JP2021140117A - Image forming apparatus and method for correcting image forming position - Google Patents

Abstract

To provide an image forming apparatus that can prevent positional shift of an image.SOLUTION: An image forming apparatus is configured comprising: an image forming unit that forms an image on a recording material; a reading unit that reads the recording material on which the image is formed by the image forming unit; and a control unit. The control unit has a printing rate calculation unit that determines a printing rate for each area set in advance on the recording material, a positional shift amount calculation unit that acquires, from a read image acquired by the reading unit, the amount of positional shift of the image formed on the recording material, a storage unit that stores the amount of positional shift in correspondence with the combinations of the areas and printing rates, and a correction unit that, according to the amount of positional shift, instructs correction of the formation position of the image to the image forming unit.SELECTED DRAWING: Figure 3

Description

The present invention relates to an image forming apparatus and a method of correcting an image forming position.

When image formation is performed by an image forming apparatus, the recording material may shrink due to the heat applied during image formation. Further, when an image is formed on both sides of the recording material, the transport path at the time of image formation differs between the front surface and the back surface. As a result, when images are formed on both sides of the recording material, the positions of the images may shift between the front surface and the back surface. In addition, the amount of image misalignment between the front and back surfaces (hereinafter referred to as position) depends on various printing conditions such as the type, size, basis weight, fixing temperature, temperature (inside and outside the machine), and humidity of the recording material. The amount of deviation) is different. Therefore, in the conventional image forming apparatus, the image forming position in the image forming portion is adjusted according to various printing conditions.

However, the misalignment of the formed image is affected not only by the above-mentioned various printing conditions but also by the characteristics of the formed image. For example, the amount of misalignment differs between the case where the image is formed under the condition of low printing rate and the case where the image is formed under the condition of high printing rate. This is because image formation with a high printing rate and a low printing rate differs in the shrinkage rate of the recording material due to the heat of the transport conditions and the fixing temperature. In this way, when images having different characteristics are formed on the recording material, misalignment occurs due to the difference in image characteristics.

An image forming apparatus has been proposed that measures the amount of misalignment according to the printing rate of the formed image and corrects the misalignment of the formed image with respect to the misalignment caused by the image characteristics (see, for example, Patent Document 1). In this image forming apparatus, a correction coefficient of an image forming position is set according to a printing rate. Therefore, the position of the formed image is corrected according to the printing rate, and the misalignment of the formed image is suppressed.

JP-A-2019-74586

In the image forming apparatus described in Patent Document 1 described above, correction is performed according to the printing rate of the entire recording material. However, the printing rate of the image actually formed on the recording material differs depending on the area of the recording material. Since the shrinkage rate of the recording material differs depending on the printing rate, the shrinkage rate changes for each region according to the printing rate. Therefore, it is not possible to sufficiently suppress the misalignment of the image simply by correcting the image formation position based on the printing rate of the entire recording material.

In order to solve the above-mentioned problems, the present invention provides an image forming apparatus capable of suppressing image misalignment and a method for correcting an image forming position.

The image forming apparatus of the present invention includes an image forming unit that forms an image on a recording material, a reading unit that reads a recording material on which an image is formed by the image forming unit, and a control unit. The control unit has a print rate calculation unit that calculates the print rate for each area preset in the recording material, and a position shift amount that acquires the position shift amount of the image formed on the recording material from the read image acquired by the reading unit. The calculation unit, the storage unit that stores the amount of misalignment corresponding to the combination of the area and the print rate, and the image forming unit that corrects the image formation position with respect to the image forming unit according to the amount of misalignment. It has a correction unit for instructing.

Further, the image forming position correction method is an image forming position correction method by the image forming apparatus, in which the reading unit reads the image formed on the recording material and the control unit performs a preset area on the recording material. A process of obtaining the print rate of each image, a process of acquiring the amount of image misalignment from the image read by the control unit, and a process of storing the amount of misalignment in the control unit corresponding to the area and the print rate. The control unit has a process of determining whether or not the amount of misalignment exceeds the threshold value, and the control unit has a process of instructing the image forming unit to correct the image forming position.

According to the present invention, it is possible to provide an image forming apparatus capable of suppressing image misalignment and a method for correcting an image forming position.

It is a figure which shows the schematic structure of the image forming apparatus. It is a system block diagram which shows the structure of an image forming apparatus. It is a functional block diagram which shows the structure of the control part of an image forming apparatus. It is a figure which shows the example of the image data received by the image receiving part of a control part. It is a figure which shows the combination of the print rate and the table of the misalignment amount stored in a storage part. It is a figure which shows the table of the combination of the print rate and the correction amount stored in the storage part. It is a flowchart which shows the correction method of the image formation position. It is a flowchart which shows the correction method of the image formation position.

