Touchscreen Developments for Industrial Control

Article courtesy of Zytronic

New developments in touch screen technology are widening their suitability for industrial control applications. Enhanced sensitivity ensures that screens perform better than ever behind protective cover glass and with gloved hands. New controllers are also less sensitive to electrical noise in the environment, and attractive new features are emerging.

One touch technology, projected capacitive or P-CAP, is dominating the industrial touch control landscape. P-CAP is also the most popular technology in high volume phones and tablets. This success has been driven by a compelling feature set, including an effectively unlimited lifespan conferred by a resistant all-glass surface, edge-to-edge design capability (with no requirement for bezels) and high levels of sensitivity. These features also appeal to industrial control applications. The volume of sales in the consumer market reduces costs, but drives R&D investment leading to capabilities, some of which are also suitable for the industrial market.  Examples include force recognition (Z-axis detection) and gesture recognition.

High Sensitivity

Fundamentally, the key attribute of P-CAP touch technologies such as PCT™ and MCPT™ is its high sensitivity. It can detect a touch through very thick overlays, protective glass and even heavily gloved hands and therefore has an unsurpassed level of Z-axis sensitivity and control.

Coupled with a well-designed touch controller P-CAP can offer a reliable and intuitive touch experience, responding precisely to up to 40 touches. Although many instrument designers believe that users will only touch the screen with one finger at a time, multi-touch functionality can still bring advantages. For example, gesture recognition such as the pinch and zoom action popular with tablet users relies on the ability to recognise more than one touch point. Palm rejection, where a screen ignores a hand resting on the screen but still recognises and responds to an intentional touch, similarly requires multi-touch support.

Force sensing

A further development as yet little used in instrument user interfaces but with great potential is force sensing . A common objection to touch screens is that they don’t provide feedback in the way a mechanical button does, if a user is looking away. Using force recognition, a verbal message can alert the user to the option selected when the screen is touched lightly. The selection can be confirmed by pressing harder. So for example an instrument can say ‘temperature’, ‘pressure’ or ‘time’ as the user’s finger moves across the screen. Once the finger is over the correct option, a firm press makes the selection. This approach also allows partially-sighted users to be accommodated.

Extending force sensing from handheld devices to larger touch screens used in commercial and industrial applications is much more than a matter of simply scaling up the same technology. Most smart phones use capacitive sensors integrated into the display. This approach would be very costly if scaled up to a large screen, and is also incompatible with the protective cover glass often fitted to kiosks and other touch screens used in public places. Zytronic’s approach is based on a measurement of the surface area of an applied touch, which changes the measured capacitive signal levels at the relative touch location on the sensor. This eliminates the need for a piezo-electric or other layers on the glass to measure applied force or pressure, and means that the technology can even be used on thick, rigid and vandal resistant toughened glass surfaces.

Improved Immunity to EMI

e (EMI) is often an issue for touch screen systems placed into industrial environments. Similarly, touch screens deployed in areas where the power supply is inconsistent or not well regulated will also be affected by transient interference coming up the power cable from the mains supply. This can create problems for touch screens and their control electronics in terms of identifying the signal (or touch) from the surrounding noise, i.e. decreasing the signal-to-noise ratio, and thereby impairing the identification of true touch events.

Major improvements to the electronic design and touch detection firmware employed by the touch controller are ensuring that signal integrity is maintained at a high level.P-CAP touch technologies such as Zytronic’s proprietary Projected Capacitive Technology (PCT™) have an X-Y matrix of micro-fine capacitors, embedded within a laminated glass substrate, and use frequency modulation to detect minute capacitance changes within the conductive tracks. One way to combat EMI is to implement a ‘smart’ frequency-scanning function in the touch controller. The operating frequency moves dynamically between 1.3MHz and 2.5MHz in order to avoid detected environmental ‘noise’ that would otherwise prevent the detection of touch events.

Zone 1 applications

Suitably designed touchscreens can even be used in hazardous and explosive (zone 1) applications such as oil rigs. Zytronic’s proprietary self-capacitive touch sensing technique induces a known frequency (around 1 MHz) within these capacitors, which in turn, is altered by a user’s body capacitance when their finger comes in proximity with that part of the touchscreen’s surface. Through sophisticated algorithms embedded within the connected touch controller’s firmware, the position of peak frequency change is interpolated. This method of touch detection is so sensitive, that the PCT sensor matrix may be embedded within a laminated, thick protective overlay. The firmware may also be easily tuned by the user via a driver to adjust touch sensitivity and threshold detection levels so that the screen will respond to the lightest of touches or full finger pressure, depending on application requirements. It can also support heavily gloved hand operation, making it highly optimised for outdoor and industrial applications.

Glass improvements

Materials technology is leading to glass that is thin and light yet very tough indeed. The latest development is to include anti-microbial elements in the glass, ensuring that any bacteria on the glass surface die away rather than multiply. Zytronic has collaborated with Corning, to use their unique Antimicrobial Corning® Gorilla® Glass, the first antimicrobial cover glass registered with the U.S. Environmental Protection Agency (EPA), as a safe and non-toxic material for display cover glass. This glass contains an ionic silver component which serves as an agent greatly reducing the ability of bacteria to proliferate, helping to keep the glass clean. Furthermore, Gorilla Glass is tough and scratch resistant, so is unlikely to develop cracks in which bacteria can multiply.  The anti-microbial agent does not affect the excellent optical clarity of the glass. For external or unattended touch screen applications, where added rigidity and impact resistance may be needed, Zytronic can laminate the chemically strengthened Antimicrobial Corning Gorilla Glass cover layer with a thicker, thermally tempered rear glass, to create an incredibly impact resistant ZyTouch™ sensor.

Combining the renowned benefits of damage resistance, optical clarity and touch sensitivity, the Antimicrobial Corning Gorilla Glass is formulated with antimicrobial properties to help keep touch surfaces clean of stain and odour causing bacteria, with a performance that will last the lifetime of the display.

Design Constraints

Space is usually at a premium in industrial and other instrument designs. There is a clear advantage if the footprint of the touch controller can be kept to a minimum. Reducing the PCB size is therefore important, as is making available the controller chip-set, so that designers can consider embedding the touch controller onto an existing system motherboard.

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