Prosthetic Lock Assembly With Cam-Guided Pin for Secure Donning

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Solution Overview

Problem

Conventional prosthetic attachment systems face issues with incorrect locking, pistoning, and difficulty in donning and doffing, especially for elderly users with limited dexterity or poor eyesight, leading to potential injury and premature wear.

Innovation Solution

A prosthetic attachment system combining vacuum suspension and mechanical suspension, utilizing a lanyard and strap mechanism to secure the prosthetic liner to the socket, with a lock assembly that includes an attachment pin and connector assembly for intuitive alignment and secure connection.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a conventional locking pin-type system is used, then mechanical locking is achieved, but incorrect locking occurs if the user does not properly insert the attachment pin

Engineering Contradiction:

Improvelocking reliabilityVSAvoidalignment difficulty

Core Design Contradiction:

ReliabilityVSEase of operation

Solution Approach 1:

The attachment pin and lock assembly use asymmetric geometric features including a cam surface and corresponding cam follower that only engage in one specific orientation. The pin has a tapered cam surface that guides it into the correct rotational position within the lock assembly, preventing incorrect insertion through geometric constraint rather than relying on user alignment skill.

Inventive Principle:

Principle #4Asymmetry

Solution Approach 2:

A cam mechanism acts as an intermediary between the attachment pin and the lock assembly. The cam surface converts linear insertion motion into rotational engagement, automatically guiding the pin into the correct orientation and providing tactile feedback to confirm proper engagement without requiring precise user alignment.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Ease of operation

If too much free play exists between the attachment pin and lock assembly, then easier insertion is achieved, but pistoning occurs causing the residual limb to move up and down

Engineering Contradiction:

Improveinsertion easeVSAvoidconnection stability

Core Design Contradiction:

Ease of operationVSStability of the object's composition

Solution Approach 1:

The lock assembly incorporates a spring-loaded cam follower that dynamically adjusts to the attachment pin during engagement. The spring allows initial free play for easy insertion, then automatically compresses to eliminate gaps and maintain constant contact pressure, preventing pistoning while preserving ease of insertion.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The system changes the contact parameter between pin and lock assembly from loose tolerance to constant spring-loaded contact. The spring force maintains optimal contact pressure that eliminates free play and prevents pistoning, while the cam geometry ensures this constant pressure is applied in the correct direction for stable connection.

Inventive Principle:

Principle #35Parameter changes

3Reliability

If conventional lock assemblies are used, then attachment is achieved, but donning and doffing becomes problematic for elderly users with limited dexterity or poor eyesight

Engineering Contradiction:

Improveattachment securityVSAvoiduser accessibility

Core Design Contradiction:

ReliabilityVSEase of operation

Solution Approach 1:

The cam mechanism provides self-aligning and self-locking functionality that eliminates the need for precise user alignment. The geometric cam surface automatically guides the attachment pin into the correct position and secures it through mechanical leverage, providing tactile feedback and visual indicators that confirm engagement without requiring user dexterity or eyesight.

Inventive Principle:

Principle #25Self-service

Solution Approach 2:

The cam surface is pre-configured with guide features that begin directing the attachment pin into the correct orientation as soon as insertion begins. This preliminary geometric guidance reduces the alignment task to a simple linear insertion motion, making the system accessible to users with limited dexterity or visual impairment.

Inventive Principle:

Principle #10Preliminary action

4Reliability

If conventional locking systems are used, then connection is achieved, but premature wear of components occurs leading to lock failure

Engineering Contradiction:

Improveconnection securityVSAvoidcomponent lifespan

Core Design Contradiction:

ReliabilityVSDuration of action of stationary object

Solution Approach 1:

The system replaces direct friction-based mechanical contact with cam-based mechanical advantage. The cam surface converts insertion force into controlled rotational engagement and locking force, distributing stresses across larger surface areas and reducing point-contact wear, thereby extending component lifespan while maintaining secure connection.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Data Source

PatentEP4387572B1Prosthetic attachment system and corresponding lock assembly

Publication Date: 2026.04.01 OSSUR ICELAND EHF

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Figure 2A
Figure 2B~2C

AI summary

A prosthetic attachment system (10) and corresponding lock assembly (12) are provided for connecting a distal end of a prosthetic liner (18) to a distal end of a prosthetic socket (16), by combining vacuum suspension and mechanical suspension. An attachment pin (20) extends from a distal end of the prosthetic liner (18). A connector assembly (21) secures to a distal end of the prosthetic socket (16) and is adapted for receiving and locking to the attachment pin (20). A lanyard assembly (15) has a first end secured to the connector assembly (21) and a second end extending outwardly from the distal end of the prosthetic socket (16) and adapted to secure to an exterior surface (E) of the prosthetic socket (16) by an external securing system (14).