Original size detecting apparatus of an image forming apparatus

摘要

When preliminary scanning is started, a reference signal is generated from a reference position sensor and a moving amount of the scanner is measured by counting. Change in intensity of the reflected light from a platen is detected by a first sensor according to movement of the scanner. When the detected intensity attains reference intensity, the moving amount of the scanner is stored. When the detected intensity attains again the reference intensity after it has been lower than the reference intensity, the stored moving amount of the scanner is updated. The time in which the detected intensity attains the reference intensity is measured and when it attains a predetermined time, absence of the original is determined and the scanner stops and returns. The size of the original is determined based on the moving amount of the scanner stored at that time.