Modelling, stability and control issues of elastic joint manipulators during contact with a stiff environment

Aspects of modelling, stability, and control of robotic manipulators with stiff joints in contact with stiff surfaces are presented. System models are cast into three time-scale formulations, both directly and by means of integral manifolds, and singular perturbation methods are employed to examine high- and low-speed characteristics of these systems. When surface and joint stiffnesses are comparable, it is seen that the corresponding subsystems are strongly coupled, indicating significant interaction between surface and joint flexibility, and that this coupling vanishes when the stiffnesses are widely disparate. It is also seen that a control system designed for low-speed behavior without regard for high-speed activity can have a deleterious effect on the overall system. With light joint or surface damping and high surface stiffness, without a high-speed stabilizing control, poor high-speed system characteristics can result which contaminate the slow subsystem, but a stabilized fast subsystem will not have this effect