JP4585868B2 - Color image forming apparatus - Google Patents

Description

  The present invention relates to a color image forming apparatus.

  FIG. 6 is a diagram illustrating an example of a configuration of a conventional color image forming apparatus (see, for example, Patent Document 1). This color image forming apparatus is a so-called tandem type in which image forming units are arranged along a conveying belt.

  As shown in FIG. 6, the image forming units that form images of different colors (magenta: M, cyan: C, yellow: Y, black: K) are arranged in a line along the conveyance belt 2 that conveys the transfer paper 1. Is arranged. The conveyor belt 2 is constructed by a driven roller 4 driven and rotated by a driving roller 3 that is driven to rotate, and is driven to rotate in the direction of the arrow by the rotation of the conveyor roller. A paper feed tray 5 in which the transfer paper 1 is stored is provided below the conveyance belt 2. The transfer sheet 1 at the uppermost position among the stored transfer sheets 1 is fed at the time of image formation and is attracted onto the transport belt 2 by electrostatic attraction. The adsorbed transfer paper 1 is conveyed to a first image forming unit (magenta), where magenta image formation is performed.

  The first image forming unit (magenta) includes a photosensitive drum 6M, a charger 7M, an exposure unit 8, a developing unit 9M, and a photosensitive cleaner 10M arranged around the photosensitive drum 6M. The surface of the photosensitive drum 6M is uniformly charged by a charger 7M, and then exposed by a laser beam 11M corresponding to a magenta image by an exposure unit 8, thereby forming an electrostatic latent image. The formed electrostatic latent image is developed by the developing device 9M, and a toner image is formed on the photosensitive drum 6M. This toner image is transferred by the transfer device 12M at a position (transfer position) where the photosensitive drum 6M and the transfer paper 1 on the transport belt 2 are in contact with each other, and forms a single color (magenta) image on the transfer paper. After the transfer, the photoreceptor drum 6M is cleaned with unnecessary toner remaining on the drum surface by the photoreceptor cleaner 10M to prepare for the next image formation.

  As described above, the transfer paper 1 on which the single color (magenta) is transferred by the first image forming unit (magenta) is transported by the transport belt 2 to the second image forming unit (cyan). In this case as well, the toner image (cyan) formed on the photosensitive drum 6 </ b> C is similarly transferred onto the transfer paper 1. The transfer paper 1 is further conveyed to a third image forming unit (yellow) and a fourth image forming unit (black), and a toner image formed with a similarly formed toner image is transferred to form a color image. I will do it. The transfer paper 1 on which a color image has been formed by passing through the fourth image forming section is peeled off from the conveying belt 2, fixed by the fixing device 13, and then discharged. Further, detection sensors 14, 15, 16 for detecting a pattern for alignment are attached on the conveyor belt 2.

  FIG. 7 is a view showing a part of the alignment toner mark row 17 formed on the transport belt 2. In FIG. 7, a set of four horizontal lines and four diagonal lines of each color is taken as one set, and eight sets are formed. By detecting the K, Y, C, and M horizontal lines and diagonal lines by the detection sensors 14, 15, and 16 arranged in the main scanning direction, skew with respect to the reference color (in this case, K), sub-scanning registration deviation, main scanning Registration shift and main scanning magnification error can be measured, and the image is shifted in the direction opposite to the position shift direction by 1/2 of the maximum-minimum position shift amount detected by each of the detection sensors 14-16. Thus, it is possible to correct the shift amount due to the magnification deviation in the main scanning direction so as not to be noticeable. Various deviation amounts, correction amount calculation and correction execution commands are executed by a main CPU described later. The detected pattern is cleaned by the cleaning means 18 (see FIG. 6).

FIG. 8 is a graph showing changes in the output voltage output from the light receiving element when the alignment toner mark row 17 is detected by the detection sensor 14 (15, 16). Prior to detection, the background portion of the conveyor belt 2 is calibrated to 4 [V], and the mark position is determined from the voltage change in each pattern. FIG. 9 is an enlarged view of the detected waveforms of BK (K) and Y in FIG. Like the BK (1) and Y (1) waveforms, the detected waveform is compared with a predetermined threshold level: Vth (= 2 [V]), and the center position of the waveform is determined from the falling intersection and the rising intersection of the waveform. Ask. On the other hand, if the background portion is not calibrated to 4 [V], the voltage level does not drop sufficiently to the Vth level as in the waveforms: BK (2) and Y (2) waveforms, Calibration is essential because the center position cannot be determined. Such misregistration correction is executed according to an instruction from the user menu, service menu or printer driver of the apparatus, or according to a predetermined execution determination condition, for example, an accumulated number of prints or a temperature rise at a location in the apparatus (not shown). Automatically executed.