Hereinafter, examples of embodiments for carrying out the present invention will be described, but the present invention is not limited to the following examples.
<1. Image forming device>
A specific embodiment of the image forming apparatus will be described.
FIG. 1 shows a schematic configuration diagram of the image forming apparatus of this embodiment. The image forming apparatus 1 shown in FIG. 1 includes a paper feeding device 40, an image forming apparatus main body 10, a reading device 20, and a post-processing device 30.

The paper feed device 40 includes a plurality of paper feed trays. Recording materials are stored in each paper feed tray. The recording material stored in the paper feed tray is supplied to the image forming apparatus main body 10.

In the image forming apparatus main body 10, a main body feeding unit 12 having a plurality of paper feeding trays is arranged on the lower side inside the housing, and recording materials are stored in each paper feeding tray. Further, a transport path 13 is provided in the housing of the image forming apparatus main body 10, and the recording material supplied from the paper feed device 40 or the main body paper feed unit 12 is conveyed downstream along the transport path 13. NS. The transport path 13 is provided with an image forming unit 11 for forming an image on the recording material.

The image forming unit 11 has a photoconductor 11a for each color (cyan, magenta, yellow, black). A charger, an exposure device, a developing device, a cleaning unit, and the like (not shown) are provided around the photoconductor 11a. Further, the image forming unit 11 has an intermediate transfer belt 11b at a position where it comes into contact with the photoconductor 11a for each color. The intermediate transfer belt 11b comes into contact with the recording material on the transport path 13 at the secondary transfer portion 11c provided in the middle of the intermediate transfer belt 11b. Further, in the transport path 13, the fixing portion 11d is provided at a position downstream of the secondary transfer portion 11c.

When the image forming unit 11 forms an image on the recording material, the photoconductor 11a is uniformly charged by the charger, and then the photoconductor 11a is irradiated with laser light from the exposure apparatus. As a result, a latent image is formed on the photoconductor 11a. The latent image on the photoconductor 11a is developed by a developing device to become a toner image. Then, the toner image on the photoconductor 11a is transferred to the intermediate transfer belt 11b. The image on the intermediate transfer belt 11b is transferred to the recording material at the secondary transfer unit 11c. After the image is transferred, the recording material is conveyed along the conveying path 13, and the fixing portion 11d fixes the image.

Further, in the transport path 13, the reverse transport path 15 is branched on the downstream side of the fixing portion 11d. In the middle of the reversing transport path 15, the downstream transport path 16 branches and is connected to the transport path 13 on the downstream side of the branch point of the reverse transport path 15. In the reverse transport path 15, the evacuation transport path 14 branches on the downstream side of the point where the downstream transport path 16 branches. The downstream end side of the inverted transport path 15 joins the transport path 13 at a position on the upstream side of the image forming portion 11. The transport path 13 is connected to the transport path 23 of the reading device 20 connected to the subsequent stage in the straight direction.

When the image is formed on one side of the recording material, the recording material after the image formation is conveyed straight through the conveying path 13 and conveyed to the conveying path 23 of the reading device 20.
When switching the face surface of the recording material after the image is formed, the recording material is transported to the reversing transport path 15, the recording material is transported beyond the branch point of the downstream transport path 16, and then the reverse transport path 15 is transported in the opposite direction. , It is transported to the downstream side of the transport path 13 through the downstream transport path 16.
When the recording material is inverted to form an image on the back surface of the recording material, the recording material is sent from the transport path 13 to the reverse transport path 15, sent to the evacuation transport path 14, and then the front and back of the recording material are changed to form the reverse transport path. It is sent to the downstream side of 15, and is recirculated to the transport path 13. After that, the image forming unit 11 forms an image on the back surface side of the recording material.

The image forming apparatus main body 10 is provided with an operation display unit 141 on the upper part of the housing. The operation display unit 141 may be configured such that the operation unit and the display unit are integrated. The operation display unit 141 has a group of operation keys such as an LCD and a numeric keypad provided with a touch panel, and can display information and accept operation input. The operation display unit 141 may not be integrated with the operation unit and the display unit. For example, the operation unit may be configured by a mouse, a tablet terminal, or the like. Further, the LCD may be movable.

Further, the image forming apparatus main body 10 has a control unit 100. The control unit 100 controls the entire image forming apparatus 1, and is composed of a CPU, a memory, and the like. The control unit 100 includes a storage unit in which the print rate for each area and the amount of misalignment for each area corresponding to the print rate are stored. Further, the control unit 100 may include a communication unit, an IO, or the like that communicates with the reading unit when acquiring the image reading result.

An automatic document feeding device (ADF) 18 is provided on the upper part of the housing of the image forming apparatus main body 10. The automatic document feeding device 18 automatically feeds the document set on the document mounting table. The document fed by the automatic document feeding device 18 is transported along the transport path 17, and is transported to the transport path 23 of the reading device 20 described later. Then, it is read by the reading units 24 and 25 of the reading device 20.

The reading device 20 has a transport path 23, and the recording material introduced from the image forming apparatus main body 10 is transported along the transport path 23. The downstream side of the transport path 23 is connected to the post-processing device 30 in the subsequent stage.
Near the middle of the transport path 23, a reading unit 24 for reading an image on the lower surface of the recording material transported by the transport path 23 and a reading unit 25 for reading an image on the upper surface of the recording material are provided. The reading unit 24 is located upstream of the reading unit 25.

