Stand-alone programmable controller for time-critical robotic systems

This paper proposes and describes a new technique in the design and implementation of stand-alone programmable controllers which implement complex control algorithms for complex systems in general and time-critical systems in particular. Unlike other existing commercially available controllers, the proposed controller is capable of implementing all kinds of simple and complex control algorithm techniques such as PIDs, adaptive, optimal, etc. The controller is designed to handle timed events accurately due to the utilization of a new software approach based on Petri net technique as well as the use of an optimized simulation language designed for control and data acquisition applications. The most significant aspects of the proposed controller are its low cost, high speed, and easy implementation. Using the new approach, it is possible to effortlessly and efficiently simulate any controller algorithm and controlled plant, verify results if they meet pre-defined system specifications and then immediately generate and save codes on EPROMs to be placed on the controller board. The proposed controller system consists of a hardware portion and a software package. The software package is written in C and assembly languages and consists of four different programs. A prototype of the proposed controller was designed, constructed and successfully tested to implement various control algorithms. The data obtained suggest that the proposed technique will significantly aid engineers to simplify the task of implementing complex algorithms industry such as robotics.     

A semi-Markovian model for low-cycle elastic-plastic fatigue crack growth

Elastic-plastic fatigue crack growth is described by a continuous time semi-Markovian stochastic process. The load on the member is considered to be deterministic and the resistance is assumed to be random. Crack growth resistance is described by an equation employing the J-integral. Quantities of interest that can be obtained from this model include emergency statistics and probability distributions on the time to reach a critical crack length. The model is tested with fatigue crack propagation data for A533B pressure vessel steel. The results indicate that the model underpredicts the mean first-passage time at the start of a test but predicts it well in the mid-ranges and towards the end of the test; the variance of the process is better predicted for specimens that undergo large plasticity than those with low plasticity.     

THE EFFECTS OF STRESS RATIO, COMPRESSIVE PEAK STRESS AND MAXIMUM STRESS LEVEL ON FATIGUE BEHAVIOUR OF 2024-T3 ALUMINIUM ALLOY

Abstract— Fatigue crack growth behaviour of 2024-T3 aluminium alloy is investigated as a function of stress ratio, compressive peak stress and maximum stress level. It is found that as the stress ratio and the magnitude of the compressive peak stress are increased, the threshold stress intensity range decreased linearly. Intermediate and near threshold growth rate data are analysed with different formulae for effective stress intensity range. The data covered different values of stress ratio, compressive peak stress and maximum stress level. A formula for the crack opening stress level is introduced as a function of stress ratio, compressive peak stress and maximum stress level. The formula permitted a good correlation between crack growth data for both positive stress ratio and negative compressive peak stress values. Using the new formula, intermediate and near threshold crack growth data for the 2024-T3 aluminium alloy yielded a unique crack growth rate vs effective stress intensity range curve for all stress ratio and compressive peak stress values investigated. This suggests that for the 2024-T3 aluminium alloy the crack growth rate vs effective stress intensity range curve does not depend on stress ratio, compressive peak stress, or maximum stress level. The significance of the new equation and the crack growth rate versus effective stress intensity range curve is that they allow a designer to find crack growth rate vs stress intensity range data for the 2024-T3 aluminium alloy in both intermediate and near threshold regions for the particular stress ratio, compressive peak stress and maximum stress level conditions of the component under investigation.     

Accumulation and implications of cadmium,cobalt and manganese in soils and vegetables irrigated with city effluent

