Markus Raab

# Development and experimental verification of a mathematical model describing the dynamic behavior of magnetic shape memory actuators

Description:

Magnetic Shape Memory Alloys (MSM) are a new group of Shape Memory Alloys (SMA). By applying a magnetic field, the MSM elongates more than 5 % and up to a maximum of 12 %, depending on the composition of the chosen alloy.

The aim of the first part of this work is to describe the basic of magnetic shape memory alloys, which converts magnetic fields and mechanical forces into mechanical elongation (working principle of magnetic shape memory alloys).

The possible uses for the material are derived from the working principle of the material. Possible uses are actuators, sensors, energy harvesting and damping. This work focuses on actuators engineering. Different types of MSM actuators are presented, the working principles of the different actuator designs are explained and the advantages as well as disadvantages are discussed.

A mathematical model of a MSM-Push-Actuator in combination with a mass-spring-damper system is built. The MSM effect in the material is described through the Helmholtz Energylandscape. Additionally other models for the magnetic circuit of the actuator and the connection between actuator and mass-spring-damper system are described. The model is implemented in Matlab/Simulink.

The mathematical model is compared with a MSM-actuator on a test bench. Several tests were planned in order to characterize the material. Derived from the requirements of the tests different concepts of test benches were developed, compared and the best concept is chosen for manufacturing.

3D CAD model of the test bench

The tests done with this test bench are divided in quasistationary and dynamic tests. In the quasistationary tests, the force-displacement curves and the current-displacement curves of the actuator are measured. The following graphs show the measured behavior of the MSM-actuator compared with the mathematical model of the system.

Comparison of the quasistationary test with the mathematical model (a) Force-Elongation Diagram, (b) Current Elongation Diagram

The dynamic test focuses on the frequency and step response of the system. A position controller is designed with the results of the frequency response of the system in open loop and the developed Simulink model.

For the qualification of the Simulink model, the model is compared with the test results. With this comparison the accuracy and the problems of the model are detected

Skills required:

• Literature review
• Design for manufacturing and assembly
• Solid modeling and drawing documentation using ProE
• Test planning, test implementation, test evaluation
• Developing of control algorithms in time – and frequency domain
• Implementation and developing of mathematical models in Matlab (Simulink and script)
• Project and work management

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