Duplex image forming apparatus

A duplex image forming apparatus includes a driving unit which has driving rollers and driven rollers to reversely feed the paper printed on the first surface to a duplex printing part or discharge the paper printed on the first and second surfaces, and a separation unit which separates the driven rollers from the driving rollers while the paper printed on the first surface is reversely fed and registered by duplex rollers of the duplex printing part. Accordingly, when the paper is registered by the duplex rollers, because the paper is not caught in the driving rollers and the driven rollers, the paper can be easily registered.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the priority benefit under 35 U.S.C. §119(a) of Korean Patent Application No. 2007-0029471, filed on Mar. 26, 2007 in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present general inventive concept relates to an image forming apparatus, and more particularly, to a duplex image forming apparatus which is capable of printing both surfaces of a printing medium, e.g., paper.

2. Description of the Related Art

An image forming apparatus is an apparatus that prints an image on a printing medium, e.g., paper, according to an inputted image signal. An image forming apparatus is classified as a simplex image forming apparatus which prints only one surface (front surface) of paper, or a duplex image forming apparatus which also prints a rear surface of paper by reversing the paper after printing a front surface.

The duplex image forming apparatus generally includes a paper supplying part to supply the paper, an image forming part to form an image on the supplied paper, and a paper discharge part to discharge the printed paper having passed through the image forming part to the outside.

The duplex image forming apparatus further includes a duplex printing part which is provided with duplex rollers so as to feed again the paper, whose front surface has been printed, to the image forming part to print a rear surface of the paper.

The duplex printing part rotates the duplex rollers to feed again the paper, which is fed by the reverse rotation of discharge rollers provided in the paper discharge part, to the image forming part. Accordingly, the paper whose front surface has been printed is fed again to the image forming part via a duplex print path, and the rear surface of the paper is printed.

The duplex rollers have a function of registering the paper fed by the duplex rollers, as well as reversely feeding the paper whose front surface has been printed.

However, because a portion of the paper fed by the duplex rollers is also caught in the discharge rollers, it is not easy for the duplex rollers to register to the paper by the discharge rollers.

For instance, the conventional duplex image forming apparatus includes center-feed type discharge rollers which are disposed at positions corresponding to a center portion of the paper, and side-feed type duplex rollers which are disposed at positions corresponding to sides of the paper. The duplex rollers are typically set to register the paper at the positions corresponding to the sides of letter paper.

Because the duplex rollers register the paper at the positions corresponding to the sides of the letter paper, in order to register the A4 paper, the paper should be shifted by a predetermined distance, e.g., 3 mm or more, in a transverse direction of the paper. However, because an end portion of the paper which is registered by the duplex rollers is caught in the discharge rollers, it is difficult to register the paper.

SUMMARY OF THE INVENTION

The present general inventive concept provides a duplex image forming apparatus that is capable of easily performing a paper registering process of duplex rollers in a duplex printing operation.

Additional aspects and/or advantages of the general inventive concept will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the general inventive concept.

The foregoing and/or other aspects and utilities of the present general inventive concept may be achieved by providing a duplex image forming apparatus, including an image forming part which forms an image on paper, a paper discharge part which reversely feeds the paper, in which the image has been formed on a first surface of the paper in the image forming part, so that the image is formed on a second surface of the paper, or discharges the paper on which the image is completely formed, and a duplex printing part which is provided with duplex rollers which feed the paper reversed from the paper discharge part toward the image forming part to form the image on the second surface of the paper, and register the paper fed to form the image on the second surface. The paper discharge part includes a driving unit which has driving rollers and driven rollers to reversely feed the paper printed on the first surface to the duplex printing part or discharge the paper printed on the first and second surfaces, and a separation unit which separates the driven rollers and the driving rollers from each other while the paper is registered by the duplex rollers.

The paper discharge part may further include a first supporting frame to which the driving rollers are mounted, and a second supporting frame which is provided below the first supporting frame and to which the driven rollers are mounted. The first supporting frame and the second supporting frame provide a paper feeding path therebetween.

The separation unit may include a cam member which is provided underneath the second supporting frame, a rotating shaft which is connected to the cam member, and a rotating motor which rotates the rotating shaft. The second supporting frame pivots by the separation unit so that the driven rollers are separated from the driving rollers.

