The degree to which an actuator can return to a reference location. Notice on the bullseye on the next page that the holes are close together, however the grouping is far from the bullseye. Repeatability can be thought of as how tight of a grouping can be made. Unidirectional repeatability, measured by approaching a position from a single direction, hides errors caused by backlash and hysteresis effects. Bidirectional repeatability, measured by approaching a position from opposing directions, includes these effects, and provides a more meaningful specification.

Repeatability & accuracy

The measure of how close to a programmed point the actuator can come, and how close it gets to that same point again. The repeatability of industrial actuators is usually much better than the accuracy. Notice on the bullseye below that the points are centered around the middle of the target and are grouped close together. This is good accuracy and repeatability.

Resolution

The smallest position increment that can be achieved.

Resolver

A feedback device consisting of a stator and rotor that provides position and velocity information to the drive for commutation.

Reverse radial load

Load where the force is acting perpendicular to the axis of actuator (bearing) in the direction opposite from actuator (bearing).

RMS Torque

In an intermittent application, this is the torque provided to generate equivalent motor heating to one operating in a steady state. Trms= where: Ti= Torque during interval i ti= Time of interval i

RS232

A standard for data communication that defines voltages and time requirements for information to be transferred on a single line in sequential format.