Sami Al Issa

Bio: Sami Al Issa is an academic researcher from Indian Institute of Technology Guwahati. The author has contributed to research in topics: Adaptive control & Backstepping. The author has an hindex of 4, co-authored 7 publications receiving 39 citations. Previous affiliations of Sami Al Issa include Damascus University.

Improved event-triggered adaptive control of non-linear uncertain networked systems

Abstract: Over the past few years, networked control systems (NCSs) have shown rapid progress and have indeed been very popular in terms of research as well as industrial applications. The issue of limited resources has been a fundamental problem in the translation of modern control techniques to NCS design. In order to address the aforesaid design challenge, an improved event-triggered adaptive backstepping control scheme is presented in this study for a class of uncertain NCSs with non-Lipschitz non-linearities under limited resources. Rather than a preselected constant threshold assumption, a well-designed and systematic triggering rule is derived based on the Lyapunov approach in order to satisfy bandwidth limitation and ensure system stability with acceptable transient performance. Relative to existing strategies in the literature, the proposed method leads to a substantially reduced number of transmissions with longer inter-event time. Thereby, the proposed algorithm exhibits more efficiency in resource utilisation. Simulation results on a networked control based robotic manipulator system illustrate the efficacy of the proposed adaptive scheme compared to benchmark control algorithms intended for a similar application.

Event-Triggered Adaptive Hybrid Position-Force Control for Robot-Assisted Ultrasonic Examination System

Abstract: In this paper, an adaptive motion-force control scheme is presented for a networked ultrasound robotic manipulator to perform a transversal abdomen scan. An adaptive backstepping position controller is designed to ensure the stability of the ultrasound robot in the presence of parametric uncertainties and external disturbances. A proportional-integral-derivative force controller is proposed to maintain a constant interaction force during the scan process. Rather than periodic time-triggered implementation, the Lyapunov-based triggering condition is derived to update the control inputs in an aperiodic manner, reduce the communication burden, and preserve the stability of the robotic system during the task. The effectiveness of the proposed control strategy is investigated based on a comparison study with different time-triggered adaptive control schemes. Moreover, the proposed event-triggered mechanism is compared with the most common triggering conditions in literature, i.e., fixed and relative thresholds. These schemes are devoted to carry out the transversal ultrasound scan in the simulation environment. Additional validation of the proposed control scheme is performed in the virtual robot experimentation platform (V-REP). From the results of simulation and experimental runs, the proposed event-triggered control scheme is found to be more promising and efficient in robot-assisted ultrasound imaging.

Event-triggered adaptive control of uncertain non-linear systems under input delay and limited resources

Abstract: In this paper, both input delay and limited bandwidth challenges in uncertain networked control systems have been tackled. For this purpose, an event-triggered adaptive controller based on backstepping technique is designed for a general class of non-linear uncertain MIMO systems. The event-triggered mechanism is placed in the sensor-to-controller channel to reduce communication burden and save computational resources. Rather than predefined fixed or simple relative triggering thresholds, the proposed triggering condition is derived based on the negative semi-definiteness of derivative of Lyapunov function. To handle input delay problem, an auxiliary compensation system based on integral of input signal is introduced in the controller design. System stability are guaranteed under proposed scheme with no Zeno behavior. Simulation results on three-link cylindrical robotic arm show that the proposed control scheme successfully compensates for input delays and ensures a substantial saving in computational and network resources characterized by number of required control updates and signal transmissions over the network.

Event-triggered Backstepping Control Scheme for Networked Mobile Robots

Abstract: Remote control of mobile robotic systems over a communication network is indeed a challenging task. With the benefit of event-triggered strategy, a dynamic tracking controller based on backstepping approach is proposed for a remotely-controlled mobile robot considering the limitation of network bandwidth. The designed controller aims to reduce the required transmissions of control update through the network while ensuring the system performance and stability of closed-loop system. For this purpose, a well-designed Lyapunov-based triggering condition is derived. Simulation results illustrate the efficacy of the proposed event-triggered scheme compared to a traditional time-triggered implementation in terms of network usage.

Event-Triggered Adaptive Hybrid Position-Force Control for Robot-Assisted Ultrasonic Examination System

Abstract: In this paper, an adaptive motion-force control scheme is presented for a networked ultrasound robotic manipulator to perform a transversal abdomen scan. An adaptive backstepping position controller is designed to ensure the stability of the ultrasound robot in the presence of parametric uncertainties and external disturbances. A proportional-integral-derivative force controller is proposed to maintain a constant interaction force during the scan process. Rather than periodic time-triggered implementation, the Lyapunov-based triggering condition is derived to update the control inputs in an aperiodic manner, reduce the communication burden, and preserve the stability of the robotic system during the task. The effectiveness of the proposed control strategy is investigated based on a comparison study with different time-triggered adaptive control schemes. Moreover, the proposed event-triggered mechanism is compared with the most common triggering conditions in literature, i.e., fixed and relative thresholds. These schemes are devoted to carry out the transversal ultrasound scan in the simulation environment. Additional validation of the proposed control scheme is performed in the virtual robot experimentation platform (V-REP). From the results of simulation and experimental runs, the proposed event-triggered control scheme is found to be more promising and efficient in robot-assisted ultrasound imaging.

Event-triggered practical finite-time output feedback stabilisation for switched non-linear time-delay systems

Abstract: This study investigates the event-triggered practical finite-time output feedback control for a class of switched high-order non-linear time-delay systems with uncertain control coefficients. A reduced-order observer is first constructed to estimate the unmeasurable states. By adding a power integrator technique, an event-triggered output feedback controller is designed for the nominal system. Subsequently, the constructed observer and controller are scaled with a suitable gain by homogeneous domination approach, which, together with an appropriate Lyapunov-Krasoviskii functional, can render that the uncertain switched high-order non-linear system with time-varying delay is practical finite-time stability. Finally, two examples are provided to demonstrate the validity of the proposed scheme.

Event-triggered communication for passivity and synchronisation of multi-weighted coupled neural networks with and without parameter uncertainties

Abstract: A multi-weighted coupled neural networks (MWCNNs) model with event-triggered communication is studied here. On the one hand, the passivity of the presented network model is studied by utilising Lyapunov stability theory and some inequality techniques, and a synchronisation criterion based on the obtained output-strict passivity condition of MWCNNs with event-triggered communication is derived. On the other hand, some robust passivity and robust synchronisation criteria based on output-strict passivity of the proposed network with uncertain parameters are presented. At last, two numerical examples are provided to testify the effectiveness of the output-strict passivity and robust synchronisation results.

Event-triggered adaptive control of uncertain non-linear systems under input delay and limited resources

Abstract: In this paper, both input delay and limited bandwidth challenges in uncertain networked control systems have been tackled. For this purpose, an event-triggered adaptive controller based on backstepping technique is designed for a general class of non-linear uncertain MIMO systems. The event-triggered mechanism is placed in the sensor-to-controller channel to reduce communication burden and save computational resources. Rather than predefined fixed or simple relative triggering thresholds, the proposed triggering condition is derived based on the negative semi-definiteness of derivative of Lyapunov function. To handle input delay problem, an auxiliary compensation system based on integral of input signal is introduced in the controller design. System stability are guaranteed under proposed scheme with no Zeno behavior. Simulation results on three-link cylindrical robotic arm show that the proposed control scheme successfully compensates for input delays and ensures a substantial saving in computational and network resources characterized by number of required control updates and signal transmissions over the network.