JP 2003-131443 A

  However, in the above prior art, the alignment operation takes time, and if a print request is made during execution of the alignment control, printing is started after waiting for the alignment control to end. There was a problem that efficiency decreased.

  In the above-described conventional technology, it takes time to calibrate the detection level of the alignment sensor, and when a print request is made during calibration execution, printing is started after the calibration is completed. Even in this respect, there is a problem that the efficiency of the printing process is reduced.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a color image forming apparatus capable of promoting efficient operation of the apparatus and improving printing processing efficiency in order to eliminate the above-described problems caused by the prior art.

In order to solve the above-described problems and achieve the object, the color image forming apparatus according to the first aspect of the present invention forms a latent image on a photoconductor by exposure, and develops, transfers, and fixes the colors to each other. A color image forming apparatus that forms a color image on a recording sheet by superimposing a plurality of images having different colors, a transfer body that transfers and conveys the recording sheet, or an intermediate that collectively transfers each color onto the recording sheet A transfer body, mark forming means for forming a mark for alignment on the transport body or the intermediate transfer body, and an alignment sensor for detecting the position of the alignment mark formed by the mark forming means; The position of another image relative to a reference image among the plurality of images having different colors based on the position of the alignment mark detected by the alignment sensor. Calibration for determining the driving condition of the positioning sensor in order to set the detection level of the positioning sensor and the detection level of the positioning sensor to a value corresponding to the background of the conveyance body or the intermediate transfer body. A calibration request to be performed and whether or not a print request has been made before operating the calibration means, and if a print request has been made, a print request has been made so that the calibration means does not operate If not, calibration means control means for controlling the calibration means to operate is characterized.

  According to the first aspect of the present invention, since it is possible to determine whether or not to perform the calibration operation according to the state of the color image forming apparatus, it is possible to improve the efficiency of the printing process.

According to a second aspect of the present invention, the color image forming apparatus according to the first aspect of the invention is characterized in that the calibration means control means operates the calibration means prior to the operation of the alignment means. To do.

  According to the third aspect of the present invention, the calibration operation can be executed prior to the alignment operation.

According to a third aspect of the present invention, in the color image forming apparatus of the first aspect, the calibration unit control unit operates the calibration unit at the end of a job after printing a predetermined number of images. Features.

  According to the fourth aspect of the present invention, the calibration operation can be executed after printing a predetermined number of images.

According to a fourth aspect of the present invention, there is provided the color image forming apparatus according to the first aspect, wherein the calibration means control means operates the calibration means at the time of system initialization immediately after the apparatus is turned on. And

  According to the fifth aspect of the present invention, the calibration operation can be executed at the time of system initialization immediately after the apparatus is turned on.

According to a fifth aspect of the present invention, there is provided the color image forming apparatus according to the first aspect, wherein the calibration means control means turns the calibration means on when a print request is made during the operation of the calibration means. It is characterized by being stopped.

  According to the sixth aspect of the present invention, when a print request is made during the calibration operation, the calibration operation can be stopped.

According to a sixth aspect of the present invention, in the color image forming apparatus according to the fifth aspect of the present invention, the driving condition of the alignment sensor is maintained when the calibration unit is stopped, and the calibration unit is reactivated. A new setting is made later.

  According to the seventh aspect of the present invention, the driving condition of the alignment sensor can be set while the calibration operation is being performed.

According to a seventh aspect of the present invention, in the color image forming apparatus of the first aspect, the calibration unit control unit selects whether or not to continue the operation during the operation of the calibration unit. It is characterized by.

  According to the eighth aspect of the present invention, it is possible to select whether or not to continue the operation during the calibration operation.

