Powered Prosthetic Elbow Gearbox for Stable Forearm Positioning
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Solution Overview
Problem
Prosthetic elbows without a powered gearbox mechanism struggle to maintain the forearm in varying angular positions due to gravity, causing the forearm to fall downward under its own weight, limiting the user's ability to control the arm effectively.
Innovation Solution
A powered gearbox mechanism is integrated into the prosthetic elbow, comprising a motor, planetary frictional drive, strain wave gear set, and optional brake mechanism, which converts motor output into rotation of the housing structure relative to the fixed member structure, allowing the forearm to move to various angular positions while balancing the moment force.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a powered gearbox mechanism is integrated into the prosthetic elbow, then the ability to maintain the forearm in varying angular positions is improved, but the device complexity increases
Solution Approach 1:
The patent employs nested gear mechanisms where a strain wave gear is integrated within a planetary frictional drive system. The strain wave gear's flexible spline is positioned inside the planetary gear assembly, creating a compact nested structure that achieves high reduction ratios while maintaining manageable complexity. This nesting allows the system to maintain forearm position reliably through combined mechanical advantage of both gear systems.
Solution Approach 2:
The patent merges two different gear mechanisms (planetary frictional drive and strain wave gear) into a single integrated powered gearbox mechanism. The planetary drive provides initial torque multiplication while the strain wave gear provides additional reduction and positioning precision. This combination of merging distinct mechanical systems resolves the contradiction by achieving reliable position maintenance through synergistic mechanical advantage while consolidating functions into one unified mechanism.
2Force
If the mass of the prosthetic arm is distributed more proximally, then the moment force on the residual limb is reduced, but the device complexity increases
Solution Approach 1:
The patent uses the gearbox mechanism and housing structure as a counterweight system positioned proximal to the user's body. By concentrating mass in the upper arm portion near the elbow joint, the system creates a counterbalancing effect that reduces the moment force acting on the residual limb. The heavy gearbox assembly acts as an artificial counterweight that offsets the gravitational moment of the forearm and hand, thereby reducing the effort required by the user.
3Manufacturing precision
If a strain wave gear set is used in the powered gearbox mechanism, then the manufacturing precision is improved, but the device complexity increases
Solution Approach 1:
The strain wave gear set is nested within the planetary frictional drive assembly, with the flexible spline positioned inside the planetary gear structure. This nested configuration allows the precision positioning capability of the strain wave gear to be integrated without significantly increasing the external dimensions or overall complexity of the mechanism. The compact nesting enables high manufacturing precision in angular positioning while maintaining a manageable device structure.
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 powered gearbox mechanism enables the user to maintain the forearm in desired positions, reduces noise, and distributes the mass more proximally, making the prosthetic feel lighter and more comfortable by minimizing the moment force on the residual limb.
Implementation Method 1
a planetary frictional drive connected to a motor shaft of the motor... The planetary frictional drive includes a sun element connected to the motor shaft, a ring element fixed to the housing structure, and a set of planet elements for driving the input of the strain wave gear set
Implementation Method 2
a strain wave gear set having an input driven by the frictional drive and an output attached to the fixed member structure... The input of the strain wave gear set may be a wave generator. The output of the strain wave gear may be a flex spline
Data Source
AI summary
A prosthetic elbow includes a fixed member structure and a powered gearbox mechanism housed in a housing structure for rotating the forearm portion to varying angular positions. The powered gearbox mechanism includes a motor attached to the housing structure, a planetary frictional drive connected to a motor shaft of the motor and the housing structure, and a strain wave gear set having an input driven by the planetary fictional drive and an output attached to the fixed member structure, where the powered gearbox mechanism is configured to convert an output of the motor into a rotation of the housing structure relative to the fixed member structure, thereby causing the rotation of the forearm portion to varying angular positions relative to the upper arm. The fixed member structure and the housing structure each are connected to one of a forearm portion and an upper arm portion and rotatable relative to one another about an axis of rotation of the forearm portion.