Optimization Strategies for Actuators of Kinematically Redundant Manipulators to Achieve High Dynamic Performance

It is known that the kinematic redundancy promotes, among other benefits, a significant reduction of the presence of singularities. However, the evaluation of the kinematic redundancy as a good solution to increase the dynamic performance was not studied. Kinematic redundancy corresponds to the introduction of an actuator in a kinematic chain. Due to this redundancy, the mechanism can reconfigure itself in order to avoid high torque levels. This can be generally achieved in two different manners: the offline and the online ways. The former manner is the simplest way to use redundancy since the position/orientation of the redundant actuator is modified before the desired trajectory is performed. This position/orientation is selected according to performance indexes via an optimization problem. The latter manner exploits the full capacity of the redundant actuators updating their position/orientation while the trajectory is being performed. The online optimization is implemented in two different methods: the simple online optimizes only the positions and the complex online optimizes the accelerations and positions of the redudant actuator. In order to evaluate these strategies, three kinematically redundant configurations of the 3RRR planar manipulator have been evaluated through kinematic and dynamic models: the (P)RRR+2RRR, the 2(P)RRR+RRR and the 3(P)RRR. The main objective of this paper is to evaluate the impact of the different levels of redundancy to design high performance parallel manipulators. Moreover, comparisons between the online and offline reconfiguration strategies have been done demonstrating a reduction on the required actuation forces.