Image forming apparatus and program

Abstract

It accurately corrects color shifts in images formed on paper. [Solution] The image forming apparatus 1 comprises an image forming unit 34 that continuously forms images of multiple colors on paper using an intermediate transfer method, a reading unit (image reading unit 42) that reads the images formed on the paper by the image forming unit 34, and a control unit (third control unit 36) that corrects color misalignment in the images formed on the paper by the image forming unit 34. The control unit corrects color misalignment based on the reading results obtained by the reading unit from the images formed on the second and subsequent sheets of paper from which images have been continuously formed by the image forming unit 34.

Description

Technical Field

[0001] The present invention relates to an image forming apparatus and a program.

Background Art

[0002] In the production printing market, the fields with high demand for thick paper are increasing. Therefore, in recent years, with the increase in demand, color misregistration in the paper feeding direction, which is a problem that thick paper is easily affected by printing in electrophotographic printing using intermediate transfer, has become prominent.

[0003] In relation to this, Patent Document 1 discloses an image forming apparatus that reads a test chart formed on a sheet and corrects the partial magnification of an image formed on the sheet by controlling the speed of a roller in a transfer unit based on the read data.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, when forming images on a plurality of sheets continuously in an image forming apparatus, since there is no preceding sheet for the first sheet, color misregistration caused by the preceding sheet does not occur. On the other hand, for the second and subsequent sheets, color misregistration caused by the preceding sheet occurs. Therefore, the amount of color misregistration that occurs in the first sheet is smaller compared to the second and subsequent sheets. Therefore, when color misregistration correction is performed based on the image formed on the first sheet, there is a possibility that the color misregistration correction for the second and subsequent sheets becomes insufficient.

[0006] An object of the present invention is to provide an image forming apparatus and a program that can accurately correct color misregistration in an image formed on a sheet. [Means for solving the problem]

[0007] To solve the above problems, the image forming apparatus described in claim 1 is An image forming unit that continuously forms multiple color images on paper using an intermediate transfer method, A reading unit reads the image formed on the paper by the image forming unit, A control unit for correcting color misalignment in the image formed on the paper by the image forming unit, Equipped with, The control unit corrects the color misalignment based on the reading results obtained by the reading unit from the second and subsequent sheets of paper on which images have been continuously formed by the image forming unit.

[0008] The invention described in claim 2 is an image forming apparatus according to claim 1, The image forming unit is A transfer unit that transfers an image onto the paper, a resist unit that transports the paper, The system includes a fixing unit for fixing an image onto the aforementioned paper, The control unit corrects color misalignment by adjusting at least one of the transport speeds in the resist section and the transport speed in the fixing section.

[0009] The invention described in claim 3 is an image forming apparatus according to claim 1, The control unit corrects color misalignment between at least two colors in the image formed on the paper.

[0010] The invention described in claim 4 is an image forming apparatus according to claim 2, The control unit measures the amount of color misalignment in the image formed on the second and subsequent sheets of paper, and corrects the color misalignment by adjusting at least one of the transport speed in the resist section and the transport speed in the fixing section so that the measured amount of color misalignment becomes smaller.

[0011] The invention described in claim 5 is an image forming apparatus according to claim 1, The reading unit reads the image on the paper that has been continuously formed by the image forming unit. The control unit corrects the color misalignment based on the reading results obtained by the reading unit from the images formed on the second and subsequent sheets of paper.

[0012] The invention described in claim 6 is an image forming apparatus according to claim 1, The reading unit reads the images formed on the second and subsequent sheets of paper from among the sheets on which images have been continuously formed by the image forming unit. The control unit corrects the color misalignment based on the reading results obtained by the reading unit from the images formed on the second and subsequent sheets of paper.

[0013] The invention described in claim 7 is an image forming apparatus according to claim 1, Before executing the print job, the control unit corrects the color misalignment based on the reading results obtained by the reading unit from the images formed on the second and subsequent sheets of paper.

[0014] The invention described in claim 8 is an image forming apparatus according to claim 1, The aforementioned paper is cardboard with a thickness or basis weight exceeding a specified amount.

[0015] The invention described in claim 9 is an image forming apparatus according to claim 1, The system includes a detection unit that detects attribute information of the aforementioned paper, The control unit corrects the color misalignment based on the attribute information detected by the detection unit.

[0016] The program described in claim 10 is An image forming unit that continuously forms multiple color images on paper using an intermediate transfer method, A reading unit reads the image formed on the paper by the image forming unit, A computer for an image forming apparatus equipped with, The control unit functions to correct color misalignment in the image formed on the paper by the image forming unit. Based on the reading result obtained by the reading unit reading the images formed on the sheets after the second sheet among the sheets on which images are continuously formed by the image forming unit, the control unit corrects the color shift.

