Sheet transport mechanism and image forming device provided with same

The sheet transport mechanism of the present disclosure is provided with drive roller, driven roller, and roller pressing mechanism. The roller pressing mechanism presses the driven roller into contact against the drive roller. The driven roller includes a central driven roller, a first rotating shaft for supporting the central driven roller, at least one pair of outside driven rollers, and second rotating shafts supporting the outside driven rollers. The roller pressing mechanism includes a central pressing mechanism, and an outside pressing mechanism. The central pressing mechanism presses the central driven roller against the drive roller. The outside pressing mechanism presses the outside driven rollers against the drive roller.

INCORPORATION BY REFERENCE

This application claims the benefit of Japanese Application No. 2013-179436, filed Aug. 30, 2013, in the Japanese Patent Office. All disclosures of the documents named above are incorporated herein by reference.

BACKGROUND OF THE INVENTION

The present disclosure relates to a sheet transport mechanism for transporting a recording medium of sheet form, such as paper or the like, in an image forming device such as a fax machine, copier, printer, or the like, and to an image forming device provided with the same.

In image forming devices such as fax machines, copiers, printers, and the like, sheet transport mechanisms in which pairs of transport rollers, composed of pairs of rollers pressed into contact with one another, rotate in order to transport a sheet while pinched in the nip of the pair of rollers, are widely employed as means for transporting sheets (recording media) such as paper, cloth, OHP sheets, and the like.

In this sort of sheet transport mechanism, one of the rollers constituting the transport roller pair is pressed into contact against the other roller at a predetermined pressure, by means of a tension spring, compression spring, or the like. In the past, the typical method for doing so was to furnish individual springs at left and right in the axial direction of the transport roller pair, and to press one roller against the other roller.

However, when individual springs are furnished at left and right in the axial direction, variability in the dimensions of the springs may cause the pressing force on the transport roller pair to differ between left and right in the axial direction. As a result, the transporting force acting on the sheet may be uneven between left and right in the axial direction, causing the sheet to experience oblique motion.

SUMMARY OF THE INVENTION

The sheet transport mechanism according to one aspect of the present disclosure is provided with transport roller pairs, and roller pressing mechanism. The transport roller pairs are composed of drive roller and driven roller. The drive roller is rotated by drive power from a drive source. The driven roller is pressed into contact against the drive roller and passively driven thereby. The roller pressing mechanism presses the driven roller into contact against the drive roller. The sheet transport mechanism transports a recording medium pinched in a nip section of the transport roller pairs. The driven roller includes a central driven roller disposed to the center side in the axial direction, with a first rotating shaft for supporting the central driven roller, at least one pair of outside driven rollers arranged symmetrically on either side of the central driven roller in an axial direction, and with second rotating shafts for supporting the outside driven rollers. The roller pressing mechanism includes a central pressing mechanism for pressing the central driven roller against the drive roller, and an outside pressing mechanism for pressing the outside driven rollers against the drive roller.

Other objects of the present disclosure, and specific advantages afforded by the present disclosure, will become more apparent from the following description of the preferred embodiments.

DETAILED DESCRIPTION OF THE EMBODIMENTS

An image forming device in which the sheet transport mechanism according to an embodiment of the present disclosure has been installed will be described with reference toFIGS. 1 to 6. Here, an ink jet printer100is described as the image forming device.

As shown inFIG. 1, the printer100is equipped with a paper supply cassette3disposed in a lower part of the interior of a printer body2, and serving as a paper receptacle. The paper supply cassette3accommodates a stack of a prescribed number of sheets (for example, about 500) of paper P, such as unprinted cut paper, by way of an exemplary recording medium. A paper feed device4is disposed to the downstream side, in the direction of paper transport, from the paper supply cassette3, and specifically above the right side of the paper supply cassette3inFIG. 1. The paper P is separated and fed one sheet at a time upward and to the right of the paper supply cassette3inFIG. 1by the paper feed device4. The paper supply cassette3is capable of being pulled out horizontally from the front face side of the printer body2, in order to be refilled with paper P.

