Evaluation of manufacturing tolerance for a model ship hull by using stitched stereo vision data sets

Abstract

As various hull forms are developed, the importance of manufacturing accurate model ship for performance test has increased. Generally, manufacturing accuracy of the model ship has been evaluated by CMM (coordinate measuring machine). However, traditional evaluating method takes long time due to measuring only single points on CMM. And it is difficult to obtain data with high resolution and to configure the freeform surface of a ship's bow and stern. A research was conducted, using 3-Dimensional stereo vision measuring instrument, to collectthe accurate data measurement of freeform surface. An optical 3-Dimensional measurement technology is known to be fast and accurate research method. However, relatively small single-measurement area of 7 m length enabled us to evaluate only limited portion of the model. Therefore, the process to stitch each data from different parts is required. When stitching 3- dimensional data, first step is to mark reference points before any process. Then, based on standard points, data is adjusted into one piece. However, the data value changes from filtering. Therefore, this method is not suitable in some cases such as determining the manufacturing tolerance, which needs every data estimate to be accurate, to meet the standard of the International Towing Tank Conference (ITTC). In this research, data stitching algorithm which only requires measured data and no reference points is proposed. The test was conducted to confirm if the algorithm can gather precise and detailed results during measuring model ship. The evaluation of the manufacturing tolerance of model ship was done using comparison of real design data and stitching data.