CONVEYANCE DEVICE AND IMAGE FORMING APPARATUS

Abstract

A conveyance device includes a sheet stacker, a pickup roller, a feed roller, a first drive source, a first encoder, a first drive controller, a separation roller, a second drive source, a second encoder, a second drive controller, a separation pressure provider, and a torque estimation device. The torque estimation device estimates a torque of the second drive source with an applied voltage to the second drive source from the second drive controller after calculating a turning angle speed from a rotation amount of the second drive source detected by the second encoder based on a relational expression between a motor rotation speed and an applied voltage that are measured beforehand for the second drive source and a torque of the second drive source.

Claims

1. A conveyance device comprising: a sheet stacker on which sheets are stacked; a pickup roller configured to contact a top sheet of the sheets stacked on the sheet stacker and to rotate in a sheet conveyance direction; a feed roller configured to rotate to feed the sheet in the sheet conveyance direction; a first drive source configured to rotate the pickup roller and the feed roller; a first encoder configured to detect a rotation amount of the first drive source; a first drive controller configured to control a speed or a position of the first drive source based on the rotation amount detected by the first encoder; a separation roller configured to nip a sheet with the feed roller; a second drive source configured to rotate the separation roller; a second encoder configured to detect a rotation amount of the second drive source; a second drive controller configured to perform torque control of the second drive source, the torque control rotating the separation roller with rotation of the feed roller in the sheet conveyance direction when a force having a predetermined value or more is applied to the separation roller from the feed roller in direct contact with the separation roller or nipping a sheet with the separation roller, and rotating the separation roller in a direction opposite the sheet conveyance direction when a force having a value less than the predetermined value is applied from the feed roller to the separation roller, to return an excess sheet to the sheet stacker if sheets are multi-fed; a separation pressure provider configured to provide a pressure by which the separation roller is pressed against the feed roller; and a torque estimation device configured to estimate a torque of the second drive source with an applied voltage to the second drive source from the second drive controller after calculating a turning angle speed from the rotation amount of the second drive source detected by the second encoder based on a relational expression between a motor rotation speed and an applied voltage that are measured beforehand for the second drive source and a torque of the second drive source.

2. The conveyance device according to claim 1, further comprising a multi-sheet feed detector configured to monitor a rotation speed of the second drive source while the sheet is being fed and to determine that sheet separation is to be started as sheets are multi-fed if the rotation speed is lower than a predetermined value, wherein the multi-sheet feed detector is configured to cause the second drive controller to increase a target torque for the torque control, if the multi-sheet feed detector determines that sheet separation is to be started as sheets including the sheet are multi-fed.

3. The conveyance device according to claim 1, further comprising a multi-sheet feed detector configured to monitor a torque estimation value of the second drive source while the sheet is being fed and to determine that sheet separation is to be started as sheets are multi-fed if the torque estimation value is lower than a predetermined value, wherein the multi-sheet feed detector is configured to cause the second drive controller to increase a target torque for the torque control, if the multi-sheet feed detector determines that sheet separation is to be started as sheets including the sheet are multi-fed.

4. The conveyance device according to claim 2, wherein the multi-sheet feed detector is configured to cause the second drive controller to maintain the increased target torque until the sheet being conveyed passes, if the multi-sheet feed detector determines that sheet separation is to be started as sheets are multi-fed.

5. The conveyance device according to claim 1, further comprising a sheet type input device configured to receive an input of a sheet type, wherein at least one of a predetermined value of rotation speed or torque estimation value, a target torque, and a value of target torque at a time of multi-sheet feeding is changeable depending on the sheet type input from the sheet type input device.

6. The conveyance device according to claim 2, wherein the multi-sheet feed detector is configured to: continue to monitor a rotation speed of the second drive source after determining that sheet separation is to be started as sheets are multi-fed; and determine that the sheet separation is completed if the rotation speed of the second drive source exceeds a predetermined value, and wherein the first drive controller is configured to: stop driving of the first drive source if the multi-sheet feed detector determines that sheet separation has been started as sheets are multi-fed; and resume driving the first drive source if the multi-sheet feed detector determines that the sheet separation is completed.

7. The conveyance device according to claim 3, wherein the multi-sheet feed detector is configured to: continue to monitor a torque estimation value of the second drive source after determining that sheet separation is to be started as sheets are multi-fed; and determine that the sheet separation is completed if the torque estimation value of the second drive source exceeds the predetermined value, and wherein the first drive controller is configured to: stop driving of the first drive source if the multi-sheet feed detector determines that sheet separation has been started as sheets are multi-fed; and resume driving the first drive source if the multi-sheet feed detector determines that the sheet separation is completed.

8. The conveyance device according to claim 2, wherein the first drive controller is configured to: reduce driving of the first drive source to a predetermined speed if the multi-sheet feed detector determines that sheet separation has been started as sheets are multi-fed; and return a speed of the first driving source to a normal speed if the multi-sheet feed detector determines that the sheet separation is completed.

9. The conveyance device according to claim 2, further comprising: a conveyance roller pair configured to nip a sheet fed from the conveyance device; a third drive source configured to rotate the conveyance roller pair; a third encoder configured to detect a rotation amount of the third drive source; a third drive controller configured to control a position or a speed of the third drive source; a sheet detector configured to detect presence or absence of a sheet in a position of the conveyance roller pair or a position downstream of the conveyance roller pair in the sheet conveyance direction; and a conveyance-roller-pair sheet nipping determiner configured to determine whether the conveyance roller pair has nipped a sheet based on detection performed by the sheet detector, wherein the conveyance roller pair, the third drive source, the third encoder, the third drive controller, the sheet detector, and the conveyance-roller-pair sheet nipping determiner are arranged downstream of the feed roller in the sheet conveyance direction in the conveyance device, and wherein the third drive controller is configured to: stop driving of the third drive source if the multi-sheet feed detector determines that sheet separation has been started as sheets are multi-fed after the conveyance-roller-pair sheet nipping determiner determines that the conveyance roller pair has nipped a sheet; and resume driving the third drive source if the multi-sheet feed detector determines that the sheet separation is completed.

