Motor Control of an Oscillating Pendulum

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Motor Control of an Oscillating Pendulum

• Nick Myers and Chirag Patel
• March 9, 2004
• Advised by Dr. James Irwin and Mr. Jose Sanchez
• Bradley University Department of Electrical
  Engineering and Technology

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Presentation Overview

• Project Objectives
• System Block Diagrams
• Step by Step Project Goals
• Work Completed - Hardware (Nick)
• Work Completed - Software (Nick)
• Work Completed - Hardware (Chirag)
• Work Completed - Software (Chirag)
• Initial PWM Design Plan
• Summary of Progress
• Possible Additions
• Questions

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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.

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System Level Block Diagram
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Subsystem Level Block Diagram
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Step by Step Project Goals

• H-bridge hardware
• EMAC to H-bridge interface hardware
• H-bridge switching software
• Initial motor pulsing software
• Incrementing motor pulsing software

• Optical sensor hardware
• Optical sensor interrupt software
• Oscillation stabilization software
• User interface software
• Pendulum construction and wiring

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H-bridge Hardware
Truth table for forward and backward states
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H-bridge Hardware

• The H-bridge uses (2) N-Channel ZVN4206
  Transistors and (2) P-Channel ZVP2106 Transistors
  
• The H-bridge operates on a supply voltage of 15V
  DC
• The inputs of the active transistors are pulled
  to Vcc
• The voltage across the motor is approximately 12V

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EMAC to H-bridge Hardware Interface

• All of the outputs from the EMAC microprocessor
  board come from Port 1
• Port 1 supplies 80uA of current
• Additional hardware must be added for EMAC to be
  able to turn the H-bridge on/off

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EMAC to H-bridge Hardware Interface
From EMAC
To H-bridge
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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
  equilibrium sensor interrupt
• The H-bridge code will switch motor polarity by
  switching on/off two pins on Port 1

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H-bridge Microprocessor Code
Flowchart
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Initial Motor Pulsing Software

• The equilibrium sensor will always be blocked
  initially
• Interrupt driven pulsing cannot be used to begin
  pendulum oscillation
• A constant pulse must be provided until the
  pendulum clears the equilibrium sensor

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Initial Motor Pulsing Software
Turn on P1.4 and P1.5 and set 31H1
31H1?
Yes
No
Turn off P1.4 and set 31H0
Turn off P1.5 and set 31H1
Delay
Delay
Flowchart
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Incrementing Motor Pulsing Software

• Once the Pendulum has successfully cleared the
  equilibrium sensor, the length of the torque
  bursts can be increased
• The bursts will only be sent when the equilibrium
  sensor is crossed
• These bursts will continue to increase in length
  until the angle sensor is crossed

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Incrementing Motor Pulsing Software
Flowchart
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Oscillation Stabilization Software

• When the pendulum reaches its desired angle of
  oscillation, it should remain constant at that
  desired angle
• Once the pendulum passes the angle sensor, the
  interrupt handler will check how many times the
  sensor is crossed
• If the pendulum is overshooting the sensor, the
  delay will be shortened

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Oscillation Stabilization Software
Flowchart
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User Interface Software

• On startup, the LCD prompts the user Press A
  to Begin
• The program is waiting to be interrupted by the
  keypad button A
• When the keypad button A is pressed, the
  initial motor pulsing software is entered and the
  pendulum begins its oscillation

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User Interface Software

• As the initial motor burst software is entered,
  the LCD display changes to Press B to Stop
• After every motor pulse, the code checks to see
  if the button B has been pressed
• If the button has been pressed, the motor is
  turned off and the the LCD is reset to the
  initial prompt

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Constructed Pendulum
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Optical Sensor

• Two optical sensors
• Equilibrium Sensor
• Predefined Angle Sensor
• RF 200
• Limits Current to 20 mA
• IF 5V/200 20mA
• Enough Current to transmit infrared signal
• Not Enough Current to Damage Optical Sensor

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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
• Equilibrium and Predefined Angle Sensor Have Same
  Values.

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Sensor Initialization

• Equilibrium Sensor
• Handled by Interrupt 3
• Once obstructed Rerouted to code in order to
  output motor burst
• Predefined Angle Sensor
• Handled by Interrupt 4
• Once obstructed Rerouted to code in order to
  count the number of obstructions
• Used to determine overshoot or undershoot

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Initial Design Plan

• 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.

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Initial Design Plan

• 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 pulsel sent to motor to control oscillation
  of pendulum.
• Faster the oscillation Smaller pulses
• Slower the oscillation Larger pulses

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Initial Design Plan

• Pulse Width Measurement
• Timer 2 used in gated mode
• When P1.7 High
• Timer begins counting
• When P1.7 Low
• Timer stops counting
• Obtain time value through pulse width measurement
  when pendulum is dropped from desired angle.
• Compare that value to value obtained each swing.
• If value obtained gt stored value - INCREASE BURST
  LENGTH
• If value obtained lt stored value DECREASE BURST
  LENGTH

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Initial Design Plan

• Initial design was not used due to the
  complications encountered
• Proved to be more time-consuming than expected
• However, this design can be used for changing
  loads.

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Summary of Progress

• Completed H-bridge hardware
• Completed EMAC to H-bridge hardware interface
• Completed H-bridge software
• Completed initial motor pulsing software
• Completed incrementing motor pulsing software

• Completed optical sensor Hardware
• Completed optical sensor interrupt software
• Completed oscillation stabilization software
• Completed user interface software
• Completed pendulum construction

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Possible Additions

• Adding additional angle sensors so that user may
  choose from multiple angles of oscillation
• Changing initial motor pulsing code so that
  changing loads could be oscillated
• Creating power storage circuitry so that system
  could run from a lower supply voltage

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Questions?