A zoom visual displacement measurement system and method based on a beam-splitting fixed-focus reference target

Abstract

This application discloses a zoom visual displacement measurement system and method based on a beam-splitting fixed-focus reference target, relating to the field of structural monitoring. The system includes: a measurement point target and a reference imaging unit respectively disposed on the first and second incident light paths of a beam-splitting component; the measurement point target is located on the surface of the structure to be measured; the zoom imaging unit is disposed on the outgoing light path of the beam-splitting component; the zoom imaging unit and the reference imaging unit are rigidly connected; a processing unit is electrically connected to the zoom imaging unit; the beam of the measurement point and the reference light are combined by the beam-splitting component, and after being zoomed by the zoom imaging unit, they are converted into electrical signals; the processing unit normalizes the signal according to the current focal length scale and calculates the attitude transformation matrix to obtain the displacement measurement result. This application achieves coordinate reference in complex scenes by constructing a self-contained optical reference benchmark at the near end; compensates for camera attitude disturbances using the same imaging light path; and improves the accuracy, adaptability, and stability of zoom visual displacement measurement by using normalization to separate zoom geometric changes.

Description

Technical Field

[0001] This application relates to the field of structural monitoring, and in particular to a zoom visual displacement measurement system and method based on a spectrophotometric fixed-focus reference target. Background Technology

[0002] Structural displacement is a crucial parameter characterizing the safety status, service performance, and disease evolution of bridges, tunnels, buildings, and other civil structures. Existing structural displacement monitoring methods mainly include contact displacement gauges, levels, total stations, GNSS, and machine vision-based displacement monitoring. Traditional contact displacement gauges typically require a mechanical connection between the measured component and a fixed reference point. While achieving high accuracy in localized scenarios, they suffer from complex installation, high maintenance requirements, limited span, and long-term reliability significantly affected by mechanical wear and environmental factors. Leveling instruments and total stations rely heavily on periodic manual observations, making them unsuitable for all-weather, long-term continuous, and automated monitoring. While GNSS methods offer advantages in large-scale deformation monitoring, they often struggle to balance cost and accuracy in scenarios with severe obstruction, limited space, or high precision requirements. With the development of image sensors, embedded processors, and image processing algorithms, machine vision-based structural displacement monitoring technology has gradually become a research and engineering application hotspot. These methods typically obtain displacement information of the measured points by placing artificial targets on the surface of the measured structure or utilizing the structure's natural texture features, through image acquisition and image coordinate calculation. Compared with traditional contact methods, visual measurement methods have advantages such as being non-contact, capable of long-distance measurement, allowing for simultaneous measurement at multiple points, and being easy to network.

[0003] In practical engineering monitoring, zoom lenses are often required for long-distance observation to balance monitoring range and spatial resolution. By adjusting the focal length, magnified imaging of key local areas can be achieved within a larger monitoring range, thus meeting the requirements of wide coverage and high-precision measurement. However, zoom visual displacement monitoring systems are typically installed on supports, columns, platforms, or other carriers, making them susceptible to factors such as wind load, micro-vibration, temperature changes, and micro-displacement of the foundation, which can cause changes in camera attitude. Cameras are highly sensitive to minute attitude changes under long-distance zoom conditions; these changes manifest as noticeable pixel displacement in the image and are superimposed on the actual displacement of the measured structure, thus affecting measurement accuracy and long-term stability.

[0004] In summary, existing technologies rely on a fixed background at a distance, making it difficult to obtain reliable references in scenarios lacking a stable distant view, such as tunnels and underground locations. Furthermore, it is difficult to accurately estimate camera attitude disturbances, resulting in displacement measurements being affected by shaking. At the same time, the geometric changes caused by zooming are coupled with attitude changes, reducing the accuracy and stability of large-area zoom monitoring. Summary of the Invention

[0005] The purpose of this application is to provide a zoom visual displacement measurement system and method based on a beam splitting fixed-focus reference target. It can realize coordinate reference in complex scenes by constructing a self-contained optical reference benchmark at the near end; compensate for camera attitude disturbances by using the same imaging optical path; and improve the accuracy, adaptability and stability of zoom visual displacement measurement by using normalization to separate zoom geometric changes.

