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Universidade do Minho Escola de Engenharia Mafalda Araújo Seara Couto 3D Modelling and Design of a Bioloid Compliant Quadruped Leg Dissertação de Mestrado Ciclo de Estudos Integrados Conducentes ao Grau

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Universidade do Minho Escola de Engenharia Mafalda Araújo Seara Couto 3D Modelling and Design of a Bioloid Compliant Quadruped Leg Dissertação de Mestrado Ciclo de Estudos Integrados Conducentes ao Grau de Mestre em Engenharia Biomédica Trabalho realizado sob a orientação de Professor Doutor José Mendes Machado Professora Doutora Cristina Manuela Peixoto dos Santos DECLARAÇÃO Nome: Mafalda Araújo Seara Couto Endereço electrónico: Telefone: Número do Bilhete de Identidade: Título dissertação: 3D Modelling and Design of a Bioloid Compliant Quadruped Leg Orientadores: Professor Doutor José Mendes Machado Professora Doutora Cristina Manuela Peixoto dos Santos Ano de conclusão: 2011 Designação do Mestrado: Mestrado em Engenharia Biomédica Área de Especialização: Biomateriais, Reabilitação e Biomecânica Escola: de Engenharia Departamento: de Engenharia Mecânica Nos exemplares das teses de doutoramento ou de mestrado ou de outros trabalhos entregues para prestação de provas públicas nas universidades ou outros estabelecimentos de ensino, e dos quais é obrigatoriamente enviado um exemplar para depósito legal na Biblioteca Nacional e, pelo menos outro para a biblioteca da universidade respectiva, deve constar uma das seguintes declarações: 1. É AUTORIZADA A REPRODUÇÃO INTEGRAL DESTA TESE/TRABALHO APENAS PARA EFEITOS DE INVESTIGAÇÃO, MEDIANTE DECLARAÇÃO ESCRITA DO INTERESSADO, QUE A TAL SE COMPROMETE; 2. É AUTORIZADA A REPRODUÇÃO PARCIAL DESTA TESE/TRABALHO (indicar, caso tal seja necessário, nº máximo de páginas, ilustrações, gráficos, etc.), APENAS PARA EFEITOS DE INVESTIGAÇÃO,, MEDIANTE DECLARAÇÃO ESCRITA DO INTERESSADO, QUE A TAL SE COMPROMETE; 3. DE ACORDO COM A LEGISLAÇÃO EM VIGOR, NÃO É PERMITIDA A REPRODUÇÃO DE QUALQUER PARTE DESTA TESE/TRABALHO Universidade do Minho, / / Assinatura: ii Acknowledgements To my parents and my brother First of all, I would like to give special thanks to my supervisor Prof. Dra. Cristina Santos for her professional support, guidance and encouragement throughout the development of this dissertation. I deeply appreciate her many efforts to proofread my dissertation over and over again. I am extremely grateful to my dissertation co-supervisor, Prof. Dr. José Machado, from the Department of Mechanical Engineering, for all the availability and orientation along the semester which has been fundamental in the elaboration of this project. To all the researchers from the Robotics Laboratory, with a special thanks to Vitor Matos and Miguel Oliveira, for their extensive knowledge and range of ideas during my work in the Webots TM software. My greatest acknowledgement goes to my family, my parents and my brother, for all the encouragement and support along the five years as a student. Love and thank for the values, the caring and trust, you are my motivation and my pride. To my academic family, with whom I have learn so much, thanks for the happiness, thanks for the brotherhood, thanks for all the sharing moments and finally thanks for the love. iii Big thanks to my friends, for the companionship, the joy, the affection, for their neverending patience, support and encouragement, but mostly for the friendship. You were fundamental during this time. Thanks for listening and accompaning me, thanks for being there. Finally, my thanks go to all those who are not particularly mentioned here. The work presented could not have been made without the support from many individuals. iv Abstract In the growing fields of rehabilitation robotics, prosthetics, and walking robots, the modeling of a real robot is a complex and passionate challenge. On the crossing point of mechanics, physics and computer-science, the development of a complete model involves multiple tasks ranging from the 3D modeling of the different body parts, the measure of the different physic properties, the understanding of the requirements for an accurate simulation, to the development of a robotic controller. In order to minimize large forces due to shocks, to safely interact with the user or the environment, and knowing the ability of passive elastic elements to store and release energy, compliant mechanisms are increasingly being applied in robots applications. This work aims to the elaboration of an accurate efficient three-dimensional model of the legs of the quadruped Bioloid robot and the development of a world showing the effect on Webots TM simulation software developed by Cyberbotics Ltd. The goal was to design a segmented pantographic leg with compliant joints, in order to actively retract the collision and the impact of the quadruped legs with the ground during locomotion. Geometrical and mechanical limits have to be evaluated and considered for the modeling setup. Finally a