Oscillator-based walking assistance

Oscillator-based walking assistance

Lintzen, C.S.

Van der Helm, F.C.T. (mentor)
Van der Kooij, H. (mentor)
Van Dijk, W. (mentor)

Mechanical, Maritime and Materials Engineering

BioMechanical Engineering

Biomechatronics

2011-07-11

A human with muscle weakness can wear a rehabilitation device, e.g. exoskeleton, to receive support during walking. How can this support be adjusted in real-time to the intention of the user? The given support should be intuitive, user-specific, compliant and robust to sensor noise. We suggest the use of an adaptive oscillator, which can detect the frequency and phase of the user's gait. The designed oscillator-based controller is capable to adjust the support in real time, based on reliable joint angle measurements. The adaptive oscillator determines the position and velocity reference trajectories, based on the measured joint angles. The controller uses these reference trajectories to attract the current angle respectively velocity. In simulations the control parameters for the oscillator-based controller are optimized: the phase shift, to determine the reference trajectories and the controller stiffness/damping trajectories, for the impedance control. All parameters are determined in a one-stage optimization minimizing the stiffness and the power to find a minimal disturbed gait. The applied phase shift is time variable. The stiffness and damping of the controller can vary in one gait cycle between two values The simulation results show that the hip and knee joint angle trajectories and the ankle joint torque in simulations are similar to recorded human data. The optimization algorithm finds the same reference angles over multiple optimization runs and retrieves a separation between swing and stance phase of the controller stiffness without explicit prior knowledge. The performance of the optimized oscillator-based controller is determined for the ankle joint using specially designed pneumatic ankle foot orthoses (PAFO). The PAFO actuate the plantar flexion movement with pneumatic muscles. The performance of the controller is analyzed measuring the activity of the Tibialis Anterior and Gastrocnemius Medialis with electromyography (EMG). The oscillator-based controller found the same reference joint angles and velocities in real time compared to the optimization. The desired exoskeleton torques are comparable to the simulations, but the amplitude is lower. The support decreased the EMG activity of the Gastrocnemius Medialis. The lack of transparency of the PAFO increased the EMG of the Tibialis Anterior. Overall the oscillator-based controller can give a user-specific support by detecting the gait frequency and learning the gait trajectory. The specially designed PAFO can be used to validate the performance of controllers on humans. The EMG of the Gastrocnemius Medialis decreases using the oscillator based controller. The EMG can even decrease more, when the transparency of the PAFO is increased.

exoskeleton
control
oscillator-based control

http://resolver.tudelft.nl/uuid:fd2aab94-b460-4ec8-a1a8-dfd1131bc5e4

2014-06-30

Student theses

master thesis

(c) 2011 Lintzen, C.S.