Sheet transport device and image forming apparatus

Abstract

To provide a sheet carrier device capable of switching the nip pressure of a roller pair in three steps or more at a low cost with a simple configuration.SOLUTION: A sheet carrier device comprises: a roller pair 42 holding a sheet carried in a first carrying route; energization means 37b of energizing one roller 42a forming the roller pair toward the other roller 42b; energization power switching means 37d, 65e of switching the energization power by the energizing means; and control means of switching the energization power by the energization power switching means. The energization power switching means switches the energization power by the energization means among three or more energization powers different from each other, interlocking with the movement of a movable member 65 moving when the sheet is carried in a second carrying route, and has detection means 65c of detecting presence or absence of a detected part 65b moving interlocking with the movement of the movable member, in a detection region. The control means specifies the energization power by the energization means on the basis of a detection result of the detection means and a movement direction of the movable member.SELECTED DRAWING: Figure 8

Description

Technical Field

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

Background Art

[0002] Conventionally, there has been known a sheet conveying apparatus comprising: a roller pair that nipping a sheet conveyed in a first conveying path; a biasing means that biases one roller constituting the roller pair 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 by the biasing force switching means.

[0003] For example, Patent Document 1 discloses a sheet conveying apparatus that switches the nip pressure (biasing force) of a pair of relay rollers in a main body sheet feeding path (first conveying path) in conjunction with the lifting and lowering operation of a manual feed bottom plate (movable member of a second conveying path) on which a sheet bundle is placed. In this sheet conveying apparatus, when the manual feed bottom plate is at the raised position, the nip pressure of the pair of relay rollers increases in conjunction therewith. At this time, the detection filler that moves in conjunction with the lifting and lowering operation of the manual feed bottom plate is positioned so as not to block the filler sensor. On the other hand, when the manual feed bottom plate is at the lowered position, the nip pressure of the pair of relay rollers decreases in conjunction therewith. At this time, the detection filler is positioned to block the filler sensor. The control unit performs lifting control of the manual feed bottom plate based on the detection result of the filler sensor, and performs control to switch the nip pressure of the pair of relay rollers.

Summary of the Invention

Problem to be Solved by the Invention

[0004] In conventional sheet conveying apparatuses, it has been difficult to realize a configuration for switching the nip pressure of a roller pair in three or more stages at low cost.

Means for Solving the Problem

[0005] To solve the above-mentioned problems, the present invention provides a sheet conveying device comprising: a pair of rollers for gripping a sheet being conveyed in a first conveying path; a biasing means for biasing one roller constituting the pair of rollers toward the other roller; a biasing force switching means for switching the biasing force by the biasing means; and a control means for switching the biasing force by the biasing force switching means, wherein the biasing force switching means, in conjunction with the operation of a movable member that operates when the sheet is conveyed in a second conveying path, switches the biasing force by the biasing means to three different values. tsu It switches between biasing forces and has a detection means for detecting whether or not a detected part that moves in conjunction with the operation of the movable member is present within the detection area. The movable member includes a rotating shaft comprising a cam portion and a detected portion that constitute the biasing force switching means. The control means is characterized by determining 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. [Effects of the Invention]

[0006] According to the present invention, it is possible to switch the nip pressure of a roller pair in three or more stages at a low cost. [Brief explanation of the drawing]

[0007] [Figure 1] A schematic diagram showing a printer according to this embodiment. [Figure 2] This is a perspective view showing the main components of the printer: the main paper feed unit, which feeds recording sheets from the paper tray, and the manual feed unit, which feeds recording sheets from the manual feed tray. [Figure 3] A perspective view showing the configuration of the drive system in the paper feed section and manual paper feed section of the main unit. [Figure 4] An explanatory diagram illustrating the paper feeding path in the main unit's paper feeding section and manual paper feeding section. [Figure 5] A flowchart illustrating the control operation when feeding and transporting paper from the main unit's paper feed section. [Figure 6] A flowchart illustrating the control operation when feeding and transporting paper from the manual paper feed unit. [Figure 7](a) is a perspective view showing the configuration when the manual feed base plate is in the lowered position. (b) is a perspective view showing the configuration when the manual feed base plate is in the raised position. [Figure 8] (a) to (c) are explanatory diagrams showing a biasing force switching means in this embodiment that switches the biasing force of the pressure spring 37b that biases the bearing portion 37a of the relay driven roller 42b toward the relay driven roller 42a side. [Figure 9] (a) and (b) are explanatory diagrams showing the detection means when the cam detection filler does not obstruct the detection area of ​​the filler sensor. [Figure 10] (a) and (b) are explanatory diagrams showing the detection means for a state in which the cam detection filler is obstructing the detection area of ​​the filler sensor. [Figure 11] (a) is an explanatory diagram showing the rotational position of the manual-inserted base plate cam shaft when the nip pressure of the intermediate roller pair is zero nip pressure. (b) is an explanatory diagram showing the rotational position of the manual-inserted base plate cam shaft when the nip pressure of the intermediate roller pair is low nip pressure. (c) is an explanatory diagram showing the rotational position of the manual-inserted base plate cam shaft when the nip pressure of the intermediate roller pair is high nip pressure. [Modes for carrying out the invention]

[0008] Hereinafter, the present invention will be described using an electrophotographic printer (hereinafter simply referred to as a printer) that forms images using an electrophotographic method as an example of an image forming apparatus to which the present invention is applied.

[0009] First, the basic configuration of the printer according to this embodiment will be described. Figure 1 is a schematic diagram showing a printer according to an embodiment. In the figure, the printer is equipped with a photoreceptor 1 as a latent image carrier, and a main paper feed tray 100 and two additional paper feed trays 100A and 100B, which are sheet storage means configured to be detachable from the main body housing 50. Inside each paper feed tray 100, 100A, and 100B, multiple recording sheets S are stored in a sheet bundle.

[0010] The recording sheet S in the main paper feed tray 100 is fed out of the paper feed tray by the rotational drive of the main paper feed roller 41. At the separation nip between the main paper feed roller 41 and the separation pad 48, only the top sheet is separated and fed out, reaching the main paper feed path R1, which is the first transport path. Subsequently, the recording sheet S is caught (held) by the transport nip of the relay roller pair 42, which is the upper transport roller pair, and transported from the upstream side to the downstream side in the transport direction within the main paper feed path R1. Note that at least one of the transport roller pair may be a belt transport body pair.

[0011] The recording sheet S in the first additional paper feed tray 100A is fed out of the paper feed tray by the rotational drive of the paper feed roller 41A, and at the separation nip between the paper feed roller 41A and the separation pad 48A, only the top sheet is separated and fed out. After that, the recording sheet S is caught (held) by the transport nip of the upper transport roller pair 42A and transported upward, passing through the main paper feed tray 100 and into the main paper feed path R1.

[0012] The recording sheet S in the second additional paper feed tray 100B is fed out of the paper feed tray by the rotational drive of the paper feed roller 41B, and at the separation nip between the paper feed roller 41B and the separation pad 48B, only the top sheet is separated and fed out. Subsequently, the recording sheet S is caught (held) by 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 arriving at the main paper feed path R1.