[0006] To achieve the above objectives, this application provides the following solution: In a first aspect, this application provides a zoom visual displacement measurement system based on a beam-splitting, fixed-focus reference target. The system includes: a measurement point target, a beam-splitting assembly, a reference imaging unit, a zoom imaging unit, and a processing unit. The measurement point target is disposed on the first incident light path of the beam-splitting assembly. The measurement point target is located on the surface of the structure to be measured. The measurement point target is used to characterize the surface displacement of the structure to be measured, forming a target image. The measurement point target includes multiple measurement points. The reference imaging unit is disposed on the second incident light path of the beam-splitting assembly. The reference imaging unit is used as a near-end optical reference, forming a reference reference feature point image. The zoom imaging unit is disposed on the beam-splitting assembly. The output light path of the device; the zoom imaging unit is rigidly connected to the reference imaging unit; the processing unit is electrically connected to the zoom imaging unit; the light rays of the target image and the reference reference feature point image are combined by the beam splitting component to obtain a composite image, the composite image is zoomed by the zoom imaging unit and converted from an optical signal to an electrical signal, and then transmitted to the processing unit, the processing unit performs scale normalization on the composite image according to the current focal length of the zoom imaging unit, obtains the compensated measurement point image coordinates by calculating the attitude transformation matrix of the surface of the structure to be measured, and outputs the displacement measurement result; the composite image includes: non-overlapping measurement point areas and reference areas.

[0007] Secondly, this application also provides a zoom visual displacement measurement method based on a beam-splitting fixed-focus reference target. This method is applied to the aforementioned zoom visual displacement measurement system based on a beam-splitting fixed-focus reference target. The method includes: a beam-splitting component transmits target image light rays incident on the measurement point target through a first incident optical path, and reflects reference reference feature point image light rays incident on the reference imaging unit through a second incident optical path, combining the light rays to form a composite image; a zoom lens performs field-of-view zoom on the composite image to obtain a zoomed composite image; an image sensor converts the zoomed composite image from an optical signal to an electrical signal and transmits it to a processing unit; the processing unit performs scale normalization on the composite image according to the current focal length of the zoom imaging unit, obtains the compensated measurement point image coordinates by calculating the attitude transformation matrix of the surface of the structure under test, and outputs the displacement measurement result.

[0008] According to the specific embodiments provided in this application, the following technical effects are disclosed: This application achieves coordinate reference in complex scenes by constructing a self-contained optical reference benchmark at the near end; compensates for camera attitude disturbances using the same imaging optical path; and improves the accuracy, adaptability, and stability of zoom visual displacement measurement by normalizing and separating zoom geometry changes. It realizes direct observation and compensation of camera attitude changes on the same image plane, while also meeting the requirements of large range, high resolution, and long-term stability in zoom working mode. It is suitable for long-distance zoom visual displacement monitoring and camera attitude error compensation for bridges, tunnels, buildings, dilapidated buildings, slopes, and other engineering structures. Attached Figure Description

[0009] To more clearly illustrate the technical solutions in the embodiments of this application or related technologies, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0010] Figure 1 This is a schematic diagram of the structural connection of a zoom visual displacement measurement system based on a beam-splitting fixed-focus reference target, provided for an embodiment of this application.

[0011] Figure 2 This is a schematic diagram of the optical path structure of the beam splitting component and the reference imaging unit provided in the embodiments of this application.

[0012] Figure 3 This is a schematic diagram of a reference target structure provided for an embodiment of this application.

[0013] Figure 4 This is a schematic diagram showing the division of the reference region and the measurement point region in the synthesized image provided in the embodiments of this application.

[0014] Figure 5 This is a schematic diagram of the algorithm flow for attitude change estimation and inverse transformation compensation based on a reference target, provided in an embodiment of this application.

[0015] Figure 6 This is a schematic diagram of the measurement system after introducing temperature compensation and attitude compensation, provided in an embodiment of this application.

