Inductive encoder bounce value detection device and interference shield error correction method

Abstract

The present application relates to rebound hammer technical field, disclose a kind of inductance encoder rebound value detection device and interference shielding error correction method, including target metal pointer piece, PCB coil board, metal shield and inductance encoder.The present application is based on the principle of eddy current effect to realize non-contact measurement, overcome the defects that traditional detection scheme is vulnerable to dust, strong light interference and temperature drift.Through setting metal shield in the non-detection surface of PCB coil board, the dynamic electromagnetic stray interference introduced by the internal metal components of rebound hammer is blocked, while cooperating with no-load zero point calibration, real-time difference deduction method eliminates the static reference bias error introduced by shield, uses multi-point piecewise linear interpolation algorithm, corrects the non-linear distortion at both ends of full range.The present application solves the problem that internal metal components of rebound hammer destroy the uniformity of alternating excitation electromagnetic field, corrects the detection deviation induced by shielding structure, realizes high-precision, long-term maintenance-free stable detection of rebound value.

Description

Technical Field

[0001] This invention relates to the field of rebound spring technology, specifically to an inductive encoder rebound value detection device and an interference shielding error correction method. Background Technology

[0002] In the field of building quality inspection, a rebound hammer is a non-destructive testing device for the compressive strength of concrete. Its working principle involves using a spring-driven hammer to strike the concrete surface via a striking rod, generating an instantaneous elastic deformation and restoring force. The hammer then moves a pointer slider to indicate the rebound distance. This rebound distance, or rebound value, is used to calculate the compressive strength grade of the concrete.

[0003] Currently, rebound hammers are widely used in concrete compressive strength testing during various stages of construction, municipal engineering, and road and bridge construction. Existing digital rebound hammers typically add an electronic detection module to a mechanical rebound hammer to obtain the displacement data of the pointer slider. To achieve non-contact detection of the pointer slider position information, existing digital rebound hammers mainly employ the following three technical solutions, but all of them have corresponding technical drawbacks: First, the grating encoding scheme. This scheme uses a grating sheet with a sawtooth array mounted on the pointer slider and multiple optocouplers arranged along the slider's movement path. The grating sheet blocks the light path by sliding between the optocouplers, and the rebound value is obtained by accumulating the number of times the optocouplers are switched on and off. However, due to limitations in the physical processing precision of the grating sheet and its susceptibility to false counting under impact and vibration conditions, the displacement detection accuracy is low. Furthermore, since the optocouplers are photoelectric conversion devices, they are susceptible to interference from dust, oil, and strong outdoor light at the construction site, leading to abnormal detection signals. This necessitates frequent cleaning of the light path and light-avoidance operations, resulting in frequent maintenance and a poor user experience.

[0004] Second, the image recognition solution. This solution uses a one-dimensional CMOS image sensor to directly scan the image data before and after the pointer slider slides, uses an image recognition algorithm to locate the pointer slider position, and then calculates the rebound value based on the sensor pixel size. CMOS image sensors, like other photoelectric conversion devices, cannot avoid interference from dust, oil, and strong light. Furthermore, the silicon wafer inside the sensor is relatively large and has weak resistance to mechanical shock, making it prone to physical damage during the high-intensity impact vibrations of the rebound hammer. In addition, the high cost of the sensor results in extremely high hardware manufacturing and maintenance costs for the equipment.

[0005] Third, the linear Hall sensor scheme. This scheme mounts a magnet on the pointer slider and arranges multiple linear Hall sensors in the sliding direction to form a detection array. The movement distance of the pointer slider is calculated by detecting the change in the spatial magnetic field strength caused by the magnet's movement. While this scheme overcomes the shortcomings of photoelectric schemes, such as susceptibility to dust, oil, and strong light interference, it calculates displacement by detecting the absolute strength of the magnetic field, resulting in poor position repeatability and susceptibility to electromagnetic interference from the external environment. More significantly, Hall sensors have inherent temperature drift characteristics, and the magnetic field strength of the magnet decreases with ambient temperature fluctuations, leading to increased measurement errors over a wide temperature range and requiring frequent temperature calibration.

[0006] Therefore, existing digital rebound hammers cannot simultaneously meet the engineering application requirements of high precision, maintenance-free operation, shock resistance, and wide temperature range.

[0007] An inductive encoder is a sensor device that uses the eddy current effect for non-contact position detection. Its working principle involves an alternating electromagnetic field generated by a signal excitation coil arranged on a circuit board. When a conductive object enters this field, eddy currents are excited. The reverse electromagnetic field generated by these eddy currents changes the magnetic flux of the signal receiving coil, and the position of the object is then demodulated by the change in the induced signal. Due to its high resolution, immunity to oil and dust, resistance to mechanical shock, and tolerance to extreme temperatures, inductive encoders are widely used in industrial robots, automotive electronics, aerospace, and other fields, such as measuring the rotation angle of robotic arms, the torque angle of steering wheels, the speed of motors, and the radian of rotary buttons.

[0008] However, applying conventional inductive encoders and their associated structures to displacement detection in rebound hammers faces significant technical obstacles. Because the core components of the rebound hammer, such as the metal casing, impact rod, impact hammer, and springs, are mostly made of aluminum alloy or stainless steel, these metal parts are irregularly distributed within a confined space and undergo high-frequency mechanical movement with the impact. These dynamic metal components severely interrupt or distort the alternating excitation electromagnetic field generated by the inductive encoder, producing extremely strong dynamic stray electromagnetic interference. This causes severe nonlinear distortion in the output signal of the conventional inductive encoder, making it unable to effectively detect the target displacement signal.

[0009] Therefore, this invention proposes an inductive encoder springback detection device and an interference shielding error correction method to address the shortcomings of existing technologies. Summary of the Invention

[0010] To address the shortcomings of existing technologies, this invention provides an inductive encoder springback value detection device and an interference shielding error correction method. This solves the problems of measurement errors caused by dust, oil, and strong light interference in the photoelectric detection structure of existing springback hammers; displacement detection deviations caused by temperature drift due to ambient temperature fluctuations in the magnetic sensing structure; decreased signal-to-noise ratio of the measurement signal due to irregular dynamic stray electromagnetic interference introduced by the internal metal components of the springback hammer onto the inductive encoder; and nonlinear distortion problems in full-range detection.

