Prosthetic Thumb Actuation With Switchable Joint Locking
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Solution Overview
Problem
Prosthetic thumbs in existing prosthetic hands have a limited range of motion, making it difficult for users to form desired positions such as a fist or pinch objects, and dual motor actuation systems increase weight and bulk, compromising watertightness.
Innovation Solution
A prosthetic hand design with a proximal thumb part and distal thumb part, each rotating about separate axes, using a rotary actuator and locking mechanism to switch between configurations, allowing sequential movement and improved robustness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If dual motor actuation systems are used to rotate the prosthetic thumb about two different axes of rotation, then the range of motion of the prosthetic thumb is improved, but the weight and bulk of the prosthetic hand increases
Solution Approach 1:
The thumb is divided into two separate rotatable parts: a proximal thumb part that rotates about a first axis of rotation relative to the palm, and a distal thumb part that rotates about a second axis of rotation relative to the proximal thumb part. This segmentation allows each part to be controlled independently to achieve complex thumb positions and gestures
Solution Approach 2:
The locking mechanism dynamically switches between locked and unlocked states based on the desired thumb configuration. When the locking mechanism is in the first state, it locks the distal thumb part relative to the proximal thumb part, allowing rotation about the first axis. When in the second state, it locks the proximal thumb part relative to the palm, allowing rotation about the second axis. This dynamic locking enables a single actuator to control two rotational degrees of freedom
2Adaptability or versatility
If dual motor actuation systems are used to rotate the prosthetic thumb about two different axes of rotation, then the range of motion of the prosthetic thumb is improved, but the bulk of the prosthetic hand increases
Solution Approach 1:
The patent combines the functions of two separate motors into a single rotary actuator by using a locking mechanism that sequentially locks different parts of the thumb to the actuator. This merging reduces the bulk associated with housing two separate motors while maintaining the capability for dual-axis rotation
Solution Approach 2:
The locking mechanism dynamically switches between locked and unlocked states based on the desired thumb configuration. When the locking mechanism is in the first state, it locks the distal thumb part relative to the proximal thumb part, allowing rotation about the first axis. When in the second state, it locks the proximal thumb part relative to the palm, allowing rotation about the second axis. This dynamic locking enables a single actuator to control two rotational degrees of freedom
3Volume of moving object
If at least one of the dual-motors is disposed adjacent to the user's wrist, then the bulk of the prosthetic hand is reduced, but electrical cables must be threaded through the prosthetic hand which compromises watertightness
Solution Approach 1:
The patent combines the functions of two separate motors into a single rotary actuator, which can be disposed adjacent to the user's wrist. This reduces the bulk of the prosthetic hand while minimizing the need for electrical cables to thread through the hand, as only one actuator is required
Data Source
Figure 1a
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Figure 2a
AI summary
According to an aspect, there is provided a prosthetic hand comprising: a palm part; a proximal thumb part coupled to the palm part to form a first joint with a first axis of rotation, wherein the proximal thumb part is configured to rotate about the first axis of rotation; a distal thumb part coupled to the proximal thumb part to form a second joint with a second axis of rotation, wherein the distal thumb part is configured to rotate about the second axis of rotation; a rotary actuator configured to rotate the proximal thumb part and distal thumb part about the first axis of rotation and the second axis of rotation respectively; and a locking mechanism having a first configuration and a second configuration, the locking mechanism being configured such that: in the first configuration, the distal thumb part is rotatably locked relative to the proximal thumb part about the second axis of rotation such that the rotary actuator rotates both the distal thumb part and proximal thumb part about the first axis of rotation, and in the second configuration, the proximal thumb part is rotatably locked relative to the palm part about the first axis of rotation such that the rotary actuator rotates the distal thumb part relative to the proximal thumb part about the second axis of rotation.