Prosthetic Knee Latch Mechanism for Reliable Stance Stability

Solution Overview

Problem

Current prosthetic knee technologies are inadequate for transfemoral amputees in developing countries, as they fail to replicate able-bodied gait efficiently, leading to metabolic inefficiencies and socio-economic discrimination due to conspicuous gait deviations, and rely on friction for locking mechanisms which are unreliable.

Innovation Solution

A prosthetic knee design incorporating a latch mechanism that uses a virtual lock axis and hydraulic dampers to provide stance stability and control during the gait cycle, allowing for adjustable early stance flexion and efficient swing phase control, eliminating the need for friction-based locking.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Device complexity

If friction-based locking mechanism is used, then device complexity is reduced, but reliability deteriorates

Engineering Contradiction:

Improvelocking mechanism complexityVSAvoidlocking reliability

Core Design Contradiction:

Device complexityVSReliability

Solution Approach 1:

The patent replaces the friction-based mechanical locking system with a geometric locking system using a latch mechanism. The latch engages with a notch on the femur component, providing positive mechanical interlocking rather than relying on friction. This substitution maintains simplicity while dramatically improving reliability, as the geometric lock cannot fail due to friction variations, wear, or contamination.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The latch mechanism is designed to automatically engage and disengage based on the ground reaction force vector. During early stance phase, when the ground reaction force is posterior to the virtual lock axis, the latch automatically engages with the notch to lock the knee. During late stance phase, when the force is anterior, the latch automatically disengages. This self-regulating mechanism eliminates the need for external control systems while ensuring reliable locking.

Inventive Principle:

Principle #25Self-service

2Ease of manufacture

If friction-based locking is used, then manufacturing cost is reduced, but performance deteriorates

Engineering Contradiction:

Improvemanufacturing costVSAvoidlocking performance

Core Design Contradiction:

Ease of manufactureVSReliability

Solution Approach 1:

The patent replaces the friction-based mechanical locking system with a geometric locking system using a latch mechanism. The latch engages with a notch on the femur component, providing positive mechanical interlocking rather than relying on friction. This substitution maintains simplicity while dramatically improving reliability, as the geometric lock cannot fail due to friction variations, wear, or contamination.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

3Device complexity

If simple gait mechanism is used, then device complexity is reduced, but productivity deteriorates

Engineering Contradiction:

Improvegait mechanism complexityVSAvoidmetabolic efficiency

Core Design Contradiction:

Device complexityVSProductivity

Solution Approach 1:

The patent incorporates a dynamic latch mechanism that automatically adapts to the gait cycle through the ground reaction force vector. The virtual lock axis is positioned to create different moment arms during different phases of the gait cycle, enabling the knee to automatically lock during stance phase for stability and unlock during swing phase for mobility. This dynamic behavior replicates natural knee function and improves metabolic efficiency without requiring complex active control systems.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The latch mechanism is designed to automatically engage and disengage based on the ground reaction force vector. During early stance phase, when the ground reaction force is posterior to the virtual lock axis, the latch automatically engages with the notch to lock the knee. During late stance phase, when the force is anterior, the latch automatically disengages. This self-regulating mechanism eliminates the need for external control systems while ensuring reliable locking.

Inventive Principle:

Principle #25Self-service

Applied Scientific Principles

This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.

Function Achieved in This Case

The design enables able-bodied gait with improved metabolic efficiency and reduced socio-economic stigma by providing reliable stance stability and adjustable flexion, while avoiding the limitations of friction-based locking mechanisms.

Implementation Method 1

a hydraulic damper configured to dampen the pivot of the prosthetic knee joint about the knee joint pivot axis

Methodology Applied

Scientific EffectHydraulic damping: Viscous Damping

Data Source

PatentUS11497627B2Locking and damping mechanism for a prosthetic knee joint

Publication Date: 2022.11.15 MASSACHUSETTS INST OF TECH

AI summary

A high performance, low-cost passive prosthetic knee includes one or more modules to enable able-bodied gait by transfemoral amputees to improve metabolic efficiency and reduce stigma from conspicuous abnormal gaits. A stance stability module includes a latch with a virtual lock axis that automatically locks and unlocks. An early stance flexion module enables able-bodied gait during stance. Hydraulic fluid dampers ensure reliable swing phase control. A swing extension energy storage module stores and returns energy as the knee locks and unlocks, respectively. These modules may be used together, in any combination, or individually.