[0011] To achieve the above objectives, the present invention provides the following technical solution: The first aspect of the present invention provides an inductive encoder springback detection device, which is disposed inside the electronic compartment of a spring hammer. The inductive encoder springback detection device includes a target metal pointer piece, a PCB coil board, a metal shielding cover, and an inductive encoder. The target metal pointer piece is fixedly mounted on the pointer slider of the rebound hammer, and moves synchronously in a straight line along the metal slide rail with the pointer slider; The PCB coil board is arranged on one side of the electronic compartment of the rebound hammer along the straight sliding direction of the pointer slider. The metal shielding cover is installed on the non-detection side of the PCB coil board; The inductive encoder is installed on the main control circuit board inside the electronic compartment of the rebound hammer, and the inductive encoder is electrically connected to the PCB coil board. When the target metal pointer moves with the pointer slider, it generates eddy current induction with the PCB coil board. The inductive encoder receives the induced electrical signal output by the PCB coil board and converts the induced electrical signal into the displacement value of the pointer slider.

[0012] The inductive encoder springback detection device utilizes the electromagnetic eddy current effect for non-contact displacement measurement. A signal excitation coil and a signal receiving coil are arranged on the surface of the PCB coil board. The signal excitation coil generates an alternating electromagnetic field into the surrounding space. When the target metal pointer enters the coverage area of ​​the alternating electromagnetic field, eddy currents are excited on its surface. These eddy currents generate a reverse electromagnetic field, which weakens the intensity of the alternating electromagnetic field and changes the magnetic flux passing through the signal receiving coil, causing a change in the induced electrical signal output from the signal receiving coil. The change in the induced electrical signal is correlated with the displacement of the target metal pointer relative to the signal receiving coil. The inductive encoder receives the induced electrical signal and demodulates it into the displacement value of the target metal pointer. The signal transmission process of the eddy current effect isolates the magnetic flux from interference by dust and oil deposits on the surface of the target metal pointer, and the deformation of the copper foil traces on the PCB coil board due to ambient temperature changes has a much lower impact on the alternating electromagnetic field than the temperature drift of a Hall sensor.

[0013] The target metal pointer piece is manufactured into an L-shaped sheet metal structure using conductive metal sheet. This L-shaped structure has a first and a second bending surface that are perpendicular to each other. The bending feature of the L-shaped sheet metal structure increases the physical structural rigidity of the target metal pointer piece, which can resist the deformation and displacement caused by the mechanical impact and vibration generated by the rebound hammer during the impact action. The first bending surface of the target metal pointer piece is rigidly fixed to the surface of the pointer slider inside the rebound hammer, and this rigid connection eliminates the relative positional offset between the target metal pointer piece and the pointer slider. The second bending surface of the target metal pointer piece extends into the alternating excitation electromagnetic field induction area of ​​the PCB coil board, and the plane containing the second bending surface of the target metal pointer piece is parallel to the surface of the PCB coil board.

[0014] A detection air gap is formed between the target detection surface of the PCB coil board and the parallel surfaces of the target metal pointer piece, with the vertical spatial distance of the detection air gap limited to ≤2mm. An inner cavity air gap is formed between the inner wall of the metal shield and the non-detection surface of the PCB coil board, with the vertical spatial distance of the inner cavity air gap limited to ≥5mm. This vertical spatial distance is strictly greater than the vertical spatial distance of the detection air gap between the PCB coil board and the target metal pointer piece. Based on this spatial distance difference matching design, the amplitude of the electromagnetic detection signal generated by the target metal pointer piece can be significantly higher than the amplitude of the eddy current signal generated by the metal shield on the non-detection surface of the PCB coil board, avoiding excessive absorption of excitation electromagnetic field energy by the metal shield. The eddy current signals generated by the shield itself can be symmetrically distributed and cancel each other out in the differential loop of the receiving coil, and will not directly drown out the effective detection signal. However, if the shield dissipates too much magnetic field flux, on the one hand, it will lead to insufficient excitation magnetic field incident on the target metal pointer piece, and the amplitude of the eddy current signal induced by the target metal will weaken accordingly, resulting in a decrease in the signal-to-noise ratio of the detection loop and a reduction in the sensitivity and resolution of position detection. On the other hand, it will increase the eddy current induction intensity of the shield, exacerbate the imbalance of the induced voltage of the two differential loops inside the receiving coil, and cause the overall static reference bias level of the system to rise, compressing the dynamic amplitude margin of the effective detection signal. When the pointer displacement enters the range of the largest amplitude of the induced signal, it is very easy to trigger signal clipping saturation, which is manifested as the pointer displacement continuously changing but the detection output value remaining constant. After the pointer moves out of this high amplitude range, the signal leaves the saturation state, and the detection value can change normally again with the displacement. This forms a segmented abnormal response of "displacement change - value stagnation - displacement change - value stagnation", which destroys the linearity of the entire detection process and reduces the effective linear detection range.

[0015] The signal excitation coils are arranged around the edge of the PCB coil board. The signal excitation coils are multi-turn inductors with closed loop traces, and these closed loop traces surround all the signal receiving coils arranged on the PCB coil board plane. This peripheral structure allows the distortion components in the alternating excitation electromagnetic field generated by the signal excitation coils, caused by trace corners and edges, to symmetrically cover the differential loops of each group of signal receiving coils. This transforms various magnetic field non-uniform flux interferences into symmetrical common-mode interference. The electromotive forces induced by the two differential receiving loops of each group of signal receiving coils cancel each other out, thus achieving self-cancellation of the alternating excitation electromagnetic field distortion interference introduced by the geometric wiring of the signal excitation coils.

