H∞ sliding mode control of discrete switched systems with time-varying delays

The finite-time boundedness issue for a class of discrete switched systems with time-varying delays is investigated via sliding mode control (SMC) approach. By employing the Lyapunov functional and average dwell time method, new sufficient conditions are derived to guarantee the finite-time boundedness of the dynamic system in the novel sliding surface. By solving an optimization problem, the sliding mode controller is synthesized such that the discrete reaching condition is satisfied and the chattering is reduced. A simulation example tests the feasibility of the provided SMC scheme.     

H∞ observer-based event-triggered sliding mode control for a class of discrete-time nonlinear networked systems with quantizations

This paper investigates the problem of H_∞ observer-based event-triggered sliding mode control (SMC) for a class of uncertain discrete-time Lipschitz nonlinear networked systems with quantizations occurring in both input and output channels. The event-triggered strategy is used to save the limited network bandwidth. Then, based on the zero-order-hold (ZOH) measurement, a state observer is designed to reconstruct the system state, which facilitates the design of the discrete-time sliding surface. Considering the effects of quantizations, networked-induced constraints and event-triggered scheme, the nonlinear state error dynamics and sliding mode dynamics are converted into a unified linear parameter varying (LPV) time-delay system with the aid of a reformulated Lipschitz property. By using the Lyapunov-Krasovskii functional and free weighting matrix, a new sufficient condition is derived to guarantee the robust asymptotic stability of the resulting closed-loop system with prescribed H_∞ performance. And then the observer gain, event-triggering parameter and sliding mode parameter are co-designed. Furthermore, a novel SMC law is synthesized to force the trajectories of the observer system onto a pre-specified sliding mode region in a finite time. Finally, a single-link flexible joint robot example is utilized to demonstrate the effectiveness of the proposed method.     

H∞ non-fragile observer-based dynamic event-triggered sliding mode control for nonlinear networked systems with sensor saturation and dead-zone input

This paper considers the problem of robust non-fragile observer-based dynamic event-triggered sliding mode control (SMC) for a class of discrete-time Lipschitz nonlinear networked control systems subject to sensor saturation and dead-zone input nonlinearity. First, an improved dynamic event-triggered scheme (DETS) in consideration of sensor saturation is proposed to reduce the number of data transmission. Next, a non-fragile observer is designed to estimate the system state, which facilitates the construction of the discrete sliding surface. By using a reformulated Lipschitz property, the error dynamics and sliding mode dynamics are modeled as a unified linear parameter varying (LPV) networked system with time-varying delays. Then, based on this model, sufficient conditions are established to guarantee the resulting closed-loop system to be asymptotically stable with a given disturbance attenuation level. Furthermore, an observer-based event-triggered SMC law is designed to drive the trajectories of the observer system onto a region near equilibrium point in a finite time in the presence of dead-zone input nonlinearity. Finally, two practical examples are employed to demonstrate the effectiveness of the proposed method.     

Multivariable robust adaptive sliding mode control of an industrial boiler–turbine in the presence of modeling imprecisions and external disturbances: A comparison with type-I servo controller

To guarantee the safety and efficient performance of the power plant, a robust controller for the boiler–turbine unit is needed. In this paper, a robust adaptive sliding mode controller (RASMC) is proposed to control a nonlinear multi-input multi-output (MIMO) model of industrial boiler–turbine unit, in the presence of unknown bounded uncertainties and external disturbances. To overcome the coupled nonlinearities and investigate the zero dynamics, input–output linearization is performed, and then the new decoupled inputs are derived. To tackle the uncertainties and external disturbances, appropriate adaption laws are introduced. For constructing the RASMC, suitable sliding surface is considered. To guarantee the sliding motion occurrence, appropriate control laws are constructed. Then the robustness and stability of the proposed RASMC is proved via Lyapunov stability theory. To compare the performance of the purposed RASMC with traditional control schemes, a type-I servo controller is designed. To evaluate the performance of the proposed control schemes, simulation studies on nonlinear MIMO dynamic system in the presence of high frequency bounded uncertainties and external disturbances are conducted and compared. Comparison of the results reveals the superiority of proposed RASMC over the traditional control schemes. RAMSC acts efficiently in disturbance rejection and keeping the system behavior in desirable tracking objectives, without the existence of unstable quasi-periodic solutions.     

Robust sliding mode control for uncertain servo system using friction observer and recurrent fuzzy neural networks?

A robust positioning control scheme has been developed using friction parameter observer and recurrent fuzzy neural networks based on the sliding mode control. As a dynamic friction model, the LuGre model is adopted for handling friction compensation because it has been known to capture sufficiently the properties of a nonlinear dynamic friction. A developed friction parameter observer has a simple structure and also well estimates friction parameters of the LuGre friction model. In addition, an approximation method for the system uncertainty is developed using recurrent fuzzy neural networks technology to improve the precision positioning degree. Some simulation and experiment provide the verification on the performance of a proposed robust control scheme.     

