Monday, 31 July 2017

Membrane or Touchscreen?

Membrane switches have for many years been the dominant choice as the method of machine control in a multitude of industries. However, in the last decade, touch screens have been slowly transferring their prominent position in consumer products into the Human Machine Interface (HMI) market. With the advent of Industry 4.0 and the IOT, which direction will machine manufacturers take for their next input system?  

Membrane switches were invented more than 40 years ago. They first appeared in the late 1970’s as a low-cost method of inputting data into toys and keyboards. The very first switches consisted of two thin layers of plastic, these were printed with a conductive ink and separated by a spacer layer of adhesive, a decorative screen printed top film then adhered to the switching layer. When a key was pressed the two conductive layers would touch, allowing a voltage to flow.

The first switches were initially labelled as unreliable, with brittle materials that would crack or turn yellow after time. These switches also lacked any tactile feedback and were prone to inconsistent contacts. However, some enterprising individuals saw the potential in this new technology and formed companies in order to focus on manufacturing these new input devices.
Within only a few years these companies had developed new materials and processes that had eliminated all of the early problems and a new generation of membrane switches emerged. The new switches were reliable, had a customisable tactile feel, embossed or domed graphic overlays and resistance to harsh environments. Over the next 30 years a host of options and variations were added, such as a range of finishes, integrated LED, large area backlighting and anti-microbial coatings all of which increased the range of potential applications even further. The offer of a fully customisable product with a low cost and fast turnaround was difficult to resist and the membrane switch quickly became the technology of choice for HMI devices across a multitude of industries.      

However, by the 1990’s a change was on the horizon and touchscreen technology was arriving in HMI devices. Touchscreens are not new, in fact, they are older than membrane switches! The first finger driven touchscreen was invented by E.A. Johnson at the Royal Radar Establishment in Malvern, UK in 1965 and touchscreens were in use in some machine terminals by the 1970’s. The first touch screens were made with resistive technology. Resistive touchscreens have 2 layers of a clear flexible material coated in a clear conductive material which when pressed together by a finger would allow a voltage to pass, the resistance of this voltage could be measured to indicate the position of the finger on the screen.

The 1990’s saw the first widespread use of resistive touchscreens, these were in the first personal digital assistant or PDA and tended to use a stylus instead of a finger to push the conductive layers together. The first of these consumer touch applications suffered from slow software and poor display attributes, however, resistive technology was now firmly on the radar of the HMI market and the first resistive products started to appear that controlled machines.

The 2000’s saw the introduction of a new capacitive touch technology, this worked not by applying pressure to the screen to make a contact, but by sensing changes in the capacitance of its surface. As no switching pressure was required, this meant the top surface no longer had to be flexible but could be hard and flat, making glass a perfect choice as a top surface. No switching pressure also meant that no moving parts were required so long life and reliability were guaranteed. Public awareness of this new technology was captivated by the apple iPhone. Using capacitive technology, it revolutionised input systems for mobile phones by replacing numerous silicon keys with just one capacitive touch screen.            

For the HMI market, forward thinking companies who had already embraced resistive touch screens began to adapt capacitive technology into the larger sized screens that would be required to control machines. The new technology offered many advantages over resistive screens such as multi-touch and the ability to swipe across the screen. 

Today the change from membrane technology to capacitive technology for machine control is rapidly gathering pace. The onset of the IOT and industry 4.0 requires the machines of the future, whether they are controlling a production line in a factory or controlling a life critical function of a patient in a hospital, will have to be “smart”. They will empower machine operators with not only live information but also predictions enabling them to take crucial decisions to produce optimal outcomes. These decisions and information exchanges will often be carried out in a live networked environment.

A customised touch screen is the perfect solution to control tomorrow’s machines. A large display with an interactive capacitive touch allows a symbiotic relationship between machine and human, this grants both the ability to transfer and receive information quickly and accurately. As the future unfolds and new needs and requirements become necessary, the information and controls can be easily changed by a software update, therefore, making the input system completely future proof.

Membrane switches will always have their place, but the machine control of the future is a touch screen.

Andy Stevens is the commercial manager for SCHURTER Electronics Ltd in the UK and has worked in the HMI industry for more than 25 years.

SCHURTER Electronics was a founding member of membrane switch technology and one of the first manufacturers of resistive touchscreen technology. Today it is leading the way in the capacitive touch systems of the future and offers its customers the solutions they require to grow in their markets. 

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