JP2019061014A - Image forming apparatus - Google Patents

Abstract

To provide an image forming apparatus capable of improving accuracy of an image formation position relative to a recording material without wasting the recording material.SOLUTION: The image forming apparatus has: a control unit for controlling an operation of forming an image on a recording material, which controls in such a manner that an inspection image is formed on the recording material at a predetermined position at a specific distance from an end of the recording material; an image forming unit for forming an image on the recording material, which forms the inspection image on the recording material; and an image detection unit for detecting a detection position of the inspection image on the recording material. The control unit detects a difference between the predetermined position and the detection position, corrects the difference, and controls to form an image on the recording material where the inspection image is formed.SELECTED DRAWING: Figure 4

Description

  The present invention relates to an image forming apparatus such as an electrophotographic copying machine and an electrophotographic printer (for example, a laser beam printer, an LED printer).

  In an electrophotographic image forming apparatus, it is general to form an image by providing a fixed margin from the end of a sheet. However, in recent years, opportunities for using printed materials as catalogs and brochures have increased, and there has been an increasing demand for narrowing the margin as much as possible.

  In order to narrow the margin, it is necessary to improve the accuracy of the image forming position with respect to the sheet, particularly the distance with respect to the distance from the edge of the sheet to the image forming position. However, in the electrophotographic image forming apparatus, an error in the image forming position with respect to the sheet may occur due to the following factors.

  For example, an error in the image forming position in the sheet conveying direction may occur due to the mounting position accuracy of the registration roller or the like. In addition, an error in the image forming position in the sheet width direction may occur due to the position accuracy of a member that regulates the sheet width direction such as a sheet feeding cassette. Furthermore, when the shape of the plastic lens and the refractive index change due to the change of the temperature inside the machine, the scanning position changes and an error of the image magnification occurs, which may cause an error of the image forming position.

  On the other hand, in Patent Document 1, the inspection image is formed on both sides of the sheet and read by the image reading unit, the magnification / position information is extracted, the correction value is calculated, and the next image formation is performed based on the correction value. A configuration has been proposed in which correction is performed to improve the image forming position accuracy with respect to a sheet.

  Further, in Patent Document 2, an image on a sheet is read as image data, and the image processing method of the image data to be overwritten is switched based on the read image data, and then the image is overwritten on the sheet. Have been described.

Japanese Patent Application Laid-Open No. 9-27879 JP, 2013-236159, A

  However, in the configuration described in Patent Document 1, a sheet serving as a recording material is wastefully consumed in order to form an inspection image, which causes a load on the environment.

  Further, in the configuration described in Patent Document 2, although it is possible to suppress the moiré phenomenon that occurs when an image is formed on a document by overwriting, the image formation position accuracy with respect to a sheet as a recording material is not taken into consideration.

  Therefore, the present invention has been made in view of such a current situation, and it is an object of the present invention to provide an image forming apparatus capable of improving the accuracy of an image forming position with respect to a recording material without wasting the recording material. .

  A representative configuration of an image forming apparatus according to the present invention for achieving the above object is a control unit that controls an operation of forming an image on a recording material, and a distance from an end of the recording material to the recording material Is a control unit that controls to form an inspection image at a predetermined position of a predetermined length, and an image forming unit that forms an image on the recording material, the image that forms the inspection image on the recording material A forming unit; and an image detecting unit configured to detect a detection position of the inspection image on the recording material, wherein the control unit detects a difference between the predetermined position and the detection position, and the difference To form an image on the recording material on which the inspection image is formed.

  According to the present invention, it is possible to improve the accuracy of the image forming position with respect to the recording material without wasting the recording material.

