JP2017151376A - Image forming apparatus, image forming method, and program - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus, image forming method, and program that are able to determine a degree of contribution of the quality of a recording medium to a difference in estimation between the surface and rear thereof.SOLUTION: An image forming apparatus including; image forming means 54, end detecting means 3, 4, 5 that detect an end position of a recording medium; recording medium size detecting means 23, 24 that detect the size of the recording medium on the basis of the result of the detection of the end detecting means; and recording medium contraction/expansion degree calculating means 25 that calculates a degree of contraction/expansion of the recording medium on the basis of a change in the size of the recording medium before and after image formation, comprises: recording medium size variation calculating means that calculates differences in size between a plurality of recording mediums or recording medium contraction/expansion degree calculation means that calculates differences in a degree of contraction/expansion between the plurality of recording mediums; and surface estimation difference degree calculating means that calculates a degree of difference in estimation between the surface and the rear, assumed due to the quality of a recording medium, on the basis of at least differences in size between the recording mediums or differences in a degree of contraction/expansion between the recording mediums.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an image forming apparatus, an image forming method, and a program.

  Conventionally, an image forming apparatus that forms images on both sides of a recording medium is known.

  Patent Document 1 discloses an image forming apparatus according to the present invention, which detects the size of the recording medium before printing the front surface of the recording medium and before printing the back surface, and calculates the expansion / contraction ratio of the recording medium, There is described what corrects the magnification of an image printed on the back surface in accordance with the expansion / contraction rate. Thereby, it is said that the misregistration of the front and back where the image magnification, the image position, etc. of the image formed on the front surface and the back surface of the recording medium deviate from each other can be reduced.

  The cause of misregistration in the image forming apparatus is roughly divided into vertical and horizontal registration errors, skew errors between the recording medium and the printed image, and magnification errors due to image length expansion and contraction during image transfer to the recording medium. it can. Further, the misalignment of the front and back sides also affects the properties of the recording medium (size, amount of expansion and contraction, etc.). For example, even for recording media of the same brand, the size of the recording medium may differ slightly from lot to lot, or the size of the recording medium may change due to humidity or the like. However, conventionally, it has not been possible to determine whether the front / back misregistration of the recording medium depends on the properties of the recording medium or on factors other than the properties of the recording medium. For this reason, if the image forming apparatus is adjusted to reduce the front / back misregistration even though the front / back misregistration depends on the properties of the recording medium, useless downtime occurs in the image forming apparatus. Problem arises.

  In order to solve the above problems, the present invention provides an image forming unit that forms an image on a recording medium, an end detection unit that detects an end position of the conveyed recording medium, and a detection by the end detection unit. A recording medium size detecting unit for detecting the size of the recording medium based on the result, and an expansion / contraction amount of the recording medium based on a change in the size of the recording medium before and after image formation detected by the recording medium size detecting unit. And a recording medium expansion / contraction amount calculating means for calculating, in an image forming apparatus capable of forming an image on both sides of the recording medium by reversing the front and back of the recording medium, detected by the recording medium size detecting means in a plurality of recording media Calculated by the recording medium size variation calculating means for calculating the recording medium size variation, and the recording medium expansion / contraction amount calculating means for a plurality of recording media. Based on at least one of the recording medium expansion / contraction amount variation calculating means for calculating the recording medium expansion / contraction amount variation and at least one of the recording medium size variation and the recording medium expansion amount variation And a surface registration amount calculation means for calculating a front and back registration amount.

  As described above, according to the present invention, it is possible to obtain an excellent effect that it is possible to determine the degree of contribution of the property of the recording medium to the front / back misregistration.

FIG. 4 is a diagram for explaining a normal printing operation flow of the image forming apparatus according to the embodiment. 1 is a diagram illustrating a schematic configuration of an image forming apparatus according to an embodiment. FIG. 4 is a diagram illustrating a sheet size inspection operation flow of the image forming apparatus according to the embodiment. FIG. 3 is a schematic cross-sectional view of a paper transport device. FIG. 3 is a schematic top view of the paper transport device. Schematic of the measurement target position of a sheet. FIG. 1 is a block diagram illustrating a functional configuration of an image forming apparatus according to an embodiment. The figure which illustrates the contribution calculation method of the paper property with respect to the front and back misregistration in this embodiment. The figure which shows the output example of the start trigger sensor in this embodiment, a stop trigger sensor, and a rotary encoder.

  FIG. 2 is a diagram illustrating a schematic configuration of the image forming apparatus 101 according to the embodiment. The image forming apparatus 101 forms an image on a sheet S as a recording medium that is a sheet material, for example, by an image forming unit including a tandem image forming unit 54, an intermediate transfer belt 15, a secondary transfer device 77, and a fixing device 50. The sheet material is not limited to paper, and may be a recording medium such as an OHP sheet.

  The intermediate transfer belt 15 is provided in the vicinity of the center of the image forming apparatus 101, and is configured to be wound around a plurality of rollers and rotate clockwise in the drawing. The intermediate transfer belt 15 rotates following the roller 61 that is driven to rotate. The tandem image forming unit 54 has a plurality of developing devices 53 arranged along the conveyance direction of the intermediate transfer belt 15. An exposure device 55 is provided above the tandem image forming unit 54. Each developing device 53 of the tandem image forming unit 54 includes a photosensitive drum 71 as an image carrier that carries toner images of respective colors. A primary transfer roller 81 is provided at a primary transfer position where the toner image is transferred from the photosensitive drum 71 to the intermediate transfer belt 15 so as to face each of the photosensitive drums 71 with the intermediate transfer belt 15 interposed therebetween. Yes.

  The secondary transfer device 77 is provided on the opposite side of the intermediate transfer belt 15 from the tandem image forming unit 54 (on the downstream side in the conveyance direction of the intermediate transfer belt 15). The secondary transfer device 77 transfers the image on the intermediate transfer belt 15 to the paper S by applying the transfer electric field by pressing the secondary transfer roller 14 against the roller 62 as a secondary transfer counter roller. The secondary transfer device 77 changes the transfer current of the secondary transfer roller 14, which is a transfer condition parameter, according to the type of the paper S and the like. The fixing device 50 includes a halogen lamp 57 as a heat source, and a pressure roller 52 is pressed against a fixing belt 56 that is an endless belt. The fixing device 50 changes the temperature of the fixing belt 56 and the pressure roller 52, the nip width between the fixing belt 56 and the pressure roller 52, and the speed of the pressure roller 52, which are parameters of the fixing conditions, according to the paper S. From the secondary transfer device 77 to the fixing device 50, the transport belt 41 transports the sheet S after the image transfer.

