Image forming device

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 machine, or a printer. [Background technology]

[0002] In recent years, the market for on-demand image forming devices has been expanding. For example, electrophotographic image forming devices are becoming more widespread in the offset printing market. In addition, the market for on-demand image forming devices is also expanding for inkjet image forming devices, which have succeeded in cultivating a wide range of markets due to their 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 previous image forming devices that have dominated that market must be maintained. In order to maintain image quality, the image forming conditions when the image forming device forms an image on a recording medium are appropriately corrected.

[0003] For example, when performing gradation correction on an image forming device, the image forming conditions are corrected so that the gradation characteristics of the image forming device match the target gradation characteristics. The gradation characteristics are corrected using a gradation correction table that links the gradation characteristics of the image forming device with the target gradation characteristics. The gradation characteristics of the image forming device vary depending on environmental conditions such as temperature and humidity, and on changes over time in the parts and materials used in image formation. For this reason, the image forming device needs to periodically adjust (calibrate) the gradation characteristics and optimize the gradation correction table.

[0004] Calibration may be performed using the results of reading a test image formed on a recording medium, or using the results of reading a test image on an image carrier before it is transferred to the recording medium. In either case, the calibration is a process for updating a tone correction table according to the error between the tone characteristics obtained from the measurement results of the test image and the target tone 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 print job. This makes it possible to prevent a decrease in productivity while maintaining appropriate tone characteristics.

[0005] The image forming apparatus disclosed in Patent Document 1 performs calibration by forming a test image in a blank area on a recording medium where an image (user image) in accordance with an instruction from a user is formed. This allows calibration to be performed in real time. The blank area where the test image is formed is an area where the outer edge of the recording medium is cut off. Therefore, the test image is not included in the deliverable. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2014-107648 A Summary of the Invention [Problem to be solved by the invention]

[0007] In electrophotographic image forming apparatuses, a product image 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 process), and then fixing the transferred toner to the recording medium in a fixing process. If the surface properties of the recording medium are not uniform, the toner may not adhere uniformly to the recording medium during the transfer process, resulting in image unevenness. Even if the transfer process is performed appropriately, pressure may not be applied uniformly when pressure is applied in the fixing process, resulting in image unevenness. When image unevenness occurs, the measurement results of the test image will vary greatly, and the image adjustment accuracy will decrease.

[0008] Furthermore, even if no image unevenness occurs 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. An on-demand image forming apparatus requires high detection accuracy from the optical sensor. 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, if 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] SUMMARY OF THE PRESENT DISCLOSURE In view of the above problems, an object of the present invention is to provide an image forming apparatus that stabilizes image adjustment precision by determining whether or not a recording medium can be used for adjusting image formation conditions. [Means for solving the problem]

[0010] The image forming apparatus of the present invention comprises: picture Based on imaging conditions Note an image forming unit that forms an image on a recording medium; and a conveying unit that conveys the recording medium on which the image has been formed from the image forming unit; A recording medium on which a test image has been formed by the image forming means, Transported by the transport means Reading while moving Means, before Note Read of the test image by the means Read The image forming conditions are updated based on the results. Perform throttling control A control means; a registration means for registering a recording medium to be used in the adjustment control, and a recording medium not yet registered in the registration means when the recording medium is to be registered; Recording medium and determining whether the recording medium is usable for the adjustment control based on the result of the reading by the reading means. Means and Yes It is characterized by the above. Effect of the Invention

[0011] According to the present invention, it is possible to stabilize the image adjustment precision by determining whether or not a recording medium can be used for adjusting image forming conditions. [Brief description of the drawings]

