JP2021081590A - Image forming apparatus - Google Patents

Abstract

To reduce a user's waiting time associated with color shift correction.SOLUTION: Image forming means superimposes a plurality of toner images different in color from each other to form a color image on a sheet. Fixing means fixes the color image to the sheet. Correction means corrects image forming positions of the plurality of toner images formed by the image forming means to correct color shift on the sheet. Especially, the correction means executes the correction of color shift in parallel with warming-up of the fixing means.SELECTED DRAWING: Figure 7

Description

The present invention relates to an image forming apparatus.

The electrophotographic color image forming apparatus forms a color image by superimposing a plurality of toner images having different colors. Therefore, if the transfer position of a plurality of toner images having different colors deviates from the ideal position, so-called color shift occurs. Therefore, the color image forming apparatus forms a test image, obtains the amount of color shift, and executes color shift correction that corrects the writing timing of the toner image according to the amount of color shift. According to Patent Document 1, it is proposed that the color shift correction is not executed when the power of the image forming apparatus is turned on, but the color shift correction is executed when a print job is input.

Japanese Unexamined Patent Publication No. 2012-168421

Patent Document 1 does not accept a print job and does not execute color shift correction unless the warm-up process, which is a process of raising the detection temperature of the sensor provided in the fuser to a predetermined temperature, is completed. Therefore, if the warm-up of the fuser and the color shift correction can be performed in parallel, it will be possible to further reduce the waiting time of the user. Therefore, an object of the present invention is to reduce the waiting time of the user due to the color shift correction.

The present invention is, for example,
An image forming means for forming a color image on a sheet by superimposing a plurality of toner images having different colors.
A fixing means for fixing the color image on the sheet,
It has a correction means for correcting color shift in the sheet by correcting the image formation position of each of the plurality of toner images in the image forming means.
The correction means
If a print job is submitted while the fixing means is performing warm-up, the color shift correction is executed in parallel with the warm-up.
If a print job is not submitted while the fixing means is performing warm-up, if a print job is submitted after the warm-up is completed, the color shift correction is executed. An image forming apparatus characterized by this is provided.

According to the present invention, the waiting time of the user due to the color shift correction is reduced.

Schematic diagram of the image forming apparatus Controller block diagram Diagram illustrating the test image Diagram explaining how to obtain the amount of color shift Flowchart showing initial adjustment processing Flowchart showing preparatory operation Timing chart showing Examples and Comparative Examples

Hereinafter, embodiments will be described in detail with reference to the accompanying drawings. The following embodiments do not limit the invention according to the claims. Although a plurality of features are described in the embodiment, not all of the plurality of features are essential to the invention, and the plurality of features may be arbitrarily combined. Further, in the accompanying drawings, the same or similar configurations are given the same reference numbers, and duplicate description is omitted.

[Image forming device]
As shown in FIG. 1, the image forming apparatus 1 is a multifunction peripheral (MFP) having an electrophotographic printer 100 and an image reader 110. The printer 100 forms a toner image on the sheet P by executing a print job input from the image reader 110 or the host computer.

● Printer 100
The image forming unit 50 forms a color image by superimposing four color developing agents (toners) of yellow (Y), magenta (M), cyan (C), and black (K). In FIG. 1, the characters of YMCK indicating the toner color are added to the end of the reference numbers, but the characters of YMCK are omitted when the matters common to the four colors are explained.

The feeding cassette 2 is a storage for storing the sheet P. The feeding roller 4 feeds the sheet P from the feeding cassette 2 to the transport path. The transport roller pair 5 transports the sheet P fed from the feed cassette 2 further downstream in the transport direction of the sheet P. The resist roller pair 6 is a transfer roller for matching the timing when the sheet P arrives at the secondary transfer roller 19 and the timing when the toner image arrives at the secondary transfer roller 19.

In the image forming unit 50, the photosensitive drum 11 is an image carrier that supports an electrostatic latent image or a toner image. The charging roller 12 charges the surface of the photosensitive drum 11 so that the potential on the surface of the photosensitive drum 11 becomes a uniform potential. The exposure apparatus 13 forms an electrostatic latent image by irradiating the surface of the photosensitive drum 11 with light. The developing device 15 develops an electrostatic latent image using toner to form a toner image. The primary transfer device 16 transfers the toner image to the intermediate transfer body 17. The secondary transfer roller 19 transfers the toner image from the intermediate transfer body 17 to the sheet P. The fuser 20 uses heat and pressure to fix the toner image on the sheet P. The discharge roller 21 discharges the sheet P to a tray provided outside the image forming apparatus 1.

