Two speed loop control arrangement

Abstract

A control system senses variations in the size of a buffer loop introduced in a magnetic recording tape or other flexible strip between a point of intermittent advance and a point of uniform advance. The control system maintains the size of the buffer loop at a selected measure by controlling the speed of the drive means which advances the tape uniformly. The control system has two response characteristics which cause the control system to react to variations in loop size either quickly or slowly depending on which response characteristic is chosen. During a first mode of operation, the faster response characteristic is chosen to establish the loop size quickly, while audio reproduction is muted. The control system then switches to a second mode of operation with the slower response characteristic which is compatible with audio reproduction. The control system employs an integrator responsive to an input signal indicative of loop size. The integrator output is a control signal which determines the speed of the drive mechanism for advancing the tape uniformly. In one embodiment, the signal indicative of loop size is provided by a circuit which produces an amplitude corresponding to the duty cycle of the output of a light detector which is illuminated via a path interrupted by the buffer loop. Preferably, the circuit includes a peak follower for the output of a gated integrator. The gated integrator provides a succession of rising output signals or 'ramps' which time the duration of a first level of the light detector output. The peak follower is reset before the end of each ramp.