JP2017007863A - Image formation apparatus and sheet conveyance device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To control a sheet interval more accurately than a conventional technique.SOLUTION: An image formation apparatus 100 determines a reduction quantity Q from the rear end of a preceding sheet to the tip of a succeeding sheet in accordance with the difference between a sheet interval from the rear end of the preceding sheet to the tip of the succeeding sheet measured on the basis of the detection result of a top sensor 107 and a target interval. The image formation apparatus 100 corrects the reduction quantity Q so as to be able to detect the rear end of the preceding sheet and the tip of the succeeding sheet by a sheet discharge sensor 109. The reduction quantity Q is corrected in accordance with an error in measurement values of a length in the conveyance direction of the preceding sheet measured on the basis of the detection result of the top sensor 107. The error is the error with respect to the nominal value of the length in the convenience direction of the preceding sheet. The image formation apparatus 100 controls a motor so that the conveyance speeds of a conveyance roller 104 and a register roller 106 temporarily increase over the time according to the reduction quantity Q.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a printing apparatus, and more particularly to an image forming apparatus such as a copying machine, a laser beam printer, and a facsimile, and a sheet conveying apparatus.

  According to Patent Document 1, the sheet interval between the preceding sheet and the succeeding sheet is measured before the sheet enters the image forming unit, and the sheet feeding motor is temporarily increased in accordance with the difference from the target interval to thereby increase the sheet interval. It has been proposed to adjust. As a result, the sheet interval can be maintained at the target interval. The sheet interval is the distance or time from the trailing edge of the preceding sheet to the leading edge of the succeeding sheet. In order to measure the sheet interval, a sheet sensor is required. According to Patent Documents 2 and 3, a flag that is rotated by being pushed by a sheet, and a photo interrupter in which a light-transmitting state and a light-shielding state are switched by the rotation of the flag are proposed.

JP 2002-132765 A JP 2014-40329 A JP 2015-16922 A

  Sheet sensors for measuring the sheet interval are arranged on the downstream side and the upstream side of the conveyance path. The sheet sensor disposed on the upstream side is mainly used to maintain the sheet interval between the preceding sheet and the succeeding sheet at a target interval. On the other hand, the sheet interval disposed on the downstream side is mainly used for detecting a jam (paper jam). Since the sheet sensor includes a mechanical mechanism, the sheet sensor cannot be detected unless the sheet interval exceeds a certain interval. Therefore, if there is an error in the sheet interval obtained by the upstream sheet sensor, the sheet interval is adjusted to be shorter than necessary, and as a result, the downstream sheet sensor cannot detect the sheet interval and a jam occurs. May be mistakenly detected. On the other hand, if the sheet interval is adjusted to be longer than necessary, the throughput (the number of images that can be formed per unit time) decreases. Therefore, an object of the present invention is to control the sheet interval with higher accuracy than in the past.

The present invention is, for example,
Conveying means for conveying the sheet in the conveying path;
First detection means for detecting a sheet in the conveyance path;
The distance from the trailing edge of the preceding sheet to the leading edge of the succeeding sheet according to the difference between the distance from the trailing edge of the preceding sheet to the leading edge of the succeeding sheet and the target distance measured based on the detection result of the first detecting means Determining means for determining the adjustment amount of
According to the error of the measured value of the length in the conveyance direction of the preceding sheet measured based on the detection result of the first detection unit with respect to the reference value of the length in the conveyance direction of the preceding sheet. Correction means for correcting the adjustment amount;
An image forming apparatus comprising: a control unit configured to control the transport unit so that the transport speed of the transport unit is increased or decreased over a time corresponding to the adjustment amount corrected by the correction unit. .

  According to the present invention, it is possible to control the sheet interval with higher accuracy than in the past.

Sectional view showing an example of an image forming apparatus Diagram showing the relationship between the roller and each motor Block diagram showing the control system Diagram explaining the structure and operation of the sheet sensor Flow chart showing processing for determining reduction amount Diagram explaining transfer speed and transfer time Flow chart showing processing for determining reduction amount Diagram explaining the structure and operation of the sheet sensor Diagram showing the relationship between the roller and each motor Diagram showing functions of the transport controller Sectional view showing an example of an image forming apparatus Block diagram showing the control system

[Example 1]
<Image forming apparatus>
FIG. 1 is a schematic sectional view of the image forming apparatus 100. The image forming apparatus 100 in this embodiment is an electrophotographic printer, but an image forming apparatus to which the present invention can be applied may employ other image forming methods such as an ink jet method and a thermal transfer method. The photosensitive drum 122 is a photosensitive member and an image carrier, and rotates clockwise at a predetermined peripheral speed (process speed) vps. The charging roller 123 uniformly charges the surface of the photosensitive drum 122. The optical scanning device 140 outputs a light beam corresponding to the image signal. The light beam is reflected by the reflection mirror 141 and irradiated on the surface of the photosensitive drum 122 to form an electrostatic latent image. The developing roller 121 attaches toner to develop the electrostatic latent image to form a toner image.

  The sheets S accommodated in the paper feed cassette are picked up by the paper feed roller 102, separated one by one by the separation roller 103, and sent out to the conveyance path. A conveyance roller 104 and a registration roller 106 provided on the upstream side of the conveyance path are an example of a conveyance unit that conveys a sheet in the conveyance path. The conveyance speeds of the conveyance roller 104 and the registration roller 106 are freely variable, and the conveyance speed of the sheet S changes as these conveyance speeds change. Thereby, the sheet interval (so-called sheet interval) from the trailing edge of the preceding sheet to the leading edge of the succeeding sheet is maintained at the target interval. The adjustment of the sheet interval is performed by the conveyance roller 104, and the registration roller 106 does not have to be involved. The target interval is a sheet interval determined at the design stage of the image forming apparatus 100 in order to achieve a desired throughput. The peripheral speed of the conveying roller 104 disposed on the downstream side of the registration roller 106 is controlled to be constant (peripheral speed vps). That is, the conveyance speed of the sheet S is variably controlled when the leading edge of the sheet S is positioned in the section from the conveyance roller 104 to the photosensitive drum 122 (or the registration roller 106).

  The transfer roller 108 conveys the sheet S while sandwiching the sheet S together with the photosensitive drum 122, so that the toner image on the photosensitive drum 122 is transferred to the sheet S. The fixing device 130 includes a fixing film 133 and a pressure roller 134. The sheet S is conveyed while being sandwiched between the fixing film 133 and the pressure roller 134, and the toner image is fixed. Thereafter, the sheet S is sent to the discharge roller 110 and discharged to the discharge tray 111. Note that the photosensitive drum 122, the transfer roller 108, the pressure roller 134, and the discharge roller 110 are also examples of the conveying unit.

  A plurality of sheet sensors for detecting a sheet are arranged in the conveyance path. The top sensor 107 is an example of a first detection unit that is disposed on the upstream side in the conveyance direction of the sheet S in the conveyance path and detects the sheet S. The top sensor 107 is used for detecting the length of the sheet S in the transport direction and detecting the sheet interval. The paper discharge sensor 109 is an example of a second detection unit that is disposed on the downstream side in the conveyance direction of the sheet S in the conveyance path and detects the sheet S. The paper discharge sensor 109 is mainly used for detecting a jam (paper jam) of the sheet S.

