| 摘要 |
PROBLEM TO BE SOLVED: To predict a failure due to wear of the brush of a DC servo motor accurately and conveniently. SOLUTION: A DC servo motor 2 is subjected to PWM driving by a controller 1 connected through a feeder line 4. A sensor 3 measuring the current of a pair of feeder lines 4 collectively outputs a current difference Ia-Ib corresponding to a leak current Ir flowing through the insulation resistor Rz of the motor 2. The sensor output is compared with two difference threshold values Th1 and Th2 by comparison circuit 6 and 7 and, depending on the comparison results, a logic circuit 8 delivers an abnormal signal if the leak current is higher than the large threshold value Th1 and delivers a caution signal if it is between Th1 and Th2. Since the leak current Ir is proportional to the insulation resistance if the drive current V is constant and the insulation resistance has a good relation with wear of brush, failure of motor due to wear of brush can be predicted accurately by monitoring the magnitude of the leak current.
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