A Lyapunov based Adaptive Control of Nonlinear Microdynamics of a Ball Screw Driven Slide for Nanometer Positioning

A desire to improve the positioning accuracy of ball screws prompted an investigation into the dynamics of nanometer motion. Characterization of the ball screw indicated that nanometer motion is possible prior to friction breakaway via elastic deformation of the frictional contacts. The observed dynamics are nonlinear, and consequently result in inconsistent and unpredictable closed-loop response while under PI position control. A model reference adaptive control (MRAC) strategy is adopted and a Lyapunov design technique is applied to derive the adaptive laws. The digital signal processor (DSP) implementation of the scheme is discussed. Experimental results show the MRAC scheme results in a more predictable and consistent closed-loop response than the PI scheme.