| 摘要 |
PROBLEM TO BE SOLVED: To reduce the size and cost of an apparatus by simplifying the structure of a change-over switch used for demagnetizing residual magnetism in a yoke chucking a work with magnetic force. SOLUTION: When a forward current and a reverse current are alternately applied to a coil 40 generating magnetic force in the yoke and a current flow is decreased, residual magnetism in the yoke disappears. Since the switch SW1, for example, only turns on and off between a positive electrode terminal (+) of a D.C. power supply circuit 30 and a terminal 41 of the coil 40, the switching speed is not needed so as to simplify the structure.
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