| 摘要 |
1,139,320. Automatic control of speed. HEBERLEIN & CO. A. G. Oct.31, 1967 [Nov. 1, 1966; March 20, 1967], No. 49434/67. Heading G3R. In a system for controlling the speed of a commutator motor supplied from an A. C. source by adjustment of the firing angle of a controlled rectifier, e. g. a thyristor, in which a triggering capacitor 17 is charged by a fast rising "pedestal" voltage and then by a slowly rising "ramp" voltage, the capacitor is connected to the point 14 of a voltage divider 10, 11, 12 across which is applied the sum of a constant voltage (from Zener 8) and a speed representative voltage. The "pedestal" voltage comprises the constant voltage minus the volt drop across 10: when the voltage on capacitor 17 reaches this a diode 15 blocks and charging continues by the "ramp" voltage which is the constant voltage applied through a high value resistor 19. Desired speed is set on variable resistor 12, which determines the magnitude of the pedestal voltage. As shown, the motor is a shunt machine having a field 2 shunted by a "flywheel" diode 7. The armature 1 is energized through a single thyristor 3 and the speed representative voltage is the back e. m.f. during the non-conducting half cycles. The thyristor is triggered directly by a unijunction transistor 18. In an alternative embodiment Fig. 2 (not shown) the motor is a series machine energized during both half cycles through back to back thyristors triggered by a transformer whose primary is in series with a unijunction transistor across a diode and resistor bridge. The triggering capacitor is also across this bridge, which provides for a triggering pulse in each half cycle. The speed representative voltage is provided by a tachogenerator. Either embodiment may additionally have current limit circuits. In Fig. 4 (not shown) there is one for limiting normal running current, in which excessive current charges a capacitor sufficiently to cause a transistor to conduct which increases the volt drop in resistor 10 and so retards the firing angle; this circuit has a long time constant, and starting current is limited by a separate circuit comprising an R C delay network which restricts the rate at which the pedestal voltage can rise. In Fig. 5 (not shown) these two functions are combined in a single limiter circuit comprising an R C network connected through diodes to the junction of resistors 11 and 12 and across the Zener diode. |
