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    A geometrical approach for configuration and singularity analysis of a new non-symmetric 2DOF 5R spherical parallel manipulator

    , Article Mechanism and Machine Theory ; Volume 147 , 2020 Alamdar, A. R ; Farahmand, F ; Behzadipour, S ; Mirbagheri, A. R ; Sharif University of Technology
    Elsevier Ltd  2020
    Abstract
    A new non-symmetric 5R-SPM is introduced and a geometrical approach is developed to analyze its configurations and singularities. The proposed methodology determines the type of configuration of a 5R-SPM, i.e. regular, singular, or out-of-workspace and also the type of singularity, i.e. instantaneous or finite, only based on geometric parameters and without solving verbose kinematic equations. It also provides insights into the workspace and singularities of 5R-SPMs, in the preliminary stage of design. The mechanism was analyzed by both the new geometrical approach and conventional methods for comparison. The geometrical approach could intuitively detect all the singularities observed by the... 

    Mechanical Systems Using Nonlinear State Feedback

    , M.Sc. Thesis Sharif University of Technology Zade Gharejehdaghi, Elahe (Author) ; Namvar, Mehrzad (Supervisor)
    Abstract
    Disturbance is one of the inseparable components of the mechanical systems which cannot be avoided. In these systems a number of inner and outer sources exist which are the cause of disturbance. Abrupt changes in torque, uncertainty in parameters, mechanical impulses and external forces on robot’s parts all can be mentioned as examples which introduce disturbance that affects the output of mechanical and robotic systems. Therefore, disturbance rejection is considered indispensable in robotic control systems. There are number of problems which are associated with disturbance rejection. In several methods, mostly optimization based methods, system fails to completely reject the disturbance and... 

    A geometric approach for separating post non-linear mixtures

    , Article European Signal Processing Conference, 3 September 2002 through 6 September 2002 ; Volume 2015-March , September , 2015 ; 22195491 (ISSN) Babaie Zadeh, M ; Jutten, C ; Nayebi, K ; Sharif University of Technology
    European Signal Processing Conference, EUSIPCO  2015
    Abstract
    A geometric method for separating PNL mixtures, for the case of 2 sources and 2 sensors, has been presented. The main idea is to find compensating nonlinearities to transform the scatter plot of observations to a parallelogram. It then results in a linear mixture which can be separated by any linear source separation algorithm. An indirect result of the paper is another separability proof of PNL mixtures of bounded sources for 2 sources and 2 sensors  

    Probability estimation in aircraft conflict detection: A simple and computationally effective method with accuracy certificates

    , Article 18th European Control Conference, ECC 2019, 25 June 2019 through 28 June 2019 ; 2019 , Pages 4319-4324 ; 9783907144008 (ISBN) Seyedi Pour, S ; Nobahari, H ; Prandini, M ; European Control Assoication (EUCA) ; Sharif University of Technology
    Institute of Electrical and Electronics Engineers Inc  2019
    Abstract
    In this paper, we address aircraft conflict detection on a mid-term horizon. We adopt a probabilistic approach and provide a simple method to estimate the probability of two aircraft getting closer than some minimum predefined distance, based on a commonly adopted Gaussian model of the deviation from their planned trajectories. A key feature of our method is that the probability estimate is accompanied by a deterministic accuracy certificate. This is achieved by adopting a geometric approach to conflict probability estimation and jointly computing a lower and an upper bound on the conflict probability. These bounds can be inspected and refined if the resulting accuracy of the probability... 

    A geometric approach to fault detection and isolation in robotic manipulators

    , Article Proceedings of the IEEE Conference on Decision and Control, 17 December 2018 through 19 December 2018 ; Volume 2018-December , 2019 , Pages 391-396 ; 07431546 (ISSN); 9781538613955 (ISBN) Karami, S ; Namvar, M ; Sharif University of Technology
    Institute of Electrical and Electronics Engineers Inc  2019
    Abstract
    We present a geometric approach for fault detection and isolation (FDI) in robotic manipulators in presence of model uncertainty. A systematic procedure is introduced for representing robotic system model being affine with respect to faults and disturbances. The proposed residual generator has smooth dynamics with freely selectable functions and it does not require high gains or threshold adjustment for the FDI purpose. No assumption on amplitude of faults and their rate is used. The solvability conditions for the FDI problem lead to a quotient observable subspace unaffected by all unknown inputs except the faults. Simulation example demonstrates localization of faults in presence of... 

