JP2009122437A - Color shift detection method in image forming apparatus, and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a color shift detection method for a color image forming apparatus that forms a full-color image by superposing toner images of a plurality of colors, whereby the separate color resist patterns are read by a reflection type density sensor that detects specular reflection light (P wave) and diffusion reflection light (S wave), and the shift of the timing of detecting the specular reflection light (P wave) and diffusion reflection light (S wave) resulting from a plurality of factors is corrected by an easy, inexpensive method, thereby enabling correct color superposition, and to provide an image forming apparatus. <P>SOLUTION: Thresholds for binarizing specular reflection light (P wave) and diffusion reflection light (S wave) read at specific densities of the corresponding color resist patterns by the reflection type density sensor are predetermined to binarize with the thresholds. Time difference in rising or falling at the same specific density is determined as an amount of offset, thereby calculating a difference between the P and S waves. On the basis of the difference, the amounts of displacements between the separate color resist patterns are corrected and the color image is formed. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color misregistration detection method and an image forming apparatus in an image forming apparatus such as a copying machine, a printer, a facsimile, or a composite machine using an electrophotographic method, and in particular, an intermediate transfer of a color misregistration detection pattern of each color. BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color misregistration detection method and an image forming apparatus in an image forming apparatus that is formed on a body or paper, and that is read by a reflection type density sensor to calculate a misregistration amount between each color, thereby enabling accurate color superposition. It is.

  As a color image forming method in a color image forming apparatus such as a copying machine, a printer, a facsimile, or a composite machine using an electrophotographic method, black (BK), yellow (Y), magenta (M ), Cyan (C), etc., toner images of multiple colors are formed in sequence, and then transferred onto the intermediate transfer body and then transferred onto the sheet in a secondary transfer in a lump, or referred to as a tandem type. An image forming unit including a photoconductor corresponding to each color such as black (BK), yellow (Y), magenta (M), and cyan (C) is arranged in the conveyance direction of the intermediate transfer member or the paper conveyance belt, A toner image formed by the plurality of image forming units is first transferred onto an intermediate transfer member, and then secondarily transferred onto a sheet or sequentially transferred onto a sheet conveyed by a sheet conveying belt. Form Those manner have been proposed.

  In these color image forming apparatuses, in order to prevent the color toner images of the respective colors from being misaligned and overlapped and to deteriorate the image quality, and to obtain good color reproducibility, color misregistration detection is performed prior to image formation. A toner pattern (hereinafter referred to as a color resist pattern) for adjusting the toner density is formed on a photosensitive member, an intermediate transfer member, or a paper or a paper transport belt (hereinafter simply referred to as an intermediate transfer member), and is formed as a reflection type. A density sensor (hereinafter, abbreviated as an ID sensor) is used to control image forming conditions, or to calculate the amount of misalignment between colors so that accurate color superposition can be performed.

  FIG. 6 shows a configuration example of an ID sensor used for reading such a color resist pattern. In the ID sensor shown in FIG. 6, the light from the light emitting element 1 using an LED or the like is split by a first beam splitter 2 that transmits P-polarized light and reflects a part thereof, The P-polarized light is directed toward the intermediate transfer body 12 having the color resist pattern 8 and the reflected light is detected by the light emitting element 1, and the first light receiving for monitoring to keep the light quantity constant by the feedback circuit. It is directed in the direction of the element (Photo Detector) 3.

  Then, the light directed toward the intermediate transfer body 12 having the color resist pattern 8 is reflected by the surface of the color resist pattern 8 (toner pattern) on the intermediate transfer body 12 to be P-polarized light and S-polarized light. In addition, the light is diffusely reflected and scattered on the surface of the intermediate transfer body 12 and is incident on the second beam splitter 4 as P-polarized light of regular reflection without being disturbed by polarization.

  The light incident on the second beam splitter 4 is divided into two polarization components, the P wave being divided into a second light receiving element (Photo Detector) 5 and the S wave being divided into a third light receiving element (Photo Detector) 6. A control device (not shown) detects the toner density and the position of each color resist pattern 8 based on the ratio of the output voltages from the respective light receiving elements 5 and 6, thereby controlling the toner density and correcting the positional deviation. Done.

