JP2024047423A - Sheet conveying device and image forming apparatus - Google Patents

Abstract

[Problem] To realize a simple configuration and low cost switching of the nip pressure of a roller pair between three or more stages. [Solution] A sheet conveying device including a roller pair 42 for nipping a sheet conveyed in a first conveying path, a biasing means 37b for biasing one roller 42a of the roller pair toward the other roller 42b, biasing force switching means 37d, 65e for switching the biasing force by the biasing means, and a control means for switching the biasing force by the biasing force switching means, the biasing force switching means switching the biasing force by the biasing means between three or more different biasing forces in conjunction with the operation of a movable member 65 that operates when a sheet is conveyed in a second conveying path, the biasing force switching means having a detection means 65c for detecting whether a detected portion 65b that moves in conjunction with the operation of the movable member is present within a detection area, and the control means specifying the biasing force by the biasing means based on the detection result of the detection means and the movement direction of the movable member. [Selected Figure] Figure 8

Description

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

Conventionally, a sheet conveying device is known that includes a pair of rollers that clamp a sheet conveyed through a first conveying path, a biasing means that biases one roller of the pair of rollers toward the other roller, a biasing force switching means that switches the biasing force applied by the biasing means, and a control means that switches the biasing force using the biasing force switching means.

For example, Patent Document 1 discloses a sheet transport device that switches the nip pressure (urging force) of the relay roller pair in the main body paper feed path (first transport path) in conjunction with the lifting and lowering of the manual feed bottom plate (movable member of the second transport path) on which the sheet stack is placed. In this sheet transport device, when the manual feed bottom plate is in the raised position, the nip pressure of the relay roller pair increases in conjunction with this. At this time, the detection filler that moves in conjunction with the lifting and lowering of the manual feed bottom plate takes a position that does not block the filler sensor. On the other hand, when the manual feed bottom plate is in the lowered position, the nip pressure of the relay roller pair decreases in conjunction with this. At this time, the detection filler takes a position that blocks the filler sensor. The control unit controls the lifting and lowering of the manual feed bottom plate based on the detection result of the filler sensor, and also controls the switching of the nip pressure of the relay roller pair.

In conventional sheet conveying devices, it was difficult to realize a configuration that allows the nip pressure of a roller pair to be switched between three or more stages at low cost.

In order to solve the above-mentioned problems, the present invention provides a sheet conveying device that includes a pair of rollers that sandwich a sheet conveyed through a first conveying path, a biasing means that biases one roller of the roller pair toward the other roller, a biasing force switching means that switches the biasing force by the biasing means, and a control means that switches the biasing force using the biasing force switching means, the biasing force switching means switching the biasing force by the biasing means between three or more different biasing forces in conjunction with the operation of a movable member that operates when a sheet is conveyed through a second conveying path, the device has a detection means that detects whether a detected part that moves in conjunction with the operation of the movable member is present within a detection area, and the control means identifies the biasing force by the biasing means based on the detection result of the detection means and the movement direction of the movable member.

According to the present invention, it is possible to switch the nip pressure of the roller pair between three or more stages at low cost.

FIG. 1 is a schematic diagram showing a printer according to an embodiment. 2 is a perspective view showing the main configuration of a main body paper feed unit that feeds recording sheets from a paper feed tray in the printer, and a manual feed unit that feeds recording sheets from a manual feed tray. FIG. FIG. 2 is a perspective view showing the configuration of a drive system in the main body paper feed unit and the manual paper feed unit. FIG. 4 is an explanatory diagram for explaining a paper feed path in the main body paper feed unit and the manual paper feed unit. 6 is a flowchart showing a control operation when feeding and conveying paper from the main body paper feeding unit. 6 is a flowchart showing a control operation when feeding and conveying paper from the manual paper feed unit. 1A is a perspective view showing a configuration when the manual feed bottom plate is in a lowered position, and FIG. 1B is a perspective view showing a configuration when the manual feed bottom plate is in an elevated position; 6A to 6C are explanatory diagrams showing a biasing force switching means for switching the biasing force of a pressure spring 37b that biases a bearing portion 37a of an intermediate driven roller 42b toward an intermediate driving roller 42a in the present embodiment. 6A and 6B are explanatory diagrams showing the detection means in a state where the cam detection feeler does not block the detection area of the feeler sensor. 6A and 6B are explanatory diagrams showing the detection means in a state in which the cam detection feeler blocks the detection area of the feeler sensor. 1A is a diagram showing the rotational position of the manual feed bottom plate cam shaft when the nip pressure of the relay roller pair is zero nip pressure, (b) is a diagram showing the rotational position of the manual feed bottom plate cam shaft when the nip pressure of the relay roller pair is low nip pressure, and (c) is a diagram showing the rotational position of the manual feed bottom plate cam shaft when the nip pressure of the relay roller pair is high nip pressure.

The following describes an image forming apparatus to which the present invention is applied, taking as an example an electrophotographic printer (hereinafter simply referred to as a printer) that forms images using an electrophotographic method.

First, the basic configuration of the printer according to the embodiment will be described.
FIG. 1 is a schematic diagram showing a printer according to an embodiment.
In the figure, the printer includes a photoconductor 1 as a latent image carrier, a main body paper feed tray 100 as a sheet storage means configured to be detachable from a main body housing 50, and two additional paper feed trays 100A and 100B. Each of the paper feed trays 100, 100A, and 100B stores a plurality of recording sheets S in the form of a sheet stack.

The recording sheet S in the main body paper feed tray 100 is sent out from the paper feed tray by the rotational drive of the main body paper feed roller 41, and only the topmost sheet is separated and sent out at the separation nip between the main body paper feed roller 41 and the separation pad 48, and reaches the main body paper feed path R1, which is the first transport path. The recording sheet S is then sandwiched (held) in the transport nip of the upper transport roller pair, the relay roller pair 42, and transported from the upstream side to the downstream side in the transport direction within the main body paper feed path R1. Note that at least one of the transport roller pairs may be a transport body pair of a belt.

The recording sheet S in the first additional paper feed tray 100A is sent out of the paper feed tray by the rotational drive of the paper feed roller 41A, and only the topmost sheet is separated and sent out at the separation nip between the paper feed roller 41A and the separation pad 48A. The recording sheet S is then sandwiched (held) in the transport nip of the upper transport roller pair 42A and transported upward, passing through the main body paper feed tray 100 and into the main body paper feed path R1.

The recording sheet S in the second additional paper feed tray 100B is sent out of the paper feed tray by the rotational drive of the paper feed roller 41B, and only the topmost sheet is separated and sent out at the separation nip between the paper feed roller 41B and the separation pad 48B. The recording sheet S is then sandwiched (held) in the transport nip of the upper transport roller pair 42B and transported upward, passing through the first additional paper feed tray 100A and the main paper feed tray 100, and into the main paper feed path R1.

The downstream end of the main body feed path R1 is connected to the common transport path R3, on which a pair of registration rollers 43 is arranged. On the common transport path R3, a registration sensor 49 that detects the recording sheet S is arranged upstream of the pair of registration rollers 43 in the transport direction. The transport of the recording sheet S is temporarily stopped when the leading edge of the recording sheet S hits the nip of the stopped registration roller pair 43. When the recording sheet S hits the nip, the skew of the recording sheet S is corrected. The registration sensor 49 is also used for initial operations and for checking the remaining sheets (jam detection operations) when the device is stopped due to an abnormal stop.

The pair of registration rollers 43 start rotating at a timing when the recording sheet S can be superimposed on the toner image on the surface of the photoconductor 1 at the transfer nip, and send the recording sheet S toward the transfer nip. At this time, the pair of relay rollers 42 start rotating at the same time, and resume the transport of the recording sheet S that was temporarily stopped.

