Automatic control of reflective-type sensors in reproduction apparatus

Abstract

A control system for an optical sheet sensor device, including at least one light emitter and at least one light detector associated therewith for sensing a sheet in a sheet travel path for automatically controlling the sheet sensor device in order to provide an intensity of light from the light emitter to compensate for varying background reflectance and background-to-light emitter distance. The control provided for determining a light emitter current level corresponding to an operating condition where a sheet is known to be absent from the sheet travel path and where there is a close, reflective background to the light emitter. A light emitter current operating level corresponding to a reduced level with respect to the above determined current level is stored. A current startup error level at a preset amount off-set from the stored current level is determined. Current is applied to a light emitter, the applied current being increased toward a level at which the threshold level for the light detector is exceeded. The instantaneous applied current level is compared with the determined startup error current level, and an error signal is provided when the light intensity threshold is reached prior to the applied current level exceeding the determined current level. If the determined startup error current level is exceeded by the applied current level prior to the light intensity reaching the light intensity threshold, the light emitter is operated at the applied current level.