Passenger and crew interaction with the air cabin and seating systems on-board has become one of the most important driving factors in the design of the customer experience. In fact, when considering the human-machine interface (HMI) the industry has even created and adopted its own language.


HMI Capabilities

Not only do they need it to be intuitive and integrate seamlessly into the overall design concept both structurally and cosmetically, more nuanced effects such as the back lighting and even the touch of the materials used can become critical to the final design of the passenger experience. ‘Cold’ metals can feel more expensive than ‘Warm’ plastics for example.


When considering HMI’s for the crew systems such as CMS – Cabin Management Systems, and the equipment used in their daily duties, for instance GAIN – Galley Insert Equipment, more ergonomic factors need to be considered. Space is usually more of a premium in these areas and haptic feel can be crucial since the operation of galley equipment can often be hidden from the operators eyeline.

In the cabin areas there is often little available appropriate space on bulkheads because of the need for storage and other essential fittings. Traditionally, curved surfaces on the inside walls, underneath overhead cabins or small amounts of room between storage units have provided the only realistic opportunities for integrating controls and displays. But as the design of the customer experience advances the curved surfaces increasingly appear in First and Business class areas for both the seating and social environments. Therefore conventional flat and rigid HMI and Mood Lighting units have to be re-thought.

The advent of smart phones and smart technologies in all aspects of our lives has driven passenger demand for easy and intuitive access to seating, comfort and entertainment system controls. When the customer steps out of his Executive Automobile into his Business Class Seat, he expects to have no diminution in his experience. Essentially, HMI technology is now required to deliver visual and haptic feedback that crew and passengers require without instruction.

Aircraft Interior designers have made extensive use of secret-until-lit panel designs to ensure crew and passengers are only aware of status lights and icons when they are illuminated. One of the longstanding problems with traditional indicator technology used for this purpose is the amount of space required behind the panel for lamps and backlighting. If the illumination were to be made compact and light enough to integrate into seats and armrests as well as in the bottom of overhead lockers, aircraft designers could make much more extensive use of the technology.

The indicators may be combined with HMI technology such as membrane and capacitive touch controls in an increasingly smaller package. Light-guide technology has existed for a number of years. The conventional method of construction for the light-guide is based around a machined clear plastic part onto which are assembled LEDs, reflectors and diffusers. However, these assemblies can be clumsy and sometimes provide a less than satisfactory result in terms of brightness, homogeneousness and light bleed between graphics.

Our patented low profile backlighting technology makes it much easier to provide panels that can be seamlessly integrated into the aircraft design, such as the side or top of an armrest or the monument of a seat.  The technology takes advantage of the same properties that make fibre-optic communication possible. Transparent materials convey light according to Fresnel’s Law of Refraction. If the light hits the surface of this transparent material at a shallow enough angle, it will reflect back into the body of the material. A larger angle lets the light escape. The refractive index of the material determines how large this angle needs to be. Using a mixture of materials with different refractive indices, it is possible to guide light precisely to defined points. This is a radical departure from moulded light-guides and demonstrates significant cost and performance benefits. It allows multiple light guides to be integrated on a single substrate through the use of an optically transparent acrylic material. The process cuts a cavity into an opaque polymer layer into which the individually printed and laser cut acrylic optics are dispensed. This optically opaque cavity material serves to isolate adjacent light-guides preventing any bleed from one indicator to another. Using this technique, LEDs can be placed anywhere across the light-guide substrate depending on the needs of the application or optically coupled to the guide at the edge. The result is a light-guide with a thickness of 1.2mm or less: a significant reduction compared with traditional approaches.

As a result, the light-guide technology provides much greater flexibility and efficiency in the mounting of LED light sources. The resulting thinness of the package construction more readily allows for the requirement for curved surfaces.

A further advantage of the technology is compatibility with capacitive sensing. With conventional display and backlighting technology, one of the major issues with integrating capacitive switches is illuminating the switch graphics – such as on/off indicators – without interfering with the electric fields needed for sensing. As the light-guide technology provides illumination from comparatively remote LEDs, there is practically no interference received by the capacitive electrodes.

Through the use of optics and smart manufacturing technologies such as light guides TT Electronics can not only support improved HMI designs but also ensure that HMI’s can keep up with the demands of the latest customer experience styling concepts.

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We are the Global Manufacturing Solutions group of TT Electronics plc. From design and engineering, to integrated manufacturing of electronic systems, we deliver a full suite of end-to-end solutions to aerospace, defense, medical, industrial and rail enterprises with highly customized, low volume high mix product requirements.

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