[0012] [Figure 1] FIG. 1 is a diagram illustrating the configuration of an image forming apparatus. [Diagram 2] FIG. [Diagram 3] FIG. 2 is a diagram illustrating the configuration of a line sensor. [Figure 4] FIG. [Diagram 5] FIG. [Figure 6] 6 is a flowchart showing a process for determining whether a recording medium is usable for adjusting image forming conditions. [Figure 7] FIG. [Figure 8]FIG. 4 is a graph showing the relationship between basis weight and the amount of noise components. [Figure 9] FIG. [Figure 10] 11 is a graph showing an example of the fluctuation amount of reflected light in a white background portion and an average reflected light amount ratio; [Figure 11] 13 is an example of a test image on an intermediate transfer member. [Figure 12] FIG. [Figure 13] FIG. [Figure 14] 6 is a flowchart showing a process for determining whether a recording medium is usable for adjusting image forming conditions. [Figure 15] FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

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

[0014] (First embodiment) 1 is a configuration diagram of an image forming apparatus according to this embodiment. The image forming apparatus 100 according to this 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. The printer 101 according to this embodiment may be an inkjet printer or a dye-sublimation printer.

[0015] Image forming apparatus 100 includes mechanisms constituting an engine section for image formation within printer 101, an engine control section 102 that controls the operation of each mechanism, and a control board storage section 104 that stores printer controller 300. An operation panel 180 is provided on the top of printer 101. Operation panel 180 is a user interface, and includes an input device that receives instructions from a user, and an output device that displays a screen such as an operation screen. The input device is various key buttons, a touch panel, etc. The output device is a display and a speaker. Reader 400 is an image reading device that reads an image from a recording medium (original) on which the image is formed.

[0016] The mechanisms that make up the engine section include a charging / exposure processing mechanism, a developing processing mechanism, a transfer processing mechanism, a fixing processing mechanism, a paper feed processing mechanism for the recording medium 110, and a transport processing mechanism for the recording medium 110. The charging / exposure processing mechanism forms an electrostatic latent image by scanning with a laser beam. The developing processing mechanism visualizes the electrostatic latent image. The transfer processing mechanism transfers the toner image generated by the visualization to the recording medium 110. The fixing processing mechanism fixes the toner image transferred to the recording medium 110. Each of these mechanisms is made up of image forming units 120, 121, 122, 123, intermediate transfer body 106, fixing unit 150, paper feed cassette 113, etc. in the printer 101.

[0017] Image forming units 120, 121, 122, and 123 have the same configuration and perform the same operations, except for the colors of the images they form. Image forming unit 120 forms a yellow (Y) image. Image forming unit 121 forms a magenta (M) image. Image forming unit 122 forms a cyan (C) image. Image forming unit 123 forms a black (K) image. Image forming units 120, 121, 122, and 123 each include a photosensitive drum 105, a charger 111, a laser scanner 107, and a developer 112.

[0018] The charging and exposing process 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 photosensitive body having a photosensitive layer on its surface, and rotates around the 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 the 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 includes a laser driver that drives the laser light emitted from the light-emitting unit 108 in accordance with image data supplied from the printer controller 300. The laser light emitted from the semiconductor laser is swung in one direction in accordance with the rotation of a rotary polygon mirror in the light-emitting unit 108. The laser light swung 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 (drum axial direction) to form an electrostatic latent image. The one direction (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 the developing device 112 to form a toner image on the photosensitive drum 105. The toner image on the photosensitive drum 105 is transferred onto the intermediate transfer body 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, the toner images of each color are transferred from the photosensitive drums 105 of the image forming units 120, 121, 122, and 123 to the intermediate transfer body 106 in order to be superimposed. In this embodiment, the intermediate transfer body 106 rotates clockwise in the figure, and the 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 body 106. The photosensitive drum 105 and the developing device 112 are detachable from the housing of the printer 101.

