Surface topography measurement of double-curved propeller blades using projected fringes

This paper studies application of the method of projected fringes on measurement of the surface topography of double-curved propeller blades, produced in liquid metal, i.e. NiAl-bronze, with surface areas of about one square meter. The measurements are performed inside a grinding hall of a propeller factory. To meet the challenges encountered in such a demanding environment, it is important to keep the equipment as simple and robust as possible. Therefore, a method is developed for locating the fringe positions with sub-pixel accuracy. To avoid the need for a physical reference plane of sufficient area, a method of extrapolating the fringes projected on a small reference plane is applied. The method has been tested on a grinded propeller blade and the results agree very well compared to a standard manual measurement method.