Monolithic SMA Actuator With Integrated Strain Sensing for Position Control
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Solution Overview
Problem
Conventional Shape Memory Alloy (SMA) actuators face challenges in obtaining position and strain feedback, limiting their application due to complexity and cost associated with external sensors, especially 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 configured as a strain gauge sensor, with a control system that adjusts current based on resistance measurements from both sections to estimate position and adapt to dynamic stresses, utilizing laser processing and thermomechanical treatment to achieve desired properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If external sensors are added to SMA actuators for position and strain feedback, then measurement precision is improved, but device complexity increases
Solution Approach 1:
The patent combines the sensing function directly into the actuator wire by creating a monolithic structure with SME and PE sections. This merging eliminates the need for separate external sensors, thereby reducing device complexity while maintaining measurement precision through the integrated resistance-based sensing mechanism.
Solution Approach 2:
The monolithic SMA wire serves multiple functions simultaneously: the SME section provides actuation while the PE section provides strain sensing through resistance measurements. This multi-functionality reduces the need for separate components, addressing both the actuation and sensing requirements within a single integrated element.
2Measurement precision
If external sensors are used for position feedback, then measurement precision is improved, but manufacturing cost increases
Solution Approach 1:
By merging the sensing functionality into the actuator wire itself through the PE section, the patent eliminates the need for separate sensor components. This integration reduces manufacturing costs by removing additional parts and simplifying the assembly process while maintaining position feedback capability through resistance measurements.
Solution Approach 2:
The actuator wire serves itself by incorporating the PE section that automatically provides strain sensing information through its resistance changes. This self-service capability eliminates the need for external sensing systems, thereby reducing manufacturing complexity and cost while maintaining measurement precision.
3Adaptability or versatility
If conventional SMA actuators operate under dynamic and unknown stress conditions, then adaptability is improved, but measurement precision deteriorates due to stress interference
Solution Approach 1:
The patent segments the monolithic wire into distinct SME and PE sections with different functional properties. The PE section is specifically designed to operate in the pseudo-elastic regime under dynamic stresses, providing stable resistance-based strain measurements that are less sensitive to stress variations, thereby maintaining measurement precision while handling dynamic conditions.
Solution Approach 2:
Different sections of the monolithic wire are given different local qualities: the SME section is optimized for actuation while the PE section is optimized for sensing under dynamic stresses. This local differentiation allows the PE section to maintain measurement precision even when the actuator operates under dynamic and unknown stress conditions.
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 complexity and cost by integrating sensing functionality, effectively addressing the limitations of conventional SMA actuators under dynamic and unknown stress conditions.
Implementation Method 1
a shape memory effect (SME) section of the monolithic shape memory alloy wire, configured for actuation
Implementation Method 2
The SME section is configured with transformation temperatures higher than an intended operating temperature of the actuator
Implementation Method 3
a pseudo-elastic (PE) section of the monolithic shape memory alloy wire, configured as a sensor for enabling position sensing
Implementation Method 4
The PE section is configured with transformation temperatures lower than an intended operating temperature of the SME section allowing the PE section to exhibit pseudo-elastic (PE) properties
Implementation Method 5
the sensor results include an estimated position of the actuator based on a first resistance of the SME section and a second resistance of the PE section
Implementation Method 6
laser processing a monolithic shape memory alloy wire to provide a shape memory effect (SME) section having a different transformation temperature than an existing pseudo-elastic (PE) section
Implementation Method 7
thermomechanically treating the laser processed monolithic shape memory alloy wire
Data Source
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Figure 3a~3b
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.