Variable structure control of systems with nonlinear friction and dynamic backlash

This paper investigates the control of systems with nonlinear friction and dynamic backlash. The study is based on the describing function (DF) of nonlinear systems. The controllers studied are the first order model and the second order model variable structure controllers (FOM-VSC and SOM-VSC). The nonlinear plants consist on a mass with kinetic plus viscous friction or two masses subjected to backlash. The worst case of the limit cycle generation is found to be the closed-loop system having two masses with backlash. On the other hand, the closed-loop system of a mass with friction is found to be amenable to control without limit cycles.N/