Image-forming device with interlockingly movable two paper guide members

An image-forming device includes a casing, a photosensitive drum, a transfer roller, a first guide member, and a second guide member. The first guide member is disposed upstream of the transfer point between the photosensitive drum and the transfer roller in a conveying direction of the recording medium and selectively movable between a first position and a second position. The second guide member is disposed between the first guide member and the transfer point and selectively movable between a third position and a fourth position farther from the photosensitive drum than the third position. The second guide member is movable in association with the movement of the first guide member in such a manner that when the first guide member is disposed in the first position, the second guide member is disposed in the third position for guiding the recording medium received from the first guide member to move toward the photosensitive drum.

CROSS REFERENCE TO RELATED APPLICATION

This application claims priority from Japanese Patent Application No. 2006-305856 filed Nov. 10, 2006. The entire content of this priority application is incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to an image-forming device such as a laser printer, and a process cartridge mounted in the image-forming device.

BACKGROUND

Normally, a process cartridge is detachably mounted in image-forming devices such as laser printers. The process cartridge includes a photosensitive drum functioning to carry an electrostatic latent image, which is developed into a toner image by developer. The photosensitive drum is disposed in confrontation with and in contact with a transfer roller. The toner image carried on the photosensitive drum is transferred onto paper passing through a nip position between the photosensitive drum and the transfer roller by a transfer bias applied to the transfer roller. In this construction, a guide member is typically provided near the photosensitive drum upstream of the nip position in the paper-conveying direction for guiding the paper to the nip position.

Japanese unexamined patent application publication No. HEI-5-53449, for example, discloses a transfer unit provided with the following type of guide member. The guide member includes a paper conveying guide, an eccentric cam for pivoting the paper conveying guide, and a photosensor. When the photosensor detects the leading edge of the paper, the eccentric cam is rotated to place the paper conveying guide near the photosensitive drum. When the photosensor detects the trailing edge of the paper, the eccentric cam is rotated to separate the paper conveying guide from the photosensitive drum.

However, the transfer unit described in Japanese unexamined patent application publication No. HEI-5-53449 requires a photosensor and eccentric cam for placing the downstream portion of the guide member near to the photosensitive drum and separating the same portion from the photosensitive drum. Moreover, the transfer unit requires a motor for rotating the eccentric cam, and a control unit for driving the motor at a prescribed timing based on signals received from the photosensor, thereby requiring a larger number of parts and a more complex construction. This construction may also be less reliable because electronic units, such as the control circuit board on which the photosensor and control unit are provided, are susceptible to electrical malfunctions.

SUMMARY

Therefore, it is an object of the present invention to provide an image-forming device and a process cartridge having a simple construction for moving a guide portion of a guide member on the downstream side relative to the paper-conveying direction toward and away from a photosensitive member.

The above objects and others will be attained by an image-forming device that includes a casing, an image-carrying member, a transfer member, a first guide member, and a second guide member. The image-carrying member carries a developer image. The transfer member is disposed in confrontation with the image-carrying member and transfers the developer image from the image-carrying member to a recording medium at a transfer point of contact with the image-carrying member. The first guide member is disposed in a predetermined position upstream of the transfer point in a conveying direction of the recording medium. The first guide member is selectively movable between a first position and a second position. The second guide member disposed between the first guide member and the transfer point along the conveying direction of the recording medium. The second guide member is selectively movable between a third position and a fourth position farther from the image-carrying member than the third position. The second guide member is movable in association with the movement of the first guide member in such a manner that when the first guide member is disposed in the first position, the second guide member is disposed in the third position for guiding the recording medium received from the first guide member to move toward the image-carrying member.

When the image-carrying member is a photosensitive drum, this photosensitive drum may be provided in a process cartridge that is detachably mounted in the image-forming device. In this case, the second guide member may also be provided in the process cartridge.

By the second guide member moving in association with the first guide member, the image-forming device can guide recording medium toward the image-carrying member without a complex structure for guiding the recording medium toward the image-carrying member, such as a motor, a sensor for detecting the leading edge of paper, and CPU for moving the motor based on the signal from the sensor, and complex control. Therefore, it can reduce the number of required parts and simplify the construction.

DETAILED DESCRIPTION

An image-forming device according to preferred embodiments of the present invention will be described while referring to the accompanying drawings.FIG. 1is a side cross-sectional view showing the relevant construction of a laser printer serving as a preferred embodiment of the image-forming device according to the present invention.

As shown inFIG. 1, a laser printer1includes a main casing2, and, within the main casing2, a feeder unit4for feeding a paper3, an image-forming unit5for forming images on the paper3supplied from the feeder unit4, and the like.

The laser printer1also includes an access opening6formed in one side wall of the main casing2for inserting and removing a process cartridge16described later, and a front cover7capable of opening and closing over the access opening6. The front cover7is rotatably supported by a cover shaft (not shown) inserted through a bottom end of the front cover7. Accordingly, when the front cover7is rotated closed about the cover shaft, the front cover7covers the access opening6. When the cover is rotated open about the cover shaft, the access opening6is exposed, enabling the process cartridge16to be mounted into or removed from the main casing2via the access opening6. A control panel (not shown), including operating keys and an LED display unit, is embedded in the front cover7.

Hereinafter, the side of the laser printer1and the process cartridge16on which the front cover7is provided will be referred to as the “front side” and the opposite side as the “rear side”. The side of the laser printer1and the process cartridge16on which the feeder unit4is provided will be referred to as the “below side” and the opposite side as the “above side”.

