Image forming apparatus

A supporting unit is mounted on a body of an image forming apparatus in a swingable manner around a swing fulcrum. A through shaft serves as the swing fulcrum, which is inserted into the supporting unit through the swing fulcrum so that both ends of the through shaft are supported by supporting members. The through shaft includes at least one of an operation member that is slidable on the through shaft in an axial direction and a biasing unit that biases a sliding force in one direction of the axial direction. When the supporting unit is opened with respect to the body, at least a part of a conveying path on which the recording medium is conveyed is exposed.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority to and incorporates by reference the entire contents of Japanese priority document 2006-344510 filed in Japan on Dec. 21, 2006.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an image forming apparatus that forms an image on a recording medium, such as a copier, a printer, a facsimile, and a multifunction product.

2. Description of the Related Art

In an image forming apparatus such as a copier, a printer, a facsimile, and a multifunction product (MFP), an image is formed by conveying a recording medium such as a sheet on a conveying path, so that a sheet may be jammed during a conveyance of the sheet. Because the sheet jam is basically cleared by a user, it is indispensable to make a jam processing easier for a user.

Japanese Patent Application Laid-open No. 2003-186371 discloses an image forming apparatus in which a cover unit that includes a transfer carrying belt unit, a guiding plate, and a registration roller on a driven side is arranged to be openable with respect to a body of the apparatus so that a sheet conveying path from a sheet feeding roller to a portion just before a fixing unit is exposed. The cover unit is supported by a swing shaft in a swingable manner with respect to the body. The cover unit needs to be detachable from the body for a maintenance or a component replacement.

FIG. 17is a perspective view of a swing shaft supporting portion for supporting a detachable cover unit. An oval-shaped shaft200with an oval section that is short in an axial direction is arranged on each inner wall of both side plates of a body of an image forming apparatus. The cover unit includes bearing members210each having a cutout portion211from which a small diameter portion201of the oval-shaped shaft200can escape. The oval-shaped shaft200is inserted into the bearing member210by allowing the small diameter portion201to pass through the cutout portion211. In this state, a large diameter portion202of the oval-shaped shaft200is supported by the bearing member210. The configuration makes it possible for the cover unit to swing with respect to the body. In addition, by appropriately positioning the cutout portion211with respect to the small diameter portion201and moving the cover unit in a direction in which the small diameter portion201can escape, the cover unit can be taken out of the body.

However, when such bearing configuration is used, a positioning accuracy of the cover unit is degraded because each end of the cover unit is independently supported by the oval-shaped shaft200, which may adversely affect a sheet conveyance or an image transfer. Specifically, a misalignment occurs in a shaft line of a conveying unit in the cover unit with respect to a conveying unit in the body that conveys sheets in cooperation with the conveying unit in the cover unit, which may cause jamming or skewing of sheets.

SUMMARY OF THE INVENTION

An apparatus for forming an image on a recording medium, according to one aspect of the present invention, includes a supporting unit that is mounted on a body of the apparatus in a swingable manner around a swing fulcrum and a through shaft that serves as the swing fulcrum, the through shaft being inserted into the supporting unit through the swing fulcrum so that both ends of the through shaft are supported by supporting members. The through shaft includes at least one of an operation member that is slidable on the through shaft in an axial direction and a biasing unit that biases a sliding force in one direction of the axial direction. When the supporting unit is opened with respect to the body, at least a part of a conveying path on which the recording medium is conveyed is exposed

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1is a schematic diagram of a full-color printer100such as a color laser printer as an example of an image forming apparatus according to the present invention.

As shown inFIG. 1, the printer100includes an intermediate transfer belt11and image forming units10M,10C,10Y, and10Bk for magenta, cyan, yellow, and black, respectively. The intermediate transfer belt11is arranged substantially in the middle of the printer100, and is stretched over a plurality of rollers. The image forming units10M,10C,10Y, and10Bk are arranged along a lower side of the intermediate transfer belt11.

