WO2021183245A1

WO2021183245A1 - Structure for compensating driving force of roller under load torque

Info

Publication number: WO2021183245A1
Application number: PCT/US2021/017168
Authority: WO
Inventors: Jangwon Seo; Hojun JANG; Junghoon Lee
Original assignee: Hewlett-Packard Development Company, L.P.
Priority date: 2020-03-13
Filing date: 2021-02-09
Publication date: 2021-09-16
Also published as: KR20210116744A

Abstract

An example paper transfer device includes first and second transfer rollers, first and second driving sources to generate first and second driving forces for rotationally driving the first and second transfer rollers, first and second power transmission structures to transmit the first and second driving forces to the first and second transfer rollers, and an optional power transmission structure to optionally connect between the first power transmission structure and the second power transmission structure and to optionally transmit the second driving force to the first transfer roller, based on a rotation speed of the first transfer roller.

Description

STRUCTURE FOR COMPENSATING DRIVING FORCE OF ROLLER UNDER

LOAD TORQUE

BACKGROUND

[0001] A printing medium transfer device, for transferring or conveying paper, may be embedded in an image forming apparatus, such as a copier, a printer, a scanner, a facsimile machine, or the like. The printing medium transfer device may include a pair of transfer rollers, which are positioned to face each other and rotate. As the pair of transfer rollers rotate at a certain rotation speed, printing medium inserted therebetween may be provided for an image forming process.

BRIEF DESCRIPTION OF THE DRAWINGS

[0002] FIG. 1 is a schematic perspective view of a paper transfer device according to an example.

[0003] FIG. 2 is a schematic plan view of the paper transfer device shown in FIG. 1 according to an example.

[0004] FIG. 3 is a view for describing an operation of a first transfer roller and a second transfer roller according to an example.

[0005] FIG. 4 is a view for describing a state in which a load torque is concentrated on some transfer rollers according to an example.

[0006] FIG. 5 is an enlarged perspective view of a part of the paper transfer device of FIG. 1 according to an example.

[0007] FIG. 6 is a side view of a part of the paper transfer device of FIG. 1 according to an example.

[0008] FIG. 7 is a cross-sectional view of the paper transfer device taken along line VII-VII of FIG. 5 according to an example.

[0009] FIG. 8 is a view for describing an operation of a one-way bearing in the paper transfer device of FIG. 5 according to an example.

[0010] FIG. 9 is a view for describing an optional power transmission structure according to an example.

[0011] FIG. 10 is a view for describing a scanner device in which a paper transfer device is employed according to an example.

[0012] FIG. 11 is a schematic view of an image forming apparatus in which a paper transfer device is employed according to an example.

[0013] FIG. 12 is a schematic view of a multi-function device according to an example.

DETAILED DESCRIPTION OF EXAMPLES

[0014] hereinafter, examples of a printing medium transfer device will be described with reference to the drawings. Like reference numerals in the drawings represent like elements, and the size or thickness of each element may be exaggerated for clarity.

[0015] A printing medium transfer device may include a pair of transfer rollers that are positioned to face each other and rotate. As the pair of transfer rollers rotate at a certain rotation speed, a printing medium, such as paper, inserted therebetween is transferred at a certain speed.

[0016] The state of the printing medium used in the printing medium transfer device may vary due to various causes, such as a user’s selection or a change in surrounding environmental factors. Examples of a changed state of the printing medium may include a different thickness of the printing medium, a different material of the printing medium, a different surface frictional force of the printing medium, or the like.

[0017] When the state of the printing medium is changed, an unintended load torque may act on any one of the pair of transfer rollers. The load torque may be transmitted to a driving source that rotates the transfer rollers. Thus, the rotation speed of the transfer rollers may be reduced. This can change the printing medium transfer speed of the printing medium transfer device. That is, the constant speed of the printing medium transfer device can be reduced.

[0018] In the following description, a printing medium transfer device may be described as a “paper transfer device” for convenience. Flowever, the described examples are not limited in application to paper but are applicable to other types of printing medium.

[0019] FIG. 1 is a schematic perspective view of a paper transfer device 1 according to an example, FIG. 2 is a schematic plan view of the paper transfer device 1 shown in FIG. 1 according to an example, and FIG. 3 is a view for describing an operation of a first transfer roller 11 and a second transfer roller 12 according to an example.

[0020] The paper transfer device 1 is a device for transferring paper P. The paper transfer device 1 may include the first transfer roller 11 and the second transfer roller 12. The paper transfer device 1 may further include a pickup member 13 (e.g., a pickup roller).

[0021] An example in which the paper transfer device 1 is a paper feeding device for feeding the paper P positioned on a loading table 10 will be mainly described. Flowever, the paper transfer device 1 is not limited thereto, and in addition to a paper feeding device, any device for transferring the paper P may be applied to various parts or devices.

[0022] The pickup member 13 may be in contact with, for example, a first paper P positioned at the top of the paper P loaded on the loading table 10. The pickup member 13 may be in the form of a roller, but is not limited thereto, and may be in various forms such as a belt form.

