JP4661142B2 - Color image forming apparatus - Google Patents

Description

  The present invention relates to an arrangement position of a detection unit with respect to an image area in a color image forming apparatus that reads a mark image formed on the surface of an image carrier by a detection unit and corrects a positional deviation and density error of a recorded image.

JP-A-8-248721

  In recent years, in order to achieve high productivity in electrophotographic color image forming apparatuses, those adopting a tandem method have become mainstream. In this tandem system, the toner images formed on the photoconductors of the respective colors are multiplex-transferred onto the image carrier, and the multiple-transferred recorded images are transferred from the image carrier to the recording sheet, and the transfer carrier In some cases, a photoconductor for each color is disposed at a position opposite to the recording sheet conveyance path, and the recording sheet is conveyed, and a toner image of each color is sequentially transferred to the recording sheet to form a recording image. In any case, due to misalignment of the exposure device, the photosensitive member, the image carrier, and the transfer carrier, the toner images of the respective colors are transferred to the recording sheet at positions that are relatively displaced, and are recorded on the recording image. Since misalignment may occur, it is essential to correct such misalignment.

  As a method of correcting the positional deviation, generally, a plurality of yellow, magenta, cyan, and black mark images are successively formed on the surface of an image carrier or transfer carrier, and the positions of these mark images are determined. There is a method of correcting the positional deviation detected by a sensor (Japanese Patent Laid-Open No. 8-248721). In this method, by calculating the average value for each color component from the detection result of the sensor, the amount of misregistration of each color is calculated, and based on this misregistration amount, image formation of ROS, LED array, laser array, etc. The timing of drawing an image is fed back to the means.

  There are several types of sensors for detecting a mark image, such as a CCD sensor, a Bi-Cell type photo sensor, and a one-channel photo sensor. Among these sensors, the CCD sensor and the Bi-Cell type photosensor have high detection accuracy but are somewhat expensive, which causes high costs. Therefore, in the tandem method in the popular price range (hereinafter referred to as “popular price range tandem machine”), the position deviation detection and the density error detection which generally have both functions of the position deviation detection and the density error detection with a one-channel photo sensor. Common sensors (hereinafter referred to as “common sensors”) have become widespread.

  In the case of this popular price tandem machine, there are no problems if there are two sensors for detecting displacement and one sensor for detecting density error, and they are common in terms of cost reduction and space saving. It is preferable to equip two sensors in total, one sensor and one sensor for detecting misalignment. However, in the detection of misalignment, in order to detect skew misalignment and main scanning magnification misalignment with high accuracy, it is required to arrange sensors at two locations near both ends of the image area. When the recording sheet is set to a symmetrical position with respect to the center line of the image carrier parallel to the sub-scanning direction of the image carrier (hereinafter referred to as “center alignment”) In this case, it is required to arrange the sensor near the center of the image area. That is, the request for the arrangement position of the shared sensor is different between the position shift detection and the density error detection.

FIG. 13 shows a sensor arrangement that places importance on improving accuracy of density error detection when center alignment is applied. In this figure, the sensor 101a disposed at the center of the image carrier 100 is a common sensor, and the sensor 101b disposed at one end in the main scanning direction of the image carrier 100 is a position shift detection dedicated sensor. The mark images on the center line C and the dotted line W ₁ indicating the center of the image carrier 100 in the main scanning direction can be read. A dotted line W ₀ indicates a position symmetrical to the dotted line W ₁ with respect to the center line C.

The sensor 101a, the arrangement of the 101b, and between the dashed lines W ₀ ~ centerline C, by the left and right portions magnification difference between the between the center line C~ dotted W _1, the detection accuracy of the total magnification difference dotted W ₀ ~ dotted W ₁ It will get worse.

Next, FIG. 14 shows a state in which a straight line L parallel to the main scanning direction of the image carrier 100 formed on the image carrier 100 and a curve Q are detected by the sensors 101a and 101b. . In this figure, the sensor 101a disposed at the center of the image carrier 100 is a common sensor, and the sensor 101b disposed at one end in the main scanning direction of the image carrier 100 is a position shift detection dedicated sensor. The mark images on the center line C and the dotted line W ₁ indicating the center of the image carrier 100 in the main scanning direction can be read. A dotted line W ₀ indicates a position symmetrical to the dotted line W ₁ with respect to the center line C.

Here, the curve Q causes a so-called skew shift and BOW shift in the sub-scanning direction of the image carrier 100 with respect to the straight line L. Therefore, the sensor 101a, when the skew of the curve Q detected in 101b, the dotted line from the relationship between the influence of BOW deviation, skew on the center line C shift amount on the dotted line W ₁ (in the case of the figure zero) On W ₀ , it is detected as a skew deviation of K ₂ . Accordingly, an erroneous skew deviation K ₂ is detected with respect to the true skew deviation K ₁ on the dotted line W ₀ , so that a detection error occurs and the detection accuracy is lowered.

  As described above, in the sensor arrangement in FIGS. 13 and 14, when center alignment is applied, a highly accurate density error detection can be performed by arranging a shared sensor near the center of the image area. it can. However, if the main scanning magnification deviation or skew deviation is detected by this common sensor and the position deviation dedicated sensor arranged at one main scanning direction end of the image carrier, the detection accuracy is reduced. End up. On the contrary, when the shared sensor is arranged at one end in the main scanning direction of the image carrier, the accuracy of detecting the position error is improved, but the accuracy of detecting the density error is lowered. In other words, it is difficult to arrange a sensor that satisfies the detection of the opposite characteristics of density error and positional deviation such as skew deviation and main scanning magnification deviation, and it is difficult to detect both characteristics with high accuracy. .

  The present invention has been made in view of such problems, and an object of the present invention is to correct a positional deviation and a density error by reading a mark image formed on the surface of an image carrier with a detection unit. At the same time, it is an object of the present invention to provide a color image forming apparatus capable of detecting contradictory characteristics with high accuracy depending on the skew misalignment and density error reading positions.

  In order to achieve the above object, a color image forming apparatus according to the present invention includes a plurality of image forming means for forming a toner image of each color on the surface of a photoconductor according to an image data signal, and a toner image of each color from the photoconductor. And a correction mode control unit for sequentially transferring a mark image of each color for sending a signal to each image forming means and correcting a positional deviation and a density error of the image on the surface of the image carrier. A first detection unit and a second detection unit that optically read mark images of each color, and a detection information extraction unit that extracts both positional deviation information and density error information of each color toner image from detection signals of these detection units; In the color image forming apparatus comprising a condition correction unit that corrects the image forming condition of the toner image in each image forming means according to the positional deviation information and density error information, the first detecting means is provided on the image carrier. Oh The second detection means is disposed at a position that is asymmetric with respect to the center line parallel to the sub-scanning direction of the image carrier. It is characterized by that.

