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Basics of cam followers (including those for linear motion)

2019-05-17

Cam followers are power-transmission devices with a rotary bearing core that bears load while serving as the interface between independently moving machine sections. Applications include those on rotary indexing tables and turntable conveyors, long-stroke robot transfer units (RTUs), and an array of highly customized machinery.

The outer diameter (OD) of the cam-follower bearing assembly is its working face — typically made of steel, nylon, urethane, polyamide, or other engineered material. This OD mates with some machine surface … traditionally this was a mechanical cam of some type — such as the precision barrel of an indexing table. Such mechanically automated indexing tables have a motion profile cut into a cam drum that engages the followers, which in turn transmits the power to an output.

Cam followers also find use in assemblies that pair them with linear tracks and other engineered paths on customized assemblies.

Cam followers assemble onto machines in one of two ways. Stud-type cam followers include a partially threaded shaft fixed to the follower inner diameter (ID) for assembly onto a machine frame with a nut or similar fastening device. Yoke cam-follower variations (identifiable by their open ID) often mate to machine frames via press fit at a hardened inner race usually held by the follower’s end plates. Because they’re not a cantilevered design, yoke followers exhibit minimal deflection. But stud cam followers are indispensable in an array of applications — including those that are subject to high loads.

The most common cam-follower design employs needle rollers to carry high radial loads; where applications require the axis to run at high speeds, a cage can separate the rollers.

Where loads are particularly high and the axis needs high dynamic load capacity, cam followers can include twin rows standard rollers. Though beyond the focus here, some light-load cam followers are even built around simple plain (sleeve) bearings.

Note that cam followers differ from their roller-bearing cousins in a few ways. Because the latter are typically interference fit into assemblies, they get circumferential reinforcement from the surrounding machine frame or housing. In contrast, the outer race of a cam follower must be thick to prevent deformation … especially under the localized line of loading. In addition, many cam followers include lubrication ports and more ruggedized surface finishes to withstand exposure to environments during operation — especially those that operate exposed on unprotected machine sections.

Many cam followers have flat outer diameter (OD) profiles, while others (especially those for linear-motion applications) include crowned, edge-flanged, or vee-shaped ODs to engage tracks and rails that are engineered with mating geometry.

Crowned cam followers can compensate for ten times the misalignment that traditional flat-profile cam followers.

Linear cam-follower (track follower) arrangement image courtesy Güdel US

Some cam followers serve as track followers by engaging rails to deliver linear motion. These designs are increasingly common in automated storage and retrieval systems (AS/RS) and seventh-axis RTUs mentioned earlier.

That’s because cam-follower-based linear systems outperform the linear bearings known as profile guides where compactness and ultra-high accuracy are less important than ruggedness, quick and forgiving installation, high-speed reversals, and long life.