Reflection type grating Moire signal reconstruction method, subdivision method and measurement method

Abstract

The invention discloses a reflective grating Moire signal reconstruction method, subdivision method and measurement method, and relates to the technical field of measurement and signal reconstruction, and the method comprises the following steps: S1, obtaining two paths of original Moire signals U1 (i) and U2 (i), and correspondingly processing the two paths of original Moire signals to obtain two initial information items; s2, subtracting the two initial information items to obtain an information item difference value, and obtaining an expected digital signal of U2 (i) according to the information item difference value and the original Moire signal U1 (i); s3, subtracting the U2 (i) from an expected digital signal to obtain an error signal, and optimizing a filter coefficient according to the error signal, the U2 (i) and the expected digital signal to obtain an optimized filter coefficient; and S4, filtering the U1 (i) and the U2 (i) by using the optimized filter coefficient to obtain two paths of reconstructed Moire signals, so that the measurement precision and the resolution of the grating displacement sensor are remarkably improved, and the production cost is reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of measurement and signal reconstruction, and in particular to a reflective grating moiré signal reconstruction method, a subdivision method and a measurement method. Background Art

[0002] Against the backdrop of continuous innovation in global industrial manufacturing technology, precision manufacturing has become a key indicator for measuring a country's high-end manufacturing capabilities. Consequently, the demand for high-precision measurement technology is becoming increasingly urgent. Grating displacement sensors, as core components for achieving precision measurement, play a vital role in high-end fields such as automotive manufacturing, aerospace, semiconductor processing, and precision machine tool control. For example, gap detection of key automotive oil pump components, precise machining of aerospace engine blade profiles, precise measurement of semiconductor wafer thickness, and real-time displacement feedback of precision machine tool worktables all rely on the high-precision measurement performance of grating sensors to ensure product quality and manufacturing process stability.

[0003] In existing technologies, outdated signal processing algorithms, insufficient subdivision technology, and flawed photoelectric receiving array performance lead to signal distortion and accumulated measurement errors. Furthermore, complex industrial environmental factors (such as temperature fluctuations and electromagnetic interference) further exacerbate the instability of grating sensor performance. This results in existing products suffering from low accuracy, poor real-time performance, and high manufacturing costs, making them unable to meet the practical needs of modern industrial manufacturing for high-precision, high-reliability measurements. Summary of the Invention

[0004] The purpose of the present invention is to provide a reflective grating moiré signal reconstruction method, subdivision method and measurement method, which reconstruct the original moiré signal, significantly improve the measurement accuracy and resolution of the grating displacement sensor, and reduce production costs.

[0005] In order to achieve the above object, the specific solution adopted by the present invention is: a reflective grating moiré signal reconstruction method, comprising the following steps:

[0006] S1, obtain two original Moiré signals U1(i) and U2(i), and process the two original Moiré signals to obtain two initial information items;

[0007] S2, the two initial information items are subtracted to obtain the information item difference, and the expected digital signal U2(i) is obtained based on the information item difference and the original moiré signal U1(i);

[0008] S3, subtracting U2(i) from the desired digital signal to obtain an error signal, and optimizing the filter coefficients based on the error signal, U2(i) and the desired digital signal to obtain optimized filter coefficients;

[0009] S4, using the optimized filter coefficients to filter U1(i) and U2(i) to obtain two reconstructed moiré signals.

[0010] As an optimization solution of the above-mentioned reflective grating moiré signal reconstruction method: in S1, two original moiré signals are subjected to arc cosine processing to obtain two initial information items.

[0011] As another optimization solution of the above-mentioned reflective grating moiré signal reconstruction method: in S2, the expected digital signal includes a forward expected signal and a reverse expected signal.

[0012] As another optimization scheme of the above-mentioned reflective grating moiré signal reconstruction method: in S2, when the information item difference is positive, all phase values of U1(i) are delayed by 90° to obtain the forward desired signal; when the information item difference is negative, all phase values of U1(i) are advanced by 90° to obtain the reverse desired signal.

