Three dimensional measurement of object´s surface in water using the light stripe projection method

In this paper, we propose a three-dimensional (3D) measurement method of objects´ shapes in liquid by using the light stripe projection method. Usually, 3D measurement by robot vision techniques is executed under the assumptions that cameras and objects are in aerial environments. However, an image distortion occurs when vision sensors measure objects in liquid. It is caused by the refraction of the light on the boundary between the air and the liquid, and the distorted image brings errors in a triangulation for the range measurement. Our proposed method can measure accurate 3D coordinates of objects´ surfaces in liquid taken for calculating the refraction effect. The effectiveness of the proposed method is shown through experiments. By considering the refraction of the light, the accuracy of the 3D measurement of objects in water becomes same as that when there is no water, although the accuracy is bad when the refraction of the light is not considered. The accuracy of the 3D measurement is about 1 mm for objects located about 400 mm from the laser range finder. The measurement speed can be also reduced as compared with the case of using a spot laser beam.