Image forming apparatus

An image forming apparatus and printer are provided. The image forming apparatus includes a plurality of side frames opposed to each other; an intermediate frame provided between the plurality of side frames; a plurality of first screws for connecting the side frames and the intermediate frame at first mutually opposed positions of the side frames; and a plurality of second screws for connecting the side frames and the intermediate frame at second mutually opposed positions of the side frames; wherein a distance between the first mutually opposed positions of the first screws is narrower than a distance between the second mutually opposed positions of the second screws.

CROSS REFERENCE TO RELATED APPLICATION

The present application claims priority from Japanese Patent Application No. 2007-157263, which was filed on Jun. 14, 2007, the disclosure of which is herein incorporated by reference in its entirety.

TECHNICAL FIELD

Apparatuses consistent with the present invention relate to an image forming apparatus and, more particularly, to an image forming apparatus having improved structural stability.

BACKGROUND

A related art image forming apparatus is described in Japanese Patent Application Nos. JP-A-9-120187, JP-A-2002-169353, and JP-A-2002-214900. The related art image forming apparatus is provided with one pair of side frames opposed to each other, and an intermediate frame that axially supports various kinds of rollers and is disposed between the pair of side frames. Screws are fastened at corresponding positions to connect between one side frame and the intermediate frame and between the other side frame and the intermediate frame.

SUMMARY

However, the related art image forming apparatus as described in the above documents has a couple of disadvantages. A distance between the thread fastened position between one side frame and the intermediate frame and the thread fastened position between the other side frame and the intermediate frame, the thread fastened positions corresponding to each other, is the same in any case. That is, since the shape formed by joining the thread fastening positions is a square or rectangle, there is a problem in that the overall strength of the frame composed of one pair of side frames and the intermediate frame is weak.

Exemplary embodiments of the present invention address the above disadvantages and other disadvantages not described above. However, the present invention is not required to overcome the disadvantages described above, and thus, an exemplary embodiment of the present invention may not overcome any of the problems described above.

It is an aspect of the invention to provide an image forming apparatus in which the overall strength of the frame composed of one pair of side frames and the intermediate frame can be increased.

According to an exemplary embodiment of the present invention, an image forming apparatus comprises a plurality of side frames opposed to each other; an intermediate frame provided between the plurality of side frames; a plurality of first screws for connecting the side frames and the intermediate frame at first mutually opposed positions of the side frames; and a plurality of second screws for connecting the side frames and the intermediate frame at second mutually opposed positions of the side frames; wherein a distance between the first mutually opposed positions of the first screws is narrower than a distance between the second mutually opposed positions of the second screws.

According to another exemplary embodiment of the present invention, an image forming apparatus comprises two side frames opposed to each other; an intermediate frame provided between the two side frames; two first screws for connecting the side frames and the intermediate frame at first mutually opposed positions of the side frames; and two second screws for connecting the side frames and the intermediate frame at second mutually opposed positions of the side frames; wherein a distance between the first mutually opposed positions of the first screws is narrower than a distance between the second mutually opposed positions of the second screws.

According to another exemplary embodiment of the present invention, a printer is provided that comprises a first side frame comprising a first projection portion; a second side frame comprising a second projection portion, wherein the first side frame and the second side frame are arranged such that the first and second projection portions project towards each other; an intermediate frame; two first connectors which connect the intermediate frame to the first projection portion and second projection portion respectively; and two second connectors which connect the intermediate frame to the first side frame and the second side frame respectively.

FIG. 1is a side cross-sectional view showing an image forming apparatus according to an exemplary embodiment of the present invention. In this exemplary embodiment, the image forming apparatus is embodied in the form of a printer1. However, the present inventive concept applies to any electronic apparatus that contains a frame that supports roller elements. In the following description, it is supposed that the left side on the paper inFIG. 1is the front side of the printer1, and the right side on the paper inFIG. 1is the back side of the printer1. InFIG. 1, the printer1comprises a main body case2comprising a feeder unit4for feeding a printing medium, in this case a paper3, and an image forming unit5for forming the image on the fed paper3in the main body case2.

