An image forming apparatus according to the present invention includes a first processing device which processes in a normal mode for dynamically driving photoelectric detectors in groups so as to sequentially read detection signals from the photoelectric detectors in the groups, second processing device...http://www.google.com/patents/US5300768?utm_source=gb-gplus-sharePatent US5300768 - Including a processing means for driving designated photoelectric detectors for the checking thereof
