JP2013171174A - Image forming apparatus, control method thereof, and program - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of reducing downtime and deterioration of throughput, while obtaining a good quality image.SOLUTION: An electrophotographic image forming apparatus stores a color shift correction amount of each color when executing a color shift correction, and determines whether or not a color is included whose retrieved color shift correction amount at the previous time is under a prescribed value. When the color is included whose previous color shift correction amount is under the prescribed value, the image forming apparatus forms no color shift correction pattern of the color when executing the color shift correction next time, but only forms color shift correction patterns for colors whose color shift correction amounts at the previous time are larger than the prescribed value.

Description

  The present invention relates to an image forming apparatus, a control method therefor, and a program, and more particularly to a color misregistration correction technique for an image forming apparatus using an electrophotographic process method.

  Conventionally, in a color image forming apparatus having independent multiple color image carriers, images of all colors are designed to overlap without shifting, but it is very difficult to eliminate all variations in parts and assembly. Therefore, a means for adjusting the color misregistration is necessary. As one of the adjusting means, a color misregistration correction pattern for detecting color misregistration is formed, and control for correcting the color misregistration amount by detecting the position of the formed pattern is performed. If this color misregistration correction control is frequently performed, the color misregistration can be maintained in a good state, but the throughput is lowered. To solve this problem, as disclosed in Patent Document 1, when the previous color misregistration correction amount is small, a proposal has been made to reduce the number of repetitions of the color misregistration correction pattern for each color to be formed next time.

JP 2005-172945 A

  However, if the number of repetitions of the color misregistration correction pattern is reduced, there is a possibility that the accuracy of color misregistration correction for the color with the reduced number of repetitions may be impaired.

  The present invention has been made in view of the above problems, and provides an image forming apparatus, a control method thereof, and a program capable of obtaining a high-quality image while reducing downtime and reducing a decrease in throughput. The purpose is to do.

  In order to achieve the above object, an image forming apparatus of the present invention comprises a plurality of image forming means for forming an image on an image carrier using a developer, and a color misregistration correction pattern formed by the image forming means. An image provided with detection means for irradiating light to detect reflected light, and color misregistration correction means for correcting color misregistration of images formed by the plurality of image forming means based on the detection results of the detection means In the forming apparatus, a storage unit that stores a color misregistration correction amount of each color when the color misregistration correction is performed by the color misregistration correction unit, and a previous color misregistration correction amount stored in the storage unit is a predetermined value or less. A determination unit configured to determine whether or not a color is present, and the color misregistration correction unit determines, based on a determination result by the determination unit, that a color having a previous color misregistration correction amount equal to or less than a predetermined value exists. Next color shift compensation Without forming the color of the color registration patterns during implementation, the color shift correction amount of the previous time and controls so as to form a color shift correction pattern of the predetermined value is greater than color only.

  According to the present invention, the previous color misregistration correction amount is stored, and for a color with a small correction amount, a pattern is not formed at the next color misregistration correction, and the misregistration correction patterns for other colors are packed. Form. Therefore, the adjustment can be performed efficiently according to the color misregistration state of each color.

1 is a schematic configuration diagram of an image forming apparatus according to an embodiment of the present invention. FIG. 2 is a schematic configuration diagram when a photo sensor and an intermediate transfer belt of the image forming apparatus in FIG. 1 are viewed from below the image forming apparatus. It is a block diagram which shows the control system relevant to the color shift correction in a control unit. It is a figure which shows schematic structure of a photosensor. (A)-(c) is a figure which shows the state transition of the spot of the incident light on an intermediate transfer belt, (d) is a figure which shows the graph of an irregular reflection detection output. It is a figure which shows an example of the pattern for color misregistration correction. It is a figure which shows the waveform of the ideal photosensor output at the time of detecting the patch of the pattern for color misregistration correction with a photosensor. (A) to (c) are diagrams showing the rotation unevenness of the intermediate transfer belt driving roller for four colors, three colors, and two colors. (A) is a diagram showing a normal color misregistration correction pattern, and (b) is a diagram showing a color misregistration correction pattern when the C color misregistration correction pattern is deleted. 6 is a flowchart illustrating a flow of color misregistration correction processing in an image forming apparatus to which the color misregistration correction method of the present embodiment is applied. It is a flowchart which shows the flow of the process which determines the predetermined value D utilized by the process of FIG.

