Image forming apparatus and program

Abstract

It accurately corrects color shifts in images formed on paper. [Solution] The image forming apparatus 1 includes an intermediate transfer belt 342 that transfers images of multiple colors transferred from multiple image carriers (photoreceptor drums 341Y, 341M, 341C, 341K) onto paper; a speed detection unit (drive roller 345 and peripheral speed detection unit 39) that contacts the inner surface of the intermediate transfer belt 342 to detect the peripheral speed of the intermediate transfer belt 342; an acquisition unit (third control unit 36) that acquires paper characteristic information indicating the paper characteristics of the paper; a correction unit (third control unit 36) that corrects the detection result by the speed detection unit based on the paper characteristic information acquired by the acquisition unit; and a determination unit (third control unit 36) that determines the amount of color shift correction based on the detection result by the speed detection unit corrected by the correction unit.

Description

Technical Field

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

Background Art

[0002] Conventionally, a technique for correcting color misregistration in the paper feed direction (sub-scanning direction) in electrophotographic printing using intermediate transfer has been known.

[0003] In relation to this, Patent Document 1 discloses an image forming apparatus that changes the writing timing of each scanning line in the sub-scanning direction on an image carrier according to the thickness of the paper.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, in the invention described in Patent Document 1, the writing timing is changed by a predetermined correction amount for each paper thickness. Therefore, due to the influence of the environment inside the image forming apparatus and the like, the correction accuracy of color misregistration may decrease. On the other hand, since the color misregistration in the sub-scanning direction is caused by the speed variation of the intermediate transfer belt, it is possible to correct the color misregistration in the sub-scanning direction by adjusting the speed of the intermediate transfer belt. However, depending on the type of paper, there may be a difference between the encoder value for detecting the speed of the intermediate transfer belt and the actual speed of the intermediate transfer belt while the paper passes through the secondary transfer nip. Thus, when the speed of the intermediate transfer belt cannot be accurately detected, the speed of the intermediate transfer belt cannot be appropriately adjusted, resulting in a problem that the color misregistration in the sub-scanning direction cannot be accurately corrected.

[0006] The present invention aims to provide an image forming apparatus and program that can accurately correct color misalignment in images formed on paper. [Means for solving the problem]

[0007] To solve the above problems, the image forming apparatus described in claim 1 is An intermediate transfer belt that transfers images of multiple colors, transferred from multiple image carriers, onto paper, A speed detection unit that contacts the inner surface of the intermediate transfer belt to detect the peripheral speed of the intermediate transfer belt, An acquisition unit that acquires paper characteristic information indicating the paper characteristics of the aforementioned paper, A correction unit corrects the detection result by the speed detection unit based on the paper characteristic information acquired by the acquisition unit, A determination unit that determines the amount of color shift correction based on the detection result by the speed detection unit corrected by the correction unit, It is equipped with.

[0008] The invention described in claim 2 is an image forming apparatus according to claim 1, The aforementioned paper characteristics include at least one of the following: paper type, paper thickness, basis weight, and moisture content.

[0009] The invention described in claim 3 is an image forming apparatus according to claim 2, It includes a media detection unit that detects the aforementioned paper characteristics, The acquisition unit acquires the detection result from the media detection unit as the paper characteristic information.

[0010] The invention described in claim 4 is an image forming apparatus according to claim 2, The acquisition unit accepts the input of the paper characteristic information.

[0011] The invention described in claim 5 is an image forming apparatus according to claim 1, The correction unit corrects the detection result by the speed detection unit based on environmental information indicating the environment inside the image forming apparatus.

[0012] The invention according to claim 6 is, in the image forming apparatus according to claim 1, The correction unit corrects the detection result by the speed detection unit based on the width of the paper.

[0013] The invention according to claim 7 is, in the image forming apparatus according to claim 1, The correction unit determines a correction value for correcting the detection result by the speed detection unit based on the detection result by the speed detection unit.

[0014] The invention according to claim 8 is, in the image forming apparatus according to claim 1, comprising an image reading unit that reads an image formed on the paper, The correction unit corrects the detection result by the speed detection unit based on the reading result by the image reading unit.

[0015] The invention according to claim 9 is, in the image forming apparatus according to claim 1, The correction unit corrects the detection result by the speed detection unit based on the mechanical characteristics of the members constituting the image forming apparatus.

[0016] The invention according to claim 10 is, in the image forming apparatus according to claim 1, The correction unit corrects the detection result by the speed detection unit based on the change in the amount of color shift accompanying the change over time.

