Optical Sensor Technology
The advent of digital camera technology and use as sensors in touch displays is a more recent development than other technologies.
Consisting of line scanning optical sensors (i.e., cameras), a glass substrate and lighting or reflective strips along three of the four borders (see image below), this type of touch system application also requires a mechanical frame or bezel be constructed and implemented onto the manufacturer's original display.
On the top two corners of the substrate two cameras are positioned, and the light strips provide a reflective border, creating a field of infra-red light slightly above the glass surface.
Introducing a finger or object touch into the field, the light path is blocked and the touch controller calculates the X-Y coordinate position.
It should be noted that the field created by this technology requires about a 1/8", or 3.5mm additional depth beyond the depth of the glass substrate, and that the resulting frame-based solution may be deeper than an infra-red sensor touch system, and certainly more than on-glass construction utilizing other sensor technologies such as 3M DST, SAW or Surface Capacitive touch.
Optical Touch: Key Points
- high opitcal clarity (depending upon substrate quality)
- use of finger, gloved hand or stylus touch
- functions with scratches or surface wear
- requires addition 3.5mm depth beyond glass substrate to acheive function
- open area created by frame collects dust, debris and other environmental influences which can compromise function
- requires mechanical frame or bezel
- obstructions, liquids or contaminants can reduce or eliminate function until removed, including "false" or inaccurate touch
- touch occurs slightly above the surface which can result in unintended touch response, or "touch parallax"
- optical sensors (cameras) introduce "wear-out" potential to touch mechanism