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Compact Linear Actuator
Copley Controls shrinks the size – but keeps the power – of its direct-drive linear actuators
Joseph Ogando, Senior Editor -- Design News, January 19, 2007
Size really does matter when it comes to direct-drive linear actuators. The smaller the actuator, the more that can be crammed side-by-side into the tight spots normally occupied by pneumatic cylinders or ball screws. But size isn't everything. Force and acceleration capabilities matter too. So does ease-of-installation.
Copley Controls recently developed a compact actuator that balances all of these needs. Sized to mount on 28-mm centers, the new ServoTube Model STA11 is the company's most compact direct-drive linear actuator to date. Yet it's no weakling. The STA11, which has an 11-mm thrust rod, offers a peak force of 92N and continuous force of 23.5N. It has maximum velocity of 5.6 m/sec, accelerates instrumentation-type loads to 25g, and provides a 14- to 232-mm stroke.
The STA11 also features an integrated solid-state position sensor capable of 8-micron repeatability. "This model eliminates the need for external position sensors, which have traditionally added cost and installation headaches," says George Procter, Copley's vice president of motion systems.
Like the company's previous ServoTube designs, the smallest of which offered 54-mm spacing, the STA11's load-positioning thrust rod houses the actuator's permanent magnets, while its electrically-powered drive coils are encapsulated in the forcer.
"It's not the smallest actuator on the market," says Procter. Nippon Pulse America, for example, has some smaller models available, even some with 4-mm thrust rods. But Procter notes that the STA11's combination of a small size with high force and acceleration capabilities sets it apart from the competition. "More than 20 Newtons of continuous force and 25g of acceleration in a package this size is significant," he says.
That view is echoed by John Odenthal of Motion By Odenthal, an integrator of motion control systems and one of the first engineers to try out the STA11. "Center line spacing is important but it's not the name of the game. Force, high acceleration and long life are just as important," he says. Odenthal recently picked the STA11 for aprinting-machine application, ruling out other compact linear actuators because they didn't offer adequate force or acceleration characteristics. Nor did he find any models with built-in encoders.
"The STA11 fills a niche that had been empty," Odenthal says. He says he would consider the STA11 as a replacement for pneumatic cylinders and ball screws for any single axis that requires up to 1.5 kW of power. "Above that, the loads tend to become high enough that I would question the STA11's axial and radial rigidity," he says.
As for the long-life of the STA11, Procter says they run for about 50-60 km. "That's at least 10 times more than what you would get from a typical ball screw," he says.
Uses for the STA11 include a variety of pick-and-place applications. Other than Odenthal's printing project, the unit has also been tested as a replacement for cams in a bottle filling line, as well as in a robotic blood analysis system. The STA11 becomes commercially available in March. For more information, visit www.copleycontrols.com.
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 Copley's latest ServoTube linear actuator is the company's most compact unit yet, with center-to-center spacing of just 28 mm. |
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