scholarly journals Robust LQR-Based Neural-Fuzzy Tracking Control for a Lower Limb Exoskeleton System with Parametric Uncertainties and External Disturbances

2021 ◽  
Vol 2021 ◽  
pp. 1-20
Author(s):  
Jyotindra Narayan ◽  
Santosha K. Dwivedy
Keyword(s):  
Lower Limb ◽  
Gait Training ◽  
Lyapunov Theory ◽  
Parametric Uncertainties ◽  
External Disturbances ◽  
Lower Limb Exoskeleton ◽  
Lqr Control ◽  
Control Scheme ◽  
Firing Strength ◽  
Neural Fuzzy

The design of an accurate control scheme for a lower limb exoskeleton system has few challenges due to the uncertain dynamics and the unintended subject’s reflexes during gait rehabilitation. In this work, a robust linear quadratic regulator- (LQR-) based neural-fuzzy (NF) control scheme is proposed to address the effect of payload uncertainties and external disturbances during passive-assist gait training. Initially, the Euler-Lagrange principle-based nonlinear dynamic relations are established for the coupled system. The input-output feedback linearization approach is used to transform the nonlinear relations into a linearized state-space form. The architecture of the adaptive neuro-fuzzy inference system (ANFIS) and used membership function are briefly explained. While varying mass parameters up to 20%, three robust neural-fuzzy datasets are formulated offline with the joint error vector and LQR control input. Thereafter, to deal with external interferences, an error dynamics with a disturbance estimator is presented using an online adaptation of the firing strength matrix. The Lyapunov theory is carried out to ensure the asymptotic stability of the coupled human-exoskeleton system in view of the proposed controller. The gait tracking results for the proposed control scheme (RLQR-NF) are presented and compared with the exponential reaching law-based sliding mode (ERL-SM) controller. Furthermore, to investigate the robustness of the proposed control over LQR control, a comparative performance analysis is presented for two cases of parametric uncertainties and external disturbances. The first case considers the 20% raise in mass values with a trigonometric form of disturbances, and the second case includes the effect of the 30% increment in mass values with a random form of disturbances. The simulation runs have shown the promising gait tracking aspects of the designed controller for passive-assist gait training.

Fault tolerant control based on backstepping nonsingular terminal integral sliding mode and impedance control for a lower limb exoskeleton

2021 ◽  
pp. 095440622110357
Author(s):  
Majied Mokhtari ◽  
Mostafa Taghizadeh ◽  
Pegah Ghaf Ghanbari
Keyword(s):  
Sliding Mode Control ◽  
Lower Limb ◽  
Fault Tolerant ◽  
Sliding Mode ◽  
Impedance Control ◽  
Fault Tolerant Control ◽  
Integral Type ◽  
Lower Limb Exoskeleton ◽  
Mode Control ◽  
Control Scheme

In this paper, an active fault-tolerant control scheme is proposed for a lower limb exoskeleton, based on hybrid backstepping nonsingular fast terminal integral type sliding mode control and impedance control. To increase the robustness of the sliding mode controller and to eliminate the chattering, a nonsingular fast terminal integral type sliding surface is used, which ensures finite time convergence and high tracking accuracy. The backstepping term of this controller guarantees global stability based on Lyapunov stability criterion, and the impedance control reduces the interaction forces between the user and the robot. This controller employs a third order super twisting sliding mode observer for detecting, isolating ad estimating sensor and actuator faults. Motion stability based on zero moment point criterion is achieved by trajectory planning of waist joint. Furthermore, the highest level of stability, minimum error in tracking the desired joint trajectories, minimum interaction force between the user and the robot, and maximum system capability to handle the effect of faults are realized by optimizing the parameters of the desired trajectories, the controller and the observer, using harmony search algorithm. Simulation results for the proposed controller are compared with the results obtained from adaptive nonsingular fast terminal integral type sliding mode control, as well as conventional sliding mode control, which confirm the outperformance of the proposed control scheme.

scholarly journals Finite-Time Path Following Control of an Underactuated Marine Surface Vessel with Input and Output Constraints

2020 ◽  
Vol 10 (18) ◽  
pp. 6447
Author(s):  
Mingyu Fu ◽  
Lulu Wang
Keyword(s):  
Finite Time ◽  
Input Saturation ◽  
Path Following ◽  
Parametric Uncertainties ◽  
External Disturbances ◽  
Time Path ◽  
Path Following Control ◽  
Control Scheme ◽  
Marine Surface ◽  
Surface Vessel