    Geometric-based fault diagnosis in a grid-connected inverter

    , Article Proceedings of the IEEE Conference on Decision and Control, 17 December 2018 through 19 December 2018 ; Volume 2018-December , 2019 , Pages 3421-3426 ; 07431546 (ISSN); 9781538613955 (ISBN) Mashreghi, A ; Namvar, M ; Sharif University of Technology
    Institute of Electrical and Electronics Engineers Inc  2019
    Abstract
    This paper presents a nonlinear geometric approach to fault detection and isolation (FDI) in grid-connected inverters. Faults are considered in inverter switches as well as in grid voltage and source current sensors. The FDI system is not sensitive to load variations or grid transients. No assumptions on balanced, zero-sum or sinusoidal form of voltages or currents are made. The resulting residual converges to zero in no-fault condition such that no threshold adjustment is needed. Simulations demonstrate performance of the proposed FDI system in presence of unknown disturbance. © 2018 IEEE  

    Geometrical approach in physical understanding of the Goos-Haenchen shift in one- And two-dimensional periodic structures

    , Article Optics Letters ; Volume 33, Issue 24 , 2008 , Pages 2940-2942 ; 01469592 (ISSN) Miri, M ; Naqavi, A ; Khavasi, A ; Mehrany, K ; Khorasani, S ; Rashidian, B ; Sharif University of Technology
    Optical Society of America (OSA)  2008
    Abstract
    The Goos-Haenchen shift of a totally reflected beam at the planar interface of two dielectric media, as if the incident beam is reflected from beneath the interface between the incident and transmitted media, has been geometrically associated with the penetration of the incident photons in the less-dense forbidden transmission region. This geometrical approach is here generalized to analytically calculate the Goos-Haenchen shift in one- and two-dimensional periodic structures. Several numerical examples are presented, and the obtained results are successfully tested against the well-known Artman's formula. The proposed approach is shown to be a fast, simple, and efficient method that can... 

    A geometric approach to fault detection and isolation in a grid-connected inverter

    , Article IEEE Transactions on Control Systems Technology ; Volume 29, Issue 6 , 2021 , Pages 2622-2629 ; 10636536 (ISSN) Mashreghi, A ; Namvar, M ; Sharif University of Technology
    Institute of Electrical and Electronics Engineers Inc  2021
    Abstract
    We present a nonlinear geometric approach to fault detection and isolation (FDI) in a grid-connected inverter system. Open-switch faults in inverter power transistors together with faults in grid voltages and source current sensors are detected and isolated in the presence of disturbance. The detection process is based on dynamic model of an inverter, including a dc-bus capacitor and an output $RL$ filter. The proposed FDI system does not rely on balanced or zero-sum conditions in the grid point and is functional under nonsinusoidal voltages and currents. © 1993-2012 IEEE  

    Geometric-Based Fault Diagnosis in a Grid-Connected Inverter

    , Ph.D. Dissertation Sharif University of Technology Mashreghi, Ali (Author) ; Namvar, Mehrzad (Supervisor)
    Abstract
    Inverters are the main utility in transmitting power from distributed generation (DG) systems toward grid and their safe and immune performance has become a major concern among the system designers. In addition to poor power transmittance, faults in inverter can harm other equipment such as DG and local load. Consequently different protections has been considered to increase the reliability of these systems. Some of these protections like fuses and varistors are implemented in the hardware while others are considered in the processor. In the later class of protections, fault detection and isolation (FDI) system has been the subject of intense investigation in inverters over the past two... 

    Nonlinear Geometric Approach to Fault Detection in Mechanical Systems

    , M.Sc. Thesis Sharif University of Technology Mashreghi, Ali (Author) ; Namvar, Mehrzad (Supervisor)
    Abstract
    The demand for safety operating systems is growing with the new developments in technology. One of the important and critical issues in system monitoring is the capability of the system to detect probable faults and hazards. In model-based fault detection one specific diagnostic signal called residual should be generated for each fault that is only sensitive to a particular fault and independent of other faults and disturbances. In this thesis we try to investigate the nonlinear geometric approach in fault detection of a class of mechanical systems. After a brief introduction to geometric tool for nonlinear inputaffine systems and conditions in which output is decoupled from input, we... 