[0023] When the pickup member 13 is rotated, the first paper P may be drawn from the loading table 10. The first paper P picked up by the pickup member 13 may be transferred by the first transfer roller 11 and the second transfer roller 12.

[0024] When the pickup member 13 is rotated, in some cases, the first paper P and one or more additional sheets of paper P positioned thereunder may be drawn together. This is referred to as multi-feeding.

[0025] The paper transfer device 1 may function as a separation device. For example, when multi-feeding occurs, the paper transfer device 1 may separate one sheet of paper, for example, paper P1 alone, and may transfer the paper P1 in a drawing direction A1 .

[0026] The second transfer roller 12 may include a feed roller to transfer the paper P1 in the drawing direction A1. The first transfer roller 11 may include a retard roller that is in contact with the second transfer roller 12 while facing the second transfer roller 12. The second transfer roller 12 and the first transfer roller 11 may be rotated in engagement with each other. The second transfer roller 12 may be rotated in a first direction B1 in which the paper P1 is transferred in the drawing direction A1. The first transfer roller 11 may be rotated in a second direction B2 in which paper P2 is transferred in an opposite direction A2 to the drawing direction A1 .

[0027] For rotation of the first transfer roller 11 in the second direction B2, the first transfer roller 11 may be connected to a first driving source 21. For rotation of the second transfer roller 12 in the first direction B1 , the second transfer roller 12 may be connected to a second driving source 22.

[0028] A first driving force of the first driving source 21 may be transmitted to the first transfer roller 11 by using a first power transmission structure 31 , and a second driving force of the second driving source 22 may be transmitted to the second transfer roller 12 by using a second power transmission structure 32. [0029] The first driving source 21 may be a direct current (DC) motor having a speed that varies according to a change in the magnitude of a certain load torque when the certain load torque is applied to the first power transmission structure 31 . For example, when the load torque applied to the first transfer roller 11 is transmitted to the first driving source 21 through the first power transmission structure 31 , the first driving source 21 may be a DC motor having a speed that varies according to the magnitude of the load torque. The first driving source 21 may be a DC motor capable of being rotated even when a certain load torque is applied to the first driving source 21 . For example, the first driving source 21 may be a brush DC motor or brushless DC motor.

[0030] A first detection unit 25 to detect a rotation speed may be coupled with the first driving source 21. The first detection unit 25 may be an encoder. Flowever, the first detection unit 25 is not limited thereto and may be variously modified for detection of the rotation speed.

[0031] The first detection unit 25 may detect the rotation speed of the first driving source 21 and may transmit the detected rotation speed to a controller 27. The controller 27 may control a voltage or current supplied to the first driving source 21 considering a change in the speed of the first driving source 21 , so that compensation may be made for the change in the speed of the first driving source 21 . For example, when the speed of the first driving source 21 is reduced as the load torque applied to the first driving source 21 increases, the controller 27 may increase a voltage applied to the first driving source 21 , thereby increasing the speed of the first driving source 21.

[0032] The second driving source 22 may be a motor having a speed that varies according to a change in a certain load torque when the certain load torque is applied to the second power transmission structure 32. The second driving source 22 may be a DC motor capable of being rotated even when a certain load torque is applied to the second driving source 22. For example, the second driving source 22 may be a brush DC motor or brushless DC motor.

[0033] A second detection unit 26 to detect a rotation speed may be coupled with the second driving source 22. The second detection unit 26 may be an encoder. Flowever, the second detection unit 26 is not limited thereto and may be variously modified for detection of the rotation speed.

[0034] The second detection unit 26 may detect the rotation speed of the second driving source 22 and may transmit the detected rotation speed to the controller 27. The controller 27 may control a voltage or current supplied to the second driving source 22 considering a change in the speed of the second driving source 22, so that compensation may be made for the change in the speed of the second driving source 22.

[0035] A torque limiter 111 may provide a threshold torque at which the first transfer roller 11 begins a driven rotation by the second transfer roller 12. That is, the torque limiter 111 may optionally allow a driven rotation of the first transfer roller 11 by the second transfer roller 12 according to the magnitude of the load torque acting on the first transfer roller 11. When the load torque applied to the first transfer roller 11 exceeds the threshold torque provided by the torque limiter 111 , a first driving force in the second direction B2 transmitted to the first transfer roller 11 may be blocked, and the first transfer roller 11 may be allowed to be driven-rotated in a third direction B3 by the second transfer roller 12. When the load torque applied to the first transfer roller 11 is less than the threshold torque provided by the torque limiter 111 , the first transfer roller 11 may be rotated by the first driving force in the second direction B2.

[0036] An example of a separation operation by the first transfer roller 11 and the second transfer roller 12 will be briefly described.

