Sheet conveying device and image forming apparatus

Abstract

To prevent even a thin sheet from being torn when a jam is removed.SOLUTION: A sheet carrier device comprises: a resister roller part which forms a register loop on a sheet by butting the sheet; a carrier roller part which is arranged upstream from the register roller part and carries the sheet; a changeover part which changes nip pressure with which the carrier roller part holds the sheet between first nip pressure and second nip pressure higher than the first nip pressure; and a control part which performs control to change the nip pressure to the second nip pressure to make the sheet abut on the register roller part with the second nip pressure once it is determined that the sheet is thinner than a predetermined value, and then performs control to change the nip pressure to the first nip pressure when the register roller part starts carrying the sheet after the sheet is made to abut on the register roller part.SELECTED DRAWING: Figure 12

Description

[Technical Field]

[0001] The present invention relates to a sheet conveying device and an image forming apparatus. [Background technology]

[0002] When transporting a sheet such as paper (hereinafter, an example will be described using paper as the sheet), a technique is known in which a loop (a slack that occurs when a sheet is abutted; a so-called resist loop; hereinafter referred to as a "resist loop") is formed in the sheet by feeding the sheet with the leading edge abutting against a roller, for the purpose of correcting skew of the transported sheet.

[0003] Specifically, in an image forming apparatus that includes a pair of loop rollers and a conveying roller upstream of the pair of loop rollers, the image forming apparatus controls the nip pressure of the pair of loop rollers. In this way, a technique is known in which the nip pressure of the pair of loop rollers is made lower than the nip pressure of the pair of registration rollers to prevent the paper from passing through the registration nip portion (see, for example, Patent Document 1). Summary of the Invention [Problem to be solved by the invention]

[0004] In conventional technology, the nip pressure that holds the sheet is not adjusted even if the sheet thickness varies. Therefore, when a thin sheet jams (also called a paper jam), the operator pulls out the sheet. In this case, if the nip pressure is not adjusted, the sheet may tear.

[0005] An object of the present invention is to prevent tearing of a sheet even when the sheet is thin, when clearing a jam or the like. [Means for solving the problem]

[0006] In order to solve the above problems, one aspect of the present invention is a sheet conveying device, a registration roller unit that abuts against the sheet to form a registration loop in the sheet; a conveying roller unit disposed upstream of the registration roller unit and configured to convey the sheet; a switching unit that switches the nip pressure at which the conveying roller unit pinches the sheet between a first nip pressure and a second nip pressure that is higher than the first nip pressure; The control unit is provided with a control unit that, when it determines that the sheet is thinner than a predetermined value, controls to switch the nip pressure to the second nip pressure, causing the sheet to abut against the registration roller unit with the second nip pressure, and when the registration roller unit starts conveying the sheet after the sheet has abutted against the registration roller unit, controls to switch the nip pressure to the first nip pressure. [Effects of the Invention]

[0007] According to the present invention, even if the sheet is thin, tearing of the sheet can be prevented when clearing a jam or the like. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a diagram illustrating an example of the overall configuration of an image reading apparatus. [Figure 2] FIG. 2 illustrates an example of a hardware configuration of a sheet conveying device. [Figure 3] FIG. 2 is a diagram illustrating an example of the configuration of a sheet conveying device. [Figure 4] 10A and 10B are diagrams illustrating an example of control for switching nip pressures. [Figure 5] FIG. 1 is a diagram (part 1) showing an example of the overall processing. [Figure 6] FIG. 2 is a diagram (part 2) showing an example of the overall processing. [Figure 7] FIG. 10 is a diagram showing an example of an operation result when thin paper is used as the target. [Figure 8] 10A and 10B are diagrams illustrating an example of forming a resist loop. [Figure 9] 10A and 10B are diagrams illustrating an example of paper transport by a pair of registration rollers. [Figure 10] FIG. 10 is a diagram showing an example of roller marks. [Figure 11] FIG. 2 is a diagram illustrating an example of a control configuration. [Figure 12] FIG. 2 is a diagram illustrating an example of a functional configuration. [Figure 13] 10A and 10B are diagrams illustrating examples of operation results when targeting cardboard or the like. [Figure 14] FIG. 10 is a diagram illustrating an example of overall processing in a comparative example. [Figure 15] FIG. 10 is a diagram illustrating an example of an operation result of a comparative example. DETAILED DESCRIPTION OF THE INVENTION

[0009] A specific example will be described below with reference to the accompanying drawings. Note that the embodiment is not limited to the specific example described below. In the following description, the sheet is a paper sheet.