The color image forming apparatus according to claim 8 forms a latent image on a photosensitive member by exposure, and forms a color image on a recording sheet by overlapping a plurality of images having different colors by developing, transferring and fixing. A color image forming apparatus that performs transfer and conveyance of the recording paper, or an intermediate transfer body that batch-transfers each color onto the recording paper after overlapping each color;
Mark forming means for forming an alignment mark on the transport body or the intermediate transfer member, an alignment sensor for detecting the position of the alignment mark formed by the mark forming means, and the alignment Alignment means for performing an alignment operation for aligning the position of another image with respect to a reference image among the plurality of images having different colors based on the position of the alignment mark detected by a sensor for alignment, and the alignment It is determined whether or not a print request has been made before operating the means. When the print request has been made, the alignment means does not operate. When the print request has not been made, the alignment means operates. It is characterized by positioning means control means for controlling so as to.

  According to the ninth aspect of the present invention, since it is possible to determine whether or not to perform the alignment operation according to the state of the color image forming apparatus, it is possible to improve the efficiency of the printing process.

According to a ninth aspect of the present invention, in the color image forming apparatus according to the eighth aspect, the alignment unit control unit operates the alignment unit at a job end after printing a predetermined number of images. Features.

  According to the eleventh aspect of the present invention, the alignment operation can be executed after printing a predetermined number of images.

According to a tenth aspect of the present invention, in the color image forming apparatus according to the eighth aspect, the alignment unit control unit operates the alignment unit at the time of system initialization immediately after the apparatus is turned on. And

  According to the twelfth aspect of the present invention, the alignment operation can be executed at the time of system initialization immediately after the apparatus is turned on.

According to an eleventh aspect of the present invention, in the color image forming apparatus according to the eighth aspect of the present invention, the alignment unit control unit is configured to switch the alignment unit when a print request is made during the operation of the alignment unit. It is characterized by being stopped.

  According to the thirteenth aspect of the present invention, when a print request is made during the alignment operation, the alignment operation can be stopped.

According to a twelfth aspect of the present invention, in the color image forming apparatus according to the eleventh aspect, the driving condition of the alignment sensor is maintained when the alignment unit is stopped, and the alignment unit is restarted. A new setting is made later.

  According to the fourteenth aspect of the present invention, the driving condition of the alignment sensor can be set while the alignment operation is being performed.

According to a thirteenth aspect of the present invention, in the invention according to the eighth aspect, the alignment unit control unit selects whether or not to continue the operation during the operation of the alignment unit. It is characterized by.

  According to the fifteenth aspect of the present invention, it is possible to select whether or not to continue the operation during the alignment operation.

  As described above, according to the first aspect of the present invention, a color image forming apparatus that forms a latent image on a photosensitive member by exposure and forms a color image on a recording sheet by developing, transferring, and fixing. A transfer body that transfers and conveys the recording paper, or an intermediate transfer body that collectively transfers the respective colors onto the recording paper and an alignment mark formed on the conveyance body or the intermediate transfer body. Mark forming means, a positioning sensor disposed in a direction (main scanning direction) perpendicular to the moving direction on the transport body or the intermediate transfer body, and detecting a displacement amount of an image fixing position; An alignment unit that aligns the fixing position of the image based on the detection result of the alignment sensor, and driving the alignment sensor to set the detection level of the alignment sensor to a predetermined value. Since a calibration unit for performing calibration for determining the condition and a calibration unit control unit for controlling the operation of the calibration unit are provided, whether the calibration operation is performed according to the state of the color image forming apparatus. It is possible to determine whether or not, and it is possible to improve the efficiency of the printing process.

  According to a second aspect of the invention, in the first aspect of the invention, the calibration means control means operates the calibration means when no print request is made. There is an effect that the calibration operation can be executed only when no is performed.

  According to the invention of claim 3, in the invention of claim 1, the calibration means control means operates the calibration means prior to the operation of the alignment means. There is an effect that the operation can be executed prior to the alignment operation.

  According to a fourth aspect of the present invention, in the first aspect of the invention, the calibration means control means operates the calibration means at the end of a job after printing a predetermined number of images. This produces an effect that the calibration operation can be executed after the image is printed.

  According to the invention described in claim 5, in the invention described in claim 1, the calibration means control means operates the calibration means at the time of system initialization immediately after the apparatus is turned on. There is an effect that the calibration operation can be executed at the time of system initialization immediately after the power is turned on.

  According to the invention described in claim 6, in the invention described in claim 1, when the calibration unit control unit makes a print request during the operation of the calibration unit, the calibration unit controls the calibration unit. Since it is stopped, when a print request is made during the calibration operation, the calibration operation can be stopped.

