A displacement measurement device, method and circuit processing unit based on a circular grating sensor

Abstract

The application discloses a kind of displacement measurement device, method and circuit processing unit based on circular grating sensor, including the two-stage processing of front-end + rear-end of grating signal, wherein front-end processing mainly realizes the first-order optimization to signal, rear-end processing carries out second compensation using software technology, wherein signal processing module uses FPGA technology, can greatly improve the speed and accuracy of signal processing, to provide guarantee for accurate measurement. By algorithm compensation to sampling data, the accuracy of displacement measurement device can be effectively improved. For the error factors such as DC component, equal amplitude, orthogonality and sinusoidal of moire signal, a system framework of front-end processing circuit + adaptive compensation algorithm is designed. Two modes of digital subdivision are designed, according to the requirements of actual working condition, one mode is selected by dial switch, the resolution of measurement can be changed, the speed and accuracy of signal processing can be greatly improved, to provide guarantee for accurate measurement.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of precision instrument measurement technology, and particularly relates to a linear displacement measurement device, method and circuit processing unit of a circular grating sensor. BACKGROUND

[0002] In the current manufacturing field, precision measurement technology is a very important key link. Ultra-precision measurement technology is one of the cutting-edge technologies in the current manufacturing industry. With the continuous development of manufacturing industry, people's requirements for the precision, range and measurement speed of the ultra-precision measurement system are increasing in the fields of national defense industry, aerospace, precision optics, biological medicine, precision machining and manufacturing, micro-operation robot, etc. The circular grating sensor takes Moiré fringes as the basic measurement unit, and completes displacement measurement through the corresponding relationship between Moiré fringes and grating pitch. The grating sensor has a larger measurement range, is more suitable for large-range measurement occasions, has lower requirements for working environment, and has a relatively simple system structure and lower manufacturing cost.

[0003] Traditional displacement measurement sensors include capacitive sensors and laser interferometers. The capacitive sensor completes displacement measurement according to the corresponding relationship between capacitance and displacement, has a relatively simple system structure and high resolution, but has a relatively low frequency response and a small measurement range, and is not suitable for occasions requiring high speed, dynamics and large range measurement.

[0004] The laser interferometer completes displacement measurement according to the corresponding relationship between interference fringes and displacement, has a larger measurement range, and is more suitable for large-range measurement occasions. However, the system has strict requirements for the environment of the measurement occasion, has a complex overall structure, and has a high manufacturing cost.

[0005] The circular grating sensor takes Moiré fringes as the basic measurement unit, and completes displacement measurement through the corresponding relationship between Moiré fringes and grating pitch. The measurement range is large, and it is more suitable for large-range measurement occasions, has lower requirements for working environment, and has a relatively simple system structure and lower manufacturing cost. The traditional grating ruler displacement measurement device is applied to the field of numerical control machine tools, and the grating ruler has a large device volume and low resolution, and is not suitable for the measurement of precision parts. The measurement of precision parts is mostly measured by a vernier caliper, and the measurement error is large.

[0006] At present, the measurement precision of the grating is improved basically from the following two aspects:

[0007] (1) This can be achieved by increasing the grating's line density, but this is very difficult and costly in terms of manufacturing process. Furthermore, the smaller the grating pitch, the stricter the requirements for the optical system and mechanical structure, and the lower the grating's maximum speed. Currently, the grating line count used in length measurement fields both domestically and internationally is 20-2000 lines / mm, corresponding to a grating pitch of 0.5-50 μm. Holographic gratings can achieve 6000 lines per millimeter, corresponding to a grating pitch of 0.17 μm. However, the fabrication method of holographic gratings also suffers from the problem of difficulty in fabricating large-range gratings because it is difficult to obtain two very wide monochromatic parallel beams. Therefore, holographic gratings are relatively short, and when the grating density is too high, there are corresponding requirements for the light source wavelength, limiting their application. Whether it's a scribed grating, a holographic grating, or their replica gratings, they cannot be made too long.

[0008] (2) Improve the accuracy of grating displacement measurement through subdivision technology. Moiré fringes optically magnify the grating pitch and have a one-to-one correspondence with the grating pitch. The problem to be solved by subdivision of moiré fringes is how to determine the accurate displacement value when the grating is within a moiré fringe, which corresponds to a grating pitch. This requires interpolation, i.e. subdivision, of the fringe signal within one period in order to achieve higher resolution and accuracy.

[0009] Currently, there are few grating signal subdivision systems on the market, resulting in insufficient practicality and scalability. Traditional hardware subdivision circuits are cumbersome, prone to interference between circuits, and difficult to modify, hindering expansion. Therefore, to better address these issues, this invention uses an FPGA chip as the core hardware architecture and leverages the FPGA's logic resources to process the grating signal. This not only reduces the complexity of hardware design and saves implementation costs, but also reduces interference between circuits by replacing hardware circuits with FPGA programmable logic devices. Furthermore, circuits designed using FPGAs can achieve new functions by modifying the program and changing the connections between FPGA logic resources, facilitating the modification and expansion of the subdivision system. Moreover, software subdivision of the grating signal is performed on top of hardware subdivision, further improving the accuracy of grating measurement.