FIG. 1 is a schematic cross-sectional view of an image forming apparatus. It is a schematic diagram which shows the internal structure of a laser scanner unit. FIG. 1 is a block diagram showing a part of a system configuration of an image forming apparatus. 5 is a flowchart of an image formation position correction sequence. It is a figure which shows the image for a test | inspection. It is a figure which shows the measurement result of the distance from the edge of the sheet | seat of the image for test | inspection. It is a table | surface which shows the measurement result of the distance from the edge of the sheet | seat of the image for test | inspection. It is a schematic diagram for demonstrating the operation | movement which detects the inclination of the image for a test | inspection, and correct | amends the inclination of an image. FIG. 6 is a view showing a first side and a second side of a sheet on which an image is formed by executing an image forming position correction sequence. 5 is a flowchart of an image formation position correction sequence. It is a figure which shows an example of the image data of the image which a user wants to obtain. It is a figure which shows the image for a test | inspection. It is a figure which shows the 1st surface and 2nd surface of the sheet | seat which an image is formed and a user finally obtains. It is the figure which illustrated other inspection images. It is the figure which illustrated other inspection images.

First Embodiment
<Image forming apparatus>
Hereinafter, the entire configuration of the image forming apparatus A according to the first embodiment of the present invention will be described together with the operation at the time of image formation with reference to the drawings. Note that the dimensions, materials, shapes, relative arrangements, and the like of the components described are not intended to limit the scope of the present invention to them unless otherwise specified.

  The image forming apparatus A is an electrophotographic color image forming apparatus capable of forming an image on a sheet with four color toners (a plurality of developers) of yellow Y, magenta M, cyan C, and black K. In the following description, members using the toners of the respective colors are suffixed with Y, M, C, and K, except that the configuration and operation of each member are different except for the color of the toner used. Since they are substantially the same, subscripts are appropriately omitted unless distinction is required.

  As shown in FIG. 1, an image forming apparatus A includes an image forming unit that transfers a toner image to a sheet as a recording material to form an image, a sheet feeding unit that supplies a sheet toward the image forming unit, A fixing unit is provided to fix a toner image on a sheet.

  The image forming unit includes a process cartridge P (PY, PM, PC, PK). In addition, electrostatic attraction as a transfer unit for transferring the sheet S, transfer rollers 19 (19Y, 19M, 19C, 19K) as transfer units, laser scanner units 17 (17Y, 17M, 17C, 17K) as exposure units A type of conveyor belt 14 is provided. The image forming unit can form an image on the sheet S using toners that are developers of four colors of yellow Y, magenta M, cyan C, and black K.

  The process cartridge P includes photosensitive drums 15 (15Y, 15M, 15C, and 15K) as rotatable photosensitive members, and charging rollers 16 (16Y, 16M, 16C, and 16K) as charging units for charging the photosensitive drums 15. . The developing device 28 (28Y, 28M, 28C, 28K) is provided as a developing unit for visualizing the electrostatic latent image formed on the photosensitive drum 15 as a photosensitive member with toner. Further, the cleaning blade 20 (20Y, 20M, 20C, 20K) for removing the toner attached to the photosensitive drum 15 is provided.

  The transport belt 14 as the transport unit is rotationally driven in the direction of the arrow R1 at a surface speed of 226.27 mm / sec by rotation of the drive roller 27. The throughput of plain paper of the image forming apparatus A is A4 size longitudinal (279.4 mm) feeding 40 ppm (page per minute), and the image interval (sheet interval) is 60 mm. Further, in synchronization with the rotation of the conveyance belt 14, the photosensitive drums 15 of the respective colors are also rotationally driven in the direction of the arrow R2.

  Next, the image forming operation will be described. First, when the control unit 70 shown in FIG. 3 receives an image forming job signal, the sheet S (recording material) stacked and stored in the sheet feeding cassette 10 by the feeding roller 11 and the separation pad 12 is sent out to the registration roller 13 one by one. Be

  Next, the sheet S abuts against the nip portion of the registration roller 13 in the stopped state, and the leading end position follows the nip portion, whereby skew feeding correction is performed. Thereafter, the sheet S is conveyed to the conveyance belt 14 by the registration roller 13 rotating in synchronization with the image writing start timing of the image forming unit. The conveying belt 14 conveys the sheet S to a transfer nip portion formed between the photosensitive drum 15 as a photosensitive member and the transfer roller 19 as a transfer portion. That is, the registration roller 13 and the conveyance belt 14 are a conveyance unit that conveys the sheet S to the transfer nip unit.

