JP5755059B2 - Image forming apparatus, control method thereof, and control program - Google Patents

Description

  The present invention relates to an image forming apparatus, a control method thereof, and a control program, and more particularly to an image forming apparatus that performs color misregistration correction using a color misregistration correction pattern.

  In general, in a color image forming apparatus such as a copying machine, a printer, or a facsimile using a so-called tandem method, a color misregistration correction pattern is used when correcting color misregistration. When performing color misregistration correction, a toner image, which is a color misregistration correction pattern, is formed on an intermediate transfer member such as an intermediate transfer belt by an image forming unit for each color. Then, color misregistration correction is performed by calculating a color misregistration amount in accordance with detection of the color misregistration correction pattern (hereinafter simply referred to as a correction pattern).

  By the way, when detecting the correction pattern, a technique of detecting using an optical sensor or the like disposed in the vicinity of the intermediate transfer member is used. In this detection method, light is emitted from a light emitting portion (light emitting element) of an optical sensor to an intermediate transfer member, and reflected light from the surface of the intermediate transfer member and a correction pattern is a photosensor (referred to as a pattern detection sensor). ). The correction pattern is recognized in accordance with the difference between the reflected light amount from the intermediate transfer member and the reflected light amount from the correction pattern.

  As a method for detecting reflected light, there are a regular reflection light detection method and a diffuse reflection (also referred to as diffuse reflection) light detection method.

  In the regular reflection light detection method, a light receiving part is arranged at a position where a regular reflection component is incident on the reflected light from the intermediate transfer body and the correction pattern, and the difference in the amount of regular reflection light from the intermediate transfer body and the correction pattern is detected. A correction pattern is detected.

  On the other hand, in the irregular reflection light detection method, a pattern detection sensor (that is, a light receiving unit) is arranged at a position where irregular reflection components are incident among the reflected light reflected by the intermediate transfer body and the correction pattern. Then, a correction pattern is detected from the difference in the amount of irregularly reflected light. Since the irregular reflection component from the surface of the intermediate transfer member is small, the output level from the pattern detection sensor is low. Since there are many irregular reflection components from the correction patterns for yellow (Y), magenta (M), and cyan (C), the output level from the pattern detection sensor is high. In this case, even if the reflectivity on the surface of the intermediate transfer member is lowered, the reflected light from the intermediate transfer member is hardly affected by the decrease in reflectivity because there are few irregular reflection components. Therefore, the irregular reflection light detection method can detect the correction pattern stably for a long time.

  However, a correction pattern (low brightness color pattern) with low reflectance such as black (K) has a small amount of irregular reflection components, and therefore the output level from the pattern detection sensor is low. For this reason, it is difficult to distinguish between the surface of the intermediate transfer member and the K pattern, and it may be difficult to detect the K pattern.

  Therefore, when detecting the K pattern, a color toner image having a high reflectance is formed as a base pattern (high brightness color pattern) on the intermediate transfer member, and a pattern in which the K pattern is superimposed on the base pattern is formed. There is something which was made to do (for example, refer to patent documents 1).

  FIG. 11 is a diagram illustrating an example of a color misregistration correction pattern used in a conventional image forming apparatus.

  As shown in FIG. 11, in order to be able to detect the K pattern, a base pattern (Y pattern in the illustrated example) 915 is formed on an intermediate transfer belt (not shown). A K pattern 906 is formed in the part. For C and M having a high reflectance, a base pattern is not used unlike the C pattern 904 and the M pattern 905.

JP 2007-156159 A

  However, the K pattern is changed from the base pattern due to a change in environment such as a place where the image forming apparatus is installed, toner deterioration, and mechanical deterioration of the developer due to durability (that is, due to aging or deterioration). There may be a significant shift. If such a shift occurs, the K pattern cannot be detected, and as a result, the color shift cannot be accurately corrected.

  Accordingly, an object of the present invention is to provide an image forming apparatus, a control method thereof, and a control program capable of accurately performing color misregistration correction even when there is a secular change.

