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    Hybrid control and motion planning of dynamical legged locomotion

    , Book ; Sadati, Nasser
    Wiley  2012
    This book provides a comprehensive presentation of issues and challenges faced by researchers and practicing engineers in motion planning and hybrid control of dynamical legged locomotion. The major features range from offline and online motion planning algorithms to generate desired feasible periodic walking and running motions and tow-level control schemes, including within-stride feedback laws, continuous time update laws and event-based update laws, to asymptotically stabilize the generated desired periodic orbits. This book describes the current state of the art and future directions across all domains of dynamical legged locomotion so that readers can extend proposed motion planning... 

    Natural and Quantum Walks on Graphs

    , M.Sc. Thesis Sharif University of Technology Khanteimouri, Payam (Author) ; Daneshgar, Amir (Supervisor)
    A Markov chain on a base graph is a stochatic process that can be visualized as a particle movement such that the probability of moving from a vertex i to a vertex j is specified by the corresponding transition kernel Ka. In this thesis, based on the result of A.Daneahgar and H.Hajiabolhassa, we recall some general necessary conditions for the existence of graph homomorphism, which holds on both directed and undirected cases. A discrete-time quantum walk on a graph is the repeated application of a unitary evolution operator. In this regard, also, we explain the quantum search algorithm on the result of Grover and the algorithms that is based on the quantum walk approach of A.Ambainis,... 

    Optimization of the switching surface for the simplest passive dynamic biped

    , Article Proceedings of the 17th International Conference on Advanced Robotics, ICAR 2015, 27 July 2015 through 31 July 2015 ; July , 2015 , Pages 363-368 ; 9781467375092 (ISBN) Safa, A. T ; Naraghi, M ; Alasty, A ; Saranli U ; Kalkan S ; Sharif University of Technology
    Institute of Electrical and Electronics Engineers Inc  2015
    Recently, it has been proved that a different switching surface can preserve the walking trajectory while varying the walking stability [1], [2]. In this paper, by employing the simplest passive dynamic biped, we optimize the switching surface to maximize the robot's stability. Here, the stability measure is preferably the size of the basin of attraction, i.e. the collection of all possible initial conditions leading to the system's equilibrium point. Numerical investigations indicate that the maximum stability is obtained for neither the highest nor the lowest walking speed  

    Optimal gaits generation of a 4-legged walking robot

    , Article Proceedings of 2003 IEEE Conference on Control Applications, Istanbul, 23 June 2003 through 25 June 2003 ; Volume 1 , 2003 , Pages 664-668 Alasty, A ; Borujeni, B. S ; Sharif University of Technology
    A novel Locomotion and gait planning method for a surface walking/climbing robot based on sequential 4-bar mechanism motions is presented. The robot moves on a surface through decoupled transverse gaits and turning gaits with desired length and angle. For implementation of turning gaits three methods of Simulated Annealing Accurate Planning (SAAP), Gradient Based Planning (GBP) and Hybrid Accurate Planning (HAP) are studied. Where the last method was found the most effective approach  

    How far is too far? Providing safe and comfortable walking environments

    , Article Transportation Research Record ; Volume 2586 , 2016 , Pages 72-82 ; 03611981 (ISSN) Ermagun, A ; Samimi, A ; Rashidi, T. H ; Sharif University of Technology
    National Research Council  2016
    The use of active modes of travel in school trips has sharply declined for a number of reasons, some of which are rooted in urban design, location of schools, and parental reservations. Thus, policy makers are keen to find practical ways to promote active modes of travel, particularly walking. This study was an effort to determine a tolerable walking distance for school trips and identify factors that made walking trips more reasonable for students. In the vein of understanding the tolerable walking distance, a two-step framework encompassing a random utility method and a hazard-based model was introduced. This framework was applied to a set of data that were collected from middle and high... 