controller based on the use of Central Pattern Generators was improved in order to adapt to the novel model and simple tests were performed in the Webots TM, rendering a 3D model simulation for the different values of spring-damping coefficients at the legs knee joint. Through the a MATLAB algorithm, the characterization of the joint angles during simulation was possible to be assessed. v vi Resumo A modelação de um robot real é um desafio complexo e fascinante na crescente área da Robótica, que engloba desde robots de reabilitação, próteses a uma diversidade de outros dispositivos locomotores. No cruzamento da mecânica com a física e as ciências computacionais, o desenvolvimento de um modelo completo envolve várias tarefas que vão desde a modelação 3D das diferentes partes do corpo, a medição das propriedades físicos inerentes, a compreensão dos requisitos para uma simulação precisa bem como a aplicação de um controlador robótico. A fim de minimizar grandes forças devido a choques, interagir com segurança com o utilizador ou o ambiente e conhecendo a capacidade de armazenagem de energia por parte de elementos elásticos passivos, um sistema de amortecimento-mola demonstra ser uma aplicação de crescente interesse na Robótica. Este trabalho visa a elaboração de um modelo tridimensional eficiente e preciso das pernas do robô quadrúpede Bioloid a ser reproduzido num mundo no software Webots TM desenvolvido pela Cyberbotics Ltd. O objectivo foi desenhar uma perna pantográfica segmentada tridimensional a ser aplicada em paralelo com um sistema de amortecimento-mola de forma a retrair activamente a colisão e o impacto das patas do quadrúpede com o solo durante a locomoção. Deste modo para uma configuração do modelo bem sucedida são tidos em conta limites geométricos e mecânicos. Por ultimo, o controlador com base no uso de Central Pattern Generators foi melhorado a fim de se adaptar ao novo modelo e por conseguinte foram realizados testes simples usando o simulador Webots TM. Nesta parte experimental é realizada a simulação do modelo permitindo avaliar o comportamento do modelo 3D para diferentes valores de coeficientes de mola e de amortecimento aplicados a nível do joelho da perna. Através de um algoritmo MATLAB é possível caracterizar e analisar o comportamento doa ângulos das juntas durante a simulação. vii viii Table of Contents Acknowledgements... iii Abstract... v Resumo... vii Table of Contents... ix Abbreviations and Acronyms... xiii List of Figures... xv List of Tables... xix 1 Introduction The work presentation and motivation Bioloid robot presentation Considerations of the model Structure of the dissertation Passive compliant actuation systems State of the art of passive compliant actuators Actuators with fixed compliance Actuators with variable compliance Comparison of the passive compliant actuators Applications of passive compliant actuators ix 3 Quadruped leg configuration Legged Robots Robotic leg mechanism Types of leg structures Cheetah robot Three-segment leg Pantographic model actuation with a passive spring mechanism Leg modeling Novel model of the Leg Kinematic analysis for the leg model Virtual Leg Step Cycle Weight factor Morphology for the Spring-Damping model Experimental simulation Webots TM modelling Model Animation Servo Physics Robot Physics plugin Locomotion control Servomotor characterization Central Pattern Generator - CPG Simulation Analysis of the quadruped behavior Results discussion Conclusions and future work General conclusions x 6.2 Future work and final remarks Bibliographic References Appendixes A. Webots TM world file B. Physics plug-in input C. AX-12 servo dimensions D. Controller main command E. Simulation Graphics xi xii Abbreviations and Acronyms DoF ODE CoM CPG SEA MACCEPA PAM PPAM VSA AMASC VSSEA Degrees of Freedom Open Dynamics Engine Center of Mass Central Pattern Generator Series Elastic Actuator Mechanically Adjustable Compliance and Controllable Equilibrium Position Actuator Pneumatic Artificial Muscles Pleated Pneumatic Artificial Muscles Variable Stiffness Actuator Actuator with Mechanically Adjustable Series Compliance Variable Stiffness Series Elastic Actuator normalized length of the first leg segment (thigh/scapula) normalized length of the second leg segment (shank/upper arm) normalized length of the third leg segment (foot/lower arm) normalized distance of the pantograph attachment to, absolute length of the first leg segment (thigh/scapula) absolute length of the second leg segment (shank/upper arm), absolute length of the third leg segment (foot/lower arm) absolute length of the pantograph to attachment, xiii leg stiffness of the virtual leg body mass gravitational acceleration: 9.81 m/s 2 leg angle between / or / fully extended total length of the leg: 0.21 m length of the leg at touchdown current leg length relative leg length angle between the leg segment and the virtual leg angle of attack of the virtual leg leg force velocity of the center of mass with respect to the coordination system time of contact half-angle of the virtual leg spring constant at the knee joint damping constant at the knee joint xiv List of Figures Figure Puppy BIOLOID robot [6] Figure Quadruped robot model rendered in Webots TM [4] Figure 1.3 Control process and disposition block diagram for Bioloid motion generation [6] Figure A conceptual schematic of fixed compliance actuator adapted from SEA [19] Figure Serial and antagonistic variable compliance actuation schemes respectively [20].. 