JP2006337962A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus equipped with a means for adjusting the transfer position of each color component image. <P>SOLUTION: One color component is set (S11), and a patch image by the set color component is formed (S12). A control part acquires the detection output V1 of regularly reflected light and the detection output V2 of irregularly reflected light at a predetermined sampling rate (S13), and calculates the passing timing T1 of the patch image by using a threshold TH1 for the detection output V1 (S14). Then, it calculates correction output V3 (=V1-V2) (S15), and calculates the passing timing T3 of the patch image by using a threshold TH3 for the correction output V3 (S16). Next, it calculates (T1-T3) as correction time ΔT for the detection output V1 (S17). The transfer position of each color component image is adjusted, based on the detection output V1 corrected by using the average value of the correction time ΔT. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an image forming apparatus including means for adjusting a transfer position of each color component image.

  In an image forming apparatus such as a digital color copying machine or a digital color printing machine, input image data is decomposed into each color component and subjected to image processing, and then an image for each color component is superimposed to form a multicolor image. . When the multi-color image is formed, if the images of the respective color components are not accurately superimposed, color misregistration occurs in the formed multi-color image, leading to a decrease in image quality. In particular, in an image forming apparatus provided with an image forming unit for each color component in order to improve the formation speed of a multicolor image, an image of each color component is formed in each image forming unit. A multicolor image is formed by superimposing. In such an image forming apparatus, the transfer position of the image of each color component is likely to shift, and the color shift of a multicolor image is a big problem.

  Therefore, an image forming apparatus has been proposed which forms a good multicolor image without color misregistration by performing color matching adjustment for correcting color misregistration of a multicolor image in order to accurately superimpose images of respective color components. . In the color matching adjustment, a deviation of the image forming positions of other color components from the image forming position of the reference color component is detected using an optical detector. Then, an adjustment value related to the image forming position is calculated based on the detection result, and the timing for forming the image of each color component is adjusted so that the transfer position of the image of each color component matches according to the adjustment value. In order to calculate the adjustment value, the images of the respective color components are transferred at the same timing, and the interval between the transfer positions of the respective color components is detected, or the density of the multicolor image in which the respective color components are superimposed is measured.

  For example, in an image forming apparatus that detects an interval between transfer positions of an image of each color component and performs correction based on the detected shift amount of the transfer position, an image formed with a reference color component and other colors The distance from the image formed by the component is detected by a detector, and the amount of shift in the transfer position of the image of each color component is determined based on the detected distance, and the color shift is corrected (for example, Patent Documents). 1).

As another method for determining the correction amount, there is a method of measuring the density of a multicolor image in which the respective color component images are superimposed. For example, the density of a multicolor image in which the correction image is superimposed on the reference image is measured, and color matching adjustment is performed so that the measured density becomes a density in a state where the correction image is accurately superimposed. This image forming apparatus repeatedly forms a plurality of identical images as a multicolor image in order to improve correction accuracy. For example, a plurality of line-like images (hereinafter referred to as line images) are formed as the same image, the density of the multicolor line image is detected by a sensor, and the overlapping state of the respective corrected images is obtained. Then, the state in which the density of the multicolor line image detected by the sensor falls within a predetermined density range is regarded as a state in which the corrected images are accurately overlapped, and the color is formed so that image formation is performed in the overlapped state. Adjustment is performed (see, for example, Patent Document 2).
JP-A-10-213940 JP 2000-81744 A JP 2004-117385 A

  In the color matching adjustment described above, the reference image, the corrected image, and the reflected light from the surface of the transfer medium on which they are formed are detected by the optical sensor, but the image formed portion and the image are not formed. Since the difference in the intensity of reflected light from the surface of the transfer medium in the state is small, the maximum or minimum of the density detection value may be erroneously detected, and color matching adjustment is performed based on the erroneous detection result, Conversely, there has been a problem that the image quality is lowered or an error occurs during the execution of the color matching adjustment, and the color matching adjustment cannot be executed normally.

  Therefore, the applicant of the present application detects specular reflection light and irregular reflection light among the reflection light reflected on the transfer medium surface, and subtracts the intensity of the irregular reflection light from the detected intensity of the regular reflection light. Has proposed a technique for improving the detection accuracy of an image for color matching adjustment (see, for example, Patent Document 3).

  FIG. 8 is an explanatory diagram for explaining a conventional detection method. When performing color matching adjustment, as shown in FIG. 8A, a plurality of adjustment images (patch images) are transferred to the transfer medium 310, and the irradiation unit 301, the irregular reflection light detection unit 302, Then, the optical sensor 300 including the regular reflection light detection unit 303 detects irregular reflection light and regular reflection light from the transfer medium 310 at a predetermined sampling rate. When the detection parts (point P on the transfer medium 310) of the irregular reflection light detection unit 302 and the regular reflection light detection unit 303 are the same, when the irregular reflection light detection unit 302 detects strong irregular reflection light, the regular reflection light detection unit 303 is detected. On the other hand, weak regular reflection light is detected. Conversely, when the regular reflection light detection unit 303 detects strong regular reflection light, the irregular reflection light detection unit 302 detects weak irregular reflection light. Therefore, by subtracting the intensity of the irregularly reflected light from the intensity of the regular reflected light, the amplitude of the detected value can be increased, and the detection accuracy of the adjustment image can be increased.

