Comparison of reduced state and full state passive control laws for flexible joint robots

Passivity based control laws have interesting features, such as robustness of stability and natural extension to passive controller-observer design. We present reduced and full state passive control laws for a flexible joint robot. We show that even though reduced state feedback guarantees global asymptotic stability, the dynamic performance is poor since it is driven by the natural modes of the mechanical structure. However, full state feedback can be used to inject damping and accelerate the link state behavior. The robustness of the control law permits the use of an approximate feedforward signal to reduce the complexity of the control algorithm.