Flex Spline Geometry for Compact High-Torque Strain Wave Drives
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Solution Overview
Problem
Conventional strain wave drives for rotary actuation of flight control surfaces in aircraft require large and heavy gear systems due to the need for high torque and compactness, and existing flex splines add complexity and cost with built-in compliance for load distribution, compromising size, weight, and manufacturing efficiency.
Innovation Solution
A straight tubular flex spline with sections of changed geometry, such as perforations, thinner sections, or corrugations, is used to provide compliance and torsional stiffness, allowing for reduced size and weight while maintaining torque and deformation capability, without compromising design space, manufacturing, or assembly costs.
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 significantly
Solution Approach 1:
The patent replaces the conventional involute gear mechanical system with a strain wave drive system that uses elastic deformation of a flex spline instead of rigid toothed gears. This substitution achieves the same torque multiplication function through elastic compliance and wave propagation, resulting in a more compact and lighter actuator design while maintaining the required torque ratio
2Reliability
If built-in compliance is added to flex spline to ensure correct load distribution, then tooth engagement is improved, but the complexity and manufacturing cost increase
Solution Approach 1:
The patent applies local quality by providing compliance features only at specific locations where needed - namely at the tooth root regions - rather than making the entire flex spline compliant. This localized approach ensures correct load distribution and tooth engagement while maintaining simplicity in the overall design and reducing manufacturing complexity compared to fully compliant structures
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 solution enables a compact, lightweight, and cost-effective strain wave drive with improved flexibility and torsional stiffness, addressing the issues of uneven loading and coning effects, while maintaining performance and reliability.
Implementation Method 1
a flexible tubular body having a first open end and a second open end; a first set of radially outwardly extending teeth around its outer periphery at the first open end; a second set of radially outwardly extending teeth around its outer periphery at the second open end; and a third set of radially inwardly outwardly teeth located axially between the first and the second sets of teeth
Implementation Method 2
A strain wave gear system includes a wave generator which is in the form of an elliptical shaft and a compliant ball bearing in which the elliptical shaft rotates
Data Source
AI summary
A flex spline for a strain wave drive. The flex spline includes: a flexible tubular body having a first open end and a second open end; a first set of radially outwardly extending teeth around its outer periphery at the first open end; a second set of radially outwardly extending teeth around its outer periphery at the second open end; and a third set of radially inwardly outwardly teeth located axially between the first and the second sets of teeth. The body also includes one or more sections of changed geometry located between the first and second sets of teeth and/or the second and third sets of teeth, the sections of changed geometry being provided with a geometric feature in the flex spline body that is not present in the remainder of the flex spline body.