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Biologically Inspired Neural Control Network for a Bipedal Walking Model

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Biologically Inspired Neural Control Network for a Bipedal Walking Model BIOLOGICALLY INSPIRED NEURAL CONTROL NETWORK FOR A BIPEDAL WALKING MODEL by WEI LI Submitted in partial fulfillment of the requirements For the degree of Doctor of Philosophy Dissertation Advisor: Dr. Roger D. Quinn Department of Mechanical and Aerospace Engineering CASE WESTERN RESERVE UNIVERSITY January, 2017 CASE WESTERN RESERVE UNIVERSITY SCHOOL OF GRADUATE STUDIES We hereby approve the dissertation of Wei Li Candidate for the degree of Doctor of Philosophy* Committee Chair Roger Quinn Committee Member Musa Audu Committee Member Kiju Lee Committee Member Richard Bachmann Date of Defense: 11/28/2016 *We also certify that written approval has been obtained for any proprietary material contained therein. Table of Contents Table of Contents ....................................................................................................... i List of Tables ............................................................................................................. v List of Figures .......................................................................................................... vi Abstract .................................................................................................................... xi Chapter 1 Introduction .......................................................................................... 1 1.1 Research Objectives .................................................................................... 4 1.2 Dissertation Structure .................................................................................. 4 Chapter 2 Background .......................................................................................... 7 2.1 Introduction of CPG .................................................................................... 7 2.1.1 CPGs in Animals .................................................................................. 7 2.1.2 CPG Models ......................................................................................... 8 2.2 Sensory Feedback in Walking ................................................................... 12 2.2.1 Roles of Sensory Feedback ................................................................ 12 2.2.2 Feedback of Leg Load and Hip Joint Movement ............................... 14 2.3 Human Gait................................................................................................ 15 2.4 Biologically Inspired Bipedal Walking Control ........................................ 18 2.4.1 Passive Dynamics ............................................................................... 18 i 2.4.2 CPG-based Control ............................................................................ 18 2.4.3 Reflex Control .................................................................................... 20 2.5 Features of This Dissertation ..................................................................... 21 Chapter 3 Neuromechanical Simulation ............................................................. 23 3.1 Challenges in Researching Locomotion .................................................... 23 3.2 The Approach: Neuromechanical Simulation ............................................ 24 3.3 The Simulation Environment: Animatlab .................................................. 26 Chapter 4 Biomechanical model ......................................................................... 29 4.1 General Structure ....................................................................................... 29 4.2 Foot Design................................................................................................ 30 4.3 Muscle Model ............................................................................................ 31 Chapter 5 Neural Control Network ..................................................................... 35 5.1 Neural Models ........................................................................................... 35 5.1.1 Leaky Integrate-and-Fire Neuron Model ........................................... 35 5.1.2 Synapse Model ................................................................................... 38 5.1.3 Neural Facilitation Model .................................................................. 39 5.2 Half-center Oscillator ................................................................................ 40 5.3 CPG Network Without Sensory Feedback ................................................ 44 ii 5.4 Neural Network with Sensory Feedback ................................................... 50 5.4.1 Feedback of Ground Contact and Hip movement .............................. 50 5.4.2 Architecture of the Neural Network ................................................... 53 5.5 Connecting Neural Network to Muscles ................................................... 56 Chapter 6 Simulation of Normal Walking .......................................................... 60 6.1 Generation of Gait Cycle ........................................................................... 60 6.2 Kinematic Analysis .................................................................................... 68 6.2.1 Joint Angle.......................................................................................... 68 6.2.2 Displacement and Velocity ................................................................. 72 6.3 Kinetic Analysis ......................................................................................... 75 6.3.1 Ground Reaction Force ...................................................................... 75 6.3.2 Muscle Force ...................................................................................... 77 6.3.3 Joint Moment...................................................................................... 79 Chapter 7 Simulation of Walking with Perturbations ......................................... 82 7.1 Changing Neural Network Configuration ................................................. 82 7.2 Walking with Different Body Weights ...................................................... 96 7.3 Walking with Horizontal Pelvis COM Displacements ............................ 100 7.4 Walking Over Obstacle ............................................................................ 103 iii 7.5 Walking On Slopes .................................................................................. 106 Chapter 8 Conclusions and Future Works ......................................................... 111 8.1 Contributions ........................................................................................... 111 8.2 Future Works ........................................................................................... 115 Appendix A: Neuron Properties ............................................................................ 119 Appendix B: Synapse Properties ........................................................................... 120 Appendix C: Synaptic Weights in the CPG Neural Network ................................ 121 Bibliography .......................................................................................................... 122 iv List of Tables Table 4.1: Mass and dimension of leg part. ............................................................ 30 Table 4.2: Muscle parameters. EXT: extensor muscle, Flex: flexor muscle. .......... 34 Table 7.1: Walking performance after cutting off one synaptic connection............ 82 v List of Figures Figure 2.1: Classic half-center CPG model............................................................... 9 Figure 2.2: Unit burst generator (UBG) model ....................................................... 10 Figure 2.3: Rybak and McCrea’s two-level CPG model ........................................ 11 Figure 2.4: Two-level CPG model containing separated networks for rhythm generating and pattern formation ................................................................................. 12 Figure 2.5: Dynamic interaction between sensory afferents, spinal neuronal networks, and muscles in human walking ................................................................... 13 Figure 2.6: Normal human gait and phase plot ....................................................... 17 Figure 3.1: Neuromechanical simulations facilitating the interaction of robotics and biology. ......................................................................................................................... 26 Figure 4.1: The biomechanical model. .................................................................... 30 Figure 4.2: Human foot during stance phase. ......................................................... 31 Figure 4.3: The structure of the two-part foot. ........................................................ 31 Figure 4.4: Hill’s muscle model. ............................................................................. 32 Figure 4.5: Modeling muscle in Animatlab. ........................................................... 33 Figure 4.6: The stimulus-tension curve (left) and the length-tension curve (right) of the hip extensor muscle. ............................................................................................... 34 Figure 5.1: Simulation of a leaky integrate-and-fire neuron in Animatlab ............. 37 Figure 5.2: Neural facilitation and depression models............................................ 40 vi Figure 5.3: Simulation of a half-center oscillator in Animatlab.............................. 41 Figure 5.4: The output of a pattern
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