JP2019105742A - Image forming apparatus and program - Google Patents

Abstract

To enable highly accurate color shift correction, when performing the formation of an image by differentiating a transfer condition.SOLUTION: An image forming apparatus includes an image forming part 40 which forms a correction pattern on a photoreceptor drum and transfers the correction pattern to an intermediate transfer belt, a signal acquisition part 90 which samples and acquires the detection signal of the correction pattern transferred to the intermediate transfer belt in a predetermined period, and a control part 100 which detects the centroid position of the correction pattern on the intermediate transfer belt on the basis of the detection signal acquired by the signal acquisition part 90, compares the centroid position with a previously set reference position, and calculates a correction value. The control part 100 executes first centroid detection processing, when the detection signal below a predetermined value among the detection signals acquired by the signal acquisition part 90 is a predetermined amount or more in the detection of the centroid position and executes second centroid detection processing whose accuracy is higher than that of the first centroid detection processing, when the detection signal below the predetermined value among the detection signals acquired by the signal acquisition part 90 is below the predetermined amount.SELECTED DRAWING: Figure 2

Description

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

  Conventionally, the electrostatic latent image formed on the photosensitive member is developed with toner to form a toner image, and the formed toner image is transferred to the intermediate transfer member (primary transfer), and the toner transferred to the intermediate transfer member There is known an electrophotographic image forming apparatus in which an image is transferred onto a sheet (secondary transfer) and the sheet is heated and pressed to form the image on the sheet.

In such an image forming apparatus, an image is formed on various types of paper such as plain paper, coated paper, and high quality paper according to the application and purpose. Since the paper has different surface irregularities depending on its type, the image forming apparatus transfers the image onto the paper by varying the secondary transfer pressure so that the pressure is suitable for the type of paper at the time of secondary transfer. To do control.
When such control is performed, the shape of the nip portion of the secondary transfer portion changes in accordance with the change of the secondary transfer pressure, so that the transfer position of the toner image on the sheet is shifted and a color shift occurs. As one of the measures, for example, in Patent Document 1, the correction pattern is formed on the intermediate transfer member under the condition in which the secondary transfer pressure is made different beforehand, and the correction data is detected from the result of detecting the correction pattern by the reflection type sensor. There has been proposed a technique for creating a color misregistration amount using correction data according to the transfer pressure setting at the time of sheet passing.

JP, 2016-133544, A

  By the way, when the paper on which an image is formed is embossed paper, in order to facilitate transfer of the toner image to the embossed paper at the time of secondary transfer, it is also necessary to lower the primary transfer pressure. That is, by reducing the primary transfer pressure, the adhesion between the toner and the intermediate transfer member is weakened to facilitate transfer of the toner image to the embossed paper at the time of secondary transfer.

As described above, even when the primary transfer pressure is varied, the shape of the nip portion changes in accordance with the pressure change as in the case where the secondary transfer pressure is varied. Since the transfer position of the image is shifted and a color shift occurs, it is necessary to correct the color shift amount.
However, when the correction pattern is formed on the intermediate transfer member as in the technique described in the above-mentioned patent document 1, the adhesion between the toner and the intermediate transfer member is weak under the condition that the primary transfer pressure is low. The toner layer becomes thin.
Then, when a correction pattern in which the toner layer is thin is detected by the reflection type sensor, the detection output weakens, correction data of sufficient accuracy can not be created, and as a result, the color misregistration amount can not be accurately corrected.

  The present invention has been made in view of the above problems, and is to enable highly accurate color misregistration correction when performing image formation under different transfer conditions.

In order to solve the above problems, the image forming apparatus of the present invention is
An image forming unit for forming a correction pattern image as a toner image on a photosensitive member and transferring the pattern image to an intermediate transfer member;
A signal acquisition unit for sampling and acquiring a detection signal of the pattern image transferred to the intermediate transfer member at a predetermined cycle;
A control unit which detects a barycentric position of the pattern image on the intermediate transfer member based on the detection signal acquired by the signal acquisition unit, and calculates a correction value by comparing with a preset reference position;
Equipped with
The control unit is configured to detect the center of gravity position.
The first gravity center detection process is executed when a detection signal below a predetermined value among the detection signals acquired by the signal acquisition unit is equal to or greater than a predetermined amount,
Among the detection signals acquired by the signal acquisition unit, a second gravity center that is more accurate than the first gravity center detection process if the detection signal below the predetermined value does not reach the predetermined amount or is estimated thereto It is characterized in that detection processing is performed.