[0013] As another optimization scheme of the above-mentioned reflective grating moiré signal reconstruction method: in S3, the iterative formula for optimizing the filter coefficient is:

[0014] Among them, α, β, γ are constants, W T (n) represents the filter coefficient vector obtained after the nth iteration; μ(n) is the step factor of the nth iteration; e(n) is the error signal generated in the nth iteration; x(n) is the original moiré signal U2(i) input to the filter in the nth iteration, y(n) is the reconstructed moiré signal U6(i) output by the filter in the nth iteration, W(n) is the weight coefficient vector of the adaptive filter in the nth iteration, W(n+1) is the weight coefficient vector of the adaptive filter in the n+1th iteration, μ, d(n) is the expected digital signal, the forward expected signal and the reverse expected signal in the nth iteration.

[0015] A reflective grating moiré signal subdivision method, comprising constructing a tangent function based on two reconstructed moiré signals and obtaining an arctangent phase value of the tangent function, wherein the two reconstructed moiré signals are obtained by the reflective grating moiré signal reconstruction method described above;

[0016] The arc tangent phase value within the moiré signal period is mapped to obtain the corresponding subdivision value.

[0017] As an optimization scheme for the above-mentioned reflective grating moiré signal subdivision method, the constructed tangent function is:

[0018]

[0019] Among them, U5(i) is the reconstructed moiré signal of the original moiré signal U1(i); U6(i) is the reconstructed moiré signal of the original moiré signal U2(i).

[0020] As another optimization scheme for the above-mentioned reflective grating moiré signal subdivision method, the inverse tangent phase value is obtained by using the coordinate rotation digital method, which is expressed as:

[0021]

[0022] Among them, U5(i) is the reconstructed moiré signal of the original moiré signal U1(i); U6(i) is the reconstructed moiré signal of the original moiré signal U2(i), S i represents the shrinkage factor, T i represents the rotation gain, d i Indicates the direction of rotation, sign indicates the sign function, z i+1 Value represents the inverse tangent phase value to be solved.

[0023] As another optimization scheme for the above-mentioned reflective grating moiré signal subdivision method, the arc tangent phase value within the moiré signal period is mapped to obtain the corresponding subdivision value. The mapping formula is:

[0024]

[0025] Where M is the subdivision multiple within the Moiré signal period, 2π is the Moiré signal period angle, and N represents the subdivision value corresponding to the arc tangent value.

[0026] A reflective grating moiré signal measurement method obtains a measurement result based on a subdivision value, a number of periods, and a moving direction within a moiré signal period, wherein the subdivision value is obtained by the above-mentioned reflective grating moiré signal subdivision method.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] 1. The present invention provides a method for reconstructing a reflective grating moiré signal, wherein an initial information item is obtained based on two original moiré signals, the two initial information items are subtracted to obtain an information item difference, a desired digital signal is obtained based on the information item difference, the filter coefficients are optimized based on U2(i), the desired digital signal and the error signal, and finally the original moiré signal is filtered using the optimized filter parameters to obtain a reconstructed moiré signal, and a measurement result is obtained by processing based on the reconstructed moiré signal. The reconstructed moiré signal suppresses and compensates for noise and interference to a certain extent, thereby significantly improving the measurement accuracy and resolution of the grating displacement sensor and reducing the production cost.

[0029] 2. In the present invention, based on the characteristic that the phase difference relationship between the two original moiré signals is the same as the amplitude of the washing machine, the direct drift, amplitude deviation and orthogonal deviation between the two original moiré signals are greatly reduced, thereby improving the stability and reliability of the entire moiré signal.

