JP4705352B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus for forming a color image by forming images on a plurality of photoconductors by scanning a plurality of light beams independently on the photoconductors and superimposing these images. It is about.

  In color laser printers and copiers, images consisting of four color toners (Y: yellow, M: magenta, C: cyan, K: black) are sequentially formed on a single photoconductor, and sequentially transferred onto the transfer body. Color images are formed by superimposing them, but this method has a problem that it takes time to form a final color image.

  Therefore, in recent years, as the image forming speed has been increased, a plurality of optical devices are independently scanned with light beams from a plurality of photoconductors to form images of the respective colors, and the images of the respective colors are formed on the belt or on the belt. A tandem method is used in which a color image is formed by superimposing and transferring on a recording material conveyed to the recording medium. Since the tandem method forms four color images at a time, the time until the final color image is formed can be greatly reduced.

  However, since the tandem system uses a plurality of photoconductors and a plurality of optical devices, the quality is good unless correction of color misregistration is performed according to variations in the mounting of the photoconductors and the optical devices and changes with time of the mechanism unit. There is a problem that not only a color image cannot be obtained, but also color unevenness occurs in some cases. For this reason, conventionally, a correction pattern for each color toner for color misregistration detection is printed along the longitudinal direction on both ends of the belt, and a correction pattern for each color toner is generated by a correction pattern detection sensor provided near both ends of the belt. Then, based on the detected misregistration amount between the color patterns, correction data of the misregistration amount is calculated, and the misregistration correction between the colors is performed.

  Next, color misregistration detection will be described in detail with reference to FIG. In general, registration sensors 42 are arranged at both ends of the belt 41, respectively. The sensor 42 is composed of a light emitting element made of, for example, an LED, a light receiving element made of, for example, a photodiode, and a comparison circuit that compares the output of the light receiving element with a threshold value and converts it into a pulse. Further, variously devised correction patterns 43 are formed along the traveling direction on both ends of the belt 41.

  By detecting the correction pattern 43 with the registration sensor 41, color misregistration detection is performed. 11A shows an example of the correction pattern 43, FIG. 11B shows an output of a light receiving element such as a photodiode, FIG. 11C shows an example of an output waveform of the registration sensor 42, FIG. 11C shows a threshold value, and FIG. In general, the belt 41 has high reflectivity, and light from the light receiving element is efficiently reflected and enters the light receiving element. Since the reflectance of the light of the correction pattern 43 by the toner is small, the output of the light receiving element is reduced only at the portion of the correction pattern 43 as shown in (b). By inputting the output of the light receiving element to a comparison circuit having a certain threshold value, a signal having a pulse waveform as shown in (d) is obtained as an output of the registration sensor 42. The interval between pulses obtained from the sensor 42 is measured and compared with a certain reference value to detect the color misregistration amount of each color pattern.

  However, if there is a scratch or the like on the surface of the belt 41 on which the correction pattern 43 is printed, the reflectance decreases due to the scratch or the like, and the output of the light receiving element decreases below the threshold value, as shown in FIG. 42 outputs a pulse. If the color misregistration correction is performed based on the interval of the pulses output due to the scratches on the belt 41, there is a problem that not only the color misregistration correction cannot be performed but also a color image having a large color misregistration is output.

  In order to avoid this problem, various methods have heretofore been proposed. For example, the technique disclosed in Patent Document 1 will be described with reference to FIG. 13A shows scratches and depressions of the correction pattern 43 and the belt 41, FIG. 13B shows the output of the light receiving element, FIG. 13C shows the threshold value, and FIG. 13D shows the output of the registration sensor 42. A CPU (not shown) extracts only the output of the correction pattern 43 from the output of the registration sensor 42 due to the correction pattern 43 and scratches and depressions. Based on the position where the leading correction pattern 43 is formed, the second and third positions are predicted, and if the output of the registration sensor 42 at a position deviating from the predicted position cannot be detected at the predicted position, the toner Judge as missing. Further, if the output width of the registration sensor 42 is larger than a predetermined value, it is determined that the belt 41 is depressed. If the number of effective detection results is less than or equal to the predetermined number, it is determined that sufficient accuracy cannot be obtained, and measurement is performed again.

