JP6186910B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus.

  In the commercial printing industry, a shift from conventional offset printing to POD (Print on Demand) by an image forming apparatus using an electrophotographic method is progressing in printing of a small lot, a variety of products, and variable data. In order to meet such a need, an image forming apparatus using an electrophotographic system is required to have front and back registration accuracy comparable to that of an offset printing machine.

  The cause of misregistration can be broadly divided into vertical and horizontal registration errors and paper (printing medium) / image skew errors. However, in an image forming apparatus having a fixing unit, the paper further expands and contracts. This adds an image magnification error.

  Therefore, conventionally, an image forming apparatus that obtains the amount of paper expansion / contraction based on the paper size detected by the measurement unit and determines the front / back image magnification to correct the image size and reduce the front / back image magnification error. It has been proposed (see, for example, Patent Documents 1 to 6).

  However, in the conventional image forming apparatus, the measurement unit for detecting the paper size is disposed in the vicinity of the upstream side of the transfer position for transferring the toner image onto the paper. For this reason, unless the processing such as monitoring the position of the toner image on the intermediate transfer belt and controlling the conveyance / stop of the sheet is executed, the expansion / contraction amount obtained based on the sheet size detected by the measurement unit is sequentially calculated. It was difficult to reflect the toner image transfer process on the paper.

  In view of this, an object of one aspect is to provide an image forming apparatus capable of reducing front and back image magnification errors for each print medium.

An image forming apparatus according to an embodiment of the present invention has the following configuration. That is,
A transfer unit that transfers an image at a transfer position via a transfer belt to a print medium supplied from a paper supply unit;
A fixing unit that thermally fixes the image transferred in the transfer unit to the print medium;
A reversing unit for reversing the first surface and the second surface of the print medium after heat fixing by the fixing unit;
An image forming apparatus for transferring an image to each of the first surface and the second surface of the print medium,
A measurement unit for measuring the size of the print medium on a conveyance path for conveying the print medium toward the transfer position;
A correction unit that corrects an image transferred to the print medium based on the size of the print medium measured by the measurement unit;
The correction unit is
Before the print medium is heat-fixed, the size of the print medium measured by the measurement unit is reversed by the reversing unit, and the measurement unit is measured by the measurement unit after the print medium is heat-fixed. based on the size of the print media, it has rows correction of an image to be transferred onto the printing medium after being thermally fixed,
The measuring unit is
The time from when the size of the print medium is measured until the print medium reaches the transfer position by being conveyed on the conveyance path, after measuring the size of the print medium, the correction unit, The image is corrected based on the measured size, and the transfer unit is disposed so as to be longer than the time required to move the transfer belt on which the corrected image is transferred to the transfer position. ,
The print medium whose size is measured by the measuring unit is transported toward the transfer position without being stopped on the transport path at a transport speed synchronized with the moving speed of the transfer belt.

  According to one aspect, it is possible to provide an image forming apparatus that can reduce front and back image magnification errors for each print medium.

1 is a diagram illustrating a schematic configuration of an image forming apparatus according to an embodiment. It is a figure which shows the relationship between the processing timing of each processing content in the image correction part and image transfer part which concerns on embodiment, and the processing timing of each processing content in a size measurement part and a conveyance means. It is a figure for demonstrating arrangement | positioning of a size measurement part. It is an upper surface schematic diagram of the paper length measurement part of the size measurement part which concerns on embodiment. It is a section schematic diagram of a paper length measurement part of a size measurement part concerning an embodiment. It is a figure which shows the output example of the start trigger sensor which concerns on embodiment, a stop trigger sensor, and a rotary encoder. It is a figure which shows the other relationship between the processing timing of each processing content in the image correction part and image transfer part which concerns on embodiment, and the processing timing of each processing content in a size measurement part and a conveyance means.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. In addition, in this specification and drawing, about the component which has the substantially same function structure, the duplicate description is abbreviate | omitted by attaching | subjecting the same code | symbol.

[First Embodiment]
<Schematic configuration of image forming apparatus>
First, a schematic configuration of the image forming apparatus 100 according to the present embodiment will be described. FIG. 1 is a diagram illustrating a schematic configuration of the image forming apparatus 100. As illustrated in FIG. 1, the image forming apparatus 100 includes a paper feed unit 110, a size measurement unit 120, an image correction unit 130, an image transfer unit 140, a fixing unit 150, and a reversing unit 160. Then, the paper (print medium) supplied from the paper supply unit 110 is conveyed to each unit along arrows 181 and 182 by a conveyance unit that forms a conveyance path 170.

