Joined Flex Spline Assembly for Low-Fatigue Compound Harmonic Drives
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing compound harmonic drives used in aircraft wing structures face challenges in reducing stress and fatigue, particularly in thin wing designs where traditional actuators and gear systems are inadequate for efficient gear reduction.
Innovation Solution
A compound harmonic drive system incorporating a flexible ring gear with radially-extending teeth, a harmonic wave generator, and flexible gears attached via brazed joints, which utilizes a bearing element and conductive windings to achieve efficient rotation and stress distribution, allowing for a high gear ratio and torque-to-weight ratio while minimizing fatigue.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If traditional actuators and gear systems are used in thin wing designs, then the structure can support standard components, but the gear reduction efficiency is inadequate and stress concentration occurs
Solution Approach 1:
The flex spline is segmented into multiple modular units (first flex spline unit, second flex spline unit, etc.) that can be assembled together. Each unit contains its own set of flexible gears and ring gears, distributing the mechanical loads across multiple independent segments rather than concentrating stress in a single large component, thereby improving both gear reduction efficiency and stress resistance
Solution Approach 2:
The patent employs flexible gears with radially-extending teeth that can elastically deform during operation. These flexible components absorb and distribute cyclic stresses through controlled deformation, reducing fatigue accumulation compared to rigid traditional gear systems while maintaining high gear reduction ratios
2Power
If a high gear ratio is achieved through compound harmonic drive, then torque-to-weight ratio improves, but device complexity increases
Solution Approach 1:
Multiple flexible gear units are nested concentrically around a central harmonic wave generator. The first flexible gear, second flexible gear, and additional units are arranged in nested configurations, sharing common rotational axes and space. This nesting approach achieves compound gear ratios through multiple stages without proportionally increasing the overall device footprint or weight
Solution Approach 2:
The harmonic wave generator serves as a universal driving element for all flexible gear units simultaneously. A single wave generator can engage multiple flexible gears with different tooth counts, providing multiple gear reduction ratios from one motor shaft, thereby reducing the need for separate drive systems for each gear stage
3Reliability
If flexible gears with radially-extending teeth are used, then stress distribution improves, but manufacturing precision requirements increase
Solution Approach 1:
The flexible gears utilize elastic deformation as a functional parameter, allowing the tooth profiles to flex and adapt during meshing. This elasticity compensates for minor manufacturing variations in tooth geometry and alignment, maintaining reliable stress distribution even when manufacturing precision is limited. The material's elastic properties become the primary mechanism for ensuring uniform stress distribution
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 system effectively reduces stress and fatigue in aircraft wing structures by distributing loads through the flexible components, enabling efficient gear reduction and maintaining a high torque-to-weight ratio, suitable for space-limited applications like thin wing aircraft control surfaces.
Implementation Method 1
The flexible ring, the first flexible gear, and the second flexible gear rotate in response to interaction between the harmonic wave generator, the flexible ring, the first flexible gear, the second flexible gear, the first ring gear, and the second ring gear when the harmonic wave generator rotates
Implementation Method 2
a bearing element radially interposed between the rotor element and the flexible ring
Implementation Method 3
the first flexible gear and second flexible gear are fixedly attached to the outer surface of the flexible ring by a brazed joint
Data Source
Figure 1
Figure 2
Figure 3~4
AI summary
A compound harmonic drive (10) including: a flexible ring (43) having an inner surface (43a) and an outer surface (43b); a first flexible gear (40a) disposed around the outer surface (43b) of the flexible ring (43) and coaxial to the flexible ring (43); a second flexible gear (40b) disposed around the outer surface of the flexible ring (43) and coaxial to the flexible ring (43); a first ring gear (20a) that meshes with the first flexible gear (40a) and is coaxial to the first flexible gear (40a); and a second ring gear (20b) that meshes with the second flexible gear (40b) and is coaxial to the second flexible gear (40b). The first flexible gear (40a) and second flexible gear (40b) are fixedly attached to the outer surface (43b) of the flexible ring (43).