Grating three-dimensional displacement measurement system based on high subdivision interpolation linear processing circuit

Abstract

The invention belongs to the technical field of micro-displacement measurement systems, and particularly relates to a grating three-dimensional displacement measurement system based on a high subdivision interpolation linear processing circuit, which comprises a grating Talbot image three-dimensional micro-displacement device, a 90-degree phase shift circuit, a direct current bias circuit and a subdivision interpolation circuit, the grating Talbot image three-dimensional micro-displacement device is electrically connected with the 90-degree phase-shifting circuit, the 90-degree phase-shifting circuit is electrically connected with the direct-current biasing circuit, and the direct-current biasing circuit is electrically connected with the subdivision interpolation circuit. By adopting the high subdivision interpolation circuit technology and combining the 90-degree phase shift circuit and the high-precision bias voltage circuit, phase, amplitude and bias errors caused by grating machining errors in the interpolation subdivision process are remarkably inhibited, and therefore the resolution ratio and precision of micro-displacement measurement are greatly improved. The high-power subdivision interpolation linearization processing circuit is adopted, high sensitivity is ensured, meanwhile, the linear range of micro-displacement measurement is expanded, and the linearity in the full-scale range is remarkably improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of micro-displacement measurement systems, and particularly relates to a grating three-dimensional displacement measurement system based on a high-resolution interpolation linear processing circuit. Background Art

[0002] High-precision micro-displacement measurement technology is widely used in precision machining and measurement fields such as numerical control machine tools, lithography machines, aircraft manufacturing, and semiconductor precision manufacturing. Currently, the mainstream displacement detection technologies mainly include capacitive, piezoelectric, grating, and laser interferometric methods. Among them, the grating displacement detection technology stands out with its significant advantages such as high precision, anti-electromagnetic interference, and fast response. Other detection methods are often limited by factors such as parasitic capacitance, external electromagnetic interference, and temperature effects, making it difficult to further improve the measurement accuracy. From a technical path perspective, the grating displacement detection technology can be divided into multi-path interferometric, sub-wavelength evanescent field coupling effect, Talbot effect, and Moiré fringe methods. Among them, the multi-path interferometric method uses the Doppler effect to detect the displacement amount through the change in the interference intensity after the diffraction and beam combination of different orders of gratings. Although it has the advantage of high precision, due to the complexity of multi-path devices, it is difficult to achieve integration. Currently, three-axis measurement is still mainly based on discrete integration, with problems such as large volume and large orthogonal error. The sub-wavelength evanescent field coupling effect refers to when the distance between two or more sub-wavelength structures is very close (usually at the nanometer scale), their evanescent fields will overlap and couple with each other, thus significantly changing the propagation characteristics of light. However, this technology is limited by problems such as strict preparation accuracy requirements and short working distance, making it difficult to be widely used in large-range displacement measurement. The Moiré fringe method is mostly used for displacement detection with a resolution of ten nanometers or more and is more applied in the field of surface topography measurement. Compared with the previous three technologies, the displacement detection technology based on the grating Talbot effect has the advantages of high integration, large measurement range, and high resolution. Currently, it has been successfully applied to single-axis micro-displacement measurement, but there is less research on the three-dimensional displacement measurement system. Summary of the Invention

[0003] Aiming at the technical problems existing in the above-mentioned traditional grating displacement detection technology, the present invention provides a grating three-dimensional displacement measurement system based on a high-resolution interpolation linear processing circuit.

[0004] In order to solve the above technical problems, the technical solution adopted by the present invention is as follows:

[0005] A grating three-dimensional displacement measurement system based on a high-resolution interpolation linear processing circuit includes a grating Talbot image three-dimensional micro-displacement device, a 90-degree phase shift circuit, a DC bias circuit, and a resolution interpolation circuit. The grating Talbot image three-dimensional micro-displacement device is electrically connected to the 90-degree phase shift circuit, the 90-degree phase shift circuit is electrically connected to the DC bias circuit, and the DC bias circuit is electrically connected to the resolution interpolation circuit.

[0006] The 90-degree phase-shifting circuit includes an adder, a feedback integrator, an integrator, a first resistor, and a second resistor. The negative input terminal of the adder is electrically connected to the first resistor, the positive input terminal of the adder is electrically connected to the output terminal of the feedback integrator, the output terminal of the adder is electrically connected to the negative input terminal of the integrator, the positive input terminal of the integrator is grounded, and the negative input terminal of the adder is electrically connected to the output terminal of the adder through the second resistor.

