Quadruped locomotion reference synthesis wıth central pattern generators tuned by evolutionary algorithms

With the recent advances in sensing, actuating and communication tecnologies and in theory for control and navigation; mobile robotic platforms are seen more promising than ever. This is so for many fields ranging from search and rescue in earthquake sites to military applications. Autonomous or teleoperated land vehicles make a major class of these mobile platforms. Legged robots, with their potential virtues in obstacle avoidance and cross-country capabilities stand out for applications on rugged terrain. In the nature, there are a lot of examples where four-legged anatomy embraces both speed and climbing characteristics. This thesis is on the locomotion reference generation of quadruped robots. Reference generation plays a vital role for the success of the locomotion controller. It involves the timing of the steps and the selection of various spatial parameters. The generated references should be suitable to be followed. They should not be over-demanding to cause the robot fall by loosing its balance. Nature tells that the pattern of the steps, that is, the gait, also changes with the speed of locomotion. A well-planned reference generation algorithm should take gait transitions into account. Central Pattern Generators (CPG) are biologically-inspired tools for legged-robot locomotion reference generation. They represent one of the main stream quadruped robot locomotion synthesis approaches, along with Zero Moment Point (ZMP) based techniques and trial–and–error methods. CPGs stand out with their natural convenience for gait transitions. This is so because of the stable limit cycle behavior inhertent in their structure. However, the parameter selection and tuning of this type of reference generators is difficult. Often, trial–and–error iterations are employed to obtain suitable parameters. The background of complicated dynamics and difficulties in reference generation makes automatic tuning of CPGs an interesting area of research. A natural command for a legged robot is the speed of its locomotion. When considered from kinematics point of view, there is no unique set of walking parameters which yield a given desired speed. However, some of the solutions can be more suitable for a stable walk, whereas others may lead to instability and cause robot to fall. This thesis proposes a quadruped gait tuning method based on evolutionary methods. A velocity command is given as the input to the system. A CPG based reference generation method is employed. 3D full-dynamics locomotion simulations with a 16-degrees-of-freedom (DOF) quadruped robot model are performed to assess the fitness of artificial populations. The fitness is measured by three different cost functions. The first cost function measures the amount of support the simulated quadruped receives from torsional virtual springs and dampers opposing the changes in body orientation, whereas the second one is a measure of energy efficiency in the locomotion. The third cost function is a combination of the firs two. Tuning results with the three cost functions are obtained and compared. Cross-over and mutation mechanisms generate new populations. Simulation results verify the merits of the proposed reference generation and tuning method

Dört bacaklı robotlarda merkezi örüntü üreteci ve genetik algoritmalar ile referans sentezi

Bu çalışmada Merkezi Örüntü Üretimi (MÖÜ) ile referansları sentezlenen dört bacaklı robotun dengeli yürüyüşü önerilmiştir. MÖÜ biyolojiden ilham alınarak oluşturulan bir referans sentezi yöntemidir. Bu yöntemde kullanılan uygun parametleri belirlemek, robotun düşmesini engellemek için önemlidir. Çalışmamızda bu parametreleri belirlemek için yine biyolojiden ilham alınarak oluşturulan Genetik Algoritma (GA) optimizasyon yöntemi kullanılmıştır. Genetik Algoritma’nın amaç fonksiyonu denge ve enerji tüketimi olarak seçilmiştir. MÖÜ yöntemi ile üretilen referanslar, 16 serbestlik dereceli dört bacaklı robotumuza üç boyutlu (3D) tam dinamikli benzetim ortamında uygulanmıştır. Benzetim sonuçları önerilen metodun geçerliliğini kanıtlamıştır

Dört bacaklı robotlar için önizlemeli kontrol ile sıfır moment noktası tabanlı yürüme yörüngesi sentezi

