VARIABLE STRUCTURE CONTROL OF TWO MANIPULATORS HANDLING A CONSTRAINED OBJECT

The control of two manipulators handling a constrained object involves the control of the position of the object, the internal force used to grasp the object, and the constraint force due to the constraint surface. The robustness of the controller must be guaranteed when the system faces parameter uncertainties and or external disturbances. In this paper, a variable structure control law is proposed. This controller guarantees the asymptotic convergence of the position of the object, internal force, and constraint force to their desired values when uncertainties on the parameters and external disturbances are present in the system. Simulation results for two planar robots moving an object along a horizontal plane illustrate the fact that the proposed controller achieves the desired asymptotic tracking.     

Electromechanical modelling of overhead cranes

A non-linear electromechanical model describing the dynamical behaviour of overhead cranes is presented. The model takes into consideration the non-linear dependence of the load sway on transients of driving motors during voltage disturbances and start-ups. This is extremely useful in practice since load sway control schemes normally utilize input voltages as control variables. The mechanical subsystem within the model is that of the load sway and has the swing angles and their derivatives as state variables. Each of the two driving motors, namely, the girder motor and the trolley motor, is represented by the classical fifth-order model of induction machines where electrical transients as well as mechanical transients are considered. The model is linearized using Taylor series expansion around a normal operating point. A numerical example is presented to illustrate the usefulness of the results.     

Linear quadratic regulators with eigenvalue placement in a horizontal strip

A method for optimally shifting the imaginary parts of the open-loop poles of a multivariable control system to the desirable closed-loop locations is presented. The optimal solution with respect to a quadratic performance index is obtained by solving a linear matrix Lyapunov equation.     

A New Approach for Manufacturing a High Porosity Ti-6Al-4V Scaffolds for Biomedical Applications

Titanium and its alloys are currently considered as one of the most important metallic materials used in the biomedical applications, due to their excellent mechanical properties and superior biocompatibility. In the present study, a new effective method for fabricating high porosity titanium alloy scaffolds was developed. Porous Ti-6Al-4V scaffolds are successfully fabricated with porosities ranging from 30% to 70% using spaceholder and powder sintering technique. Based on its acceptable properties, spherical carbamide particles with different diameters （0.56, 0.8, and 1mm） were used as the space-holder material in the present investigation. The Ti-6Al-4V scaffolds porosity is characterized by using scanning electron microscopy. The results show that the scaffolds spherical-shaped pores are depending on the shape, size and distribution of the space-holder particles. This investigation shows that the present new manufacturing technique is promising to fabricate a controlled high porosity and high purity Ti-6Al-4V scaffolds for hard tissue replacement.     

Inactivation and Injury of Listeria monocytogenes in a Minimal Medium as Affected by Benzoic Acid and Incubation Temperature

The population of Listeria monocytogenes in a minimal medium (lacking a nitrogen source) at pH 5.5 decreased logarithmically during incubation. Rate of death of the pathogen, indicated by D-values, was greatly affected by changes in the temperature of incubation (4–35°C), but to a much lesser extent by the presence of benzoic acid (3000 ppm). Injury of L. monocytogenes during incubation was equally detectable on tryptose agar containing 6% salt and McBride Listeria Agar containing 0.5% lithium chloride. A greater degree of injury was detected at the lower than the higher temperatures of incubation, but presence of benzoic acid (3000 ppm) did not seem to affect the extent of injury.     

Formal proof of integer adders using all-prefix-sums operation

Addition of two binary numbers is a fundamental operation in electronic circuits.Several integer adder architectures have been proposed.Their formal properties are well known,but the proofs are either incomplete or difficult to find.In this paper,we present a formal proof for the correctness of prefix adders.Both sequential and parallel algorithms are formalized and proved.In contrast to previous proofs using higher order functions and rewriting systems,our work is based on first order recursive equations,which are familiar to the computer arithmetic community and are therefore understandable by people working on VLSI circuit design.This study sets up a basis for further work on formal proofs of computer arithmetic algorithms.     

A floating point conversion algorithm for mixed precision computations

The floating point number is the most commonly used real number representation for digital computations due to its high precision characteristics. It is used on computers and on single chip applications such as DSP chips. Double precision (64-bit) representations allow for a wider range of real numbers to be denoted. However, single precision (32-bit) operations are more efficient. Recently, there has been an increasing interest in mixed precision computations which take advantage of single precision efficiency on 64-bit numbers. This calls for the ability to interchange between the two formats. In this paper, an algorithm that converts floating point numbers from 64- to 32-bit representations is presented. The algorithm was implemented as a Verilog code and tested on field programmable gate array (FPGA) using the Quartus II DE2 board and Agilent 16821A portable logic analyzer. Results indicate that the algorithm can perform the conversion reliably and accurately within a constant execution time of 25 ns with a 20 MHz clock frequency regardless of the number being converted.     

Extraction of Niobium and Tantalum from Nitrate and Sulfate Media by Using MIBK

Abstract

The niobium-tantalum ore material obtained from Ras Baroud locality in the central Eastern Desert of Egypt, consists mainly of two minerals namely: columbite and alvarolite. The extractive separation of niobium(V) and tantalum(V) from the acid media HF-HNO₃or HF-H₂SO₄ have been worked out using methyl isobutyl ketone (MIBK) as an extractant.

The extraction system HF-H₂SO₄-MIBK proved to have the most promising separation effect with the highest purity of each niobium and tantalum oxides.

The optimum loading conditions in HF-H₂SO₄-MIBK system were: O/A = 10/1.15 minutes contact time, 100% MIBK. while the feed solution assayed 4.3 N HF and 5.7 N H₂SO₄. Moreover, the stripping process was performed with 1.0 N HF and distilled water in subsequent steps.