  In such an image forming apparatus of the present invention, the image forming means may be any means as long as it can transfer images of each color onto the image carrier, and is used in an image forming apparatus using an electrophotographic method. However, the present invention is not limited to the electrophotographic method as long as it is an apparatus that forms a full-color image by superimposing images of respective colors. In addition to the four colors of cyan, yellow, magenta, and black, a special color such as a corporate color may be added.

  As the image carrier, an intermediate transfer body belt on which a recording image formed on the surface of each color photoreceptor is transferred in a tandem color image forming apparatus can be applied. Alternatively, a photosensitive belt of each color is disposed at a position opposite to the conveyance belt that electrostatically attracts and conveys the recording sheet, and a conveyance belt that sequentially transfers the recorded images of each color onto the recording sheet as the recording sheet is conveyed. It is also possible to apply.

  The correction mode control unit is set to send an image data signal for transferring the mark image to the surface of the image carrier to the image forming means of each color when the mark image needs to be detected. That's fine. The mark image formation position preferably corresponds to the reading position of the detection means disposed at the position facing the image carrier.

  The first detection means and the second detection means for detecting the mark image formed on the image carrier combine a light emitting element and a light receiving element, and when the mark image is irradiated by the light emitting element, to the light receiving element. There is no problem as long as it is arranged at a position where the reflected light from the mark image or the transmitted light transmitted through the mark image can enter. In the present invention, the first detection unit may be disposed in the vicinity of one end of the image carrier in the main scanning direction. And it is preferable to make the said 1st detection means function only for position shift detection. Further, since skew deviation and main scanning magnification deviation can be detected only by using two detection means capable of detecting positional deviation, the second detection means can detect positional deviation and also has density error. In order to detect, it is good to function as both misalignment detection and density error detection. Further, the second detection means passes through a center point of the image carrier in the main scanning direction and is opposite to the first detection means with respect to a center line parallel to the sub-scanning direction of the image carrier. In addition, it is preferable that the first detection means is disposed at a position that is asymmetric. The arrangement positions of the first detection means and the second detection means, while the detection accuracy is somewhat sacrificed for both the positional deviation detection and the density error detection, even if two detection means are used, the minimum accuracy is maintained. It is possible to achieve both misalignment detection and density error detection.

  The detection information extraction unit can detect the mark image formed on the surface of the image carrier by performing arithmetic processing based on the interval and output value of the output signals detected by the first detection unit and the second detection unit. It is only necessary to send the detection result to the condition correction unit. Specifically, the positional deviation is detected based on the detected output signal interval, and the density error is detected based on the detected output value.

  The condition correction unit is configured to generate an image forming position of a recording image formed on the surface of the image carrier by the image forming unit based on positional deviation information and density error information of each color toner image derived from the detection result of the detecting unit. In order to reflect the corrected image forming position in the recorded image, any signal can be used as long as it can output a signal corrected to adjust the image forming position to the image forming means.

  In the image forming apparatus, for the alignment of the recording sheet with respect to the width of the image carrier in the main scanning direction, in addition to center alignment, one of the widths in the main scanning direction of the conveyance path orthogonal to the conveyance direction of the recording sheet is used. At the end, there is a type in which one side of all the recording sheets is set together (hereinafter referred to as “side alignment”). When side alignment is applied, the end portion in the main scanning direction of the image carrier on which one side of the recording sheet is aligned is defined as a reference side.

  Here, when the side alignment is applied as the alignment of the recording sheet, the arrangement position of the second detecting means is preferably set in the vicinity of the reference side main scanning direction end of the recording sheet. Thereby, the second detection means can always read the mark image in the image area of the recording sheet of any size, and can detect the positional deviation and the density error with high accuracy. It becomes possible.

  In the image forming apparatus, in order to accurately detect the skew deviation, the mark image is read at both ends of the image carrier in the main scanning direction, and the skew deviation is detected from the amount of positional deviation at each reading position. Is preferred. However, in the arrangement position of the second detection means of the present invention, the skew deviation detection accuracy is lower than when the mark image is read at both ends in the main scanning direction of the image carrier and the skew deviation is detected. Become. Therefore, it is preferable that the second detection means includes a moving means for moving the second detection means in the main scanning direction width region of the image carrier. And it is good to provide the memory | storage part which memorize | stores the detection result in each reading position in the said condition correction | amendment part. Thereby, the difference between the skew deviation detected by moving the second detection means to the end of the image carrier in the main scanning direction and the skew deviation detected at the position where the second detection means is arranged is stored in advance. By storing this information in the unit and adding the stored information to the detection result to correct the skew deviation, it is possible to eliminate a decrease in detection accuracy of the skew deviation due to the arrangement position of the second detection means. .

  Further, when center alignment is applied as the alignment of the recording sheet, it is preferable to detect the density error at the center of the image area of the recording sheet. However, in this case, since the density error cannot be detected at the center of the image area of the recording sheet at the position where the second detection means of the present invention is arranged, a detection error occurs. Therefore, it is preferable to store the difference between the density error detected by moving the second detection means to the center of the image area of the recording sheet and the density error detected at the arrangement position of the second detection means in the storage unit. . Thereby, it is possible to perform highly accurate correction by adding the information stored in the storage unit to the density error detected at the arrangement position of the second detection means.

  The timing for detecting the mark image by moving the second detection means is when the image forming apparatus is adjusted at the time of factory shipment or in the service mode, or when a consumable part such as a toner cartridge or an intermediate transfer belt is replaced. Etc. are preferred. Then, it is preferable to store in advance skew deviation, BOW deviation, linearity deviation, main scanning magnification balance deviation, main scanning partial magnification deviation, density distribution in the image area, and the like. Thereby, each detection information memorize | stored in the said memory | storage part and the newly detected detection information can be compared, and the said characteristic, position shift, and / or density | concentration error can be correct | amended based on the difference.

  According to the color image forming apparatus of the present invention configured as described above, when correcting the positional deviation and density error by reading the mark image formed on the surface of the image carrier by the detecting means, skew deviation or the like is performed. Depending on the reading position of the density error, it is possible to detect the contradictory characteristics with high accuracy.

