JP2006003726A - Color image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a color image forming apparatus with which displacement and density error of recorded images formed on the surface and the backside of a recording sheet and, in addition, displacement of the recorded image on each side of the recording sheet can be corrected by using a single sensor. <P>SOLUTION: The color image forming apparatus transfers recorded images onto both sides of the recording sheet at the same time by conveying the recording sheet between the intermediate transfer members of the first and second image forming sections, each of which includes image forming means for respective colors for forming toner images onto the surfaces of respective photoreceptors according to image data signals and the intermediate transfer member to which the toner images of respective colors are transferred one on another from the photoreceptors. The first image forming section includes a detecting means. In correction mode, a reference mark image formed in the second image forming section is transferred to the intermediate transfer member of the first image forming section, both of the reference mark images are detected in the first image forming section, and displacement and/or density error of both of the recorded images are corrected. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a recording sheet in a color image forming apparatus in which two intermediate transfer members are brought into contact with each other, arranged at opposing positions, a recording sheet is conveyed between these intermediate transfer members, and a recorded image is simultaneously transferred to both sides of the recording sheet. The present invention relates to a technique for correcting a positional deviation and a density error of a recorded image formed on the front surface and the back surface.

JP-A-63-63057 JP-A-2-259670

  Conventionally, as a method for forming a recorded image on both sides of a recording sheet in an image forming apparatus to which an electrophotographic method is applied, first, a recorded image on a surface formed on a photoreceptor (hereinafter referred to as a `` surface image '') is used. The recording sheet is transferred to the surface of the recording sheet conveyed to the image forming unit, and further, the recording sheet on which the surface image is transferred is passed through a fixing device, whereby the surface image is fixed on the recording sheet. Thereafter, the recording paper is reversed in the image forming apparatus, re-fed to the transfer unit, and then the back side recorded image (hereinafter referred to as “back side image”) formed on the photosensitive member is conveyed again to the image forming unit. Transfer to the back side of the recording sheet and, like the front image, pass the recording sheet with the back side image transferred to the fixing device, thereby fixing the back side image to the recording sheet and forming the recording image on both sides of the recording sheet. The As described above, a method of forming a front image and a back image on a recording sheet by one image forming unit is common.

  However, this method requires two times of transfer and fixing in order to form a recorded image on both sides of the recording sheet, and the productivity per recording sheet in the image forming apparatus forms a recorded image on one side of the recording sheet. It will drop to half or less. Further, since pressure and heat are applied to the recording sheet at the time of fixing, a phenomenon (hereinafter referred to as “curl”) of trying to curl the recording sheet occurs after the first fixing. As a result, not only a problem occurs in the second transfer, but also the recording sheet may be wrinkled during fixing, and the recording sheet is likely to be jammed (hereinafter referred to as “jam”) in the recording sheet conveyance path. . Furthermore, there is a problem that noise is generated when the recording sheet is reversed in the image forming apparatus. Furthermore, when the front surface image is fixed, the paper expands and contracts due to pressure and heat, and when the back surface image is transferred and fixed thereafter, the size, shape, and position of the image are shifted on the front and back sides. To do.

  Therefore, in order to solve these problems, two image forming units are arranged at opposite positions, and the recording sheet is conveyed between the respective photosensitive members that are in contact with each other, thereby simultaneously recording the recording images on both sides of the recording sheet. An image forming apparatus to be formed has been proposed (Japanese Patent Laid-Open Nos. 63-63057 and 2-259670). With these image forming apparatuses, the recording sheet can be formed on both sides of the recording sheet by passing the recording sheet once between the two photoconductors, and the recording sheet can be curled and wrinkled. It is possible to prevent accompanying jamming and noise accompanying reversal of the recording sheet.

  For example, when this prior art image forming apparatus is applied to a color image forming apparatus, each image forming unit forms a toner image on a photoreceptor of each color of yellow, magenta, cyan, and black, and each color toner image on an intermediate transfer member. Can be formed by a tandem method in which a recorded image is transferred to a recording sheet after multiple transfer is performed, and color images can be formed on both sides of the recording sheet. However, in this configuration, a positional deviation occurs in the recorded image depending on the alignment of each photoconductor and the intermediate transfer body, and an error occurs in the density of the recorded image due to a change in temperature and humidity. And correction of density error must be performed.

