Compact Wrist Rotator and Flexor Mechanism for Prosthetic Hands

Resolve Bottlenecks,
Find Innovative SolutionsGenerate Solutions

Solution Overview

Problem

Prosthetic wrist devices are often excluded from prosthetic hands due to their bulkiness and weight, which reduces their adoption, despite studies showing that they can enhance upper limb functionality by providing an additional degree of freedom.

Innovation Solution

A compact wrist rotator and flexor mechanism that includes a rotator motor with an inverted gearbox and worm gear system, combined with a lead screw actuator, allowing for non-backdrivable rotation and flexion, thereby reducing size and weight while maintaining torque and preventing unintentional counter-rotation.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If a wrist device is incorporated into a prosthesis to provide additional degree of freedom, then functionality is improved, but size and weight increase

Engineering Contradiction:

ImprovefunctionalityVSAvoidweight

Core Design Contradiction:

Adaptability or versatilityVSWeight of moving object

Solution Approach 1:

The patent combines the rotator motor and flexor motor into a single integrated wrist device assembly, merging multiple functions (rotation and flexion) into one compact unit. This consolidation reduces overall size and weight compared to separate devices, while maintaining both degrees of freedom for enhanced functionality.

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The patent employs a nested configuration where the lead screw actuator is positioned within the housing of the rotator motor assembly, and the flexor motor is integrated into the same structural envelope. This nesting arrangement maximizes space utilization and minimizes the overall footprint and weight of the wrist device.

Inventive Principle:

Principle #7Nested doll (Nesting)

2Adaptability or versatility

If a wrist device is incorporated into a prosthesis to provide additional degree of freedom, then functionality is improved, but device size increases

Engineering Contradiction:

ImprovefunctionalityVSAvoidsize

Core Design Contradiction:

Adaptability or versatilityVSVolume of moving object

Solution Approach 1:

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The patent utilizes a three-dimensional spatial arrangement where the rotator motor, flexor motor, and lead screw actuator are positioned in different spatial dimensions and orientations. This allows efficient packing of components within a compact volume, reducing the overall device size while maintaining full functionality.

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

3Weight of moving object

If a compact design is used to reduce size and weight, then device appeal is improved, but torque capability may be reduced

Engineering Contradiction:

ImproveweightVSAvoidtorque

Core Design Contradiction:

Weight of moving objectVSForce

Solution Approach 1:

The patent replaces traditional direct-drive motor configurations with a lead screw actuator system for the flexor function. This mechanical substitution provides high torque multiplication through the lead screw mechanism, enabling compact motor sizing while maintaining sufficient torque output for wrist flexion against gravitational and resistive forces.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The patent selects motor parameters (torque, speed, gear ratios) specifically optimized for the compact wrist device application. The rotator motor and flexor motor are chosen with torque characteristics matched to the reduced moment arms of the compact design, ensuring adequate torque capability despite the smaller size and weight.

Inventive Principle:

Principle #35Parameter changes

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 compact design increases the likelihood of the prosthetic wrist device being incorporated into a prosthesis, enhancing user functionality and usability by providing two degrees of freedom with reduced size and weight, making it more appealing for regular use.

Implementation Method 1

A compact wrist rotator and flexor mechanism that includes a rotator motor with an inverted gearbox and worm gear system, combined with a lead screw actuator

Methodology Applied

Scientific EffectLead screw mechanism: Screw

Implementation Method 2

worm gear system, allowing for non-backdrivable rotation and flexion, thereby reducing size and weight while maintaining torque and preventing unintentional counter-rotation

Methodology Applied

Scientific EffectFriction: Friction

Data Source

PatentUS11612504B2Compact wrist rotator and flexor

Publication Date: 2023.03.28 REHABILITATION INST OF CHICAGO D B A SHIRLEY RYAN ABILITYLAB

AI summary

The present disclosure is directed to a compact wrist rotator and flexor mechanism for use with a prosthetic hand. The wrist rotator and flexor uses a set of motors to provide a driven mechanism having two degrees of freedom, a wrist rotation and a wrist flexion. The rotator uses a motor with an inverted shaft gearbox combined with a worm gear and a face gear transmission to generate continuous and non-backdrivable rotation. The rotator is integrated into a flexor that uses a lead screw acting as a linear actuator to provide strong non-backdrivable flexion and extension. Due to the arrangement of the drives, the resulting wrist rotator and flexor mechanism has a low and compact profile.