Elevator door stall mode with hysteresis

Elevator door apparatus, comprising:

• a motor driven elevator door mechanism;
• demand means for providing signals indicative of demands to open or close said elevator door;
• position means providing signals related to the position of said elevator door;
• and
• control means for controlling said door mechanism in response to said demand signals and said position signals;
• characterized by:
• said position means comprising a transducer for providing signals which vary as a function of the position of said door mechanism;
• and
• said control means comprising cyclically operative signal processing means for providing, in response to said transducer, signal indications of the position and velocity of said door, and, in response to said demand means and said position and velocity signal indications, for controlling said door in either a motion mode of operation or a stall mode of operation, and, when operating in said motion mode of operation, for providing a dictated door motion control signal to effect desired motion of the door in response to said position and velocity signal indications and providing driving signals to said door mechanism in response to the difference between said signal indications and said door motion control signal, and, when operating in said stall mode of operation, providing driving signals to said door mechanism to provide a desired force on said door, for comparing said velocity signal indication with a signal indicative of a predetermined stall velocity, for operating in said motion mode of operation when the velocity of said door is greater than said predetermined stall velocity, and for operating in said stall mode of operation when said door velocity is less than said predetermined stall velocity for a predetermined hysteresis interval of time.