[0007] The DC bias circuit uses an LM399H voltage reference chip, which generates a standard DC bias voltage and has excellent temperature stability.

[0008] The subdivision interpolation circuit uses a DSP microprocessor of iC-TW8. The DSP microprocessor has a digital self-calibration function and continuously adjusts the digital gain, bias, and phase during operation to maintain stability and minimize errors. After digital calibration and correction, the arctangent and interpolation algorithms are used to process two differential input signals to achieve high-resolution subdivision. The DSP microprocessor adjusts the interpolation factor, adaptive mode, and filter mode parameters through an external configuration circuit.

[0009] The grating Talbot image three-dimensional micro-displacement device includes a first support frame, a movable grating layer, a fixed grating layer, a second support frame, and a housing. The first support frame is slidably connected to the top of the housing. The movable grating layer is fixedly connected below the first support frame. The fixed grating layer is arranged below the movable grating layer. The second support frame is fixed inside the housing, and the fixed grating layer is fixed on the second support frame.

[0010] A silicon wafer is arranged on the movable grating layer, and a first grating, a second grating, and a third grating are prepared on the silicon wafer by a magnetron sputtering process.

[0011] The movable grating layer is arranged at an integer multiple of the Talbot image distance from the fixed grating layer, and the grating parameters of the movable grating layer and the fixed grating layer are the same.

[0012] A photodetector is arranged below the fixed grating layer, and the photodetector is electrically connected to the 90-degree phase-shifting circuit.

[0013] Compared with the prior art, the beneficial effects of the present invention are:

[0014] The present invention proposes a monolithic integrated grating Talbot image three-dimensional micro-displacement measurement system, effectively solving the problems of the existing grating three-dimensional micro-displacement measurement system such as large volume and large orthogonal error in discrete integration. By adopting high-subdivision interpolation circuit technology and combining a 90-degree phase-shifting circuit and a high-precision bias voltage circuit, the present invention significantly suppresses the phase, amplitude, and bias errors caused by grating processing errors during the interpolation subdivision process, thereby greatly improving the resolution and accuracy of micro-displacement measurement. The present invention uses a high-magnification subdivision interpolation linearization processing circuit, which expands the linear range of micro-displacement measurement while ensuring high sensitivity, and realizes a significant improvement in linearity within the full measurement range. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are only exemplary, and those of ordinary skill in the art can also obtain other implementation drawings according to the provided drawings without creative efforts.

[0016] The structures, ratios, sizes, etc. shown in this specification are only used to cooperate with the content disclosed in the specification for those skilled in this technology to understand and read, and are not used to limit the limiting conditions under which the present invention can be implemented. Therefore, they do not have a substantial technical meaning. Any modification of the structure, change of the proportional relationship, or adjustment of the size, without affecting the effects that the present invention can produce and the purposes that can be achieved, should still fall within the scope covered by the technical content disclosed in the present invention.

[0017] Figure 1 It is a flowchart of the linear processing circuit of the present invention;

[0018] Figure 2 It is a schematic diagram of the 90-degree phase-shifting circuit of the present invention;

[0019] Figure 3 It is a schematic diagram of the DC bias circuit of the present invention;

[0020] Figure 4 It is a schematic diagram of the subdivision interpolation circuit of the present invention.

[0021] Figure 5 It is a schematic diagram of the structure of the grating Talbot image three-dimensional micro-displacement device of the present invention;

[0022] Figure 6 It is a schematic diagram of the structure of the movable grating layer of the present invention;

[0023] Among them: 101 is a 90-degree phase shift circuit, U1A is an adder, U2A is a feedback integrator, U1B is an integrator, R1 is a first resistor, R2 is a second resistor, 102 is a DC bias circuit, 103 is a subdivision interpolation circuit, 1 is a first support frame, 2 is a movable grating layer, 3 is a fixed grating layer, 4 is a second support frame, 5 is a housing, 6 is a first grating, 7 is a second grating, 8 is a third grating, 9 is a silicon wafer, and 10 is a photodetector. Detailed implementation manners

[0024] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Apparently, the described embodiments are only a part rather than all of the embodiments of the present application. These descriptions are only for further explaining the features and advantages of the present invention rather than limiting the claims of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in the present application without creative efforts shall fall within the scope of protection of the present application.

