JP7425988B2 - Image forming device - Google Patents

Description

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

2. Description of the Related Art Conventionally, sheet conveyance devices are known that include a pair of rollers that sandwich a sheet to be conveyed, and a biasing means that biases one roller constituting the pair of rollers toward the other roller.

For example, Patent Document 1 discloses a sheet conveyance device that includes a pair of rollers in which a conveyance roller is brought into pressure contact with a conveyance roller to form a nip. In this device, when a jam is detected, the arm member is operated by the solenoid of the nip release mechanism, and the shaft of the conveying roller moves in a direction away from the conveying roller. As a result, the nip pressure between the conveyance roller and the conveyance roller is released, and the nip pressure (contact pressure) acting between the conveyance roller and the conveyance roller becomes low.

Generally, when a jam occurs and it is attempted to pull out a sheet held between a pair of rollers, if the contact pressure between the pair of rollers is low, it is possible to pull out the sheet without tearing the sheet. However, with the conventional mechanism that operates a solenoid, which is a means for releasing the nip between the roller pairs, based on the detection result of the jam detection sensor to separate the roller pairs, the problem may occur due to false detection or failure of the jam detection sensor, or failure of the solenoid. In some cases, it becomes impossible to release the contact pressure between the roller pair even though a jam has occurred. In other words, if the conventional structure is such that the contact pressure between the pair of rollers is released after detecting a jam, the sheet may be torn when it is pulled out.
Furthermore, in the case where the image forming apparatus has a mechanism that separates the roller pair by operating a solenoid as described above, the solenoid becomes inoperable (hereinafter referred to as "immediate decision") as soon as a jam occurs. Similarly to the above, a problem arises due to the inability to release the contact pressure between the roller pair.
Furthermore, since a solenoid is used, the mechanism for separating the roller pair becomes complicated, resulting in problems such as an increase in the size and cost of the device.

In order to solve the above-mentioned problems, the present invention provides an image forming apparatus that forms an image on a sheet conveyed by a sheet conveyance device, wherein the sheet conveyance device is configured such that rollers cannot be separated from each other, and a pair of rollers that sandwich a sheet conveyed through a first conveyance path of a plurality of conveyance paths ; a biasing means that biases one roller constituting the pair of rollers toward the other roller ; and biasing force switching means for switching the biasing force of the biasing means depending on the type of the sheet before the sheet is sandwiched between the pairs, and the biasing force switching means is configured to switch the biasing force of the biasing unit according to the type of the sheet, and the biasing force switching unit is configured to switch the biasing force of the biasing unit depending on the type of the sheet. The present invention is characterized in that the urging force of the urging means is switched in conjunction with the operation of a movable member that operates when the sheet is conveyed through the second conveyance path .

According to the present invention, even if the contact pressure of the roller pair cannot be released due to false detection or failure of the jam detection sensor, failure of the separation mechanism, or immediate decision of the image forming apparatus, the contact pressure of the roller pair can be prevented after a jam occurs. Since the operation of weakening the pressure is not required, it is possible to suppress sheet tearing when the sheet is pulled out from the pair of rollers.

1 is a schematic diagram showing a printer according to an embodiment. FIG. 2 is an enlarged schematic diagram showing an enlarged configuration of a photoreceptor and its surroundings in the same printer. FIG. 2 is a perspective view showing the main configurations of a main body paper feeding section that feeds recording sheets from a paper cassette in the printer, and a manual paper feeding section that feeds recording sheets from a manual tray. FIG. 3 is a perspective view showing the configuration of a drive system in the main body paper feeding section and the manual paper feeding section. FIG. 3 is an explanatory diagram for explaining paper feeding paths in the main body paper feeding section and the manual paper feeding section. 5 is a flowchart showing a control operation when feeding and transporting paper from the paper feeding section of the main body. FIG. 3 is a perspective view of the appearance of the manual paper feed section with the manual feed tray removed. FIG. 3 is a perspective view showing the main parts of the manual paper feed section. 7 is a flowchart showing a control operation when feeding and transporting paper from the manual paper feed section. FIG. 7 is a perspective view showing a state in which the manual feed bottom plate is separated from the manual paper feed roller. (a) and (b) are perspective views showing a state in which the opening/closing door to which the manual feed tray is attached is opened from the printer main body. (a) and (b) are perspective views showing a state in which the opening/closing door to which the manual feed tray is attached is closed in the printer main body. (a) and (b) are perspective views showing a state in which the opening/closing door is closed in the printer body and the manual feed tray is opened. (a) and (b) are explanatory views showing a biasing force switching means that switches the biasing force of a pressure spring that biases the bearing portion of the relay driven roller toward the relay drive roller. (a) and (b) are perspective views showing the main configuration of the biasing force switching means. (a) is a front view showing a mechanism that supports a relay driven roller. (b) is a perspective view of the same mechanism. (a) to (c) are explanatory diagrams showing locations where the pressing portion on the manual feed bottom plate camshaft presses the pressure plate. (a) and (b) are explanatory views showing the shape of a pressing part on the manual feed bottom plate camshaft. FIG. 7 is an explanatory diagram showing a deflection suppressing means for suppressing deflection of a manual feed bottom plate camshaft that includes a pressing portion that presses a pressure plate. 5 is a flowchart showing the flow of processing when the printer according to the embodiment stops abnormally. Here is an example where the maximum load operating position of the manual feed bottom plate camshaft when feeding recording sheets from the manual feed tray matches the maximum load operating position of the manual feed bottom plate camshaft when switching the nip pressure of the relay roller pair. Graph showing. This example shows an example where the maximum load operating position of the manual feed bottom plate camshaft when feeding recording sheets from the manual feed tray is different from the maximum load operating position of the manual feed bottom plate camshaft when switching the nip pressure between the relay roller pair. graph. Another example where the maximum load operating position of the manual feed bottom plate camshaft when feeding a recording sheet from the manual feed tray is different from the maximum load operating position of the manual feed bottom plate camshaft when switching the nip pressure of the relay roller pair. Graph showing. A graph showing another example in which the amount of deviation is further increased. (a) and (b) are perspective views showing the main structure of biasing force switching means. FIG. 3 is an enlarged view showing a location where a pressure plate contacts a mounting member attached to a support frame of a manual paper feed unit. FIG. 3 is an external perspective view of the relay roller pair viewed diagonally from below.

DESCRIPTION OF THE PREFERRED EMBODIMENTS An example of an image forming apparatus to which the present invention is applied is 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 photoreceptor 1 as a latent image carrier, a paper feed cassette 100 as a sheet storage means configured to be removably attached to a main body housing 50, and the like. Inside the paper feed cassette 100, a plurality of recording sheets S are stored in the form of a sheet bundle.

The recording sheets S in the paper feed cassette 100 are fed out from the cassette by rotation of the main body paper feed roller 41, and only the uppermost sheet is separated and sent out at the separation nip between the main body paper feed roller 41 and the separation pad 48. Then, it reaches the main paper feed path R1, which is the first conveyance path. Thereafter, the recording sheet S is sandwiched (pinched) by the conveyance nip of the relay roller pair 42, which is the upper pair of conveyance rollers, and conveyed from the upstream side to the downstream side in the conveyance direction within the main body paper feed path R1. . Note that the pair of conveying rollers may be a pair of conveying bodies in which at least one of them is a belt.

The downstream end of the main body paper feed path R1 communicates with a common transport path R3, and a registration roller pair 43 is disposed in the common transport path R3. In the common conveyance path R3, a registration sensor 49 for detecting the recording sheet S is arranged upstream of the pair of registration rollers 43 in the conveyance direction. Conveyance of the recording sheet S is temporarily stopped with the leading end of the recording sheet S hitting the nip between the stopped pair of registration rollers 43. During the abutment, the skew of the recording sheet S is corrected. Note that the registration sensor 49 is also used for initial operations and operations for checking remaining sheets (jam detection operations) when canceling an abnormal stop of the apparatus.

The registration roller pair 43 starts rotating 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, and feeds the recording sheet S toward the transfer nip. At this time, the relay roller pair 42 starts rotating at the same time, and restarts the temporarily stopped conveyance of the recording sheet S.

The main body casing 50 of this printer is provided with a manual paper feed unit 30 as a manual feed unit, which 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, etc. ing. Details of the manual paper feed section 30 will be described later. The recording sheet S manually fed into the manual feed tray 31 of the manual feed section 30 is sent out from the manual feed tray 31 to the manual feed path R2, which is a second conveyance path, by the rotation of the manual feed roller 32. The downstream end of the manual paper feed path R2 joins the common conveyance path R3 together with the downstream end of the main body paper feed path R1. The recording sheet S sent out by the manual paper feed roller 32 passes through a separation nip due to contact between the manual paper feed roller 32 and the separation pad 33 in the manual paper feed path R2, and is then fed into the common conveyance path R3. It is transported to a pair of registration rollers 43. Thereafter, like the recording sheet S sent out from the paper feed cassette 100, the recording sheet S is sent to the transfer nip after passing through a pair of registration rollers 43.

FIG. 2 is an enlarged schematic diagram showing the photoreceptor 1 and its surrounding structure in this printer.
A cleaning blade 2, a collection screw 3, a charging roller 4, a charging cleaning roller 5, a scraper 6, a latent image writing device 7, a developing device 8, a transfer roller 10, etc. are provided. A charging roller 4 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 4 from a charging power source. Thereby, 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 4 in the charging nip.

The latent image writing device 7 includes an LED array, and performs optical writing on the uniformly charged surface of the photoreceptor 1 using LED light. Among the uniformly charged surface portions of the photoreceptor 1, the potential of the area irradiated with the writing light is attenuated, and an electrostatic latent image is formed on the surface of the photoreceptor 1.

As the photoreceptor 1 rotates, the electrostatic latent image passes through a developing area facing the developing device 8 . The developing device 8 includes a circulating transport section and a developing section, and the circulating transport section accommodates a developer containing toner and magnetic carrier. The circulation conveyance section includes a first screw 8b that conveys the developer to be supplied to the developing roller 8a, and a second screw 8c that conveys the developer in an independent space located directly below the first screw 8b. There is. Furthermore, it also has an inclined screw 8d for transferring the developer from the second screw 8c to the first screw 8b. The developing roller 8a, the first screw 8b, and the second screw 8c are arranged parallel to each other. On the other hand, the inclined screw 8d is arranged in an attitude inclined from them.