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

  FIG. 1 is a schematic configuration diagram of an image forming apparatus according to an embodiment of the present invention.

  The illustrated image forming apparatus is an electrophotographic color image forming apparatus in which a plurality of image forming units are arranged in parallel.

  The color image forming apparatus according to the present embodiment includes an image reading unit 1R and an image output unit 1P. The image reading unit 1R optically reads a document image, converts it into an electrical signal (image signal), and transmits it to the image output unit 1P. The image output unit 1P includes a plurality (four in this embodiment) of image forming units 10 (10a to 10d) arranged in parallel, a paper feeding unit 20, an intermediate transfer unit 30, a fixing unit 40, and a cleaning unit. 50, 70, a photosensor 60, and a control unit 80.

  The image forming units 10a to 10d are configured as described below. Photosensitive drums 11a to 11d as image carriers are rotatably supported at the center and are driven to rotate in the direction of the arrow. The primary chargers 12a to 12d, the laser scanner units 13a to 13d, the developing devices 14a to 14d, the cleaning devices 15a to 15d, and the folding mirrors 16a to 16d are arranged in the rotation direction facing the outer peripheral surfaces of the photosensitive drums 11a to 11d. Has been.

  The primary chargers 12a to 12d respectively apply a uniform charge amount to the surfaces of the photosensitive drums 11a to 11d. Next, the laser scanner units 13a to 13d output laser beams modulated according to the image signal from the image reading unit 1R. The outputted laser beam exposes the photosensitive drums 11a to 11d through the folding mirrors 16a to 16d, and electrostatic latent images are formed on the photosensitive drums 11a to 11d.

  The electrostatic latent image formed on the image carrier is developed by the developer of the developing devices 14a to 14d, and a visible image is formed. The visible image is transferred by the intermediate transfer unit 30 to the transfer material P supplied to the photosensitive drums 11 a to 11 d via the paper supply unit 20. Thereafter, the transfer material P is conveyed to the fixing unit 40 and heated and pressurized. The transfer material P on which the visible image is fixed is discharged to the outside of the apparatus, and the image formation is completed.

  The photosensor 60 is disposed downstream of the photosensitive drums 11 a to 11 d as a detection unit for a toner pattern (color misregistration correction pattern and density adjustment pattern) formed on the intermediate transfer unit 30. FIG. 2 shows a schematic configuration when the photosensor 60 and the intermediate transfer belt 31 are viewed from below the image forming apparatus.

  In FIG. 2, a photosensor 60 irradiates light to an endless intermediate transfer belt 31 that is an intermediate transfer member, and a color misregistration correction pattern 203 and density formed on the intermediate transfer belt 31 by photosensitive drums 11a to 11d. The reflected light from the adjustment pattern 204 is detected. Two photosensors 60 are also arranged to detect patterns formed on both ends of the intermediate transfer belt 31.

  FIG. 3 is a block diagram showing a control system related to color misregistration correction in the control unit 80.

  In FIG. 3, the control board 100 is connected to the laser scanner units 13 a to 13 d, the photo sensor 60, and the temperature sensor 108. On the control board 100, a CPU 101, an ASIC 102, a light receiving circuit 104, a sensor driving circuit 105, a ROM 106, and a RAM 107 are arranged. The CPU 101 includes an A / D converter 103.

