Digital control of a magnetic levitation system

Abstract

Nowadays, conservation of energy is one of the most important and challenging tasks engineers face. In most mechanical systems, the most common energy loss is due to friction. Magnetic levitation allows new designs to be more energy efficient since it greatly reduces friction, which in tum lowers the consumption of energy by the system. Magnetic levitation now has numerous applications ranging from magnetic bearing to more complex and elaborate designs such as high speed maglev trains. The aim of this thesis was to design and implement a magnetic levitation system controlled by a microcontroller. The concept is to levitate an object using a magnetic transducer and keep it suspended in the air for an indefinite amount of time at a fixed position. This cannot be achieved by simply using a permanent magnet to provide the force. With the force of a magnet on a ferromagnetic object being inversely proportional to the distance square, the whole system would instantly go unstable exponentially, with the slightest change in the distance from equilibrium. An electromagnet was used instead, whose magnetic field strength varies with the current supplied. The benefit of using a microcontroller is the facility to implement and test various digital controllers by simply modifying the program. An electromagnet will produce the force of attraction required to lift the mass and control it in midair. An Infrared LED and a photodiode will provide the feedback to the system. By creating an imaginary line between the sender and receiver, the system will monitor the movement in that field, by measuring the intensity of the light on the photodiode. As the ball starts to descend less light will be blocked by the mass, and thus the control system will counter this change by increasing the current in the electromagnet to increase the magnetic field. The current is controlled by a control equation designed specifically for this model. The microcontroller will read the voltage from the sensor using its analogue to digital converter, and the output will be given in a Pulse Width Modulation signal which will drive the transistor of the magnet.