[0017] The program according to claim 11 is an intermediate transfer belt that transfers images of a plurality of colors transferred from a plurality of image carriers to a paper, a speed detection unit that contacts the inner surface of the intermediate transfer belt and detects the peripheral speed of the intermediate transfer belt, a computer of an image forming apparatus including an acquisition unit that acquires paper characteristic information indicating the paper characteristics of the paper, a correction unit that corrects the detection result by the speed detection unit based on the paper characteristic information acquired by the acquisition unit, A determination unit that determines a color shift correction amount based on the detection result of the speed detection unit corrected by the correction unit, is made to function as.

Effect of the Invention

[0018] According to the present invention, color shift in an image formed on a sheet can be accurately corrected.

Brief Description of the Drawings

[0019] [Figure 1] It is a front view showing a schematic configuration of an image forming apparatus according to the present embodiment. [Figure 2] It is a functional block diagram showing a control structure of an image forming apparatus according to the present embodiment. [Figure 3] It is a diagram showing an intermediate transfer unit before the sheet enters the secondary transfer nip. [Figure 4] It is a diagram showing an intermediate transfer unit after the sheet enters the secondary transfer nip. [Figure 5] It is a diagram showing the detection result of the peripheral speed detection unit and the actual speed fluctuation of the intermediate transfer belt when a thin sheet is passed. [Figure 6] It is a diagram showing the detection result of the peripheral speed detection unit and the actual speed fluctuation of the intermediate transfer belt when a thick sheet is passed. [Figure 7] It is a diagram showing an example of a peripheral speed correction table. [Figure 8] It is a diagram showing the detection result of the peripheral speed detection unit and the actual speed fluctuation of the intermediate transfer belt when sheets of different stiffnesses are passed. [Figure 9] It is a diagram showing the amount of color shift in the sub-scanning direction between two colors. [Figure 10] It is a flowchart showing the flow of print control processing. [Figure 11] It is a flowchart showing the flow of the first adjustment process. [Figure 12] It is a flowchart showing the flow of the second adjustment process. [Figure 13] It is a flowchart showing the flow of encoder value correction processing. [Figure 14] This flowchart shows the flow of the third adjustment process. [Figure 15] This is a flowchart showing the flow of the fourth adjustment process. [Modes for carrying out the invention]

[0020] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

[0021] (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.

[0022] (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.

[0023] 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.

[0024] 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.

[0025] (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 paper characteristic information that indicates the characteristics of the paper. The detection device 20 detects physical properties of multiple types of paper, including paper type, thickness, basis weight, stiffness, moisture content, and surface properties. The physical properties may be information that can be converted into physical properties.

[0026] The detection device 20 includes a second control unit 21, a media detection unit 22, a transport unit 23, and the like.

[0027] 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 media detection unit 22 detect the paper 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 by the transport unit 23.

[0028] The media detection unit 22 detects the physical properties of the paper. The media detection unit 22 has sensors for detecting paper properties such as paper thickness, basis weight, stiffness, moisture content, and surface properties.

[0029] For example, a sensor for detecting paper thickness includes a pair of transport rollers, at least one of which moves according to the thickness of the paper passing through the roller nip, and a measuring unit that measures the distance between the axes of the transport roller pair. The measuring unit includes, for example, an actuator, an encoder, a light-emitting unit, a light-receiving unit, etc. The axis position of the driven roller, which moves according to the thickness of the paper held between the transport roller pair, is displaced. The sensor measures the paper thickness by measuring the height of this displaced axis. The media detection unit 22 outputs the thickness as a physical property value to the second control unit 21.

[0030] The sensor for detecting the basis weight of the 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 media detection unit 22 outputs the basis weight as a physical property value to the second control unit 21.

[0031] 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 media 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.

[0032] 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. This 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 deflection filter. The media detection unit 22 outputs the moisture content as a physical property value to the second control unit 21.

[0033] 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 media detection unit 22 outputs the surface properties as physical properties to the second control unit 21.

[0034] The transport unit 23 is equipped with multiple roller pairs and transports the paper transported from the paper feed device 10 to the media detection unit 22. Next, the transport unit 23 transports the paper detected by the media detection unit 22 to the main unit 30.

[0035] (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 a peripheral speed detection unit 39.

[0036] 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.

[0037] 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.

[0038] 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.

[0039] 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 that has undergone image processing. In this embodiment, the paper is a single sheet. The image forming unit 34 includes photoreceptor 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 tension roller 344, a drive roller 345, an opposing roller 346, a fixing unit 347, an inversion path 348, a resist unit 349, 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. The photoreceptor drums 341Y, 341M, 341C, and 341K are multiple image carriers.

[0040] 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.

[0041] The intermediate transfer belt 342 is an endless belt, stretched by multiple rollers, and driven in a circular motion in the direction of travel AR. These multiple rollers include opposing rollers 346, drive rollers 345, driven rollers, tension rollers 344, etc. The tension roller 344 contacts the inner surface of the intermediate transfer belt 342 and moves vertically to maintain a constant tension on the intermediate transfer belt 342. The drive roller 345 contacts the inner surface of the intermediate transfer belt 342 and drives the intermediate transfer belt 342 in a circular motion in the direction of travel AR. The opposing roller 346 is positioned opposite the secondary transfer roller 343, with the intermediate transfer belt 342 in between.