  That is, the diffuse reflection type scattered light reflected on the surface of the color resist pattern 8 on the intermediate transfer body 12 has irregularly shaped toner particles and large irregularities, so that the vibration direction of the reflected light changes randomly. The amounts of light incident on the second light receiving element 5 for waves and the third light receiving element 6 for S waves are substantially equal. On the other hand, the light reflected by the intermediate transfer body 12 and the reflected light reflected by the color resist pattern 8 are incident on the second light receiving element 5 for P wave and detected from the second light receiving element 5 for P wave. The value is the sum of the light reflected by the surface of the color resist pattern 8 and the light reflected by the intermediate transfer body 12, whereas the third light receiving element 6 for S wave has a value on the surface of the color resist pattern 8. Since only the reflected diffuse reflection type scattered light reaches and there is a difference between them, the amount of light reflected by the intermediate transfer body 12 can be detected by calculating this difference.

  Therefore, when the amount of reflected light from the intermediate transfer body 12 is large, the amount of toner attached on the intermediate transfer body 12 is small, and when the amount of reflected light is small, the amount of toner attached on the intermediate transfer body 12 is large. It is possible to detect the toner adhesion amount from the amount of light reflected by the body 12.

  Further, since the output voltages from the second light receiving element 5 and the third light receiving element 6 thus obtained are waveforms having a certain width and height, the center of gravity position of the waveform is detected. It is also a value representative of the position of the color resist pattern 8 for each color, and the amount of color misregistration between each color can be obtained by calculating the position of the center of gravity of the output voltage waveform. Therefore, it is possible to obtain a color image with no color shift by correcting the shift amount of the toner image to be formed based on the detected color shift amount.

  However, in the ID sensor configured as described above, the variation in mounting of the second light receiving element 5 and the third light receiving element 6 for detecting the light reflected by the intermediate transfer body 12 and the light reflected by the color resist pattern 8 can be reduced. The detection timing of the P wave and the S wave is shifted due to variations in the optical arrangement caused by the chip position variation of the light receiving element, the mounting accuracy of the first beam splitter 2 and the second beam splitter 4, and the like. The same applies to the case where the resin system constituting the sensor undergoes thermal expansion due to a change in ambient temperature of the sensor.

  Further, when the toner amount of the color resist pattern 8 increases or decreases, the output ratio of the P wave and the S wave fluctuates, and the difference signal of the P wave and the S wave is further influenced, so that the detection timing of the color resist pattern 8 is erroneously detected. Will cause.

  Therefore, for example, Patent Document 1 includes a first light receiving device that receives P wave components arranged in parallel to each other, and a second light receiving device that receives S wave components, and information on arrangement positions of these light receiving devices. Of the first and second light receiving devices based on the system speed information of the image forming apparatus and the first or second light receiving device. An image forming apparatus is provided that includes a calculation unit that calculates the difference between the output signal of the output signal and the detection output delayed by the delay unit as information on the amount of reflected toner on the image carrier.

  Further, in Patent Document 2, when an inexpensive sensor is used, a detection waveform is distorted due to the influence of diffuse reflected light when detecting a pattern, thereby causing a measurement error. Therefore, diffuse reflection that occurs when an inexpensive sensor is used. There is shown a color image forming apparatus in which a distortion amount is measured and the measurement error is corrected by paying attention to the fact that the distortion amount of the detected waveform due to light has a certain relationship with the measurement error amount.

JP 2005-134778 A JP 2007-025315 A

  However, the image forming apparatus disclosed in Patent Document 1 delays the detection output of the light receiving device that has previously entered to obtain a difference in output between the first light receiving device and the second light receiving device. The outputs of the first light receiving device and the second light receiving device are both analog signals, and no specific method of how to delay the analog signals is shown. Analog signals are easily affected by noise, and there is a possibility that accuracy may be reduced due to deformation due to delay. Therefore, for example, variations in the optical arrangement due to variations in mounting of the first and second light receiving devices described above, variations in the chip position of the light receiving elements, and the like, the first beam splitter 2 and the second beam splitter 4 Timing deviations due to mounting accuracy can be accommodated to some extent because the amount of delay is known during device assembly, but for thermal expansion due to changes in the environmental temperature of the resin system that constitutes the sensor. The amount of change may change each time, and in order to deal with these, it is difficult to implement concretely unless you know how to delay the signal.

