Optical Methods in Engineering Metrology

Edited by D. C. Williams Division of Mechanical and Optical Metrology UK National Physical Laboratory

В CHAPMAN & HALL London . Glasgow . New York . Tokyo . Melbourne . Madras

Contents

List of contributors xv

Preface x v i i

1 Introduction 1 J. M. Burch 1.1 The optical metrologist 1 1.2 Optical measurement 3 1.3 A wider view 7

References 9

2 Laser beam geometry and its applications 11 D. С Williams 2.1 Analysis of laser beam size 11

2.1.1 Characteristics of a laser beam 11 2.1.2 Analysis using skew rays 16 2.1.3 Some applications of the theory 21

2.2 Increasing the precision 25 2.2.1 Three-point alignment system 25 2.2.2 Fresnel zone plates 27 2.2.3 Variable-focus zone plate 31 2.2.4 Variable-focus lens systems 36 2.2.5 Afocal lens systems 38 2.2.6 Bessel beam 40

2.3 The effect of the atmosphere 43 2.3.1 Bending of a light beam 44 2.3.2 Effect of temperature and pressure gradients 45 2.3.3 Two-colour methods 47

2.4 Detection of beam position 49 2.4.1 Photoelectric detection methods 49 2.4.2 Phase-sensitive systems 50 2.4.3 Bore straightness measurements 52 2.4.4 Quadrant detectors 57

Contents vii

2.4.5 Axial position detection 58 2.4.6 Photopotentiometers 60 2.4.7 Intensity-modulation methods 61 2.4.8 Measurement of large movements 63

2.5 Problem solving with optical devices 65 2.5.1 Scanning and triangulation techniques 65

67 74 76 78 79 82 85

87

93 94 95 98 99 99 100 101 103 103 105 106 107 108 108 109 110 112 112

Photogrammetry in industrial measurement 113 R. A. Hunt 4.1 The technique of photogrammetry 113 4.2 How to make a measurement 116

4.2.1 Choice of method 1

2.5.2 Two-mirror and related devices 2.5.3 Surface profilometer 2.5.4 Profilometry in two dimensions 2.5.5 Profilometry refinements 2.5.6 Roller parallelism measurements 2.5.7 Intensity-based measurements References

Alignment metrology B. S 3.1

3.2

3.3

3.4

3.5

. Pearn Instrumentation for alignment 3.1.1 Micro-alignment telescope 3.1.2 Lasers Telescope applications 3.2.1 Crankshaft bearings 3.2.2 Transport and process rollers 3.2.3 Coaxial spindles Flatness or level 3.3.1 Flatness on-board ship 3.3.2 Alignment on an offshore platform Autocollimation 3.4.1 Straightness by autocollimation 3.4.2 Electronic autocollimators 3.4.3 Flatness of surface tables 3.4.4 Angle comparison Practical problems 3.5.1 Environmental problems 3.5.2 Obstructed sight line 3.5.3 Parallax 3.5.4 Conclusion Reference

via Contents

4.2.2 Mathematical modelling 117 4.2.3 Experimental design 118 4.2.4 Prediction of uncertainties 118 4.2.5 Assessment of the method 118 4.2.6 The experiment 118 4.2.7 Estimation of experimental uncertainties 119

4.3 Mathematical formulation 119 4.3.1 The bundle solution 123 4.3.2 Least squares revisited 123 4.3.3 The Newton-Raphson method 124 4.3.4 Treatment of distortions 125 4.3.5 Error ellipsoids: fact or fiction? 126 4.3.6 Singularities in the solution 127 4.3.7 Design of experiments 128 4.3.8 Calculation of initial values 129

4.4 Imaging devices 129 4.4.1 Metric and semi-metric cameras 130 4.4.2 The NPL monocentric axicon camera 132 4.4.3 The role of the measuring machine 134 4.4.4 Finding the image centres 134

4.5 Towards real time 135 4.5.1 The coming of computer vision 136 4.5.2 Video theodolites 138 4.5.3 Location of images 139 4.5.4 True video photogrammetry 141

