Image reading device and image forming device

Abstract

To provide an image formation device, image reading device and calibration method that can calibrate each imaging sensor more easily and precisely.SOLUTION: An image formation device comprises: a conveyance part of a medium M; an imaging unit that has a plurality of imaging sensors 251, and captures a surface of the medium on a conveyance route of the medium; a color measurement unit 26 that measures a color of the surface of the medium on the conveyance route; and a control unit. An imaging range each of the plurality of imaging sensors has overlapped parts D1 and D3 between adjacent imaging sensors as for a width direction. The control unit is configured to: calibrate a first imaging sensor on the basis of a color measurement result of an inspection image It1 within a reference imaging range of a first imaging sensor 2511, and a reference imaging result of an inspection image It2 within the reference imaging range; compare imaging results by a plurality of imaging sensors 2511 and 2512 in the overlapped part D1; and calibrate other imaging sensor different from the first imaging sensor with the reference imaging result as a reference.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] This invention is Image reading device and The present invention relates to an image forming apparatus. [Background technology]

[0002] Image forming devices that form images on media, especially those used for commercial applications that require high quality, require highly accurate calibration and rapid detection of abnormalities. To achieve this, there are technologies that capture images of the formed images to detect density variations and image quality defects. To capture images, an imaging sensor is used, which has multiple imaging elements arranged in a plane parallel to the media transport direction, across a width perpendicular to the media transport direction, to capture a two-dimensional image.

[0003] In such image forming devices, if a single image sensor is lengthened to match the size of the formed image, problems arise such as increased costs and reduced manufacturing yield. To address this issue, there is a technology in which multiple image sensors are arranged in parallel to capture images across the entire width of the medium (Patent Document 1). In this case, adjustments are made to align the sensitivity characteristics between the image sensors. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2012-4868 Summary of the Invention [Problem to be solved by the invention]

[0005] However, when it becomes necessary to adjust absolute values ​​such as color tone as image quality improves, adjustments between image sensors are insufficient, and conventionally, there has been a problem in that it has become necessary to perform processing outside the image forming device.

[0006] The object of the present invention is to provide a method for calibrating each image sensor more easily and accurately. Image reading device and An object of the present invention is to provide an image forming apparatus. [Means for solving the problem]

[0007] In order to achieve the above object, the invention described in claim 1 is as follows: a transport unit that moves the medium along a predetermined transport path; a first image sensor that captures an image of the surface of the medium on the transport path; a second imaging sensor that images the surface of the medium on the transport path; a third image sensor that images the surface of the medium on the transport path; a fourth image sensor that images the surface of the medium on the transport path; the first imaging sensor in the conveying direction of the conveying unit 、 the second imaging sensor , the third imaging sensor and the fourth imaging sensor a color measurement unit that is provided downstream of the conveyance path and that measures the color of the surface of the medium on the conveyance path; A control unit; Equipped with a first overlapping portion in which a portion of the first image sensor and a portion of the second image sensor overlap in a width direction perpendicular to a conveying direction along the conveying path; a second overlapping portion in which a portion of the third image sensor and a portion of the fourth image sensor overlap in a width direction perpendicular to a conveying direction along the conveying path; While the medium is positioned within a color measurement range of the color measurement unit, the color measurement unit moves in the width direction, and Side By position The first test image Color measurement and measuring the color of the second test image at a position downstream of the second overlapping portion. , The control unit calibrating the first image sensor based on the color measurement result of the colorimetric measurement unit of the first test image and the imaging result of the first image sensor, and calibrating the second image sensor based on the imaging result of the first test image of the first image sensor and the imaging result of the second image sensor; calibrating the third image sensor based on the colorimetric result of the second test image by the colorimetric unit and the imaging result of the third image sensor, and calibrating the fourth image sensor based on the imaging result of the second test image by the third image sensor and the imaging result of the fourth image sensor; It is an image reading device.

[0009] Also, claims 2 The invention described is 1 In the image reading device described above, The color measurement unit is movable in the width direction across a portion of the first imaging sensor that does not overlap with the second imaging sensor, the first overlapping portion, and a portion of the second imaging sensor that does not overlap with the first imaging sensor.

[0010] Also, claims 3 The invention described in claim 1 is an image reading device, The color measurement unit is capable of reciprocating movement.

[0011] Also, claims 4 The invention described in claim 1 is an image reading device, The color measurement unit is fixed during color measurement.

[0012] Also, claims 5 The invention described is 1 In the image reading apparatus described in The color measurement unit is movable in the width direction along a support member.

[0013] Also, claims 6 The invention described is 5 In the image reading apparatus described in The support member is longer in the width direction than the imaging range of the first imaging sensor and the imaging range of the second imaging sensor.

[0015] Also, claims 7 The invention described herein comprises an image reading device according to claim 1, a forming operation unit that is provided upstream of the image reading device in the transport direction and that forms an image on the surface of the medium on the transport path; The image forming apparatus includes: [Effects of the Invention]

[0022] According to the present invention, it is possible to more easily and accurately calibrate each image sensor. [Brief explanation of the drawings]

[0023] [Figure 1] 1 is a schematic front view of an overall configuration of an image forming apparatus according to an embodiment of the present invention; [Figure 2] FIG. 2 is a diagram illustrating a head unit, an imaging unit, and a color measurement unit. [Figure 3] FIG. 2 is a block diagram showing the functional configuration of the image forming apparatus. [Figure 4] FIG. 10 is a diagram illustrating calibration of an image sensor. [Figure 5] FIG. 10 is a diagram illustrating the positional relationship of test images. [Figure 6] 10 is a flowchart showing a control procedure of a calibration control process. [Figure 7] 10A and 10B are diagrams illustrating a first modification of the test image formation position and calibration operation. [Figure 8] 10 is a flowchart showing a control procedure of a calibration control process according to the first modification. [Figure 9] 10A and 10B are diagrams illustrating a second modification of the test image formation position and calibration operation. [Figure 10] 10 is a flowchart showing a control procedure of a calibration control process according to a second modification. [Figure 11] FIG. 10 is a diagram showing a third modification of the calibration operation. [Figure 12] 10 is a flowchart showing a control procedure of a calibration control process according to a third modification. DETAILED DESCRIPTION OF THE INVENTION

[0024] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a schematic diagram showing the overall configuration of an image forming apparatus 1 according to an embodiment of the present invention, as viewed from the front.

[0025] The image forming apparatus 1 includes a medium supply unit 10, a formation unit 20, a medium discharge unit 30, and a control unit 40 (see FIG. 3). In this image forming apparatus 1, based on the control operation of the control unit 40, a medium M on which an image is to be formed is sent from the medium supply unit 10 to the formation unit 20, and after the image is formed, the medium M is discharged to the medium discharge unit 30.

