| 摘要 |
PURPOSE:To prevent a device from malfunction when current stops flowing to a motor, by furnishing a means to sense the current to the motor and a means to sense the decelerative operating limit of the motor, and by deengaging a magnet clutch through generation of a sensing signal about operating limit. CONSTITUTION:After a motor attains its decelerative operating limit and a magnet clutch 24 is deengaged, a decelerative drive signal is generated for sensing of decelerative drive current of the motor 25 after a certain period of time t. When a decelerative limit switch 30 is in failure in closed condition due to trouble which has occurred before passage of the period t, the above- mentioned decelerative drive signal causes current to flow in the motor 25. Accordingly the CPU judges the decelerative limit switch 30 as close failure upon motor current sensing signal from a motor current sensing circuit 6 to perform cancel treatment in the automatic constant-speed running condition. In normal time, however, the switch 30 is in opened state even though a decelerative drive signal is emitted, so that no current will flow in the motor 25.
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