A stress monitoring device and method based on permanent magnet effect

Abstract

The application relates to a stress monitoring device and method based on a permanent magnet effect, and belongs to the technical field of bridge detection. The stress monitoring device mainly comprises a permanent magnet and a Hall sensor, the Hall sensor is fixed on a sliding block together with an AD converter and a microprocessor, and the permanent magnet is fixed on a permanent magnet supporting plate left to a right baffle of a sliding rail. When the stress change of a detected device is detected, the force-magnetic relationship is calibrated first, the detected device is installed after the calibration is completed, the lower hole of the sliding block device is tightly connected with the detected device; when the detected device is strained, the magnetic signals detected by the Hall probe at different positions on the central axis of the permanent magnet are input, output after being processed by the Hall sensor, and data is extracted by an external magnetic solution equipment, and the stress change of the detected device is fed back through the force-magnetic relationship. The stress of a stay cable, a stress bar, a steel bar and the like can be monitored through the permanent magnet, that is, the Hall sensor, the structure is simple, and the sensitivity is high.

Description

Technical Field

[0001] This invention belongs to the field of bridge inspection technology and relates to a stress monitoring device and method based on the permanent magnet effect. Background Technology

[0002] Prestressed steel strands, as the main load-bearing components in prestressed structures, primarily provide prestress and critical loads, and their stress state directly determines the overall performance of the structure. During tensioning, construction, and subsequent operation, factors such as material properties, construction conditions, and environmental conditions can lead to a series of problems, including stress loss, degradation, and uneven stress distribution, resulting in a decrease in the overall stress level of the structure. Once such conditions occur in the steel strands of a prestressed member (e.g., excessive stress loss or fracture failure), the structure may rapidly fail without warning. Therefore, to ensure the safe operation of the structure and subsequent maintenance and reinforcement management, it is necessary to monitor the stress state of the steel strands to detect problems affecting structural safety and health hazards as early as possible, and to take timely preventative and reinforcement measures to nip safety issues and adverse accidents in the bud.

[0003] Existing conventional methods for monitoring rebar stress mainly include fiber optic sensor monitoring, vibrating wire sensor monitoring, and magnetic flux sensor monitoring. Among them, fiber optic sensor monitoring, although compact in structure and highly sensitive, has disadvantages such as easy damage to optical fibers, high cost, and unsuitability for complex and harsh environments. Vibrating wire sensors have a simple, compact, stable, and reliable structure, and are easy to install and debug. However, vibrating wire sensors still have drawbacks such as short lifespan, low reliability of monitoring data, and great susceptibility to the influence of surrounding vibration factors. Magnetic flux sensors provide relatively reliable measurement results, but they require large excitation equipment and complex circuit parameter tuning. They are also susceptible to the influence of material factors (such as chemical composition, microstructure, impurities, defects, material inhomogeneity, and temperature). Summary of the Invention

[0004] In view of this, the purpose of the present invention is to provide a stress monitoring device and method for stay cables or prestressed steel strands that is simple in structure, low in cost, and highly sensitive.

[0005] To achieve the above objectives, the present invention provides the following technical solution:

[0006] A stress monitoring device based on permanent magnet effect includes a permanent magnet and a Hall effect integrated module; the Hall effect integrated module is fixed on a slider device, the slider device is mounted on a slide rail, and baffles are provided on both sides of the slide rail; the permanent magnet is fixed on a permanent magnet support plate on the left side of the baffle on the right side of the slide rail.

[0007] The movement of the slider drives the Hall integrated module to move. The Hall probe in the Hall integrated module detects the magnetic signal at different positions on the central axis of the permanent magnet. The magnetic signal is processed by the microcontroller and output to the external device. The external device calculates the stress of the device under test based on the pre-calibrated force-magnetic relationship.