[0026] The medium supply unit 10 includes a medium supply tray 11 and a supply conveying unit 12 . The medium supply tray 11 is a plate-like member that can hold one or more media M. The medium supply tray 11 moves up and down depending on the amount of media M placed on it, and the topmost medium M is held at a position where the supply and conveyance unit 12 starts conveying the media. Various materials such as printing paper of various thicknesses, cells, films, and fabrics can be used as the medium M. The medium M may have a surface made of a non-absorbent material that prevents ink from penetrating into the interior. The supply conveying unit 12 has a plurality of (for example, two) rollers 121, 122, a circular belt 123 supported on the inner surface by the rollers 121, 122, and a supply unit (not shown) that transfers the topmost medium M placed on the medium supply tray 11 to the belt 123. The supply conveying unit 12 transports the medium M transferred onto the belt 123 by the supply unit as the belt 123 moves in a circular motion due to the rotation of the rollers 121, 122, and sends it to the forming unit 20.

[0027] The forming section 20 includes an image forming drum 21, a delivery unit 22, a head unit 23 (forming operation section), a fixing section 24, an imaging section 25, a color measurement section 26, a delivery section 27, and the like.

[0028] The image forming drum 21 has a cylindrical outer periphery, and the medium M is placed on the outer periphery (transport surface) of the image forming drum 21, which moves the medium M along a (predetermined) transport path according to its rotation. A heater is provided on the inner surface of the image forming drum 21, and the transport surface can be heated so that the medium M placed on the transport surface reaches a predetermined set temperature.

[0029] The transfer unit 22 transfers the medium M transferred from the supply conveyance section 12 to the image forming drum 21. The transfer unit 22 is provided at a position between the supply conveyance section 12 of the medium supply section 10 and the image forming drum 21. The transfer unit 22 has a claw section 221 that grips one end of the medium M sent by the supply conveyance section 12, and a cylindrical transfer drum 222 that guides the medium M gripped by the claw section 221. When the medium M obtained from the supply conveyance section 12 by the claw section 221 is sent to the transfer drum 222, it moves along the outer peripheral surface of the rotating transfer drum 222 and is guided and transferred to the outer peripheral surface of the image forming drum 21.

[0030] The head unit 23 forms an image by ejecting ink droplets from multiple nozzle openings provided on an ink ejection surface facing the medium M to various locations on the surface of the medium M, which moves along a transport path in accordance with the rotation of the image forming drum 21 on which the medium M is placed. In the image forming apparatus 1 of this embodiment, four head units 23 are arranged at predetermined intervals, separated a predetermined distance from the outer circumferential surface of the image forming drum 21. The four head units 23 output, for example, ink of four colors, CMYK (cyan, magenta, yellow, and black). Here, the C, M, Y, and K color inks are ejected in order from the upstream side in the transport direction of the medium M, but this is not limited to this. Any ink may be used, but here, ink is used that changes phase between a sol state and a gel state depending on temperature and that hardens and fixes when exposed to predetermined actinic energy rays, such as ultraviolet rays. When ink is ejected from the head unit 23 in a sol state and lands on the medium M, its temperature drops, it quickly gels, and its viscosity increases, and the ink is fixed to the medium M by ultraviolet light irradiated from the fixing unit 24. Here, each of the head units 23 has a line head that can form an image across the image forming width on the medium M in combination with the rotation of the image forming drum 21 .

[0031] The fixing unit 24 irradiates the surface of the medium M with predetermined active energy rays, in this case, ultraviolet rays as described above. The fixing unit 24 has, for example, an LED lamp that emits ultraviolet rays. The fixing unit 24 is positioned near the outer peripheral surface of the image forming drum 21 so that it can irradiate ultraviolet rays onto the medium M in a range after ink is ejected from the head unit 23 onto the medium M transported by the rotation of the image forming drum 21 and before the medium M is transferred from the image forming drum 21 to the delivery unit 27. The fixing unit 24 has a shielding member that sufficiently reduces the amount of ultraviolet rays irradiated onto areas other than a predetermined area of ​​the medium M on the transport surface compared to the predetermined area.

[0032] The imaging unit 25 captures an image of the surface of the medium M downstream of the head unit 23 and the fixing unit 24 in the transport direction on the transport path, and outputs the image as read data to the control unit 40. The imaging unit 25 has multiple line sensors (image sensors). The line sensors are not particularly limited, but may be, for example, CMOS sensors. The imaging unit 25 measures the amount of incident light at the three wavelengths of RGB, and acquires each as a brightness value.

[0033] The colorimetry unit 26 measures the color of the surface of the medium M downstream of the head unit 23 and the fixing unit 24 in the transport direction on the transport path, further downstream than the imaging unit 25 in this case, and outputs the colorimetry results to the control unit 40. The colorimetry position of the colorimetry unit 26 is not on the image forming drum 21 but on the belt 273 of the delivery unit 27, but is not limited to this. The color space obtained by measurement by the colorimetry unit 26 may be changeable, and for example, color values ​​in the L*a*b* color space can be output.

[0034] The delivery unit 27 transports the medium M, on which the ink has been ejected and fixed, from the image forming drum 21 to the medium discharge unit 30. The delivery unit 27 has a plurality of (for example, two) rollers 271 and 272, a ring-shaped belt 273 supported on the inner surface by the rollers 271 and 272, and a cylindrical delivery roller 274. The delivery unit 27 guides the medium M on the image forming drum 21 onto the belt 273 using the delivery roller 274, and transports the delivered medium M by moving it together with the belt 273, which moves in circles as the rollers 271 and 272 rotate, and sends it out to the medium discharge unit 30.

[0035] The medium discharge unit 30 stores the medium M after image formation sent from the formation unit 20 until the medium M is removed by a user. The medium discharge unit 30 has a plate-shaped medium discharge tray 31 on which the medium M transported by the delivery unit 27 is placed.

[0036] Figure 2 shows (a) a bottom view of the head unit 23 seen from the conveying surface side of the image forming drum 21, (b) a view of the light incident surface of the imaging unit 25 seen from the side facing the outer peripheral surface of the image forming drum 21, and (c) a view of the colorimetric unit 26 seen from above the outer peripheral surface of the belt 273.

[0037] As shown in FIG. 2(a), the head unit 23 has a plurality of inkjet heads 231 on the bottom surface, in which the openings of a plurality of nozzles N are arranged within a predetermined range (arrangement range). Here, one head unit 23 has eight inkjet heads 231, but this is not limited to this. Each of the eight inkjet heads 231 has two nozzle rows arranged in the transport direction, in which the openings of the nozzles N are aligned in the width direction perpendicular to the transport direction, and the opening positions of the nozzles N in these two rows are staggered in a houndstooth check pattern in the width direction. Note that the size and number of the openings of the nozzles N are shown large and small here for the sake of explanation, and are different from the actual size and number.

