SHEET CONVEYING DEVICE THAT SEPARATES MULTI-FED SHEETS, AND IMAGE READING APPARATUS

Abstract

A sheet conveying device which makes it possible to facilitate separation of multi-fed sheets. A separation pad and a separation roller separate sheets from a sheet bundle placed on a sheet tray, on a one-by-one basis. A pull-off roller section formed by a pair of conveying rollers nips and conveys a fed sheet. The two conveying rollers of the pull-off roller section have rotational axes extending in respective different directions. A registration roller further conveys the sheet conveyed by the pull-off roller section. One roller of the pull-off roller section is disposed such that the roller conveys a sheet in a direction in which the sheet is to be conveyed by the registration roller, and the other roller of the pull-off roller section is disposed such that the roller conveys a sheet obliquely with respect to the sheet conveying direction of the registration roller.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a sheet conveying device and an image reading apparatus, and more particularly to a separating technique for separating multi-fed sheets when multi-feed occurs in a conveying mechanism that conveys sheets while separating the sheets one by one from a sheet bundle placed on a sheet tray.

2. Description of the Related Art

In an image reading apparatus provided with a conventional sheet conveying device, when two or more sheets are conveyed in a state overlapping each other, i.e. when multi-feed occurs, a sheet jam or defective image reading can take place. In either case, a user has to carry out work e.g. for removing sheets and setting sheets again, and hence the apparatus is inevitably stopped during execution of the work. To solve this problem, there has been proposed a sheet conveying device configured to be operable when multi-feed is detected, to convey multi-fed sheets in the reverse direction, i.e. toward a sheet tray by a predetermined distance and separate the sheets one from another using a separation mechanism again (see e.g. U.S. Patent Publication No. 5,384,631).

In the above-described conventional sheet conveying device, however, multi-feed occurs due to high adhesiveness between sheets, so that re-use of the same separation mechanism cannot reliably ensure separation of the sheets.

SUMMARY OF THE INVENTION

The present invention provides a sheet conveying device and an image reading apparatus, which make it possible to facilitate separation of multi-fed sheets to thereby improve sheet conveyance efficiency.

In a first aspect of the present invention, there is provided a sheet conveying device comprising a sheet feed unit configured to feed a sheet from a plurality of sheets placed on a sheet tray, on a one-by-one basis, by separating the sheets, a first conveying unit having a pair of conveying rollers configured to convey the sheet fed from the sheet feed unit in a state nipped therebetween, the conveying rollers having rotational axes extending in respective different directions, and a second conveying unit configured to further convey the sheet conveyed by the first conveying unit, wherein one roller of the conveying roller pair is disposed such that the roller conveys the fed sheet in a direction in which the sheet is to be conveyed by the second conveying unit, and the other roller of the conveying roller pair is disposed such that the roller conveys the sheet obliquely with respect to the sheet conveying direction of the second conveying unit.

In a second aspect of the present invention, there is provided an image reading apparatus comprising a sheet tray on which a plurality of sheets are placed, a sheet feed unit configured to feed a sheet from the sheets placed on the sheet tray, on a one-by-one basis, by separating the sheets, a first conveying unit having a pair of conveying rollers configured to convey the sheet fed from the sheet feed unit in a state nipped therebetween, the conveying rollers having rotational axes extending in respective different directions, a second conveying unit configured to further convey the sheet conveyed by the first conveying unit, and a reading unit configured to read an image from the sheet conveyed by the second conveying unit, wherein one roller of the conveying roller pair is disposed such that the roller conveys the fed sheet in a direction in which the sheet is to be conveyed by the second conveying unit, and the other roller of the conveying roller pair is disposed such that the roller conveys the sheet obliquely with respect to the sheet conveying direction of the second conveying unit.

According to the present invention, one of the pair of conveying rollers different in axial direction is disposed such that the roller performs sheet conveyance in a sheet conveying direction, and the other roller of the conveying roller pair is disposed such that the roller performs sheet conveyance obliquely with respect to the sheet conveying direction. This makes it easy to separate the multi-fed sheets, and makes it possible to improve sheet conveying efficiency.

Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of an image reading apparatus provided with a sheet conveying device according to a first embodiment of the present invention.

FIG. 2 is a schematic block diagram of the control systems of an ADF and a reader section appearing in FIG. 1 and an image controller.

FIGS. 3A and 3B are schematic views of a pull-off roller section appearing in FIG. 1, in which FIG. 3A schematically shows the pull-off roller section as viewed in a direction indicated by an arrow A in FIG.

1, and FIG. 3B schematically shows the pull-off roller section as viewed in a direction indicated by an arrow B in FIG. 1.