The reading units 24 and 25 are composed of a CCD sensor, a CMOS sensor, or the like. The reading units 24 and 25 can read the recording material transported in the transport path 23 over the entire direction orthogonal to the transport direction. The reading results read by the reading units 24 and 25 are transmitted to the control unit 100. When images are formed on both sides of the recording material, the control unit 100 can calculate the amount of misalignment according to the misalignment of the front and back images. Further, the control unit 100 can calculate the print rate for each area of the recording material from the read image.

When calculating the amount of misalignment of the front and back images, it is preferable to use a recording material printed with a chart image such as a grid. In the chart image, the amount of deviation between the front and back images can be easily grasped. In this embodiment, the front-back deviation correction amount of the front-back image can be acquired in advance, stored in a storage unit or the like, and can be called and provided as needed.

The image forming apparatus 1 has a configuration in which the reading apparatus 20 reads the images of the front and back surfaces of the recording material by the two reading units 24 and 25. The image forming apparatus 1 may be configured to read the images of the front and back surfaces of the recording material by one reading unit 25 by providing an inversion transfer path in front of and behind the reading unit 25 and performing reverse transfer of the recording material.

The aftertreatment device 30 includes a transport path 33 capable of transporting the recording material. The transport path 33 transports the recording material introduced from the reading device 20 to the downstream side. A post-processing unit 34 for post-processing the recording material is provided in the middle of the transport path 33. The post-processing unit 34 executes a predetermined post-processing. As the post-processing, for example, the staple processing and the punch processing perform processing including folding, for example, processing such as inner tri-folding, saddle stitching, Z-folding, Kannon folding, and four-folding.

The transport path 33 branches in the middle and is connected to the first paper ejection unit 31 and the second paper ejection unit 32. The recording material that has passed through the post-processing unit 34 is discharged to the second paper ejection unit 32, and the recording material that has not been post-processed is discharged to the first paper ejection unit 31. The recording material that is not post-processed may be discharged to the second paper ejection unit 32.

In this embodiment, the image forming apparatus 1 is composed of the paper feeding device 40, the image forming apparatus main body 10, the reading device 20, and the post-processing apparatus 30, but the configuration of the image forming apparatus is limited to the above configuration. It's not a thing. For example, the image forming apparatus may be configured by the image forming apparatus main body 10 and the reading apparatus 20. Further, even if the image forming apparatus is composed of only the image forming apparatus main body 10 and the image forming apparatus main body 10 is provided with various functions such as a reading device 20, a post-processing device 30, and a paper feeding device 40. good.

[Configuration of image forming apparatus]
FIG. 2 shows a system block diagram of the image forming apparatus 1.
The image forming apparatus 1 includes a main body feeding unit 12, an operation display unit 141, an image forming unit 11, a control unit 100, a storage unit 140, and a communication I / F (Interface) 150. Each part in the image forming apparatus 1 is connected via a bus.

The control unit 100 includes a CPU (Central Processing Unit) 110, a ROM (Read Only Memory) 120, and a RAM (Random Access Memory) 130.
The CPU 110, ROM 120, and RAM 130 are used as an example of a computer that controls the operation of each part in the image forming apparatus 1. For example, the CPU 110 controls the image forming process (printing operation) of the image forming unit 11 based on the user's printing instruction performed through the operation display unit 141, controls the supply of the recording material by the main body feeding unit 12, and controls the image. Performs data objectification processing, etc. Further, the CPU 110 receives the job setting by the user, the registration of the post-processing function using the post-processing device 30, and the like from the operation display unit 141.
The ROM 120 is used as an example of a non-volatile memory, and stores programs, data, and the like executed and referenced by the CPU 110.
The RAM 130 is used as an example of a volatile memory, and temporarily stores information (data) required for each process performed by the CPU 110.

The storage unit 140 is composed of, for example, a storage device such as an HDD (Hard Disk Drive), and stores a program for the CPU 110 to control each unit, a program such as an OS (Operating System), a controller, and data. Further, the storage unit 140 stores image information read by the reading units 24 and 25, a print rate for each area, and a data table or the like in which the amount of misalignment for each area corresponding to the print rate is stored. .. A part of the program and data stored in the storage unit 140 may be stored in the ROM 120. The storage unit 140 is used as an example of a computer-readable non-transient recording medium that stores a program executed by the CPU 110. The computer-readable non-transient recording medium in which the program executed by the image forming apparatus 1 is stored is not limited to the HDD, and is, for example, an SSD (Solid State Drive), a CD-ROM, or a DVD-ROM. It may be a recording medium such as.
The communication I / F 150 is composed of a NIC (Network Interface Card), a modem, or the like, establishes a connection between the image forming apparatus 1 and a PC terminal (not shown), and executes transmission / reception of various data.

