Optical Techniques for Industrial Inspection P. Cielo National Research Council of Canada Industrial Materials Research Institute Boucherville, Quebec, Canada ACADEMIC PRESS, INC. Harcourt Brace Jovanovich, Publishers Boston San Diego New York Berkeley London Sydney Tokyo Toronto
Contents Preface Chapter 1. Need and Functions of Industrial Inspection 1 1.1 Definition and scope of inspection activities in industry... 1 1.2 Human versus automated inspection 3 1.3 Economic factors 5 1.3.1 Quality and income 5 1.3.2 Quality and costs 9 1.4 Statistical techniques 11 1.4.1 The control chart 11 1.4.2 Statistical analysis 12 1.4.3 Sampling 15 1.5 Inspection requirements in the materials processing and manufacturing industries 17 1.5.1 Metallurgical industry 17 1.5.2 Metal fabricating and automotive industry 18 1.5.3 Pulp and paper 19 1.5.4 Chemical process industries 19 1.5.5 Plastics forming 20 1.5.6 Electronic components 20 xi v
vi CONTENTS Chapter 2. Overview of Nonoptical Inspection Techniques.... 23 2.1 Mechanical techniques 24 2.1.1 Mechanical gaging 24 2.1.2 Tactile sensors 26 2.2 Ultrasonic inspection 29 2.2.1 Active air propagation techniques 30 2.2.2 Passive airborne techniques 32 2.2.3 Active solid propagation techniques 35 2.2.4 Passive structure borne techniques 40 2.3 Radiographic inspection 44 2.3.1 Radiographic imaging 45 2.3.2 Thickness gaging 47 2.4 Electromagnetic techniques 53 2.4.1 Direct current methods 53 2.4.2 Eddy current inspection 55 2.4.3 Magnetic particle inspection 57 2.4.4 Microwave inspection 58 2.5 Sensors for industrial process control 61 2.5.1 Pressure sensors 61 2.5.2 Fluid sensors 65 2.5.3 Temperature sensors 70 2.5.4 In-process analyzers 72 Chapter 3. Fundamentals of Optical Technology 79 3.1 Light sources 79 3.1.1 Incoherent sources 80 3.1.2 Coherent sources 88 3.2 Lasers and safety 97 3.3 Optical detectors 103 3.3.1 Thermal detectors 104 3.3.2 Photoemissive detectors 104 3.3.3 Photoconductive and photovoltaic devices 106 3.4 Image sensing devices 108 3.4.1 Discrete detector arrays 108 3.4.2 Television tubes 113 3.5 Detection and noise 115 3.5.1 Environmental noise 115 3.5.2 Light-source noise 116 3.5.3 Electronic noise 121 3.6 Noise reduction techniques 124 3.6.1 Environmental noise reduction 124 3.6.2 Light source noise compensation 125 3.6.3 Reduction of electronic noise 128
CONTENTS vii 3.7 Optical elements 130 3.7.1 Imaging Systems 132 3.7.2 Optical materials 141 3.7.3 Holographie optical elements 144 3.8 Scanning techniques 148 3.9 Fiber optics 166 3.10 Speckle under coherent illumination 175 Chapter 4. Surface Inspection 185 4.1 Random surface profilometry 186 4.1.1 Surface roughness statistics 186 4.1.2 Tactile profilometry 190 4.1.3 Interferometric optical profilometry 192 4.1.4 Geometrical optics based profilometry 195 4.2 Surface monitoring by light-scattering techniques 203 4.2.1 Angular spectrum of the scattered light 203 4.2.2 Polarization and coherence properties of the scattered light 212 4.3 On-line surface inspection 219 4.3.1 Roughness analysis in rolled produets 221 4.3.2 On-line surface-defect detection 225 4.4 Techniques for automatic focusing 243 4.4.1 Angular sensing methods. 244 4.4.2 Sonar based approach 250 4.4.3 Image sharpness monitoring 251 Chapter 5. Optical Gaging and Profiling 257 5.1 On-line optical metrology 258 5.1.1 Part sizing 258 5.1.2 Alignment techniques 265 5.1.3 Thickness measurement 268 5.2 Two-dimensional imaging 278 5.2.1 Principles of image-processing techniques 279 5.2.2 Industrial applications 288 5.3 Three-dimensional imaging by incoherent techniques.... 294 5.3.1 Flying spot scanning methods 294 5.3.2 Pattern projeetion techniques 300 5.3.3 Passive techniques 305 5.3.4 Time-of-flight ranging 307 Chapter 6. Optical Techniques for Nondestructive Testing.... 311 6.1 Holographie nondestructive testing 312 6.1.1 Optical holography 313
viii CONTENTS 6.1.2 Strain analysis by holographic interferometry 316 6.1.3 Part loading methods and NDT applications 321 6.1.4 Heterodyne holographic interferometry 328 6.2 Speckle metrology 333 6.2.1 Speckle photography 334 6.2.2 Speckle interferometry 340 6.3 Focused beam testing 350 6.3.1 Vibration sensing by interferometric devices 351 6.3.2 Thermoelastic testing 361 6.3.3 Laser generation and detection of ultrasound 372 6.4 Thermal inspection 380 6.4.1 Single spot techniques 383 6.4.2 Thermal imaging techniques 392 6.5 A comparative assessment 397 Chapter 7. Optical Sensing for Process Control 401 7.1 Fundamentals of process control 402 7.1.1 Elements of automatic control 403 7.1.2 Stability of control loops 410 7.2 On-line optical sensing of temperature 413 7.2.1 Infrared thermal sensing 414 7.2.2 On-line industrial applications 418 7.3 Optical sensing of flow and speed 427 7.3.1 Doppler velocimetry sensors 428 7.3.2 Other optical techniques for fluid and motion sensing.. 431 7.4 Fiber optic sensors 437 7.4.1 Phase sensors 438 7.4.2 Amplitude sensors 441 7.5 An example of an optically controlled process: robotic welding 445 7.5.1 Fundamentals of robotic arc welding 447 7.5.2 Active optical sensors for robotic welding monitoring.. 451 7.5.3 Passive optical inspection 455 Chapter 8. Optical Techniques for Material Analysis 461 8.1 Spectroscopic techniques 462 8.1.1 Overview of the most common optical spectroscopy methods 462 8.1.2 Transmission and reflection spectroscopy 467 8.1.3 Raman and luminescence spectroscopy 472 8.2 Spectroscopy of industrial materials 478 8.2.1 Analysis of surface layers 478
CONTENTS IX 8.2.2 Quality control of epoxy-based products 485 8.2.3 Laser-induced breakdown spectroscopy 492 8.3 Nondispersive process analyzers 498 8.3.1 Basic principles 498 8.3.2 In-process material analysis 503 8.3.3 Combustion monitoring 508 8.4 Light scattering methods 514 8.4.1 Light scattering by an aggregate of particles 514 8.4.2 Industrial inspection of quasi spherical particles.... 518 8.4.3 Fiber monitoring in the pulp and paper industry... 525 8.5 Conclusion 530 References 533 Index 585