Three-dimensional stress ball sensor and monitoring method

Abstract

The invention discloses a three-dimensional stress ball sensor and a monitoring method, the three-dimensional stress ball sensor comprises a ball body, a central light source, a photosensitive unit and a signal processing unit, the ball body can be elastically deformed and is made of an optical transparent or semitransparent material; the light source can emit light to the periphery and penetrate through the ball body; the light-sensitive units are used for receiving light rays which come from the central light source and penetrate through the ball body and converting the intensity of the light rays into measurable electric signals, and the multiple light-sensitive units are evenly distributed on the surface of the ball body or evenly embedded into preset positions, close to the surface, in the ball body; the signal processing unit is used for collecting signals of the photosensitive unit, processing and calculating the signals, and finally outputting three-dimensional stress information. The complete three-dimensional stress state at the measuring point can be independently and accurately measured, and the measuring result does not depend on the specific spatial orientation relative to the main stress direction when the sensor is installed.

Description

Technical Field

[0001] The present invention relates to the technical field of engineering measurement, and in particular to a three-dimensional stress ball sensor and a monitoring method. Background Art

[0002] Accurately obtaining information on the stress state within geotechnical structures is crucial for geotechnical engineering monitoring, geological exploration, and related structural safety assessments. Currently, a widely used sensor in this field is the vibrating wire earth pressure cell. While this sensor is mature and widely used, its primary function is to measure pressure in the direction normal to the sensor's mounting plane—in other words, unidirectional stress or normal stress. It cannot independently provide complete information on the stress state at the measurement point.

[0003] To overcome the limitations of unidirectional measurements and obtain more comprehensive stress data, one attempt has emerged in the art: combining multiple (usually six) traditional unidirectional earth pressure cells in specific spatial orientations to create a combined measurement device, sometimes referred to as a "true 3D earth pressure cell." This device is designed to infer the 3D stress state at the measuring point by measuring pressure components in three mutually perpendicular directions.

[0004] However, this combined "true 3D earth pressure cell" has an inherent and difficult-to-overcome flaw: the accuracy of its measurement results is highly dependent on the device's installation orientation. Only when its three measurement directions exactly align with the three actual principal stress directions at the measuring point can the measurement results accurately reflect the magnitude of the principal stresses. In actual geotechnical engineering sites, the principal stress directions of the in-situ stresses are often unknown, complex, and subject to change over time and with operating conditions. Therefore, accurately predicting and aligning the principal stress directions during installation is virtually impossible. If the installation orientation deviates from the actual principal stress directions, the measurement data will incur significant errors and will fail to truly reflect the 3D stress state of the measuring point.

[0005] Given this, combined earth pressure measurement devices, which rely on a specific installation orientation and require extremely high installation accuracy, cannot reliably and accurately measure the true three-dimensional stress state at any point in practical applications. Therefore, there is an urgent need to develop a new sensor that can overcome the shortcomings of existing technologies and accurately measure the complete three-dimensional stress state at any point within the rock and soil mass without relying on a specific installation orientation. Summary of the Invention

[0006] In order to solve the above technical problems, the present invention provides a three-dimensional stress sphere sensor that can independently and accurately measure the complete three-dimensional stress state at the measuring point, and its measurement results are independent of the specific spatial orientation of the sensor relative to the main stress direction when it is installed.

[0007] In order to achieve the above object, the present invention adopts the following technical solutions: A three-dimensional stress ball sensor includes a sphere, a central light source, a photosensitive unit and a signal processing unit. The sphere is elastically deformable and is made of an optically transparent or translucent material; The light source can emit light in all directions and penetrate the sphere; The photosensitive unit is used to receive light from the central light source after passing through the sphere and convert its intensity into a measurable electrical signal. The photosensitive unit is multiple and evenly distributed on the surface of the sphere or evenly embedded in predetermined positions near the surface of the sphere. The signal processing unit is used to collect the signal of the photosensitive unit, process and calculate it, and finally output three-dimensional stress information.

[0008] Preferably, the optically transparent or translucent material is a mixture of one or more of silicone, polyurethane elastomer and engineering plastic.

[0009] Preferably, the central light source is one or more light emitting diodes.

[0010] Preferably, the photosensitive unit is a photodiode or a phototransistor.

[0011] Preferably, the signal processing unit is located inside the sphere or on the surface of the sphere or is connected to the outside of the sphere via a lead.

