Stacker Crane from Klinkhammer: 

Moving safely through the aisles

Safety technology from Bihl+Wiedemann not only enables conveyor lines to be safely controlled and monitored up to SIL3/PLe, but also storage and retrieval machines (SRMs) in automated high-bay warehouses.

Together with Klinkhammer, Bihl+Wiedemann implemented the safety technology for a 2-ton, approximately 8 meter high stacker crane for containers, moving through an aisle on a rail and using a load handling device (LHD) to automatically load and unload shelves to the right and left at different heights.

For (safe) communication between the control cabinet outside the active area of the S/RM and the stacker crane itself two ASi-5/ASi-3 PROFINET gateways with integrated safety monitor are used. Both gateways are connected to each other via Safe Link from Bihl+Wiedemann. Safe Link can be transmitted over standard Ethernet or the fieldbus. This way, no additional wiring is necessary for the safety communication, and the gateway can be expanded locally over AS-Interface with additional safe and standard I/Os. For the area between the barrier and the S/RM, i.e. where no hardwired communication is possible, a data light barrier is used. With this data light barrier, the Safe Link data and the non-safe signals can be stably transmitted optically over a distance of up to 120 m. A safety gateway monitors the stationary safety technology and makes data available to the gateway on the stacker crane via Safe Link, with the gateway itself controlling the safety technology of the S/RM.

For safe position and motion monitoring of the S/RM, which accelerates at 3.5 m/s²  and reaches a speed of 6 m/s, an ASi Speed Monitor (BWU2849) from Bihl+Wiedemann is used. In addition to the position of the S/RM the device, together with the gateway, also monitors additional safety requirements: depending on the operating mode, these can be speed, acceleration and braking ramps, rotation direction, standstill as well as safe end positions. For diagnostic and control purposes these data are sent non-safe over the fieldbus to the control. 

The LHD on the S/RM can remove materials from the high-bay or place them there and hand over materials at the aisle entrance to the conveyor belt for further transport or remove them for storage. To ensure that the throughput of goods is as high as possible, it is essential that the S/RM accelerates and decelerates as quickly as possible. However, the mechanical buffers at the beginning and at the end of the aisle can only absorb part of the maximum kinetic energy of the stacker crane. Therefore, the speed at the edge areas must be safely monitored and reduced at the right time. Ideally, this is achieved using monitored brake ramps, which can also be safely evaluated by the Speed Monitor. If the acceleration or braking behavior is not correct, the safety technology also intervenes here and ensures that the S/RM comes to a safe stop. 

In contrast to the travel path within the aisle, which must be safely monitored because a person may be present, safe monitoring of the stroke is not necessary for a container S/RM system, since only boxes are transported on the LHD. The situation is different for a palletized S/RM system, where a person can also travel upwards in a cabin. However, using the safety solution from Bihl+Wiedemann, this can also be implemented with relatively little effort by simply using a second Speed Monitor for the stroke.

Read the full article here.

More information: Bihl+Wiedemann, AS-Interface