A high-precision absolute capacitive displacement sensor and signal demodulation method

Abstract

A high-precision absolute capacitive displacement sensor and its signal demodulation method are disclosed. The sensor includes a fixed electrode plate and a moving electrode plate. The fixed electrode plate has two sets of transmitting grid electrodes for precise and coarse measurements, and the moving electrode plate also has two sets of receiving electrodes for precise and coarse measurements. The two electrodes are capacitively coupled to jointly measure the absolute displacement. The invention also discloses the signal demodulation method for this sensor. The sensor of this invention has advantages such as simple structure, long lifespan, high accuracy, low power consumption, and good environmental adaptability.

Description

Technical Field

[0001] This invention relates to the field of precision displacement measurement technology, specifically to a high-precision absolute capacitive displacement sensor and a signal demodulation method. Background Technology

[0002] With the continuous development of science and technology, higher demands are being placed on precision displacement measurement devices in important industrial fields such as national defense, aerospace, and machinery manufacturing. Advances in science and technology have led researchers to focus on developing various high-precision displacement measurement devices, whose applications have expanded to aerospace, microelectronics, biomedicine, optics, and other fields. Currently, photoelectric and electromagnetic sensors still dominate in the measurement of precision linear displacement. Among them, photoelectric grating displacement sensors are the most widely used due to their mature technology and high precision; however, due to the presence of optical components, they have poor vibration resistance, are sensitive to dust and oily environments, and have high environmental requirements. Electromagnetic grating displacement sensors measure displacement through electromagnetic induction, are sensitive to electromagnetic interference, and struggle to achieve high-precision measurements in harsh electromagnetic environments. In contrast, capacitive grating displacement sensors are sensor devices that measure displacement using capacitive coupling. They can be applied in harsh working environments such as vibration, high temperature, dust, and oil, and feature simple structure, high reliability, low power consumption, high precision, and programmable resolution. Therefore, they have received increasing attention and are widely used in mechanical manufacturing, optics, and other fields, playing an increasingly important role.

[0003] However, most existing capacitive grating displacement sensors use simple rectangular or triangular electrode plates, which introduces severe harmonic interference into the sensor's output signal, resulting in a large number of harmonic components. This reduces the signal-to-noise ratio of the effective information during measurement, severely reducing the accuracy of this type of sensor. Furthermore, most existing capacitive grating displacement sensors are relative displacement sensors. When the sensor is powered off, the absolute zero point is lost, making it impossible to measure absolute displacement, which greatly affects the application scenarios of this type of sensor. Summary of the Invention

[0004] In order to overcome the technical problems existing in the prior art, the present invention aims to provide a high-precision absolute capacitive grating displacement sensor and signal demodulation method with high signal-to-noise ratio, high measurement accuracy, simple structure, and the ability to realize absolute displacement measurement.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] A high-precision absolute capacitive displacement sensor includes a fixed plate 1 and a moving plate 2, wherein the moving plate 2 is located above the fixed plate 1 and can move horizontally relative to the fixed plate 1. To meet the requirements of absolute displacement measurement, two sets of periodically arranged electrodes are provided on the fixed plate 1 and the moving plate 2, including a precise position measuring transmitting grid electrode 3 located on the fixed plate 1 and a precise position measuring receiving electrode 5 located on the moving plate 2 for precise displacement measurement; and a coarse position measuring transmitting grid electrode 4 located on the fixed plate 1 and a coarse position measuring receiving electrode 6 located on the moving plate 2 for coarse displacement measurement. When the relative position between the fixed plate 1 and the moving plate 2 changes, the capacitive coupling between the two sets of transmitting grid electrodes and receiving electrodes changes. After the electrical signals on the precise position measuring receiving electrode 5 and the coarse position measuring receiving electrode 6 are demodulated by the peripheral signal demodulation circuit 7 located outside the sensor, the distance moved by the moving plate 2 relative to the fixed plate 1 is measured, thus completing the high-precision displacement measurement.

