“Instantaneous Trucks” vs “TUM Trucks”
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In reality, trucks do not respect the TUM in an instant in time - in any one instant, the truck is either available or unavailable, not a mixture of the two. There’s a probability of whether a truck will be operating at an instant in time in the future (the TUM is the average over an extended period of time). This is the most correct way to think about trucks on an instantaneous basis, and for very short term scheduling. The TUM accounts for but does not explicitly contain, the frequency and duration of downtime events (a cyclone vs a broken bucket tooth).
APS now supports both methods to accommodate either paradigmsupports TUM trucks, and an approximation of instantaneous trucks (with Dispatch mode, explained below).
Truck Hours Calculation
Truck hours are based on the cycle time of the truck (when being loaded by the specific digger), the truck’s payload, the quantity and type of material moved, and the time usage model (TUM) which applies to the truck.
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Note that the way this is done in APS is to rotate through the trucks in a round-robin fashion. Dispatch Enabled: In each step the trucks will be used in the order specified. If in a steady steady state on a single loader a truck is exhausted, it will then go on to the next truck - and will use multiple truck types in the same instant (but it does not use the longer of the two cycle times). Dispatch Disabled: For each movement the loader does, a different truck will be used, thus approximating equal use while only using a single truck for each movement, going through the list in the order the trucks are specified in the Site Lists. In each steady state, the loader will choose a different truck from the previous steady state, thus approximating equal use while only using a single truck for each movement. |
If none of the trucks in the rule can be used anymore (because they have no more truck hours left), the loader will then choose the next rule that applies out of its priority list and use the trucks in that one. In this manner, it’s possible to specify that a loader should prefer to use one type of truck, but once that’s exhausted, start using a lower priority truck.
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The Instant Units is a calculated field that is equal to the number of units entered, multiplied by the PA, UPA, OE, and PF. the PA, UPA, OE, and PF.
Although the Instant Units is the mode of the number of trucks that are expected to be available, the number of trucks that will be available on any day is based on a binomial probability distribution. However, there’s no practical way of using this probability distribution in APS, so we are just using an approximation of the mode (not an integer).
Notably, UA is not included, as the Use of Availability is determined by the schedule. Conceptually, the Instant Units is the exact number of trucks expected to be available for use at any instant over the schedule.
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If UA is specified, it is still possible to run out of hours at the end of each period. Therefore, if Dispatch mode is enabled, it is strongly recommended to set UA to be 100%. |
Fleet Use of Availability
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In each instant, APS will go through the diggers in order and assign trucks to diggers as it goes. If a specific route needs 5.2 trucks to haul at the maximum rate, and only has 2.3 left to assign, the digger will be derated. If there are no trucks available at all, the digger will be shut down.
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Dispatch Deadlocks
While this dispatch logic will work well in most circumstances, there are a few shortcomings. It is possible in some edge cases for APS to choose to do nothing even though if fully trucked it would do something. As an example, consider three diggers, EX1 on 62% Fe, EX2 mining 58% Fe, and EX3 on waste. There is also a strict Fe target of 60% on the crusher.
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To determine whether the schedule is achievable with the truck fleet on site, use the Dispatch mode, and consider the Fleet Use Of Availability (UoAUA) which is reported for each truck in the Calendar. Although many sites have a historical UoAUA, this should not be an input (and is not when Dispatch mode is enabled). There is nothing wrong with varying the UoA UA for the truck fleet each day, provided the objectives of the schedule are met. The reported fleet use of availability gives an indication of how close to the edge the schedule is running. If the UoA UA is at 100% fleet use of availability, then if a truck goes down, the schedule may not be achievable (it still may be if there’s an opportunity to catch up later). If it’s at 50%, half the expected trucks could be inoperable, and the schedule is still achievable.
Note that if UoA UA for your site also includes times like when a truck driver does not show up for work, that should be instead be accounted for in either unplanned availability or one of the other availability fields. APS assumes that UoA UA is historically the percentage of time that the truck could be used, but intentionally wasn’t.
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