| 摘要 |
<p>There are provided two kinds of nuts of a ball thread nut 20 and a non-ball thread nut 30 which is rotatable in synchronization with the ball thread nut 20 and in which a thread groove in rectangular or trapezoidal shape in section is formed. In a thread rod 10, two kinds of thread grooves are formed at the same pitch, one 11 of the thread grooves being in an arc shape in section so as to be meshed with the ball thread nut 20 through balls B and the other thread groove 12 being in a rectangular or trapezoidal shape in section so as to be meshed with the non-ball thread nut 30. When load is less than a predetermined value, the thread ridge of the non-ball thread nut 20 and the thread ridge 13 of the thread rod 10 are separated and are out of contact with each other so that the thread rod 10 is moved in the axial direction thereof by only the ball thread nut 20. In contrast, when the load exceeds the predetermined value, the thread ridge 31 of the non-ball thread nut 30 and the thread ridge 13 of the thread rod 10 are made in contact with each other so that the thread rod 10 is moved in the axial direction by the non-ball thread nut 30.</p> |