[0030] 3. In the present invention, the filter coefficients are optimized, and the original moiré signal is filtered by the optimized filter parameters, that is, the moiré signal can be filtered in real time, the noise can be quickly suppressed, and a clear model can be output in time, meeting the measurement and control scenarios with high real-time requirements; at the same time, the method is simple, has a small amount of calculation, and can make the grating moiré signal clearer and more stable, further improving the measurement accuracy of the grating displacement sensor.

[0031] 4. The present invention provides a reflective grating moiré signal subdivision method, which further subdivides the signal output by the grating sensor, thereby improving the measurement resolution without increasing the grating line density; at the same time, further suppressing the influence of noise on the measurement results. DETAILED DESCRIPTION

[0032] The technical solution of the present invention is further elaborated in detail below in conjunction with specific embodiments. Parts not described and disclosed in detail in the following embodiments of the present invention should be understood as existing technologies known or should be known to those skilled in the art.

[0033] Example 1

[0034] A method for reconstructing a reflective grating moiré signal, comprising the following steps:

[0035] S1, obtain two original moiré signals U1(i) and U2(i), and perform arc cosine processing on the two original moiré signals to obtain two corresponding initial information items; specifically:

[0036] A reflective grating is fixed below the grating head, positioned on a parallel-movable object to be measured. The reflective surface of the reflective grating is parallel to the light source emission point of the grating head, and the distance between the reflective surface and the light source emission point is 1.5 ± 0.15 mm. The light beam emitted by the grating head impinges on the reflective surface of the reflective grating. Based on the principle of grating diffraction interference, the interaction between the measuring grating and the indicator grating, which have the same grating pitch, produces a Moire fringe effect. Ultimately, the grating head converts the optical signal into an electrical signal approximately equal to sine and cosine. When the grating head and the reflective grating move relative to each other by one grating pitch, l, the Moire fringe also moves one cycle, and the grating head outputs one cycle of sine and cosine signals.

[0037] In this embodiment, the STM32F446RET6 model single-chip microcomputer is combined with an operational amplifier circuit, a differential amplifier circuit, a power management circuit, a USB interface, a CH340 communication circuit, and a magnetic bead circuit to draw a complete PCB four-layer board. Among them, the power management circuit provides reliable and stable 3.3V and 5V voltages for the normal operation of the circuit. The operational amplifier circuit and the differential amplifier circuit organize the four-way sine and cosine signals output by the grating reading head into two original Moiré signals. The USB interface is responsible for external power supply. At the same time, combined with the CH340 communication, it is responsible for sending data to the host computer through the USART communication protocol. The magnetic bead circuit is responsible for stabilizing the power signal. The PA4 and PA5 pins of the STM32F446RET6 microcontroller are used as ADC sampling pins to sample the two original moiré electrical signals, obtaining the data sampling values U1(i) and U2(i) of the original moiré signals, where U1(i) is the i-th sampling value of the first original moiré signal U1, and U2(i) is the i-th sampling value of the second original moiré signal U2. The ADC sampling rate is set to 2MHz, and the ADC bit width accuracy is set to 12. This allows more moiré signals to be acquired per unit time, thereby more accurately capturing the details of signal changes, reducing sampling errors, and ultimately improving detection resolution. Simultaneously, the two original moiré signals can be acquired synchronously, ensuring temporal consistency between the two original moiré signals, which is beneficial for suppressing noise. Due to interference from circuit noise, environmental noise, and light source noise, the acquired original moiré signals deviate from the theoretical moiré signals. Directly processing the original moiré signals results in inaccurate detection results. Therefore, the original moiré signals need to be reconstructed. The reconstructed moiré signals are closer to the theoretical moiré signals, improving measurement accuracy.

