Non-contact linear displacement sensor

Abstract

The invention discloses a non-contact linear displacement sensor, which comprises an inductance coil, a signal generator, a signal sampling module and a signal processing module, and is characterized in that the signal generator outputs an excitation signal with a preset frequency; after an excitation signal output by the signal generator acts on the inductance coil, the inductance coil generates inductance change related to the position of a measured object according to an electromagnetic induction principle, so that electric signals at the two ends of the inductance coil are changed; the signal sampling module collects voltage signals at the two ends of the inductance coil in real time, conducts amplitude conditioning on the collected voltage signals and then sends the voltage signals to the signal processing module. The signal processing module converts the conditioned analog voltage signal into a digital signal. The non-contact linear displacement sensor does not need to be in direct contact with a measured object, the problems of abrasion and friction caused by mechanical contact of a traditional contact type sensor can be effectively solved, meanwhile, signal interference caused by contact type measurement is reduced, the measurement accuracy and reliability are remarkably improved, and the service life of the sensor is prolonged.

Description

Technical Field

[0001] This invention relates to the field of non-contact sensors, and in particular to a non-contact linear displacement sensor. Background Technology

[0002] Displacement sensors detect displacement by converting displacement into voltage changes. They are a crucial technological foundation for the new technological revolution and the information society, and a vital component in testing and automatic control. Displacement sensors play a very important role in practical engineering applications. Currently, the most commonly used displacement sensors on the market include: The first type is a wire-wound potentiometer displacement sensor: Operating principle: The wire-wound potentiometer consists of a resistance wire wound on an insulating frame. A brush draws in an input corresponding to the resistance at the sliding point. The brush is driven by the displacement being measured, and the output is a change in resistance or voltage proportional to the displacement.

[0003] Defects: It is easily damaged by physical friction and has low precision.

[0004] The second type is the resistance strain gauge displacement sensor: Working principle: The resistance strain gauge displacement sensor uses a spring and a cantilever beam connected in series as elastic elements. Four strain gauges are attached to the front and back sides of the root of the rectangular interface cantilever beam to form a full-bridge circuit. One end of the tension spring is connected to the measuring rod. When the measuring rod moves with the specimen, it drives the spring to bend the root of the cantilever beam. The strain generated by the bending is linearly related to the displacement of the measuring rod.

[0005] Disadvantages: Small displacement measurement range and low accuracy.

[0006] The third type is the capacitive displacement sensor: Working principle: The capacitive displacement sensor is based on an ideal parallel plate capacitor. The two parallel plates are formed by the sensor probe and the surface of the object being measured. Based on the operational amplifier measurement circuit principle, when a constant frequency sinusoidal excitation current passes through the sensor capacitor, the voltage amplitude generated on the sensor is proportional to the gap between the capacitor plates.

[0007] Disadvantages: Capacitive sensors have parasitic capacitance and distributed capacitance, which leads to a small displacement measurement range, low accuracy, and nonlinear errors.

[0008] The fourth type is the Hall effect displacement sensor. Operating principle: The Hall displacement sensor mainly consists of a gradient magnetic field formed by two semi-annular magnets and a germanium semiconductor Hall plate (sensing element) located at the center of the magnetic field. When a constant current flows through the Hall element, a Hall potential is output in the direction perpendicular to both the magnetic field and the current. As the Hall element moves up and down in the gradient magnetic field, the output Hall potential V depends on its displacement x in the magnetic field. By measuring the magnitude of the Hall potential, the static displacement of the Hall element can be determined.

[0009] Disadvantages: The signal changes with temperature, and the displacement measurement range is small.

[0010] The fifth type is the LVDT displacement sensor. Operating principle: LVDT is an abbreviation for Linear Variable Differential Transformer, which is a linear displacement sensor. It consists of an iron core, an armature, a primary coil, and a secondary coil. When the armature is in the middle position, the induced electromotive forces generated by the two secondary coils are equal, so the output voltage is 0. When the armature moves inside the coil and deviates from the center position, the induced electromotive forces generated by the two coils are not equal, and there is a voltage output. The magnitude of the voltage depends on the magnitude of the displacement.

[0011] Disadvantages: Complex structure, high cost, and inability to measure nonlinear displacement.

[0012] The above-mentioned types of sensors all have varying degrees of shortcomings in terms of accuracy, reliability, and displacement measurement range. Therefore, the market urgently needs a new displacement sensor to overcome the deficiencies of current solutions. Summary of the Invention

[0013] In order to overcome the shortcomings and deficiencies of the existing technology, the purpose of this invention is to provide a non-contact linear displacement sensor.

