AUTOMATION CONCEPTS – CENTRALIZED AND DECENTRALIZED
Automation concepts play an increasingly important role in the modern world aligned with climate protection and flexibility. The decision for one concept or another one depends on the complexity and the necessity of a precise temporal control of processes. Centralized and decentralized automation concepts are however not being separated by a clear line: Every centralized concept also has decentralized components and every decentralized network also features a kind of central control, even if the importance is by far not rated as high as with the central concepts.
What are the Trends?
The trend in general is more likely towards decentralized networks. Our life is also becoming “more decentralized” – we take work home, and are available via smartphone or tablet PC almost always and everywhere and hardly separate privacy and work.
For some time, there has also been the trend towards M-to-M communication. M-to-M stands for Machine-to-Machine communication. This means that even vending machines have their own small mobile phones installed. In this way, the drinks dispenser at the train station can send its concrete filling condition to the supplier companies, then these only come when they have to and no longer in fixed intervals. Thus possibly unnecessary trips can be cut, or the vacantness of vending machines can be prevented.
Even in agriculture, the first centralized and decentralized automation concepts have been developed by now. Precisely speaking, this also includes the milking machine as a well-established classic centralized automation concept, but smarter ways are possible:
The irrigation of fields normally occurs in certain intervals, for example every morning at 6 a.m., again in the early afternoon, and then, as the case may be, again in the evening, at night and so on – however the farmer plans it. By the insertion into the ground of sensors checking the soil composition for certain minerals and moisture, the field irrigation does not have to work inflexible like a clockwork mechanism any more, but complies with the needs of the field. By means of such and similar centralized and decentralized automation concepts, resources can therefore be saved at the right places, and even agricultural yields can be increased.
Centralized and Decentralized Automation Concepts in the Industry
In addition to the building automation in residential buildings, the industry also realized the possibility to increase the efficiency of operation by centralized and decentralized automation concepts. Thereby, the ratio between the expenditure of time and money during production and the finished product should be increased.
The increased complexity of manufacturing processes, as well as the increased importance of precision to the split second and millisecond of certain work steps overtaxes the field bus systems that have been considered as high tech 20 years ago. The developed and most modern networks for centralized and decentralized automation concepts since 2010 are these:
- Sercos III
- Profinet IO
These Ethernet and field bus systems are the current elite class for centralized and decentralized automation concepts. A distinction is been made between the just mentioned categories “fieldbus” and “Ethernet”. However, as the transition between these two automation concepts is almost a hundred per cent transparent by means of Ethernet adapters, a combination of Ethernet and fieldbus is no problem at all.
Centralized and Decentralized Automation Concepts: The Advantages
Because of the steadily increasing pressure of globalisation, more and more companies change to the use of centralized and decentralized automation concepts. The first users of these technologies can possibly hope for advantages in the market from it, soon, however, this high technology will be essential in the severe worldwide competition.
Users can benefit from the following advantages:
Savings through less waste by more precise control of the production processes. Among other things, dosage processes can be carried out more precisely that way.
The central control will be relieved and this saves primary energy. The electricity costs and the costs for CO2 certificates will be reduced by this.
The high flexibility obtained through centralized and decentralized automation concepts also creates the possibility of short-term and medium-term predictability towards the previous planning times. In this way you can reduce goods in stock because you can deal with new orders even better.
That supports the reduction in downtimes.
Furthermore there are advantages for the clients of users of centralized and decentralized control systems:
The quality of the products can be increased extremely, as constant monitoring of the processes spots mistakes faster.
Centralized and Decentralized Automation Concepts: The Maintenance
For many things, the purchase in most cases is less expensive than the long-term costs. For Ethernet and fieldbus systems, it is different:
As the users have demanded simple and, if possible, standard maintenance measures, three large providers have developed three concepts with which the field components and the systems of all manufacturers can be examined and maintained:
- FDI : Field Device Control
- TCI: Tool Calling interface
- ECCL : Electronic Device Description Language
For the future of maintenance, even plans for only one technology regarding the maintenance are under consideration for centralized and decentralized automation concepts.
What are Centralized and Decentralized Automation Concepts?
It should be clarified what is meant by both concepts to provide clarity. The decentralized concept means in detail “distributed intelligence” because many distributed controls take over a big part of the task processing here. Even though such concepts usually permit higher speeds and allow modular machine concepts. For this reason, decentralized automation concepts are often more suitable for machine automation with many drive functions. Just to give one example, POWERLINK is such a system which can be also suitable for centralized solutions. In plain language, this concept means that the main part of the tasks goes to one or a few centralized controls and are being performed there, and only small working parts are being outsourced and assigned to network nodes. The big advantage of such centralized concepts lies in the application to the process industry because plants require a very high degree of automation and can be operated safe and secure by only a few required persons. These are only some nuances in definitions to differentiate between both concepts. Which concept is recommended specifically for which area depends on the required application speed.
Essential Criterion: The Application Speed
The time control of such processes and the determination of this control primarily decide whether a centralized or a decentralized system should and can be used. You can talk about a so-called “degree of hardness” of real-time because principally you can say that with an increase of this degree the control moves away from a centralized structure and to a decentralized structure.
The boundary of both concepts is not clearly drawn and intermingles, because a centralized automation concept also includes decentralized components and vice versa, a decentralized concept also has some centralized features. The differences between the concepts are in the scope of the tasks which have been allocated for control. The decentralized control outsources whole tasks, while in the decentralized structure only smaller “working parts” are mentioned. A decentralized concept consequently relieves the centralized control through this outsourcing to intelligent components. With this, a higher and better communication link of these components with the centralized system it is necessary.
The decision regarding the concepts also depends on which network structures can fulfil the timing demands best and with the least effort. For centralized systems for example, it can be assumed that with high data traffic there is only a moderate demand on the total computer performance and the transmission speed. The real-time therefore represents only a “soft” component, i.e. the period of time between the triggering and the occurrence of the event has a duration between one hundredth and one thousandth second. The requirements are therefore more likely suitable for a centralized automation concept and can be well applied in the process industry. Contrary to this, in the process industry “hard” real-times are also often required. The duration is in the µ-second range, which is why only decentralized concepts are suitable and are being applied for these processes. The advantage of distributed intelligence comes take effect with such complex systems.
Modular Machine Concepts – which Concepts can be applied better?
As processes require a higher flexibility and higher speed at the same time, and as these features only exist partly in centralized systems, this resulted in the development of modular machine concepts. These expand the scope of functions in general by connecting independent components without the need to modify the machine core.
With these, the drive control has to perform a variety of tasks which comprise for example regulation of the speed or calculation of the axis acceleration per phase. These calculations take place at exactly two different places: In the drive itself, which implies that corresponding processing units also exist there, or in the centralized control itself. It is obvious here that a centralized calculation requires a wide bandwidth of the bus and an immense processing power of the centralized control is required. It is also obvious that the data volumes can take on an extreme extent, which has a negative effect on the speed. The calculations would only be done by the master to send the results afterwards to the slave that has to give continuous feedback over the bus about its present condition. This fact results in an increasing susceptibility of the application function.
Having the computing power take place external is nevertheless hardly practicable, which is why the advantages of a decentralized concept are obvious in this application. Faster computing and reaction times exist, as well as a relief of the master is given. This in turn relieves the data traffic of the bus. An easier, modular expandability of the machinery through decentralized concepts is also given, as well as a safe application. To generate all these advantages, a correspondingly good communication connection must exist.