JP7775690B2 - Sheet conveying device and image forming apparatus - Google Patents

Description

The present invention relates to a sheet conveying device and an image forming apparatus.

When transporting a sheet such as paper (hereinafter, an example will be described using paper as the sheet), a technique is known in which the leading edge of the sheet is abutted against a roller while being fed in, forming a loop in the sheet (a slack that occurs when the sheet is abutted; this is a so-called "resist loop"; hereinafter referred to as a "resist loop") in order to correct any skew in the transported sheet.

Specifically, in an image forming device equipped with a loop roller pair and a conveying roller upstream of the loop roller pair, the image forming device controls the nip pressure of the loop roller pair. In this way, a technology is known that makes the nip pressure of the loop roller pair lower than the nip pressure of the registration roller pair, preventing paper from passing through the registration nip (see, for example, Patent Document 1).

With conventional technology, the nip pressure that holds the sheet is not adjusted even if the sheet thickness varies. As a result, when a jam occurs with a thin sheet, the worker pulls out the sheet. In this case, if the nip pressure is not adjusted, there is a problem that the sheet may tear.

The purpose of this invention is to prevent sheet tearing even when clearing a jam, etc., even with thin sheets.

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 at 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.

This invention prevents even thin sheets from tearing when clearing jams, etc.

FIG. 1 is a diagram illustrating an example of the overall configuration of an image reading apparatus. FIG. 2 illustrates an example of a hardware configuration of a sheet conveying device. FIG. 2 is a diagram illustrating an example of the configuration of a sheet conveying device. 10A and 10B are diagrams illustrating an example of control for switching nip pressures. FIG. 1 is a diagram (part 1) showing an example of the overall processing. FIG. 10 is a diagram (part 2) showing an example of the overall processing. FIG. 10 is a diagram showing an example of an operation result when thin paper is used as the target. 10A and 10B are diagrams illustrating an example of forming a resist loop. 10A and 10B are diagrams illustrating an example of paper transport by a pair of registration rollers. FIG. 10 is a diagram showing an example of roller marks. FIG. 2 is a diagram illustrating an example of a control configuration. FIG. 2 is a diagram illustrating an example of a functional configuration. 10A and 10B are diagrams illustrating examples of operation results when targeting cardboard or the like. FIG. 10 is a diagram illustrating an example of overall processing in a comparative example. FIG. 10 is a diagram illustrating an example of an operation result of a comparative example.

Specific examples will be described below with reference to the accompanying drawings. Note that the embodiment is not limited to the specific examples described below. In addition, the following description will be given assuming that the sheets are paper.

[Overall configuration example]
Fig. 1 is a diagram showing an example of an image forming apparatus. The following description will be given using 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 using an example of the electrophotographic method.

The image forming apparatus 100 includes an image forming unit 2 that forms an image using an image carrier 1, a transfer device 9, an exposure device, and the like. Note that the image forming unit 2 may also include other devices.

The image forming device 100 is equipped with 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 transported one sheet at a time from a stack of paper P1 stored in the main body paper feed tray 3 or a stack of paper P2 stored in the manual paper feed tray 4 toward the image forming device 2. The paper is also transported by the paper feed roller 5 or the paper feed roller 6.

The image forming device 100 is equipped with a registration sensor S and a registration roller pair 8. The registration sensor S detects whether or not paper is present. After the registration sensor S detects the paper, the registration roller pair 8 transports the paper to the transfer device 9. The transfer device 9 then transfers the image onto the paper. After transfer, the paper is sent to the fixing device 10.

The fixing device 10 performs a fixing process to fix the image onto the paper. After fixing, the paper is ejected outside the image forming apparatus 100.

The following explanation uses the sheet conveying device 200 as an example. In this example, the sheet conveying device 200 is composed 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 has the following hardware resources:

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

The CPU 201 is an example of a calculation device and a control device. Below, an example will be described in which the CPU 201 controls the various devices included in the image forming apparatus 100 and the sheet conveying device 200.

The storage device 202 includes a main storage device and an auxiliary storage device.

The input device 203 inputs operations and data from outside.

The output device 204 outputs processing results, etc.

