A Hybrid System Framework for Unified Impedance and Admittance Control

Impedance Control and Admittance Control are two distinct implementations of the same control goal but their stability and performance characteristics are complementary. Impedance Control is better suited for dynamic interaction with stiff environments and Admittance Control is better suited for interaction with soft environments or operation in free space. In this paper, we use a hybrid systems framework to develop an entire family of controllers that have Impedance Control and Admittance Control at two ends of its spectrum; and intermediate controllers that have stability and performance characteristics that are an interpolation of those of Impedance Control and Admittance Control. The hybrid systems framework provides the scope for maintaining stability and achieving the best performance by choosing a specific controller for a given environment and by continuously changing the controller to adapt to a changing environment. The advantage of our approach is demonstrated with an extensive case study of a one-dimensional system and through experiments with the joint of a lightweight robotic arm.