First grate detector for an optical scanning system

Abstract

In an optical scanning system the position of a scanning beam is determined by a grating across which the beam is traced and then retraced to start again. The first grate is detected by first filtering the relatively low frequency input signals generated as the beam traces across the grating and the relatively high frequency signals generated as the beam retraces across the grating. The filter passes the low frequency signals, excludes the high frequency signals and accentuates the changes between high and low frequency signals which occur as the beam reaches either end of the grating. By applying the filtered signal to a gating arrangement, it is possible to eliminate one plurality of the signals generated as the beam falls upon the end of the grating. The remaining plurality of signals is further applied to a gate which detects the first grate signal to the exclusion of all others for providing an accurate indication of the start of scan of the optical system.

Dependencies are inferred from the claim text.