Profibus is being used by CSi for its customised flexible palletisers, enabling assembly operations to be simplified and time saved, plus the need for cabinet space is reduced.
CSi is a mechanical engineering company based in Raamsdonksveer, the Netherlands, that specialises in designing, producing, supplying and implementing fully integrated logistic systems for materials handling and product distribution. Palletisers are incorporated in many of the company's projects, and these are generally constructed from standard modules. A 'Machine Control Concept' is used to integrate Profibus communications, soft PLCs, mechanics, hardware and software to create customised mechatronic systems.
Large-scale users of production systems today are demanding greater flexibility as a result of the continual reduction in life of products and their packaging. An additional need is for tracking and tracing - ie the ability to identify the complete supply chain for a product on a retailer's shelf, and the ability to identify the destination of all products manufactured at a given time and date. Consequently, the complexity and scope of the data processing is such that it requires the use of industrial PCs and soft PLCs.
All these requirements render the construction of traditional tailor-made systems extremely costly. Mark van de Klundert, CSi's Research and Development Manager, explains how his company is able to build tailor-made systems for an acceptable cost: "In fact this is possible only by virtue of the use of a modular system; this enables us to manufacture a standard product that possesses a high degree of flexibility. Moreover, we can achieve more rapid production times on the basis of proven technology."
The standardisation process also applies to the control of complex lines. For CSi, the construction and installation of a control system is now merely a question of 'plug and play'. "The control of the units has now become so simple that training of the operators is no longer required - and that is inclusive of operator adjustments to the settings and the routings."
An additional benefit offered by the modular design is the opportunity it provides to convert or expand the entire palletiser without the need for complex programming work.
According to Mark van de Klundert, the advance of fieldbus and remote I/O technology is now an unstoppable trend. "At present some 25 per cent of the new units are equipped with fieldbuses. Within five years the proportion will have increased to 75 per cent."
Most importantly, all I/O points on CSi's Machine Control Concept make use of Profibus, which results in cabling being reduced to a minimum. All sensors and actuators are connected with plugs, so the production staff can assemble the plug-and-play system without the assistance of electricians.
"We achieve our time savings by virtue of the fact that everything is right first time; without banks of terminals, it is impossible to make an incorrect connection", says Mark van de Klundert. The safety controls are also incorporated in the control concept in accordance with category 3 of EN 954-1.
A second trend is the shift from PLCs to soft PLCs installed on an industrial PC. CSi adopted the universal IEC 61131-3 programming language for its Machine Control Concept, as a result of which systems from different suppliers are now virtually compatible with each other. "The great benefit offered by the 61131 is the combination of old and new languages, integrated in one standard. It enables programmers to switch readily from old to new language, and vice versa."
Moreover Mark van de Klundert is of the opinion that it is an extremely powerful programming language. In particular, it has enabled CSi to continue offering customers state-of-the-art features such as graphical interfaces and links to modems, an intranet or the internet. IEC 61131-3 provides for the I/O and the machine's functions, and Visual Basic takes care of the graphical interfaces. In CSi's new concept these interfaces are linked to each other in real-time via OCX/ADS (OLE Control Extension and Alternate Data Stream, a function of Microsoft's NTFS file system that enables files to be embedded in other files and remain invisible to the user through Windows Explorer).
CSi's approach is a good example of the continually increasing integration of industrial automation and ICT (information and communications technology). Mark van de Klundert explains: "For us integration involves the combination of the Visual Basic software, the IEC 61131 software, the TwinCat Soft PLC platform, the IPC hardware, the standard control cabinet, the standard plug-and-play Profibus cabling, and the complete mechanics into one system."
Both the Scada software and the control system run on the industrial PC. CSi has developed software for a Human Machine Interface (HMI) in Visual Basic, known as the Eagle 2000+ system. This interface encompasses graphical information for the operator, an edit module and a maintenance program. Thanks to the intuitive user interface, the machines can be operated without training. All instructions are displayed in a logical manner, and online help is always available.
In addition, a maintenance program maintains records of the hours of operation, warns when maintenance is required, and logs malfunctions. This software can be linked to the internet or other forms of communications so as to automatically transmit a message to an external maintenance department or service provider in the event of maintenance being required. The maintenance fitter can also refer to all manuals, such as for the servo systems, on line; these are either stored locally on the IPC or accessed via hyperlinks.
The standard control platform consists of a Beckhoff industrial PC, together with one or more 12 MB Profibus loops and, on request, an RS 422 interface for a barcode reader. All systems make use of a standard touchscreen interface. The standardisation also extends to the control cabinet; all models have a cabinet of the same dimensions and with the same layout. The contents consist of a standard IPC configuration and 24 and 400 V power supplies. Cabinet space is provided for standard servos for the motion control systems. CSi has found that the use of Profibus results in a considerably smaller and much less complex cabinet that can readily be drawn using AutoCAD.
The use of soft PLCs in an industrial PC offers virtually unlimited space for the program and data. Moreover, the response time of a soft PLC is much shorter than that of an 'ordinary' PLC - and the cycle time is always of the same length. According to Industrial Automation Link, in Haarlem, this is one of the great benefits offered by a soft PLC such as TwinCat that works with real-time multi-tasking.
A conventional PLC scans all the I/O in each cycle and, depending, on the load, adjusts the cycle time. Therefore the cycle time can steadily increase - and will almost certainly do so while the PLC is communicating - which will have a detrimental affect on the machine functions. However, Beckhoff's TwinCat can carry out these tasks simultaneously and, in terms of the load, independently from each other. The consequence for the control system is that each task is guaranteed to be carried out within the specified scan time.
CSi makes use of scan times of between 2 to 5 milliseconds, which would be virtually impossible with conventional PLCs. Two channels (scan rates) are available for scanning, as a result of which the scan time for some elements of the processes can be reduced even further. An additional benefit offered by TwinCat is the ability to program the soft PLC without any additional equipment; programming can simply be performed directly on the screen.
But without a doubt, Profibus is the crucial element that enables CSi to create cost-effective customised palletisers that deliver the flexibility, ease of use and ease of maintenance demanded by its customers today.