Formation-containment control of networked Euler–Lagrange systems: An event-triggered framework

To improve the concurrency of leaders’ formation and followers’ containment, a difficult problem of designing the formation controller and the containment controller simultaneously should be addressed for networked systems. Motivated by this, this paper presents an even-triggered control framework for networked Euler–Lagrange systems to achieve formation-containment control even in the presence of uncertain parameters. An event-triggered formation controller is firstly designed for leaders to achieve the desired configuration. An event-triggered containment control law is then developed to guarantee that all the followers can converge to the convex hull formed by leaders. The key feature of the containment control law is that it does not necessitate any relative velocity information with respect to neighbor followers. Each controller’s gains are adaptively tuned using only local information. The parametric uncertainties are accommodated by using the adaptive updating law. Zeno behaviors of the triggering time sequences are also excluded. As a result, the communication burden of formation-containment system can be reduced. Numerical simulation is finally presented to verify the effectiveness of the proposed event-triggered formation-containment control framework.     

Improving control and estimation for distributed parameter systems utilizing mobile actuator–sensor network

This paper proposes a scheme for non-collocated moving actuating and sensing devices which is unitized for improving performance in distributed parameter systems. By Lyapunov stability theorem, each moving actuator/sensor agent velocity is obtained. To enhance state estimation of a spatially distributes process, two kinds of filters with consensus terms which penalize the disagreement of the estimates are considered. Both filters can result in the well-posedness of the collective dynamics of state errors and can converge to the plant state. Numerical simulations demonstrate that the effectiveness of such a moving actuator–sensor network in enhancing system performance and the consensus filters converge faster to the plant state when consensus terms are included.     

Discrete-time direct adaptive control for robotic systems based on model-free and if–then rules operation

An adaptive controller for a class of nonlinear discrete-time systems is proposed for robotic systems under the assumption that the parameters and structure of system dynamics are all unknown. This controller is designed with the concept of model-free adaptive control requiring only the input–output of the unknown plant. The robotic system has been generalized to be a nonaffine discrete-time system under reasonable assumptions. The adaptive scheme called fuzzy rules emulated network (FREN) is implemented as a direct controller. The IF–THEN rules for FREN have been defined by the knowledge according to the relation between input and output of the robotic system without any compensator for the unknown mathematical model or nonlinearities. The underlying physical specifications of robotic system such as the operating range, maximum joint velocity, and so on have been considered to initialize the membership functions and adjustable parameters of FREN. The adaptation scheme is developed according to convergence analysis established for both adjustable parameters and the tracking error. The performance of the proposed controller is validated by the experimental system with a 7-degrees-of-freedom robotic arm operated in velocity-mode control.     

Micro-to-Nano Indentation and Scratch Hardness in the Ni–Co System: Depth Dependence and Implications for Tribological Behavior

Although size effects in hardness have been extensively reported and analyzed for the static (indentation) case, much less attention has been given to these effects in non-static (scratch) hardness measurements. In the present work, size effects in the indentation and scratch hardness response of the Ni–Co system are evaluated by performing tests at several penetration depths, from the micro to the nanometer range. It is shown that, for all the range of compositions, the hardness response of these materials is strongly affected by the depth of penetration of the indenter: when the depth decreases, both the indentation and scratch hardness increase several times. This result denotes that, when studying the wear behavior of materials, special care must be taken concerning the scale one is dealing with, since the tribo-mechanical response of the material may change significantly from the micrometric to the nanometric contact scale.     

Fatigue properties of the pantograph–insulator system of metro trains: Experiments and the design for improvement

Journal of Mechanical Science and Technology - The power of a metro vehicle is supplied by the pantograph on the vehicle roof. During pantograph lifting, the insulator set of the pantograph is...     

Influence of the Addition of Vanadium Nitride on the Structure and Specifications of a Diamond–(Fe–Cu–Ni–Sn) Composite System

This article discusses the influence of the addition of vanadium nitride on the mechanical and operational properties of diamond composite material based on metallic bond comprised of iron, copper, nickel, and tin obtained by sintering in a mold at 800°C for 1 h with subsequent hot repressing. It has been established that the addition of vanadium nitride in the amount of 2 wt % to diamond–(51Fe–32Cu–9Ni–8Sn) increases the ultimate compressive strength from 846 to 1640 MPa and bending strength from 680 to 1120 MPa, as well as decreases the wear intensity of the composite material from 0.0069 to 0.0033 g/km. The mechanism of improving the tribological properties has been revealed.     

Resilient guaranteed cost control for uncertain T–S fuzzy systems with time-varying delays and Markov jump parameters

This paper aims to investigate the problem of resilient guaranteed cost control for uncertain Takagi–Sugeno fuzzy systems with Markov jump parameters and time-varying delay. A resilient mode-dependent fuzzy controller is designed and a weak sufficient condition is developed to ensure that the resulting closed-loop system is robust almost surely asymptotically stable with guaranteed cost index not exceeding the specified upper bound. Subsequently, the controller gain and upper bound of the guaranteed cost index can be obtained by solving a set of linear matrix inequalities. Finally, numerical and practical examples of the single-link robot arm system are provided to demonstrate the performance of the proposed approach.     

