Modeling and control of micropositioning systems using Stewart platforms

The modeling and control of a 6‐DOF Stewart micropositioning system with each leg actuated by a respective piezoelectric actuator are considered in this paper. The 12 multi‐DOF passive joints are assumed to be well designed and fabricated so that guaranteed guiding precision and lack of backlash can be obtained. The dynamics model of the micropositioning system is derived first, and then a composite control strategy consisting of moving platform model‐based feedback linearization and two sets of simple SISO fuzzy systems is proposed. By considering the internal axial forces of the six legs on the six spherical joints at the moving end as the virtual control inputs of the moving platform, feedback linearization can be easily used to derive the desired control forces for the moving platform. The corresponding desired linear displacement of each piezoelectric actuator can then be computed based on the derived leg model, and each piezoelectric actuator's control voltage can be generated by the first set of independent leg fuzzy controls. The second set of fuzzy controls is suggested for the further enhancement of robustness with respect to uncertainty. Computer simulations are presented to illustrate the effectiveness of the suggested micropositioning control strategy. ©2000 John Wiley & Sons, Inc.     

Note on the multiple scattering in an IEM model

The authors derive the multiple scattering expression within the framework of an IEM model for rough surface scattering. The complementary field coefficients are rederived based on a new surface slope expressions which are dependent on spatial variables. This leads to a more complete expression of the multiple scattering terms, thus allowing the authors to account for multiple effects more accurately. Numerical calculations and comparisons with numerical simulation are provided to demonstrate the results     

Comments on `Discrete optimal control with eigenvalue assignedinside a circular region'

The commenters claim that the perturbation bound for the stability of a linear optimal system derived in the paper by T.T. Lee et al. (see ibid., vol.AC-31, p.958-62 (1986)) is incorrect. The source of the error is identified and a corrected result is given. Furthermore, it is pointed out that an even more fundamental problem exists before the derivation process is started. A remedy is suggested     

Radiative transfer simulation of dust-like aerosols: Uncertainties from particle shape and refractive index

The composition, particle shape, number concentration, size distribution, and spatial and temporal distributions of dust aerosols cause significant uncertainties in relevant radiative transfer simulations. The spherical particle approximation has been generally recognized to introduce errors in radiative transfer calculations involving dust aerosols. Although previous studies have attempted to quantify the effect of non-spherical particles, no consensus has been reached as to the significance of the dust aerosols non-spherical effect on flux calculations. For this study, we utilize a newly developed ultra-violet-to-far-infrared spectral database of the single-scattering properties of tri-axial ellipsoidal, mineral dust-like aerosols to study the non-spherical effect on radiative forcing. The radiance and flux differences between the spherical and ellipsoidal models are obtained for various refractive indices and particle size distributions. The errors originating from using the spherical model and the uncertainties in the refractive indices are quantified at both the top and bottom of the atmosphere. The dust non-spherical effect on the net flux and heating rate profile is obtained over the entire range of the solar spectrum. The particle shape effect is found to be related to the dust optical depth and the surface albedo and can be an important uncertainty source in radiative transfer simulation. The particle shape effect is largest over water surfaces and can cause up to a 30% difference in dust forcing at the top of the atmosphere.     

Properties of polyurethane oligomeric blends versus high molecular weight block copolymers

Segmental compatibility has been investigated in both oligomeric polyurethane blends and polyurethane block copolymers. The block copolymers are formed by linking a hard segment, composed of three MDI and two butane diol units on average with various macroglycols. The monodisperse oligomeric hard segment, H₃, with its chain ends reacted with ethanol is used as the urethane component in blends with macroglycols. The macroglycols used in both the blend and block copolymer systems include polyethylene oxide (PEO), polypropylene oxide (PPO), polytetramethylene oxide (PTMO), and polybutadiene (PBD). Blends of H₃ and PEO form a eutectic at a weight ratio of $\text{≈20}\text{80}\text{(}\text{H}{}_3\text{/}\text{PEO}\text{)}$ with a T_m,e = 34°C. H₃ and PTMO blends also give rise to a eutectic composition at $\text{≈20}\text{80}\text{(}\text{H}{}_3\text{/}\text{PTMO}\text{)}$ but with a T_m,e = 10°C. Both PPO and PBD mix with H₃ to form a crystalline—amorphous blend. The miscibility of H₃ and the soft segments at the melting point of H₃ is in the order of PEO > PTMO > PPO > PBD. In the block copolymer systems, stress—strain and dynamic mechanical testing indicate that the block copolymerization of a hard segment with each soft segment results in a microphase separated elastomer as expected. The extent of phase separation increases in the order of PBD > PTMO > PPO > PEO which is coincident with the trend predicated by the application of Hilderbrand's solubility parameter concept. All the soft segments used occur in an amorphous phase in the block copolymers while PEO and PTMO crystallize in a blend with H₃. The differences between the properties of the blends and block copolymers suggest that the phase separation, segment crystallization and domain coalescence are substantially restricted by the urethane—polyol junction points.     

