Comparison of linear control algorithms for a class of nonlinear mechanical actuators

This paper presents a comparison between various control strategies for a class of mechanical actuators common in heavy-duty industry. Typical actuator components are hydraulic or pneumatic elements with static nonlinearities, which are commonly referred to as Hammerstein systems. Such static nonlinearities may vary in time as a function of the load and hence classical inverse-model based control strategies may deliver sub-optimal performance. This paper investigates the ability of classical linear control strategies as lead, P, PI and PID control to satisfy tolerance interval for position error values, overshoot and settling time specifications. Due to the presence of static nonlinearity, control effort is also evaluated in terms of zero crossing frequency (up-down or left-right movement). Simulation and experimental data from a lab setup suggest that advanced control strategies may be needed to improve global performance parameters

Finite-time extended state observer and fractional-order sliding mode controller for impulsive hybrid port-Hamiltonian systems with input delay and actuators saturation: Application to ball-juggler robots

This paper addresses the robust control problem of mechanical systems with hybrid dynamics in port-Hamiltonian form. It is assumed that only the position states are measurable, and time-delay and saturation constraint affect the control signal. An extended state observer is designed after a coordinate transformation. The effect of the time delay in the control signal is neutralized by applying Pade ́ approximant and augmenting the system states. An assistant system with faster convergence is developed to handle actuators saturation. Fractional-order sliding mode controller acts as a centralized controller and compensates for the undesired effects of unknown external disturbance and parameter uncertainties using the observer estimation results. Stability analysis shows that the closed-loop system states, such as the observer tracking error, and the position/velocity tracking errors, are finite-time stable. Simulation studies on a two ball-playing juggler robot with three degrees of freedom validate the theoretical results’ effectiveness

A Fuzzy Logic-based Cascade Control without Actuator Saturation for the Unmanned Underwater Vehicle Trajectory Tracking

An intelligent control strategy is proposed to eliminate the actuator saturation problem that exists in the trajectory tracking process of unmanned underwater vehicles (UUV). The control strategy consists of two parts: for the kinematic modeling part, a fuzzy logic-refined backstepping control is developed to achieve control velocities within acceptable ranges and errors of small fluctuations; on the basis of the velocities deducted by the improved kinematic control, the sliding mode control (SMC) is introduced in the dynamic modeling to obtain corresponding torques and forces that should be applied to the vehicle body. With the control velocities computed by the kinematic model and applied forces derived by the dynamic model, the robustness and accuracy of the UUV trajectory without actuator saturation can be achieved

Fractional Order Fault Tolerant Control - A Survey

In this paper, a comprehensive review of recent advances and trends regarding Fractional Order Fault Tolerant Control (FOFTC) design is presented. This novel robust control approach has been emerging in the last decade and is still gathering great research efforts mainly because of its promising results and outcomes. The purpose of this study is to provide a useful overview for researchers interested in developing this interesting solution for plants that are subject to faults and disturbances with an obligation for a maintained performance level. Throughout the paper, the various works related to FOFTC in literature are categorized first by considering their research objective between fault detection with diagnosis and fault tolerance with accommodation, and second by considering the nature of the studied plants depending on whether they are modelized by integer order or fractional order models. One of the main drawbacks of these approaches lies in the increase in complexity associated with introducing the fractional operators, their approximation and especially during the stability analysis. A discussion on the main disadvantages and challenges that face this novel fractional order robust control research field is given in conjunction with motivations for its future development. This study provides a simulation example for the application of a FOFTC against actuator faults in a Boeing 747 civil transport aircraft is provided to illustrate the efficiency of such robust control strategies

Fault accommodation controller under Markovian jump linear systems with asynchronous modes

We tackle the fault accommodation control (FAC) in the Markovian jump linear system (MJLS) framework for the discrete-time domain, under the assumption that it is not possible to access the Markov chain mode. This premise brings some challenges since the controllers are no longer allowed to depend on the Markov chain, meaning that there is an asynchronism between the system and the controller modes. To tackle this issue, a hidden Markov chain ((Formula presented.), (Formula presented.)) is used where θ(k) denotes the Markov chain mode, and (Formula presented.) denotes the estimated mode. The main novelty of this work is the design of H∞ and H2 FAC under the MJLS framework considering partial observation of the Markov chain. Both designs are obtained via bilinear matrix inequalities optimization problems, which are solved using coordinate descent algorithm. As secondary results, we present simulations using a two-degree of freedom serial flexible joint robot to illustrate the viability of the proposed approach

Pitch angle control with fault diagnosis and tolerance for wind turbine generation systems

To enhance the reliability of wind turbine generation systems that are generally located in the remote area and subjected to harsh environment, we design the pitch angle control for variable speed wind turbines with the function of fault diagnosis and fault tolerance. The main fault targeted in this research is the mechanical wear and possible break of the blade, pitch gear set or shaft, which cause shaft rotary friction change. The proposed method uses a disturbance observer to diagnose the fault. The estimated fault is used for component assessment and later maintenance. The fault-tolerant control is achieved using a full-order terminal sliding mode control combined with an adaptive neural network estimator. With the compensation of the adaptive estimator, the post-fault states can be driven onto the sliding surface and converge to a small area around the origin. The full-order terminal sliding mode control ensures the state convergence in finite time. The Lyapunov method is used to derive the control law, so that the closed-loop post-fault stability and the convergence of the adaptive estimator adaptation are both guaranteed. The computer simulations of the pitch angle control based on a 5-MW variable-speed variable-pitch angle wind turbine model are conducted with different types of fault simulated. A third-order nonlinear state space model with fault term is derived, and real physical parameters are applied in the simulations. The simulation results demonstrate the feasibility and effectiveness of the proposed scheme and the potential of real-world applications. © IMechE 2021

Bilateral control: a sliding mode control approach

Bilateral control is bi-directional control of force-position between two systems connected by a communication link. It is typically used for teleoperation with forcefeedback, such that the master system is handled by an operator. Motions of the operator are fed forward to the slave system, generally remote to the operator and forces encountered are fed back to the master system, enabling a telepresence of the operator in the remote environment. The necessity of bilateral control lies in its applicability to the tasks that cannot be handled by autonomous manipulators and/or reached by human beings. Main issues of consideration for bilateral control, namely transparency, scaling and time delay, are addressed and two discrete-time sliding-mode approaches are presented as solutions to highly transparent bilateral controllers that support scaling. First approach has a force-hybrid architecture, where the cascaded sliding mode hybrid force/position controller on the slave side reacts to the external forces directly. Therefore, it provides a protection (reflex) mechanism on the slave side to large external forces, that the operator cannot respond in time due to the time delay. Second approach has a decentralized nature. Virtual systems are devised by a linear transformation from the plant space to the task space and sliding mode control has been applied to those virtual systems, hence sides of bilateral control are interchangable. The decentralized structure of the controller makes it possible to generalize the problem to a coordination and/or cooperation of more than two plants. High precision has been achieved on experiments for both approaches designed and discussed in detail

Sliding mode control with system constraints for aircraft engines

This paper proposes a constraint-tolerant design with sliding mode strategy to improve the stability of aircraft engine control. To handle the difficulties associated with the high-frequency switching laws, merely attenuating the chattering is far from satisfactory. System constraints on input, output, and input rate should be addressed in the design process. For a sort of uncertain nonlinear systems subjected to the constraints, sliding mode regulators are designed using Lyapunov analysis. A turbofan engine is adopted for simulation, which shows that the methodology developed in this paper can handle the speed tracking and limit protection problem in a stable fashion, despite the negative influence posed by the system constraints