Monitored robust force control of a milling process

With global aging people and patients with lower-limb dysfunction growing, motion control of the omnidirectional lower-limb rehabilitation robot during centre-of-gravity shift is becoming more and more important. This paper proposes a robust trajectory tracking control strategy for omnidirectional lower-limb rehabilitation robot during centre-of-gravity shift. The main contents of this paper consist of three parts: 1) The kinematic and dynamic model that considered centre-of-gravity shift are presented firstly. 2) A robust control strategy with H ∞ tracking performance is developed and used to achieve the desired trajectories. 3) Simulation tests are performed and demonstrate the feasibility and efficacy of the proposed approach.

In this paper, robust adaptive control strategies are designed for Underwater Remotely Operated Vehicles (ROVs) with velocity constraints. First, robust control strategies are investigated for under-water ROVs, and then adaptive robust control strategies are further developed with online parameter estimation. To prevent the velocity constraint violation, the Barrier Lyapunov Function (BLF) is employed in Lyapunov synthesis. By ensuring the boundedness of the BLF, we also guarantee that the velocity constraints are not transgressed. The stability analysis of the closed-loop system is provided and all closed-loop signals are ensured to be bounded. Simulation results for 5 degree-of-freedom (DOF) underwater ROV demonstrate the effectiveness of the proposed approach.

The objective is to control a web transport system with winder and unwinder for elastic material. A physical modeling of this plant is made based on the general laws of physics. For this type of control problem, it is extremely important to prevent the occurrence of web break or fold by decoupling the web tension and the web velocity. Due to the wide-range variation of the radius and inertia of the rollers the system dynamics change considerably during the winding/unwinding process. Different strategies for web tension control and linear transport velocity control are presented. First, an H/sub /spl infin// robust control strategy which reduces the coupling between tension and velocity, is compared to the decentralized control strategy with proportional integral derivative (PID) controllers commonly used in the industry. Second, an H/sub /spl infin// robust control strategy with varying gains is shown to render the control more robust to the radius variations. Then, a linear parameter varying (LPV) control strategy with smooth scheduling of controllers is synthesized for different operating points and compared to the previous methods. Finally, this LPV control and the H/sub /spl infin// robust control strategy with varying gains are combined to give the best results on an experimental setup, for the rejection of the disturbances introduced by velocity variations and for the robustness to radius and inertia changes.

Connected and Autonomous Vehicles (CAVs) in a platoon can exchange real-time information using Vehicle-to-Vehicle (V2V) communication technology to enhance platoon control performance. However, the V2V communication technology also provides opportunities for cyber-attacks, where falsified information can be injected into vehicle controllers to disrupt the platoon operation and even induce vehicle collisions. To address this problem, this study proposes a robust platoon control strategy for CAVs to mitigate the impacts of the falsified information to maneuver the CAV platoon to achieve consensus safely. The proposed control strategy consists of three components: (i) a robust control law, which consistently negates the disturbance induced by falsified information; (ii) a state observer which estimates the vehicle states and disturbance induced by falsified information and inputs the estimated results into the robust control law to compute a synthesized control decision; and (iii) a control decision regulator which applies a Control Barrier Function-based Quadratic Programming (CBF-QP) to regulate the control decision computed by the robust control law to avoid actuator saturation issue and ensure safe spacing for each vehicle in the platoon. Numerical experiments demonstrate that the proposed control strategy can effectively drive the CAV platoon to the desired consensus safely and efficiently under the impacts of falsified information injection.

Application of μ theory in compliant force control system is studied. Compliant force control strategy is developed based on the inner loop position control of 6-DOF parallel robot in order to simulate pushing and pulling procedure of forcible alignment of space docking. The cascade structure of "out-force-loop containing inner-position-loop" is depicted, and the method is set forth using classical control strategy to realize compliant force control. Considering uncertainties such as parameter perturbations, model perturbations and external disturbances, etc, robust force controller is designed using μ synthesis theory. It is listed in detail that the selection method of weighting functions in robust compliant force control loop and the designing procedure of robust force controller. Robust stability and robust performance are compared between robust force controller and classical force controllers by μ analysis. Experiment of robust force controller and classical force controllers is presented. The results indicate that the designed robust force controller is of efficiency and superiority.

