Date: 26 Jan 2013

Forward kinematic singularity avoiding design of a Schönflies motion generator by asymmetric attachment of subchains

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In most of the previous studies on parallel mechanisms (PMs), architectural design mainly relying on symmetric geometry was investigated without in-depth analysis of its performance. This work demonstrates that such a symmetric geometry of multiple subchains sometimes induces a forward kinematic singularity which degrades the overall kinematic performance of PMs within the desired workspace and claims that an asymmetric attachment of those subchains on a moving platform can effectively resolve such a singularity problem. A 4-Degree-of-Freedom (DOF) PM exhibiting Schönflies motions is examined as an example device. First, its mobility analysis and kinematic modeling via screw theory are conducted. Then a singularity analysis based on Grassmann line geometric conditions is carried out, and the forward kinematic singularities of the mechanism are identified and verified by simulations. Based on these analysis and simulations, a forward kinematic singularity-free design is suggested. To show the high potential of the device in practical applications, its output stiffness and dynamic motion capability are examined. Then a prototype is built and its motions capability is verified through experiments.

Recommended by Editorial Board member Yangmin Li under the direction of Editor Hyouk Ryeol Choi.
This research was in part supported by Basic Science Research Program through the National Research Foundation of Korea(NRF) funded by the Ministry of Education, Science and Technology(2011-0010708), and in part supported by the Converging Research Center Program funded by the Ministry of Education, Science and Technology (2012K001328). Also, this work is in part supported by GRRC program of Gyeonggi Province (GRRC HANYANG 2010-A02), and in part financially supported by the Ministry of Knowledge Economy (MKE) and Korea Institute for Advancement in Technology (KIAT) through the Workforce Development Program in Strategic Technology.
Sung Mok Kim received his M.S. degree in Control and Instrumentation Engineering from Korea University at SeoJong in 2011. He is currently a graduate student at department of Control and Instrumentation Engineering, Korea University. His research interests includes robot kinematics, singularity analysis, parallel robot design, and medical robot.
Byung-Ju Yi received his Ph.D. degree in Mechanical Engineering from The University of Texas at Austin in 1991. He is currently a professor in the Department of Electronic Systems Engineering at Hanyang University. His research interests include robot kinematics, parallel mechanism, medical robot, pipeline robot, and biomimetic robot design.
Wheekuk Kim received his Ph.D. degree in Mechanical Engineering from The University of Texas at Austin, in 1990. Since 1991, he has been working as a professor at the Department of Control and Instrumentation Engineering, Korea University at Seojong. His current research interests include parallel robot design, screw theory, singularity analysis, parallel robot synthesis, robot kinematics, medical robot, mobile robot, haptics, etc.