10. The conveyance device according to claim 2, further comprising: a conveyance roller pair configured to nip a sheet fed from the conveyance device; a third drive source configured to rotate the conveyance roller pair; a third encoder configured to detect a rotation amount of the third drive source; a third drive controller configured to control a position or a speed of the third drive source; a sheet detector configured to detect presence or absence of a sheet in a position of the conveyance roller pair or a position downstream of the conveyance roller pair in the sheet conveyance direction; and a conveyance-roller-pair sheet nipping determiner configured to determine whether the conveyance roller pair has nipped a sheet based on detection performed by the sheet detector, wherein the conveyance roller pair, the third drive source, the third encoder, the third drive controller, the sheet detector, and the conveyance-roller-pair sheet nipping determiner are arranged downstream of the feed roller in the sheet conveyance direction in the conveyance device, and wherein the third drive controller is configured to: reduce driving of the third drive source to a predetermined speed if the multi-sheet feed detector determines that sheet separation has been started as sheets are multi-fed after the conveyance-roller-pair sheet nipping determiner determines that the conveyance roller pair has nipped a sheet; and return a speed of the third drive source to a normal speed if the multi-sheet feed detector determines that the sheet separation is completed.

11. The conveyance device according to claim 9, wherein the first drive controller is configured to stop driving of the first drive source if the conveyance-roller-pair sheet nipping determiner determines that the conveyance roller pair has nipped a sheet.

12. The conveyance device according to claim 9, wherein the second drive source is a direct current motor.

13. An image forming apparatus comprising the conveyance device according to claim 1.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0007] The aforementioned and other aspects, features, and advantages of the present disclosure are better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein:

[0008] FIG. 1 is a sectional view illustrating a schematic configuration of a sheet conveyance device according to an embodiment of the present disclosure;

[0009] FIG. 2 is a block diagram illustrating a control system of a separation motor of the sheet conveyance device;

[0010] FIG. 3 is a diagram illustrating an example of a reaction force estimation observer;

[0011] FIG. 4 is a diagram illustrating an example of a configuration in which a multi-sheet feed detector that detects multi-sheet feeding is disposed in the sheet conveyance device;

[0012] FIG. 5 is a diagram illustrating times at which the multi-sheet feed detector illustrated in FIG. 4 determines that sheet separation is to be started as sheets are multi-fed and the sheet separation is completed from a change in rotation speed of a separation motor;

[0013] FIG. 6 is a schematic diagram illustrating one example of the sheet conveyance device in which a target torque of the separation motor is increased if the multi-sheet feed detector illustrated in FIG. 4 monitors a torque estimation value of the separation motor and determines that sheet separation is to be started as sheets are multi-fed;

[0014] FIG. 7 is a diagram illustrating times at which the sheet conveyance device illustrated in FIG. 6 determines that sheet separation is to be started as sheets are multi-fed and the sheet separation is completed from a change in torque estimation value;

[0015] FIGS. 8A and 8B are diagrams illustrating leading end positions of a first sheet and a multi-fed sheet if a sheet feed motor is not stopped and is stopped, respectively, according to one embodiment of the present disclosure;

[0016] FIG. 9 is a sectional view illustrating a schematic configuration of a sheet conveyance device according to one embodiment of the present disclosure;

[0017] FIG. 10 is a sectional view illustrating a schematic configuration of a sheet conveyance device according to the embodiment (if a single controller is disposed);

[0018] FIG. 11 is a sectional view illustrating a schematic configuration of the sheet conveyance device according to the embodiment (if the single controller is disposed);

[0019] FIG. 12 is a diagram illustrating an example of a sheet type input device according to the embodiment; and

[0020] FIG. 13 is a sectional view illustrating an image forming apparatus according to one embodiment of the present disclosure.

[0021] The accompanying drawings are intended to depict embodiments of the present disclosure and should not be interpreted to limit the scope thereof. The accompanying drawings are not to be considered as drawn to scale unless explicitly noted.

DETAILED DESCRIPTION

[0022] In describing embodiments illustrated in the drawings, specific terminology is employed 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 have the same function, operate in a similar manner and achieve similar results.

[0023] Referring now to the drawings, embodiments of the present disclosure are described below. In the drawings for explaining the following embodiments, the same reference codes are allocated to elements (members or components) having the same function or shape and redundant descriptions thereof are omitted below.