  The photosensor 60 is a diffuse reflection detection type photosensor. The light emitting unit 901 emits light in response to a signal from the CPU 101, and the light receiving unit 902 detects diffuse reflection light diffusely reflected by the intermediate transfer belt 31 or the toner pattern. The detection light of the light receiving unit 902 is IV converted, and the light receiving circuit 104 transmits the signal to the A / D converter 103 in the CPU 101. The A / D converter 103 sequentially converts signals from the light receiving circuit 104. The CPU 101 calculates color misregistration correction information by performing calculations based on the information A / D converted by the A / D converter 103. The calculated color misregistration correction information is reflected in the settings at the time of image formation. At the time of image formation, the CPU 101 instructs the laser scanner units 13a to 13d to form an image under conditions according to the settings.

  Here, a method for detecting the color misregistration correction pattern 203 using the photosensor 60 will be described with reference to FIGS.

  The photosensor 60 includes a light emitting unit 901 and a light receiving unit 902. For example, an LED is used for the light emitting unit 901, and a photodiode is used for the light receiving unit 902, for example. The light output from the light emitting unit 901 is incident on the intermediate transfer belt 31. At this time, when the color misregistration correction pattern 203 is formed on the intermediate transfer belt 31, the incident light hitting the toner pattern (color misregistration correction pattern 203) is scattered in all directions as shown in FIG. Of these scattered light, the light reaching the light receiving unit 902 is converted into an electric signal and detected as a change in voltage value by the light receiving circuit 104 on the control board 100 shown in FIG. This change in voltage value will be described with reference to FIG.

  In FIG. 5A to FIG. 5C, a spot 501 represents a spot of incident light on the intermediate transfer belt 31. FIGS. 5A to 5C show the positional relationship between the color misregistration correction pattern 203 formed on the intermediate transfer belt 31 and the incident light spot 501. FIG. 5A shows a state in which the color misregistration correction pattern 203 is not included in the incident light spot 501. FIG. 5B shows a state where the color misregistration correction pattern 203 is half in the incident light spot 501. FIG. 5C shows a state in which the color misregistration correction pattern 203 is in the incident light spot 501. In this embodiment, it is assumed that the density of the color misregistration correction pattern 203 is uniformly formed in the surface. The change in voltage value in each state is shown in FIG.

  In FIG. 5D, since the color misregistration correction pattern 203 is not included in the incident light spot 501 at the time point (a), and only irregularly reflected light from the surface of the intermediate transfer belt 31 is obtained. The voltage level does not rise. At the time of (b), since the color misregistration correction pattern 203 is in the half incident light spot 501, irregularly reflected light is obtained to some extent, and the voltage value increases. At the time of (c), since the color misregistration correction pattern 203 is in the incident light spot 501, the amount of irregular reflection light obtained is increased and a large voltage value is obtained. In this manner, when the color misregistration correction pattern 203 passes through the incident light spot 501, a change in diffuse reflection light is obtained, and thereby the edge position of the output waveform when the color misregistration correction pattern is detected can be detected. By utilizing such a characteristic of the detection system, a color misregistration correction pattern 203 as shown in FIG. 6 is read to correct the color misregistration.

  The laser power (control information) for forming the color misregistration correction toner pattern is stored in the RAM 107 on the control board 100. The output of the photosensor 60 is sent to the ASIC 102 or the CPU 101 via the light receiving circuit 104 and temporarily stored in the RAM 107 as a photosensor output value. From the photosensor output value and the laser power (control information) stored in the RAM 107, the laser power for realizing the target density is calculated. The laser power calculated in this way is set in the ASIC 102, and the laser scanner units 13a to 13d are driven by the laser driver in the laser scanner 109 to emit light.

  FIG. 6 is a diagram illustrating an example of the color misregistration correction pattern 203.

  As illustrated, the color misregistration correction pattern 203 is a pattern in which a plurality of parallelogram patches are arranged in the sub-scanning direction of the intermediate transfer belt 31. In addition, by arranging two types of patches that are mirror-symmetrical with respect to the main scanning direction, it is possible to detect color misregistration in both the sub-scanning direction and the main scanning direction from the relationship between the target patches. Yes.

