Usage determination of multi-feed prevention roller

A sheet feeding apparatus includes a sheet stacker to stack at least one sheet; a sheet feed roller disposed at one side of the sheet stacker and to feed a sheet fed from the sheet stacker; a multi-feed prevention roller disposed to face the sheet feed roller and to prevent multi-feed of the sheet fed from the sheet stacker; a magnetic torque limiter disposed coaxially with the multi-feed prevention roller; a hall sensor disposed at one side of the magnetic torque limiter and to detect rotation of the magnetic torque limiter; and a controller configured to rotate the sheet feed roller in a state in which the sheet feed roller and the multi-feed prevention roller are in contact with each other without a sheet and to identify a lifetime of the multi-feed prevention roller by using a signal output from the hall sensor.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is filed under 35 U.S.C. § 371 as a PCT national stage of PCT International Application No. PCT/KR 2018/000242, filed on Jan. 5, 2018, which claims the priority benefit of Korean Patent Application No. 10-2017-0004184, filed on Jan. 11, 2017 and Korean Patent Application No. 10-2017-0099208, filed on Aug. 4, 2017, the contents of the International Application and the Korean Patent Applications are incorporated by reference herein in their entirety.

BACKGROUND ART

Generally, an image forming apparatus includes a sheet feeding apparatus for feeding sheets one by one to an image former.

Since a pickup roller, a sheet feeding roller, and a multi-feed prevention roller of the sheet feeding apparatus which feeds stacked sheets one by one are worn out, sheet feeding failure such as miss-feed, jam, multi-feed, and the like may occur if the pickup roller, the sheet feeding roller, and the multi-feed prevention roller are not replaced with new ones after a predetermined number of sheets, for example, 200,000 sheets are fed.

Further, when the lifetime of one or more of the rollers is over and two or more sheets stacked on the sheet feeding apparatus are fed to the image former, an appropriate image may not be properly formed on the sheets. Therefore, the sheet feeding apparatus may be provided with a multi-feed detecting apparatus capable of detecting the multi-feed of sheets.

MODE FOR INVENTION

Hereinafter, certain exemplary examples of the present disclosure will be described in detail with reference to the accompanying drawings.

The matters defined herein, such as a detailed construction and elements thereof, are provided to assist in a comprehensive understanding of this description. Thus, it is apparent that exemplary examples may be carried out without those defined matters. Also, well-known functions or constructions are omitted to provide a clear and concise description of exemplary examples. Further, dimensions of various elements in the accompanying drawings may be arbitrarily increased or decreased for assisting in a comprehensive understanding.

The terms “first”, “second”, etc. may be used to describe diverse components, but the components are not limited by the terms. The terms are only used to distinguish one component from the others.

The terms used in the present application are only used to describe the exemplary examples, but are not intended to limit the scope of the disclosure. The singular expression also includes the plural meaning as long as it does not differently mean in the context. In the present application, the terms “include” and “consist of” designate the presence of features, numbers, steps, operations, components, elements, or a combination thereof that are written in the specification, but do not exclude the presence or possibility of addition of one or more other features, numbers, steps, operations, components, elements, or a combination thereof.

FIG. 1is a view schematically illustrating an example of a sheet feeding apparatus according to an example of the present disclosure, andFIG. 2is a view illustrating a multi-feed prevention roller and a sheet feed roller of the sheet feeding apparatus ofFIG. 1.

Referring toFIGS. 1 and 2, a sheet feeding apparatus1according to an example of the present disclosure may include a sheet stacker10, a sheet feed roller20, and a multi-feed prevention roller30.

The sheet stacker10stacks at least one sheet S, picks up the stacked sheets S one by one, and feeds the picked sheet S toward the sheet feed roller20. The sheet stacker10may include a sheet cassette11and a pickup roller13provided above the sheet cassette11. The sheet cassette11is configured to accommodate a predetermined number of sheets S. The pickup roller13is formed to convey the sheet S positioned at the top of the sheets S stacked on the sheet cassette11toward the sheet feed roller20.

The sheet feed roller20is provided at the front end of the sheet stacker10and moves the sheet S stacked on the sheet stacker10to a conveying roller201. In detail, the sheet feed roller20is formed to move the sheet S picked up by the pickup roller13in the sheet stacker10to the conveying roller201.

The conveying roller201is formed in a pair of rollers facing each other and moves the sheet S fed by the sheet feed roller20to an image former220.FIG. 1shows a case where the sheet feeding apparatus1according to an example of the present disclosure is disposed in an image forming apparatus200(seeFIG. 15).

The sheet feed roller20is disposed to be rotated by a driving source100. As an example, the driving source100may use a sheet feed motor. Since the structure in which the sheet feed motor rotates the sheet feed roller20is general, the illustration and description thereof are omitted.

The multi-feed prevention roller30is provided to face the sheet feed roller20and to prevent the multi-feed of sheets S fed from the sheet stacker10. For example, the multi-feed prevention roller30is provided to be in contact with the sheet feed roller20at a predetermined pressure and is rotated by the rotation of the sheet feed roller20when a single sheet S is fed from the sheet stacker10so that the sheet S is conveyed to the conveying roller201.

The multi-feed prevention roller30may be elastically supported by a multi-feed prevention roller holder33so that the multi-feed prevention roller30is in contact with the sheet feed roller20at a predetermined pressure. The multi-feed prevention roller holder33is elastically supported by elastic members35provided on a frame3.

When two or more sheets S enter between the multi-feed prevention roller30and the sheet feed roller20, the multi-feed prevention roller30prevents the two or more sheets S from passing in between the multi-feed prevention roller30and the sheet feed roller20. Hereinafter, preventing two or more sheet S from passing between the sheet feed roller20and the multi-feed prevention roller30is referred as multi-feed prevention.

A magnetic torque limiter40is provided in the multi-feed prevention roller30for preventing the multi-feed of the sheets S. In detail, the magnetic torque limiter40is disposed coaxially with a rotation shaft31of the multi-feed prevention roller30and has a predetermined torque threshold value. Therefore, when a sheet conveyance frictional force generated between the multi-feed prevention roller30and the sheet feed roller20is larger than the torque threshold value, the multi-feed prevention roller30rotates in the direction of interlocking with the rotation of the sheet feed roller20, that is, in a sheet conveying direction. However, when the sheet conveyance frictional force generated between the multi-feed prevention roller30and the sheet feed roller20is smaller than the torque threshold value, the multi-feed prevention roller30does not rotate with the sheet feed roller20, but rotates in the opposite direction or remains stationary.

Accordingly, when a single sheet S enters between the multi-feed prevention roller30and the sheet feed roller20, the sheet conveyance frictional force between the multi-feed prevention roller30and the sheet S becomes larger than the torque threshold value of the magnetic torque limiter40and the multi-feed prevention roller30rotates in the sheet conveying direction so that the sheet S is normally conveyed. However, when two or more sheets S enter between the multi-feed prevention roller30and the sheet feed roller20, the sheet conveyance frictional force becomes smaller than the torque threshold value and the multi-feed prevention roller30rotates in the direction opposite to the sheet conveying direction or stops so that the conveyance of the sheet S is interrupted.

Hereinafter, the structure of the magnetic torque limiter40provided on one side of the multi-feed prevention roller30will be described with reference toFIGS. 3 and 4.

FIG. 3is a cross-sectional view illustrating a structure of a magnetic torque limiter of a sheet feeding apparatus according to an example of the present disclosure, andFIG. 4is a cross-sectional view illustrating the magnetic torque limiter ofFIG. 3taken along a line I-I.

Referring toFIGS. 3 and 4, the magnetic torque limiter40includes a plurality of permanent magnets41provided in the circumferential direction on the rotation shaft31of the multi-feed prevention roller30. Each of the plurality of permanent magnets41is formed in a bar shape and is provided on the circumferential surface of a magnet support portion32provided coaxially with the rotation shaft31so that N poles and S poles are alternately arranged in the circumferential direction of the rotation shaft31. The magnet support portion32is formed in a cylindrical shape larger in diameter than the rotation shaft31and may be formed integrally with the rotation shaft31of the multi-feed prevention roller30.

In the present example, the plurality of permanent magnets41are provided on the outer circumferential surface of the magnet support portion32connected to the rotation shaft31of the multi-feed prevention roller30. However, as another example, the plurality of permanent magnets41may be provided on the outer circumferential surface of a hollow cylindrical boss and the boss may be coaxially connected to the rotation shaft31of the multi-feed prevention roller30.

The magnetic torque limiter40may include a housing43enclosing the plurality of permanent magnets41provided on the rotation shaft31. A housing shaft47is provided on one side of the housing43and an opening44into which the rotation shaft31of the multi-feed prevention roller30is inserted is provided on the other side of the housing43.

In addition, a magnetic member45is provided on the inner surface of the housing43to face the plurality of permanent magnets41so that a magnetic force is generated between the plurality of permanent magnets41and the magnetic member45. The magnetic member45is formed in a hollow cylindrical shape. The magnetic member45is spaced apart in the radial direction by a predetermined distance from the plurality of permanent magnets41.

The housing43is formed of a non-magnetic material such as plastic. The length L1of the magnetic member45is formed to be shorter than the length L2of the housing43. Therefore, as illustrated inFIG. 3, portions41aof the plurality of permanent magnets41directly face the inner surface of the housing43without facing the magnetic member45. Accordingly, the magnetic force of the plurality of permanent magnets41is radiated to the outside of the housing43through a portion43aof the housing43where the magnetic member45is not provided. Therefore, the portion43aof the housing43through which the magnetic force of the plurality of permanent magnets41is radiated to the outside of the housing43over the entire circumference of the housing43may be referred to as a magnetic force emitting region. The magnetic force of the plurality of permanent magnets41is not radiated to the outside at the portion of the housing43where the magnetic member45is provided.

The housing shaft47is rotatably supported by a rotation support member (not illustrated) such as a bearing. The housing shaft47may be configured to receive or not to receive rotational force from the driving source100.

When the housing shaft47is configured to receive the rotational force from the driving source100, the multi-feed prevention roller30is rotatable by the driving source100. At this time, the housing shaft47is connected to the driving shaft that receives the rotational force from the driving source100and rotates. The housing shaft47and the driving shaft of the driving source100may be coupled using a coupling such as a universal joint.

In the case where the multi-feed prevention roller30is configured to be rotated by the separate driving source100as described above, the multi-feed prevention roller30may be referred to as an active multi-feed prevention roller. As another example, the housing shaft47may be provided to only support the rotation of the multi-feed prevention roller30without receiving power from the driving source100. When the housing shaft47is not connected to the driving source100as described above, the multi-feed prevention roller30can be rotated only by the rotation of the sheet feed roller20. Such a multi-feed prevention roller30may be referred to as a semi-active multi-feed prevention roller.

A sensor50may be provided in the outer side of the housing43and may detect the magnetic force of the plurality of permanent magnets41radiated to the outside of the housing43. A hall sensor capable of detecting a magnetic force may be used as the sensor50.

The hall sensor50is provided in the outside of the housing43to face the portion43aof the housing43where the magnetic member45is not provided on the inner surface of the housing43. In other words, the hall sensor50is disposed in the outside of the housing43to face the portion43aof the housing43facing the portions41aof the plurality of permanent magnets41which do not overlap with the magnetic member45, that is, a magnetic force emitting region.

For example, as illustrated inFIG. 4, the hall sensor50is disposed outside the magnetic torque limiter40in the radial direction of the magnetic torque limiter40. The hall sensor50is provided on a separate bracket55and does not interfere with the magnetic torque limiter40. The bracket55may be fixed to a frame3in which the sheet feeding apparatus1is provided. Therefore, when the magnetic torque limiter40rotates, the hall sensor50does not interfere with the magnetic torque limiter40, and can detect the magnetic force emitted from the plurality of permanent magnets41of the magnetic torque limiter40.

The hall sensor50may include two hall sensors51and52which are provided in the circumferential direction of the magnetic torque limiter40to detect the rotational direction of the magnetic torque limiter40. For example, a first hall sensor51may be disposed on a horizontal line H passing the rotation center C of the magnetic torque limiter40, and a second hall sensor52may be disposed at a predetermined angle from the first hall sensor51in the circumferential direction of the magnetic torque limiter40.

When the first hall sensor51and the second hall sensor52are provided in the circumferential direction of the magnetic torque limiter40as described above, whether the magnetic torque limiter40, that is, the plurality of permanent magnets41are rotated or not, and the rotational direction and displacement of the magnetic torque limiter40may be detected. Since the plurality of permanent magnets41are provided integrally with the multi-feed prevention roller30, whether the multi-feed prevention roller30rotates or not, and the rotational direction and displacement of the multi-feed prevention roller30may be detected through the two hall sensors51and52.

Although the case where the hall sensor50is composed of two hall sensors51and52has been described above, the hall sensor50is not limited thereto. For example, the hall sensor50may use a hall IC sensor50′ in which the two hall sensors51and52are embedded and integrated in a single body. The hall IC sensor50′ may be implemented in a form capable of detecting changes in the number of revolutions and the rotational direction of the magnetic torque limiter40from the number of pulses and the phase difference of the embedded two hall sensors51and52.

As another example, the hall IC sensor50′ may be implemented so that the hall IC sensor50′ is arranged in the vertical direction or the horizontal direction with respect to the magnetic flex direction, and the pulse output and the switching of the rotational direction are detected from the magnetic flux phase difference of each of the embedded two hall sensors51and52.