The first screw 8b transports the developer from the back side toward the front side in a direction perpendicular to the plane of the drawing as it rotates. At this time, a part of the developer is supplied to the developing roller 8a disposed opposite to the developing roller 8a. The developer transported by the first screw 8b to the vicinity of the near end in the direction perpendicular to the plane of the drawing is dropped onto the second screw 8c.

The second screw 8c, while receiving the used developer from the developing roller 8a, transports the received developer from the back side to the front side in the direction perpendicular to the plane of the drawing in accordance with its own rotational drive. . The developer transported by the second screw 8c to the vicinity of the near end in the direction perpendicular to the plane of the drawing is transferred to the inclined screw 8d. Then, as the inclined screw 8d is rotated, it is transported from the front side to the back side in the direction perpendicular to the plane of the drawing, and then is transferred to the first screw 8b near the end on the back side in the same direction. It is handed over.

The developing roller 8a includes a rotatable developing sleeve made of a cylindrical non-magnetic member, and a magnet roller fixed within the sleeve so as not to rotate along with the developing sleeve. Then, a part of the developer being conveyed by the first screw 8b is drawn up on the surface of the developing sleeve by the magnetic force of the magnet roller. The developer supported on the surface of the developing sleeve is transported as the developing sleeve rotates, and its layer thickness is regulated when it passes through a position where the developing sleeve and the doctor blade face each other. Thereafter, the toner is transported to a developing area facing the photoreceptor 1 while rubbing against the surface of the photoreceptor 1 .

A developing bias having the same polarity as the uniform charging potential (background potential) of the toner and the photoreceptor 1 is applied to the developing sleeve. The absolute value of this developing bias is larger than the absolute value of the latent image potential and smaller than the absolute value of the background potential. Therefore, in the development region, a development potential acts between the electrostatic latent image on the photoconductor 1 and the development sleeve to electrostatically move the toner from the development sleeve side to the photoconductor 1 side. On the other hand, a background potential that electrostatically moves toner from the photoconductor 1 side to the development sleeve side acts between the background portion of the photoconductor 1 and the developing sleeve. As a result, in the development area, toner selectively adheres to the electrostatic latent image on the photoreceptor 1, and the electrostatic latent image is developed.

The developer that has passed through the developing area enters the opposing area between the developing sleeve and the second screw 8c as the developing sleeve rotates. In this opposing region, a repulsive magnetic field is formed by two magnetic poles having the same polarity among the plurality of magnetic poles included in the magnet roller. The developer that has entered the opposing area is separated from the surface of the developing sleeve by the action of the repulsive magnetic field and is collected by the second screw 8c.

The developer conveyed by the inclined screw 8d contains the developer recovered from the developing roller 8a, and since this developer contributes to development in the development area, the toner concentration is reduced. The developing device 8 includes a toner concentration sensor that detects the toner concentration of the developer conveyed by the inclined screw 8d. A control unit 51 including a semiconductor circuit such as a CPU outputs a replenishment operation signal for replenishing toner to the developer transported by the inclined screw 8d, as necessary, based on the detection result by the toner concentration sensor.

A toner cartridge 9 is disposed above the developing device 8 . This toner cartridge 9 agitates the toner contained therein by an agitator 9b fixed to a rotating shaft member 9a. The toner replenishing member 9c is rotationally driven in response to a replenishment operation signal output from the control unit 51, thereby replenishing the inclined screw 8d of the developing device 8 with an amount of toner corresponding to the amount of rotational drive.

As the photoreceptor 1 rotates, the toner image formed on the photoreceptor 1 by development enters a transfer nip where the photoreceptor 1 and the transfer roller 10 come into contact. A voltage having a polarity opposite to the potential of the latent image on the photoreceptor 1 is applied to the transfer roller 10, thereby forming a transfer bias within the transfer nip.

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 photoreceptor 1 within the transfer nip. The toner image on the photoreceptor 1 is transferred to the recording sheet that is brought into close contact with the toner image at the transfer nip due to the action of transfer bias and nip pressure.

Transfer residual toner that was not transferred to the recording sheet S adheres to the surface of the photoreceptor 1 after passing through the transfer nip. After the transfer residual toner is scraped off from the surface of the photoreceptor 1 by a cleaning blade 2 that is in contact with the photoreceptor 1, it is conveyed by a collection screw 3 and sent to a waste toner bottle.

The surface of the photoreceptor 1 that has been cleaned by the cleaning blade 2 is neutralized by a neutralizing means, and then uniformly charged by a charging roller 4 again. Foreign matter such as toner additives and toner that has not been completely removed by the cleaning blade 2 adheres to the charging roller 4 that is in contact with the surface of the photoreceptor 1 . After this foreign matter is transferred to the charging cleaning roller 5 which is in contact with the charging roller 4, it is scraped off from the surface of the charging cleaning roller 5 by the scraper 6 which is in contact with the charging cleaning roller 5. The scraped foreign matter falls onto the recovery screw 3 mentioned above.

In FIG. 1, the recording sheet S that has passed through the transfer nip where the photoreceptor 1 and the transfer roller 10 are in contact with each other is sent to the fixing device 44. The fixing device 44 forms a fixing nip by abutting a fixing roller 44a containing a heat generating source such as a halogen lamp with a pressure roller 44b that is pressed against the fixing roller 44a. A toner image is fixed on the surface of the recording sheet S sandwiched in the fixing nip by the action of heat and pressure. Thereafter, the recording sheet S that has passed through the fixing device 44 passes through a paper discharge path R4, and is then nipped in a paper discharge nip between a pair of paper discharge rollers 46.

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 images are formed on both sides of the recording sheet S. In the case of single-sided mode or double-sided mode where images have already been formed on both sides of the recording sheet, the pair of paper ejection rollers 46 continues to rotate in the normal direction, thereby removing the recording sheet S in the paper ejection path R4. is discharged outside the machine. The ejected recording sheets S are stacked in a stack section provided on the top surface of the main body casing 50.

On the other hand, when the duplex mode is used and an image is formed only on one side of the recording sheet S, at the timing when the rear end of the recording sheet S enters the paper ejection nip of the paper ejection roller pair 46, The paper ejection roller pair 46 is driven in the reverse direction. At this time, the switching claw 47 disposed near the downstream end of the sheet discharge path R4 is activated to close the sheet discharge path R4 and open the entrance of the reverse refeed path R5. The recording sheet S, which has started to move backward by the reverse drive of the pair of paper discharge rollers 46, is sent into the reverse refeed path R5. The downstream end of the reversal retransmission path R5 merges with the upstream side of the pair of registration rollers 43 of the common transport path R3, and after being transported within the reversal retransmission path R5, it is retransmitted to the pair of registration rollers 43 of the common transport path R3. be done. Thereafter, after the toner image is transferred to the other side in the transfer nip, the sheet is discharged outside the machine via the fixing device 44, the sheet discharge path R4, and the pair of sheet discharge rollers 46.

Next, the configuration and operation related to feeding the recording sheet S will be explained.
FIG. 3 is a perspective view showing the main configurations of a main body paper feeding section that feeds recording sheets S from the paper cassette 100 and a manual paper feeding section 30 that feeds recording sheets S from the manual tray 31. .
FIG. 4 is a perspective view showing the structure of the drive system in the main paper feeding section and the manual paper feeding section 30.

As shown in FIGS. 3 and 4, the drive system in the main body paper feeding section and the manual paper feeding section 30 transfers the driving force from a single main motor 61 to the main body paper feeding roller 41, the relay roller pair 42, and the manual feeding section. It is configured to drive the paper roller 32 and the manual feed bottom plate cam 35 in a distributed manner. Specifically, the driving force output from the motor shaft 61a of the main motor 61 is transmitted via each idler gear to the paper feed roller shaft 62 where the main paper feed roller 41 is provided, and the relay roller where the relay roller pair 42 is provided. It is configured to be transmitted to a shaft 63, a manual paper feed roller shaft 64 on which the manual paper feed roller 32 is provided, and a manual bottom plate cam shaft 65 on which the manual bottom plate cam 35 is provided.

The paper feed roller shaft 62, the relay roller shaft 63, the manual paper feed roller shaft 64, and the manual bottom plate cam shaft 65 are each provided with clutches 62a, 63a, 64a, and 65a for turning on/off transmission of driving force. There is. When the power to each clutch is turned on, the driving force is transmitted and each shaft 62, 63, 64, 65 is rotated, and when the power to each clutch is turned off, the transmission of the driving force is cut off, and each shaft is rotated. 62, 63, 64, and 65 are not rotationally driven. Note that 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 each clutch on/off by the control unit 51.

FIG. 5 is an explanatory diagram for explaining paper feeding paths in the main body paper feeding section and the manual paper feeding section 30.
First, the case where paper is fed and conveyed from the main body paper feeding section will be described with reference to the flowchart shown in FIG.
Since the main body paper feed bottom plate 101 is biased upward toward the main body paper feed roller 41, the main body paper feed roller 41 can collect the plurality of records placed in the form of a sheet bundle on the main body paper feed bottom plate 101. It is in contact with the uppermost recording sheet S among the sheets S. When starting feeding and conveying paper from the paper feed section of the main body, the control section 51 first checks whether the initial operation has been completed (S1), and if the initial operation has not been completed (No in S1), , starts the initial operation (S2). Here, the "initial operation" is an operation that brings the manual feed bottom plate 34 to the lowest position (see FIGS. 10, 14(a), and 15(a)). After completing this initial operation, the nip pressure between the relay roller pair 42 is set to a low state.

After the initial operation is completed (Yes in S1), 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 operation panel of the printer to select the recording sheet S stored in the paper cassette 100, for example, plain paper (a sheet with low strength), thin paper (a sheet with low strength), thick paper ( One of the sheet types that can be printed by the printer, such as a high-strength sheet), is selected, and the selection result is stored in the storage section of the control section 51. In processing step S4 of this embodiment, the control section 51 refers to the contents of this storage section and determines whether the recording sheet S to be fed is thin paper or plain paper.

Note that the method for determining whether paper is thin paper or plain paper is not limited to this, and for example, the thickness of the recording sheet S stored in the paper feed cassette 100 or the recording sheet S fed from the paper feed cassette 100 may be used. may be detected by a thickness detection sensor, and the judgment may be made based on the detection result.