[0013] The downstream end of the main paper feed path R1 is connected to the common transport path R3, where a pair of register rollers 43 is installed. A register sensor 49 for detecting the recording sheet S is located upstream of the register roller pair 43 in the transport direction on the common transport path R3. The transport of the recording sheet S is temporarily stopped when its leading edge comes into contact with the nip of the stopped register roller pair 43. At this point, the skew of the recording sheet S is corrected. The register sensor 49 is also used for initial operation and for checking the remaining sheets (jam detection operation) when the device malfunctions and stops are resolved.

[0014] The registration roller pair 43 starts rotational driving at a timing that allows the recording sheet S to be superimposed on the toner image on the surface of the photoreceptor 1 at the transfer nip, and feeds the recording sheet S toward the transfer nip. At this time, the relay roller pair 42 also starts rotational driving simultaneously, and resumes the conveyance of the recording sheet S that has been temporarily suspended.

[0015] The main body housing 50 of the printer is provided with a manual paper feed unit 30 serving as a manual feeding unit that includes a manual feed tray 31, a manual paper feed roller 32, a separation pad 33, a manual feed bottom plate 34, a manual feed bottom plate cam 35, and the like. Details of the manual paper feed unit 30 will be described later. The recording sheet S manually fed into the manual feed tray 31 of the manual paper feed unit 30 is fed from the manual feed tray 31 to the manual paper feed path R2, which is the second conveyance path, by the rotational driving of the manual paper feed roller 32. The downstream end of the manual paper feed path R2 merges into the common conveyance path R3 together with the downstream end of the main body paper feed path R1. The recording sheet S fed out by the manual paper feed roller 32 passes through a separation nip formed by the contact between the manual paper feed roller 32 and the separation pad 33 in the manual paper feed path R2, then is fed into the common conveyance path R3 and conveyed to the registration roller pair 43. Thereafter, similarly to the recording sheet S fed out from the paper feed tray 100, the recording sheet S is fed to the transfer nip after passing through the registration roller pair 43.

[0016] Around the drum-shaped photoreceptor 1 that is rotationally driven in the clockwise direction in the figure, a cleaning blade, a recovery screw, a charging roller, a charging cleaning roller, a scraper, a latent image writing device 7, a developing device 8, a transfer roller 10, and the like are disposed. The charging roller including a conductive rubber roller portion rotates while contacting the photoreceptor 1 to form a charging nip. A voltage is applied to this charging roller from a charging power supply. Accordingly, in the charging nip, 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.

[0017] The latent image writing device 7 includes an LED array, and performs optical writing with LED light on the uniformly charged surface of the photoconductor 1. Among the uniformly charged surface portion of the photoconductor 1, the potential of the area irradiated with writing light attenuates, and an electrostatic latent image is formed on the surface of the photoconductor 1.

[0018] The electrostatic latent image passes through the development region facing the developing device 8 as the photoconductor 1 rotates. The developing device 8 includes a circulation conveyance section and a development section, and the circulation conveyance section accommodates a developer containing toner and a magnetic carrier. In the development region, toner selectively adheres to the electrostatic latent image on the photoconductor 1 to develop the electrostatic latent image. A toner cartridge 9 is disposed above the developing device 8.

[0019] The toner image formed on the photoconductor 1 through development enters the transfer nip where the photoconductor 1 and the transfer roller 10 abut against each other as the photoconductor 1 rotates. A voltage having a polarity opposite to the latent image potential of the photoconductor 1 is applied to the transfer roller 10, thereby forming a transfer bias in the transfer nip.

[0020] As described above, the registration roller pair 43 feeds 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 photoconductor 1 within the transfer nip. The toner image on the photoconductor 1 is transferred onto the recording sheet brought into close contact with the toner image at the transfer nip by the action of the transfer bias and nip pressure.

[0021] In FIG. 1, the recording sheet S that has passed through the transfer nip where the photoconductor 1 and the transfer roller 10 abut is sent to a fixing device 44. The fixing device 44 forms a fixing nip by the abutment between a fixing roller 44a containing a heat generating source such as a halogen lamp and a pressure roller 44b pressed toward the fixing roller 44a. The toner image is fixed onto the surface of the recording sheet S sandwiched in the fixing nip by the action of heating and pressing. Thereafter, 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 paper discharge roller pair 46.

[0022] This printer can switch 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 single-sided mode, or in double-sided mode when an image has already been formed on both sides of the recording sheet, the paper output roller pair 46 continues to rotate in the forward direction, ejecting the recording sheet S from the paper output path R4 to the outside of the machine. The ejected recording sheet S is stacked in a stack section provided on the top surface of the main unit housing 50.

[0023] On the other hand, in double-sided mode, when an image is formed on only one side of the recording sheet S, the output roller pair 46 is driven in reverse when the rear end of the recording sheet S enters the output nip of the output roller pair 46. At this time, a switching claw 47 located near the downstream end of the output path R4 is activated, blocking the output path R4 and opening the entrance to the reverse re-feed path R5. The recording sheet S, which has started to move backward due to the reverse drive of the output roller pair 46, is fed into the reverse re-feed path R5. The downstream end of the reverse re-feed path R5 merges with the upstream side of the registration roller pair 43 of the common transport path R3, and after being transported within the reverse re-feed path R5, it is re-feeded to the registration roller pair 43 of the common transport path R3. After that, the toner image is transferred to the other side at the transfer nip, and then it is discharged outside the machine via the fuser 44, the output path R4, and the output roller pair 46.

[0024] Next, we will explain the configuration and operation related to the paper feeding of the recording sheet S. Figure 2 is a perspective view showing the main configuration of the main paper feeding unit, which feeds recording sheets S from the main paper tray 100, and the manual feed unit 30, which feeds recording sheets S from the manual feed tray 31. Figure 3 is a perspective view showing the configuration of the drive system in the main paper feed section and the manual paper feed section 30.

[0025] As shown in Figures 2 and 3, the drive system in the main paper feed section and the manual feed section 30 is configured to distribute the driving force from a single main motor 61 to the main paper feed roller 41, the intermediate 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 and the like to the paper feed roller shaft 62 on which the main paper feed roller 41 is located, the intermediate roller shaft 63 on which the intermediate roller pair 42 is located, the manual feed roller shaft 64 on which the manual feed roller 32 is located, and the manual feed bottom plate cam shaft 65 on which the manual feed bottom plate cam 35 is located.

[0026] The paper feed roller shaft 62, the intermediate roller shaft 63, the manual feed paper feed roller shaft 64, and the manual feed bottom plate cam shaft 65 are each provided with clutches 62a, 63a, 64a, and 65a for switching the transmission of driving force on and off. When power is turned on to each clutch, driving force is transmitted and each shaft 62, 63, 64, and 65 rotates. When power is turned off to each clutch, the transmission of driving force is interrupted and each shaft 62, 63, 64, and 65 does not rotate. The driving force from the main motor 61 is also transmitted to the register roller pair 43 via the clutches. In this embodiment, the paper feeding and transport of the recording sheet S is achieved by using the driving force of the main motor 61 and controlling the on / off state of each clutch by the control unit 51.

[0027] Figure 4 is an explanatory diagram illustrating the paper feeding path in the main paper feeding section and the manual paper feeding section 30. First, we will explain the process of feeding and transporting paper from the main paper feed unit, referring to the flowchart shown in Figure 5. The main paper feed base plate 101 is biased upward toward the main paper feed roller 41, so that the main paper feed roller 41 is in contact with the uppermost recording sheet S among the multiple recording sheets S placed on the main paper feed base plate 101 in a sheet stack. When paper feeding from the main paper feed section is to begin, the control unit 51 first performs an initial operation (S1) and checks whether the initial operation is completed successfully (S2). Here, the "initial operation" is the operation of setting the manual feed base plate 34 to its lowest position, and after the initial operation is completed, the nip pressure of the intermediate roller pair 42 is set to a low state.