  Further, the image forming apparatus 101 includes a paper transport device 100 as an example of a measuring unit that measures the paper size of the paper S. Then, by using the sheet conveying apparatus 100, the distance (sheet length) from the leading end to the trailing end of the sheet S in the configuration and method to be described later, one end from the other end in the width direction orthogonal to the sheet S conveying direction. Measure the distance (paper width).

  In the image forming apparatus 101, when image data is sent and an image formation start signal is received, the drive motor rotates the roller 61 to rotate the other plurality of rollers to rotate the intermediate transfer belt 15. At the same time, each developing device 53 forms a single color image on each photosensitive drum 71. Then, the single color image formed by the developing device 53 is sequentially superimposed and transferred onto the rotationally driven intermediate transfer belt 15 to form a composite color image. In addition, the sheet S is selectively rotated by one of the sheet feeding rollers 72 of the sheet feeding table 76, is fed out from one of the sheet feeding cassettes 73, is conveyed by the conveying roller 74, and is a registration roller 75 as an example of a registration unit. Stopped by being hit by. The registration roller 75 corrects the conveyance posture of the paper S, and rotates in accordance with the timing at which the composite color image on the intermediate transfer belt 15 reaches the secondary transfer device 77 to convey the paper S. The composite color image formed on the intermediate transfer belt 15 is transferred onto the surface of the paper S conveyed to the secondary transfer device 77.

  The sheet S after the image transfer is transported by the transport belt 41 and sent to the fixing device 50, where heat and pressure are applied, and the transferred image is melted and fixed. After the image is fixed on the front side, the sheet S is conveyed to the sheet reversing path 93 by the branching claw 91 and the flip roller 92 in the case of duplex printing. Thereafter, the sheet S is switched back by a branching claw, a roller pair, and the like, and conveyed to the double-sided conveyance path 94, and a composite color image is formed on the back side. When the paper S is reversed and discharged, the branching claw 91 guides the paper S to the paper reversing path 93, and the paper S is reversed from the front surface to the back surface and discharged. In the case of single-sided printing and no paper reversal, the paper S is conveyed to the paper discharge roller 95 by the branch claw 91. Thereafter, the paper S is conveyed to the decurler unit 96 by the paper discharge roller 95, and the decurler unit 96 changes the decurler amount according to the paper S. The decurler amount is adjusted by changing the pressure of the decurler roller 97, and the paper S is discharged by the decurler roller 97. The purge tray 40 is disposed below the reverse paper discharge unit.

  For example, a registration gate and a skew correction mechanism may be provided instead of the registration roller 75 as a registration mechanism for correcting the position in the conveyance direction of the paper S and the position in the width direction orthogonal to the conveyance direction. In this case, the paper transport device 100 controls the transport timing of the paper S to the secondary transfer unit between the roller 62 and the secondary transfer roller 14. Specifically, the timing between the registration mechanism and the paper transport device 100 is such that the timing at which the toner image on the intermediate transfer belt 15 reaches the secondary transfer portion matches the timing at which the paper S reaches the secondary transfer portion. The transport speed of the paper S is controlled based on the detection result of the paper detection sensor in FIG.

  Note that the image forming apparatus 101 according to the present embodiment is configured to transfer the color toner image formed on the intermediate transfer belt 15 to the paper S, but the single color toner images formed on the plurality of photosensitive drums 71 are used as the paper. A configuration in which the image is directly superimposed on S may be used. It can also be applied to a monochrome image forming apparatus.

  FIG. 1 is a diagram illustrating an example of a normal printing operation flow of the image forming apparatus 101 according to the present embodiment. FIG. 3 is a diagram illustrating an example of a sheet size inspection operation flow of the image forming apparatus 101 according to the present embodiment. The operation flow of the image forming apparatus 101 according to the present embodiment includes a normal printing operation flow and a paper size inspection operation flow. In the normal printing operation flow, the image forming apparatus 101 performs the image forming operation described above with reference to FIG. 2 and follows the general flow of the image forming apparatus 101 that discharges the paper S outside the apparatus. In the flow, the paper size is measured. For example, in FIG. 1, when paper is set in a paper feed cassette (S1) and normal single-sided printing is performed (S2), the paper is automatically conveyed to the position measuring device (S3), and the size of the first side of the paper Is measured (S4). Then, image formation is performed on the first surface of the paper (S5). Thereafter, variations in the paper size and the amount of expansion / contraction on the first surface are calculated (S13), and the paper is discharged out of the apparatus (S14). When performing normal double-sided printing (S6), the paper is automatically conveyed to the position measuring device (S7), and the size of the first surface of the paper is measured (S8). Then, image formation is performed on the first surface of the sheet (S9). After that, the paper with the front and back reversed is automatically conveyed again to the position measuring device (S10), and the size of the second surface of the paper is measured (S11). Then, image formation is performed on the second side of the sheet (S12). Thereafter, variations in the paper size and expansion / contraction amount of each side are calculated (S13), and the paper is discharged out of the apparatus (S14).

  In the paper size inspection operation flow, the normal printing operation flow and the operation of the image forming apparatus 101 are different, and image formation is not performed on the front surface, which is the first surface of the paper S, and the back surface, which is the second surface. For example, in FIG. 3, the paper is set in the paper feed cassette (S1), and in the initial paper size inspection mode (S2), the paper is automatically conveyed to the position measuring device (S3), and the size of the first surface of the paper is measured. (S4). Then, the paper size variation is calculated (S10), and the paper is discharged out of the apparatus (S11). In the sheet expansion / contraction amount measurement mode (S5), the sheet is automatically conveyed to the position measuring device (S6), and the size of the first surface of the sheet is measured (S7). Thereafter, the paper whose front and back are reversed is automatically conveyed again to the position measuring device (S8), and the size of the second surface of the paper is measured (S9). Then, the variation of the expansion / contraction amount of the paper is calculated (S10), and the paper is discharged out of the apparatus (S11).

  In the initial paper size inspection mode, the fixing device 50 may not be heated. In both the normal printing operation flow and the paper size inspection operation flow, the position measuring device measures the position of the paper edge and calculates the paper size. The position measuring device refers to a sheet conveying device 100 as an example of a measuring unit that measures the size of the sheet S in FIG. The image forming apparatus 101 according to the present embodiment has a function capable of arbitrarily determining the number of sheets S to be automatically conveyed in the sheet size inspection operation flow. For example, ten sheets S are continuously passed. Execute the paper size inspection operation flow.