  On the other hand, in the image forming unit, first, the surface of the photosensitive drum 15 as the photosensitive member is charged by the charging roller 16 as the charging unit. Thereafter, the laser scanner unit 17 as an exposure unit irradiates the surface of the photosensitive drum 15 of each color with a laser beam according to the image data transmitted from an external device or the like (not shown) to form an electrostatic latent image on the surface of the photosensitive drum 15 Do.

  Thereafter, a bias is applied to the developing rollers 18 (18Y, 18M, 18C, 18K) included in the developing device 28 as the developing unit. As a result, toners of respective colors are attached to the electrostatic latent image formed on the surface of the photosensitive drum 15, and a toner image (developer image) is formed on the surface of the photosensitive drum 15. The toner images of the respective colors formed on the surface of each photosensitive drum 15 are sequentially applied to the sheet S conveyed by the conveyance belt 14 by applying a transfer bias having a polarity opposite to the charge polarity of the toner to the transfer roller 19 as a transfer portion. It is superimposed and transferred. As a result, a full color toner image is formed on the sheet S.

  Next, the sheet S on which the toner image has been transferred is subjected to heat and pressure processing in the fixing device 21, whereby the toner image on the sheet S is fixed to the sheet S. Thereafter, the sheet S on which the toner image is fixed is discharged to the discharge tray 23 by the discharge roller 22 which discharges the sheet S to the outside of the image forming apparatus A as a discharge unit.

  When an image is formed on both sides of the sheet S, the sheet S is conveyed to the discharge roller 22 as a discharge unit after the fixing process to the first surface of the sheet S by the fixing device 21. Thereafter, when the trailing end of the sheet S passes the flapper 24, the position of the flapper 24 as a guide portion is switched by an actuator (not shown), and the discharge roller 22 is reversely rotated. As a result, the sheet S is switched back in the reverse direction by the discharge roller 22 and is guided to the both-side conveying path 25 by the flapper 24 as a guiding portion in a state where the front and back are reversed. That is, the flapper 24 is a guiding unit which switches the conveyance path of the sheet S and guides the sheet S to the discharge roller 22 as a discharge unit and the contact image sensor 2 described later.

  Thereafter, the sheet S guided to the duplex conveying path 25 by the flapper 24 serving as the guiding portion passes the U-turn portion 26 and is transported to the transport belt 14 again via the registration roller 13. Thereafter, in the image forming unit, the toner image is transferred to the second surface as in the first surface. Thereafter, the toner image is fixed on the second surface of the sheet S by the fixing device 21, and the sheet S is discharged to the discharge tray 23 by the discharge roller 22 as a discharge unit.

  Further, the double-sided conveyance path 25 is provided with a contact image sensor 2 as an image detection unit. The contact image sensor 2 can read the image data of the entire sheet S by passing the image through the image reading elements arranged in the longitudinal direction 220 mm.

<Laser Scanner Unit>
Next, the configuration of the laser scanner unit 17 as an exposure unit will be described.

  FIG. 2 is a schematic view showing an internal configuration of the laser scanner unit 17. As shown in FIG. 2, the laser scanner unit 17 includes a semiconductor laser 173, a collimator lens 174, a rotating polygon mirror 175, an fθ lens 176, and a BD sensor 177.

  Next, the basic operation of the laser scanner unit 17 will be described. First, when the semiconductor laser 173 emits the laser beam L, the laser beam L is converted into substantially parallel light by the collimator lens 174, and forms an image on the reflecting surface 175a of the rotating polygon mirror 175 with a predetermined diameter.

  Next, as the rotating polygon mirror 175 is rotated, the laser beam L is deflected and scanned while being reflected by the reflecting surface 175 a. The rotary polygon mirror 175 performs constant angular velocity rotation of 890.8 rotations / sec in the direction of arrow R3 shown in FIG.

  The laser beam L deflected and scanned by the rotary polygon mirror 175 first enters the BD sensor 177 disposed one line upstream of the laser beam L from the photosensitive drum 15. At this time, with reference to the BD signal serving as the scan start reference signal of each line of the same cycle output from the BD sensor 177, the write start timing of the image on the photosensitive drum 15 is determined.