[0028] If the initial operation does not complete normally (No. S2), the control unit 51 displays a fault message on the printer's control panel (S14) and executes a process to notify the system of an abnormality in the switching operation of the nip pressure of the relay roller pair 42. This notification method is not limited to notifying the system of the abnormality visually, such as by displaying a fault message on the control panel; it may also be notified aurally, for example, by sound. Furthermore, the notification may be given immediately, or it may be given at a delayed time, such as after the completion of the image forming apparatus operation.

[0029] If the initial operation is completed successfully (Yes in S2), the control unit 51 turns on the main motor 61 (S3) and determines whether the recording sheet S to be fed is thin paper or plain paper (S4). In this embodiment, the user operates the printer's control panel to select one of the types of sheets that can be printed on by the printer, such as plain paper (low strength (thin) sheet), thin paper (low strength (thin) sheet), or thick paper (high strength (thick) sheet), 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 and determines whether the recording sheet S to be fed is thin paper or plain paper.

[0030] The method for determining whether paper is thin, regular, or thick is not limited to this. For example, the thickness of the recording sheets S stored in the paper tray 100 or the recording sheets S fed from the paper tray 100 may be detected by a thickness detection sensor, and the determination may be made based on the detection result.

[0031] Furthermore, in this embodiment, the type of recording sheet S to be judged is determined by the difference in thickness of the recording sheet S, but it may also be determined by 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.

[0032] In this embodiment, if it is determined that the paper is thin paper or plain paper (Yes in S4), the control unit 51, because the nip pressure of the relay roller pair 42 is already low due to the initial operation described above, turns on the main paper feed clutch 62a and the relay clutch 63a while maintaining this low nip pressure state (S5). As a result, the main paper feed roller 41 rotates, and the uppermost recording sheet S in the main paper feed tray 100 is sent to the separation pad 48. At this time, even if the second and subsequent recording sheets are sent out together with the uppermost recording sheet S, the transport of the second and subsequent recording sheets is hindered by the frictional force with the separation pad 48, and only the uppermost recording sheet S can pass through the separation pad 48. Note that while paper is being transported from the main paper feed unit, paper is not being transported from the manual feed unit 30, so the manual feed clutch 64a and the manual feed bottom plate cam clutch 65a remain in the OFF state.

[0033] On the other hand, if it is determined that the paper is not thin paper or plain paper (i.e., it is determined to be thick paper) (No. S4), the control unit 51 performs a process to increase the nip pressure of the intermediate roller pair 42. Specifically, during the initial operation, the nip pressure of the intermediate roller pair 42 is low (low nip pressure), so the control unit 51 also turns on the manual feed bottom plate cam clutch 65a (S6). As a result, the manual feed bottom plate cam shaft 65 rotates clockwise in Figure 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.

[0034] As shown in Figure 4, the other relay driven roller 42b, which constitutes the relay roller pair 42, has a bearing portion 37a that supports its roller shaft 66, which is biased by a compression spring 37b, and this biasing force causes it to contact the relay driven roller 42a. When the manual insertion bottom plate cam shaft 65 is stopped at the rotation position described above, the amount of compression of the compression 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.

[0035] In this embodiment, when feeding paper from the main paper feed unit, the timing for turning on the manual feed bottom plate cam clutch 65a is the same as the timing for turning on the main paper feed clutch 62a and the relay clutch 63a (S6). This is for the following reason.

[0036] The switching of the nip pressure of the intermediate roller pair 42 must be completed from the start of paper feeding of the recording sheet S until before the leading edge of the recording sheet S reaches the intermediate roller pair 42. When feeding from the main paper tray 100, the transport distance from the main paper tray 100 to the intermediate roller pair 42 is short. Therefore, if the switching operation of the nip pressure of the intermediate roller pair 42 is not started simultaneously with the start of paper feeding from the main paper tray 100, the switching of the nip pressure cannot be completed before the leading edge of the recording sheet S reaches the intermediate roller pair 42.

[0037] In this embodiment, the fed recording sheet S is transported along the main paper feed path indicated by the reference numeral R1 in Figure 4. At this time, one of the relay drive rollers 42a constituting the relay roller pair 42 is rotationally driven by the driving force from the main motor 61. The other relay driven roller 42b constituting the relay roller pair 42 has its bearing portion 37a, which supports its roller shaft 66, biased by a pressure spring 37b with a low biasing force when using thin or plain paper, and with a high biasing force when using thick paper, and contacts the relay drive roller 42a due to this biasing force. As a result, the relay driven roller 42b rotates together with the relay drive roller 42a. The recording sheet S being transported along the main paper feed path R1 is transported while being held between the nip of the relay drive roller 42a and the relay driven roller 42b.

[0038] When the leading edge of the recording sheet S reaches the resist sensor 49 and the resist sensor 49 turns on (Yes in S8), after a predetermined time has elapsed (before the leading edge of the recording sheet S reaches the resist roller pair 43) (for example, 100 ms after the resist sensor 49 turns on), the main paper feed clutch 62a and the relay clutch 63a are turned off (S9), and the transport of the recording sheet S is temporarily stopped. As a result, the leading edge of the recording sheet S comes into contact with the nip of the stopped resist roller pair 43, and the skew of the recording sheet S is corrected.

[0039] The control unit 51 turns on the relay clutch 63a and the resist clutch (S10) at a timing when the recording sheet S can be superimposed on the toner image on the surface of the photoreceptor 1 at the transfer nip (for example, 200 ms after turning off the main paper feed clutch 62a and the relay clutch 63a). As a result, the resist 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, the main paper feed clutch 62a remains off, so the main paper feed roller 41 does not rotate. Even when the rear end of the recording sheet S is still held between the main paper feed roller 41 and the separation pad 48, the main paper feed roller 41 rotates along with the recording sheet S being transported by the transport force of the resist roller pair 43 and the relay roller pair 42, and does not obstruct transport. Then, when the rear end of the recording sheet S reaches the resist sensor 49 and the resist sensor 49 turns off (Yes in S11), the relay clutch 63a is turned off (S12), and the rotational drive of the relay roller pair 42 is stopped.

[0040] In this embodiment, the biasing force provided by the pressure spring 37b is switched depending on whether the recording sheet S is thin paper or regular paper or thick paper, and the nip pressure of the relay roller pair 42 is changed to a pressure appropriate for each. As a result, stable transport is achieved for thick paper by using a high nip pressure, and stable transport is also achieved for thin paper or regular paper by using a low nip pressure.

[0041] Next, the case of feeding and transporting paper from the manual feed unit 30 will be explained with reference to Figure 6. Figure 6 is a flowchart showing the control operation when feeding and transporting paper from the manual feed unit 30. Figure 7(a) is a perspective view showing the configuration when the manual feed base plate 34 is in the lowered position, and Figure 7(b) is a perspective view showing the configuration when the manual feed base plate 34 is in the raised position.