The feeder unit4includes a paper supply tray8that is detachably mounted in a lower section of the main casing2, a feeding roller9and separating pad10disposed above the front end of the paper supply tray8, a pickup roller11disposed on the rear side of the feeding roller9, a pinch roller12disposed in opposition to the feeding roller9on the lower front side thereof, and a pair of registration rollers13disposed on the above rear side of the feeding roller9.

A paper pressing plate14is provided inside the paper supply tray8for supporting the paper3in a stacked state. The paper pressing plate14is pivotably supported on the rear end thereof, so that the front end can move vertically. When the front end of the paper pressing plate14is lifted, the topmost sheet of the paper3stacked on the paper pressing plate14is pressed against the pickup roller11. The pickup roller11rotates to begin conveying the topmost sheet of the paper3between the feeding roller9and separating pad10. The registration rollers13convey the sheet of the paper3to a transfer point in the image-forming unit5. The transfer point is a position between a photosensitive drum23and a transfer roller26. The photosensitive drum23and the transfer roller26are described later.

A paper-guiding plate55is provided in the main casing2along a conveying path of the paper3extends from the registration rollers13, through the image-forming unit5, to a fixing unit17described later. The paper-guiding plate55is formed in a flat plate-shape and disposed above the paper tray8.

The paper-guiding plate55is configured of a recessed part56, a front guiding plate57, and a rear guiding plate58. The recessed part56is formed in a center portion of the paper-guiding plate55relative to the front-to-rear direction. The front guiding plate57extends from the front end of the paper-guiding plate55to the recessed part56for conveying the paper3from the registration rollers13to the transfer point. The front guiding plate57slopes downward toward the rear side. A device-side slit59(seeFIG. 7) is formed in a left-to-right center of the front guiding plate57. The side of the laser printer1and the process cartridge16on which a photosensor75(as described later) is provided will be referred to as the “left side”, and the opposite side as the “right side” inFIG. 5. The device-side slit59is substantially rectangular in shape and extends in the front-to-rear direction into the recessed part56.

The rear guiding plate58extends from the recessed part56to the rear edge of the paper-guiding plate55for conveying the paper3from the transfer point to the fixing unit17. The rear guiding plate58slopes upward toward the rear side.

The image-forming unit5includes a scanning unit15, the process cartridge16, the fixing unit17, and the like.

The scanning unit15is disposed in the top section of the main casing2and includes a laser light source (not shown), a polygon mirror18that can be driven to rotate, fθ lenses19, reflecting mirrors20, and the like. The laser light source emits a laser beam based on image data. As illustrated by a dotted line inFIG. 1, the laser beam is deflected by the polygon mirror18, passes through the fθ lens19, and is reflected rearward by the reflecting mirror20. After passing through the fθ lenses19, the laser beam is reflected downward by the reflecting mirrors20and irradiated on the surface of the photosensitive drum23described later in the process cartridge16.

The process cartridge16is detachably mounted in the main casing2below the scanning unit15.

FIG. 2is a cross-sectional side view of the process cartridge16. As shown inFIG. 2, the process cartridge16includes a drum cartridge21, and a developer cartridge32that is detachably mounted on the drum cartridge21. The drum cartridge21includes a drum frame22, a photosensitive drum23, a scorotron charger24, a cleaning brush25, and a transfer roller26.

As shown inFIG. 5, the drum frame22extends in the front-to-rear direction and is partitioned into a front part and a rear part. The front part is a developer-cartridge-accommodating section27for accommodating the developer cartridge32(seeFIG. 2), while the rear part is a photosensitive-drum-accommodating section28for accommodating the photosensitive drum23(seeFIG. 2). A transfer-roller-accommodating section29is provided in the drum frame22below the photosensitive-drum-accommodating section28for accommodating the transfer roller26(seeFIG. 2).

As shown inFIG. 2, a charger-supporting section31is provided in the drum frame22above the rear side of the photosensitive-drum-accommodating section28for supporting the scorotron charger24. A plate-shaped chute30is also provided in the drum frame22for guiding the paper3to the transfer point.

The chute30forms the bottom wall on the rear part of the developer-cartridge-accommodating section27. The chute30is separated a prescribed distance from the front end of the transfer-roller-accommodating section29and slopes downward toward the front. The chute30is formed a step lower than the bottom wall on the front part of the developer-cartridge-accommodating section27. A paper inlet46is formed between the front end of the chute30and the bottom wall on the front part of the developer-cartridge-accommodating section27for introducing the paper3into the drum cartridge21.

As shown inFIG. 5, a drum-side slit53is formed in a portion of the chute30opposing the device-side slit59(seeFIG. 7). The drum-side slit53is substantially rectangular in shape and disposed in the left-to-right center (widthwise center) of the chute30.

As shown inFIG. 2, a paper outlet47is formed in the rear end of the transfer-roller-accommodating section29for guiding the paper3out of the drum cartridge21.

When the drum frame22is mounted in the main casing2, as shown inFIG. 1, the transfer-roller-accommodating section29and chute30are accommodated in the recessed part56of the paper-guiding plate55. At this time, the front part of the bottom wall of the developer-cartridge-accommodating section27opposes the front guiding plate57of the paper-guiding plate55and is separated slightly therefrom in the vertical direction.

