Under tension

Article of 25 august 2017 

Under tension

A sprained ankle or a stiff neck can afflict anyone, in which case support bandages are a great relief for the patient. Elastic dressings in bright colours have become standard in medical care, but high-tech bandages are also available – for example, with integrated sensor technology for measuring a person’s temperature. They are produced by specialist weavers such as Wernli AG from Switzerland, which rely on innovative automation technology with muscular power.

336 tonnes of yarn: this is the impressive quantity that Wernli AG made into 51,000 kilometres of various types of bandage in 2014. In order to maintain a consistently high quality, the company uses the very latest technology on its looms. When producing the elastic fabrics, it is particularly important that the yarn is kept under constant tension while it is being processed. Only in this way is it possible to weave uniformly elastic bandages.

Muscles instead of weights

This tension is normally ensured by lead weights on the weaving machines. They compensate for the reducing weight caused by the yarn being used up on the so-called warp beams, from which the yarn is gradually wound off for the warp threads in the fabric. Without using them, the warp beams would move at increasing speed as more yarn is wound off, thus producing an uneven fabric. The weights of between 2.5 and 15 kilograms previously had to be suspended from the warp beams manually by employees. In the meantime, the company uses the DMSP Fluidic Muscle from Festo instead, which continuously keeps the tension and whose retention force can be regulated very precisely.

The DMSP Fluidic Muscle from Festo keeps the yarn under constant tension while being processed.
The DMSP Fluidic Muscle from Festo keeps the yarn under constant tension while being processed.

Flowing elastic movements

The fluidic muscle essentially consists of an elastomer hose with embedded aramid yarns. If it is filled with air, the diameter of the elastic hose increases and its length simultaneously contracts. This creates a flowing elastic movement, which enables operations that come very close to human movements. With no seals or bearings, the fluidic muscle moves without jerking and enables a sensitive and consistent application of force.

At a comparable size, the fluidic muscle achieves ten times the force of a conventional pneumatic cylinder. It is very robust and can even be used under extreme conditions such as in sand or dust. Its design as a hermetically sealed hose makes it resistant to particles or dirt – a property that makes it particularly suitable for use in the dusty surroundings of a textile factory.

Thanks to the precise ‘muscular power’, not only the quality of the woven bandages has improved, but the risk of accidents in the production department at Wernli has gone down: the employees are no longer able to injure themselves when suspending and removing the weights or bang themselves on them when walking past.

The fluidic muscle is based on the biological role model.
The fluidic muscle is based on the biological role model.