[0038] The acquired original moiré signals U1(i) and U2(i) are subjected to arccosine processing to obtain initial information items P1(i) and P2(i), where P1(i) is the i-th arccosine phase value of the first original moiré signal, and P2(i) is the i-th arccosine phase value of the second original moiré signal. Arccosine processing of the original moiré signals can effectively reduce the occupancy of single-chip microcomputer resources and improve the calculation speed. In this embodiment, the coordinate rotation digital method is used for arccosine processing, and the formula is as follows:

[0039]

[0040] Where A is the peak value of the cosine function to be solved, d i The direction of rotation is determined by the relationship between yi and the known cosine value A. i is the x-axis coordinate value of the vector in the plane rectangular coordinate system at the i-th iteration, T i is the modulus of the rotation gain after the i-th iteration, z iis the cumulative angle value at the i-th iteration. The iteration goal is to make the final value close to the target angle. i+1 is the x-axis coordinate value of the vector in the plane rectangular coordinate system at the i+1th iteration, and y i+1 is the y-axis coordinate value of the vector in the plane rectangular coordinate system at the i+1th iteration, z i+1 To solve the arc cosine phase value, S i is the shrinkage factor, T i+1 is the modulus of the rotation gain after i+1 iterations. In order to avoid misjudging the direction due to zi exceeding the range during the iteration process, zi is greater than π.

[0041] In this embodiment, the initial information items P1(i) and P2(i) are both in the range of [0, 1.57], and the unit is rad.

[0042] S2, the difference between the two initial information items is obtained to obtain the information item difference P3(i), P3(i) represents the difference between P1(i) and P2(i), and based on the information item difference and the original Moiré signal U1(i), the expected digital signal U2(i) is obtained. The original Moiré signal is generated by the relative movement of the reflective grating plate and the grating reading head. Therefore, the phase of the original Moiré signal is related to the displacement of the reflective grating plate. Therefore, the change in the arc cosine phase value of the original Moiré signal can reflect the movement direction of the grating reading head. Therefore, the positive and negative value of P3(i) can be used to determine the movement direction of the grating reading head relative to the reflective grating plate. When the grating reading head moves in the positive direction, P1(i) leads P2(i) by 90°; when the grating reading head moves in the negative direction, P1(i) lags P2(i) by 90°.

[0043] The expected digital signal includes a forward expected signal and a reverse expected signal. When the information item difference is positive, all phase values of U1(i) are delayed by 90° to obtain the forward expected signal; when the information item difference is negative, all phase values of U1(i) are advanced by 90° to obtain the reverse expected signal. Specifically, the arc cosine values P1(i) and P2(i) of U1(i) and U2(i) are calculated respectively. The sizes of P1(i) and P2(i) are compared to determine the direction of the grating relative to the reading head. Based on the direction of motion, the coordinate rotation digital reconstruction method is used to construct the forward expected signal U3(i) and the reverse expected signal U4(i) with a 90° phase difference. Specifically, the coordinate rotation digital reconstruction method is as follows:

[0044]

[0045] Among them, x1 is the initial value of the x-axis, that is, A is the amplitude of U1(i), z1 is the phase value of the desired signal to be reconstructed, d i The direction of rotation is determined by the size of zi, xi is the x-axis coordinate value in the plane rectangular coordinate system at the i-th iteration, z i is the cumulative angle value at the i-th iteration, x i+1 is the x-axis coordinate of the vector in the plane rectangular coordinate system at the i+1th iteration, that is, the expected digital signal U3(i) or U4(i), y i+1 The y-axis coordinate value of the vector in the plane rectangular coordinate system at the i+1th iteration greatly reduces the DC drift, amplitude deviation and orthogonality deviation of the two original Moiré signals, thereby improving the stability and reliability of the entire signal system.

[0046] In this embodiment, U3(i) represents the i-th discrete value of the positive desired signal, and the phase of U1(i) leads the phase of U3(i) by 90°, and the values of U1(i) and U3(i) are both within [-1000, 1000]; U4(i) represents the i-th discrete value of the negative desired signal, and the phase of U1(i) lags the phase of U4(i) by 90°, and the values of U1(i) and U4(i) are both within [-1000, 1000].

