Compliant systems: Flexible yet strong materials allow aircraft wings to flex with air flow

Flavio Campanile, head of a research group in Empa's Mechanics for Modeling and Simulation Laboratory, is convinced that aircraft can be made which move more elegantly and, above all, more economically through the air. "Sooner or later it will be possible to make wings without ailerons, flaps and thousands of individual parts. They will have in principle only one component, which continually changes shape."

Biomimetic wings -- that is, those based on designs seen in nature -- adapt perfectly to the airflow around them, and are light and energy efficient.

In order to put his ideas into practice, Campanile developed so-called "compliant systems" at Empa and the ETH, initially by himself and thereafter with a team of twelve colleagues. But aerodynamic surface design is not the only field in which the engineer is active. Campanile also intends to tackle concrete problems facing industry by making use of compliant systems. "Wherever machines are at work, compliant structures can be used to bring improvements," Campanile is convinced. In order to persuade industry of the gains to be made by using compliant systems, he has been financially supported by the Gebert Ruef Foundation for three years.

Solutions to industrial problems

As a result of his efforts, Campanile has succeeded in convincing diverse industrial partners from the medical technology and robotics fields of the advantages in using these novel systems based on innovative materials. In cooperation with these companies he has developed a range of solutions for instruments and tools which are made in one piece and therefore superior to the conventional devices they replace which use joints and hinges. The latter are complicated and expensive to produce and assemble, and also not cheap to maintain.

Compliant systems made of materials such as plastics, metal and composites are so designed that they transmit forces without using joints. They change shape because the material from which they are made undergoes elastic deformation, not through the use of rigid components which slide or roll over each other. This means that the new instruments suffer less wear and tear.

A robot gripper arm developed by Campanile's team consists of only 32 individual parts, is 60 per cent lighter than a conventional equivalent and costs about 98 per cent less to manufacture. "These figures must make car designers and mechanical engineers ears' prick up. To date they have made use of hardly any compliant structures," maintains Campanile. Success and the next steps

Michael Sauter, a colleague of Flavio Campanile, is one person who has successfully used the new technology. In a feasibility study he showed how a special bed using compliant structures could be used to prevent bedridden patients from developing bed sores. His idea has already won him several awards. Sauter is now working in his Empa spin-off firm, compliant concept GmbH, to bringing the nursing bed to the market in the near future.

Campanile himself prefers to carry on his research. "Designers and manufacturers expect a great deal, and the solutions are often very complex;" he explains. Currently two of his co-workers are working on doctoral dissertations at the ETH Zurich's Centre of Structure Technologies under the guidance of Paolo Ermanni. One is investigating ways to combine compliancy and lightweight construction techniques; the other is developing "active aeroelastic" wings which adapt to aerodynamic flow by changing shape, requiring practically no external energy to do so.