[0010] In summary, this invention utilizes a circular grating sensor to design a small-volume displacement measuring device capable of measuring the dimensions of precision parts. The measuring device comprises two stages of processing: a front-end and a back-end for the grating signal. The front-end processing primarily performs primary signal optimization, while the back-end processing employs software technology for secondary compensation. The signal processing module utilizes FPGA (Field-Programmable Gate Array) technology, which significantly improves the speed and accuracy of signal processing, thereby ensuring precise measurement. Summary of the Invention

[0011] The purpose of the present application is to solve the problems existing in the prior art measurement technology, and provide a small displacement measurement device based on a circular grating sensor, which realizes the compensation and subdivision functions of signals, improves the resolution of measurement, and converts the angular displacement measured by the circular grating sensor into linear displacement.

[0012] In order to achieve the above-mentioned purpose, the present application adopts the following technical solutions:

[0013] The circuit processing unit of the high-precision linear displacement measurement device based on the circular grating sensor comprises a circular grating sensor, a voltage stabilizing power supply module, a raw signal pre-processing circuit module, a single-channel high-speed AD signal acquisition module, a double-channel high-speed AD signal acquisition module, an FPGA signal processing unit, a digital display and a key function switching module, a high-precision screw thread conversion module, and a grating signal subdivision module. Firstly, the circular grating sensor is driven to do linear displacement by the high-precision screw thread conversion module through mechanical rotation. The circular grating sensor outputs two grating signals, which are transmitted to the raw signal pre-processing circuit module. After signal conditioning and filtering, the signals are divided into two paths. One path is transmitted to the single-channel AD signal acquisition module, and the other path is transmitted to the double-channel AD signal acquisition module. After signal sampling, the signals are processed by the FPGA signal processing unit. By distinguishing the forward and reverse rotation of the circular grating sensor, the number of pulses is calculated, and the large numerical part is calculated. The subdivision small numerical value is obtained by the minimum period construction function method. Finally, the displacement value is equal to the sum of the two parts, and the corresponding displacement value is displayed through the digital display module.

[0014] The circular grating sensor displacement measurement device is as shown in Figure 1 .

[0015] The circular grating sensor outputs A and B two-way differential signals, A+ and A- are one-way differential mode signals, B+ and B- are another way differential mode signals, A and B two-way signals are phase difference 90 degree sine signals, and the circular grating sensor is a hollow circular structure installed at one end of the high-precision screw thread. The circular grating sensor adopts a Heidhann ERN1381 incremental grating sensor, and its power supply voltage is 5V. The output A+ and A-, B+ and B-, and R+ and R- three signals are output, wherein A and B are sine output signals, and R is a zero signal for one rotation. The two grating signals are as shown in Figure 2 .

[0016] The voltage stabilizing power supply module provides a stable voltage source for the circular grating sensor and the entire unit. The size of the voltage source can be adjusted by a knob. The power supply voltage of the circular grating encoder is 5V, and the size of the input and output voltage and current is displayed by a digital tube.

[0017] The original signal pre-processing circuit comprises a differential amplification circuit module, a low-pass filter circuit module, a secondary amplification circuit module, a comparator circuit module, a multiplexing selection circuit, a direction discrimination circuit and an absolute value circuit module.

[0018] The differential amplification circuit module has two modules, which are connected to A+ and A-, B+ and B- two-way differential signals output by the circular grating sensor. A+ and A-, B+ and B- are called differential mode signals. The differential amplification circuit is beneficial to suppress common mode interference and reduce temperature drift. The chip used is OPA2604, which has the characteristics of ultra-low harmonic distortion, low noise, high gain bandwidth, etc. The built-in double channel has negative feedback characteristics, so the bandwidth, impedance and input characteristics of the circuit do not affect the changes in the manufacturing process and the temperature coefficient.

[0019] The low-pass filter circuit module adopts a second-order low-pass Butterworth filter, and the RC link can narrow the transition band of the filter and increase the attenuation slope value, thereby improving the filtering capability of the system. The quality factor Q of the Butterworth filter is 0.707, and the amplitude-frequency characteristic curve is monotonous near , the amplitude-frequency characteristic curve is monotonous near .

[0020] The secondary amplification circuit is used to amplify the voltage amplitude of the circuit after the preliminary noise processing circuit and the differential circuit, so that the peak voltage is stabilized at 5V, thereby facilitating the processing of the subsequent comparator circuit and A / D sampling circuit.

[0021] The comparator circuit is used to convert the original sinusoidal signal into a square wave signal to realize fine direction discrimination. The zero-crossing comparator amplifier is used to output two square wave signals with a phase difference of 90° from two sinusoidal signals with a phase difference of 90°, thereby improving the flat signal basis for the subsequent multiplexing circuit and FPGA fine direction discrimination.