[Control unit configuration]
FIG. 3 shows a functional block diagram of the configuration of the control unit 100 of the image forming apparatus 1. The control unit 100 includes an image receiving unit 101, a misalignment amount calculation unit 102, a print rate calculation unit 103, a storage processing unit 104, a determination unit 105, a correction unit 106, and an input image processing unit 107.

The image receiving unit 101 receives the image data read by the reading units 24 and 25 of the image forming apparatus 1. An example of the image data received by the image receiving unit 101 is shown in FIG. In FIG. 4, the image 50 based on the image data input by the user on the recording material S and the reference images 51, 52, 53, 54, 55, 56 for measuring the image formation position on the recording material S, 57 and 58 are formed. In FIG. 4, in the margin position of the recording material S, the reference image 51 is on the upper left side, the reference image 52 is on the upper center, the reference image 53 is on the upper right side, the reference image 54 is on the left center, the reference image 55 is on the right center, and the lower left side. A reference image 56 is formed, a reference image 57 is formed in the lower center, and a reference image 58 is formed in the lower right side. Further, as reference images 51, 52, 53, 54, 55, 56, 57, 58, cross-shaped register marks for image position measurement are formed.

In the example shown in FIG. 4, four regions of the upper left region S1, the upper right region S2, the lower left region S3, and the lower right region S4 are preset as the regions of the recording material S. The number of areas set in the recording material S is not particularly limited. The area of the recording material S may be set to 2 or more, and preferably 4 or more.
Further, in FIG. 4, only the image formed on one surface (front surface) side of the recording material S is shown, but similarly, the image 50 based on the image data and the recording are also shown on the other surface (back surface) side. Reference images 51, 52, 53, 54, 55, 56, 57, 58 for measuring the image formation position on the material S are formed. The front surface and the back surface of the recording material S are such that the surface on which the image is formed first in the image forming apparatus 1 is the front surface and the surface formed later is the back surface.

In FIG. 4, the boundary of each region S1, S2, S3, S4 set in the recording material S is shown by a broken line. This broken line is not actually formed as an image. Further, the characters "large", "medium", and "small" shown in FIG. 4 are also symbols indicating the classification of the printing rate in each of the areas S1, S2, S3, and S4, which will be described later, and are actually formed as an image. It has not been.

Further, the misalignment amount calculation unit 102 shown in FIG. 3 calculates the misalignment amount of the image from the image data received by the image receiving unit 101.
For example, the misalignment amount calculation unit 102 measures the distance from the end of the recording material S to the feature points of the reference images 51, 52, 53, 54, 55, 56, 57, 58. As a result, the position where the image is formed on the recording material S is calculated. In the example shown in FIG. 4, the image formation position can be measured by measuring the distance from the upper end of the recording material S to the center (intersection) of the crosses of the reference images 51, 52, and 53. Similarly, the distance from the left end of the recording material S to the reference images 51, 54, 56, the distance from the right end to the reference images 53, 55, 58, and the distance from the lower end to the reference images 56, 57, By measuring the distance to 58, the image formation position can be measured.
Further, the misalignment amount calculation unit 102 also looks at the image on the back surface side of the recording material S from the end of the recording material S to the feature points of the reference images 51, 52, 53, 54, 55, 56, 57, 58. Measure the distance to. As a result, the position where the image is formed on the back surface side of the recording material S is calculated.
Further, the misalignment amount calculation unit 102 may calculate the misalignment amount from the measurement result of one recording material S. Further, an average value may be calculated from the measurement results of the plurality of recording materials S, and this average value may be calculated as the amount of misalignment.

In the example shown in FIG. 4, the image formation position can be measured by measuring the distance from the upper end of the recording material S to the center (intersection) of the crosses of the reference images 51, 52, and 53. Similarly, the distance from the left end of the recording material S to the reference images 51, 54, 56, the distance from the right end to the reference images 53, 55, 58, and the distance from the lower end to the reference images 56, 57, By measuring the distance to 58, the image formation position can be measured. The end of the recording material S, which is the reference for measurement, may be either the upper end or the lower end, and either the right end or the left end.

Then, the formed position of the image on the front surface side on the measured recording material S and the formed position of the image on the back surface side are compared. As a result, the amount of misalignment between the image formed on the front surface side of the recording material S and the image formed on the back surface side is calculated. It is preferable to compare the image formation positions for each reference image. By performing this for each reference image, it is possible to quantify the deformation state and the positional deviation of the entire image due to the deformation of the recording material S.
Further, the amount of misalignment may be calculated by comparing the formation positions of the images on the front surface side and the back surface side with the image positions in the input image data. By comparing the positions of the formed images with reference to the image positions in the input image data, it is possible to calculate the amount of misalignment of the images formed on the front surface side and the back surface side.

