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Electric ram takes on hydraulics

01 November, 1999

Electric ram takes on hydraulics

A British engineer has developed an electromagnetic linear actuator that he says can replace hydraulic rams in many applications. The ServoRam, designed by London-based Phillip Denne, has only one moving part - a cylinder that moves freely along the axis of the motor, instead of rotating.

Denne, who has been working on the technology for eight years, was originally looking for an alternative to the hydraulic rams used to drive amusement park rides such as flight simulators.

"Until recently, the only way to produce precise and powerful motion for simulation has been by using hydraulics," he explains. "Electric motors driving screwjacks can be beefed up to produce a large thrust, but they cannot be designed also to have the extreme sensitivity and the fast response that is vital to the simulation illusion."

Denne says that the technology has many potential industrial and military applications including packaging machinery, passenger lifts, machine tools, vehicle suspensions, pile drivers, and aircraft carrier catapults.

The ServoRam is a free-piston, linear, three-phase, brushless servomotor. In effect, it consists of a multipole, permanent magnet motor split down the middle, rolled flat, and rolled back up again by taking the long edges and bringing them around to form a cylinder. The armature is treated in a similar way and the armature shaft is inserted along the axis of the cylinder to form a piston shaft.

Finally, the outer surface of the armature is sealed to the inner surface of the cylindrical stator so that it acts simultaneously as a fluid piston and an electromagnetic force generator.

Denne claims that the resulting actuator is clean, simple, silent, fast-acting, easy to control, precise, reliable, and free of stray electromagnetic fields. Unlike costly hydraulic rams, the ServoRam does not leak oil and can be used safely indoors.

Denne asserts that the ServoRam`s lifecycle costs are lower than those of hydraulics because it has just one moving part - the piston - and low maintenance.

The electrical actuator can move at speeds of up to 100m/s and position to an accuracy of a few microns. There are six versions of the ServoRam with piston travel lengths from 10mm to more than 100m and thrusts from 1kg to more than 100 tonnes.

Denne is the founder and chief scientist of US-based Advanced Motion Technologies which owns the patents to the ServoRam and is offering the technology for licenced manufacture worldwide.

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