  The size measuring unit 120 is disposed on the downstream side of the paper feeding unit 110 and the reversing unit 160 in the conveyance path 170, and the paper supplied from the paper feeding unit 110 and the paper after reversing conveyed from the reversing unit 160. Measure each size. As described above, by sharing the size measuring unit 120 in the measurement of the paper size before inversion and the measurement of the paper size after inversion, the cost of the image forming apparatus 100 can be reduced.

  The size measuring unit 120 has a contact image sensor (CIS) that measures the paper width. CIS measures the sheet width by detecting the position of the side edge of the sheet (the position of the right end and the position of the left end in the transport direction).

  The size measuring unit 120 further includes a start trigger sensor, a stop trigger sensor, and a driven roller with an encoder disk as a paper length measuring unit that measures the paper length. In the paper length measurement unit, the number of rotations from when the leading edge of the paper passes the start trigger sensor to when the trailing edge of the paper passes the stop trigger sensor is detected by a driven roller with an encoder disk (rotation amount detection unit). Thus, the paper length is measured. Details of the paper length measuring unit will be described later.

  The image correction unit 130 calculates the expansion / contraction amount of each sheet based on the sheet length and the sheet width measured by the size measurement unit 120, and corrects the image size using the calculated expansion / contraction amount.

  The image transfer unit 140 includes an intermediate transfer belt (intermediate transfer member / belt member) and a photosensitive drum corresponding to each color (Y: yellow, M: magenta, C: cyan, K: black). The image transfer unit 140 forms a toner image on each photosensitive drum based on image data to be printed, and then sequentially transfers the toner image to and from each primary transfer roller on the intermediate transfer belt (primary). Transfer process). Then, the intermediate transfer belt on which the toner images of the respective colors are transferred in an overlapping manner is moved to a position opposite to the secondary transfer roller (secondary transfer position), and the surface of the conveyed paper (supplied from the paper feeding unit 110 and first supplied). The toner image on the intermediate transfer belt is transferred to the transfer surface to be transferred onto the intermediate transfer belt.

  The fixing unit 150 includes a heating roller and a pressure roller, and pressurizes the toner image transferred on the surface of the sheet while heating. As a result, the toner image transferred to the surface of the paper is thermally fixed. Note that the paper after heat fixing contracts compared to the paper before heat fixing by being heated and pressed by the heat roller and the pressure roller.

  The reversing unit 160 reverses the front and back surfaces of the paper conveyed from the fixing unit 150. The reversed paper is conveyed again to the size measuring unit 120 using the back surface (the surface on which transfer is performed next) as a transfer surface, and the size measuring unit 120 measures the paper width and the paper length.

  As described above, since the paper after heat fixing is contracted compared with the paper before heat fixing, when the paper width and paper length of the paper reversed by the reversing unit 160 are measured, the measurement result is First, the sheet width and the sheet length measured by the size measuring unit 120 are different values.

  Here, the paper width first measured by the size measuring unit 120 is W1, the paper length is L1, the paper width measured by the size measuring unit 120 after being inverted by the reversing unit 160 is W2, and the paper length is L2. To do. In this case, the image transfer unit 140 calculates L2-L1 and W2-W1 as the amount of expansion / contraction of the paper. Then, the image size is corrected based on the expansion / contraction amount. Thereby, image data corresponding to the amount of expansion / contraction of the paper can be generated on the back surface of the paper.

  The paper that has been reversed by the reversing unit 160 and whose paper width and length have been measured by the size measuring unit 120 is conveyed again to the image transfer unit 140 by the conveying unit, and the image size is corrected by the image transfer unit 140. The transferred toner image is transferred to the back side of the paper.

  The sheet having the toner image transferred on the back side is further conveyed to the fixing unit 150, where the toner image on the back side is thermally fixed, and then discharged outside the apparatus.

<Arrangement of size measuring unit>
Next, in the image forming apparatus 100, the image data is corrected according to the expansion / contraction amount of the paper, and the process of transferring the toner image to the surface of the paper based on the corrected image data is realized for each paper. The arrangement of the size measuring unit 120 will be described. FIG. 2 is a diagram schematically illustrating the relationship between the processing timing of each processing content in the image correction unit 130 and the image transfer unit 140 and the processing timing of each processing content in the size measurement unit 120 and the transport unit. In FIG. 2, the horizontal axis indicates time, and the length of each bar indicates the time required for each process. Hereinafter, an appropriate arrangement of the size measuring unit 120 will be examined with reference to FIG.

