Abstract

Performance evaluation is one of the most important issues in the field of parallel kinematic manipulators (PKMs). As a very important class of PKMs, the redundant PKMs have been studied intensively. However, the performance evaluation of this type of PKMs is still unresolved and a challenging endeavor. In this paper, indices that assimilate motion/force transmissibility are proposed to evaluate the performance of redundant PKMs. To illustrate the application of these indices, three PKMs with different kinds of redundancies are taken as examples, and performance atlases are plotted based on the definitions of the indices. Transmissibility comparisons between redundant PKMs and the corresponding non-redundant ones are carried out. To determine the inverse solutions of the PKMs with kinematic redundancy, an optimization strategy is presented, and the rationality of this method is demonstrated. The indices introduced here can be applied to the performance evaluation of redundant parallel manipulators.

Highlights

  • As an important complementary counterpart of serial manipulators, parallel kinematic manipulators (PKMs) have been studied intensively for more than twenty years for their advantages of compact structure, high stiffness, lower moving inertia, high load‐to‐weight ratio, high dynamic performance, and high accuracy potential

  • Screw theory has been successfully used in the analysis of motion/force transmissibility of the non‐redundant PKMs [28,29,30], in the analysis of both kinematics and dynamics [33,34,35], and in type synthesis [36]

  • In order to introduce the applications of the proposed indices and demonstrate their effectiveness in the analysis of the motion/force transmissibility of redundant PKMs, three PKMs with different kinds of redundancy are taken as examples and the corresponding atlases of the indices are plotted

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Summary

Introduction

As an important complementary counterpart of serial manipulators, parallel kinematic manipulators (PKMs) have been studied intensively for more than twenty years for their advantages of compact structure, high stiffness, lower moving inertia, high load‐to‐weight ratio, high dynamic performance, and high accuracy potential. Due to the extra DOFs, kinematically redundant PKMs are inherently capable of more dexterous manipulation [23], and can execute the original output task and perform additional tasks such as singularity elimination, workspace enlargement, dexterity improvement, obstacle avoidance, force transmission optimization and unexpected impact compensation [2, 6, 7]. Optimal kinematic design is always an important and challenging subject in designing PKMs due to the closed‐loop structures, and this problem becomes more complex with the introduction of redundancy to non‐redundant PKMs. In general, there are two issues involved: performance evaluation and dimension synthesis.

Transmissibility analysis of non‐redundant PKMs
Definitions of transmission indices for redundant PKMs
Examples
Actuation redundancy: redundantly‐actuated
Actuation redundancy: branch‐redundant
Kinematic redundancy
Conclusions
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