11 Figure Jack Spring TM Actuator s active and inactive regions [15] Figure MACCEPA actuator working principle [18] Figure The Simple, Cross-coupled and Bi-directional antagonist setups [19] Figure 2.6 Schematic of a rotational joint actuated by an antagonist pair of McKibbens [23]. 14 Figure Schematic of the Migliore's actuator [25] Figure 2.8 Variable Stiffness Actuator CAD views and schematic mechanism of one of the antagonistic pairs [19] Figure Simplified schematic overview of the AMASC [19] [26] Figure 2.10 Examples of SEA application. Spring flamingo [32], M2V2 bipedal [30] and anklefoot prosthesis [31] respectively Figure 2.11 Robot legs with antagonistic elastic actuators [12] Figure 2.12 a)one of the BiMASC s legs, partially assembled [33], b) Bipedal walking robot Lucy actuated by PPAM s [34], c) Bipedal walking robot Veronica actuated by MACCEPA s [34]21 xv Figure Concept of the pantograph leg of small mammals [48] Figure The tri-segmented limb abstraction for small mammals. The limbs are segmented in three parts Fore-limbs/Hind-limbs : scapula/femur, humerus/shank and lower arm/foot [12] Figure 3.3 Schematic description of a bi-segmented system configuration with a single joint and a tri-segmented with a par of joints respectively [49] Figure a) insect-type and b) mammal-type articulated legs respectively [42] Figure Orthogonal configuration RPP [42] Figure Two-dimensional pantograph mechanism legs [42] Figure Three-dimensional pantograph leg [42] Figure Cheetah robot prototype and side view of the architecture schematics respectively [11] Figure Diagram of the performance of the compliant mechanism of the pantographic leg (u v w) [50] Figure Pantographic three-segmentation for the Bioloid leg Figure Thigh segment of Bioloid leg model in Webots TM Figure Hardware sketch of the angles and the different points and segment lengths for the side view of the leg. The red line is the virtual single-segmented leg [50] [57] Figure 4.4 Variation on the virtual SLIP leg model during one step [12] [56] Figure 4.5 Trajectory expected for the hip (red line) and knee (blue line) angles during the step cycle of 16% Figure Diagram of the virtual leg variation during retraction Figure 4.7- Schematic representation of the torsional spring and damping parallel system at the knee joint Figure New quadruped robot model rendered in Webots TM Figure Webots TM specification of the Servo node [65] Figure Mechanical Diagram of a Servo [65] Figure Webots TM specification of the Physics node [65] Figure Webots TM specification of the Robot node [65] xvi Figure Schematic representation of the extra joints to be added in the physics plugin (green down arrow ) Figure AX-12 servomotors from Dynamixel and module rearview of actuation position [6]. 59 Figure 5.8 Simulation trajectory of the theoretical (black line) and practical knee angles during the step cycle with spring constant of 1.0 N.m/rad for different damping constant values Figure Simulation trajectory of the theoretical (black line) and practical knee angles during the step cycle with damping constant of 0.02 N.m.s/rad for different spring constant values Figure Mean deviation at the swing-to-stance point of the knee angles during the step cycle as function of the spring and damping constant values Figure C.1 - Servo AX-12 schematic dimensions (mm) [6] Figure E.1 - Simulation trajectory of the theoretical (black line) and practical knee angles during the step cycle with spring constant of 0.5 N.m/rad for different damping constant values Figure E.2 Simulation trajectory of the theoretical (black line) and practical knee angles during the step cycle with spring constant of 1.5 N.m/rad for different damping constant values Figure E.3 - Simulation trajectory of the theoretical (black line) and practical knee angles during the step cycle with spring constant of 2.0 N.m/rad for different damping constant values Figure E.4 - Simulation trajectory of the theoretical (black line) and practical knee angles during the step cycle with spring constant of 2.5 N.m/rad for different damping constant values Figure E.5 - Simulation trajectory of the theoretical (black line) and practical knee angles during the step cycle with damping constant of N.m.s/rad for different spring constant values. 92 Figure E.6 - Simulation trajectory of the theoretical (black line) and practical knee angles during the step cycle with damping constant of N.m.s/rad for different spring constant values. 