[0021] The transfer mechanism transfers a visible image (toner image) formed on the intermediate transfer body 106 to the recording medium 110 fed from a paper feed cassette 113. The transfer mechanism includes a transfer roller 114 for transferring the toner image from the intermediate transfer body 106 to the recording medium 110. The toner images transferred from the image forming units 120, 121, 122, and 123 to the intermediate transfer body 106 are conveyed to the transfer roller 114 by the intermediate transfer body 106 rotating clockwise in the figure. The recording medium 110 is conveyed to the transfer roller 114 in accordance with the timing at which the toner image is conveyed to the transfer roller 114. The transfer roller 114 presses the recording medium 110 against the intermediate transfer body 106 and simultaneously applies a bias of the opposite polarity to the toner image, thereby transferring the toner image to the recording medium 110.

[0022] An image formation start position detection sensor 115 and an image density sensor 117 are disposed around the intermediate transfer body 106. The image formation start position detection sensor 115 is used to determine the transfer start position of the toner image onto 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 body 106. The image density sensor 117 is used to detect a test image for gradation correction formed on the intermediate transfer body 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 body 106.

[0023] The feeding process mechanism includes a paper feed cassette 113 that stores the recording medium 110, a transport path along which the recording medium 110 is fed, and various rollers for transporting the recording medium 110. The recording medium 110 is fed from the paper feed cassette 113, and while being transported along the transport path, a toner image is transferred and fixed onto the recording medium 110 to form an image, and the recording medium 110 is discharged outside the printer 101. The transport direction of the recording medium 110 is the sub-scanning direction perpendicular to the main scanning direction.

[0024] The recording medium 110 is fed from a paper feed cassette 113 and conveyed along a conveying path to a transfer roller 114. A paper feed timing sensor 116 for adjusting the conveying timing of the recording medium 110 is provided midway along the conveying path from the paper feed cassette 113 to the transfer roller 114. The timing at which the recording medium 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 body 106 and the timing at which the paper feed timing sensor 116 detects the recording medium 110. As a result, the toner image is transferred from the intermediate transfer body 106 to a predetermined position on the recording medium 110.

[0025] The recording medium 110 onto which the toner image has been transferred is transported to a fixing mechanism. The fixing mechanism of this embodiment includes a fixing device 150. The fixing device 150 includes a fixing roller 151 for heating the recording medium 110 in order to thermally and compress 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 completion of fixing. The fixing roller 151 is a hollow roller having an internal heater and configured to transport 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 fixing device 150 may be discharged as is or may be conveyed to a conveying path 135. For this purpose, a flapper 132 is provided after the fixing device 150. The flapper 132 guides the recording medium 110 to either the conveying path 135 or a conveying path 201. The conveying path 201 includes conveying rollers 140 and 141. The recording medium 110 guided to the conveying path 201 is conveyed by the conveying rollers 140 and 141, and is discharged from the printer 101 to the processing device 600 with the surface on which the image has been formed facing up. A color measurement unit 138 is provided between the conveying rollers 140 and 141 of the conveying path 201 at a position where the image on the recording medium 110 can be detected.

[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 conveyed on the conveying path 201 by the conveying rollers 140 and 141. The color measurement unit 138 outputs a read signal including luminance values ​​of each color of red (R), green (G), and blue (B) as a reading result. The luminance values ​​of these read signals are converted into density values ​​of each color of cyan (C), magenta (M), yellow (Y), and black (K) for use. In general, cyan is calculated from the luminance value of a red sensor, magenta from the luminance value of a green sensor, yellow from the luminance value of a blue sensor, and black from the luminance value of a green sensor. At this time, the conversion from each luminance value to each color density value is performed using a look-up table (LUT) that is generated by acquiring in advance the relationship between each luminance value of RGB and each density value of CMYK. Such an LUT is stored in the image forming apparatus 100 in advance.

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

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

[0030] (Color measurement unit) 2 is an explanatory diagram of the color measurement unit 138. The color measurement unit 138 includes two line sensors 138a, 138b arranged to overlap in the main scanning direction perpendicular to the transport direction of the recording medium 110. Line sensors are generally expensive because there is little demand for a size capable of reading recording media 110 of A3 size or larger. By using two inexpensive line sensors of a size capable of reading recording media 110 of A3 size or smaller, it becomes possible to read the recording media 110 of A3 size or larger while keeping costs down.

