| 摘要 |
Paper P has a detection pattern 10a having a length in a main scanning direction M, the length becoming shorter from upstream to downstream along a paper feeding direction F. An image sensor 4 detects the detection pattern and outputs a detection signal including data in the main scanning direction (length y). A control unit 5 calculates a position x of a vertex V of the detection pattern, by using the detection signal, a feeding speed v, an angle ¸ being half of the vertex angle of the pattern, and an imaging time t, so as to correct an image forming position on the back side to coincide with an image on the front side. The detection signal from the sensor with a low operation speed is processed according to a method utilizing a shape feature and the like of the detection pattern, thereby precisely detecting the position of the paper in the feeding direction. |
