CMM with tunable focal lens

A coordinate measuring machine for measuring a number of measuring points on a surface, the coordinate measuring machine comprising:

• a base,
• a probe head with an optical probe,
• a machine structure with structural components for linking the probe head to the base,
• at least one drive mechanism for providing movability of the machine structure and of the probe head relative to the base,
• at least one encoding unit configured to provide positional data concerning a position of the machine structure and/or of the probe head relative to the base,
• an optical overview sensor unit arranged at the machine structure and configured to acquire surface information, the optical overview sensor unit provides a field of view which is significantly greater than the field of view of the optical probe, and
• a controlling and processing unit that includes a processor and that is adapted at least for controlling the drive mechanism,
• the optical probe comprising:
• an optical detection unit, in particular a sensor,
• a variable focal length lens modifying its focal length, and
• an actuating unit configured and arranged relative to the variable focal length lens so that the actuating unit provides setting and varying the focal length as a function of a controlling signal, wherein the actuating unit includes at least one of a mechanical unit or an electronic unit,
• the controlling and processing unit comprises a measuring functionality configured to derive auxiliary distance information and effective surface information for measuring points, wherein the auxiliary distance information is derived by:
• controlling the optical overview sensor unit as to acquire surface information related to at least one point of the number of measuring points, and
• determining the auxiliary distance information related to the at least one measuring point based on the surface information, and
• wherein the effective surface information is derived by:
• deriving a controlling signal based on the auxiliary distance information,
• providing an adjusted measuring state of the optical probe by applying the controlling signal to the actuating unit and thus providing a distance-related focal length, and
• determining the effective surface information for the at least one measuring point by means of the optical probe in the adjusted measuring state.