characterization of the accuracy in a reverse engineering process

135 Pages·2011·3.61 MB·English

CHARACTERIZATION OF THE ACCURACY IN A REVERSE ENGINEERING
PROCESS EMPLOYING WHITE LIGHT SCANNED DATA TO DEVELOP
CONSTRAINT-BASED THREE DIMENSIONAL COMPUTER MODELS

By

Christopher W. Rhoades

A Thesis
Submitted to the
Faculty of the Graduate School
of
Western Carolina University
in Partial Fulfillment of the
Requirements for the Degree
of
Master of Science in Technology

Committee:
_____________________________________________ Director

_____________________________________________

_____________________________________________

_____________________________________________ Dean of the Graduate School

Date: ________________________________________

Spring 2011
Western Carolina
University
Cullowhee, North Carolina
CHARACTERIZATION OF THE ACCURACY IN A REVERSE ENGINEERING
PROCESS EMPLOYING WHITE LIGHT SCANNED DATA TO DEVELOP
CONSTRAINT-BASED THREE DIMENSIONAL COMPUTER MODELS

A thesis presented to the faculty of the Graduate School of Western
Carolina University in partial fulfillment of the requirements for the
degree of Master of Science in Technology

By

Christopher W. Rhoades

Director: Dr. Chip Ferguson
Associate Professor
Department of Engineering Technology

Committee Members:
Dr Wesley Stone, Engineering Technology
Dr. Aaron Ball, Engineering Technology

March 2011
Acknowledgements

I would like to thank my committee members, Dr. Chip Ferguson, Dr. Aaron Ball,
and Dr. Wes Stone for their guidance and assistance during the time of my research. I
would also like to t show appreciation to my fellow graduate students Jason Proffitt, Josh
Ellis, Tyler Bennett, Andrew J. Punch, and Matthew Proffitt for their support and
encouragement throughout my graduate studies. I would also like to express thanks to my
sister Andrea Still for her help and suggestions while writing my thesis, and the rest of
my family for their help and support during my research.
TABLE OF CONTENTS

ACKNOLOGEMENTS ........................................................................................................ ii
TABLE OF CONTENTS ................................................................................................... iii
LIST OF FIGURES ............................................................................................................ v
LIST OF TABLES ............................................................................................................ vii
ABSTRACT ..................................................................................................................... viii
CHAPTER 1: Introduction ................................................................................................. 9
Purpose and Objective ................................................................................................... 9
Problem Statement ....................................................................................................... 10
Background .................................................................................................................. 11
The ATOS system. .................................................................................................. 11
Methodology ................................................................................................................ 12
Overview of Measurement Procedure. ................................................................... 13
Analysis of measurements. ..................................................................................... 14
Terms and Definitions.................................................................................................. 15
Limitations and Delimitations ...................................................................................... 16
CHAPTER 2: Literature Review ...................................................................................... 18
Metrology & Reverse Engineering .............................................................................. 18
Computer Aided Design (CAD) .................................................................................. 19
Solid models............................................................................................................ 20
Contact Metrology ....................................................................................................... 21
Coordinate measuring machine. .............................................................................. 21
Non-Contact metrology ............................................................................................... 23
Interferometry. ........................................................................................................ 23
Photogrammetry. ..................................................................................................... 24
Moiré metrology. .................................................................................................... 26
Structured Light Scanning ........................................................................................... 28
Projection patterns. ................................................................................................. 31
Gray coding ........................................................................................................ 32
ATOS System .............................................................................................................. 34
Reference points. ..................................................................................................... 35
Calibration............................................................................................................... 37
Gage Blocks ................................................................................................................. 39
Post-Processing ............................................................................................................ 39
CHAPTER 3: Methodology .............................................................................................. 44
Overview of Testing Procedure .................................................................................. 44
Equipment Used ........................................................................................................... 46
ATOS system. ......................................................................................................... 46
Sensor configurations ......................................................................................... 47
Calibration.......................................................................................................... 48
Gage block selection & preparation. ....................................................................... 49
Point Cloud Acquisition ............................................................................................... 53
Post-Processing ............................................................................................................ 56
Polygonization using ATOS software. ................................................................... 57
Developing constraint based solid 3D models. ....................................................... 59
Measurement Method .................................................................................................. 64
Procedure for Analyzing Data ..................................................................................... 65
CHAPTER 4: Analyisis and Results................................................................................. 68
Normal Probability Test ............................................................................................... 68
One Sample t-test ......................................................................................................... 71
F-test ............................................................................................................................ 74
Two Sample t-test ........................................................................................................ 76
General Linear Model .................................................................................................. 79
Analysis of Variance (ANOVA) .................................................................................. 84
Chapter 5: Conclusion and Future Work .......................................................................... 87
Analysis of Statistical Results ...................................................................................... 87
Discussion of Results of t-tests .................................................................................... 88
One sample t-test..................................................................................................... 88
Two sample t-test. ................................................................................................... 90
GLM Discussion of Results ......................................................................................... 91
Conclusion ................................................................................................................... 92
Future Work ................................................................................................................. 93
REFERENCES ................................................................................................................. 96
APPENDIX A: Deviations Within Polygonization ........................................................ 101
APPENDIX B: Data Collected ....................................................................................... 102
APPENDIX C: One Sample t-test .................................................................................. 105
APPENDIX D: F-test ...................................................................................................... 108
APPENDIX E: Two Sample t-test Results ..................................................................... 114
APPENDIX F: General Linear Model ............................................................................ 120
APPENDIX G: ANOVA Results.................................................................................... 130
LIST OF FIGURES

