The dragline’s repositioning is a large component of its operation. This relates to the dragline’s walking sequence, that is, to where the dragline should stand, dig and dump to, and to when and where it moves. A trade-off exists as to whether to remain digging at a particular location or whether to reposition in order to achieve more favourable dig-conditions or swing-angles. Since the dragline’s repositioning requires a major loss of productive cycling- hours, more feasible, dig and swing conditions are essential in order to achieve a higher productivity.
The dragline’s operators or supervisors currently make many repositioning decisions during its operation. This is still very costly in terms of time and operation, although different repositioning strategies and various computer software programs for the comparison of multiple scenarios of the mine plan are available. Feedback to the operator can indicate the ideal time for the relocation of the dragline and can thus enable a large reduction in the cost of repositioning actions.
Previous research has analysed this trade-off by developing a cost function per horizontal bucket-foot of movement. It has also recommended the repositioning of the dragline by the operators if the expected cost of continuing to dig at a certain position exceeds the delay and dig-costs that are associated with a repositioning. This approach doesn’t, however, consider the cost penalties, which are associated with hoist-limited cycles.
An algorithm has been developed in this research for advising the operators on how to improve the dragline dig-sequences. Dragline, repositioning information was analysed after collecting cycle-data over a representative, one-year period. A cost model has been derived from the collected data to monitor the operator performance at each stage of the excavation sequence. Repositioning suggestions and dig-sequence improvements, which are based on the current master mine-plan and operation, can thus be provided using a search, heuristic, optimisation model.
There are benefits of providing this repositioning information and this optimised dig- sequence capability to the dragline operators. The dragline’s utilisation and productivity will be enhanced as a result of making the operators aware of the consequence of non-optimal dig-sequences. A reduction in the dragline’s energy consumption will be a potential consequence of decreasing the incidence of hoist-limited cycles. Its asset life can also be extended since fewer, hoist-limited cycles will minimise boom and gearbox stresses and will also enhance the life of the components.