CN108303016A - A kind of measurement method of Ultra-high Accuracy Displacement amount - Google Patents

Abstract

The invention discloses a method for measuring ultra-high-precision displacement. The fitting capacitance formed by the measuring sensor is connected in parallel with the varactor diode of the phase-locked loop circuit, and the phase detector cooperates with the LPF to generate the local oscillation frequency value and the value of the VCO oscillation. The comparison of the set frequency value transmitted by the MCU generates a phase-locked error voltage. The error voltage uses negative feedback to adjust the local oscillator frequency to track and equal to the set frequency of the phase-locked loop PLL and achieve the same accuracy as the PLL crystal oscillator, infinitely approaching or equal to a phase-locked Using the error voltage and the variable value of the error voltage to measure the real-time value of _{the total} capacitance of C in the phase-locked loop LC oscillator, the real-time value of the fitting capacitance and the variable value, and calculate the displacement or angle from the fitting capacitance variable value Or the measured value of the hysteresis signal, using the correction coefficient correction to achieve ultra-high-precision measurement. The invention has a wide measurement range, ultra-high stability, relatively low cost, a measurement accuracy of 0.05%, a resolution of 20nm, a measurement range of 300mm, and a repeatability of 0.1%.

Description

A Measuring Method of Ultra-high Precision Displacement

technical field

The invention relates to a method for measuring displacement, in particular to a method for measuring ultrahigh-precision displacement.

Background technique

Measurement is to use data to describe the observed phenomenon according to a certain law, that is, to make a quantitative description of things. Measurement is the process of quantifying non-quantified objects. In mechanical engineering, measurement refers to the experimental cognition process of comparing the measured value with a standard quantity with a unit of measurement in order to determine the ratio between the two.

The object of measurement mainly refers to geometric quantities, including length, area, shape, elevation, angle, surface roughness, and shape and position errors. Among them, for the measurement of displacement, angle and torque, especially for the ultra-high-precision measurement of the above three quantities, the main methods used in the prior art are: as measuring displacement, a capacitive displacement sensor is used, and the capacitive sensor is divided into variable There are three types: polar distance type, variable area type and variable medium type. Among the three types of sensors, the variable pole-pitch type is better. This type of sensor contacts and drives the target body that needs displacement measurement, such as the moving body of a precision machine tool, in a transmission manner, and finally forms a voltage difference on the two poles of the capacitive sensor. The coaxial cable is led out, and then amplified by operational amplifier, filter, AD conversion, CPU data processing, display communication, and finally output the data corresponding to the displacement variable. It has the characteristics of high sensitivity, wide linear range and high stability.

However, the current capacitive sensors still have the problems of poor accuracy, stability, reliability, and low consistency of measurement data when the measurement requires ultra-high precision. The measurement accuracy is about ±50nm (this accuracy does not consider the repeatability F.S, such as Considering the repeatability, the accuracy will drop), which leads to the fact that the above-mentioned sensors cannot meet the accuracy requirements when they are used in the processing of ultra-high-precision machine tools, precision parts of robots (such as joint transmission parts) and other products. Moreover, the measurement displacement range of the existing technology is too small, only about 10 mm. In order to solve this problem, some solutions have been given in the prior art. However, these solutions have the problem of high cost and cannot be popularized. When ultra-high precision is achieved, the stability and repeatability decrease, and it cannot be taken into account at the same time, resulting in low consistency of measurement data. Therefore, the prior art requires a measurement method with a wide measurement range, ultra-high precision, ultra-high stability, and relatively low cost.

Contents of the invention

In order to solve the problems existing in the current technology, the object of the present invention is to provide an ultra-high precision displacement measurement method with wide measurement range, ultra-high stability and relatively low cost.

