SafetyBUS p applications grow from wood processing

Otto Baier, head of maintenance at Wiesner Hager in Altheim, Austria, describes how his company's SafetyBUS p implementation has developed since it was first installed in April 1999.

SafetyBUS p, the safe, open fieldbus system, was first used in the Wiesner Hage wood processing centre in Austria in April 1999.

Since then, numerous SafetyBUS p applications have been added from the widest range of industries.

SafetyBUS p is based on an event-driven bus procedure: data is only sent when the status changes at the input/output modules or field module.

For this reason, SafetyBUS p is well suited for networking within plants with different signalling rates and high requirements for response time.

It can be used to network a maximum of 64 subscribers with a range of up to 3.5km.

Via the inputs and outputs on the decentralised I/O modules it is possible to poll input devices such as emergency stops or safety gates and also to set actuators such as contactors.

What's more, field modules such as robots or light guards can be connected directly to SafetyBUS p.

Whether the programmable safety system is centralised or decentralised, users view the plant configuration as a process image of inputs and outputs.

It is therefore possible to use all the BG and/or TUV-tested software blocks available for the PSS programmable safety system (such as E-stop, safety gate).

The integration of optoelectronic protection devices such as light curtains into the safe bus system offers the user additional benefits.

These include the transmission of additional diagnostic information, as well as the classic reports on the status of the protected field.

Wiesner Hager's plant in Altheim, Austria, produces glued beams, made up of individual glued boards.

The procedure for creating the glued beams begins by sorting and selecting the wooden boards to be processed.

This ensures that the finished beams contain wood of similar quality.

The sorted boards are then planed, de-stacked and fed through the first saw.

The boards are sawed lengthwise and are then finger-jointed on their end face.

At the next workstation, the individual boards are glued and pressed.

After they have been planed one final time, the finished beams are transported to a temporary storage area.

The potential risk from the production process comes from both the individual processing stations and the transportation between them.

For this reason emergency stop buttons, among other devices, are fitted along the whole length of the plant, enabling the entire plant or sections thereof to be switched off in the case of danger.

Under conventional technology, to ensure that the relevant drive could be switched off via safety relay logic, each and every one of these emergency stop buttons would have to be wired in the local control cabinet and connected to a safety relay there or at the E-stop control point.

On a plant extending up to 300m in length, this would involve a considerable amount of wiring.

This is why the Austrian company decided to use SafetyBUS p.

The whole plant is made up of individual machines from different manufacturers, supplied with ready-wired I/O modules.

The company programmed the safety system itself and also laid the bus cable between the individual plant sections.

Safety-related data is transmitted to the programmable safety system via a single bus cable.

The logic from the original safety relay wiring is reproduced in the user program software.

The plant's safe control technology consists of a PSS SB 3100 programmable safety system and eleven safe, decentralised I/O modules, positioned locally within the relevant control cabinet.

The emergency stop buttons are wired into the I/O modules, as are the local actuators.

In order to guarantee high availability within the plant, each bus subscriber was assigned to its own group.

This way it will not affect the other subscribers, should an error occur.

A PX30 text display is also used for diagnostic purposes.

This plant structure gives the Austrian company the greatest possible flexibility, both in terms of commissioning and operation of the plant.

Two more machines were added to the plant at the end of 2003.

The flexibility of the safe bus system could therefore be put to good use.

Again, safe decentralised I/O modules were integrated into the control cabinets of the new machines.

The new safety functions were easily incorporated into the existing safety concept through connection to the bus system and an extension to the user program.

"By using SafetyBUS p we were able to keep the amount of wiring required for the E-STOP concept to a minimum.

"The flexibility of the safe bus system was clear, not just when we created the E-stop concept but also when we came to extend the plant.

"For our application, SafetyBUS p was the right, forward-looking decision".

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