  The correction of the positional deviation and the density error is performed by forming a reference mark image of each color on the intermediate transfer member and reading the reference mark image by a detecting means such as a sensor. Therefore, it is necessary to equip each image forming unit with a sensor. is there. In addition, it is a heavy load on the image forming apparatus to simultaneously process the signals detected by the sensors of the image forming units in parallel. For this reason, it is not preferable in terms of space and cost to equip sensors with two systems for the front image and the back image. In addition, when the positional deviation between the front image and the rear image is corrected independently by the sensor of each image forming unit, the position of the front image and the rear image with respect to the recording sheet may be shifted due to a difference in the attachment state of each sensor. is there.

  The present invention has been made in view of such problems, and the object of the present invention is to provide a positional deviation and / or density error of a recorded image formed on the front and back surfaces of a recording sheet by a set of sensors. Another object of the present invention is to provide a color image forming apparatus capable of correcting the positional deviation of the recorded image on each side with respect to the recording sheet.

  In order to achieve the above object, a color image forming apparatus according to the present invention includes an image forming unit for forming a toner image on the surface of a photoconductor in accordance with an image data signal, and a toner image of each color from the photoconductor. A first image forming unit and a second image forming unit each formed of an intermediate transfer member to be disposed are opposed to each other, and a recording sheet is conveyed between both of the intermediate transfer members in contact with each other, and the recording In a color image forming apparatus that simultaneously transfers a recorded image to both sides of a sheet, the first image forming unit includes a detecting unit that optically reads the reference mark image. In the correction mode, the first image is formed by the correction mode control unit. A signal is sent to the image forming means of the image forming unit and the second image forming unit, and a reference mark image of each color is formed on the surface of the intermediate transfer member of each image forming unit and formed on the intermediate transfer member of the second image forming unit The The reference mark image is transferred to the intermediate transfer member of the first image forming unit, and the detection unit detects the reference mark image formed in both the first image forming unit and the second image forming unit. Further, correction of misalignment and / or density error in each recorded image formed in the first image forming unit and the second image forming unit is performed.

  In such an image forming apparatus of the present invention, the image forming means is not limited as long as it can form a toner image on the surface of the photosensitive member of each color, and the image forming apparatus applied to an electrophotographic image forming apparatus. Preferably means are applied. In addition to the four colors of cyan, yellow, magenta, and black, a special color such as a corporate color may be added.

  The intermediate transfer member is not particularly limited as long as it can multiplex-transfer toner images formed on the surface of the photosensitive member of each color, and an intermediate transfer member belt used in a tandem color image forming apparatus can be applied. . The toner images that are multiple-transferred onto the surface of the intermediate transfer body of both the first image forming unit and the second image forming unit disposed at the opposing positions are so that the charged polarity is in a reverse polarity relationship. One charging polarity must be positive (+) and the other charging polarity must be negative (-). In addition, the intermediate transfer members of the image forming units that are in contact with each other must have a transfer electric field formed between their contact surfaces. With this configuration, when the recording sheet is conveyed between the contact surfaces of both of the intermediate transfer members, the recorded images formed on the surfaces of both of the intermediate transfer members are attracted to each other and simultaneously onto both surfaces of the recording sheet. The recorded image can be transferred.

  The detection means provided in the first image forming unit combines a light emitting element and a light receiving element, and displays the reference mark image of each color formed on the intermediate transfer body of the first image forming unit as a light emitting element. If it is arranged at a position where the reflected light from the reference mark image or the transmitted light that has passed through the reference mark image can be incident upon the light receiving element when it is irradiated by.

  When the reference mark image needs to be detected in the correction mode, the correction mode control unit sends an image data signal for forming the reference mark image on the photoconductor to the image forming unit for each color. It suffices if it is set as follows. Further, it is preferable that the formation position of the reference pattern image corresponds to the reading position of the detection means disposed at the position facing the intermediate transfer member. Further, in the correction mode, the correction mode control unit is configured to transfer the reference mark image formed on the surface of the intermediate transfer body of the second image forming unit to the first image forming unit. An image data signal for forming the reference mark image is sent to the image forming means of each image forming unit at different timings so that the reference mark images of both the image forming unit and the second image forming unit do not overlap. It is good to set.