[0024] Hereinafter, exemplary embodiments of the present disclosure are described. The present disclosure relates to a sheet supplying device (also referred to as a conveyance device) that separates and feeds sheets one by one from a tray on which the sheets (recording media such as paper) are stacked, and to an image forming apparatus including the sheet supplying device. The image forming apparatus is, for example, a copier, a printer, a facsimile machine, a multifunction peripheral having two or more copying, printing, and facsimile functions, and an offset printing machine. Particularly, the sheet supplying device as a conveyance device includes a feed roller that is rotated to feed a sheet in a sheet conveyance direction, and a separation roller that nips the sheet with a feed roller against which the separation roller is pressed. The separation roller is driven by torque control. The separation roller is rotated in the sheet conveyance direction with rotation of the feed roller when a force having a predetermined amount or more is applied from the feed roller in direct contact with the separation roller or nipping the sheet with the separation roller. The separation roller is rotated in a direction opposite the sheet conveyance direction when a force having a predetermined amount or less is applied. Accordingly, if a plurality of sheets is fed from the tray with the sheets overlapped, a sheet that is excessively fed is returned to the sheet stacker, so that the sheets are separated and fed one by one. The sheet supplying device and the image forming apparatus have the following characteristics. Based on a relational expression between a motor rotation speed and an applied voltage that are measured beforehand for a direct current (DC) motor as a separation motor and a torque of the DC motor, a torque is estimated from a detection result of the motor rotation speed and an output (a motor drive voltage) of a controller, and a determination is made on control based on the estimated torque to set a target value. Thus, torque control is performed without an electric current detector (a sensor). In addition, not only the separation motor is controlled, but also control of a feed motor is adjusted depending on the presence or absence of multi-feed sheeting, so that multi-sheet feeding can be prevented more easily. Hence, enhancement of sheet separability of the sheet supplying device and reduction of characteristic degradation of a component (reverse-roller abrasion) can be achieved at lower cost. Such characteristics of the present disclosure are hereinafter described in detail with reference to the drawings.

[0025] FIG. 1 is a sectional view illustrating a schematic configuration of a sheet conveyance device 1201 as a conveyance device according to an embodiment. The sheet conveyance device 1201 includes a sheet feed roller C2 as a feed roller, a separation roller C1, a sheet feed motor M2, and a separation motor M1 that form a sheet conveyance mechanism. The sheet conveyance mechanism causes a sheet to be nipped between the sheet feed roller C2 and the separation roller C1, and rotates the sheet feed roller C2 to convey the sheet. The sheet conveyance device 1201 also includes a sheet stacking tray T on which sheets are stacked, a sheet raising plate that raises the sheet stacked on the sheet stacking tray T toward a pickup roller C3, a timing belt that transmits rotation of the sheet feed motor M2 to the pickup roller C3, and the separation motor M1. The separation motor M1 rotates the separation roller C1 in a direction opposite a sheet conveyance direction D1. In addition, the sheet conveyance device 1201 includes a sensor that detects a sheet conveyed in a sheet conveyance direction D1, and a separation roller urging member 103 that urges the separation roller C1 toward the sheet feed roller C2. The sensor is disposed directly below a shaft of the sheet feed roller C2 or slightly downstream from the sheet feed roller C2 in the sheet conveyance direction.

[0026] With such a configuration, when a sheet is to be supplied, the sheet conveyance device 1201 raises the sheet raising plate disposed inside the sheet stacking tray T to raise the sheets stacked on the sheet stacking tray T, so that the top sheet of the stack is pressed against the pickup roller C3. Herein, the raising of the sheet raising plate stops when the top sheet is pressed against the pickup roller C3 with a pressure within a predetermined range. A sensor is disposed to detect that the top sheet is pressed against the pickup roller C3. When a sheet is not to be supplied, the sheet raising plate can be lowered.

[0027] When the sheet conveyance device 1201 rotates the pickup roller C3 in the sheet conveyance direction D1 with the top sheet pressed against the pickup roller C3, a sheet is fed from the sheet stacking tray T. Rotation of the sheet feed motor M2 as a drive source of the sheet feed roller C2 is transmitted to the pickup roller C3 via the timing belt, so that the pickup roller C3 is rotated. The sheet fed from the sheet stacking tray T enters a portion (a nip portion) in which the sheet feed roller C2 and the separation roller C1 are pressed against each other. The sheet feed roller C2 is rotated by the sheet feed motor M2 such that the sheet is fed in the sheet conveyance direction D1. The sheet feed roller C2 and the separation roller C1 pressed against each other nip the sheet. A controller 102 controls a position or a speed of the sheet feed motor M2.

[0028] The separation roller C1 is driven by the separation motor M1 via a predetermined driving force transmitter. In the present embodiment, a controller 101 controls a return force to control the separation roller C1 via the separation motor M1 for the separation roller C1 without arraignment of a torque limiter as a predetermined driving force transmitter on a separation roller shaft. The separation motor M1 rotates the separation roller C1 in a direction opposite the sheet conveyance direction. However, when a single sheet is fed, the controller 101 controls the separation motor M1 by using torque to rotate the separation roller C1 in the sheet conveyance direction (a direction D2 illustrated in FIG. 1 while applying a return force). When two or more sheets are fed to the nip portion, the controller 101 controls the separation motor M1 by using torque to stop or rotate the separation roller C1 in an opposite direction (a direction D3 illustrated in FIG. 1).

[0029] If a plurality of sheets is fed from the pickup roller C3 with the sheets overlapped, rotation of the separation roller C1 in the direction D3 functions to return an excess sheet to the sheet stacking tray T since a friction between sheets is smaller than a friction between the separation roller C1 and a sheet. Accordingly, the sheet conveyance mechanism feeds the sheets one by one. A drive source for the separation roller C1 can be shared with the sheet feed motor M2, instead of arranging a drive source as the separation motor M1 dedicated to the separation roller C1.

[0030] The present embodiment has been described using one example (a spring) of the separation roller urging member 103 as a device that gives a pressure (a separation pressure) by which the separation roller C1 as a reverse roller is pressed to the sheet feed roller C2. However, as for such a device, a mechanism that causes a gear attached to a separation roller shaft to sprig up by a gear connected to a drive source may be used, or a configuration similar to a configuration of a conventional sheet conveyance device may be employed, instead of the spring.

