Inductive Sensors Reliably Detect Position of AGVs

A smooth material flow is essential for efficient production. Small, autonomous transport vehicles (automated guided vehicles, or AGVs) are increasingly being used to distribute the parts needed at different locations within a plant. The components they transport are usually on metal trolleys. When a trolley must be moved, an AGV loads, transports, and unloads it. Driving, loading, and unloading take place automatically. Errors during pickup can become a safety risk and slow down the material flow.

Material trolleys can only be lifted when positioned correctly. They must be securely positioned on AGVs during transport. Trolleys that tilt or slip can become hazards on their own or because of falling material. Since they are equipped with their own transport rollers, the trolleys can also roll away and collide with people, other AGVs, and sensitive plant parts. In addition to the risk of injury, this can also lead to far-reaching disruptions in the production process. Such errors must be reliably prevented.

Inductive safety sensors ensure that material trolleys are correctly positioned on AGVs. They detect the presence of the trolleys and check the position of the lift. When an AGV drives the loading platform under a trolley, the incorporated sensor only detects the trolley when it is in a safe position above the platform. A corresponding switching signal triggers the lifting process. The material trolley can be brought right up to the sensor; one of the trolley’s metal struts serves as target. 

The loading platform lifts the metal trolley high enough so that its wheels no longer touch the ground. Two M12 sensors, mounted one above the other, determine the position of the platform. The lower sensor emits a switching signal when the platform is in the lower starting position. This signal only allows loading and unloading. The upper sensor indicates if the platform has reached the raised driving position. The loaded AGV can only drive off when the platform is in the correct position. The target is integrated into the platform.

The compact sensors can be easily integrated into AGVs. Since they have no dead band, no minimum distance to the target must be maintained. There is no need for time-consuming adjustment during assembly. Standard metal actuators are sufficient, so no coded targets are required. The sensors can be easily and directly connected to existing safety controllers via an OSSD interface. With regard to functional safety, the sensors comply with SIL 2 and PL d in accordance with the Machinery Directive and are certified accordingly. They can also achieve SIL 3/PLe in redundant design. The high safety characteristic values allow longer operating intervals.

• Compact cubic and cylindrical designs (M12, M18, M30); flush and non-flush mounting
• Cylindrical sensors with extended temperature range, E1 approval, and stainless steel models available
• Applications up to Cat. 2, PL d/SIL 2 possible (can be used redundantly up to Cat. 3, PL e/SIL 3)

• Reliable detection of material trolley position
• Space-saving design for easy integration into AGVs
• No dead band, no minimum distance between sensor and target
• Extended test cycles due to high safety characteristics