In Machinery, what is a Roller Screw?

A roller screw is a mechanical device that converts rotational motion into linear motion. They are mainly known as roller screw actuators, being very similar in construction to ball screw actuators. Roller screws consist of three main components, which are the nut, the rollers and the shaft. The rollers, shaft and the inside of the nut are all threaded so that the rotation of the nut will create linear motion within the screw. Roller screws are a more expensive, higher-quality alternative to ball screw actuators.

Ball screw actuators are very similar to roller screw actuators, each with three main components. Their biggest difference lies in the area between the nut housing and the shaft. Instead of having threaded rollers, a ball screw will have balls. These balls operate in a very similar manner to the threads of a roller, as their rotation pushes the shaft in and out of the nut housing. Roller screws are typically more expensive than ball screws, mainly due to their increased longevity, quality, precision, and maximum capacity.

Roller screw design is considered simple, the actual transmission device itself consisting of only three major components. On the outside lies the nut housing, which is often coupled with the motor or engine that rotates it. Oftentimes, the housing itself will serve as the armature of an electric motor. Doing so makes the device far more compact and efficient, allowing it to be used in a wider variety of applications.

The inside of the nut housing is an internal thread, which comes in contact with the matching threads of the rollers. There are multiple rollers inside every roller screw, usually enough to fill in the gap between the nut and shaft. The number and size of these rollers varies depending on the size of the actuator. Regardless of size, all rollers have threading which allows for contact between both the nut and the shaft. As the nut housing turns, the rollers move around the shaft; as a result, they are often referred to as orbital rollers.

The shaft is usually larger than the rollers and moves linearly. Much like the other components, the shaft also has a threading which can join with the rollers. As the internal thread of the nut housing rotates, as do the rollers. The rotation of these rollers "pushes" the thread of the shaft, which moves it either forwards or back. The direction in which the shaft moves depends entirely upon the rotational direction of the nut housing.