On Robust Control of Flexible Joint Robots Using Describing Function and Sector Bounded Nonlinearity Descriptions

Abstract

This work is directed towards improving the performance of flexible jointrobots equipped with harmonic drive (HD) as gear train mechanism. Harmonicdrive in robot joint exhibits joint flexibility, nonlinear stiffness andhysteresis that result in deterioration of robot motion performance. Theobjective of this paper is to provide a control synthesis strategy tocompensate for these effects. In this work, nonlinear properties of HD thathave been widely observed in experiments are analyzed. Then, the describingfunction and conic sector bounded nonlinearity descriptions are used tomodel the effects of nonlinearities in robust H ∞-based control designprocedure. Finally, a two-fold control design procedure to compensate forthe above effects is proposed: a link-level motion control and anactuator-level torque control.