The Discontinuous Unloading AC consists of two interacting participants - a rock crusher and hauling machine. Goal of this AC is to position the hauling machine in a suitable way to the rock crusher to then unload the hauling machine’s truck-bed. To support an autonomous, decentralized discontinuous unloading process, the following Use Cases describe the required machine communication between the two participants for queueing, positioning, loading procedures and parameter sharing and are depicted in Figure 1.
This UC starts once the hauling machine indicates to the rock crusher, that it intends to start the Application Case Loading by calling the RequestForUnloading-Method. In case the rock crusher signals the hauling machine, that it can also start the Application Case Loading, it reads the current payload of the hauling machine.
Next, the Queueing and Positioning Use Cases for this Application Case take place, please refer to Chapter 4.2.2 and Chapter 4.2.3 respectively. After this, the hauling machine should be positioned so that it can unload into the rock crusher.
The unloading procedure can now start. By calling the StartUnloading-Method, the rock crusher indicates to the hauling machine, that it can start unloading its truck-bed. At any point in time, the rock crusher can inform the hauling machine to stop unloading using the StopLoading-Method. This could be, for example, due to an internal error within the rock crusher.
Once the unloading procedure has finished, the rock crusher requests the hauling machine to leave the unloading spot. A graphical representation of the UC is depicted in Figure 2.
The Queueing UC is part of the Unloading Use Case. Therefore, it takes place after the rock crusher has read the current payload of the hauling machine. As there could be multiple hauling machines queueing up for one or more rock crushers, this UC determines the queueing position of the hauling machines. Thereby, the rock crusher assigns a QueuePriority-Number to each hauling machine. The hauling machines can determine their respective queue position accordingly. Once the QueuePriority of a hauling machine is set to 1 this Use Case ends and the Positioning Use Case starts. A sequence diagram of this UC interaction is shown in Figure 3.
The Use Case Positioning starts as soon as the hauling machine has been assigned a QueuePriority (see Chapter 4.2.2) of 1. The hauling machine shall then position itself in front of the rock crusher so that it can start unloading its truck-bed in the next process step.
First, the hauling machine waits for the rock crusher to trigger its StartPositioning-Method, indicating, that the hauling machine can now start the positioning procedure. If the hauling machine is not yet ready to start the procedure, the rock crusher may trigger the StartPositioning -Method again after a short period of time. In case the hauling machine is ready to start the positioning procedure, the hauling machine reads the area from the rock crusher, it is not permitted to enter while positioning itself. After having received this information, the hauling machine can compute its trajectories and start the positioning procedure.
In case the rock crusher has an internal error during the loading procedure, it can always inform the truck to stop its positioning using the StopPositioning-Method. In case the hauling machine has successfully positioned itself, it can inform the rock crusher by calling the PositioningComplete-Method. A sequence diagram of this UC interaction is shown in Figure 4.
The ParameterSubscription UC allows any mobile machine to request meta-information, such as AssetId or DeviceClass of another mobile machine. As mobile mining machines, such as a hydraulic excavator or a dump truck, typically roam around freely, it becomes necessary, in the context of an autonomous, decentralized operation, for machines to inform each other about their current location and device type. Using the variables described in this UC, this information can be requested or subscribed. A sequence diagram of this UC is depicted in Figure 5.