Electro-Mechanical Actuator With Ball-Ramp Failsafe Reconfiguration
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Solution Overview
Problem
Aircraft electro-mechanical actuators face challenges in reliably moving flight critical components to a safe position in case of failure, particularly in engine stator vane control systems, where continued airflow is essential without mechanical obstruction.
Innovation Solution
A failsafe electro-mechanical actuator design featuring a motor shaft with a harmonic drive and ball bearings that transition between engagement and disengagement modes, allowing controlled rotation and axial movement to ensure safe positioning of components, even in the event of motor failure, by utilizing a solenoid to disengage the harmonic drive and engage helical grooves for controlled movement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the actuator uses a harmonic drive to transfer motion from the motor shaft to the output shaft, then the actuator can operate in a controlled manner under its own power, but the system becomes vulnerable to complete failure if the motor or harmonic drive fails
Solution Approach 1:
The actuator employs a dynamic mechanism where the motor shaft can axially displace between two positions: first position engaging the harmonic drive for controlled operation, and second position disengaging the harmonic drive while engaging ball bearings with helical grooves for failsafe operation. This dynamic reconfiguration allows the system to switch between normal and failsafe modes, resolving the contradiction between reliability and device complexity.
Solution Approach 2:
The ball bearings serve as an intermediary mechanism that can engage with either the harmonic drive (via cage) or the helical grooves on the output shaft. This intermediary element enables seamless transition between the motor-driven controlled mode and the mechanical spring-driven failsafe mode, allowing the system to maintain functionality even when the motor or harmonic drive fails.
2Reliability
If the motor shaft axially displaces to disengage the harmonic drive and engage ball bearings, then the actuator can transition to failsafe mode, but the mechanism requires additional components and structural complexity
Solution Approach 1:
The design merges the motor shaft, ball bearings, harmonic drive, and spring mechanism into a compact integrated assembly. The motor shaft simultaneously serves as both the driver for the harmonic drive and the carrier for the ball bearings. The spring is integrated within the housing to provide the necessary axial force. This merging reduces the number of separate components and simplifies the overall structure despite the dual-mode functionality.
3Reliability
If the ball bearings engage the helical grooves to rotate the output shaft independently, then the actuator can move to a safe position without motor power, but the mechanism requires precise geometric alignment
Solution Approach 1:
The helical grooves are pre-formed on the output shaft during manufacturing with precise geometry and orientation. The ball bearings are pre-configured on the motor shaft with their cage structure designed to engage these grooves at the correct angle. This preliminary preparation ensures that when the motor shaft displaces axially to the second position, the ball bearings automatically engage the helical grooves at the correct orientation, enabling immediate independent rotation of the output shaft without requiring complex real-time alignment mechanisms.
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
Enables the actuator to independently isolate failures and move components to a predetermined safe position, ensuring continued safe flight by maintaining airflow and preventing mechanical obstruction, even when primary power sources fail.
Implementation Method 1
the actuator includes a solenoid that surrounds, and is axially aligned with, 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
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
Implementation Method 4
outwardly facing helical grooves formed along the first end; the ball bearings engage the helical grooves in the output shaft, whereby the output shaft rotates
Data Source
AI summary
A failsafe electro-mechanical actuator, the actuator having: an output shaft having a first and second ends spaced apart from each other along a shaft axis, and outwardly facing helical grooves formed along the first end; a motor shaft surrounding the output shaft; a harmonic drive between the motor and output shafts that transfers motion between these shafts in a first mode of operation; ball bearings seated at the first end of the motor shaft and project inwardly from the motor shaft; in the first mode of operation: the ball bearings are disengaged from the output shaft and the output shaft rotates with the motor shaft, 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.