HMI solutions for extreme environments

Freezing cold, summer heat or thunderstorms – in extreme weather conditions, many input systems quickly reach their limits. Increased protection against vandalism also plays an important role in the use of robust input systems.

In addition, the high demands on hygiene pose a further requirement. Therefore, input systems that are used in highly specialised HMI applications under harsh environmental conditions require extensive experience in development and design.

Applications in demanding environments always require special solutions. Input systems are used with appropriately qualified materials that guarantee maximum reliability in order to meet all requirements. These input systems are manufactured using state-of-the-art production technology and meet the highest industrial and medical standards.

Touch panels have proven their importance as an interface between man and machine in many applications for years. For new developments in the industrial sector, they are the most important operating concept. For extreme requirements, robust and durable input systems are used. When selecting the appropriate touch technology and developing and designing such HMI touch panels, the required specifications of the application must be taken into account.

In addition to a visually appealing and easy-to-install design, the requirements for touch panels in industry are above all durability and robustness. Industrial applications demand scratch-resistant and mirror-free surfaces. They also have to withstand high stresses caused by water jets, steam and dirt in order to maintain tightness against aggressive harmful gases. The complete surface of the input system must be resistant to oil, solvents and aggressive chemicals and meet the IP67 protection class. In addition, perfect operation with gloves must be guaranteed. 

A continuously closed front structure without soiled edges is required. This design facilitates cleaning of the touch panels, which is of great importance in the food industry, for example. In process visualisation, a reflection-free surface with optimal image brilliance and sharpness is primarily required. All components of the input system must meet EMC conformity.

In the field of medical technology, special challenges arise for the operating units with regard to lighting options, salt water resistance, EMC shielding, antimicrobial surfaces and chemical resistance.

Outdoor applications require sunlight-readable touch displays with increased UV resistance and weather-resistant materials. The input systems must withstand extreme temperature changes and the influence of humidity and water. An extended temperature range of -40 to +85°C is required.

Industrial applications

Capacitive PCAP touch technology is a mature technology designed to meet industrial requirements comprehensively. Capacitive multi-touch film sensors are laminated optically which is highly transparent behind printed front glasses. Glass-based sensors are bonded with special materials. Robustness against mechanical stress is guaranteed by the selection of hardened glasses. In combination with a laminated glass panel laminated on the back, vandal-proof touch panels for public applications can be realized.

For touch panels in hazardous areas, special sensors have been developed for use behind 10 mm thick front glass. For use in food production, splinter-free front materials are used. In addition to PMMA, polymer composite materials are available as unbreakable front material with extreme impact resistance with IK 10 specification. Furthermore, for such applications, the front glasses are laminated with a shatter-proof film.

EMC conformity is fully guaranteed by the use of pre-qualified controller systems in accordance with the industry standard.  The front glass is integrated all around by means of a chemical-resistant gap encapsulation. Front glasses with an antiglare surface reduce reflections and are resistant to mechanical and chemical influences. Operating temperatures from -40 to +85°C are made possible by the selection of qualified materials.

Medical applications

PCAP technology is qualified for medical applications and meets the requirements for water and salt water resistance, EMC immunity, glove operability, antimicrobial surfaces and chemical resistance. For optimal visualisation of the screen content, the display is integrated with optical bonding.

The integration of the PCAP sensors behind a printed cover glass enables an attractive design in customised colours, a variety of backlighting options and an easy- to-clean, closed surface. The structure of the cover glass is optimally adapted to requirements such as antireflection, antimicrobial effect, pleasant haptics or dirt repellency. Antimicrobial and antiviral mechanisms based on silver ion particles are coated onto the surface of the cover glass in a special process. This coating is stable over the entire lifetime of the application.

The front-integrated cover glass is sealed around the circumference with a chemical- resistant gap seal. In addition to the sensor, the most important component of a PCAP system for medical applications is a functionally reliable touch controller. EMC influences occurring in the environment of the application, for example in HF surgical devices, are reliably eliminated by special firmware algorithms.

For applications in radiation-critical areas, such as MRI devices, an additional metal mesh foil is integrated into the sensor structure to shield the radiation. Furthermore, resistive touchscreen solutions in special designs such as glass- film-glass (GFG) or low reflection (LR – sunlight readable) and as resistive multi- touch are used for mobile medical devices for outdoor use.

A combination with capacitive switch elements (CapKeys) such as buttons, sliders and wheels or haptic membrane switches can be realized with all touch technologies.

For example, the combination or use of membrane switches in medical applications enables solutions with backlighting or in night design without glare or overdriving of the lighting. Furthermore, key point and key surface illumination as well as symbol printing in the so-called disappearing effect (black panel) are available. EMC shielding is integrated by means of an additionally printed foil that is laminated into the layer structure of the keypad and contacted to the electronics. The design and integration of chemically resistant membrane switches is carried out without soiled edges and facilitates the cleaning of the application.

Outdoor applications

For extreme outdoor applications, resistive GFG (glass-film-glass) touch screen technology is used in addition to specially developed PCAP sensors. Reliable function in snow and ice as well as daily sunlight UV radiation can be realized with this technology. In combination with the Low Reflective (LR) design, the reflection rate is minimized to 1.5%. This makes the display content of the application optimally readable even in direct sunlight.

If the application requires multi-touch functionality, the resistive multitouch (RMT) design is available. This RMT can be shielded with a metal mesh film on the front for medical applications.

An optically highly transparent bonding (optical bonding) of the displays with the front glass and sensor results in excellent readability by preventing reflections and increases the mechanical robustness of the panel. By using this technique, an improvement in the viewing angle based on reduction of the reflections is being created, which is particularly used in medical applications.

Optical bonding increases the shock resistance and vibration resistance of the touch panel. The filling of the air gap prevents condensation and the penetration of dirt and dust particles. UV- stable optical bonding materials are used. The constant distance in the structure also improves the touch performance of the PCAP sensors. Optical bonding is carried out in liquid or dry bonding processes. Qualified, UV- resistant and silicone-free materials are available according to the requirements of the application.

Especially for applications with extreme operating conditions, the realisation of an optimal solution requires a high degree of know-how and experience. All specifications and their special requirements in the application must be verified and qualified.

Based on its know-how, Schurter Electronics finds the optimal solution even for the most demanding applications and areas. With the company’s experience, it develops and designs the perfect input system together with customers, for use under harsh and demanding conditions.