Protection of safety devices in the packaging industry
ASIsafe is a simple solution that can cover a number of protective devices. "We had to wait quite a long time for what we consider the best solution in terms of distributed automation. But it was worth the wait." Which explains why Christian Dunkel is so happy. Christian works in the electrical department at Jürgens Maschinenbau GmbH & Co. KG in Emsdetten near Münster, and he used the extremely compact Siemens Simatic ET 200SP distributed I/O for the first time in a packaging system for fleece fabrics.
In this project he also decided to use AS-Interface in conjunction with an ASIsafe safety concept for the first time. The reason why this solution is so simple to realize is that the CM AS-i Master ST devices and the F-CM AS-i Safety fail-safe versions are available as modules for the distributed I/O. "It is a perfect combination because it saves space in the control cabinet and gives us lots of advantages in terms of engineering, installation and flexibility in connection with our safety equipment," the specialist reports. "It is really worth having AS-i as a bus under Profibus and Profinet - and AS-i is simpler than we thought."
90 percent time-saving with AS-i
The doors of the packaging system's safety fence used to be safeguarded with mechanical switches connected to the fail-safe controller via conventional direct wiring. "That was laborious, complicated and led to a lot of faults," Dunkel explains. And so it is not surprising that the total amount of engineering work that went into the safety fence up to preliminary commissioning and re-assembly on site took up a lot of time. Many machinery manufacturers are familiar with this scenario and therefore appreciate flexible solutions based on ASIsafe under Profinet for their centralized automation.
"Compared to the conventional wiring we used in the past, we can now achieve a 90-percent time-saving in our cabling work thanks to the AS-i solution," says Christian Dunkel. Previously, simply constructing the installation channels involved a great deal of work. Each control station took up to three hours, but with AS-i this has now been reduced to practically zero thanks to the easy-to-handle insulation piercing method. They also save time by avoiding errors as they do not need any terminals and can always position the profiled yellow cable correctly.
Fast installation of position switch and control station
The packaging system is situated at the end of a several-hundred-meter-long fleece manufacturing system. It includes six protective doors secured by Siemens Sirius 3SE5 position switches with tumblers. In the interests of quick assembly, the safety fence manufacturer supplies an adapter plate, thus providing a further opportunity to save a considerable amount of time. Beside each protective door there is a control station with a fail-safe emergency stop button and three control keys for "Access Request", "Area Acknowledgement" and "Restart". They are connected as spur lines to the AS-i line via AS-i-M12 round connectors. Standard and safety-related signals can then be transmitted through a single two-wire cable. "That makes installation transparent, fast and flexible," summarizes the specialist.
In addition to the time-saving aspect, flexibility is a further major benefit to be gained by using ASIsafe in conjunction with the distributed I/O. That is because it becomes easy to incorporate other safety devices into the safety concept. These may include light curtains on the transport sections or accessible openings like those found on the system described above. Furthermore, by means of hardware contact transfer, the upstream part of the system can be easily integrated into the safety concept of the packaging system through fail-safe input and output modules in the ET 200SP, thus providing yet another easily realizable safety feature.
Fast programming in a program
Instead of using a separate safety controller, those responsible for designing the packaging system opted for a Siemens Simatic S7-300 with a fail-safe F-CPU. "We are following the TIA philosophy with all of its advantages," adds Christian Dunkel. One of these advantages is that Totally Integrated Automation (TIA) can reduce the number of interfaces. The associated time benefit alone is absolutely immense, as the automation expert knows from experience: Depending on the design of the housing on such systems, there are three to five safety areas that can be programmed with the new TIA solution in just one hour.
The expert therefore sees the safety concept and fast configuration of the safety equipment for the safety fence as a major benefit in this packaging system project. Standard and safety equipment are therefore configured centrally in the SIMATIC in STEP 7, thereby significantly reducing the amount of work involved in engineering. Just one engineering software is required for connecting AS-i Master, ASIsafe as well as the digital and analog inputs and outputs, counters for incremental encoders and SSI modules for absolute encoders. Around three hours had to be planned for this work with the previously used separate safety controller, and two to three days would have been realistic using conventional safety equipment with safety relays.
Maintenance benefits thanks to fail-safe PLC
Both standard and fail-safe signals can be processed on the same hardware thanks to the use of the fail-safe controller in conjunction with the distributed I/O. A fail-safe exchange of data with end-to-end diagnostics is able to take place without interfaces from the controller level to the field level thanks to the PROFIsafe connection of the AS-i network. "That is why we can now take a look at or even adjust the safety equipment by remote maintenance if that is what the customer wants," Christian Dunkel happily reports. For example, when the additional safety area was incorrectly shut down at one customer's factory, it was possible to check or readjust the programming via a remote link and the programming error was soon discovered. That could save end-customers in foreign countries two days in terms of time and costs. With a global export share of around 75 percent, that represents an important competitive advantage for this medium-sized company with its staff of around 250.
Drive technology with integrated safety engineering
In addition to the above, around 20 Sinamics S120 converters bring movement to the packaging system, where they bundle huge rolls of fleece into towers, stand them up, turn them and give them a protective covering before they are finally wrapped in protective film ready for shipping. The advantage of these devices is that they integrate fail-safe functions and again require little wiring work compared to alternative solutions. If someone presses the emergency stop button on the system, the Profisafe telegram is activated via Profinet to trigger the safe stop function by means of Safety Torque Off (STO). Taken as a whole, Performance Level PLd is reached according to EN ISO 13849.
A further advantage of ASIsafe: In the packaging system concerned, a simple method was used to program three different areas so that unaffected areas can continue to run in the event of a safety mechanism being triggered. "Here again the consistent, simple architecture of the safety engineering gives us the flexibility that the equipment operator demands." The process engineering for non-woven products demands consistency and it should not come to a halt because of every little interruption that only affects the conveyor belt at the end, for example.
Modular AS-i Master in distributed I/O
The task to be mastered at Jürgens Maschinenbau involved separating individual segments from the mother roll - a wound, four-meter-wide and pre-cut roll of fleece - and packaging them in individual units. A safety fence measuring around 60 meters in length had to be installed for the enclosure, whereby operator protection is ensured by means of light curtains at the openings and by six access doors.
Siemens 3SE5 devices were used as position switches with tumbler; these are connected to the controller via ASIsafe. This simple, quick-to-install safety concept was made possible with the aid of the fail-safe F-CM AS-i Safety ST module, an add-on module to the Simatic ET 200SP distributed I/O. "It is modular and can therefore be installed in different positions on the system, in every junction box, just the way I need it," explains Dunkel. Thanks to the solution's consistency based on the model of Totally Integrated Automation, teleservice right down to field level is also available for the safety equipment.
The future benefits for Jürgens Maschinenbau became immediately apparent upon the initial deployment of ASIsafe in conjunction with this new version of the distributed I/O. The solution described here, whose advantages benefit both the safety engineering and standard automation, can serve as a standardized set-up for the future. That simplifies engineering, installation and global service for the packaging systems, which is a very important aspect in view of the dynamic development in this area of the Emsdetten machinery manufacturer's business.
(Images: Siemens)