Diagnosis for improved maintenance services: Analysis of standards related to Condition Based Maintenance

Abstract

Depending on the maintenance strategy there can be enormous differences how much energy the machinery uses and how much waist it produces. It has become a common practise to study the efficiency of production machinery together with the quality of production and availability of this machinery i.e. the overall effectiveness is studied. In order to reach high efficiency, high availability and good quality, the production machinery has to be in the condition to fulfil these goals. In principle there are two questions that need to be answered when maintenance is planned for tackling the above described situation: 1) What do we have to do? 2) When do we need to take action? The maintenance strategy that has been developed to answer these questions in an optimal way is Condition Based Maintenance (CBM) i.e. the maintenance actions are based on the need of the machinery. Up to this level everything is very logical and clear but unfortunately the current reality in the industry is far from optimal. It is not an easy task to define the condition of production machinery and it is not easy to say what needs to be done and when. This paper is oriented to help to answer the What question i.e. diagnosis of the condition of machinery and When question i.e. prognosis of wear development is not discussed in detail. However, the What question as such is already very demanding. The reason for this is that automatic diagnosis should be based on measurements of the condition and this becomes very difficult in practise due to the differences in the production machinery and the difficulty in separating the condition information from information that is related to the production parameters.

The paper provides an ontology of diagnosis in order to support the building of diagnostic tools. The motivation for relying on defining ontology is based on the fact that it takes a lot of work to define a reliable diagnosis tool and it also is very demanding to be able to keep the system working when changes in the machinery or the software environment take place. The ontology is built in such a way that diagnosis of similar machinery can be identified and new type of machinery as well, based on the similarity of components. One of the most important findings, in the development of this process has been that in order to make the development of ontology possible in practise and in order to be able to keep the system up to date, is to rely on available definitions in the form of standards and practices that other developers are prepared to support and update.

The main focus of this paper is in defining the environment that supports the development of the ontology of diagnosis of the condition of rotating machinery. To build the ontology both references related with standards for exchange of information in a CBM system [1] and upper ontologies are analysed. Upper ontologies define toplevel classes such as physical objects and activities from which more specific classes and relations can be defined. For example following the scope of this paper ISO 15926-2 [2] is analysed. The using of upper ontologies to develop a more specific domain ontology enables to define concepts based on the more general concepts provided by the upper ontology, avoiding reinventing the wheel, while having better integration [3] and standardization.