CN112782948A - Sheet conveying device and image forming apparatus - Google Patents

Abstract

A sheet conveying device and an image forming apparatus. The sheet conveying device includes a pair of rollers and a biasing unit. The pair of rollers is configured to nip the conveyed sheet. The biasing unit is configured to bias one roller of the pair of rollers toward the other roller of the pair of rollers. The pair of rollers are configured not to be separated from each other. The sheet conveying device further includes a biasing force switching unit configured to switch a biasing force of the biasing unit according to a type of the sheet before the sheet is nipped by the pair of rollers.

Description

Sheet conveying device and image forming apparatus

Technical Field

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

Background

There is known a sheet conveying device including a pair of rollers for nipping a sheet being conveyed and a biasing unit for biasing one roller of the pair of rollers toward the other roller.

For example, japanese unexamined patent application publication No. 2006-. If a paper jam is detected in the apparatus, the solenoid of the nip release mechanism operates the arm member, and therefore, the shaft of the conveying roller moves in a direction away from the drive roller. Therefore, the nip pressure between the conveying roller and the conveying roller is released, and a state is achieved in which the nip pressure (contact pressure) acting between the conveying roller and the conveying roller is low.

When attempting to pull out a sheet nipped by a pair of rollers after a jam occurs, and if the contact pressure of the pair of rollers is low, the sheet is not generally torn when the sheet is pulled out. In a mechanism in which a solenoid as a nip release unit is activated in a conventional manner based on a detection result of a jam detection sensor to separate a pair of rollers, even if a jam occurs, the conventional mechanism may not be able to release the contact pressure of the pair of rollers due to a detection error or a jam detection sensor malfunction or a solenoid malfunction. That is, in the configuration in which the contact pressure of the pair of rollers is released after the jam is detected, the sheet may be torn when the sheet is pulled out.

As described above, if a mechanism that separates a pair of rollers by the operation of a solenoid and when the image forming apparatus includes a configuration that deactivates the solenoid while a paper jam (hereinafter referred to as "immediate stop") occurs, a problem occurs in that the contact pressure of the pair of rollers cannot be released as described above.

Further, since the solenoid is used, a mechanism for separating the pair of rollers is complicated. Therefore, the size and cost of the apparatus increase.

Disclosure of Invention

According to one aspect of the present invention, a sheet conveying apparatus includes a pair of rollers and a biasing unit. The pair of rollers is configured to nip the conveyed sheet. The biasing unit is configured to bias one roller of the pair of rollers toward the other roller of the pair of rollers. The pair of rollers are configured not to be separated from each other. The sheet conveying device further includes a biasing force switching unit configured to switch a biasing force of the biasing unit according to a type of the sheet before the sheet is nipped by the pair of rollers.

According to an aspect of the present invention, even if the contact pressure of the pair of rollers cannot be released due to a detection error or a malfunction of the jam detection sensor, a malfunction of the separation mechanism, or an immediate stop of the image forming apparatus, since an operation of reducing the contact pressure of the pair of rollers is not required after the occurrence of the jam, it is possible to prevent the sheet from tearing when the sheet is pulled out from the pair of rollers.

Drawings

FIG. 1 is a schematic diagram illustrating a printer according to one embodiment;

fig. 2 is an enlarged schematic view showing the photosensitive body and the configuration around the photosensitive body in the printer according to the embodiment;

fig. 3 is a perspective view showing the main configuration of a main sheet feeding unit that feeds a recording sheet from a sheet feeding cassette and a bypass sheet feeding unit that feeds a recording sheet from a bypass sheet feeder in the printer according to the embodiment;

fig. 4 is a perspective view showing the configuration of a main body sheet feeding unit according to the embodiment and a drive system of a bypass sheet feeding unit according to the embodiment;

fig. 5 is an explanatory diagram showing a main body sheet feeding unit according to the embodiment and a sheet feeding path of a bypass sheet feeding unit according to the embodiment;

fig. 6 is a flowchart showing a control operation for sheet-feed conveyance from the main body sheet-feed unit according to the embodiment;

fig. 7 is an external perspective view of the bypass sheet feeding unit according to the embodiment, in which the bypass sheet feeder is removed from the bypass sheet feeding unit;

fig. 8 is a perspective view showing a main part of the bypass sheet feeding unit according to the embodiment;

fig. 9 is a flowchart showing a control operation for sheet-feed conveyance from the bypass sheet-feed unit according to the embodiment;

fig. 10 is a perspective view showing a bypass bottom plate separated from a bypass sheet feeding roller;

fig. 11A is a perspective view showing an opening and closing door with a bypass paper feeder attached, opened from the main body of the printer;

fig. 11B is a perspective view showing the opening and closing door with the bypass paper feeder attached, opened from the main body of the printer;

fig. 12A is a perspective view showing the opening and closing door with a bypass paper feeder attached, closed on the main body of the printer;

fig. 12B is a perspective view showing the opening and closing door with the bypass paper feeder attached, closed on the main body of the printer;

fig. 13A is a perspective view showing an opening and closing door closed on the printer main body in a state where the bypass paper feeder is opened;

fig. 13B is a perspective view showing an opening and closing door closed on the printer main body in a state where the bypass paper feeder is opened;

fig. 14A is an explanatory view showing a biasing force switching unit that switches a biasing force of a pressing spring that biases a bearing of the driven relay roller toward the driving relay roller;

fig. 14B is an explanatory view showing a biasing force switching unit that switches the biasing force of the pressing spring that biases the bearing of the driven relay roller toward the driving relay roller;

fig. 15A is a perspective view showing a main configuration of the biasing force switching unit;

fig. 15B is a perspective view showing the main configuration of the biasing force switching unit;

fig. 16A is a front view showing a mechanism that supports the driven relay roller;

fig. 16B is a perspective view showing a mechanism that supports the driven relay roller;

fig. 17A is an explanatory diagram showing the position of the pressure plate urged by the urging unit on the bypass floor camshaft;

fig. 17B is an explanatory diagram showing the position of the pressure plate urged by the urging unit on the bypass floor camshaft;

fig. 17C is an explanatory view showing the position of the pressure plate urged by the urging unit on the bypass floor camshaft;

fig. 18A is an explanatory diagram showing the shape of the pressing unit on the bypass floor camshaft;

fig. 18B is an explanatory diagram showing the shape of the pressing unit on the bypass floor camshaft;

fig. 19 is an explanatory view showing a warp prevention unit that prevents warp of a bypass floor camshaft including a pressing unit that presses a pressing plate;

FIG. 20 is a flowchart illustrating processing of the printer at an abnormal stop according to one embodiment;

fig. 21 is a graph showing an example in which, when the recording paper is fed from the bypass paper feeder, the maximum load operation position of the bypass bottom plate cam shaft corresponds to the maximum load operation position of the bypass bottom plate cam shaft when the nip pressure of the pair of relay rollers is switched;

fig. 22 is a graph showing an example in which, when the recording paper is fed from the bypass paper feeder, the maximum load operation position of the bypass floor cam shaft is shifted from the maximum load operation position of the bypass floor cam shaft when the nip pressure of the pair of relay rollers is switched;

fig. 23 is a graph showing another example in which, when the recording paper is fed from the bypass paper feeder, the maximum load operation position of the bypass floor cam shaft is offset from the maximum load operation position of the bypass floor cam shaft when the nip pressure of the pair of relay rollers is switched;

fig. 24 is a graph showing another example of further increasing the offset amount;

fig. 25A is a perspective view showing a main configuration of the biasing force switching unit;

fig. 25B is a perspective view showing the main configuration of the biasing force switching unit;

fig. 26 is an enlarged view showing a portion where the pressing plate contacts with an attaching member attached to the support frame of the bypass sheet feeding unit; and

fig. 27 is an external perspective view of the pair of relay rollers as viewed obliquely from below.

The drawings are intended to depict exemplary embodiments of the invention, and should not be construed as limiting the scope thereof. In the various drawings, like or similar reference numbers indicate like or similar elements.

Detailed Description

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.

As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise.

In describing the preferred embodiments illustrated in the drawings, specific terminology may be resorted to for the sake of clarity. However, the disclosure of this patent specification is not intended to be limited to the specific terminology so selected, and it is to be understood that each specific element includes all technical equivalents that perform the same function, operate in a similar manner, and achieve a similar result.

Embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Hereinafter, an electrophotographic printer (hereinafter simply referred to as a printer) will be given as an example of an image forming apparatus to which the present invention is applied. The printer forms an electrophotographic image.

First, a basic configuration of a printer according to one embodiment will be described.

Fig. 1 is a schematic diagram showing a printer according to this embodiment.

In fig. 1, the printer includes, for example, a photoreceptor 1 and a paper supply cassette 100. The photoreceptor 1 is a latent image carrier. The paper supply cassette 100 is a paper accommodating unit attachable to and detachable from the main body case 50. The sheet feed cassette 100 accommodates a stack of a plurality of recording sheets S.

The recording paper S is fed from the inside of the paper feed cassette 100 by driving the main paper feed roller 41 to rotate. At the separation nip between the main body sheet feed roller 41 and the separation pad 48, only the top sheet of the recording sheet S is separated, and fed to enter the main body sheet feed path R1 as the first conveying path. Then, the recording paper S is held (nipped) between the conveying nips of the pair of relay rollers 42 as the upper pair of conveying rollers, and is conveyed from upstream to downstream through the main body paper feed path R1. The pair of relay rollers 42 is a pair of conveying rollers above the main body paper feed roller 41. Note that at least one pair of rollers of the pair of conveying rollers may be a pair of conveying belts.

The downstream end of the main body sheet feed path R1 is connected to the common conveying path R3. A pair of registration rollers 43 is arranged in the common conveying path R3. The registration sensor 49 is provided in the common conveyance path R3. The registration sensor 49 is located upstream of the pair of registration rollers 43 in the conveying direction. The registration sensor 49 detects the recording sheet S. The conveyance of the recording sheet S is temporarily stopped while the leading end of the recording sheet S is abutted against the nip of the pair of registration rollers 43 that are stopped. Skew of the recording sheet S is corrected while the leading end of the recording sheet S is abutted against the nip. Note that the registration sensor 49 is used, for example, for an initial operation and an operation of determining whether or not a sheet stays at the time of restart after an abnormal stop of the apparatus (jam detection operation).

At a timing allowing the recording sheet S to be placed on the toner image on the surface of the photoconductor 1 at the transfer nip, the pair of registration rollers 43 starts to be driven to rotate. A pair of registration rollers 43 feeds the recording sheet S to the transfer nip. At this time, the pair of relay rollers 42 simultaneously starts to be driven to rotate, and resumes the conveyance of the recording sheet S that was temporarily stopped.

The main body casing 50 of the present printer includes a bypass sheet feeding unit 30 as a bypass sheet feeder unit including a bypass sheet feeder 31, a bypass sheet feeding roller 32, a separation pad 33 and a bypass bottom plate 34, a bypass bottom plate cam 35. Details of the bypass sheet feed unit 30 will be described later. The recording sheet S is manually loaded onto the bypass sheet feeder 31 of the bypass sheet feeding unit 30. The recording sheet S is fed from the bypass paper feeder 31 to the bypass paper feed path R2 by the bypass paper feed roller 32 being driven to rotate. The bypass sheet supply path R2 is a second conveyance path. The downstream end of the bypass sheet supply path R2 and the downstream end of the main body sheet supply path R1 merge into a common conveyance path R3. The recording sheet S fed by the bypass sheet-feed roller 32 passes through the separation nip in the bypass sheet-feed path R2, and then is fed to the common transport path R3, and is transported to the pair of registration rollers 43. The separation nip is formed by the bypass sheet feed roller 32 and the separation pad 33 contacting each other. Then, the recording sheet S passes through a pair of registration rollers 43 and is then conveyed to the transfer nip, similarly to the recording sheet S fed from the sheet feed cassette 100.