[0008] The force-magnetic relationship is as follows:

[0009]

[0010] Among them, B z The vector representing the magnetic flux density of a permanent magnet is denoted by σ, where h represents the dimension of the permanent magnet in the magnetization direction, and E represents the magnetic flux density vector of the permanent magnet. P Let x, y, and z represent the stress and elastic modulus of the device under test, respectively; x, y, and z represent the three-dimensional coordinates of the measurement point or the position vectors pointing from the origin to any point in space; x0, y0, and z0 represent the integral constants of the current element vector pointing from the origin; a and b represent the length and width of the permanent magnet, respectively; and K is given by the following formula:

[0011]

[0012] In the formula, μ0 represents the free permeability, J S This represents the current density.

[0013] Preferably, the Hall integrated module includes a Hall sensor, an AD converter, and a microcontroller, wherein the Hall sensor includes a voltage regulation circuit, a differential amplifier, a temperature acquisition module, and a Hall probe;

[0014] The voltage regulation circuit is connected to the differential amplifier, AD converter, microcontroller and Hall probe respectively to provide continuous voltage output; one end of the Hall probe is placed at the central axis of the permanent magnet, and the other end is connected to the differential amplifier, the differential amplifier, AD converter and microcontroller are connected in sequence; the temperature acquisition module is connected to the microcontroller.

[0015] The Hall probe is used to acquire magnetic signals, which are then converted into electrical signals and amplified by a differential amplifier. The digital signals are then converted into digital signals by an AD converter and transmitted to a microcontroller to calculate the magnitude of the magnetic field strength. The signal output by the microcontroller is then output to an external device through a serial interface.

[0016] The temperature acquisition module is used to collect temperature data, and the microcontroller corrects the effect of temperature drift on the magnetic field strength measurement value to reduce errors.

[0017] Preferably, the lower part of the slider is provided with a spring-type hole, which is shaped like a pointed cone when closed; the lower part of the permanent magnet support plate is provided with a hole for the device under test to pass through.

[0018] Preferably, the device further includes upper and lower outer shells, the outer shells are designed to be elliptical or semi-circular, and there are two latches on the front and rear sides of each outer shell; the outer shells also have the function of shielding magnets.

[0019] Preferably, the outer shell is also designed with a sandwich layer filled with heat insulation material.

[0020] Preferably, the stress monitoring method applicable to this device is as follows: Before using the device, a force-magnetic relationship calibration is performed. After calibration, the stress monitoring device is installed on the device under test and tightly connected to the device under test through the spring-type hole at the bottom of the slider. When the device under test experiences strain, the slider moves synchronously and drives the Hall probe to move. The Hall probe inputs the detected magnetic signal at different positions on the central axis of the permanent magnet into the microcontroller. The microcontroller calculates the magnetic field strength at the corresponding position and outputs it to an external magnetic analysis device. The external device then extracts the data and feeds back the stress change of the device under test through the force-magnetic relationship.

[0021] The beneficial effects of this invention are as follows: the sensor of this invention is easy to manufacture, has a simple structure, low cost, high sensitivity, and does not require large excitation equipment. It can also be applied to the stress monitoring of stay cables, external prestressed tendons, and internal steel bars in structures.

[0022] Other advantages, objectives, and features of the invention will be set forth in part in the description which follows, and in part will be apparent to those skilled in the art from the following examination, or may be learned from practice of the invention. The objectives and other advantages of the invention can be realized and obtained through the following description. Attached Figure Description

[0023] To make the objectives, technical solutions, and advantages of the present invention clearer, the preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings, wherein:

[0024] Figure 1 The monitoring principle and internal composition of the monitoring device;

[0025] Figure 2 This is a schematic diagram of the detection circuit;

[0026] Figure 3 The monitoring mechanism is based on the permanent magnet effect;

[0027] Figure 4 This is a schematic diagram showing the monitoring device installed on the device under test.

[0028] Figure 5 This is a diagram of the internal structure of the monitoring device.