Each of the image forming units10M,10C,10Y, and10Bk includes a photosensitive drum1as an image carrier, and a charging unit, a developing unit, a cleaning unit, and the like that are arranged around the photosensitive drum1. A transfer roller12is arranged as a primary transfer unit inside the intermediate transfer belt11opposite to the photosensitive drum1. The image forming units10M,10C,10Y, and10Bk have the same configuration using different developers for different colors. The image forming units10M,10C,10Y, and10Bk are arranged in the order of magenta, cyan, yellow, and black from the left inFIG. 1. Each of the image forming units10M,10C,10Y, and10Bk is detachably mounted on a body50of the printer100as a process cartridge.

An optical writing unit14is arranged below the image forming units10M,10C,10Y, and10Bk. The optical writing unit14that includes a polygon mirror and a mirror group (not shown) emits an optically-modulated laser beam on a surface of each of the photosensitive drums1. A plurality of optical writing units can be respectively arranged for the image forming units10M,10C,10Y, and10Bk. However, it is advantageous in cost to use a single optical writing unit in common for the image forming units10M,10C,10Y, and10Bk. The intermediate transfer belt11and the optical writing unit14are each formed as a unit, so that each of them can be detached from the body50.

Two stages of sheet feeding cassettes15aand15bfor sheet feeding units16aand16bare installed at a lower portion of the printer100. Each of the sheet feeding units16aand16bincludes a pick-up roller, a feeding roller, and a separating roller. Pairs of a driving roller17aand a driven roller17b(conveying rollers17) are arranged to convey a recording medium (hereinafter, “a sheet”) such as a printing paper fed by the sheet feeding units16aand16b. A pair of registration rollers18is arranged above the upper pair of conveying rollers17(on a downstream side in a sheet conveying direction). A transfer roller19serving as a secondary transfer unit is arranged above the registration rollers18opposite to a transfer roller13that is one of the rollers over which the intermediate transfer belt is stretched.

A fixing unit20is arranged above the secondary transfer unit, and first to third switching claws21,22, and23for switching sheet conveying directions are arranged above the fixing unit20. Each of the switching claws21to23is switched between the positions indicated by a solid line and a broken line inFIG. 2by a driving force of an actuator such as a solenoid (not shown). Pairs of conveying rollers24to27and sheet sensors35to41are appropriately arranged on a sheet conveying path. The sheet conveying path is appropriately formed by members such as guiding plates.

A sheet discharging tray30is arranged on top of the body50, and a pair of sheet-discharging rollers29for discharging sheets to the sheet discharging tray30is arranged on the upper left of the fixing unit20.

A sheet reversing unit60serving as a supporting unit is arranged on a right side of the body50shown inFIG. 1. The sheet reversing unit60includes a sheet reversing path61and a sheet returning path62. A pair of first reversing rollers31is arranged at an inlet of the sheet reversing path61(at an upper portion of the apparatus), and a pair of second reversing rollers32is arranged in the middle of the sheer reversing path61. The first and the second reversing rollers31and32can rotate in both clockwise and counterclockwise directions inFIG. 1. Pairs of conveying rollers26and27are arranged at positions at which the sheet returning path62are divided equally into three portions. The third switching claw23just next to the first reversing rollers31is positioned at an inlet to the sheet returning path62from the sheet reversing path61.

A manual tray33is arranged on a side of the sheet reversing unit60so that the manual tray33can be pulled out and accommodated. InFIG. 1, the manual tray33is pulled out. A sheet feeding unit34including a pick-up roller, a feeding roller, and a separating roller is arranged to feed sheets from the manual tray33. A sheet feeding roller28is positioned next to the sheet feeding unit34to be inner side of the body50. Driven rollers come into close contact with the sheet feeding roller28on both up and down sides thereof. The sheet feeding roller28can be rotated in both clockwise and counterclockwise directions inFIG. 1. When a sheet is fed from the sheet returning path62, the sheet feeding roller28is driven to rotate counterclockwise, and when a sheet is fed from the manual tray33, the sheet feeding roller28is driven to rotate clockwise.

An image forming operation of the above-constituted full-color printer100is explained.