[0007] The peripheral signal demodulation circuit 7 includes a signal excitation circuit, a bandpass filter circuit, a shaping circuit, and a phase detector circuit connected in sequence. In the signal excitation circuit, four SPWM sinusoidal modulation waves with different phases are generated by FPGA control and applied to the precise position measurement transmitting grid electrode 3 and the coarse position measurement transmitting grid electrode 4 as the sensor input signals. When the relative position between the fixed electrode plate 1 and the moving electrode plate 2 changes, the capacitive coupling between the two sets of transmitting grid electrodes and the receiving electrodes changes. The output signals on the precise position measurement receiving electrode 5 and the coarse position measurement receiving electrode 6 are acquired by the signal demodulation circuit 7. The signal is filtered by a bandpass filter to remove harmonic components, leaving only the fundamental sinusoidal component of the SPWM sinusoidal modulation wave. Then, a shaping circuit amplifies and shapes this fundamental sinusoidal waveform, converting it into a square wave, which facilitates phase discrimination of the output signal in the subsequent phase detector circuit. The phase detector circuit compares and demodulates the processed output signal with a reference signal generated by the FPGA. Finally, the FPGA uses a high-frequency clock pulse counting method to process the demodulated phase signal, obtaining the corresponding displacement value and completing the high-precision displacement measurement.

[0008] The precise position measurement transmitting grid electrode 3 is composed of N1 groups of small rectangular electrode plates of the same size and equal spacing, arranged in equal periods of four small rectangular electrode plates per group, i.e., one cycle, on the fixed electrode plate 1, where N1 is an integer multiple of 4; and within each cycle, four SPWM sinusoidal modulation waves generated by the peripheral signal demodulation circuit 7 are applied to the four small rectangular electrode plates respectively, and the phases of these four SPWM sinusoidal modulation waves are 0°, 90°, 180° and 270° respectively; correspondingly, the transmitting grid electrode 4 used for coarse position measurement is composed of two groups of small rectangular electrode plates of the same size and equal spacing, which are also arranged in equal periods of four small rectangular electrode plates per group, i.e., one cycle, on the fixed electrode plate 1; and within each cycle, four SPWM sinusoidal modulation waves generated by the peripheral signal demodulation circuit 7 are applied to the four small rectangular electrode plates respectively, and the phases of these four SPWM sinusoidal modulation waves are 0°, 90°, 180° and 270° respectively;

[0009] The precise position measurement receiving electrode 5 is made of N f The electrode plate 2 is composed of four identical, equally spaced, sinusoidal petal-shaped electrode plates. The upper and lower envelope equations of the sinusoidal petal-shaped electrode plates are sinusoidal. These sinusoidal petal-shaped electrode plates are arranged periodically on the moving electrode plate 2, where N... f =N1 / 2; The coarse position measurement receiving plate 6 is composed of a full sinusoidal envelope petal-shaped electrode plate arranged on the moving electrode plate 2; by demodulating the output signals generated by the precise position measurement receiving electrode 5 and the coarse position measurement receiving electrode 6 through capacitive coupling in the peripheral signal demodulation circuit 7, accurate displacement information can be obtained, and displacement measurement can be completed.

[0010] For precise measurements, the precise position measurement grid electrode 3 is formed by periodically arranging N1 small rectangular electrode plates, where the length of each small rectangular electrode plate is a. f The width of each is 4A. f The corresponding equations for the upper and lower sinusoidal envelopes of the precise position measurement receiving electrode 5 are as follows: L represents the entire measurement range of the corresponding sensor, N f To determine the number of receiving electrodes for precise position measurement; at this time, when the moving electrode 2 moves Δx horizontally relative to the fixed electrode 1, the precise position measurement receiving electrode 5 and the four small rectangular electrode plates of the precise position measurement transmitting grid electrode 3 in each cycle form a variable capacitor C. a (Δx),C b (Δx),C c (Δx),C d (Δx);

[0011] At this point, based on the equivalent circuit of the sensor, the output signal on the precise position measurement receiving electrode 5 is obtained:

[0012] In the formula, A is the amplitude of the SPWM sinusoidal modulation wave, ω is the angular frequency of the SPWM sinusoidal modulation wave; and according to the parallel plate capacitance expression (2), S is the relative surface area of ​​the electrode plates, and d is the distance between the electrode plates.

[0013]

[0014] Simplifying equation 1, we get:

[0015]

[0016] Here S a S b S c S d To accurately measure the surface area of ​​the four small rectangular electrode plates of the receiving electrode 5 and the transmitting grid electrode 3 in each cycle, the upper and lower sinusoidal envelope equations of the receiving electrode 5 are then used to determine the position of the moving electrode 2 relative to the fixed electrode 1 when it moves Δx in the horizontal direction.

