Research On Interferometric Method For Measuring The Topography Of Cylinder’s Outer Surface

With the development of precision instrument technology and the improvement of optical system,cylindrical elements with high-precision optical surfaces have been widely used.However,there are fewer methods for measuring the topography of cylinder’s exterior,and it is difficult to solve the task for measuring the topography of cylinder’s closed-loop outer surface.The traditional method is to use a cylindricity meter to measure the sample,which often damages the surface during measurement.In the optical non-destructive interferometric measurement methods,such as computer-generated holography CGH(Computer-Generated Holograms),the surface that can be measured at a time is very small,and splicing measurement technology is needed.The efficiency is very low when it involves large area.In this paper,a conical mirror and phase-shifting interference technology are combined to design an improved interference system in order to measure the closed-loop cylinder’s outer surface.The measurement system adopts the Fizeau interference structure,has good stability,can measure large area with high precision in short time,which greatly improves the efficiency of measurement.The paper analyzes the three different misalignment errors that are easily introduced in the interference system.The relationships are established between the three misalignment errors and the interference optical path difference.Draw the interference fringe diagram based on the optical path difference.According to the characteristics of the interference fringes produced by the three misalignment errors,which type of misalignment error in the system is identified,and the interference optical path is adjusted to reduce the misalignment error.Derive the data mapping transformation matrix and convert the ring shape data into rectangular shape data to restore the true topography of the cylinder.The CGH is used to measure the same area on the exterior of the cylindrical sample,and the topography data of the cylindrical sample are compared with the data measured by the improved interference system.The results show that the morphological features measured by the two methods are consistent and the PV(Peak-to-Valley)values are close.In order to verify the stability of the measurement system,the same area of the measured sample was continuously measured 40 times.The results showed that the standard deviation of the PV value of the measured topography is 0.0808 wavelength and the standard deviation of the RMS(Root-Mean-Square)is 0.0106 wavelength.In summary,the improved interferometric measurement system designed in this paper can achieve a one-time measurement for the cylinder’s closed-loop outer surface.Establish the data mapping relationship and convert the circular topography data into rectangular topography data to restore the true topography of the cylinder’s outer surface.