Figure 2.1: Coordinate Measuring Machine .................................................................. 22
Figure 2.2: Simple diagram for interferometry ............................................................. 24
Figure 2.3: Diagram of photogrammetry center of projection principle ....................... 25
Figure 2.4: Coded target ................................................................................................ 26
Figure 2.5: Moiré pattern of two identical line patterns superimposed at an angle on a
flat surface .................................................................................................. 28
Figure 2.6: Out-of-plane Moiré pattern ......................................................................... 26
Figure 2.7: Triangulation of point P .............................................................................. 30
Figure 2.8: Distortion of coded light when projected onto an object ............................ 30
Figure 2.9: Gray code using four projection patterns . .................................................. 33
Figure 2.10: Gray code + phase shift .............................................................................. 34
Figure 2.11: Reference points, five 5mm on top, 3mm in the middle, and .8mm on
the bottom ................................................................................................... 36
Figure 2.12: Measured point cloud around a reference point .......................................... 37
Figure 2.13: Calibration object for the 120mm measurement volume ............................ 38
Figure 2.14: Transformation of a point cloud into a parametric solid model .................. 40
Figure 2.15: Polygon mesh abnormalities ....................................................................... 41
Figure 2.16: Repaired polygon mesh .............................................................................. 42
Figure 3.1: Lenses for the 90mm, 500mm, and, 250mm for the projector and left
and right cameras ........................................................................................ 46
Figure 3.2: ATOS IIe SO (left) and ATOS IIe 400 (right) ............................................ 47
Figure 3.3: False color mode for left and right cameras during aperture adjustment ... 48
Figure 3.4: Mitutoyo ceramic square gage blocks, sizes 1 inch, 0.5 inch, and 2 inch,
certified by NIST used during data collection ............................................ 50
Figure 3.5: 3mm reference points placed on the surface of the three gage blocks ........ 51
Figure 3.6: Front surface of polygon mesh ................................................................... 52
Figure 3.7: Two inch gage block inside the 120mm measurement volume .................. 54
Figure 3.8: Gage block orientation for each scan (left) and local point clouds of the
five corresponding scans (right) ................................................................. 55
Figure 3.9: Change in point density in curved regions, image created using scan data
from a gear acquired using the ATOS system ............................................ 59
Figure 3.10: Three planes used to locate the CAD data in 3D space ............................. 60
Figure 3.11: Readjusted position of the gage block within the Cartesian coordinate
system ......................................................................................................... 61
Figure 3.12: Polygon mesh after data were removed from the edges ............................. 63
Figure 3.13: Parametric model measured in Pro/Engineer .............................................. 64
Figure 3.14: Position of the four measurements taken from gage block scan data ......... 65
Figure 4.1: Normal probability plot for 90mm measurement volume .......................... 69
Figure 4.2: Normal probability plot for 120mm measurement volume ........................ 69
Figure 4.3: Normal probability plot for 250mm measurement volume ........................ 70
Figure 4.4: Normal probability plot for 500mm measurement volume ........................ 70
Figure 4.5: Interactions plot for measurement volume, object size and measurement
location ....................................................................................................... 80
Figure 4.6: Main effects plot from the GLM on the main effects ................................. 82
Figure 4.7: Box plot for measurement volume .............................................................. 85
Figure 4.8: Box plot for object size ................................................................................ 86
Figure 5.1: Normal distributions for the one inch object size ....................................... 89
Figure 5.2: Normal distributions for the two inch object size ....................................... 90
Figure 5.3: Normal distributions for the half inch object size ....................................... 90
LIST OF TABLES

