Image forming device

Abstract

To provide an image forming device that reduces false detection of transport failure caused by a skewed paper.SOLUTION: Image forming device is equipped with a transport path, a paper width sensor 104, a register sensor 109, a discharge sensor 112, and a jam detection unit 807 that detects a paper jam of a recording material S based on the timing when the recording material S is detected by the register sensor 109 and the timing when the recording material S is detected by the discharge sensor 112. The jam detection unit 807 corrects the deviation of the timing of detecting the recording material S by the discharge sensor 112 based on the skew amount.SELECTED DRAWING: Figure 8

Description

[Technical field]

[0001] The present invention relates to an image forming apparatus, and more particularly to conveyance control of an image forming apparatus including a sheet conveying device that detects skew of a sheet by using a plurality of sensors. [Background technology]

[0002] Conventional image forming devices detect the posture of a sheet of paper using a sensor arranged in the width direction of the sheet on the transport path, and estimate the skew of the sheet (see, for example, Patent Document 1). Meanwhile, a control that detects a paper jam based on the detection timing of a plurality of sensors arranged in the transport direction of the sheet on the transport path and stops the transport of the sheet is also widely known. For example, a paper jam is generally detected based on the detection timing of a sensor arranged upstream in the transport direction, and whether or not the detection of a sensor arranged downstream in the transport direction is within a predetermined range. Also, in an image forming device that performs double-sided transport, a configuration is known in which the timing of reversing the sheet of paper is determined based on the detection timing of a sensor on the transport path. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent Publication No. 2022-141424 Summary of the Invention [Problem to be solved by the invention]

[0004] However, if the deviation in detection timing due to skewed paper becomes large, the difference in the configuration between the upstream sensor and the downstream sensor may cause the detection timing to be shifted due to the skew, which may result in a false detection due to a factor other than the actual paper jam detection. Also, if the detection timing of the downstream sensor is shifted, for example, the timing of paper inversion may be shifted due to the skew, so the paper will be inverted at a timing different from the timing at which the inversion was originally intended to start. This may result in the paper not being properly fed into the duplex conveying path, or the edge of the skewed paper being bent when inverted.

[0005] The present invention has been made under such circumstances, and has an object to reduce erroneous detection of transport failure caused by skewed paper. [Means for solving the problem]

[0006] In order to solve the above-mentioned problems, the present invention has the following configuration.

[0007] (1) An image forming apparatus that forms an image on a recording material, comprising: a transport path along which the recording material is transported; a first sensor that is disposed on the transport path and detects the leading and trailing ends of the recording material; a second sensor that is disposed on the transport path downstream of the first sensor in the transport direction of the recording material and at a position different from the first sensor in the direction perpendicular to the transport direction and detects the leading and trailing ends of the recording material; an acquisition unit that acquires an amount of skew of the recording material based on detection results of the first sensor and the second sensor; a third sensor that is disposed on the transport path downstream of the second sensor in the transport direction and at a position different from the second sensor in the direction perpendicular to the transport direction and detects the leading and trailing ends of the recording material; and a detection unit that detects a paper jam of the recording material based on a timing at which the recording material is detected by the first sensor or the second sensor and a timing at which the recording material is detected by the third sensor, wherein the detection unit corrects a deviation in the timing at which the recording material is detected by the third sensor based on the amount of skew acquired by the acquisition unit.

[0008] (2) An image forming apparatus for forming an image on a recording material, the apparatus comprising: a transport path along which the recording material is transported; a discharge section to which the recording material transported on the transport path is discharged; a rotating member disposed on the transport path and transporting the recording material, the rotating member being capable of switching its rotation direction to a first direction in which the recording material is guided to the discharge section or a second direction opposite to the first direction; a reversing section to which the recording material is guided by the rotating member rotating in the second direction; a first sensor disposed on the transport path and for detecting leading and trailing ends of the recording material; and a second sensor disposed on the transport path downstream of the first sensor in a transport direction of the recording material, the second sensor being disposed at a position different from the first sensor in a direction perpendicular to the transport direction, the first sensor being disposed at a position different from the first sensor in a direction perpendicular to the transport direction, the second ... an acquisition unit that acquires an amount of skew of the recording material based on a detection result of the first sensor or the second sensor; a third sensor that is arranged on the conveying path downstream of the second sensor in the conveying direction and at a position different from the second sensor in a direction perpendicular to the conveying direction, for detecting the leading and trailing ends of the recording material; and a control unit that switches the rotation direction of the rotating member based on a timing at which the recording material is detected by the third sensor, wherein the control unit predicts a deviation in timing at which the recording material is detected by the third sensor based on the amount of skew acquired by the acquisition unit, and corrects the switching timing for switching the rotation direction of the rotating member. Effect of the Invention

[0009] According to the present invention, it is possible to reduce erroneous detection of transport failure caused by skewed paper. [Brief description of the drawings]

[0010] [Figure 1] Cross-sectional view of an image forming apparatus according to embodiments 1 to 3. [Diagram 2] 1 is a perspective view and a cross-sectional view of a paper width sensor according to an embodiment of the present invention; [Diagram 3] FIG. 13 is a diagram showing detection of the trailing end of a recording material by a paper width sensor in the first to third embodiments. [Figure 4] 1 is a perspective view and a cross-sectional view of a registration sensor according to an embodiment of the present invention; [Diagram 5] FIG. 13 is a diagram showing detection of the trailing end of a recording material by a registration sensor in the first to third embodiments; [Figure 6] Cross-sectional view of the discharge sensor of Examples 1 to 3 [Figure 7] FIG. 13 is a diagram showing detection of the trailing end of a recording material by a discharge sensor in Examples 1 to 3. [Figure 8] Control block diagram of an image forming apparatus according to a first embodiment [Figure 9] Schematic diagram of detection of skew amount by a paper width sensor and a registration sensor in the first embodiment. [Figure 10] 1 is a timing chart showing the control of the clogging detection unit according to the first embodiment. [Figure 11] 3 is a cross-sectional view of a fixing unit, a discharge unit, and a reversing unit according to the second embodiment; [Figure 12] Control block diagram of an image forming apparatus according to a second embodiment [Figure 13] Schematic diagram of a discharge sensor and a timing for reversing a recording material according to the second embodiment. [Figure 14] FIG. 11 is a schematic diagram showing detection of the amount of skew by a registration sensor and a discharge sensor according to the second embodiment; [Figure 15] Timing chart showing the inversion control in the second embodiment [Figure 16] Flowchart showing the inversion control of the third embodiment DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS EXAMPLES

[0011] A first embodiment of the present invention will be described. The first embodiment is a monochrome laser beam printer using an electrophotographic method, which forms a toner image on a recording material S in response to image information transmitted from an external device such as a personal computer. Examples of the recording material S include recording paper, label paper, OHP sheets, cloth, etc.