[0016] The signal receiving coil includes a first group of signal receiving coils and a second group of signal receiving coils, both arranged within a planar region enclosed by the traces of the signal excitation coil. The traces of both groups are designed as continuous sinusoidal curves. The first group of signal receiving coils has an initial spatial geometric phase of 0 degrees, and the second group has an initial spatial geometric phase of 90 degrees. The traces of the two groups of signal receiving coils are orthogonally arranged on the plane of the PCB coil board with a 90-degree geometric phase difference. When the target metal pointer moves linearly, the orthogonal arrangement modulates the amplitude of the excitation carrier magnetic field, causing the two groups of signal receiving coils to output modulated induced voltage signals with sinusoidal and cosine envelopes, respectively. After demodulation and arctangent ratio calculation, the amplitude ratio of the two induced voltage signals is converted into an absolute electrical angle parameter characterizing the physical spatial position of the target metal pointer. The two induced voltage signals with a 90-degree phase difference serve as a dynamic reference for each other in the arctangent ratio calculation. This calculation mechanism can offset the common-mode bias error caused by the fluctuation of the alternating excitation electromagnetic field intensity.

[0017] As a replacement coil arrangement structure, the signal receiving coil includes a first group of signal receiving coils, a second group of signal receiving coils, and a third group of signal receiving coils. The traces of the first group of signal receiving coils, the second group of signal receiving coils, and the third group of signal receiving coils are all set to a continuous sine curve shape. The first group of signal receiving coils has an initial spatial geometric phase of 0 degrees, the second group of signal receiving coils has an initial spatial geometric phase of 120 degrees, and the third group of signal receiving coils has an initial spatial geometric phase of 240 degrees. The traces of the three groups of signal receiving coils are arranged with a 120-degree geometric phase difference on the plane of the PCB coil board, and the endpoints on one side of the three groups of signal receiving coils are electrically connected using a three-phase star connection structure. When the target metal pointer moves linearly to any position, the algebraic sum of the instantaneous values ​​of the three induced voltages is always zero. The fluctuation of the alternating excitation electromagnetic field intensity and the external stray magnetic field will act synchronously on the three groups of coils, introducing common-mode interference components from the same source into the three induced voltages. These common-mode interference components can be filtered out by performing three-phase differential decoding calculations through the digital processing unit inside the inductive encoder.

[0018] Both the target detection surface and non-detection surface of the PCB coil board are tightly covered with an insulating protective layer, which is made of a non-magnetic insulating polymer film. The exposed area of ​​the solder pads formed by the physical connection between the pins of the inductive encoder and the terminals of the PCB coil board is completely wrapped with a resin potting layer. The physical isolation structure prevents moisture, oil, and dust particles from directly contacting the electrical traces.

[0019] The second aspect of the present invention provides an interference shielding error correction method, which is applied to an inductive encoder springback detection device. The interference shielding error correction method includes steps S1, S2 and S3.

[0020] Step S1 executes a physical-level interference shielding and conversion mechanism: A metal shield is fixedly installed on the non-detection side of the PCB coil board to block dynamic stray interference introduced by the internal metal components of the rebound spring to the alternating excitation electromagnetic field. The metal shield itself is within the range of the alternating excitation electromagnetic field, and eddy current signals are excited on the side of the PCB coil board near the metal shield. These eddy currents form a reverse magnetic field with a relatively stable amplitude and opposite direction to the alternating excitation electromagnetic field. This reverse magnetic field induces voltage signals in the two signal loops of the signal receiving coil. Due to the influence of processing and assembly tolerances such as the assembly gaps and installation tilt of the metal shield, the induced voltages in the two signal loops cannot be completely balanced, thus generating an asymmetrical bias voltage signal. This asymmetrical bias voltage signal constitutes the static reference bias error.

[0021] Step S2 executes the software-level reference error elimination mechanism: During the target metal pointer piece moving out of the target detection area of ​​the PCB coil board, the inductive encoder reads the asymmetric bias voltage signal introduced by the metal shield on the signal receiving coil. The non-volatile storage module inside the inductive encoder saves this asymmetric bias voltage signal as a static zero-point calibration parameter. As the target metal pointer piece enters the target detection area of ​​the PCB coil board with the pointer slider and slides along the metal rail, the signal input terminal of the inductive encoder acquires the mixed induced voltage signal output by the signal receiving coil in real time. The digital processing unit inside the inductive encoder performs a difference subtraction algorithm on the mixed induced voltage signal, subtracting the static zero-point calibration parameter stored in the non-volatile storage module from the mixed induced voltage signal value in real time, separating the target displacement voltage parameter that directly characterizes the physical displacement of the target metal pointer piece. The inductive encoder performs spatial geometric position calculation on the target displacement voltage parameter, outputting the target displacement voltage parameter as the absolute linear displacement value of the target metal pointer piece, obtaining a preliminary absolute linear displacement value.

[0022] Step S3 executes a full-range multi-point piecewise linear interpolation compensation mechanism: During the system calibration phase of the device, multiple standard physical position reference points and corresponding preliminary absolute linear displacement values ​​are collected at equal intervals along the linear detection stroke of the target metal pointer piece. A nonlinear error compensation mapping table is then generated and stored in the non-volatile memory module inside the inductive encoder. During real-time displacement detection, the digital processing unit inside the inductive encoder matches two adjacent position reference points in the nonlinear error compensation mapping table based on the currently acquired preliminary absolute linear displacement value. A multi-point piecewise linear interpolation algorithm is then used to calculate the dynamic compensation parameters. The preliminary absolute linear displacement value is superimposed with the dynamic compensation parameters for correction, eliminating the nonlinear distortion error caused by the metal shield at both ends of the full linear displacement detection range.

