No-Back Ball Screw Actuator for Bidirectional Backdrive Resistance
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing electromechanical actuators face challenges in resisting large back driving forces, especially when driving heavy loads at high speeds, and may fail to maintain position if the motor fails.
Innovation Solution
A compact and efficient electromechanical actuator design that incorporates a ball screw system with a no-back device, utilizing a sprag clutch and skewed roller assemblies 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 adjusted to drive loads at faster rates of speed, then the speed increases, but back driving forces become larger and more difficult to resist
Solution Approach 1:
The no-back device is segmented into two independent one-way clutch assemblies: a first one-way clutch assembly for resisting compression back driving forces and a second one-way clutch assembly for resisting tension back driving forces. Each assembly operates independently to handle specific directional forces, allowing the actuator to maintain high speed capability while effectively resisting back driving forces in both directions.
Solution Approach 2:
One-way clutch assemblies serve as intermediary mechanical elements between the ball screw mechanism and the load. These clutches mediate the force transmission by allowing motion in the driving direction while blocking reverse motion, thereby resisting back driving forces without interfering with the forward motion capability needed for high speed operation.
2Reliability
If a no-back device is added to resist back driving forces, then the reliability improves, but the device complexity increases
Solution Approach 1:
The no-back device uses universal one-way clutch assemblies that can resist both compression and tension back driving forces through two independently configured assemblies. This multi-functional approach allows a single no-back device structure to handle multiple force conditions (compression, tension, static, dynamic) without requiring entirely separate mechanisms for each condition, thereby improving reliability while limiting complexity growth.
Solution Approach 2:
The one-way clutch assemblies provide self-service by automatically engaging to resist back driving forces without requiring external control signals or additional actuation mechanisms. The clutches self-activate based on the direction of force applied, providing reliable back driving resistance through their inherent mechanical design rather than requiring complex control systems.
3Reliability
If a ball screw system with no-back device is used, then the ability to resist back driving forces improves, but the manufacturing complexity increases
Solution Approach 1:
The manufacturing process is segmented into modular assembly steps: first the ball screw mechanism is manufactured and tested, then the first and second one-way clutch assemblies are separately manufactured and configured, and finally they are assembled together with the housing and drive shaft. This segmentation allows each component to be manufactured using standard processes and then integrated, reducing overall manufacturing complexity compared to creating a fully integrated custom mechanism.
Solution Approach 2:
The one-way clutch assemblies serve as intermediary components that can be manufactured using established clutch manufacturing processes and then integrated into the ball screw system. This approach avoids the need to develop entirely new manufacturing processes for the no-back functionality, as the clutch assemblies are mature, well-understood mechanical components that can be produced through conventional methods.
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 back driving forces in both static and dynamic states, maintaining position and preventing movement if the motor fails, thus ensuring reliable operation across various applications such as aircraft flap control.
Implementation Method 1
The sprag clutch is oriented to resist relative rotation of the first static disk and the housing in a first direction and allows free relative rotation of the first static disk and the housing in a second direction
Implementation Method 2
a first compression skewed roller assembly positioned between the radially extending ball screw flange and the first static disk first compression skewed roller engagement surface
Data Source
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.