[0037] Referring to FIG. 3, when there is no paper P between the second transfer roller 12 and the first transfer roller 11 or one sheet of paper P alone is supplied therebetween, the load torque applied to the first transfer roller 11 may be greater than the threshold torque of the torque limiter 111. In that case, a driving force applied to the first transfer roller 11 may be blocked by the torque limiter 111. Thus, the first transfer roller 11 may be rotated in the third direction B3 in which the paper P is transferred in the drawing direction A1 together with the second transfer roller 12.

[0038] When two or more sheets of paper P, i.e., paper P1 and paper P2, are supplied between the second transfer roller 12 and the first transfer roller 11 , the paper P1 and the paper P2 may be in contact with the second transfer roller 12 and the first transfer roller 11 , respectively. In that case, a frictional force between the paper P1 and the paper P2 may be less than a frictional force between the paper P2 and the first transfer roller 11. Thus, a slip may occur between the paper P1 and the paper P2. The load torque that acts on the first transfer roller 11 may be less than the threshold torque provided by the torque limiter 111. The first transfer roller 11 may be rotated in the second direction B2, and the paper P2 may be transferred by the first transfer roller 11 in the opposite direction A2 to the drawing direction A1. Thus, the paper P1 alone may pass between the second transfer roller 12 and the first transfer roller 11 and may be transferred in the drawing direction A1.

[0039] When two or more sheets of paper are supplied between the second transfer roller 12 and the first transfer roller 11 , the second transfer roller 12 may be rotated by the second driving source 22 in the first direction B1 , and the first transfer roller 11 may be rotated by the first driving source 21 in the second direction B2.

[0040] Referring again to FIGS. 1 and 2, the second transfer roller 12 may be connected to the second driving source 22 by the second power transmission structure 32, and the first transfer roller 11 may be connected to the first driving source 21 by the first power transmission structure 31 .

[0041] The first power transmission structure 31 may include at least one first rotating member (e.g., 310 of FIG. 6). The second power transmission structure 32 may include at least one second rotating member (e.g., 320 of FIG. 5).

[0042] The first power transmission structure 31 and the second power transmission structure 32 may have a structure in which at least parts thereof are connected to each other by a belt transmission method.

[0043] The first power transmission structure 31 may include a plurality of pulleys 311 (e.g., 311 A, 311 B, 311 C, and 311 D) that may be rotated in association with rotation of the first driving source 21 , and belts 312 (e.g., 312A and 312B) that may be wound on at least a part of the plurality of pulleys 311. A first rotating member 310 may be any one of the pulleys 311 A, 311 B, 311 C, and 311 D or the belts 312A and 312B. For example, the first rotating member 310 may be the pulley 311 C.

[0044] In order to stably transmit a driving force, a plurality of protrusions may be arranged on outer circumferential surfaces of the pulleys 311 of the first power transmission structure 31 , and a plurality of grooves into which the plurality of protrusions are insertable may be arranged in inner surfaces of the belts 312 of the first power transmission structure 31 .

[0045] The second power transmission structure 32 may include a plurality of pulleys 321 that may be rotated in association with rotation of the second driving source 22, a belt 322 that may be wound on at least a part of the plurality of pulleys 321 , and a rotation shaft 323 that rotatably supports at least one of the plurality of pulleys 321 and extends in a direction perpendicular to a drawing direction of paper (e.g., P1 ). The second rotating member 320 may be any one of the pulleys 321 , the belt 322, or the rotation shaft 323. For example, the second rotating member 320 may be the rotation shaft 323.

[0046] In order to stably transmit a driving force, a plurality of protrusions may be arranged on outer circumferential surfaces of the pulleys 321 of the second power transmission structure 32, and a plurality of grooves into which a plurality of protrusions are insertable may be arranged on an inner surface of the belt 322 of the second power transmission structure 32.

[0047] The first and second power transmission structures 31 and 32 are not limited to the above described example. When a different power transmission method, for example, a chain transmission method, a friction transmission method, a gear transmission method, or the like, is applied to the first and second power transmission structures 31 and 32, the first and second power transmission structures 31 and 32 may be accordingly changed to a different configuration or may further include the different configuration.

[0048] The second power transmission structure 32 may transmit a part of the second driving force to a different transferring roller 15. For example, the second power transmission structure 32 may transmit the second driving force to the different transferring roller 15 through an additional pulley 325 and an additional belt 326.

[0049] Through the above-described example, the first driving source 21 may rotate the first transfer roller 11 in the second direction B2, and the second driving source 22 may rotate the second transfer roller 12 and the different transferring roller 15 in the first direction B1. Thus, some paper P1 may be transferred by the second transfer roller 12 and the different transferring roller 15 in the drawing direction A1 , and some other paper P2 may be transferred by the first transfer roller 11 in the opposite direction A2 to the drawing direction A1 . [0050] However, while the paper P may be transferred by the transfer rollers in the drawing direction A1 or the opposite direction A2 to the drawing direction A1 , a load torque may be unintentionally concentrated on some of the transfer rollers.

[0051] FIG. 4 is a view for describing a state in which a load torque is concentrated on some transfer rollers according to an example.