[0029] Reference numerals in the attached diagram: 1-Hall integrated module; 2-Permanent magnet; 3-Slider; 4-Slide rail; 5-Hall probe; 6-Lock. Detailed Implementation

[0030] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the illustrations provided in the following embodiments are only schematic representations of the basic concept of the present invention. Unless otherwise specified, the following embodiments and features can be combined with each other.

[0031] The accompanying drawings are for illustrative purposes only and are schematic diagrams, not actual pictures. They should not be construed as limiting the invention. To better illustrate the embodiments of the invention, some parts in the drawings may be omitted, enlarged, or reduced, and do not represent the actual product dimensions. It is understandable to those skilled in the art that some well-known structures and their descriptions may be omitted in the drawings.

[0032] In the accompanying drawings of the embodiments of the present invention, the same or similar reference numerals correspond to the same or similar components. In the description of the present invention, it should be understood that if terms such as "upper," "lower," "left," "right," "front," and "rear" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, they are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, the terms used to describe positional relationships in the drawings are only for illustrative purposes and should not be construed as limiting the present invention. For those skilled in the art, the specific meaning of the above terms can be understood according to the specific circumstances.

[0033] like Figure 1 The diagram illustrates the monitoring principle and internal components of the stress monitoring device. The device mainly comprises the following parts:

[0034] 1. The permanent magnet has three main functions in the detection device of this embodiment: first, it is responsible for providing a magnetic source for a permanent and stable magnetic field; second, it serves as a magnetic source element that reacts to changes in the magnetic field; and third, it can serve as a marker for measurement points. In the stress monitoring device, the permanent magnet is fixed on the permanent magnet support plate on the left side of the right baffle.

[0035] 2. Hall sensor, whose main function is to detect changes in magnetic signal and input them into magnetic decomposition equipment to convert them into measurable numerical signals. Finally, through the pre-calibrated force-magnetic coupling relationship, it achieves the purpose of monitoring structural stress and strain. The sensor itself has a voltage regulation circuit, operational amplifier, temperature compensator and linear Hall element.

[0036] 3. Detection circuit, such as Figure 2 As shown, the voltage regulation circuit in this part is connected to the Hall probe, differential amplifier, AD converter, microcontroller, and serial interface, respectively, to provide a continuous voltage output for the entire circuit, improve the load-carrying capacity of the entire circuit, and reduce the impact caused by direct connection between circuits. In this embodiment, the serial interface can be RS485 or RS232. The detection circuit works by the Hall probe acquiring the magnetic signal, converting the magnetic signal into an electrical signal, amplifying it by the differential amplifier, and then converting it into a digital signal by the AD converter and transmitting it to the microprocessor for processing. The signal output by the microprocessor is output through the serial interface. The temperature acquisition module connected to the microcontroller acquires temperature data according to the instructions of the microcontroller, and corrects the influence of temperature drift on the magnetic field strength measurement value in the internal calculation of the microcontroller based on the temperature data, reducing errors. In this embodiment, the preferred model of the temperature acquisition module is DS18B20. Finally, the output signal is extracted and displayed by an external device, and the entire signal acquisition process is completed.

[0037] 4. Slider and rail: The slider is equipped with a Hall sensor, an AD converter, and a microcontroller. The slider moves along the rail. A spring-loaded hole is located at the bottom of the slider. When material does not pass through, the hole is closed in a pointed cone shape. When material passes through, the pointed corner is opened, and the spring is compressed, ensuring that the slider moves synchronously with the material when it experiences strain or displacement. The rail provides the slider's movement path, and its zero-zone (closed area) has a baffle to restrict the slider's movement area, ensuring that the slider moves within the designated area.

[0038] 5. Outer casing, such as Figure 4 As shown, the outer shell consists of upper and lower parts, both designed in an elliptical or semi-circular shape. This design aims to reduce the impact of concrete compression when used for monitoring the stress of steel strands within a structure, protecting the internal components and ensuring normal structural operation. The outer shell also serves as a magnetic shield. Furthermore, the outer shell is designed with a sandwich structure filled with thermal insulation material to prevent or reduce the impact of external temperature on the sensor's measurement performance.

