| 摘要 |
PROBLEM TO BE SOLVED: To minimize the switching frequency of exciting current by making the extendable speed of an extendable means into electric signals whose waveforms are different from each other on extension side and contraction side with one of the first and second fixing means excited and the other non- excited when the extendable means moves in one direction. SOLUTION: Exciting current is supplied to a fixing device 18, for example, so that the magnetic attracting surfaces 22 of the fixing devices 18, 20 may be attracted to a movement reference part constituted of magnetic material, and the saw tooth waveform voltage which goes up rapidly and goes down gradually is applied to an expandable device 16 repetitively with the exciting current not supplied to the fixing device 20. As a result, the fixing device 18 displaces gradually to the fixing device 20 side in a nonexciting condition and in the opposite direction. The fixing device 20 reciprocates to the fixing device 18 by the expandable action of the expandable means 16 and displaces by a distance corresponding to the displacement amount of the fixing device 18. It is thus possible to minimize switching frequency of exciting current and eliminate need for synchronizing the switching of exciting current with the supply of an electric signal to the expandable means. |
