Search for: trajectories
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    Vehicle trajectory challenge in predictive active steering rollover prevention

    , Article International Journal of Automotive Technology ; Volume 18, Issue 3 , 2017 , Pages 511-521 ; 12299138 (ISSN) Ghazali, M ; Durali, M ; Salarieh, H ; Sharif University of Technology
    High center of mass vehicles are likely to rollover in extreme maneuvers. Available works present control strategies to prevent rollover. In these works, however, other important parameters such as path trajectory tracking are not a main concern. In this paper conflicts between rollover prevention and trajectory tracking is investigated. Model predictive control (MPC) is adopted to predict and avoid rollover while tracking desired trajectory. For this regard a model based future error estimation is introduced. The control framework predicts both rollover and trajectory error simultaneously. It avoids rollover while tries to track the trajectory. Simulation results for two controllers with... 

    Covariance-based multiple-impulse rendezvous design

    , Article IEEE Transactions on Aerospace and Electronic Systems ; Volume 55, Issue 5 , 2019 , Pages 2128-2137 ; 00189251 (ISSN) Shakouri, A ; Kiani, M ; Pourtakdoust, S. H ; Sharif University of Technology
    Institute of Electrical and Electronics Engineers Inc  2019
    A novel trajectory design methodology is proposed in the current work to minimize the state uncertainty in the crucial mission of spacecraft rendezvous. The trajectory is shaped under constraints utilizing a multiple-impulse approach. State uncertainty is characterized in terms of covariance, and the impulse time as the only effective parameter in uncertainty propagation is selected to minimize the trace of the covariance matrix. Furthermore, the impulse location is also adopted as the other design parameter to satisfy various translational constraints of the space mission. Efficiency and viability of the proposed idea have been investigated through some scenarios that include constraints on... 

    An open loop walking on different slopes for NAO humanoid robot

    , Article Procedia Engineering ; Volume 41 , 2012 , Pages 296-304 ; 18777058 (ISSN) Massah, B. A ; Sharifi, K. A ; Salehinia, Y ; Najafi, F ; Sharif University of Technology
    Dynamic gait planning for humanoid robots encounters difficulties such as stability, speed, and smoothness. In most of previous studies, joints' trajectories are calculated in 3D Cartesian space, then, introducing boundary conditions and using polynomials, the first and second derivatives of the motion are ensured to be continuous. Then, the stability of the motion is guaranteed using Zero Moment Point (ZMP) stability criterion. In this study, a trajectory planner is presented using the semi-ellipse equations of the motion; the continuity of the derivatives is preserved. Stabilization of motion is attained through using ZMP criterion and 3d inverted pendulum equations in three slope... 

    A Survey on Bohm’s Theory Without Quantum Potential

    , M.Sc. Thesis Sharif University of Technology Hosseini, Zahra (Author) ; Shafiee, Afshin (Supervisor)
    Bohm-de Broglie theory is an alternative for standard quantum mechanics for explaining the bizarreness of micro-phenomena. This theory is casual and deterministic,but endows with nonlocal and contextual characters. Up to now,two different approaches presented: One is known as Bohm-Hiley (BH) formalism and the other is Dürr-Goldstein-Zanghí (DGZ) representation. In BH formalism, quantum potential has a significant role, according to witch peculiar phenomena such as quantum tunneling, two-slit interference and chemical bond are explained. Active information is also another important rotion introduced by quantum potential. In DGZ approach, however, the foundation of Bohm theory is based on... 

    Trajectory planning of mobile robots using indirect solution of optimal control method in generalized point-to-point task

    , Article Frontiers of Mechanical Engineering ; Volume 7, Issue 1 , 2012 , Pages 23-28 ; 20950233 (ISSN) Nazemizadeh, M ; Rahimi, H. N ; Amini Khoiy, K ; Sharif University of Technology
    This paper presents an optimal control strategy for optimal trajectory planning of mobile robots by considering nonlinear dynamic model and nonholonomic constraints of the system. The nonholonomic constraints of the system are introduced by a nonintegrable set of differential equations which represent kinematic restriction on the motion. The Lagrange's principle is employed to derive the nonlinear equations of the system. Then, the optimal path planning of the mobile robot is formulated as an optimal control problem. To set up the problem, the nonlinear equations of the system are assumed as constraints, and a minimum energy objective function is defined. To solve the problem, an indirect... 

