Inverse cartesian trajectory control and stabilization of a three-axis flexible manipulator

This article treats the question of end point trajectory control of a flexible manipulator based on the nonlinear inversion technique. The manipulator has two rigid links and the third link is elastic. A parameterization of the Cartesian coordinates of a point close to the end effector position is suggested. Using these coordinates as output variables, an inverse feedback control law is derived for tracking reference Cartesian trajectories. The stability of the zero dynamics associated with the end point motion control is examined. It is shown that inverse control of the end point causes divergent oscillatory flexible modes. In addition, for regulating the end point to a fixed position, a linear stabilizer is designed to damp the elastic vibration. Simulation results are presented to show that in the closed-loop system, reference end point trajectories can be accurately followed in spite of the parameter uncertainty in the arm dynamic model. © 1994 John Wiley & Sons, Inc.     

An integrated CAE system for dynamic stress and fatigue life prediction of mechanical systems

This paper presents computer simulation methodology for dynamic stress time history computation to predict the fatigue life of machine components using flexible multi-body dynamics. A hybrid method which employes stress superposition as a function of constraint loads and component accelerations that are predicted by flexible body dynamic simulation is utilized and implemented using established codes. A system integration methodology for dynamic stress computation of mechanical system components is described to provide a usable environment for an engineer. It uses a database management system such as the IAC and the established dynamics and finite element analysis codes.     

Constrained doubly coprime factorization for all stabilizing ℋ∞ controllers

The conventional Youla parameterization (equivalently Q-Parameterization) approach to solve ?_∞ optimal control problems requires solving the well-known matrix dilation optimization as a method for satisfying the ?_∞-norm constraint of the closed-loop transfer matrix. As an alternative, this paper presents a constrained doubly coprime factorization so that the ?_∞-norm constraint of the closed-loop transfer matrix can be satisfied without the need for matrix dilation optimization. For a given ?_∞-norm constraint, a constrained plant is suggested from a state estimator that includes the worst-case disturbance and estimation effects. Then, the constrained doubly coprime factorization is derived from the constrained plant model. All the stabilizing ?_∞ controllers are expressed by using the constrained coprime factors. Finally, an application example is provided to demonstrate the effectiveness of the proposed method.     

Effects of processing variables on melt cleanliness of AZ31B magnesium alloy investigated by quantitative evaluation of Fe and non-metallic inclusions

Impurities such as Fe, Ni and Cu and non-metallic inclusions such as oxides, nitrides, carbides, sulfides and fluorides are harmful to the quality and various properties of magnesium alloy sheets produced by twin-roll casting. In this study, the changes of the content of Fe and non-metallic inclusions in AZ31B magnesium alloys with melt temperature and isothermal holding time were quantitatively evaluated using EPMA and the metallographic method. The Fe content did not increase above the Fe content in the raw material, which implies that the dissolution of Fe from a steel crucible was suppressed effectively. The content of non-metallic inclusions, mainly consisting of oxide, fluoride and Fe-rich intermetallic compounds, did not change remarkably with the melt temperature but it increased with the isothermal holding time due to the continuous oxidation of the magnesium alloy melt on the melt surface.     

Use of Self-assembled Monolayers at Variable Coverage to Control Interface Bonding in a Model Study of Interfacial Fracture: Pure Shear Loading

The relationships between fundamental interfacial interactions, energy dissipation mechanisms, and fracture stress or fracture energy in a glassy thermoset/inorganic solid joint are not well understood. This subject is addressed with a model system involving an epoxy adhesive on a polished silicon wafer containing its native oxide. The proportions of physical and chemical interactions at the interface, and the in-plane distribution, are varied using self-assembling monolayers of octadecyltrichlorosilane (ODTS). The epoxy interacts strongly with the bare silicon oxide surface, but interacts only weakly with the methylated tails of the ODTS monolayer. The fracture stress is examined as a function of ODTS coverage in the napkin-ring (nominally pure shear) loading geometry. The relationship between fracture stress and ODTS coverage is catastrophic, with a large change in fracture stress occurring over a narrow range of ODTS coverage. This transition in fracture stress does not correspond to a wetting transition of the epoxy. Rather, the transition in fracture stress corresponds to the onset of large-scale plastic deformation within the epoxy. We postulate that the transition in fracture stress occurs when the local stress that the interface can support becomes comparable to the yield stress of the epoxy. The fracture results are independent of whether the ODTS deposition occurs by island growth (T _dep = 10°C) or by homogeneous growth (T _dep = 24°C).     

