Showing papers by "Harbin Institute of Technology published in 1997"

The model-free learning adaptive control of a class of SISO nonlinear systems

Abstract: The model-free learning adaptive control of a class of nonlinear systems is presented in this paper based on a new concept of partial derivative called 'pseudo-partial-derivative'. The BIBO stability of the regulator are proved.

Adaptive control of chaos in Lorenz system

Abstract: This paper treats the control of chaos in Lorenz systemsin the presence of system parameter uncertainty. An adaptivecontrol law is derived such that in the closed-loop system thestate of the system can be regulated to a specified point inthe state space. Simulation results are presented which showthe suppression of chaotic behavior and the regulation of statevector to the desired terminal point in spite of the uncertaintyin system parameters.

Precipitation behaviour of Al-Mg-Si alloys with high silicon content

Abstract: The precipitation behaviour of three Al-Mg-Si alloys has been studied by differential scanning calorimetry (DSC) and transmission electron microscopy. Seven exothermic peaks are usually observed in DSC thermograms of Al-Mg-Si alloys with high silicon contents. These peaks are believed to be caused by the formation of clusters of silicon and magnesium atoms, Guinier-Preston zones, small precipitates with an unknown structure, β″ phase, B′ phase, silicon precipitates and β phase. The silicon content has no obvious effect on the precipitation of β″ and B′ phases in these alloys, but it has a pronounced influence on the formation of silicon precipitates. The cold-rolling reduction before solution heat treatment is also found to affect the precipitation process appreciably.

Technical note Simple criteria for stability of neutral systems with multiple delays

Abstract: The stability of linear neutral delay-differential systems with multiple delays is investigated, which is an extension of the work reported in the literature. The case of delay-independent stability is considered. Some simple stability criteria through the evaluation of the measure and norm of corresponding matrices are presented.

Study on a new kind of combined machining technology of ultrasonic machining and electrical discharge machining

Abstract: An analysis on the mechanisms of ultrasonic machining and electrical discharge machining has been carried out, and a technology, which combines the advantages of both of them, has been proposed in this paper. It can be used to machine all conductive hard and brittle materials with high efficiency and surface integrity. The mechanism of this combined technology has been studied by the authors. The experimental results show that the efficiency of it is over three times greater than that of ultrasonic machining, and the surface integrity is not significantly different.

On-line tool condition monitoring system with wavelet fuzzy neural network

Abstract: In manufacturing systems such as flexible manufacturing systems (FMS), one of the most important issues is accurate detection of the tool conditions under given cutting conditions. An investigation is presented of a tool condition monitoring system (TCMS), which consists of a wavelet transform preprocessor for generating features from acoustic emission (AE) signals, followed by a high speed neural network with fuzzy inference for associating the preprocessor outputs with the appropriate decisions. A wavelet transform can decompose AE signals into different frequency bands in the time domain. The root mean square (RMS) values extracted from the decomposed signal for each frequency band were used as the monitoring feature. A fuzzy neural network (FNN) is proposed to describe the relationship between the tool conditions and the monitoring features; this requires less computation than a back propagation neural network (BPNN). The experimental results indicate the monitoring features have a low sensitivity to changes of the cutting conditions and FNN has a high monitoring success rate in a wide range of cutting conditions; TCMS with a wavelet fuzzy neural network is feasible.

Radio-frequency plasma nitriding and nitrogen plasma immersion ion implantation of Ti-6A1-4V alloy

Abstract: Nitrogen ion implantation improves the wear resistance of Ti-6A1-4V alloys by forming a hard TiN superficial passivation layer. However, the thickness of the layer formed by traditional ion implantation is typically 100–200 nm and may not be adequate for many industrial applications. We propose to use radio-frequency (RF) plasma nitriding and nitrogen plasma immersion ion implantation (PIII) to increase the layer thickness. By using a newly designed inductively coupled RF plasma source and applying a series of negative high voltage pulses to the Ti-6A1-4V samples, RF plasma nitriding and nitrogen PIII can be achieved. Our process yields a substantially thicker modified layer exhibiting more superior wear resistance characteristics, as demonstrated by data from micro-hardness testing, pin-on-disc wear testing, scanning electron microscopy (SEM), as well as Auger electron spectroscopy (AES). The performance of our newly developed inductively coupled RF plasma source which is responsible for the success of the experiments is also described.

Self-learning fuzzy neural networks for control of uncertain systems with time delays

Abstract: We address the problem of control of uncertain systems with time delays. Using the fuzzy logic control and artificial neural network methodologies, we present a self-learning fuzzy neural control scheme for general uncertain processes. In this scheme, a neural network compensator is designed instead of the classical Smith predictor for attenuating the adverse effects of time delays of the uncertain systems. The scheme has been used in control of welding pool dynamics of the arc welding process, and the experiment results show the control scheme available.

