Motor Control of an Oscillating Pendulum

Nick Myers and Chirag PatelMarch 9, 2004

Advised by: Dr. James Irwin and Mr. Jose SanchezBradley University Department of Electrical Engineering

and Technology

Presentation Overview•Project Objectives

•System Block Diagrams

•Original Schedule of Tasks to be completed

•Work Completed (Nick)

•Work to be Completed (Nick)

•Work Completed (Chirag)

•Work to be Completed (Chirag)

•Revised Schedule of Tasks to be completed

•Summary of Progress

•Questions

Objectives

To initialize the oscillation of a weighted pendulum using microprocessor controlled motor bursts.

To oscillate the pendulum to a predefined angle and, using optical sensor outputs, maintain the angle of oscillation.

System Level Block Diagram

EMAC Motor Control and Sensor Reading

User Input: Start/StopPendulum Oscillation

Angle

Subsystem Level Block Diagram

Pendulum Swing Angle

Pendulum Arm

Optical Sensors

8051 MicroController Board

EMAC to Hardware Interface

DC Motor

Motor Power Supply

User Input

Feedback

Schedule of Tasks

Goals Accomplished to Date

Motor control switch to allow user to switch motor on/off

H-bridge hardware to allow motor to turn in both directions

H-bridge microprocessor code to switch H-bridge automatically based on pendulum location and direction

Construction of our pendulum unit

H-bridge Hardware

A B C D Motor Direction1 0 0 1 Forward0 1 1 0 Backward

H-bridge Hardware

The H-bridge uses (4) N-Channel Power Transistors

The H-bridge operates on a supply voltage of +15V DC

The H-bridge ideally accepts input voltages of 0V or +15V DC

Finding the appropriate transistors to power our motor was difficult

H-bridge Microprocessor Code

The H-bridge will switch motor burst direction every time the pendulum passes equilibrium.

Once the direction is switched, a burst will immediately be sent.

The H-bridge code will be called by the sensor input interrupt.

H-bridge Microprocessor Code

Yes No

Initialization of H-bridge by setting 31H to 1

Output P1.4Set 31H to 0

31H=1?

Output P1.5Set 31H to 1

Constructed Pendulum

Goals to be Accomplished

Complete hardware interface for EMAC to H-bridge

Calculate timing for motor burst lengths to be called by H-bridge code

Create timing code that will burst the motor with increasing lengths as pendulum period increases

Compile H-bridge code with all other project codes

Goals Accomplished to Date

Optical Sensor with desired switching times and code to read the sensors through EMAC.

PWM Signal Code to initiate oscillation.

Pulse Width Measurement Code to control speed of oscillation

Design of Pendulum Structure

Optical Sensor

Two sensors to be used– One at equilibrium

– Another at desired swing of oscillation

RF = 200 to limit current to 20 mA– Enough current to transmit infrared

signal

– Not enough current to damage Optical Sensor

R1 = 4700 to account for desired on/off switching times– ON Switching Time

• 8us * 1.7 = 14.4 us

– OFF Switching Time• 50us * 1.6 = 80us

PWM Signal

Current PWM signal = 1khz @ 33% Duty cycle. – Actual frequency will be

much smaller. PWM signal will be used to

initiate the oscillation of the pendulum.– Once pendulum is beyond

the equilibrium sensor, timed pulse signals will be used to oscillate the pendulum.

Pulse Width Measurement

Pulse Width Measurement code used to measure length of time sensor is obstructed by pendulum.– This time will be used to

control the length of the pulse sent to motor to control oscillation of pendulum.

• Faster oscillation = Smaller pulses

• Slower oscillation = Larger pulses

Goals to be Accomplished

Construct code for the timed pulses of constant length in order to sustain oscillation beyond the equilibrium sensor.

Construct code to adjust the length of the timed pulses which will be dependent upon the pulse width measurement.

Construct code to maintain oscillation once the predefined height sensor is reached.

Software FlowchartPWM SIGNAL TO

INIT. OSCILLATION

PULSE WIDTH MEASUREMENT

TIMED PULSES OF LENGTH TO BE DETERMINED UPON

PULSE WIDTH

OUT OF

EQ.? SENSO

R

PRESET

SENSOR??

MAINTAIN OSCILLATION

NO

NO

Revised Schedule of Tasks

WEEK SCHEDULED TASKS7

8

9

10

11

12

13

Code to output pulses of constant length.Complete interfacing of EMAC and H-Bridge

Design and build power supply circuit to hold/release charge.Code to adjust the length of the pulses, dependent upon speed of oscillation.

Code to adjust the length of the pulses, dependent upon speed of oscillation.

Design and build power supply circuit to hold/release charge.

Troubleshoot/Prepare for student expo

Prepare for student expo and project presentation

Code to maintain speed of oscillation once predefined sensor is reachedKeypad/LCD/Initialization Code

Prepare for student expo and project presentation

Code to maintain speed of oscillation once predefined sensor is reached.Compile all code and Troubleshoot.Troubleshoot/Prepare for student expo

Progress to Date

Completed motor on/off switch

Completed H-bridge hardware

Completed H-bridge software

Partially completed EMAC to H-bridge interfacing

Completed Optical sensor timing values and code

Completed PWM signal code

Completed pulse width measurement code

Completed pendulum construction

Questions?