IMAGE FORMING APPARATUS HAVING GUIDE PORTIONS ARRANGED IN A DIRECTION CROSSING A TRANSPORTATION DIRECTION OF A RECORDING MEDIUM

An image forming apparatus includes a fixing device including a pressing unit and a heating unit that opposes the pressing unit; and plural guide portions disposed downstream of the fixing device and arranged in a direction crossing a transporting direction of a recording medium. An amount of projection of the guide portions is smaller in a region near a center of the fixing device than in a region near an end of the fixing device.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based on and claims priority under 35 USC 119 from Japanese Patent Application No. 2017-165042 filed Aug. 30, 2017.

BACKGROUND

Technical Field

SUMMARY

According to an aspect of the invention, there is provided an image forming apparatus including a fixing device including a pressing unit and a heating unit that opposes the pressing unit, and plural guide portions disposed downstream of the fixing device and arranged in a direction crossing a transporting direction of a recording medium. An amount of projection of the guide portions is smaller in a region near a center of the fixing device than in a region near an end of the fixing device.

DETAILED DESCRIPTION

Exemplary embodiments of the present invention will now be described with reference to the drawings. Image forming apparatuses according to the exemplary embodiments described below are merely examples in which the technical idea of the present invention is embodied, and are not intended to limit the present invention. The present invention may be similarly applied to other exemplary embodiments within the scope of the claims.

First Exemplary Embodiment

An image forming apparatus10according to a first exemplary embodiment will be described with reference toFIGS. 1 to 4B. As illustrated inFIG. 1, the image forming apparatus10according to the first exemplary embodiment includes an image forming apparatus body12. A recording-medium supplying device18, an image forming device14, and a fixing device36are mounted in the image forming apparatus body12. The recording-medium supplying device18supplies a recording medium104, such as a recording paper sheet, which serves as a transfer material. The image forming device14forms an image to be transferred onto the recording medium104. A discharge tray16to which the recording medium104is discharged is provided at the top of the image forming apparatus body12. A transport path56along which the recording medium104is transported is arranged to extend through the above-mentioned components. The structure of each component will now be described.

The recording-medium supplying device18includes a recording-medium container50that contains a stack of recording media104; a transport roller52that extracts the top recording medium104of the stack contained in the recording-medium container50and transports the extracted recording medium104toward the image forming device14; and a retard roller54that separates the recording media104from each other to prevent the recording media104from being transported to the image forming device14in a stacked state.

The image forming device14includes, for example, four image forming units20corresponding to four colors, which are yellow (Y), magenta (M), cyan (C), and black (K); an optical writing device22; and a transfer device24. The image forming units20and components thereof have the same structures except for the color of the images formed thereby.

Each image forming unit20is a replaceable member that is removably attached to the image forming apparatus body12. The image forming units20for Y, M, C, and K are arranged in that order from the back (right inFIG. 1) of the image forming apparatus body12.

The image forming units20constitute, for example, an electrophotographic system that forms a color image. Each image forming unit20includes an image forming unit body26, in which an image carrier28, a charging device30, a developing device32, and a cleaning device34are provided. The image carrier28is drum-shaped and carries a developer image. The charging device30serves as a charging unit and includes a charging roller that uniformly charges the image carrier28. The developing device32develops a latent image formed on the image carrier28by using developer (toner). The cleaning device34cleans the image carrier28by scraping off waste developer that remains on the image carrier28.

The developing device32develops the latent image formed on the image carrier28by using Y, M, C, or K developer contained therein.

The optical writing device22serves as a latent-image forming device, and is composed of, for example, a laser scanning exposure device. The optical writing device22forms a latent image on the surface of each image carrier28. Other examples of the optical writing device22include an LED and a surface emitting laser.

The transfer device24includes a transfer member38that serves as a transfer body, first transfer rollers40that serve as first transfer devices, a second transfer roller42that serves as a second transfer device, and a cleaning device44.

The transfer member38is, for example, endless-belt-shaped, and is supported by five support rollers46a,46b,46c,46d, and46esuch that the transfer member38is rotatable in the direction shown by the arrow inFIG. 1. At least one of the support rollers46a,46b,46c,46d, and46eis connected to a power source (not shown), such as a motor, and rotates upon receiving a driving force from the power source, so that the transfer member38is rotated.

The support roller46ais arranged to oppose the second transfer roller42, and functions as a back-up roller for the second transfer roller42. A position between the second transfer roller42and the support roller46aserves as a second transfer position.

Each first transfer roller40transfers the developer image formed on the surface of the corresponding image carrier28by the corresponding developing device32onto the transfer member38.