[0010] [Overall configuration example] Fig. 1 is a diagram showing an example of an image forming apparatus. The following description will be given taking the image forming apparatus 100 shown in Fig. 1 as an example. The image forming apparatus 100 forms an image on paper using an electrophotographic method or an inkjet method. The following description will be given taking the electrophotographic method as an example.

[0011] The image forming apparatus 100 includes an image forming unit 2 that forms an image using an image carrier 1, a transfer unit 9, an exposure unit, etc. The image forming unit 2 may further include other devices.

[0012] The image forming apparatus 100 includes a main body paper feed tray 3, a manual paper feed tray 4, a paper feed roller 5, and a paper feed roller 6. Paper is conveyed one sheet at a time toward the image forming device 2 from a stack of paper P1 accumulated in the main body paper feed tray 3 or a stack of paper P2 accumulated in the manual paper feed tray 4. The paper feed roller 5 or the paper feed roller 6 also conveys the paper.

[0013] The image forming apparatus 100 includes a registration sensor S and a registration roller pair 8. The registration sensor S detects whether or not a sheet is present. After the registration sensor S detects the sheet, the registration roller pair 8 transports the sheet to a transfer device 9. The transfer device 9 then transfers the image onto the sheet. After transfer, the sheet is sent to a fixing device 10.

[0014] The fixing device 10 performs a fixing process to fix the image on the paper. After fixing, the paper is discharged outside the image forming apparatus 100.

[0015] The following description will be given taking the sheet conveying device 200 as an example. In this example, the sheet conveying device 200 is made up of a pair of conveying rollers 7, a pair of registration rollers 8, and a paper feed roller 5. The sheet conveying device 200 also includes the following hardware resources.

[0016] 2 is a diagram showing an example of the hardware configuration of a sheet conveying device 200. Specifically, the sheet conveying device 200 includes a central processing unit (hereinafter referred to as a "CPU 201"), a storage device 202, an input device 203, an output device 204, and an interface 205.

[0017] The CPU 201 is an example of a calculation device and a control device. An example in which the CPU 201 controls each device included in the image forming apparatus 100 and the sheet conveying device 200 will be described below.

[0018] The storage device 202 is a main storage device, an auxiliary storage device, or the like.

[0019] The input device 203 inputs operations, data, etc. from the outside.

[0020] The output device 204 outputs the processing results and the like.

[0021] The interface 205 transmits and receives data to and from external devices.

[0022] The sheet conveying device 200 executes processing by causing a CPU 201, a storage device 202, and the like to cooperate with each other based on a program or the like.

[0023] The hardware configuration may further include an auxiliary device, a calculation device, a control device, a storage device, an input device, or an output device inside or outside the hardware configuration in addition to the devices described above.

[0024] [Example of sheet transport device configuration] 3 is a diagram showing an example of the configuration of a sheet conveying device. The main body paper feed bottom plate 101 urges upward toward the paper feed roller 5. Next, the paper feed roller 5 comes into contact with the uppermost sheet of the paper stack P1.

[0025] When starting the transport of paper, the CPU 201 first checks whether the initial operation has been completed, and then, if the initial operation has not been completed, the CPU 201 starts the initial operation.

[0026] The initial operation is an operation to set the manual feed bottom plate 34 to the lowest position. After the initial operation is completed, the nip pressure (hereinafter simply referred to as "nip pressure") at which the conveying roller pair 7 pinches the paper is set.

[0027] Hereinafter, the nip pressure is assumed to be switched between two levels, "first nip pressure" and "second nip pressure", under the control of the CPU 201.

[0028] The first nip pressure is a nip pressure lower than the second nip pressure. On the other hand, the second nip pressure is a nip pressure higher than the first nip pressure. Note that there may be three or more levels of nip pressure. Of the multiple levels of nip pressure, the second nip pressure may be a nip pressure higher than the first nip pressure.

[0029] After the initial operation is completed, the CPU 201 turns on the main motor, and then determines whether the paper is thin paper.

[0030] Thin paper and regular paper (hereinafter collectively referred to as "thin paper") are papers that are thinner than a predetermined value. Cardboard is thick paper that is thicker than a predetermined value. Therefore, thin paper is weaker and more easily torn than cardboard. The predetermined value is a value that is set in advance.

[0031] The user operates the operation panel to select the type of paper. Multiple types of paper are prepared, such as plain paper, thin paper, and thick paper. The thickness of each type is input in advance. The user then selects one of these types. When this operation is performed, the storage device 202 stores the selection result. Thereafter, the CPU 201 refers to the selection result stored in advance to determine whether the paper is thin paper or thick paper.

[0032] The CPU 201 may determine the type of paper by measuring the thickness with a sensor, etc. The CPU 201 may also determine the type of paper based on characteristics such as the material or size of the paper, for example.