As shown inFIG. 2, the photosensitive drum23is accommodated in the photosensitive-drum-accommodating section28. The photosensitive drum23includes a main drum body33that is cylindrical in shape and has a positively charged photosensitive layer on its outer surface, and a metal drum shaft34extending along the axial center of the main drum body33in the longitudinal direction thereof. The drum shaft34can be rotatably supported in both side plates of photosensitive-drum-accommodating section28, while the main drum body33is rotatably supported on the drum shaft34.

The scorotron charger24is mounted on the charger-mounting unit31diagonally above and rearward of the photosensitive drum23. The scorotron charger24is disposed in opposition to but separated a prescribed distance from the photosensitive drum23so as not to contact the same. The scorotron charger24is a positively charging scorotron charger that generates a corona discharge from a wire formed of tungsten or the like, and can form a uniform charge of positive polarity over the surface of the photosensitive drum23.

The cleaning brush25is mounted on the rear side of the photosensitive drum23. The cleaning brush25is disposed so that a tip of the cleaning brush25is in contact with the surface of the main drum body33of the photosensitive drum23.

The transfer roller26is rotatably supported on both side plates of the drum cartridge21and contacts the photosensitive drum23in the above-to-below direction from the bottom thereof. The transfer roller26is configured of a metal roller shaft36that is covered with a roller35formed of a conductive rubber material. During a transfer operation, a transfer bias is applied to the transfer roller26.

When the laser printer1is printing, the drive force from a motor (not shown) is transmitted to the roller shaft36for driving the transfer roller26to rotate together with the roller shaft36.

The developer cartridge32is formed in a box shape that is open on the rear side. Within the developer cartridge32are provided a developer frame37, an agitator38accommodated in the developer frame37, a supply roller39, a developing roller40, and a layer-thickness regulating blade41.

The developer frame37is formed in a box shape open on the rear side. A partition42is provided for partitioning the developer frame37into a toner-accommodating chamber43on the front side, and a developing chamber44on the rear side. A passage45is formed in the partition42for providing communication between the toner-accommodating chamber43and developing chamber44. The toner-accommodating chamber43accommodates toner.

The agitator38is provided in the toner-accommodating chamber43. The supply roller39is disposed rearward of the passage45in the developing chamber44. The developing roller40is disposed rearward of the supply roller39in the developing chamber44and contacts the supply roller39so that both are compressed by the force.

The layer-thickness regulating blade41is provided above the developing roller40in the developing chamber44and contacts the surface of the developing roller40with pressure.

With this construction, the agitator38stirs toner in the toner accommodating chamber43, discharging toner toward the developing chamber44. Discharged toner is supplied onto the developing roller40by the rotating supply roller39. At this time, the toner is positively tribocharged between the supply roller39and developing roller40. As the developing roller40rotates, toner supplied to the surface of the developing roller40passes between the developing roller40and the layer-thickness regulating blade41, thereby maintaining a uniform thickness of toner layer on the surface of the developing roller40.

As the photosensitive drum23rotates, the scorotron charger24charges the surface of the photosensitive drum23with a uniform positive polarity. Subsequently, a laser beam emitted from the scanning unit19(seeFIG. 1) is scanned at a high speed over the surface of the photosensitive drum23, forming an electrostatic latent image corresponding to an image that will be formed on the paper3.

Next, positively charged toner carried on the surface of the developing roller40comes into contact with the photosensitive drum23as the developing roller40rotates and is supplied to areas on the surface of the positively charged photosensitive drum23that were exposed to the laser beam and, therefore, have a lower potential. In this way, the latent images on the photosensitive drum23are transformed into visible images so that a reverse toner image is carried on the surface of the photosensitive drum23.

As shown inFIG. 1, when the registration rollers13convey the paper3to a transfer point between the photosensitive drum23and transfer roller26, the toner image carried on the surface of the photosensitive drum23is transferred onto the paper3by a transfer bias applied to the transfer roller26. After the toner image is transferred, the paper3is conveyed to the fixing unit17. Toner remaining on the photosensitive drum23after the transfer operation is recovered by the developing roller40. Further, paper dust deposited on the photosensitive drum23from the paper3is recovered by the cleaning brush25after the transfer operation.

The fixing unit17is disposed on the rear side of the process cartridge16and includes a heating roller48and a pressure roller49. The pressure roller49is disposed below and contacts the heating roller48with pressure.

In the fixing unit17, toner transferred onto the paper3at the transfer point is fixed to the paper3by heat as the paper3passes between the heating roller48and pressure roller49. After the fixing process, the paper3is conveyed along a discharge path50that leads up to the top surface of the main casing2. Discharge rollers51provided at the top of the discharge path50discharge the paper3onto a discharge tray52formed on the top surface of the main casing2.

Next, a transfer position guiding mechanism61(seeFIG. 9) for guiding the paper3to the transfer point will be described with reference toFIGS. 3 through 10. As shown inFIG. 3, the transfer position guiding mechanism61includes a first pivoting member62and a second pivoting member63.

The first pivoting member62is disposed in a predetermined position upstream (on the front side) of the transfer point. The first pivoting member62pivotably is supported on the paper-guiding plate55of the main casing2. In other words, the first pivoting member62is selectively movable between a non-passing position and a passing position. The non-passing position and passing position are described later. The first pivoting member62functions to guide the paper3toward the second pivoting member63.

