Laser distance measurement by triangular-wave amplitude modulation based on the least squares

Abstract

Phase ranging method of distance measurement usually sacrifices the simplicity of the ranging system by adding complex circuit and multi-frequency ruler to achieve high accuracy. Laser pulse ranging has the counting error of the number of round-trip pulses which affects the accuracy of flight time calculation. Hence a novel method to measure a distance by triangular-wave amplitude modulation laser based on the least squares is proposed in this article. The triangular-wave is adopted to modulate the laser amplitude linearly, which improves the signal to noise ratio (SNR) of the ranging system effectively. The proposed system designs two identical channels for referenced and measured signals with certain length of optical distance. Their return signals are fitted with improved straight-line fitting algorithm based on the least square. Then a series of fitting parameters and singular characteristic points of triangular wave were obtained. The detection distance is calculated with the proposed theoretical algorithm based on the relationship between the two signals and the time shift information of the characteristic point. The average measuring error of this laser ranging system is maintained within 2.8 mm with the detection distance in 10 m according to experimental results.