  The image forming apparatus 101 has a function of calculating the sheet expansion / contraction amount of the sheet S due to fixing heating in normal double-sided printing in the normal printing operation flow. Thus, for example, the writing image size is enlarged or reduced so as to cancel out the average expansion / contraction amount with respect to the front surface image and the back surface image of the succeeding paper S, and it is automatically controlled to the ideal image position. Is possible. Note that, regarding the correction for calculating the amount of expansion and contraction and canceling out the amount, if the paper transport device S shown in FIG. It is also possible to apply corrections in real time.

  Next, the configuration of the sheet conveying apparatus 100 included in the image forming apparatus 101 will be described with reference to FIGS. 4, 5, and 6. FIG. 4 is a schematic cross-sectional view of the paper transport apparatus 100. FIG. 5 is a schematic top view of the sheet conveying apparatus 100. FIG. 6 is a schematic view of the measurement target position of the paper. FIG. 7 is a schematic view of the position of the sheet conveying apparatus 100.

  The paper transport apparatus 100 transports the paper S and measures the transport distance and the width direction position of the paper S. The sheet conveying apparatus 100 is provided immediately upstream of the secondary transfer apparatus 77 as an image forming unit that transfers an image onto the sheet S in the conveying path of the sheet S. The sheet conveying apparatus 100 includes a driving roller 12 that is rotated by receiving a driving force of a driving unit (for example, a motor), and a driven roller 11 that is driven to rotate while sandwiching the sheet S between the driving roller 12. A registration roller 75 is provided on the upstream side of the driven roller 11 and the driving roller 12 in the sheet conveying direction. A roller 62 facing the secondary transfer roller 14 via the secondary transfer roller 14 and the intermediate transfer belt 15 is provided on the downstream side of the driven roller 11 and the driving roller 12 in the sheet conveying direction.

  As shown in FIG. 5, the length Wr of the driven roller 11 in the width direction orthogonal to the transport direction of the paper S is configured to be smaller than the minimum width Ws of the paper S corresponding to the paper transport device 100. Therefore, the driven roller 11 does not come into contact with the driving roller 12 when the paper S is conveyed, and therefore the driven roller 11 is driven to rotate only by friction generated between the driven roller 11 and the paper S. Therefore, when the paper S is transported, the driven roller 11 can measure the distance (paper length) from one end to the other end in the transport direction of the paper S more accurately by the method described later without being affected by the driving roller 12. It becomes possible to do.

  As shown in FIGS. 4 and 5, a rotary encoder 18 is provided on the rotation shaft of the driven roller 11 of the paper transport apparatus 100. The pulse measuring means 21 as the transport amount measuring means detects the slit formed in the rotating encoder disk 18a and counts the pulse signal generated by the encoder sensor 18b, whereby the driven roller 11 is used as the transport amount of the paper S. Measure the amount of rotation.

  In this embodiment, the rotary encoder 18 is provided on the rotating shaft of the driven roller 11, but it can also be provided on the rotating shaft of the driving roller 12. Note that the smaller the diameter of the roller to which the rotary encoder 18 is attached, the more the number of pulses to be counted as the number of rotations associated with the sheet conveyance increases, and the more the number of pulses to be counted increases. . In addition, the driven roller 11 or the driving roller 12 to which the rotary encoder 18 is attached is preferably composed of a metal roller in order to ensure axial deflection accuracy. By suppressing the rotation of the rotating shaft, it becomes possible to measure the transport distance of the paper S described later with high accuracy.

  In the vicinity of the downstream side of the driven roller 11 and the driving roller 12 in the transport direction of the paper S, a start trigger sensor 3 is disposed as a downstream detection unit that detects the leading edge of the paper S. Further, a stop trigger sensor 4 as an upstream detection unit that detects passage of the trailing end of the sheet S is disposed in the vicinity of the upstream side in the transport direction of the sheet S of the driven roller 11 and the driving roller 12. Note that the start trigger sensor 3 and the stop trigger sensor 4 can also detect the passage of the edge of the image formed on the paper S. As the start trigger sensor 3 and the stop trigger sensor 4, for example, a transmissive optical sensor or a reflective optical sensor with high detection accuracy of the paper edge can be used. In the present embodiment, a reflective optical sensor is used.

  As shown in FIG. 5, the start trigger sensors 3a and 3b and the stop trigger sensors 4a and 4b are provided at substantially the same position in the width direction orthogonal to the transport direction of the sheet S and at positions separated by Tw in the width direction. ing. By providing in this way, the size of the paper S can be measured by the calculation formula described later, and the transport distance of the paper S can be measured, and the paper lengths La and Lb shown in FIG. 6 can be calculated. Become. By setting the average value of the paper lengths La and Lb as the paper length, when the shape of the paper S is not rectangular, it is possible to calculate the paper length of the paper S with less error on average. The start trigger sensor 3 and the stop trigger sensor 4 are not limited to two sets, and may be one set or three or more sets.

  In the present embodiment, the two start trigger sensors 3a, 3b and stop trigger sensors 4a, 4b are arranged symmetrically from the center position in the width direction orthogonal to the transport direction of the paper S. If it is within the region through which the paper S passes, the paper S can be shifted from the central position in any direction in the width direction. Further, the sheet conveying apparatus 100 includes a line sensor 5 such as a contact image sensor (CIS) on the upstream side of the registration roller 75 in the conveying direction of the sheet S. As shown in FIG. 5, the line sensor 5 includes two line sensors 5 a and 5 b that detect both ends of the sheet S in the width direction.

  The sheet conveying apparatus 100 measures the sheet widths Wl and Wb shown in FIG. 6 based on both ends in the width direction of the sheet S detected by the line sensor 5. It is desirable for the line sensor 5 to keep the distance from the opposing parts within a certain range. This is because the accuracy of detection of the sheet S by the line sensor 5 may be reduced if the sheet S greatly fluctuates during sheet conveyance. In order to suppress fluttering of the paper S, a part for controlling the transport position of the paper S may be provided before and after the line sensor 5 in the paper transport direction.

  A distance A shown in FIG. 5 is a distance between the start trigger sensor 3 and the driven roller 11 and the driving roller 12 in the conveyance path of the sheet S, and a distance B is a distance between the stop trigger sensor 4, the driven roller 11 and the driving roller 12. Is the distance between. The distances A and B are preferably made as small as possible because the pulse count range described later becomes large.

  The driving roller 12 is rotated in the direction of the arrow shown in FIG. 4, and the driven roller 11 is driven and rotated by the driving roller 12 when the paper S is not conveyed (during idling) and the paper S is conveyed. Is driven to rotate by the paper S. When the driven roller 11 rotates, a pulse is generated from the rotary encoder 18 provided on the rotating shaft. The pulse measuring means 21 connected to the rotary encoder 18 starts the pulse counting of the rotary encoder 18 when the start trigger sensor 3 detects that the paper S has been conveyed in the direction of the arrow in the figure and the leading edge has passed. When the stop trigger sensor 4 detects that the trailing edge of the paper S has passed, the pulse counting is finished. Calculation of the pulse count by the start trigger sensors 3a and 3b and the stop trigger sensors 4a and 4b will be described with reference to FIG.