[0052] Referring to FIG. 4, when the state of the paper P2, such as the thickness, material, surface frictional force, or the like of the paper P2, differs from the state of the previous paper P 1 , a large load torque may be unintentionally applied to the first transfer roller 11 that is in contact with the paper P2. Thus, the rotation speed of the first transfer roller 11 may be at least temporarily reduced. In other words, even when the rotation speed of the first transfer roller 11 is managed by the controller 27, the rotation speed of the first transfer roller 11 may be temporally reduced due to an unintended load torque while departing from a range of a reference speed. In this case, the load torque applied to the second transfer roller 12 may be less than the load torque applied to the first transfer roller 11.

[0053] The paper transfer device 1 may have a structure in which a reduction of the rotation speed of the first transfer roller 11 due to the unintended load torque is minimized, by using the driving force for driving the second transfer roller 12 having a relatively small speed reduction.

[0054] The paper transfer device 1 may further include an optional power transmission structure 100 for connecting the first transfer roller 11 to the second driving source 22.

[0055] The optional power transmission structure 100 may prevent a reduction of the rotation speed of the first transfer roller 11 by using a mechanical structure when the rotation speed of the first transfer roller 11 is about to be lower than a certain reference speed.

[0056] FIG. 5 is an enlarged perspective view of a part of the paper transfer device 1 of FIG. 1 according to an example, FIG. 6 is a side view of a part of the paper transfer device 1 of FIG. 1 according to an example, and FIG. 7 is a cross- sectional view of the paper transfer device taken along line VII-VII of FIG. 5 according to an example.

[0057] Referring to FIGS. 5 and 6, the optional power transmission structure 100 may optionally connect between the first power transmission structure 31 and the second power transmission structure 32 and optionally transmit the second driving force to the first transfer roller 11 , based on the rotation speed of the first transfer roller 11 .

[0058] The optional power transmission structure 100 may include a connecting rotating member 110 that rotates in association with the first power transmission structure 31 , and a one-way bearing 130 arranged between the connecting rotating member 110 and the second power transmission structure 32. [0059] The connecting rotating member 110 may rotate in association with the first rotating member 310. The one-way bearing 130 may be arranged between the connecting rotating member 110 and the second rotating member 320.

[0060] The one-way bearing 130 may allow rotation of the connecting rotating member 110 relative to the second rotating member 320 when the rotation speed of the connecting rotating member 110 is greater than the speed of the second rotating member 320.

[0061] When the rotation speed of the connecting rotating member 110 is less than the speed of the second rotating member 320, the one-way bearing 130 may block rotation of the connecting rotating member 110 relative to the second rotating member 320. As rotation of the connecting rotating member 110 relative to the second rotating member 320 is blocked, the connecting rotating member 110 may be rotated by the second rotating member 320, and a part of the second driving force may be transmitted to the first power transmission structure 31 . [0062] The connecting rotating member 110 may include a first connecting rotating member 116 that interlocks with the pulleys 311 B and 311 C of the first power transmission structure 31 , and a second connecting rotating member 112 coupled to the first connecting rotating member 116 by a connecting member 113. [0063] The second connecting rotating member 112 may be installed on the rotation shaft 323 of the second power transmission structure 32 by using the one-way bearing 130.

[0064] The first connecting rotating member 116 and the second connecting rotating member 112 may be in the form of a pulley, and the connecting member 113 may be in the form of a belt. In an example, the first connecting rotating member 116 and the second connecting rotating member 112 may be pulleys having outer circumferential surfaces on which a plurality of protrusions are formed, and the connecting member 113 may be a belt having an inner surface in which a plurality of grooves are formed.

[0065] The first connecting rotating member 116 may be arranged to be coaxially fixed to at least one of the pulleys 311 of the first power transmission structure 31 . The first connecting rotating member 116 and the pulleys 311 B and 311C of the first power transmission structure 31 may be rotated together.

[0066] The second connecting rotating member 112 may be coaxially arranged on at least one pulley 321 B of the pulleys 321 of the second power transmission structure 32. For example, the second connecting rotating member 112 may be coaxially arranged on the pulley 321 B of the second power transmission structure 32 through the rotation shaft 323 of the second power transmission structure 32.

[0067] To prevent a slip between the rotation shaft 323 of the second power transmission structure 32 and the pulley 321 B of the second power transmission structure 32, a cross-sectional shape of the rotation shaft 323 and an insertion hole of the pulley 321 B into which the rotation shaft 323 is inserted may not have a circular shape. For example, as shown in FIG. 7, the cross- sectional shape of the rotation shaft 323 and the insertion hole of the pulley 321 B may have a D-shape.

[0068] The one-way bearing 130 may prevent the rotation speed of the second connecting rotating member 112 from being less than the rotation speed of the rotation shaft 323. The second driving force may be optionally transmitted to the first power transmission structure 31 according to the relationship between the rotation speed of the second connecting rotating member 112 and the rotation speed of the rotation shaft 323. In a normal state, i.e. , when an unintended load torque does not act on the first driving source 21 , the rotation speed of the second connecting rotating member 112 that rotates in association with the first driving source 21 may be set to be greater than the rotation speed of the rotation shaft 323.