A manual paper feed tray5is provided to the outside of the right side face of the printer body2. Into the manual paper feed tray5is placed paper of sizes different from the paper P inside the paper supply cassette3, thick paper, OHP sheets, envelopes, postcards, invoices, or other such recording media that do not readily pass over a transport path inflected, or recording media desired to feed one sheet at a time, and the like. A paper feed device6is disposed to the downstream side, in the direction of paper transport, from the manual paper feed tray5, specifically, to the left side of the manual paper feed tray5inFIG. 1. Paper positioned on the manual paper feed tray5is separated and fed one sheet at a time to the left inFIG. 1by this paper feed device6.

The printer100is additionally provided in the interior thereof with a first paper transport path7. The first paper transport path7, in relation to the paper supply cassette3, is located above and to the right which is the paper feed direction; and in relation to the manual paper feed tray5is located leftward. The paper P fed out from the paper supply cassette3is transported vertically upward along a side face of the printer body2by the first printer paper transport path7, while paper fed out from the manual paper feed tray5is transported horizontally leftward.

A resist roller pair8is provided at the downstream end of the first printer paper transport path7in relation to the paper transport direction. A first belt transport part20and a recording part30are disposed in proximity to the downstream side of the resist roller pair8. The paper P fed out from the paper supply cassette3(or from the manual paper feed tray5) reaches the resist roller pair8through the first printer paper transport path7. The resist roller pair8, while correcting diagonal feed of the paper P, feeds the paper P towards the first belt transport part20, at a timing coordinated with an ink ejection operation executed by the recording part30. Transport roller pairs13afor transporting the paper P are furnished at appropriate locations along the first printer paper transport path7.

In order to prevent ink ejection failure due to clogging or drying out of the print head, the recording part30, when commencing a print operation after being idle for a prolonged period, executes a purge, doing so from all of the ink ejection nozzles (not illustrated) of the recording head, or during the interim between printing operations, from ink ejection nozzles for which the quantity of ink ejected therefrom is equal to or less than a prescribed value, in order to eject ink that has increased in viscosity within the nozzles, and prepare for the next printing operation.

A second belt transport part40is disposed to the downstream side (the left side inFIG. 1) from the first belt transport part20in relation to the paper transport direction. The paper P on which an ink image has been recorded by the recording part30is feed to the second belt transport part40, and the ink ejected onto the paper P surface is dried during passage through the second belt transport part40.

A decurler part9is provided to the downstream from the second belt transport part40in relation to the paper transport direction, in proximity to the left side face of the printer body2. The paper P onto which the ink has been dried in the second belt transport part40is fed to the decurler part9, where curling is corrected by a plurality of rollers lined up in the paper width direction.

A second paper transport path10is provided to the downstream side (the upper side inFIG. 1) of the decurler part9in relation to the paper transport direction. In cases in which the paper P passing through the decurler part9has not been printed on both sides, it is discharged, via discharge rollers, from the second paper transport path10into a paper discharge tray11furnished outside the left side of the printer100. The second paper transport path10, like the first paper transport path7, is furnished at appropriate locations with transport roller pairs13bfor transporting the paper P.

A maintenance unit50is disposed below the second transport part40. During execution of a purge as discussed above, the maintenance unit50moves to below the recording part30, wipes the ink ejected from the ink discharge nozzles of the recording head, and recovers the wiped ink.

A reverse transport path12for performing duplex recording is provided above the recording part30and the second belt transport part40, in an upper part of the printer body2. In the case of performing duplex recording, once recording of the first side is finished, the paper P having passed through the second belt transport part40and the decurler part9is fed onto the reverse transport path12through the second transport path10. The transport direction of the paper P fed onto the reverse transport path12is then switched in order to record the second side, and is fed towards the right side while passing through the upper part of the printer body2, and again fed into the first belt transport part20through the resist roller pair8, with the second side facing up. The reverse transport path12, like the first paper transport path7, is furnished at appropriate locations with transport roller pairs13cfor transporting the paper P.

Next, the sheet transport mechanism of an embodiment of the present disclosure will be described. Here, a case in which the transport roller pairs13aare employed as the sheet transport mechanism of the present disclosure will be described.

As shown inFIG. 2, the sheet transport mechanism of the embodiment of the present disclosure includes transport roller pairs13a, and a roller pressing mechanism80for pressing a driven roller70, discussed later, against a drive roller60of the transport roller pairs13a, which transport the paper P while pinched in the nip part of the transport roller pairs13a.