  As shown in FIG. 7, the sheet conveying apparatus 100 has a photosensitive element in which the distance Ds between the start trigger sensor 3 and the secondary transfer apparatus 77 is the most upstream in the rotation direction of the intermediate transfer belt in the conveying path of the sheet S. The electrostatic latent image and toner image moving distance Dt from the position P1 where the electrostatic latent image is formed on the body drum 71 by the exposure device 55 to the position P2 where the toner image is transferred to the paper S by the secondary transfer device 77 It is preferable to configure so as to be less than. Further, it is preferable that the sheet conveying apparatus 100 is provided immediately upstream of the secondary transfer apparatus 77 as an image forming unit for the sheet S in the conveyance path of the sheet S and as close as possible to the secondary transfer apparatus 77.

  FIG. 8 is a block diagram illustrating a functional configuration of the image forming apparatus 101 according to this embodiment. As illustrated in FIG. 8, the image forming apparatus 101 includes a start trigger sensor 3, a stop trigger sensor 4, a line sensor 5, a rotary encoder 18, a control unit 20, and a storage unit 31. The control unit 20 includes, for example, a CPU, and includes a pulse counting unit 21, a transport distance calculating unit 22, a sheet length calculating unit 23, a sheet width calculating unit 24 at a sheet end, a sheet expansion / contraction amount calculating unit 25, and image data correction. Means 26 are provided.

  The control unit 20 is an arithmetic device that controls the operation of the image forming apparatus 101 by reading a program and data from the storage unit 31 and executing processing. The pulse counting means 21 counts a pulse signal generated from the encoder sensor 18b by the rotation of the encoder disk 18a of the rotary encoder 18 provided on the driven roller 11, and rotates the driven roller 11 as the transport amount of the paper S. Measure the amount. The transport distance calculating unit 22 calculates the transport distance of the paper S based on the detection result of the paper S by the start trigger sensor 3 and the stop trigger sensor 4 and the rotation amount of the driven roller 11 measured by the pulse counting unit 21. To do.

  The paper length calculator 23 calculates the paper length of the paper S to be transported based on the transport distance calculator 22. The paper width calculation unit 24 calculates the paper width of the conveyed paper S based on the detection result of the line sensor 5. The sheet expansion / contraction amount calculation unit 25 is based on the sheet length and sheet width of the sheet S calculated by the sheet length calculation unit 23 and the sheet width calculation unit 24, and is used for the second surface transfer during the first surface transfer of the sheet S. The difference in paper size with respect to is calculated. The image data correction unit 26 corrects the image data based on the paper expansion / contraction amount obtained by the paper expansion / contraction amount calculation unit 25. The storage unit 31 is, for example, an HDD or ROM as a nonvolatile storage device that stores programs and data, and a volatile RAM that temporarily stores programs and data. Then, the paper size and paper expansion / contraction amount data obtained by the paper length calculation unit 23, the paper width calculation unit 24, and the paper expansion / contraction amount calculation unit 25 are accumulated.

  FIG. 9 is a diagram exemplifying a method for calculating the contribution degree of the sheet property to the front / back misregistration in this embodiment. It is assumed that the images are arranged at the four corners of the paper S. Hereinafter, the sheet S is described as a sheet, but is not limited to the sheet.

  With respect to the front / back misregistration, the contribution of the paper property is calculated on the premise that the detection of the image positional deviation and the real-time correction of the deviation are not performed. It is assumed that the paper size is calculated as follows by a paper size calculation method described later.

-First side paper length = L ₁
-First side paper width = W ₁
-Second side paper length = L ₂
-Second side paper width = W ₂

Assume general double-sided printing in which the paper is reversed so that the front end direction of the paper is reversed between the first side and the second side during image formation. When the number of sheets used for calculating the degree of contribution of the sheet property to the front / back misregistration is i, the measured variation L ₁ of the length _L1 of the first-side sheet length can be expressed by Expression 1.

If the L ₁ is uneven, for inverting the sheet to duplex printing, the image writing start position of the second surface varies with respect to the image position in the transport direction rear end side of the first surface. Thus, front and back misregistration amount _D lu conveyance direction shown in FIG. _9, can represent the contribution _{CR L1} of the sheet properties _{L 1} for _{D ru} several 2.

On the other hand, with respect to the variation of the first surface sheet width W _1, by fixing the image write reference of the first surface and a second surface in the same place (for example, left or right end, the paper center of paper), front and back misregistration Can be made to not affect.

Then, the amount of expansion or contraction of the sheet length and C _{d =} L ₁ -L _2, with respect to expansion amount C _d of the calculated sheet length, it is possible to calculate the amount of expansion and contraction variation VC _d using equation 3.

If there are variations in expansion amount C _d of paper length, the image position in the transport direction rear end side of the second surface is varied with respect to the paper leading edge of the first surface. That is, the image position on the rear end side in the transport direction of the second surface is deviated from the image writing position of the first surface. Therefore, the degree of contribution CR _Cd of the paper property C _d to the front and back misregistration amounts D _ld and D _{rd in the} transport direction shown in FIG.

On the other hand, when the expansion / contraction amount of the paper width is C _w = W ₁ −W ₂ , the contribution can be calculated in the same manner as the expansion / contraction amount C _d of the paper length, but the calculation method differs depending on the image writing reference. When the image writing reference is the left end of the sheet, the contribution _{CRC Cw} can be estimated by _Equation 5.

If the image writing reference is the right edge of the sheet, the contribution _{CRC Cw} can be calculated in the same manner using _Equation 5 if the subscript “r” in Equation 5 is “l”.

When the image writing reference is centered on the paper, the contribution _{CRC Cw} can be estimated by _Equation 6.

  From the above, it is possible to estimate the contribution of the initial paper size and paper expansion / contraction amount, which are paper properties, to the front / back misregistration, and it is possible to determine whether the main cause of the front misregistration is the paper properties. Become. For example, depending on the allowable amount of misregistration required by the user, when the allowable amount is within 0.5 [mm], the contribution degree is 50 [%] or more and the length conversion is 0.25 [mm] or more. Sometimes, it is determined that the main cause of the misregistration of the surface is the paper properties. It is also possible to store the size data of various brands obtained by the above formulas. For this reason, an image forming apparatus which uses a recommended appropriate brand of paper S having a property with relatively little misregistration (for example, less than 50 [%] contribution or less than 0.25 [mm] in terms of length). It is also possible to present it on a display unit of an operation panel provided in.