[0042] The manual feed base plate 34 is biased upward toward the manual feed paper roller 32 by a base plate spring 36. The manual feed base plate 34 is also provided with a base plate guide portion 34a at a location corresponding to the manual feed base plate cam 35. When the manual feed base plate cam shaft 65 rotates and the manual feed base plate cam 35 comes into contact with the base plate guide portion 34a and pushes it down, the manual feed base plate 34 descends against the biasing force of the base plate spring 36 and moves away from the manual feed paper roller 32, as shown in Figure 7(a).

[0043] When starting paper feeding from the manual feed section 30, the control unit 51 first performs an initial operation (S1) and checks whether the initial operation is completed successfully (S2). If the initial operation is completed successfully (Yes in S2), the control unit 51 turns on the main motor 61 (S3), first turns on the manual feed bottom plate cam clutch 65a (S41), and then turns off the manual feed bottom plate cam clutch 65a after a specified time has elapsed (S42). As a result, the manual feed bottom plate cam shaft 65 rotates, and as shown in Figure 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 comes into contact with the uppermost recording sheet S among the multiple recording sheets S placed in a sheet stack on the manual feed tray 31 and manual feed bottom plate 34.

[0044] Next, the control unit 51 turns on the manual feed clutch 64a (S43). This causes the manual feed roller 32 to rotate, and the topmost recording sheet S on the manual feed bottom plate 34 is fed towards the separation pad 33. At this time, even if the second and subsequent recording sheets are fed out together with the topmost recording sheet S, the transport of the second and subsequent recording sheets is hindered by the frictional force with the separation pad 33, and only the topmost recording sheet S can pass through the separation pad 33.

[0045] During paper feeding from the manual feed unit 30, paper feeding from the main unit's paper feed unit does not occur, so the main unit's paper feed clutch 62a and the relay clutch 63a remain in the off state.

[0046] Subsequently, the fed recording sheet S is transported along the manual feed path indicated by the symbol R2 in Figure 4. When the leading edge of the recording sheet S reaches the resist sensor 49 and the resist sensor 49 turns on (Yes in S44), after a predetermined time has elapsed (before the leading edge of the recording sheet S reaches the resist roller pair 43), the manual feed clutch 64a is turned off (S45), and the transport of the recording sheet S is temporarily stopped. As a result, the leading edge of the recording sheet S comes into contact with the nip of the stopped resist roller pair 43, and the skew of the recording sheet S is corrected.

[0047] The control unit 51 turns on the resist clutch (S46) at the timing when the recording sheet S can be superimposed on the toner image on the surface of the photoreceptor 1 by the transfer nip. As a result, the resist roller pair 43 starts rotating and the recording sheet S is transported toward the transfer nip.

[0048] In this embodiment, the manual feed section 30 is 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 this unit is fixed to the main body housing 50 by screws. On the other hand, 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.

[0049] More specifically, as described above, the manual feed mechanism supporting the relay driven roller 42b is fixed to the main body housing 50 by screws. As shown in Figure 1, the opening / closing door 39 is attached to the manual feed mechanism via a hinge mechanism so as to be openable and closable. The manual feed tray 31 is also attached to the opening / closing door 39 via a hinge mechanism so as to be openable and closable. In this embodiment, by opening the opening / closing door 39, the process cartridge containing the photoreceptor 1 can be attached or detached, or a jammed recording sheet S can be removed.

[0050] However, since the relay driven roller 42b is supported not by the opening / closing door 39, but by the manual feed mechanism screwed to the main housing 50, the relay driven roller 42b and the relay drive roller 42a provided on the main housing 50 are configured to be unable to separate from each other.

[0051] In this case, if a device malfunction occurs in the printer, such as a jam, that should stop the transport of the recording sheet S (the following will be explained using an example of a device malfunction due to a jam), the recording sheet S remaining inside the device must be removed. Specifically, in this embodiment, the paper feed tray 100 is removed from the device in the direction of the recording sheet S's paper feed or in a direction intersecting the paper feed direction, and the remaining recording sheet is taken out (pulled out) from the main paper feed section. At this time, in order to prevent the recording sheet S, such as thin paper or plain paper with low strength, from tearing when it is pulled out, it is preferable to release (separate) the points that hold the recording sheet S (such as the transport nip of the intermediate roller pair 42, or the point where the manual feed roller 32 and the manual feed bottom plate 34 are held).

[0052] One configuration for separating the rollers of the relay roller pair 42 is to support the relay driven roller 42b with an opening / closing door that is movably 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, since the relay driven roller 42a and the relay driven roller 42b that make up the relay roller pair 42 are configured so that they cannot be separated from each other, the relay roller pair 42 cannot be opened (separated).

[0053] In this embodiment, when transporting a recording sheet S of a low strength type (thin paper or plain paper) that is easily torn, the nip pressure (contact pressure) of the intermediate roller pair 42 is switched to a low nip pressure. Therefore, even if a jam occurs when transporting a thin paper or plain paper recording sheet S, the nip pressure of the intermediate roller pair 42 is low, so even if the recording sheet S is pulled out from the intermediate roller pair 42 in that state, the sheet is relatively less likely to tear.

[0054] However, when transporting thin paper or plain paper recording sheets S, the nip pressure (contact pressure) of the intermediate roller pair 42 is lower than when transporting thick paper recording sheets S, but the necessary nip pressure for transporting thin paper or plain paper recording sheets S must be maintained. Therefore, if a thin paper or plain paper recording sheet S jams and the recording sheet S is pulled out of the intermediate roller pair 42 while maintaining the low nip pressure of the intermediate roller pair 42, there is a risk that the recording sheet S will tear.

[0055] Furthermore, when transporting a highly durable, tear-resistant type of recording sheet S (cardboard), a high nip pressure is used as the nip pressure (contact pressure) of the intermediate roller pair 42. In the case of cardboard recording sheets S, a low nip pressure of the intermediate roller pair 42 is likely to cause transport failures. However, in this embodiment, the intermediate roller pair 42 is set to a high nip pressure state to transport the cardboard recording sheet S, thus reducing the likelihood of transport failures and ensuring stable transport. On the other hand, if a jam occurs, with cardboard recording sheets S, even if the nip pressure of the intermediate roller pair 42 remains high, it is less likely that the recording sheet S will tear when it is pulled out from the intermediate roller pair 42. However, if the nip pressure of the intermediate roller pair 42 remains high, there is a risk that the recording sheet S may tear when it is pulled out from the intermediate roller pair 42.

[0056] Furthermore, if the intermediate roller pair 42 is set to a high nip pressure state, it is possible that plain paper or thin paper may be accidentally transported. In such cases, if a jam occurs during paper feeding, the risk of the plain paper or thin paper tearing when it is pulled out from the intermediate roller pair 42 becomes even higher.

[0057] Therefore, in this embodiment, the nip pressure (contact pressure) of the relay roller pair 42 is configured to be switchable not only to the high nip pressure and low nip pressure described above, but also to a nip pressure even lower than the low nip pressure (in this embodiment, a zero nip pressure where the nip pressure is substantially zero). With this configuration, 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 suppress the tearing of the recording sheet S when it is pulled out from the relay roller pair 42.

[0058] Next, we will describe the configuration for switching the nip pressure between the intermediate roller and 42. In this embodiment, the operation of switching the nip pressure of the relay roller pair 42 in the main paper feed path R1 is performed in conjunction with the operation of the movable member used for sheet transport in the manual paper feed path R2. In this embodiment, when transporting the recording sheet S using the main paper feed path R1, the manual paper feed path R2 is not used for sheet transport. Therefore, when transporting the recording sheet S using the main paper feed path R1, operating the movable member used for sheet transport in the manual paper feed path R2 does not cause any problems.