The first pivoting member62is integrally configured of a first rotational shaft64, a paper contact part65, a first contact part66, a sensor arm67(seeFIG. 5), and a pivot-restricting protrusion68.

FIG. 8is a perspective view from the bottom side of the paper-guiding plate (during the transfer operation). As shown inFIG. 8, the first rotational shaft64extends in the left-to-right direction below the front guiding plate57. More specifically, a right bearing part69is provided on the bottom surface of the paper-guiding plate55in a left-to-right center region thereof, on the right side of the device-side slit59. A side plate80is provided on the left end of the paper-guiding plate55extending downward. A left bearing part70is provided on the side plate80at a position along a plane passing through the right bearing part69in the left-to-right direction.

The first rotational shaft64is inserted into and rotatably supported by the right bearing part69and left bearing part70. More specifically, the first rotational shaft64is supported in the right bearing part69and left bearing part70with a midpoint of the first rotational shaft64in the left bearing part70and the left end of the first rotational shaft64protruding leftward from the left bearing part70. Thereby, the first rotational shaft64can rotate about an axial center of the first rotational shaft64. The first rotational shaft64is also disposed to intersect the device-side slit59in the left-to-right direction.

As shown inFIG. 3, the paper contact part65protrudes radially outward from the first rotational shaft64. The paper contact part65is formed of a slender plate piece slightly narrower than the device-side slit59and is disposed opposite the device-side slit59. The paper contact part65is configured to protrude through the device-side slit59farther than the top surface of the front guiding plate57.

FIG. 9is a side view of the transfer position guiding mechanism61. As shown inFIGS. 3 and 9, the first contact part66protrudes radially outward from the first rotational shaft64in a different direction from the paper contact part65and, more specifically, forms an obtuse angle (100-130°, for example) with the paper contact part65. The first contact part66is formed of a slender plate piece having substantially the same width as the paper contact part65, and is also disposed in a position on the first rotational shaft64corresponding to the device-side slit59, i.e. the same left-to-right position as the paper contact part65.

As shown inFIGS. 8 and 9, the first contact part66is formed substantially in the shape of the letter J in a side view. More specifically, the first contact part66includes a protruding rod71that protrudes radially outward from the first rotational shaft64, and an engaging piece72that protrudes further from the protruding portion. The engaging piece72bents from the free end of the protruding rod71toward a second contact part83described later at an acute angle (30-60°, for example). The engaging piece72is shorter than the protruding rod71, and the distal end of the engaging piece72is rounded into a circular shape when viewed from the side.

As shown inFIGS. 8 and 9, the sensor arm67is formed substantially in an L-shape having an arm part73disposed on the left end of the first rotational shaft64, and a light-interrupting piece74provided on the distal end of the arm part73.

The arm part73protrudes radially outward from the left end of the first rotational shaft64in a different direction from the paper contact part65when viewed from the side, and more specifically forms an acute angle (5-45°, for example) with the paper contact part65.

As shown inFIGS. 5 and 9, the light-interrupting piece74projects slightly leftward from the distal end of the arm part73, then extends from the left end of the projected part in a circumferential direction around the first rotational shaft64, forming an arc shape that is curved in the front-to-rear direction. As shown inFIGS. 5,6,9and10, the light-interrupting piece74pivots in the circumferential direction about the center of the first rotational shaft64when the first rotational shaft64rotates.

The photosensor75is also provided in the main casing2. As shown inFIGS. 5 and 6, the photosensor75is disposed in the same position as the light-interrupting piece74relative to the left-to-right direction and is positioned in the front-to-rear direction for allowing the light-interrupting piece74to be interposed therein and retracted therefrom as the first rotational shaft64rotates. The photosensor75is shaped substantially like three sides of a rectangle and includes a light-emitting element76and a light-receiving element77that are separated but confront each other vertically. A detection position P shown inFIGS. 9 and 10is a position at which the photosensor75detects a detection light transmitted between the light-emitting element76and light-receiving element77.

Through rotation of the first rotational shaft64, the light-interrupting piece74pivots between a retracted position shown inFIGS. 5 and 9, when the light-interrupting piece74is retracted from the light-emitting element76and light-receiving element77, and an advanced position shown inFIGS. 6 and 10, when the light-interrupting piece74is interposed between the light-emitting element76and light-receiving element77.

When the light-interrupting piece74is in the retracted position shown inFIGS. 5 and 9, the light-interrupting piece74is separated from the detection position P, allowing the light-receiving element77to receive detection light emitted from the light-emitting element76.

When the light-interrupting piece74is in the advanced position shown inFIGS. 6 and 10, the light-interrupting piece74overlaps the detection position P, thereby blocking the detection light emitted from the light-emitting element76and preventing the light-receiving element77from receiving this detection light.

As shown inFIG. 8, the pivot-restricting protrusion68has a substantially rectangular plate shape and is provided near the right side of the left bearing part70. As shown inFIGS. 9 and 10, the pivot-restricting protrusion68protrudes radially outward from the first rotational shaft64in a different direction than the paper contact part65, and more specifically in a direction forming an obtuse angle (120-180°, for example) with the paper contact part65.