[0033] For example, the CPU 201 controls the mechanisms and the like as follows to switch the nip pressure.

[0034] 4A and 4B are diagrams showing an example of control for switching nip pressure. Fig. 4A shows the state of the initial operation. Fig. 4B shows the state shown in Fig. 4A after the manual feed bottom plate cam clutch is turned on and the manual feed bottom plate cam shaft 65 is rotated clockwise.

[0035] The conveying roller pair 7 is made up of a relay drive roller 42a, a relay driven roller 42b, etc. The relay driven roller 42b has a bearing portion 37a that bears a roller shaft 66, and is biased by a pressure spring 11, which is a compression spring. The biasing force of the pressure spring 11 causes the relay driven roller 42b to come into contact with the relay drive roller 42a.

[0036] When the manual feed bottom plate cam shaft 65 is stopped, the compression amount of the pressure spring 11 increases, and the nip pressure is therefore switched to a high state, that is, the second nip pressure.

[0037] The paper is transported along the paper feed path R1, and the relay drive roller 42a is rotated by the driving force from the main motor.

[0038] On the other hand, when the pressure spring 11 presses the bearing portion 37a with a biasing force based on the thickness of the paper, etc., the relay driven roller 42b comes into contact with the relay drive roller 42a due to the biasing force. As a result, the relay driven roller 42b rotates in conjunction with the relay drive roller 42a. Then, the paper transported along the paper feed path R1 is sandwiched by the nip pressure between the relay drive roller 42a and the relay driven roller 42b and transported.

[0039] The registration sensor S detects that the paper has arrived. Next, the CPU 201 turns off the paper feed clutch to temporarily halt the transport of the paper. As a result, when the leading edge of the paper hits the nip of the stopped registration roller pair 8, any skew caused by the paper being skewed is corrected.

[0040] Hereinafter, as with the paper feed clutch, the paper feed roller 5, the pair of conveying rollers 7, and the pair of registration rollers 8 are described using an example in which the main motor is used as a drive source, and the state of each roller is switched between "driven" and "stopped" by switching the clutch "ON" and "OFF." However, the control of switching the drive of the rollers may be realized by a device other than the clutch.

[0041] The CPU 201 transports the paper to the image forming device 2 at the timing when the paper is to be superimposed on the toner image formed on the photosensitive member.

[0042] [Overall processing example] Fig. 5 is a diagram (part 1) showing an example of the overall processing. Of the overall processing shown in Fig. 5, the processing from step S0512 onwards is shown in Fig. 6.

[0043] FIG. 6 is a diagram (part 2) showing an example of the overall processing.

[0044] The overall process will be explained below with reference to the timing chart shown in FIG.

[0045] 7 shows an example of the operation results for thin paper. Below, the operation results are explained using the main motor signal SG1, paper feed clutch signal SG2, nip pressure signal SG3, registration sensor signal SG4, registration loop detection signal SG5, and registration clutch signal SG6.

[0046] The main motor signal SG1 indicates the driving state of the main motor. Specifically, the main motor signal SG1 is a high active signal (high level is "ON"; the same applies below). Therefore, when the main motor signal SG1 is "ON", the main motor is in a driving state.

[0047] The paper feed clutch signal SG2 is a high active signal. When the paper feed clutch signal SG2 is "ON", it indicates that the drive force of the main motor is being transmitted to the paper feed roller 5.

[0048] The nip pressure signal SG3 indicates the result of switching between the nip pressure being the "first nip pressure" and the nip pressure being the "second nip pressure." In the following, when the nip pressure signal SG3 is "ON," the nip pressure is assumed to be the second nip pressure (i.e., a control result of a high nip pressure).

[0049] The registration sensor signal SG4 is a high active signal. Therefore, when a sheet is present within the detection range of the registration sensor S, that is, when the sheet is present immediately before the pair of registration rollers 8, the registration sensor signal SG4 is a signal that becomes “ON.”

[0050] The registration loop detection signal SG5 is a high active signal. Therefore, the registration loop detection signal SG5 is a signal that indicates the detection result of whether or not the sheet is abutting against the registration roller pair 8. Specifically, it can be estimated that the sheet is abutting against the registration roller pair 8 when a predetermined time has elapsed since the registration roller pair 8 stopped and the sheet was conveyed to the registration roller pair 8. If this estimation indicates that the sheet is abutting against the registration roller pair 8, the registration loop detection signal SG5 becomes "ON." Whether or not the sheet is abutting against the registration roller pair 8 may also be determined by detecting it using a sensor installed in the registration roller pair 8.