[0059] In this embodiment, the sheet feeding means for manual paper feeding involves pressing the recording sheet S on the manual feed base plate 34 against the manual feed roller 32 to feed it out. Therefore, in this embodiment, the manual feed base plate cam shaft 65 for moving the manual feed base plate 34 is made a movable member, and the nip pressure of the relay roller pair 42 is switched in conjunction with the operation of this manual feed base plate cam shaft 65.

[0060] More specifically, as described above, the means for operating the manual feed base plate 34 is to rotate the manual feed base plate cam shaft 65 by the driving force of the main motor 61. When the manual feed base plate cam shaft 65 is in a rotational position where the manual feed base plate cam 35 pushes down the base plate guide portion 34a against the biasing force of the base plate spring 36, the manual feed base plate 34 is in a lowered position and moves away from the manual feed paper roller 32 (see Figure 7(a)). On the other hand, when the manual feed base plate cam shaft 65 is in a rotational position where the manual feed base plate cam 35 moves away from the base plate guide portion 34a, the manual feed base plate 34 is in an elevated position due to the biasing force of the base plate spring 36 and makes contact with the manual feed paper roller 32 (see Figure 7(b)).

[0061] The biasing force switching means of this embodiment changes the nip pressure of the relay roller pair 42 by moving a pressure plate 37d, which is a biasing support part that supports a pressure spring 37b that biases the bearing portion 37a of the relay driven roller 42b, one of the rollers of the relay roller pair 42, toward the relay drive roller 42a, in accordance with the rotation of the manual feed bottom plate cam shaft 65. A slider is fastened to the pressure plate 37d and is configured to move along a guide portion provided on the support frame of the manual feed paper section 30, thereby enabling linear movement in the direction of approaching and moving away from the relay drive roller 42a.

[0062] Figures 8(a) to 8(c) are explanatory diagrams showing a 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 driven roller 42a in this embodiment.

[0063] The roller shaft 66 of the relay driven roller 42b is held in a position where it can slide relative to the support frame of the manual feed section 30, moving toward and away from the relay driven roller 42a. Furthermore, as described above, the bearing portion 37a of the relay driven roller 42b is biased toward the relay driven roller 42a by the pressure spring 37b.

[0064] The pressure spring 37b is a compression spring positioned such that one end contacts the bearing portion 37a of the intermediate 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 intermediate driven roller 42b toward the intermediate drive roller 42a. On the back surface of the pressure plate 37d opposite to the spring contact surface, a pressing portion 65e is in contact with the pressure plate 37d, capable of pressing the pressure plate 37d toward the intermediate drive roller 42a. This pressing portion 65e rotates in conjunction with the rotation of the manual insertion bottom plate cam shaft 65.

[0065] When the rotational position of the manual feed base plate cam shaft 65 is in a position that raises the manual feed base plate 34 (the position where the manual feed base plate 34 contacts the manual feed paper roller 32), the pressing portion 65e on the manual feed base plate cam shaft 65 is in a high-pressure position as shown in Figure 8(c). At this time, the pressure plate 37d moves toward the intermediate drive roller 42a against the biasing force of the pressure spring 37b. As a result, the pressure spring 37b compresses, and the amount of compression increases, so the biasing force of the pressure spring 37b increases. Consequently, the biasing force that biases the intermediate driven roller 42b toward the intermediate drive roller 42a increases, so the nip pressure between the intermediate rollers 42 increases. Note that manual feeding is not possible because the manual feed base plate 34 remains in contact with the manual feed paper roller 32, but this does not cause any problems as manual feeding is not performed during main paper feeding.

[0066] On the other hand, when the rotational position of the manual feed base plate cam shaft 65 is in a position that lowers the manual feed base plate 34 (a position in which the manual feed base plate 34 is separated from the manual feed paper roller 32), the pressing portion 65e on the manual feed base plate cam shaft 65 is in either the non-pressing position shown in Figure 8(a) or the low-pressure position shown in Figure 8(b).

[0067] When the pressing portion 65e on the manual feed bottom plate cam shaft 65 is in the low-pressure position shown in Figure 8(b), the pressure plate 37d moves away from the relay drive roller 42a due to the biasing force of the pressure spring 37b, causing the pressure spring 37b to stretch and reducing its compression, thus lowering the biasing force of the pressure spring 37b. As a result, the biasing force that pushes the relay driven roller 42b toward the relay drive roller 42a decreases, and the nip pressure between the relay roller 42 weakens. Note that the manual feed bottom plate 34 remains separated from the manual feed paper roller 32, so manual feeding is not possible, but this does not cause any problems as manual feeding is not performed during main paper feeding.

[0068] When the pressing portion 65e on the manual insertion bottom plate cam shaft 65 is in the non-pressed position shown in Figure 8(a), the pressure plate 37d moves away from the intermediate drive roller 42a due to the biasing force of the pressure spring 37b, the pressure spring 37b stretches to its free length, its compression becomes zero, and the biasing force of the pressure spring 37b becomes zero. As a result, the biasing force that biases the intermediate driven roller 42b toward the intermediate drive roller 42a becomes zero, and the nip pressure between the intermediate rollers 42 becomes zero nip pressure.

[0069] According to this embodiment, the operation of the manual feed bottom plate cam shaft 65 of the manual feed bottom plate 34, which is a movable member used for sheet transport in the manual feed path R2, can be used to switch the nip pressure (biasing force of the pressure spring 37b) of the intermediate roller pair 42 in the main paper feed path R1 in three stages. This makes it possible to achieve this switching with a simple configuration that does not require a dedicated operating means for switching the nip pressure of the intermediate roller pair 42.

[0070] Next, we will describe a detection means that uses a filler sensor 65c to detect whether or not the cam detection filler 65b, which is a detected part that moves in conjunction with the rotational movement of the manual insertion bottom plate cam shaft 65, is present within the detection area. Figures 9 and 10 are explanatory diagrams showing a detection means for detecting the cam detection filler 65b with a filler sensor 65c.

[0071] In this embodiment, by rotating the manual insertion bottom plate cam shaft 65, the pressing portion 65e, which is integrally formed with the manual insertion bottom plate cam 35, can take a position in which it contacts and presses down the push-down lever 65d that presses down the cam detection filler 65b, as shown in Figures 9(a) and (b), and a position in which it does not press down the push-down lever 65d, as shown in Figures 10(a) and (b). As a result, the cam detection filler 65b can take a state in which it does not obstruct the detection area of ​​the filler sensor 65c, as shown in Figures 9(a) and (b), and a state in which it obstructs 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.

[0072] As shown in Figures 9(a) and (b), when the cam detection filler 65b obstructs 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 base plate cam shaft 65 is such that the manual feed base plate 34 is lowered (the manual feed base plate 34 is separated from the manual feed paper roller 32). On the other hand, as shown in Figures 10(a) and (b), when the cam detection filler 65b does not obstruct 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 base plate cam shaft 65 is such that the manual feed base plate 34 is raised (the manual feed base plate 34 is in contact with the manual feed paper roller 32).