  In addition, each patch has a pattern of yellow (Y), magenta (M), and cyan (C) of measurement colors as a background, and a black (Bk) pattern as a reference color is superimposed on the background. When the irregular reflection detection type sensor as shown in FIG. 4 is used for the photosensor 60, the black (Bk) developer absorbs the light output from the LED of the light emitting unit 901, and therefore the detection is sufficient. I can't. Therefore, a black (Bk) pattern is superimposed on a color (Y, M, C) pattern. As a result, as shown in FIG. 5A, the background portion has a low diffuse reflection output (photosensor output voltage), the color portion has a high diffuse reflection output, and the black (Bk) portion has a low diffuse reflection output. Is used to detect black (Bk). Depending on how much the relative positional relationship between the colors (Y, M, C) and black (Bk) deviates from what should originally be, the amount of color misregistration in each of the main scanning direction and the sub-scanning direction can be calculated. it can.

  Next, the detection timing shift that occurs when the color misregistration correction pattern 203 is detected will be described.

  In the present embodiment, it is determined that the color misregistration correction pattern 203 has been detected at the timing when the output voltage of the photosensor exceeds the threshold voltage. For this reason, when the rise or fall of the photosensor output waveform is slow, it takes time to exceed the threshold voltage, and the detection timing of the color misregistration correction pattern may be shifted.

  FIG. 7 is a diagram illustrating an ideal photosensor output waveform when a patch of the color misregistration correction pattern 203 is detected by the photosensor 60.

  The ideal photosensor output means that the sensor output is Low when the intermediate transfer belt 31 and the black (Bk) patch are detected, and the output is High when the color (Y, M, C) patch is detected. It should be short enough. When the photosensor output is ideal, the time from when the waveform of the photosensor output starts to rise or after it starts to fall until the threshold voltage is exceeded is sufficiently short, so that the detection timing does not shift.

  However, the rising speed or falling speed of the photosensor output actually depends on the conveyance speed of the intermediate transfer belt 31, the toner density of the color misregistration correction pattern, the optical characteristics of the photosensor 60, and the like. Therefore, it takes some time to detect the output change. In addition, since detection timing may be shifted due to uneven driving of the intermediate transfer belt driving rollers 32 and 33 for driving the intermediate transfer belt 31, a plurality of color misregistration correction patterns 203 are formed and detected. Data correction is performed by averaging the data. A method for forming the color misregistration correction pattern 203 will be described with reference to FIGS. 8A to 8C.

  The waveforms shown in FIGS. 8A to 8C represent uneven rotation of the intermediate transfer belt driving roller, and the uneven rotation appears as the speed unevenness of the intermediate transfer belt 31 as it is. This speed unevenness is detected as a timing shift when the color misregistration correction pattern 203 is read. In order to cancel such rotation unevenness, the driving roller cycle is divided into N (N: integer), and the color misregistration correction pattern 203 is formed at intervals of M / N cycle (M: integer).

  In FIG. 8A, the formation position (formation timing) of the color misregistration correction pattern 203 in the 7/6 cycle of the driving roller is indicated by ★. When the six color misregistration correction patterns 203 shown in FIG. 6 are set as one set, for example, when the length of one set is 130 mm and the driving roller cycle is 120 mm, the color misregistration is performed at a cycle as shown in FIG. A correction pattern 203 is formed. In this case, the first set of color misregistration correction pattern 203 is formed up to the position of one round of driving roller (120 mm) +10 mm. The second set is formed from a position of 7/6 cycle, and the third set is formed from a position of 7/6 × 2 cycle. Thus, since the color misregistration correction pattern 203 is formed in a period of 7/6 with respect to the driving roller period, when the first pattern is formed at the position of the phase 0, the second pattern has the phase 1/6, The third pattern is formed at the position of phase 2/6, and the fourth pattern is formed at the position of phase 3/6. When the six patterns are formed, the color misregistration correction pattern 203 is formed from all positions obtained by dividing the circumference of the driving roller into six parts, so that it is possible to cancel the uneven rotation of the intermediate transfer belt driving roller. Note that the length of six patterns at this time is 120 mm × 7/6 × 6 times = 840 mm.