The main body housing 50 of the printer is provided with a manual feed section 30 as a manual feed section including a manual feed tray 31, a manual feed roller 32, a separation pad 33, a manual feed bottom plate 34, and a manual feed bottom plate cam 35. Details of the manual feed section 30 will be described later. A recording sheet S manually fed into the manual feed tray 31 of the manual feed section 30 is sent from the manual feed tray 31 to the manual feed path R2, which is the second transport path, by the rotational drive of the manual feed roller 32. The downstream end of the manual feed path R2 merges with the downstream end of the main body feed path R1 into the common transport path R3. The recording sheet S sent out by the manual feed roller 32 passes through a separation nip caused by the contact between the manual feed roller 32 and the separation pad 33 in the manual feed path R2, and is then sent to the common transport path R3 and transported to the registration roller pair 43. Then, like the recording sheet S sent from the paper feed tray 100, it passes through the registration roller pair 43 and is sent to the transfer nip.

A cleaning blade, recovery screw, charging roller, charging cleaning roller, scraper, latent image writing device 7, developing device 8, transfer roller 10, etc. are arranged around the drum-shaped photoreceptor 1, which is rotated clockwise in the figure. The charging roller, which has a conductive rubber roller portion, rotates while in contact with the photoreceptor 1 to form a charging nip. A voltage is applied to this charging roller from a charging power source. As a result, the surface of the photoreceptor 1 is uniformly charged by the charging bias generated between the surface of the photoreceptor 1 and the surface of the charging roller in the charging nip.

The latent image writing device 7 is equipped with an LED array and performs optical writing using LED light on the uniformly charged surface of the photoconductor 1. The potential of the area of the uniformly charged surface of the photoconductor 1 that is irradiated with the writing light decays, and an electrostatic latent image is formed on the surface of the photoconductor 1.

As the photoconductor 1 rotates, the electrostatic latent image passes through a development area facing the developing device 8. The developing device 8 has a circulating transport section and a developing section, and the circulating transport section contains a developer containing toner and magnetic carriers. In the developing area, the toner selectively adheres to the electrostatic latent image on the photoconductor 1, developing the electrostatic latent image. A toner cartridge 9 is disposed above the developing device 8.

The toner image formed on the photoconductor 1 by development enters the transfer nip where the photoconductor 1 and the transfer roller 10 come into contact as the photoconductor 1 rotates. A voltage of the opposite polarity to the latent image potential of the photoconductor 1 is applied to the transfer roller 10, which creates a transfer bias in the transfer nip.

As described above, the pair of registration rollers 43 sends the recording sheet S toward the transfer nip at a timing that allows the recording sheet S to be superimposed on the toner image on the photoreceptor 1 in the transfer nip. The toner image on the photoreceptor 1 is transferred to the recording sheet, which is brought into close contact with the toner image in the transfer nip, by the action of the transfer bias and nip pressure.

In FIG. 1, the recording sheet S that has passed through the transfer nip where the photoconductor 1 and transfer roller 10 come into contact is sent to the fixing device 44. The fixing device 44 forms a fixing nip by the contact between the fixing roller 44a, which contains a heat source such as a halogen lamp, and the pressure roller 44b, which is pressed against it. A toner image is fixed to the surface of the recording sheet S that is sandwiched in the fixing nip by the action of heat and pressure. After that, the recording sheet S that has passed through the fixing device 44 passes through the paper discharge path R4 and is then sandwiched in the paper discharge nip of the pair of paper discharge rollers 46.

This printer can be switched between a single-sided mode, in which an image is formed on only one side of the recording sheet S, and a double-sided mode, in which an image is formed on both sides of the recording sheet S. In the single-sided mode, or in the double-sided mode in which images have already been formed on both sides of the recording sheet, the pair of discharge rollers 46 continues to rotate in the forward direction, thereby discharging the recording sheet S in the discharge path R4 outside the machine. The discharged recording sheet S is stacked in a stack section provided on the top surface of the main body housing 50.

On the other hand, in the double-sided mode, when an image is formed only on one side of the recording sheet S, the pair of discharge rollers 46 is driven in reverse when the trailing end of the recording sheet S enters the discharge nip of the pair of discharge rollers 46. At this time, the switching claw 47 arranged near the downstream end of the discharge path R4 is activated to block the discharge path R4 and open the entrance of the reverse re-sending path R5. The recording sheet S that starts to return due to the reverse drive of the pair of discharge rollers 46 is sent into the reverse re-sending path R5. The downstream end of the reverse re-sending path R5 joins the upstream side of the pair of registration rollers 43 of the common conveying path R3, and after being conveyed through the reverse re-sending path R5, it is re-sent to the pair of registration rollers 43 of the common conveying path R3. After that, the toner image is transferred to the other side at the transfer nip, and the sheet is discharged outside the machine via the fixing device 44, the discharge path R4, and the pair of discharge rollers 46.

Next, the configuration and operation relating to feeding of the recording sheets S will be described.
FIG. 2 is a perspective view showing the main configuration of a main body paper feed section which feeds recording sheets S from a main body paper feed tray 100 and a manual feed section 30 which feeds recording sheets S from a manual feed tray 31. As shown in FIG.
FIG. 3 is a perspective view showing the configuration of the drive system in the main body paper feed unit and the manual paper feed unit 30. As shown in FIG.

As shown in Figs. 2 and 3, the drive system in the main body feed section and manual feed section 30 is configured to distribute the driving force from a single main motor 61 to drive the main body feed roller 41, the relay roller pair 42, the manual feed roller 32, and the manual feed bottom plate cam 35. Specifically, the driving force output from the motor shaft 61a of the main motor 61 is transmitted via idler gears, etc. to the feed roller shaft 62 on which the main body feed roller 41 is provided, the relay roller shaft 63 on which the relay roller pair 42 is provided, the manual feed roller shaft 64 on which the manual feed roller 32 is provided, and the manual feed bottom plate cam shaft 65 on which the manual feed bottom plate cam 35 is provided.

The feed roller shaft 62, the relay roller shaft 63, the manual feed roller shaft 64, and the manual bottom plate cam shaft 65 are provided with clutches 62a, 63a, 64a, and 65a for turning on and off the transmission of the driving force. When the power to each clutch is turned on, the driving force is transmitted and the shafts 62, 63, 64, and 65 are rotated, and when the power to each clutch is turned off, the transmission of the driving force is cut off and the shafts 62, 63, 64, and 65 do not rotate. The driving force from the main motor 61 is also transmitted to the registration roller pair 43 via the clutch. In this embodiment, the recording sheet S is fed and conveyed by using the driving force of the main motor 61 and controlling the on/off of each clutch by the control unit 51.

FIG. 4 is an explanatory diagram for explaining the paper feed paths in the main body paper feed section and the manual paper feed section 30. As shown in FIG.
First, the process of feeding and conveying paper from the main body paper feed section will be described with reference to the flow chart shown in FIG.
Since the main paper feed bottom plate 101 is biased upward toward the main paper feed roller 41, the main paper feed roller 41 abuts against the uppermost recording sheet S among the multiple recording sheets S placed in a sheet stack on the main paper feed bottom plate 101. When starting paper feed conveyance from the main paper feed unit, the control unit 51 first executes an initial operation (S1) and checks whether the initial operation is completed normally (S2). Here, the "initial operation" refers to an operation of bringing the manual feed bottom plate 34 to the lowest position, and after the initial operation is completed, the nip pressure of the relay roller pair 42 is set to a low state.

If the initial operation is not completed normally (No in S2), the control unit 51 displays a fault message on the operation panel of the printer (S14) and executes a process to notify the user of an abnormality in the switching operation of the nip pressure of the relay roller pair 42. Note that this notification method is not limited to a visual notification of the abnormality, such as displaying a fault message on the operation panel, but may also be an audible notification of the abnormality, for example, by sound. The notification may be immediate, or may be delayed, such as after the image forming device has finished operating.