[0038] As shown in FIG. 2(b), the imaging unit 25 has multiple imaging sensors 251, each with a light entrance opening for a plurality of imaging elements P positioned within a predetermined range in the width direction. Here, the imaging unit 25 has four sensors: a first imaging sensor 2511, a second imaging sensor 2512, a third imaging sensor 2513, and a fourth imaging sensor 2514. However, this is not limited to this. In this embodiment, at least the first imaging sensor 2511 is the first sensor, and the third imaging sensor 2513 may also be included in the multiple first sensors. The second imaging sensor 2512 and the fourth imaging sensor 2514 are included in the other sensors (second sensors). The imaging sensors 251 are arranged in a staggered pattern, and the light entrance range of the light entrance opening of each imaging sensor 251, i.e., the imaging range, has overlapping portions D1 to D3 between adjacent imaging sensors 251. The positions of the light entrances of the imaging elements P and the positions of the light-receiving sensors may be the same in the width direction. For example, they may be contact image sensors (CIS), or a reduction optical system using mirrors and lenses may be formed so that the light-receiving sensors are grouped together near the center in the width direction. Furthermore, when primarily capturing color images using RGB, the imaging elements P of the line sensor do not need to be linearly arranged in the width direction. While the light entrances are shown here as being roughly divided into several sections for the sake of explanation, they may actually be continuous, or may be divided into smaller sections depending on the resolution (number of elements) of the light-receiving sensors. The magnitude relationship between the imaging resolution of the imaging unit 25 and the image formation resolution of the head unit 23 is not particularly limited here.

[0039] 2(c), the colorimetric unit 26 measures the color of a portion of the area of ​​the medium M in the width direction. The colorimetric unit 26 is movable in the width direction along a support member 261. The support member 261 may be provided with, for example, a rail and a belt, and the colorimetric unit 26 may move back and forth on the rail in accordance with the movement of the belt. The colorimetric unit 26 is fixed during colorimetric measurement and measures the color of the colorimetric range.

[0040] FIG. 3 is a block diagram showing the functional configuration of the image forming apparatus 1 of this embodiment. In addition to the above-mentioned forming unit 20, the image forming apparatus 1 includes a control unit 40, a conveying drive unit 45, an image processing unit 46, a memory unit 50, a communication unit 61, a display unit 62, an operation reception unit 63, a bus 90, etc.

[0041] In addition to the above-mentioned imaging unit 25, color measurement unit 26, and nozzle N (included in the head unit 23), the forming unit 20 also has a head driving unit 28 that ejects ink from the nozzle N, and a fixing driving unit 29 that operates the fixing unit 24.

[0042] The head driver 28 operates a mechanism that applies pressure to ink in an ink flow path that communicates with each nozzle N and supplies ink, causing the head unit 23 (inkjet head 231) to perform an image formation operation. For example, the head driver 28 generates a drive voltage signal for a piezoelectric element that deforms the wall surface of a pressure chamber (pressure chamber) provided in the ink flow path, and outputs the drive voltage signal to the piezoelectric element. The head driver 28 selects a pre-stored voltage waveform pattern based on a control signal from the control unit 40, generates a power-amplified drive voltage signal, and switches whether to output the drive voltage signal to each piezoelectric element according to the image data to be formed input from the storage unit 50. The deformation of the piezoelectric element deforms the pressure chamber, applying pressure fluctuations to the ink in a predetermined pattern, and in response, a desired volume of ink droplets is ejected from the opening of the nozzle N at a desired speed toward a predetermined ink landing position (position in a plan view).

[0043] The fixing driver 29 outputs a drive signal to the fixing unit 24 to cause it to emit (emit) predetermined active energy rays (ultraviolet rays in this case).

[0044] The control unit 40 controls the overall operation of the image forming apparatus 1 and the operations of each unit. The control unit 40 includes a CPU 41 (Central Processing Unit), a RAM 42 (Random Access Memory), and the like.

[0045] The CPU 41 performs various types of calculation processing and controls the transport of the medium M, ink supply, temperature management and ejection, imaging, color measurement, and maintenance operations in the image forming apparatus 1. The CPU 41 also performs various processes related to image formation based on image data, status signals and clock signals of each unit, etc., in accordance with a program read from the storage unit 50.

[0046] The RAM 42 provides a working memory space for the CPU 41 and stores temporary data. The RAM 42 may include a non-volatile memory, and the data stored in this non-volatile memory and the data stored in the storage unit 50 are allocated appropriately.

[0047] The image processing unit 46 performs various types of processing on the image data. These types of processing include processing related to calibration of the image sensor 251 based on the imaging results of the imaging unit 25 and the colorimetric results of the colorimetric unit 26. The image processing unit 46 may have a CPU and RAM, and may also have a dedicated hardware circuit in addition to or instead of these. Furthermore, the hardware configuration of the image processing unit 46 may be configured so that the CPU 41 and RAM 42 of the control unit 40 serve as both the CPU 41 and RAM 42.

[0048] When an image formed on the medium M is captured by the imaging unit 25, the image processing unit 46 generates one piece of imaging data by connecting the images obtained by the multiple imaging sensors 251. In the overlapping portions D1 to D3 shown in FIG. 2, it is determined in advance which of the two adjacent imaging sensors 251 captures the data, and the unused data may be discarded.

[0049] The storage unit 50 stores job data 52 related to image formation acquired from an external device via the communication unit 61, as well as control programs and setting data related to various control operations of the control unit 40 and image processing unit 46. DRAM is primarily used to temporarily store the job data 52 and its processing data, while a hard disk drive (HDD) or nonvolatile memory is used to store the control programs and setting data, but this is not limiting. For example, the job data 52 may be stored in nonvolatile memory, and the initial program and initial setting data may be stored in a non-rewritable mask ROM or the like. Furthermore, data on specific images, such as those for inspection rather than normal images, and setting data for forming the specific images may be stored in nonvolatile memory. The control program includes a calibration program 51 for adjusting the sensitivity between the image sensors 251.

[0050] The data stored in the storage unit 50 also includes calibration data 53 obtained by executing the program 51. For example, the image data captured by the image capturing unit 25 is calibrated using the calibration data 53 before being analyzed.

[0051] The conveying drive unit 45 has a medium conveying unit 71 that operates each unit that conveys the medium M, such as the supply conveying unit 12, the image forming drum 21, the transfer unit 22, and the delivery unit 27, and a colorimetry moving unit 72 that moves the colorimetry unit 26.

[0052] The medium transport unit 71 includes a motor that rotates the rollers, drums, etc., and also operates the claw portion 221. Of the above components, at least the image forming drum 21 and the transport drive unit 45 constitute a transport unit that moves the medium M along a predetermined transport path in the image forming apparatus 1 of this embodiment.