Interface 205 sends and receives data to and from external devices.

The sheet conveying device 200 executes processing by causing the CPU 201, storage device 202, etc. to operate in cooperation with each other based on programs, etc.

In addition to the devices listed above, the hardware configuration may also include internal or external auxiliary devices, arithmetic units, control units, storage devices, input devices, or output devices.

[Configuration example of sheet conveying device]
3 is a diagram showing an example of the configuration of the 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.

When starting paper transport, the CPU 201 first checks whether the initial operation has been completed. If the initial operation has not been completed, the CPU 201 starts the initial operation.

The initial operation is the operation of bringing the manual feed bottom plate 34 to its lowest position. After this 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.

In the following, the nip pressure is assumed to be switched between two levels, "first nip pressure" and "second nip pressure," based on the control of the CPU 201.

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. 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.

After the initial operation is complete, the CPU 201 turns on the main motor. Then, the CPU 201 determines whether the paper is thin paper.

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

The user operates the operation panel to select the type of paper. Several types of paper are available, such as regular paper, thin paper, and thick paper. The thickness of each type is also entered 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.

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

The CPU 201 controls the mechanisms, etc., as follows, for example, and switches the nip pressure.

Figure 4 shows an example of control for switching nip pressure. Figure 4(a) shows the initial operation state. Figure 4(b) shows the state in Figure 4(a) after the manual feed bottom plate cam clutch is turned on and the manual feed bottom plate cam shaft 65 is rotated clockwise.

The conveying roller pair 7 is composed of a relay drive roller 42a and a relay driven roller 42b. The relay driven roller 42b has a bearing portion 37a that supports the roller shaft 66, which is biased by a compression spring 11. The biasing force of the pressure spring 11 causes the relay driven roller 42b to abut against the relay drive roller 42a.

When the manual feed bottom plate cam shaft 65 is stopped, the compression amount of the pressure spring 11 increases. Therefore, the nip pressure is switched to a high state, i.e., the second nip pressure.

The paper is transported along paper feed path R1. The relay drive roller 42a is then rotated by the driving force from the main motor.

On the other hand, when the pressure spring 11 presses against 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.

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 between the stopped registration roller pair 8, any skew caused by the paper being skewed is corrected.

In the following, we will explain an example in which, like the paper feed clutch, the paper feed roller 5, the pair of transport rollers 7, and the pair of registration rollers 8 are driven by the main motor, and each roller is controlled to be "driven" or "stopped" by switching the clutch "ON" or "OFF." However, the control to switch the drive of the rollers may also be achieved by a device other than the clutch.

The CPU 201 transports paper to the image forming device 2 at the timing required to overlay the toner image formed on the photosensitive member.

[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.

Figure 6 is a diagram (part 2) showing an example of the overall processing.

The overall process is explained below using the timing chart shown in Figure 7.

Figure 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.

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.

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.

The nip pressure signal SG3 indicates the result of switching between the "first nip pressure" and the "second nip pressure." Below, we will use the example where, when the nip pressure signal SG3 is "ON," the nip pressure is the second nip pressure (i.e., a control result of a high nip pressure).

The registration sensor signal SG4 is a high active signal. Therefore, when paper is present within the detection range of the registration sensor S, that is, when paper is present immediately in front of the registration roller pair 8, the registration sensor signal SG4 is an "ON" signal.

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 paper is abutting against the registration roller pair 8. Specifically, it can be assumed that the paper is abutting against the registration roller pair 8 after a predetermined time has passed since the registration roller pair 8 stopped and the paper was transported to the registration roller pair 8. If this assumption indicates that the paper is abutting against the registration roller pair 8, the registration loop detection signal SG5 becomes "ON." Whether or not the paper is abutting against the registration roller pair 8 can also be detected by installing a sensor on the registration roller pair 8.

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

In step S0501, the sheet conveying device 200 acquires printer information. Therefore, the CPU 201 can subsequently determine the thickness and type of paper, etc.

In step S0502, the sheet conveying device 200 determines whether the paper is thinner than a predetermined value. Specifically, the CPU 201 references printer information to determine the thickness of the paper, i.e., whether it is thin paper.