  Another technique disclosed in Patent Document 2 will be described with reference to FIG. When the image forming apparatus enters the color misregistration correction operation mode, a correction pattern 43 is generated, and the correction pattern 43 is detected by the registration sensor 42. At this time, the number of pulses of the generated correction pattern detection signal is counted by a counter. Here, the counted count value s is compared with the predetermined correction pattern detection signal pulse number n that should be generated when only the correction pattern 43 is detected. If s = n is not satisfied, the belt 41 is detected. A command for displaying a warning such as belt replacement, a command for stopping the image forming apparatus, and the like, judging that a false detection signal is included in addition to the original correction pattern detection signal due to a scratch on the sensor or a failure of the registration sensor 42, In this method, a command such as a command for prohibiting color image formation or a command for prohibiting color misregistration correction is input to the device to be controlled.

JP 2003-66677 A (page 3-4, FIG. 1)

JP 2003-167404 A (page 2-4, FIG. 2)

  As described in Patent Document 1, the second and third positions are predicted based on the position where the leading correction pattern 43 is formed, and the output of the registration sensor 42 at a position outside the predicted position is a flaw. In the method in which it is determined that toner is missing if the predicted position cannot be detected, it is necessary to narrow the time width of the predicted position as much as possible in order to avoid erroneous detection. However, narrowing the time width of the predicted position narrows the detection width, and as a result, narrows the correction width for color misregistration correction. When the correction range for color misregistration correction is narrowed, there is a problem that the mechanical attachment accuracy of an optical device, a developing machine, or the like is increased or human adjustment is required, and the cost of the device is increased.

  In general, the correction pattern is formed in a non-printing area on the belt. However, in the method described in Patent Document 2, a command for stopping the image forming apparatus by a single scratch in the non-printing area, or a color image. Since a command for prohibiting formation and a command for prohibiting color misregistration correction are issued, it is impossible to form a color image corrected for color misregistration even if there is no problem in forming a color image other than scratches in the non-printing area. There's a problem.

  The present invention relates to a photoconductor, a charger for charging the surface of the photoconductor, an optical device for exposing the charged surface of the photoconductor according to image data, and developing the exposed image area. An image forming apparatus having a plurality of image forming units each having a developing device for forming a visual image, and sequentially transferring the visible images formed on the respective photosensitive members to an image carrier passing through the plurality of image forming units. Correction pattern forming means for forming a plurality of correction patterns used for detecting color misregistration between the visible images on the image carrier, and a correction pattern for detecting the correction pattern formed on the image carrier Color misregistration correction based on detection means, a plurality of discriminating means for discriminating whether the color misregistration amount detected by the correction pattern detecting means is valid, and a plurality of correction pattern detection results determined to be valid by the discrimination means Calculate the data Means out, characterized in that a correcting means for correcting, based color shift on the calculated color shift correction data.

  According to the present invention, the number of correction patterns is counted in a predetermined section to determine whether or not a normal correction pattern has been detected. When the number of correction patterns is determined to be abnormal, the correction pattern is detected. Take the difference between the means that does not use the result and the average value of the detection result and the average value of the detection result. Since the color misregistration correction data is calculated using the normal value from which the color misregistration has been removed, there is an effect that the color misregistration correction can be performed while maintaining a wide correction range of the color misregistration correction.

  In addition, when the number of correction patterns determined to be abnormal is within a predetermined number of times, a warning is given to belt deterioration while permitting the formation of a color image. There is an effect that the user can be notified in advance.

  FIG. 1 is a schematic configuration diagram showing the overall configuration of a tandem image forming apparatus according to an embodiment of the present invention. In the image forming apparatus shown in FIG. 1, the black (K), yellow (Y), magenta (M), and cyan (C) color components are converted into independent optical devices 13, the photoconductor 11, and the latent image of the photoconductor. A developing device 14 for attaching and visualizing toner is provided, and a multiple image is printed on the intermediate transfer member 17 and a color image is obtained by transferring the multiple image onto a sheet.

  A registration sensor 22 is provided at a position close to the conveyance path of the intermediate transfer member 17, and this detection signal is applied to the positional deviation correction control unit 30. The control signal generated by the positional deviation correction control unit 30 is supplied to, for example, the optical device 13 and is used for controlling the generation timing of the laser light.

  The visible toner image forming units K, Y, M, and C having different colors are arranged vertically as shown in the figure. The visible toner image forming units K, Y, M, and C include drum-shaped photoconductors 11k, 11y, 11m, and 11c, respectively. Around each of the photoconductors 11k, 11y, 11m, and 11c, charging devices 12k, 12y, 12m, and 12c, optical devices 13k, 13y, 13m, and 13c, developing devices 14k, 14y, 14m, and 14c, a transfer device 15k, 15y, 15m, 15c and cleaning devices 16k, 16y, 16m, 16c are arranged as shown in the figure, and the photoconductor 11 rotates in the direction A in the figure.

