Magnetic Shape Memory Alloy Actuator Self-Sensing via Resistance Feedback
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Solution Overview
Problem
Conventional shape memory alloy actuators face challenges with temperature-actuated systems, including hysteresis and the need for heating and cooling, which complicates control and slows response times, and existing magnetic shape memory alloy self-sensing methods are limited in accurately tracking static position and are not fully independent of the driving signal.
Innovation Solution
A method utilizing the internal electrical resistance of magnetic shape memory alloy elements to measure and control strain, allowing for accurate position sensing and feedback without external sensors, using a 4-point constant current and voltage drop measurement, and a coil structure to apply a magnetic field, enabling efficient control and detection of fatigue-induced defects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If temperature-actuated shape memory alloy is used for actuation, then large strain output and force are achieved, but response time is slowed and control is complicated due to hysteresis and heating/cooling requirements
Solution Approach 1:
The patent changes the actuation parameter from temperature to magnetic field. By applying magnetic field instead of thermal energy, the alloy achieves rapid actuation without the thermal inertia and hysteresis that limit temperature-actuated systems. This parameter change enables fast response times while maintaining large strain output and force generation capabilities.
2Measurement precision
If electrical resistance measurement is used for strain sensing in temperature-actuated shape memory alloy, then strain information is obtained, but measurement precision is reduced due to temperature-induced resistivity changes
Solution Approach 1:
The patent changes the actuation parameter from temperature to magnetic field, which eliminates the temperature-induced resistivity changes that corrupt strain measurements. Since the alloy is not heated for actuation, the electrical resistance measurement accurately reflects only the strain-induced geometric changes, providing precise strain sensing without temperature interference.
3Speed
If magnetic shape memory alloy is used for actuation, then fast response and high frequency operation are achieved, but accurate static position sensing is limited
Solution Approach 1:
The patent implements a feedback control system that continuously measures the electrical resistance of the magnetic shape memory alloy element. Since resistance changes with strain, this provides real-time position feedback that enables accurate static position sensing. The measured resistance value is used to determine the actual position, allowing the system to maintain precise positioning even during static holding phases.
4Measurement precision
If external strain gauges or sensors are used for position measurement, then strain measurement is possible, but device complexity increases
Solution Approach 1:
The patent makes the magnetic shape memory alloy element itself serve dual functions: actuation and sensing. The same alloy element that responds to magnetic field for actuation also provides strain information through its electrical resistance. This eliminates the need for separate external strain gauges or sensors, reducing device complexity while maintaining measurement capability.
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
This approach enables fast, accurate, and reliable control of magnetic shape memory alloy actuators, providing both movement and position data, and allows for early detection of fatigue, enabling preventive maintenance and precise positioning, suitable for various applications including medical and industrial uses.
Implementation Method 1
They are simultaneously shape memory and ferromagnetic alloys. In MSM-alloys it is possible to obtain a new type of behaviour called magnetic shape memory effect (MSME)
Implementation Method 2
Shape memory alloys possess unique characteristics that permit them to generate a large strain output and force, i.e. an actuation stroke, by an intrinsic mechanism called a martensite to austenite phase transformation
Implementation Method 3
Deformation of a bar or rod etc. results in a change of its length and cross-section. This causes a change in its electrical resistance, which is detectable. Thus, the electrical resistance of the alloy changes as a function of strain
Data Source
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AI summary
The present invention relates to a method and system for sensing and controlling the strain induced in a magnetic shape memory alloy element, and to a magnetic shape memory alloy actuator and sensor. The actuating element (5a) is operated by a control unit (10) having an input control signal (6a) and an input signal (7a) representative of the strain of the actuating element, consisting of a magnetic shape memory alloy. The strain of the actuating element (5a) is determined by measuring its internal electrical resistance, and the control of the same is provided by applying a magnetic field across it, having a magnitude corresponding to the input control signal (6a) and the feedback (7a) information, thereby altering the length of said actuating element (5a) to achieve the desired actuation.