PACKING PORK is no picnic. Despite adding automation where practical and appropriate in recent decades, meat processing and packing still involves a tremendous amount of repetitive manual labor. So, as is the case with most chores, any assistance and respite is extremely welcome.
Providing some added relief and efficiency was the basic mission the developers, engineers, and machine builders at the Cryovac food packaging division of Sealed Air began a three-year project to reinvent its bag-dispensing machine for food processors. These users typically are packaging fresh, red meat, usually large cuts of pork, which often are shipped to locations such as restaurants for further processing. As the product comes through the line, operators cut it, bag it, and vacuum seal it.
Cryovac makes a variety of bags used in packing houses. However, one of the main problems had been that the meat packers boxes of pre-printed bags often had to be switched as different products were processed. Consequently, the packers wanted a bagger with print capability, so they wouldnt have to change rolls as frequently. On-machine printing also would allow them to add date and time stamps, as well as more-specific product-grade information. The U.S. Department of Agriculture (USDA) requires increasingly more detailed documentation and better traceability from many food and beverage manufacturers.
|FIGURE 1: PRINTING AND DISPENSING|
Cryovacs BL135 Smart Rack Roll serrated bag printer and dispenser has in-line, thermal transfer capabilities, and is designed to work with manual loading systems.
Papas Brand New Bag
Launched about a year ago, BL135 Smart Rack roll serrated bag dispenser provides the plant-floor printing that Cryovacs customers were seeking (See Figure 1). BL135 prints up to a 2x4-in. monochrome graphic image on bags, which means it can add required date codes and other text directly onto the bags. Each printer typically can produce as many as 15 different labels.
A human-machine interface displays the packers fixed label before printing, which allows the operator to make sure the proper label will be dispensed, says Workman. This means a lot less wasted bag inventory, but it also gives users a lot more flexibility. We now can print a different label on every bag if necessary. This is the first machine we know of that can do on-the-fly changes.
Networking Aids Expandability
Not content with merely adding printing functions to one machine, Cryovac next sought to organize its bag dispensers into modular head units that could be linked and expanded as needed by particular packers. Each unit would have one printer and one-sized roll of bags, and could then be combined into a machine with up to four total units, allowing up to four different bag sizes (See Figure 2 below).
These units originally were designed to operate with discrete I/O and point-to-point wiring, but that meant we couldnt combine them into an expanded machine, explains Workman. To accomplish this expansion, we evaluated using a fieldbus such as DeviceNet. We looked at having PLCs with their software programs run the four dispensers, but we found that we couldnt physically connect our I/O to it. We found that EtherNet/IP was able to make this system easily expandable.
|FIGURE 2: COMBINING UNITS|
Cryovac can combine up to four printer/dispenser units, which allows packers to choose up to four different bag sizes.
Once they settled on EtherNet/IP, Cryovacs engineers chose an Allen-Bradley FlexLogix processor to run it. This made it simple to add on units without extra programming, because we had the remote I/O on Ethernet, says Workman. For example, if we already had a machine with two or three dispensers on it, we could simply add another because the overall system would already have all the remote I/O in it to accept that fourth device.
Even though theyd decided to go with EtherNet/IP, Workman says Cryovacs builders also knew theyd need tougher wire and connectors than those typically used with Ethernet. Regular RJ45 wasnt robust enough, wasnt shielded enough, and didnt have the good connections that BL135 was going to need in our customers facilities, says Workman. For instance, while we were developing BL135, we once used a 1-ft., Cat 5, Ethernet patch cable, but it wasnt able to withstand the vibrations--its connections didnt hold, and eventually the machine communications were affected.
|FIGURE 3: ETHERNET CABLING|
BL135s unit use Ethernet/IP and an Allen-Bradley FlexLogix processor, communicating via Lumbergs EtherMate Ethernet cable.
BL135s main panel runs two dispensers, says Workman. There is one man PLC, and then remote I/O points and stepper drives that communicate via Ethernet. These drives run the dispenser, set the dip rollers, and spit out the bags. The printers controllers are tied to Ethernet too. We even have an Ethernet modem in our panels, so we can that dial in and examine our units remotely. In fact, I just did some remote troubleshooting work two weeks ago for one of our customers in Brazil.
Workman says all of BL135s components are coordinated and work well together. Its like the machine has its own little virtual private network (VPN), he states. We havent had any communication problems. We did have some concerns at the beginning, but EtherNet/IP has worked out very well for us.
How to Compare DeviceNet and EtherNet/IP
Heres a brief comparison of DeviceNet and EtherNet/IP. ODVA says its two network protocols are complimentary technologies, and that they dont compete with each other.
- DeviceNet puts simple devices on a network to replace hardwiring; provide device diagnostics; and control, configure, and collect data.
- EtherNet/IP ties to plant management systems (materials and planning); controls, configures, and collects data on one high-speed network; and networks time-critical applications that don't require a user-established schedule.
Typical Devices on the Network
- DeviceNet handles processors/adapters; valves, pushbuttons, sensors, and motor starters; and also simple drives.
- EtherNet/IP manages computers, processors, HMIs, I/O, and adapters.
- DeviceNet covers a single work area or machine; has limited distance due to its controller area network (CAN)-based architecture and chipset speed and power design; and allows multiple networks to feed into and communicate across a common backbone.
- EtherNet/IP can cover an entire plant using routers, bridges and switches; allows connections between plants via high-speed data lines and satellites; but non-manufacturing networks need to be separated to eliminate unnecessary traffic.
- DeviceNet has a low perceived cost due to CAN chip costs, and its actual costs also are low.
- EtherNet/IP has low perceived costs due to commercial components; actual costs may be relatively high, however, due to point-to-point architecture and switch costs
Parts Needed to Build a Network
- DeviceNet requires a main network cable, in flat or round media, to carry power and signal (four-wire); allows devices to hang directly on the wire or be attached to a drop cable; has connectors available in open and sealed designs; and distributes power supplies on the network based on the number of devices and power requirements.
- EtherNet/IP requires a 10-Mbaud bus configuration, including thick or thin cable in star topology; accepts commercially available routers, bridges, switches and other elements; supports 100 Mbaud configured in a star topology; and requires switches for control applications.