Patent GB-1365312-A (GB)
Title: Processes and apparatus for controlling stepping motors
IPC: G05B19/40
Filed: 1971-07-08
Abstract: 1365312 Waveform generators CARL ZEISS JENA VEB 8 July 1971 32126/71 Heading H3T [Also in Division H2] A control system for a stepping motor comprises an impulse generator 7 which produces a variable frequency output to supply the motor (not shown) in response to a variable voltage applied to its input A1 as a result of the charge or discharge of a capacitor C1, the arrangement being such that the motor is accelerated to a final stepping frequency in accordance with a desired time/stepping frequency exponential function independent of the final stepping frequency, at which the acceleration is automatically interrupted, and the motor is decelerated in accordance with a time/stepping frequency characteristic which approximates to an exponential function with a positive exponent but a negative sign, the characteristic being obtained by the superimposition of a time/stepping frequency linear function and a time/stepping frequency exponential function. Figure 1 shows time/stepping frequency acceleration characteristics 1b, 2b to final stepping frequencies of f 1 , f 2  respectively, which characteristics are identical with the permissible characteristics la, 2a and an improvement on the characteristics 1c, 2c obtained by known control systems. The Figure also shows the deceleration characteristics 1b, 2b from the stepping frequencies f 1 , f 2  and the corresponding permissible and known characteristics 1a, 2a and 1c, 2c, the motor being slowed ,down to a crawl frequency f cr  which is maintained constant until the desired stop position is reached. In Fig. 2 the operation is as follows:- Acceleration.-A signal at E2 closes a switch 1 to apply a D.C. voltage from a source E1 to capacitor C1 through a resistor R8, the capacitor C1 charging to a maximum voltage determined by a limiter element 2 controlled by a signal E5 corresponding to the desired final stepping frequency. Deceleration.-The signal E2 is removed to open the switch 1 and a signal E3 (previously absent) is applied to a time function element 6 controlling the operation of a current source 5 for discharging the capacitor C1 in a predetermined manner to provide the desired deceleration characteristic. When the voltage has fallen to a value corresponding to the crawl frequency f cr , set by a signal E4, a comparator 4 opens a switch 3 to interrupt the discharge of the capacitor C1. Alternatively E4 may be set to zero to completely discharge C1. Figure 3 shows a circuit diagram of the embodiment of Fig. 2, all the switches being in the form of transistors actuated by 0/1 signals at inputs E2 and E6. The element 2 takes the form of a diode D4 controlled by a potentiometer P1 to set the final stepping frequency corresponding to the charging of capacitor C1 when switch 1, formed by members R1, R2, R3, T1, is closed. Members P2, T2, R5 limit the maximum charging voltage of capacitor C1 and members D3, R20 produce a "dead zone" in the characteristic control curve of the impulse generator. The element 6 is formed by members T3, R6, R7, R11...R14 and C2, whilst the transistor T4 acting as the current source 5 also functions as the switch 3 and comparator 4. During deceleration the transistor T3 is blocked and members R11...R16 and T4 maintain the voltage across resistor R14 substantially constant, so that the resistor carries an almost constant current arising out of the addition of the emitter current of the transistor T4 and the discharge current of capacitor C2 via an adjustable resistor R7, the capacitor C2 being charged through a diode D2 and resistor R6 during the acceleration of the motor. Hence the discharge current of the capacitor C1 follows the collector current of the transistor T4, whose emitter current varies as the difference between the current through resistor R14 and the exponentially decaying discharge current of the capacitor C2. Mathematical expressions are derived for the action of the element 6 and the various voltages and currents associated with members C1, C2 and T4, it being shown that the deceleration characteristics 1b, 2b of Fig. 1 are obtained by superimposing the linear characteristics 1b<SP>11</SP>, 2b<SP>11</SP>, corresponding to discharge of capacitor C1 without the capacitor C2, with the voltage characteristic produced by integration of the discharge current of capacitor C2. Variations of the shape of the acceleration and deceleration characteristics may be produced by altering or adjusting the members D3, P1, P2, R4, R7, R8, R14 and R16, Fig. 4 (not shown). The capacitors C1, C2 may be interconnected by a resistor, transistor, diode circuit, Fig. 5 (not shown) to cause the voltage of capacitor C2 to follow that of the capacitor C1 at all times, thereby adapting the deceleration to the final acceleration frequency.