[0016] Figure 7 This is a schematic diagram illustrating the application of multi-point monitoring in tunnels as provided in the embodiments of this application.

[0017] Figure label: 10. Zoom imaging unit; 11. Zoom lens; 12. Image sensor; 20. Beam splitter; 30. Reference imaging unit; 31. Fixed-focus lens; 32. Reference target; 40. Measurement point target; 60. Processing unit; 70. Temperature sensing unit; 80. Inertial measurement unit. Detailed Implementation

[0018] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0019] In existing technologies, the following methods are commonly used to compensate for measurement errors caused by changes in camera attitude: 1. This method relies on fixed background features or distant reference targets in the far-field scene to estimate camera perturbation through methods such as image registration, optical flow estimation, or affine transformation, and then corrects the displacement of the measurement point. This method depends on a stable and observable far-field background or rigid benchmark, but in scenarios such as tunnels, underground spaces, inside dilapidated buildings, and concrete surfaces with simple textures, there is often a lack of long-term stable and easily identifiable background references.

[0020] 2. The camera attitude change is measured and fused with image data for compensation. Although this approach can alleviate the problem of no far-end reference to some extent, the pure inertial measurement scheme suffers from drift, noise, complex calibration, and insufficient long-term consistency, especially in low-cost embedded terminals.

[0021] 3. Deploy a dedicated reference target at a remote location to achieve differential measurement. This approach works in open environments, but in practical engineering, it is often difficult to deploy a rigid reference point at a remote location or to ensure it remains stationary for a long period, which also increases on-site construction and maintenance costs.

[0022] To make the above-mentioned objectives, features and advantages of this application more apparent and understandable, this application will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0023] Example 1, such as Figures 1-2 As shown, this embodiment provides a zoom visual displacement measurement system based on a beam splitting fixed-focus reference target. The system includes: a measurement point target 40, a beam splitting component 20, a reference imaging unit 30, a zoom imaging unit 10, and a processing unit 60.

[0024] The measuring target 40 is set on the first incident light path of the beam splitter 20; the measuring target 40 is located on the surface of the structure to be measured; the measuring target 40 is used to characterize the displacement of the surface of the structure to be measured and form a target image; the measuring target 40 includes multiple measuring points.

[0025] Optionally, the marking form of the measuring point target 40 includes at least one of the following: high reflectivity markers, coded targets, point targets, and area targets.

[0026] In practical applications, such as Figure 7 As shown, the arrangement of multiple measuring points enables synchronous displacement monitoring at multiple points. For example, in a tunnel monitoring scenario, multiple measuring points can be arranged along the tunnel cross-section outline, arch crown, arch waist, or sidewalls to represent convergence deformation, arch crown settlement, or local displacement changes.

[0027] The reference imaging unit 30 is disposed in the second incident light path of the beam splitter 20; the reference imaging unit 30 is used as a near-end optical reference reference to form a reference reference feature point image.

[0028] The zoom imaging unit 10 is disposed in the output light path of the beam splitter 20; the zoom imaging unit 10 is rigidly connected to the reference imaging unit 30.

[0029] Optionally, the rigid connection can be achieved through a bracket or an integral structure.

[0030] In practical applications, when the system as a whole undergoes translation, pitch, yaw, roll, or attitude changes caused by temperature or micro-vibrations, both the reference feature point image in the reference region and the target image in the measurement point region will be affected accordingly. By utilizing the geometric changes of the reference feature points in the reference region, common disturbances can be explicitly estimated, and compensation can be achieved by applying an inverse two-dimensional geometric transformation matrix to the coordinates of the measurement point image.

[0031] The processing unit 60 is electrically connected to the zoom imaging unit 10.

[0032] The light rays from the target image and the reference feature point image are combined by the beam splitter 20 to obtain a composite image. The composite image is zoomed by the zoom imaging unit 10 and converted from an optical signal to an electrical signal before being transmitted to the processing unit 60. The processing unit 60 performs scale normalization on the composite image according to the current focal length of the zoom imaging unit 10, obtains the compensated coordinates of the measurement point image by calculating the attitude transformation matrix of the surface of the structure to be measured, and outputs the displacement measurement result. The composite image includes: non-overlapping measurement point areas and reference areas.