  According to the invention described in claim 7, in the invention described in claim 6, the driving condition of the alignment sensor is maintained when the calibration unit is stopped, and the calibration unit is restarted. Since it is newly set later, the driving condition of the alignment sensor can be set while the calibration operation is being performed.

  According to the invention described in claim 8, in the invention described in claim 1, the calibration means control means selects whether or not to continue the operation during the operation of the calibration means. Thus, it is possible to select whether or not to continue the operation during the calibration operation.

  According to a ninth aspect of the present invention, there is provided a color image forming apparatus for forming a latent image on a photoreceptor by exposure and forming a color image on a recording paper by developing, transferring and fixing, And a conveyance body that conveys the recording paper, or an intermediate transfer body that batch-transfers the respective colors onto the recording paper, and a mark forming unit that forms a mark for alignment on the conveyance body or the intermediate transfer body A positioning sensor that is arranged in a direction (main scanning direction) perpendicular to the moving direction on the transport body or the intermediate transfer body, and that detects a displacement amount of the fixing position of the image, and the positioning sensor Since the image forming apparatus includes an alignment unit that aligns the fixing position of the image based on the detection result, and an alignment unit control unit that controls the operation of the alignment unit. , It can determine whether to perform the positioning operation, an effect that it is possible to improve the efficiency of the printing process.

  According to the invention of claim 10, in the invention of claim 9, since the alignment means control means operates the alignment means when no print request is made, a print request There is an effect that the alignment operation can be executed only when no is performed.

  According to the invention of claim 11, in the invention of claim 9, the alignment means control means operates the alignment means at the end of a job after printing a predetermined number of images. There is an effect that the alignment operation can be executed after printing a predetermined number of images.

  According to a twelfth aspect of the invention, in the ninth aspect of the invention, the alignment means control means operates the alignment means at the time of system initialization immediately after the apparatus is turned on. There is an effect that the alignment operation can be executed at the time of system initialization immediately after the power is turned on.

  According to a thirteenth aspect of the present invention, in the ninth aspect of the invention, when the alignment means control means makes a print request during the operation of the alignment means, the alignment means is Since the operation is stopped, if a print request is made during the alignment operation, the alignment operation can be stopped.

  According to the invention described in claim 14, in the invention described in claim 13, the driving condition of the alignment sensor is maintained when the alignment means is stopped, and the alignment means is reactivated. Since it is newly set later, the driving condition of the alignment sensor can be set while the alignment operation is being performed.

  According to the invention of claim 15, in the invention of claim 9, the alignment means control means selects whether or not to continue the operation during the operation of the alignment means. It is possible to select whether or not to continue the operation during the alignment operation.

  Exemplary embodiments of a color image forming apparatus according to the present invention will be explained below in detail with reference to the accompanying drawings.

  FIG. 1 is a diagram showing a configuration of a control unit of a color image forming apparatus according to an embodiment of the present invention. First, the light reception signal obtained from the detection sensor 14 is amplified by the AMP 19, and the frequency component higher than the frequency required by the filter 20 is cut. Next, the A / D converter 21 converts the analog data into digital data. Sampling of data is controlled by the sampling control unit 22. In this embodiment, the sampling rate is 100 KHz. The sampled data is sequentially stored in the FIFO memory 23. Here, only the configuration of one detection sensor 14 is shown, but the description of the other detection sensors 15 and 16 is omitted because the same configuration can be adopted.

  After the pattern detection is completed, the stored data is loaded to the CPU 26 and the RAM 27 via the I / O port 24 by the data bus 25, arithmetic processing for calculating various shift amounts, and image formation. Arithmetic processing for condition optimization is executed.

  On the other hand, the ROM 28 stores various programs including a program for calculating various deviation amounts and a program for performing calculation processing for optimizing image forming conditions. The address bus 29 is used to specify a ROM address, a RAM address, and various input / output devices. Further, the CPU 26 monitors the detection signal from the detection sensor 14 at an appropriate timing, and the light emission amount control unit 30 ensures that even if the conveyance belt 2 and the light emission unit of the sensor are deteriorated or the like is detected. The amount of light emission is controlled so that the level of the light reception signal from the light receiving unit is always constant.

  Based on the correction amount obtained from the detection result of the alignment pattern, the CPU 26 sets the setting for the write control board 31 in order to change the image frequency based on the change of the main and sub resists, the correction of the skew, and the magnification error. Do. The write control board 31 includes a device that can set an output frequency very finely, for example, a clock generator using a VCO (Voltage Controlled Oscillator) for each color including a reference color, and uses this output as an image clock. Yes.

