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Mechatronics Honours Project 2005 School of Mechanical Engineering Stumpy An autonomous bipedal robot Michael Cowling | Andrew Jeffs | Nathan Kaesler Supervisors: Dr Frank Wornle | Mr George Osborne 2 Background Mechanical Engineering • History of bipedal walking robots • 1968~1969: first functional robot: WL-3 • Current: fully functioning humanoids such as Honda ASIMO and Sony QRIO • Applications “Bipedal walking robots” www.humanoid.rise.waseda.ac.jp • Prosthetics for the disabled • Entertainment • Human assistance “Multifunctional Sony 2005 Above-knee Honda 2005 Prosthesis” www.humanoid.rise.waseda.ac.jp 3 Motivation Mechanical Engineering • University of Adelaide designed pneumatic muscles • Stimulate robotics research at the University 4 Seminar Outline • Project aims • Control techniques • Traditional method: biomechanical • Contemporary method: gait synthesis • Passive dynamic design concept • Design process • Passive biped for downhill walking • Pneumatic muscle actuated biped • Results and future directions Mechanical Engineering 5 • • • • Aims Mechanical Engineering Design and build a unactuated biped Extend design to incorporate muscle actuation Make self-contained Extension goal: incorporate standing still, stopping and starting 6 Design Methodologies Mechanical Engineering • Two main design methods • Biomechanical control • Traditional control method • Robust and versatile • ‘Robotic’ looking gait • Difficult and expensive to implement • Unnecessarily complex • Inefficient and heavy “Asimo X2 at Robodex 2003” http://www.plyojump.com/asimo.html • Control based on gait synthesis 7 Control by Gait Synthesis • Simulate natural kinematics of walking • Begins with essentials of walking • Actuate only when required • Relatively new approach • McGeer 1990, Wisse 2004 • • • • Inherent sequential design Suited to muscle actuation Simple control required Very efficient Collins et al 2005 Mechanical Engineering 8 Control by Gait Synthesis Mechanical Engineering • Passive dynamic concept • Gravitational power only • • • • Perfect starting point Natural looking gait Simple and light Leads to human-like behaviour • Only dynamically stable Collins et al 2005 Collins et al 2005 9 Preliminary Design Mechanical Engineering • Gait synthesis approach chosen • Simplifications to human physiology • Fewer degrees of freedom • Minimal actuators • Simplest walker concept • Natural starting point • Prototypes for feasibility • ‘Mancano’ promising • ‘Legoman’ unsuccessful ‘Mancano’ “Simplest Walker” ‘Legoman’ http://mms.tudelft.nl/dbl/research/biped 10 Design of Stumpy Mechanical Engineering • Extremely difficult task • Discrete events and varying configuration • Non-linear and naturally unstable dynamics • Complex mathematical model • Empirical results required • Design based on McGeer’s kneed walking model • Unactuated kneed biped • Made goals achievable McGeer 1990 11 Mechanical Design Mechanical Engineering • Simple mechanical layout • Four legs in pairs • Pinned knee joints • Curved feet • Consideration for tuning and actuation Muscle clamp • Limb lengths • Weight distribution • Muscle mounting • Foot position and radius Mass Clamp 12 Final Design Mechanical Engineering 13 Testing and Results • Many variables • Limb lengths • Foot radius • Mass distribution • Ramp angle • Starting conditions • Success! Mechanical Engineering 14 Testing and Results • Poor repeatability • Knee bounce main failure mechanism • Knee damping ineffective • Latch required • Very promising for next design stage Mechanical Engineering 15 Biped Actuation • Passive biped has limited functionality • Only walks downhill • Cannot start, stop or stand still • Actuation can overcome these • Modify passive biped • Add actuation • Add associated power and control Mechanical Engineering 16 Muscle Actuation Mechanical Engineering • Pneumatic muscle operation • Mains air or bottled CO2 supply (~2 bar) • Power required for switching • Preserves passive dynamic action • Other benefits • Simple construction • Light and powerful Valve assembly Gas supply • Low cost • Efficient Power Bladder 17 Mechanics Mechanical Engineering • Various muscle configurations possible • Actuate knees only • Actuate hips, and use knee latches • Actuate all joints, with either 1 or 2 muscles on each • Five muscles used • Antagonistic hip arrangement Inner leg lever arm • Only two actuators required • Simple lever arm attachment • Muscle-spring system for knees 2 1 3 4 5 Outer leg lever arm 18 Electronics and Control Mechanical Engineering • Motorola 9S12C32 microcontroller on-board • H-Bridge muscle switching • On/off muscle sequencing • Real-time tuning via PC Micro • On-board user controls • Foot switch cycle initialisation H-Bridge • Li-ion batteries for power and electronics 19 Final design Mechanical Engineering 20 Results Mechanical Engineering • Stumpy walks successfully with some assistance 21 Achievements • Stumpy walked passively • Actuated walking successful • Will improve with fine tuning • Self-contained, but with mobile gas supply Mechanical Engineering 22 • • • • Future Directions Standing still, starting and stopping Turning Incorporating upper body More degrees of freedom • Two legs • Active ankles Mechanical Engineering 23 Conclusion Mechanical Engineering • Gait synthesis instead of biomechanical control • Two prototypes built • Passive biped Stumpy based on existing design • Walked successfully • Muscle actuation added to Stumpy • Powered biped walked with some assistance 24 Acknowledgements • Supervisors • Dr Frank Wornle and Mr George Osborne • Mechanical engineering workshop staff • Electronics and instrumentation staff Mechanical Engineering 25 Questions Mechanical Engineering
