João Vitor de Carvalho Fontes

The Influence of Kinematic Redundancies in the Energy Efficiency of Planar Parallel Manipulators

Parallel manipulators present advantages compared to serial ones, such as higher load-carrying capacity, improved accuracy and increased stiffness. However, parallel manipulators possess limitations due to the presence of singularities. It has been proved that kinematic and actuation redundancy promote a significant reduction in the singularities and homogenization on the actuation forces. This paper evaluates the effect of the addition of kinematic redundancy in the energy efficiency of parallel manipulators. In order to do so, the required mechanical energy consumed by a 3RRR non-redundant planar parallel manipulator and their kinematically redundant versions, to perform several predefined trajectories is minimized using a genetic algorithm. The result of the comparison shows that the required mechanical energy to perform a given trajectory can be reduced with the addition of kinematic redundancy.Copyright

Numerical Analysis and Prototyping Details of a Planar Parallel Redundant Manipulator

Important drawbacks of parallel kinematic machines can be partially overcome by the use of redundancy. Despite of some trade off issue, redundancy is a promising solution to achieve improved dynamic performance and energy efficiency. This manuscript describes preliminary numerical results on the rational use of three levels of kinematic redundancy of a 3 (P)R RR parallel planar manipulator. Moreover, this manuscript describes some practicalities on the design and prototyping of such manipulator. Based on the numerical results, one can conclude that if the redundancy is considered accordingly, the manipulator may present improved dynamic performance and may be more energy efficient. The insights on the design and prototyping of the manipulator have shown that this is a versatile setup. Diverse research topics may be studied using this experimental setup: the use of redundancy, the control of induced vibrations, the role of uncertainties on the manipulators accuracy, among others.

Robust Critical Inverse Condition Number for a 3 R RR Robot Using Failure Maps

Industrial manipulators must be robust with regard to manufacturing tolerances and uncertainties. This paper presents a study of the effects of geometrical uncertainties of a planar parallel manipulator on its kinematic performance and robustness, regarding possible failures. The parallel manipulator under study is a 3RRR, which is composed of a single end-effector connected to the ground by three identical kinematic chains. Each kinematic chain is composed of two passive and one active revolute joints. Among others, parallel manipulators may suffer from two important failures: when the end-effector reaches (i) the workspace’s limitation and (ii) a singular region. Both failures can be assessed by calculating the inverse of the condition number of the Jacobian matrix. In order to evaluate geometrical uncertainties, a Monte Carlo simulation is performed to estimate the probability of both types of failures. Failure Maps are depicted by plotting the probability of failure on the workspace, exhibiting the most affected regions. Based on this information, a robust inverse critical condition number is proposed. This information can be exploited for robustifying the control design and the motion planning of parallel manipulators.

The Impact of Kinematic Redundancies on the Conditioning of a Planar Parallel Manipulator

Parallel manipulators present drawbacks such as singularities inside their workspace. In order to measure these drawbacks, the condition number of the Jacobian matrix can be used either as a measurement of the distance between the end effector and singularities or as an isotropy index. In this paper, a study of the impact of kinematic redundancies on the improvement of a planar manipulator’s isotropicity and on the reduction of singularities is presented. In order to do so, conditioning maps are exploited for the non-redundant 3RRR and for the kinematically redundant 3PRRR manipulators. The outcome of this evaluation supports evidences in favor of kinematic redundancies regarding kinematic characteristics.

Simulation and Experimental Verification of a Global Redundancy Resolution for a 3PRRR Prototype

Parallel manipulators have kinematic chains connected to each other in a common point, the end effector. This design grants desirable characteristics to parallel manipulators, for instance high rigidity and load distribution. However they suffer from singularities inside their workspace which may cause low precision and high efforts. Aiming to overcome this problem, kinematic redundancy can be used to design new redundant manipulators which can avoid singularities and improve some manipulator’s characteristics with a proper redundancy resolution. Two approaches of a global redundancy resolution to avoid singularities and improve the manipulator’s dynamic performance in a 3PRRR manipulator prototype are presented. The experimental results show that the implemented redundancy resolution is suitable for the application.