    Stability improvement of a dynamic walking system via reversible switching surfaces

    , Article Multibody System Dynamics ; Volume 43, Issue 4 , 2018 , Pages 349-367 ; 13845640 (ISSN) Tehrani Safa, A ; Mohammadi, S ; Naraghi, M ; Alasty, A ; Sharif University of Technology
    Inspired by the effects of a switching surface on the stability of passive dynamic walking (Safa and Naraghi in Robotica 33(01):195–207, 2015; Safa et al. in Nonlinear Dyn. 81(4):2127–2140, 2015), this paper suggests a new control strategy for stabilization of dynamic bipedal locomotion. It verifies that the stability improvement of a dynamic walking system is feasible while preserving the speed, step-length, period, natural dynamics, and the energy effectiveness of the gait. The proposed control policy goes behind the three primary principles: (i) The system’s switching surface has to be replaced by a new one if an external disturbance is induced. (ii) The new switching surface has to be... 

    Design of an Active Exoskeleton Robot to Assist Human Walking

    , M.Sc. Thesis Sharif University of Technology Soltani Hekmat, Shima (Author) ; Zohoor, Hassan (Supervisor) ; Selk Ghaffari, Ali (Supervisor)
    Walking is one of the most important physical activities in daily life and it plays an important role on body health. Despite the importance of this issue, today many people suffering from walking abnormalities. This thesis aims at designing an exoskeleton for the rehabilitation in order to help patient’s lower limb movement. The hip joint is crucial for walking and is problematic for a large number of aged people or the patients who suffered from paralysis. A number of hip and knee model checked, one model for knee and one for hip selected to combine in order to achieve a unique model for walking exoskeleton. A mechanism consisting of six link and seven joints with four degrees of freedom... 

    Gait analysis of a six-legged walking robot using fuzzy reward reinforcement learning

    , Article 13th Iranian Conference on Fuzzy Systems, IFSC 2013 ; August , 2013 , Page(s): 1 - 4 ; ISBN: 9781479912278 Shahriari, M ; Khayyat, A. A ; Sharif University of Technology
    IEEE Computer Society  2013
    Free gait becomes necessary in walking robots when they come to walk over discontinuous terrain or face some difficulties in walking. A basic gait generation strategy is presented here using reinforcement learning and fuzzy reward approach. A six-legged (hexapod) robot is implemented using Q-learning algorithm. The learning ability of walking in a hexapod robot is explored considering only the ability of moving its legs and using a fuzzy rewarding system telling whether and how it is moving forward. Results show that the hexapod robot learns to walk using the presented approach properly  

    Using a saddle-assistive device equipped with mechanical orthosis for walking of the person with incomplete spinal cord injury

    , Article Proceedings of the Institution of Mechanical Engineers, Part H: Journal of Engineering in Medicine ; Volume 235, Issue 9 , May , 2021 , Pages 1088-1095 ; 09544119 (ISSN) Hojjati Najafabadi, A ; Amini, S ; Farahmand, F ; Sharif University of Technology
    SAGE Publications Ltd  2021
    The majority of the people with incomplete spinal cord injury lose their walking ability, due to the weakness of their muscle motors in providing torque. As a result, developing assistive devices to improve their conditionis of great importance. In this study, a combined application of the saddle-assistive device (S-AD) and mechanical medial linkage or thosis was evaluated to improve the walking ability in patients with spinal cord injury in the gait laboratory. This mobile assistive device is called the saddle-assistive device equipped with medial linkage or thosis (S-ADEM). In this device, a mechanical orthosis was used in a wheeled walker as previously done in the literature. Initially,... 

    Local Community Detection in Social

    , M.Sc. Thesis Sharif University of Technology Rajabi, Arezoo (Author) ; Rabiee, Hamid Reza (Supervisor)
    The fast growth of social networks and their wide range of applications have made the anal-ysis of them an interesting field of research. The growth of concern in modeling large social networksand investigation of their structural features leads studies towards community detec-tion in such networks. In recent years, a great amount of effort has been done for introducing community detection algorithms, many of which are based on optimization of a global cri-terion which needs network’s topology. However, because of big size of most of the social networks , accessing their global information tends to be impossible. Hence, local commu-nity detection algorithms have been introduced. In this... 