[0012] (Configuration of image forming device) FIG. 1 is a schematic diagram showing the configuration of an image forming apparatus 100 according to a first embodiment. The image forming apparatus 100 is a monochrome printer that forms an image on a recording material S based on image information input from an external device. The image forming apparatus 100 includes a pickup roller 101 for feeding the recording material S from an open tray. The fed recording material S is separated into only one sheet by a conveying roller 102 that separates and conveys the recording material S and a separation roller 103 that is driven in an opposing manner. After the recording material S is separated, the paper width can be detected by a paper width sensor 104. Here, the paper width refers to the length in a direction (width direction) perpendicular to the conveying direction of the recording material S.

[0013] The separated recording material S is conveyed while its skew is corrected by a registration roller 105 and a registration shutter roller 106 driven opposite to the roller. The cartridge 107 includes a photosensitive drum 108, and forms an electrostatic latent image on the photosensitive drum 108 by a general electrophotographic method to form a toner image. The toner image is transferred to the recording material S by the photosensitive drum 108 in synchronization with the conveyance timing of the recording material S by a registration sensor 109. The recording material S with the transferred toner image is thermally fixed by a pressure roller 110 and a heating film 111. A discharge sensor 112 is provided to detect the recording material S being wrapped around the heating film 111 and a conveyance failure. The recording material S with the thermally fixed toner image is discharged outside the machine by a pair of discharge rollers 113 as a rotating member. When double-sided printing is instructed, the pair of discharge rollers 113 is reversed based on the timing when the recording material S passes the discharge sensor 112, and the recording material S is drawn into the double-sided conveyance path by a drawing operation. The pulled-in recording material S is again transported to the nip portion formed by the registration roller 105 and the registration shutter roller 106 by the driven double-sided transport roller 114 and the registration roller 105, and a toner image is transferred to the back surface in the same manner as the front surface. The image forming apparatus 100 also includes a display unit 120. The display unit 120 displays various information related to the image forming apparatus 100. The above configuration is one form for explaining the embodiment, and the scope of the present invention is not limited to the above configuration.

[0014] (About the configuration of the paper width sensor) Next, the configuration and operation of the paper width sensor 104 as the first sensor in the first embodiment will be described with reference to FIG. 2. FIG. 2(a) is a perspective view of the paper width sensor 104. The photointerrupter 200 is in a transparent state when there is no recording material S (hereinafter, this is referred to as a normal state). The paper width sensor 104 has the photointerrupter 200, flags 201a and 201b, a link member 202, and a light-shielding portion 202a that interlocks with the link member 202. The flags 201a and 201b are provided at positions symmetrical in the width direction with respect to the center position in the width direction perpendicular to the conveying direction of the recording material S. The flags 201a and 201b are also collectively referred to as flags 201. When there is no recording material S, the light-shielding portion 202a is supported upward by the flags 201a and 201b provided at positions corresponding to both ends of the link member 202 in the width direction, and the photointerrupter 200 is in a transparent state. When the recording material S is conveyed here, the flags 201a and 201b are pushed by the recording material S, causing the link member 202 to rotate. In conjunction with this, the light-shielding portion 202a also rotates and blocks the light of the photointerrupter 200. In other words, the light-shielding portion 202a rotates as the recording material S passes through and blocks the light of the photointerrupter 200, thereby detecting that the width of the recording material S is wider than the distance between the flags 201a and 202b.

[0015] 2(b) and 2(c) are views of the paper width sensor 104 as viewed from the cross-sectional direction of FIG. 1. When the light-shielding portion 202a of the link member 202 is pushed up by the flag 201 as in FIG. 2(b), the photointerrupter 200 is in a light-transmitting state. When the recording material S passes, the flag 201 is knocked down and rotated as in FIG. 2(c), and in conjunction with this, the link member 202 rotates, and the photointerrupter 200 enters a light-shielding state.

[0016] In FIG. 2(d), (i) shows the state of flag 201a (no paper, paper present), (ii) shows the state of flag 201b (no paper, paper present), and (iii) shows the state of photointerrupter 200. The horizontal axis in each case is time. Note that the photointerrupter 200 is in the OFF (low level) state when in the transmitting state and in the ON (high level) state when in the light-blocking state. As shown in FIG. 2(d), when both flag 201a and flag 201b are knocked down by the recording medium S, the photointerrupter 200 is blocked from light, and when the recording medium S has finished passing either flag 201a or 201b, the photointerrupter 200 becomes transmissive.

[0017] (Relationship between the flag and the recording medium) Subsequently, the relationship between the detection by the flag 201 of the paper width sensor 104 in Example 1 and the recording medium S is shown with reference to FIG. 3. FIG. 3(a) shows a state in which the recording medium S has passed and knocked down the flag 201. As shown in FIG. 3(b), when the recording medium S has passed to the position of S_dtct and passed through the flag 201, the photointerrupter 200 becomes in the light-transmitting state. FIG. 3(c) shows the detection timing in a state where the recording medium S is skewed. Flag 201b has been knocked down by the recording medium S, but since the end portion (rear end portion) of the skewed recording medium S has passed through flag 201a, flag 201a has rotated and the photointerrupter 200 has returned to the light-transmitting state. At this time, the rear end position on the central axis Cn of the conveyance path of the recording medium S lags behind by L_over with respect to the phase at which the flag 201 passes through (the timing at which the photointerrupter 200 changes from light-blocking to light-transmitting).

[0018] (Regarding the configuration of the registration sensor) Next, the configuration and operation of the registration sensor 109 as the second sensor in the first embodiment will be described with reference to Fig. 4. Fig. 4(a) is a perspective view of the registration sensor 109. The recording material S passes through a nip portion formed by a driven registration roller 105 and a driven registration shutter roller 106. A registration shutter 400 is provided downstream of the nip portion in the conveying direction so as to block the path of the recording material S, and rotates when the leading edge of the recording material S is pushed in. The rotation of the registration shutter 400 also rotates a light-shielding portion 400a, and the photointerrupter 401 changes from a transmitting state to a light-shielding state, thereby detecting the leading edge of the recording material S.

[0019] Fig. 4(b) is a cross-sectional view of the registration sensor 109 in a light-transmitting state. When the registration shutter 400 blocks the path of the recording material S, the photointerrupter 401 is in a light-transmitting state. When the recording material S is transported by the registration roller 105 as shown in Fig. 4(c), the registration shutter 400 is pushed up and rotates, and the photointerrupter 401 enters a light-blocking state. As described above, the registration sensor 109 is linked to the rotation of the registration shutter 400, so that the leading edge of the recording material S is detected at the timing when the transport force of the leading edge of the recording material S pushes up the registration shutter 400.

[0020] (Relationship between the register shutter and the recording material) Next, the relationship between detection by the registration sensor 109 and the recording material S in the first embodiment will be shown with reference to Fig. 5. Fig. 5(a) shows a state in which the recording material S pushes up the registration shutter 400 and the photointerrupter 401 is blocking light. S_dtct is the position at which the recording material S passes through the registration shutter 400 and the photointerrupter 401 switches from blocking light to transmitting light. As shown in Fig. 5(b), when the rear end of the recording material S passes the position of S_dtct and the registration shutter 400 falls, the photointerrupter 401 becomes in a light transmitting state and the rear end of the recording material S can be detected.

