Experimental Results on the Robust and Adaptive Control of Robot Manipulators Without Velocity Measurements

To achieve accurate tracking control of robot manipulators, many schemes have been proposed. Some common approaches are based on robust and adaptive control techniques, while when necessary velocity observers are employed. Robust techniques have the advantage of requiring few prior information of the robot model parameters/structure or disturbances while tracking can be achieved, for instance, by using sliding mode control. On the contrary, adaptive techniques guarantee trajectory tracking but under the assumption that the robot model structure is perfectly known and it is linear in the unknown parameters, while joint velocities are also available. In this letter, some experiments are carried out to find out whether combining a robust and an adaptive controller may increase the performance of the system, as long as the adaptive term can be treated as a perturbation by the robust controller. The results are compared with an adaptive robust control law, showing that the proposed combined scheme performs better than the separated algorithms, working on their own and then the comparison laws.