Real-time data messaging and displays aid detergent packing
Real-time data can't aid users if they can't see it. Based on this simple logic, engineers and technicians at Unilever Home and Personal Care (Cartersville, Ga.) recently developed a low-cost, flexible, real-time message display that presents status and efficiency of the plant's eight dry laundry detergent packing lines.
Real-time data can't aid users if they can't see it. Based on this simple logic, engineers and technicians at Unilever Home and Personal Care (Cartersville, Ga.) recently developed a low-cost, flexible, real-time message display that presents status and efficiency of the plant's eight dry laundry detergent packing lines. Requested by the packing department's self-directed production team, the new display system's message boards present variable data—not more than 1 sec old—to help operators improve plant productivity.
The plant produces and packs all of Unilever's dry laundry detergents, including its Wisk, All, and Surf consumer brands. Carton sizes range from 18 to 150 washer loads. Previously, the packing team overseeing the eight lines couldn't determine from observation how efficiently the lines were performing minute-to-minute. Without hard, real-time numbers, it was difficult to balance resources among lines to make sure each met its shift goals. Line efficiency was only calculated weekly from marginally accurate, hand-kept records.
To access PLC data for the messaging system, Unilever's packing team began by calculating real-time production data from coil statuses and register values in the lines' eight Modicon PLCs from Schneider Electric's Automation Business (North Andover, Mass.).
The team subsequently developed a messaging system architecture that uses the plant's Ethernet TCP/IP IT LAN and Modicon Modbus Plus control LAN. New hardware required was a recently introduced Modbus Plus Ethernet bridge to link the IT and control networks, eight 4 x 4-ft message boards from Display Solutions Inc. (Kennesaw, Ga.), and a Microsoft Windows NT Pentium II display server. Essentially a host that collects PLC data and drives the message boards, this server is programmed with Visual Basic to poll the PLCs every 1/8 NNNsec for coil statuses indicating on/off information, and every 1 sec for register values, such as carton counts.
Maximum throughput on the Ethernet LAN, including new display-related traffic, is less than 20% of capacity. However, the LAN is heavily loaded and efforts are underway to move existing packing line HMI-to-PLC traffic onto dedicated Modbus Plus segments. Polled requests from the display server to the PLCs and the resulting replies, pass through the Modbus Plus Ethernet bridge, a small, diskless PC loaded with bridging software. The bridge also contains a power supply and can access nearly all PLC functions.
Raw data gathered by the display server is converted into readable values, which are sent to the message boards over one serial link without repeaters. Though serial links are typically restricted to 50 ft, the Unilever plant's furthest board is 587 ft from the server. This long run was accomplished by transmitting at 9.6 kbit/sec and minimizing interference by specifying Category 5 cabling enclosed in dedicated steel conduit.
Display and benefits
Unilever's team chose message boards, rather than PC monitors, because the boards can be viewed at a distance, alerting operators more quickly about packing line progress and problems. Real-time data displayed on the boards include:
Product code being packed;
Scheduled carton total for the product run;
Carton count for the run;
Scheduled carton total for the 12-hour shift in progress;
Carton count for the shift;
Line efficiency (as a percent of maximum theoretical output for the shift);
Line uptime/downtime for the shift; and
Number of line stops for that shift.
In addition, a real-time overpack total has been added to the packing line HMIs and will soon be transferred to the message boards.
Since installing its display system, the packing department's output and efficiency have increased substantially. For example, no packing line in the plant's nine-year history had ever run for more than an hour or two without a stop. With help from the display system, one line has already reached 7.5 hours. The improvement is a result of better line management, while maintaining the plant's safety record. Some packing team members are even competing informally for awards based on improved efficiency.
As a result, several other Unilever departments, such as scheduling, production, shipping/receiving, and traffic, have asked how to obtain information from PLCs in the packing line and in other departments. The plant's other PCs are being programmed to allow a browser to request PLC data from either the display server or from the PLCs directly.
Felix Perruci, P.E., senior plant controls engineer, and Michael Smith, senior business systems analyst, Unilever Home & Personal Care—USA, Cartersville, Ga.