[0021] FIG. 5C shows the detection timing when the recording material S is skewed. Since the registration shutter 400 cannot rotate until the rear end of the recording material S has passed, the timing when the rear end passes S_dtct and the registration shutter 400 falls is delayed by the amount of skew. In FIG. 5C, the left corner in the width direction of the rear end of the recording material S is the rear end. At this time, the rear end position of the recording material S, when considered from the central axis Cn of the conveying path of the skewed recording material S, will be advanced by L_delay with respect to the phase at which the recording material S passes through the registration shutter 400 (the timing at which the photointerrupter 401 changes from light-shielding to light-transmitting).

[0022] (About the configuration of the emission sensor) Next, the configuration and operation of the discharge sensor 112 as the third sensor in the first embodiment will be described with reference to FIG. 6. FIG. 6(a) is a cross-sectional view showing the fixing and discharging section of the image forming apparatus 100. The unfixed toner image on the recording material S is thermally fixed by the pressure roller 110 and the heating film 111. The flag 600 constituting the discharge sensor 112 is located downstream of the nip section between the pressure roller 110 and the heating film 111, and detects the passage of the recording material S. The pair of discharge rollers 113 discharges the recording material S after thermal fixing to the outside of the machine. When the pair of discharge rollers 113 operates to discharge the recording material S to the outside of the machine, the pair of discharge rollers 113 rotates in a counterclockwise direction in FIG. 6(a), which is called a forward rotation state. On the other hand, when the pair of discharge rollers 113 operates to pull the recording material S into the machine, the pair of discharge rollers 113 rotates in a clockwise direction in FIG. 6(a), which is called a reverse rotation state (reverse state).

[0023] Fig. 6(b) shows a cross-sectional view of the discharge sensor 112 in a light-shielding state. When the flag 600 is in the initial position, the photointerrupter 601 is in a light-shielding state due to the light-shielding portion 600a. Fig. 6(c) shows a cross-sectional view of the discharge sensor 112 in a light-transmitting state. When the recording material S passes, the light-shielding portion 600a also rotates in conjunction with the rotation of the flag 600, and the photointerrupter 601 becomes in a light-transmitting state.

[0024] (Relationship between flags and recording materials) Next, the relationship between detection by the discharge sensor 112 and the recording material S in the first embodiment will be shown with reference to Fig. 7. Fig. 7(a) shows a state in which the recording material S pushes up the flag 600 and the photointerrupter 601 is in a light-transmitting state. S_dtct is the position at which the trailing edge of the recording material S passes the flag 600 and the photointerrupter 601 switches from the light-transmitting state to the light-shielding state. As shown in Fig. 7(b), when the trailing edge of the recording material S passes the flag 600, the flag 600 returns to its original position and the photointerrupter 601 enters a light-shielding state, making it possible to detect the trailing edge of the recording material S.

[0025] 7C shows the detection timing when the recording material S is skewed. The image forming apparatus 100 is capable of forming images on various recording materials S having different widthwise lengths. In order to detect a paper jam in the fixing unit without being affected by the widthwise length of the recording material S, the flag 600 is attached at approximately the center of the position on the conveying path where the recording material S passes. Therefore, even when the recording material S is skewed, the detection timing of the flag 600 is configured such that L_over is not significantly delayed with respect to the actual trailing edge of the recording material S when considered at the center of the conveying path.

[0026] As described above, the paper width sensor 104, the registration sensor 109, and the discharge sensor 112 differ in the position of the flag in the width direction and the mechanism of switching between light transmission and light blocking of the photointerrupter. For this reason, a difference in magnitude occurs between the timing when each sensor detects the trailing end of the recording material S and the timing when the trailing end portion located on the central axis Cn of the recording material S, which is being transported in a skewed state, actually passes S_dtct. Furthermore, this difference is expressed as a delay of L_over for the paper width sensor 104 and the discharge sensor 112, and an advance of L_delay for the registration sensor 109, based on the detection timing of each sensor. Hereinafter, L_over will be referred to as the trailing end position delay amount, and L_delay will be referred to as the trailing end position advance amount.

[0027] (Control block diagram of an image forming apparatus) Next, a configuration related to the transport control of the recording material S in the first embodiment will be described with reference to Fig. 8. Fig. 8 is a block diagram related to the control of the image forming apparatus 100 in the first embodiment. The image forming control unit 800 is provided in the image forming apparatus 100, and includes a transmitting / receiving unit 801, a transport control unit 802, and an image control unit 803. The transmitting / receiving unit 801 transmits and receives information to and from a controller 804 that receives image information from a host device such as a personal computer (not shown), and in the first embodiment, receives, for example, condition information necessary for image formation instructions from the controller 804.

[0028] When the transmitting / receiving unit 801 receives an instruction for image formation, the conveyance control unit 802 drives the main motor 805. When the main motor 805 drives, the pickup roller 101, the conveyance roller 102, the registration roller 105, the photosensitive drum 108, the pressure roller 110, and the pair of discharge rollers 113 are driven. When the image formation control unit 800 determines that image formation preparation is complete, the conveyance control unit 802 controls the paper feed solenoid 806. By the operation of the paper feed solenoid 806, the pickup roller 101 descends to the surface of the recording material S stacked on the open tray, and the uppermost recording material S is fed by the driving force of the pickup roller 101.

[0029] When the fed recording material S is conveyed, the inputs of the paper width sensor 104, the registration sensor 109, and the discharge sensor 112 on the conveying path are switched. The jam detection unit 807 judges whether the recording material S is being conveyed normally or not from the switching timing of each sensor. More specifically, the jam detection unit 807 functions as a detection unit that detects a paper jam of the recording material S based on the timing at which the recording material S is detected by the paper width sensor 104 or the registration sensor 109 and the timing at which the recording material S is detected by the discharge sensor 112. The judgment specific to the first embodiment will be described in detail later.

[0030] The size detection unit 808 determines whether the specified image size matches the size of the recording material S based on the width information from the paper width sensor 104 and the length information converted from the ON time of the registration sensor 109, and notifies the image control unit 803. The timing synchronization unit 809 calculates the start timing of the image forming operation of the image control unit 803 from the ON timing of the registration sensor 109 and notifies the image control unit 803.

[0031] (Detection of skew amount by combination of sensors) Subsequently, the detection of the skew amount of the recording material S in the first embodiment will be described. FIG. 9 is a schematic diagram showing the arrangement (sensor arrangement) and detection timing of the paper width sensor 104 and the registration sensor 109 in the first embodiment. The diagonal line S1 indicates the detection position (rear end detection position) of the rear end of the skewed recording material S in the paper width sensor 104. The diagonal line S2 indicates the rear end detection position of the skewed recording material S in the registration sensor 109. The distance between the sensors is shown as L_ref, the detection width position of the paper width sensor 104 is shown as L_width, and the detection width position of the registration sensor 109 is shown as L_reg. Note that the detection width positions L_width and L_reg are both positions from the center in the width direction.

