FEM and experimental investigation of the thermal drift in ultra-high precision measuring machines for dimensional metrology

The thermal drifts induced by the power dissipated by mechanical guiding systems represent the main limitation on the accuracy of ultra-high precision cylindricity machines. Thus, a high precision compact prototype (high precision set-up) was designed such as to simulate the behaviour of a cylindricity machine and to insure in-situ calibration of capacitance probes with regards to four laser interferometers. The set-up is equipped with three heating wires simulating the power dissipated by the mechanical guiding systems and nineteen temperature Pt100 probes to monitor the temperature distribution. A time-independent and a time-dependent thermal Finite Elements Models (FEM) of the set-up were achieved, and the results were compared to experimental ones. This comparison presents a global agreement. The simulations of cylindricity measurements reveal that the thermal expansion is equivalent to few nanometres.