FIGS. 4A to 4D are views useful in explaining the behavior of a sheet in the pull-off roller section.

FIG. 5 is a flowchart of a sheet separation process executed in the first embodiment by a CPU using the pull-off roller section.

FIGS. 6A to 6C are views useful in explaining a multi-feed determination method.

FIG. 7 is a diagram illustrating different degrees of change in sheet width detected on sheets by a sheet width detection section.

FIGS. 8A to 8D are views useful in explaining push-in operation performed by the pull-off roller section to push a sheet into a registration roller.

FIG. 9 is a partially see-through view of an ADF, as viewed from above, of an image reading apparatus provided with a sheet conveying device according to a second embodiment of the present invention.

FIGS. 10A to 10C are views useful in explaining the behavior of a sheet in the pull-off roller section.

DESCRIPTION OF THE EMBODIMENTS

The present invention will now be described in detail below with reference to the accompanying drawings showing embodiments thereof.

FIG. 1 is a schematic view of an image reading apparatus provided with a sheet conveying device according to a first embodiment of the present invention.

In FIG. 1, the image reading apparatus comprises an automatic document feeder (hereinafter acronymized as “the ADF”) 100 and an image reading section (hereinafter referred to as “the reader section”) 200. The ADF 100 has a sheet tray 30 on which a sheet bundle S formed by one or more sheets is placed. Before the start of a sheet feeding operation, the sheets of the sheet bundle S are restricted by a separation pad 21 from entering the ADF 100. When the sheet feeding operation is started, a sheet feed roller 1 urged on the sheet bundle S is driven to pull the sheets into the ADF 100, and only an uppermost sheet of the sheet bundle S is fed onto a conveying path by the separation pad 21 and a separation roller 2.

In actuality, a case where the separation pad 21 and the separation roller 2 fail to separate only an uppermost sheet can occur depending on a sheet type or due to a difference in surface frictional force between sheets. In the present embodiment, sheets which are not separated one from another at the above-mentioned time and are fed in a state overlapping each other will be referred to as “multi-fed sheets”.

A separation sensor 10 is disposed downstream of the separation pad 21 and the separation roller 2 in the sheet conveying direction. The separation sensor 10 is used for detection of an interval between sheets after separation, which is performed based on an output therefrom. Downstream of the separation sensor 10 is disposed a sheet width detection section 11 comprising a plurality of sheet detectors arranged in a direction intersecting with (e.g. orthogonal to) the sheet conveying direction (hereinafter simply referred to as “the conveying direction”). The sheet width detection section 11 detects the width of each fed sheet based on whether or not the fed sheet has been detected by the sheet detection sensors in predetermined timing before the sheet is brought into abutment with a registration roller 4. Note that the sheet width detection section 11 may be implemented by an array sensor, such as a CCD or a CIS.

A sheet having passed the sheet width detection section 11 is conveyed by a pull-off roller section 3 and is brought into abutment with the registration roller 4. At a time point when the sheet reaches the registration roller 4, the registration roller 4 is in a state not being driven but at rest, so that the leading edge of the sheet is prevented from being advanced. The sheet in this state is pushed toward the registration roller 4 by pushing operation of the pull-off roller section 3, whereby it is warped. Even when the conveying process up to this time has brought the sheet into a skewed state where the leading edge of the sheet is in an oblique relation to the conveying direction, the skew of the sheet is corrected by warping the sheet with its leading edge held in abutment with the registration roller 4. Then, the registration roller 4 is rotated to convey the sheet to a first conveying roller 5 and a roller 7, whereafter the sheet is conveyed by these rollers onto a platen glass 201. The reader section 200 reads a front-surface image from the sheet through the platen glass 201.

Then, the sheet is conveyed by a second conveying roller 6, and is passed through between a roller 16 and a back surface-reading glass 18. Then, the sheet is discharged onto a discharge tray 31 via a discharge flapper 20 and a discharge roller pair 8.

A back-surface image reading section 17 is a unit configured to optically read image information from a sheet and output an image signal subjected to photoelectric conversion to a subsequent stage. The back-surface image reading section 17 is disposed on the back side of the back surface-reading glass 18 opposed to the roller 16. The back-surface image reading section 17 reads a back-surface image on the sheet while the sheet is passing through a clearance between the roller 16 and the back surface-reading glass 18.

Each of sheet detection sensors 12, 13, and 14 detects whether or not there is a sheet at an associated sensor position. Further, conveyance guides, not shown, are disposed along the sheet conveying path so as to restrict a sheet from deviating from a predetermined range in a direction (hereinafter also referred to as “the main scanning direction) orthogonal to the conveying direction.

