Door operator system using counter circuit for determining limit positions

摘要

The shaft driven by a reversible motor for opening and closing a door is provided with at least one reflective surface. An optical source/detector senses rotation of the shaft and generates a pulse each time one of the reflective surfaces passes. A programmable counter circuit counts the pulses in one direction when the door is opened and de-energizes the motor when a predetermined count is reached without the use of mechanical switches. The counter is decremented when the door is closed, and de-energizes the motor when the count returns to zero. Any obstruction will cause the system to stop the door if sensed during opening, or to reverse the door's direction if sensed during closing. Provision is made to account for any "coasting" the door may experience due to inertia; and the system will also track and permit small changes in the closed position of the door, as might occur if snow accumulates beneath the door.