Observers for stabilization of systems with matched uncertainty

In this article, we study the design of observer-based robust linear feedback controllers. The uncertainty, which can enterA, and either theB orC matrices, is assumed to satisfy certain matching conditions. Lyapunov techniques are used to establish sufficient conditions for stability, given an uncertainty bound. In particular, sufficient conditions are obtained that, if met, result in stabilizing controllers regardless of the size of the uncertainty entering the system matrix, as long as the standard constraints on the uncertainty entering the input or output matrices are met. As with the case of more general forms of uncertainty, the resulting observers often have high gains. To study performance, the problem of disturbance rejection is considered. Sufficient conditions are presented for obtaining control laws that stabilize the closed loop system, regardless of the size of the uncertainty entering the system matrix, while simultaneously guaranteeing arbitrarily small infinity norm for the transfer function from the plant disturbances to the outputs.     

Effect of solution chemistry and operating conditions on the nanofiltration of acid dyes by a nanocomposite membrane

A composite nanofiltration membrane was developed by a poly(acrylic acid) in situ ultraviolet (UV) graft polymerization process using an ultrafiltration polysulfone membrane as a porous support, by a phase inversion method. SEM images showed that the PSf membranes had numerous finger-like pores. Atomic force microscopy (AFM) showed that the roughness of the surface was reduced by an increase in UV irradiation times. The rejections of sodium chloride and sodium sulfate were moderate and declined with the increase of concentration. We observed that by increasing UV irradiation time and nanofiltration pressure applied, retention of dyes was enhanced and in the most irradiated membrane (M-4 membrane) at 4 bars, color removal with a high rejection of about 99.80% was achieved. It was found that the separation efficiency of dyes in the mixture of salt and dyes decreased with the salt concentration due to a decrease in the Donnan effect. It was also found that by varying the pH, the membrane surface and the dyes' charges are changed, which meant that the membrane surface and dyes had different interactions at various pHs.     

Neural network-based asymptotic tracking control of unknown nonlinear systems with continuous control command

ABSTRACT

This paper proposes a robust tracking controller for a class of nonlinear second-order systems with time-varying uncertainties. The controller is mainly based on the robust integral of the sign of the error (RISE) control approach to achieve an asymptotic stability result with a continuous control command in the presence of additive uncertainties. An adaptive feedforward neural network control term is blended with a new RISE controller to improve the system's transient performance. The proposed RISE controller is a modified version of the existing saturated RISE controller such that only sign of the derivative of the output is needed. The stability of the closed-loop system is well studied, where a local asymptotic stability is proven. The controller performance is validated through simulations on a two-degree-of-freedom lower limb robotic exoskeleton.     

Bounded‐Input Control of the Quadrotor Unmanned Aerial Vehicle: A Vision‐Based Approach

In this paper, a bounded‐input controller is designed for the quadrotor vertical take‐off and landing unmanned aerial vehicle (UAV). Visual information is used to localize the aircraft with respect to its environment and an image‐based visual servo scheme is developed to navigate the motion of it. The visual features are selected from perspective image moments and projected on a rotated image plane, which simplifies the controller design. The flow of the features is used as the linear velocity information, and the controller assumes angular velocity and attitude information available for feedback. To design the controller, the dynamics of the quadrotor are decoupled into two parts: translational dynamics and rotational dynamics. First visual data are used to design a bounded‐input controller for the translational dynamics, and then a saturated controller is designed for the rotational dynamics. The boundedness of the controller increases the chance of keeping the visual features in the field of view of the camera. Furthermore, the controllers also cope with the unknown depth of the image, and the external disturbances. The complete stability analysis of the overall system is presented to show that all states are bounded and the error signals converge to zero asymptotically. Simulation examples are provided in both nominal and perturbed conditions which show the effectiveness of the proposed theoretical results.     

Experimental and numerical results of dynamics behavior of a nonlinear piezoelectric beam

This article presents a numerical formulation and experimental implementation for the dynamics behavior verification of the nonlinear piezoelectric beam through harmonic excitation. The nonlinear piezoelectric beam dynamic analysis program is developed with MATLAB software. To verify the nonlinear piezoelectric beam dynamic analysis results, the experimental results are used for the vibration analysis of a piezoelectric beam to the harmonic excitation of the base of the beam. Then, the piezoelectric effect on the output voltage, velocity, acceleration values, and the time response are obtained. Afterwards, the effects of the excitation velocity and the position of concentrated mass on the output voltage are verified.     

Using scales in the multiobjective approach

Scales are used to reduce the conservatism encountered in most multiobjective approaches to control design. The most general case (i.e., matrix scales) results in a nonconvex problem, though the use of scalar scales leads to convex searches in the analysis and state feedback problems. Output feedback synthesis and other extensions are discussed. Numerical examples are provided to show the effectiveness of the suggested approach. The article considers, in particular, H^∞ control     

Vibration Suppression with Resettable Device

Novel low-power or semiactive devices are developed for vibration suppression applications. By manipulating the structural stiffness, the resisting forces generated by the devices are quite large and independent of velocity. Experimental results are presented to demonstrate the feasibility of the devices and to justify the main assumptions used. The critical design issue of device placement is addressed analytically and verified. While much of the development here applies to the case of variable stiffness devices, we focus on resettable devices in which the device behaves like a linear spring. However, at appropriate times, the effective unstretched length of the device is changed—or reset—to extract energy from the vibrating structure.     

Oxovanadium(IV) salicylidene Schiff base complex anchored on mesoporous silica MCM-41 as hybrid materials: a robust catalyst for the oxidation of sulfides

Oxovanadium(IV) Schiff base complex have been anchored onto the surface of purely siliceous MCM-41 and tested for its activity as catalyst for the oxidation of sulfides. This catalyst could alter this oxidation reaction extremity, exhibiting excellent yields with 100 % selectivity. The intercalation of the complex inside the silica matrix was supported by various characterization techniques like X-ray diffraction, differential thermogravimetric (TG-DTA), BET measurements, UV–Vis diffuse reflectance spectroscopy and Fourier transform infrared spectroscopy (FT-IR). The stability of the catalyst during the course of the reaction was confirmed from its post catalytic FT-IR and XRD analysis. The catalyst could be reused five times without notable loss of its catalytic activity and efficiency which indicates that the metal-Schiff base moiety is intact and the coordination environments are not altered during the reaction.     

A Numerical Study of Suspension Injection in Plasma-Spraying Process

Suspension feedstock in plasma spraying opened a new chapter in coating process with enhanced characteristics. The suspension carrying sub-micron up to few micron-sized particles is radially injected into an atmospheric plasma plume. Understanding the trajectory, velocity, and temperature of these small particles upon impacting on the substrate is a key factor to produce repeatable and controllable coatings. A three dimensional two-way coupled Eulerian-Lagrangian scheme is utilized to simulate the flow field of the plasma plume as well as the interactions between the evaporative suspension droplets with the gas phase. To model the breakup of droplets, Kelvin-Helmholtz Rayleigh-Taylor breakup model is used. After the breakup and evaporation of suspension is complete, the solid suspended particles are tracked through the domain to determine the characteristics of the coating particles. The numerical results are validated against experiments using high-speed imaging.