[0031] 3 is a diagram illustrating the configuration of line sensor 138a. Line sensor 138b has a similar configuration. Line sensor 138a is an optical sensor that detects the spectral reflectance of test image 520 formed on recording medium 110 to perform color measurement. Line sensor 138a includes white LED (Light Emitting Diode) 501, diffraction grating 502, light receiving element array 503, calculation unit 504, memory 505, and lens 506.

[0032] The white LED 501 is a light emitting unit that irradiates light onto the recording medium 110 transported on the transport path 201. The diffraction grating 502 separates the reflected light from the test image 520 into wavelengths. The lens 506 focuses the light emitted from the white LED 501 onto the test image 520, and also focuses the reflected light from 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 of the light receiving elements 503-1 to 503-n of the light receiving element array 503 receives the reflected light that has been separated into wavelengths by the diffraction grating 502. Each of the light receiving elements 503-1 to 503-n outputs a detection result, for example a voltage (electrical signal) that is correlated with the intensity of the received reflected light.

[0033] The calculation unit 504 converts the voltage value output from each of the light receiving elements 503-1 to 503-n into a digital signal (light intensity value). 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 value of each of the light receiving elements 503-1 to 503-n corresponds to the reflected light intensity (spectral data) for each wavelength. The calculation unit 504 performs spectral calculation of the light intensity value and calculation of Lab values. As a result, the calculation unit 504 generates a read signal including the luminance value of each color of 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 reflected light from a reference member (not shown).

[0034] In the present embodiment, the color measurement unit 138 performs forced emission of light from the light source (white LED 501) before color measurement. Since the output value of the light receiving element array 503 is stabilized by the forced emission, the color measurement unit 138 is configured to be less susceptible to the effects of temperature characteristics.

[0035] (Printer Controller) 4 is an explanatory diagram of the printer controller 300 of this 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 communicatively connected via a communication line such as USB 2.0 High-Speed ​​or 1000Base-T / 100Base-TX / 10Base-T (IEEE 802.3 compliant) or wirelessly.

[0036] The printer controller 300 controls the overall operation of the printer 101. To this end, 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 formation 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 in 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 configured, for example, by 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 read only memory (ROM) 304, and a random access memory (RAM) 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 working area for the printer controller 300 to execute processes.

[0039] The program ROM 304 has, as modules, an image information generating unit 305, a main scanning unevenness correction table generating unit 306, an automatic tone correction generating unit 307, a multi-color table generating unit 308, and an image defect detecting unit 309. The image information generating unit 305 generates various image objects by setting data acquired from the host computer 301. The main scanning unevenness correction table generating unit 306 generates a main scanning unevenness correction table for suppressing image density unevenness in the main scanning direction by correcting laser emission intensity. The automatic tone correction generating unit 307 generates a tone correction table (γLUT) for performing density tone correction of a single color. The multi-color table generating unit 308 generates an ICC profile, which is a multidimensional LUT, in order to correct fluctuations in multi-colors. The image defect detecting unit 309 detects image defects in an image read by the color measurement unit 138.

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

[0041] The printer controller 300 includes a RIP (Raster Image Processor) unit 315, a color processing unit 316, a tone correction unit 317, and a pseudo-halftone processing unit 318. The RIP unit 315 develops an image object (image data) into a bitmap image. The color processing unit 316 performs a multi-color color conversion process on the image data developed into the bitmap image by the RIP unit 315, using an ICC profile. The tone correction unit 317 performs a monochromatic tone correction process on the image data that has been color converted by the color processing unit 316, using a γLUT. The pseudo-halftone processing unit 318 performs pseudo-halftone processing such as a dither matrix or an error diffusion method on the image data that has been tone corrected by the tone correction unit 317. The image data that has been subjected to the pseudo-halftone process by the pseudo-halftone processing unit 318 is transmitted to the engine unit 1011 via an engine I / F 319. The engine control unit 102 of the engine unit 1011 performs an image formation process 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 a system bus 320 and can communicate with each other 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 makes it possible to output an image in a desired color by having the color processing unit 316, gradation correction unit 317, etc. reflect the latest tables.

