Variable bandwidth low-pass filter for line tracer accuracy control

A circular scanning optical pattern tracer including an optical scanner, means in said scanner to produce a reference sine wave, a reference cosine wave and a sensing pulse indicative of the time the scan intercepts the pattern, a pair of sample and hold circuits for producing coordinate signals representative of the coordinate velocities required to drive a servo system which moves the machine tangential to the pattern, means to apply said sine wave to one of said sample and hold circuits and means to apply said cosine wave to the other of said sample and hold circuits, means to derive a first and a second sampling pulse from said sensing pulse means and to selectively apply said first or said second sampling pulse to said sample and hold circuits and means to alter the duration of said first sampling pulse over a range of values such that the duration of said sampling pulse determines the frequency response of said sample and hold circuits.