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Torque distribution optimization of redundantly actuated planar parallel mechanisms based on a null-space solution

Published online by Cambridge University Press:  15 January 2014

Jung Hyun Choi ,
TaeWon Seo  and
Jeh Won Lee
Jung Hyun Choi
Affiliation:
School of Mechanical Engineering, Yeungnam University, Gyeongsan 712-749, Republic of Korea
TaeWon Seo
Affiliation:
School of Mechanical Engineering, Yeungnam University, Gyeongsan 712-749, Republic of Korea
Jeh Won Lee*
Affiliation:
School of Mechanical Engineering, Yeungnam University, Gyeongsan 712-749, Republic of Korea
*
*Corresponding author. E-mail: jwlee@yu.ac.kr
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Summary

Redundant actuation for the parallel kinematic machine (PKM) is a well-known technique for overcoming general drawbacks of the PKM by helping it to avoid singularity and enhance stiffness characteristics, among others. Torque distribution plays a critical role in redundant actuation because this actuation causes the PKM to consume too much energy or put a substantial amount of stress on joints and links. This paper proposes a new torque distribution method for reducing the maximum torque of the actuator of a planar PKM. Here the main idea behind the proposed method is the use of superposition of a particular solution for a non-redundant case and an optimized null-space solution for a redundant case with a constant coefficient. The optimal value of a null-space solution can be easily determined by checking only the intersection points of the profile of the actuator's torque as the coefficient varies. We consider three cases of planar PKMs—2-, 3-, and 4-RRR PKMs—and present a detailed procedure for deriving a kinematic solution for the 2-RRR PKM based on Screw theory. We compare the proposed method with the minimum-norm pseudo-inverse method and assess a limitation of the proposed method. The torque distribution algorithm can be used to determine the number of actuators in an efficient manner and to reduce energy consumption.

Keywords

Torque distributionOptimizationRedundant actuationParallel mechanismParticular solutionNull-space solution
Type
Articles
Information
Robotica , Volume 32 , Issue 7 , October 2014 , pp. 1125 - 1134
Copyright
Copyright © Cambridge University Press 2014 

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