[0047] S3, subtract U2(i) from the expected digital signal to obtain an error signal, and optimize the filter coefficients based on the error signal, U2(i) and the expected digital signal to obtain optimized filter coefficients; in this embodiment, an adaptive filter algorithm based on the least mean square method is used to process the input signal (original moiré signal U2(i)), and then the filter coefficients are optimized to achieve the best filtering effect.

[0048] In this embodiment, the filter order of the adaptive filter algorithm based on the least mean square method is set to 2, and the iterative formula is:

[0049] Among them, α, β, γ are constants, W T (n) represents the filter coefficient vector obtained after the nth iteration. The initial filter coefficient vector is [0.8, 0.5] T ; e(n) is the error signal generated in the nth iteration; x(n) is the original moiré signal U2(i) input to the filter in the nth iteration, y(n) is the reconstructed moiré signal U6(i) output by the filter in the nth iteration, W(n) is the weight coefficient vector of the adaptive filter in the nth iteration, W(n+1) is the weight coefficient vector of the adaptive filter in the n+1th iteration, μ(n) is the step factor, which controls the update amplitude of the weight vector in each iteration, d(n) is the expected signal, the forward expected signal and the reverse expected signal in the nth iteration.

[0050] S4, using the optimized filter coefficients to filter U1(i) and U2(i) to obtain two reconstructed moiré signals.

[0051] An adaptive filter algorithm based on the least mean square method can be used to filter the grating moiré signal in real time. While acquiring the signal, it can quickly suppress noise and output a clear signal in a timely manner, meeting measurement and control scenarios with high real-time requirements. This method is relatively simple, requires little computation, and is easy to implement in hardware. The algorithm can make the grating moiré signal clearer and more stable, reduce the interference of noise on the signal characteristics, and help to more accurately extract information such as displacement and phase in the signal, thereby improving measurement accuracy.

[0052] Example 2

[0053] A reflective grating moiré signal subdivision method is provided, wherein a tangent function is constructed based on two reconstructed moiré signals, and an arctangent phase value of the tangent function is obtained. The two reconstructed moiré signals are obtained by a reflective grating moiré signal reconstruction method described in Example 1. The constructed tangent function is:

[0054]

[0055] Among them, U5(i) is the reconstructed moiré signal of the original moiré signal U1(i); U6(i) is the reconstructed moiré signal of the original moiré signal U2(i), and tanθ is the ratio of the two reconstructed moiré signals.

[0056] The coordinate rotation digital method is used to obtain the arc tangent limit value of the above tangent function, and the expression is:

[0057]

[0058] Among them, U5(i) is the reconstructed moiré signal of the original moiré signal U1(i); U6(i) is the reconstructed moiré signal of the original moiré signal U2(i), S i represents the shrinkage factor, T i represents the rotation gain, d i Indicates the direction of rotation, sign indicates the sign function, z i+1 Value represents the inverse tangent phase value to be solved.

[0059] The arc tangent phase value within the moiré signal period is mapped to obtain the corresponding subdivision value. The mapping formula is:

[0060]

[0061] Where M is the subdivision multiple within the Moiré signal period, 2π is the Moiré signal period angle, and N represents the subdivision value corresponding to the arc tangent value.

[0062] Subdivision is performed based on the reconstructed Moiré signal, which improves the measurement resolution without increasing the grating line density. The subdivision multiple can be flexibly selected according to needs, effectively suppressing the influence of noise and interference on the measurement results.

[0063] Example 3

[0064] A reflective grating moiré signal measurement method is provided, wherein a measurement result is obtained based on a subdivision value, a number of periods, and a movement direction within a moiré signal period. The subdivision value is obtained by a reflective grating moiré signal subdivision method described in Example 2. The measurement result is:

[0065]

[0066] Where S represents the measurement result, t represents the number of cycles of the Moiré signal, l represents the pitch of a grating, and D represents the moving direction.