In order to achieve the above-mentioned purpose, the technical means adopted in the present invention is: a kind of measuring method of ultra-high-precision displacement, the fitting capacitor formed by the sensor of measuring displacement or angle variable or hysteresis signal variable and phase-locked loop circuit The varactor diodes are connected in parallel, and the phase detector cooperates with the LPF to compare the local oscillator frequency value generated by the VCO oscillation with the set frequency value transmitted by the MCU to generate a phase-locked error voltage. The error voltage adjusts the local oscillator frequency in the form of a negative feedback closed loop to make it Track and be equal to the PLL setting frequency of the phase-locked loop, and achieve the same accuracy as the PLL crystal oscillator, infinitely approach or equal to the central value of a phase-locked voltage in the form of differential integral and median value theorem, and the calibrated real-time error voltage determines the local oscillator Frequency value, use the error voltage and error voltage variable value to reversely measure the real-time value of _{the total} capacitance of C in the phase-locked loop LC oscillator, the real-time value of the fitting capacitance and the variable value, and calculate the displacement or angle or variable value from the fitting capacitance variable value The measured value of the hysteresis signal is corrected by using the stored temperature, correction capacitance and the correction coefficient of the measured value to further obtain an ultra-high-precision measured value, and realize ultra-high-precision measurement of displacement or angle or hysteresis signal.

Further, the ultra-high precision refers to: the measurement accuracy is 0.05%, the resolution is 20nm, the measurement range is 300mm, and the repeatability reaches 0.1%.

Further, the error voltage adjusts the local oscillator frequency in the form of a negative feedback closed-loop to make it track and equal to the set frequency of the phase-locked loop PLL means: the capacity of the varactor diode is changed by the phase-locked comparator in cooperation with the adjustment voltage of the PLL, Make it follow the increase or decrease, and adjust the local oscillator frequency up and down until it is equal to the set frequency value. When the frequency is locked, the real-time value of the adjusted voltage is used to deduce the current capacity of the varactor diode; the displacement or angle Or the variable signal generated by the pressure sensor is converted into a capacitance signal to form a fitting capacitance sensor. The fitting capacitance sensor is connected in parallel with the varactor diode, and the varactor diode increases the capacitance of the fitting capacitance. The phase-locked loop maintains the original frequency value. Then reduce the current capacitance value of the varactor diode. At this time, the adjusted voltage increases, and the variable of the current capacitance value of the varactor diode is calculated from the increased value of the adjusted voltage, and the current capacitance value of the fitting capacitor is obtained, which is compared with the previous pre-stored fitting Compared with the current capacitance value of the capacitor, the variable value of the fitted capacitor is increased or decreased, and the measured value of the displacement or angle or pressure is further calculated.

Furthermore, the phase detector cooperates with the LPF to compare the local oscillator frequency value generated by the VCO oscillation with the set frequency value transmitted by the MCU, and to generate a phase-locked error voltage means: when the two frequency values are different, an error is generated Voltage, the error voltage is fed back to the negative terminal of the varactor diode of the VCO circuit. When the local oscillator frequency value is lower than the set frequency value, the error voltage increases. Since the error voltage is loaded on the negative terminal of the varactor diode, the capacitance of the varactor diode decrease, causing the local oscillator frequency signal to increase; otherwise, the error voltage decreases, causing the local oscillator frequency to decrease until the phase-locked loop tracks and locks to a set frequency center value, reaching the same or higher frequency than the crystal oscillator of the phase-locked loop. High precision.

Further, _{the total value} of C of the LC oscillator is correspondingly reduced by the same amount as the fitting capacitance, and at the same time, the adjustment voltage value is correspondingly increased. When the parallel fitting capacitance increases due to displacement or angle change Or decrease, so that the adjusted voltage value increases or decreases accordingly.

Further, the correction using the stored temperature, correction capacitance and the correction coefficient of the measured value refers to storing the correction system of the error caused by the temperature, capacitance and measured value in the MCU, and using these correction systems to correct the measured value. Calibration, in which the calibration capacitor is measured twice by the relative measurement method, and the obtained two voltage values are subtracted, and the difference obtained is the current capacity value of the calibration capacitor, and the current calibration capacitor capacity is combined with the stored calibration value of the calibration capacitor. Calculate the correction coefficient; use this correction coefficient to correct the real-time variable value of the fitting capacitance, and improve the accuracy, stability and repeatability of the variable value.

Further, the VCO circuit adopts a temperature-compensated crystal oscillator with an accuracy of at least 10e-16 power, and uses a constant temperature bath VCO circuit with a power accuracy of not less than 0.01%.

Further, the variable value of the fitting capacitor is the positive terminal of the fitting capacitor connected to a switch and connected to the negative pole of the varactor diode, and the phase-locking error voltage difference obtained by turning on and off the switch is the error The variable value of the voltage is calculated at the same time as the variable value of the fitted capacitance.

