JP2006023468A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus easily correcting color shift even when a scratch or a hollow exists in a belt or when some toner void exists in a portion of a correction pattern. <P>SOLUTION: Visual images developed by two or more photoreceptors are sequentially transferred to an endless belt or a recording medium travelling so that two or more image forming units are sequentially passed in the image forming apparatus. The image forming apparatus is provided with a means for forming two or more sets of correction patterns on the endless belt or the recording medium for detecting color shift between the visual images transferred superposed by the two or more image forming units, a means to detect the correction patterns formed on the endless belt or the recording medium, a means to calculate color shift correction data from the detected result of the two or more sets of correction patterns, a means to compensate the color shift based on the correction data, a means to count the number of the correction patterns in a specified section and a means to discriminate whether detection of the correction patterns is carried out normally based on the counted number of correction patterns. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus for forming a color image by forming a plurality of images on a plurality of photoconductors by independently scanning a plurality of light beams on the plurality of photoconductors. Is.

  In color laser printers and copiers, images consisting of four colors of toner (Y: yellow, M: magenta, C: cyan, K: black) are sequentially formed on a single photoconductor, and transferred sequentially 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 method 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 attachment of the photoconductors and the optical devices and changes over 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 detected by a correction pattern detection sensor provided near both ends of the belt. Then, based on the detected misregistration amount between the respective color patterns, correction data of the misregistration amount is calculated, and the misregistration correction between the respective 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 41 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 non-printing areas. There's a problem.

  An object of the present invention is to provide an image forming apparatus that solves the above-described problems.

  Specifically, it is an object of the present invention to provide an image forming apparatus that can easily perform color misregistration correction even when there are scratches or dents on a belt or some toner is missing from a correction pattern.

  Another object of the present invention is to provide an image forming apparatus capable of informing a user of belt deterioration before image formation becomes impossible due to belt deterioration or the like.

  In order to achieve the above object, the present invention provides a photoconductor, a charger for charging the surface of the photoconductor, an optical device for exposing the charged photoconductor surface according to image data, and developing the exposed image area. A plurality of image forming units each having a developing machine, and sequentially displaying the visible images developed on the plurality of photosensitive members on an endless belt or a recording medium that travels so as to pass through the plurality of image forming units sequentially. In the image forming apparatus to be transferred, means for forming a plurality of correction patterns for detecting color misregistration between visible images superimposed and transferred by the plurality of image forming units on an endless belt or a recording medium; Means for detecting correction patterns formed on the recording medium; means for calculating color misregistration correction data from detection results of the plurality of sets of correction patterns; and color based on the correction data Means for correcting this, means for counting the number of the correction patterns in a predetermined section, and means for determining whether or not the correction pattern was normally detected based on the number of correction patterns counted. There is one feature.

  Another feature of the present invention is that, when the determination unit determines that the value obtained by counting the number of correction patterns in a predetermined section is abnormal, the detection result of the plurality of sets of correction patterns is used to calculate color misregistration correction data. There is to not use.

  Another feature of the present invention is that the number of correction patterns detected by the determination unit is determined to be abnormal, and the correction pattern determined to be abnormal is not the last correction pattern set of a plurality of correction patterns. The detection result of the plurality of sets of correction patterns is not used for calculation of color misregistration correction data, but the detection result of the next detected correction pattern is used.

  Another feature of the present invention is that, when the number of correction patterns detected by the determination unit is determined to be abnormal, and the correction pattern determined to be abnormal is not the first correction pattern set of a plurality of correction patterns. The detection result of the plurality of sets of correction patterns is not used for calculating the color misregistration correction data, but the detection result of the correction pattern detected before is used.

  Another feature of the present invention is that, when it is determined that the number of correction patterns detected by the determination unit is abnormal, the detection result of the plurality of sets of correction patterns is not used for calculation of color misregistration correction data, but an ideal value is used. There is.

  Another feature of the present invention is to issue a warning notifying the deterioration of the endless belt or the like after the color misregistration correction is performed when the number of correction pattern groups determined to be abnormal by the determination means is N2 or more. It is in that.

  Another feature of the present invention is that the color misregistration correction and the color image formation are stopped and the color misregistration is stopped when the number of correction pattern sets determined to be abnormal by the determining means is equal to or greater than the predetermined number N1 greater than N2. This is to warn of a failure of correction or an abnormality of the endless belt.

  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. If it is determined that the number of correction patterns is abnormal, (1) correction is performed. Do not use pattern detection result, (2) Use detection result of correction pattern detected next, (3) Use detection result of correction pattern detected before, (4) Instead of detection result of correction pattern Since the color misregistration correction data is calculated using any one of the ideal values for the color misregistration, there is an effect that the color misregistration correction can be performed while keeping the correction range of the color misregistration correction wide.

  If the number of correction patterns determined to be abnormal is within a predetermined number of times, a warning is given to the deterioration of the belt while permitting the formation of a color image. It is possible to notify the user 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 the photoreceptors 11k, 11y, 11m, and 11c, there are chargers 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. Each developed toner image is 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, 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, so that the count value of the counter 34 can be counted up, the count value can be read, 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, and 6.

  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 is detected.

  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 the correction patterns 21, it is determined that the correction patterns 21 are not normally detected.

  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.

  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 embodiment of the control flow of the control unit 30 for correcting the misalignment 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 has been detected normally. If it is detected normally, the value of the color misregistration counter 32 is stored in the memory of the CPU 31 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, 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, the count values of the color misregistration counters 32 stored in the memory of the CPU 31 are averaged in step S16. And various color misregistration corrections are executed based on the color misregistration counter values averaged in step S17. 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. When the detection of the plurality of sets of correction patterns 21 has not been completed, the operation is repeated again from step S12.

