Patent ID: 7798757
Filing Date: 2010-09-21
Classification: B23P,B25B,F16B

Abstract:
1. A screw on which a screw driving device performs a tightening operation and a loosening operation and a loosening operation with respect to a screw hole that is correspondingly formed in a member to be fastened, the screw driving device comprising: a device body in which is provided a piezoelectric element that generates predetermined ultrasonic oscillations upon being impressed with a predetermined alternating current, and an oscillating end surface on which mechanical oscillations are excited based on the ultrasonic oscillations; and an oscillation transmission means that is integrally fixed to the device body on the oscillating end surface and that transmits the mechanical oscillations to the screw by contact with the screw, and the oscillation transmission means including a frictional material that is provided with a screw contact surface that is correspondingly formed to be capable of surface contact with a top end face formed on the screw head of the screw to transmit ultrasonic mechanical oscillations to the screw by frictional contact with the top end face, wherein the top end face of the screw head has a flat surface that includes only of a disc-shaped flat element without a “+” or “−” recess corresponding to the frictional material of the screw driving device, and the top portion circumferential side portion of the screw head has a circumferential side surface including only of a circular surface element.