This technique projects accurate patterns onto a target and then measures the displacement or distortion in order to calculate the shape, size or position of the object. In the easiest form, a line is projected onto a target and observed under a known angle from a camera. The distortions in the line can then be translated into height variations. This technique is often referred to as laser triangulation. Structured illumination is often used to obtain height information and especially for 3D inspection tasks.
Uses for this technique include: inspection of food items to check for correct volume or product deformations and foreign object inclusion. It can also be used to check the surface profile of objects against known good examples or a golden template to ensure perfect product quality.
To obtain the most accurate 3D information, very narrow and sharp illuminated lines are required. This is usually achieved by using laser technology or structured LED illumination. In addition a narrow pass filter is fixed on the camera, only transmitting the reflected laser or LED light with no ambient light.
The image shows a regular squared pattern being projected onto a component to allow a comparision with a sample, or for accurate measurements to be taken.
Structured lighting is also widely used in alignment applications where markers are required to adjust tools or components and is also employed in medical applications such as the placement of patients for X-ray or radiation.