A Large-Motion Po Wered Wheelchairs

LAMASS: A LARGE-MOTION ACTIVE SUSPENSION SYSTEM FOR PO WERED WHEELCHAIRS William W. Li B.A.Sc., Simon Fraser University, 1993 THESIS SUBMITTED IN PARTIAL, FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF APPLIED SCENCES in the School of Engineering Science O William W. Li 1997 SIMON FRASER UNIVERSITY December 1997 Ali rights reserved. This work may not be reproduced in whole or in part, by photocopy or other means, without permission of the author. National Library Bibliothèque nationale 1*1 of Canada du Canada Acquisitions and Acquisitions et Bibliographie Services services bibliographiques 395 Wellington Street 395. rue Wellington dttawaON KIAONQ Ottawa ON KIA ON4 CaMda Canada The author bas granted a non- L'auteur a accordé une licence non exclusive licence allowing the exclusive permettant à la National Library of Canada to Bibliothèque nationale du Canada de reproduce, loan, distribute or sell reproduire, prêter, distri'buer ou copies of this thesis in microform, vendre des copies de cette thèse sous paper or elecîronic fonnats. la forme de microfichelfilm, de reproduction sur papier ou sur format électronique. The author retains ownership of the L'auteur conserve la propriété du copyright in this thesis. Neither the droit d'auteur qui protège cette thèse. thesis nor substantial extracts fkom it Ni la thèse ni des extraits substantiels may be p~tedor otherwise de celle-ci ne doivent être imprimés reproduced without the author's ou autrement reproduits sans son permission. autorisation. ABSTRACT The design of a large-motion active suspension system for powered wheelchairs is described and discussed. A common problem with powered wheelchairs is their inability to navigate steep or rough terrain. As the seat support is typically ngidly fixed to the chassis, travelling dong or across a slope can result in the wheelchair's user sliding uncomfortably Erorn side to side. In more extreme cases, it is possible to lose control of the wheelchair as the center of gravity of the combined user and wheelchair system tilts out beyond the footprint formed by the wheels contacting with the ground. By moving the seat and user, which typically comprise half of the rnass of the wheelchair, relative to the wheelchair chassis, it is possible to maintain equivalent stability with a smaller footprint or enhanced stability for a given chassis as the wheelchair tilts according to the terrain it moves across. Any device which accomplishes this type of motion, though, must satisfy strict constraints with regards to safety, reliability, production cost, power consurnption, and size. One important constraint is the need to devise the mechanism such tliat it fits within the space already beneath the wheelchair's seat without adding bulk. One solution is to use a self-levelling type of active suspension to provide the motion. A proof-of-concept of the Large Motion Active Suspension System (LaMASS) has been built to test out this idea. LaMASS moves a scde mode1 of a human user according to input from inertial sensors mounted on the wheelchair chassis, attempting to keep the user level regardless of the extemai acceleration input. A design technique to satisfy the design constraints is discussed, and the resuIts of the LaMASS controller are anal yzed. Dedication This thesis is dedicated to the memory of Dr. Tom Richardson, whose example inspired me to leam more, whose support brought out my best, and whose Iessons will guide me for the rest of my life. Acknowledgements 1 would like to thank the guidance, support, and encouragement of my supervisor, Dr. Payandeh, without whom this work would not have been completed. 1 would also like to thank Simon Fraser University for providing the funding which made the construction of the proof-of-concept for the LaMASS system possible, through the Prototype Development Fund and the Wighton Endowrnent Fund. The wheelchair platform was kindly donated by Dr. Andrew Rawicz. As well, Dick and the rest of the guys in the Science Shop have always been helpfui to me whenever 1 needed anything quickly. I would also Like to thank Hamy Boehm for hdping me through the inevitable experimental blowups. Boiko Rawicz and Greg Hall also deseme a vote of thanks for working with me in the early stages of this project. Last, but not least, I want to thank my lovely significant other Jennifer for always believing in me. Table of Contents .. Approval .......................... ....... ................................................... ii ... ABSTRACT .................. .. ..... ... ......,................*..*............111 Dedication ...................................................................................... iv List of Tables ......................... .., .................................................... x List of Figures ............ ,. ..........*.... ...................................... xi Foreword ...................... ................................................................ xiv Chapter 1 Introduction ............................................................ 1 1.1 MOTIVATION.......................................................................................................... -3 Chapter 2 Background ...................... .... ..... ............................. 13 3.1 WHEELCHAIRMECHANICS: TERMS AND CONCEPTS....................................,..... 13 2.1.7 Co-ordinate S'rems ..................................................................................... 16 2.2.3 Types of Powered Wheelchairs................................................................... 17 2.2 PHYS~OLOGYOF MOBILITY DISABILITY ................................................................. 19 2.3 EFFECTSOF VIBRATION ON THE HUMANBODY ............................................. 20 2.4. I Passive Suspension ................................. .... .................................................. 24 2.4.2 Active Strspension....................................................................................... 23' 2.4. 3 Semi-Active Suspension ................. ..... ... ,.... ......................................... 30 2.1.4 Self-Levelling Sysrems ................................................................................. 30 Chapter 3 Theory and Modelling ..................... ....... ......... ....31 3.1 MODELLING........................................................................................................... 31 3.2.1 Stafic Tipping Criferion................................................................................ 37 3.2.2 Relafionship Berween S'stem Centre of Graviiy and Tipping Stability ........ 38 3.2.3 Formulation of Dynamic Tipping Sfabilio.............................................. 39 3.2.4 Threshold Unrecoverable Tipping Speed ..................................................... 40 3.2.j Maximum Tip Criterion ................................................................................ 43 3.2.6 Effect of Active Control on Sfability ............................................................. 43 Chapter 4 Mechanical Design ....................................... .......... 50 4.1 PROBLEMDEFINITION ............................................................................................ 50 4.4 DIMENSIONALCALCULATION AND OPT~MIZATION................................................ 68 Chapter 5 Implementation ...................... ....................... .......... 75 5.1 SYSTEMOVERVIEW ........................ ,........ ....................................................... 75 5.2 HARDWARESUBSYSTEMS ...................................................................................... 78 2 Z Power Supply ................................................................................................ 80 2 Inertial Sensor Platfarm ............................................................................... 81 vii Data Acquisition Board ................................................................................ 83 Supervisory Controllet-.................................................................................. 84 Motor Control Board .................................................................................... 8.5 Motor and Motor Position Board ................................. ... 87 Chapter 6 Results ......................................................................... 95 Chapter 7 Conclusions and Future Work ............................... 110 7.1 CONCLUSIONS...................................................................................................... 110 7.2.1 Hardware Design Considerdons .............................................................. 112 7.2.1.1 Safety and Reliability ............................................................................ 112 7.2.1.2 Power Consumption ............................................................................. 113 7.2.1.3 Size.......................................................................................................... 113 7.2.2 Addition oflnstrumentaiion Sensors ........................................................... II4 7.2.3 Use ofLarger Human Mass Model ............................................................. 114 7.2.4 Extension io Spatial Mechanism ................................................................. 114 viii 7.2. 5 UtiZizing a Serni-Active Suspension ............................................................ 114 Appendix 1 Electronic Schematics ........................................ 116 Appendix II Code for Acquiring Data ..................................

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