[0043] (Test image for gradation correction formed on recording medium 110) FIG. 5 is an example diagram of a test image for gradation correction formed on the recording medium 110 together with a user image according to an instruction from a user. The recording medium 110 is conveyed in the direction of the arrow (conveyance direction) shown in FIG. 5. The test image for gradation correction (gradation correction pattern 1104) formed on the recording medium 110 is formed in an end region (non-image region 1102) of the recording medium 110 except for an image region 1101 where a user image is formed. The gradation correction pattern 1104 of this embodiment is formed in an end region (non-image region 1102) of the recording medium 110 in the conveyance direction. The image region 1101 is an area indicated by dots in FIG. 5. A cutting mark 1103 is provided in advance on the recording medium 110. The cutting mark 1103 is configured by combining two L-shaped marks and is provided at the four corners of the image region 1101. The recording medium 110 is cut at the cutting mark 1103. It should be noted that the dots in the image area 1101 are shown for the purpose of explanation, and are not actually printed on the recording medium 110.

[0044] The gradation correction pattern 1104 is formed for each color on one side of the recording medium 110. The gradation correction pattern 1104 is usually formed in a non-image area 1102 outside the image area 1101 so as not to overlap the image area 1101. However, when the CPU 314 determines that the gradation correction pattern 1104 is to be formed so as to overlap the image area 1101, the gradation correction pattern 1104 may be formed so as to overlap the image area 1101. In this embodiment, overlapping the image area 1101 includes not only the case where the gradation correction pattern is formed so as to overlap only the image area 1101, but also the case where the gradation correction pattern is formed across the image area 1101 and the non-image area 1102.

[0045] The gradation correction pattern 1104 may be formed anywhere on the periphery of the recording medium 110. In this embodiment, the gradation correction pattern 1104 is formed on both ends of the recording medium 110 in a direction (short side direction of the recording medium 110) perpendicular to the conveying direction of the recording medium 110 (longitudinal direction of the recording medium 110). That is, the gradation correction pattern 1104 of two colors is formed on one end of the recording medium 110 in the short side direction, and the gradation correction pattern 1104 of the remaining two colors is formed on the other end of the recording medium 110 in the short side direction. In this embodiment, the gradation correction pattern 1104 of cyan and magenta is formed on one end of the recording medium 110 in the short side direction, and the gradation correction pattern 1104 of yellow and black is formed on the other end of the recording medium 110 in the short side direction. As a result, the gradation correction pattern 1104 is not formed on the leading end of the recording medium 110 in the conveying 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) in which the gradation values ​​of each color are gradually changed. Each of the plurality of gradation patches is, for example, a square with one side measuring approximately 8 mm, and is arranged in a line in the transport direction.

[0047] The tone patches of each color are arranged at both ends of the recording medium 110 in the conveying direction, with tone patches for detecting the texture of the recording medium 110 (i.e., tone patches with a tone value of 0). Nine tone patches with equally-allocated tone values ​​are arranged between tone patches with a tone value of 0. When tone values ​​are expressed as 0 to 255, the tone correction pattern 1104 is composed of tone patches of each color with tone values ​​of 0, 16, 32, 64, 86, 104, 128, 176, 224, 255, and 0. Note that the tone correction pattern 1104 is not limited to yellow, magenta, cyan, and black, and may be composed of red, green, and blue colors or process black. Furthermore, the size and tone order are not limited.