[0022] The multiplexing selection circuit compares the amplitudes of the output signals of the absolute value circuit 、 , and outputs the selected signal to the input end of the follower after the selection of the input signal of the analog selector. 、 The selected analog selector model is DG409, which has eight input channels. DG409 controls the selection channel through the port. If the high The potential of the two ends, so as to realize the selection of DG409 channel. =0, that is , the channel S1A and S1B open, S1A input signal, S1B input signal; when =1, that is , the channel S2A and S2B open, S2A input , S2B input signal. Two signal respectively by DA and DB two port output, wherein DA end always output after comparison of large voltage, DB output after comparison of small voltage, then again input to high speed A / D sampling chip analog voltage input terminal, will input to A / D sampling chip reference input terminal.

[0023] The direction discrimination circuit, the phase difference of 90° two square wave signals A and B, first carry out synchronous dithering processing, and extract the rising edge and falling edge of A signal after dithering, control the left turn flag and the right turn flag to pull up and pull down through judging condition, carry out rising edge detection to the left turn and the right turn flag, when left turn, control the counter to add one, when right turn, control the counter to subtract one. The judging condition is as follows: 1) A signal is rising edge, B signal is low level, then the grating sensor right turn, when A signal is falling edge, B signal is high level, then one right turn ends; 2) when A signal is rising edge, B signal is high level, then the grating sensor left turn, when A is falling edge, B is low level, then one left turn ends.

[0024] The absolute value circuit, in order to construct new function formula 3, need to do absolute value processing to the sine signal output by grating, so as to carry out subsequent sampling processing. Because the displacement measured is constantly changing. If the simple absolute value circuit is selected, the waveform is easy to distort. In order to make the system work stably under the condition that the input signal frequency is constantly changing, the high-precision absolute value circuit is selected. Compared with the ordinary absolute value circuit, the ability of filtering processing and power decoupling of the circuit has been greatly improved, and the system can still work stably under the condition of dynamic measurement.

[0025] ​The high-speed AD signal sampling module is divided into single and double channels: when the dial switch selects mode one, after analog circuit function construction, one AD sampling channel is used, and the selected AD chip is AD9280, which is a single-chip, 8-bit, 32MSPS analog-to-digital converter produced by ADI, with high performance and low power consumption; when the dial switch selects mode two, two AD sampling channels are used, the high-speed AD conversion chip is produced by Enrui company, the model is 3PA1030, the input analog voltage conversion range of 3PA1030 chip is 0V~2V, so the voltage input end needs to pass through the voltage attenuation circuit first, so that the input voltage between-5V~+5V is attenuated to 0V~2V, and then the analog voltage signal is converted into digital signal by 3PA1030 chip. 3PA1030 is a single voltage chip of 10 bits, 50MSPS (Million Samples Per Second, Million Samples Per Second) analog-to-digital converter, integrated on-chip sampling holding amplifier and reference voltage source. It has the characteristics of high performance and low power consumption.

[0026] The FPGA signal processing module: FPGA is a high-precision programmable logic device, connected to the high-speed AD sampling module, when the screw rotates, the middle hub of the circular grating sensor rotates, thereby generating angular displacement and grating signal. The FPGA chip model is EP4CE10F17C8, the FPGA signal processing unit samples the grating analog signal and converts it into a digital signal, the software compensation module processes the sampled signal, and the consistency of the two signals needs to be ensured, the processed signal is further operated by the data processing logic circuit module, and the entire subdivision data is obtained. The software compensation module includes direct current component compensation, equal amplitude compensation, sinusoidal compensation and quadrature compensation four modules, among which the sinusoidal output signal of the Heidhann ERN1381 type grating encoder has been adjusted at the factory, so the signal sinusoidal compensation is not processed in the present application.

[0027] The direct current component compensation module is mainly used to make the two signals have the same direct current component. Because the two sinusoidal signals of the grating Moiré signal have different sizes, the direct current error compensation is needed. The direct current error compensation generally has two methods, analog circuit compensation and digital compensation. The analog compensation method usually uses the differential circuit structure to eliminate the interference of common-mode voltage in the original signal. Because the analog device is easily affected by temperature change, the device performance changes with temperature, so the direct current error component in the Moiré signal cannot be completely removed. The digital error compensation method is to compare the sampled signal amplitude point by point, and then calculate the direct current error by taking the maximum value in the whole period. The direct current error of the grating Moiré signal is equal to the average of the maximum value and the minimum value of the signal in the whole period, and the expression is:

[0028]

[0029] For the direct current error of the grating Moiré signal, according to the continuity of the grating Moiré signal parameters, the signal parameter change is smooth and slow, the direct current error amount detected in the current period is used to compensate the direct current error of the signal point by point in the next signal period, so as to realize the direct current error compensation of the signal.