The second supporting frame may be hingedly coupled to the first supporting frame so as to pivot when the cam member rotates.

The duplex printing part may further include a duplex sensor which detects that the paper is fed by the duplex rollers, and when the duplex sensor detects that the paper is fed by the duplex rollers, the rotating motor of the separation unit operates.

The separation unit include a cam member which is provided underneath the second supporting frame, a rotating shaft which is connected to the cam member, and a gear member provided to be connected to the rotating shaft and receiving rotational force from a driving source which drives overall the image forming part, the paper discharge part and the duplex printing part. The second supporting frame may pivot by the separation unit so that the driven rollers are separated from the driving rollers.

The foregoing and/or other aspects and utilities of the present general inventive concept may be achieved by providing a duplex image forming apparatus, including an image forming part which forms an image on paper, a paper discharge part to discharge the paper in a discharging direction and to feed the paper in a reverse direction, and a duplex printing part to receive the paper from the paper discharge part in the reverse direction, and to register the paper when feeding the paper toward the image forming part, wherein the paper discharge part stops feeding the paper when the duplex printing part registers the paper.

The paper discharge part may include a driving roller to contact the paper to feed the paper in the reverse direction, and not to contact the paper to stop feeding the paper in the reverse direction when a portion of the paper is registered by the duplex printing part.

The paper discharge part may include a driving roller and a driven roller to feed the paper in the reverse direction, and to stop feeding the paper when a portion of the paper is registered by the duplex printing part.

The paper discharge part may include a driving roller and a driven roller to form a paper feeding path therebetween and to feed the paper in the reverse direction through the paper feeding path, and at least one of the driving roller and the driven roller moves away from the paper feeding path when the paper is registered by the duplex printing part.

The paper discharge part may include a driving roller disposed in a first position to feed the paper in the reverse direction, the paper may include a first paper having a first size and a second paper having a second size, and the driving roller may move to a second position from the first position when the first paper is registered by the duplex printing part and may not move to the second position from the first portion when the second paper is registered by the duplex printing part.

The driving roller may be spaced-apart from the duplex printing part by a distance different from the first size and the second size.

The distance between the driving roller and the duplex printing part may be longer than the second size and shorter than the first size.

The paper discharge part may further include a first supporting frame having a driving roller rotatably mounted thereon, and a second supporting frame having a driven roller rotatably mounted thereon to form a paper feeding path therebetween, and at least one of the first supporting frame and the second supporting frame may move to separate one of the driving roller and the driven roller from the paper when the paper is registered.

The paper may include first and second end portions opposite to each other in the reverse direction, and the paper discharge part may be separated from the first end portion when the duplex printing part registers the paper by feeding the second end portion of the paper.

The paper discharge part may selectively stop feeding the paper according to a size of the paper in the reverse direction.

The foregoing and/or other aspects and utilities of the present general inventive concept may be achieved by providing a duplex image forming apparatus, including an image forming part which forms an image on a first paper having a first size and a second paper having a second size, a paper discharge part disposed in a first position to discharge the first paper and the second paper in a discharging direction and to feed the first paper and the second paper in a reverse direction, and a duplex printing part to receive the first paper and the second paper from the paper discharge part in the reverse direction, and to register the first paper and the second paper when feeding the first paper and the second paper toward the image forming part, wherein the paper discharge part moves to a second position from the first position not to feed the first paper in the reverse direction when the first paper is registered by the duplex printing part, and does not move to the second position when the second paper is registered by the duplex printing part.

The first size may be longer than the first size in the reverse direction.

The paper discharge part may include a driving roller to feed the first paper and the second paper in the reverse direction, the duplex printing part may include a register roller to register the first paper and the second paper during feeding the first paper and the second paper to the image forming part, and the driving roller may be spaced-apart from the register roller by a distance different from the first size and the second size.

The paper discharge part may not catch the first paper and the second paper when the duplex printing part registers the first paper and the second paper.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1is a sectional view illustrating a duplex image forming apparatus according to an exemplary embodiment of the present general inventive concept.

