A large range broadband absolute displacement sensor and method without reference point

Abstract

The application discloses a wide-range broadband absolute displacement sensor without reference point, which comprises a negative stiffness system, a positive stiffness system and a displacement monitoring system. The negative stiffness system is a bistable structure, which can generate linear negative stiffness with large stroke. The linear negative stiffness is compensated by the positive stiffness spring, so that a linear quasi-zero stiffness interval with large range can be obtained. At this time, the absolute displacement of the bridge deck can be represented by the relative displacement collected by the laser displacement sensor, so that the absolute displacement monitoring of the bridge in a large displacement range can be realized. The guide rod shaft and the upper plate are in contact through a flange type linear bearing, so that the frictional damping in the working process of the sensor is significantly reduced, and the starting frequency of the sensor is reduced. The absolute displacement of the bridge is directly monitored, compared with the traditional displacement monitoring method, the fixed reference point is not needed, the displacement monitoring frequency bandwidth is longer, the displacement monitoring range is larger, and the absolute displacement monitoring of the large-span bridge can be performed.

Description

Technical Field

[0001] This invention belongs to the field of civil engineering structural health monitoring technology, specifically relating to a large-range wide-frequency domain absolute displacement sensor and method that does not require a reference point. Background Technology

[0002] Bridge vibration displacement is a crucial indicator for assessing bridge health and service performance, directly impacting its operational capability. Long-span bridges, such as cable-stayed and suspension bridges, are characterized by low vibration frequencies and large vibration displacements. Traditional displacement sensors, such as LVDTs (Linear Variable Differential Transformers) and LDVs (Laser Doppler Vibration Meters), can directly measure absolute displacement, but they require a fixed reference point, significantly limiting their application in long-span bridges. Optical cameras and digital image-based methods can monitor bridge absolute displacement non-contactly, but they require compensation for their own displacement effects, and the monitoring accuracy is affected by equipment and weather conditions, making them unsuitable for long-term monitoring. Indirect measurement methods, such as using double integration of acceleration signals or single integration of velocity signals, can obtain absolute displacement, but the estimation accuracy is greatly affected by initial values ​​and suffers from low-frequency drift and delay, resulting in low accuracy for low-frequency vibrations. GPS (Global Positioning System) can monitor bridge absolute displacement, but it suffers from low monitoring frequency and low accuracy. Therefore, finding a high-accuracy absolute displacement measurement method that is not overly dependent on environmental conditions is crucial.

[0003] The quasi-zero stiffness principle has gained popularity among researchers in recent years. It uses a positive stiffness system to compensate for a negative stiffness system, creating a near-zero stiffness working space within a certain displacement range, thus creating a vibration-free point. The absolute displacement of the structure can be monitored by directly measuring the relative displacement between the vibrating structure and the vibration-free point. The realization of negative stiffness mainly includes the following types: mechanical springs, pre-buckling beams, electromagnetic negative stiffness, negative stiffness materials, and biomimetic negative stiffness. Since negative stiffness structures are inherently unstable, corresponding positive stiffness compensation is needed to achieve quasi-zero stiffness. Traditional positive stiffness units include positive stiffness springs and electromagnetic positive stiffness units. Existing research on quasi-zero stiffness mainly focuses on vibration isolation; research applying the quasi-zero stiffness principle to monitor the absolute displacement of bridges is relatively limited.

[0004] Chinese patent application CN113324465A discloses an absolute displacement sensor and its design method. It employs an electromagnetic negative stiffness system and elastic positive stiffness to create a quasi-zero stiffness working space, and uses a resistance strain gauge to measure absolute displacement. Chinese patent application CN113091587A discloses a quasi-zero stiffness absolute displacement sensor based on electromagnetic positive stiffness, which simultaneously employs electromagnetic positive and negative stiffness. The magnitude of the electromagnetic positive and negative stiffness is adjusted by changing the geometric parameters of the coil and permanent magnet, as well as the coil current. However, both of these patented technologies suffer from the inability to monitor large deformations, and the resistance strain gauge requires rebalancing of the bridge circuit once power is lost, resulting in weak resistance to sudden events.

[0005] For long-span bridges such as cable-stayed bridges and suspension bridges, the vibration frequency is relatively low, which requires sensors with a wide displacement monitoring bandwidth. Existing sensors perform well in monitoring high-frequency displacements, but poorly in monitoring low-frequency displacements, and may even produce errors. Therefore, it is more valuable to develop a bridge absolute displacement sensor with a large range, high monitoring accuracy, and applicability to most bridge types. Summary of the Invention

[0006] In view of the above, the present invention provides a large-range wide-frequency domain absolute displacement sensor and method that does not require a reference point. The sensor can provide a vibration-free point over a long stroke range, and the device has a low natural frequency, enabling direct measurement of low-frequency, large-amplitude absolute vibration displacement of long-span bridges.