The image sensor 25 is a sensor that reads a test image for color shift correction formed on the intermediate transfer body 17. A plurality of image sensors 25 may be arranged side by side in a direction (main scanning direction) orthogonal to the moving direction of the intermediate transfer body 17.

[controller]
As shown in FIG. 2, the controller 200 may have a CPU 201 and a memory 202. The CPU 201 may have a plurality of CPU cores. Here, the CPU 201 may be any of a processor circuit, an ASIC (application specific integrated circuit), an FPGA (field programmable gate array), or an aggregate thereof.

The CPU 201 realizes various functions by executing a control program stored in the ROM area of the memory 202. One or more of the various functions may be realized by a hardware circuit different from the CPU 201. The CPU 201 controls the image sensor 25 to read the test image. The CPU 201 drives the motor 232 through the drive circuit 231. As a result, the photosensitive drum 11 and the intermediate transfer body 17 rotate. The CPU 201 controls the power supply circuit 234 to generate a charging voltage and a transfer voltage. The CPU 201 controls the environment sensor 235 and measures the environmental temperature and the environmental humidity. The fixing control unit 213 of the CPU 201 detects the temperature by the thermistor 237 provided in the fixing device 20, and controls the heater 236 so that the detected temperature reaches the target temperature.

Among the functions realized by the CPU 201, the state control unit 211 controls the operating state of the image forming apparatus 1. For example, the state control unit 211 shifts the image forming apparatus 1 to the power saving state, or returns the image forming apparatus 1 from the power saving state to the non-power saving state (standby state). The adjusting unit 212 adjusts the charging voltage and the transfer voltage generated by the power supply circuit 234 according to the environmental temperature measured by the environment sensor 235. The flag management unit 221 manages whether or not color shift correction is necessary by using the flag. For example, if the color shift correction has already been executed when the power of the image forming apparatus 1 is turned on or when the image forming apparatus 1 returns to the standby state, the flag management unit 221 sets the flag to on (High or 1). On the other hand, if the color shift correction is not executed when the power of the image forming apparatus 1 is turned on or when the image forming apparatus 1 returns to the standby state, the flag management unit 221 sets the flag to off (Low or 0). The flag may be 1-bit data stored in the memory 202. The job reception unit 222 receives a print job from the host computer or the image reader 110.

The color shift correction unit 214 creates a test image, measures the test image, calculates the amount of color shift, and determines the amount of correction. The pattern generation unit 215 creates an image signal for generating a test image and outputs it to the exposure devices 13Y, 13M, 13C, and 13K of the image forming unit 50. As a result, the image forming unit 50 forms a test image on the intermediate transfer body 17. The deviation amount calculation unit 216 controls the image sensor 25 to cause the image sensor 25 to read the test image, and acquires the reading result of the test image. Further, the deviation amount calculation unit 216 calculates the color deviation amount of the attention color (example: yellow, cyan, black) with respect to the reference color (example: magenta) based on the reading result of the test image. The correction amount determining unit 217 determines a correction amount such as an image writing position in the main scanning direction, an image writing position in the sub-scanning direction, and an image magnification for each of the yellow, magenta, cyan, and black colors based on the color shift amount. As a method for calculating the amount of color shift and a method for calculating the amount of correction, a method already known in the technical field of the image forming apparatus may be adopted.

The temperature sensor 238 is a sensor that measures the temperature of the exposure apparatus 13. When the temperature of the exposure apparatus 13 changes, the exposure position changes. Therefore, when the difference between the temperature of the exposure apparatus 13 when the color shift correction is executed and the temperature of the current exposure apparatus 13 exceeds the threshold value, the CPU 201 may execute the color shift correction again. RTC223 is a real-time clock that clocks the current time.

[Color shift correction]
The cause of the color shift is mainly the fluctuation of the exposure position with respect to the photosensitive drum 11 depending on the heat generated by the heat sources such as the motor 232, the heater 236, and the power supply circuit 234 and the change in the environment in which the image forming apparatus 1 is installed. Is. The amount of fluctuation in the exposure position can be obtained by measuring the test image. Since the exposure position on the photosensitive drum 11 and the transfer position on the intermediate transfer body 17 are correlated, the exposure position and the transfer position may be referred to as an image formation position.