As illustrated inFIG. 1, the duplex image forming apparatus includes a main body10which forms an exterior appearance, a paper supply part20, an image forming part, a duplex printing part60, and a paper discharge part100. The paper supply part20, the image forming part, the duplex printing part60, and the paper discharge part100are provided inside the main body10.

The paper supply part20includes a paper cassette21which is removably mounted in a lower portion of the main body10, a paper supporting plate23which is pivotably coupled to the paper cassette21and on which printing media P, such as paper sheets, are stacked, an elastic member25which is provided under the paper supporting plate23and elastically supports the paper supporting plate23to bias the same upward, and a pickup roller27which is disposed at a position corresponding to a front end portion of the paper sheets stacked on the paper supporting plate23and picks up a sheet of paper.

The image forming part to form an image on the paper supplied from the paper supply part20includes a developing unit30, a transfer unit40, and a fusing unit50.

The developing unit30includes a photosensitive body31, a charge roller32which charges the photosensitive body31with a uniform electric potential, an exposure member35which irradiates a laser beam to the photosensitive body31to form an electrostatic latent image on the photosensitive body31charged by the charge roller32, and developer cartridges33which supply developers to the electrostatic latent image formed on the photosensitive body31to transform the electrostatic latent image into a visible image.

The developer cartridges33are configured as four developer cartridges33Y,33M,33C and33K in which developers of different colors, e.g., yellow, magenta, cyan and black developers, are respectively stored. Each of the developer cartridges33Y,33M,33C and33K includes a developing roller37which develops the electrostatic latent image formed on the photosensitive body31by supplying the developer to the electrostatic latent image, and a supply roller38which rotates while contacting the developing roller37to supply the developer to the developing roller37.

The transfer unit40includes an intermediate transfer belt41which is supported by supporting rollers42aand42band runs at the same velocity as a rotational linear velocity of the photosensitive body31, a first transfer roller43which is disposed opposite to the photosensitive body31with respect to the intermediate transfer belt41and transfers the visible image developed on the photosensitive body31onto the intermediate transfer belt41, and a second transfer roller44which is disposed opposite to the intermediate transfer belt41with respect to a transferring of the paper and transfers the visible image transferred onto the intermediate transfer belt41onto the paper.

The fusing unit50fuses the visible image formed by the developing unit30to the paper by applying heat and pressure, and includes a heat roller51which contains a heat source, and a press roller52which is disposed opposite to the heat roller51and maintains the constant fusing pressure with the heat roller51.

The duplex printing unit60feeds the paper printed on a front surface in a reverse direction so as to be subsequently printed on a rear surface thereof. The duplex printing unit60includes a duplex path61, duplex rollers63,66which are mounted on the duplex path61to feed the paper, and a duplex sensor65which detects the paper which is fed by the duplex rollers63,66.

The duplex rollers63have a function of feeding the paper printed on the front surface to the image forming part so as to be subsequently printed on the rear surface, and at the same time have a function of registering the fed paper as register rollers. The duplex rollers63are disposed at positions corresponding to the sides of the fed paper.

The duplex sensor65determines whether the paper is caught in the duplex rollers63, and operates a separation unit120of the paper discharge part100, which will be described later.

The paper discharge part100reversely feeds the paper, which is printed on the front surface in the image forming part, to the duplex printing part60, and discharges the duplex-printed paper. The paper discharge part100feeds the paper in a feeding direction, so that the paper is discharged, and feeds the paper in a reverse direction opposite to the feeding direction, so that the paper is fed back to a printing path through the duplex path61.

As illustrated inFIGS. 1 and 2, the paper discharge part100includes a driving unit110which reversely feeds the paper printed on the front surface to the duplex printing part60or discharges the duplex-printed paper, and a separation unit120which makes the reversely fed simplex (front surface)-printed paper by the driving unit110to be easily registered by the duplex rollers63.

The driving unit110includes a first supporting frame111to which driving rollers112are mounted, and a second supporting frame116which is provided below the first supporting frame111and to which driven rollers117are mounted to face the driving rollers112. A paper feeding path115is provided between the first supporting frame111and the second supporting frame116, to guide the paper when reversely feeding the paper printed on the front surface to the duplex printing part60or discharging the duplex-printed paper.

