Synchronization of pendulum like systems

Ankara : The Department of Electrical and Electronics Engineering and the Graduate School of Engineering and Science of Bilkent University, 2011.Thesis (Master's) -- Bilkent University, 2011.Includes bibliographical references leaves 92-96.Synchronization is a phenomenon that is widely encountered in nature, life sciences and engineering. There exist various synchronization definitions in various research fields. The general definition for synchronization is the adjustment of rhythms of oscillating systems due to their weak interaction. Synchronization problem depends on the type of applications that require suitable properties and comparison functions. Different applications require different properties and comparison functions. Throughout our study, we choose the comparison function to be the difference of the states variables of the systems in hand. In this thesis, we will present types and methods of synchronization which has practical applications, i.e. mechanical systems. Then, we will investigate the passive controlled in-phase synchronization of spring-damper coupled single and double pendulum systems by using various stability analysis for both the system in hand and its appropriately defined error dynamics. We mostly achieved in-phase synchronization in these coupled pendulum systems with a few exceptions which are based on several conditions. Finally, we will explain the masterslave synchronization of two ball hoppers using two different gait controllers, namely, fully-actuated and under-actuated controllers. By using fully-actuated controller for the slave hopper, we achieved apex state synchronization and by using under-actuated controller for the slave hopper, we achieved apex position synchronization between these two hoppers in master slave configuration.Kerimoğlu, DenizM.S

Pergel yürüme modelinin bilekte seri yaylı eyleyici ile denetimi ve kontrolü

Cataloged from PDF version of article.Thesis (Ph.D.): Bilkent University, Department of Electrical and Electronics Engineering, İhsan Doğramacı Bilkent University, 2017.Includes bibliographical references (leaves 94-100).Passive dynamic walking models are capable of capturing basic properties of walking behaviors and can generate stable human-like walking without any actuation on downhill surfaces. The passive compass gait model is among the simplest of such models, consisting of a planar point mass and two stick legs. A number of di erent actuation methods have been proposed both for this model and its more complex extensions to eliminate the need for a downhill sloped ground, balancing collision losses using gravitational potential energy. In this thesis, we introduce and investigate an extended compass gait model with series-elastic actuation at the ankle towards a similar goal, realizing stable walking on various terrains such as level ground, inclined surfaces and rough terrains. Our model seeks to capture the basic structure of how humans utilize toe push-o prior to leg lifto , and is intended to eventually be used for controlling the ankle joint in a lower-body robotic orthosis. We derive hybrid equations of motion for this model and obtain limit cycle walking on level and inclined grounds. We then numerically identify xed points of this system and and show numerically through Poincar e analysis that it can achieve asymptotically stable walking on level and inclined ground for certain choices of system parameters. The dependence of limit cycles and their stability on system parameters such as spring precompression and sti ness for level ground walking is identi ed by studying the bifurcation regimes of period doubling of this model, leading to chaotic walking patterns. We show that feedback control on the initial extension of the series ankle spring can be used to improve and extend system stability on level ground walking. Then, we investigate and identify the period doubling bifurcation regions of our model for spring precompression and ground slope parameter leading to various maps that we utilize for rough terrainwalking. Furthermore, we evaluate the performance of our model on rough terrains by applying ground slope feedback controllers on the spring precompression. Thereafter, we demonstrate that slope feedback along with stance leg apex velocity feedback control on the extension of the series ankle spring improves walking performance on rough terrains. The implementation of series elastic actuation on the ankle joint is realized with an experimental instantiations of active ankle foot orthosis system for the patients walking unnaturally and ine ciently with impaired ankles. Finally, we integrate the active ankle foot orthosis platform with an active knee orthosis platform where the experimentation results indicate that the integrated platform can generate e cient walking patterns.by Deniz Kerimoğlu.Ph. D