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.

In step S0503, the sheet conveying device 200 conveys the paper using the paper feed roller 5. Specifically, the sheet conveying device 200 first starts driving the main motor (first timing T1 in Figure 7). Next, the sheet conveying device 200 turns the paper feed clutch "ON" (second timing T2 in Figure 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.

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

In step S0505, the sheet conveying device 200 switches the nip pressure to the second nip pressure. Therefore, the sheet conveying device 200 clamps the paper with a high nip pressure.

In step S0506, the sheet conveying device 200 performs image formation on the paper. Note that in step S0506, the sheet conveying device 200 may also perform processing other than image formation.

In step S0507, the sheet conveying device 200 ejects the paper.

In step S0508, the sheet conveying device 200 determines whether or not the abutment of the paper has begun. Specifically, in step S0504, the paper is conveyed and arrives at the conveying roller pair 7. Next, when the paper arrives at the conveying roller pair 7, the sheet conveying device 200 conveys the paper to the registration roller pair 8 using the conveying roller pair 7.

As shown in Figure 3, the registration sensor S is installed upstream of the registration roller pair 8. Therefore, the registration sensor S detects when the paper is transported before it hits the registration roller pair 8, i.e., when the paper has reached the position immediately before the registration roller pair 8.

After that, when a predetermined time has passed since the registration sensor S began to detect the paper (the third timing T3 in Figure 7) and the registration roller pair 8 is stopped, the paper will strike the registration roller pair 8, forming a registration loop.

The specified time is calculated and set in advance through experiments, etc.

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. In other words, the sheet conveying device 200 continues to convey the sheet until a predetermined time has elapsed.

In step S0509, the sheet conveying device 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.

In step S0510, the sheet conveying device 200 forms a registration loop on the paper. In Figure 7, the formation of the registration loop begins at the fifth timing T5.

In step S0511, the sheet conveying device 200 resumes conveying the paper. In Figure 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 paper conveyance begins.

Furthermore, when the registration roller pair 8 starts rotating, the registration roller pair 8 transports 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 turns "OFF." In other words, in Figure 7, a registration loop is formed between the fifth timing T5 and the sixth timing T6.

In step S0512, when paper transport begins, the sheet transport device 200 switches the nip pressure to the first nip pressure. In FIG. 7, when a certain period of time (determined by the motor start time, etc.) has passed since the resist clutch signal SG6 turned "ON" (i.e., at the seventh timing T7, which is the point at which a certain period of time has passed based on the sixth timing T6), the sheet transport device 200 determines that paper transport has begun. Therefore, the nip pressure signal SG3 turns "OFF" at the seventh timing T7.

In step S0513, the sheet conveying device 200 determines whether a first time has elapsed since paper conveyance was resumed.

The first time is a time that is set in advance. Furthermore, the sheet conveying device 200 makes the determination in step S0513 based on whether the time counted from the resumption of paper conveyance (which is the sixth timing T6 in Figure 7) has reached the first time.

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

In step S0514, the sheet conveying device 200 switches the nip pressure to the second nip pressure. In Figure 7, this is the eighth timing T8.

In step S0515, the sheet conveying device 200 stops the paper feed roller 5. In Figure 7, this is the ninth timing T9. Specifically, the paper feed clutch signal SG2 becomes "OFF."

In step S0516, the sheet conveying device 200 determines whether a second time has elapsed since the paper feed roller 5 was stopped.

The second time is a time that is set in advance. Furthermore, the sheet conveying device 200 makes a determination in step S0516 based on whether the time counted from the time when the paper feed roller 5 was stopped (the time at the ninth timing T9 in Figure 7) has reached the second time.

Next, if it is determined that the second time has elapsed since the paper feed roller 5 was stopped (YES in step S0516), the 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 paper feed roller 5 was stopped (NO in step S0516), the sheet conveying device 200 repeats step S0516.

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 use a sensor to determine whether the paper has passed through the paper feed roller 5.

In step S0517, the sheet conveying device 200 switches the nip pressure to the first nip pressure. In Figure 7, this is the tenth timing T10.

