World Scientific Series in Robotics and Automated Systems - Vol. 5

ADVANCED TACTILE SENSING FOR ROBOTICS

edited by Howard R. Nicholls

Universlfy College of Wales Aberystwyth, UK

** World Scientific Singapore • New Jersey • London • Hong Kong

Contents

Preface v

1 Introduction to Tactile Sensing 1 1.1 Sensing and Robotics 1 1.2 A Sensing Taxonomy 2 1.3 What Is Tactile Sensing? 4 1.4 Some Attributes of the Tactile Domain 5 1.5 Haptic Sensing 8 1.6 Tasks For Tactile Sensors 9 References 11

2 Tactile Sensor Designs 13 2.1 Introduction 13 2.2 Methods of Transduction 15

2.2.1 Resistive 15 2.2.2 Piezoelectric and Pyroelectric Effects 20 2.2.3 Capacitive Techniques 23 2.2.4 Magnetic Transduction Methods 26 2.2.5 Mechanical Transduction Methods 29 2.2.6 Optical Transduction Methods 31 2.2.7 Other Techniques 36

2.3 Summary 37 2.3.1 Resistive and Conductive 38 2.3.2 Piezoelectric and Pyroelectric Effects 38 2.3.3 Capacitive Techniques 38 2.3.4 Magnetic Transduction Methods 39 2.3.5 Mechanical Transduction Methods 39 2.3.6 Optical Transduction Methods 40

References 40

3 Processing and Using Tactile Sensor Data 49 3.1 Introduction 49 3.2 Basic Tactile Sensing Issues 50

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x Advanced Tactile Sensing For Robotics

3.2.1 Parameters of Contact 50 3.2.2 Grasping and Tactile Sensing 51 3.2.3 Stahle Grasping With Intrinsic Tactile Sensing 54

3.3 Object Recognition Using a Single Tactile Image 55 3.4 Active Tactile Sensing 60

3.4.1 Shape Description Without Specific Models 61 3.4.2 Model Matching 62

3.5 Haptic Sensing 64 3.6 Conclusion 67 References 67

4 Planar Elasticity for Tactile Sensing 75 4.1 Introduction 75 4.2 Stresses and Strains in Plane Stress 77

4.2.1 Deflections for Plane Strain 80 4.2.2 Strain and Deflection Given Surface Traction 81 4.2.3 Determining Surface Tractions from Object Shape and Loading 83

4.3 Tactile Signal Processing 84 4.3.1 Deflection vs. Strain Measurements 85 4.3.2 Sensor Modelling 85 4.3.3 Filter Methods for Obtaining Surface Pressure and Deflection 85 4.3.4 Force Angle Estimation 86 4.3.5 Sampling Density 87 4.3.6 Finger Softness 90

4.4 Summary 91 References 91

5 Integrating Tactile Sensors - E S P R I T 278 95 5.1 Introduction 95 5.2 Project Structure 95 5.3 The Manufacturing Requirement 96 5.4 The Sensing Problem 97 5.5 An Integrated Approach 98

5.5.1 System Architecture 98 5.5.2 Tactile and Gripper System 99 5.5.3 Vision System . 103 5.5.4 Communications Infrastructure 103 5.5.5 System Operation 104

5.6 Conclusion 105 References 106

6 Distributed Touch Sensing 107 6.1 An Alternative To Regulär Array Sensing 107 6.2 The InFACT Project: Flexible Assembly 108

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6.3 The InFACT Machine Configuration 109 6.4 Sensing Philosophy and Sensor Integration 111 6.5 The Touch Probes 112 6.6 Assembly Sequence Specification 114

6.6.1 Measurement Tasks 115 6.6.2 Measurement Task Design 118 6.6.3 Uncertainties 118

6.7 Two Example Measure Tasks 120 6.7.1 The "Translate Until" Task 120 6.7.2 The "Find Hole Centre" Task 120

6.8 Conclusion 121 References 122

7 The Human Tactile System 123 7.1 Introduction . ., ,v 123 7.2 The Peripheral Nerve 124

7.2.1 Organisation of a Peripheral Nerve 124 7.2.2 Classification of Afferent Nerves 125 7.2.3 Afferent Fibre Distribution in a Peripheral Nerve 126 7.2.4 Nerve Conduction 126 7.2.5 Fast Adapting and Slowly Adapting Receptors 128

7.3 Nerve Terminals in the Skin 129 7.3.1 Structure of the Skin 129 7.3.2 Dermal-Epidermal Environment 129 7.3.3 Distinction Between Hairy Skin and Glabrous Skin 130 7.3.4 Glabrous Skin 131

