Dynamic Analysis of Compliant Joint for Assistive Exoskeleton
Author
Paul, Elizabeth Napoleon
Term
4. term
Education
Publication year
2020
Submitted on
2020-06-03
Pages
54
Abstract
This thesis investigates the nonlinear dynamics of a compliant revolute joint for an assistive exoskeleton within the Exo-aider project. The joint is modeled as a one-degree-of-freedom pendulum using a Lagrangian formulation, and the resulting equation of motion is solved numerically with fourth-order Runge-Kutta and analytically with the Harmonic Balance Method (HBM). These methods are used to characterize nonlinear behaviors, including chaotic responses and jump phenomena, assessed via phase and frequency response plots. The model is validated through MSC Adams simulations, showing good agreement with the Runge-Kutta solution (errors from 0 to 0.09 rad), and HBM closely matches Runge-Kutta as well (errors around +/- 0.008 rad). The model is then extended to include an actuator, considering both series elastic (SEA) and parallel elastic (PEA) configurations. Power analysis based on inverse dynamics indicates that increasing stiffness from softening to hardening reduces the system’s power requirement. The results provide a dynamic basis to guide design and actuator selection for safe and energy-efficient exoskeleton joints.
Denne afhandling undersøger den ikke-lineære dynamik af et eftergivende (compliant) drejeled til en assisterende exoskeletarm som led i Exo-aider-projektet. Leddet modelleres som et 1-DOF pendul ved brug af Lagrange-formulering, og bevægelsesligningen løses både numerisk med fjerdeordens Runge-Kutta og analytisk med Harmonic Balance Method (HBM). De to metoder anvendes til at karakterisere ikke-lineære fænomener, herunder kaotisk adfærd og spring (jump) i systemets respons, vurderet via fase- og frekvensplots. Modellen valideres i MSC Adams, hvor resultaterne viser god overensstemmelse med Runge-Kutta (fejl 0 til 0,09 rad), og HBM matcher ligeledes tæt med Runge-Kutta (fejl omkring +/- 0,008 rad). Modellen udvides efterfølgende med en aktuator, hvor både serieelastiske (SEA) og parallelelstiske (PEA) konfigurationer betragtes. En inverse-dynamik-baseret effektaflæsning indikerer, at en stivhedsstigning fra blødgørende til hærdende karakter reducerer systemets effektbehov. Arbejdet giver et dynamisk grundlag for design og aktuatormæssige valg i sikre og energieffektive exoskeletled.
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