The triangulation is a well known technique of classical optics, especially used in geodesy. The combination of the laser with the triangulation created a new field of application for laser distance measurement. In principle, the laser distance measurement can be classified to three major sections where each one uses a particular property of the laser. For distance or length measurement with interferometers, the low divergence and the coherence of the laser is used. In laser range finding applications, the low divergence of the laser beam and the defined speed of light is used. In the case of the laser triangulation, only the low divergence of the laser beam is exploited. Each technique has a particular measuring range and accuracy:

1. Triangulation 1 to 50 cm with an accuracy of 10-3
2. Interferometer up to 50 m / 10-8
3. Range Finder 1 m up to several km /10-3.

Therefore the laser triangulation is qualified for the absolute distance measurement in industrial applications. It should be mentioned that the triangulation technique cannot cover the entire range from 1 to 50 cm because the principle of the measurement is based on optical imaging.
However, the costs of a triangulation head compared to laser interferometer are so small that one can use a number of units to cover the desired range. In the automobile industry for example it is common to equip a car body measuring cabinet with nearly one hundred triangulation heads in defined positions.
The car is driven into the cabinet and in a very short time the dimensions of interest can be measured. Since the laser triangulation works without contact, a lot of other applications in automated production processes exist.

Principle of Operation

The set-up consists of:
1. Diodelaser
2. Object (A)
3. Imaging lens (L1)
4. Position sensitive photo detector (DP)
The beam of the laser hits the object A and is scattered or reflected, depending on the surface properties of the object. The scattered light enters the lens L1 and the laser spot of the object is imaged onto the position sensitive device (DP). The laser exit, the centre of the detector and the object are arranged in such a way that they form a triangle. The distance H of the centre of the detector to the laser exit is known and stays constant. If the object A moves by dx, the imaged spot moves by dS which is measured. By using the known parameters H, the measured value of dS and the focal length of the lens the value for x+dx, the distance of the object from the unit, can be calculated.