  When a photograph or the like with a clear outline of a recorded image is formed on both sides of the recording sheet, or one of the two-page designs is formed on the back side of the recording sheet and the other is formed on the front side of the next recording sheet. When the recording sheets are overlapped, the front image and the back image are formed on the front and back sides of the recording sheet so as to be shifted from each other or compared to the case where the document is formed on both sides of the recording sheet. If the back image and the other front image are overlaid in a shifted state, the shift becomes conspicuous. Therefore, in the correction mode, not only correction of the positional deviation and / or density error of the front image and the back image, but also correction of the positional deviation and / or shape between the front image and the back image is performed. Good. In this case, the position data obtained from the reference mark image formed on the intermediate transfer member of either the first image forming unit or the second image forming unit is used as a reference, and the position data Configuration for executing positional correction and / or shape correction between front and back images by detecting a relative shift amount of position data obtained from the reference mark image formed on the other intermediate transfer member It is preferable that

  Further, when correcting the positional deviation between the front and back images, the positional deviation and / or shape of the recorded image of either the first image forming unit or the second image forming unit may be changed. is there. In this case, the positional deviation and / or shape change of one recorded image and the positional deviation and / or shape change of the other recorded image are interlocked to cancel the positional deviation between the front and back images. It is better to set to automatically correct. As a result, when the positional deviation and / or shape of either the front image or the back image is changed, the other recorded image is changed in conjunction with the change. Correction of both the front image and the back image can be performed only by executing a positional shift and / or a shape change of any one of the recorded images.

  According to the color image forming apparatus of the present invention configured as described above, the positional deviation and / or density error of the recording image formed on the front and back surfaces of the recording sheet by one set of sensors, It is possible to correct the displacement of the recorded image with respect to the recording sheet.

  Since the reference mark image of the second image forming unit is transferred to the first image forming unit, it is unavoidable that the density is slightly lower than the density of the original reference mark image as long as the transfer efficiency is not 100%. Absent. For this reason, when correcting the density error of the second image forming unit, it is necessary to calculate the correction amount in consideration of the density reduction.

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

  FIG. 1 shows an example of a color image forming apparatus to which the present invention can be applied. This color image forming apparatus includes a first image forming section A, a second image forming section B, a fixing device 43, a sheet feeding path 45, and an inverter path 46, and recording on both sides of the recording sheet P simultaneously. An image is to be formed.

  The first image forming unit A includes four image forming engines 10aY, 10aM, 10aC, and 10aK for forming yellow, magenta, cyan, and black color toner images, and the toner images are primarily transferred from the respective photoreceptors. An intermediate transfer belt 20a is provided, and a toner image that has been multiple transferred to the intermediate transfer belt 20a is secondarily transferred to a recording sheet P to form a full color image. The intermediate transfer body belt 20a is formed in an endless shape and is wound around four belt transporting rolls 21a to 24a including a driving roll 21a. The image forming engine of each color is rotated while rotating in the direction of the arrow. It is configured to receive primary transfer of toner images formed with 10aY, 10aM, 10aC, and 10aK.

  The intermediate transfer belt 20a is stretched around four belt conveying rolls 21a to 24a, and a substantially flat image receiving span is formed between the belt conveying rolls 21a and 22a, on the opposite side of the image receiving span. A third belt conveyance roll 23a for forming an image transfer portion is disposed between the fourth belt conveyance roll 24a and the second image forming portion B with the intermediate transfer belt 20a interposed therebetween. It is stretched in a square shape.

  The above-described image forming engines 10aY, 10aM, 10aC, and 10aK are arranged in parallel on the image receiving span of the intermediate transfer belt 20a, and a toner image formed according to image information of each color is intermediate transferred. Primary transfer is performed on the body belt 20a. These four image forming engines are arranged in the order of yellow 10aY, magenta 10aM, cyan 10aC and black 10aK along the rotational direction of the intermediate transfer belt 20a, and the most frequently used black image forming engine is arranged. The image engine 10aK is disposed closest to the image transfer portion.

  Here, each image forming engine is provided with a raster scanning unit (not shown) that performs exposure according to image information, and laser light modulated according to image information of each color is applied to the image forming engine of each color. The body (not shown) is exposed. Then, a charger (not shown) for charging the photoreceptors to a uniform background portion potential, and developing the electrostatic latent images formed on the photoreceptors by the laser light exposure to form toner images. A developing device (not shown) to be formed, a drum cleaner (not shown) for removing residual toner and paper dust from the surface of each photoconductor after the toner image is transferred to the intermediate transfer belt 20a, and this drum cleaner And a pre-cleaning static eliminator (not shown) that neutralizes residual toner prior to cleaning by the above-described cleaning, and is configured to form a toner image corresponding to image information of each color on each photoconductor. Note that the exposure apparatus is not limited to the raster scanning unit, and an exposure apparatus using a light emitting element array such as an LED may be used.

