Abstract

In an apparatus for controlling operation of an automatic door with minimum error in a detected door position, a motion sensor is positioned relative to a movable driving member coupled to the door. Pulses having a pulse repetition rate are created in direct proportion to a velocity of movement of the driving member. The pulses are counted and current position of the door determined. Any error arising from a loss or slip in an intermediate transmission mechanism which couples a motor with the final driving member is substantially eliminated. A pair of motion sensing elements as opto-electronic couplers may be provided for sensing a phase relationship between the sensing elements defining a direction of door movement. A pulse interval monitor adapted to generate a signal indicative of a long lapse of time between adjacent pulses from the sensing element may be provided. A sequence control circuit responsive to this generated signal generates a stop command for the motor.