Constrained identification of virtual CNC drives using a genetic algorithm

This paper presents a genetic algorithm (GA) for identifying virtual models of machine tool drives with minimal intervention to the production machine. The proposed solution builds on the “rapid identification” concept reported earlier in literature, in which a short series of motion data is captured from the Computer Numerical Control (CNC) and used for closed-loop transfer function identification subject to stability constraints. Compared to the Lagrange multipliers solution that was used in the original implementation of rapid identification, the proposed GA is both significantly faster and better suited for industrial use. The novel contributions in the paper include the reduction of the search space from eight unknown variables down to three, which also enables stability constraints to be incorporated in a natural manner, and the re-formulation of the objective function, which streamlines the convergence of the GA by two to three orders of magnitude. Following initial verification in simulations, the GA has been used to identify the closed-loop dynamics of a stand-alone ball screw drive and the x- and y-axes of a five-axis machining center. In experimental results, it is shown that drive models constructed using the GA can be successfully used to predict the tracking and contouring errors for different part programs in a virtual process planning environment.     

Interferometry Measurement of Lubricating Films in Slider-On-Disc Contacts

Interferometry proves to be an efficient way to measure thin lubricant film thickness. However, there are very few reports on the film thickness measurement of conformal lubricated contacts using optical interferometry due to experimental difficulties. In this article, a custom-built test apparatus is introduced, in which a lubricated conformal contact is made between a stationary fixed-incline slider and a moving transparent disc. With a flexible holder, the slider can be positioned in such a way that a specified inclination with respect to the flat disc plane can be obtained. When the disc rotates and the slider is loaded against it, lubricating films are generated. The minimum film thickness h _m at the exit can be determined by interference intensity changes. Measurement error correction in the film thickness was discussed. Case experiments were carried out using the new test apparatus. The credibility of the measurement system is validated by good correlation between the experiments and the theoretical results. The applicability is demonstrated by the film thickness measurement under different inclinations, loads, velocities, lubricants and slider materials. Amongst those case experiments, it is highlighted that the influences of solid/liquid interface properties on the lubrication behaviours can be clearly identified in terms of film thickness.     

Byte-Level Parametric Wavelength Exchange for Narrow Pulsewidth Return-to-Zero Signal

We investigate the feasibility of switching return-to-zero signals with 3-ps pulsewidth by byte-level parametric wavelength exchange (PWE) numerically and experimentally. Square-wave modulated pumps are used in PWE for pump gating. Simultaneous bit swapping for two signals at the same time slot is achieved. Error-free operation is achieved for both signal channels with ap3.5-dB power penalty at 10^-9 bit-error rate.     

Robust Collaborative-Relay Beamforming

Relay communications is a promising technique to extend the range of wireless communications by forwarding the message from the sender to the intended destination. While fixed or variable-power relays have been previously investigated, this paper addresses the collaborative use of variable-phase variable-power amplify-and-forward (AF) relays for robust beamforming, with the aid of imperfect channel state information (CSI) at the sender. In particular, the maximization of the worst-case signal-to-noise ratio (SNR) at the destination terminal is studied under a bounded spherical region for the norm of the CSI error vector from the relays to the destination. Our main contribution is that we prove, under a condition on the quality of the estimated CSI, the robust-optimal collaborative-relay beamforming (CRBF) can be obtained by S-procedure and rank relaxation techniques. In addition, a distributed algorithm is developed by examining the structure of the optimal CRBF solution. Results demonstrate a significant gain of CRBF over non-robust approaches.     

Effects of periphery encapsulation material on the characteristics of micro vacuum dielectric capacitor

The effects of the periphery sealant on the electrical characteristics of vacuum dielectric capacitors (VDCs) are modeled. For the square shape VDCs, their characteristics are predominantly determined by the ratio of capacitor side length versus the width of boundary sealant layer, r. The smaller of the r value, the smaller of the dissipation factor, and the better frequency response of the VDCs are found. To achieve a dissipation factor of less than 10⁻⁵ at 1 GHz, the dimension parameter, r, should be smaller than 0.05 which has been achieved based on the present technology for a capacitor with size larger than 4 mm × 4 mm. The leakage current can also be reduced significantly in the VDCs. We found that the leakage current is mainly governed by the Poole-Frenkel emission of electrons over the periphery region. The present results have demonstrated that the VDC structure is a promising technology option for making high-frequency micro capacitors.     

Design and performance evaluation of an adaptive FPGA for network applications

This paper presents the design, implementation and performance evaluation of a coarse-grain dynamically reconfigurable FPGA platform for multi-service edge and access network devices. The platform consists of two MicroBlaze RISC processors and a number of hardware co-processors used for the processing of packet payloads (Data Encryption Standard (DES) and Lempel-Ziv Compression). The co-processors can be connected either directly to the processors or using a shared bus. The functionality of the co-processors is dynamically reconfigured to meet the requirements of the network workload. The system has been implemented on the Xilinx Virtex II Pro platform and the network traces from real passive measurements have been used for performance evaluation. The use of dynamically reconfigurable co-processors for network applications shows that the performance speedup versus a static version varies from 12% to 35% in the best case and from 10% to 15% on average, depending on the network traffic fluctuation.     