    Swing up and arm trajectory tracking of the furuta pendulum with sliding mode control

    , Article 5th RSI International Conference on Robotics and Mechatronics, IcRoM 2017, 25 October 2017 through 27 October 2017 ; 2018 , Pages 346-351 ; 9781538657034 (ISBN) Karamin Manesh, M. J ; Nikzad Goltapeh, A ; Sharif University of Technology
    In this paper, the swing-up problem of the Furuta pendulum has been solved by introducing a new combined method based on the frequency response, and the sliding mode method. Furthermore, a trajectory tracking controller has been introduced and applied to the Furuta pendulum; which the pendulum remained regulated at the upward position, while the arm tracks a desired time-varying trajectory. The hierarchical sliding mode control (HSMC) approach has been employed to achieve the mentioned goals. The Furuta system is made up of two subsystems. Based on this physical structure, the hierarchical structure of the sliding surfaces is designed as follows: first, the sliding surface of each subsystem... 

    Optimal trajectory planning for flight through microburst wind shears

    , Article Aerospace Science and Technology ; Volume 15, Issue 7 , October , 2011 , Pages 567-576 ; 12709638 (ISSN) Pourtakdoust, S. H ; Kiani, M ; Hassanpour, A ; Sharif University of Technology
    Microburst wind shear is a potential hazard for aviation safety, especially in some crucial phases of flight like take-off and landing. Optimal trajectories could be useful for suitable retrieval of transport aircrafts encountering microburst. These types of trajectories are investigated in this paper for landing phase in two scenarios of escape and landing utilizing the most recent realistic analytical model of the microburst. In this regard, a set of complete six degrees of freedom aircraft's equations of motion is taken in a variation formulation of this problem. This approach is particularly useful for determination of optimal escape or approach trajectories constrained with respect to... 

    Trajectory design for cooperative combat missions

    , Article 2008 IEEE Aerospace Conference, AC, Big Sky, MT, 1 March 2008 through 8 March 2008 ; 2008 ; 1095323X (ISSN) ; 1424414881 (ISBN); 9781424414888 (ISBN) Tavakoli Kashi, A ; Sharif University of Technology
    In this paper, a hierarchical method for trajectory design for cooperative combat missions (CCM) is presented. In a military environment, in addition to physical constraints (aircraft dynamics and mountains) there are threats made by Radars or Artillery. So an important constraint, "Avoid Threats", is added to physical constraints. Major steps in trajectory design are: "Target Assignment", "Path Planning", "Path Smoothing and Trajectory Design". The most important points and a brief algorithm for each step is presented in this paper. Finally the method is applied to special case and the results presented. ©2008 IEEE  

    Optimal-time quadcopter descent trajectories avoiding the vortex ring and autorotation states

    , Article Mechatronics ; Volume 68 , 2020 Talaeizadeh, A ; Antunes, D ; Nejat Pishkenari, H ; Alasty, A ; Sharif University of Technology
    Elsevier Ltd  2020
    It is well-known that helicopters descending fast may enter the so-called Vortex Ring State (VRS), a region in the velocity space where the blade's lift differs significantly from regular regions and high amplitude fluctuations are often present. These fluctuations may lead to instability and, therefore, this region is avoided, typically by increasing the horizontal speed. This paper researches this phenomenon in the context of small-scale quadcopters. The region corresponding to the VRS is identified by combining first-principles modeling and wind-tunnel experiments. Moreover, we propose that the so-called Windmill-Brake State (WBS) or autorotation region should also be avoided for... 

    Minimum time trajectory optimization of a tail-sitter aerial vehicle using nonlinear programming

    , Article 2012 International Conference onAdvanced Mechatronic Systems, ICAMechS 2012 ; 2012 , Pages 275-280 ; 9780955529382 (ISBN) Banazadeh, A ; Assadian, N ; Saghafi, F ; Sharif University of Technology
    Aerial tail-sitters have drawn many attentions in recent years. The main challenge of employing these vehicles is to ensure safe and efficient takeoff and landing. The aim of the current study is to develop a gradient-base optimization algorithm for a jet aerial tail-sitter in order to obtain minimum time trajectories in transition flight phases. The vehicle is supposed to utilize thrust vectoring system instead of conventional control surfaces that will pose minimal drawbacks in terms of low speed efficiency and complexity. The time-optimal trajectories are computed using the nonlinear dynamic equations of motion of the vehicle in order to make sure that the vehicle can follow the optimum... 

