Image forming device having protection member for protecting peeling claw

An image forming device includes a frame, a photosensitive drum, a developing roller, a transfer roller, a heating roller, a backup roller, a peeling claw, and a protection member. The photosensitive drum has a surface on which a latent image is formable. The developing roller develops the latent image to provide a toner image. The transfer roller transfers the toner image onto a recording medium. The heating roller has a heating surface and a shaft supported to the frame and extending in a direction. The backup roller has a shaft supported to the frame and extending in the direction. The backup roller is in pressure contact with the heating roller. The peeling claw has a tip end in sliding contact with the heating surface of the heating roller. The protection member is configured to protect the peeling claw and prevent a user from accessing to the peeling claw.

CROSS REFERENCE TO RELATED APPLICATION

This application claims priority from Japanese Patent Application No. 2008-261313 filed Oct. 8, 2008. The entire content of the priority application is incorporated herein by reference.

TECHNICAL FIELD

The invention relates to a fixing device capable of fixing an image formed of developing agent onto a sheet-type recording medium. More specifically, the invention relates to arrangements in the vicinity of the fixing device.

BACKGROUND

Conventionally, an electrophotographic image forming device is provided with a fixing device. The fixing device is so as to be capable of fixing a toner image onto a sheet of paper. The fixing device includes a heating roller and a pressure roller disposed opposite to the heating roller.

A conveying roller pair is disposed in a downstream side of the heating roller and the pressure roller in a paper conveying direction to convey the sheet further towards the downstream side. A paper separating claw is provided to separate the sheet from the heating roller.

SUMMARY

In order to downsize the image forming device, it is necessary to downsize the fixing device. However, downsizing of the fixing device tends to cause a paper jam.

Accordingly, it is desirable that, when a paper jam has occurred in the fixing device, jammed paper be easily removed from the fixing device without damaging the same.

In view of the foregoing, it is an object of the invention to provide an image forming device. The image forming device includes a frame, a photosensitive drum, a developing roller, a transfer roller, a heating roller, a backup roller, a peeling claw, and a protection member. The photosensitive drum has a surface on which a latent image is formable. The developing roller develops the latent image to provide a toner image. The transfer roller transfers the toner image onto a recording medium. The heating roller has a heating surface and a shaft supported to the frame and extending in a direction. The backup roller has a shaft supported to the frame and extending in the direction. The backup roller is in pressure contact with the heating roller. The peeling claw has a tip end in sliding contact with the heating surface of the heating roller. The protection member is configured to protect the peeling claw and prevent a user from accessing to the peeling claw.

DETAILED DESCRIPTION

<Overall Structure of Laser Printer>

A laser printer1as an image forming device according to an embodiment of the invention will be described with reference toFIG. 1. As shown inFIG. 1, the laser printer1is configured to form a toner image on a sheet of paper while conveying the sheet along a paper conveying path PP. A direction of paper to be conveyed along the paper conveying path PP will hereinafter be referred to as “paper conveying direction.”

Throughout the specification, the terms “above”, “below”, “right”, “left”, “front”, “rear” and the like will be used assuming that the laser printer1is disposed in an orientation in which it is intended to be used. More specifically, inFIG. 1a left side and a right side are a front side and a rear side, respectively.

A paper width direction is defined by a direction perpendicular to a frontward/rearward direction of the laser printer1and a hightwise direction of the laser printer1.

The laser printer1has a main casing11. Within the main casing11, provided are a feeder unit2, a process cartridge3, a scanner unit4, a sheet conveying unit5and a fixing unit6.

The feeder unit2is positioned at a lower portion of the main casing11. The feeder unit2is mountable to detachable from the main casing11in a frontward/rearward direction.

The process cartridge3is detachably mounted in the main casing11. The process cartridge3forms a toner image on a sheet of paper in cooperation with the scanner unit4.

The sheet conveying unit5conveys the sheet along the paper conveying path PP. The fixing unit6fixes the toner image on the sheet.

Each part of the laser printer1will be described below in detail.

The main casing11is formed substantially in a box shape. The main casing11integrally formed of resin is formed over an outer surface of a main frame (not shown) for supporting various parts and components mounted in the main casing11.