[0033] In practical applications, the processing unit 60 extracts the image coordinates of multiple measuring point targets 40 in parallel from each frame of the synthesized image, and applies the inverse transformation of the two-dimensional geometric transformation matrix to the image coordinates of each measuring point to obtain the compensated displacement results of multiple measuring points. Subsequently, the processing unit 60 can upload the displacement time history, statistical characteristics, and early warning parameters of multiple measuring points to a host computer, cloud platform, or monitoring center via wired or wireless communication to achieve long-term tracking and anomaly early warning of the tunnel structure deformation state.

[0034] Furthermore, the reference imaging unit 30 specifically includes: a fixed-focus lens 31 and a reference target 32; both the fixed-focus lens 31 and the reference target 32 ​​are located on the second incident light path of the beam splitter 20; the fixed-focus lens 31 is disposed between the reference target 32 ​​and the beam splitter 20; the reference target 32 ​​is disposed on the object-side focal plane of the fixed-focus lens 31.

[0035] Optionally, the reference target 32 ​​is positioned on the object-side focal plane of the fixed-focus lens 31, which enables the light rays emitted from the reference target 32 ​​through the fixed-focus lens 31 to be parallel beams.

[0036] Optionally, the reference target 32 ​​can be configured as a reflector or mask containing multiple highly reflective reference feature points.

[0037] Furthermore, such as Figure 3 As shown, the reference target 32 ​​includes at least: n highly reflective reference feature points, where n is greater than or equal to 4; the n highly reflective reference feature points are distributed asymmetrically in the corner and / or edge regions of the synthetic image (to form a larger geometric baseline).

[0038] Optional, such as Figure 4 As shown, the reference target 32 ​​adopts a four-corner reference layout, that is, the four main reference feature points are arranged in an asymmetrical four-corner structure on the reference target 32, so that they fall in the vicinity of the four corners of the image after imaging. This layout is beneficial to improving the recognition capability of the two-dimensional geometric transformation matrix under different disturbance modes such as translation, pitch, yaw and roll.

[0039] Optionally, a supplementary reference light source, such as a ring-shaped narrow-band LED light source, can be placed near the reference target 32 ​​to improve the imaging brightness and recognition stability of the reference area under low-light or nighttime conditions. Combining this with highly reflective reference feature points can further improve the sub-pixel positioning accuracy of the reference points.

[0040] In practical applications, asymmetric distribution can avoid geometric symmetry ambiguity when matching feature points, and improve the uniqueness of feature recognition and the stability of transformation matrix solution.

[0041] Furthermore, the beam splitting component 20 is either a planar beam splitting prism or a polarizing beam splitting prism.

[0042] Furthermore, when the beam splitting component 20 is a polarizing beam splitter prism, at least one quarter-wave plate is provided in the second incident light path. The quarter-wave plate is used to perform polarization state conversion on the light rays of the reference reference feature point image.

[0043] Furthermore, the zoom imaging unit 10 specifically includes: a zoom lens 11 and an image sensor 12; the zoom lens 11 is disposed in the output light path of the beam splitting assembly 20; the zoom lens 11 is used to zoom the composite beam; the image sensor 12 is disposed in the output light path of the zoom lens 11; the image sensor 12 is electrically connected to the processing unit 60; the image sensor 12 is used to convert the zoomed composite beam from an optical signal into an electrical signal and transmit it to the processing unit 60.

[0044] Optionally, the image sensor 12 is a CMOS sensor.

[0045] Furthermore, such as Figure 6 As shown, the system also includes an inertial measurement unit 80; the inertial measurement unit 80 is disposed on the image sensor 12, and the inertial measurement unit 80 is used to perform pose measurement on the image sensor 12, obtain the body pose parameters, and transmit the body pose parameters to the processing unit 60 to provide pose compensation for the processing unit 60 when calculating the displacement measurement results.

