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Lower-limb exoskeleton emulator to be employed in estimation of hip impedance in normal gait, A
Lee, Jason Y.
Lee, Jason Y.
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2017
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Abstract
Recent progress in robotic control and technology has contributed to an increase in interest and applications of wearable robotics, also known as exoskeletons. Identification of exoskeleton mechanical and control parameters that will provide the best performance for specific tasks remains as a significant challenge. Exoskeleton emulators, which allow real-time adjustment of device parameters (such as stiffness of an emulated spring) have emerged as valuable tools that enable fast, iterative experimentation and testing. This thesis presents design, implementation, and characterization results of a lower-limb exoskeleton emulator system with offloaded actuation. The emulator is able to apply controlled torques in the ankle, knee and hip joint sagittal degrees of freedom through five braces that were developed. A PID controller was implemented for the emulator to control the torques applied at the brace joints. Characterization of hip joint impedance is essential to the groundwork for design and control system of exoskeletons, orthoses, and prostheses. A pilot test with a single healthy subject was conducted, using the emulator as a perturbation source and focusing on identification of hip impedance parameters during normal walking. A model, that incorporated stiffness, damping, and inertia parameters as polynomial coefficients, was used to calculate the impedance values from the collected data. The results showed that the perturbation amplitudes were inadequate and soft tissues at the leg attachment points prevented effective delivery of the torques to the leg. Future work on impedance estimation of hip will focus on improving brace leg attachments and enhancing the delivered torque. In conclusion, an exoskeleton emulator for the lower-limb was successfully designed, constructed, characterized, and tested. The exoskeleton emulator will enable a variety of future studies on gait augmentation and assistance.
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