(1) Feeder Unit

The feeder unit4comprises a storage cassette, in this case a sheet feed tray6, a sheet feed roller8, a separation roller9, and a registration roller12. The paper3on the top of the sheet feed tray6is fed by the feed roller8, and fed one by one with the rotation of the separation roller9. The fed paper3is registered by the registration roller12and fed to a transfer position.

(2) Image Forming Unit

The image forming unit5comprises a scanner unit16, a process cartridge17and a fixing unit18. The scanner unit16has a laser emitting unit and a polygon mirror (not shown) A laser beam emitted from the laser emitting unit is deflected by the polygon mirror, and applied onto the surface of a photosensitive drum27.

Also, the process cartridge17has a developing unit, in this case a developing roller31, a photosensitive drum27, a scorotron type charger unit29and a transfer roller30. The charger unit29positively charges the surface of the photosensitive drum27uniformly. Thereafter, the surface of the photosensitive drum27is exposed by the laser beam from the scanner unit16so that an electrostatic latent image is formed thereon. Then, the toner carried on the surface of the developing roller31is supplied to the electrostatic latent image formed on the photosensitive drum27, so that the electrostatic latent image is developed.

When the paper3passes through the transfer position, a transfer voltage is applied to the transfer roller30, so that a toner image on the photosensitive drum27is transferred onto the paper3. The fixing unit18thermally fixes the toner on the paper3while the paper3passes between a heating roller41and a pressing roller42. Thereafter, the paper3after thermal fixing is exhausted onto a sheet discharging tray44.

FIG. 2is a front view of a frame structure of the printer1according to an exemplary embodiment of the present invention as seen from the front (i.e., a front side of the paper is the front side of the printer1), andFIG. 3is a bottom view of the frame structure of the printer1(i.e., the upper side of the paper is the front side of the printer1). The printer1has a structure in which an intermediate frame, in this case a paper feed frame54and a scanner unit16are sandwiched between a pair of side frames50,52disposed on the left and right side of the intermediate frame, respectively.

FIG. 4is a side view of a left side frame50as seen from the outside (left side), andFIG. 5is a side view of the left side frame50as seen from the inside (right side).

Each of the side frames50,52has a box shape in which an outer surface directed to the outside of the printer1is opened, and an inner wall directed to the inside of the printer1has a convex portion56,58, respectively, swollen like a rectangle in its front portion. Also, a collar portion60,62is provided under the respective convex portion56,58(seeFIG. 2). On the other hand, the paper feed frame54has a shape like a plate as a whole, and hollow in a portion corresponding to each convex portion56,58. The paper feed frame54has a smooth and uneven upper portion to guide the paper3smoothly.

The paper feed frame54is secured to the convex portions56and58of the side frames50and52by a pair of first screws64and66, and secured to the back ends of the side frames50and52by a pair of second screws68and70, as shown inFIGS. 2 and 3. The thread fastening positions of the first screws64and66and the thread fastening positions of the second screws68and70have different heights, as shown inFIG. 2.

The thread fastening positions of the first screws64and66are located on a straight line along the lateral direction of the printer1. In other words, the thread fastening positions of the first screws64and66are located at the opposed positions, i.e., a pair of positions with the shortest distance, of the side frames50and52. Likewise, the thread fastening positions of the second screws68and70are located on a straight line along the lateral direction of the printer1. In other words, the thread fastening positions of the second screws68and70are located at the opposed positions, i.e., a pair of positions with the shortest distance, of the side frames50and52.

Also, the paper feed frame54is provided with the registration roller12(on the lower side) together with the separation roller9, as shown inFIG. 3. This registration roller12comprises a pair of roller portions12A,12A arranged in the lateral direction, and a roller shaft12B, and is provided near the thread fastening positions of the first screws64and66in the hollow portions corresponding to the convex portions56and58.

Specifically, a bearing portion80is provided within the paper feed frame54to bear one end of the roller shaft12B. The other end of the roller shaft12B projects outward via a through hole55provided through a side wall of the paper feed frame54. On the other hand, the convex portion56of the left side frame50has an outwardly hollow portion56A, and a bearing portion82is provided in the hollow portion56A. The other end of the roller shaft12B, which projects through the through hole55, is borne by the bearing portion82, and has a gear84for receiving a driving force from a drive motor M, not shown. In the figures, a mechanism for transmitting the driving force from the drive motor M to the gear84is omitted.

