Determination of a movable gantry position including a dual measurement module

摘要

The position of a working point relative to a working space, such as a working point of a carriage on a gantry beam of an XY positioning table, is determined by measuring at least two sets of displacements. A first set of displacements, of the working point relative to an intermediate component, such as the gantry beam, includes a relatively large displacement (X) in a first linear degree of freedom and relatively small displacements (Y₁', Y₂'), in at least two of the five degrees of freedom other than the first. The second set of displacements, of the intermediate component relative to the working space, includes a relatively large displacement (Y₁, Y₂), in a second linear degree of freedom, and relatively small displacements (X₁', X₂'), in at least two of the five degrees of freedom other than the second.