[0073] Since the manual feed base plate 34 only moves to two positions, an upward position and a downward position, the detection means only needs to be able to distinguish and detect these two positions. For this reason, a simple configuration is adopted for the detection means, consisting of a cam detection filler 65b that moves in conjunction with the rotational movement of the manual feed base plate cam shaft 65 of the manual feed base plate 34, and a filler sensor 65c, which is an optical sensor that detects the presence or absence of the cam detection filler 65b within the detection area.

[0074] In a conventional configuration where the nip pressure (biasing force of the pressure spring 37b) of the intermediate roller pair 42 is switched between two stages, high nip pressure and low nip pressure, each position of the manual insertion base plate (up position and down position), which is also switched between two stages, is matched one-to-one with each nip pressure (high nip pressure and low nip pressure) of the intermediate roller pair 42. This makes it possible to determine the nip pressure (biasing force of the pressure spring 37b) of the intermediate roller pair 42 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 insertion base plate 34.

[0075] However, with this conventional configuration, it is not possible to distinguish and identify the nip pressure (biasing force of the pressure spring 37b) of the intermediate roller pair 42 in three or more stages, and therefore it is not possible to switch the nip pressure (biasing force of the pressure spring 37b) of the intermediate roller pair 42 in three or more stages. While it would be possible to switch the nip pressure of the intermediate roller pair 42 in three or more stages by providing a new component (such as a new sensor) to distinguish and identify the nip pressure in three or more stages, this would increase costs.

[0076] Therefore, in this embodiment, the nip pressure of the relay roller pair 42 (biasing force of the pressure spring 37b) is determined not only by the detection result (on or off) of the detection means composed of the cam detection filler 65b and filler sensor 65c described above, but also by utilizing information on the direction of movement of the cam detection filler 65b (i.e., the rotation direction of the manual insertion bottom plate cam shaft 65). As a result, even with a simple detection means that can only distinguish and detect two states, whether or not the cam detection filler 65b is within the detection area of ​​the filler sensor 65c, it becomes possible to distinguish and determine the nip pressure of the relay roller pair 42 in three or more stages by combining it with information on the direction of movement of the cam detection filler 65b.

[0077] In other words, by using this combination, it is possible to distinguish and understand the rotational position of the manual feed bottom plate cam shaft 65 when the cam detection filler 65b exits and stops from one side of the detection area, the rotational position of the manual feed bottom plate cam shaft 65 when the cam detection filler 65b enters and stops from one side of the detection area, the rotational position of the manual feed bottom plate cam shaft 65 when the cam detection filler 65b exits and stops from the other side of the detection area, and the rotational position of the manual feed bottom plate cam shaft 65 when the cam detection filler 65b enters and stops from the other side of the detection area. As a result, it becomes possible to distinguish and identify the nip pressure (biasing force of the pressure spring 37b) of the intermediate roller pair 42, which switches in conjunction with the rotational movement of the manual feed bottom plate cam shaft 65, in three or more stages, and to switch the nip pressure (biasing force of the pressure spring 37b) of the intermediate roller pair 42 in three or more stages without providing any new components.

[0078] Figure 11(a) is an explanatory diagram showing the rotational position of the manual insertion bottom plate cam shaft 65 when the nip pressure of the intermediate roller pair 42 is zero nip pressure, Figure 11(b) is an explanatory diagram showing the rotational position of the manual insertion bottom plate cam shaft 65 when the nip pressure of the intermediate roller pair 42 is low nip pressure, and Figure 11(c) is an explanatory diagram showing the rotational position of the manual insertion bottom plate cam shaft 65 when the nip pressure of the intermediate roller pair 42 is high nip pressure. Furthermore, Table 1 below shows the relationship between the position of the manual feed base plate 34, the nip pressure of the relay roller pair 42, and the output state of the filler sensor 65c.

[0079] [Table 1]

[0080] In this embodiment, the rotational position of the manual feed bottom plate cam shaft 65 when the nip pressure of the intermediate roller pair 42 is low is defined as the home position, and the output of the filler sensor 65c is turned on. More specifically, in this embodiment, the home position is the stopping 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 rotation direction B2 shown in Figure 11(b).

[0081] When the manual feed bottom plate cam shaft 65 stops in this home position, the manual feed bottom plate cam 35 on the manual feed bottom plate cam shaft 65 pushes down the bottom plate guide portion 34a, causing the manual feed bottom plate 34 to take the lowered position (the position where the manual feed bottom plate 34 is separated from the manual feed paper roller 32). At this time, the pressing portion 65e on the manual feed bottom plate cam shaft 65 is in a low-pressure position as shown in Figure 11(b), the pressure spring 37b stretches, its compression is reduced, and the biasing force of the pressure spring 37b becomes low. As a result, the biasing force that biases the intermediate driven roller 42b toward the intermediate driven roller 42a becomes low, and the nip pressure between the intermediate rollers 42 becomes low nip pressure.

[0082] When controlling the manual feed bottom plate 34 to move to the raised position, or when controlling the nip pressure of the intermediate roller pair 42 to switch to a high nip pressure, the control unit 51 rotates the manual feed bottom plate cam shaft 65 in the forward direction B2 shown in Figure 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 (Figure 11(c)).

[0083] When the manual insertion bottom plate cam shaft 65 stops at this rotational position, the manual insertion bottom plate cam 35 on the manual insertion bottom plate cam shaft 65 separates from the bottom plate guide portion 34a, and the manual insertion bottom plate 34 takes an elevated position due to the biasing force of the bottom plate spring 36. At this time, the pressing portion 65e on the manual insertion bottom plate cam shaft 65 is in a high-pressure position as shown in Figure 11(c), and the pressure spring 37b compresses, and the amount of compression increases, so the biasing force of the pressure spring 37b increases. As a result, the biasing force that biases the intermediate driven roller 42b toward the intermediate driven roller 42a increases, and the nip pressure between the intermediate rollers 42 becomes high nip pressure.

[0084] On the other hand, when controlling the system to switch the nip pressure of the intermediate roller pair 42 to zero nip pressure from the home position (the manual feed base plate 34 is in the lowered position and the nip pressure of the intermediate roller pair 42 is low nip pressure), the control unit 51 rotates the manual feed base plate cam shaft 65 in the reverse direction B1 shown in Figure 11(b). Then, immediately after the output of the filler sensor 65c switches from on to off, the rotation of the manual feed base plate cam shaft 65 is stopped (Figure 11(a)).

[0085] When the manual insertion bottom plate cam shaft 65 stops at this rotational position, the manual insertion bottom plate cam 35 on the manual insertion bottom plate cam shaft 65 remains in the same position as in the home position, pressing down the bottom plate guide portion 34a, and the manual insertion bottom plate 34 takes the same lowered position as in the home position. However, the pressing portion 65e on the manual insertion bottom plate cam shaft 65 is in the unpressed position as shown in Figure 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 that biases the relay driven roller 42b toward the relay drive roller 42a becomes zero, and the nip pressure between the relay rollers 42 becomes zero nip pressure.

[0086] The above configuration can be achieved by appropriately adjusting the arrangement and shape of the manual insertion bottom plate cam 35 and pressing portion 65e provided on the manual insertion bottom plate cam shaft 65, as well as the arrangement and shape of the cam detection filler 65b.