[0069] FIG. 8 is a view for describing an operation of the one-way bearing 130 in the paper transfer device 1 of FIG. 5 according to an example. FIG. 9 is a view for describing an optional power transmission structure according to an example.

[0070] Referring to FIG. 8, the one-way bearing 130 may be installed in the second connecting rotating member 112 so as to be rotatable in one direction (e.g., A direction) and to be not rotatable in an opposite direction (e.g., B direction). By using the one-way bearing 130, the second driving force for rotating the rotation shaft 323 may be optionally transmitted to the second connecting rotating member 112.

[0071] When a rotation speed V11 of the second connecting rotating member 112 is greater than a rotation speed V2 of the rotation shaft 323, the second connecting rotating member 112 may allow a force to act on the rotation shaft 323 in the one direction (e.g., A direction). In this case, because the one way bearing 130 is rotatable in the one direction (e.g., A direction), the second connecting rotating member 112 and the rotation shaft 323 may rotate according to each of the rotation speeds V11 and V2.

[0072] On the other hand, when the rotation speed V11 of the second connecting rotating member 112 is reduced and is less than the rotation speed V2 of the rotation shaft 323, the second connecting rotating member 112 may allow a force to act on the rotation shaft 323 in an opposite direction (e.g., B direction). In this way, because the one-way bearing 130 does not allow rotation in the opposite direction (e.g., B direction), driving force transmission occurs between the rotation shaft 323 and the second connecting rotating member 112. When the second driving force for rotating the rotation shaft 323 is greater than a force transmitted through the second connecting rotating member 112, the second connecting rotating member 112 rotates together with the rotation shaft 323. That is, the second connecting rotating member 112 rotates in a same direction and at a same speed as the rotation shaft 323.

[0073] The second driving force transmitted to the second connecting rotating member 112 is transmitted to the first transfer roller 11 . In this way, the first transfer roller 11 on which the load torque is relatively concentrated may be connected to a driving source having a higher speed among the first driving source 21 and the second driving source 22 through the optional power transmission structure 100 having a mechanical configuration.

[0074] Thus, by the second driving force transmitted to the first power transmission structure 31 , the unintended load torque that acts on the first transfer roller 11 may be offset to some extent, and compensation may be made for the lowering of the speed of the first transfer roller 11. That is, through the optional power transmission structure 100 having a mechanical configuration, the paper transfer device 1 may prevent the rotation speed of the first transfer roller 11 from being reduced to a level less than the reference speed. The paper transfer device 1 may implement uniform paper transfer without installation of an additional motor or complex firmware.

[0075] In the above-described example, a case in which the optional power transmission structure 100 is connected to the first power transmission structure 31 by the first and second connecting rotating members 116 and 112 and the connecting member 113 has been mainly described. However, the optional power transmission structure 100 may be variously modified to have any structure in which power transmission between the first power transmission structure 31 and the second power transmission structure 32 is optionally performed. For example, as shown in FIG. 9, the optional power transmission structure 100 may be connected to the first power transmission structure 31 without the first connecting rotating member 116 and the connecting member 113, and the second connecting rotating member 112 installed on the rotation shaft 323 may be connected to the first power transmission structure 31 by a different connecting member 114. [0076] In the above-described example, a case in which the one-way bearing 130 is installed between the second connecting rotating member 112 and the rotation shaft 323 has been mainly described. However, the arrangement of the one-way bearing 130 is not limited thereto, and may be variously applied as necessary. Although not shown, unlike in the above-described example, the one way bearing 130 may be arranged on the first connecting rotating member 116, and the second connecting rotating member 112 may be coaxially fixed to the rotation shaft 323. In this case, power transmission between the first connecting rotating member 116 and the first power transmission structure 31 may optionally occur according to the speed of the first connecting rotating member 116.

[0077] FIG. 10 is a view for describing a scanner device 600 in which the paper transfer device 1 is employed according to an example.

[0078] Referring to FIG. 10, the scanner device 600 may include a medium processing unit to read an image while transferring the paper P supplied from a paper feeding device, to which the paper transfer device 1 is applied.

[0079] The medium processing unit may include a paper transfer unit 600a and a reading unit 600b to read an image from paper P. The paper transfer device 1 described in FIGS. 1 through 9 may be employed as the paper transfer device 1 . Because the scanner device 600 is a device for reading an image recorded on the paper P, the paper transfer device 1 may transfer the paper P.

[0080] A reading member 650 for reading an image from the paper P may be arranged on the reading unit 600b. The reading member 650 may irradiate light on the paper P, may receive light reflected from the paper P, and may read an image of the paper P. For example, a contact type image sensor (CIS), a charge coupled device (CCD), or the like may be employed as the reading member 650.

