Strain Wave Gear Disconnect Mechanism for Reverse Operation
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Solution Overview
Problem
Strain wave gearing systems have limited reversibility, which restricts their application in scenarios requiring reverse operation, such as in rotary electromechanical actuators for flight control surfaces, due to their low back drive capability.
Innovation Solution
A strain wave gear mechanism with a solenoid-operated disconnect gear that allows the outer ring to be selectively disconnected from the casing, enabling reverse operation by rotating a cam between two positions to engage or disengage the teeth of the flexible ring with the outer ring, thereby enhancing reversibility.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If strain wave gearing is used to achieve high gear ratio and compact size, then the gearbox becomes smaller and lighter, but reversibility capability deteriorates
Solution Approach 1:
The outer ring is made rotatable relative to the casing through the disconnect mechanism, transforming it from a static component to a dynamic one. This allows the system to switch between engaged and disengaged states, enabling reverse operation while maintaining the compact strain wave gearing structure.
Solution Approach 2:
The disconnect mechanism acts as an intermediary between the outer ring and the casing. It includes a disconnect mechanism flexible ring with teeth that can engage with or disengage from the outer ring teeth, controlled by a cam mechanism. This intermediary allows selective connection and disconnection to achieve reversibility.
2Strength
If the outer ring is fixed to the casing to maintain structural stability, then mechanical strength is improved, but reversibility is lost
Solution Approach 1:
The connection between the outer ring and casing is made dynamic rather than fixed. The disconnect mechanism allows the outer ring to be securely fixed during forward operation for mechanical strength, but can be rotated to disengage when reverse operation is needed, providing both strength and adaptability.
Solution Approach 2:
The system changes the engagement parameter of the disconnect mechanism. When engaged, the teeth of the disconnect mechanism flexible ring mesh with the outer ring teeth, providing strong mechanical connection. When disengaged, the cam rotates to misalign the teeth, allowing reverse operation. This parameter change enables both strength and reversibility.
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 mechanism provides improved reversibility while maintaining the compactness and high gear ratio benefits of strain wave gearing, making it suitable for applications like aircraft flight control surfaces where reverse operation is necessary.
Implementation Method 1
a solenoid operated disconnect gear configured to selectively disconnect the outer ring from the casing
Implementation Method 2
a rotatable cam having an elliptical cross-section and arranged coaxial with and radially inwards of the disconnect mechanism outer ring
Implementation Method 3
a flexible ring mounted around the elliptical drive shaft radially inwards of the outer ring, the flexible ring having a toothed outer circumference
Data Source
AI summary
A strain wave gear mechanism includes: a casing; an elliptical drive shaft; an outer ring arranged coaxially around the elliptical drive shaft and rotationally fixed to the casing, the outer ring having a toothed inner circumference; a flexible ring mounted around the elliptical drive shaft radially inwards of the outer ring, the flexible ring having a toothed outer circumference. Rotation of the elliptical drive shaft causes elliptical rotation of the flexible ring relative to the outer ring such that teeth of the flexible ring engage with teeth of the outer ring at points corresponding to the major axis of the ellipse of the drive shaft to cause movement of the flexible ring in a direction opposite to rotation of the drive shaft. The outer ring is rotationally fixed to the casing via a solenoid operated disconnect gear configured to selectively disconnect the outer ring from the casing.