Also, the program of the present invention is
An image forming unit for forming a correction pattern image as a toner image on a photosensitive member and transferring the pattern image to an intermediate transfer member;
A signal acquisition unit for sampling and acquiring a detection signal of the pattern image transferred to the intermediate transfer member at a predetermined cycle;
A computer of the image forming apparatus, equipped with
The position of the center of gravity of the pattern image on the intermediate transfer member is detected based on the detection signal acquired by the signal acquisition unit, and a correction value is calculated by comparing it with a preset reference position.
In detecting the center of gravity position,
The first gravity center detection process is executed when a detection signal below a predetermined value among the detection signals acquired by the signal acquisition unit is equal to or greater than a predetermined amount,
Among the detection signals acquired by the signal acquisition unit, a second gravity center that is more accurate than the first gravity center detection process if the detection signal below the predetermined value does not reach the predetermined amount or is estimated thereto It is a program that functions as control means for executing detection processing.

  According to the present invention, when performing image formation with different transfer conditions in an image forming apparatus, highly accurate color misregistration correction is possible.

FIG. 1 is a diagram showing a schematic configuration of an image forming apparatus. FIG. 2 is a block diagram showing the main functional configuration of the image forming apparatus. It is a flowchart which shows correction value calculation processing. It is a figure which shows an example of a structure of a correction pattern. It is a flowchart which shows a 1st gravity center detection process. It is a figure for demonstrating a 1st gravity center detection process. It is a flow chart which shows the 2nd gravity center detection processing. It is a figure for demonstrating a 2nd gravity center detection process. It is a figure for demonstrating a 2nd gravity center detection process. It is a figure for demonstrating the shift | offset | difference detection of a subscanning direction. It is a figure for demonstrating the shift | offset | difference detection of the main scanning direction. It is a flowchart which shows the correction value calculation process of a modification. It is a flowchart which shows the correction value calculation process of 2nd Embodiment.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. However, the scope of the invention is not limited to the illustrated example.

First Embodiment
[Configuration of image forming apparatus]
FIG. 1 is a view schematically showing an entire configuration of an image forming apparatus 1 according to the present embodiment. FIG. 2 is a block diagram showing the main functional configuration of the image forming apparatus 1.

  As shown in FIGS. 1 and 2, the image forming apparatus 1 is an intermediate transfer type color image forming apparatus using an electrophotographic process technology. That is, the image forming apparatus 1 forms an intermediate transfer belt (intermediate transfer belt) on the toner images of Y (yellow), M (magenta), C (cyan), and K (black) reference colors formed on the photosensitive drum 413. After transferring (primary transfer) onto the body 421 and superimposing toner images of four colors on the intermediate transfer belt 421, a color image is formed by transferring (secondary transfer) onto a sheet of paper.

  As shown in FIG. 2, the image forming apparatus 1 includes an image reading unit 10, an operation display unit 20, an image processing unit 30, an image forming unit 40, a sheet conveyance unit 50, a fixing unit 60, a communication unit 70, a storage unit 80. A signal acquisition unit 90 and a control unit 100 are provided.

  The control unit 100 includes a central processing unit (CPU) 101, a read only memory (ROM) 102, a random access memory (RAM) 103, and the like. The CPU 101 reads out a program according to the processing content from the ROM 102, develops it in the RAM 103, and cooperates with the developed program to centrally control the operation of each part of the image forming apparatus 1 shown in FIG.

The image reading unit 10 includes an automatic document feeder 11 called an ADF (Auto Document Feeder), a scanner 12 and the like.
The automatic document feeder 11 conveys the document D placed on the document tray by the conveyance mechanism to the scanner 12.
The scanner 12 optically scans the document D transported from the automatic document feeder 11 onto the contact glass or the document D placed on the contact glass, reads the document image of the document D, and acquires image data Do. The image processing unit 30 applies predetermined image processing to the image data.

The operation display unit 20 is configured of, for example, a liquid crystal display (LCD) with a touch panel, and functions as the display unit 21 and the operation unit 22.
The display unit 21 displays various operation screens, image status display, operation status of each function, and the like according to a display control signal input from the control unit 100.
The operation unit 22 includes various operation keys such as a ten key and a start key, receives various input operations by the user, and outputs an operation signal to the control unit 100.

