| 摘要 |
1531490 Control of DC motors CABLEFORM Ltd 14 Dec 1976 [24 Dec 1975] 52782/75 Heading H2J A D.C. series motor 4, 5 is controlled by a system having a section I operating in a manner described in Specification 1,328,800, a section II operating to vary the mark/space ratio of the pulses in section I in accordance with a demand signal from section III, and a section IV responsive to the signal from a motor-current sensing resistor 8 to reduce the maximum mark/space ratio of the pulses that may be applied to the motor when the current is below a predetermined limit, thereby preventing the motor overspeeding on light loads without the need to add a shunt winding to overcome this problem. The current signal determines the conductivity of transistors 11, 12, 13, 14 and hence the voltage across the track of a potentiometer 9, 10 supplying the demand signal. The maximum mark-space ratio may be proportional to the motor current when it is below the limit I 0 determined by the setting of a resistor 25, typical characteristics of mark/space ratio and motor speed against current being discussed for various settings of the wiper 9, Figs. 3 and 4 (not shown). To obtain modified characteristics for wiper settings below the maximum, Figs. 6 and 7 (not shown), the series combination of transistor 14 and a resistor (31) is connected in parallel with the potentiometer 10, the wiper 9 and resistor (31) being connected through diodes (32) to section II, Fig. 5 (not shown), which diodes select the least positive signal for application to section II. The latter also limits the maximum motor current as described in Specification 1,330,131. |