Similarly, the reader section 200 is a unit configured to optically read image information from a sheet and output an image signal subjected to photoelectric conversion to a subsequent stage. The reader section 200 comprises the platen glass 201, a platen glass 202, a scanner unit 209, a second mirror 205, a third mirror 206, a lens 207, and a CCD (charge coupled device) 208. Note that the scanner unit 209 comprises an illuminating lamp 203 and a first mirror 204.

In reading a front-surface image from a sheet, the scanner unit 209 is moved to a position below the platen glass 201 in advance. Then, the illuminating lamp 203 is turned on in this state, and reflected light from the front surface of the sheet passing on the moving reading glass is guided to the lens 207 via the first to third mirrors 204, 205, and 206, whereby it is caused to form an image on the CCD 208. After this process, the front-surface image from the sheet is photoelectrically converted to a digital image signal by the CCD 208.

FIG. 2 is a schematic block diagram of the control systems of the ADF 100 and the reader section 200 appearing in FIG. 1 and an image controller 300.

In the reader section 200, a central processing unit (hereinafter acronymized as “the CPU”) 251 controls the ADF 100 and the reader section 200. Connected to the reader section 200 are a ROM 252 as a memory for storing programs and a RAM 253 as a memory for providing work areas. The ROM 252 stores control programs for the reader section 200 and the ADF 100, and the RAM 253 stores input data for use in control and working data.

Connected to the CPU 251 are a motor driver section 256 as a driver circuit for driving an optical motor that moves the scanner unit 209 and a front-surface image reading section 260. The front-surface image reading section 260 comprises the illuminating lamp 203 and the CCD 208 mentioned above, and a signal controller 259 for converting an output from the CCD 208 to a digital image signal. The CPU 251 controls the motor driver section 256 and the front-surface image reading section 260 to read an image from the front surface of an original.

A sheet interval correction section 254 corrects parameters of the signal controller 259 according to a sheet interval (i.e. an interval between the trailing edge of a preceding sheet and the leading edge of the following sheet) between fed sheets. Although in the present embodiment, the sheet interval is handled as a time parameter, it may be handled as a distance parameter. An image processing section 255 processes an image signal read by the front-surface image reading section 260 or the back-surface image reading section 17, generates a timing signal, and transmits the signals to the image controller 300. An image buffer 261 is controlled by the image processing section 255. The image buffer 261 is provided for temporarily storing the image signal read by the front-surface image reading section 260 or the back-surface image reading section 17.

The ADF 100 is connected to the input/output ports of the CPU 251. Connected to the output port are a motor group 103 for driving the conveying rollers, a solenoid group 101, and a clutch group 102. On the other hand, connected to the input port are a sensor group 104 for generating sheet conveying timing signals and the sheet width detection section 11 for detecting the size of each sheet during sheet conveyance.

The CPU 251 executes a control program stored in the ROM 252, to thereby control sheet conveying operation in the ADF 100. The back-surface image reading section 17 comprises an illuminating lamp 307 for back-surface image reading, a CIS (contact image sensor) 308, and a signal controller 107. The back-surface image reading section 17 is connected to the CPU 251. The back-surface image reading section 17 reads a back-surface image from a sheet according to a control signal from the CPU 251 and transfers the read image to the image processing section 255.

Image signals stored in the image buffer 261 are read out into the image processing section 255 in synchronism with a timing signal, and is sequentially transferred to the image controller 300 via a controller interface section 350.

The image controller 300 has a CPU 301, a ROM 302, and a RAM 303 for image control, independently of the reader section 200. The image signals delivered from the image processing section 255 to the image controller 300 are subjected to input/output control by an image input/output unit 304, and are sequentially stored and accumulated as image data in an image memory 305.

An image processing section 310 performs various kinds of image processing on image signals input from the image input/output unit 304 or image data accumulated in the image memory 305. A console section 309 is capable of notifying a user of the status of the apparatus by screen display. Further, the console section 309 receives operation instructions given by the user to the apparatus. In response to the instructions received via the console section 309, the CPU 301 reads out image data from the image memory 305 and executes processing e.g. for transferring an image and information to an external apparatus or a personal computer through a telephone line or a network connected to an external interface 312.

Although in the present embodiment, the front-surface image reading section of the reader section 200 is provided with the CCD and the back-surface image reading section of the ADF 100 is provided with the CIS, this is not limitative, but any other sensor which is capable of image reading may be used in place of the CCD or the CIS.

Next, the pull-off roller section 3 will be described in detail.

FIGS. 3A and 3B are schematic views of the pull-off roller section 3 appearing in FIG. 1. FIG. 3A schematically shows the pull-off roller section 3 as viewed in a direction indicated by an arrow A in FIG. 1, and FIG. 3B schematically shows the same as viewed in a direction indicated by an arrow B in FIG. 1.