  Primary transfer rolls 25aY, 25aM, 25aC, and 25aK are disposed at positions facing the image forming engines 10aY, 10aM, 10aC, and 10aK of the respective colors so as to sandwich the intermediate transfer belt 20a. These primary transfer rolls 25aY, By applying a predetermined transfer bias voltage to 25aM, 25aC, and 25aK, an electric field is formed between the image forming engines 10aY, 10aM, 10aC, and 10aK of the respective colors and the primary transfer rolls 25aY, 25aM, 25aC, and 25aK. The toner images charged on the image forming engines 10aY, 10aM, 10aC, and 10aK for the respective colors are transferred to the intermediate transfer belt 20a by Coulomb force.

  Therefore, in forming a full color image by the first image forming unit A, first, toner images corresponding to the image information of each color are formed on the image forming engines 10aY, 10aM, 10aC, and 10aK of the respective colors. The toner images formed on the image forming engines 10aY, 10aM, 10aC, and 10aK of the respective colors are sequentially transferred to the rotating intermediate transfer belt 20a, and the toner images of the respective colors overlap on the intermediate transfer belt 20a. A multiple toner image is formed.

  On the other hand, the second image forming unit B includes the four photoconductors 10bY, 10bM, 10bC, and 10bK on which toner images of yellow, magenta, cyan, and black are formed, as in the first image forming unit A. An intermediate transfer body belt 20b to which a toner image is primarily transferred from each photoconductor is provided, and the toner image multiple-transferred to the intermediate transfer body belt 20b is secondarily transferred to a recording sheet P to form a full color image. Has been. The intermediate transfer body belt 20b is formed in an endless shape and is wound around four belt transport rolls 21b to 24b including a drive roll 21b. Each color photoconductor 10bY, It is configured to receive a primary transfer of a toner image formed with 10 bM, 10 bC, and 10 bK.

  Similarly to the intermediate transfer belt 20a, the intermediate transfer belt 20b is also stretched around four belt transport rollers 21b to 24b, and a substantially flat image receiving span is formed between the belt transport rollers 21b and 22b. On the other hand, on the opposite side of the image receiving span, a third belt conveying roll that forms an image transfer portion between the fourth belt conveying roll 24b and the first image forming portion A with the intermediate transfer belt 20b interposed therebetween. 23b is disposed and stretched in a square shape as a whole.

  Further, the image forming engines 10bY, 10bM, 10bC, 10bK of the respective colors described above are arranged in parallel on the image receiving span of the intermediate transfer belt 20b, and toner images formed according to the image information of the respective colors are arranged. Primary transfer is performed on the intermediate transfer belt 20b. These four image forming engines are arranged in the order of yellow 10bY, magenta 10bM, cyan 10bC and black 10bK along the rotation direction of the intermediate transfer belt 20b, and the most frequently used black image forming engine is formed. The image engine 10bK is disposed closest to the image transfer portion.

  Here again, as with the first image forming unit A, each image forming engine is provided with a raster scanning unit (not shown) that performs exposure according to image information, and is modulated according to image information of each color. Laser light exposes a photoreceptor (not shown) of each color image forming engine. Then, a charger (not shown) for charging the photoreceptors to a uniform background portion potential, and developing the electrostatic latent images formed on the photoreceptors by the laser light exposure to form toner images. A developing device (not shown) to be formed, a drum cleaner (not shown) for removing residual toner and paper dust from the surface of each photoconductor after the toner image is transferred to the intermediate transfer belt 20b, and this drum cleaner And a pre-cleaning static eliminator (not shown) that neutralizes residual toner prior to cleaning by the above-described cleaning, and is configured to form a toner image corresponding to image information of each color on each photoconductor.

  Further, similarly to the first image forming unit A, primary transfer rolls 25bY, 25bM, 25bC, and 25bK are arranged at positions facing the image forming engines 10bY, 10bM, 10bC, and 10bK for the respective colors so as to sandwich the intermediate transfer belt 20b. By applying a predetermined transfer bias voltage to the primary transfer rolls 25bY, 25bM, 25bC, and 25bK, the image forming engines 10bY, 10bM, 10bC, and 10bK for the respective colors and the primary transfer rolls 25bY, 25bM, An electric field is formed between 25bC and 25bK, and the toner images charged on the image forming engines 10bY, 10bM, 10bC, and 10bK of the respective colors are transferred to the intermediate transfer belt 20b by Coulomb force. Yes.