In the example shown in FIG. 4, the formation positions of the reference images 51, 52, 53, 54, 55, 56, 57, 58 are preset with respect to the recording material S. The number of reference images set in the recording material S is not particularly limited. It is preferable that there are a plurality of reference images set in the recording material S. Further, the number of reference images provided on the recording material S is one or more in each region, and it is preferable that a plurality of reference images are provided in each region. For example, in the example shown in FIG. 4, three reference images of reference images 51, 52, and 54 are formed in the region S1. Similarly, the reference images 52, 53, 55 are formed in the region S2, the reference images 54, 56, 57 are formed in the region S3, and the reference images 55, 57, 58 are formed in the region S4, respectively.

Further, as the reference image, instead of the reference images 51, 52, 53, 54, 55, 56, 57, 58 formed in the margin shown in FIG. 4, the feature points in the image 50 in the image forming region are used as the reference image. May be good. For example, the end portion of the line portion in the image 50, the intersection, the corner portion, or the like may be used as a feature point of the reference image. Even when the image 50 is used as the reference image, the number of reference images in each region may be one or a plurality. The reference images 51, 52, 53, 54, 55, 56, 57, 58 formed in the above margin and the feature points in the image 50 may be used facing each other.

The input image processing unit 107 converts the image data input by the user or the like into image data for image formation by the image forming unit 11. For example, the input image data is RIP-converted to create RIP data. Further, the image forming engine or the like generates image forming data (data immediately before being input to the exposure apparatus) to be actually input to the exposure apparatus of the image forming unit 11 based on the RIP data.

The print rate calculation unit 103 calculates the print rate for each area of the recording material S from the image data converted into RIP data by the input image processing unit 107. Further, the print rate calculation unit 103 calculates the print rate for each area of the recording material S from the image data read by the reading units 24 and 25. When calculating the print rate from the image data input by the user or the like, for example, the print rate for each preset area is calculated based on the RIP data and the image image data processed by the input image processing unit 107. .. When calculating the print rate from the scanned image data, the print rate for each preset area is calculated based on the image data acquired by the image receiving unit 101.

The print rate calculation unit 103 may calculate the print rate of each area on both sides of the recording material S, or may calculate the print rate of each area only on the front surface side. The recording material S forms an image on the surface, and when it first passes through the fixing portion 11d, a large shrinkage due to heat occurs. On the other hand, when the image is formed on the back surface side and then passes through the fixing portion 11d for the second time, the shrinkage due to heat is small. That is, the misalignment of the image also occurs significantly in the image on the surface side that first passes through the fixing portion 11d. Positional deviation is unlikely to occur in the image on the back side. Therefore, the print rate calculation unit 103 may calculate the print rate only in each region of the surface of the recording material S.

Further, the print rate calculation unit 103 may calculate the print rate from 0 to 100% and then manage the print rate according to the print rate classification set for each predetermined range. FIG. 4 shows an example in which the print rate of each area is managed by three print rate categories of “large”, “medium”, and “small”. For example, when the calculated print rate is less than 30%, the print rate category is managed as "small". When the calculated print rate is 30% or more and less than 60%, the print rate category is managed as "medium". When the calculated print rate is 60% or more, the print rate category is managed as "large".
By dividing and managing the print rate for each preset area, it is possible to prevent an increase in the amount of data managed by the storage processing unit 104. Therefore, by setting the print rate classification, it becomes easy to correspond to the amount of misalignment and to determine the correction process. Setting the print rate classification The range of the print rate and the number of divisions are not particularly limited. By setting the number of print rate divisions to about 2 to 4, it is possible to improve the accuracy of misalignment correction while suppressing the amount of data.

The storage processing unit 104 stores in the storage unit 140 the print rate calculated by the print rate calculation unit 103 and the position shift amount calculated by the position shift amount calculation unit 102. For example, the print rate and the amount of misalignment are stored as a table corresponding to each area set in the recording material S. FIG. 5 shows an example of a table in which the amount of misalignment is matched for each combination of printing rates.

In the table shown in FIG. 5, the print rates of the areas S1, S2, S3, and S4 are managed as a combination of the print rate categories "large", "medium", and "small" in the left column. Therefore, when the area is set to 4 and the print rate division is set to 3 as shown in FIG. 4, 81 combinations are set as the print rate. In the example shown in FIG. 4, the print rate classification of the upper left area S1 is "large", the print rate classification of the upper right area S2 is "medium", the print rate classification of the lower left area S3 is "medium", and the print rate of the lower right area S4 is "medium". Since the classification is "small", No. 5 in FIG. It corresponds to 15 combinations.

Further, in the table shown in FIG. 5, the amount of misalignment is managed in the column on the right side. The amount of misalignment is managed according to the combination of print rate classifications in each area. Further, the misalignment amount is managed by a combination (xn, yn) of the misalignment amount "xn" in the x direction (main scanning direction) and the misalignment amount "yn" in the y direction (secondary scanning direction). In addition, n corresponds to the combination "No." in FIG.
When calculating the misalignment amount of each region using a plurality of reference images, the average value or the maximum value of the misalignment amount of each reference image is managed as the misalignment amount.