In addition, in this embodiment, the type of recording sheet S to be determined is based on the difference in the thickness of the recording sheet S, but for example, the type of recording sheet S is determined based on the difference in the thickness of the recording sheet S. This may be due to a difference in characteristics that affects the strength of the recording sheet S or the transport load of the recording sheet S.

In this embodiment, when it is determined that the paper is thin paper or plain paper (Yes in S4), the control unit 51 controls the nip pressure of the relay roller pair 42 to be in a low state due to the above-mentioned initial operation. Maintain low pressure.

On the other hand, if it is determined that the paper is not thin paper or plain paper (if it is determined that it is thick paper) (No in S4), the control unit 51 executes a processing operation to increase the nip pressure between the relay roller pair 42. Specifically, during the initial operation, the nip pressure between the pair of relay rollers 42 is low, so the control unit 51 turns on the manual feed bottom plate cam clutch 65a (S5), and moves the manual feed bottom plate cam shaft 65 in the direction shown in FIG. When the filler sensor 65c is turned off (Yes in S6) (see FIGS. 8, 14(b), and 15(b)), the manual feed bottom plate cam clutch 65a is turned off ( S7), the rotation of the manual feed bottom plate camshaft 65 is stopped.

As shown in FIG. 5, the other relay driven roller 42b constituting the relay roller pair 42 has a bearing portion 37a that supports the roller shaft 66, and is biased by a pressure spring 37b, which is a compression spring. It is in contact with the relay drive roller 42a. When the manual feed bottom plate camshaft 65 is stopped at the rotational position described above, the amount of compression of the pressure spring 37b increases, and the nip pressure between the rollers of the relay roller pair 42 is switched to a high state. Note that the configuration for switching the nip pressure between the relay roller pair 42 will be described later.

After that, the control unit 51 turns on the main paper feed clutch 62a and the relay clutch 63a (S8). As a result, the main paper feed roller 41 is driven to rotate, and the uppermost recording sheet S in the paper feed cassette 100 is sent out to the separation pad 48 side. 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 conveyance of the second and subsequent recording sheets is hindered by the frictional force with the separation pad 48, and the topmost recording sheet Only the sheet S can pass through the separation pad 48. Note that while paper is being fed and transported from the main body paper feeding section, since paper is not being fed and transported from the manual paper feeding section 30, the manual paper feeding clutch 64a and the manual feeding bottom plate cam clutch 65a remain in the off state.

After that, the fed-out recording sheet S is conveyed along the main body paper feeding path indicated by the symbol R1 in FIG. At this time, one relay drive roller 42a constituting the relay roller pair 42 is rotationally driven by the driving force from the main motor 61. In addition, the other relay driven roller 42b constituting the relay roller pair 42 has a low urging force when using thin paper or plain paper, and a high urging force when using thick paper, and the bearing portion 37a that supports the roller shaft 66 is pressed by the pressure spring 37b. It is biased and contacts 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 conveyed through the main body paper feed path R1 is conveyed in a state where it is nipped (nipped) 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 turns on the registration sensor 49 (Yes in S9), after a predetermined period of time (before the leading edge of the recording sheet S reaches the pair of registration rollers 43) (for example, the registration sensor 49 49), the main paper feed clutch 62a and the relay clutch 63a are turned off (S10), and conveyance 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 between the stopped pair of registration rollers 43, and the skew of the recording sheet S is corrected.

The control unit 51 activates the relay clutch 63a and the relay clutch 63a at a timing when the recording sheet S can be superimposed on the toner image on the surface of the photoreceptor 1 in the transfer nip (for example, 200 ms after turning off the main paper feed clutch 62a and the relay clutch 63a). Turn on the registration clutch (S11). As a result, the registration roller pair 43 and the relay roller pair 42 start rotating, and the recording sheet S is conveyed toward the transfer nip. At this time, the main body paper feed clutch 62a remains off, so the main body paper feed roller 41 is not rotationally driven. Even when the trailing end of the recording sheet S is still held between the main body paper feed roller 41 and the separation pad 48, the main body paper feed roller 41 is able to hold the recording sheet S conveyed by the conveyance force of the registration roller pair 43 and the relay roller pair 42. It rotates along with the transport, and does not interfere with transportation. When the rear end of the recording sheet S reaches the registration sensor 49 and the registration sensor 49 is turned off (Yes in S12), the relay clutch 63a is turned off (S13) and the rotational drive of the relay roller pair 42 is stopped. .

Next, the case where paper is fed and conveyed from the manual paper feed section 30 will be described with reference to FIGS. 7 to 9.
FIG. 7 is an external perspective view of the manual paper feed section 30 with the manual tray 31 removed.
FIG. 8 is a perspective view showing the main parts of the manual paper feed section 30.
FIG. 9 is a flowchart showing a control operation when feeding and transporting paper from the manual paper feed section 30.

The manual feed bottom plate 34 is urged upward toward the manual feed roller 32 by a bottom plate spring 36. Furthermore, as shown in FIG. 8, the manual feed bottom plate 34 is 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 comes into contact with the bottom plate guide portion 34a and pushes it down (see FIG. 10), the manual feed bottom plate 34 descends against the biasing force of the bottom plate spring 36. It moves away from the manual feed roller 32.

When starting feeding and conveying paper from the manual paper feed unit 30, the control unit 51 first checks whether the initial operation is completed (S21), and if the initial operation is not completed (No in S21). starts the initial operation (S22). After the initial operation is completed (Yes in S21), the control unit 51 turns on the main motor 61 (S23), and then first turns on the manual feed bottom plate cam clutch 65a (S24). As a result, the manual feed bottom plate cam shaft 65 is rotationally driven, and the manual feed bottom plate cam 35 changes from a state in which it is in contact with the bottom plate guide portion 34a (a state in which the manual feed bottom plate 34 is separated from the manual feed roller 32) (see FIG. 10). ), the manual feed bottom plate cam 35 transitions to a state in which it does not come into contact with the bottom plate guide portion 34a (see FIGS. 5 and 8).

Specifically, when the manual feed bottom plate cam shaft 65 is rotationally driven, the protruding plate 35a integrally formed with the manual feed bottom plate cam 35 comes into contact with the push-down lever 65d that pushes down the cam detection filler 65b, and moves the cam detection filler 65b from the push-down position (see FIG. 10). ), it rotates to a position where it does not come into contact with the push-down lever 65d. As a result, the cam detection filler 65b is raised by a predetermined urging force, and transitions to a state in which it blocks the filler sensor 65c (see FIG. 8). Note that the state in which the cam detection filler 65b blocks the filler sensor 65c (see FIG. 8) means that the filler sensor 65c is off, and the state in which the cam detection filler 65b does not block the filler sensor 65c (see FIG. 10) indicates that the filler sensor 65c is off. Sensor 65c is in an off state.

Then, when the filler sensor 65c is turned off (Yes in S25), the control unit 51 turns off the manual feed bottom plate cam clutch 65a (S26). As a result, the rotation of the manual feed bottom plate cam shaft 65 is stopped in a state where the manual feed bottom plate cam 35 does not contact the bottom plate guide portion 34a, and the manual feed bottom plate 34 is urged toward the manual feed roller 32 by the urging force of the bottom plate spring 36. become in a state of being As a result, the manual feed roller 32 comes into contact with the uppermost recording sheet S of the plurality of recording sheets S placed in a sheet bundle on the manual tray 31 and the manual feed bottom plate 34. .

Subsequently, the control unit 51 turns on the manual paper feed clutch 64a (S27). As a result, the manual feed roller 32 is driven to rotate, and the uppermost recording sheet S on the manual feed bottom plate 34 is sent out to the separation pad 33 side. 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 conveyance of the second and subsequent recording sheets is hindered by the frictional force with the separation pad 33, and the topmost recording sheet Only the sheet S can pass through the separation pad 33.

Note that while paper is being fed and conveyed from the manual paper feed section 30, since paper is not fed and conveyed from the main body paper feed section, the main body paper feed clutch 62a and the relay clutch 63a remain in the off state.

Thereafter, the fed-out recording sheet S is conveyed along a manual paper feed path indicated by the symbol R2 in FIG. Then, when the leading edge of the recording sheet S reaches the registration sensor 49 and the registration sensor 49 is turned on (Yes in S28), after a predetermined period of time has elapsed (before the leading edge of the recording sheet S reaches the pair of registration rollers 43), manually feed the recording sheet S. The paper feed clutch 64a is turned off (S29), and conveyance 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 between the stopped pair of registration rollers 43, and the skew of the recording sheet S is corrected.

The control unit 51 turns on the resist clutch at a timing when the recording sheet S can be superimposed on the toner image on the surface of the photoreceptor 1 in the transfer nip (S30). As a result, the registration roller pair 43 starts rotating, and the recording sheet S is conveyed toward the transfer nip.

As shown in FIG. 7, the manual paper feed section 30 in this embodiment has a unit structure in which a relay driven roller 42b, which is one of the rollers constituting the relay roller pair 42, is integrally supported with a manual paper feed mechanism. The unit is screwed and fixed to the main body casing 50. 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 casing 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 casing 50 are configured so that they cannot be separated from each other.

This point will be explained in more detail.
FIGS. 11A and 11B are perspective views showing a state in which the opening/closing door 39 to which the manual tray 31 is attached is opened from the printer main body.
FIGS. 12A and 12B are perspective views showing a state in which the opening/closing door 39 to which the manual tray 31 is attached is closed in the printer body.
FIGS. 13A and 13B are perspective views showing a state in which the opening/closing door 39 is closed in the printer body and the manual feed tray 31 is opened.

As described above, the manual paper feed mechanism that supports the relay driven roller 42b is fixed to the main body casing 50 by screws. The opening/closing door 39 is attached via a hinge mechanism to the manual paper feeding mechanism so that it can be opened and closed. Further, the manual tray 31 is attached via a hinge mechanism to the opening/closing door 39 so as to be openable and closable. In this embodiment, by opening the opening/closing door 39, the process cartridge including the photoreceptor 1 can be attached and detached, and the jammed recording sheet S can be taken out.