Bacakları üzerinde hareket eden robotların engel aşma konusunda önemli avantajları söz konusudur. Özellikle dört bacaklı robotların değişken arazi yapıları üzerinde birçok uygulamaları düşünülmektedir. Bu çalışmada, dört bacaklı bir robotun düz zemin üzerinde hızlı yol almasına yönelik tırıs türü ilerleme üzerinde durulmaktadır. Sıfır Moment Noktası (SMN) karalılık kriterine ve Doğrusal Ters Sarkaç Modeli’ne (DTSM) dayalı bir yürüme referansı sentez yöntemi sunulmaktadır. Tırıs ilerleme için bir SMN referans yörüngesi önerilmiş, bu yörüngeden, önizlemeli kontrol yaklaşımı ile Robot Ağırlık Merkezi (RAM) için bir referans yörünge elde edilmiştir. Oluşturulan ağırlık merkezi yörüngesi ters kinematik yöntemi ile bacak eklemlerinin konum referanslarının hesaplanmasında kullanılmıştır. Önerilen referans sentezi yöntemi, 16 serbestlik dereceli bir robot modeli ile üç boyutlu ve tam dinamikli bir simülasyon ortamında denenmiştir. Simülasyon sonuçları sunulan yaklaşımın başarılı olduğunu göstermektedir

Dört bacaklı robotlar için önizleme kontrolü ve sıfır moment noktası esaslı yürüyüş yörüngesi üretimi

Robota verilen görevde engel aşımı gerektiğinde bacaklı robotların geri kalan mobil robotlara göre önemli avantajları bulunmaktadır. Bu makalede dört bacaklı robotların düz bir yüzeyde yürüyüşü için bir ölçümleme üretimi yöntemi sunuldu. Bu yaklaşım sıfır moment noktası (SMN) temelli kararlılık ve doğrusal ters sarkaç modeli (DTSM) üzerinedir. Yürüyüş için SMN referans gezingeleri ileri sürülüp oradan önizleme kontorü vasıtasıyla robotun ağırlık merkezi (RAM) referansı için referans gezingeleri elde edildi. Bacak eklemlerinin pozisyonları RAM referans gezingeleri üzerine ters kinematik uygulanarak hesaplandı. Öne sürülen referans gezinge üretimi sentezi, tamamen dinamik 3 boyutlu benzetimle test edildi. Benzetimde 16 serbestlik derecesine (SD) sahip dört bacaklı robot modeli kullanıldı. Benzetim sonuçları, yürüyüş için yapılan referans üretim tekniğinin başarıya ulaştığını gösteriyor

Whole-body bound gait control of a quadruped robot equipped with an active spine joint

Legged robots stand out with their maneuverability and terrain adaptability potential owing to their articulated limb structure. Quadrupeds have considerable advantages on rugged terrain over wheeled and tracked robotic land platforms. They have virtues when employed for tasks in diverse environments. Still, commissioning quadruped robots is not a straightforward process. These robots have not only high degrees of freedom but also complex and non-linear dynamics. Nature provides us knowledge about how animals choose and vary their gait according to their locomotion speed while keeping their balance and utilizing their energy efficiently. Hence, quadruped robots need to perform a variety of gaits, including static and dynamic ones, during their assignments. Spine articulation is mainly put to work for fast, dynamic animal gaits. Spinal motion is also instrumental in gait to gait transitions. Therefore, adding an active spine to a quadruped robot is an effective way to boost its dynamic motion performance. Nonetheless, the additional degrees of freedom increase the complexity of the system. A complicated set of challenges has to be met for employing spine joints effectively. This dissertation presents a study on the dynamic bound gait of a quadruped robot equipped with a spinal joint. Motion generation is carried out by forming reference contact forces. Contact forces are planned with linear and angular momentum laws and impulse equations. Suitable contact forces are produced by an optimization algorithm. As an optimization solver, sequential quadratic programming is utilized. A hybrid force-motion control framework is created in the operational space for tracking generated references. A gait phase transition method is devised for the application of force and position controllers. To test the proposed method, a full-dynamics 3D simulation environment is built. The equations of motion of the quadruped robot are obtained by the Newton-Euler and the Lagrangian approaches. A linear complementarity problem is cast to develop constraint-based contact physics for ground interaction modeling. Simulation results verify the performance of the proposed whole-body motion control method

Bound gait reference generation of a quadruped robot via contact force planning

This paper presents a reference generation technique for bounding quadruped locomotion. Synthesis of the reference is carried out by forming contact forces. Contact forces are planned with the aid of linear and angular momentum conservation and impulse laws. For the purpose of obtaining a stable and continuous bound gait, linear and angular momentum changes are set to be equal to zero over a full gait cycle. This condition allows the robot body to keep its initial dynamics at the end of the cycle, thus, producing a stable bound gait throughout the cycles. Periodicity in vertical linear velocity and angular velocity is obtained. These settings also result in almost constant horizontal body linear velocity. Suitable contact forces are produced with an optimization algorithm. Sequential Quadratic Programming (SQP) is utilized as an optimization solver. Linear and angular momentum laws and a non-slipping condition are applied as constraints of optimization. A full-dynamics simulation environment is employed to test the proposed reference generation algorithm. Results verify the validity of the proposed reference generation method for quadruped bounding