  However, in the method described in Patent Document 3, the difference between the intensity of the regular reflection light detected at a predetermined sampling rate and the intensity of the irregular reflection light has to be calculated. There is a problem that it takes a burden.

  Further, as shown in FIG. 8B, when the optical sensor 300 is installed in an inclined state with respect to the transfer medium 310 for some reason, a detection site (on the transfer medium 310) by the specular reflection light detection unit 303 is provided. Point P1) differs from the detection part (point P2 on the transfer medium 310) by the irregularly reflected light detection unit 302, and a phase difference occurs between the outputs of both detection units. Therefore, when the difference between the intensity of the regular reflection light and the intensity of the irregular reflection light is calculated in this state, there is a problem that the detection accuracy is deteriorated due to the influence of the phase difference caused by the difference in the detection part. .

  The present invention has been made in view of such circumstances, and calculates a phase difference between an output when specular reflection light is detected and a correction output corrected by irregular reflection light, and a first detection in which the calculated phase difference is corrected. Provided is an image forming apparatus capable of accurately adjusting the transfer position of a color component image without increasing the amount of calculation by adopting a configuration in which the transfer position of the color component image is adjusted based on the output of the means. With the goal.

  An image forming apparatus according to the present invention irradiates light onto a transfer medium to which a color component image is transferred in an image forming apparatus that forms an image by transferring each of a plurality of color component images on a transfer medium. Means, and first and second detection means for detecting specularly reflected light and irregularly reflected light, respectively, of the light reflected by the transfer medium or the color component image when light is emitted by the means, and the first Means for calculating a correction output obtained by correcting the output of the detection means by the output of the second detection means; means for calculating a phase difference between the output of the first detection means and the calculated correction output; and And a means for adjusting the transfer position of the color component image on the basis of the output of the first detection means corrected for the above.

  In the present invention, the phase difference between the output of the first detection means when the regular reflection light is detected and the correction output corrected by the irregular reflection light is calculated, and the output of the first detection means is corrected by the calculated phase difference. Since the transfer position of the color component image is adjusted based on the corrected output, the phase difference caused by the positional relationship between the first and second detection means and the transfer medium is corrected, and the color component image is corrected. The transfer position is adjusted with high accuracy. In addition, since the phase difference is stored and the subsequent color matching adjustment can correct the detection output based on this phase difference, the amount of calculation is greatly reduced.

  In the image forming apparatus according to the present invention, the first and second detection units measure time changes in the intensity of the specular reflection light and the irregular reflection light, respectively, and the time of the intensity of the specular reflection light and the correction output is measured. The phase difference is calculated based on the change.

  In the present invention, the temporal change of the intensity of the regular reflection light and the irregular reflection light is measured, and the phase difference is calculated based on the temporal change of the intensity of the regular reflection light and the correction output. Therefore, a threshold value is set for each intensity, a median value of detection times when each intensity is equal to or greater than the threshold value is obtained, and a phase difference is obtained by taking a difference between the two median values. Further, the maximum value or the minimum value of each intensity is detected, and the phase difference is obtained from the time lag of the maximum value or the minimum value.

  The image forming apparatus according to the present invention is characterized in that the phase difference is a phase difference caused by a difference in a portion on the transfer medium where the regular reflection light and irregular reflection light are generated.

  In the present invention, the first and second detection means are ideal for the transfer medium because the phase difference caused by the difference between the portions on the transfer medium where the regular reflection light and the irregular reflection light are generated is corrected. Even when it is not installed in a state, it is possible to perform highly accurate color matching adjustment.

  An image forming apparatus according to the present invention includes: a unit that detects presence / absence of a transfer unit that transfers the color component image to a transfer medium; and a unit that determines whether the transfer unit is mounted based on a detection result of the unit. And a means for calculating a phase difference between the output of the first detection means and the correction output when it is determined that the transfer means is mounted.

  In the present invention, the phase difference is calculated only when the arrangement relationship between the first and second detection means and the transfer medium may change.

  The image forming apparatus according to the present invention determines a means for detecting presence / absence of the first and second detection means, and determines whether the first and second detection means are mounted based on the detection means of the means. And a means for calculating a phase difference between the output of the first detection means and the correction output when it is determined that the first and second detection means are attached.

  In the present invention, the phase difference is calculated only when the arrangement relationship between the first and second detection means and the transfer medium may change.

  In the image forming apparatus according to the present invention, the color component image transferred to the transfer medium includes a chromatic color component image, and the phase difference between the output of the first detection unit and the correction output for the color component image. Is calculated.

