Real time data used to optimise production control

Using standard control components, a company employs real time production data as probably the most potent tool for optimising control of production processes like assembly and packaging.

Real time production data is probably the most potent tool for optimising control of production processes such as assembly and packaging, and Richard Armstrong of Ritech Systems has developed a low cost system based on standard Mitsubishi control components that brings this ideal within reach of many plant operators' budgets.

The viability of many industrial processes is based on the production of large quantities of the product.

If the manufacturing volumes drop, perhaps due to plant downtime or slow product changeovers the overall margins can be eroded severely.

Excessive product giveaway, reworking and substandard quality can also be equally compromising.

Conversely, a small gain multiplied through the production run can bolster bottom line profits considerably.

It is not uncommon in the food packing industry for instance to reckon that a half-to-one percent improvement in productivity will put thousands of pounds an hour onto the bottom line, giving payback in months rather than years.

Ritech has developed its system from a modest base, as Armstrong recalls: "We were talking to a customer about extracting production data automatically instead of using the conventional paper trail method, when it struck me that as the data would be 'live' there was no reason for waiting until the end of the day to calculate performance.

Further, displaying the information on an immediate basis would highlight production problems easily.

We also started creating hourly Excel reports, initially thinking that this would help us with commissioning, but soon realised that the production managers were diving on the reports as soon as they appeared!" This initial system was based simply on communicating with a pair of weighers at the beginning of a packaging line, and a check weigher at the end using serial comms blocks under the local control of modest Mitsubishi FX1N micro PLCs.

The PLCs in turn were linked together via a CC-Link, to a larger Mitsubishi A1SJ supervisory PLC in the production control office.

The distance from the packaging hall to the production office was considerable, so the CC-Link's twisted pair field bus was an economic choice as well as providing fast and secure data transfer.

CC Link also provides the expandability that will be required to eventually service all the production lines across the factory.

The architecture is such that much of the calculation load is undertaken by the local micro PLCs so that the central A1SJ is free to communicate with a SCADA (supervisory control and data acquisition) system monitoring the whole site.

At this point Armstrong's creativity took over and he started brainstorming with the client for ways to further enhance the system, so that comprehensive data could be collected and used effectively.

One of the first ideas was to use another RS232 communications block to drive a giant LED display above the packaging line, so that the operatives could monitor their own progress.

This shows information such as quantity packed, percentage giveaway, yield and efficiency and had the immediate effect of encouraging the line workers to constantly improve their own productivity.

Data is actually fed to the display in ASCI code which it converts to update the display every 10 seconds.

The LEDs are tricolour, red, amber and green; with the colours cascading as performance tolerances are approached and exceeded.

Another idea was to install a Mitsubishi E910T HMI (human machine interface) at the checkweigher end of the packaging line and to connect it via Ethernet to the office based PC in order to update the latest production information centrally.

When complete, every line will be connected to a central hub and addressed using its own individual TCP/IP address.

Program modifications to the attached micro PLC can also be performed transparently across the Ethernet from the office without disturbing line personnel.

Refinements to the system include a reworking loop for efficient handling of packs and raw materials that are out of tolerance, and the recording of downtime events along with the appropriate report.

The system is very flexible and new ideas can be incorporated and trialled in very short timescales.

The system has been up and run for some weeks now, and significant productivity gains and improvements in asset management and utilisation have been realised - far beyond our original expectations," says Armstrong.

"Our next task is to clone the system onto the 12 parallel lines elsewhere in the company.

"We are also demonstrating the technology to lots of other potential users, some of whom stand to make massive strides in production efficiency as a result of simply installing some basic hardware and state of the art data handling.".

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