Protection field switching of rail-guided transport trolley for rolls of paper independent of position and direction using DME5000.
For a rail-mounted truck that travels in two directions, a precise and robust system was sought for switching between and activating the protective fields of two safety laser scanners mounted on the truck.
Two SICK DME5000 laser distance measurement systems mounted on the truck are used. When the truck is moving, the two sensors continuously measure (redundantly in the related direction) the time taken by the light pulses emitted to travel to the end of the track and back. From this information the electronics determine the position of the truck and provide this information to the truck’s PLC over Profibus. The data are processed in the PLC and the related binary signals generated. These signals are used for protective field switching on the laser scanners.
The proximity switches originally used for the protective field switching did not last long, as the switching lugs for the proximity switches were bonded to the floor and were frequently damaged by the fork lift trucks in the building. The DME5000 + PLC solution has proven to be extremely reliable in comparison. Furthermore, the measurement accuracy is extraordinarily high at +/- 2 mm with a reproducibility of 0.5 mm. A current measured value is output every millisecond – it is hardly possible to measure distances more precisely in such applications.