Machine Control Thinks Inside of the Box

July 1, 2004
Logic and motion control, human-machine interaction, diagnostics—even intelligence—in a single device is today’s machine control. Examples from packaging machinery manufacturers reveal the new directions of machine control.

Like most technologies, machine control has had its twists and turns over its life time. But it has rotated from historically simple, and large, systems to today’s small multi-function systems that integrate machine and motion control and communications in one package.

In the beginning were first-generation machines for packaging applications. Dubbed Gen1, these machines are simple and purely mechanical. One motor turns a line shaft to which motions are cammed. For control, programmable logic controllers (PLCs), also simple, are typically the operator’s only connection to the machine. For the most part, human-machine interface (HMI) technology is absent.

Then came Gen2. Birthed a decade ago, this technology still has main drive shafts, but is more complicated because of servo motors slaved to speed commands for specific activities, and more complex PLC demands. Yes, Gen2 allows more adjustable machines, but that benefit came with higher costs. Those include more wiring, much input/output (I/O) for PLCs—which were large and complex—more sensors and more programming, even more peripherals. Also, there is more difficulty in troubleshooting.

Mechatronics

Now Gen3 machines are available. Gen3 embodies the concepts of so-called “mechatronics”—using servos and simple mechanics—to execute complex motion. Not surprisingly, vendors pursue the design goal of cheaper, faster and better machines having smaller footprints. “If you can make that machine, you’ve got a winner,” says Tom Jensen, senior technical evangelist at Schaumburg, Ill.-based Elau Inc.

With Gen3’s arrival about four years ago, the focus shifted to developing single-box control technologies having ladder logic, PLC functionality and I/O and, where possible, HMI and even fieldbus, Ethernet and Web Services communications capabilities for enterprise connectivity. Gen2 needs an encoder and programmable limit switch (PLS) to ascertain a servo’s position, explains Jensen. Now, because of Gen 3’s I/O, servo control exists in one processor, which senses when the servo is in position and then sends a signal via a fieldbus to start whatever process is required, he notes. Also, “SERCOS (serial real-time communications system), which is connected to the controller, is the bus used for servo control.”

Gen3 represents what some call packaging automation control, or PAC, which Jensen says is “inherently motion-based.” One example is Forest, Va.-headquartered Sentry Equipment & Erectors Inc. The company builds conveying systems, palletizers, de-palletizers, rinsers and elevators for Coca-Cola, Pepsi, Tropicana and other bottlers, as well as for canned-food producers. North American chemical and household-products companies also use Sentry’s equipment. This original equipment manufacturer (OEM) incorporated Gen3 technology in a new family of packagers, launched in early summer, which will shrink wrap, tray pack and case pack. A North American bottled-water company will be a first user, says Steven Prance, Sentry’s director of packer engineering. The Gen3 technology, he explains, allows end-users the flexibility of multiple formats on the same chassis, with intuitive and quick changeovers rather than typical extended ones. The traditional mechanical drive train is eliminated by placing a servo axis on each motion axis, Prance adds, and that reduces part count, allowing a smaller machine.

Improved maintainability of machines is a benefit of the technology, which Prance describes as “a personal computer that combines all of the conventional PLC capabilities with motion control and intelligent motion.” Also, he notes, the distributed-intelligence I/O runs on bus networks. “We’re using Profibus DP, but we could use DeviceNet.” His product, using PacDrive, can communicate with factory-level data acquisition systems and management control systems in a variety of formats, he says, including Ethernet, TCP/IP (transmission control protocol/internet protocol), OPC (an open connectivity standard) and Web-based services.

Programming compliant with International Electrotechnical Commission (IEC) standard 61131-3—“Guidelines for the application and implementation of programming languages”—is another technology benefit, he says. “It means that we should be able to have a single program for the entire range of equipment, so regardless of whether you have a 30 cycles-per-minute machine or a 120 cycles-per-minute machine, with the same level of accessibility, it’s going to appear the same to the technician.” By using the Gen3 technology’s standardized programming techniques, he adds, “we’ve actually reduced our design cycle. We’ve saved about three to six months of a (traditional) design cycle of anywhere from nine months to two years, and it’s produced a smaller, more elegant program.”

Another technology that might find use in pick-and-place applications in which servos might operate in different planar environments, or in places where products might be collated, such as wrapping candy bars or filling bags, is Schneider Electric’s TwinLine. Primarily a servo system that eliminates a separate controller, the unit offers full machine control and can have analog and digital I/O wired directly into the unit. The technology “addresses the market segment where the user doesn’t need eight-axis servo controls, but (where) they do need servo controls,” says Kevin Hamilton, Knightdale, N.C.-based market-applications development manager for packaging. Through its connectivity feature, he adds, TwinLine “has the ability to connect to other user equipment that can speak DeviceNet, CANopen, Profibus and Interbus-S.”

Revolutionary

A West Plains, Mo., OEM is incorporating the technology into a custom control system it is engineering for Monet Desauw Inc., which builds roof-trusses cutting machines. A to-be-patented machine is scheduled for mid-year production, says West Plains Electric Motor Service Inc. design engineer Steve Kellett. This first use of TwinLine by the OEM is to manage a single-blade saw, which is a “revolutionary design that no one has ever tried in the industry,” Kellet contends. “We’re actually cutting across the board with the X-Y axis. We have a linear positioner that feeds in the lumber and we have two pinch-rollers on servos that actually speed lumber through. We have to coordinate all servos together because the cut has to be precise,” he explains.

The technology permits lumber length and width to be fed into a Windows-based personal computer. It then optimizes the cut based on a customer cut-list. Other advantages of the Gen3 technology, Kellett says, include user-friendly setup and its ability to link to different servos at different times.

Another Gen3 technology is Siemens’ Simotion family, which has motion control with integrated object functionality, as well as temperature, pressure and other controls in the same box. The technology, which is capable of proportional-integral-derivative control, finds use in packaging, plastics, printing, converting and other applications. “We’re also talking about connection to the Internet or Ethernet, from each point, for maintenance and diagnostics,” adds Joseph Hammer, Norcross, Ga.-based product manager for Siemens Energy & Automation.

Cloud Packaging Solutions, in Des Plaines, Ill., is using Simotion to build a machine for Dr. Oetker, a European-based food processor. The OEM, which also builds high-speed form-fill-seal packaging machines for companies such as General Foods, Procter & Gamble and Sara Lee, chose that Gen3 technology, says control engineer Todd Hartmann, in part because Cloud wanted to put its remote HMI system on a swing arm, thus avoiding placing the processor on it or installing an industrial computer. “We were able to do that on MPI bus, which is similar to Profibus. It’s built into (the Siemens) S-7 processor. It’s basically peer-to-peer communications.”

Safety included

Cloud implements safety controls on the machine through the Gen3 technology’s PLC function. New this year, the functionality eliminates discrete safety relays, greatly simplifies wiring and integrates fault diagnostics into the safety system, says Hartmann. Those data display on the HMI, he adds.

An issue the technology resolves is handling cycle times of separate motion controllers and PLCs, states Hartmann. “The widely different cycle or update times of the processors creates ‘racing conditions,’ where data are even missed between the two platforms. You’d have to be very careful in those situations. And even just trying to set up those databases for communications protocols is difficult,” he explains.

One control box. One program. One place to troubleshoot. “The complexity of machine control has gone from very complicated in Gen2 to a simple, single control in Gen3,” remarks Elau’s Jensen. “We’ve completely taken the mechanical hard-coding out of the metal of the machine. We replaced it with the simple mechanics that are highly flexible.”

See sidebar to this article: Say What? GenNext?