Research Papers

Design and Modeling of a Compliant Link for Inherently Safe Corobots

[+] Author and Article Information
Yu She

Department of Mechanical and
Aerospace Engineering,
The Ohio State University,
Columbus, OH 43210
e-mail: she.22@osu.edu

Hai-Jun Su

Fellow ASME
Department of Mechanical and
Aerospace Engineering,
The Ohio State University,
Columbus, OH 43210
e-mail: su.298@osu.edu

Deshan Meng

Department of Mechanical and Automation,
Shenzhen Graduate School,
Harbin Institute of Technology,
Guangdong, Shenzhen 518055, China
e-mail: dsmeng@hit.edu.cn

Siyang Song

Department of Mechanical and
Aerospace Engineering,
The Ohio State University,
Columbus, OH 43210
e-mail: song.1252@osu.edu

Junmin Wang

Fellow ASME
Department of Mechanical and
Aerospace Engineering,
The Ohio State University,
Columbus, OH 43210
e-mail: wang.1381@osu.edu

1Corresponding author.

Manuscript received April 3, 2017; final manuscript received November 10, 2017; published online December 20, 2017. Assoc. Editor: K. H. Low.

J. Mechanisms Robotics 10(1), 011001 (Dec 20, 2017) (10 pages) Paper No: JMR-17-1087; doi: 10.1115/1.4038530 History: Received April 03, 2017; Revised November 10, 2017

In this paper, we propose a variable width compliant link that is designed for optimal trade-off of safety and control performance for inherently safe corobots. Intentionally introducing compliance to mechanical design increases safety of corobots. Traditional approaches mostly focus on the joint compliance, while few of them study the link compliance. Here, we propose a novel method to design compliant robotic links with a safety constraint which is quantified by head injury criterion (HIC). The robotic links are modeled as two-dimensional beams with a variable width. Given a safety threshold, i.e., HIC constraint, the width distribution along the link is optimized to give a uniform distribution of HIC, which guarantees inherent safety for human operators. This solution is validated by a human–robot impact simulation program built in matlab. A static model of the variable width link is derived and verified by finite element simulations. Not only stress in the link is reduced, this new design has a better control and dynamic performance quantified by a larger natural frequency and a larger bandwidth compared with designs made of uniform beams and compliant joints (CJs). The proposed variable width link takes full advantage of the link rigidity while keeps inherent safety during a human–robot impact. This paper demonstrates that the compliant link solution could be a promising alternative approach for addressing safety concerns of human–robot interactions.

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Grahic Jump Location
Fig. 1

Impact between the robot and the human operator occurs anywhere on the robotic links

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Fig. 2

A typical robotic link (a) and its mass–spring–mass impact model (b)

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Fig. 3

The mechanical model of the robot impact system

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Fig. 4

Distribution of HIC versus impact position for several link designs: (a) a RL gives HIC∝r2.5, (b) a rigid link with a CJ gives HIC∝r, (c) a flexible link with a uniform bending stiffness (U) results in HIC∝r0.25, and (d) a flexible link with variable bending stiffness (V) results in a constant HIC. (e) Comparison of HIC/HICmax for the four compliance designs.

Grahic Jump Location
Fig. 5

The plot width w versus radius r for four representative width distribution function

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Fig. 6

The plot HIC as a function of radius r for the four width distribution functions given in Fig. 4

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Fig. 7

The continuous link model versus the discrete rigid segment model

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Fig. 8

The optimized width distribution of the link

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Fig. 9

The optimized bending stiffness EI

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Fig. 10

The optimized HIC distribution along the link direction

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Fig. 11

The Simmechanics model for impact simulation

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Fig. 12

The static model of the variable width link

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Fig. 13

Trajectory of the deflected tip point according to the FEA simulation and static model

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Fig. 14

Normalized displacement at the tip of the link given sinusoidal input signal at the joint angle

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Fig. 15

Compare the bandwidth of the four systems

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Fig. 16

Stress evaluation

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Fig. 17

Safety evaluation



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