High-resolution range finder with wide dynamic range of 0.2 m to 1 m using a frequency-modulated laser diode

The authors describe a compact range-finder that uses a frequency-modulated self-mixing laser diode which measures the averaged time interval of successive external-mode hops to give a short distance from the laser diode to a resting target with rough surface. With a triangular current modulation of an optimum amplitude, the measured dynamic range is from 0.2 m to 0.5 m; the standard deviation and the repeatability are less than ±0.25 mm and ±1.1 mm, respectively. With a decreased amplitude, i.e. half of the optimum, the dynamic range is widened to the range of 0.2 m to 1 m; the standard deviation and the repeatability are less than ±1.6 mm and ±2.8 mm, respectively. This type of range-finder is suitable for application as a visual sensor of an industrial robot