Stacker crane from Klinkhammer: MOVING SAFELY THROUGH THE AISLES

According to Alexander Ruhmann, responsible for electronic design at Klinkhammer, an essential consideration in choosing Bihl+Wiedemann was the fact that the ASi gateways (ASi master and fieldbus connection in one stainless steel housing), in contrast to the devices from other manufacturers, were early to include a display, making them significantly more maintenance- friendly.

And the safety technology, even for larger material handling applications, is ideally implemented using ASi Safety according to A. Ruhmann, since it is often the case that only the data from simple sensors needs to be collected but from widely different locations in the field. “Light barriers, here and there a safety light curtain, every few meters an E-STOP button, perhaps a protective door or two – ASi Safety is simply perfect for this, especially in the field of material handling”.

Based on the positive experiences, the company has made over the past few years with ASi and ASi Safety solutions, as well as the possibilities that these offer, Klinkhammer decided for the first time on the safety technology of a stacker crane (S/RM) for an automated high-bay warehouse with a safety solution from Bihl+Wiedemann.

In designing an approximately 2-ton and approximately 8 meter high stacker crane for containers, moving through an aisle on a rail at a speed of up to 6 m/s and using a load handling device (LHD) to automatically load and unload shelves to the left and right of the aisle at different heights, the following requirements had to be met:

• The safety concept had to meet the requirements of the new EN 528 for storage and retrieval cranes
• Safe communication between the inside (the S/RM on the rail) and the outside (the control cabinet in front of the safe area at the aisle entrance and the non-travelling buffers) had to be possible to implement 
• The safety solutions should function without expensive sliding contacts and without the use of an additional safety control
• Safe position and motion monitoring had to be ensured within the aisle
• Safe position and motion monitoring should be implemented using a barcode positioning system
• The safety technology should be capable of being processed locally on the S/RM
• Communication between the S/RM and control cabinet should be via data light barrier - The position of the S/RM must be known by the control unambiguously and at all times

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 (BWU3863) are used. Both gateways are connected to each other via Safe Link, the safe coupling technology from Bihl+Wiedemann.

Safe Link can be transmitted over standard Ethernet or the fieldbus. 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.

The second ASi-5/ASi-3 PROFINET Safety Gateway monitors the stationary safety technology. These data are made available to the second 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 stacker crane the ASi Speed Monitor, together with the gateway, also monitors additional safety requirements specified in EN 528. 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 nonsafe over the fieldbus to the control.

The load handling device (LHD) on the stacker crane can remove materials from a defined location in the high-bay or precisely place them in that same location. In addition it can hand over materials removed at the aisle entrance to the conveyor belt for further transport or remove them from the belt for storage. To ensure that the throughput of goods in the high-bay warehouse is as high as possible, it is essential that the S/RM accelerates and also decelerates again 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 (‘X-direction’), which must be safely monitored because, for example, in manual operation or commissioning mode an operator may be present in the aisle, safe monitoring of the stroke (‘Y-direction’) 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, which is usually much larger and where a person can also travel upwards in a cabin. In this case, the lift also needs to be monitored in terms of safety. What at first glance sounds like a significantly more complex application can, on closer inspection, be implemented with relatively little effort using the safety solution from Bihl+Wiedeman by simply using a second ASi Speed Monitor for the ‘Y direction’ in addition to the Speed Monitor for the aisle.

Whether in material handling or in storage and retrieval machines – the ASi and (ASi Safety) solutions from Bihl+Wiedemann have proven and established themselves in many safe and non-safe applications. And if Alexander Ruhmann has anything to say about it, this will not change in the future – on the contrary, existing and new products as well as further technological developments still offer great potential.