[0012] A monitoring method for a three-dimensional stress ball sensor comprises the following steps: S1 measures the stress-strain relationship of the sphere; S2 When the three-dimensional stress ball sensor is not under stress or is under a known reference stress state, start the central light source, measure and record the initial light intensity value received by all photosensitive units as I 0,i , where i is the photosensitive unit number, and these initial light intensity values ​​constitute the benchmark data set; S3 When the sphere is deformed by force, the real-time light intensity value received by all photosensitive units is measured again and recorded as I t,i ; S4 calculates the light intensity change or change rate of each photosensitive unit to obtain a distribution map reflecting the light intensity change on the entire sphere surface; S5 Construct a mathematical model of the relationship between the overall three-dimensional deformation field and the distribution of light intensity changes; S6: The sensor is installed in the environment to be tested, and the signal processing unit collects the real-time light intensity value of each photosensitive unit periodically or according to instructions; S7: Input the light intensity value measured in step S6 into the mathematical model constructed in step S4 to invert the overall three-dimensional deformation field of the sphere; S8 calculates the external three-dimensional stress state that causes the deformation based on the overall three-dimensional deformation field obtained by inversion in step S7 and using the stress-strain relationship of the sphere measured in S1.

[0013] Compared with existing technologies, this invention offers the following technical advantages: it can independently and accurately measure the complete three-dimensional stress state at a measuring point, and its measurement results are independent of the specific spatial orientation of the sensor relative to the principal stress direction. The sensor, which is insensitive to installation posture and can accurately reflect the three-dimensional stress information at any point within the rock or soil mass, significantly improves the accuracy, reliability, and practicality of stress measurement in geotechnical engineering and simplifies on-site installation requirements. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for describing the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be derived from these drawings without inventive effort. Among them: Figure 1 It is a structural schematic diagram of the present invention; Figure 2 : Schematic diagram of the deformation of a sphere under the action of external non-uniform stress, where the solid line is the undeformed outline and the dotted line is the deformed outline; Sphere 1, central light source 2, multiple photosensitive units 3, signal processing unit 4. DETAILED DESCRIPTION

[0015] In order to make the above-mentioned objects, features and advantages of the present invention more clearly understood, the specific embodiments of the present invention are described in detail below in conjunction with the accompanying drawings. In the following description, many specific details are set forth to facilitate a full understanding of the present invention. However, the present invention may also be implemented in other ways different from the description. Those skilled in the art may make similar generalizations without violating the connotation of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0016] Secondly, the term "one embodiment" or "embodiment" herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in various places throughout this specification does not necessarily refer to the same embodiment, nor does it refer to a separate or selective embodiment that is mutually exclusive of other embodiments.

[0017] A three-dimensional stress sphere sensor of the present invention mainly comprises: a sphere 1, a central light source 2, a plurality of photosensitive units 3 distributed on the surface of the sphere, and a signal processing unit 4.

[0018] Sphere 1: Sphere 1 is made of an optically transparent or translucent material with good elastic deformation, such as silicone, polyurethane elastomer, or specific engineering plastics. Sphere 1 deforms when subjected to pressure from the external environment (e.g., rock or soil). The optical properties of the material (e.g., refractive index, absorption coefficient) change predictably under stress.

[0019] Central Light Source 2: Central Light Source 2 is one or more light-emitting diodes (LEDs) or other miniaturized light sources, fixed at the geometric center of sphere 1. This light source 2 emits light in all directions and penetrates sphere 1. Central Light Source 2 can emit light of a specific wavelength and stable intensity.

[0020] Photosensitive units 3: Photosensitive units 3 are multiple (e.g., dozens to hundreds) photodiodes, phototransistors, or other light-sensing devices. They are precisely fixed to the surface of sphere 1 in a nearly uniform grid or a specifically optimized array, or embedded within sphere 1 at a predetermined location near the surface. Each photosensitive unit 3 is used to receive light from central light source 2 after it passes through the sphere material and convert its intensity into a measurable electrical signal (e.g., voltage or current).

[0021] Signal processing unit 4: The signal processing unit 4 is used to collect the signals from all photosensitive units 3, process and calculate them, and ultimately output three-dimensional stress information. This unit can be located inside the sensor or connected to the outside via leads.

[0022] Working principle and measurement process The operating principle of the present invention is that when the sensor sphere 1 is subjected to three-dimensional stress from the external environment, it undergoes global and local deformation. This deformation changes the light propagation path from the central light source 2 to each photosensitive element 3 and / or the optical properties of the propagation medium (the sphere's material), resulting in changes in the light intensity received by each photosensitive element 3. By precisely measuring these light intensity changes through the signal processing unit 4 and combining them with a pre-calibrated model or algorithm, the 3D stress state of the sphere can be inferred.

[0023] The monitoring process of a three-dimensional stress ball sensor is as follows: Step S1: measuring the stress-strain relationship (such as elastic modulus, Poisson's ratio, etc.) of the sphere.

[0024] Step S2: When the sensor is not under stress or is in a known reference stress state (such as hydrostatic pressure), start the central light source 2, measure and record the initial light intensity value (I 0，i , where i is the photosensitive unit number). These light intensity values ​​constitute the benchmark dataset.