  In the present invention, since the phase difference is calculated using the chromatic color component image, the phase difference calculation process can be omitted for the achromatic color component image in which irregular reflection does not occur.

  In the image forming apparatus according to the present invention, the color component image transferred to the transfer medium includes a plurality of chromatic color component images, and the output of the first detection unit and the correction output for each of the color component images. And a means for calculating an average value of the calculated phase differences.

  In the present invention, the phase difference is calculated using each of a plurality of chromatic color component images, and the average value of the calculated phase differences is calculated. Since the phase difference calculated due to the magnitude of the output value of the irregularly reflected light due to the sensitivity characteristics for each wavelength of the first and second detection means and the unexpected situation may fluctuate for each color component, in the present invention, these fluctuations Impact is reduced.

  In the case of the present invention, the phase difference between the output of the first detection means when the regular reflection light is detected and the correction output corrected by the irregular reflection light is calculated, and the output of the first detection means is corrected by the calculated phase difference. The transfer position of the color component image is adjusted based on the corrected output. Therefore, it is possible to correct the phase difference due to the arrangement relationship between the first and second detection means and the transfer medium, and to adjust the transfer position of the color component image with high accuracy. Further, the phase difference is stored, and in the subsequent color matching adjustment, the detection output can be corrected based on this phase difference, and the amount of calculation can be greatly reduced.

  According to the present invention, the temporal change in the intensity of the regular reflection light and the irregular reflection light is measured, and the phase difference is calculated based on the temporal change in the intensity of the regular reflection light and the correction output. Therefore, a threshold value is set for each intensity, a median value of detection times when each intensity is equal to or greater than the threshold value is obtained, and a phase difference can be obtained by taking a difference between the two median values. Further, the maximum value or the minimum value of each intensity can be detected, and the phase difference can be obtained from the time lag of the maximum value or the minimum value. In either case, it is not necessary to take the difference between detection outputs every time color adjustment is performed, and the amount of calculation can be greatly reduced.

  In the case of the present invention, the first and second detection means are in an ideal state with respect to the transfer medium because the phase difference caused by the difference between the portions on the transfer medium where the regular reflection light and the irregular reflection light are generated is corrected. Even if it is not installed in, highly accurate color matching adjustment is possible.

  In the present invention, the phase difference is calculated only when the arrangement relationship between the first and second detection means and the transfer medium may change. Therefore, when the detection unit is replaced or when the transfer unit is replaced, the phase difference calculation process is performed and stored, and the subsequent color matching adjustment is performed by correcting with the stored phase difference. Accurate color matching adjustment is possible.

  In the present invention, since the phase difference is calculated using the chromatic color component image, the phase difference calculation process can be omitted for the achromatic color component image in which irregular reflection does not occur.

  In the present invention, the phase difference is calculated using each of a plurality of chromatic color component images, and the average value of the calculated phase differences is calculated. Since the phase difference calculated due to the magnitude of the output value of the irregularly reflected light due to the sensitivity characteristics for each wavelength of the first and second detection means and the unexpected situation may fluctuate for each color component, in the present invention, these fluctuations The influence can be reduced.

Hereinafter, the present invention will be specifically described with reference to the drawings illustrating embodiments thereof.
Embodiment 1 FIG.
FIG. 1 is a cross-sectional view showing the overall configuration of an image forming apparatus according to the present invention. The image forming apparatus according to the present invention is specifically a digital color printer, a digital color copying machine, or a complex machine thereof. The image forming apparatus includes an image forming station 100 and a transfer unit 7.

  The image forming station 100 of the image forming apparatus forms four colors according to each color in order to form a multicolor image using each color of black (K), cyan (C), magenta (M), and yellow (Y). Exposure devices 1a, 1b, 1c, 1d for forming latent images, developing devices 2a, 2b, 2c, 2d for developing latent images of the respective colors, photosensitive drums 3a, 3b, 3c, 3d, cleaners 4a, 4b, 4c, 4d and chargers 5a, 5b, 5c and 5d. Note that the symbols a, b, c, and d attached to the respective symbols are described so as to correspond to the respective colors of black (K), cyan (C), magenta (M), and yellow (Y). In the following description, except for the case where a member corresponding to a specific color is specified and described, the members provided for each color are collectively shown as an exposure unit 1, a developing unit 2, a photosensitive drum unit 3, and a cleaner unit 4. Will be referred to as the charging unit 5.

  The exposure unit 1 is a laser scanning unit (LSU) including a writing head or a laser irradiation unit in which light emitting elements such as EL (Electro Luminescence) and LED (Light Emitting Diode) are arranged in an array, and a reflection mirror. The image forming apparatus shown in FIG. 1 uses LSU. The exposure unit 1 forms an electrostatic latent image corresponding to the image data on the photosensitive drum unit 3 by performing exposure according to the input image data. The developing unit 2 visualizes the electrostatic latent image formed on the photosensitive drum unit 3 with each color toner. The photosensitive drum unit 3 is disposed at the center of the image forming apparatus, and forms an electrostatic latent image and a toner image corresponding to the input image on the drum surface. The cleaner unit 4 removes and collects the toner remaining on the photosensitive drum unit 3. The charging unit 5 uniformly charges the surface of each of the photosensitive drums 3a to 3d to a predetermined potential. As the charging unit 5, a charger type that does not contact the drum surface is used in addition to a roller type or a brush type that contacts the drum surface. The image forming apparatus shown in FIG. 1 uses a charger type charger.