FIG. 5is a view illustrating a structure of a sheet feeding apparatus according to an example of the present disclosure provided with a single hall IC sensor.

Referring toFIG. 5, the hall IC sensor50′ is disposed on a substrate53, and the substrate53is fixed to a substrate holder54. The substrate holder54may be fixed to a bracket57secured to the frame of the sheet feeding apparatus1. Accordingly, when the magnetic torque limiter40rotates, the hall IC sensor50′ can detect the magnetic force radiated from the plurality of permanent magnets41of the magnetic torque limiter40in a stable state.

When a change in the magnetic force of the magnetic torque limiter40is detected using the single hall IC sensor50′ as illustrated inFIG. 5, it may be easy to arrange the hall sensor50in comparison with the case where a change in the magnetic force is detected using the two hall sensors51and52provided along the circumferential direction of the magnetic torque limiter40as illustrated inFIG. 4.

Hereinafter, another example of the magnetic torque limiter that can be used in the sheet feeding apparatus according to an example of the present disclosure will be described with reference toFIGS. 6 and 7.

FIG. 6is a cross-sectional view illustrating another magnetic torque limiter of a sheet feeding apparatus according to an example of the present disclosure, andFIG. 7is a cross-sectional view illustrating the magnetic torque limiter ofFIG. 6taken along a line II-II.

Referring toFIGS. 6 and 7, the magnetic torque limiter40may include a plurality of permanent magnets41, a housing43, and a magnetic member45′.

The plurality of permanent magnets41are disposed in the circumferential direction on the outer circumferential surface of the magnet support portion32provided on the rotation shaft31of the multi-feed prevention roller30, and are the same as or similar to the plurality of permanent magnets41of the magnetic torque limiter40according to the example illustrated inFIGS. 3 and 4; therefore, a detailed description thereof is omitted.

The housing43is disposed to surround the plurality of permanent magnets41provided on the rotation shaft31and is the same as or similar to the housing43of the magnetic torque limiter40according to the example illustrated inFIGS. 3 and 4; therefore, a detailed description thereof is omitted.

The magnetic member45′ is provided on the inner surface of the housing43and is formed to have substantially the same length as each of the plurality of permanent magnets41. A plurality of slits46are formed in the circumferential direction near one end of the magnetic member45′. The magnetic force generated in the plurality of permanent magnets41may be radiated to the outside of the housing43through the plurality of slits46. Therefore, a portion43aof the housing43corresponding to the plurality of slits46of the magnetic member45′ may be referred to as a magnetic force emitting region.

The hall sensor50as described above is disposed in the outside of the housing43and is provided to face the plurality of slits46through the side surface of the housing43. In other words, the hall sensor50is disposed outside the housing43to face the portion43aof the housing43facing the plurality of slits46, that is, the magnetic force emitting region. Accordingly, when two hall sensors51and52are provided in the circumferential direction in the outside of the magnetic torque limiter40, that is, in the outside of the housing43, the hall sensors51and52can detect the magnetic force of the plurality of permanent magnets41that are radiated through the plurality of slits46.

Therefore, the magnetic torque limiter40and the hall sensor50may constitute a roller self-diagnosis portion capable of diagnosing the life span of the multi-feed prevention roller30.

The sheet feeding apparatus1according to an example of the present disclosure may include a controller9(seeFIG. 9). For example, the controller9may include at least one processing circuit, various electronic components such an ASIC, ROM, RAM, and the like, or at least one program module.

The controller9may be configured to control the sheet feeding apparatus1to feed the sheets S stacked on the sheet cassette11one by one. In addition, the controller9may perform the roller self-diagnosis using the hall sensor50. For example, the controller9may determine whether to replace the multi-feed prevention roller30by identifying the wear state of the multi-feed prevention roller30by using a signal input from the hall sensor50.

When the controller9determines that the replacement of the multi-feed prevention roller30is required due to the lifetime of the multi-feed prevention roller30, the controller9may also inform a user that the sheet feed roller20and the pickup roller13are required to be replaced together with the multi-feed prevention roller30. Since the sheet feed roller20and the pickup roller13pickup and feed the sheets S stacked on the sheet cassette11one by one together with the multi-feed prevention roller30, when the lifetime of the multi-feed prevention roller30is over, the sheet feed roller20and the pickup roller13may be determined to have reached the end of the their lifetime and may be required to be replaced together with the multi-feed prevention roller30.

In addition, when the multi-feed prevention roller30of the sheet feeding apparatus1can be driven, the controller9may identify the connection state of the magnetic torque limiter40. For example, when the assembled state of the magnetic torque limiter40and the drive shaft49(seeFIG. 14) is poor, a regular rotation fluctuation may be detected by the hall sensor50. When the rotation fluctuation detected by the hall sensor50exceeds a reference value, the controller9may determine that the connection state of the magnetic torque limiter40is poor.

In addition, the controller9may determine whether the multi-feed occurs in the multi-feed prevention roller30of the sheet feeding apparatus1. A method by which the controller9detects the multi-feed will be described later.

When it is necessary to replace the multi-feed prevention roller30, the sheet feed roller20, and the pickup roller13or when the multi-feed of the sheets S occur, the controller9may be configured to inform the outside of the roller replacement and the occurrence of the multi-feed. When the sheet feeding apparatus1is disposed in an image forming apparatus200(seeFIG. 15), the controller9may be configured as a part of a main controller209to control the operation of the image forming apparatus200.

Hereinafter, a roller self-diagnosis method of a sheet feeding apparatus according to an example of the present disclosure will be described in detail with reference toFIGS. 8 and 9.

FIG. 8is a view for explaining operation of a sheet feeding motor, a pickup roller, a sheet feed roller, and a multi-feed prevention roller of a sheet feeding apparatus according to an example of the present disclosure, andFIG. 9is a functional block diagram of a sheet feeding apparatus according to an example of the present disclosure.

Referring toFIGS. 8 and 9, the sheet feeding apparatus1may include a sheet cassette11, a pickup roller13, a sheet feed roller20, a multi-feed prevention roller30, a sheet feed motor100, a sheet feed clutch81, a pickup clutch82, a hall sensor50, a controller9, a storage portion9-1, and a transmission portion9-2.

The sheet cassette11is configured to receive a predetermined number of sheets S, and the pickup roller13is configured to move the sheet S positioned on the top of the sheets S stacked on the sheet cassette11toward the sheet feed roller20.

The sheet feed roller20is provided at the leading end of the sheet cassette11and moves the sheet S picked up by the pickup roller13toward the conveying roller201(seeFIG. 1).

The multi-feed prevention roller30is provided to face the sheet feed roller20and to prevent the multi-feed of the sheets S fed from the sheet cassette11. In detail, the multi-feed prevention roller30is provided to be in contact with the sheet feed roller20at a predetermined pressure, and a magnetic torque limiter40is provided coaxially with the multi-feed prevention roller30(seeFIG. 3). Accordingly, when one sheet S is conveyed from the sheet cassette11, the multi-feed prevention roller30is rotated in the sheet conveying direction by the rotation of the sheet feed roller20so that the sheet S is conveyed toward the conveying roller201. However, when two or more sheets S are conveyed, the multi-feed prevention roller30is rotated in the direction opposite to the sheet conveying direction or stops by the magnetic torque limiter40, thereby preventing the multi-feed of the sheets S.

The sheet feed motor100generates rotational force capable of rotating the sheet feed roller20, the pickup roller13, and the multi-feed prevention roller30. As another example, the rotational force of the sheet feed motor100may not be transmitted to the multi-feed prevention roller30. However, the sheet feeding apparatus1as illustrated inFIG. 8is configured so that the rotational force of the sheet feed motor100is transmitted to the multi-feed prevention roller30.

The rotational force of the sheet feed motor100is transmitted to the sheet feed roller20through the sheet feed clutch81. For example, when the sheet feed clutch81is turned on, the rotational force of the sheet feed motor100is transmitted to the sheet feed roller20and the pickup roller13so that the sheet feed roller20and the pickup roller13rotate. Conversely, when the sheet feed clutch81is turned off, the rotational force of the sheet feed motor100is not transmitted to the sheet feed roller20so that the sheet feed roller20and the pickup roller13do not rotate. In other words, the pickup roller13is configured to rotate together with the sheet feed roller20when the sheet feed roller20rotates.

When the sheet feed clutch81is turned on, the rotational force of the sheet feed motor100is transmitted to a pickup roller cam83through the pickup clutch82, thereby lowering the pickup roller13. For example, when the pickup clutch82is turned on while the sheet feed clutch81is turned on, the rotational force of the sheet feed motor100is transmitted to the pickup roller cam83so that the pickup roller cam83rotates. The pickup roller13is lowered by the rotation of the pickup roller cam83and is brought into contact with the sheet S of the sheet cassette11.

Conversely, when the pickup clutch82is turned off, the rotational force of the sheet feed motor100is not transmitted to the pickup roller cam83, so that the pickup roller cam83does not press the pickup roller13downward. Accordingly, the pickup roller13is kept spaced apart from the sheet S of the sheet cassette11by a pickup roller spring14. When the sheet feed clutch81is turned off, the pickup roller13is spaced apart from the sheet S of the sheet cassette11by the pickup roller spring14regardless of whether the pickup clutch82is turned on or off.

Each of the sheet feed clutch81and the pickup clutch82may be implemented with an electromagnetic clutch whose on/off is controlled by the controller9.

The rotational force of the sheet feed motor100is transmitted to the multi-feed prevention roller30to rotate the multi-feed prevention roller30. Since the multi-feed prevention roller30is directly connected to the sheet feed motor100, when the sheet feed motor100operates, the multi-feed prevention roller30also rotates in one direction.

A sheet feed sensor86capable of detecting the leading end of the sheet S having passed between the sheet feed roller20and the multi-feed prevention roller30may be provided in front of the sheet feed roller20in the conveying direction of the sheet S. A lift sensor87may be provided at one side of the multi-feed prevention roller30to detect that the multi-feed prevention roller30is raised and contacted with the sheet feed roller20. In addition, a cam position sensor88for detecting the position of the cam may be provided at one side of a multi-feed prevention roller lowering cam84for lowering the multi-feed prevention roller30.

The hall sensor50is disposed at one side of the magnetic torque limiter40that is provided coaxially with the multi-feed prevention roller30and is configured to detect the magnetic force radiated from the magnetic torque limiter40and to output a pulse signal corresponding to the magnetic force. The magnetic torque limiter40and the hall sensor50are described above; therefore, the detailed descriptions thereof are omitted.

The controller9is configured to perform the roller self-diagnosis and to store the result in the storage portion9-1or to output the result to the outside. A user or a maintenance service engineer may set the controller9to perform the roller self-diagnosis at a predetermined time interval. For example, the user or the maintenance service engineer may set the controller9to perform the roller self-diagnosis when the sheet feeding apparatus1is turned on, or when the image forming apparatus200(seeFIG. 15) is turned on in the case where the sheet feeding apparatus1is disposed in the image forming apparatus200.

If the image forming apparatus200including the sheet feeding apparatus1is always on, the controller9may be set to perform the roller self-diagnosis every predetermined time every morning.

The controller9of the sheet feeding apparatus1according to an example of the present disclosure may perform two types of roller self-diagnoses, that is, a first self-diagnosis and a second self-diagnosis. The roller self-diagnosis performed by the controller9will be described in detail below.

The storage portion9-1is configured to store the result of the roller self-diagnosis performed by the controller9. In addition, the storage portion9-1may store the roller self-diagnosis program and reference values necessary for the roller self-diagnosis so that the controller9can perform the roller self-diagnosis. As the storage portion9-1, various memories, for example, a random access memory (RAM) may be used.

The transmission portion9-2is configured to transmit information on the state of the sheet feeding apparatus1, for example, a replacement request of the multi-feed prevention roller30, the sheet feed roller20, and the pickup roller13to an external device under the control of the controller9.

The transmission portion9-2may be connected to the external device wirelessly or by wire. For example, the transmission portion9-2may be connected to a personal computer or a mobile device by wire or wirelessly. The mobile device may include a notebook computer, a tablet computer, a smartphone, and the like. In this case, the roller replacement request generated by the controller9may be output to the external device through the transmission portion9-2.

When a program or an application connected to the service center of the image forming apparatus200is installed in the personal computer or the mobile device, the roller replacement request information may be provided to the service center via communication or the Internet. Also, when the roller replacement request is not made, the service center may acquire information on the state of each of the multi-feed prevention roller30, the sheet feed roller20, and the pickup roller13via the personal computer or the mobile device.

In addition, since the service center can detect the rotation state of the multi-feed prevention roller30, the service center may grasp the operation status of the image forming apparatuses200and the plurality of sheet cassettes11provided in the respective image forming apparatuses200of all the users managed by the service center through communication in real time.

As another example, the transmission portion9-2may be configured to be connected to the cloud and web hard via the Internet. In this case, the roller replacement request generated in the controller9may be output to the cloud or web hard.

Also, as another example, the transmission portion9-2may be configured to receive a signal form the external device and to transmit the received signal to the controller9of the sheet feeding apparatus1. In other words, the transmission portion9-2may be configured to exchange signals with the external device. In this case, the transmission portion9-2is implemented as a transmitting/receiving portion.

