| Capacitive grid sensor based on capacitance coupling principle has a wide market in the field of measurement because of its advantages of good measurement accuracy and low cost.The measuring tool designed based on capacitive gate sensor has excellent performance in small displacement measurement with complex environment.With the advent of Industry 4.0 era,higher requirements are put forward for intelligent,miniaturized and digitized measuring equipment.Compared with foreign countries,domestic capacitive grid sensor technology is relatively backward,the measurement accuracy and stability are relatively poor.In order to improve the measurement accuracy of capacitance gate sensor,it is necessary to analyze the factors affecting the measurement accuracy of capacitance gate sensor,optimize the signal processing process on the basis of existing capacitance gate sensor,and reduce the influence of grid line error.Firstly,the ranging principle of capacitive grating sensor is analyzed.The effects of fixed grid and moving grid on resolution and measurement accuracy of capacitive grid sensor are studied.The optimal width ratio of emitter to reflector is determined by simulation software calculation and actual error test.,that is,each group of reflector corresponds to 8 emitters,and the optimal ratio between emitter width and the gap between adjacent emitters is determined to be 4:1.According to the current domestic manufacturers’ processing capacity of PCB board,combined with the theoretical calculation formula of capacitance grid sensor,determine to use a high resolution ring plate structure and design 10 groups of emitter.The transmitting plate and receiving plate are designed on the same grid for the transmission of excitation signals and the reception of modulation signals with displacement information,and the reflecting pole is designed on the moving grid plate.The angular displacement measured by the ring capacitive grating sensor is converted into linear displacement by a lead screw with 0.5mm pitch.The capacitive gate sensor designed in this paper achieves the theoretical resolution of 0.1 μm.Secondly,EDA tool is used to design the hardware circuit and capacitive gate sensor,and a complete measurement scheme is designed according to the requirements of the measuring instrument,including Bluetooth,British conversion,screen display,upper computer and so on.In order to avoid the loss of initial position data of capacitance gate sensor during battery replacement,a dual power supply mode consisting of rechargeable lithium battery and external power supply is designed.The battery power collection circuit is designed to avoid inaccurate measurement data when the power is too low.A power module that can be used independently is designed to reduce the power consumption of the measuring tool.The waveform of common signals is analyzed by simulation software,and 8 complex pulse sequences with adjacent phase difference of 45° are selected as excitation signals.The circuit of modulation,filtering,amplification and shaping is designed to process the received signal,and the phase difference is measured by XOR gate.Finally,the measuring results of the volumetric grating measuring tool are checked and calibrated by using the standard measuring block and grating measuring instrument with measuring error less than 1μm in the full range.In order to ensure that the geometric size of the capacitive grid sensor meets the design goal,the dynamic and fixed grid of capacitive grid sensor is checked and screened by the imager of the quadratic device.The source of measurement error is analyzed,the gross error is identified and eliminated by Dixson criterion,and the system error is compensated by piecewise linear interpolation function.The actual test results show that the maximum measurement error of capacitive grating measuring tool is ±2μm in the range of 25mm. |