The beneficial effects of the present invention are: because the phase-locked error voltage has ultra-high precision, resolution and repeatability, the real-time value of _{the total} capacitance of C in the phase-locked loop LC oscillator is reversely measured by using the error voltage and the variable value of the error voltage, The measurement value of displacement or angle or hysteresis signal is calculated from the fitting capacitance variable value. This measurement value also achieves ultra-high precision, resolution and repeatability, and then uses the stored temperature, correction capacitance and correction coefficient of the measurement value to perform Calibrate, and further obtain ultra-high-precision measurement values, and realize ultra-high-precision measurement of displacement or angle or hysteresis signals.

Description of drawings

The present invention will be further defined below in conjunction with the accompanying drawings and embodiments.

Fig. 1 is a schematic diagram of the principle of the present invention.

Detailed ways

Example 1

A method for measuring ultra-high-precision displacement. The fitting capacitive sensor formed by the displacement or angle variable or hysteresis signal variable is connected in parallel with the varactor diode of the phase-locked loop circuit. The phase detector cooperates with the LPF to detect the VCO oscillation The frequency value of the local oscillator is compared with the set frequency value transmitted by the MCU to generate a phase-locked error voltage. The error voltage adjusts the frequency of the local oscillator in the form of a negative feedback closed loop to make it track and equal to the set frequency of the phase-locked loop PLL, and achieve the same value as the PLL crystal oscillator. Accuracy, and in the form of differential integral and mean value theorem infinitely approach or equal to a phase-locked voltage center value, and the calibrated real-time error voltage determines the local oscillator frequency value, using the error voltage and the error voltage variable value to measure back The real-time value of _{the total} capacitance of C in the phase-locked loop LC oscillator, the measured value of the displacement or angle or hysteresis signal is calculated from the fitting capacitance variable value, and the stored temperature, correction capacitance and correction coefficient of the measured value are used for correction. Further obtain ultra-high-precision measurement values, and realize ultra-high-precision displacement or angle or hysteresis signal measurement.

The ultra-high precision refers to: the measurement accuracy is 0.05%, the resolution is 20nm, the measurement range is 300mm, and the repeatability reaches 0.1%.

Example 2

As a preferred or specific implementation of Embodiment 1, the error voltage adjusts the local oscillator frequency in the form of a negative feedback closed loop to make it track and equal to the set frequency of the PLL of the phase-locked loop. Next, change the capacity of the varactor diode to make it increase or decrease accordingly, and adjust the local oscillator frequency up and down until it is equal to the set frequency value. When the frequency is locked, the real-time value of the adjusted voltage is used to calculate the varactor The current capacity of the diode; where the variable signal generated by the displacement or angle or pressure sensor is converted into a capacitance signal to form a fitting capacitance sensor, the fitting capacitance sensor is connected in parallel with the varactor diode, and the varactor diode increases the capacitance of the fitting capacitance, locking In order to maintain the original frequency value of the phase loop, the current capacitance value of the varactor diode is reduced. At this time, the adjusted voltage increases, and the variable of the current capacitance value of the varactor diode is calculated from the increased value of the adjusted voltage to obtain the current capacitance value of the fitted capacitor. , compared with the current capacitance value of the last fitting capacitor pre-stored before, whether the variable value of the fitting capacitance is increased or decreased, and the measured value of the displacement or angle or pressure is further calculated.

The phase detector cooperates with the LPF to compare the local oscillator frequency value generated by the VCO oscillation with the set frequency value delivered by the MCU, and to generate a phase-locked error voltage means: when the two frequency values are different, an error voltage is generated, and the error voltage Feedback to the negative terminal of the varactor diode of the VCO circuit. When the local oscillator frequency value is lower than the set frequency value, the error voltage increases. Since the error voltage is loaded on the negative terminal of the varactor diode, the capacitance of the varactor diode decreases, resulting in The local oscillator frequency signal increases; otherwise, the error voltage decreases, causing the local oscillator frequency to decrease until the phase-locked loop tracks and locks to a set frequency center value, achieving the same or higher precision as the crystal oscillator of the phase-locked loop.

The total value of C of the LC oscillator is correspondingly reduced by the same amount as the fitting capacitance, and at the same time, the adjustment voltage value is correspondingly increased. When the fitting capacitance of the parallel connection increases or decreases due to displacement or angle , so that the adjustment voltage value increases or decreases accordingly.

