JP4890941B2 - Image forming apparatus - Google Patents

Description

The present invention relates to an image forming equipment such as copiers and printers. In particular, double-sided image formation and an image formed on the first surface and the second surface of the recording medium, but about the multiple composite images formed an image forming equipment for forming an image on the first surface of the recording medium.

  An image forming apparatus according to a conventional example will be described with reference to FIG. 12, taking an electrophotographic image forming apparatus using a laser beam exposure method as an example. FIG. 12 is a schematic configuration diagram of an image forming apparatus according to a conventional example.

  The image forming apparatus includes a photosensitive drum 505 as an image carrier, a developing unit 506 as a developing unit, a cleaner 507, a charger 508 as a charging unit, a transfer roller 509 as a transfer unit, and a laser optical unit 510 as an exposure unit. An image forming unit.

  The image forming operation is performed according to the following steps.

  (1) Charging: The photosensitive drum 505 is uniformly charged by the charger 508.

  (2) Laser exposure: Laser light is irradiated by the laser optical unit 510 toward the photosensitive drum 505 (broken line B) to form an electrostatic latent image on the photosensitive drum 505.

  (3) Development: A developing device 506a causes toner as a developer contained in the toner container 506b to adhere to the electrostatic latent image formed on the photosensitive drum 505 to form a toner image.

  (4) Transfer: The transfer roller 509 transfers the toner image on the photosensitive drum 505 to a recording sheet as a recording medium.

  (5) Fixing: A fixing device 511 serving as a fixing unit heats and presses the recording paper to fix the unfixed toner on the recording paper.

  The recording paper is loaded on the paper feed cassette 513 or the manual feed tray 514. Then, the paper is fed to the image forming unit by the paper feed roller 515, and after being fixed by the fixing device 511, is discharged to the paper discharge tray 512 (broken line A) or is transported to a double-sided conveyance path described later (broken line C). .

  In a conventional image forming apparatus, as an image forming mode, in addition to a normal mode in which a single image is formed on one side of a recording paper, a composite mode in which an image is formed on one side of the recording paper and an image on both sides of the recording paper. And a double-sided mode for forming an image is known. In the composite image forming mode and the double-sided image forming mode, image formation is performed by repeating image transfer and fixing on the same recording paper a plurality of times.

  Here, the composite image forming mode and the double-sided image forming mode will be described. The recording paper on which image formation has been performed on the first surface in the above-described steps is placed on the downstream side of the fixing device 511 and conveyed to the lower part of the apparatus by a flapper 516 that opens and closes up and down. The recording paper conveyed to the lower part of the apparatus is conveyed by the flapper 521 to the recording paper reversing unit 517 in the double-sided image forming mode, and directly without passing through the recording paper reversing unit 517 in the composite image forming mode. It is conveyed to the double-sided conveyance roller 518. The recording paper conveyed to the recording paper reversing unit 517 is conveyed to the double-sided conveying roller 518 with the leading end of the recording paper reversed at the recording paper reversing unit 517. The recording paper conveyed to the double-sided conveyance roller 518 passes through the double-sided conveyance path driven by the double-sided conveyance rollers 518, 519, and 520, and is conveyed again to the image forming unit, and the second and subsequent image formation is performed.

  However, in the composite image forming mode and the double-sided image forming mode, since transfer and fixing are repeatedly performed on the same recording paper a plurality of times, the recording paper is heated and pressed by the first fixing, so that the recording paper is shrunk. Elongation occurs. For this reason, if the image is transferred and fixed at the same magnification as the first image formation at the second and subsequent image formation, there is a problem in that a proper image cannot be obtained due to a discrepancy between the images. It was.

In order to solve such a problem, the image correction magnification is calculated by detecting the size of the recording paper before and after fixing, and the image correction is performed based on the image correction magnification. In such an image forming apparatus, the following methods have been proposed as methods for detecting the size of the recording paper on the recording paper conveyance path. That is, during the recording paper transport, the passing time from the leading edge to the trailing edge of the recording paper is measured by the output signal of the sensor arranged on the recording paper transport path, and the size of the recording paper is determined from the passing time and the recording paper transport speed. (See, for example, Patent Document 1).
Japanese Patent Laid-Open No. 03-172255

  However, the actual recording paper conveyance speed in the image forming apparatus is uneven in speed due to the eccentricity of the recording paper conveyance roller, and may not match the preset conveyance speed. For this reason, the conventional example has a problem that the recording paper size cannot be accurately detected.