  In order to achieve the above object, an image forming apparatus according to the present invention is an image forming apparatus in which an image of each color is superimposed on an image carrier conveyed in a predetermined direction to form a color image on the image carrier. A pattern forming means for forming, on the image carrier, a correction pattern that exists on a ground pattern in which a low brightness color pattern of a low color is a color pattern having a higher brightness than the low brightness color pattern, and the image carrier A detecting unit comprising: a light emitting unit for irradiating light on the surface of the body and the correction pattern; and a light receiving unit for detecting irregularly reflected light on the surface of the image carrier and the correction pattern based on the light irradiated by the light emitting unit; Correction means for correcting the color misregistration by correcting the overlapping timing of the images of the respective colors according to the detection result by the detection means, and based on the detection result by the detection means The determination means for determining whether or not the low lightness color pattern can be detected, and when the determination means determines that the low lightness color pattern cannot be detected, the width of the base pattern in the predetermined direction is expanded. And a control unit that causes the pattern forming unit to form a correction pattern.

  According to the present invention, when performing color misregistration correction, if the low brightness color pattern on the base pattern is shifted due to aging or deterioration, and the low brightness color pattern cannot be detected, the width of the base pattern is expanded. Thus, the low brightness color pattern can be detected with certainty. As a result, color misregistration correction can be performed accurately.

1 is a diagram schematically showing the configuration of an example of an image forming apparatus according to an embodiment. FIG. 2 is a diagram for explaining an example of a color misregistration correction pattern formed on an intermediate transfer belt in the image forming apparatus illustrated in FIG. 1. It is a figure which shows the optical relationship of a light emission part and a irregular reflection light light-receiving part in the pattern detection sensor shown in FIG. It is a block diagram for demonstrating the structure of the control part shown in FIG. FIG. 2 is a diagram for explaining a signal waveform when an example of a correction pattern formed on the intermediate transfer belt shown in FIG. 1 is detected. FIG. 5 is a diagram for explaining a relationship between a color misregistration amount obtained by a control unit shown in FIG. 4 and a writing start timing. 3 is a flowchart for explaining image formation in the image forming apparatus shown in FIG. 1. It is a flowchart for demonstrating the color misregistration correction process shown in FIG. FIG. 2 is a diagram for explaining an example of a color misregistration correction pattern used in the image forming apparatus illustrated in FIG. 1. 6 is a time chart for explaining timings of signals given to the image forming unit by the CPU shown in FIG. FIG. 10 is a diagram illustrating an example of a color misregistration correction pattern used in a conventional image forming apparatus.

  Hereinafter, an example of an image forming apparatus according to an embodiment of the present invention will be described with reference to the drawings. However, the dimensions, materials, shapes, relative arrangements, and the like of the components described in this embodiment are not intended to limit the scope of the present invention only to those unless otherwise specified.

  FIG. 1 is a diagram schematically showing the configuration of an example of an image forming apparatus according to the present embodiment.

  The image forming apparatus illustrated in FIG. 1 is a so-called tandem type color image forming apparatus, and includes yellow (Y), cyan (C), magenta (M), and black (K) image forming units 101a to 101d. ing. In the image forming unit 101a, the exposure device 15a exposes the photosensitive drum 1a according to image data to form an electrostatic latent image. The electrostatic latent image is developed by the developing device 16a to become a Y toner image. Similarly, in the image forming units 101b to 101d, the exposure devices 15b, 15c, and 15d expose the photosensitive drums 1b, 1c, and 1d according to the image data to form electrostatic latent images. These electrostatic latent images are developed by developing units 16b, 16c, and 16d, respectively, to become C toner images, M toner images, and K toner images.

  Although not shown, each of the exposure apparatuses 15a to 15d includes a laser, a control driver, and a polygon mirror. Further, each of the exposure devices 15a to 15d includes a polygon mirror driving motor and various optical mirrors for guiding laser light to the photosensitive drum via the polygon mirror.