Effect of iron particle addition on the pseudocapacitive performance of sol–gel derived manganese oxides film

Manganese oxide electrodes with promising behavior were prepared successfully by sol–gel process. Manganese oxide films were also modified with the addition of submicron-crystalline iron powders. Effects of post heat treatment and iron submicron-powder addition on the material characteristics and electrochemical capacitance of the manganese oxide electrodes were investigated. The experimental results showed that manganese oxide films composed from metal-organic precursors at 250 °C heat treatment, while formation of MnO₂, Mn₂O₃, Mn₃O₄, Fe₂O₃, and Fe₃O₄ phases were observed after heat treatment at a temperature higher than 300 °C. The specific capacitances were 48.9, 140.1, 212.7, and 81.1 F g⁻¹ for manganese oxide films heat treated at 250, 300, 350, and 400 °C, respectively. The specific capacitances were 75.7, 227.3, 247.9, and 152.9 F g⁻¹ for manganese/iron oxide films (Mn:Fe = 100:1) heat treated at 250, 300, 350, and 400 °C, respectively. The manganese/iron oxide films (Mn:Fe = 100:1) treated at 350 °C exhibited the highest specific capacitance 247.9 F g⁻¹ of the electrodes investigated in the present study. After 1000 cyclic voltammetry tests, the specific capacitance decreased by only 10 percent. The surface morphology of this film exhibited powders with linked nano-sized particles. The number of special particles reached a maximum after heat treatment at 350 °C. The experimental results showed that post heat treatment and iron submicron-particle addition may change the surface morphology and structure, increase the specific capacitance, and improve the electrochemical performances of the manganese oxide electrodes.     

Nonconvex economic dispatch by integrated artificial intelligence

This paper presents a new algorithm by integrating evolutionary programming (EP), tabu search (TS) and quadratic programming (QP) methods to solve the nonconvex economic dispatch problem (NED). A hybrid EP and TS were used for quality control, and Fletcher's quadratic programming technique for solving. EP and TS determines the segment of a cost curve used, which is piecewise quadratic natured. Operation constraints are modeled as linear equality or inequality equations, resulting in a typical QP problem. Fletcher's QP was chosen to enhance the performance. The fitness function is constructed from priorities without penalty terms. Numerical results show that the proposed method is more effective than other previously developed evolutionary computation algorithms     

Effect of preheating process on crystallization and optical properties of sol-gel derived ZnO semiconductor thin films

Highly transparent ZnO semiconductor thin films were deposited onto alkali-free glass substrates by a sol-gel spin coating process. This research investigated the effects of different preheating rates (4 or 10°C/min) on the various surface morphologies, crystallization characteristics, and optical properties of these thin films. The ZnO sol was synthesized by dissolving the zinc acetate dihydrate in isopropanol (IPA), and then adding monoethanolamine (MEA). These as-coated films were preheated at 300°C for 10 min and annealed in an air ambiance at 500°C for 1 h. Experimental results revealed that the as-prepared films had a hexagonal wurtzite structure, and that the heating rates of the preheating process obviously affected the surface morphologies, crystallization qualities, and transparency levels of the thin films. A ZnO thin film preheated at 10°C/min exhibited preferential orientation along the (002) plane, a flat surface, and also achieved a high transmittance value, 92.5%, for light with a wavelength of 550 nm.     

Load–frequency control of interconnected power system with governor backlash nonlinearities

In this paper, the stability-equation method is applied to the analysis and design of an interconnected power system with governor backlash nonlinearities. The considered system is a nonlinear multivariable feedback control system. The governor nonlinearities tend to produce a sustaining oscillation in area frequency and tie-line power transient responses. Most conventional linear design techniques are usually unable to find the sustaining oscillation in design phase and need simulation verifications to check the validations after designs. However, the proposed method can consider effects of nonlinearities in the design phase. Some nonlinear design techniques need parameters optimization method by Lyapunov theorem or Integral of Square Errors (ISE) criteria. They are effective. However, they need large computation efforts. The proposed method can choice frequency bias parameters and integrator gains of supplementary controllers for avoiding the oscillation or reducing the amplitude of the oscillation to be acceptable. Simulation verifications show that the proposed method can provide a simple and effective way for the considered system.     

Second-Order Radiation Boundary Condition for Water Wave Simulation with Large Angle Incidence

A finite-element method (FEM) is used to simulate water wave propagation with large angle incidence at exterior boundaries. In this paper, the radiation boundary condition is expanded to a second-order approximation and a quadratic shape function is used in the FEM wave model. Cases used for verifications include wave scattering around a vertical cylinder and wave propagation over a submerged circular shoal with concentric contours. Numerical calculations based on this second-order radiation boundary condition are found to be in good agreement with theoretical and experimental results available. The numerical predictions show that this model has made a very good improvement over the first-order radiation boundary conditions for oblique wave incidence in coastal engineering.