Numerical and experimental investigation of the influences of the kinematic redundancy on the performance of a kinematically redundant parallel planar manipulator

Author(s)

João Cavalcanti Santos

• Document type: Master's Dissertation
• Press: São Carlos.
• Institution: Universidade de São Paulo (USP). Escola de Engenharia de São Carlos (EESC/SBD)
• Defense date: 2017-07-03

Examining board members

Maíra Martins da Silva; Juan Francisco Camino; Eduardo Fontoura Costa

• Advisor: Maíra Martins da Silva

Abstract

As a consequence of their reduced inertia, parallel manipulators present superior energetic efficiency and they are able to reach high accelerations. Nevertheless, their workspace has a poorly uniform performance. Indeed, the presence of parallel singularities is a strong limitant for this kind of robots. On the one hand, actuation redundancy is well-known as a good choice in an effort to solve this issue. On the other hand, kinematic redundancy still have unclear consequences on this matter. A kinematically redundant manipulator presents an end-effector with fewer degrees of freedom than the mechanism as a whole. Considering this gap, the objective of this research is to analyze the influence of kinematic redundancy on the performance of parallel manipulators through simulations and experimental tests. This issue turns out to be complex, once traveling actuators sum additional inertia to the system. Metrics are defined in order to evaluate how favourable is a given position, and redundancy resolution strategies are analyzed using them. The main proposed strategy is composed of two steps. In the first one, a movement is defined so that the position for each instant is optimum for a given multiobjective performance metric. This procedure delivers a refererence movement which generally presents high accelerations. On the second step, a global optimization is applied, seeking for a trade-off between the proximity to the reference and the acceleration levels. In addition, several local methods (which resolve the inverse kinematics for each instant independently) and one truncated global strategy were addressed. These configurations were compared numerically and experimentally, delivering a objective analysis of the influence of kinematic redundancy on the performance of the parallel manipulator. The experimental campaign was executed with a physical prototype built at the São Carlos School of Engineering. This is a planar manipulator with 6 degrees of freedom, consequently presenting up to 3 degrees of redundancy. The mechanism is actuated by 6 rotating motors, of which 3 are coupled to leadscrews, resulting in linear actuators. These leadscrews can be locked, defining different degrees of redundancy and granting the versatility of the prototype. (AU)

• FAPESP's process: 14/21946-2 - Numerical and experimental investigation on the dynamic performance of kinematically redundant parallel planar manipulator
• Grantee: João Cavalcanti Santos
• Support Opportunities: Scholarships in Brazil - Master