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

Here, if an abnormality occurs in the printer that requires the conveyance of the recording sheet S to be stopped, such as when a jam occurs in this printer (hereinafter, an example of an abnormality in the apparatus due to the occurrence of a jam occurs), the recorded Sheet S must be removed. Specifically, in this embodiment, the paper feed cassette 100 is removed from the apparatus in the paper feeding direction of the recording sheets S or in the direction crossing the paper feeding direction, and the remaining recording sheets are taken out (pulled out) from the paper feeding section of the main body. At this time, in order to prevent the recording sheet S made of thin paper or plain paper with low strength from being torn when pulled out, it is necessary to It is preferable to open (separate) the sandwiched portion between the paper roller 32 and the manual feed bottom plate 34, etc.).

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

Therefore, in this embodiment, when a jam occurs during paper feeding in the main body, the recording sheet S having low strength is prevented from being torn when taking out (pulling out) the recording sheet sandwiched between the pair of relay rollers 42. In order to suppress this, the nip pressure (contact pressure) of the pair of relay rollers 42 is switched to a low nip pressure when conveying a recording sheet S of a low-strength type (thin paper or plain paper) that is easily torn. As a result, even if a jam occurs while transporting a thin or plain paper recording sheet S, the nip pressure between the relay roller pair 42 is low, so even if the recording sheet S is pulled out from the relay roller pair 42 in that state, It is possible to suppress the sheet from tearing.

At this time, since the nip pressure between the relay roller pair 42 is low, if the conveyance load of the recording sheet S (sliding friction with the conveyance guide, conveyance resistance when the leading edge of the sheet enters the roller pair, etc.) is large, the relay roller pair 42 There is a possibility that the recording sheet S slips in the conveyance nip, causing a conveyance failure that prevents proper conveyance. However, since the recording sheet S made of thin paper or plain paper is usually relatively thin and has relatively low elasticity, transportation defects occur even when the transportation load is small and the nip pressure between the pair of relay rollers 42 is low. It's hard to do. Therefore, if the recording sheet S is thin paper or plain paper, stable conveyance can be achieved even when the nip pressure between the relay roller pair 42 is low.

On the other hand, when transporting a recording sheet S of a strong type (cardboard paper) that is hard to tear, a high nip pressure is used as the nip pressure (contact pressure) of the pair of relay rollers 42. In the case of a cardboard recording sheet S, if the nip pressure between the relay roller pair 42 is low, it is likely to cause a conveyance failure, but in this embodiment, the relay roller pair 42 is set to a high nip pressure state to handle the cardboard recording sheet S. Since the material is transported, transport defects are less likely to occur and stable transport is achieved. Furthermore, even if a jam occurs, if the recording sheet S is made of thick paper, the recording sheet S will be torn when the recording sheet S is pulled out from the relay roller pair 42 even if the nip pressure between the relay roller pair 42 remains high. Situations are unlikely to occur.

In addition, when adopting the conventional operation of weakening the nip pressure (contact pressure) of the relay roller pair 42 after a jam occurs, if this operation is properly executed after the jam occurs, the sheet pull-out This can prevent the recording sheet S, which has low strength, from being torn at times. However, depending on the timing at which a jam occurs, the configuration for realizing a jam removal operation, etc., the operation of weakening the nip pressure between the pair of relay rollers 42 may not be executed after a jam occurs. For example, if the above-mentioned jam detection sensor (registration sensor 49) erroneously detects or malfunctions, or if the image forming apparatus suddenly shuts down, the drive sources for the main motor 61 and clutches 62a, 63a, 64a, and 65a should be driven normally. Therefore, it is not possible to lower the nip pressure between the pair of relay rollers 42 when pulling out the sheet.

In contrast, in the present embodiment, in the case of the recording sheet S made of thin paper or plain paper, the relay driven roller 42b is activated before the jam occurs, specifically, before the recording sheet S is sandwiched between the relay roller pair 42. The nip pressure between the relay roller pair 42 is weakened by switching the urging force of the pressure spring 37b that urges the relay drive roller 42a to a weak urging force (see S1-4 in FIG. 6). Therefore, since there is no need to perform an operation to weaken the nip pressure between the relay roller pair 42 after a jam occurs, the relay roller pair 42 can be removed when a jam occurs, without depending on the jam occurrence timing or the configuration contents for realizing the jam clearing operation. The recording sheet S of thin paper or plain paper can be pulled out while the nip pressure of 42 is weak.

Next, a configuration for switching the nip pressure between the relay roller pair 42 will be described.
In this embodiment, the operation of switching the nip pressure of the pair of relay rollers 42 in the main paper feed path R1 is performed in conjunction with the operation of the movable member used for conveying sheets in the manual paper feed path R2. In this embodiment, when the recording sheet S is transported using the main body paper feed path R1, the manual paper 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 problem occurs even if the movable member used for sheet transport in the manual paper feed path R2 is operated.

In this embodiment, the sheet feeding means during manual paper feeding is one that presses the recording sheet S on the manual feed bottom plate 34 against the manual paper feed roller 32 and feeds it out. Therefore, in this embodiment, 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 movement of the manual feed bottom plate 34.

Specifically, the operating means for operating the manual feed bottom plate 34 rotates the manual feed bottom plate camshaft 65 by the driving force of the main motor 61, as described above. When the manual feed bottom plate cam shaft 65 is located at the rotational position where the manual feed bottom plate cam 35 pushes down the bottom plate guide portion 34a against the biasing force of the bottom plate spring 36, the manual feed bottom plate 34 is lowered and removed from the manual feed roller 32. (See FIGS. 10 and 15(a)). On the other hand, when the manual feed bottom plate cam shaft 65 is located at the rotational position where the manual feed bottom plate cam 35 is separated from the bottom plate guide portion 34a, the manual feed bottom plate 34 is raised by the urging force of the bottom plate spring 36 and comes into contact with the manual feed roller 32 ( (See FIGS. 8 and 15(b)).

The biasing force switching means of this embodiment is a biasing support that supports a pressure spring 37b that biases a bearing portion 37a of a relay driven roller 42b, which is one roller of the relay roller pair 42, toward the relay drive roller 42a. By moving the pressure plate 37d as a part with the rotation of the manual feed bottom plate camshaft 65, the biasing force of the pressure spring 37b is switched and the nip pressure between the relay roller pair 42 is changed. A slider is fastened to the pressure plate 37d, and the slider is configured to move along a guide section provided on the support frame 38 of the manual paper feed section 30. It is configured to move linearly along the direction of contact and separation.

FIGS. 14(a) and 14(b) illustrate 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 drive roller 42a in this embodiment. It is a diagram.
FIGS. 15(a) and 15(b) are perspective views showing the main structure of the biasing force switching means.
FIGS. 16A and 16B are explanatory diagrams showing a mechanism that supports the relay driven roller 42b.

As shown in FIGS. 16(a) and 16(b), the roller shaft 66 of the relay driven roller 42b is attached to a projection 38a provided on the support frame 38 of the manual paper feed section 30 and to a bearing portion 37a of the relay driven roller 42b. By fitting the guide groove 37a1, the relay driven roller 42b is held slidably in the direction toward and away from the relay drive roller 42a. Further, 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 such that one end thereof contacts the bearing portion 37a of the relay driven roller 42b and the other end contacts the pressure plate 37d. The bearing portion 37a of the relay driven roller 42b is urged toward the relay drive roller 42a by the urging force of the pressure spring 37b supported by the pressure plate 37d. A pressing portion 65e that can press the pressure plate 37d toward the relay drive roller 42a is formed on the back surface of the pressure plate 37d opposite to the spring contact surface with which the pressure spring 37b contacts. This pressing portion 65e rotates as the manual feed bottom plate camshaft 65 rotates.

When the rotational position of the manual feed bottom plate camshaft 65 is at the position where the manual feed bottom plate 34 is lowered (the 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 camshaft 65 moves as shown in FIG. a) and the non-pressed position as shown in FIG. 15(a). At this time, the pressure plate 37d moves in a direction away from the relay drive roller 42a by the urging force of the pressure spring 37b. As a result, the pressure spring 37b expands, the amount of contraction thereof decreases, and the biasing force of the pressure spring 37b decreases. As a result, the urging force that urges the relay driven roller 42b toward the relay drive roller 42a becomes lower, so that the nip pressure between the relay roller pair 42 is weakened. Note that the manual feed bottom plate 34 remains separated from the manual paper feed roller 32, so manual paper feeding is not possible, but there is no problem since manual paper feeding is not performed during main body paper feeding.

On the other hand, when the rotational position of the manual feed bottom plate camshaft 65 is at the 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 portion 65e on the manual feed bottom plate camshaft 65 is 14(b) and the pressed position as shown in FIG. 15(b). At this time, the pressure plate 37d moves in a direction approaching the relay drive roller 42a against the biasing force of the pressure spring 37b. As a result, the pressure spring 37b contracts and the amount of compression increases, so that the biasing force of the pressure spring 37b increases. As a result, the urging force that urges the relay driven roller 42b toward the relay drive roller 42a increases, so that the nip pressure between the relay roller pair 42 increases. Note that the manual feed bottom plate 34 remains in contact with the manual paper feed roller 32, so manual paper feeding is not possible, but since manual paper feeding is not performed during main body paper feeding, there is no problem.

According to the present embodiment, the nip pressure of the pair of relay rollers 42 (pressure spring 37b (biasing force) can be switched. Thereby, the switching can be realized with a simple configuration that does not require a dedicated operating means for switching the nip pressure between the pair of relay rollers 42.

FIGS. 17(a) to 17(c) are explanatory diagrams showing locations where the pressing portion 65e on the manual feed bottom plate camshaft 65 presses the pressing plate 37d.
As shown in FIG. 17(a), the pressing portion 65e on the manual feed bottom plate camshaft 65 is at the same position B' as the supporting position A of the pressing spring 37b on the pressing plate 37d, and in the biasing direction of the pressing spring 37b. The pressure plate 37d may be pressed along the line. In this case, since the amount of pushing of the pressure plate 37d by the pressing portion 65e and the amount of contraction of the pressure spring 37b substantially match, it becomes easy to set the biasing force.

However, in this embodiment, since the arrangement as shown in FIG. 17(a) is difficult due to constraints on the device layout, the pressure spring 37b is placed at a position B shifted from the support position A of the pressure spring 37b on the pressure plate 37d. 37d is pressed along the biasing direction of the pressure spring 37b. In this case, as shown in FIG. 17(b), the pressure plate 37d is tilted, and the amount of compression of the pressure spring 37b is smaller than the amount of pushing of the pressure plate 37d by the pressing portion 65e, so that the actual biasing force does not reach the desired value. It is insufficient than the urging force.

