Automatic window/door system

Claim 1

A motor-driven window/door system comprising: a pressure responsive sensor arranged in association with a window or door; detector circuit means coupled to said pressure responsive sensor for detecting a squeezed object caught in the way of said window or door; an electric motor for driving said window or door to open/close said window or door; and control circuit means for controlling said motor; wherein said pressure responsive sensor comprises a coaxial sensor having an inner electrode, an outer electrode and a pressure responsive element interposed bewteen said inner and outer electrodes and having a variable resistance responsive to pressure on said pressure responsive sensor; said detector circuit means comprises pressure detector means coupled to said pressure responsive sensor for generating a signal indicative of a pressure on said pressure responsive sensor, and differentiation means coupled to said pressure detector means for generating a signal indicative of a rate of change of said pressure; and said control circuit means comprises direction control means coupled to said detector circuit means for controlling said motor in response to the squeezed object to release said object from said window or door, overload detector means coupled to said motor for detecting an overload condition of said motor including means for repeatedly interrupting the power supplied to said motor, electromotive force detector means for detecting a voltage appearing across said motor upon interruption by said interrupting means and having a magnitude essentially proportional to the rotational speed of said motor, and comparator means coupled to said electromotive force detector means, for comparing the voltage with a predetermined reference voltage and power-down means including deenergizing means, coupled to said comparator means, for deenergizing said motor in response to a signal from said overload detector means indicative of an overload of said motor.