  As shown in FIG. 2, when the paper size measurement by the size measuring unit 120 is completed for the paper being conveyed, the measurement results (paper length, paper width) are transmitted to the image correction unit 130. The image correction unit 130 calculates the amount of expansion / contraction based on the measurement result transmitted from the size measurement unit 120 and corrects the image size. During this time, the sheet is continuously conveyed by the conveying means.

  The image transfer unit 140 exposes each photosensitive drum based on the image data that has been subjected to size correction. The toner image formed on each photosensitive drum by exposure is transferred to the intermediate transfer belt. The intermediate transfer belt moves at a speed synchronized with the conveyance speed of the paper by the conveyance means, and reaches the secondary transfer position at the timing when the paper reaches the secondary transfer position.

Here, the time T _d ′ from when the measurement result is received by the image correction unit 130 to when the correction of the image data based on the measurement result is completed is assumed. Further, the time T _d ″ is set until the toner image transferred to the intermediate transfer belt reaches the secondary transfer position after the photosensitive drum is exposed by the image transfer unit 140. Further, the total time of both is defined as T _d (= T _d ′ + T _d ″). Also, T _p is the time until the paper whose paper size has been measured in the size measuring unit 120 is transported by the transport means and reaches the secondary transfer position.

Under such a definition, the size measuring unit 120 is arranged on the conveyance path 170 so that T _d = T _p is established in a state where the moving speed of the intermediate transfer belt is maximized. Image size correction based on the amount of paper expansion / contraction can be realized for each paper.

  In other words, the image correction unit 130 that receives the measurement result corrects the image size, and the image transfer unit 140 conveys the intermediate transfer belt onto which the toner image has been transferred until it reaches the secondary transfer position. The distance the sheet is conveyed by the means. Then, the size measuring unit 120 is arranged at a position that goes back upstream from the secondary transfer position by the distance. Accordingly, it is possible to realize image size correction for each sheet based on the amount of expansion / contraction of the sheet without stopping the conveyance.

With reference to FIG. 2, it demonstrates concretely using FIG. FIG. 3 is a diagram for explaining the arrangement of the size measuring unit 120. In FIG. 3, T _d ″ indicates that the toner image formed on the photosensitive drum (Y) by exposure to the photosensitive drum on the most upstream side (photosensitive drum (Y) in the example of FIG. 3) is an intermediate transfer belt. The time until the secondary transfer position is reached is shown. As described above, the intermediate transfer belt moves at a speed synchronized with the conveyance speed of the sheet by the conveyance unit. Therefore, if the movement speed of the intermediate transfer belt is V, the sheet will be T during the time T _d ″. Only _d ″ × V is conveyed.

Further, in the time (T _d ′) until the correction of the image data based on the measurement result by the size measuring unit 120 is completed, the maximum distance that the sheet is conveyed is, assuming that the maximum moving speed of the intermediate transfer belt is V _max . T _d ′ × V _max .

Therefore, in FIG. 3, the distance L (the distance from the position at which the measurement of the paper size by the size measuring unit 120 is completed (the position of the stop trigger sensor in this embodiment) to the secondary transfer position) is T _d ′ × V _max + T _d ″ × V. That is, the size is set so that the position of the stop trigger sensor of the size measuring unit 120 is located at a distance L (= T _d ′ × V _max + T _d ″ × V) from the secondary transfer position back along the conveyance path 170. The measurement unit 120 is disposed on the conveyance path 170. Accordingly, it is possible to realize image data correction for each sheet based on the amount of expansion / contraction of the sheet without stopping the conveyance.

In the case where the size measuring unit 120 is arranged in this way, when the actual moving speed of the intermediate transfer belt is V _x (where V _x <V _max ), the image transfer unit 140 performs the following: Process. That is, after the image correction unit 130 receives the measurement result from the size measurement unit 120 and the time calculated by (T _d ′ × V _max ) / V _x elapses, the photosensitive drum on the most upstream side ( Start exposure to Y). Thereby, the timing to reach the secondary transfer position can be matched.

<Configuration of size measuring unit>
Next, a detailed configuration of the size measuring unit 120 will be described. Here, a paper length measuring unit that prescribes completion of measurement of the paper size will be described in detail.