  Accordingly, in forming a full color image by the second image forming unit B, first, toner images corresponding to the image information of each color are formed on the image forming engines 10bY, 10bM, 10bC, and 10bK for each color. The toner images formed on the image forming engines 10bY, 10bM, 10bC, and 10bK for the respective colors are sequentially transferred to the rotating intermediate transfer belt 20b, and the toner images for the respective colors overlap on the intermediate transfer belt 20b. A multiple toner image is formed.

  In this embodiment, the charging polarity of the toner image of the first image forming unit A is minus (−), and the charging electrode of the toner image of the second image forming unit B is plus (+). The negative (−) and plus (+) charged multiple toner images formed on the intermediate transfer belts 20a and 20b at the timing approach the image transfer section as the intermediate transfer belts 20a and 20b rotate. It has become a thing.

  Next, after the recording sheet P is pulled out from the sheet cassette 40 one by one by the sheet feeding roll 41, the recording sheet P passes through a predetermined sheet feeding path 45 indicated by a solid line in the drawing and the intermediate transfer belt 20a and the intermediate transfer body. The image is fed to an image transfer portion in contact with the belt 20b. A registration roll 42 is provided on the front side of the image transfer portion, and the recording sheet P is controlled by the registration roll 42 to enter the image transfer portion, so that the recording sheet P is placed on the intermediate transfer belts 20a and 20b. The toner image is primarily aligned with each toner image.

  The belt conveyance rolls 23a and 23b that form the image transfer portion by facing each other with the intermediate transfer belts 20a and 20b interposed therebetween are formed by covering the surface of the insulating roll with a semiconductive sheet. A conductive contact roll 30 to which a predetermined transfer bias voltage is applied is in contact with the surface of 23a. Accordingly, the power supply 31 applies a transfer bias voltage having the same polarity as that of the toner image of the first image forming unit A to the contact roll 30, that is, a minus (−) transfer bias voltage, and charges the surface of the belt transport roll 23 a. When applied, a transfer electric field is formed between the belt conveyance roll 23b located on the opposite side of the intermediate transfer belt 20a, 20b and the belt conveyance roll 23a, and is held on the intermediate transfer belt 20a, 20b. The negative (−) and positive (+) charged toner images are electrostatically transferred so as to be attracted to both surfaces of the recording sheet P.

  Thereafter, the recording sheet P on which each toner image has been electrostatically transferred is conveyed to the fixing device 43 by the rotation of the intermediate transfer belts 20a and 20b. The recording sheet P is fixed on both sides of the recording sheet P by the fixing unit 43 and then discharged to the paper discharge tray 44. Thus, the formation of a full color image on both sides of the recording sheet P is completed. In this color image forming apparatus, an inverter passage 46 for inverting the front and back of the recording sheet P is formed between the fixing device 43 and the paper discharge tray 44. This is because when the toner image is formed only on one side of the recording sheet P, the toner image is mainly formed in the first image forming unit A, so that the image surface of the recording sheet P is directed downward. Face down discharge becomes possible.

  In such a color image forming apparatus, there is a displacement in the mounting position of a raster scanning unit (not shown) included in each image forming engine, or along the circumferential direction of the intermediate transfer belt of each image forming engine. If there is a displacement in the attached position, the toner images primarily transferred from the image forming engines 10aY, 10aM, 10aC, 10aK, and 10bY, 10bM, 10bC, 10bK to the intermediate transfer belts 20a, 20b for the respective colors The transfer belts 20a and 20b cannot be accurately superimposed.

  For this reason, this color image forming apparatus is configured to periodically form a reference mark image on the surface of the intermediate transfer belt 20a, 20b, and the reference mark image is disposed in the first image forming unit A. It is detected using the detection apparatus 1 which is. At this time, a correction mode control unit (not shown) is configured to send signals to the color image forming engines of the first image forming unit A and the second image forming unit B at different timings in order to form a reference mark image. When the reference mark image formed on the surface of the intermediate transfer belt 20b of the second image forming portion B is transferred to the intermediate transfer belt 20a of the first image forming portion A, the intermediate transfer belt 20a By continuously forming the reference mark images of both the first image forming unit A and the second image forming unit B, the detection device 1 can detect both of the reference mark images continuously. Further, a guide roll 26a that is in contact with the intermediate transfer belt 20a and disposed at a position facing the detection device 1 keeps the distance between the detection device 1 and the intermediate transfer belt 20a substantially constant, and also on the belt surface. Detection accuracy can be ensured by suppressing the occurrence of wrinkles, swells, and the like.

