Interference Signal Processing Technology And System Research Based On Miniature Nano-displacement Sensor

Today, the rapid development of ultra-precision machining technology contributedthe birth of nano coordinate measuring machine (nano CMM), one of the keytechnologies in which is to develop displacement sensor with nanometer resolution.This research studies interference signal processing technology based on lab-developedminiature nano-displacement sensors, and develops a DSP microprocessor system forthe research of fringe counting and phase subdivision technologies. Finally, with thefeedback of lab-made displacement sensor and corresponding signal processing board,this study completed motion control on the lab-developed nano CMM moving stage.Our laboratory developed two miniature nano-displacement sensors, which arePolarizing Michelson Interferometer (PMI) using Michelson interferometric principleand Linear Diffraction Grating Interferometer (LDGI) using grating diffraction theory.For the PMI, the two back light beams from the reference mirror and the measuringmirror after a series of the optical conversion produce interference fringes. In differentway, the LDGI uses the grating Doppler phase shift principle for generating1orderdiffracted light beams to produce interference fringers. Although the principles aredifferent between PMI and LDGI, they all eventually produce four interference signalswith phase shift of0degrees,90degrees,180degrees and270degrees.This thesis studies the signal processing technology based on miniaturenano-displacement sensor. Firstly, the compositon of the sensor signal errors is analyzedand appropriate correction methods are proposed. Secondly, the corresponding circuitboard by using operational amplifiers and analog muiltipliers and other devices toachieve the interference signal processing is designed. The processed quadrature signalsare respectively sent into the comparative counting module and ADC module on theDSP microprocessor system, in which the core device named bidirectional reversiblequadrature pulse counter of the comparative counting module is for pulse counting andADC module is for phase subdivision. Then DSP program calculates system’s totaldisplacement. Efficient displacement measurement software is developed for twodifferent testing platforms. The output signals of two nano-displacement sensors arerespectively measured by the designed software and compared with previously verifiedPC program. The comparision results show that residual error is less than±4.8nm.The hardware circuit portion of motion control is developed on DSP microprocessorsystem. The analysis of BP neural networks and PID controller derives signal propagation equations, status updating equations and incremental PID controllerequations. On this basis, the programming implements the core algorithm of stagemotion control. The USB interface serving as a communication bridge between the PCand the DSP microprocessor system is also developed. Finally, by a series of tests andcorrection, this reasearch realized the USB-based stage motion control and controllederrors of every mode were even better than the control performance of PC-basedsoftware.This research is sponsored by the “Cheung Kong Scholars Program” of HefeiUniversity of Technology and the “Key technology and system research of3D nanomeasurement(50420120134)” by the National Natural Science Foundation of China（NSFC）.