| 摘要 |
PURPOSE:To effectively prevent a motor from being rocked on a low speed, by enlarging the slope of saw-tooth wave when the actual speed of the motor becomes lower than a specified low speed. CONSTITUTION:By a photo-transistor PT1, voltage V3 according to the speed electromotive force of a motor M is applied to resistances R1, R2, and a diode D1, and speed voltage V5 is obtained. By a comparator CP1, trigger signal is applied to thyristors SCR1, SCR2 when the speed voltage V5 is made equal to saw-tooth wave V6 from a speed command section B. When the motor M is put in a rocking state, then voltage V9 is heightened with characteristic determined by resistances R31, 32, 35 and a diode. When the motor M is not removed from the rocking state even after a given time, then V4>V11 is shown, and the output V12 of a comparator CP2 comes to a low level, and the slope of the saw-tooth wave is enlarged, and the conductive phase angles of the thyristors are led.
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