  A transfer unit 7 is disposed below the photosensitive drum unit 3. The transfer unit 7 includes a transfer belt 70, a transfer belt driving roller 71, a transfer belt tension roller 73, transfer belt driven rollers 72 and 74, transfer rollers 6 a, 6 b, 6 c and 6 d, and a transfer belt cleaning unit 9.

  The transfer belt driving roller 71, the transfer belt tension roller 73, the transfer rollers 6a to 6d, the transfer belt driven rollers 72 and 74, and the like stretch the transfer belt 70, and the transfer belt 70 is indicated by the white arrow shown in FIG. It is rotationally driven in the direction. The transfer rollers 6a to 6d are rotatably supported by the housing of the transfer unit 7, and are based on a metal shaft having a diameter of 8 to 10 mm. The surface thereof is a conductive material such as EPDM (Ethylene Propylene Diene Monomer) or urethane foam. Covered with elastic material. The transfer rollers 6 a to 6 d can uniformly apply a high voltage having a polarity opposite to the charging polarity of the toner to the recording paper by the conductive elastic material, and the toner formed on the photosensitive drum unit 3. The image is transferred onto the transfer belt 70 or a recording sheet that is attracted onto the transfer belt 70 and conveyed. The transfer belt 70 is formed of polycarbonate, polyimide, polyamide, polyvinylidene fluoride, polytetrafluoroethylene polymer, ethylenetetrafluoroethylene polymer or the like having a thickness of about 100 μm, and is in contact with the surface of each of the photoreceptor drums 3a to 3d. It is provided to do. A multicolor toner image is formed by sequentially transferring the toner images of the respective colors formed by the photosensitive drum unit 3 onto the transfer belt 70 or a recording sheet that is sucked and conveyed on the transfer belt 70. The transfer belt 70 has a thickness of about 100 μm and is formed endlessly using a film. The transfer belt cleaning unit 9 removes and collects the toner image directly transferred to the transfer belt 70 and the toner adhering to the contact with the photosensitive drum unit 3.

  The image forming apparatus includes a paper feed tray 10 for supplying recording paper to the image forming station 100 and the transfer unit 7 described above, a fixing unit 12 for fixing a multicolor toner image transferred onto the recording paper, and recorded recording. A paper discharge tray 15, 33 or the like for placing paper is provided.

  The paper feed tray 10 is a tray for accumulating recording paper. The paper discharge trays 15 and 33 are trays on which recording paper on which images are recorded are placed. The paper discharge tray 15 is provided in the upper part of the image forming apparatus, and places printed recording paper face down. The paper discharge tray 33 is provided on the side of the image forming apparatus, and places printed recording paper face up. The fixing unit 12 includes a heat roller 31 and a pressure roller 32. The heat roller 31 is controlled based on a temperature detection value of a temperature detector (not shown) so as to reach a predetermined temperature by turning on / off heating means such as a heater lamp. The heat roller 31 and the pressure roller 32 are rotated while sandwiching the recording paper on which the toner image is transferred, and the toner image is thermocompression bonded to the recording paper by the heat of the heat roller 31.

  The operation of the image forming apparatus having the above configuration will be described. When image data is input to the image forming apparatus, the exposure unit 1 exposes according to the input image data and forms an electrostatic latent image on the photosensitive drum unit 3. This electrostatic latent image is developed by the developing unit 2 to generate toner images of the respective color components. On the other hand, the recording paper accumulated in the paper feed tray 10 is separated one by one by the pickup roller 16, transported to the paper transport path 11, and temporarily held by the registration roller 14. Based on a detection signal from a pre-registration detection switch (not shown), the registration roller 14 controls the timing so that the leading edge of the toner image on the photosensitive drums 3a to 3d is aligned with the leading edge of the image forming area of the recording paper. The sheet is conveyed to the transfer belt 70 in accordance with the rotation of the photosensitive drums 3a to 3d. The recording paper is sucked onto the transfer belt 70 and conveyed.

  Transfer of the toner image from the photosensitive drum unit 3 to the recording paper is performed by transfer rollers 6 a to 6 d provided to face the photosensitive drum unit 3 via the transfer belt 70. A high voltage having a polarity opposite to that of the toner is applied to the transfer rollers 6a to 6d, whereby a toner image is transferred to the recording paper. Since the transfer belt 70 is rotationally driven by the transfer belt driving roller 71, the transfer belt tension roller 73, the transfer belt driven rollers 72 and 74, and the transfer roller 6, the transfer belt 70 is adsorbed on the transfer belt 70 and is conveyed onto the recording sheet. The toner images of the respective color components are sequentially transferred and transferred to form a multicolor toner image.

