Structured LED illumination
Some of the more common reasons for this follow:
- Speckles (light granulation) might cause a laser line to look much wider for the camera sensor than it really is, thus reducing the resolution of measurement results significantly.
- Laser use has strict safety rules and relatively low light output with narrow fan angles mean lasers could get defined as class 3R. This could result in a much higher effort in the system design to comply with user safety regulations (see chapter 2.9 illumination safety classes).
The advantage of using LED illumination is the lack of speckles and the fact that illumination in the visible range is usually classified in LED class 1 or 2, not requiring complex precaution measures.
Structured LED illumination consists of
- LED light source, usually a spot light with a single LED as emitter
- pattern template for creation of the desired light pattern
- lens for reproduction/projection of the pattern
LED light sources produce a homogeneous spot and are usually available in different colours, ranging from red to blue, including ultraviolet, infrared and white. As white light is not available as laser light, but might be important for colour applications. LED structured light offers a viable alternative option.
Using a pattern template, different patterns such as single lines, multi- lines, crosses or spots with crisp edges can be created. Customised pattern templates for structured LED lights can be produced at far lower cost, compared to optical elements for laser solutions.
Using a lens allows scaling of the pattern to the right size for a defined working distance. When selecting the correct lens, the main focus should be given to the quality of the lens to deliver maximum resolution at the same time as reducing image defects such as distortion.
Despite the possibilities the use of structured LED illumination offers, lasers are often indispensable for many triangulation tasks, as line width of 10µm can be achieved, compared to LED lines being minimum 50µm wide.
Beside the structured LED spots there is the possibility to project multiline pattern with a flat dome light. With this method, line are projected onto the reflective object Surface. The line pattern Lights highlight the irregularities as curved lines. When there is no irregularity, the lines are reflected evenly (without curves). The line pattern Comes with 1 mm interval and with a 2 mm interval.