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Eliminating the ghosts in the machine
Machinery safety design in high-speed corrugated cardboard production is particularly challenging because a machine can be more than 100 metres long and made up of complex, modular elements that must integrate many levels of safety protection.
Board24, a leading producer of corrugated packaging, sheet board and boxes, is committed to maintaining the exceptional health and safety record at its production facilities in Preston, Lancashire. So, when the company made an £7.5m investment in a new corrugating machine, it also took on the challenge of updating the safety systems on its existing machinery to be best-in-class.
As a result, Board24 has achieved an exemplary integrated safety system for its Mitsubishi corrugator with a design developed by industry-specialist systems integrator JKSP and enabled with Sick Flexi safety controllers and software. JKSP was able to deliver a safety upgrade that achieved Board24’s objectives. These included compliance with the latest UK and European safety standards, and a cost-effective, streamlined implementation of integrated safety circuits and wiring. The solution offered increased machine availability by eliminating non-safety-related E-stops, and improved fault-finding and diagnostics.
“Board24 is committed to the highest standards of health and safety for our workforce,” says Lee Bullen, corrugated services manager of Board24. “Investment in new machinery prompted us to undertake a safety audit according to PUWER98 and as a result we identified an opportunity to upgrade the safety system on the existing machine to bring it right up to date with current standards.” Installed in 1995, the 120m-long Mitsubishi corrugator has a line speed of up to 300m a minute and a maximum sheet width of 2.5 metres. The machine is capable of manufacturing corrugated sheet with up to seven different flute types – either as a single wall sheet with three layers, or a double wall sheet with five layers, trimmed, cut to size and stacked, with each order completed to individual customer specifications.
Corrugating machine processes
The corrugating machine comprises a ‘wet end’ and a ‘dry end’ process during which the paper is fluted, laminated, glued, cut and stacked. The different machine processes include preheaters to aid the gluing process; steam-heaters for curing the glue; shear, slitter and knife cutting processes; mill roll stands and traction sections which maintain the correct line speed and tension on the papers and board for productivity and safety. PLCs are positioned locally with a separate low voltage panel room situated on the floor above the machine, where all the main drives are sited which completes the line.
Dr Martin Kidman, Sick (UK) safety specialist, explains: “The key challenge facing JKSP and Board24 was that the machine had only basic zone E-stops with local safety switching which was standard technology in 1995 for such a long corrugating machine with so many different sections. JKSP have designed the system to bring it up to date and, in the process, have also upgraded the safety circuits to be more robust, improved productivity through safety and increased the diagnostics capabilities of the system.”
Bullen added: “An important problem that we needed to fix as part of the system upgrade was the amount of production time being lost through use of the emergency stop for non-safety reasons. The corrugator line operatives used to press the E-stops for incidents that were not emergencies, for example to deal with a breakage or misfeed.
“It might happen that someone would hit an E-stop on a Sunday run. Then, maintenance would come in on Monday and spend many hours trying to find the E-stop that had been activated, while the line remained down. We had a word for it: we called it a ‘ghost stop’. We would need to spend a lot of time going around the machine opening and closing gates to try to reset the system. Even when the operator in the control room would confirm the E-stop had been deactivated, it was often not possible to identify which switch had stopped the machine.”
Board24 turned to JKSP, a Warrington-based systems integrator with specialist knowledge of installing safety systems for packaging and corrugating machinery all over the UK, and briefed them to improve their safety system to meet current safety regulations. As designed by JKSP, the function of the new safety system is to control all safety devices and actuators within the corrugator zone. The layout has been designed to deliver the full capability of the corrugator, while offering the highest levels of safety to ensure protection to operators in the event of a hazard occurring.
Ellis Brown, electrical design engineer, JKSP, explains: “A key requirement was to have a global emergency stop. As the safety system spans over a great distance, it also required zoning for non-emergency stops. This is organised as a global stop loop and stop loops for each zone. A major benefit of the global emergency stop system is that it gives the operators of the ‘wet end’ and ‘dry end’ the ability to hit an emergency stop at one end of the corrugator knowing that it will disable the other end also.
“Global emergency stop pushbuttons positioned at strategic points along the machine act as a total system stop. Each zone has local safety and the information needs to be shared between zones. This creates a global network so, if an E-stop pushbutton was pressed on zone 1, then every zone would react by operating full system safety shutdowns.”
Kidman explains: “To upgrade the line safety required the utilisation of Sick Flexi Soft. Flexi Soft is the Sick family of machinery safety controllers including Flexi Loop, Flexi Link and Flexi Line multi-switch and multi-station options for fully-automated central control. “All Flexi Soft systems share a safe global process image, so information about the safety status can be exchanged between Flexi Soft stations to a safety level of PLe/SIL3. Essential to such advanced installations is Flexi Soft’s versatile communications capability allowing connection to all common networks. The Flexi Soft PLC is configured using the associated software Flexi Soft Designer, which can be downloaded free of charge from the Sick website.”