    Trajectory optimization for a high speed planing boat based on Gauss pseudospectral method

    , Article Proceedings - 2011 2nd International Conference on Control, Instrumentation and Automation, ICCIA 2011 ; 2012 , Pages 195-200 Salarieh, H ; Ghorbani, M. T ; Sharif University of Technology
    In this paper, the problem of Optimal Trajectory Planning for a high speed planing boat under nonlinear equality and inequality path constraints, is addressed. First, a nonlinear mathematical model of the craft's dynamic is constructed. To solve a trajectory optimization problem, we can utilize the indirect or direct methods. In the indirect methods, the maximum principle of Pontryagin is used to transform the optimal control problem into Euler-Lagrange equations, on the other hand, in the direct methods it is necessary to transcribe the optimal control problem into a nonlinear programming problem (NLP) by discretization of states and controls. The resulted NLP can be solved by... 

    Nonholonomic motion planning based on optimal control for flight phases of planar bipedal running

    , Article Electronics Letters ; Volume 47, Issue 20 , 2011 , Pages 1120-1122 ; 00135194 (ISSN) Sadati, N ; Akbari Hamed, K ; Dumont, G. A ; Graver, W. A ; Sharif University of Technology
    Presented is a novel approach for online trajectory modification of joint motions to transfer a free open kinematic chain, undergoing flight phase, from a specified initial configuration to a specified final configuration. Formally, it is assumed that a nominal trajectory, computed offline, can reorient the kinematic chain (reconfiguration problem) for a given angular momentum on a time interval. A modification algorithm of body joints, based on optimal control, is developed such that for different angular momentums and time intervals, the same reconfiguration problem can be solved online. This approach can be utilised for space robotics applications and online computation of planar running... 

    Constrained optimization of sensors trajectories for moving source localization using TDOA and FDOA measurements

    , Article International Conference on Robotics and Mechatronics, ICROM 2015, 7 October 2015 through 9 October 2015 ; 2015 , Pages 200-204 ; 9781467372343 (ISBN) Adelipour, S ; Hamdollahzadeh, M ; Behnia, F ; Sharif University of Technology
    This paper examines the problem of determining optimal sensors trajectories for localization of a moving radio source based on Time Difference of Arrival (TDOA) and Frequency Difference of Arrival (FDOA) measurements in situations in which sensors are constrained both in their movements and regions of operation. By considering the movement of the source and constrained movement of the sensors, a constraint problem is formed which is solved to determine optimal trajectories of the sensors for source tracking. The validity of the proposed algorithm is assessed by two different simulation scenarios and the results verify its proper operation with estimation error decreasing in consecutive steps... 

    Near-optimal trajectories to manage landing sequence in the vicinity of controlled aerodromes

    , Article Journal of Aircraft ; Volume 47, Issue 1 , 2010 , Pages 129-140 ; 00218669 (ISSN) Malaek, S. M ; Nabavi, S. Y ; Sharif University of Technology
    A comprehensive approach is proposed to manage landing sequences and their associated trajectories for an arbitrary number of aircraft in the vicinity of a controlled aerodrome. The current approach, similar to that of "first come, first served," could consider different types of priorities as well as emergencies. The approach is especially useful to combine unstructured free-flight trajectories with structured ones during the approach phase of the flight A comprehensive cost function considers the relative size of all aircraft together with their relative speeds and flight directions. This helps optimize the amount of fuel consumption while respecting separation minima. Resulting... 

    Robust decentralized control of consensus-based formations of leader-follower networks with uncertain directed topologies on bounded velocity trajectories unde ned for followers via backstepping method

    , Article Scientia Iranica ; Volume 23, Issue 3 , 2016 , Pages 1064-1072 ; 10263098 (ISSN) Sayyaadi, H ; Soltani, A ; Sharif University of Technology
    Sharif University of Technology  2016
    In this paper, decentralized control of formation of a special category of leaderfollower networks on bounded velocity trajectories is addressed. The network of the agents in this study is supposed to have a directed graph with a spanning tree rooted at the leader agent. Moreover, follower agents do not receive online or have offine velocity of the desired trajectory, such as in tracking problem of trajectories which are not predefined or when the total bandwidth is narrow. Furthermore, the leader does not receive any information from any agent and its control is fully centralized. In the present study, formation problem is considered a consensus problem. The controller is designed for... 