Therefore, in this embodiment, as shown in FIG. 17(c), the amount of pushing of the pressure plate 37d by the pressing portion 65e is set to be greater than the target amount of contraction of the pressure spring 37b. As a result, even if the pressure plate 37d is pressed at a position B that deviates from the support position A of the pressure spring 37b on the pressure plate 37d, the pressure spring 37b can be compressed to the target amount of contraction, and the desired urging force can be achieved. can be obtained.

FIGS. 18A and 18B are explanatory diagrams showing the shape of the pressing portion 65e on the manual feed bottom plate camshaft 65.
In this embodiment, the pressing portion 65e is a cam. In this embodiment, even if the rotational position (phase) of the pressing part 65e of the manual feed bottom plate camshaft 65 deviates due to component tolerances or errors in control stop time, the predetermined angle including the target rotation angle of the pressing position can be maintained. The pressing portion 65e is configured such that the outer diameter of the cam is constant within the width α. Thereby, for example, the amount of pushing of the pressure plate 37d by the pressing portion 65e becomes the same when the rotation position shown in FIG. 18(a) is stopped and when the rotation position is stopped as shown in FIG. 18(b). . As a result, even if the rotational position at the pressing position deviates due to component tolerances or errors in control stop time, the target biasing force (nip pressure between the pair of relay rollers) can be obtained.

FIG. 19 is an explanatory diagram showing a deflection suppressing means for suppressing deflection of the manual feed bottom plate camshaft 65, which includes a pressing portion 65e that presses the pressure plate 37d.
Since the reaction force of the urging force of the pressure spring 37b that urges the relay driven roller 42b toward the relay drive roller 42a side acts on the pressure plate 37d, the reaction force is applied via the pressing portion 65e that contacts the pressure plate 37d. is transmitted to the manual feed bottom plate camshaft 65. As a result, if the manual feed bottom plate camshaft 65 is bent, the amount of pushing of the pressure plate 37d by the pressing portion 65e will decrease, making it impossible to obtain the target biasing force (nip pressure between the pair of relay rollers).

Therefore, in the present embodiment, as a deflection suppressing means for suppressing the deflection of the manual feed bottom plate camshaft 65, a contact portion 37e is provided that comes into contact with the manual feed bottom plate camshaft 65 to suppress the bending. This contact portion 37e is a part of the support frame 38 of the manual paper feed unit 30, and although two contact portions 37e are provided in this embodiment, it may be one, three or more.

Next, a processing flow when the printer stops abnormally (a jam occurs) will be described.
FIG. 20 is a flowchart showing the flow of processing when the printer stops abnormally.
In this printer, when a device abnormality such as a conveyance failure (jam) that should stop the conveyance of the recording sheet S is detected (S41), the control unit 51 first controls the main body paper feed clutch 62a, the relay clutch 63a, and the manual feed clutch. Turn off the paper clutch 64a (S42). Thereafter, the control unit 51 determines from the control information whether manual paper feeding is in progress (S43).

If manual paper feeding is in progress (Yes in S43), in this embodiment, the recording sheet S is held between the manual paper feed roller 32 and the manual paper feed bottom plate 34, that is, the manual paper feed bottom plate 34 is held between the manual paper feed roller 32 and the manual paper feed roller 34. 32 (see FIGS. 8 and 14(b)), the manual feed roller 32 and the manual bottom plate 34 are separated from each other.

In other words, when the manual feed bottom plate 34 is in contact with the manual feed roller 32, the filler sensor 65c is in the off state, so the control unit 51 first turns on the manual feed bottom plate cam clutch 65a (S44), and the manual feed bottom plate cam shaft 65 is rotated. Thereafter, the manual feed bottom plate camshaft 65 continues to rotate until the filler sensor 65c is turned on, and when the filler sensor 65c is turned on (S45), the manual feed bottom plate cam clutch 65a is turned off (S46), and the manual feed bottom plate camshaft The rotation of 65 is stopped. Thereafter, the control unit 51 turns off the main motor 61 (S51), stops the apparatus (S52), and makes it possible for the user to remove the recording sheet S.

With the above-described control, when an abnormality occurs in the device that requires stopping the conveyance of the recording sheet S during manual paper feeding, the manual feed bottom plate 34 becomes separated from the manual paper feed roller 32, and the manual paper feed path R2 The operation for removing the recording sheet S remaining inside (the recording sheet S held between the manual feed roller 32 and the manual feed bottom plate 34) becomes easy.

Further, if the main body is feeding paper (No in S43), there is a possibility that the recording sheet S is being held between the rollers of the relay roller pair 42. At this time, if the type of recording sheet S is determined to be thick paper and the sheet is being conveyed, the nip pressure between the pair of relay rollers 42 is in a high state.

Here, if the recording sheet S that is actually being conveyed is thick paper (a strong sheet), as described above, even if the nip pressure between the relay roller pair 42 is high, the sheet cannot be pulled out without tearing. can be removed. However, if the recording sheet S that is actually being conveyed is thin paper or plain paper (a sheet with low strength) due to a user's operation error or setting error, the nip pressure between the relay roller pair 42 will not be high. , the recording sheet S is torn when the sheet is pulled out. Therefore, it is desirable to lower the nip pressure between the relay roller pair 42. Furthermore, even if the recording sheet S that is actually being conveyed is thick paper (a strong sheet), when the nip pressure between the relay roller pair 42 is high, a large force is required to pull out the sheet, making it difficult to clear the jam. In order to improve workability, it is desirable to lower the nip pressure between the relay roller pair 42.

Therefore, in the present embodiment, in the case of main body paper feeding (No in S43), when the type of recording sheet S is determined to be thick paper and the sheet is being conveyed, that is, when the manual feed bottom plate 34 is If the nip pressure of the relay roller pair 42 is high (No in S47) due to contact with the filler sensor (the filler sensor is in the OFF state), the manual feed bottom plate cam clutch 65a is turned on (S48), and the manual feed bottom plate cam clutch 65a is turned on (S48). 65 is rotated. Then, the manual feed bottom plate camshaft 65 continues to rotate until the filler sensor 65c is turned on, that is, the manual feed bottom plate 34 is at the lowest position, and the nip pressure between the relay roller pair 42 becomes low, and the filler sensor 65c is turned on. When the manual feed bottom plate cam clutch 65a is turned off (S50), rotation of the manual feed bottom plate cam shaft 65 is stopped. Thereafter, the control unit 51 turns off the main motor 61 (S51), stops the apparatus (S52), and makes it possible for the user to remove the recording sheet S.

As a result, the nip pressure between the relay roller pair 42 is switched from a high state to a low state, so even if the recording sheet S that is actually being conveyed is thin paper or plain paper (a sheet with low strength), the sheet will not be torn. It can be pulled out without any problem. In addition, if the recording sheet S that is actually being conveyed is cardboard (a sheet with high strength), it can be easily pulled out without requiring a large force to pull out the sheet, which improves the workability of jam removal. will improve.

Further, in this embodiment, when feeding the recording sheet S from the manual feed tray 31, the manual feed bottom plate cam shaft 65 is moved to the rotational position where the manual feed bottom plate cam 35 pushes down the bottom plate guide portion 34a against the biasing force of the bottom plate spring 36. , the maximum driving load L1 is generated on the manual feed bottom plate camshaft 65. Therefore, when feeding the recording sheet S from the manual feed tray 31, the rotational position where the manual feed bottom plate cam 35 pushes down the bottom plate guide portion 34a against the biasing force of the bottom plate spring 36 is the position at which the manual feed bottom plate cam shaft 65 is driven to the maximum. This is the maximum load operating position P1 where the load L1 occurs.

When switching the nip pressure between the pair of relay rollers 42, the manual feed bottom plate camshaft 65 is moved to a rotational position in which the pressing portion 65e moves the pressing plate 37d toward the relay drive roller 42a against the urging force of the pressing spring 37b. , the maximum driving load L2 is generated on the manual feed bottom plate camshaft 65. Therefore, when switching the nip pressure between the pair of relay rollers 42, the rotation position at which the pressing portion 65e moves the pressing plate 37d in the direction approaching the relay drive roller 42a against the urging force of the pressing spring 37b is set to the manual feed bottom plate camshaft. 65 is the maximum load operating position P2 where the maximum drive load L2 occurs.

In this embodiment, as described above, the rotational position of the manual feed bottom plate camshaft 65 is the position where the manual feed bottom plate 34 is raised (the position where the minimum driving load occurs when feeding the recording sheet S from the manual feed tray 31). ), the pressing part 65e on the manual feed bottom plate camshaft 65 moves the pressing plate 37d in the direction toward the relay drive roller 42a against the urging force of the pressing spring 37b (the position of the relay roller pair 42). The position P2) where the maximum drive load L2 occurs when switching the nip pressure is taken. That is, in the present embodiment, the maximum load operating position P1 of the manual feed bottom plate camshaft 65 when feeding the recording sheet S from the manual feed tray 31 and the maximum load operation position P1 of the manual feed bottom plate camshaft 65 when switching the nip pressure of the relay roller pair 42. and the maximum load operating position P2 are shifted from each other.

FIG. 21 shows the maximum load operation position P1 of the manual feed bottom plate camshaft 65 when feeding recording sheets S from the manual feed tray 31, and the maximum load of the manual feed bottom plate camshaft 65 when switching the nip pressure of the relay roller pair 42. There is a graph showing an example in which the operating position P2 matches.
In this graph, the load torque of the manual feed bottom plate camshaft 65 is plotted on the vertical axis, and the rotation angle of the manual feed bottom plate camshaft 65 is plotted on the horizontal axis. (The same applies to FIGS. 22 to 24 described later.)

In the example of FIG. 21, since the two maximum load operating positions P1 and P2 coincide (overlap) with each other, the total driving load (load torque) generated on the manual feed bottom plate camshaft 65 is at most the two maximum load operating positions P1 and P2. The drive load L is the sum of the operating positions P1 and P2. When such a large drive load L is applied, a drive mechanism (such as a motor or a clutch) for driving the manual feed bottom plate camshaft 65 that can handle the large drive load L is required, leading to increased costs. Furthermore, the parts that make up the manual feed bottom plate camshaft 65 and the manual paper feed section 30 also require parts that can withstand larger loads (thick and heavy parts, etc.), which leads to higher costs and weight. .