[0046] Optionally, the inertial measurement unit 80 is used to output preliminary estimates of angular velocity, acceleration, or attitude change. The processing unit 60 can fuse the attitude change estimate output by the inertial measurement unit 80 with the attitude change estimate obtained based on the changes in the reference feature point image to correct the two-dimensional geometric transformation matrix or further compensate the coordinates of the measurement point image.

[0047] Optionally, the information output by the inertial measurement unit 80 can be used as prior information for solving the two-dimensional geometric transformation matrix, or it can be used to further correct the coordinate compensation results of the measurement point image after the solution is completed.

[0048] Furthermore, such as Figure 6 As shown, the system also includes: a temperature sensing unit 70; the temperature sensing unit 70 is disposed at the position of the beam splitting component 20 and / or the reference imaging unit 30; the temperature sensing unit 70 is electrically connected to the processing unit 60; the temperature sensing unit 70 is used to acquire temperature data and transmit the temperature data to the processing unit 60, so as to provide temperature compensation for the processing unit 60 when calculating the displacement measurement results.

[0049] Optionally, the temperature sensing unit 70 is used to acquire temperature information near the optical components and mechanical support structure. The temperature sensing unit 70 can be a digital temperature sensor, a thermistor, or other temperature sensing element suitable for embedded devices. During factory calibration or laboratory calibration, reference image coordinates of reference feature points can be acquired at multiple temperature points, and a compensation relationship between the temperature and the drift of the reference coordinates can be established. The compensation relationship can be implemented using linear fitting, polynomial fitting, piecewise models, or lookup table interpolation.

[0050] In actual operation, the processing unit 60 performs temperature compensation on the reference image coordinates of the reference feature points under the calibration reference state based on the current temperature value output by the temperature sensing unit 70 before performing scale normalization, and then performs the two-dimensional geometric transformation matrix solution step to reduce the slow zero-point drift caused by thermal expansion and contraction.

[0051] Example 2: This example also provides a zoom visual displacement measurement method based on a beam-splitting fixed-focus reference target. This method is applied to the above-described zoom visual displacement measurement system based on a beam-splitting fixed-focus reference target. The method includes: S1. The beam splitter 20 transmits the target image light incident on the measuring target 40 through the first incident optical path and reflects the reference reference feature point image light incident on the reference imaging unit 30 through the second incident optical path, and then combines the beams to form a composite image.

[0052] S2. Zoom lens 11 zooms the field of view of the composite image to obtain the zoomed composite image.

[0053] S3. The image sensor 12 converts the zoomed composite image from light signals into electrical signals and transmits them to the processing unit 60.

[0054] S4. The processing unit 60 performs scale normalization on the synthesized image based on the current focal length of the zoom imaging unit 10, obtains the compensated measurement point image coordinates by calculating the attitude transformation matrix of the surface of the structure to be measured, and outputs the displacement measurement result.

[0055] Furthermore, such as Figure 5 As shown, step S4 specifically includes: S41. Processing unit 60 extracts the coordinates of all measurement points in the measurement point region of the composite image.

[0056] S42. Based on the current focal length of the zoom imaging unit 10, the coordinates of all measuring points are scaled to obtain the normalized coordinates of all measuring points.

[0057] In practical applications, scale normalization is used to separate deterministic geometric changes caused by zoom.

[0058] Optionally, the current focal length can be adjusted according to the monitoring distance, target size, and resolution requirements.

[0059] S43. Based on the normalized coordinates of the measurement points and the coordinates of the reference feature points in the reference area, obtain the two-dimensional geometric transformation matrix; the two-dimensional geometric transformation matrix is ​​used to characterize the current attitude change of the structure under test.

[0060] S44. Perform an inverse transformation on the two-dimensional geometric transformation matrix to obtain the compensated coordinates of the measurement point image.

[0061] In practical applications, inverse transformation of the two-dimensional geometric transformation matrix can achieve synchronous displacement compensation and monitoring of multiple measurement points.

