Periodic Reporting for period 1 - SmartANKLE (Smart Mechatronic Ankle-Foot Orthosis Platform for Gait Assistance and Augmentation)
Période du rapport: 2023-10-01 au 2025-09-30
Mechatronic ankle foot orthoses have recently attracted significant attention as a means for assisting or augmenting gait functions of impaired and healthy individuals. However, this technology has seldom translated into products that are available to clinicians and the general public. To solve this issue, we aim at training six high-skilled professionals who can design and develop solutions that satisfy the needs of all stakeholders and can translate into products. SmartANKLE will establish a comprehensive training program that will provide the six Doctoral Candidates (DCs) with all the skills required to bring the mechatronic ankle foot orthosis concept into the market. The SmartANKLE group brings together four internationally recognized universities, one hospital and three companies. The SmartANKLE DCs will be trained in all the aspects of the development of a radically new Smart Mechatronic Ankle Foot Orthoses (SMAFO) platform. The components of this platform will be used to assemble different SMAFO configurations able to provide positive torque during gait and that can be utilized in different applications, spanning from gait assistance of stroke survivor, training of sport practitioners and human augmentation. The training will cover all phases of product development: from conceptualization, to design, to translation and testing. The DCs will learn to identify the needs of the different users and to investigate the requirements of all stakeholders. The DCs will formulate a tailored career development plan which includes the acquisition of engineering, research, and management skills, in a training that will foster teamwork, open science practices and gender aspects. The DCs will undergo outreach activities aiming at disseminating SmartAnkle’s impact to a wide array of audiences. SmartANKLE will greatly enhance the career perspectives of the DCs in academia and industry and will set an example for a novel
research-intensive industrial doctoral network
research-intensive industrial doctoral network
VUB investigated new methodologies for system identification and tuning of remote actuation in wearable robotics, focusing on flexible shafts for ankle–foot orthoses. These components can reduce distal mass and improve efficiency compared to Bowden cables or pneumatic systems, but their behaviour under dynamic use has been poorly understood. To address this, the work concentrated on system-level characterisation of flexible shafts, analysing how performance depends on mechanical constraints, bending, and routing.
Three experimental campaigns were conducted:
- Out-of-plane motion tests showed that restricting helical buckling increases stiffness, reduces hysteresis, and improves efficiency, while excessive freedom of movement introduces nonlinearities. This highlighted the importance of controlling shaft deformation when designing wearable systems.
- Fully constrained translation tests revealed that stiffness and torque transmission efficiency remain high even at large bend angles if translation is tightly constrained. This finding contradicted common assumptions in the literature that bending itself reduces stiffness, demonstrating instead that translation and buckling are the dominant factors. These insights suggest that careful mechanical routing can enable lighter, thinner shafts to achieve the required torque capacity, directly contributing to reduced device weight and improved wearability.
- Motion capture tests demonstrated that bending and endpoint translation have similar effects when measured as deviations from an ideal reference plane, reinforcing the importance of routing strategies to minimise deviations rather than focusing solely on bend radius. The experiments also revealed a consistent relationship between tensile forces and transmitted torque, which may provide a practical proxy for system monitoring in future implementations.
Together, these results establish a clear design principle: maximising translation constraint yields more predictable and efficient torque transmission. This challenges supplier data and prior models, shifting design focus from bend radius to routing and support structures.
In addition to these experimental outcomes, the project explored future methodologies for system identification and tuning. Depending on the observed degree of nonlinearity in final device prototypes, different approaches are recommended:
- For near-linear behaviour: frequency-domain methods.
- For moderate nonlinearities: polynomial state-space or nonlinear autoregressive models.
- For strongly nonlinear behaviour: hybrid strategies combining physics-based models with machine learning.
- Human-in-the-loop tuning methods are proposed to refine controller parameters based on user feedback and physiological signals, ensuring personalised and safe performance.
The main achievements of this work are:
- Demonstration that translation constraint, not bending angle, is the dominant factor affecting stiffness, hysteresis, and efficiency.
- Identification of promising pathways for system identification, modelling and tuning, adaptable to varying levels of system nonlinearity.
- Development of design guidelines for shaft routing, enabling lighter, more efficient ankle–foot orthoses.