FIG. 2 is a diagram illustrating a configuration of the light emission amount control unit 30 of the detection sensor 14. The square wave generated from the PWM waveform generator 32 is integrated by an integrator 33 to become a voltage signal having only a DC component from which a high-frequency component is cut. Light up with. The light irradiated onto the surface of the conveyor belt 2 by the LED 35 is reflected by the photo Tr 36 and output to the I / F circuit at the next stage. The light emission amount of the LED 35 can be controlled by changing the ON / OFF duty of the PWM waveform.

In the calibration operation, the CPU 26 monitors the output voltage of the photo Tr 36 and changes the duty of the PWM waveform so as to be 4 [V]. Since the calibration operation is conventionally performed prior to the alignment operation, when the print request is made, the printing operation of the apparatus is interrupted by performing both the calibration operation and the alignment operation. The downtime increased and the print processing efficiency was reduced. Therefore, in the color image forming apparatus of this embodiment, the alignment operation and the calibration operation are not performed when the print request is made, and the alignment operation and the calibration operation are performed while the print request is not made. It was decided.

  Here, calibration and alignment processing will be described. FIG. 3 is a flowchart showing the procedure of the calibration and alignment process. In the flowchart shown in FIG. 3, it is first determined whether or not a print request has been made (step S301). If a print request has been made (step S301: Yes), RETURN is performed. On the other hand, if no print request has been made (step S301: No), calibration processing is performed (step S302), and then alignment processing is performed (step S303), and then RETURN is performed. The calibration operation is executed prior to the alignment process.

  Next, the calibration process will be described. FIG. 4 is a flowchart showing the procedure of the calibration process. In the flowchart shown in FIG. 4, first, it is determined whether or not the system is initialized when the power is turned on (step S401). In the case of system initialization at power-on (step S401: Yes), calibration is executed (step S403), and RETURN is performed. On the other hand, if it is not at the time of system initialization at power-on (step S401: No), it is determined whether or not the job (JOB) end after printing 200 sheets (step S402). Here, in the case of JOB end after printing 200 sheets (step S402: Yes), after executing calibration (step S403), RETURN is performed. On the other hand, if it is not at the end of JOB after printing 200 sheets (step S402: No), RETURN is immediately performed.

  In the color image forming apparatus according to this embodiment, when a print request is made by the user during calibration, the CPU 26 interrupts the calibration process by an interrupt process. When the operation is interrupted, the detection operation and the alignment operation are performed using the duty of the PWM waveform at the time of the interruption as it is until the next calibration operation. In addition, during calibration execution, it is possible to select whether the calibration operation is interrupted or continued by the operation unit of the apparatus or a printer driver.

  Next, the alignment process will be described. FIG. 5 is a flowchart showing the procedure of this alignment process. In the flowchart shown in FIG. 5, it is first determined whether or not the system is initialized when the power is turned on (step S501). In the case of system initialization at power-on (step S501: Yes), alignment is executed (step S503), and RETURN is performed. On the other hand, if it is not at the time of system initialization at the time of power-on (step S501: No), it is determined whether or not it is a JOB end after printing 200 sheets (step S502). Here, in the case of JOB end after printing 200 sheets (step S502: Yes), after performing alignment (step S503), RETURN is performed. On the other hand, if it is not at the time of JOB end after printing 200 sheets (step S502: No), RETURN is immediately performed.

  Note that, when a print request is made by the user during the alignment, the CPU 26 interrupts the alignment process by an interrupt process. When interrupted, until the next alignment is performed, image formation is performed using the current image formation conditions (skew correction conditions, main and sub-registration positions, magnification adjustment image frequency conditions) as they are. In addition, during alignment, it is possible to select whether the alignment operation is interrupted or continued by the operation unit of the apparatus or a printer driver.

  As described above, according to the color image forming apparatus of the present invention, it is possible to determine whether or not to execute the calibration operation and the alignment operation according to the apparatus status at the time of the printing process. Efficiency can be improved.

  As described above, the color image forming apparatus according to the present invention is useful for printing a color image, and is particularly suitable when an efficient printing process is desired.

