Image forming apparatus including a belt-shaped image carrier

1. An image forming apparatus including an image carrier, shaped like a belt, that holds toner images of a plurality of colors, and a transfer portion that transfers the toner images of a plurality of colors held on the image carrier onto a recording medium, wherein the image carrier is made of an elastic material, comprising:

a pattern image forming unit that repeatedly forms a pattern image for color misregistration detection on the image carrier at a constant interval so as to set the pattern images within a length range of the recording medium in the rotating direction of the image carrier,

wherein one of the pattern images includes a first toner image group in which a plurality of toner images of a first color is formed at a first interval in the rotating direction of the image carrier, and a second toner image group in which a plurality of toner images of a second color is formed at a second interval in the rotating direction of the image carrier.

2. The image forming apparatus according to claim 1 , further comprising:

a control portion that corrects a color misregistration distance detected based on the pattern images.

3. The image forming apparatus according to claim 1 ,

wherein the pattern image forming unit forms the pattern image in which the second interval is different from the first interval, and the second toner image group is closed to the first toner image group.

4. The image forming apparatus according to claim 1 ,

wherein the pattern image forming unit forms the pattern image in which the second interval is different from the first interval, and the second toner image group is superimposed on the first toner image group at same position.

5. The image forming apparatus according to claim 1 ,

wherein the pattern image forming unit forms a first pattern image in which the second interval is equivalent to the first interval, and the second toner image group is superimposed on the first toner image group, forms second pattern images in which the second interval is equivalent to the first interval, and the second toner image group is superimposed on the first toner image group with shifting the second toner image group by ±1 pixel respectively in the rotating direction of the image carrier on both lateral sides of the first pattern image, and forms N+1-th pattern images in which the second interval is equivalent to the first interval, and the second toner image group is superimposed on the first toner image group with shifting the second toner image group by ±N pixels (N is an integer greater than or equal to 2) respectively in the rotating direction of the image carrier next to Nth pattern images.

6. The image forming apparatus according to claim 1 ,

wherein each toner image group included in the pattern images is formed by identifiable signs with which misregistration-distance is enabled to be identified.

7. The image forming apparatus according to claim 6 ,

wherein the identifiable signs are numeric or alphabetic characters.

8. The image forming apparatus according to claim 1 ,

wherein a group of the pattern images is repeatedly formed a plurality of times at a predetermined interval in the rotating direction of the image carrier.

9. The image forming apparatus according to claim 1 ,

wherein a load is made to touch and leave to and from the image carrier at predetermined timing, while the pattern images are repeatedly formed a plurality of times at an interval corresponding to the touching/leaving timing of the load in the rotating direction of the image carrier.

10. The image forming apparatus according to claim 1 ,

wherein the toner image of the first color is magenta, and the toner image of the second color is yellow.

11. The image forming apparatus according to any one of claims 1 to 4 ,

wherein the toner image of the first color is one of yellow and black, and the toner image of the second color is one of cyan and magenta.