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Volume 21 Issue 05/06 - Publication Date: 1 May 2002
 
Nonholonomy on Purpose
 
Design, Analysis and Control of a Wheeled Mobile Robot with a Nonholonomic Spherical CVT
 
Jungyun Kim and F. C. Park School of Mechanical and Aerospace Engineering Seoul National University Seoul 151-742, Korea and Yeongil Park Institute of Precision Machinery Technology Seoul National University of Technology Seoul 139-743, Korea
 
This article reports on the design, analysis and control of a new type of wheeled mobile robot based on a nonholonomic spherical continuously variable transmission (S-CVT). Our S-CVT based mobile robot is designed to increase the run time (i.e., the length of time in which the robot can be operated), and to achieve full planar accessibility with the design of a novel pivoting device that takes advantage of the flexibility of the S-CVT. We examine the sources of power loss in the S-CVT, in particular spin loss. For a quantitative analysis of spin loss of the S-CVT, we develop a friction model for the S-CVT, and perform an in-depth contact analysis based on the relative velocity field and normal pressure distribution. We also present a nonlinear shifting controller based on feedback linearization that takes into account the dynamics of the S-CVT. To evaluate the energy efficiency of our mobile robot and the performance of the S-CVT as a machine element, we perform experiments with a hardware prototype. The results are benchmarked numerically with a differential drive type mobile robot equipped with a reduction gear.
 
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