An Analytical Model for the Transfer Characteristics of a Polycrystalline Silicon Thin-Film Transistor With a Double Exponential Grain-Boundary Trap-State Energy Dispersion

For a thin-film transistor (TFT) built on excimer-laser crystallized polycrystalline silicon, the dependence of the effective ldquograin-boundary mobilityrdquo on the gate-to-source voltage can be divided into two subregimes exhibiting different power-law characteristics. An expression for the effective mobility is developed using a procedure previously proposed for a TFT built on polycrystalline silicon exhibiting only single power-law dependence. The additional power-law component is reflected in the model by a pair of measurable and physically meaningful parameters. The procedure for determining these parameters is described and demonstrated. Both the measured and calculated transfer characteristics are reported and compared. The double power-law dependence implies a grain-boundary trap-state energy dispersion characterized by two exponential functions. This is presently verified.     

Interferential lithography of 1D thin metallic sinusoidal gratings: Accurate control of the profile for azimuthal angular dependent plasmonic effects and applications

Nonlinear processes involved in the manufacture of nominally sinusoidal surface relief diffraction gratings generated by interference lithography can introduce distortions into the profile of these surfaces. Such distortions may dramatically affect both the specular reflectivity and diffracted efficiencies from such a surface [H. Raether, Phys. Thin Film 9 (1977) 145–261]. We shall consider in particular the case of metallic gratings used to investigate plasmonic effects that can be engineered for bio-sensing applications. To investigate these effects, interference lithography (IL) has been used for the generation of profile controlled sinusoidal plasmonic crystals. IL exposure contrast study has been performed to control the amplitude oscillation and the surface roughness quality. Bi-metallic layer of silver and gold have been systematically deposited with different film thicknesses. A comprehensive numerical model that studies the optical coupling to surface plasmon polaritons on Ag/Au gratings has been undertaken for the simulation of the reflectivity and azimuthal angle dependence [Z. Chen, I.R. Hooper, J.R. Sambles, J. Opt. A: Pure Appl. Opt. 10 (1) (2008) 015007]. This computation illustrates the sensitivity of individual features to specific harmonic components of the surface, for surface plasmon resonances recorded in both the zeroth and higher diffracted orders. The roughness surface control after development and after bi-metallic evaporation strongly contributes to tighten the width of the reflectivity peak. Optimization process has shown that for an Ag (37 nm) and Au (7 nm) metallic bilayer, a semi-amplitude of 20 nm provides the best reflectivity.     

Effect of Electromigration on the Mechanical Performance of Sn-3.5Ag Solder Joints with Ni and Ni-P Metallizations

The effect of moderate electric current density (1 × 10³ to 3 × 10³ A/cm²) on the mechanical properties of Ni-P/Sn-3.5Ag/Ni-P and Ni/Sn-3.5Ag/Ni solder joints was investigated using a microtensile test. Thermal aging was carried out at 160°C for 100 h while the current was passed. The interfacial microstructure and intermetallic compound (IMC) growth were analyzed. It was found that, at these levels of current density, there were no observable voids or hillocks. Samples aged at 160°C without current stressing failed mostly inside the bulk solder with significant prior plastic deformation. The passage of current was found to cause brittle failure of the solder joints and this tendency for brittle failure increased with increasing current density. Fractographic analysis showed that, in most of the electrically stressed samples, fracture occurred at the interface region between the solder and the joining metals. The critical current density that caused brittle fracture was about 2 × 10³ A/cm². Once brittle fracture occurred, the tensile toughness, defined as the energy per unit fractured area, was usually lower than ~5 kJ/m², compared with the case of ductile fracture where this value was typically greater than ~9 kJ/m². When comparing the two types of joint, the brittle failure was found to be more severe with the Ni than with the Ni-P joint. This work also found that the passage of electric current affects the IMC growth rate more significantly in the Ni than in the Ni-P joint. In the case of the Ni joint, the Ni₃Sn₄ IMC at the anode side was appreciably thicker than that formed at the cathode side. However, in the case of electroless Ni-P metallization, this difference was much smaller.     

A New Method for Blocking Probability Evaluation in OBS/OPS Networks With Deflection Routing

In this paper, we present a new method for the estimation of blocking probabilities in bufferless optical burst or packet switched networks. In such networks, deflection routing is used to reduce blocking probability. However, it requires certain wastage due to trunk reservation that must be used to avoid instability. We provide a wide range of simulation and numerical results to validate our new approximation method and demonstrate various effects on blocking probability and utilization, such as network size, trunk size, the maximal number of allowable deflections, and burst/packet length.