The Sick Flexi Soft system made design, installation, diagnostics and commissioning of a complex system easier and quicker. Brown continues: “We were looking for a networked safety solution that offered communication both between and across safety zones. Sick Flexi Line and Flexi Loop delivered both of these, where other manufacturers could only offer one or other. So, we were able to complete a fully compliant update of the whole line and use zoning to create spans of control.”
Sick Flexi Loop
The Sick Flexi Loop is a fully open system and allows a designer to connect any safety system in series with another without any compromise of the safety system performance. With a capacity to cascade up to 32 safety sensors or switches on one loop and to create up to eight separate loops, Sick Flexi Loop will provide up to 256 sensors on eight dual channel inputs, reducing the clutter of traditional connections.
The operating range allows each Flexi Loop to be up to 960m and the distance between Flexi Loop modules 30m apart. Each Flexi Loop module assures PLe/SIL3 as long as the sensor can fulfil the same level, and makes calculating complex SIL or PL parameters easy.
Sick Flexi Line enables up to 32 Flexi Soft stations to be easily connected via twisted pair cable allowing a virtual safe process image to be linked to all zones. This enables the simple status communication of safety parameters such as global E-stop, global reset and zonal stop, both between the individual zones of the machine safety HMIs, and with the master control panel in the LV panel room that contains all of the large drives, whilst allowing local Flexi Soft systems to deal with local safety control.
Connecting stations in this way offers a very simple, cost-effective method of connecting E-stop information between different parts of machines to high safety levels (PLe/SIL3). It also allows easy implementation of span control using function block logic rather than complicated wiring.
With the previous safety system, Board24 had experienced excessive downtime to deal with E-stops that were not safety related. The E-stop pushbuttons positioned at key points in the machine are now clearly understood by operators to be used for personnel safety reasons only and not to deal with production errors. To avoid misuse in future, JKSP also took advantage of the ability within Sick Flexi Loop to add auxiliary circuits and developed a ‘fast stop’ system, as a non-safe machine stop condition for production issues such as machine jams and threading/spooling. For example, across the single facer 1, pushbuttons are provided as a fast stop procedure for the main drive to shut down, if a paper jamming problem occurs.
The Flexi Soft gateways enable diagnostic information to be displayed on local HMIs identifying which safety device has been pressed. HMI viewpoints local to the production line aid rapid location of the cause of stoppages. In this way, time spent checking an entire line or zone for an unidentified fault is saved, so there is less production downtime.
“If someone does hit an E-Stop and then walks away from it, the action is on an HMI indicating which one’s been hit,” adds Bullen. “Then the operator can easily identify the cause of the stop and reset it, rather than having to go around the whole machine checking all of the emergency stop buttons.”
Sick Flexi Line demonstrated particular benefits in the upstairs LV panel room where all the main drive motors are located. Without Flexi Line, it would have been necessary to run 20 cables through the room wall and a large cable entry would have needed to be constructed. Instead, the Flexi Line installation required just one Flexi Line cable and one Profinet cable, to carry all the control, diagnostics and feedback information.
For operating the threading up process at the wet end, JKSP have also added Safe Speed Monitoring to PLe/SIL 3 using two Sick DFS60 encoders. The encoders guarantee the safety-limited speed of the corrugators in accordance with EN ISO 61800-5-2. Sick also provided full training to JKSP to enable them to implement the system.
In consultation with Board24 and Sick, JKSP devised a safety zoning plan with different spans of control for the global and local safety functions so that the machine can run more safely and efficiently. This design and implementation of the zoning plan was made simple using Sick’s wide range of products:
Bullen says: “At Board24, E-stop testing has always been done historically by a guy with a clipboard. To complete the register he has to test all the E-stops: start the machine and stop it, over and again. It was long process to test the full corrugators. To start and reset every type of safe stop can take about 8 hours. It was a monthly maintenance task meaning Saturday or Sunday work while the machine is not in production, often undertaken while trying to fit in other jobs.
Brown adds: “Our next step is to look at a further development on the HMI that can automatically output a record of when and where E-stops have been pressed so that any patterns can be spotted for possible action.”
Bullen concludes: “JKSP’s knowledge of the Sick safety system was fantastic. In fact, we depended on it, as E-stop systems, zoning and legislation have to be implemented correctly. When added to their thorough knowledge of corrugators, it meant were able to carry out the full installation for us, allowing our production and maintenance teams to concentrate on our job of manufacturing quality products to our customers.”
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