SHEET CONVEYING DEVICE, IMAGE FORMING APPARATUS, AND METHOD OF DETECTING DOUBLE-FEED OF SHEET

Abstract

According to an embodiment, a sheet conveying device includes: a first roller configured to correct a tilt of a sheet to be conveyed; a first detecting unit located further on an upstream side in a conveying direction of the sheet than the first roller and configured to detect information concerning double-feed of the sheet; a second roller configured to convey the sheet to the first roller; a driving unit configured to drive the second roller; and a controller configured to control the driving unit to thereby temporarily stop the conveyance of the sheet in order to perform the detection by the first detecting unit in a state in which an end of the sheet on a downstream side in the conveying direction of the sheet is located further on the upstream side in the conveying direction of the sheet than a nip position of the first roller.

Description

CROSS-REFERENCE TO RELATED APPLICATION

This application is also based upon and claims the benefit of priority from U.S. provisional application 61/248910, filed on Oct. 6, 2009; the entire contents of which are incorporated herein by reference.

FIELD

Embodiments described herein relate generally to a technique for performing double-feed detection for a sheet.

BACKGROUND

In the past, double-feed detection for an original document conveyed in an auto document feeder is performed in a state in which the original document is bent by bringing the original document into contact with an aligning roller that corrects a tilt of the original document.

However, since a positional relation between a sensor that performs the double-feed detection and the original document is unstable, stable double-feed detection cannot be performed.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view of an image forming apparatus;

FIG. 2 is a sectional view of an auto document feeder;

FIG. 3 is a block diagram of components related to document conveyance by the auto document feeder;

FIG. 4 is a flowchart for explaining the operation of the auto document feeder;

FIG. 5 is a sectional view of the auto document feeder, wherein an original document located in a double-feed detection position is schematically shown; and

FIG. 6 is a sectional view of the auto document feeder, wherein a position of the original document at the time when a motor driving unit stops is schematically shown.

DETAILED DESCRIPTION

In general, according to an embodiment, a sheet conveying device includes: a first roller configured to correct a tilt of a sheet to be conveyed; a first detecting unit located further on an upstream side in a conveying direction of the sheet than the first roller and configured to detect information concerning double-feed of the sheet; a second roller configured to convey the sheet to the first roller; a driving unit configured to drive the second roller; and a controller configured to control the driving unit to thereby temporarily stop the conveyance of the sheet in order to perform the detection by the first detecting unit in a state in which an end of the sheet on a downstream side in the conveying direction of the sheet is located further on the upstream side in the conveying direction of the sheet than a nip position of the first roller.

FIG. 1 is a sectional view of an image forming apparatus. An image forming apparatus 1 may be a MFP (Multi Function Printer).

Referring to FIG. 1, the image forming apparatus 1 includes an image reading unit R and an image forming unit P. The image reading unit R scans and reads images of a sheet document and a book document.

The image forming unit P forms a developer image on a sheet on the basis of an image read from an original document by the image reading unit R or print data transmitted to the image forming apparatus 1 by an external apparatus.

The image reading unit R includes an auto document feeder (ADF) 9 configured to automatically convey an original document to a predetermined image reading position. The image reading unit R reads, with a scanning optical system 10, an image of an original document automatically conveyed by the auto document feeder 9 and placed on a document tray (a predetermined document placing table) Rt or an original document placed on a not-shown document table.

The image forming unit P includes toner cartridges 1Y to 1K, photoconductive members 2Y to 2K, developing rollers 3Y to 3K, mixers 4Y to 4K, an intermediate transfer belt 6, a fixing device 7, and a discharge tray 8.

The image forming apparatus 1 according to this embodiment includes a controller 801, a memory 803, an operation display unit 805, and a communication unit 807.

The controller 801 has a role of performing various kinds of processing in the image forming apparatus 1 and also has a role of realizing various functions by executing computer programs stored in the memory 803. The memory 803 may be, for example, a RAM (Random Access Memory), a ROM (Read Only Memory), a DRAM (Dynamic Random Access Memory), an SRAM (Static Random Access Memory), or a VRAM (Video RAM). The memory 803 has a role of storing various kinds of information and computer programs used in the image forming apparatus 1.