In this case, even when the user or the maintenance service engineer does not directly input the condition of the roller self-diagnosis to the image forming apparatus200, the service center can input the roller self-diagnosis conditions of the multi-feed prevention roller30, the sheet feed roller20, and the pickup roller13by a remote operation.

When the sheet feeding apparatus1according to an example of the present disclosure is disposed in the image forming apparatus200, the roller replacement request may be output through a display91or a speaker92provided in an operation panel90of the image forming apparatus200.

Hereinafter, the case where the controller performs the first self-diagnosis will be described in detail with reference toFIGS. 10 to 12.

FIG. 10is a view for explaining operation of a sheet feed motor, a pickup roller, a sheet feed roller, and a multi-feed prevention roller when a sheet feeding apparatus according to an example of the present disclosure performs a first self-diagnosis.FIG. 11is a diagram illustrating a pulse signal output from a hall sensor when a sheet feeding apparatus according to an example of the present disclosure performs a first self-diagnosis.FIG. 12is a perspective view illustrating a multi-feed prevention roller of a sheet feeding apparatus according to an example of the present disclosure which is unevenly worn.

The first self-diagnosis refers to that the controller9determines the lifetime of the multi-feed prevention roller30by using a signal output from the hall sensor50while the sheet feed motor100is rotating the sheet feed roller20in the state where the sheet feed roller20and the multi-feed prevention roller30are in contact with each other without the sheet S between the sheet feed roller20and the multi-feed prevention roller30.

For example, in order to perform the first self-diagnosis, the controller9turns on the sheet feed motor100, and then turns on the sheet feed clutch81. Then the sheet feed motor100rotates and the rotational force of the sheet feed motor100is transmitted to the sheet feed roller20through the sheet feed clutch81so that the sheet feed roller20rotates.

At this time, since the pickup roller13is connected to the sheet feed roller20, when the sheet feed roller20rotates, the pickup roller13also rotates. However, since the pickup clutch82is in the off state, the pickup roller13is positioned at the raised position by the pickup roller spring14and is spaced apart from the sheet S of the sheet cassette11. Therefore, even when the pickup roller13rotates, the sheet S of the sheet cassette11is not fed between the sheet feed roller20and the multi-feed prevention roller30.

Also, since the multi-feed prevention roller lowering cam84for lowering the multi-feed prevention roller30is at a position where the multi-feed prevention roller30is not pressed, the multi-feed prevention roller30is pressed upward by the elastic member35and is brought into contact with the sheet feed roller20at a predetermined pressure.

At this time, the rotational force of the sheet feed motor100is transmitted to the magnetic torque limiter40provided coaxially with the multi-feed prevention roller30. At this time, the rotational force is transmitted to the magnetic torque limiter40in a direction opposite to the rotational direction of the sheet feed roller20. The housing shaft47of the magnetic torque limiter40is connected to the drive shaft49which receives the rotational force from the sheet feed motor100by the coupling48. Therefore, the housing43of the magnetic torque limiter40that receives the rotational force from the sheet feed motor100through the coupling48rotates in the direction opposite to the sheet feed roller20.

However, since the sheet feed roller20and the multi-feed prevention roller30made of rubber having a high coefficient of friction are in contact with each other without a sheet, and the magnetic torque limiter40is configured to slip at a predetermined load or more, when the sheet feed roller20rotates, the multi-feed prevention roller30rotates along the sheet feed roller20. For example, when the sheet feed roller20rotates in the clockwise direction inFIG. 10, the multi-feed prevention roller30rotates in the counter-clockwise direction by the sheet feed roller20.

When the multi-feed prevention roller30rotates in the counter-clockwise direction, the plurality of permanent magnets41of the magnetic torque limiter40connected to the rotation shaft31of the multi-feed prevention roller30rotates at the same speed as the multi-feed prevention roller30. Then, the hall sensor50disposed on one side of the magnetic torque limiter40outputs a pulse signal corresponding to the plurality of rotating permanent magnets41(seeFIG. 11).

The controller9may detect the number of rotations of the multi-feed prevention roller30by using the pulse signal output from the hall sensor50.

Accordingly, the controller9compares the number of rotations of the sheet feed roller20with the number rotations of the multi-feed prevention roller30. When the difference between the number of rotations of the multi-feed prevention roller30and the number of rotations of the sheet feed roller20is greater than a predetermined value, that is, a reference number of rotations, the controller9may determine that the lifespan of the multi-feed prevention roller30is over. At this time, the number of rotations of the sheet feed roller20is determined by a power transmission mechanism (not illustrated) between the sheet feed motor100and the sheet feed roller20, so that the controller9can rotate the sheet feed roller20at a desired number of rotations. The number of rotations of the sheet feed roller20may be kept constantly under the control of the controller9regardless of the abrasion of the sheet feed roller20. The power transmission mechanism for transmitting the rotational force of the sheet feed motor100to the sheet feed roller20may be variously configured including gears, pulleys, and belts.

In general, when the sheet feed roller20and the multi-feed prevention roller30are new, the multi-feed prevention roller30rotates by a few percent less than the number of rotations of the sheet feed roller20due to the load of the magnetic torque limiter40.

However, when the sheet feed roller20and the multi-feed prevention roller30are uniformly worn by repetition of a large number of sheet feeding operations, the number of rotations of the multi-feed prevention roller30may be reduced by several tens of percent (%) or more as compared with the number of rotations of the sheet feed roller20due to a reduction in the diameter and change in the friction coefficient of each of the sheet feed roller20and the multi-feed prevention roller30.

When the multi-feed prevention roller30is worn, slip occurs between the multi-feed prevention roller30and the sheet feed roller20, so that the pulse signal output from the hall sensor50has a wider pulse width T1′ as the pulse signal indicated by the worn roller inFIG. 11. In other words, the pulse width T1′ of the pulse signal of the worn roller is wider than the pulse width T1of the pulse signal of the new roller as illustrated inFIG. 11. When the pulse width of the pulse signal is widened, the number of rotations of the roller calculated by using the pulse signal decreases.

Therefore, when the number of rotations of the multi-feed prevention roller30is reduced by several tens of percent compared with the number of rotations of the sheet feed roller20, the controller9may determine that the lifespan of the multi-feed prevention roller30has expired. For example, when the number of rotations of the multi-feed prevention roller30is reduced by 30% or more compared to the number of rotations of the sheet feed roller20, the controller9may determine that the lifetime of the multi-feed prevention roller30is over.

For example, when the controller9rotates the sheet feed roller20at 600 rpm and the number of rotations of the multi-feed prevention roller30measured using the hall sensor50is 400 rpm, the controller9may determine that the lifetime of the multi-feed prevention roller30is over because the decrease in the number of rotations of multi-feed prevention roller30is 200 rpm and about 33.3%. When it is determined that the lifetime of the multi-feed prevention roller30is over, the controller9may output an indication to request replacement of the multi-feed prevention roller30to the outside. At this time, since the sheet feed roller20is worn equally or similarly to the multi-feed prevention roller30, the controller9may request the sheet feed roller20to be replaced with the multi-feed prevention roller30. Further, since the pickup roller13is worn equally or similarly to the sheet feed roller20, the controller9may indicate the pickup roller13to be replaced with the multi-feed prevention roller30as well.

In other words, in the case of the first self-diagnosis, the controller9drives the sheet feed motor100and controls the sheet feed clutch81and the pickup clutch82so that the sheet feed roller20is rotated by the rotational force of the sheet feed motor100and the pickup roller13is blocked from picking up and feeding the sheet S to the sheet feed roller20. Then, the controller9may calculate the number of rotations of the multi-feed prevention roller30using the signal output from the hall sensor50and compare the number of rotations of the multi-feed prevention roller30and the number of rotations of the sheet feed roller20, thereby determining the lifespan of the multi-feed prevention roller30.

In addition, when the multi-feed prevention roller30is unevenly worn, the controller9may detect a section where the rotation fluctuation becomes larger during one rotation of the multi-feed prevention roller30. Here, that the multi-feed prevention roller30is unevenly worn refers to the case in that the outer circumferential surface of the multi-feed prevention roller30is not uniformly worn, but a portion30aof the multi-feed prevention roller30is worn more than the other portion thereof as illustrated inFIG. 12. InFIG. 12, reference numeral30adenotes an unevenly worn portion of the multi-feed prevention roller30.

When the multi-feed prevention roller30is unevenly worn, the pulse interval T of the unevenly worn portion becomes very large as illustrated inFIG. 11. Accordingly, when the interval T between the adjacent two pulses among the plurality of pulses corresponding to one rotation of the multi-feed prevention roller30output from the hall sensor50is greater than the reference pulse interval T′, the controller9may determine that uneven wear occurs on the multi-feed prevention roller30.

When the uneven wear generated on the multi-feed prevention roller30is equal to or larger than the reference value, the controller9may determine that the lifespan of the multi-feed prevention roller30is over and may output a replacement request for the multi-feed prevention roller30to the outside.

Hereinafter, the case where the controller performs the second self-diagnosis will be described in detail with reference toFIGS. 13 and 14.

FIG. 13is a view for explaining operation of a sheet feeding motor, a pickup roller, a sheet feed roller, and a multi-feed prevention roller when a sheet feeding apparatus according to an example of the present disclosure performs a second self-diagnosis.FIG. 14is a view illustrating a coupling connecting a magnetic torque limiter and a drive shaft of a sheet feeding apparatus according to an example of the present disclosure.

The second self-diagnosis refers to that the controller9identifies a connection state of the magnetic torque limiter40by using the signal output from the hall sensor50while the sheet feed motor100is rotating in the state where the sheet feed roller20and the multi-feed prevention roller30are in contact with each other without a sheet S between the sheet feed roller20and the multi-feed prevention roller30and the rotational force of the sheet feed motor100is blocked not to be transmitted to the sheet feed roller20and the pickup roller13.

For example, in order to perform the second self-diagnosis, the controller9turns off the sheet feed clutch81and turns on the sheet feed motor100. Then, although the sheet feed motor100rotates, the rotational force of the sheet feed motor100is blocked by the sheet feed clutch81and is not transmitted to the sheet feed roller20. Therefore, the sheet feed roller20can freely rotate.

At this time, since the pickup roller13is connected to the sheet feed roller20, when the sheet feed roller20does not rotate, the pickup roller13also does not rotate. Further, since the sheet feed clutch81is in the off state, the pickup roller13is kept in a raised position by the pickup roller spring14and is spaced apart from the sheet S of the sheet cassette11. Accordingly, even when the sheet feed motor100rotates, the sheet S of the sheet cassette11in not fed between the sheet feed roller20and the multi-feed prevention roller30.

In addition, since the multi-feed prevention roller lowering cam84for lowering the multi-feed prevention roller30is at a position where the multi-feed prevention roller30is not pressed, the multi-feed prevention roller30is pressed upward by the elastic member35and is brought into contact with the sheet feed roller20at a predetermined pressure.

At this time, the rotational force of the sheet feed motor100is transmitted to the magnetic torque limiter40provided coaxially with the multi-feed prevention roller30. In detail, the housing shaft47of the magnetic torque limiter40is connected to the drive shaft49that receives the rotational force from the sheet feed motor100by the coupling48so that the housing43of the magnetic torque limiter40rotates. When the housing43of the magnetic torque limiter40rotates, the plurality of permanent magnets41provided inside the housing43also rotate. When the plurality of permanent magnets41rotate, the rotation shaft31provided with the plurality of permanent magnets41rotates, and therefore, the multi-feed prevention roller30also rotates. In the example illustrated inFIG. 13, when the sheet feed motor100rotates, the multi-feed prevention roller30rotates in the clockwise direction.

The sheet feed roller20and the multi-feed prevention roller30are in contact with each other and the sheet feed roller20is freely rotatable, so that when the multi-feed prevention roller30rotates, the sheet feed roller20is rotated along with the multi-feed prevention roller30. For example, inFIG. 13, when the multi-feed prevention roller30rotates in the clockwise direction, the sheet feed roller20is rotated in the counter-clockwise direction by the multi-feed prevention roller30.

The magnetic torque limiter40is connected to the drive shaft49that receives the rotational force of the sheet feed motor100by the coupling48. The coupling48is a joint that connects a shaft and another shaft, such as a universal joint. For example, as illustrated inFIG. 14, the housing shaft47of the magnetic torque limiter40is connected to the drive shaft49that is rotated by the rotational force from the sheet feed motor100by the coupling48. Accordingly, when the drive shaft49is rotated by the sheet feed motor100, the housing shaft47of the magnetic torque limiter40coupled to the drive shaft49by the coupling48rotates.

In the case where the housing shaft47of the magnetic torque limiter40and the drive shaft49are arranged in a straight line by coupling48, when the magnetic torque limiter40rotates, the pulse signal output from the hall sensor50is uniform.

However, when there is a large unacceptable positional error between the housing shaft47and the drive shaft49, a regular variation may occur in the pulse signal output from the hall sensor50. For example, when there is a positional error in the joint between the housing shaft47and the drive shaft49, an abnormal pulse that the interval between two adjacent pulses among the plurality of pulses corresponding to one rotation of the magnetic torque limiter40is narrower or wider than the interval between the other pulses (a reference pulse interval) may occur. In this case, when the magnetic torque limiter40rotates, such an abnormal pulse is regularly generated every one rotation.

Such a regular rotation fluctuation due to the defective joint may cause vibration so that the upward contact pressure of the multi-feed prevention roller30fluctuates. When the upward contact pressure of the multi-feed prevention roller30fluctuates, the multi-feed of the sheets S is likely to occur.