The photosensitive drum1of each of the image forming units10M,10C,10Y, and10Bk is driven to rotate clockwise by a driving unit (not shown) inFIG. 1, and the surface of the photosensitive drum1is uniformly charged to a predetermined polarity by the charging unit. The optical writing unit14irradiates the uniformly charged surface of each of the photosensitive drums1with a laser beam, so that an electrostatic latent image is formed on the surface. The desired full-color image information is separated into four pieces of single-color image information for magenta, cyan, yellow, and black, each of which is exposed on each of the photosensitive drums1. A toner of each color is applied to the electrostatic latent image from each developing unit, so that a toner image of each color is developed.

The intermediate transfer belt11is driven counterclockwise as shown by an arrow inFIG. 1. The toner images of four colors are sequentially transferred one above the other to the intermediate transfer belt11from the photosensitive drums1through operations of the first transfer rollers12at the image forming units10M,10C,10Y, and10Bk. In this manner, the intermediate transfer belt11carries a full-color toner image on its surface.

A single-color image or a two or three-color image can be formed by using one or some of the image forming units10M,10C,10Y, and10Bk. For monochrome printing, the image forming unit10Bk on the rightmost side of the image forming units10M,10C,10Y, and10Bk inFIG. 1is used.

A residual toner adhered to a surface of the photosensitive drum1after a toner image is transferred to the intermediate transfer belt11is removed by the cleaning unit. Then, the surface of the photosensitive drum1is neutralized by a neutralizing unit to have an initial potential, whereby the photosensitive drum1is prepared for the next image forming.

A sheet is selectively fed from the manual tray33or one of the sheet feeding cassettes15aand15b, and sent to the secondary transfer section through the registration rollers18at which the timing for conveying the sheet is adjusted to synchronize with the movement of the intermediate transfer belt11carrying the toner image. In this example, a transfer voltage having a polarity opposite to that of the charged toners of the toner images on the surface of the intermediate transfer belt11is applied to the transfer roller19, so that the toner images on the surface of the intermediate transfer belt is transferred to the sheet all at once. When the sheet on which the toner image is transferred passes through the fixing unit20, the toner image is fused and fixed on the sheet by heat and pressure. The sheet with the toner image fixed thereon is discharged onto the sheet discharging tray30by the sheet-discharging rollers29. A sheet conveying path for a single-side printing is indicated by a solid line [1] inFIG. 2(when a sheet is fed from the sheet feeding cassettes15aand15b).

A sheet discharging tray (for example, a four-bin tray having a sorting function) can be optionally mounted on the top surface of the printer100that is above the second switching claw22, and the sheet with the toner image fixed thereon can be discharged on the optionally-mounted sheet discharging tray. A sheet conveying path for discharging a sheet to the optionally-mounted sheet discharging tray (after passing through the fixing unit20) is indicated by a broken line [2] inFIG. 2.

When performing a double-side printing, the sheet with the toner image fixed on one side is sent into the sheet reversing path61by properly switching the first to the third switching claws21to23. In this case, the first and the second switching claws21and22are switched to the positions indicated by the broken lines inFIG. 2. The third switching claw23is switched to the position indicated by the solid line inFIG. 2. The first and the second reversing rollers31and32are rotated clockwise shown inFIG. 1. A sheet conveying path for sending the sheet into the sheet reversing path61(after passing through the conveying rollers25) is indicated by a two-dot chain line [3] inFIG. 2.

When the sheet sensor40detects a rear end of the sheet sent into the sheet reversing path61, the first and the second reversing rollers31and32are rotated counterclockwise inFIG. 1, so that the sheet is reversed. At this time, the third switching claw23is switched to the position indicated by the broken line inFIG. 2to send the sheet into the sheet returning path62.

The sheet returning path62is combined with the sheet conveying path from the manual tray33at its lower end, and is also combined with the sheet conveying path from the sheet feeding cassettes15aand15bon a left side of the sheet feeding roller28. The sheet is conveyed through the sheet returning path62by the conveying rollers26and27, and is further conveyed to the registration rollers18by the sheet feeding roller28. A sheet conveying path that passes through the sheet returning path62(from the third switching claw23to the junction with the solid line [1]) is indicated by a one-dot chain line [4] inFIG. 2. A sheet conveying path for sending a sheet from the manual tray33(to a point at which the sheet finishes passing through the sheet feeding roller28) is indicated by a one-dot chain line [5] inFIG. 2.