Deformation and fracture behavior of two Al-Mg-Si alloys

Abstract: Deformation and fracture behavior of two Al-Mg-Si alloys in different aging conditions has been studied by tensile testing, transmission electron microscope (TEM), and scanning electron microscope (SEM) observation. Tensile test results show that the strain hardening exponents (n values) of the two alloys decrease sharply at the early stage of artificial aging and are only 0.045 and 0.06, respectively, in the overaged condition. The sharp decrease of work hardening rate is believed to be one major reason that results in the rapid decrease of elongation to failure at the early stage of artificial aging. In fully aged conditions, dislocations are concentrated in narrow bands during plastic deformation of these alloys, which is responsible for the very low n values of the Al-Mg-Si alloys in peak aged and overaged conditions. The Si particles formed in the interior of grains of the higher Si containing alloy reduce the inhomogeneous deformation behavior. The TEM results show that large precipitates and precipitate-free zones (PFZs) along grain boundaries are formed in peak aged and overaged conditions, and SEM observations demonstrate that the tensile fracture modes of the two alloys in these aging conditions are completely intergranular with many small cusps decorated on facets of the fractured grain boundaries. Thus, the fracture process of both alloys is suggested to be that in which the high local stresses, built up where the slip band impinges on the grain boundaries, nucleate voids at the grain boundary precipitates by decohesion of the particle/PFZ interface, and then coalescence of these voids within the PFZ leads to the final fracture of these alloys.

Sinewave fit algorithm based on total least-squares method with application to ADC effective bits measurement

Abstract: Sinewave fit is a fundamental task in many test and measurement systems. The characterizations of analog-digital converters and digital oscilloscopes are two examples. In this paper, we present a high-performance (i.e., high-precision and high-speed) algorithm to estimate the four parameters of a sinewave from a sample data record. By the use of trigonometric identity, we propose a frequency estimator that turns the nonlinear estimation problem into a linear one. Thus, the difficulty of the traditional nonlinear least-squares sinewave fit method is attenuated. The total least-squares method is used to estimate four parameters of a sinewave in order to minimize the estimation errors in the sense of l/sub 2/ norm. Simulation results exhibit that the proposed method gives superior performance over traditional ones and achieves excellent estimation of the true resolution of the simulated ideal ADC. This new algorithm is noniterative and gives swift and consistent results.

Electric discharge milling of polycrystalline diamond

Abstract: Polycrystalline diamond (PCD) has been used widely in modern industry. However, the manufacture of PCD blanks is not an economical and efficient process. The shaping of PCD blanks with conventional machining methods (such as grinding), is a long, labour-intensive and costly process. Electromachining processes promise to be effective and economical techniques for the production of tools and parts from PCD blanks. Wire electric discharge machining is able to effectively slice PCD. Electrical discharge machining (EDM) and electrical discharge grinding (EDG) shape PCD blanks at a lower cost. However, EDM and EDG of a large surface area on PCD show lower efficiency. This paper presents a new process of machining PCD using electrical discharge (ED) milling. ED milling employs a DC source instead of the pulse generator used in EDM, and uses a water-based emulsion as the machining fluid. This process is able to effectively machine a large surface area on PCD, and effectively machine other advanced conduct...

Improvement of the corrosion property of Cr4Mo4V bearing steel using plasma immersion ion implantation

Abstract: The working conditions of aerospace bearings such as engine bearings are quite harsh and prolonging the life span of these components is thus very important to the aerospace industry. Previous results have shown that the main failure mechanism of aerospace bearings is corrosion, and enhancing their corrosion resistance is a key. Cr4Mo4V, which is equivalent to AISI M50 bearing steel, is usually used in aerospace bearings in China. In this study, Cr4Mo4V components are treated in a new generation plasma immersion ion implanter in which ion implantation and sputter deposition can be carried out in the same chamber without breaking vacuum. Three treatment processes involving Cr, Mo, and N are evaluated. Our test results indicate that Cr is the main element enhancing the corrosion resistance and the addition of nitrogen improves the properties further. The non line-of-sight advantage of PIII is important to the processing of complex-shaped samples such as engine bearings.

Modeling, scheduling and control of flexible manufacturing systems by extended high-level evaluation Petri nets

Abstract: This paper proposes an extended high level evaluation Petri nets (EHLEP-N) for modeling and control of flexible manufacturing systems (FMSs). This new class of models is simple, perceivable and descriptive, having the capability of inference and making decisions. When applied to FMSs, the EHLEP-N can model real-time decisions with which dynamic scheduling rules can be investigated and evaluated. Experimental results show that the throughput for such systems with the new scheduling strategies can increase on an average of 7% by decreasing no-inputs and blockings compared with that of the traditional strategies.

Fractional Gabor transform.

Abstract: A fractional Gabor transform (FRGT) is proposed. This new transform is a generalization of the conventional Gabor transform (GT) based on the Fourier transform to the windowed fractional Fourier transform (FRFT). The FRGT provides analyses of signals in both the real space and the FRFT frequency domain simultaneously. The space-FRFT frequency pattern can be rotated as the fractional order changes. The FRGT has an additional freedom, compared with the conventional GT, i.e., the transform order. The FRGT may offer a useful tool for guiding optimal filter design in the FRFT domain in signal processing.

Image-scaling problem in the optical fractional Fourier transform.

Abstract: The significance of scale factors and cascade of optical fractional Fourier transform is emphasized. Exact and cascadable fractional Fourier transforms in practical applications mandate that the image scale be the reciprocal of the scale of the input plane controlled by the optical setup. The practical setup of the optical fractional Fourier transform must be without any quadratic phase term at the spectrum plane.