The table managed by the storage processing unit 104 is updated every time the misalignment amount calculation unit 102 calculates the misalignment amount of the image. For example, when an image is formed by the image forming apparatus 1, the printing rate calculating unit 103 first calculates the printing rate of each area. Then, from the calculated printing rate, the combination of the printing rates for each area of the recording material S is determined. Further, the result of image formation is read, and the misalignment amount calculation unit 102 calculates the misalignment amount of the image in each region. Then, the table of the combination of the print rates of the corresponding areas is updated by the calculated misalignment amount.

In addition, the storage processing unit 104 stores the threshold value of the amount of misalignment that serves as a reference for correction. The threshold is preset. The threshold value may be set corresponding to the combination of the print rate divisions of each area, or may be set uniformly regardless of the print rate. Further, the user may operate the operation display unit 141 to arbitrarily set the threshold value.

The determination unit 105 determines whether or not to correct the image formation position in the image formation unit 11. The determination in the determination unit 105 is different depending on whether the image formation position is corrected by the initial adjustment or the image formation position is corrected by the change with time.

For example, in the case of initial adjustment, the threshold value of the amount of misalignment is set to 0, or the minimum value allowed by the image forming apparatus 1 (that is, 0 or substantially 0). Therefore, when the calculated misalignment amount is not 0, it is determined to correct the image formation position. That is, in the case of the initial adjustment, the determination unit 105 corrects the image formation positions on the front surface side and the back surface side of the recording material so that the misalignment amount becomes substantially 0 regardless of the magnitude of the misalignment amount. To determine to execute.

On the other hand, in the case of a change with time, when the magnitude of the amount of misalignment exceeds the threshold value stored in the storage processing unit 104, the image formation positions on the front surface side and the back surface side of the recording material are corrected. Judge to. At this time, the determination unit 105 determines to execute the correction when the misalignment amount of any one region exceeds the threshold value. Alternatively, it may be determined to execute the correction when the amount of misalignment of all the regions exceeds the threshold value.

The correction unit 106 instructs the image forming unit 11 to correct the image forming position according to the determination result of the determination unit 105. In the case of initial adjustment, the correction unit 106 instructs the image forming unit 11 to correct the image forming position so that the amount of misalignment becomes substantially zero. In the case of a change with time, the image forming unit 11 is instructed to correct the image forming position so that the amount of misalignment becomes substantially 0 or the amount of misalignment becomes equal to or less than the threshold value.
Further, the correction unit 106 calculates the amount of misalignment from the measurement result of one recording material S, and based on the calculated amount of misalignment (for example, so that the amount of misalignment becomes 0), corrects the value. You may set it. Further, the average value of the misalignment amount is calculated from the measurement results of the plurality of recording materials S, and the correction value is set based on the average misalignment amount (for example, so that the average misalignment amount becomes 0). You may.

For example, the correction unit 106 calculates the correction amount of the image formation position from the calculated position shift amount. The correction amount is calculated for each area according to the combination of the print rates of each area. Then, the correction unit 106 instructs the image formation unit 11 to correct the image formation position at the time of the next image formation based on the calculated correction amount. The image forming unit 11 corrects the image forming position according to the instructed correction amount.
The correction unit 106 may store the calculated correction amount in the storage processing unit 104 in correspondence with the combination of the print rates of each area. FIG. 6 shows an example of a table of correction amounts stored in the storage processing unit 104 corresponding to the combination of printing rates. In the table shown in FIG. 6, the combination of printing rates of each area is managed in the left column. Further, in the column on the right side, the correction amount of the image formation position corresponding to the combination of the print rates of each area is managed. The image forming unit 11 can perform image forming by correcting the forming position based on the correction amount of the table stored in the storage processing unit 104.

[Image formation position correction method (1)]
Next, a method of correcting the image forming position using the image forming apparatus 1 will be described. FIG. 7 shows a flowchart of a method for correcting the image formation position. The flowchart shown in FIG. 7 is a method of correcting an image formation position, which calculates a print rate of each area from image data input by a user.

First, the user inputs image data into the image forming apparatus 1 (step S1). Next, RIP processing is performed on the image data input by the input image processing unit 107 (step S2). Further, if necessary, image data for actually inputting to the exposure apparatus of the image forming unit 11 is generated from the RIP data.

The print rate calculation unit 103 calculates the print rate based on the RIP-processed image data and the like (step S3). The printing rate is calculated for each area preset in the recording material. Further, the print rate calculation unit 103 obtains a print rate category in which the print rate of each area is set for each predetermined range, if necessary. The print rate calculation unit 103 may calculate the print rate of each area based on the image image data input to the exposure apparatus instead of the RIP-processed image data.

The storage processing unit 104 stores the print rate of each area calculated by the print rate calculation unit 103 (step S4). When the print rate is managed as the print rate category, the storage processing unit 104 stores the print rate of each area in the print rate category.