[0031] In the configuration illustrated in FIG. 1, the sheet conveyance device 1201 includes the sheet stacking tray T, the pickup roller C3, the sheet feed roller C2, the sheet feed motor M2, a first encoder, the controller 102, the separation roller C1, the separation motor M1, a second encoder, the controller 101, and the separation roller urging member 103. The sheet stacking tray T serves as a sheet stacker on which sheets are stacked. The pickup roller C3 contacts the top sheet of the stack on the sheet stacker, and is rotated in the sheet conveyance direction D1. The sheet feed roller C2 as a feed roller is rotated to feed a sheet in the sheet conveyance direction D1. The sheet feed motor M2 as a first drive source rotates the pickup roller C3 and the sheet feed roller C2, and the first encoder detects a rotation amount of the sheet feed motor M2. The controller 102 as a first drive controller controls a speed or a position of the first drive source based on the rotation amount detected by the first encoder. The separation roller C1 nips a sheet with the sheet feed roller C2 against which the separation roller C1 is pressed. The separation motor M1 as a second drive source rotates the separation roller C1, and the second encoder detects a rotation amount of the separation motor M1. The controller 101 as a second drive controller performs torque control of the separation motor M1, and the separation roller urging member 103 as a separation pressure provider provides a pressure (a separation pressure) by which the separation roller C1 is pressed against the sheet feed roller C2. The torque control performed by the second drive controller controls a torque (a return force) such that the separation roller C1 is rotated with rotation of the sheet feed roller C2 in the direction D2 which is the same direction as the sheet conveyance direction D1 when a force having a predetermined value or more is applied from the sheet feed roller C2 in direct contact with the separation roller C1 or nipping a sheet with the separation roller C1. Moreover, the torque control performed by the second drive controller controls a torque (a return force) such that the separation roller C1 is rotated in a direction D3 opposite the sheet conveyance direction D1 when a force having a value less than the predetermined value is applied. With such control, a sheet that has been excessively fed is returned to the sheet stacking tray T as a sheet stacker if sheets are multi-fed. Thus, sheets are separated and fed one by one. In such a configuration, the separation motor M1 as the second drive source is a DC motor. Based on a relational expression between a motor rotation speed and an applied voltage that are measured beforehand for the DC motor and a torque of the DC motor, a reaction force estimation observer 201 (described below) as a torque estimation device calculates a turning angle speed from a rotation amount of the separation motor M1 detected by the second encoder, and then estimates a torque of the DC motor with an applied voltage to the DC motor from the controller 101 as the second drive controller. Such a configuration enables detection of multi-sheet feeding and control of multi-fed sheet separation to be performed in sheet conveyance (paper feeding) based on a torque of a motor that drives one roller contributed to the sheet conveyance. Thus, torque control is performed without an electric current detector (a sensor), and torque control of a reverse motor can be performed at lower cost than a conventional manner.

[0032] FIG. 2 is a block diagram illustrating a control system of the separation motor M1 of the sheet conveyance device 1201. The sheet conveyance device 1201 does not use an electric current detector (a sensor) to detect an electric current of a motor. The sheet conveyance device 1201 inputs an output (a motor applied voltage) of the controller 101 and a motor shaft rotation speed measured by a sensor to the reaction force estimation observer 201 to calculate an estimation value of a return force to a sheet as a reaction force estimation value, and performs feedback control. A plant C10 includes the separation motor M1 and a drive module such as the separation roller C1. An example of the reaction force estimation observer 201 may have a known configuration as illustrated in FIG. 3. In the example illustrated in FIG. 3, a motor applied voltage and a motor shaft rotation speed are input to output an estimation value of a reaction force (torque).

[0033] In addition, as illustrated in FIG. 4, the sheet conveyance device 1201 can include a multi-sheet feed detector 401 that detects multi-sheet feeding. The multi-sheet feed detector 401 monitors a rotation speed of the separation motor M1 to determine whether sheet separation is to be started as sheets are multi-fed. If the multi-sheet feed detector 401 determines that sheet separation is to be started, a target torque of the separation motor M1 is increased. In FIG. 4, the multi-sheet feed detector 401 receives a rotation speed from the separation motor M1. If the rotation speed is a predetermined threshold value or greater and remains unchanged for a certain time period, the multi-sheet feed detector 401 determines that sheet separation is to be started as sheets are multi-fed, and instructs the controller 101 to change a target torque.

[0034] Accordingly, the sheet conveyance device 1201 illustrated FIG. 1 includes the multi-sheet feed detector 401 which monitors a rotation amount (a rotation speed) of the separation motor M1 as the second drive source during sheet feeding. If the rotation speed falls below a predetermined value, the multi-sheet feed detector 401 determines that sheet separation is to be started as sheets are multi-fed. If sheet separation is to be started as sheets are multi-fed, the multi-sheet feed detector 401 controls the controller 101 as the second drive controller to increase a target torque for torque control. Such control enables multi-sheet feeding to be detected without arrangement of a dedicated multi-sheet feed detection sensor. Moreover, since a return force is increased when only sheets are multi-fed, unnecessary return force is not applied during single-sheet feeding in which sheets are not multi-fed. Thus, a rubbing amount of a separation roller against a sheet can be reduced, and the lifetime of a component of the separation roller can be extended.