[0025] The following will further describe in detail the specific implementation manners of the present invention in conjunction with the accompanying drawings and embodiments. The following embodiments are used to illustrate the present invention but are not intended to limit the scope of the present invention.

[0026] The terms "first" and "second" are only used for descriptive purposes and cannot be construed as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, features defined with "first" and "second" may explicitly or implicitly include one or more of such features. In the description of the present application, unless otherwise specified, the meaning of "a plurality" is two or more.

[0027] In the description of the present application, it should be noted that, unless otherwise clearly defined and limited, the terms "installed", "connected", and "coupled" should be understood in a broad sense. For example, it may be a fixed connection, a detachable connection, or an integral connection; it may be a mechanical connection or an electrical connection; it may be directly connected or indirectly connected through an intermediate medium, and it may be the internal communication of two components. For those of ordinary skill in the art, the specific meanings of the above terms in the present application can be understood according to specific circumstances.

[0028] This embodiment provides a grating three-dimensional displacement measurement system based on a high-subdivision interpolation linear processing circuit. The linear processing circuit of this measurement system is as Figure 1As shown in the figure, it includes a 90-degree phase-shifting circuit 101, a DC bias circuit 102, and a subdivision interpolation circuit 103. The grating Talbot image three-dimensional micro-displacement device is electrically connected to the 90-degree phase-shifting circuit 101. The 90-degree phase-shifting circuit 101 is electrically connected to the DC bias circuit 102. The DC bias circuit 102 is electrically connected to the subdivision interpolation circuit 103.

[0029] Furthermore, as Figure 2 shown, the 90-degree phase-shifting circuit 101 includes an adder U1A, a feedback integrator U2A, an integrator U1B, a first resistor R1, and a second resistor R2. The negative input terminal of the adder U1A is electrically connected to the first resistor R1. The positive input terminal of the adder U1A is electrically connected to the output terminal of the feedback integrator U2A. The output terminal of the adder U1A is electrically connected to the negative input terminal of the integrator U1B. The positive input terminal of the integrator U1B is grounded. The negative input terminal of the adder U1A is electrically connected to the output terminal of the adder U1A through the second resistor R2.

[0030] Furthermore, as Figure 3 shown, the DC bias circuit 102 uses an LM399H voltage reference chip. The LM399H voltage reference chip generates a standard DC bias voltage and has excellent temperature stability.

[0031] Furthermore, as Figure 4 shown, the subdivision interpolation circuit 103 uses a DSP microprocessor of iC-TW8. The DSP microprocessor has a digital self-calibration function. During operation, it continuously adjusts the digital gain, bias, and phase to maintain stability and minimize errors. After digital calibration and correction, the arctangent and interpolation algorithms are used to process two differential input signals to achieve high-resolution subdivision. The DSP microprocessor adjusts the interpolation factor, adaptive mode, and filter mode parameters through an external configuration circuit.

[0032] Furthermore, as Figure 5 shown, the grating Talbot image three-dimensional micro-displacement device includes a first support frame 1, a movable grating layer 2, a fixed grating layer 3, a second support frame 4, and a housing 5. The first support frame 1 is slidably connected to the top of the housing 5. The movable grating layer 2 is fixedly connected below the first support frame 1. The fixed grating layer 3 is arranged below the movable grating layer 2. The second support frame 4 is fixed inside the housing 5. The fixed grating layer 3 is fixed on the second support frame 4. A silicon wafer 9 is arranged on the movable grating layer 2. The first grating 6, the second grating 7, and the third grating 8 are prepared on the silicon wafer 9 by magnetron sputtering. The movable grating layer 2 is arranged at an integer multiple of the Talbot image distance from the fixed grating layer 3. The grating parameters of the movable grating layer 2 and the fixed grating layer 3 are the same.