The sheet reversed in the sheet reversing path61is passed through the sheet returning path62, whereby the sheet is turned upside down. Then, a toner image is transferred on a back side of the sheet from the intermediate transfer belt11, and the toner image is fixed on the sheet at the fixing unit. The sheet carrying an image on each side is discharged to the sheet discharging tray30or the optionally-mounted tray, whereby the double-side printing is finished.

The sheet reversing unit60is mounted in a swingable manner about a swing shaft63arranged at its lower portion as a fulcrum, and can be opened or closed with respect to the body50.FIG. 3is a schematic diagram of the sheet reversing unit60in an open state.

The sheet reversing unit60includes a guiding plate forming the sheet reversing path61, part of the guiding plate66forming the sheet returning path62, a transfer unit64, the third switching claw23, the first and the second reversing rollers31and32, the manual tray33, the sheet feeding unit34, the sheet feeding roller28, and the driven rollers17bthat are opened or closed with respect to the body50.

Thus, because the sheet reversing unit60can be opened, a sheet conveying path from a position just after a sheet is fed to a position just before an image on the sheet is fixed thereto is opened. Therefore, even a user can easily clear a sheet jamming. The sheet reversing unit60can be detached from the body50for maintenance or component replacement. For making the sheet reversing unit60detachable from the body50, if the swing shaft63is composed of the bearing members210as shown inFIG. 17, the accuracy in positioning the cover unit and the accuracy in positioning the driven rollers17band the transfer roller19decrease, thereby adversely affecting a sheet conveyance or an image transfer.

As shown inFIG. 4, the sheet reversing unit60according to the first embodiment uses the swing shaft63that works as a through shaft penetrating through the sheet reversing unit60. The swing shaft63that works as the through shaft is formed of a hard metal, both ends of which are rotatably supported by bearings51and52mounted on the body50. The sheet reversing unit60is supported by the swing shaft63that can move in the axial direction via a bearing unit73.

The through shaft is used as the swing shaft63, so that the sheet reversing unit60can be securely held by the through shaft, and positioned with high accuracy. Consequently, the driven rollers17band the transfer roller19are positioned with high accuracy, which results in preventing a sheet conveyance or an image transfer from being adversely affected. For example, because a large load is imposed on the driven rollers17bwhen conveying a thick sheet, and a positioning accuracy of the transfer roller19affects a positioning accuracy of an image on the recording medium, the swing shaft63is used to position the sheet reversing unit60while the sheet reversing unit60securely holding the swing shaft63, thereby significantly contributing to the thick paper conveyance or the high-quality image formation.

Although the problems in the sheet conveyance or the image transfer can be avoided by using the swing shaft63that works as the through shaft, the sheet reversing unit60needs to be detachable from the body50for a maintenance or a component replacement, as described above. However, when the through shaft is used as the swing shaft63, it is difficult to pull out the swing shaft63from the bearings51and52and detach the sheet reversing unit60from the body50.

According to a second embodiment of the present invention, a sliding lever70serving as an operation member is fixed to the swing shaft63inFIG. 5. The sliding lever70includes a fixing unit71fixed to the swing shaft63and a lever unit72serving as an operation unit both of which are integrated. As shown inFIG. 5, when the swing shaft63is properly supported by the bearings51and52, the tip of the lever unit72protrudes outside the side of the sheet reversing unit60. When the lever unit72is moved to a position at which the tip aligns with the side of the sheet reversing unit60as shown inFIG. 6by pushing the lever unit72in a direction indicated by an arrow A, a right end63R of the swing shaft63is pulled out of the bearing52.

In the image forming apparatus in which the sliding lever70is fixed to the swing shaft63, the right end63R of the swing shaft63is extracted from the bearing52simply by pushing the lever unit72in the direction of the arrow A, so that the sheet reversing unit60can be pulled out of the body50in a direction indicated by an arrow B. In this case, as shown inFIG. 7, a chamfered groove52ais formed at an upper portion of the bearing52to easily pull out the sheet reversing unit60.