Accordingly, when the controller9detects a regular rotation fluctuation from the pulse signal output from the hall sensor50, the controller9may identify that a joint failure occurs and may output the occurrence of joint failure to the outside.

The second self-diagnosis may be used as a shipment inspection of the sheet feeding apparatus1at the factory. As a result of performing the second self-diagnosis, when a joint failure occurs, an operator may not shipment the sheet feeding apparatus1, and may adjust the joint state between the housing shaft47of the magnetic torque limiter40and the drive shaft49.

According to the sheet feeding apparatus1according to an example of the present disclosure as described above, the self-diagnosis is carried out by itself without feeding the actual sheet S to the multi-feed prevention roller30, the sheet feed roller20, and the pickup roller13which are required to be replaced due to the sheet feeding, and then the replacement of the multi-feed prevention roller30, the sheet feed roller20, and the pickup roller13may be requested before a sheet feeding failure occurs. Therefore, the miss-feed, jam, multi-feed, and the like of sheets may be prevented.

Hereinafter, an image forming apparatus provided with a sheet feeding apparatus according to an example of the present disclosure will be described with reference toFIG. 15.

FIG. 15is a cross-sectional view schematically illustrating an image forming apparatus according to an example of the present disclosure including two sheet feeding apparatuses.

Referring toFIG. 15, an image forming apparatus200according to an example of the present disclosure may include a main body210, two sheet feeding apparatuses1, an image former220, and a sheet discharger230.

The main body210forms the appearance of the image forming apparatus200, and accommodates and supports the two sheet feeding apparatuses1, the image former220, and the sheet discharger230therein.

The sheet feeding apparatus1accommodates a predetermined number of sheets S and is formed to pick up the sheets S one by one and supply the picked sheet to the image former220. In the present example, two sheet feeding apparatuses1are stacked in the vertical direction. The structure and operation of the two sheet feeding apparatuses1are described above; therefore, detailed description thereof is omitted.

The image former220forms a predetermined image on the sheet S supplied from the sheet feeding apparatus1. The image former220may include an exposure member225for forming an electrostatic latent image corresponding to the print data on an image carrier222, a developing cartridge221for developing the electrostatic latent image formed on the image carrier222into a developer image, a transfer member223for transferring the developer image formed on the image carrier222to the sheet, and a fixing portion224for fixing the developer image onto the sheet. The image former220may be the same as or similar to the image former of the conventional image forming apparatus, and a detailed description thereof is omitted.

FIG. 15shows the image forming apparatus200that forms a monochrome image using one image carrier222. However, the sheet feeding apparatus1according to an example of the present disclosure may be used in a color image forming apparatus that prints a color image using a plurality of image carriers.

Further, the sheet feeding apparatus1according to an example of the present disclosure may be applied to an inkjet printer. Therefore, although not illustrated, the image former may be formed by an ink ejection head which ejects predetermined ink according to print data.

The sheet discharger230discharges the sheet having a predetermined image formed thereon through the image former220to the outside of the main body210of the image forming apparatus200. The sheet discharger230may be configured as a pair of discharge rollers.

The main controller209is configured to control the image forming apparatus200and to form an image on the sheet S. The main controller209may include the above-described controller9that performs the roller self-diagnosis for each of the two sheet feeding apparatuses1. The main controller209may perform the roller self-diagnosis for the sheet feeding apparatus1in the same manner as the controller9as described above, and thus a detailed description thereof is omitted.

The main controller209performs the roller self-diagnosis for each of the two sheet feeding apparatuses1. When it is necessary to replace the multi-feed prevention roller30, the sheet feed roller20, and the pickup roller13, the main controller209may inform the outside of it. For example, the main controller209may inform that it is necessary to replace the multi-feed prevention roller30, the sheet feed roller20, and the pickup roller13of any one of the two sheet feeding apparatuses1using the display91and the speaker92of the operation panel90(seeFIG. 9) of the image forming apparatus200.

InFIG. 15, the image forming apparatus200having two sheet feeding apparatuses1is described as an example. However, the sheet feeding apparatus1according to an example of the present disclosure may be applied to an image forming apparatus having three or more sheet feeding apparatuses. Also, the sheet feeding apparatus1according to an example of the present disclosure may be applied to an automatic document scanning apparatus and a sheet feeding apparatus of a large capacity provided separately from the image forming apparatus in which miss-feed, jamming, multi-feed, and the like of sheets are troublesome.

According to the sheet feeding apparatus of an example of the present disclosure as described above, in the image forming apparatus having a plurality of sheet feeding apparatuses, it is possible to identify the wear state of the multi-feed prevention roller or the joint failure with respect to each of the sheet feeding apparatuses. Therefore, the multi-feed prevention roller30, the sheet feed roller20, and the pickup roller13of the sheet feeding apparatus that need to be replaced may be replaced at an appropriate time. In other words, instead of replacing the rollers of all of the plurality of sheet feeding apparatuses, the multi-feed prevention roller, the sheet feed roller, and the pickup roller of only the sheet feeding apparatus frequently used by the user may be replaced, thereby enabling efficient maintenance.

In the above description, the sheet feeding apparatus according to an example of the present disclosure performs the roller self-diagnosis and requests replacement of the multi-feed prevention roller, the sheet feed roller, and the pickup roller. However, the sheet feeding apparatus according to an example of the present disclosure may be configured to detect the multi-feed of the sheets.

Hereinafter, a sheet feeding apparatus according to an example of the present disclosure configured to detect the multi-feed of sheets will be described.

FIG. 16is a view schematically illustrating an example of a sheet feeding apparatus according to an example of the present disclosure.

Referring toFIGS. 16 and 2, the sheet feeding apparatus1according to an example of the present disclosure may include a sheet stacker10, a sheet feed roller20, and a multi-feed prevention roller30.

The sheet stacker10stacks at least one sheet S, picks up the stacked sheets S one by one, and feeds the picked sheet S toward the sheet feed roller20. The sheet stacker10may include a sheet cassette11and a pickup roller13provided above the sheet cassette11. The sheet cassette11is configured to accommodate a predetermined number of sheets S. The pickup roller13is formed to move the sheet S positioned at the top of the sheets S stacked on the sheet cassette11toward the sheet feed roller20.

The sheet feed roller20is disposed on one side of the sheet stacker10and moves the sheet S fed from the sheet stacker10toward the conveying roller201. In detail, the sheet feed roller20is formed to move the sheet S picked up by the pickup roller13in the sheet stacker10toward the conveying roller201. The conveying roller201moves the sheet S fed by the sheet feed roller20to the image former220.FIG. 16illustrates a case where the sheet feeding apparatus1according to an example of the present disclosure is disposed in the image forming apparatus.

The sheet feed roller20is disposed to be rotatable by the driving source100. As an example, the driving source100may use a drive motor. The structure in which the drive motor100rotates the sheet feed roller20is general; therefore, the illustration and description thereof are omitted.

The multi-feed prevention roller30is provided to face the sheet feed roller20and to prevent the multi-feed of the sheets S fed from the sheet stacker10. In detail, the multi-feed prevention roller30is provided to be in contact with the sheet feed roller20at a predetermined pressure. When one sheet S is fed from the sheet stacker10, the multi-feed prevention roller30is rotated by the sheet feed roller20to move the sheet S to the conveying roller201. The multi-feed prevention roller30may be elastically supported by the multi-feed prevention roller holder33so that the multi-feed prevention roller30is in contact with the sheet feed roller20at a predetermined pressure. The multi-feed prevention roller holder33is elastically supported by an elastic member35provided on the frame3.

When two or more sheets S enter between the multi-feed prevention roller30and the sheet feed roller20, the multi-feed prevention roller30prevents the two or more sheets S from passing between the multi-feed prevention roller30and the sheet feed roller20. Hereinafter, the prevention of the two or more sheets S from passing between the sheet feed roller20and the multi-feed prevention roller30is referred to as multi-feed prevention.

For the multi-feed prevention, a magnetic torque limiter40is provided in the multi-feed prevention roller30. In detail, the magnetic torque limiter40is provided on the rotation shaft31of the multi-feed prevention roller30and has a predetermined threshold torque value. Therefore, when the sheet conveyance frictional force generated between the multi-feed prevention roller30and the sheet feed roller20is larger than the threshold torque value, the multi-feed prevention roller30rotates in a direction of interlocking with the rotation of the sheet feed roller20, that is, in the sheet conveying direction. However, when the sheet conveyance frictional force generated between the multi-feed prevention roller30and the sheet feed roller20is smaller than the threshold torque value, the multi-feed prevention roller30does not rotate along with the sheet feed roller20, but rotates in the opposite direction or remains stationary.

Accordingly, when one sheet S enters between the multi-feed prevention roller30and the sheet feed roller20, the sheet conveyance frictional force between the multi-feed prevention roller30and the sheet S becomes larger than the threshold torque value of the magnetic torque limiter40. Therefore, the multi-feed prevention roller30rotates in the sheet conveying direction, so that the sheet S is normally conveyed. However, when two or more sheets S enter between the multi-feed prevention roller30and the sheet feed roller20, the conveyance of the sheet S is blocked by the multi-feed prevention roller30.

The structure of the magnetic torque limiter40provided at one side of the multi-feed prevention roller30is described above; therefore, detailed description thereof is omitted.

The magnetic torque limiter40and the hall sensor50, which is disposed at one side of the magnetic torque limiter40and detects the magnetic force radiated from the magnetic torque limiter40, may constitute a multi-feed detector capable of detecting whether or not the multi-feed of the sheets S occurs in the multi-feed prevention roller30.

The sheet feeding apparatus1according to an example of the present disclosure may include a controller9(seeFIG. 24). The controller9may identify whether the multi-feed occurs in the multi-feed prevention roller30of the sheet feeding apparatus1by using signals input from the hall sensors51and52. When the multi-feed of the sheets S occurs, the controller9may be configured to stop the driving source100that rotates the pickup roller13of the sheet stacker10and the sheet feed roller20and to inform the outside of the occurrence of the multi-feed. When the sheet feeding apparatus1is disposed in the image forming apparatus, the controller9may be formed as a part of a main controller to control the operation of the image forming apparatus.

Hereinafter, the operation of the sheet feeding apparatus according to an example of the present disclosure will be described with reference toFIGS. 17A to 19B.

First, a case in which the sheet feeding apparatus normally feeds one sheet will be described with reference toFIGS. 17A and 17B.

FIG. 17Ais a view illustrating a case where a sheet feeding apparatus according to an example of the present disclosure normally feeds a sheet, andFIG. 17Bis a view illustrating signals output from a first hall sensor and a second hall sensor in the case ofFIG. 17A.

Referring toFIG. 17A, one sheet S is picked up by the pickup roller13and enters between the sheet feed roller20and the multi-feed prevention roller30. In this case, since the sheet conveyance frictional force generated between the multi-feed prevention roller30and the sheet S is larger than the threshold torque value of the magnetic torque limiter40, the multi-feed prevention roller30is rotated by the sheet feed roller20. For example, as illustrated inFIG. 17A, when the sheet feed roller20rotates in the clockwise direction, the multi-feed prevention roller30rotates in the counter-clockwise direction due to the frictional force against the sheet S and causes the sheet S to be conveyed in the sheet conv (a direction of arrow A).

At this time, the two hall sensors51and52provided on one side of the magnetic torque limiter40output pulse signals in the order of A-phase and B-phase as illustrated inFIG. 17B. For example, the first hall sensor51outputs the A-phase pulse signal, and then the second hall sensor52outputs the B-phase pulse signal delayed by t time with respect to the A-phase pulse signal. When the A-phase pulse signal and the B-phase pulse signal are output from the first and second hall sensors51and52as illustrated inFIG. 17B, the controller9determines that the sheet S is normally fed.

Next, a case where the sheet stacker10feeds two sheets S will be described with reference toFIGS. 18A and 18B.

FIG. 18Ais a view illustrating a case where two sheets are fed to a multi-feed prevention roller of a sheet feeding apparatus according to an example of the present disclosure, andFIG. 18Bis a view illustrating signals output from a first hall sensor and a second hall sensor in the case ofFIG. 18A.

Referring toFIG. 18A, two sheets S are picked up by the pickup roller13and enter between the sheet feed roller20and the multi-feed prevention roller30. In this case, since the sheet conveyance frictional force generated between the multi-feed prevention roller30and the sheet S is smaller than the threshold torque value of the magnetic torque limiter40, the multi-feed prevention roller30is not rotated by the sheet feed roller20, but is rotated by the driving source100connected to the multi-feed prevention roller30. For example, as illustrated inFIG. 18A, when the sheet feed roller20rotates in the clockwise direction, the multi-feed prevention roller30is rotated in the clockwise direction by the driving source100, so that the lower sheet is conveyed to the sheet cassette11. Therefore, when the multi-feed of the sheets S occurs, the multi-feed prevention roller30rotates in the opposite direction with respect to the direction in which the sheet S is normally conveyed.

