Compound Harmonic Drive With Nested Flexible Ring Gears
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Solution Overview
Problem
Conventional rotary actuators with planetary gear drives are too large and heavy for thin-winged aircraft designs, as reducing gear size to fit within the wing cross-section compromises torque-to-weight ratio and increases manufacturing costs.
Innovation Solution
A compound harmonic drive system with a wave generator, bearing element, and integral internal ring gears that rotate together, allowing for a high reduction ratio and torque-to-weight ratio while maintaining a compact size, using a flexible material and unique gear configurations to manage stress and deformation.
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 employs nested gearing where a first planetary gear set is positioned within the outer gear of a second planetary gear set. This nesting allows multiple stages of reduction in a single compact package, achieving high reduction ratios without proportionally increasing the overall size or weight of the gear drive.
Solution Approach 2:
The patent combines multiple planetary gear stages into a single integrated structure where the inner gear of one stage serves as the outer gear of another stage. This merging of components reduces the total number of separate parts, simplifies the overall structure, and decreases both size and weight while maintaining high torque-to-weight ratio.
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 size of the teeth must also be decreased which lowers torque-to-weight ratio and increases manufacturing tolerances and cost
Solution Approach 1:
By nesting planetary gear stages, the patent achieves high reduction ratios in a compact diameter suitable for thin-winged aircraft. The nested configuration allows multiple gear meshes within a single planetary carrier, maximizing the use of available radial space without requiring proportionally smaller teeth.
Solution Approach 2:
The patent utilizes the axial dimension by stacking planetary gear stages along the axis rather than simply reducing radial dimensions. This allows the gear drive to fit within the wing cross-section while maintaining adequate tooth sizes through efficient three-dimensional space utilization.
3Productivity
If the size of the teeth is decreased to maintain high reduction ratio in smaller gear drive, then the reduction ratio is maintained, but the torque-to-weight ratio is lowered and manufacturing tolerances and cost increase
Solution Approach 1:
The nested planetary gear configuration allows the patent to achieve high reduction ratios through multiple stages rather than relying on a single stage with excessively small teeth. Each stage uses adequately sized teeth while the cumulative effect of multiple stages provides the required high reduction ratio, maintaining torque-to-weight ratio and reducing manufacturing complexity.
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 compound harmonic drive effectively steps down rotational speed and increases torque, providing a compact, lightweight solution for aircraft actuators that maintains performance comparable to conventional planetary gear drives.
Implementation Method 1
a compound flex spline comprising: a first internal ring gear and a second internal ring gear, wherein the first and second internal ring gears are integral and comprise a radially-inward extending rib... the first internal ring gear and the second internal ring gear are composed of a flexible material... rotate in response to interaction between the wave generator, the first internal ring gear, the second internal ring gear
Implementation Method 2
a bearing element radially interposed between the harmonic wave generator and the first internal ring gear and the second internal ring gear
Data Source
Figure 1
Figure 2
Figure 3~4
AI summary
A compound harmonic drive including: a first internal ring gear (130); a second internal ring gear (140), the second internal ring gear (140) being coaxial to the first internal ring gear (130); a first external gear (150) located within the first internal ring gear (130) and coaxial to the first internal ring gear (130), the first external gear meshes with the first internal ring gear (130); and a second external gear (170) located within the second internal ring gear (140) and coaxial to the second internal ring gear (140), the second external gear (170) meshes with the second internal ring gear (140). The first internal ring gear (130) and the second internal ring gear (140) are composed of a flexible material.