Image forming apparatus

An image forming apparatus includes a body, a conveyance unit, an image carrier, a transfer unit, and a pre-transfer guide. The body has a sheet passage for conveying sheets along inner and outer conveyance surfaces mutually facing. The conveyance unit includes the outer conveyance surface and is supported pivotably between an open position and a closed position relative to the inner conveyance surface. The transfer unit rotatably supports a transfer roller. The pre-transfer guide includes a first guide on the outer conveyance surface and a second guide on the inner conveyance surface. The first guide has a contact segment protruding toward the second guide. The first guide and the transfer unit are supported independently swingably relative to the transfer unit. The first guide is urged toward the second, and the distance between the two guide surfaces is restricted by the contact segment touching a contacted portion.

INCORPORATION BY REFERENCE

This application is based on and claims the benefit of priority from Japanese Patent Application No. 2020-199984 filed on Dec. 2, 2020, the contents of which are hereby incorporated by reference.

BACKGROUND

The present disclosure relates to image forming apparatuses, such as copiers, printers, and facsimile machines as well as multifunction peripherals incorporating their functions.

Many known image forming apparatuses such as copiers and printers have a sheet conveyance passage provided vertically near a side surface of the apparatus body to achieve compactness of the apparatus as a whole. In the vertically provided conveyance passage, a pair of conveyance rollers is disposed. It is common to provide a conveyance unit fitted with one of such a pair of conveyance rollers, or a transfer roller kept in pressed contact with an image carrying member to form a transfer nip, or the like and to configure the conveyance unit openable and closable with respect to the apparatus body. This construction permits the conveyance passage to be widely exposed for jam disposal and maintenance work.

Just short of the transfer nip, a pre-transfer guide is provided, and a sheet is guided along the pre-transfer guide to the transfer nip. One important target to be managed in image formation at the transfer nip is the gap between a conveyance unit-side guide, which is a part of the pre-transfer guide, and a body-side guide, which is disposed at a position opposite the conveyance unit-side guide.

SUMMARY

According to one aspect of the present disclosure, an image forming apparatus includes an apparatus body, a cover member, a conveyance unit, an image carrying member, a transfer roller, a transfer unit, a first urging member, and a pre-transfer guide. The apparatus body has a sheet conveyance passage through which sheets are conveyed along a pair of conveyance surfaces that face each other. The cover member is supported so as to be openable and closable with respect to the apparatus body. The conveyance unit is disposed inside the cover member in the apparatus body, includes an outer conveyance surface forming an outer surface of the sheet conveyance passage, and is supported so as to be pivotable between an open position and a closed position with respect to the inner conveyance surface forming an inner surface of the sheet conveyance passage. The image carrying member is rotatably disposed on the inner conveyance surface, and has a toner image formed on its surface. The transfer roller is disposed on the outer conveyance surface of the conveyance unit so as to face the image carrying member such that, with the conveyance unit in the closed position, the transfer roller is in pressed contact with the image carrying member to form a transfer nip, thereby to allow the toner image to be transferred to the sheet passing through the transfer nip. The transfer unit is supported so as to be swingable with respect to the outer conveyance surface of the conveyance unit, and rotatably supports the transfer roller. The first urging member urges the transfer unit in a direction in which the transfer roller is pressed against the image carrying member. The pre-transfer guide is disposed closely upstream of the transfer nip with respect to the sheet conveyance direction, and includes a first guide disposed on the outer conveyance surface and a second guide disposed opposite the first guide on the inner conveyance surface. The first guide is supported on the outer conveyance surface so as to be movable in directions approaching and receding from the second guide, and has a first guide surface that guides a sheet toward the transfer nip and a contact segment that protrudes from the first guide surface toward the second guide. The second guide has a second guide surface that faces the first guide surface and a contacted portion that is formed at a position on the second guide surface opposite the contact segment. The first guide and the transfer unit are supported so as to be swingable independently of each other with respect to the outer conveyance surface. The first guide is urged by a second urging member in a direction approaching the second guide such that, with the conveyance unit disposed in the closed position, the distance between the first and second guide surfaces is restricted by the contact segment making contact with the contacted portion.