The second transfer roller42transfers the Y, M, C, and K developer images that have been transferred to the transfer member38onto the recording medium104.

The cleaning device44includes a scraping member48that scrapes off the developers of the respective colors that remain on the surface of the transfer member38after the developer images of the respective colors have been transferred to the recording medium104by the second transfer roller42. The developers that have been scraped off by the scraping member48are collected in the cleaning device44.

The transport path56includes a first transport path56aand a second transport path56b.

The first transport path56aallows the recording medium104supplied from the recording-medium supplying device18to be transported to the image forming device14, and then be discharged to the discharge tray16after an image is formed thereon. The transport roller52, the retard roller54, registration rollers58, the transfer device24, the fixing device36, and discharge rollers60, which serve as a discharge unit, are arranged along the first transport path56ain that order from the upstream side in a transporting direction in which the recording medium104is transported.

The registration rollers58temporarily stop the leading end of the recording medium104that has been transported from the recording-medium supplying device18, and then transports the recording medium104toward the transfer device24at a time that matches the time at which the image is formed.

The fixing device36includes a heating roller66that serves as a heating unit and a pressing unit76that opposes the heating roller66. The heating roller66and the pressing unit76heat and press the recording medium104that passes therebetween, so that the developer image is fixed to the recording medium104. The fixing device36will be described in detail below.

The discharge rollers60discharge the recording medium104to the discharge tray16after the developers are fixed to the recording medium104by the fixing device36.

The second transport path56breverses the recording medium104having the developer image formed on one side thereof, and supplies the recording medium104to the image forming device14again. Two pairs of reversing transport rollers62aand62b, for example, are arranged along the second transport path56b.

After the recording medium104is transported from the first transport path56ato the discharge rollers60, the discharge rollers60are rotated in the reverse direction while the trailing end portion of the recording medium104is nipped therebetween, so that the recording medium104is supplied to the second transport path56b. The recording medium104that has been supplied to the second transport path56bis transported to a location upstream of the registration rollers58by the reverse transport rollers62aand62b.

The fixing device36according to the first exemplary embodiment will now be described. As illustrated inFIGS. 2 to 5C, the fixing device36includes the heating roller66; an endless belt72that serves as an endless band-shaped member; guide members74that guide the endless belt72in a rotatable manner; and the pressing unit76. The pressing unit76is disposed inside the endless belt72and pressed against the heating roller66together with the endless belt72. A releasing member, for example, for releasing the recording medium104that is transported may be disposed downstream of the fixing device36.

The heating roller66includes a cylindrical roller portion84and a heater86disposed in the roller portion84. The roller portion84is rotatably supported by heating roller bearings (not shown), and rotates in the direction of arrow A (seeFIG. 2). The roller portion84is, for example, a so-called hard roller and includes a core88made of a metal material, such as iron, stainless steel, or aluminum, and a releasing layer90formed on or applied to the core88. The releasing layer90is made of an insulating material having high releasability, such as PFA.

The heater86includes, for example, two lamps. A thermostat94is arranged to oppose the heating roller66at a side opposite to the side at which the endless belt72is disposed.

The roller portion84is not limited to the above-described hard roller, and may instead be a soft roller including an elastic layer on the core thereof.

The endless belt72is disposed between the heating roller66and the pressing unit76, and is moved in the direction of arrow C (seeFIG. 2) by the rotation of the heating roller66. The heating roller66and the endless belt72are pressed against each other by the pressing unit76, so that a pressing region102is formed therebetween. The toner image is fixed to the recording medium104in the pressing region102. The endless belt72is obtained by forming a synthetic resin, such as polyimide, into an endless belt shape.

An entrance unit96, which guides the transported recording medium104to the fixing device36, is disposed upstream of the fixing device36, more specifically, upstream of the pressing region102. The entrance unit96guides the recording medium104transported in the direction of arrow B so that the leading end of the recording medium104moves toward the pressing region102(seeFIG. 2). An entrance blocking member97is provided in the gap between the entrance unit96and the pressing unit76to prevent entrance of the recording medium104through the gap.

As illustrated inFIGS. 3 to 5C, plural guide portions200for guiding the recording medium104to the discharge rollers60are disposed downstream of the fixing device36, more specifically, downstream of the pressing region102. In the first exemplary embodiment, the guide portions200are formed on an exit unit98, which is provided downstream of the fixing device36.

