Iterative learning control for vibration reduction in industrial robots with link flexibility

This paper proposes an iterative learning control (ILC) scheme for the reduction of the end-effector vibration caused by the flexible link deflection in large-size robot manipulators. A 6-DoF LCD substrate transfer robot with two long vertical links is used as the testing example to study the end-effector vibration reduction. Due to the beam flexibility of the long vertical links, the precision performance of the end-effector may be severely degraded especially when robots are out-stretching. Normally there is no actuation degree of freedom on the link of deflection to directly compensate for the vibration. Hence, control action is applied to other actuation degrees of freedom based on the kinematic study of the vibration. Specifically, an ILC scheme is employed to off-line modify the reference trajectory of these robot joints for the next iteration based on prior position measurements of the end-effector and the kinematic relationships between the joints and the end-effector. Simulation results demonstrate the superior performance of the proposed scheme in reducing the vibration of the end-effector.