  In the case of the color image forming apparatus disclosed in Patent Document 2, it is a method for dealing with the distortion of the detected waveform when an inexpensive sensor is used, and copes with the deviation caused in the detection timing of the P wave and the S wave. Not a way.

  Therefore, in the present invention, in a color image forming apparatus that forms a full-color image by superimposing a plurality of separately formed toner images, a color misregistration detection pattern (color resist pattern) for each color is used as a regular reflection light (P wave). ) And diffuse reflection light (S wave) is detected by a reflection type density sensor, and a deviation amount between colors is calculated in a color deviation detection method in which a light receiving element constituting the reflection type density sensor is attached. Specularly reflected light (P) due to multiple factors such as variations in optical arrangement due to variations in the chip position of the light receiving element, variations due to mounting accuracy, variations due to thermal expansion due to changes in the operating environment temperature, etc. Waves) and diffuse reflected light (S waves) detection timing shifts are corrected by a simple and inexpensive method to enable accurate color overlay It is an object to provide a color shift detecting method and an image forming apparatus in the deposition apparatus.

In order to solve the above problems, a color misregistration detection method in an image forming apparatus according to the present invention is as follows.
A color resist pattern formed by toner of each color formed by an electrophotographic method is read by a reflection type density sensor that detects regular reflection light (P wave) and diffuse reflection light (S wave) to detect a color misregistration amount. A color misregistration detection method in an image forming apparatus that corrects and superimposes toner image forming positions and forms a color image,
A threshold value for binarizing each of regular reflection light (P wave) and diffuse reflection light (S wave) read by the reflection density sensor at a specific density in each color resist pattern of each color is determined in advance, and the reflection is performed. Each of the P wave and S wave read by the mold density sensor is binarized with the threshold value, and the difference between the P wave and the S wave is obtained using the time difference between rising and falling at the same specific density as an offset amount. The color resist pattern shift amount of each color is corrected based on the above, and a color image is formed.

An image forming apparatus that implements the method includes:
A plurality of image forming units arranged in the conveyance direction of the intermediate transfer member or the sheet conveying belt, each of which includes a photosensitive member that forms a toner image by electrophotography corresponding to each color, and is formed by the plurality of image forming units. A reflective density sensor that reads the color resist pattern transferred to the intermediate transfer body or the paper transport belt, and a positional deviation of the color resist pattern is calculated based on a reading result of the reflective density sensor, and the plurality of image forming units In an image forming apparatus comprising a control unit that adjusts the position of a toner image formed in
A threshold value storage device for storing a threshold value for binarizing each of regular reflection light (P wave) and diffuse reflection light (S wave) read by the reflection type density sensor at a specific density in the color resist pattern of each color; A binarization circuit that binarizes each of the P wave and the S wave read by the reflective density sensor based on the threshold value stored in the threshold value storage device, and the control unit is binarized. The difference between the P wave and the S wave is obtained using the time difference between the rising and falling edges of the P wave and the S wave as an offset amount, and the shift amount of the color resist pattern of each color is calculated based on the difference, and the plurality of images The position of the toner image formed in the forming unit is adjusted.

  As described above, a threshold value for binarizing each of the P wave and the S wave at a specific density in each color resist pattern is determined in advance, and each of the P wave and the S wave is binarized by the threshold value. The time difference between the wave and the S wave can be easily detected, and the amount of deviation can be easily and accurately detected by correcting the amount of deviation of the color resist pattern of each color using the time difference as an offset amount. Therefore, variations in the light receiving elements that make up the reflective density sensor, variations in the optical arrangement due to variations in the chip position of the light receiving elements, variations due to mounting accuracy, and thermal expansion due to changes in the operating environment temperature Colors that can be accurately overlaid by correcting the deviation in the detection timing of specularly reflected light (P wave) and diffusely reflected light (S wave) due to multiple factors such as variations due to A displacement detection method and an image forming apparatus can be provided.

  The threshold value corresponds to each of the P wave and the S wave, and is determined corresponding to two densities of the high density and the low density in the color resist pattern of each color, whereby the background of the intermediate transfer body on which the color resist pattern is formed. The color resist pattern itself can be discriminated with high accuracy, and the detection accuracy of the P wave and the S wave, and thus the color misregistration amount can be accurately detected.