  Thereafter, the recording paper is conveyed to the fixing unit 12, and the toner image is fixed on the recording paper by thermocompression bonding. The conveyance switching guide 34 switches the conveyance path, and conveys the recording paper on which the toner image is fixed to the paper discharge tray 33 or the paper conveyance path 35. The recording paper transported to the paper transport path 35 is transported along the paper transport path 37 by the transport rollers 36 and 38 and discharged to the paper discharge tray 15 by the paper discharge rollers 39.

  When the transfer to the recording paper is completed, the residual toner on the photosensitive drum unit 3 is removed and collected by the cleaner unit 4. Further, the transfer belt cleaning unit 9 removes and collects the toner adhering to the transfer belt 70 and ends a series of image forming operations.

  In the present embodiment, a direct transfer method is employed in which a recording sheet is carried on the transfer belt 70 and the toner images formed on the photosensitive drum unit 3 are superimposed on the recording sheet. The present invention can also be applied to an intermediate transfer type image forming apparatus in which toner images formed on the respective photosensitive drum units 3 are transferred in a superimposed manner and then transferred again onto a recording sheet to form a multicolor image. Needless to say, an effect can be obtained.

  As described above, the image forming apparatus according to the present embodiment controls the timing for driving the exposure units 1a to 1d, that is, the timing for writing the electrostatic latent images on the photosensitive drums 3a to 3d, respectively. A multicolor toner image is formed by superimposing the toner images of the respective color components on the transfer belt 70. Therefore, when the timing for writing the electrostatic latent image is not appropriate, a shift occurs in the transfer position of the toner image of each color component, causing a color shift.

  Therefore, in the present embodiment, a registration detection sensor 21 that detects the transfer position of the toner image of each color component is installed, and the photosensitive drums 3a, 3b, 3c, and so on are based on the detection result of the registration detection sensor 21. The timing for writing the electrostatic latent image in 3d is adjusted.

  FIG. 2 is a schematic diagram illustrating the configuration of the registration detection sensor 21. The registration detection sensor 21 is a position where the transfer belt 70 has passed through the image forming station 100 in order to detect an image for color matching adjustment (hereinafter referred to as a patch image) transferred onto the transfer belt 70. In addition, it is provided at a position before reaching the transfer belt cleaning unit 9. The registration detection sensor 21 includes a rectangular parallelepiped housing 210, in which a light emitting unit 21a, a detection unit 21b that detects irregular reflection light, and a detection unit 21c that detects regular reflection light are arranged. . The light emitting unit 21a is, for example, an LED (Light Emitting Diode), and the detection units 21b, 21c are, for example, PD (Photo Diode). In the present embodiment, the light emitting part 21 a and the detection parts 21 b and 21 c are arranged along the moving direction of the transfer belt 70. When light is emitted from the light emitting unit 21a to the transfer belt 70, irregularly reflected light and regular reflected light generated by the transfer belt 70 or the patch image on the transfer belt 70 are detected simultaneously by the detecting units 21b and 21c, respectively.

  The housing 210 of the registration detection sensor 21 is detachably attached to a base 200 fixed inside the image forming apparatus. Therefore, when the sensor output decreases due to a change with time, or when a failure occurs in the sensor, the entire housing 210 can be replaced. A micro switch 205 is installed on the pedestal 200 (see FIG. 4) so that the presence or absence of the registration detection sensor 21 can be detected.

  FIG. 3 is a graph showing an output example of the registration detection sensor 21. The graph shown in FIG. 3A shows the outputs of the detection units 21 b and 21 c when a plurality of rectangular patch images are generated at the image forming station 100 and sequentially transferred to the transfer belt 70. The horizontal axis of the graph represents the elapsed time from the start of detection, and the vertical axis represents the outputs (for example, voltage values) of the detection units 21b and 21c. In other words, from the graph shown in FIG. 3, it is possible to acquire information on the timing at which the patch image transferred to the transfer belt 70 passes a predetermined detection point.

  When detecting regular reflection light, the intensity (light quantity) of regular reflection light differs depending on the surface of the transfer belt 70, the black (K) toner image, and the chromatic (C, M, Y) toner image. There is a large difference in the intensity of reflected light between the black toner image and the chromatic toner image, and the black toner image is weaker. On the other hand, the intensity of specularly reflected light from the surface of the transfer belt when no image is formed is substantially the same as that of the chromatic toner image and is stronger than that of the black toner image. By utilizing these properties, it is possible to acquire information on the timing at which the patch image transferred to the transfer belt 70 passes a predetermined detection point.