In the first exemplary embodiment, the exit unit98, on which the guide portions200are formed, is provided between the fixing device36and the discharge rollers60. More specifically, the exit unit98is provided downstream of the fixing device36and upstream of the discharge rollers60, which discharge the recording medium104to the discharge tray16. In the case where no discharge rollers are provided, the exit unit98is provided upstream of a mechanism such as a discharge hole through which the recording medium is discharged.

As illustrated inFIG. 2, the pressing unit76includes a holder100disposed inside the endless belt72, an elastic member80provided on the holder100, and frames82and83that support the holder100. A sliding member for reducing friction may be provided between the endless belt72and the holder100. The holder100is made of a resin material, for example, liquid crystal polymer (LCP), which is highly heat-resistant. The elastic member80is substantially as long as the holder100in the longitudinal direction, and is obtained by forming a heat-resistant resin material, such as silicon rubber, into a substantially rectangular parallelepiped shape.

Referring toFIG. 2, the guide members74are provided at respective ends of the endless belt72and the pressing unit76. The pressing unit76is supported by the guide members74.

Referring toFIG. 2, the frames82and83support the holder100, and are supported by the guide members74at both ends thereof so that the holder100is pressed against the heating roller66. Both end portions of each of the frames82and83extend through the guide members74, and are urged toward the heating roller66by urging units, such as springs (not shown).

The exit unit98and the guide portions200formed on the exit unit98will now be described with reference toFIGS. 2 to 5C. As illustrated inFIGS. 2 to 4B, the exit unit98is provided downstream of the fixing device36, and the guide portions200are formed thereon. The recording medium104to which toner is fixed is discharged from the fixing device36, transported along the guide portions200on the exit unit98, and guided to the discharge rollers60.

In the first exemplary embodiment, the recording medium104is transported in such a manner that the side on which the image is formed faces the guide portions200.

The exit unit98is composed of a block having a predetermined width, for example, a width substantially equal to that of the heating roller66of the fixing device36in the width direction (direction crossing the transporting direction) and a predetermined length in the transporting direction. The exit unit98may be integrated with the fixing device36or be formed as a separate component that is attached to the image forming apparatus body12at a location between the fixing device36and the discharge rollers60.

The guide portions200are plate-shaped members that substantially perpendicularly project from the exit unit98at a side along which the recording medium104is transported. The guide portions200have a predetermined length in the transporting direction of the recording medium104. Thus, the guide portions200formed on the exit unit98have a predetermined length in the direction from the fixing device36toward the discharge rollers60.

As illustrated inFIG. 5A, the guide portions200on the exit unit98, which is disposed downstream of the fixing device36, are arranged with predetermined gaps therebetween in the direction crossing the transporting direction of the recording medium104(width direction). In the first exemplary embodiment, eighteen guide portions200are arranged substantially symmetrically about a center220of the exit unit98.

The guide portions200are arranged so as to project toward the transported recording medium104by different amounts depending on the positions of portions of the recording medium that pass thereby. More specifically, in the first exemplary embodiment, as illustrated inFIGS. 4A, 4B, and 5A, the guide portions200include guide portions202near the center220of the exit unit98in the direction crossing the transporting direction, more specifically, at a position where a substantially central portion106of the recording medium104in the direction crossing the transporting direction passes. The guide portions202have a smallest amount of projection that is smaller than amounts of projection of guide portions204and206near both ends222and224, which will be described below, and other guide portions208. Here, the other guide portions208are guide portions other than the guide portions202near the center220and the guide portions204and206near both ends222and224. Although a pair of guide portions202are arranged symmetrically about the center220as the guide portions202near the center220in the first exemplary embodiment, a single guide portion202may instead be provided at the center220.

The guide portions204and206are respectively formed near a first end222and a second end224(hereinafter sometimes referred to simply as both ends222and224) of the exit unit98in the width direction, more specifically, at positions where a first end portion108and a second end portion110(hereinafter sometimes referred to simply as both end portions108and110) of the recording medium104in the direction crossing the transporting direction pass. The guide portion204near the first end222and the guide portion206near the second end224(hereinafter sometimes referred to simply as the guide portions204and206near both ends222and224) project by an amount larger than the amounts of projection of the guide portions202near the center220and the other guide portions208. In other words, the guide portions204and206near both ends222and224of the exit unit98have a largest amount of projection, which is larger than the amounts of projection of the guide portions202near the center220and the other guide portions208.

The guide portions200according to the first exemplary embodiment are formed so that the amount of projection thereof gradually decreases from the guide portions204and206near both ends222and224toward the guide portions202near the center220. More specifically, in the first exemplary embodiment, the guide portions200are formed so that the guide portions202near the center220have a smallest amount of projection and that the amount of projection gradually increases toward both ends222and224so as to form a curved or substantially curved bowl shape.