Fig. 2 is an enlarged schematic view showing the photoconductor 1 and the configuration around the photoconductor 1 in the present printer.

In fig. 2, the photoconductor 1 is drum-shaped and is driven to rotate clockwise. Around the photoreceptor 1, a cleaning blade 2, a collecting 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, and the like are arranged. The charging roller 4 includes a conductive rubber roller. The charging roller 4 rotates while contacting the photoreceptor 1 and forms a charging nip. The charging power supply applies a voltage to the charging roller 4. Therefore, at the charging nip, a charging bias is generated between the surface of the photoreceptor 1 and the surface of the charging roller 4. The charging bias uniformly charges the surface of the photoreceptor 1.

The latent image writing device 7 includes a Light Emitting Diode (LED) array. The latent image writing device 7 writes a latent image on the surface of the uniformly charged photoconductor 1 using LED light. Although the surface of the photoconductor body 1 has been uniformly charged, the potential is reduced at the region of the surface irradiated with the writing light. An electrostatic latent image is formed on the surface of the photoreceptor 1.

As the photoreceptor 1 rotates, the electrostatic latent image passes through the development region. The developing area is opposed to the developing device 8. The developing device 8 includes a circulation and conveyance unit and a developing unit. The circulation and conveyance unit contains a developer containing a toner and a magnetic carrier. The circulation and conveyance unit includes a first screw 8b and a second screw 8 c. The first screw 8b conveys the supplied developer to the developing roller 8 a. The second screw 8c conveys the developer in a separate space directly below the first screw 8 b. The circulation and conveyance unit further includes an inclined screw 8d, and the inclined screw 8d transfers the developer from the second screw 8c to the first screw 8 b. The developing roller 8a, the first screw 8b, and the second screw 8c are arranged in parallel with each other. In contrast, the inclined screw 8d is inclined with respect to the developing roller 8a, the first screw 8b, and the second screw 8 c.

In a case where the first screw 8b itself is driven to rotate, the first screw 8b conveys the developer from the far side to the near side of fig. 2 in a direction perpendicular to fig. 2. At this time, the first screw 8b supplies a part of the developer to the developing roller 8a disposed opposite to the first screw 8 b. The first screw 8b conveys the developer in the direction perpendicular to fig. 2 to the vicinity of one end on the near side in fig. 2. The developer falls on the second screw 8 c.

While the second screw 8c receives the used developer from the developing roller 8a, the second screw 8c rotates. In a case where the second screw 8c itself is driven to rotate, the second screw 8c conveys the received developer from the far side to the near side in fig. 2 in a direction perpendicular to fig. 2. The second screw 8c conveys the developer in the direction perpendicular to fig. 2 to the vicinity of one end on the near side in fig. 2. The developer is transferred to the inclined screw 8 d. Then, with the oblique screw 8d driven to rotate, the developer is conveyed from the near side to the far side in fig. 2 in the direction perpendicular to fig. 2. Then, the developer is transferred to the first screw 8b around one end on the far side in the direction.

The developing roller 8a includes a developing sleeve and a magnetic roller. The developing sleeve includes a tubular nonmagnetic member. The developing sleeve may be rotated. The magnetic roller is fixed inside the sleeve and thus does not rotate with the developing sleeve. A part of the developer conveyed by the first screw 8b is attracted to the surface of the developing sleeve by the magnetic force of the magnetic roller. The rotation of the developing sleeve conveys the developer carried on the surface of the developing sleeve. The thickness of the developer layer is regulated when the developer passes through a facing position where the developing sleeve and the doctor blade face each other. Then, the developer is conveyed through a developing region where the developer opposes the photoreceptor 1 while the developer and the surface of the photoreceptor 1 are rubbed together.

A developing bias is applied to the developing sleeve. The polarity of the developing bias is the same as the polarity (background potential) for uniformly charging the toner and the photoreceptor 1. The absolute value of the developing bias is larger than the absolute value of the latent image potential. Further, the absolute value of the developing bias is smaller than the absolute value of the background potential. Therefore, in the developing region, a developing potential acts between the electrostatic latent image on the photoreceptor 1 and the developing sleeve. The developing potential electrostatically transfers the toner from the developing sleeve to the photoreceptor 1. On the other hand, the background potential acts between the background of the photoreceptor 1 and the developing sleeve. The background potential electrostatically transfers the toner from the photoreceptor 1 to the developing sleeve. Accordingly, in the developing region, the toner selectively adheres to the electrostatic latent image on the photoreceptor 1, and develops the electrostatic latent image.

The developer having passed through the development region is conveyed to the facing region between the development sleeve and the second screw 8c by the rotation of the development sleeve. In the facing region, of the plurality of magnetic poles of the magnetic roller, two magnetic poles having the same polarity form a repulsive magnetic field. The developer having entered the facing area is caused to exit from the surface of the developing sleeve by the action of the repulsive magnetic field. Then, the developer is collected by the second screw 8 c.

The developer conveyed by the inclined screw 8d contains the developer collected from the developing roller 8 a. Since the developer contributes to development in the development area, the developer has a lower toner concentration. The developing device 8 includes a toner concentration sensor. The toner concentration sensor detects the toner concentration of the developer conveyed by the inclined screw 8 d. Based on the detection result of the toner concentration sensor, the control unit 51 including a semiconductor circuit such as a Central Processing Unit (CPU) outputs a supply operation signal for supplying toner to the developer conveyed by the inclined screw 8d, as necessary.

The toner cartridge 9 is disposed above the developing device 8. The toner cartridge 9 includes an agitator 9b fixed to the rotation shaft member 9 a. The agitator 9b fixed to the rotary shaft member 9a agitates the toner contained in the toner cartridge 9. The toner supplying member 9c is driven to rotate in response to a supply operation signal output from the control unit 51, thereby supplying an amount of toner corresponding to the amount by which the toner supplying member 9c is driven to rotate to the inclined screw 8d of the developing device 8.

A toner image is formed on the photoreceptor 1 by development. The toner image is conveyed into the transfer nip by the rotation of the photoreceptor 1. The photoreceptor 1 contacts the transfer roller 10 at the transfer nip. A voltage is applied to the transfer roller 10. The polarity of the voltage is opposite to the polarity of the latent image potential of the photoreceptor 1. Thus, a transfer bias is formed in the transfer nip.

As described above, the pair of registration rollers 43 feeds the recording sheet S to the transfer nip at a timing allowing the recording sheet S to be placed on the toner image on the photoconductor 1 in the transfer nip. The recording paper is brought into close contact with the toner image at the transfer nip. The toner image on the photoreceptor 1 is transferred onto the recording paper by the action of the transfer bias and the nip pressure.

After the surface of the photoreceptor 1 passes through the transfer nip, the toner that has not been transferred onto the recording sheet S remains on the surface. The untransferred toner is scraped off from the surface of the photoreceptor 1 by the cleaning blade 2 in contact with the photoreceptor 1. Then, the scraped-off toner is conveyed to the waste toner bottle by the collection screw 3.

The discharge unit discharges from the surface of the photoreceptor 1 that has been cleaned by the cleaning blade 2. Then, the charging roller 4 uniformly charges the surface again. Foreign matter adheres to the charging roller 4 that is in contact with the surface of the photoreceptor 1. The foreign matter includes the toner additive and the toner not removed by the cleaning blade 2. The foreign matter is transferred to the charging cleaning roller 5 which is in contact with the charging roller 4. Then, foreign matter is scraped off from the surface of the charging cleaning roller 5 by the scraper 6 in contact with the charging cleaning roller 5. The scraped foreign matter falls on the above-mentioned collection screw 3.

In fig. 1, the recording sheet S having passed through a transfer nip where the photosensitive body 1 is in contact with the transfer roller 10 is conveyed to a fixing device 44. The fixing device 44 includes a fixing roller 44a and a pressure roller 44 b. The fixing roller 44a contains a heat source such as a halogen lamp. The pressure roller 44b is pushed toward the fixing roller 44 a. The fixing roller 44a and the pressure roller 44b contacting each other form a fixing nip. The toner image is fixed onto the surface of the recording sheet S held between the fixing nips by the action of heat and pressure. Then, the recording sheet S passes through the fixing device 44 and a sheet discharge path R4. Then, the recording sheet S is held between the sheet discharging nips of the pair of sheet discharging rollers 46.

The present printer can switch between a single-sided mode for forming an image on one side of the recording sheet S and a double-sided mode for forming an image on both sides of the recording sheet S, and execute the single-sided mode or the double-sided mode. In the case of the single-sided mode, the pair of sheet-discharge rollers 46 continues to rotate normally, and therefore the recording sheet S in the sheet-discharge path R4 is discharged from the printer. Alternatively, if images have been formed on both sides of the recording sheet in the duplex mode, the pair of sheet-discharge rollers 46 continues to rotate normally, and thus the recording sheet S in the sheet-discharge path R4 is discharged from the printer. The discharged recording sheet S is stacked on a stacking unit on the top surface of the main body casing 50.

On the other hand, if an image is formed on only one side of the recording sheet S in the duplex mode, the pair of sheet-discharge rollers 46 are rotated reversely at the timing when the trailing end of the recording sheet S enters the sheet-discharge nip of the pair of sheet-discharge rollers 46. At this time, the switching claw 47 is activated to close the sheet discharging path R4 and open the opening of the reverse rotation returning path R5. The switching claw 47 is provided in the vicinity of the downstream end of the sheet discharge path R4. The recording sheet S starts to be returned by the pair of sheet-discharge rollers 46 which rotate in the reverse direction. The recording sheet S is fed to the reverse-rotation return path R5. The downstream end of the reverse-rotation return path R5 merges with the common conveying path R3 at a position upstream of the pair of registration rollers 43. The recording sheet S is conveyed through the reverse-rotation return path R5. Then, the recording sheet S is conveyed again to the pair of registration rollers 43 in the common conveying path R3. Then, the toner image is transferred to the other side at the transfer nip. Then, the recording sheet S passes through the fixing device 44, the sheet discharge path R4, and the pair of sheet discharge rollers 46, and is discharged from the printer.

Next, the configuration and operation relating to the feeding of the recording sheet S will be described.

Fig. 3 is a perspective view showing the main configuration of the main body sheet feeding unit and the bypass sheet feeding unit 30. The main sheet feeding unit supplies recording sheets S from the sheet feeding cassette 100. The bypass sheet feeding unit 30 feeds the sheet of recording paper S from the bypass paper feeder 31.

Fig. 4 is a perspective view showing the configuration of the drive system of the main body sheet feeding unit and the bypass sheet feeding unit 30.

As shown in fig. 3 and 4, the driving system of the main body sheet feeding unit and the bypass sheet feeding unit 30 distributes driving force from one main motor 61 to the main body sheet feeding roller 41, the pair of relay rollers 42, the bypass sheet feeding roller 32, and the bypass floor cam 35 to drive the main body sheet feeding roller 41, the pair of relay rollers 42, the bypass sheet feeding roller 32, and the bypass floor cam 35. Specifically, the driving force output from the motor shaft 61a of the main motor 61 is transmitted to the sheet feed roller shaft 62, the relay roller shaft 63, the bypass sheet supply roller shaft 64, and the bypass floor cam shaft 65 through, for example, respective idler gears. The main body sheet feed roller 41 is attached to the sheet feed roller shaft 62. A pair of relay rollers 42 are attached to the relay roller shaft 63. The bypass sheet feeding roller 32 is attached to the bypass sheet feeding roller shaft 64. The bypass floor cam 35 is attached to a bypass floor camshaft 65.