  Hereinafter, a color image forming apparatus of the present invention will be described in detail with reference to the accompanying drawings.

  FIG. 1 is a schematic configuration diagram of a color image forming apparatus using an electrophotographic system to which the present invention is applied. In this schematic configuration diagram, the surface of the photoconductor is charged by a contact charger, an electrostatic latent image is formed by irradiation with a laser beam, and the xerographic engine that develops the electrostatic latent image with toner is yellow, magenta, cyan. 1 shows an overview of an IOT (image output terminal: image output unit) of a tandem color electrophotographic image forming apparatus provided for each color of black. In the drawing, the image reading unit and the image processing unit of the image forming apparatus are omitted.

  The IOT of this image forming apparatus includes four photoconductors 1Y, 1M, 1C, and 1K that rotate in the direction of arrow A in the figure, and contact chargers 2Y, 2M, 2C, and 2K that charge the surface of each photoconductor. ROS (laser output units) 3Y, 3M, 3C, which expose the charged photoreceptor surfaces with exposure light modulated based on the image information of each color and form electrostatic latent images on the photoreceptors. 3K and developing units 4Y, 4M, 4C, and 4K that develop the electrostatic latent image on each photoconductor with each color developer to form a toner image on the photoconductor, and intermediate transfer each color toner image on the photoconductor The primary transfer units 5Y, 5M, 5C, and 5K that transfer to the body belt 6, the secondary transfer unit 7 that transfers the toner image on the intermediate transfer body belt 6 to the paper P, and the toner image transferred to the paper P are fixed. The fixing device 9 for carrying out the paper, the paper tray T for containing the paper P, and the surface of each photoconductor. A cleaner (not shown) for cleaning, a static eliminator (not shown) for removing residual charges on the surface of each photoconductor, a photosensor 10 for detecting a mark image transferred to the surface of the intermediate transfer belt 6, and an intermediate The belt cleaner 8 is configured to clean the surface of the transfer belt 6.

  As an image forming operation in the image forming apparatus shown in the configuration diagram, first, an original image signal read from an original by an image reading unit (not shown) or an external computer (not shown) is used. The original image signal is input to an image processing unit (not shown). The input image signal is decomposed into image information of each color and then input to ROS (laser output units) 3Y, 3M, 3C, and 3K, and the laser beam L is modulated. The modulated laser beam L is applied to the surfaces of the photoreceptors 1Y, 1M, 1C, and 1K that are uniformly charged by the contact chargers 2Y, 2M, 2C, and 2K. When the laser beam L is raster-irradiated on the surface of each photoconductor, an electrostatic latent image corresponding to the input image signal is formed on each photoconductor. Subsequently, the electrostatic latent images on the photoconductors are developed with toner by the color developing devices 4Y, 4M, 4C, and 4K, and toner images are formed on the photoconductors. The toner image formed on each photoconductor is transferred to the intermediate transfer belt 6 by the primary transfer units 5Y, 5M, 5C, and 5K. Each photoreceptor after the transfer of the toner image to the intermediate transfer belt 6 is cleaned of adhering matter such as residual toner adhering to the surface by a cleaner, and the residual charge is removed by a static eliminator.

  Next, the toner image on the intermediate transfer belt 6 is transferred onto the paper P sent from the paper tray by the secondary transfer device 7 and then transferred onto the paper P by the fixing device 9. Is fixed and a desired image is obtained. The intermediate transfer belt 6 on which the transfer of the toner image onto the paper P has been completed is cleaned of adhering matters such as residual toner adhering to the surface by the belt cleaner 8, and one image forming operation is completed.

  In an electrophotographic color image forming apparatus, image fluctuations such as image density, positional deviation of each color toner image, color reproduction, gradation, and fogging occur due to environmental conditions such as temperature and humidity and deterioration over time. For this reason, it is necessary to correct misalignment and density error before outputting an image to the paper P or while waiting for output. As the method, first, a mark image is formed on the intermediate transfer belt 6. Then, the mark image is detected by the photosensor 10 and an output signal is sent to the control unit. Further, the positional deviation and the density error are corrected as necessary from the result of the positional deviation amount and the density error obtained from the output signal (this correction operation is hereinafter referred to as “correction mode”).

  A color image forming apparatus to which the present invention is applied is equipped with two photosensors, a position shift detection dedicated sensor and a position shift detection and density error detection shared sensor (one is shown in FIG. 1). The shift detection dedicated sensor is disposed in the vicinity of one main scanning direction end of the intermediate transfer belt 6. The shared sensor may include a moving means (not shown) and move the shared sensor to a position other than the arrangement position. In this case, the shared sensor moves on a straight line parallel to the main scanning direction of the intermediate transfer belt 6. As a result, it is possible to detect positional deviation and density error at a plurality of positions of the intermediate transfer belt 6.

  FIG. 2 is a block diagram showing a flow of correction of positional deviation and density error in the color image forming apparatus shown in FIG. The photosensitive member 1 is charged by the contact charger 2, and an electrostatic latent image is formed by exposing the photosensitive member 1 with the ROS 3 according to the signal of the mark image output from the correction mode control unit 11. After development, the mark image is transferred to the intermediate transfer belt 6. Then, the mark image transferred onto the intermediate transfer belt 6 is read by the photosensor 10.

  The detection information extraction unit 12 detects positional deviation and density error from the signal output from the photosensor 10, and the storage unit 13 stores the positional deviation information and density error information sent from the detection information extraction unit 12. Then, the condition correction unit 14 applies information suitable for correction based on the positional deviation information and density error information stored in the storage unit 13, and corrects the image forming position by controlling the writing timing of the ROS 3. At the same time, the image density is corrected by controlling the laser power of the ROS 3.

  FIG. 3 shows an arrangement of mark images applied to the present invention. In this embodiment, cyan is used as a reference color, a reference mark image (Mc) of the reference color cyan is combined with other comparative colors, a combination of cyan (Mc) and yellow (My), cyan (Mc) and A combination of magenta (Mm) and a combination of cyan (Mc) and black (Mb) are sequentially arranged. These mark images move in the direction of the arrow in the figure, and sequentially pass through the detection field of view (not shown) of the photosensor 10 from the mark image Mc to the mark image Mb, thereby detecting misalignment and density error. It has a configuration. In the description of the mark image, all combinations are collectively referred to as a pattern image M.

