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Research Papers

A Flexible Multibody Model of a Safety Robot Arm for Experimental Validation and Analysis of Design Parameters

[+] Author and Article Information
J. López-Martínez

Department of Engineering,
University of Almería,
Almería 04004, Spain
e-mail: javier.lopez@ual.es

D. García-Vallejo

Department of Mechanical
and Materials Engineering,
University of Seville,
Seville 41092, Spain
e-mail: dgvallejo@us.es

J. L. Torres-Moreno

Department of Engineering,
University of Almería,
Almería 04004, Spain

Contributed by the Design Engineering Division of ASME for publication in the JOURNAL OF COMPUTATIONAL AND NONLINEAR DYNAMICS. Manuscript received January 26, 2013; final manuscript received July 25, 2013; published online September 25, 2013. Assoc. Editor: Aki Mikkola.

J. Comput. Nonlinear Dynam 9(1), 011003 (Sep 25, 2013) (10 pages) Paper No: CND-13-1019; doi: 10.1115/1.4025285 History: Received January 26, 2013; Revised July 25, 2013

Service robots must comply with very demanding safety requirements in order to guarantee that a human can be assisted without any risk of injury. This paper presents a detailed multibody model of the interaction between a single link manipulator and a human head–neck to study the different and more significant parameters involved in the design of the manipulator. The multibody model is first validated through comparison with experimental results obtained in a testbed, which has been built for this purpose. The testbed consists of a flexible pendulum with an inertial wheel attached to the pendulum shaft and a head–neck dummy of 1 degree of freedom (DOF). A phenomenological model of the robot-arm foam soft cover has been developed by fitting experimental results obtained in a compressive test performed on the foam. Once the multibody model is qualitatively validated, several simulations are carried out. The aim of the simulations is to study the effect of different design parameters in the head injury. In particular, the effects of the link flexibility, of the joint compliance, and of the soft cover are detailed.

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Figures

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Fig. 1

Human head–robot impact model. The flexible arm includes a mass Me at the end point of the link. The contact force Fc is expressed as a function of the cover compression.

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Fig. 2

Stress–strain relation of the polyurethane foam specimen

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Fig. 3

Comparison between the compression part of the experimental stress–strain curve and the curve predicted by the Avalle et al. [44] model

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Fig. 4

Comparison between the decompression part of the experimental stress–strain curve and the curve predicted by the Rusch model [43]

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Fig. 6

Equivalence between rotational and translational head–neck models

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Fig. 7

Translational head–neck dummy

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Fig. 8

Acceleration of the extreme of the link at contact point, head acceleration, and contact force. Experimental data and simulation results for a 36.2 deg initial link angle.

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Fig. 9

Acceleration of the extreme of the link at contact point, head acceleration, and contact force. Experimental data and simulation results for a 41.0 deg initial link angle.

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Fig. 10

Acceleration of the extreme of the link at contact point, head acceleration, and contact force. Experimental data and simulation results for a 36.2 deg initial angle link. Simulation results are obtained for Avalle et al. [44] model at compression and decompression phase (discontinuous line); and for Avalle et al. model at compression and Rusch model [43] at decompression phase (dotted line).

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Fig. 11

Acceleration of the extreme of the link at contact point, head acceleration and contact force. Experimental data and simulation results for a 51.0 deg initial link angle, and inertial disk coupled at the pendulum shaft.

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Fig. 12

Acceleration of the extreme of the link at contact point, head acceleration, and contact force. Experimental data and simulation results for a 61.6 deg initial link angle, and inertial disk coupled at the pendulum shaft.

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Fig. 13

Contact force for different link models (Link 2)

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Fig. 14

Contact force for different link flexibility

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Fig. 15

Contact force peak for different joint stiffness and ideally rigid link

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Fig. 16

Contact force for different joint stiffness, Kr (Link 1)

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Fig. 17

Contact force for different joint stiffness, Kr (Link 2)

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Fig. 18

Contact force for different cover thickness values (Link 1). Contact area cover of 4 cm2 of polyurethane foam.

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Fig. 19

Peak contact force versus cover thickness for different link flexibility

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Fig. 20

HIC36 versus cover thickness for different link flexibility

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