Screw drives are some of the most common methods of mechanical linear actuation. And planetary roller screws are one of several screw types, including lead screws and ball screws. Planetary roller screws use threaded rollers that are toothed to mesh with geared rings at each end of a nut. The rollers spin on their axes and orbit around the nut, in a planetary configuration.
Planetary roller screws are capable of higher force transmission because the rollers have more contact with screw threads. (Image via Tolomatic)
One of the benefits to planetary roller screws is that they have high force transmission capabilities because the rollers have significant contact with the screw threads. They deliver high force, operate at high speeds, are long lasting and require little maintenance.
The geometry of a planetary roller screw provides more contact points than a ball screw. As a result, roller screws typically have higher dynamic load capacities and rigidity than similarly sized ball screws. And the fine threads provide a higher mechanical advantage, so less input torque is required for a given load.
One downside is that the increased contact area creates more heat with the same amount of work. Ball screws, because they have fewer contact points, can operate slightly cooler in high duty cycle and high-speed applications due to somewhat more efficient heat management.
A typical planetary roller screw showing the nut enclosing the rollers. (Image via Tolomatic)
However, planetary roller screws offer higher dynamic load ratings and longer life even in repeated stress applications like pressing, inserting or riveting. In fact, planetary roller screws are being specified in applications that were once powered by hydraulic cylinders.