[0051] The resist clutch signal SG6 is a high active signal. When the resist clutch signal SG6 is "ON," it indicates that the drive of the main motor is being transmitted to the resist roller pair 8. Therefore, when the resist clutch signal SG6 is "ON," the paper passes through the resist roller pair 8. On the other hand, when the resist clutch signal SG6 is "OFF," the paper cannot pass through the resist roller pair 8, and the paper hits the resist roller pair 8.

[0052] In step S0501, the sheet conveying apparatus 200 acquires printer information, so that the CPU 201 can subsequently determine the thickness and type of paper.

[0053] In step S0502, the sheet conveying apparatus 200 determines whether the paper is thinner than a predetermined value. Specifically, the CPU 201 refers to the printer information to determine the thickness of the paper, that is, whether the paper is thin paper.

[0054] Next, if it is determined that the paper is thinner than the predetermined value (YES in step S0502), the sheet conveying device 200 proceeds to step S0504. On the other hand, if it is determined that the paper is not thinner than the predetermined value (NO in step S0502), the sheet conveying device 200 proceeds to step S0503.

[0055] In step S0503, the sheet conveying device 200 conveys the paper by the paper feed roller 5. Specifically, the sheet conveying device 200 first starts driving the main motor (first timing T1 in FIG. 7). Next, the sheet conveying device 200 turns the paper feed clutch "ON" (second timing T2 in FIG. 7). In this way, when the main motor signal SG1 and the paper feed clutch signal SG2 are both "ON", the sheet conveying device 200 conveys the paper to the conveying roller pair 7.

[0056] In step S0504, the sheet conveying device 200 conveys the paper by the paper feed roller 5. For example, step S0504 is the same process as step S0503.

[0057] In step S0505, the sheet conveying apparatus 200 switches the nip pressure to the second nip pressure, so that the sheet conveying apparatus 200 nip the paper with a high nip pressure.

[0058] In step S0506, the sheet conveying apparatus 200 performs image formation on the paper, etc. Note that in step S0506, the sheet conveying apparatus 200 may also perform processing other than image formation.

[0059] In step S0507, the sheet conveying device 200 discharges the paper.

[0060] In step S0508, the sheet conveying device 200 determines whether or not the abutment of the sheet has started. Specifically, in step S0504, the sheet is conveyed and arrives at the pair of conveying rollers 7. Next, when the sheet arrives at the pair of conveying rollers 7, the sheet conveying device 200 conveys the sheet to the pair of registration rollers 8 by the pair of conveying rollers 7.

[0061] 3, the registration sensor S is installed upstream of the registration roller pair 8. Therefore, the registration sensor S detects the sheet before it hits the registration roller pair 8, that is, when the sheet is transported to just before the registration roller pair 8.

[0062] After that, when a predetermined time has passed since the timing at which the registration sensor S begins to detect the paper (the third timing T3 in Figure 7) and the registration roller pair 8 is stopped, the paper hits the registration roller pair 8 and a registration loop is formed.

[0063] The predetermined time is calculated and set in advance through experiments or the like.

[0064] Next, if it is determined that the sheet has started to be butted (YES in step S0508), the sheet conveying device 200 proceeds to step S0509. On the other hand, if it is determined that the sheet has not started to be butted (NO in step S0508), the sheet conveying device 200 repeats step S0508. That is, the sheet conveying device 200 continues to convey the sheet until a predetermined time has elapsed.

[0065] In step S0509, the sheet conveying apparatus 200 switches the nip pressure to the second nip pressure. For example, step S0509 is the same process as step S0505. In the example shown in FIG. 7, the nip pressure is switched to the second nip pressure at the fourth timing T4.

[0066] In step S0510, the sheet conveying apparatus 200 forms a registration loop on the sheet. In Fig. 7, the formation of the registration loop starts from the fifth timing T5.

[0067] In step S0511, the sheet conveying device 200 resumes conveying the sheet. In Fig. 7, this is at the sixth timing T6. Specifically, from the sixth timing T6, the registration clutch signal SG6 turns "ON" and the pair of registration rollers 8 changes from a stopped state to a rotating state, and sheet conveyance begins.

[0068] Furthermore, when the pair of registration rollers 8 starts rotating, the pair of registration rollers 8 conveys the paper, completing the process of forming a registration loop on the paper. Therefore, from the sixth timing T6, the registration loop detection signal SG5 becomes "OFF." That is, in FIG. 7, the registration loop is formed between the fifth timing T5 and the sixth timing T6.

[0069] In step S0512, when sheet conveyance starts, sheet conveying device 200 switches the nip pressure to the first nip pressure. In FIG. 7, when a certain period (determined by the motor start time, etc.) has passed since registration clutch signal SG6 turned "ON" (i.e., at seventh timing T7, which is the point at which a certain period has passed from sixth timing T6), sheet conveying device 200 determines that sheet conveyance has started. Therefore, nip pressure signal SG3 turns "OFF" at seventh timing T7.

