Design of Dissipative and Stable Assist Robots

[+] Author and Article Information
Sunil K. Agrawal1

Mechanical Systems Laboratory, Department of Mechanical Engineering, University of Delaware, Newark, Delaware 19716agrawal@udel.edu

Ji-Chul Ryu

Mechanical Systems Laboratory, Department of Mechanical Engineering, University of Delaware, Newark, Delaware 19716jcryu@udel.edu


Corresponding author.

J. Mech. Des 129(12), 1251-1255 (Dec 14, 2006) (5 pages) doi:10.1115/1.2779891 History: Received May 22, 2006; Revised December 14, 2006

This paper presents a methodology for design of dissipative assist robots with proven stability during set-point control. A dissipative assist robot is defined as one where the actuators continuously dissipate energy from the robot until the robot reaches the desired set point. We have discussed in this paper that, under well known control laws, it is hard to characterize dissipativity of a general assist robot. However, by appropriately designing the robot through inertia redistribution, the dynamic equations can be modified so that the control laws can now be proven to be both dissipative and stable under set-point control. The proposed method is demonstrated through simulation of a three-link planar manipulator used as an assist robot to modify human functional movements in a vertical plane.

Copyright © 2007 by American Society of Mechanical Engineers
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Figure 3

A three-link planar manipulator and its parameters

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Figure 4

Simulation result showing the stability of the trajectory in phase space (ei,q̇i)

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Figure 5

Simulation results showing the input power from the actuator and the user

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Figure 6

Simulation results showing the total power of the system, which remains negative as the robot reaches the equilibrium point

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Figure 1

A schematic of a robot used as an assist device

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Figure 2

A schematic of an n-link planar manipulator. Here, qi is the ith joint angle and Oi is the joint axis i.




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