[0062] S45. Calculate and output the displacement measurement results of the structure under test based on the compensated coordinates of the measuring point image.

[0063] In practical applications, the actual operation of step S4 is as follows: 1) Acquire the composite image; the composite image is formed as follows: the parallel reference beam emitted from the reference target 32 ​​in the reference imaging unit 30 through the fixed-focus lens 31 and the reflected beam from the measuring point target 40 on the surface of the structure to be measured are combined by the beam splitting component 20 set on the light-incident side of the zoom lens 11 and imaged onto the same image sensor 12 by the zoom lens 11; the reference imaging unit 30 and the zoom lens 11 are rigidly connected; the images of the measuring point target 40 and the reference target 32 ​​in the composite image form non-overlapping measuring point areas and reference areas, respectively.

[0064] 2) Extract the current image coordinates of multiple reference feature points within the reference region. Reference feature point extraction can employ threshold segmentation, connected component analysis, corner detection, centroid calculation, 2D fitting, or other sub-pixel localization methods.

[0065] 3) Based on the current focal length parameter of the zoom lens 11, scale normalize the current image coordinates to separate the deterministic geometric changes caused by zooming. The focal length parameter can be derived from the zoom drive encoding value, lens internal parameters, or a pre-calibrated correspondence.

[0066] Let the calibration reference focal length be Current focal length is Scaling ratio Then the coordinates of the reference feature point after scale normalization can be expressed as: .

[0067] The correspondence between focal length parameters and scale normalization coefficients can be established using lookup tables, linear fitting, polynomial fitting, or piecewise fitting.

[0068] 4) Compare the normalized current image coordinates with the reference image coordinates of the reference feature points under the calibration reference state to obtain the two-dimensional geometric transformation matrix representing the attitude change of the zoom imaging unit 10. The two-dimensional geometric transformation matrix can be a two-dimensional affine transformation matrix or a two-dimensional perspective transformation matrix.

[0069] 5) Apply the inverse transformation of the two-dimensional geometric transformation matrix to the image coordinates of the target 40 in the measurement area to obtain the compensated image coordinates of the measurement point.

[0070] 6) Output the displacement measurement results based on the compensated measurement point image coordinates. The compensated measurement point image coordinates can be compared with the measurement point reference coordinates under the calibration reference state, and then combined with the current focal length, imaging ratio, or geometric calibration relationship to convert the pixel displacement into a physical displacement.

[0071] Furthermore, before scale normalization, temperature compensation can be performed on the reference image coordinates of the reference feature points under the calibration reference state based on the temperature data collected by the temperature sensing unit 70. Temperature compensation can be implemented using a lookup table method, a linear model, a polynomial model, or a piecewise fitting model. Let the temperature drift of the reference image coordinates of the reference feature points be... The change in ambient temperature is A linear compensation model is adopted: .

[0072] Where α is the pre-calibrated temperature drift coefficient. During compensation, the coordinates of the reference feature point in the baseline image are first corrected based on the current temperature value, and then scale normalization and two-dimensional geometric transformation matrix solving steps are performed.

[0073] The attitude change estimate obtained based on the reference feature points can also be fused with the attitude change estimate output by the inertial measurement unit 80 to improve the robustness of the compensation results under high-frequency vibration conditions.

[0074] The technical effects of this application are as follows: 1. Constructing a near-end self-contained optical reference benchmark enhances usability in complex scenes. This application constructs an optical reference benchmark at the near end of the camera that changes synchronously with the camera body through a rigid connection between the reference imaging unit and the zoom imaging unit. A beam splitter is then used to combine the reference optical path and the measurement point optical path onto the same image sensor for imaging. Compared to schemes that rely on distant background features or fixed targets at a distance, this application can still provide stable and observable reference information in environments lacking a stable, rigid distant background, such as tunnels, underground spaces, dilapidated buildings, or environments with monotonous textures, thereby improving the system's applicability.

