Strain Wave Drive With Barrel-Profile Compliance for Lightweight Torque
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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 additional components for compliance to manage uneven loading, which increases cost, complexity, and weight.
Innovation Solution
The strain wave drive incorporates a modified design with barrel-shaped roller bearings and longitudinally curved flex spline teeth to provide compliance, allowing for uniform load distribution and reduced interference between meshing teeth, thereby eliminating the need for additional compliance components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If conventional involute gears are used to provide high torque ratio, then the required torque multiplication is achieved, but the size and weight of the actuator system increases
Solution Approach 1:
The patent replaces conventional involute gear mechanisms with a strain wave drive system that uses elastic deformation of a flex spline instead of rigid toothed gears. The wave generator creates an elliptical motion that causes the flex spline to deform and engage with the circular spline, providing the required torque multiplication through elastic compliance rather than rigid mechanical gearing.
Solution Approach 2:
The patent employs a flexible splined ring (flex spline) that can elastically deform to accommodate the elliptical shape of the wave generator. This flexible component replaces rigid intermeshing gears, enabling compact torque transmission while reducing overall actuator size and weight compared to conventional gear systems.
2Weight of moving object
If conventional strain wave drives are used for compact actuation, then size and weight are reduced, but additional compliance components are required which increases complexity and cost
Solution Approach 1:
The patent merges the compliance function directly into the flex spline component itself, which inherently possesses elastic properties due to its thin-walled cylindrical structure. This eliminates the need for separate compliance components or mechanisms, simplifying the overall drive system while maintaining the compact advantages of strain wave gearing.
Solution Approach 2:
The flex spline serves dual functions: it transmits torque through its splined engagement with the circular spline and simultaneously provides the necessary compliance through its elastic deformation capability. This self-service approach eliminates the need for additional dedicated compliance components, reducing system 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
This design results in a more compact, lightweight, and cost-effective strain wave drive with improved stress distribution and reduced wear, maintaining performance while minimizing size and weight.
Implementation Method 1
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
Figure 1A~1B
Figure 2~3
AI summary
A strain wave drive comprising: an elliptical wave generator shaft (100) rotatable about an axis (X); a flexible 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 set of 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 first set of teeth of the flex spline; and wherein 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, 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 second set of teeth of the output ring gear at the major diameter of the ellipse, causing the output ring gear to rotate; and wherein the wave generator shaft is provided with a radially outer surface defining the elliptical shape and arranged to engage with an inner surface of the flex spline; the strain wave drive further comprising roller bearing supports provided between the cam surface and the flex spline, and wherein the roller bearing supports and/or the teeth of the flex spline define a longitudinal barrel profile, are formed with a longitudinal barrel shape to define a convex curved surface at the interface between the bearings and the flex spline.