[0023] This invention provides an inductive encoder springback detection device and an interference shielding error correction method. It has the following beneficial effects: 1. This invention establishes a non-contact measurement structure by setting the target metal pointer piece and the PCB coil board as an eddy current induction device. A non-magnetic insulating protective layer is applied to the surface of the PCB coil board, and a resin potting layer is wrapped around the terminals. Based on the non-contact detection principle of electromagnetic induction, it is naturally unaffected by dust, oil, and ambient light. The insulating layer and potting structure physically block the intrusion of moisture and dust particles. Furthermore, the differential loop wiring mechanism of the inductive encoder signal receiving coil naturally resists common-mode interference such as alternating excitation electromagnetic field symmetry distortion, temperature drift, and changes in excitation signal strength. These features enable the detection device to adapt to harsh construction site environments, eliminate the interference of ambient temperature fluctuations on displacement measurement, and solve the problems of traditional rebound hammer photoelectric or magnetic sensing modules being easily contaminated and experiencing data anomalies due to temperature changes, thus reducing the frequency of equipment cleaning and maintenance.

[0024] 2. This invention, by installing a metal shield on the non-detection surface of the PCB coil board and running a difference subtraction algorithm and a multi-point piecewise linear interpolation program within the inductive encoder, blocks dynamic electromagnetic stray interference radiated from irregular metal components such as the impact rod and spring inside the rebound hammer. It actively introduces fixed differential mode offset interference caused by assembly tolerances, transforming external random stray interference, which is difficult to suppress directly, into a static reference bias error that can be eliminated through zero-point calibration. This combination of physical shielding and algorithmic correction eliminates the disruption of the alternating induced magnetic field by the metal material of the rebound hammer body, enabling the inductive encoding technology to be stably applied within the limited space of the rebound hammer and ensuring high-resolution accuracy of rebound displacement detection.

[0025] 3. This invention fabricates the target metal pointer piece into an L-shaped sheet metal structure with double vertical bending surfaces, and sets a signal receiving coil group with a fixed spatial geometric phase difference on the surface of the PCB coil board. The L-shaped sheet metal structure provides physical rigidity to resist mechanical impact. The differential loop routing of the multiple signal receiving coils and the orthogonal or three-phase arrangement between the signal receiving coils can cancel the common-mode interference caused by the transient vertical jump of the target metal pointer piece caused by the impact vibration of the rebound hammer in real time. At the same time, this detection device eliminates complex optical components and magnet assemblies, and the overall structure is flat and compact, reducing assembly and alignment requirements and facilitating direct integration and installation inside the electronic compartment of existing digital rebound hammers. Attached Figure Description

[0026] Figure 1 This is an oblique view of the assembly of the present invention, excluding the main control circuit board.

[0027] Figure 2 This is an assembly side view of the present invention, including the main control circuit board.

[0028] Figure 3 This is a three-dimensional structural view of the present invention.

[0029] Figure 4 This is a schematic diagram of the PCB layout for the dual receiving coils of the present invention.

[0030] Figure 5 This is a schematic diagram of the PCB layout for the three receiving coils of the present invention.

[0031] Among them, 1. Target metal pointer piece; 2. PCB coil board; 3. Metal shielding cover; 4. Inductive encoder; 5. Lithium battery; 6. Metal slide rail; 7. Pointer slider; 8. Rebound spring; 9. Main control circuit board; 21. Signal excitation coil; 22. First group of receiving coils; 23. Second group of receiving coils; 24. Third group of receiving coils. Detailed Implementation

[0032] The technical solutions in 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 some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0033] Example 1

[0034] Combination Figures 1 to 4 This embodiment discloses an inductive encoder rebound value detection device, applied to the non-destructive testing of concrete compressive strength in building engineering. It is suitable for the high-frequency impact, continuous reciprocating vibration, confined and enclosed machine body, dusty and oily construction sites, and wide temperature fluctuations of the rebound hammer. Existing mainstream digital rebound hammer detection structures have limitations in adaptability: photoelectric imaging detection structures are easily affected by dust, oil, strong light, and water mist, resulting in poor imaging stability and high maintenance costs; magnetic Hall effect detection structures are affected by device temperature drift and permanent magnet temperature decay characteristics, leading to large detection deviations in wide temperature environments and requiring frequent manual calibration; conventional inductive detection structures, when applied to the metal enclosed body of the rebound hammer, generate a large amount of dynamic stray electromagnetic interference due to the reciprocating motion of the dense internal metal components, easily causing a decrease in the signal-to-noise ratio and full-range nonlinear distortion, making high-precision and stable detection impossible. This device is integrated entirely within the electronic compartment of the rebound hammer 8, with a flat and compact structure. It requires no modification to the main mechanical and external structure of the rebound hammer, and can be adapted for upgrades and modifications of existing digital rebound hammers, demonstrating good versatility. This device mainly includes a target metal pointer piece 1, a PCB coil board 2, a metal shield 3, and an inductive encoder 4. Through a dedicated hardware structure and a matching error correction method, it achieves high-precision and high-stability spring displacement detection in the case of a small metal body.

[0035] Each functional component is assembled in a separate layout, ensuring precise positioning and stable motion. The target metal pointer 1 is fixedly mounted on the pointer slider 7 of the rebound spring 8, and can synchronously complete linear reciprocating motion along the metal slide rail 6 with the pointer slider 7, without relative slippage or motion lag during the movement. The PCB coil board 2 is fixedly arranged inside the electronic compartment along the sliding direction of the pointer slider 7, and the coil sensing area completely covers the effective detection stroke of the pointer. The metal shield 3 is mounted on the non-detection surface of the PCB coil board 2 to block stray electromagnetic interference from the outside and inside the machine body. The inductive encoder 4 is fixedly mounted on the main control circuit board 9 and establishes a stable electrical connection with the PCB coil board 2. This layout physically isolates the analog sensing acquisition area from the digital signal processing area, effectively avoiding coupling interference from the high-frequency operating signals of the digital circuit to the weak analog sensing signals, and ensuring the stability of the signal acquisition, demodulation, and displacement calculation processes.

