3-D Scanning Robot

1. 3-D Scanning Robot Steve Alexander Jeff Bonham John Johansson Adam Mewha Faculty Advisor: Dr. C. Macnab

2. Overview of Presentation • Project Goal • Background of 3D Scanning • Structural and Mechanical Design • Software Design • Control • Communication • Visualization • Results

3. Project Goal • Create an autonomous robot which will scan an object and create a 3-D representation of that object on a computer

4. Background of 3-D Scanning Basic Idea • Create a 3-D representation of an object which can be viewed on a computer

5. Background of 3D Scanning Existing Scanning Methods • Laser • Photogrammetry • Direct Contact • Sound Waves

6. BackgroundMechanics • Decided to go with a three-joint arm using a direct-contact method • Using Lego for the design • Advantages • Low Cost • C Programming Interface • Wide Variety of Parts Leading to Easier Structural Design And Redesign

7. BackgroundMechanics • Disadvantages • Limited Number of Input And Output Connections • Limited Processing Power • Gear Backlash And Structural Flexibility • Result: Poor Accuracy

8. Background Mechanics • Sample gears and gear reduction Diagrams from D. Baum, "Definitive Guide to Lego Mindstorms",2nd ed.

9. Mechanics of the Current Design • Successfully implemented stated goal of designing a robot arm with 3 Degrees of Freedom on a linear tracking base

10. Kinematics/Mechanics of the Current Design Side view representation of the finished arm. Equation to convert the above angles and lengths into Cartesian coordinates

11. Mechanics of the Current Design • January 2003 identified three main areas which required significant changes to be able to have a functional unit • Complete redesign of Wrist/End-Effector • Redesign/manufacture of axel support • Complete redesign of drive system

12. Wrist / End-Effector • Problems Identified • End wheel too large • Length not easily adjusted • Not enough reduction on rotation sensor

13. Wrist / End-Effector • 1 and 2 easily fixed • Smallest available gear used as most distal point (finger) • Axel used as attachment of distal point to main arm

14. Wrist / End-Effector Third design change more difficult. Tried to implement above design (8.3X reduction). Excessive torque at rotation sensor, wrist joint unable to move freely.

15. Wrist / End-Effector • Settled on this final design giving a reduction of 5

16. Drive System Original Base December 2003 Original Single wheel drive December 2003

17. Drive System New centrally mounted guide for base (left) and robot (right) Final design for drive system

18. Axels • In order to support weight of Chassis employed #10 threaded rod as axels. Attached wheels via threaded inserts and lock nuts.

19. Final Mechanical Design

20. Control Software Control Software Progression • Version 1.1 • Turned the motors on and off, varied the speed • Version 1.2 • Rotary encoders used as an input to control the stop position of each motor

21. Control Software Control Software Progression • Version 1.3 • A Proportional controller was implemented. This enabled us to have the motor speed slow as the target position was approached. 

22. Control Software Additions in Version 1.5 to Version 2.3 • Incorporated feedback loop control for the Elbow joint which tracks the position of the shoulder • Single direction communication added between RCX and PC • Multiplexing functionality using external multiplexing board

23. Control Software Additions in Version 1.5 to Version 2.3 • Added functions for recording data during a scan pass • Extensive calibration was carried out to optimize all portions of a scan

24. Control Software Calibrate Move Base to Next Scan Region Reset Arm To Scan Start Position Turn on Shoulder Motor Calculate Elbow Position If Scan Finished Transmit Data to PC

25. Communication Software • Need to transmit scan data from robot to PC for processing • LegOS Networking Protocol (LNP) too complex • Use IR program by Pavel Petrovic • Based on small subset of LNP • Simple unidirectional communication • Basic CRC

26. Communication Software First Version • Batch file to call IR multiple times • Very unreliable • Manually timed • No flexibility

27. Communication Software Second Version • IRG (IR Good) Program • Total solution • Fully automated • High complexity • Many issues • Abandoned

28. Communication Software Third Version • IRR (IR Redone) • C equivalent of first version • Calls IR four times with a delay • Worked perfectly • Only works for one scan

29. Communication Software Start Loop Listen for Start of Scan Receive Travel Delay Receive Wrist Delay Receive Elbow Delay Receive Shoulder Delay

30. Communication Software Need a program to listen for the start of a scan • Developed Listen Program • Continuously read serial port • Listen for a 4-byte start-of-scan message • Message is simply “SCAN” • Return to IRR when done

31. Communication Software Start Open Com Port Loop Check For Data New Data No Delay Yes Read New Data No Search For Message Found Yes Quit

32. Communication Software Final version (IRR + Listen) • Fully automated scan • Errors in transmission are unrecoverable • Must discard an entire pass

33. Visualization Software Matlab software • Load in all scan files • Compute the position of the arm based on rotation sensors • Polyfit data to smooth results • Layer scan passes • Use Matlab “mesh” command

34. Visualization Software Raw and fitted data for shoulder, elbow, and wrist

35. Results

36. Results • Scanning works • Accuracy is poor • Largely due to Lego limitations • Polyfitting smoothes result but wrecks sharp edges • Can be improved with better construction • No 4th-dimensional data • Time and resource constraints

37. Questions?