The correction using the stored temperature, correction capacitance and the correction coefficient of the measured value refers to storing the correction system of the error caused by the temperature, capacitance and measured value in the MCU, and using these correction systems to correct the measured value, wherein The correction capacitance is measured twice by the relative measurement method, and the obtained two voltage values are subtracted, and the difference obtained is the current capacity value of the correction capacitance. The correction is calculated by combining the current correction capacitance with the stored calibration value of the correction capacitance. Coefficient; use this correction coefficient to correct the real-time variable value of the fitting capacitance, and improve the accuracy, stability and repeatability of the variable value.

Example 3

The variable value of the fitting capacitor is obtained by connecting the positive terminal of the fitting capacitor to a switch and connecting to the negative pole of the varactor diode, and the phase-locking error voltage difference obtained according to the switching on and off of the switch is the variable of the error voltage value, and calculate the variable value of the fitted capacitance at the same time. Calculate the measured value of the displacement or angle or hysteresis signal from the fitting capacitance variable value, and use the stored temperature, correction capacitance and correction coefficient of the measured value to correct, and further obtain ultra-high-precision measured values to achieve ultra-high-precision Measurement of displacement or angle or hysteresis signals. Further, a temperature-compensated crystal oscillator is used with an accuracy of 10e-16 power or above, and a constant temperature bath VCO circuit is used to maximize the accuracy, repeatability, and resolution of the phase-locked error voltage, and by selecting 0.01% or The above-mentioned high-precision power supply, higher resolution, and smaller varactor diodes for phase-locking error voltage steps, and because the fitting capacitor excitation frequency of this scheme is about 100MHz, which is the highest excitation frequency of the existing TDR method. About 1000 times of 100KHz, the higher the excitation frequency, the higher the accuracy, resolution and repeatability of the measured value, and then use the temperature, correction capacitance and correction coefficient of the measured value stored in the system to correct and correct to obtain ultra-high precision Finally, combined with the characteristics of the phase-locked error voltage and related algorithms, the above parameter indicators with a resolution of about 20nm, a measurement range of 300mm, an accuracy of 0.05%, and a repeatability of 0.1% or higher are finally realized. Based on the range of phase-locking error voltage from zero to more than ten volts and approaching multiple central values with ultra-high resolution, it is reflected that the variation range of the fitting capacitance is about 0 to 6p, which is converted into the signal that is displacement or The measurement range of the angle or hysteresis signal will be extremely high, and the measurement range of this technology for displacement can be about 30CM while ensuring ultra-high precision.

Example 4

Referring to Figure 1, the micro-displacement measuring instrument is based on the principle of plate capacitance to realize the capacitance variable corresponding to the linear displacement or angular displacement and magnetostrictive change measured by the phase-locked loop method. After calculation, calibration and conversion, the micro-displacement amount of bits. The existing micro-displacement measuring instrument is easily affected by external electromagnetic interference, hardware such as LC sensor head, parameter drift of A/D devices, etc., that is, there is an error in the final measurement result.

The displacement sensor is a sensor that converts the measured mechanical quantity, such as displacement, pressure, etc., into capacitance, that is, fitting the change of capacitance. Its sensitive part is the plate capacitor with variable parameters. Its most common structures include plate and cylinder, referred to as plate capacitors or cylindrical capacitors. The structure of traditional displacement measuring instruments consists of a fitted plate capacitive sensor head, op amp amplification, filtering, AD conversion, CPU data processing, Displays components such as communication. Capacitive sensors are divided into three types: variable pole pitch type, variable area type and variable medium type. These three types are based on the shape and composition of the sensor plate, especially the differential sensor, which has the characteristics of high sensitivity, wide linear range, and high stability. The moving body contacts and drives, and finally forms a voltage difference on the two poles of the capacitive sensor, which is led out by the coaxial cable, and then amplified by the op amp, filtered, AD converted, CPU data processing part, display communication, and finally output corresponding to the displacement (distance or angle, magnetostrictive change) variable data. This data, that is, the amount of change corresponding to the distance or angle, can be displayed locally or sent to the host computer (computer) by the communication part, and further processed and stored by the pre-installed software, so as to realize the displacement of dynamic bodies such as precision machine tools For measurement purposes of even small displacements. It is pointed out that this technology has increased the phase-locked loop technology, back-tested and fitted capacitance and calculated the displacement and angle changes.