DETAILED DESCRIPTION

Hereinafter, an embodiment of the present disclosure will be described with reference to the accompanying drawings.FIG.1is a sectional view of an image forming apparatus100according to one embodiment of the present disclosure, showing an outline of its construction. In the embodiment, the image forming apparatus100is a four-stage tandem-type color copier that performs image formation with four photosensitive drums1a,1b,1c,and1ddisposed side by side for four different colors (magenta, cyan, yellow, and black).

In the apparatus body of the image forming apparatus100, four image forming portions Pa, Pb, Pc, and Pd are arranged in this order from left to right inFIG.1. These image forming portions Pa to Pd are provided for images of the four different colors (magenta, cyan, yellow, and black), and sequentially form a magenta, a cyan, a yellow, and a black image each through the processes of electrostatic charging, exposure to light, image development, and image transfer.

In these image forming portions Pa to Pd respectively, the above-mentioned photosensitive drums1ato1dare arranged for carrying visible images (toner images) of the different colors. An intermediate transfer belt8that rotates counter-clockwise inFIG.1is provided adjacent to the image forming portions Pa to Pd. Toner images formed on these photosensitive drums1ato1dare sequentially transferred to the intermediate transfer belt8that moves while in contact with the photosensitive drums1ato1d.The toner images transferred to the intermediate transfer belt8are, at a secondary transfer roller9, at once transferred to a sheet P, and are, in a fixing device15, fixed to the sheet P, which is then discharged out of the image forming apparatus100. While the photosensitive drums1ato1dare rotated clockwise inFIG.1, an image forming process is performed with respect to each of the photosensitive drums1ato1d.

Sheets P to which toner images are to be transferred are stored in a sheet cassette16disposed in a lower part of the body of the image forming apparatus100, and are conveyed via a sheet teed roller12, a pair of registration rollers13, and a sheet conveyance passage14to the secondary transfer roller9. Used as the intermediate transfer belt8is a sheet made of a dielectric resin, and typically is a belt with no seams (seamless belt). The intermediate transfer belt8and the secondary transfer roller9are driven by a belt drive motor (not illustrated) to rotate at the same linear velocity as the photosensitive drums1ato1d.Downstream of the secondary transfer roller9, a blade-form belt cleaner19is disposed for removing the toner and other residues that are left behind on the surface of the intermediate transfer belt8.

Next, the image forming portions Pa to Pd will be described. Around and under the photosensitive drums1ato1d,which are rotatably arranged, there are provided charging devices2a,2b,2c,and2dfor electrostatically charging the photosensitive drums1ato1d,an exposure unit5for exposing the photosensitive drums1ato1dto light based on image data, developing devices3a,3b,3c,and3dfor developing, with toner, electrostatic latent images formed on the photosensitive drums1ato1d,and cleaning devices7a,7b,7c,and7dfor collecting and removing the developer (toner) that is left behind on the photosensitive drums1ato1dafter the transfer of the toner images.

An image reading portion23includes (though none is illustrated) a scanning optical system comprising a scanner lamp for illuminating a document during copying and a mirror for deflecting the optical path of the light reflected from the document, a converging lens for converging and focusing the light reflected from the document, and a CCD sensor for converting the focused image light into an electrical signal, or the like. The image reading portion23reads the document image and converts it into image data.

In copying operation, the image reading portion23reads the image data of a document and converts it into a read image signal. On the other hand, the charging devices2ato2delectrostatically charges the surfaces of the photosensitive drums1ato1duniformly. Subsequently, the exposure unit5irradiates the surfaces of the photosensitive drums1ato1dwith light based on the image data, and thereby forms electrostatic latent images based on the image data on the photosensitive drums1ato1d.The developing devices3ato3dinclude developing rollers (developer carrying members) disposed opposite the photosensitive drums1ato1d,and are loaded with predetermined amounts of two-component developer containing toner of different colors, namely magenta, cyan, yellow, and black.

As toner images are formed as will be described later, when the proportion of toner in the two-component developer loaded in the developing devices3ato3dfalls below a prescribed value, developer is supplied from containers4ato4dto the developing devices3ato3d.The toner in the developer is fed by the developing devices3ato3donto the photosensitive drums1ato1dand electrostatically attaches to them; this forms toner images based on the electrostatic latent images formed through exposure to the light from the exposure unit5.

