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Research Papers

Design and Static Analysis of Elastic Force and Torque Limiting Devices for Safe Physical Human–Robot Interaction

[+] Author and Article Information
Meiying Zhang

Département de Génie Mécanique,
Université Laval,
Québec, QC G1V 0A6, Canada
e-mail: meiying.zhang.1@ulaval.ca

Thierry Laliberté

Département de Génie Mécanique,
Université Laval,
Québec, QC G1V 0A6, Canada
e-mail: thierry@gmc.ulaval.ca

Clément Gosselin

Département de Génie Mécanique,
Université Laval,
Québec, QC G1V 0A6, Canada
e-mail: gosselin@gmc.ulaval.ca

Manuscript received October 3, 2016; final manuscript received December 20, 2016; published online March 9, 2017. Assoc. Editor: Venkat Krovi.

J. Mechanisms Robotics 9(2), 021003 (Mar 09, 2017) (8 pages) Paper No: JMR-16-1287; doi: 10.1115/1.4035683 History: Received October 03, 2016; Revised December 20, 2016

This paper presents the static analysis of elastic force and torque limiters that aim at limiting the forces that a robotic manipulator can apply on its environment. First, the design of one-degree-of-freedom force and torque limiting mechanisms is presented. It is shown that a single elastic component (spring) can be used to provide a prescribed preload and stiffness in both directions of motion along a given axis. Then, the mechanisms are analyzed in order to determine the nonlinear relationships between the motion of the mechanism and the extension of the spring. These relationships can then be used in the design of the force and torque limiters. Finally, the force capabilities of the mechanisms are investigated and numerical results are provided for example designs.

Copyright © 2017 by ASME
Topics: Torque , Design , Springs
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References

Figures

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Fig. 1

Elastic return force limiter based on a pivoting mechanism: (a) locked and (b) unlocked

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Fig. 2

Elastic return force limiter based on guided sliding (from Ref. [10]): (a) locked and (b) unlocked

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Fig. 3

Geometry of the force limiter based on guided sliding

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Fig. 4

Increase of the spring extension as a function of angle ϑ, with b = 50 mm. For the design of Fig. 1, l0 = 25 mm. For the design of Fig. 2, x1 = x2 = 10 mm and R2 = 30 mm.

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Fig. 5

Distribution of the contact force on the two sliding surfaces for the force limiter of Fig. 2, when the limiter is displaced from its reference configuration

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Fig. 6

External force with respect to angle ϑ, with a = b = 50 mm, k = 1 N/mm and F0 = 10 N. For the design of Fig. 1, l0 = 25 mm. For the design of Fig. 2, x1 = x2 = 10 mm and R2 = 30 mm. The force required to overcome the notch of the design of Fig. 2 is computed by setting, x1 = 10 mm, x2 = 25 mm and R2 = 25 mm and is represented as a circle on the force axis.

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Fig. 7

Qualitative comparison of the force behavior of the two types of proposed elastic return force limiters

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Fig. 8

Force limiting module comprising two orthogonally mounted guided sliding force limiters

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Fig. 9

Schematic representation of an elastic return torque limiter based on a pivoting mechanism

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Fig. 10

Force transmission of the mechanism of Fig. 9

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Fig. 11

Guided sliding torque limiter (from [10]): (a) locked and (b) unlocked

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Fig. 12

Schematic representation of the mechanism of Fig. 11

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Fig. 13

The spring force transmission of the mechanism represented schematically in Fig. 12(b)

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Fig. 14

Increase of the external force for both types of elastic return torque limiters, where a=60 mm, b=80 mm, x1=x2=10 mm, R2=30 mm, ϕ=π/9, k=1 N/mm, F0=10 N and ϑ=0. From the geometric parameters, lC = 109.9 mm: (a) force increase as a function of ϑ where l = 30 mm and (b) force increase as a function of l where ϑ=π/18.

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Fig. 15

Example of the use of torque limiters in the design of a robot link to limit the forces isotropically in all directions (taken from Ref. [11])

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