Various kinds of setting are displayed on the operation display unit 805. The operation display unit 805 may be an LCD (Liquid Crystal Display), an EL (Electronic Luminescence), a PDP (Plasma Display Panel), or a CRT (Cathode Ray Tube).

The various kinds of setting are changed by operating the operation display unit 805. The operation display unit 805 may be a touch panel type.

An overview of copying is explained below as an example of processing in the image forming apparatus according to this embodiment.

First, sheets picked up from cassettes enter a sheet conveying path. The sheets entered the sheet conveying path are moved in a predetermined conveying direction by plural roller pairs.

Images of plural sheet documents continuously automatically conveyed by the auto document feeder 9 are read by the scanning optical system 10 in the predetermined image reading position.

On the basis of print data of the images read from the original documents by the image reading unit R, electrostatic latent images are formed on photoconductive surfaces of the photoconductive members 2Y, 2M, 2C, and 2K for transferring developer images of yellow (Y), magenta (M), cyan(C), and black (K) onto the sheets.

Subsequently, developers agitated by the mixers 4Y to 4K in a developing device are deposited by the developing rollers 3Y to 3K on the photoconductive members 2Y to 2K on which the electrostatic latent images are formed as explained above. Consequently, the electrostatic latent images formed on the photoconductive surfaces of the photoconductive members are visualized.

Developer images formed on the photoconductive members in this way are transferred onto a belt surface of the intermediate transfer belt 6 (so-called primary transfer). The developer images conveyed by the rotation of the intermediate transfer belt 6 are transferred onto the conveyed sheets in a predetermined secondary transfer position T.

The developer images transferred onto the sheets are heated and fixed on the sheets by the fixing device 7. The sheets having the developer images heated and fixed thereon are conveyed in the conveying path by plural conveying roller pairs and sequentially discharged onto the discharge tray 8.

The auto document feeder 9 is explained below. FIG. 2 is an enlarged sectional view of the auto document feeder. An original document is set on a document tray 11. The document may be plural documents or one document.

A pickup roller 12 as a third roller picks up the original document located on the document tray 11 and conveys the original document to a paper feeding roller 13 as a second roller. The paper feeding roller 13 conveys the original document picked up by the pickup roller 12 to downstream in the conveying direction. Rotating shaft sections of the pickup roller 12 and the paper feeding roller 13 are connected to each other via a transmission mechanism 18. The transmission mechanism 18 may be a belt or a pulley.

FIG. 3 is a block diagram of components related to document conveyance by the auto document feeder 9. Referring to the figure, the pickup roller 12 moves up and down according to the operation of a solenoid driving unit 40. The solenoid driving unit 40 includes a solenoid driver 41 and a pickup solenoid 42.

Referring to FIG. 2, a separation roller 14 as a fourth roller is located to be opposed to the paper feeding roller 13. When the pickup roller 12 picks up two or more original documents, a load of a torque limiter of the separation roller 14 is increased by frictional force of the original documents and the separation roller 14 stops. The stopped separation roller 14 comes into contact with the original document on the lower side to thereby suppress the original document on the lower side from being conveyed further down stream.

An aligning roller 15 as a first roller comes into contact with the original document conveyed by the paper feeding roller 13 to correct a tilt of the original document. The aligning roller 15 includes two roller set in contact with each other. The aligning roller 15 brings the original document into contact with a nip section where the rollers are in contact with each other to be bent to thereby correct the tilt of the original document.

Referring to FIG. 3, a motor driving unit 30 drives the pickup roller 12, the paper feeding roller 13, and the aligning roller 15. The motor driving unit 30 includes a motor driver 31 and a document feeding motor 32.

The document feeding motor 32 may be a stepping motor. The controller 801 outputs a pulse signal to the motor driver 31. The motor driver 31 supplies driving current to the document feeding motor 32 on the basis of the received pulse signal.

