Coil Velocities Error Reduction in the French Kibble Balance Experiment

Determination of the Planck constant in the Kibble balance experiment requires, among other things, a precise control and knowledge of the speed and position of its major sensor: a coil immerged in a magnetic field. This paper presents our method to measure the coil unwanted angular movements during its vertical travel and a way to reduce it by controlling piezoelectric actuators. By this way we were able to reduce the contribution to the global uncertainty of the angular parasitic forces from 2μrad/s to less than 1μrad/s.