<Drive mechanism>
FIG. 2 is a diagram illustrating the relationship between each roller and a drive source that drives each roller. In the image forming apparatus 100, a paper feed motor 301 and a main motor 302 are used as drive sources. The paper feed motor 301 and the main motor 302 may also be understood as part of the transport unit. The paper feed motor 301 drives the paper feed roller 102 and the separation roller 103 via the paper feed clutch 310. Further, the paper feed motor 301 drives the transport roller 104 and the registration roller 106. The main motor 302 drives the photosensitive drum 122, the developing roller 121, the pressure roller 134, and the discharge roller 110. The sheet interval is adjusted by controlling the rotation speed of the paper feed motor 301. Note that a stepping motor is employed as the paper feed motor 301 in order to facilitate the explanation of sheet interval adjustment by acceleration (hereinafter referred to as acceleration control). However, a DC brushless motor, a brush motor, or the like can be used as the paper feed motor 301. In the period when the sheet interval adjustment is not executed, the peripheral speeds of the conveying roller 104 and the registration roller 106 are also controlled to the peripheral speed vps. When the peripheral speed of the registration roller 106 is always controlled to the peripheral speed vps, the registration roller 106 may be driven by the main motor 302. In this case, a sheet sensor for detecting the sheet interval is disposed near the conveyance roller 104.

<Control system>
FIG. 3 is a block diagram showing the control system. The conveyance control unit 202 includes a computing device such as a microprocessor, an ASIC (application specific integrated circuits), and an FPGA (Field Programmable Gate Array), and a storage device such as a RAM and a ROM. The conveyance control unit 202 uses the top sensor 107 and the paper discharge sensor 109 to detect or measure the length of the sheet S and the sheet interval in the conveyance direction. The conveyance control unit 202 controls the sheet feeding motor 301 based on the measured value of the sheet interval, temporarily changes the sheet conveyance speed, and controls the sheet interval to the target interval. Further, the conveyance control unit 202 uses the timing at which the top sensor 107 detects the leading edge of the sheet S as the image formation start timing. The conveyance control unit 202 detects a jam based on the detection result of the paper discharge sensor 109. For example, the conveyance control unit 202 determines that a jam has occurred if the paper discharge sensor 109 cannot detect the leading edge of the sheet S even after a predetermined period has elapsed from the timing when the top sensor 107 detects the leading edge of the sheet S. . In particular, the conveyance control unit 202 determines that a jam has occurred in the fixing device 130 if the trailing edge cannot be detected even after a predetermined period of time has elapsed after the discharge sensor 109 detects the leading edge of the sheet S. The conveyance control unit 202 appropriately controls the main motor 302 and the paper feed clutch 310. The conveyance control unit 202 specifies the sheet size based on information input by the operator through the operation panel 211.

  In particular, the conveyance control unit 202 detects the following sheet from the trailing end of the preceding sheet according to the difference between the target interval and the sheet interval from the trailing end of the preceding sheet to the leading end of the succeeding sheet measured based on the detection result of the top sensor 107. The amount of reduction Q of the interval to the tip of is determined. Furthermore, the conveyance control unit 202 corrects the reduction amount Q so that the paper discharge sensor 109 can detect the trailing edge of the preceding sheet and the leading edge of the succeeding sheet. The reduction amount Q is corrected according to an error in the measured value of the length in the conveyance direction of the preceding sheet measured based on the detection result of the top sensor 107. This error is an error with respect to the nominal value (reference value) of the length of the preceding sheet in the conveyance direction. The conveyance control unit 202 controls the paper feed motor 301 so that the conveyance speeds of the conveyance roller 104 and the registration roller 106 temporarily increase over a time corresponding to the reduction amount Q.

<Seat sensor>
4A to 4F are diagrams illustrating the structure and operation of the sheet sensor 400 such as the top sensor 107 and the paper discharge sensor 109. FIG. The sheet sensor 400 includes a flag 402 that is pressed by the sheet S and rotates about a rotation shaft 403, a photo interrupter 401 that switches between a light-transmitting state and a light-blocking state by the rotation of the flag 402, and a flag 402 with a predetermined value. A spring 407 for returning to the position is provided. As shown in FIG. 4D, the photo interrupter 401 includes a light emitting element 405 and a light receiving element 406. A state where the flag 402 is between the light emitting element 405 and the light receiving element 406 is a light shielding state, and a state where the flag 402 is not between the light emitting element 405 and the light receiving element 406 is a light transmitting state.

  Next, how to obtain the sheet interval using the sheet sensor 400 will be described. The sheet S is conveyed along the conveyance guide 404 from the upstream side (right side) to the downstream side (left side). FIG. 4A shows the home position of the flag 402. In a period in which the sheet S is not involved in the flag 402, the flag 402 is stopped at the home position by the force of the spring 407. When the flag 402 is stopped at the home position, the flag 402 blocks light from the light emitting element 405 toward the light receiving element 406. As shown in FIG. 4B, when the sheet S reaches the sheet sensor 400, the leading edge of the sheet S pushes the flag 402, thereby rotating the flag 402 around the rotation shaft 403. As a result, the photo interrupter 401 changes from the light shielding state to the light transmitting state. By receiving the detection signal output when the light receiving element 406 receives light from the light emitting element 405, the conveyance control unit 202 recognizes that the leading edge of the sheet S has arrived at the end detection position P1. Thus, when the leading edge of the sheet S arrives at the edge detection position P1, the light receiving element 406 of the photo interrupter 401 outputs a detection signal. When the leading edge of the sheet S arrives at the end detection position P1, the rotation angle of the flag 402 is set to θ1. As shown in FIG. 4C, the sheet S is further conveyed downstream, and finally the trailing end of the sheet S exits the flag 402. When the rear end of the sheet S passes the removal position P2, the flag 402 starts to return to the home position by the spring 407. The rotation angle of the flag 402 when the rear end of the sheet S passes the removal position P2 is defined as θ2. When the time Tb elapses from the timing when the return is started, the flag 402 passes the end detection position P1 (the rotation angle returns to θ1), and the photo interrupter 401 changes from the light transmitting state to the light blocking state. The conveyance control unit 202 recognizes the trailing edge of the sheet S when the detection signal from the light receiving element 406 is interrupted.

  Since the conveyance speed of the sheet S coincides with the circumferential speed vps, the conveyance speed of the sheet S is also set to vps. The distance from the end detection position P1 to the removal position P2 is Lf. In the light shielding period Tx from the timing when the trailing edge of the preceding sheet is detected to the timing when the leading edge of the succeeding sheet is detected, the photo interrupter 401 maintains the light shielding state. Therefore, the conveyance control unit 202 can determine the sheet interval Lintrvl using the following equation.