[0014] The objective of this invention is achieved through the following technical solution: a non-contact linear displacement sensor, comprising an inductor coil, a signal generator, a signal sampling module, and a signal processing module. The signal generator outputs an excitation signal at a preset frequency; After the excitation signal output by the signal generator is applied to the inductor, the inductor generates an inductance change related to the position of the object being measured based on the principle of electromagnetic induction, thereby changing the electrical signal at both ends of the inductor. The signal sampling module acquires the voltage signal across the inductor coil in real time, and after amplitude conditioning, sends the acquired voltage signal to the signal processing module; the signal processing module converts the conditioned analog voltage signal into a digital signal.

[0015] As an improvement to the non-contact linear displacement sensor of the present invention, the excitation signal of the preset frequency output by the signal generator is a sine wave or a square wave excitation signal.

[0016] As an improvement of the non-contact linear displacement sensor of the present invention, when the measured object moves within the effective sensing range of the inductor coil, the change in the relative position of the measured object and the inductor coil will cause a change in the magnetic coupling area between them: when the magnetic coupling area increases, the magnetic reluctance of the magnetic circuit in which the inductor coil is located decreases, and the inductance and reactance of the inductor coil increase accordingly; when the magnetic coupling area decreases, the magnetic reluctance of the magnetic circuit in which the inductor coil is located increases, and the inductance and reactance of the inductor coil decrease accordingly.

[0017] As an improvement to the non-contact linear displacement sensor of the present invention, the inductor coil is manufactured using PCB or flexible printed circuit board printing technology, and the winding shape of the inductor coil is racetrack-shaped. This type of inductor coil possesses good durability, thereby enhancing the sensor's accuracy and environmental adaptability under complex working conditions.

[0018] As an improvement to the non-contact linear displacement sensor of the present invention, the signal processing module's processing method is as follows: (1) Filtering algorithm: A composite filtering algorithm combining Kalman filtering and moving average filtering is adopted. The moving average filtering is used to initially filter out high-frequency random noise in the signal. Its principle is to select digital signals of N consecutive sampling periods and calculate the average value as the effective signal at the current time. The formula is: y k = (x k + x k-1 +... + x k-n+1 ) / N; Where y k This is the filtered signal value at the current moment. x k The sampled value at the current moment. x k-1 To x k-n+1 These are the sampled values ​​from the first N-1 time steps. N is the preset sampling window length; After the initial processing of the moving average filter, the amplitude of high-frequency noise can be quickly attenuated, thereby improving the smoothness of the signal. On this basis, Kalman filtering is introduced for secondary noise reduction. Kalman filtering predicts the theoretical value of the signal in real time by constructing the state equation and observation equation of the signal, and performs error correction in combination with the current sampled value, thereby obtaining the optimal estimate. The Kalman filter consists of three stages: state prediction, observation update, and error covariance update. This composite filtering algorithm can effectively balance noise reduction and signal response speed. It can filter out invalid components such as high-frequency random noise and electromagnetic interference, while avoiding the signal lag problem caused by a single filtering algorithm.

[0019] (2) Integral operation algorithm: The effective signal after filtering is sent to the integration operation module, and the trapezoidal integration algorithm is used to realize the integration processing of the signal; As an improvement to the non-contact linear displacement sensor of the present invention, the trapezoidal integration algorithm treats the signal values ​​at two consecutive sampling times as the two bases of a trapezoid, and the sampling interval as the height of the trapezoid. The integration result is obtained by calculating and summing the area of ​​the trapezoid. The formula is: S k = S k-1 + (x k + x k-1 )×T / 2, in: S k This is the accumulated value of the integral at the current moment. S k-1 This is the accumulated value of the integral from the previous moment. x k and x k-1 These are the filtered signal values ​​at the current and previous moments, respectively. T represents the sampling interval. Compared to the traditional rectangular integration algorithm, the trapezoidal integration algorithm offers higher computational accuracy, a fact verified in related research. The core purpose of integration is to convert the change in voltage signal across the inductor coil into a cumulative quantity directly related to the displacement of the induced element. Since the change in voltage signal is linearly related to the rate of change of displacement of the induced element, integrating the change in voltage signal yields the cumulative displacement value of the induced element. This allows for the extraction of feature signals directly related to the absolute position of the induced element, ultimately achieving accurate detection of the absolute position of the induced element within the effective stroke of the inductor coil.