The sheet feed roller shaft 62 includes a clutch 62 a. The relay roller shaft 63 includes a clutch 63 a. The bypass sheet feed roller shaft 64 includes a clutch 64 a. The bypass floor camshaft 65 includes a clutch 65 a. The clutches 62a, 63a, 64a, and 65a respectively turn on or off the transmission of the driving force. If the electric power of each clutch is turned on, the driving force is transmitted to each of the shafts 62, 63, 64, and 65, and each of the shafts 62, 63, 64, and 65 is driven to rotate. If the electric power of each clutch is disconnected, the driving force is not transmitted to each of the shafts 62, 63, 64, and 65, and each of the shafts 62, 63, 64, and 65 is not driven to rotate. Note that the driving force from the main motor 61 is also transmitted to the pair of registration rollers 43 through the clutch. In the present embodiment, in order to feed and convey the recording sheet S, the driving force of the main motor 61 is used, and the control unit 51 turns each clutch on or off.

Fig. 5 is an explanatory diagram showing the sheet feeding paths of the main body sheet feeding unit and the bypass sheet feeding unit 30.

First, sheet feeding conveyance from the main body sheet feeding unit will be described with reference to a flowchart shown in fig. 6.

The main body sheet supply base plate 101 is biased upward toward the main body sheet feed roller 41. Thus, the main body sheet feed roller 41 comes into contact with the top recording sheet S of the stack of a plurality of recording sheets S loaded on the main body sheet feed base plate 101. If the sheet-feed conveyance from the main body sheet feed unit is started, the control unit 51 first determines whether the initial operation has been completed (S1). If the initial operation has not been completed (NO in S1), the initial operation is started (S2). Here, the "initial operation" is an operation of positioning the bypass substrate 34 at the lowermost position (see fig. 10, 14A, and 15A). After the initial operation is completed, the nip pressure of the pair of relay rollers 42 is set to a low nip pressure.

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 paper sheet S to be fed is thin paper or plain paper (S4). In the present embodiment, the user operates the operation panel of the present printer to select a paper type as the recording paper S accommodated in the paper supply cassette 100 from among paper types that can be printed with the printer. Types of paper include, for example, plain paper (low-strength paper), thin paper (low-strength paper), and thick paper (high-strength paper). The selection result is stored in the storage unit of the control unit 51. In the processing step S4 in the present embodiment, the control unit 51 refers to the contents of the storage unit, and determines whether the recording paper sheet S to be fed is thin paper or plain paper.

Note that the method of determining whether the recording paper is thin paper or plain paper is not limited to this method. For example, the thickness detection sensor may detect the thickness of the recording sheet S accommodated in the paper supply cassette 100, or may detect the thickness of the recording sheet S fed from the paper supply cassette 100. Based on the detection result, it is possible to determine whether the recording sheet S to be fed is thin paper or plain paper.

In the present embodiment, the type of the recording sheet S as the determination target depends on the difference in thickness of the recording sheet S. However, the type of the recording sheet S as the determination target may depend on a difference in characteristics that affect a difference in strength of the recording sheet S or a difference in conveyance load of the recording sheet S, such as a difference in material of the recording sheet S or a difference in size of the recording sheet S.

In the present embodiment, if it is determined whether the recording sheet S to be fed is thin paper or plain paper (yes in S4), the control unit 51 maintains the low nip pressure of the pair of relay rollers 42 since the nip pressure has been set to the low nip pressure by the above-described initial operation.

Alternatively, if it is determined that the recording sheet S to be fed is not thin paper or plain paper (if it is determined that the recording sheet S to be fed is thick paper) (no in S4), the control unit 51 performs a processing operation of increasing the nip pressure of the pair of relay rollers 42. Specifically, since the nip pressure of the pair of relay rollers 42 is set to the low nip pressure at the initial operation, the control unit 51 turns on the bypass floor cam clutch 65a (S5) to drive the bypass floor cam shaft 65 to rotate clockwise in fig. 5. If the filler sensor 65c is turned off (yes in S6) (see fig. 8, 14B, and 15B), the control unit 51 turns off the bypass floor cam clutch 65a (S7) to stop the rotation of the bypass floor camshaft 65.

The driven relay roller 42b as the other roller of the pair of relay rollers 42 has a roller shaft 66 supported by the bearing 37 a. As shown in fig. 5, the bearing 37a is biased by a compression spring 37b as a compression spring. This biasing force brings the driven relay roller 42b into contact with the driving relay roller 42 a. When the bypass floor camshaft 65 stops at the above-described rotational position, the compression amount of the compression spring 37b is large. Thus, the nip pressure of the pair of relay rollers 42 is switched to the high nip pressure. Note that, a configuration of switching the nip pressure of the pair of relay rollers 42 will be described later.

Then, the control unit 51 turns on the main body sheet feed clutch 62a and the relay clutch 63a (S8). Accordingly, the main-body sheet feeding roller 41 is driven to rotate, and the top recording sheet S in the sheet feeding cassette 100 is fed toward the separation pad 48. At this time, even if the second and subsequent recording sheets are fed from the top together with the top recording sheet S, the second and subsequent recording sheets are not conveyed due to the friction of the separation pad 48. Only the top recording sheet S passes through the separation pad 48. Note that, during the sheet-feed conveyance from the main body sheet-feed unit, the sheet-feed conveyance from the bypass sheet-feed unit 30 is not performed. Therefore, the bypass sheet feed clutch 64a and the bypass floor cam clutch 65a remain open.

Then, the fed recording sheet S is conveyed along a main body sheet feeding path indicated by symbol R1 in fig. 5. At this time, the driving relay roller 42a, which is one of the pair of relay rollers 42, is driven to rotate by the driving force from the main motor 61. The driven relay roller 42b as the other roller of the pair of relay rollers 42 has a roller shaft 66 supported by the bearing 37 a. In the case of thin paper or plain paper, the bearing 37a is biased with a low biasing force by the compression spring 37 b. In the case of thick paper, the bearing 37a is biased with a large biasing force by the pressing spring 37 b. This biasing force brings the driven relay roller 42b into contact with the driving relay roller 42 a. Therefore, the driven relay roller 42b is rotated by the rotating drive relay roller 42 a. While holding (nipping) the recording sheet S between the nips of the drive relay roller 42a and the driven relay roller 42b, the recording sheet S is conveyed through the main body sheet feed path R1.

If one end of the recording sheet S reaches the registration sensor 49 and the registration sensor 49 is turned on (yes in S9), the main body sheet feed clutch 62a and the relay clutch 63a are turned off (S10) after a predetermined period of time has elapsed (before the end of the recording sheet S reaches the pair of registration rollers 43) (e.g., after 100ms after the registration sensor 49 is turned on), thereby temporarily stopping the conveyance of the recording sheet S. Thus, the end of the recording sheet S is brought into abutment against the nip of the pair of registration rollers 43 that have stopped, and the skew of the recording sheet S is corrected.

At timing that allows the recording sheet S to be placed on the toner image on the surface of the photosensitive body 1 at the transfer nip (for example, 200ms after the main body sheet feed clutch 62a and the relay clutch 63a are turned off), the control unit 51 turns on the relay clutch 63a and the registration clutch (S11). Accordingly, the pair of registration rollers 43 and the pair of relay rollers 42 start to be driven to rotate, and the recording sheet S is conveyed to the transfer nip. At this time, the main body sheet feed clutch 62a remains off. Therefore, the main body sheet feed roller 41 is not driven to rotate. Even if the trailing end of the recording sheet S is nipped by the main body sheet feed roller 41 and the separation pad 48, the main body sheet feed roller 41 is rotated by the recording sheet S conveyed by the conveying forces of the pair of registration rollers 43 and the pair of relay rollers 42. The main body paper feed roller 41 does not prevent the conveyance. Then, if 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) to stop driving the pair of relay rollers 42 to rotate.

Next, the sheet feeding conveyance from the bypass sheet feeding unit 30 will be described with reference to fig. 7 to 9.

Fig. 7 is an external perspective view of the bypass sheet feeding unit 30 from which the bypass sheet feeder 31 is removed.

Fig. 8 is a perspective view showing a main part of the bypass sheet feeding unit 30.

Fig. 9 is a flowchart showing a control operation for sheet-feed conveyance from the bypass sheet-feed unit 30.

The bypass floor 34 is biased upward toward the bypass sheet feed roller 32 by a floor spring 36. As shown in fig. 8, the bypass substrate 34 has a substrate guide rail 34a at a position corresponding to the position of the bypass substrate cam 35. If the bypass floor cam shaft 65 is rotated and the bypass floor cam 35 is brought into contact with the floor rail 34a and pressed downward (see fig. 10), the bypass floor 34 is moved downward against the biasing force of the floor spring 36 and separated from the bypass sheet feeding roller 32.

If the sheet-feed conveyance from the bypass sheet-feed unit 30 is started, the control unit 51 first determines whether the initial operation has been completed (S21). If the initial operation has not been completed (NO in S21), the initial operation is started (S22). After the initial operation is completed (yes in S21), the control unit 51 turns on the main motor 61 (S23). Then, the control unit 51 first turns on the bypass floor cam clutch 65a (S24). Accordingly, the bypass floor cam shaft 65 is driven to rotate, and the bypass floor cam 35 is separated from the floor rail 34a (see fig. 5 and 8). Before the bypass floor cam shaft 65 rotates, the bypass floor cam 35 has come into contact with the floor rail 34a (the bypass floor 34 has been separated from the bypass paper-feeding roller 32) (see fig. 10).

Specifically, if the bypass floor camshaft 65 is driven to rotate, the projecting plate 35a integrated with the bypass floor cam 35 rotates from a position where the projecting plate 35a is in contact with and presses down the pressing down lever 65d that presses down the cam detection packing 65b to a position where the projecting plate 35a is not in contact with the pressing down lever 65d (see fig. 10). Therefore, the cam detection packing 65b is moved upward by a predetermined biasing force, and shifts to a state in which the cam detection packing 65b blocks the packing sensor 65c (see fig. 8). Note that when the cam detects that the filler 65b blocks the filler sensor 65c (see fig. 8), the filler sensor 65c is turned off. On the cam detection packing 65b not obstructing the packing sensor 65c (see fig. 10), the packing sensor 65c is turned off.

Then, if the filler sensor 65c becomes off (yes in S25), the control unit 51 turns off the bypass floor cam clutch 65a (S26). Therefore, when the rotation of the bypass floor cam shaft 65 is stopped, the bypass floor cam 35 does not contact the floor rail 34 a. Further, the bypass bottom plate 34 is biased toward the bypass sheet-feed roller 32 by the biasing force of the bottom plate spring 36. Therefore, the bypass-sheet feeding roller 32 comes into contact with the top recording sheet S of the stack of the plurality of recording sheets S loaded on the bypass feeder 31 and the bypass bottom plate 34.

Next, the control unit 51 turns on the bypass sheet-supply clutch 64a (S27). Accordingly, the bypass-sheet feeding roller 32 is driven to rotate, and the top recording sheet S on the bypass bottom plate 34 is sent toward the separation pad 33. At this time, even if the second and subsequent recording sheets are fed from the top together with the top recording sheet S, the second and subsequent recording sheets are not conveyed due to the friction of the separation pad 33. Only the top recording sheet S passes through the separation pad 33.

Note that, during the sheet-feed conveyance from the bypass sheet-feed unit 30, the sheet-feed conveyance from the main body sheet-feed unit is not performed. Therefore, the main body sheet feed clutch 62a and the relay clutch 63a remain off.

