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Improving the man/machine interface in industrial control systems

13 June 2023

Membrane switch and FFC technologies can help enable reliable human-machine interfaces in industrial applications, explains Phil McDavitt

MACHINES IN industrial plants, from power generation to manufacturing or food processing, are frequently situated in harsh environments. This means their control panels and HMIs (human-machine interface) must be able to cope with extremes of temperature, humidity and particulate matter - as well as ideally being easily wipe-clean and potentially resistant to high-pressure steam cleaning and washdown protocols. Here, explains how… 

Industrial HMIs 

Machines and industrial automation equipment found in production settings, including manufacturing, assembly and processing plants, typically require some type of interactive control system in the form of an HMI. While back-office systems may feature standard electronic and computing kit (including, for instance, PCs, keyboards and mice, touchscreens and displays), HMIs on the shop floor must be more rugged, combining ease-of-use with a sturdy form factor that can deal with the extremes of industrial environments. 

Touchscreen panels, LEDs, membrane switch keypads and electromechanical controls (such as joysticks) are more commonly used interfaces in industrial automation settings. They offer greater robustness, simpler and more reliable ease-of-use, and longer lifetimes. IP-rated protection guarantees resistance to extreme environmental influences, including the unintentional ingress of foreign bodies, including dust, dirt, liquids, moisture and even aggressive media. 

Flat flexible cables 

'Under the hood', flat flexible cables (FFCs) provide the board-to-board connections between the electrical switches and other sub-assemblies and PCBs (printed circuit boards) in the system, integrating cables into complete interconnect solutions. FFCs offer mechanically strong, reliable signal and power connections, alongside significant space savings and easier cable management.

They also deliver superior EMI/RFI shielding, which is crucial in electrically noisy industrial environments (caused by a multitude of power cabling, communications networks and motors). Nicomatic-patented Crimpflex connectors provide solid, dependable electrical and mechanical connections between the FFCs and other system components. 

Membrane switches 

With electrical switches deployed throughout diverse applications and environments, many factors can affect their lifecycle, which may vary considerably from that achieved under strictly controlled testing conditions. Metal domes are used in membrane switch keypads to enable the electrical connection from the switch or keypad, enabling end-users to initiate specific functions. The switch domes are mounted on PCBs, FPCs (flexible printed circuits) or silver-printed flex membranes. 

To ensure the most suitable dome is selected for each application and environment, design engineers should consider: 

  • How many cycles will the dome be used for? Will the switch last the expected lifetime of the HMI?
  • How much force will a typical user press the switch with? And how much tactile feedback does the user need? 
  • What environment will the HMI be deployed in? 
  • What size and shape of dome fits the application? 

Novel approaches address challenges 

New approaches in dome technology can help solve common problems. Nicomatic's patented Switch Air Domes are four-legged metal domes with a notch that creates a cushion of air between the domes to prevent them sticking to each other, a common issue. They are also very low profile, making them ideal for many domestic products, including microwave ovens, dishwashers and washing machines – as well as for industrial HMI control panels. They are even used in cash machines - a consumer application in which users take robustly functioning keys for granted! 

Reliable technologies for industrial control interfaces 

HMIs and control panels in manufacturing production, processing and industrial automation applications must often endure harsh environments, ranging from extremes of temperature, humidity and electrical noise to frequent exposure to grease, dirt and debris. To ensure robust and reliable operation, they employ interface technologies that can handle these demanding requirements - including ruggedised touch panels, electromechanical controls and membrane switches. FFCs provide the connectivity between these system elements. Interconnect specialist, Nicomatic can help design engineers identify and specify the ideal components for such HMI systems. 

Phil McDavitt is UK MD at Nicomatic

For more information: 

www.nicomatic.com

Tel: 01183 801 033

 
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