Lintrvl = (Tx + Tb) * vps + Lf ... Eq.1
A distance obtained by multiplying the light shielding period Tx by the conveyance speed vps is a distance from which the sheet interval Lintrvl is based. However, the time lag of the photo interrupter 401 must be taken into consideration for this distance, as shown in FIGS. 4A to 4C. When the leading edge of the succeeding sheet reaches the edge detection position P1, the trailing edge of the preceding sheet advances the distance Lf from the edge detection position P1, and the distance obtained by multiplying the return time Tb by the conveyance speed vps is also downstream. Is going on. Therefore, Eq.1 is established.

  Here, the distance Lf and the return time Tb of the flag 402 are measured by experiments at the time of factory shipment or are obtained by simulation, and are held in a ROM or the like built in the transport control unit 202. However, as shown in FIG. 4E and FIG. 4F, in reality, the removal position P2 varies due to the strain or curl of the sheet S. There are individual differences in the spring constant of the spring 407. Therefore, the distance Lf and the return time Tb may differ from the design values. In such a case, a difference occurs in the sheet interval Lintrvl obtained from the actual sheet interval Lact and Eq.1. If the sheet interval Lintrvl obtained from Eq.1 is longer than the actual sheet interval Lact, the reduction amount of the sheet interval will be excessive. There is a lower limit for the sheet interval that can be detected by the sheet sensor 400. That is, when the actual sheet interval Lact becomes shorter than the lower limit interval Lmin_intrvl, the sheet sensor 400 cannot detect the trailing edge of the preceding sheet and the leading edge of the succeeding sheet. The conveyance control unit 202 determines that the preceding sheet has jammed because the trailing edge of the preceding sheet cannot be detected even after a predetermined period has elapsed since the leading edge of the preceding sheet has been detected. Although the jam does not actually occur, the conveyance control unit 202 erroneously detects the jam, stops the image forming operation, and displays a jam message on the operation panel 211. This will reduce usability. Conversely, if the sheet interval Lintrvl is calculated to be shorter than the actual interval, the actual sheet interval Lact exceeds the target interval Lt. That is, the throughput decreases. Therefore, in the present embodiment, the following improvements may be applied.

<Sheet spacing adjustment>
Sheet spacing adjustment (hereinafter referred to as acceleration control) by increasing the speed of the paper feed motor 301 during continuous printing will be described. The conveyance control unit 202 obtains the sheet presence distance L1 by counting the number of steps of the sheet feeding motor 301 from the sheet leading edge detection to the sheet trailing edge detection by the top sensor 107. That is, the conveyance control unit 202 continuously counts the number of steps of the paper feed motor 301 while the light receiving element 406 of the photo interrupter 401 outputs a detection signal. Further, the conveyance control unit 202 obtains the sheet absence distance L2 by counting the number of steps from the trailing edge detection of the preceding sheet to the leading edge detection of the succeeding sheet. That is, the conveyance control unit 202 continuously counts the number of steps of the paper feed motor 301 while the light receiving element 406 of the photo interrupter 401 stops outputting the detection signal. As shown in FIG. 4C, the distance from the end detection position P1 of the top sensor 107 to the removal position P2 is Lf. Further, the return time until the flag 402 returns from the missing position P2 to the end detection position P1 is Tb. The sheet length measurement result Lmsr for the preceding sheet and the sheet interval Lintrvl between the preceding sheet and the succeeding sheet are expressed using these parameters.

Lmsr = L1-Lf-Tb * vps ... Eq. 2
Lintrvl = L2 + Lf + Tb * vps ... Eq. 3
The sheet presence distance L1 includes the distance that the leading edge of the sheet S travels after the leading edge of the sheet S arrives at the edge detection position P1 and before the flag 402 returns to the edge detection position P1. That is, the sheet presence distance L1 includes the distance (Tb * vps) that the leading edge has advanced during the return time Tb in addition to the distance Lf from the end detection position P1 to the removal position P2. Therefore, the measurement result Lmsr of the length of the sheet S can be obtained by subtracting the distance Lf and Tb * vps from the sheet presence distance L1. Eq. 3 is Eq. It is obtained from 1. That is, the sheet absence distance L2 corresponds to the distance that the trailing edge of the preceding sheet travels during the light shielding period Tx.

  By the way, the distance Lf and the return time Tb are values obtained at the time of shipment from a factory through experiments and simulations of conveying a typical sheet. As described above, an error occurs between these values and the actual values. Therefore, in order to adjust the sheet interval more accurately, these errors must be taken into consideration.

  The sheet discharge sensor 109 is also realized by the sheet sensor 400 in the same manner as the top sensor 107. Here, how to obtain the lower limit interval Lmin_intrvl that can be detected by the paper discharge sensor 109 will be described. For the lower limit interval Lmin_intrvl, in addition to the distance Lf and the return time Tb, the noise countermeasure time Tc may be considered. The noise countermeasure time Tc is the time from when the photo interrupter 401 of the paper discharge sensor 109 is in a no sheet state until the conveyance control unit 202 determines that there is no sheet. Therefore, the lower limit interval Lmin_intrvl is equal to Eq. 4 is obtained.

Lmin_intrvl = Lf + (Tb + Tc) * vps ... Eq. 4
Here, the distance Lf and the return time Tb are values that maximize the lower limit interval Lmin_intrvl among the values determined by the combination of the tolerance of the mechanism constituting the paper discharge sensor 109 and the type of the sheet S. These are determined at the time of factory shipment through experiments and simulations. The finally obtained lower limit interval Lmin_intrvl is stored in a ROM built in the conveyance control unit 202.

<Determination of reduction amount>
A method for determining the reduction amount Q by the acceleration control will be described using the flowchart of FIG. The reduction amount Q is determined according to an error between the measured sheet interval Lintrvl and the target interval Lt, and is a reduction amount of the sheet interval. When the top sensor 107 detects the leading edge of the succeeding sheet, the conveyance control unit 202 executes the following processing.

  In S <b> 1, the conveyance control unit 202 determines a length (hereinafter referred to as a nominal value L <b> 0) in the conveyance direction of the preceding sheet from the sheet size designated by the operator through the operation panel 211. The conveyance control unit 202 holds in advance in the ROM a nominal value L0 corresponding to the sheet size (eg, B5, B5R, A4, A4R, B4, A3, etc.). Here, the nominal value L0 is a reference value or standard value of the sheet size, for example, 297 mm for A4 and 420 mm for A3. Therefore, the conveyance control unit 202 reads the nominal value L0 corresponding to the designated size from the ROM.

  In step S2, the conveyance control unit 202 acquires the measurement result Lmsr of the length of the preceding sheet from the RAM. The conveyance control unit 202 is Eq. 2 is used to obtain the measurement result Lmsr of the length of the preceding sheet, and is stored in advance in a RAM built in the conveyance control unit 202.

  In S3, the conveyance control unit 202 subtracts the nominal value L0 from the measurement result Lmsr to obtain the length difference Δ.

  In S4, the conveyance control unit 202 determines whether or not the difference Δ is 0 or more, that is, whether or not the measurement result Lmsr is greater than or equal to the nominal value L0. If the difference Δ is equal to or greater than 0, the measurement result Lmsr is equal to or greater than the nominal value L0, and the transport control unit 202 proceeds to S5. On the other hand, if the difference Δ is less than 0, since the measurement result Lmsr is less than the nominal value L0, the transport control unit 202 proceeds to S8.