  Next, the electrophotographic process will be described. First, in the dark place, the surfaces of the photoreceptors 11k, 11y, 11m, and 11c are uniformly charged by the chargers 12k, 12y, 12m, and 12c. Next, each optical device 13k, 13y, 13m, and 13c applies a light beam in accordance with the image data, removes the charged electric charge in the portion irradiated with the light beam, and removes the charge on the photoconductors 11k, 11y, 11m, and 11c. A latent electrostatic image is formed. In the developing devices 14k, 14y, 14m, and 14c, a toner, which is charged colored fine particles, is attached to the latent image to form a visible image. The developed toner images are transferred by the transfer units 15k, 15y, 15m, and 15c so as to be superimposed on the intermediate transfer member 17 formed of an endless belt as an image carrier, thereby forming a color image. The formed color image is secondarily transferred from the intermediate transfer member 17 to a sheet conveyed from a sheet cassette (not shown) and discharged to a stack unit (not shown).

  FIG. 2 is an explanatory diagram of a color misregistration detection correction pattern used in the image forming apparatus according to the present invention. In order to detect the color misregistration amount, the correction pattern 21 is printed on the intermediate transfer body 17, and this correction pattern 21 is detected by the registration sensors 22 installed at both ends of the intermediate transfer body 17. Here, the sensor 22 can be composed of a light emitting element, for example, an LED, a light receiving element, for example, a photodiode, and a comparison circuit that compares the output of the photodiode with a threshold value and converts it into a pulse as in the conventional case. The correction pattern 21 is, for example, a black (hereinafter abbreviated as K) correction pattern 21a serving as a reference color, cyan (hereinafter abbreviated as C), magenta (hereinafter referred to as M), which is a color for measuring a color shift amount other than the reference color (Abbreviated), yellow (hereinafter abbreviated as Y) correction patterns 21b, 21c, 21d, and a plurality of sets of correction patterns 21 arranged in the order of KK-K-C-KM-K-Y. They are arranged in pairs. The purpose of the correction pattern 21 is the reference color KK interval ΔtK-K and the CK, KM, and KY intervals ΔtK-C, ΔtK-M, and ΔtK-Y. The difference is detected as a color shift.

  FIG. 3 is a configuration diagram of a misregistration correction control unit of the image forming apparatus of the present invention. The output of the registration sensor 22 is applied to the CPU 31, the color misregistration counters 32 a, 32 b, 32 c, 32 d, and the pulse counter 33 constituting the misregistration correction control unit 30. Further, the CPU 31 is connected to the color misregistration counters 32a, 32b, 32c, 32d and the pulse counter 33 by a bus, and the CPU 31 can read the count value of each counter or clear the count value. Further, the CPU 31 is connected to the abnormality correction pattern counter 34 by a bus. The count value of the counter 34 can be counted up, the count value can be read out, and the count value can be cleared.

  Next, the correction pattern detection operation in the image forming apparatus of the present invention will be described with reference to FIGS. 4, 5, 6, and 7.

  First, the operation when a set of correction patterns 21 is normally detected will be described with reference to FIG. The registration sensor 22 detects KK-K-C-K-M-K-Y of the correction pattern 21, and measures the interval between the K-K pulses by the color misregistration counter 32a. Similarly, the intervals K-C, KM, and KY are measured by the color misregistration counters 32b, 32c, and 32d. On the other hand, the pulse counter 33 counts the number of pulses of KKKKCKMKY. Further, the CPU 31 detects the head of the set of correction patterns 21 and, after a predetermined time has elapsed from the head, that is, after all the correction patterns KKKKK-MKY have been detected, Hereinafter, the values of the color misregistration counters 32a, 32b, 32c, 32d and the pulse counter 33 are read. In the example of FIG. 4, since the value 8 of the pulse counter 33 matches the number of correction patterns 21, it is determined that a normal correction pattern 21 has been detected, and the count value is stored in the memory 35.