If the initial operation is completed normally (Yes in S2), the control unit 51 turns on the main motor 61 (S3) and judges whether the recording sheet S to be fed is thin paper or plain paper (S4). In this embodiment, the user operates the operation panel of the printer to select the type of sheet from among the types of sheets that can be printed by the printer, such as plain paper (low strength (thin) sheet), thin paper (low strength (thin) sheet), thick paper (high strength (thick) sheet), etc., for the recording sheet S stored in the main body paper feed tray 100, and the selection result is stored in the memory unit of the control unit 51. In processing step S4 of this embodiment, the control unit 51 refers to the contents of this memory unit to judge whether the recording sheet S to be fed is thin paper or plain paper.

The method of determining whether the paper is thin, regular, or thick is not limited to this. For example, the thickness of the recording sheets S stored in the paper feed tray 100 or the recording sheets S fed from the paper feed tray 100 may be detected by a thickness detection sensor, and the determination may be made based on the detection results.

In addition, in this embodiment, the type of recording sheet S to be judged is determined based on differences in the thickness of the recording sheet S, but it may also be determined based on differences in characteristics that affect the strength of the recording sheet S or the transport load of the recording sheet S, such as differences in the material or size of the recording sheet S.

In this embodiment, when it is determined that the paper is thin or normal (Yes in S4), the control unit 51 turns on the main body paper feed clutch 62a and the relay clutch 63a while maintaining the nip pressure low (S5), since the nip pressure of the relay roller pair 42 is already low (low nip pressure) due to the above-mentioned initial operation. This rotates the main body paper feed roller 41, and the topmost recording sheet S in the main body paper feed tray 100 is sent to the separation pad 48 side. At this time, even if the second or subsequent recording sheets from the top are sent out together with the topmost recording sheet S, the second or subsequent recording sheets are hindered from being conveyed by the frictional force with the separation pad 48, and only the topmost recording sheet S can pass through the separation pad 48. Note that during paper feed conveyance from the main body paper feed unit, paper feed conveyance from the manual paper feed unit 30 is not performed, so the manual paper feed clutch 64a and the manual bottom plate cam clutch 65a remain in the off state.

On the other hand, if it is determined that the paper is not thin or normal (if it is determined that the paper is thick) (No in S4), the control unit 51 executes a processing operation to increase the nip pressure of the relay roller pair 42. Specifically, since the nip pressure of the relay roller pair 42 is low (low nip pressure) during the initial operation, the control unit 51 also turns on the manual feed bottom plate cam clutch 65a (S6). This causes the manual feed bottom plate cam shaft 65 to rotate clockwise in FIG. 4, and after a specified time has elapsed, the manual feed bottom plate cam clutch 65a is turned off (S7), stopping the rotation of the manual feed bottom plate cam shaft 65.

As shown in FIG. 4, the bearing portion 37a of the other relay driven roller 42b that constitutes the relay roller pair 42 is biased by the pressure spring 37b, which is a compression spring, and the biasing force of the bearing portion 37a that bears the roller shaft 66 of the relay driven roller 42b contacts the relay drive roller 42a. When the manual feed bottom plate cam shaft 65 is stopped in the above-mentioned rotation position, the compression amount of the pressure spring 37b increases, and the nip pressure of the rollers of the relay roller pair 42 is switched to a high state (high nip pressure). The configuration for switching the nip pressure of the relay roller pair 42 will be described later.

In this embodiment, when feeding paper from the main body paper feed section, the timing at which the manual feed bottom plate cam clutch 65a is turned on is the same as the timing at which the main body paper feed clutch 62a and the relay clutch 63a are turned on (S6). This is for the following reasons.

The switching of the nip pressure of the rollers of the relay roller pair 42 must be completed from the start of feeding the recording sheet S until the leading edge of the recording sheet S reaches the relay roller pair 42. When feeding from the main paper feed tray 100, the transport distance from the main paper feed tray 100 to the relay roller pair 42 is short, so if the switching operation of the nip pressure of the rollers of the relay roller pair 42 is not started at the same time as feeding from the main paper feed tray 100 begins, the switching of the nip pressure cannot be completed before the leading edge of the recording sheet S reaches the relay roller pair 42.

In this embodiment, the sent recording sheet S is transported along the main paper feed path indicated by the symbol R1 in FIG. 4. At this time, the relay drive roller 42a, one of the relay roller pair 42, is rotated by the driving force from the main motor 61. The other relay driven roller 42b, which is the other of the relay roller pair 42, is biased by the pressure spring 37b at the bearing portion 37a that bears the roller shaft 66 with a low biasing force for thin or normal paper and a high biasing force for thick paper, and is in contact with the relay drive roller 42a due to the biasing force. As a result, the relay driven roller 42b rotates together with the relay drive roller 42a. The recording sheet S transported along the main paper feed path R1 is transported in a state of being sandwiched (clamped) in the nip between the relay drive roller 42a and the relay driven roller 42b.

When the leading edge of the recording sheet S reaches the registration sensor 49 and the registration sensor 49 turns on (Yes in S8), after a predetermined time has elapsed (before the leading edge of the recording sheet S reaches the registration roller pair 43) (for example, 100 ms after the registration sensor 49 turns on), the main body paper feed clutch 62a and relay clutch 63a are turned off (S9) and the transport of the recording sheet S is temporarily halted. This causes the leading edge of the recording sheet S to abut against the nip of the stopped registration roller pair 43, and the skew of the recording sheet S is corrected.

The control unit 51 turns on the relay clutch 63a and the registration clutch at a timing when the recording sheet S can be superimposed on the toner image on the surface of the photoconductor 1 at the transfer nip (for example, 200 ms after the main feed clutch 62a and the relay clutch 63a are turned off) (S10). As a result, the registration roller pair 43 and the relay roller pair 42 start to rotate, and the recording sheet S is transported toward the transfer nip. At this time, since the main feed clutch 62a remains off, the main feed roller 41 does not rotate. Even if the rear end side of the recording sheet S is still sandwiched between the main feed roller 41 and the separation pad 48, the main feed roller 41 rotates in a manner that is accompanied by the recording sheet S transported by the transport force of the registration roller pair 43 and the relay roller pair 42, and does not hinder transport. Then, when the rear end of the recording sheet S reaches the registration sensor 49 and the registration sensor 49 is turned off (Yes in S11), the relay clutch 63a is turned off (S12) and the rotation drive of the relay roller pair 42 is stopped.

In this embodiment, the biasing force of the pressure spring 37b is switched between when the recording sheet S is thin paper or plain paper and when it is thick paper, and the nip pressure of the relay roller pair 42 is changed to a pressure appropriate for each case. As a result, for thick paper, a high nip pressure is used to achieve stable transportability, and for thin paper or plain paper, a low nip pressure is used to achieve stable transportability.

Next, the case where paper is fed from the manual paper feed unit 30 will be described with reference to FIG.
FIG. 6 is a flow chart showing a control operation when feeding and conveying paper from the manual paper feed unit 30. In FIG.
FIG. 7A is a perspective view showing the configuration when the manual feed bottom plate 34 is located in the lowered position, and FIG. 7B is a perspective view showing the configuration when the manual feed bottom plate 34 is located in the raised position.

The manual feed bottom plate 34 is biased upward toward the manual feed roller 32 by the bottom plate spring 36. The manual feed bottom plate 34 is also provided with a bottom plate guide portion 34a at a location corresponding to the manual feed bottom plate cam 35. When the manual feed bottom plate cam shaft 65 rotates and the manual feed bottom plate cam 35 abuts against and pushes down the bottom plate guide portion 34a, the manual feed bottom plate 34 descends against the biasing force of the bottom plate spring 36 and separates from the manual feed roller 32, as shown in FIG. 7(a).

