Robox AGV and plant simulation: the value of the Digital Twin in design

When it comes to AGVs (Automatic Guided Vehicles), the main question that arises in every plant is how many vehicles are required to meet demand and perform all assigned tasks. Defining this number can be challenging, as many factors may have an impact: from AGV performance, such as speed and acceleration, through to the size of the plant and the characteristics of the traffic routes available. All these data can be assessed in the best possible way through a digital plant simulation, i.e. by emulating the system production times and the AGVs on a computer using the Digital Twin.

Configure virtual AGVs with real parameters

The emulated AGVs can be configured exactly like the real ones by setting the same parameters, including:

• velocità,
• acceleration,
• jerk,
• maximum rotation speed.

In this way, the travel time of the emulated AGVs will reflect that of the real vehicles in the final plant, allowing the cycle time to be calculated.

The digital map of the plant

Another useful element to develop is the plant map, which allows the system operation to be simulated and tested even when the building housing the actual plant is still under construction.

This makes it possible to significantly optimize the program development and debugging times. No on-site surveys are required; a DXF file containing the project to be imported into the RAT (Robox AGV Tool) is sufficient. The RAT is the small CAD tool provided by the Robox environment and allows the map to be designed and drawn with:

• AGV lanes,
• curves,
• workstations.

AGV Manager: fleet management and communications

The map is then loaded into the fleet manager, the Robox AGV Manager.

This tool enables communication with the AGVs and with the plant systems, managing different levels of integration.

AGV Manager enables communication with the AGVs via:

• radio modem with serial connection,
• wireless LAN with TCP/IP protocol,
• wireless LAN with UDP protocol.

Communication with the plant PLCs via:

• RS232 serial interface,
• OPC server,
• Ethernet with send/receive protocol,
• Ethernet with fetch/write protocol,
• generic file reading and writing.

AGV Manager also supports communication with databases, including:

• SQL Server,
• MySQLm
• PostgreSQL,
• ODBC.

Plant logic and mission assignment

The Robox Fleet Manager allows the developer to describe the plant logic and the assignment of missions to the vehicles in text format (x-script), together with the management of input/output signals with the plant PLC.

In addition to all this, the true major advantage of AGV Manager lies in its autonomous navigation management, which requires no intervention by the developer or installer. The manager follows the same logic as the highway code, controlling:

• vehicle priority rules,
• queuing,
• one-way routes,
• traffic lights.

This allows the fleet behavior within the plant to be simulated and managed realistically.

An application case in the textile industry

In 2019, a large company operating in the textile industry commissioned Robox to design an AGV system to manage the loading of finished products from the winding machines and unloading at the storage and warehousing stations. The AGVs used the RP-2 controller to manage their 9 axes and adopted Robox inertial navigation (see Navigation Systems for AGVs).

The designer followed the steps listed above, requiring:

• the drawing of the plant under construction,
• the number of reels that would be produced,
• the different characteristics of the various production lines,
• the rules to be followed for unloading management.

AGV fleet simulation

Once the map had been drawn, the technician started the AGV Manager and set the kinematic parameters of the individual AGV, then instantiated several vehicles of the same type with the same characteristics. In order to correctly simulate the cycle, the various timings were required, including:

• the time required to enable unloading from the winding machines,
• the battery charging time of the vehicles,
• pickup times,
• deposit times.

The simulation with the virtualized AGVs started with a fleet of 20 AGVs.

After the initial tests, it immediately became clear that this number was insufficient; furthermore, some of the one-way routes selected during plant design did not allow good vehicle mobility, forcing the AGVs headed towards the pickup area to take a long detour that was unsustainable in terms of timing.

Map and AGV fleet size optimization

La mappa è stata quindi modificata, cambiando i sensi unici di alcune linee di transito. Anche il numero di AGV è aumentato. Le nuove simulazioni hanno dato esito positivo, dimostrando che 26 veicoli erano sufficienti per gestire tutto l’impianto e sostenere il rateo di produzione.
Considerando la manutenzione ordinaria dei veicoli e gli imprevisti che potrebbero ridurre il numero di AGV realmente operativi, alla fine son stati adottati altri due veicoli, in modo da operare normalmente con una mole lavorativa ottimale senza rischiare di andare in sovraccarico nel caso di uno o anche due veicoli fermi.

Simulation also in the RDE environment

In addition to AGV Manager, simulation is also possible within the RDE (Robox Development Environment), allowing system logic, movements, and interactions to be verified directly during the development phase, without the need for an RP-family controller on the desk: a PC is all that is required.

Since this feature was implemented, it has helped technicians from various users of the Robox system to simulate the axes of their machines in order to predict the behavior of the future real applications. In this way, it is possible to:

• test the cycles,
• debug the programs,
• calculate the plant cycle times.

This feature is useful for every type of user, considering that the Robox system is adopted by companies operating in many sectors, including robotics, packaging and beverage, CNC machines, and laser cutting.

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