A microprocessor‐based electrohydraulic servo system

Abstract

A microprocessor‐based electrohydraulic servo system has been constructed and tested. It is implemented with an 8‐bit single‐chip microcomputer to control a hydraulic motor. The control algorithm is based on variable structure control principles. The experimental results show that the system is under good control and possesses a great potential for electrohydraulic servo control.     

Parameter identification of discrete systems via discrete Chebyshev transformation

Abstract

A new method is proposed for the parameter identification of linear time‐invariant discrete single‐input‐single‐output systems by the application of the discrete Chebyshev transformation. The input and output data sequences of a system represented by difference equation are first transformed into discrete Chebyshev spectra. Using spectrum matching, the parameter identification problem becomes the solution of a set of overdetermined simultaneous linear algebraic equations. Examples with and without noise contamination are given to illustrate the new method.     

Adsorption of perfluorooctanesulfonate (PFOS) and perfluorooctanoate (PFOA) on alumina: influence of solution pH and cations

The persistent nature of perfluorochemicals (PFCs) has attracted global concern in recent years. Perfluorooctanesulfonate (PFOS) and perfluorooctanoate (PFOA) are the most commonly found PFC compounds, and thus their fate and transport play key roles in PFC distribution in the natural environment. As most solid phases in natural water contain alumina, an investigation of PFOS and PFOA adsorption behavior on alumina should prove useful in evaluating the environmental impact of this type of persistent pollutant. Systematic experiments were carried out in this study to investigate the adsorption behavior of PFOS and PFOA onto alumina. The results of adsorption kinetics on alumina show that it takes 48 h to reach equilibrium. The adsorption isotherms reveal maximum adsorption capacities of 0.252 μg/m² for PFOS and 0.157 μg/m² for PFOA at pH = 4.3, with the difference primarily due to their different functional groups. An increase in pH leads to a decrease in PFOS and PFOA adsorption on alumina, which may be attributed to the reduction in electrostatic interaction. The adsorption of both PFOS and PFOA decreases with an increase in ionic strength for all four types of cations (Na⁺, K⁺, Mg²⁺, and Ca²⁺), due to the compression of the electrical double layer. Furthermore, the results also indicate that both Ca²⁺ and Mg²⁺ can form bridges with PFOA anions in solution, whereas only PFOS can be bridged by Ca²⁺ due to the higher covalent nature of magnesium.     

Auto-referencing of notational labels in working drawings

This paper presents an auto-referencing framework and method applicable to notational labels in working drawings. The framework cross-references drawing information and updates label contents distributed in drawings. The method is applied to drawing labels, which are mainly the types or numbers of finishes, openings, or equipment, to represent the attributes or specifications of certain building components. Auto-referencing extends the functionality of traditional schedules in referencing inter-relationships between labels and drawing contents. The referencing method can also prevent mistakes due to draftspersons' mis-coordination, improve drawing management efficiency, and reduce reviewing time. One case is presented with created notational symbols, which can be easily used by most architectural firms. Demonstrations are illustrated accordingly.     

Derivation of optimal processing parameters of polypropylene foam thermoforming by an artificial neural network

The effects of processing parameters on the thermoforming of polymeric foam sheets are highly nonlinear and fully coupled. The complex interconnection of these dominant processing parameters makes the process design a difficult task. In this study, the optimal processing parameters of polypropylene foam thermoforming are obtained by the use of an artificial neural network. Data from tests carried out on a lab‐scale thermoforming machine were used to train an artificial neural network, which serves as an inverse model of the process. The inverse model has the desired product dimensions as inputs and the corresponding processing parameters as outputs. The structure, together with the training methods, of the artificial neural network is also investigated. The feasibility of the proposed method is demonstrated by experimental manufacturing of cups with optimal geometry derived from the finite element method. Except the dimension deviation at one location, which amounts to 17.14%, deviations of the other locations are all below 3.5%. POLYM. ENG. SCI., 45:375–384, 2005. © 2005 Society of Plastics Engineers     

Effect of nitrogen ion implantation on impact wear

The effect of nitrogen ion implantation on the impact wear of several metals and alloys with different hardnesses was studied. An impact testing machine was built for this study. In this machine, bullet-shaped projectiles are bounced against a metal surface which is either stationary or rotating. Wear was determined by weight loss measurements. Scanning electron microscopy pictures were taken to study the surface damage. It was found that nitrogen ion implantation improved the impact wear of most of the materials studied. With sliding motion added during the impact, nitrogen ion implantation has little effect.     

A dual-probe approach for evaluation of gypsum crystallization in response to antiscalant treatment

An experimental system was developed to assess and rank the performance of commercial antiscalants designed to inhibit mineral scale formation on reverse osmosis membrane surfaces. The study focused on calcium sulfate dihydrate (gypsum) precipitation to illustrate an approach to antiscalant ranking based on its ability to retard the observed onset (i.e., induction time) of gypsum crystallization from supersaturated solutions. The experimental method consisted of on-line monitoring solution turbidity rise and calcium ion concentration decline to signal the onset of gypsum crystallization. Significant differences were found among commercial antiscalants with respect to achievable levels of induction time retardation. Moreover, antiscalant effectiveness with respect to dosage also varied significantly among antiscalants. The present approach enables a relatively simple and robust initial screening of candidate antiscalants based on their induction time as a function of the applied dose.     

Specific interactions in miscible polymer blends of poly(2‐hydroxypropyl methacrylate) with polyvinylpyrrolidone

The miscibility behaviour and hydrogen‐bonding interaction in blends of poly(2‐hydroxypropyl methacrylate) (PHPMA) with polyvinylpyrrolidone (PVP) were characterized using differential scanning calorimetry and Fourier‐transform infrared spectra. This polymer blend was miscible over the whole composition range and an unusually large positive deviation of T_g from the linearity rule was observed, indicating strong hydrogen bonding between the hydroxyl group of PHPMA and the carbonyl group of PVP. Infrared spectroscopic analysis provided positive evidence for the intra‐molecular hydrogen bonding of PHPMA and inter‐molecular hydrogen bonding between PHPMA and PVP at various compositions and temperatures. Furthermore, equilibrium constants and enthalpies of self‐association and inter‐association between functional groups in the blend of PHPMA and PVP were calculated to explain the results. Copyright © 2004 Society of Chemical Industry     

IPNs based on unsaturated polyester/epoxy: IV. Investigation on hydrogen bonding,compatability and interaction behavior

A series of interpenetrating polymer networks (IPNs) based on unsaturated polyester/epoxy have been developed. The compatibility and interaction behavior of these IPNs have been investigated by DMA, DSC, SEM, FTIR and solid‐state NMR spectroscopies. The glass transition temperatures of IPNs were decreased and their transitions became broader as the content of unsaturated polyester increased in IPNs, based on our DMA and DSC study. The results of FTIR indicate that hydrogen bonding is present between the unsaturated polyester and epoxy. Insufficient degree of hydrogen bonding brought about immiscibility between IPN components. The analysis of proton spin‐lattice relaxation time in the rotating frame of the IPNs was also utilized to investigate molecular interaction between unsaturated polyester and epoxy. From relaxation curves, phase separation was found for the IPN samples with unsaturated polyester content higher than 30 %. This corroborates the DMA and SEM study. Copyright © 2004 Society of Chemical Industry