[0039] 6. Locks, such as Figure 4 , Figure 5 It is installed on the front and rear sides of the upper and lower outer shells. When installing the monitoring device on the device under test, the bolt is passed through the lock and then secured with a nut.

[0040] 7. Connectors and other accessories: Connectors such as bolts serve to connect and fasten the upper and lower shells. Other accessories include permanent magnet support plates (the lower part of the permanent magnet support plate has holes, which are different from the holes under the slider. The holes under the permanent magnet support plate are only used for the device under test to pass through), baffles in the zero zone of the device, and springs in the channels under the slider.

[0041] This embodiment provides an example of using a stress monitoring device for measuring the stress of reinforcing bars. First, the stress monitoring device needs initial position correction and initial strength calibration. Then, the reinforcing bar is passed through the hole under the slider and permanent magnet support plate, ensuring that the slider can move synchronously when the reinforcing bar deforms. Next, bolts are used to tighten the pre-drilled bolt holes on the stress monitoring device to prevent slippage. Then, force-magnetic relationship calibration is performed. After calibration, it is installed on the reinforcing bar. Figure 4 As shown, when the reinforcing bar retracts due to strain and generates stress loss, the reinforcing bar drives the slider to move synchronously. Since the measurement position of the Hall sensor probe on the central axis of the permanent magnet changes, the magnetic induction intensity monitored by the Hall sensor changes. The output data of the Hall sensor is processed by an external device (such as a computer) connected to the tail of the Hall sensor through the wire. Based on the pre-calibrated force and magnetic relationship, the stress change of the reinforcing bar is fed back.

[0042] When using the stress monitoring device for monitoring the stress of steel strands within a structure, epoxy resin can be applied appropriately between the steel strands and the holes below the slider and permanent magnet support plate. This can prevent concrete, mortar, etc., from entering the stress monitoring device and affecting its performance.

[0043] like Figure 3 To establish a monitoring mechanism based on the permanent magnet effect, a three-dimensional coordinate system is constructed with the central axis of the permanent magnet as the x-axis. Different measurement positions correspond to different magnetic field intensities. By establishing a relationship between the variation of the magnetic field intensity along the central axis and the strain of the device under test, the strain of the device under test can be measured using the magnetic signal of the permanent magnet, as detailed below:

[0044] When the device under test generates strain ε, the probe of the Hall sensor on the central axis AOB of the permanent magnet is displaced synchronously with the device under test, and the measurement point moves from point O to point D. The probe acquires the magnetic field strength B. z It also changes accordingly, with the change being ΔB = B z2 -B z1 The stress changes from σ1 to σ2, and a force-magnetic coupling theory can be established based on this process. When the measured device undergoes a small deformation, the displacement generated at a single measurement point is Δx = ε. Therefore, the deformation ε of the measured device is related to B. z The relation is:

[0045]

[0046] According to the relationship between material properties:

[0047]

[0048] The stress σ and B can be obtained z The relation is:

[0049]

[0050] The parameters in the above formula: B z E represents the Z-axis component of the magnetic field strength vector of the permanent magnet, h represents the dimension of the permanent magnet in the magnetization direction, and E represents the magnetic field strength vector of the permanent magnet. P Let x, y, and z represent the elastic modulus of the device under test, respectively; x, y, and z represent the three-dimensional coordinates of the measurement point or the position vectors pointing from the origin to any point P in space; x0, y0, and z0 represent the integral constants of the current element vector pointing from the origin; a, b, and c represent the length, width, and height of the magnet, respectively; and K is given by the following formula:

[0051]

[0052] In the formula, μ0 represents the free permeability, J S This represents the current density.