As shown inFIG. 8, a stopper78is provided on the bottom surface of the paper-guiding plate55near the right side of the left bearing part70so as to be capable of contacting the pivot-restricting protrusion68. The stopper78is substantially rectangular in shape and extends in the front-to-rear direction. As shown inFIG. 9, the stopper78is disposed on the bottom surface of the paper-guiding plate55at an angle for contacting the pivot-restricting protrusion68when the first rotational shaft64rotates so that the paper contact part65is erected vertically. Hereafter, the first pivoting member62is said to be in a “non-passing position” when the paper contact part65is erected vertically.

As shown inFIGS. 8 and 10, a spring79is also connected to the first pivoting member62for positioning the first pivoting member62in the non-passing position. More specifically, the spring79urges the pivot-restricting protrusion68so that the first pivoting member62moves from the passing position toward the non-passing position. The spring79is configured of a coil spring (tension spring) and extends in the front-to-rear direction between the side plate80(seeFIG. 8) on the left end of the paper-guiding plate55and the stopper78. One end of the spring79is engaged in a spring-engaging part (not shown) protruding from the first rotational shaft64in substantially the same radially direction as the pivot-restricting protrusion68, while the other end is engaged with the side plate80.

The urging force of the spring79urges the first pivoting member62in a direction for rotating the first rotational shaft64clockwise inFIG. 9. Hence, when no external forces are applied, the first rotational shaft64rotates clockwise until the pivot-restricting protrusion68contacts the stopper78, placing the first pivoting member62in the non-passing position. By contacting the stopper78, the pivot-restricting protrusion68restricts the first rotational shaft64from rotating past the non-passing position in the clockwise direction. In other words, the first pivoting member62can pivot from the passing position to the non-passing position in the clockwise direction without overrunning the non-passing position.

When the first pivoting member62is disposed in the non-passing position, the paper contact part65is in the erect state shown inFIGS. 3 and 5, protruding upward from the front guiding plate57through the device-side slit59, and is received in the drum-side slit53on the drum side (seeFIG. 5). Further, the first contact part66is arranged so that the protruding rod71extends rearward, while the sensor arm67is arranged with the light-interrupting piece74in the retracted position shown inFIG. 9.

As shown inFIG. 3, the second pivoting member63is disposed between the first pivoting member62and the transfer point along the conveying direction of paper3(front-to-rear direction). The second pivoting member63guides a sheet of paper3received from the first pivoting member62to the photosensitive drum23. The second pivoting member63is pivotably supported by the chute30of the process cartridge16(seeFIG. 2). More specifically, the second pivoting member63is selectively movable between a separated position and a proximal position. The separated position is farther from the photosensitive drum23than the proximal position, described later.

As shown inFIGS. 3 and 5, the second pivoting member63is integrally configured of a second rotational shaft81, a transfer guide part82, and the second contact part83.

As shown inFIG. 3, the transfer guide part82and second contact part83form an inverted V-shape over the second rotational shaft81. The transfer guide part82and the second contact part83protrude forward from the second rotational shaft81.

Shaft-supporting parts84are provided on the rear end of the chute30for rotatably supporting the second rotational shaft81. As shown inFIG. 5, the second rotational shaft81is formed slightly longer than the drum-side slit53in the left-to-right direction. The second rotational shaft81is inserted through the shaft-supporting parts84and rotates about its axial center, serving as a second support point.

The shaft-supporting parts84are formed in the left-to-right center of the chute30on the rear end of the drum-side slit53so that the drum-side slit53is interposed between the shaft-supporting parts84in the left-to-right direction.

As shown inFIGS. 5 and 9, the transfer guide part82includes a guide-supporting part85protruding from the second rotational shaft81toward the transfer point, and film members86extending from the rear edge of the guide-supporting part85toward the transfer point.

As shown inFIG. 9, the guide-supporting part85is formed in a flat plate-shape extending in the left-to-right direction and is disposed on the rear side of the chute30(seeFIG. 5). The center of the front edge on the guide-supporting part85is fixed to the second rotational shaft81via a mounting plate87. The rear edge of the guide-supporting part85extends to a point between the second rotational shaft81and photosensitive drum23and confronts the photosensitive drum23with a gap formed therebetween.

As shown inFIG. 5, two of the film members86are disposed adjacent to each other in the left-to-right direction with a gap formed therebetween in the left-to-right center of the guide-supporting part85. The film members86are flexible film formed of a synthetic resin or the like in a substantially rectangular shape. The film members86are affixed to the top surface of the guide-supporting part85, extending in the left-to-right direction along the rear edge thereof. The rear edges of the film members86extend from the guide-supporting part85of the second pivoting member63.

As shown inFIG. 5, the second contact part83is formed in a substantially rectangular shape slightly narrower than the drum-side slit53, and extends in the front-to-rear direction. The second contact part83is disposed inside the drum-side slit53, with the rear end of the second contact part83affixed to the second rotational shaft81via the mounting plate87(seeFIG. 9). As shown inFIG. 9, the second contact part83protrudes from the second rotational shaft81toward the first contact part66of the first pivoting member62such that the distal end of the second contact part83can contact the engaging piece72from above.

The second pivoting member63is formed to satisfy the equation L1·F1<L2·F2, where L1is the distance from the second rotational shaft81to the rear end of the guide-supporting part85, F1is the force that the weight of the transfer guide part82generates at the rear end of the guide-supporting part85, L2is the distance from the second rotational shaft81to the front end of the second contact part83, and F2is the force that the weight of the second contact part83generates at the front edge of the second contact part83.

