Converting the rotary motion of a stepping motor into linear motion can be accomplished by several mechanical means, including rack and pinion, belts and pulleys and other mechanical linkages.
All of these designs require various mechanical components. The most effective way to accomplish this conversion is within the motor itself.
The basic stepper motor creates rotary motion. The rotary to linear conversion is done by a screw-nut system, usually external to the motor. For obvious reasons of design simplicity, it makes sense to accomplish the rotary to linear conversion right inside the motor.
In Haydon’s linear actuators the nut is located inside the rotor and a corresponding screw is engaged in that nut. In order for the screw to move axially, the screw must be prevented from rotating with the nut and rotor assembly by some means. That can be done inside the motor as well (captive design) or externally (non-captive design).
Haydon offers also more conventional configurations with external screw and nut (called an external linear motor).
Haydon Motion Europe is based in Coueron, France. www.haydoneurope.com