  The figure schematically shows how the reference mark image formed on the surface of the intermediate transfer belt 20b of the second image forming section B is transferred to the intermediate transfer belt 20a of the first image forming section A. 2. In this figure, the belt conveying rolls 23a and 23b are rotated in the directions of the arrows in the drawing, respectively, and the intermediate transfer belts 20a and 20b are rotated while being in contact with each other (not in the drawing for convenience). A sheet feeding path 45 for conveying the recording sheet P is formed between the intermediate transfer belts 20a and 20b. A conductive contact roll 30 to which a predetermined transfer bias voltage is applied is in contact with the belt transport roll 23a, and has the same polarity as the reference mark image formed on the surface of the intermediate transfer belt 20a by the switching power supply 31a. That is, a minus (−) transfer bias voltage is applied. The switching power supply 31a and the belt transport roll 23b are connected to grounds 32 and 33, respectively, and are grounded.

  When the reference mark image formed on the surface of the intermediate transfer belt 20b is transferred to the intermediate transfer belt 20a in the correction mode, the negative (−) charge reference formed on the surface of the intermediate transfer belt 20a is transferred. After the mark image has passed through the contact portions of the intermediate point transfer belts 20a and 20b, the switching power supply 31a gives a negative (−) potential to the contact roll 30 that is lower than the belt conveying roll 23b set to zero potential. It is done. Then, a potential difference is generated between the belt conveyance roll 23a and the belt conveyance roll 23b, and the reference mark image charged to the plus (+) on the surface of the intermediate transfer belt 20b becomes a contact portion between the intermediate transfer belts 20a and 20b. Is approached and transferred to the intermediate transfer belt 20a. Accordingly, the reference mark images of both the intermediate transfer belts 20a and 20b can be formed on the surface of the intermediate transfer belt 20a, and both of the reference mark images can be detected by one set of the detection device 1. .

  When the reference mark image formed on the surface of the intermediate transfer member belt 20b of the second image forming unit B is transferred to the surface of the intermediate transfer member belt 20a of the first image forming unit A, the transfer efficiency is 100. %is not. Therefore, the density of the reference mark image transferred to the surface of the intermediate transfer belt 20a is slightly lower than the density of the reference mark image formed on the surface of the intermediate transfer belt 20b. It cannot be avoided. Therefore, when the reference mark image of the second image forming unit B transferred to the intermediate transfer belt 20a is detected and correction of the density error in the second image forming unit B is performed, the correction is performed in consideration of the reduced density. You have to calculate the quantity.

Intermediate transfer the first image forming portion is formed on the surface of the belt 20a A and the second image forming unit B each reference mark image M _A, that illustrates an M _B is Fig. In the color image forming apparatus in the present embodiment, a two-point detecting device (not shown) is disposed on the main scanning line. Then, the reference mark image M _A, M _B is formed on the detection field dashed line indicates the centerline structured R S of the detection device. The reference mark image M _A, M _B is advanced in the direction of the arrow in the figure, the reference mark image M _A, the order of the reference mark image M _B has become one that passes through the detection field R.

The detection results of the read reference mark image M _A and the reference mark image M _B by detector, firstly, positional deviation of the recording image formed in each of the first image forming unit A and the second image forming unit B and / Alternatively, the density error is corrected. Then, each of the difference in the main scanning direction magnification W _A and W _B of the first image forming unit A and the second image forming section B, a difference in the sub scanning direction magnification L _A and L _B, a skew difference Q correction As a result, the formation positions of the recording images formed in the first image forming unit A and the second image forming unit B with respect to the recording sheet P can be matched, and the positional deviation of the recording images on the front and back of the recording sheet P and / or It becomes possible to correct the shape of the recorded image.