  Further, the correction of the image on the second side or the second and subsequent times in the double-sided image formation or the composite image formation is usually performed according to the expansion / contraction ratio of the recording paper after fixing, and the position and magnification of the second side or the second image. Is adjusted to match the image of the first surface. For this reason, it is necessary to detect the size of the recording paper before forming the second or second image, and the size detection position of the recording paper is necessarily arranged upstream of the skew correction portion of the recording paper. The Rukoto. Therefore, it has been required to accurately detect the size of the skewed recording paper.

The present invention has been made in view of such problems, and is an image that can detect the size of the recording paper with higher accuracy regardless of the skew amount of the recording paper and the unevenness in the conveyance speed of the recording paper. and to provide a forming equipment.

  The present invention has been made to solve the above-described problems, and includes the following configuration.

(1) In an image forming apparatus capable of performing an image forming operation for transferring and fixing a developer image formed on an image carrier a plurality of times on the same recording medium, the position of the recording medium on the conveyance path is set. A plurality of position detection means to detect, a skew amount calculation means for calculating a skew amount of the recording medium based on a detection result of the position detection means, a detection result of the position detection means, and the skew amount Based on the skew amount calculated by the calculation means, the transport direction of the recording medium and the length in the direction perpendicular to the transport direction are calculated, and the size of the recording medium before fixing as the first recording medium size A size detection means for detecting the size of the recording medium after fixing as a second recording medium size,
Calculating a scaling factor of the recording medium before and after the fixing from the first and second recording medium size, possess control means for controlling the image forming operation, a based on the expansion ratio, of the plurality of position sensing means at least two out, the in position in the diagonal direction of the recording medium, the image forming apparatus according to claim line sensor der Rukoto arranged inclined with respect to the transport direction.

According to the present invention, it is possible to provide a skew amount and regardless of the speed fluctuation of the conveying speed of the recording paper, the image forming equipment which can detect more accurately the size of the recording sheet of the recording paper .

  The best mode for carrying out the present invention will be described based on the following examples.

  However, the dimensions, materials, shapes, relative arrangements, and the like of the components described in this embodiment are not intended to limit the scope of the present invention only to those unless otherwise specified. .

  An image forming apparatus according to this embodiment will be described with reference to FIGS. 1 to 6 and 11.

  FIG. 11 is a schematic configuration diagram of an image forming apparatus according to the present embodiment. As shown in FIG. 11, the image forming apparatus according to this embodiment includes a recording paper size detection unit 100 at a downstream position of the double-sided conveyance path. However, the arrangement position of the recording paper size detection unit 100 is not particularly limited to this, and it may be present at a position (timing) that can reflect the expansion / contraction ratio of the recording paper when generating image data. The recording paper size detection unit 100 includes line sensors 10, 11, and 12 as position detection means.

1. Recording Paper Size Detection Method FIG. 1 is a schematic configuration diagram of a main part of the recording paper size detection unit 100, and FIG. 2 is a block diagram illustrating a control configuration of the image forming apparatus according to the present embodiment.

  The line sensors 10 and 11 are arranged in a diagonal direction of the recording paper 7 as the conveyed recording medium, and the line sensor 12 is perpendicular to the recording paper conveyance direction (sub-scanning direction) (main scanning direction). It is arranged at a position facing the line sensor 10. The recording paper 7 conveyed in the conveyance direction by a conveyance roller (not shown) detects six points from the edge 1 to 6 of the recording paper shown in FIG. Thereby, the skew amount of the recording paper 7 and the lengths in the main scanning direction and the sub scanning direction are calculated, and the recording paper size can be detected.

  Here, as shown in FIG. 6, the line sensors 10 to 12 are arranged at predetermined intervals and angles. Therefore, the main scanning direction distance Lm0 between the leftmost detection point of the line sensor 10 and the leftmost detection point of the line sensor 12, and the sub-scanning direction between the rightmost detection point of the line sensor 12 and the leftmost detection point of the line sensor 11 The distance Ls0 is also a predetermined distance. Further, a main scanning direction distance Lmn between the rightmost detection point of the line sensor 10 and the rightmost detection point of the line sensor 12, and a sub-scanning direction distance between the leftmost detection point of the line sensor 12 and the rightmost detection point of the line sensor 11. Lsn is also a predetermined distance. Similarly, the main scanning direction distance and the sub-scanning direction distance between the arbitrary detection points of the line sensors 10 to 12 are predetermined distances.