It is a figure which shows the structure of the control part of the color image forming apparatus concerning embodiment of this invention. It is a figure which shows the structure of the light emission amount control part of the detection sensor shown in FIG. It is a flowchart which shows the procedure of a calibration and an alignment process. It is a flowchart which shows the procedure of a calibration process. It is a flowchart which shows the procedure of the alignment process. It is a figure which shows an example of a structure of the conventional color image forming apparatus. FIG. 7 is a diagram illustrating a part of an alignment toner mark row formed on the conveyance belt illustrated in FIG. 6. 6 is a graph showing a change in output voltage output from a light receiving element when a toner mark row for alignment is detected by a detection sensor. It is an enlarged view of the detection waveform of BK and Y in FIG.

Explanation of symbols

14 Detection sensor 19 AMP
20 Filter 21 A / D Converter 22 Sampling Control Unit 23 FIFO Memory 24 I / O Port 25 Data Bus 26 CPU
27 RAM
28 ROM
29 Address Bus 30 Light Emission Control Unit 31 Write Control Board 32 PWM Waveform Generator 33 Integrator 34 Constant Current Circuit 35 LED
36 Photo Tr

Claims (13)

A color image forming apparatus that forms a latent image on a photoreceptor by exposure and forms a color image on a recording sheet by superimposing a plurality of images having different colors by developing, transferring, and fixing;
A transfer body that transfers and conveys the recording paper, or an intermediate transfer body that collectively transfers each color onto the recording paper after being overlaid,
Mark forming means for forming a mark for alignment on the transport body or the intermediate transfer body;
A sensor for alignment for detecting the position of the mark for the alignment formed by the mark forming means,
Alignment means for aligning the position of another image with respect to a reference image among the plurality of images having different colors based on the position of the alignment mark detected by the alignment sensor;
Calibration means for performing calibration for determining a driving condition of the alignment sensor in order to set a detection level of the alignment sensor to a value corresponding to a background of the transport body or the intermediate transfer body;
It is determined whether or not a print request has been made before operating the calibration means. If the print request has been made, the calibration means will not operate. A color image forming apparatus comprising calibration means control means for controlling the means to operate.     The color image forming apparatus according to claim 1, wherein the calibration unit control unit operates the calibration unit prior to the operation of the alignment unit.     The color image forming apparatus according to claim 1, wherein the calibration unit control unit operates the calibration unit at a job end after printing a predetermined number of images.     2. The color image forming apparatus according to claim 1, wherein the calibration means control means operates the calibration means at the time of system initialization immediately after the apparatus is turned on.     The color image forming apparatus according to claim 1, wherein the calibration unit control unit stops the calibration unit when a print request is made during the operation of the calibration unit.     6. The color image forming apparatus according to claim 5, wherein the driving condition of the alignment sensor is maintained when the calibration unit is stopped, and is newly set after the calibration unit is restarted.     2. The color image forming apparatus according to claim 1, wherein the calibration unit control unit selects whether or not to continue the operation of the calibration unit. A color image forming apparatus that forms a latent image on a photoreceptor by exposure and forms a color image on a recording sheet by superimposing a plurality of images having different colors by developing, transferring, and fixing;
A transfer body that transfers and conveys the recording paper, or an intermediate transfer body that collectively transfers each color onto the recording paper after being overlaid,
Mark forming means for forming a mark for alignment on the transport body or the intermediate transfer body;
A sensor for alignment for detecting the position of the mark for the alignment formed by the mark forming means,
Alignment means for performing an alignment operation for aligning the position of another image with respect to a reference image among the plurality of images having different colors based on the position of the alignment mark detected by the alignment sensor;
It is determined whether or not a print request has been made before operating the alignment means. If the print request has been made, the alignment means is not operated. If the print request has not been made, the alignment is made. A color image forming apparatus comprising: an alignment means control means for controlling the means to operate.     9. The color image forming apparatus according to claim 8, wherein the alignment unit control unit operates the alignment unit at a job end after printing a predetermined number of images.     9. The color image forming apparatus according to claim 8, wherein the alignment unit control unit operates the alignment unit at the time of system initialization immediately after the apparatus is turned on.     9. The color image forming apparatus according to claim 8, wherein the alignment unit control unit stops the alignment unit when a print request is made during operation of the alignment unit.     12. The color image forming apparatus according to claim 11, wherein the driving condition of the alignment sensor is maintained when the alignment unit is stopped, and is newly set after the alignment unit is restarted.     9. The color image forming apparatus according to claim 8, wherein the positioning unit control unit selects whether or not to continue the operation of the positioning unit.

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