Bradley University

Name: Marwan Karrar Abbadi

Advisor: Dr. Winfred Anakwa

System Block Diagram

Date: November 5, 2002

Overview: The objectives of this project are modeling and control of a laboratory scalemagnetic levitation system. The magnetic levitation system facilitates the suspension of ahollow steel sphere with the aid of electromagnetism. Figure 1 displays a picture of sucha system.

Figure1: Magnetic levitation system

Figure 2: General System Block Diagram

Figure 2 shows a high-level block diagram of the system. The user adjusts theset point and applies the reference signal; the system is affected by disturbance signals that could be internal fluctuation in the power supply voltage or signals applied by the user. An error signal would be generated corresponding to the difference between the desired and actual ball position. This error signal is fed into a microcontroller that generates a control signal to place the ball at the desired vertical position.

There are six major subsystems in this project. These subsystems are as follows:

I. Error Generator Subsystem

Figure 3: Subsystem I

The first subsystem generates an error signal for the microcontroller. Thissubsystem, shown in figure 3, accepts three inputs: set point, reference signal and actual ball position to produce the error signal.

MagneticLevitation System

and Controller

Set point

Reference input signal

Actual Ballposition

Error Generator

Signalcorrespondingto actual ballposition (fedfrom output)

Error signal

Set point

Reference input signal

II. Amplifier and Protective Circuitry

This subsystem amplifies the error signal and provides any protective circuitryneeded for the microcontroller. This subsystem includes a level shifter circuit whichbrings the error signal to the microcontroller voltage range. Figure 4 shows the block

Figure 4: Subsystem II

III. Microcontroller

The position error signal is sent to a microcontroller through a multiplexed A/D converter. A PC is used to develop, debug and compile control algorithm code. The compiled code will be downloaded to an 8051microcontroller for execution. The A/Dconverter samples the error signal through channel 1. The microcontroller solves the discrete-time equations of the control algorithm andproduces a control signal via the D/A converter.

A subsystem block diagram is shown in figure 5.

Figure 5: Subsystem III

Amplifier andProtective Circuitry

Error signalfrom

Subsystem IAmplified error

signal

Microcontroller

A/D

D/A Controlsignal

PCcontainingcontroller

code

Controllerw/discrete

timeEquations

IV. Coil driver and electromagnet

The control signal, produced by the microcontroller, is amplified and fed to a coildriver to produce a current. This current is fed to an electromagnet, which produces therequired force to suspend the ball at the desired position. A subsystem block diagram isshown in figure 6.

Figure 6: Subsystem IV V. Sensor

The photo-emitter/detector sensor is used for detecting the vertical position of theball. It generates an analog signal, corresponding to the actual ball position; which is fedback for closed-loop control. A block diagram for this subsystem is shown below in figure 7.

Figure 7: Ball position sensor

The overall closed-loop system block diagram with subsystems is shown in figure 8:

Figure 8: Overall system

Coil Driver &

Electromagnet

Control signal Electromagneticforce

Ball PositionSensor

Actual ball

position

Analog signalcorresponding to ball

position

ErrorGenerator

Amplifier&

ProtectiveCircuitry

CoilDriver

&Electromagnet

BallPositionSensor

Reference inputsignal Disturbances

Ball positionMicrocontroller

PC

Flow Chart

Figure 9 represents hardware and procedure for controller implementation.

set point- actual position

Reference input signal

Error signalHardware Components

Sampled Error signal

Microcontroller

Figure 9: Flow Chart

ErrorGenerator

A/D Converter

Protective and amplifier circuitry

e(k)

Control Algorithmu(k) =ƒ[e(k)]

D/AAnalogcontrolsignalu(t)

Output of controller u(k)