[0042] 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 intermediate transfer belt 342 and the secondary transfer roller 343 form a secondary transfer nip 343a.

[0043] The fixing unit 347 includes a heating roller for heating the paper onto which the color toner image has been transferred, a pressure roller for applying pressure to the paper, and the like. The fixing unit 347 holds the paper between fixing nip formed by a heating roller and a pressure roller, and fixes the color toner image to the paper by heating and pressurizing.

[0044] 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 347 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 347 to the reversal path 348 to reverse the paper surface. Next, the third control unit 36 ​​feeds the paper again upstream of the resist unit 349 in the paper transport direction.

[0045] The resist section 349 is equipped with resist rollers and transports the paper to the secondary transfer nip 343a. The resist unit 349 corrects the tilt of the paper transported from the detection device 20 and adjusts the timing of paper transport.

[0046] 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.

[0047] The third control unit 36 ​​determines the type of paper (paper grade) based on the physical properties of the paper obtained from the detection device 20. Specifically, the third control unit 36 ​​calculates the density of the paper by dividing the basis weight of the paper by the thickness of the paper. Next, the third control unit 36 ​​determines the type of paper based on the surface properties and density of the paper.

[0048] 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.

[0049] 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. The memory unit 37 stores a peripheral speed correction table that corrects the speed difference between the detection result of the peripheral speed detection unit 39 and the actual peripheral speed of the intermediate transfer belt 342. The peripheral speed correction table will be described in detail later.

[0050] 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).

[0051] The peripheral speed detection unit 39 is an encoder that detects the peripheral speed of the intermediate transfer belt 342 by detecting the amount of mechanical displacement of the rotation of the drive roller 345. The peripheral speed detection unit 39 outputs the encoder value, which is the detected peripheral speed of the intermediate transfer belt 342, to the third control unit 36. The drive roller 345 and the peripheral speed detection unit 39 are collectively referred to as the "speed detection unit."

[0052] (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.

[0053] 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.

[0054] 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.

[0055] 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.

[0056] 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.

[0057] 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.

[0058] 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.

[0059] (2. Speed ​​difference between the detection result of the peripheral speed detection unit and the actual peripheral speed of the intermediate transfer belt) Next, we will explain the speed difference between the detection result of the peripheral speed detection unit 39 and the actual peripheral speed of the intermediate transfer belt 342. Figure 3 shows the intermediate transfer unit before the paper S enters the secondary transfer nip 343a. Figure 4 shows the intermediate transfer unit after the paper S enters the secondary transfer nip 343a. The intermediate transfer unit includes an intermediate transfer belt 342, a secondary transfer roller 343, a tension roller 344, a drive roller 345, an opposing roller 346, and the like.

[0060] As shown in Figure 3, the tension of the intermediate transfer belt 342 is kept constant by the tension roller 344 before the paper S enters the secondary transfer nip 343a.

[0061] As shown in Figure 4, when the paper S enters the secondary transfer nip 343a, the opposing roller 346 lifts due to the thickness of the paper S, causing the tension of the intermediate transfer belt 342 to loosen. When the tension of the intermediate transfer belt 342 loosens, the tension roller 344 begins to move upward to restore the tension of the intermediate transfer belt 342. However, depending on the sliding properties of the tension roller 344, it may take a predetermined amount of time for the tension of the intermediate transfer belt 342 to return to normal. The sliding properties of the tension roller 344 vary depending on the physical properties of the paper S, the mechanical properties of the intermediate transfer unit, the deterioration of the durability of the intermediate transfer unit, the environmental conditions inside the main body 30, etc. When the tension of the intermediate transfer belt 342 has not returned to its original state and is loose, the contact between the drive roller 345 and the intermediate transfer belt 342 decreases. As a result, the peripheral speed detection unit 39 is unable to accurately detect the peripheral speed of the intermediate transfer belt 342. In this case, a speed difference occurs between the detection result of the peripheral speed detection unit 39 and the actual peripheral speed of the intermediate transfer belt 342.