  When detecting irregularly reflected light (diffuse reflected light), it is possible to obtain a difference in intensity between the image of the chromatic toner and the surface of the transfer belt 70, and the characteristic of irregularly reflected light is the characteristic of regular reflected light. It becomes the opposite characteristic. For example, when the detection value of regular reflection light is a maximum, the detection value of diffuse reflection light is a minimum. Conventionally, in order to improve the detection accuracy of each patch image, the influence of the irregularly reflected light component included in the detection output of the detection unit 21c has been removed. That is, when the detection output of the detection unit 21c that detects regular reflection light is V1, and the detection output of the detection unit 21b that detects diffuse reflection light is V2, a correction output V3 obtained by subtracting the detection output V2 from the detection output V1 (FIG. 3). The transfer position of each patch image is detected based on (b).

  However, when the registration detection sensor 21 is not installed in an ideal state with respect to the transfer belt 70, the detection point of the regular reflection light detected by the detection unit 21c and the irregular reflection light detected by the detection unit 21b. There is a possibility that a difference occurs between the detection point and the detection point. At this time, as shown in FIG. 3A, between the time when the detection output V1 of specular reflection light is maximum (or minimum) and the time when the detection output V2 of diffuse reflection light is minimum (or maximum). A difference (phase difference) occurs. In the present embodiment, in order to reduce the error based on this time difference (phase difference), the phase difference between the detection output V1 and the correction output V3 is obtained in advance as the correction time ΔT, and thereafter a patch image is used. When performing color misregistration adjustment, the output of the detection unit 21c is corrected with the correction time ΔT.

  Specifically, a threshold value TH1 is set for the detection output V1, and first, the times Ta and Tb when the detection output V1 matches the threshold value TH1 are obtained, and the median value T1 of the times Ta and Tb is calculated. The calculated median value T1 serves as an index indicating the transfer position of the patch image. For example, as shown in FIG. 3A, when the detected output V1 is in the vicinity of the maximum value at the calculated median value T1, the calculated median value T1 is the center of two adjacent patch images of the detection unit 21c. This corresponds to the timing of passing the detection point. Conversely, when the detected output V1 is near the minimum value at the calculated median value T1, the median value T1 corresponds to the timing at which the patch image passes the detection point of the detection unit 21c.

  Similarly, a threshold value TH3 is set for a correction output V3 obtained by subtracting the detection output V2 from the detection output V1, and times Tc and Td at which the correction output V3 and the threshold value TH3 match are obtained. Then, a median value T3 of the times Tc and Td is calculated. At this time, the phase difference between the detection output V1 of the regular reflection light and the correction output V3 can be obtained by T1−T3 (= ΔT), and this value is stored as the correction time ΔT for the detection output V1.

  The operation of the image forming apparatus when adjusting the exposure timing using the output of the registration detection sensor 21 will be described below. FIG. 4 is a block diagram illustrating the configuration of the control system of the image forming apparatus. A CPU 51 is mounted on the control unit 50 that controls the image forming station 100, and a ROM 52, a RAM 53, a clock unit 54, and A / D converters 55, 56, and 57 are connected to the CPU 51. The CPU 51 loads the control program stored in advance in the ROM 52 onto the RAM 53 and executes it, thereby controlling the various hardware as described above and operating as the image forming apparatus according to the present invention. In addition to such a control program, the ROM 52 previously stores image data for generating a patch image, threshold values TH1 and TH3 for the detection output V1 and the correction output V3, and the like.

  The registration detection sensor 21 is connected to the A / D converter 55, and the outputs of the detection units 21b and 21c of the registration detection sensor 21 are acquired at a predetermined sampling rate (for example, 2 msec). A micro switch 205 is connected to the A / D converter 56 and acquires a signal indicating whether or not the registration detection sensor 21 is attached to the pedestal 200. For example, the micro switch 205 outputs an off signal when the registration detection sensor 21 is mounted on the pedestal 200, and outputs an on signal when the registration detection sensor 21 is not mounted. A transfer unit detection switch 7a is connected to the A / D converter 57, and a signal indicating whether or not the transfer unit 7 is installed is acquired. The transfer unit detection switch 7a is, for example, a press-type switch provided so as to contact the transfer unit 7, and outputs an off signal when the transfer unit 7 is installed at a predetermined position inside the apparatus, and is removed. If ON, an ON signal is output.

  FIG. 5 is a flowchart illustrating a processing procedure by the control unit 50 when calculating a correction value for the output of the detection unit 21c. First, the CPU 51 of the control unit 50 sets one color component (step S11). Here, since irregular reflection by a black patch image is hardly observed, any one of chromatic colors (C, M, Y) is set.

  The CPU 51 controls the image forming station 100 to form a patch image with the set color components on the transfer belt 70 (step S12). Specifically, the image data related to the patch image is read from the ROM 52, and the exposure device 1b (or the exposure devices 1c and 1d) is controlled based on the read image data, and the photosensitive drum 3b (or the photosensitive drum 3c). , 3d) to generate an electrostatic latent image. Then, the electrostatic latent image is developed by supplying toner from the developing device 2b (or the developing devices 2c and 2d), and a patch image having a set color component is generated. The generated patch images are sequentially transferred onto the transfer belt 70 under the action of the transfer roller 6b (or transfer rollers 6c and 6d).