Three experimental campaigns were conducted:
- Out-of-plane motion tests showed that restricting helical buckling increases stiffness, reduces hysteresis, and improves efficiency, while excessive freedom of movement introduces nonlinearities. This highlighted the importance of controlling shaft deformation when designing wearable systems.
- Fully constrained translation tests revealed that stiffness and torque transmission efficiency remain high even at large bend angles if translation is tightly constrained. This finding contradicted common assumptions in the literature that bending itself reduces stiffness, demonstrating instead that translation and buckling are the dominant factors. These insights suggest that careful mechanical routing can enable lighter, thinner shafts to achieve the required torque capacity, directly contributing to reduced device weight and improved wearability.
- Motion capture tests demonstrated that bending and endpoint translation have similar effects when measured as deviations from an ideal reference plane, reinforcing the importance of routing strategies to minimise deviations rather than focusing solely on bend radius. The experiments also revealed a consistent relationship between tensile forces and transmitted torque, which may provide a practical proxy for system monitoring in future implementations.
Together, these results establish a clear design principle: maximising translation constraint yields more predictable and efficient torque transmission. This challenges supplier data and prior models, shifting design focus from bend radius to routing and support structures.
In addition to these experimental outcomes, the project explored future methodologies for system identification and tuning. Depending on the observed degree of nonlinearity in final device prototypes, different approaches are recommended:
- For near-linear behaviour: frequency-domain methods.
- For moderate nonlinearities: polynomial state-space or nonlinear autoregressive models.
- For strongly nonlinear behaviour: hybrid strategies combining physics-based models with machine learning.
- Human-in-the-loop tuning methods are proposed to refine controller parameters based on user feedback and physiological signals, ensuring personalised and safe performance.
The main achievements of this work are:
- Demonstration that translation constraint, not bending angle, is the dominant factor affecting stiffness, hysteresis, and efficiency.
- Identification of promising pathways for system identification, modelling and tuning, adaptable to varying levels of system nonlinearity.
- Development of design guidelines for shaft routing, enabling lighter, more efficient ankle–foot orthoses.
Until now, flexible shafts were considered unsuitable for highly dynamic, human-interactive devices due to their variability and nonlinear behaviour under bending. Supplier data typically highlighted minimum bend radius as the decisive parameter, while most research relied on simplified models without accounting for the real-world constraints of wearable systems.
This project has overturned these assumptions by demonstrating that translation constraint, rather than bending angle, is the key factor governing stiffness, hysteresis, and efficiency. This insight challenges conventional design guidelines and establishes new principles for routing and supporting flexible shafts in wearable robotic platforms. Crucially, the results show that high efficiency and predictable torque transmission are achievable even at large bend angles, provided that the shaft is properly constrained.
The potential impacts of these findings are significant:
The project delivers the first systematic framework for analysing flexible shaft transmissions in wearable robotics, addressing a major gap in the field.
The new design guidelines enable integration of flexible shafts into commercial orthoses and exoskeletons, supporting lighter devices with improved efficiency compared to traditional cable-driven systems.
Looking ahead, we will further develop intellectual property around routing methods, characterisation metrics, and control strategies tailored to lower-limb orthoses. Protection of this IP may be pursued to facilitate technology transfer and uptake by industrial partners.
This project has overturned these assumptions by demonstrating that translation constraint, rather than bending angle, is the key factor governing stiffness, hysteresis, and efficiency. This insight challenges conventional design guidelines and establishes new principles for routing and supporting flexible shafts in wearable robotic platforms. Crucially, the results show that high efficiency and predictable torque transmission are achievable even at large bend angles, provided that the shaft is properly constrained.
The potential impacts of these findings are significant:
The project delivers the first systematic framework for analysing flexible shaft transmissions in wearable robotics, addressing a major gap in the field.
The new design guidelines enable integration of flexible shafts into commercial orthoses and exoskeletons, supporting lighter devices with improved efficiency compared to traditional cable-driven systems.
Looking ahead, we will further develop intellectual property around routing methods, characterisation metrics, and control strategies tailored to lower-limb orthoses. Protection of this IP may be pursued to facilitate technology transfer and uptake by industrial partners.