In this technical solution, the ultra-high-precision micro-displacement measuring instrument based on phase-locked loop technology achieves high stability, high resolution, and high Reliable, high-precision displacement

Or angle change measurement, ultra-high-precision micro-displacement measuring instrument based on phase-locked loop technology, has made breakthroughs in several parameters such as measurement accuracy, resolution and repeatability.

A set of phase-locked high-frequency generator is composed of PLL phase-locked loop circuit, VCO and varactor diode. There are different types or structures of plate capacitors and installed in the tested such as precision machine tools, concrete to be tested, space body docking, etc. On the moving body, the physical structure where the plate is placed and the spacing is changing, and then the plate capacitor is excited by the high-frequency electric field and fitted to the Cx fitting capacitor as shown in the figure. It is well known that the phase-locked loop is coordinated by the varactor diode and controlled by the MCU. Through the communication between the I²C bus and the phase-locked loop chip, the frequency data of a frequency point such as 100MHz can be set by the MCU, and the VCO voltage can be used, and then the phase-locked loop circuit cooperates with the oscillator to lock the frequency, and at the same time, the two ends of the varactor diode are also The oscillation frequency can be measured. According to the principle of the phase-locked loop, the oscillation frequency will be changed and locked by different setting frequencies. The locking ground is extremely accurate, such as 100MHz, and at the negative terminal (-) of the varactor diode, the VCO presented Voltage (that is, voltage-controlled oscillation voltage), the voltage value is extremely stable in a certain time domain, that is, infinitely approaching a "central value"; at the same time, the Cx fitting capacitor is also connected in parallel at both ends of the varactor diode. The two ends of the combined capacitor are connected to the varactor diode, and the high-frequency oscillation signal is connected. In fact, it is equal to the fitting capacitor being highly correlated with the medium and the distance between the two poles under the action of the high-frequency excitation frequency, and then generating a fitting capacitor Cx, which has a certain According to the principle of the phase-locked loop, the capacity change of the varactor diode will cause the output frequency of the VCO to change. This frequency is input into the phase-locked loop chip. The phase loop chip compares the set frequency to get an error voltage, which will be fed back to the negative terminal (-) of the diode to readjust the output frequency of the VCO and repeat the above process until the output frequency of the VCO is 100MHz and reaches The same frequency accuracy as the set frequency, that is, the two crystal oscillators of MCU and PLL (at least the crystal oscillator effect of PLL), can reach an order of magnitude greater than or equal to 10 ^-9 . When the VCO outputs an extremely precise frequency, it is stable at this frequency point. Then the negative terminal voltage of the varactor diode will be relatively extremely stable at a value in a certain time domain. Since Cx is connected in parallel at both ends of the varactor diode, it belongs to the change value of Cx fitting capacitance, which is the above-mentioned varactor diode The amount of change in the total capacity, this change value is the above-mentioned steady state obtained by the phase-locked loop circuit, and reflected to a real-time voltage value on the varactor diode, and this value just corresponds to the Cx fitting capacitance A variable capacity, compared to the Cx value before measurement, is either greater or less than, and the difference is the voltage value, which is then converted into the capacitance value of the Cx fitting capacitance by the corresponding algorithm, so the capacitance value actually corresponds to the displacement, angle, etc. amount of change. At the same time, Cx fits the capacitance value and combines other parameters such as temperature data, hardware drift data of VCO voltage, various interference data, and combines certain previous experience table data (such as temperature coefficient, iterative correction of fitting capacitance and VCO) , look-up table coefficient) for calibration, and then converted into actual soil displacement according to the corresponding data model.

The voltage of the varactor diode load is the VCO voltage. This voltage is an important parameter in the phase-locked loop. This voltage is actually a phase-locked adjustment voltage generated by the phase detector PD inside the phase-locked loop and input to the attached drawing. The negative terminal of the varactor diode shown in 1, this voltage determines the frequency value of the VCO output frequency signal. According to the principle of the phase-locked loop, this voltage is initially a basic voltage value, and finally controlled by the PD unit of the phase-locked loop. Combined with the above, it will eventually approach a central voltage value infinitely. This central voltage value is not an absolute 0 value, but a relatively stable value for a certain instantaneous time period. This period actually includes two states: locked frequency and unlocked frequency. , before locking, its PD voltage oscillates on a certain "central line" voltage and changes with time, but when the parameters of the phase-locked loop circuit are correct and there is a correct setting frequency value, it will reach the final let The phase-locked voltage tends to an actual PD voltage value, which actually reaches a frequency-locked state. As mentioned above, the current phase-locked voltage is highly correlated with the measured displacement. It is important to point out that due to the use of a phase-locked loop, the representative Measure the voltage AD value of the phase-locking capacitor, approaching infinitely, and approaching a center line that satisfies the median theorem in the form of differential integration, which is relatively stable, reliable and credible within tens or several milliseconds, and has a strong reproducibility.

