Ball Screw Drive, Slide Guide

Ball Screw Drive, Slide Guide

Ball Screw Drive

A ball screw is made up of a rotating screw and a moving ball nut. The ball nut is attached to the carriage of the unit. It does not have a normal thread, instead balls circulate inside the nut making it work as an efficient ball bearing that travels along the screw. Ball screws come in a large variety of leads, diameters and tolerance classes. The tolerance class (T3, T5, T7 or T9) indicates the lead tolerance of the screw. The lower the number, the higher the tolerance. High load capability and high accuracy are typical of ball screw driven units.

Slide Guides

A slide guide consist of a guide attached to the inside of the profile and a slide bushing attached to the carriage. The guide can be made of different materials (e.g. polished hardened steel, anodized aluminium) while the bushing is made of a polymer material. There are two types of bushings, fixed and prism. Prism bushings can move in relation to the guide which results in longer life and higher load capabilities. Slide bushings are silent, simple, reliable and robust and can be used in dirty and dusty environments. They are also resistant to shock loads, have a long life expectancy and require little or no maintenance.

Ball Screw Units with Double Ball Nuts

Using double ball nuts will increase the repeatability of the unit. The ball nuts are installed so that they are pre-tensioned against each other eliminating the play between the nuts and the screw. A double nut unit will have a slightly shorter stroke for a given overall length.

Single Carriage

Single carriage units have one carriage. Some linear unit models also have the option of long or short single carriage. The long carriage handle higher loads but will have a longer overall length for a given stroke.

Double Carriages

Double carriage units have two carriages which gives them higher load capabilites than single carriage units. When ordering a double carriage unit the distance between the two carriages needs to be defined. This distance is called LA or Lc depending on the model.

3D CAD models are available at this link : www.tollo.com/3d_cad_drawings.htm