Abstract: A tape tension control system is provided which controls the rotation of two tape reels to maintain substantially constant tension of the tape over its full length for all operational modes. The device utilizes inputs from two reel tachometers and a tape counter-roller for controlling the torque applied to each reel by AC induction motors. The tape counter-roller effectively measures the linear velocity of the tape which is driven by a capstan and the tachometers measure the rotational velocity of each reel. Appropriate logic circuitry, supplied with these velocity readings, enables the system effectively to sense tape diameter on each reel for providing the necessary torque to each reel to maintain uniform tape tension. This system provides for rapid start of the reels to allow for fast lock-in of the capstan and also controlled starts in fast modes such as rewind and fast-forward to prevent high stresses on the tape.

Abstract: A tape tension control system for a video tape recorder in which a first motor is coupled to a supply reel, a second motor is coupled to a takeup reel and a capstan is provided for driving the tape between supply and takeup reels in a normal running mode. Tachometers are associated with each reel and with the capstan. Signal processing circuits are provided for indirectly sensing diameters of tape on the respective reels. The required torque of each motor is determined by comparing the signals representing tape diameter with a reference sawtooth waveform. The sawtooth waveform is provided across a first capacitor coupled via a first transistor switching means to a source of charging current. A second capacitor is coupled to the current source for biasing the transistor into conduction after a predetermined time delay. A biasing supply is coupled to the alternating voltage source for varying the time delay in response to variations in the alternating voltage.