[0062] Figure 5 shows the speed fluctuations between the detection result F1 of the peripheral speed detection unit 39 and the actual peripheral speed F2 of the intermediate transfer belt 342 from the time the A3-sized thin paper enters the secondary transfer nip 343a until it separates from it. Figure 6 shows the speed fluctuations between the detection result G1 of the peripheral speed detection unit 39 and the actual peripheral speed G2 of the intermediate transfer belt 342 from the time the A3-sized cardboard enters the secondary transfer nip 343a until it separates from it. The change in tension of the intermediate transfer belt 342 when thin paper enters the secondary transfer nip 343a is smaller compared to that of thick paper. Therefore, as shown in Figure 5, the speed difference between the detection result F1 of the peripheral speed detection unit 39 and the actual peripheral speed F2 of the intermediate transfer belt 342 when the paper is thin paper is smaller than in the case of thick paper. The thicker the paper, the greater the change in tension of the intermediate transfer belt 342 when the paper enters the secondary transfer nip 343a. Therefore, as shown in Figure 6, the speed difference between the detection result G1 of the peripheral speed detection unit 39 and the actual peripheral speed G2 of the intermediate transfer belt 342 when the paper is thick is larger than when the paper is thin.

[0063] Figure 7 shows an example of a peripheral speed correction table that corrects the speed difference between the detection result of the peripheral speed detection unit 39 and the actual peripheral speed of the intermediate transfer belt 342. The peripheral speed correction table stores correction coefficients that correct the detection results of the peripheral speed detection unit 39, which are associated with the distance from the leading edge of the paper and the thickness of the paper.

[0064] Figure 8 shows the speed fluctuations between the detection results of the peripheral speed detection unit 39 and the actual peripheral speed of the intermediate transfer belt 342 from the time multiple types of paper enter the secondary transfer nip 343a until they detach. The multiple types of paper are A3 size, have the same thickness, and have different stiffnesses. Specifically, this shows the speed fluctuation between the detection result H1 of the peripheral speed detection unit 39 and the actual peripheral speed H2 of the intermediate transfer belt 342, from the time a sheet of paper with standard stiffness enters the secondary transfer nip 343a until it separates from it. Furthermore, the speed fluctuations between the detection result I1 of the peripheral speed detection unit 39 and the actual peripheral speed I2 of the intermediate transfer belt 342, from the time the paper, which has a higher rigidity than standard, enters the secondary transfer nip 343a until it separates from it, are shown. Furthermore, the speed fluctuations between the detection result J1 of the peripheral speed detection unit 39 and the actual peripheral speed J2 of the intermediate transfer belt 342, from the time a paper with lower-than-standard stiffness enters the secondary transfer nip 343a until it separates from it, are shown. As shown in Figure 8, the position where the peak occurs in speed fluctuations changes depending on the difference in paper stiffness. Therefore, it is necessary to adjust the correction coefficient stored in the peripheral speed correction table based on characteristic values ​​such as paper stiffness.

[0065] (3. Amount of color shift in the sub-scanning direction) Next, we will explain the amount of color shift in the sub-scanning direction that occurs when the peripheral speed detection unit 39 cannot accurately detect the peripheral speed of the intermediate transfer belt 342. Since the photoreceptor drums 341Y, 341M, 341C, and 341K are arranged in series along the running direction AR of the intermediate transfer belt 342, the distances between each photoreceptor drum are different. Specifically, with black (K) as the reference, the distance between photoreceptor drum 341C and photoreceptor drum 341K is shortest, followed by the distance between photoreceptor drum 341M and photoreceptor drum 341K, and then the distance between photoreceptor drum 341Y and photoreceptor drum 341K.

[0066] Figure 9 shows the amount of color shift in the sub-scanning direction between two colors, with black (K) as the reference, on an A3 size sheet of paper. As shown in Figure 9, the greater the distance between the photoreceptor drums, the greater the amount of color misalignment in the sub-scanning direction that occurs when the peripheral speed detection unit 39 cannot accurately detect the peripheral speed of the intermediate transfer belt 342.

[0067] (4. Operation of the image forming apparatus) Next, the print control process performed in the image forming apparatus 1 will be described. The third control unit 36 ​​works in cooperation with the program stored in the memory unit 37 to execute print control processing. The third control unit 36 ​​executes print control processing, for example, when the main unit 30 receives print job information from an external device via the communication unit 38. The external device is, for example, a personal computer. Figure 10 shows a flowchart of the print control process.

[0068] (Print control processing) The third control unit 36 ​​determines, for example, whether the first adjustment process is enabled based on the received job information (step S1). If the first adjustment process is enabled (step S1; YES), the third control unit 36 ​​executes the first adjustment process shown in Figure 11 (step S2).

[0069] (First adjustment process) The third control unit 36 ​​feeds the target paper for the print job from the paper feed device 10 based on the received job information (step A1). Next, the third control unit 36 ​​acquires the detection result of the peripheral speed detection unit 39 from the time the target paper enters the secondary transfer nip 343a until it separates from it (step A2). Next, the third control unit 36 ​​adjusts the correction timing and correction amount in the correction coefficient to suppress the speed difference between the detection result of the peripheral speed detection unit 39 and the actual peripheral speed of the intermediate transfer belt 342, based on the detection result of the peripheral speed detection unit 39 obtained in step A2 (step A3). Next, the third control unit 36 ​​reflects the correction coefficient adjusted in step A3 into the peripheral speed correction table (step A4), and terminates the first adjustment process.