The measurement principle mentioned above is actually to obtain the negative terminal of the varactor diode, a changing "central line" voltage, the central line voltage is locked after a certain period of time, in fact very quickly, this voltage actually corresponds to the current The accurate oscillation frequency of the VCO, that is, frequency locking, the current VCO voltage is extremely stable, this contribution also comes from the accuracy and stability of the respective crystal oscillators of the PLL and MCU unit, and its general accuracy can reach 10 ^-9 , or even 10 ^-18 , it is conceivable that combined with the precision of this crystal oscillator, and relying on the error correction obtained by the PD phase-locked loop comparator unit, that is, the "difference pump", the final VCO key voltage obtained is very stable and Accurate, that is to obtain the voltage of the negative terminal of the varactor diode, note that this VCO phase-locking voltage is only a relatively stable voltage, its corresponding capacitance value is the current total capacity value, and the current measured displacement and angle corresponding to this phase-locking voltage value Equal variable with the current varactor base capacitance value. Actually inductively speaking, if the distance is changed by 1nm, since Cx is connected in parallel with the varactor diode, the varactor diode will actually increase the capacitance value step of the fitting capacitor Cx corresponding to the increment of 1nm, and the PLL phase locks In order to ensure the output of the original set frequency, the phase-locked loop voltage will make the voltage of the phase-locked loop infinitely approach a "center line" VCO voltage value under the framework of integral and differential or even Laplace's median value theorem, which is actually a gate Grid voltage, each grid voltage actually corresponds to each measured value of displacement.

As mentioned above, the solution in the technical field can realize high-precision and high-resolution measurement, but this is only for the uninterrupted measurement after the instrument is turned on. That is, dynamic high-precision and high-resolution are realized. Regarding the situation of restarting after shutdown, regardless of temperature and hardware drift factors, there will be a complete fitting capacitance Cx corresponding to the measured displacement, angle and other variables. In the case of no change, there will be a deviation problem during repeated measurements, that is, after it is connected in parallel with the varactor diode, the measured "center line" VCO phase-locked voltage at the negative end of the varactor diode will have zero drift or the same as the previous time. The starting values are inconsistent, although the error is very small, if certain measures are not taken, the instrument will not be able to exert its highest accuracy, resolution and repeatability accuracy, thus introducing the "relative measurement method" and adding The calibration part composed of calibration capacitors, it is emphasized that this part is just to make the instrument achieve the highest performance specification, but it is not a limitation of this patent.

The implementation method of the specific principle of the relative measurement method:

The basic principle of the relative measurement method is that there are two measured values, 1. One of the most basic basic values, such as the varactor diode shown in Figure 1, when _the external C and Cx are disconnected through the switch as shown in the figure, the varactor will be measured separately. The AD value of the voltage measured at the negative terminal of the capacitor diode is the current real-time basic measured value. 2. The so-called other measurement value is when C _or Cx are respectively closed through the switch as shown in the figure, and then measure the negative terminal of the varactor diode at this time to obtain a real-time measurement value. Actually, at least two capacitors are connected in parallel. The resulting voltage AD value.

In fact, the value obtained after the subtraction of these two values is the relative measurement value of Cx (fitting capacitance) or the relative measurement value of C _calibration (calibration capacitance). The value obtained by the principle measurement has extremely high stability, high repeatability and high reproducibility, and has high precision, and at the same time eliminates the varactor diode, which is caused by various factors The various influences brought about by the zero drift, especially the influence brought about by the basic capacitance measurement, this is the technical principle and the technical effect brought by this relative measurement method.

Let's discuss why the calibration capacitor should be used to calibrate the measured value.

Although the above-mentioned relative measurement of the measured value has high accuracy, resolution and stability, due to the influence of many factors such as the nonlinearity of the VCO voltage of the varactor diode, it will affect the accuracy, resolution, especially those with super When high precision is required, it will be more or less affected, so the technical structure of calibrating capacitors is introduced.