When starting paper feed from the manual feed unit 30, the control unit 51 first performs an initial operation (S1) and checks whether the initial operation is completed normally (S2). If the initial operation is completed normally (Yes in S2), the control unit 51 turns on the main motor 61 (S3), then turns on the manual feed bottom plate cam clutch 65a (S41), and turns off the manual feed bottom plate cam clutch 65a after a specified time has elapsed (S42). This causes the manual feed bottom plate cam shaft 65 to rotate, and as shown in FIG. 7(b), the manual feed bottom plate 34 is biased toward the manual feed roller 32 by the biasing force of the bottom plate spring 36. As a result, the manual feed roller 32 is in contact with the uppermost recording sheet S of the multiple recording sheets S placed in the sheet stack on the manual feed tray 31 and the manual feed bottom plate 34.

Then, the control unit 51 turns on the manual feed clutch 64a (S43). This rotates the manual feed roller 32, and the topmost recording sheet S on the manual feed bottom plate 34 is sent out toward the separation pad 33. At this time, even if the second and subsequent recording sheets from the top are sent out together with the topmost recording sheet S, the second and subsequent recording sheets are prevented from being conveyed by the frictional force with the separation pad 33, and only the topmost recording sheet S can pass through the separation pad 33.

Note that while paper is being fed from the manual paper feed unit 30, no paper is being fed from the main paper feed unit, so the main paper feed clutch 62a and relay clutch 63a remain in the off state.

Then, the sent recording sheet S is transported along the manual feed path indicated by the symbol R2 in FIG. 4. Then, when the leading edge of the recording sheet S reaches the registration sensor 49 and the registration sensor 49 turns on (Yes in S44), after a predetermined time has elapsed (before the leading edge of the recording sheet S reaches the registration roller pair 43), the manual feed clutch 64a is turned off (S45) and the transport of the recording sheet S is temporarily halted. This causes the leading edge of the recording sheet S to abut against the nip of the stopped registration roller pair 43, and the skew of the recording sheet S is corrected.

The control unit 51 turns on the registration clutch at a timing when the recording sheet S can be superimposed on the toner image on the surface of the photoconductor 1 at the transfer nip (S46). This causes the registration roller pair 43 to start rotating, and the recording sheet S is transported toward the transfer nip.

The manual feed section 30 in this embodiment has a unit structure in which the relay driven roller 42b, which is one of the rollers constituting the relay roller pair 42, is supported integrally with the manual feed mechanism, and the unit is fixed to the main body housing 50 by screws. Meanwhile, the relay drive roller 42a, which is the other roller constituting the relay roller pair 42, is supported by the main body housing 50. Therefore, in this embodiment, the relay driven roller 42b provided in the unit and the relay drive roller 42a provided in the main body housing 50 are configured so that they cannot be separated from each other.

In more detail, as described above, the manual feed mechanism that supports the relay driven roller 42b is fixed to the main body housing 50 by screws. As shown in FIG. 1, the opening and closing door 39 is attached to the manual feed mechanism via a hinge mechanism so that it can be opened and closed. The manual feed tray 31 is also attached to the opening and closing door 39 via a hinge mechanism so that it can be opened and closed. In this embodiment, by opening the opening and closing door 39, it is possible to attach and detach the process cartridge including the photosensitive member 1, and to remove jammed recording sheets S.

However, the relay driven roller 42b is supported not by the opening and closing door 39 but by a manual paper feed mechanism that is screwed to the main body housing 50, so the relay driven roller 42b and the relay drive roller 42a provided on the main body housing 50 are configured so that they cannot be separated from each other.

When a device abnormality occurs in which the transport of the recording sheet S should be stopped, such as when a jam occurs in this printer (an example of a device abnormality due to a jam will be described below), the recording sheet S remaining in the device must be removed. Specifically, in this embodiment, the paper feed tray 100 is removed from the device in the feed direction of the recording sheet S or in a direction intersecting the feed direction, and the remaining recording sheets are taken out (pulled out) from the main body paper feed section. At this time, in order to prevent the recording sheet S, such as thin paper or plain paper, which has low strength, from being torn when it is pulled out, it is preferable to open (separate) the areas where the recording sheet S is clamped (such as the transport nip of the relay roller pair 42 or the clamped area between the manual feed roller 32 and the manual feed bottom plate 34).

As an example of a configuration for separating the rollers of the relay roller pair 42, there is a configuration in which the relay driven roller 42b is supported by an opening/closing door that is openably attached to the main body housing 50 of the printer. With this configuration, the relay roller pair 42 can be separated by opening the opening/closing door. However, as described above, the relay drive roller 42a and the relay driven roller 42b that constitute the relay roller pair 42 are configured so that they cannot be separated from each other, so the relay roller pair 42 cannot be opened (separated).

In this embodiment, when transporting a recording sheet S of a type with low strength that is easily torn (thin paper or plain paper), the nip pressure (contact pressure) of the relay roller pair 42 is switched to a low nip pressure. Therefore, even if a jam occurs when transporting a recording sheet S of thin paper or plain paper, the nip pressure of the relay roller pair 42 is low, so even if the recording sheet S is pulled out from the relay roller pair 42 in this state, the sheet is relatively unlikely to tear.

However, the nip pressure (contact pressure) of the relay roller pair 42 when transporting a thin or plain paper recording sheet S is a lower nip pressure than when transporting a thick paper recording sheet S, but the nip pressure required for transporting a thin or plain paper recording sheet S must be ensured. Therefore, if the recording sheet S is pulled out from the relay roller pair 42 while maintaining the low nip pressure of the relay roller pair 42 when a thin or plain paper recording sheet S jams, there is a risk that the recording sheet S will be torn.

When conveying a recording sheet S of a type (cardboard) that is strong and resistant to tearing, a high nip pressure (contact pressure) is used as the nip pressure (contact pressure) of the relay roller pair 42. In the case of a recording sheet S of cardboard, a low nip pressure of the relay roller pair 42 is likely to cause a transport failure. In this embodiment, however, the relay roller pair 42 is set to a high nip pressure state to convey the recording sheet S of cardboard, so that transport failure is unlikely to occur and stable transport is achieved. On the other hand, if a jam occurs, if the recording sheet S of cardboard is a recording sheet S, even if the nip pressure of the relay roller pair 42 remains high (high nip pressure), the recording sheet S is unlikely to tear when the recording sheet S is pulled out from the relay roller pair 42. However, if the nip pressure of the relay roller pair 42 remains high, there is a risk that the recording sheet S will tear when the recording sheet S is pulled out from the relay roller pair 42.

In addition, when the relay roller pair 42 is set to a high nip pressure, it is possible that plain paper or thin paper may be mistakenly transported. In such a case, if a jam occurs during paper transport, there is an even higher risk that the plain paper or thin paper will tear when it is pulled out from the relay roller pair 42.

Therefore, in this embodiment, the nip pressure (contact pressure) of the relay roller pair 42 is configured to be switchable between the high nip pressure and low nip pressure described above, as well as a nip pressure even lower than the low nip pressure (in this embodiment, zero nip pressure, where the nip pressure is essentially zero). By switching the nip pressure (contact pressure) of the relay roller pair 42 to zero nip pressure after a jam occurs, it is possible to prevent the recording sheet S from being torn when the recording sheet S is pulled out from the relay roller pair 42.

Next, a configuration for switching the nip pressure of the relay roller pair 42 will be described.
In this embodiment, the operation of switching the nip pressure of the relay roller pair 42 in the main body paper feed path R1 is performed in conjunction with the operation of a movable member used for sheet transport in the manual feed path R2. In this embodiment, when the recording sheet S is transported using the main body paper feed path R1, the manual feed path R2 is not used for sheet transport. Therefore, when the recording sheet S is transported using the main body paper feed path R1, no problems will occur even if the movable member used for sheet transport in the manual feed path R2 is operated.