FIG. 22 shows the maximum load operation position P1 of the manual feed bottom plate camshaft 65 when feeding the recording sheet S from the manual feed tray 31, and the maximum load of the manual feed bottom plate camshaft 65 when switching the nip pressure of the relay roller pair 42. It is a graph which shows an example where operation position P2 deviates.
In the example of FIG. 22, since the two maximum load operating positions P1 and P2 are shifted from each other (do not overlap), the total drive load (load torque) generated on the manual feed bottom plate camshaft 65 is at most The drive load L' is smaller than the maximum drive load L in the example. Therefore, as a drive mechanism for driving the manual feed bottom plate camshaft 65, a drive mechanism that can handle a relatively small drive load L' is sufficient, so that cost and weight reductions can be achieved.

FIG. 23 shows the maximum load operation position P1 of the manual feed bottom plate camshaft 65 when feeding the recording sheet S from the manual feed tray 31, and the maximum load of the manual feed bottom plate camshaft 65 when switching the nip pressure of the relay roller pair 42. It is a graph which shows another example where operation position P2 deviates.
In the example of FIG. 23 as well, the two maximum load operating positions P1 and P2 are shifted from each other (do not overlap). However, the drive load on the manual feed bottom plate camshaft 65 that occurs when feeding the recording sheet S from the manual feed tray 31, and the drive load on the manual feed bottom plate camshaft 65 that occurs when switching the nip pressure between the relay roller pair 42, It is always smaller than the larger of the maximum driving load L1 when feeding the recording sheet S from the tray 31 and the maximum driving load L2 when switching the nip pressure between the relay roller pair 42.

Therefore, in the example of FIG. 23, the driving load that may occur on the manual feed bottom plate camshaft 65 is the maximum driving load L1 when feeding the recording sheet S from the manual feed tray 31 and the maximum driving load L1 when switching the nip pressure between the relay roller pair 42. and the maximum driving load L2, whichever is greater. Therefore, as a drive mechanism for driving the manual feed bottom plate camshaft 65, a drive mechanism that can handle a smaller drive load is sufficient, so that cost and weight reductions can be achieved.

In particular, in the example shown in FIG. 23, the driving load on the manual feed bottom plate camshaft 65 that occurs when feeding the recording sheet S from the manual feed tray 31 also applies to the drive load on the manual feed bottom plate camshaft 65 that occurs when switching the nip pressure between the relay roller pair 42. The driving load is also smaller than the maximum driving load L1 when feeding the recording sheet S from the manual feed tray 31 or the maximum driving load L2 when switching the nip pressure between the relay roller pair 42. , always small. Therefore, in the example shown in FIG. 23, a drive mechanism that can handle a smaller drive load is sufficient as the drive mechanism for driving the manual feed bottom plate camshaft 65, so that cost reduction can be achieved and weight reduction can be achieved. I can do it.

FIG. 24 is a graph showing another example in which the amount of deviation is further increased.
The example in FIG. 24 shows the maximum pressing force rotation position P1 of the manual feed bottom plate cam shaft 65 where the maximum pressing force of the manual feed bottom plate cam 35 occurs when feeding the recording sheet S from the manual feed tray 31, and the nip between the relay roller pair 42. The maximum pressing force rotation position P2 of the manual feed bottom plate camshaft 65, where the maximum pressing force of the pressing portion 65e occurs when changing the pressure, is shifted by 180°. In this embodiment, since the maximum pressing force rotation positions P1 and P2 each have a constant width, the deviation angle is defined as the deviation angle between the center positions (rotation angles) of the respective widths.

According to the example in FIG. 24, even if the rotational position of the manual feed bottom plate camshaft 65 varies slightly due to dimensional errors of parts, control errors, etc., the two maximum load operating positions P1 and P2 coincide with each other (overlapping ) is unlikely to occur. Therefore, it is possible to stably suppress excessive driving load from being applied to the manual feed bottom plate camshaft 65.

According to the example of FIG. 24, the operation of the manual feed bottom plate 34 when feeding the recording sheet S from the manual feed tray 31 is controlled by simple control of switching the rotation angle of the manual feed bottom plate camshaft 65 in 180° increments; The operation of switching the nip pressure between the pair of relay rollers 42 can be realized. In particular, since the switching times for these operations are all the same, it is possible to maintain control such as making it possible to keep the waiting time for switching image forming operations constant when, for example, image forming operations are performed consecutively for different paper thicknesses. It becomes easier.

Further, in this embodiment, when the pressing portion 65e on the manual feed bottom plate camshaft 65 is located at the non-pressing position as shown in FIGS. 14(a) and 15(a), the pressing plate 37d is It moves in the direction away from the relay drive roller 42a by the urging force of 37b. At this time, the movement of the pressure plate 37d may be regulated by coming into contact with the pressing part 65e, but as shown in FIGS. 25(a) and 26, a member other than the pressing part 65e, for example, It may be regulated by coming into contact with a mounting member 38b attached to the support frame 38 of the paper feed section 30.

If the configuration is such that the movement of the pressure plate 37d is restricted by contacting only the pressure portion 65e, the pressure portion 65e will wear out over time, and the position where the movement of the pressure plate 37d is restricted will change over time. It is difficult to obtain a stable biasing force. On the other hand, as shown in FIGS. 25(a) and 26, if the movement of the pressure plate 37d is restricted by coming into contact with the mounting member 38b, which is a member different from the pressing part 65e, the mounting member Since the pressure plate 37d does not rub against the pressure plate 38b, there is no wear caused by use over time, and it is easy to obtain a biasing force that is stable over time. As a result, stable nip pressure between the relay roller pair 42 can be obtained.

In particular, in this embodiment, the mounting member 38b restricts the movement of the pressure plate 37d by making surface contact with the pressure plate 37d, as shown in FIGS. 25(a) and 26. If the mounting member 38b is configured to locally contact the pressure plate 37d, the posture of the pressure plate 37d is likely to change due to misalignment of the contact position between the mounting member 38b and the pressure plate 37d, resulting in a stable biasing force over time. difficult to obtain. On the other hand, with a configuration in which surface contact is made, even if the contact position between the mounting member 38b and the pressure plate 37d is shifted, the posture of the pressure plate 37d is difficult to change, and it is easy to obtain a stable biasing force over time.

Note that here, a member different from the pressing portion 65e is the mounting member 38b attached to the support frame 38 of the manual paper feeder 30, but it may be the support frame 38, for example.

FIG. 27 is an external perspective view of the relay roller pair 42 when viewed diagonally from below.
In this embodiment, the attachment member 38b that is attached to the support frame 38 of the manual paper feeder 30 is a member different from the pressing portion 65e, so that the configuration is highly easy to assemble. That is, the support frame 38 of the manual paper feed section 30 includes a pressure plate 37d that is inserted into a guide portion formed in the support frame 38, a manual feed bottom plate cam shaft 65, and a pressure plate 37d that is attached to the manual feed bottom plate cam shaft 65. It is necessary to assemble various cams such as the pressing part 65e and the manual bottom plate cam 35. At this time, it is desirable that the support frame 38 is provided with an opening having a sufficient width for inserting and assembling the pressure plate 37d into the guide portion. However, when such an opening is provided, the rigidity of the support frame 38 is reduced, so it is common to attach a structural component such as a stay to the support frame 38 to ensure rigidity.

In this embodiment, an opening with a sufficient width is formed in the support frame 38 to improve ease of assembly, and a mounting member 38b is provided which functions as a structural component to be attached to ensure rigidity. This restricts the movement of the pressure plate 37d. Therefore, the number of parts is smaller than when securing rigidity and regulating the movement of the pressure plate 37d are performed by separate members, and it is possible to achieve reductions in size and weight.

As described above, 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 applied to the manual feed bottom plate 34 as a movable member used in the manual feed path R2. It is switched in conjunction with the operation, but is not limited to this. For example, when the manual paper feed section 30 employs a sheet feeding mechanism that presses the manual paper feed roller 32 against the recording sheet on the manual tray to feed it by lowering the manual paper feed roller 32. Alternatively, the manual paper feed roller 32 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 paper feed roller 32. Further, for example, the switching may be performed in conjunction with the operation of a movable member used in a paper feed path other than the manual paper feed path R2 (for example, the reverse refeed path R5, etc.).

Further, in the present embodiment, a configuration has been described in which the nip pressure (biasing force of the pressure spring 37b) of the relay roller pair 42 used in the main body paper feed path R1 is switched, but for example, other conveyance roller pairs (e.g. It is also possible to apply the present invention to a configuration in which the nip pressure of a pair of paper ejection rollers 46, etc. is switched. Further, the relay roller pair 42, which was the target of switching the nip pressure in this embodiment, is a conveying roller pair in which one is a driving roller and the other is a driven roller, but both may be driving rollers or both may be driven rollers. It may also be a pair of conveyance 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 also be a copying machine equipped with an image reading device or a multifunction device also equipped with functions such as facsimile. Good too. In addition, the application is not limited to image forming apparatuses that form images using an electrophotographic method, but also applies to image forming apparatuses that form images using other methods such as an inkjet method or a toner projection method described in Japanese Patent Laid-Open No. 2002-307737. Applicable. Further, the image forming apparatus is not limited to an image forming apparatus, and may be an image reading apparatus equipped with an automatic feeder (ADF) as long as it is equipped with a sheet conveying device.