Then, the fed recording sheet S is conveyed along a bypass sheet feeding path indicated by symbol R2 in fig. 5. Then, if the one end 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 (before the end of the recording sheet S reaches the pair of registration rollers 43), the bypass sheet supply clutch 64a is turned off (S29) to temporarily stop the conveyance of the recording sheet S. Therefore, a state is reached in which the end of the recording sheet S abuts against the nip of the pair of registration rollers 43 that have stopped, and the skew of the recording sheet S is corrected.

At the timing of allowing the recording sheet S to be placed on the toner image on the surface of the photosensitive body 1 at the transfer nip, the control unit 51 turns on the registration clutch (S30). Thus, the pair of registration rollers 43 starts to be driven to rotate, and the recording sheet S is conveyed to the transfer nip.

In the present embodiment, the bypass sheet feeding unit 30 is of a unit structure. As shown in fig. 7, the unit structure includes a driven relay roller 42b and a bypass sheet feeding mechanism supporting the driven relay roller 42 b. The driven relay roller 42b is one roller of the pair of relay rollers 42. The unit is screwed to the main body case 50. On the other hand, a drive relay roller 42a as the other roller of the pair of relay rollers 42 is supported by the main body casing 50. Therefore, in the present embodiment, the driven relay roller 42b of the unit and the drive relay roller 42a of the main body casing 50 are not separated from each other.

This configuration will be described in detail.

Fig. 11A and 11B are perspective views showing the opening and closing door 39 of the printer main body. The opening and closing door 39 is opened in fig. 11A and 11B. The bypass paper feeder 31 is attached to the opening and closing door 39.

Fig. 12A and 12B are perspective views showing the opening and closing door 39 of the printer main body. The opening and closing door 39 is closed in fig. 12A and 12B. The bypass paper feeder 31 is attached to the opening and closing door 39.

Fig. 13A and 13B are perspective views showing the opening and closing door 39 of the printer main body. In fig. 13A and 13B, the opening-closing door 39 is closed, and the bypass paper feeder 31 is opened.

As described above, the bypass sheet feeding mechanism that supports the driven relay roller 42b is screwed to the main body casing 50. The opening and closing door 39 is attached to the bypass sheet feeding mechanism by a hinge mechanism. The opening and closing door 39 can be opened and closed. In addition, the bypass paper feeder 31 is attached to the opening and closing door 39 by a hinge mechanism. The bypass paper feeder 31 can be opened and closed. In the present embodiment, opening the opening and closing door 39 allows the process cartridge including the photosensitive body 1 to be attached and removed, and allows the jammed recording sheet S to be removed.

However, the driven relay roller 42b is not supported by the opening/closing door 39, but is supported by a bypass sheet feeding mechanism screwed to the main body casing 50. Therefore, the driven relay roller 42b is not separated from the drive relay roller 42a of the main body casing 50.

If an apparatus failure occurs that requires stopping conveyance of the recording sheet S, for example, if a paper jam occurs in the present printer (hereinafter, a case where a paper jam occurs will be taken as an example of an apparatus failure), the recording sheet S remaining in the apparatus needs to be removed. Specifically, in the present embodiment, the paper supply cassette 100 is removed from the apparatus in the feeding direction of the recording paper S or a direction intersecting the feeding direction of the recording paper S. Then, the remaining recording sheet is removed (pulled out) from the main body sheet feeding unit. At this time, it is preferable that the portion that nips the recording sheet S (for example, the conveying nip of the pair of relay rollers 42 and the portion that nips the recording sheet S by the bypass-sheet feeding roller 32 and the bypass bottom plate 34) be opened (separated) in order to prevent the recording sheet S such as thin paper or plain paper having low strength from being torn when the recording sheet S is pulled out.

As an example of a configuration of separating the pair of relay rollers 42 from each other, the driven relay roller 42b is supported by an opening and closing door that is attached to the main body casing 50 of the printer, and the opening and closing door can be opened and closed. This configuration allows the pair of relay rollers 42 to be separated from each other by opening the opening and closing door. However, as described above, the drive relay roller 42a and the driven relay roller 42b constituting the pair of relay rollers 42 are not separated from each other. Therefore, the pair of relay rollers 42 are not opened (separated from each other).

Therefore, in the present embodiment, when the recording paper S (thin paper or plain paper) of a kind which is low in strength and easy to tear is conveyed, the nip pressure (contact pressure) of the pair of relay rollers 42 is switched to the low nip pressure to prevent the recording paper S low in strength from being torn when a jam occurs during the main body paper feeding, and the recording paper S nipped by the pair of relay rollers 42 is removed (pulled out). Therefore, even if the recording sheet S of thin paper or plain paper is conveyed and jammed, when the recording sheet S is pulled out from the pair of relay rollers 42, since the nip pressure of the pair of relay rollers 42 is low, the sheet can be prevented from being torn without changing the state.

At this time, the nip pressure of the pair of relay rollers 42 is low. Therefore, a conveyance failure may occur, that is, the recording sheet S may not be conveyed properly, and for example, if a conveyance load of the recording sheet S (for example, the recording sheet S rubs against a conveyance guide and a conveyance resistance when the tip of the sheet enters a pair of rollers) is large, the recording sheet S may slip at a conveyance nip of the pair of relay rollers 42. However, the recording sheet S, which is thin paper or plain paper, is generally relatively thin and generally has relatively low rigidity. Therefore, the transport load is low. Even if the nip pressure of the pair of relay rollers 42 is low, conveyance failure is less likely to occur. Therefore, even if the nip pressure of the pair of relay rollers 42 is low, the recording sheet S as thin paper or plain paper can be stably conveyed.

On the other hand, when the recording paper sheet S of a type having high strength and less likely to tear (thick paper) is conveyed, the nip pressure (contact pressure) of the pair of relay rollers 42 is high. If the nip pressure of the pair of relay rollers 42 is low, the recording sheet S as thick paper may cause conveyance failure. However, in the present embodiment, the nip pressure of the pair of relay rollers 42 is high when the recording sheet S as thick paper is conveyed. Therefore, a conveyance failure is less likely to occur, and stable conveyance is performed. Even if a jam occurs, when the recording sheet S is pulled out from the pair of relay rollers 42 having a high nip pressure, the recording sheet S as thick paper is less likely to tear.

Note that if a configuration is adopted in which the operation of reducing the nip pressure (contact pressure) of the pair of relay rollers 42 is conventionally performed after the occurrence of a jam and the operation of reducing the nip pressure (contact pressure) of the pair of relay rollers 42 is appropriately performed after the occurrence of a jam, it is possible to prevent the recording paper S having a low strength from tearing when the paper is pulled out. However, due to a configuration such as the timing at which the jam occurs or the operation of performing the jam processing, after the jam occurs, the operation of reducing the nip pressure of the pair of relay rollers 42 may not be performed. For example, if a detection error or malfunction of the above-described jam detection sensor (registration sensor 49) occurs, or an immediate stop of the image forming apparatus occurs, the driving power source of the main motor 61 and the clutches 62a, 63a, 64a, and 65a is not normally driven. Therefore, when the sheet is pulled out, the nip pressure of the pair of relay rollers 42 is not reduced.

In contrast to this configuration, in the present embodiment, in the case where the recording sheet S is thin paper or plain paper, the biasing force of the pressing spring 37b that biases the driven relay roller 42b toward the driving relay roller 42a is switched to the low biasing force to reduce the nip pressure of the pair of relay rollers 42 before the jam occurs, more specifically, before the recording sheet S is nipped by the pair of relay rollers 42 (see S1 to S4 in fig. 6). Therefore, after the occurrence of the jam, it is not necessary to perform an operation of reducing the nip pressure of the pair of relay rollers 42. Therefore, in the event of a jam, for example, the recording sheet S as thin paper or plain paper is pulled out from the pair of relay rollers 42 having a low nip pressure regardless of, for example, the timing at which the jam occurs or the configuration in which the jam processing operation is performed.

Next, a configuration of switching the nip pressure of the pair of relay rollers 42 will be described.

In the present embodiment, the operation of the movable member for sheet conveyance by the bypass sheet feeding path R2 performs the operation of switching the nip pressure of the pair of relay rollers 42 in the main body sheet feeding path R1. In the present embodiment, when the main body sheet supply path R1 is used for conveying the recording sheet S, the bypass sheet supply path R2 is not used for sheet conveyance. Therefore, when the main body sheet feeding path R1 is used to convey the recording sheet S, the operation of the movable member for sheet conveyance in the bypass sheet feeding path R2 does not cause any obstacle.

The sheet feeding unit during bypass sheet feeding in the present embodiment presses the recording sheet S on the bypass bottom plate 34 against the bypass sheet feeding roller 32 to feed the recording sheet S. Therefore, in the present embodiment, the bypass substrate 34 functions as a movable member, and the nip pressure of the pair of relay rollers 42 is switched in conjunction with the operation of the bypass substrate 34.

In detail, as described above, the operation unit that operates the bypass floor 34 rotates the bypass floor camshaft 65 with the driving force of the main motor 61. Then, when the bypass floor cam shaft 65 is located at a rotational position where the bypass floor cam 35 presses the floor guide 34a downward against the biasing force of the floor spring 36, the bypass floor plate 34 moves downward and is separated from the bypass sheet feeding roller 32 (see fig. 10 and 15A). Alternatively, when the bypass floor cam shaft 65 is in the rotational position in which the bypass floor cam 35 is separated from the floor guide 34a, the bypass floor 34 is moved upward by the biasing force of the floor spring 36 and is brought into contact with the bypass sheet feeding roller 32 (see fig. 8 and 15B).

The biasing force switching unit according to the present embodiment moves the pressing plate 37d as a biasing and supporting unit that supports the pressing spring 37b, the pressing spring 37b biases the bearing 37a of the driven relay roller 42b as one roller of the pair of relay rollers 42 toward the driving relay roller 42 by the rotation of the bypass floor cam shaft 65, thereby switching the biasing force of the pressing spring 37b and changing the nip pressure of the pair of relay rollers 42. The driven relay roller 42b is one roller of the pair of relay rollers 42. Note that the slider is screwed to the pressing plate 37 d. The slider is configured to move along a guide rail portion of the support frame 38 that bypasses the sheet feeding unit 30. Thus, the platen 37d is configured to move linearly toward and away from the drive relay roller 42 a.

Fig. 14A and 14B are explanatory views showing the biasing force switching unit in the present embodiment. The biasing force switching unit switches the biasing force of the pressing spring 37b that biases the bearing 37a of the driven relay roller 42b toward the driving relay roller 42 a.

Fig. 15A and 15B are perspective views showing the main configuration of the biasing force switching unit.

Fig. 16A and 16B are explanatory views showing a mechanism of supporting the driven relay roller 42B.

As shown in fig. 16A and 16B, the guide groove 37a1 of the bearing 37a of the driven relay roller 42B is fitted to the projection 38a of the support frame 38 of the bypass sheet feeding unit 30. Therefore, the roller shaft 66 of the driven relay roller 42b is held and can slide in the direction in which the driven relay roller 42b moves toward the driving relay roller 42a, and can slide in the direction in which the driven relay roller 42b moves away from the driving relay roller 42 a. Further, as described above, the pressing spring 37b biases the bearing 37a of the driven relay roller 42b to bias the driven relay roller 42b toward the driving relay roller 42 a.

