Original Publication Date: 1986-Aug-01
Included in the Prior Art Database: 2005-Mar-09
In sensing a mark by optically scanning a mark area on a medium, a scanning output for each scan line is sampled at a predetermined period and digitized for storing in a memory and then comparing with a scanning output similarly digitized for the next scan line, so that the mark can be sensed by checking the amount of difference in the comparison. Referring to the drawing, the mark area is scanned by a CCD scanner and its output signal is amplified and clock-noise removed in the differential amplifier and then passed through the limiter to the sample and hold circuit which samples the signal at a predetermined time period. Further, the sampled signal is digitized at the AD (analog-to-digital) converter and supplied to the microprocessor for storing and comparing, as stated above.