7.4 Nerve Terminals in Glabrous Skin 131 7.4.1 Thermoreceptors and Nociceptors 133 7.4.2 Mechanoreceptors 134

7.5 Limb Proprioception 140 7.5.1 Afferents of the Joints 140 7.5.2 Afferents of the Muscles 142

7.6 Conclusion 143 References 144

8 Lessons From the Study of Biological Touch for Robotic Tactile Sensing 151 8.1 Introduction 151

8.1.1 What Is Touch Good For? 151 8.1.2 Definitions: Tactile, Kinesthetic, Haptic 152 8.1.3 Focus and Chapter Outline 152 8.1.4 What Can the Study of Biological Touch Contribute to

Robotics 153

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8.1.5 A Mini-tutorial on the Scientific Method in Biological Research 155 8.2 Skin Mechanics 158 8.3 Cutaneous Sensitivity 160

8.3.1 Amplitude Resolution 160 8.3.2 Spatial Sensitivity 162 8.3.3 Temporal Sensitivity 165 8.3.4 Spatiotemporal Transfer Function 168

8.4 Texture Perception 169 8.4.1 Psychophysics 169 8.4.2 Neural Basis 171 8.4.3 Static Touch vs. Scanning 173

8.5 Processing 2-dimensional Patterns 174 8.5.1 Behavioural 174 8.5.2 Neural Coding 178

8.6 Thermal Sensing 180 8.6.1 Psychophysics 180 8.6.2 Neural Coding 181 8.6.3 Robotic Applications 181

8.7 Processing Spatially Distributed Inputs 181 8.7.1 Fingers as Separate Processing Sites 182 8.7.2 Are Two Hands Better Than One? 182 8.7.3 Limited Cutaneous Field of View 182 8.7.4 Selective Attention 183 8.7.5 Preattentive vs. Attentive Tactile Processing 183 8.7.6 Features for Computational Models of Early Tactile Processing 184

8.8 Conclusion 185 References 185

9 Lessons From The Study Of Biological Touch For Robot ic Haptic Sensing 193 9.1 Introduction, Focus and Chapter Outline 193 9.2 Haptic Perception 194

9.2.1 Processing Raised 2-dimensional Spatial Patterns & Homoge-neous 3-dimensional Objects 195

9.2.2 Processing Common 3-dimensional Objects 197 9.2.3 Patterns of Manual Exploration: "Exploratory Procedures" . . 198 9.2.4 Constraints on the Selection of Exploratory Procedures . . . . 200 9.2.5 Two-stage Sequence of Manual Exploration During Haptic

Object Recognition 205 9.2.6 Towards a Computational Model of Constraint-driven Explo­

ration and Haptic Object Identification 206 9.2.7 The Development of Manual Exploration and Haptic Object

Perception 207

Contents xiii

9.2.8 Haptic Perception Through Wielding a Rod 207 9.3 Sensory-guided Motor Control 208

9.3.1 Cutaneous Information for Motor Control 208 9.3.2 Haptic Volumetrie Attributes for Lifting an Unknown Object . 213 9.3.3 Contour Exploration Procedures (CEPs) for Grasping/Manipulation

and the Role of the Second Hand 213 9.4 Conclusion 214 References 215

10 Object Recognition Using Active Tactile Sensing 221 10.1 Introduction 221 10.2 Early Work in Active Tactile Object Recognition 222 10.3 Interpretation Tree Methods 223

10.3.1 Eliminating Interpretations by Constraints 223 10.3.2 Strategies for Active Search 225

10.4 Intrinsic Tactile Sensing 228 10.4.1 Surface Recovery Using Intrinsic Tactile Sensing 229

10.5 Shape Interpretation Using Active Touch 232 10.5.1 Related Methods 233

10.6 Integrated Methods 234 10.6.1 Recognition Using Vision and Touch 234 10.6.2 Apprehension Using Vision and Touch 240

10.7 Summary 243 References 244

11 Experiments In Active Haptic Perception With The Utah-MIT Dextrous Hand 249 11.1 Introduction 249 11.2 A Haptic Perception Framework 250 11.3 The Columbia Hand-Arm System 253

11.3.1 Tactile Sensors 254 11.4 Exploratory Procedures for Object Recognition Tasks 256

11.4.1 Exploratory Procedure 1: Grasping by Containment 257 11.4.2 Exploratory Procedure 2: Planar Surface Explorer 261 11.4.3 Exploratory Procedure 3: Surface Contour Following 264

11.5 Summary 268 References 269

12 Future Trends in Tactile Sensing 273 12.1 Progress To Date 273 12.2 Some Key Trends in Tactile Sensing 274 12.3 Major Outstanding Issues 275 12.4 Conclusion 276 References 276

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Appendix. Basic Linear Elasticity 277 A.l Definitions of Stress and Strain 277 A.2 Stress and Strain Relations 279 A.3 Coordinate Transformations for Stresses 281 A.4 Elastic Equilibrium: Navier's Equation 283 A.5 Solution for Line Load on Half-Space 287

A.5.1 Normal Strain for Line Load 289 A.5.2 Surface Displacement for Line Load 289

A.6 Solution for Load on Half Space 290 References 290

Index 291