    A novel model for wellbore stability analysis during reservoir depletion

    , Article Journal of Natural Gas Science and Engineering ; 2016 , Pages 935-943 ; 18755100 (ISSN) ; Volume 35, Issue Part A Behnoud far, P ; Hassani, A. H ; Al Ajmi, A. M ; Heydari, H ; Sharif University of Technology
    Elsevier B.V 
    It is not common to build a geomechanical model for depleted reservoirs as logging and coring are costly and time consuming in such reservoirs. On the other hand, in regular analysis of wellbore stability, the effect of time is completely ignored. As a result, with time there will be some errors in the evaluation of wellbore stability in depleted reservoirs. In order to determine the optimum wellbore trajectory during the reservoir life, it is necessary to have a model which can estimate the rock properties based on the first full logging suite and also consider the depletion effect. In this study, a novel model is proposed which combines a mechanical earth model, borehole circumferential... 

    Simultaneous joint and object trajectory templates for human activity recognition from 3-D data

    , Article Journal of Visual Communication and Image Representation ; Volume 55 , 2018 , Pages 729-741 ; 10473203 (ISSN) Ghodsi, S ; Mohammadzade, H ; Korki, E ; Sharif University of Technology
    Academic Press Inc  2018
    Availability of low-cost range sensors and the development of relatively robust algorithms for the extraction of skeleton joint locations have inspired many researchers to develop human activity recognition methods using 3-D data. In this paper, an effective method for the recognition of human activities from the normalized joint trajectories is proposed. We represent the actions as multidimensional signals and introduce a novel method for generating action templates by averaging the samples in a “dynamic time” sense. Then, in order to deal with the variations in speed and style of performing actions, we warp the samples with action templates by an efficient algorithm and employ wavelet... 

    Optimal stair climbing pattern generation for humanoids using virtual slope and distributed mass model

    , Article Journal of Intelligent and Robotic Systems: Theory and Applications ; Volume 94, Issue 1 , 2019 , Pages 43-59 ; 09210296 (ISSN) Shahrokhshahi, A ; Yousefi Koma, A ; Khadiv, M ; Mansouri, S ; Mohtasebi, S. S ; Sharif University of Technology
    Springer Netherlands  2019
    This study addresses optimal walking pattern generation for SURENA III humanoid robot in a stair-climbing scenario. To this end, the kinematic configuration of the 31-DOF humanoid robot is studied. Integrating the detailed dynamic properties of the robot, a comprehensive and precise dynamic model is developed for its lower-limb. In order to generate the optimal walking pattern for the considered humanoid robot, trajectories for feet and pelvis are first designed, and then joint angles are derived by means of inverse kinematics. Such a complete model provides the designer with the necessary tools to optimize the trajectory generation. Using two different types of objective functions, namely... 

    Trajectory planning of spine motion during flexion using a stability-based optimization

    , Article ASME 2010 10th Biennial Conference on Engineering Systems Design and Analysis, ESDA2010, 12 July 2010 through 14 July 2010 ; Volume 1 , 2010 , Pages 747-755 ; 9780791849156 (ISBN) Khorsand Vakilzadeh, M ; Salarieh, H ; Asghari, M ; Parnianpour, M ; Sharif University of Technology
    A central problem in motor control is to understand how the many biomechanical degrees of freedom are coordinated to achieve a goal. A common assumption is that Central Nervous System (CNS) would minimize a performance index to achieve this goal which is called objective function. In this paper, two popular objective functions are utilized to design the optimal trajectory of trunk movements. A 3D computational method incorporated with 18 anatomically oriented muscles is used to simulate human trunk system. Inverse dynamics allows us to compute torque which is generated around Lumbosacral joint. This torque is divided among muscles by static stability-based optimization. Trunk movement from... 

    A new dissimilarity index of EEG signals for epileptic seizure detection

    , Article Final Program and Abstract Book - 4th International Symposium on Communications, Control, and Signal Processing, ISCCSP 2010, 3 March 2010 through 5 March 2010 ; March , 2010 ; 9781424462858 (ISBN) Niknazar, M ; Mousavi, S. R ; Vosoughi Vahdat, B ; Shamsollahi, M. B ; Sayyah, M ; Sharif University of Technology
    Epileptic seizures are generated by an abnormal synchronization of neurons. Since epileptic seizures are unforeseeable for the patients, epileptic seizures detection is an interesting issue in epileptology, that novel approaches to understand the mechanism of epileptic seizures. In this study we analyzed invasive electroencephalogram (EEG) recordings in patients suffering from medically intractable focal epilepsy with a nonlinear method called, dissimilarity index. In order to detect epileptic seizures Bhattacharyya distance between trajectory matrix of reference window during an interval quite distant in time from any seizure and trajectory matrix of present window is employed to measure...