4.6 Applications for photogrammetry 144 4.6.1 Survey of an infrared telescope 145 4.6.2 The destruction of a bridge 148 4.6.3 Measurement of a fuel tank 149 References 152

5 Laser interferometry for precision engineering metrology 153 P. Gill 5.1 General principles 153

5.1.1 Optical interference by amplitude division 153 5.1.2 Limitations to fringe formation 154 5.1.3 Refractive index compensation 156 5.1.4 Single-wavelength fringe-counting interferometry 157

5.2 Stabilized laser wavelength sources 158 5.2.1 International definition of the metre 158 5.2.2 He-Ne stabilization techniques 159 5.2.3 Laser wavelength calibration and traceability 162

5.3 Heterodyne interferometry 163

Contents ix

5.4 Machine tool characterization 164 5.4.1 Angle measurement 164 5.4.2 Straightness measurement 165 5.4.3 Plane mirror interferometers 165

5.5 Laser interferometer measurement errors 166 5.5.1 System specification 166 5.5.2 Laser wavelength errors 166 5.5.3 Compensation errors 166 5.5.4 Interferometer verification 167 5.5.5 Operator errors 167

5.6 Multiple wavelength interferometry 168 5.6.1 Method of excess fractions 168 5.6.2 The NPL gauge-block interferometer 169

5.7 Multiple- and swept-wavelength interferometry using laser diodes 171 5.7.1 Laser diode properties and stabilization 171 5.7.2 EDM equivalence 174 5.7.3 Multiple-wavelength diode theory and application 175 5.7.4 Swept-wavelength diode theory and application 176 5.7.5 Future trends 176 References 177

Laser vibrometry 179 N. A. Halliwell 6.1 Laser Doppler velocimetry 179

6.1.1 Principles of operation 180 6.1.2 Frequency-shifting devices 183 6.1.3 Doppler signal processing 186

6.2 Solid surface vibration measurement 187 6.2.1 Laser speckle effects and theory of operation 188 6.2.2 Measurements on rotating targets 190 6.2.3 Choice of vibrometer: practical considerations 191

6.3 Torsional vibration measurement 194 6.3.1 Cross-beam torsional vibrometer 195 6.3.2 The laser torsional vibrometer 197 6.3.3 Practical considerations 201

6.4 Fibre optic vibration sensors 203 6.4.1 Intrinsic vibration sensors 204 6.4.2 Extrinsic vibration sensors 206 6.4.3 A practical all-fibre laser vibrometer 207 6.4.4 The fibre optic vibrometer: practical considerations 208 References 210

Laser Doppler velocimetry texts 210 Other references 210

x Contents

Industrial application of holographic interferometry R.J. 7.1

7.2

7.3

7.4

7.5

7.6

7.7

7.8

Parker Holography 7.1.1 Recording the whole picture 7.1.2 Two-beam interference and holography 7.1.3 Recording transmission holograms 7.1.4 Viewing in white light Equipment for holography 7.2.1 Lasers 7.2.2 Laser safety 7.2.3 Recording materials 7.2.4 Other holographic equipment Measurement with holograms 7.3.1 Holographic interferometry 7.3.2 Fringe pattern interpretation and analysis 7.3.3 Resolving components of displacement 7.3.4 Automatic analysis Applications of holographic interferometry 7.4.1 Non-destructive testing Vibration analysis by holography 7.5.1 Time-averaged holograms 7.5.2 Large-object or large-amplitude analysis 7.5.3 Holography of rotating objects Flow visualization 7.6.1 Fringe interpretation 7.6.2 Two-dimensional flows 7.6.3 Three-dimensional flows 7.6.4 Real-time flow visualization 7.6.5 Rotating flows Holographic contouring 7.7.1 Two-angled illumination 7.7.2 Two-refractive-index techniques 7.7.3 Two-wavelength techniques 7.7.4 Holographic contouring - new potential Conclusion References and bibliography

Television holography and its applications J. С 8.1

8.2

Davies and C. H. Buckberry Limitations of conventional holography 8.1.1 The need for holography 8.1.2 The benefits and limitations of holographic analysis Principles of television holography

