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Research Papers

Force Capabilities of Two-Degree-of-Freedom Serial Robots Equipped With Passive Isotropic Force Limiters

[+] 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 September 12, 2015; final manuscript received November 25, 2015; published online May 4, 2016. Assoc. Editor: Andrew P. Murray.

J. Mechanisms Robotics 8(5), 051002 (May 04, 2016) (9 pages) Paper No: JMR-15-1250; doi: 10.1115/1.4032120 History: Received September 12, 2015; Revised November 25, 2015

This paper proposes the use of passive force and torque limiting devices to bound the maximum forces that can be applied at the end-effector or along the links of a robot, thereby ensuring the safety of human–robot interaction. Planar isotropic force limiting modules are proposed and used to analyze the force capabilities of a two-degree-of-freedom (2DOF) planar serial robot. The force capabilities at the end-effector are first analyzed. It is shown that, using isotropic force limiting modules, the performance to safety index remains excellent for all configurations of the robot. The maximum contact forces along the links of the robot are then analyzed. Force and torque limiters are distributed along the structure of the robot in order to ensure that the forces applied at any point of contact along the links are bounded. A power analysis is then presented in order to support the results. Finally, examples of mechanical designs of force/torque limiters are shown to illustrate a possible practical implementation of the concept.

Copyright © 2016 by ASME
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References

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Figures

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Fig. 1

Architecture of a planar RP force limiter

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Fig. 2

Force polytope for the manipulator of Fig. 1. In this example, the force and torque thresholds are chosen such that an isotropic force module is obtained.

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Fig. 3

Architecture of PP force module

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Fig. 4

Planar 2DOF manipulator with torque and force limiters

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Fig. 5

Achievable force polygons for some configurations: (a) θ2 = π/6, (b) θ2 = π/2, (c) θ2 = 3π/4, and (d) θ2 = 8π/9

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Fig. 6

The index μ for the best optimal situation of the robot

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Fig. 7

Distribution of contact forces along the robot links

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Fig. 8

Contact force spaces at the different points of robot links: (a) Along L1, (b) along L2, (c) along L′2, (d) along L3, (e) along L4, and (f) along L5

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Fig. 9

Maximum forces in all directions contacting along thelinks (where τp,max = 140 N m, τ1,max = 60 N m, and f1,max = f2,max = f3,max = 100 N)

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Fig. 10

Maximum power for contacts along the links with θ˙max=[0.1,1.1] (rad/s)

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Fig. 11

Maximum power at the tool center of the end-effector with θ˙max=[0.1,1.1] (rad/s)

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Fig. 12

Design principle of the force/torque limiters

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Fig. 13

Torque limiter: (a) locked and (b) unlocked

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Fig. 14

Limit force as a function of the lever arm l for the torque limiter

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Fig. 15

Force limiter, based on a parallelogram linkage: (a) locked and (b) unlocked

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Fig. 16

Force thresholds for different limiter designs

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Fig. 17

Limit forces measured experimentally and expected force thresholds for an isotropic module comprising two orthogonal force limiters

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Fig. 18

Robot links with isotropic modules

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Fig. 19

Examples of the experimental force spaces at the end-effector with θ1 = 0. (a) θ2 = π/4, (b) θ2 = π/2, and (c) θ2 = 2π/3.

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