Concentric Harmonic Drive for Thin-Wing Aircraft Actuators
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Solution Overview
Problem
Conventional rotary actuators with planetary gear drives face challenges in thin-winged aircraft designs due to increased size, weight, and complexity, making it difficult to fit them within reduced wing cross-sections while maintaining a high torque-to-weight ratio.
Innovation Solution
A harmonic drive assembly utilizing a first and second flexible gear with ring gears and a wave generator to achieve a compact, high reduction ratio and torque-to-weight ratio, replacing the conventional planetary gear drive.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a conventional planetary gear drive with multiple stages is used to increase reduction ratio and torque-to-weight ratio, then the torque-to-weight ratio is improved, but the size, weight, and complexity of the gear drive increase
Solution Approach 1:
The patent divides the single flexible gear into multiple concentric flexible gears (first flexible gear, second flexible gear, third flexible gear) that can be independently configured. Each flexible gear engages with its own ring gear, allowing the system to achieve high reduction ratios through multiple concentric stages rather than sequential planetary stages, thereby reducing overall complexity while maintaining torque multiplication.
Solution Approach 2:
The patent implements a nested configuration where multiple flexible gears are arranged concentrically within each other. The first flexible gear is positioned at the center, with the second and third flexible gears nested around it in successive concentric layers. This nesting allows multiple gear reductions to occur within a compact radial space, reducing the overall size and complexity compared to traditional multi-stage planetary gears.
2Volume of moving object
If the diameter of the planetary gear drive is decreased to fit within reduced wing cross-section, then the size is reduced, but the tooth size must also be decreased which lowers torque-to-weight ratio and increases manufacturing tolerances
Solution Approach 1:
The patent transitions from a single-dimension planetary gear arrangement to a multi-dimensional concentric configuration. By stacking multiple flexible gears and ring gears in concentric layers along the radial dimension, the system achieves high reduction ratios and maintains large effective tooth sizes within a compact overall diameter, fitting within reduced wing cross-sections without sacrificing torque capacity.
Solution Approach 2:
The patent utilizes flexible gears with thin, elastic tooth structures that can deform elastically during engagement. This flexibility allows the gears to maintain large effective tooth sizes for high torque capacity while the overall gear assembly remains compact. The elastic deformation enables smooth engagement and disengagement, reducing the need for large clearance tolerances.
3Productivity
If the tooth size is decreased to maintain high reduction ratio in reduced diameter gear drive, then the reduction ratio is maintained, but the torque-to-weight ratio is lowered and manufacturing tolerances increase
Solution Approach 1:
The patent employs flexible gear materials with composite-like properties, combining elasticity with structural integrity. The flexible gears are made from materials that can be molded into precise tooth profiles while maintaining elastic flexibility. This allows for tight manufacturing tolerances to be achieved through molding processes rather than precision machining, reducing cost while maintaining high reduction ratios with adequately sized teeth.
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 harmonic drive assembly provides a compact, high torque-to-weight ratio and reduction ratio, enabling efficient conversion of high-speed input from an electric motor to a manageable output speed and torque, suitable for thin-winged aircraft applications.
Implementation Method 1
a first flexible gear and a second flexible gear... A wave generator can rotate both the first flexible gear and the second flexible gear
Data Source
Figure 1
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Figure 3
AI summary
A harmonic drive (30) includes a first flexible gear (20) and a second flexible gear (22) disposed around the first flexible gear (20) and coaxial with the first flexible gear (20). A first ring gear (24-1) meshes with the first flexible gear (20), and a second ring gear (24-2) meshes with the second flexible gear (22).