  There are two cases where the measurement result Lmsr is greater than or equal to the nominal value L0. The first case is a case where the sheet length is actually longer than the nominal value L0. The second case is the case shown in FIG. 4F. In this case, the nominal value L0 matches the sheet length, but Eq. 2 is a case where the behavior of the sheet S assumed in 2 does not match the actual behavior. In the former case, the subsequent sheet may be accelerated by the difference between the target interval Lt and the sheet interval measurement result Lintrvl. However, in the latter case, the sheet interval measurement result Lintrvl is calculated to be as short as the error included in the sheet S length measurement result Lmsr. Therefore, even if the succeeding sheet is accelerated by the difference between the target interval Lt and the sheet interval measurement result Lintrvl, the sheet interval becomes longer than the target by Δ, and the throughput decreases. Therefore, if the reduction amount Q is positively corrected by Δ, the throughput can be appropriately maintained. However, if the reduction amount Q is positively corrected by Δ in the former case as well, the sheet interval becomes too tight and the sheet discharge sensor 109 may not be able to detect the sheet interval. That is, misdetection of a jam can occur. Therefore, in this embodiment, it is considered whether or not the sheet discharge sensor 109 can detect the sheet interval when the reduction amount Q is positively corrected (when the reduction amount of the sheet interval is increased).

  In step S5, the conveyance control unit 202 determines whether the sheet discharge sensor 109 can detect the sheet interval when the reduction amount Q is positively corrected (when the reduction amount of the sheet interval is increased). For example, the conveyance control unit 202 may determine whether the target interval Lt−difference Δ is equal to or greater than the lower limit interval Lmin_Intrvl that can be detected by the paper discharge sensor 109. If the paper discharge sensor 109 can detect the sheet interval even if the reduction amount Q is positively corrected, the process proceeds to S6.

  In step S6, the conveyance control unit 202 corrects the reduction amount Q to be positive. For example, the conveyance control unit 202 determines the reduction amount Q by subtracting the target interval Lt from the sheet interval measurement result Lintrvl, and corrects the reduction amount Q by adding the difference Δ to the reduction amount Q.

  On the other hand, if the paper discharge sensor 109 cannot detect the sheet interval when the reduction amount Q is positively corrected in S5, the conveyance control unit 202 proceeds to S9. The conveyance control unit 202 does not correct the reduction amount Q using the difference Δ. That is, the conveyance control unit 202 determines the reduction amount Q by subtracting the target interval Lt from the sheet interval measurement result Lintrvl.

  By the way, if the difference Δ is less than 0 in S4, the measurement result Lmsr is less than the nominal value L0, so the transport control unit 202 proceeds to S8. There are also two cases where the measurement result Lmsr is less than the nominal value L0. The first case is a case where the sheet length is actually shorter than the nominal value L0. In the second case, although the nominal value L0 matches the sheet length, as shown in FIG. 2 is a case that does not match the actual behavior of the sheet. In the former case, the subsequent sheet may be accelerated by the difference between the target interval Lt and the sheet interval measurement result Lintrvl. However, in the latter case, the sheet interval measurement result Lintrvl is calculated to be longer by an amount corresponding to the sheet length error. Therefore, if the succeeding sheet is accelerated by the difference between the target interval Lt and the sheet interval measurement result Lintrvl, the sheet interval is excessively clogged, and the sheet discharge sensor 109 cannot detect the sheet interval. That is, misdetection of a jam can occur. Therefore, it is considered whether or not the sheet discharge sensor 109 can detect the sheet interval when the reduction amount Q is not corrected according to the difference Δ.

  In step S8, the conveyance control unit 202 determines whether or not the sheet discharge sensor 109 can detect the sheet interval when the reduction amount Q is not corrected according to the difference Δ. For example, the conveyance control unit 202 determines whether or not a value obtained by subtracting −Δ from the target interval Lt is equal to or greater than the lower limit interval Lmin_intrvl. Note that since Δ is determined to be a negative value in S4, −Δ is a positive value. If the sheet discharge sensor 109 can detect the sheet interval when the reduction amount Q is not corrected according to the difference Δ, the conveyance control unit 202 proceeds to S9.

  In step S9, the conveyance control unit 202 does not correct the reduction amount Q using the difference Δ. That is, the conveyance control unit 202 determines the reduction amount Q by subtracting the target interval Lt from the sheet interval measurement result Lintrvl.

  On the other hand, if there is a possibility that the paper discharge sensor 109 cannot detect the sheet interval unless the reduction amount Q is corrected according to the difference Δ, the conveyance control unit 202 proceeds to S10.

  In step S10, the conveyance control unit 202 negatively corrects the reduction amount Q. For example, the conveyance control unit 202 determines the reduction amount Q by subtracting the target interval Lt and −Δ from the sheet interval measurement result Lintrvl.

<Acceleration control>
The acceleration control will be described with reference to FIG. In the present exemplary embodiment, the conveyance control unit 202 increases the rotation speed of the sheet feeding motor 301 during acceleration control, thereby increasing the conveyance speed of the sheet S from vps to vacc. As shown in FIG. 6, the acceleration time required to accelerate from vps to vacc is Tacc [msec]. A deceleration time required for decelerating from vacc to vps is Tdec [msec]. The amount of reduction during the acceleration period is Qacc [mm], and the amount of reduction during the deceleration period is Qdec [mm]. These values are determined from the speed-up table and slow-down table of the paper feed motor 301 held in the ROM. In order to simplify the explanation, a case where the reduction amount Q is larger than Qacc + Qdec is taken as an example. In order to obtain the desired reduction amount Q by the acceleration control, it is only necessary to shorten the sheet interval by Q-Qacc-Qdec [mm] after reaching the speed vacc. Let this be Qsteady. The conveyance control unit 202 obtains the conveyance time Tsteady [msec] at the speed vacc from the following equation.
Tsteady = (Q−Qacc−Qdec) / (vacc−vps)... Eq. 5
As described above, for the second and subsequent sheets of continuous printing, the reduction amount Q is determined at the timing when the top sensor 107 detects the leading edge of the sheet. Then, the conveyance control unit 202 determines the acceleration period Tsteady from the reduction amount Q. When the conveyance control unit 202 starts accelerating the paper feed motor 301 at time t1, the conveyance control unit 202 starts decelerating the paper feed motor 301 when Tacc + Tsteady [msec] has elapsed from time t1. As a result, the transport speed returns from vacc to vps.

  Although the acceleration control has been described with reference to FIG. 6, the same applies to the case where the sheet interval is increased by the deceleration control. By performing the acceleration control in this manner, the case where the sheet interval cannot be detected by the paper discharge sensor 109 due to the measurement error of the top sensor 107 is reduced, and the throughput is also maintained.

[Example 2]
In the first embodiment, the method of determining the reduction amount Q is selected using the difference Δ between the measurement result Lmsr of the preceding sheet and the nominal value specified by the operator. This is based on the premise that the operator correctly specifies the size of the sheet S. Therefore, if the operator specifies an incorrect size, the reduction amount Q cannot be determined correctly. Therefore, in the second embodiment, an example in which the reduction amount is determined from the measurement error range measured in advance will be described. In the second embodiment, description of matters common to the first embodiment is omitted.

