Control of pre-sliding friction using nonlinear state observer

The novel nonlinear state observer for control of pre-sliding friction is proposed. The parameter-varying state-space representation of motion dynamics is derived as a function of the variable pre-sliding distance. The proposed Luenberger-type asymptotic state observer, obtained in the closed analytic form, is analyzed and evaluated by experiments. When augmenting the common PD and PID position feedback controllers, the proposed observer clearly improves the reference tracking performance within pre-sliding operation range.