[0030] The equal amplitude compensation module is mainly used to realize the consistency of the amplitudes of the two signals. The Moiré signal amplitude error compensation can be realized by building an operational amplifier circuit to realize the error compensation, but due to the limitation of the hardware circuit itself, it is difficult to realize high-precision error compensation. Moreover, due to the interference of external noise, it is difficult to realize precise multiplication and division operation, so the signal amplitude under different working conditions cannot be accurately compensated. The Moiré signal digital amplitude error compensation adopted by the present application is to calculate the amplitude deviation of the two Moiré signals relative to the standard signal amplitude by taking the maximum value of the sampled Moiré signal and taking the standard signal amplitude as the reference. The amplitude error detection expression is:

[0031]

[0032]

[0033]

[0034]

[0035] In the formula, a is the number of sampling points in each period, is the standard signal amplitude, , ... and , ... the measured voltage value of the two signals, the maximum value of the two signals, respectively, the amplitude deviation coefficient of the two moire signals relative to the standard signal.

[0036] The moire fringe signal has parameter continuity, and according to the amplitude deviation coefficient detected in the current period, the linear displacement of the screw rod can be calculated.

[0037] The orthogonality compensation module is mainly used to ensure that the phase difference of the two sinusoidal signals is 90 degrees. The key problem of orthogonal error compensation is to calculate the trigonometric function value of the sine and cosine moire signals. In view of the advantage of pipeline operation of FPGA, the CORDIC algorithm is used to calculate the angle value.

[0038] In the phase error detection link, the arcsine and arccosine values of the two sinusoidal signals and cosine signals are calculated respectively, and the phase deviation of the cosine signal is obtained by calculating the difference between the two signals. When detecting the phase difference, the sine signal is taken as the reference to improve the system detection accuracy and speed, reduce the calculation amount and resource consumption, and calculate the phase difference by selecting the corresponding grating cosine signal in the grating sinusoidal signal interval.

[0039] In the phase compensation, the arccosine value of the grating cosine signal is calculated in the whole period, and then the point-to-point compensation of the grating cosine signal phase is carried out according to the detection result of the phase difference. The phase information of the compensated grating cosine signal is converted into amplitude information to achieve the purpose of signal reconstruction, which is convenient for the subsequent amplitude subdivision module to calculate the subdivision value of the grating moire signal.

[0040] The digital display and key function module: code conversion and nixie tube display function, the key module function mainly plays the role of unit conversion, position zero, initialization device, zero adjustment, etc.

[0041] The high-precision screw rod conversion module: through the mechanical transmission action of the high-precision screw rod, combined with the pitch of the screw rod and the angular displacement of the circular grating sensor, the linear displacement of the screw rod can be calculated. The high-precision screw rod conversion module is connected with the circular grating sensor, and is fixed on the bottom of the base to maintain the stability of the whole device.

[0042] ​​The grating signal subdivision module: the electronic amplitude segmentation subdivision method is adopted in the scheme, the sine and cosine signals cannot be directly quantified and subdivided, the sine and cosine signals have nonlinearity, therefore, a grating signal with good linearity is constructed to improve the accuracy of grating signal measurement. The tangent function subdivision method constructed in the amplitude segmentation subdivision method basically overcomes the nonlinearity error of the signal and does not need to measure the amplitude of the signal. The tangent function method mainly uses the ratio of the two-phase sine signals of the grating signal with a phase difference of 90 degrees, basically eliminates the nonlinearity error caused by the amplitude fluctuation, and accordingly the corresponding displacement value can be derived. The grating signal tangent function construction is as shown in Figure 3 The grating signal and the constructed tangent function formula are as follows,

[0043]

[0044]

[0045]

[0046]

[0047] The function amplitude is calculated by sampling Or The corresponding is calculated by arctangent, so that the displacement value can be determined. The constructed approximate linear function equally divides one period 8 of the original grating signal, and the area value of each interval is π / 4. It is necessary to determine the extreme value and the absolute value of the two signals And , so as to realize 8 equal division and divide one period into 8 intervals. In an interval, according to the absolute value ratio, several subdivisions can also be realized. The eight subdivision gu limit subdivision is as shown in Figure 4 The formula is used in the intervals 1, 4, 5 and 8, and the formula is used in the intervals 2, 3, 6 and 7. The value of Or in the above interval changes between 0 and 1, so it can be represented by the value between 0° and 45°. In this way, a ROM table is fixed in the FPGA, the subdivision multiple N is set, then N tangent values between 0° and 45° are fixed in N storage units, and the processor queries the storage unit closest to the calculated Or value in the ROM table. If the measured value is the kth unit of the storage unit, the subdivision multiple interval is found according to the subdivision formula, so that the displacement value is calculated. The circular grating sensor grating signal subdivision system is as shown in Figure 5 The single-channel AD sampling subdivision program flow of the circular grating sensor is asFigure 6 The application is shown.

