GB1404774A - Controlling a stepping motor by a variable frequency oscillator - Google Patents

Abstract

1404774 Automatic control of movement ELEKTROMAT VEB 14 Sept 1972 42655/72 Heading G3N [Also in Division H2] A stepping motor 4 is controlled by a circuit comprising a variable frequency oscillator 1, a controller 3, a reversible counter 2 and a variable impedance network 5, the arrangement being such that the oscillator frequency is determined by the state of the counter 2 whose outputs 2‹ - - - 2n control respective switching transistors To - - - T n of the network 5 to vary the conductance G of the latter and hence the time constant of the oscillator. The controller 3 includes a pulse-shaping unit, a reference counter, comparator and coincidence stages, a pulse distributor and a pulse amplifier feeding the windings of the motor 4. Members 2, 3 receive a squarewave pulse train from the oscillator 1 and the controller 3 sets a predetermined pulse value a corresponding to a desired number of motor steps, for example as obtained from a punched tape. In a typical operation involving acceleration, constant speed running and braking of the motor, pulses are fed to members 2, 3 and the oscillator frequency progressively increases until the reference counter reaches a value b, whereupon the controller 3 stops the counter 2. The motor then runs at a speed dependent on the value b (in counter 2) and fixed and variable oscillator time constants dependent on elements R', C', R"' and G, C". The reference counter counts up to a value a/2 and then counts down. When a count value (a-b) has been reached, the counter 2 is restarted I in the reverse direction and the oscillator frequency progressively decreases until both counters simultaneously reach zero and the motor stops. Thus the frequency/time characteristics for acceleration and braking are mirror symmetrical, Fig. 2 (not shown). If b is greater than a/2, there is no steady speed condition since the counter is not stopped but counts down with the reference counter when its value reaches a/2.