[0070] In step S0513, the sheet conveying apparatus 200 determines whether or not the first time has elapsed since the sheet conveyance was resumed.

[0071] The first time is a time that is set in advance. The sheet conveying device 200 determines in step S0513 whether the time counted from the time when the sheet conveyance is resumed (the sixth timing T6 in FIG. 7) has reached the first time.

[0072] Next, if it is determined that the first time has elapsed since the sheet conveyance was resumed (YES in step S0513), sheet conveying device 200 proceeds to step S0514. On the other hand, if it is determined that the first time has not elapsed since the sheet conveyance was resumed (NO in step S0513), sheet conveying device 200 repeats step S0513.

[0073] In step S0514, the sheet conveying apparatus 200 switches the nip pressure to the second nip pressure, which is the eighth timing T8 in FIG.

[0074] In step S0515, the sheet conveying apparatus 200 stops the sheet feed roller 5. This is the ninth timing T9 in Fig. 7. Specifically, the sheet feed clutch signal SG2 is turned "OFF."

[0075] In step S0516, the sheet conveying apparatus 200 determines whether or not a second time has elapsed since the sheet feed roller 5 was stopped.

[0076] The second time is a time set in advance. The sheet conveying device 200 determines in step S0516 whether the time counted from the time when the sheet feed roller 5 was stopped (the time at the ninth timing T9 in FIG. 7) has reached the second time.

[0077] Next, if it is determined that the second time has elapsed since the sheet feed rollers 5 were stopped (YES in step S0516), sheet conveying device 200 proceeds to step S0517. On the other hand, if it is determined that the second time has not elapsed since the sheet feed rollers 5 were stopped (NO in step S0516), sheet conveying device 200 repeats step S0516.

[0078] The sheet conveying device 200 may determine whether the paper has passed through the paper feed roller 5 at a time other than the second time elapsed since the paper feed roller 5 was stopped. For example, the sheet conveying device 200 may determine whether the paper has passed through the paper feed roller 5 using a sensor.

[0079] In step S0517, the sheet conveying apparatus 200 switches the nip pressure to the first nip pressure, which corresponds to the tenth timing T10 in FIG.

[0080] Thereafter, the sheet conveying device 200 performs image formation (step S0506 in FIG. 5), paper discharge (step S0507 in FIG. 5), and the like.

[0081] 8 is a diagram showing an example of forming a resist loop 300. FIG. 8 shows a state in which a resist loop 300 is formed in step S0510.

[0082] In the sheet conveying device 200, the conveying roller pair 7 conveys the thin sheet P10 and causes it to strike the stopped registration roller pair 8. When the thin sheet P10 strikes the registration roller pair 8 in this manner, a registration loop 300 is formed. For example, the registration loop 300 is formed to be about 3 mm. The size of the registration loop 300 is set in advance.

[0083] As described above, when the registration loop 300 is formed, it is possible to correct the tilted posture of the paper due to skew, etc. Furthermore, when the posture can be corrected, it is possible to prevent the image formed on the paper from being formed at an angle, thereby improving image quality. In this way, when the registration loop 300 is formed and the paper can be corrected, no special device or the like is required for correction, and the sheet conveying device 200 can easily correct the posture of the paper.

[0084] Then, to form the registration loop 300, the sheet conveying device 200 switches the nip pressure to the second nip pressure (step S0509). In this way, the sheet conveying device 200 performs control to switch the nip pressure to the second nip pressure, and forms the registration loop 300 at the second nip pressure even for thin paper P10. In FIG. 7, the nip pressure is the second nip pressure (i.e., the nip pressure signal SG3 is "ON") from the fifth timing T5 to the sixth timing T6. After that, when the registration roller pair 8 rotates and the paper is conveyed, the paper becomes in the following state.

[0085] Fig. 9 is a diagram showing an example of paper transport by a pair of registration rollers. Compared to Fig. 8, Fig. 9 differs in that the pair of registration rollers 8 is rotating. When the pair of registration rollers 8 rotates, the paper is transported and processed, such as for ejection.

[0086] The sheet conveying device 200 conveys a sheet by nipping it between a pair of conveying rollers 7. When a sheet jams while being conveyed in this manner and the nip pressure is the second nip pressure, i.e., a strong pressure, it is often difficult to pull out the jammed sheet. Furthermore, if you try to pull out the jammed sheet by force, it will often tear because thin paper is easily torn.