[0033] Furthermore, the first grating 6 detects the displacement in the y-axis direction, the second grating 7 detects the displacement in the x-axis direction, and the grating 8 detects the displacement in the z-axis direction. AsFigure 6 As shown. The first grating 6 and the second grating 7 are used for in-plane (X-, Y-direction) micro-displacement measurement. Its working principle is that when a plane wave is perpendicularly incident on the fixed nano-grating layer, the positive and negative images of the grating will be periodically formed in the near-field region behind the grating. The movable grating layer is placed at an integer multiple of the Talbot image distance from the fixed grating layer. The change of in-plane displacement can be converted into a sine signal with a period equal to the grating constant by a photodetector, thus realizing the measurement of in-plane micro-displacement. The third grating 8 is dedicated to out-of-plane (Z-direction) micro-displacement detection. Its working principle is that when a plane wave is perpendicularly incident on the fixed nano-grating layer, the positive and negative images of the periodic grating are formed in the near-field region behind the grating. When the movable grating layer is placed in the near-field region of the fixed grating layer, the out-of-plane displacement change will be converted into a sine signal with a period of 2d 2 / λ (d is the grating period and λ is the laser wavelength). The high-precision measurement of out-of-plane displacement can be realized through this signal. Due to the limited linear region of the signal, it is impossible to ensure linear measurement within the full range during the micro-displacement measurement process. At the same time, at the peak and trough positions of the sine signal, the amplitude is not sensitive to the micro-displacement amount, resulting in inconsistent resolution and low linearity at different positions.

[0034] The interpolation subdivision method is a common method for converting sine and cosine signals into digital square wave signals. To achieve subdivision interpolation, a four-quadrant detection mode is usually adopted to realize the output of multiple orthogonal detection signals. For in-plane detection, by setting the grating array spacing of the four quadrants to (N + 1 / 4)d, the four signals can be ensured to be orthogonal to each other; for out-of-plane detection, the grating arrays of the four quadrants ensure the orthogonality between signals by having a thickness difference of (N + 1 / 4)z T where z T = 2d 2 / λ is the Talbot distance, d is the grating constant, and λ is the laser wavelength. However, errors are inevitable in the processing and assembly alignment process of the double-layer grating, resulting in phase, amplitude, and offset errors between the four output signals. These errors will cause subdivision interpolation errors and affect the resolution and accuracy of micro-displacement detection.

[0035] To reduce these three types of errors, the present invention proposes a high-magnification subdivision interpolation technique. A photodetector 10 is provided below the fixed grating layer 3. The photodetector 10 is electrically connected to a 90-degree phase-shifting circuit. The 90-degree phase-shifting circuit is electrically connected to a DC bias circuit. The DC bias circuit is electrically connected to a subdivision interpolation circuit... The four-quadrant grating scheme is replaced by a one-dimensional grating, and a 90-degree phase-shifting circuit is used to realize the output of two orthogonal signals. The specific schematic diagram is as Figure 2As shown in the figure. In the phase shift module, an adder U1A is set to compare the output sine signal and the feedback signal of the feedback integrator U2A. By adjusting the ratio of the first resistor R1 and the second resistor R2, the magnitude of the phase shift signal is controlled. The integrator U1B achieves a 90° phase shift, and its output signal is a cosine wave, with a phase 90° ahead of the input signal. The feedback integrator U2A, as a linear low-pass filter, can eliminate the bias voltage generated by the integrator U1B. The transfer function of the entire circuit is expressed as:

[0036]

[0037] It can be seen from the above formula that the phase angle of the transfer function is Arg[H(jω)] = 90°, which means that when the frequency of the input signal changes, the two output signals can still maintain a 90° phase difference, ensuring that the subdivision interpolation factor is not affected by the phase error.

[0038] According to the arctangent subdivision principle, when there is a bias error between the two signals, it will also affect the magnitude of the subdivision multiple and the stability of the output signal. And the input end of the subsequent subdivision interpolation circuit is a differential input, and its bias voltage needs to be adjusted to +2.5V. Based on this, a high-precision DC bias circuit is designed, as Figure 3 shown. This part of the circuit uses the LM399H voltage reference chip to generate a standard DC bias voltage, and this chip has excellent temperature stability.

[0039] The design of the subdivision interpolation circuit is based on the DSP microprocessor of iC-TW8 of iC-Haus company. It has a digital self-calibration function, which can continuously adjust the digital gain, bias and phase during operation to maintain stability and minimize errors. After digital calibration and correction, the arctangent and interpolation algorithms are used to process the two differential input signals to achieve high-resolution subdivision. This processor can adjust parameters such as the interpolation factor, adaptive mode, and filtering mode through an external configuration circuit. Specifically, using the arctangent algorithm to achieve high-multiple interpolation subdivision is to perform the arctangent operation through the cotangent function to directly obtain the phase information of the input signal. At this time, 8-fold coarse and fine subdivision of the input signal is achieved. Two ADCs convert the analog sine and cosine signals into 14-bit digital quantities for processing. After ADC conversion, the arctangent and interpolation algorithms are used to process the differential input signals. Then, digital subdivision is completed in the DSP interpolator. The DSP interpolator continuously corrects the digital gain, offset, gain matching and phase to minimize errors and jitter. The corrected differential input signals are processed again by the arctangent and interpolation algorithms to generate equally spaced displacement output signals. The function of high-subdivision interpolation linear processing is realized through the above steps, as Figure 4 shown.