    A novel approach for recovering 2-valued independent sparse components from whitened data in noisy environments

    , Article Proceedings - 2016 UKSim-AMSS 18th International Conference on Computer Modelling and Simulation, UKSim 2016, 6 April 2016 through 8 April 2016 ; 2016 , Pages 155-160 ; 9781509008889 (ISBN) Keshavarzi, M ; Bayat, S ; Keshavarzi, S ; Sharif University of Technology
    Institute of Electrical and Electronics Engineers Inc  2016
    Abstract
    Some sources transmit periodic and quasi periodic sparse pulse trains in the environment and a number of sensors might receive them through a single channel simultaneously. It is usually our interest to know which pulse belongs to which source. This identification process has wide applications in communications, radar system, medical applications, and neural systems. Blind source separation (BSS) is one solution for this problem. This paper proposed a geometrical approach to solve BSS problem when observations are whitened data and are obtained from the linear mixtures of 2-valued sparse signals (such as sparse pulse trains). In other words, the proposed approach aims to estimate a rotation... 

    Smooth residual generation for robust isolation of faults in manipulators using joint torque sensors

    , Article 58th IEEE Conference on Decision and Control, CDC 2019, 11 December 2019 through 13 December 2019 ; Volume 2019-December , 2019 , Pages 2922-2927 ; 07431546 (ISSN); 9781728113982 (ISBN) Karami, S ; Namvar, M ; Sharif University of Technology
    Institute of Electrical and Electronics Engineers Inc  2019
    Abstract
    Reliability of model-based failure detection and isolation (FDI) methods depends on the amount of uncertainty in a system model. Recently, it has been shown that the use of joint torque sensing results in a simplified manipulator model that excludes hardly identifiable link dynamics and other nonlinearities. We present a geometric approach to fault detection and isolation (FDI) for robotic manipulators using joint torque sensor in presence of model uncertainty. A systematic procedure is introduced for representing a robotic system model using joint torque sensor being affine with respect to faults and disturbances. The proposed FDI filter has smooth dynamics with freely selectable functions... 

    A geometric approach to fault detection and isolation in a grid-connected inverter

    , Article IEEE Transactions on Control Systems Technology ; November , 2020 , Pages: 1-8 Mashreghi, A ; Namvar, M ; Sharif University of Technology
    Institute of Electrical and Electronics Engineers Inc  2020
    Abstract
    We present a nonlinear geometric approach to fault detection and isolation (FDI) in a grid-connected inverter system. Open-switch faults in inverter power transistors together with faults in grid voltages and source current sensors are detected and isolated in the presence of disturbance. The detection process is based on dynamic model of an inverter, including a dc-bus capacitor and an output RL filter. The proposed FDI system does not rely on balanced or zero-sum conditions in the grid point and is functional under nonsinusoidal voltages and currents. IEEE  

    A simple geometrical approach for deinterleaving radar pulse trains

    , Article Proceedings - 2016 UKSim-AMSS 18th International Conference on Computer Modelling and Simulation, UKSim 2016, 6 April 2016 through 8 April 2016 ; 2016 , Pages 172-177 ; 9781509008889 (ISBN) Keshavarzi, M ; Pezeshk, A. M ; Sharif University of Technology
    Institute of Electrical and Electronics Engineers Inc  2016
    Abstract
    Some periodic and quasi-periodic pulse trains are emitted by different sources in the environment and a number of sensors receive them through a single channel simultaneously. We are often interested in separating these pulse trains for source identification at sensors. This identification process is termed as deinterleaving pulse trains. Deinterleaving pulse trains has wide applications in communications, radar systems, neural systems, biomedical engineering, and so on. This paper studies the deinterleaving problem with the assumption that both sources and sensors are fixed. In this study, the problem of deinterleaving pulse trains is modeled as a blind source separation (BSS) problem. To...