[0048] (Processing for determining usable recording media) Due to surface characteristics and other reasons, the recording medium 110 may have a large variation in the measurement results of the test image by the color measurement unit 138. This causes a decrease in the accuracy of image adjustment. For this reason, the recording medium 110 used for adjusting image formation conditions such as gradation correction is selected from those that can be used. FIG. 6 is a flowchart showing the process of determining whether the recording medium 110 can be used for adjusting image formation conditions. When storing a different type of recording medium in the paper feed cassette 113, the user registers the recording medium 110 using the operation panel 180.

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

[0050] In addition to determining whether the recording medium 110 is to be used for image adjustment, the basis weight is also used to optimize various control values ​​(for example, high pressure settings during transfer and temperature settings during fixing) in the image forming apparatus 100. In this embodiment, when the recording medium 110 is fine paper, the range of basis weights 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 fine paper and the amount of noise components in the amount of reflected light from a white background portion (a portion on which an image is not formed) detected by the color measurement unit 138. As is clear from Fig. 8, the amount of noise components in the white background portion increases as the basis weight decreases. 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, causing the amount of reflected light by the recording medium 110 to become unstable.

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

[0053] After acquiring the basis weight information, the CPU 314 displays a setting screen for the surface properties of the recording medium 110, as shown in Fig. 9, on the operation panel 180, and prompts the user to input the surface properties. The user inputs the relevant surface properties 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 example diagram of the average reflected light rate for each type of surface property of the recording medium 110 and the amount of fluctuation in the amount of reflected light in the white background. The average reflected light rate is calculated based on the amount of reflected light when high-quality paper that meets a specified standard is detected by the color measurement unit 138. As is clear from Fig. 10, the amount of fluctuation is large for embossed paper and some 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 that form the recording medium 110.

[0055] In this embodiment, the necessary condition (threshold) for the recording medium 110 used to adjust the image formation conditions is an average reflected light rate of 85% or more. If it is lower than this value, the signal value difference (dynamic range) between the white background and the test image becomes small, and the correction accuracy does not meet the target. In addition, the signal value fluctuation 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 the acquired basis weight and surface property as registration information in a non-volatile storage area of ​​the program ROM 304 or RAM 310 in association with the brand of the recording medium 110. This storage area also stores registration information of brands that have already been registered. In the process of S2, this storage area is referenced to determine whether or not a brand has been registered.

[0057] If the accepted brand has already been registered (S2: Y), or after new registration information is registered, the CPU 314 refers to the registered information (basis weight, surface property) of the brand (S5). The CPU 314 judges whether the recording medium 110 of the brand can be used for adjusting the image formation conditions based on the referenced registered information (S6). The CPU 314 compares the basis weight and surface property with their respective threshold values, and judges usability based on the comparison result. For example, the CPU 314 judges that the recording medium 110 of the brand can be used if the basis weight is such that the variation in detection accuracy of the white background is equal to or less than a target value, the reflected light amount rate is equal to or more than a predetermined value, and the surface property is such that the variation in detection accuracy of the white background is equal to or less than a target value.

[0058] If it is not available (S6:N), the CPU 314 adjusts the image forming conditions using the intermediate transfer body 106 (S8). FIG. 11 is an example of a test image for gradation correction formed on the intermediate transfer body 106 in this embodiment. Four image density sensors 117 are arranged in a direction perpendicular to the rotation direction of the intermediate transfer body 106, and each measurement color is determined. The test image (gradation correction pattern) is composed of 10 gradation patches with different gradation values ​​for each color, and the gradation correction pattern is read by the image density sensor 117. The image density is stably maintained 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. In this embodiment, the image quality is stabilized by adjusting the image forming conditions using the intermediate transfer body 106 by widening the paper gap every time 200 sheets of the recording medium 110 are passed.

