【正文】 system. It is not trivial to access the status of sometimes moving ponents of a belt conveyor. The same experienced person should therefore carry out inspections on a regular basis. To overe operational problems caused by a lack of experience of external maintenance personnel, the inspection of belt conveyor ponents can be automated. In this way knowledge of for example wear rates and replacement schedules can be built up in a data base system. The external maintenance crew then can be used to replace the worn off ponents. Alternatively, replacement of ponents can be automated as well. This paper discusses strategies and techniques for automated maintenance of belt conveyor systems. Section 2 defines the concept of intelligent maintenance, Section 3 discusses existing inspection systems that can be used in automated maintenance systems. Section 4 discusses means of assessing the status of rotating ponents of belt conveyors based on vibration based monitoring concepts. Section 5 presents a case study and section 6 finally lists the conclusions and remendations. INTELLIGENT MAINTENANCE Maintenance on belt conveyor systems can be divided in condition monitoring of the total system and servicing of its ponents. Condition monitoring is defined as the continuous or periodic measurement and interpretation of data to indicate the condition of a ponent to determine the need for replacement or servicing. Condition monitoring therefore deals with the acquirement of data (data acquisition or DAQ) from sensors, the interpretation of that data (data mining or DAM) and with taking corrective actions (ACT) on ponents that are to fail, thus preventing fail systems from developing and propagating. The basic concept of condition monitoring is to identify subtle changes in operation, such as increased vibration levels, that indicate a mechanical (or electrical) problem is starting to develop. These early messages provide more time to plan for machine downtime and repair. There are four typical types of maintenance: ? preventive maintenance: calendar based, . activities are planned depending on working hours or at certain time intervals (scheduled maintenance)。 nothing is repaired but preventive jobs are done. ? random maintenance: opportunity based, . maintenance is done when the opportunity arises。 this may cause a general shutdown of the system。 it is a planned and corrective maintenance. From the above given four types of maintenance it is clear that only a predictive maintenance concept qualifies for application in an intelligent maintenance system that enables maintenance automation. Intelligence here is defined as the ability to make decisions based on information gathered through sensors in the equipment or provided by the control system of the total transport system. Applied to belt conveyor systems the information gathered from a system is information on the life expectancy of individual ponents as for example idler rolls. This information leads to a decision either to inspect a certain idler station and its rolls more frequently or to change a roll for a new roll. Repairing in fact here means changing one roll for another. Whether or not a roll can be repaired and the effect of that on the belt conveyor’s performance is outside the scope of this study. The main issue in this study is the question how an automated inspection strategy is affected by the accuracy of the data acquired. In theory there are two outer limits in predictive maintenance. The first is that no accurate information of the rolls is available at all, basically meaning that an assessment of the remaining lifetime is made purely on the basis of historical data provided by the roll or bearing manufacturers (predictive maintenance based on statistics). The second is that during inspection very accurate information on the status of rolls is generated enabling an accurate assessment of the remaining lifetime of an individual roll (predictive maintenance based on data). A logistic simulation model is made to determine the effect of the accuracy of data acquired on automated inspection strategies. This model is discussed in Section 5. EXISTING INSPECTION SYSTEMS One problem faced with inspection or condition monitoring of ponents of belt conveyors, including the belt, pulleys and idler rolls, is that they rotate. Since the condition of ponents like rolls and pulleys can only be assessed when they are rotating, only condition monitoring systems based on vibration analysis or acoustical monitoring can be used. The opposite holds for the belt. The belt’s condition can only be inspected when the belt conveyor system is not operating. Either way, an inspector has to walk the full length of the conveyor to inspect its ponents. An associated problem is that pulleys may be far apart from each other or that the conveyor has a great length. To ease inspection in these cases a powered maintenance trolley can be used for inspection purposes. The concept of a powered maintenance trolley is not new. An early example of a maintenance trolley used on a belt conveyor system was the trolley used on the 100 km Phosboucraa overland system built by Krupp in the 70ties to transport raw phosphate across a distance of 100 km from inside the west Sahara across a desert of stones to the loading point on the coast. This longdistance conveyor system, consisting of belt systems with centre distances of to 11,7 km. applied a maintenance trolley concept to allow for inspection also see Figure 1. The Kruppdesign turned out to be occasionally liable to instability. Figure 1 Powered maintenance trolley on Krupp system in Sahara. A revitalised version of a maintenance trolley is shown in Figure 2. This concept, designed and developed by CKIT of South Africa, is quite robust and stable. It has been ins