  4 and 5 show the configuration of the paper length measurement unit of the size measurement unit 120 according to the present embodiment (hereinafter referred to as the paper length measurement unit 400). 4 is a schematic top view of the paper length measuring unit 400, and FIG. 5 is a schematic cross-sectional view of the paper length measuring unit 400.

  On the conveyance path of the paper P, the paper P is sandwiched between a driving roller 414 that is driven to rotate by a driving means (for example, a motor) and a driving force transmission means (for example, a gear, a belt, etc.) (not shown) and the driving roller 414. A driven roller 413 that is driven to rotate is provided.

  Further, a rotary encoder 415 serving as a rotation amount detection unit is provided on the rotation shaft of the driven roller 413 of the paper length measurement unit 400 according to the present embodiment. Pulse signals generated by the rotating encoder disk 415a and encoder sensor 415b can be counted by a pulse counter (not shown).

  Sensors 411 and 412 are provided on the upstream side and downstream side of the driven roller 413 and the drive roller 414 in the conveyance path of the paper P. Sensors 411 and 412 detect the end of the sheet P being transported. As the sensors 411 and 412, for example, a transmissive or reflective optical sensor with high detection accuracy of the paper edge can be used. In the present embodiment, a reflective optical sensor is used.

  A sensor 411 on the downstream side of the driven roller 413 and the driving roller 414 in the transport direction of the paper P is a start trigger sensor 411 serving as a leading edge detecting unit that detects passage of the leading edge of the paper P. A sensor 412 on the upstream side of the driven roller 413 and the driving roller 414 in the conveyance direction of the paper P is a stop trigger sensor 412 as a trailing edge detection unit that detects passage of the trailing edge of the paper P.

  A distance A shown in FIG. 4 is a distance between the start trigger sensor 411 and the driven roller 413 and the driving roller 414, and a distance B is a distance between the stop trigger sensor 412 and the driven roller 413 and the driving roller 414. is there.

  The driving roller 414 rotates in the direction of the arrow shown in FIG. 5, and the driven roller 413 is driven to rotate by the driving roller 414 and transports the paper P when the paper P is not transported (when idling). In this case, the paper P is driven to rotate. When the driven roller 413 rotates, a pulse is generated from the rotary encoder 415 provided on the rotation shaft.

  When the start trigger sensor 411 detects that the paper P has been conveyed in the direction of arrow X and the leading edge has passed, the pulse counting of the rotary encoder 415 is started, and the stop trigger sensor 412 indicates that the trailing edge of the paper P has passed. When counting is detected, the pulse counting is terminated.

<Paper length measurement method>
FIG. 6 shows an output example of the start trigger sensor 411, stop trigger sensor 412, and rotary encoder 415 of the paper length measuring unit 400.

  As described above, when the driven roller 413 rotates, a pulse is generated from the rotary encoder 415 provided on the rotation shaft of the driven roller 413.

  After the stop trigger sensor 412 detects that the paper P has been conveyed and the leading edge of the paper P has passed at time t1, the start trigger sensor 411 detects that the leading edge of the paper P has passed at time t2. .

  Subsequently, after the stop trigger sensor 412 detects that the trailing edge of the paper P has passed at time t3, the start trigger sensor 411 detects that the trailing edge of the paper P has passed at time t4.

  At this time, after the start trigger sensor 411 detects that the leading edge of the paper P has passed at time t2, until the stop trigger sensor 412 detects that the trailing edge of the paper P has passed at time t3. During this period, the rotary encoder 415 performs pulse counting.

  Let r be the radius of the driven roller 413 provided with the rotary encoder 415 as the rotation amount detection unit, N be the number of encoder pulses for one rotation of the driven roller 413, and n be the number of pulses counted in the pulse count time. Further, as shown in FIG. 5, when the distance between the start trigger sensor 411 and the stop trigger sensor 412 in the transport path of the paper P is a, the length L in the transport direction of the paper P is expressed by the following formula (1 ).

L = (n / N) × 2πr + a (1)
n: Number of counted pulses N: Number of encoder pulses for one rotation of the driven roller 413 [/ r]
r: radius of the driven roller 413 [mm]
a: Distance [mm] between the start trigger sensor 411 and the stop trigger sensor 412
In general, the paper conveyance speed depends on the mechanical accuracy such as the external accuracy of the roller (particularly the driving roller) that conveys the paper P, 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 414 and the paper P, a slack phenomenon caused by a difference in paper transport force or paper transport speed of the upstream and downstream transport means, and the like. For this reason, the pulse period and pulse width of the rotary encoder 415 always change, but the number of pulses does not change.