  The image processing unit 30 includes a circuit or the like that performs digital image processing according to settings on the input image data. For example, under the control of the control unit 100, the image processing unit 30 performs various types of image processing such as shading correction, color conversion, gradation correction, and compression processing. The image forming unit 40 is controlled based on the image data subjected to these processes.

  The image forming unit 40 forms an image forming unit 41C, 41M, 41Y, 41K for forming an image with toner of each of the reference colors of C component, M component, Y component, and K component based on the image data subjected to image processing. , The intermediate transfer unit 42 and the like.

  The image forming units 41C, 41M, 41Y, and 41K for the C component, the M component, the Y component, and the K component have the same configuration. For convenience of illustration and description, common components are denoted by the same reference numerals, and when the components are distinguished, they are indicated by appending C, M, Y, or K to the reference. In FIG. 1, reference numerals are attached only to the components of the image forming unit 41Y for the Y component, and reference numerals of the components of the other image forming units 41M, 41C, and 41K are omitted.

  The image forming unit 41 includes an exposure device 411, a developing device (developing unit) 412, a photosensitive drum 413, a charging device 414, a drum cleaning device 415, and the like. The intermediate transfer unit 42 includes an intermediate transfer belt 421, a primary transfer roller (primary transfer member) 422, a plurality of support rollers (including a drive roller and a follow roller) 423, a secondary transfer roller 424, a belt cleaning device 425, and the like. .

  The surface of the photosensitive drum 413 is uniformly charged by the charging device 414, and a latent image is formed by scanning exposure by the exposure device 411, and the developing device 412 forms a latent image of any of C, M, Y, and K. The latent image is visualized by the adhesion of the toner. As a result, a toner image of a predetermined color is formed on the photosensitive drum 413. The toner image formed on the photosensitive drum 413 is sequentially transferred to a predetermined position on the rotating intermediate transfer belt 421 by the primary transfer roller 422 (primary transfer). The transfer residual toner remaining on the surface of the photosensitive drum 413 after the primary transfer is removed by the drum cleaning device 415.

  The primary transfer roller 422 is biased against the intermediate transfer belt 421 by a biasing mechanism 422a, and is configured to be capable of changing the nip pressure in primary transfer under the control of the control unit 100.

  The toner images of the respective colors transferred onto the intermediate transfer belt 421 are transferred by the secondary transfer roller 424 onto the sheet transported at a predetermined timing by the sheet transport unit 50 described later (secondary transfer). Further, transfer residual toner remaining on the surface of the intermediate transfer belt 421 is removed by a belt cleaning device 425.

  The secondary transfer roller 424 is biased against the intermediate transfer belt 421 by a biasing mechanism 424a, and is configured to be capable of changing the nip pressure in secondary transfer under the control of the control unit 100.

The paper conveyance unit 50 includes a paper feed unit 51, a paper discharge unit 52, a conveyance path unit 53, and the like. In the three sheet feeding tray units 51a to 51c constituting the sheet feeding unit 51, sheets (standard sheets, embossed sheets, etc.) identified based on basis weight, size, etc. are accommodated for each preset type. There is.
The sheets stored in the sheet feeding tray units 51 a to 51 c are sent out one by one from the top and conveyed by the conveyance path unit 53 to the image forming unit 40. Then, in the image forming unit 40, the toner images of the intermediate transfer belt 421 are secondarily transferred collectively on one side of the sheet, and the sheet on which the toner image has been transferred is conveyed toward the fixing unit 60.

The fixing unit 60 fixes the toner image on the sheet by heating and pressing the sheet on which the toner image has been secondarily transferred and conveyed at the fixing nip.
The fixed sheet is discharged to the outside of the apparatus by the discharge unit 52 provided with a discharge roller 52a.

  The communication unit 70 includes, for example, a communication control card such as a LAN (Local Area Network) card, and communicates with an external device (for example, a personal computer) connected to a communication network such as a LAN or WAN (Wide Area Network). Send and receive various data.

The storage unit 80 is configured of, for example, a non-volatile semiconductor memory (so-called flash memory), a hard disk drive, or the like. The storage unit 80 stores various data including various setting information related to the image forming apparatus 1.
For example, the storage unit 80 stores image forming data and the like of a correction pattern used in a correction value calculation process described later.
In addition, the storage unit 80 accumulates the numerical values calculated in the correction value calculation process.

