At the Touch of a Button: Wipe-Clean Moulded Switches for Medical Engineering

For electronic medical devices, control components such as switches and buttons must not only be easy to operate—they must also be easy to clean. They are notorious for attracting germs and dirt particles, particularly in and around the tiny crevices and gaps between the various components and connections. The development of smart plastics—moulded components with capacitive electronic functionality—offers device manufacturers the opportunity to develop wipe-clean electronic buttons and switches while improving production efficiency and achieving better and more complex designs.

Some people have earmarked smart plastics as a converging technology where capacitive electronics have been combined with injection moulding. Others have described them as a new type of composite technology. Fundamentally, they consist of a plastic part moulded over a film which has had electronic components printed onto it (see image below left). The result is an aesthetically pleasing part with smooth lines and a clean shiny finish. The part has electronically interactive parts built in to it to form switches and buttons.

The electronics components consist of capacitive sensors which utilise the principle of electrical capacity—the reciprocation between two spatial points (as in the electric force field between two electrodes). The electric flux lines within an electric field may be changed by introducing a conductive object (such as a fingertip). The capacitive sensors pick up these changes and respond with a voltage variation that can be used to initiate a particular function—such as an on/off or up/down command. Since the field lines penetrate non-conductive solid bodies, the sensor effect also works from a distance through a thin surface layer such as a thermoplastic or an operator's gloves.

The films can be configured in three dimensions and cut before being overmoulded or back-injected with thermoplastic. In this way, capacitive electronics can replace mechanical switches, buttons and control knobs. The operating elements are covered by a continuous, even and highly resistant interface.

Smart Plastics in Cars

According to Austrian injection moulding machine manufacturer Engel, smart plastics have undergone most development in the automotive sector. Michael Fischer (pictured right overleaf), sales manager (technologies) believes: “The cars of the future will be easier to operate than smartphones, simply by touch, feel and interaction.”

At its open house in June 2012, Engel presented its first close-to-production application for smart plastics (see image). Centre consoles for cars with a sensitive interface were manufactured using an Engel duo 350 injection moulding machine with reversing plate and combination mould. A capacitive, three-dimensional pre-formed film was placed into the mould by a robot and overmoulded with PC/ABS. The component was then flow-coated with polyurethane to protect the surface and produce a high quality impression.

The technology will now be marketed under the name Sensitive Surface by Engel and its project partners. “We are in discussion with various automobile companies and OEMs with a view to mass-producing the first sensitive surface applications in three to four years”, reveals Fischer.

In the case of vehicle construction, the hygiene aspects of a continuously sealed interface are less important than ease of use and high efficiency in the manufacturing process. Whereas conventional manufacturing often involves the individual production and assembly of more than 100 small parts, capacitive films and plastic granulate facilitate the production of functional, ready-to-install components in a single work step. “Taking the centre consoles as an example, production costs are reduced by at least 30% if we look at the whole process”, emphasises Michael Fischer. Since no assembly is required, productivity is also increased sharply.

Pushing the Boundaries of Product Design

Ample scope for design through injection moulding is a real benefit here. The flexible print production for the films makes it possible to position sensors almost anywhere; films can also be formed into virtually any shape. Sensitive surface technology is therefore the ideal means by which to develop operator control units cost effectively—units that Engel say are unbeatable in terms of usability and ergonomics.

Of course, ergonomics and cost-effectiveness have been key considerations in other sectors of industry for many years. With this in mind, a design study for the control panel of a washing machine was recently presented. Meanwhile, Engel and its partners are starting to field enquiries from the medical engineering sector.

“I think the fact that this technology addresses a whole set of requirements at a stroke represents a major opportunity for medical engineering”, says Christoph Lhota (pictured middle overleaf), the head of Engel's medical business unit. “Firstly we're doing more to address stringent hygiene requirements, secondly we're improving the ergonomics of medical engineering products and thirdly we're drastically cutting production costs. Pressure on costs is rising in the medical engineering sector too.”

At present, lessons learned from the automobile industry are being developed and applied to the medical engineering field. Alongside Engel, a company heavily involved in the specialist development and production of intelligent, multi-layered interfaces is Austria-headquartered smart plastics technology developer plastic electronic. One key development issue at present is the sterilisability of intelligent electronic components. “We successfully carried out function tests for the automobile industry in the temperature range of -40°C to +85°C”, reports Philipp Weissel (pictured left overleaf), CEO of plastic electronic. “We're now working on raising the temperature range for critical applications in medical engineering.”

Upper Austria Hailed as Epicentre of Smart Plastics Evolution

As far as the future research activity of Engel and plastic electronic is concerned, Upper Austria promises ideal conditions. Few places elsewhere in the world are such a high concentration of companies and research institutes to be found alongside the infrastructure needed for smart plastics. Early in 2011, this density of specialist expertise led to the foundation of a smart plastics networking group, the Smart Plastics initiative. The aim of this group is to accommodate the entire value chain for intelligent electronic plastic products within Upper Austria so that world-leading system solutions may be developed in partnership. To further this goal, Smart Plastics is hosting a congress in Linz, Upper Austria—the same place where Engel’s headquarters are—on June 10-11, 2013.

Editor’s Outlook

Plastic electronics may help designers find an alternative to conventional membrane keyboards in medical situations. These membranes attempt to integrate a continuous seal over an interface, but are said to be less than robust in practice and constitute a source of infection in sterile environments like operating theatres. Thanks to the commitment in Austria for smart plastics and Engel’s lead in the moulding expertise, observers can expect product designers to turn to smart plastics for improved functionality, aesthetic design, not to mention the wow factor of a highly sensitive button which requires absolutely no pressure to activate. It takes the phrase “at the touch of a button” to a whole new level.

Caption: Sensors and conducting paths are printed onto the film; the malleability of the film gives product designers ample scope.