Control of Flexible-Link Multiple Manipulators

In this paper, we consider the object trajectory tracking control for flexible-link cooperating manipulators. In particular, we develop a stable inversion control law which is commonly known as the inverse dynamics control or the computed torque method for rigid manipulators. Difficulties in applying this method to the control of flexible link manipulators are due to the fact that the inverse dynamics system is generally unstable because of the inherently unstable zero dynamics. As such, bounded actuator torques cannot be guaranteed. For multiple manipulators handling a common object, there are more actuators than the degrees of freedom of the system. Through decomposing the manipulator end-effector wrenches into resultant and internal force components, control laws are derived such that the internal forces are used to stabilize the system zero dynamics. Consequently, nonlinear inversion control can be applied for the object trajectory tracking control. Numerical simulations are performed to illustrate the performance of the control strategy developed in the paper.