# Design of a rotational bistable mechanism: a parametric and ergonomic study

Kéliane Megret, Justin Dirrenberger, Jocelyn Monnoyer, Cyrille Sollogoub, Benjamin Goislard de Monsabert, Laure Fernandez, Stéphane Delalande, Stéphane Viollet

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Kéliane Megret, Justin Dirrenberger, Jocelyn Monnoyer, Cyrille Sollogoub, Benjamin Goislard de Monsabert, et al.. Design of a rotational bistable mechanism: a parametric and ergonomic study. 14th International Conference on the Mechanical Behaviour of Materials, Jul 2023, Santiago de Chile, Chile. hal-04869825

HAL Id: hal-04869825

https://hal.science/hal-04869825v1

Submitted on 7 Jan 2025

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# Design of a rotational bistable mechanism : a parametric and ergonomic study

Kéliane MEGRET<fnref n="1" />,<fnref n="2" />,<fnref n="3" />*, Justin DIRRENBERGER<fnref n="1" />, Jocelyn MONNOYER<fnref n="2" />,<fnref n="3" />, Cyrille SOLLOGOUB<fnref n="1" />, Benjamin GOISLARD DE MONSABERT<fnref n="2" />, Laure FERNANDEZ<fnref n="2" />, Stéphane DELALANDE<fnref n="1" />, Stéphane VIOLLET<fnref n="2" />

## Motivation

* In the automotive industry, several means exist to lower the carbon footprint: reduce weight, fuel consumption, aerodynamics.

* Specific design, lightweight system, produced in one part.

* Bistability applied to human-centered approach interfaces.

Reduced carbon footprint

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Lightweight

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Single-part with same properties

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Human-centered

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### Need for new mechanisms

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* Optimize affordance with a smart and user friendly design.

* Evaluate the best way to grasp and actuate the mechanism.

* Find the human perception coupling and maximize hedonism.

Affordance

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Grasping and holding [1]

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## Literature review

Most innovative mechanisms are usually made of origami, kirigami, trusses, ... Here, bistable mechanisms are made of living hinges and compliant beams. They can be classified by their global motion : translation or rotation.

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A : First stable position

B : Unstable position

C : Second stable position

A system having two stable positions is called bistable. The force-displacement curve is plotted to characterize them. Bistable systems store and release energy during use. A change in the sign of the force testifies this behaviour and a critical force is required to initiate the motion.

Rotating bistable mechanisms are less studied and tend to be more symmetric [2].

$$ \epsilon_{in} = \epsilon_{out} \Leftrightarrow \text{symmetric behaviour} $$

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## Parametric study

<figure><img src="image_22.png" /><figcaption>CAD model of the bistable
Inspired by [3]</figcaption></figure>

<figure><img src="image_23.png" /><figcaption>Experimental setup</figcaption></figure>

<figure><img src="image_24.png" /><figcaption>Geometry and parameters</figcaption></figure>

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<figure><img src="image_26.png" /><figcaption>Human torque limitations without arm lever: 16 N.m [4]</figcaption></figure>

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Mmax ↓
Angular range ↑
Stable if > 20

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Mmax ↑
Angular range =

## Conclusion & future works

* Out-of-plane thickness only influences the maximum value of the torque to switch from one stable position to the other.

* Slenderness ratio influences the maximum moment and the position of the second stable equilibrium.

* Energy stored and released by the mechanism fully determines the behaviour of the bistable.

* Increase the number of papers studied to improve the energy maps.

* Set up an experiment, human-centered and assess the bistable behaviours : affordance, muscles activation, pleasure of use.

PhD started in November 2022

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<footnote n="1">¹: Laboratoire PIMM, Arts et Métiers, CNRS, HESAM Université, 75013 Paris, France</footnote>

<footnote n="2">²: Institut des Sciences du Mouvement, Aix-Marseille Université, CNRS, F-13288 Marseille, France</footnote>

<footnote n="3">³: Stellantis, Paris, France</footnote>

<footnote>[1] M. R. Cutkosky, IEEE Trans. Robot. Automat. 5, 269-279 (1989).</footnote>

<footnote>[2] K. Megret et al., "Design of a rotational bistable mechanism : a parametric and ergonomic study", in prep</footnote>

<footnote>[3] Y. Oh, "Synthesis of multistable equilibrium compliant mechanisms," thesis, 2008</footnote>

<footnote>[4] L. W. O'Sullivan, T. J. Gallwey, Proceedings of the Human Factors and Ergonomics Society Annual Meeting. 45, 1128-1132 (2001)</footnote>

<footnote>*: keliane.megret@stellantis.com</footnote>