  The toner images formed on the photosensitive drums 1a to 1d are sequentially transferred to and superposed on an intermediate transfer belt 5 as an intermediate transfer member by a primary transfer roller (not shown). As a result, a color toner image 6 is formed on the intermediate transfer belt 5.

  The intermediate transfer belt 5 is stretched around a driving roller 2a, a driven roller 2, and a tension roller (belt support roller) 3, and is driven to rotate in a direction indicated by a solid arrow by driving of the driving roller 2a. The tension roller 3 and the transfer roller (secondary transfer roller) 4 are arranged to face each other with the intermediate transfer belt 5 interposed therebetween.

  The sheet is conveyed on the conveyance path 11 by the conveyance roller 10. When the leading edge of the sheet being conveyed is detected by the registration sensor 8, the sheet is temporarily held by the registration roller 13. Then, in synchronization with the rotational drive of the intermediate transfer belt 5, the sheet is conveyed by the registration roller 13 to the secondary transfer position defined by the nip portion between the tension roller 3 and the secondary transfer roller 4.

  At the secondary transfer position, the color toner image on the intermediate transfer belt 5 is transferred to a sheet, and the sheet on which the toner image is transferred is conveyed to a fixing unit (not shown) by the conveyance belt 12. In the fixing unit, the toner image is fixed on the paper, and the paper on which the toner image is fixed is discharged onto a paper discharge tray or the like.

  The optical sensor (pattern detection sensor) 7 is disposed to face the intermediate transfer belt 5.

  Although not shown, residual toner remaining on the intermediate transfer belt 5 is collected by a belt cleaner, and toner of each color remaining on the photosensitive drums 1a to 1b is collected by a drum cleaner.

  The illustrated control unit 19 executes image formation by controlling the image forming units 101a to 101d, and responds to a received light detection signal output from the optical sensor (pattern detection sensor) 7 when performing color misregistration correction, which will be described later. To calculate the color misregistration amount. Then, the control unit 19 controls the image forming units 101a to 101d based on the color misregistration amount so that the color misregistration is reduced as described later.

  By the way, in the tandem type color image forming apparatus, it is unavoidable due to an attachment error of the photosensitive drums 1a to 1d and the exposure apparatuses 15a to 15d and deformation due to temperature fluctuations of an optical mirror in the exposure apparatuses 15a to 15d. Color misregistration occurs. Therefore, it is necessary to perform color misregistration correction during standby or between image formations.

  FIG. 2 is a diagram for explaining an example of a color misregistration correction pattern (hereinafter simply referred to as a correction pattern) formed on the intermediate transfer belt 5.

  As shown in FIG. 2, when performing color misregistration correction, first, correction patterns 990a and 990b are formed in at least two places in a direction crossing the conveyance direction of the intermediate transfer belt 5. In forming the correction patterns 990a and 990b, the control unit 19 controls the image forming units 101a to 101d to form the correction patterns 990a and 990b at positions that can be read by the pattern detection sensor 7. The correction patterns 990a and 990b are the same pattern.

  The pattern detection sensor 7 is provided corresponding to each of the correction patterns 990a and 990b. That is, two pattern detection sensors 7 are provided. These pattern detection sensors 7 are arranged near the intermediate transfer belt 5 and read correction patterns 990a and 990b formed on the intermediate transfer belt 5.

  Each of the correction patterns 990a and 990b is formed such that the Y, C, and K patterns are sandwiched between M patterns that are reference colors (reference patterns), and the patterns of each color are substantially in the direction perpendicular to the belt conveyance direction. It has two patterns inclined at 45 degrees. Note that each of the Y, C, M, and K patterns is called a color pattern.

  As shown, the Y pattern follows the M pattern, followed by the M pattern. Further, following this M pattern, patterns are formed in the order of C pattern, M pattern, and K pattern.