  FIG. 4 is a schematic configuration diagram of the photosensor 10 in the color image forming apparatus to which the present invention is applied. The photosensor 10 includes an illumination unit, a light receiving optical system, and a light receiving element. This illumination means consists of two LEDs 10a, 10b. The light receiving optical system includes a lens 10c and a mask 10e. In this figure, the left-right direction is the main scanning direction. FIG. 5 is a block diagram showing a flow in which the output signal from the photodiode 10d is processed by the detection information extraction unit 12, and includes an AMP, a peak detection circuit, an under-peak detection circuit, and two sample-and-holds. The output signal from each circuit is sent to the storage unit 13 in FIG.

  In order for the photosensor 10 to detect a positional shift and a density error, it is necessary to irradiate the pattern image M shown in FIG. Accordingly, the illumination unit emits a pattern image M composed of mark images arranged in the order of cyan, yellow, cyan, magenta, cyan, and black. However, the reflected light from the cyan, yellow, and magenta mark images differs from the reflected light from the black mark image. Therefore, in order to detect these two types of reflected light with one light receiving element (photodiode 10d), it is necessary to irradiate the mark image from a position where each reflected light can enter the light receiving element. Two illumination means are used properly according to the mark image.

  The lens 10c of the light receiving optical system is arranged so that one of the two types of reflected light can be imaged on the light receiving surface of the photodiode 10d. However, when the reflected light is incident on the photodiode 10d, it is not limited to whether the reflected light is imaged or not formed on the light receiving surface, and reflected light that is unnecessary for the detection of positional deviation and density error also enters. End up. Therefore, it is necessary to block this unnecessary reflected light and guide only the reflected light component effective for each detection onto the light receiving surface of the photodiode 10d. Therefore, a mask 10e for restricting the detection visual field of the light receiving surface of the photodiode 10d is provided immediately before the photodiode 10d. The mask 10e is black to prevent stray light. The lens 10c and the mask 10e constituting the light receiving optical system can make the detection visual field of the light receiving surface of the photodiode 10d substantially equal regardless of which reflected light is incident.

  When the reflected light from the mark image is projected onto the light receiving surface of the photodiode 10d, the photodiode 10d outputs a current corresponding to the amount of reflected light, that is, the density of the mark image. As shown in FIG. 5, the current output from the photodiode 10 d is subjected to current-voltage conversion / amplification by the AMP 20 and then stored as a sensor output signal in a storage unit (not shown), a peak detection circuit 21, and an under-peak detection circuit 23. , And two sample and hold circuits 22 and 24.

  The peak detection circuit 21 detects the maximum position of the sensor output signal, supplies it to the sample & hold circuit 22 as a peak detection signal, and outputs it to the storage unit. By using this peak detection circuit 21 to detect the maximum position of the sensor output signal, the center position in the thickness direction of the mark image can be detected. And in the memory | storage part, this peak detection signal is memorize | stored as positional offset information of each color mark image.

  The sample & hold circuit 22 holds the sensor output signal output from the AMP 20 with the peak detection signal output from the peak detection circuit 21 as a trigger. As a result, the maximum value of the sensor output signal is held and output to the storage unit as a peak hold signal. In the storage unit, the hold signal of the maximum value of the output signal is stored as density error information of each color mark image of cyan, yellow, and magenta.

  The under peak detection circuit 23 detects the minimum position of the sensor output signal and supplies it to the sample and hold circuit 24 as an under peak detection signal. The sample and hold circuit 24 holds the sensor output signal output from the AMP 20 with the under peak detection signal output from the under peak detection circuit 23 as a trigger. As a result, the minimum value of the sensor output signal is held and output to the storage unit as an under-peak hold signal. In the storage unit, this minimum value hold signal is stored as density error information of the black mark image. Note that a general electric circuit may be applied to the AMP 20, the peak detection circuit 21, the under peak detection circuit 23, and the sample and hold circuits 22 and 24, and the description thereof is omitted.

  In order to detect the density of the pattern image M by the output signal from the photodiode 10d, the reference output signal and the output signal detected from the pattern image M must be compared. For this reason, a means capable of switching between the case where the reference light is incident on the photodiode 10d and the case where the reflected light from the pattern image M is incident is required. Therefore, a shutter 10f as shown in FIG. 6 is attached to the photosensor 10 in a slidable state on the housing of the photosensor 10 facing the intermediate transfer belt 6 (FIG. 4). . This figure is a plan view of the shutter 10f as seen from the LED side. The shutter 10f is provided with a measurement window 10g and a reference plate 10h for obtaining a reference for the output voltage of the sensor. A mechanism is provided that moves by a drive device (not shown) in the direction of the arrow in the figure in accordance with the reflected light incident on the photodiode 10d. The shutter 10f is in such a position that the reference plate 10h is disposed on the light receiving system optical axis in the normally closed state, and the shutter 10f is opened only when the pattern image M is measured, and the measurement window 10g is disposed on the light receiving system optical axis. Move to be.

FIG. 7 shows the positional relationship between the mark image m formed on the intermediate transfer belt 6 and the detection visual field R of the photosensor 10 on the intermediate transfer belt 6 with the passage of time. Graph (a) shows the waveform of the sensor output signal corresponding to the position of the detection visual field R of the photosensor 10. The lowermost graph (b) shows the peak detection signal of the mark image m output from the peak detection circuit in correspondence with the passage of time. Here, the mark image is formed such that the thickness t of each of the sides m ₁ and m ₂ is slightly smaller than the diameter d (1 mm) of the detection visual field R.

The mark image m primarily transferred onto the intermediate transfer belt 6 passes through the front surface of the photosensor 10 as the intermediate transfer belt 6 rotates, and crosses the detection visual field R of the photosensor 10. When the mark image m moves with the intermediate transfer body belt 6 and the detection field R of the photosensor 10 reaches the point A on the intermediate transfer body belt 6 shown in FIG. Since the side m ₁ enters, the sensor output signal starts changing. When the mark image m further moves, the area of the mark image m included in the detection visual field R, that is, the overlapping area between the detection visual field R and one side m ₁ of the mark image m increases, so that the sensor output signal gradually increases. The sensor output signal becomes maximum at the point B where the detection visual field R is substantially covered with the mark image m.

As described above, since the thickness t of each side m ₁ and m ₂ of the mark image m is formed slightly smaller than the diameter d of the detection field R of the photosensor 10, the mark image m passes the B point. Then, since the area of the mark image m included in the detection visual field R, that is, the overlapping area of the detection visual field R and the mark image m decreases, the sensor output signal gradually decreases and the mark image m becomes a photosensor. The sensor output signal becomes the minimum (point C) when it completely leaves the 10 detection visual fields R.