The pull-off roller section 3 comprises a conveying roller pair formed by upper and lower rollers 3a and 3b. The upper roller 3a and the lower roller 3b rotate with a sheet P nipped therebetween, to thereby convey the sheet P in the conveying direction. The upper roller 3a and the lower roller 3b are driven by respective different motors (included in the motor group 103 in FIG. 2).

The upper roller 3a and the lower roller 3b have respective rotational axes extending in different directions, respectively. Specifically, the lower roller 3b is a conveying roller having a rotational axis extending in the same direction as the rotational axes of the sheet feed roller 1 and the separation roller 2 and that of the registration roller (i.e. in the direction orthogonal to the sheet conveying direction) and configured to convey a sheet P straight in the downstream direction. On the other hand, the upper roller 3a is an obliquely conveying roller having a rotational axis horizontally inclined with respect to the direction orthogonal to the sheet conveying direction. In the present embodiment, the inclination angle of the upper roller 3a with respect to the lower roller 3b is set to 20 degrees. Note that the inclination angle can be changed according e.g. to the material, size, or frictional force of a roller, and therefore it is not limited to 20 degrees. Further, the directional relationship between the rotational axis of the upper roller 3a and that of the lower roller 3b may be reversed.

The upper roller 3a and the lower roller 3b are configured to apply respective different conveying forces to a sheet. The reason for this will be described hereinafter.

Further, the upper roller 3a and the lower roller 3b are constructed such that switching can be performed between contact and separation states. This is because if the two rollers different in axial direction are rotated in direct contact with each other in a state where no sheet exists therebetween, abrasion or deformation can occur to cause damage to the rollers. Switching between contact and separation between the upper roller 3a and the lower roller 3b is performed by driving a specific solenoid of the solenoid group 101 according to a control signal from the CPU 251. In short, the specific solenoid functions as a switching unit for switching between contact and separation between the upper roller 3a and the lower roller 3b. Note that any other construction and method may be employed for switching between contact and separation between the upper roller 3a and the lower roller 3b.

Next, a description will be given, with reference to FIGS. 4A to 4D, of the behavior of a sheet P in the pull-off roller section 3. Although in FIGS. 4A to 4D, only the obliquely conveying roller (upper roller 3a) is shown as the pull-off roller section 3, it is assumed that the conveying roller (lower roller 3b), not shown, is disposed at a location opposed to the obliquely conveying roller. Further, in the vicinity of the pull-off roller section 3 is disposed the sheet width detection section 11 for detecting sheet width in the direction intersecting with the sheet conveying direction of the registration roller 4 (or the lower roller 3b).

FIG. 4A shows a state before the sheet P reaches the pull-off roller section 3. In the state shown in FIG. 4A, it is not apparent whether the sheet P has been conveyed in a state normally separated as a single sheet or in a multi-fed state in which the sheet P overlaps another sheet. When the sheet P reaches the pull-off roller section 3, control is performed to switch the upper roller 3a and the lower roller 3b from the separation state to the contact state.

Now, a description will be given of conveying forces of the respective upper and lower rollers 3a and 3b for conveying a sheet. It is assumed that the conveying forces are determined using, as parameters, driving forces of the motors for driving the respective upper and lower motors 3a and 3b, the frictional forces of the respective two rollers, angle difference between the rotational axes of the respective rollers, and so forth.

First, a case where the sheet P has been conveyed as a single sheet will be described.

FIG. 4B shows an example of a state where the conveying forces have been set in advance such that the conveying force of the upper roller 3a is larger than that of the lower roller 3b. In this case, since the conveying force of the upper roller 3a is larger, the sheet P is skewed and conveyed obliquely. On the other hand, FIG. 4C shows a state where the conveying forces have been set in advance such that the conveying force of the upper roller 3a is smaller than that of the lower roller 3b. In this case, since the conveying force of the lower roller 3b is larger, the sheet P is conveyed straight forward.

Next, a description will be given of a case where the sheet P has been conveyed in a state overlapping another sheet.

When the upper roller 3a and the lower roller 3b are switched to the contact state, the upper sheet P of the multi-fed sheets receives a force acting in an oblique direction from the upper roller 3a. On the other hand, a lower sheet Pa receives a force acting straight in the conveying direction from the lower roller 3b. As a consequence, a twist occurs between the upper sheet and the lower sheet of the multi-fed sheets, which causes separation between the sheet P and the sheet Pa fed together with the sheet P, as shown in FIG. 4D. In this case, whichever of the upper roller 3a and the lower roller 3b applies a larger force, it is known that the behavior for separation is substantially the same. Note that a skew of a sheet caused by the conveying force of the upper roller 3a is corrected by the registration roller 4. A sheet having its skew corrected and conveyed by the registration roller 4 may have its position in a transverse direction orthogonal to the conveying direction adjusted by shifting of the registration roller 4 in its axial direction.