The recording medium104is discharged from the fixing device36after being heated and pressed by the heating roller66and the pressing unit76of the fixing device36. Accordingly, the discharged recording medium104is curved as illustrated inFIG. 5B, that is, such that the central portion106thereof in the direction crossing the transporting direction of recording medium104is warped toward the guide portions200with respect to both end portions108and110.

If the guide portions are formed so as to project by the same amount, a portion of the recording medium104, in particular, a central portion of the recording medium104receives a large contact force from the guide portions, and there is a risk that defects such as streaks will be formed on the image due to the guide portions immediately after the image is fixed.

In contrast, in the first exemplary embodiment, the guide portions200on the exit unit98are formed so that the amount of projection of the guide portions202near the center220is smaller than that of the guide portions204and206near both ends222and224. Accordingly, as illustrated inFIG. 5B, the recording medium104discharged from the fixing device36in a curved state also comes into contact with the guide portions204and206near both ends222and224. As a result, the risk that only the central portion106of the recording medium104will receive a large contact force and that defects such as streaks will be formed on the image due to the guide portions may be reduced.

When the guide portions200are formed so that parts thereof near the discharge rollers60are flat, the curved recording medium104may be substantially flattened when the recording medium104is transported along the flat parts of the guide portions200.

Alternatively, a device for flattening the curved recording medium may be provided between the exit unit98and the discharge rollers. Alternatively, the curved recording medium may be flattened by the discharge rollers.

In the first exemplary embodiment, the recording medium104is transported while the side on which the image is formed faces the guide portions200. However, the recording medium104may instead be transported while the side opposite to the side on which the image is formed faces the guide portions200.

As illustrated inFIG. 5C, the guide portions200may instead be formed so that the guide portions202near the center220have a smallest amount of projection, that the guide portions204and206near both ends222and224have a largest amount of projection, and that the amount of projection of the guide portions200substantially linearly increases from the guide portions202near the center220toward the guide portions204and206near both ends222and224. In other words, the guide portions200may be arranged so as to form a V-shape.

First Modification

The guide portions200of the first exemplary embodiment extend substantially linearly in the transporting direction and are formed so that the guide portions202near the center220have a smallest amount of projection and that the amount of projection gradually increases toward the guide portions204and206near both ends222and224. However, the guide portions are not limited to this. As in a first modification illustrated inFIG. 6, guide portions200A may be formed so that parts thereof near the fixing device36have different amounts of projection but parts thereof near the discharge rollers60are formed as flat parts200Aa (202Aa,204Aa,206Aa, and208Aa) that project so as to form a substantially flat shape. Here, the phrase “substantially flat” means that the difference in the amount of projection between the guide portions near both ends and the guide portions near the center is small, and it is not necessary that all the guide portions have the same amount of projection.

More specifically, according to the first modification, in a region near the fixing device36, the guide portions200A on an exit unit98A are formed so that guide portions202A near the center220have a smallest amount of projection and that guide portions204A and206A near both ends222and224have an amount of projection larger than that of the guide portions202A near the center220(seeFIGS. 6A, 6C, and 6D). However, as the distance from the fixing device36increases, the amount of projection of the guide portions202A near the center220and the amount of projection of the guide portions204A and206A near both ends222and224become closer to each other and the difference therebetween decreases. In a region near the discharge rollers60, the guide portions202A near the center220and the guide portions204A and206A near both ends222and224have substantially the same amount of projection (seeFIGS. 6B, 6C, and 6D).

Other guide portions208A, which are disposed between the guide portions202A near the center220and the guide portions204A and206A near both ends222and224, are also formed so that they have different amounts of projection in the region near the fixing device36and that as the distance from the fixing device36increases, the guide portions200A project by amounts with smaller differences to form a substantially flat shape.

In the first modification, parts of the guide portions200A near the discharge rollers60are formed as the flat parts200Aa that project by substantially the same amount to form a substantially flat shape. The flat parts200Aa include flat parts202Aa of the guide portions202A near the center220, flat parts204Aa and206Aa of the guide portions204A and206A near both ends222and224, and flat parts208Aa of the other guide portions208A, and have substantially the same amount of projection (seeFIGS. 6B, 6C, and 6D).

In the first modification, the guide portions200A are formed so that the amount of projection of the flat parts200Aa near the discharge rollers60is equal to the amount of projection of the guide portions204A and206A near both ends222and224. With this structure, the curved recording medium104may be substantially flattened by transporting the recording medium104along the guide portions200A.

