GB1043491A - Motor control circuit - Google Patents

Abstract

1,043,491. Automatic tension control. MINNESOTA MINING & MANUFACTURING CO. Feb. 4. 1965, No. 4963/65. Heading G3R. In a system for controlling the tension of a magnetic tape, an oscillator 10 supplies a differential transformer 11 associated with a movable vane whereby the output signal of the transformer undergoes a change of phase when the tension passes from below a desired value to above that value. The output signal passes to an A.C. amplifier 12 which is biased to produce a signal having a single polarity despite deviations in tension from the desired value. A phase detector 13 compares signals from the amplifier 12 and the oscillator 10 to afford a unipolar direct voltage having a magnitude directly dependent upon the tension of the tape. This D.C. signal is applied to a differential amplifier 14 producing V-shaped characteristic signals of equal amplitude for corresponding deviations in tension on opposite sides of the desired value. These signals then pass through a D.C. amplifier 15 which biases the signals to locate the vertex of the characteristic at a reference potential. The output of the amplifier 15 is applied to reversing relay 17. The output of phase detector 13 is also applied to relay amplifier 16 which operates the relay in one direction or the other in accordance with the magnitude of the D.C. signal. The reversing relay is connected in circuit with motor 304 which drives a pay-out reel in a direction and at a speed to maintain the tension constant at the desired value. The tape-tension at the takeup reel may be controlled in a similar manner. Another arrangement comprises a photo-sensitive detector in which a movable vane is subjected to tape-tension and controls the amount of light received by two photo-cells.