  FIG. 5 shows an example in which a set of correction patterns 21 could not be normally detected because extra pulses were detected due to scratches or depressions in the intermediate transfer member 17. The correction pattern 21 and the flaw, KK-K-C-K-flaw-MKY are detected by the registration sensor 22, and the interval between the KK pulses is measured by the color misregistration counter 32a. Similarly, the K-C pulse interval is measured by the color misregistration counter 32b. Since there are scratches between the KM patterns, a pulse due to the scratches is generated, and the interval between the K-scratches is measured by the color misregistration counter 32c. Further, the color misregistration counter 32d measures the M-K interval as shown in the figure. On the other hand, the pulse counter 33 counts the number of pulses of KKKKK wound / MKY. Further, the CPU 31 detects a set of correction patterns 21 at the beginning, and reads the values of the color misregistration counters 32a, 32b, 32c, 32d and the pulse counter 33 after all the correction patterns 21 have been detected, that is, at the timing of checking. Here, since the value of the pulse counter 33 is larger than the number of correction patterns 21, it is determined that the correction pattern 21 has not been detected normally, and the count value is not stored in the memory 35.

  FIG. 6 shows an example in which the M toner image of the correction pattern 21 disappears for some reason and only a predetermined number of pulses or less can be detected, so that the set of correction patterns 21 cannot be detected normally. The registration sensor 22 detects KKKKCKY of the correction pattern 21, and the interval between the KK pulses is measured by the color misregistration counter 32a. K-C is similarly measured by the color misregistration counter 32b. However, since the M correction pattern 21 is missing, the interval K-K is measured by the color misregistration counter 32c. Since the color misregistration counter 32d does not receive a pulse for ending the measurement, it continues counting. On the other hand, the pulse counter 33 counts the number of pulses of KKKKCKY. Further, the CPU 31 detects a set of correction patterns 21 at the beginning, and reads the values of the color misregistration counters 32a, 32b, 32c, and 32d and the pulse counter 33 after all the correction patterns 21 are detected, that is, at the timing of checking. Here, since the value of the pulse counter 33 is smaller than the normal value of the correction pattern 21, it is determined that the correction pattern 21 has not been detected normally, and the count value is not stored in the memory 35.

  FIG. 7 shows an example in which an extra pulse is detected due to scratches or dents in the intermediate transfer member 17, and the M toner image of the correction pattern 21 disappears simultaneously for some reason, resulting in normal detection. Show. KK-scratches-CK-KY of the correction pattern 21 is detected by the registration sensor 22, and the interval between the KK pulses is measured by the color misregistration counter 32a. Since there is a flaw between the K-C patterns, a pulse due to the flaw is generated, and the K-flaw interval is measured by the color misregistration counter 32b. Next, CK is measured by the color misregistration counter 32c, and since the M correction pattern is missing, the KY interval is measured by the color misregistration counter 32d. On the other hand, KK-K-scratches-CK-KY is measured by the pulse counter 33. Further, the CPU 31 detects a set of correction patterns 21 at the beginning, and reads the values of the color misregistration counters 32a, 32b, 32c, and 32d and the pulse counter 33 after all the correction patterns 21 are detected, that is, at the timing of checking. Here, since the value of the pulse counter 33 matches the normal value of the correction pattern 21, it is determined that the correction pattern 21 has been detected normally, and the count value is stored in the memory 35.

  In order to avoid this erroneous detection, the second filtering is performed. The CPU 31 averages the count values for each color stored in the memory 35, takes a difference from the data stored in the memory 35 for each color, and if the difference value exceeds a predetermined value D, an abnormal The data is determined to be erased from the memory 35.

  When determining whether or not the correction pattern is normally detected as described above, the second and third patterns come based on the position where the leading correction pattern 21 is formed as in the conventional case. If the position of the registration sensor 22 predicts the position and the output from the registration sensor 22 at the position deviated from the predicted position is scratched and cannot be detected at the predicted position, it is not necessary to provide a time width of the predicted position as compared with the method of determining that the toner is missing. The correction pattern can be detected at

  Next, an example of the control flow of the control unit 30 for correcting the misregistration in the image forming apparatus of the present invention will be described with reference to FIG. When the color misregistration correction is started, printing of a plurality of sets of correction patterns 21 is started in step S11. Next, in step S <b> 12, a set of correction patterns 21 is detected, and count values are input to the color misregistration counter 32 and the pulse counter 33. In step S13, it is determined whether the value of the counter 33 is detected normally. If it is detected normally, the value of the color misregistration counter 32 is stored in the memory 35 in step S14, and the process proceeds to step S15. If it is not normal detection, the value of the color misregistration counter 32 is not stored in the memory 35, and the process proceeds to step S15.

