Innovative Short-stroke Electric Cylinder Uses Tubular Linear Motor

Believed to be the first of its type on the market, the ADNE-LAS cylinder is extremely easy to install and commission. It has an IP65 rating and an ISO standard form factor, which means that it can use the same mounting brackets and accessories as other similarly-sized Festo products, making it very easy for machine designers to mix and match different drive technologies to create task-optimised automation. And although the cylinder uses closed-loop control to ensure positioning accuracy, there are no servo parameters to set up – instead, users simply teach the controller the two required end positions of the piston rod.

Festo’s new ADNE-LAS electric cylinders offer a choice of two 32 mm profile models with stroke lengths of 15 and 35 mm, and two 40 mm profile models with stroke lengths of 20 and 45 mm. The 32 mm profile models can produce a thrust force of 35 N peak and 8 N continuous, whilst the 40 mm profile models are capable of generating a thrust force of 52 N peak and 12 N continuous. All four models provide ±0.5 mm positioning repeatability.

The ADNE-LAS cylinder’s heavily patented linear motor is 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 the 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 motor’s 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 has developed a special cost-optimised end-position controller to partner the ADNE-LAS electric cylinder. Known as the CMFL, the controller accepts feedback from the cylinder’s built-in magnetic encoder and maintains its drive output signal until the piston rod has reached the desired end position. Unlike a solenoid actuator, the ADNE-LAS has a very high power density and produces a constant force throughout the entirety of its stroke – much like a pneumatic actuator, though without the same extremely high force levels. Self-adaptive loop gain control decelerates actuator movement as it nears the end of its stroke, to provide completely automatic end-position cushioning.

The CMFL controls the movement of the cylinder’s piston rod in both directions and is capable of storing four different movement patterns, any of which can be selected and initiated via digital inputs; the controller also produces a ‘motion complete’ output signal when the piston rod reaches its end position. The combination of controller and cylinder can handle stroke cycles – movement in and out – as high as 20 Hz, for periods of up to 10 minutes at a time without interruption. The entire system operates from a single safety extra-low voltage (SELV) 48 Vdc source, and can also be run from 24 Vdc, with suitable de-rating.