Experimental Study on a Fast Tracking and Smooth Constrained Motion Controller for Robot Arms

Lots of constrained motion control schemes have been proposed for robots. However, since constrained motion demands fast tracking with smooth control, few of these schemes are convenient in practice for many tasks, such as hand-control, polishing, grinding, and assembly operations. In particular, adaptive control is quite slow due to its overparametrization, while first order sliding mode control cannot be implemented because its chattering. On the other hand, second order sliding mode control demands knowledge of upper bounds. Recently, to ameliorate these limitations, the theoretical framework and simulations, a synergetic combination of adaptive and second order sliding mode control has been proposed. This controller achieves simultaneous exponential convergence of position/force tracking errors with chattering-free control and without any knowledge of upper bounds. Then, it stands as a viable control technique that exhibits the best of adaptive and sliding mode control. In this paper, the real-time, Linux RTAI-based, experimental results of this controller is presented on a direct-drive robot manipulator equipped with six axis JR3 force sensor. Comparative results suggest its superior performance.