[0017]

[0018] Substituting equation 4 into equation 3, we obtain the output signal U. o (Δx,t)

[0019]

[0020] Therefore, when the moving electrode 2 moves in the horizontal direction, the output signal U on the precise position measuring receiving electrode 5 is generated by the capacitive coupling between the precise position measuring transmitting grid electrode 3 and the precise position measuring receiving electrode 5 in each cycle. o (Δx,t) will change in phase, and this change is linear. Therefore, by using U o By comparing (Δx,t) with the reference signal sinωt of the SPWM sinusoidal modulation wave, the phase of the output signal is demodulated to obtain the corresponding displacement information, thus completing the precise displacement measurement.

[0021] By observing formula (5) and the above signal demodulation method, the measurement method is a relative measurement, that is, the absolute displacement measurement cannot be achieved in multiple electrode cycles. That is, when the sensor is powered off, the absolute zero point will be lost. If the position of the moving plate 2 changes during the period, the sensor cannot obtain accurate absolute displacement information after being powered on again. Therefore, in order to achieve the measurement of absolute displacement, a coarse measurement component is set on the basis of accurate measurement. The coarse measurement component has only one spatial cycle in the entire sensor range, so that the phase change of the output signal of the coarse measurement component is a single cycle in the entire range of sensor measurement. Therefore, the coarse measurement of absolute position can be achieved in the entire range of sensor measurement. Then, in the peripheral signal demodulation circuit 7, the position information of the coarse measurement is combined with the position information of the accurate measurement to achieve high-precision measurement of absolute displacement in the entire range.

[0022] The electrode plates mentioned are all printed on circuit boards.

[0023] Sensor resolution is closely related to the single-cycle length of the transmitting grid electrode and the high-frequency clock frequency used for pulse counting; that is, the displacement resolution R is... Where f T f is the frequency of the SPWM modulated wave. t This is a high-frequency clock frequency.

[0024] The precise position measurement emission grid electrode 3 is composed of 16 groups of small rectangular electrode plates of the same size and with equal spacing, i.e., N1 = 16.

[0025] Compared with existing technologies, the high-precision absolute capacitive grating displacement sensor and signal demodulation method of the present invention have the following advantages:

[0026] 1. The high-precision absolute capacitive displacement sensor and signal demodulation method described in this invention use capacitive coupling to complete displacement measurement, which has high resolution, high precision, high reliability, and can adapt to harsh environments.

[0027] 2. Compared with a semi-sinusoidal receiving plate, the high-precision absolute capacitive grating displacement sensor and signal demodulation method of the present invention improves the capacitive coupling area, increases the signal-to-noise ratio, and enhances the sensor's anti-interference capability by adopting a full sinusoidal envelope petal-shaped receiving plate.

[0028] 3. The high-precision absolute capacitive displacement sensor of the present invention achieves absolute displacement measurement by adding a coarse measurement component with a single spatial cycle to the full range of the sensor and combining it with a precision measurement component. This allows the sensor to maintain its absolute zero point even after power failure, thus enabling precise measurement of absolute displacement and expanding its application scenarios.

[0029] 4. The high-precision absolute capacitive grating displacement sensor and signal demodulation method described in this invention uses an FPGA in the peripheral signal demodulation circuit to complete the generation of signal excitation and the calculation of final displacement data, so that the resolution of the sensor can reach the nm level, which greatly improves the resolution of the sensor and expands its application scenarios.

[0030] 5. The electrode plate in the high-precision absolute capacitive displacement sensor of the present invention is made of printed circuit board, which has a simple and compact structure and is easy to process and install. Attached Figure Description

[0031] Figure 1 This is a three-dimensional schematic diagram of the absolute capacitive displacement sensor of the present invention.

[0032] Figure 2 This is a top view of the absolute capacitive displacement sensor of the present invention.

[0033] Figure 3 This is the signal demodulation process for the absolute capacitive displacement sensor of the present invention.

[0034] Figure 4 This is a schematic diagram of the fixed electrode plate of the absolute capacitive displacement sensor of the present invention.

