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Quadruped robot control and variable legtransmissions

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    Quadruped robot control and variable leg

    transmissions

    JOHAN INGVAST

    Doctoral ThesisStockholm, Sweden 2006

  • TRITA MMK 2006-02ISSN 1400-1179ISRN KTH/MMK/R--06/02--SEISBN 9171782575

    KTH, School of Industrial Engineering and ManagementSE-100 44 Stockholm

    Sweden

    Akademisk avhandling som med tillstnd av Kungl Tekniska hgskolan framlggestill offentlig granskning fr avlggande av teknologie doktorsexamen i maskinkon-struktion fredagen den 10 februari 2006 klockan 10.00 i M2, KTH, Brinellvgen 64,Stockholm.

    Johan Ingvast, Januari 2006

    Tryck: Universitetsservice US AB

  • Till

    Monica

    Moa och Jakob

  • Abstract

    The research presented in this thesis regards walking of quadruped robots,and particularly the walking of the WARP1 robot. The motivation for therobot is to provide a platform for autonomous walking in rough terrain.

    The thesis contains six papers ranging from development tools to actua-tion of robot legs. The first paper describes the methods and tools made forcontrol development. These tools feature: programming of the robot with-out low level coding (C-code); that the controller has to be built only oncefor simulation and experiments; and that names of variables and constantsare unchanged through the chain of software Maple Matlab Simulink Real Time Workshop xPCTarget.

    Three controllers, each making the robot walk are presented. The firstcontroller makes the robot walk using the crawl gait. The method usesstatic stability as method for keeping balance and the instantaneous trunkmotions are given by a concept using the so called weight-ratios. A methodfor planning new footholds based on the positions of the existing footholdsis also proposed and the controller experimentally verified.

    The second walking controller shows that the robot also can walk dynami-cally using the trot gait. The method proposed uses information from groundcontact sensors on the feet as input to control balance, instead of, which iscommon, inertial sensors. It is experimentally verified that WARP1 can trotfrom level ground onto a slope and turn around while staying balanced.

    The main ideas of these two walking controllers are fused in the thirdwhich enables smooth transitions between crawl and trot. The idea of usingthe ground contact sensors from the first controller is here used to estimatethe position of the center of mass. This controller uses weight-ratios in thegait crawl as well as in the dynamic gait trot. Hence, the method of usingweight-ratios is not only useful for static stability for which it was originallyintended. The controller is experimentally verified on WARP1.

    The WARP1 robot weighs about 60 kg, has 0.6 m long legs with threeactuated joints on each. The speed and strength is sufficient only for slowwalking, even though the installed power indicates that it should be enoughfor faster walking. The reason is that a walking robot often needs to be strongbut slow when the feet are on the ground and the opposite when in the air.This can not be achieved with the motors and transmissions currently used.

    A transmission called the passively variable transmission (PVT) is pro-posed which enhance motor capabilities of robot joints. It is elastic, nonlinearand conservative. Some general properties for elastic transmissions are de-rived such that they can be compared with conventional transmissions. ThePVT gives strong actuation at large loads and fast actuation at small loads.The proposed transmission is compared to a conventional transmission for aspecific task, and the result is that a smaller motor can be used.

    v

  • Preface

    PhD studies have been a fantastic experience for me, of course lots of hard work,late hours and desperation, but also great friends, parties and enthusiasm. TheCAS research group was pretty large when I joined in 1999. Head of the researchwas Tom, who later went to Canada and now works with banking. Lennart handedin his Licentiate thesis just a few months after I arrived and then left for theindustry. Freyr received his PhD a few years later and went home to Island, wherehe now works with banking. Christian is still in the Stockholm area and sticks tomechatronics, designing satelite equipment. Others have also been involved in theresearch group: PhD students from other departments; technicians Micke, JohanW. and Andreas; master students . . . most of them I dont know where they aretoday. Thanks all, it has been enjoyable to work with you. Well see where I goafter finishing abroad?1

    At the moment Im writing this, I have Johan T. in the same room, and Fredrikin the next where also Magnus should be. Thanks for being there. Some occasionsrelated to my years at the department are more memorable than others:

    Lunches at Restaurant Cypern. Thanks Payam, Peter and Christian for mak-ing those lunches so special

    Johan T. organized a ski weekend in Kittelfjll. We had some days of greatskiing Johan stayed home being ill.

