Method and device for determining the speed of a member

Claim 1

In an apparatus for controlling the speed of a motor including means for observing the actual speed of said motor and for providing a signal corresponding to such observed motor speed, means for providing a reference speed signal, a comparator receiving said actual and reference speed signals for determining the different therebetween and providing an error signal corresponding to such difference, and a controller receiving said error signal from said comparator and controlling the speed of said motor accordingly, an improved observed speed measuring means comprising a pulse producing member rotated by said motor, said member having a plurality of radiation-intercepting elements arranged in spaced relation thereon, an electromagnetic radiation source disposed on the path of said radiation-intercepting eLements and impinging radiation on said intercepting elements in succession to produce by the intermittent interception of said radiation by said elements a series of radiation pulses, two radiation-sensitive detectors arranged in spaced relation along the path of said intercepting elements to receive said radiation pulses, said detectors being arranged such that both receive the pulse corresponding to the same intercepting element before receiving the pulse corresponding to any other element, and means for determining the interval of time elapsing between the instant said pulse is first detected by said first detector and the instant the same pulse is first detected by said second detector, said time interval being indicative to the speed of said pulseproducing member and thus of said motor.