The transport roller pairs13aare composed of the drive roller60which is rotated by drive power from a drive source, and the driven roller70which is rotated by being driven while pressed against the drive roller60. The driven roller70includes a central roller (central driven roller)71disposed towards the center side in an axial direction, and a pair of outside rollers (outside driven rollers)72disposed symmetrically on either side of the central roller71in an axial direction.

The drive roller60includes a rotating shaft60aand a plurality (in this instance, four) of roller elements60bsecured about the outside peripheral face of the rotating shaft60ain the paper width direction (the axial direction of the rotating shaft60a). The rotating shaft60aof the drive roller60is rotatably supported by a pair of side panel frames (not illustrated) disposed in the longitudinal direction (a direction perpendicular to the plane of the page inFIG. 1) of the printer body2, with drive power from a power source such as a motor or the like (not illustrated) input to one end of the rotating shaft60a.

The central roller71includes a rotating shaft (first rotating shaft)71a, and two roller elements71bsecured along the outside peripheral face of the rotating shaft71ain the paper width direction. The roller elements71bare disposed at locations facing the central roller elements60bof the drive roller60. Each of the outside rollers72includes a rotating shaft (second rotating shaft)72aand a single roller element72bsecured to the outside peripheral face of the rotating shaft72a. The roller elements72bare disposed at locations facing the outside roller elements60bof the drive roller60. As shown inFIG. 3, the two rotating shafts72aare arranged in mutually coaxial fashion, as well as being arranged positioned coaxially to the rotating shaft71awhen central roller71and the outside rollers72are pressed against the drive roller60.

The roller elements60bof the drive roller60are formed from elastic material such as rubber or the like, and the roller elements71band72bof the driven roller70are formed of resin material having higher hardness than the roller elements60b. In so doing, the transporting force produced during transport of the multifunction paper through frictional force of the drive roller60and the driven roller70can be enhanced.

The roller pressing mechanism80includes a central pressing mechanism81for pressing the central roller71against the drive roller60, and an outside pressing mechanism82for pressing the pair of outside rollers72against the drive roller60under uniform pressing force.

The central pressing mechanism81has a pair of central pressing members83for pressing on both ends of the rotating shaft71aof the central roller71towards the drive roller60side, and a central urging member84linked to the pair of central pressing members83and urging the central pressing members83to impart pressing force. The central urging member84is designed such that the pressing force of the central pressing members83exceeds the pressing force of outside pressing members88, discussed below.

Each of the central pressing members83includes a first lever85, and a second lever86abutting the first lever85.

As shown inFIG. 4, the first lever85is supported on a frame (not illustrated) of the printer body2so as to be pivotable about a first pivot shaft85a. The first pivot shaft85aextends in a direction parallel to the rotating shaft60aof the drive roller60and the rotating shafts71aand72aof the driven roller70(a direction perpendicular to the plane of the page inFIG. 1).

In an approximate center portion of the first lever85there is formed a bearing portion85badapted to rotatably support an end of the rotating shaft71aof the central roller71, making it possible for the end of the rotating shaft71ato be pressed towards the drive roller60side. By pivoting of the first lever85about the first pivot shaft85ain a counterclockwise direction or clockwise direction inFIG. 5, the central roller71pivots in a direction approaching or moving away from the drive roller60.

As shown inFIG. 4, the second lever86is supported on the frame (not illustrated) of the printer body2so as to be pivotable about a second pivot shaft86aorthogonal to the first pivot shaft85a. The second lever86is of crank shape having a first arm portion (abutting portion)86bthat protrudes out towards an axial end of the central roller71from the second pivot shaft86aand abuts the first lever85, and a second arm portion (linking portion)86cthat protrudes out in an “L” shape towards an axial center portion of the central roller71from the second pivot shaft86a. A hook portion87is formed at the distal end of the second arm portion86cof each of the second levers86, and the central urging member84is linked at both ends thereto.

The second pivot shaft86aextends in a direction orthogonal to the rotating shaft60aof the drive roller60and the rotating shafts71a,72aof the driven roller70.

The central urging member84comprises a tension spring, and urges the second lever86in a direction parallel to the rotating shaft71aof the central roller71.