The signal acquisition unit 90 is provided at a position downstream of the image forming unit 41 K and upstream of the secondary transfer roller 424 with respect to the rotation direction of the intermediate transfer belt 421. The signal acquisition unit 90 can also be provided on the downstream side of the secondary transfer roller 424.
The signal acquiring unit 90 includes two reflective sensors 90A and 90B (see FIG. 4) provided along the width direction on the intermediate transfer belt 421, and the intermediate transfer belt 421 is mounted on the intermediate transfer belt 421 in the correction value calculation process described later. When the correction patterns PY, PM, PC, and PK (pattern images for correction) are formed, the detection signals for detecting the correction patterns are sampled and acquired at a predetermined cycle.
The arrangement and number of reflective sensors are not limited to those described above. For example, it may be provided at the central portion in the width direction on the intermediate transfer belt 421.

[Operation of image forming apparatus]
Next, the operation of the image forming apparatus 1 in the present embodiment will be described.
In the image forming apparatus 1 according to the present embodiment, control for changing the transfer conditions is executed in accordance with the type of paper.
Specifically, the control unit 100 controls the biasing mechanism 422a and the biasing mechanism 424a to change the nip pressure in primary transfer and secondary transfer, for example, when the type of paper is embossed paper. Then, when the nip pressure in the primary transfer and the secondary transfer is changed, the control unit 100 calculates the correction value for preventing the occurrence of the positional deviation of the image along with the change of the nip pressure. Execute calculation processing.
Hereinafter, the correction value calculation process will be described in detail.

FIG. 3 is a flowchart showing the correction value calculation process.
Such processing is executed, for example, at the time of activation of the image forming apparatus 1 or at the time of reaching a predetermined correction value calculation timing.

  First, the control unit 100 reads the image data of the correction pattern stored in the storage unit 80, and causes the image forming unit 40 to form the correction pattern on the intermediate transfer belt 421 (step S11).

FIG. 4 is a diagram showing an example of the configuration of the correction patterns PY, PM, PC, and PK formed on the intermediate transfer belt 421 in step S11.
As shown in FIG. 4, the correction patterns PY, PM, PC, and PK are formed on both ends of the width direction (main scanning direction) on the intermediate transfer belt 421 orthogonal to the conveyance direction (sub scanning direction). . Each of the correction patterns PY, PM, PC, and PK is formed along the sub-scanning direction, for example, five in each color. The correction patterns PY, PM, PC, and PK are configured by combining a pattern extending in the main scanning direction and a pattern extending in an oblique direction with respect to the main scanning direction. In this example, for example, the correction patterns PY and PM , PC, and PK are configured in a “フ” shape. The shape of the correction pattern is not limited to this.
As described above, since the correction patterns PY, PM, PC, and PK are formed at both ends in the width direction on the intermediate transfer belt 421, the reflection type sensors 90A and 90B are configured to receive the correction patterns PY, PM, PC, and It is provided at a position corresponding to the PK. The correction pattern may be provided also at the central portion in the width direction on the intermediate transfer belt 421, and in this case, the reflection type sensor is also provided at a position corresponding to the correction pattern.

  Next, the control unit 100 causes the signal acquisition unit 90 to read the correction pattern image formed in step S11, and samples a detection signal of the correction pattern image at a predetermined cycle (step S12).

  Next, the control unit 100 determines whether a detection signal whose value is less than a predetermined threshold (predetermined value) is equal to or greater than a predetermined amount (step S13).

And when it judges that it is more than predetermined amount (Step S13: YES), control part 100 performs the 1st gravity center detection processing (Step S14).
Here, when the primary transfer pressure (pressing force set by the biasing mechanism 422a) is a preset default value, the detection signal below the predetermined threshold becomes a predetermined amount or more.
That is, the toner layer of the correction pattern on the intermediate transfer belt 421 has a sufficient thickness, and the detection signal below the threshold value becomes a predetermined amount or more.
At this time, since the number of effective data (the number of detection signals below the threshold) is sufficient, the control unit 100 executes the first gravity center detection process with a small load due to the process.

