Technical terms

Absolute accuracy [mm or mrad]

Specification of the difference between an expected set position and the mean value of the actual position resulting from approaching the set position from different directions (multi-directional). The absolute accuracy is valid within a tile and is defined as the difference between the set position and the actual position of the positioning system.

Standstill repeatability [mm or mrad]

Specification of how accurately the system positions when approaching a position from the two directions (bidirectionally). The standstill repeatability is to be evaluated as the average difference between the actual position and the set position and is the most important measure for the assessment of a positioning system. It defines the variance around the mean value of the actual positions for a large number of positionings.

The variance of the positions is illustrated by the Gauss distribution or normal distribution. The standstill repeatability is defined by three standard deviations (3σ) with a probability of 99.74 %.

Synchronization accuracy [mm or mrad]

Specification of the fluctuations that the system exhibits in the position during a position-controlled movement at a constant set velocity of 200 mm/s. The synchronization accuracy depends on the load on the movers and the associated inertias in all 6 spatial directions, the controller settings, the target velocity and also any mechanical misalignment between the tiles.