How does an AGV know, when and where it should drive?
It needs a “Pick up from A, bring to B” transport order.
The vehicle receives this transport order from the AGV Interface Controller (AIC), which also selects the most suitable vehicle in the fleet for the corresponding order. This is comparable to a dispatcher in a taxi center who selects a free taxi near the pick-up location and sends it to the passenger.
Create a transport order
You can create transport orders in many different ways, from simple and manual to fully automated. In the figure above, several of these possibilities are shown.
- Call button: The transport robots can be requested and sent to a destination simply by pressing a button. This easy form of transport control is a good solution, when operators work at stations and want to have finished assemblies or finished parts transported to a limited amount of destinations, e.g. warehouse, quality control or shipping.
- Operating panel: An operating panel considerably increases the number of available destinations. The transfer stations can be represented by a selection button or by a visual item. The target selection is done manually.
- Detection sensors: With this solution, sensors are installed at the points where loads get collected for transport. These sensors then detect when a load is dropped at this point and the system automatically generates the transport order for the AIC.
- Bar code scanner: This solution can be used both manually and automatically. Here, all important information about a pending transport order is communicated to the AIC via a barcode. This barcode can be scanned automatically at specific points or manually by an employee.
- ERP/MES: By communicating with a customer’s production or order control system, the transport orders can also be transmitted to the AIC fully automatically. An interface is used to report the material requirements of machines or the arrival of products directly to the AIC after completion.
As a supplier of complete solutions, InSystems Automation delivers all the solutions described above. Below you will find more information about how the entire communication system works in the practice and how exactly the AIC operates.
Interfaces to receive transport orders
The AIC is the interface to the environment that generates the transport requests. It provides a Web interface (API) as a standard interface. In addition, InSystems Automation also offers connections via customer-specific interfaces. Previously implemented examples of this are:
- Customer-specific protocols via TCP/IP
- Communication via Modbus or Profibus
- Communication via OPC
Transport order data
Essential components of a transport request are the source and destination of the transport. You can use any name that uniquely identifies the various transportation elements. The only condition is that the destinations with the same name are stored in the map of the navigation system.
In addition to these mandatory fields, the following data can also be transferred:
- SU number: Number of the load carrier. If the vehicles are equipped with bar code scanners, a bar code can be scanned on the load carrier to check whether the correct transport unit was picked up by the AGV.
- SU type: Type of load carrier. If several models of transport vehicles are used in the application, the load carrier to be transported can be specified here (for example, pallets or KLT containers).
- Deadline: Time by which the shipment must be delivered.
- Earliest pickup time: Earliest time from which the load can be picked up.
- Production order: not used by AIC, but may be relevant for visualization or for the host system.
- Material number: not used by AIC, but may be relevant for visualization or for the host system.
Distribution of the transport orders to the available transport vehicles
The AIC lists the received transport orders in an internal database. Periodically, the AIC tries to distribute the transfer orders with the status “replanned” to the available vehicles.
Various planning algorithms can be useful for this. These are explained below:
- FIFO (First In First Out): the orders are processed in the sequence in which they were created.
- FIFO with priorities: as above, but some orders can get higher priorities.
- Maximum throughput: the vehicles next take the order whose source is closest to their current position.
- After deadline: each transport is delivered with a deadline. The transport with the next deadline is always executed.
The development of a dispatching and planning algorithm is the main focus of our work in the research project CrESt.