[0053] The colorimetry moving unit 72 moves in the width direction the colorimetry range measured by the colorimetry unit 26. For example, if a rail and a belt are provided on the support member 261 as described above, the colorimetry moving unit 72 moves the belt a desired distance at a predetermined speed, thereby moving the colorimetry unit 26 fixed to the belt a desired distance.

[0054] The communication unit 61 is a communication interface that controls communication operations with external devices. The communication interface may include one or more devices compatible with various communication protocols, such as a LAN card. The communication unit 61 acquires image data of the image to be formed and setting data (job data) related to image formation from the external device under the control of the control unit 40, and can also transmit status information and the like to the external device.

[0055] The display unit 62 displays the status of the image forming apparatus 1, an operation menu, and the like, in response to a control signal from the control unit 40. The display unit 62 has a display screen such as a liquid crystal display. The display unit 62 may also have an LED or the like used for notification operations.

[0056] Furthermore, the operation reception unit 63 receives user operations and outputs them to the control unit 40. The operation reception unit 63 has, for example, a touch sensor that is provided over the display screen. The control unit 40 associates information about the content and position of the menu displayed on the display screen with information about the type and position of the user's touch operation received by the operation reception unit 63, and performs control operations to cause each unit of the image forming apparatus 1 to perform processing according to the operation. The operation reception unit 63 may also include push button switches, a numeric keypad, etc.

[0057] The bus 90 is a signal transmission path that electrically connects the control unit 40 and each of the above components to exchange signals. Of the above components, the image reading device of this embodiment is configured by the conveying unit, the imaging unit 25, the colorimetric unit 26, and the control unit 40. The image reading device of this embodiment may also include a colorimetric moving unit 72.

[0058] Next, the operation and adjustment of the imaging sensor 251 of the imaging unit 25 in the image forming apparatus 1 of this embodiment will be described.

[0059] FIG. 4 is a diagram illustrating the calibration of the image sensor 251. When the imaging results of the four imaging sensors 251 are stitched together to generate a single piece of integrated imaging data, the output characteristics of the imaging data are matched because there are differences in the imaging characteristics of these imaging sensors 251. In the image forming apparatus 1 of this embodiment, first, as shown in Figure 4(a), test images It1 and It2 (predetermined test images) of the same pattern are formed at the same position in the transport direction within the imaging range (reference imaging range) of the first imaging sensor 2511, and the first imaging sensor 2511 is calibrated by comparing the imaging result (reference imaging result) of test image It2 by the first imaging sensor 2511 with the colorimetric result of test image It1 in range W1 within the imaging range of the first imaging sensor 2511. Next, the calibration degree of the second imaging sensor 2512 is set based on the deviation (difference) of the imaging result by the second imaging sensor 2512 relative to the imaging result by the first imaging sensor 2511 of the test image It2 in the overlapping portion D1 (first overlapping portion overlapping with the first imaging sensor 2511), and calibration is performed. Note that relative adjustment (correction) of sensitivity unevenness at each position in the width direction within the first imaging sensor 2511 and the second imaging sensor 2512 may be performed using a separately known technique.

[0060] 4(b), test images It3 and It4 are formed at the same position in the transport direction, and the third image sensor 2513 is calibrated by comparing the image capture result of test image It4 by the third image sensor 2513 with the colorimetric result of test image It3 in range W3 within the imaging range of the third image sensor 2513. Next, the calibration degree of the fourth image sensor 2514 is set based on the deviation of the image capture result of the fourth image sensor 2514 from the image capture result of the test image It4 by the third image sensor 2513 in the overlapping portion D3, and calibration is performed. That is, in this embodiment, the second imaging sensor 2512 is included in the range defined for the first imaging sensor 2511, and the fourth imaging sensor 2514 is included in the range defined for the third imaging sensor 2513.

[0061] The calibration operation is performed by combining the results of reading the test images It1 and It2 by the imaging sensor 251 and the colorimetric unit 26. For example, the image processing unit 46 converts the colorimetric values ​​in the L*a*b* color space measured by the colorimetric unit 26 into RGB luminance values, and approximates these RGB values ​​to the RGB values ​​obtained by the imaging sensor 251, thereby calculating the calibration amount.

[0062] After measuring the colors in the range W1, the colorimetric unit 26 moves to the range W3. Therefore, the test images It1 and It2 and the test images It3 and It4 are formed at different positions in the transport direction.

[0063] FIG. 5 is a diagram illustrating the positional relationship between the test images It1 to It4. As shown in FIG. 5A, compared to the positions of test images It1 and It2 in the transport direction, test images It3 and It4 are located at different positions along the transport path, i.e., downstream, by the time required to move the colorimetric unit 26 and start reading. Based on the distance dw13 (movement distance of the colorimetric unit 26) between ranges W1 and W3 (e.g., between their respective center positions), the movement speed V2 of the colorimetric unit 26, and the transport speed V1 of the medium M (movement speed of the medium M), the distance dt13 between the most upstream (rear end) position of test image It1 and the most downstream (leading end) position of test image It3 can be determined as dt13≧dw13×(V2 / V1). To shorten the distance dt13, the transport speed V1 can be reduced (changed) depending on the relationship between the desired distance dt13 and the distance dw13 (the positional relationship between the test images It1 to It4), the movement speed V2, and other factors.

[0064] The test images It1 to It4 are, for example, small regions (patch images) of each color (each density) required for calibration arranged in order in the transport direction. As shown in Fig. 5(b), the colorimetric measurement range of the colorimetric unit 26 is moved to a range W3 after the colorimetric measurement of the test image It1 in a range W1 is completed and before the test image It2 reaches the colorimetric measurement position due to the transport movement of the medium M. Then, the colorimetric measurement of the test image It2 is performed in the range W3.

[0065] FIG. 6 is a flowchart showing a control procedure by the control unit 40 of a calibration control process including the calibration method of this embodiment. When the calibration control process is started, the control unit 40 (CPU 41) adjusts the color measurement range of the colorimetric unit 26 to the range W1 (step S101). The control unit 40 sets the transport speed of the medium M by the medium transport unit 71, starts the transport operation, and forms the test images It1 to It4 on the transported medium M in the above positional relationship (step S102).

[0066] The control unit 40 sequentially captures the test images It2 and It4 as the formed test images It2 and It4 reach the imaging range of the imaging unit 25 (step S103). The control unit 40 causes the test image It1 to be colorimetrically measured as the formed test image It1 reaches the colorimetric range of the colorimetric unit 26 (step S104).

[0067] The control unit 40 moves the colorimetric unit 26 into the range W3 at a moving speed V2 (step S105). After the movement is completed, the control unit 40 causes the colorimetric unit 26 to measure the color of the test image It3 as the test image It3 reaches the colorimetric range of the colorimetric unit 26 (step S106).