  The Y, C, and M patterns are directly formed on the intermediate transfer belt 5, while the K pattern (that is, the low brightness color pattern) is formed on a part of the base pattern formed on the intermediate transfer belt 5. In the illustrated example, a Y pattern which is a high brightness color pattern having a brightness higher than that of the K pattern is used as the base pattern.

  When the correction patterns 990a and 990b are read by the pattern detection sensor 7, the amount of color misregistration in the main scanning direction and the sub-scanning direction of the Y, M, and K patterns based on the M pattern is grasped from the pattern spacing of each color. Can do. Calculation of the amount of color misregistration in the main scanning and sub-scanning directions will be described later.

  The control unit 19 controls the image forming units 101a, 101b, and 101d so as to eliminate the color misregistration according to the calculated color misregistration amount. FIG. 3 is a diagram showing an optical relationship between the light emitting unit 208 and the irregularly reflected light receiving unit 202 in the pattern detection sensor 7 shown in FIG.

  In FIG. 3, the pattern detection sensor 7 (detection means) has a light emitting unit 208 and a diffusely reflected light receiving unit 202. Light is emitted from the light emitting unit 208 to the intermediate transfer belt 5 and the correction pattern formed on the intermediate transfer belt 5. Of the reflected light from the surface of the intermediate transfer belt 5 and the correction pattern, irregularly reflected light (also referred to as diffusely reflected light) is received by the irregularly reflected light receiving unit 202.

  That is, the light emitting unit 208 and the irregularly reflected light receiving unit 202 are arranged at positions where the irregularly reflected light receiving unit 202 can receive diffusely reflected light. The irregular reflection light receiving unit 202 outputs an analog signal (light reception detection signal) 301 having a voltage value (output level) corresponding to the amount of received light (diffuse reflection light).

  FIG. 4 is a block diagram for explaining the configuration of the control unit 19 shown in FIG.

  In FIG. 4, the control unit 19 has a CPU 109, and the CPU 109 controls the image forming apparatus shown in FIG. Note that the CPU 109 executes control based on a program (control program) stored in the ROM 110.

  The CPU 109 controls the image forming units 101 a to 101 d to perform normal image formation and forms the above-described correction patterns 990 a and 990 b on the intermediate transfer belt 5 when performing color misregistration correction. Here, as described above, the amount of shift in the main scanning direction and the sub-scanning direction of the Y, C, and K patterns with respect to the M pattern as the reference color is detected. Therefore, the correction pattern 990a is formed on the front side in FIG. 2 and the correction pattern 990b is formed on the back side in FIG.

  Two pattern detection sensors 7 are provided. Here, the pattern detection sensors 7a and 7b are used. The pattern detection sensors 7a and 7b correspond to the correction patterns 990a and 990b, respectively. The CPU 109 performs light emission control of the light emitting unit 208 in the pattern detection sensors 7a and 7a.

  The irregularly reflected light of the light irradiated on the surface of the intermediate transfer belt 5 and the correction pattern 990a is incident on the irregularly reflected light receiving unit 202 of the pattern detection sensor 7a. The irregular reflection light receiving unit 202 outputs an analog signal (light reception detection signal) having a voltage value corresponding to the amount of incident light (diffuse reflection light) received.

  This light reception detection signal is given to the comparator 204a, and the comparator 204a compares a predetermined threshold level (threshold level) 921 with the output level of the light reception detection signal. Then, the comparator 204a gives the difference to the CPU 109 as a first digital signal.

  Similarly, the reflected light of the light irradiated on the surface of the intermediate transfer belt 5 and the correction pattern 990b is incident on the irregularly reflected light receiving unit 202 of the pattern detection sensor 7b. The irregularly reflected light receiving unit 202 outputs a light reception detection signal having a voltage value corresponding to the amount of incident light received. This light reception detection signal is given to the comparator 204b, and the comparator 204b compares a predetermined threshold level (threshold level) 921 with the output level of the light reception detection signal. Then, the comparator 204b gives the difference to the CPU 109 as a second digital signal.

