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Pneumatic membranes muscle in on new applications

01 May, 2000

Pneumatic membranes muscle in on new applications

A novel pneumatic actuator that mimics the behaviour of human muscles could open up new applications for fluid power. The "fluidic muscle", developed by Festo, is said to deliver ten times the force of a conventional pneumatic cylinder of a similar size, while weighing only a tenth as much.

The "muscle" consists of a watertight, flexible hose around which non-stretchable fibres are arranged to form a three-dimensional grid. When compressed air is forced into the system, the grid deforms and a pulling force is generated along the hose, shortening it.

The actuator has several attractive characteristics. It can react rapidly, or it can produce extremely slow movements because it is not affected by the "stiction" (stick-slip) effect. Contamination of the air supply does not affect the actuator`s performance and the muscle does not suffer from mechanical wear. Its consumption of compressed air is minimal.

After working on the technology for several years, Festo is now ready to put the fluidic muscle into production. The company plans to offer the actuators in lengths of up to 10m, and internal diameters of 10-40mm.

But Festo will not have the market to itself. London-based Shadow Robot has been working on a similar technology since 1982 and is now offering a range of "air muscles" with the smallest weighing just 10g yet delivering a maximum pull of 7kg. The air muscles have power-to-weight ratios as high as 400:1 compared to the 16:1 of a typical pneumatic cylinder or DC motor.

Shadow claims that a 50mm-diameter muscle is powerful enough to pull down a brick wall. The company asserts that its muscles, which operate from compressed air supplies of 0-5bar, are cheaper to buy and install than conventional actuators and pneumatic cylinders.

The muscles respond almost immediately to changes in pressure, contracting by up to 40% of their original length. They can operate even when bent around a corner or twisted axially.

Shadow developed the air muscles originally for use in its own robots but it envisages many other potential applications. One simple example is to use a muscle to operate a lever with a spring return. A pair of muscles can be used to pull the lever in two directions.

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