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Blurring the control boundaries

01 November 2011

To both efficiently and cost-effectively handle the increasing complexity of automation, more users now expect a complete and consistent automation system, together with advanced engineering tools and support from their automation suppliers.

Boundaries that have grown over time between the various control disciplines – CNC, motion control, sequence control, visualisation platform – are starting to disappear. Hardware and engineering costs are being reduced thanks to this integration of systems.

“Traditionally, PLCs were not able to handle motion control and motion controllers were unable to handle logic functions,” said Geoff Janes, Lenze UK automation business development manager. “Furthermore centralised controllers were limited in the fieldbus systems they offered, meaning that customers were restricted to the range of drives, HMIs and peripherals that they could choose.”

Today, however, that is changing. “Now, a modern centralised controller can offer connection to most popular fieldbuses, as well as handling both motion and logic. Although it is not always desirable to have several fieldbus systems on one machine, the controller does make this possible by acting as a gateway. It is now quite common, for example, for the machine pneumatics to be controlled in this way by fieldbus instead of inputs and outputs, offering savings in machine wiring.”

“The real advantages of centralised control, however, only becomes available and practical when the operating software is intuitive and uses common standards such as IEC 61131-3 and CoDeSys,” said Janes. “Lenze software L-force Engineer meets these requirements giving cost-saving benefits right through the machine building process."


Decentralised or central control?
Which architecture works best for a certain automation task is less a question of philosophy than that of the task at hand and the fundamental performance criteria. In many cases, a decentralised topology a good choice for cyclic processes, as these are typically made up of largely autonomous units. Here a good option is to modularise the control system accordingly.

One advantage offered by this approach is being able to test run the modules before they are assembled to form a production line. For units that are not too complex, intelligent drives have been proving themselves for a long time as decentralised control platforms. Today, thanks to ever more powerful processors, these devices can also perform sophisticated control and motion functions, such as positioning or an electronic cam. This allows synchronised motion sequences to be implemented simply and with minimal component costs. However, this architecture often reaches its limits in applications with more than four axes. As such, it is used predominantly in the fields of materials handling or intralogistics.

More complex cases, such as robots, packaging machines and handling systems require a powerful central control system which allows coordinated movements along many axes. In addition to this, a central control system is also capable of taking over the control functions of a linear process. The central architecture offers the advantage to project engineers that they only need to develop and manage one control program. Although this makes the project more extensive, it also becomes more uniform and easier to understand. Commissioning is also simpler, as the control application only needs to be installed and maintained on one device.

PC-based control systems have also now established themselves as hardware platforms in central control architectures. However, one issue is that many applications do not fully exploit the resources of PC-based control systems, which are typically equipped with numerous interfaces and particularly high computing power even in basic form. For cases such as these, a device from Lenze's new L-force Controller 3200 C range can offer an easy to use and cost-effective alternative. The controllers, designed for DIN rail mounting, have been developed specifically for applications that require a central control system.

They are based on a newly developed platform, at the heart of which lies an energy-efficient Intel Atom processor, allowing for space-saving and robust controller construction, as no fans are needed. Also, because the conventional hard disk has been replaced by flash memory and a UPS has been integrated, the devices do not have any rotating parts or batteries and are therefore largely maintenance-free. The integrated, deterministic 48 MHz backplane bus allows modules from the I/O System 1000 to be directly side-mounted to the controller. This works with a time stamp mechanism, making the controller, in connection with fast I/O modules, suitable for the implementation of complete automation systems which require fast measurement and control functions.

The functionality and costs of automation solutions are increasingly being determined by the software employed in this area. Lenze has embedded the controllers in a powerful software environment and further improved handling. This involved a revision of its PLC Designer engineering environment and integration of version 3 of the CoDeSys programming system for PLCs and industrial controllers. In addition to this, the drive and automation specialist also chose to exploit the opportunities offered by the new CoDeSys with its object orientation and plug-in technology to optimise and extend the standard system, as well as secure reliable continuous operation in automation systems. For implementation of motion control, the PLC Designer contains libraries with certified motion modules based on PLCopen Part I and II, as well as functions for implementation of electronic cam groups and a 3D NC or robot control, all integrated at no extra cost.

Conclusion
Flexibility and productivity are becoming increasingly important in production processes. As such, the requirements of automation solutions are also constantly growing. Due to the increasing complexity of automation, integrated complete systems have become more popular in recent years. Lenze offers tailor-made software tools and a uniform, end-to-end system solution that covers everything from electromechanical components, through controlled drives, all the way up to complete automation systems. And users have access to a uniform product portfolio that offers unrestricted freedom in selecting the right control architecture.


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