92 xvii xviii List of Tables Table An overview of some of the properties for the different compliant actuators [15] Table Leg length and angle variation during step cycle Table Weight of the different body parts Table Servo Forces [65] Table 5.2 AX-12 technical specifications [4] [6] Table 5.3 Mean deviation at the swing-to-stance point of the knee angles during the step cycle with spring constant of 1.0 N.m/rad for different damping constant values Table Mean deviation at the swing-to-stance point of the knee angles during the step cycle with damping constant of 0.02 N.m.s/rad for different spring constant values Table 5.5 Mean deviation at the swing-to-stance point of the knee angles during the step cycle as function of the spring and damping constant values xix xx 1 Introduction This chapter presents the context of the framework, defining objectives to the development, as well as the motivations of the global project. This section ends with a brief description of the dissertations structure. 1.1 The work presentation and motivation The work developed in the present dissertation had the duration of one semester, being developed in the Control, Automation and Robotics Group of the University of Minho, in Guimarães. Nowadays, Robotics is growing fast and in the most fields, making a significant impact on many aspects of modern life. Locomotive robots are no exception and became an attractive field of research. Walking machines have a major interest in a large range of applications, from industry to healthcare, transportation, military applications, space and sea exploration, providing many advantages over human faculties in many of these situations in terms of safety and effectiveness [1] [2] [3]. Currently, the biomechanical models are very complex and their application in modeling keeps being applied on several areas. In robotics there are several studies and projects 3D Modelling and Design of a Bioloid Compliant Quadruped Leg 1 mimicking the human and animal behavior to improve the knowledge about their mechanisms and ultimately succeed in the many significant fields, like rehabilitation. The modeling and design of a robot is a complex and interesting challenge, therefore in order to minimize large forces due to shocks and to safely interact with the user or the environment, the motivation of this work aims to the elaboration of an accurate efficient threedimensional model of a quadruped robot with compliant legs. The main goal of this project is to improve the leg design of the Bioloid quadruped robot, from a three-dimensional model developed by Fillion-Robin [4]. For this purpose a new segmented pantographic robotic leg design was created using the Webots TM simulation software, with passive compliant knee joints associated. Focusing on a main issue which is the leg retraction, the design features to be implemented are essential for the performance of the quadruped when it contacts the ground. Thus, the use of well-designed passive compliant system comes as a benefit in order to obtain a successful operative leg. This component is not only useful to store energy and reducing power consumption, it also helps to make a segmented leg safe and robust when faced with external perturbations [5]. This project aim to a final leg incorporated in the Bioloid quadruped robot in order to perform a stable and linear locomotion. With the goal of a future real assembling of the developed mechanism the objective was to achieve a stable simulation of the novel quadruped using a qualified virtual software. 1.2 Bioloid robot presentation The ROBOTIS is a well-known, specialized company developer of robotic kits with a wide set of advantageous features, thus it holds an academic interest on research in many fields, greatly due to its robustness and versatility. The kit used in this project is named BIOLOID. Figure 1.1 illustrates the dog assembly known as Puppy. 2 3D Modelling and Design of a Bioloid Compliant Quadruped Leg Figure Puppy BIOLOID robot [6]. The basis of this project was the model created by Fillion-Robin [4], which holds a threedimensional model that closely resembles a real dog robot, as illustrated in Figure 1.2. Therefore some of the main characteristics (orientations, weight, etc.) presented in the Webots TM world from [4] were maintained. Figure Quadruped robot model rendered in Webots TM [4]. The robot design aim for the development of an accurate leg model both efficient and robust for a quadruped, using the same Webots TM simulator software to the rendering of a 3D model. The Webots TM platform, developed by Cyberbotics Ltd, in collaboration with the Swiss Federal Institute of Technology in Lausanne, performs a rapid prototyping environment for modeling, programming and simulating mobile robots models, demonstrating the different phases of the reproduction of the motion [4]. 3D Modelling and Design of a Bioloid Compliant Quadruped Leg 3 Webots TM reproduces several accurate properties, very important for modeling such as shape, color, mass, friction or density. The core of this software is based on the robust and pow
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