The controller 801 controls the number of pulses of the pulse signal output to the motor driver 31 to thereby control an amount of driving of the document feeding motor 32.

The document feeding motor 32 normally rotates, whereby the pickup roller 12 and the paper feeding roller 13 rotate. The document feeding motor 32 reversely rotates, whereby the aligning roller 15 rotates.

An aligning sensor 16 is located between the separation roller 14 and the aligning roller 15. The aligning sensor 16 detects arrival of the original document conveyed by the separation roller 14.

A double-feed detecting unit 17 is located between the aligning roller 15 and the aligning sensor 16. The double-feed detecting unit 17 may be a non-contact sensor. The non-contact sensor may be an ultrasonic sensor.

When the double-feed detecting unit 17 is the ultrasonic sensor, the double-feed detecting unit 17 includes an ultrasound generating unit 17a and an ultrasound receiving unit 17b. The ultrasound generating unit 17a and the ultrasound receiving unit 17b are opposed to each other across the conveying path for the original document. The ultrasound generating unit 17a is located further on a downstream side in the conveying direction of the original document than the ultrasound receiving unit 17b. The ultrasound generating unit 17a and the ultrasound receiving unit 17b may be obliquely opposed to each other with respect to the conveying path for the original document. Since the ultrasound sound generating unit 17a and the ultrasound receiving unit 17b are obliquely opposed to each other, detection accuracy is improved.

The ultrasound receiving unit 17b receives ultrasound output by the ultrasound generating unit 17a. The ultrasound penetrated into the original document is attenuated. When the number of original documents increases, a degree of the attenuation increases. The ultrasound receiving unit 17b outputs a signal corresponding to the intensity of the received ultrasound to the controller 801.

When original documents entered a position for detection by the double-feed detecting unit 17 are superimposed, the intensity of the ultrasound received by the ultrasound receiving unit 17b is smaller than that of the ultrasound received in a normal case, i.e., when one original document is detected. The controller 801 discriminates, according to the intensity of the signal output from the ultrasound receiving unit 17b, whether the original documents are double-fed.

The controller 801 controls driving timing for the aligning roller 15 such that the original document coming into contact with the aligning roller 15 to be bent is conveyed to be timed to coincide with a toner image formed on the intermediate transfer belt 6.

The operation of the auto document feeder 9 is explained with reference to a flowchart of FIG. 4. In Act 101, the controller 801 controls the solenoid driving unit 40 to thereby move down the pickup roller 12 toward a pickup position for picking up an original document placed on the document tray 11.

In Act 102, the controller 801 controls the motor driving unit 30 to thereby drive the pickup roller 12 and the paper feeding roller 13. The original document picked up by the pickup roller 12 moves downstream. In Act 103, the controller 801 determines whether the aligning sensor 16 detects the original document.

If the aligning sensor 16 detects the original document, the controller 801 proceeds to Act 104. In Act 104, the controller 801 starts counting of the number of pulses output to the motor driver 31.

In Act 105, the controller 801 determines whether the counted number of pulses reaches N1. If the number of pulses reaches N1, the controller 801 proceeds to Act 106.

The controller 801 stops the driving of the motor driving unit 30 and stops the conveyance of the original document. A position where the conveyance of the original document is stopped is a double-feed detection position where double-feed detection is performed by the double-feed detecting unit 17.

N1 is set such that an end of the original document on the downstream side in the conveying direction of the original document is located further on an upstream side in the conveying direction than the nip section of the aligning roller 15. FIG. 5 is a sectional view of the auto document feeder, wherein the original document located in the double-feed detection position is schematically shown. Referring to the figure, the original document stops before coming into contact with the aligning roller 15 and is located along the conveying path without being bent.

Even if a slip occurs when the original document is conveyed by the pickup roller 12 and the paper feeding roller 13, the slip does not affect the stop control for the original document. Specifically, the stop control for the original document is performed by using a detection result of the aligning sensor 16 located between the paper feeding roller 13 and the aligning roller 15. Therefore, fluctuation in the double-feed detection position is suppressed.