[0068] The control unit 40 converts the colorimetric results of the test images It1 and It3 measured by the colorimetric unit 26 into RGB luminance values ​​(step S107). The control unit 40 compares the colorimetric results of the test image It1 with the imaging result of the test image It2 measured by the first imaging sensor 2511, and calculates a correction amount for reading by the first imaging sensor 2511 (step S108; first calibration step). The control unit 40 compares the imaging results of the test image It2 measured by the first imaging sensor 2511 and the second imaging sensor 2512, and calculates a correction value for the second imaging sensor 2512 based on the imaging result of the first imaging sensor 2511 (step S109; second calibration step).

[0069] The control unit 40 compares the color measurement result of the test image It3 with the imaging result of the test image It4 by the third imaging sensor 2513, and calculates a correction amount for reading by the third imaging sensor 2513 (step S110). The control unit 40 compares the imaging results of the test image It4 by the third imaging sensor 2513 and the fourth imaging sensor 2514, and calculates a correction value for the fourth imaging sensor 2514 based on the imaging result of the third imaging sensor 2513 (step S111).

[0070] The control unit 40 performs calibration settings for each of the test images It1 to It4 (step S112), and then the control unit 40 ends the calibration control process.

[0071] [Variation 1] FIG. 7 is a diagram showing the formation positions of the test images It1 to It4 and a first modification of the calibration operation. In the above embodiment, test images It1 to It4 are formed at different positions in the transport direction as the medium M is transported. However, if the medium M is transported backward after reading test images It1 and It2, and the medium transport unit 71 is operated so that the medium M passes through a predetermined colorimetric range multiple times in the transport direction, allowing the remaining test images It3 and It4 to be read, test images It1 to It4 may be formed at the same position in the transport direction of the medium M. Alternatively, the colorimetric unit 26 may be positioned opposite the outer circumferential surface of the image forming drum 21 so that the image on the medium M can be measured. The medium M may then be rotated multiple times (twice) without being peeled off the image forming drum 21, and the test images It1 to It4 at the same position in the transport direction of the medium M may be measured each time they pass through the colorimetric range. Furthermore, even if the colorimetric unit 26 can simultaneously measure the colors in both ranges W1 and W3, the test images It1 to It4 may be at the same position in the transport direction.

[0072] 8 is a flowchart showing the control procedure by the control unit 40 of the calibration control process for the test images It1 to It4 of this modified example 1. The calibration control process is the same as the calibration control process of the above embodiment except that steps S121 and S122 have been added, and the same process contents are denoted by the same reference numerals and detailed description thereof will be omitted.

[0073] In the process of step S104, after the colorimetry of the test image It1 is completed, but before the upstream end of the medium M leaves the delivery roller 274 (and the outer circumferential surface of the image forming drum 21), the control unit 40 stops the conveying operation in the normal conveying direction by the medium conveying unit 71 and conveys the medium M backward until the downstream ends (leading edges) of the test images It1 to It4 return upstream in the conveying direction from the colorimetry range of the colorimetry unit 26 (step S121). Then, the process of the control unit 40 proceeds to step S105.

[0074] After the process of step S105, the control unit 40 resumes transport of the medium M in the transport direction (step S122). Then, the process of the control unit 40 proceeds to step S106. Note that the process of step S105 may be performed in parallel with the processes of step S121 and / or step S122.

[0075] [Variation 2] FIG. 9 is a diagram showing a second modification of the formation positions of the test images It11 to It13 and the calibration operation. In the above embodiment and modification 1, the ratio between the image sensor that is directly configured by color measurement and the image sensor that is comparatively calibrated between the image sensors is 1:1, but here it is 1:2.

[0076] As shown in Figure 9(a), of the three imaging sensors 251a, the first imaging sensor 2511a (the second sensor in this modified example) and the second imaging sensor 2512a (the first sensor in this modified example) have an overlapping portion D11 (the first overlapping portion in this modified example), and the second imaging sensor 2512a and the third imaging sensor 2513a (the fourth sensor in this modified example) have an overlapping portion D12 (the third overlapping portion in this modified example).

[0077] 9(b), a range W11 in which colorimetry is performed by the colorimetry unit 26 is determined within the imaging range of the image sensor 2512a at the center in the width direction. Additionally, both overlapping portions D11 and D12 are used for comparative calibration between the image sensors 251a. Accordingly, test images It11 to It13 are formed within the colorimetry range W11 and the overlapping portions D11 and D12.

[0078] Here, since colorimetry is performed in only one location in range W11 for calibration of the three imaging sensors 251a, there is no need to move the colorimetry unit 26 and it may be fixed. Note that if there are four or more (e.g., six) imaging sensors 251a, it may be moved to the imaging ranges of the imaging sensors other than the three.

[0079] The second imaging sensor 2512a is calibrated based on a comparison result between the colorimetry result and the imaging result (reference imaging result in this modification) by the second imaging sensor 2512a in the overlapping portion D11 or D12. Furthermore, by comparing the imaging results by the first imaging sensor 2511a and the second imaging sensor 2512a in the overlapping portion D11, the first imaging sensor 2511a is calibrated for the second imaging sensor 2512a for which a calibration result has been obtained. Furthermore, by comparing the imaging results by the second imaging sensor 2512a and the third imaging sensor 2513a in the overlapping portion D12, the third imaging sensor 2513a is calibrated for the second imaging sensor 2512a for which a calibration result has been obtained.

[0080] FIG. 10 is a flowchart showing the control procedure of the calibration control process of the second modification. When the calibration control process is started, the control unit 40 adjusts the colorimetry range to the range W11 (step S121). As described above, this process is not necessary when the colorimetry unit 26 is fixed.

[0081] The control unit 40 sets the transport speed of the medium M by the medium transport unit 71 and starts the transport operation. The control unit 40 also causes the test images It11 to It13 to be formed on the transported medium M in the above-described positional relationship (step S122). The control unit 40 causes the test images It11 and It13 to be captured when the test images It11 to It13 reach the imaging range of the imaging unit 25 (step S123). The control unit 40 causes the colorimetric unit 26 to perform colorimetry within the range W11 (step S124).

[0082] The control unit 40 converts the color measurement results of the test image It12 obtained by the colorimeter 26 into RGB luminance values ​​(step S125). The control unit 40 compares the color measurement results of the test image It12 with the image capture results of the test image It11 (or test image It13) obtained by the second imaging sensor 2512a, and calculates a correction amount for the reading by the second imaging sensor 2512a (step S126).

[0083] The control unit 40 compares the imaging results of the first imaging sensor 2511a and the second imaging sensor 2512a for the test image It11 and calculates a correction value for the first imaging sensor 2511a based on the imaging result of the second imaging sensor 2512a (step S127).The control unit 40 compares the imaging results of the second imaging sensor 2512a and the third imaging sensor 2513a for the test image It13 and calculates a correction value for the third imaging sensor 2513a based on the imaging result of the second imaging sensor 2512a (step S128).

[0084] The control unit 40 sets the amount of calibration for each imaging sensor 251a (step S129), and then the control unit 40 ends the calibration control process.