[0075] 2. Achieving explicit estimation and compensation of attitude changes under the same imaging link and the same image sensor. In this application, the reference target and the measurement target enter the same image sensor through the same zoom imaging link, and both are affected by camera attitude disturbances. By extracting reference feature points within the reference region and obtaining the two-dimensional geometric transformation matrix relative to the calibration reference state, and then applying inverse transformation compensation to the image coordinates of the measurement target within the measurement region, the common disturbances introduced by camera attitude changes can be explicitly separated within the image plane, thereby improving the accuracy of displacement measurement.

[0076] 3. Separating deterministic geometric changes during zooming through scale normalization to adapt to zoom working modes. This application performs scale normalization on the image coordinates of reference feature points based on the current focal length parameters, separating the deterministic geometric changes caused by zooming from the attitude change estimation. Therefore, this application can maintain the consistency and interpretability of the attitude compensation process under varying focal lengths of zoom lenses, making it more suitable for applications involving large-scale zoom and long-distance monitoring.

[0077] 4. Parallel reference optical paths are beneficial for improving reference imaging stability. By setting the reference target on the object-side focal plane of the fixed-focus lens, the reference rays enter the beam splitter and zoom lens in a parallel manner. This facilitates the establishment of stable and calibrable reference imaging relationships at different working focal lengths, providing a basis for subsequent scale normalization and geometric compensation.

[0078] 5. It is compatible with multiple preferred enhancement schemes to improve system robustness. This application can further combine asymmetric high-reflectivity reference feature point layout to improve the stability of reference point extraction and two-dimensional geometric transformation matrix solution; it can further adopt a combination of polarization beam splitter prism and quarter-wave plate; and it can also combine temperature compensation and inertial measurement unit fusion to improve compensation performance under long-term operation and high-frequency vibration conditions.

[0079] 6. Supports single-point or multi-point synchronous displacement measurement, facilitating engineering application. This application is applicable to both high-precision displacement measurement at a single measuring point and synchronous compensation and monitoring of multiple measuring points, making it suitable for expanded applications in bridge, tunnel, building, and other structural monitoring scenarios, and possessing significant engineering practical value.

[0080] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

[0081] This document uses specific examples to illustrate the principles and implementation methods of this application. The descriptions of the above embodiments are only for the purpose of helping to understand the methods and core ideas of this application. Furthermore, those skilled in the art will recognize that, based on the ideas of this application, there will be changes in the specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of this application.

Claims

1. A zoom visual displacement measurement system based on a beam-splitting fixed-focus reference target, characterized in that, The system includes: a measurement target, a beam splitting component, a reference imaging unit, a zoom imaging unit, and a processing unit; The measuring point target is disposed on the first incident light path of the beam splitter; the measuring point target is located on the surface of the structure to be measured; the measuring point target is used to characterize the surface displacement of the structure to be measured and constitute a target image; the measuring point target includes multiple measuring points. The reference imaging unit is disposed on the second incident light path of the beam splitter; the reference imaging unit is used as a near-end optical reference reference to form a reference reference feature point image. The zoom imaging unit is disposed in the output light path of the beam splitter; the zoom imaging unit is rigidly connected to the reference imaging unit; The processing unit is electrically connected to the zoom imaging unit; The light rays from the target image and the reference feature point image are combined by the beam splitter to obtain a composite image. The composite image is zoomed by the zoom imaging unit and converted from an optical signal to an electrical signal before being transmitted to the processing unit. The processing unit performs scale normalization on the composite image according to the current focal length of the zoom imaging unit, obtains the compensated coordinates of the measurement point image by calculating the attitude transformation matrix of the surface of the structure under test, and outputs the displacement measurement result. The composite image includes non-overlapping measurement point regions and a reference region.

2. The zoom visual displacement measurement system based on a beam-splitting fixed-focus reference target according to claim 1, characterized in that, The reference imaging unit specifically includes: a fixed-focus lens and a reference target; The fixed-focus lens and the reference target are both located on the second incident light path of the beam splitter; the fixed-focus lens is disposed between the reference target and the beam splitter; the reference target is disposed on the object-side focal plane of the fixed-focus lens.