[0087] Next, I will explain what happens when jam occurs. When a jam occurs when the nip pressure of the intermediate roller pair 42 is low (when transporting thin paper or regular paper), the rotation position of the manual feed bottom plate cam shaft 65 is at the home position at the time of the jam. Therefore, the control unit 51 rotates the manual feed bottom plate cam shaft 65 in the reverse direction B1 shown in Figure 11(b), and when the output of the filler sensor 65c switches from on to off, it controls the rotation of the manual feed bottom plate cam shaft 65. As a result, the nip pressure of the intermediate roller pair 42 switches to zero nip pressure.

[0088] After completing jam removal, such as removing the recording sheet S held between the relay roller pair 42, the control unit 51 rotates the manual feed bottom plate cam shaft 65 in the forward direction B2 shown in Figure 11(b) to return the nip pressure of the relay roller pair 42 to its 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. As a result, the rotation position of the manual feed bottom plate cam shaft 65 returns to the home position, and the nip pressure of the relay roller pair 42 switches to low nip pressure. Printing is then resumed.

[0089] On the other hand, if a jam occurs when the nip pressure of the intermediate roller pair 42 is high (when transporting cardboard), the control unit 51 first rotates the manual feed bottom plate cam shaft 65 in the forward direction B2 shown in Figure 11(b) to return its rotational position 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. This returns the rotational position of the manual feed bottom plate cam shaft 65 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 Figure 11(b), and when the output of the filler sensor 65c switches from on to off, it controls the rotation of the manual feed bottom plate cam shaft 65 to stop. This switches the nip pressure of the intermediate roller pair 42 to zero nip pressure.

[0090] After completing jamming procedures such as removing the recording sheet S held between the relay roller pair 42, the control unit 51 rotates the manual feed bottom plate cam shaft 65 in the forward direction B2 shown in Figure 11(b) to return the nip pressure of the relay roller pair 42 to its original nip pressure, i.e., 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. This returns the rotation position of the manual feed bottom plate cam shaft 65 to the home position. Subsequently, the control unit 51 rotates the manual feed bottom plate cam shaft 65 further in the forward direction B2 shown in Figure 11(b), and when the output of the filler sensor 65c switches from on to off, it stops the rotation of the manual feed bottom plate cam shaft 65. This switches the nip pressure of the relay roller pair 42 to high nip pressure.

[0091] In this embodiment, the nip pressure (biasing force of the pressure spring 37b) of the relay roller pair 42 used in the main paper feed path R1 is switched in conjunction with the operation of the manual feed bottom plate cam shaft 65, which is a movable member used in the manual feed path R2, but this is not limited to this. For example, if the manual feed section 30 employs a sheet feeding means that lowers the manual feed roller 32 to press the manual feed roller 32 against the recording sheet on the manual feed tray and feed it out, the manual feed roller 32 or its drive member may be made 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 drive member. Alternatively, for example, the switch may be linked to the operation of a movable member used in a paper feed path other than the manual feed path R2 (e.g., the reverse refeed path R5).

[0092] Furthermore, although this embodiment describes a configuration for switching the nip pressure (biasing force of the pressure spring 37b) of the intermediate roller pair 42 used in the main paper feed path R1, it is also possible to apply this to other configurations, such as switching the nip pressure of other transport roller pairs (for example, the paper discharge roller pair 46). Also, although the intermediate roller pair 42 whose nip pressure was switched in this embodiment is a transport roller pair in which one is a drive roller and the other is a driven roller, it may also be a transport roller pair in which both are drive rollers or both are driven rollers.

[0093] Furthermore, although this embodiment uses a printer as an example of an image forming apparatus, it may also be an image forming apparatus such as a copier equipped with an image reading device or a multifunction device that also has functions such as a facsimile. Moreover, it is not limited to image forming apparatuses that form images using the electrophotographic method, but can also be applied to image forming apparatuses that form images using other methods, such as the inkjet method or the toner projection method described in Japanese Patent Application Publication No. 2002-307737.In addition, it is not limited to image forming apparatuses, but may also be an image reading device equipped with an automatic feeder (ADF), as long as it is equipped with a sheet transport device.

[0094] The above is just one example; each of the following embodiments produces its own unique effects. [First aspect] The first embodiment is a sheet conveying device comprising: a pair of rollers (e.g., a pair of relay rollers 42) that grips a sheet (e.g., a recording sheet S) being conveyed in a first conveying path (e.g., a main paper feed path R1); a biasing means (e.g., a pressure spring 37b) that biases one roller constituting the roller pair (e.g., a relay drive roller 42a) toward the other roller (e.g., a relay driven roller 42b); a biasing force switching means (e.g., a pressure plate 37d, a pressing part 65e, etc.) that switches the biasing force by the biasing means; and a control means (e.g., a control unit 51) that switches the biasing force by the biasing force switching means, wherein the biasing force switching means is located in a second conveying path (e.g., a manual feed path R2) The system switches the biasing force applied by the biasing means 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., a manual insertion bottom plate cam shaft 65) that operates when the sheet is transported. The system also includes a detection means (e.g., a filler sensor 65c) that detects whether a detected part (e.g., a cam detection filler 65b) that moves in conjunction with the operation of the movable member is within a detection area. The control means is characterized in that it identifies the biasing force applied by the biasing means based on the detection result of the detection means and the direction of operation of the movable member (e.g., the rotation direction of the manual insertion bottom plate cam shaft 65). Conventional sheet transport devices switch the biasing force (nip pressure of the roller pair) in two stages by a biasing means that biases one roller of a roller pair in the main paper feed path (first transport path) toward the other roller, in conjunction with the raising and lowering movement of the manual feed bottom plate (movable member) in the manual feed path (second transport path). At this time, the control means that performs this switching utilizes a detection means that detects the position of the manual feed bottom plate. Since the manual feed bottom plate only moves to two positions, an raised position and a lowered position, the detection means only needs to be able to distinguish and detect these two positions. For this reason, a simple configuration is adopted for this detection means, for example, a detection filler (detected part) that moves in conjunction with the movement of the manual feed bottom plate, and an optical sensor that detects the presence or absence of the detection filler within the detection area. Conventional sheet conveying devices have a one-to-one correspondence between two possible positions for the manual feed base plate and two possible biasing forces (two nip pressures that a roller pair can take) that the biasing means can apply. This allows the control means to use a detection means that detects the position of the manual feed base plate to identify which of the two biasing forces the biasing means is applying, thereby enabling appropriate control of the switching of the nip pressure. However, with this configuration, it was not possible to distinguish and identify three or more biasing forces applied by the biasing means, and therefore it was not possible to switch the biasing force applied by the biasing means (nip pressure of the roller pair) in 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 from the biasing means, it would be possible to switch between biasing forces from the biasing means in three or more stages, but this would lead to increased costs. In this embodiment, a configuration is adopted in which the biasing force provided by the biasing means is switched between three or more different biasing forces in conjunction with the movement of the movable member. The control means that performs this switching uses not only the detection result of a conventional detection means that detects whether or not the detected part, which moves in conjunction with the movement of the movable member, is within the detection area, but also information on the direction of movement (direction of movement) of the movable member to determine the biasing force provided by the biasing means. From the detection result of the detection means, only two operating positions of the movable member corresponding to two states, whether or not the detected part is within the detection area, can be distinguished and understood. However, by also using information on the direction of movement of the movable member, it becomes possible to distinguish and understand at least three operating positions of the movable member. For example, it is possible to distinguish and understand the operating position of the movable member when the detected part is within the detection area, the operating position of the movable member when the movable member moves in one direction and the detected part leaves the detection area, and the operating 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 provided 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 understood, it becomes possible to distinguish and identify at least three biasing forces provided by the biasing means. According to this embodiment, it is possible to distinguish and identify three or more biasing forces provided by the biasing means without adding any new components, and therefore it is possible to switch the biasing force provided by the biasing means (nip pressure of the roller pair) in three or more stages at low cost.