[0085] [Variation 3] FIG. 11 is a diagram showing a third modification of the calibration operation. In this third modification, relative calibration operations between the imaging sensors are performed in series in multiple stages. When the range W21 in which the colorimetry unit 26 performs colorimetry is within the imaging range of the first imaging sensor 2511a (the first sensor in this modification), which is the end of the imaging unit 25, calibration of the second imaging sensor 2512a (the second sensor in this modification) is performed by comparing it with the first imaging sensor 2511a in the overlapping portion D11. Furthermore, calibration of the third imaging sensor 2513a (the third sensor in this modification) is performed by comparing the second imaging sensor 2512a with the third imaging sensor 2513a in the overlapping portion D12 (the second overlapping portion). In addition to the test images It11 and It13, a test image It21 is formed in place of the test image It12, aligned with the range W21.

[0086] That is, the calibration of the third imaging sensor 2513a is performed indirectly based on the degree of calibration of the second imaging sensor 2512a and a comparison with the imaging results of the second imaging sensor 2512a, which are not directly compared with the colorimetric results of the colorimetric unit 26. Note that such calibration operations can be performed in multiple stages, not just up to the third imaging sensor 2513a, but since accuracy typically decreases with increasing stages, an appropriate maximum number of stages may be set.

[0087] 12 is a flowchart showing the control procedure of the calibration control process of Modification 3. In this calibration control process, steps S121 to S124, S126, and S127 in the calibration control process of Modification 2 are replaced with steps S121a, S122a, S124a, S126a, and S127a, respectively. The other processes are the same, and the same process contents are denoted by the same reference numerals.

[0088] When the calibration control process is started, the control unit 40 adjusts the color measurement range of the colorimetric unit 26 to the range W21 (step S121a). This process is also unnecessary when the colorimetric unit 26 is fixed, as in the second modification.

[0089] The control unit 40 sets the transport speed of the medium M by the medium transport unit 71 and starts the transport operation. The control unit 40 also causes the test images It11, It13, and It21 to be formed on the transported medium M in the above-described positional relationship (step S122a). The control unit 40 causes the test images It11 and It13 to be captured when they reach the imaging range of the imaging unit 25 (step S123). The control unit 40 also causes the colorimetric unit 26 to perform colorimetry within the range W21 (step S124a).

[0090] The control unit 40 converts the colorimetric result of the test image It12 measured by the colorimetric unit 26 into RGB luminance values ​​(step S125). The control unit 40 compares the colorimetric result of the test image It21 with the image pickup result of the test image It11 measured by the first image pickup sensor 2511a, and calculates the amount of correction related to the reading by the first image pickup sensor 2511a (step S126a).

[0091] The control unit 40 compares the imaging results of the first imaging sensor 2511a and the second imaging sensor 2512a for the test image It11 and calculates a correction value for the second imaging sensor 2512a based on the imaging result of the first imaging sensor 2511a (step S127a).The control unit 40 compares the imaging results of the second imaging sensor 2512a and the third imaging sensor 2513a for the test image It13 and calculates a correction value for the third imaging sensor 2513a based on the imaging result of the second imaging sensor 2512a (step S128).

[0092] The control unit 40 sets the amount of calibration for each imaging sensor 251a (step S129), and then the control unit 40 ends the calibration control process.

[0093] As described above, the image forming apparatus 1 of this embodiment includes the medium transport unit 71 and image forming drum 21 as a transport unit that moves the medium M along a predetermined transport path, an imaging unit 25 having multiple image sensors 251 (2511-2514) that captures an image of the surface of the medium M along the transport path, a colorimetric unit 26 that measures the color of the surface of the medium M along the transport path, and a control unit 40. The imaging ranges of each of the multiple image sensors 2511-2514 have overlapping portions D1-D3 between adjacent image sensors in the width direction (in a plane parallel to the transport surface) perpendicular to the transport direction along the transport path. The control unit 40 performs a calibration operation of the first imaging sensor 2511 based on the color measurement results of the test image It1 within the reference imaging range of the first imaging sensor 2511 among the multiple imaging sensors 251 and the reference imaging results of the test image It2 of the same pattern within the reference imaging range, and compares the imaging results of the multiple imaging sensors 2512, 2513 in the overlapping portion D1 to perform a calibration operation of another sensor different from the first imaging sensor 2511 (third imaging sensor 2513), in this case the second imaging sensor 2512 (fourth imaging sensor 2514), based on the reference imaging results of the first imaging sensor 2511 (third imaging sensor 2513). In this way, some of the imaging sensors 251 are calibrated with high precision using the colorimetric unit 26, while other imaging sensors 251 are adjusted relatively by comparing the imaging results of test images It2, It4, etc., using overlapping portions of the imaging ranges of the imaging sensors 251. This achieves both precision and the effort and time required for adjustment, making it possible to calibrate each imaging sensor 251 in the image forming device 1 more easily and accurately.

[0094] The color measurement range of the color measurement unit 26 is the area other than the overlapping portion of the reference imaging range of the first imaging sensor 2511 (third imaging sensor 2513). That is, in the calibration operation, color measurement and imaging may be performed at different positions.

[0095] The other sensors also include a second imaging sensor 2512 that has an overlapping portion D1 with the first imaging sensor 2511. The control unit 40 determines the degree of calibration of the second imaging sensor 2512 relative to the calibrated first imaging sensor 2511 based on the difference between the imaging results of the second imaging sensor 2512 obtained at the overlapping portion D1 and the imaging results of the first imaging sensor 2511. In this way, calibration of the first imaging sensor 2511 that has been calibrated with high precision and the second imaging sensor 2512 that has the overlapping portion D1 is performed by comparing the imaging results of the same test image It2 at the overlapping portion D1. This makes it possible to calibrate multiple imaging sensors 251 with greater precision than conventional methods while reducing the time and effort required compared to performing colorimetry separately for each sensor.

[0096] Furthermore, as in Modification Example 3, the other sensors may include a third imaging sensor 2513a having an overlapping portion D12 with the second imaging sensor 2512a. The control unit 40 determines the calibration degree of the third imaging sensor 2513a based on the difference between the imaging results of the second imaging sensor 2512a and the third imaging sensor 2513a obtained at the overlapping portion D12 and the calibration degree determined based on a comparison between the second imaging sensor 2512a and the first imaging sensor 2511a. In this way, the comparison between the image sensors 251a using the overlapping portions may be performed in multiple stages. This allows absolute value calibration for three or more image sensors 251a based on a single color measurement result, enabling more efficient and accurate calibration in the image forming apparatus 1.