FIG. 5 is a flowchart showing the first centroid detection process.
FIG. 6 is a diagram for explaining the first centroid detection process. In FIG. 6, the horizontal axis indicates the sampling position of the detection signal, and the vertical axis indicates the output value.
As shown in FIG. 5, in step S141, the control unit 100 extracts a detection signal whose output value is less than a threshold (for example, 2 V) to obtain a total area (S) (hatched portion in FIG. 6). Specifically, the control unit 100 obtains a total value obtained by adding the heights to the threshold value at each point sequentially as a total area (S) from point A to point B in FIG.
Next, in step S142, the control unit 100 sends the next detection signal (point C in FIG. 6) beyond the position (dotted line in FIG. 6) that is half (S / 2) of the calculated total area (S). The corresponding position is detected as the position of the center of gravity, and the process ends.

On the other hand, when it is determined that the detection signal below the predetermined threshold (predetermined value) does not reach the predetermined amount (step S13: NO), the control unit 100 executes the second gravity center detection process (step S15). .
Here, when the primary transfer pressure (pressing force set by the biasing mechanism 422a) is a value lower than a preset default value, a detection signal below a predetermined threshold does not reach a predetermined amount.
That is, the toner layer of the correction pattern on the intermediate transfer belt 421 does not have a sufficient thickness, and the detection signal below the threshold does not reach a predetermined amount.
At this time, in the present embodiment, since the control unit 100 has a small number of effective data (the number of detection signals below the threshold), the processing load is higher than that of the first gravity center detection processing, but high accuracy A second centroid detection process is performed that can perform centroid detection.

FIG. 7 is a flowchart showing the second gravity center detection process.
FIG. 8 is a diagram for explaining the second gravity center detection process. In FIG. 8, the horizontal axis indicates the sampling position of the detection signal, and the vertical axis indicates the output value.

  As shown in FIG. 7, in step S151, the control unit 100 extracts a detection signal whose output value is less than a threshold (for example, 2 V) to obtain a total area (S) and a voltage (V) at the lowest point. (The shaded area and point P in FIG. 8).

Next, in step S152, the control unit 100 calculates the center of gravity (C) by the least squares method.
Here, in the three-dimensional space as shown in FIG. 9, a plane which minimizes the errors from all the points in three dimensions is determined by approximation using the least squares method. That is, the coefficients (u, v, w) in the following arithmetic expression (1) are determined by the least squares method.
C = uS + vV + w (1)
In addition, it is also preferable to include the parameter regarding environmental conditions, such as temperature and humidity, in arithmetic expression (1).

  Next, in step S153, the control unit 100 stores the numerical values (S, V, C, u, v, w) calculated in the second gravity center detection process in the storage unit 80, and ends the present process.

Note that, for example, when the first gravity center detection process is performed by increasing the threshold value to increase the number of effective data, there is a possibility of erroneous detection of dust or the like. Also, if the sensor itself is changed to increase the number of valid data, the cost will be increased.
However, according to the second center-of-gravity detection process described above, the center of gravity can be accurately determined without causing a problem of false detection or cost increase.

Further, the numerical value calculated in the second gravity center detection process may be stored in the storage unit 80 in association with the environmental condition (temperature and / or humidity) at the time of the numerical value calculation.
Then, when the second barycenter detection processing is performed next, it is also preferable to extract a numerical value corresponding to the environmental condition at the time of the execution and execute the least square method using this.
This makes it possible to calculate the center of gravity more accurately.
Further, in addition to the environmental conditions at the time of numerical value calculation, the number of sheets at the time of numerical value calculation, toner density, transfer pressure, and the like may be correlated.

Returning to FIG. 3, the control unit 100 calculates a correction value using the gravity center obtained by the first gravity center detection process or the second gravity center detection process (step S16).
Specifically, of the correction patterns PY, PM, PC, and PK detected by the signal acquisition unit 90, for example, the control unit 100 sets the correction pattern PY of the other color to the correction pattern PK based on the black correction pattern PK, for example. The shift amount of the image forming position of PM and PC is calculated as a correction value. Examples of the correction value include a correction value for correcting the deviation of the writing position in the sub scanning direction, and a correction value for correcting the deviation of the writing position in the main scanning direction.

FIG. 10 is a view for explaining calculation of a correction value for correcting the deviation of the writing position in the sub scanning direction.
In FIG. 10, ideal distances from the reference (correction pattern PK) to C, M, and Y are set as reference distances a, 2a, and 3a, respectively. Then, the distance from the actually calculated reference barycenter to the barycenter of each color is compared with the reference distances a, 2a and 3a, and the difference is calculated as a correction value. In the example of FIG. 8, correction values are calculated for C and Y.