  Next, the deflected and scanned laser beam L enters the fθ lens 176. The fθ lens 176 is a lens for forming an image of the laser beam L on the photosensitive drum 15, and the scanning speed on the photosensitive drum 15 in the main scanning direction (rotational axis of photosensitive drum 15, arrow K1 direction) is equal. It is designed to be kept fast. The laser beam L that has passed through the fθ lens 176 is imaged on the photosensitive drum 15.

By rotating the rotary polygon mirror 175 in this manner, scanning of the laser beam L in the main scanning direction is performed on the photosensitive drum 15. Further, as the photosensitive drum 15 rotates in the direction of arrow R2, scanning in the sub scanning direction of the laser beam L (rotational direction of the photosensitive drum 15, a direction orthogonal to the main scanning direction) is performed. Thus, an electrostatic latent image is formed on the surface of the photosensitive drum 15.
<Control unit>
Next, an outline of a system configuration of the image forming apparatus A will be described.

  FIG. 3 is a block diagram showing a part of the system configuration of the image forming apparatus A. As shown in FIG. As shown in FIG. 3, the image forming apparatus A includes a control unit 70 including a CPU and a memory. Further, to the control unit 70, the contact image sensor 2, the resist motor 74, the drive motor 73, the video controller 171, the BD sensor 177 and the like are connected.

  The contact image sensor 2 as an image detection unit reads the image data formed on the sheet S and outputs the image data to the control unit 70. The image data output to the control unit 70 is taken in, for example, as RGB information encoded at 24 bpp (24 bits per pixel), and indicates the brightness of red, green, and blue (r value, g value, b value). Represented by two 8-bit unsigned integers (0 to 255).

  The video controller 171 processes image data input from an external device (not shown) or the like, and outputs an electrical signal (video signal) corresponding to the image data to the laser driver 172. The laser driver 172 controls the light emission of the semiconductor laser 173 in accordance with the input video signal to form an electrostatic latent image corresponding to the image data on the photosensitive drum 15.

  The control unit 70 controls the drive motor 73 and the registration motor 74 to control the drive of the drive roller 27 and the registration roller 13 respectively.

  The control unit 70 is also connected to devices of the image forming unit other than the laser scanner unit 17 and controls an image forming operation on the sheet S by the image forming unit.

<Image formation position correction sequence>
Next, an image forming position correction sequence for forming an image after correcting the image forming position on the sheet S will be described with reference to the flowchart shown in FIG.

  As shown in FIG. 4, when the image forming job signal is received, the control unit 70 first controls each device of the image forming unit to perform the above-described image forming operation on the first surface of the sheet S as shown in FIG. An inspection image is formed (S1). In the inspection image of the present embodiment, dots D1 to D4 of yellow color and size 2 pixels × 2 pixels are formed at the four corners of the sheet S as target values 5.0 mm of the margin in both the main scanning direction and the sub scanning direction. That is, the dots D1 to D4 are formed with the positions S1 to S4 and F1 to F4 from the end of the sheet S shown in FIG. 5 as 5.0 mm (predetermined length) as the target positions (predetermined positions). That is, as the inspection image, dots D1 to D4 are formed at predetermined positions where the distance from the end of the sheet S is a predetermined length.

  Note that, by forming an inspection image with the yellow toner having the highest lightness among the toners used in the image forming apparatus A, the user can secure the dot reproducibility in development and the reading reliability in the contact image sensor 2 It can be made inconspicuous on visual observation.

  Next, the sheet S on which the inspection image is formed on the first surface is conveyed to the duplex conveying path 25 (S2). Then, in the double-sided conveyance path 25, the inspection image formed on the sheet S is read by the contact image sensor 2 as an image detection unit (S3). The read result is sent to the control unit 70.