The separation unit120includes a cam member121which is mounted underneath the second supporting frame116while contacting the same, a rotating shaft122which is connected to the cam member121, and a rotating motor123which rotates the rotating shaft122. When the cam member121rotates about the rotating shaft122by the rotating motor123, the second supporting frame116pivots by the cam member121. In order for the second supporting frame116to pivot by the rotation of the cam member121, an end of the second supporting frame116is hingedly coupled to the first supporting frame111through a shaft116a.

This embodiment describes that the rotating motor123is provided to rotate the rotating shaft122and the cam member121connected thereto. However, an exemplary embodiment, as illustrated inFIG. 5, may be modified such that a gear member124is provided to be connected to the rotating shaft122so as to receive the rotational force of a driving source125for driving the overall duplex image forming apparatus.

Hereinafter, an operation of the duplex image forming apparatus ofFIGS. 1 and 2according to an exemplary embodiment will be described with reference toFIGS. 3 and 4.

As illustrated inFIG. 3, the paper loaded on the paper supply part20is fed to the image forming part to form a visible image on the front surface of the paper. The paper printed on the front surface is fed to a region between the driving rollers112and the driven rollers117in the paper discharge part100.

If the paper printed on the front surface is fed to the region between the driving rollers112and the driven rollers117by a predetermined extent or more, the driving rollers112rotate in the reverse direction to reversely feed the paper printed on the front surface to the duplex path61of the duplex printing part60.

As shown inFIG. 4, the paper is fed to the duplex path61in a reversed direction and then fed back to the image forming part by the rotation of the duplex rollers63, so that the image is formed on the rear surface of the paper. While being fed by the duplex rollers63, the paper is registered to prevent twisting.

In the above process, the duplex sensor65of the duplex printing part60detects whether the paper is caught in the duplex rollers63. If the duplex sensor65detects the paper caught in the duplex rollers63, the duplex sensor65transmits a signal to the rotating motor123of the separation unit120to rotate the rotating motor123. If the rotating motor123rotates, the rotational force of the rotating motor123is transmitted to the cam member121to separate the second supporting frame116from the first supporting frame111. In other words, the driven rollers117mounted to the second supporting frame116are separated from the driving rollers112mounted to the first supporting frame111.

As described above, since the driven rollers117are separated from the driving rollers112in the paper discharge part100in the process of registering the paper by the duplex rollers63, the paper can be easily registered, when compared to a conventional apparatus in which the paper is caught in the driving rollers and the driven rollers while being registered.

Specifically, even when registering a sheet of paper, such as A4 size paper, by the duplex rollers of the duplex image forming apparatus, which are typically set for letter paper, since the paper is not caught in the paper discharge part, the paper can be easily registered.

When a first printing medium having a first size, such as the A4 size paper, is fed, a length L between the duplex roller63and a position between the driving roller112and the driven roller117may be shorter than a length of the sheet of the A4 size paper in the direction to feed the paper from the paper discharging part100to the duplex path61. In this case, a leading edge (previously trailing edge) and a trailing edge (previously leading edge) of the A4 size paper fed in the reversed direction may contact the driving roller112and the duplex roller63, respectively, for a period corresponding to a difference between the length L and the length of the A4 size paper. However, the driving roller112and the driven roller are separated immediately after the duplex roller63registers and feeds the A4 size paper. Accordingly, the driving roller112and the driven roller117do not interfere the registering operation of the duplex roller63.

When the printing medium is a second printing medium having a second size different from the first size in a feeding direction, such as a letter size paper, is fed, the driving roller112and the driven roller117do not interfere the registering operation of the duplex roller63since the length L between the duplex roller63and a position between the driving roller112and the driven roller117may be equal or longer than a length of the sheet of the letter size paper in the direction to feed the paper from the paper discharging part100to the duplex path61. It is possible that when the letter size paper is fed, the letter size paper can be registered by the duplex roller63without separating the driving roller112and the driven roller117to avoid interference of the driving roller112and the driven roller117.

As apparent from the above description, the duplex image forming apparatus according to an exemplary embodiment can easily register the paper because when the paper is registered by the duplex rollers, the paper is not caught in the driving rollers and the driven rollers.