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Summary: A model predictive cascade controller is proposed in this article to resolve the actuator saturation problem of underwater human‐occupied vehicle (HOV) trajectory tracking. For the kinematic model, a grasshopper optimization‐based model predictive control (MPC) is developed to obtain control velocities with small fluctuations in allowable regions. Based on the desired velocities obtained from the improved kinematic control, the HOV dynamic model is used to generate the corresponding torques and forces using sliding mode control. With the control velocities and forces given by the cascade control strategy, the elimination of actuator saturation during the HOV trajectory tracking can be realized. The proposed controller is verified by simulations using a numerical example based on a four degrees of freedom (4‐DOFs) HOV. [ABSTRACT FROM AUTHOR]

A distributed control policy is designed for a group of Euler–Lagrange (EL) agents in a leader–follower-based communication network with time-varying delays. The nonsingular terminal sliding mode control (NTSMC) policy is integrated with mixed-type feedback and time-varying, adaptive control parameters. The control gain and proportions of feedback with and without estimated self-delays are tuned online with fuzzy logic control (FLC). The total and maximum tracking errors of a group of EL agents are assessed to demonstrate an improvement in synchronization performance with the proposed NTSMC+FLC approach compared to the NTSMC approach with constant parameters. Simulation and experimental results of a group of Phantom Omni manipulators are presented to validate the proposed control policy. [ABSTRACT FROM AUTHOR]

Common assumptions in most of the previous nonlinear networked leader–follower systems are that the leader is provided as a constant signal and that the controllers are designed for either the joint-space regulation or the translational Cartesian-space motion control. This article addresses the control issue of the delay-induced horizontal shift effect when the leader is moving with a changing speed. A novel mixed-type feedback is introduced to reduce the horizontal shift effect so as to minimize tracking errors experienced by the follower agents. In this article, we also study the complete pose control using a nonsingular terminal sliding mode (NTSM) method. A stability analysis is provided to prove the finite-time boundedness of the tracking error signals. Quantitative evaluations of the multiple effects on the error bound are conducted to facilitate the subsequent control design to improve the performance. Numerical simulation results of a team of two degree-of-freedoms (DOFs) manipulators demonstrate the improved tracking performance of the end effectors with small bounded errors which are affected by network delays, maximum assigned accelerations, and the selection of control gains. The experimental results are provided to demonstrate the performance of the developed controller. [ABSTRACT FROM AUTHOR]

In this article, we focus on the experimental validation of the developed adaptive nonsingular terminal sliding mode (ANTSM) controller for a networked manipulator system. The proposed control approach is designed to deal with a combination of adverse and inexactly known conditions in practice, including parametric uncertainties, frictions, exogenous disturbances, and random time-varying network delays. Another issue addressed in this article is the tradeoff between achieving a smooth convergence and a high tracking accuracy in the physical implementation of the ANTSM controller. Hence, a novel time-varying gain in a form of logistic function is introduced to provide converging smoothness and meanwhile improve the tracking accuracy. Experimental results and empirical analysis are provided to demonstrate the effectiveness and performance improvement of the proposed controller with a time-varying gain. [ABSTRACT FROM AUTHOR]

Bilateral teleoperation technology has caused wide attentions because of its applications in various remote operation systems. However, there exist some challenging control issues such as communication delay, unmeasurable environmental force, and various manipulator modelling uncertainties. In this study, the disturbance observer is designed based on the slave manipulator dynamics to observe the unmeasurable environmental force. When the environmental force is modelled as a general linear regression form, its unknown parameters can be estimated online by the least square adaptation law. A novel communication structure is proposed where only the master trajectory is transmitted to the slave side, and the transmission signal from the slave to the master is replaced by those estimated environmental parameters. Since these parameters are not power signals, the passivity problem of the communication channel and the trade‐off limitation between the transparency performance and robust stability in traditional teleoperation control are essentially avoided. The sliding mode control and the force compensation of disturbance observer are integrated subsequently to deal with various manipulator modelling uncertainties, so that the excellent synchronisation performance can be realised. Thus, the proposed control algorithm can guarantee the robust stability and the good control performance simultaneously under arbitrary time delays. The simulation and experiment on two single degree‐of‐freedom manipulators are carried out and the results show the effectiveness of the proposed control algorithm. [ABSTRACT FROM AUTHOR]

In this work two main robust control strategies, the sliding mode control (SMC) and nonlinear H 8 control, are integrated to function in a complementary manner for tracking control tasks. The SMC handles matched L 8 [0,8) type system uncertainties with known bounding functions. H 8 control deals with unmatched disturbances of L 2 [0,8) type where the upper-bound knowledge is not available. The new control method is designed for a class of nonlinear uncertain systems with two cascade subsystems. Nonlinear H 8 control is applied to the first subsystem in the presence of unmatched disturbances. Through solving a Hamilton-Jacoby inequality, the nonlinear H 8 control law for the first subsystem well defines a nonlinear switching surface. By virtue of nonlinear H 8 control, the resulting sliding manifold in the sliding phase possesses the desired L 2 gain property and to a certain extend the optimality. Associated with the new switching surface, the SMC is applied to the second subsystem to accomplish the tracking task, and ensure the L 2 gain robustness in the reaching phase. Two illustrative examples are given to show the effectiveness of the proposed robust control scheme. [ABSTRACT FROM AUTHOR]

It is well known by equivalent control theory, that in the sliding mode a low-pass filter, working as an average operator, can capture the desired control fairly well from the switching control signals. However, directly adding the filtered signals in parallel with the switching control does not warrant any improvement in the control system performance. In this work, we make clear the underlying reason why the sliding mode control (SMC) system does not function properly with such a simple closed-loop filtering structure. The correct way of incorporating the closed-loop filtering into SMC requires a second low-pass filter, which works concurrently with the first low pass filter to scale down the gain of the switching control. The SMC system with the new closed-loop filtering is able to realize the acquisition of equivalent control or estimate the disturbance, effectively reduce the switching gain to the minimum level, and as a result to eliminate chattering. Complementary to existing SMC, the proposed control system can easily incorporate feed-forward control into the closed-loop for bounded system perturbations. In addition, the frequency-domain knowledge can be easily used to construct the two filters. [ABSTRACT FROM AUTHOR]

In this paper, via describing function techniques, sliding mode control of DC servo mechanisms is analyzed in the presence of unmodeled dynamics. We first show that, a conventional sliding mode controller with signum function will inevitably generate a limit cycle where a second or higher order unmodeled dynamics exists. A fractional interpolation based smoothing scheme is then proposed to eliminate the limit cycle, and maintain a reasonable tracking precision bound. In particular, a DC servo motor with unmodeled stator and sensor dynamics is taken into consideration. Both theoretical analysis and simulation results verify the effectiveness of the proposed new fractional interpolation control scheme. [Copyright &y& Elsevier]