[0087] If torn paper remains inside the device, it becomes difficult to recover from the jam. On the other hand, if the nip pressure is set to the first nip pressure, i.e., a weak pressure, to prevent tearing even if a jam occurs, the sheet conveying device 200 may not be able to pass thick paper.

[0088] Therefore, the sheet conveying device 200 switches the nip pressure depending on the thickness of the paper. Specifically, the sheet conveying device 200 uses a first nip pressure to convey thin paper. This switching can reduce the risk of paper tearing, even for thin paper. On the other hand, the sheet conveying device 200 uses a second nip pressure to convey thick paper. This switching can convey even thick paper.

[0089] However, when a sheet is pressed against the pair of registration rollers 8 with a weak nip pressure such as the first nip pressure, the reaction force of the registration loop 300 may cause slippage in the pair of conveying rollers 7. When such slippage occurs, the following phenomenon occurs.

[0090] 10 is a diagram showing an example of roller marks. If slippage occurs while forming the registration loop 300, a slip mark (hereinafter referred to as "first roller mark 50") is likely to appear at the leading edge of the paper. Therefore, the sheet conveying device 200 switches the nip pressure to the second nip pressure to abut the paper against the pair of registration rollers 8, even for thin paper.

[0091] If the nip pressure is strong like the second nip pressure, slippage is unlikely to occur even with the reaction force of the registration loop 300. Therefore, the first roller mark 50 can be prevented from occurring.

[0092] Next, when the sheet conveying device 200 resumes conveying the sheet after the sheet abuts against the pair of registration rollers 8 (step S0511), it switches the nip pressure to the first nip pressure (step S0512). In this way, if the sheet is conveyed at the first nip pressure, even if a jam occurs while conveying the thin sheet P10, the sheet is less likely to tear when the sheet is pulled out because the nip pressure is weak.

[0093] Furthermore, it is desirable that the sheet conveying device 200 performs control to stop the feed rollers 6 before the trailing edge of the paper passes through the feed rollers 6 (step S0515). In this way, stopping the feed rollers 6 before the trailing edge of the paper passes through the feed rollers 6 can prevent the next paper from being conveyed in a continuous state.

[0094] The rear end portion of the paper is, for example, the portion behind the center of the paper in the transport direction (indicated by center line 52 in FIG. 10) (the portion to the right of center line 52 in FIG. 10). On the other hand, the front end portion is the portion to the left of center line 52 in FIG. 10. However, the ranges to be defined as the front end portion and the rear end portion are set in advance.

[0095] When the paper tries to pass through the paper feed roller 6 while the paper feed roller 6 is stopped, a load is placed on the paper during conveyance because the paper feed roller 6 is stopped. Therefore, if the nip pressure is weak, slippage may occur in the conveyance roller pair 7.

[0096] If slippage occurs while the paper feed roller 6 is stopped before the trailing end of the thin paper P10 passes through the paper feed roller 6, a slip mark (hereinafter referred to as the "second roller mark 51") is likely to appear on the trailing end of the paper, as shown in Figure 10.

[0097] 7, the nip pressure is switched to the second nip pressure at eighth timing T8, which is before ninth timing T9 at which the paper feed roller 6 is stopped (step S0514). Note that the timing at which the nip pressure is switched to the second nip pressure, i.e., the eighth timing T8, may be the same as when the paper feed roller 6 is stopped. In other words, as long as the nip pressure is the second nip pressure when the paper feed roller 6 is stopped and the trailing edge of the paper leaves the paper feed roller 6, the timing at which the nip pressure is switched is not limited to the eighth timing T8.

[0098] By switching the nip pressure to the second nip pressure at this timing, the sheet conveying device 200 can convey the paper at the second nip pressure before the trailing edge of the paper passes through the paper feed roller 6 and while the paper feed roller 6 is stopped.

[0099] If the nip pressure is strong like the second nip pressure, slippage is unlikely to occur even if there is a load that tries to cause the paper to pass through the paper feed roller 6. Therefore, the second roller marks 51 can be prevented from occurring.

[0100] When it is determined that the paper has passed through the paper feed roller 6 (YES in step S0516), the sheet conveying device 200 switches the nip pressure to the first nip pressure (step S0517). In FIG. 7, this is the tenth timing T10. In this way, if the paper is conveyed at the first nip pressure, even if a jam occurs while conveying the thin paper P10, the nip pressure is weak, so the paper is less likely to tear even when the paper is pulled out.

[0101] [Control configuration example] 11 is a diagram showing an example of a control configuration. A CPU 201 is connected to a main motor 500, a paper feed clutch 501, a nip pressure switch 502, a resist clutch 503, and the like.

[0102] The CPU 201 controls each device by transmitting a main motor signal SG1, a paper feed clutch signal SG2, a nip pressure signal SG3, and a registration clutch signal SG6.