Thus, in the example shown in FIG. 7, when one side m ₁ of the mark image m passes through the detection field R of the photosensor 10 (between points A and B), the detection field R and the mark image m Are overlapped with the progress of the intermediate transfer belt 6, and the sensor output signal having the same intensity is not continuously output from the photosensor 10. That is, the maximum value is instantaneously generated in the sensor output signal. The waveform of the sensor output signal is such that the detection visual field R of the photosensor 10 is formed in a circular shape, and the thickness of the mark image m is the same as or smaller than the diameter d of the detection visual field R. Can be easily obtained.

  In multi-color printing machines, color copiers, color printers, etc., when the mark image m is formed on a moving body such as an intermediate transfer belt, the thickness of the mark image m changes depending on the environmental conditions such as temperature and humidity. In other words, it is difficult to form a mark image m having the same thickness as the diameter d of the detection visual field R of the photosensor 10. Therefore, as described above, even when the thickness of the mark image m is smaller than the diameter d of the detection visual field R, the instantaneous maximum value is generated in the waveform of the sensor output signal. It is advantageous when constructing.

As shown in FIG. 7, when a momentary maximum value occurs in the waveform of the sensor output signal, the maximum value is detected by the photosensor 10 in the center position (center of gravity position) in the thickness direction of _one side m ₁ of the mark image m. Occurs when it matches the center position of the field of view R. Therefore, if the peak detection circuit detects the maximum value (peak) of the sensor output signal and, as shown in FIG. 7B, a pulse-shaped peak detection signal is output in accordance with this maximum value. The rising edge portion of the peak detection signal indicates the center position (center of gravity position) of one side m ₁ of the mark image m, and the position of m ₁ can be accurately detected.

Further, the mark image m shown in FIG. 7 is formed in a V shape having two sides m ₁ and m ₂ inclined at approximately 45 degrees in different directions with respect to the moving direction of the intermediate transfer belt 6. Therefore, by detecting one of the mark images m with the photosensor 10 of the present embodiment, it is possible to grasp the amount of positional deviation in the main scanning direction and the sub-scanning direction at a time. That is, the sensor output signal is once minimized when the detection visual field R reaches the point C, but when the detection visual field R passes the point D, the side m _{2 of the} mark image m and the detection visual field R start to overlap again. Then, it starts to rise again, and the maximum value is shown at point E where the center position of the side m _{2 in} the thickness direction overlaps the center position of the detection visual field R. As the overlapping area of m ₂ and the detection field of view R decreases, the sensor output signal also decreases, and the mark image m returns to the minimum output at point F where the mark image m leaves the detection field of view R.

For this reason, when the V-shaped mark image m is read by the photosensor 10, as shown in FIG. 7B, the center position (center of gravity position) of each side m ₁ and m _{2 in the} thickness direction of the mark image m is obtained. A pair of pulsed peak detection signals are output from the peak detection circuit corresponding to the points B and E overlapping the center position of the detection visual field R.

  Subsequently, the operation of the positional deviation correction and the density error correction in the correction mode of the present invention will be described with reference to the flowchart of FIG. 8 by taking as an example the case where the photosensor in this flowchart is a common sensor. First, in step S1, the photosensor 10 is moved to the reading position. In step S 2, the pattern image M shown in FIG. 3 is formed on the intermediate transfer body belt 6. Thereafter, in step S3, the pattern image M is measured by the photosensor 10, and the positional deviation and density error are corrected based on the output signal of the photodiode 10d.

  In the misalignment correction, in step S11, the detection information extraction unit 12 outputs the peak detection signal output from the peak detection circuit 21 based on the output signal of the photodiode 10d to the target value of the reference color cyan in the main scanning direction. Measurement and calculation of the absolute position displacement amount and the relative displacement amounts of yellow and magenta with respect to the reference color cyan.

  In this embodiment, the amount of misalignment of the mark image is obtained by calculation from the timing chart at the time of mark image measurement shown in FIG. In FIG. 9, from the top, the waveforms of the operation signal of the shutter 10f of the photo sensor 10, the lighting signals of the LEDs 10a and 10b of the photo sensor 10, the sensor output signal, the peak detection signal, the peak hold signal, the under peak detection signal, and the under peak hold signal. It is shown.

  As shown in FIG. 9, in the correction mode, first, the LED 10b is turned on with the shutter 10f closed, and the reflected light of the reference plate 10h is measured for density error correction. Thereafter, before the mark image arranged at the head with respect to the moving direction of the intermediate transfer belt 6 passes through the detection visual field of the photosensor 10, the shutter 10f is opened, and the reflected light from the mark image can be incident on the photodiode 10d. Put it in a state. At this time, the sensor output signal is 0V. This is because the intermediate transfer belt 6 used in this embodiment has a black surface and has a mirror surface or gloss, and the LED illumination light is almost diffused in the non-image portion on the surface of the intermediate transfer belt 6. Therefore, the sensor output signal is 0V.

  The sensor output signal has a pulse-like waveform corresponding to the amount of cyan toner by passing one side of the cyan mark image while the shutter 10f is open. At this time, as shown in FIG. 5, the peak detection circuit 21 detects the maximum value of the sensor output signal and outputs the peak detection signal. Here, the time from the start of misalignment measurement until the peak detection signal is output is tA1. The time until the peak detection signal detected by the peak detection circuit 21 is output with the passage of the remaining one side of the mark image is defined as tA2. Thereafter, in the same manner, the times tT1, tT2, tB1, and tB2 until the peak detection signal is output as the yellow, cyan, magenta, cyan, and black mark images pass are sequentially measured.

  As described above, since the reflected light of the black mark image is different from the reflected light of the cyan, yellow, and magenta mark images, the LED 10b is turned off and the LED 10a is turned on simultaneously with the passage of the black mark image. At this time, the sensor output signal is output at a voltage value corresponding to the reflected light from the intermediate transfer belt 6. As the black mark image passes, the output voltage of the sensor has a pulse-like waveform that decreases according to the amount of black toner. Here, as shown in FIG. 5, the under peak detection circuit 23 detects the minimum value of the sensor output signal, and measures the times tU1 and tU2 until the under peak detection signal is output. In FIG. 9, cyan, yellow, cyan, and some of them are omitted, and a black mark image, that is, a state until one pattern image M passes through the detection visual field of the photosensor 10 is shown. In the correction mode, a plurality of pattern images M having different densities are continuously formed on the intermediate transfer belt 6.

