NEWS JULY 2023
Smart Cover Len's Design for Smart HMI.
By Richard Applin.
 01/07/2023
For HMI Designers the Cover Lens forms the outer surface of the product, and the first point of interaction for the user.
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Custom Cover Lenses fulfill the unique aesthetic and material requirements of any industrial application.
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Incorporating impact resistance requirements, toughness and scratch resistance, as well as moisture and dust ingress protection, the Cover Lens and method of bonding are critical to successful HMI Design.
How Does Halo Deliver Seemless HMI Cover Lens Integration?
Whether a product is Touch or Non Touch based, the Cover Lens is integral to the design. Halo places significant emphasis on consultative design with our client's , defining form, fit and function, material properties and special features. Here are some of the main design considerations:
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IK Rating. IK ratings help to classify products by their
resistance to impacts, which is especially useful when
considering hand held devices, which can be dropped from
height. Halo utilises Chemically Strengthened Glass to ensure
even our standard lens materials meet IK06 ratings. For very
rugged applications, we can use IK09, thicker substrates,
and even tailor the PCT Sensor IC to enable Touch
Activation at thicknesses of 6mm or greater.
Optical Bonding: Halo deploys Optical Bonding in almost all client
projects. Filling the air gap with an Optical Clear Adhesive or Film
/Resin, depending on the size and weight of the combined layers,
provides moisture and dust ingress protection, higher contrast ratio,
and impact resistance.
The Optical Bond is made between the Cover Lens and the Display
and is usually 0.1mm or thereabouts in thickness. The process is not
considered re-workable, and careful attention must be paid to curing
to ensure that small bubbles do not evolve over time, when subject
to changes in pressure during transportation or operation.
Once the preserve of higher value niche product design, in Military
and Medical applications, Optical Bonding is now widespread.
Curved Lens design is increasingly relevant with the advent
of Smart Controls for Industrial and Home Automation design.
Combined with rounding or corners of beveled edges, Design
Engineer's are increasingly experimenting with unique shapes,
form factors and sizes.
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Often the Design Engineer will specify an oversized border
lens design with large rounded edges for form an oval or
significantly rounded front design, combing hidden till lit
black Silk Screen Printing with smoked effects delivering
varying levels of opacity.
ESD Design Engineers will be required to meet certification for EMC
and ESD related to their specific sector. For instance, 15 KV ESD for
Air Discharge and 8 KV ESD for Contact Discharge is common in
ISO13486 Medical product design certification.
Halo often advises clients to add some overlap in the boredr of the
Cover Lens, to ensure that the charge path is located further from the
risk components and display IC.
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The diagram on the left clearly shows an identified discharge path, where ESD is able to contact the TFT FPC. Analysing various materials to fill the gap with, the table below demonstrates the required thicknesses to mitigate an 8KV discharge event. The best performing material for thickness would be an ESD Acrylic Tape.
The tape can be implemented to fill the gap . 3M provide suitable gasket DST (Double Sided Tape) , which can be deployed to adhere the display within a recess, but also tackle 8 KV discharge events. Halo often consults clients to design a Double SIded Adhesive Gasket for their lens.
Speak to us today to understand more about designing smart and novel Cover Lenses to enhance your HMI Design.
Holes and Cut Through Features. As a Design Engineer you may be challenged to deliver tactile controls which need to protrude through the border of the Display Cover Lens.
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This could be in the form of a Rotary Switch, or a physical button. Either way Halo is able to use laser cutting techniques to machine holes straight through the lens material delivering a unique integrated tactile HMI Design.
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Consideration is given to mechanical integrity, as holes created too close to the edge of the Cover Lens could lead to weakening mechanically. Holes are also recommended to integrate rounded internal edges to aid stability.
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