Advantages of the Invention

[0017] According to the present invention, the color shift in the image formed on the sheet can be accurately corrected.

Brief Description of the Drawings

[0018] [Figure 1] It is a front view showing the schematic configuration of the image forming apparatus according to the present embodiment. [Figure 2] It is a functional block diagram showing the control structure of the image forming apparatus according to the present embodiment. [Figure 3] It is a diagram showing a case where the paper conveyance speed in the fixing unit is faster than the paper conveyance speed in the transfer unit. [Figure 4] It is a diagram showing a case where the paper conveyance speed in the fixing unit is slower than the paper conveyance speed in the transfer unit. [Figure 5] It is a diagram showing the image forming unit at the timing immediately before the leading end of the first sheet enters the fixing nip portion. [Figure 6] It is a diagram showing the area where color shift occurs in the first sheet. [Figure 7] It is a diagram showing the image forming unit at the timing when the trailing end of the first sheet exits from the transfer unit. [Figure 8] It is a diagram showing the area where color shift occurs in the sheets after the second sheet. [Figure 9] It is a flowchart showing the flow of the color shift correction process.

Embodiments for Carrying Out the Invention

[0019] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

[0020] (1. Configuration of the Image Forming Apparatus) As shown in Figures 1 and 2, the image forming apparatus 1 according to this embodiment comprises a paper feeder 10, a detection device 20, a main body 30, and an image reading device 40. In the image forming apparatus 1, the paper feeder 10, detection device 20, main unit 30, and image reading device 40 are arranged in the following order from the upstream side along the paper transport direction.

[0021] (1-1. Configuration of the paper feed device) The paper feeding device 10 includes a first control unit 11, a transport unit 12, a paper feeding unit 13, and the like.

[0022] The first control unit 11 includes a CPU (Central Processing Unit), ROM (Read Only Memory), RAM (Random Access Memory), and the like. The CPU of the first control unit 11 reads the program stored in ROM, loads it into RAM, and then controls each part of the paper feed device 10 according to the loaded program. For example, the first control unit 11 transports paper from the paper trays 131 to 133 of any of the paper feeding units 13 to the detection device 20 according to the print job.

[0023] The transport unit 12 is equipped with a transport path 121 that connects the paper feeding unit 13 to the detection device 20, and transports paper. The paper feeding unit 13 has paper trays 131 to 133 for storing paper according to predetermined paper types, sizes, etc. For example, paper tray 131 stores paper larger than the paper stored in paper tray 132. Paper tray 133 stores paper thicker than the paper stored in paper trays 131 and 132.

[0024] (1-2. Configuration of the detection device) The detection device 20 is located downstream of the paper feed device 10 in the paper transport direction, and upstream of the main body 30 in the paper transport direction. The detection device 20 detects the physical properties of the paper transported from the paper feed device 10 and outputs the detected physical property values ​​to the third control unit 36, which will be described later. The physical property values ​​of the paper are attribute information of the paper. The detection device 20 detects values ​​(physical property values) related to the physical properties of multiple types of paper, including basis weight, stiffness, moisture content, and surface properties. The physical property values ​​may be information that can be converted into physical properties.

[0025] The detection device 20 includes a second control unit 21, a detection unit 22, a transport unit 23, and the like.

[0026] The second control unit 21 includes a CPU, ROM, RAM, etc. The CPU of the second control unit 21 reads the program stored in ROM, loads it into RAM, and then controls each part of the detection device 20 according to the loaded program. For example, the second control unit 21 has the detection unit 22 detect the paper being transported from the paper feed device 10 and outputs the obtained physical property values ​​to the third control unit 36. Next, the second control unit 21 transports the detected paper to the main unit 30 using the transport unit 23.

[0027] The detection unit 22 detects the physical properties within the paper. The detection unit 22 has sensors for detecting the paper's physical properties, such as basis weight, stiffness, moisture content, and surface properties.

[0028] For example, a sensor for detecting the basis weight of paper comprises a light-emitting unit and a light-receiving unit, and measures the basis weight by the amount of attenuation of light transmitted through the paper. The detection unit 22 outputs the basis weight as a physical property value to the second control unit 21.

[0029] A sensor that detects the stiffness of paper detects physical properties corresponding to the rigidity of the paper. For example, when paper is transported along a curved transport path, the sensor mechanically measures the force or displacement exerted by the paper on one of the outer guide plates that make up the transport path. The detection unit 22 outputs the stiffness as a physical property value based on the force or displacement exerted by the paper to the second control unit 21.

