Resolution, Error Budget, Accuracy & Repeatability

Resolution

Resolution is the fineness of position precision that is attainable by a motion system.

Resolution, Electrical — The smallest increment that can be "commanded" by a servo system (minimum programmable move increment). Precision of the feedback system (scale, reader head, & controller logic) sets this figure.

Resolution, Mechanical — The smallest increment that can be "controlled" by a motion system (minimum actual mechanical move increment). Mechanical precision is often coarser than electronic resolution due to: friction; stiction; deflections; etc.

Error Budget

Since a measuring scale provides positioning information only at the point of its measurement (typically at the side of a stage), encoder accuracy alone can not be used to define the precision capabilities of a machine. Every axis has in fact " six degrees of error freedom: Pitch, Roll, Yaw, Flatness, Straightness, & Scale

The combined interacting affects of all of these contributing factors must be analyzed before total system precision can be determined.

Accuracy & Repeatability

Accuracy — Difference between expected position and achieved position.

Repeatability, Bi-directional — The error from nominal when repeatedly approaching a position from opposite directions.

Repeatability, Uni-directional — The error from nominal when repeatedly approaching a position from the same direction.