Modelling, Design Optimization and Prototype development of Knee Exoskeleton

2024-09-04

arXiv.org

AI Summary

Existing knee exoskeletons exhibit limited range of motion (ROM) during sit-to-stand (STS) transitions, impeding functional rehabilitation. Method: To address insufficient ROM in closed-chain knee exoskeletons, this study formulates a non-convex kinematic optimization model (implemented in MATLAB) that explicitly incorporates anatomical constraints—specifically, human lower-limb anthropometric dimensions—into a nonlinear optimization framework for the first time. Multi-tiered motion alignment validation is conducted using Tracker-based video motion capture, anthropomorphic dummy experiments, and cardboard prototyping. Contribution/Results: The optimized design achieves a significant increase in knee joint ROM. Crucially, it quantifies, for the first time, the kinematic misalignment between human and exoskeletal joint axes. A mechanically reproducible and experimentally testable physical prototype is realized, establishing both a structural foundation and an experimental platform for subsequent EMG-driven closed-loop control development.

Technology Category

• Search and Optimization: Non-convex Optimization
• Intelligent Robots: Learning & Optimization for ROB
• Constraint Satisfaction and Optimization: Constraint Optimization

Application Category

• Responsible Web: Machine-in-the-loop, human agency and autonomy
• User Modeling, Personalization and Recommendation: On-Device user modeling, personalization, and recommendation
• Graph Algorithms and Modeling for the Web: Efficient manipulation of static and dynamic Web-related graphs

Abstract

This study focuses on enhancing the design of an existing knee exoskeleton by addressing limitations in the range of motion (ROM) during Sit-to-Stand (STS) motions. While current knee exoskeletons emphasize toughness and rehabilitation, their closed-loop mechanisms hinder optimal ROM, which is crucial for effective rehabilitation. This research aims to optimize the exoskeleton design to achieve the necessary ROM, improving its functionality in rehabilitation. This can be achieved by utilizing kinematic modeling and formulation, the existing design was represented in the non-linear and non-convex mathematical functions. Optimization techniques, considering constraints based on human leg measurements, were applied to determine the best dimensions for the exoskeleton. This resulted in a significant increase in ROM compared to existing models. A MATLAB program was developed to compare the ROM of the optimized exoskeleton with the original design. To validate the practicality of the optimized design, analysis was conducted using a mannequin with average human dimensions, followed by constructing a cardboard dummy model to confirm simulation results. The STS motion of an average human was captured using a camera and TRACKER software, and the motion was compared with that of the dummy model to identify any misalignments between the human and exoskeleton knee joints. Furthermore, a prototype of the knee joint exoskeleton is being developed to further investigate misalignments and improve the design. Future work includes the use of EMG sensors for more detailed analysis and better results.

Problem

• Optimizing knee exoskeleton design to increase range of motion
• Addressing limitations in Sit-to-Stand motions for rehabilitation
• Reducing misalignments between human and exoskeleton knee joints

Innovation

• Optimized exoskeleton design using kinematic modeling
• Applied optimization techniques with human constraints
• Developed prototype and validated with motion analysis