After this, the sheet conveying device 200 performs image formation (step S0506 in Figure 5), paper ejection (step S0507 in Figure 5), etc.

Figure 8 is a diagram showing an example of forming a registration loop. Figure 8 shows the state in which the registration loop 300 is formed in step S0510.

In the sheet conveying device 200, the conveying roller pair 7 conveys the thin paper P10 and abuts it against the stopped registration roller pair 8. When the thin paper P10 abuts in this way, 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.

By forming the registration loop 300 as described above, it is possible to correct the tilted posture of the paper caused by skew, etc. Furthermore, correcting the posture prevents the image formed on the paper from being formed at an angle, improving image quality. In this way, by forming the registration loop 300 and correcting the paper, special devices are not required for correction, and the sheet conveying device 200 can easily correct the posture of the paper.

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 controls the nip pressure to be switched 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. Thereafter, when the registration roller pair 8 rotates and the paper is conveyed, the paper is in the following state.

Figure 9 shows an example of paper transport by a pair of registration rollers. Compared to Figure 8, Figure 9 differs in that the pair of registration rollers 8 is rotating. As the pair of registration rollers 8 rotates, the paper is transported and processed, such as for ejection.

The sheet conveying device 200 conveys paper by nipping it between a pair of conveying rollers 7. When conveying paper in this manner, if a jam occurs when the nip pressure is the second nip pressure, i.e., a strong pressure, it is often difficult to pull out the jammed paper. Furthermore, if you try to forcibly pull out the jammed paper, it will often tear because thin paper is prone to tearing.

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 through.

The sheet conveying device 200 therefore 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 reduces the risk of paper tearing, even with thin paper. On the other hand, the sheet conveying device 200 uses a second nip pressure to convey thick paper. This switching allows paper to be conveyed even with thick paper.

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 from the registration loop 300 can cause slippage in the pair of conveying rollers 7. When such slippage occurs, the following phenomenon occurs:

Figure 10 shows an example of roller marks. If slippage occurs while forming the registration loop 300, slip marks (hereinafter referred to as "first roller marks 50") are likely to appear on the leading edge of the paper. Therefore, the sheet conveying device 200 switches the nip pressure to the second nip pressure, even for thin paper, to force the paper against the registration roller pair 8.

When the nip pressure is strong, like the second nip pressure, slippage is unlikely to occur even with the reaction force from the registration loop 300. This prevents the first roller marks 50 from occurring.

Next, when the sheet conveying device 200 resumes conveying the sheet after abutting it against the registration roller pair 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 nip pressure is weak, so the sheet is less likely to tear when pulled out.

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

The trailing edge of the paper is, for example, the portion behind the center of the paper in the transport direction (indicated by center line 52 in Figure 10) (the portion to the right of center line 52 in Figure 10). On the other hand, the leading edge is the portion to the left of center line 52 in Figure 10. However, the ranges that will be considered the leading edge and trailing edge are set in advance.

When the paper attempts to pass through the paper feed roller 6 while the paper feed roller 6 is stopped, the paper feed roller 6 is stopped, which places a load on the paper during transport. Therefore, if the nip pressure is weak, slippage may occur in the transport roller pair 7.

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

In FIG. 7, the nip pressure is switched to the second nip pressure at the eighth timing T8, which is before the 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 of the switch is not limited to the eighth timing T8.

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.

When the nip pressure is strong, like the second nip pressure, slippage is unlikely to occur even when there is a load that tries to cause the paper to pass through the paper feed roller 6. This prevents the second roller marks 51 from occurring.

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 Figure 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 thin paper P10, the nip pressure is weak, so the paper is less likely to tear when the paper is pulled out.

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

The CPU 201 then 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.

Note that the sheet conveying device 200 may be configured to use devices other than those shown in the figure. For example, it may use a mechanism other than a clutch, or the control device may be something other than the CPU 201.

[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.

The registration roller unit 200F1 abuts 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, etc.

The transport roller unit 200F2 is located upstream of the registration roller unit 200F1. The transport roller unit 200F2 transports the sheet. This is realized, for example, by a transport roller pair 7.

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, etc.