[0030] A sensor for detecting the moisture content of paper optically detects the amount of light absorbed by OH groups using a near-infrared method, for example. The sensor irradiates the paper with light of a predetermined wavelength in the near-infrared region and detects the amount of light absorbed by utilizing the property that the light absorption rate changes according to the moisture content of the paper. Alternatively, the sensor may measure the moisture content by measuring the change in the amount of light of the reflective component inside the paper using reflected light separated by a polarizing filter. The detection unit 22 outputs the moisture content as a physical property value to the second control unit 21.

[0031] A sensor for detecting the surface properties (smoothness, degree of smoothness) of paper includes, for example, a reflection sensor that outputs the intensity and / or intensity ratio of specularly reflected light and scattered reflected light irradiated onto the paper. The sensor measures the surface properties based on this intensity ratio. The detection unit 22 outputs the surface properties as physical properties to the second control unit 21.

[0032] In addition to the above-mentioned sensors, the detection unit 22 may also have sensors for detecting the specific gravity and conductivity of the paper.

[0033] The transport unit 23 is equipped with multiple roller pairs and transports the paper transported from the paper feed device 10 to the detection unit 22. Next, the transport unit 23 transports the paper detected by the detection unit 22 to the main unit 30.

[0034] (1-3. Main body configuration) The main body 30 is located downstream of the detection device 20 in the paper transport direction and upstream of the image reading device 40 in the paper transport direction. The main unit 30 forms a color image using an electrophotographic method based on image data obtained by reading an image from a document, or job image data of a print job received from an external device (not shown). Next, the main unit 30 transports the paper with the formed image to the image reading device 40. As shown in Figures 1 and 2, the main unit 30 includes an operation unit 31, a display unit 32, a document reading unit 33, an image forming unit 34, a third control unit 36, a storage unit 37, a communication unit 38, and an image processing unit 39.

[0035] The operation unit 31 includes a touch panel formed to cover the display screen of the display unit 32, and various operation buttons such as number buttons and a start button. The operation unit 31 outputs an operation signal based on the user's operation to the third control unit 36.

[0036] The display unit 32 includes an LCD (Liquid Crystal Display) or the like. The display unit 32 displays various screens according to the instructions of the display signals input from the third control unit 36.

[0037] The document reading unit 33 is equipped with an automatic document feeder (ADF), a scanner, and the like. The document reading unit 33 reads the image of the document and outputs the resulting image data to the third control unit 36.

[0038] The image forming unit 34 forms an image on the paper transported from the detection device 20 using an intermediate transfer method, based on the image data processed by the image processing unit 39. In this embodiment, the paper is a single sheet. The image forming unit 34 includes photosensitive drums 341Y, 341M, 341C, and 341K corresponding to yellow (Y), magenta (M), cyan (C), and black (K), an intermediate transfer belt 342, a secondary transfer roller 343, a fixing unit 344, an inversion path 345, a resist unit 346, and the like. The photoreceptor drums 341Y, 341M, 341C, and 341K are arranged in this order in series along the travel direction AR of the intermediate transfer belt 342, starting from the upstream side of the travel direction AR.

[0039] The image forming unit 34 uniformly charges the photoreceptor drum 341Y, then scans and exposes it with a laser beam based on yellow image data to form an electrostatic latent image. Next, the image forming unit 34 deposits yellow toner onto the electrostatic latent image on the photoreceptor drum 341Y and performs development. The photoconductor drums 341M, 341C, and 341K are the same as the photoconductor drum 341Y, except for the different colors they handle, so we will omit their explanation.

[0040] The image forming unit 34 sequentially transfers the toner images of each color formed on the photoreceptor drums 341Y, 341M, 341C, and 341K onto the rotating intermediate transfer belt 342 (primary transfer). In other words, the image forming unit 34 forms a color toner image on the intermediate transfer belt 342 by superimposing the four toner images. The image forming unit 34 transfers the color toner image on the intermediate transfer belt 342 onto the paper in one go using the secondary transfer roller 343 (secondary transfer). The transfer nip formed by the intermediate transfer belt 342 and the secondary transfer roller 343 is the transfer section 343a.

[0041] The fixing unit 344 includes a heating roller for heating the paper onto which the color toner image has been transferred, and a pressure roller for applying pressure to the paper. The fixing unit 344 holds the paper between fixing nip sections 344a formed by a heating roller and a pressure roller, and fixes the color toner image to the paper by heating and pressurizing.

[0042] In the case of single-sided printing, where an image is formed on one side of the paper in the main unit 30, the third control unit 36 ​​transports the paper from the fuser unit 344 to the image reading device 40. On the other hand, in the case of double-sided printing, where an image is formed on both sides of the paper, the third control unit 36 ​​transports the paper from the fuser unit 344 to the reversal path 345 to reverse the paper surface. Next, the third control unit 36 ​​feeds the paper again upstream of the resist unit 346 in the paper transport direction.

