A manufacturing execution system is helping to improve consistency of quality of paintwork on massive 40 tonne earth moving machinery, by recording critical metrics from the production process to provide detailed traceability.
ITT Contracts was tasked with automating the plant, which consisted of three combined spray booth and curing ovens. There were also requirements to interface the control system to the existing IT network, to allow access to production data for quality control and development purposes, to monitor and control energy consumption and to design in capacity for future expansion.
Despite all of this the budget was tight and an elegantly simple solution was required so that the planned interfacing and expansion could proceed without undue difficulty.
Ian Hatch, the project leader, first considered a SCADA (supervisory control and data acquisition) but quickly rejected the idea because it would be too expensive to interface to the IT networks as access to the data was required across the entire site’s PC network. He could also see that expanding such a system at a later date would be very expensive.
“I knew that Mitsubishi was launching some exciting new control kit and invited their Steve Thornton to float a few ideas at me,” he says.
Mitsubishi’s new Q series programmable automation controller (PAC) certainly offered considerable potential, and the two engineers started sketching out possible control system architectures with Q as the backbone.
Q is based on dual CPUs, power supplies and bases. It combines ‘out of the box’ system building using standard components with customisation by simple parameter setting. The Q has a level of simplicity normally expected of smaller PLCs combined with the power and flexibility of many very sophisticated control technologies.
It is configured for total data tracking and extensive physical redundancy so that ultra high system availability can be guaranteed. This is complemented by the ease of use provided by a powerful engineering environment that Mitsubishi has created around the Q concept.
Thornton explains further: "Q is in fact a technology platform that builds on the power of the core PAC with a range of control modules which interface directly with business information systems to deliver true top-to-bottom plant and enterprise control.
“Modularised manufacturing execution system (MES) hardware allows control engineers to configure complete bespoke systems in a very simple way. Modules are available that provide interfaces to business systems, thus allowing simple integration with enterprise management systems.”
This adaptable and powerful control platform enabled Thornton and the ITT engineers to take a strategic approach to automation and control of the paint shop, giving full integration of all business functions.
There are fives stages in the painting process: washing, preparation, spraying, baking, and combined decal application and final checking. These are carried out by a relatively large number of operatives working over several shifts.
Each operator was assigned a unique code number and logs onto the system at each stage of the process. The system also logs various parameters in the first three production stages.
For the fourth stage it records the gas usage and temperature at six different points in each of the ovens every minute and also controls four variable speed fans for each oven to provide rapid temperature control whilst also optimising energy use.
Yet more information is collected and archived in the final stage, so that a complete record is created for every body going through the paint shop.
All this information is collated and made available to the business systems via a simple web interface, from where it can be analysed and viewed in user-friendly MicroSoft formats such as Excel spreadsheets and PDF files.
“Earth moving vehicles have a hard working life,” explains Hatch. The system was developed to alert key personnel of issues that can affect the quality of the finish via email by constantly monitoring production variables. “The whole idea is to give them a rugged paint job, but we have to be realistic and accept that occasionally the paint fails in the field. If a problem occurs, we can go back to the production database and pull out the precise details of the affected part(s) and also check the other parts in that batch”.
“Given that the vehicle cost upwards of £250,000, we need to offer the best possible customer care packages to their users. The new control system is enabling us to take this to a new level.”
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