Specifically, see Figure 1. _School C uses high-precision mica capacitors. Under normal conditions, its stability can reach ±0.01%. It can be seen that its ultra-high stability can be used to correct the measurement of the above-mentioned fitting capacitance. Value, this C _calibration is also closed or disconnected through the switch shown in the figure, and at the same time the switch of the fitting capacitor is also disconnected. At this time, the relative measurement value of C _calibration is obtained, and further compared with the previous design experience C _calibration value, A new calibration coefficient is obtained, and this coefficient is used for multiplication or division or a certain function operation. After further accuracy correction of the above relative measurement value, the relative measurement value is the obtained fitting capacitance value, which has super High precision, resolution, repeatability accuracy.

Finally, the capacitance value of the fitting capacitor is calibrated in combination with certain previous empirical table data (such as temperature coefficient, iterative correction of fitting capacitor and VCO, table look-up coefficient), and then converted into actual displacement according to the corresponding data model, At the same time, it is further corrected and calibrated to further improve the precision and accuracy of the measured value.

Example 5

Utilizing the above-mentioned scheme, principle and algorithm, a super-high-precision displacement accuracy measuring instrument is designed and manufactured. Of course, other measuring instruments with the same accuracy of angle and hysteresis expansion can be manufactured. Get ready to import ultra-high-speed oscilloscopes, spectrum analyzers, logic analyzers, a micro-motion ultra-precision milling machine with ultra-high-precision (nano-level) ultra-high precession of the screw screw, and choose a micro-precision milling machine imported from Germany that is currently in the international market. Compared with capacitive micro-displacement sensors with extremely high technical indicators and performance. In the specific process of the experiment, the moving body of the milling machine is closely connected to the capacitive moving piece of the capacitance sensor made according to this technology, and the moving piece of the imported measuring instrument is also connected to the moving body of the milling machine. This product And imported products are powered on, first reset the precision milling machine to zero, and record the current data of the machine and imported equipment, and then move the moving body of the machine tool with a certain load to the end point of 20nm, 220nm, 2um, 30cm, and at the same time Record the data of the two sensors, use the above-mentioned instruments to measure, directly read and calculate, and obtain the accuracy of the measured value of this machine is 0.05%, the resolution is 20nm, the measurement range is 300mm, and the repeatability is 0.1%. Compared with imported sensors, the above three parameters Both exceeded 3 to 5 orders of magnitude. In addition, according to the above experiment process, the static and variable values of the angle and hysteresis signals were measured by the capacitance method of the local machine and the imported machine, and the indicators of the three parameters of the local machine were all 3 to 5 orders of magnitude higher than the imported machine.

This technical solution uses phase-locked loop technology to measure small changes in capacitance and reflect and measure changes in macro distances and micro angles, reaching or even exceeding the accuracy and sensitivity of similar foreign products, and achieving high stability and Reliability, product cost is basically less than 1/3 of similar foreign products, and the measurement range of imported products from Europe, America, Japan, etc. does not exceed 10mm, which also limits its application range. The technical solution makes full use of the phase-locked loop technology and the cyclic accumulation measurement technology to realize a large-scale ultra-high-precision measurement, and even achieve ultra-high-precision measurement of any distance and any n*360 degree range.

The embodiments of the application are only used to illustrate the technical features disclosed in the application, and changes made by those skilled in the art through simple replacements still fall within the protection scope of the application.

Claims (8)