    Feasibility of a powered knee joint in providing stance and swing phase knee flexion when using a knee-ankle-foot orthosis

    , Article Journal of Prosthetics and Orthotics ; Volume 29, Issue 4 , 2017 , Pages 177-182 ; 10408800 (ISSN) Rafiaei, M ; Arazpour, M ; Bahramizadeh, M ; Farahmand, F ; Jamshidi, N ; Samadian, M ; Sharif University of Technology
    Background The aim of this study was to develop a new stance control knee-ankle-foot orthosis (SCKAFO) and determine its efficacy on specific spatiotemporal and kinematic parameters. Method Seven healthy volunteer subjects participated in this study. After orthotic gait training, subjects participated in a four-part data collection session that consisted of gait evaluation with normal walking, SCKAFO with locked knee joint, SCKAFO without initial flexion (IF) mode, and SCKAFO with IF mode. Results Walking with any of the control knee-ankle-foot orthoses (KAFOs) produced a significant reduction in walking speed compared with normal walking. There was no significant difference in walking speed... 

    Active control of a passive bipedal walking robot

    , Article International Journal of Dynamics and Control ; Volume 5, Issue 3 , 2017 , Pages 733-740 ; 2195268X (ISSN) Ebrahimi, A ; Heydari, M ; Alasty, A ; Sharif University of Technology
    A passive bipedal walking robot can descend down a small slope without any exertion of external force and only by using the gravity force. By exerting a proper energy to a passive biped robot, its walking speed can be controlled and also it can be forced to walk on flat planes and ascending slopes. In this paper, the proper energy is applied to the robot in three different methods: applying a proper moment to the robot joints, applying a proper moment to the robot’s stance leg, and applying a proper movement to the robot’s upper body. It is found that the first method is not practical, but the second and third methods enhance the stability and speed regulation of the robot. Additionally, the... 

    Design, construction, and evaluation of “sensor lock”: an electromechanical stance control knee joint

    , Article Disability and Rehabilitation: Assistive Technology ; 2017 , Pages 1-8 ; 17483107 (ISSN) Arazpour, M ; Ahmadi Bani, M ; Baniasad, M ; Samadian, M ; Golchin, N ; Sharif University of Technology
    Background and aim: Most currently-available stance control knee ankle foot orthoses (SCKAFOs) still need full knee extension to lock the knee joint, and they are still noisy, bulky, and heavy. Therefore, the aim of this study was to design, construct, and evaluate an original electromechanical SCKAFO knee joint that could feasibly solve these problems, and thus address the problems of current stance control knee joints with regards to their structure, function, cosmesis, and cost. Method: Ten able-bodied (AB) participants and two (knee ankle foot orthosis) KAFO users were recruited to participate in the study. A custom SCKAFO with the same set of components was constructed for each... 

    Biased Random Walk On Galton-Watson Tree With Leaves

    , M.Sc. Thesis Sharif University of Technology Khaniha, Sayeh (Author) ; Haji Mirsadeghi, Mir Omid (Supervisor)
    We consider a biased random walk Xn on a Galton-watson tree with leaves in the subballistic regime. We prove that there exists an explicit constant ϒ = ϒ(β) ε (0,1),such that |Xn| is of order n. If Δn be the hitting time of level n, we prove that Δn{n1{ is tight. More ever we show thatΔn{n1{ does not converge in law. We prove that along the sequences npkq Xk\ , Δn{n1{ converges to certain infinity divisible laws. Key tools for the proof are the classical Harris decomposition for Galton-Watson trees, a new variant of regeneration times and the careful analysis of triangular arrays of i.i.d. random variables  

    A different switching surface stabilizing an existing unstable periodic gait: an analysis based on perturbation theory

    , Article Nonlinear Dynamics ; Volume 81, Issue 4 , 2015 , Pages 2127-2140 ; 0924090X (ISSN) Safa, A. T ; Alasty, A ; Naraghi, M ; Sharif University of Technology
    Kluwer Academic Publishers  2015
    Limit cycle walkers are known as a class of walking robots capable of presenting periodic repetitive gaits without having local controllability at all times during motion. A well-known subclass of these robots is McGeer’s passive dynamic walkers solely activated by the gravity field. The mathematics governing this style of walking is hybrid and described by a set of nonlinear differential equations along with impulses. In this paper, by applying perturbation method to a simple model of these machines, we analytically prove that for this type of nonlinear impulsive system, there exist different switching surfaces, leading to the same equilibrium points (periodic solutions) with different... 

    How local slopes stabilize passive bipedal locomotion?