A top cover12is formed with a concave portion of which depth is gradually decreased towards the front side of the top cover12. The concave portion has a bottom surface constituting a discharge tray12ato accommodate the image-bearing sheets. Specifically, the discharge tray12ais defined by a slant surface extending from the front side of the top cover12diagonally downward towards the rear side of the top cover12.

An upper rear end of the discharge tray12ais formed with a discharge opening12b. The discharge tray12ais so configured as to be capable of receiving the image-bearing sheets discharged from the discharge opening12b.

A rear cover13is movable between an open position and a closed position. When the rear cover13is at the open position, the fixing unit6is exposed to allow a user to access the same. By opening the rear cover13, a user can remove jammed paper from the fixing unit6when a paper jam has occurred in the fixing unit6.

The feeder unit2has a feeder casing21. The feeder casing21is capable of accommodating a plurality of stacked sheets of paper therein. The feeder casing21includes a sheet pressing plate22, a separation pad23, and a coil spring24allowing the separation pad23to urge against a sheet supply roller51.

The sheet pressing plate22has front and rear ends. The rear end of the sheet pressing plate22is fixed to a bottom surface of the feeder casing21to move pivotally about the same. The front end of the sheet pressing plate22is urged upward when supplying the sheet.

The separation pad23is positioned immediately frontward of the sheet pressing plate22, and disposed at a downstream side of the sheet pressing plate22in the paper conveying direction. An upper surface of the separation pad23is formed of material having a friction coefficient higher than paper, such as rubber. The coil spring24is positioned immediately below the separation pad23to urge the separation pad23upward.

The process cartridge3has a process casing31. Within the process casing31, provided are a photosensitive drum32, a charger33, a developing roller34, and a transfer roller35.

The photosensitive drum32is a cylindrical member formed with a photosensitive layer at its outer peripheral surface. The photosensitive drum32is rotatable about an axis parallel to the paper width direction as indicated by an arrow inFIG. 1.

The charger33is disposed above the photosensitive drum32and opposes the outer peripheral surface of the photosensitive drum32. The charger33is configured to uniformly charge the outer peripheral surface of the photosensitive drum32.

The developing roller34is rotatably disposed frontward with respect to the photosensitive drum32. The developing roller34is rotatable in a direction indicated by an arrow inFIG. 1, so as to supply charged toner onto the outer peripheral surface of the photosensitive drum32.

The transfer roller35is disposed opposite to the photosensitive drum32across the paper conveying path PP. The transfer roller35rotates in a direction opposite to a rotational direction of the photosensitive drum32. Further, a predetermined voltage is applied to the transfer roller35so as to transfer a toner image formed on the outer peripheral surface of the photosensitive drum32onto the sheet of paper.

The scanner unit4is disposed above the process casing31. The scanner unit4includes a polygon mirror41, a motor42, and an optical system43.

The polygon mirror41is operatively coupled to a rotational drive shaft of the motor42. While drivingly rotated by the polygon motor42, the polygon mirror41deflects with its one facet a laser beam generated from a laser generating unit (not shown), thereby scanning over the outer peripheral surface of the photosensitive drum32with the laser beam.

The optical system43includes an f-θ lens, a cylindrical lens, a reflecting mirror and the like. The optical system43functions to compensate for scanning intervals and the cross sectional shape of the laser beam deflected by the polygon mirror41.

The sheet conveying unit5includes the sheet supply roller51, a conveying roller52, a registration roller53, and a discharge roller54. The sheet conveying unit5is configured to convey the sheet along the paper conveying path PP.

The sheet supply roller51is rotatably supported at a lower portion of the main casing11. The sheet supply roller51is disposed above the separation pad23and opposes the separation pad23, so that edge portions of the sheets accommodated in the feeder casing21are brought into contact with the sheet supply roller51. The sheet supply roller51picks up each sheet accommodated in the feeder unit2in cooperation with the separation pad23so as to convey the sheet toward the conveying roller52.

The conveying roller52is provided at a position downstream of the sheet supply roller51. The conveying roller52conveys the sheet picked up by the sheet supply roller51towards the registration roller53.