A stroke is a common disease that can easily lead to lower limb motor dysfunction in the elderly. Stroke survivors can effectively train muscle strength through leg flexion and extension training. However, available lower limb rehabilitation robots ignore the knee soft tissue protection of the elderly in training. This paper proposes a human–robot cooperative lower limb active strength training based on a robust admittance control strategy. The stiffness change law of the admittance model is designed based on the biomechanics of knee joints, and it can guide the user to make force correctly and reduce the stress on the joint soft tissue. The controller will adjust the model stiffness in real-time according to the knee joint angle and then indirectly control the exertion force of users. This control strategy not only can avoid excessive compressive force on the joint soft tissue but also can enhance the stimulation of quadriceps femoris muscles. Moreover, a dual input robust control is proposed to improve the tracking performance under the disturbance caused by model uncertainty, interaction force and external noise. Experiments about the controller performance and the training feasibility were conducted with eight stroke survivors. Results show that the designed controller can effectively influence the interaction force; it can reduce the possibility of joint soft tissue injury. The robot also has a good tracking performance under disturbances. This control strategy also can enhance the stimulation of quadriceps femoris muscles, which is proved by measuring the muscle electrical signal and interaction force. Human–robot cooperative strength training is a feasible method for training lower limb muscles with the knee soft tissue protection mechanism.

In this paper, an integrated tube robust iterative learning model predictive control (Tube‐RILMPC) strategy based on the dynamic partial least squares (DyPLS) identified algorithm is proposed. The problems of large amount of online data calculation and input and output variable dimensions disaster in the original variable space are solved. This integrated Tube‐RILMPC strategy enhances the tracking performance and robustness of two‐dimensional (2D) control system. The output trajectories of system are located in the tube the nominal trajectory, which reduces the modelling error caused by the uncertain model. Based on the worst‐case performance index of ellipsoidal uncertainty and polytopic uncertainty, a robust iterative learning control (ILC) strategy is designed. Finally, the superiority of the proposed control algorithm is verified by comparative simulation.

The purpose of this chapter is to redesign the standard adaptive control schemes by using hybrid structure composed by Model Reference Adaptive Control (MRAC) or Adaptive Pole Placement Control (APPC) strategies, associated to Variable Structure (VS) schemes for achieving non-standard robust adaptive control strategies. The both control strategies is now on named VS-MRAC and VS-APPC. We start with the theoretical base of standard control strategies APPC and MRAC, discussing their structures, as how their parameters are identified by adaptive observers and their robustness properties for guaranteeing their stability. After that, we introduce the sliding mode control (variable structure) in each control scheme for simplifying their design procedure. These design procedure are based on stability analysis of each hybrid robust control scheme. With the definition of both hybrid control strategies, it is analyzed their behavior when controlling system plants with unmodeled disturbances and parameter variation. It is established how the adaptive laws compensates these unmodeled dynamics. Furthermore, by using simple systems examples it is realized a comparison study between the hybrid structures VS-APPC and VSMRAC and the standard schemes APPC and MRAC. As the hybrid structures use switching laws due to the sliding mode scheme, the effect of chattering is analyzed on the implementation and consequently effects on the digital control hardware where sampling times are limiting factor. For reducing these drawbacks it is also discussed possibilities which kind of modifications can employ. Finally, some practical considerations are discussed on an implementation on motor drive systems.