[0043] The resist section 346 is equipped with resist rollers and transports the paper to the transfer section 343a. The resist unit 346 corrects the tilt of the paper transported from the detection device 20 and adjusts the timing of paper transport.

[0044] The third control unit 36 ​​includes a CPU, RAM, ROM, etc. The CPU of the third control unit 36 ​​reads various processing programs stored in ROM and loads them into RAM. The third control unit 36 ​​then comprehensively controls the operation of the main unit 30 in cooperation with the various programs loaded into RAM.

[0045] The memory unit 37 is a non-volatile storage device such as an HDD (Hard Disk Drive) or semiconductor memory that stores various types of data, such as programs and image data. The memory unit 37 stores data such as program data and various setting data so that it can be read and written by the third control unit 36.

[0046] The memory unit 37 stores information such as the basis weight, size, and type of paper stored in the paper feed trays 131 to 133, associating them with each other.

[0047] The communication unit 38 includes, for example, a communication control card such as a LAN (Local Area Network) card. The communication unit 38 transmits and receives various types of data with external devices (such as personal computers) connected to communication networks such as LANs and WANs (Wide Area Networks).

[0048] The image processing unit 39 performs necessary image processing on image data stored in the storage unit 37, image data obtained by reading an image from a document by the document reading unit 33, and image data input from an external device. Next, the image processing unit 39 transmits the processed image data to the image forming unit 34. The image processing includes gradation processing, halftone processing, and color conversion processing. Gradation processing is the process of converting the gradation value of each pixel of image data into gradation values ​​that have been corrected so that the density characteristics of the image formed on the paper match the density characteristics of the target. Halftone processing includes error diffusion processing and screen processing using systematic dithering. Color conversion processing is the process of converting each RGB gradation value into each CMYK gradation value.

[0049] (1-4. Configuration of the image reading device) The image reading device 40 is located downstream of the main unit 30 in the paper transport direction. The image reading device 40 reads the paper transported from the main unit 30 and outputs the obtained read image data to the third control unit 36. The image reading device 40 includes a fourth control unit 41, an image reading unit 42, a transport unit 43, a paper output tray 44, and the like.

[0050] The fourth control unit 41 includes a CPU, ROM, RAM, etc. The CPU of the fourth control unit 41 reads the program stored in ROM, loads it into RAM, and then controls each part of the image reading device 40 according to the loaded program. For example, the fourth control unit 41 has the image reading unit 42 read the paper transported from the main unit 30 and outputs the obtained read image data to the third control unit 36. Next, the fourth control unit 41 discharges the read paper into the output tray 44 using the transport unit 43.

[0051] The image reading unit 42 has reading units 421 and 422. The reading unit 421 reads the image from one side of the paper and acquires the read image data. The reading unit 422 reads the image on the other side of the paper and acquires the read image data.

[0052] The reading units 421 and 422 include a line image sensor, an illumination unit, and the like. In a line image sensor, multiple image sensors (for example, CCDs (Charge Coupled Devices)) that perform photoelectric conversion for each pixel are arranged in a one-dimensional manner in the width direction of the paper. The width direction of the paper is perpendicular to the paper transport direction. The illumination unit irradiates light onto the paper to enable proper reading. The illumination unit consists of, for example, an LED and a diffusion member that evenly spreads the emitted light within the reading area. The reading units 421 and 422 may include a CIS (Contact Image Sensor) integrating a line image sensor and an illumination unit, or a two-dimensional area sensor and an illumination unit, etc.

[0053] The image reading unit 42 reads either the upper side, the lower side, or both sides of the paper transported from the main unit 30 using reading units 421 and 422. Next, the image reading unit 42 outputs the read image generated as a result of the reading to the fourth control unit 41. The image reading unit 42 may include a background member that serves as the background for the paper image when the paper is read by a line image sensor or the like.

[0054] The transport unit 43 is equipped with multiple roller pairs and transports the paper transported from the main unit 30 to the image reading unit 42. Next, under the control of the fourth control unit 41, the transport unit 43 discharges the paper read by the image reading unit 42 into the output tray 44.

[0055] In this embodiment, the third control unit 36 ​​of the main unit 30 comprehensively controls the entire image forming apparatus 1, but this is not limited to this configuration. The second control unit 21 of the detection device 20, or the fourth control unit 41 of the image reading device 40, may also comprehensively control the entire image forming apparatus 1.

[0056] (2. Color shift caused by the difference in speed between fixing speed and transfer speed) Next, we will explain the color misalignment caused by the speed difference between the paper transport speed (fixing speed) in the fixing unit 344 and the paper transport speed (transfer speed) in the transfer unit 343a. In this embodiment, the color misalignment is a color misalignment between at least two colors in an image formed on paper.

