Variable Gains Research Articles

Signal-to-Noise Ratio Enhancement of MR Images With Variable Gains and K-Space Splicing Method

Signal-to-Noise Ratio Enhancement of MR Images With Variable Gains and K-Space Splicing Method

Design of sliding mode control with state varying gains for a Benchmark Twin Rotor MIMO System in Horizontal Motion

In this paper, a sliding mode control (SMC) with state-varying gains is proposed to control the yaw orientation of the Twin Rotor MIMO System (TRMS). This proposed SMC algorithm reduces the chattering effect without affecting the properties of the robustness of the sliding modes. The salient feature of this control is that the magnitude of the variable gains depends on the absolute values of the states and tracking error. This design exhibits a relation between first-order and higher-order sliding mode control algorithms. Besides, the developed control strategy does not overestimate disturbances. Hence, the energy utilized by the control effort is reduced significantly. The stability analysis is accomplished by considering the TRMS model in the horizontal plane to illustrate the asymptotic stability condition. Further, a comparison between the twisting algorithm and the proposed control law is highlighted. However, it is evinced that the proposed variable gain SMC is a combination of a twisting algorithm and conventional SMC. Simulations studies are carried out to highlight the efficacies of the proposed controller using MATLAB/Simulink environment.

Combining FD‐UAV and NOMA technologies in IoT sensor network with millimeter‐wave communications

SummaryIn this article, we exploit the huge advantages of full‐duplex (FD) transmission, nonorthogonal multiple access (NOMA) technique, unmanned aerial vehicle (UAV), and millimeter‐wave (mmWave) communications in an Internet of things (IoT) sensor network. Specifically, the UAV operates as a FD amplify‐and‐forward (AF) relay to aid communications between an IoT sensor and multiple NOMA users. Moreover, the FD‐UAV (FDU) adopts both fixed and variable gains. We obtain exact expressions of outage probability (OP) and throughput of IoT‐FDU‐NOMA‐mmWave network with fixed and variable gains at FDU over Nakagami‐ fading channels. Numerical illustrations clearly show that the OP and throughput performance of the IoT‐FDU‐NOMA‐mmWave network with variable gain are considerably higher than those with fixed gain. Since mmWave bands are used, the OP and throughput of the IoT‐FDU‐NOMA‐mmWave network are greatly affected by carrier frequency and communication distances. Consequently, when the carrier frequency or/and the distances between the IoT sensor and the users increase, the transmit power of the IoT sensor and the FDU should be increased to maintain the network performance. On the other hand, the effects of residual loop interference (LI) induced by FD transmission are remarkable. Thus, more efforts to reduce the residual LI power have to be continuously performed. Moreover, the specific impacts of the key parameters such as fading order , the positions of the FDU, and data rates are clarified. More importantly, in practice, according to the fixed gain or the variable gain that is used, we can locate the position of FDU to achieve the best performance for the IoT‐FDU‐NOMA‐mmWave network.

Generalized Variable Gain ADRC for Nonlinear Systems and Its Application to Delta Parallel Manipulators

In this paper, a novel generalized variable gain active disturbance rejection control (VGADRC) method is proposed for the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$n$ </tex-math></inline-formula> -th order nonlinear system. The generalized VGADRC, including generalized variable gain tracking differentiator (VGTD), generalized variable gain extended state observer (VGESO), and generalized variable gain controller (VGC), incorporates error-based variable gains to achieve desired control performance. Moreover, the stability analysis of VGADRC is performed, and the existence of feasible solutions are discussed and expressed explicitly. Finally, the generalized VGADRC method is applied to delta parallel manipulators, and the numerical simulation results and experiment results are presented to illustrate the effectiveness of the proposed method.

Family of Bounded Regulators with Variable Gains and Lyapunov Asymptotic Stability for Robot Manipulators

In this paper, the regulation problem for robot manipulators in joint space through the proposal of a new family of bounded regulators with variable gains is presented. The proposed regulators have bounded functions that replace the classical position error and the velocity; moreover, the variable gains are formed by a family of Lipchitz functions with the position error and the velocity as their arguments. This structure avoids exceeding the physical limits of the servomotors. A strict Lyapunov function is proposed to demonstrate the global and asymptotic stability. Finally, the functionality and performance of the proposal are examined by experimental results on a direct-drive-robot of 3-degrees-of-freedom against the PD regulator

Trajectory tracking control for four‐mecanum‐wheel mobile vehicle: A variable gain active disturbance rejection control approach