Stability of Planar Compass Gait Walking with Series Elastic Ankle Actuation

Passive dynamic walking models capture the natural dynamics of stable human-like walking. The passive compass gait (PCG) model, consisting of a point mass and two rigid legs, is among the simplest of such models. The fully passive nature of these models, however, necessitates a sloped ground to recover the energy lost during the ground collisions [1]. A variety of methods have been proposed to eliminate this requirement through different actuation methods. Among these are impulsive energy injection after foot collision, torque actuation on the hip, active ankle joints or tunable compliance in the leg [2, 3]. In this study, we propose a simple model to investigate how series elastic actuation (SEA) at the ankle can be used to achieve stable walking on level ground. The structure we propose is designed to behave in a similar fashion to how humans utilize toe push-off prior to leg liftoff, and is intended for eventual use within a lower-body robotic orthosis

Pars Plana Vitrektomi ve Endolazer Tedavisi Uygulanan Regmatojen Retina Dekolmanlı Olgularda İntraoküler Silikon Yağının Retinal Sinir Lifi Kalınlığına Etkisinin Değerlendirilmesi

Purpose: To evaluate the effect of silicone oil (SiO) on retinal nerve fi ber layer thickness (RNFLT) by using optical coherence tomog-raphy in patients who underwent pars plana vitrectomy and SiO injection for retinal detachment.Material and Methods: A total of 50 eyes of 50 patients were retrospectively enrolled in this study. 34 patients (68%) were male,16patients (32%) were female. SiO was injected in 50 eyes and the healty fellow eyes (50 eyes) were evaluated as controls. RNFLT mea-surements were compared with the control eyes,one and three months after PPV and one month after SiO removal.Results: In siliconized eyes the temporal, inferotemporal,nasal,inferonasal quadrants and global measurements were signifi cantly thi-cker at fi rst month after PPV compared to controls (p0.001,p0.001,p0.044,p0.002,p0.001 respectively). Temporal quadrantand global measurements were signifi cantly thicker at third month after PPV (p0.001,p0.034). At fi rst month after SiO removal, thetemporal, nasal quadrants, global measurements were signifi cantly thicker (p0.004,p0.01,p0.018). Also siliconized eyes RNFLTmeasurements were evaluated between fi rst, second and third visit separately. Almost there was no signifi cant difference in quadrantsfor the measurements of the subsequent visits.Conclusions: A transient increase in RNFLT in some of the quadrants compared to the control eyes was found in the study due to thepresence of SiO in the globe.Amaç: Retina dekolmanı nedeniyle pars plana vitrektomi yapılıp silikon yağı tamponadı verilen hastalarda silikon yağının retinal sinirlifi tabakası (RSLT) kalınlığına etkisinin optik koherens tomagrafi ile değerlendirilmesi.Materyal ve Metod: 50 hastanın 50 gözü çalışmaya katıldı. 34 hasta (%68) erkek,16 hasta (%32) kadındı. 50 göze silikon verildi vediğer sağlam gözler (50 göz) kontrol olarak değerlendirildi. Silikonize gözlerin PPV’den bir ay ve üç ay sonra ve silikon alımından biray sonraki RSLT ölçümleri kontrol gözlerin ölçümleriyle kıyaslandı.Bulgular: Silikonize gözlerin PPV’den bir ay sonraki RSLT ölçümlerinde kontrol gözlere kıyasla temporal,inferotemporal,nazal,infe-ronazal kadranlarının ve global olarak istatistiksel olarak anlamlı kalın olduğu görüldü (p0.001,p0.001,p0.044,p0.002,p0.001 sırasıyla). PPV’den üç ay sonraki ölçümlerde global olarak ve özellikle temporal kadranın istatistiksel olarak anlamlı kalın olduğugörüldü (p0.034,p0.001). Silikon alımından bir ay sonra temporal,nazal kadranın ve global olarak RSLT ölçümlerinin anlamlı kalınolduğu görüldü (p0.004,p0.01,p0.018). Birinci,ikinci ve üçüncü vizitte yapılan silikonize gözlerin RSLT ölçümleri ayrıca kendiiçlerinde de değerlendirildi ve ayrı ayrı kıyaslandığında istatisitksel olarak anlamlı kalınlık farklılığı olmadığı görüldü.Sonuç: Silikonun göz içinde bulunduğu süre içerisinde bazı kadranlarda kısa süreli olsa da kontrol gözlere kıyasla kalınlık artışı olduğugörülmüştür