Reducing the undesirable effects of joints clearance on the behavior of the planar 3-RRR parallel manipulators

Clearance imposes some uncontrollable degrees of freedom to a manipulator. Therefore, poor dynamic performance, low accuracy, reduction in components lifetime and generation of undesirable vibrations result in the impacts of mating parts in a clearance joint. In this study, the effects of clearance on the dynamics of a planar 3-RRR parallel manipulator are investigated. Then, an optimization algorithm for simultaneously kinematic and dynamic synthesis has been carried out to reduce these effects and improve the performance and the accuracy of the manipulator. The algorithm is based on changing the lengths and the mass distribution of the links. By combining the Lagrange equations with Lankarani-Nikravesh contact force model, a series of dynamic equations are established. Then, the highly nonlinear optimization problem is tackled via a PSO method. The last but not the least, the efficiency of the algorithm and its superiority have been demonstrated by a numerical example. We claim that the linear and angular accelerations of the links and the contact forces in the joints are bounded and evolve very smoothly in the optimal design. Finally, to verify the validity of the optimization algorithm, the planar 3-RRR parallel manipulator is modeled in MSC.ADAMS software and the simulation results are compared for the original and the optimal manipulators.