saim ahmed - Academia.edu (original) (raw)

Papers by saim ahmed

Entropy

In this investigation, the adaptive fractional-order non-singular fixed-time terminal sliding mod... more In this investigation, the adaptive fractional-order non-singular fixed-time terminal sliding mode (AFoFxNTSM) control for the uncertain dynamics of robotic manipulators with external disturbances is introduced. The idea of fractional-order non-singular fixed-time terminal sliding mode (FoFxNTSM) control is presented as the initial step. This approach, which combines the benefits of a fractional-order parameter with the advantages of NTSM, gives rapid fixed-time convergence, non-singularity, and chatter-free control inputs. After that, an adaptive control strategy is merged with the FoFxNTSM, and the resulting model is given the label AFoFxNTSM. This is done in order to account for the unknown dynamics of the system, which are caused by uncertainties and bounded external disturbances. The Lyapunov analysis reveals how stable the closed-loop system is over a fixed time. The pertinent simulation results are offered here for the purposes of evaluating and illustrating the performance o...

Actuators

This paper presents a fault tolerant scheme employing adaptive non-singular fixed-time terminal s... more This paper presents a fault tolerant scheme employing adaptive non-singular fixed-time terminal sliding mode control (AFxNTSM) for the application of robotic manipulators under uncertainties, external disturbances, and actuator faults. To begin, non-singular fixed-time terminal sliding mode control (FxNTSM) is put forth. This control method uses non-singular terminal sliding mode control to quickly reach fixed-time convergence, accomplish satisfactory performance in tracking, and produce non-singular and non-chatter control inputs. Then, without knowing the upper bounds beforehand, AFxNTSM is used as a reliable fault tolerant control (FTC) to estimate actuator faults and unknown dynamics. The fixed-time stability of the closed-loop system is established by the theory of Lyapunov analysis. The computer simulation results of the position tracking, control inputs, and adaptive parameters are presented to verify and illustrate the performance of the proposed strategy.

Computer Physics Communications

International Journal of Modelling, Identification and Control

Sir Syed University Research Journal of Engineering & Technology

This paper presents a low cost and portable mechanical ventilator in order to contribute towards ... more This paper presents a low cost and portable mechanical ventilator in order to contribute towards the increasing demand of mechanical ventilators all over the world due to the global pandemic of COVID-19. The proposed system’s portability makes it different from the other ventilators which are currently in use in different hospitals. It could be easily carried from one place to another without facing any difficulty because of its small size and low weight as compared to the previous versions of ventilators. Moreover, the aim is to design provide an adequate amount of oxygen and clears CO2 simultaneously to the patients and it will also prevent infection. The proposed ventilator is one of the simplest variations of a mechanical ventilator and the idea behind this vision is to make it too simple so that any ward nurse or a common man can easily operate it as efficiently so an expert can also invest his/her time while looking after much more severe cases as compared to not making much o...

2019 IEEE 8th Data Driven Control and Learning Systems Conference (DDCLS), 2019

Generally model-reference adaptive control (MRAC) is designed using known regression matrix. Howe... more Generally model-reference adaptive control (MRAC) is designed using known regression matrix. However, the formulation of regression matrix is difficult for more degree of freedoms (DOFs) of robot manipulator and sometime impossible to compute for many applications. In this work, MRAC using time delay estimation (TDE) named (MRAC-TDE) is proposed to avoid complex calculation of regression matrix and provides model-free control. Therefore, TDE is devised to estimate the unknown dynamics and MRAC is used to update the control gains. The closed-loop stability of system is investigated using the Lyapunov stability criterion. In the end, to validate the effectiveness of the proposed method, simulations are illustrated the appropriateness of proposed MRAC-TDE.

tutor: Daniele Marini ; correlatore: Alessandro Rizzi ; direttore della Scuola di Dottorato in In... more tutor: Daniele Marini ; correlatore: Alessandro Rizzi ; direttore della Scuola di Dottorato in Informatica: Ernesto Damiani

Iranian Journal of Science and Technology, Transactions of Electrical Engineering, 2020

