Prosthetic Digit Actuation Using Linear Expansion and Worm Wheel
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Solution Overview
Problem
Existing prosthetic digits do not adequately mimic natural fingers, resulting in incomplete restoration of functionality for amputees.
Innovation Solution
The development of prosthetic digits with three articulating segments (proximal, middle, and distal) articulated by an actuator and mechanical links, allowing for multiple degrees of freedom and enhanced gripping capabilities, utilizing a compact actuator that expands linearly to rotate the digit, and incorporating a spring-biased worm wheel transmission for manual mode protection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If multiple actuators are used for each digit segment, then articulation precision is improved, but device complexity and weight increase
Solution Approach 1:
The digit is divided into three articulating segments (proximal, middle, and distal) that can rotate independently relative to each other. This segmentation allows each segment to contribute to the overall articulation, achieving natural finger-like movement with a single actuator rather than requiring multiple actuators for each segment.
Solution Approach 2:
A single actuator is designed to control the rotation of multiple digit segments through a shared mechanical linkage system. The actuator performs the universal function of controlling articulation for the entire digit, eliminating the need for separate actuators for each segment and reducing overall device complexity.
2Weight of moving object
If a compact actuator is used, then space and weight are reduced, but power output capability is limited
Solution Approach 1:
A mechanical linkage system acts as an intermediary between the compact actuator and the digit segments. The linkage multiplies the force and motion from the small actuator, enabling it to produce sufficient power for articulation despite the actuator's compact size and limited direct power output.
Solution Approach 2:
The actuator is designed with a nested structure where components are arranged concentrically or in compact configurations. This nesting reduces the actuator's overall size and weight while maintaining its power output capability, allowing it to fit within the constrained space of the prosthetic digit.
3Ease of operation
If manual rotation is allowed, then ease of operation is improved, but reliability decreases due to potential damage from external forces
Solution Approach 1:
A spring-biased worm wheel transmission is incorporated to provide preliminary protection against harmful external forces. The worm wheel's inherent back-driving resistance and the spring bias create a mechanical barrier that prevents unwanted rotation from external forces while still allowing intentional manual rotation when needed.
Solution Approach 2:
The transmission system is designed to be dynamic, allowing manual rotation in the forward direction while automatically resisting reverse rotation from external forces. The spring-biased worm wheel engages and disengages based on the direction of applied force, providing ease of operation for intentional movement while protecting against unintentional damage.
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 solution provides enhanced gripping functionality, space, weight, and power savings by using a single actuator, mimicking natural finger movement, and protecting against external forces, thereby restoring dexterity to amputees.
Implementation Method 1
A spring-biased worm wheel transmission provides a manual mode for rotation of the digit and prevents damage due to rotation induced by external forces acting on the digit
Implementation Method 2
A spring-biased worm wheel transmission provides a manual mode for rotation of the digit and prevents damage due to rotation induced by external forces acting on the digit
Implementation Method 3
A motor may rotate a leadscrew. The leadscrew may engage and move axially a housing or other member. Axial movement of the housing or member causes the proximal digit segment to pivot and thus the digit to articulate
Data Source
Figure 1A~1B
Figure 2A~2B
Figure 3A~3B
AI summary
Features for prosthetic digits are described. The digits mimic natural fingers by having multiple articulating segments, for example three, that can rotate varying amounts. Actuation systems for the prosthetic digits may include a compact actuator that expands linearly to rotate the digit. Each digit may have its own actuator, which may be housed in the digit and/or the palm. A motor may rotate a leadscrew. The leadscrew may engage and move axially a housing or other member. Axial movement of the housing or member causes the proximal digit segment to pivot and thus the digit to articulate. In some embodiments, the leadscrew may rotate a wheel to actuate a tendon. An actuation tendon may cause a closing rotation of the digit segments, and a return tendon may cause an opening rotation.