| This paper aims at the development of practical measuring system using high measuring speed dual-frequency laser interferometer with two longitudinal modes. Attention has been focused on the following six parts:(1) Based on the well understanding of domestic and foreign laser interferometry situations, the status quo, tendency and problems of the development of high speed laser interferometry were analyzed. Then, the research goal was put forward on the basis of the existing dual-frequency laser interferometer with two longitudinal modes which already has some advantages. This high measuring speed laser interferometer has improved circuitry, higher measuring speed (not less than 1000mm/s), better anti-interference ability, and higher extent in intelligence and automatization.(2) The structure of dual-frequency laser interferometer with two longitudinal modes was described in detail. Then, the principles of measurement and optical heterodyne of dual-frequency laser interferometer were analyzed theoretically, and three structural characteristics of light paths were introduced. In order to secure the parallelity of mixed beam from measuring light and reference light, prism is used for both measuring lens and reference lens. Because reversed positioned binoculars and pinhole are used for beam collimating, expanding and space filter system, Gaussian laser beam waist is enlarged M times (M=f'2/f'1), and diffusion is reduced 1/M and equivalent length of bore is enlarged M2 times. Since the frequency of beat frequency is as high as 728 MHz, 80mm syv type of polyethylene coaxial cable is used as delay line to shift phase and such obtained two signals with phase difference 90°. It is easier than the traditional method of photo-mask phase shift. According to all the features discussed above, such interferometer can meet various requirements of high precisionmeasurement and has been applied extensively.(3) The signal always has dc shift and the observation of signal is inconvenient when adjusting light paths. Aiming at the above deficiency of original circuitry, the settlement was presented. The signal of frequency v, which is output by high frequency oscillator of high stability, is divided into two path by power divider in order to mix measuring signal and reference signal. The frequency of measuring signal and reference signal is the beat frequency Av , so measuring signal |ν-△ν|+△f modulated by the movement of measuring mirror and reference signal |ν-△ν| can be gained, where △f is Doppler frequency shift. Then, the two signals are magnified and shaped by AGC circuits respectively, and square-wave pulse signals that can be directly counted by counters are available. The difference of values of the two counters, which is operated by CPU, multiplied by the pulse equivalence is the expectative length. Also, this paper has shown the basic formulas of the selection of oscillators, and the concrete circuit of AGC.(4) According to the research goal, the design formulas of the counting system were list, which are the basis of 8254 and 74HC161 counting systems. The two systems both have their own features, and their applications are not same. The system based on 8254 has large counting range singly and high integration level of circuits, and is convenient to connect 89C51. But the measuring speed will be limited when resolving power is high. The other one based on 74HC161 is quite the contrary.(5) The measuring, control and data processing system centering on 89C51 has been designed, which has sixteen keys and 12 bits LED. By pressing these keys, the measurement can be started and stopped, the length be displayed, the dynamic or static sampling mode be chosen, and the environmental parameters be input to correct wavelength error. All of the above improves the intelligence and automatization of the system. The communication with computer has also been realized, and the max baud rate is up to 19.2Kbps.(6) After the design, processing and debug of circuitry being finished... |
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