Sensors for Mechatronics Paul P.L Regtien Hertgelo The Netherlands AMSTERDAM BOSTON HEIDELBERG LONDON NEW YORK' OXFORD ELSEVIER PARIS SAN DIEGO SAN FRANCISCO SINGAPORE SYDNEY TOKYO
Contents Preface xi 1 Introduction 1 1.1 Sensors in Mechatronics 1 1.1.1 Definitions 1 1.1.2 Sensor Development 3 1.1.3 Sensor Nomenclature 4 1.1.4 Sensors and Information 6 1.2 Selection of Sensors 13 2 Sensor Fundamentals 19 2.1 Physical Quantities 19 2.1.1 Classification of Quantities 19 2.1.2 Relations Between Quantities 23 2.2 Sensor Classifications 26 2.2.1 Classification Based on Measurand and Application Field 26 2.2.2 Classification Based on Port Models 26 2.2.3 Classification Based on Conversion Principles 30 2.2.4 Classification According to Energy Domain 31 3 Uncertainty Aspects 35 3.1 Sensor Specification 35 3.1.1 Sensitivity 36 3.1.2 Non-linearity and Hysteresis 36 3.1.3 Resolution 37 3.1.4 Accuracy 38 3.1.5 Offset and Zero Drift 38 3.1.6 Noise 38 3.1.7 Response Time 39 3.1.8 Frequency Response and Bandwidth 39 3.1.9 Operating Conditions 39 3.2 Sensor Error Reduction Techniques 40 3.2.1 Compensation 41 3.2.2 Feedback Methods 44 3.2.3 Filtering 47 3.2.4 Modulation 48 3.2.5 Demodulation 51 3.2.6 Correction Methods 53
vi Contents 4 Resistive Sensors 57 4.1 Resistivity and Resistance 57 4.2 Potentiometric Sensors 58 4.2.1 Construction and General Properties 58 4.2.2 Electrical Characteristics 59 4.2.3 Interfacing 61 4.2.4 Contact-Free Potentiometers 64 4.2.5 Applications of Potentiometers 66 4.3 Strain Gauges 67 4.3.1 Construction and Properties 67 4.3.2 Interfacing 71 4.3.3 Applications of Strain Gauges 73 4.4 Piezoresistive Sensors 77 4.4.1 Piezoresistivity 77 4.4.2 Micromachined Piezoresistive Sensors 81 4.4.3 Applications of Piezoresistive Sensors 83 4.5 Magnetoresistive Sensors 87 4.5.1 Magnetoresistivity 87 4.5.2 Applications of Magnetoresistive Sensors 91 4.6 Thermoresistive Sensors 91 4.6.1 Thermoresistivity 91 4.6.2 Resistance Thermometer 92 4.6.3 Thermistors 93 4.7 Optoresistive Sensors 95 5 Capacitive Sensors 101 5.1 Capacitance and Permittivity 101 5.2 Basic Configurations of Capacitive Sensors 105 5.2.1 Flat-Plate Capacitive Sensors 105 5.2.2 Multiplate Capacitive Sensors 109 5.2.3 Silicon Capacitive Sensors 110 5.3 Interfacing 113 5.4 Applications 116 5.4.1 Capacitive Sensors for Position-and Force-Related Quantities 116 5.4.2 Particular Applications 118 6 Inductive and Magnetic Sensors 125 6.1 Magnetic and Electromagnetic Quantities 125 6.1.1 Magnetic Field Strength, Magnetic Induction and Flux 125 6.1.2 Permeability 127 6.1.3 Eddy Currents 128 6.1.4 Magnetic Resistance (Reluctance) and Self-Inductance 128 6.1.5 Magnetostriction 129