AbstractIn this article, a novel variable gain active disturbance rejection control (ADRC) approach is developed for the trajectory tracking control of four‐mecanum‐wheel mobile vehicle. The proposed variable gain ADRC approach includes three parts, variable gain tracking‐differentiator (VGTD), variable gain extended state observer (VGESO), and composite disturbance rejection controller. The error‐based variable gains are, respectively, incorporated in VGTD, VGESO, and controller to improve the transient performances. Moreover, stability analysis of the VGTD tracking error system, VGESO estimation error system, and the closed‐loop system are also provided. Finally, simulation and experiment results show the effectiveness of the proposed control approach.

Variable Gain for Iterative Learning Control

Background: At present, the gain of most ILC algorithms is fixed, and the convergence speed of the system depends on the learning law, which will lead to the complexity of the structure of the learning law, and variable gain can accelerate the convergence speed without changing the structure of the learning law as variable gains are introduced into ILC. Objective: In this paper, the D-type learning law is used. Firstly, the variable gain iterative learning controller is designed. Secondly, the convergence of the learning law is analyzed. Methods: Finally, in order to illustrate the effectiveness of this method, the simulation is carried out using MATLAB. Results and Conclusion: The simulation results show that the variable gain iterative learning control can improve the convergence speed of the iteration, and weaken the restrictions on the initial input.

Nonlinear PID global regulators with selftuned PD gains for robot manipulators: theory and experimentation

It is known that the Proportional Integral and Derivative (PID) regulator with constant and symmetric positive definite gain matrices (Kp, Kv and Ki), in closed loop with robotic manipulators, guarantees semiglobal asymptotic stability of the equilibrium point. In this paper, a fresh approach for control of robots manipulators based on a class of PID regulators with variable gain matrices Kp and Kv, which guarantee global asymptotic stability, is proposed. This PID control scheme, proposed with PD variable gains and fixed integral gains, improves the performance of the transient response and the handling of constraints, such as the limits of the actuator torques. Based on the authors experience, our proposal is the first scheme of a nonlinear PID regulator for robot manipulators whose PD gains are variable and its stability proof is global asymptotic in the sense of Lyapunov. The PD variable gains are directly dependent on the joint position errors and are fine tuned by fuzzy logic methodology. Good results were obtained on an experimental direct-drive robot arm of two degrees of freedom, when it was tested in order to verify the effectiveness of the new controller.

Global Saturated Regulator with Variable Gains for Robot Manipulators

In this paper, we propose a set of saturated controllers with variable gains to solve the regulation problem for robot manipulators in joint space. These control schemes deliver torques inside the prescribed limits of servomotors. The gamma of variable gains is formed by continuous, smooth, and differentiable functions of the joint position error and velocity of the manipulator. A strict Lyapunov function is proposed to demonstrate globally asymptotic stability of the closed-loop equilibrium point. Finally, the functionality and performance of the proposal are illustrated via simulation results and comparative analysis against Proportional-Derivative (PD) control scheme on a two-degrees-freedom direct-drive robot manipulator.

Global Saturated Regulator with Variable Gains for Robot Manipulators

In this paper, we propose a set of saturated controllers with variable gains to solve the regulation problem for robot manipulators in joint space. These control schemes deliver torques inside the prescribed limits of servomotors. The gamma of variable gains is formed by continuous, smooth, and differentiable functions of the joint position error and velocity of the manipulator. A strict Lyapunov function is proposed to demonstrate globally asymptotic stability of the closed-loop equilibrium point. Finally, the functionality and performance of the proposal are illustrated via simulation results and comparative analysis against Proportional-Derivative (PD) control scheme on a two-degrees-freedom direct-drive robot manipulator.

On the performance of roadside unit-assisted energy harvesting full-duplex amplify-and-forward vehicle-to-vehicle relay systems