3. The zoom visual displacement measurement system based on a beam-splitting fixed-focus reference target according to claim 2, characterized in that, The reference target includes at least n highly reflective reference feature points, where n is greater than or equal to 4; the n highly reflective reference feature points are distributed asymmetrically in the corner and / or edge regions of the synthesized image.

4. The zoom visual displacement measurement system based on a beam-splitting fixed-focus reference target according to claim 1, characterized in that, The beam splitting component is either a planar beam splitting prism or a polarizing beam splitting prism.

5. The zoom visual displacement measurement system based on a beam-splitting fixed-focus reference target according to claim 3, characterized in that, When the beam splitting component is a polarizing beam splitter prism, at least one quarter-wave plate is provided in the second incident light path. The quarter-wave plate is used to perform polarization state conversion on the light rays of the reference feature point image.

6. The zoom visual displacement measurement system based on a beam-splitting fixed-focus reference target according to claim 1, characterized in that, The zoom imaging unit specifically includes: a zoom lens and an image sensor; The zoom lens is disposed in the output light path of the beam splitter; the zoom lens is used to zoom the composite beam. The image sensor is disposed in the output light path of the zoom lens; the image sensor is electrically connected to the processing unit; the image sensor is used to convert the zoomed composite beam from an optical signal into an electrical signal and transmit it to the processing unit.

7. The zoom visual displacement measurement system based on a beam-splitting fixed-focus reference target according to claim 6, characterized in that, The system further includes an inertial measurement unit; the inertial measurement unit is disposed on the image sensor, and the inertial measurement unit is used to perform pose measurement on the image sensor to obtain body pose parameters, and transmit the body pose parameters to the processing unit to provide pose compensation for the processing unit when calculating the displacement measurement results.

8. The zoom visual displacement measurement system based on a beam-splitting fixed-focus reference target according to claim 1, characterized in that, The system further includes: a temperature sensing unit; the temperature sensing unit is disposed at the position of the beam splitting component and / or the reference imaging unit; the temperature sensing unit is electrically connected to the processing unit; the temperature sensing unit is used to acquire temperature data and transmit the temperature data to the processing unit to provide temperature compensation for the processing unit when calculating displacement measurement results.

9. A method for measuring zoom visual displacement based on a beam-splitting fixed-focus reference target, wherein the method is applied to the zoom visual displacement measurement system based on a beam-splitting fixed-focus reference target as described in any one of claims 1-8, characterized in that... The method includes: The beam splitter transmits the target image light incident on the target at the measurement point through the first incident optical path and reflects the reference reference feature point image light incident on the reference imaging unit through the second incident optical path. The beams are then combined to form a composite image. The zoom lens zooms the field of view of the composite image to obtain the zoomed composite image; The image sensor converts the zoomed composite image from light signals into electrical signals and transmits them to the processing unit; The processing unit performs scale normalization on the synthesized image based on the current focal length of the zoom imaging unit, obtains the compensated coordinates of the measurement point image by calculating the attitude transformation matrix of the surface of the structure to be measured, and outputs the displacement measurement result.

10. The zoom visual displacement measurement method based on a beam-splitting fixed-focus reference target according to claim 9, characterized in that, The processing unit performs scale normalization on the synthesized image based on the current focal length of the zoom imaging unit, obtains the compensated coordinates of the measurement point image by calculating the attitude transformation matrix of the surface of the structure under test, and outputs the displacement measurement result, specifically including: The processing unit extracts the coordinates of all measurement points in the measurement point region of the synthesized image; Based on the current focal length of the zoom imaging unit, the coordinates of all measuring points are scaled and normalized to obtain the normalized coordinates of all measuring points. Based on the normalized coordinates of the measurement points and the coordinates of the reference feature points in the reference area, a two-dimensional geometric transformation matrix is ​​obtained; the two-dimensional geometric transformation matrix is ​​used to characterize the current attitude change of the structure under test. Perform an inverse transformation on the two-dimensional geometric transformation matrix to obtain the compensated coordinates of the measurement point image; The displacement measurement results of the structure under test are calculated and output based on the compensated coordinates of the measuring point images.

Images