At this time, the order of the pulse signals output from the two hall sensors51and52provided on one side of the magnetic torque limiter40changes. For example, as illustrated inFIG. 18B, the pulse signals, which output in the order of A-phase and B phase from the first and second hall sensors51and52during forward rotation, changes in the order of B-phase and A-phase when the multi-feed prevention roller30is rotated in the opposite direction due to the occurrence of the multi-feed. In detail, when the multi-feed occurs, the second hall sensor52outputs the B-phase pulse signal, and then the first hall sensor51outputs the A-phase pulse signal delayed by the t time with respect to the B-phase pulse signal. When a predetermined period time (T1msec) elapses after the order of the A-phase pulse signal and the B-phase pulse signal is changed, the controller9may stop the sheet feed roller20and the multi-feed prevention roller30and inform the outside of the occurrence of the multi-feed.

Finally, a case where the sheet stacker10feeds three or more sheets S will be described with reference toFIGS. 19A and 19B.

FIG. 19Ais a view illustrating a case where three or more sheets are fed to a multi-feed prevention roller of a sheet feeding apparatus according to an example of the present disclosure, andFIG. 19Bis a view illustrating signals output from a first hall sensor and a second hall sensor in the case ofFIG. 19A.

Referring toFIG. 19A, a large number of sheets S, for example, three or more sheets S are picked up by the pickup roller13and enter between the sheet feed roller20and the multi-feed prevention roller30. In this case, since the frictional force applied to the multi-feed prevention roller30by the large number of sheets S inserted between the sheet feed roller20and the multi-feed prevention roller30is larger than the threshold torque value of the magnetic torque limiter40, the multi-feed prevention roller30rotates in conjunction with the sheet feed roller20. For example, as illustrated inFIG. 19A, when the sheet feed roller20rotates in the clockwise direction, the multi-feed prevention roller30is rotated in the sheet conveying direction (the direction of arrow A), that is, in the counter-clockwise direction by the frictional force against the large number of sheets S. At this time, since the large number of sheets S are inserted between the sheet feed roller20and the multi-feed prevention roller30, a lower side displacement amount (arrow B), which is the distance that the multi-feed prevention roller30moves downward, increases. The lower side displacement of the multi-feed prevention roller30may be detected by the two hall sensors51and52.

At this time, the two hall sensors51and52provided on one side of the magnetic torque limiter40output pulse signals in the order of A-phase and B-phase as illustrated inFIG. 19B. However, the pulse interval of each of the A-phase pulse signal and the B-phase pulse signal becomes shorter than in the case of normal rotation. For example, when the multi-feed prevention roller30rotates in the forward direction, the first hall sensor51outputs the A-phase pulse signal, and the second hall sensor52outputs the B-phase pulse signal delayed by t times with respect to the A-phase pulse signal. At this time, the pulse interval of each of the A-phase pulse signal and the B-phase pulse signal is T1. When the large number of sheets S are inserted between the multi-feed prevention roller30and the sheet feed roller20, as illustrated inFIG. 19B, the order of the A-phase pulse signal and the B-phase pulse signal output from the first and second hall sensors51and52is the same, but the pulse interval of each of the A-phase pulse signal and the B-phase pulse signal is shortened to T2(msec). When a predetermined period time (T3msec) elapses after detecting that the pulse interval of each of the A-phase pulse signal and the B-phase pulse signal is shorten, the controller9may stop the sheet feed roller20and the multi-feed prevention roller30and inform the outside of the occurrence of the multi-feed of the large number of sheets.

Hereinafter, a sheet feeding apparatus configured to return the sheet S to the sheet stacker10and to retry the sheet feeding operation when the controller9recognizes the occurrence of multi-feed in the multi-feed prevention roller30will be described with reference toFIGS. 20 to 24.

FIG. 20is a plan view schematically illustrating a sheet feeding apparatus according to an example of the present disclosure having a sheet return function.FIG. 21is a side view illustrating a case where the sheet feeding apparatus ofFIG. 20does not operate.FIG. 22is a side view illustrating a case where the sheet feeding apparatus ofFIG. 20normally feeds a sheet, andFIG. 23is a side view illustrating a case where the sheet feeding apparatus ofFIG. 20returns the sheet to a retrying position.FIG. 24is a functional block diagram of the sheet feeding apparatus ofFIG. 20.

Referring toFIGS. 20 and 21, the sheet feeding apparatus1according to an example of the present disclosure may include a sheet cassette11and a pickup roller13. The pickup roller13is provided over the sheet cassette11, picks up one sheet stacked on the sheet cassette11and feeds the picked sheet to a sheet feed roller20. The pickup roller13is provided on a pickup roller shaft13awhich is rotatably disposed in a sheet feed roller holder21. A pickup roller gear13bis coaxially disposed on the pickup roller shaft13aat one side of the pickup roller13. Accordingly, when the pickup roller gear13brotates, the pickup roller13rotates.

On one side of the pickup roller13, that is, downstream of the sheet conveying direction, the sheet feed roller20is provided. The sheet feed roller20is provided on a sheet feed roller shaft20awhich is rotatably disposed on the sheet feed roller holder21. A sheet feed roller gear20bis coaxially disposed on the sheet feed roller shaft20aat one side of the sheet feed roller20. At this time, the pickup roller shaft13aand the sheet feed roller shaft20aare provided parallel to each other, and the pickup roller gear13band the sheet feed roller gear20bare spaced apart from each other. At one side of the sheet feed roller holder21, there is provided an idle gear15which is engaged with the pickup roller gear13band the sheet feed roller gear20b. The idle gear15is rotatably disposed on an idle gear shaft15aprovided in the sheet feed roller holder21. Therefore, when the sheet feed roller gear20brotates, the pickup roller gear13brotates through the idle gear15. Accordingly, when the sheet feed roller20rotates, the pickup roller13rotates together.

A sheet feed pulley23is provided at one end of the sheet feed roller shaft20a, that is, at an end opposite to the side where the sheet feed roller20is disposed. A drive clutch27may be provided between the sheet feed pulley23and the sheet feed roller shaft20a. The drive clutch27selectively blocks the rotation of the sheet feed pulley23from being transmitted to the sheet feed roller shaft20a. For example, when the drive clutch27is turned on, the rotation of the sheet feed pulley23is transmitted to the sheet feed roller shaft20a. When the drive clutch27is turned off, the rotation of the sheet feed pulley23is prevented from being transmitted to the sheet feed roller shaft20a. Therefore, when the drive clutch27is turned off, the sheet feed roller20does not rotate even when the sheet feed pulley23rotates. The on/off of the drive clutch27may be controlled by the controller9.

The sheet feed pulley23receives rotational force from a first drive motor101through a sheet feed belt24. For example, a feed drive pulley25is provided on a motor shaft101aof the first drive motor101, and the feed drive pulley25is connected with the sheet feed pulley23by the sheet feed belt24. Thus, when the motor shaft101aof the first drive motor101rotates, the feed drive pulley25rotates. The rotation of the feed drive pulley25is transmitted to the sheet feed pulley23through the sheet feed belt24, so that the sheet feed pulley23rotates.

A pickup roller spring120to apply a force to pull the sheet feed roller holder21in the upward direction is provided at one side of the sheet feed roller holder21. One end of the pickup roller spring120is fixed to a frame (not illustrated) where the sheet feeding apparatus is disposed, and the other end of the pickup roller spring120is fixed to one side surface of the sheet feed roller holder21. At this time, the other end of the pickup roller spring120is fixed to the opposite side of the pickup roller13about the sheet feed roller shaft20a. Thus, the pickup roller spring120causes the pickup roller13to move downward.

The multi-feed prevention roller30is rotatably disposed below the sheet feed roller20. The magnetic torque limiter40is provided on the rotation shaft31of the multi-feed prevention roller30. A multi-feed prevention pulley48is provided on the housing shaft47of the magnetic torque limiter40. Accordingly, when the multi-feed prevention pulley48rotates, the magnetic torque limiter40rotates and the multi-feed prevention roller30rotates.

The multi-feed prevention roller30is rotatably disposed in a multi-feed prevention roller holder33. The multi-feed prevention roller holder33is provided to receive an elastic force in the upward direction by the elastic member35. Therefore, the multi-feed prevention roller30is kept in contact with the sheet feed roller20at a predetermined pressure by the elastic member35.

A first intermediate pulley131is rotatably disposed on one side of the multi-feed prevention roller holder33. In detail, the first intermediate pulley131is disposed coaxially with an intermediate shaft130, which is rotatably disposed on one side of the multi-feed prevention roller holder33. The first intermediate pulley131is connected with the multi-feed prevention pulley48through a multi-feed prevention belt135. Therefore, when the first intermediate pulley131rotates, the multi-feed prevention pulley48is rotated by the multi-feed prevention belt135. When the multi-feed prevention pulley48rotates, the multi-feed prevention roller30rotates through the magnetic torque limiter40.

A second intermediate pulley132is coaxially disposed at the other end of the intermediate shaft130. Therefore, when the second intermediate pulley132rotates, the intermediate shaft130rotates, and thereby the first intermediate pulley131rotates. The second intermediate pulley132is provided to be rotatable by the rotational force transmitted from the first drive motor101through an intermediate belt136. For example, a multi-feed prevention drive pulley133may be provided on the motor shaft101aof the first drive motor101. The multi-feed prevention drive pulley133is connected with the second intermediate pulley132through the intermediate belt136. Therefore, when the multi-feed prevention drive pulley133rotates, the second intermediate pulley132is rotated by the intermediate belt136. The multi-feed prevention drive pulley133is disposed on the motor shaft101aof the first drive motor101coaxially with the feed drive pulley25. Therefore, when the motor shaft101aof the first drive motor101rotates, the feed drive pulley25and the multi-feed prevention drive pulley133rotates integrally. Accordingly, the first drive motor101can rotate the sheet feed roller20and the multi-feed prevention roller30.

A multi-feed prevention roller release cam140may be provided on one side of the multi-feed prevention roller holder33. One end of the multi-feed prevention roller release cam140is fixed to a release cam shaft141, and the other end is provided to be in contact with a protrusion33aof the multi-feed prevention roller holder33. Therefore, when the multi-feed prevention roller release cam140rotates in the counter-clockwise direction, the protrusion33aof the multi-feed prevention roller holder33is pivoted upward. When the protrusion33ais pivoted upward, the multi-feed prevention roller holder33is rotated in the clockwise direction about the intermediate shaft130so that the multi-feed prevention roller30is moved away from the sheet feed roller20. When the multi-feed prevention roller release cam140rotates in the opposite direction, the force applied to the protrusion33aof the multi-feed prevention roller holder33is removed, so that the multi-feed prevention roller holder33is pivoted upward by the elastic member35and the multi-feed prevention roller30is brought close to the sheet feed roller20.

A release cam pulley142is provided at one end of the release cam shaft141, that is, at the end opposite to where the multi-feed prevention roller release cam140is disposed. When the release cam pulley142rotates, the release cam shaft141rotates, whereby the multi-feed prevention roller release cam140rotates.

The release cam pulley142is configured to receive the rotational force from a second drive motor102. In other words, a release cam drive pulley144is coaxially disposed on a motor shaft102aof the second drive motor102, and the release cam drive pulley144is connected with the release cam pulley142through a release cam belt143. Therefore, when the motor shaft102aof the second drive motor102rotates, the release cam drive pulley144rotates, whereby the release cam belt143rotates. Then, the release cam pulley142is rotated by the release cam belt143.

In addition, a pickup roller lifting cam150may be provided on one side the sheet feed roller holder21. One end of the pickup roller lifting cam150is fixed to a lifting cam shaft151, and the other end is provided to be in contact with a protruding portion21aof the sheet feed roller holder21. Therefore, when the pickup roller lifting cam150rotates in the clockwise direction, the protruding portion21aof the sheet feed roller holder21may be pivoted downward. When the protruding portion21aof the sheet feed roller holder21is pivoted downward, the sheet feed roller holder21is rotated in the counter-clockwise direction about the sheet feed roller shaft20aso that the pickup roller13is moved away from the sheet stacked on the sheet cassette11. When the pickup roller lifting cam150rotates in the opposite direction, the force applied to the protruding portion21aof the sheet feed roller holder21is removed so that the sheet feed roller holder21receives a force in the upward direction by the sheet feed roller spring120. Therefore, the sheet feed roller holder21rotates in the clockwise direction, and the pickup roller13comes into contact with the sheet.

A lifting cam pulley152is disposed on one side of the pickup roller lifting cam150coaxially with the lifting cam shaft151. When the lifting cam pulley152rotates, the lifting cam shaft151rotates, whereby the pickup roller lifting cam150rotates.

The lifting cam pulley152is configured to receive the rotational force from the second drive motor102. In other words, a lifting cam drive pulley154is coaxially disposed on the motor shaft102aof the second drive motor102, and the lifting cam drive pulley154is connected with the lifting cam pulley152through the lifting cam belt153. Therefore, when the motor shaft102aof the second drive motor102rotates, the lifting cam drive pulley154rotates, and thereby the lifting cam belt153rotates. Then, the lifting cam pulley152is rotated by the lifting cam belt153. The lifting cam drive pulley154is disposed on the motor shaft102aof the second drive motor102coaxially with the release cam drive pulley144as described above. Therefore, when the motor shaft102aof the second drive motor102rotates, the lifting cam drive pulley154and the release cam drive pulley144rotate integrally. Thus, the second drive motor102can rotate the multi-feed prevention roller release cam140and the pickup roller lifting cam150at the same time.

Hereinafter, the operation of the sheet feeding apparatus having the sheet return function will be described with reference toFIGS. 20 to 24attached hereto.