[0070] The third control unit 36 ​​performs a first adjustment process to adjust the peripheral speed correction table based on the detection results of the peripheral speed detection unit 39 from the time the target paper enters the secondary transfer nip 343a until it leaves it. As a result, the third control unit 36 ​​can accurately correct the detection results of the peripheral speed detection unit 39 using the adjusted peripheral speed correction table in the encoder value correction process described later, starting from the time the image forming process is executed for the first target paper of the print job. Therefore, the third control unit 36 ​​can suppress the occurrence of color misalignment from the first target sheet of the print job by controlling the peripheral speed of the intermediate transfer belt 342 based on the detection result of the peripheral speed detection unit 39, which has been accurately corrected.

[0071] Returning to Figure 10, if the first adjustment process is set to disabled (step S1; NO), the third control unit 36 ​​moves the print control process to step S3.

[0072] Next, the third control unit 36 ​​starts the print job based on the received job information (step S3). Next, the third control unit 36 ​​feeds the target paper for the print job from the paper feeder 10 (step S4). Next, the third control unit 36 ​​determines, for example, whether the second adjustment process is enabled based on the received job information (step S5). If the second adjustment process is enabled (step S5; YES), the third control unit 36 ​​executes the second adjustment process shown in Figure 12 (step S6).

[0073] (Second adjustment process) The third control unit 36 ​​acquires paper characteristic information indicating the paper characteristics of the target paper (step B1). The third control unit 36 ​​functions as an acquisition unit. Specifically, the third control unit 36 ​​detects the target paper using the detection device 20 and acquires detection results such as the paper thickness, basis weight, stiffness, and moisture content of the target paper as paper characteristic information. Furthermore, the third control unit 36 ​​determines the type of the target paper based on the thickness, basis weight, and surface properties of the target paper acquired from the detection device 20, thereby acquiring the type of paper as paper characteristic information for the target paper. Paper characteristics may include at least one of the following: paper type, thickness, basis weight, and moisture content.

[0074] Next, the third control unit 36 ​​adjusts the correction timing and correction amount in the correction coefficient to suppress the speed difference between the detection result of the peripheral speed detection unit 39 and the actual peripheral speed of the intermediate transfer belt 342, based on the difference between the paper characteristic information of the target paper acquired in step B1 and the reference paper characteristic information (step B2). Next, the third control unit 36 ​​reflects the correction coefficient adjusted in step B2 into the peripheral speed correction table (step B3), and terminates the second adjustment process.

[0075] The third control unit 36 ​​adjusts the peripheral speed correction table based on the paper characteristics information of the target paper by executing the second adjustment process. As a result, the third control unit 36 ​​can accurately correct the detection result of the peripheral speed detection unit 39 using the adjusted peripheral speed correction table in the encoder value correction process described later. Therefore, the third control unit 36 ​​can suppress the occurrence of color misalignment by controlling the peripheral speed of the intermediate transfer belt 342 based on the detection result of the peripheral speed detection unit 39, which has been accurately corrected.

[0076] Returning to Figure 10, if the second adjustment process is set to disabled (step S5; NO), the third control unit 36 ​​proceeds to step S7 of the print control process.

[0077] Next, the third control unit 36 ​​starts acquiring the detection result of the peripheral speed detection unit 39 at the timing when the target paper enters the secondary transfer nip 343a (step S7). Next, the third control unit 36 ​​determines, for example, whether the encoder value correction process is enabled based on the received job information (step S8). If the encoder value correction process is enabled (step S8; YES), the third control unit 36 ​​executes the encoder value correction process shown in Figure 13 (step S9).

[0078] (Encoder value correction process) The third control unit 36 ​​acquires the detection result of the peripheral speed detection unit 39 at the current time (step C1). Next, the third control unit 36 ​​corrects the detection result of the peripheral speed detection unit 39 acquired in step C1 using the peripheral speed correction table (step C2). Next, the third control unit 36 ​​adjusts the peripheral speed of the intermediate transfer belt 342 based on the detection result of the corrected peripheral speed detection unit 39 (step C3).

[0079] The third control unit 36 ​​corrects the detection result by the peripheral speed detection unit 39 based on the paper characteristic information by performing the second adjustment process and the encoder value correction process. The third control unit 36 ​​functions as a correction unit. The third control unit 36 ​​performs encoder value correction processing and determines a color shift correction amount to correct the color shift based on the detection result of the corrected peripheral speed detection unit 39. The third control unit 36 ​​functions as a determination unit. Next, the third control unit 36 ​​can suppress the occurrence of color shift by controlling the peripheral speed of the intermediate transfer belt 342 based on the determined color shift correction amount.