In this embodiment, the sheet feeding means during manual feeding presses the recording sheet S on the manual feed bottom plate 34 against the manual feed roller 32 to feed it. Therefore, in this embodiment, the manual feed bottom plate cam shaft 65 for moving the manual feed bottom plate 34 is a movable member, and the nip pressure of the relay roller pair 42 is switched in conjunction with the operation of this manual feed bottom plate cam shaft 65.

In more detail, the operating means for operating the manual feed bottom plate 34 is, as described above, the driving force of the main motor 61 to rotate the manual feed bottom plate cam shaft 65. When the manual feed bottom plate cam shaft 65 is located in a rotational position where the manual feed bottom plate cam 35 presses down the bottom plate guide portion 34a against the biasing force of the bottom plate spring 36, the manual feed bottom plate 34 is located in a lowered position and separates from the manual feed roller 32 (see FIG. 7(a)). On the other hand, when the manual feed bottom plate cam shaft 65 is located in a rotational position where the manual feed bottom plate cam 35 separates from the bottom plate guide portion 34a, the manual feed bottom plate 34 is located in an upper position by the biasing force of the bottom plate spring 36 and contacts the manual feed roller 32 (see FIG. 7(b)).

The biasing force switching means of this embodiment switches the biasing force of the pressure spring 37b and changes the nip pressure of the relay roller pair 42 by moving the pressure plate 37d, which serves as a biasing support part supporting the pressure spring 37b that biases the bearing part 37a of the relay driven roller 42b, one of the rollers of the relay roller pair 42, toward the relay drive roller 42a, in association with the rotation of the manual feed bottom plate cam shaft 65. A slider is fastened to the pressure plate 37d, and the slider is configured to move along a guide part provided on the support frame of the manual feed section 30, thereby allowing it to move linearly in the direction of approaching and separating from the relay drive roller 42a.

Figures 8(a) to (c) are explanatory diagrams showing the biasing force switching means for switching the biasing force of the pressure spring 37b that biases the bearing portion 37a of the relay driven roller 42b toward the relay drive roller 42a in this embodiment.

The roller shaft 66 of the relay driven roller 42b is held slidably in a direction in which the relay driven roller 42b approaches and separates from the relay drive roller 42a relative to the support frame of the manual paper feed unit 30. In addition, as described above, the bearing portion 37a of the relay driven roller 42b is biased toward the relay drive roller 42a by the pressure spring 37b.

The pressure spring 37b is a compression spring arranged so that one end contacts the bearing portion 37a of the relay driven roller 42b and the other end contacts the pressure plate 37d. The biasing force of the pressure spring 37b supported by the pressure plate 37d biases the bearing portion 37a of the relay driven roller 42b toward the relay drive roller 42a. A pressing portion 65e capable of pressing the pressure plate 37d toward the relay drive roller 42a abuts on the back surface of the pressure plate 37d opposite the spring contact surface with which the pressure spring 37b contacts. This pressing portion 65e rotates with the rotation of the manual feed bottom plate cam shaft 65.

When the rotation position of the manual feed bottom plate cam shaft 65 is in a position where the manual feed bottom plate 34 is raised (the position where the manual feed bottom plate 34 contacts the manual feed roller 32), the pressing part 65e on the manual feed bottom plate cam shaft 65 is in a high pressing position as shown in FIG. 8 (c). At this time, the pressure plate 37d moves in a direction approaching the relay drive roller 42a against the urging force of the pressure spring 37b. This causes the pressure spring 37b to contract, and since the amount of contraction increases, the urging force of the pressure spring 37b becomes stronger. As a result, the urging force that urges the relay driven roller 42b toward the relay drive roller 42a becomes stronger, and the nip pressure of the relay roller pair 42 becomes stronger. Note that since the manual feed bottom plate 34 remains in contact with the manual feed roller 32, manual feed is not possible, but since manual feed is not performed during main body feed, there is no problem.

On the other hand, when the rotational position of the manual feed bottom plate cam shaft 65 is in a position that lowers the manual feed bottom plate 34 (a position where the manual feed bottom plate 34 is separated from the manual feed roller 32), the pressing portion 65e on the manual feed bottom plate cam shaft 65 is in the non-pressing position shown in FIG. 8(a) or in the low pressing position shown in FIG. 8(b).

When the pressing portion 65e on the manual feed bottom plate cam shaft 65 is located in the low pressing position shown in FIG. 8(b), the pressing plate 37d moves in a direction away from the relay drive roller 42a due to the biasing force of the pressure spring 37b, the pressure spring 37b expands, the amount of contraction decreases, and the biasing force of the pressure spring 37b decreases. As a result, the biasing force biasing the relay driven roller 42b toward the relay drive roller 42a decreases, and the nip pressure of the relay roller pair 42 weakens. Note that since the manual feed bottom plate 34 remains separated from the manual feed roller 32, manual feed is not possible, but since manual feed is not performed during main body feed, there is no problem.

When the pressing portion 65e on the manual feed bottom plate cam shaft 65 is located in the non-pressing position shown in FIG. 8(a), the pressing plate 37d moves in a direction away from the relay drive roller 42a due to the biasing force of the pressing spring 37b, the pressing spring 37b extends to its free length, its contraction amount becomes zero, and the biasing force of the pressing spring 37b becomes zero. As a result, the biasing force biasing the relay driven roller 42b toward the relay drive roller 42a becomes zero, and the nip pressure of the relay roller pair 42 becomes zero nip pressure.

According to this embodiment, the nip pressure (the biasing force of the pressure spring 37b) of the relay roller pair 42 of the main body paper feed path R1 can be switched between three levels by utilizing the operation of the manual feed bottom plate cam shaft 65 of the manual feed bottom plate 34 as a movable member used for sheet transport in the manual feed path R2. This makes it possible to realize the switching with a simple configuration that does not require a dedicated operating means for switching the nip pressure of the relay roller pair 42.

Next, a detection means for detecting whether or not the cam detection feeler 65b, which serves as a detected part that moves in conjunction with the rotational movement of the manual-feed bottom plate cam shaft 65, is present within the detection area by the feeler sensor 65c will be described.
9 and 10 are explanatory diagrams showing a detection means for detecting the cam detection feeler 65b by the feeler sensor 65c.

In this embodiment, by rotating the manual feed bottom plate cam shaft 65, the pressing portion 65e formed integrally with the manual feed bottom plate cam 35 can be in a position where it abuts against the push-down lever 65d that pushes down the cam detection feeler 65b as shown in Figures 9(a) and (b) and pushes down the push-down lever 65d as shown in Figures 10(a) and (b). As a result, the cam detection feeler 65b can be in a state where it does not block the detection area of the filler sensor 65c as shown in Figures 9(a) and (b) and a state where it blocks the detection area of the filler sensor 65c as shown in Figures 10(a) and (b). The output of the filler sensor 65c is acquired by the control unit 51.

9(a) and (b), when the cam detection feeler 65b blocks the detection area of the filler sensor 65c, the output of the filler sensor 65c is OFF, and the rotational position of the manual feed bottom plate cam shaft 65 is a position that lowers the manual feed bottom plate 34 (a position where the manual feed bottom plate 34 is separated from the manual feed roller 32). On the other hand, when the cam detection feeler 65b does not block the detection area of the filler sensor 65c, the output of the filler sensor 65c is ON, and the rotational position of the manual feed bottom plate cam shaft 65 is a position that raises the manual feed bottom plate 34 (a position where the manual feed bottom plate 34 abuts against the manual feed roller 32) as shown in FIG. 10(a) and (b).

Since the manual feed bottom plate 34 can only move to two positions, the raised position and the lowered position, the detection means only needs to be able to distinguish between these two positions. Therefore, the detection means has a simple configuration, consisting of a cam detection feeler 65b that moves in conjunction with the rotation of the manual feed bottom plate cam shaft 65 of the manual feed bottom plate 34, and a feeler sensor 65c, which is an optical sensor that detects the presence or absence of the cam detection feeler 65b within the detection area.