What has been described above is just an example, and each of the following aspects has its own unique effects.
[First aspect]
In the first aspect, a pair of rollers (for example, a pair of relay rollers 42) that sandwich a sheet to be conveyed (for example, a recording sheet S), and one roller (for example, a relay driven roller 42b) constituting the pair of rollers sandwich the other roller (for example, a pair of relay rollers 42b). For example, the sheet conveyance device includes a biasing means (for example, a pressure spring 37b) that biases toward the relay drive roller 42a), the rollers of the pair of rollers are configured so that they cannot be separated from each other, and the rollers It is characterized by having a biasing force switching means (for example, a pressure plate 37d, a pressing part 65e, etc.) that switches the biasing force of the biasing means depending on the type of the sheet before the sheet is sandwiched between the pairs. be.
In this aspect, since the rollers of the roller pair cannot be separated from each other, when a jam occurs and the sheet sandwiched between the roller pair is to be removed, the sheet sandwiched between the roller pair is pulled out. Work is required. At this time, if a sheet with low strength (for example, thin paper) is jammed, the sheet may be torn when the sheet is pulled out if the contact pressure between the pair of rollers is too high.
If a conventional configuration is adopted in which the contact pressure of the roller pair is weakened after a jam is detected, if the operation of weakening the contact pressure is properly executed after a jam occurs, the strength will be increased when the sheet is pulled out. It is possible to prevent sheets with low temperatures from being torn. However, depending on the timing of occurrence of a jam and the content of the configuration for realizing the jam removal operation, it may not be possible to perform an operation of weakening the contact pressure after a jam has occurred. In this case, it is not possible to drive a drive source that weakens the contact pressure acting between the rollers of the pair of rollers, and it is not possible to reduce the contact pressure of the pair of rollers when the sheet is pulled out. It should be noted that even in an emergency situation where the operation of weakening the contact pressure cannot be performed after a jam occurs, even if a configuration is adopted in which the drive source that performs the operation of weakening the contact pressure acting between the rollers of a pair of rollers can be driven. This is good, but there is a concern that it will lead to higher costs.
Another option is to lower the contact pressure between the pair of rollers from the beginning of conveying the sheet, but in this case, when conveying sheets with a high conveyance load such as cardboard, there is a risk that the contact pressure will be insufficient and cause conveyance failure. There is.
In view of the above problems, in this embodiment, a configuration is adopted in which the urging force of the urging means is switched depending on the type of the sheet before the sheet is held between the pair of rollers. According to this configuration, for example, when conveying a type of sheet with low strength, by switching to a low urging force and keeping the contact pressure of the roller pair low, even if a jam occurs, the contact pressure of the roller pair is low, so even if the sheet is pulled out from the pair of rollers in that state, the sheet can be prevented from being torn. In addition, since the conveyance load of a low-strength type of sheet is usually small, conveyance defects will not occur even if the sheet is conveyed with a low contact pressure between the pair of rollers. On the other hand, for example, when conveying a type of sheet with high strength, by switching to a high urging force and increasing the contact pressure between the roller pair, it is possible to convey the sheet without causing conveyance defects even if the conveyance load is large. is possible. Moreover, if the sheet is of a high strength type, it is possible to pull the sheet out without tearing it even if the contact pressure between the pair of rollers remains high.
As described above, according to this aspect, it is possible to suppress sheet tearing when the sheet is pulled out from the roller pair without requiring an operation of weakening the contact pressure between the roller pair after a jam occurs.

[Second aspect]
A second aspect of the present invention is that in the first aspect, the types of sheets include types of sheets having different strengths.
According to this, it is possible to suppress sheet tearing when a sheet with low strength is pulled out from the roller pair.

[Third aspect]
A third aspect of the present invention is that in the second aspect, the types of sheets include types of sheets having different thicknesses.
According to this, it is possible to suppress sheet tearing when a thin sheet is pulled out from the roller pair.

[Fourth aspect]
In a fourth aspect, in the second or third aspect, the biasing force switching means switches the biasing force such that the lower the strength of the sheet, the weaker the biasing force.
According to this, it is possible to appropriately suppress sheet tearing when a sheet with low strength is pulled out from the roller pair.

[Fifth aspect]
A fifth aspect is an image forming apparatus (for example, a printer) that forms an image on a sheet conveyed by a sheet conveying device, and the sheet conveying device according to any one of the first to fourth aspects is used as the sheet conveying device. It is characterized by this.
According to this aspect, it is possible to provide an image forming apparatus that can suppress sheet tearing when the sheet is pulled out from the roller pair without requiring an operation of weakening the contact pressure of the roller pair after a jam occurs.

[Sixth aspect]
In a sixth aspect, based on the fifth aspect, the pair of rollers of the sheet conveying device is arranged such that the first conveyance path (for example, the main body paper feed path R1 and the manual paper feed path R2) of the plurality of conveyance paths (for example, the main body paper feed path R1 and the manual paper feed path R2) The biasing force switching means is configured to nip a sheet conveyed through a path R1), and the biasing force switching means is configured to nip a sheet conveyed through a second conveyance path (for example, manual paper feed path R2) among the plurality of conveyance paths. The device is characterized in that the urging force of the urging means is switched in conjunction with the operation of a movable member (for example, the manual feed bottom plate 34) that operates in response to the pressing.
In this aspect, the operation of switching the contact pressure (biasing force by the biasing means) of the roller pair in the first conveyance path is performed in conjunction with the operation of the movable member used for sheet conveyance in the second conveyance path. In the image forming apparatus according to this aspect, when a sheet is being transported using a transport path selected from a plurality of transport paths, other transport paths are not used for sheet transport. Therefore, when switching the contact pressure between the pair of rollers on the first conveyance path, there is no problem even if the movable member used for conveying the sheet on the second conveyance path is operated.
According to this aspect, the contact pressure of the pair of rollers on the first conveyance path can be switched using the operation of the movable member used for conveying the sheet on the second conveyance path, so an operation means dedicated for switching is provided. This is not necessary, and it is possible to downsize the device and reduce costs.

[Seventh aspect]
A seventh aspect is characterized in that in the sixth aspect, the sheet placed on the sheet placement section (for example, the manual feed bottom plate 34) is fed to the second conveyance path by operating the movable member. It is something to do.
According to this, the contact pressure of the pair of rollers on the first conveyance path can be switched in conjunction with the operation of the movable member for feeding the sheet to the second conveyance path.

[Eighth aspect]
An eighth aspect is the seventh aspect, wherein the sheet feeding is performed by raising or lowering the movable member and bringing the sheet into contact with a feeding roller.
According to this, the contact pressure of the pair of rollers on the first conveyance path can be switched in conjunction with the movement of raising or lowering the movable member for feeding the sheet to the second conveyance path.

[Ninth aspect]
In a ninth aspect, in any one of the sixth to eighth aspects, the movable member operates by rotating a rotating shaft (for example, the manual feed bottom plate cam shaft 65), and the biasing force switching means The biasing force of the biasing means is switched by moving a biasing support part (for example, a pressure plate 37d) that supports the biasing means in conjunction with the rotation of the biasing means.
According to this, a configuration in which the operation of switching the contact pressure of the roller pair in the first conveyance path is performed in conjunction with the operation of the movable member used for sheet conveyance in the second conveyance path can be realized with a simple configuration.

[Tenth aspect]
In a tenth aspect, based on the ninth aspect, the biasing force switching means changes the pressing state in which a cam on the rotating shaft presses the biasing support section by rotating the rotating shaft. The support part is moved to a first movement position (for example, a pressed position) and a second movement position (for example, a non-pressed position), and the biasing support part is moved to one of the first movement position and the second movement position. When located at one of the movement positions, the movement is regulated by a member other than the cam (for example, the mounting member 38b).
According to this, it is easy to realize stable movement restriction over time, and it is possible to realize a stable biasing force when located at one of the moving positions.

[Eleventh aspect]
An eleventh aspect is the tenth aspect, wherein the another member restricts movement of the biasing support by making surface contact with the biasing support.
According to this, even if a contact position shift between the other member and the biasing support section occurs, the posture of the biasing support section is unlikely to change, making it easy to obtain a stable biasing force over time.

[Twelfth aspect]
A twelfth aspect is that in the tenth or eleventh aspect, the another member is a mounting member 38b attached to a support member (for example, the support frame 38) that movably supports the biasing support part. It is something to do.
According to this, for example, when forming an opening with a sufficient width in the support member to improve ease of assembly, rigidity can be ensured and the movement of the biasing support part can be restricted without increasing the number of parts. be able to.

[13th aspect]
In a 13th aspect, in any one of the 9th to 12th aspects, the biasing force switching means is configured to cause the pressing portion 65e on the rotating shaft to apply the biasing force on the biasing support portion by rotation of the rotating shaft. The device is characterized in that the biasing support portion is moved by pressing the biasing support portion at a position B shifted from the support position A of the means.
According to this aspect, it is possible to cope with the case where there is a restriction that the pressing part on the rotating shaft cannot press the biasing support part at the same position B' as the support position A of the biasing means in the bias support part.

[Fourteenth aspect]
In a fourteenth aspect, in the thirteenth aspect, the pressing part is a cam, and the pressing part is a cam within a predetermined angular width α including a rotation angle of the rotation shaft when obtaining a biasing force according to the type of the sheet. It is characterized by a constant diameter.
According to this aspect, even if the rotational position of the pressing part deviates due to component tolerances or errors in control stop time, the target biasing force (contact pressure of the roller pair) can be obtained. .

[15th aspect]
In a fifteenth aspect, in any one of the ninth to fourteenth aspects, when the pressing part on the rotating shaft presses the biasing support part and moves the biasing support part by rotation of the rotating shaft. It is characterized in that it has a deflection suppressing means (for example, the contact portion 37e) that suppresses the deflection of the rotating shaft due to the reaction force that the rotating shaft receives.
According to this aspect, the deflection of the rotating shaft is suppressed so that the pressing part on the rotating shaft can appropriately press the urging support part, and the target urging force (contact pressure of the roller pair) is achieved. Obtainable.

[16th aspect]
A 16th aspect is characterized in that, in any of the 6th to 15th aspects, the second conveyance path is a manual feeding conveyance path (for example, manual paper feeding path R2).
According to this, the operation of the movable member of the manual feeding path can be used to switch the contact pressure of the roller pair within the apparatus main body in order to remove the sheet remaining within the apparatus main body.

[Seventeenth aspect]
A seventeenth aspect is one of the sixth to sixteenth aspects, characterized in that the movable member is operated when a conveyance failure occurs in the sheet conveyed in the first conveyance path. be.
According to this aspect, when a conveyance failure occurs in a sheet conveyed in the first conveyance path, the contact pressure between the pair of rollers in the first conveyance path is reduced to reduce the force required to pull out the sheet. By weakening it, it is possible to suppress sheet tearing and improve workability when removing the sheet.