Nanomechanical thermal analysis of the effects of physical aging on glass transitions in PS/PMMA blend and PS-PMMA diblock copolymers

The effects of physical aging on the thermomechanical properties of polymers were investigated using silicon microcantilever deflection measurements. Polystyrene (PS), polymethylmethacrylate (PMMA), a PS/PMMA blend, or PS-PMMA diblock copolymer were applied to one side of a microcantilever, and the temperature-dependent thermal stress in the polymers was measured. A maximum compressive stress peak was observed for the PS- and PMMA-coated cantilevers during heating but not during cooling, which produced hysteresis. Physical aging of the polymers was found to contribute to the development of the hysteresis properties. The two distinct maximum compressive stress peaks in the PS/PMMA blend coincided with the temperatures at which the pure PS and PMMA peaks occurred, indicating that the glass transitions of each polymer were independent. In contrast, the thermal stress profiles of the PS-PMMA copolymer exhibited a single broad peak at a position intermediate between the peak positions of the pure PS and PMMA, indicating that the PS and PMMA polymers interacted during the glass transition.     

Role of coagulation in membrane filtration of wastewater for reuse

This study explains the role of coagulation in membrane filtration of wastewater for reuse. For this purpose, a coagulation-ultrafiltration (UF) membrane system was used to treat secondary effluent from a nearby wastewater treatment plant using a rotating biological contactor. The study proceeded with the hypothesis that coagulation could affect membrane filtration through two phenomena: change in particle characteristics and contaminant loading reduction. If fouling reduction were observed at a low alum dosage, coagulation would affect membrane performance by changing particle characteristics because contaminant reduction could not be possible at low dosage. If fouling reduction were observed only at a high alum dosage, the role of coagulation would be contaminant loading reduction. Results showed that both phenomena were important. Coagulation improved the membrane performance by changing particle characteristics at a low alum dosage. The improvement was achieved through both a change in particle characteristics and contaminant loading reduction at a high alum dosage. Particle size among various characteristics was found the most important for membrane fouling. Coagulation increased particle size, which led to a reduction of fouling. The beneficial effect from coagulation was observed at both fouling steps of pore blocking/adsorption and cake formation. Coagulation pretreatment was also beneficial for the improvement of the permeate quality in terms of organic matter.     

Membrane Profiling by Free Flow Electrophoresis and SWATH-MS to Characterize Subcellular Compartment Proteomes in Mesembryanthemum crystallinum

The study of subcellular membrane structure and function facilitates investigations into how biological processes are divided within the cell. However, work in this area has been hampered by the limited techniques available to fractionate the different membranes. Free Flow Electrophoresis (FFE) allows for the fractionation of membranes based on their different surface charges, a property made up primarily of their varied lipid and protein compositions. In this study, high-resolution plant membrane fractionation by FFE, combined with mass spectrometry-based proteomics, allowed the simultaneous profiling of multiple cellular membranes from the leaf tissue of the plant Mesembryanthemum crystallinum. Comparisons of the fractionated membranes’ protein profile to that of known markers for specific cellular compartments sheds light on the functions of proteins, as well as provides new evidence for multiple subcellular localization of several proteins, including those involved in lipid metabolism.     

Effect of the Ca content on the microstructural evolution of Ca containing AZ31 cast alloys

Microstructural changes with varying amounts of Ca in cast AZ31-xCa (x: 0.7 wt.%, 2.0 wt.%, 5.0 wt.%) alloys were investigated. According to transmission electron microscopy (TEM) analyses, it was experimentally confirmed that the C36-(Mg,Al)₂Ca phase with a di-hexagonal structure formed at interdendritic regions in as-cast AZ31 alloys with no more than 2 wt.% Ca. On the other hand, as the Ca content exceeded 2 wt.%, the lamellar structure consisting of the α-Mg phase and the Mg₂Ca phase with a C14 structure formed at interdendritic regions instead of C36 phase. Plate-like Al₂Ca precipitates with a C15 structure also formed on the basal plane inside the α-Mg grains.     

Electrochemical stability of bis(trifluoromethanesulfonyl)imide-based ionic liquids at elevated temperature as a solvent for a titanium oxide bronze electrode

Four different electrolytes are prepared by dissolving a Li salt in three different room-temperature ionic liquids (RTILs) and also in a conventional organic solvent. The cathodic (electrochemical reduction) stability of these electrolytes is compared at both ambient and elevated temperature by potential cycling on a TiO₂-B electrode. At room temperature, the stability of pyrrolidinium- and piperidinium-based RTILs is comparable with that of the carbonate-based organic solvent, which is in contrast to the severely decomposed imidazolium-based RTIL. At elevated temperature (120 °C), the imidazolium-based RTIL undergoes even more significant cathodic decomposition that results in the deposition of a resistive surface film and leads to eventual cell degradation. By contrast, the cathodic decomposition and concomitant film deposition are not serious with pyrrolidinium- and piperidinium-based RTILs even at this high-temperature, so that the TiO₂-B/Li cell operates with reasonably good cycle performance. The latter two RTILs appear to be promising solvents for lithium-ion batteries that are durable against occasional exposure to high-temperature.