No-Back Ball Screw Actuator for Tension and Compression Loads
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Solution Overview
Problem
Electromechanical actuators face challenges in resisting large back driving forces, especially when driving heavy loads at high speeds, and existing no-back systems may not effectively maintain position in the event of motor failure.
Innovation Solution
A compact and efficient electromechanical actuator with a no-back system that incorporates a ball screw type actuator and a no-back device, utilizing a combination of skewed roller assemblies and sprag clutches to resist both tension and compression back driving forces without relying on electrical power, ensuring the actuator holds its position even if the motor fails.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the pitch of a ball screw actuator is increased to drive loads at faster rates of speed, then the speed of actuation is improved, but the back driving forces become larger and harder to resist
Solution Approach 1:
The no-back system is divided into two separate assemblies: a first compression skewed roller assembly for resisting compressive back driving forces and a second tension skewed roller assembly for resisting tensile back driving forces. Each assembly independently handles one type of force, allowing the system to effectively resist larger back driving forces even at high speeds.
Solution Approach 2:
Skewed roller assemblies act as intermediary mechanical elements between the ball screw drive shaft and the housing. These rollers convert axial back driving forces into radial forces that are resisted by the housing, effectively blocking back driving forces without requiring electrical power.
2Reliability
If a no-back device is added to resist back driving forces, then the reliability is improved, but the device complexity increases
Solution Approach 1:
The no-back system merges the functions of resisting compressive and tensile back driving forces into a single integrated assembly mounted on the ball screw drive shaft. The first and second skewed roller assemblies are combined with sprag clutches and bearings in one compact unit, reducing the need for separate components and simplifying installation while maintaining high reliability.
Solution Approach 2:
The no-back system is designed to be self-actuating through mechanical means only. The skewed rollers and sprag clutches automatically engage and disengage based on the direction of back driving forces, eliminating the need for electrical sensors, motors, or control systems to maintain position, thus improving reliability without requiring complex electronic controls.
3Volume of moving object
If a compact no-back system is designed, then the volume is reduced, but the ability to resist large back driving forces may be compromised
Solution Approach 1:
The no-back system uses dynamic skewed roller assemblies that can tilt and adjust their orientation based on the direction and magnitude of back driving forces. The rollers are mounted on bearings that allow them to self-align with the force vector, enabling the compact assembly to effectively resist large forces in both compression and tension without requiring oversized components.
Solution Approach 2:
The no-back system employs composite structural design combining multiple functional elements (skewed rollers, sprag clutches, bearings, and retainers) into an integrated assembly. This composite approach allows the compact structure to achieve high force resistance by distributing loads across multiple interacting components rather than relying on a single large element.
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 resists large back driving forces in both static and dynamic states, maintaining position and preventing unwanted movement even in the absence of electrical power, thus ensuring reliability and safety in applications like aircraft flap control.
Implementation Method 1
sprag clutches to resist both tension and compression back driving forces
Implementation Method 2
utilizing a combination of skewed roller assemblies and sprag clutches to resist both tension and compression back driving forces
Data Source
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AI summary
A compact, efficient, and reliable electromechanical actuator that is capable of driving heavy loads at a high rate of speed and also capable of resisting large back driving forces. The actuator resists tension and compression back driving forces in a static state as well as when the actuator extends and retracts. The back driving forces are resisted even if the electronics (e.g., motor) fail.