Linear Motion Moves Up and Out

Machine Builders Use Variations on Basic Linear Motion Technologies to Bring Precision and Accuracy to Non-Traditional Applications

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By Jim Montague, Executive Editor

It's a pain in the neck to reinvent the wheel. That's why it's useful to preserve human know-how, so one generation's gains can be built on by the next.

Such is the case with our knowledge of linear motion. Many of its traditional ballscrews, pulleys, rails and guides, and even newer electrical cylinders, have stayed basically the same, but they're steadily tweaked and accessorized for new and unexpected applications. Not surprisingly, linear motion is being assisted by servo motors and drives and more PC-based control, too.

Belts Shape Up Surfboards

To build less costly and more capable surfboard shaping and routing machines, Precision Shapes Northwest (www.psnwsurf.com) in Seattle added a Harmonic Linear Drive (HLD60-H3) belt-type linear actuator with a built-in smart motor to its machines. It combines six pulleys, and uses their resulting harmonic principle to accomplish internal gear reduction and braking without a gearhead (Figure 1). This belt-driven linear actuator allows the company's inventor and owner, Mike Ewaliko, and his Precision Shaper machine to follow CAD designs more accurately, and cut and shape the boards' polyurethane and expanded polystyrene (EPS) blanks more precisely—even over very long lengths.

The company has been building shaping machines since 2004, and is now on Version 8. HLD60-H3 also enables Precision Shaper V.8 to be 25% smaller and more durable. "Shaping a surfboard is a lot like creating airplane wings," Ewaliko says. "Each little concave or convex change in the hull can dramatically affect performance. There's a lot going on hydrodynamically, so shapers must get in tune with their designs and build their boards from the inside."

Serving Smaller Shops

Ewaliko reports that small surfboard shaping shops use his Precision Shaper machine to fight off economic demons on several fronts. "Big production houses use $65,000 to $100,000 shaping machines, but the little guys can't afford them," he explains. "So hand shapers have to get their designs produced by a production house, but they lose profit that way, too. More recently, Asian manufacturers have started mass producing surfboards and making them much cheaper, and this squishes the small shops even more. We build shaping machines that are compact, rugged and attainable for small shops—about $25,000 to $45,000—so they can still do 6–18 ft custom boards, but then record and repeat designs, or do a custom design for each one.

"Of course, there are still many curves on surfboards, so we've also honed in on holding blanks better—not too rigidly and not too loosely—for better registering and better transfer of the design. We're still matching the usual three to three and a half boards per hour that the big machines do. However, where we all used to reject three of every 10 boards for being a fraction of an inch off spec, our improved registration and accuracy means we're rejecting few to no boards now. This ability lets our users realize the true value of their shaping machines as extensions of their minds and their designs."

This happy ending is thanks in large part to the HLD60-H3 linear actuator, but the journey there wasn't easy. This is because previous Precision Shaper versions used stepper motors and servo motors, which used a lot more cabling, had more potential failure points, and were more costly. HLD60-H3 is built by the OEM Dynamics (www.oemdynamics.com) division of Animatics (www.animatics.com), which also supplies a SmartMotor with a 32-bit RISC controller. Precision Shaper also uses Animatics' JenCNC software and CANbus and RS-232 connectivity (Figure 2). These features cost more, but Ewaliko reports they cut job setup time to 30 seconds from 3–4 minutes, and enable more intuitive customization and remote troubleshooting.

It took Animatics several years to develop the HLD60-H3's six pulleys and continuous, steel-reinforced belt, according to Chuck Searcy, senior applications engineer. "Most belt drives have two pulleys, but they need a planetary gearhead. The trick with our six pulleys is that their gears are slightly different sizes, and this design is able to accomplish that planetary gearhead capability and gear reduction by itself," he explains. "Our belt module is also more precise over very long lengths, and has unidirectional repeatability of less than 22 µm over 3.2 m. This allows Precision Shaper to cut precisely over much longer lengths than a ballscrew can handle. Ballscrews are precise at shorter lengths, but at longer lengths they start to vibrate and whip around like a jump rope."

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