Next, the image forming unit 11 forms an image based on the image data input by the user (step S5).
After image formation, the reading units 24 and 25 read the image formed on the recording material and transmit the read image data to the image receiving unit 101 (step S6). When an image is formed on both sides of the recording material, the recording material and the formed image are read by the reading units 24 and 25 after the image is formed on both sides. In addition, image formation and reading may be performed on each side.

The misalignment amount calculation unit 102 calculates the misalignment amount of the formed image based on the read image data received by the image receiving unit 101 (step S7). First, the misalignment amount calculation unit 102 acquires the positions of the reference images on the front surface side and the back surface side formed on the recording material from the read image data. Then, the positions (x, y) of each reference image are obtained by obtaining the distance between the position of each reference image and the end portion of the recording material on the front surface side and the back surface side. Then, the position of each reference image formed on the front surface side of the recording material is compared with the position of each reference image formed on the back surface side corresponding to the position, and the difference is calculated. As a result, the amount of misalignment of the formed image is calculated. The amount of misalignment is calculated for each area of the recording material.
At this time, the misalignment amount calculation unit 102 may calculate the misalignment amount from the measurement results of one recording material S, calculate the average value from the measurement results of the plurality of recording materials S, and calculate the average value. May be calculated as the amount of misalignment

Next, the storage processing unit 104 stores the misalignment amount calculated by the misalignment amount calculation unit 102 (step S8). The storage processing unit 104 stores the amount of misalignment corresponding to the combination of print rates in each area. As a result, the amount of misalignment stored in the storage processing unit 104 corresponding to the combination of print rates in each area is updated.

Next, the determination unit 105 determines whether or not the executed image formation is performed as the initial adjustment of the image forming apparatus 1 (step S9). The initial adjustment is performed by the user or the like in advance using the operation display unit 141 or the like to switch to a mode for setting the image forming apparatus 1 as the initial adjustment at the time of image formation. Therefore, the determination unit 105 determines whether or not the image formation has been performed as the initial adjustment by confirming the mode at the time of image formation.

When the image formation is not the initial adjustment (NO in step S9), the determination unit 105 determines whether or not the amount of misalignment corresponding to the combination of print rates stored in the storage processing unit 104 exceeds the threshold value. (Step S10).

When the image formation is the initial adjustment (YES in step S9) or when the amount of misalignment exceeds the threshold value (YES in step S10), the correction unit 106 instructs the image formation unit 11 to correct the image formation position. (Step S11). The image forming unit 11 adjusts the image forming position according to the instruction of the correction unit 106. At this time, the correction unit 106 calculates the amount of misalignment from the measurement result of one recording material S, and forms an image based on the calculated amount of misalignment (for example, so that the amount of misalignment becomes 0). A correction value may be instructed to the unit 11. Further, the average value of the misalignment amount is calculated from the measurement results of the plurality of recording materials S, and the image forming unit is based on the average misalignment amount (for example, so that the average misalignment amount becomes 0). A correction value may be instructed for 11.
Further, after instructing the image forming unit 11 to correct the image forming position, the correction unit 106 may store the correction amount in the table shown in FIG. 6 as necessary. The correction amount is stored for each area corresponding to the combination of the print rates of each area. Then, after the correction of the image formation position, the formation position may be corrected and the image is formed based on the correction amount stored for each combination of the print rates of each area.

After instructing the correction of the image formation position, the process according to this flowchart is terminated. If the amount of misalignment does not exceed the threshold value (NO in step S10), the process according to this flowchart ends.

By performing the above processing, the print rate and the amount of misalignment of the formed image are calculated for each area set in the recording material, and the amount of misalignment according to the combination of the print rates of each area is managed. be able to. As a result, it is possible to acquire the amount of misalignment according to the printing rate for each area, not for the entire recording material, and to correct the amount of misalignment for each area. Therefore, even when the recording material is deformed due to fixing heat or the like, it is possible to correct the image formation position with higher accuracy.

[Image formation position correction method (2)]
Next, a method of correcting the image formation position, which calculates the print rate of each region from the scanned image data after image formation, will be described. FIG. 8 shows a flowchart of a method for correcting the image formation position. The following processing is the same as the flowchart shown in FIG. 7 above, except that the processing for calculating the printing rate and the execution order of each processing are different. Therefore, in the following description, detailed description of each processing content will be omitted except for processing different from the flowchart shown in FIG. 7 described above.

First, the user inputs image data into the image forming apparatus 1 (step S20). Next, RIP processing is performed on the image data input by the input image processing unit 107 (step S21).
Next, the image forming unit 11 forms an image based on the image data input by the user (step S22).
After image formation, the reading units 24 and 25 read the recording material and the image formed on the recording material, and transmit the read image data to the image receiving unit 101 (step S23).

Next, the print rate calculation unit 103 calculates the print rate based on the read image data received by the image receiving unit 101 (step S24).
Next, the misalignment amount calculation unit 102 calculates the misalignment amount of the formed image based on the read image data received by the image receiving unit 101 (step S25).
The storage processing unit 104 stores the print rate and the misalignment amount calculated by the misalignment amount calculation unit 102 (step S26).

