Development of a Lower Limb Exoskeleton with Flexible Links via Additive Manufacturing

• Grant number: 25/02598-8
• Support Opportunities: Regular Research Grants
• Start date: August 01, 2025
• End date: July 31, 2028
• Field of knowledge: Engineering - Mechanical Engineering
• Principal Investigator: Wilian Miranda dos Santos
• Grantee: Wilian Miranda dos Santos
• Host Institution: Faculdade de Engenharia. Universidade Estadual Paulista (UNESP). Campus Experimental São João da Boa Vista. São João da Boa Vista , SP, Brazil
• Associated researchers: Adriano Almeida Gonçalves Siqueira ; Andres Felipe Galvis Rodriguez ; Crystopher Cardoso de Brito ; Felix Mauricio Escalante Ortega ; João Pedro de Sousa Oliveira ; Julian Arnaldo Avila Diaz ; Murilo Sartorato ; Thiago Boaventura Cunha

Abstract

This research project aims to develop a lower limb exoskeleton with flexible links, designed to assist individuals with disabilities or reduced mobility. Traditionally, link flexibility has been considered an undesirable effect; however, in this project, it will be treated as a feature that enables high levels of stability, robustness, and transparency in interaction control. The exploration of link flexibility in interaction control applications is scarcely addressed in the literature, and this study aims to fill that gap. Additive manufacturing (AM) technology will enable the development of optimized flexible links, designed using topological and parametric optimization techniques through finite element analysis. These links will be engineered to meet desired requirements, such as maximum allowable load and bandwidth, which are essential for walking assistance while ensuring low stiffness and a compact, lightweight device. The study will investigate different materials for the construction of flexible links, including carbon fiber, titanium, and aerospace-grade aluminum. Macro- and microstructural characterization, as well as corrosion tests, will be conducted to assess the surface integrity of the components, while mechanical tests will be performed to validate the structural design. Regarding control, studies will be carried out to analyze how link flexibility influences the stability and passivity parameters of the controllers. Additionally, the approach of time-varying parameter linear system representations will be used in modeling the exoskeleton-user system, allowing the incorporation of user impedance parameters into the control strategy. This approach will enable modeling of the user's parameter variations during movement, resulting in a more comprehensive dynamic representation of the interaction between the exoskeleton and the user, providing greater safety and comfort during use. To address the complexity of controlling flexible robots, robust control techniques, such as h-infinity, will be evaluated to ensure the system's robustness against parametric uncertainties and external disturbances. Optical fiber sensors will be employed to measure the deformation of the flexible links, allowing the control system to account for variations in the physical properties of the links. In summary, this project aims to develop a lower limb exoskeleton with flexible links via AM and explore the flexibility of these links as an advantage in interaction control. Robust control techniques, such as h-infinity, and optical fiber sensors will be used to ensure precise and robust system control. This study has the potential to significantly contribute to the advancement of exoskeleton technology, expanding its applications in rehabilitation and assistance. (AU)