| 摘要 |
PURPOSE:To reduce the shift of each color in the transfer paper carrying direction with simple constitution, by producing warning signals when the calculating result of a shifting quantity of an arithmetic means exceeds a prescribed value and inhibiting image forming operations when the image forming mode of >= colors is selected. CONSTITUTION:Means for generating image signal for pattern which form the pattern image of each color in areas other than the transfer paper placing area on a transfer belt 21, a detecting means 27 for detecting the passing of the pattern image of each color, and counting means CNT1-CNT4 which count the detecting timing of the detecting means 27 are provided. In addition, an arithmetic means 60 which calculates the shifting quantities by comparing the count values of the detecting timing counting means CNT1-CNT4 with set values and means for generating writing timing signals of each color which can be variably set in accordance with the output value of the arithmetic means 60, are provided. Moreover, the warning signals are produced when the shifting quantity calculating result of the arithmetic means 60 exceeds a prescribed value and, at the same time, image forming operations are inhibited when the picture forming mode of two or more colors is selected. Therefore, color shifts can be measured and compensated accurately without receiving any influences from the contamination of the transfer belt 21 and contamination and variance of sensitivity of a sensor.
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