Tractable Quantification of Metastability for Robust Bipedal Locomotion

This work develops tools to quantify and optimize performance metrics for bipedal walking, toward enabling improved practical and autonomous operation of two-legged robots in real-world environments. While speed and energy efficiency of legged locomotion are both useful and straightforward to quantify, measuring robustness is arguably more challenging and at least as critical for obtaining practical autonomy in variable or otherwise uncertain environmental conditions, including rough terrain. The intuitive and meaningful robustness quantification adopted in this thesis begins by stochastic modeling of disturbances such as terrain variations, and conservatively defining what a failure is, for example falling down, slippage, scuffing, stance foot rotation, or a combination of such events. After discretizing the disturbance and state sets by meshing, step-to-step dynamics are studied to treat the system as a Markov chain. Then, failure rates can be easily quantified by calculating the expected number of steps before failure. Once robustness is measured, other performance metrics can also be easily incorporated into the cost function for optimization.For high performance and autonomous operation under variations, we adopt a capacious framework, exploiting a hierarchical control structure. The low-level controllers, which use only proprioceptive (internal state) information, are optimized by a derivative-free method without any constraints. For practicability of this process, developing an algorithm for fast and accurate computation of our robustness metric was a crucial and necessary step. While the outcome of optimization depends on capabilities of the controller scheme employed, the convenient and time-invariant parameterization presented in this thesis ensures accommodating large terrain variations. In addition, given environment estimation and state information, the high-level control is a behavioral policy to choose the right low-level controller at each step. In this thesis, optimal switching policies are determined by applying dynamic programming tools on Markov decision processes obtained through discretization. For desirable performance in practice from policies that are formed using meshing-based approximation to the true dynamics, robustness of high-level control to environment estimation and discretization errors are ensured by modeling stochastic noise in the terrain information and belief state while solving for behavioral policies

Model following control with discrete time SMC for time-delayed bilateral control systems

This paper proposes a new algorithm based on model following control to recover the uncompensated slave disturbance on time delayed motion control systems having contact with environment. In the previous works, a modified Communication Disturbance Observer (CDOB) was shown to be successful in ensuring position tracking in free motion under varying time delay. However, experiments show that due to the imperfections in slave plant Disturbance Observer (DOB) when there is rapid change of external force on the slave side, as in the case of environment contact, position tracking is degraded. This paper first analyzes the effect of environment contact for motion control systems with disturbance observers. Following this analysis, a model following controller scheme is proposed to restore the ideal motion on the slave system. A virtual plant is introduced which accepts the current from the master side and determines what the position output would be if there was no environment. Based on the error bet ween actual system and model system, a discrete time sliding mode controller is designed which enforces the real slave system to track the virtual slave output. In other words, convergence of slave position to the master position is achieved even though there is contact with environment. Experimental verification of the proposed control scheme also shows the improvement in slave position tracking under contact forces

Obstrüktif uyku apneli ve horlayan erişkin erkek hastaların dentofasiyal özelliklerinin değerlendirilmesi

Amaç: Bu çalışmanın amacı obstrüktif uyku apne sendromu (OUAS) olan erişkin erkek hastaların kraniofasiyal morfolojik özellikleri değerlendirmektir. Gereç ve Yöntem: Çalışmada 80 erkek hastanın (60 sefalogramları değerlendirildi. Bireyler Grup 1: horlama (AHİ5); Grup 2: hafif OUAS (5AHİ15); Grup 3: orta OUAS(15 AHİ30) ; Grup 4: şiddetli OUAS (AHİ30) olarak değerlendirildi. Sefalogramlar üzerinde hyoid, dil kökü ve yumuşak damak konumu, kranioservikal postür ve havayolu genişliğini belirleyen ölçümler yapıldı. Gruplar arasındaki farklar normal dağılım gösteren değişkenlerde tek yönlü varyans analizi ve Duncan testiyle, normal dağılım göstermeyen değişkenlerde Kruskal düzeltmesi uygulanarak Mann Whitney U testiyle yapıld

Quantifying the trade-offs between stability versus energy use for underactuated biped walking

Abstract — In this paper, we address the problem of incor-porating both energy consumption and stability into a cost function for bipedal walking. To solve the problem, we also propose a basic framework and demonstrate its effectiveness in simulation. This framework allows one to use a scalar coefficient to adjust the trade-off between stability and energy use. The optimal scalar value depends on the robot, terrain, task and priorities. In order to implement the methods in this paper, multiple low-level walking controllers and meshing of a ten-dimensional state space are needed. This latter requirement would normally be impractical for a 10D system; however, we exploit the observation that our low-level controllers cause the step-to-step dynamics to fill only a small, quasi-2D region, thus enabling meshing and, correspondingly, dynamic programming based on the resulting Markov Decision Process (MDP). Both the introduction of the energy/stability trade-off problem and our proposed framework for its solution have potential for significant utility in the future, as robot locomotion is developed to operate in increasingly less structured (stochastic) environ-ments. I