FIG. 11 is a diagram for explaining calculation of a correction value for correcting the deviation of the writing position in the main scanning direction.
In this case, the distance between two points in the pattern of the reference (correction pattern PK) is determined. Also in the C, M and Y patterns, the same distance between two points is obtained.
Then, the reference distance is compared with each distance of C, M, and Y, and the difference is calculated as a correction value. In the example of FIG. 11, the color misregistration is detected for C and M, and the difference is corrected.

Next, the control unit 100 changes the image forming conditions using the calculated correction value (step S17), and ends the present process.
As described above, it is also preferable to calculate the correction value a plurality of times and change the image forming conditions using the average value.

As described above, according to the present embodiment, the image forming apparatus forms correction patterns PY, PM, PC, and PK as toner images on the photosensitive drum 413 and transfers the correction patterns to the intermediate transfer belt 421. The intermediate transfer is performed based on the detection signal acquired by the signal acquisition unit 90 and the signal acquisition unit 90 which samples and acquires the detection signal of the correction pattern transferred to the intermediate transfer belt 421 at a predetermined cycle. The control unit 100 detects the center of gravity position of the correction pattern on the belt 421 and calculates a correction value by comparing with a preset reference position, and the control unit 100 detects the center of gravity position by detecting the signal acquisition unit. When the detection signal below the predetermined value among the detection signals acquired by 90 is equal to or more than the predetermined amount, the first gravity center detection processing is executed and acquired by the signal acquisition unit 90 Among the detection signals, the detection signal falls below a predetermined value if less than the predetermined amount, executing the highly accurate second centroid detection processing than the first centroid detecting process.
For this reason, when the acquisition amount of the detection signal is less than the predetermined amount by changing the transfer condition, the second gravity center detection process with higher accuracy than the first gravity center detection process is executed, and the transfer condition is Even when performing image formation differently, color misregistration correction with high accuracy is possible.

Further, according to the present embodiment, as the first gravity center detection process, the control unit 100 detects the gravity center position using the total value of the values of the detection signals less than the predetermined value, and performs the second gravity center detection process. The position of the center of gravity is detected using the method of least squares from the value of the detection signal below a predetermined value.
Therefore, when the detection signal below the predetermined value does not reach the predetermined amount, the barycentric position is detected by the least squares method, so that the correction value can be calculated with high accuracy.

Further, according to the present embodiment, the control unit 100 is provided to face the photosensitive drum 413 via the intermediate transfer belt 421, and transfers the toner image on the photosensitive drum 413 to the intermediate transfer belt 421. The primary transfer roller 422, and an urging mechanism 422a that sets the pressing force of the primary transfer roller 422 against the intermediate transfer belt 421 according to the type of paper, and the control unit 100 is set by the urging mechanism 422a. If the pressing force is a preset default value, the first gravity center detection process is executed, and if the pressing force set by the biasing mechanism 422a is a value lower than the default value, a second gravity center detection process Run.
For this reason, when the nip pressure at the time of primary transfer is lower than the default value and toner hardly adheres on the intermediate transfer belt 421, the second gravity center detection process is performed.

Further, according to the present embodiment, the storage unit 80 is provided which stores the numerical value calculated in the second gravity center detection process.
Therefore, each time the second center-of-gravity detection process is executed, a numerical value is stored, and the accuracy of the second center-of-gravity detection process can be improved.

Further, according to the present embodiment, storage unit 80 stores the numerical value and the environmental condition at the time of calculation of the numerical value in association with each other, and control unit 100 executes the second gravity center detection process, From the numerical values stored in the storage unit 80, the numerical value corresponding to the environmental condition at the time of execution of the second gravity center detection process is extracted, and the second gravity center detection process is executed using the extracted numerical value.
Therefore, the accuracy can be further improved in the second centroid detection process.

<Modification>
In the first embodiment, in step S3 of FIG. 3, it is determined whether or not the detection signal below the threshold is equal to or greater than a predetermined amount. Instead, as shown in FIG. It may be determined whether or not it is different from normal (step S13A).
Then, when the image forming condition is different from the normal condition (step S13A: YES), the second gravity center detection process is executed (step S15).
Here, "image forming conditions are different from normal" means, for example, that the type of paper on which an image is to be formed is set to embossed paper, or that the development bias is set to a predetermined value (default value) or less. In the case where the developing bias is set to a predetermined value (default value) or less at the time of adjusting the toner concentration by the user operation, or the like.
That is, the control unit 100 determines that the pressing force set by the biasing mechanism 422a is lower than the default value in the case of the above-described image forming condition, and the detection signal below the threshold does not reach a predetermined amount. It is estimated that the second gravity center detection process is to be performed.