As shown inFIG. 3, the outside pressing mechanism82has a pair of outside pressing members88for pressing the rotating shafts72aof the pair of outside rollers72towards the drive roller60side, and an outside urging member89linked to the pair of outside pressing members88, and urging the outside pressing members88to impart pressing force.

Each of the outside pressing members88includes a third lever90, and a fourth lever91abutting the third lever90.

As shown inFIG. 6, the third lever90is supported on the frame (not illustrated) of the printer body2so as to be pivotable about a third pivot shaft90a. The third pivot shaft90aextends in a direction parallel to the rotating shaft60aof the drive roller60and the rotating shafts71aand72aof the driven roller70.

In an approximate center portion of the third lever90there is formed bearing portions90badapted to rotatably support both ends of the rotating shaft72aof the outside roller72, making it possible for both ends of the rotating shaft72ato be pressed towards the drive roller60side. By pivoting of the third lever90about the third pivot shaft90ain the clockwise direction or counterclockwise direction inFIG. 5, the outside roller72pivots in a direction approaching or moving away from the drive roller60.

The fourth lever91is supported on the frame (not illustrated) of the printer body2so as to be pivotable about a fourth pivot shaft91aorthogonal to the third pivot shaft90a. The fourth lever91is of crank shape having a third arm portion91bthat protrudes out towards an axial end of the driven roller70from the fourth pivot shaft91aand abuts the third lever90, and a fourth arm portion91cthat protrudes out in an “L” shape towards an axial center portion of the driven roller70from the fourth pivot shaft91a. A hook portion92is formed at the distal end of the fourth arm portion91cof each of the fourth levers91, and the outside urging member89is linked at both ends thereto.

The fourth pivot shaft91aextends in a direction orthogonal to the rotating shaft60aof the drive roller60and the rotating shafts71a,72aof the driven roller70.

The outside urging member,89comprises a tension spring, and urges the fourth lever91in a direction parallel to the rotating shaft72aof the outer roller72. As shown inFIG. 3, the outside urging member89is disposed to the opposite side from the central urging member84with respect to the driven roller70, and the third pivot shaft90aof the third lever90is disposed to the opposite side from the first pivot shaft85aof the first lever85with respect to the driven roller70.

Turning to a description of operation of the roller pressing mechanism80, the second arm portion86cis pulled in the direction of arrow A1by the urging force of the central urging member84. In so doing, the second lever86pivots, and the first arm portion86bpresses the first lever85in the downward direction ofFIG. 3, whereby the first lever85pivots in the counterclockwise direction inFIG. 5about the first pivot shaft85a. In so doing, the central roller71, which is supported by the bearing portion85bof the first lever85, is pressed into contact against the drive roller60.

Likewise, the fourth arm portion91cis pulled in the direction of arrow B1by the urging force of the outside urging member89. In so doing, the fourth lever91pivots, and the third arm portion91bpresses the third lever90in the downward direction ofFIG. 3, whereby the third lever90pivots in the clockwise direction inFIG. 5about the third pivot shaft90a. In so doing, the outside roller72, which is supported by the bearing portion90bof the third lever90, is pressed into contact against the drive roller60.

In the present embodiment, in the aforedescribed manner, the driven roller70includes the central roller71which is disposed to the center side in the axial direction, and the pair of outside rollers72which are disposed to the outside in the axial direction, while the roller pressing mechanism80includes the central pressing mechanism81for pressing the central roller71against the drive roller60, and the outside pressing mechanism82for pressing the outside rollers72against the drive roller60. In so doing, even in cases in which the rotating shaft60aof the drive roller60flexes due to low rigidity of the rotating shaft60a, the central roller71can be pressed into contact against the drive roller60by the central pressing mechanism81. For this reason, diminished pressing force at the center side can be avoided, and therefore small-sized paper (for example, postcards or envelopes) can be transported with good accuracy.

Additionally, the central pressing mechanism81has the pair of central pressing members83for pressing on both ends of the rotating shaft71aof the central roller71towards the drive roller60side, and the central urging member84which is linked to the pair of central pressing members83and urges the central pressing members83to impart pressing force. In so doing, both ends of the central roller71can be pressed uniformly, whereby variability of the central pressing force at either side in the axial direction can be minimized. Moreover, the outside pressing mechanism82has the pair of outside pressing members88for pressing the pair of outside rollers72towards the drive roller60side, and the outside urging member89linked to the pair of outside pressing members88, and urging the outside pressing members88to impart pressing force. In so doing, the pair of outside rollers72can be pressed uniformly, whereby variability of the outside pressing force at either side in the axial direction can be minimized. As a result, variability of the pressing force of the transport roller pairs13aat either side in the axial direction can be minimized.