[0057] Figure 3 shows the case where the fixing rate is faster than the transfer rate. In this case, the paper S is pulled in the direction of A1 shown in Figure 3 by the fixing nip portion 344a formed by the heating roller and pressure roller of the fixing unit 344. As a result, the speed of the intermediate transfer belt 342 becomes faster than the normal value at which no color misalignment occurs, causing the primary transfer position to shift and resulting in color misalignment in the image formed on the paper S.

[0058] Figure 4 shows the case where the fixation rate is slower than the transfer rate. In this case, the paper S sags between the fixing unit 344 and the transfer unit 343a, and the reaction force of this sag causes the speed of the intermediate transfer belt 342 to be slower than the normal value at which no color misalignment occurs. As a result, the position of the primary transfer shifts, and color misalignment occurs in the image formed on the paper S. If the paper S is thick paper, the reaction force of this sag is greater than in the case of thin paper, so the speed of the intermediate transfer belt 342 tends to be slower. Thick paper is, for example, paper with a thickness of a predetermined value or a basis weight of a predetermined value or more.

[0059] (3. Color shift during sequential image formation) Next, we will explain the color misalignment that occurs when the main unit 30 continuously forms images on multiple sheets of paper. Figure 5 shows the image forming unit 34 at the moment just before the leading edge of the first sheet of paper S1 enters the fixing nip section 344a. As shown in Figure 5, the photoreceptor drums 341Y, 341M, 341C, and 341K are arranged in series along the running direction AR of the intermediate transfer belt 342. Therefore, the distances from the fixing nip section 344a to each photoreceptor drum 341Y, 341M, 341C, and 341K via the transfer section 343a are different. Specifically, the distances are shortest in the order of KL1, CL1, ML1, and YL1. Distance KL1 is the distance from the fixing nip section 344a to the photoreceptor drum 341K via the transfer section 343a. Distance CL1 is the distance from the fixing nip section 344a to the photoreceptor drum 341C via the transfer section 343a. Distance ML1 is the distance from the fixing nip section 344a to the photoreceptor drum 341M via the transfer section 343a. Distance YL1 is the distance from the fixing nip section 344a to the photoreceptor drum 341Y via the transfer section 343a.

[0060] When the leading edge of the first sheet of paper S1 enters the fixing nip section 344a, the intermediate transfer belt 342 is affected by the fixing speed via the paper S1, causing the speed of the intermediate transfer belt 342 to change. As a result, color shifts may occur in the image formed on the first sheet of paper S1 due to the speed difference between the fixing speed and the transfer speed.

[0061] Region R1 in the first sheet of paper S1 shown in Figure 6 is the region from the leading edge of paper S1 to a distance KL1. Region R1 is the region where the black (K) toner image is primarily transferred before the leading edge of paper S1 enters the fuser nip 344a. In region R1, paper S1 is not held by the fuser nip 344a, so it is not affected by the fuser speed. Therefore, color shifts due to the speed difference between the fuser speed and the transfer speed are less likely to occur in region R1. On the other hand, the area of ​​paper S1 behind region R1 is the area where the black (K) toner image is primarily transferred after the leading edge of paper S1 enters the fixing nip portion 344a. Therefore, in the area of ​​paper S1 behind region R1, color misalignment between black (K) and other colors may occur due to the speed difference between the fixing speed and the transfer speed.

[0062] Specifically, region R21 on paper S1 is a region affected by the difference between distance KL1 and distance CL1. In region R21, color shifts between black (K) and cyan (C) are likely to occur in the image formed on paper S1 due to the difference in speed between the fixing speed and the transfer speed that occurs when paper S1 enters the fixing nip 344a. Region R22 on paper S1 is a region affected by the difference between distance KL1 and distance ML1. In region R22, color shifts between black (K) and magenta (M) are likely to occur in the image formed on paper S1 due to the difference in speed between the fixing speed and the transfer speed that occurs when paper S1 enters the fixing nip 344a. Region R23 on paper S1 is a region affected by the difference between distance KL1 and distance YL1. In region R23, color shifts between black (K) and yellow (Y) are likely to occur in the image formed on paper S1 due to the difference in speed between the fixing speed and the transfer speed that occurs when paper S1 enters the fixing nip portion 344a.