  The detection points 1 to 6 detected by the line sensors 10 to 12 are detected by the main scanning direction extraction unit 22. Similarly, detection points 3, 4, 5, and 6 are extracted by the sub-scanning direction extraction unit 23.

  In the main scanning direction calculation unit 24 as the skew amount calculation means, first, the inclination α of the side of the recording paper 7 in the main scanning direction is calculated from the detection points 2 and 6 extracted by the main scanning direction extraction unit 22. In addition, the recording paper length Lm1 between the detection point 2 and the detection point 6 is calculated by the main scanning direction calculation unit 24 as a size detection unit. Since the main scanning direction distance d and the sub-scanning direction distance e between the detection point 2 and the detection point 6 are determined in advance, the inclination α and the length Lm1 are calculated based on the following calculation formula.

  Next, the recording paper length Lm3 between the detection point 6 and the corner of the recording paper 7 on the side of the line sensor 12 is calculated from the detection points 5 and 6 and the inclination α. Since the distance a between the detection point 5 and the detection point 6 is determined in advance, the recording paper length Lm3 is calculated based on the following calculation formula.

  Similarly, the recording paper length Lm2 between the detection point 2 and the corner of the recording paper 7 on the side of the line sensor 10 is calculated from the detection points 1 and 2 and the inclination α.

  From the thus calculated recording paper lengths Lm1, Lm2, and Lm3, the main scanning direction length Lm of the recording paper 7 is calculated as Lm = Lm1 + Lm2 + Lm3.

  On the other hand, in the sub-scanning direction calculation unit 25 as the skew amount calculation means, the inclination β of the side in the sub-scanning direction of the recording paper 7 is calculated from the detection points 4 and 5 extracted by the sub-scanning direction extraction unit 23. . At the same time, the recording paper length Ln1 between the detection point 4 and the detection point 5 is calculated by the sub-scanning direction calculation unit 25 as a size detection unit. Here, when the recording paper 7 has a substantially accurate rectangular shape, the inclination β coincides with the above-described inclination α. Since the main scanning direction distance c and the sub scanning direction distance f between the detection point 4 and the detection point 5 are determined in advance, the inclination β and the length Ln1 are calculated based on the following calculation formula.

  Next, from the detection points 5 and 6 and the inclination β, the recording paper length Ln3 between the detection point 5 and the corner of the recording paper 7 on the side of the line sensor 12 is recorded from the detection points 3 and 4 and the inclination β. The recording paper length Ln2 between the corners of the line 7 on the line sensor 11 is calculated. Since the distance a between the detection points 5 and 6 and the distance b between the detection points 3 and 4 are determined in advance, the recording paper lengths Ln2 and Ln3 are calculated based on the following calculation formulas. .

  From the recording sheet lengths Ln1, Ln2, and Ln3 calculated in this way, the length Ln of the recording sheet 7 in the sub-scanning direction is calculated as Ln = Ln1 + Ln2 + Ln3.

  As described above, the main scanning direction length Lm and the sub-scanning direction length Ln of the recording paper 7 are calculated, and the recording paper size of the recording paper 7 is thereby detected. In the recording sheet size detection method of the present embodiment, a plurality of recording sheets are simultaneously detected by a plurality of line sensors. For this reason, even when the recording paper is being conveyed, it is possible to detect the recording paper size without the influence of the speed variation of the recording paper conveyance speed.

2. Recording Paper Size Detection and Image Correction Procedure Next, the recording paper size detection and image correction procedure in this embodiment will be described with reference to FIG. FIG. 3 is an operation control flowchart for explaining a recording paper size detection and image correction procedure.

  First, the line sensors 10 to 12 are moved by a line sensor movement control mechanism described later (step S101). Subsequently, the skew amount and the recording paper lengths Lm and Ln of the recording paper 7 before fixing are calculated by the above-described recording paper size detection method, and the recording paper size is detected (step S102). In this embodiment, since the recording paper size detection unit 100 exists on the duplex conveyance path, image formation and fixing by the image forming unit are not performed on the first recording paper.

  Subsequently, the recording paper size of the recording paper 7 after fixing is detected in the same manner (step S103). Thereafter, in the image correction control unit 26 as the control means, the expansion / contraction ratio of the recording paper 7 before and after fixing is calculated from the recording paper sizes detected in steps S102 and S103, respectively (S104). If the expansion rate in the main scanning direction of the recording paper 7 is Cm, the expansion rate in the sub-scanning direction is Cn, the recording paper length before fixing is Lma, Lna, and the recording paper length after fixing is Lmb, Lnb. The rates Cm and Cn are calculated based on the following equations.