  Further, after the analog / digital conversion is performed on the reading results of the regular reflection light (P wave) and the diffuse reflection light (S wave) by the reflection type density sensor, the processing is performed. It is a preferred embodiment of the present invention to have an analog / digital conversion circuit for analog / digital conversion of reading results of specular reflection light (P wave) and diffuse reflection light (S wave) by a density sensor. .

  As described above, the color misregistration detection method and the image forming apparatus in the image forming apparatus according to the present invention are a simple and inexpensive method, and the variation in mounting the light receiving element constituting the reflection type density sensor and the chip position variation of the light receiving element. Regular reflection light (P wave) and diffuse reflection light (P-wave) and diffuse reflection light (variation due to variations in optical arrangement due to, etc., variation due to mounting accuracy, variation due to thermal expansion due to changes in operating environment temperature, etc.) S-wave) detection timing shift can be easily detected, and the color shift amount can be detected easily and accurately, and the color image of each color to be formed can be accurately overlaid to produce a high-quality color image. Can be provided, and a color misregistration detection method and an image forming apparatus can be provided.

  Hereinafter, exemplary embodiments of the present invention will be described in detail 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 unless otherwise specified, but are merely illustrative examples. Not too much.

  First, an example of an image forming apparatus for carrying out the present invention will be described with reference to the schematic sectional view shown in FIG. The image forming apparatus shown in FIG. 7 has a plurality of 10M, 10C, 10Y, and 10K provided corresponding to each color of magenta (M), cyan (C), yellow (Y), and black (K). Photoconductors, charging devices 18M, 18C, 18Y, 18K, developing devices 19M, 19C, 19Y, 19K, photoconductor cleaning devices 9M, 9C, 9Y, 9K, which are provided corresponding to the respective photoconductors, are illustrated. A tandem type color image forming apparatus in which a photosensitive unit composed of a static eliminator that is not disposed is arranged in the running direction of the intermediate transfer body (belt) 12.

  In the tandem color image forming apparatus shown in FIG. 7, the intermediate transfer belt 12 is stretched around a driving roller 13 and a backup roller 15, and is driven to rotate by driving of the driving roller 13. When this image forming apparatus is a printer, for example, image forming data sent from an external computer is a control device including a CPU (not shown), and magenta (M), cyan (C), yellow (Y), and black (K). Each color is divided into data. Then, the surfaces of the photoconductors 10M, 10C, 10Y, and 10K are uniformly charged by the charging devices 18M, 18C, 18Y, and 18K, and each of the light exposure apparatuses indicated by 20 is used by the image forming data divided into the respective colors. The photoreceptors 10M, 10C, 10Y, and 10K are exposed to form an electrostatic latent image.

  Then, the electrostatic latent images on the photoconductors 10M, 10C, 10Y, and 10K are developed by the developing devices 19M, 19C, 19Y, and 19K, respectively, and a magenta (M) toner image, a cyan (C) toner image, and a yellow (Y ) A toner image and a black (K) toner image are formed.

  On the other hand, the primary transfer rollers 11M, 11C, 11Y, and 11K are opposed to the photoconductors 10M, 10C, 10Y, and 10K with the intermediate transfer belt 12 interposed therebetween. The color toner images are sequentially transferred to the intermediate transfer belt 12 by the transfer bias applied to the primary transfer rollers 11M, 11C, 11Y, and 11K, and a color toner image is formed on the intermediate transfer belt 12.

  Then, a CPU (not shown) instructs the paper take-out roller 27 to take out the paper from the paper feeding device 26, and the paper is conveyed to the registration roller pair 17 through the paper conveyance path. Then, the toner image on the intermediate transfer belt 12 is sent out by the registration roller pair 17 at the timing when the toner image reaches the secondary transfer position where the secondary transfer roller 16 is located.