BACKGROUND: In most parts of Pakistan, untreated city effluent is utilised for growing vegetables around large urban settlements such as Faisalabad. Farmers use it as a source of irrigation water and plant nutrients. However, its continuous use may have serious environmental implications, since it also contains heavy metals. In this study the Faisalabad city effluent was examined for irrigation quality and its impact on irrigated soils and vegetables. RESULTS: Irrigation hazard of the effluent was moderate (electrical conductivity (EC) 1.1–1.7 dS m^?1, Sodium adsorption ratio (SAR) 5.9–17.4 mmol^1/2 L^?1/2, Residual sodium carbonate (RSC) 1.0–2.1 mmol_c L^?1) at site 1 and strong (EC 3.7–4.1 dS m^?1, SAR 16.1–21.8 mmol^1/2 L^?1/2, RSC 4.0–9.1 mmol_c L^?1) at site 2. Mean concentrations of ammonium bicarbonate/diethylene triamine pentaacetic acid (AB/DTPA)‐extractable Cd, Co and Mn at upper soil depth (0.0–0.2 m) were respectively 0.080, 0.057 and 217.4 mg kg^?1 at site 1 and 0.101, 0.076 and 164.1 mg kg^?1 at site 2. CONCLUSION: The concentrations of Cd and Mn were above the permissible limits but that of Co was below the permissible limit for irrigation. The concentrations of Cd, Co and Mn tended to decrease with increasing soil depth. Accumulation of metals was higher in leaves irrespective of whether leaves were the edible or non‐edible component of shoots. Use of untreated city effluent for irrigation without risk assessment and management could be a serious hazard, impacting soil and crop quality and ultimately human health. Copyright © 2007 Society of Chemical Industry     

Assessment of reservoir temperatures of thermal springs of the northern areas of Pakistan by chemical and isotope geothermometry

Chemical and isotope geothermometers, i.e. the Na–K, K–Mg, quartz and δ¹⁸O(SO₄–H₂O), have been applied to estimate the reservoir temperature of the thermal springs in the northern areas of Pakistan. The chemical types of the thermal waters and the effects of mixing of shallow cold water with the thermal end-members are discussed. These waters are neutral to slightly alkaline and have low dissolved contents. Sodium is the dominant cation in almost all the cases. In terms of anions, the hot waters of Budelas are of the SO₄ type, those of Tatta Pani are of mixed character (SO₄ and HCO₃), and the waters from the remaining areas show HCO₃ domination. An absence of tritium in Tatta Pani and Tato thermal springs indicates that they do not have any contribution of shallow young water. In the case of the Murtazabad springs, the wide range of tritium concentrations, negative correlations with surface temperature and Cl, and positive correlation between Na and Cl show that the shallow cold groundwater is mixing with thermal water in different proportions. For the mixed water of Murtazabad thermal springs, ‘isochemical modelling’ using the Na–K, K–Mg and quartz geothermometers indicates an equilibrium temperature in the range 185–200 °C. The δ¹⁸O(SO₄–H₂O) geothermometer gives relatively low temperatures for three springs, whereas two samples are close to the 185–200 °C temperature interval. The reservoir temperatures of Tatta Pani springs (100–120 °C), determined by Na–K and quartz geothermometers, are in good agreement. The δ¹⁸O(SO₄–H₂O) geothermometer gives a relatively higher range (140–150 °C) for most of the Tatta Pani springs. For Tato spring, the isotope and chemical geothermometers (except for the K–Mg) agree on an equilibrium temperature of about 170 °C. Reservoir temperatures of the remaining minor fields are not conclusive due to the lack of sufficient data.     

Process Optimization and Characterization of Popped Brown Rice

The popping process was optimized for brown rice based on an expansion ratio. A central composite design with interactive effect of three independent variables, including salt content (1–2.5 g/100 g raw material), moisture content (13–17 g/100 g raw material), and popping temperature (210–240°C) was used to study their effects on the expansion ratio of rice using response surface methodology. The experimental values of expansion ratio were ranged from 5.24 to 6.85. On fitting the experimental values of expansion ratio to a second order polynomial equation, a mathematical model with the predictability was developed with the statistical adequacy and validity (p ? 0.05). From the model, the optimal condition including salt content (1.75 g/100 g raw material), moisture content (15 g/100 g raw material), and popping temperature (225°C) were predicted for a maximum expansion ratio of 6.79, which was then proved to be 6.85 through experiment. Raw and popped brown rice were investigated for physical properties including hardness, L*, a*, and b* value, length/breadth ratio, bulk density, and minerals, which showed the significant differences. The optimized popped rice sample was evaluated for structural, spectroscopic, and thermal properties, which showed the significant difference from raw rice.