APPARATUS AND METHOD FOR CALIBRATING A SCANNING HEAD

摘要

A method of calibrating an angular measurement scale in a motorised articulated scanning head (16) using a reference artefact (40; 60; 80) is described. The method comprises the step of rotating a surface sensing device, such as a scanning probe (28), mounted on the scanning head (16) about at least one axis (A1, A2) of the scanning head (16) to move the surface sensing device into a plurality of different angular orientations relative to the reference artefact (40; 60; 80). A step is then performed of measuring, with the surface sensing device, at least one property of the reference artefact (40; 60; 80) at each of the different angular orientations. An error map or function is then created for at least one measurement scale of the scanning head using the properties of the reference artefact (40; 60; 80) measured and optionally known or calibrated properties of that reference artefact (40; 60; 80). The method may comprise use of co-ordinate positioning apparatus, such as a co-ordinate measuring machine (14), to move the scanning head (16). The reference artefact (40; 60; 80) may comprise a single feature or an array of features (46; 66).