May 22, 2008 by craftadmin
The spread of touch enabled products, like the Apple ITouch and the self service check-in terminals at most airports is familiarising the general public with the concept of touch systems, encouraging more and more similar applications. Having worked with electronic displays and touch for more than 20 years Craft Data has seen the increase in the need for touch in a host of different projects. Touch technology has gone from, in many cases a luxury aspect of the application to now being a necessity.
There are a number of different touch technologies however we have focused on the main players. Each technology has advantages and disadvantages when compared so hopefully this blog will help you understand what will and won’t work for you in your particular application.
The simplest and probably the most widespread is the low cost Analogue Resistive. This is basically a flexible polymer front sheet and a glass backing substrate (although now an acrylic backer can be made available), both having their inners surfaces coated with a conductive layer sealed together but separated by tiny clear rubber balls/spacers. Electrical connections are made to all four sides so when the front flexible polymer surface is pressed against the rear substrate compressing the clear rubber balls, current flows side to side and top to bottom, the magnitude of which indicates the point of contact. When the touch pressure is removed the rubber balls return to normal and separate the two surfaces. Any stylus can be used to make the touch, although something that will not scratch or puncture the front film is preferred.
If ruggedization or vandal proofing is part of your specification whilst still requiring a tactile touch response then possibly the resistive hybrid “Ultra Touch” could be suitable. The usual flexible front polymer sheet is replaced by a flexible glass/polymer laminate sheet and coupling this with a chemically strengthened glass or polycarbonate backing substrate makes this technology ideally suited for public kiosk type applications.
Infrared is a long established technology originally developed for schools and children with dexterity/mobility problems. It utilises infrared emitters on two sides of a PCB frame and detectors on the opposite two sides creating and invisible array across the display screen’s surface. Any non-transparent stylus touching the screen breaks both the vertical and horizontal beams, defining the touch point. The touch frames can be fitted to most popular monitors with screen sizes up to a huge 108” diagonal, retrospectively if necessary. A 2M diagonal version is the largest frame size to date, designed for a TV game show.
Surface Acoustic Wave systems (SAW) have transducers mounted on two corners of a sheet of glass which has machined reflectors on all four sides. Acoustic waves are transmitted across the surface of the glass both vertically and horizontally which are reflected back. Since the distance is fixed and the frequency of the wave is known, if a finger touches the glass, part of the energy wave is absorbed and the point of touch/absorption can be computed.
The stylus needs to be energy absorbing, a finger is ideal and possibly even a gloved finger but a pointer or a pencil for example are not. For vandal protection the sensors can be made from 6mm or more toughened glass.
Capacitive systems are also based on a sheet of glass but here the outer surface has a conductive coating. Electrodes at the corners generate an energy field across this surface so when a conductive stylus e.g. a finger, makes contact, a small current is drawn from each electrode and the relative values indicate the touch point.
More and more industries are making use of touch interfaces, any type of menu, POS, medical and public information systems are just a few common applications. If you have a possible requirement for a touch from 2.8” through to 108” and want help with deciding which technology is right for your application and budget please contact us by phone, email or fax. We are not just pushing one of the preceding technologies from one manufacturer but will listen to your needs and make a recommendation on what we feel is right for you.
Posted in Touch