[0048] The application has the following advantages:

[0049] 1、The original signal pre-processing circuit module is designed, which can greatly reduce the influence of interference signals and noise, and complete the early conversion processing of the grating original signal. After the processing of the differential amplification circuit, the common-mode signal interference is suppressed, but the noise signals caused by the uncertain disturbance of the experimental environment, electronic devices and experimental equipment are amplified. These signals are obviously not what we need, and the strength of these signals will affect our processing of normal signals, so it is necessary to filter out these noise signals. After the first two module circuits, the disturbance noise caused by the common-mode signal and environmental factors in the system is removed. In order to adjust the signal amplitude, a new amplification circuit is designed to amplify the obtained signal twice, so that the amplitudes of the two signals are the same.

[0050] 2、The FPGA chip is used as a processor in the application, which can greatly speed up the data processing speed and improve the stability of the whole system. The CORDIC algorithm is used to realize the inverse tangent angle solving function of the constructor. The CORDIC algorithm is a numerical approximation iterative algorithm, which can realize the calculation of trigonometric functions through simple addition and subtraction and shift operation. Through the non-cyclic pipeline structure, the iteration process of the CORDIC algorithm is realized. The pipeline structure is one of the commonly used design architectures of FPGA. In each link of the pipeline, FPGA only processes one iteration operation. This method improves the system running frequency by consuming the internal register resources of FPGA and simplifies the design.

[0051] 3、The application can effectively improve the accuracy of the displacement measuring device by compensating the algorithm for the sampling data. A cascade relationship model is established for the error factors of the Moiré signal direct current component, equal amplitude, orthogonality and sinusoidal, and a model of front-end processing circuit + adaptive compensation algorithm is designed.

[0052] 4、Since the Moiré fringe signal obtained after conditioning is a sinusoidal signal, the amplitude of the sinusoidal signal cannot be uniformly divided according to the phase angle, and the linearity is too poor. The closer to the peak value, the greater the phase change is required for the same amplitude change. Obviously, this is not conducive to system calculation, and other methods need to be found to solve the problem of poor linearity of the Moiré fringe signal. In view of this problem, a new function can be constructed to solve the problem, that is, a function with good linearity is used to replace the Moiré fringe signal. The function is constructed into a function with good linearity, which can reduce the nonlinear error of subdivision and improve the measurement accuracy. The method of constructing function is through tangent method, that is, the two orthogonal sinusoidal signals after conditioning are divided.

[0053] 5、The present application proposes a method of combining a circular grating sensor with a screw rod, wherein the screw rod adopts a ball screw rod, and the ball screw rod is composed of a screw rod, a nut, a steel ball, a pre-pressing piece, a reverser and a dustproof device. The function of the ball screw rod is to convert rotary motion into linear motion, and to convert angular displacement into linear displacement through mechanical transmission. Since there are many steel balls between the screw rod shaft and the screw nut of the ball screw pair to make rolling motion, high motion efficiency can be obtained. The device of the present application has small size, high resolution and good transmission efficiency, and is suitable for the measurement of precision parts.

[0054] 6、The measuring device in the present application includes two modes of digital subdivision system. According to the requirements of actual working conditions, one mode is selected through a code switch. Mode one adopts the construction of hardware function algorithm, and realizes the purpose of subdivision through the processing of grating signals. Mode two realizes the first-level optimization of signals through a front-end processing module, and the second-level compensation is realized through software technology in the back-end processing. After signal acquisition, the COEDIC algorithm is realized in the FPGA (Field Programmable Gate Array) inside. The signal processing module adopts FPGA technology. The two modes can be freely switched, the resolution of measurement can be changed, the speed and accuracy of signal processing can be greatly improved, and thus the accurate measurement is guaranteed. BRIEF DESCRIPTION OF DRAWINGS

[0055] Figure 1 It is a schematic diagram of a circular grating sensor displacement measuring device.

[0056] Figure 2 It is a schematic diagram of grating signal subdivision interval.

[0057] Figure 3 It is a schematic diagram of tangent function construction of grating signals.

[0058] Figure 4 It is a schematic diagram of eight subdivision gua limit.

[0059] Figure 5 It is a schematic diagram of a grating signal subdivision system of a circular grating sensor.

[0060] Figure 6 It is a single-channel AD sampling subdivision program flow chart of a circular grating sensor. DETAILED DESCRIPTION

[0061] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all the embodiments.