[0063] Figure 7 shows the image forming unit 34 at the moment when the rear end of the first sheet of paper S1 is removed from the transfer unit 343a. At this time, the second sheet of paper S2 is held in place by the resist unit 346. As shown in Figure 7, the distances from the transfer unit 343a to each photoreceptor drum 341Y, 341M, 341C, and 341K are different. Specifically, the distances are shortest in the order of KL2, CL2, ML2, and YL2. Distance KL2 is the distance from the transfer unit 343a to the photoreceptor drum 341K. Distance CL2 is the distance from the transfer unit 343a to the photoreceptor drum 341C. Distance ML2 is the distance from the transfer unit 343a to the photoreceptor drum 341M. Distance YL2 is the distance from the transfer unit 343a to the photoreceptor drum 341Y.

[0064] When the trailing edge of the first sheet of paper S1 leaves the transfer section 343a, the intermediate transfer belt 342 is no longer affected by the fixing speed via the paper S1, and therefore its speed changes. As a result, in the image formed on the second sheet of paper S2, color misalignment may occur due to the speed difference between the fixing speed and the transfer speed caused by the trailing edge of the first sheet of paper S1 leaving the transfer section 343a.

[0065] Region R31 on the second sheet of paper S2 shown in Figure 8 is a region affected by the difference between distance KL2 and distance CL2. In region R31, color shifts between black (K) and cyan (C) are likely to occur in the image formed on paper S2 due to the difference in speed between the fixing speed and the transfer speed, which occurs when the trailing edge of the first sheet of paper S1 leaves the transfer section 343a. Region R32 on paper S2 is an area affected by the difference between distance KL2 and distance ML2. In region R32, color shifts between black (K) and magenta (M) are likely to occur in the image formed on paper S2 due to the difference in speed between the fixing speed and the transfer speed, which occurs when the trailing edge of the first sheet of paper S1 leaves the transfer section 343a. Region R33 on paper S2 is a region affected by the difference between distance KL2 and distance YL2. In region R33, color shifts between black (K) and yellow (Y) are likely to occur in the image formed on paper S2 due to the difference in speed between the fixing speed and the transfer speed, which occurs when the trailing edge of the first sheet of paper S1 leaves the transfer section 343a. In the second sheet of paper S2, similar to the first sheet of paper S1, a color misalignment between black (K) and other colors may occur in region R21-R23 due to the speed difference between the fixing speed and the transfer speed caused by paper S2 entering the fixing nip section 344a.

[0066] As described above, the area where color misalignment may occur is larger on the second sheet of paper S2 than on the first sheet of paper S1. Similarly to the second sheet of paper S2, the area where color misalignment may occur is larger on the third and subsequent sheets of paper than on the first sheet of paper S1. Therefore, when the image forming apparatus 1 of this embodiment forms images on multiple sheets of paper in succession, the image forming unit 34 corrects the color misalignment in the images formed on the paper based on the amount of color misalignment on the second and subsequent sheets of paper.

[0067] (3. Operation of the image forming apparatus) Next, we will explain the color misalignment correction process performed in the image forming apparatus 1 before executing a print job. The third control unit 36 ​​of the image forming apparatus 1 performs color shift correction processing in cooperation with the program stored in the storage unit 37. The third control unit 36 ​​performs color misalignment correction processing, for example, when the main unit 30 receives job information for a print job from an external device via the communication unit 38. This external device is, for example, a personal computer. The third control unit 36 ​​corrects color misalignment in the image formed on the paper by the image forming unit 34 by performing color misalignment correction processing. The third control unit 36 ​​functions as a control unit. Figure 9 shows a flowchart of the color shift correction process.

[0068] (Color shift correction processing) The third control unit 36 ​​feeds multiple sheets of paper for the print job from the paper feeder 10 in succession based on the received job information (step B1). Next, the third control unit 36 ​​obtains the detection results of the physical properties of the target paper by having the detection device 20 detect the target paper (step B2).

[0069] Next, the third control unit 36 ​​controls the image forming unit 34 to continuously form a chart on multiple sheets of target paper (step B3). This chart is used to measure the amount of color shift between at least two of the yellow (Y), magenta (M), cyan (C), and black (K) colors in the image formed by the image forming unit 34.

[0070] Next, the third control unit 36 ​​reads the chart formed on the paper using the image reading device 40 and acquires the read image data, which is the result of the reading (step B4). In step B4, the third control unit 36 ​​may use the image reading device 40 to read all the sheets on which the chart is formed and acquire the read image data of all the sheets. Alternatively, in step B4, the third control unit 36 ​​may use the image reading device 40 to read the second and subsequent sheets of paper on which the chart is formed, and acquire the read image data of the second and subsequent sheets.

[0071] Next, the third control unit 36 ​​measures the amount of color misalignment in the chart formed on the second and subsequent sheets of paper based on the image data read from the second and subsequent sheets of paper acquired in step B4 (step B5). In step B5, the third control unit 36 ​​may measure the amount of color shift between each color, or it may measure the integral value, mean, maximum, median, mode, etc., of the amount of color shift between each color.

