GB1313972A - Servo-mechanisms - Google Patents

Abstract

1313972 Control of stepping motors YOKOGAWA ELECTRIC WORKS Ltd 28 April 1971 [30 April 1970 24 March 1971] 11924/71 Heading H2J [Also in Division H3] A pulse motor is controlled to stop at a position corresponding to the value of input signal E i . Comparator amplifier 3 of linear integrated circuit type receives as input the signal E i opposed by the signal E f corresponding to actual rotor position. For one sign of the difference E i -E f , transistor Q 41 conducts, causing the signal level at a to have digital level unity and establishing a direction of rotation for motor 6 decreasing the value of | E i -E f |. Transistor Q 42 also conducts, and, as | E i -E f | tends to zero, Q 41 cuts off before Q 42 , the output b of NAND G 40 thus becoming zero and cutting off the pulse motor energization. For rotation in the opposite sense, Q 42 comes on before Q 41 to de-energize the motor. A subsequent change in the value of E i will engender further motor movement causing E f to follow E i . Motor energization.-Rectangular clock pulses are generated at CP and divided by two in frequency, by flip-flop FF. NAND gates G 51 -G 54 receive rectangular pulses at the flipflop frequency, and, depending upon the digital value of signal a, the pulses e lead or lag those at f by 90 degrees, respectively to establish the direction of motor rotation. Gates G 51 -G 54 are enabled only when signal b is unity. Development of actual motor position signal E f .-Two coils W b in series aiding, and two coils W d in series opposition are wound on both limbs of a saturable core T forming a balanced magnetic circuit which is completed through magnet M rotated by the motor, see Fig. 7 (not shown). Coils Wb, W d are coupled to form an oscillator whose output is rectified, and via Darlington pair 24, produces a steady current in coils W f , in series opposition, on the core T. The voltage E f across R L in series with coils W f thus corresponds to the magnet position, as does the amplitude of the oscillations. In an alternative driving circuit (not shown) the signal d may feed gate G 52 directly, signal f being fed to EOR 1 , and, in Fig. 8 (not shown), only two NAND gates (G 51 , G 52 ) are used, generator CP and flip-flop FF being reset whenever signal b attains zero. In the embodiment of Fig. 1 (not shown), the rotor drives the wiper of a potentiometer (R 20 ) to derive the signal (E f ) signals (E i ) and (E f ) being fed to the respective inputs of comparator (3), the breakdown voltage of a zener diode D 24 defines the magnitude of ( | E i -E f | ) beyond which the enabling signal (b) is provided and the NAND gates G 51 -G 54 are in the circuits of the motor windings. The system is used in an automatic balancing recording meter.