Selectively Self-Locking Actuator for Thermal Management
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Solution Overview
Problem
Current electromechanical actuators (EMAs) in aircraft generate excessive waste heat due to high friction and motor current requirements, especially when holding static loads or overcoming stiction forces, which complicates thermal management in thermally stressful missions.
Innovation Solution
A selectively self-locking actuator design featuring a threaded shaft with both semicircular ball screw and power screw threadforms, a split nut with spring-biased portions, and a nut coupler plate to secure the ball nut and split nut at a fixed distance, allowing for reduced or zero motor current usage when holding static loads and low friction during motion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If a self-locking screw is used to eliminate motor torque for holding loads, then energy consumption is reduced, but friction losses increase significantly during motion
Solution Approach 1:
The actuator is segmented into two distinct drive mechanisms: a ball screw mechanism for motion phases and a self-locking screw mechanism for holding phases. This segmentation allows each mechanism to operate in its optimal performance regime, with the ball screw providing low-friction motion and the self-locking screw providing zero-power holding, thereby resolving the contradiction between energy consumption during holding and friction losses during motion
Solution Approach 2:
The system dynamically transitions between two operational modes: during motion, the ball screw is engaged to minimize friction; during static holding, the self-locking screw is engaged to eliminate motor current requirements. This dynamic switching allows the system to optimize energy efficiency for each operational phase, resolving the contradiction between the energy benefits of self-locking and the friction penalties during motion
2Loss of energy
If a non-self-locking ball screw is used to reduce friction during motion, then energy efficiency improves, but motor torque is required to hold static loads
Solution Approach 1:
The actuator is segmented into two distinct drive mechanisms: a ball screw mechanism for motion phases and a self-locking screw mechanism for holding phases. This segmentation allows each mechanism to operate in its optimal performance regime, with the ball screw providing low-friction motion and the self-locking screw providing zero-power holding, thereby resolving the contradiction between energy consumption during holding and friction losses during motion
Solution Approach 2:
The system dynamically transitions between two operational modes: during motion, the ball screw is engaged to minimize friction; during static holding, the self-locking screw is engaged to eliminate motor current requirements. This dynamic switching allows the system to optimize energy efficiency for each operational phase, resolving the contradiction between the energy benefits of self-locking and the friction penalties during motion
3Reliability
If high friction is used to achieve self-locking capability, then holding position becomes passive, but waste heat generation increases during operation
Solution Approach 1:
The actuator is segmented into two distinct drive mechanisms: a ball screw mechanism for motion phases and a self-locking screw mechanism for holding phases. This segmentation allows each mechanism to operate in its optimal performance regime, with the ball screw providing low-friction motion and the self-locking screw providing zero-power holding, thereby resolving the contradiction between energy consumption during holding and friction losses during motion
Solution Approach 2:
The invention converts the harmful high-friction characteristic into a beneficial feature by using it specifically for the holding function where friction is advantageous for self-locking, while using the low-friction ball screw for motion to minimize heat generation. This selective application transforms what is typically a harmful effect into a context-specific benefit, resolving the contradiction between holding reliability and waste heat generation
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 solution effectively minimizes waste heat generation by eliminating the need for motor torque to hold static loads and leveraging low friction benefits during actuator motion, enhancing thermal management and reducing energy consumption in aerospace applications.
Implementation Method 1
The spring is configured to bias the first split nut portion and the second split nut portion either radially inward or radially outward with respect to the threaded shaft
Implementation Method 2
In such self-locking configurations, the drive motor is not required to generate any torque to hold a load in a fixed position
Data Source
AI summary
A selectively self-locking actuator includes a threaded shaft having a first threaded portion and a second threaded portion. The first threaded portion includes a semicircular ball screw threadform and the second threaded portion includes a power screw threadform. The actuator further includes a ball nut mated to the first threaded portion, a split nut selectively mated with the second threaded portion, and a nut coupler plate configured to secure the ball nut and split nut at a fixed distance from each other. The split nut includes at least a first split nut portion and a second split portion each mated to a spring and a driver. The spring is configured to bias the first split nut portion and the second split nut portion either radially inward or radially outward with respect to the threaded shaft, and wherein the driver is configured to selectively oppose the bias of the spring.