Output-feedback 2-time Scale Control of Multilink Flexible Arms

Lightweight flexible arms will most likely constitute the next generation robots. The design key is the adoption of flexible links, rather than rigid links like in today's industrial robots. Despite all the potential advantages achievable with a flexible arm, the control problem is complex, due to the introduction of increasingly more complex dynamics. This paper represents an effort toward the goal of designing efficient control systems for multilink flexible arms. A two-time scale approach is pursued which allows the adoption of a composite control strategy. First a slow control can be designed for the slow (rigid) sybsystem, then a fast stabilizing control for the fast (flexible) subsystem. The main contribution of the paper is to address the problem of lack of full state measurements concerned with the fast control design. An output feedback dynamic compensator of fixed order is designed. Its optimal gains are computed according to a loop transfer recovery technique in order to obtain a robust design. The control is tested by means of simulation results for a nonlinear model of a two-link flexible arm.