[0035] FIG. 5 is a diagram illustrating times at which the multi-sheet feed detector illustrated in FIG. 4 determines that sheet separation is to be started as sheets are multi-fed and the sheet separation is completed from a change in rotation speed of the separation motor.

[0036] As illustrated in FIG. 5, in the sheet conveyance device 1201, after activation of the separation motor M1 is completed, a rotation speed of the separation motor M1 exceeds a threshold value V1, and the multi-sheet feed detector 401 starts monitoring the rotation speed of the separation motor M1 at a time T0. Subsequently, the rotation speed of the separation motor M1 may remain constant for a certain time period. In such a case, at a time T1, the multi-sheet feed detector 401 determines that sheets are multi-fed and instructs the controller 101 to change a target torque. Accordingly, the controller 101 changes the target torque such that the separation motor M1 is rotated in reverse for a certain time period. Then, the multi-sheet feed detector 401 increases the rotation speed of the separation motor M1 as similar to the situation prior to the time T1. When the rotation speed of the separation motor M1 exceeds a threshold value V2 that is used for determination of completion of the sheet separation, the multi-sheet feed detector 401 determines that the sheet separation is completed at a time T2 at which the rotation speed exceeds the threshold value V2, and conveyance of the sheet continues.

[0037] A threshold value (V1) to be used for determination of the start of sheet separation as sheets are multi-fed and a threshold value (V2) to be used for determination of completion of the sheet separation can be same value or different values. In FIG. 5, the separation motor M1 intends to rotate the separation roller C1 in a direction opposite the sheet conveyance direction. Thus, when separation of sheets is started as the sheets are multi-fed, the separation roller C1 is decelerated and rotated in reverse. When the separation is completed and the separation roller C1 is again rotated with a first sheet (the top layer sheet), the separation roller C1 is rotated in the sheet conveyance direction.

[0038] FIG. 6 is a schematic diagram illustrating one example of the sheet conveyance device 1201 in which the multi-sheet feed detector 401 illustrated in FIG. 4 monitors a torque estimation value of the separation motor M1 to increase a target torque of the separation motor M1 if the multi-sheet feed detector 401 determines that sheet separation is to be started as sheets are multi-fed. In FIG. 6, the multi-sheet feed detector 401 receives a torque estimation value of the separation motor M1 from the controller 101. If the torque estimation value is a predetermined threshold value or greater and remains unchanged for a certain time period, the multi-sheet feed detector 401 determines that sheet separation is to be started as sheets are multi-fed, and instructs the controller 101 to change a target torque.

[0039] Accordingly, the sheet conveyance device 1201 illustrated FIG. 6 includes the multi-sheet feed detector 401. The multi-sheet feed detector 401 monitors torque (an estimation value provided by the reaction force estimation observer 201 as a torque estimator) of the separation motor M1 as the second drive source during sheet feeding. The multi-sheet feed detector 401 determines that sheet separation is to be started as sheets are multi-fed, if the toque estimation value falls below a predetermined value. If the multi-sheet feed detector 401 determines that sheet separation is to be started as sheets are multi-fed, a target torque for torque control to be performed by the controller 101 as the second drive controller is increased. Hence, with such a multi-sheet feed detector 401, multi-sheet feeding can be detected by a method different from the method described with reference to FIG. 4 without a dedicated multi-sheet feed detection sensor. Moreover, since a return force is increased when only sheets are multi-fed, unnecessary return force is not applied during single-sheet feeding in which sheets are not multi-fed. Thus, a rubbing amount of a separation roller against a sheet can be reduced, and the lifetime of a component of the separation roller can be extended.

[0040] FIG. 7 is a diagram illustrating times at which the sheet conveyance device 1201 illustrated in FIG. 6 determines that sheet separation is to be started as sheets are multi-fed and the sheet separation is completed from a change in torque estimation value. As illustrated in FIG. 7, in the sheet conveyance device 1201, after activation of the separation motor M1 is completed, a torque estimation value of the separation motor M1 exceeds the threshold value V1, and the multi-sheet feed detector 401 starts monitoring the torque estimation value of the separation motor M1 at a time T0. Afterward, the torque estimation value of the separation motor M1 may remain constant for a certain time period without increasing. In such a case, the multi-sheet feed detector 401 determines that sheets are multi-fed at a time T3 at which the certain time has elapsed, and instructs the controller 101 to change a target torque. Accordingly, the controller 101 changes the target torque such that the separation motor M1 is rotated in reverse for a certain time period. Subsequently, the multi-sheet feed detector 401 increases the torque estimation value of the separation motor M1, as similar to the situation prior to the time T3. When the torque estimation value of the separation motor M1 exceeds a threshold value V2 that is used for determination of completion of the sheet separation, the multi-sheet feed detector 401 determines that the sheet separation is completed at a time T4 at which the torque estimation value exceeds the threshold value V2, and conveyance of the sheet continues. If a torque estimation value of the separation motor M1 is constant without increasing, the multi-sheet feed detector 401 can make a determination based on the presume that a slip of a lower sheet of multi-fed sheets with respect to an upper sheet by a return force from the separation roller C1 reduces a reaction force estimated by the reaction force estimation observer 201. Accordingly, a time at which such a determination is made can be determined as a time T3 at which sheet separation is started as sheets are multi-fed. A threshold value (V1) to be used for determination of the start of sheet separation as sheets are multi-fed and a threshold value (V2) for determination of completion of the sheet separation can be same value or different values.