Also, the scanner unit16is secured between the side frames50and52by a pair of third screws72and74and a pair of fourth screws76and78(seeFIG. 2).

Effects of the First Exemplary Embodiment

According to the first exemplary embodiment of the present invention, the paper feed frame54is secured between the side frames50and52by the first screws64and66and the second screws68and70. The distance spacing D1between the thread fastening positions of the first screws64and66is shorter than the distance spacing D2between the thread fastening positions of the second screws68and70, as shown inFIGS. 2 and 3. As shown inFIG. 2andFIG. 3, a distance between positions where the first screws64and66connect the side frames50and52and the paper feed frame54is the distance spacing D1between first mutually opposed positions of the side frames50and52. And, a distance between positions where the second screws68and70connect the side frames50and52and the paper feed frame54is the distance spacing D2between second mutually opposed positions of the side frames50and52. That is, a shape formed by joining the first screws64and66and the second screws68and70is trapezoidal. Accordingly, the strength of the frame structure which comprises one pair of side frames50and52and the paper feed frame54can be greater than a case in which a shape formed by joining the thread fastening positions is square or rectangular. In addition, although there is a clearance between the side frames50and52and the paper feed frame54inFIG. 2andFIG. 3, the side frames50and52could be firmly connected to the paper feed frame54by the first screws64and66and the second screws68and70such that there is substantially no clearance between the side frames50and52and the paper feed frame54.

As show inFIG. 2andFIG. 4, the sign “h1” denotes a distance between the thread fastening positions of the first screws (64,66) and a bottom face of the printer1, in a direction perpendicular to the bottom face of the printer1. The sign “h2” denotes a distance between the thread fastening positions of the second screws (68,70) and the bottom face of the printer1, in the direction perpendicular to the bottom face of the printer1. As shown inFIG. 2andFIG. 4, the distance h1is larger than the distance h2. In other words, a height of the thread fastening positions of the first screws (64,66) is higher than a height of the thread fastening positions of the second screws (68,70). According to the first exemplary embodiment of the present invention, the thread fastening positions of the first screws64and66and the thread fastening positions of the second screws68and70have different heights. Accordingly, the strength of the frame structure can be further greater than a case in which the first screws and the second screws have a same height.

According to the first exemplary embodiment of the present invention, the registration roller12is provided nearer to the thread fastening positions of the first screws64and66than the positions of the second screws68and70. Since the strength is stronger near the thread fastening positions of the first screws64and66than near the thread fastening positions of the second screws68and70, it is possible to suppress influence of the load of the frame due to distortion on the rotational motion of the registration roller12.

According to the first exemplary embodiment of the present invention, the other end of the roller shaft12B for the registration roller12receives a driving force from the drive motor M outside the thread fastening position of the second screw68in the first exemplary embodiment. In this case, the other end of the roller shaft12B is borne at the same position as the thread fastening position of the second screw68. Thereby, the other end of the roller shaft12B can be borne at a position near the gear84receiving the driving force form the drive motor M, so that the registration roller12can be rotated stably.

According to the first exemplary embodiment of the present invention, the lower surfaces of the convex portions56and58function as a guide for inserting or extracting the sheet feed tray6, as shown inFIG. 5. Accordingly, the sheet feed tray6can be taken in or out smoothly without providing a special guide.

Other Exemplary Embodiments

The present invention is not limited to the exemplary embodiment as described above.

Although the intermediate frame is exemplified as the paper feed frame54in the above exemplary embodiment, it may be the scanner unit16or the fixing unit18as far as it can be sandwiched between a pair of side frames.

Although the conveying roller is exemplified as the registration roller12in the above exemplary embodiment, it may be other rollers for conveying the paper3.

Although the convex portion is provided on each of the side frames in the above exemplary embodiment, the convex portion may be provided on one side frame. Also, each convex portion may have a different protruding length in the case where the convex portion is provided on each of the side frames.

According to the above-described exemplary embodiments of the present invention, the overall strength of the frame comprising a pair of side frames and the intermediate frame can be increased.