3-D shape measurement of free-form machined surfaces by optical ring imaging system

The purpose of this paper is to develop an advanced 3-D profile sensor system which will be able to accurately measure 3-D free-form machined metal surfaces. The proposed sensor system has many advantages as compared with conventional measuring systems. First, a new detecting system of optical ring images utilized by the rotating image detector is developed to measure 3-D profiles in the long measuring range with high accuracy. Second, processing time can be shortened within 0.5 second by using the proposed detecting system. Third, the speckle noise is eliminated effectively by the rotating mechanism. Finally, it is concluded that this sensor system makes it possible to measure the profiles within an accuracy of +/- 50 mu m in the measuring range of 100 mm. In this paper, the measurement principle of the proposed sensor system is analyzed and the performance of the system is experimentally measured and discussed not only for both diffuse reflection surface and specular reflection surface, but also for reduction of the laser speckle noise which has direct influence on the measurement accuracy.