[0032] Here, as described above, the rear end position delay amount L_over is the delay amount of the rear end position of the recording material S on the central axis Cn in the width direction of the conveyance path of the recording material S with respect to the phase (timing) at which the flag 201 is passed. Also, the rear end position leading amount L_delay is the leading amount of the rear end position of the skewed recording material S when considered on the central axis Cn in the width direction of the conveyance path of the recording material S with respect to the phase (timing) at which the registration shutter 400 is passed. When there is no change in the skew amount during the conveyance of the recording material S, the relationship between the rear end position delay amount L_over and the rear end position leading amount L_delay can be expressed as the following formula (1). L_delay:L_over = L_reg:L_width Formula (1)

[0033] Furthermore, when the conveying speed is PS, the detection time T, which is the time difference between the detection timing by the paper width sensor 104 and the detection timing by the registration sensor 109, can be expressed by the following formula (2). T=(L_ref+L_delay+L_over)÷PS Equation (2) A detection time T_ref, which is a time difference between the detection timing by the paper width sensor 104 and the detection timing by the registration sensor 109 when the recording material S is not skewed, is expressed by equation (3). T_ref=L_ref÷PS formula (3)

[0034] In other words, if the detection time related to the paper width sensor 104 and the registration sensor 109 is affected by the skew, ΔT can be expressed as the following formula (4) from formulas (2) and (3). ΔT corresponds to the amount of skew of the recording material S. ΔT=T-T_ref=(L_delay+L_over)÷PS Equation (4)

[0035] From the simultaneous equations of equation (4) and equation (1), it is possible to obtain the skew influence time of each sensor from the time ΔT. The skew influence time is the time difference when a difference occurs in the detection timing of each sensor due to the recording material S being skewed, and the detection timing becomes earlier or later than when there is no skew. For this reason, the skew influence time can also be called the detection deviation time. When the skew influence time of the paper width sensor 104 is T_width_skew and the skew influence time of the registration sensor 109 is T_reg_skew, the formula for obtaining T_reg_skew can be expressed as the following formula (5). T_reg_skew=ΔT(1-(L_width÷(L_reg+L_width))) Equation (5) The jam detection unit 807 functions as an acquisition unit that acquires the amount of skew of the recording material S based on the detection results of the paper width sensor 104 and the registration sensor 109 .

[0036] (Clogging Detection Control in Fixing Unit by Clogging Detection Unit 807) Based on the configuration described above, detection of a clogging in the fixing unit by the clogging detection unit 807 will be described. Fig. 10 is a timing chart of clogging detection using the registration sensor 109 and the discharge sensor 112. In Fig. 10, (i) shows the change over time in the output signal of the registration sensor 109, and (ii) shows the change over time in the output signal of the discharge sensor 112. In both cases, when the leading edge of the recording material S arrives, the signal changes from low level to high level, and when the trailing edge of the recording material S passes by, the signal changes from high level to low level.

[0037] Fig. 10(a) is a basic timing chart. Using the timing tr (hereinafter referred to as reference timing tr) when the registration sensor 109 detects the trailing edge, the section from timing tf (hereinafter referred to as fastest timing tf) when the trailing edge of the recording material S leaves the discharge sensor 112 the fastest is defined as section T1. Also, the section from the reference timing tr to timing ts (hereinafter referred to as latest timing ts) when the trailing edge of the recording material S leaves the discharge sensor 112 the latest is defined as section T2. ​​Furthermore, the section from the fastest timing tf to the latest timing ts, i.e., the difference between section T2 and section T1, is defined as section T3 (predetermined time) (T3 = T2 - T1).

[0038] The fastest timing tf and the slowest timing ts are calculated in advance from the drop time of the flag or the shutter, the time to remove electrical noise, and the tolerance variation and wear state of each roller. When the conveyance of the recording material S is normal, the detection timing t01 of the trailing end of the recording material S by the discharge sensor 112 is within the section T3. On the other hand, when the discharge sensor 112 cannot detect the trailing end of the recording material S within the section T3, the jam detection unit 807 notifies the conveyance control unit 802 of the abnormality. Hereinafter, the section T3 is also referred to as the trailing end detection window T3. When the conveyance control unit 802 is notified of the abnormality by the jam detection unit 807, it stops the main motor 805. Note that in the example of FIG. 10(a), the jam detection unit 807 does not detect a paper jam because the discharge sensor 112 detects the trailing end of the recording material S at the detection timing t01, that is, within the trailing end detection window T3.

[0039] FIG. 10B is a timing chart when the jam detection unit 807 operates in the conventional manner with respect to the skewed recording material S. The detection of the trailing end of the recording material S by the discharge sensor 112 is affected by the detection deviation time T_reg_skew due to the skew of the registration sensor 109 and the detection deviation time T_fsr_skew due to the skew of the discharge sensor 112. The jam detection unit 807 performs correction based on a first deviation amount due to the skew when the trailing end of the recording material S is detected by the registration sensor 109 and a second deviation amount due to the skew when the trailing end of the recording material S is detected by the discharge sensor 112. Here, the first deviation amount corresponds to the detection deviation time T_reg_skew, and the second deviation amount corresponds to the detection deviation time T_fsr_skew. The timing t11 affected by the detection deviation time T_reg_skew due to the skew of the registration sensor 109 is advanced due to the configuration of the registration shutter 400. That is, the discharge sensor 112 detects the trailing edge of the recording material S at an earlier timing than when there is no skew. For this reason, there is a possibility that the timing t11 will be earlier than the fastest timing tf by the amount of the detection deviation time T_reg_skew.

[0040] On the other hand, the detection deviation time T_fsr_skew of the discharge sensor 112 due to skew may be either advanced or delayed depending on the angle of skew. If it is advanced, as shown in FIG. 10B, the detection timing t12 of the recording material S by the discharge sensor 112 may be earlier than the fastest timing tf by the sum of the detection deviation time T_fsr_skew and the detection deviation time T_reg_skew. Note that, as shown in FIG. 7C, the influence of skew of the discharge sensor 112 is sufficiently smaller than the influence of skew of the registration sensor 109. Therefore, even if the detection deviation time T_fsr_skew is delayed, the detection timing t12 of the trailing edge by the discharge sensor 112 from the reference timing tr of the trailing edge detection by the registration sensor 109 will be advanced overall due to the influence of skew by the registration sensor 109. At this time, if the discharge sensor 112 detects the trailing end of the paper in a time shorter than the section T1, that is, at a timing earlier than the fastest timing tf, the trailing end cannot be detected within the trailing end detection window T3. This causes the jam detection unit 807 to erroneously detect abnormal transport.

[0041] (Control of clogging detection in fixing unit by clogging detection unit 807 in embodiment 1) 10C is a control timing chart of the jam detection unit 807 for the skewed recording material S in the first embodiment. The transport control unit 802 can obtain the detection deviation time T_reg_skew of the registration sensor 109 from equation (5) by using the detection time T of the paper width sensor 104 and the registration sensor 109 in advance. The transport control unit 802 shifts the trailing end detection window T3 of the discharge sensor 112 by applying the detection deviation time T_reg_skew to sections T1 and T2. Specifically, the transport control unit 802 shifts the trailing end detection window T3 to be earlier by the amount of the detection deviation time T_reg_skew of the registration sensor 109.