The pressing spring 37b is a compression spring arranged in such a manner that an end portion of the pressing spring 37b is in contact with the bearing 37a of the driven relay roller 42b, and the other end portion of the pressing spring 37b is in contact with the pressing plate 37 d. The biasing force of the pressing spring 37b held by the pressing plate 37d biases the bearing 37a of the driven relay roller 42b toward the driving relay roller 42 a. The pressing plate 37d has a spring contact surface with which the pressing spring 37b is in contact. The pressing plate 37d has a rear surface opposite to the spring contact surface. A pressing unit 65e is formed on the rear surface. The pressing unit 65e presses the platen 37d toward the drive relay roller 42 a. The pressing unit 65e is rotated by the rotation of the bypass floor camshaft 65.

As shown in fig. 14A and 15A, when the bypass floor cam shaft 65 is in the rotational position where the bypass floor 34 is moved downward (the position where the bypass floor 34 is separated from the bypass paper-feeding roller 32), the pressing unit 65e on the bypass floor cam shaft 65 is in the non-pressing position. At this time, the pressing plate 37d is moved away from the drive relay roller 42a by the biasing force of the pressing spring 37 b. Therefore, the pressing spring 37b is extended. The compression amount of the compression spring 37b decreases. The biasing force of the pressing spring 37b is reduced. Therefore, the biasing force biasing the driven relay roller 42b toward the driving relay roller 42a is reduced. Therefore, the nip pressure of the pair of relay rollers 42 is reduced. Note that the bypass bottom plate 34 is kept separate from the bypass sheet-feed roller 32. Therefore, the bypass sheet feeding cannot be performed. However, the bypass sheet feeding is not performed during the main body sheet feeding. Therefore, there is no obstacle.

Alternatively, as shown in fig. 14B and 15B, when the bypass floor cam shaft 65 is in the rotational position where the bypass floor 34 is moved upward (the position where the bypass floor 34 is in contact with the bypass paper-feeding roller 32), the pressing unit 65e on the bypass floor cam shaft 65 is in the pressing position. At this time, the platen 37d moves toward the drive relay roller 42a against the biasing force of the pressing spring 37 b. Thus, the pressing spring 37b is compressed. The compression amount of the pressing spring 37b increases. Therefore, the biasing force of the pressing spring 37b increases. Therefore, the biasing force biasing the driven relay roller 42b toward the driving relay roller 42a increases. Therefore, the nip pressure of the pair of relay rollers 42 increases. Note that the bypass bottom plate 34 is held in contact with the bypass sheet-feed roller 32. Therefore, the bypass sheet feeding cannot be performed. However, the bypass sheet feeding is not performed during the main body sheet feeding. Therefore, there is no obstacle.

According to the present embodiment, the operation of the bypass bottom plate 34 is for switching the nip pressure of the pair of relay rollers 42 (the biasing force of the pressing spring 37b) in the main body sheet feeding path R1. The bypass bottom plate 34 is a movable member for sheet conveyance through the bypass sheet supply path R2. Therefore, the simple configuration switches the nip pressure of the pair of relay rollers 42. The simple configuration does not include a dedicated operation unit that switches the nip pressure of the pair of relay rollers 42.

Fig. 17A to 17C are explanatory views showing the position of the pressing plate 37d pressed by the pressing unit 65e on the bypass floor camshaft 65.

As shown in fig. 17A, the pressing unit 65e on the bypass floor camshaft 65 can press the position B' on the pressing plate 37d in the direction in which the pressing spring 37B is biased. The position B' corresponds to the support position a on the platen 37d on which the pressing spring 37B is supported. In this case, the pressing unit 65e presses the pressing plate 37d by a pressing amount substantially equal to the compression amount of the pressing spring 37 b. Therefore, the biasing force is easily set.

However, in the present embodiment, the arrangement shown in fig. 17A is difficult due to the limitation of the device layout. Therefore, the pressing plate 37d is pressed in the direction in which the pressing springs 37B are biased at the position B, which is shifted from the supporting position a on the pressing plate 37d, at which the pressing springs 37B are supported. In this case, as shown in fig. 17B, the platen 37d is inclined. The pressing unit 65e presses the pressing plate 37d by a smaller amount than the compression amount of the compression spring 37 b. The actual biasing force is less than the desired biasing force.

Therefore, in the present embodiment, as shown in fig. 17C, the amount of pressing by the pressing unit 65e against the platen 37d is set to an amount larger than the target compression amount of the compression springs 37 b. Therefore, even if the position B on the platen 37d is pressed and the position B is shifted from the supporting position a on the platen 37d at which the pressing spring 37B is supported, the pressing spring 37B is compressed by the target compression amount. The desired biasing force is obtained.

Fig. 18A and 18B are explanatory views showing the shape of the pressing unit 65e on the bypass floor camshaft 65.

In the present embodiment, the pressing unit 65e is a cam. In the present embodiment, the pressing unit 65e is configured such that the cam has a uniform diameter within a predetermined angular range α including the target rotation angle of the pressing position even if the rotational position (phase) of the pressing unit 65e of the bypass floor camshaft 65 varies due to a tolerance of components or an error in the stop time for control. Therefore, for example, if the pressing unit 65e stops at the rotational position shown in fig. 18A, the pressing amount by which the pressing unit 65e presses the platen 37d is equal to the pressing amount by which the pressing unit 65e presses the platen 37d if the pressing unit 65e stops at the rotational position shown in fig. 18B. Therefore, even if the rotational position varies at the pressing position due to a tolerance of a component or an error of a stop time for control, a target biasing force (nip pressure of the pair of relay rollers) can be obtained.

Fig. 19 is an explanatory view showing a warp prevention unit that prevents warp of the bypass floor camshaft 65 of the pressing unit 65e including the pressing plate 37 d.

A reaction force of a biasing force of the pressing spring 37b that biases the driven relay roller 42b toward the driving relay roller 42a acts on the pressing plate 37 d. Therefore, the reaction force is transmitted to the bypass floor camshaft 65 through the pressing unit 65e in contact with the pressure plate 37 d. Therefore, the bypass floor camshaft 65 may be bent. The pressing amount by which the pressing unit 65e presses the pressing plate 37d can be reduced. The target biasing force (nip pressure of the pair of relay rollers) may not be obtained.

Therefore, in the present embodiment, as the bending prevention unit that prevents the bypass floor camshaft 65 from bending, the contact unit 37e that contacts the bypass floor camshaft 65 to prevent bending is disposed. The contact unit 37e is a part of the support frame 38 that bypasses the sheet feeding unit 30. In the present embodiment, the number of the contact units 37e is two. However, the number of the contact units 37e may be one or three or more.

Next, the processing of the present printer at the time of abnormal stop (occurrence of a paper jam) will be described. Fig. 20 is a flowchart showing the processing of the present printer at the time of abnormal stop. If an apparatus trouble requiring stopping of the conveyance of the recording sheet S, such as a conveyance trouble (paper jam), is detected in the present printer (S41), the control unit 51 first disconnects the main body sheet-feed clutch 62a, the relay clutch 63a, and the bypass sheet-feed clutch 64a (S42). Then, the control unit 51 determines whether bypass sheet feeding is being performed according to the control information (S43).

If the bypass sheet feeding is being performed (yes in S43), in the present embodiment, the recording sheet S is nipped between the bypass sheet-feeding roller 32 and the bypass bottom plate 34. That is, the bypass bottom plate 34 is in contact with the bypass sheet-feed roller 32 (see fig. 8 and 14B). Therefore, the bypass bottom plate 34 is separated from the bypass sheet-feed roller 32.

That is, when the bypass bottom plate 34 comes into contact with the bypass paper feed roller 32, the filler sensor 65c is turned off. Therefore, the control unit 51 first turns on the bypass floor cam clutch 65a (S44) to drive the bypass floor camshaft 65 to rotate. Then, the bypass floor camshaft 65 continues to rotate until the charge sensor 65c is turned on. If the charge sensor 65c is turned on (S45), the bypass floor cam clutch 65a is turned off (S46) to stop the rotation of the bypass floor camshaft 65. Then, the control unit 51 turns off the main motor 61(S51), and stops the apparatus (S52) to reach a state where the user can remove the recording sheet S.

When an apparatus failure that requires stopping the conveyance of the recording sheet S occurs during bypass paper feeding, the above-described control separates the bypass bottom plate 34 from the bypass paper feeding roller 32. The recording sheet S remaining in the bypass sheet-feed path R2 (the recording sheet S sandwiched between the bypass sheet-feed roller 32 and the bypass bottom plate 34) is easily removed.

Alternatively, if the main body sheet feeding is being performed (no in S43), the recording sheet S may be nipped between a pair of relay rollers 42. At this time, if it is determined that the recording paper S is of a thick paper type and paper conveyance is being performed, the nip pressure of the pair of relay rollers 42 is high.

Here, if the actually conveyed recording paper S is thick paper (paper with high strength), the paper will not tear when pulled out and removed even if the nip pressure of the pair of relay rollers 42 is high, as described above. However, if the user performs an erroneous operation or setting so that the actually conveyed recording sheet S is thin paper or plain paper (a sheet of low strength), and the nip pressure of the pair of relay rollers 42 is high, the recording sheet S tears when the sheet is pulled out. Therefore, it is preferable to reduce the nip pressure of the pair of relay rollers 42. Further, even if the recording paper S actually conveyed is thick paper (paper having high strength), if the nip pressure of the pair of relay rollers 42 is high, a large force is required to pull out the paper. Preferably, the nip pressure of the pair of relay rollers 42 is reduced to effectively deal with the jam.

Therefore, in the present embodiment, if the main body sheet feeding is being performed (no in S43), and if it has been determined that the recording sheet S is of the thick sheet type, and sheet conveyance is being performed, that is, if the bypass bottom plate 34 is in contact with the bypass sheet supply roller 32 (the filler sensor is off), and therefore the nip pressure of the pair of relay rollers 42 is high (no in S47), the bypass bottom plate cam clutch 65a is turned on (S48) to drive the bypass bottom plate cam shaft 65 to rotate. Then, the bypass floor cam shaft 65 continues to rotate until the filler sensor 65c becomes on, that is, until the bypass floor 34 is located at the lowest position, thereby making the nip pressure of the pair of relay rollers 42 low. If the charge sensor 65c becomes on (yes in S49), the bypass floor cam clutch 65a is turned off (S50) to stop the rotation of the bypass floor camshaft 65. Then, the control unit 51 turns off the main motor 61(S51), and stops the apparatus (S52) to reach a state where the user can remove the recording sheet S.

Thus, the nip pressure of the pair of relay rollers 42 is switched from the high nip pressure to the low nip pressure. Therefore, even if the recording paper S actually conveyed is thin paper or plain paper (paper with low strength), the paper does not tear when the paper is pulled out. Alternatively, if the actually conveyed recording paper S is thick paper (paper having high strength), a large force is not required to pull out the paper, and thus the paper is easily pulled out. The paper jam can be effectively handled.

Further, in the present embodiment, if the recording sheet S is fed from the bypass sheet feeder 31, the maximum driving load L1 is applied to the bypass floor cam shaft 65 when the bypass floor cam shaft 65 is at the rotational position at which the bypass floor cam 35 presses the floor guide 34a downward against the biasing force of the floor spring 36. Therefore, when the recording sheet S is fed from the bypass sheet feeder 31, the rotational position of the bypass floor cam 35 pressing the floor guide 34a downward against the biasing force of the floor spring 36 is the maximum load operating position P1 where the maximum driving load L1 is applied to the bypass floor cam shaft 65.

Further, if the nip pressure of the pair of relay rollers 42 is switched, when the bypass floor cam shaft 65 is at a rotational position where the pressing plate 37d is moved toward the drive relay roller 42a by the pressing unit 65e against the biasing force of the pressing spring 37b, the maximum driving load L2 is applied to the bypass floor cam shaft 65. Therefore, when the nip pressure of the pair of relay rollers 42 is switched, the rotation position at which the pressing plate 37d is moved toward the drive relay roller 42a against the biasing force of the pressing spring 37b by the pressing unit 65e is the maximum load operation position P2 at which the maximum driving load L2 is applied to the bypass floor camshaft 65.