[0041] In the sheet conveyance device 1201 illustrated in each of FIGS. 4 and 6, if determining that sheet separation is to be started as sheets are multi-fed, the multi-sheet feed detector 401 can perform control such that a target torque remains large until a sheet being conveyed passes. When such control can return the multi-fed sheet to the tray side, the separation roller C1 is rotated with a sheet in a sheet conveyance direction D1. In the sheet conveyance device 1201 illustrated in FIGS. 4 and 6, if a rotation speed or a torque estimation value exceeds a predetermined value again, a target torque level is controlled to return to an initial value. However, in one embodiment of the present disclosure, even if a rotation speed or a torque estimation value exceeds a predetermined value again, a target torque level is controlled not to return to an initial value. Thus, a return operation can be performed promptly, even if sheets are multi-fed again.

[0042] In the sheet conveyance device 1201 according to one embodiment of the present disclosure, as illustrated in FIG. 5 or 7, after determining that sheet separation is to be started as sheets are multi-fed, the multi-sheet feed detector 401 continue to monitor a rotation amount (a rotation speed) of the separation motor M1 as the second drive source, or torque (an estimation amount provided by the torque estimation device) of the separation motor M1 as the second drive source. If the rotation amount (the rotation speed) of the second drive source or the torque (the estimation amount provided by the torque estimation device) of the second drive source exceeds a predetermined value, the multi-sheet feed detector 401 determines that the sheet separation is completed. The controller 102 as a first drive controller stops the driving of the sheet feed motor M2 as the first drive source if the multi-sheet feed detector 401 determines that sheet separation is to be started as sheets are multi-fed. The controller 102 resumes driving of the first drive source if the multi-sheet feed detector 401 determines that the sheet separation is completed.

[0043] In the sheet conveyance device 1201 according to one embodiment of the present disclosure, as illustrated in each of FIGS. 5 and 7, the controller 102 as the first drive controller can reduce driving of the sheet feed motor M2 as the first drive source to a predetermined speed if the multi-sheet feed detector 401 determines that separation of sheets has been started as the sheets are multi-fed. The controller 102 can control a speed of the first drive source to return to a normal speed if the multi-sheet feed detector 401 determines that the sheet separation is completed. Although such control provides lower multi-sheet feeding prevention effects than a configuration illustrated in each of FIGS. 4 and 6, a delay of sheet feeding operation when multi-sheet feeding prevention operation is performed can be reduced, and influence on a latter system can be reduced.

[0044] FIG. 8A is diagram illustrating leading end positions 801 and 802 of a first sheet and a multi-fed sheet if the sheet feed motor M2 is not stopped, and FIG. 8B is a diagram illustrating leading end positions 803 and 804 of a first sheet and a multi-fed sheet if the sheet feed motor M2 is stopped according to one embodiment of the present disclosure. As illustrated in FIGS. 8A and 8B, the controller 101 stops the sheet feed motor M2 if multi-sheet feeding is detected from a position (P2) of a sheet feed separation portion as a nip portion formed by the separation roller C1 and the sheet feed roller C2 to a position (P1) of a conveyance roller disposed downstream in a conveyance direction. As illustrated in FIG. 8A, if the sheet feed motor M2 is not stopped, the leading end position 801 of the first sheet moves with time to the position (P1) of the conveyance roller disposed downstream in the conveyance direction. Meanwhile, as for the leading end position 802 of a lower sheet that is prevented by the separation roller C1 from being multi-fed, after the leading end position 802 intends to move to the position (P1) of the conveyance roller disposed downstream in the conveyance direction with the first sheet, the leading end position 802 remains unchanged even after a certain time period has elapsed. On the other hand, as illustrated in FIG. 8B, if the sheet feed motor M2 is stopped for a certain time period (TT), the leading end position 804 of a lower sheet does not intend to move to the position (P1) of the conveyance roller disposed downstream in the conveyance direction, and is not changed even after the certain time period has elapsed. That is, the sheet feed motor M2 is stopped, so that a multi-fed sheet is prevented from moving excessively, and a possibility that the multi-fed sheet may reach a downstream roller pair (a conveyance roller pair) can be reduced even more.

[0045] FIG. 9 is a sectional view illustrating a schematic configuration of the sheet conveyance device 1201 according to one embodiment of the present disclosure. In FIG. 9, the sheet conveyance device 1201 includes a conveyance-roller-pair sheet nipping determiner 903 in addition to the configuration illustrated in FIG. 4. The conveyance-roller-pair sheet nipping determiner 903 determines whether a conveyance roller pair has nipped a sheet. In FIG. 9, the sheet conveyance device 1201 includes a conveyance roller pair (a conveyance roller R1 and a counter roller R2), a conveyance motor M3 as a third drive source, a third encoder, a controller 902 as a third drive controller, and the conveyance-roller-pair sheet nipping determiner 903 that are disposed downstream of the sheet conveyance device 1201 in the sheet conveyance direction D1 illustrated in FIG. 1. The conveyance roller pair is pressed against each other to nip a sheet fed from the sheet conveyance device 1201. The conveyance motor M3 rotates the conveyance roller pair (or the conveyance roller R1). The third encoder detects a rotation amount of the conveyance motor M3. The controller 902 controls a position or a speed of the conveyance motor M3. The conveyance-roller-pair sheet nipping determiner 903 uses a sheet detector 901 such as a sensor to determine whether the conveyance roller pair has nipped a sheet. The sheet detector 901 detects the presence or absence of a sheet in a position of the conveyance roller pair or a position slightly downstream of the conveyance roller pair. In the sheet conveyance device 1201 illustrated in FIG. 9, if the multi-sheet feed detector 401 determines that a time at which sheet separation is to be started as sheets are multi-fed has come after the conveyance-roller-pair sheet nipping determiner 903 determines that the conveyance roller pair has nipped a sheet, the controller 902 stops the driving of the sheet feed motor M2. If the multi-sheet feed detector 401 determines that the sheet separation is completed, the controller 902 resumes the driving of the conveyance motor M3. Such control enables effects similar to FIGS. 4 and 6 to be obtained even when a second sheet or subsequent sheets enter a portion in which the sheet feed roller C2 and the separation roller C1 forming a sheet feed separation portion are in contact with each other after a first sheet reaches the conveyance roller pair.

