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Magnetically Preloaded Wheels Alexander Slocum, Jeffrey Lang, Shorya Awtar, Anastasios John Hart, Kabir Mukaddam
 

Summary: Magnetically Preloaded Wheels
Alexander Slocum, Jeffrey Lang, Shorya Awtar, Anastasios John Hart, Kabir Mukaddam
Massachusetts Institute of Technology, 77 Mass. Ave Rm 3-445, Cambridge, MA 02139 USA, slocum@mit.edu
Abstract
Friction drives require preloading and this often results in large loads on shafts and bearings which can increase
system cost and reduce efficiency. Using the principle of self-help, a friction drive wheel can be coupled to a surface or the
motor output by magnetic attraction: One wheel is made from a sandwich of a steel disk, magnet, and a second steel disk. A
second wheel or surface with low permeability is placed in contact with the magnetic wheel, the two are attracted to each
other, thereby establishing preload without the need for external preload systems. A first-order analytical solution does well to
predict the attraction force, where the primary trade-off is the sensitivity to the gap between the wheels. If a rubber layer is
used to increase the coefficient of friction, the magnetic attraction force drops rapidly. A flexure allows one wheel to have a
degree of freedom in the radial direction, while being stiff in the tangential direction, thereby allowing a motor shaft to be
preloaded to a drive wheel to obtain a transmission effect. An application is for an overhead robotic system, dubbed
"Magnebots" that allows small autonomous robots to drive across ceilings and up and down walls, such as for hospital
automation.
Introduction
Friction drives have had many applications from controlling paper motion in printers to actuating large precision machine tool
axes [1,2,3]. In light load applications, it is not difficult to provide the preload force needed in order to develop the necessary
traction forces [4]. However, friction drives required to provide large forces, such as to machine tool axes, the preload forces
must typically be an order of magnitude greater than the actuation force, and this creates a need for complex preload and

  

Source: Awtar, Shorya - Department of Mechanical Engineering, University of Michigan

 

Collections: Engineering