The mechanism of Screw - nut is a mechanism of transformation of movement. In general it allows the transformation of a movement of Rotation into a movement of Translation. It is for example the device most commonly adopted on the vice X, and others Pressoir S but also the reversible Cric S. Rarement as on the objective of a Camera, it can however constitute the reverse transformation.
To obtain a dispositf transformation of movement, it is necessary to associate with the couple female screw a third part. Then there exist two families of solutions, structurally symmetrical:
- the screw and the nut are bound by a helicoid connection of axis (O, Z) (here horizontal)
- a connection (1) binds the screw (or the nut) in translation, and must thus authorize rotation around the axis (O, Z). The pivot is the most obvious model.
- a connection (2) binds the nut (or the screw) in rotation, and must thus authorize the translation in direction Z. the glissère is the most obvious model.
The principle is always the same one: it is a question of blocking the rotation of the screw (or of the nut) and conversely the translation of the nut (or of the screw). The report/ratio of transformation is then of a value of the Pas of screw for a turn of the revolving element.
With a slide and a pivot the model is strongly hyperstatic; there exist other solutions less constraining kinematics. The choice will depend on the required efforts to the guidance of the elements.
In a jack automoblie of the type Parallelogram, dispotif the female screw allows the control of a diagonal, the other ensuring the lifting of the vehicle. The structure is then more complex with at least 6 parts.
- conversion couples thorough
- reversibility and output
Technology and examples
- screw/nut standart
- screw ball
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