Metastable Markov chains

Abstract — In this paper, we discuss the dynamics of metastable systems. Such systems exhibit interesting long-living behaviors from which they are guaranteed to inevitably escape (e.g., eventually arriving at a distinct failure or success state). At the heart of this work, we emphasize (1) that for our goals, hybrid systems can be approximated as Markov Decision Processes, (2) that although corresponding Markov chains may include a very large number of discrete states, much of their dynamic behavior is well-characterized simply by the second-largest eigenvalue, which is directly analogous to a dominant pole for a discrete-time system and describes both the mean and higher-order modes of the escape statistics, and (3) that for many systems, one can accurately describe initial conditions as being rapidly forgotten, due to a significant separation in slow and fast decay rates. We present both theory and intuitive toy examples that illustrate our approach in analyzing such systems, toward enabling and encouraging other researchers to adopt similar methods. I

Obstrüktif uyku apneli ve horlayan erişkin erkek hastaların dentofasiyal özelliklerinin değerlendirilmesi

<p><strong>ÖZET </strong></p> <p><strong>Amaç:</strong> Bu çalışmanın amacı obstrüktif uyku apne sendromu (OUAS) olan erişkin erkek hastaların kraniofasiyal morfolojik özellikleri değerlendirmektir.</p> <p><strong>Gereç ve Yöntem</strong>: Çalışmada 80 erkek hastanın (60 OUAS, 20 horlama hastası) lateral sefalogramları değerlendirildi. Bireyler Grup 1: horlama (AHİ<5); Grup 2: hafif OUAS (5£ AHİ<15); Grup 3: orta OUAS(15£ AHİ<30) ; Grup 4: şiddetli OUAS (AHİ<strong> </strong>³30) olarak değerlendirildi. Sefalogramlar üzerinde hyoid, dil kökü ve yumuşak damak konumu, kranioservikal postür ve havayolu genişliğini belirleyen ölçümler yapıldı. Gruplar arasındaki farklar normal dağılım gösteren değişkenlerde tek yönlü varyans analizi ve Duncan testiyle, normal dağılım göstermeyen değişkenlerde Kruskal Wallis testi  ve Bonferroni düzeltmesi uygulanarak Mann Whitney U testiyle yapıldı.</p> <p><strong>Bulgular:</strong> Gruplar karşılaştırıldığında hyoid pozisyonu, yumuşak damak konumu, kranioservikal postür ve havayolu genişliğini gösteren ölçümlerde istatistiksel anlamlılık gösteren bir fark bulunmadı (p>0.05). Dil kökü konumunu gösteren PNS-V (mm) değeri şiddetli OUAS grubu ile diğer gruplar arasında istatistiksel olarak anlamlı fark gösterdi (p<0.05). Dil kökü ile ilgili diğer ölçümlerde ise gruplar arasında anlamlı fark bulunmadı (p>0.05).</p> <p><strong>Sonuçlar: </strong>İncelenen popülasyonda şiddetli OUAS grubunda dil kökünün daha aşağıda konumlandığı belirlenmiş, diğer kraniofasiyal değişkenlerde gruplar arasında fark görülmemiştir.</p> <p><strong>Anahtar kelimeler:</strong> Obstrüktif uyku apnesi sendromu, horlama, sefalometri, kraniofasiyal.</p> <p><strong> </strong></p> <p><strong> </strong></p> <p><strong>ABSTRACT</strong></p> <p><strong>Objectives: </strong>The aim of this study was to evaluate the craniofacial morphology of adult male patients with obstructive sleep apnea syndrome (OSAS).</p> <p><strong>Materials and Methods:</strong> Cephalograms of 80 male patients (60 OSAS, 20 snoring) were evaluated. Subjects were grouped as, Group 1: snoring (AHI<5); Group 2: mild OSA (5£ AHI<15);  Group 3: moderate OSA (15£ AHI<30) ; Group 4: severe OSA (AHI ³30). Measurements were made to evaluate hyoid bone position, tongue base and soft palate, craniocervical extension and the airway width. Statistical significance was determined with one-way ANOVA and Duncan test for variables showing normal distribution. Kruskal Wallis test and Mann Whitney U test with Bonferroni correction were used to evaluate the variables that were not normally distibuted.</p> <p><strong>Results:</strong> No significant differences were found in hyoid bone position, soft palate position, craniocervical extension and the airway width (p>0.05). PNS-V (mm), was significantly different between severe OSA group and the other groups (p<0.05). The other measurements on tongue base showed no difference between groups (p>0.05).</p> <p><strong>Conclusions:</strong> In this study population, the tongue base was more inferiorly positioned in the severe OSA group whereas the other craniofacial variables showed no difference between groups.</p> <strong>Key words: </strong>Obstructive sleep apnea syndrome, snoring, cephalometry, craniofacial