The positions of the pickup roller13, the sheet feed roller20, and the multi-feed prevention roller30when the sheet feeding apparatus1does not operate are illustrated inFIG. 21.

In detail, since the pickup roller lifting cam150is spaced apart from the protruding portion21aof the sheet feed roller holder21, the sheet feed roller holder21is rotated in the clockwise direction around the sheet feed roller shaft20aby the sheet feed roller spring120so that the pickup roller13comes into contact with the sheet S.

Further, since the multi-feed prevention roller release cam140pushes the protrusion33aof the multi-feed prevention roller holder33upwardly, the multi-feed prevention roller holder33rotates in the clockwise direction around the intermediate shaft130. Therefore, the multi-feed prevention roller30is spaced apart from the sheet feed roller20. When the multi-feed prevention roller30and the sheet feed roller20are separated from each other before the sheet feeding apparatus1stops operating, deformation that occurs when the multi-feed prevention roller30and the sheet feed roller20are in contact with each other for a long time may be prevented.

In this state, when the controller9receives a sheet feed command, the controller9controls the first drive motor101and the second drive motor102to change the sheet feeding apparatus1to the state as illustrated inFIG. 22, thereby conveying the sheet S.

In detail, the controller9rotates the second drive motor102in one direction, and thereby the multi-feed prevention roller release cam140is positioned in a horizontal state. For example, inFIG. 21, the motor shaft102aof the second drive motor102is rotated in the clockwise direction so that the multi-feed prevention roller release cam140is positioned in a horizontal state. Thus, since the force of pushing the protrusion33aof the multi-feed prevention roller holder33upward is removed, the elastic member35provided below the multi-feed prevention roller holder33presses the multi-feed prevention roller holder33upward so that the multi-feed prevention roller30comes into contact with the sheet feed roller20.

When the motor shaft102aof the second drive motor102rotates in the clockwise direction, the pickup roller lifting cam150rotates in the clockwise direction. Accordingly, when the multi-feed prevention roller release cam140is positioned in the horizontal state, the pickup roller lifting cam150is also positioned in the horizontal state. At this time, since the pickup roller lifting cam150does not apply a force to the protruding portion21aof the sheet feed roller holder21, the pickup roller13keeps in contact with the sheet S.

In this state, the controller9rotates the motor shaft101aof the first drive motor101in one direction so that the pickup roller13and the sheet feed roller20feed the sheet S. For example, the controller9controls the first drive motor101to rotate the motor shaft101ain the clockwise direction. Then, the feed drive pulley25provided on the motor shaft101aof the first drive motor101rotates, thereby rotating the sheet feed belt24. When the sheet feed belt24rotates, the sheet feed pulley23provided on the sheet feed roller shaft20arotates in the clockwise direction. At this time, since the drive clutch27connecting the sheet feed pulley23and the sheet feed roller shaft20ais in the on state, when the sheet feed pulley23rotates, the sheet feed roller shaft20arotates integrally.

Therefore, when the sheet feed roller shaft20arotates in the clockwise direction, the sheet feed roller gear20band the sheet feed roller20rotate integrally in the clockwise direction. When the sheet feed roller gear20brotates, the pickup roller gear13bconnected by the idle gear15rotates. At this time, when the sheet feed roller gear20brotates in the clockwise direction, the idle gear15rotates in the counter-clockwise direction and the pickup roller gear13brotates in the clockwise direction. Therefore, the pickup roller13provided on the pickup roller shaft13aintegrally with the pickup roller gear13balso rotates in the clockwise direction. Then, one of the sheets S stacked on the sheet cassette11is picked up by the pickup roller13and conveyed between the sheet feed roller20and the multi-feed prevention roller30.

When one sheet S enters between the multi-feed prevention roller30and the sheet feed roller20, the sheet conveyance frictional force generated between the sheet S and the multi-feed prevention roller30is larger than the threshold torque value of the magnetic torque limiter40so that the multi-feed prevention roller30is rotated in the counter-clockwise direction by the sheet feed roller20. Therefore, the sheet S that enters between the sheet feed roller20and the multi-feed prevention roller30is conveyed in the sheet conveying direction (the direction of arrow A).

When the sheet stacker10picks up and feeds the sheet S, two or more sheets S may enter between the sheet feed roller20and the multi-feed prevention roller30, resulting in the multi-feed of the sheets. At this time, the controller9may perform a retry mode in which the sheets S positioned between the sheet feed roller20and the multi-feed prevention roller30are returned to the sheet cassette11and then the sheet S is fed again.

A state in which the controller9returns the sheets S positioned between the sheet feed roller20and the multi-feed prevention roller30to the sheet cassette11is illustrated inFIG. 23.

In detail, the controller9rotates the motor shaft102aof the second drive motor102in the clockwise direction so that the pickup roller lifting cam150presses the protruding portion21aof the sheet feed roller holder21downward. When the pickup roller lifting cam150presses the protruding portion21aof the sheet feed roller holder21downward, the sheet feed roller holder21rotates in the counter-clockwise direction about the sheet feed roller shaft20aso that the pickup roller13is spaced apart from the sheet cassette11. At this time, the multi-feed prevention roller release cam140also rotates in the clockwise direction so that the multi-feed prevention roller release cam140is spaced apart from the protrusion33aof the multi-feed prevention roller holder33. Accordingly, the multi-feed prevention roller holder33is not subjected to the force by the multi-feed prevention roller release cam140, so that the multi-feed prevention roller30keeps to press the sheet feed roller20.

In addition, the controller9controls the drive clutch27provided on the sheet feed roller shaft20ato be turned off.

In this state, the controller9rotates the motor shaft101aof the first drive motor101in the clockwise direction. Then, the feed drive pulley25provided on the motor shaft101aof the first drive motor101rotates, thereby rotating the sheet feed belt24. When the sheet feed belt24rotates, the sheet feed pulley23provided on the sheet feed roller shaft20arotates in the clockwise direction. At this time, since the drive clutch27connecting the sheet feed pulley23and the sheet feed roller shaft20ais in the off state, the sheet feed roller shaft20adoes not rotate even when the sheet feed pulley23rotates. Therefore, the sheet feed roller gear20band the sheet feed roller20integrally provided on the sheet feed roller shaft20aare not rotated either. When the sheet feed roller gear20bdoes not rotate, the pickup roller gear13bconnected by the idle gear15also does not rotate. At this time, the sheet feed roller20connected to the sheet feed roller shaft20aby the one-way clutch20ccan freely rotate in the counter-clockwise direction.

When the motor shaft101aof the first drive motor101rotates in the clockwise direction, the multi-feed prevention drive pulley133rotates integrally with the motor shaft101atogether with the feed drive pulley25. When the motor shaft101aof the first drive motor101rotates in the clockwise direction, the multi-feed prevention drive pulley133also rotates in the clockwise direction. When the multi-feed prevention drive pulley133rotates in the clockwise direction, the second intermediate pulley132provided on the intermediate shaft130also rotates in the clockwise direction by the intermediate belt136. When the second intermediate pulley132rotates in the clockwise direction, the first intermediate pulley131provided on the intermediate shaft130also rotates in the clockwise direction. When the first intermediate pulley131rotates in the clockwise direction, the multi-feed prevention pulley48disposed on one side of the magnetic torque limiter40rotates in the clockwise direction. When the multi-feed prevention pulley48rotates in the clockwise direction, the magnetic torque limiter40rotates in the clockwise direction, and thereby the multi-feed prevention roller30rotates in the clockwise direction.

Since the multi-feed prevention roller30presses the sheet feed roller20by the elastic member35, when the multi-feed prevention roller30rotates in the clockwise direction, the sheet S positioned between the multi-feed prevention roller30and the sheet feed roller20may be returned to the sheet cassette11. At this time, the sheet feed roller20rotates in the counter-clockwise direction by the friction between the sheet feed roller20and the sheet S, so that the sheet S can be moved in the direction (a direction of arrow C) opposite to the sheet conveying direction.

Therefore, the drive clutch27for selectively blocking the rotational force transmitted to the sheet feed roller20, the first drive motor101for rotating the multi-feed prevention roller30, and the multi-feed prevention roller30may constitute a sheet return unit that returns two or more sheet S conveyed between the multi-feed prevention roller30and the sheet feed roller20to the sheet cassette11.

When the operation of returning the sheets S positioned between the multi-feed prevention roller30and the sheet feed roller20to the sheet cassette11is completed, the controller9controls the first drive motor101and the second drive motor102so that the sheet feed roller20, the pickup roller13, and the multi-feed prevention roller30are brought into the state shown inFIG. 22as described above, and thereby the sheet S stacked on the sheet stacker10is conveyed to the sheet feed roller20again.

When the feeding operation of the sheet S is completed, the controller9controls the first drive motor101and the second drive motor102so that the sheet feed roller20, the pickup roller13, and the multi-feed prevention roller30are brought into the state ofFIG. 21from the state ofFIG. 22as described above.

In detail, the controller9rotates the second drive motor102in one direction so that the multi-feed prevention roller release cam140is rotated in the counter-clockwise direction. For example, inFIG. 22, the motor shaft102aof the second drive motor102is rotated in the counter-clockwise direction so that the multi-feed prevention roller release cam140is rotated in the counter-clockwise direction from the horizontal state. Then, the multi-feed prevention roller release cam140presses the protrusion33aof the multi-feed prevention roller holder33upward, so that the multi-feed prevention roller holder33rotates in the clockwise direction about the intermediate shaft130. Then, the elastic member35provided below the multi-feed prevention roller holder33is compressed, and the multi-feed prevention roller30is spaced apart from the sheet feed roller20.

When the motor shaft102aof the second drive motor102rotates in the counter-clockwise direction, the pickup roller lifting cam150also rotates in the counter-clockwise direction. Then, the pickup roller lifting cam150does not apply a force to the protruding portion21aof the sheet feed roller holder21, so that the pickup roller13remains in contact with the sheet S.

When the sheet S is jammed between the sheet feed roller20and the multi-feed prevention roller30, the controller9controls the first drive motor101and the second drive motor102so that the sheet feed roller20and the multi-feed prevention roller30are spaced apart from each other as illustrated inFIG. 21.

With the sheet feeding apparatus1according to an example of the present disclosure as described above, when a multi-feed occurs between the multi-feed prevention roller30and the sheet feed roller20, the sheet S may be automatically returned to the sheet cassette11, and then the sheet feeding operation may be performed again.

The sheet feeding apparatus as described above is configured to transmit rotation of the first drive motor and the second drive motor by using belts and pulleys, but the power transmission structure is not limited thereto. The belt power transmission structure may be changed to a gear power transmission structure.

Hereinafter, a sheet feeding apparatus according to another example of the present disclosure will be described with reference toFIGS. 25 and 26.

FIG. 25is a view schematically illustrating a sheet feeding apparatus according to another example of the present disclosure, andFIG. 26is a plan view illustrating a multi-feed prevention roller of the sheet feeding apparatus ofFIG. 25.

Referring toFIGS. 25 and 26, a sheet feeding apparatus1according to an example of the present disclosure may include a sheet stacker10, a sheet feed roller20, a multi-feed prevention roller30, and a multi-feed detector.

The sheet stacker10stacks at least one sheet S, picks up the stacked sheets S one by one, and feeds the picked sheet toward the sheet feed roller20. The sheet stacker10may include a sheet cassette11and a pickup roller13provided above the sheet cassette11. The sheet cassette11is configured to accommodate a predetermined number of sheets S. The pickup roller13is formed to move the sheet S positioned at the top of the sheets S stacked on the sheet cassette11toward the sheet feed roller20.

The sheet feed roller20is disposed on one side of the sheet stacker10and feeds the sheet S stacked on the sheet stacker10toward the conveying roller201. In detail, the sheet feed roller20is formed to move the sheet S picked up by the pickup roller13in the sheet stacker10toward the conveying roller201. The conveying roller201moves the sheet S fed by the sheet feed roller20to an image former (not illustrated).

The sheet feed roller20is disposed to be rotatable by a driving source (not illustrated). As an example, the driving source may use a drive motor. The structure in which the drive motor rotates the sheet feed roller20is general; therefore, the illustration and description thereof are omitted.

The multi-feed prevention roller30is provided to face the sheet feed roller20and to prevent the multi-feed of the sheets S fed from the sheet stacker10. In detail, the multi-feed prevention roller30is provided to be in contact with the sheet feed roller20at a predetermined pressure. When one sheet S is fed between the multi-feed prevention roller30and the sheet feed roller20from the sheet stacker10, the multi-feed prevention roller30is rotated by the sheet feed roller20to allow the sheet S to convey to the conveying roller201. However, when two or more sheets S enter between the multi-feed prevention roller30and the sheet feed roller20, the multi-feed prevention roller30prevents the two or more sheets S from passing between the multi-feed prevention roller30and the sheet feed roller20.

For the multi-feed prevention, a magnetic torque limiter40is provided in the multi-feed prevention roller30. In detail, the magnetic torque limiter40is provided on the rotation shaft31of the multi-feed prevention roller30and has a predetermined threshold torque value. The structure of the magnetic torque limiter40is the same as or similar to that of the above-described example. Accordingly, when one sheet S enters between the multi-feed prevention roller30and the sheet feed roller20, the magnetic torque limiter40allows the multi-feed prevention roller30to be rotated by the sheet feed roller20so that the sheet S is normally conveyed. However, when two or more sheets S enter between the multi-feed prevention roller30and the sheet feed roller20, the magnetic torque limiter40blocks two or more sheets S from being conveyed.

