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The future of machine control

The future of machine control Back in the early 1970s when PLCs first became accepted as the way to automate a machine or process, very few users would have considered the cost of developing the "logic control" software as part of the overall machine cost. In fact, it is estimated that in 1970, the cost of the man hours to write the machine control code accounted for just 1-2% of the overall cost.

As the capabilities of traditional PLCs have expanded to meet the demands of the OEM machine builders and their end-user customers, such as the inclusion of complex motion control, integrated safety and vision inspection, and data storage and manipulation, so the cost of software developed has also increased proportionally. Even just a decade ago, up to 40% of the cost of any machine was attributable to the cost of its control software development. Today, that figure is likely to be even higher.

Of course, it is not just the complexity of machines that has changed over the years; flexibility and re-configurability often become top priorities for any OEM. The evidence of this is the ever-increasing number of servo axes per machine, automating traditional, manual "change parts" processes, reducing product changeover times and increasing throughput speeds.

To minimise the cost of software development and, indeed, the time taken to create the working solution, reusability of existing code is key, along with the ability for several engineers to work on the same piece of code without the risk of conflict. It must also be structured in such a way that it is understandable for everyone, including those who will have to maintain the system in the future.

'Traditional' methods of one continuous, often uncommented, ladder logic program using meaningless physical I/O addresses are now giving way to symbol-based programming, often using Sequential Flow Chart (SFC) structures to provide a clear picture of how the machine or process operates (understandable by everyone, even non-programmers) and helping to break-down the code into individual tasks and requisite disciplines (mechanical handling, process control, etc), thus facilitating the aforementioned ideal of several developers working on the control software at the same time.

IEC standards (IEC61131-3) have helped to provide some commonality in programming methodologies and go some way to providing familiarity for software developers (or at least a familiar "look and feel" of the programming environment), even between different automation equipment vendors.

In the world of motion control, the PLCopen organisation has provided the standards for a complete set of motion-related software function blocks that work in exactly the same way in the controllers of those companies that implement and comply with them within their programming environment.

This has really positive implications for the re-use of motion control code between different manufacturers; in the past, an OEM faced with having to fit another automation vendor's control system on his machine, maybe as a result of end-user specification, would have been faced with a complete re-write of the control software. Now, it is feasible that much of the code can be re-used and the learning curve of a new supplier's equipment is greatly reduced.

Similarly, the use of software 'libraries', the introduction of non-address specific data structures and arrays, the ability to use in-line Structured Text or "C" code, and the introduction of 'Namespaces' are all greatly helping to reduce the time taken to develop machine control software, and allow it to be easily maintained and enhanced throughout its life cycle.

However, as the complexity, flexibility and openness of this software expands, the hardware platform needs to expand with it and must be equally flexible in its speed to adopt these new ideals.

Traditionally, PLCs have been based around 'ASIC' (Application-specific Integrated Circuit) "chips", designed to run a set of instructions very quickly with great repeatability.

ASIC design is one of the most costly (and time consuming) disciplines for any manufacturer and, once a device has gone into production, it remains the same forever.

The introduction of new features or improvements in performance means a partial or complete ASIC re-design, which is why most PLC models remain exactly the same for a good many years!

It is not just PLCs that employ this technology; motion controllers, safety systems and vision systems are often based on ASICs and, although they may appear to be an integrated part of a PLC or control system, are really disparate items each utilising their own programming packages and often require a great deal of effort to connect them all together in an efficient manner to ensure that data can be passed between them within the necessary time frame.

Our industry has talked of "Soft PLCs" for many years, with semi-industrialised PCs running operating systems that use high-level language code (such as C or VisualBasic) to create the process control. These have brought their own problems; unreliability of hardware, lack of continuity of supply due to ever-changing specifications and performance and frequently "crashing" operating systems, which is why they have not been widely adopted in machine control applications where reliability is paramount.

However, for all the negatives, the Soft PLC offered one big advantage; it was "open"; new functionality could be easily added as the control 'engines' were software-based and not dictated by fixed-form hardware.

Over the last couple of years we have started to see more and more PLC vendors turning towards this more "open" concept.

Omron's recently-introduced Sysmac NJ-series Machine Automation Controllers use an Intel Atom hardware platform running 'QNX' real-time operating system (RTOS) with Omron's own logic, motion and vision software 'engines'.

A global partnership between Intel and Omron ensures consistency and guarantee of supply of industrialised CPUs and the ability for Omron to work with Intel developers on forthcoming technologies.

QNX RTOS is renowned for its reliability and stability, being the OS of choice in many aerospace, telecommunications, industrial and defence system applications. Omron's pedigree in producing ultra-reliable PLCs for over thirty years has been used as the cornerstone for the development of the Sysmac NJ-series, to eliminate the issues associated with semi-industrial Soft PLCs.

Such an open control platform demands open networks to ensure the trouble-free connection of hardware such as servo systems, inverters and I/O, and robust data communication between devices (e.g., PLC to PLC or PLC to PC/HMI). For its Sysmac platform, Omron chose EtherCAT for motion control and EtherNet/IP for data communications, both of which feature as standard on every NJ-series controller.

EtherCAT is widely accepted as being the fastest motion control network on the market and is supported by more manufacturers than any other motion network; Omron's implementation of Distributed Clocks on its EtherCAT devices ensure network synchronicity (or "jitter") of less than one microsecond,  with a network of 16 servos axes being serviced in less than 0.5ms

EtherNet/IP caters for the exchange of large amounts of data between devices at high speed and uses 'tag-based' addressing to expose the names of all I/O points and variables across the network, greatly simplifying programming effort.

Omron's "Sysmac Studio" software brings logic, motion, kinematic and vision control into a single programming environment, resulting in one project file for the entire machine.  EtherCAT network configuration is simply a 'drag and drop' exercise, whilst devices such as servo amplifiers, inverters and vision sensors can be parameterised within the same workspace.

However, perhaps the most exciting feature for the motion aspect of the machine control is the in-built 3D simulation; motion paths can be visualised on-screen to check correct movements and avoid costly mechanical damage on the 'real' machine, while the graphical cam profiler allows the user to create movement relationships between servo axes without resorting to complex mathematics or data tables.
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