Maintenance management is to design, operate, and maintain the reliability and availability of assets at a required performance level using the lowest possible cost. The standby redundancy is one of the means to achieve highly reliable system with less dependable units. As commonly used performance indicator, the reliability and availability should be precisely analysed for a repairable standby system. The reliability of a standby system is mainly studied in the framework of lifetime approach. Most existing models are developed for a two-unit standby system and a Kout- of-N system with identical units. The system units are assumed to be binary-state and the failures of system units are modelled as sudden failures. The deteriorations of units are modelled as time-dependent failure rate and are assumed to be independent. In addition, most of the existing models do not consider maintenance is carried out on the system. In reality, the deteriorations and the resultant failures in real-world systems are often interactive with each other. The systems normally experience several, often imperfect, restorations before a complete renewal. Therefore, the study of different repair policies, such as opportunistic and individual policies, in multi-unit systems need also be investigated. To address the problem, the reliability and availability models for a 2-out-of-3 cold standby system will be studied in a multi-state system reliability framework. A multistate multi-path failure mode is proposed to model the interactive deteriorations. The concept of repair matrix will be adopted to model the effect of unit level restorations on system reliability. The availabilities under individual repair policy and opportunistic repair policy will be developed.

Abstract  Purpose – The purpose of the study is to investigate how distribution centers can prevent delays to achieve higher on-time delivery.  To fulfill the purpose of the study three study questions have been conducted:  • What factors causes delays in distribution centers?  • Why do delays occur in distribution centers?  • How can distribution centers prevent delays to achieve higher on-time delivery?  Method – A qualitative approach has been used throughout the study to enable fulfilment of the study´s purpose. The study has implemented a case study at a distribution center to investigate what factors causes delays. A theoretical framework that attends the research areas of on-time delivery, distribution centers function, operational problems and classification of factors was used to conduct suggestions addressing how businesses can prevent delays.  Findings – The study emphasizes that all delays that effect on-time delivery could be classified as individual- or system dependent. The study suggests that businesses should focus on preventing delays classified as system dependent, since they may also prevent individual dependent delays. By improving education and prioritize development of education and standards businesses should be able to improve their on-time delivery.  Implications – The study maps factors that causes delays in distribution centers. Categorization and classification could be used to identify where factors occur and explain their dependencies. This study focuses on how on-time delivery is affected by distribution centers performance. The study indicates the possibility to applicate already presented theories in this context but also that categorization and classification of factors is possible. Furthermore, the study has identified problems due to non-used standards, even though they are available for the user.  Limitations – The delimitations of the study mark the study’s focus to stocked goods in distribution centers and do not attend economic aspects of on-time delivery.  Key words: On-time delivery, distribution centers, delays, individual dependent, system dependent / Sammanfattning  Syfte – Syftet med studien är att undersöka hur distributionscentraler kan förhindra förseningar för att uppnå högre leveransprecision.  För att uppfylla syftet har tre frågeställningar utformats:  • Vilka faktorer orsakar förseningar i distributionscentraler?  • Varför uppstår förseningar i distributionscentraler?  • Hur kan distributionscentraler förhindra förseningar för att uppnå högre leverans-precision?  Metod – För att uppnå syftet har studien använt en kvalitativ ansats där en fallstudie har genomförts på en distributionscentral i syfte att undersöka vilka faktorer som kan orsaka förseningar. Ett teoretiskt ramverk som behandlar leveransprecision, distributionscentralers funktion, verksamhetsproblem och klassificering av faktorer har använts för att ta fram förslag på hur distributionscentraler kan förhindra faktorer som orsakar förseningar.  Resultat – Studien indikerar att alla identifierade faktorer som orsakar förseningar och därmed påverkar leveransprecision kan vara antingen individ- eller systemberoende. Studien föreslår att verksamheter bör fokusera på att förhindra systemberoende faktorer som orsakar förseningar eftersom de även kan förhindra individberoende förseningar. Studien föreslår; genom att förbättra utbildning samt prioritera utveckling av utbildning och standarder skulle verksamheters leveransprecision kunna öka.  Implikationer – Det har kartlagts faktorer som kan orsaka förseningar i distributions-centraler. Kategoriseringen tillsammans med klassificering kan användas för att identifiera var faktorer uppstår och vad de beror på. Kategoriseringen tillsammans med klassificering kan användas för att identifiera var faktorer uppstår och vad de beror på. Vidare identifierar studien problem på grund av att standarder inte används, trots att de finns tillgängliga för användare.  Begränsningar – Studien är avgränsad till att endast studera produkter som lagerförs i distributionscentraler och tar inte hänsyn till ekonomiska aspekter kopplat till leverans-precision.  Nyckelord: Leveransprecision, distributionscentraler, förseningar, individberoende, systemberoende.