[0020] As an improvement to the non-contact linear displacement sensor of the present invention, the voltage across the inductor coil is calculated using the following formula: U L =U X L / R+X L

[0021] in: U L The voltage across the inductor coil; U is the excitation voltage input to the signal generator; R is the resistance value; XL This is the inductive reactance of the inductor coil.

[0022] The above formula clarifies the quantitative relationship between the voltage across the inductor, the input excitation voltage, and the resistance. In practical applications, based on this formula, and combined with parameters such as the input excitation voltage U and the total equivalent resistance R of the circuit collected by the signal sampling module, the voltage U across the inductor can be accurately calculated. L ; and then based on U L The correspondence between the inductive reactance of the inductor coil (and consequently the position of the sensed component) provides core data support for the signal processing module and the accurate detection of the sensed component's position. Furthermore, based on the quantitative relationship of this formula, parameters such as resistance and excitation voltage can be optimized in reverse, thereby further improving the sensor's detection accuracy and stability.

[0023] The beneficial effects of this invention are as follows: The non-contact linear displacement sensor of this invention can accurately capture changes in inductance and reactance, and convert them into quantifiable electrical signals with the help of a signal processing module, thereby achieving accurate detection of parameters such as the absolute position and moving speed of the measured object within the effective stroke of the inductor coil. Furthermore, this inductor coil has a significant inductive response to metal or alloy components with different magnetic permeability, making it adaptable to various magnetically permeable objects and applicable to a wide range of applications.

[0024] This non-contact linear displacement sensor, based on the principle of electromagnetic induction, accurately measures the position of an object by detecting changes in inductance. Since it does not require direct contact with the object being measured, it effectively avoids the wear and friction problems caused by mechanical contact in traditional contact sensors. It also reduces signal interference associated with contact measurements, significantly improving measurement accuracy and reliability, and extending the sensor's lifespan. Furthermore, this non-contact linear displacement sensor boasts advantages such as fast response speed, strong anti-interference capability, and convenient installation, making it widely applicable in robotics, automation control, machinery manufacturing, aerospace, and other fields. Attached Figure Description

[0025] Figure 1 This is a control module diagram of the present invention; Figure 2 This is a schematic diagram of the inductor coil structure of the present invention; The attached figures are labeled as follows: 1. Inductor coil, 2. Signal generator, 3. Signal sampling module, 4. Signal processing module, 5. Object under test, 6. Inductor coil substrate. Detailed Implementation

[0026] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0027] It should be noted that all directional indications (such as up, down, left, right, front, back, etc.) in the embodiments of the present invention are only used to explain the relative positional relationship and movement of the components in a specific posture (as shown in the figure). If the specific posture changes, the directional indication will also change accordingly.

[0028] Furthermore, the use of terms such as "first" and "second" in this invention is for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. Additionally, the technical solutions of the various embodiments can be combined with each other, but only on the basis of being achievable by those skilled in the art. If the combination of technical solutions is contradictory or impossible to implement, such a combination of technical solutions should be considered non-existent and not within the scope of protection claimed by this invention.

[0029] like Figure 1 and Figure 2 As shown, a non-contact linear displacement sensor includes an inductor coil 1, a signal generator 2, a signal sampling module 3, and a signal processing module 4; Signal generator 2 outputs an excitation signal at a preset frequency; After the excitation signal output by the signal generator 2 is applied to the inductor coil 1, the inductor coil 1 generates an inductance change related to the position of the measured object according to the principle of electromagnetic induction, thereby changing the electrical signal at both ends of the inductor coil 1. The signal sampling module 3 collects the voltage signal across the inductor coil 1 in real time, and after amplitude conditioning, sends the collected voltage signal to the signal processing module 4; the signal processing module 4 converts the conditioned analog voltage signal into a digital signal.

[0030] Preferably, the excitation signal of the preset frequency output by the signal generator 2 is a sine wave or a square wave excitation signal.

[0031] Preferably, when the object under test 5 moves within the effective sensing range of the inductor coil 1, the change in the relative position of the object under test 5 and the inductor coil 1 will cause a change in the magnetic coupling area between the two: when the magnetic coupling area increases, the magnetic reluctance of the magnetic circuit where the inductor coil 1 is located decreases, and the inductance and reactance of the inductor coil 1 increase accordingly; when the magnetic coupling area decreases, the magnetic reluctance of the magnetic circuit where the inductor coil 1 is located increases, and the inductance and reactance of the inductor coil 1 decrease accordingly.

