Electric actuators require screw mechanisms to move loads linearly, with ball screws (or ballscrews) and roller screws the most commonly used. They each have their own advantages and disadvantages that will make either of them more suitable for certain applications, so let’s look at each screw type and the important differences between them.
Ballscrews Manufacture and Design
Ball screws are so-called because they use re-circulating ball bearings within the screw’s arch-shaped threads and the corresponding nut threads. These bearings rolling through the nut’s circuits are what generates and transmits the required power and motion created by the electric actuator.
Actuators using ball screws generally have a high thrust capacity and will usually have a long service life. They are noisy but usually have an efficiency rating around 80%. They can also be backdriven and thus are ideal for applications that produce high duty cycles and relatively high thrust.
The best ballscrews distributors will supply a wide variety of ball screw sizes, with options for leads and accuracies as well as diameters.
Roller Screws Manufacture and Design
When electric actuators use roller screws, the power is transmitted via multiple threaded rollers in the nut, hence the name. The nut threads are usually triangular, with the rollers rotating within the nut in direct contact with the screw’s threads. This contact generates the power and the motion, and also necessitates that roller screws be hardened before being precision ground. This hardening during the manufacturing process provides them with a deeper hardness which gives them a higher dynamic load rating. The extra hardness and increased contact reduces the efficiency rating to around 75%, though some roller screws are designed to have a slightly higher efficiency rating.
There are also different types of roller screw, such as the inverted planetary roller screw. This type inverts the functions of the nut and screw, though otherwise operates in the same way as standard roller screws. Inverted roller screws allow the electric actuator to be significantly smaller which benefits applications operating in limited space.
Ball Screws vs. Roller Screws
Ballscrews distributors will advise buyers that this design has a long service life when used correctly, even in high-force applications. However, this is not in direct comparison roller screws as the roller type’s service life can be even longer thanks to the increased number of points of contact with distributes the force more evenly.
Roller screws have a distinct advantage when it comes to generating high force, as they can do it more easily than ball screws. While ball screws can indeed compete with roller screws when it comes to generating force, they do so at an increased cost to energy consumption and service life.
The advantage switches to ball screws when used for low to moderate-force applications, as they incur lower initial costs, are more versatile and consume less power than roller screws.
If you require any ballscrews or roller screws, then contact YB Components who are the UK’s leading ballscrews suppliers.