1. A method of measuring ultra-high-precision displacement, characterized in that: the fitting capacitance formed by the sensor of measurement displacement or angle variable or hysteresis signal variable is connected in parallel with the varactor diode of phase-locked loop circuit, phase discrimination The device cooperates with the LPF to compare the local oscillator frequency value generated by the VCO oscillation with the set frequency value delivered by the MCU to generate a phase-locked error voltage. The error voltage adjusts the local oscillator frequency in the form of a negative feedback closed loop to make it track and equal to the PLL setting of the phase-locked loop Frequency, and achieve the same accuracy as the PLL crystal oscillator, infinitely approaching or equal to the center value of a phase-locked voltage in the form of differential integral and median theorem, and the calibrated real-time error voltage determines the local oscillator frequency value, using this error voltage and The real-time value of _{the total} capacitance of C in the phase-locked loop LC oscillator, the real-time value of the fitting capacitance and the variable value are reversely measured by the variable value of the error voltage, and the measured value of the displacement or angle or hysteresis signal is calculated from the variable value of the fitting capacitance, and Use the stored temperature, correction capacitance and correction coefficient of the measured value to perform correction, and further obtain ultra-high-precision measured values, and realize ultra-high-precision measurement of displacement or angle or hysteresis signals. 2. The method for measuring ultra-high-precision displacement according to claim 1, characterized in that: said ultra-high-precision means: the accuracy of the measured value is 0.05%, the resolution is 20nm, the measurement range is 300mm, and the repeatability reaches 0.1%. 3. the measuring method of ultra-high-precision displacement according to claim 1, it is characterized in that: described error voltage adjusts local oscillator frequency with negative feedback closed-loop form to make it track and be equal to phase-locked loop PLL setting frequency means: by Under the cooperation of the PLL adjustment voltage, the phase-locked comparator changes the capacity of the varactor diode to make it increase or decrease accordingly, and adjust the local oscillator frequency up and down until it is equal to the set frequency value. When using the locked frequency, The real-time value of the adjusted voltage is reversely calculated to calculate the current capacity of the varactor diode; the variable signal generated by the displacement or angle or pressure sensor is converted into a capacitance signal to form a fitted capacitance sensor, and the fitted capacitance sensor is connected in parallel with the varactor diode to form a fitted capacitance The capacitance value of the varactor increases, and the phase-locked loop maintains the original frequency value, then reduces the current capacitance value of the varactor diode, and at this time the adjusted voltage increases, and the variable of the current capacitance value of the varactor diode is calculated from the increased value of the adjusted voltage. The current capacitance of the fitting capacitor is obtained, and compared with the current capacitance of the last fitting capacitor pre-stored before, the variable value of the obtained fitting capacitance is increased or decreased, and the measured value of the displacement or angle or pressure is further calculated. 4. The measuring method of ultra-high-precision displacement according to claim 1, characterized in that: said phase detector cooperates with LPF to compare the local oscillator frequency value generated by VCO oscillation with the set frequency value delivered by MCU to generate a The phase-locked error voltage means: when the two frequency values are different, an error voltage is generated, and the error voltage is fed back to the negative terminal of the varactor diode of the VCO circuit. When the local oscillator frequency value is lower than the set frequency value, the error voltage increases. Because the error voltage is loaded on the negative terminal of the varactor diode, the capacitance of the varactor diode decreases, resulting in an increase in the local oscillator frequency signal; otherwise, the error voltage decreases, resulting in a decrease in the local oscillator frequency until the phase-locked loop tracks and locks to a When the frequency center value is set, it can achieve the same or higher precision as the crystal oscillator of the phase-locked loop. 5. The measuring method of ultra-high-precision displacement according to claim 1, characterized in that: when the fitting capacitance of the LC oscillator in parallel is increased or decreased due to displacement or angle variation, the adjustment voltage The value increases or decreases accordingly. 6. The measuring method of ultra-high-precision displacement according to claim 1, characterized in that: said utilizing stored temperature, correction capacitance and the correction coefficient of the measured value to correct refers to storing the temperature and capacitance in the MCU. And the correction system of the error caused by the measurement value, use these correction systems to correct the measurement value, in which the correction capacitance is measured twice by the relative measurement method, and the two voltage values obtained are subtracted, and the difference obtained is the current value of the correction capacitance. Capacitance value, using the current correction capacitance combined with the stored calibration value of the correction capacitance to calculate the correction coefficient; use this correction coefficient to correct the real-time variable value of the fitting capacitance, and improve the accuracy, stability and repeatability of the variable value. 7. The method for measuring ultra-high-precision displacement according to claim 2, characterized in that: the VCO circuit adopts a temperature-compensated crystal oscillator with an accuracy of at least 10e-16 power, and uses a constant temperature bath VCO circuit, and the accuracy of the power supply is not less than 0.01%. 8. The measuring method of ultra-high-precision displacement according to claim 1, characterized in that: the variable value of the fitting capacitor is connected with a switch by the positive terminal of the fitting capacitor and connected with the negative pole of the varactor diode , the phase-locking error voltage difference obtained by turning on and off the switch is the variable value of the error voltage, and the variable value of the fitting capacitance is calculated at the same time.