FIG. 5 is a flowchart of a sheet separation process executed in the present embodiment by the CPU 251 using the pull-off roller section 3.

First, in response to a reading operation start instruction from the image controller 300, the CPU 251 performs control such that a sheet pickup operation for picking up a sheet on the ADF is started (step S800). Specifically, the sheet feed roller 1 is turned on whereby it is driven and lowered into contact with the upper surface of a sheet bundle S to convey sheets P to the separation roller 2. The separation roller 2 attempts to separate an uppermost sheet P and then conveys the separated sheet P into the apparatus.

Then, when a predetermined time period elapses after the start of the pickup operation, the CPU 251 causes the sheet width detection section 11 to start sheet width detection (step S801).

Thereafter, the CPU 251 waits until the sheet P reaches the pull-off roller section 3 (step S802). Immediately before the sheet P reaches the pull-off roller section 3, the CPU 251 switches the pull-off roller section 3 held in the separation state in advance to the contact state, and causes rotation of the upper roller 3a and the lower roller 3b (step S803). Then, the CPU 251 drivingly controls the upper roller 3a and the lower roller 3b to pull off (separate) the sheet P as shown in FIG. 4D (step S803).

Next, the CPU 251 terminates the pickup operation in timing substantially synchronous with execution of the step S803 to thereby facilitate the sheet pull-off operation by the pull-off roller section 3 (step S804). Specifically, the CPU 251 stops driving of the sheet feed roller 1 to allow the same to move upward away from the sheet bundle S, and stops driving of the separation roller 2 at the same time to thereby facilitate the sheet pull-off operation by the pull-off roller section 3.

Then, the CPU 251 determines, based on a change in sheet width detected by the sheet width detection section 11, whether or not the sheet P currently conveyed is in a state overlapping another sheet (step S805).

Now, a description will be given of determination of multi-feed of sheets with reference to FIGS. 6A to 6C.

In the present embodiment, multi-feed determination is performed based on a sheet width detected by the sheet width detection section 11.

FIG. 6A shows an example of a state before a sheet P reaches the pull-off roller section 3.

In the illustrated example, a detected sheet width L0 of the sheet P detected by the sheet width detection section 11 is the same as the actual sheet width of the sheet P.

FIG. 6B shows a case where under a condition that the conveying force of the upper roller 3a is larger than that of the lower roller 3b, a single sheet P reaches the pull-off roller section 3, and since the conveying force of the upper roller 3a is larger than that of the lower roller 3b, the single sheet P is brought into a skewed state.

Now, a detected sheet width of the sheet P detected by the sheet width detection section 11 in the FIG. 6B example is represented by L1. In this example, since the sheet P is caused to be skewed, L1 is larger than L0 (L1>L0). Note that under a condition that the conveying force of the upper roller 3a is smaller than that of the lower roller 3b, if a single sheet P reaches the pull-off roller section 3, the sheet P advances straight forward. Therefore, in this case, a detected sheet width of the sheet P detected by the sheet width detection section 11 is equal to L0 similarly to FIG. 6A.

FIG. 6C shows a state where multi-fed sheets reach the pull-off roller section 3 and the sheets start to be separated.

Now, a detected sheet width of the sheet P detected by the sheet width detection section 11 in the FIG. 6C example is represented by L2. The apparent sheet width L1 or L2 detected by the sheet width detection section 11 changes in the sheet conveyance and separation process. FIG. 7 is a graph showing the different degrees of change in each sheet width detected by the sheet width detection section 11 after each sheet reaches the pull-off roller section 3. In the FIG. 7 graph, the vertical axis represents detected sheet width, and the horizontal axis represents elapsed time t. A time point t0 indicates a timing in which the sheet width detection section 11 detects the sheet width at a leading end of the sheet, and a time point t1 indicates a timing in which the sheet reached the pull-off roller section 3.

Referring to FIG. 7, when the sheet is single, the detected sheet width L1 is constant after the leading end of the sheet has started to be detected by the sheet width detection section 11 until the sheet reaches the pull-off roller section 3. After the sheet reaches the pull-off roller section 3, the detected sheet width L1 of the single sheet, under the condition that the conveying force of the upper roller 3a is set to be larger than that of the lower roller 3b, progressively increases as the sheet is further skewed. Note that the increase in the detected sheet width L1 stops when the skew of the sheet P becomes equal in value to the inclination of the upper roller 3a. On the other hand, when sheets are multi-fed, an upper sheet P is conveyed while being skewed, whereas a lower sheet Pa is conveyed straight. For this reason, the amount of change in the detected sheet width L2, i.e. the inclination of the graph associated with the detected sheet width L2 is larger than that of the detected sheet width L1. Note that the value of the detected sheet width L2 is maximized when the skew of the sheet P becomes equal in value to the inclination of the upper roller 3a.

