Mechanical Finger Screw Nut Assembly for Compact Prosthetic Design
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Solution Overview
Problem
Existing prosthetic fingers face challenges in achieving a natural appearance, high strength, light weight, reliability, adequate speed, and reduced complexity, particularly due to the small space constraints within the finger, which limits market acceptance and increases costs.
Innovation Solution
A mechanical finger design featuring a knuckle, proximal element, screw nut boss, force generator, and elastic element, with a screw nut assembly that allows for free longitudinal movement while preventing rotation, enabling a shorter build height and reduced part count, thus improving fit and affordability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a traditional force generator and drive mechanism are placed inside the prosthetic finger, then the finger can achieve high strength and reliability, but the build height extends beyond the natural envelope of the finger, reducing market acceptance
Solution Approach 1:
The screw nut assembly is nested within the proximal element cavity, with the left and right pivot bosses extending through slots in the cavity wall. This nesting arrangement allows the force generator and drive mechanism to be contained within the natural envelope of the finger, reducing the build height while maintaining structural strength and reliability.
2Reliability
If a complex drive mechanism with multiple components is used, then the prosthetic finger can achieve reliable operation, but the device complexity and production cost increase
Solution Approach 1:
The left and right pivot bosses are merged into a single screw nut assembly that moves as one unit within the proximal element cavity. This merging reduces the number of separate components and simplifies the overall mechanism while maintaining reliable operation through the coordinated movement of the combined structure.
Solution Approach 2:
The screw nut assembly serves multiple functions simultaneously: it acts as both the driving mechanism for finger movement and the structural connection between the proximal and distal elements. The left and right pivot bosses provide both rotational guidance and longitudinal movement constraints, eliminating the need for separate guidance mechanisms.
3Manufacturing precision
If the screw nut assembly is constrained to prevent rotation, then longitudinal movement is controlled, but the assembly may become stuck or experience increased friction
Solution Approach 1:
The guide slots in the proximal element cavity provide localized guidance only in the longitudinal direction, while allowing free rotation of the screw nut assembly. This local quality approach ensures precise control of longitudinal movement without imposing rotational constraints that would cause sticking or increased friction.
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 enhances market acceptance by providing a prosthetic finger that is more aesthetically and functionally suitable for a wider range of users, including females and teenagers, while reducing production costs through simplified components and improved functionality.
Implementation Method 1
an axial screw drive... as the screw nut assembly is moved longitudinally in the proximal element cavity by a an axial screw drive
Implementation Method 2
The left and right pivot boss are each sized to provide free longitudinal movement within its respective left guide and right slots so as to prevent the screw nut assembly from rotating in the proximal element cavity
Data Source
Figure 1a~1b
Figure 1c
Figure 2a~2b
AI summary
The invention relates to a mechanical finger comprising, a knuckle, a proximal element, a rod, a motor, a motor driven screw and a distal element. The knuckle has a first and second pivot. The proximal element knuckle end is coupled to the first pivot. The proximal element also has a third pivot at a variable longitudinal distance from the first pivot. The rod has a near end pivotally coupled to the second pivot and a far end pivotally coupled to the third pivot. A motor is coupled to and referenced to the proximal element. A screw is driven to change the distance between the third pivot and the first pivot in response to a command from a controller to the motor. A distal element is pivotally coupled to the proximal element. The distal element rotates with respect to the proximal element in response to a change in the variable distance between the third pivot and the first pivot.