İki ayaklı yürüyen robot tasarımı ve prototip imalatı
Design and contruction of 12 dof biped robot
Yazar: ALPER GERÇEK
Danışman: PROF. DR. HİKMET KOCABAŞ ; YRD. DOÇ. DR. ZEKİ YAĞIZ BAYRAKTAROĞLU
İstanbul Teknik Üniversitesi / Fen Bilimleri Enstitüsü / Makine Ana Bilim Dalı / Konstrüksiyon ve İmalat Bilim Dalı
Derece: Yüksek Lisans, 2012
Konu: Makine Mühendisliği = Mechanical Engineering
Dizin: Makine mühendisliği = Mechanical engineering

Özet:
Bu tezde, on iki serbestlik derecesinden oluşan yürüyen bir robotun prototip imalatının yapılması hedeflenmiştir. İnsansı robot araştırmaları içinde iki ayaklı yürüme en zorlu mühendislik problemlerinden biridir. Bu projenin, iki ayaklı yürüme konusunda tecrübe sağlaması ve bundan sonraki insansı robot projeleri için bir ön çalışma teşkil etmesi amaçlanmıştır. Bu nedenle robot tasarımında, kollar ve kafa uzuvları bulunmamaktadır.Robotun, gövde, kalça eklem grubu, diz eklemi ve bilek eklem grubu olmak üzere dört ana montaj grubundan oluşması planlanmıştır. Montaj gruplarına ait tasarım kriterlerini belirleyebilmek için, boyutları ve kütlesi öngörülmüş bir çubuk modelin, bilgisayar ortamındaki benzetiminden faydalanılmıştır. Çubuk modelin fiziksel parametreleri belirlenirken, projenin hedefleri ve literatürdeki insansı robotların mevcut değerleri göz önüne alınmıştır. Analizler sonucunda çubuk modele ait eklem açısal yer değişimleri, tork ve açısal hız değerlerine ulaşılmıştır. Elde edilen bu değerler ve hazırlanan istekler listesi sayesinde tasarımı yapılacak robot için tasarım kriterlerini oluşturmuştur.Ödevin açık şekilde tasvir edilmesi ve projenin çerçevesinin oluşturulmasından sonra eklemlere ait mekanik sistemlerin verbal yapı strüktürleri oluşturulmuştur. Bu şemalar sistemlerin sahip olduğu giriş ve çıkış büyüklüklerini enerji, sinyal ve madde olmak üzere üç farklı birimde tanımlayarak, birimlerin birbiri arasındaki ilişkileri gösterir. Verbal yapı strüktürleri kullanılarak sistemin elemanter fonksiyon strüktürü, Koller elemanter fonksiyon simgeleriyle ifade edilip gösterilmiştir.Tasarım kriterlerine ve ödev tanımına cevap veren bir konsept tasarımı ortaya atılmış, detaylandırma bu konsept tasarım üzerinden yapılmıştır.Robot eklemlerine ait detaylı tasarım bölümünde, kullanılan hazır elemanlar ve mekanik yapı ayrıntılı şekilde ele alınmıştır. Tasarım sırasında, konumu ve yapısı sebebiyle riskli görünen parçaları, sonlu elemanlar yöntemiyle statik yapısal analizine tabi tutulmuş, gerekli görülen parçalarda iyileştirmeye gidilmiştir.Mekanik tasarımın ve hazır elemanların belirlenmesinden sonra, robot üstüne konuşlandırılmış elektrik ve kontrol ekipmanlarının tanıtımı yapılmış, bir biriyle olan ilişkileri belirlenmiştir. Ayrıca çubuk model için yapılan bilgisayar benzetimi, tasarlanan model ile tekrar edilerek doğruluğu yüksek yer değişimi, tork ve hız değerleri hesaplanmıştır. Bu değerler kullanılarak, seçilen hazır elemanların ve tasarımın doğrulaması yapılmıştır.Tasarımı biten parçaların, imalat ve montaj resimlerinin oluşturulması, uygun imalat yöntemleri ve toleransların seçimi yapılmıştır. İmalat listesini, teknik resimleri ve imalat sırasında gerekli tüm bilgileri içeren imalat klasörü oluşturulmuştur. Akabinde montaj ve ilk denemeler sırasında karşılaşılan sorunlar ve ek önlemler için robot tasarımı üzerinde belirli güncellemeler yapılarak, robota son hali verilmiştir.

