Short-stroke cylinder replaces solenoid actuators

Paul Boughton

Festo is launching an innovative short-stroke electric cylinder that uses a patented tubular linear motor and end-position controller to provide exceptional dynamic performance. Initially available in two sizes with peak thrust force ratings of 35 N and 52 N, the new ADNE-LAS cylinder offers a choice of four stroke lengths from 15 to 45mm. The cylinders are said to be good alternatives to solenoid actuators - and they are especially suitable for process-type applications demanding fast and controllable movement, such as selectively ejecting faulty parts in high-throughput testing stations.
Believed to be the first of its type on the market, the ADNE-LAS cylinder is claimed to be extremely easy to install and commission. It is sealed to IP65 and uses 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 piston rod end positions.
Festo's new ADNE-LAS electric cylinders offer a choice of two 32mm profile models with stroke lengths of 15 and 35mm, and two 40mm profile models with stroke lengths of 20 and 45mm. The 32mm profile models can produce a thrust force of 35N peak and 8N continuous, while the 40mm profile models are capable of generating a thrust force of 52N peak and 12N continuous. All four models provide +/-0.5mm positioning repeatability.
The ADNE-LAS cylinder's patented linear motor is based on an 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 says its new design offers a number of significant advantages, including low moving mass and an 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 high force levels. Self-adaptive loop gain control decelerates the actuator as it nears the end of its stroke, thereby providing 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 - at rates as high as 20Hz for periods of up to 10 minutes at a time without interruption. The entire system operates from a single safety extra-low voltage (SELV) 48V DC source, and can also be run from 24V DC, albeit with suitable de-rating.
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