Dependability assurance for automatic load haul dump machines
Abstract: Load Haul Dump (LHD) machines are used in underground mines to load and transport ore and minerals. Loading and hauling blasted ore from drawpoint to dumping point constitute a significant portion of the production costs for mining companies. There are a number of operation modes available for LHDs, and there are many criteria to consider when selecting the best one. The use of automated LHDs has been widely discussed due to the potential to increase productivity. The increasing focus on safety and ergonomics also gives an edge to automatically operated loaders over manually operated ones. Mine managers must decide when it is preferable to use manually operated loaders and when to complement or replace these with automatic ones. Automation focus has over the years gradually shifted from having automated fleets of vehicles to the more flexible solutions with semi-automatic LHDs gaining safety as one of the main goals. Several issues must be resolved to maximize the benefits of automation. One is to improve maintenance, and moving from operatorassisted “fail and fix” to planned maintenance. Since the operator is removed from the machine during automatic operation and maintenance staff is not always available on short notice, it is crucial to increase planned maintenance to maximize the investment in automation. Another issue is the complexity of the mining environment, including both the infrastructure and external disturbances like oversized boulders and road maintenance, as these can throw the entire investment in automation into question. The purpose of this thesis is to explore the maintenance actions connected to automated LHDs as well as the factors influencing the dependability of the machine. Research methods include a literature review, interviews, and data collection and analysis. Real time process data, operation and maintenance data have been refined, integrated and aggregated to make a comparative analysis of manual and automatic LHDs. The analysis show that 75% of the stop occasions causing idle time for LHDs relate to the operating environment, 21.5% pertain to machine related issues and 3.5% are related to the infrastructure of the automatic system installed in the mine. There is no difference in what kind of maintenance actions that are taken for manually and automatically operated LHDs, but there is a difference in what type of failures that occurs more frequently for the different operation modes. For automation of LHDs too much unplanned repairs and maintenance work significantly reduces the overall availability and can jeopardize the entire investment in automation. The difference between the semi-automatic and the manual LHD was found to be very small in terms of maintenance cost versus produced number of tons. However, a semi-automated LHD is an optimal machine regarding the ability to adapt to reconfiguring the operation mode to meet demands such as safety, flexibility and productivity.
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