Computer controlled truck dispatching systems is a newly-developed
technical system in surface mines with shovel-truck technology. The real
time dispatching criteria, as the core of optimal truck dispatching
software, are analysed and a new criterion, complex dispatching criterion,
is put forward. Dispatching criteria previously proposed include: 1. `Earliest Loading' (EL) - to assign a truck to the shovel at which
the truck can be loaded earliest. 2. `Max Truck' (MT) - to assign a truck to the shovel at which the
truck will have the shortest waiting time. 3. `Max Shovel' (MS) - to assign a truck to the shovel which has
been waiting for the longest time. 4. `Minimum Saturation Degree' (MSD) - to assign a truck to the
shovel at the branch where the truck flow saturation degree is
minimum. 5. `Minimum Saturation Degree with Truck Cycle time consideration'
(MSDTC) - as the MSD principle, with the truck travel cycle also
considered. 6. `Fixed Dispatching' (FIX) - to assign trucks to fixed shovels. A system simulation model has been set up for truck dispatching
system analysis. A few surface coal mines have been selected for case
studies. Equipment waiting times and shift production of the system are
obtained as the main outputs of the model. Simulation results show that each dispatching criterion has its own
applicable range, no one can absolutely dominate the others. For example,
when under-trucked, EL and MT criterion can obtain higher production
than the MS criterion; when over-trucked, it is vice versa; while for MSD
criteria, better results can be obtained no matter how the truck numbers
fluctuate. From the view point of shovel output balance, large
fluctuations occur for EL and MT criteria, while a good balance can be
obtained for other criteria. In the light of dynamic change of mining system conditions, a single
dispatching criterion is not necessarily reasonable. A complex dispatching
criterion has been put forward to seek the complex optimum effect.
Taking the advantage of each dispatching criteria, the dispatching result
of a complex dispatching criterion dominates over individual dispatching
criterion and a comprehensive optimum effect can be reached.