Electric cylinders use linear motors to deliver high performance

The heavily patented linear motors are based on an 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 is said to offer a number of significant advantages, including low moving mass and no 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 use in 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 32mm profile models with stroke lengths of 100, 200 and 320mm, and four 40mm profile models with stroke lengths of 100, 200, 320 and 400mm. The cylinders offer a variety of acceleration, speed and thrust ratings - the largest model can accelerate at up to 90m/s2, achieves a velocity of 3m/s, and is capable of producing a thrust force of 202N peak and 55N continuous. All seven models provide exceptionally high positioning repeatability to within +/-0.02mm. Pressurised air cooling and pneumatic clamping unit options are available.

Guided versions

These DNCE-LAS electric cylinders are suitable for applications involving loads up to about 1kg 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 is launching the DFME-LAS series guided electric cylinders (pictured right). 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 400mm. The most powerful DFME-LAS series guide electric cylinder can accommodate twisting moments in excess of 6Nm, has a payload capacity of 6kg, and can accelerate at up to 54m/s2.

All Festo DNCE-LAS and DFME-LAS electric cylinders are intended for closed-loop control, hence they feature a built-in magnetic encoder to provide feedback to the motor controller. Festo has also launched a new SFC-LAC motor controller to partner its new electric cylinders, which is supplied as a complete ready-to-run unit incorporating a power output stage and all necessary control interfaces, as well as an optional HMI (pictured right). It features a built-in digital I/O interface as standard with CANopen, DeviceNet and Profibus interfaces available as options. The controller is said to be 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, 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 independently of the host PLC. Additional move profiles can also be specified via the fieldbus connection whenever required.

Festo's Drives Manager, Nigel Dawson, comments: "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."

In addition to the DNCE-LAS and DFME-LAS electric cylinders, Festo produces a wide range of accessories - including cylinder rod ends, foot mounts and clamping brackets.

Follow the links for more information about the DNCE-LAS and DFME-LAS electric cylinders.

Other products Festo has recently launched include the ELGL-LAS ultra-precise linear motor axis with an air bearing and, previously, the DNCE series electrical cylinders.