Active Impedance Controller for Exoskeleton Energy Assistance
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Solution Overview
Problem
Current assistive exoskeletons are limited by their passive behavior, which restricts their ability to provide continuous energy assistance for movements that elevate the center of mass, such as walking or standing up, and rely on inaccurate and variable EMG signals for control.
Innovation Solution
The development of an active impedance control system for exoskeletons that modifies the mechanical properties of user extremities, allowing the exoskeleton to act as an energy source by transitioning from passive to active behavior, reducing muscle effort through virtual impedance parameters and eliminating the need for EMG control signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If passive mechanical devices like springs are used for exoskeleton assist, then the device structure is simple, but the assistive capability is limited and cannot supply continuous energy
Solution Approach 1:
The patent replaces passive mechanical energy storage devices (springs) with an active control system that uses motors and sensors to provide continuous energy assistance. The controller actively regulates motor torque based on desired trajectory and actual position feedback, enabling the exoskeleton to supply energy continuously rather than relying on passive mechanical energy storage.
Solution Approach 2:
The exoskeleton system uses the user's own motion intent (detected through position sensors) to automatically regulate the assistance provided. The controller compares desired trajectory with actual position and adjusts motor output accordingly, allowing the system to adaptively provide energy assistance without external control input.
2Adaptability or versatility
If myoelectrical control using EMG signals is used, then the control can assist any attempted motion, but the control accuracy is poor due to EMG signal variability
Solution Approach 1:
The patent replaces EMG-based myoelectrical control with a position-based control system using mechanical sensors. Instead of estimating torque from electrical signals, the system directly measures joint position and uses this information to regulate motor torque, eliminating the inaccuracies associated with EMG signal interpretation.
Solution Approach 2:
The system implements closed-loop feedback control where the controller continuously compares the desired trajectory with the actual joint position measured by sensors. Based on this feedback, the controller adjusts the motor torque to achieve the desired motion, providing accurate and reliable control without relying on variable EMG signals.
Data Source
AI summary
A system and method are presented to provide assist to a user by means of an exoskeleton with a controller capable of making the exoskeleton display active impedance. The exoskeleton assists the user by reducing the muscle effort required by the user to move his or her extremities. In one embodiment, a single-degree-of-freedom (1-DOF) exoskeleton assists a user with single-joint movement using an active impedance controller. In another embodiment, a multiple-degree-of-freedom (multi-DOF) exoskeleton assists a user with multiple-joint movement using an active impedance controller.