MRO Magazine

Focus on Linear Motion: Reducing System Complexity

Production machinery such as spraying equipment, measuring systems, winding machines and cutting/slitting equipment often includes a positioning or reciprocating linear motion assembly. Operating and ...

November 1, 2003 | By MRO Magazine

Production machinery such as spraying equipment, measuring systems, winding machines and cutting/slitting equipment often includes a positioning or reciprocating linear motion assembly. Operating and maintaining these assemblies can require engineering and production personnel to become familiar with a variety of components and devices, including multi-speed direct braked reversible motors, valves, solenoids, gear head assemblies, PLCs and other complex controls.

Even though handling these devices is routine, it can nonetheless increase the complexity and cost of machine operation and maintenance. For some applications, a “rolling ring” linear drive system can eliminate most — and in some cases all — of these devices from production machinery. This simplifies operation and maintenance to save time and money, and makes production processes more efficient.

In a rolling ring assembly, automatic, instantaneous reversal of the drive head is mechanically controlled. No programming or electronics are needed, and no additional motors or controls are required. All changes to the travel direction and the linear pitch of the tool head are automatic and completely independent of the drive motor speed or rotational direction.

Hardware “end stops” are positioned on the assembly. When the drive unit reaches an end stop, the mechanical reversal mechanism is triggered and reversal is instantaneous. There is no need to slow down or stop the motor when changing drive head travel direction. Reversal points are easily and quickly changed by moving the manually-adjustable end stops.


Rolling ring linear motion assemblies also reduce the downtime associated with routine operating and maintenance tasks that usually are taken for granted. These tasks include gearing down and up, replacing bent piston rods, replacing leaky seals and training personnel to operate electronic controls.

A rolling ring system operates on a smooth, threadless shaft. There is no place where dirt or debris can become trapped, which eliminates the chance of clogging or jamming. Additionally, there is no need to interrupt production and stop the system to clean the shaft.

The rolling ring linear drive operating principle is a simple concept which uses a specially machined bearing assembly inside the linear drive unit to convert rotary input motion into backlash-free linear output. The user-adjustable angle of the bearing assembly, relative to the shaft, can be used to precisely control the drive head’s linear pitch and travel direction. It’s all done completely without complex electronic controls.

Rolling ring linear drive units are available separately, or in custom-designed assemblies ready for installation into production machinery. The systems are used for a wide range of converting, finishing, machining and assembly processes, including slitting, welding, coating, x-y table movement, rewinding, spreading, grinding and spraying. The drives provide backlash-free linear motion, and the only maintenance needed is periodic light lubrication of the drive shaft.

The anti-backlash engineering of the bearing assembly makes it unnecessary to purchase extra anti-backlash solutions such as preloaded nuts, shims or double enveloping gears. Depending on the make and model, rolling ring drive assemblies can deliver up to 800 lb of axial thrust.

Travel length may be up to 16 ft at speeds of up to 13 fps. Typical accuracy is to within 0.005 in. Greater accuracy may be achieved with options such as linear scale attachments.

For more information, contact Amacoil Inc. at 610-485-8300, or visit its website at The company offers a full range of linear motion solutions.



Rolling ring assemblies are available from a number of suppliers, as the original patents on the technology have expired. The most prominent of these are Zero Max Inc., Plymouth, Minn., Cemanco Inc., Pompano Beach, Fla., and Uhing. Amacoil, Aston, Penn., is the North American value-added distributor for Uhing.

The technology was invented in the late 1940s by a German factory worker named Joachim Uhing.

The original invention came about when Uhing was working in a factory where much of the machinery was driven by a common drive belt/shaft arrangement. The belts and shaft ran across the ceiling. One day a belt slipped off its bearing and began moving linearly along the rotating shaft. When the belt reached the end of the shaft, it moved back the other way. This is what got Uhing thinking about creating a linear drive using a similar “smooth shaft/bearing” principle.


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