  Next, a trial calculation example of the contribution degree of the paper property to the front / back misregistration will be described. Table 1 shows the measurement results of the sheet length of 10 sheets.

The measured variation V _L1 of the first side paper length L1 is calculated as shown in Equation 7.

When the front and back registration in the transport direction displacement amount _D lu = 1.00 [mm] shown in FIG. _9, it is possible to calculate the contribution _{CR L1} of the sheet properties _{L 1} for _{D lu} as Expression 8.

Next, the variation V _cd of the sheet length expansion / contraction amount C _d is calculated as shown in Equation 9.

Assuming that the front / back registration misalignment amount D _ld = 0.75 [mm] in the transport direction shown in FIG. 9, the degree of contribution CR _Cd of the paper property C _d to D _ld can be calculated as shown in Equation 10.

As described above, it is possible to calculate the degree of paper property contribution to the surface misregistration. Actually, the front and back misregistration amount of such front and back misregistration amount D _lu and front and back misregistration amount D _ld, for example, by using a start trigger sensor 3 and the stop trigger sensor 4, detecting an image edge position on the sheet S You may make it measure by doing. Further, the actual front / back misregistration amount may be measured by the user from the sheet S after image formation. Then, for example, the front and back misregistration amount measured by the user from the sheet S after image formation is input from an operation panel provided in the image forming apparatus, a computer that can communicate with the image forming apparatus, or the like. It is sufficient to calculate the degree of contribution of the paper property to the front / back misregistration. Further, the calculated degree of contribution of the sheet property to the front / back misregistration may be displayed on a display unit such as an operation panel provided in the image forming apparatus or a computer capable of communicating with the image forming apparatus.

  Next, a paper size calculation method for the paper S in the image forming apparatus 101 will be described. FIG. 10 shows an output example of the start trigger sensor 3, the stop trigger sensor 4, and the rotary encoder 18 in the present embodiment. As described above, when the driven roller 11 rotates, a pulse signal is generated from the rotary encoder 18 provided on the rotation shaft of the driven roller 11. In the example shown in FIG. 10, after the conveyance of the paper S is started, the start trigger sensor 3b detects passage of the leading edge of the paper S at time t1, and the start trigger sensor 3a detects passage of the leading edge of the paper S at time t2. doing.

  Subsequently, the stop trigger sensor 4a detects passage of the trailing edge of the sheet S at time t3, and the stop trigger sensor 4b detects passage of the trailing edge of the sheet S at time t4. At this time, the start trigger sensor 3b detects the passage of the leading edge of the paper S at time t1, and the pulse counting means at the pulse cant time until the stop trigger sensor 4b detects the passage of the rear short part of the paper S at time t4. 21 counts the number of pulses n1 of the rotary encoder 18. At time t2, the start trigger sensor 3a detects passage of the leading edge of the sheet S, and at time t3, the pulse counting means 21 rotates at a pulse counting time until the stop trigger sensor 4a detects passage of the trailing edge of the sheet S. The number of pulses n2 of the encoder 18 is counted.

The radius of the driven roller 11 to the rotary encoder 18 is provided as r, the number of encoder pulses one rotation of the driven roller 11 N, the number of pulses counted in the pulse count time n _x. At this time, the transport distance L _dx of the paper S between the time t _i and the time t _j can be obtained by the following equation (11).

In general, the paper conveyance speed depends on the mechanical accuracy such as the external accuracy of the roller (particularly the driving roller 12) that conveys the paper S, the core flutter accuracy, the rotational accuracy of the motor, and the accuracy of the power transmission mechanism such as the gear and belt. fluctuate. Further, it fluctuates due to a slip phenomenon between the driving roller 12 and the paper S, a slack phenomenon due to a difference in paper transport force or paper transport speed of the upstream and downstream transport means, and the like. Therefore, the pulse period and pulse width of the rotary encoder 18 always fluctuate, but the number of pulses does not change. Accordingly, the transport distance calculating means 22 provided in the paper transport apparatus 100 can transport the paper S by the driven roller 11 and the driving roller 12 as the paper transport means L _dx without depending on the paper transport speed according to the above equation (11). Can be obtained with high accuracy.

Based on the calculation result of the transport distance calculation means 22, the length L _s of the paper S can be obtained from the distance A and the distance B shown in FIG.

  On the other hand, the width W of the paper S can be accurately obtained by, for example, the following two methods. The first is to cover the line sensors 5 a and 5 b with a single line sensor 5. In this case, the difference between the paper edge detection positions (pixel positions at which the paper edge is detected) is the width of the paper S. The second is a method of calibrating the calculation result of the sheet edge between the two line sensors 5a and 5b with a jig having an accurate size. As a result, the width of the paper S can be accurately obtained from the calculation result of the paper edge regardless of the attachment accuracy of the line sensors 5a and 5b. In addition, as shown in FIG. 10, when measuring the size of several places using several sensors, it is desirable to make each average value paper size.

<Image magnification shift correction method based on paper expansion / contraction amount>
The sheet expansion / contraction amount calculation means 25 obtains the expansion / contraction rate R in the sheet length direction by the following equation 13 from the relative ratio of the sheet conveyance distances between both ends of the front and back surfaces obtained by the conveyance distance calculation means 22, for example. Can do.

  Since the image on the first surface is also expected to shrink at the same magnification as the paper expands and contracts, the value obtained by the paper expansion / contraction amount calculation means 25 is estimated as the relative ratio of the front and back lengths of the printed image. .

Here, an example calculated in the present embodiment will be described below. In this embodiment, N = 2800 [/ r], r = 9 [mm], and the sheet S when the number of pulses counted on the surface when an A3 size sheet is conveyed vertically is n1a = 17716. The transport distance Ld _1a is 357.79 [mm] from Equation 14.

Further, when the number of pulses counted again at the time of transporting the back surface of the paper S is n _1b = 17698, the transport distance Ld _1b of the paper S is 357.42 [mm] from Equation 15.

Therefore, the paper length difference (paper expansion / contraction amount) ΔLd ₁ during the first surface transfer with respect to the second surface transfer of the paper S is −0.37 [mm] from Equation 16.

  As the sheet expands and contracts, the image on the first side is also contracted at the same magnification. Therefore, based on the value obtained by the sheet expansion / contraction amount calculation means 25, the sheet length direction expansion / contraction ratio Lr (the estimated front and back of the print image) The relative ratio of the length can be obtained as 99.90 [%] using Equation 17.

