Study On Coaxial Displacement Detection Technology Of Focus Adjustment In Ultra-precise Optical Measurement

This research is a crucial technique in the provincial technical project named "Flexible Circuit FPC Non-electrical Quantity Parameter Online Quality Control Technology". It can accomplish the coaxial detection of focus adjustment displacement in the ultra-precise optical measurement system, which solves the problem of theoretical error in the system and increases the measurement accuracy of the optical measuring system.In the process of the geometrical dimensional measurement to the Ultra-precise finish surface via the theory of confocal microscopy measurement, which is recorded by the displacement sensor. Capacitive displacement sensor has lots of advantages and it is the key part which applied to detect the focusing displacement. According to the request of miniaturization and minimizing the influence of edge effect in optical measurement system, plate capacitive displacement sensor succeeds in coaxial detection of focus displacement. The thesis has put forward a new-style capacitive sensor. This orbicular capacitive sensor with a middle-hole and double equipotential rings improves the structural constraint of the ordinary plate one. This new-style structure makes the light path of plain shaft pass through the centre hole of the orbicular polar plate, and then the measurement of the directional of displacement is coincident with plain shaft, which is in accordance with the Abbe Rule. Breaking though the traditional mechanical processing technique, the design applies MEMS technique to process the orbicular polar plate with double equipotential rings, which can make the thickness of the plate very thin (about 1mm), and the gap between the equipotential rings and the polar plate (about 10μm). This technique effectively decreases the edge effect influence of stray capacitance and increases the measurement accuracy of linearity. What's more, it has devised an improved measure of operational amplifier to detect the circuit. In conclusion, the data recording chip collects the signal voltage to the computer and output the information through computer, which intelligentizes the whole system.The research includes the following five subjects: 1.The qualitative analysis of the edge effect in flat capacitive displacement transducer and the nonlinear influence in output characteristics;2.In accordance with the request of research, design the structure of orbicular polar plate with double equipotential rings via the AutoCAD software;3.Confirm the procedure of MEMS technique and complete the polar plate;4.On the basis of the simulation testing, design the test circuit of capacitive displacement sensor and experiment the displacement measurement;5.Calibrating testing of capacitive displacement sensor;On the basis of the successful simulation testing and dynamic testing on the experiment table, it concludes that the capacitive sensor's resolving capability outgoes 0.02μm and the nonlinear error is less than 1%, which is in correspondence with the design objective.