Nonlinear control with end‐point acceleration feedback for a two‐link flexible manipulator: Experimental results

Experimental results for end‐point positioning of multi‐link flexible manipulators through end‐point acceleration feedback are presented in this article. The advocated controllers are implemented on a two‐link flexible arm developed at the Control/Robotics Research Laboratory at Polytechnic University. The advocated approach in this article is based on a two‐stage control design. The first stage is a nonlinear (1) feedback linearizing controller corresponding to the rigid body motion of the manipulator. Because this scheme does not utilize any feedback from the end‐point motion, significant vibrations are induced at the end effector. To this effect, and to enhance the robustness of the closed‐loop dynamics to parameter variations, the inner loop is augmented with an outer loop based on a linear output LQR design that utilizes an end‐point acceleration feedback. The forearm of the manipulator is significantly more flexible as compared with the upper arm. Experimental and simulation results validate the fact that the end‐effector performance is significantly better with the proposed (1) feedback linearizing control as compared with the linear independent joint PD control. In addition, the nonlinear control offers other advantages in terms of smaller and smoother actuator torques and reducing the effects of nonlinearities. Close conformation between simulation and experimental results validates the accuracy of the model.