IMAGE FORMING APPARATUS

Abstract

An image forming apparatus has: an intermediate transfer member to which a toner image developed on a photosensitive material is transferred while the intermediate transfer member rotates plural times; a transfer roller that is provided to be able to move into contact with and apart from the intermediate transfer member and transfers the toner image on the intermediate transfer member to a paper sheet while conveying the paper sheet pressed to the intermediate transfer member; a grooved cam having different grooves formed respectively in front and back surfaces of the grooved cam. A link mechanism for color image printing and a link mechanism for monochrome printing are reciprocated independently from each other, with ends of the link mechanism engaged respectively in the grooves of the grooved cam, thereby to control contact and separation of the transfer roller and the intermediate transfer member.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic structure of a color copier according to an embodiment of the invention;

FIG. 2 is a perspective view showing a schematic structure of an intermediate transfer belt unit, viewed from a front side;

FIG. 3 shows a position of the intermediate transfer belt unit in a full-color mode;

FIG. 4 shows a position of the intermediate transfer belt unit in a monochrome mode;

FIG. 5 shows a position of the intermediate transfer belt unit in a full separation mode;

FIG. 6 shows motion of a link and a lever which is caused by a grooved cam according to the embodiment;

FIG. 7 schematically shows a structure of grooved cams and link mechanisms, viewed from the top;

FIG. 8A and FIG. 8B show examples of shapes of grooves in the grooved cams;

FIG. 9 is a timing chart showing operation of the grooved cams; and

FIG. 10 is a timing chart showing operation of the grooved cams.

Claims

1. An image forming apparatus having an intermediate transfer member to which a toner image developed on a photosensitive material is transferred while the intermediate transfer member rotates plural times, and a transfer roller that is provided to be able to move into contact with and apart from the intermediate transfer member and transfers the toner image on the intermediate transfer member to a paper sheet while conveying the paper sheet pressed to the intermediate transfer member, the apparatus comprising: a grooved cam having different grooves formed respectively in front and back surfaces of the grooved cam, whereina link mechanism for color image printing and a link mechanism for monochrome printing are reciprocated independently from each other, with ends of the link mechanism engaged respectively in the grooves of the grooved cam, thereby to control contact and separation of the transfer roller and the intermediate transfer member.

2. The image forming apparatus according to claim 1, wherein each of the link mechanism includes:a link member having one end engaged in one of the grooves of the grooved cam; anda lever member having one end pivoted, to be swingable, on the link member and the other end attached to an end of an axle of the transfer roller.

3. The image forming apparatus according to claim 1, wherein three modes of a full-color mode, monochrome mode, and full separation mode are available for moving the transfer roller into contact with and apart from the intermediate transfer member, and positions of the grooved cam corresponding respectively to the three modes can be switched repeatedly in order of the full-color mode to the monochrome mode to the full separation mode.

4. The image forming apparatus according to claim 3, wherein in the full-color mode, all transfer rollers and the intermediate transfer member are in contact with transfer drums;in the monochrome mode, only one transfer roller for monochrome printing and the intermediate transfer member are in contact with one of the a transfer drums; andin the full separation mode, all the transfer rollers are separated from the intermediate transfer member and the transfer drums.

5. The image forming apparatus according to claim 1, wherein the link mechanisms and the grooved cam are positioned so as to generate a load which acts to raise the transfer roller if the link mechanisms are moved in a direction toward a position where the grooved cam is located.

6. The image forming apparatus according to claim 5, wherein if the transfer roller is raised, outer circumferential parts of the grooves of the grooved cam are used, andif the transfer roller is lowered, inner circumferential parts of the grooves of the grooved cam are used.