[0036] This device achieves non-contact displacement detection based on the eddy current effect. The signal excitation coil 21 arranged on the PCB coil board 2 and the matching capacitor of the main control circuit board 9 form an LC resonant circuit, which can output an alternating excitation signal with stable amplitude and frequency, forming a regularly distributed alternating excitation electromagnetic field on the outer side of the detection surface of the PCB coil board 2. Due to the limitations of PCB planar wiring technology, the alternating excitation electromagnetic field suffers from local uneven field strength and slight edge distortion. This invention adopts an outer-encircling coil wiring structure, which can convert magnetic field distortion disturbances into symmetrical common-mode interference and cancel them out, balancing the magnetic field distribution and weakening the magnetic field disturbances caused by the process. When the pointer slider 7 drives the target metal pointer piece 1 into the area covered by the alternating excitation electromagnetic field, the metal target is excited by the alternating magnetic field to generate eddy currents. The reverse magnetic field derived from the eddy currents can change the magnetic flux in the signal receiving coil area, causing the signal receiving coil to output an induced electrical signal that continuously corresponds to the target displacement. The inductive encoder 4 collects and demodulates the induced electrical signal, calculates the real-time linear displacement value of the pointer slider 7, and then converts it into the concrete rebound value. This detection method is not affected by dust, oil, or water stains on the surface of the target metal pointer piece. Combined with the common-mode suppression characteristics of the differential coil, it has good adaptability to working conditions and detection stability.

[0037] The target metal pointer piece 1 is an integral L-shaped sheet metal structure formed by a single bending of conductive metal sheet, with a first bending surface and a second bending surface that are perpendicular to each other. The L-shaped structure can improve the overall structural rigidity of the target metal pointer piece, enhance its resistance to impact and vibration deformation, avoid micro-deformation of the target metal pointer piece and displacement of the detection reference caused by the high-frequency impact vibration of the rebound spring, and has a simple forming process, good processing consistency, and is suitable for mass production. The first bending surface is rigidly fixed to the surface of the pointer slider 7, ensuring that the target metal pointer piece and the pointer slider 7 move completely synchronously; the second bending surface is arranged parallel to the surface of the PCB coil board 2 and extends into the effective sensing area of ​​the alternating excitation electromagnetic field, serving as an eddy current sensing target to convert mechanical displacement into magnetic field flux change, and establishing a stable correspondence between displacement parameters and induced electrical signals.

[0038] This device features a dual-layer differentiated air gap structure. By defining a specific spatial dimension, it ensures electromagnetic coupling efficiency and detection linearity. A detection air gap is formed between the detection surface of the PCB coil board 2 and the opposing surface of the target metal pointer piece 1. The vertical spatial distance of the detection air gap is no greater than 2mm, and in this embodiment, 0.5mm is preferred. This dimension ensures that the target metal pointer piece is within the effective penetration depth range of the alternating excitation electromagnetic field, resulting in sufficient and stable electromagnetic coupling. This avoids signal attenuation and detection linearity degradation caused by an excessively large air gap, while also mitigating mechanical risks such as vibration, rubbing, and assembly interference caused by an excessively small air gap.

[0039] An internal air gap is formed between the non-detection surface of the PCB coil board 2 and the inner wall of the metal shield 3. The vertical spatial distance of the internal air gap is not less than 5mm, preferably 9.5mm in this embodiment, and the vertical spatial distance of the internal air gap is always greater than the vertical spatial distance of the detection air gap, forming a differentiated air gap ratio structure. Relying on the characteristic that the alternating magnetic field decays exponentially with the propagation distance, this ratio can reduce the eddy current induction intensity on the shield side, so that the effective detection signal amplitude generated by the target metal pointer piece dominates, reducing the ineffective absorption and magnetic flux loss of the excitation magnetic field by the shield. Theoretically, the eddy current magnetic field generated by the shield can be symmetrically canceled in the differential loop inside the receiving coil, and will not directly suppress the effective detection signal. If the internal air gap is too small and the eddy current of the shield is too strong, on the one hand, it will shunt the excitation magnetic flux, weaken the pointer induction signal, and reduce the system signal-to-noise ratio, resulting in a decrease in detection sensitivity and resolution; on the other hand, due to the influence of assembly tolerance, the induced voltage of the two sets of differential loops inside the receiving coil cannot be completely balanced and canceled, the overall static reference bias level rises, and the range of dynamic signal changes is squeezed. Once the target metal pointer moves into the signal peak range, voltage clipping and saturation occur, resulting in a plateau segment where the displacement continuously changes but the sampled value remains unchanged. After the pointer moves out of this range, the signal resumes its linear following characteristic, exhibiting an overall discontinuous nonlinear response, and the compression system can use a linear stroke. This embodiment suppresses the above two types of defects at the source by setting a larger air gap in the inner cavity of the shielding cover, ensuring linear and stable displacement detection throughout the entire stroke.

[0040] The signal excitation coil 21 is arranged in a closed loop multi-turn trace structure around the edge of the PCB coil board 2 plane, completely surrounding all the signal receiving coils on the board surface. This wiring method can symmetrically cover each group of differential receiving loops with the magnetic field distortion disturbances generated at the edges and corners of the signal excitation coil, so that the process-induced magnetic field non-uniform disturbances are transformed into symmetrical common-mode interference. The interferences are canceled out by the induced electromotive force of the differential coils, effectively weakening the problem of uneven distribution of alternating excitation electromagnetic field and improving the stability and linearity of the detection signal.

[0041] Combination Figure 4 This embodiment employs a two-phase orthogonal differential signal receiving coil structure. The PCB coil board 2 houses a first set of signal receiving coils 22 and a second set of signal receiving coils 23 within the area enclosed by the signal excitation coils. Both sets of coils utilize continuous sinusoidal curve traces, with initial spatial geometric phases of 0° and 90° respectively, and are arranged orthogonally to each other. During the linear reciprocating motion of the target metal pointer 1, the two sets of orthogonal coils modulate the amplitude of the excitation carrier magnetic field, outputting two phase difference induced voltage signals with sinusoidal and cosine envelopes, respectively.

[0042] The inductive encoder 4 synchronously acquires two orthogonal induced voltage signals. Through a built-in arctangent ratio calculation algorithm, it converts the dynamic ratio of the two voltage amplitudes into the corresponding absolute electrical angle parameter. Combined with the coil geometric period parameters, it calculates the absolute linear displacement value of the target metal pointer piece 1, thus completing the springback value calculation. The two orthogonal signals act as dynamic references to each other during the ratio calculation process, offsetting common-mode bias errors introduced by fluctuations in the amplitude of the alternating excitation electromagnetic field and power supply offset. This eliminates the need for frequent on-site zeroing calibration, effectively improving detection repeatability and long-term operational stability.