FIG. 3 shows a test image formed on the intermediate transfer body 17. The test image has a plurality of color shift detection patterns (hereinafter referred to as patterns) for yellow, magenta, cyan, and black. Patterns 300Ya and 300Yb are yellow putters. Patterns 300Ca and 300Cb are cyan putters. The patterns 300Ka1, 300Ka2, 300Kb1 and 300Kb2 are black putters. The patterns 300M to 307M, 300Mak, and 300Mbk are magenta patterns. The reason why there are many magenta patterns is that the magenta patterns are the standard colors.

As shown in FIG. 3, the test image has three rows of pattern groups. The image sensor 25a detects the pattern group located on the leftmost side in the main scanning direction. The image sensor 25b detects a pattern group located in the center in the main scanning direction. The image sensor 25c detects the pattern group located on the far right in the main scanning direction.

By the way, when the surface color of the intermediate transfer body 17 is close to black, it becomes difficult for the image sensor 25 to detect the black pattern. This is because the reflectance of the intermediate transfer member 17 and the reflectance of the black pattern are substantially equal to each other. Therefore, the black pattern is partially superimposed on the magenta pattern. Since there is a significant difference between the reflectance of the magenta pattern and the reflectance of the black pattern, the black pattern can be detected.

FIG. 4 illustrates a method of calculating the amount of yellow color shift with respect to magenta.
Main scanning deviation amount = {(d2Ya-d1Ya) /2-(d2Yb-d1Yb) / 2} / 2 ... (1)
Sub-scanning deviation amount = {(d2Ya-d1Ya) / 2+ (d2Yb-d1Yb) / 2} / 2 ... (2)
Here, d1Ya is the distance between the magenta pattern 300M and the yellow pattern 300Ya. d2Ya is the distance between the magenta pattern 301M and the yellow pattern 300Ya. d1Yb is the distance between the magenta pattern 304M and the yellow pattern 300Yb. d2Yb is the distance between the magenta pattern 305M and the yellow pattern 300Yb. These operations are also performed on cyan and black.

The plurality of patterns shown in FIG. 4 may be referred to as subgroups. That is, the one-round pattern group of the intermediate transcript 17 includes N subgroups (eg, N = 10). The deviation amount calculation unit 216 may calculate the main scan deviation amount and the sub-scan deviation amount for each subgroup, and obtain the average value thereof. Further, this average value is calculated for the image sensors 25a, 25b, and 25c. The correction amount determination unit 217 corrects the main scan writing position, the main scanning magnification, the sub scanning writing position, the sub scanning tilt, and the like based on these calculation results.

[Execution timing of color shift correction]
The color shift correction unit 214 can execute the color shift correction in either the initial adjustment process or the preparatory operation. The initial adjustment process is a process of shifting the image forming apparatus 1 to a state in which an image can be formed. For example, the initial adjustment process is executed when the power supply of the image forming apparatus 1 is switched from off to on and when the image forming apparatus 1 returns from the power saving state to the non-power saving state (standby state). The preparatory operation is a preparatory operation of the image forming apparatus 1 that is executed immediately before executing the print job. Therefore, the preparatory operation is executed when the print job is received in the standby state. Below, the color shift correction will be described separately for the initial adjustment process and the preparatory operation.

● Initial adjustment process Fig. 5 shows the initial adjustment process. The CPU 201 executes the following processing when the power of the image forming apparatus 1 is turned on or when the image forming apparatus 1 returns to the non-power saving state.

In S1, the CPU 201 (fixing control unit 213) starts warming up the fixing device 20. The warm-up is a process of activating the fixing device 20 so that the toner image can be fixed on the sheet P. For example, the fixing control unit 213 detects the temperature by the thermistor 237 and controls the heater 236 so that the detected temperature reaches the target temperature. Here, the target temperature may be a fixing temperature at which the toner image can be fixed to the sheet P, or may be a standby temperature lower than the fixing temperature. When the standby temperature is adopted as the target temperature, a power saving effect is expected. On the other hand, when the fixing temperature is adopted as the target temperature, image formation can be started as soon as the warm-up is completed.

In S2, the CPU 201 (adjustment unit 212) starts the adjustment process of the image drawing condition. The image formation conditions are, for example, a charging voltage and a transfer voltage. Appropriate charging voltage and transfer voltage differ depending on environmental conditions such as environmental temperature. Further, when the film thickness of the surface layer of the photosensitive drum 11 changes or the electrical resistance between the intermediate transfer body 17 and the primary transfer device 16 changes, the appropriate charging voltage and transfer voltage also change. Therefore, the adjustment unit 212 executes the adjustment process of the image formation condition in parallel with the warm-up. For example, the adjusting unit 212 measures environmental conditions (eg, temperature, humidity) using the environmental sensor 235, and determines the charging voltage and the transfer voltage according to the environmental conditions.