  As shown in FIG. 4, the light reception detection signals output from the pattern detection sensors 7a and 7b are given to the CPU 109. These light reception detection signals are digitized by an A / D converter (not shown) provided in the CPU 109. Hereinafter, signals obtained by digitizing the light reception detection signals output from the pattern detection sensors 7a and 7b are referred to as first and second digital detection signals, respectively.

  FIG. 5 is a diagram for explaining a signal waveform when an example of a correction pattern formed on the intermediate transfer belt 5 shown in FIG. 1 is detected. As described above, although two correction patterns are formed, only one is shown here for convenience of explanation, and a light reception detection signal is received from the pattern detection sensor 7a corresponding to the illustrated correction pattern. The case will be described. The operation when receiving a light reception detection signal from the pattern detection sensor 7b is the same.

  4 and 5, comparator 204a compares the output level of the received light detection signal with the threshold level and outputs the first digital signal as described above. The threshold level is set lower than the output level corresponding to the Y, M, and C patterns, and higher than the output level corresponding to the surface of the intermediate transfer belt 5 and the K pattern.

  The CPU 109 receives the first digital signal and measures the time interval for each color. It is assumed that pattern data indicating the order and interval (that is, arrangement) of each color pattern in the correction pattern is set in the CPU 109 in advance. Here, as shown by the first digital signal in FIG. 5, the CPU 109 measures the time intervals Y1, Y2, M1, M2, K1, K2, Y3, Y4... And stores them in the RAM 119 as time interval data. To do. Since the M pattern is the reference color, the time interval between M and another color is measured.

  The CPU 109 obtains the color misregistration amount of the other color pattern with respect to the M pattern according to the time interval data (detection result). For example, the color misregistration of the Y pattern with respect to the M pattern can be obtained by the following expressions (1) and (2).

Main scanning direction deviation amount ΔHy = {(Y4-Y3) / 2- (Y2-Y1) / 2} / 2 (1)
Sub-scanning direction deviation amount ΔVy = {(Y4-Y3) / 2 + (Y2-Y1) / 2} / 2 (2)
FIG. 6 is a diagram for explaining the relationship between the color misregistration amount obtained by the control unit 19 shown in FIG. 4 and the writing start timing.

  Assume that a line segment having a width of 1 pixel and a length of 1 pixel is drawn for Y, M, C, and K. In this case, if there is no color shift, Y, M, C, and K overlap. On the other hand, when there is a color shift, as described above, the CPU 109 obtains the main scanning direction shift amount ΔHy, the sub-scanning direction shift amount ΔVy, and the like. These color shifts due to the shift amounts ΔHy and ΔVy appear in the image.

  The CPU 109 corrects the color shift in the main scanning direction by controlling the exposure timing in units of the image clock or the unit obtained by dividing the image clock by 1/16 according to the amount of shift in the main scanning direction. Further, the CPU 109 controls the exposure timing in units of BD periods or 1/16 divisions of the BD period in accordance with the amount of deviation in the sub-scanning direction, and corrects color misregistration in the sub-scanning direction.

  In this way, the CPU 109 controls the image forming unit 101a according to the main scanning direction deviation amount ΔHy and the sub-scanning direction deviation amount ΔVy to adjust the image writing timing and correct the color deviation. Similarly, for C and K, the CPU 109 controls the image forming units 101b and 101d in accordance with the color misregistration correction amount to correct the color misregistration.

  Further, as described above, the CPU 109 detects the surface state (gloss) of the intermediate transfer belt 5 in accordance with the first digital detection signal obtained by digitizing the light reception detection signal. In the pattern detection sensor 7a, if the gloss is high (the surface state is rough), the irregular reflection light received by the irregular reflection light receiving unit 202 decreases, and the output level of the light reception detection signal output from the irregular reflection light reception unit 202 decreases. . On the other hand, if the gloss is low, the amount of diffusely reflected light received increases, so that the output level of the received light detection signal increases.

  FIG. 7 is a flowchart for explaining image formation in the image forming apparatus shown in FIG.

