| In the field of high-precision positioning technology,nano-piezoelectric positioning platform has a wide range of applications as one of the main research directions at present.The capacitive displacement sensor,as the feedback link of the nano-piezoelectric positioning platform system,determines the performance of the control system to a large extent.At present,strain gauge type sensors are mostly used in nano-piezoelectric positioning platform,but the accuracy of strain gauge and the poor temperature stability directly restrict the positioning accuracy of the system.As a noncontact measuring instrument,the capacitance sensor has the advantages of high sensitivity,good dynamic performance and high resolution,which is very suitable for the detection of tiny displacement.Because of the edge effect and the difficulty of detecting the tiny capacitance,the optimization of the capacitance sensor structure and the implementation of the detection circuit are one of the important topics in the study of capacitance sensors.(1)Analysis of the detection principle and scheme design of capacitive sensors.Firstly,the principle analysis of the capacitive sensor in the electrostatic field,and then the preliminary design of the capacitive sensor structure scheme by analyzing the characteristics of different types of capacitive sensors and combining with the design requirements.In order to compensate the error caused by the non-linearity of piezoelectric ceramic hysteresis,a PID closed-loop control strategy is designed with the capacitive sensor as the position feedback and with feed-forward compensation.Finally,by analyzing the principles of several weak capacitance detection techniques,a system detection scheme for measuring small displacements is designed.(2)Research on the probe structure of capacitive sensors.the capacitive sensor with protective ring structure is designed and simulated to improve the electric field distribution between the poles in response to the edge effect problem inherent in capacitive sensors.In order to study the effect of the change of the relevant structural parameters on the capacitance sensor,the simulation software COMSOL is used to derive the capacitance values and nonlinear errors for different parameters,so that the sensor structure can be optimized.The magnitude of the edge added capacitance of the capacitive sensor is also related to the electrode thickness,the thicker the electrode,the more obvious the edge effect,so the metal conductive film electrode is prepared on the insulating substrate by vacuum vapor deposition technology.The simulation results show that the capacitive sensor with a protective ring structure can effectively reduce the influence of the edge effect.(3)Design and implementation of a weak capacitance signal detection circuit.To address the problem of difficult detection and transmission of tiny capacitance,an improved capacitance detection circuit is designed on the basis of operational amplifier detection technology,and a zeroing circuit is designed to improve the linearity of the detection circuit.The shielding technology is used for the transmission cable to reduce the influence of parasitic capacitance on the sensor capacitance to a large extent.Finally,the schematic of the capacitance detection circuit is designed using Altium Designer circuit software,and the circuit module is simulated by NI Multisim software.The results show that the improved capacitance detection circuit leads to a greater improvement in the linearity and sensitivity of the output signal.(4)The performance of the capacitance sensor was tested by building an experimental platform.The experimental results show that the measurement range is within 0.90 mm,the sensitivity is 6.09 m V/μm,the linearity is 0.76%,and the repeatability is 0.55% using the modified capacitance detection circuit after ensuring that the sensor meets the stability requirements. |
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