[0007] A large-range, wide-frequency-domain absolute displacement sensor requiring no reference point includes a negative stiffness system, a positive stiffness system, a laser displacement sensor, and a counterweight, wherein:

[0008] The negative stiffness system is used to provide linear negative stiffness, and the positive stiffness system is used to compensate for the linear negative stiffness generated by the negative stiffness system, thereby obtaining a large range of linear quasi-zero stiffness. It includes a compression spring, a guide rod shaft, and a spring seat. One end of the guide rod shaft is fixed at the center point of the lower plate of the negative stiffness system, and the other end passes through the upper plate of the negative stiffness system. The spring seat is fixed on the lower plate and sleeved around the guide rod shaft. The compression spring is wound around the guide rod shaft between the upper and lower plates, with one end fixed inside the spring seat and the other end fixed to the bottom of the upper plate.

[0009] The laser displacement sensor is installed at the bottom of the upper plate and is used to measure the relative displacement between the upper and lower plates.

[0010] The counterweight is placed on the upper plate to press the upper plate down to a static equilibrium position within the linear quasi-zero stiffness range.

[0011] Furthermore, the negative stiffness system includes an upper plate, a lower plate, diagonal braces, horizontal support rods, tension springs, optical axis seats, fixed optical axes, and articulated optical axes. The optical axis seats are distributed and fixed on the surface of the lower plate and the bottom of the upper plate, with two pairs on the left, two pairs on the right, and four pairs on each side. Each pair of optical axis seats is used to install the corresponding fixed optical axis. The diagonal braces have through holes at both ends for the optical axes to pass through. Each fixed optical axis is connected to two diagonal braces at the front and back. The diagonal braces are divided into upper and lower layers. One end of the upper layer's diagonal brace is connected to the upper plate via a fixed optical axis, and the other end is connected to the corresponding support rod via an articulated optical axis. One end of the lower diagonal rod is connected, and the other end of the lower diagonal rod is connected to the lower plate through a fixed optical axis; a total of 4 horizontal support rods are set in the middle of the upper and lower plates, one on the left front and one on the right front and one on the right. One end of the horizontal support rod is connected to the upper and lower diagonal rods on the inner side through a joint optical axis, and the other end is connected to the upper and lower diagonal rods on the outer side through a joint optical axis. Thus, each joint optical axis passes through the 4 upper and lower diagonal rods and the 2 horizontal support rods on the front and back; one end of the tension spring is hung on the fixed optical axis on the inner side, and the other end is hung on the joint optical axis on the outer side.

[0012] Furthermore, the joint optical axis is connected to the inclined rod and the horizontal support rod via ball bearings, and the fixed optical axis is connected to the inclined rod via ball bearings to reduce friction; snap rings are provided on both sides of the joint optical axis to limit the movement of the inclined rod and the horizontal support rod.

[0013] Furthermore, the upper plate of the negative stiffness system has a through hole for the guide rod shaft to pass through. A flange-type linear bearing is concentrically installed in the through hole. The bearing consists of a linear bearing body, a flange, and balls. The balls are located on the inner wall of the linear bearing body. The end of the linear bearing body is connected to the flange. The flange has a nut hole for bolts to pass through and is fixed to the upper plate by bolts. This design ensures that the guide rod shaft always maintains a vertical linear motion, reduces friction between the guide rod shaft and the through hole of the upper plate, and avoids contact and collision between the guide rod shaft and the upper plate when the sensor is working.

[0014] Furthermore, a spring hook groove is provided on the optical axis of the suspension tension spring to fix the spring position and prevent the spring from shifting during operation. The spring seat has a spring hole that mates with the compression spring to fix the spring in the spring hole, which can avoid the compression spring from directly contacting the lower plate and causing unwanted slippage and buckling during vibration displacement monitoring.

[0015] Furthermore, the guide rod shaft has multiple pin holes in the vertical direction for bolt insertion. By inserting bolts into the corresponding pin holes to lock the compression spring, the effective working length of the compression spring is changed, thereby adjusting the stiffness of the compression spring during operation.

[0016] Furthermore, the lower plate of the negative stiffness system has several threaded holes for fixing the lower plate to the bridge deck with bolts.

[0017] The design method for the above-mentioned large-range wide-frequency domain absolute displacement sensor includes the following steps:

[0018] (1) Determine the natural frequency of vertical vibration and the maximum vibration displacement amplitude of the target bridge;

[0019] (2) Determine the length of the diagonal rod based on the maximum vibration displacement amplitude. And thickness, and initially estimate the length of the horizontal support rod. And thickness, and calculate the rod length ratio. ;

[0020] (3) Select the stiffness of the tension spring And calculate the stiffness of the compression spring used to compensate for the negative stiffness. And the mass of the counterweight required to press the upper plate down to the static balance position;

[0021] (4) Perform simulation calculations to verify whether the requirements are met. If the requirements are met, the device can be installed, tested, and put into use. If the requirements are not met, return to step (2) to adjust the rod length ratio. and stiffness Then recalculate.

