In smart factories, the flow of goods is fully automated. This means that material for production is made available in prepared containers on staging areas, also known as "supermarkets". Material requirement notifications are sent digitally directly from the production area. Automated guided vehicles (AGVs) are used to supply the robot cells with the required parts and to collect the processed components. The automated processes at these transfer stations, where AGVs interact with robot cells, must be designed to be both safe and efficient. This can only be achieved with reliable safety solutions: AGVs pass through the hazardous areas without the robot cells interrupting their work, and people must not be allowed to enter these areas unnoticed at any time. This is why Leuze has developed an innovative safety concept that is tailored to such transfer stations in smart production environments. The approach is based on dynamic adaptation of the protective field around the AGV during material transfer.

Automated material transfer between AGVs and robots requires a holistic view of the safety functions at the transfer stations. Relevant in this context are the entry of the AGV into the station, reaching the transfer position and the exit. The AGVs themselves are secured by their integrated sensors. And the robot cells in turn use sensors to detect whether a person is approaching the dangerous work area. However, for automated material transfer between AGVs and robots, the different control units of the systems involved in the process (robot cell, AGV and material flow control) must be able to communicate with each other. They must be coordinated in such a way that safety and reliability are guaranteed throughout the entire cycle. This can only be achieved through close coordination with the specialist departments involved. In addition to the (plant) planners, logistics managers and occupational safety officers, the IT department also makes a significant contribution to success in this phase.

Requirements for fully automatic handovers

Traditional approaches often work with light curtains to safeguard access to the transfer area between the AGV and the robot cell. Although this is technically feasible, the possibilities are limited: The presence of people within the transfer area cannot be monitored automatically. In order to separate people from the danger zone, these classic concepts require additional protective measures - such as mechanical separating elements like fences or grids. A fully automated, safe transfer between AGVs and robot cells without physical barriers is more efficient. A reliable distinction must be made between people and AGVs. The following requirements apply to this approach:

- The danger zone of the AGV transfer station must be secured during the entire process.

- Fixed AGVs should be able to enter and leave the work area axially (optionally also radially) fully automatically.

- Persons or deviations from the defined AGV contour must be detected at all times and trigger a safe stop signal.

AGVs enclosed by protective fields

The solution developed by Leuze for safeguarding robot / AGV transfer stations ensures two safety functions:

- stopping the dangerous movement of the robot cell

- the dynamic adaptation of safety fields around the AGV

Leuze uses safety laser scanners to safeguard the entire area of the transfer station. These use protective fields to detect access and the presence of people in the transfer area. If this is the case, the system triggers a stop signal. At the same time, the position of the AGV in the monitored area is detected at all times. To prevent the AGV itself from triggering a stop signal, the safety program hides its outline from the protected area. The protective field therefore adapts dynamically around the moving AGV. To do this, the laser scanners switch their preconfigured protective fields step by step.

The AGV, which is "enclosed" by protective fields, can therefore automatically enter the station, transfer the material at the parking position and then leave the station again. The safety level is maintained throughout the entire cycle. The advantage: the rest of the environment is covered at all times by the remaining protective field - providing all-round protection. In principle, only the AGV contours defined in advance in the system are able to pass through the protective field. To detect tampering or scanner misalignment, Leuze uses the spirit level function integrated in the device and additional external reference contours.

Axial or radial entry possible

Only a few components are required for the safety solution: these include two safety laser scanners from the RSL 400 series, which are characterized by their performance, robustness and ease of use. With their long range of 8.25 meters, they can even monitor large areas. The solution is completed by a safety program from Leuze and the Siemens Simatic S7 system controller. The optimum positioning of the RSL400 laser scanners in the application depends on various factors.

The following must be taken into account:

- Application layout and any constructive shading

- AGV specifications (e.g. dimensions)

- Entry and exit positions of the AGVs in the protective field area

- Travel paths and speed of the AGVs in the protective field (axial and/or radial)

Depending on this, diagonal or linear positioning of the laser scanners around the protective field is preferable. In special cases (such as corner layouts with shadowing by the building or cell structure), the system network can also be operated with more than two laser scanners.

Easy to implement

Only a few specifications need to be observed for this intelligent type of protection, such as the minimum width of the AGV and the maximum travel speed in the protective field. The route accuracy of the AGV should also be around 50 millimetres. In addition, there must be sufficient space in front of the hazardous area to be able to move the AGV within it and to be able to implement a sufficiently large scanner protective field (required minimum distance to the hazard from all access sides).

To initiate an AGV entry or passage, the AGV control system of the material flow control system must first register its route with the safety solution. Depending on the risk assessment of the application, it may also be necessary to stop the AGV in the event of a protective field violation in addition to stopping the robot cell. This requires safe communication between the cell and the AGV.

Flexibility in transport material

This concept for safeguarding robot/ AGV transfer stations provides plant operators with a cost-effective solution that offers seamless safety throughout the entire cycle. It meets Performance Level d in accordance with ISO 13849-1 and SILCL 2 in accordance with IEC 62061, reliably minimizing the risk of accidents. The safety solution works autonomously once the AGV has been registered by the AGV control system.

And it offers maximum flexibility: there are no restrictions when transporting parts. The safety system and the protective fields are based on the outline of the AGV and not on the material being transported on it. Even parts protruding at the front or side are transported reliably. The integration also eliminates the need for mechanical safeguards such as fences or grids. This saves valuable space in production.

From the risk assessment to the result

If you want to implement this concept for your automated system, you need an experienced partner at your side. It is important that the entire process is accompanied by the security technology provider. In this way, a tailor-made solution can be developed and implemented. The first step is the risk assessment: the hazards (e.g. in the area of the robot) must be clearly defined. It must also be known how quickly the robot cell stops. On this basis, the size of the protective field and the time sequences can be determined.

Leuze is the right partner for these steps. The employees assess the situation on site, coordinate the requirements and develop a safety concept. Once the components have been installed, Leuze provides support with the associated documentation, sensor parameterization and commissioning. Final validation of the application is also part of the service portfolio. Last but not least, CE conformity provides legal certainty. Innovative material logistics systems can thus be implemented without compromise.