Precision Machine Design

Rotary to Linear Motion Conversion

Ballscrews and ballnuts are the conventional technologies.

Watch out for backlash where the ballscrew screws into the ballnut. Even if the ballscrew rotates, the nut will not move until the ballthread tolerance is cleared. Anti-backlash/zero-backlash technology is the solution.

Watch out for thermal expansion/contraction. Ballscrews will expand and contract in size if the temperature rises or falls. This will affect linear precision as well as the fit between the ballscrew and the ballnut. Thermal compensation hardware is the solution.

Watch out for kinetic tension. Ballscrews that experience great axial forces will deflect whatever is supporting the ballscrew at either end. This is why the ballscrew mounts at each end of the ballscrew must be firmly mounted. Also, pre-loading tension into the mount-ballscrew-mount assembly will increase the rigidity of the system because the force-deflection curve of the assembly is non-linear in a good way (more deflection with low forces than later on with higher forces).

How the ballnut connects with the moving element is important. If the ballnut is "hanging off" too much for a given load-time curve during normal operation, then the ballnut will heavily deflect; also, the ballnut and ballscrew will suffer uneven wear, especially with shock forces.

How the ballscrew connects to the rotating element is important. Conventionally, the rotating element to be interfaced is a shaft, aka round bar; rod.