[0062] As Figure 1As shown in the schematic diagram of the physical structure of the present application, the device of the present application comprises a circular grating sensor 1, a high-precision threaded screw 2, a metal cylindrical head 3, a baffle 4, a fixing screw 5, a supporting leg 6, a circuit processing unit 7, an adjusting button 8, a digital display nixie tube 9, a bottom plate 10, a threaded knob 11, a screw rod fixing support 12, and a locking button 13. The circular grating sensor 1 is a hollow structure, the middle hub is connected with the high-precision threaded screw 2, and the high-precision threaded screw 2 rotates to drive the rotation of the hub in the middle of the circular grating sensor 1. The high-precision threaded screw 2 is connected with the screw rod fixing support 12, and the screw rod fixing support is connected with the bottom plate 10, thereby ensuring the stability of the device. The baffle 4 is connected with the bottom plate 10, and the baffle 4 is used for fixing one end of the measured object and is connected with the metal cylindrical head 3 to fix the measured object at the middle position. The threaded knob 11 adopts a threaded protruding structure, is installed at the tail of the high-precision threaded screw 2, and can be rotated clockwise or counterclockwise. The rotation of the threaded knob 11 can drive the rotation of the high-precision threaded screw 2. The locking button 13 is installed on the screw rod fixing support 12 and can mechanically limit the rotation of the screw rod by rotating. The locking button 13 is used for switching between the locking state and the working state of the measuring device. When the locking button 13 is twisted clockwise, the device is in the working state, and when the locking button 13 is twisted counterclockwise, the device is in the locked state. The metal cylindrical head 3 is installed at the front end of the high-precision threaded screw 2, and its main function is to contact the measured object and fix the measured object. The circuit processing unit 7 is fixed below the bottom plate 10 and comprises a power module, a signal processing module, a data acquisition module, an FPGA processor module, a nixie tube display module, and a key control module. The digital display nixie tube 9 is installed outside the box of the circuit processing unit 7 and has six nixie tubes arranged in sequence, which are used to display the size of the measured displacement. The adjusting button 8 is installed at the lower right of the digital display nixie tube 9 and has three buttons from left to right. The first button is used for zero setting, the second button is used for code switching, and the third button is used for value locking.

[0063] More specifically, the supporting mechanism comprises the supporting leg 6, which is connected with the bottom plate 10 through the fixing screw 5. The two ends of the supporting leg 6 have screw holes corresponding to the fixing screw 5, and the bottom of the bottom plate 10 has adjustable screw holes connected with the fixing screw. The supporting leg 6 is connected with the bottom plate 10 through the fixing screw 5, and the purpose is to adjust the position of the supporting leg 9 on the bottom plate 7 to facilitate the adjustment of the distance between the two supporting legs 9 for use in different situations.

[0064] The measuring process of the device: firstly, rotate the lock button 13 to switch to the working state, set the initial position, measurement resolution, measurement code conversion, etc. through the adjusting button 8, then place the measured object between the baffle 4 and the metal cylindrical head 3, move the high-precision threaded rod 2 forward and backward by rotating the threaded knob 11, and the circular grating sensor 1 also rotates at the same time, when the measured object is pressed by the baffle 4 and the metal cylindrical head 3, the signal of the circular grating sensor 1 is processed by the circuit processing unit 7, and the displacement measurement data is displayed on the digital display tube 9, completing a complete measurement process.

[0065] The above series of detailed descriptions are only specific descriptions of the feasible embodiments of the present application, and are not used to limit the protection scope of the present application, and any equivalent means or changes without departing from the present application should be included in the protection scope of the present application.

Claims

1. A circuit processing unit for displacement measurement, characterized in that It comprises: Stabilized power supply module, raw signal pre-processing circuit, high-speed AD signal sampling module, FPGA signal processing module, digital display module, high-precision screw rod conversion module, grating signal subdivision module; The high-precision screw rod conversion module drives the linear displacement of the circular grating sensor, and the circular grating sensor outputs two grating signals which are transmitted to the raw signal pre-processing circuit module. After signal conditioning and filtering, the signals are transmitted in two ways. One is transmitted to the single-channel AD signal acquisition module of the high-speed AD signal sampling module, and the other is transmitted to the dual-channel AD signal acquisition module of the high-speed AD signal sampling module. After signal sampling, the signal is processed by the FPGA signal processing unit. By distinguishing the forward and reverse rotation of the circular grating sensor, the number of pulses is calculated, and the large value part is calculated. The minimum period of the grating signal subdivision module is obtained by the construction function method to get the small decimal value. Finally, the displacement value is equal to the sum of the two parts, and the corresponding displacement value is displayed through the digital display module. The stabilized power supply provides power for each module. The FPGA signal processing module is connected to the high-speed AD signal sampling module. When the middle hub of the circular grating sensor rotates, the angular displacement generates a grating signal. The FPGA signal processing module samples the grating analog signal and converts it into a digital signal. The software compensation module processes the sampled signal to ensure the consistency of the two signals. The entire subdivision data is obtained based on the processed signal. The high-precision screw rod conversion module is connected to the circular grating sensor. Through the mechanical transmission of the high-precision screw rod, combined with the pitch of the screw rod and the angular displacement of the circular grating sensor, the linear displacement of the screw rod can be calculated.