As described with reference to FIGS. 4A to 4F, the top sensor 107 includes a flag 402, a photo interrupter 401, a spring 407, and the like. Therefore, the following factors exist in the measurement error of the sheet interval.
The tolerance of the shape of the flag 402 The attachment tolerance of the flag 402 and the photo interrupter 401 The tolerance of the spring constant of the spring 407 By performing the experiment while passing through the side (FIG. 4F) or changing these combinations, the range in which the measurement error of the sheet interval can be determined. The measurement result of the sheet length Lp varies in the range from Lp−ΔLmin to Lp + ΔLmax. The difference ΔL between the lower limit value and the upper limit value of the sheet length Lp for one sheet is ΔLmin + ΔLmax. Therefore, the possible range of the measurement error of the sheet length measurement result Lmsr is a range from −ΔLmax to + ΔLmin.

  FIG. 7 is a flowchart illustrating a determination process of the adjustment amount (reduction amount Q) of the sheet interval in the second embodiment.

  In step S11, the conveyance control unit 202 acquires a lower limit interval Lmin_intrvl, a target interval Lt, and ranges ΔLmax and ΔLmin that can be taken by measurement errors. For example, the conveyance control unit 202 reads these parameters from the ROM. Alternatively, the conveyance control unit 202 may calculate the target interval Lt from the throughput.

  In S12, the conveyance control unit 202 determines whether or not the lower limit interval Lmin_intrvl can be secured even when the measurement error becomes maximum. The initial value of the reduction amount Q is the difference between the sheet interval measurement result Lintrvl and the target interval Lt. The sheet interval measurement error is in the range of -ΔLmin to + ΔLmax because the same component as the sheet length measurement error is included. When the error component is maximized, the corrected sheet interval becomes the target interval Lt−ΔLmin. If this value is equal to or greater than the lower limit interval Lmin_intrvl, a sheet interval equal to or greater than the lower limit interval Lmin_intrvl is ensured even if the error is maximized. Therefore, the conveyance control unit 202 may determine whether (target interval Lt−ΔLmin) is equal to or greater than the lower limit interval Lmin_intrvl. If (target interval Lt−ΔLmin) is equal to or greater than the lower limit interval Lmin_intrvl, even if the succeeding sheet is further accelerated by ΔL and the sheet interval is reduced, the lower limit interval Lmin_intrvl is ensured. .

  In step S13, the conveyance control unit 202 positively corrects the reduction amount Q. For example, the conveyance control unit 202 may calculate the reduction amount Q by subtracting the target interval Lt from the sheet interval measurement result Lintrvl and further adding ΔLmax.

  On the other hand, if it is determined that the lower limit interval Lmin_intrvl cannot be secured when the measurement error is maximized, the transport control unit 202 proceeds to S14. In step S14, the conveyance control unit 202 negatively corrects the reduction amount Q. For example, the conveyance control unit 202 determines the reduction amount Q by subtracting the target interval Lt from the sheet interval measurement result Lintrvl, and corrects the reduction amount Q by subtracting ΔLmin from the reduction amount Q.

  By correcting the reduction amount Q in this way, it is possible to appropriately correct the reduction amount Q. By the way, ΔLmin and ΔLmax are obtained experimentally in consideration of where the sheet S passes in the conveyance path. However, ΔLmin and ΔLmax differ depending on the type of sheet (basis weight, presence / absence of coat, etc.). By using various types of sheets for the experiment, ΔLmin and ΔLmax independent of the types may be obtained and stored in the ROM. Alternatively, an experiment may be performed for each type of sheet S, and ΔLmin and ΔLmax may be obtained for each type and stored in the ROM. In this case, the conveyance control unit 202 may read ΔLmin and ΔLmax corresponding to the type designated by the operator through the operation panel 211 from the ROM and add them to obtain ΔL.

  As described above, in the second embodiment, a possible range of measurement error is obtained at the time of factory shipment, and the reduction amount Q is determined according to this range. Therefore, the case where the sheet interval cannot be detected by the paper discharge sensor 109 due to the measurement error of the top sensor 107 is reduced, and the throughput is also maintained.

[Example 3]
In the first and second embodiments, the sheet sensor 400 having the photo interrupter 401 and the flag 402 has been described as the top sensor 107. However, other types of sheet sensors may be employed in the present invention. In Embodiment 3, a rotary sheet sensor will be described. In the third embodiment, description of matters common to the first and second embodiments is omitted.

  8A to 8F are views for explaining the structure and operation of the rotary sheet sensor 400 '. The sheet sensor 400 ′ includes a shaft 904 serving as a rotation center, a flag 902 for detecting the sheet S, a photo interrupter flag 903, and a photo interrupter 901. The flag 902 and the flag 903 are fixed to the shaft 904 and rotate together. The sheet S is conveyed from the right side to the left side along the conveyance guide 404.

  FIG. 8A shows the sheet sensor 400 ′ in a state where the sheet S is not passed. In FIG. 8A, the flag 902 is located at the home position. When the sheet S is not passed, the flag 902 is returned to the home position by the cam mechanism and a power source such as a spring. When the flag 902 is located at the home position, the photo interrupter 901 is maintained in a light-shielded state by the flag 903.

  As shown in FIG. 8B, when the sheet S reaches the sheet sensor 400 ′, the leading end of the sheet S pushes the flag 902, so that the shaft 904 rotates counterclockwise. When the leading edge of the sheet S reaches the leading edge detection position P3, the photo interrupter 901 changes from the light shielding state to the light transmitting state. Accordingly, the conveyance control unit 202 can detect the leading edge of the sheet S. When the sheet S is further conveyed, the leading edge of the sheet S does not engage with the protruding portion of the flag 902.

  As shown in FIG. 8C, the central portion of the sheet S is engaged with the protrusion. At this time, although the peripheral speed of the protrusion is smaller than the conveying speed of the sheet S, the flag 902 rotates counterclockwise by a cam mechanism (not shown). The flag 902 is provided with three projections at intervals of 120 degrees. Each time one sheet S passes through the sheet sensor 400 ', the flag 902 rotates 120 degrees by the action of the cam.

  As shown in FIG. 8D, the photo interrupter 901 changes from the light-transmitting state to the light-blocking state at the timing when the rear end of the sheet S reaches the rear end detection position P4. Thereby, the conveyance control unit 202 can detect the trailing edge of the sheet S.

  In the first embodiment, an error occurs in the measurement result of the sheet interval Lintrvl depending on the return time Tb of the flag 402 of the top sensor 107 in addition to the distance Lf between the edge detection position P1 and the removal position P2. On the other hand, in the case of the rotary sheet sensor 400 ′, as shown in FIGS. 8E and 8F, the posture of the sheet S due to the strain and curl of the sheet S is a main factor of error.

  FIG. 9 illustrates a relationship between each roller of the image forming apparatus 100 according to the third exemplary embodiment and a motor that drives the roller. The cam 1001 rotates the shaft 904 of the sheet sensor 400 'by 120 degrees.

