Analysis and control problems in highly nonlinear robot drive systems

The dynamics of a typical robot arm, along with many other multiple degree of freedom mechanisms, can be considered in two parts, those due to the interactions between the links and those of the actuation and transmission system. Of these, the major control problem is the dynamics present in many actuation and transmission systems, particularly in low cost systems where non-ideal characteristics cannot be engineered out. The major factors which cause undesirable characteristics are flexibility and nonlinear friction. The RTX, a low cost 6 DOF robot with many undesirable characteristics is presented. The shoulder and elbow joints have the most complex dynamics. The variable structure control strategy is considered since this gives behaviour which is robust to certain plant nonlinearities and parameter variations. The aim of the control system is to introduce discontinuous state feedback to force the phase plane trajectory onto some predefined switching surface and to keep it within an infinitesimal distance of that surface