2. A circuit processing unit for displacement measurement according to claim 1, characterized in that The raw signal pre-processing circuit includes a differential amplifier circuit module, a low-pass filter circuit module, a secondary amplifier circuit module, a comparator circuit module, a multiplexing selection circuit module, a direction discrimination circuit, and an absolute value circuit module. The differential amplifier circuit module has two modules, which are connected to the A+ and A-, B+ and B- two-way differential signals output by the circular grating sensor. OPA2604 is used, which has a built-in dual-channel and negative feedback feature. The low-pass filter circuit module adopts a second-order low-pass Butterworth filter, increases an RC link, narrows the transition band of the filter, increases the attenuation slope value, improves the filtering capacity, the quality factor Q of the Butterworth filter is 0.707, the amplitude-frequency characteristic has no peak value, the amplitude-frequency characteristic curve near is monotonically decreasing, is the cut-off frequency of the second-order low-pass Butterworth filter. The secondary amplifier circuit module is used to amplify the voltage amplitude of the signal processed by the raw signal pre-processing circuit and the differential amplifier circuit. The peak voltage is stabilized at 5V to enable subsequent circuit processing. The comparator circuit module is used to convert the original sinusoidal signal into a square wave signal to achieve signal subdivision and direction discrimination. A zero-crossing comparator amplifier is used to output two square wave signals A and B with a phase difference of 90°. The direction discrimination circuit processes the two square wave signals A and B with a phase difference of 90° synchronously and removes the jitter. The rising edge and falling edge of the A signal after jitter removal are extracted. The left and right turn flags are pulled up and pulled down by judging the conditions. The left and right turn flags are detected by the rising edge. When the left turn is detected, the counter is incremented. When the right turn is detected, the counter is decremented. The judgment conditions are as follows: 1) A signal is rising edge, B signal is low level, then grating sensor turns right, when A signal is falling edge, B signal is high level, then one right turn ends; 2) when A signal is rising edge, B signal is high level, then grating sensor turns left, when A is falling edge, B is low level, then one left turn ends; The absolute value circuit processes the cosine signals output by the grating to absolute value, so as to be sampled subsequently; The multiplexing selection circuit module compares the amplitude of the output signal of the absolute value circuit , , the selected analog selector model is DG409, which has 8 input channels, DG409 controls the selection channel through , port, if the high end is at low potential, the potential of the end is controlled by the signal output by the comparator to realize the selection of the DG409 channel, when =0, , , channels S1A and S1B are open, S1A inputs signal, S1B inputs signal; when =1, , channels S2A and S2B are open, S2A inputs , S2B inputs signal, two signals are respectively output by DA and DB two ports, wherein DA port always outputs the large voltage after comparison, DB port outputs the small voltage after comparison, then is input to the analog voltage input end of the high-speed A / D sampling chip, and is input to the reference input end of the A / D sampling chip.

3. A circuit processing unit for displacement measurement according to claim 1, characterized in that The high-speed AD signal sampling module is divided into single and double channels: when the dial switch selects mode one, after analog circuit function construction, a single AD sampling channel is used, and the selected AD sampling chip is AD9280; when the dial switch selects mode two, a double AD sampling channel is used, and the high-speed AD sampling chip adopts 3PA1030, the voltage input end needs to be first passed through a voltage attenuation circuit, so that the input voltage between-5V~+5V is attenuated to 0V~2V, and then the analog voltage signal is converted into a digital signal through the 3PA1030 chip.

4. The circuit processing unit for displacement measurement according to claim 1, characterized in that, The software compensation module includes a direct current component compensation module, an equal amplitude compensation module, a sinusoidal compensation module and a quadrature compensation module, The DC component compensation module is used to ensure that the DC components of the two signals are of equal magnitude. DC error compensation includes both analog and digital compensation. Analog compensation typically uses a differential circuit structure to eliminate common-mode voltage interference in the original signal. Digital compensation calculates the DC error by comparing the amplitude of the sampled signal point by point and then finding the maximum value over the entire cycle. The DC error of the grating moiré signal is equal to the maximum value of the signal over the entire cycle. and minimum value The mean, expressed as: For the DC error of the grating Moiré signal, according to the continuity of the grating Moiré fringe signal parameters, the DC error compensation is realized by using the slow variation of the adjacent period signal parameters and compensating the signal point by point in the next signal period according to the DC error detected in the current period. The equal amplitude compensation module is used to realize the consistency of the amplitudes of the two signals, and a Moore signal digital amplitude error compensation is adopted, the maximum value of the sampled Moore signal is calculated, and the amplitude deviation of the two Moore signals relative to the standard signal is calculated based on the standard signal amplitude, and the amplitude error detection expression is: where a is the number of sampling points per cycle, is the standard signal amplitude, , ... and , ... is the measured voltage value of the two-channel signal, and are the maximum values of the two-channel signal, and are the amplitude deviation coefficients of the two-channel Moire signal relative to the standard signal; The Moire fringe signal has parameter continuity, and according to the amplitude deviation coefficient detected in the current period, the grating Moire signal of the next period can be compensated point by point; The sinusoidal compensation module is used to realize the consistency of the sinusoidal shapes of the two sinusoidal signals. The quadrature compensation module is used to realize that the phase difference of the two sinusoidal signals is 90 degrees, and the CORDIC algorithm is used for angle value calculation in the quadrature error compensation, in the phase error detection link, the arcsine and arccosine values of the two sinusoidal signals and the cosine signal are calculated respectively, the phase deviation of the cosine signal is obtained by calculating the difference between the two signals, and when detecting the phase difference, the sinusoidal signal is taken as the reference, the corresponding grating cosine signal in the grating sinusoidal signal interval range is selected, and the phase difference is calculated; in the phase compensation, the arccosine value of the grating cosine signal is calculated in the whole period, and then the grating cosine signal phase is compensated point by point according to the detection result of the phase difference, the phase information of the compensated grating cosine signal is converted into amplitude information, and signal reconstruction is realized.

