Tunable Magnets: Modeling and Validation for Dynamic and Precision Applications

Tunable Magnets: Modeling and Validation for Dynamic and Precision Applications

Viëtor, Silvan (TU Delft Mechanical, Maritime and Materials Engineering; TU Delft Mechatronic Systems Design)

Hossein Nia Kani, Hassan (mentor)
Spronck, Jo (mentor)

Delft University of Technology

2018-08-28

Actuator self-heating limits achievable force and can cause unwanted structural deformations that adversely affect the accuracy in precision actuation systems. This is especially apparent in quasi-static applications that require the actuator to maintain a stable position over an extended period. As a solution, we propose the use of Tunable Magnets (TMs). TMs rely on in-situ magnetization state tuning of AlNico to create an infinitely adjustable magnetic flux. They consist of an AlNiCo low coercivity permanent magnet together with a magnetizing coil. After tuning, the AlNiCo retains its magnetic field without further energy input, thus eliminating static heat dissipation. To enable implementation in actuation systems, the AlNiCo needs to be robustly tunable in the presence of a dynamically varying system air-gap. We achieve this by developing a magnetization state tuning method, based on a magnetic circuit model of the actuator, measured AlNiCo BH data and air-gap flux feedback control. A measurement setup is built to test the proposed tuning method. For an AlNiCo 5 TM, we have accomplished magnetization tuning with an accuracy in the mT range and a sub mT precision. With this obtained performance, actuator heating is already almost eliminated during static periods.
The second part of the thesis consists of investigating TM actuator applications. By comparing a TM actuator to a conventional actuator of similar geometry, we have derived a metric called the Break-Even Tuning Time. This can be used to evaluate what actuation applications can be made more energy efficient using a TM actuator. The results are very sensitive to assumptions made, but they do provide some useful qualitative conclusions. Actuation systems where these actuators can improve energy efficiency can be characterized by a low actuation bandwidth or only incidentally required actuation, together with large air-gaps and/or large required constant bias forces. Also, scaling analysis shows that TM actuators are more energy efficient compared to conventional reluctance actuators at small length scales.

tunable magnets
electropermanent magnets
precision actuation
magnetization state tuning
thermal stability
AlNiCo
recoil permeability

http://resolver.tudelft.nl/uuid:b4f375ee-c52c-45de-b40a-37d5722407d2

Student theses

master thesis

© 2018 Silvan Viëtor