  Accordingly, in this case, the length in the transport direction of the print image is about 0.1 [%], and there is a difference between the front and back. For example, when the reference image length is 400 [mm], the length is about 0.4 [mm]. Front / back registration misalignment (image position misalignment) occurs. Therefore, the image data correction unit 26 can improve the front / back registration accuracy by correcting the image length to be printed on the back surface of the paper S based on the estimated front / back image magnification deviation Lr.

Further, the sheet expansion / contraction amount calculating unit 25 calculates, for example, an average width from the measurement results of the first and second surfaces of the widths W ₁ and W _b of the sheet S shown in FIG. 6 calculated by the sheet width calculating unit 24. The paper expansion / contraction rate Wr in the direction is calculated. Then, the image data correction unit 26 corrects the image width to be printed on the back surface of the paper S based on the paper width direction expansion / contraction rate Wr of the paper S calculated by the paper expansion / contraction amount calculation unit 25.

In the above example, the sheet expansion / contraction amount calculation unit 25 calculates the conveyance distances L _1b and L _2b of the sheet S on the front and back surfaces to obtain the sheet length direction expansion / contraction ratio L _r. The ratio of the pulse numbers n _2a and n _2b counted during the conveyance of the sheet on the back side may be obtained as the sheet length direction expansion / contraction rate Lr.

For example, in the above example, when the number of pulses n _2a = 17716 counted during the conveyance of the front sheet S and the number of pulses n _2b = 17698 counted during the conveyance of the front sheet S, the sheet length direction expansion / contraction rate L _r Can be obtained as shown in Equation 18 below.

  The function of the image forming apparatus according to the above embodiment is to execute each processing procedure described above on a computer as a program coded in a programming language suitable for the image forming apparatus according to the above embodiment. Can be realized. Therefore, a program for realizing the image forming apparatus according to the above embodiment can be stored in a computer-readable storage medium.

  Therefore, the program according to each of the above embodiments can be installed in the image forming apparatus from these recording media by being stored in a storage medium such as a floppy (registered trademark) disk, CD, or DVD. Further, by providing the image forming apparatus with a network I / F, the program according to the above embodiment can be downloaded and installed via a telecommunication line such as the Internet.