[0025] Step S3: When the sphere 1 is deformed by force, the real-time light intensity values ​​received by all photosensitive units 3 are measured again (I t,i ).

[0026] Step S4: Calculate the light intensity variation (ΔI i = I t,i - I 0,i ) or rate of change (ΔI i / I 0,i ). A distribution map reflecting the changes in light intensity on the entire sphere surface is obtained.

[0027] Possible causes of light intensity variations include: 1. Changes in optical path length: the linear distance between the central light source 2 and certain photosensitive elements 3 changes. 2. Changes in material density / refractive index: compression or stretching of the spherical material can cause local density changes, potentially altering the refractive index and affecting the light propagation path and speed. 3. Changes in absorption / scattering: deformation of the material can alter the absorption or scattering characteristics of light during propagation. 4. Changes in relative position: the relative angular relationship between the light source and a specific sensor can change, affecting reception efficiency.

[0028] Step S5: Constructing a mathematical model of the relationship between the overall three-dimensional deformation field and the light intensity variation distribution.

[0029] Step S6: The sensor is installed in the environment to be tested (such as buried in the soil), and the signal processing unit collects the real-time light intensity value of each photosensitive unit periodically or according to instructions.

[0030] Step S7: Input the light intensity value measured in step S6 into the mathematical model constructed in step S4, and calculate the light intensity change (ΔI i The sphere's overall three-dimensional deformation field (strain field) is then inverted using a collection of inverted images. This step draws on the concept of computed tomography (CT), treating changes in light intensity as projection data and using specific reconstruction algorithms (such as finite element analysis-based optical-mechanical coupling model inversion or machine learning models) to determine the internal strain distribution.

[0031] S8 calculates the external three-dimensional stress state that causes the deformation based on the global three-dimensional deformation field obtained by inversion in step S7 and the stress-strain relationship of the sphere measured in step S1. This involves solving an inverse problem of mechanical equilibrium, and ultimately the average stress tensor acting on the sphere can be obtained, or the magnitude and direction of the three principal stresses can be calculated. Output the calculated three-dimensional stress information (for example, σ x , σ y , σz, τ xy , τ yz , τ zxsix stress components, or three principal stresses P1, P2, P3 and their directions).

[0032] The core advantage of this technical solution lies in that, regardless of the initial orientation of the sensor during installation, as long as the sphere deforms due to external stress, the changes in the internal light field distribution can be fully captured. By analyzing the changing pattern of the entire light field, rather than relying on a single measurement value in a specific direction, the complete three-dimensional stress state at the measurement point can be decoupled and calculated, thus overcoming the strict dependence of existing modular earth pressure cells on installation orientation. Example

[0033] like Figure 1 As shown in this embodiment, a three-dimensional stress sphere sensor is provided, wherein the sphere 1 is injection-molded from a transparent silicone material with a diameter of 50 mm. The silicone material has good elasticity (elastic modulus of approximately 0.5 MPa, Poisson's ratio of approximately 0.48) and light transmittance (visible light transmittance >90%).

[0034] At the geometric center of sphere 1, a high-brightness white light LED is suspended and fixed via a thin, low-optical-absorption support structure (e.g., a thin fluoroplastic wire, not shown in detail in the figure) as central light source 2. The LED is connected to an external power supply and control circuit via leads.

[0035] Sphere 1 has 64 micro-silicon photodiodes evenly spaced and attached to its surface, serving as photosensitive elements 3. These photodiodes are integrated onto a flexible printed circuit board (FPC) designed to conform to the curved surface of the sphere's outer wall. Each photodiode has a photosensitive area of ​​approximately 1 mm². The signal outputs from all photodiodes are combined via fine wires on the FPC and routed through a sealed channel within sphere 1 via a flexible flat cable (FFC) to the outside of the sensor, where they are connected to a signal processing unit 4.

[0036] Signal processing unit 4 consists of a multi-channel data acquisition card (including an amplifier and an analog-to-digital converter (ADC)) and a microprocessor. The data acquisition card is responsible for synchronously collecting the analog photocurrent signals output by all 64 photodiodes, amplifying them, and converting them into digital signals. The microprocessor is responsible for subsequent data processing and executing the stress reconstruction algorithm.

[0037] Usage example: 1. Pre-calibration and model building: The sensor is loaded and calibrated under laboratory conditions. For example, it is placed in a triaxial pressure chamber and subjected to a series of known uniform confining pressures and deviatoric stresses of different directions and magnitudes. The light intensity readings of 64 photosensitive cells3 are recorded under each stress state. Using this data, a precise mathematical model is established through machine learning methods (such as neural networks) or inversion algorithms based on finite element models. The model can predict the light intensity change (ΔI) based on a set of light intensity change values ​​(ΔI i ) to inversely calculate the three-dimensional stress state (e.g., six independent stress components or three principal stresses and their directions) applied to the sphere. The model is stored in the microprocessor of the signal processing unit 4.

