When a customer such as Wal-Mart decides to put your cereals on sale next Friday, not only do you deliver the brands that the giant retailer orders on time, but you also deliver them in the packages it wants. Making the cereal is relatively straightforward, given the state of today’s automation. Once Wal-Mart places its order into your enterprise resource planning (ERP) system, the order propagates itself throughout the organization so that purchasing can ensure the raw materials are on hand and production can adjust its batch sizes. The difficult part is finding the capacity to put the last-minute order in the right packages.
If you’re like many manufacturers of consumer goods, you’re still using packaging machines driven by a central shaft and mechanical linkages. Cartoners, for example, that are built this way require as long as six hours to reconfigure to accommodate another kind of cereal box. Consequently, they are cumbersome in the short-lot, high-mix production environment that characterizes manufacturing for consumer markets today.
These and other mechanical packaging machines cause delays in other ways too. Because packaging machines contain a large number of components, not only do producing and assembling them take months, but the quantity of components also increases the potential failure points and the routine maintenance necessary to ensure that all mechanical parts remain in good operating condition. Making matters worse, these designs are unable to exploit the advanced diagnostics and troubleshooting tools available on modern controllers to minimize unscheduled downtime.
Virtual line shafts
As innovative packages continue to grow in importance, and as lot sizes and lead times continue to shrink, captive and contract packagers alike have been discovering that the conventional mechanical design is simply not conducive to the competitive nature of today’s consumer marketplace. “They need to run products faster and more efficiently, and they’re increasingly asking OEMs (original equipment manufacturers) to build intelligent machines with shorter delivery and installation times, at lower costs,” explains Darren Elliott, chief engineer, R. A. Jones & Co. Inc., a Cincinnati-based builder of cartoners and other packaging machines.
To satisfy this need, Elliott and his design team, like their counterparts at other machine builders, have been replacing the mechanical power trains on their machines with virtual line shafts. Rather than relying on the central line shaft for power transmission and timing, they actuate the axes with servo motors, and coordinate their activities with integrated computerized controls. For Jones & Co.’s newest cartoner, the Criterion 2000, the design team specified the Kinetix integrated motion-control system from
Milwaukee-based Rockwell Automation as a standard option. The system actuates the machine’s axes with servo motors, links them with an internal digital Serial Real-time Communication System, or SERCOS, network, and coordinates their activities with ControlLogix controllers.
The result is a modular machine that has 30 percent fewer components, making it not only flexible and fast, but also faster to build and easier to maintain. “The control system has greatly reduced the complexities and problems of previous machines,” adds Elliott. “We’ve been able to shift from around 100 input/output (I/O) points down to about 50, just by streamlining the architecture.” Fewer points, as well as simplified ladder logic and integrated motion and sequential control, reduce programming time by more than a third. Changeovers can take as little as 15 minutes because they often occur at a push of a button, and downtime is low because advanced diagnostics built into the control system accept feedback from the various I/O points and predict or diagnose failure.
Although servo technology has been driving machine tools and other machinery for quite a while now, its reliability and repeatability at faster speeds have improved only recently to the point where it can replace the line shafts in packaging machines. Combined with the controller and internal communications network, the electromechanical actuation creates a kind of virtual line shaft that users can reconfigure by reprogramming the motion.
“Rather than changing a mechanical cam profile, you have the ability to change parameters on the fly,” explains Kenneth Ryan, Ph.D., director of the Manufacturing Automation Research Lab at Alexandria Technical College, in Alexandria, Minn. “You can stop packing one size box and, with very little accumulation, start packing the next size simply by changing the recipe. The recipe is loaded into the machine, and all the servos make the appropriate adjustments—and you keep packaging.”
Computing capacity is a key reason that servo motors and the ability to “program and go” are practical in packaging. Today’s digital signal processors are much faster, smarter and cheaper than their predecessors. Consequently, distributing the processors throughout a machine is not cost prohibitive and builders can deploy the computing capacity necessary for controlling complex motion occurring at high speeds.
“Although velocity control is important in packaging, especially for conveyors, we’re more interested in having servos that can solve position loops relative to some kind of virtual 360-degree master in a certain time,” explains Ryan. “Sometimes you can’t close a torque or velocity loop fast enough for the required accuracy, no matter how fast your network is. So the solution is to put as much of that intelligence in the drive as possible and let the drive close all of these loops between itself and the motors using position information from the controller.”