What was demonstrated above is an example, and there exists an effect peculiar for every following aspect.
(Aspect A)
An image forming unit such as a tandem image forming unit 54 that forms an image on a recording medium such as the paper S, an end detection unit such as sensors 3, 4, and 5 that detect the end position of the conveyed recording medium; Recording medium size detecting means such as paper length calculating means 23 and paper width calculating means 24 for detecting the size of the recording medium based on the detection result of the edge detecting means, and an image detected by the recording medium size detecting means Recording medium expansion / contraction amount calculation means such as a paper expansion / contraction amount calculation means 25 for calculating the expansion / contraction amount of the recording medium based on a change in the size of the recording medium before and after the formation, In an image forming apparatus such as the image forming apparatus 101 capable of forming an image on both sides of a recording medium, the recording medium size detected by the recording medium size detecting unit in a plurality of recording media. Recording medium size variation calculating means such as the control means 20 for calculating the variation of the recording medium and recording means such as the controlling means 20 for calculating the variation of the recording medium expansion / contraction amount calculated by the recording medium expansion / contraction amount calculating means in a plurality of recording media. Control for calculating a front / back misregistration amount that is assumed depending on the properties of the recording medium, based on at least one of the medium expansion / contraction amount variation calculating means and at least one of the recording medium size variation and the recording medium expansion / contraction amount variation. Surface registration amount calculation means such as means 20.
The inventor of the present application has found that even when recording media of the same brand are used, the larger the variation in the size of the recording medium and the variation in the amount of expansion / contraction of the recording medium, the greater the misregistration between the front and the back. Then, by estimating the amount of misregistration due to the characteristics of the recording medium from the variation in the size of the recording medium and the amount of expansion / contraction of the recording medium, how much the property of the recording medium contributes when the misregistration occurs. It was found that it was possible to judge whether
In (Aspect A), the front and back misregistration amount assumed by the properties of the recording medium is calculated by the surface registration misregistration amount calculation means based on at least one of the recording medium size variation and the recording medium expansion / contraction variation. . Then, by comparing the assumed front / back registration deviation amount calculated by the surface registration deviation amount calculation unit with the actually generated front / back registration deviation amount, the property of the recording medium with respect to the front / back registration deviation is determined. It becomes possible to judge whether it contributes to a certain extent.
(Aspect B)
In (Aspect A), the contribution degree of the control means 20 or the like that calculates the contribution degree of the properties of the recording medium to the actual front / back registration deviation amount based on the front / back registration deviation amount calculated by the front / back registration amount calculation means. It has a calculation means. According to this, as described in the above embodiment, it is possible to determine the degree of contribution of the property of the recording medium to the front / back misregistration.
(Aspect C)
Image forming means for forming an image on a recording medium, end detection means for detecting end positions at a plurality of positions on each side of the conveyed recording medium, and the recording medium based on the detection result of the end detection means Recording medium size detecting means for detecting the size of the recording medium, and recording medium expansion / contraction amount calculation for calculating the expansion / contraction amount of the recording medium based on a change in size of the recording medium before and after image formation detected by the recording medium size detection means And a recording medium size variation detected by the recording medium size detection means in a plurality of recording media in an image forming apparatus capable of forming images on both sides of the recording medium by inverting the recording medium. Variation of the recording medium expansion amount calculated by the recording medium expansion amount calculation means for the plurality of recording media The degree of contribution for calculating the contribution degree of the property of the recording medium to the front / back registration deviation based on at least one of the recording medium size variation and the recording medium expansion amount variation It has a calculation means. According to this, as described in the above embodiment, it is possible to determine the contribution of the property of the recording medium to the front / back misregistration.
(Aspect D)
In any one of (Aspect A) to (Aspect C), an image such as an image data correction unit 26 that corrects an image magnification shift accompanying expansion / contraction based on the expansion / contraction amount of the recording medium calculated by the recording medium expansion / contraction amount calculation unit. Magnification deviation correction means is provided. According to this, as described in the above embodiment, it is possible to suppress an image magnification shift.
(Aspect E)
In (Aspect D), the image magnification deviation correction unit is configured to form an image on the recording medium based on an image magnification deviation of the recording medium conveyed before the image formation on the recording medium is started based on the image data. The image data used is corrected. According to this, as described in the above embodiment, it is possible to improve the front and back registration accuracy.
(Aspect F)
In any one of (Aspect A) to (Aspect E), the paper length calculation unit 23 calculates the distance between the downstream end in the recording medium conveyance direction and the upstream end in the recording medium conveyance direction, which is detected by the edge detection unit. A sheet width calculating unit 24 for calculating a distance between both ends in the recording medium width direction orthogonal to the recording medium conveying direction detected by the recording medium conveying direction length calculating unit, and the like. Recording medium width calculation means, wherein the recording medium size detection means is based on the calculation result of the recording medium conveyance direction length calculation means and the calculation result of the recording medium width calculation means. Detect the size of. According to this, as described in the above embodiment, the recording medium transport direction length and the recording medium width can be detected as the size of the recording medium.
(Aspect G)
In (Aspect F), the recording medium expansion / contraction amount calculation unit uses the calculation result of the recording medium conveyance direction length calculation unit and the calculation result of the recording medium width calculation unit to calculate the recording medium conveyance direction of the recording medium and The amount of expansion / contraction in each recording medium width direction is calculated. According to this, as described in the above embodiment, the expansion and contraction amounts of the recording medium in the recording medium conveyance direction and the recording medium width direction can be calculated.
(Aspect H)
In any one of (Aspect A) to (Aspect G), the image forming unit is formed based on an image carrier such as a photosensitive drum 71 that rotates with a latent image formed on the surface, and the latent image. And a transfer means such as a secondary transfer device 77 for transferring the toner image to the recording medium, and the end detection means has a distance between the transfer means in the conveyance path of the recording medium and the image carrier. It is preferably provided at a position that is less than the moving distance of the latent image and the toner image from the position where the latent image is formed on the body to the position where the toner image is transferred to the recording medium by the transfer means.
(Aspect I)
In any one of (Aspect A) to (Aspect H), there is a registration unit such as a registration roller 75 that corrects the conveyance posture of the recording medium and conveys the recording medium in accordance with the image formation timing of the image forming unit. The recording medium size detecting means has recording medium transport distance measuring means such as a pulse measuring means 21 for measuring the transport distance of the recording medium, and the recording medium transport distance measuring means is provided in the recording medium transport path. Preferably, it is provided between the image forming means and the resist means.
(Aspect J)
In (Aspect A) to (Aspect I), a recording medium conveying unit such as a driven roller 11 and a driving roller 12 that conveys a recording medium, a pulse measuring unit 21 that measures a conveyance distance of the recording medium by the recording medium conveying unit, and the like The end detection means includes downstream detection means such as a start trigger sensor 3 for detecting the leading edge of the recording medium on the downstream side of the recording medium conveyance direction in the recording medium conveyance direction. And upstream detection means such as a stop trigger sensor 4 for detecting the trailing edge of the recording medium on the upstream side in the recording medium conveyance direction of the recording medium conveyance means, and the conveyance amount measuring means and the downstream detection Recording medium transport distance calculating means such as transport distance calculating means 22 for calculating the transport distance of the recording medium based on the detection results of the recording medium and the upstream detection means, and the recording medium transport distance Based on the calculation result of the detecting means, having a recording medium length calculation means such as a sheet length calculation unit 23 for calculating a recording medium length in the recording medium conveying direction. According to this, as described in the above embodiment, the recording medium length in the transport direction can be calculated.
(Aspect K)
In (Aspect A) to (Aspect J), the recording medium conveying means includes a driven roller 11 that is driven and rotated by nipping and conveying the recording medium between a driving roller such as a driving roller 12 that is rotationally driven and the driving roller. And a driven roller. According to this, as described in the above embodiment, it is possible to more accurately measure the distance (recording medium length) from one end of the recording medium in the conveyance direction to the other end.
(Aspect L)
An image forming step of forming an image on a recording medium by an image forming unit; an end detecting step of detecting end positions of a plurality of portions on each side of the conveyed recording medium by an end detecting unit; and the end detecting unit A recording medium size detecting step of detecting the size of the recording medium based on the detection result of the recording medium, and a change of the recording medium size before and after image formation detected by the recording medium size detecting unit, And a recording medium expansion / contraction amount calculating step for calculating the expansion / contraction amount of the recording medium by a recording medium expansion / contraction amount calculating unit. In the forming method, the variation in the recording medium size detected by the recording medium size detecting means in a plurality of recording media is calculated as the recording medium size variation calculation. Recording medium size variation calculation step calculated by the means, and recording medium expansion / contraction amount calculation means for calculating a recording medium expansion / contraction amount variation calculated by the recording medium expansion / contraction amount calculation means in a plurality of recording media. Based on at least one of the variation calculation step and at least one of the variation in the recording medium size and the variation in the recording medium expansion / contraction amount, the front / back registration deviation amount assumed by the properties of the recording medium is calculated. And a contribution degree calculating step of calculating a contribution degree of the property of the recording medium to the front and back registration deviation by the contribution degree calculating means. According to this, as described in the above embodiment, it is possible to determine the degree of contribution of the properties of the recording medium to the front / back misregistration.
(Aspect M)
A program for causing an image forming apparatus to execute the image forming method described in (Aspect L) can be provided.

2 Recording medium measuring end 3 Start trigger sensor 3a Start trigger sensor 3b Start trigger sensor 4 Stop trigger sensor 4a Stop trigger sensor 4b Stop trigger sensor 5a Line sensor 5b Line sensor 11 Drive roller 12 Drive roller 14 Secondary transfer roller 15 Intermediate transfer belt DESCRIPTION OF SYMBOLS 18 Rotary encoder 18a Encoder disk 18b Encoder sensor 20 Control means 21 Pulse counting means 22 Conveyance distance calculation means 23 Paper length calculation means 24 Paper width calculation means 25 Paper expansion / contraction amount calculation means 26 Image data correction means 31 Storage means 40 Purge tray 41 Conveyance belt DESCRIPTION OF SYMBOLS 50 Fixing device 52 Pressure roller 53 Developing device 54 Tandem image forming part 55 Exposure device 56 Fixing belt 57 Halogen lamp 61 Roller 62 Roller 71 Photosensitive drum 72 Paper feed roller 73 Paper feed cassette 74 Transport roller 75 Registration roller 76 Paper feed table 77 Secondary transfer device 81 Primary transfer roller 91 Branch claw 92 Flip roller 93 Paper reversing path 94 Double-sided transport path 95 Paper discharge roller 96 Curler unit 97 Decurler roller 100 Paper transport device 101 Image forming device

JP 2014-079777 A

Claims (13)

