Bipedal Exoskeleton Gait Control for Stable Speed Changes

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Solution Overview

Problem

Existing exoskeletons face instability during unexpected accelerations or decelerations, limiting the ability to freely adjust assistance to a patient's efforts and requiring excessive physiotherapist intervention to maintain stability.

Innovation Solution

A method for stabilizing exoskeleton movement by estimating leg speed, determining a setpoint for center of mass trajectory through optimization, and adjusting actuator commands to maintain balance, using a control unit to iteratively adjust movements to match patient speed while ensuring stability.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If the exoskeleton operates at nominal speed with equilibrium control, then the system remains stable, but the physiotherapist cannot freely adjust assistance to reward patient efforts and excessive effort is required to maintain position during significant slowing

Engineering Contradiction:

Improveexoskeleton stabilityVSAvoidability to adjust assistance to patient efforts

Core Design Contradiction:

ReliabilityVSAdaptability or versatility

Solution Approach 1:

The control system dynamically adapts the center of mass trajectory based on real-time estimation of leg speed. When the patient moves the leg faster or slower than nominal speed, the controller computes a new trajectory that maintains stability while accommodating the speed variation. This dynamic adaptation allows the system to remain stable across a range of speeds rather than requiring exact nominal speed maintenance.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The system uses feedback from motion sensors to continuously estimate the actual speed of the patient's leg movement. This speed estimation is fed back to the controller, which then adjusts the center of mass trajectory accordingly. The feedback loop enables the system to respond to patient efforts in real-time, maintaining stability while allowing free adjustment of assistance levels.

Inventive Principle:

Principle #23Feedback

2Reliability

If the physiotherapist holds the exoskeleton to prevent falling during trajectory acceleration or deceleration, then stability is maintained, but the patient's movement freedom is restricted and rehabilitation effectiveness is reduced

Engineering Contradiction:

Improveexoskeleton stabilityVSAvoidpatient movement freedom

Core Design Contradiction:

ReliabilityVSEase of operation

Solution Approach 1:

The exoskeleton performs self-stabilization through automated control without requiring external physical support from the physiotherapist. The control unit independently computes and executes trajectory adjustments based on sensed leg speed, enabling the system to maintain balance autonomously during acceleration and deceleration phases. This eliminates the need for the therapist to physically hold the device.

Inventive Principle:

Principle #25Self-service

Solution Approach 2:

The patent replaces the mechanical intervention of the physiotherapist (physically holding the exoskeleton) with an automated control system that uses sensors and algorithms to maintain stability. This substitution of mechanical support with electronic control frees the patient's movements while maintaining system stability.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

3Adaptability or versatility

If rapid trajectory replanning is implemented to handle various speeds, then flexibility is improved, but the methodology may not find an equilibrium trajectory for certain exoskeleton speeds generated by the patient during exertion

Engineering Contradiction:

Improvehandling of various experimental conditions and patient morphologiesVSAvoidequilibrium trajectory availability

Core Design Contradiction:

Adaptability or versatilityVSReliability

Solution Approach 1:

The controller changes the parameters of the center of mass trajectory (position, velocity, acceleration profiles) based on the estimated leg speed. By adjusting these trajectory parameters dynamically, the system can find a valid equilibrium trajectory for a wider range of speeds. The optimization problem computes trajectory parameters that satisfy both the stability constraints and the desired speed accommodation.

Inventive Principle:

Principle #35Parameter changes

Data Source

PatentEP4584051B1Method for stabilized movement of a bipedal exoskeleton

Publication Date: 2026.02.18 WANDERCRAFT

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AI summary

Method for movement of an exoskeleton (1) receiving a human operator (2), for executing a step during which a first leg (30) of the exoskeleton (1) passes from a first control point to a second control point, and during which a second leg (31) of the exoskeleton (1) remains on the ground, the method comprising, at each iteration of a plurality of iterations implemented during the step, the following method steps: - estimation of a speed of the first leg (30); - determination of a trajectory of the centre of mass of the exoskeleton (1) guaranteeing the equilibrium of the exoskeleton (1), and of a speed-of-movement setpoint closest to the estimated speed; - based on the setpoint, determination of a first command to be applied to the first leg (30); and - based on the trajectory, determination of a second command to be applied to the second leg (31).