[0053] Equation (3) is the force-magnetic coupling relationship under the mathematical theoretical model. When the measurement conditions are determined, the basic constant parameters and integral constants in the equation can be directly obtained. In the actual measurement process, the magnitude of the magnetic field strength measured by the Hall sensor is a certain value. That is, when the strain stress value is determined, there is a unique solution to the corresponding equation, which is the corresponding magnitude of the magnetic field strength.

[0054] Finally, 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 it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A stress monitoring device based on the permanent magnet effect, characterized in that: It includes a permanent magnet and a Hall effect integrated module; the Hall effect integrated module is fixed on the slider, the slider is mounted on the slide rail, and baffles are provided on both sides of the slide rail; the permanent magnet is fixed on the permanent magnet support plate on the left side of the baffle on the right side of the slide rail; The lower part of the slider is provided with a spring-type hole, which is a pointed cone shape when closed; the stress monitoring device is installed on the device under test, and the slider is tightly connected to the device under test through the spring-type hole; When the device under test is strained, the slider moves synchronously and drives the Hall probe to move. In the Hall integrated module, the Hall probe detects magnetic signals at different positions on the central axis of the permanent magnet. The magnetic signals are processed by the Hall sensor and output to the external device. The external device calculates the stress of the device under test based on the pre-calibrated force-magnetic relationship. The force-magnetic relationship is as follows: in, The Z-axis component represents the magnetic flux density vector of a permanent magnet. The dimension indicating the direction of magnetization of the permanent magnet. , These represent the stress and elastic modulus of the measured device, respectively. , , These represent the three-dimensional coordinates of the measurement point or the radius vector pointing from the origin to any point in space. , , This represents the integral constant pointing from the origin of the coordinate system to the current element vector. , These represent the length and width of the permanent magnet, respectively. It is given by the following formula: In the formula, Represents the permeability of free space. This represents the current density.

2. The stress monitoring device based on permanent magnet effect according to claim 1, characterized in that: The Hall integrated module includes a Hall sensor, an AD converter, and a microcontroller, wherein the Hall sensor includes a voltage regulation circuit, a differential amplifier, a temperature acquisition module, and a Hall probe; The voltage regulation circuit is connected to the differential amplifier, AD converter, microcontroller and Hall probe respectively to provide continuous voltage output; one end of the Hall probe is placed at the central axis of the permanent magnet, and the other end is connected to the differential amplifier, the differential amplifier, AD converter and microcontroller are connected in sequence; the temperature acquisition module is connected to the microcontroller. The Hall probe is used to acquire magnetic signals, which are then converted into electrical signals and amplified by a differential amplifier. The digital signals are then converted into digital signals by an AD converter and transmitted to a microcontroller to calculate the magnitude of the magnetic field strength. The signal output by the microcontroller is then output to an external device through a serial interface. The temperature acquisition module is used to collect temperature data, and the microcontroller corrects the effect of temperature drift on the magnetic field strength measurement value to reduce errors.

3. The stress monitoring device based on permanent magnet effect according to claim 1, characterized in that: The device also includes upper and lower outer shells, which are designed to be elliptical or semi-circular, with two latches on the front and rear sides of each outer shell; the outer shells also serve as magnetic shields.

4. The stress monitoring device based on permanent magnet effect according to claim 3, characterized in that: The outer shell is also designed with a sandwich layer, which is filled with heat insulation material.

5. A stress monitoring method applicable to the device described in any one of claims 1 to 4, characterized in that: Before using the device, the force-magnetic relationship is calibrated. After calibration, the stress monitoring device is installed on the device under test and tightly connected to the device under test through the spring-type hole at the bottom of the slider. When the device under test experiences strain, the slider moves synchronously and drives the Hall probe to move. The Hall probe detects magnetic signals at different positions on the central axis of the permanent magnet and inputs them into the microcontroller. The microcontroller calculates the magnetic field strength at the corresponding position and outputs it to the external device. The external device then extracts the data and feeds back the stress change of the device under test through the force-magnetic relationship.

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