Festo's new electric linear motors look like their pneumatic counterparts

Author : M Babb

05 September 2009

You could be forgiven if you thought these photos show pneumatic motors, which is, after all, the flagship product of Festo. However, they are actually electrically-driven actuators, purposefully designed by clever Festo engineers to look like their pneumatic counterparts.

DNCE-LAS with both versions of the new SFC-LAC motor controller
DNCE-LAS with both versions of the new SFC-LAC motor controller

(For main article "Direct Drive Linear Motors" enter 26721 in the LINK CODE box above.)

The electric cylinders employ the company’s new—and, as it hastens to add, ‘heavily patented’—tubular linear motor technology. They feature similar dimensions and mechanical interfaces as their pneumatic counterparts, making them true ‘drop-in’ electrically-driven alternatives. Even the names are similar: DNCE-LAS electric cylinders have the same form factors as the company’s DNC series of piston rod pneumatic cylinders.

The tubular design uses high flux annular magnets on the actuator rod, closely surrounded by a series of specialised windings on a long stator coil. This approach effectively turns conventional linear motor design inside out: in most linear motors, the fixed stator contains the permanent magnets and the moving element contains the coil windings.

The design offers a number of significant advantages, including low moving mass and a complete absence of flexible cabling to the moving parts—both of which, says Nigel Dawson, Festo’s drives manager in the U.K., contribute to the motors’ high reliability and dynamic performance capabilities. Furthermore, the cylinders have no external magnetic field which makes them suitable for environments subject to swarf, such as in machine tool applications.

The cylinders, which come in a variety of profiles and stroke lengths, offer a variety of acceleration, speed and thrust ratings.
The largest model can accelerate up to 90  m/s2, handle a velocity of 3 m/s, and is capable of producing a thrust force of 202 N peak and 55 N continuous.
All models provide positioning repeatability to within ±0.02 mm. Pressurised air cooling and pneumatic clamping unit options are available.

DNCE-LAS electric cylinders are ideal for applications involving loads up to about 1 kg that do not exert twisting forces on the actuator, such as small parts unloading, sorting and packaging machines.

For applications that demand a higher load capacity and resistance to twisting forces, Festo has launched the DFME-LAS series guided electric cylinders which use the same tubular linear motor but are equipped with two ball race guide assemblies to provide extra rigidity. The most powerful DFME-LAS series guide electric cylinder can accommodate twisting moments in excess of 6 Nm, has a payload capacity of 6 kg, and can accelerate at up to 54 m/s2.

All Festo electric cylinders are intended for closed-loop control: they feature a built-in magnetic encoder to provide feedback to the SFC-LAC motor controller (shown in the photo), which is also being launched at the same time.

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