In Act 107, the controller 801 determines, on the basis of a signal output by the ultrasound receiving unit 17b, whether the original documents are double-fed. Since the original document is located flat along the conveying path without being bent, accuracy of double-feed detection is improved.

If the original documents are double-fed, in Act 108, the controller 801 displays indication of the double-feed on the operation display unit 805. If the original documents are not double-fed, the controller 801 proceeds to Act 109.

In Act 109, the controller 801 drives the motor driving unit 30 again and rotates the paper feeding roller 13. In Act 110, the controller 801 starts counting of the number of pulses output to the motor driver 31.

In Act 111, the controller 801 determines whether the counted number of pulses reaches N2. If the number of pulses reaches N2, the controller 801 proceeds to Act 112 and stops the driving of the motor driving unit 30.

FIG. 6 is a sectional view of the auto document feeder 9, wherein the position of the original document at the time when the motor driving unit 30 stops is schematically shown. Referring to the figure, the original document is bent because the original document is prevented from being conveyed downstream by coming into contact with the aligning roller 15.

In Act 113, the controller 801 discriminates whether scanning timing is reached. The scanning timing means timing when the original document is located in the image reading position at the start of scanning by the scanning optical system 10.

In Act 114, the controller 801 controls the motor driving unit 30 to thereby reversely rotate the driving of the document feeding motor 32 and rotate the aligning roller 15. The original document is nipped by the aligning roller 15 and moves to the image reading position. A conveying operation performed until the original document reaches from the aligning roller 15 to the image reading position is omitted.

First Modification

As a method of stopping an original document in the double-feed detection position, the controller 801 counts the number of pulses output to the motor driver 31 after the detection by the aligning sensor 16. However, the controller 801 may count driving time of the paper feeding roller 13. Specifically, the controller 801 may measure time in which the paper feeding roller 13 performs the rotation operation and stop the motor driving unit 30 when the measured time reaches a predetermined time. It is also possible that the predetermined time is calculated from rotating speed of the paper feeding roller 13, the calculated predetermined time is stored in the memory 803, and the controller 801 reads out information concerning the predetermined time from the memory 803 and performs the control.

Second Modification

The double-feed detecting unit 17 may be another non-contact sensor. The other non-contact sensor may be an optical sensor. The optical sensor includes a light emitting element and a light receiving element. The light emitting element and the light receiving element are located across an original document. The controller 801 discriminates presence or absence of double-feed from a light amount of light received by the light receiving element.

Third Modification

The document feeding motor 32 may be a DC motor. The DC motor includes a photointerrupter in an output shaft. The controller 801 controls a driving amount of the DC motor according to the number of times the photointerrupter interrupts light.

Fourth Modification

In the embodiment, the auto document feeder 9 configured to convey an original document to the image reading position is explained. However, the embodiment can also be applied to a conveying system for a sheet fed from a cassette tray or a manual feed tray. Specifically, it is also possible to temporarily stop conveyance of the sheet in a position further on the upstream side in the conveying direction than an aligning roller included in the conveying system for the sheet fed from the cassette tray or the manual feed tray and perform the double-feed detection.

While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of invention. Indeed, the novel apparatus and methods described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the apparatus and methods described herein may be made without departing from the sprit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the inventions.

Claims

1. A sheet conveying device comprising:

a first roller configured to correct a tilt of a sheet to be conveyed;

a first detecting unit located further on an upstream side in a conveying direction of the sheet than the first roller and configured to detect information concerning double-feed of the sheet;

a second roller configured to convey the sheet to the first roller;

a driving unit configured to drive the second roller; and

a controller configured to control the driving unit to thereby temporarily stop the conveyance of the sheet in order to perform the detection by the first detecting unit in a state in which an end of the sheet on a downstream side in the conveying direction of the sheet is located further on the upstream side in the conveying direction of the sheet than a nip position of the first roller.

2. The device according to claim 1, further comprising a second detecting unit located between the second roller and the first detecting unit and configured to detect entrance of the sheet, wherein

the controller starts, when the second detecting unit detects the entrance of the sheet, control for stopping the sheet in a position of the detection by the first detecting unit.

