Efficient Path Determining Robot

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Efficient Path Determining Robot

• Jamie Greenberg
• Jason Torre

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General Description

• Maze is set up as shown
• PC Analyzes maze through webcam
• PC Determines best path for robot to get from
  start position to end using Dijkstra's Least Cost
  Path Algorithm

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General Description (continued)

• PC translates path into a set of commands and
  sends them to the HCS12 through the serial port
• Robot follows commands to travel the best path to
  the finish

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Image Processing

• Laptec Webcam connected to PC through USB port
• Image is captured through Java Media Framework
• Pixel information is pulled from the image using
  Java PixelGrabber class
• Pixel data for areas of interest is analyzed to
  determine if color best represents a wall (white)
  or a blank space (black)
• Use this data to determine what grid positions
  have a blank space (no wall) and designate them
  as nodes

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Dijkstras Algorithm

• Start with a cost of zero for the start node
  and infinity at every other node.
• Iterate through every node and determine its
  distance from the start node (if directly
  connected)
• Mark the node with the least cost and determine
  the costs of all unmarked nodes to this node
• Repeat for every node until least cost node is
  the finishing node.
• Once this is determined, the shortest path is the
  reverse order of the nodes previously marked

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Getting the data to the robot

• Once the best path is found, the path is
  converted on the PC to a set of binary commands
• This data is sent to the Motorola 68HCS12 through
  the serial port on the PC and the SCI port on the
  HCS12.
• When a FINISHED command has been received by
  the robot a command will be sent back to the PC
  that will notify the user to remove the serial
  cable and press the Go button on the robot. When
  GO is pressed, the robot should begin its path
  towards the finish.

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Commands

• The following commands will be used to guide the
  robot through the maze

Commands Bit Setup Description
LEFT 001 xxxxx Move the robot left xxxxx grid coordinates. This location will never be larger than 7, as the grid has only 8 coordinates.
RIGHT 010 xxxxx Move the robot right xxxxx grid coordinates. This location will never be larger than 7, as the grid has only 8 coordinates.
FORWARD 011 00000 Move the robot forward 1 row.
FINISHED 100 00000 Notify robot that it has reached its destination and adjust status LEDs.
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Communications Test

• At the beginning of the program (before web
  capture), the serial connection will be tested
• A binary test sequence will be sent to the
  robot and it will be echoed back to the PC.
• If the echo is not received in 5 seconds an error
  message will be displayed

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PC User Interface

• The PC will be used to guide the user through the
  process
• Instruct the user to attach the serial cable and
  reset the robot
• Notify user if communications test was successful
• Notify user that image analysis is in progress
• Notify user if path does not exist
• Notify user that commands are being sent to the
  HCS12
• Ask user to remove serial connection and press
  the GO button

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Robot Design

• Tamiya Robot kit
• The DC motor is FA-130 by Tamiya
• The whole kit measured 6.5 X 4.25 X 3.75
  height, available surface area after the bottom
  deck is covered is 4.5 X 2.5

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Chassis and Actuators
Robot Tank by Budget Robotics Two gear ratio to
choose from 581 , 2031
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Hardware Utilized

• Proximity Sensors
• Opto-reflectors
• Chasis and DC motors
• H bridges
• Batteries

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Proximity sensors
Sharp GP2D15 IR Proximity Sensor Range between 0
cm and 80 cm Beam width of 45-50
This model can be adjusted to yield a digital
output when the robot comes to close to the wall
( 2 cm) No external circuitry is needed
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Opto-reflector
Optek OPB745 opto reflector Responsible for
informing that the vehicle has arrived reached a
mrker
The sensor will yield a digital input value when
the robot crosses a piece of reflective tape, and
modifications are done on the signal handling
circuit that was completed previously (IDE).
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Battery and power

• 4 AA sized battery for the vehicle (in the kit)
• Additional D Cell battery cells used to drive all
  the sensors and HCS12 board

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Block Diagram
HCS12
DC Motor
PWM 0-2
H bridges
PT 0-5
DC Motor
Opto-reflectors
Proxy Sensors
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Overhead view
Hole for wires
Top Level
Bottom Level
Proxy sensor
Sensor Circuitry
Opto-reflector and circuitry
H Bridges, DC Motors and voltage regulator
Batteries
HCS12
User Interface
Proxy sensor
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User interface
Error
Moving
Finished
On/Off
GO
Download Complete complete
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Difficulties

• The camera must be nearly perfectly calibrated so
  that the rectangular arrays of pixels sampled are
  always the correct ones
• Calibrating the opto reflector correctly because
  it has been known to be unreliable
• Calibrating the proxy sensors so as not to give
  too large a range

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Webcam Alignment Utility

• A small utility will be created to assist in
  positioning of the webcam
• The utility will display a snapshot of the grid
  with boxes around the areas that should contain
  the edges of each grid position (either a wall or
  an opening)
• If the camera needs to be moved, the user can
  retry the calibration until it is satisfactorily
  lined up

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Cost
Item Cost
Labtec Webcam 19.80 from staples
Java API Free from java.sun.com
Motorolla 68HCS12 Microcontroller 180.00 from CE department
Remote Control Tank 35.95 from budgetrobotics.com
LM298 H bridges (2) 10.90 from digikey.com
Optek OPB745 Opto-Isolators(2) 12.00 from CE department
Various other power circuitry and batteries 30.00
Maze for Robot 20.00 Approx
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Questions?