[0035] Figure 5 This is a schematic diagram of the moving electrode plate of the absolute capacitive displacement sensor of the present invention.

[0036] Figure 6 This is a schematic diagram showing the relationship between the moving distance and the phase of the output signal of the absolute capacitive displacement sensor of the present invention. Specific implementation methods

[0037] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0038] like Figure 1 and Figure 2As shown, a high-precision absolute capacitive displacement sensor includes a fixed electrode plate 1 and a moving electrode plate 2. The moving electrode plate 2 is located directly above the fixed electrode plate 1 and can move horizontally relative to the fixed electrode plate 1. To meet the requirements of absolute position measurement, two sets of periodically arranged electrodes are provided on the fixed electrode plate 1 and the moving electrode plate 2. These include a precise position measuring transmitting grid electrode 3 located on the fixed electrode plate 1 and a precise position measuring receiving electrode 5 located on the moving electrode plate 2 for precise position measurement; and a coarse position measuring transmitting grid electrode 4 located on the fixed electrode plate 1 and a coarse position measuring receiving electrode 6 located on the moving electrode plate 2 for coarse position measurement. When the relative position between the fixed electrode plate 1 and the moving electrode plate 2 changes, the capacitive coupling between the two sets of transmitting grid electrodes and receiving electrodes changes. After the electrical signals on the precise position measuring receiving electrode 5 and the coarse position measuring receiving electrode 6 are demodulated by the external signal demodulation circuit 7, the distance moved by the moving electrode plate 2 relative to the fixed electrode plate 1 can be measured, thus completing the high-precision displacement measurement.

[0039] like Figure 3 As shown, the peripheral signal demodulation circuit 7 includes a signal excitation circuit, a bandpass filter circuit, a shaping circuit, and a phase detector circuit connected in sequence. In the signal excitation circuit, four SPWM sinusoidal modulation waves with different phases are generated by FPGA control and applied to the precise position measurement transmitting grid electrode 3 and the coarse position measurement transmitting grid electrode 4 as the input signals of the sensors. When the relative position between the fixed plate 1 and the moving plate 2 changes, the capacitive coupling between the two sets of transmitting grid electrodes and the receiving electrodes changes. The output signals on the precise position measurement receiving electrode 5 and the coarse position measurement receiving electrode 6 are acquired by the signal demodulation circuit 7. The bandpass filter circuit eliminates the harmonic components of this signal, leaving only the corresponding sinusoidal fundamental component of the SPWM sinusoidal modulation wave. Then, the shaping circuit amplifies and shapes the sinusoidal fundamental waveform, converting it into a square wave waveform, which is beneficial for the phase discrimination of the output signal in the subsequent phase detector circuit. Here, the reference signal generated by the FPGA is subjected to the same filtering and shaping process. Then, the processed output signal and the reference signal are compared and demodulated by the digital phase detector circuit. Finally, a high-frequency clock pulse counting method is used in the FPGA to process the phase signal after demodulation by the phase detector circuit. The corresponding displacement value is obtained through this phase signal, thus completing the high-precision displacement measurement.

[0040] like Figure 4 and Figure 5As shown, the transmitting grid electrode 3 for precise position measurement consists of N1 groups of small rectangular electrode plates of the same size and equal spacing, arranged in equal periods of four small rectangular electrode plates per group (one cycle). Within each cycle, four SPWM modulated sine waves generated by the peripheral signal demodulation circuit 7 are applied to the four transmitting grid electrodes 3-1, 3-2, 3-3, and 3-4, respectively, with phases of 0°, 90°, 180°, and 270°. Similarly, the transmitting grid electrode 4 for coarse position measurement consists of two groups of small rectangular electrode plates of the same size and equal spacing, also arranged in equal periods of four small rectangular electrode plates per group (one cycle) on the fixed electrode 1. In each cycle, four SPWM modulated sine waves generated by the peripheral signal demodulation circuit 7 are applied to the four transmitting gate electrodes 4-1, 4-2, 4-3 and 4-4 respectively, and the phases of these four SPWM modulated sine waves are 0°, 90°, 180° and 270° respectively.

