Control of a flexible-joint robot using a stable adaptive introspective CMAC

Abstract

This paper proposes an adaptive control for a rigidlink, flexible-joint robot using the Cerebellar Model Articulation Controller (CMAC) and the backstepping method, which is a suitable method when joints are underdamped and exhibit a large amount of flexibility. A previously proposed robust weight update method, deemed the introspective method, is placed into a Lyapunov-stable framework. In the introspective method, each local CMAC cell measures the output error in its own domain and over the domain of several sequentially activated cells on the same CMAC array. The cell then votes on whether it appears its previous weight update has reduced this error or not. The sum of all votes from the activated cells determines whether weight updates continue. In order to ensure uniformly ultimately bounded signals, a robust CMAC operates in parallel using a conservative e-modification weight update. Simulations with a two link flexible-joint arm show significantly improved performance over e-modification and a model-based LQR control.