Trajectory Tracking in Flexible Robot Arms

Abstract

We consider the problem of controlling the end-effector motion of flexible robot arms. Main difficulties arise both from the typical nonlinearities of robot dynamics and from the non-minimum phase nature of the flexible arm when tip position is chosen as output. This bars the straight application of inversion control solving the trajectory tracking problem in robots with rigid links. Three alternative strategies are presented: inversion control based on a suitable minimum phase output, nonlinear regulation of the tip output, and iterative learning control. The control laws are discussed from the point of view of system requirements and complexity, while their performance is compared by simulation on a simple but significative example. Finally, we report on the experimental activity in controlling flexible robots carried out in the Robotics Laboratory at DIS.