The second test image is characterized by including more non-image forming portions than the test image. The image forming apparatus according to claim 8.

10. The control means is characterized in that a determination result as to whether or not the recording medium can be used for adjusting image forming conditions is registered in a predetermined registration means. The image forming apparatus according to any one of claims 7 to 9.

Images