The Preliminary Study Of The Non-contact Measurement Of The Micro-variation In The Thickness Of The Ring Laser Gyroscope Substrate

In our laboratory, the measurement of the micro-variation in the thickness of the ring laser gyroscope(RLG) substrate has always been using traditional method in the production of RLG, such as micrometer. Because the contact measurement may damage chip's surface, a new high-precision and non-contact measurement system with high range has been developed in this paper.Although the traditional method of geometry optics probe is accurate, the range is limited. The method of physics optics probe has wide range, the structure of which is complex and it request for more strict condition. This method has been developed through analyzing advantages and disadvantages of those two non-contact measurements. The scheme of the measurement system is as follow: First, the focusing error optical signal is gotten based on heterodyne astigmatic principle. Second, the result of the micro-variation is obtained by laser interferometry to get the value of the change in the position of the lens. The new system obviously widens the range from±5μm to±50μm.The major work of this paper as follow: In the optical section, the measurement plan of the focusing error optical signal is designed and the optical parameters influence to the focusing error optical signal is analyzed by using MATLAB according to optical model based on the theory of the transport matrix. During the period of analyzing, the parameters are also gained. The focus of the lens and the cylinder lens is 4 .51mmand 50 mm, while the distance between the two should be 60 mm. One four-quadrant photodetector should be placed in front of the focus of the cylinder lens, while the other should be behind the focus and the distance should be both 10mm. In the electronic section, photoelectric transferor and operation circuit, 300V D.C. stabilized source and piezoelectric ceramics driven circuit, communication circuit and sampling circuit based on DSP are designed and debugged successfully. Some measures are also taken to prevent from disturbing and reduce the noise during the period of designing circuit and making the circuit board. In the arithmetic and software section, the digital filter, PID control programme and the communication between SCI and LabVIEW are implemented.In the end, a series of tests have been carried out on the accomplished system and the experimental data is analyzed and processed. The result shows that the orientation precision can be less than 50 nm and the accomplished system can meet the need of the measurement well.