In the late 1940s, Joachim Uhing was working in a factory in Germany that made thread guides and other parts for industrial knitting machines. As in many plants at the time, most of the machines in Uhing's facility were driven by a common shaft running along the ceiling. At various points, belts ran from the shaft, carrying mechanical power down to the equipment.

One day, as Uhing was making his rounds, a shaft-support bearing slipped from its mounting and began traveling along the rotating drive shaft. When it reached the end, it bumped a stop and began moving back in the opposite direction. It was obvious to the engineer Uhing that the force causing the bearing to run back and forth was friction.

Uhing thought further about what he had observed, and how he might apply it to create a linear drive from a smooth rotating shaft like the one in his plant. The timing couldn't have been better — knitting machine manufacturers were looking for a device to automate the traversing movements of the carriages on their equipment.

Within a year, Uhing came up with a design based on a smooth shaft and a drive nut consisting of three slightly oversized bearings angled relative to the shaft. The operating principle is relatively simple: The spring-loaded bearings generate friction force at their point of contact with the shaft. The angle of the bearing rings relative to the shaft determines the net force and, hence, the speed and direction of travel.

Today, rolling-ring linear drives are used in a wide variety of linear motion applications, involving winding, slicing, spooling, slitting, spraying, and scanning; in general, any process that requires positioning, indexing, or reciprocating motion.

Special thanks to Uhing Co. and Amacoil Inc., Aston, Pa., for providing information used in this article. For specs and other data on rolling-ring linear drives, contact Bob Eisele at beisele@amacoil.com or (800) 252-2645.