[18th aspect]
An 18th aspect is that in any one of the 6th to 17th aspects, a maximum load L1 occurs during a sheet conveyance operation of the movable member that operates when the sheet is conveyed in the second conveyance path. Maximum load operation position P1 of the member and maximum load operation position P2 of the movable member where the maximum load L2 occurs during the urging force switching operation of the movable member when the urging force by the urging means is switched by the urging force switching means. It is characterized by the fact that they are shifted from each other.
If the two maximum load operating positions P1 and P2 match (overlap) each other, the maximum load that can be generated on the movable member is the maximum load L1 and L2 at the two maximum load operating positions P1 and P2. It is the sum of When such a large load is generated, a drive mechanism that can handle the large load is required as a drive mechanism for operating the movable member, leading to increased costs. Furthermore, various components must be able to withstand large loads, which leads to higher costs and weight.
According to this aspect, since the two maximum load operating positions P1 and P2 are shifted from each other (do not overlap), the maximum load that can be generated on the movable member is at most the two maximum load operating positions P1 and P2. This is smaller than the sum of the maximum loads L1 and L2 at . Therefore, compared to the case where the two maximum load operating positions P1 and P2 match (overlap) each other, it is possible to reduce the cost and weight.

[19th aspect]
In a 19th aspect, in the 18th aspect, a load occurring during the sheet conveying operation and a load occurring during the urging force switching operation are equal to the maximum load L1 occurring during the sheet conveying operation and the urging force. It is characterized in that it is always smaller than the larger of the maximum loads L2 occurring during the switching operation.
According to this, cost reduction and weight reduction can be achieved.

[Twentieth aspect]
In a 20th aspect, in the 19th aspect, a load occurring during the sheet conveying operation and a load occurring during the urging force switching operation are equal to the maximum load L1 occurring during the sheet conveying operation and the urging force. It is characterized in that it is always smaller than the smaller of the maximum loads L2 occurring during the switching operation.
According to this, further cost reduction and weight reduction can be achieved.

[21st aspect]
In a twenty-first aspect, in any one of the sixth to seventeenth aspects, the movable member rotates a rotation shaft (for example, the manual feed bottom plate cam shaft 65) when the sheet is conveyed in the second conveyance path. The biasing force switching means operates by changing the pressing state of the first cam (for example, the manual bottom plate cam 35) on the rotating shaft, and the biasing force switching means operates by changing the pressing state of the first cam (for example, the manual feed bottom plate cam 35) on the rotating shaft. By changing the pressing state in which the pressing part (for example, the pressing part 65e) presses the urging support part (for example, the pressure plate 37d) that supports the urging means, the urging support part is moved and the urging force is applied by the urging means. a maximum pressing force rotation position P1 of the movable member where the maximum pressing force of the first cam occurs during the sheet conveying operation of the movable member when the sheet is conveyed in the second conveying path by switching the force; A maximum pressing force rotation position P2 of the movable member at which the maximum pressing force of the second cam occurs during the urging force switching operation of the movable member when switching the urging force by the urging means by the urging force switching means, They are characterized by being shifted from each other.
If the two maximum pressing force rotation positions P1 and P2 match (overlap) each other, the maximum load that can be generated on the movable member will be at the maximum pressing force at the two maximum pressing force rotation positions P1 and P2. It is the sum of the loads when pressure is generated. When such a large load is generated, a drive mechanism that can handle the large load is required as a drive mechanism for operating the movable member, leading to increased costs. Furthermore, various components must be able to withstand large loads, which leads to higher costs and weight.
According to this aspect, since the two maximum pressing force rotation positions P1 and P2 are shifted from each other (do not overlap), the load that may be generated on the movable member is at most the maximum pressing force rotation position P1, P2. , P2, each of which is smaller than the sum of the loads when the maximum pressing force is generated. Therefore, compared to the case where the two maximum pressing force rotation positions P1 and P2 match (overlap) each other, it is possible to reduce the cost and weight.

[22nd aspect]
In a twenty-second aspect, in the twenty-first aspect, a deviation angle between a maximum pressing force rotation position P1 of the movable member during the sheet conveying operation and a maximum pressing force rotation position P2 of the movable member during the urging force switching operation. is 180°.
According to this aspect, even if the rotational position of the movable member varies somewhat due to dimensional errors of parts, control errors, etc., the two maximum pressing force rotational positions P1 and P2 coincide (overlap) with each other. Such a situation is unlikely to occur. Therefore, it is possible to stably suppress an excessive load from being applied to the operation of the movable member.

1: Photoconductor 30: Manual feed section 31: Manual feed tray 32: Manual feed roller 33: Separation pad 34: Manual feed bottom plate 34a: Bottom plate guide section 35: Manual feed bottom plate cam 36: Bottom plate spring 37a: Bearing section 37b: Pressure Spring 37c: Slide elongated hole 37d: Pressure plate 37e: Contact portion 38: Support frame 38b: Mounting member 39: Opening/closing door 41: Main body paper feed roller 42: Relay roller pair 42a: Relay drive roller 42b: Relay driven roller 43: Registration Roller pair 44: Fixing device 46: Paper ejection roller pair 47: Switching claw 48: Separation pad 49: Registration sensor 50: Main body housing 51: Control unit 61: Main motor 61a: Motor shaft 62: Paper feed roller shaft 62a: Main body Paper feed clutch 63: Relay roller shaft 63a: Relay clutch 64: Manual paper feed roller shaft 64a: Manual paper 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 part 66: Roller shaft 100: Paper feed cassette 101: Main body paper feed bottom plate R1: Main body paper feed path R2: Manual paper feed path R3: Common conveyance path R4: Paper discharge path R5: Reverse refeed path S: Recording sheet

Japanese Patent Application Publication No. 2006-39336

Claims (17)

An image forming apparatus that forms an image on a sheet conveyed by a sheet conveying device,
The sheet conveying device includes:
a pair of rollers configured such that the rollers cannot be separated from each other, and which sandwich a sheet conveyed through a first conveyance path of the plurality of conveyance paths;
urging means for urging one roller constituting the roller pair toward the other roller;
and urging force switching means for switching the urging force of the urging means depending on the type of the sheet before the sheet is held between the pair of rollers;
The urging force switching means switches the urging force of the urging means in conjunction with the operation of a movable member that operates when the sheet is conveyed through a second conveyance path among the plurality of conveyance paths. Features of the image forming device . The image forming apparatus according to claim 1 ,
An image forming apparatus characterized in that the sheet placed on the sheet placement section is fed to the second conveyance path by operating the movable member. The image forming apparatus according to claim 2 ,
The image forming apparatus is characterized in that the sheet feeding is performed by raising or lowering the movable member and bringing the sheet into contact with a feeding roller. The image forming apparatus according to any one of claims 1 to 3 ,
The movable member operates by rotating a rotating shaft,
The image forming apparatus is characterized in that the biasing force switching unit switches the biasing force of the biasing unit by moving a biasing support portion that supports the biasing unit in conjunction with rotation of the rotating shaft. . The image forming apparatus according to claim 4 ,
The biasing force switching means changes the pressing state in which a cam on the rotary shaft presses the biasing support portion by rotating the rotary shaft, thereby moving the biasing support portion between a first movement position and a second movement position. Move to the moving position,
The biasing support section is characterized in that its movement is regulated by a member different from the cam when it is located at one of the first and second movement positions. Image forming device. The image forming apparatus according to claim 5 ,
The image forming apparatus is characterized in that the another member restricts movement of the biasing support section by making surface contact with the biasing support section. The image forming apparatus according to claim 5 or 6 ,
The image forming apparatus is characterized in that the other member is an attachment member attached to a support member that movably supports the urging support section. The image forming apparatus according to any one of claims 4 to 7 ,
The biasing force switching means is configured such that, due to rotation of the rotating shaft, a pressing portion on the rotating shaft presses the biasing support portion at a position shifted from a support position of the biasing means in the biasing support portion; An image forming apparatus characterized in that the biasing support section is moved. The image forming apparatus according to claim 8 ,
The pressing part is a cam,
An image forming apparatus characterized in that the diameter of the cam is constant within a predetermined angular width including a rotation angle of the rotation shaft when obtaining a biasing force according to the type of sheet. The image forming apparatus according to any one of claims 4 to 9 ,
When the rotation of the rotation shaft causes a pressing part on the rotation shaft to press the biasing support part and move the bias support part, the rotation shaft is prevented from being bent by a reaction force received by the rotation shaft. An image forming apparatus characterized by having a deflection suppressing means. The image forming apparatus according to any one of claims 1 to 10 ,
The image forming apparatus is characterized in that the second conveyance path is a manual feeding conveyance path. The image forming apparatus according to any one of claims 1 to 11 ,
An image forming apparatus characterized in that the movable member is operated when a conveyance failure occurs in a sheet conveyed through the first conveyance path. The image forming apparatus according to any one of claims 1 to 12 ,
The maximum load operation position of the movable member where the maximum load occurs during the sheet conveyance operation of the movable member that operates when the sheet is conveyed in the second conveyance path, and the biasing force switching means An image forming apparatus characterized in that the maximum load operating positions of the movable member where the maximum load is generated during the biasing force switching operation of the movable member when switching the biasing force are shifted from each other. The image forming apparatus according to claim 13 ,
The load generated during the sheet conveyance operation and the load generated during the urging force switching operation are the maximum load generated during the sheet conveyance operation and the maximum load generated during the urging force switching operation. An image forming apparatus characterized in that the image forming apparatus is always smaller than the larger of the two. The image forming apparatus according to claim 14 ,
The load generated during the sheet conveyance operation and the load generated during the urging force switching operation are the maximum load generated during the sheet conveyance operation and the maximum load generated during the urging force switching operation. An image forming apparatus characterized in that the image forming apparatus is always smaller than the smaller of the two. The image forming apparatus according to any one of claims 1 to 12 ,
The movable member operates by rotating a rotating shaft and changing the pressing state of the first cam on the rotating shaft when the sheet is transported through the second transporting path,
The biasing force switching means changes the pressing state in which the second cam on the rotating shaft presses the biasing support unit that supports the biasing unit by rotating the rotating shaft. to switch the urging force of the urging means,
A maximum pressing force rotation position of the movable member at which the maximum pressing force of the first cam occurs during sheet conveying operation of the movable member when the sheet is conveyed in the second conveying path, and the urging force switching means The maximum pressing force rotation position of the movable member at which the maximum pressing force of the second cam occurs during the urging force switching operation of the movable member when switching the urging force of the urging means is shifted from each other. Features of the image forming device. The image forming apparatus according to claim 16 ,
Image formation characterized in that a deviation angle between a maximum pressing force rotation position of the movable member during the sheet conveying operation and a maximum pressing force rotation position of the movable member during the urging force switching operation is 180°. Device.

Images