[0072] Next, the third control unit 36 ​​calculates and corrects correction values ​​for the resist speed and / or fixing speed in the image formation process of the main unit 30 based on the detection results of the physical properties of the target paper acquired in step B2 and the amount of color shift measured in step B5 (step B6), and then terminates the color shift correction process. The resist speed is the paper transport speed in the resist unit 346. In step B6, the third control unit 36 ​​corrects the resist speed and / or fixing speed so that the amount of color shift measured in step B5 is below a predetermined threshold.

[0073] (4. Other) The image forming apparatus 1 may interrupt the print job while it is running, then perform the color misalignment correction process described above, and resume the print job after the color misalignment correction process is completed. In step B2 of the above color shift correction process, the detection unit for detecting the physical properties of the target paper may be provided in the paper feed trays 131 to 133, respectively. The third control unit 36 ​​of the image forming apparatus 1 may omit step B2 of the color shift correction process. In this case, in step B6, the third control unit 36 ​​calculates and corrects correction values ​​for the resist speed and / or fixing speed based on the amount of color shift measured in step B5.

[0074] (5. Effects) As described above, the image forming apparatus 1 according to this embodiment includes an image forming unit 34 that continuously forms images of multiple colors on paper using an intermediate transfer method. The image forming apparatus 1 according to this embodiment includes a reading unit (image reading unit 42) that reads an image formed on paper by the image forming unit 34. The image forming apparatus 1 according to this embodiment includes a control unit (third control unit 36) that corrects color misalignment in the image formed on the paper by the image forming unit 34. The control unit corrects color misalignment based on the reading results obtained by the reading unit from the second and subsequent sheets of paper on which images have been continuously formed by the image forming unit 34. Therefore, when an image forming apparatus forms images on multiple sheets of paper in succession, the amount of color shift that occurs on the first sheet of paper is smaller than that on subsequent sheets. However, by performing color shift correction based on the images formed on the second and subsequent sheets of paper, sufficient color shift correction can be performed on the subsequent sheets. This allows for accurate correction of color shifts in images formed on paper.

[0075] In the image forming apparatus 1 according to this embodiment, the image forming unit 34 includes a resist unit 346 that transports paper to a transfer unit 343a that transfers an image onto the paper, and a fixing unit 344 that fixes the image onto the paper. The control unit (third control unit 36) corrects color misalignment by adjusting at least one of the transport speeds in the resist unit 346 and the fuser unit 344. Therefore, color misalignment can be accurately corrected by adjusting the resist speed and / or fixing speed.

[0076] In the image forming apparatus 1 according to this embodiment, the control unit (third control unit 36) corrects color misalignment between at least two colors in the image formed on the paper. Therefore, color misalignment between at least two colors in an image formed on paper can be corrected with high accuracy.

[0077] In the image forming apparatus 1 according to this embodiment, the control unit (third control unit 36) measures the amount of color misalignment in the image formed on the second and subsequent sheets of paper. The control unit corrects the color misalignment by adjusting at least one of the transport speed in the resist unit 346 and the transport speed in the fixing unit 344 so that the measured amount of color misalignment becomes smaller. Therefore, by correcting the color shift based on the amount of color shift in the image formed on the second and subsequent sheets of paper, the color shift in the image formed on the paper can be corrected with high accuracy.

[0078] In the image forming apparatus 1 according to this embodiment, the reading unit (image reading unit 42) reads the image on the paper that has been continuously formed by the image forming unit 34. The control unit (third control unit 36) corrects color misalignment based on the reading results obtained by the reading unit from the second and subsequent sheets of paper. Therefore, the reading unit (image reading unit 42) can omit the process of identifying the second and subsequent sheets of paper from among the sheets on which images have been continuously formed by the image forming unit 34.

[0079] In the image forming apparatus 1 according to this embodiment, the reading unit (image reading unit 42) reads the images formed on the second and subsequent sheets of paper from which images have been continuously formed by the image forming unit 34. The control unit (third control unit 36) corrects color misalignment based on the reading results obtained by the reading unit from the second and subsequent sheets of paper. Therefore, the reading unit (image reading unit 42) can omit the process of reading the image on the first sheet of paper, which is unnecessary for correcting color misalignment.

[0080] In the image forming apparatus 1 according to this embodiment, the control unit (third control unit 36) corrects color misalignment based on the reading results obtained by the reading unit (image reading unit 42) from the second and subsequent sheets of paper before executing the print job. Therefore, a print job can be executed in the image forming apparatus 1 with color misalignment corrected to a high degree of accuracy.