Cm = Lmb / Lma
Cn = Lnb / Lna

  Then, an image correction magnification in the second or subsequent image formation is determined from the expansion / contraction ratios Cm and Cn (step S105). Thereafter, the image forming unit 27 forms an image on the recording paper 7 according to the image correction magnification determined by the image correction control unit 26 (step S106).

  Next, the movement control mechanism of the line sensors 10 to 12 will be described.

  FIG. 4 is a diagram for explaining movement control of the line sensors 10 to 12. The line sensors 10 to 12 are in an initial position before the image forming operation, for example, a position where the size of the smallest recording paper 7 among a plurality of types of recording paper 7 that can be fed can be detected (solid line position in FIG. 4). is there. From this state, the line sensor 10 moves in the main scanning direction (in the direction of arrow 43 in FIG. 4) and the sub-scanning direction (in the direction of arrow 44 in FIG. 4) according to the standard sizes of various recording papers 7.

  The movement control of the line sensors 10 to 12 will be described with reference to FIG. FIG. 5 is a block diagram of the movement control mechanism of the line sensors 10-12.

  When the standard size of the fed recording paper 7 is confirmed by the recording paper size confirmation unit 51, a predetermined movement distance predetermined for each standard size is determined by the line sensor movement control unit 52. The standard size of the recording paper 7 is selected by, for example, a panel unit (not shown) by the user, and the result is confirmed by the recording paper size confirmation unit 51. Next, the line sensor movement control unit 52 transmits a signal of a predetermined movement amount to the main scanning movement unit 53 and the sub scanning movement unit 54 as driving means. The main scanning movement unit 53 and the sub scanning movement unit 54 move the line sensors 10 to 12 to predetermined positions based on the signal transmitted from the line sensor movement control unit 52. This makes it possible to calculate the skew amount and length of the recording paper 7 of various standard sizes. A pulse motor or the like can be used for the main scanning moving unit 53 and the sub scanning moving unit 54.

  In the present embodiment, the case where the line sensor 10 moves has been described. However, the present invention is not particularly limited to this, and the line sensors 11 and 12 may be set to move. Further, it is possible to shorten the movement time by moving the plurality of line sensors 10 to 12 at the same time.

  The main scanning direction extraction unit 22, the sub scanning direction extraction unit 23, the main scanning direction calculation unit 24, the sub scanning direction calculation unit 25, and the image correction control unit 26 are configured by a controller including, for example, a CPU, a ROM, a RAM, and the like. However, a program for performing various controls may be recorded.

  The image forming apparatus according to the present embodiment will be described with reference to FIGS.

  In the image forming apparatus according to the first embodiment, the skew amount and length of the recording paper 7 are calculated using the line sensors 10 to 12. However, in the image forming apparatus according to the present embodiment, a photo is used instead of the line sensor 12. The point which used the sensor 13 differs from Example 1. FIG. The other points are the same as those of the image forming apparatus according to the first embodiment, and the same reference numerals are given to the same configurations as those of the first embodiment, and the description thereof is omitted.

  FIG. 7 is a schematic configuration diagram of a main part of the recording paper size detection unit 100 arranged in the recording paper conveyance path of the image forming apparatus according to the present embodiment.

7, the line sensor 10 and 11 is disposed on the conveyed diagonal direction of the recording paper 7, the photosensor 1 3, arranged in vertical position of the line sensor 10 and symmetrically with respect to the recording sheet conveying direction Has been. The recording paper 7 conveyed in the conveyance direction by a conveyance roller (not shown) is detected by the line sensors 10 and 11 and the photo sensor 13 at five points 1 to 4 and 8 of the recording paper 7 shown in FIG. A point is detected.

  Here, as shown in FIG. 8, the line sensors 10 and 11 and the photosensor 13 are arranged at predetermined intervals and angles. The photosensor 13 is disposed at the intersection of the center detection points of the line sensors 10 and 11, and the line sensors 10 and 11 are disposed at an angle of 45 degrees with respect to the transport direction. Accordingly, the main scanning direction distance Lm0 between the center detection point of the line sensor 10 and the detection point of the photosensor 13 and the sub-scanning direction distance Ls0 between the detection point of the photosensor 13 and the center detection point of the line sensor 11 are also determined in advance. Distance. The main scanning direction distance and the sub-scanning direction distance between the arbitrary detection points of the line sensors 10 and 11 and the photosensor 13 are also predetermined distances. Also, at this timing when the photosensor 13 detects the recording paper 7, the line sensors 10 and 11 detect the four points 1 to 4 of the recording paper and calculate the skew amount and length of the recording paper 7. Can do.