[0046] In the sheet conveyance device 1201 illustrated in FIG. 9, as one embodiment of the present disclosure, if the multi-sheet feed detector 401 determines that separation of sheets has been started as the sheets are multi-fed after the conveyance-roller-pair sheet nipping determiner 903 determines that the conveyance roller pair has nipped a sheet, the controller 902 reduces the driving of the conveyance motor M3 to a predetermined speed. If the multi-sheet feed detector 401 determines that the sheet separation is completed, the controller 902 returns the speed of the conveyance motor M3 to a normal speed. Such control enables effects similar to FIGS. 4 and 6 to be obtained, even if a second sheet or subsequent sheets enter a portion in which the sheet feed roller C2 and the separation roller C1 forming a sheet feed separation portion are in contact with each other after a first sheet reaches the conveyance roller pair.

[0047] Moreover, in the sheet conveyance device 1201 illustrated in FIG. 9, as one embodiment of the present disclosure, if the conveyance-roller-pair sheet nipping determiner 903 determines that the conveyance roller pair has nipped a sheet, the controller 102 as the first drive controller can stop the driving of the sheet feed motor M2 as the first drive source. Such control enables a sheet to be conveyed by only the conveyance roller pair, so that energy saving effect can be obtained. As illustrated in FIGS. 10 and 11, a function of the controller 102 can be included in the controller 101, so that the sheet conveyance device 1201 can include a single controller. With such arrangement, the sheet conveyance device 1201 can be made more compact

[0048] FIG. 12 is a diagram illustrating an example of a sheet type input portion 1202 according to the present embodiment. The sheet conveyance device 1201 includes a sheet stacking tray 1203, a sheet ejection port tray 1204 to which a sheet is ejected, and a sheet type input device including the sheet type input portion 1202. The sheet type input portion 1202 is used to input (select) a sheet type.

[0049] The sheet conveyance device 1201 which has been described with reference to the drawings can include the sheet type input device including the sheet type input portion 1202 to which a sheet type can be input by a user. At least one of a predetermined value of rotation speed or torque estimation value, a target torque, and a value of target torque at the time of multi-sheet feeding can be changed depending on the sheet type input from the sheet type input device. Such a configuration enables a suitable return force to be set according to a sheet type (characteristic), so that multi-sheet feed prevention performance (separability) can be enhanced, and a rubbing amount of a separation roller against a sheet can be reduced.

[0050] FIG. 13 is a sectional view illustrating an image forming apparatus 1000 according to one embodiment. The image forming apparatus 1000 illustrated in FIG. 13 is an electrophotographic tandem-type indirect-transfer color copier (hereinafter simply referred to as a copier), and a schematic configuration illustrated in FIG. 13 is one example of an internal mechanical part of the copier. The image forming apparatus 1000 includes a copier body 100 as an image forming apparatus body, a sheet conveyance device 200 on which the copier body 100 is placed, a scanner 300 that is attached on the copier body 100, and an automatic document feeder (ADF) 400 that is attached on the scanner 300.

[0051] In a middle portion of the copier body 100, an intermediate transfer body 10 of an endless belt is stretched by a drive roller 14 and two driven rollers 15 and 16, and is rotatable clockwise in FIG. 13. The intermediate transfer body 10 may be stretched by four or more rollers including a roller that adjusts deviation of the intermediate transfer body 10. In the example illustrated in FIG. 13, the intermediate transfer body 10 is stretched in a substantially horizontal manner. However, the intermediate transfer body 10 may be diagonally stretched, instead of being horizontally stretched.

[0052] In the example illustrated in FIG. 13, the copier body 100 also includes a belt cleaning device 17 on the left side of the driven roller 15 which is one of the driven rollers. The belt cleaning device 17 removes residual toner remaining on the intermediate transfer body 10 subsequent to transfer of an image.

[0053] A tandem image formation device 20 is disposed on the intermediate transfer body 10 which is horizontally stretched between the drive roller 14 and the driven roller 15. The tandem image formation device 20 includes four single-color image formation devices 18Y, 18C, 18M, and 18K for yellow, cyan, magenta, and black that are aligned along a direction of movement of the intermediate transfer body 10. In addition, an exposure device 21 is disposed above the tandem image formation device 20.

[0054] A secondary transfer device 22 is disposed below an area in which the intermediate transfer body 10 is stretched. In the example illustrated in FIG. 13, the secondary transfer device 22 includes a secondary transfer belt 24 of an endless belt that is stretched between two rollers 23 and is pressed against the driven roller 16 to transfer an image on the intermediate transfer body 10 to a recording medium.

[0055] A fixing device 25 that fixes the transferred image on the recording medium is disposed beside the secondary transfer device 22. The fixing device 25 is configured to press a pressure roller 27 against a fixing belt 26 of an endless belt. In the example illustrated in FIG. 13, one portion of the fixing device 25 is (the entire portion of the fixing device 25 can be) arranged below the area in which intermediate transfer body 10 is stretched. The secondary transfer device 22 also has a recording medium conveyance function of conveying the recording medium with the transferred image to the fixing device 25. Alternatively, a non-contact charger may be disposed as the secondary transfer device 22. In such a case, however, the non-contact charger as the secondary transfer device 22 has a difficulty in having such a recording medium conveyance function.