In the aforedescribed manner, the pressing force produced by the central pressing member83exceeds the pressing force produced by the outside pressing member88. In so doing, the central roller71can be pressed into contact against the drive roller60in a more reliable manner, even in cases in which the rotating shaft60aof the drive roller60flexes due to low rigidity of the rotating shaft60a.

Moreover, in the aforedescribed manner, the central urging member84is linked to the pair of second levers86and urges the second levers86in the direction parallel to the rotating shaft71a, whereupon the second levers86, under the urging force of the central urging member84, pivot in a direction of pressing the first levers85, thereby pressing the central roller71into contact against the drive roller60. In so doing, both ends of the central roller71can be readily pressed in uniform fashion by the central urging member84, the pair of second levers86, and the pair of first levers85.

Moreover, in the aforedescribed manner, the outside urging member89is linked to the pair of fourth levers91and urges the fourth levers91in the direction parallel to the rotating shaft72a, whereupon the fourth levers91, under the urging force of the outside urging member89, pivot in a direction of pressing the third levers90, thereby pressing the pair of outside rollers72into contact against the drive roller60. In so doing, the pair of outside rollers72can be readily pressed in uniform fashion by the outside urging member89, the pair of fourth levers91, and the pair of third levers90.

Moreover, in the aforedescribed manner, the third pivot shaft90ais disposed to the opposite side from the first pivot shaft85awith respect to the driven roller70. In so doing, as compared with a case in which the third pivot shaft90aand the first pivot shaft85aare disposed at a side lying in the same direction with respect to the driven roller70, the force bearing on drive roller60in the paper transport direction (radial direction) can be minimized. Therefore, deviation in the alignment of the drive roller60can be minimized.

Moreover, in the aforedescribed manner, the central urging member84and the outside urging member89are tension springs. In so doing, the pair of central pressing members83can readily be urged in uniform fashion by the central urging member84, and the pair of outside pressing members88can readily be urged in uniform fashion by the outside urging member89.

The embodiment disclosed herein is in all respects exemplary and should not be construed as limiting. The scope of the disclosure is that indicated by the claims, not the preceding description of the embodiments, and shall be considered to further include any modification equivalent in significance to the claims and falling within the scope thereof.

For example, the sheet transport mechanism of the present disclosure is not limited to application in a color printer of inkjet recording type such as that shown inFIG. 1, and application is possible in various other kinds of image forming devices, such as monochrome copiers, digital multifunction printers, fax machines, laser printers, and the like.

In the aforedescribed embodiment, the transport roller pair13adisposed on the first paper transport path7was described as an example of the transport roller pair of the sheet transport mechanism of the present disclosure, but there is no limitation thereto. For example, the transport roller pair could be applied in completely analogous fashion to the transport roller pair13bdisposed on the second paper transport path10, the transport roller pair13cdisposed on the reverse transport path12, the resist roller pair8, the discharge rollers, or the like.

In the aforedescribed embodiment, a case in which the central roller has two roller elements was shown; however, the present disclosure is not limited thereto, and the central roller may have a single roller element instead.

Moreover, in aforedescribed embodiment, an example in which one outside roller was furnished at each axial side of the central roller was shown; however, the present disclosure is not limited thereto, and additional outside rollers may be furnished at each axial side of the outside rollers.

Moreover, in aforedescribed embodiment, an example in which, in order to press the pair of outside roller72against the drive roller60under uniform pressing force, the outside pressing mechanism82is constituted by the pair of outside pressing members88for pressing the pair of outside rollers72against the drive roller60, and the outside urging member89linked to the pair of outside pressing members88, for urging the outside pressing members88to impart pressing force, but the present disclosure is not limited thereto. For example, a configuration in which the pair of outside pressing members88are bridged by an elongated rigid plate, the center of the rigid plate being urged by a compression spring, can also be employed to press the pair of outside roller72against the drive roller60under uniform pressing force.