    To all the friends that I should have cared about but not had the strength now,Ill be less involved, please accept me as a friend again.

    Jan, my supervisor, thanks for letting me follow my own research compass, andfor always taking the time, but most of all thanks for letting me do research onwalking robots.

    Christian, we have written a number of papers together. It has been a pleasureto work with you and I hope we will do it again.

    Mom and dad, thanks for all the support.My largest appreciation goes to my family: Moa, Jakob and particularly Monica.

    Thanks for coping with me during these years.

    Stockholm, January 2006Johan Ingvast

    Acknowledgment

    This work was supported by the Foundation for Strategic Research through theCentre of Autonomous Systems (CAS) at the Royal Institute of Technology.

    1No, I could not stand working at a bank.

    vii

  • List of published papersChristian Ridderstrm, Johan Ingvast, Freyr Hardarson, Mats Gudmundsson,Mikael Hellgren, Jan Wikander, Tom Wadden, and Henrik Rehbinder. The basicdesign on the quadruped robot Warp1. In Professional Engineering PublishingLimited, editor, 3rd International Conference on Climbing and Walking Robots,pages 87 94, Madrid, Spain, October 2000.

    Johan Ingvast, Christian Ridderstrm, Freyr Hardarson, and Jan Wikander. Im-proving a trotting robots gait by adapting foot reference offsets. In ProfessionalEngineering Publishing Limited, editor, 4th International Conference on Climbingand Walking Robots, pages 711718, Karlsruhe, Germany, September 2001.

    Christian Ridderstrm and Johan Ingvast. Combining control design tools from modeling to implementation. In Int. Conf. on Robotics and Automation,pages 13271333, 2001.

    Christian Ridderstrm and Johan Ingvast. Quadruped posture control based onsimple force distribution a notion and a trial. In IEEE/RSJ Int. Conf. onIntelligent Robots and Systems, pages 23262331, Hawaii, USA, 2001.

    Johan Ingvast. Derivation of ground interaction models for plastic soils speciallysuited for walking robots. Technical Report TRITA-MMK 2002:14, Dept. of Ma-chine Design, Brinellv. 83, 100 44 Stockholm, Sweden, June 2002.

    Johan Ingvast. A two dimensional bidirectional ground interaction model. InProfessional Engineering Publishing Limited, editor, 5th International Conferenceon Climbing and Walking Robots, pages 547 554, Paris, France, September 2002.

    Johan Ingvast and Jan Wikander. A passive load-sensitive revolute transmission.In Professional Engineering Publishing Limited, editor, 5th International Confer-ence on Climbing and Walking Robots, pages 603 610, Paris, France, September2002.

    Christian Ridderstrm and Johan Ingvast. Warp1: Towards walking in roughterrain smooth foot placment. In Professional Engineering Publishing Limited,editor, 6th International Conference on Climbing and Walking Robots, pages 467 474, Catania, Italy, September 2003.

    Johan Ingvast, Christian Ridderstrm, Freyr Hardarson, and Jan Wikander.Warp1: Towards walking in rough terrain control of walking. In ProfessionalEngineering Publishing Limited, editor, 6th International Conference on Climbingand Walking Robots, pages 197 204, Catania, Italy, September 2003.

    Johan Ingvast. PVT The passively variable transmission. Technical ReportTRITA-MMK 2005:17, Dept. of Machine Design, Royal Institute of Technology,S-100 44 Stockholm, Sweden, December 2005.

  • Contents

    Introduction 11 The science of walking . . . . . . . . . . . . . . . . . . . . . . . . . 32 The WARP1 robot . . . . . . . . . . . . . . . . . . . . . . . . . . . . 203 Methods and tools . . . . . . . . . . . . . . . . . . . . . . . . . . . . 254 Transmissions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 265 Summary of papers . . . . . . . . . . . . . . . . . . . . . . . . . . . 386 Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44Bibliography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47

    A Combining control design tools from modeling to implemen-tation 53A 1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54A 2 Development tools and methods . . . . . . . . . . . . . . . . . . . . . 55A 3 Models . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60A 4 Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62A 5 Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64Bibliography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67

    B The basic design of the quadruped robot WARP1 69B 1 Introduction . . . . . .