  In step S15, it is determined whether or not the detection of the plurality of sets of correction patterns 21 has been completed. If all have been completed, in step S16, the CPU 31 calculates the count values of the plurality of color misregistration counters 32 stored in the memory 35. Average things. In the next step 17, the CPU 31 takes the difference from the count value stored in the memory 35 and compares it with the predetermined value D. If the difference is larger than the predetermined value D, the CPU 31 stores the difference in the memory 35 in step 18. Clear the count value. In step 19, it is determined whether the comparison of all the data stored in the memory 35 has been completed. If all of the data have been completed, various data are counted based on the color misregistration counter values averaged in step S20. Perform color misregistration correction. That is, based on the signal generated by the CPU 31, the optical devices 13k, 13y, 13m, and 13c of the image forming units K, Y, M, and C are controlled as shown in FIG. If the comparison of all the data stored in the memory 35 has not been completed, the operation is repeated from step S17 again.

  As described above, while maintaining a wide correction range for color misregistration correction, pulses other than the correction pattern 21 such as belt scratches and dents are generated, or toner missing in a part of the correction pattern 21 occurs less than a predetermined number of times. Even in this case, it is possible to form a color image corrected for color misregistration.

  Next, another embodiment of the control flow of the control unit 30 will be described with reference to FIG. When the color misregistration correction is started, printing of a plurality of sets of correction patterns 21 is started in step S31. Next, in step S 32, the above-described set of correction patterns 21 is detected, and the count values are input to the color misregistration counter 32 and the pulse counter 33. In step S33, it is determined whether or not the correction pattern is normally detected. In the case of normal detection, the color misregistration counter value is stored in the memory in step S34, and the process proceeds to step S36.

  If it is not normal detection, the color misregistration counter value is not stored in the memory, but the process proceeds to step S35, and the abnormality correction pattern counter 34 is counted up. Next, in step S36, it is determined whether or not the detection of the plurality of sets of correction patterns 21 has been completed. If all the detection patterns have not been completed, the operation is repeated from step S32. If all are completed, a plurality of color misregistration counter values stored in the memory 35 are averaged in step S39, and the process proceeds to step S40.

  In step S40, the plurality of color misregistration counters stored in the memory 35 are compared with the above-mentioned average value. If the difference is not more than the predetermined value D, the process proceeds to step S46, and if the difference is not less than the predetermined value D. After erasing the color misregistration counter value in step S41, the abnormality correction pattern counter 34 is counted up in step S42, and the process proceeds to step S43. In step S43, it is determined whether or not the count value of the abnormality correction pattern counter 34 is equal to or greater than a predetermined value N1, and if it is equal to or smaller than the predetermined value N1, the process proceeds to step S46. If it is equal to or greater than the predetermined value N1, color misregistration correction and color image formation are stopped in step S44, and a warning such as failure of color misregistration correction or belt abnormality is issued in step S45.

  In step S46, it is asked whether or not all color misregistration counters have been compared. If not, the operation is repeated from step S40. If all have been completed, the process proceeds to step S47. In step S47, it is determined whether or not the count value of the abnormality correction pattern counter 34 is equal to or greater than a predetermined value N2. If the count value is equal to or smaller than the predetermined value N2, the process proceeds to step S49. The process proceeds to step S49. Finally, a plurality of color misregistration counter values stored in the memory 35 are averaged in step S49, and various color misregistration corrections are executed in step S50.

According to the above embodiment, the number of times detected is determined to be abnormal in a set of correction patterns, if it is on a predetermined number of times N2 than, after the color shift correction performed, deterioration of the belt or the like while allowing the formation of a color image When the predetermined number of times N1 (N1> N2) is exceeded, the color misregistration correction and the color image formation are stopped, and the color misregistration correction failure and the belt abnormality are warned. Accordingly, it is possible to notify the user of the belt deterioration or the like in advance before the situation where the color image formation of the image forming apparatus is stopped due to the belt deterioration or the like.

  Although the tandem image forming apparatus using the endless belt intermediate transfer member 17 has been described above, the present invention is similarly applied to a tandem image forming apparatus in which a sheet is conveyed on the endless belt. Can do.