[0081] In the image forming apparatus 1 according to this embodiment, the paper is cardboard with a predetermined thickness or basis weight. Therefore, even when forming images on thick paper, which is prone to color misalignment in the paper feeding direction (paper transport direction), color misalignment can be corrected with high accuracy.

[0082] The image forming apparatus 1 according to this embodiment includes a detection unit 22 for detecting attribute information of the paper. The control unit (third control unit 36) corrects the color misalignment based on the paper attribute information detected by the detection unit 22. Therefore, highly accurate color shift correction can be performed according to the attribute information of the paper.

[0083] Although the present invention has been specifically described above based on embodiments, the present invention is not limited to the above embodiments and can be modified without departing from its spirit. For example, the image forming apparatus 1 may be configured to send and receive information for mutual cooperation with a print controller (not shown) that generates and manages print jobs, other image forming systems (not shown), a business management system, etc.

[0084] In this embodiment, the third control unit 36 ​​of the main unit 30 comprehensively controls the entire image forming apparatus 1, but this is not limited to this. A separate control device may be provided, and the control unit of the control device comprehensively controls the entire image forming apparatus 1.

[0085] Furthermore, the detailed configuration and detailed operation of each device constituting the image forming apparatus 1 can also be modified as appropriate without departing from the spirit of the present invention. [Explanation of Symbols]

[0086] 1. Image forming apparatus 10 Paper feeder 11 First Control Unit 12 Conveying section 121 Transport Route 13 Paper feed section 131, 132, 133 Paper feed tray 20 Detection device 21 Second Control Unit 22 Detection unit 23 Conveying section 30 Main body 31 Operation section 32 Display section 33 Manuscript Reading Unit 34 Image forming unit 341Y, 341M, 341C, 341K Photoconductor Drum 342 Intermediate Transfer Belt 343 Secondary Transfer Roller 344 Fixing section 345 Reversal Path 346 Resist section 36 Third Control Unit (Control Unit) 37 Memory section 38 Communications Department 39 Image Processing Unit 40 Image reading device 41 Fourth Control Unit 42 Image reading unit (reading unit) 43 Conveying section 44 Paper output tray

Claims

1. An image forming unit that continuously forms multiple color images on paper using an intermediate transfer method, A reading unit reads the image formed on the paper by the image forming unit, A control unit for correcting color misalignment in the image formed on the paper by the image forming unit, Equipped with, The control unit corrects the color misalignment based on the reading result obtained by the reading unit from the second and subsequent sheets of paper on which images have been continuously formed by the image forming unit.

2. The image forming unit is A transfer unit that transfers an image onto the paper, a resist unit that transports the paper, The system includes a fixing unit for fixing an image onto the aforementioned paper, The image forming apparatus according to claim 1, wherein the control unit adjusts at least one of the transport speed in the resist section and the transport speed in the fixing section to correct color misalignment.

3. The image forming apparatus according to claim 1, wherein the control unit corrects color misalignment between at least two colors in the image formed on the paper.

4. The image forming apparatus according to claim 2, wherein the control unit measures the amount of color shift in the image formed on the second and subsequent sheets of paper, and corrects the color shift by adjusting at least one of the transport speed in the resist section and the transport speed in the fixing section so that the measured amount of color shift becomes smaller.

5. The reading unit reads the image on the paper that has been continuously formed by the image forming unit. The image forming apparatus according to claim 1, wherein the control unit corrects the color misalignment based on the reading result obtained by reading the images formed on the second and subsequent sheets of paper by the reading unit.

6. The reading unit reads the images formed on the second and subsequent sheets of paper from among the sheets on which images have been continuously formed by the image forming unit. The image forming apparatus according to claim 1, wherein the control unit corrects the color misalignment based on the reading result obtained by reading the images formed on the second and subsequent sheets of paper by the reading unit.

7. The image forming apparatus according to claim 1, wherein the control unit corrects the color misalignment based on the reading result obtained by reading the images formed on the second and subsequent sheets of paper by the reading unit before executing the print job.

8. The image forming apparatus according to claim 1, wherein the paper is cardboard of a predetermined thickness or basis weight.

9. The system includes a detection unit that detects attribute information of the aforementioned paper, The image forming apparatus according to claim 1, wherein the control unit corrects the color shift based on the attribute information detected by the detection unit.

10. An image forming unit that continuously forms multiple color images on paper using an intermediate transfer method, A reading unit reads the image formed on the paper by the image forming unit, A computer for an image forming apparatus equipped with, The control unit functions to correct color misalignment in the image formed on the paper by the image forming unit. The control unit is a program that corrects the color misalignment based on the reading results obtained by the reading unit from the second and subsequent sheets of paper on which images have been continuously formed by the image forming unit.

Images