Then primary transfer rollers6ato6dapply a predetermined transfer voltage between the primary transfer rollers6ato6dand the photosensitive drums1ato1d.This causes the magenta, cyan, yellow, and black toner images on the photosensitive drums1ato1dto be primarily transferred to the intermediate transfer belt8. These images of four colors are formed in a predetermined positional relationship that is prescribed to form a predetermined full-color image. The primary transfer rollers6ato6dare driven by a primary transfer motor (not illustrated) to rotate at the same linear velocity as the photosensitive drums1ato1dand the intermediate transfer belt8. Then, in preparation to the subsequent formation of new electrostatic latent images, the toner that is left behind on the surfaces of the photosensitive drums1ato1dis removed by the cleaning devices7ato7d.

The intermediate transfer belt8is stretched around a driven roller10and a driving roller11. When, as the driving roller11is driven to rotate by the belt drive motor, the intermediate transfer belt8starts to rotate counter-clockwise, a sheet P is conveyed from the pair of registration rollers13, with predetermined timing, to the nip (secondary transfer nip N inFIG.2) between the secondary transfer roller9, which is provided adjacent to the intermediate transfer belt8, and the intermediate transfer belt8. At the nip, the full-color image is secondarily transferred to the sheet P. The sheet P having the toner images transferred to it is conveyed through the sheet conveyance passage14to the fixing device15. Through the sheet conveyance passage14, the sheet P is conveyed along a pair of conveyance surfaces (an outer conveyance surface14aand an inner conveyance surface14binFIG.2) that face each other in the horizontal direction.

While the sheet P conveyed to the fixing device15passes through the nip (fixing nip) in a pair of fixing rollers15a,the sheet P is heated and pressed, so that the toner images are fixed to the surface of the sheet P; thus the predetermined full-color image is formed. The sheet P having the predetermined full-color image firmed on it is diverted in an appropriate conveyance direction by a branch portion17that branches into a plurality of directions. In a case where an image is to be formed on only one side of a sheet P, the sheet P is discharged as it is onto a discharge tray20by a pair of discharge rollers18.

By contrast, in a case where images are to be formed on both sides of a sheet P, part of the sheet P having passed through the fixing device15is momentarily stuck out of the apparatus through the pair of discharge rollers18. Then the pair of discharge rollers18is rotated reversely, so that the sheet P is diverted by the branch portion17into a reversal conveyance passage21; thus the sheet P is conveyed, now with the image side reversed, once again to the secondary transfer roller9. Then the next image formed on the intermediate transfer belt8is transferred by the secondary transfer roller9to the side of the sheet P on which no image has been formed yet. The sheet P is then conveyed to the fixing device15, where the toner images are fixed to it, and is then discharged by the pair of discharge rollers18onto the discharge tray20.

FIG.2is a sectional view around the sheet conveyance passage14and the reversal conveyance passage21in the image forming apparatus100.FIG.3is a perspective view of a side cover33and a conveyance unit35as seen from inside the image forming apparatus100(from the left side inFIG.2).

The side cover33constitutes a side surface102of the image forming apparatus100, and is pivotably supported on a pivot33aprovided in a lower part of the body of the image forming apparatus100. The inner side surface of the side cover33constitutes one conveyance surface of the reversal conveyance passage21. Pivoting only the side cover33in the opening direction with respect to the image forming apparatus100permits the reversal conveyance passage21to be widely exposed. By contrast, pivoting the side cover33along with the conveyance unit35in the opening direction results in the outer conveyance surface14a,which is the inner side surface of the conveyance unit35, moving away from the inner conveyance surface14bof the body of the image forming apparatus100, and thus permits the sheet conveyance passage14to be widely exposed. On the other hand, pivoting the side cover33along with the conveyance unit35in the closing direction causes the outer conveyance surface14aof the conveyance unit35to face the inner conveyance surface14bof the body of the image forming apparatus100, and thus results in the secondary transfer roller9being pressed against the driving roller11.

