Three-line high-power three-dimensional sensor

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Abstract
This paper describes a sensor that employs three laser beams in order to measure the 3-D distress characteristics of road surfaces at highway speed. The 3-D feature extraction is done by means of a combination of two measuring techniques: triangulation and defocusing. In order to generate a pattern of transverse profiles spaced by 11 cm at a speed of about 20 m/s, three transverse profiles are acquired in a single frame, at a frame rate of 60 Hz. This approach led to the three laser beam solution and the use of a standard CCD camera as detector. Subject analysis emphasized as a 'must have': a wide field of view, low blurring, a more even distribution of the laser line intensity, a low power consumption along with simplicity and low cost. The use of a modified reversed prism provided a more uniform distribution, even with a single laser for each projected line. High power laser diodes were needed in order to operate at 1/10,000s shutter speed. An accurate sensor calibration provides 256 points of z (range), x (position) and I (intensity) for each profile. Calibration data as well as range and intensity of measured profiles are provided. Sensor's accuracy is also observed.

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