[0095] [Second aspect] The second embodiment is characterized in that, in the first embodiment, when a jam occurs in the sheet in the first transport path, the control means switches to the smallest biasing force among the three or more biasing forces (for example, zero nip pressure). According to this, it is possible to prevent the sheet from tearing when it is pulled out from between the roller pair during jamming.

[0096] [Third aspect] The third aspect is characterized in that, in the second aspect, the control means switches to the biasing force immediately before switching to the smallest biasing force after the jam has been resolved. According to this method, after the jam is cleared, the nip pressure of the roller pair is returned to the original nip pressure just before the jam occurred, allowing sheet conveying to be resumed quickly.

[0097] [Fourth aspect] The fourth aspect is characterized in that, in any of the first to third aspects, the smallest biasing force among the three or more biasing forces is zero. According to this, it is possible to prevent the sheet from tearing when it is pulled out from between the roller pair during jamming.

[0098] [Fifth aspect] The fifth embodiment is characterized in that, in any of the first to fourth embodiments, the movable member operates between a first position (for example, a position in which the manual insertion base plate 34 is in a lowered position) and a second position (for example, a position in which the manual insertion base 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 (biasing force by the biasing means) of the roller pair in the first transport path is performed in conjunction with the operation of the movable member used for sheet transport in the second transport path. When a sheet is being transported using a transport path selected from among multiple transport paths, no other transport paths are used for sheet transport. Therefore, when switching the nip pressure of the roller pair in the first transport path, operating the movable member used for sheet transport in the second transport path does not cause any problems. According to this embodiment, the contact pressure of the roller pair in the first transport path can be switched by utilizing the operation of the movable member used for sheet transport in the second transport path. Therefore, there is no need to provide a dedicated operating means for switching, which enables miniaturization of the device and reduction of costs.

[0099] [Sixth aspect] The sixth embodiment is characterized in that, in any of the first to fifth embodiments, it has a sheet mounting section (e.g., manual feed bottom plate 34) on which a sheet bundle is placed, and the movable member moves the sheet mounting section between a contact position (e.g., an upward position) in which the sheet bundle is brought into contact with a feeding member (e.g., a manual feed paper roller 32) that feeds the uppermost sheet of the sheet bundle, and a separation position (e.g., a downward position) in which the sheet bundle is separated from the feeding member. According to this, the contact pressure of the roller pair can be switched by using a means to move the sheet mounting section.

[0100] [Seventh aspect] The seventh embodiment is characterized in that, in any of the first to sixth embodiments, the movable member includes a rotating shaft (e.g., a manual insertion bottom plate cam shaft 65) having a cam portion (e.g., a pressing portion 65e) and a detected portion (e.g., a cam detection filler 65b) that constitute the biasing force switching means, and the control means performs the identification based on the detection result of the detection means and the operating direction of the movable member (e.g., the rotation direction of the manual insertion bottom plate cam shaft 65). According to this, the above-mentioned identification can be performed with a simple configuration.

[0101] [8th aspect] The eighth aspect is an image forming apparatus for forming an image on a sheet conveyed by a sheet conveying device, characterized in that the sheet conveying device is one of the sheet conveying devices of the first to seventh aspects. According to this embodiment, when switching the nip pressure of a pair of rollers that grip a sheet being transported in the first transport path in conjunction with the operation of a movable member that operates when a sheet is being transported in the second transport path, it is possible to provide an image forming apparatus that can switch the nip pressure in three or more stages at low cost. [Explanation of Symbols]

[0102] 1: Photoreceptor 30: Manual feed section 31: Manual feed tray 32: Manual feed roller 33: Separation pad 34: Manual bottom plate 35: Manual insertion bottom plate cam 36: Bottom plate spring 37a: Bearing part 37b: Compression spring 37d: Pressure plate 39: Opening and closing doors 41: Main paper feed roller 41A, 41B: Paper feed rollers 42: Relay Laura vs. 42A, 42B: Conveyor roller pair 42a: Relay drive roller 42b: Relay-driven roller 43: Resistola vs. 44: Fixing device 46: Paper output roller pair 48: Separation pad 48A, 48B: Separation pads 49: Resist Sensor 50: Main unit 51: Control Unit 61: Main motor 61a: Motor shaft 62: Paper feed roller shaft 62a: Main paper feed clutch 63: Relay roller shaft 63a: Relay clutch 64: Manual feed roller shaft 64a: Manual feed clutch 65: Manual insertion bottom plate cam shaft 65a: Manual bottom plate cam clutch 65b: Cam detection filler 65c: Filler sensor 65d: Push-down lever 65e: Pressing part 66: Roller shaft 100: Main paper feed tray 100: Paper feed tray 101: Main body paper feed bottom plate B1: Reverse direction B2: Forward rotation direction R1: Main paper feed path R2: Manual feed path R3: Common transport path R4: Paper ejection path R5: Reversal and retransmission path S: Record Sheet [Prior art documents] [Patent Documents]

[0103] [Patent Document 1] Japanese Patent Publication No. 2021-113105

Claims

1. A pair of rollers that grip the sheet being transported along the first transport path, A biasing means for biasing one roller constituting the roller pair toward the other roller, A biasing force switching means for switching the biasing force by the biasing means, A sheet conveying device comprising a control means for switching the biasing force using the biasing force switching means, The biasing force switching means switches the biasing force provided by the biasing means between three different biasing forces in conjunction with the operation of the movable member that operates when the sheet is transported along the second transport path. The system includes a detection means for detecting whether or not a detected part, which moves in conjunction with the operation of the movable member, is located within the detection area. The movable member includes a rotating shaft comprising a cam portion and a detected portion that constitute the biasing force switching means. The sheet conveying device is characterized in that the control means determines the biasing force by the biasing means based on the detection result of the detection means and the operating direction of the movable member.

2. In the sheet conveying device according to claim 1, The sheet conveying device is characterized in that, when a jam occurs in the sheet in the first conveying path, the control means switches to the smallest biasing force among the three biasing forces.

3. In the sheet conveying device according to claim 2, The sheet conveying device is characterized in that, after the jam is cleared, it switches to the biasing force immediately before switching to the smallest biasing force.

4. In the sheet conveying device according to any one of claims 1 to 3, A sheet conveying device characterized in that the smallest of the three biasing forces is zero.

5. In the sheet conveying device according to any one of claims 1 to 3, The aforementioned movable member moves between a first position and a second position, The sheet conveying device is characterized in that the control means performs movable member control to position the movable member at the first position or the second position based on the detection result of the detection means.

6. In the sheet conveying device according to any one of claims 1 to 3, It has a sheet mounting section on which a sheet bundle is placed, The sheet conveying device is characterized in that the movable member moves the sheet placement portion between a contact position in which the sheet bundle is brought into contact with a feeding member that feeds the uppermost sheet of the sheet bundle, and a separation position in which the sheet bundle is separated from the feeding member.

7. An image forming apparatus for forming an image on a sheet conveyed by a sheet conveying device, An image forming apparatus characterized in that the sheet transport device is the sheet transport device described in any one of claims 1 to 3.

Images