Next, the determination unit 105 determines whether or not the image formation performed is performed as the initial adjustment of the image forming apparatus 1 (step S27).
When the image formation is not the initial adjustment (NO in step S27), the determination unit 105 determines whether or not the amount of misalignment corresponding to the combination of print rates stored in the storage processing unit 104 exceeds the threshold value. (Step S28).
When the image formation is the initial adjustment (YES in step S27) or when the amount of misalignment exceeds the threshold value (YES in step S28), the correction unit 106 instructs the image formation unit 11 to correct the image formation position. (Step S29). The image forming unit 11 adjusts the image forming position according to the instruction of the correction unit 106.
After instructing the correction of the image formation position, the process according to this flowchart is terminated. If the amount of misalignment does not exceed the threshold value (NO in step S28), the process according to this flowchart ends.
By performing the above processing, the print rate can be calculated from the scanned image data, and the amount of misalignment according to the combination of the print rates in each area can be managed. Then, even when the recording material is deformed due to fixing or the like, it is possible to correct the image formation position with higher accuracy.

The present invention is not limited to the configuration described in the above-described embodiment, and various modifications and changes can be made without departing from the configuration of the present invention.

1 Image forming device, 10 Image forming device main body, 11 Image forming part, 11a Photoreceptor, 11b Intermediate transfer belt, 11c Secondary transfer part, 11d Fixing part, 12 Paper feeding part, 13, 17, 23, 33 Transport path, 14 Evacuation transport path, 15 Reverse transport path, 16 Downstream transport path, 18 Automatic document feeder, 20 Reader, 24, 25 Reader, 30 Post-processing device, 31 First paper discharge section, 32 Second paper discharge section , 34 Post-processing unit, 40 Paper feed device, 50 images, 51, 52, 53, 54, 55, 56, 57, 58 Reference image, 100 control unit, 101 image receiving unit, 102 misalignment amount calculation unit, 103 printing Rate calculation unit, 104 storage processing unit, 105 judgment unit, 106 correction unit, 107 input image processing unit, 110 CPU, 120 ROM, 130 RAM, 140 storage unit, 141 operation display unit, S1 upper left area, S2 upper right area, S3 Lower left area, S4 Lower right area

Claims (11)

An image forming part that forms an image on the recording material,
A reading unit that reads the recording material on which an image is formed by the image forming unit,
With a control unit
The control unit
A print rate calculation unit that obtains a print rate for each area preset in the recording material, and a print rate calculation unit.
A position shift amount calculation unit that acquires the position shift amount of the image formed on the recording material from the read image acquired by the reading unit, and
A storage unit that stores the amount of misalignment in correspondence with the combination of the area and the printing rate, and
An image forming apparatus having a correction unit for instructing the image forming unit to correct an image forming position according to the amount of misalignment. The image forming apparatus according to claim 1, wherein the print rate calculation unit obtains the print rate for each area from the data of the read image acquired by the reading unit. The image forming apparatus according to claim 1, wherein the printing rate calculating unit obtains a printing rate for each of the regions from the rasterized data of an input image for forming an image by the image forming unit. The image forming apparatus according to claim 1, wherein the printing rate calculation unit obtains a printing rate for each area based on image data input to an exposure unit of the image forming unit. The image forming apparatus according to any one of claims 1 to 4, wherein the storage unit manages the print rate for each area according to the print rate classification set for each area. A determination unit for determining whether or not the amount of misalignment exceeds a threshold value is provided.
The image forming apparatus according to claim 1 to 5, wherein when the determination unit determines that the amount of misalignment exceeds a threshold value, the correction unit corrects the formation position of the image. Any one of claims 1 to 6, wherein the misalignment amount calculation unit acquires the positions of one or more reference images in order to calculate the misalignment amount for each region of the image formed on the recording material. The image forming apparatus according to. The image forming according to claim 7, wherein the misalignment amount calculation unit acquires the positions of a plurality of the reference images in order to calculate the misalignment amount for each region of the image formed on the recording material. Device. The image forming apparatus according to claim 7 or 8, wherein the misalignment amount calculation unit acquires the position of a feature point in the image data as a reference for acquiring the misalignment amount. The image forming apparatus according to any one of claims 1 to 9, wherein the printing rate calculating unit obtains a printing rate only for an image formed on the surface of the recording material. It is a method of correcting the image forming position by the image forming apparatus.
The process of reading the image formed on the recording material with the reading unit,
In the control unit, a process of obtaining the print rate of the image for each area preset in the recording material, and
A process of acquiring the amount of misalignment of the image from the read image by the control unit, and
In the control unit, a process of storing the misalignment amount in correspondence with the area and the print rate, and
A process of determining whether or not the amount of misalignment exceeds a threshold value in the control unit,
A method for correcting an image forming position, which comprises a process in which the control unit instructs an image forming unit to correct the image forming position.

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