  Next, the control unit 70 measures the distances from the edge of the sheet S of the inspection image (S1 to S4 and F1 to F4 shown in FIG. 5) from the reading result of the inspection image. Then, the difference between the target value and the measured value is calculated and detected (S4). That is, the contact image sensor 2 detects a detection position, which is the position of the inspection image on the sheet S (on the recording material), and the control unit 70 detects the difference between the detection position and the target position. FIG. 6 and FIG. 7 are diagrams and tables showing measurement results of the present embodiment. The broken line in FIG. 6 is a 1 mm square. Also, this measurement result is an example of the measurement result used to explain the algorithm, and is not a unique value determined by the device configuration.

  Next, the control unit 70 uses the measurement result of the inspection image as a correction value for correcting the difference between the target value and the measurement value, the writing position of the image in the main scanning direction and the sub scanning direction with respect to the photosensitive drum 15; A correction value regarding the magnification of the image in the main scanning direction and the sub scanning direction is calculated (S5). These correction values are calculated using the following equations 1 to 6.

Correction value of the writing position of the image in the main scanning direction = −ΔS1 (1)
Correction value of the writing position of the image in the sub scanning direction = −ΔF1 (2)

With regard to the correction value x and the correction value y of the magnification of the image in the main scanning direction and sub scanning direction, the sheet length = the current margin and the image because the length of the sheet S is obtained by adding the margin and the image length first. The following equations 3 and 4 are established as the sum of the length = the sum of the target margin and the corrected image length. In Equations 3 and 4, Ps is the image length in the main scanning direction, and Pf is the image length in the subscanning direction.
Sheet length = S1 + Ps + S2 = 5.0 + xPs + 5.0 (3)
Sheet length = F1 + Pf + F2 = 5.0 + yPf + 5.0 (4)

Next, the correction value x and the correction value y are calculated by the following formulas 5 and 6 which are formulas 3 and 4 respectively.
x = 1 + (S1 + S2-10) / Ps (5)
y = 1 + (F1 + F2-10) / Pf (6)

  Here, the image length Ps in the main scanning direction can be directly measured by the contact image sensor 2, and in the present embodiment, Ps = 200.0 mm. The image length Py in the sub scanning direction can be calculated by approximating the image length by multiplying the time when the contact image sensor 2 detects the image by the absolute value of the transport speed of the sheet S. In the present embodiment, Pf = 287.0 mm. The absolute value of the transport speed of the sheet S may include an error such as tolerance variation of mechanical parts.

  As a result of calculation using Equations 1 to 6, the correction values of the writing position of the image in the main scanning direction and the writing position of the sub scanning direction were both 0.6 mm. The correction value of the magnification of the image in the main scanning direction was 99.8%, and the correction value of the magnification of the image in the subscanning direction was 99.9%.

  Next, the control unit 70 corrects the image writing timing and the magnification from the calculated correction value as follows (S6).

  The writing start position of the image in the main scanning direction (exposure start position to the photosensitive drum 15) is delayed by 0.6 mm from the detection timing of the BD sensor 177 by 0.6 mm of the writing timing of the laser beam L to the photosensitive drum 15 of the laser scanner unit 17. Correct by doing.

  The writing start position of the image in the sub scanning direction is corrected by delaying the rotation start timing of the registration roller 13 as the conveyance unit by 0.6 mm. In the present embodiment, since the transport speed of the sheet S by the transport belt 14 is 226.27 mm / sec, the speed is advanced by 0.6 ÷ 226.27 = 0.0027 sec.

  The magnification of the image in the main scanning direction is corrected by shortening the scanning time (exposure time) of the laser beam L by the laser scanner unit 17 as the exposure unit to 99.8%.

  The magnification of the image in the sub scanning direction is corrected by controlling the drive motor 73 to set the rotational speeds of the photosensitive drum 15 and the transport belt 14 to 99.9%, that is, 225.95 mm / sec.

  Next, the control unit 70 detects the inclination of the inspection image to correct the difference between the target value and the measurement value from the measurement result of the inspection image (S7). Then, the inclination of the image is corrected based on the inclination of the detected inspection image (S8). In the present embodiment, the inclination of the inspection image is detected by the method described below, and the inclination of the image is corrected.

