Hip Exoskeleton Admittance Switching for Natural Gait Support

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Solution Overview

Problem

Existing human-in-the-loop optimization methods for exoskeletons alter gait kinematics while attempting to reduce metabolic cost, which is undesirable for healthy users.

Innovation Solution

A novel approach using admittance control with reinforcement learning to optimize switching times between predetermined admittance parameters, maintaining hip kinematics and reducing human exertion by modulating compliance in the system.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Use of energy by moving object

If human-in-the-loop optimization is used to minimize metabolic cost, then energy expenditure is reduced, but gait kinematics are altered from natural patterns

Engineering Contradiction:

Improvemetabolic costVSAvoidgait kinematics

Core Design Contradiction:

Use of energy by moving objectVSStability of the object's composition

Solution Approach 1:

The patent applies dynamics by making the exoskeleton's admittance parameters switchable between different sets (first set and second set) at optimized switching times during the gait cycle. This dynamic adjustment allows the system to provide assistance that reduces metabolic cost while maintaining natural gait kinematics, resolving the contradiction between energy reduction and gait stability.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The patent changes physical parameters by optimizing the switching times between different admittance parameter sets. By adjusting when the exoskeleton transitions between stiffness and compliance modes during specific gait phases, the system achieves metabolic cost reduction without altering natural hip joint kinematics, thus resolving the technical contradiction.

Inventive Principle:

Principle #35Parameter changes

2Force

If exoskeleton provides mechanical energy assistance, then human exertion is reduced, but control complexity increases

Engineering Contradiction:

Improvemechanical energyVSAvoidcontrol complexity

Core Design Contradiction:

ForceVSDevice complexity

Solution Approach 1:

The patent segments the gait cycle into distinct phases and applies different admittance parameter sets to specific phases. By dividing the control strategy into phase-specific segments with predetermined switching times, the system provides mechanical energy assistance to reduce human exertion while managing control complexity through structured phase-based control.

Inventive Principle:

Principle #1Segmentation

Data Source

PatentUS20250352421A1Method to reduce human exertion during walking without affecting gait kinematics

Publication Date: 2025.11.20 NORTH CAROLINA STATE UNIV

AI summary

Various examples are provided related to gait kinematics. A methodology for human in the loop optimization (HILO) for use of a hip exoskeleton is presented. In one example, a method includes monitoring a gait phase of an exoskeleton and controlling switching time between admittance parameters associated with actuator control of the exoskeleton, where the switching time is controlled based upon the monitored gait phase. The admittance parameters can be predetermined and can be user specific. The time of the switching can be determined from use of the exoskeleton and can be determined using reinforcement learning.