When the control unit 200F4 determines that the sheet is thinner than a predetermined value, it controls the nip pressure to switch to the second nip pressure, abutting 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 begins 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, etc.

The supply roller unit 200F5 is located upstream of the transport roller unit 200F2. The supply roller unit 200F5 supplies the sheet to the transport roller unit. For example, the supply roller unit 200F5 can be realized by the paper feed roller 5, etc.

Image forming unit 100F1 performs an image formation procedure to form an image on a sheet. For example, image forming unit 100F1 is realized by image forming device 2, etc.

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 with thin sheets, the first nip pressure prevents the sheet from tearing when pulling out the sheet due to a jam, etc.

In addition, 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's posture. This prevents slippage and other problems from occurring when the sheet abuts against the registration roller unit 200F1.

[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 onward. As a result of such processing, i.e., in the case of thick paper, the operation result is as shown in FIG.

The sheet conveying device 200 sets the nip pressure to the second nip pressure at the 20th timing T20 (step S0505). Therefore, the nip pressure signal SG3 becomes "ON" at the 20th timing T20.

Compared to the case of thin paper (i.e., the operational result of the control shown in Figure 7), the difference with thick paper is that from the 20th timing T20 onwards, the nip pressure is basically the second nip pressure.

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

Figure 15 shows an example of the operational results of the comparative example. Compared to Figure 7, the comparative example differs in that the nip pressure signal SG3 is consistently "OFF." Note that in the example shown in Figure 15, the initial nip pressure setting is the first nip pressure, so the nip pressure signal SG3 is not switched "ON" or "OFF" in step S1408.

This type of overall processing is likely to result in the results shown in Figure 10.

[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.

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

Specifically, the recording medium may be a recording medium such as paper, film, or cloth, an electronic circuit board, 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. As such, the recording medium may be made of any material that can accept a liquid, such as paper, thread, fiber, fabric, leather, metal, plastic, glass, wood, ceramics, or a combination of these.

Each device may be multiple devices. That is, each device may be configured to perform distributed, redundant, or parallel processing across multiple devices. Alternatively, each device may be integrated. That is, the multiple devices described above may be implemented in a single device.

The image reading method 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 operate in cooperation with each other to realize the image reading method. The image reading program may also be distributed via a computer-readable recording medium or via a telecommunications line, etc.

The above embodiments are preferred examples, but those skilled in the art will be able to realize various modifications based on the disclosed content. Such modifications are also within the technical scope described in the claims.

2: Image forming device 5: Paper feed roller 7: Conveying roller pair 8: Registration roller pair 50: First roller trace 51: Second roller trace 52: Center line 100: Image forming device 100F1: Image forming section 200: Sheet conveying device 200F1: Registration roller section 200F2: Conveying roller section 200F3: Switching section 200F4: Control section 200F5: Supply roller section 300: Registration loop SG1: Main motor signal SG2: Paper feed clutch signal SG3: Nip pressure signal SG4: Registration sensor signal SG5: Registration loop detection signal SG6: Registration clutch signal T1: First timing T2: Second timing T3: Third timing T4: Fourth timing T5: Fifth timing T6: Sixth timing T7: Seventh timing T8: Eighth timing T9: Ninth timing T10 : 10th timing T20 : 20th timing

Japanese Patent Application Laid-Open No. 2018-058682

Claims (6)

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. The control unit
2. The sheet conveying device according to claim 1, wherein the nip pressure that forms the registration loop is the second nip pressure. 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
3. The sheet conveying device according to claim 1, wherein the nip pressure is switched to the second nip pressure before the trailing edge of the sheet passes through the supply roller unit and when the supply roller unit is stopped. The control unit
The sheet conveying device according to claim 3 , wherein the nip pressure is switched to the first nip pressure when the trailing end portion passes through the supply roller portion. 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,
5. The sheet conveying device according to claim 1, wherein the sheet is nipped by the second nip pressure and the leading edge is abutted against the registration roller portion to form the registration loop and correct the attitude of the sheet. The sheet conveying device according to any one of claims 1 to 5,
The image forming apparatus further includes an image forming unit that forms an image on the sheet.