Muscling in on manufacturing

Festo’s Fluidic muscle, an unusual pneumatic actuator based on 100-year-old prosthetic research, is finally making its mark in industrial applications.

Many attempts have been made to commercialise ‘pneumatic muscle’ technology. In the 1980s, Bridgestone Rubber in Japan launched the unsuccessful ‘rubbertuator’, and more recently UK roboticist Shadow developed its own version, dubbed the air muscle, for use on its biped project.

However, with its fluidic muscle, Festo claims to have developed the technology to the stage where it is a commercially viable alternative to existing technologies.In its most basic form, the device consists of a rubber tube wrapped in a plastic weave that shortens in a scissor action when pulled out, mimicking the action of a biological muscle.

When actuated with compressed air, the muscle contracts by up to 40 per cent of its original length. The contraction is accompanied by a force inversely proportional to the degree of contraction. The first few per cent of travel provides a large force: a small muscle filled by low-pressure air cannot be stopped by hand.

The simplest use is for moving a lever. For example, a muscle can be used to pull a lever in one direction and a spring can return it. Two muscles will allow the lever to be pulled in either direct- ion and because a muscle contracts over a known distance, it can be used to provide a safe movement, only moving the lever through the angle it is set up to.

Festo’s fluidic muscle, officialy launched a couple of years ago, is only now beginning to find its way on to the factory floor.

Middlesex-based starter motor maker Hamlyn Engineering has built the muscles into a production machine designed to crop copper conductors.

During motor production, 27 strips of copper conductor need to be cut to length in situ. For speed and consistency, cropping all 27 conductors simultaneously was the optimum solution, as long as the system could apply the required force and control. Cutting copper requires between 22,000 and 30,000lb ft/in2 force, and the combined cross-sectional area of the 27 conduct-ors is 1.125 sq in.

Rather than using six 125mm diameter cylinders of 50mm travel, Hamlyn opted for eight of Festo’s Fluidic Muscles, each 40mm in diameter. At just £74 each – a total of £592 – they provided a cost saving of almost £800 over standard cylinders.

Head of Hamlyn’s design team Mac Ghadially said that another advantage is that it gives the muscles superb accuracy upon return in the relax mode. ‘This attribute eliminates the need for a stopping cylinder to reposition the cutter at the start point, but I didn’t expect to get it from the muscle,’ he said.

It also kept the bar cropper machine simple and cost-effective by eliminating the need for control electronics. ‘It is a completely pneumatic solution with no need for sensors or PLCs,’ said Ghadially.

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