As described above, in the present modification, when the type of paper is embossed paper, or when the developing bias of the developing device 412 is equal to or less than the predetermined value, the control unit 100 sets the pressing force set by the biasing mechanism 422a. Is determined to be a value lower than the default value, and in this case, it is estimated that the detection signal below the predetermined value among the detection signals acquired by the signal acquisition unit 90 is less than the predetermined amount, and the second gravity center detection Execute the process
Even with such processing, it is possible to correct color misregistration amount with high accuracy.

Second Embodiment
Next, a second embodiment of the present invention will be described focusing on differences from the first embodiment. The same components as those of the first embodiment are denoted by the same reference numerals, and the description thereof is omitted.

FIG. 13 is a flowchart showing a correction value calculation process according to the second embodiment.
Such processing is executed, for example, before an image is formed on a sheet when an image forming job is input.

  First, the control unit 100 receives an image forming job (step S21), and reads sheet information from the image forming job (step S22).

  Next, the control unit 100 reads out the image data of the correction pattern stored in the storage unit 80, and causes the image forming unit 40 to form the correction pattern on the intermediate transfer belt 421 under the transfer pressure corresponding to the sheet information Step S23).

  Next, the control unit 100 causes the signal acquisition unit 90 to read the correction pattern image formed in step S23, and samples a detection signal of the correction pattern image at a predetermined cycle (step S24).

  Next, the control unit 100 determines whether a detection signal whose value is less than a predetermined threshold (predetermined value) is equal to or more than a predetermined amount (step S25).

  When it is determined that the detection signal below the threshold is equal to or greater than the predetermined amount (step S25: YES), the control unit 100 determines whether the type of paper included in the sheet information is plain paper (step S26). .

  Then, if the type of sheet is plain paper (step S26: YES), the control unit 100 executes a first gravity center detection process (step S27), and proceeds to step S31 described later.

  On the other hand, when it is determined that the detection signal below the threshold value does not reach the predetermined amount (step S25: NO), the control unit 100 determines whether the type of sheet included in the sheet information is embossed (step S28). .

  When the type of sheet is embossed (YES in step S28), the control unit 100 executes the second gravity center detection process (step S29), and proceeds to step S31 described later.

If the paper type is not plain paper at step S26 (step S26: NO), and if the paper type is not embossed paper at step S28 (step S28: NO), the control unit 100 sends the image forming apparatus 1 It notifies that abnormality has occurred (step S30), and ends this processing.
The notification can be performed by displaying a message of abnormality occurrence by the display unit 21 or the like, but the method of notification is not limited to this, and for example, a sound may be output.

  Next, the control unit 100 calculates a correction value using the centroid obtained by the first centroid detection processing or the second centroid detection processing (step S31).

  Next, the control unit 100 changes the image forming conditions using the calculated correction value, executes the image forming process (step S32), and ends the process.

As described above, according to the present embodiment, the control unit 100 determines that the sheet information included in the job information is a sheet other than the embossed sheet and is less than the predetermined value among the detection signals acquired by the signal acquisition unit 90. When the detection signal does not reach the predetermined amount, or when the sheet information included in the job information is embossed paper, and the detection signal below the predetermined value among the detection signals acquired by the signal acquisition unit 90 is the predetermined amount or more, The notification is given by the display unit 21.
Therefore, the user can recognize the abnormality of the device.

  In addition, the detailed configuration of the image forming apparatus and the detailed operation of each apparatus can be appropriately modified without departing from the spirit of the present invention.