This paper considers the performance of a full-duplex (FD) vehicle-to-vehicle (V2V) relay system where the relay uses amplify-and-forward (AF) protocol and harvests the energy from the radio frequency (RF) signals transmitted by source. Unlike previous reports, we investigate the case that both relay and destination are moving vehicles. Therefore, the channel between source and relay is Rayleigh fading while the channel between relay and destination is cascade (double) Raleigh fading. In addition, both fixed and variable gains are used at the FD relay. Based on mathematical analysis, we successfully derive the exact closed-form expressions of the outage probability (OP) and symbol error probability (SEP) to evaluate the system performance. Monte-Carlo simulations are exploited to demonstrate the correctness of all derived mathematical expressions. Numerical results clearly indicate that the OP and SEP performance of the considered energy harvesting (EH)-FD-V2V relay system with variable gain is much better than that with fixed gain. Moreover, the OP and SEP performance are strongly impacted by residual self-interference (RSI) due to the incomplete noise cancellation during the FD transmission. Besides the RSI, the OP and SEP performance is greatly reduced because of the cascade Rayleigh fading. We also observe that there is an optimal EH time duration to minimize the OP and SEP and this optimal value is different for fixed and variable gains. Therefore, from the transmission power of source and the type of gains used at FD relay, we can choose a suitable time EH time duration to get the best system performance.

PID Principles to Obtain Adaptive Variable Gains for a Bi-order Sliding Mode Control

A new model to obtain adaptive variable gains for a bi-order Sliding Mode Control is proposed in this work. The variable gains for the controller are designed to dynamically adapt their values, using principles of the well-known Proportional-Integral-Derivative control technique, where the magnitude of the tracking error is the signal feedback. According the way to tune parameters, it can become a first-order or a second-order controller. This design takes into account the actuators constraints (operational limits of the plant to control). As a result of the adaptive properties of the proposed scheme, the new controller significantly reduces the energy consumption in control processes, and it rejects the so called chattering-effect, simultaneously maintaining the main robust properties of the Sliding Mode strategy. In order to show the feasibility and effectiveness of the proposed design, simulation results are presented, where the performance of the proposed controller is compared with the conventional Sliding Modes of order one and two, and also with the classical PID controller. A strong stability analysis in the sense of Lyapunov is presented, showing global exponential stability for the equilibrium point of the closed-loop control system when the proposed control design is used.

Output constrained sliding mode control: A variable gain approach

In this paper output constrained sliding mode control of nonlinear relative degree two systems is considered. The constraints are formulated with respect to the first derivative of the control variable. The system may be effected by matched disturbances. Only the uncertainty bounds are required to be known. A multi-controller approach with variable gains is proposed. The controller guarantees that the constraints can at most be violated for a finite-time, which can be shortened by tuning the controller parameters. Despite the action of the multiple controllers the tracking error of the approach is guaranteed to be bounded.

Observer-Based Fault Detection With Fuzzy Variable Gains and Its Application to Industrial Servo System

In this paper, an adaptive high-accurate observer-based fault detection approach for industrial applications is proposed. The proposed fault detection algorithm employs a fuzzy logic-based approach with the objective of finding the appropriate observer gains that could cope with the different working conditions. The flexibility and adaptability represent the main objectives of the proposed observer. This work is interested in proposing an observer with fuzzy variable gains for a general nonlinear system. Furthermore, a linear model has been built to facilitate the accomplishment of the fault detection of the industrial servo system by using the proposed observer. In order to evaluate the proposed approach, eleven realistic sensor fault scenarios are created under varying conditions: fault parameters (e.g., multiple fault profiles, location, and magnitudes), unknown inputs (e.g., disturbers and sensor noises) for performance testing. Also, a scoring algorithm has been implemented, to evaluate the classification ability of the algorithm and the early fault detection ability. The experimental results demonstrate the effectiveness of the proposed observer approach in detecting sensor faults in the industrial servo systems, with 88.8% classification accuracy. Furthermore, the obtained results confirm the proposed algorithm superiority when compared to classical Luenberger observer with constant gains.

Robust control design for air breathing proton exchange membrane fuel cell system via variable gain second‐order sliding mode

AbstractThe nonlinear and time‐dependent characteristic and unknown modeling uncertainty of proton exchange membrane fuel cell (PEMFC) such as complex electro‐chemical, thermal, and fluid mechanic phenomena make its controller design quite challenging. In this paper, a controller based on a super twisting algorithm (STA) with variable gains is proposed to control the air breathing system of PEMFC. The strategy includes regulating the oxygen excess ratio () for preventing the stack oxygen starvation and maintaining optimum net power output in spite of external disturbances and model uncertainties. The proposed algorithm has the main advantages of the fixed gain STA, such as robustness against the disturbance and parametric uncertainties with the unknown boundary, chattering reduction, and finite time convergence. The Lyapunov analysis was proposed to assess the stability of the Variable Gain Super Twisting Algorithm (VGSTA). The results verified the effectiveness of the proposed controller with attaining robust regulation against uncertainties, disturbances, and noisy circumstance compared to fixed gain SOSM controllers.