[0042] As a result, the trailing end detection window T3 is adjusted by the detection deviation time T_reg_skew of the registration sensor 109, and the trailing end detection window T3 can be optimized to the original detection timing of the discharge sensor 112. The adjusted trailing end detection window T3 includes the detection timing t12 when skew exists. This allows the jam detection unit 807 to properly detect a paper jam. That is, even if the recording material S reaches the discharge sensor 112 early (or late) due to skew, the jam detection unit 807 does not erroneously detect a paper jam.

[0043] At the timing when the detection deviation time T_reg_skew by the registration sensor 109 is calculated, the discharge sensor 112 is not yet able to detect the trailing edge of the recording material S. Also, since the skew angle of the recording material S is unknown, the section T3 cannot be corrected by the detection deviation time T_fsr_skew by the discharge sensor 112. However, due to the attachment position of the discharge sensor 112, the detection deviation time T_fsr_skew is sufficiently small compared to the detection deviation time T_reg_skew (T_fsr_skew << T_reg_skew). That is, the second deviation amount is smaller than the first deviation amount. Also, the sections T1 and T2 are based on the timing when the registration sensor 109 detects the trailing edge of the recording material S, but are not limited to this. For example, the timing when the paper width sensor 104 detects the trailing edge of the recording material S may be based on the interval.

[0044] By controlling as described above, the image forming apparatus 100 does not erroneously detect a jam of the recording material S even when the recording material S is significantly skewed, so that it is possible to reduce the frequency of the user's access to the inside of the machine. As described above, according to the first embodiment, it is possible to reduce erroneous detection of a transport failure caused by a skew of the paper. EXAMPLES

[0045] In the first embodiment, a method for suppressing erroneous detection by the jam detection unit 807 was described by reflecting the detection time difference between the paper width sensor 104 and the registration sensor 109 in the jam detection timing of the jam detection unit 807. In the second embodiment, a control in which the detection time difference between the paper width sensor 104 and the registration sensor 109 is reflected in the double-sided reversal control is described. The cross-sectional configuration of the image forming apparatus 100 and the detection configurations of the paper width sensor 104 and the registration sensor 109 are omitted since they are the same as in the first embodiment.

[0046] (About the configuration of the discharge sensor and the reverse transport path) Fig. 11 is a cross-sectional view showing the relationship between the fixing section and the discharge section and the recording material S. Fig. 11(a) is a cross-sectional view showing the timing when fixing of the surface of the recording material S is completed, and the recording material S is conveyed in a conveying direction Dr1 as a first direction and discharged. The flag 600 is pushed up by the recording material S, and the discharge roller pair 113 is in a forward rotation state. The rotation direction of the discharge roller pair 113 can be switched between forward and reverse by a reversing solenoid 1200 (see Fig. 12).

[0047] 11B, the flag 600 falls, allowing the discharge sensor 112 to detect the rear end of the recording material S. In addition, since the recording material S also follows the upper surface Pu of the conveying path, the recording material S does not flow back toward the flag 600 when it is reversed, and can access the reverse conveying path Pr.

[0048] If the discharge roller pair 113 continues to convey the recording material S in the forward rotating state, the recording material S will be discharged outside the apparatus by the discharge roller pair 113. When the reverse solenoid 1200 reverses the discharge roller pair 113, the recording material S is switched back to the reverse conveying path Pr as shown in FIG. 11C, and conveyed in the conveying direction Dr2 as the second direction. The timing of reversing the discharge roller pair 113 is determined based on the detection of the trailing end by the discharge sensor 112. However, the reverse operation of the discharge roller pair 113 needs to be performed between the time when the trailing end of the recording material S is properly in a state where it can be switched back to the reverse conveying path Pr and the time when the recording material S is discharged outside the apparatus by the discharge roller pair 113. In addition, in determining the timing of the reverse operation of the discharge roller pair 113, it is necessary to take into consideration the suction time of the reverse solenoid 1200, the time required to switch the rotation direction, and the variation in the timing of the detection of the trailing end by the discharge sensor 112.

[0049] (Control block diagram of an image forming apparatus) A reversal control block diagram of the image forming apparatus 100 of the second embodiment will be described with reference to FIG. 12. Explanation of parts that overlap with FIG. 8 will be omitted. The transport control unit 802 can switch between forward and reverse rotation of the pair of discharge rollers 113 using a reversal solenoid 1200. The reversal control unit 1201 as a control unit can obtain the amount of skew from the detection time difference between the paper width sensor 104 and the registration sensor 109 as in the first embodiment. The reversal control unit 1201 can also calculate the reversal timing based on the detection of the rear end by the discharge sensor 112 and instruct the transport control unit 802 on the reversal timing.

[0050] (Influence of the reversing conveyance path and the skew of the recording material S) So far, we have explained the basic configuration of the reversing unit and the relationship between control. In the following, we will explain the effect of skew in this reversing configuration and the control to deal with it. Figure 13 is a diagram showing the relationship between the reversing unit and the recording material S in terms of the positional relationship in the conveying direction of the recording material S. Figure 13(a) shows the positional relationship between the reversing unit and the recording material S with no skew.

[0051] Reverse Entry indicates the position where the recording material S faces the reverse conveying path Pr and can start to be reversed, and Reverse Exit indicates the position where the recording material S is discharged by the discharge roller pair 113. In other words, if the discharge roller pair 113 starts to reverse before Reverse Entry, the recording material S will flow back toward the discharge sensor 112. Also, even if the discharge roller pair 113 starts to reverse after Reverse Exit, the recording material S will be discharged to the discharge section. The range (predetermined range) from Reverse Entry to Reverse Exit will be referred to as the reverse window below. If the recording material S starts to reverse within this reverse window, it is possible to switch back normally. Reverse Timing is the distance required for the recording material S to reach the reverse entry position, where it can be reversed, based on the detection of the trailing end by the discharge sensor 112.

[0052] FIG. 13B shows the positional relationship with the reversing portion when the recording material S is skewed. In the case of the recording material S that is significantly skewed as shown in FIG. 13B, the skew-affecting distance Reverse skew margin is required until the recording material S passes the Reverse Entry. If the skew-affecting distance Reverse skew margin cannot be secured, the following problems may occur, depending on the material of the recording material S and the reversing timing. For example, the recording material S may not be able to face the reversing conveying path Pr and may flow back again in the fixing direction, or the corners of the recording material S may be bent. In addition, if the reversing timing is simply delayed to ensure reversing, one end of the recording material S may pass the Reverse Exit, and the reversing conveying force required for pulling in may be lost.