[0041] Preferred, such as Figure 5 As shown, in order to reduce the interference of a large number of harmonic components in the output signals of the precise position measurement receiving electrode 5 and the coarse position measurement receiving electrode 6, increase the facing area of ​​the plates between the transmitting grid electrode and the receiving electrode during capacitive coupling, further improve the signal-to-noise ratio of the effective information in the output signal, and enhance the measurement accuracy of the sensor, the receiving electrodes 5 and 6 in this invention adopt a full sinusoidal envelope petal-shaped plate. The precise position measurement receiving electrode 5 is composed of N... f (N in this invention) f The moving electrode plate 2 is composed of 8 identical, equally spaced, sinusoidal petal-shaped electrode plates. The upper and lower envelope equations of these plates are sinusoidal. These plates are arranged periodically on the moving electrode plate 2. The coarse position measurement receiving electrode plate 6 is composed of a single sinusoidal petal-shaped electrode plate (meaning it exists only for a single period throughout the entire sensor measurement range), arranged on the moving electrode plate 2. Accurate displacement information is obtained by demodulating the output signals generated by capacitive coupling on the precise position measurement receiving electrode 5 and the coarse position measurement receiving electrode 6 in the external signal demodulation circuit 7, thus completing the displacement measurement. Furthermore, all the electrode plates are printed on a circuit board.

[0042] Taking precise measurement as an example, the precise position measurement emission grid electrode 3 is composed of 16 groups of small rectangular electrode plates arranged in a periodic manner, and the length of each small rectangular electrode plate is a. f The width of each is 4A. f The corresponding equations for the upper and lower sinusoidal envelopes of the precise position measurement receiving electrode 5 are as follows: L represents the entire measurement range of the corresponding sensor, N f To accurately measure the number of receiving electrodes, when the moving electrode 2 moves horizontally relative to the fixed electrode 1, the accurate position measuring receiving electrode 5 forms a variable capacitor C with the transmitting grid electrodes 3-1, 3-2, 3-3, and 3-4 in each cycle. a (Δx),C b (Δx),C c (Δx),C d (Δx).

[0043] At this point, based on the equivalent circuit of the sensor, the output signal on the precise position measurement receiving electrode 5 is obtained:

[0044]

[0045] In the formula, A is the amplitude of the SPWM sinusoidal modulation wave, and ω is the angular frequency of the SPWM sinusoidal modulation wave. Furthermore, according to the parallel plate capacitance expression (2), S is the relative surface area of ​​the electrode plates, and d is the distance between the electrode plates.

[0046]

[0047] Simplifying equation (1) yields:

[0048]

[0049] Here S a S b S c S d To accurately measure the facing surface area of ​​the receiving electrode 5 and the transmitting grid electrodes 3-1, 3-2, 3-3, and 3-4 in each cycle, the equation of the upper and lower sinusoidal envelope of the receiving electrode 5 can be used to obtain the result when the moving electrode 2 moves Δx relative to the fixed electrode 1 in the horizontal direction.

[0050]

[0051] Substituting equation (4) into equation (3), we obtain the output signal U. o (Δx,t)

[0052]

[0053] like Figure 6 As shown, when the moving electrode 2 moves in the horizontal direction, the output signal U on the precise position measuring receiving electrode 5 is generated by the capacitive coupling between the precise position measuring transmitting grid electrode 3 and the precise position measuring receiving electrode 5 in each cycle. o(Δx,t) will change in phase, and this change is linear. Therefore, by using U o By comparing (Δx,t) with the reference signal sinωt of the SPWM sinusoidal modulation wave, the corresponding displacement information can be obtained by demodulating the phase of the output signal, thus completing the precise displacement measurement.

[0054] Preferably, through observation formula (5), Figure 6 Compared to the aforementioned signal demodulation method, this measurement method is a relative measurement, meaning it cannot achieve absolute displacement measurement over multiple electrode cycles. Specifically, when the sensor is powered off, the absolute zero point is lost. If the position of the moving electrode 2 changes during this period, accurate absolute displacement information cannot be obtained when the sensor is powered on again. Therefore, to achieve absolute displacement measurement, a coarse measurement component is included in addition to the precise measurement. This coarse measurement component exists for only one spatial cycle across the entire sensor range, ensuring that the phase change of the output signal of the coarse measurement component is a single cycle throughout the entire sensor measurement range. Thus, a coarse measurement of the absolute position can be achieved across the entire sensor range. Subsequently, in the external signal demodulation circuit 7, the coarsely measured position information is combined with the precise measured position information through program identification, thereby achieving high-precision measurement of the absolute displacement across the entire range.

