A Classification for Hoist Scheduling Problems

Electroplating lines are totally automated manufacturing systems that are used to cover parts with a coat of metal. They consist of a set of tanks between which the parts to be treated are transported by one or several hoists. Scheduling the movements of these hoists is commonly called a hoist scheduling problem (HSP) in the literature. But the assumptions and constraints that must be taken into account greatly depend on the production environment (physical system, manufacturing specifications, and management policies). Consequently, there exist several classes of HSPs. The systematic frameworks usually used to classify deterministic scheduling problems do not allow distinguishing between these various kinds of HSPs. Therefore, identifying the scope of each published work and comparing the various proposed scheduling methods turn out to be difficult. Thus, this article presents notation for scheduling problems in electroplating systems, to make the specification of problem types and the identification of studied problem instances easier. An associated typology gives a survey of the literature and demonstrates the usefulness of the proposed classification scheme.     

Influence of physico-chemical,mechanical and morphological fingerpad properties on the frictional distinction of sticky/slippery surfaces

This study investigates how the fingerpad hydrolipid film, shape, roughness and rigidity influence the friction when it rubs surfaces situated in the slippery psychophysical dimension. The studied counterparts comprised two ‘real’ (physical) surfaces and two ‘virtual’ surfaces. The latter were simulated with a tactile stimulator named STIMTAC. Thirteen women and 13 men rubbed their right forefingers against the different surfaces as their arms were displaced by a DC motor providing constant velocity and sliding distance. Tangential and normal forces were measured with a specific tribometer. The fingerpad hydrolipid film was characterized by Fourier transform infrared spectroscopy. The shape and roughness of fingers were extrapolated from replicas. Indentation measurements were carried out to determine fingerpad effective elastic modulus. A clear difference was observed between women and men in terms of friction behaviour. The concept of tactile frictional contrast (TFC) which was introduced quantifies an individual''s propensity to distinguish two surfaces frictionally. The lipids/water ratio and water amount on the finger skin significantly influenced the TFC. A correlation was observed between the TFC and fingerpad roughness, i.e. the height of the fingerpad ridges. This is essentially owing to gender differences. A significant difference between men''s and women''s finger topography was also noted, because our results suggested that men have rougher fingers than women. The friction measurements did not correlate with the fingerpad curvature nor with the epidermal ridges'' spatial period.     

A linear optimization approach to the heterogeneous r-cyclic hoist scheduling problem

The cyclic hoist scheduling problem is encountered in electroplating facilities, when mass production is required. This class of problems is a branch stemming from the Hoist Scheduling Problem (HSP) where automatic hoist is used for moving electroplates through chemical baths. A repetitive sequence of moves is searched for the hoist in cyclic schedule. To minimize the cycle time of r different part-jobs, we propose a linear optimization approach. An illustrative example is given in order to show some feedback of our exact solving method. Afterward, two comparisons are presented: firstly, between a two 1-cycle homogenous schedule and a 2-cycle heterogeneous part-job and secondly, between 2-cycle and 4-cycle heterogeneous part-job. These comparisons show how, by considering r-cyclic scheduling, we can optimize the cycle length considerably and then the throughput rate of the electroplating line.     

Prevalence and characterization of antibiotic resistant Enterococcus faecalis in French cheeses

Prevalence of enterococci and antibiotic resistance profiles of Enterococcus faecalis was analyzed in 126 French cheeses from retail stores. Forty-four percent of pasteurized or thermised-milk cheeses, and up to 92% of raw-milk cheeses contained detectable enterococci. A total of 337 antibiotic resistant enterococci were isolated in 29% and 60% of pasteurized-milk and raw-milk cheeses, respectively. E. faecalis was the predominant antibiotic resistant species recovered (81%), followed by Enterococcus faecium (13%), and Enterococcus durans (6%). The most prevalent antibiotic resistances were tetracycline (Tet) and minocycline (Min), followed by erythromycin (Ery), kanamycin (Kan) and chloramphenicol (Cm). The most common multiple antibiotic resistance phenotype was Cm Ery Kan Min Tet. The occurrence of antibiotic genes, as searched by PCR, was 100 % for aph3′IIIa, 96 % for ermB, 90 % for tetM and 80 % for catA in isolates resistant to Kan, Ery, Tet or Cm, respectively. MLST analysis of 30 multidrug resistant E. faecalis revealed that ST19, CC21, CC25 and CC55 isolates were the most common in cheeses. In conclusion, as in many other European countries, French cheeses do contain enterococci with multiple antibiotics resistances. However, low occurrence of high-level gentamicin resistant or sulfamethoxazole/trimethoprim-resistant enterococci and absence of vancomycin- or ampicillin- resistant enterococci indicate that cheeses cannot be considered as a major reservoir for nosocomial multi-drug resistant enterococci.     

Meteorologische Probleme bei der Bestimmung von Schornstein-Mindesthöhen

Meteorological problems in determining minimum stack height . In the Federal Republic of Germany the minimum stack height must be determined with the aid of the “TA Luft” code. The method of determination has been developed with a number of simplifications concerning constancy and homogeneity of emission data, meteorological parameters, and topographical structure. The influences of these simplifications are discussed, and improved methods of determining necessary stack heights are described.     

Filtre intégré à transferts récursifs

A new fully integrated mos frequency filter is suggested, using passive charge routing structure. The principle of operation, the synthesis procedure, and the first experimental results are discussed. This new device has to be compared with finite impulse CCD-filters and switched capacitor filters. Large improvements are expected in terms of silicon area and power consumption. Finally, this solution should be of large economical interest for digital communications.     

机械性刺激感受作用传入装置的感应及机械表征

为了提高织物手感的机械性能表征,把人看作是测量手感的机械传感器.由皮肤的机械性刺激感受器对织物刺激引起的触觉传入信息,可由应用显微神经检查法记录下来.实验结果突显出机械测量法的弱点.为了获得更多关于织物手感的专有信息,设备的传感器和信号处理已作了改进.     

A genetic algorithm approach for a single hoist scheduling problem with time windows constraints

This study considers a cyclic scheduling of hoist movements in electroplating industry. Several jobs have to flow through a production line according to an ordered bath sequence. They firstly enter the line at a loading buffer. Then they will be soaked sequentially in a series of tanks containing specific chemical baths. Finally, they will leave the line at the unloading buffer. The processing time duration of each job in each tank is not constant but confined within a time window bounded by a minimum and a maximum duration. If a job spends less than the minimum duration or more than the maximum duration it is considered defective. Moreover, not only the job operations in the soaking tanks have to be scheduled, but also the transportation of the jobs between tanks has to be considered. The problem now is to find an optimum or near optimum feasible cyclic scheduling such that the hard resource and time-window constraints are respected and the cycle time duration is minimized. A mathematical formulation is proposed for the multi-jobs cyclic hoist scheduling problem with a single transportation resource, and a Genetic Algorithm (GA) approach is presented to solve it. The performance of the proposed algorithm is evaluated with the objective value obtained with a linear programming model, on several literature instances. Computational experiments show the good performance of our GA in terms of solution quality, convergence and computation time.