Normal force control for a pin-on-disk tribometer including active or passive suppression of vertical vibrations

This paper presents the design of a computer-controlled pin-on-disk tribometer for friction characterization of various sliding pairs. The pin-on-disk setup comprises two high-bandwidth servomotors for the control of the rotating disk and the normal load-related spindle drive, as well as a high-precision tri-axial piezoelectric force sensor for normal and tangential forces measurement. Since the spindle drive system is characterized by notable compliance effects, the normal force cascade control system is designed with the aim of vertical vibrations active damping. In order to account for notable unevenness of the rotating disk surface and related high-level perturbations in the specimen normal force, the normal force control system is extended with a feedforward compensator of the disk unevenness disturbance, and, in particular, a dedicated leaf spring suspension system is designed. The effectiveness of the proposed system of vertical vibrations damping is verified experimentally.