[0055] By observing equation (5) and the signal demodulation method, the sensor resolution of this invention is closely related to the single cycle length of the transmitting grid electrode and the high-frequency clock frequency used for pulse counting. That is, the displacement resolution R is... Where f T f is the frequency of the SPWM modulated wave. t This is a high-frequency clock frequency.

Claims

1. A high-precision absolute capacitive displacement sensor, characterized in that: It comprises two parts: a fixed electrode plate (1) and a moving electrode plate (2), wherein the moving electrode plate (2) is located above the fixed electrode plate (1) and can move horizontally relative to the fixed electrode plate (1); in order to meet the requirements of absolute displacement measurement, two sets of periodically arranged electrodes are provided on the fixed electrode plate (1) and the moving electrode plate (2), including a precise position measuring transmitting grid electrode (3) located on the fixed electrode plate (1) and a precise position measuring receiving electrode (5) located on the moving electrode plate (2) for precise displacement measurement; and a coarse displacement measuring electrode located on the fixed electrode plate (1) The coarse position measurement transmitting grid electrode (4) and the coarse position measurement receiving electrode (6) located on the moving electrode plate (2) are used. When the relative position between the fixed electrode plate (1) and the moving electrode plate (2) changes, the capacitive coupling between the two sets of transmitting grid electrodes and receiving electrodes changes. After the electrical signals on the precise position measurement receiving electrode (5) and the coarse position measurement receiving electrode (6) are demodulated by the peripheral signal demodulation circuit (7) located outside the sensor, the distance of the moving electrode plate (2) relative to the fixed electrode plate (1) is measured, and the high-precision displacement measurement is completed. The precise position measurement emission grid electrode (3) is composed of The plates are composed of small rectangular electrode plates of the same size and with equal spacing. Four small rectangular electrode plates form a group, which is one cycle. They are arranged periodically on the fixed electrode plate (1). The four SPWM sinusoidal modulation waves generated by the peripheral signal demodulation circuit (7) are applied to the four small rectangular electrode plates respectively in each cycle, and the phases of the four SPWM sinusoidal modulation waves are 0°, 90°, 180° and 270° respectively. Correspondingly, the transmitting grid electrode (4) used for coarse position measurement is composed of two sets of small rectangular electrode plates of the same size and equal spacing. They are also arranged on the fixed plate (1) in equal cycles of four small rectangular electrode plates as a group. In each cycle, the four SPWM sinusoidal modulation waves generated by the peripheral signal demodulation circuit (7) are applied to the four small rectangular electrode plates respectively, and the phases of the four SPWM modulated sinusoidal waves are 0°, 90°, 180° and 270° respectively. The precise position measurement receiving electrode (5) is composed of The electrode plate consists of four identical, equally spaced, sinusoidal petal-shaped electrode plates. The upper envelope equation of the sinusoidal petal-shaped electrode plates is a sine equation, and the lower envelope equation is also a sine equation. The sinusoidal petal-shaped electrode plates are arranged periodically on the moving electrode plate (2). ; The coarse position measurement receiving plate (6) is composed of a full sinusoidal envelope petal-shaped electrode plate arranged on the moving electrode plate (2). By demodulating the output signals generated by the precise position measurement receiving electrode (5) and the coarse position measurement receiving electrode (6) through capacitive coupling in the peripheral signal demodulation circuit (7), accurate displacement information can be obtained and displacement measurement can be completed. For precise measurements, The precise position measurement emission grid electrode (3) is composed of a group of small rectangular electrode plates arranged in a periodic manner, and the length of the small rectangular electrode plates is... The width is 4 The corresponding equations for the upper and lower sinusoidal envelopes of the precise position measurement receiving electrode (5) are as follows: , , L This represents the entire measurement range of the corresponding sensor. To accurately measure the number of receiving electrodes; at this time, when the moving electrode (2) moves horizontally relative to the fixed electrode (1). At the same time, the precise position measurement receiving electrode (5) and the four small rectangular electrode plates of the precise position measurement transmitting grid electrode (3) in each cycle form a variable capacitor. ; At this point, based on the equivalent circuit of the sensor, the output signal on the precise position measurement receiving electrode (5) is obtained: (1) In the formula, A The amplitude of the SPWM sinusoidal modulation wave. Let be the angular frequency of the SPWM sinusoidal modulation wave; and according to the expression for the parallel plate capacitance (2), where S This represents the relative surface area of ​​the electrode plates. d The distance between the plates; (2) Simplifying equation (1) yields: （3） here To accurately measure the surface area of ​​the four small rectangular electrode plates of the receiving electrode (5) and the transmitting grid electrode (3) in each cycle, the upper and lower sinusoidal envelope equations of the receiving electrode (5) are then used to obtain the horizontal movement of the moving electrode plate (2) relative to the fixed electrode plate (1). hour Substituting equation (4) into equation (3) yields an output signal. (5) Therefore, when the moving plate (2) moves in the horizontal direction, the output signal on the precise position measuring receiving electrode (5) is obtained by capacitive coupling between the precise position measuring transmitting grid electrode (3) and the precise position measuring receiving electrode (5) in each cycle. A change will occur in the phase, and this change is linear; therefore, by... Reference signal with SPWM sinusoidal modulation wave In contrast, demodulating the phase of the output signal yields the corresponding displacement information, thus completing the precise displacement measurement. By observing formula (5) and the above signal demodulation method, the measurement method is a relative measurement, that is, the absolute displacement measurement cannot be achieved in multiple electrode cycles. That is, when the sensor is powered off, the absolute zero point will be lost. If the position of the moving plate (2) changes during the period, the sensor cannot obtain accurate absolute displacement information after being powered on again. Therefore, in order to achieve the measurement of absolute displacement, a coarse measurement component is set on the basis of accurate measurement. The coarse measurement component has only one spatial cycle in the entire sensor range, so that the phase change of the output signal of the coarse measurement component is a single cycle in the entire range of sensor measurement. Therefore, the coarse measurement of absolute position can be achieved in the entire range of sensor measurement. Then, in the peripheral signal demodulation circuit (7), the position information of the coarse measurement is combined with the position information of the accurate measurement to achieve high-precision measurement of absolute displacement in the entire range.

