Product category:
Switches and Keyboards
News Release from: Danielson (UK) | Subject: Membrane switches
Edited by the Electronicstalk Editorial
Team on 16 August 2004
Membranes improve performance and
functionality
Developments in membrane switch technology have opened up new areas of application in the automotive sector, says Andy Birch, Production Manager for Danielson.
Although membrane switches and keyboards are widely used in industrial and consumer products they have, until recently, had limited application in the automotive sector This has largely been due to the limitations in technology when compared with conventional methods of switching and backlighting and to the protracted process of achieving accreditation to automotive standards
This article was originally published on Electronicstalk on 6 Feb 2004 at 8.00am (UK)
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Perhaps as importantly, the complexity of selling this technology to specifiers and buyers in all tiers in the industry has further added to the slow take up of technology that otherwise offers exciting and innovative possibilities to automotive system designers.
To date, it has generally been concerns about long term durability in what is an extremely demanding operating environment that has caused specifiers to shy way from the use of membrane switches and keypads.
Now, however, to overcome the challenges of widely fluctuating temperatures and often high humidity, suppliers are now developing membrane technology specifically for in-car or in-cab systems.
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A new touch screen is billed as ideal for use in bank cash points, public kiosks or other applications where the interface has to withstand excessive use and possible surface damage.
Key developments have been made in the actual design and construction of the switches and the use of high specification manufacturing techniques and of materials, such as the latest generation of high performance coated polyesters from UK suppliers such as Autotype.
Polyester substrates and overlays are now deemed essential for most automotive applications as they provide the necessary mechanical and chemical properties.
This is especially true for tactile keys, where heat stabilised domes are formed within the polyester.
Previously, formed domes have had a limited life expectancy, due either to stress fractures around the base of each dome, or a tendency for domes to invert or collapse in extreme operating conditions.
Now, these limitations have been overcome through the advent of much more tightly controlled manufacturing processes, so that, for example, areas of potential stress in and around each dome are eliminated, and by better utilisation of the physical characteristics of hard coated polyester materials.
Hard-coated polyester also has the advantage of being resistant to most oils, greases and solvents, making it ideal for use as a tough keypad overlay material.
In addition, the latest polyesters are available with a range of textured surface finishes and with extremely efficient anti-glare and anti-reflective surfaces, typically with less than 1% visible light reflection, enabling them to be used with instrument displays and touch screens.
Similarly, a new range of high temperature and moisture resistant adhesives are now being used in the construction of membrane keypads and overlays.
These materials are capable of withstanding wide fluctuations in temperature, often from -20 to +50C and are easy and cost effective to apply during production.
Production techniques have also changed dramatically in recent years.
Operations such as the location of spacer layers, the insertion of LEDs and formation of switch domes that were once manual are now highly automated, enabling consistent, high quality and large volume production to be achieved.
The combined impact of these changes is to extend significantly switch operating life and reliability.
Circuit design and construction have also evolved considerably.
For example, in keypads where tactile metal domes are used, the use of redesigned circuit layers have made considerable improvements to switch reliability and functionality.
Such constructions effectively allow the entire switch mechanism to be confined to within the diameter of the dome, reducing the total area required by up to 50%.
The advantage of this type of switch design is that it retains all the features of tactile metal domes, without affecting keyboard performance, functionality or reliability; it also frees up more space for the switch circuits.
Another key development is low voltage backlighting solutions that can be used in conjunction with all types of membrane switches and keyboards for seat controls and foot wells, plus instrumentation, PRND and dashboard panels.
Until recently, backlighting for membrane keyboards has generally been achieved using point light sources, light guides or electroluminescent lamps.
These, however, have their limitations, typically producing hot spots, being complex to assemble reliably or, in the case of EL, have relatively short operating lives and require additional components to be used.
By contrast, the new low voltage backlighting development offers consistent and even light distribution, without affecting tactile response or other properties of the keyboard.
It also has an exceptionally long operating life and can easily be produced in both high and low volumes.
In essence, the new system comprises a custom designed layer, inserted directly beneath the graphics and, depending on requirements, switch and tactile layers of a standard membrane keyboard.
LEDs are then positioned within machined pockets in the base of the custom layer to act as a light source for individual switches, groups of switches or graphics areas.
Although this construction is similar to normal light guides, the new system incorporates innovative switch actuators that, through a special shape and coating, allow the light path and degree of diffusion to be carefully controlled.
This effectively eliminates bright spots and, as importantly, allows light to be directed precisely into those areas that require illumination.
In addition, the structure enables fewer LEDs to be used than would normally be the case and provides the option of using different coloured LEDs within the same keyboard.
One final point worth noting is that developments in sophisticated print technology now make it possible to enhance key and keyboard graphics and finishes.
This is a critical factor in the automotive sector where high quality is essential.
The latest developments in membrane switch technology are becoming increasingly suitable for use in the automotive sector.
Indeed, many of these latest systems are already being used in the cabs of tractors and trucks, for both primary and secondary instrumentation, and ICE and associated units in low and medium volume cars.
The key to success is for automotive designers and manufacturers to work closely with the membrane supplier from the outset.
This ensures that the membrane system is developed to match precisely the specific parameters of each application, eliminates possible problems and maximises the potential of the latest technology.
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