Traceable tactile, active, force and torque measuring coordinate measuring system sensor head

• Applicants: Professor Dr.-Ing. Thomas Fröhlich; Professor Dr.-Ing. Tino Hausotte
• Subject Area: Measurement Systems
• Term: since 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 505063926

The planned project involves the conception and design, the realisation and verification of a novel tactile, active, force and torque measuring coordinate measuring system-measuring head as well as accompanying fundamental investigations including the traceability of the measurement of the probing force and deflection of the stylus. The innovations of measuring head are the omission of elastic spring systems and the levitation of the probe, the probing force generation completely with Lorentz forces, the in situ force calibration according to the Kibble principle as well as the special arrangement of the actuators as parallel kinematics and of the position sensors as parallel metrology. In addition to the position and force measurement, the additional measurement of the orientation and occurring torques at the stylus changing plate should enable the investigation of new correction approaches to reduce the measurement uncertainty for measurements with projecting and long styli. The shortened traceability of the force and torque measurement and the intended low measurement uncertainty of the probing force should allow to vary the probing force over several orders of magnitude in a targeted way with new probing strategies to be developed. On the one hand, this should enable a significant reduction of the minimum probing sphere diameter and accurate measurements of objects made of aluminium or plastic as well as with sensitive surfaces in conventional coordinate measuring machines on the other hand. The generation and traceable measurement of probing forces up to 2 N with uncertainties of 20 micro N + measured value·0.0001 as well as the calibration of the probing forces without additional, external force calibration devices shall be made possible. The changing plate with stylus is to be coupled to a levitating flotor (derived from fly and rotor) and its position and orientation controlled using the signals from three 2D optoelectronic position sensors to be researched as parallel metrology and at least six voice coil actuators as parallel kinematics. The actuators serve both to maintain the levitation state of the flotor and to measure the forces and torques acting on the stylus and the levitating flotor, which occur in case of a probing or scanning on a measuring object surface. The primary measurement of the probing force according to the Kibble principle enables traceability to fundamental constants in accordance to the new SI system of units, valid since May 2019. The traceability of the measurement of the position and orientation shall be done via the primary laser interferometric length measurement of the coordinate measuring system used for the investigations and displacement calibration. Special challenges are posed to the measurement data acquisition and controller concept in order to keep the flotor in equilibrium of forces and torques, even during probing, and to be able to perform open-loop, closed-loop and free-form scans.

• DFG Programme: Research Grants