Prosthetic Digit Locking Rack Mechanism for Grip Stability
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Solution Overview
Problem
Conventional prosthetic technologies for partial hand amputees struggle to provide effective opposition grasp and efficient object manipulation due to limitations in force output and speed, often requiring substantial gear-down ratios and non-backdriveable gear pairs, which lead to inefficiencies and cumbersome designs.
Innovation Solution
The development of an electronic prosthetic digit with a locking rack mechanism that disengages the geared power drivetrain upon opposition, allowing for quick movement and passive resistance of large forces, thereby optimizing battery capacity and integrating motor, battery, and controls within the digit itself.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If conventional geared power drivetrains are used to provide force output, then gripping force is improved, but speed and efficiency deteriorate due to substantial gear-down ratios
Solution Approach 1:
The system dynamically transitions between two operational modes: a powered mode with engaged gear train for low-speed high-force gripping, and a passive mode with disengaged gear train for high-speed low-force movement. This dynamic reconfiguration allows the prosthetic digit to optimize performance characteristics based on task requirements, achieving both high gripping force and quick movement speeds.
Solution Approach 2:
The drivetrain engagement and disengagement occurs periodically during operation - engaged during gripping phases requiring force, disengaged during movement phases requiring speed. This periodic switching between powered and passive states enables the system to achieve high average speed while maintaining peak force capability when needed.
2Reliability
If non-backdriveable gear pairs are used to prevent reverse motion, then gripping stability is improved, but energy efficiency deteriorates
Solution Approach 1:
The invention extracts the anti-backdrive function from the power train by implementing a separate passive locking mechanism (ratchet and pawl system) that engages only when needed. This allows the powered drivetrain to use efficient backdriveable gear pairs during powered operation, while the passive lock provides grip stability during unpowered phases, eliminating the need for continuously engaged non-backdriveable gears.
Solution Approach 2:
A spring-loaded detent mechanism acts as an intermediary between the powered drivetrain and the passive locking system. This intermediary automatically engages the ratchet lock when opposition force is detected, providing grip stability without requiring the main gear train to be non-backdriveable, thus maintaining energy efficiency during powered operation.
3Adaptability or versatility
If high-power motors and gear trains are integrated within the digit, then functionality is improved, but battery size and weight increase
Solution Approach 1:
The system uses a lightweight motor paired with a passive mechanical locking mechanism, dynamically switching between powered and passive modes. This allows high functionality to be achieved without requiring a large, heavy battery, as the motor only needs to provide power during brief activation periods rather than continuous operation.
Solution Approach 2:
The motor operates periodically rather than continuously - activating briefly to position the digit, then disengaging while the passive lock maintains position. This periodic operation dramatically reduces average power consumption, enabling the use of smaller, lighter batteries while maintaining full functional capability.
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
This solution enables the prosthetic digit to achieve quick flexion speeds and resist significant extension forces, mimicking natural hand movement while minimizing battery size and weight, thus enhancing the prosthetic's functionality and usability in daily tasks.
Implementation Method 1
a spring-loaded detent mechanism that automatically engages a locking pawl with the rack teeth upon opposition
Data Source
AI summary
This disclosure provides systems, apparatuses, and devices for a powered prosthetic digit. The disclosed devices restore prehension in a person with missing fingers or thumb by providing motor-driven extension and flexion, and opposition to forces in the extension direction via a pawl and locking rack ratchet mechanism, thereby allowing an individual to manipulate or stabilize objects. In one embodiment, a digit comprises a base configured to be removably couplable to an anchor, a first segment pivotably coupled to the base, and a second segment removably coupled to the first segment. The first segment comprises a rack with a plurality of rack teeth and a pawl with a nose configured to engage with the rack to prevent pivoting of the first segment in a rotational direction corresponding to extension of the prosthetic digit. The second segment comprises a drive gear operable to pivot the first segment with respect to the base.