Hence, the second pivoting member63is urged by its own weight to pivot so that the transfer guide part82pivots upward and the second contact part83pivots downward. Specifically, the second pivoting member63is urged to rotate clockwise inFIG. 9about the second rotational shaft81. Thereby, the second contact part83is moved in interlocking relation with the engaging piece72of first contact part66.

However, since the first pivoting member62is disposed in the non-passing position shown inFIG. 9by the urging force of the spring79, as described above, the first contact part66is oriented with the protruding rod71extending rearward and the engaging piece72protruding upward.

Accordingly, the second pivoting member63is disposed in the separated position when the first pivoting member62is disposed in the non-passing position. The separated position is the state of the second pivoting member63when the film members86are separated from the photosensitive drum23. In other words, the film members86are oriented farther from the photosensitive drum23when the second pivoting member63is moved to the non-passing position. When the second pivoting member63is in the separated position, the transfer guide part82protrudes rearward and slightly downward from the second rotational shaft81. At this time, the rear edges of the film members86are positioned toward the transfer roller26and separated from the photosensitive drum23. Further, the second contact part83protrudes forward from the second rotational shaft81, and the front-to-rear center portion of the second contact part83contacts the top of the engaging piece72.

As described above, the first pivoting member62is in the non-passing position and the second pivoting member63is in the separated position when the paper3is not passing over the first pivoting member62. When the paper3is conveyed from the registration rollers13so that the leading edge of the paper3in the conveying direction (hereinafter simply referred to as “leading edge”) contacts the paper contact part65positioned in the conveying path, as shown inFIG. 9, the pressure applied to the paper contact part65by the paper3causes the paper contact part65to rotate rearward, and the first rotational shaft64rotates counterclockwise against the urging force of the spring79.

When the paper contact part65rotates rearward about the center of the first rotational shaft64, as shown inFIG. 10, the paper3is conveyed over the paper contact part65toward the photosensitive drum23. In other words, abutting the paper3conveyed against the paper contact part65rotates the paper contact part65to move the first pivoting member62to the passing position from the non-passing position. The passing position is the orientation of the first pivoting member62when the paper contact part65is laid downward toward the rear.

The first pivoting member62remains in the passing position while the paper3passes over the paper contact part65. While the first pivoting member62is in the passing position and the paper contact part65is angled rearward, a gap is formed above the paper contact part65for allowing passage of the paper3, as shown inFIGS. 4 and 10. At this time, the first contact part66is arranged with the protruding rod71extending downward, and the sensor arm67is oriented with the light-interrupting piece74in the advanced position.

When in the advanced position, the light-interrupting piece74overlaps the detection position P in the optical path of the detection light, thereby preventing the light-receiving element77from receiving the detection light. The photosensor75inputs a light-interruption signal to a CPU (not shown) provided in the main casing2to indicate that the light-receiving element77is not receiving light. This light-interruption signal is inputted into the CPU while the paper3is in contact with the paper contact part65.

Based on the timing that the light-interruption signal is inputted, the CPU controls the scanning unit15to begin scanning a laser beam at high speed. Accordingly, before the paper3comes into contact with the photosensitive drum23, the scanning unit15forms an electrostatic latent image on the photosensitive drum23that is subsequently developed into a toner image.

In the meantime, since the second contact part83contacts the engaging piece72due to its own weight when the paper3presses against and rotates the paper contact part65, rotating the first contact part66downward, the second contact part83pivots downward by its own weight following the engaging piece72of the light-emitting element76. Since the second rotational shaft81rotates clockwise at this time, the second pivoting member63pivots from the separated position to the proximal position in association with the pivoting of the first pivoting member62as shown inFIG. 10.

In other words, the second pivoting member63is disposed in the proximal position while the paper3passes over the paper contact part65. The proximal position denotes the orientation of the second pivoting member63when the rear edges of the film members86are disposed in proximity to the photosensitive drum23. In other words, the film members86are oriented toward photosensitive drum23when the second pivoting member63is moved to the passing position. When the second pivoting member63is in the proximal position, the transfer guide part82protrudes rearward and upward from the second rotational shaft81, as shown inFIGS. 4 and 10. At this time, the second contact part83slopes downward toward the front from the second rotational shaft81with the front end of the second contact part83contacting the top of the engaging piece72.

Accordingly, after the leading edge of the paper3passes over the paper contact part65, the film members86guides the paper3so that the leading edge of the paper3contacts the photosensitive drum23upstream of the transfer point. As a result, instead of a gap being formed between the paper3and photosensitive drum23on the upstream side of the transfer point, the paper3is conveyed to the transfer point in close contact with the photosensitive drum23.

When the trailing edge of the paper3in the conveying direction (hereinafter simply referred to as the “trailing edge”) subsequently passes over the paper contact part65, the paper3no longer applies a force to the paper contact part65. At this time, the urging force of the spring79rotates the first rotational shaft64clockwise so that the first pivoting member62pivots from the passing position to the non-passing position. Hence, the first pivoting member62once again returns to the non-passing position shown inFIG. 3.

Further, as the protruding rod71pivots upward together with the pivoting of the first pivoting member62, the engaging piece72pivots upward while sliding rearward along the second contact part83of the second pivoting member63. The force with which the engaging piece72presses against the second contact part83causes the second contact part83to pivot upward against its own weight. Since the second rotational shaft81rotates counterclockwise at this time, the second pivoting member63pivots from the proximal position to the separated position along with the pivoting of the first pivoting member62. Hence, the second pivoting member63is again placed in the separated position shown inFIGS. 3 and 9.