[0043] The front and back sides of PCB coil board 2 are fully covered with a non-magnetic insulating polymer protective film, achieving physical isolation between the coil traces and the external environment. The exposed solder pad areas of the inductive encoder pin 4 and the terminals of PCB coil board 2 are encapsulated with epoxy resin for overall protection. This protective structure effectively blocks moisture, oil, and dust corrosion, preventing circuit oxidation, leakage, contact resistance drift, and solder joint failure, thus improving the equipment's weather resistance and maintenance-free performance. Simultaneously, all protective materials are non-magnetic, not altering the distribution of the alternating excitation electromagnetic field or interfering with the eddy current induction process, preserving the equipment's high-precision detection characteristics while ensuring protective performance.

[0044] Example 2

[0045] Combination Figure 5 This embodiment discloses another signal receiving coil topology. The assembly relationship of the fuselage, the dimensions of the L-shaped target metal pointer sheet, the double-layer differentiated air gap parameters, the layout of the surrounding signal excitation coil, and the board insulation protection structure are all consistent with Embodiment 1. Only the topology arrangement and wiring logic of the signal receiving coil are optimized. This invention provides two alternative signal receiving coil schemes: two-phase orthogonal and three-phase symmetrical, to adapt to different application scenarios. The two-phase coil structure is simple, has low hardware cost, and lightweight supporting algorithms, making it suitable for conventional working conditions and popular rebound hammer equipment. The three-phase symmetrical topology can improve the equipment's anti-interference performance, detection linearity, and operational fault tolerance, making it suitable for high-precision, harsh working condition detection scenarios. The two schemes complement each other, broadening the applicability of this technology.

[0046] In this embodiment, three sets of sinusoidal signal receiving coils are arranged: a first set of signal receiving coils 22, a second set of signal receiving coils 23, and a third set of signal receiving coils 24. The initial spatial geometric phases of the three sets of coils are 0°, 120°, and 240°, respectively, and they are arranged symmetrically in pairs. The ends of the three sets of coils on the same side are electrically connected in a three-phase star connection to form a common contact, while the other end is an independent signal output terminal, which is electrically connected to the signal acquisition port of the inductive encoder 4, realizing the independent acquisition and joint decoding of the three induced voltage signals.

[0047] Compared to the two-phase orthogonal structure of Example 1, this three-phase symmetrical topology has significant technical advantages in terms of measurement resolution accuracy and operational fault tolerance reliability. Both the two-phase orthogonal and three-phase symmetrical architectures have excellent common-mode interference suppression capabilities, which can effectively offset detection errors caused by fixed assembly bias, excitation amplitude fluctuations, uniform temperature changes, and symmetrical magnetic field disturbances. However, the two-phase orthogonal topology is limited by the dual-channel signal processing mechanism, resulting in limited angle subdivision density, relatively low resolution accuracy for minute displacements, and lacks hardware fault tolerance capabilities; any abnormality in the signal of any single coil will lead to displacement calculation failure. This example adopts a 120° three-phase symmetrical arrangement structure, relying on the closed-loop characteristics of the three-channel signal vector, which provides richer signal sampling dimensions and higher angle subdivision accuracy, effectively improving the identification and resolution capability of minute displacements and the linearity of full-range detection. Meanwhile, this topology possesses hardware fault-tolerant degradation operation characteristics that are not available in two-phase orthogonal architectures. When any single coil fails due to open circuit, poor soldering, signal loss, or other faults, the remaining two effective coil signals with a fixed phase difference can still complete the displacement calculation. The equipment will not experience problems such as detection downtime, data interruption, or functional failure. It only slightly reduces the anti-interference level, greatly improving the operational stability and service life of the equipment under harsh conditions such as high-frequency continuous construction, strong vibration fatigue, and complex electromagnetic environments. It is more suitable for high-precision engineering acceptance, long-term uninterrupted on-site testing, and other high-requirement application scenarios.

[0048] Example 3

[0049] This embodiment discloses an interference shielding error correction method applied to the aforementioned inductive encoder springback detection device. This method addresses technical problems existing in the confined, enclosed metal casing of the springback encoder, such as dynamic stray electromagnetic interference, static reference bias errors introduced by the metal shielding assembly process, and full-range nonlinear distortion caused by the boundary effects of alternating excitation electromagnetic fields. It constructs a hierarchical closed-loop correction mechanism that includes controllable conversion of physical interference, software zero-point error elimination, and full-range interpolation compensation. This mechanism eliminates multi-dimensional detection errors step by step, improving the accuracy of springback displacement detection and its full-range linearity. Specifically, this method includes steps S1, S2, and S3: Step S1: Implement physical interference shielding and error conversion mechanisms The metal shield 3 is fixedly mounted on the non-detection side of the PCB coil board 2, forming a closed electromagnetic isolation structure. This structure can isolate the electromagnetic coupling path between the metal shell of the rebound hammer, the reciprocating impact rod, the energy storage spring, the metal slide rail 6, the main control circuit board 9, the lithium battery 5, and the sensing area of ​​the PCB coil board 2 in three-dimensional space. It effectively blocks the dynamic and irregular stray electromagnetic interference generated by the high-frequency movement of the metal components during equipment operation, avoids the distortion, cutting, and attenuation of the alternating excitation electromagnetic field, and suppresses the problem of electromagnetic interference-induced signal distortion and signal-to-noise ratio reduction, providing a stable alternating excitation electromagnetic field environment for induction detection.

