FEATURE SWITCHES & RELAYS IT’S A MATTER OF TASTE AND STYLE
Robert Davies, marketing manager of EAO offers an overview of electro-mechanical switch-based human machine interfaces and how they are defining the latest generation of electronic devices
H
MI component technology has undergone major changes over the
years to serve the increasingly specialised needs of machinery. Today’s HMI typically comprises a number of electromechanical switches that control critical functions and deliver the tactile feedback (haptics) and full switch travel essential for intuitive equipment operation. Available in a wide variety of shapes, sizes, and electrical specifications, with a choice of environmental sealing, mounting and termination styles, today’s switches are precisely crafted devices, made to exacting design specifications. Very close tolerances and carefully
calibrated springs ensure a typical mechanical life of between 1 million and 10 million operations. The use of high-grade plastics and metals available in wide range of colour options, including metallised plastic and anodised aluminium match or complement front panel designs while switches manufactured in durable stainless-steel meet the needs of equipment used by the public and/or in hygienic applications.
ERGONOMICS Designers of HMI systems have always had to determine critical parameters such as electrical rating; switch action; operating mode; contact configuration and terminal connection method, but ergonomics have become just as important. Intuitive operation is part of any modern HMI design, so operator controls must be designed and arranged for maximum user- friendliness and to ensure error-free switching between the various production steps. Size, illumination and visual and tactile ‘feel’ are becoming increasingly important and special requirements such as switch illumination and lens marking (symbols\legends etc.) must be readily available. Additional design considerations include
panel mounting style - raised bezel, or bezel flush with the front panel; the physical mounting hole and the available front/back panel space. The use of mixed technology such as the integration of a touch screen and electromechanical switching in a panel means that a switch will often need to be positioned close to an
24 SEPTEMBER 2018 | ELECTRONICS Figure 1:
Size, illumination and visual and tactile ‘feel’ are becoming increasingly important and help define brand and quality
LCD screen and so needs to be broadly similar in depth. Flush-mount switches that protrude only a few mm from the front panel meet this requirement and go a long way towards avoiding inadvertent actuation.
Figure 2:
Push-buttons featuring bright illumination and laser marking, etching and engraving of icons or text on to coloured lenses ensures the clear identification of each button's function
PUSH-BUTTON SWITCHES Push-buttons featuring bright illumination and laser marking, etching and engraving of icons or text on to coloured lenses ensures the clear identification of each button's function, and ‘secret-‘till-lit’ legends avoid confusion by becoming visible only when a particular function is available to the operator. By incorporating the latest LED lighting technology into switches designers are able to create dynamic multi-coloured lighting effects that deliver a satisfying and reassuring response to the user. In industrial applications such as machine
tool control and food processing, control panels have to tolerate harsh daily usage by operators using gloved hands and must
resist the harsh chemicals and/or high- pressure hose downs used in periodic intensive cleaning. Industrial water- and oil-tight switches provide front- and back- panel protection against the ingress of dust, dirt, water, solvents, and other foreign materials and are tested to meet international IP rating such as IP65, IP67 and even IP69K.
IT’S AN EMERGENCY - STOP! A fault condition in machinery or equipment will often threaten the equipment, its operator or other people in the vicinity. It’s essential therefor to have a clear, reliable and fool proof means to bring about an ‘emergency stop’ when necessary. Emergency Stop switches have evolved to provide the designer with a vast choice, ranging from compact 16mm mount fully waterproof switches suitable for hand held control boxes through to large 22mm mount metal body products that are resistant to harsh environments and operator abuse. Each application has its own special
requirements, but E-Stop switches today must meet EN 60947-5-5 and the new IEN 13850 regulations, which mandates that they feature a trigger action - where the switch must latch-in past a point of no return as the contacts open. In addition, the contacts in a dedicated E-Stop switch must have a forced opening action to guard against contact welding. Illuminated E-Stops are available for use in low-light environments and/or for night time operation Equipment builders today need to concentrate on their ‘core competencies’ – ensuring that their products do what they are designed to do in the most cost- efficient way. In this they are being helped by forward-thinking HMI specialists offering fully integrated front-panels complete with added value products such as cables and connectors, supplied as a fully assembled and tested package. By working closely with an expert HMI partner, the design, manufacture and supply of the complete HMI can be reliably outsourced.
EAO
www.eao.com T: 01444 236 000
/ ELECTRONICS
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