When calculating a correction value for the output of the detection unit 21c, the registration detection sensor 21 detects reflected light from the transfer belt 70 or a patch image on the transfer belt 70 at a predetermined sampling rate. That is, the control unit 50 acquires the detection output V1 of specular reflection light and the detection output V2 of irregular reflection light through the A / D converter 55 (step S13). Next, the CPU 51 calculates the patch image passage timing T1 using the threshold value TH1 for the detection output V1 (step S14). For example, the passage timing T1 may be calculated as a median value of the time when the difference (V1−TH1) between the detection output V1 and the threshold value TH1 changes from plus to minus and the next time when it changes from minus to plus. it can.
Note that the value calculated in step S14 is not necessarily the passage timing of the patch image, and as shown in FIG. 3A, the center position of two adjacent patch images passes the detection point of the detection unit 21c. It may be timing.

  Next, the CPU 51 calculates the correction output V3 by calculating the difference between the detection output V1 and the detection output V2 (step S15), and calculates the patch image passage timing T3 using the threshold value TH3 for the correction output V3. (Step S16). That is, the passage timing T3 can be calculated as the median value of the time when the difference (V3−TH3) between the correction output V3 and the threshold value TH3 changes from plus to minus and the next time when it changes from minus to plus. it can. In step S14, when the passage timing of the center position of the two patch images is detected instead of the passage timing of the patch images, the difference (V3-TH3) between the correction output V3 and the threshold value TH3 is obtained. It can be calculated as a median value of the time from the minus to the plus and the time from the plus to the minus.

  Next, the CPU 51 calculates the correction time ΔT by calculating the difference (T1−T3) between the patch image passage timing T1 calculated in step S14 and the patch image passage timing T3 calculated in step S16 (step S17). ). The calculated correction time ΔT is stored in the RAM 53.

  Next, the CPU 51 determines whether other color components need to be corrected (step S18). When there is a color component other than black (K) for which the calculation of the correction time ΔT has not been completed, it is determined that correction is required for the other color components (S18: YES), and the CPU 51 has completed the correction. Other color components that are not present are set (step S19), and the process returns to step S12.

  When it is determined that there is no need to correct other color components (S18: NO), the CPU 51 calculates an average value ΔTave of correction times ΔT calculated for each color component excluding black (K) (step S20). Then, the CPU 51 stores the calculated average value ΔTave in the RAM 53 (step S21). The stored average value ΔTave is used as a correction value for the detection unit 21c during color matching adjustment described later.

  In the present embodiment, the correction time ΔT is calculated for each color component (C, M, Y) excluding black and the average value ΔTave is obtained. However, the phase difference between the detection output V1 and the correction output V3 is For example, a correction time ΔT may be calculated for a cyan color component, and the correction time ΔT may be used when adjusting the color misregistration of magenta and yellow because of the inclination when the registration detection sensor 21 is attached. Good. Further, with respect to the phase difference, there is almost no change over time, so the above-described processing is performed at the time of manufacturing or shipping the image forming apparatus, and the obtained correction value (ΔTave) is stored in advance. Good.

  Next, an operation when color misregistration adjustment is performed using the correction value calculated by the above-described method will be described. FIG. 6 is a flowchart illustrating a procedure of processing executed by the control unit 50 during color misregistration adjustment. The CPU 51 of the controller 50 forms a patch image by controlling the image forming station 100 (step S31). Next, the CPU 51 detects the passage timing T of the patch image based on the output from the registration detection sensor 21 input through the A / D converter 55 (step S32). The patch image passage timing T can be detected in the same manner as described above. That is, a threshold value is set for the detection output of the detection unit 21c (hereinafter, the detection output of the detection unit 21c is V and the threshold value is TH), and the difference between the detection output V and the threshold value TH (V−TH). The passage timing T of the patch image can be detected as the median value of the time when the shift from plus to minus and the difference between the detection output V and the threshold TH (V-TH) shifts from minus to plus.

  Next, the detected value, that is, the passage timing T is corrected by the average value ΔTave calculated by the above-described flowchart, and the corrected passage timing is obtained. The corrected passage timing is obtained by T-ΔTave (step S33). Next, the difference between the corrected passage timing and the reference passage timing is calculated (step S34). Here, the reference passage timing is, for example, from when the electrostatic latent image is generated on the photosensitive drums 3 a to 3 d to when the toner image transferred onto the transfer belt 70 passes a detection point by the registration detection sensor 21. This means the theoretical value or set value of the time. The reference passage timing is stored in advance in the ROM 52, for example.

  Then, the CPU 51 corrects the image forming position using the calculation result of step S34 (step S35). Specifically, the image forming position is corrected by adjusting the exposure timing of each of the exposure devices 1a to 1d by ΔTave.

