Quality Applications

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Controllers Boost Chocolate Production
Rockwell RSView32

Although Cadbury's Crunchie Bar plant is modern, the existing distributed control system (DCS) that was installed in 1981 was becoming outdated, forcing Cadbury to look for a replacement. Cadbury couldn't afford to let consumers switch to a competitor's product while old equipment was being removed and the new control system was being installed. Due to the critical time schedule and the scope of the project, Cadbury looked to Rockwell Automation's, Allen-Bradley and Rockwell Software products and support to get the job done.

 "Although the Ferranti ARGUS DCS had served us well for a number of years, we were starting to have problems with support against a background of increasing downtime and pressure to continue to enhance the automation of the process," says David Williams, a systems engineer at Cadbury. "Added to this, Ferranti had gone out of business, and we had concerns with Year 2000 compatibility. Something needed to be done quickly."

 The original Ferranti system had taken two years to commission and install and cost about $3.4 million. The original software had taken 10 labor-years to develop, and an additional five labor-years had been spent on testing. The old system also had more than 1,000 control devices and a menu of about 100 different operator screens. Due to the system's complexity, maintenance and repair were slow, inhibiting development.

 The demand for Cadbury's Crunchie Bars gave management no choice but to stipulate a very tight project schedule of 10 weeks with a budget of about $1.5 million. The scale of the task was daunting, with more than 3,000 input/output (I/O) points to be replaced.

 The new system is based around four Allen-Bradley PLC5/80C ControlNet programmable controllers. Installed within the same panels, and connected via ControlNet, is the Allen-Bradley 1771 range of I/O points. Although the new system was considerably rationalized, there are still more than 2,500 I/O points. The 1771 range provides signal interfaces to suit AC and DC applications, with a wide range of signal levels, including standard analog inputs and outputs.

 Ethernet and DeviceNet communication modules exchange data with the various other devices. Ethernet provides backbone communications between the programmable logic controllers (PLCs) and computers running Rockwell Software RSView32 human-machine interface (HMI) software. The system also runs Rockwell Software RSTune, a Microsoft Windows-based software package that optimizes PID control loops. Using RSTune, Cadbury is able to analyze, simulate, document and download optimal tuning parameters.

 There are 24 Allen-Bradley 1305 drives located in the electrical panels and connected to the PLCs using DeviceNet. The drives range from 0.37 kW to 7.5 kW, providing reliable and flexible speed control of motors positioned around the plant. With the help of RSView32, the whole Crunchie Bar process is monitored and controlled from a central control room. Two operators work the plant 24 hours a day and are able to monitor the process using RSView32 to show the status of individual stations around the plant. There are also CCTVs positioned at critical points to give immediate warning of manufacturing problems.

 "We started to plan in January although the changeover was not scheduled until November," Williams says. "We were able to use this time to build up stocks of finished product and prepare for the changeover. This included identifying all of the existing cabling and devices and preparing 5,000 cables in looms ready for installation. We were able to save time by running many tasks in parallel--for example, software specification, development and testing. Another benefit provided by RSView32 was the ability to simulate the production process using software, and this was used to train the operators before we went live."

 The new system required more than four tons of cable, and there were 2,500 I/O points to be wired. On the system side, there were 200 operator screens to be configured and 20,000 lines of software to be written--the equivalent of four labor-years of work.

 While the plant was being recommissioned, the production and packaging shifts had to be redeployed to other plants in the factory. The plant was manufacturing product after only four weeks--well within the revised target of six weeks. The running efficiencies that Cadbury was experiencing with the old system were soon exceeded, and many long-standing problems were quickly resolved. Not only were the time schedules met, the project was also completed well within the budget and without any safety incidents.

 "Rockwell Automation is able to supply a wide range of industrial control products as well as software systems, and this total package made a considerable contribution to the success of this project," Williams concludes. "The changeover was not without its problems, and we challenged Rockwell Automation's expertise and support on a number of occasions. Some of the questions we raised were complex, but someone in their organization could always provide an answer. We are continuing to enjoy the benefits of increased production and enhanced reliability provided by the new control system."