[0032] Preferably, the inductor coil 1 is manufactured using a flexible printed circuit board (FPC) process, and its winding shape is racetrack-shaped. The use of FPC not only improves the sensor's detection sensitivity and measurement accuracy but also gives the inductor coil good flexibility and corrosion resistance, thereby enhancing the sensor's durability and environmental adaptability under complex operating conditions. The inductor coil 1 is printed on an inductor coil substrate 6, which can be wound without damaging the inductor coil 1.

[0033] The effective travel range of the inductor coil 1 can be customized according to the requirements of the actual application scenario. During the detection process, a preset gap is maintained between the inductor coil 1 and the object being measured 5. The size of this gap will affect the measurement accuracy and sensitivity within a certain range. To address this effect, this invention can minimize the interference of gap fluctuations on the measurement results through parameter matching of the signal processing module 4 and compensation correction of the signal processing algorithm. At the same time, the linearized inductor coil 1 maintains stable induction characteristics throughout the entire effective travel range and will not experience significant performance degradation due to changes in the position of the object being measured 5, providing a core guarantee for the stable and reliable operation of the sensor.

[0034] Preferably, the processing method of signal processing module 4 is as follows: (1) Filtering algorithm: A composite filtering algorithm combining Kalman filtering and moving average filtering is adopted. The moving average filtering is used to initially filter out high-frequency random noise in the signal. Its principle is to select digital signals of N consecutive sampling periods and calculate the average value as the effective signal at the current time. The formula is: y k = (x k + x k-1 +... + x k-n+1 ) / N; Among them, y k This is the filtered signal value at the current moment. x k The sampled value at the current moment. x k-1 To x k-n+1 These are the sampled values ​​from the first N-1 time steps. N is the preset sampling window length; After the initial processing of the moving average filter, the amplitude of high-frequency noise can be quickly attenuated, thereby improving the smoothness of the signal. On this basis, Kalman filtering is introduced for secondary noise reduction. Kalman filtering predicts the theoretical value of the signal in real time by constructing the state equation and observation equation of the signal, and performs error correction in combination with the current sampled value, thereby obtaining the optimal estimate. The Kalman filter consists of three stages: state prediction, observation update, and error covariance update. This composite filtering algorithm can effectively balance noise reduction and signal response speed. It can filter out invalid components such as high-frequency random noise and electromagnetic interference, while avoiding the signal lag problem caused by a single filtering algorithm.

[0035] (2) Integral operation algorithm: The effective signal after filtering is sent to the integration operation module, and the trapezoidal integration algorithm is used to realize the integration processing of the signal; Preferably, the trapezoidal integral algorithm treats the signal values ​​at two consecutive sampling times as the two bases of a trapezoid, and the sampling interval as the height of the trapezoid. The integral result is obtained by calculating and summing the area of ​​the trapezoid. The formula is: S k = S k-1 + (x k + x k-1 )×T / 2, Where S k This is the accumulated value of the integral at the current moment. S k-1 This is the accumulated value of the integral from the previous moment. x k and x k-1 These are the filtered signal values ​​at the current and previous moments, respectively. T represents the sampling interval. Compared to the traditional rectangular integration algorithm, the trapezoidal integration algorithm offers higher computational accuracy, a fact verified in related research. The core purpose of integration is to convert the change in voltage signal across the inductor coil into a cumulative quantity directly related to the displacement of the induced element. Since the change in voltage signal is linearly related to the rate of change of displacement of the induced element, integrating the change in voltage signal yields the cumulative displacement value of the induced element. This allows for the extraction of feature signals directly related to the absolute position of the induced element, ultimately achieving accurate detection of the absolute position of the induced element within the effective stroke of the inductor coil.

[0036] Preferably, the formula for calculating the voltage across inductor 1 is: U L =U X L / R+X L

[0037] in: UL The voltage across the inductor coil; U is the excitation voltage input to the signal generator; R is the resistance value; X L This is the inductive reactance of the inductor coil.