In this study, trajectory tracking of robotic manipulators with uncertainties and external distur... more In this study, trajectory tracking of robotic manipulators with uncertainties and external disturbances is obtained by proposing model-free adaptive fractional super-twisting sliding mode control (AOFSTSM). The proposed AOFSTSM method is composed of an adaptive super-twisting sliding mode control integrated with fractional-order (FO) control. An adaptive tuning control is utilized to evaluate the uncertain unknown dynamics of the system without relying on the prior knowledge of the upper bounds. Moreover, FO control and super-twisting sliding mode control are used to achieve the fast finite-time convergence, chatter-free control inputs, better tracking performance and robustness. An output feedback (OF) is proposed and the state estimation is obtained by robust exact differentiator. Furthermore, the stability of the overall system is investigated and derived from the Lyapunov stability criterion. Finally, to validate the effectiveness and robustness of the developed control method, comparative simulations of state-feedback and OF of proposed method with fractional-order nonsingular fast terminal sliding mode control are realized to demonstrate the performance of AOFSTSM.

Asian Journal of Control, 2020

In this study, trajectory tracking of robotic manipulators under varying loads with uncertainties... more In this study, trajectory tracking of robotic manipulators under varying loads with uncertainties and external disturbances is obtained by proposing model‐independent adaptive fractional high‐order terminal sliding mode control (AFO‐HoTSMC). The proposed AFO‐HoTSMC method is composed of an adaptive high‐order terminal sliding mode control integrated with fractional‐order (FO) control. An adaptive tuning control is utilised to evaluate the uncertain unknown dynamics of the system without relying on the prior knowledge of the upper bounds. FO control and HoTSMC are used to achieve the fast finite‐time convergence, chatter‐free control inputs, better tracking performance and robustness. The finite‐time stability of the overall system is investigated and derived from the Lyapunov stability criterion. Finally, to validate the effectiveness and robustness of the developed control method, comparative simulations with H∞‐Adaptive control, intelligent PD (iPD), intelligent PID (iPID) and adaptive third‐order SMC (ATOSMC) are realized to demonstrate the performance of AFO‐HoTSMC.

IEEE Transactions on Systems, Man, and Cybernetics: Systems, 2019

This paper presents the results for model-independent control of uncertain n-degree of freedom ro... more This paper presents the results for model-independent control of uncertain n-degree of freedom robotic manipulators in the presence of external disturbances and backlash hysteresis. In order to improve the response characteristics of the system and attenuate the uncertainties, the developed robust model-free controller incorporates time delay control (TDC) as well as adaptive terminal sliding mode control (ATSMC) methods. Particularly, the time delay estimation is designed to estimate the unknown dynamics of the robotic manipulators by adopting the theory of TDC. Further, the ATSMC is utilized to obtain the robustness, finite-time convergence, and an adaptive tuning is exploited to deal with bounded derivative of unknown dynamics. The overall system stability is investigated by the Lyapunov theorem application and computed the finite convergence rate thereafter. Finally, a simulation comparison with an existing adaptive fractional-order terminal sliding mode control under backlash hysteresis is provided to illustrate the effectiveness and the superiority of the proposed method.

Asian Journal of Control, 2018

This paper introduces a robust adaptive fractional-order non-singular fast terminal sliding mode ... more This paper introduces a robust adaptive fractional-order non-singular fast terminal sliding mode control (RFO-TSM) for a lower-limb exoskeleton system subject to unknown external disturbances and uncertainties. The referred RFO-TSM is developed in consideration of the advantages of fractional-order and non-singular fast terminal sliding mode control (FONTSM): fractional-order is used to obtain good tracking performance, while the non-singular fast TSM is employed to achieve fast finite-time convergence, non-singularity and reducing chattering phenomenon in control input. In particular, an adaptive scheme is formulated with FONTSM to deal with uncertain dynamics of exoskeleton under unknown external disturbances, which makes the system robust. Moreover, an asymptotical stability analysis of the closed-loop system is validated by Lyapunov proposition, which guarantees the sliding condition. Lastly, the efficacy of the proposed method is verified through numerical simulations in comparison with advanced and classical methods.