3. The device according to claim 2, wherein

the driving unit includes: a pulse motor; and a driver for the pulse motor, and

the controller stars, when the second detecting unit detects the entrance of the sheet, counting of a number of pulses output to the driver and stops the sheet in the position of the detection by the first detecting unit on the basis of a result of the counting.

4. The device according to claim 1, wherein the first detecting unit is a non-contact detecting unit.

5. The device according to claim 4, wherein

the first detecting unit includes: an ultrasound generating unit configured to generate ultrasound; and an ultrasound receiving unit configured to receive the ultrasound generated by the ultrasound generating unit, and

the ultrasound generating unit and the ultrasound receiving unit are opposed to each other across a conveying path for the sheet.

6. The device according to claim 5, wherein the ultrasound generating unit is located further downstream in the conveying direction of the sheet than the ultrasound receiving unit.

7. The device according to claim 2, wherein the second detecting unit is located below a conveying path for the sheet.

8. The device according to claim 1, further comprising a third roller configured to pick up the sheet to the second roller, wherein

the second and third rollers are connected by a transmission mechanism.

9. The device according to claim 8, wherein the second roller is opposed to a fourth roller, the fourth roller inhibits double-feed of the sheet picked up by the third roller.

10. An image forming apparatus comprising:

a document conveying unit including: a first roller configured to correct a tilt of an original document to be conveyed; a first detecting unit located further on an upstream side in a conveying direction of the original document than the first roller and configured to detect information concerning double-feed of the original document; a second roller configured to convey the original document to the first roller; and a driving unit configured to drive the second roller;

a reading unit configured to optically read the original document conveyed by the document conveying unit;

an image forming unit configured to form an image on a sheet on the basis of image data read by the reading unit; and

a controller configured to control the driving unit to thereby temporarily stop the conveyance of the original document in order to perform the detection by the first detecting unit in a state in which an end of the original document on a downstream side in the conveying direction of the original document is located further on the upstream side in the conveying direction of the original document than a nip position of the first roller.

11. The apparatus according to claim 10, wherein

the document conveying unit further includes a second detecting unit located between the second roller and the first detecting unit and configured to detect entrance of the original document, and

the controller starts, when the second detecting unit detects the entrance of the original document, control for stopping the original document in a position of the detection by the first detecting unit.

12. The apparatus according to claim 11, wherein

the driving unit includes: a pulse motor; and a driver for the pulse motor, and

the controller stars, when the second detecting unit detects the entrance of the original document, counting of a number of pulses output to the driver and stops the original document in the position of the detection by the first detecting unit on the basis of a result of the counting.

13. The apparatus according to claim 10, wherein the first detecting unit is a non-contact detecting unit.

14. The apparatus according to claim 13, wherein

the first detecting unit includes: an ultrasound generating unit configured to generate ultrasound; and an ultrasound receiving unit configured to receive the ultrasound generated by the ultrasound generating unit, and

the ultrasound generating unit and the ultrasound receiving unit are opposed to each other across a conveying path for the original document.

15. The apparatus according to claim 14, wherein the ultrasound generating unit is located further downstream in the conveying direction of the original document than the ultrasound receiving unit.

16. The apparatus according to claim 11, wherein the second detecting unit is located below a conveying path for the original document.

17. The apparatus according to claim 10, wherein

the document conveying unit further includes a third roller configured to pick up the original document to the second roller, and

the second and third rollers are connected by a transmission mechanism.

18. The apparatus according to claim 17, wherein the second roller is opposed to a fourth roller, the fourth roller inhibits double-feed of the original document picked up by the third roller.

19. A method of detecting double-feed of a sheet comprising performing double-feed detection for the sheet in a state in which an end of the sheet on a downstream side in a conveying direction of the sheet is located further on an upstream side in the conveying direction of the sheet than a nip position of a roller configured to correct a tilt of the sheet.

20. The method according to claim 19, wherein the double-feed detection is performed by a non-contact sensor.