[0038] 2. On-site installation and benchmark acquisition: The three-dimensional stress ball sensor is buried at the designated measuring point inside the rock and soil body to be monitored. After the installation position is stable, the central light source 2 is powered on and the initial light intensity readings (I 0,i ), as the benchmark for the initial stress state (or reference zero) of the measuring point.

[0039] 3. Stress monitoring: During the monitoring period (e.g., due to excavation, loading or environmental changes causing the stress of the soil to change), the sphere 1 is subjected to the new stress and deforms (e.g. Figure 2 At this time, the signal processing unit collects the real-time light intensity readings of each photosensitive unit 3 periodically or according to instructions (I t,i The microprocessor calculates the light intensity change ΔI for each channel. i = I t,i - I 0,i These 64 light intensity variations are then fed into a pre-established mathematical model for calculation. The model output is the three-dimensional stress state information at the current measurement point, for example, given as the magnitudes of the three principal stresses P1, P2, and P3 in the sensor's own coordinate system and their direction cosines relative to the sensor's coordinate axes.

[0040] Because the sensor infers stress by analyzing the overall pattern of changes in the light field caused by the deformation of the entire sphere, rather than relying on measurements in a specific direction, regardless of the spatial orientation of the sensor sphere during initial installation (even if the user cannot predict or align the principal directions of the in-situ stress), as long as it is fully embedded in the deforming medium, the 3D stress output (principal stress magnitude and orientation relative to the sensor itself) objectively reflects the true stress state at the measurement point. Coordinate transformations can also be used to obtain stress components in the geodetic coordinate system or other reference coordinate systems.

[0041] This embodiment successfully demonstrates a three-dimensional stress ball sensor and its working method, which can accurately measure the three-dimensional stress state of any point without being aligned with the main stress direction, overcomes the shortcomings of the existing technology, and improves the accuracy and convenience of measurement.

[0042] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present invention, which should all be included in the scope of the claims of the present invention.

Claims

1. A three-dimensional stress ball sensor, characterized in that: Including sphere, central light source, photosensitive unit and signal processing unit, The sphere is elastically deformable and is made of an optically transparent or translucent material; The light source can emit light in all directions and penetrate the sphere; The photosensitive unit is used to receive light from the central light source after passing through the sphere and convert its intensity into a measurable electrical signal. The photosensitive unit is multiple and evenly distributed on the surface of the sphere or evenly embedded in predetermined positions near the surface of the sphere. The signal processing unit is used to collect the signal of the photosensitive unit, process and calculate it, and finally output three-dimensional stress information.

2. A three-dimensional stress ball sensor according to claim 1, characterized in that: The optically transparent or translucent material is a mixture of one or more of silicone, polyurethane elastomer and engineering plastic.

3. The three-dimensional stress ball sensor according to claim 1, characterized in that: The central light source is one or more light emitting diodes.

4. The three-dimensional stress ball sensor according to claim 1, characterized in that: The photosensitive unit is a photodiode or a phototransistor.

5. The three-dimensional stress ball sensor according to claim 1, characterized in that: The signal processing unit is located inside the sphere or on the surface of the sphere or is connected to the outside of the sphere through a lead.

6. A monitoring method for a three-dimensional stress ball sensor according to any one of claims 1 to 5, characterized in that: The following steps are involved: S1 measures the stress-strain relationship of the sphere; S2 When the three-dimensional stress ball sensor is not under stress or is under a known reference stress state, start the central light source, measure and record the initial light intensity value received by all photosensitive units as I 0,i , where i is the photosensitive unit number, and these initial light intensity values ​​constitute the benchmark data set; S3 When the sphere is deformed by force, the real-time light intensity value received by all photosensitive units is measured again and recorded as I t,i ; S4 calculates the light intensity change or change rate of each photosensitive unit to obtain a distribution map reflecting the light intensity change on the entire sphere surface; S5 Construct a mathematical model of the relationship between the overall three-dimensional deformation field and the distribution of light intensity changes; S6: The sensor is installed in the environment to be tested, and the signal processing unit collects the real-time light intensity value of each photosensitive unit periodically or according to instructions; S7: Input the light intensity value measured in step S6 into the mathematical model constructed in step S4 to invert the overall three-dimensional deformation field of the sphere; S8 calculates the external three-dimensional stress state that causes the deformation based on the overall three-dimensional deformation field obtained by inversion in step S7 and using the stress-strain relationship of the sphere measured in S1.

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