Experiments toward MRAC design for linkage system

In most machine design, a planar linkage is synthesized to achieve a specific trajectory of motion. However, the dynamics of the planar linkage is shown to be highly nonlinear due to the asymmetry of the geometrical structure and external loads are often present in the output link; thus, the tracking of the prescribed trajectory is difficult to achieve perfectly. A model reference adaptive control (MRAC) with a nonlinear feedback loop and a disturbance compensation loop is proposed to suppress the nonlinear dynamics of the linkage and external force, respectively, while other feedback loops are designed to achieve the desired specifications. Furthermore, switching control is applied to the derivation of the adaptation rule to obtain a satisfactory transient behavior; meanwhile, modifications are proposed to alleviate the chattering due to the switching adaptive mechanism. Experimental studies are performed in a four-bar linkage system to demonstrate the effectiveness of the proposed method.