Although the detection time is longer than that in which the detection device is provided in each of the first image forming unit A and the second image forming unit B, the reference mark image M is continuously provided on the surface of the intermediate transfer belt 20a. _a, by forming M _B, it is possible in a short time to detect the reference mark image M _a, M _B, compares both. Further, when the detection device is disposed in the second image forming unit B in the same manner as the first image forming unit A, it is necessary to perform correction in consideration of an attachment error between the detection device and the detection device 1. by detecting the mark image M _a and the reference mark image M _B in the first image forming unit a, but need not. Therefore, it is possible to detect and position displacement correction of the recorded image in the front and back sides of the recording sheet P of the reference mark image M _A and the reference mark image M _B with a simple configuration.

  Here, there are two methods for correcting the positional deviation and / or the shape of the recorded images on the front and back of the recording sheet P. First, one of the first image forming unit A and the second image forming unit B is used. This is a method for detecting the relative shift amount of the position data obtained from the other reference mark image with respect to the position data, based on the position data obtained from the reference mark image. The other method corrects the positional deviation and / or shape of one of the recorded images of the first image forming unit A or the second image forming unit B, and the other recorded image is linked to the correction, This is a method of automatically correcting so as to cancel the positional deviation of the recorded images between the first image forming unit A and the second image forming unit B, and it is possible to select which one to apply as appropriate.

  In this embodiment, two detection devices are arranged on the main scanning line. For example, a detection device is also arranged at the center, and a reference mark image is formed at three locations on the intermediate transfer belt. As a result, the partial magnification difference in the main scanning direction of each of the first image forming unit A and the second image forming unit B and the linearity in the sub-scanning direction in which the reference mark image is displaced in a bow shape with respect to the main scanning line ( A (BOW deviation) difference can also be corrected.

1 is a diagram illustrating an example of a color image forming apparatus to which the present invention is applicable. FIG. 6 is a diagram schematically illustrating a state in which a reference mark image formed on the surface of an intermediate transfer body belt of a second image forming unit is transferred to an intermediate transfer body belt of a first image forming unit. FIG. 6 is a diagram illustrating reference mark images of the first image forming unit and the second image forming unit formed on the surface of the intermediate transfer body belt of the first image forming unit.

Explanation of symbols

A ... first image forming unit, B ... second image forming unit, 1 ... detection device, 10aY, 10aM, 10aC, 10aK, 10bY, 10bM, 10bC, 10bK ... image forming engine, 20a , 20b... Intermediate transfer belt, 21a, 22a, 23a, 24a, 21b, 22b, 23b, 24b... Belt conveying roll, 25aY, 25aM, 25aC, 25aK, 25bY, 25bM, 25bC, 25bK. Primary transfer roll, 26a ... guide roll, 30 ... contact roll, 31 ... power supply, 40 ... paper feed cassette, 41 ... paper feed roll, 42 ... registration roll, 43 ... ..Fixer, 44 ... discharge tray, 45 ... sheet feeding path, 46 ... inverter path, P ... recording sheet

Claims (3)

A first image forming section comprising: image forming means for forming each color image on the surface of the photoconductor in response to an image data signal; and an intermediate transfer body on which the toner images of each color are transferred from the photoconductor. In a color image forming apparatus in which a second image forming unit is disposed at a facing position, a recording sheet is conveyed between both of the intermediate transfer members that are in contact with each other, and a recorded image is simultaneously transferred to both sides of the recording sheet.
The first image forming unit includes detection means for optically reading a reference mark image of each color formed on the surface of the intermediate transfer member,
In the correction mode, a signal is sent from the correction mode control unit to the image forming means of the first image forming unit and the second image forming unit, and the reference mark image of each color is formed on the surface of the intermediate transfer member of each image forming unit. The reference mark image formed on the intermediate transfer member of the second image forming unit is transferred to the intermediate transfer member of the first image forming unit, and the first image forming unit and the second image forming unit are formed by the detecting unit. The reference mark image formed in both of the image forming portions is detected, and the positional deviation and / or the density error in the respective recorded images formed in the first image forming portion and the second image forming portion are corrected. A color image forming apparatus. 2. The correction of misalignment and / or shape of mutually recorded images transferred to both surfaces of the recording sheet by the first image forming unit and the second image forming unit is performed. Color image forming apparatus. When the positional deviation and / or shape of either one of the first image forming unit or the second image forming unit is changed, the positional deviation and / or shape of the other recorded image is linked with the change, The color image forming apparatus according to claim 2, wherein the color image forming apparatus is automatically corrected so as to cancel the positional deviation between the front and back recorded images.

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