Inward of the side cover33, the conveyance unit35is disposed. The conveyance unit35is supported on the body of the image forming apparatus100so as to be pivotable about a pivot shaft35a,and constitutes the reversal conveyance passage21and the outer conveyance surface14aof the sheet conveyance passage14. The reversal conveyance passage21extends vertically along the side surface102of the image forming apparatus100between the side cover33and the conveyance unit35, and then curves substantially in a C-shape to meet the sheet conveyance passage14.

Closely upstream of the secondary transfer nip N in the sheet conveyance direction, a pre-transfer guide40is provided that guides the leading end of a sheet P that is about to enter the secondary transfer nip N. The pre-transfer guide40comprises a first guide41disposed on the outer conveyance surface14aof the conveyance unit35and a second guide42disposed on the inner conveyance surface14bof the body of the image forming apparatus100. The structure of the first and second guides41and42will be described in detail later.

The outer conveyance surface14a,which is the inner side surface of the conveyance unit35, is fitted with, in order from upstream in the sheet conveyance direction (from bottom inFIG.2), a first roller13ain the pair of registration rollers13, the first guide41in the pre-transfer guide40, and the secondary transfer roller9. The secondary transfer roller9is pressed against the driving roller11with the intermediate transfer belt8in between.

When a jam in the reversal conveyance passage21has to be coped with, pivoting only the side cover33clockwise from the state inFIG.2leaves the reversal conveyance passage21open. By contrast, when a jam in the sheet conveyance passage14has to be coped with, pivoting the side cover33along with the conveyance unit35clockwise results in the conveyance unit35being disposed in a position (an open position) where its outer conveyance surface14ais located away from the inner conveyance surface14bof the body of the image forming apparatus100, leaving the sheet conveyance passage14open. In this state, the secondary transfer roller9is located away from the driving roller11, and the first roller13ain the pair of registration rollers13is located away from a second roller13b.

After the removal of the sheet P, pivoting the conveyance unit35and the side cover33counter-clockwise inFIG.2back to the state inFIG.2(a closed position) results in the conveyance unit35being disposed at such a position that the secondary transfer roller9is in pressed contact with the driving roller11and the first roller13ais in pressed contact with the second roller13b.

FIG.4is a perspective view of a secondary transfer unit43that is mounted on the conveyance unit35.FIG.5is a side sectional view around a lever45of the secondary transfer unit43accommodated in an accommodating recess35bin the conveyance unit35.FIG.6is a perspective view of the conveyance unit35with the secondary transfer unit43removed. As shown inFIG.4, the secondary transfer unit43(transfer unit) includes the secondary transfer roller9that is kept in pressed contact with the intermediate transfer belt8to form the secondary transfer nip N, a holder44that rotatably supports the secondary transfer roller9, and a pair of levers45that keeps the secondary transfer roller9in pressed contact with the driving roller11with the intermediate transfer belt8in between.

The secondary transfer roller9has a roller portion9athat is formed of an electrically conductive elastic material and a rotary shaft9bthat extends along the axial direction of the roller portion9a.The secondary transfer roller9is electrically connected to a transfer voltage source (not illustrated), and is fed with a predetermined secondary transfer voltage of the polarity opposite to that of toner when the full-color toner image formed on the intermediate transfer belt8is secondarily transferred to the sheet P at the secondary transfer nip N.

The holder44has an accommodating portion44athat is provided along part of the circumferential surface of the secondary transfer roller9and that is arc-shaped as seen in a cross-sectional view and a pair of pivot portions44bthat are provided respectively in opposite end parts of the accommodating portion44a.The pivot portions44bhave respectively formed in them bearing holes (not illustrated) that pivotally support opposite end parts of the rotary shaft9bof the secondary transfer roller9.

The pair of levers45are mounted on opposite end parts of the holder44in the axial direction, and each have a bearing part45athat pivotally supports one end part of the rotary shaft9bof the secondary transfer roller9, a spring seat part45bthat holds one end of a compression spring50(first urging member) fitted to the conveyance unit35, and a swing fulcrum45cthat is provided at the side of the bearing part45aopposite from the spring seat part45b.