In S3, the CPU 201 (job reception unit 222) determines whether or not a print job has been submitted from the host computer, the image reader, or the like. If no print job has been submitted, the CPU 201 advances the process to S8. If the print job has been submitted, the CPU 201 advances the process to S4.

In S4, the CPU 201 (flag management unit 221) determines whether or not the flag is off. That is, the CPU 201 determines whether or not the color shift correction has already been executed in the initial adjustment process. If the flag is on, the color shift correction has already been executed, so the CPU 201 advances the process to S8. If the flag is off, the color shift correction has not yet been executed, and the CPU 201 advances the process to S5.

In S5, the CPU 201 (adjustment unit 212) determines whether or not the adjustment process of the image drawing condition has been completed. If the adjustment process is not completed, the CPU 201 advances the process to S8. However, the time required for warming up shall be longer than the time required for the adjustment process. If the adjustment process is completed, the CPU 201 advances the process to S6.

In S6, the CPU 201 (color shift correction unit 214) executes color shift correction. The details of the color shift correction have already been described.

In S7, the CPU 201 (flag management unit 221) sets the flag on. As a result, the flag indicates that the color shift correction has been performed. The CPU 201 may store the data at the time when the color shift correction is executed in the memory 202. Along with the flag, the time data may be used to suppress the execution of multiple color shift corrections in a short period of time. Time data can be obtained from RTC223.

In S8, the CPU 201 (fixing control unit 213) determines whether or not the warm-up of the fixing device 20 is completed. If the warm-up is completed, the CPU 201 ends the initial adjustment process and transitions to the standby state. On the other hand, if the warm-up is not completed, the CPU 201 returns the process to S3.

As described above, in this embodiment, the color shift correction is executed in parallel with the warm-up of the fuser 20. Therefore, in this embodiment, the waiting time of the user due to the color shift correction is reduced.

The fixing control unit 213 maintains the detection temperature of the fixing device 20 at the target temperature so that the print job can be started immediately in the standby state. In FIG. 5, it is described that the adjustment process of the image formation condition and the color shift correction are executed in the initial adjustment process. However, the CPU 201 may skip the image formation condition adjustment process and the color shift correction depending on the stop time of the image forming apparatus 1. The stop time may be, for example, the time from the time when the image forming apparatus 1 shifts to the power saving state to the time when the image forming apparatus 1 returns to the non-power saving state. This time may be measured by the state control unit 211.

● Preparation operation FIG. 6 shows the preparation operation of the image forming apparatus 1. Immediately before the image forming apparatus 1 starts the print job in the non-power saving state (standby state), the preparatory operation is executed.

In S11, the CPU 201 (job reception unit 222) determines whether or not a print job has been submitted. When the print job is submitted, the CPU 201 advances the process to S12.

In S12, the CPU 201 (flag management unit 221) determines whether or not the flag is off. If the print job is not submitted in the initial adjustment process, the color shift correction is not executed. In this case, the flag is off. On the other hand, when a print job is submitted in the initial adjustment process, color shift correction is executed. In this case, the flag is on. If the flag is on, it is not necessary to execute the color shift correction, so the CPU 201 advances the process to S15. In S15, the CPU 201 (flag management unit 221) turns off the flag. Here, the CPU 201 may turn off the flag when the difference between the time when the color shift correction held in the memory 202 is executed and the current time exceeds the threshold value. Further, the CPU 201 may keep the flag on when this difference does not exceed the threshold value. This is to suppress the execution of color shift correction multiple times in a short period of time. After that, the CPU 201 advances the process to S14. On the other hand, if the flag is off, it is necessary to execute the color shift correction, so the CPU 201 advances the process to S13.

In S13, the CPU 201 (color shift correction unit 214) executes color shift correction. In S14, the CPU 201 executes a print job. The CPU 201 forms a toner image on the sheet P according to the print job. The CPU 201 may store the data at the time when the color shift correction is executed in the memory 202.