[0081] A flatbed method, whereby the paper P is positioned at a fixed position and for example, the reading member 650, such as a CIS or CCD, is moved to read an image, a document feed method, whereby the reading member 650 is positioned at a fixed position and the paper P is transferred, and a complex method thereof may be used in the scanner device 600. The scanner device 600 according to the illustrated example is a complex type scanner device in which the flatbed method and the document feed method are combined.

[0082] A platen glass 660, on which the paper P is positioned, may be provided on the reading unit 600b so as to read an image from the paper P by using the flatbed method. Also, a reading window 670 for reading an image from the paper P may be provided on the reading unit 600b by using the document feed method. The reading window 670 may be a transparent member, for example. In an example, a top surface of the reading window 670 may be a surface having a same height as that of a top surface of the platen glass 660. [0083] When the document feed method is applied, the reading member 650 may be positioned under the reading window 670. When the flatbed method is applied, the reading member 650 may be moved from a lower portion of the platen glass 660 in a sub-scanning direction S, i.e. , a lengthwise direction of the paper P by using a moving unit (not shown). Also, when the flatbed method is applied, the platen glass 660 may be exposed to the outside so that the paper P may be positioned on the platen glass 660. To this end, the paper transfer unit 600a may be rotated relative to the reading unit 600b so as to expose the platen glass 660.

[0084] The paper transfer unit 600a may transfer the paper P so that the reading member 650 may read an image recorded on the paper P and may discharge the paper P that has been read. To this end, a paper transfer path 610 may be provided on the paper transfer unit 600a, and the reading member 650 may read an image from the paper P transferred along the paper transfer path 610. The paper transfer path 610 may include a supply path 611 , a reading path 612, and a discharge path 613, for example. The reading member 650 may be arranged on the reading path 612, and while the reading member 650 passes through the reading path 612, the image recorded on the paper P may be read by the reading member 650. The supply path 611 may be a path on which the paper P is supplied to the reading path 612. The paper P loaded on the loading table 10 may be supplied to the reading path 612 via the supply path 611. The discharge path 613 may be a path on which the paper P passing through the reading path 612 is discharged. Thus, the paper P loaded on the loading table 10 may be transferred along the supply path 611 , the reading path 612, and the discharge path 613, and may be discharged to a discharge tray 630.

[0085] Transfer rollers 621 and 622 may be arranged on the paper transfer path 610 so as to transfer the paper P drawn from the loading table 10 by using the paper transfer device 1 . Each of the transfer rollers 621 and 622 may have a structure in which a driving roller and a driven roller are engaged with each other so as to rotate.

[0086] Transfer rollers 623 and 626 for transferring the paper P may be arranged on the reading path 612. For example, the transfer rollers 623 and 626 for transferring the paper P may be arranged on both sides of the reading member 650. Each of the transfer rollers 623 and 626 may have a structure in which a driving roller and a driven roller are engaged with each other so as to rotate. A reading guide member 624 facing the reading member 650 may be arranged on the reading path 612. The reading guide member 624 may be pressed by gravity toward the reading window 670 or an elastic member 625 may press the reading guide member 624 toward the reading window 670. The paper P may be transferred between the reading window 670 and the reading guide member 624. Although not shown, the reading window 670, instead of the reading guide member 624, may be elastically pressed and rotated, and a reading roller for transferring the paper P supplied therebetween may also be employed.

[0087] A discharge roller 627 for discharging the paper P that has been read may be arranged on the discharge path 613. The discharge roller 627 may have a structure in which a driving roller and a driven roller are engaged with each other so as to rotate.

[0088] Through this configuration, the paper P supplied from the paper transfer device 1 may be transferred along the supply path 611 , the reading path 612, and the discharge path 613, and the reading member 650 may read an image from the paper P.

[0089] FIG. 11 is a schematic view of an image forming apparatus 700 in which the paper transfer device 1 is employed according to an example.

[0090] Referring to FIG. 11 , the image forming apparatus 700 may include a printing unit (e.g., a medium processing unit) 700a for printing an image on a paper P supplied from a paper feeding device. As shown by solid lines in FIG. 11 , the paper feeding device may be positioned under the printing unit 700a in the form of a cassette feeding device 1 b in which the paper transfer device 1 is employed. Also, as shown in by dotted lines in FIG. 11 , the paper transfer device 1 may be applied to a multi-purpose tray (MPT) 1c positioned at one side of the printing unit 700a.

[0091] The printing unit 700a may print an image on the paper P by using various methods, such as an electrophotographic method, an inkjet method, a thermal transfer method, a heat sublimation method, and the like. The image forming apparatus 700 may print a color image on the paper P by using an electrophotographic method. Referring to FIG. 14 the printing unit 700a may include a plurality of developing units 710, an exposure unit 720, a transfer unit, and a fusing unit 740.

[0092] For color printing, the plurality of developing units 710 may include four developing units 710 for developing color images of cyan (C), magenta (M), yellow (Y), and black (K), for example. Toners of C, M, Y, and K may be respectively accommodated in the four developing units 710. The printing unit 700a may further include a developing unit 710 for accommodating and developing toners of various colors, such as light magenta, black, and the like in addition to the above-described colors.