When the second pivoting member63is in the separated position, the light-interrupting piece74is in the retracted position. Since the light-interrupting piece74is separated from the detection position P at this time, the light-receiving element77can receive the detection light. Hence, the photosensor75inputs a light-transmission signal to the CPU in the main casing2indicating that the light-receiving element77is receiving the detection light. The photosensor75inputs this light-transmission signal into the CPU as long as the paper3is not contacting the paper contact part65.

Hence, the light-transmission signal is inputted into the CPU while the paper3is not contacting the paper contact part65, and a light-interruption signal is inputted into the CPU when the light contacts the paper contact part65.

When the second pivoting member63is disposed in the separated position, the film members86are separated from the photosensitive drum23, with the rear edges of the film members86disposed near the transfer roller26side.

The image-forming device having the construction described above can obtain the following effects.

(1) When the paper3is conveyed by the registration rollers13toward the transfer position guiding mechanism61, the leading edge of the paper3first contacts the paper contact part65and begins to pass over the paper contact part65. When the paper3passes over the paper contact part65, the first pivoting member62pivots about the first rotational shaft64into the passing position.

Next, the paper3passes over the film members86. At this time, the second pivoting member63is disposed in the proximal position having pivoted about the second rotational shaft81together with the pivoting of the first pivoting member62. Hence, the paper3is guided along the film members86while being conveyed to the photosensitive drum23.

After the paper3has passed over the paper contact part65, the first pivoting member62pivots about the first rotational shaft64and returns to the non-passing position, and the second pivoting member63pivots about the second rotational shaft81in association with the pivoting of the first pivoting member62and returns to the separated position separated from the photosensitive drum23. When the trailing edge of the paper3has passed the paper contact part65, the film members86are brought into the separated position, so that the second pivoting member63guides the recording medium without the paper3pressing the film members86downward. Hence, when the trailing edge of the paper3separates from the film members86, it is prevented that the film members86generate abnormal noise.

Further, since the transfer position guiding mechanism61is configured to pivot the first pivoting member62and the second pivoting member63based only on passing or non-passing of the paper3, there is no need to provide a complex structure for placing the guide member near and separating from the photosensitive drum, such as a sensor for detecting the leading edge of paper, motor, and CPU for moving the motor based on the signal from the sensor, and complex control, thereby reducing the number of required parts and simplifying the construction.

(2) Further, when the paper3contacts the paper contact part65extending into the paper-conveying path above the front guiding plate57, the first rotational shaft64rotates about its axial center, pivoting the first contact part66into the passing position. As the first contact part66pivots, the second contact part83of the second pivoting member63slides along the engaging piece72. At this time, the second rotational shaft81rotates about its axial center, pivoting the transfer guide part82and placing the second pivoting member63in the proximal position, with the film members86of the transfer guide part82in proximity to the photosensitive drum23.

After the paper3passes over the paper contact part65, removing contact between the paper3and paper contact part65, the first rotational shaft64rotates about its axial center, pivoting the first contact part66and placing the first pivoting member62in the non-passing position.

As the first contact part66pivots, the second contact part83of the second pivoting member63slides along the engaging piece72. At this time, the second rotational shaft81rotates about its axial center, pivoting the transfer guide part82and placing the second pivoting member63in the separated position in which the film members86of the transfer guide part82are separated from the photosensitive drum23.

Hence, this construction can achieve reliable operations through simple formation of the first pivoting member62and the second pivoting member63.

(3) When the paper3is conveyed through the transfer position guiding mechanism61toward the photosensitive drum23, the paper3passes over the film members86on the transfer guide part82. Therefore, the transfer position guiding mechanism61can reliably place the paper3in contact with the photosensitive drum23.

(4) When the paper3does not contact the paper contact part65, the second pivoting member63is disposed in the separated position by the weight of the second contact part83, since the second contact part83always contacts the engaging piece72by its own weight in the transfer position guiding mechanism61described above. However, when the paper3contacts the paper contact part65, the first pivoting member62is moved to the passing position. Hence, the engaging piece72is rotated downward so that the second pivoting member63moves to the proximal position allowing the second contact part83to pivot down. Accordingly, through a simple construction that eliminates the need for a coupling member for coupling the first contact part66and the second contact part83, it is possible to pivot the second pivoting member63into the proximal position or the separated position in association with pivoting of the first pivoting member62.

(5) In the transfer position guiding mechanism61described above, the second pivoting member63is formed to satisfy the equation L1·F1<L2·F2, where L1is the distance from the second rotational shaft81to the rear end of the guide-supporting part85, F1is the force that the weight of the transfer guide part82generates at the rear end of the guide-supporting part85, L2is the distance from the second rotational shaft81to the front end of the second contact part83, and F2is the force that the weight of the second contact part83generates at the front edge of the second contact part83. Hence, the second pivoting member63can be reliably placed in contact with the first contact part66at all times through the weight of the second contact part83.

(6) Further, after the paper3passes over the paper contact part65, removing contact between the paper contact part65and paper3, the first pivoting member62pivots about the axial center of the first rotational shaft64until the pivot-restricting protrusion68contacts the stopper78, placing the first pivoting member62in the non-passing position. In this way, the first pivoting member62can be placed in a prescribed non-passing position while the second pivoting member63can be placed in prescribed separated position.