[0059] The arrangement of the image density sensor 117 and the gradation patches is not limited to this, and they may be located outside the range in which the image is formed on the intermediate transfer body 106 in the direction perpendicular to the rotation direction. In this case, it becomes possible to adjust the image formation conditions using the intermediate transfer body 106 while performing normal image formation. This makes it possible to maintain productivity.

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

[0061] In this way, based on the characteristics of the recording medium 110, it is determined whether the recording medium 110 can be used for adjusting the image forming conditions. If the recording medium 110 cannot be used, the adjustment of the image forming conditions using the recording medium 110 is not performed. This makes it possible to prevent the measurement results of the test image from varying greatly depending on the type of recording medium 110, and to prevent a decrease in the accuracy of the image adjustment. In addition to the basis weight and surface properties, the characteristics of the recording medium 110 may also include the color of the recording medium 110. FIG. 13 is an example of a setting screen for the color of the recording medium 110. If the color of the recording medium 110 is dark, the dynamic range of the result of measuring the image density of the gradation patch of the test image of a specific color becomes small, and the adjustment accuracy may decrease. For this reason, the recording medium 110 with a dark color is determined to be unusable for adjusting the image forming conditions.

[0062] Second embodiment In recent years, recording media 110 with various characteristics are used for image formation in order to meet user needs. In this case, in addition to registering the characteristics of the recording medium 110, the characteristics of the recording medium 110 may be detected from the detection results of the color measurement unit 138. Fig. 14 is a flowchart showing a process for determining whether or not the recording medium 110 can be used for adjusting the image formation conditions based on the detection results of the color measurement unit 138. Note that the configurations of the image forming apparatus 100 and the printer controller 300 of the second embodiment are similar to those of the first embodiment, and therefore description thereof will be omitted.

[0063] When the recording medium 110 is placed in the paper feed cassette 113, the user registers the recording medium 110 through the operation panel 180. The CPU 314 receives brand information of the recording medium 110 placed in the paper feed cassette 113 from the operation panel 180 (S11). The CPU 314 judges whether the received brand is already registered or not (S12). If it is registered (S12: Y), the CPU 314 has already judged whether the recording medium 110 can be used for image adjustment, and the judgment result is also registered. If it cannot be used (S16: N), the CPU 314 adjusts the image formation conditions using the intermediate transfer body 106 in the same manner as the process of S8 in FIG. 6 (S18). If it can be used (S16: Y), the CPU 314 displays a selection screen exemplified in FIG. 12 on the operation panel 180 (S17). The CPU 314 judges which adjustment method has been selected from the selection screen (S19). When the in-engine adjustment is selected (S19: in-engine adjustment), the CPU 314 performs the process of S18. When the on-paper adjustment is selected (S9: on-paper adjustment), the CPU 314 adjusts the image forming conditions using the recording medium 110 (S20), similar to the process of S20 in FIG.

[0064] If not registered (S12:N), the CPU 314 passes the recording medium 110 and determines whether it is usable 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 is usable for adjusting the image forming conditions (S13). FIG. 15 is an example of a test image. In the test image of FIG. 15, the position of the gradation correction pattern 1105 is the same as the position of the gradation correction pattern 1104 in the test image of FIG. 5. No user image is formed in the image area 1101. The color of the gradation patch of the gradation correction pattern 1105 is different from the color of the gradation patch of the gradation correction pattern 1104.

[0065] Specifically, the gradation patches include many white areas (non-image forming areas). In order to detect image density with high accuracy, it is important that the level of the white areas in the reflected light amount is stable. Therefore, the gradation correction pattern 1105 is configured such that six of the eleven gradation patches are white areas, making the white area wide. In addition, the colored gradation patches are arranged with many high image densities of the same gradation value. In the example of FIG. 15, five of the eleven gradation patches have a gradation value of 255 level. With such a gradation correction pattern 1105, it is possible to determine whether the transferability, which depends on the resistance of the recording medium 110, and the fixability, which depends on the heat capacity, are stable.

