| 摘要 |
1286107 Automatic control WARNER & SWASEY CO 9 Sept 1969 [26 Sept 1968] 44480/69 Heading G3R [Also in Division H2] An A.C. source 10 is connected to a D.C. motor 11 through silicon controlled rectifiers 12, 13, which are arranged back-to-back. A sawtooth generator 14 produces signals on lines 15, 16, for controlling the rectifiers 12, 13 respectively, these sawtooth signals being inverted and phase displaced by 180 degrees with respect to each other. A summing network 17 receives a reference signal on line 18 and a feedback signal on line 19 representing the speed of the motor. The resultant error signal is combined with a level adjustment signal and the sawtooth signal on line 15. When the instantaneous value of the error signal plus the sawtooth signal exceeds the adjustment signal, a level detector 20 triggers the rectifier 12 provided that is anode is positive with regard to its cathode at the time. A summing network 21 is similarly associated with a level detector 22 for controlling the rectifier 13. The effect of back EMF having a polarity opposed to the source voltage is retard the firing time and to advance the turn-off time of the rectifier 12. If the motor rotates in the opposite direction, as a result of rectifier 13 being fired or due to the motor being driven by the load, the motor is stopped or driven in the forward direction by firing the rectifier 12. The back EMF then aids the source voltage to advance the firing-time of the rectifier 12 into the preceding negative half-cycle and to retard the turn-off time into the following negative half-cycle. When the error and back EMF signals are both at zero, the motor receives alternate pulses of opposite polarity and short duration so that it does not rotate. Alternatively, the level adjustment signals may be altered to provide a dead-band effect. In modifications, the variable controlled may be other than speed. For example, the load may consist of heating and cooling elements for stabilizing temperature, and two rectifiers providing bidirectional control.
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