Monolithic SMA Actuator With Integrated Strain Sensing Feedback
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Solution Overview
Problem
Conventional Shape Memory Alloy (SMA) actuators face challenges in obtaining position and strain feedback, limiting their applications due to the complexity and cost of external position sensors and the difficulty in sensing under dynamic and unknown stress conditions.
Innovation Solution
A monolithic SMA actuator design incorporating a shape memory effect (SME) section for actuation and a pseudo-elastic (PE) section as a strain gauge sensor, controlled by a system that calculates position based on resistance measurements from both sections, with laser processing and thermomechanical treatment to achieve desired properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If external position sensors are used with SMA actuators, then position feedback can be obtained, but the complexity and cost of the system increases
Solution Approach 1:
The patent combines the actuator and sensor into a single integrated SMA element. The SMA wire serves dual functions: actuation through shape memory effect and sensing through resistance measurement. This eliminates the need for separate external position sensors, thereby reducing system complexity while maintaining position feedback capability.
Solution Approach 2:
The SMA element is designed to perform multiple functions simultaneously - it acts as both the actuator that generates motion and the sensor that provides position feedback. The same material and structure are used for both actuation and sensing, making the system more compact and less complex.
2Device complexity
If conventional SMA actuators are used without integrated sensing, then the actuator structure remains simple, but position and strain sensing becomes difficult under dynamic stress conditions
Solution Approach 1:
The sensing capability is merged directly into the SMA actuator element itself. By measuring the electrical resistance of the SMA wire, which changes with strain and temperature, the system can detect position and strain information without adding complex external sensing apparatus, thus maintaining structural simplicity while enabling measurement.
Solution Approach 2:
The patent implements a feedback mechanism where the resistance measurement of the SMA element provides real-time information about its state (position and strain). This feedback is used to control the actuator, enabling closed-loop control that improves measurement accuracy under dynamic conditions.
3Measurement precision
If a monolithic SMA design with PE section is used, then position sensing capability is improved, but the manufacturing process becomes more complex
Solution Approach 1:
The monolithic SMA element is segmented into two functional sections: an SME section for actuation and a PE section for sensing. This segmentation allows each section to be optimized for its specific function while maintaining a single integrated structure, balancing manufacturing complexity with sensing performance.
Solution Approach 2:
Different sections of the SMA element have different material properties tailored to their specific functions. The SME section has properties optimized for shape memory actuation, while the PE section has properties optimized for pseudo-elastic sensing. This local differentiation of material properties enables precise position sensing while maintaining manufacturability through controlled material processing.
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 reliable position control and strain sensing within the actuator, reducing the need for external sensors and improving performance under dynamic stress conditions, enhancing the applicability of SMA actuators.
Implementation Method 1
a shape memory effect (SME) section of the monolithic shape memory alloy, configured for actuation
Implementation Method 2
a pseudo-elastic (PE) section of the monolithic shape memory alloy, configured as a sensor for enabling position sensing
Implementation Method 3
measuring a first resistance of a shape memory effect (SME) section of the actuator; measuring a second resistance of a pseudo-elastic (PE) section of the actuator; calculating an estimated position of the actuator, via the control system, based on the first and second resistances
Data Source
AI summary
A shape memory actuator including: a monolithic shape memory alloy; a shape memory effect (SME) section of the alloy, configured for actuation; a pseudo-elastic (PE) section of the alloy, configured as a sensor for enabling position sensing; and a control system configured to control the actuator by controlling a current through at least the SME section based on the sensor results of the PE section. A method of controlling a shape memory actuator, the method including: applying a predetermined current through the actuator; measuring a first resistance of the SME section; measuring a second resistance of the PE section; calculating an estimated position of the actuator based on the first and second resistances; and adapting the current applied to the actuator based on the estimated position. A method of manufacturing a shape memory actuator, the method including: laser processing; thermomechanically treating; and training the shape memory alloy.