  FIG. 9 is a block diagram illustrating a control configuration of the image forming apparatus according to the present embodiment.

  Detection points 1 to 4 and 8 detected by the photo sensor 13 and the line sensors 10 and 11 are extracted by the main scanning direction extraction unit 92. Similarly, detection points 1 to 4 and 8 are extracted by the sub-scanning direction extraction unit 93.

  First, the main scanning direction calculation unit 94 calculates the inclination α of the recording paper 7 and the recording paper length Lm1 from the detection points 2 and 8 extracted by the main scanning direction extraction unit 92 by the same calculation method as in the first embodiment. The Next, the recording paper length Lm2 is calculated from the detection points 1 and 2 and the inclination α by the same calculation method as in the first embodiment. Finally, the recording paper length Lm3 is calculated from the detection points 4 and 8, the intersection 9 of the line sensor 11 drawn from the detection point 8 in parallel with the recording paper conveyance direction (see FIG. 7), and the inclination α.

  Since the distance g between the detection point 8 and the intersection 9 is determined in advance, and the distance h between the detection point 4 and the intersection 9 is also determined in advance, the recording paper length Lm3 is calculated based on the following calculation formula.

  From the thus calculated recording paper lengths Lm1, Lm2, and Lm3, the main scanning direction length Lm of the recording paper 7 is calculated as Lm = Lm1 + Lm2 + Lm3.

  On the other hand, the sub-scanning direction calculation unit 95 calculates the recording paper length Ln2 from the detection points 3 and 4 and the inclination α extracted by the sub-scanning direction extraction unit 93 by the same calculation method as in the first embodiment. Next, the recording paper length Ln1 between the detection point 4 and the corner of the photosensor 13 side of the recording paper 7 is calculated from the detection points 4 and 8, the intersection 9 and the inclination α based on the following calculation formula.

  From the recording sheet lengths Ln1 and Ln2 calculated in this way, the sub-scanning direction length Ln of the recording sheet 7 is calculated as Ln = Ln1 + Ln2.

  Subsequent image correction control and line sensor moving operation and control are performed in the same manner as in the first embodiment.

  As described above, the image forming apparatus according to the present embodiment uses the photo sensor 13 instead of the line sensor 12, and therefore can detect the size of the skewed recording paper 7 at a relatively low cost.

  The image forming apparatus according to this embodiment will be described with reference to FIG.

  In the image forming apparatus according to the first embodiment, the skew amount and the length of the recording sheet 7 are calculated using the line sensors 10 to 12. However, in the image forming apparatus according to the present embodiment, in addition to the line sensors 10 to 12, The difference from the first embodiment is that the line sensor 14 is used. The other points are the same as those of the image forming apparatus according to the first embodiment, and the same reference numerals are given to the same configurations as those of the first embodiment, and the description thereof is omitted.

  FIG. 10 is a schematic configuration diagram of a main part of the recording paper size detection unit 100 in the image forming apparatus according to the present embodiment.

  In this embodiment, the line sensors 10 and 11 are arranged in the diagonal direction of the recording paper 7, and the line sensors 12 and 14 are respectively perpendicular to the recording paper conveyance direction (sub-scanning direction) (main scanning direction). It is arranged at a position facing the line sensors 10 and 11. That is, in the present embodiment, a total of four line sensors 10 to 12 and 14 are arranged one by one at the four corners of the recording paper 7, and from the eight detection points 1 to 6, 8 and 9 on the recording paper 7, The skew amount and the length of the four sides of the recording paper 7 are calculated by the same calculation method as in 1. The calculated lengths of the two sides in the main scanning direction and the two sides in the sub-scanning direction are averaged to detect the recording sheet size of the recording sheet 7.

  As described above, in the image forming apparatus according to the present embodiment, the lengths of the four sides of the recording paper 7 are calculated using four line sensors and averaged. For this reason, warpage and deflection of the recording paper 7 after fixing and variations in size detection are reduced, and the size of the recording paper 7 can be detected with higher accuracy.