Abstract:
This thesis presents design and construction details of a 12 Dofs biped walking robot. Bipedal walking is one of the most challenging research fields on humanoid robots. So this work aimed at providing experience on bipedal walking and to be pre-study of design and construction of a full humanoid robot. Therefore, biped robot design has no head and arms. Robot structure is formed by four subassemblies with torso, hip, knee and ankle. Kinematic structure is 6-Dof at the leg, 3 Dof at the hip, one at the knee and two at the ankle. The biped robot?s total weight is 55 kg and its height is 142 cm.Humanoid robots are autonomous robots, because they can adapt to changes in their environments or their self and continue to reach their goal. This is the main difference between humanoid and other kinds of robots. In this context, some of the capacities of a humanoid robot may include, among others: self-maintenance, autonomous learning, avoiding harmful situations to people, property and itself, safe interacting with human beings and the environment.Humanoid robots are created to imitate some of the same physical and mental tasks that humans undergo daily. Scientists and engineers from many different fields combine their efforts to create a robot as human-like as possible. The main goal for the robot is that one day it will be able to both understand human intelligence, reason and act like humans. If humanoids are able to do so, they could eventually work in collaboration with humans to create a more productive and higher quality future. Another important benefit of developing humanoid robot is to understand the human body's biological and mental processes.Asimo is one of the most successful humanoid robot project for all times. Honda and Wako Fundamental Technical Research Center develop it since middle of the 1980?s. Until today, 12 different prototypes are developed and manufactured. The most popular one of these prototypes is announced in 2005 with name of New Asimo.HRP is another milestone humanoid robot prototype, is developed by AIST, METI and NEDO in Japan. In the past several years, successful prototypes HRP4-C and HRP-4 are announced to public.In order to define design criteria belongs to assembly groups; hip, knee and ankle, a beam model simulation is used with a pre-defined dimensions and mass. Bipedal robots in literature are considered in defining masses and dimensions for beam model simulation.Beam robot model has 12 Dofs and 35 kg mass totally. Joints? angular displacements, angular velocities and torques are revealed form results of computer simulation based on beam model. Simulated walking speed of the beam model is 1 km/h under condition of predefined foot trajectories. In the presence of the simulation results, an inquiry list is generated and design criteria of bipedal robot studied in this thesis is derived from results and that inquiry list.After clarification of the goals and defining the frame of the project, verbal construction structures of joints? mechanical systems are derived. These schemes, states systems inputs and outputs in terms of energy, signal, matter, and defines interactions between them. System?s elementary function structure is expressed with Koller elementary function figures using the verbal construction structure.A concept design that meets the requirements of design criteria and project goals, is introduced and improvements and detailing of project is made based of this concept design. Concept design describes location, shapes, manufacturing techniques and power transmission system of the joints.Mechanical structure and units such as motors, couplings etc. are explained in the section of robots joints detailed design. During the design phase, parts that are seem to be critical according to their structure, are analyzed with finite element methods and necessary improvements are done.All Dofs are driven by dc motors. Harmonic drive units are used to reduce the velocity which is provided by motors. Also, it provides stiff and robust mechanical structure because of it has no backlash. Axes of the at hip joint, intersect at one point. Thus, inverse kinematic calculations are fairly straightforward. Incremental encoders are mounted to motor shafts to feedback the system. Moreover, initial conditions are defined by absolute encoders, are located to rotary axes of the each hip joints.Lower and upper legs consist of U-profiles containing all actuation and transmission mechanism of the knee and ankle joints. An industrial computer with real-time operating system, all motor drivers and sensors interfaces and a battery are situated on an upper body upon the hip joints.Knee and ankle joints are driven by vertically placed actuators through ball screw mechanism. Actuators and transmission driving higher than the driven rotating Dofs. In such a kinematic configuration, the center of mass of the robot moves also higher in vertical with respect to that of robots with direct driven joints.The knee