Optical System Compensation for ADF Document Position
Original Publication Date: 1988-Aug-01
Included in the Prior Art Database: 2005-Feb-15
When an automatic document feeder (ADF) is used on a copier, the object plane can be anywhere between the top of the document glass and the bottom of the ADF vacuum belt. This distance can be greater than the depth of the field of the lens, creating a possible out-of-focus condition. A method is described to compensate for this condition. In the figure, the copier's scanning optical system 10 consists of focal length adjusting mirrors 11 and 12, lens 13 and fixed mirror 14. For magnification and reduction modes, lens 13 and mirrors 11 and 12 change positions to achieve the proper focal length. In this design, optical system 10 is set up with the top of document glass 15 as the object plane. The bottom of ADF vacuum belt 16 is set at a known and fixed distance, for example, 1.