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- Type of Document: M.Sc. Thesis
- Language: Farsi
- Document No: 58187 (08)
- University: Sharif University of Technology
- Department: Mechanical Engineering
- Advisor(s): Behzadipour, Saeed
- Abstract:
- Walking with lower-limb exoskeletons, particularly in individuals with limited motor abilities, presents numerous challenges. One of the most critical limitations is the absence of an active ankle joint in many commercial exoskeletons. This deficiency prevents users from naturally transferring their center of mass over the peak of potential energy, as the ankle normally plays a crucial role in generating forward propulsion and transferring energy between steps. The lack of this energy source forces users to adopt compensatory strategies that have not yet been thoroughly identified or analyzed. In this study, aiming to precisely analyze the gait mechanism in the presence of an exoskeleton lacking an active ankle, two datasets were used: a publicly available dataset from the ReWalk exoskeleton and a custom-collected dataset from a user of the Exoped exoskeleton walking with an instrumented crutch. Following biomechanical modeling and the development of a simplified inverted pendulum model, the model was validated by comparing the longitudinal component of the center of pressure (CoP) and ground reaction forces (GRFs). The mean deviation of the pendulum model from the reference full-body model was found to be less than 8.1% for CoP position and 27.9% and 2.9% in the respective GRF components. Through this analysis, a specific region of the gait cycle was identified as the “critical phase,” during which additional mechanical energy is required. It was found that only the active degrees of freedom in the exoskeleton, particularly the stance-side hip joint, contributed significantly to energy input, while the ground reaction forces, crutches, and even upper body contributed minimally or counterproductively. Furthermore, eight mechanical energy indices were evaluated, revealing a clear deviation from normal gait. Notably, the energy recovery index was approximately 40%, and the mean total mechanical work variation exceeded 0.04 J/kg per cycle, reflecting a high level of dynamical discordance with natural walking patterns. These findings can inform the optimization of future exoskeleton designs, the development of control strategies focused on the critical phase of gait, and the formulation of more effective rehabilitation training programs
- Keywords:
- Exoskeleton ; Inverted Pendulum ; Dynamic Analysis ; Energy Index ; Critical Phase ; Gait Analysis ; Lower Limb Exoskeleton
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