Embodiment 2. FIG.
In the first embodiment, the phase difference caused by the inclination of the registration detection sensor 21 is calculated at the time of manufacture or shipment of the image forming apparatus. For example, when the transfer unit 7 is replaced, Alternatively, the phase difference may be calculated again when the registration detection sensor 21 is replaced.

  FIG. 7 is a flowchart illustrating a processing procedure performed by the control unit 50 when calculating a correction value for the output of the detection unit 21c. First, the CPU 51 of the control unit 50 determines whether or not the replacement of the transfer unit 7 is detected by monitoring a signal input through the A / D converter 57 (step S41). A transfer unit detection switch 7a is connected to the A / D converter 57. When the transfer unit 7 is installed at a predetermined position inside the apparatus, an off signal is input, and when the transfer unit 7 is removed, it is turned on. A signal is input. Therefore, when the CPU 51 detects a change from the ON signal to the OFF signal through the A / D converter 57, it is determined that the transfer unit 7 has been replaced (S41: YES), and the correction is performed again according to the flowchart shown in FIG. Is executed (step S43).

  If it is determined that the replacement of the transfer unit 7 has not been detected (S41: NO), the CPU 51 monitors the signal input through the A / D converter 56 to replace the registration detection sensor 21. It is determined whether or not it has been detected (step S42). A micro switch 205 is connected to the A / D converter 56, and an off signal is input when the registration detection sensor 21 is attached to the pedestal 200, and an on signal is input when it is removed. . Therefore, when the CPU 51 detects a change from the ON signal to the OFF signal through the A / D converter 56, it is determined that the replacement of the registration detection sensor 21 has been detected (S42: YES), and again according to the flowchart shown in FIG. Is corrected (S43). If it is determined that the replacement of the registration detection sensor 21 has not been detected (S42: NO), the processing according to this flowchart is terminated.

  As described above, in this embodiment, only when the inclination of the registration detection sensor 21 with respect to the transfer unit 7 changes, the phase difference between the regular reflection output and the correction output can be calculated again.

1 is a cross-sectional view showing an overall configuration of an image forming apparatus according to the present invention. It is a schematic diagram explaining the structure of a registration detection sensor. It is a graph which shows the example of an output of a registration detection sensor. 2 is a block diagram illustrating a configuration of a control system of the image forming apparatus. FIG. It is a flowchart explaining the process sequence by the control part at the time of calculating the correction value with respect to the output of a detection part. It is a flowchart which shows the procedure of the process which a control part performs at the time of color shift adjustment. It is a flowchart explaining the process sequence by the control part at the time of calculating the correction value with respect to the output of a detection part. It is explanatory drawing explaining the conventional detection method.

Explanation of symbols

1 Exposure unit
2 Development Unit 3 Photosensitive Drum Unit 4 Cleaner Unit 5 Charging Unit 7 Transfer Unit 7a Transfer Unit Detection Switch 21 Registration Detection Sensor 51 CPU
52 ROM
53 RAM
205 micro switch

Claims (7)

In an image forming apparatus that forms an image by transferring each of a plurality of color component images on a transfer medium,
A means for irradiating light to the transfer medium to which the color component image has been transferred, and specularly reflected light and irregularly reflected light among light reflected by the transfer medium or the color component image when light is emitted by the means. First and second detection means for detecting, respectively, means for calculating a correction output obtained by correcting the output of the first detection means by the output of the second detection means, and an output of the first detection means and a corrected output calculated An image forming apparatus comprising: means for calculating a phase difference between the first and second detection means; and means for adjusting a transfer position of the color component image based on an output of the first detection means that corrects the phase difference.   The first and second detectors measure temporal changes in the intensity of the regular reflection light and the irregular reflection light, respectively, and calculate the phase difference based on the temporal change in the intensity of the regular reflection light and the correction output. The image forming apparatus according to claim 1, wherein the image forming apparatus is configured as described above.   The image forming apparatus according to claim 1, wherein the phase difference is a phase difference caused by a difference in a portion on the transfer medium where the regular reflection light and irregular reflection light are generated. .   Means for detecting the presence or absence of transfer means for transferring the color component image to a transfer medium; means for determining whether or not the transfer means is attached based on a detection result of the means; and the transfer means is attached. 4. The image formation according to claim 1, further comprising means for calculating a phase difference between the output of the first detection means and the correction output when the determination is made. 5. apparatus.   Means for detecting the presence or absence of the first and second detection means, means for determining whether or not the first and second detection means are mounted based on the detection means of the means, and the first and second 4. The apparatus according to claim 1, further comprising means for calculating a phase difference between the output of the first detection means and the correction output when it is determined that the detection means is attached. The image forming apparatus described in 1.   The color component image transferred to the transfer medium includes a chromatic color component image, and the phase difference between the output of the first detection means and the correction output is calculated for the color component image. The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus.   The color component image transferred to the transfer medium includes a plurality of chromatic color component images, and the phase difference between the output of the first detection means and the correction output is calculated for each of the color component images. 6. The image forming apparatus according to claim 1, further comprising means for calculating an average value of the calculated phase differences.

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