As described above, in the present embodiment, when the rotational position of the bypass bottom plate cam shaft 65 is at the position where the bypass bottom plate 34 is moved upward (the position where the minimum driving load is applied when the recording sheet S is fed from the bypass sheet feeder 31), the pressing unit 65e on the bypass bottom plate cam shaft 65 is located at the position where the pressing unit 65e moves the pressing plate 37d toward the drive relay roller 42a against the biasing force of the pressing spring 37b (the position P2 where the maximum driving load L2 is applied when the nip pressure of the pair of relay rollers 42 is switched). That is, in the present embodiment, when the recording sheet S is fed from the bypass sheet feeder 31, the maximum load operation position P1 of the bypass floor cam shaft 65 is shifted from the maximum load operation position P2 of the bypass floor cam shaft 65 when the nip pressure of the pair of relay rollers 42 is switched.

Fig. 21 is a graph showing an example in which, when the recording sheet S is fed from the bypass sheet feeder 31, the maximum load operation position P1 of the bypass floor cam shaft 65 corresponds to the maximum load operation position P2 of the bypass floor cam shaft 65 when the nip pressure of the pair of relay rollers 42 is switched.

On the graph, the load torque of the bypass floor camshaft 65 is on the vertical axis, and the rotation angle of the bypass floor camshaft 65 is on the horizontal axis. (fig. 22 to 24 described later are similar to fig. 21.)

In the example of fig. 21, the two maximum load operating positions P1 and P2 correspond to (are identical to) each other. Therefore, the maximum value of the total drive load (load torque) applied to the bypass floor camshaft 65 is the drive load L that is the sum of the two maximum load operation positions P1 and P2. If such a large drive load L is applied to the bypass floor camshaft 65, a drive mechanism (e.g., a motor and a clutch) that drives the bypass floor camshaft 65 is required to handle the large drive load L. And thus the cost increases. Further, the parts bypassing the chassis cam shaft 65 and the parts bypassing the sheet feeding unit 30 are required to bear a large load (thick and heavy parts). The cost increases and the weight of the parts increases.

Fig. 22 is a graph showing an example in which, when the recording sheet S is fed from the bypass sheet feeder 31, the maximum load operation position P1 of the bypass bottom plate cam shaft 65 is offset from the maximum load operation position P2 of the bypass bottom plate cam shaft 65 when the nip pressure of the pair of relay rollers 42 is switched.

In the example of fig. 22, the two maximum load operating positions P1 and P2 are offset (not identical) from each other. Therefore, even the maximum value of the total driving load (load torque) L' applied to the bypass floor camshaft 65 is smaller than the maximum driving load L in the example of fig. 21. Thus, the drive mechanism driving the bypass floor camshaft 65 handles a relatively small drive load L'. Thus, the cost is reduced. The weight of the drive mechanism is reduced.

Fig. 23 is a graph showing another example in which, when the recording paper sheet S is fed from the bypass paper feeder 31, the maximum load operation position P1 of the bypass bottom plate cam shaft 65 is offset from the maximum load operation position P2 of the bypass bottom plate cam shaft 65 when the nip pressure of the pair of relay rollers 42 is switched.

In the example of fig. 23, the two maximum load operating positions P1 and P2 are offset (not identical) from each other. However, when the recording sheet S is fed from the bypass paper feeder 31, the driving load applied to the bypass floor cam shaft 65 is always smaller than the larger of the maximum driving load L1 when the recording sheet S is fed from the bypass paper feeder 31 and the maximum driving load L2 when the nip pressure of the pair of relay rollers 42 is switched. Further, the driving load applied to the bypass bottom plate cam shaft 65 when switching the nip pressure of the pair of relay rollers 42 is always smaller than the larger of the maximum driving load L1 when the recording sheet S is fed from the bypass sheet feeder 31 and the maximum driving load L2 when switching the nip pressure of the pair of relay rollers 42.

Therefore, in the example of fig. 23, the drive load that can be applied to the bypass floor cam shaft 65 does not exceed the larger of the maximum drive load L1 when the recording sheet S is fed from the bypass sheet feeder 31 and the maximum drive load L2 when the nip pressure of the pair of relay rollers 42 is switched. Therefore, the drive mechanism that drives the bypass floor camshaft 65 bears a small drive load. Thus, the cost is reduced. The weight of the drive mechanism is reduced.

Particularly in the example of fig. 23, when the recording sheet S is fed from the bypass sheet feeder 31, the driving load applied to the bypass floor cam shaft 65 is always smaller than the smaller of the maximum driving load L1 when the recording sheet S is fed from the bypass sheet feeder 31 and the maximum driving load L2 when the nip pressure of the pair of relay rollers 42 is switched. Further, the driving load applied to the bypass floor cam shaft 65 when switching the nip pressure of the pair of relay rollers 42 is always smaller than the smaller of the maximum driving load L1 when feeding the recording sheet S from the bypass sheet feeder 31 and the maximum driving load L2 when switching the nip pressure of the pair of relay rollers 42. Thus, in the example of fig. 23, the drive mechanism driving the bypass floor camshaft 65 carries even less drive load. Thus, the cost is reduced. The weight of the drive mechanism is reduced.

Fig. 24 is a graph showing another example of further increasing the offset amount.

In the example of fig. 24, when the recording sheet S is fed from the bypass sheet feeder 31, the maximum thrust rotational position P1 of the bypass floor cam shaft 65 that generates the maximum thrust of the bypass floor cam 35 is 180 ° different from the maximum thrust rotational position P2 of the bypass floor cam shaft 65 that generates the maximum thrust of the pushing unit 65e when the nip pressure of the pair of relay rollers 42 is switched. Note that, in the present embodiment, the maximum thrust rotation positions P1 and P2 have respective predetermined ranges. Therefore, the offset angle is an angle (rotation angle) between the center of the range and the center of the range.

In the example of fig. 24, even if the rotational position of the bypass floor camshaft 65 slightly varies due to a component size error or a control error, the two maximum load operation positions P1 and P2 are unlikely to correspond to (be the same as) each other. Therefore, it is possible to stably prevent an excessive driving load from being applied to the bypass floor camshaft 65.

According to the example in fig. 24, simple control of switching the rotation angle of the bypass bottom plate cam shaft 65 in units of 180 ° performs the operation of the bypass bottom plate 34 and the operation of switching the nip pressure of the pair of relay rollers 42 when the recording sheet S is fed from the bypass paper feeder 31. In particular, since the switching period between these operations is the same, control becomes easy. For example, if a series of image forming operations are performed on sheets having different thicknesses, the time period for switching the image forming operations may be the same.

In the present embodiment, as shown in fig. 14A and 15A, when the pressing unit 65e on the bypass floor cam shaft 65 is in the non-pressing position, the pressing plate 37d is moved away from the drive relay roller 42a by the biasing force of the pressing spring 37 b. At this time, the movement of the platen 37d may be restricted by the pressing unit 65e in contact with the platen 37 d. However, as shown in fig. 25A and 26, the movement of the pressing plate 37d may be restricted by another member (for example, an attachment member 38b with which the pressing plate 37d is in contact) different from the pushing unit 65 e. The attachment member 38b is attached to the support frame 38 of the bypass sheet feeding unit 30.

If the movement of the pressing plate 37d is restricted only by the pressing unit 65e in contact with the pressing plate 37d, the pressing unit 65e is worn out after using the pressing unit 65e for a certain time. Therefore, the supporting position that restricts the movement of the platen 37d is restricted from changing over a period of time. It is difficult to obtain a stable biasing force over a period of time. In contrast to this configuration, if the movement of the platen 37d is restricted by the attachment member 38b that is in contact with the platen 37d, and the attachment member 38b is another member different from the pushing unit 65e, as shown in fig. 25A and 26, the attachment member 38b does not rub against the platen 37 d. Therefore, the pressing unit 65e is not worn after being used for a certain period of time. A stable biasing force is easily obtained over a period of time. Thus, a stable nip pressure of the pair of relay rollers 42 is obtained.

Particularly in the present embodiment, as shown in fig. 25A and 26, the attachment member 38b is in surface contact with the platen 37d to restrict the movement of the platen 37 d. If the attachment member 38b is locally in contact with the platen 37d, the orientation of the platen 37d may change because the attachment member 38b and the platen 37d that are in contact with each other are misaligned. It is difficult to obtain a stable biasing force over a period of time. In contrast to this configuration, in the case of the surface contact configuration, even if the attachment member 38b and the pressing plate 37d that are in contact with each other are misaligned, the orientation of the pressing plate 37d is unlikely to change. A stable biasing force is easily obtained over a period of time.

Here, another member other than the pushing unit 65e is an attaching member 38b attached to the support frame 38 of the bypass sheet feeding unit 30. However, another member other than the pushing unit 65e may be, for example, the support frame 38.

Fig. 27 is an external perspective view of the pair of relay rollers 42 as viewed obliquely from below.

In the present embodiment, another member other than the pressing unit 65e is an attaching member 38b attached to the support frame 38 of the bypass sheet feeding unit 30. Therefore, the ease of assembly is high. That is, it is necessary to attach the pressing plate 37d, the bypass floor cam shaft 65, and various cams attached to the bypass floor cam shaft 65 to the support frame 38 of the bypass sheet feeding unit 30. The pressing plate 37d is fitted in the rail portion of the support frame 38. The various cams include, for example, the pushing unit 65e and the bypass floor cam 35. At this time, it is preferable that the support frame 38 has an opening wide enough to enable the platen 37d to be fitted into the rail portion. However, such openings reduce the rigidity of the support frame 38. Therefore, structural members such as brackets are generally attached to the support frame 38 to ensure rigidity.

In the present embodiment, since the support frame 38 has a sufficiently wide opening, the convenience of assembly is increased. Further, the attachment member 38b is attached to the support frame 38. The attachment member 38b serves as a structural component attached to ensure rigidity. The attachment member 38b restricts the movement of the platen 37 d. Therefore, the number of parts is less than that in the case where the member ensures rigidity and the other member restricts the movement of the platen 37 d. Therefore, the size and weight are small.

As described above, in the present embodiment, the movable member as used in the bypass sheet feeding path R2 switches the nip pressure of the pair of relay rollers 42 (the biasing force of the pressing spring 37b) used in the main body sheet feeding path R1 in conjunction with the operation of the bypass bottom plate 34. However, other configurations are possible. For example, in the case where the bypass sheet feeding unit 30 includes a sheet feeding unit that presses the bypass sheet feeding roller 32 against the recording sheet on the bypass sheet feeder by an operation of lowering the bypass sheet feeding roller 32, thereby feeding the recording sheet, the bypass sheet feeding roller 32 may be used as a movable member, and the nip pressure of the pair of relay rollers 42 may be switched in conjunction with the operation of the bypass sheet feeding roller 32. Alternatively, the switching may be performed in conjunction with the operation of a movable member that is not used in the bypass sheet feeding path R2 but is used in, for example, a sheet feeding path other than the bypass sheet feeding path R2 (e.g., the reverse rotation return path R5).

In addition, in the present embodiment, a configuration of switching the nip pressure (the biasing force of the pressing spring 37b) of the pair of relay rollers 42 used in the main body sheet feeding path R1 is described. However, a configuration of switching the nip pressure of, for example, another pair of conveying rollers (for example, a pair of paper discharge rollers 46) may be applied. In the present embodiment, the nip pressure of the pair of relay rollers 42 is switched. The pair of relay rollers 42 is a pair of conveying rollers including one driving roller and one driven roller. However, the pair of relay rollers 42 may be a pair of conveying rollers in which the pair of relay rollers 42 are both driving rollers or both driven rollers.

