| 摘要 |
PROBLEM TO BE SOLVED: To provide an image forming apparatus that correctly determines whether or not the positional relation between the focal point of an exposure means and the surface of a photoreceptor is correct, without using an intermediate gradation mark. SOLUTION: When patches P shown on the conveyance belt (A) of a tandem system printer are formed, a sensor output when the patches P are passed results in as shown in (B). A comparator output obtained by comparing the sensor output with a comparator threshold results in as shown in (C). However, if the width of the patch P increases due to focus displacement of an exposure means, the sensor output does not decrease below the comparator threshold between the patches P, as shown in (D) and (E). Consequently, the number of detected patches P decreases, or the patch width Wtc becomes wider than a normal patch width Wta, as shown in (H) and (I), and a patch interval Wtd becomes smaller than a regular patch interval Wtb. To counteract this, the presence or absence of focus displacement is determined on the basis of the result of the detection of the end edge of each patch P. COPYRIGHT: (C)2010,JPO&INPIT
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