Research Of Micro Displacement Measurement Technology Based On Capacitance Method

As the main means of non-contact measurement technology, capacitance micrometer technology is widely used in the domains of precision machining, high precision orientation and precision measurement. With the structure of parallel plate, traditional capacitance displacement sensor has the difficulty of alignment, and it is difficult to operate and achieve accurate measurement. capacitance detection circuits always use lots of discrete components, such as filters, operational amplifiers, circuit structure is complex and vulnerable to impact by environment, the measurement and stability is hard to guarantee. All these factors have restricted the development of capacitance displacement sensor.This paper designed a kind of spherical electrode capacitive displacement sensor with the characteristics of three-dimensional isotropic, solving the difficulty of alignment effectively in the principle. And based on the analysis of common micro capacitance detection circuit, design a micro capacitance detection circuit with a core of capacitor digital conversion chip, it effectively solves the bad stability and easily influenced by environment of traditional capacitance detection system. This paper’s main research is given as follows:Firstly, the mechanical structure and size of the probe are designed, and using COMSOL Multiphysics finite element simulation software to research the electric field distribution, to verify the rationality of its design. Secondly, on the basis of analysis and comparison by the working principal of commonly used micro capacitance detection circuit, propose a detection design by using digital conversion chip AD7747, and the capacitance hardware detection control circuit based on CY7C6801A is designed which includes external storage circuit, communication interface circuit, power circuit and filter circuit. Thirdly, analyse and calculate the characteristics of the capacitance displacement sensor by the method of electrical images and separation variables, and Mathematica 9.0 software is used to get the relationship curve between the capacitance and displacement. Finally, the experiment is carried out to realize the static calibration by using the designed test-bed. By using the least squares polynomial fitting method, get the relationship between capacitance and displacement.Results show that, spherical electrode capacitive displacement sensor can effective-ly avoid the influence of edge effect, it has good stability, high repeat precision. The designed four different diameter probe has the lowest stability of 0.002pF/u m, and maximum repeatability error is 0.953%. The sensitivity of the sensor increases with the increase of probe diameter. And through the analysis and calculation of the experiment data, find that the resolution of 20nm can be achieved in the range of 0.5-10μ m for the designed four different sensors.