Research On Contact And Noncontact Hybrid Measurement System Of Profile Based On White Light Interferometry

In surface morphology there are two main families of technology, the first of which requires contact between a stylus tip and the surface, whereas the second is non-contact technique without any contact between the sensor and the object. It is known that these two types of instrument are complementary to each other in many aspects and each of them has their own application areas. So it is needful to integrate the two techniques into one surface measuring instrument. A novel hybrid instrument capable of contact and non-contact measurements with large range is developed, and both measurement systems are based on a Linnik interference microscope and on white-light interference measuring techniques. The creative points and main research contants are as follows.A contact surface profile measurement system which is based on white-light interference measuring technique is proposed. The mathematic model for the contact measuring method is established by wave theory, the sensitivity and the non-linear measuring error are discussed accordingly.A hybrid surface profile measurement system capable of contact and non-contact measurements with large range is proposed. Both measuring methods are based on white- light interference measuring technique, and both systems are built on Linnik microscope configuration. Compared with other counterparts, the system has a simpler structure and a lower cost, and is of high accuracy and suitable for a wide range of applications. As adopting white-light interference measuring technique, the ambiguity presented in conventional monochromatic interferometers is not present for both contact and non-contact measurements, and it can be used for large range measurements in combination with the vertical scanning stage and x-y stage. On the basis of analysis and summary for fringe identifying techniques of non-congtact measurement, it is proposed that two methods of determination of zero-order fringe are used in the system to respectively meet the demands for different measuring speeds and accuracy ranges.The main parts and assemblies of the system are designed and analysed. After discussing the characteristics of white-light sources, the simple design formula for two-synthesized source and three -synthesized source are obtained in accordance with the proposed judgment criterion, and the design effects are simulated with computer. The results of computer simulation demonstrate that the use of the synthesized sources with the optimized parameters results in the more accurate determination of zero-order fringe. The cross-spring pivot of the lever mechanism in the contact measuring system is designed, and the dynamic characteristics of the lever mechanism are studied. On the basis of the relationship deduced between the traverse speed and the roughness of test surface and between the measuring force and the roughness, three grades of the traverse speeds are setted for the system, which can be used for the rapid and effective measurement of the surfaces of different roughness. The processing circuit and a software method of fine dividing of grating sensor in the stages are designed, and the error analysis for the beamsplitter in Linnik interference microscope is discussed.The dynamic characteristic, the filter characteristic, the stability and the repeatability of the system are also discussed. The errors of the contact and noncontact measuring systems are analysed, respectively. The calibration methods for the dynamic characteristics of the lever mechanism and for the contact and noncontact measurements are designed seperately, and the calibration results for them are also shown.