The sheet reversing unit60using the swing shaft63can be pulled out of the body50, so that it is possible to perform a maintenance of the sheet reversing unit60, a component replacement in the sheet reversing unit60, or the like. After performing the maintenance, the component replacement, or the like, the sheet reversing unit60needs to be mounted again. The operation is performed in the order opposite to the operation of pulling out the sheet reversing unit60from the body50. However, it is difficult to return the swing shaft63from a state shown inFIG. 6to a state shown inFIG. 5in which the swing shaft63is properly supported by the bearings51and52.

According to a third embodiment of the present invention, the operation of mounting the sheet reversing unit60is simplified by effectively utilizing a biasing of an biasing unit shown inFIG. 7.

As shown inFIG. 7, a rigid body74(for example, a molded component made from SECC) is fixed to the swing shaft63, a spring75serving as an biasing unit is arranged between the rigid body74and the sheet reversing unit60, thereby obtaining a moving force for moving the swing shaft63to the right inFIG. 7. The spring75is wound around the swing shaft63; however, the spring75can be mounted between the rigid body74and the sheet reversing unit60as shown inFIG. 8.

When the swing shaft63reaches a position at which the swing shaft63is aligned with the bearings51and52in a state the spring75is compressed by pushing the swing shaft63to the left as shown inFIG. 9, the swing shaft63is moved to the right by the action of the spring75, and both ends of the swing shaft63are supported by the bearings51and52. More specifically, as shown inFIG. 10, a left end63L of the swing shaft63is first fitted into the bearing51. At this time, the right end63R is positioned higher than the left end63L, so that the sheet reversing unit60is askew. In addition, the right end63R hits a side wall of the body50, and the spring75is compressed. When the sheet reversing unit60is moved to a horizontal position as shown inFIG. 9, the swing shaft63automatically moves to a position properly supported by the bearings51and52by the action of the compressed spring75as shown inFIG. 7. In this manner, the sheet reversing unit60can be easily mounted on the body50.

According to a fourth embodiment of the present invention, for mounting the sheet reversing unit60on the body50more smoothly by dropping it downward, a slope surface53that is formed to slope to the left toward its bottom is formed on the upper portion of the bearing52as shown inFIGS. 11 and 12. At least the right end63R is chamfered as shown inFIG. 13.

With this configuration, when the left end63L is fitted into the bearing51, the sheet reversing unit60moves to a proper position by its own weight, and the swing shaft63is properly supported by the bearings51and52by the action of the spring75, thereby enabling the sheet reversing unit60to automatically be mounted.

According to a fifth embodiment of the present invention, as shownFIGS. 14 to 16, the sliding lever70shown inFIG. 5and the spring75shown inFIG. 7are provided. The sliding lever70also works as the rigid body74, so that the sliding lever70is formed of SECC steel plate.

With this configuration, for mounting the sheet reversing unit60on the body50, when the left end63L of the swing shaft63is fitted into the bearing51, the sheet reversing unit60moves to a proper position by its own weight. Furthermore, the swing shaft63is properly supported by the bearings51and52by the action of the spring75. In this manner, mounting of the sheet reversing unit60is completed.

For detaching the sheet reversing unit60from the body50, the right end63R is pulled out of the bearing52by pushing the lever unit72of the sliding lever70against the action of the spring75in a direction opposite to a direction indicated by an arrow inFIG. 14. Thus, the sheet reversing unit60can be taken out upward from the body50.

As described above, exemplary embodiments of the present invention are explained. However, the present invention is not limited to the embodiments and can be modified in various manners. For example, the sheet reversing unit60is used as a supporting unit in the embodiments; however, it is possible to use an image carrier that can carry an image transferred to a sheet instead of a supporting unit.

According to an aspect of the present invention, it is possible to securely hold a shaft of a supporting unit because the supporting unit is supported by one through shaft and to position the supporting unit with high accuracy. Furthermore, it is possible to easily mount and detach even the supporting unit supported by the through shaft with respect to the apparatus.