Therefore, when it is determined, by referring to time-varying change in the sheet width detected after a sheet P reaches the pull-off roller section 3, that the degree of the change has exceeded e.g. a predetermined threshold value T, it is possible to judge that the conveyed sheet P is in a state overlapping another sheet.

Although in the present embodiment, multi-feed determination is performed based on a change in sheet width detected by a sheet width detection sensor, this is not limitative, but a dedicated sensor for detecting multi-feed may be additionally provided.

Referring again to FIG. 5, if it is determined in a step S806 that multi-feed has occurred, the CPU 251 stops driving of the lower roller 3b of the pull-off roller section 3 and performs sheet conveyance by driving the upper roller 3a alone (step S807). As a consequence, only the upper one of the sheets to be separated is conveyed first. Then, the CPU 251 waits until the upper sheet reaches the registration roller 4 (step S808). When the upper sheet reaches the registration roller 4 and is pushed against the registration roller 4 to have the skew of the upper sheet corrected, the CPU 251 causes the upper roller 3a to be spaced from the lower roller 3b and stops the driving of the upper roller 3a (step S809).

Now, a description will be given, with reference to FIGS. 8A to 8D, of the push-in operation performed by the pull-off roller section 3 for pushing a sheet into the registration roller 4.

FIG. 8A shows a skewed state of the sheet P before reaching the registration roller 4. Note that the upper portion of each of FIGS. 8A to 8D shows the registration roller 4, the pull-off roller section 3, and the sheet P, as viewed from above, and the lower portion shows these as viewed just from a side.

Note that in FIGS. 8A to 8D hatching provided on a roller indicates that the roller is in a driven state.

In a state shown in FIG. 8B, the leading edge of the sheet P has reached the registration roller 4, but since the registration roller 4 is at rest, the sheet P cannot advance. On the other hand, the sheet P is pushed from behind by the pull-off roller section 3, so that the sheet P starts to be warped.

FIG. 8C shows a state where the push-in operation by the pull-off roller section 3 has been completed and the sheet P has been warped. In this stage, the leading edge of the sheet has been brought into abutment with the registration roller 4 by sheet stress and restriction of conveying guides (not shown), whereby the skew of the sheet has been eliminated. The registration roller 4 is driven for rotation in predetermined timing to convey the sheet having its skew eliminated downstream toward an image reading position, as shown in FIG. 8D.

Referring again to FIG. 5, in a step S810, the CPU 251 waits until the sheet P is conveyed downstream by the registration roller 4 and the separation is completed. The completion of the separation is judged from time elapsed after the start of driving of the registration roller 4 until passing of the trailing end of the upper sheet through the registration roller 4. After confirming completion of the sheet separation, the CPU 251 stops driving of the registration roller 4, terminates the spacing of the upper roller 3a from the lower roller 3b, and restarts driving of both the upper and lower rollers 3a and 3b of the pull-off roller section 3 (step S811) to cause the lower one of the multi-fed sheets to be conveyed toward the registration roller 4, and then proceeds to a step S812. Processing in the step S812 et seq. is the same as in a case where it is determined in the step S806 that multi-feed has not occurred.

If it is determined in the step S806 that multi-feed has not occurred, the CPU 251 continues sheet conveyance to cause the sheet to reach the registration roller 4. Then, after confirming arrival of the sheet at the registration roller 4 (step S812), the CPU 251 stops driving of the pull-off roller section 3 in a predetermined timing to thereby return the upper roller 3a and the lower roller 3b to the separation state (step S813). Finally, the CPU 251 stops operation of the sheet width detection section 11 (step S814) to thereby terminate sheet width detection and multi-feed detection based on time-varying change of a width detection signal. This completes a sequence of sheet-pulling off operations.

Although in the sheet conveying device of the present embodiment, the conveying force of the lower roller 3b configured to convey a sheet in the same conveying direction as the registration roller 4 does is set to be smaller than that of the upper roller 3a, the upper roller 3a may have a smaller conveying force than the lower roller 3b.

As described above, according to the above-described embodiment, one roller of the pair of conveying rollers different in axial direction is disposed such that it conveys a sheet in the conveying direction, and the other roller is disposed such that it conveys a sheet obliquely with respect to the conveying direction so as to separate multi-fed sheets. This makes it possible to facilitate separation of multi-fed sheets to thereby improve sheet conveyance efficiency. Further, it is not required to stop the apparatus, and hence it is possible to further improve sheet conveyance efficiency.