The registration roller53is provided at a position upstream of a transfer position (a position that the photosensitive drum32opposes the transfer roller35) in the paper conveying direction. While adjusting an orientation and conveying timing of the sheet, the registration roller53supplies the sheet towards the transfer position.

The discharge roller54is positioned frontward of the discharge opening12bso as to allow the sheet past the fixing unit6to discharge onto the discharge tray12a.

The fixing unit6is provided at a position downstream of the above transfer position. That is, the fixing unit6is disposed at a rear side of the main casing11of the laser printer1.

The fixing unit6includes a fixing roller pair61. The fixing roller pair61includes a heating roller61aand a backup roller61b. The heating roller61ahas a heating surface, and a shaft supported to a main fixing unit frame65and extending in a direction parallel to the paper width direction. The heating roller61aheats toner deposited on the sheet. Further, the heating roller61ais of a hollow cylindrical shape made of metal, in which a heater is accommodated to generate heat.

The backup roller61bhas a shaft supported to the main fixing unit frame65and juxtaposed with the shaft of the heating roller61a. Further, the backup roller61bis disposed opposite to the heating roller61ainterposing the paper conveying path PP therebetween. The backup roller61bincludes a roller portion made of silicon rubber, and is in pressure contact with the heating roller61a.

A peeling claw62is provided at a position downstream of the fixing roller pair61in the paper conveying direction. The peeling claw62has a tip end in sliding contact with the heating surface of the heating roller61aso as to peel the sheet off from the heating surface of the heating roller61awith its tip end. Further, the peeling claw62is rotatably movable about a pivot shaft62apositioned at an end opposite to the tip end, and is also linearly movable in an upward/downward direction. The tip end of the peeling claw62is movable towards and away from the heating surface of the heating roller61a. A plurality of the peeling claws62(four peeling claws in this embodiment) is disposed substantially at an equi-pitch in the paper width direction.

A conveying roller pair63conveys the sheet to be away from the fixing roller pair61. The conveying roller pair63includes a drive roller63bsupported on a drive shaft63aand a driven roller63ddisposed in pressure contact with the drive roller63b. A plurality of the conveying roller pairs63(four pairs in this embodiment) is disposed substantially at an equi-pitch along the drive shaft63a.

As shown inFIG. 3, the drive shaft63ais positioned below the paper conveying path PP. Rotations of the drive shaft63aconvey the sheet in the sheet conveying direction. As shown inFIG. 2, the drive shaft63aextends in the paper width direction, and has a first end and a second end. The first and second ends are rotatably supported to a sub fixing unit frame66. Further, the drive shaft63ais rotatably supported by a bearing64provided substantially at an intermediate position between the first end and the second end.

The drive roller63bis formed with a cylindrical member made of rubber, that is, a rubber roller. The drive roller63bis fixed to the drive shaft63aso as to coaxially rotatable therewith.

As shown inFIG. 2, a peeling claw opposing roller63c, which functions as a protection member with respect to the peeling claw62, is coaxially provided on the drive shaft63a. The peeling claw opposing roller63cis fixed to the drive shaft63aso as to rotatable therewith. The peeling claw opposing roller63cis disposed in confrontation with the peeling claw62. The peeling claw opposing roller63cis positioned below the paper conveying path PP, while the peeling claw62is positioned above the paper conveying path PP.

The peeling claw opposing roller63cis formed with a cylindrical member made of rubber, that is, a rubber roller.

A plurality of the peeling claw opposing rollers63c(two rollers in this embodiment) is provided at a position where a flexure amount of the drive shaft63ais larger. In this embodiment, one peeling claw opposing roller63cis provided at an intermediate position between the first end and the bearing64, and another peeling claw opposing roller63cat an intermediate position between the bearing64and the second end. In other words, the peeling claw opposing roller63cis not provided at a position where the flexure amount of the drive shaft63ais not relatively large, for example, at a position in confrontation with the peeling claw62positioned closer to the bearing64. The four drive rollers63bis provided in the embodiment. That is, the first drive roller63bis disposed between the first end and one peeling claw opposing roller63cthat is provided at the intermediate position between the first end and the bearing64. The second drive roller63bis disposed between the bearing and the one peeling claw opposing roller63cthat is provided at the intermediate position between the first end and the bearing64. The third drive roller63bis disposed between the bearing64and another peeling claw opposing roller63cthat is provided at the intermediate position between the bearing64and the second end. The fourth drive roller63bis disposed between the second end and another peeling claw roller63cthat is provided at the intermediate position between the bearing64and the second end.