The bearing part45ahas a cylindrical shape, and is so formed that one end part of the rotary shaft9bis inserted through the bearing part45aand that the bearing part45ais insertable through the bearing hole formed in the pivot portion44bof the holder44. The spring seat part45bis formed in the shape of a circular recess at the rear side (right side inFIG.5) of the lever45. At the tip end of the spring seat part45b,a hook portion46is provided. As shown inFIG.4, the swing fulcrum45chas the shape of a boss that protrudes inward from a lower end part of the lever45. The secondary transfer unit43is supported so as to be swingable about the swing fulcrum45cwith respect to the conveyance unit35.

As shown inFIGS.5and6, the accommodating recess35bis formed so as to he recessed from the outer conveyance surface14a.In lower parts of the opposite side surfaces of the accommodating recess35b,a pair of engagement holes (not illustrated) is provided for rotatable engagement with the swing fulcrums45c.On opposite end parts of the bottom surface of the accommodating recess35b,one ends of the compression springs50as an urging member for urging the levers45are supported respectively. Over the compression springs50respectively, engagement portions37are formed.

Inserting the swing fulcrums45cformed on the pair of levers45from above into the engagement holes formed in the opposite side surfaces of the accommodating recess35bpermits the secondary transfer unit43to be supported such that the secondary transfer unit43is slidable vertically along the engagement holes and in addition that the secondary transfer unit43is pivotable about the swing fulcrums45c.Then locking the hook portions46of the pair of levers45in the engagement portions37formed in the accommodating recess35bpermits the other ends of the compression springs50to rest in the spring seat parts45bin the levers45respectively.

The compression spring50urges the lever45counter-clockwise inFIG.5about the swing fulcrum45c.The lever45urges the secondary transfer roller9toward the rotational center of the driving roller11. The direction in which the secondary transfer roller9is urged is restricted by a rail-like structure (not illustrated) formed on the body of the image forming apparatus100. The upward movement of the secondary transfer unit43is restricted by the hook portion46and the engagement portion37, and the downward movement of the secondary transfer unit43is restricted by the accommodating recess35b.

As shown inFIG.6, the first guide41is fitted to a downstream end part (left end part inFIG.6) of the accommodating recess35bwith respect to the rotation of the conveyance unit35in the closing direction. The first guide41has a guide surface41athat is formed so as to curve obliquely upward rightward along the sheet conveyance passage14, a pair of swing shafts41bthat are formed in opposite end parts of the guide surface41ain its longitudinal direction (sheet width direction) and that are swingably supported on the conveyance unit35, and a pair of contact segments41cthat protrude toward the second guide42(leftward inFIG.6) from a position away from the swing shafts41btoward the swinging end (upward inFIG.6).

The swing shaft41bis fitted with a torsion spring51(second urging member seeFIG.8). The first guide41is urged by the urging force of the torsion spring51in a direction approaching the second guide42(counter-clockwise inFIG.6). The contact segment41cis configured to protrude by a dimension greater than the clearance between the first and second guides41and42as observed with the first guide41closest to the second guide42within the swingable range. Thus, with the conveyance unit35disposed in the closed position (seeFIG.2, the contact segment41cis always in contact with a contacted portion42b(seeFIG.7) of the second guide42, and thereby restricts the clearance between the first guide41, which is urged by the torsion spring51, and the second guide42.

FIG.7is a perspective view of the second guide42in the pre-transfer guide40as seen from the direction of the first guide41. The second guide42is fastened with screws to the inner conveyance surface14bof the body of the image forming apparatus100, and has a second guide surface42athat faces the first guide surface41aof the first guide41and a contacted portion42bthat is formed at a position on the second guide surface42aopposite the contact segment41c.The contacted portion42bis a recess formed in the second guide surface42a.The second guide42rotatably supports the second roller13bin the pair of registration rollers13.

Next, the operation of pivoting the conveyance unit35to close the sheet conveyance passage14will be described. Pivoting counter-clockwise inFIG.2the side cover33and the conveyance unit35in the open state brings the first and second rollers13aand13bin the pair of registration rollers13into pressed contact with each other. Meanwhile the secondary transfer roller9is brought into pressed contact with the driving roller11to form the secondary transfer nip N against the intermediate transfer belt8.

