Strain Wave Drive Ring Gear Layout for Lightweight Torque Transfer
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional strain wave drives for rotary actuation of flight control surfaces in aircraft are bulky and heavy due to the need for multiple intermeshing gears, and they require built-in compliance to ensure correct load distribution, which increases complexity and cost.
Innovation Solution
A strain wave drive design featuring a straight tubular flex spline and a ring gear assembly with two earth ring gears on either side of an output ring gear, eliminating the need for flanges and compliance in other components, allowing for a compact and lightweight configuration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If conventional involute gears are used to provide high torque ratio, then the required torque can be achieved, but the size and weight of the actuator system increases
Solution Approach 1:
The gear system is segmented into a wave generator, flex spline, and circular spline, replacing the conventional multi-gear involute system. This segmentation allows for a more compact arrangement that achieves the same torque ratio with reduced weight and size.
Solution Approach 2:
The wave generator uses an elliptical (curved) cross-section that deforms the flex spline into a wave pattern, creating variable meshing points with the circular spline. This curved geometry enables compact high-ratio gearing without the bulk of conventional straight-toothed gears.
2Weight of stationary object
If strain wave gearing is used to reduce size and weight, then compactness is improved, but built-in compliance is required which increases complexity and cost
Solution Approach 1:
Compliance is localized specifically to the flex spline component rather than requiring built-in compliance throughout the entire drive system. The flex spline's flexible material and cross-section provide the necessary elasticity locally at the meshing interface, while other components remain rigid and simple.
Solution Approach 2:
The material properties and cross-sectional dimensions of the flex spline are optimized to provide the required compliance. By changing the parameters of the flex spline (material elasticity, wall thickness, cross-section shape), the system achieves correct load distribution and tooth engagement without adding complexity to other components.
3Reliability
If built-in compliance is added to ensure correct load distribution, then tooth engagement is improved, but manufacturing cost and complexity increases
Solution Approach 1:
The flex spline is designed as a thin-walled flexible tube with a specific cross-section that allows it to deform elastically under load. This flexible shell structure naturally provides the compliance needed for correct tooth engagement and load distribution, simplifying manufacturing compared to complex compliant mechanisms.
Solution Approach 2:
The flex spline utilizes composite construction or material selection that combines rigidity where needed with flexibility where required. This allows the component to provide necessary compliance for reliable tooth engagement while maintaining structural integrity and ease of manufacture.
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
This design reduces the size and weight of the actuator system, eliminates coning effects, and simplifies manufacturing and assembly, while maintaining the compactness and reliability of strain wave gearing.
Implementation Method 1
the flex spline will only engage with the inner teeth of the outer ring at the major axes of the ellipse
Data Source
Figure 1A~1B
Figure 2~3
Figure 4
AI summary
A strain wave drive comprising: an elliptical wave generator shaft (100) rotatable about an axis (X); a flexible tubular flex spline (500) mounted around the wave generator shaft; a ring gear assembly mounted around the flex spline, the ring gear assembly comprising an output ring gear (200) having a circular inner periphery and being sandwiched between two earth ring gears (300, 400) each having a circular inner periphery; wherein the flex spline has a first number of radially outwardly extending teeth around its outer periphery; and wherein each earth ring gear has the first number of radially inwardly extending teeth to engage with the teeth of the flex spline; and wherein the output ring gear has a second number of radially inwardly extending teeth, wherein the second number is greater than the first number, such that as the wave generator shaft rotates, it causes the flex spline to take up the elliptical form of the wave generator shaft and the teeth of the flex spline engage with teeth of the output ring gear at the major diameter of the ellipse, causing the output ring gear to rotate.