[0103] The sheet conveying device 200 may be configured to use devices other than those shown in the drawings. For example, a mechanism other than a clutch may be used, or a control device other than the CPU 201 may be used.

[0104] [Example of functional configuration] 12 is a diagram showing an example of a functional configuration. Specifically, the sheet conveying device 200 includes a registration roller unit 200F1, a conveying roller unit 200F2, a switching unit 200F3, a control unit 200F4, and a supply roller unit 200F5. The image forming apparatus 100 includes the sheet conveying device 200 and an image forming unit 100F1.

[0105] The registration roller unit 200F1 abuts against the sheet to form a registration loop in the sheet. For example, the registration roller unit 200F1 is realized by a pair of registration rollers 8 or the like.

[0106] The conveying roller unit 200F2 is disposed upstream of the registration roller unit 200F1 and conveys the sheet. For example, the conveying roller unit 200F2 is realized by a pair of conveying rollers 7 or the like.

[0107] The switching unit 200F3 performs a switching procedure to switch the nip pressure between the first nip pressure and the second nip pressure. For example, the switching unit 200F3 is realized by the CPU 201 or the like.

[0108] When the control unit 200F4 determines that the sheet is thinner than a predetermined value, it performs control to switch the nip pressure to the second nip pressure, and abuts the sheet against the registration roller unit 200F1 at the second nip pressure. After the sheet abuts against the registration roller unit 200F1, when the registration roller unit 200F1 starts conveying the sheet, it performs a control procedure to switch the nip pressure to the first nip pressure. For example, the control unit 200F4 is realized by the CPU 201 or the like.

[0109] The supply roller unit 200F5 is disposed upstream of the conveyance roller unit 200F2. The supply roller unit 200F5 supplies a sheet to the conveyance roller unit. For example, the supply roller unit 200F5 is realized by the paper feed roller 5 or the like.

[0110] The image forming unit 100F1 performs an image forming procedure for forming an image on a sheet. For example, the image forming unit 100F1 is realized by an image forming device 2 or the like.

[0111] With the above configuration, after the sheet hits the registration roller unit 200F1, the sheet conveying device 200 conveys the sheet with the first nip pressure. Therefore, even if the sheet is thin, the first nip pressure can prevent the sheet from being torn when pulling out the sheet due to a jam or the like.

[0112] Furthermore, the sheet conveying device 200 uses the second nip pressure to abut the sheet against the registration roller unit 200F1, form a registration loop, and correct the sheet posture, thereby preventing slippage and the like from occurring when the sheet abuts against the registration roller unit 200F1.

[0113] [Example of processing cardboard, etc.] 13 is a diagram showing an example of the operation result for thick paper. When the sheet conveying device 200 determines that the paper is not thinner than a predetermined value (i.e., the paper is thick paper) (NO in step S0502), it performs the processing from step S0503 onwards. As a result of such processing, that is, in the case of thick paper, the operation result is as shown in FIG.

[0114] The sheet conveying device 200 sets the nip pressure to the second nip pressure at the twentieth timing T20 (step S0505). Therefore, the nip pressure signal SG3 is turned "ON" at the twentieth timing T20.

[0115] Compared with the case of thin paper (that is, the operation result under the control shown in FIG. 7), the difference with thick paper is that the nip pressure is basically the second nip pressure after the twentieth timing T20.

[0116] [Comparative Example] 14 is a diagram showing an example of overall processing in the comparative example. Compared with FIGS. 5 and 6, the comparative example differs in that in the case of thin paper (YES in step S1402), the nip pressure is consistently the first nip pressure. In other words, in the comparative example, after the nip pressure is switched to the first nip pressure in step S1408, there is no process of switching the nip pressure.

[0117] 15 is a diagram showing an example of the operation result of the comparative example. Compared to FIG. 7, the comparative example differs in that the nip pressure signal SG3 is consistently "OFF." Note that in the example shown in FIG. 15, the initial setting of the nip pressure is the first nip pressure, so the nip pressure signal SG3 is not switched "ON" or "OFF" in step S1408.

[0118] Such global processing is likely to result in the results shown in FIG.

[0119] [Other embodiments] The sheet may be something other than paper (also called "plain paper"). That is, the sheet conveying device may be applied to an apparatus other than an image forming apparatus. For example, the sheet conveying device may be a pre-processing device that performs pre-processing before image formation.

[0120] In an image forming apparatus, a sheet is a recording medium. For example, the recording medium may be paper, coated paper, label paper, an overhead projector sheet, a film, or a flexible thin plate. In other words, the material of the recording medium may be any material to which toner or ink droplets can adhere, be temporarily adhered, adhere and fix, or adhere and penetrate.