Image forming means for forming an image on a recording medium;
End detection means for detecting the end position of the recording medium being conveyed;
A recording medium size detecting means for detecting the size of the recording medium based on a detection result of the edge detecting means;
A recording medium expansion / contraction amount calculating means for calculating an expansion / contraction amount of the recording medium based on a change in size of the recording medium before and after image formation detected by the recording medium size detection means;
In an image forming apparatus capable of forming images on both sides of the recording medium by inverting the front and back of the recording medium,
Recording medium size variation calculating means for calculating the recording medium size variation detected by the recording medium size detecting means in a plurality of recording media, and recording calculated by the recording medium expansion / contraction amount calculating means in the plurality of recording media. At least one of the recording medium expansion / contraction amount variation calculating means for calculating the variation of the medium expansion / contraction amount;
Characterized in that it has a surface registration deviation amount calculating means for calculating a front / back registration deviation amount assumed depending on the properties of the recording medium based on at least one of the recording medium size variation and the recording medium expansion / contraction amount variation. Image forming apparatus. The image forming apparatus according to claim 1.
Image formation comprising: contribution calculation means for calculating the contribution degree of the properties of the recording medium to the actual front / back registration deviation amount based on the front / back registration deviation amount calculated by the front / back registration deviation calculation means apparatus. Image forming means for forming an image on a recording medium;
End detection means for detecting the end position of the recording medium being conveyed;
A recording medium size detecting means for detecting the size of the recording medium based on a detection result of the edge detecting means;
A recording medium expansion / contraction amount calculating means for calculating an expansion / contraction amount of the recording medium based on a change in size of the recording medium before and after image formation detected by the recording medium size detection means;
In an image forming apparatus capable of forming images on both sides of the recording medium by inverting the front and back of the recording medium,
Recording medium size variation calculating means for calculating the recording medium size variation detected by the recording medium size detecting means in a plurality of recording media;
A recording medium expansion / contraction amount variation calculating means for calculating a variation in the recording medium expansion / contraction amount calculated by the recording medium expansion / contraction amount calculating means in a plurality of recording media;
An image forming apparatus comprising: a contribution degree calculating unit that calculates a contribution degree of a property of the recording medium to the front / back misregistration based on at least one of the recording medium size variation and the recording medium expansion / contraction amount variation. . The image forming apparatus according to any one of claims 1 to 3,
An image forming apparatus, comprising: an image magnification shift correcting unit that corrects an image magnification shift accompanying expansion / contraction based on the expansion / contraction amount of the recording medium calculated by the recording medium expansion / contraction amount calculation unit. The image forming apparatus according to claim 4.
The image magnification shift correcting unit corrects image data used for image formation on the recording medium based on the image magnification shift of the recording medium conveyed before the image formation on the recording medium is started based on the image data. An image forming apparatus. The image forming apparatus according to any one of claims 1 to 5,
A recording medium transport direction length calculating means for calculating a distance between the downstream end in the recording medium transport direction and the upstream end in the recording medium transport direction detected by the end detection means;
Recording medium width calculating means for calculating a distance between both ends of the recording medium width direction, which is detected by the recording medium edge detection means, perpendicular to the recording medium conveyance direction,
The recording medium size detecting unit detects the size of the recording medium based on a calculation result of the recording medium conveyance direction length calculation unit and a calculation result of the recording medium width calculation unit. . The image forming apparatus according to claim 6.
The recording medium expansion / contraction amount calculation means uses the calculation result of the recording medium conveyance direction length calculation means and the calculation result of the recording medium width calculation means, respectively for the recording medium conveyance direction and the recording medium width direction of the recording medium. An image forming apparatus that calculates an expansion / contraction amount. The image forming apparatus according to claim 1,
The image forming unit includes an image carrier that rotates with a latent image formed on a surface thereof, and a transfer unit that transfers a toner image formed based on the latent image to a recording medium.
The edge detection unit is configured such that the toner image is transferred to the recording medium by the transfer unit from the position where the latent image is formed on the image carrier, so that the distance between the end detection unit and the transfer unit in the conveyance path of the recording medium. An image forming apparatus, wherein the image forming apparatus is provided at a position that is less than a moving distance of the latent image and the toner image to a certain position. The image forming apparatus according to claim 1,
A registration unit that corrects the conveying posture of the recording medium and conveys the recording medium in accordance with the image forming timing of the image forming unit;
The recording medium size detecting means has a recording medium transport distance measuring means for measuring the transport distance of the recording medium,
The image forming apparatus according to claim 1, wherein the recording medium conveyance distance measuring unit is provided between the image forming unit and the registration unit in a recording medium conveyance path. The image forming apparatus according to claim 1, wherein
A recording medium conveying means for conveying the recording medium;
A conveyance amount measuring means for measuring a conveyance distance of the recording medium by the recording medium conveyance means,
The end detection means is
A downstream side detection means for detecting the leading edge of the recording medium on the downstream side in the recording medium conveyance direction of the recording medium conveyance means;
Upstream detection means for detecting the trailing edge of the recording medium on the upstream side in the recording medium conveyance direction of the recording medium conveyance means,
A recording medium conveyance distance calculation unit that calculates a conveyance distance of the recording medium based on detection results of the conveyance amount measurement unit, the downstream detection unit, and the upstream detection unit;
An image forming apparatus comprising: a recording medium length calculation unit that calculates a recording medium length in a recording medium conveyance direction based on a calculation result of the recording medium conveyance distance calculation unit. The image forming apparatus according to claim 10.
2. The image forming apparatus according to claim 1, wherein the recording medium conveying unit includes: a driving roller that is rotationally driven; and a driven roller that is rotated while the recording medium is nipped and conveyed between the driving rollers. An image forming step of forming an image on a recording medium by an image forming unit;
An edge detection step of detecting an edge position of the recording medium to be conveyed by an edge detection means;
A recording medium size detecting step of detecting a size of the recording medium by a recording medium size detecting means based on a detection result of the edge detecting means;
A recording medium expansion / contraction amount calculating step for calculating an expansion / contraction amount of the recording medium by a recording medium expansion / contraction amount calculation unit based on a change in recording medium size before and after image formation detected by the recording medium size detection unit;
In the image forming method of the image forming apparatus capable of forming images on both sides of the recording medium by reversing the front and back of the recording medium,
A recording medium size variation calculating step for calculating a recording medium size variation detected by the recording medium size detecting unit in a plurality of recording media by a recording medium size variation calculating unit, and the recording medium expansion / contraction amount in the plurality of recording media At least one of the recording medium expansion / contraction amount variation calculating step for calculating the recording medium expansion / contraction amount variation calculated by the calculation unit by the recording medium expansion / contraction amount variation calculating unit;
A surface registration deviation amount calculating step of calculating a front / back registration deviation amount assumed by a property of the recording medium by a surface registration deviation amount calculating means based on at least one of the recording medium size variation and the recording medium expansion / contraction variation. Or a contribution degree calculating step of calculating a contribution degree of the property of the recording medium with respect to the front / back misregistration by a contribution degree calculating means.   A program for causing an image forming apparatus to execute the image forming method according to claim 12.

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