Prosthetic Digit Ratcheting Lock for Opposition Grasp
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Solution Overview
Problem
Conventional prosthetic solutions for partial hand amputations, particularly those involving the transmetacarpal region, struggle to provide effective opposition grasp and are often restricted in their use environments due to weak forces and sensitive componentry.
Innovation Solution
A three-segment prosthetic digit with a spring-loaded pawl and locking rack ratchet mechanism, allowing for adjustable opposition and robust grasping capabilities, is designed to replace a finger or thumb and provide natural movement patterns.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If conventional passive prostheses are used, then the device is simple and robust, but the opposition grasp force is weak and the device is restricted in use environments
Solution Approach 1:
The prosthetic digit employs a spring-loaded pawl mechanism that dynamically adjusts the engagement with rack teeth based on load conditions. The spring allows the pawl to flex and maintain contact under varying forces, enabling the mechanism to transition from a static rigid structure to a dynamic system that adapts to different grasp forces and environmental conditions.
Solution Approach 2:
The prosthetic digit is divided into multiple segments (phalanges) connected by joints, each capable of independent movement. This segmentation allows for more complex opposition motions and grasp patterns while maintaining mechanical simplicity through modular construction, resolving the contradiction between force capability and device complexity.
2Adaptability or versatility
If adjustable opposition systems are implemented, then the prosthetic can adapt to different postures, but the mechanism becomes more complex and sensitive
Solution Approach 1:
The spring-loaded pawl mechanism is designed to automatically engage and disengage from the rack teeth based on the natural motion and loading of the prosthetic digit. This self-service mechanism eliminates the need for external actuators or complex control systems to maintain adjustability, thereby improving reliability while preserving adaptability to different postures.
Solution Approach 2:
The mechanism uses simple, durable components such as spring steel for the pawl and hardened rack teeth that can withstand repeated engagement cycles. These robust, easily replaceable parts ensure reliable operation in demanding environments without requiring complex maintenance or adjustment systems.
3Strength
If a ratchet mechanism is used to lock positions, then the load-bearing capacity increases, but the device complexity increases
Solution Approach 1:
The locking function is merged with the existing joint structure by integrating the rack and pawl mechanism directly into the phalange connections. This eliminates the need for separate locking devices while providing robust load-bearing capacity through the interlocking teeth, thereby increasing strength without proportionally increasing device complexity.
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 prosthetic digit achieves robust and adjustable opposition, enabling effective object manipulation and stabilization, with enhanced load-bearing capacity and reduced deflection, thus improving the functionality and usability of partial hand prosthetics.
Implementation Method 1
a spring-loaded pawl and locking rack ratchet mechanism
Data Source
Figure 1A
Figure 1B
Figure 2A
AI summary
This disclosure provides systems, apparatuses, and devices for a prosthetic digit usable with persons with amputations at or proximal to the metacarpophalangeal joint. The device restores prehension in a person with missing fingers or thumb by providing opposition to forces in the extension direction via a spring-loaded pawl and locking rack ratchet mechanism, thereby allowing an individual to manipulate or stabilize objects. The digit may be spring-loaded in the extension direction by a torsion spring or other biasing member. The pawl may be automatically disengaged from the rack when the digit reaches full flexion, and the full flexion disengage stop may be adjustable. The pawl may be automatically engaged with the rack when the digit reaches full extension, and the extension stop may be adjustable. The pawl may contain a lateral feature that creates interference with the anchoring linkage under load and limits deflection of the structure.