In the present embodiment, a printer is exemplified as an example of the image forming apparatus. However, the image forming apparatus may include: a copier including a scanner; and a multifunction peripheral including a function such as a facsimile function. The present invention is applicable not only to an image forming apparatus that forms an electrophotographic image, but also to an image forming apparatus that uses other image forming methods. Other image forming methods include an ink jet method and a toner projection method. A toner projection method is disclosed in japanese unexamined patent application publication No. 2002-307737 and the like. The present invention is applicable not only to an image forming apparatus but also to an apparatus including a sheet conveying device such as a scanner including an Automatic Document Feeder (ADF).

The above is one example. The following aspects have respective characteristic effects.

First aspect

A first aspect is a sheet conveying apparatus including: a pair of rollers (e.g., a pair of relay rollers 42) that nip a sheet (e.g., recording sheet S) to be conveyed; and a biasing unit (for example, a pressure spring 37b) that biases one roller (for example, the driven relay roller 42b) of the pair of rollers toward the other roller (for example, the driving relay roller 42a) of the pair of rollers. The pair of rollers are configured not to be separated from each other. The sheet conveying device further includes a biasing force switching unit (e.g., the pressing plate 37d and the pushing unit 65e) that switches the biasing force of the biasing unit according to the type of the sheet before the sheet is nipped between the pair of rollers.

In the present aspect, the pair of rollers are not configured to be separated from each other. Therefore, if a paper jam occurs and a sheet nipped by a pair of rollers is removed, the sheet held between the pair of rollers needs to be pulled out. At this time, if a sheet (e.g., thin paper) having low strength is jammed and a contact pressure of a pair of rollers is excessively high when the sheet is pulled out, the sheet may be torn when the sheet is pulled out.

If a configuration is adopted in which the contact pressure of the pair of rollers is conventionally reduced after a jam is detected, and the operation of reducing the contact pressure is appropriately performed after the jam occurs, it is possible to prevent the sheet having low strength from tearing at the time of sheet pulling-out. However, due to a configuration such as the timing/timing at which the jam occurs or the operation of performing the jam processing, after the jam occurs, the operation of reducing the contact pressure may not be performed. In this case, the driving power source that performs the operation of reducing the contact pressure acting between the pair of rollers cannot be driven. Therefore, when the sheet is pulled out, the contact pressure of the pair of rollers cannot be reduced. Note that, even in an emergency where the operation of reducing the contact pressure cannot be performed after the occurrence of a sheet, a configuration of driving a power source that drives the operation of performing the operation of reducing the contact pressure acting between the rollers of the pair of rollers may be used. However, this configuration may increase cost.

The contact pressure of a pair of rollers may be small from the start of sheet conveyance. In this case, the reduced contact pressure is insufficient to convey a paper sheet having a high conveyance load, such as thick paper. Therefore, a conveyance failure may occur.

In view of the above, the present aspect includes a configuration that switches the biasing force of the biasing unit based on the type of the sheet before the sheet is nipped by the pair of rollers. This configuration reduces the contact pressure of the pair of rollers by switching the biasing force to a lower biasing force when, for example, a type of paper having low strength is conveyed. Therefore, even if a paper jam occurs, the contact pressure of the pair of rollers is low, and therefore, even if a paper is pulled out from the pair of rollers having a low contact pressure, the paper may be torn. In addition, a sheet having low strength is generally small in conveyance load. Therefore, even if the sheet having low strength is conveyed when the contact pressure of the pair of rollers is low, no conveyance failure occurs. On the other hand, when a type of paper having high strength is conveyed, for example, the contact pressure of a pair of rollers is increased by switching the biasing force to a higher biasing force. Therefore, even when the conveyance load is large, conveyance failure does not occur when conveying a type of paper having high strength. Further, even if the contact pressure of the pair of rollers is high, the paper of the type having high strength does not tear when the paper is pulled out.

As described above, the present aspect does not require an operation of reducing the contact pressure of the pair of rollers after the occurrence of a jam, and therefore can prevent tearing of the sheet when the sheet is pulled out from the pair of rollers.

Second aspect of the invention

In the second aspect, the types of paper include different strength types of paper described in the first aspect.

Therefore, when the sheet having low strength is pulled out from the pair of rollers, the sheet can be prevented from being torn.

Third aspect of the invention

In the third aspect, the types of paper include different thickness types of paper in the second aspect.

Therefore, when a thin sheet is pulled out from the pair of rollers, the sheet can be prevented from being torn.

Fourth aspect of the invention

In the fourth aspect, since the type of paper described in the second or third aspect has low strength, the biasing force switching unit switches the biasing force to a lower biasing force.

Therefore, when the sheet having low strength is pulled out from the pair of rollers, the sheet can be appropriately prevented from being torn.

Fifth aspect of the invention

A fifth aspect is an image forming apparatus (e.g., a printer) that forms an image on a sheet conveyed by a sheet conveying device, the sheet conveying device according to any one of aspects 1 to 4 serving as the sheet conveying device according to any one of the first to fourth aspects.

The present aspect provides an image forming apparatus that can prevent tearing of a sheet when the sheet is pulled out from a pair of rollers without an operation of reducing a contact pressure of the pair of rollers after a jam occurs.

Sixth aspect

In the sixth aspect, a pair of rollers of the sheet conveying device nips the sheet conveyed through a first conveying path (e.g., the main body sheet conveying path R1) of the plurality of conveying paths (e.g., the main body sheet feeding path R1 and the bypass sheet feeding path R2), and the biasing force switching unit switches the biasing force of the biasing unit in conjunction with the operation of a movable member (e.g., the bypass bottom plate 34) that is operated to convey the sheet through a second conveying path (e.g., the bypass sheet feeding path R2) of the plurality of conveying paths in the first aspect.

In the present aspect, the operation of switching the contact pressure of the pair of rollers (the biasing force of the biasing unit) in the first conveying path is performed in conjunction with the operation of the movable member for conveying the sheet through the second conveying path. In the image forming apparatus according to the present aspect, when a conveyance path selected from the plurality of conveyance paths is used to convey a sheet, the other conveyance paths are not used for sheet conveyance. Therefore, even when the contact pressure of the pair of rollers in the first conveying path is switched, the movable member for sheet conveyance through the second conveying path is operated, no obstacle is caused.

According to the present aspect, the operation of the movable member for sheet conveyance through the second conveyance path is for switching the contact pressure of the pair of rollers in the first conveyance path. Therefore, a dedicated operation unit is not required. The size and cost of the apparatus are reduced.

Seventh aspect

In the seventh aspect, the image forming apparatus causes the movable member to operate to feed the sheet loaded on the sheet loading portion (e.g., the bypass bottom plate 34) to the second conveyance path in the sixth aspect.

Therefore, the contact pressure of the pair of rollers in the first conveying path can be switched in conjunction with the operation of the movable member that feeds the sheet to the second conveying path.

Eighth aspect of the invention

In the eighth aspect, the movable member is moved up and down to bring the sheet into contact with the feed roller to perform feeding of the sheet in the seventh aspect.

Therefore, the contact pressure of the pair of rollers in the first conveying path can be switched in conjunction with the operation of moving the movable member that feeds the sheet to the second conveying path up and down.

Ninth aspect

In the ninth aspect, the movable member is operated by rotating the rotating shaft (e.g., the bypass floor cam shaft 65), and the biasing force switching unit supports the biasing force of the biasing unit and the supporting unit (e.g., the pressing plate 37d) in conjunction with the rotational movement of the rotating shaft to switch the biasing force of the biasing unit in any one of the sixth to eighth aspects.

Therefore, this realizes a configuration in which the operation of switching the contact pressure of the pair of rollers in the conveying path is performed in a simple configuration in conjunction with the operation of the movable member for conveying the sheet through the second conveying path.

Tenth aspect of the invention

In the tenth aspect, the biasing force switching unit changes the urging state in which the cam on the rotary shaft urges the biasing and supporting unit with rotation of the rotary shaft to move the biasing and supporting unit to the first movement position (e.g., the urging position) and the second movement position (e.g., the non-urging position), and when the biasing and supporting unit is in the first movement position or the second movement position, the movement of the biasing and supporting unit is restricted by another member (e.g., the attaching member 38b) different from the cam in the ninth aspect.

Thus, the movement is stably restricted for a period of time. Further, the biasing force is stable when the biasing and supporting unit is in the first or second moving position.

Eleventh aspect of the invention

In the eleventh aspect, another member is in surface contact with the biasing and supporting unit to restrict movement of the biasing and supporting unit in the tenth aspect.

Therefore, even if another member that contacts each other and the biasing and supporting unit are misaligned, the orientation of the biasing and supporting unit is unlikely to change. It is easy to obtain a stable biasing force over a period of time.

Twelfth aspect of the invention

In the twelfth aspect, the other member is an attachment member 38b, and the attachment member 38b is attached to a support member (e.g., a support frame 38) that movably supports the biasing and supporting unit in the tenth and eleventh aspects.

Therefore, for example, if the support member has a sufficiently wide opening to increase the convenience of assembly, the number of parts is not increased, rigidity is ensured, and the biasing and movement of the support unit are restricted.

Thirteenth aspect of the invention

In the thirteenth aspect, the biasing force switching unit is configured to cause the urging unit 65e on the rotation shaft to urge the biasing and supporting unit 65e at a position B offset from a supporting position a of the biasing and supporting unit that supports the biasing unit with rotation of the rotation shaft to move the biasing and supporting unit in any one of the ninth to twelfth aspects.

The present aspect relates to a case where there is a constraint that the urging unit on the rotary shaft cannot urge the biasing and supporting unit at a position B' corresponding to a supporting position a of the biasing and supporting unit that supports the biasing unit.

Fourteenth aspect of the invention

In the fourteenth aspect, the urging unit is a cam, and the cam has a uniform diameter within a predetermined angular range α including a rotation angle of the rotary shaft when the biasing force obtained in the thirteenth aspect is in accordance with the type of paper.

According to the present aspect, even if the rotational position at the time of pushing by the pushing unit varies due to the tolerance of the component or the error of the stop time for control, it is possible to obtain the target biasing force (the contact pressure of the pair of rollers).

Fifteenth aspect of the invention

In the fifteenth aspect, a bending prevention unit (for example, a contact unit 37e) that prevents the rotation shaft from bending, which is acted by a reaction force received by the rotation shaft when the pressing unit on the rotation shaft presses the biasing and supporting unit to move the biasing and supporting unit with the rotation of the rotation shaft, is further included in any one of the ninth to fourteenth aspects.

According to the present aspect, the bending of the rotating shaft is prevented, thus allowing the pressing unit on the rotating shaft to appropriately press the biasing and supporting unit, and thus obtaining the target biasing force (contact pressure of the pair of rollers).

Sixteenth aspect of the invention

In the sixteenth aspect, the second conveyance path is the bypass-feed conveyance path (e.g., the bypass sheet-feed path R2) in any one of the sixth to fifteenth aspects.

Therefore, the operation of the movable member in the bypass conveying path serves to switch the contact pressure of the pair of rollers in the apparatus main body to remove the paper remaining in the apparatus main body.

Seventeenth aspect of the present invention

In the seventeenth aspect, the movable member is operated when a conveyance failure of the sheet conveyed through the first conveyance path occurs in any one of the sixth to sixteenth aspects.

According to the present aspect, when a conveyance failure of the sheet conveyed through the first conveyance path occurs, the contact pressure of the pair of rollers in the first conveyance path is reduced, and therefore, the force required to pull out the sheet is reduced, and therefore, it is possible to prevent the sheet from tearing and improve the operability of removing the sheet.