  The Eq. 2, Eq. In Example 3 instead of Eq. 6, Eq. 7 is adopted.

Lmsr = L1 + Lf ′... Eq. 6
Lintrvl = L2−Lf ′... Eq. 7
Here, Lf ′ is a distance from the front end detection position P3 to the rear end detection position P4 as shown in FIG. 8D. Lf ′ is obtained by executing an experiment for conveying a typical sheet S at the time of factory shipment. Therefore, as described above, an error may occur with respect to the distance from the actual front end detection position P3 to the rear end detection position P4. The third embodiment is the same as the first embodiment except that the method for obtaining the sheet length measurement result Lmsr and the sheet interval measurement result Lintrvl is different. The following factors affect the possible range of measurement error of the sheet interval using the rotary sheet sensor 400 ′.
The tolerance of the shape of the flag 902 The tolerance of the shape of the flag 903 The attachment tolerance of the shaft 904 The attachment tolerance of the photo interrupter 901 The range in which the measurement error can be taken is obtained in advance by experiments through the lower side (FIG. 8F) or depending on the combination thereof. Therefore, the second embodiment can also be applied to the rotary sheet sensor 400 ′.

  Thus, even if the rotary sheet sensor 400 ′ is employed as the top sensor 107, the ideas of the first and second embodiments can be applied. That is, in the third embodiment, similarly to the first and second embodiments, the case where the sheet interval cannot be detected by the paper discharge sensor 109 due to the measurement error of the top sensor 107 is reduced, and the throughput is also maintained.

<Summary>
The function of the conveyance control unit 202 related to the first to third embodiments will be described with reference to FIG. These functions may be realized by a microprocessor executing a program, or may be realized by ASIC or FPGA hardware. Alternatively, some functions may be realized by software, and the remaining functions may be realized by hardware. The length measurement unit 501 measures the length Lmsr from the leading edge to the trailing edge of the sheet S based on the detection result of the top sensor 107. The designation unit 506 functions as an acquisition unit that acquires the nominal value L0 of the length in the transport direction of the preceding sheet based on the sheet size specified by the operator. The interval measurement unit 502 measures the sheet interval Lintrvl from the trailing edge of the preceding sheet to the leading edge of the succeeding sheet based on the detection result of the top sensor 107. The jam detection unit 503 detects the occurrence of a jam based on the detection result of the paper discharge sensor 109.

  The determination unit 504 determines the following sheet from the trailing end of the preceding sheet according to the difference d between the sheet interval Lintrvl from the trailing end of the preceding sheet to the leading end of the succeeding sheet measured based on the detection result of the top sensor 107 and the target interval Lt. An adjustment amount (e.g., reduction amount Q) of the interval to the tip of the is determined. The correction unit 505 corrects the adjustment amount so that the discharge sensor 109 can detect the trailing edge of the preceding sheet and the leading edge of the succeeding sheet. For example, the correction unit 505 adjusts according to the error Δ of the measurement value of the length in the conveyance direction of the preceding sheet measured based on the detection result of the top sensor 107 with respect to the nominal value of the length in the conveyance direction of the preceding sheet. Correct the amount. As described with reference to FIG. 6, the motor control unit 507 controls the paper feed motor 301 so that the transport speed of the transport roller 104 or the registration roller 106 temporarily increases or decreases over a time corresponding to the corrected adjustment amount. To do. As a result, the sheet interval can be controlled more accurately than in the past. In other words, it will be possible to reduce false detection of jam while maintaining throughput.

  As described with respect to S5, the determination unit 510 determines whether the leading edge of the preceding sheet and the leading edge of the succeeding sheet are detected even if the sheet interval is reduced based on the target interval Lt, the error Δ, and the lower limit interval that is a predetermined interval. It may be determined whether it can be detected at 109. Here, it may be determined whether the difference between the target interval Lt and the error Δ is greater than or equal to the lower limit interval Lmin_intrvl. This corresponds to determining whether the value obtained by reducing the difference d between the sheet interval Lintrvl and the target interval Lt and the error Δ from the sheet interval Lintrvl is equal to or greater than the lower limit interval Lmin_intrvl. The correction unit 505 increases, maintains, or decreases the reduction amount Q according to the determination result of the determination unit 510.

  As described regarding S4, the first determination unit 511 determines that the measured value Lmsr of the length in the transport direction of the preceding sheet measured based on the detection result of the top sensor 107 is equal to or greater than the nominal value of the length in the transport direction of the preceding sheet. It is determined whether it is (reference value or more). As described with respect to S5, the second determination unit 512 determines whether the difference obtained by subtracting the error Δ from the target interval Lt is equal to or greater than the lower limit interval Lmin_intrvl when the measured value Lmsr is equal to or greater than the nominal value. May be. The correction unit 505 increases the reduction amount Q when the measured value Lmsr is equal to or greater than the nominal value and the difference obtained by subtracting the error Δ from the target interval Lt is equal to or greater than the lower limit interval Lmin_intrvl. That is, as described for S6, the correction unit 505 increases the reduction amount Q by the error Δ. This improves the throughput. On the other hand, the correction unit 505 does not correct the reduction amount Q when the measured value Lmsr is equal to or larger than the nominal value but the difference obtained by subtracting the error Δ from the target interval Lt is not equal to or greater than the predetermined interval. In this case, the reduction amount Q = the difference d. This will allow the paper discharge sensor 109 to detect the sheet spacing and reduce false jam detection.

  As described with respect to S8, when the measured value Lmsr is not greater than or equal to the nominal value, the third determination unit 513 determines that the difference obtained by subtracting the difference Δ between the measured value and the nominal value from the target interval Lt is equal to or less than the predetermined interval (or It is determined whether it is less than a predetermined interval. The predetermined interval is the lower limit interval Lmin_intrvl. When the measured value Lmsr is not greater than the nominal value and the difference obtained by subtracting the measured value difference Δ from the nominal value from the target interval Lt is equal to or less than the lower limit interval Lmin_intrvl, the correction unit 505 Is not corrected. This will allow the paper discharge sensor 109 to detect the sheet spacing and reduce false jam detection. On the other hand, when the measured value Lmsr is not greater than the nominal value and the difference obtained by subtracting the measured value difference Δ from the nominal value from the target interval Lt is not less than the lower limit interval Lmin_intrvl, the correction unit 505 reduces the reduction amount Q. To reduce. For example, the correction unit 505 may reduce the reduction amount Q by the difference Δ obtained by subtracting the measured value Lmsr from the nominal value. This improves the throughput.

  As described with reference to FIG. 6, the motor control unit 507 increases the transport speed of the transport roller 104 and the like over the time corresponding to the reduction amount Q from the first transport speed vps to the second transport that is faster than the first transport speed. Increase to speed vacc. The first transport speed vps is a speed determined based on the throughput of the image forming apparatus 100. This reduces sheet spacing and improves throughput. For example, the motor control unit 507 linearly increases the conveyance speed in the first period Tacc starting from the timing t1 at which the increase in the conveyance speed is started. These can be easily realized by storing a speed-up table in the ROM as a control table. Further, the motor control unit 507 maintains the transport speed at the second transport speed vass in the second period Tsteady starting from the timing when the transport speed reaches the second transport speed vacc. Further, the motor control unit 507 linearly decreases the transport speed and returns it to the first transport speed vps in the third period Tdec following the second period. These can be easily realized by holding a slow-down table in the ROM as a control table.

