Study On Planar Capacitive Sensors For Multiple-Dimensional Precision Displacement Measurement

Multiple degree-of-freedom (DOF) precision displacement measurement as an indispensable part of precision manufacturing and assembly, is now widely used for the fabrication of semiconductors and optical elements, the positioning and manipulation of cells, the actuation of precision machine tools and etc. However, multiple DOF precision measurement is conventionally realized by stacking multiple single-DOF stage systems, resulting in a bulky metrology prototype involving a complicated structure, errors superposition and high cost. Thus, it is of paramount meaning to propose a fast, simple, effective cost multiple DOF metrology system. On the basis of planar capacitive sensor, thorough study on large scale, high resolution, multiple-DOF precision displacement measurement was presented in this dissertation. The research work is supported by the National Natural Science Foundation of China (Grant No.50875241),"Study on two dimensional long range direct decoupling precision displacement measuring system based on planar capacitive sensor", and the National Natural Science Foundation of China (Grant No.51275465),"Study on cylindrical capacitive sensors for on-line monitoring rotation error of high precision spindle"The dissertation is organized as follows:In chapter1, the backgrounds and significant achievements of precision measurement were introduced. Further discussion on the advantages and shortcomings of multiple DOF precision displacement measurement was then presented. The motivation, meaning and research contents were proposed in the end.In chapter Ⅱ. the basic principle of capacitive displacement sensor was introduced firstly, based on which, a single DOF encoder-like planar capacitive sensor(EPCDS) is proposed for large scale precision displacement measurement, with the discussion of the shortcomings of single DOF precision measurement, a two dimensional long range direct decoupling precision displacement measuring system is constructed, the experimental results implied that two dimensional precision displacement measurement was realized with a single capacitor. Finally, the merits and withdraws were both concluded, potential solutions were proposed.In chapter III, the influences of electric field fringe component was introduced. Feasible methods to diminish whose influences on measuring accuracy is presented either. For EPCDS, a capacitance model with the consideration of electric field fringe component was calculated under MAXWELL’S equations. With an optimized geometric layout, influences of electric field fringe component was reduced.In chapter IV, the major errors of the two dimensional EPCDS were analyzed firstly. Based on the analysis, the sensor model against errors was built. Measurement errors were precisely calculated; and approaches have been carried out to diminish the measurement errors.In chapter V, based on the two dimensional EPCDS, a five-DOF precision displacement measurement system was presented. The capacitor electrodes were rearranged and symmetrically positioned, X-Y long range linear displacement measurement was decoupled from the measurement errors, and extra roll, yaw, pitch angular readouts(θx,θy,θz) were achieved. Finite element analysis(FEA) authenticated the five-DOF precision displacement measurement system.In chapter VI, the signal acquisition system of the five-DOF EPCDS was proposed, including the weak capacitive signal sampling system and signal interpretation algorithm. Firstly, phase locked-in correlation detection was adopted to reduce the effects of noises. Secondly, arctangent phase shifted (APS) interpretation algorithm was presented under Lab VIEW(?) to increase measurement resolution and accuracy.In chapter VII, the five-DOF precision displacement measurement system based on EPCDS was constructed firstly, the stability of signal acquisition system was investigated secondly. Then, experiments of five-DOF displacement measurement were carried out. The experimental results indicated that X-Y-θx-θy-θz displacements measurement was successfully achieved, accuracy and resolution have both been increased.In chapter VIII, the key achievements and innovations of this dissertation were offered, and potential researches in the future were presented in the end.