The calculation of the positional deviation amount is performed by obtaining the absolute positional deviation amount with respect to the target value of the reference color cyan in the main scanning direction and the relative positional deviation amounts of yellow and magenta with respect to the reference color cyan. First, the absolute value position shift amount of the reference color cyan in the main scanning direction is
Absolute value position deviation amount in main scanning direction = {(tA2−tA1) −target value} / 2
The relative positional deviation of yellow relative to the reference color cyan is
Sub-scanning direction positional deviation = [(tT2 + tT1) / 2 − ((tA2 + tA1) / 2 + (tB2 + tB1) / 2) / 2] × PS
= [(tT2 + tT1) / 2- (tA2 + tA1) / 4- (tB2 + tB1) / 4] × PS
Position deviation in main scanning direction = [((tB1 + tA1) / 2−tT1 + sub scanning direction error
+ TT2− (tB2 + tA2) / 2−sub-scanning direction error) / 2] × PS
= [((tB1 + tA1) / 2-tT1 + tT2- (tB2 + tA2) / 2) / 2] × PS
Can be obtained. Here, tA1, tA2, tT1, tT2, tB1, and tB2 are times (μs) from the start of positional deviation measurement until the peak detection signal is output, and PS is a process speed (mm / s). The relative misregistration amounts of magenta and black with respect to the reference color cyan are similarly calculated. This calculation corresponds to step S11 in FIG. If this is detected at two locations in the main scanning direction, it is possible to detect a skew deviation in the sub-scanning direction and a total magnification deviation in the main scanning direction in addition to the offset deviation in the main scanning and sub-scanning. Furthermore, if the detection is performed at three or more locations, it is possible to detect a positional deviation (BOW deviation or linearity deviation) due to the bending of the scanning line, a partial magnification deviation in the main scanning direction, or the like.

  Next, in the density error correction, in step S21 of FIG. 8, the hold information output from the sample & hold circuit in the detection information extraction unit 12 based on the detection signal of the photodiode 10d at the center of the intermediate transfer belt 6 is shown. From the signal, the density error of the mark image is calculated.

  In this embodiment, the density error of the mark image is obtained by calculation from the timing chart when measuring the mark image shown in FIG. As described above, in the correction mode, first, the LED 10b is turned on with the shutter 10f closed. As a result, a voltage value corresponding to the reflected light from the reference plate 10h of the shutter 10f is output as the sensor output signal, and this is measured as the reference plate output voltage (Vref) of the sensor. Then, before the mark image arranged at the head with respect to the moving direction of the intermediate transfer belt 6 passes through the measurement position of the sensor, the shutter 10f is opened so that the reflected light from the mark image can enter the photodiode 10d. To do.

  The sensor output signal has a pulse-like waveform corresponding to the cyan toner amount due to the passage of the cyan mark image after the shutter 10f is opened. At this time, the peak detection circuit 21 detects the maximum value of the sensor output signal and outputs a peak detection signal. The sample and hold circuit 22 uses the rising pulse of the peak detection signal output from the peak detection circuit 21 as a trigger to hold the maximum value of the sensor output signal corresponding to the amount of cyan toner, whereby the cyan density voltage (Vc) is held. ) Is measured. Thereafter, in the same manner, yellow density voltage (Vy) and magenta density voltage (Vm) are measured by passing mark images of yellow, cyan, magenta (not shown) and cyan (not shown).

  Next, the LED 10b is turned off and the LED 10a is turned on simultaneously with the passage of the black mark image. At this time, the sensor output signal is output at a voltage value corresponding to the reflected light from the intermediate transfer belt 6. As the black mark image passes, the output voltage of the sensor has a pulse-like waveform that decreases according to the amount of black toner. Here, as shown in FIG. 5, the under peak detection circuit 23 detects the minimum value of the sensor output signal and outputs the under peak detection signal. The sample & hold circuit 24 holds the minimum value of the sensor output signal corresponding to the amount of black toner by using the rising pulse of the under peak detection signal output from the under peak detection circuit 23 as a trigger, thereby causing the black density voltage to be held. (Vk) is measured. Next, after passing the black mark image, the sensor output signal again indicates a voltage value corresponding to the specularly reflected light from the intermediate transfer body belt 6, and this value is measured as a belt surface voltage (Vbelt). And after this belt surface voltage measurement, while turning off LED10a, turning on LED10b, a sensor output signal will be set to 0V.

The image density is calculated differently between black and color (CYM). The image density of black is a relative value with respect to the non-image surface of the intermediate transfer belt 6. Image density: Dk = Vk / Vbelt
And calculate. On the other hand, the color (CYM) image density is a relative value to the output of the reference plate 10h.
Image density: Dn = ((Vn average value) / Vref)
Where n = toner color (c, y, m)
Define and calculate.

  As described above, the reason why the relative value for the output of the intermediate transfer belt 6 or the reference plate 10h is used as the image density is that the sensor light is fouled, changes with time, changes in temperature, changes in LED light quantity, PD sensitivity, and the like occur. This is because the density of the pattern image M is measured with high accuracy. In this way, the image density of the pattern image M is calculated in step S21 of FIG. 8, and the error between the predetermined density target value and the calculated image density is calculated in step S22.

  After the detection information extraction unit 12 calculates the positional deviation amount and the density error, the calculation results are stored in the storage unit 13 in step S31. Thereafter, in step S32, it is confirmed whether or not the shared sensor has read the pattern image M at all reading positions. If reading at all reading positions is not completed, the process returns to step S1, the photosensor 10 is moved to the next reading position, and the pattern image M is read at the reading position. Similarly, the positional deviation amount and the density error at the next reading position are calculated, and the calculation result is stored in the storage unit 13.

On the other hand, when the pattern images M are read at all the reading positions and the calculation results are stored in the storage unit 13, the condition correction unit 14 corrects the positional deviation and the density error based on the calculation results of the respective reading positions. I do. Specifically, in step S41 of FIG. 8, the image formation position at the time of output image formation, that is, the exposure timing in the main scanning direction and the sub-scanning direction by ROS is set, and the positional deviation is corrected. In step S51, the correction amount of the ROS laser power: ΔLP is
Laser power correction amount: ΔLP = ΔDn / An
Where n = toner color (k, c, y, m)
Is required. Here, ΔDn is the density error of the pattern image M obtained in step S22, and An is a coefficient indicating the correspondence between the laser power and the image density of the pattern image M. This coefficient is obtained in advance by experiments or the like. .