Knee Impedance Modulation to Control an Active Orthosis Using Insole Sensors.

Robotic devices for rehabilitation and gait assistance have greatly advanced with the objective of improving both the mobility and quality of life of people with motion impairments. To encourage active participation of the user, the use of admittance control strategy is one of the most appropriate approaches, which requires methods for online adjustment of impedance components. Such approach is cited by the literature as a challenge to guaranteeing a suitable dynamic performance. This work proposes a method for online knee impedance modulation, which generates variable gains through the gait cycle according to the users’ anthropometric data and gait sub-phases recognized with footswitch signals. This approach was evaluated in an active knee orthosis with three variable gain patterns to obtain a suitable condition to implement a stance controller: two different gain patterns to support the knee in stance phase, and a third pattern for gait without knee support. The knee angle and torque were measured during the experimental protocol to compare both temporospatial parameters and kinematics data with other studies of gait with knee exoskeletons. The users rated scores related to their satisfaction with both the device and controller through QUEST questionnaires. Experimental results showed that the admittance controller proposed here offered knee support in 50% of the gait cycle, and the walking speed was not significantly different between the three gain patterns (p = 0.067). A positive effect of the controller on users regarding safety during gait was found with a score of 4 in a scale of 5. Therefore, the approach demonstrates good performance to adjust impedance components providing knee support in stance phase.

Three-axis attitude stabilization of a flexible satellite using non-linear PD controller

In this paper, after complete modelling of a flexible satellite equipped with a control moment gyroscope (CMG) actuator, it is shown that a PD-like controller can globally asymptotically stabilize this satellite by using Lyapunov’s direct method. Despite the simplicity, simulations show that the controller can stabilize the flexible satellite in a three-axis manoeuvre even in the presence of external disturbances. Then, using a non-linear variable gains PD controller, which only uses angular velocity of the rigid body and the attitude parameters as the inputs, the performance of the control system is improved in some important aspects such as reducing maximum control torque, reducing maximum peak of deflection of the appendages and increasing robustness of the controller against the orbital disturbances. In addition, locally asymptotically stability of the non-linear variable gain PD controller is guaranteed using a novel Lyapunov candidate function. Considering the difficulty in measuring the appendages’ deflection and the primarily existence of parameter uncertainties, and as this controller is independent of changes in these parameters, such a control system is very useful and applicable. In order to validate the system’s mathematical model and the control system performance, an exact model of the satellite is constructed in the ADAMS/View software that is linked to the MATLAB software. The efficacy of the proposed approach is demonstrated by several numerical examples.

New variable gain super-twisting sliding mode observer for sensorless vector control of nonsinusoidal back-EMF PMSM

This paper presents a new discrete-time super-twisting sliding mode observer with variable gains for sensorless nonsinusoidal vector control of permanent magnet synchronous motors. This observer is adopted to estimate the back electromotive forces (back-EMF) that are required for the rotor speed estimation and for the nonsinusoidal vector control. In addition, their gains are time-varying to minimize the chattering. So, they are adjusted based on internal states of the super-twisting algorithm. The stability analysis is investigated from the Lyapunov theory for discrete-time systems. Finally, simulation and experimental results are presented to demonstrate the good performance and the effectiveness of the proposed observer.

Predictive Variable Gain Iterative Learning Control for PMSM

A predictive variable gain strategy in iterative learning control (ILC) is introduced. Predictive variable gain iterative learning control is constructed to improve the performance of trajectory tracking. A scheme based on predictive variable gain iterative learning control for eliminating undesirable vibrations of PMSM system is proposed. The basic idea is that undesirable vibrations of PMSM system are eliminated from two aspects of iterative domain and time domain. The predictive method is utilized to determine the learning gain in the ILC algorithm. Compression mapping principle is used to prove the convergence of the algorithm. Simulation results demonstrate that the predictive variable gain is superior to constant gain and other variable gains.

Application of a New Membership Function in Nonlinear Fuzzy PID Controllers with Variable Gains

This paper proposes a nonlinear fuzzy PID control algorithm, whose membership function (MF) is adjustable, is universal, and has a wide adjustable range. Appling this function to fuzzy control theory will increase system’s tunability. The continuity of this function is proved. This method was employed in the simulation and HIL experiments. Effectiveness and feasibility of this function are demonstrated in the results.