Monday, February 22, 2010

Model of Magnetic Levitation System



MODEL OF THE MAGNETIC LEVITATION SYSTEM
Figure shows the experiment model for the
Maglev system that has been carried out in a
project at National key lab for Digital Control &
System Engineering, Vietnam.








Diagram of magnetic levitation


The Maglev system in the model contains two
feedback sensors. One is a small current sense
resistor in series with the coil. The other is a
phototransitor embedded in the chamber pedestal
and providing the ball position signal. After
amplifying, both current sensor and phototransitor
are wired to analog inputs of card PCI-1711. The
control signal from the computer is sent to the
controllable voltage source through the analog
output of card PCI-1711.
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EXPERIMENTAL APPARATUS AND CONTROL MODEL
Figure 1 shows the single-axis magnetic levitation
system used in the experiment. The levitation object is a
ping-pong ball with a permanent magnet attached inside it
to provide an attractive force. The attraction force is
controlled by means of a computer-controlled electromagnet
mounted directly above the ball. A light source and a
linear image sensor (LIS, Hamamatsu S5462-512Q) are
used to determine the displacement of the ball. There are
512 photo diode cells in LIS, and the length of each cell is
0.05mm. The light source and the sensor are tuned such
that the outputs of the photocells are saturated when the






Schematic diagram of the magnetic levitation system.


ball does not cover the cells. A comparator is used to
compare the outputs of each cell with a preset voltage to
judge whether the cell is saturated or not. We then obtain
the levitation displacement of the ball by utilizing a counter
to count the numbers of saturated cells. The sampling rate
used is 200 Hz. This low sampling rate is used due to the
bandwidth limitation of LIS. The control computer is an
industrial personal computer with a Pentium processor
and an Advantech PCL818H analog I/O and counter
board.
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MAGNETIC LEVITATION SYSTEM
In this section, a physical maglev system and its components are described. Presenting system equations nonlinear and linear models are developed for the plant. The schematic of the MAGLEV plant is presented in Fig. 3.1 below:






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MODEL OF THE MAGNETIC LEVITATION SYSTEM
Diagram of the magnetic levitation system.








Consider the magnetic levitation system shown in Fig. 1. this
is a popular gravity-based one degree-of-freedom magnetic
levitation system, in which an electromagnet exerts attractive
force to levitate a steel ball (in some references a steel plate is
levitated). The system dynamics can be described in the
following equations
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