Here, the preparatory operation shown in FIG. 6 may be a preparatory operation for the first print job submitted after the initial adjustment process is completed. In this case, in S13, the CPU 201 measures the temperature of the exposure apparatus 13 by the temperature sensor 238, and saves the measurement result in the RAM area of the memory 202. When the second and subsequent print jobs are submitted, the CPU 201 again measures the temperature of the exposure apparatus 13 with the temperature sensor 238, and calculates the difference between this measurement result and the measurement result held in the memory 202. .. If the difference exceeds the threshold value, the CPU 201 executes the color shift correction immediately before executing the print job. In this way, the temperature of the exposure apparatus 13 may be adopted as an execution condition for color shift correction. As described above, the execution condition may be that the time difference between the current time and the time when the color shift correction is executed exceeds the threshold value.

[Effect of Examples]
In order to explain the effect of this example, this example and a comparative example are compared. In the comparative example, when a print job is submitted in the initial adjustment process, color shift correction is executed after the initial adjustment process is completed.

● FIG. 7A shows a case where a print job is submitted during execution of the image formation condition adjustment process. As shown in FIG. 7A, in the comparative example, the color shift correction is executed after the warm-up of the fuser 20 is completed, and then the print job is further executed. On the other hand, in this embodiment, after the adjustment process is completed, the color shift correction is executed in parallel with the warm-up. Further, in this embodiment, the print job is executed when the color shift correction and the warm-up are completed. Therefore, in this embodiment, the print job can be started earlier than in the comparative example, and the waiting time of the user is reduced.

● FIG. 7B shows a case where the print job is submitted after the adjustment process of the image formation conditions is completed. The operation of the comparative example in this case is the same as the operation shown in FIG. 7 (A). On the other hand, in this embodiment, when the print job is submitted after the adjustment process is completed, the color shift correction can be executed immediately. Therefore, even in the case shown in FIG. 7B, in this embodiment, the print job can be started earlier than in the comparative example, and the waiting time of the user is reduced.

The invention is not limited to the above embodiments, and various modifications and modifications can be made without departing from the spirit and scope of the invention. Therefore, claims are attached to make the scope of the invention public.

<Summary>
[Viewpoints 1 and 11]
The image forming unit 50 is an example of an image forming means for forming a color image on a sheet by superimposing a plurality of toner images having different colors. The fixing device 20 is an example of a fixing means for fixing a color image on a sheet. The CPU 201 (color shift correction unit 214) functions as a correction means for correcting color shift in the sheet by correcting the image formation positions of the plurality of toner images in the image forming means. The color shift correction unit 214 corrects the color shift in parallel with the warm-up of the fixing means. As a result, the waiting time of the user due to the color shift correction is reduced.

[Viewpoint 2]
If a print job is submitted while the fixing means is performing warm-up, the color shift correction unit 214 may perform color shift correction in parallel with the warm-up. The color shift correction unit 214 may be configured not to perform color shift correction in parallel with the warm-up if a print job is not submitted while the fixing means is performing the warm-up. If the color shift correction is executed immediately before the print job is executed, the color shift is accurately reduced.

[Viewpoint 3]
If the print job is not submitted while the fixing means is warming up, the color shift correction unit 214 may wait until the print job is submitted before executing the color shift correction. If the color shift correction is executed immediately before the print job is executed, the color shift is accurately reduced.

[Viewpoint 4]
The fuser 20 may perform warm-up when the power is turned on to the image forming apparatus 1 and when the image forming apparatus 1 returns from the power saving state to the non-power saving state. As a result, the fixing device 20 can appropriately fix the toner image on the sheet.

[Viewpoints 5 and 6]
The CPU 201 (flag management unit 221) functions as a management means for managing whether or not the color shift correction has already been executed. The color shift correction unit 214 may skip the color shift correction when the management means indicates that the color shift correction has already been executed. The color shift correction unit 214 may execute the color shift correction when the management means does not indicate that the color shift correction has already been executed. As a result, it is possible to suppress the occurrence of unnecessary waiting time caused by executing the color shift correction many times. In addition, toner consumption will be reduced. The flag management unit 221 may include a flag that turns on when the color shift correction is executed and turns off when the color shift correction is not executed.

[Viewpoint 7]
The photosensitive drum 11 is an example of a photoconductor. The charging roller 12 functions as a charging means for charging the surface of the photoconductor by applying a charging voltage to the photoconductor. The exposure apparatus 13 functions as an exposure means for exposing the photoconductor to form an electrostatic latent image. The developing device 15 functions as a developing means for developing an electrostatic latent image to form a toner image. The primary transfer device 16 functions as a transfer means for transferring a toner image to an intermediate transfer body using a transfer voltage. The CPU 201 (adjusting unit 212) functions as an adjusting means for adjusting the charging voltage and the transfer voltage. When the color shift correction is executed in the warm-up, the color shift correction unit 214 may execute the color shift correction after the adjustment of the charging voltage and the transfer voltage is completed. By appropriately adjusting the charging voltage and the transfer voltage, the toner image is appropriately transferred to the intermediate transfer body 17. Therefore, if the color shift correction is executed after the adjustment of the charging voltage and the transfer voltage is completed, the accuracy of the color shift correction is improved.