joint has 90 degrees motion range, and it is driven by a ball screw mechanism which is actuated by a dc actuator placed in the upper leg. To provide the required conversion ratio, ball screw mechanism is used to as velocity reducer. In a same way to the hip joint, the incremental encoder is mounted to the dc motor shaft of the knee joint, and also, the absolute encoder is placed on the knee joint shaft to get rid of the measurement errors which may occur because of transmission mechanisms.In the lower leg, 2 Dofs of the ankle joints are driven by dc electrical actuators. Driving torque of the actuators is transmitted to the ankle joints by ball screw mechanism similar to the knee joint.The ball screw mechanism are guided on a polyamide part which is mounted on lower leg, therefore only linear displacements are allowed to the mechanism. Complexity of the power transmission of the ankle joint causes uncertain feedback by only incremental encoder. Therefore, additional absolute encoders are mounted to each ankle joints. Besides, 6 axes force-torque sensors are placed over feet to measure the forces and torques which are required for the control loop.The sensory system of the biped robot includes incremental and absolute encoders at all 12 joints and two force-torque sensors at each ankle. The components of the interaction forces exerted by the ground on the biped robot will be measured.The incremental encoders attached to the motor shafts to measure the angular displacements relative to initial values of each joint. Resolution of the incremental encoder which is 500 increments per revolution satisfies qualified measurement with highly stiff harmonic drive gears.Since an incremental encoder measures differentiation of angular positions, initial angular position of all joints must be measured by absolute encoders. The absolute encoders which are integrated to shafts of joints measure the initial values of joints before the biped robot stars walking. Measurement errors of the absolute encoders are negligible thanks to its 12-bit resolution pre revolutions.The biped robot consist of 12 Maxon dc motors driven by Epos motor drivers. The motor drivers drive dc motors with respect to trajectory data which is received from the computer via canbus.The embedded computer receives data from absolute encoders and force-torque sensors and transmits data to motor drivers via canbus. The computer which is installed embedded real time Linux operating system will provide the trajectories for static walking and control algorithms for dynamic walking.To simulate the biped robot model and control algorithm, Msc-Adams and Matlab-Simulink software packages are used. Simulink is responsible for the pattern generation and the dynamic controller, and Adams is responsible for the biped robot model. Reference joint trajectories are generated by Simulink and are sent to Adams. Adams solves the inverse dynamics of the biped robot and sends joint torques and contact forces back to Simulink.Feet paths are generated off-line and also desired ZMP references are generated off-line in accordance with the foot placements. To solve the inverse kinematics problem of the biped robot model, feet and torso paths must be known simultaneously. Torso path is generated to ensure dynamic balance of the robot. In torso path generation model predictive control and linear inverted pendulum model is used.Adams takes reference joint trajectories as inputs and gives joint torques and contact forces as outputs. CAD drawings of the parts are imported into Adams and all material properties and constraints are defined in Adams environment.Subsequent to selection of ready to use units and final design, electronic components and control equipments that takes place in the project are defined and interactions between each other is explained.Besides, computer simulation derived for beam model, is rerun for new designed model and angular displacements, angular velocities and torques are calculated with a high accuracy. Design and selection of ready to use units are validated with new simulation results.Following to design cycle, technical drawings for manufacturing and assemblies are drawn according to convenient manufacturing techniques and tolerances are defined. Manufacturing folder which contains technical drawings and all necessary information for manufacturing is created. Sequent, in the light of problems encountered during assemblies and first trials, some modifications are done and final design is released.After construction and assembly process and integration electrical components, joint?s basic functions and control system has been tested with movements in the air. The transmission mechanism of the hip, knee and ankle joints, are tested under various input. All sensors have been put in use and joint position references successfully controlled. The next step is, put the robot on ground and perform the actions are done in air. After test stage, experimentation of biped walking will start.