| 摘要 |
PURPOSE:To suppress a noise due to high-speed running at the time of no-load running by automatically changing a circuit voltage according as there is any load, and by making a rotational speed variable. CONSTITUTION:When it is started, a motor 1 is driven with a low noise by a TRIAC 3 and low-voltage firing angle circuit 10. Each voltage-reduced value of the output current of a load current reference value-setting circuit 7 and the current to a current detector 4 coincide with each other, e.g. at the time of a thread cutting work. Then, operation is switched from a low-voltage no- load current reference circuit 7 to a high-voltage no-load current reference value circuit 8. When the thread cutting work ends and the current of a circuit 2 lowers to the reference current of the high-voltage time no-load current reference circuit 8 by the release of the load of the motor 1, voltage values of a comparison circuit 12 coincide with each other. Then, setting of the high-voltage firing angle holding circuit 13 is canceled and the signal of an output circuit 15 is eliminated. Thus, both voltage and noise of the circuit 2 are reduced by the TRIAC 3 and low-voltage firing angle circuit 10. |