[0050] The metal shield 3 is located within the range of the alternating electromagnetic field of the PCB coil board 2. Its metal surface is excited by the alternating magnetic field, generating steady-state eddy currents, which in turn form a reverse magnetic field. This induces a fixed voltage signal in the differential circuit of the signal receiving coil. Under ideal assembly conditions, the induced voltage amplitudes of the two differential loops are balanced and cancel each other out, resulting in no reference error. However, due to process factors such as stamping tolerances, assembly gap deviations, installation tilt, and alignment deviations in actual production, the magnetic coupling matching degree of the two differential loops cannot be completely consistent, leading to a fixed asymmetric bias voltage and forming an inherent static reference bias error in the equipment.

[0051] This step achieves a controllable transformation of detection interference. The dynamic electromagnetic interference within the confined, enclosed body of the rebound hammer is random and unpredictable, making it impossible to compensate for using conventional algorithms. It is the primary source of random error in inductance detection within confined spaces. This structure completely blocks this type of random electromagnetic interference through a metal shield 3, eliminating uncertain operating condition errors. Simultaneously, it transforms unavoidable process deviations from manufacturing and assembly into static reference bias errors with fixed amplitude, stable state, and calibrable modeling capabilities. This provides a quantifiable, calibrable, and compensable basis for the previously difficult-to-detect stable inductance detection conditions within confined spaces, offering a stable correction benchmark for subsequent precise error elimination in the software.

[0052] Step S2: Execute the software baseline error difference subtraction and elimination mechanism During the target detection area where the target metal pointer piece 1 moves out of the PCB coil board 2, the inductive encoder 4 reads the asymmetric bias voltage signal introduced by the metal shield 3 on the signal receiving coil. The non-volatile storage module inside the inductive encoder 4 saves the asymmetric bias voltage signal as a static zero-point calibration parameter. This parameter has good stability and does not require repeated calibration and on-site zeroing calibration during subsequent use of the equipment.

[0053] When the target metal pointer piece 1 enters the target detection area of ​​the PCB coil board 2 along with the pointer slider 7 and slides along the metal slide rail 6, the signal input terminal of the inductive encoder 4 acquires the mixed induced voltage signal output by the signal receiving coil in real time. The digital processing unit inside the inductive encoder 4 performs a difference subtraction algorithm on the mixed induced voltage signal. The difference subtraction algorithm subtracts the static zero-point calibration parameters stored in the non-volatile storage module from the mixed induced voltage signal value in real time, and separates the target displacement voltage parameter that directly represents the physical displacement of the target metal pointer piece 1. The inductive encoder 4 performs spatial geometric position calculation on the target displacement voltage parameter. Combined with the preset spatial geometric calculation model, the spatial geometric position calculation process outputs the target displacement voltage parameter as the absolute linear displacement value of the target metal pointer piece 1, and obtains the preliminary absolute linear displacement value.

[0054] Step S3: Execute the full-range multi-point piecewise linear interpolation compensation mechanism During the system calibration phase of the device, multiple standard physical position reference points and preliminary absolute linear displacement values ​​corresponding to the standard physical position reference points are collected at equal intervals along the linear detection stroke of the target metal pointer piece 1, and a nonlinear error compensation mapping table is generated and stored in the non-volatile storage module inside the inductive encoder. During real-time displacement detection, the digital processing unit inside the inductive encoder 4 matches two adjacent position reference points in the nonlinear error compensation mapping table based on the currently acquired preliminary absolute linear displacement value, and calculates the dynamic compensation parameters using a multi-point piecewise linear interpolation algorithm. The preliminary absolute linear displacement value is then superimposed and corrected with the dynamic compensation parameters to eliminate the nonlinear distortion error caused by the metal shield 3 at both ends of the full range of linear displacement detection, outputting a high-precision, highly repeatable rebound displacement value, and completing the concrete rebound value calculation.

[0055] This invention achieves controllable conversion of random interference through physical shielding, and combines software zero-point error elimination and full-range interpolation compensation to construct a hierarchical closed-loop error correction system. This solves the technical problems of signal distortion, low signal-to-noise ratio, data drift, and poor full-range linearity in inductive detection under the confined metal casing of rebound hammers. This technical solution requires no on-site manual calibration, has strong environmental adaptability, effectively balances equipment detection accuracy and long-term operational stability, and improves the reliability and engineering applicability of digital rebound hammers for non-destructive testing.

Claims

1. A device for detecting the springback value of an inductive encoder, characterized in that, It includes a target metal pointer piece (1), a PCB coil board (2), a metal shield (3), and an inductive encoder (4). The target metal pointer piece (1) is fixedly installed on the pointer slider (7) of the rebound spring (8) and moves synchronously in a straight line along the metal slide rail (6) with the pointer slider (7); The PCB coil board (2) is arranged on one side of the electronic compartment of the rebound device (8) along the straight sliding direction of the pointer slider (7); The metal shield (3) is installed on the non-detection side of the PCB coil board (2); The inductive encoder (4) is installed on the main control circuit board (9) inside the electronic compartment of the rebounder (8), and the inductive encoder (4) is electrically connected to the PCB coil board (2); When the target metal pointer piece (1) moves with the pointer slider (7), it generates an eddy current induction with the PCB coil board (2). The inductive encoder (4) receives the induced electrical signal output by the PCB coil board (2) and converts the induced electrical signal into the displacement value of the pointer slider (7), and then converts it into a rebound value.

2. The inductive encoder springback detection device according to claim 1, characterized in that, The target metal pointer piece (1) is an L-shaped sheet metal structure made of conductive metal sheet. The L-shaped sheet metal structure has a first bending surface and a second bending surface that are perpendicular to each other. The first bending surface of the target metal pointer piece (1) is rigidly fixed to the surface of the pointer slider (7) inside the rebound spring (8). The second bending surface of the target metal pointer piece (1) extends into the alternating excitation electromagnetic field induction area of ​​the PCB coil board (2). The plane where the second bending surface of the target metal pointer piece (1) is located is parallel to the surface of the PCB coil board (2).

3. The inductive encoder springback detection device according to claim 1, characterized in that, A detection air gap is formed between the target detection surface of the PCB coil board (2) and the parallel and opposite surface of the target metal pointer piece (1), and the vertical spatial distance of the detection air gap is limited to ≤2mm; An inner cavity air gap is formed between the inner wall of the metal shield (3) and the non-detection surface of the PCB coil board (2). The vertical spatial distance of the inner cavity air gap is limited to ≥5mm. The vertical spatial distance of the inner cavity air gap is strictly greater than the vertical spatial distance of the detection air gap between the PCB coil board (2) and the target metal pointer piece (1).