FIG.8is a perspective view showing the first and second guides41and42in a state in contact with each other.FIG.9is a side sectional view around the secondary transfer nip N between the first and second guides41and42in a state in contact with each other. With the conveyance unit35disposed in the closed position, as shown inFIGS.8and9, the contact segment41con the first guide41is in contact with the contacted portion42bof the second guide42, maintaining a fixed distance between the first and second guide surfaces41aand42a.

In this state, a hook on the side cover33engages with an engagement pin on the body of the image forming apparatus100(neither is illustrated), so that the side cover33is held in the closed state. Thus the conveyance unit35is positioned in a predetermined position (closed position) inside the body of the image forming apparatus100.

In a known construction where the first guide41is fitted directly to the secondary transfer unit43, variations in the hardness and the outer diameter of the roller portion9aof the secondary transfer roller9cause variation of the position of the secondary transfer unit43. This may in turn cause variation of the position of the first guide41fitted to the secondary transfer unit43and hence variation of the clearance (distance) between the first and second guide surfaces41aand42a.Too small a clearance can lead to an increased load (braking force) in sheet conveyance, and too large a clearance can lead to variation of the behavior of the trailing end of a sheet and hence an image defect.

In the embodiment, the secondary transfer unit43, which holds the secondary transfer roller9, and the first guide41, which is a part of the pre-transfer guide40, are separately fitted to the outer conveyance surface14aof the conveyance unit35, and the secondary transfer unit43and the first guide41are supported so as to be swingable independently of each other with respect to the outer conveyance surface14a,of the conveyance unit35.

The first guide41is urged by the torsion spring51in a direction approaching the second guide42, and the first guide41has formed on it the contact segment41cthat makes contact with the contacted portion42bof the second guide42. The contact segment41cis configured to protrude by a dimension greater than the clearance between the first and second guide surfaces41aand42aas observed with the conveyance unit35disposed in a predetermined position.

With this structure, regardless of variations in the hardness and the outer diameter of the secondary transfer roller9, simply positioning the conveyance unit35determines the position of the first guide41. This makes it possible to maintain a fixed clearance between the first and second guide surfaces41aand42ait is thus possible to suppress image defects resulting from variation of the load in sheet conveyance, and variation of the clearance between the first and second guides41and42in the pre-transfer guide40.

The contact segment41cis configured to protrude by a dimension greater than the clearance between the first and second guide surfaces41aand42aas observed with the first guide41closest to the second guide42within the swingable range. Thus the contact segment41cis always in contact with the contacted portion42b.Hence the first guide41is held in a state pushed back in a direction receding from the second guide42against the urging force of the torsion spring51. It is thus possible to accurately restrict the clearance between the first and second guides41and42with the dimension of protrusion of the contact segment41c.

Configuring the contacted portion42bof the second guide42as a recess formed in the second guide surface42apermits the contact segment41cto be reliably held on the contacted portion42bas the first guide41swings. That is, the position at which the contact segment41cmakes contact with the second guide surface42adoes not change, and this makes it possible to stably maintain the clearance between the first and second guide surfaces41aand42a.

The embodiment described above is not meant to limit the scope of the present disclosure, which thus allows for any modifications within the spirit of the present disclosure. For example, while in the embodiment described above the levers45are fitted to opposite end parts of the secondary transfer unit43and the secondary transfer unit43is urged toward the driving roller11via the levers45with the compression springs50, the levers45may be omitted, in which case the secondary transfer unit43can be urged directly with the compression springs50.

While the embodiment described above deals with application to clearance adjustment for the pre-transfer guide40at the secondary transfer nip N between the secondary transfer roller9and the intermediate transfer belt8, application is also possible to clearance adjustment for a pre-transfer guide at the transfer nip between a transfer roller and a photosensitive drum in an image forming apparatus of a direct-transfer type.

The present disclosure finds applications in image forming apparatuses, such as copiers, printers, and facsimile machines as well as multifunction peripherals incorporating their functions. Based on the present disclosure, it is possible to provide an image forming apparatus that can suppress variation of the position of a guide member for guiding a sheet to the transfer nip and that can thus guide the sheet to the transfer nip with a fixed alignment during conveyance.