Table 2.1: Measurement uncertainty of Geomagic’s algorithm based on the
ASME B89.4.10-2000 Standard Default Test ............................................. 43
Table 4.1: Descriptive statistics ..................................................................................... 71
Table 4.2: Results from one sample t-test using an alpha of 0.01 ................................. 73
Table 4.3: F-test results .................................................................................................. 76
Table 4.4: Results from t-tests ....................................................................................... 78
Table 4.5: Results of ANOVA for general linear model of main effects and
Interactions .................................................................................................... 80
Table 4.6: Results of ANOVA for general linear model of main effects only .............. 81
Table 4.7: Results from Tukey post hoc comparison test .............................................. 83
Table 4.8: Results from ANOVA on measurement volume .......................................... 84
Table 5.1: Accuracy table .............................................................................................. 93
ABSTRACT

The statistical accuracy of constraint-based three-dimensional (3D) models
created using reverse engineering software to post process scan data collected by an
Advanced Topometric Sensor (ATOS) system is currently unpublished information
useful to the end-user. Throughout the process of scanning an object and converting the
scanned data into a constraint-based 3D model, error can be introduced into the final
model. The error introduced into the constraint-based 3D model is difficult to calculate
due to a large number of variables and factors. The current study sought to characterize
the accuracy of this process based on different measurement volumes and object sizes.
Optical 3D metrology techniques have become an accepted method in the field of
reverse engineering. The popularity of optical 3D metrology is due in large part to the
non-contact approach, which can quickly produce a dense point cloud. Using post-
processing software, these point clouds can be converted into a constraint-based 3D
model and used in much the same manners as 3D models created using CAD software.
To simulate a variety of measurement conditions, four measurement volumes and
three object sizes were selected generating a total of 36-point clouds. The 36-point clouds
were converted into constraint-based 3D models. Four measurements were collected from
each 3D model. To analyze the data collected, hypothesis testing was conducted to
compare the data and inferential statistics were applied. The statistical tests include one-
sample t-tests, two-sample t-tests, a General Linear Model (GLM), and multiple 1-way
ANOVA. The statistical test found that a difference existed between the measured values
and the actual values for both the object size and measurement volume.
9
CHAPTER 1: INTRODUCTION

The purpose of the current thesis was to characterize the accuracy of a reverse
engineering process to develop constraint-based three-dimensional (3D) models. These
3D models were created using scan data collected by an Advanced Topometric Sensor
(ATOS) system and Geomagic Studio reverse engineering software. Throughout the
process of scanning an object and converting the scanned data into a constraint-based 3D
model, error was introduced into the final 3D model. Error within the reverse engineering
process is difficult to calculate due to a large number of variables. The current study
seeks to characterize the accuracy of the reverse engineering process contingent on
varying measurement volumes and object sizes. With the growing popularity in
commercial scanners used for applications such as reverse engineering and industrial
inspection, the demand for a greater understanding of the accuracy and precision of
reverse engineered 3D models is increasing.
Purpose and Objective
Optical 3D metrology using structured light scanning techniques has become an
accepted method in the field of reverse engineering, due in large part to the non-contact
approach, which can quickly produce a dense point cloud (Gesellschaft für Optische
Messtechnik [GOM mbH], 2006). Optical 3D measurement devices, such as the ATOS
system, generate 3D computer models that contain dimensional measurement information
of real world objects. According to V. Raja (2008), the ATOS system and other similar
systems convert the geometry of a physical object into a digital 3D point cloud for use in
computer-aided design (CAD) and computer-aided manufacturing (CAM) software