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Tuesday 12pm, 29 November 2016

Kkim

On the Locomotion of Spherical Tensegrity Robots

Kyunam Kim

PhD candidate - UC Berkeley

Abstract

This work studies novel robotic systems based on tensegrity structures, with an emphasis on their locomotion capabilities. Naturally compliant tensegrity structures have several unique properties that are advantageous for co-robotic or soft robotic platforms; they are lightweight, deployable, robust and safe. By leveraging these distinctive features of tensegrity structures, tensegrity robots are expected to overcome the barrier that today's robots have difficulties with. In this regard, tensegrity robots have been envisioned for a wide range of new applications that have not been explored before, including assistive and rehabilitative healthcare, search and rescue, and planetary space exploration, to name a few.

In order to be actually deployed for these applications, tensegrity robots should have mobility in the first place. In this work, two modes of locomotion are examined for spherical tensegrity robots: rolling and hopping. A spherical tensegrity robot rolls by deforming its shape and by shifting its center of mass. The study of tensegrity deformation, however, is not trivial and poses a unique problem because kinematics and statics of tensegrity structures are tightly coupled and need to be solved concurrently. This work presents a method based on a dynamic relaxation technique that can solve for the deformation of tensegrity robots in an efficient manner. Also presented are methods for discovering control strategies that realize desired deformations. The methods exploit grid-based search and multi-generation Monte Carlo based learning algorithms. Several prototypes of hardware tensegrity robots are developed and their successful rolling is demonstrated.

Another viable option for locomotion of tensegrity robots is hopping. Hopping could be especially useful when the robots are deployed for planetary exploration missions, because it allows the robots to quickly travel long distances and to be less affected by ground conditions. To enable hopping, a tensegrity robot with a cold-gas thruster system is studied and its motion is simulated. Different hopping profiles are investigated in simulation for a safe and energy-efficient delivery of a scientific payload on the Moon. Furthermore, to increase the fuel efficiency, a reaction wheel based system is proposed for thrust vectoring and an associated controller that globally and asymptotically orients the thrust to any desired direction is developed based on the (z,w)-parameterization of rotation and Lyapunov method.

Bio

Kyunam Kim is a Ph.D. candidate in Mechanical Engineering at the University of California, Berkeley. Previously, he received the M.S. degree in Mechanical Engineering from the University of California, Berkeley in 2012, and the B.S. degree in Mechanical and Aerospace Engineering from Seoul National University in 2010. His research interests include tensegrity robots, robotic locomotion systems, control theories, dynamics, artificial intelligence and wireless sensor networks. He was a recipient of the Samsung Scholarship from 2010 to 2015.