24 EKSPLOATACJA I NIEZAWODNOÆ NR 4/2002 Václav LEGÁT Frantiek MONA Vratislav ÈERVENKA Vladimír JURÈA OPTIMIZATION OF PREVENTIVE MAINTENANCE AND INFORMATION SYSTEM The paper presents a method for determining the optimal interval for preventive mainte- nance/replacement using either an age related or a diagnostic related renewal strategy. Addi- tionally, the authors rise the question: "How does preventive maintenance influence the probability of failure and the mean life-time of preventively maintained elements of a technical system?" They answer the question using analytical and simulation computing approaches to arrive at the solution. The results are in quantitative form, giving relationships between pre- ventive maintenance intervals and survival probability functions and mean life-time characte- ristics. Examples demonstrate suitability of the method for typical engineering components with Weibull life distributions. Applications offer substantial benefits to both the manufacturer and the user of technical equipment. Keywords: preventive maintenance, maintenance interval optimization, reliability improvement, information system 1. Introduction Results of proper Quality and Dependability Pro- gram (QDP) implemented in manufacturing organi- sations should be reliable and maintainable products including very good maintenance support using dif- ferent internal and external maintenance echelons and lines. Nevertheless, no one has yet been able to pro- duce absolutely reliable and maintainable machines and equipment (repairable) without need of mainte- nance. Therefore, the topic of maintenance manage- ment is still very relevant and its further development is of theoretical and practical importance. So far, many maintenance strategies and methods (e. g. different optimization methods of preventive maintenance, to- tal productive maintenance (TPM), reliability centred maintenance (RCM) etc.) have been developed aimed at making maintenance cheaper and more effective. Such a program will have as its main objective the minimisation of downtime and losses due to failure of critical components of the equipment and thus the improvement of the effectiveness and profitability of the organisation. An essential part of the QDP is an efficient system of data collection and analysis, related to the failures of critical components and the corresponding opera- ting conditions with feedback to the original suppliers of the equipment, and co-operation in design modifi- cations in order to improve the inherent and operatio- nal reliability and safety of the components involved. The objectives of the paper are to contribute to the calculation of the preventive maintenance inte- rval and to the computation of impact of preventive maintenance on reliability of the preventively main- tained machine component and to demonstrate both by using an example. 2. Optimization of preventive maintenance Regarding machine maintenance strategy, it is custo- mary to distinguish between the following methods [1]: a) corrective (unplanned) maintenance where repla- cement or repair is performed only after failure, b) traditional preventive maintenance, based on a predetermined replacement interval, to be ap- plied either periodically or depending on the age of the component under consideration (perio- dic or age-related preventive maintenance), c) diagnostic preventive maintenance based on monitoring and prediction of the technical state of the equipment. Additional findings of this paper deal with opti- mization of age-related preventive maintenance for non-repairable two-state items with the potential use of diagnostic signal information on the change in tech- nical state. For such items we assume the ability to collect and process test or field data from a popula- tion of similar items that have been allowed to opera- te to the point of failure under identical conditions. Assuming that the technical state of the item can be