  Therefore, the length L in the transport direction of the paper P can be obtained with high accuracy without depending on the transport speed of the paper by the expression (1).

<Summary>
As is clear from the above description, in the image forming apparatus 100 according to the present embodiment, the size measuring unit that measures the sizes of the paper supplied from the paper feeding unit 110 and the paper after reversing conveyed from the reversing unit 160. 120,
A time T _p until the paper that has passed the size measuring unit 120 reaches the secondary transfer position;
A time T _d until the intermediate transfer belt onto which the toner image has been transferred reaches the secondary transfer position after the image size is corrected based on the measurement result by the size measuring unit 120;
Are arranged to be equal at the maximum moving speed of the intermediate transfer belt.

  Accordingly, it is possible to realize image size correction for each sheet based on the amount of expansion and contraction of the sheet without stopping the conveyance of the sheet. As a result, the image magnification error due to the expansion and contraction of the paper can be reduced for each paper, and the front and back registration accuracy can be improved.

[Second Embodiment]
In the first embodiment, the size measuring unit 120 is arranged such that the time T _d = time T _{p at} the maximum moving speed of the intermediate transfer belt. However, the present invention is not limited to this, and the time T _{d <may} be arranged the size measurement unit 120 such that the time T _p. Details of this embodiment will be described below. Note that the schematic configuration of the image forming apparatus according to the present embodiment is the same as that of the image forming apparatus 100 described with reference to FIG. 1 in the first embodiment, and thus the description thereof is omitted here.

<Arrangement of size measuring unit>
FIG. 7 is a diagram schematically illustrating the relationship between the processing timing of each processing content in the image correction unit 130 and the image transfer unit 140 and the processing timing of each processing content in the size measurement unit 120 and the transport unit. In the example of FIG. 7, the size measurement unit 120 is arranged on the conveyance path 170 so that T _d (= T _d ′ + T _d ″) <T _{p at} the maximum moving speed of the intermediate transfer belt. ing.

  As shown in FIG. 7, when the paper size measurement by the size measurement unit 120 is completed for the paper being conveyed, the measurement results (paper length and paper width) are transmitted to the image correction unit 130. The image correction unit 130 corrects the image size based on the measurement result transmitted from the size measurement unit 120. During this time, the sheet is continuously conveyed by the conveying means.

Here, when the size measurement unit 120 is arranged so that T _d (= T _d ′ + T _d ″) <T _p , a predetermined time has elapsed after the image size is corrected based on the measurement result. Later, exposure of each photosensitive drum by the image transfer unit 140 is started. That is, it is possible to secure a sufficient time to reflect the expansion / contraction amount calculated based on the measurement result by the size measurement unit 120 in the transfer process of the toner image on the paper. Further, the timing at which the intermediate transfer belt onto which the toner image has been transferred reaches the secondary transfer position can be matched with the timing at which the sheet reaches the secondary transfer position by the conveying means.

Note that the start of exposure to the most upstream photosensitive drum, the distance from the secondary transfer position of the size measuring section 120 L, if the actual moving speed of the intermediate transfer belt was V _x, receives the measurement result To (L−V _x × T _d ″) / V _x at the timing when time has elapsed.

<Summary>
As is clear from the above description, in the image forming apparatus 100 according to the present embodiment, the size measuring unit that measures the sizes of the paper supplied from the paper feeding unit 110 and the paper after reversing conveyed from the reversing unit 160. 120,
A time T _p until the paper that has passed the size measuring unit 120 reaches the secondary transfer position;
A time T _d until the intermediate transfer belt onto which the toner image has been transferred reaches the secondary transfer position after the image size is corrected based on the measurement result by the size measuring unit 120;
Is arranged such that T _d <T _p .

Accordingly, it is possible to realize image size correction for each sheet based on the amount of expansion and contraction of the sheet without stopping the conveyance of the sheet. As a result, the image magnification error due to the expansion and contraction of the paper can be reduced for each paper, and the front and back registration accuracy can be improved.
[Third Embodiment]
In the first and second embodiments, the image size is measured and the image data is corrected according to the measurement result when the image is transferred to the paper reversed by the reversing unit 160. It is not limited to. According to the arrangement of the size measuring unit 120 described in the first and second embodiments, the measurement result by the size measuring unit 120 can be used to correct the image data even for the paper before being reversed by the reversing unit 160. It is possible to reflect.