  Next, the color misregistration correction method in this embodiment will be described.

  Color misregistration correction processing using the color misregistration correction pattern 203 is performed every time the number of printed sheets reaches a predetermined number, or when the temperature change amount at a predetermined position of the apparatus becomes a predetermined value or more. This is a control process performed at a predetermined frequency while the apparatus is operating. A temperature change amount at a predetermined position of the apparatus is detected by a temperature sensor 108 as an apparatus temperature detecting means. Further, the temperature at the predetermined position of the apparatus may be either the temperature inside the apparatus or the temperature outside the apparatus as long as it affects the color misregistration correction (hereinafter, the temperature at the predetermined position of the apparatus is referred to as the apparatus temperature).

  As described with reference to FIG. 8A, when the color misregistration correction pattern is formed every time in the 7/6 cycle of the intermediate transfer belt driving roller, a down time of 840 mm is generated each time. This makes the user feel uncomfortable. Therefore, as will be described later, the number of color misregistration correction patterns formed during the color misregistration correction processing is reduced, leading to a reduction in downtime.

  When the color misregistration correction process is performed, it is determined how large the previous color misregistration correction amount of each color is, and it is determined whether or not a color misregistration correction pattern is to be formed in the next color misregistration correction process. Specifically, for example, when the previous color misregistration correction amount for cyan (C) is 20 μm and the limit value to be determined is set to a predetermined value 40 μm, the C color misregistration correction amount is smaller than the predetermined value. Determines that C color misregistration correction processing is not necessary. Then, the color misregistration correction pattern is set not to be formed. FIG. 9B shows a Y / M misregistration correction pattern formed by deleting the C misregistration correction pattern in this way.

  Comparing the Y, M color misregistration correction pattern shown in FIG. 9B with the Y, M, C misregistration correction pattern shown in FIG. The pattern has a shorter length along the transport direction than the Y, M, and C color misregistration correction patterns. In this way, when there is a color whose previous color misregistration correction amount is equal to or smaller than a predetermined value, the color misregistration correction pattern for the color is not formed at the next color misregistration correction execution, and the previous color misregistration correction amount exceeds the predetermined value. A color misregistration correction pattern for only a large color is formed. At this time, the total length for forming the color misregistration correction pattern can be further shortened by narrowing the color spaces that are not formed.

  Next, a pattern formation cycle when a predetermined color is reduced will be described with reference to FIGS. 8A to 8C.

  As described above, the period for forming the color misregistration correction pattern is a period for canceling the rotation unevenness of the intermediate transfer belt driving roller. Therefore, it is necessary to consider this even when shortened. If the length of one set of color misregistration correction patterns formed by deleting C is 90 mm, the pattern can be formed at an interval of 100 mm, which is 5/6 times the driving roller period of 120 mm in FIG. When the formation position of the color misregistration correction pattern in the 5/6 cycle of the driving roller is the position of the asterisk in FIG. 8B, the color misregistration correction pattern from which C is deleted is formed. When six sets are formed, the rotation unevenness of one cycle of the driving roller can be canceled. The length of 6 patterns at this time is 120 mm × 5/6 × 6 times = 600 mm.

  Further, if one set of patterns when another color is reduced is 50 mm, the pattern can be formed at 60 mm (3/6 period of the driving roller) as shown in FIG. In this case as well, if six sets are formed, the rotation unevenness of one cycle of the driving roller can be canceled, and the length of the six patterns is 120 mm × 3/6 × 6 times = 360 mm. In this case, since the color misregistration correction pattern is formed in 3/6 = 1/2 period, the rotation unevenness in one period of the driving roller is canceled if two sets of color misregistration correction patterns are formed. Is possible. The pattern length of the two sets at this time is 120 mm. As described above, it is possible to further reduce the downtime by forming the pattern with a cycle that cancels the uneven rotation of the intermediate transfer belt driving roller well while reducing the color misregistration correction pattern. .

