- August 12, 2011
- Case Study
Cerutti selected EtherNet/IP and Rockwell Automation to automate its flexographic printing machines. The system handles 500 nodes and 13,000 I/O.
Faced with all the obvious management and maintenance difficulties involved in such a complex system, Paolo Di Santo and his co-workers opted to invest in a standardized solution, designed to control each individual machine using a single network; only opting for a second protocol in exceptional cases. This choice was made possible thanks to the steady development of Ethernet, whose spread in the field of telecommunications has encouraged investments in Research & Development, making solutions and expertise available at more competitive prices. Ethernet is now, without doubt, an indispensable protocol, as demonstrated by the fact that, today, almost all the existing devices are capable of communicating through Ethernet. “Certainly,” admits Di Santo, “adopting EtherNet/IP for such large systems was not an easy decision. Partly because we had considerable doubts as to whether this solution would be able to meet all the requirements of automation, especially at such high speeds.” Especially considering that, for printing machines, determinism is a fundamental characteristic.
A winning combination
The close collaborative relationship that Cerutti has built up over the past years with Rockwell Automation made it easier to tackle this challenge. Indeed, the technicians of the American multinational, which includes some of the most prestigious brands in the field of automation, worked closely with Cerutti to design an architecture capable of supporting the exchange of data between the control systems involved in a flexographic system of this kind.
Thanks to the resulting developments, it was possible to operate in real time, thus overcoming all the initial concerns and fears. Obviously, in order to achieve such a result in a piece of equipment with nearly 500 nodes and 13,000 I/Os, it was necessary to use a series of specific tools including a set of sub-networks. 100 managed switches were used for this purpose, and the individual components were connected using Category 5E copper cables. A series of choices made it possible to overcome the problems associated with the lack of determinism, taking advantage of the protocol speed.
“The results of this work,” explains Di Santo, “were the fruit of close collaboration, bringing together the individual experiences and expertise of the various team members. Today, in view of the results achieved in the field, we can honestly say that the EtherNet/IP solution meets the increasing requirements, in the field of industrial communications, for convergence towards a single control network. In addition, Ethernet supports the I/Os, drives and HMI system of the network itself, which can also be shared with the company’s Information Technology resources and connected to the Internet, thus providing the possibility of communication and control on a world scale. Finally, using a single infrastructure, it is possible to reduce the complexity and increase the integration and performance of the system, with a significant impact on costs.”
Results…in black and white
The first large-scale application was carried out on a flexographic machine, used for printing a well-known English newspaper, capable of simultaneously printing up to 192 pages for four fullcolour newspapers – an impressive achievement for a solution that allows variable configurations and features no less than 498 EtherNet/IP nodes. Of course, in order to ensure the required determinism with these figures, it was necessary to subdivide the infrastructure of 34 inter connected Ethernet sub-networks responsible for controlling specific sections of the machine.
In this way, and using 36 Rockwell Automation ControlLogix PLCs, it is now possible to operate with a lower RPI between the controllers than the 15ms requested by the client. This speed, in practice, offers performances comparable with those of a real-time system. Naturally, to prevent any risk of interference from outside and a consequent reduction in performance, Cerutti opted to protect the field network, stopping any unauthorized access. Also for this purpose, the individual controllers were connected using a second, separate Ethernet network which has eight industrial PCs used for HMI functions but which cannot affect the preset time cycles that control the printing operations. The wireless access points used for maintenance can also be connected to this infrastructure.
The idea of developing a shared project was conceived at the 2005 Automation Fair, when the heads of the two companies decided to combine their respective expertise in an ambitious project. This proved to be a winning idea even during the first tests, immediately yielding positive results. “Of course,” confesses Di Santo, “there was some debate as to the best options to choose. In particular, the technicians from the IT sector would have preferred to use cables and connectors that can be used in an office environment, while those of us from the field of automation opted for industrial solutions capable of tolerating aggressive environments such as those in which printing machines operate.
“This operating method allowed us to develop not only the solution selected for the creation of the English machine but also six other machines based exclusively on Ethernet networks, some of which have been exported to China. The creation of such solutions, which are less complex but feature between five and nine controllers, allowed us to gain important experience which was then transferred to larger machines as well.”
The courage to believe in ourselves
“Believing in a complete EtherNet/IP solution,” explains Di Santo, “allowed us to cut down the variety of solutions used in a large machine, which requires a series of specific series of connections with all the components. And this is not all: an EtherNet/IP network not only replaces other solutions, but also noticeably reduces the problems of management and cabling, which often have a significant impact on the cost of the machine.”
Putting its money on such an innovative and untested technique in the field enabled Cerutti to market an extremely high-performing and yet easily managed solution. “We were not put off by the skeptics, even though many technicians, still today, do not believe in using Ethernet as a field network. Given the results we have achieved, we at Cerutti have great belief in protocols such as this one. I must stress, however, that Rockwell Automation provided us with the best possible support during this process, supplying technicians and cutting-edge technologies that other competitors, even three years down the line, still cannot boast.”
The positive results achieved using these solutions are, therefore, an ideal basis for future developments, although Di Santo emphasizes that Cerutti generally works on commission, so it is necessary to understand the market demands, “especially since the next challenges will be noticeably conditioned by the costs of the network infrastructure,” he concludes. “Specifically,” he says, “we are testing out a series of switches which, although they have limited functionality, possess all the characteristics, also in terms of reliability, required by the industrial sector. I am convinced, in any case, that by 2010, all new applications will follow Rockwell Automation’s example and implement an EtherNet/IP network, since the prices will inevitably drop”.
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