PURPOSE:To increase the speed and to improve grip force by arranging two laminated piezoelectric elements and turning a driving arm toward a driving shaft to increase contacting strength and setting a voltage, which is applied to piezoelectric elements, in accordance with the rise curve of a displacement increasing mechanism. CONSTITUTION:One end of each of laminated piezoelectric elements 3 and 4 is stuck to one side of a space 2 of a frame 1, and the other ends are brought into contact with driving shafts 7 and 8. When a voltage is applied to laminated piezoelectric elements 3 and 4, driving shafts 7 and 8 are pushed up and a moment of rotation acts on driving arms 11 and 12, and thread restraining parts 19 and 20 are pressed to thread to restrain it. Pre-pressure springs 13 and 14 and driving arms 11 and 12 are pressed and driving shafts 11 and 12 and driving shafts 7 and 8 are pressed, and they are moved as one body to suppress the occurrence of a fretting phenomenon, and a defect that the durability against tensile force is low is solved. The rise characteristic of the voltage to a laminated piezoelectric element 25 is set along that of the displacement increasing mechanism to suppress overshoot and residual oscillation.
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