  The secondary transfer roller 16 at the secondary transfer position is disposed at a position facing the backup roller 15 with the intermediate transfer belt 12 interposed therebetween, and the toner image on the intermediate transfer belt 12 is secondarily transferred to the conveyed paper. . The sheet onto which the toner image has been transferred is sent to the fixing device 21, where the toner image on the sheet is fixed and discharged onto a discharge tray. After the secondary transfer, the intermediate transfer belt 12 is cleaned by the cleaning device 14, and the remaining toner is also removed by the photoconductor cleaning devices 9M, 9C, 9Y, and 9K in the photoconductors 10M, 10C, 10Y, and 10K. For image formation.

  Also, the fixing device 21 forms a nip with a fixing roller including a heater and a pressure roller, and conveys the paper onto which the toner image has been transferred to the nip portion so that the toner is heated and pressurized to be fixed on the paper. To.

  The image forming apparatus described above is an example, and as described above, a toner image of a plurality of colors is sequentially formed on a single photoconductor, and is primarily transferred onto an intermediate transfer member and superimposed on each other. In this case, secondary transfer is performed collectively on the paper, and even in the case of a tandem type image forming apparatus, the image is directly transferred from each photoconductor directly to the paper conveyed by the paper conveyance belt instead of the intermediate transfer belt. Therefore, the present invention can be applied to various forms of image forming apparatuses such as those that form full-color images.

  The ID sensor described in FIG. 6 is finally transferred to the intermediate transfer belt 12 among the four photoconductors arranged in the running direction of the intermediate transfer belt indicated by 12 in FIG. The black (B) photoconductor 10 </ b> K and the secondary transfer position (position where the secondary transfer roller 16 is located) are provided and indicated by the number 22.

  As described above, the density sensor 22 prevents the color toner images of the respective colors from being shifted and overlapped to prevent the image quality from deteriorating and to obtain good color reproducibility. A color resist pattern for detection and toner density adjustment is formed on the intermediate transfer belt 12, and is read by the ID sensor 22 to control the image forming conditions, or the amount of misalignment between each color is calculated to accurately overlay colors. This is to make it possible.

  This ID sensor 22 has already been described, but again briefly described here. 1 is a light emitting element using an LED or the like, 2 is a P-polarized light, and a part of the light emitting element 1 emits light. A first beam splitter 4 for directing light toward the first light-receiving element 3 for monitoring in order to keep the light constant, 4 is a regular reflection of the light transmitted through the first beam splitter 2 and reflected by the color resist pattern (toner pattern) 8 A second beam splitter that divides light (P wave) and diffusely reflected light (S wave), 5 is a second light receiving element that detects P wave, 6 is a third light receiving element that detects S wave, and 12 is intermediate. The P-polarized light which is a transfer body and has passed through the first beam splitter 2 is reflected from the color resist pattern 8, and the P wave is detected by the second light receiving element 5 and the S wave is detected by the third light receiving element 6. The

  As described above, a control device (not shown) detects the toner density and the position of each color resist pattern 8 based on the ratio of output voltages from the respective light receiving elements 5 and 6, thereby controlling the toner density. And misalignment correction. It should be noted that the ID sensor is not limited to the above-described position, and it is obvious that the ID sensor may be disposed at a position where the color resist pattern 8 can be detected, corresponding to the various types of image forming apparatuses described above.

  However, as shown in FIG. 5, the outputs from the light receiving elements 5 and 6 vary in optical arrangement due to variations in mounting the light receiving elements constituting the ID sensor 22, chip position variations in the light receiving elements, and the like. Deviations in the detection timing of specularly reflected light (P wave) and diffusely reflected light (S wave) due to multiple factors, such as variations due to mounting accuracy and variations due to thermal expansion due to changes in the operating environment temperature, etc. .

FIG. 5 shows a voltage waveform of the detection result of the color resist pattern by the reflection type density sensor (ID sensor). The horizontal axis is time, the vertical axis is voltage, and reference numeral 501 in FIG. (P wave) waveform, (B) 511 is a diffuse reflected light (S wave) waveform, 57 and 58 are thresholds for binarizing the regular reflected light (P wave) waveform 501, and 59 and 60 are diffused. A threshold value for binarizing the waveform 511 of the reflected light (S wave), 55 and 56 are waveforms obtained by binarizing the waveform 501 of the regular reflected light (P wave) and the waveform 511 of the diffuse reflected light (S wave), respectively. It is. FIG. 5 shows a case where the detection timing of the regular reflection light (P wave) waveform 501 is delayed by t ₁₁ −t _{10 with} respect to the waveform 511 of diffuse reflection light (S wave).