  That is, if the image forming apparatus 100 according to the first and second embodiments is used, for example, a configuration in which correction for increasing the image size on the surface is performed for each sheet in consideration of the amount of expansion and contraction of the sheet. Is possible.

  In the first and second embodiments, the image forming apparatus capable of color printing has been described. However, the present invention is not limited to this and can be applied to an image forming apparatus for monochrome printing. Not too long.

  In the first and second embodiments, the size measuring unit 120 measures the paper length and the paper width. However, the present invention is not limited to this, and either the paper length or the paper width is used. It is good also as a structure which calculates the amount of expansion / contraction by measuring only one of them.

  Further, the configuration of the size measuring unit 120 shown in the first and second embodiments is merely an example, and a method of measuring by another measuring method (for example, a method of calculating the paper length from the sensor passing time). Needless to say, may be used.

  The size measuring unit 120 is preferably modularized and configured to be movable upstream and downstream on the conveyance path 170. This is because convenience when adjusting the arrangement of the size measuring unit 120 on the transport path 170 is improved.

  In the first and second embodiments, the case where paper is used as the print medium has been described. However, the print medium is not limited to paper, and other materials (for example, metal, cloth, resin) are used. Needless to say, it may be.

  It should be noted that the present invention is not limited to the configuration shown here, such as a combination with other elements in the configuration described in the above embodiment. These points can be changed without departing from the spirit of the present invention, and can be appropriately determined according to the application form.

DESCRIPTION OF SYMBOLS 100 Image forming apparatus 110 Paper feed part 120 Size measurement part 130 Image correction part 140 Image transfer part 150 Fixing part 160 Inversion part 170 Conveyance path

JP 2004-045476 A Japanese Patent Application Laid-Open No. 2004-129069 JP 2004-287210 A JP 2007-072094 A JP 2007-079262 A JP 2013-053004 A

Claims (3)

A transfer unit that transfers an image at a transfer position via a transfer belt to a print medium supplied from a paper supply unit;
A fixing unit that thermally fixes the image transferred in the transfer unit to the print medium;
A reversing unit for reversing the first surface and the second surface of the print medium after heat fixing by the fixing unit;
An image forming apparatus for transferring an image to each of the first surface and the second surface of the print medium,
A measurement unit for measuring the size of the print medium on a conveyance path for conveying the print medium toward the transfer position;
A correction unit that corrects an image transferred to the print medium based on the size of the print medium measured by the measurement unit;
The correction unit is
Before the print medium is heat-fixed, the size of the print medium measured by the measurement unit is reversed by the reversing unit, and the measurement unit is measured by the measurement unit after the print medium is heat-fixed. based on the size of the print media, it has rows correction of an image to be transferred onto the printing medium after being thermally fixed,
The measuring unit is
The time from when the size of the print medium is measured until the print medium reaches the transfer position by being conveyed on the conveyance path, after measuring the size of the print medium, the correction unit, The image is corrected based on the measured size, and the transfer unit is disposed so as to be longer than the time required to move the transfer belt on which the corrected image is transferred to the transfer position. ,
The print medium whose size is measured by the measuring unit is transported toward the transfer position without being stopped on the transport path at a transport speed synchronized with the moving speed of the transfer belt. apparatus. The measuring unit is
Of the transport paths for transporting the print medium toward the transfer position, on a common transport path for transporting both the print medium supplied from the paper feeding section and the print medium reversed by the reversing section. In the case where the common conveyance path conveys the printing medium at a conveyance speed synchronized with the movement speed of the transfer belt, the distance to the transfer position is determined by the movement speed of the transfer belt and the printing medium. It is arranged to be equal to a value calculated based on the time from when the size is measured until the transfer belt on which the image corrected based on the measured size is transferred is moved to the transfer position. The image forming apparatus according to claim 1, wherein: The measurement unit has a distance to the transfer position on the common conveyance path,
A multiplication value of the maximum moving speed of the transfer belt and the time from when the size of the print medium is measured until the correction unit corrects the image based on the measured size;
A multiplication value of a moving speed of the transfer belt and a time until the transfer unit moves the transfer belt on which the corrected image has been transferred to the transfer position;
The image forming apparatus according to claim 2, wherein the image forming apparatus is arranged to be equal to a total value of the image forming apparatus.

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