Inside Machines: Wireless Ethernet, PLCs add productivity to Blue Bell Creameries
Blue Bell Creameries opened its doors in Brenham, Texas, in 1907. While its automated storage and retrieval system (ASRS) doesn’t date back quite that far, it was beginning to show its age, with 20-year-old components starting to fail and causing significant delays. (ONLINE extra: Four additional images, not in the print or digital edition, appear at the end of this posting, along with useful links.)
Keith Jenkins, project systems designer for Blue Bell, made the case for an upgrade. He replaced five PLCs on each of three ASRS units with one Siemens S7 PLC, and Siemens HMI with a new Siemens Scalance W wireless LAN. The setup is easier for operators to use; Jenkins estimated the company gained more than an hour and a half per crane per day in increased ASRS productivity.
Reliability is required in the harsh Blue Bell warehouse environment where the temperature is a constant -20 degrees F. Jenkins, with 25 years of experience in PLC programming, said Siemens PLCs were “the easiest to program, easiest to negotiate, and the most stable.” Jenkins worked with Siemens distributor AWC Inc.
The PLCs were used to drive the ASRS units, which are large, manned cranes that run on a train track to move pallets of ice cream around the Blue Bell warehouse. Each of the three cranes was outfitted with five PLCs. A pair of “breadboard” PLCs communicated with a back-end warehouse management system—a database containing information on which ice cream is stored in each warehouse location—and communicated with the other PLCs on the crane. The other three PLCs controlled vertical and horizontal crane movements and pallet deposit and pickups.
The PLCs were about 18 to 20 years old, with some running DOS-based programs. The infrared communications system that communicated from the cranes to the warehouse management system server made it difficult to get replacement parts. “If more than one device failed, we could be down days without one of our ASRS units, which would take out one-third of our capacity,” Jenkins said.
Each crane had an interface unit that “looked like a point of sale terminal from 1982,” said Adam Bailey, a senior engineer with Premier Automation, the system integrator on the project (Premier has since been acquired by Tegron). The 6- to 8-inch green CRT screen was difficult to read and operators also had to learn a complex series of keyboard commands to move the ASRS units: F1 to move one way, control/F1 to move another, shift/F1 for yet another, and so on. Precise instructions were mandatory, given the size and scope of the warehouse environment, with cranes running on a track more than 500 feet long with pallets running 7 high and 4 deep—more than 7,000 spaces in all.
“It would take two to three weeks of training to get a new operator going,” Jenkins said.
Blue Bell suffered a major ASRS breakdown every three to four months. “We’d blow a fuse on a power supply or have one of the PLCs or other pieces of equipment go out,” Jenkins said. “It’d take 30 to 45 minutes, sometimes an hour to fix depending on what went wrong.”
For the quote, AWC brought in Premier Automation and Bailey to help with the solution design.
“Blue Bell wanted to have an integrated solution, with all the components from one manufacturer,” Bailey said.
Premier’s proposal included one Siemens Simatic S7-300 PLC on each crane to replace all the existing PLCs along with a Siemens SCD1297 HMI, with a 12-inch color touch screen. The configuration also called for Siemens Scalance Industrial Ethernet Wireless LAN and Simatic ET 200M remote I/O, to replace the existing infrared communications system. The solution was about half the price of the competing proposal, Jenkins said.
For the installation, Jenkins, Bailey, and his team had to work quickly; the Blue Bell warehouse operates more than 18 hours per day, save for a break from Friday night until Sunday afternoon.
“We worked about 20 hours both the first day and the second,” Adams says. After installing and testing the first unit in February 2007, Blue Bell and Premier spent about a month testing and tweaking it. The team used the same procedure to upgrade the second crane in March and the third in April.
Premier integrated the Siemens PLCs with the existing Blue Bell warehouse management system. The system resulted from years of work by Blue Bell to optimize routes around the warehouse to determine the most efficient position for each pallet.
“There was a tremendous amount of knowledge and learning in that database; it had to be kept,” Bailey says.
The warehouse management system ran on a Microsoft Windows-based server in the warehouse offices. With the Siemens WLAN equipment in place, it was simple to establish an Ethernet network connection with the server. Bailey chose a third-party driver allowing the PLC to talk to the Microsoft Windows server. The Siemens S7 programming language eased translation of the warehouse map (text file format), so PLCs could understand it. AWC upgraded the encoders that track the warehouse crane positioning.
ASRS operators found the HMI touch screen simple to use. “You just touch one button and the crane goes where it’s supposed to,” Jenkins said, noting operators can also easily flip from one page to another to see what’s next on the agenda.
Ease of operation saves time in each crane movement, reducing time to input each command from 15 seconds to 5 seconds or less. That adds up to 90 minutes of increased efficiency for each of the three cranes. Over an 18.5-hour day, the total savings is 4.5 hours. Ease of use decreased operator training time from about a week 2 to 3 days, he said.
Other benefits include increased uptime and reliability, Jenkins said. “It’s also cut down on our inventory of spare parts because we no longer have to go out and find used pieces of equipment that we can use for parts,” he says.
Servicing the new equipment is easier. In August 2009, after about a year, Jenkins changed the vertical and horizontal coordinates that the ASRSs use. “It took me about an hour and away we went,” he said. “In my eyes, serviceability was the biggest benefit,” Bailey said; “Reliability has been good, because I haven’t gotten any phone calls.”
More images (mouse over for captions) and additional useful links follow.