[0038] The above formula clarifies the quantitative relationship between the voltage across the inductor, the input excitation voltage, and the resistance. In practical applications, based on this formula, and combined with parameters such as the input excitation voltage U and the total equivalent resistance R of the circuit collected by the signal sampling module, the voltage U across the inductor can be accurately calculated. L ; and then based on U L The correspondence between the inductive reactance of the inductor coil (and consequently the position of the sensed component) provides core data support for the signal processing module and the accurate detection of the sensed component's position. Furthermore, based on the quantitative relationship of this formula, parameters such as resistance and excitation voltage can be optimized in reverse, thereby further improving the sensor's detection accuracy and stability.

[0039] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and structure of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A non-contact linear displacement sensor, characterized in that, It includes an inductor (1), a signal generator (2), a signal sampling module (3), and a signal processing module (4). The signal generator (2) outputs an excitation signal of a preset frequency; After the excitation signal output by the signal generator (2) is applied to the inductor coil (1), the inductor coil (1) generates an inductance change related to the position of the object under test (5) according to the principle of electromagnetic induction, thereby changing the electrical signal at both ends of the inductor coil (1). The signal sampling module (3) collects the voltage signal at both ends of the inductor coil (1) in real time, and sends the collected voltage signal to the signal processing module (4) after amplitude conditioning; the signal processing module (4) converts the conditioned analog voltage signal into a digital signal.

2. The non-contact linear displacement sensor according to claim 1, characterized in that, The excitation signal output by the signal generator (2) at a preset frequency is a sine wave or a square wave excitation signal.

3. The non-contact linear displacement sensor according to claim 1, characterized in that, When the object under test (5) moves within the effective sensing range of the inductor coil (1), the change in the relative position of the object under test and the inductor coil (1) will cause the magnetic coupling area between them to change: when the magnetic coupling area increases, the magnetic resistance of the magnetic circuit where the inductor coil (1) is located decreases, and the inductance and reactance of the inductor coil (1) increase accordingly; when the magnetic coupling area decreases, the magnetic resistance of the magnetic circuit where the inductor coil (1) is located increases, and the inductance and reactance of the inductor coil (1) decrease accordingly.

4. The non-contact linear displacement sensor according to claim 1, characterized in that, The inductor coil (1) is manufactured using a flexible printed circuit board printing process.

5. The non-contact linear displacement sensor according to claim 1, characterized in that, The processing method of the signal processing module (4) is as follows: (1) Filtering algorithm: A composite filtering algorithm combining Kalman filtering and moving average filtering is adopted. The moving average filtering is used to initially filter out high-frequency random noise in the signal. Its principle is to select digital signals of N consecutive sampling periods and calculate the average value as the effective signal at the current time. The formula is: y k = (x k + x k-1 +... + x k-n+1 ) / N; in: y k This is the filtered signal value at the current moment. x k The sampled value at the current moment. x k-1 To x k-n+1 These are the sampled values ​​from the first N-1 time steps. N is the preset sampling window length; After the initial processing of the moving average filter, the amplitude of high-frequency noise can be quickly attenuated, thereby improving the smoothness of the signal. On this basis, Kalman filtering is introduced for secondary noise reduction. Kalman filtering predicts the theoretical value of the signal in real time by constructing the state equation and observation equation of the signal, and performs error correction in combination with the current sampled value, thereby obtaining the optimal estimate. The Kalman filter consists of three stages: state prediction, observation update, and error covariance update. This composite filtering algorithm can effectively balance noise reduction and signal response speed. It can filter out invalid components such as high-frequency random noise and electromagnetic interference, while avoiding the signal lag problem caused by a single filtering algorithm.

6. (2) Integral operation algorithm: The effective signal after filtering is sent to the integration operation module, and the trapezoidal integration algorithm is used to realize the integration processing of the signal.

7. The non-contact linear displacement sensor according to claim 5, characterized in that, The trapezoidal integral algorithm treats the signal values ​​at two consecutive sampling times as the two bases of a trapezoid, and the sampling interval as the height of the trapezoid. It calculates the area of ​​the trapezoid and sums these values ​​to obtain the integral result. The formula is: S k = S k-1 + (x k + x k-1 )×T / 2, in: S k This is the accumulated value of the integral at the current moment. S k-1 This is the accumulated value of the integral from the previous moment. x k and x k-1 These are the filtered signal values ​​at the current and previous moments, respectively. T is the sampling interval.

8. The non-contact linear displacement sensor according to claim 1, characterized in that, The formula for calculating the voltage across the inductor coil (1) is as follows: U L =U X L / R+X L in: U L The voltage across the inductor coil; U is the excitation voltage input to the signal generator; R is the resistance value; X L This is the inductive reactance of the inductor coil.

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