Safety Minus the Downtime

September 5, 2005

9 Min Read
Safety Minus the Downtime

Belgian folding carton maker Van Genechten Packaging has developed a new multipack machine through OEM builder Cambopak that wraps single and double rows of beverage bottles in cardboard. What's new is the machine's use of so-called integrated safety to quicken its response in emergencies. In addition to the integrated safety system, the machine provides two more benefits called "safe standstill" and "safely reduced velocity," which, according to drives-supplier Bosch Rexroth, helps packagers shorten downtime by eliminating servo homing after a machine's been stopped.

The multipack machine consists of an infeed chain and accumulator area, where bottles feed and form in groups one or two wide by two or three long. As product groups move through the machine, cardboard blanks form around each bunch. The machine glues the cardboard wrapper to itself, then folds the ends in to enhance stability.

According to Owen McGuire, an applications engineer with Bosch Rexroth in Germany, the continuous-motion machine includes four servo axes that control rotary infeed, carton forming, carton tensioning and gluing, and end folding.

Machine safety is managed by the individual drives, McGuire says. The system meets IEC safety integrity level 2 by guaranteeing an axis will not move when it's in safe standstill mode, McGuire says. The system does this with dual-channel monitoring of the servo encoders.

The continuous motion cartoner makes a full range of multipacks. Changeovers are push-button easy.

When an operator opens a gate, the servos enter safe standstill. At this time, an operator can move freely within the machine's protected areas, even though the servos are still, in effect, live. Dual monitors watch the servo encoder. As long as the monitor outputs correspond with each other, the safe standstill condition remains valid. If a discrepancy between them occurs, the system flags out of safe standstill, McGuire explains.

The Safety on Board system requires both processors to agree on the position of the servo encoder to maintain safe standstill mode.

Before the advent of the "Safety on Board" system—as Bosch Rexroth calls it—a machine could not be under power whenever a door or guard opened without a special operator present who was authorized to bypass safeties. The new system, through technology, avails any operator of this authority.

Slow Roll

It gets even better: Armed with a switch on a pendant, an operator can access the machine and jog it at a safely reduced velocity. As with safe standstill, dual channel monitoring of each servo encoder ensures the system drops out if disparities arise when both signals are compared.

The new cartoner uses integrated safety to limit the time lost in restarting. Safety is localized at the drives.

Says John Wenzler, a U.S. based Bosch Rexroth packaging account executive, safely reduced velocity allows access to a machine while avoiding the "large time suck" that ordinarily accompanies a guard opening, after which a machine must take time to reset its servos. This problem manifests itself particularly on machines that aren't using absolute encoders, he says. Ten minutes to home all a machine's actuators is not uncommon; 60 minutes is not unheard of.

According to McGuire, the Cambopak machine uses absolute encoders. But Safety on Board will work with either absolute or incremental encoders, he says. The drive monitors the feedback position signal of the encoder by two separate, independent channels.

The thinking behind safe standstill and safely reduced velocity actually mirrors the philosophy that drive redundant switches onto gates and guards. If one switch welds shut, the other detects any guard opening and puts the machine in a safe state, Wenzler explains.

The Bosch Rexroth IndraDrive family of servo drives.

According to Bosch Rexroth, the system, available on its IndraDrive servo drives and IndraDyn servomotors, actually shortens the time it takes to respond to faults. Safety resides locally on each drive rather than centrally. When a safety function is invoked, the local drive can respond without having to route through additional hardware or the machine control system. It eliminates the need for power contactors in motor supply lines and reduces the amount of cabling going to a control cabinet, the company says.The system relies on a PPC-R22 integrated motion and logic controller. According to the company, the logic portion coordinates motion and the operating sequence while the motion portion synchronizes the motors. The company's VisualMotion 10 software provides programming. An HMI serves as an entry terminal for loading recipes.

The Bosch Rexroth PPC-R22 integrated motion and logic controller.

Will it Play in Peoria?

Europe and the U.S. approach safety differently, Wenzler says. While European codes such as the IEC have allowed safety to be a networked function for some time, it was only recently that U.S. standard NFPA 79 was corrected to permit this—in 2002. Before then, the regulation insisted that e-stops be hard wired.

Joseph Lazzara, president of Scientific Technologies Inc., a U.S. safety integrator, has argued that safety progress here has been hampered by outdated regulatory standards and a lack of appropriate devices. More devices have become available recently, he says.

American standards have been slowly harmonizing with European ones, he says, which, while a painful transition for U.S. builders, will ultimately benefit them by no longer holding them to two sets of regulations.

Lazzara calls the safely reduced velocity pendant an enabling device, and it's probably familiar hardware to robot users, he says. This kind of switch is expressly permitted in the U.S. by the robot standard ANSI RIA-15.06 for setting up robots during a teach cycle or to verify a program.

John Peabody, vice president of safety integration sales at STI, says the idea is to let the operator or mechanic in close to the point of operation to see what's going on. The concept of an enabling device actually comes from Europe, he says, and was harmonized into the ANSI robot standard.

Peabody distinguishes between a safe stop and an e-stop. A safe stop allows a machine to return to a known position from which it can commence working without an elaborate reset process. An e-stop removes power to the machine immediately, stopping it but possibly scrambling programs. After an e-stop, a machine needs time to gather its wits.

With robots, an operator can push a safe stop button and a locked perimeter guarding will remain that way until the robot has come to a controlled stop. Only then will the guard unlock.

According to Wenzler, IndraDrive sings a similar song.

Integrated safety keeps an operator safe while remaining out of the way.

Would it work for U.S. packagers? Much of the push for safety there comes from the users of packaging machines themselves, Wenzler says. This holds true especially in pharmaceutical and medical device industries, where large concerns such as Johnson & Johnson ask their machine suppliers to build equipment to meet a company's own internal safety standard.

Tom Piantek, director of J&J Worldwide Health and Safety, says his organization made an effort to make its machines safer by adopting some of the EU requirements and philosophy as far back as 1996. "This simplified our approach from a global perspective," he says.

Where the law of a country mandates something different—or less stringent, specific, or safe—J&J will supplement the EU requirements, Piantek says.

"There's nothing in OSHA regulations that says you can't make a machine safer than the minimum requirement," Lazzara explains.

"The European standards have advanced the machine safeguarding state-of-the-art," Piantek adds. Safe standstill and safely reduced velocity are the latest examples of these advancements. The standards have encouraged the development of many safety products.

Specially safeguarded servo drives like those from Bosch Rexroth, as with other new safety devices, "will bring machine safety control to a new level," he says.

By integrating safety components into the control hardware of the drive, these devices simplify installation of "fail to safe" control systems, he says. Integrated safety reduces the chance of design error, installation mistakes, or maintenance mishaps that might plague similar systems built of discrete components.

So, is integrated safety coming here or not? "Absolutely," says STI's Peabody. It's only a matter of time before the ANSI standards adopt this new technology, he adds. The whole point of safeguarding is to protect an operator without interfering with his job. If you interfere with his job, he'll find a way around the safeties. "Integrated safety is practically transparent to him," Peabody says.

Reach Senior Editor Paul Sharke at [email protected].

Web Resources

For an interesting discussion of integrated safety, read the ARC white paper

The following companies offer integrated safety technologies and resources:

Siemens calls its system Safety Integrated

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