The Ring Screw Mechanism

a high-speed alternative to the ball screw

Our First Prototype

What is it?

The ring screw mechanism is a mechanical device that achieves an almost frictionless screwing motion between a screw rod and a nut.  It does this by means of a set of three or more rings that are mounted in ball bearings inside the nut.  These rings rotate as the rod moves, so that the contact between each ring and the rod is a theoretically perfect rolling contact.  The result is a movement that is almost completely frictionless, except for a small amount of friction within the ball bearings.  The two videos above show how little friction there is in our first prototype.

What is it for?

The ring screw performs the same function as a ball screw, but is able to operate at higher speeds.  This means that a ring screw can be connected directly to the shaft of a modern high-speed brushless DC motor, whereas a ball screw would have to be connected via a reduction gear.

What's new about it?

There are several examples in the patent literature of mechanisms involving rotating rings and screw rods.  The special feature of the ring screw, which sets it apart from all previous mechanisms of this kind, is that it has been designed using a branch of mathematics called screw theory so that the contact between each ring and the rod is a theoretically perfect rolling contact, not just at one or two points, but at every point along a line.  The fact that each ring makes a line contact with the rod means that larger forces can be transmitted; and the absence of sliding means that the loss due to sliding friction is zero.



Also, ball screws are standard mechanical components, whereas the ring screw is new, and needs further development and testing before it too can become a standard mechanical component.

What's next?

We are building a second prototype, which will be tested at high speeds and high thrust forces in order to measure its performance (especially its efficiency).  We anticipate doing these experiments in February and March of 2018, and publishing the results thereafter.  In the meantime, we are pursuing patent applications in several countries, and we are looking for an industrial partner.


The ring screw is being developed at the Italian Institute of Technology (IIT) by Roy Featherstone, Elco Heijmink and Sep Driessen.  So far, the only published document is the patent application PCT/IB2016/052739, but better documentation is on the way.  If you want to know more about the ring screw, or are interested in possibly bringing it to market, then contact Roy Featherstone.
Page last modified:  January 2018
Author: Roy Featherstone