  FIG. 8A is a schematic view for explaining the inclination of the image. Here, in FIG. 8A, the main scanning line 81 is a scanning line of the laser scanner unit 17 and shows an ideal scanning line in the main scanning direction without inclination. The main scanning line 82 indicates a scanning line that inclines upward to the right due to the positional accuracy or the diameter of the photosensitive drum 15, the positional accuracy of the optical system of the laser scanner unit 17, or the like.

  As shown in FIG. 8A, in the inspection image, when the dot D1 at the left end which is the scan start position is a reference point, the dot D2 at the right end deviates 0.13 mm in the sub-scanning direction from D1. That is, the amount of deviation of the main scanning line 82 in the sub scanning direction with respect to the main scanning line 81 is 0.13 mm. When this inclination is linearly approximated, since the length Ps in the main scanning direction from the dots D1 to D2 is 200.0 mm as described above, the inclination is 0.13 ÷ 200.0 = 0.0065.

  FIG. 8B is a bitmap image in which the tilt of the image is corrected. As shown in FIG. 7B, the corrected bitmap image is formed in a stepwise manner while being shifted by three lines from the left end to the right end of the image area. When the image resolution is 600 dpi, the distance for three lines is 25.4 mm ÷ 600 dpi × 3 lines = 0.132 mm.

  As a result, as shown in FIG. 8C, the inclination of the scanning line is offset to form a substantially horizontal straight line. In this manner, the correction position for correcting the deviation amount in the sub scanning direction at each main scanning position is calculated from the image bitmap, and the main scanning line is inclined by reconstructing a correction image bitmap according to the calculation result. It is possible to create an image in which color shift due to distortion is corrected.

  The method of correcting the inclination of the image is not limited to the method of the present embodiment. For example, the correction optical system including the semiconductor laser 173 and the fθ lens 176, the mirror in the optical path, etc. are mechanically operated to It may be a method of aligning the position of.

  Next, the control unit 70 controls the image forming unit to form an image that the user wants to obtain on the second surface of the sheet S (S9). That is, the sheet S passes through the U-turn portion 26 in a state in which the front and back sides are reversed, is conveyed again to the registration roller 13, and in the same process as image formation on the first surface of the sheet S Etc., and an image is formed on the second surface.

  FIG. 9 is a view showing the first surface and the second surface of the sheet S on which the image is formed by executing the image forming position correction sequence. As shown in FIG. 9, yellow dots, which are inspection images, remain on the first surface of the sheet S. However, as described above, the inspection image for yellow dots is difficult to visually recognize and inconspicuous. Further, on the second surface of the sheet S, an image which the user wants to obtain and which has high accuracy of the image forming position with respect to the sheet S is formed.

  By executing the image forming position correction sequence in this manner, it is possible to form an image with high accuracy of the image forming position on the sheet S. In the image formation position correction sequence, an image that the user wants to obtain is formed on the sheet S on which the inspection image is formed. Therefore, it is possible to improve the accuracy of the image forming position with respect to the sheet S without wasting the sheet S and exerting a load on the environment.

  The timing of executing the image formation position correction sequence may be performed each time an image is formed, for example, immediately after the sheet S is replenished to the sheet feeding cassette 10 or when the environmental temperature changes significantly, or This can be performed, for example, when the predetermined number of image formations has been reached. As described above, the image forming apparatus A executes the image forming position correction sequence at a predetermined timing set in advance to correct the image forming position accuracy in real time, and to form the image according to the size variation of the sheet S. Position accuracy can be corrected.

Second Embodiment
Next, the configuration of the image forming apparatus A according to the second embodiment of the present invention will be described. About the part which overlaps with the said 1st Embodiment, the same code | symbol is attached | subjected and description is abbreviate | omitted.

  In the first embodiment, in the image formation position correction sequence, a configuration is described in which a yellow inspection image which is difficult for the user to visually recognize is formed on the first surface of the sheet S, and an image desired to be obtained by the user is formed on the second surface. did. In the present embodiment, a configuration will be described in which an image that the user wants to obtain is overwritten on the first surface of the sheet S from the inspection image.