[0056] A recording medium reverse device 28 is disposed below the secondary transfer device 22 and the fixing device 25. The recording medium reverse device 28 is disposed parallel to a direction in which the intermediate transfer body 10 is stretched. The recording medium reverse device 28 reverses a recording medium to form images on two sides of the recording medium.

[0057] When such a copier is used to make a copy, a document is set on a document tray 30 of the ADF 400 or the ADF 400 is opened to directly set a document on an exposure glass 32, and the ADF 400 is closed to hold the document with the ADF 400. Subsequently, a start switch is pressed. If the document is set on the ADF 400, the document is conveyed and moved to the exposure glass 32, and then the scanner 300 is driven to read the contents of the document. If the document is directly set on the exposure glass 32, the content of the document is read by the scanner 300 without conveyance of the document.

[0058] Moreover, when the start switch is pressed, the drive roller 14 is rotated by a drive motor and the driven rollers 15 and 16 are rotated by rotation of the drive roller 14 to rotate the intermediate transfer body 10. At the same time, in the single-color image formation devices 18Y, 18C, 18M, and 18K, image bearers 40Y, 40C, 40M and 40K are respectively rotated to form single color images of respective colors (yellow, cyan, magenta, and black) on the image bearers 40Y, 40C, 40M and 40K. Then, the single-color images are primarily transferred and sequentially overlapped with movement of the intermediate transfer body 10, so that combined color images are formed on the intermediate transfer body 10.

[0059] Meanwhile, one of pickup rollers 42 of the sheet conveyance device 200 is selected and rotated at an appropriate time after the start switch is pressed. Then, recording media are fed from one of a plurality of sheet stacking trays 44 in a sheet bank 43. The recording media are separated one by one by a separation roller 45 and enter separately a sheet conveyance path 46. The recording medium is then conveyed by a conveyance roller 47 and is guided to a sheet feed path 48 inside the copier body 100. When the recording medium contacts a registration roller 49, the conveyance of the recording medium stops. If recording media are manually fed, the recording media set on a manual feed tray 51 that is opened with rotation of a sheet feed roller 50 are fed. Then, the recording media are separated one by one by a separation roller 52 and enter separately a manual feed sheet conveyance path 53. As similar to the above, the recording medium contacts the registration roller 49, and the conveyance of the recording medium stops.

[0060] The registration roller 49 is rotated to time with the combined color images on the intermediate transfer body 10, and the recording medium is fed between the intermediate transfer body 10 and the secondary transfer device 22. The secondary transfer device 22 secondarily transfers the combined color images on the intermediate transfer body 10 to the recording medium in a collective manner to form a color image on the recording medium.

[0061] The recording medium with the transferred image is conveyed by the secondary transfer device 22 to the fixing device 25. After the fixing device 25 applies heat and pressure to the recording medium to fix the transferred image, a conveyance direction of the recording medium is switched by a switching pawl 55 and the recording medium is ejected by an ejection roller 56. The ejected recording medium is stacked on an ejection tray 57. If images are to be formed on two sides of the recording medium, a conveyance direction of the recording medium is switched by the switching pawl 55 and the recording medium enters the recording medium reverse device 28. The recording medium is reversed in the recording medium reverse device 28. The reversed recording medium is guided to a transfer position again, and an image is formed on the back surface of the recording medium. Subsequently, the recording medium is ejected by the ejection roller 56 to the ejection tray 57.

[0062] The belt cleaning device 17 removes a residual toner remaining on the intermediate transfer body 10 after the image is transferred, and the intermediate transfer body 10 becomes ready again for image formation to be performed by the tandem image formation device 20.

[0063] In such an image forming apparatus 1000, a device that supplies sheet-type recording media such as paper is disposed. The sheet conveyance device 1201 according to the embodiment can be applied to such a device for supplying recording media. The application of the sheet conveyance device 1201 can provide an image forming apparatus that reduces a degree of degradation of a separation roller at lower cost while maintaining or enhancing multi-sheet feed prevention performance (separability).

[0064] The present disclosure has been described above with reference to specific embodiments but is not limited thereto. Various modifications and enhancements are possible without departing from scope of the disclosure. It is therefore to be understood that the present disclosure may be practiced otherwise than as specifically described herein. For example, elements and/or features of different illustrative embodiments may be combined with each other and/or substituted for each other within the scope of the present disclosure.

[0065] Any one of the above-described operations may be performed in various other ways, for example, in an order different from the one described above.

[0066] Each of the functions of the described embodiments may be implemented by one or more processing circuits or circuitry. Processing circuitry includes a programmed processor, as a processor includes circuitry. A processing circuit also includes devices such as an application specific integrated circuit (ASIC), digital signal processor (DSP), field programmable gate array (FPGA), and conventional circuit components arranged to perform the recited functions.

[0067] Program codes executed by the image processing apparatus to achieve the functions of the described embodiments may be provided in files in an installable format or an executable format that are recorded on computer-readable recording media such as a CD-ROM, a flexible disk (FD), a CD-R, and a digital versatile disk (DVD). The program codes executed by the image processing apparatus may be stored on a computer connected to a network such as the Internet and provided by being downloaded via the network, or be provided or distributed via a network such as the Internet.