  As described with reference to FIG. 7, the determination unit 510 may determine whether the value obtained by subtracting ΔLmin from the target interval Lt is equal to or greater than a predetermined interval. ΔLmin is an upper limit value of an error in the measured value Lmsr of the length in the conveyance direction of the preceding sheet that may occur in the top sensor 107, and is obtained in advance at the time of factory shipment. As described with respect to S13, the correction unit 505 increases the reduction amount Q by the upper limit ΔL when the value obtained by subtracting from the target interval Lt is equal to or greater than the predetermined interval. This improves the throughput. On the other hand, as described with respect to S14, the correction unit 505 reduces the reduction amount Q by the upper limit value ΔL when the value obtained by subtracting ΔLmin from the target interval Lt is not equal to or greater than the predetermined interval. As a result, the sheet interval can be detected by the paper discharge sensor 109. The upper limit value ΔL may be determined in advance based on variations in the shapes of the plurality of members constituting the top sensor 107, mounting tolerances of the plurality of members, and variations in the posture of the seat when passing through the top sensor 107. .

  As the top sensor 107, various types of sheet sensors can be used. As described with reference to FIG. 4A and the like, the top sensor 107 may include a flag 402 that is pressed by the leading edge of the sheet S and rotates about the rotation shaft 403. Further, the top sensor 107 may include a photo interrupter 401 that switches between a light shielding state and a light transmitting state according to the phase of the flag 402. As described with reference to FIG. 4A and the like, the flag 402 is pushed by the leading end of the sheet S and rotates in the first direction, and when the trailing end of the sheet S passes the flag 402, the second direction is opposite to the first direction. You may rotate to. As described with reference to FIG. 8A and the like, a cam 1001 may further be provided that restricts the flag 903 to rotate by a certain angle while the sheet S passes.

  In the embodiment described above, it has been described that when the top sensor 107 detects the succeeding sheet, the succeeding sheet is accelerated to reduce the interval between the preceding sheet and the succeeding sheet. However, the conveyance control unit 202 may increase the interval between the preceding sheet and the succeeding sheet by decelerating the succeeding sheet when the top sensor 107 detects the succeeding sheet. In this case, the adjustment amount described above is an increase amount or an enlargement amount. In any case, the present invention can be applied to conveyance control for accelerating or decelerating a sheet in order to adjust the sheet interval to a specified interval. The above embodiment is based on the premise that the minimum paper interval that can be detected by the top sensor 107 is shorter than the minimum paper interval that can be detected by the paper discharge sensor 109. However, this restriction is not essential for the present invention. The conveyance control unit 202 detects that the error of the measured value of the length of the preceding sheet with respect to the length (nominal value) in the conveyance direction of the preceding sheet is too large (the error exceeds a predetermined threshold). May be. In such a case, the conveyance control unit 202 determines that an error (size error) that the sheet sizes do not match has occurred, and stops the image forming operation including the conveyance of the sheet. The error described in the above-described embodiment is an error that does not cause a size error.

  FIG. 11 shows the image forming apparatus 100 with the paper feed option 150 attached. The sheet feeding option 150 is a sheet feeding device or a sheet conveying device that stores and feeds sheets S having the same size as the standard cassette or sheets S having a different size. When the paper feed roller 152 rotates, the sheets S are fed one by one. The conveyance roller 153 sends the sheet S delivered from the paper supply roller 152 to the conveyance roller 104. The conveyance roller 104 feeds the sheet S to the registration roller 106. As a result, an image is also formed on the sheet S supplied from the paper feed option 150. The paper feed sensor 154 is a sheet sensor that detects a sheet fed from the paper feed option 150 to the image forming apparatus 100, and can function as the first detection unit described above. In this case, the top sensor 107 and the paper discharge sensor 109 described above may function as the second detection unit.

  FIG. 12A shows an option control unit 250 that controls the paper feed option 150. When the sheet feeding instruction is issued from the conveyance control unit 202, the option control unit 250 drives the sheet feeding motor 251 to rotate the sheet feeding roller 152 by the sheet feeding motor 251. Thereby, the sheet S is fed. Further, the option control unit 250 rotates the transport roller 153 by driving the main motor 252. As a result, the sheet S is conveyed to the image forming apparatus 100. The option control unit 250 notifies the conveyance control unit 202 that the leading edge of the sheet S has been detected by the paper feed sensor 154 and the trailing edge has been detected. As a result, the conveyance control unit 202 can recognize the positions of the leading and trailing edges of the sheet S supplied from the sheet feeding option 150.

  FIG. 12B shows that the option control unit 250 is omitted, and the conveyance control unit 202 is connected to the paper feed motor 251, the main motor 252, and the paper feed sensor 154 and directly controls them. As described above, the conveyance control unit 202 provided in the image forming apparatus 100 may directly control the paper feed option 150.

  The above-described sheet conveyance control can also be applied to the sheet feeding option 150. The conveyance roller 153 is an example of a conveyance unit that conveys a sheet in the conveyance path. The paper feed sensor 154 is an example of a detection unit that detects a sheet in the conveyance path. The option control unit 250 or the conveyance control unit 202 starts from the trailing end of the preceding sheet according to the difference between the target interval and the distance from the trailing end of the preceding sheet measured based on the detection result of the paper feed sensor 154 to the leading end of the succeeding sheet. It is an example of a determination unit (for example, a determination unit 504) that determines the adjustment amount of the interval to the leading edge of the subsequent sheet. The option control unit 250 or the conveyance control unit 202 responds to an error in the measurement value of the length in the conveyance direction of the preceding sheet measured based on the detection result of the detection unit with respect to the reference value of the length in the conveyance direction of the preceding sheet. It is an example of the correction means (example: correction unit 505) for correcting the adjustment amount. The option control unit 250 or the conveyance control unit 202 controls the conveyance unit so that the conveyance speed of the conveyance unit increases or decreases over the time corresponding to the adjustment amount corrected by the correction unit (for example, the motor control unit 507). It is an example. Note that some or all of the functions of the transport control unit 202 illustrated in FIG. 10 may be realized by the option control unit 250.

  Although only one sheet sensor (paper feed sensor 154) is provided in FIG. 11, the paper feed option 150 may include a plurality of sheet sensors. In this case, the sheet sensor disposed on the upstream side in the sheet conveyance direction functions as the first detection unit described above, and the sheet sensor disposed on the downstream side functions as the second detection unit described above. The option control unit 250 uses these two sheet sensors to execute sheet conveyance control, but this conveyance control may be the same as the conveyance control executed by the conveyance control unit 202.