  As described above, according to the image forming apparatus according to the first to third embodiments, it is possible to simultaneously calculate the lengths in the main scanning and sub-scanning directions with respect to the skewed recording paper while transporting the recording paper while eliminating the uneven speed of the conveying speed. . Therefore, it is possible to detect the size of the recording paper with higher accuracy, and therefore it is possible to perform image correction with higher accuracy.

1 is a schematic configuration diagram of a main part of a recording paper size detection unit according to a first embodiment. Block diagram explaining control configuration Operation control flowchart for explaining recording paper size detection and image correction procedure The figure explaining movement control of a line sensor Block diagram of line sensor movement control mechanism Diagram explaining the arrangement of line sensors Schematic configuration diagram of a main part of a recording paper size detection unit according to the second embodiment. The figure explaining arrangement | positioning of a line sensor and a photo sensor Block diagram explaining control configuration Schematic configuration diagram of the main part of the recording paper size detection unit of the third embodiment 1 is a schematic configuration diagram of an image forming apparatus according to a first embodiment. Schematic configuration diagram of an image forming apparatus according to a conventional example

Explanation of symbols

7 Recording paper (compatible with recording media)
10, 11, 12, 14 Line sensors (corresponding to position detection means)
13 Photosensor (corresponding to position detection means)
24 main scanning direction calculation unit (corresponding to skew amount calculation means and size detection means)
25 Sub-scanning direction calculation unit (corresponding to skew amount calculation means and size detection means)
26 Image correction control unit (corresponding to control means)
27 Image forming unit 53 Main scanning moving unit (corresponding to driving means)
54 Sub-scanning moving part (corresponding to driving means)
505 Photosensitive drum (corresponding to image carrier)

Claims (7)

In an image forming apparatus capable of performing an image forming operation of transferring and fixing a developer image formed on an image carrier multiple times to the same recording medium,
A plurality of position detecting means for detecting the position of the recording medium on the conveyance path;
A skew amount calculating means for calculating a skew amount of the recording medium based on a detection result of the position detecting means;
Based on the detection result of the position detection unit and the skew amount calculated by the skew amount calculation unit, the transport direction of the recording medium and the length in the direction perpendicular to the transport direction are calculated, and the first Size detection means for detecting the size of the recording medium before fixing as the recording medium size of the recording medium, and the size of the recording medium after fixing as the second recording medium size,
Calculating a scaling factor of the recording medium before and after the fixing from the first and second recording medium size, possess control means for controlling the image forming operation, a based on the scaling factor,
At least two, said at positions in the diagonal direction of the recording medium, the image forming apparatus according to claim line sensor der Rukoto arranged inclined with respect to the transport direction of the plurality of position sensing means . The image forming apparatus according to claim 1, made from the position detecting means three line sensors, the two are located in the diagonal direction of the recording medium of said line sensor, the remaining one of the transport direction An image forming apparatus, wherein the image forming apparatus is disposed at a position facing one of the two line sensors in the vertical direction and detects six end portions of the recording medium. The image forming apparatus according to claim 1, wherein the position consists of detecting means and two line sensors one photosensor, the position of the diagonal direction of the two line sensors are the recording medium, wherein the photo sensor is the An image forming apparatus, wherein the image forming apparatus is arranged at a position facing one of the two line sensors in a direction perpendicular to a conveyance direction and detects five end portions of the recording medium. 2. The image forming apparatus according to claim 1, wherein the position detection unit includes first to fourth line sensors, and the first and second line sensors are located at diagonal positions of the recording medium. It is disposed at a position where the third and fourth line sensor facing the first and second line sensors respectively in a direction perpendicular to the transport direction, and characterized by detecting 8 points the end of the recording medium Image forming apparatus. 5. The image forming apparatus according to claim 1, further comprising a drive unit that moves the position detection unit.
An image forming apparatus, wherein at least one of the position detecting means is moved by a predetermined distance for each standard size of the recording medium by the driving means.   6. The image forming apparatus according to claim 1, wherein the control unit forms a second surface in a double-sided image forming operation in which an image is formed on both sides of the recording medium based on an expansion / contraction ratio of the recording medium. An image forming apparatus for controlling a second and subsequent image forming operations in a composite image forming operation for forming an image on the same surface.   The image forming apparatus according to claim 1, wherein the control unit performs control to correct a magnification of an image on which image formation is performed based on an expansion / contraction ratio of the recording medium. Image forming apparatus.

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