Failsafe Electromechanical Actuator With Helical Groove Backup Drive
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Solution Overview
Problem
Aircraft actuators face challenges in safely moving critical components like flight control surfaces and engine stator vanes to a safe position during failures, requiring a controlled movement under their own power without relying on air loads.
Innovation Solution
A failsafe electro-mechanical actuator design featuring a motor shaft with a harmonic drive mechanism that transitions between modes, using ball bearings and a solenoid to ensure the actuator moves to a predetermined position in case of failure, ensuring continued safe flight.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a harmonic drive is used to transfer motion from motor shaft to output shaft, then motion transfer efficiency is improved, but device complexity increases due to additional components
Solution Approach 1:
The patent implements a dynamic coupling mechanism where the motor shaft can axially move between two positions: first position for engaged mode (harmonic drive active) and second position for disengaged mode (harmonic drive inactive). This dynamic reconfiguration allows the system to switch between high-efficiency power transfer and simplified failure-safe operation, resolving the contradiction between motion transfer efficiency and device complexity.
2Speed
If ball bearings are disengaged from output shaft in first mode, then friction is reduced for smooth rotation, but reliability decreases during motor failure
Solution Approach 1:
The ball bearings are designed to dynamically change their engagement state with the output shaft based on operational mode. In normal operation (first mode), bearings are disengaged for smooth rotation. Upon motor failure detection, the motor shaft axially moves to the second position, causing the ball bearings to engage with the helical grooves on the output shaft, providing mechanical advantage for failsafe operation. This dynamic adaptation resolves the contradiction between rotation smoothness and failsafe reliability.
Solution Approach 2:
The helical grooves on the output shaft work in conjunction with the ball bearings to automatically provide mechanical advantage during failure conditions without requiring external intervention. The geometry of the helical grooves converts the axial movement of the motor shaft into rotational movement of the output shaft, enabling the system to self-correct and move to a failsafe position.
3Reliability
If motor shaft axially moves toward output shaft in second mode, then failsafe positioning is achieved, but device complexity increases due to additional movement mechanism
Solution Approach 1:
The motor shaft serves multiple functions: it acts as both the rotating element for normal operation and as an actuating element for failsafe positioning. By making the motor shaft itself capable of axial movement, the design eliminates the need for separate actuating mechanisms, achieving multi-functionality that reduces overall device complexity while maintaining failsafe capability.
Solution Approach 2:
The ball bearings serve as an intermediary mechanism that couples the axial movement of the motor shaft with the rotational movement of the output shaft during failsafe operation. Through the helical grooves, the ball bearings translate the axial displacement into useful rotational motion, providing a simple yet effective mediation that avoids complex direct-coupling mechanisms.
4Power
If harmonic drive components are engaged, then motion transfer is efficient, but ease of operation decreases due to locking mechanism requirements
Solution Approach 1:
The patent merges the mode switching function with the existing solenoid locking mechanism. The same solenoid that locks the output shaft in position during normal operation also controls the axial movement of the motor shaft between engaged and disengaged modes. This consolidation of functions eliminates the need for separate switching mechanisms, improving ease of operation while maintaining efficient motion transfer when engaged.
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 actuator effectively isolates failures and moves components to a safe position, maintaining flight safety by transitioning to a failsafe mode upon motor or reduction gearing failure.
Implementation Method 1
The actuator may include a solenoid that surrounds, and is axially aligned with, the first end of the output shaft, wherein the solenoid may be rotationally fixed, and in the second mode, the solenoid may be activated to move the motor shaft toward the first end of the output shaft.
Implementation Method 2
a harmonic drive between the motor shaft and the output shaft that transfers motion from the motor shaft to the output shaft in a first mode of operation
Implementation Method 3
ball bearings seated at the first end of the motor shaft such that the ball bearings project inwardly from the motor shaft
Data Source
Figure 1
Figure 2
Figure 3~4
AI summary
A failsafe electro-mechanical actuator (130), the actuator having: an output shaft (250) having a first and second ends (250A, 250B) spaced apart from each other along a shaft axis, and outwardly facing helical grooves (360) formed along the first end; a motor shaft (180) surrounding the output shaft (250); a harmonic drive (270) between the motor and output shafts that transfers motion between these shafts in a first mode of operation; ball bearings (200D) seated at the first end (180A) of the motor shaft (180) and project inwardly from the motor shaft; in the first mode of operation: the ball bearings (200D) are disengaged from the output shaft (250) and the output shaft rotates with the motor shaft (180), and in a second mode of operation, the motor shaft axially moves toward the first end of the output shaft; the motor shaft is rotationally fixed; and the ball bearings engage the helical grooves in the output shaft, whereby the output shaft rotates.