Application of mu theory in the electrohydraulic load simulator is studied. Robust control strategy of the electrohydraulic load simulator is put forward. The electrohydraulic load simulator is a complicated mechanical-electronic-hydraulic compound system, moreover it is a strong coupling and time-varying controlled object. Synthetically considering uncertainties such as parameter perturbations, model perturbations and external disturbances etc., robust force controller of the electrohydraulic load simulator is designed using mu synthesis theory. Robust stability and robust performance are analyzed by mu values of the system in which robust force controller is used. Moreover, experiment results of systems using robust force controller and classical force controllers are shown. The results indicate that the designed robust force controller is efficiency and superiority

Robust control for a networked direct-drive linear motion control system: Design and experiments

Robust control of a HESG for a wind energy application

Exact linearization is a traditional method for nonlinear system in the nonlinear system theory, the basic idea of which is to linearize the whole or parts of a nonlinear system using nonlinear coordinate transformation and nonlinear state feedback method. The input-output relationship of the nonlinear system can be represented by a linearized model which can be built using linear system design method. In order to enhance the robustness of an established system which has been linearized via feedback method, the robust control strategy should be adopted. As a result, the control law is composed of feedback linearization control and robust control. Sliding mode variable structure control is a robust control method which is proposed in this paper as a robust control strategy for the exact linearization system.

This paper presents a new robust adaptive current control strategy for induction motor drive systems. This control scheme is based on an adaptive pole placement control strategy (APPC) integrated to a sliding mode control scheme (SMC). The proposed APPC employs the internal model principle for achieving a zero steady state tracking error of machine stator currents. Moreover, this current controller can be implemented on the stator reference frame transformations. With this control scheme, fast transient response and robustness to parametric uncertainties and unmodeled disturbances are obtained. These disturbance can be owing to saturation, temperature changes or loading conditions. Simulation and experimental results are presented for showing the effectiveness of the proposed close-loop current control strategy.

This thesis develops a robust output-tracking control strategy for autonomous rover systems with redundant control directions. Taking advantage of their redundancy, an optimal distribution of control actions is proposed to enhance the dynamic traction of such systems. In the first phase, a robust optimal output-tracking control strategy for underactuated mechanical systems subject to mixed holonomic and nonholonomic constraints is presented. I perform a comprehensive control analysis of this large class of nonlinear systems in terms of local reachability, input-output linearizability, and local observability. Based on the input-output linearization of the holonomically restricted nominal system, I develop a sliding mode control strategy that is robust against projected effects of uncertainties and disturbances on the system's output. Asymptotic stability of the output towards a bounded desired trajectory is proved using Lyapunov's direct method while the system's internal stability (in the sense of boundedness) is investigated based on the notion of tracking-error zero dynamics. Time-dependent bounded matched uncertainties in the inertia parameters and disturbance forces arising in the unrestricted system are considered in this study. I propose an optimal sliding manifold according to the finite-horizon linear-quadratic regulator design problem with split boundary value condition.

In the distributed power generation system (DPGS), there may be a large range perturbation values of equivalent grid impedance at the point of common coupling (PCC). Perturbation of the impedance will cause resonant frequency variation of the Inductance Capacitance Inductance (LCL) filter on a large scale, affecting the quality of the grid current of the grid-connected inverter (GCI) and even causing resonance. To deal with this problem, a novel H∞ robust control strategy based on mixed-sensitivity optimization is proposed in this paper. Its generalized controlled object is augmented by properly selecting weighting functions in order to consider both tracking performance around power frequency and the stability margin in a high frequency of the GCI. For convenient implementation, the H∞ robust controller is simplified by model reduction from the seventh order to the third order. By comparison with a traditional control strategy with a quasi-proportional resonance controller, the proposed H∞ robust control strategy avoids crossing 180 degrees at the resonant frequency point in the phase frequency characteristic of current loop, and moves the phase frequency characteristic left. It guarantees a sufficient margin of stability throughout the designed range of grid impedance perturbation values and avoids the difficulty of parameter setting. Finally, the experimental results support the theoretical analyses and demonstrate the feasibility of the proposed strategy.