In the above-described embodiment, since the registration roller 4 is disposed downstream of the pull-off roller section 3 in the conveying direction, it is determined in the steps S808 and S812 whether or not a sheet has reached the registration roller 4. However, a roller that can be disposed downstream of the pull-off roller section is not limited to the registration roller, but another kind of roller may be disposed downstream of the pull-off roller section.

Next, a second embodiment of the present invention will be described with reference to drawings.

FIG. 9 is a partially see-through view of an ADF 1100, as viewed from above, of an image reading apparatus provided with a sheet conveying device according to the second embodiment of the present invention.

As shown in FIG. 9, the ADF 1100 has a sheet tray 1030 on which a sheet bundle S formed by one or more sheets can be placed. The sheet tray 1030 is disposed such that a front side (lower side as viewed in FIG. 9) thereof obliquely extends in an expanding manner, i.e. along with a sheet guide member 1040 provided in a manner angled with respect to a conveying direction (left-right direction as viewed in FIG. 9). This configuration of the sheet tray 1030 enables a user standing in front of the apparatus (at the lower side as viewed in FIG. 9) to place the sheet bundle S on the sheet tray 1030 without stretching out his/her arms. In short, the user can place a sheet bundle on the sheet tray 1030 in an ergonomically comfortable fashion.

At the rear (upper side as viewed in FIG. 9) of the sheet tray 1030, there is a space formed in a manner extending along the conveying direction. The space is thus formed so as to enable the trailing end of a sheet, which was pulled in obliquely with respect to the conveying direction from the sheet bundle S placed along the front side of the sheet tray 1030, to freely move when the sheet turns its direction to the conveying direction.

Each of separation rollers 1002 has its pull-in angle set such that the axis of the separation roller 1002 is directed in a direction orthogonal to the gradient of a portion of the sheet guide member 1040 with which a sheet bundle side is brought into contact. The cross-sectional view of the ADF 1100 is substantially the same as FIG. 1 as described in the first embodiment, and therefore it is omitted. Note that in addition to the sheet tray 30 appearing in FIG. 1, the sheet feed roller 1, the separation pad 21, the separation roller 2, and the separation sensor 10 are arranged obliquely according to the angle of the sheet tray 1030 with respect to the conveying direction.

A conveying roller pair of a pull-in roller section 1003 is disposed such that an upper roller as one of the rollers conveys a sheet in the sheet conveying direction and a lower roller as the other of the rollers conveys a sheet in the same direction as a direction in which a sheet bundle S on the sheet tray is pulled in. In short, the lower roller is disposed so as to convey a sheet obliquely with respect to the sheet conveying direction.

The conveying forces of the two conveying rollers of the pull-in roller section 1003 are set such that the conveying force of the upper roller for conveying a sheet in the conveying direction is larger than that of the lower roller.

Note that the image reading apparatus of the present embodiment is identical in configuration to that of the first embodiment, and therefore a control block diagram thereof and description thereof are omitted.

Next, the behavior of a sheet P in the pull-in roller section 1003 will be described with reference to FIGS. 10A to 10C. Although not shown, the lower roller is disposed such that the roller conveys a sheet in the direction in which the sheet is pulled in from the sheet tray 1030. A sheet width detecting section 1011 is disposed in a manner orthogonal to the sheet guide 1040, and has the same construction as that of the sheet width detection section 11 in the first embodiment.

FIG. 10A shows a state before the sheep P reaches the pull-in roller section 1003. Similarly to the first embodiment, in this state, it is not apparent whether or not the sheet P has been conveyed as a single sheet or in a state overlapping another sheet. At this time point, the pull-in roller section 1003 is held in the separation state as in the first embodiment.

FIG. 10B shows a case where the sheet P has been conveyed as a single sheet. In this case, the pull-in roller section 1003 is switched to the contact state, but since the conveying force of the upper roller is larger, the sheet P has its direction turned in the sheet conveying direction.

FIG. 10C shows a case where the sheet P is in a state overlapping another sheet. In this case as well, the pull-in roller section 1003 is switched to the contact state in timing synchronous with arrival of the sheet P. In the present case, the upper one of the multi-fed sheets receives a force from the upper roller whereby it is directed in the conveying direction. On the other hand, the lower sheet receives a force from the lower roller so that it remains directed in the sheet feed direction. As a consequence, a twist occurs between the upper and lower ones of the multi-fed sheets, whereby separation of the multi-fed sheets is achieved.