Studies in Informatics and Control, 2018

In this paper, Fractional-order Non-singular Fast Terminal Sliding Mode Control based Fault Toler... more In this paper, Fractional-order Non-singular Fast Terminal Sliding Mode Control based Fault Tolerant Control (FONFTSM-FTC) is investigated for robotic manipulators in the presence of uncertainties, unknown external load disturbances and actuator faults. Firstly, Fractional-order Non-singular Fast Terminal Sliding Mode Control (FONFTSM) is proposed, in which Fractional-order is used to obtain good tracking performance, and Non-singular Fast Terminal Sliding Mode Control is utilized to achieve fast finite-time convergence, non-singularity and chatter-free control inputs. Secondly, FONFTSM with Adaptive scheme is used as a robust Fault Tolerant Control (FTC) to estimate the uncertainties as well as actuator faults without prior knowledge of the upper bounds. Asymptotical stability of the closed-loop system is obtained by Lyapunov analysis. Finally, corresponding simulation results with compared recent methods of adaptive FONFTSM (AFONTSM) and Non-singular Fast Terminal Sliding Mode Control based Active FTC (NFTSMC-FTC) are made to validate and demonstrate the effectiveness of the proposed method.

$Research paper thumbnail of Model-free control using time delay estimation and fractional-order nonsingular fast terminal sliding mode for uncertain lower-limb exoskeleton$

Journal of Vibration and Control, 2018

A robotic exoskeleton is a nonlinear system, which is subjected to parametric uncertainties and e... more A robotic exoskeleton is a nonlinear system, which is subjected to parametric uncertainties and external disturbances. Due to this reason, it is difficult to obtain the exact model of the system, and without knowledge of the system, it cannot be compensated accurately. In this study, time delay estimation (TDE)-based model-free fractional-order nonsingular fast terminal sliding mode control (MFF-TSM) is proposed for the lower-limb robotic exoskeleton in the existence of uncertainties and external disturbance. The main characteristic of the proposed scheme is that it controls the system without relying on the knowledge of exoskeleton dynamics. At first, the fractional-order (FO) with nonsingular fast terminal sliding mode control (NFTSM) is adopted to provide a precise trajectory tracking performance, fast finite-time speed of convergence, singularity-free and chatter-free control inputs. And then, the proposed controller employs TDE, to make the controller model independent, which d...

2016 35th Chinese Control Conference (CCC), 2016

This paper presents a modified methodology based on the model reference adaptive control (MRAC) f... more This paper presents a modified methodology based on the model reference adaptive control (MRAC) for tracking and stability with gravity compensation for the 5-link single support phase lower limb exoskeleton with external disturbance. Different from conventional methods, the proposed method is based on MRAC with adaptive error gain in the presence of external disturbance. Asymptotical stability of the system is investigated by choosing an appropriate lyapunov function, that ensures the convergence of tracking error to zero. The effectiveness of proposed method has been verified with the help of simulation example.

Journal of Biomedical Engineering and Medical Imaging, 2015

In this paper we have presented results for classification of electroencephalograph (EEG) signals... more In this paper we have presented results for classification of electroencephalograph (EEG) signals produced by the random visual exposure of primary colours i.e. red, green and blue to the subject while sitting in a dark room. Event-related spectral perturbations (ERSP) are used as features for support vector machine (SVM). Our objective was to classify the EEG signals as Red, Green and Blue classes and we have successfully classified the three visual conditions having accuracy of 84%, 89% and 98% with linear, polynomial and radial basis function kernels respectively with in all the groups of data among all the subjects.

International Journal of Adaptive Control and Signal Processing, 1992

A new adaptive controller is presented here for rigid-body robotic manipulators. It is stable and... more A new adaptive controller is presented here for rigid-body robotic manipulators. It is stable and robust with respect to a class of external disturbances. The robustness of the adaptive controller is established without the ‘slow-varying’ assumption and the computationally demanding regressor matrix. The control law consists of a non-adaptive PD control part and an adaptive control part. It uses two adaptive matrices to compensate two uniformly bounded coefficient matrices derived from the original dynamics. A α σ|q|-modified adaptive law is designed to adjust the adaptive matrices. A Lyapunov-type stability analysis indicates that the closed-loop system is uniformly ultimately bounded. The tracking error and compensation error will eventually converge into a closed region, which can be made arbitrarily small by adjusting the controller parameters. Simulation results are included to demonstrate the performance of the proposed controller.