PACs for Packaging
Another way that builders are exploiting modern computing technology is by fitting their machines with flexible controllers, sometimes called PACs, for Programmable Automation Controllers. These devices combine the reliability and ruggedness of programmable logic controllers (PLCs) with the open systems computing and communications technology found on personal computers (PCs). An advantage of these controllers in packaging is that they perform both logic and motion control. “Traditionally, motion [of a packaging machine] would have been controlled by a stand-alone motion controller that communicated somehow with a stand-alone logic controller,” says Ryan. Integrating the two functions into one unit streamlines internal communications.
PACs also promote open-architecture networking. “Instead of using PLC-based control, you’re using a PC-based control,” says Ryan. “So now you’re capable of controlling a system from a PCI (Peripheral Component Interconnect) communication interface card in a standard PC.” The machines also can talk to the outside world using the Ethernet local area network, the chosen external interface for SERCOS III, which is the latest version of the international communications standard for high-speed deterministic motion-control networks, such as those found in the packaging industry.
Modular Machines
Greater use of automation controllers in packing machines is helping to drive standards for a modular, object-oriented approach to programming. The microprocessors on these controllers have the computing power to process programs composed from function blocks written in the programming languages specified in IEC 61131-3, an open-systems standard for controllers. These function blocks are objects, or stand-alone subroutines packaged to perform a specific task when called by a program.
“A PLC processor has difficulty using many function blocks,” says John Kowal, global marketing manager at Elau Inc., a supplier of packaging automation in Schaumburg, Ill., that uses industrial-grade Pentium microprocessors in its controllers. Moreover, the sequential nature of the ladder-logic programs makes them dependent on earlier sections of code. They, therefore, are inflexible and quite convoluted, which makes inserting, moving, deleting or skipping sections of code difficult.
Programming with function blocks, on the other hand, is mostly a matter of pulling function blocks from the controller’s library and linking them together in the correct order, much as a child would create a toy from Lego blocks. “Eighty percent or more of an application can be programmed with objects in our software library,” says Kowal. “The last 10 percent to 20 percent is just tying them
together.” He notes that his estimates assume that the controller is handling motion control, process logic and information processing on one microprocessor. Although automation controllers can do both motion and logic control, some users prefer to keep motion and logic separate, a choice that will require devoting about 30 percent of the total code to communications between the two control programs.
Nevertheless, the ability to create programs from function blocks has tremendous ramifications. Builders can encode and validate their best practices and package and store them in a library for use in applications that might need them. The ability to use code that is already written and validated shortens the lead-time for delivering new machines and reconfiguring old ones. And because the code comes pre-packaged, programming is much more straightforward than spaghetti-like ladder logic. So the machines are easier to use, update and troubleshoot.
They also are easier to build and update mechanically, because builders often develop their software modules for mechanical modules that they mix and match to construct their machines. By being able to design each type of mechanism only once and produce it in quantity, builders lower their costs by amortizing their development and production costs over many more machines. Moreover, having access to a mechanism that has already been designed and perhaps is already sitting on the shelf can save a tremendous amount of time. The design effort involves connecting the modules and creating any necessary tooling for the job.
The microprocessors in automation controllers, or PACs, also can link the machine to the outside world through the Ethernet ports and other communications protocols now standard on PCs. The hardened real-time operating system (not Windows) running on the Pentium microprocessors in Elau’s machines, for example, can package information about the machines in a standard format and upload it over the local area network to the databases used by management software. Doing that with a PLC is much more difficult. “Systems integrators say that 60 percent of the work is finding information in the PLC,” says Kowal.
Avoiding work
Controllers that can comply with IEC standards—as well as the draft ISA 88 Part 5 series batch standard being proposed by the Instrumentation, Systems and Automation Society (ISA), in Research Triangle Park, N.C.—avoid that extra work. Moreover, they encourage users to connect their packaging operations to their manufacturing execution systems (MES) and other management software and schedule packaging as automatically as they do production.
“Imagine a day when you can just push a button for an order to be sent to the process and propagate all the way down to the packaging line,” says Mike Wagner, OEM business development manager at Rockwell Automation, in Milwaukee.
Such a system then could schedule as much as the in-house packaging operation can handle. If its MES and enterprise resource planning (ERP) systems speak the same language as the software at its pool of sub-contractors, the software would be able to check the available capacity among those contractors, take bids from them, and award an order to one or more to handle the rest of the job. In such a scenario, flexible packaging machines with virtual line shafts and links to the company’s network will have no problem accommodating those last-minute orders from Wal-Mart and other customers.
For more information please search on keywords “packaging” and “flexible” at www.automationworld.com.
