High performance electric cylinders use innovative tubular linear motor

The heavily patented linear motors are based on a highly innovative tubular design, using 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. Festo’s 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 contribute to the motors’ high reliability and dynamic performance capabilities. Furthermore, the cylinders have no external magnetic field and are therefore suitable for environments subject to swarf, such as in machine tool applications.

Festo’s new DNCE-LAS electric cylinders have the same form factors as the company’s popular DNC series of piston rod pneumatic cylinders. There is a choice of three 32 mm profile models with stroke lengths of 100, 200 and 320 mm, and four 40 mm profile models with stroke lengths of 100, 200, 320 and 400 mm. The cylinders offer a variety of acceleration, speed and thrust ratings – the largest model can accelerate at 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 seven models provide exceptionally high 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. These employ the same innovative tubular linear motor as the DNCE-LAS series, but are equipped with two ball race guide assemblies to provide extra rigidity. Again, there is a choice of seven different models, spanning stroke lengths from 100 to 400 mm. 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 DNCE-LAS and DFME-LAS electric cylinders are intended for closed-loop control – they feature a built-in magnetic encoder to provide feedback to the motor controller. Festo has launched a new motor controller – known as the SFC-LAC – to partner its new electric cylinders, which is supplied as a complete ready-to-run unit which incorporates a power output stage and all necessary control interfaces, as well as an optional HMI. It features a built-in digital I/O interface as standard with CANopen, DeviceNet and Profibus interfaces available as options. The controller is very easy to commission: all set-up parameters – including complete move profiles defining velocity, acceleration and deceleration – can be developed off-line on a PC, using Festo's intuitive Windows-based FCT software, and then downloaded to the controller. As many as 31 move profiles can be stored on the controller, and linked together, so that entire motion control sequences can be executed entirely independently of the host PLC. Additional move profiles can of course also be specified via fieldbus whenever required.

Festo’s Drives Manager, Nigel Dawson, points out that: “We believe that Festo’s entry into the linear motor based actuator market could prove disruptive, and hopefully cause people to re-evaluate their opinions about this type of technology. Until now, the use of linear motors for highly dynamic positioning applications, especially those requiring accurate repeatability, has proved something of a black art. We intend to change this, so that system designers eventually come to regard our linear motors as just another actuation technology choice.”

Festo’s DNCE-LAS and DFME-LAS electric cylinders have the same form factors and mechanical interfaces as their pneumatic counterparts, making it very easy for system designers to mix and match different drive technologies to create task-optimised automation. The company produces a wide range of accessories – including cylinder rod ends, foot mounts and clamping brackets – to further simply this task.