The motions for most assembly operations are measured in centimeters or millimeters. It's not hard to find an actuator to match the application. But, when the application calls for moves measured in microns or nanometers, engineers have fewer options.
When assembly equipment must be guarded, the best safety measure is one that provides the most protection with the least affect on normal machine operation.
The term plain bearings is a misnomer. True, these bearings are not as mechanically complex as antifriction bearings, but don't let their simplicity fool you.