  Therefore, in the present invention, each of the regular reflection light (P wave) 501 and diffuse reflection light (S wave) 511 read by the ID sensor 22 is binarized in advance at a specific density in each color resist pattern of each color. The threshold values 57, 58, 59, and 60 are determined for each of the high density and low density in the color resist pattern, and the P wave and S wave read by the ID sensor 22 are binarized by the threshold values 57, 58, 59, and 60, respectively. The difference between the P wave and the S wave is obtained by using the time difference between rising and falling at the same specific density as an offset amount, and the color resist pattern shift amount of each color is corrected based on the difference to form a color image. It is what I did.

That is, for the waveform 501 of the specularly reflected light (P wave) in FIG. 5A, threshold levels of levels 57 and 58 are determined in advance, and the reading result of 501 is the threshold value 58. As illustrated at t ₁₁ , the binarized waveform of 55 is set to, for example, “0” level, then to the same “1” level at t ₁₃ when the same threshold 58 is reached, and then at t ₁₅ when the threshold 57 is reached. It is binarized to the “0” level, and so on. The same applies to the case of the waveform 511 of (B) diffuse reflected light (S wave). The threshold values 59 and 60 are set in advance, and the reading result of 511 is the threshold 60 t _10. As shown in FIG. 5, the 56 binarized waveforms are set to “0” level, for example, then to “1” level at t ₁₂ when the same threshold 60 is reached, and then “0” at t ₁₄ when the threshold 59 is reached. The level is binarized such as ....

Here, since the threshold values 57, 58, 59 and 60 are the values of the P wave and the S wave at the same density of the color resist pattern as described above, the waveform 501 of the regular reflection light (P wave) is binarized 55. and falling t ₁₁ in the waveform of the falling of t ₁₀ at 56 the waveform of the waveform 511 obtained by binarizing the diffuse reflection light (S wave), should the timing at the same density of the color resist pattern. Therefore, the time difference between the t ₁₁ and t ₁₀ is the time difference between the reading timing in the P and S waves.

Therefore, this (t ₁₁ -t ₁₀ ) is used as an offset amount, and the difference between the waveform 511 of the diffuse reflected light (S wave) and the waveform obtained by shifting the waveform 501 of the regular reflected light (P wave) by this offset amount is taken. Since the difference is the amount of light reflected by the intermediate transfer body 12 as described above, the color between each color from the toner adhesion amount on the intermediate transfer body 12 and the barycentric position obtained from the width and height of the waveform. The amount of misregistration can be obtained, and by correcting the amount of color misregistration at the time of toner image formation, a color image without color misregistration can be obtained.

  In this way, the waveform 501 of the regular reflection light (P wave) and the waveform 511 of the diffuse reflection light (S wave) are shifted by this offset amount, and the resulting difference waveform is shown in FIG. It is. 4, the horizontal axis represents time, the vertical axis represents voltage (unit: V), 50 in (A) represents the waveform of specularly reflected light (P wave) read by the ID sensor 22 indicated by 501 in FIG. 51 is a waveform of diffusely reflected light (S wave) indicated by 511 in FIG. 5, 52 in (B) is a waveform of the difference between this P wave and S wave, 53 is a binarized waveform, and 54 is a P wave. This is a threshold value for binarization in the waveform 52 of the difference between the S wave and the S wave, and this is also a value corresponding to the specific density in each color resist pattern of each color, similar to the threshold values 57 to 60 described above.

The waveform 50 of specularly reflected light (P wave) and the waveform 51 of diffusely reflected light (S wave) shown in FIG. 4A are waveforms shifted by an offset amount by the method described with reference to FIG. The difference waveform 52 in FIG. 4B is the amount of light reflected by the intermediate transfer body 12 (the toner amount in the color resist pattern when considered in reverse as described above). If the binarization is performed for the color resist patterns of all colors as in the above, for example, by comparing the time corresponding to the time t ₁ of each color resist pattern, the shift amount of the color resist pattern can be easily grasped. Therefore, if the toner image forming position is adjusted based on the value, a color image without color misregistration can be obtained.

