Which Screw? Picking the Right Technology

Many industrial linear motion systems employ a screw mechanism of some type to achieve a desired linear motion. The intention of this pamphlet is to supply an explanation of typical terminology used, explain the various types of screw mechanisms available, and provide a better understanding of what is involved in making the best screw selection as it relates to electro-mechanical actuation.

So, just what is a screw mechanism? A screw mechanism provides the means to produce linear motion by the rotation of either the screw or nut in an assembly. The screw is a cylindrical element upon which are formed threads; the nut is a matching component to the screw. Each component is capable of rotating independently upon the other. By restraining one element linear motion occurs. A lead screw is a generic designation that in its broadest sense may be applied to multiple screw mechanisms. There are three primary types of screws used in linear actuators: acme, ball and roller. The differences are in the design of the thread shape along with the design and operation of a matching nut. These differences within each type of screw design will be detailed later in the following sections. To provide an overall understanding of screw selection, it is first necessary to define common screw terminology and explain the different types of screws.