[0053] (Skewing detection and reversal control by combining sensors) In the above explanation, it has been described that in order to perform suitable control, the reverse skew margin must be accurately detected. A method for accurately determining the reverse skew margin will be described below. Fig. 14 is a schematic diagram showing the sensor arrangement of the registration sensor 109 and the discharge sensor 112 and the detection timing in the second embodiment. The diagonal line S2 indicates the detection position of the trailing end of the skewed recording material S in the registration sensor 109. The diagonal line S3 indicates the detection position of the trailing end of the skewed recording material S in the discharge sensor 112. The distance between the sensors is indicated as L_ref, the detection width position of the registration sensor 109 as L_reg, and the detection width position of the discharge sensor 112 as L_fsr.

[0054] At this time, the trailing edge position advance amount L_delay of the recording material S when considered on the central axis Cn of the conveying path can be calculated by the means of the first embodiment. The registration shutter 400 is disposed over the entire width direction of the recording material S on the conveying path. Therefore, the trailing edge position advance amount L_delay of the recording material S when considered on the central axis Cn of the conveying path is equal to the position of the rear end of the recording material S. On the other hand, when the attachment position of the discharge sensor 112 is disposed at a position shifted by the detection width position L_fsr instead of the central axis Cn of the conveying path, the detection timing of the discharge sensor 112 is affected by skew even if only slightly. In this case, the skew-affected distance L_fsr_delta can be calculated as in the calculation method of the first embodiment from the ratio of the detection width position L_reg of the registration sensor 109 to the central axis Cn of the conveying path and the installation distance L_fsr of the flag 600, as shown in Equation (6). L_fsr_delta=(L_fsr×L_delay)÷L_reg Formula (6)

[0055] On the other hand, since the flag 600 is a single flag, the detection timing may be delayed or advanced depending on the skew angle. The skew angle means whether the trailing end of the recording material S is skewed downward to the right or downward to the left. When the trailing end of the recording material S is skewed downward to the left as shown in FIG. 14, the detection timing by the discharge sensor 112 is advanced from the trailing end portion on the central axis Cn. On the other hand, when the trailing end of the recording material S is skewed downward to the right, the detection timing by the discharge sensor 112 is delayed from the trailing end portion on the central axis Cn. In the case of jam detection in the first embodiment, the trailing end detection timing of the discharge sensor 112 was predicted, so the influence of the skew of the discharge sensor 112 could not be taken into consideration, but when the amount of skew is large, it is necessary to perform feedback to the reversal timing more accurately. Therefore, a method of optimizing the reversal timing taking the skew angle into consideration will be described in detail below.

[0056] Fig. 15 is a timing chart showing the detection timing and reversal timing of the sensor in the second embodiment. Note that (i) and (ii) in Fig. 15 are the same as (i) and (ii) in Fig. 10. (iii) is a diagram showing the state of the reverse solenoid 1200, with ON indicated by a high level and OFF indicated by a low level. Also shown is the above-mentioned reverse window Wr (from reverse entry to reverse exit).

[0057] 15A is a timing chart of the reversal timing (switching timing) when the influence of skew is not taken into consideration. Time T11 indicates the time from timing t21 when the registration sensor 109 detects the rear end to timing t22 when the discharge sensor 112 detects the rear end. Using timing t22 when the discharge sensor 112 detects the rear end as a reference, the reversal solenoid 1200 is turned on at timing t23 after time T12 has elapsed. For time T12, the timing when the rear end of the recording material S passes through the Reverse Entry is calculated from an equation of distance and conveying speed. By finding the timing with the shortest switching without considering delay factors such as a delay in the reversal timing of the discharge roller pair 113, reversal is possible even if there is a delay of the distance of the Reverse Exit when a delay factor occurs.

[0058] FIG. 15B is a timing chart of reversal control without considering the influence of skew when the recording material S is conveyed skewed as shown in FIG. 14. The timing t31 of detection of the trailing end by the registration sensor 109 is delayed by the detection deviation time T_reg_skew. Furthermore, the timing t32 of detection of the trailing end by the discharge sensor 112 is advanced by the detection deviation time T_fsr_skew. The reversal solenoid 1200 is turned on at the predicted timing t33 ​​after the time T12 has elapsed from the timing t32 of detection of the trailing end by the discharge sensor 112. The predicted timing t33 ​​is outside the range of the above-mentioned reversal window Wr. If the reversal solenoid 1200 is turned on (pulled) at the predicted timing t33, the following problem may occur. That is, since the reversal of the discharge roller pair 113 starts at the predicted timing t33 ​​without considering the early detection by the discharge sensor 112 and the timing when the trailing end of the recording material S actually leaves the sheet, the recording material S may flow backward or have a corner bent.

[0059] (Inversion control by the inversion control unit 1201 in the second embodiment) 15C is a timing chart of the reversal control in the second embodiment, taking into account the influence of skew. The reversal control unit 1201 calculates the detection deviation time T_reg_skew of the registration sensor 109 from the timing of detection of the rear end by the paper width sensor 104 and the registration sensor 109. The time obtained by subtracting the detection deviation time T_reg_skew from the time T11 is the predicted timing t34 of the passage of the rear end of the recording material S at the central axis Cn of the conveyance path of the discharge sensor 112.

[0060] If the actual timing at which the discharge sensor 112 detects the rear end is later than this time, i.e., the predicted timing t34, the reversal control unit 1201 can determine that the rear end is on the side where the flag 600 is located (sloping downward to the right). On the other hand, if the actual timing at which the discharge sensor 112 detects the rear end is earlier than the predicted timing t34 (rear end detection timing t32) as shown in Fig. 15(c), the reversal control unit 1201 can determine that the rear end is on the side where the flag 600 is not located (sloping downward to the left).

[0061] The inversion control unit 1201 can calculate the amount of detection deviation of the discharge sensor 112, i.e., the absolute amount of the detection deviation time T_fsr_skew, from formula (6) and the conveying speed of the recording material S. Therefore, when the detection timing is earlier than the predicted timing t34, the inversion control unit 1201 extends the time T12 by the detection deviation time T_fsr_skew (T12+T_fsr_skew). On the other hand, when the detection timing is later than the predicted timing t34, the inversion control unit 1201 shortens the time T12 by the detection deviation time T_fsr_skew (T12-T_fsr_skew).

[0062] This allows the inversion control unit 1201 to correct the timing of passing the trailing edge of the recording material S at the central axis Cn of the conveying path. Furthermore, the inversion control unit 1201 adds the detection deviation time T_reg_skew, which is the amount of skew of the recording material S itself, to the corrected timing of passing the trailing edge (T12+T_fsr_skew+T_reg_skew). This allows the inversion control unit 1201 to perform inversion control at timing t35 when the trailing edge of the recording material S has advanced to a position where it can be completely inverted. The timing t35 is included in the range of the inversion window Wr described above. Note that, if the detection timing is later than the predicted timing t34, the inversion control unit 1201 performs the following. That is, the inversion control unit 1201 adds the detection deviation time T_reg_skew to the time T12 shortened by the detection deviation time T_fsr_skew (T12-T_fsr_skew+T_reg_skew).