  Assume that the image forming apparatus is in a standby state. The CPU 109 determines whether a print job (JOB) instruction (input) has been received from the user (step S601). The determination is repeated until a print job is input (NO in step S601).

  On the other hand, when a print job is input (YES in step S601), the image forming apparatus starts a printing operation (step S602), and the image forming apparatus outputs a print (step S603). The CPU 109 counts the number of prints, and determines whether or not the count value is equal to or greater than a predetermined value (step S604).

  When the number of prints exceeds a predetermined value (YES in step S604), CPU 109 causes color misregistration correction processing (step S605). When the color misregistration correction is finished, the CPU 109 determines whether or not the print job is finished (step S606). If the print job has not ended (NO in step S606), CPU 109 executes the print process in step S603. On the other hand, when the print job is completed (YES in step S606), the CPU 109 determines whether or not there is a next print job (step S607).

  If there is no next print job (YES in step S607), the image forming apparatus ends the printing operation and returns to the standby state. If there is a next print job (NO in step S607), the process returns to step S602. If the number of prints is less than the predetermined value (NO in step S604), CPU 109 proceeds to the process in step S606.

  FIG. 8 is a flowchart for explaining the color misregistration correction processing shown in FIG.

  In step S605 shown in FIG. 7, when the color misregistration correction process is started, the CPU 109 suspends the print job and controls the image forming units 101a to 101d to transfer the correction pattern to the intermediate transfer belt as described above. 5 (step S622). Subsequently, the pattern detection sensors 7a and 7b detect a correction pattern (step S623). Then, the CPU 109 calculates the deviation amounts of the Y, C, and K patterns with respect to the M pattern, which is the reference color, in accordance with the received light detection signal (step S624).

  Subsequently, the CPU 109 determines whether or not the shift amount of the K pattern has been calculated. That is, the CPU 109 determines whether or not the K pattern has been detected (step S628). If it is determined that the K pattern can be detected (YES in step S628), the CPU 109 stores the calculated shift amount in a memory (for example, the RAM 119 shown in FIG. 4), and then forms an image based on the shift amount. The image formation timing in the sections 101a, 101b, and 101d (that is, Y, C, and K) is corrected (step S629). Then, the CPU 109 proceeds to the process of step S606 shown in FIG.

  If it is determined that the K pattern cannot be detected (NO in step S628), CPU 109 detects the K pattern again (step S625). At this time, the CPU 109 increases the width of the base pattern (here, the Y pattern) of the K pattern by a predetermined width. That is, the CPU 109 increases the width of the base pattern by a predetermined width from the previous width (step S626: width expansion setting).

  After enlarging the width of the base pattern, the CPU 109 controls the image forming units 101a to 101d to form a correction pattern on the intermediate transfer belt 5 (step S627). In this correction pattern, the width of the base pattern is enlarged by a predetermined width from the previous time. Then, the CPU 109 proceeds to the process of step S623.

  If the K pattern cannot be detected again in step S628, the CPU 109 further increases the width of the base pattern by a predetermined width in step S626. In this way, the CPU 109 increases the width of the base pattern by a predetermined width until the K pattern can be detected.

  By the way, when the correction pattern is formed by the image forming units 101a to 101d due to aging degradation of the image forming apparatus, the K pattern is shifted from the center of the base pattern. That is, as shown in FIG. 11, when the K pattern 906 is shifted from the center of the base pattern (Y pattern 915) and formed on the front side in the transport direction, the area of the base pattern portion 915 a positioned on the front side of the K pattern 906 Becomes extremely small.

  For this reason, when the pattern detection sensor 7 detects the correction pattern, the output level of the light reception detection signal (analog signal), which is the result of detecting the base pattern portion 915a, may be lower than the threshold level. For this reason, the CPU 109 cannot recognize (identify) the base pattern portion 915a, and as a result, the CPU 109 cannot recognize (identify) the K pattern 906 as well.