  Next, the flow of color misregistration correction processing in the image forming apparatus to which the above-described color misregistration correction method is applied will be described with reference to the flowchart of FIG.

  When the color image forming apparatus main body is turned on (step S101), the CPU 101 detects the apparatus temperature at a predetermined timing by the temperature sensor 108, and calculates the temperature difference ΔT from the previous color misregistration correction (step S102). .

  The CPU 101 determines whether or not the temperature difference ΔT calculated in step S103 is equal to or higher than a predetermined temperature. If it is determined that ΔT is lower than the predetermined temperature, the previous color misregistration correction value is set (step S106), and step S116. Migrate to On the other hand, if it is determined that ΔT is equal to or higher than the predetermined temperature, the process proceeds to step S104.

  In step S104, color misregistration correction is started. First, the CPU 101 reads out the previous color misregistration correction value of each color from the RAM 107 (step S106). The color misregistration correction values read at this time are denoted by ΔM, ΔC, and ΔK, respectively. In this embodiment, since Y is used as a reference color for color misregistration correction, M, C, and K color misregistration correction values are read. However, if the reference color is M, for example, Y, C, and K colors are read out. The deviation correction value is read out. The same applies when C or K is the reference color. Further, in the present embodiment, the previous color misregistration correction value is read out, but the same effect can be obtained by taking the average value of the past color misregistration correction values as ΔM, ΔC, ΔK.

  The Δ * (* = M, C, K) obtained in this way is compared with a predetermined value D for each color. For example, the CPU 101 determines whether ΔM is greater than a predetermined value D, that is, whether ΔM> D (step S107). If it is determined that ΔM ≦ D, the process proceeds to step S109, and the CPU 101 determines whether M has been corrected last time. That is, when there is a color whose previous color misregistration correction amount is equal to or smaller than a predetermined value, it is determined whether or not the color smaller than the predetermined value has been corrected last time. The predetermined value D is a predetermined value, for example, a value of 42 um for one pixel.

  On the other hand, if it is determined in step S107 that ΔM> D, the CPU 101 performs setting for forming a color misregistration correction pattern of a color to be compared (here, M) (step S108).

  As a result of the determination in step S109, when it is determined that M has been corrected last time, the CPU 101 performs a setting not to form the M color misregistration correction pattern for the next correction (step S110). On the other hand, if it is determined in step S109 that M has not been corrected last time, the CPU 101 proceeds to step S108 and performs setting for forming an M color misregistration correction pattern for the next correction.

  In this way, when the setting of whether or not to form the M color misregistration correction pattern at the time of the next correction is completed, the CPU 101 determines whether or not the setting of the color misregistration correction pattern has been set for all colors. (Step S111). If it is determined that the color misregistration correction pattern is not set for all colors, the CPU 101 returns to step S107 and determines whether to form a C color misregistration correction pattern, for example, for another color ( For example, ΔC) is used.

  On the other hand, if it is determined in step S111 that the setting for forming the color misregistration correction patterns for all colors has been completed, the CPU 101 counts the number of colors that form the color misregistration correction pattern, and calculates the number. n (step S112). For example, when an M and C color misregistration correction pattern is formed and a K color misregistration correction pattern is not formed, n = 2.

  Next, in step S113, the CPU 101 sets the pattern formation interval to (2 × 2 + 1) / 6 = 5/6 of the driving roller cycle. Here, the driving roller is divided into six integers, but this number is a factor that affects the speed unevenness of the intermediate transfer belt 31 such as a numerical value close to the common divisor of the intermediate roller belt driving roller circumference and the drum circumference. Is determined in consideration of Therefore, the color misregistration correction pattern may be formed not only by 6 divisions but by an integer multiple of 7 divisions.

