Robust-Adaptive Control of Mechanical Systems with Friction: Application to an Industrial Emulator

In control of mechanisms, friction has been recognized as the source of tracking errors, limit cycles, and stick- slip motions, among other friction phenomena, degrading the performance of the controlled mechanism. Friction compensation design schemes deal with mitigating the undesired effects of friction. The objective of this paper is to give a friction compensator design for control of mechanisms that is robust against the friction model and adaptive with respect to parameter uncertainties in the mechanical plant. The performance of the obtained control law is evaluated numerically making use of the LuGre model. Very accurate position tracking has been obtained also experimentally on an industrial plant emulator. Because our controller incorporates a signum term, in the numerical experiments this produces a chattering effect that persists just for a short time span, during which the position error is highly reduced, and after it disappears. In addition, in the experiment realization, an improvement of the controller performance, yielding to high-precision positioning, is obtained when a velocity observer is used.