  FIG. 10 is a flowchart of an image forming position correction sequence according to the present embodiment. In FIG. 10, the same reference numerals are given to steps performing the same processes as the steps described using FIG. 4 in the first embodiment, and the description will be simplified.

  As shown in FIG. 10, first, the control unit 70 first acquires image data of an image that the user wants to obtain based on an image formation instruction signal and the like transmitted from the user (S101). FIG. 11 is a diagram showing an example of image data of an image that the user wants to obtain. As shown in FIG. 11, in the present embodiment, the image that the user wants to obtain has a margin of 5 mm and a solid black image around the four corners.

  Next, an inspection image is determined based on the acquired image data (S102). Specifically, the inspection image is an image composed of an image pattern and a color in which the same color portion is overlapped between the image that the user wants to obtain and the inspection image. In the present embodiment, a black test image is formed at a position overlapping the black portion in the image desired to be obtained by the user obtained in step S101.

  FIG. 12 is a view showing an inspection image according to the present embodiment. As shown in FIG. 12, in the inspection image of this embodiment, dots D1 to D4 of black color and size 2 pixels × 2 pixels at the four corners of the sheet S are used as target values for the margin in both the main scanning direction and the sub scanning direction. It is .0 mm. That is, dots D1 to D4 are formed with a position where distances S1 to S4 and F1 to F4 from the end of the sheet S shown in FIG. 11 are 7.0 mm (predetermined length) as target positions (predetermined positions). That is, as the inspection image, dots D1 to D4 are formed at predetermined positions where the distance from the end of the sheet S is a predetermined length.

  Next, each device of the image forming unit is controlled to form the inspection image determined in step S102 on the first surface of the sheet S by the above-described image forming operation (S103).

  Next, in the same manner as in the first embodiment, the control unit 70 conveys the sheet S to the duplex conveyance path 25 (S2). Then, in the double-sided conveyance path 25, the inspection image formed on the sheet S is read by the contact image sensor 2 as an image detection unit (S3). Then, the distance from the edge of the sheet S of the inspection image is measured from the reading result of the inspection image, and the difference between the target value and the measurement value is calculated and detected (S4). That is, the contact image sensor 2 detects a detection position, which is the position of the inspection image on the sheet S (on the recording material), and the control unit 70 detects the difference between the detection position and the target position.

  Next, from the measurement result of the inspection image, the control unit 70 first writes the image writing position in the main scanning direction and the sub scanning direction with respect to the photosensitive drum 15 as a correction value for correcting the difference between the target value and the measurement value. Correction values regarding the magnification of the image in the main scanning direction and the sub scanning direction are calculated (S5). Thereafter, the control unit 70 corrects the image writing timing and the magnification from the calculated correction value (S6).

  Next, the control unit 70 detects the inclination of the inspection image to correct the difference between the target value and the measurement value from the measurement result of the inspection image (S7). Then, the inclination of the image is corrected based on the inclination of the detected inspection image (S8).

  Next, the control unit 70 controls the flapper 24 to cause the sheet S to pass through the duplex conveying path 25 again (S104). As a result, the sheet S is turned upside down twice in total, and the first surface on which the inspection image is formed becomes the image forming surface. Thereafter, the first surface of the sheet S is overwritten with the image that the user wants to obtain from the inspection image (S105).

  FIG. 13 is a view showing the first surface and the second surface of the sheet S on which an image is formed and finally obtained by the user. As shown in FIG. 13, since the dots D1 to D4 of the inspection image are overwritten on the image that the user wants to obtain, the inspection image is not recognized by the user. Therefore, it is not necessary to form the inspection image in an inconspicuous color such as yellow, so that the inspection image can be formed in black and it can be compatible with a monochrome image forming apparatus.

  In addition, as shown to Fig.14 (a), also when an image does not exist in the edge part vicinity of the sheet | seat S in the image which a user wants to obtain, it is assumed. In this case, as shown in FIG. 14B, the dots D1 to D4 may be formed as inspection images at positions corresponding to positions outside the sheet as much as possible in the image desired by the user.