  FIG. 1 is a flowchart of Example 1 of the color misregistration detection method of the present invention that corrects the color misregistration amount according to such a concept. FIG. 2 is a diagram of color misregistration correction that implements the color misregistration amount detection method. It is a circuit block diagram for this purpose. In FIG. 2, 5 and 6 are the second light receiving element and the third light receiving element constituting the ID sensor 22 shown in FIG. 6, 41 and 42 are analog / digital conversion circuits, and 43 and 44 are the above figure. 5 is a threshold value storage circuit for storing the threshold values indicated by 57 to 60, 45 and 46 are binarization circuits, 47 is a shift amount of the P wave and the S wave, and the shift amount of the color resist pattern is calculated based on the shift amount. A P-wave S-wave shift amount calculation and color shift amount calculation circuit 48 for calculating the amount is a control circuit of the image forming apparatus.

  When the process starts in step S10 in FIG. 1, the ID sensor 22 is calibrated in step S11. In this calibration, for example, the background of the portion of the intermediate transfer body (belt) 12 where the color resist pattern is formed is detected by the ID sensor 22 and the output level of the ID sensor 22 in the intermediate transfer body 12 is adjusted. In the next step S12, a color resist pattern is drawn, that is, a color resist pattern is formed on the intermediate transfer body 12.

  In the next step S13, the color sensor pattern is detected by the ID sensor 22, and the control device 48 in FIG. 2 converts the signal into a digital signal by the analog / digital conversion circuits 41 and. In the next step S14, the control circuit 48 causes the binarization circuits 45 and 46 to read out the thresholds 57 to 60 stored in the threshold storage circuits 43 and 44, and based on them, 55 and 56 in FIG. As shown, binarization of P wave and S wave is performed.

  In step S15, the control circuit 48 causes the P-wave S-wave shift amount calculation / color shift amount calculation circuit 47 to determine whether there is a timing shift in the binarized signals indicated by 55 and 56 in FIG. If not, the process proceeds to step S17. If there is, the time difference between the two is set as an offset amount in step S16.

  In the next step S17, the control circuit 48 calculates the difference between the P wave and the S wave shown by 52 in FIG. 4 (B) based on this offset amount. Is calculated and binarized based on the threshold value 54. In step S19, the color misregistration amount of the color resist pattern is calculated. In step S20, the control circuit 48 corrects the position of the toner image of each color to be formed based on the calculated color misregistration amount, and ends the process. That is why.

  By doing so, it is caused by variations in the optical arrangement due to variations in the light receiving elements constituting the reflection type density sensor when mounting the light receiving elements, chip position variations in the light receiving elements, and mounting accuracy in a simple and inexpensive manner. It is possible to easily detect a difference in detection timing between specularly reflected light (P wave) and diffusely reflected light (S wave) caused by a plurality of factors such as variations and variations due to thermal expansion caused by changes in the use environment temperature. Accordingly, the amount of color misregistration can be easily and accurately detected, and therefore a color misregistration detection method and an image forming apparatus capable of accurately overlaying the formed color images of the respective colors can be provided.

  In step S14 in the flowchart shown in FIG. 1, for example, the pulse width of the binarization result of the P wave and the S wave of a specific color binarized by the binarization circuits 45 and 46 for some reason is greatly increased. Accordingly, if the binarization result of the difference waveform between the P wave and the S wave in step S17 is equal to or larger than the width of the color resist pattern or a pulse having a very narrow width, an accurate color misregistration is performed. Detection is not possible. The routine in such a case is added to the flowchart of the second embodiment of the present invention shown in FIG.

  In the flowchart of the second embodiment of FIG. 3, based on the differential waveform of the P wave and the S wave binarized in step S17 in the first embodiment of FIG. Alternatively, step S18 for detecting whether or not there is a pulse having a very narrow width is added. If an error is detected in step S18, the process returns to the color resist pattern drawing in step S12, and the same process is performed again. It is what I do. By doing so, it is possible to detect a color shift with high reliability and to obtain an image forming apparatus that always forms a high-quality color image with no color shift.

  The other routines are exactly the same as those in the first embodiment and will not be described. However, if a detection error occurs even if the detection process is performed again in this way, it is assumed that there is a detection failure or an apparatus abnormality and the external You may make it alert | report to.