[0080] Returning to Figure 10, the case where the encoder value correction process is disabled (step S8; NO) will be explained. In this case, the third control unit 36 ​​adjusts the peripheral speed of the intermediate transfer belt 342 to suppress color shift in the sub-scanning direction by a correction ratio corresponding to the difference in distance between the photoreceptor drums 341Y, 341M, 341C, and 341K (step S10).

[0081] Next, the third control unit 36 ​​transfers the toner image to the paper at the secondary transfer nip 343a (step S11).

[0082] Next, the third control unit 36 ​​determines, for example, whether the third adjustment process is enabled based on the received job information (step S12). If the third adjustment process is enabled (step S12; YES), the third control unit 36 ​​executes the third adjustment process shown in Figure 14 (step S13).

[0083] (Third adjustment process) The third control unit 36 ​​acquires the detection result of the peripheral speed detection unit 39 from the time the target paper on which the toner image was transferred in step S11 enters the secondary transfer nip 343a until it separates from it (step D1). Next, the third control unit 36 ​​adjusts the correction timing and correction amount in the correction coefficient to suppress the speed difference between the detection result of the peripheral speed detection unit 39 and the actual peripheral speed of the intermediate transfer belt 342, based on the detection result of the peripheral speed detection unit 39 acquired in step D1 (step D2). Next, the third control unit 36 ​​reflects the correction coefficient adjusted in step D2 into the peripheral speed correction table (step D3), and terminates the third adjustment process.

[0084] Returning to Figure 10, if the third adjustment process is set to disabled (step S12; NO), the third control unit 36 ​​proceeds to step S14 of the print control process.

[0085] Next, the third control unit 36 ​​determines, for example, whether the fourth adjustment process is enabled based on the received job information (step S14). If the fourth adjustment process is enabled (step S14; YES), the third control unit 36 ​​executes the fourth adjustment process shown in Figure 15 (step S15).

[0086] (Fourth adjustment process) The third control unit 36 ​​reads the image formed on the target paper using the image reading device 40 and acquires the read image data, which is the reading result (step E1). Next, the third control unit 36 ​​measures the amount of color shift in the image formed on the target paper based on the read image data acquired in step E1 (step E2). In step E2, 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.

[0087] Next, the third control unit 36 ​​adjusts the correction timing and correction amount in the correction coefficient to suppress the speed difference between the detection result of the peripheral speed detection unit 39 and the actual peripheral speed of the intermediate transfer belt 342, based on the amount of color shift measured in step E2 (step E3). Next, the third control unit 36 ​​reflects the correction coefficient adjusted in step E3 into the peripheral speed correction table (step E4), and then terminates the fourth adjustment process.

[0088] The third control unit 36 ​​adjusts the peripheral speed correction table based on the amount of color shift in the image formed on the target paper by executing the fourth adjustment process. As a result, the third control unit 36 ​​can accurately correct the detection result of the peripheral speed detection unit 39 using the adjusted peripheral speed correction table in the subsequent encoder value correction process for the target paper in the print job. Therefore, the third control unit 36 ​​can suppress the occurrence of color misalignment by controlling the peripheral speed of the intermediate transfer belt 342 based on the detection result of the peripheral speed detection unit 39, which has been accurately corrected.

[0089] Returning to Figure 10, if the fourth adjustment process is set to disabled (step S14; NO), the third control unit 36 ​​proceeds to step S16 of the print control process.

[0090] Next, the third control unit 36 ​​determines whether or not the print job has been completed (step S16). If the print job is completed (step S16; YES), the third control unit 36 ​​terminates the print control process. On the other hand, if the print job is not completed (step S16: NO), the third control unit 36 ​​moves the print control process to step S4 and feeds the subsequent target paper for the print job.

[0091] (5. Other) The third control unit 36 ​​may perform the following processing in the second adjustment process described above. Specifically, the third control unit 36 ​​acquires environmental information within the image forming apparatus 1, such as measured temperature and humidity near the intermediate transfer unit. Next, based on the difference between the acquired environmental information and the reference environmental information, the third control unit 36 ​​adjusts the correction timing and correction amount in the correction coefficient to suppress the speed difference between the detection result of the peripheral speed detection unit 39 and the actual peripheral speed of the intermediate transfer belt 342. Next, the third control unit 36 ​​reflects the adjusted correction coefficient in the peripheral speed correction table. In this case, the third control unit 36 ​​corrects the detection result of the peripheral speed detection unit 39 based on environmental information during the encoder value correction process.