The multi-feed detector may include a rotary encoder60coaxially disposed on the rotation shaft31at one side of the multi-feed prevention roller30and a sensor65to detect rotation and displacement of the rotary encoder60. The sensor65may be disposed on one side of the rotary encoder60.

The rotary encoder60is formed in the shape of a disk, and a plurality of slots61are formed on the disk at regular intervals in the circumferential direction. The sensor65outputs a pulse signal corresponding to the rotation of the rotary encoder60and may be implemented by optical sensors66and67including light emitting portions66aand67band light receiving portions66band67b. The light receiving portions66band67bof the optical sensors66and67may output pulse signals in accordance with the rotation of the rotary encoder60. The sensor65may include two optical sensors66and67to detect the rotational direction of the rotary encoder60. The two optical sensors66and67, that is, a first optical sensor66and a second optical sensor67may be provided adjacent to each other in the circumferential direction of the rotary encoder60. The first and second optical sensors66and67may be formed as a single body.

For example, the first optical sensor66and the second optical sensor67may be disposed above and below the horizontal line H passing through the rotation center C of the rotary encoder60. As described above, by providing the first optical sensor66and the second optical sensor67in the circumferential direction of the rotary encoder60, it is possible to detect the rotation state, the rotation direction, and the displacement of the rotary encoder60. Since the rotary encoder60is integrally provided with the multi-feed prevention roller30, it is possible to detect the rotation state, the rotation direction, and the displacement of the multi-feed prevention roller30through the two optical sensors66and67. The two optical sensors66and67may be disposed on a bracket69provided separately from the sheet feeding apparatus1so as not to interfere with the rotation of the rotary encoder60.

Hereinafter, the operation of the sheet feeding apparatus according to an example of the present disclosure will be described with reference toFIGS. 27A to 29B.

First, a case in which the sheet feeding apparatus normally feeds one sheet will be described with reference toFIGS. 27A and 27B.

FIG. 27Ais a view illustrating a case where a sheet feeding apparatus according to an example of the present disclosure normally feeds a sheet, andFIG. 27Bis a view illustrating signals output from a first optical sensor and a second optical sensor in the case ofFIG. 27A.

Referring toFIG. 27A, one sheet S is picked up by the pickup roller13and enters between the sheet feed roller20and the multi-feed prevention roller30. In this case, since the sheet conveyance frictional force generated between the multi-feed prevention roller30and the sheet S is larger than the threshold torque value of the magnetic torque limiter40, the multi-feed prevention roller30is rotated by the sheet feed roller20. For example, as illustrated inFIG. 27A, when the sheet feed roller20rotates in the clockwise direction, the multi-feed prevention roller30rotates in the counter-clockwise direction due to the frictional force against the sheet S and causes the sheet S to be conveyed in the sheet conveying direction (the direction of arrow A).

At this time, the two optical sensors66and67provided on one side of the rotary encoder60output pulse signals in the order of A-phase and B-phase as illustrated inFIG. 27B. For example, the first optical sensor66outputs the A-phase pulse signal, and then the second optical sensor67outputs the B-phase pulse signal delayed by t times with respect to the A-phase pulse signal. When the A-phase pulse signal and the B-phase pulse signal are output from the first and second optical sensors66and67as illustrated inFIG. 27B, the controller9determines that the sheet S is normally fed.

Next, a case where the sheet feeding apparatus1feeds two sheets S will be described with reference toFIGS. 28A and 28B.

FIG. 28Ais a view illustrating a case where two sheets are fed to a multi-feed prevention roller of a sheet feeding apparatus according to an example of the present disclosure, andFIG. 28Bis a view illustrating signals output from a first optical sensor and a second optical sensor in the case ofFIG. 28A.

Referring toFIG. 28A, two sheets S are picked up by the pickup roller13and enter between the sheet feed roller20and the multi-feed prevention roller30. In this case, since the sheet conveyance frictional force generated between the multi-feed prevention roller30and the sheet S is smaller than the threshold torque value of the magnetic torque limiter40, the multi-feed prevention roller30is not rotated by the sheet feed roller20, but is rotated by the driving source connected to the multi-feed prevention roller30. For example, as illustrated inFIG. 28A, when the sheet feed roller20rotates in the clockwise direction, the multi-feed prevention roller30is rotated in the clockwise direction by the driving source, so that the lower sheet is conveyed to the sheet cassette11of the sheet stacker10. Therefore, when the multi-feed of the sheets S occurs, the multi-feed prevention roller30rotates in the opposite direction with respect to the rotation direction in which the sheet S is normally conveyed.

At this time, the order of the pulse signals output from the two optical sensors66and67provided on one side of the rotary encoder60changes. For example, as illustrated inFIG. 28B, the pulse signals, which output in the order of A-phase and B phase from the first and second optical sensors66and67during forward rotation, changes in the order of B-phase and A-phase when the multi-feed prevention roller30rotates in the reverse direction due to the occurrence of the multi-feed. In detail, when the multi-feed occurs, the second optical sensor67outputs the B-phase pulse signal, and then the first optical sensor66outputs the A-phase pulse signal delayed by the t times with respect to the B-phase pulse signal. When a predetermined period time (T1msec) elapses after the order of the A-phase pulse signal and the B-phase pulse signal is changed, the controller9may stop the sheet feed roller20and the multi-feed prevention roller30and inform the outside of the occurrence of the multi-feed of the sheets S.

Finally, a case where the sheet feeding apparatus1feeds three or more sheets S will be described with reference toFIGS. 29A and 29B.

FIG. 29Ais a view illustrating a case where three or more sheets are fed to a multi-feed prevention roller of a sheet feeding apparatus according to an example of the present disclosure, andFIG. 29Bis a view illustrating signals output from a first optical sensor and a second optical sensor in the case ofFIG. 29A.

Referring toFIG. 29A, a large number of sheets S, for example, three or more sheets S are picked up by the pickup roller13and enter between the sheet feed roller20and the multi-feed prevention roller30. In this case, since the frictional force applied to the multi-feed prevention roller30by the large number of sheets S inserted between the sheet feed roller20and the multi-feed prevention roller30is larger than the threshold torque value of the magnetic torque limiter40, the multi-feed prevention roller30rotates in conjunction with the sheet feed roller20. For example, as illustrated inFIG. 29A, when the sheet feed roller20rotates in the clockwise direction, the multi-feed prevention roller30is rotated in the sheet conveying direction (the direction of arrow A), that is, in the counter-clockwise direction by the frictional force against the large number of sheets S. At this time, since the large number of sheets S are inserted between the sheet feed roller20and the multi-feed prevention roller30, a lower side displacement amount (arrow B) of the multi-feed prevention roller30increases. The lower side displacement B of the multi-feed prevention roller30may be detected by the two optical sensors66and67.

At this time, the two optical sensors66and67provided on one side of the rotary encoder60output pulse signals in the order of A-phase and B-phase as illustrated inFIG. 29B. However, the pulse interval of each of the A-phase pulse signal and the B-phase pulse signal becomes shorter than in the case of normal rotation. For example, when the multi-feed prevention roller30rotates in the forward direction, the first optical sensor66outputs the A-phase pulse signal, and the second optical sensor67outputs the B-phase pulse signal delayed by t times with respect to the A-phase pulse signal. At this time, the pulse interval of each of the A-phase pulse signal and the B-phase pulse signal is T1.

When the large number of sheets S are inserted between the multi-feed prevention roller30and the sheet feed roller20, as illustrated inFIG. 29B, the order of the A-phase pulse signal and the B-phase pulse signal output from the first and second optical sensors66and67and52is the same, but the pulse interval of each of the A-phase pulse signal and the B-phase pulse signal is shortened to T2(msec). When a predetermined period time (T3msec) elapses after detecting that the pulse interval of each of the A-phase pulse signal and the B-phase pulse signal is shorten, the controller9may stop the sheet feed roller20and the multi-feed prevention roller30and inform the outside of the occurrence of the multi-feed of the large number of sheets.

In the above description, the sheet feeding apparatus1has an active multi-feed prevention roller30that the multi-feed prevention roller30is configured to be rotated by the driving source. However, the sheet feeding apparatus1may use a semi-active multi-feed prevention roller that the multi-feed prevention roller is configured not to receive the power from the driving source as the multi-feed prevention roller.

The structure of the sheet feeding apparatus including the semi-active multi-feed prevention roller is the same as or similar to that of the sheet feeding apparatus according to the example illustrated inFIGS. 25 and 26except that the driving shaft for transmitting the rotational force from the separate driving source is not connected to the housing shaft of the magnetic torque limiter. Therefore, the description of the structure of the sheet feeding apparatus including the semi-active multi-feed prevention roller is omitted.

Hereinafter, the operation of the sheet feeding apparatus including the semi-active multi-feed prevention roller will be described.

First, when one sheet S enters between the sheet feed roller20and the multi-feed prevention roller30, the multi-feed prevention roller30is rotated by the sheet conveyance frictional force, so that the two optical sensors66and67output the A-phase pulse signal and the B-phase pulse signal in the same manner as illustrated inFIG. 27B. When the A-phase pulse signal and the B-phase pulse signal are output from the first and second optical sensors66and67as illustrated inFIG. 27B, the controller9determines that the sheet S is normally fed.

Next, a case where the sheet stacker10feeds two sheets S will be described with reference toFIGS. 30A and 30B.

FIG. 30Ais a view illustrating a case where two sheets are fed to a multi-feed prevention roller of a sheet feeding apparatus including a semi-active multi-feed prevention roller according to an example of the present disclosure, andFIG. 30Bis a view illustrating signals output from a first optical sensor and a second optical sensor in the case ofFIG. 30A.

Referring toFIG. 30A, two sheets S are picked up by the pickup roller13and enter between the sheet feed roller20and the multi-feed prevention roller30. In this case, since the sheet conveyance frictional force generated between the multi-feed prevention roller30and the sheet S is smaller than the threshold torque value of the magnetic torque limiter40, the multi-feed prevention roller30is not rotated by the sheet feed roller20, and remains in a stationary state. For example, as illustrated inFIG. 30A, in the case where the sheet feed roller20rotates in the clockwise direction, when the two sheets S are conveyed between the multi-feed prevention roller30and the sheet feed roller20, the multi-feed prevention roller30is stopped regardless of the rotation of the sheet feed roller20.

At this time, the pulse signals are not output from the two optical sensors66and67provided on one side of the rotary encoder60. For example, as illustrated inFIG. 30B, during forward rotation, the pulse signals are output in the order of A-phase and B phase from the first and second optical sensors66and67. However, when the multi-feed prevention roller30does not rotate due to the occurrence of the multi-feed of the sheets S, the A-phase pulse signal and the B-phase pulse signal are not output. When a predetermined period of time (T1msec) elapses after the pulse signal is not output after any one of the A-phase pulse signal and the B-phase pulse signal is output, the controller9may stop the sheet feed roller20and inform the outside of the occurrence of the multi-feed of the sheets S.

Finally, a case where the sheet stacker10feeds three or more sheets S between the multi-feed prevention roller30and the sheet feed roller20will be described with reference toFIGS. 31A and 31B.

FIG. 31Ais a view illustrating a case where three sheets or more are fed to a multi-feed prevention roller of a sheet feeding apparatus including a semi-active multi-feed prevention roller according to an example of the present disclosure, andFIG. 31Bis a view illustrating signals output from a first optical sensor and a second optical sensor in the case ofFIG. 31A.

Referring toFIG. 31A, a large number of sheets S, for example, three or more sheets S are picked up by the pickup roller13and enter between the sheet feed roller20and the multi-feed prevention roller30. In this case, since the frictional force applied to the multi-feed prevention roller30by the large number of sheets S inserted between the sheet feed roller20and the multi-feed prevention roller30is larger than the threshold torque value of the magnetic torque limiter40, the multi-feed prevention roller30rotates in conjunction with the sheet feed roller20. For example, as illustrated inFIG. 31A, when the sheet feed roller20rotates in the clockwise direction, the multi-feed prevention roller30is rotated in the sheet conveying direction (the direction of arrow A), that is, in the counter-clockwise direction by the frictional force against the large number of sheets S. At this time, since the large number of sheets S are inserted between the sheet feed roller20and the multi-feed prevention roller30, a lower side displacement amount (arrow B) of the multi-feed prevention roller30increases. The lower side displacement B of the multi-feed prevention roller30may be detected by the two optical sensors66and67.

At this time, the two optical sensors66and67provided on one side of the rotary encoder60output pulse signals in the order of A-phase and B-phase as illustrated inFIG. 31B. However, the pulse interval of each of the A-phase pulse and the B-phase pulse becomes shorter than in the case of normal rotation. For example, when the multi-feed prevention roller30rotates in the forward direction, the first optical sensor66outputs the A-phase pulse signal, and the second optical sensor67outputs the B-phase pulse signal delayed by t times with respect to the A-phase pulse signal. At this time, the pulse interval of each of the A-phase pulse signal and the B-phase pulse signal is T1. When the large number of sheets S are inserted between the multi-feed prevention roller30and the sheet feed roller20, as illustrated inFIG. 31B, the order of the A-phase pulse signal and the B-phase pulse signal output from the first and second optical sensors66and67and52is the same, but the pulse interval of each the A-phase pulse signal and the B-phase pulse signal is shortened to T2(msec). When a predetermined period (T3msec) elapses after detecting that the pulse interval of each of the A-phase pulse signal and the B-phase pulse signal is shorten, the controller9may stop the sheet feed roller20and inform the outside of the occurrence of the multi-feed of the large number of sheets.

