Scanning and sheet feed control for electrostatic copier - by sheet position sensing and sheet-size related processing to prevent reverse charging of imaging drum, toner waste and contamination

摘要

To prevent reverse polarity charging of the imaging drum (107) the copy sheet feed (109) is commenced and then energisation of the charging unit (104), position sensor (111) and light source (105). The image transfer unit (106) is energised coincident with the arrival of the copy sheet front edge. When the position sensor (111) is de-activated the exit of the copy sheet rear edge is signalled. A time interval dependent on copy sheet size is determined to allow the sheet to clear the image transfer stage (106). The latter is switched off, the image (103) fixed and the charging unit (104) de-energised. ADVANTAGE - Prevents unnecessary scanning duration e.g. for small dimension work which wastes toner and contaminates processing. Prevents reduction in service life when processing irregularly sized copy paper.