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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
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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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.

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Copyright © Cambridge University Press 2014