| 摘要 |
PURPOSE:To prevent tightening torque from exceeding the preset value by an influence of inertia, by providing a speed change ring in the periphery of a planet cone so that the speed change ring can be turned in accordance with the torque engaging by friction with a conical surface of the planet cone. CONSTITUTION:As load torque is applied to a driver bit 14, reaction torque in accordance with a load is applied to a speed change ring 25. Then the speed change ring 25 turns in a reverse direction to the rotary direction of the driver bit 14, and an arm 32 is titled while turning respectively for the speed change ring 25 and a flange part 17a. As a screw is seated to a work, tightening torque rapidly increases, and the speed change ring 25, which rapidly moves, reaches the edge part of a conical surface 23c. Then a cam disc 24, whose rotation decreases to zero despite that an input disc 21 rotates, stops in a condition that fixed output torque is output, and screw tightening is completed.
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