(1) Field of the Invention
The present invention relates to an image forming device and an image forming method, and especially to an image forming device that includes an image carrier in the shape of an endless belt such as an intermediate transfer belt, and to an image forming method for the image forming device.
(2) Description of the Related Art
A what is called 4-cycle color printer uses a technology of transferring toner images of yellow (Y), magenta (M), cyan (C), and black (K) in layers onto an intermediate transfer belt via one photosensitive drum, so as to obtain a color image formed on a recording sheet or the like. In the 4-cycle color printer, a detecting unit detects, for example, a hole or a cut provided in the intermediate transfer belt so as to recognize a standard position of the belt. The timing at which the toner images are to be formed on the intermediate transfer belt is then controlled based on the recognized standard position.
In the above-described construction, however, a space for the hole or cut needs to be secured in the intermediate transfer belt. This would increase the intermediate transfer belt in width and thus would increase the image forming device in size. Also, providing such a hole or cut in the intermediate transfer belt would reduce the durability of the belt, making the belt easy to crack.
On the other hand, U.S. Pat. No. 5,499,092 discloses an image forming device that forms a toner patch on the intermediate transfer belt so that a detecting unit can detect the toner patch for recognition of the standard position of the belt. This construction eliminates the need to secure an extra space for a hole or a cut in the intermediate transfer belt, and therefore restricts the belt from becoming wider and the image forming device from enlarging. Also, it avoids crack formation in the belt since it avoids reduction in the belt durability.
Meanwhile, the intermediate transfer belt would have an electric resistance unevenness that is caused by a link of the belt generated during production or by a flaw generated during use. If a toner image is formed in an area having an electric resistance unevenness, a transfer density unevenness, which would reduce the image quality, occurs. Accordingly, to prevent the reduction of the image quality, it is preferable that the toner image is formed in an area that does not have an electric resistance unevenness.
The above-mentioned image quality reduction may occur even to the image forming device disclosed in U.S. Pat. No. 5,499,092, for the following reasons. In case the intermediate transfer belt has a toner patch thereon, a toner image should not be formed in an area having the toner patch. However, there may be a case where to avoid the toner patch, a toner image needs to be formed in an area that has an electric resistance unevenness.