Tubular linear motor offers alternative to solenoids

A short-stroke electric cylinder based on a tubular linear motor could provide a high power alternative to solenoid actuators, its developer Festo has claimed.

The ADNE-LAS device has a number of advantages, including low moving mass and the absence of flexible cabling to the moving parts, both of which contribute to its high reliability and dynamic performance capabilities, said Festo. In addition, the cylinders have no external magnetic field and are therefore suitable for environments subject to swarf, such as in machine tool applications.

The cylinder’s heavily patented linear motor used high flux annular magnets on the actuator rod, closely surrounded by a series of specialised windings on the stator coil. This approach in effect 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.

Initially available in two sizes with peak thrust force ratings of 35N and 52N (or 8N and 12N continuous, respectively), the ADNE-LAS cylinder offers a choice of four stroke lengths from 15 to 45 mm. Festo said the devices are especially suitable for process-type applications demanding fast and controllable movement, such as selectively ejecting faulty parts in a high throughput testing station.

Unlike a solenoid actuator, the ADNE-LAS has a high power density and produces a constant force throughout 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.

Festo 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.

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.

The ADNE-LAS cylinder 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 products, making it easy for machine designers to mix and match different drive technologies to create task-optimised automation, said Festo. 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. All four models provide ±0.5 mm positioning repeatability.

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