(A) laser scanning based 3D object sensing method using dual frequency modulation

Abstract

3D-depth map is a map of 3D spatial information which contains position and orientation information of objects. Such 3D spatial information is essential in various engineering applications such as providing a user interface through gesture recognition, face recognition, obstacle detection of unmanned vehicle and intelligent robot, and its necessity is gradually increasing. Specifically, in the field of computer vision, 3D depth maps are very widely used for many purposes. Time of flight measurement method of measuring the 3D depth map is a method of measuring the distance by using traveling time of the light. Among this time of flight measurement technologies, the time of flight measurement method using amplitude modulated continuous wave (AMCW) has emerged in that it has a small amount of calculation and an advantage in terms of miniaturization. However, many commercialized time of flight measurement sensors which use AMCW have a disadvantage in that the measurement time is long due to the sequential phase demodulation. In addition, it can be used indoors only due to the limitation of the measurement distance. Although many previous studies have investigated the method to increase the measurement distance, all the studies have been applied to the sequential phase demodulation method. These methods result in the longer measurement time, which make it difficult to apply the investigated method to commercial sensors. This thesis overcomes these shortcomings by proposing a combination of the parallel phase demodulation method and dual-frequency modulation method. The proposed method dramatically reduces the measurement time for one-point distance by using parallel demodulation and simultaneously increases the measurement distance and measurement accuracy by using dual-frequency modulation method. Thanks to this measurement method, the proposed method can be combined with scanning type hardware which uses scanner for steering illumination source. The advantages of using scanning type hardware is wide and variable field of view. In this thesis, the formula for using the proposed method is derived and the performance of the proposed method is verified through the one-point distance measurement experiments. In addition, a scanner that can be combined with the proposed method is developed and the performance of the scanner is verified. After verification of the scanner, the scanner is combined with the proposed distance measurement method to measure 1D line shape of the object. As results of this research, it is possible to measure an object at long distance with high accuracy even by using the AMCW, thereby the application field of AMCW based time of flight measurement system can be expanded.