[0093] The developing unit 710 may include a photoconductive drum 7a. The photoconductive drum 7a is an example of a photoconductor having a surface on which an electrostatic latent image may be formed and may include a conductive metallic pipe and a photoconductive layer formed on an outer circumference of the conductive metallic pipe. A charging roller 7c is an example of a charger for charging the photoconductive drum 7a to have a uniform surface electric potential. A cleaning blade 7d is an example of a cleaning unit for removing a residual toner and foreign substances from the surface of the photoconductive drum 7a after a transfer process that will be described below is performed.

[0094] The developing unit 710 may supply toner accommodated therein to the electrostatic latent image formed on the photoconductive drum 7a and may develop the electrostatic latent image into a visible toner image. As a developing method, there are a one-component developing method using a toner and a two- component developing method using a toner and a carrier. In the illustrated example, the developing unit 710 employs a one-component developing method. A developing roller 7b is used to supply the toner to the photoconductive drum 7a. A developing bias voltage for supplying the toner to the photoconductive drum 7a may be applied to the developing roller 7b.

[0095] The one-component developing method may be classified into a contact developing method, whereby the developing roller 7b and the photoconductive drum 7a are in contact with each other and rotate, and a non- contact developing method, whereby the developing roller 7b and the photoconductive drum 7a are apart from each other by several tens or several hundreds of microns and rotate. A supply roller 7e may supply toner in the developing unit 710 to the surface of the developing roller 7b. A supply bias voltage for supplying the toner in the developing unit 710 to the surface of the developing roller 7b may be applied to the supply roller 7e.

[0096] The exposure unit 720 may irradiate light modulated in correspondence with image information on the photoconductive drum 7a so as to form an electrostatic latent image on the photoconductive drum 7a. A laser scanning unit (LSU) using a laser diode as a light source, a light emitting diode (LED) exposure unit using an LED as a light source, and the like may be employed as the exposure unit 720.

[0097] The transfer unit may include an intermediate transfer belt 731 , a primary transfer roller 732, and a secondary transfer roller 733. The toner images developed on the photoconductive drum 7a of the four developing units 710 may be temporarily transferred on the intermediate transfer belt 731 . The intermediate transfer belt 731 may be supported by support rollers 734, 735, and 736 so as to circulate. Four primary transfer rollers 732 may be arranged to face the photoconductive drum 7a of four developing units 710 with the intermediate transfer belt 731 therebetween. A primary transfer bias voltage for primarily transferring a toner image developed on the photoconductive drum 7a onto the intermediate transfer belt 731 may be applied to the four primary transfer rollers 732. The secondary transfer roller 733 may face the intermediate transfer belt 731. A secondary transfer bias voltage for transferring the primarily-transferred toner image onto the intermediate transfer belt 731 onto the paper P may be applied to the secondary transfer roller 733.

[0098] When a printing command is received from a host (not shown), a controller (not shown) may charge the surface of the photoconductive drum 7a to a uniform electric potential by using the charging roller 7c. The exposure unit 720 may scan four light beams modulated according to image information of colors on the photoconductive drum 7a of the four developing units 710 so as to form an electrostatic latent image on the photoconductive drum 7a. The developing roller 7b may supply C, M, Y, and K toners to the corresponding photoconductive drum 7a and may develop an electrostatic latent image into a visible toner image. The developed toner images may be primarily transferred onto the intermediate transfer belt 731. The paper P from the paper feeding device 1 b or 1c may be transferred to a transfer nip formed by the secondary transfer roller 733 and the intermediate transfer belt 731 . The primarily-transferred toner images onto the intermediate transfer belt 731 may be secondarily transferred onto the paper P by the secondary transfer bias voltage applied to the secondary transfer roller 733. When the paper P passes through the fusing unit 740, the toner images may be fused on the paper P by heat and pressure. The paper P that has been fused may be discharged to the outside by the discharge roller 750.

[0099] The scanner device 600 and the image forming apparatus 700 may be separately used or may be used in the form of a multi-function device in which the scanner device 600 and the image forming apparatus 700 are combined with each other.

[00100] FIG. 12 is a schematic view of a multi-function device according to an example.

[00101] Referring to FIG. 12, a scanner device 600 may be arranged above a printing unit 700a. An example structure of the scanner device 600 and the printing unit 700a is as shown in FIGS. 10 and 11. The paper transfer device 1 for supplying the paper P to the printing unit 700a may be implemented in various forms. For example, the examples of the paper transfer device 1 shown in FIGS.

1 through 9 may be applied to the MPT positioned at the side of the printing unit 700a, as shown in FIG. 11 , and a main cassette feeder 810 installed under the printing unit 700a, a secondary cassette feeder 820 installed under the main cassette feeder 810, a high capacity feeder 830 installed under the main cassette feeder 810 or under the secondary cassette feeder 820, or a high capacity feeder 840 installed at the side of the printing unit 700a, as shown in FIG. 12.