[0063] In the second embodiment, the detection deviation time T_fsr_skew, which is the correction amount of the discharge sensor 112, is corrected, but this is merely an example and other configurations may be used. For example, there may be a case where the actual timing of detection of the trailing edge by the discharge sensor 112 does not differ significantly from the predicted timing t34 of the passage of the trailing edge of the recording material S. In this case, the reversal control unit 1201 may determine that the influence of the sensor detection variation is large and may not correct the detection deviation time T_fsr_skew, which is the correction amount of the discharge sensor 112.

[0064] As described above, according to the second embodiment, it is possible to reduce erroneous detection of transport failure caused by skew of paper. EXAMPLES

[0065] In Example 2, how the inversion control unit 1201 optimizes the inversion timing was described. In Example 3, a method of controlling so as to achieve a suitable operation even when there is a possibility that the inversion control cannot be performed in the process of the inversion control unit 1201 calculating the inversion timing will be described. Regarding the configuration of the image forming apparatus 100, the control block diagram, the sensor configuration, and the detection of the skew amount by the combination of sensors, since they are the same as the descriptions in Example 1 and Example 2, the description will be omitted.

[0066] FIG. 16 is a flowchart of the inversion control by the inversion control unit 1201. In step (hereinafter referred to as S) 1601, the inversion control unit 1201 determines whether or not the trailing edge of the recording material S has been detected by the paper width sensor 104. If, in S1601, the inversion control unit 1201 determines that the trailing edge of the recording material S has not been detected by the paper width sensor 104, the process returns to S1601, and if it determines that it has been detected, the process proceeds to S1602. In S1602, the inversion control unit 1201 starts measuring the time from when the trailing edge of the recording material S is detected by the paper width sensor 104 until the trailing edge of the recording material S is detected by the registration sensor 109 using a timer (not shown).

[0067] In S1603, the inversion control unit 1201 determines whether or not the trailing edge of the recording material S has been detected by the registration sensor 109. If, in S1603, the inversion control unit 1201 determines that the trailing edge of the recording material S has not been detected by the registration sensor 109, the process returns to S1603, and if it determines that it has been detected, the process proceeds to S1604. In S1604, the inversion control unit 1201 completes the measurement of the time from the detection of the trailing edge by the paper width sensor 104 to the detection of the trailing edge by the registration sensor 109.

[0068] In S1605, the inversion control unit 1201 calculates the detection deviation time T_reg_skew of the registration sensor 109 and the detection deviation time T_fsr_skew of the discharge sensor 112 according to the formula described in Example 1. In S1606, the inversion control unit 1201 starts measuring the time from when the trailing edge of the recording material S is detected by the registration sensor 109 until the trailing edge of the recording material S is detected by the discharge sensor 112.

[0069] In S1607, the reversal control unit 1201 determines whether or not the trailing edge of the recording material S has been detected by the discharge sensor 112. If the reversal control unit 1201 determines in S1607 that the trailing edge of the recording material S has not been detected by the discharge sensor 112, the process returns to S1607, and if the reversal control unit 1201 determines that the trailing edge of the recording material S has been detected, the process proceeds to S1608. In S1608, the reversal control unit 1201 completes measurement of the time from when the registration sensor 109 detects the trailing edge of the recording material S to when the discharge sensor 112 detects the trailing edge of the recording material S. In S1609, the reversal control unit 1201 calculates the correction amount of the reversal timing as described in the second embodiment (T12+T_fsr_skew+T_reg_skew, or T12-T_fsr_skew+T_reg_skew).

[0070] In S1610, the inversion control unit 1201 determines whether the inversion timing corrected by the correction amount calculated in S1609 falls within the range of the inversion window Wr. If the inversion control unit 1201 determines in S1610 that the inversion timing falls within the range of the inversion window Wr, the process proceeds to S1611, and if the inversion control unit 1201 determines that the inversion timing does not fall within the range of the inversion window Wr, the process proceeds to S1612.

[0071] In S1611, the reversal control unit 1201 turns on the reversal solenoid 1200 and reverses the pair of discharge rollers 113 when the reversal timing is reached based on the timing when the trailing end of the recording material S is detected by the discharge sensor 112, and ends the process. On the other hand, if the corrected reversal timing is not within the range of the reversal window Wr, in S1612, the reversal control unit 1201 determines that the recording material S cannot be reversed normally, and notifies the conveyance control unit 802 of that effect. Using the determination result (reversal not possible) notified from the reversal control unit 1201, the conveyance control unit 802 discharges the recording material S outside the apparatus while keeping the pair of discharge rollers 113 in the forward rotation state, without turning on the reversal solenoid 1200. The image formation control unit 800 uses the transmission / reception unit 801 to notify the controller 804 that the recording material S could not be reversed normally due to skew (reversal failure). The image formation control section 800 may notify the user that the recording material S could not be normally reversed due to skew by, for example, displaying an error message on the display section 120.

[0072] By controlling as described above, it is possible to provide an image forming apparatus 100 that conveys the recording material S outside the apparatus without damaging the recording material S by folding corners or causing clogging due to backflow, and does not require the user to handle the jam. Also, by notifying the user via the controller 804 that a skew has occurred, it is possible to have the user reconsider how the recording material S is set.

[0073] As described above, according to the third embodiment, it is possible to reduce erroneous detection of transport failure caused by skew of paper.