  The CPU 101 forms a color misregistration correction pattern at the interval set in step S113, and calculates a color misregistration correction value from the photosensor output value (step S114). Since the number of patterns formed at this time is divided into six, the number of patterns is a multiple of six. For example, six patterns are formed, and the total is 5/6 × 6 = 5, and a color misregistration correction pattern is formed on the intermediate transfer belt 31 over the length of five rotations of the driving roller. The correction value calculated in step S114 is set for the color in which the color misregistration correction pattern is formed, and the previous correction value is set for the color in which the color misregistration correction pattern is not formed (step S115). The CPU 101 reflects the set correction value to form an image (step S116). When the image formation or job is completed (step S117), the apparatus is stopped (step S118), and a series of color misregistration correction processing is completed. .

  Next, a process of determining the predetermined value D used in the process of FIG. 10 will be described using the flowchart of FIG.

  When the process for determining the predetermined value D is started (step S201), the CPU 101 determines whether or not the remaining number of prints of the print job executed by the image forming apparatus is equal to or less than the predetermined number X (step S202). The predetermined number X at this time may be determined by the output speed (PPM) of the apparatus, but is a small number such as 10 sheets. If it is less than the predetermined number, the CPU 101 determines that the color misregistration correction process should be shortened, and the CPU 101 sets a predetermined value D = 100 μm, which is larger than the normal predetermined value D = 40 μm (step S205). Make it easier to make decisions to reduce the number of patterns used.

  On the other hand, when the remaining number of print jobs exceeds the predetermined number X, the CPU 101 determines in step S203 whether or not the time priority mode is set. The time priority mode is a mode set in advance by the user or the like for the image forming apparatus. When the time priority mode is set, the CPU 101 sets a larger value than usual, for example, D = 60 μm in step S206.

  On the other hand, when the time priority mode is not set, the CPU 101 determines whether or not the image quality priority mode is set in step S204. Similar to the time priority mode, the image quality priority mode is a mode set in advance by the user or the like for the image forming apparatus. When the image quality priority mode is set, the CPU 101 sets a smaller value than normal, that is, D = 20 μm in step S207, and corrects frequently without reducing the color misregistration correction pattern as much as possible, thereby improving the image quality. It becomes possible to keep.

  On the other hand, if the image quality priority mode is not set, the CPU 101 determines that the normal mode is set, and sets a normal value such as D = 40 um (step S208).

  The color misregistration correction process described above is performed using the predetermined value D determined as described above.

  According to the present embodiment, the color misregistration correction amount of each color when the color misregistration correction is performed is stored, and it is determined whether or not there is a color whose read previous color misregistration correction amount is a predetermined value or less. When there is a color whose previous color misregistration correction amount is equal to or less than a predetermined value, the color misregistration correction pattern for the color is not formed at the next color misregistration correction execution, and the previous color misregistration correction amount exceeds the predetermined value. A color misregistration correction pattern for only a large color is formed. As a result, for colors that do not require color misregistration correction, color misregistration correction can be performed with high accuracy while reducing toner consumption and reducing downtime by not forming a color misregistration correction pattern. Image quality can be maintained.

  In the above-described embodiment, it is determined whether or not the next color misregistration correction is performed using the previous color misregistration correction value. However, for example, it may be determined using an average of a plurality of past color misregistration correction values. . Further, it may be determined whether or not the pattern is formed by the next color misregistration correction using the previous or several previous color misregistration correction values and the temperature change amount at a predetermined position of the apparatus. In this case, the color misregistration correction value is 40 μm or less and the temperature change from the previous time is within 3 ° C., but the numerical values of 40 μm and 3 ° C. are due to the characteristics of the apparatus and are not limited to this.

  For example, the predetermined value 40 um is set to a small value in the image quality priority mode to perform correction while minimizing the reduction of the pattern, or is set to a large value in the time priority mode to reduce the pattern. The frequency may be increased to reduce downtime.