[0066] The test image formed on the recording medium 110 is transported along a normal transport path. The CPU 314 detects the test image using 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 is usable for on-paper image adjustment based on the detection accuracy (S16).

[0067] In this embodiment, the detection accuracy is expressed by two items, the variation of the white background part of the detection result and the dynamic range. When the conditions of both items are satisfied, the CPU 314 judges that the recording medium 110 can be used for image adjustment. The judgment criterion (threshold) for each is the detection error ΔE≦1. The variation of the white background part is determined using the detection results of a predetermined number of white background parts (here, five) of each color. The CPU 314 judges the variation of the white background part depending on whether the variation of each detection result is within a predetermined range (for example, 2[%] or less). The CPU 314 also detects the image density from the detection result of the white background part, and judges the variation of the dynamic range depending on whether the difference (dynamic range) between the image density of the solid part and that of the image density is smaller than a predetermined value. If the dynamic range is smaller than the predetermined value, the sensitivity for reading the amount of change in the image density decreases, and the correction accuracy decreases. In this embodiment, the dynamic range of high-quality paper that meets a predetermined standard is set as a reference value, and the variation of the dynamic range is judged depending on whether 90[%] or more of the reference value is secured.

[0068] If it is not available (S16: N), the CPU 314 performs the process of S 18. If it is available (S16: Y), the CPU 314 performs the processes of S17 to S20.

[0069] Even if the characteristics of the recording medium 110 are not input in this way, it is possible to appropriately determine whether or not the recording medium 110 is usable for image adjustment based on the detection result by the color measurement unit 138. If the recording medium 110 is unusable, the image formation conditions using the recording medium 110 are not adjusted. Note that the criteria for determining usability are only an example, and for example, in order to more accurately determine the behavior of the recording medium 110 at the reading position of the color measurement unit 138, the gradation correction pattern 1104 may be entirely white. Also, in order to use the transferability and fixability of the recording medium 110 as the criteria for determination, the entire recording medium 110 may be a solid image. Furthermore, the number of recording media 110 passed through may be increased to add a determination in another gradation range.

Claims

1. An image forming means for forming an image on a recording medium based on image forming conditions; a conveying means for conveying the recording medium on which the image is formed from the image forming means; a reading means for reading the recording medium on which the test image is formed by the image forming means while conveying the recording medium by the conveying means; a control unit that executes an adjustment control for updating the image forming conditions based on a result of reading the test image by the reading unit; a registration means for registering a recording medium to be used for the adjustment control; and a determination means for, when registering an unregistered recording medium in the registration means, reading the recording medium with the reading means and determining whether or not the recording medium is usable for the adjustment control based on a reading result of the reading means. Image forming device.

2. The control means causes the image forming means to form a judgment image on the recording medium to be registered, The determination unit obtains characteristics of the recording medium to be registered based on a result of reading the determination image by the reading unit, The determination unit determines whether the recording medium to be registered in the adjustment control is usable or not based on the characteristics.

2. The image forming apparatus according to claim 1.

3. The determination means calculates a detection accuracy of the test image when the recording medium to be registered is used based on the reading result of the determination image, the determining unit determines whether the recording medium is usable for the adjustment control based on the detection accuracy.

3. The image forming apparatus according to claim 2.

4. The detection accuracy is represented by the variation and dynamic range of the white background portion of the reading result.

4. The image forming apparatus according to claim 3.

5. An image carrier carrying another test image formed by the image forming means; and another reading means for reading the other test image on the image carrier, The control means If the recording medium to be registered in the adjustment control is usable, the image forming conditions are updated based on the result of reading the test image by the reading means; if the recording medium to be registered in the adjustment control is not usable, the image forming means is caused to form the other test image on the image carrier, the other reading means is caused to read the other test image, and the image forming conditions are updated based on a result of reading the other test image by the other reading means.

2. The image forming apparatus according to claim 1.

Images