[0121] Specifically, the recording medium is a recording medium such as paper, film, or cloth, an electronic substrate, an electronic component such as a piezoelectric element (also referred to as a "piezoelectric member"), a powder layer (also referred to as a "powder layer"), an organ model, or a test cell, etc. As such, the material of the recording medium may be any material that can accept a liquid, such as paper, thread, fiber, fabric, leather, metal, plastic, glass, wood, ceramics, or a combination of these.

[0122] Each device may be a plurality of devices. That is, each device may be configured to perform distributed, redundant, or parallel processing using a plurality of devices. On the other hand, each device may be integrated. That is, the plurality of devices described above may be realized by a single device.

[0123] The image reading method as described above may be realized by an image reading program. That is, the image reading program causes devices such as an arithmetic unit, a control unit, and a storage unit provided in a computer to cooperate with each other to realize the image reading method. The image reading program may also be distributed via a computer-readable recording medium or a telecommunications line.

[0124] The above-described embodiment shows a preferred example, but a person skilled in the art can realize various modifications from the disclosed content. Such modifications are also included in the technical scope described in the claims. [Explanation of symbols]

[0125] 2: Image forming device 5: Paper feed roller 7: Transport roller pair 8: Registration roller pair 50: First roller mark 51: Second Coro Remains 52: Chuo Line 100: Image forming device 100F1: Image forming unit 200: Sheet transport device 200F1: Registration roller section 200F2: Transport roller section 200F3: Switching section 200F4: Control unit 200F5: Supply roller section 300: Resist Loop SG1: Main motor signal SG2: Paper feed clutch signal SG3: Nip pressure signal SG4: Resist sensor signal SG5: Register loop detection signal SG6: Resist clutch signal T1: First timing T2: Second timing T3: Third timing T4: Fourth timing T5: 5th timing T6: 6th timing T7: 7th timing T8: 8th timing T9: 9th timing T10: 10th timing T20: 20th timing [Prior art documents] [Patent documents]

[0126] [Patent Document 1] Japanese Patent Application Publication No. 2018-058682

Claims

1. a registration roller unit that abuts against the sheet to form a registration loop in the sheet; a registration sensor disposed upstream of the registration roller unit and configured to detect the sheet; a conveying roller unit disposed upstream of the registration sensor and configured to convey the sheet; a switching unit that switches the nip pressure at which the conveying roller unit pinches the sheet between a first nip pressure and a second nip pressure that is higher than the first nip pressure; a control unit that controls the conveyance of the sheet, When determining that the sheet is thinner than a predetermined value, the control unit controls the nip pressure to be the first nip pressure until a predetermined time has elapsed since the conveying roller unit started conveying the sheet to the registration roller unit and the registration sensor detected the sheet, After the predetermined time has elapsed since the sheet was detected by the registration sensor, control is performed to switch the nip pressure to the second nip pressure; When the registration roller unit starts conveying the sheet after the sheet has been abutted against the registration roller unit, the nip pressure is controlled to be switched to the first nip pressure. Sheet transport device.

2. The control unit The nip pressure that forms the resist loop is set to the second nip pressure. The sheet transport device according to claim 1 .

3. a supply roller unit disposed upstream of the conveying roller unit and configured to supply the sheet to the conveying roller unit; The control unit Before the trailing end portion of the sheet passes through the supply roller unit and when the supply roller unit is stopped, the nip pressure is switched to the second nip pressure.

3. The sheet conveying device according to claim 1 or 2.

4. The control unit When the trailing end portion passes through the supply roller portion, the nip pressure is switched to the first nip pressure. The sheet transport device according to claim 3 .

5. the sheet is paper, The registration loop is a slack formed when the sheet strikes the registration roller unit, When the leading edge of the paper abuts against the registration roller unit and the registration roller unit is stopped, the registration loop is formed, The conveying roller unit includes: the sheet fed from downstream is nipped with the nip pressure and conveyed toward the registration roller unit; The switching unit is switching to one of a plurality of nip pressures including at least the first nip pressure and the second nip pressure; The control unit When it is determined that the sheet is thick paper that is not thinner than the predetermined value, the nip pressure is controlled to be the second nip pressure so as to convey the sheet; If it is determined that the paper is thin paper thinner than the predetermined thickness, The paper is nipped with the second nip pressure, and the leading edge is abutted against the registration roller portion to form the registration loop and correct the posture of the paper. The sheet transport device according to claim 1 .

6. The sheet conveying device according to any one of claims 1 to 5, The image forming unit further includes an image forming unit for forming an image on the sheet. Image forming device.

Images