Research On Bidirectional Inductance Micro-displacement Sensing Technology

High precision inductive displacement sensor is widely used in the measurement of the size and surface topography of precision parts because of its advantages of high accuracy,simple structure and good linearity.Bidirectional measurement and nanoresolution are required for inductance displacement sensor in measuring the dimensions and surface topography of grooves and cavities of complex parts represented by scroll compressors.Traditional inductive displacement sensor probes can only realize one-way measurement,but can not take both nano-resolution and bidirectional measurement into account.The signal processing circuits of inductive sensor is very sensitive to noise,and there are large high-frequency noises in commonly used digital phase-sensitive detection and switched phase-sensitive detection schemes.The mechanical structure of sensor probes is sensitive to temperature changes.the change of ambient temperature will cause the thermal drift of sensor probe,but there are few studies on the drift suppression of sensor probe.In this paper,aiming at the requirement of measuring the surface size and shape of special parts such as scroll compressor,and the existing problems of inductance displacement sensor,a structure of inductance displacement sensor which can realize bidirectional measurement and effectively suppress temperature drift is proposed.The high precision signal processing scheme of inductance displacement sensor is designed,and the constant temperature control system of the probe is designed.The main contents of this paper are as follows:Firstly,a new type of bi-directional inductance displacement sensor probe structure is designed,which expands the measurement direction of inductance displacement sensor so that it can be used as bi-directional measurement.The cross flexible hinge of double leaf spring is used as the elastic support element of the sensor probe.The measurement errors caused by the drift and hysteresis of the hinge shaft are analyzed in detail.Aiming at the measurement non-linearity caused by the machining error and installation positioning error of the probe mechanical parts,the non-linearity error model of the processing error and installation error is analyzed.In view of the influence of ambient temperature fluctuation on the stability of the probe,the influence of thermal deformation of the mechanical structure of the probe on the measurement results is analyzed.Secondly,in view of the strict requirements of digital phase-sensitive detection on ADC sampling timing,the introduction of non-linear errors,and the low detection accuracy of commonly used analog phase-sensitive detection methods,this paper designs a signal processing scheme based on multiplier phase-sensitive detection.Using resistance balance arm bridge as modulation circuit reduces the volume of signal circuit and electromagnetic radiation,and improves the anti-interference ability of the circuit;demodulating the AM modulation signal by multiplier phase sensitive detection circuit effectively reduces the high frequency interference introduced by switching signal in the circuit,reduces the timing requirements of ADC sampling circuit,and reduces the nonlinearity of signal processing circuit.The complete noise model of signal processing circuit is established,the influence of circuit parameters on the total output noise of signal processing circuit is quantitatively analyzed,and the main parameters of the circuit are optimized according to the circuit noise model.According to the non-linear error model of machining error and installation error,the compensation link of sensing characteristic is designed,which reduces the measurement non-linearity caused by the machining and installation error of the probe's mechanical structure.Then,a constant temperature control unit of sensor based on PID control is designed.The system model of constant temperature control system of inductive displacement sensor probe is analyzed.The open-loop transfer function of constant temperature control system is determined by system identification,and the main parameters of PID controller are determined according to system identification results.Under the set working temperature,the temperature control stability is better than 0.1?/1h.The stability of inductive displacement sensor system is improved from 80nm/30 min before adding temperature control unit to 40nm/1h.Finally,an experimental platform is built to test the performance of the highprecision bi-directional inductance displacement sensor probe and signal processing board.The experimental results show that the measurement resolution of the two-way inductive displacement sensor system is 5nm,the stability is 40nm/1h,the system nonlinearity is 0.4%,and the measurement repeatability is 60 nm in the measurement range of ±100?m.The measurement system of bi-directional inductance displacement sensor designed in this paper has good performance.