2. The high-precision absolute capacitive displacement sensor according to claim 1, characterized in that: The peripheral signal demodulation circuit (7) includes a signal excitation circuit, a bandpass filter circuit, a shaping circuit and a phase detection circuit connected in sequence. In the signal excitation circuit, four SPWM sinusoidal modulation waves with different phases are generated by FPGA control and applied to the precise position measurement emission grid electrode (3) and the coarse position measurement emission grid electrode (4) as the input signal of the sensor. When the relative position between the fixed plate (1) and the moving plate (2) changes, the capacitive coupling between the two sets of transmitting grid electrodes and receiving electrodes changes. The output signals on the precise position measurement receiving electrode (5) and the coarse position measurement receiving electrode (6) are acquired by the signal demodulation circuit (7). The signal is filtered by the bandpass filter circuit to eliminate the harmonic components and only the corresponding sinusoidal fundamental component of the SPWM sinusoidal modulation wave is obtained. Then, the sinusoidal fundamental waveform is amplified and shaped by the shaping circuit to convert it into a square wave waveform, which is beneficial for the identification of the output signal phase in the phase detection circuit. In the phase detection circuit, the processed output signal is compared with the reference signal generated by the FPGA and demodulated. Finally, a high-frequency clock pulse counting method is used in the FPGA to process the phase signal after demodulation by the phase detector circuit. The corresponding displacement value is obtained through this phase signal, thus completing the high-precision displacement measurement.

3. The high-precision absolute capacitive displacement sensor according to claim 1, characterized in that: The electrode plates mentioned are all printed on circuit boards.

4. A high-precision absolute capacitive displacement sensor according to claim 1, characterized in that: Sensor resolution is closely related to the single-cycle length of the transmitting grid electrode and the high-frequency clock frequency used for pulse counting; that is, the displacement resolution R is... ,in The frequency of the SPWM modulated wave, This is a high-frequency clock frequency.

5. A high-precision absolute capacitive displacement sensor according to claim 1, characterized in that: The precise position measurement emission grid electrode (3) consists of 16 groups of small rectangular electrode plates of the same size and equal spacing, i.e. =16.

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