Eighteenth aspect of the invention

In the eighteenth aspect, when the biasing force switching unit switches the biasing force of the biasing unit in any one of the sixth to seventeenth aspects, during a sheet conveying operation in which the movable member is operated to convey a sheet through the second conveying path, the maximum load operating position P1 of the movable member, at which the maximum load L1 is applied, is shifted from the maximum load operating position P2 of the movable member, at which the maximum load L2 is applied during the biasing force switching operation of the movable member.

If the two maximum load operating positions P1 and P2 correspond to (are identical to) each other, the maximum load that can be applied to the movable member will be the sum of the maximum loads L1 and L2 of the two maximum load operating positions P1 and P2. If such a large load is applied, it is necessary to operate the drive mechanism of the movable member to handle the large load. The cost will increase. In addition, various components are required to withstand large loads. The cost will increase and the weight of the components will increase.

According to the present aspect, since the two maximum load operating positions P1 and P2 are offset (not identical) from each other, the maximum load that can be applied to the movable member is less than the sum of the maximum loads L1 and L2 at the two maximum load operating positions P1 and P2. Therefore, the cost and weight are less than in the case where the two maximum load operation positions P1 and P2 correspond to (are the same as) each other.

Nineteenth aspect

In the nineteenth aspect, the load applied during the sheet conveying operation and the load applied during the biasing force switching operation are always smaller than the larger of the maximum load L1 applied during the sheet conveying operation and the maximum load L2 applied during the biasing force switching operation in the eighteenth aspect.

Thus, the cost and weight are even less.

Twentieth aspect of the present invention

In the twentieth aspect, the load applied during the sheet conveying operation and the load applied during the biasing force switching operation are always smaller than the smaller of the maximum load L1 applied during the sheet conveying operation and the maximum load L2 applied during the biasing force switching operation in the nineteenth aspect.

Therefore, the cost and weight are further reduced.

Twenty-first aspect

In the twenty-first aspect, when the sheet is conveyed through the second conveying path, the rotary shaft (e.g., the bypass floor cam shaft 65) is rotated to change the pressing state of the first cam (e.g., the bypass floor cam 35) on the rotary shaft to operate the movable member, the biasing force switching unit is configured to change the pressing state of the second cam (e.g., the pressing unit 65e) on the rotary shaft with the rotation of the rotary shaft to press the biasing force of the supporting unit (e.g., the pressing plate 37d) to move the biasing force and the supporting unit to switch the biasing force of the biasing unit, and when the sheet is conveyed through the second conveying path, the maximum-thrust rotational position P1 of the movable member that generates the maximum thrust of the first cam during the sheet conveying operation of the movable member switches the biasing force of the biasing unit from when the biasing force switching unit switches the biasing force in any one of the sixth aspect to the seventeenth aspect, the maximum thrust rotational position P2 of the movable member that generates the maximum thrust of the second cam during the biasing force switching operation of the movable member is offset.

If the two maximum thrust rotational positions P1 and P2 correspond to (are the same as) each other, the maximum load that can be applied to the movable member will be the total load at which the maximum thrust generation occurs at the two maximum thrust rotational positions P1 and P2. If such a large load is applied, it will be necessary to operate the drive mechanism of the movable member to handle the large load. The cost will increase. Furthermore, the various components will need to carry a large load. The cost will increase and the weight of the components will increase.

According to the present aspect, since the two maximum thrust rotational positions P1 and P2 are offset (not identical) from each other, the maximum load that can be applied to the movable member is smaller than the total load when the maximum thrust is generated at the two maximum thrust rotational positions P1 and P2. Therefore, the cost and weight are less than those in the case where the two maximum thrust rotation positions P1 and P2 correspond to (are the same as) each other.

Twenty-second aspect of the present invention

In the twenty-second aspect, the offset angle between the maximum thrust rotational position P1 of the movable member during the sheet conveying operation and the maximum thrust rotational position P2 of the movable member during the biasing force switching operation in the twenty-first aspect is 180 °.

According to the present aspect, even if the rotational position of the movable member slightly varies due to a dimensional error or a control error of the component, the two maximum thrust rotational positions P1, P2 are unlikely to correspond to (be the same as) each other. Therefore, it is possible to stably prevent an excessive load from being applied to the operation of the movable member.

The above embodiments are illustrative and not limiting of the invention. Accordingly, many additional modifications and variations are possible in light of the above teaching. For example, at least one element of the various illustrative and exemplary embodiments herein may be combined with or substituted for one another within the scope of this disclosure and the appended claims. Further, features of the components of the embodiments, such as the number, position, and shape, do not limit the embodiments, and thus may be preferably provided. It is therefore to be understood that within the scope of the appended claims, the disclosure of the present invention may be practiced otherwise than as specifically described herein.

The method steps, processes, and operations described herein are not to be construed as necessarily requiring their performance in the particular order discussed or illustrated, unless specifically identified as an order of performance or otherwise clearly indicated by the context. It is also understood that additional or alternative steps may be employed.

Furthermore, any of the above-described devices, means or units may be implemented as a hardware device, such as a dedicated circuit or device, or as a hardware/software combination, such as a processor executing a software program.

Further, as described above, any of the above-described methods and other methods of the present invention may be implemented in the form of a computer program stored in any kind of storage medium. Examples of the storage medium include, but are not limited to, a floppy disk, a hard disk, an optical disk, a magneto-optical disk, a magnetic tape, a nonvolatile memory, a semiconductor memory, a Read Only Memory (ROM), and the like.

Alternatively, any of the above-described and other methods of the invention may be implemented by an Application Specific Integrated Circuit (ASIC), a Digital Signal Processor (DSP) or a Field Programmable Gate Array (FPGA) manufactured by interconnecting a network of suitable conventional component circuits or by combining one or more correspondingly programmed conventional general purpose microprocessors or signal processors.

Each function of the described embodiments may be implemented by one or more processing circuits or circuitry. The processing circuitry includes programming the processor, such that the processor includes circuitry. The processing circuitry also includes devices such as Application Specific Integrated Circuits (ASICs), Digital Signal Processors (DSPs), Field Programmable Gate Arrays (FPGAs), and conventional circuit elements arranged to perform the enumerated functions.

Claims (22)

1. A sheet conveying apparatus comprising:

a pair of rollers configured to nip a sheet being conveyed; and

a biasing unit configured to bias one of the pair of rollers toward the other of the pair of rollers, wherein,

the pair of rollers are configured not to be separated from each other, an

The sheet conveying device further includes a biasing force switching unit configured to switch a biasing force of the biasing unit according to a type of the sheet before the sheet is nipped by the pair of rollers.

2. The sheet conveying apparatus according to claim 1, wherein the types of the sheets include sheet types having different strengths.

3. The sheet conveying apparatus according to claim 2, wherein the types of the sheets include sheet types having different thicknesses.

4. The sheet conveying device according to claim 2 or 3, wherein the biasing force switching unit is configured to switch the biasing force to a lower biasing force when the type of the sheet has a lower strength.

5. An image forming apparatus configured to form an image on a sheet conveyed by a sheet conveying device, wherein the sheet conveying device according to any one of claims 1 to 4 is used as the sheet conveying device.

6. The image forming apparatus according to claim 5,

the pair of rollers of the sheet conveying device is configured to nip the sheet conveyed through a first conveying path of a plurality of conveying paths, and

the biasing force switching unit is configured to switch the biasing force of the biasing unit in conjunction with an operation of a movable member configured to be operated to convey a sheet through a second conveying path of the plurality of conveying paths.

7. An image forming apparatus according to claim 6, wherein said image forming apparatus is configured to cause said movable member to operate to feed the sheet loaded on the sheet loading portion toward said second conveying path.

8. The image forming apparatus according to claim 7, wherein the movable member is moved up or down to bring a sheet into contact with a feed roller to perform the feeding of the sheet.

9. The image forming apparatus according to any one of claims 6 to 8,

operating the movable member by rotating a rotating shaft, an

The biasing force switching unit is configured to move a biasing force configured to support the biasing unit and a supporting unit in conjunction with rotation of the rotation shaft to switch the biasing force of the biasing unit.

10. The image forming apparatus according to claim 9,

the biasing force switching unit is configured to change a pressing state in which the cam on the rotation shaft presses the biasing and supporting unit with rotation of the rotation shaft, and move the biasing and supporting unit to a first moving position and a second moving position, an

When the biasing and supporting unit is in any one of the first moving position and the second moving position, the movement of the biasing and supporting unit is restricted by another member different from the cam.

11. The image forming apparatus according to claim 10, wherein the other member is configured to make surface contact with the biasing and supporting unit to restrict movement of the biasing and supporting unit.

12. The image forming apparatus according to claim 10 or 11, wherein the other member is an attachment member attached to a support member that movably supports the biasing and supporting unit.

13. The image forming apparatus according to claim 9, wherein the biasing force switching unit is configured to cause the urging unit on the rotating shaft to urge the biasing and supporting unit at a position offset from a position on the biasing and supporting unit where the biasing unit is supported, with rotation of the rotating shaft, to move the biasing and supporting unit.

14. The image forming apparatus according to claim 13,

the pushing unit includes a cam, an

The cam has a uniform diameter within a predetermined angular range including a rotation angle of the rotation shaft at a timing of obtaining the biasing force according to the type of the sheet.

15. The image forming apparatus according to claim 9, further comprising a bending prevention unit configured to prevent the rotation shaft from being bent by a reaction force received by the rotation shaft when the pressing unit on the rotation shaft presses the biasing and supporting unit to move the biasing and supporting unit with rotation of the rotation shaft.

16. The image forming apparatus according to claim 6, wherein the second conveyance path is a bypass feed conveyance path.

17. The image forming apparatus according to claim 6, wherein the movable member operates in response to occurrence of a conveyance failure of the sheet conveyed through the first conveyance path.

18. An image forming apparatus according to claim 6, wherein when the biasing force switching unit switches the biasing force of the biasing unit, a maximum load operation position of the movable member when a maximum load is applied during a sheet conveying operation in which the movable member is operated to convey a sheet through the second conveying path is shifted from a maximum load operation position of the movable member when a maximum load is applied during the biasing force switching operation of the movable member.

19. An image forming apparatus according to claim 18, wherein a load applied during the sheet conveying operation and a load applied during the biasing force switching operation are always smaller than the larger of the maximum load applied during the sheet conveying operation and the maximum load applied during the biasing force switching operation.

20. An image forming apparatus according to claim 19, wherein a load applied during said sheet conveying operation and a load applied during said biasing force switching operation are always smaller than the smaller of said maximum load applied during said sheet conveying operation and said maximum load applied during said biasing force switching operation.

21. The image forming apparatus according to claim 6,

a rotating shaft rotates to change a pushing state of a first cam on the rotating shaft to operate the movable member when the sheet is conveyed through the second conveying path,

the biasing force switching unit is configured to change a biasing state in which a second cam on the rotary shaft biases the biasing unit and the supporting unit with rotation of the rotary shaft to move the biasing unit to switch the biasing force of the biasing unit, and

a maximum thrust rotational position of the movable member at which a maximum thrust of the first cam is generated during a sheet conveying operation of the movable member when conveying a sheet through the second conveying path is offset from a maximum thrust rotational position of the movable member at which a maximum thrust of the second cam is generated during a biasing force switching operation of the movable member when the biasing force switching unit switches the biasing force of the biasing unit.

22. An apparatus according to claim 21, wherein an offset angle between the maximum thrust rotational position of the movable member during the sheet conveying operation and the maximum thrust rotational position of the movable member during the biasing force switching operation is 180 °.

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