Directional Stiffness Modulation of Parallel Robots with Kinematic Redundancy and Variable Stiffness Joints

[+] Author and Article Information
Andrew L. Orekhov

2201 West End Ave Nashville, TN 37235 andrew.orekhov@vanderbilt.edu

Nabil Simaan

405 Olin Hall Department of Mechanical Engineering PMB 351592 Na nashville, TN 37235 nabil.simaan@vanderbilt.edu

1Corresponding author.

Contributed by the Mechanisms and Robotics Committee of ASME for publication in the Journal of Mechanisms and Robotics. Manuscript received July 2, 2018; final manuscript received April 26, 2019; published online xx xx, xxxx. Assoc. Editor: Shaoping Bai.

ASME doi:10.1115/1.4043685 History: Received July 02, 2018; Accepted April 26, 2019


Parallel robots have been primarily investigated as po- tential mechanisms with stiffness modulation capabilities through the use of actuation redundancy to change internal preload. This paper investigates real-time stiffness modula- tion through the combined use of kinematic redundancy and variable stiffness actuators. A known notion of directional stiffness is used to guide the real-time geometric reconfig- uration of a parallel robot and command changes in joint- level stiffness. A weighted gradient-projection redundancy resolution approach is demonstrated for resolving kinematic redundancy while satisfying the desired directional stiffness and avoiding singularity and collision between the legs of a Gough/Stewart parallel robot with movable anchor points at its base and with variable stiffness actuators. A simulation study is carried out to delineate the effects of using kinematic redundancy with or without the use of variable stiffness ac- tuators. In addition, modulation of the entire stiffness matrix is demonstrated as an extension of the approach for modulating directional stiffness.

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