The present invention relates to an image forming apparatus that operates on the basis of electrophotographic technology, such as a copying machine, a printer and a fax machine; and, more particularly, the invention relates to an image forming apparatus for obtaining a color image by superimposing multi-color toner images on an endless intermediate transfer belt.
One example of a known image forming apparatus using an intermediate transfer unit is a field sequential type image forming apparatus wherein, by repeating a series of processes which consist of forming a toner image on a photosensitive drum serving as a first image carrier and performing a primary transfer of this toner image on the intermediate transfer drum, four or five toner images are superimposed on the intermediate transfer drum, whereby multiplex image transfer is carried out. These steps are followed by secondary collective transfer of four or five toner images onto a transfer material, thereby obtaining a color image (or multi-color image) on the transfer material.
Such an image forming apparatus using an intermediate transfer unit is known to be capable of face-down stacking (sequential stacking with the recording surface facing downward), without the need for a special operation changing the paper position, wherein a paper back vacuuming type feed mechanism is used in the transfer material feed path (hereinafter referred to as “paper feed path”) from a transfer section to a fixing section.
As shown in
Patent Document 1: Japanese Application Patent Laid-Open Publication No. Sho 63-240577
In the aforementioned apparatus, when thick transfer material is fed from a straight path to the fixing apparatus, the shock of the paper hitting the fixing apparatus is directly applied to the transfer section, with the result that the image fluctuates on the transfer material during the transfer step. This problem is particularly conspicuous in multi-color printing. Further, if the transfer material consists of thin paper, the stability of the transfer material cannot be maintained when the leading edge of the transfer material is detached from the vacuum feed section, because the vacuum feed section is not equipped with a guide for leading the paper. This is likely to cause wrinkles in the transfer material.
In view of the problems described above, it is an object of the present invention to ensure that there will be a stable feed of the transfer material when a paper back vacuuming feed mechanism is employed in the path from the transfer section to the fixing section in an image forming apparatus.
The foregoing object of the present invention can be achieved by an image forming apparatus which has a transfer section arranged over a transfer material feed path; a transfer material feed apparatus provided for vacuum transfer of a transfer material from the transfer section to a fixing apparatus; a guide tilted by a predetermined angle downward of the transfer material feed surface, which guide is provided at the outlet of the fixing apparatus of the transfer material feed apparatus, wherein the nip portion of a fixing roller pair of the fixing apparatus is positioned downward of the extension line of the guide; and the tangent with respect to the nip portion of the fixing roller is tilted by a predetermined angle downward of the transfer material feed surface of the transfer material feed apparatus.
Referring to
The intermediate transfer belt 6 is supported on a series of rollers and is rotated in the direction of the arrow by a driver roller 9. Four image forming sections Py, Pm, Pc and Pk are installed adjacent to the vertical path along the intermediate transfer belt 6 so as to be disposed in parallel to each other.
The image forming sections Py, Pm, Pc and Pk are basically designed to have the same configuration, and each has a photosensitive drum 1 serving as a first image carrier, a primary charging device 2, a laser exposure device 3, a developing device 4, a transfer roller 7 and a cleaner 5. The developing device 4 of each of the image forming sections Py, Pm, Pc and Pk contains one of yellow (Y), magenta (M), cyan (C) and black (K) developers.
During the rotation of the photosensitive drum 1, the first image forming section Py allows the surface of the photosensitive drum 1 to be uniformly charged by the primary charging device 2 so as to have a predetermined polarity and potential. Then, the surface is exposed by the exposure device 3 (an optical exposure system for color decomposition and image formation of a color document image, a scanning exposure system by laser scanning that produces laser beams modulated in response to the time series digital pixel signal of image formation, or others), whereby an electrostatic latent image corresponding to the first color component (yellow component) of the color image is formed on the surface of the photosensitive drum 1. Then the electrostatic latent image is developed by the developing device 4, using a yellow developer, and is turned into a visible image as a yellow toner image. The yellow toner image formed on the photosensitive drum 1 proceeds to enter the primary transfer nip portion opposite the intermediate transfer belt 6. The transfer roller 7 is arranged on the back of the intermediate transfer belt 6 of the primary transfer nip portion and is held in engagement on the downstream side inside the transfer nip portion. The yellow toner image on the photosensitive drum 1 is primarily transferred onto the intermediate transfer belt 6 when primary transfer bias is applied to the transfer roller 7 from a primary transfer power supply (not illustrated). To ensure that the primary transfer bias can be applied independently to the transfer roller 7 of each of the image forming sections Py, Pm, Pc and Pk, a respective primary transfer power supply is provided independently for each image forming section.
In a manner similar to the above, a magenta toner image, a cyan toner image and a black toner image are formed by the second, third and fourth image forming sections Pm, Pc and Pk, and a color image obtained by superimposing the four color toner images of yellow, magenta, cyan and black is formed on the intermediate transfer belt 6.
Where the secondary opposite transfer roller 6a of the intermediate transfer belt 6 is located, a secondary transfer roller 8 is installed on the outer surface side of the intermediate transfer belt 6, where a secondary transfer section is formed. The full color image that is carried on the intermediate transfer belt 6 collectively undergoes secondary transfer onto the transfer material P, that is supplied to the secondary transfer section of the intermediate transfer belt 6 from the paper feed section (not illustrated), by means of the transfer roller 8. Then, the transfer material P, which has received the image by secondary transfer, is transported to the fixing device 10, where heat and pressure are applied to the four-color toner, so that the transfer material P is fused and fixed. Thus, a color print image is obtained.
Subsequent to the secondary image transfer, the intermediate transfer belt 6 is cleaned by means of a belt cleaner in such a way that the toner remaining on the surface thereof after the secondary image transfer is removed to ensure that the next image formation can be started at any time. After the aforementioned primary transfer, the photosensitive drum 1 of each image forming section is cleaned by the drum cleaner 5 in such a way that the toner remaining on the surface after primary image transfer is removed to ensure that the next image formation can be started at any time.
As described above, the present invention avoids the formation of wrinkles in thin paper and fluctuation of an image caused by the use of thick paper during paper feed by a back vacuuming mechanism.
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2003-154170 | May 2003 | JP | national |
2004-053089 | Feb 2004 | JP | national |
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20040240917 A1 | Dec 2004 | US |