Differential Roller Screws

The trend towards hydraulic-free actuators especially with optimal efficiency has brought into focus what was previously a niche principle: the differential roller screw. Not only is the operation of such electromechanical actuators oil-free and highly efficient, they also combine these benefits with simple construction, high reliability and highly variant designs. In terms of construction, the differential roller screw resembles the well-known planetary roller screw but with one important difference. The nut of the differential roller screw only has grooves but no lead. Only the shaft has a lead. The name comes from the resulting differential between the shaft and nut speed. Although the development of the differential roller screw occurred decades ago, it is only now gaining importance with the increasing replacement of hydraulic power systems by electromechanical drive technology.

Minimal wear paired with high efficiency

Compelling arguments include very straightforward construction, high efficiency, robustness and the ability to transfer very high forces. The principle of operation is based on a rolling movement with a low sliding friction component. This minimizes wear and leads to high efficiency. The rotational movement of all components is continuous since there is no return or shifting of rolling elements.  The result is extremely low noise emission and smooth operation.

High efficiency actuation using differential roller screws

Differential roller screws are used where rotational movements need to be converted into linear movements in a straightforward, reliable and efficient manner. They are superior to conventional lead screw drives with a trapezoidal or acme profile as they exhibit significantly better efficiency and less wear. Compared with ball screw drives, the main difference is slippage in the rolling movement which affects the advance per shaft rotation. This means differential roller screw applications always require feedback on the nut's position. Depending on the required accuracy, the simplest way to implement this is to use a limit switch. Differential roller screws can be used for precision positioning only if linear position sensing is available. The preload capability of differential roller screws facilitates positioning here.