| 摘要 |
PURPOSE:To cut off power supply to an electric motor, by detecting presence of sparks and noises, etc. occurring between a brush and a commutator during operation of a DC motor and also detecting thereby condition of stop of the motor with accuracy. CONSTITUTION:When a switch S is turned on, a full-wave rectification voltage is supplied from a rectifying unit 1 to a DC motor M through a rotating speed setting resistance R1 and a thyrister SCR1. During operation of the motor, sparking noises continuously occur between a brush and a commutator, and a monostable multivibrator 3 is driven by a pulselike noise signal coming through a differential circuit 2 whereby a low-level signal output is maintained. When tightening of screw is completed and the motor M became in stopped position, the sparking noise between the brush and the commutator stops, and when the thyrister SCR1 is turned on and a thyrister SCR2 is turned off by a high-level signal of the monostable multivibrator 3, power supply is cut off. |