Reference Signs List 1 image forming apparatus 10 image reading unit 20 operation display unit 21 display unit 22 operation unit 30 image processing unit 40 image forming units 41Y, 41M, 41C, 41K image forming unit 411 exposure device 412 developing device (developing unit)
413 Photosensitive drum (Photosensitive body)
414 charging device 415 drum cleaning device 42 intermediate transfer unit 421 intermediate transfer belt (intermediate transfer member)
422 Primary transfer roller (primary transfer member)
422a biasing mechanism (pressure setting means)
424 Secondary Transfer Roller 424a Biasing Mechanism 90 Signal Acquisition Unit 90A, 90B Reflective Sensor 426 Belt Cleaning Device 50 Paper Transport Unit 60 Fixation Unit 70 Communication Unit 80 Storage Unit 100 Control Unit PK, PY, PM, PC, PK Correction Pattern (Pattern image for correction)

Claims (9)

An image forming unit for forming a correction pattern image as a toner image on a photosensitive member and transferring the pattern image to an intermediate transfer member;
A signal acquisition unit for sampling and acquiring a detection signal of the pattern image transferred to the intermediate transfer member at a predetermined cycle;
A control unit which detects a barycentric position of the pattern image on the intermediate transfer member based on the detection signal acquired by the signal acquisition unit, and calculates a correction value by comparing with a preset reference position;
Equipped with
The control unit is configured to detect the center of gravity position.
The first gravity center detection process is executed when a detection signal below a predetermined value among the detection signals acquired by the signal acquisition unit is equal to or greater than a predetermined amount,
Among the detection signals acquired by the signal acquisition unit, a second gravity center that is more accurate than the first gravity center detection process if the detection signal below the predetermined value does not reach the predetermined amount or is estimated thereto An image forming apparatus characterized by executing detection processing. The control unit
As the first center-of-gravity detection processing, the center-of-gravity position is detected using a total value of values of detection signals below the predetermined value,
The image forming apparatus according to claim 1, wherein, as the second gravity center detection process, the gravity center position is detected using a least squares method from the value of the detection signal that is less than the predetermined value. A primary transfer member provided opposite to the photosensitive member via the intermediate transfer member to transfer a toner image on the photosensitive member to the intermediate transfer member;
A pressure setting unit configured to set a pressing force of the primary transfer member to the intermediate transfer member according to the type of sheet;
The control unit
If the pressing force set by the pressure setting means is a preset default value, the first gravity center detection process is executed,
The image forming apparatus according to claim 1, wherein when the pressing force set by the pressure setting unit is a value lower than the default value, the second gravity center detection process is performed. The control unit
4. The image forming apparatus according to claim 3, wherein the pressing force set by the pressure setting unit is determined to be a value lower than the default value when the type of the sheet is an embossed sheet. A developing unit for developing the electrostatic latent image on the photosensitive member with toner;
The control unit may determine that the pressing force set by the pressure setting unit is a value lower than the default value when the developing bias of the developing unit is equal to or less than a predetermined value. Image forming apparatus as described.   The image forming apparatus according to claim 2, further comprising: a storage unit configured to store the numerical value calculated by the second gravity center detection process. The storage unit associates and stores the numerical value and an environmental condition at the time of calculation of the numerical value;
The control unit extracts the numerical value corresponding to the environmental condition at the time of execution of the second gravity center detection process out of the numerical values stored in the storage unit when the second gravity center detection process is executed. 7. The image forming apparatus according to claim 6, wherein the second gravity center detection process is executed using the extracted numerical value. It has a notification unit that notifies the user of an error,
The control unit
When the sheet information included in the job information is a sheet other than the embossed sheet and the detection signal below the predetermined value among the detection signals acquired by the signal acquisition unit does not reach the predetermined amount,
Alternatively, when the sheet information included in the job information is embossed paper, and the detection signal below the predetermined value among the detection signals acquired by the signal acquisition unit is the predetermined amount or more,
The image forming apparatus according to any one of claims 1 to 7, wherein notification is performed by the notification unit. An image forming unit for forming a correction pattern image as a toner image on a photosensitive member and transferring the pattern image to an intermediate transfer member;
A signal acquisition unit for sampling and acquiring a detection signal of the pattern image transferred to the intermediate transfer member at a predetermined cycle;
A computer of the image forming apparatus, equipped with
The position of the center of gravity of the pattern image on the intermediate transfer member is detected based on the detection signal acquired by the signal acquisition unit, and a correction value is calculated by comparing it with a preset reference position.
In detecting the center of gravity position,
The first gravity center detection process is executed when a detection signal below a predetermined value among the detection signals acquired by the signal acquisition unit is equal to or greater than a predetermined amount,
Among the detection signals acquired by the signal acquisition unit, a second gravity center that is more accurate than the first gravity center detection process if the detection signal below the predetermined value does not reach the predetermined amount or is estimated thereto A program that functions as control means for executing detection processing.

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