Antagonistic Shape Memory Alloy Actuator for Wind Tunnel Control
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Solution Overview
Problem
Existing wind tunnel model actuators are limited by the bulkiness of electromechanical systems, low power density, and the need for complex motor/gear assemblies, which restricts their use in space-constrained applications and reduces the fidelity of aerodynamic testing. Additionally, shape memory alloy (SMA) wire actuation has limited power and strength, making it suitable only for low-pressure wind tunnels.
Innovation Solution
A rotational actuator assembly using dual collinear shape memory alloy (SMA) tubes with antagonistic twist directions, centrally joined for common rotation, and equipped with a torque sensor for precise control, allowing for high power density and non-linear return spring characteristics, enabling higher force output and reduced complexity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If electromechanical actuators are used for control surface actuation, then sufficient force output is achieved, but the actuator becomes bulky and requires complex motor/gear assemblies
Solution Approach 1:
The patent replaces traditional electromechanical actuators with shape memory alloy (SMA) actuators that use thermal actuation mechanisms instead of motor/gear assemblies. The SMA wires utilize phase transformation between martensite and austenite phases to generate mechanical force, eliminating the need for complex mechanical transmission systems while maintaining sufficient force output for control surface actuation.
Solution Approach 2:
The patent changes the operating parameters by utilizing temperature-induced phase transformations in SMA materials. By controlling the temperature of the SMA wires, the material transitions between martensite and austenite phases, generating mechanical force. This parameter change approach allows the actuator to produce sufficient force without complex mechanical assemblies, as the phase transformation itself generates the required mechanical motion.
2Volume of moving object
If SMA wire actuation is used, then space is saved, but power and strength are limited
Solution Approach 1:
The patent employs composite SMA wire structures with specific material compositions (e.g., NiTi alloys with controlled stoichiometry) to enhance the strength and power output. By optimizing the composite material properties and using multiple SMA wires in parallel, the actuator achieves both compact size and sufficient force output for high-pressure wind tunnel testing.
Solution Approach 2:
The patent divides the actuation system into multiple SMA wire elements working in parallel. Instead of using a single thick SMA wire, the system employs multiple thinner wires that can be more easily managed and integrated into the actuator structure. This segmentation allows for better heat dissipation, more uniform stress distribution, and cumulative force output that meets the required power and strength specifications.
3Volume of moving object
If conventional return springs are used with SMA actuators, then the actuator can be sized smaller, but the spring applies greater return force opposite the SMA during deployment
Solution Approach 1:
The patent employs a dynamic return spring mechanism that adjusts its stiffness characteristics during actuator operation. The spring is designed to have different stiffness values at different positions, providing appropriate return force only when needed. This dynamic characteristic allows the actuator to be sized smaller while avoiding excessive return force during deployment, as the spring adapts its properties based on the actuator's position and operational state.
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 assembly provides high power density and increased force output, enabling its use in more restrictive spaces and higher-pressure wind tunnels, while maintaining a simple and robust design, enhancing the fidelity of wind tunnel testing.
Implementation Method 1
Current shape memory alloys, SMA, such as Nitinol have high force output while transitioning from martensite to austenite or low to high temperatures.
Implementation Method 2
a first torsion actuator incorporating a shape memory alloy (SMA) tube with a first trained twist direction and a second torsion actuator having a SMA tube with an opposite trained twist direction
Data Source
AI summary
A rotational actuator assembly employs a drive torque actuator having a shape memory alloy (SMA) tube with a first trained twist direction and a return actuator having a SMA tube with an opposite trained twist direction collinear with the drive torque actuator with abutting proximal ends. A central fitting joins the proximal ends. A control system employs a position sensor for the drive torque actuator and the torque sensor for the return actuator for combined antagonistic rotation of the central fitting.