[0040] The above only elaborates in detail on the preferred embodiments of the present invention. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those of ordinary skill in the art, various changes can be made without departing from the gist of the present invention, and all such changes should be included within the protection scope of the present invention.

Claims

1. A grating three-dimensional displacement measurement system based on a high-precision interpolation linear processing circuit, characterized in that: It includes a three-dimensional micro-displacement device for grating Talbot images, a 90-degree phase-shifting circuit (101), a DC bias circuit (102), and a subdivision interpolation circuit (103). The three-dimensional micro-displacement device for grating Talbot images is electrically connected to the 90-degree phase-shifting circuit (101), the 90-degree phase-shifting circuit (101) is electrically connected to the DC bias circuit (102), and the DC bias circuit (102) is electrically connected to the subdivision interpolation circuit (103).

2. The grating three-dimensional displacement measurement system based on the high-subdivision interpolation linear processing circuit according to claim 1, characterized in that: The 90-degree phase-shifting circuit (101) includes an adder (U1A), a feedback integrator (U2A), an integrator (U1B), a first resistor (R1), and a second resistor (R2). The negative input terminal of the adder (U1A) is electrically connected to the first resistor (R1), the positive input terminal of the adder (U1A) is electrically connected to the output terminal of the feedback integrator (U2A), the output terminal of the adder (U1A) is electrically connected to the negative input terminal of the integrator (U1B), the positive input terminal of the integrator (U1B) is grounded, and the negative input terminal of the adder (U1A) is electrically connected to the output terminal of the adder (U1A) through the second resistor (R2).

3. The grating three-dimensional displacement measurement system based on the high-subdivision interpolation linear processing circuit according to claim 1, wherein: The DC bias circuit (102) uses an LM399H voltage reference chip, which generates a standard DC bias voltage and has excellent temperature stability.

4. The grating three-dimensional displacement measurement system based on the high-subdivision interpolation linear processing circuit according to claim 1, wherein: The subdivision interpolation circuit (103) uses a DSP microprocessor of iC-TW8. The DSP microprocessor has a digital self-calibration function. During operation, it continuously adjusts the digital gain, bias, and phase to maintain stability and minimize errors. After digital calibration and correction, it processes two differential input signals using the arctangent and interpolation algorithms to achieve high-resolution subdivision. The DSP microprocessor adjusts the interpolation factor, adaptive mode, and filter mode parameters through an external configuration circuit.

5. The grating three-dimensional displacement measurement system based on the high-subdivision interpolation linear processing circuit according to claim 1, characterized in that: The three-dimensional micro-displacement device for grating Talbot images includes a first support frame (1), a movable grating layer (2), a fixed grating layer (3), a second support frame (4), and a housing (5). The first support frame (1) is slidably connected to the top of the housing (5), the movable grating layer (2) is fixedly connected below the first support frame (1), the fixed grating layer (3) is arranged below the movable grating layer (2), the second support frame (4) is fixed inside the housing (5), and the fixed grating layer (3) is fixed on the second support frame (4).

6. The grating three-dimensional displacement measurement system based on the high-subdivision interpolation linear processing circuit according to claim 5, characterized in that: A silicon wafer (9) is arranged on the movable grating layer (2), and a first grating (6), a second grating (7), and a third grating (8) are prepared on the silicon wafer (9) through a magnetron sputtering process.

7. The grating three-dimensional displacement measurement system based on the high-subdivision interpolation linear processing circuit according to claim 5, wherein: The movable grating layer (2) is arranged at an integer multiple of the Talbot image distance from the fixed grating layer (3), and the grating parameters of the movable grating layer (2) and the fixed grating layer (3) are the same.

8. The grating three-dimensional displacement measurement system based on the high-subdivision interpolation linear processing circuit according to claim 5, characterized in that: A photodetector (10) is arranged below the fixed grating layer (3), and the photodetector (10) is electrically connected to the 90-degree phase-shifting circuit (101).

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