[Viewpoint 8]
The image sensor 25 is an example of a detection means for detecting a test image for color shift correction formed on the intermediate transfer body 17. The color shift correction unit 214 may control the image forming means to form a test image on the intermediate transfer body 17, and execute the color shift correction based on the test image detected by the detection means.

[Viewpoint 9]
The temperature sensor 238 may function as a measuring means for measuring the temperature of the exposure means. The memory 202 may function as a temperature storage means for storing the temperature of the exposure means measured by the measuring means when the color shift correction is executed. The color shift correction unit 214 skips the color shift correction if the difference between the temperature of the exposure means when the print job is input and the temperature of the exposure means stored in the temperature storage means does not exceed the temperature threshold. You may. This reduces the user's waiting time.

[Viewpoint 10]
The RTC223 may function as a clock means for timekeeping. The memory 202 may function as a time storage means for storing the time when the color shift correction is executed. The color shift correction unit 214 may skip the color shift correction if the difference between the time when the print job is input and the time stored in the time storage means does not exceed the time threshold value. This reduces the user's waiting time.

1: Image forming apparatus, 50: Image forming unit, 20: Fixer, 201: CPU

Claims (9)

An image forming means for forming a color image on a sheet by superimposing a plurality of toner images having different colors.
A fixing means for fixing the color image on the sheet,
It has a correction means for correcting color shift in the sheet by correcting the image formation position of each of the plurality of toner images in the image forming means.
The correction means
If a print job is submitted while the fixing means is performing warm-up, the color shift correction is executed in parallel with the warm-up.
If a print job is not submitted while the fixing means is performing warm-up, if a print job is submitted after the warm-up is completed, the color shift correction is executed. An image forming apparatus characterized in that. If a print job is not submitted while the fixing means is performing warm-up, the correction means is configured to wait until the print job is submitted and then execute the color shift correction. The image forming apparatus according to claim 1. The fixing means is
1. The image forming apparatus is configured to perform the warm-up when the power is turned on and when the image forming apparatus returns from the power saving state to the non-power saving state. Or the image forming apparatus according to 2. Further having a management means for managing whether or not the color shift correction has already been performed,
The correction means
If the control means indicates that the color shift correction has already been performed, the color shift correction is skipped.
The invention according to any one of claims 1 to 3, wherein the control means is configured to perform the color shift correction when it does not indicate that the color shift correction has already been performed. Image forming device. The image forming apparatus according to claim 4, wherein the management means includes a flag that is turned on when the color shift correction is executed and is turned off if the color shift correction is not executed. The image forming means
Photoreceptor and
A charging means for charging the surface of the photoconductor by applying a charging voltage to the photoconductor,
An exposure means that exposes the photoconductor to form an electrostatic latent image,
A developing means for developing the electrostatic latent image to form a toner image, and
It further has a transfer means for transferring the toner image to the intermediate transfer body using the transfer voltage, and an adjusting means for adjusting the charging voltage and the transfer voltage.
When the color shift correction is executed in the warm-up, the correction means executes the color shift correction after the adjustment of the charging voltage and the transfer voltage is completed, according to claims 1 to 5. The image forming apparatus according to any one of the above. Further, it has a detection means for detecting a test image for color shift correction formed on the intermediate transfer body.
The correction means is configured to control the image forming means to form the test image on the intermediate transfer body, and execute the color shift correction based on the test image detected by the detection means. The image forming apparatus according to claim 6. A measuring means for measuring the temperature of the exposure means and
Further, it has a temperature storage means for storing the temperature of the exposure means measured by the measuring means when the color shift correction is executed.
If the difference between the temperature of the exposure means when the print job is input and the temperature of the exposure means stored in the temperature storage means does not exceed the temperature threshold, the correction means corrects the color shift. The image forming apparatus according to claim 6 or 7, wherein the image forming apparatus is configured to skip. Clock means to measure the time and
Further, it has a time storage means for storing the time when the color shift correction is executed.
The correction means is configured to skip the color shift correction if the difference between the time when the print job is input and the time stored in the time storage means does not exceed the time threshold. The image forming apparatus according to any one of claims 1 to 8.

Images