  Next, in step S52, the laser power set value is corrected by subtracting the laser power correction amount ΔLP obtained in step S51 from the laser power when the pattern image M is formed, thereby correcting the density error. The laser power setting value obtained at this time is supplied to the ROS 3 as the laser power at the time of output image formation. Accordingly, the positional deviation is corrected by setting the exposure timing, and the density error is corrected by setting the laser power. As described above, the positional deviation correction and the density error correction are simultaneously performed in the correction mode, and these corrections are periodically repeated, whereby the image forming position and the output image density are kept constant.

  In the flowchart of FIG. 8, the operation of the positional deviation correction and the density error correction is described by taking the case where the photosensor is a common sensor as an example. However, if the photosensor is a position deviation detection dedicated sensor, The sensor does not move (step S1), and the exposure timing is set immediately after calculating the misregistration amount in the detection information extraction unit 12 (step S11) and storing the misregistration information in the storage unit 13 (step S31). Then, the positional deviation is corrected (step S41).

FIG. 10 shows the arrangement positions of the recording sheet and the sensor in the center alignment. The positional relationship between the intermediate transfer belt 6 and the two sensors arranged at the opposed positions, and further the recorded image. The positional relationship between the intermediate transfer belt 6 and the recording sheet at the time of formation is schematically shown. In this figure, since the recording sheet P ₁ (A4 size) and the recording sheet P ₂ (A3 size) are applied with center alignment, each indicates the center of the intermediate transfer belt 6 in the main scanning direction. The position of the belt 6 is aligned symmetrically with respect to a center line C parallel to the sub-scanning direction of the belt 6. The sensor 10 </ b> X is a position shift detection dedicated sensor and is disposed in the vicinity of the main scanning direction end of the intermediate transfer belt 6. On the other hand, the sensor 10Y is a shared sensor, and is disposed at the main scanning direction end of the recording sheet P ₁ on the opposite side of the sensor 10X with respect to the center line C. The sensor 10Y may be provided with a moving means (not shown) and moved in the main scanning direction area of the intermediate transfer belt 6 at a predetermined timing.

As shown in this figure, position of the sensor 10Y, the recording sheet P ₁ and the recording sheet is set to P ₂ in the image area, but commonly used frequent main scanning, such as A4 size It is preferable to set near the direction end. As a result, it is possible to detect a density error in a general image region and to ensure sufficient accuracy for detecting a positional deviation.

FIG. 11 shows the arrangement positions of the recording sheet and the sensor in the side alignment. Similar to FIG. 10, the positional relationship between the intermediate transfer belt 6 and the two sensors arranged at the opposed positions. Furthermore, the positional relationship between the intermediate transfer belt 6 and the recording sheet during recording image formation is schematically shown. In this figure, since the recording sheet P ₁ (A4 size) and the recording sheet P ₂ (A3 size) are applied with side alignment, the recording sheet P ₁ (A4 size) is on one side (left side in the figure) of the intermediate transfer belt 6 serving as the reference side. Their positions are matched. The sensor 10 </ b> X is a position shift detection dedicated sensor and is disposed at the end of the intermediate transfer belt 6 in the main scanning direction. In contrast, sensor 10Y is a shared sensor and a moving means (not shown), with respect to the center line C, the main scanning direction end of the recording sheet P ₁ and the recording sheet P ₂ on the opposite side to the sensor 10X It is arranged in the part. The sensor 10Y moves in the main scanning direction within the main scanning direction area of the intermediate transfer belt 6 at a predetermined timing, but remains at the arrangement position during normal recording image formation.

As shown in the figure, the arrangement position of the sensor 10Y is set to the reference side in the side alignment. Therefore, not only the recording sheet P ₁ and the recording sheet P _2, but also the positional deviation and density error can always be detected at the same main scanning direction end in the image area for recording sheets of all sizes.

  As shown in FIGS. 10 and 11, the sensor 10 </ b> X which is a position shift dedicated sensor in both the center alignment and the side alignment is provided at one end in the main scanning direction of the intermediate transfer body belt 6. Be placed. The sensor 10X and the sensor 10Y are different in distance from the end in the main scanning direction of the intermediate transfer belt 6 close to each sensor, and are disposed in an asymmetric positional relationship with respect to the center line C.

FIG. 12 shows the positional relationship between the two sensors arranged at the position facing the intermediate transfer belt and the reading position of the common sensor provided with the moving means. In this figure, the sensor 10X is a sensor dedicated to misalignment detection, and the sensor 10Y is a sensor for detecting misalignment and density error. The sensor 10X is disposed at an end of the intermediate transfer belt 6 in the main scanning direction, whereas the sensor 10Y is moved within a region in the main scanning direction of the intermediate transfer belt 6 by a moving unit (not shown). Are moved in the main scanning direction, the pattern image M is detected at a plurality of reading positions, and the detection result at each reading position is stored in the storage unit 13. The sensor when reading the center of the main scanning direction of the center line C is the intermediate transfer belt 6, the sensor 10Y is stopped at the central portion of the intermediate transfer belt 6 (shown by the dotted line rectangle 10Y _3), the mark image The detection field center of 10Y is shown. Further, the dotted line W ₀ indicates the detection visual field center at the position where the sensor 10X is disposed, the dotted line W ₁ indicates the detection visual field center at the position where the sensor 10Y is disposed, and the dotted line W ₂ indicates that the sensor 10Y is opposite to the sensor 10X. stop of the main scanning direction end portion of the intermediate transfer belt 6 (shown by the dotted line rectangle 10Y _2), illustrates the detection center of the field of view of the sensor 10Y when loading mark image. Further, a dotted line T is a main scanning line indicating the main scanning direction of the intermediate transfer belt 6.