[0097] Furthermore, as in Modification 2, the other sensors may include a third imaging sensor 2513a having an overlapping portion D12 with the first imaging sensor 2511a, which is the first sensor to be subjected to comparative calibration with the reference second imaging sensor 2512a, that is different from the overlapping portion D11. The control unit 40 determines the calibration level of the third imaging sensor 2513a relative to the second imaging sensor 2512a that has undergone the calibration operation based on the difference between the imaging results of the second imaging sensor 2512a and the third imaging sensor 2513a obtained at the overlapping portion D12. In other words, using the second imaging sensor 2512a, which has overlapping portions at both ends, as a reference, the first imaging sensor 2511a and the third imaging sensor 2513a can be accurately calibrated using the overlapping portions D11 and D12 on both sides based on the colorimetry results of a single run of the second imaging sensor 2512a. This enables more efficient and accurate calibration. Furthermore, particularly when there are three image sensors, color measurement is possible near the center of the image capture width, making it easier to perform color measurement stably and accurately compared to near the edges.

[0098] In addition, multiple reference imaging sensors are provided, for example, two, a first imaging sensor 2511 and a third imaging sensor 2513, and colorimetry is performed for each of these imaging sensors 2511, 2513 by the colorimetry unit 26. The control unit 40 performs calibration operations for other sensors within ranges determined for each of the imaging sensors 2511, 2513. When the number of image sensors 251 is three or four or more and it is difficult to cover the entire range by comparing with a single color measurement result, multiple image sensors may be selectively used as the color measurement targets. This allows sufficient calibration accuracy to be obtained without significantly reducing the efficiency of the calibration operation.

[0099] The image forming apparatus 1 also includes a colorimetry moving unit 72 that moves the colorimetry unit 26 in the width direction. The control unit 40 causes colorimetry to be performed at colorimetry positions that are respectively determined for a plurality of reference imaging sensors (first imaging sensor 2511, third imaging sensor 2513). By making the colorimetry unit 26, which is not used frequently, movable in this way, efficient and accurate calibration can be performed when colorimetry is required at multiple locations during calibration.

[0100] The image forming apparatus 1 also includes a head unit 23 that forms an image on the surface of the medium M along the transport path. The control unit 40 varies the positions of the test images formed at each of the multiple colorimetric positions in the direction along the transport path based on the moving speed of the medium M by the transport unit and the moving speed of the colorimetric unit 26 by the colorimetric moving unit 72. When measuring the color at different positions by moving the color measurement unit 26 as described above, it is not possible to simultaneously measure the color at these different positions while transporting the medium M. Therefore, by appropriately shifting the position of the test image according to the movement time of the color measurement unit 26, it is possible to perform calibration operations efficiently and accurately without hassle within the flow of transporting the medium M.

[0101] The control unit 40 can also change the speed at which the medium M is moved by the transport unit, and determines the speed at which the medium M is moved based on the speed at which the colorimetry unit 26 is moved by the colorimetry moving unit 72 and the positional relationship of multiple test images formed on the medium M by the head unit 23. Therefore, when there are restrictions on the placement of test images due to the size of the medium M or when it is desired to reduce the length of the test images formed on the medium M, the movement speed can be changed, particularly reduced, to easily adjust the calibration operation appropriately according to the placement of the test images.

[0102] Furthermore, as in Modification 1, when performing the calibration operation, the transport unit may move the medium M so that the medium M passes a position in the transport direction where the color is measured by the colorimetric unit 26 multiple times. That is, the transport unit may rotate the transport drum or reverse the transport of the medium M. This eliminates the need to shift the positions of the test images It1 to It4 during the calibration operation while transporting the medium M, and thus reduces the area in which the test images It1 to It4 are formed in the transport direction of the medium M.

[0103] Furthermore, the control unit 40 causes the head unit 23 to form a plurality of test images It1 to It4 on the medium M. By causing the image forming apparatus 1 itself to form the test images, the positions of the plurality of test images It1 to It4 can be easily adjusted.

[0104] Furthermore, the control unit 40 can change the speed at which the medium is moved by the transport unit, which allows for flexible response, such as allowing processing at a speed different from that of normal image formation operations during calibration.

[0105] The test image It1, which is colorimetrically measured within the reference imaging range of the first imaging sensor 2511, and the test image It2 used to obtain the reference imaging result are at the same position in the transport direction of the medium M. This allows for a high-precision comparison of the separate images without being affected by factors such as the density of the recording due to transport unevenness in the test images It1 and It2 to be compared.

[0106] Furthermore, even an image reading device having a configuration that excludes the head unit 23 from the image forming device 1 described above has a color measurement unit 26, which can be used to perform calibration operations through inline processing, thereby enabling adjustment of the reading sensitivity of the imaging unit 25 with greater accuracy and less hassle.

[0107] In addition, the calibration method for the imaging sensor 251 of this embodiment includes a first calibration step in which a calibration operation of the first imaging sensor 2511 is performed based on the colorimetric results of the colorimetric unit 26 of a predetermined test image It1 within a reference imaging range of the first imaging sensor 2511, which is a reference among the multiple imaging sensors 251, and the reference imaging result of a test image It2 of the same pattern as the test image It1 within the reference imaging range; and a second calibration step in which the imaging results of the multiple imaging sensors 251 at overlapping portions D1, D3, etc. are compared, and a calibration operation of a second imaging sensor 2512, etc., which is different from the first imaging sensor 2511, is performed based on the reference imaging result. In this way, by comparing the in-line color measurement results from the colorimetric unit 26 provided in the image forming apparatus 1 with the imaging results and calibrating each imaging sensor 251, it is possible to eliminate the trouble of alignment and data transmission / reception and easily calibrate the imaging sensors 251. In particular, since color measurement is performed on only some of the multiple imaging sensors 251 and adjustments are made for the rest by comparing the imaging results from the multiple imaging sensors in overlapping areas D1, D2, etc., it is possible to calibrate the multiple imaging sensors 251 efficiently and accurately in a short amount of time.

[0108] The present invention is not limited to the above-described embodiment, and various modifications are possible. For example, although the multiple image sensors 251 have been described as being arranged in a staggered pattern, there are no particular limitations on the arrangement as long as there are overlapping portions in the width direction.

[0109] In the above embodiment, the imaging sensor is described as a line sensor, but it may be a two-dimensional sensor that can capture images of a predetermined width in the conveyance direction as well. Furthermore, the colorimetric unit 26 is not limited to having one colorimeter, but may be provided in multiple locations corresponding to overlapping portions.

[0110] Furthermore, in the above embodiment, the moving speed V2 by the colorimetry moving unit 72 has been described as being constant, but the speed may be such that it gradually increases at the start of the movement and gradually decreases at the end of the movement. On the other hand, the transport speed V1 of the medium M by the medium transport unit 71 does not have to be variable. "Variable" here means that the medium M can be selectively transported at one of a plurality of speeds, and does not take into account the speed during the gradual increase / decrease at the start and end of transport.