[0092] The third control unit 36 ​​may perform the following processing in the second adjustment process described above. Specifically, the third control unit 36 ​​obtains information on the width of the target paper from the received job setting information. Next, the third control unit 36 ​​adjusts the correction timing and correction amount in the correction coefficient to suppress the speed difference between the detection result of the peripheral speed detection unit 39 and the actual peripheral speed of the intermediate transfer belt 342, based on the difference between the width of the target paper and the width of the reference paper. Next, the third control unit 36 ​​reflects the adjusted correction coefficient in the peripheral speed correction table. In this case, the third control unit 36 ​​corrects the detection result of the peripheral speed detection unit 39 based on the width of the target paper during the encoder value correction process.

[0093] The third control unit 36 ​​may perform the following processing in the fourth adjustment process described above. Specifically, the third control unit 36 ​​adjusts the correction timing and correction amount in the correction coefficient to suppress the speed difference between the detection result of the peripheral speed detection unit 39 and the actual peripheral speed of the intermediate transfer belt 342, based on the difference between the amount of color shift measured in step E2 and the amount of color shift measured when the fourth adjustment process was performed in the past. Next, the third control unit 36 ​​reflects the adjusted correction coefficient in the peripheral speed correction table. In this case, the third control unit 36 ​​corrects the detection result of the peripheral speed detection unit 39 based on the change in the amount of color shift due to changes over time in the encoder value correction process for the subsequent target paper in the print job.

[0094] The third control unit 36 ​​may perform the following processing in the above-mentioned printing control processing. Specifically, the third control unit 36 ​​adjusts the correction timing and correction amount in the correction coefficient to suppress the speed difference between the detection result of the peripheral speed detection unit 39 and the actual peripheral speed of the intermediate transfer belt 342, based on the difference between the current mechanical characteristics of the components constituting the intermediate transfer unit and the mechanical characteristics during production (initial). Next, the third control unit 36 ​​reflects the adjusted correction coefficient in the peripheral speed correction table. In this case, the third control unit 36 ​​corrects the detection result of the peripheral speed detection unit 39 based on the mechanical characteristics of the components constituting the image forming apparatus 1 during the encoder value correction process.

[0095] (6. Effects) As described above, the image forming apparatus 1 according to this embodiment includes an intermediate transfer belt 342 that transfers multiple color images transferred from multiple image carriers (photoreceptor drums 341Y, 341M, 341C, 341K) onto paper. The image forming apparatus 1 according to this embodiment includes a speed detection unit (drive roller 345 and peripheral speed detection unit 39) that contacts the inner surface of the intermediate transfer belt 342 to detect the peripheral speed of the intermediate transfer belt 342. The image forming apparatus 1 according to this embodiment includes an acquisition unit (third control unit 36) that acquires paper characteristic information indicating the paper characteristics of the paper. The image forming apparatus 1 according to this embodiment includes a correction unit (third control unit 36) that corrects the detection result by the speed detection unit based on the paper characteristic information acquired by the acquisition unit. The image forming apparatus 1 according to this embodiment includes a determination unit (third control unit 36) that determines the amount of color shift correction based on the detection result from the speed detection unit which has been corrected by the correction unit. Therefore, the detection result of the peripheral speed detection unit 39 can be accurately corrected based on the paper characteristics information. This allows for precise correction of color misalignment in the image formed on the paper by controlling the peripheral speed of the intermediate transfer belt 342 based on the detection results of the precisely corrected peripheral speed detection unit 39.

[0096] In the image forming apparatus 1 according to this embodiment, the paper characteristics include at least one of the following: paper type, paper thickness, basis weight, and moisture content. Therefore, the detection result of the peripheral speed detection unit 39 can be accurately corrected based on at least one of the paper type, paper thickness, basis weight, and moisture content of the paper.

[0097] The image forming apparatus 1 according to this embodiment includes a media detection unit 22 that detects paper characteristics. The acquisition unit (third control unit 36) acquires the detection result from the media detection unit 22 as paper characteristic information. Therefore, paper characteristic information can be easily obtained.

[0098] In the image forming apparatus 1 according to this embodiment, the acquisition unit (third control unit 36) receives input of paper characteristic information. Therefore, paper characteristic information can be easily obtained.

[0099] In the image forming apparatus 1 according to this embodiment, the correction unit (third control unit 36) corrects the detection results by the speed detection unit (drive roller 345 and peripheral speed detection unit 39) based on environmental information indicating the environment inside the image forming apparatus 1. Therefore, the detection result of the peripheral speed detection unit 39 can be accurately corrected based on environmental information.

[0100] In the image forming apparatus 1 according to this embodiment, the correction unit (third control unit 36) corrects the detection results from the speed detection unit (drive roller 345 and peripheral speed detection unit 39) based on the width of the paper. Therefore, the detection result of the peripheral speed detection unit 39 can be accurately corrected based on the paper width.