In the above description, two optical sensors66and67of the multi-feed detector are disposed adjacent to each other. However, the arrangement of the two optical sensors66and67is not limited thereto. For example, the two optical sensors66and67may be arranged at intervals of about 90 degrees.

Hereinafter, a sheet feeding apparatus including a multi-feed detector in which two optical sensors are arranged at about 90 degrees will be described with reference toFIGS. 32 and 33.

FIG. 32is a view schematically illustrating a sheet feeding apparatus according to another example of the present disclosure, andFIG. 33is a plan view illustrating a multi-feed prevention roller of the sheet feeding apparatus ofFIG. 32.

Referring toFIGS. 32 and 33, a sheet feeding apparatus1according to an example of the present disclosure may include a sheet stacker10, a sheet feed roller20, a multi-feed prevention roller30, and a multi-feed detector.

The sheet stacker10, the sheet feed roller20, and the multi-feed prevention roller30are the same as or similar to the sheet stacker10, the sheet feed roller20, and the multi-feed prevention roller30of the sheet feeding apparatus1as illustrated inFIGS. 25 and 26; therefore, detailed descriptions thereof are omitted.

The multi-feed detector may include a rotary encoder70coaxially disposed on the rotation shaft31at one side of the multi-feed prevention roller30and sensors76and77to detect rotation and displacement of the rotary encoder70. The sensors76and77may be disposed on one side of the rotary encoder70.

The rotary encoder70is formed in the shape of a disk, and a plurality of slots71are formed on the disk at regular intervals in the circumferential direction. The sensors76and77output a pulse signal corresponding to the rotation of the rotary encoder70and may be implemented by optical sensors including light emitting portions76aand77aand light receiving portions76band77b.

The light receiving portions76band77bof the optical sensors76and77may output pulse signals in accordance with the rotation of the rotary encoder70. The sensors76and77may include two optical sensors66and67, that is, a first optical sensor76and a second optical sensor77to detect the rotational direction of the rotary encoder70.

The two optical sensors76and77may be disposed at intervals of about 90 degrees with respect to the rotation center C of the rotary encoder70. For example, the first optical sensor76is disposed on a horizontal line H passing through the center C of the rotary encoder70and the second optical sensor77is disposed on a vertical line V passing through the center C of the rotary encoder70. In the case of the sheet feeding apparatus1as illustrated inFIG. 32, the first optical sensor76is disposed on the left side of the rotary encoder70and the second optical sensor77is disposed on the lower side of the rotary encoder70.

When the first optical sensor76and the second optical sensor77are provided at intervals of about 90 degrees with respect to the center C of the rotary encoder70as described above, the rotation state, the rotation direction, and the displacement of the rotary encoder70may be detected. Since the rotary encoder60is provided to rotate integrally with the multi-feed prevention roller30, it is possible to detect the rotation state, the rotation direction, and the displacement of the multi-feed prevention roller30through the two optical sensors76and77. The two optical sensors76and77may be disposed on a bracket79provided separately from the sheet feeding apparatus1so as not to interfere with the rotation of the rotary encoder70.

Hereinafter, the operation of the sheet feeding apparatus according to an example of the present disclosure will be described with reference toFIGS. 34A to 36B.

FIG. 34Ais a view illustrating a case where a sheet feeding apparatus according to an example of the present disclosure normally feeds a sheet, andFIG. 34Bis a view illustrating signals output from a first optical sensor and a second optical sensor in the case ofFIG. 34A.

Referring toFIG. 34A, one sheet S is picked up by the pickup roller13and enters between the sheet feed roller20and the multi-feed prevention roller30. In this case, since the sheet conveyance frictional force generated between the multi-feed prevention roller30and the sheet S is larger than the threshold torque value of the magnetic torque limiter40, the multi-feed prevention roller30is rotated by the sheet feed roller20. For example, as illustrated inFIG. 34A, when the sheet feed roller20rotates in the clockwise direction, the multi-feed prevention roller30rotates in the counter-clockwise direction due to the frictional force against the sheet S and causes the sheet S to be conveyed in the sheet conveying direction (the direction of arrow A).

At this time, the two optical sensors76and77provided on one side and lower side of the rotary encoder70output pulse signals in the order of A-phase and B-phase as illustrated inFIG. 34B. For example, the first optical sensor76outputs the A-phase pulse signal, and then the second optical sensor77outputs the B-phase pulse signal delayed by t times with respect to the A-phase pulse signal. When the A-phase pulse signal and the B-phase pulse signal are output from the first and second optical sensors76and77as illustrated inFIG. 34B, the controller9determines that the sheet S is normally fed.

Next, a case where the sheet stacker10feeds two sheets S will be described with reference toFIGS. 35A and 35B.

FIG. 35Ais a view illustrating a case where two sheets are fed to a multi-feed prevention roller of a sheet feeding apparatus according to an example of the present disclosure, andFIG. 35Bis a view illustrating signals output from a first optical sensor and a second optical sensor in the case ofFIG. 35A.

Referring toFIG. 35A, two sheets S are picked up by the pickup roller13and enter between the sheet feed roller20and the multi-feed prevention roller30. In this case, since the sheet conveyance frictional force generated between the multi-feed prevention roller30and the sheet S is smaller than the threshold torque value of the magnetic torque limiter40, the multi-feed prevention roller30is not rotated by the sheet feed roller20, but is rotated by the driving source connected to the multi-feed prevention roller30. For example, as illustrated inFIG. 35A, when the sheet feed roller20rotates in the clockwise direction, the multi-feed prevention roller30is rotated in the clockwise direction by the driving source, so that the lower sheet is conveyed to the sheet cassette11of the sheet stacker10. Therefore, when the multi-feed of the sheets S occurs, the multi-feed prevention roller30rotates in a direction opposite to the rotation direction when the sheet S is normally conveyed.

At this time, the order of the pulse signals output from the two optical sensors76and77provided on one side and lower side of the rotary encoder70changes. For example, as illustrated inFIG. 35B, the pulse signals, which output in the order of A-phase and B phase from the first and second optical sensors76and77during forward rotation, changes in the order of B-phase and A-phase when the multi-feed prevention roller30rotates in the opposite direction due to the occurrence of the multi-feed of the sheets S. In detail, when the multi-feed occurs, the second optical sensor77outputs the B-phase pulse signal, and then the first optical sensor76outputs the A-phase pulse signal delayed by the t times with respect to the B-phase pulse signal. When a predetermined period of time (T1msec) elapses after the order of the A-phase pulse signal and the B-phase pulse signal is changed, the controller9may stop the sheet feed roller20and the multi-feed prevention roller30and inform the outside of the occurrence of the multi-feed of the sheet S.

Finally, a case where the sheet stacker10feeds three or more sheets S will be described with reference toFIGS. 36A and 36B.

FIG. 36Ais a view illustrating a case where three or more sheets are fed to a multi-feed prevention roller of a sheet feeding apparatus according to an example of the present disclosure, andFIG. 36Bis a view illustrating signals output from a first optical sensor and a second optical sensor in the case ofFIG. 36A.

Referring toFIG. 36A, a large number of sheets S, for example, three or more sheets S are picked up by the pickup roller13and enter between the sheet feed roller20and the multi-feed prevention roller30. In this case, since the frictional force applied to the multi-feed prevention roller30by the large number of sheets S inserted between the sheet feed roller20and the multi-feed prevention roller30is larger than the threshold torque value of the magnetic torque limiter40, the multi-feed prevention roller30rotates in conjunction with the sheet feed roller20. For example, as illustrated inFIG. 36A, when the sheet feed roller20rotates in the clockwise direction, the multi-feed prevention roller30is rotated in the sheet conveying direction (the direction of arrow A), that is, in the counter-clockwise direction by the frictional force against the large number of sheets S. At this time, since the large number of sheets S are inserted between the sheet feed roller20and the multi-feed prevention roller30, a lower side displacement amount (arrow B) in which the multi-feed prevention roller30moves downward increases. The lower side displacement B of the multi-feed prevention roller30may be detected by the two optical sensors76and77.

At this time, the two optical sensors76and77provided on one side and lower side of the rotary encoder70output pulse signals in the order of A-phase and B-phase as illustrated inFIG. 36B. The pulse interval of the A-phase pulse signal is shorter than that of the normal rotation but the pulse interval of the B-phase pulse signal is the same as that of the normal rotation. For example, when the multi-feed prevention roller30rotates in the forward direction, the first optical sensor76outputs the A-phase pulse signal, and the second optical sensor77outputs the B-phase pulse signal delayed by t times with respect to the A-phase pulse signal. At this time, the pulse interval of each of the A-phase pulse signal and the B-phase pulse signal is T1. When the large number of sheets S are inserted between the multi-feed prevention roller30and the sheet feed roller20, as illustrated inFIG. 36B, the order of the A-phase pulse signal and the B-phase pulse signal output from the first and second optical sensors76and77is the same, but the pulse interval of the A-phase pulse signal is shortened to T2(msec). However, since the second optical sensor77is disposed on the vertical line V passing through the center C of the rotary encoder70, even when the multi-feed prevention roller30moves downward, the second optical sensor77cannot detect a change in the position of the slots71of the rotary encoder70. Therefore, the second optical sensor77outputs a normal B-phase pulse signal. When the difference between the A-phase pulse signal and the B-phase pulse signal occurs, the controller9determines that the multi-feed of a large number of sheet occurs.

As another example, the frequency of the pulse signal output from each of the first optical sensor76and the second optical sensor77may be converted into a voltage to determine whether the multi-feed of a large number of sheets occurs.

FIG. 36Cis a view illustrating a case where a frequency of a pulse signal output from each of a first optical sensor and a second optical sensor is converted into a voltage in the case ofFIG. 36A.

Referring toFIG. 36C, the A phase represents that the frequency of the A-phase pulse signal ofFIG. 36Bis converted into a voltage. When the rotary encoder70rotates normally, the first optical sensor76outputs pulse signals at T1time intervals as illustrated inFIG. 36B. When the pulse signals in this case is converted into a voltage, it may be represented by a voltage of Δa as illustrated inFIG. 36C. When the multi-feed of a large number of sheets occurs, the first optical sensor76outputs pulse signals at T2time intervals as illustrated inFIG. 36Bso that the number of pulses increases. When the frequency of the pulse signal in this case is converted into a voltage, it may be shown that the voltage is increased by Δb as in the portion K inFIG. 36C. Therefore, when the multi-feed of a large number of sheets occurs, the voltage of the A phase pulse signal becomes Δa+Δb.

When the multi-feed of a large number of sheets occurs, the B-phase pulse signal output from the second optical sensor77does not change as illustrated inFIG. 36B. Therefore, when the frequency of the pulse signal in this case is converted into a voltage, it may be represented by a voltage of Δa as illustrated inFIG. 36C.

Accordingly, in the case where the frequency of the pulse signal output from each of the first optical sensor76and the second optical sensor77is converted into a voltage, when the voltage difference between the output signals of the first optical sensor76and the second optical sensor77is Δb, the controller9may determine that the multi-feed of a large number of sheets occurs.

In the above description, the sheet feeding apparatus includes the active multi-feed prevention roller configured to be rotatable by the driving source as the multi-feed prevention roller. However, the sheet feeding apparatus may use a semi-active multi-feed prevention roller configured not to receive the power from the driving source as the multi-feed prevention roller, and its operation is similar to the above-described example. Therefore, a detailed description thereof is omitted.

As described above, the sheet feeding apparatus according to an example of the present disclosure can detect the rotation state, the rotation direction, and the downward displacement of the multi-feed prevention roller by using the magnetic torque limiter and the hall sensor provided on one side of the multi-feed prevention roller. Therefore, the multi-feed of the sheets may be reliably detected with a simple configuration.

Further, the sheet feeding apparatus according to an example of the present disclosure can detect the rotation state, the rotation direction, and the downward displacement of the multi-feed prevention roller by using the rotary encoder and the optical sensors provided on one side of the multi-feed prevention roller. Therefore, the multi-feed of the sheets may be reliably detected with a simple configuration. Accordingly, with an example of the present disclosure, it is possible to provide a sheet feeding apparatus having a low-cost, small-sized, and highly reliable multi-feed detecting function.

In addition, the sheet feeding apparatus according to an example of the present disclosure automatically returns the sheets positioned between the sheet feed roller and the multi-feed prevention roller to the sheet stacker and then performs the sheet feeding operation again. Therefore, the operation ratio of the sheet feeding apparatus according to an example of the present disclosure may be improved.

In the above description, the sheet feeding apparatus according to an example of the present disclosure is applied to an image forming apparatus. However, the sheet feeding apparatus according to an example of the present disclosure is not limited thereto. The sheet feeding apparatus according to an example of the present disclosure may be used for facsimile, an automatic document scanning apparatus, a large capacity paper feeding apparatus, and the like in which a large amount of sheets need to be fed.

While the examples of the present disclosure have been described, additional variations and modifications of the examples may occur to those skilled in the art once they learn of the basic inventive concepts.

Therefore, it is intended that the appended claims shall be construed to include both the above examples and all such variations and modifications that fall within the spirit and scope of the inventive concepts.