| 摘要 |
PURPOSE:To prevent a decrease in holding power by intervention of foreign matter between an electromagnet which selectively attracts an armature fixed to the top end of a control element and said armature by forming rugged parts to at least either of the attraction faces of the armature and the electromagnet. CONSTITUTION:The armature 36 is attracted to the electromagnet 38 formed with the rugged parts 105, 105a, 104, 104a on the attraction face 101 when electric current is passed to a coil 41 by an energizing device 103. The coolant between both is displaced at this time to flow from the projecting parts 105, 105a toward the recesses 104, 104a and magnetic particles 106 are attracted into the recesses 104, 104a and, therefore, the generation of a spacing between the attraction faces 101 and 102 is obviated. Alternating magnetic fields different from the magnetic fields generated at the time of attraction are generated when the backward current is passed to the coil 41 by the device 103 after the armature 36 is detached by de-energizing the electromagnet. The particles 106 can be detached by decreasing the current value down to zero.
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