[00102] In the above-described examples, an example in which a paper transfer device is applied to a paper feeding device has been mainly described. Flowever, the paper transfer device is not limited thereto and may be variously applied to any device for transferring paper in addition to the paper feeding device. [00103] It should be understood that examples described herein should be considered in a descriptive sense only and not for purposes of limitation. Descriptions of features or aspects within each example should typically be considered as available for other similar features or aspects in other examples. While one or more examples have been described with reference to the figures, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope as defined by the following claims.

Claims

WHAT IS CLAIMED IS:

1 . A paper transfer device comprising: a first transfer roller; a second transfer roller; a first driving source to generate a first driving force for rotationally driving the first transfer roller; a second driving source to generate a second driving force for rotationally driving the second transfer roller; a first power transmission structure to transmit the first driving force to the first transfer roller; a second power transmission structure to transmit the second driving force to the second transfer roller; and an optional power transmission structure to optionally connect between the first power transmission structure and the second power transmission structure and to optionally transmit the second driving force to the first transfer roller, based on a rotation speed of the first transfer roller.

2. The paper transfer device of claim 1 , wherein the first power transmission structure comprises at least one first rotating member, wherein the second power transmission structure comprises at least one second rotating member, and wherein the optional power transmission structure comprises a connecting rotating member to rotate in association with the first rotating member and a one way bearing arranged between the connecting rotating member and the second rotating member.

3. The paper transfer device of claim 2, wherein, when a rotation speed of the connecting rotating member is greater than a speed of the second rotating member, the one-way bearing allows rotation of the connecting rotating member relative to the second rotating member, and wherein, when a rotation speed of the connecting rotating member is less than a speed of the second rotating member, the one-way bearing prevents rotation of the connecting rotating member relative to the second rotating member.

4. The paper transfer device of claim 3, wherein, when a rotation speed of the connecting rotating member is less than a speed of the second rotating member, the connecting rotating member is rotated by the second rotating member and a part of the second driving force is transmitted to the first power transmission structure.

5. The paper transfer device of claim 2, wherein the second power transmission structure comprises: a plurality of pulleys to be rotated in association with rotation of the second driving source; a belt wound on at least a part of the plurality of pulleys; and a rotation shaft to rotatably support at least one of the plurality of pulleys and to extend in a direction perpendicular to a drawing direction of paper.

6. The paper transfer device of claim 5, wherein the connecting rotating member may be rotated in one direction on the rotation shaft by using the one-way bearing.

7. The paper transfer device of claim 5, wherein a cross-sectional shape of an insertion hole of a pulley into which the rotation shaft is inserted, and the rotation shaft has a D-shape.

8. The paper transfer device of claim 5, wherein a plurality of protrusions are arranged on outer circumferential surfaces of the pulleys, and wherein a plurality of grooves into which the plurality of protrusions are insertable are arranged on an inner circumferential surface of the belt.

9. The paper transfer device of claim 1 , wherein the first driving source comprises a direct current (DC) motor of which a speed varies according a change in a magnitude of a load torque that acts on the first driving source.

10. The paper transfer device of claim 1 , wherein the first driving source comprises a brush direct current (DC) motor or a brushless DC motor.

11 . The paper transfer device of claim 9, further comprising: a first detection unit to detect a rotation speed of the first driving source; and a controller to control a voltage or a current applied to the first driving source based on the detected rotation speed.

12. The paper transfer device of claim 1 , wherein the first transfer roller is to rotate in an opposite direction to a paper drawing direction, and wherein the second transfer roller is to rotate in the paper drawing direction.

13. The paper transfer device of claim 1 , further comprising a torque limiter to allow driven rotation of the first transfer roller by the second transfer roller according to a magnitude of a load torque that acts on the first transfer roller.

14. A scanner device comprising: a first transfer roller; a second transfer roller; a first driving source to generate a first driving force for rotationally driving the first transfer roller; a second driving source to generate a second driving force for rotationally driving the second transfer roller; a first power transmission structure to transmit the first driving force to the first transfer roller; a second power transmission structure to transmit the second driving force to the second transfer roller; an optional power transmission structure to optionally connect between the first power transmission structure and the second power transmission structure and to optionally transmit the second driving force to the first transfer roller, based on a rotation speed of the first transfer roller; and a reading unit to read an image from a paper.

15. An image forming apparatus comprising: a first transfer roller; a second transfer roller; a first driving source to generate a first driving force for rotationally driving the first transfer roller; a second driving source to generate a second driving force for rotationally driving the second transfer roller; a first power transmission structure to transmit the first driving force to the first transfer roller; a second power transmission structure to transmit the second driving force to the second transfer roller; an optional power transmission structure to optionally connect between the first power transmission structure and the second power transmission structure and to optionally transmit the second driving force to the first transfer roller, based on a rotation speed of the first transfer roller; and a printing unit to print an image on paper.