A control member of image forming unit controls a driving motor so as to move a unit of combined developing devices in accordance with a developing mode or a specific operational condition which is set when the unit is moved to a toner supply position due to a shortage of toner. The control member functions...http://www.google.de/patents/US5070362?utm_source=gb-gplus-sharePatent US5070362 - Image forming apparatus having a plurality of selectively operable developers
