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Problemy modelowania niezawodności systemów logistycznych

Nowakowski T.

Systems : journal of transdisciplinary systems science

2005

Vol. 10, nr 1

122--133

Omówiono podstawowe pojęcia związane z niezawodnością systemów technicznych. Przeanalizowano sposób definiowania niezawodności w literaturze poświęconej systemom logistycznym. Zwrócono uwagę na występujące różnice i sposoby budowania oceny syntetycznej. Pokazano przykład oceny systemu zaopatrzenia.

Reliability of logistics system is mentioned as one of the most important factors indecision making. The definition of logistics system is discussed. Two levels of definition are underlined: physical level connected with materials distribution and information level concerning information flow. Definitions of technical system dependability are shown according to the standards. The differences between dependability, reliability, availability and maintainability are discussed. That definition are compared with these which are used for logistics system assessment. It is shown how reliability and quality is understood in logistic literature. The differences are proved. They concern: reliability of logistics system is understood in narrow sense (not like dependability) only according to the possibility of the logistics task realization in I correct time, "logistic" and "technical" understood of availability sense is very similar, there is no maintainability characteristics use to asses logistics system (no discussion how to develop the system resistant to the mistake), only factors are used, no other characteristics (functions) are proposed but the j analyzed processes are random. The proposition of OTIF factor is discussed. It means delivery on-time, in-full, error-free. It is one of the examples of synthetic measure which take into consideration all requirements of the system client. These requirement are often defined by 7R formula (right product, right quantity, right quality, right place, right time, right customer, right price). The example of delivery reliability assessment is shown. The data were taken from engineering machines industry and one parts producer was taken into account. Total number of deliveries between January 2003 and March 2004 are discussed and delivery precision charts are shown. Sometimes the data can not be taken as a reflection of a real situation because of two important factors. The delivery date is modified because of production plan changes and usually the supplier is informed about the data change via the phone. Thus the data modification has to be done also in the system. There is no certainty that it was done in the right way during the period from which the data for the purpose of this re-1 port were taken. The second problem with delivery precision is that only closed orders are taken into consideration. The open orders are excluded from the statistics and this can lead to incorrect measurement's results. The chart of the percent of dispatches with right quantity received on time indicates that there were huge fluctuations in the results during the examined period. However, comparison of these data with the late orders quantity shows a clear correlation between I late orders and late deliveries which began in August 2003. The delivery precision for the supplier is presented but it is not know to which extent these results I represent the real situation so they can lead to incorrect conclusions. Analysis of | Missing Lists from the period between January 2003 and March 2004 shows that I 30,8% of all supplied parts were not delivered on time. Most of items were only I one day on the Missing List, so they were not a real danger to the production. The paper is concluded that it is necessary to follow the discussion on mathematical formula of logistics system reliability measure.