Color image forming apparatus and a method for operating

An image forming apparatus comprising:

• a plurality of image carriers;
• an intermediate transfer body;
• a plurality of transfer units for transferring toner images formed on said plurality of image carriers onto said intermediate transfer body, each of which is provided corresponding to each of said plurality of image carriers, each of said plurality of transfer units being contacted under pressure with each of said plurality of image carriers through said intermediate transfer body by the application of pressure when each of said plurality of transfer units is operating and not contacting each of said plurality of image carriers when each of said plurality of transfer units is not operating;
• a driving unit for driving said intermediate transfer body to rotate at a rotary speed;
• and
• a control unit for controlling said driving unit to drive said intermediate transfer body under a feed-forward control and a feed-back control,
• the control unit controlling said driving unit according to correction information, wherein correction information used for the feed-forward control is different depending upon a kind of image,
• wherein said control unit makes said plurality of transfer units to be selectively operated according to the kind of image and said control unit changes a speed control method for said driving unit according to the kind of image,
• wherein the kind of image includes a full-color image, a mono-chrome image, or a uni-color image.

A method for operating a color image forming apparatus comprising the steps of:

• selectively actuating a transfer unit according to a kind of image;
• reading correction information related to control of the rotational speed of each image carrier from a storage unit according to the kind of image;
• controlling the rotational speed of each image carrier under a feed-forward control and a feed-back control based on the read correction information, wherein the correction information used for the feed-forward control is different depending upon the kind of image;
• and
• transferring a toner image of a specific color on the image carrier onto an intermediate transfer body at a controlled rotational speed.