Higher order sliding mode precision-limit positioning of a direct drive system

This paper considers the application of a higher order sliding mode control algorithm to the problem of precision-limit positioning of a direct drive system in the presence of friction. Precision-limit positioning requires that the precision error is equal to the resolution of the sensor. Such high levels of control performance have not been generally considered possible because of the problems encountered in accurately modelling static friction. This paper employs a recently developed model of static friction and develops a higher order sliding mode position control algorithm. This algorithm does not require the output derivative (or velocity) to be measured or observed and merely employs the position error measurement to generate the control signal. This coincides with a fundamental requirement of precision limit positioning that only digital position measurement is used by the controller. Simulation and experimental results show good correlation. It is demonstrated that higher order sliding mode control is an appropriate technique for such precision limit position control.