1 is an overall configuration diagram illustrating an embodiment of an image forming apparatus according to the present invention. Explanatory drawing of the correction pattern in this invention. FIG. 3 is a configuration diagram of a color misregistration correction control unit in the image forming apparatus according to the present invention. FIG. 6 is an operation explanatory diagram when a set of correction patterns is normally detected in the present invention. Explanatory drawing of operation | movement in case this invention has a damage | wound and a hollow in a set of correction patterns. FIG. 6 is an operation explanatory diagram when toner is missing in a set of correction patterns in the present invention. FIG. 10 is an explanatory diagram of an operation when a set of correction patterns includes scratches, dents, and toner missing in the present invention. 5 is a flowchart illustrating a first embodiment of a control flow of a color misregistration correction control unit according to the present invention. 9 is a flowchart showing a second embodiment of the control flow of the color misregistration correction control unit of the present invention. Explanatory drawing of general color misregistration correction operation. Explanatory drawing of general correction pattern detection. Explanatory drawing when there is a flaw in a general correction pattern. Operation | movement explanatory drawing of the conventional method when there exists a crack and a hollow in a correction pattern. Operation | movement explanatory drawing of the conventional method when there exists a crack and a hollow in a correction pattern.

Explanation of symbols

11k, 11y, 11m, 11c, 32, 61 Photoconductors 12k, 12y, 12m, 12c Chargers 13k, 13y, 13m, 13c, 31, 51, 64 Optical devices 14k, 14y, 14m, 14c Developing devices 15k, 15y, 15m, 15c Transfer device 16k, 16y, 16m, 16c Cleaning device 17 Intermediate transfer member 21, 43 Correction pattern 22, 42 Registration sensor 41 Belt 30 Controller 31 CPU
32 Color shift counter 33 Pulse counter 34 Abnormality correction pattern counter 35 Memory

Claims (4)

A photoreceptor, a charger that charges the surface of the photoreceptor, an optical device that exposes the charged photoreceptor surface according to image data, and developing the exposed image area to form a visible image on the photoreceptor. In an image forming apparatus that has a plurality of image forming units each including a developing machine and sequentially transfers a visible image formed on each photosensitive member to an image carrier that passes through the plurality of image forming units. The image forming apparatus includes a CPU, a plurality of color misregistration counters, a pulse counter, and a misregistration correction control unit including a memory, a light emitting element, a light receiving element, a comparison circuit that compares the output and threshold value of the light receiving element, and converts them into pulses. The image carrier is composed of a reference color correction pattern and a color correction pattern for measuring a color misregistration amount other than the reference color. Standard A plurality of sets of correction patterns in which colors whose color misregistration amounts are measured are alternately arranged are formed, and the one set of correction patterns is included in the set of correction patterns. the resist is detected by translation sensors, spacing of the pulses of the color correction pattern to be measured the pulses and the color shift amount other than the reference color correction pattern of the reference color sequentially at the plurality of color shift counter When the number of pulses is counted by the pulse counter and the count value of the pulse counter matches the normal value of the set of correction patterns, the measured value of the color misregistration counter is stored in the memory. When the control flow that is not stored in the case of non-coincidence is repeated for all of the plurality of sets of correction patterns and is finished, the CPU The measured value of the color misregistration counter stored in the memory is averaged for each color, and the difference between the averaged average value and the stored measured value of the color misregistration counter is taken and compared with a predetermined value. , Erasing the measured value of the color misregistration counter stored in the memory where the difference is greater than the predetermined value, and after the comparison is completed for all the measured values of the misregistration counter stored, An image forming apparatus, wherein color misregistration correction is executed based on a value obtained by averaging the measured values of the color misregistration counter stored in a memory for each color.   The misregistration correction control unit has an abnormality correction pattern counter, erases the measured value of the color misregistration counter stored in the memory with the difference larger than a predetermined value, and counts up the abnormality correction pattern counter. The image forming apparatus according to claim 1. 2. The apparatus according to claim 1, wherein when the number of correction patterns stored in the abnormality correction pattern counter is equal to or greater than a predetermined number N2, a warning is issued to notify deterioration of the image carrier after the color misregistration correction. 2. The image forming apparatus according to 2.   If the number of correction patterns stored in the abnormality correction pattern counter is equal to or greater than the predetermined number N1 greater than the predetermined number N2, the color misregistration correction and color image formation are stopped, and the color misregistration correction fails. 4. The image forming apparatus according to claim 3, wherein a warning is given to the abnormality of the image carrier.

Images