This paper develops a finite-time path following control scheme for an underactuated marine surface vessel (MSV) with external disturbances, model parametric uncertainties, position constraint and input saturation. Initially, based on the time-varying barrier Lyapunov function (BLF), the finite-time line-of-sight (FT-LOS) guidance law is proposed to obtain the desired yaw angle and simultaneously constrain the position error of the underactuated MSV. Furthermore, the finite-time path following constraint controllers are designed to achieve tracking control in finite time. Additionally, considering the model parametric uncertainties and external disturbances, the finite-time disturbance observers are proposed to estimate the compound disturbance. For the sake of avoiding the input saturation and satisfying the requirements of finite-time convergence, the finite-time input saturation compensators were designed. The stability analysis shows that the proposed finite-time path following control scheme can strictly guarantee the constraint requirements of the position, and all error signals of the whole control system can converge into a small neighborhood around zero in finite time. Finally, comparative simulation results show the effectiveness and superiority of the proposed finite-time path following control scheme.

Robust Guidance Control for Nonholonomic AGV Based on First Order Dynamic Sliding Mode Techniques

2013 ◽  
Vol 709 ◽  
pp. 583-588
Author(s):  
Jin Hua Ye ◽  
Di Li ◽  
Shi Yong Wang ◽  
Feng Ye
Keyword(s):  
High Performance ◽  
Sliding Mode ◽  
Path Following ◽  
Lyapunov Theory ◽  
External Disturbances ◽  
Guidance Control ◽  
First Order ◽  
Control Scheme ◽  
The Impact ◽  
Dynamic Sliding Mode

This paper develops a high performance guidance controller for automated guided vehicle (AGV) with nonholonomic constraint. In this controller, the path following method in the Serret-Frenet frame is used for driving the AGV onto a predefined path at a constant forward speed. Moreover, a first order dynamic sliding mode controller is proposed, not only to overcome the impact of unknown model uncertainties and external disturbances of the system, but also to weaken the chattering in the standard sliding mode control. The global asymptotic stability and robustness of the system is proven by the Lyapunov theory and LaSalles invariance principle. Simulation results show the validity of the proposed guidance control scheme.

scholarly journals An Adaptive Hierarchical Sliding Mode Controller for Autonomous Underwater Vehicles

Electronics ◽  
2021 ◽  
Vol 10 (18) ◽  
pp. 2316
Author(s):  
Quang Van Vu ◽  
Tuan Anh Dinh ◽  
Thien Van Nguyen ◽  
Hoang Viet Tran ◽  
Hai Xuan Le ◽  
...  
Keyword(s):  
Adaptive Learning ◽  
Autonomous Underwater Vehicle ◽  
Sliding Mode ◽  
Autonomous Underwater Vehicles ◽  
Lyapunov Theory ◽  
Control Technique ◽  
External Disturbances ◽  
Control Scheme ◽  
Hierarchical Sliding Mode ◽  
Over Time

The paper addresses a problem of efficiently controlling an autonomous underwater vehicle (AUV), where its typical underactuated model is considered. Due to critical uncertainties and nonlinearities in the system caused by unavoidable external disturbances such as ocean currents when it operates, it is paramount to robustly maintain motions of the vehicle over time as expected. Therefore, it is proposed to employ the hierarchical sliding mode control technique to design the closed-loop control scheme for the device. However, exactly determining parameters of the AUV control system is impractical since its nonlinearities and external disturbances can vary those parameters over time. Thus, it is proposed to exploit neural networks to develop an adaptive learning mechanism that allows the system to learn its parameters adaptively. More importantly, stability of the AUV system controlled by the proposed approach is theoretically proved to be guaranteed by the use of the Lyapunov theory. Effectiveness of the proposed control scheme was verified by the experiments implemented in a synthetic environment, where the obtained results are highly promising.

scholarly journals Backstepping Control of an Unmanned Helicopter Subjected to External Disturbance and Model Uncertainty