Contents vii 6.2 Magnetic Field Sensors 130 6.2.1 Coil 131 6.2.2 Hall Plate Sensors 131 6.2.3 Fluxgate Sensors 134 6.3 Magnetic and Induction Based Displacement and Force Sensors 136 6.3.1 Magnetic Proximity Switches 137 6.3.2 Inductive Proximity and Displacement Sensors 138 6.3.3 Eddy Current Displacement Sensors 139 6.3.4 Variable Differential Transformers 141 6.3.5 Resolvers and Synchros 143 6.3.6 Magnetostrictive or Elastomagnetic Sensors 145 6.4 Applications 147 6.4.1 Interfacing Inductive Sensors 148 6.4.2 Contact-Free Sensing Using Magnetic and Inductive Sensors 149 6.4.3 Applications of Variable Reluctance and Eddy Current Sensors 150 6.4.4 Applications of Other Inductive Sensors 153 7 Optical Sensors 161 7.1 Electro-Optical Components 161 7.1.1 Light Emitters 162 7.1.2 Light Sensors 165 7.1.3 Position Sensitive Diode 167 7.2 Optical Displacement Sensors 170 7.2.1 Intensity Measurement 170 7.2.2 Triangulation 173 7.2.3 Optical Encoders 176 7.2.4 Interferometry 182 7.2.5 Time-of-Flight 188 7.3 Interfacing 188 7.3.1 LEDs and Photo Diodes 188 7.3.2 Interfacing PSDs 190 7.4 Applications 191 7.4.1 Linear Displacement Sensing 192 7.4.2 Angular Displacement Sensing 199 7.4.3 Object Tracking 201 7.4.4 Object Shape 204 7.4.5 Navigation 208 7.4.6 Force, Torque and Strain Sensing 211 8 Piezoelectric Sensors 219 8.1 Piezoelectricity 219 8.1.1 Piezoelectric Materials 219 8.1.2 Piezoelectric Parameters 221
viii Contents 8.2 Force, Pressure and Acceleration Sensors 228 8.2.1 Construction 228 8.2.2 Characteristics of Accelerometers 230 8.3 Interfacing 232 8.4 Applications 234 8.4.1 Stress and Pressure 235 8.4.2 Acceleration 235 8.4.3 Tactile Sensors 236 9 Acoustic Sensors 241 9.1 Properties of the Acoustic Medium 241 9.1.1 Sound Intensity and Pressure 242 9.1.2 Sound Propagation Speed 242 9.1.3 Acoustic Damping 243 9.1.4 Acoustic Impedance 244 9.2 Acoustic Sensors 245 9.2.1 General Properties 245 9.2.2 Electrostatic Transducers 248 9.2.3 Piezoelectric Transducers 249 9.2.4 Arrays 251 9.3 Measurement Methods 252 9.3.1 Burst 253 9.3.2 Continuous Sine Wave (CW) 255 9.3.3 Frequency-Modulated Continuous Waves (FMCW) 256 9.3.4 Other Signal Types 259 9.4 Applications 259 9.4.1 Navigation 259 9.4.2 Inspection 264 Appendix A Symbols and Notations 275 A.1 The Electrical Domain 275 A.2 The Thermal Domain 277 A.3 The Mechanical Domain 277 A.4 The Optical Domain 280 A.4.1 Optical Quantities 280 A.4.2 Radiant Energy from a Unit Surface with Lambertian Emission 283 A.4.3 Derivation of Relations Between Intensity and Distance 284 Appendix B Relations Between Quantities 287 B. l Generalized Equations 287 B.2 Application to Four Domains 289 B.3 Heckmann Diagrams 292
Contents ix Appendix C Basic Interface Circuits 295 C.l Operational Amplifier 295 C.2 Current-to-Voltage Converter 297 C.3 Non-Inverting Amplifier 298 C.4 Inverting Amplifier 300 C.5 Comparator and Schmitttrigger 301 C.5.1 Comparator 301 C.5.2 Schmitttrigger 302 C.6 Integrator and Differentiator 303 C.6.1 Integrator 304 C.6.2 Differentiator 304 C.7 Filters 307