[0074] The disclosure of this embodiment includes the following configuration. (Configuration 1) An image forming apparatus for forming an image on a recording material, a conveying path along which the recording material is conveyed; a first sensor disposed on the conveying path for detecting a leading edge and a trailing edge of the recording material; a second sensor that is disposed on the conveying path downstream of the first sensor in a conveying direction of the recording material and at a position different from the first sensor in a direction perpendicular to the conveying direction, for detecting a leading edge and a trailing edge of the recording material; an acquisition unit that acquires an amount of skew of a recording material based on detection results of the first sensor and the second sensor; a third sensor that is disposed on the conveying path downstream of the second sensor in the conveying direction and at a position different from the second sensor in a direction perpendicular to the conveying direction, for detecting a leading edge and a trailing edge of the recording material; a detection unit that detects a paper jam of the recording material based on a timing when the recording material is detected by the first sensor or the second sensor and a timing when the recording material is detected by the third sensor; Equipped with The image forming apparatus, wherein the detection unit corrects a deviation in timing at which the third sensor detects the recording material based on the amount of skew acquired by the acquisition unit. (Configuration 2) The image forming apparatus described in configuration 1, characterized in that the detection unit detects the paper jam when the third sensor does not detect the trailing end of the recording material within a predetermined time based on the timing at which the first sensor or the second sensor detects the trailing end of the recording material, or when the third sensor detects the trailing end of the recording material outside the predetermined time. (Configuration 3) The image forming apparatus according to configuration 2, characterized in that the specified time is determined based on the timing at which the trailing end of the recording material is detected by the first sensor or the second sensor as a reference, and based on the earliest timing at which the trailing end of the recording material is detected by the third sensor when there is no skew, and the latest timing at which the trailing end of the recording material is detected by the third sensor. (Configuration 4) The image forming apparatus according to any one of configurations 1 to 3, wherein the detection unit performs correction based on a first amount of deviation due to skew when the trailing end of the recording material is detected by the second sensor and a second amount of deviation due to skew when the trailing end of the recording material is detected by the third sensor. (Configuration 5) 5. The image forming apparatus according to any one of configurations 1 to 4, wherein the third sensor detects the trailing edge of a skewed recording material at an earlier timing than when there is no skew. (Configuration 6) 5. The image forming apparatus according to configuration 4, wherein the second amount of deviation is smaller than the first amount of deviation. (Configuration 7) An image forming apparatus for forming an image on a recording material, a conveying path along which the recording material is conveyed; a discharge section to which the recording material conveyed on the conveying path is discharged; a rotating member that is disposed on the conveying path and conveys the recording material, the rotating member being capable of switching a rotation direction between a first direction in which the recording material is guided to the discharge portion, or a second direction opposite to the first direction; a reversing section to which the recording material is guided by the rotating member rotating in the second direction; a first sensor disposed on the conveying path for detecting a leading edge and a trailing edge of the recording material; a second sensor that is disposed on the conveying path downstream of the first sensor in a conveying direction of the recording material and at a position different from the first sensor in a direction perpendicular to the conveying direction, for detecting a leading edge and a trailing edge of the recording material; an acquisition unit that acquires an amount of skew of a recording material based on a detection result of the first sensor or the second sensor; a third sensor that is disposed on the conveying path downstream of the second sensor in the conveying direction and at a position different from the second sensor in a direction perpendicular to the conveying direction, for detecting a leading edge and a trailing edge of the recording material; a control unit that switches the rotation direction of the rotating member based on a timing at which the third sensor detects the recording material; Equipped with The control unit predicts a deviation in timing at which the recording material is detected by the third sensor based on the amount of skew acquired by the acquisition unit, and corrects a switching timing for switching the rotation direction of the rotating member. (Configuration 8) The image forming apparatus according to configuration 7, characterized in that, when the skew amount acquired by the acquisition unit exceeds a predetermined range, the control unit maintains the rotation direction of the rotating member in the first direction and discharges the recording material to the discharge unit. (Configuration 9) The image forming apparatus according to configuration 8, further comprising a display unit that displays information that the recording material has been discharged to the discharge unit when the skew amount exceeds the predetermined range. (Configuration 10) The image forming apparatus according to any one of configurations 7 to 9, wherein the control unit corrects the switching timing based on a first amount of deviation due to skew when the trailing end of the recording material is detected by the second sensor and a second amount of deviation due to skew when the trailing end of the recording material is detected by the third sensor. [Explanation of symbols]

[0075] 100 Image forming device 104 Paper width sensor 109 Cash register sensor 112 Emission sensor 807 Clogging detector

Claims

1. An image forming apparatus for forming an image on a recording material, a conveying path along which the recording material is conveyed; a first sensor disposed on the conveying path for detecting a leading edge and a trailing edge of the recording material; a second sensor that is disposed on the conveying path downstream of the first sensor in a conveying direction of the recording material and at a position different from the first sensor in a direction perpendicular to the conveying direction, for detecting a leading edge and a trailing edge of the recording material; an acquisition unit that acquires an amount of skew of a recording material based on detection results of the first sensor and the second sensor; a third sensor that is disposed on the conveying path downstream of the second sensor in the conveying direction and at a position different from the second sensor in a direction perpendicular to the conveying direction, for detecting a leading edge and a trailing edge of the recording material; a detection unit that detects a paper jam of the recording material based on a timing when the recording material is detected by the first sensor or the second sensor and a timing when the recording material is detected by the third sensor; Equipped with The image forming apparatus according to claim 1, wherein the detection unit corrects a deviation in timing at which the third sensor detects the recording material based on the amount of skew acquired by the acquisition unit.

2. The image forming apparatus according to claim 1, characterized in that the detection unit detects the paper jam when the trailing end of the recording material is not detected by the third sensor within a predetermined time based on the timing at which the trailing end of the recording material is detected by the first sensor or the second sensor, or when the trailing end of the recording material is detected outside the predetermined time.

3. The image forming apparatus according to claim 2, characterized in that the specified time is determined based on the timing at which the trailing end of the recording material is detected by the first sensor or the second sensor, and on the timing at which the trailing end of the recording material is detected by the third sensor when there is no skew, the timing at which the trailing end is detected at the earliest and the timing at which the trailing end is detected at the latest.

4. 2. The image forming apparatus according to claim 1, wherein the detection unit performs correction based on a first amount of deviation due to skew when the trailing end of the recording material is detected by the second sensor, and a second amount of deviation due to skew when the trailing end of the recording material is detected by the third sensor.

5. 5. The image forming apparatus according to claim 4, wherein the third sensor detects the trailing edge of a skewed recording material at an earlier timing than when there is no skew.

6. 5. The image forming apparatus according to claim 4, wherein the second amount of deviation is smaller than the first amount of deviation.

7. An image forming apparatus for forming an image on a recording material, a conveying path along which the recording material is conveyed; a discharge section to which the recording material conveyed on the conveying path is discharged; a rotating member that is disposed on the conveying path and conveys the recording material, the rotating member being capable of switching a rotation direction between a first direction in which the recording material is guided to the discharge portion or a second direction opposite to the first direction; a reversing section to which the recording material is guided by the rotating member rotating in the second direction; a first sensor disposed on the conveying path for detecting a leading edge and a trailing edge of the recording material; a second sensor that is disposed on the conveying path downstream of the first sensor in a conveying direction of the recording material and at a position different from the first sensor in a direction perpendicular to the conveying direction, for detecting a leading edge and a trailing edge of the recording material; an acquisition unit that acquires an amount of skew of a recording material based on a detection result of the first sensor or the second sensor; a third sensor that is disposed on the conveying path downstream of the second sensor in the conveying direction and at a position different from the second sensor in a direction perpendicular to the conveying direction, for detecting a leading edge and a trailing edge of the recording material; a control unit that switches the rotation direction of the rotating member based on a timing at which the third sensor detects the recording material; Equipped with The control unit predicts a timing shift in detecting the recording material by the third sensor based on the amount of skew acquired by the acquisition unit, and corrects the switching timing for switching the rotation direction of the rotating member.

8. The image forming apparatus according to claim 7, characterized in that, when the skew amount acquired by the acquisition unit exceeds a predetermined range, the control unit maintains the rotation direction of the rotating member in the first direction and discharges the recording material to the discharge unit.

9. 9. The image forming apparatus according to claim 8, further comprising a display unit that displays information that the recording material has been discharged to the discharge unit when the skew amount exceeds the predetermined range.

10. The image forming apparatus according to claim 7, characterized in that the control unit corrects the switching timing based on a first amount of deviation due to skew when the trailing end of the recording material is detected by the second sensor, and a second amount of deviation due to skew when the trailing end of the recording material is detected by the third sensor.

Images