Control of the pull-in roller section 1003 in the present embodiment is performed following the same control procedure as in the first embodiment, and therefore description thereof is omitted.

As described above, also in the sheet conveying device having the sheet tray extending in a manner expanding toward the front side so as to facilitate user operation for placing sheets on the sheet tray, the pull-in roller section 1003 is formed by the pair of rollers different in conveying direction. This makes it possible to switch the sheet conveying direction to the direction of conveyance by a downstream conveying roller (e.g. the registration roller 4) and positively perform separation of multi-fed sheets.

Although in the above-described first and second embodiments, the image reading apparatus provided with the sheet conveying device is described, this is not limitative, but the present invention is also applicable to an image forming apparatus including an image forming section (printer section) in addition to an image reading section having the above-described construction.

While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.

This application claims priority from Japanese Patent Application No. 2011-069970 filed Mar. 28, 2011, and Japanese Patent Application No. 2012-064026 filed Mar. 21, 2012, which are hereby incorporated by reference herein in their entirety.

Claims

1. A sheet conveying device comprising:

a sheet feed unit configured to feed a sheet from a plurality of sheets placed on a sheet tray, on a one-by-one basis, by separating the sheets;

a first conveying unit having a pair of conveying rollers configured to convey the sheet fed from said sheet feed unit in a state nipped therebetween, the conveying rollers having rotational axes extending in respective different directions; and

a second conveying unit configured to further convey the sheet conveyed by said first conveying unit,

wherein one roller of the conveying roller pair is disposed such that the roller conveys the fed sheet in a direction in which the sheet is to be conveyed by said second conveying unit, and the other roller of the conveying roller pair is disposed such that the roller conveys the sheet obliquely with respect to the sheet conveying direction of said second conveying unit.

2. The sheet conveying device according to claim 1, further comprising a multi-feed determination unit configured to determine whether or not multi-feed has occurred in which the sheet conveyed by said first conveying unit is in a state overlapping another sheet, and

a control unit configured to be operable when said multi-feed determination unit determines that multi- feed has occurred, to perform control such that rotation of one roller of the conveying roller pair nipping the multi-fed sheets is stopped or decelerated.

3. The sheet conveying device according to claim 2, further comprising a sheet width detection unit disposed close to said first conveying unit and configured to detect a sheet width in a direction intersecting with a sheet conveying direction of said first conveying unit, and

wherein said multi-feed determination unit determines whether or not multi-feed has occurred, based on a change in the sheet width which is detected by said sheet width detection unit during sheet conveyance by said first conveying unit.

4. The sheet conveying device according to claim 3, wherein said sheet width detection unit comprises a plurality of detectors arranged in the direction intersecting with the sheet conveying direction of said second conveying unit.

5. The sheet conveying device according to claim 1, further comprising a switching unit configured to switch the conveying roller pair between a contact state in which one roller and the other roller of the conveying roller pair are brought into contact with each other and a separation state in which the one roller and the other roller of the conveying roller pair are spaced from each other.

6. The sheet conveying device according to claim 5, wherein in synchronism of the sheet reaching the conveying roller pair, said switching unit switches the conveying roller pair held in the separation state in advance to the contact state.

7. The sheet conveying device according to claim 1, wherein the one roller of the conveying roller pair and the other of the conveying roller pair are configured to have respective different conveying forces.

8. The sheet conveying device according to claim 7, further comprising a guide member for guiding the plurality of sheets which are placed on the sheet tray, a portion of said guide member with which a sheet bundle side is brought into contact being angled with respect to the sheet conveying direction.

9. The sheet conveying device according to claim 8, wherein a direction in which a sheet is conveyed by the one roller of the conveying roller pair is the same as the sheet conveying direction of said second conveying unit, and the conveying force of the one roller of the conveying roller pair is larger than the conveying force of the other roller of the conveying roller pair.

10. An image reading apparatus comprising:

a sheet tray on which a plurality of sheets are placed;

a sheet feed unit configured to feed a sheet from the sheets placed on said sheet tray, on a one-by-one basis, by separating the sheets;

a first conveying unit having a pair of conveying rollers configured to convey the sheet fed from said sheet feed unit in a state nipped therebetween, the conveying rollers having rotational axes extending in respective different directions;

a second conveying unit configured to further convey the sheet conveyed by said first conveying unit; and

a reading unit configured to read an image from the sheet conveyed by said second conveying unit,

wherein one roller of the conveying roller pair is disposed such that the roller conveys the fed sheet in a direction in which the sheet is to be conveyed by said second conveying unit, and the other roller of the conveying roller pair is disposed such that the roller conveys the sheet obliquely with respect to the sheet conveying direction of said second conveying unit.