Touch Me!

click here to read this article in ProSystems Africa News magazine July/August 2016.

These days the words ‘screen’ and ‘touch’ go together like bacon and eggs. It’s nothing new to touch a display screen and expect a relevant response. Consumer grade mobile phones, tablets and most notebooks are all touch-enabled. Interacting with a display has become part of our daily lives.

Many moons ago the idea of touching a display to initiate a command was only known from Hollywood sci-fi. Touch Screen technologies have been experimented with from as early as the late 1960s. However it was only around the turn of the century that we saw touch enabled point of sale systems and interactive information kiosks become more customary in retail spaces. High-end meeting and conference venues utilized state of the art touch overlays over LCD and plasma screens, and back then homes-of-the-future had touch panels with processors controlling their environments. Interactive projection also grew in prevalence, but has never entertained the same levels of attention as touch LCD screens. In the case of interactive projection, ultra-short throw projectors are paired with infra-red or radar devices which cast a separate grid over a projected image. A stylus pen or finger is then used to interact with the grid on a solid surface such as a white board with a low reflective surface.

LCD touch technologies have seen many iterations over the years. Each variation of touch screen architecture focused on the key features - accurate touch and near instant response time - but with an objective of improving a previous result. The biggest challenge in any touch technology is for interaction to be acknowledged by the system and then another challenge is to determine the precise location of the touch on the screen.

The aesthetics of modern day touch overlays such as capacitive and resistive technologies used in smart phones, tablets and kiosks mask very well any visible hint of external technologies. Capacitive Touch screens consist of a conductive coating over a transparent insulator, such as glass. The human body, being an electrical conductor itself, then disturbs the screen’s electrostatic field when touching it. Many variations of capacitive technologies are available, but essentially these function in a similar way. A grid array of sensors is continuously scanned to determine the location of the touch. Resistive Touch screens consist of two layers, each with a fine grid of conductive material placed over each other with a micro cavity in between. The top layer is typically softer, and, when pressed down, makes contact with the bottom layer. A short-circuit registers a resistance in the voltage which will indicate a touch. The X and Y coordinates of the grid determines the location. Not all touch screens are as smooth looking. Alternative technologies have equipment integrated into the bezel of the screen, with protective glass covering the display surface. Because of the integration in the bezel, the latter sits proud from the display surface and could be perceived as a bulky finish.

Surface Acoustic Wave (SAW) and Dispersive Signal Touch (DST) are vastly different technologies but both utilize wave interference by finger touch. SAW systems emit ultrasonic waves over a display from two sides and then measure the same waves from the remaining two sides. An object interfering with these waves will absorb a percentage of the energy and the relevant touch controller then measures the change in amplitude in order to determine the touch location.  DST in turn, measures the bending waves created by a finger touching a display surface from all around the surface area. This is similar to the ripple effect of a water surface when disturbed. Neither of these technologies is very popular because of substantial interference of surface particles such as dust or humidity.

Infra-red (IR) touch systems have IR emitters and sensors around the bezel of the display to form a grid in front of the touch surface. When touched, one or more light paths are broken and based on XY coordinates, a touch, and its location, is registered. Optical Touch systems have LED lights integrated into the bezel, which creates an invisible light layer over the display area. Two cameras from the top corners are monitoring disturbance in the light plane and thus determine touch and location. These technologies do not perform well in very bright environments.

Shadow Sense Touch (SST) is the newest kid on the block. LED lights are integrated into the sides and bottom of a display bezel, with optical sensors in the top corners and top bezel. These sensors measure a shadow created by the interference of a light path. Because of SST architecture being positioned in the bezel, the product, like other optical touch technologies, is also available as a video wall over-frame kit. Individual bezel pieces are mounted around the perimeter displays in a video wall up to 6m in width. These bezels then function collectively to create a touch capable video wall.

SST not only determines a touch and its location, but also identifies the shape of the touch-object used. Software then allows the user to configure a set of parameters in order to accept certain shapes, and ignore others. This feature revolutionized the world of annotations because fingers and pens can be recognized, whilst suit cuffs and hand palms can be dismissed. This in turn reduces headaches, frustration and violence in the workplace.