  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 misregistration correction controller 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 S21. Next, in step S22, a set of correction patterns is detected, and the count values are input to the color misregistration counter 32 and the pulse counter 33. In step S23, it is determined whether or not the correction pattern is normally detected. In the case of normal detection, the value of the color misregistration counter 32 is stored in the memory of the CPU 31 in step S24, and the process proceeds to step S26. If it is not normal detection, the process proceeds to step S25, and one of the following is performed to store an alternative value in the memory.
(1) Value to be detected next time (Condition: When not the last correction pattern set)
Next, the color misregistration counter value detected normally next time is stored in the memory twice in step S24. (2) The value detected last time (condition: not the last correction pattern set)
The color misregistration counter value detected normally last time is stored in the memory in step S25. (3) Ideal value The ideal value when there is no color misregistration is stored in the memory in step S25.

Next, in step S26, it is determined whether or not the detection of a plurality of sets of correction patterns 21 has been completed. If all the detections have been completed, a plurality of color misregistration counter values stored in the memory are averaged in step S27. Then, various color misregistration corrections are executed based on the color misregistration counter value averaged in step S28. If the detection of the plurality of sets of correction patterns 21 has not been completed, the operation is repeated again from step S22.

  With the contents described above, the same effects as in the first embodiment can be obtained.

  Next, another embodiment of the control flow of the misregistration correction control unit of 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 S31. Next, in step S 32, the above-described 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 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 S39. If it is not normal detection, the color misregistration counter 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 36, 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. If it is equal to or smaller than the predetermined value, the process proceeds to step S39. If it is equal to or greater than the predetermined value, the color misregistration correction and the color image formation are stopped in step S37, and a warning such as failure of color misregistration correction or belt abnormality is given in step 38. In step S39, it is determined whether or not the detection of a 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 the processing has been completed, a plurality of color misregistration counter values stored in the memory are averaged in step S40. In step S41, when the value of the abnormality correction pattern counter is out of the predetermined number of times, various color misregistration corrections are executed based on the color misregistration counter value averaged in step S43. When the value of the abnormality correction pattern counter 34 is within the predetermined number of times, after executing a warning such as belt deterioration in step S42, various color shifts are performed based on the color shift counter values averaged in step S43. Perform correction.

  According to the above-described embodiment, when the number of times that the detection of a set of correction patterns is determined to be abnormal is equal to or less than the predetermined number N2, after the color misregistration correction is performed, belt deterioration or the like is permitted while allowing 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. Explanatory drawing of operation | movement at the time of detecting a set of correction patterns normally in this invention apparatus. Operation | movement explanatory drawing in case this invention apparatus 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 apparatus of the present invention. 3 is a flowchart showing a first embodiment of a control flow of a color misregistration correction control unit of the device of the present invention. The flowchart which shows the 2nd Example of the control flow of the color misregistration correction control part of this invention apparatus. The flowchart which shows the 3rd Example of the control flow of the color shift correction control part of this invention apparatus. 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: photoreceptors 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 units 16k, 16y, 16m, 16c: cleaning device 17: intermediate transfer member 21, 41: correction pattern 22, 42: registration sensor 43: belt 31: CPU
32: Color misregistration counter 33: Pulse counter 34: Abnormality correction pattern counter

Claims (7)

  There are a plurality of image forming units having 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 a developing unit for developing the exposed image area. In the image forming apparatus for sequentially transferring the visible images developed on the plurality of photoconductors to an endless belt or a recording medium that travels so as to sequentially pass through the plurality of image forming units. Means for forming a plurality of correction patterns on the endless belt or recording medium for detecting color misregistration between visible images superimposed and transferred by the unit, and detecting the correction pattern formed on the endless belt or recording medium Means for calculating color misregistration correction data from detection results of the plurality of sets of correction patterns, means for correcting color misregistration based on the correction data, and the correction pattern An image forming apparatus comprising means for counting the number of predetermined intervals, that the detection of the normal correction pattern based on the number of correction patterns is counted and means for determining whether or not made of.   The detection result of the plurality of sets of correction patterns is not used for calculation of color misregistration correction data when the determination unit determines that the value obtained by counting the number of correction patterns in a predetermined section is abnormal. Item 2. The image forming apparatus according to Item 1.   When the number of correction patterns detected by the determination unit is determined to be abnormal, and the correction pattern determined to be abnormal is not the last correction pattern group of the plurality of correction patterns, 2. The image forming apparatus according to claim 1, wherein the detection result is not used for calculating the color misregistration correction data, but the detection result of the next detected correction pattern is used.   When the number of correction patterns detected by the determination unit is determined to be abnormal, and the correction pattern determined to be abnormal is not the first correction pattern group of the plurality of correction patterns, 2. The image forming apparatus according to claim 1, wherein the detection result is not used for calculating the color misregistration correction data, but the detection result of the correction pattern detected previously is used.   The ideal value is used instead of calculating the color misregistration correction data when the determination unit determines that the number of detected correction patterns is abnormal. The image forming apparatus according to 1.   2. A warning for informing deterioration of the endless belt or the like is issued after color misregistration correction is performed when the number of correction pattern groups determined to be abnormal by the determination means is a predetermined number of times N2 or more. The image forming apparatus described. When the number of correction patterns determined to be abnormal by the determination means is greater than or equal to the predetermined number N1 greater than N2, the color misregistration correction and the color image formation are stopped, the color misregistration correction fails, and the endless belt. The image forming apparatus according to claim 6, wherein an abnormality in the image is warned.

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