[0101] In the image forming apparatus 1 according to this embodiment, the correction unit (third control unit 36) determines a correction value (correction timing and correction amount) to correct the detection result by the speed detection unit (drive roller 345 and peripheral speed detection unit 39) based on the detection result by the speed detection unit. Therefore, the detection result of the peripheral speed detection unit 39 can be corrected with high accuracy.

[0102] The image forming apparatus 1 according to this embodiment includes an image reading unit 42 that reads an image formed on a sheet of paper. The correction unit (third control unit 36) corrects the detection results from the speed detection unit (drive roller 345 and peripheral speed detection unit 39) based on the reading results from the image reading unit 42. Therefore, the detection result of the peripheral speed detection unit 39 can be accurately corrected based on the reading result of the image reading unit 42.

[0103] In the image forming apparatus 1 according to this embodiment, the correction unit (third control unit 36) corrects the detection results from the speed detection unit (drive roller 345 and peripheral speed detection unit 39) based on the mechanical characteristics of the components constituting the image forming apparatus 1. Therefore, the detection result of the peripheral speed detection unit 39 can be accurately corrected based on the mechanical properties of the components constituting the image forming apparatus 1.

[0104] In the image forming apparatus 1 according to this embodiment, the correction unit (third control unit 36) corrects the detection results by the speed detection unit (drive roller 345 and peripheral speed detection unit 39) based on the change in the amount of color shift due to changes over time. Therefore, the detection result of the peripheral speed detection unit 39 can be accurately corrected based on the change in the amount of color shift due to time.

[0105] 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.

[0106] 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.

[0107] In this embodiment, the image forming apparatus 1 is provided with a detection device 20 for detecting the physical properties of the paper, but it is not limited to this. The image forming apparatus 1 may not be provided with the detection device 20. In this case, the paper feed device 10 is provided with a detection unit for detecting the physical properties of the paper.

[0108] 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]

[0109] 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 Media 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 Tension Roller 345 Drive Roller 346 Opposing Roller 347 Fixing section 348 Reversal Path 349 Resist section 36. Third Control Unit (Acquisition Unit, Correction Unit, Determination Unit) 37 Memory section 38 Communications Department 39 Peripheral speed detection unit 40 Image reading device 41 Fourth Control Unit 42 Image reading unit 43 Conveying section 44 Paper output tray

Claims

1. An intermediate transfer belt that transfers images of multiple colors, transferred from multiple image carriers, onto paper, A speed detection unit that contacts the inner surface of the intermediate transfer belt to detect the peripheral speed of the intermediate transfer belt, An acquisition unit that acquires paper characteristic information indicating the paper characteristics of the aforementioned paper, A correction unit corrects the detection result by the speed detection unit based on the paper characteristic information acquired by the acquisition unit, A determination unit that determines the amount of color shift correction based on the detection result by the speed detection unit corrected by the correction unit, An image forming apparatus equipped with the following features.

2. The image forming apparatus according to claim 1, wherein the paper characteristics include at least one of the paper type, paper thickness, basis weight, and moisture content of the paper.

3. It includes a media detection unit that detects the aforementioned paper characteristics, The image forming apparatus according to claim 2, wherein the acquisition unit acquires the detection result by the media detection unit as the paper characteristic information.

4. The image forming apparatus according to claim 2, wherein the acquisition unit receives input of the paper characteristic information.

5. The image forming apparatus according to claim 1, wherein the correction unit corrects the detection result by the speed detection unit based on environmental information indicating the environment inside the image forming apparatus.

6. The image forming apparatus according to claim 1, wherein the correction unit corrects the detection result by the speed detection unit based on the width of the paper.

7. The image forming apparatus according to claim 1, wherein the correction unit determines a correction value to correct the detection result by the speed detection unit based on the detection result by the speed detection unit.

8. The system includes an image reading unit that reads an image formed on the aforementioned paper, The image forming apparatus according to claim 1, wherein the correction unit corrects the detection result by the speed detection unit based on the reading result by the image reading unit.

9. The image forming apparatus according to claim 1, wherein the correction unit corrects the detection result by the speed detection unit based on the mechanical characteristics of the components constituting the image forming apparatus.

10. The image forming apparatus according to claim 1, wherein the correction unit corrects the detection result by the speed detection unit based on the change in the amount of color shift due to changes over time.

11. An intermediate transfer belt that transfers images of multiple colors, transferred from multiple image carriers, onto paper, A speed detection unit that contacts the inner surface of the intermediate transfer belt to detect the peripheral speed of the intermediate transfer belt, A computer for an image forming apparatus equipped with, An acquisition unit that acquires paper characteristic information indicating the paper characteristics of the aforementioned paper. A correction unit corrects the detection result by the speed detection unit based on the paper characteristic information acquired by the acquisition unit. A determination unit that determines the amount of color shift correction based on the detection result by the speed detection unit corrected by the correction unit, A program that makes it function as such.

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