The peeling claw opposing roller63cis provided to reduce an open space formed between the peeling claw62and the drive shaft63ain the frontward/rearward direction as well as to protect the peeling claw62to prevent the user from accessing to the peeling claw62.

The driven roller63dis supported to the main fixing unit frame65, and rotatable in association with rotations of the drive roller63b. The driven roller63dis positioned above the paper conveying path PP.

The driven roller63dand the peeling claw62are disposed in positions offset from each other in the paper width direction. Further, as shown inFIGS. 3 to 5, the peeling claw62overlaps at least partially with the driven roller63dwhen projected onto a plane perpendicular to the paper width direction regardless of a position of the peeling claw62.

As shown inFIGS. 3 to 5, the main fixing unit frame65is provided with a peeling claw supporting portion65a. The peeling claw supporting portion65ais of a generally U-shaped shape. The peeling claw supporting portion65ais engageable with the pivot shaft62aso as to allow the peeling claw62to be rotatably movable about the pivot shaft62aand to be upwardly and downwardly movable.

As shown inFIG. 6, the main fixing unit frame65further includes a stopper65b. According to the embodiment, the driven roller63dis removably provided with respect to the drive roller63b. The stopper65bis provided to regulate a displacement amount of the driven roller63din a direction removing from the drive roller63b(in a diagonally upward and frontward direction inFIG. 6).

The sub fixing unit frame66supports the drive shaft63aby fixing the first end, the second end and the bearing64thereto. As shown inFIGS. 4 and 5, the sub fixing unit frame66has a lower portion provided with a shaft extending in the paper width direction, and is pivotably movable between a closed position and an open position about the shaft with respect to the main fixing unit frame65.

<<Operation of Laser Printer>>

An operation of the laser printer1having the structure as described above will be described while referring toFIG. 1.

The edge portions downstream in the paper conveying direction of the stacked sheets of paper accommodated in the feeder casing21are urged upwardly towards the sheet supply roller51by the sheet pressing plate22, so that a first few sheets from the top of the stacked paper are brought into contact with a peripheral surface of the sheet supply roller51.

In this state, when the sheet supply roller51is rotated, the edges of the sheets are conveyed to be pinched between the sheet supply roller51and the separation pad23. Only the topmost sheet being in contact with the peripheral surface of the sheet supply roller51is supplied to the conveying roller52in association with rotation of the sheet supply roller51.

The leading edge of the sheet conveyed in the paper conveying direction by the conveying roller52impinges against the registration roller53. The resist roller53is provided to compensate for the orientation of the sheet. Then, rotation of the registration roller53at predetermined timing allows the sheet to be conveyed to the transfer position where the photosensitive drum32opposes the transfer roller35.

While the sheet is conveyed to the transfer position as described above, a toner image is formed on the outer peripheral surface of the photosensitive drum32as described below.

The outer peripheral surface of the photosensitive drum32is uniformly charged by the charger33. While the outer peripheral surface of the photosensitive drum32charged by the charger33moves towards the downstream side in the rotational direction of the photosensitive drum32, the charged surface of the photosensitive drum32is irradiated with the laser beam. The laser beam is modulated according to image data. By scanning the modulated laser beam over the outer peripheral surface of the photosensitive drum32, an electrostatic latent image is formed on the outer peripheral surface of the photosensitive drum32.

The outer peripheral surface of the photosensitive drum32on which the electrostatic latent image is formed reaches a position opposite to an outer peripheral surface of the developing roller34. Here, the outer peripheral surface of the photosensitive drum32is brought into contact with or brought to a position closer to the outer peripheral surface of the developing roller34on which the charged toner is deposited. The toner is deposited on the peripheral surface of the photosensitive drum32to form a toner image corresponding to the electrostatic latent image. That is, the electrostatic latent image formed on the outer peripheral surface of the photosensitive drum32is developed by the toner.

The toner image formed on the peripheral surface of the photosensitive drum32as described above is transferred onto the sheet at the transfer position.