5. The circuit processing unit for displacement measurement according to claim 1, characterized in that, The digital display module is used for code conversion and nixie tube display functions.

6. The circuit processing unit for displacement measurement according to claim 1, characterized in that, The grating signal subdivision module adopts an electronic amplitude segmentation subdivision method, the tangent function subdivision in the amplitude segmentation subdivision method overcomes the nonlinear error of the signal without measuring the amplitude of the signal, the tangent function is constructed by using the ratio of the two-phase 90-degree sinusoidal signals of the grating signal, the nonlinear error caused by the amplitude fluctuation is eliminated, and the displacement value can be calculated accordingly; wherein the grating signal and the constructed tangent function formula are as follows, The function amplitude is calculated by sampling Or The corresponding is calculated by arctangent, so that the displacement value can be determined, wherein the construction of the approximate linear function is to divide one period 8 of the original grating signal into equal parts, and the area value of each interval is π / 4, it is necessary to determine the extreme value and the absolute value of the two signals And in advance, so as to realize 8 equal division, and in an interval, according to the absolute value ratio, a number of sub-divisions can be realized, 1, 4, 5, 8 intervals use formula , 2, 3, 6, 7 intervals use formula The value of Or in the above interval varies between 0 and 1, so it can be represented by the value of between 0° and 45°, and the ROM table is fixed in FPGA, set the subdivision multiple N, then use N storage units to fix N tangent values between 0° and 45°, the processor queries the storage unit closest to the calculated Or value in this ROM table, if the measured value is the kth unit of the storage unit, then according to the subdivision formula, the subdivision multiple interval is found, so as to calculate the displacement value.

7. A displacement measuring device based on a circular grating sensor, characterized in that It includes: round grating sensor (1), high-precision screw rod (2), metal cylindrical head (3), baffle (4), fixed screw (5), support leg (6), circuit processing unit (7), adjusting button (8), digital display (9), bottom plate (10), threaded knob (11), screw rod fixed support (12), locking button (13), screw hole; wherein the round grating sensor (1) is a hollow structure, the middle hub is connected with the high-precision screw rod (2), the high-precision screw rod (2) can drive the middle hub of the round grating sensor (1) to rotate, the high-precision screw rod (2) is connected with the screw rod fixed support (12), the screw rod fixed support (12) is connected with the bottom plate (10), to ensure the stability of the device; the threaded knob (11) is provided with a threaded protrusion structure, is installed at the tail of the high-precision screw rod (2), and can rotate clockwise or counterclockwise; the locking button (13) is used for switching the locking and working states of the measuring device, clockwise twisting is in the working state, and counterclockwise twisting is in the locked state; the metal cylindrical head (3) is installed at the front end of the high-precision screw rod (2), and functions to contact and fix the measured object; the circuit processing unit (7) is fixed below the bottom plate (10), and is the circuit processing unit of any one of claims 1-6; the digital display (9) is installed outside the circuit processing unit (7) box, has six digital tubes arranged in sequence, and is used for displaying the size of the measured displacement; the adjusting button (8) is installed below the right of the digital display (9), has three buttons from left to right, the first button is used for zero setting, the second button is used for code switching, and the third button is used for value locking. The support leg (6) is connected with the bottom plate (10) through the fixed screw (5), the two ends of the support leg (6) are provided with screw holes corresponding to the fixed screw (5), the bottom of the bottom plate (10) is provided with adjustable screw holes connected with the fixed screw (5), the support leg (6) is connected with the bottom plate (10) through the fixed screw (5), and the purpose is to adjust the position of the support leg (6) on the bottom plate (10), so as to conveniently adjust the distance between the two support legs (6) for use in different situations.

8. A method of displacement measurement based on a circular grating sensor, the method being applied to the displacement measurement apparatus based on a circular grating sensor according to claim 7, characterized by, First, rotate the locking button (13) to switch to the working state, set the initial position, measurement resolution, measurement code conversion and the like through the adjusting button (8), then place the measured object between the baffle (4) and the metal cylindrical head (3), rotate the threaded knob (11) to drive the high-precision screw rod (2) to move forward and backward, and the round grating sensor (1) also rotates at the same time, when the measured object is pressed by the baffle (4) and the metal cylindrical head (3), the signal of the round grating sensor (1) is processed through the circuit processing unit (7), and the displacement measurement data is displayed on the digital display (9), so that a complete measurement process is completed.

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