  DESCRIPTION OF SYMBOLS 100 ... Image forming apparatus 104 ... Conveyance roller 106 ... Registration roller 107 ... Top sensor 109 ... Paper discharge sensor 301 ... Paper feed motor 302 ... Main motor 401 ... Photo interrupter 402 ... Flag

Claims (17)

Conveying means for conveying the sheet in the conveying path;
First detection means for detecting a sheet in the conveyance path;
The distance from the trailing edge of the preceding sheet to the leading edge of the succeeding sheet according to the difference between the distance from the trailing edge of the preceding sheet to the leading edge of the succeeding sheet and the target distance measured based on the detection result of the first detecting means Determining means for determining the adjustment amount of
The adjustment amount is corrected according to an error in the measured value of the length in the transport direction of the preceding sheet measured based on the detection result of the first detection unit with respect to the reference value of the length in the transport direction of the preceding sheet. Correction means for
An image forming apparatus comprising: a control unit configured to control the transport unit so that a transport speed of the transport unit is increased or decreased over a time corresponding to the adjustment amount corrected by the correction unit. The second detection means for detecting the sheet is further disposed on the downstream side of the conveyance direction of the sheet with respect to the first detection means in the conveyance path,
The correction means corrects the adjustment amount according to the error so that the second detection means can detect the trailing edge of the preceding sheet and the leading edge of the succeeding sheet. Image forming apparatus. The distance from the trailing edge of the preceding sheet to the leading edge of the succeeding sheet based on the target distance, the error, and the predetermined distance that can be detected by the second detection means from the trailing edge of the preceding sheet and the leading edge of the succeeding sheet. Further comprising a determination means for determining whether the second detection means can detect the trailing edge of the preceding sheet and the leading edge of the succeeding sheet even if the difference and the error are reduced from
The image forming apparatus according to claim 2, wherein the correction unit increases, maintains, or decreases the adjustment amount according to a determination result of the determination unit. First determination means for determining whether a measured value of the length in the conveyance direction of the preceding sheet measured based on the detection result of the first detection means is equal to or greater than a reference value of the length in the conveyance direction of the preceding sheet. When,
When the measured value is greater than or equal to the reference value, the difference obtained by subtracting the error from the target interval can be detected by the second detection means from the trailing edge of the preceding sheet and the leading edge of the succeeding sheet. And second determination means for determining whether or not the predetermined interval is exceeded,
The correction means increases the adjustment amount when the measured value is equal to or greater than the reference value and a difference obtained by subtracting the error from the target interval is equal to or greater than the predetermined interval, 3. The image according to claim 2, wherein the adjustment amount is not corrected when a value obtained by subtracting the error from the target interval is not equal to or greater than the predetermined interval although the value is equal to or greater than the reference value. Forming equipment.   When the measured value is equal to or greater than the reference value, and the difference obtained by subtracting the error from the target interval is equal to or greater than the predetermined interval, the correction means reduces the adjustment amount by the amount of the error. The image forming apparatus according to claim 4, wherein the number is increased. Third determination means for determining whether or not a difference obtained by subtracting a difference of the measurement value with respect to the reference value from the target interval is equal to or less than the predetermined interval when the measurement value is not equal to or more than the reference value. Have
The correcting means adjusts the adjustment when the measured value is not equal to or greater than the reference value and the difference obtained by subtracting the difference of the measured value with respect to the reference value from the target interval is equal to or less than the predetermined interval. The adjustment is performed when the amount is not corrected, the measured value is not greater than or equal to the reference value, and the difference obtained by subtracting the difference of the measured value with respect to the reference value from the target interval is not less than or equal to the predetermined interval. The image forming apparatus according to claim 4, wherein the amount is reduced.   The correction means, when the measured value is not greater than or equal to the reference value and the difference obtained by subtracting the difference of the measured value with respect to the reference value from the target interval is not less than or equal to the predetermined interval. The image forming apparatus according to claim 4, wherein the adjustment amount is reduced by a difference obtained by subtracting the measurement value from the image.   The control means has a second transport speed that is higher than the first transport speed from a first transport speed determined based on a throughput of the image forming apparatus over a time corresponding to the adjustment amount. The image forming apparatus according to claim 1, wherein the image forming apparatus is accelerated.   The control means linearly increases the transport speed of the transport means in a first period starting from the timing at which the transport speed of the transport means is started, and the transport speed of the transport means is the second transport speed. The transport speed of the transport means is maintained at the second transport speed in the second period starting from the timing at which the speed is reached, and the transport speed of the transport means is linearly reduced in the third period following the second period. The image forming apparatus according to claim 8, wherein the image forming apparatus returns to the first conveyance speed.   The image forming apparatus according to claim 1, further comprising an acquisition unit configured to acquire a reference value of a length in the conveyance direction of the preceding sheet based on a size of the sheet designated by an operator. The value obtained by subtracting the upper limit of the error in the length measurement value in the conveyance direction of the preceding sheet that can occur in the first detection unit from the target interval is the trailing edge of the preceding sheet and the subsequent sheet. A determination means for determining whether or not the tip is equal to or longer than a predetermined interval detectable by the second detection means;
The correction means increases the adjustment amount when a value obtained by subtracting from the target interval is equal to or greater than the predetermined interval, and when the value obtained by subtracting from the target interval is not equal to or greater than the predetermined interval, The image forming apparatus according to claim 2, wherein the adjustment amount is decreased.   The correction means increases the adjustment amount by the upper limit when the value obtained by subtracting from the target interval is equal to or greater than the predetermined interval, and the value obtained by subtracting from the target interval is the predetermined value. 12. The image forming apparatus according to claim 11, wherein the adjustment amount is decreased by an amount corresponding to the upper limit value when the interval is not greater than the interval.   The upper limit value is determined in advance based on variations in the shapes of the plurality of members constituting the first detection means, attachment tolerances of the plurality of members, and variations in the posture of the sheet when passing through the first detection means. The image forming apparatus according to claim 11. The first detection means includes
A flag that is pushed by the leading edge of the sheet and rotates around the rotation axis;
The image forming apparatus according to claim 1, further comprising: a photo interrupter that switches between a light shielding state and a light transmitting state in accordance with a phase of the flag.   The flag is pushed by the leading end of the sheet and rotates in a first direction, and when the trailing end of the sheet passes through the flag, the flag rotates in a second direction opposite to the first direction. Item 15. The image forming apparatus according to Item 14.   The image forming apparatus according to claim 14, further comprising a cam mechanism that restricts the flag to rotate by a predetermined angle while the sheet passes. Conveying means for conveying the sheet in the conveying path;
Detecting means for detecting a sheet in the conveying path;
Adjustment of the distance from the trailing edge of the preceding sheet to the leading edge of the succeeding sheet according to the difference between the distance from the trailing edge of the preceding sheet to the leading edge of the succeeding sheet and the target distance measured based on the detection result of the detecting means A determining means for determining the amount;
Correction for correcting the adjustment amount according to an error in the measured value of the length in the transport direction of the preceding sheet measured based on the detection result of the detection unit with respect to the reference value of the length in the transport direction of the preceding sheet Means,
And a control unit that controls the conveyance unit so that the conveyance speed of the conveyance unit is increased or decreased over a period of time corresponding to the adjustment amount corrected by the correction unit.