In the conventional configuration in which the nip pressure of the relay roller pair 42 (the biasing force of the pressure spring 37b) is switched between two levels, high nip pressure and low nip pressure, each position of the manual feed bottom plate (upper position and lower position), which also switches between two levels, corresponds one-to-one to each nip pressure (high nip pressure and low nip pressure) of the relay roller pair 42. This makes it possible to identify the nip pressure of the relay roller pair 42 (the biasing force of the pressure spring 37b) based on the output state (on or off) of the filler sensor 65c, which is a detection means for detecting the position of the manual feed bottom plate 34.

However, in this conventional configuration, the nip pressure of the relay roller pair 42 (the biasing force of the pressure spring 37b) cannot be specified in three or more stages, and therefore the nip pressure of the relay roller pair 42 (the biasing force of the pressure spring 37b) cannot be switched between three or more stages. If a new component (such as a new sensor) is provided to specify the nip pressure of the relay roller pair 42 in three or more stages, it would be possible to switch the nip pressure of the relay roller pair 42 between three or more stages, but this would result in higher costs.

Therefore, in this embodiment, the nip pressure (the biasing force of the pressure spring 37b) of the relay roller pair 42 is determined using not only the detection result (on or off) of the detection means consisting of the above-mentioned cam detection feeler 65b and filler sensor 65c, but also information on the movement direction of the cam detection feeler 65b (i.e., the rotation direction of the manual feed bottom plate cam shaft 65). In this way, even if a simple detection means is used that can only distinguish and detect two states, that is, whether or not the cam detection feeler 65b is present within the detection area of the filler sensor 65c, by combining this with information on the movement direction of the cam detection feeler 65b, it is possible to distinguish and determine the nip pressure of the relay roller pair 42 in three or more stages.

In other words, by using this combination, for a detection area having a certain range, the rotational position of the manual feed bottom plate cam shaft 65 at which the cam detection feeler 65b exits one side of the detection area and stops, the rotational position of the manual feed bottom plate cam shaft 65 at which the cam detection feeler 65b enters one side of the detection area and stops, the rotational position of the manual feed bottom plate cam shaft 65 at which the cam detection feeler 65b exits the other side of the detection area and stops, and the rotational position of the manual feed bottom plate cam shaft 65 at which the cam detection feeler 65b enters the other side of the detection area and stops can be distinguished and grasped from each other. As a result, it becomes possible to distinguish and specify the nip pressure (the biasing force of the pressure spring 37b) of the relay roller pair 42, which is switched in conjunction with the rotational movement of the manual feed bottom plate cam shaft 65, in three or more stages, and the nip pressure (the biasing force of the pressure spring 37b) of the relay roller pair 42 can be switched in three or more stages without providing a new component.

Figure 11(a) is an explanatory diagram showing the rotational position of the manual-feed bottom plate cam shaft 65 when the nip pressure of the relay roller pair 42 is zero nip pressure, Figure 11(b) is an explanatory diagram showing the rotational position of the manual-feed bottom plate cam shaft 65 when the nip pressure of the relay roller pair 42 is low nip pressure, and Figure 11(c) is an explanatory diagram showing the rotational position of the manual-feed bottom plate cam shaft 65 when the nip pressure of the relay roller pair 42 is high nip pressure.
Moreover, the following Table 1 shows the relationship between the position of the manual feed bottom plate 34, the nip pressure of the relay roller pair 42, and the output state of the filler sensor 65c.

In this embodiment, the rotational position of the manual feed bottom plate cam shaft 65 when the nip pressure of the relay roller pair 42 is low nip pressure is set as the home position, and the output of the filler sensor 65c is turned on. More specifically, in this embodiment, the stop rotational position of the manual feed bottom plate cam shaft 65 immediately after the output of the filler sensor 65c switches from off to on when the manual feed bottom plate cam shaft 65 rotates in the forward direction B2 shown in FIG. 11(b) is the home position.

When the manual feed bottom plate cam shaft 65 stops at this home position, the manual feed bottom plate cam 35 on the manual feed bottom plate cam shaft 65 presses down the bottom plate guide portion 34a, and the manual feed bottom plate 34 takes the lowered position (the position where the manual feed bottom plate 34 is separated from the manual feed roller 32). At this time, the pressing portion 65e on the manual feed bottom plate cam shaft 65 is in the low pressing position as shown in FIG. 11(b), and the pressure spring 37b expands and contracts less, so that the biasing force of the pressure spring 37b is low. As a result, the biasing force biasing the relay driven roller 42b toward the relay drive roller 42a is low, and the nip pressure of the relay roller pair 42 becomes low nip pressure.

When controlling the manual feed bottom plate 34 to move to the raised position from this home position state (manual feed bottom plate 34 in the lowered position, and the nip pressure of the relay roller pair 42 at low nip pressure), or when controlling the nip pressure of the relay roller pair 42 to be switched to high nip pressure, the control unit 51 rotates the manual feed bottom plate cam shaft 65 in the forward direction B2 shown in FIG. 11(b). Then, immediately after the output of the filler sensor 65c switches from on to off, the rotation of the manual feed bottom plate cam shaft 65 is stopped (FIG. 11(c)).

When the manual-feed bottom plate camshaft 65 stops at this rotational position, the manual-feed bottom plate cam 35 on the manual-feed bottom plate camshaft 65 separates from the bottom plate guide portion 34a, and the manual-feed bottom plate 34 takes the raised position due to the biasing force of the bottom plate spring 36. At this time, the pressing portion 65e on the manual-feed bottom plate camshaft 65 is in a high pressing position as shown in FIG. 11(c), and the pressure spring 37b contracts. Since the amount of contraction increases, the biasing force of the pressure spring 37b increases. As a result, the biasing force biasing the relay driven roller 42b toward the relay drive roller 42a increases, and the nip pressure of the relay roller pair 42 becomes high.

On the other hand, when controlling the nip pressure of the relay roller pair 42 to be switched to zero nip pressure from the home position state (manual feed bottom plate 34 in the lowered position, low nip pressure state of the relay roller pair 42), the control unit 51 rotates the manual feed bottom plate cam shaft 65 in the reverse direction B1 shown in FIG. 11(b). Then, immediately after the output of the filler sensor 65c switches from on to off, the rotation of the manual feed bottom plate cam shaft 65 is stopped (FIG. 11(a)).

When the manual feed bottom plate cam shaft 65 stops at this rotational position, the manual feed bottom plate cam 35 on the manual feed bottom plate cam shaft 65 keeps pressing down the bottom plate guide portion 34a, just as in the home position, and the manual feed bottom plate 34 takes the same lowered position as in the home position. However, the pressing portion 65e on the manual feed bottom plate cam shaft 65 is in the non-pressing position as shown in FIG. 11(a), the pressure spring 37b extends to its free length, and the biasing force of the pressure spring 37b becomes zero. As a result, the biasing force biasing the relay driven roller 42b toward the relay drive roller 42a becomes zero, and the nip pressure of the relay roller pair 42 becomes zero nip pressure.

The above configuration can be achieved by appropriately adjusting the arrangement and shape of the manual feed bottom plate cam 35 and the pressing portion 65e provided on the manual feed bottom plate cam shaft 65, and the arrangement and shape of the cam detection feeler 65b, etc.

Next, the operation when a jam occurs will be described.
If a jam occurs when the nip pressure of the relay roller pair 42 is low (when conveying thin paper or plain paper), the rotation position of the manual-feed bottom plate cam shaft 65 is the home position when the jam occurs. Therefore, the control unit 51 controls the manual-feed bottom plate cam shaft 65 to rotate in the reverse direction B1 shown in Fig. 11(b) and to stop the rotation of the manual-feed bottom plate cam shaft 65 when the output of the filler sensor 65c switches from on to off. This switches the nip pressure of the relay roller pair 42 to zero nip pressure.