[0067] The above description of the disclosed embodiments is intended to enable one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be readily apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention is not limited to the embodiments shown herein but is intended to conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for reconstructing a reflective grating moiré signal, characterized in that: The following steps are involved: S1, obtain two original Moiré signals U1(i) and U2(i), and process the two original Moiré signals to obtain two initial information items; S2, the two initial information items are subtracted to obtain the information item difference, and the expected digital signal U2(i) is obtained based on the information item difference and the original moiré signal U1(i); S3, subtracting U2(i) from the desired digital signal to obtain an error signal, and optimizing the filter coefficients based on the error signal, U2(i) and the desired digital signal to obtain optimized filter coefficients; S4, using the optimized filter coefficients to filter U1(i) and U2(i) to obtain two reconstructed moiré signals.

2. The method for reconstructing a reflective grating moiré signal according to claim 1, wherein: In S1, two original moiré signals are processed by arc cosine to obtain two initial information items.

3. The method for reconstructing a reflective grating moiré signal according to claim 1, wherein: In the above S2, the expected digital signal includes a forward expected signal and a reverse expected signal.

4. The method for reconstructing a reflective grating moiré signal according to claim 3, wherein: In S2, when the information item difference is positive, all phase values of U1(i) are delayed by 90° to obtain the forward desired signal; when the information item difference is negative, all phase values of U1(i) are advanced by 90° to obtain the reverse desired signal.

5. The method for reconstructing a reflective grating moiré signal according to claim 1, wherein: In S3, the iterative formula for optimizing the filter coefficients is: Among them, α, β, γ are constants, W T (n) represents the filter coefficient vector obtained after the nth iteration; μ(n) is the step factor of the nth iteration; e(n) is the error signal generated in the nth iteration; x(n) is the original moiré signal U2(i) input to the filter in the nth iteration, y(n) is the reconstructed moiré signal U6(i) output by the filter in the nth iteration, W(n) is the weight coefficient vector of the adaptive filter in the nth iteration, W(n+1) is the weight coefficient vector of the adaptive filter in the n+1th iteration, d(n) is the expected digital signal, the forward expected signal and the reverse expected signal in the nth iteration.

6. A reflective grating moiré signal subdivision method, characterized by: Constructing a tangent function based on the two-path reconstructed moiré signals and obtaining an arctangent phase value of the tangent function, wherein the two-path reconstructed moiré signals are obtained by a reflective grating moiré signal reconstruction method according to any one of claims 1 to 5; The arc tangent phase value within the moiré signal period is mapped to obtain the corresponding subdivision value.

7. The reflective grating moiré signal subdivision method according to claim 6, wherein: The constructed tangent function is: Among them, U5(i) is the reconstructed moiré signal of the original moiré signal U1(i); U6(i) is the reconstructed moiré signal of the original moiré signal U2(i).

8. The reflective grating moiré signal subdivision method according to claim 1, wherein: The inverse tangent phase value is obtained by using the coordinate rotation digital method, and the expression is: Among them, U5(i) is the reconstructed moiré signal of the original moiré signal U1(i); U6(i) is the reconstructed moiré signal of the original moiré signal U2(i), S i represents the shrinkage factor, T i represents the rotation gain, d i Indicates the direction of rotation, sign indicates the sign function, z i+1 Value represents the inverse tangent phase value to be solved.

9. The reflective grating moiré signal subdivision method according to claim 1, wherein: The arc tangent phase value within the moiré signal period is mapped to obtain the corresponding subdivision value. The mapping formula is: Where M is the subdivision multiple within the Moiré signal period, 2π is the Moiré signal period angle, and N represents the subdivision value corresponding to the arc tangent value.

10. A method for measuring a reflective grating moiré signal, characterized in that: The measurement result is obtained based on the subdivision value, the number of periods and the moving direction within the moiré signal period, wherein the subdivision value is obtained by a reflective grating moiré signal subdivision method according to any one of claims 6 to 9.

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