  According to the present invention, it is possible to provide an image forming apparatus capable of forming a high-quality color image with accurately corrected color misregistration.

It is a flowchart of Example 1 of the color shift detection method in the image forming apparatus which becomes this invention. FIG. 2 is a block diagram of a color misregistration detection circuit for implementing a color misregistration detection method in the image forming apparatus according to the present invention. It is a flowchart of Example 2 of the color shift detection method in the image forming apparatus which becomes this invention. The voltage waveform of the detection result of the color resist pattern by the reflection type density sensor (ID sensor), (A) is the waveform of specular reflection light (P wave) and diffuse reflection light (S wave), and (B) is the difference waveform. It is. It is a figure for demonstrating binarizing the voltage waveform of the detection result of the color resist pattern by a reflection type density sensor (ID sensor), (A) is regular reflection light (P wave), (B) is diffuse reflection. It is a waveform of light (S wave). It is a figure of one structural example of the reflection type sensor used for reading of a color shift detection toner pattern. 1 is a schematic cross-sectional view of an example of an image forming apparatus for carrying out the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Light emitting element 2 1st beam splitter 3 1st light receiving element 4 2nd beam splitter 5 2nd light receiving element 6 3rd light receiving element 8 Color shift detection toner pattern 12 Intermediate transfer bodies 41 and 42 Analog / digital conversion circuit 43, 44 Threshold memory circuits 45, 46 Binary circuit 47 P-wave S-wave shift amount calculation, Color shift amount calculation circuit 48 Control circuit

Claims (5)

A color resist pattern formed by toner of each color formed by an electrophotographic method is read by a reflection type density sensor that detects regular reflection light (P wave) and diffuse reflection light (S wave) to detect a color misregistration amount. A color misregistration detection method in an image forming apparatus that corrects and superimposes toner image forming positions and forms a color image,
A threshold value for binarizing each of regular reflection light (P wave) and diffuse reflection light (S wave) read by the reflection density sensor at a specific density in each color resist pattern of each color is determined in advance, and the reflection is performed. Each of the P wave and S wave read by the mold density sensor is binarized with the threshold value, and the difference between the P wave and the S wave is obtained using the time difference between rising and falling at the same specific density as an offset amount. A color misregistration detection method in an image forming apparatus, wherein a color image is formed by correcting a misregistration amount of the color resist pattern of each color based on the above.   2. The image forming apparatus according to claim 1, wherein the threshold value corresponds to each of a P wave and an S wave, and is determined to correspond to two densities of a high density and a low density in each color resist pattern. Color misregistration detection method.   3. The process according to claim 1, wherein the processing is performed after analog / digital conversion is performed on the reading result of the regular reflection light (P wave) and diffuse reflection light (S wave) by the reflection type density sensor. Color misregistration detection method in an image forming apparatus. A plurality of image forming units arranged in the conveyance direction of the intermediate transfer member or the sheet conveying belt, each of which includes a photosensitive member that forms a toner image by electrophotography corresponding to each color, and is formed by the plurality of image forming units. A reflective density sensor that reads the color resist pattern transferred to the intermediate transfer body or the paper transport belt, and a positional deviation of the color resist pattern is calculated based on a reading result of the reflective density sensor, and the plurality of image forming units In an image forming apparatus comprising a control unit that adjusts the position of a toner image formed in
A threshold value storage device for storing a threshold value for binarizing each of regular reflection light (P wave) and diffuse reflection light (S wave) read by the reflection type density sensor at a specific density in the color resist pattern of each color; A binarization circuit that binarizes each of the P wave and the S wave read by the reflective density sensor based on the threshold value stored in the threshold value storage device, and the control unit is binarized. The difference between the P wave and the S wave is obtained using the time difference between the rising and falling edges of the P wave and the S wave as an offset amount, and the shift amount of the color resist pattern of each color is calculated based on the difference, and the plurality of images An image forming apparatus that adjusts a position of a toner image formed by a forming unit.   The image forming apparatus includes an analog / digital conversion circuit that performs analog / digital conversion of reading results of specular reflection light (P wave) and diffuse reflection light (S wave) by the reflective density sensor. The image forming apparatus according to claim 4.

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