  FIG. 9 is a diagram for explaining an example of a color misregistration correction pattern used in the image forming apparatus shown in FIG.

  As described with reference to FIG. 8, if the K pattern 906 cannot be detected, the CPU 109 increases the width of the base pattern (Y pattern 915) and tries to detect the K pattern 906 again. For this reason, when the correction pattern is formed by the image forming units 101a to 101d due to aging degradation of the image forming apparatus or the like, the K pattern 906 is shifted from the center of the base pattern (Y pattern 915) and is formed on the front side in the transport direction. However, since the width of the base pattern is enlarged, the area of the base pattern portion 915a located on the front side of the K pattern is sufficiently large for detection.

  As a result, when the pattern detection sensor 7 detects the correction pattern, the output level of the light reception detection signal, which is the result of detecting the background pattern portion 915a, exceeds the threshold level, so the CPU 109 recognizes the background pattern portion 915a, A K pattern 906 can also be recognized.

  Here, the timing of signals given by the CPU 109 to the image forming units 101a to 101d will be described.

  FIG. 10 is a time chart for explaining timings of signals given to the image forming units 101a to 101d by the CPU 109 shown in FIG.

  When the user inputs a copy start from an operation unit (not shown), the CPU 109 turns on a copy start signal to be given to the image forming units 101a to 101d. Subsequently, the CPU 109 sequentially turns on the Y image write signal, the M image write signal, the C image write signal, and the K image write signal, and sends the Y image data signal, the M image data signal, and the C image to the image forming units 101a to 101d, respectively. A data signal and a K image data signal are sent.

  At this time, the Y image write signal, the M image write signal, the C image write signal, and the K image write signal that are the primary transfer timing according to the color shift amount (that is, color shift correction data) stored in the CPU 109 memory. The on-timing (t1, t2, t3, t4) time is adjusted.

  As described above, in the above-described embodiment, when the color misregistration correction is performed using the correction pattern for forming the K pattern on the base pattern, the base pattern and the K pattern are caused by the secular change of the image forming apparatus. If the K pattern is not detected because the positional relationship is shifted, the width of the base pattern is expanded. Therefore, the K pattern can be detected regardless of the secular change of the image forming apparatus, and color misregistration correction can always be performed accurately.

  In the above-described embodiment, the example in which the correction pattern is formed on the intermediate transfer belt 5 (that is, the image carrier) to perform the color misregistration correction is described. The present invention can be similarly applied to a type in which a correction pattern is formed on a sheet conveyed by a sheet conveying belt.

  Furthermore, in the above-described embodiment, the image forming apparatus using the electrophotographic process has been described. However, the image forming apparatus is not limited to the electrophotographic process, and can be applied to, for example, an ink jet printing apparatus.

  In the above-described embodiment, the output level and the threshold level of the light reception detection signal are compared, and the color misregistration amount is detected according to the comparison result (difference). The center of gravity position or peak position may be calculated to calculate the color misregistration amount.

  As is clear from the above description, in FIGS. 1 and 4, the CPU 109 and the image forming units 101a to 101d function as a pattern forming unit and a correcting unit. The CPU 109 functions as a determination unit. Further, the CPU 109 also functions as a control unit.

  As mentioned above, although this invention was demonstrated based on embodiment, this invention is not limited to these embodiment, Various forms of the range which does not deviate from the summary of this invention are also contained in this invention. .

  For example, the function of the above-described embodiment may be used as a control method, and the control method may be executed by the image forming apparatus. Further, a program having the functions of the above-described embodiments may be used as a control program, and the control program may be executed by a computer included in the image forming apparatus. The control program is recorded on a computer-readable recording medium, for example.

  At this time, the control method and the control program have at least a pattern formation step, a light emission step, a light reception step, a correction step, a determination step, and a control step.

