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Electric cylinder is based on `inside-out` linear motor

10 October, 2010

Festo has launched a novel short-stroke electric cylinder with a patented tubular linear motor and end-position controller that provides highly dynamic movements. The ADNE-LAS cylinders, thought to be the first of their type, can replace solenoid actuators. They are said to be especially suitable for applications demanding fast, controllable movements, such as ejecting faulty parts from high-throughput test stations.

The cylinder`s patented linear motor uses high-flux annular magnets on the actuator rod, surrounded by special windings on the stator coil. This 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.)

The new design is said to offer several significant advantages, including a low moving mass and the avoidance of flexible cabling to the moving parts. The cylinders have no external magnetic field and can be used in environments, such as machine tools, where swarf may be present.

Initially, the IP65-protected cylinders are available in two sizes – with 32mm and 40mm profiles and peak thrust force ratings of 35N and 52N – and in four stroke lengths from 15–45mm. Positioning repeatability is said to be ±0.5mm.

The cylinders can use the same mounting accessories as other similarly-sized Festo products, making it easy to mix and match different drive technologies. Although the cylinders use closed-loop control to ensure positioning accuracy, there are no servo parameters to set up – users simply teach the controller the two end-positions for the piston rod.

Festo has also produced a controller to partner the ADNE-LAS cylinders. The CMFL controller accepts feedback from the cylinder’s built-in magnetic encoders and maintains its drive output signal until the piston rod has reached the desired end-position. Unlike a solenoid actuator, the cylinders have a high power density and produce a constant force throughout their stroke – like a pneumatic actuator, though with lower force levels. Self-adaptive loop gain control decelerates the actuator movement as it nears the end of its stroke, providing automatic end-position cushioning.

The CMFL controls the movement of the piston rod in both directions and can store 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 (movements in and out) at up to 20Hz for up to 10 minutes without interruption. The system operates from a 48V DC SELV (safety extra-low voltage) source, and can also be run from 24V DC, with suitable de-rating.

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