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Obstruction detection in automatic portal control apparatus employing induction motor power factor

  • US 4,855,653 A
  • Filed: 03/03/1988
  • Issued: 08/08/1989
  • Est. Priority Date: 03/03/1988
  • Status: Expired due to Fees
First Claim
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1. An automatic portal operator comprising:

  • a portal closing member movable between a closed position blocking a portal and an open position not blocking said portal;

    an induction motor mechanically coupled to said portal closing member for controllably moving said portal closing member between said closed position and said open position;

    a motor controller electrically coupled to said induction motor for supplying electrical power to said induction motor for controllably moving said portal closing member toward said closing position or toward said open position, said motor controller including a safety operation for supplying electric power to said induction motor to render said portal closing member safe; and

    a power factor sensor connected to said induction motor and said motor controller includinga current sensor for generating a current square wave signal having the phase of the current supplied to said induction motor by said motor controller,a pulse stretching circuits connected to said current sensor for generating a extended current square wave signal having a trailing edge a predetermined length of time after the trailing edge of said current square wave signal,a voltage sensor for generating a voltage square wave signal having the phase of the voltage supplied to said induction motor by said motor controller,a clamping circuit connected to said pulse stretching circuit and said voltage sensor for clamping the reading edge of said extended current square wave signal to the leading edge of said voltage square wave signal, thereby producing a clamped extended current square wave signal,an inclusive or circuit connected to said voltage sensor and said clamping circuit for generating a phase output signal when said clamped extended current square wave signal differs from said voltage square wave signal, andan output circuit connected to said motor controller and said exclusive OR circuit for triggering said motor controller to execute said safety operation if the duty cycle of said phase output signal exceeds a predetermined amount.

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