Date of Award
Master of Science
Electrical and Computer Engineering
Recent advances in non-contact manipulation of magnetic objects by external magnetic fields have made significant impact on the development of new generations of minimally invasive medical procedures in which magnetized objects such as drug carriers, surgical tools, etc., are guided inside the patients' body by precise control of external magnetic fields. The magnetic fields can be generated and controlled by arrays of either electro- or permanent magnets. Such controllable array of electromagnets is called non-contact magnetic manipulator. Although the magnetic fields of electromagnets are easier to control, permanent magnets have a larger magnetic field to size ratio that promotes compactness and/or larger workspace of the manipulator. In a magnetic manipulator with permanent magnets, the generated magnetic field is controlled by changing the translational or rotational position of its magnets by use of mechanical actuators. To stabilize the position of a magnetized object inside magnetic fields, feedback control of these actuators is necessary by the very nature of magnetic fields. The ability of feedback to stabilize the object substantially depends on the bandwidth and rate-of-change (or slew rate) limitations of the utilized actuators, the size of object and the viscosity of the medium it movies in, and the strength of the permanent magnets used. The study of these effects is crucial for the proper design of non-contact manipulation using permanent magnets. This research investigates the impact of bandwidth and rate-of-change limitations on the stability properties of the feedback loop within a magnetic levitation framework. A magnetic levitation system relying on permanent magnets provides an appropriate example while the simple structure of this system provides deeper understanding of the nature of limitations imposed by mechanical actuators.For this system, two controller designs are developed and their stability properties are studied: first, a linear feedback law based on an approximate linearized model of the actual system, and second, a nonlinear feedback law using the concept of feedback linearization. In the latter case, the nonlinear nature of magnetic fields is involved in the control design procedure to improve the close-loop stability. Finally, the region of attraction associated with each controller is constructed for different values of system parameters. These parameters are experimentally extracted from a real-world mechanical actuator (servomotor) and permanent magnet using system identification techniques. The stability properties of developed controllers are examined in terms of the size of constructed region of attraction.
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