Research On Theory And Key Technologies Of Long-range Displacement Measuring With Nanometer Resolution By Grating

In contemporary industrial field such as microelectronics and ultra-precision manufacture.the displacement measuring with high precision is in great demand. The measuring resolution needs to reach nanometer level in some applications.and the measure distance gets longer and longer. In this dissertation.The theory and key technologies to measure long-range displacement with nanometer resolution by metrology grating is studied.1. Firstly.the existing theories and methods for displacement measure with nanometer resolution are presented. Based on this. the displacement measurement with nonsymmetrical doubly blazed grating (DMNG) is studied in detail and corresponding experiments are done. The principle of acquiring high optical subdivision is analyzed.and the mathematical model of optical structure is established. The formation of moire fringes in DMNG is also explained. Besides.the function of blazed grating in DMNG and the influence of incidence angle variation are discussed.2. The fundamentality of fringe multiplication in DMNG is pointed out.and the means to realize optical subdivision with high multiple is simplified. On the basis of this.a measuring method with single metrology grating (SMG) that can replace DMNG is proposed. By utilizing this method.not only high optical subdivision is obtained.but also many disadvantages of DMNG are avoided. The measure principle is analyzed with several kinds of theories. A displacement measuring system.which resolution is Inm and measure range is 400mm.is set up. And the experiment results of the system on twist roller friction platform are introduced.3. The diffraction efficiency is studied by scale diffraction theory and vector diffraction theory. The relationships of diffraction efficiency with grating profile and system configuration are investigated to get high signal to noise ratio of moire fringes. In the process of the research.a new kind of blazed grating.isosceles blazed grating is put forward and its diffraction characteristics is analyzed and simulated.4. A DSP (Digital Signal Processor) based counting and subdivision method of moire fringes with wide dynamic and high precision is provided. The hardware platform.time sequence of process and operation means is described in detail. Because of utilizing highspeed data acquisition and digital signal process.the moire signals from 0 to 1M hertz can be processed by dual-threshold double counting.segment subdivision and combination of them. The method is of zero frequency response and can count fringes with very lowfrequency. And it is insensitive to the orthogonality of the signal A and B.which can resist strong disturbance and shows sound reliability.5. The theory of adaptive signal process is introduced to process the optoelectronic converting signals of moire fringes. For channel A and B.an adaptive process model is established to eliminate disturbance and enhance the signal quality. Several effective realtime adaptive algorithms are respectively provided. By these solutions.the unwanted drift is eliminated.the harmonics is filtered.the amplitude of the signals can be kept constant and the orthogonality of two channels can be improved. At last.a compare algorithm between correlation coefficient and threshold is proposed to recognize and eliminate fault signals.6. The factors that influence the measure precision are systematically discussed in single metrology grating (SMG) system. The maximums of all kinds of errors are calculated and corresponding correction and compensation methods are provided. The precision parameters in various operating conditions are deduced. It is concluded that.when installed.the SMG system is insensitive to the gap and angle of taper between grating and readout. It is very convenient to fix and use. After modifying the cumulating errors of grating and compensating to the environment temperature.the displacement measure precision of SMG can reach 0.1 um/100mm.