(7) In the transfer position guiding mechanism61described above, the light-interrupting piece74of the sensor arm67pivots between the passing position and non-passing position through rotation of the first rotational shaft64so that the light-interrupting piece74overlaps or separates from the detection position P. The photosensor75detects whether the light-interrupting piece74is in an overlapped state or separated state relative to the detection position P and inputs the detected state into the CPU as a light-interruption signal or a light-transmission signal. Accordingly, the CPU can detect the timing for beginning to write an image on the photosensitive drum23based on the timing of the inputted light-interruption signal. By controlling the scanning unit15to begin scanning a laser beam at a high speed based on the inputted timing of the light-interruption signal, the CPU can reliably transfer a toner image onto the paper3. As a result, through the pivoting of the first pivoting member62, this construction can simultaneously guide the paper3to the photosensitive drum23by the pivoting of the second pivoting member63and detect a timing to begin writing an image on the photosensitive drum23.

(8) In the laser printer1of the preferred embodiment, the drum cartridge21is detachably mounted in the main casing2. This construction can simplify operations for removing paper jams and for replacing the drum cartridge21.

(9) Since the first pivoting member62is provided in the main casing2rather than in the drum cartridge21, which is a consumable product, this construction reduces the cost of the drum cartridge21. Further, if the first pivoting member62were provided in the drum cartridge21, the first pivoting member62could be damaged when mounting or removing the drum cartridge21. However, such damage can be avoided by providing the first pivoting member62in the main casing2.

(10) On the other hand, the second pivoting member63is provided in the drum cartridge21. This construction can improve the accuracy for placing the second pivoting member63in a proximal position and separated position relative to the photosensitive drum23, making it possible to reliably transfer a toner image onto the paper3.

In the preferred embodiment described above, the second contact part83contacts the engaging piece72of the first contact part66by its own weight. However, the second contact part83may be slidably engaged with the first contact part66, as shown inFIG. 11. InFIG. 11, like parts and components to those in the preferred embodiment described above are designated with the same reference numerals to avoid duplicating description.

As shown inFIG. 11, the first contact part66is formed substantially in the shape of the letter J in a side view, and is configured of a protruding rod91that protrudes along a straight line radially outward from the first rotational shaft64, and an engaging piece92that is bent from the free end of the protruding rod91at a prescribed angle (45-135°, for example) toward the second contact part83. The engaging piece92is shorter than the protruding rod91. Both widthwise edges on the distal end of the engaging piece92protrude slightly outward in the width direction.

The second contact part83includes an engaging piece93that is substantially rectangular in a plan view. The engaging piece93extends in the front-to-rear direction and is slightly narrower than the drum-side slit53. An elongated groove94is formed at a midpoint in the engaging piece93relative to the longitudinal direction and extends along the conveying direction of the paper3(the longitudinal direction) and receives the engaging piece92to slide therewithin.

The elongated groove94is formed with a front-to-rear length corresponding to the range in which the first pivoting member62pivots between the non-passing position and the passing position. The distal end of the engaging piece92penetrates and engages with the elongated groove94. Through this construction, the engaging piece92is slidably fitted into the elongated groove94and is allowed to slide within the elongated groove94a distance corresponding to the range in which the first pivoting member62pivots between the non-passing position and the passing position.

When the paper3passes over the paper contact part65causing the first rotational shaft64to rotate about its axial center in the transfer position guiding mechanism61, the engaging piece92of the first contact part66slides rearward relative to the elongated groove94of the second contact part83. Hence, the second pivoting member63rotates about the axial center of the second rotational shaft81into the proximal position.

After the paper3passes over the paper contact part65, the first rotational shaft64rotates about its axial center, sliding the engaging piece92of the first contact part66forward relative to the elongated groove94of the second contact part83. At this time, the second pivoting member63rotates about the axial center of the second rotational shaft81back to the separated position.

In the transfer position guiding mechanism61shown inFIG. 11, the elongated groove94has a length in the front-to-rear direction corresponding to the range in which the first pivoting member62pivots between the non-passing position and the passing position. Hence, when the engaging piece92slides rearward in the elongated groove94and contacts the rear edge of the elongated groove94, the second pivoting member63is disposed in the proximal position. When the engaging piece92slides forward in the elongated groove94and contacts the front edge of the elongated groove94, the second pivoting member63is disposed in the separated position.

Through the simple construction of the preferred embodiment described above, the first pivoting member62can be reliably placed in the non-passing position or passing position and the second pivoting member63can be reliably placed in the proximal position or separated position through contact between the pivot-restricting protrusion68and stopper78, rather than requiring special positioning.

Although the present invention has been described with respect to specific embodiments, it will be appreciated by one skilled in the art that a variety of changes may be made without departing from the scope of the invention. For example, although the embodiment has been described so that the first and second members62and63are pivotally movable about their own rotational shafts64and81, these two members may be arranged to move differently, e.g., vertically. Further, in the above-described embodiment, the first pivoting member62has been described to have the paper contact part65and the first contact part66both protruding radially outward from angularly displaced positions on the same portion in the axial direction of the first rotational shaft64. However, the paper contact part65and the first contact part66may be provided on different portions in the axial direction of the first rotational shaft64with the paper contact part65being disposed in the paper conveying path. The first contact part66may be disposed in a position offset from the paper conveying path.