Influence of graphite content on the dry sliding and oil impregnated sliding wear behavior of Al 2024–graphite composites produced by in situ powder metallurgy method

The influence of graphite content on the dry sliding and oil impregnated sliding wear characteristics of sintered aluminum 2024 alloy–graphite (Al/Gr) composite materials has been assessed using a pin-on-disc wear test. The composites with 5–20 wt.% flake graphite particles were processed by in situ powder metallurgy technique. For comparison, compacts of the base alloy were made under the same consolidation processing applied for Al/Gr composites. The hardness of the sintered materials was measured using Brinell hardness tester and their bending strength was measured by three-point bending tests. Scanning electron microscopy (SEM) was used to analyze the debris, wear surfaces and fracture surfaces of samples. It was found that an increase in graphite content reduced the coefficient of friction for both dry and oil impregnated sliding, but this effect was more pronounced in dry sliding. Hardness and fracture toughness of composites decreased with increasing graphite content. In dry sliding, a marked transition from mild to severe wear was identified for the base alloy and composites. The transition load increased with graphite content due to the increased amount of released graphite detected on the wear surfaces. The wear rates for both dry and oil impregnated sliding were dependent upon graphite content in the alloy. In both cases, Al/Gr composites containing 5 wt.% graphite exhibited superior wear properties over the base alloy, whereas at higher graphite addition levels a complete reversal in the wear behavior was observed. The wear rate of the oil impregnated Al/Gr composites containing 10 wt.% or more graphite particles were higher than that of the base alloy. These observations were rationalized in terms of the graphite content in the Al/Gr composites which resulted in the variations of the mechanical properties together with formation and retention of the solid lubricating film on the dry and/or oil impregnated sliding surfaces.     

MAGE Spectrometer for the Investigation of Hadron–Nucleus Interactions and the Identification of Final Nuclear States

A combined spectrometer is composed of a wide-aperture magnetic spectrometer with proportional chambers and a -spectrometer based on a Ge(Li) detector. The respective momentum and the angular resolutions of the magnetic spectrometer are FWHM/p(%) = 0.59p (GeV/c) + 1.1 and 0.5–1 mrad; its average efficiency for 0°–5° angles is 85%. The energy resolution of the -spectrometer is 8 and 16 keV for 0.5- and 2.0-MeV photons, respectively; the average angular acceptance is 1.5 msr.     

Application of Computational Fluid Dynamics and Fluid–Structure Interaction Method to the Lubrication Study of a Rotor–Bearing System

Computational methods were used to analyse the elasto-hydrodynamic lubrication of a complex rotor–bearing system. The methodology employed computational fluid dynamics (CFD), based on the Navier–Stokes equation and a fluid–structure interaction (FSI) technique. A series of models representing the system were built using the CFD–FSI methodology to investigate the interaction between the lubrication of the fluid film, and elastic dynamics of the rotor and journal bearing. All models followed an assumption of isothermal behaviour. The FSI methodology was implemented by setting nodal forces and displacements to equilibrium at the fluid–structure interface, therefore allowing the lubrication of the fluid and the elastic deformation of structures to be solved simultaneously. This is significantly different to the more common techniques—such as the Reynolds equation method—that use an iterative solution to balance the imposed load and the force resulting from the pressure of the fluid film to within a set tolerance. Predictions using the CFD–FSI method were compared with the results of an experimental study and the predictions from an ‘in-house’ lubrication code based on the Reynolds equation. The dynamic response of the system was investigated with both rigid and flexible bodies for a range of different bearing materials and dynamic unbalanced loads. Cavitation within the fluid film was represented in the CFD–FSI method using a simplified phase change boundary condition. This allowed the transition between the liquid and vapour phases to be derived from the lubricant’s properties as a function of pressure. The combination of CFD and FSI was shown to be a useful tool for the investigation of the hydrodynamic and elasto-hydrodynamic lubrications of a rotor–bearing system. The elastic deformation of the bearing and dynamic unbalanced loading of the rotor had significant effects on the position of its locus.     

Quality control of the injection molding process using an EWMA predictor and minimum–variance controller

This study presents an exponentially weighted moving average predictor and minimum–variance controller for the quality control of plastic injection molding processes. This is a slow drifting problem of quality control during plastic injection molding processes. In order to have good product quality for plastic injection molding process, a proposed approach was applied to achieve the desired process control quality during the control process. To simplify the process model and reduce system loads, design of experiments technique was adopted to analyze the important factors that had significant effects on the product quality and their relative correlations. The results of this research showed that the proposed approach was effective for a quality control of plastic injection molding process. This cannot only steadily control the manufacturing process to reduce product loss and maintenance time due to unforeseen malfunctions, but they can also increase the efficiency of the equipment and the process.