Continuous improvements help Alabama cotton gin increase yields
The cotton gin facility owned by Milstead Farm Group Inc. in Shorter, Ala., requires a production process that can run at optimum levels 24 hours a day, six days a week, until all the growing season’s cotton is in bales. When Milstead Farm Group first started processing loose cotton into bales (ginning), it produced 15,000 (500 lb.) bales a year. Their volumes have increased over the years, topping 65,000 bales in 2018.
As a result, production rates have had to increase to achieve those numbers. Increasing production demands required better equipment and more finely tuned process controls, a more powerful programmable logic controller (PLC) and local input/output (I/O) rack at the end of the 2017 ginning season, and installing a new Profinet communications backbone after the 2018 season.
Working against the clock
Because the factory can only run three months out of the year, there’s no question the factory’s primary mission must be to get the maximum yield out of its raw materials. The cotton gin facility owned by Milstead Farm Group requires a production process that can run at optimum levels 24 hours a day, six days a week, until all the growing season’s cotton is in bales.
Cotton ginning facility
When Milstead Farm Group first started ginning, it wasn’t able to produce what it can now. Investing in new equipment and maintaining existing systems has pushed production from 25 bales an hour in 1998 to 50 bales an hour. This has required tighter process controls, PLC and I/O updates, and communications upgrades.
“By investing in these technologies, we’re able to provide our customers with a better return on their crop,” said general manager Joey Scarborough. “One thing we’re seeing at Milstead and across the ginning industry is a large push for more process controls. As gins try to increase capacity to be more efficient, controls often have to be relied on to get it done.
Upgrading the network
The latest network upgrade project had two goals: first was replacing an obsolete PLC on an existing piece of equipment that provides moisture control to the air, which is then fed to the cotton as it moves to the bale press. The second was to provide an interface to a new piece of equipment that was purchased to supplement the moisture unit, which didn’t have sufficient capacity to deal with the increased production output.
Cotton is priced according to several characteristics including moisture content. In addition to providing additional moisture during baling, the facility also uses air dryers to dry the cotton when it comes in from the fields, where it may have been stored for many weeks. Summer droughts, such as the one experienced in 2019, can make achieving the right moisture balance complicated.
David Adams, a system integrator for Design Automated Controls who has worked with Milstead since 2006, was on a tight timeline to complete the project between May and September, before the start of the 2019 ginning season.
“We needed to decide which hardware we would use, determine how much of the I/O needed to be replaced, and how much could be moved to the human-machine interface (HMI) we planned on adding to the machinery we were updating,” he said. “The first step in the project was actually taken at the end of 2017 ginning season, when we proposed replacing the existing PLC and local rack with a PLC and local rack that uses the modules as is. This ensured we would have spare parts available in case of breakdowns.”
“Profinet was added to provide a means to network the two controllers in the plant without adding to the existing Profibus system,” Adams said. “It was also chosen to allow for future upgrades, especially for the five aging HMIs that reside on the Profibus network. As they are replaced by Ethernet-based HMIs in the coming years, they will reside on the Profinet network.”
Seamless step-wise migration
While many machines in the facility are still running with the Profibus protocol, they interface seamlessly with the control system. The new CPU that’s been installed has onboard Profibus and Profinet interfaces, which made installation and commissioning very efficient, and has the memory capacity to support the existing code after conversion. Profinet I/O also replaced the I/O for the controls for an existing piece of equipment
Since Milstead Farm is continuously improving equipment and process controls, Profinet’s ease of expansion and installation, as well as higher data transfer rates, were factors in the switch to the new network. It only required 200 feet of cable to install Profinet to service the new I/O and controller.
“A sideline of this project and the PLC upgrade is to provide more and better troubleshooting tools from the HMIs to assist operators and maintenance personnel,” Adams said. “They need to be producing finished product instead of working on the machines. The in-depth status-of-operation capabilities that will be added to the HMIs will assist them in troubleshooting problems, which will reduce downtime and lead to increased productivity and a lower operating cost.”
Keywords: Profinet, programmable logic controller, Ethernet
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