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

1a to 1d Photosensitive drum 5 Intermediate transfer belt 7 Pattern detection sensor 101a to 101d Image forming unit 109 CPU
110 ROM
119 RAM
204a, 204b Comparator 202 Diffuse reflected light receiving unit 208 Light emitting unit

Claims (6)

In the image forming apparatus for forming a color image on the image carrier by superimposing the images of the respective colors on the image carrier conveyed in a predetermined direction,
A pattern forming means for forming a correction pattern on the image carrier, the low lightness color pattern having a low lightness color existing on a ground pattern that is a color pattern having a lightness higher than that of the low lightness color pattern;
A light emitting unit configured to irradiate light on the surface of the image carrier and the correction pattern; and a light receiving unit configured to detect irregularly reflected light on the surface of the image carrier and the correction pattern based on the light irradiated by the light emitting unit. Detection means;
Correction means for correcting the color misregistration by correcting the overlay timing of the images of the respective colors according to the detection result by the detection means;
Determining means for determining whether or not the low lightness color pattern has been detected based on a detection result by the detecting means;
And a control unit that causes the pattern forming unit to form the correction pattern in which the width of the base pattern in the predetermined direction is increased when the determination unit determines that the low brightness color pattern cannot be detected. An image forming apparatus. Each color is yellow, cyan, magenta, and black,
The correction pattern has the yellow, cyan, magenta, and black patterns,
When the correction pattern is formed on the image carrier by the pattern forming unit, the black pattern is used as the low brightness color pattern, and any of the yellow, cyan, or magenta pattern is used as the base pattern. Is used,
The correction means is set with a threshold level for identifying the yellow, cyan, and magenta patterns,
When the correction pattern is formed on the image carrier, the correction unit compares the output level of the received light detection signal, which is the detection result of the detection unit, with the threshold level, and uses the comparison result as a comparison result. The image forming apparatus according to claim 1, wherein the yellow, cyan, magenta, and black patterns are detected and the color misregistration correction is performed in accordance with the detection result.   The image forming apparatus according to claim 2, wherein the base pattern is the yellow pattern.   The image forming apparatus according to claim 3, wherein the correction pattern includes the magenta pattern as a reference pattern, and the reference pattern is arranged between the remaining color patterns. A method of controlling an image forming apparatus for forming a color image on an image carrier by superimposing an image of each color on an image carrier carried in a predetermined direction,
A pattern formation step of forming a correction pattern on the image carrier, the low lightness color pattern having a low lightness color existing on a ground pattern that is a color pattern having a lightness higher than the low lightness color pattern;
A light emitting step of irradiating light from the sensor to the surface of the image carrier and the correction pattern;
A light receiving step of detecting irregularly reflected light of the surface of the image carrier and the correction pattern with the sensor;
A correction step for correcting the color misregistration by correcting the overlay timing of the images of the respective colors according to the detection result of the light receiving step;
A determination step of determining whether or not the low brightness color pattern has been detected based on the detection result of the light receiving step;
And a control step of forming the correction pattern in which the width of the base pattern in the predetermined direction is increased by the pattern forming step when it is determined in the determination step that the low brightness color pattern cannot be detected. Characteristic control method. A control program used in an image forming apparatus for superimposing an image of each color on an image carrier carried in a predetermined direction to form a color image on the image carrier,
In the computer provided in the image forming apparatus,
A pattern formation step of forming a correction pattern on the image carrier, the low lightness color pattern having a low lightness color existing on a ground pattern that is a color pattern having a lightness higher than the low lightness color pattern;
A light emitting step of irradiating light from the sensor to the surface of the image carrier and the correction pattern;
A light receiving step of detecting irregularly reflected light of the surface of the image carrier and the correction pattern with the sensor;
A correction step for correcting the color misregistration by correcting the overlay timing of the images of the respective colors according to the detection result of the light receiving step;
A determination step of determining whether or not the low brightness color pattern has been detected based on the detection result of the light receiving step;
If it is determined in the determination step that the low-lightness color pattern cannot be detected, a control step of forming the correction pattern in which the width of the base pattern in the predetermined direction is increased by the pattern formation step is executed. A control program characterized by

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