213

213 214 214 216 217 218 218 219 220 226 228 228 231 232 233 235 236 242 242 247 250 253 254 255 259 259 261 262 264 266 268 270 270 270

275

275 276 277 278

8.3

8.4

8.5

8.6

8.2.1 Resolution requirements 8.2.2 Forming TV holograms 8.2.3 The effect of the aperture stop 8.2.4 Operating modes 8.2.5 Fringe formation Systems and their operation 8.3.1 Optical arrangement 8.3.2 Operating parameters 8.3.3 Fibre optic systems 8.3.4 Setting up a system 8.3.5 Alternative operating geometries Modulation techniques 8.4.1 Limitations of a basic system 8.4.2 Intensity modulation 8.4.3 Phase modulation 8.4.4 Combined modulation Automatic fringe analysis 8.5.1 Digital processing 8.5.2 The engineering need 8.5.3 Phase-measurement algorithms 8.5.4 Application of phase stepping to TV holography 8.5.5 Practical considerations 8.5.6 Practical examples 8.5.7 Conclusions Examples of applications 8.6.1 Automobile applications 8.6.2 In-situ measurement of stone degradation 8.6.3 Structural integrity testing 8.6.4 Pulsed TV holography 8.6.5 Surface contouring 8.6.6 Future developments Acknowledgements References

Contents xi

278 279 281 284 284 286 286 289 291 292 293 295 296 296 298 300 301 301 302 302 306 308 311 316 316 316 325 328 330 332 335 336 337

Moire methods in strain measurement 339 C. Forno 9.1 Conventional moire measurements 339

9.1.1 The moire phenomenon 339 9.1.2 Out-of-plane moire techniques 340 9.1.3 Imaged moire 342 9.1.4 In-plane measurement analysis 344 9.1.5 In-plane measurement techniques 347

9.2 High-resolution moire photography 348

Contents

9.2.1 Tuning the lens response 349 9.2.2 Photographic recording 352

9.3 Application of modified camera 354 9.3.1 Spatial filtering of moire fringe patterns 355 9.3.2 Fringe-pattern analysis 356 9.3.3 Examples of engineering structures 358 9.3.4 Deformation measurement in a timber structure 358

9.4 Types of surface pattern 362 9.4.1 Printed pattern 362 9.4.2 Stencilled patterns 366 9.4.3 Random patterns 369

9.5 Additional features of the technique 372 9.5.1 Optical differentiation 372 9.5.2 Three-dimensional movement 374 9.5.3 Pattern frequency multiplication 374 9.5.4 Optical regeneration of defective gratings 374 9.5.5 Displacement sensitivity direction 375

9.6 Moire interferometry 375 9.6.1 Two-beam interference 375 9.6.2 Surface grating 379 9.6.3 Moire fringe analysis 381 Acknowledgement 382 References 383

Automatic analysis of interference fringes 385 G. T. Reid 10.1 Intensity-based methods 386

10.1.1 Dedicated systems 386 10.1.2 Fringe tracking 390

10.2 Phase-based methods 395 10.2.1 Electronic heterodyning 395 10.2.2 Phase stepping 397 10.2.3 Spatial phase measurements 405 References 410

Monomode fibre optic sensors 415 J. D. C. Jones 11.1 Measurement using optical fibres 415 11.2 Transduction mechanisms 417

11.2.1 Sensor transfer function 418 11.2.2 Phase modulated sensors 418 11.2.3 Polarization-modulated sensors 419

Contents xiii

Optical processing 11.3.1 Two-beam interferometers 11.3.2 Multiple-beam interferometers 11.3.3 Polarimetrie techniques 11.3.4 Spectral techniques Modulators and components 11.4.1 Phase modulation 11.4.2 Polarization modulation 11.4.3 Frequency modulation 11.4.4 Directional couplers Electronic processing 11.5.1 Active homodyne processing 11.5.2 Passive homodyne processing 11.5.3 Heterodyne processing 11.5.4 Noise considerations Applications 11.6.1 Intrinsic sensors 11.6.2 Extrinsic sensors References

420 421 425 427 429 430 431 432 434 436 439 440 442 445 445 450 450 457 459

Index 465