  Further, the determination criterion may be changed according to the number of sheets, such as setting a large predetermined value so that the downtime can be shortened when the number of remaining sheets is small in a job for printing a plurality of sheets.

  The above-described embodiments are merely examples, and are not intended to limit the scope of the present invention.

  The present invention can also be realized by executing the following processing. That is, software (program) that realizes the functions of the above-described embodiments is supplied to a system or apparatus via a network or various storage media, and a computer (or CPU, MPU, etc.) of the system or apparatus reads the program. It is a process to be executed.

31 Intermediate transfer belt 32, 33 Intermediate transfer belt driving roller 60 Photo sensor 100 Control board 101 CPU
102 ASIC
104 light receiving circuit 105 sensor drive circuit 901 light emitting unit 902 light receiving unit

Claims (7)

A plurality of image forming means for forming an image on an image carrier using a developer; a detection means for detecting reflected light by irradiating light to a color misregistration correction pattern formed by the image forming means; and An image forming apparatus comprising: a color misregistration correction unit that performs color misregistration correction of an image formed by the plurality of image forming units based on a result of detection by the detection unit.
Storage means for storing a color misregistration correction amount of each color when color misregistration correction is performed by the color misregistration correction means;
Determination means for determining whether or not there is a color having a previous color misregistration correction amount stored in the storage means that is equal to or less than a predetermined value;
The color misregistration correction means determines that the color misregistration correction pattern for the color is corrected when the next color misregistration correction is performed if there is a color whose previous color misregistration correction amount is equal to or less than a predetermined value based on the result of determination by the determination means. An image forming apparatus that controls to form a color misregistration correction pattern for only a color whose previous color misregistration correction amount is larger than the predetermined value without forming.   The color misregistration correction unit forms the color misregistration correction pattern by filling a space for a color not to be formed when forming a color misregistration correction pattern for only a color whose previous color misregistration correction amount is larger than the predetermined value. The image forming apparatus according to claim 1, wherein the image forming apparatus is controlled as follows. An endless intermediate transfer body to which a color misregistration correction pattern is transferred from the image carrier;
The color misregistration correction unit cancels the cycle of the driving roller of the intermediate transfer member that affects color misregistration when forming a color misregistration correction pattern for only colors whose previous color misregistration correction amount is greater than the predetermined value. 3. The image forming apparatus according to claim 1, wherein control is performed so that the color misregistration correction pattern is formed at a possible cycle. An apparatus temperature detecting means for detecting a temperature at a predetermined position of the image forming apparatus;
The color misregistration correction unit performs the color misregistration correction only when a temperature difference between the previous and next color misregistration corrections is less than a predetermined temperature based on a result of detection by the apparatus temperature detecting unit. The image forming apparatus according to 1 or 2.   The color misregistration correction unit changes the predetermined value for determining a previous color misregistration correction amount to a large value when the remaining number of prints of a print job executed by the image forming apparatus is equal to or less than a predetermined number. The image forming apparatus according to any one of claims 1 to 4. A plurality of image forming means for forming an image on an image carrier using a developer; a detection means for detecting reflected light by irradiating light to a color misregistration correction pattern formed by the image forming means; and In a control method of an image forming apparatus comprising: a color misregistration correction unit that performs color misregistration correction of an image formed by the plurality of image forming units based on a detection result by a detection unit;
A storage step of storing, in a storage unit, a color shift correction amount of each color when the color shift correction is performed by the color shift correction unit;
A determination step of determining whether or not there is a color whose previous color misregistration correction amount stored in the storage unit is a predetermined value or less;
As a result of the determination in the determination step, if there is a color whose previous color misregistration correction amount is equal to or less than a predetermined value, the color misregistration correction pattern for the color is not formed at the next color misregistration correction, and the previous color And a control step of controlling the color misregistration correction means so as to form a color misregistration correction pattern for only colors having a misregistration correction amount larger than the predetermined value.   A computer-readable program for causing an image forming apparatus to execute the control method according to claim 6.

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