Rotary servo drive and its first cousins, linear motors, may be coming to packaging—or maybe not, depending on whom you talk to. A few packaging machine builders are looking at the super flexibility linear motors can give to an industry where package designs last as long as the highly preserved products inside that package.
Claude Chirignan, a senior applications engineer for Anorad of Shirley, NY, says the linear motor division of parent company Rockwell Automation is now in discussion with a major European manufacturer of packaging equipment. Packaging engineers, he says, aren't necessarily going to be attracted to linear motors for their high precision or their smooth motion—two traits that help meet the specs for semiconductor equipment and machine tools. Instead, it's their capacity to stretch that precision out to almost any imaginable length—unlike ball screw actuators, which can encounter crippling shaft windup and other problems at longer lengths, Chirignan says.
Yet, linear motors are overkill for most packaging machines, says George Gulalo, president of Motion Tech Trends, a technical analysis and market research firm that specializes in motor and motion control technologies. Packaging machines make primarily "gross" moves—moves that conventional pneumatic cylinders and air motors handle readily.
New motor enters the fray
Still, at least one packaging-biz veteran imagines places where linear motors could fit. Kevin Jacobs of Jacobs Automation LLC has taken a keen look at vertical and horizontal form, fill, and seal machines, and thinks he sees ways in which his freshly patented linear motor design could be applied. Unlike traditional linear motor systems, in which the forcer, thruster, and mover traverse back and forth in a line, Jacob's design resembles a slot car oval having two straightaways and two turns. PackTrak's running of multiple movers simultaneously is also unconventional. The track controls each mover independently.
With this type of arrangement, PackTrak could replace a rotary servo and transmission with two opposed racetracks on rotary servo motors to drive the mechanical links of opposing sealing heads on a form, fill, and sealing machine, Jacobs says. Pairs of counter-rotating movers—as many as are needed— would synchronize their movement with the motion of the bag. Sealing time would no longer limit the machine cycle time as a sealing head could remain heated, touching the two sides of the film for whatever time was needed to finish fusing them.
Linear motor innovations also could help manufacturers meet increasing demands for flexibility. Jacobs remembers 20 years ago when a cookie maker might have packaged the same product in but two package sizes. Today, that company might offer 40 package types for the same cookie.
Substituting a linear motor raceway for the fixed pitch, chain-and-lug carriers common on flow wrappers today could help engineers cope with package dimensions that are ever in flux. Changeover to any other package would be a mere panel function.
A Different Move: In this linear
motor system by Jacobs Automation LLC, the forcer, thruster, and mover
traverse back and forth in a line, differing from traditional systems. The
track is also unconventional, controlling each mover independently.
Flexibility is important to packaging equipment engineers, agrees Gary
Schultze, a senior electrical engineer with Carlsbad-based California Linear
Devices Inc. But a packager might run 50 or even 75 percent of a product at the
same settings, he says. The linear actuator that couples a rotary servo motor to
a ball screw is going to stop and start at the same places over many, many
cycles, eventually leading to wear spots. A linear motor, because contact is
limited—at most—to a shaft and a couple of bushings, won't wear over repeated
cycling. That spells increased longevity and better throughput, he says, which
helps convince the engineers of their value.
He says his company's tubular linear motors claim an edge in some packaging applications where high accelerations are paramount. He mentions a number of examples—a web brake, a destacker, a fast back conveyor, a box gluer, a bottle ejector—that his company has developed or is looking at now.
But John Kowal, global marketing manager with the packaging automation company Elau, says 50 percent of the linear motor market remains in semiconductors—what he calls the "perfect" application because of the requirement for light and consistent loads. Most of the demand for the bigger linear motors comes from machine tools. A few years ago, packaging was expected to become the next big thing for the linear motor industry. That hasn't happened. A linear motor still costs more than rotary motor and gearbox, he notes.
Even linear motors' rapid accelerations—usually measured in G's—aren't necessary for packaging something like milk, he says. A fifth-degree polynomial control easily handles the deceleration needed to prevent sloshing, he adds.
The packaging industry's next-generation all-servo machines may not even be enough to spawn linear motor adoption. Their use may always be relegated to special duties requiring fast, small strokes, he says.