  Further, the inspection image is not limited to the one described above, and the position and the shape can be freely changed. For example, as shown in FIG. 15A, the number of dots may be increased, or as shown in FIG. By devising the pattern of the inspection image in this manner, correction with higher positional accuracy can be performed.

2 ... Contact image sensor (image detection unit)
15: Photosensitive drum (photosensitive body)
16: Charging roller (charging unit)
17: Laser scanner unit (exposure unit)
19: Transfer roller (transfer unit)
22: Discharge roller (discharge unit)
24 ... flapper (guidance part)
28: Developing device (developing unit)
70: Control unit A: Image forming apparatus S: Sheet (recording material)

Claims (12)

A control unit that controls an operation of forming an image on a recording material, and controls the recording material to form an inspection image at a predetermined position at a predetermined distance from the end of the recording material. When,
An image forming unit for forming an image on the recording material, wherein the image forming unit forms the inspection image on the recording material;
An image detection unit that detects a detection position of the inspection image on the recording material;
The image forming apparatus, wherein the control unit detects a difference between the predetermined position and the detection position, corrects the difference, and forms an image on the recording material on which the inspection image is formed. A discharge unit that discharges the recording material on which an image is formed to the outside of the image forming apparatus;
A guide unit which switches the conveyance path of the recording material and guides the recording material to the discharge unit and the image detection unit;
The image forming apparatus according to claim 1, further comprising:   The control unit forms the inspection image on a first surface of the recording material, and forms an image formed after correcting the difference on a second surface of the recording material. The image forming apparatus according to 2.   The image forming unit can form an image using developers of a plurality of colors, and the inspection image is formed using a developer having the highest lightness among the developers of the plurality of colors. The image forming apparatus according to claim 3, characterized in that:   The control unit forms the inspection image and the image to be formed after correcting the difference on the same surface of the recording material, and the same color portion of the image to be formed after correcting the inspection image and the difference. The image forming apparatus according to claim 1, wherein the image forming apparatus is formed so as to overlap each other.   The image forming apparatus according to any one of claims 1 to 5, wherein the control unit corrects the writing start position of the image with respect to the recording material to correct the difference.   The image forming apparatus according to any one of claims 1 to 6, wherein the control unit corrects the magnification of the image to correct the difference.   The image forming apparatus according to any one of claims 1 to 7, wherein the control unit corrects the inclination of the image to correct the difference. The image forming unit is
A rotatable photoreceptor,
A charging unit for charging the photosensitive member;
An exposure unit that exposes the charged photosensitive member to form an electrostatic latent image;
A developing unit for developing the electrostatic latent image with a developer to form a developer image;
A transfer unit for transferring the developer image to the recording material;
Equipped with
The control unit is characterized in that the control unit controls the exposure unit to correct the exposure start position with respect to the photosensitive member, thereby correcting the writing position of the image with respect to the recording material in the direction orthogonal to the rotation direction of the photosensitive member. The image forming apparatus according to claim 6. The image forming apparatus further includes a conveyance unit that conveys the recording material to a nip formed between the photosensitive member and the transfer unit.
The control unit is characterized in that the writing position of the image with respect to the recording material in the rotational direction of the photosensitive member is corrected by controlling the conveyance unit to correct the timing of conveying the recording material to the nip portion. The image forming apparatus according to claim 9. The image forming unit is
A rotatable photoreceptor,
A charging unit for charging the photosensitive member;
An exposure unit that exposes the charged photosensitive member to form an electrostatic latent image;
A developing unit for developing the electrostatic latent image with a developer to form a developer image;
A transfer unit for transferring the developer image to the recording material;
Equipped with
The image forming apparatus according to claim 7, wherein the control unit corrects the magnification of the image in the direction orthogonal to the rotation direction of the photosensitive member by correcting the exposure time of the exposure unit.   12. The image forming apparatus according to claim 11, wherein the control unit corrects the magnification of the image in the rotation direction of the photosensitive member by correcting the rotational speed of the photosensitive member.

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