In this configuration, if only the positional deviation at the arrangement position is detected by the sensor 10Y provided with the moving means, there is a problem when highly accurate skew deviation detection is required. When detecting the skew deviation amount of the curved line Q ₁ and the curved line Q ₂ where the scanning line is bent with respect to the dotted line T in the figure, the position of the dotted line circle Z ₀ where the sensor 10X is arranged and the dotted line circle Z ₁ When the mark image is read at the position, that is, the arrangement position of the sensor 10Y, the dotted line T intersects the curve Q ₁ and the curve Q ₂ at points U ₀ and U, and each of the dotted lines T is in the sub-scanning direction. Since the amount of deviation is zero, it is detected that no skew deviation has occurred. Therefore, moving the sensor 10Y by the moving means, it may read the mark images in dotted rectangle 10Y _2. Here, since the positions of the dotted circle Z ₂ are shifted in the sub-scanning direction with respect to the dotted line T, the shift amounts of the curve Q ₁ and the curved line Q ₂ with respect to the dotted line T are detected at each position, and the storage unit 13 By storing them in the skew, it is possible to accurately detect the skew deviation. Furthermore, bending of the scanning line (linearity), since hardly changed, to detect the bending of the scanning line at a time position and the position of the dotted rectangle 10Y ₂ sensor 10Y, the sub-scanning direction with respect to the dotted line T at each position It is preferable to store the difference in the amount of deviation in the storage unit 13. As a result, the skew deviation can be corrected with high accuracy only by taking the difference in deviation amount into account.

  In addition to skew deviation, BOW deviation, linearity deviation, main scanning magnification balance deviation, main scanning partial magnification deviation, density distribution in an image area, and the like may be stored in advance.

  Incidentally, regarding the position where the sensor 10Y is stopped within the width direction of the intermediate transfer belt 6 in the main scanning direction, even if center alignment or side alignment is applied, positional deviation and density error may occur. It is possible to set appropriately according to the detection accuracy required for detection.

1 is a schematic configuration diagram of a color image forming apparatus using an electrophotographic system to which the present invention is applied. FIG. 5 is a diagram illustrating a flow of correction of positional deviation and density error in a color image forming apparatus. It is a figure which shows the arrangement | sequence of the mark image applied to this invention. 1 is a diagram illustrating a schematic configuration diagram of a photosensor in a color image forming apparatus to which the present invention is applied. It is a block diagram which shows the flow by which the output signal from a photodiode is processed by the detection information extraction part. It is the plain view which looked at the shutter attached to the photo sensor from the LED side. FIG. 4 is a diagram showing a positional relationship between a mark image formed on an intermediate transfer belt and a detection visual field of the photosensor on the intermediate transfer belt along the time course. It is a flowchart which shows the operation | movement of position shift correction and density | concentration error correction in the correction mode of this invention. 6 is a timing chart showing waveforms of a shutter operation signal, a photosensor lighting signal, a sensor output signal, a peak detection signal, a peak hold signal, an under-peak detection signal, and an under-peak hold signal when measuring a mark image. It is a figure which shows the arrangement | positioning position of the recording sheet and sensor in center alignment. It is a figure which shows the arrangement | positioning position of the recording sheet and sensor in side position alignment. FIG. 4 is a diagram illustrating a positional relationship between two sensors disposed at positions facing an intermediate transfer belt and a reading position of a common sensor including a moving unit. It is a figure which shows the sensor arrangement | positioning which weighted the accuracy improvement of the density | concentration error detection in the case of applying center position alignment. It is a figure which shows a mode that the straight line parallel to the main scanning direction of the said image carrier formed on the image carrier and a curve are detected by two sensors.

Explanation of symbols

6 ... intermediate transfer belt, 10X, 10Y ... sensor, P _1, P ₂ ··· recording sheet

Claims (4)

A plurality of image forming means for forming an image of each color on the photoconductor in accordance with an image data signal;
A correction mode control unit that sends a signal to the image forming means for each color, forms a mark image on the photoconductor for correcting positional deviation and density error, and sequentially transfers the mark image to the image carrier;
First detection means and second detection means for optically reading mark images of respective colors;
A detection information extraction unit that extracts both positional deviation information and density error information of each color image from the detection signals of these detection means;
In a color image forming apparatus including a condition correction unit that corrects an image forming condition of each image forming unit according to the positional deviation information and density error information.
When forming a recording image on a recording sheet, the recording sheet is positioned symmetrically with respect to a center line passing through the center point of the image carrier in the main scanning direction and parallel to the sub-scanning direction. Set to be transported,
The first detection means is a detection means dedicated to misregistration detection, and the second detection means is a detection means for both misalignment detection and density error detection,
The first detection means is disposed in the vicinity of any end portion in the main scanning direction of the image carrier, while the second detection means is arranged with respect to a center line parallel to the sub-scanning direction of the image carrier. A color image forming apparatus, wherein the color image forming apparatus is disposed in a position near an end portion in a main scanning direction of a recording sheet having a size that is frequently used in an image area that is asymmetric with the first detection unit. A plurality of image forming means for forming an image of each color on the photoconductor in accordance with an image data signal;
A correction mode control unit that sends a signal to the image forming means for each color, forms a mark image on the photoconductor for correcting positional deviation and density error, and sequentially transfers the mark image to the image carrier;
First detection means and second detection means for optically reading mark images of respective colors;
A detection information extraction unit that extracts both positional deviation information and density error information of each color image from the detection signals of these detection means;
A condition correction unit that corrects the image forming condition of each image forming unit in accordance with the positional deviation information and the density error information;
In a color image forming apparatus comprising:
In forming a recorded image on a recording sheet, on one end in the main scanning direction width of the conveying path which is perpendicular to the conveying direction of the recording sheet, conveyed Intention one side of all of the recording sheet, the reference side one side and to have been set,
The first detection means is a detection means dedicated to misregistration detection, and the second detection means is a detection means for both misalignment detection and density error detection,
The first detection means is disposed in the vicinity of any end portion in the main scanning direction of the image carrier, while the second detection means is arranged with respect to a center line parallel to the sub-scanning direction of the image carrier. A color image forming apparatus, wherein the color image forming apparatus is disposed in an image region that is asymmetric with the first detection means and in the vicinity of the end portion on the reference side of the recording sheet . The second detection means includes a moving means for moving the second detection means in a main scanning direction width region of the image carrier,
The moving means can stop the second detecting means at a plurality of reading positions including an arrangement position of the second detecting means, and the movement is performed when the image forming apparatus is adjusted or when consumable parts are replaced. Item 3. The color image forming apparatus according to Item 1 or 2. The condition correction unit includes each detection information at the plurality of reading positions of the second detection unit, or detection information at an arrangement position of the second detection unit, and detection information at the plurality of reading positions. A storage unit for storing the difference,
4. The color image according to claim 3 , wherein a positional deviation and / or a density error is corrected by adding information stored in the storage unit to detection results of the first detection unit and the second detection unit. Forming equipment.

Images