2021 ◽  
Vol 11 (12) ◽  
pp. 5331
Author(s):  
Wenlong Zhao ◽  
Zhijun Meng ◽  
Kaipeng Wang ◽  
Haoyu Zhang
Keyword(s):  
External Disturbance ◽  
Flight Test ◽  
Lyapunov Theory ◽  
Outdoor Environment ◽  
Wind Gust ◽  
External Disturbances ◽  
Attitude Tracking ◽  
Control Scheme ◽  
Highly Nonlinear ◽  
The Stability

A helicopter is a highly nonlinear system. Its mathematical model is difficult to establish accurately, especially the complicated flapping dynamics. In addition, the forces and moments exerted on the fuselage are very vulnerable to external disturbances like wind gust when flying in the outdoor environment. This paper proposes a composite control scheme which consists of a nonlinear backstepping controller and an extended state observer (ESO) to handle the above problems. The stability of the closed-loop system can be guaranteed based on Lyapunov theory. The external disturbances and model nonlinearities are treated as a lumped disturbance. Meanwhile, the ESO is employed to compensate the influence by estimating the lumped disturbance in real-time. Numerical simulation results are presented to demonstrate that the algorithm can achieve accurate and agile attitude tracking under the external wind gust disturbances even with model uncertainties. When coming to the flight test, a block dropping device was designed to generate a quantifiable and replicable disturbance, and the experimental results indicate that the algorithm introduced above can reject the external disturbance rapidly and track the given attitude command precisely.

scholarly journals A Multiposture Locomotor Training Device with Force-Field Control

2014 ◽  
Vol 6 ◽  
pp. 173518 ◽  
Author(s):  
Jianfeng Sui ◽  
Yali Liu ◽  
Runze Yang ◽  
Linhong Ji
Keyword(s):  
Lower Limb ◽  
Closed Loop ◽  
Closed Loop Control ◽  
Locomotor Training ◽  
Training Device ◽  
Loop Control ◽  
Lower Limb Exoskeleton ◽  
Weight Support ◽  
Control Scheme ◽  
Field Control

This paper introduces a multiposture locomotor training device (MPLTD) with a closed-loop control scheme based on joint angle feedback, which is able to overcome various difficulties resulting from mechanical vibration and the weight of trainer to achieve higher accuracy trajectory. By introducing the force-field control scheme used in the closed-loop control, the device can obtain the active-constrained mode including the passive one. The MPLTD is mainly composed of three systems: posture adjusting and weight support system, lower limb exoskeleton system, and control system, of which the lower limb exoskeleton system mainly includes the indifferent equilibrium mechanism with two degrees of freedom (DOF) and the driving torque is calculated by the Lagrangian function. In addition, a series of experiments, the weight support and the trajectory accuracy experiment, demonstrate a good performance of mechanical structure and the closed-loop control.

scholarly journals A hierarchical Lyapunov-based cascade adaptive control scheme for lower-limb exoskeleton

2019 ◽  
Vol 50 ◽  
pp. 198-208 ◽  
Author(s):  
Xinglong Zhang ◽  
Wei Jiang ◽  
Zhizhong Li ◽  
Shengli Song
Keyword(s):  
Adaptive Control ◽  
Lower Limb ◽  
Lower Limb Exoskeleton ◽  
Control Scheme ◽  
Adaptive Control Scheme

scholarly journals Integral Backstepping Control of Induction Machine

2021 ◽  
Vol 23 (4) ◽  
pp. 345-351
Author(s):  
Abdelhak Benheniche ◽  
Farid Berrezzek
Keyword(s):  
High Speed ◽  
Induction Machine ◽  
Lyapunov Theory ◽  
System Stability ◽  
External Disturbances ◽  
Control Approach ◽  
Integral Action ◽  
Resistance Variation ◽  
Control Scheme ◽  
Rotor Flux

The goal of this work is to propose a latest design of a rotor speed and rotor flux modulus control approach for an induction machine using a Backstepping corrector with an integral action. The advantage of the Backstepping Strategy is the ability to manage a nonlinear system. The Lyapunov theory has been used to ensure the system stability. To improve the controller robustness proprieties the integral action is used, despite the system uncertainties and the existence of external disturbances. The unavailable rotor flux is recovered by estimation of the rotor flux of the machine based on the integration of the stator voltage expressions. The simulation results illustrate the effectiveness of the proposed control scheme under load disturbances, rotor resistance variation and low and high speed.

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