Multistable Series Elastic Actuators

CARAPACE: Compliant Advanced Robotic Actuation Powering Assistive Composite Exoskeleton

This project aims to propose an unconventional and bio-inspired approach to robotic assistive/augmenting design, able to provide a superior wearability, to deliver assistance as needed or to enhance physical performance, continuously monitoring subject’s interaction due to its extraordinary ergonomics. The principal aim is the development of a new generation of adaptive/multifunctional structures working in nonlinear regimes taking inspiration from nature. The purpose is to study compliant exoskeleton architectures in order to overcome the joint misalignment problem, allowing a gentle interaction between humans and robotic devices by lightweight and human friendly solutions. The main idea is studying flexible structures and developing Shape-Morphing Compliant Mechanisms with embedded actuators which can be integrated in the exoskeleton at the level of joint or even providing motion and torque by a tendon driven transmission or Novel Multistable Composite Structures . A distributed compliant architecture will allow to overcome the problem of joint misalignment providing a more comfortable lightweight and human friendly structure. The benefits of this approach are twofold:
•    It would allow removing unnecessary stiffness thus realizing substantial weight reduction.
•   It would allow structures to deform in a well-behaved manner by incorporating a functional  kinematics that so far have been distinctive of mechanical devices.


The revolutionary idea is to introduce flexible structures able to deform in a well-behaved manner by incorporating a functional kinematics which can be integrated in the rehabilitation devices at the level of joint and providing motion and torque by novel transmission elements based on Multistable Composite Carbon Fiber Structures. Exploitation of nonlinear behaviors in such kind of mechanisms will lead to design novel generation of multifunctional compliant devices based on a continuous and variable mechanical impedance modulation at the end effector mimicking to the biological systems where the muscles have the inherent ability to regulate stiffness (and impedance) over a wide range of loads and motions, enabling control of acceleration and force in a highly efficient manner.
The possibility to finely modulate and predict the mechanical impedance and the strain energy offered by Multistable Composite Structures is achieved by using fibre-reinforced plastic in combination with of residual stresses induced during the cure cycle and the lamination (lay-up). The use of this solution may provide several advantages in robotics regard the implementation of a robust and biologically inspired approach to human machine interaction: my initial design consisted in a novel type of muscle-like actuator employing classical electric motor and Multistable Composite Structure (MCS) to transmit motion, capable of large rotary-linear deformations, by using pre-stressed carbon fiber flanges joined to introduce multiple stable configurations (see figure).


Cappello L, Xiloyannis M, Dinh BK,  Pirrera A, Mattioni F and Masia L. "Multistable Series Elastic Actuators: Design and Control".  Robotics and Autonomous Systems (RAS), Volume 118, August 2019, Pages 167-178.

Masia L., Lachenal X., Pirrera A., Cappello L., Mattioni F., Morasso P. and Waver P. “CARAPACE: a novel Composite Advanced Robotic Actuator Powering Assistive Compliant Exoskeleton: Preliminary Design” IEEE International Conference on Robotic Rehabilitation 2013, Seattle, USA, June 24-26, 2013

Cappello L, Pirrera A, Weaver P, Masia L. 'A Series Elastic Composite Actuator for Soft Arm Exosuits Design and Preliminary Test'.

Best Student Paper Award at the IEEE International Conference on Robotic Rehabilitation 2015 (ICORR), Singapore 11th-14th August 2015.

Leonardo Cappello, Khanh Dinh Binh and Lorenzo Masia. 'Design of SARCOMEX: a Soft ARm COMpliant Exoskeleton'. In 2016 6th IEEE International Conference on Biomedical Robotics and Biomechatronics (BioRob) 26-26 June, Singapore.

Cappello L, Lachenal L, Pirrera A, Mattioni F, Weaver P and Masia L. "Design, characterization and stability test of a Multistable Composite Actuator for Exoskeletons" . IEEE BioRob 2014 IEEE International Conference on Biomedical Robotics and Biomechatronics. August 12-15, 2014, São Paulo, Brazil.