Monitoring system improves machine safety

Fitting a modular safety system to a corrugator has enabled a fibreboard packaging manufacturer to improve machine safety and reduce costs and complexity. Dean Palmer reports A manufacturer of fibreboard packaging sheet has improved the safety of its two, 100-metre long corrugator machines by installing a modular safety system with multiple safety interlocks that now provides faster alert signalling and improved monitoring. The company is Mondiboard Coalville based in Leicestershire, which produces fibreboard packaging sheet, mainly for box manufacturing customers and packaging assembly firms. The board is produced from raw paper material and then graded in terms of thickness and strength to suit client requirements and is supplied flat and scored ready for assembly. The board is produced on two 100-metre long corrugator machines, each having 17 safety trip devices including stop switches, emergency push button switches, guard locks, proximity sensors for belt alignment and power overload trips. Both machines have now been converted from a system employing a series of safety relays wired individually to a PLC in a control room, to an Allen Bradley Guardmaster MSR200 modular safety system supplied by EJA. This module wires directly to the safety trip devices on the corrugator and directly to a display in the control room via a simple shielded two-wire connection, an arrangement that eliminates the need for a PLC. The problem with the original PLC-based system was that large amounts of wiring and programming were necessary. This meant any maintenance, changes, upgrades and replacement of parts on the machines was complex and time consuming and so had to be carried out in the company's planned plant shutdown periods. The MSR200 can be updated and added to quickly and easily because of its simplicity. Even the unit's display can be programmed quickly. The 'alert' descriptions and positions on the machine are carried out using a Windows-based software tool downloaded from the Guardmaster website. The maintenance team at Mondiboard are currently planning to replace pad locks on the main machine gate access doors with Guardmaster trapped key interlock systems. Integrating these with the safety system using the MSR200 will be an easy, fast operation, requiring just a simple rail mounted plug-in module and a brief display update using a laptop and an RS232 connection to the display. This means no more wiring, no more PLC programming or lengthy installation times. The system has also improved machine safety. The 'alert' signal is faster and more informative than the previous system and provides information about which safety circuits have been broken. This means faults can be identified and rectified faster, and just as important, the machine itself can be up and running more quickly in the case of false alarms. The MSR200 is a Safety Category 4 (Stop Category 0/1) system that is easily expandable. It enables the required number of safety control outputs to be configured exactly to the specific application using a combination of auto-configuration modules (which require no programming) and simple plug-and-play technology. Pointers * Using a modular safety system eliminates the cost, maintenance and system update problems associated with multiple wiring of safety trip devices to a central controller * The module eliminates the need for PLCs as it wires directly to the safety trip devices on the corrugator and directly to a display in the control room via a shielded two-wire connection * The engineers at Mondiboard plan to replace pad locks on the main machine gate access doors with trapped key interlock systems, then integrating these with the safety system using the MSR200