PURPOSE: To detect increase in the contacting resistance between the first brush and a main shaft by providing the second brush which is designed to contact the main shaft besides the first brush which is contacted with the main shaft for contact detecting.
CONSTITUTION: The second brush 20 is mounted on the back surface of a column 12 through an insulating plate 19 and is connected with a power source +Vcc through a resistance R1 in an abnormality discriminating circuit 2. The column 12 is connected with an earth of the circuit 2, and the electricity flows from the power source +Vcc to the earth through the second brush 20, the main shaft 13, and the first brush 16. Being thus constituted, the electricity potential of a contacting point P of the resistsnce R1 and the second brush 20 values corresponding to the contacting resistance between the second brush 20 and the first brush 16 and the main shaft 13, and the increase in the electric potential at the contacting point P being accompanied by the increase in the contacting resistance is detected by a comparator 21 to output abnormal signal ABS.
YOKOE ISAMU
OWA KAORU
ETOU KUNIHIKO