After that, when the jam processing, such as removing the recording sheet S sandwiched between the relay roller pair 42, is completed, the control unit 51 rotates the manual feed bottom plate cam shaft 65 in the forward direction B2 shown in FIG. 11(b) to return the nip pressure of the relay roller pair 42 to the original nip pressure, i.e., low nip pressure. Then, when the output of the filler sensor 65c switches from off to on, the control unit 51 stops the rotation of the manual feed bottom plate cam shaft 65. This returns the rotation position of the manual feed bottom plate cam shaft 65 to the home position, and the nip pressure of the relay roller pair 42 switches to low nip pressure. Then, printing is resumed.

On the other hand, if a jam occurs when the nip pressure of the relay roller pair 42 is high (when transporting thick paper), the control unit 51 first rotates the manual feed bottom plate cam shaft 65 in the forward direction B2 shown in FIG. 11B to return the rotation position of the manual feed bottom plate cam shaft 65 to the home position. Then, when the output of the filler sensor 65c switches from off to on, the control unit 51 stops the rotation of the manual feed bottom plate cam shaft 65. As a result, the rotation position of the manual feed bottom plate cam shaft 65 returns to the home position. After that, the control unit 51 rotates the manual feed bottom plate cam shaft 65 in the reverse direction B1 shown in FIG. 11B, and controls the manual feed bottom plate cam shaft 65 to stop rotating when the output of the filler sensor 65c switches from on to off. As a result, the nip pressure of the relay roller pair 42 switches to zero nip pressure.

After that, when the jam processing, such as removing the recording sheet S sandwiched between the relay roller pair 42, is completed, the control unit 51 rotates the manual feed bottom plate cam shaft 65 in the forward direction B2 shown in FIG. 11B in order to return the nip pressure of the relay roller pair 42 to the original nip pressure, i.e., the high nip pressure. Then, when the output of the filler sensor 65c switches from off to on, the control unit 51 stops the rotation of the manual feed bottom plate cam shaft 65. As a result, the rotation position of the manual feed bottom plate cam shaft 65 returns to the home position. After that, the control unit 51 further rotates the manual feed bottom plate cam shaft 65 in the forward direction B2 shown in FIG. 11B, and when the output of the filler sensor 65c switches from on to off, the control unit 51 stops the rotation of the manual feed bottom plate cam shaft 65. As a result, the nip pressure of the relay roller pair 42 switches to the high nip pressure.

As described above, in this embodiment, the nip pressure (the biasing force of the pressure spring 37b) of the relay roller pair 42 used in the main body paper feed path R1 is switched in conjunction with the operation of the manual feed bottom plate cam shaft 65 as a movable member used in the manual feed path R2, but is not limited to this. For example, if the manual feed unit 30 adopts a sheet feeding means that presses the manual feed roller 32 against the recording sheet on the manual feed tray by the operation of lowering the manual feed roller 32, the manual feed roller 32 or its driving member may be a movable member, and the nip pressure of the relay roller pair 42 may be switched in conjunction with the operation of the manual feed roller 32 or its driving member. Also, for example, it may be switched in conjunction with the operation of a movable member used in a paper feed path other than the manual feed path R2 (for example, the reverse return path R5, etc.).

In the present embodiment, the configuration for switching the nip pressure (the biasing force of the pressure spring 37b) of the relay roller pair 42 used in the main body paper feed path R1 has been described, but the present invention can also be applied to a configuration for switching the nip pressure of other conveying roller pairs (such as the paper discharge roller pair 46). In addition, the relay roller pair 42, which is the subject of the nip pressure switching in this embodiment, is a conveying roller pair in which one is a drive roller and the other is a driven roller, but it may also be a conveying roller pair in which both are drive rollers or both are driven rollers.

In addition, in this embodiment, a printer has been described as an example of an image forming apparatus, but the image forming apparatus may be a copier equipped with an image reading device, or a multifunction device equipped with a facsimile function or the like. The present invention is not limited to image forming apparatuses that form images using an electrophotographic method, but may also be applied to image forming apparatuses that form images using other methods, such as an inkjet method or a toner projection method as described in JP-A-2002-307737. The present invention is not limited to image forming apparatuses, but may also be image reading devices equipped with an automatic feeder (ADF) as long as they are equipped with a sheet transport device.

The above description is merely an example, and each of the following aspects provides unique effects.
[First aspect]
The first aspect is a sheet conveying device including a roller pair (e.g., relay roller pair 42) that sandwiches a sheet (e.g., recording sheet S) conveyed in a first conveying path (e.g., main body paper feed path R1), a biasing means (e.g., pressure spring 37b) that biases one roller (e.g., relay drive roller 42a) constituting the roller pair toward the other roller (e.g., relay driven roller 42b), a biasing force switching means (e.g., pressure plate 37d, pressing portion 65e, etc.) that switches the biasing force by the biasing means, and a control means (e.g., control unit 51) that switches the biasing force by the biasing force switching means, and the biasing force switching means is configured to bias the sheet (e.g., recording sheet S) conveyed in a second conveying path (e.g., manual paper feed path R2). The biasing force applied by the biasing means is switched between three or more different biasing forces (e.g., high nip pressure, low nip pressure and zero nip pressure) in conjunction with the operation of a movable member (e.g., manual feed bottom plate cam shaft 65) that operates when a sheet is transported, and the device has a detection means (e.g., a filler sensor 65c) that detects whether a detected portion (e.g., a cam detection feeler 65b) that moves in conjunction with the operation of the movable member is present within a detection area, and the control means identifies the biasing force applied by the biasing means based on the detection result of the detection means and the operating direction of the movable member (e.g., the rotational direction of the manual feed bottom plate cam shaft 65).
In a conventional sheet conveying device, the biasing force (nip pressure of the roller pair) by the biasing means for biasing one roller of the roller pair in the main body paper feed path (first conveying path) toward the other roller is switched between two stages in conjunction with the lifting and lowering operation of the manual feed bottom plate (movable member) in the manual feed path (second conveying path). At this time, the control means for this switching utilizes a detection means for detecting the position of the manual feed bottom plate. Since the manual feed bottom plate moves only to two positions, the raised position and the lowered position, the detection means only needs to be capable of distinguishing and detecting these two positions. For this reason, the detection means may have a simple configuration, for example, a detection feeler (detected portion) that moves in conjunction with the operation of the manual feed bottom plate and an optical sensor that detects the presence or absence of the detection feeler in the detection area.
In the conventional sheet conveying device, the two positions where the manual feed bottom plate can be located correspond one-to-one to the two biasing forces that the biasing means can apply (the two nip pressures that the roller pair can apply). This allows the control means to use a detection means for detecting the position of the manual feed bottom plate to identify which of the two biasing forces is being applied by the biasing means, and therefore allows appropriate control of switching the nip pressure. However, in this configuration, it is not possible to distinguish and identify three or more biasing forces applied by the biasing means, and therefore it is not possible to switch the biasing force applied by the biasing means (the nip pressure of the roller pair) between three or more stages.
On the other hand, if a new component (such as a new sensor) is provided to distinguish and identify three or more biasing forces by the biasing means, it would be possible to switch the biasing force by the biasing means between three or more stages, but this would result in increased costs.
In this embodiment, a configuration is adopted in which the biasing force of the biasing means is switched between three or more different biasing forces in conjunction with the movement of the movable member. The control means for performing this switching uses not only the detection result of the detection means, which is the same as in the conventional case, that detects whether the detected part, which moves in conjunction with the movement of the movable member, is present within the detection area, but also information on the movement direction (direction of movement) of the movable member to specify the biasing force of the biasing means. From the detection result of the detection means, only two movement positions of the movable member corresponding to two states, that is, whether the detected part is present within the detection area or not, can be distinguished and grasped, but if information on the movement direction of the movable member is also used, it becomes possible to distinguish and grasp at least three movement positions of the movable member. For example, it is possible to distinguish and grasp the movement position of the movable member when the detected part is within the detection area, the movement position of the movable member when the movable member moves in one direction and the detected part leaves the detection area, and the movement position of the movable member when the movable member moves in the other direction and the detected part leaves the detection area. Furthermore, since the biasing force applied by the biasing means differs depending on the operating position of the movable member, if the operating positions of at least three movable members can be distinguished and grasped, it will be possible to distinguish and identify at least three biasing forces applied by the biasing means.
According to this aspect, it is possible to distinguish and identify three or more biasing forces applied by the biasing means without adding any new components, so that it is possible to switch the biasing force applied by the biasing means (nip pressure of the roller pair) between three or more stages at low cost.