    , Article Mechanism and Machine Theory ; Volume 100 , 2016 , Pages 63-82 ; 0094114X (ISSN) Tehrani Safa, A ; Mohammadi, S ; Hajmiri, S. E ; Naraghi, M ; Alasty, A ; Sharif University of Technology
    Elsevier Ltd 
    By employing a few simple models of passive dynamic walking mechanism, we have shown the possibility of extending the boundaries of the maximum stable speed of these autonomous robots merely by changing their terrain. The replaced terrain consists of a series of parallel local slopes and is recognized as a general form of a ramp-stair surface. Although here, the mechanism of stabilization of the unstable locomotion patterns is not clearly known, the technique is quite simple and works effectively. The merit to the method over other strategies, could be described in two separate aspects: First, it is still completely passive; so we do not need any external energy to control the robot. Second,... 

    Stability improvement of a dynamic walking system via reversible switching surfaces

    , Article Multibody System Dynamics ; 2017 , Pages 1-19 ; 13845640 (ISSN) Tehrani Safa, A ; Mohammadi, S ; Naraghi, M ; Alasty, A ; Sharif University of Technology
    Inspired by the effects of a switching surface on the stability of passive dynamic walking (Safa and Naraghi in Robotica 33(01):195–207, 2015; Safa et al. in Nonlinear Dyn. 81(4):2127–2140, 2015), this paper suggests a new control strategy for stabilization of dynamic bipedal locomotion. It verifies that the stability improvement of a dynamic walking system is feasible while preserving the speed, step-length, period, natural dynamics, and the energy effectiveness of the gait. The proposed control policy goes behind the three primary principles: (i) The system’s switching surface has to be replaced by a new one if an external disturbance is induced. (ii) The new switching surface has to be... 

    Numerical simulation of the effect of visitor's movement on bacteria-carrying particles distribution in hospital isolation room

    , Article Scientia Iranica ; Volume 24, Issue 3 , 2017 , Pages 1160-1170 ; 10263098 (ISSN) Eslami, J ; Abbassi, A ; Saidi, M. H ; Sharif University of Technology
    The aim of this paper is to simulate numerically the airflow induced by a walking visitor and its effects on the contaminant transport and ventilation system effectiveness. To this end, the following models will be used in this study: the Lagrangian Discrete Random Walk (DRW) model to trace the motion of BCPs, the dynamic mesh method to simulate the visitor movement, and the Reynolds Averaged Navier-Stokes (RANS) model to solve the airflow. The validation results of the numerical method are in full agreement with the available experimental data in the literature. The findings of the present study indicate that the visitor's movement has remarkable effect on the basic airflow, and the... 

    Boundary-induced coherence in the staggered quantum walk on different topologies

    , Article Physical Review A ; Volume 98, Issue 1 , July , 2018 ; 24699926 (ISSN) Khatibi Moqadam, J ; Tayefeh Rezakhani, A ; Sharif University of Technology
    American Physical Society  2018
    The staggered quantum walk is a type of discrete-time quantum-walk model without a coin which can be generated on a graph using particular partitions of the graph nodes. We design Hamiltonians for potential realization of the staggered dynamics on a two-dimensional lattice composed of superconducting microwave resonators connected with tunable couplings. The naive generalization of the one-dimensional staggered dynamics generates two uncoupled one-dimensional quantum walks; thus more complex partitions need to be employed. However, by analyzing the coherence of the dynamics, we show that the quantumness of the evolution corresponding to two independent one-dimensional quantum walks can be... 

    Efficiency of long-range navigation on Treelike fractals

    , Article Chaos, Solitons and Fractals ; Volume 122 , 2019 , Pages 102-110 ; 09600779 (ISSN) Khajehnejad, M ; Sharif University of Technology
    Elsevier Ltd  2019
    To get a deep understanding of a diffusion process and realizing the most efficient methods for investigating a real network, has always been of great interest and utility to us. In this work, we aim to study and compare our mobility in a network using a normal random walk and a long-range navigation strategy such as Lévy Walk. We study the Global Mean First Traverse Distance (GMFTD) and the entropy rate for this long-range navigation process and later, compare with a normal walk strategy. For this study, GMFTD is utilized instead of Global Mean First Passage Time (GMFPT). The reason for such a choice is the fact that for more accurate and precise results, we need to also take into account...