[0111] In the above embodiment, the ranges W1 and W3 are defined near the center of the imaging range of each imaging sensor 251, but this is not limiting. They may be defined as appropriate. For example, they may overlap with the overlapping portions D1 and D3. In this case, the test images It1 and It3 in the above embodiment may be used in conjunction with the test images It2 and It4, respectively.

[0112] The widths of the test images It1 to It4 may be adjusted independently as appropriate. The test images It2 and It4 may be formed according to the widths of the overlapping portions D1 and D3, or the test images It1 and It3 may be formed according to the widths that the colorimetry unit 26 can measure.

[0113] In the above modification, the medium M is transported in the reverse direction, and the second and subsequent colorimetry is performed while the medium M is being transported in the forward direction again, but colorimetry may also be performed during the reverse transport. In particular, when performing colorimetry three or more times, the number of round trips can be reduced by enabling colorimetry on both the forward and backward paths.

[0114] Furthermore, the test images It1 to It4 are not limited to those formed by the image forming apparatus 1 itself. As long as the overlapping portions D1 and D3 and the colorimetry ranges W1 and W3 can be properly aligned, the test images It1 to It4 on a test sheet prepared in advance may be captured and colorimetrically measured, and a test sheet that has been formed once may be reused multiple times.

[0115] Furthermore, the image formation in the above embodiment is not limited to flat images formed with colored inks. Colorless ink or transparent (light-transmitting) ink may be included, and the image may have a three-dimensional structure. The medium M does not have to be transported by the cylindrical image forming drum 21, and a belt member or the like that transports the medium M along a flat surface may be used.

[0116] In the above embodiment, the calibration is performed all at once after all the calibration degrees have been determined, but the calibration may be performed as needed in the order in which the calibration degrees are determined. When comparing images captured by an image sensor, the calibration of one may be performed, and then the calibrated image may be compared with the image captured before calibration.

[0117] In the above embodiment, the test image It1 (It3) for color measurement and the test image It2 (It4) for image capture are formed at the same position in the transport direction, but this is not limited to this. If it is not necessary to consider density variations in the transport direction due to transport irregularities, etc., they may be formed at different positions in the transport direction. Furthermore, as long as they have the same pattern (combination of colors in small regions), the order may be different. Furthermore, the number of small regions may be adjusted appropriately as needed. Furthermore, the shape of the small regions is not limited to rectangular. It is sufficient that they can be read with the required accuracy. Furthermore, the read result may be a representative value, such as an average value at multiple points in the small region.

[0118] Furthermore, in the above embodiment, an image forming device having a line head has been described as an example, but even if the type is one in which an image is formed by scanning the head unit 23 across the medium M, the contents of the above disclosure can be applied to calibration as long as multiple image sensors are connected to form a long image capturing section 25.

[0119] In the above embodiment, an inkjet type image forming apparatus (inkjet recording apparatus) has been described as an example, but other types of image forming apparatuses, such as electrophotographic types, may also be used. The ink ejection method may be any type, such as a piezo type using a piezoelectric element or a thermal type using a heating element.

[0120] Furthermore, the configurations and processing operations shown in the above embodiment and modifications 1 to 3 may be arbitrarily combined or excluded as long as they do not contradict each other or eliminate or cancel out the features of the present invention. In addition, the specific configurations, contents and procedures of the processing operations, etc. shown in the above embodiments can be modified as appropriate without departing from the spirit of the present invention. The scope of the present invention includes the scope of the invention described in the claims and its equivalents. [Explanation of symbols]

[0121] 1. Image forming device 10 Media supply section 11 Media supply tray 12 Supply and conveying section 20 Formation part 21 Image forming drum 22 units 23 Head Unit 24 Fixing section 25 Imaging unit 251, 251a image sensor 2511, 2511a First imaging sensor 2512, 2512a Second imaging sensor 2513, 2513a 3rd imaging sensor 2514 4th imaging sensor 26 Color measurement section 261 Support member 27 Delivery Department 28 Head drive unit 29 Fixing drive unit 30 Media discharge section 31 Media output tray 40 Control Unit 41 CPU 42 RAM 45 Conveyor drive unit 46 Image processing section 50 Storage section 51 Programs 52 Job Data 53 Calibration Data 61 Communications Department 62 Display section 63 Operation reception section 71 Media transport unit 72 Color measurement moving part 90 Bus D1~D3, D11, D12, D21 overlapped parts It1~It4, It11~It13, It21 inspection images M medium V1 Conveying speed V2 Movement speed

Claims

1. a transport unit that moves the medium along a predetermined transport path; a first image sensor that captures an image of the surface of the medium on the transport path; a second image sensor that images the surface of the medium on the transport path; a third image sensor that images the surface of the medium on the transport path; a fourth image sensor that images the surface of the medium on the transport path; a colorimetric unit that is provided downstream of the first image sensor, the second image sensor, the third image sensor, and the fourth image sensor in a conveying direction by the conveying unit and that measures the color of the surface of the medium on the conveying path; A control unit; Equipped with a first overlapping portion in which a portion of the first image sensor and a portion of the second image sensor overlap in a width direction perpendicular to a conveying direction along the conveying path; a second overlapping portion in which a portion of the third image sensor and a portion of the fourth image sensor overlap in a width direction perpendicular to a conveying direction along the conveying path; the colorimetry unit moves in the width direction while the medium is positioned within a colorimetry range measured by the colorimetry unit, and measures the colorimetry of a first test image at a position downstream of the first overlapping portion on the conveying path, and measures the colorimetry of a second test image at a position downstream of the second overlapping portion; The control unit calibrating the first image sensor based on the color measurement result of the colorimetric measurement unit of the first test image and the imaging result of the first image sensor, and calibrating the second image sensor based on the imaging result of the first test image of the first image sensor and the imaging result of the second image sensor; calibrating the third image sensor based on the color measurement result of the second test image by the colorimetric measurement unit and the imaging result of the third image sensor, and calibrating the fourth image sensor based on the imaging result of the second test image by the third image sensor and the imaging result of the fourth image sensor; Image reading device.

2. 2. The image reading device according to claim 1, wherein the color measurement unit is movable in the width direction across a portion of the first image sensor that does not overlap with the second image sensor, the first overlapping portion, and a portion of the second image sensor that does not overlap with the first image sensor.

3. 2. The image reading device according to claim 1, wherein the color measurement unit is capable of reciprocating movement.

4. The image reading device according to claim 1 , wherein the color measurement unit is fixed during color measurement.

5. The image reading device according to claim 1 , wherein the color measurement unit is movable in the width direction along a support member.

6. The image reading device according to claim 5 , wherein the support member is longer in the width direction than the imaging range of the first imaging sensor and the imaging range of the second imaging sensor.

7. The image reading device according to claim 1; a forming operation unit that is provided upstream of the image reading device in the transport direction and that forms an image on the surface of the medium on the transport path; An image forming apparatus comprising:

Images