The sheet on which the toner image is transferred is conveyed to the fixing unit6along the paper conveying path PP. The sheet is fed between the heating roller61aand the backup roller61bto be pressed and heated, and therefore, the toner image is thermally fixed on the sheet. Subsequently, the sheet is conveyed to the discharge roller54, and discharged from the discharge opening12bto the discharge tray12a.

<<Operation and Effect According to Embodiment>>

Next, operations and effects according to the embodiment will be described while referring toFIGS. 1 to 6.

According to the embodiment, the peeling claw62overlaps at least partially with the driven roller63dwhen projected onto a plane perpendicular to the paper width direction regardless of a position of the peeling claw62. Accordingly, downsizing of the fixing unit6can be attained.

A paper jam may occur at a position between the fixing roller pair61and the conveying roller pair63. Such a paper jam tends to occur as the fixing unit6is downsized. According to the embodiment, as shown inFIGS. 4 and 5, the peeling claw62is pivotally movable and upwardly slidable. Accordingly, damages on the surface of the heating roller61acaused by the tip end of the peeling claw62can be prevented as much as possible when the paper jam has occurred.

If such a paper jam has occurred, a user opens the rear cover13to remove the jammed paper. In case a relatively minor paper jam has occurred, the jammed paper is removed from the fixing unit6in a state that the sub fixing unit frame66is in the closed position.

According to the embodiment, the peeling claw opposing roller63cis provided to reduce an open space formed between the peeling claw62provided at a position where a flexure amount of the drive shaft63ais larger and the drive shaft63a, and to protect the peeling claw62to prevent the user from accessing to the peeling claw62.

When removing the jammed paper, the user may insert his fingers in the open space formed between the peeling claw62and the drive shaft63ato remove the jammed paper. In such a situation, fingers of the user may accidentally press the peeling claw62against the heating roller61a, thereby damaging the surface of the heating roller61awith the peeling claw62. Further, foreign material may be introduced into a portion around the peeling claw62, in particular, around the pivot shaft62a. According to the embodiment, such problems can be prevented by the peeling claw opposing roller63cas much as possible, since the peeling claw opposing roller63cminimizes the open space formed between the peeling claw62and the drive shaft63a. Accordingly, the jammed paper can be appropriately removed.

In case a serious paper jam has occurred and foreign material or a small piece of paper remains inside the fixing unit6, the jammed paper is removed from the fixing unit6in a state that the sub fixing unit frame66is in the open position, as shown inFIG. 5.

(1) The invention is not limited to be applied to a monochromatic laser printer. For example, the invention may be applied to an electrophotographic type color laser printer, monochromatic copying machine and color copying machine. Further, in the above embodiment, the photosensitive drum is employed. However, a flat plate type photosensitive member and an endless belt type photosensitive member are also available.

Further, with regard to the configuration of the feeder unit2, process cartridge3and the scanner unit4, various configurations may be adopted other than the configuration described above. For example, the invention may be applied to an image forming device in which the feeder unit2is omitted and sheets of paper are only fed manually.

The invention is applicable to an image forming device of toner jet type, an ion flow type and a multi-stylus electrode type, other than the electrophotographic type image forming device.

(2) The configurations of the heating roller and the backup roller according to the invention are not limited to ones as described above. For example, instead of the heating roller61a, a sleeve type fixing film made of rubber or synthetic resin may be used. If this is the case, a heating unit such as a ceramic heater is provided inside the fixing film so that the opposing roller (a pressure roller) is opposite to the heating unit interposing the fixing film therebetween. The heating unit extends along the paper width direction (an axial direction of the above sleeve) with a length corresponding to a maximum paper width.

(3) The peeling claw opposing roller63cmay be formed of a material different from that of the drive roller63b. More specifically, the peeling claw opposing roller63cmay be formed of synthetic resin (preferably fluororesin).

The peeling claw opposing roller63cmay be rotatable relative to the drive shaft63aand the drive roller63b. That is, the peeling claw opposing roller63cmay be supported by the drive shaft63ato rotate about the drive shaft63a.

(4) Four peeling claws62are provided in the embodiment. However, the number of the peeling claw62is not limited to four.