4. The inductive encoder springback detection device according to claim 1, characterized in that, The PCB coil board (2) has a signal excitation coil (21) and a signal receiving coil arranged in a plane. The signal excitation coil (21) is arranged around the edge area of ​​the plane of the PCB coil board (2). The signal excitation coil (21) is a multi-turn inductor coil with a closed loop. The closed loop trace of the signal excitation coil (21) surrounds all the signal receiving coils arranged on the plane of the PCB coil board (2) in the plane. The signal excitation coil (21) generates an alternating excitation electromagnetic field to the surrounding space.

5. The inductive encoder springback detection device according to claim 4, characterized in that, The signal receiving coil includes a first group of signal receiving coils (22) and a second group of signal receiving coils (23); The first group of signal receiving coils (22) and the second group of signal receiving coils (23) are both arranged inside the planar area surrounded by the trace of the signal excitation coil (21); The traces of the first group of signal receiving coils (22) and the second group of signal receiving coils (23) are both set to a continuous sine curve shape; The first group of signal receiving coils (22) is set with an initial spatial geometric phase of 0 degrees, and the second group of signal receiving coils (23) is set with an initial spatial geometric phase of 90 degrees. The traces of the two groups of signal receiving coils are arranged orthogonally with a geometric phase difference of 90 degrees on the plane of the PCB coil board (2).

6. The inductive encoder springback detection device according to claim 4, characterized in that, The signal receiving coil includes a first group of signal receiving coils (22), a second group of signal receiving coils (23) and a third group of signal receiving coils (24); The traces of the first group of signal receiving coils (22), the second group of signal receiving coils (23), and the third group of signal receiving coils (24) are all set to a continuous sine curve shape; The first group of signal receiving coils (22) is set with an initial spatial geometric phase of 0 degrees, the second group of signal receiving coils (23) is set with an initial spatial geometric phase of 120 degrees, and the third group of signal receiving coils (24) is set with an initial spatial geometric phase of 240 degrees. The traces of the three groups of signal receiving coils are arranged in a geometric phase difference of 120 degrees on the plane of the PCB coil board (2), and the endpoints on one side of the three groups of signal receiving coils are electrically connected by a three-phase star connection structure.

7. The inductive encoder springback detection device according to claim 1, characterized in that, The target detection surface and the non-detection surface of the PCB coil board (2) are both tightly covered with an insulating protective layer, which is a non-magnetic insulating polymer film. The exposed area of ​​the solder pad formed by the physical connection between the pins of the inductive encoder (4) and the terminals of the PCB coil board (2) is entirely covered with a resin potting layer.

8. An interference shielding error correction method, applied to the inductive encoder springback value detection device according to any one of claims 1-7, characterized in that, It includes steps S1, S2, and S3; Step S1 executes a physical-level interference shielding and conversion mechanism: The metal shield (3) is fixedly installed on the non-detection side of the PCB coil board (2) to block the dynamic stray interference introduced by the internal metal parts of the rebound tester to the alternating excitation electromagnetic field. The metal shield (3) body is within the range of action of the alternating excitation electromagnetic field, and an eddy current signal is generated on the side of the PCB coil board (2) near the metal shield (3). The eddy current forms a reverse magnetic field with a relatively stable amplitude and opposite direction to the alternating excitation electromagnetic field. The reverse magnetic field induces voltage signals in the two signal loops of the signal receiving coil. Due to the influence of processing and assembly tolerances such as the gap in the metal shield assembly and the installation tilt, the induced voltages in the two signal loops cannot be completely balanced, thus generating an asymmetrical bias voltage signal. This asymmetrical bias voltage signal constitutes the static reference bias error. Step S2 executes a software-level benchmark error elimination mechanism: During the stage when the target metal pointer piece (1) moves out of the target detection area of ​​the PCB coil board (2), the inductive encoder (4) reads the asymmetric bias voltage signal introduced by the metal shield (3) on the signal receiving coil, and the non-volatile storage module inside the inductive encoder (4) saves the asymmetric bias voltage signal as a static zero-point calibration parameter. When the target metal pointer piece (1) enters the target detection area of ​​the PCB coil board (2) along with the pointer slider (7) and slides along the metal slide rail (6), the signal input terminal of the inductive encoder (4) acquires the mixed induced voltage signal output by the signal receiving coil in real time. The digital operation unit inside the inductive encoder (4) performs a difference subtraction algorithm on the mixed induced voltage signal. The difference subtraction algorithm subtracts the static zero-point calibration parameter stored in the non-volatile storage module from the mixed induced voltage signal value in real time, and separates the target displacement voltage parameter that directly represents the physical displacement of the target metal pointer piece (1). The inductive encoder (4) performs spatial geometric position calculation on the target displacement voltage parameter. The spatial geometric position calculation process outputs the target displacement voltage parameter as the absolute linear displacement value of the target metal pointer piece (1) to obtain the preliminary absolute linear displacement value. Step S3 executes a full-range multi-point piecewise linear interpolation compensation mechanism: During the system calibration phase of the device, multiple standard physical position reference points and the preliminary absolute linear displacement values ​​corresponding to the standard physical position reference points are collected at equal intervals along the straight detection stroke of the target metal pointer piece (1), and a nonlinear error compensation mapping table is generated and stored in the non-volatile storage module. During real-time displacement detection, the digital processing unit inside the inductive encoder (4) matches two adjacent position reference points in the nonlinear error compensation mapping table based on the currently acquired preliminary absolute linear displacement value, and calculates the dynamic compensation parameter using a multi-point piecewise linear interpolation algorithm. The preliminary absolute linear displacement value is then superimposed and corrected with the dynamic compensation parameter to eliminate the nonlinear distortion error caused by the metal shield (3) at both ends of the full range of linear displacement detection.

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