In the first modification, the guide portions200A are formed so that the difference in the amount of projection gradually decreases with increasing distance toward the downstream side of the exit unit98. However, the guide portions are not limited to this, and may instead be formed so that parts thereof that are closer to the discharge rollers60than a predetermined point on a downstream section of the exit unit in the transporting direction of the recording medium104form a substantially flat shape. In this case, it is not necessary that the amount of projection of the guide portions be substantially equal to that of the guide portions near both ends, and may be any amount according to the design.

Second Exemplary Embodiment

The guide portions200according to the first exemplary embodiment are formed so that the amount of projection thereof decreases from the guide portions204and206near both ends222and224toward the guide portions202near the center220. In contrast, as illustrated inFIGS. 7, 8A, and 8B, guide portions200B according to a second exemplary embodiment are formed so that only guide portions204B and206B near both ends222and224have an amount of projection larger than those of guide portions202B near the center220and other guide portions208B. Components that are the same as those in the first exemplary embodiment are denoted by the same reference numerals, and detailed description thereof is thus omitted.

As illustrated inFIGS. 7, 8A, and 8B, the guide portions200B on an exit unit98B according to the second exemplary embodiment are formed so that the amount of projection of the guide portions204B and206B near both ends222and224is larger than those of the guide portions202B near the center220and the other guide portions208B. In other words, the amounts of projection of the guide portions202B near the center220and the other guide portions208B are smaller than that of the guide portions204B and206B near both ends222and224. The guide portions202B near the center220and the other guide portions208B are formed so as to project by substantially the same amount to form a substantially flat shape, that is, so that the difference in the amount of projection between the guide portions200B is small.

In this case, after the recording medium104is discharged from the fixing device36, both end portions108and110of the recording medium104in the direction crossing the transporting direction of the recording medium104come into contact with the guide portions204and206near both ends222and224, which have an amount of projection larger than those of the guide portions202near the center220and the other guide portions208B.

With this structure, the recording medium104discharged from the fixing device36in the curved state may be guided while both end portions108and110on both sides of the central portion106in the direction crossing the transporting direction are in contact with the guide portions204and206near both ends222and224. Accordingly, the risk that only the central portion106of the recording medium104will receive a large contact force and that defects such as streaks will be formed on the image may be reduced.

Third Exemplary Embodiment

To prevent the central portion106of the recording medium104discharged from the fixing device36in the curved state from receiving a high contact pressure from the guide portions, the guide portions may be formed so that only a guide portion202C near the center220of an exit unit98C has an amount of projection smaller than those of guide portions204C and206C near both ends222and224and other guide portions208C.

A third exemplary embodiment will now be described with reference toFIGS. 9A and 9B. In the third exemplary embodiment, the guide portion202C near the center220of the exit unit98C has an amount of projection smaller than those of the guide portions204C and206C near both ends222and224and the other guide portions208C. Components that are the same as those in the first exemplary embodiment are denoted by the same reference numerals, and detailed description thereof is thus omitted.

As illustrated inFIG. 9A, guide portions200C according to the third exemplary embodiment are formed so that the guide portion202C near the center220of the exit unit98C has an amount of projection smaller than those of the guide portions204C and206C near both ends222and224and the other guide portions208C. The guide portion202C that is closest to the center220has an amount of projection smaller than that of one of the other guide portions208C that is closest to the guide portion202C near the center220in the direction crossing the transporting direction.

With the above-described structure, as illustrated inFIG. 9B, even when, for example, a recording medium104C having a small width is transported, a central portion106C of the recording medium104C comes into contact with the guide portion202C near the center220, and both end portions108C and110C of the recording medium104C come into contact with the guide portions208C having an amount of projection larger than that of the guide portion202C near the center220. Accordingly, the risk that only the central portion106C of the recording medium104will receive a large contact pressure and that image defects will be formed may be reduced.

In each of the first and second exemplary embodiments, a total of eighteen guide portions200,200B are provided. In the third exemplary embodiment, a total of five guide portions200C are provided. However, the number of guide portions is not limited to this, and a total of at least three guide portions may be provided, the three guide portions including guide portions near both ends of the exit unit and a guide portion that is near the center and that has an amount of projection smaller than that of the guide portions near both ends. Furthermore, four or more guide portions may be provided as long as guide portions near both ends of the exit unit have an amount of projection larger than those of other guide portions, that is, as long as guide portions near the center has an amount of projection smaller than those of other guide portions.