Operasyonel uzayda hibrit kuvvet-hareket kontrolüne sahip tek bacaklı robot [A one-legged robot with hybrid force-motion control in operational space]

Bu çalışma, tek bacaklı bağımsız kaideli bir robot için dinamik hareketin nasıl oluşturulacağını açıklamaktadır. Referans sentezini gerçekleştirmek için hem ayağın salınım hareketinin hem de yerden etki eden temas kuvvetlerinin planlanması kullanılmıştır. Darbe kuvvetlerini azaltmak, salınım ve duruş fazları arasında yumuşak bir geçiş sağlamak için konum referansı olarak beşinci dereceden bir polinom kullanılmıştır. Temas kuvveti referanslarını sağlamak için momentum korunumu kuralları ve dürtü kullanılmıştır. Operasyonel alanda, üretilen referansları izlemek için hibrit bir kuvvet- hareket kontrol sistemi oluşturulmuştur. Kuvvet ve hareket kontrolörleri arasındaki geçişe yardımcı olmak için yürüyüş faz geçişi geliştirilmiştir. Önerilen kontrol metodu, tam dinamik simülasyon ortamı kullanılarak test edilmiştir. Sonuçlar, bağımsız kaideli tek bacaklı robot için önerilen kontrol sisteminin doğru çalıştığını destekler niteliktedir

Hybrid force-motion control for one-legged robot in operational space

This paper presents a dynamic locomotion generation for a one-legged floating-base robot. Reference synthesis is performed by planning both swing motion of the foot and contact forces acting from the ground. A fifth-order polynomial is employed as the position reference to reduce the impact forces and ensure a steady transition between the swing and stance phases. Contact force references are designed utilizing the laws of momentum conservation and impulse. A hybrid force-motion control framework is created in the operational space for tracking generated references. Gait phase transition is proposed to assist the transition between the force and motion controller. A full-dynamics simulation environment is utilized to test the proposed control framework. Results supported the competence of the proposed control framework for the floating-base one-legged robot

Push recovery of a quadrupedal robot in the flight phase of a long jump

Legged robots are well-suited for operation in challenging natural environments, such as steep obstacles or vast gaps in the ground. Aside from difficult terrain, robots may also encounter unanticipated impact forces while performing jumping gaits. When performing their gaits, legged robots should be able to maintain and regain their stability in the face of external perturbations. External disturbances should be detected, and necessary actions should be taken to maintain the robot's balance in order to ensure optimum landing conditions. This paper considers flight phase disturbances in the form of a push on the robot body and introduces a novel push recovery algorithm that uses angular momentum to generate reference trajectories for a quadrupedal robot with waist joints during the flight phase of a long jump. This method creates joint position reference trajectories for the quadrupedal robot's waist and rear hip joints in order to achieve the required orientation of the robot in the air. In order to track reference trajectories, PID joint control is utilized. The robot model employed for the computations is comprehensive because components of the robot body - the leg links and three torso sections - are represented with independent mass values. The proposed push recovery trajectory generation approach is computationally efficient and hence suitable to be employed in real-time applications. The suggested method is used to simulate a quadrupedal robot to test the push recovery algorithm following external disturbances in the flight phase of a long jump. The results demonstrate that the suggested approach performs well in terms of angular position and angular velocity accuracy and it can achieve a posture suitable for landing

Whole-body pace gait control based on centroidal dynamics of a quadruped robot

This paper studies the full-body motion generation of a quadruped robot for pace gait. A motion planning algorithm is designed based on the centroidal dynamics of the robot. The motion planning algorithm generates both position and force reference trajectories. These reference trajectories serve as a guide for the swing motion of feet during the swing phase, while they also serve as a guide for the ground contact forces during the stance phase. A hybrid force-motion control framework is constructed using the operational space formulation (OSF) in order to track generated reference trajectories. We contribute further to the OSF of floating-base robots by decoupling the dynamics of the right and left leg pairs to facilitate pace gait. The proposed motion generation method for pace gait is validated using a full-dynamics simulation environment. The results reveal the competence of the proposed whole-body pace gait control for a quadruped robot