[Second aspect]
A second aspect is characterized in that, in the first aspect, the control means switches to the smallest biasing force (e.g., zero nip pressure) among the three or more biasing forces when a jam occurs in the sheet in the first conveying path.
This can prevent the sheet held between the roller pair from being torn when it is pulled out during jam clearance.

[Third aspect]
A third aspect is the second aspect, characterized in that, after the jam is cleared, the control means switches the urging force to a force immediately before switching to the smallest urging force.
According to this, after the jam is cleared, the nip pressure of the roller pair is returned to the original nip pressure immediately before the jam occurred, so that sheet transport can be quickly resumed.

[Fourth aspect]
A fourth aspect is the device according to any one of the first to third aspects, characterized in that the smallest biasing force among the three or more biasing forces is zero.
This can prevent the sheet held between the roller pair from being torn when it is pulled out during jam clearance.

[Fifth aspect]
The fifth aspect is characterized in that, in any of the first to fourth aspects, the movable member operates between a first position (e.g., a position where the manual feed bottom plate 34 is in a lowered position) and a second position (e.g., a position where the manual feed bottom plate 34 is in an raised position), and the control means controls the movable member to position the movable member at the first position or the second position based on the detection result of the detection means.
In this embodiment, the operation of switching the nip pressure of the roller pair in the first conveying path (the biasing force by the biasing means) is performed in conjunction with the operation of the movable member used for sheet conveying in the second conveying path. When a sheet is conveyed using a conveying path selected from a plurality of conveying paths, the other conveying paths are not used for sheet conveying. Therefore, when switching the nip pressure of the roller pair in the first conveying path, no problems will occur even if the movable member used for sheet conveying in the second conveying path is operated.
According to this aspect, the contact pressure of the roller pair in the first conveying path can be switched by utilizing the operation of the movable member used for sheet transport in the second conveying path, so there is no need to provide an operating means dedicated to switching, and the device can be made smaller and less costly.

[Sixth aspect]
The sixth aspect is characterized in that, in any of the first to fifth aspects, it has a sheet placement portion (e.g., manual feed bottom plate 34) on which a stack of sheets is placed, and the movable member moves the sheet placement portion between a contact position (e.g., raised position) where the stack of sheets is brought into contact with a feed member (e.g., manual feed roller 32) that abuts against the top sheet of the stack of sheets and feeds it, and a separation position (e.g., lowered position) where the stack of sheets is separated from the feed member.
According to this, the contact pressure of the roller pair can be switched by utilizing the operating means for moving the sheet placement portion.

[Seventh aspect]
The seventh aspect is characterized in that, in any of the first to sixth aspects, the movable member includes a rotating shaft (e.g., manual feed bottom plate cam shaft 65) having a cam portion (e.g., pressing portion 65e) and the detectable portion (e.g., cam detection feeler 65b) that constitutes the force switching means, and the control means performs the determination based on the detection result of the detection means and the operating direction of the movable member (e.g., the rotational direction of the manual feed bottom plate cam shaft 65).
This allows the identification to be performed with a simple configuration.

[Eighth aspect]
An eighth aspect is an image forming apparatus that forms an image on a sheet transported by a sheet transporting device, characterized in that the sheet transporting device is any of the sheet transporting devices of the first to seventh aspects.
According to this aspect, when the nip pressure of a pair of rollers clamping a sheet transported through the first transport path is switched in conjunction with the operation of a movable member that operates when the sheet is transported through the second transport path, an image forming device can be provided that can switch the nip pressure between three or more levels at low cost.

1: Photoconductor 30: Manual feed section 31: Manual feed tray 32: Manual feed roller 33: Separation pad 34: Manual feed bottom plate 35: Manual feed bottom plate cam 36: Bottom plate spring 37a: Bearing section 37b: Pressure spring 37d: Pressure plate 39: Opening and closing door 41: Main body feed roller 41A, 41B: Feeding roller 42: Relay roller pair 42A, 42B: Transport roller pair 42a: Relay driving roller 42b: Relay driven roller 43: Registration roller pair 44: Fixing device 46: Discharge roller pair 48: Separation pad 48A, 48B: Separation pad 49: Registration sensor 50: Main body housing 51: Control section 61: Main motor 61a: Motor shaft 62: Feeding roller shaft 62a: Main body feed clutch 63: Relay roller shaft 63a: Relay clutch 64 : Manual feed roller shaft 64a : Manual feed clutch 65 : Manual feed bottom plate cam shaft 65a : Manual feed bottom plate cam clutch 65b : Cam detection filler 65c : Filler sensor 65d : Push-down lever 65e : Pressing section 66 : Roller shaft 100 : Main body feed tray 100 : Paper feed tray 101 : Main body feed bottom plate B1 : Reverse direction B2 : Forward direction R1 : Main body feed path R2 : Manual feed path R3 : Common transport path R4 : Discharge path R5 : Reverse return path S : Recording sheet

JP 2021-113105 A

Claims (8)

a pair of rollers for holding a sheet conveyed through the first conveying path;
a biasing means for biasing one of the rollers constituting the roller pair toward the other roller;
a biasing force switching means for switching the biasing force of the biasing means;
a control unit that switches the biasing force by the biasing force switching unit,
the biasing force switching means switches the biasing force applied by the biasing means among three or more different biasing forces in response to an operation of a movable member that operates when the sheet is transported through the second transport path,
a detection means for detecting whether a detected part that moves in conjunction with the movement of the movable member is present within a detection area;
The sheet conveying device according to claim 1, wherein the control means specifies the biasing force applied by the biasing means based on the detection result of the detection means and the movement direction of the movable member. 2. The sheet conveying apparatus according to claim 1,
The sheet transport device according to claim 1, wherein the control unit switches the urging force to the smallest one of the three or more urging forces when a jam occurs in the sheet in the first transport path. 3. The sheet conveying apparatus according to claim 2,
The sheet conveying device according to claim 1, wherein the control means switches the urging force to a value immediately before the switching to the smallest urging force after the jam is cleared. 4. The sheet conveying device according to claim 1,
The sheet conveying device according to claim 1, wherein the smallest biasing force among the three or more biasing forces is zero. 4. The sheet conveying device according to claim 1,
the movable member is movable between a first position and a second position;
The sheet conveying device, wherein the control means performs movable member control to position the movable member at the first position or the second position based on a detection result of the detection means. 4. The sheet conveying device according to claim 1,
a sheet stacking section on which a sheet bundle is placed,
The movable member is configured to move the sheet loading section between a contact position where the sheet stack is brought into contact with a feeding member that abuts against the top sheet of the sheet stack and feeds it, and a separation position where the sheet stack is separated from the feeding member. 4. The sheet conveying device according to claim 1,
the movable member includes a rotating shaft having a cam portion constituting the biasing force switching means and the detected portion,
The sheet conveying device according to claim 1, wherein the control means performs the determination based on a detection result of the detection means and a moving direction of the movable member. An image forming apparatus that forms an image on a sheet conveyed by a sheet conveying device,
4. An image forming apparatus, comprising: the sheet transport device according to claim 1.

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