Strain Wave Drive With Barrel-Profiled Flex Spline Teeth
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Solution Overview
Problem
Conventional strain wave drives for rotary actuation in aircraft require additional components for compliance, increasing cost, complexity, size, and weight due to uneven load distribution and coning effects in the flex spline.
Innovation Solution
The strain wave drive incorporates compliant design features by modifying the shape of bearing rollers and/or flex spline teeth to a longitudinal barrel profile, providing uniform stress distribution and reducing interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional strain wave drives use standard cylindrical bearing rollers and straight teeth, then the structure is simple, but uneven load distribution and coning effects occur in the flex spline, requiring additional compliance components that increase size, weight, and complexity
Solution Approach 1:
The bearing rollers are given a barrel shape with curved contact surfaces instead of cylindrical shapes, and the flex spline teeth are given a longitudinal barrel profile instead of straight profiles. This local modification of geometry at the contact interfaces creates compliant behavior that ensures uniform load distribution across the tooth contacts, eliminating the need for additional compliance components.
Solution Approach 2:
The invention applies curved surfaces by forming the bearing rollers with a longitudinal barrel shape and the flex spline teeth with a longitudinal barrel profile. This curvature at the contact interfaces allows for compliant engagement that accommodates misalignment and ensures uniform stress distribution, replacing the need for separate compliance mechanisms.
2Reliability
If conventional strain wave drives are designed with additional compliance components to ensure correct load distribution, then load distribution improves, but costs, complexity, size, and weight increase
Solution Approach 1:
The compliance function is merged into the bearing rollers and flex spline teeth themselves through their modified barrel shapes. Instead of having separate compliance components, the compliant behavior is integrated directly into the load-bearing elements, ensuring correct engagement while minimizing additional weight.
Solution Approach 2:
The invention changes the geometric parameters of the bearing rollers and flex spline teeth from cylindrical/straight to barrel-shaped profiles. This parameter modification inherently provides the compliance needed for correct load distribution and engagement, eliminating the need for additional heavy compliance components.
3Reliability
If strain wave drives use modified barrel-shaped bearing rollers and teeth, then uniform stress distribution and reduced interference are achieved, but manufacturing complexity increases
Solution Approach 1:
The invention modifies the geometric parameters of the bearing rollers and teeth to barrel shapes with specific curvature radii. While this changes the manufacturing process from simple cylindrical forms, the barrel shape can be achieved through standard forming and machining operations, and the resulting uniform stress distribution improves reliability and reduces wear.
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 modified design achieves compactness, reduced weight, and improved load capability with minimal drag and wear, while maintaining efficient gear ratio and reliability.
Implementation Method 1
a compliant design which incorporates roller bearing supports provided between the cam surface and the flex spline, and wherein the roller bearing supports are formed with a longitudinal barrel shape and/or the teeth of the flex spline define a longitudinal barrel profile, to define a convex curved surface at the interface between the bearings and the flex spline
Data Source
AI summary
A strain wave drive includes: an elliptical wave generator shaft rotatable about an axis (X); a flexible flex spline mounted around the wave generator shaft; a ring gear assembly mounted around the flex spline, the ring gear assembly comprising an output ring gear having a circular inner periphery and being sandwiched between two earth ring gears each having a circular inner periphery. The flex spline has a first set of a first number of radially outwardly extending teeth around its outer periphery. Each earth ring gear has the first number of radially inwardly extending teeth to engage with the first set of teeth of the flex spline. The flex spline has a second set of the first number of radially outwardly extending teeth around its outer periphery wherein the output ring gear has a second number of radially inwardly extending teeth.