[0022] Furthermore, the specific implementation of step (3) is as follows: First, determine the following relationship. K and y Relationship curve:

[0023] ;

[0024] , ;

[0025] ;

[0026] ;

[0027] in: K For the stiffness of a negative stiffness system, y This represents the downward displacement of the upper plate after applying counterweights of varying weights. A and B To simplify the parameters, and For about y Simplified function, θ The initial assembly angle is the angle between the diagonal rod and the horizontal plane when no counterweight is applied.

[0028] Then, the stiffness is determined based on this relationship curve. K minimum value K min and its corresponding yValue, that y The value corresponds to the static equilibrium position within the linear quasi-zero stiffness range, and this value is used to determine the mass of the counterweight; finally, the stiffness of the compression spring is calculated. .

[0029] Preferably, the initial assembly angle θ The angle is set to 80°, which results in the longest linear quasi-zero stiffness range, the highest material utilization rate, and a wider monitoring range.

[0030] A method for monitoring bridge vibration displacement specifically involves: firstly, installing the aforementioned large-range, wide-frequency-domain absolute displacement sensor at the corresponding position on the bridge deck, i.e., fixing the lower plate to the bridge deck with bolts; then, pressing the upper plate down to the static equilibrium position within the linear quasi-zero stiffness range by applying counterweights; when the bridge experiences vertical vibration, measuring the relative displacement between the upper and lower plates using a laser displacement sensor; since the linear quasi-zero stiffness range creates a vibration-free point, the upper plate will not displace within this range, and the relative displacement measured by the laser displacement sensor at this time is the absolute displacement of the lower plate. Since the lower plate is fixedly connected to the bridge deck, the absolute displacement of the lower plate at this time is the vibration displacement of the bridge.

[0031] Based on the above technical solution, the inventiveness of this invention is mainly reflected in the following aspects:

[0032] (1) The negative stiffness system of the present invention is a bistable structure, and the linear negative stiffness accounts for a large proportion of the total stroke. Therefore, the linear segment of quasi-zero stiffness after positive stiffness compensation is relatively long, which can be used for vibration displacement monitoring of bridges with large displacement.

[0033] (2) Due to the “high static and low dynamic” characteristics of the quasi-zero stiffness itself (high static stiffness and low dynamic stiffness), the inherent frequency of the sensor of the present invention is very low. Therefore, its displacement measurement frequency range is wider, and it can monitor bridge frequencies that are lower, making it more suitable for monitoring bridges with low inherent frequencies, such as long-span bridges.

[0034] (3) On the one hand, the guide rod shaft passes through the flange-type linear bearing fixed on the upper plate, which greatly reduces the frictional damping in the vertical direction; on the other hand, the connection between the sensor connecting rod and the optical axis is made of ball bearings, which have low rotational friction, low starting frequency, and are easier to monitor absolute displacement under low frequency load.

[0035] (4) Since the quasi-zero stiffness characteristic creates a fixed point over a wide range of strokes, it can be used with a laser displacement sensor to directly monitor the absolute displacement of the lower plate (bridge deck) without the need for additional data conversion, thus improving monitoring efficiency.

[0036] (5) The present invention changes the effective working length of the spring by drilling pin holes from bottom to top below the guide rod shaft and configuring pins. This makes it easier to adjust the mismatch between the actual stiffness and the design stiffness caused by the spring manufacturing process and errors, and improves the accuracy of the device test.

[0037] Therefore, compared with the prior art, the present invention has at least the following beneficial technical effects:

[0038] (1) This invention utilizes the quasi-zero stiffness principle for absolute displacement monitoring. By creating a fixed point, the relative displacement between the upper and lower plates is converted into the absolute displacement of the lower plate (such as a bridge deck), thus eliminating the need for a fixed reference point. This invention can be applied to displacement measurement scenarios where sensors such as LVDT and LDV cannot be used.

[0039] (2) The present invention uses mechanical principles to monitor the absolute displacement of bridges. Compared with displacement monitoring methods that use optical methods such as optical cameras and digital image-based methods, the sensor is less affected by weather.

[0040] (3) Because the quasi-zero stiffness characteristic of this invention creates a fixed point over a wide range of strokes, it can be used with a laser displacement sensor to directly monitor the absolute displacement of the base plate (bridge deck). Compared with the second integral of the acceleration signal or the first integral of the velocity signal, no additional data conversion processing is required, and the dependence on the initial value is small.

[0041] (4) Since the sampling frequency of the sensor of the present invention depends on the sampling frequency of the laser displacement sensor, it can adapt to the sampling requirements of high and low frequencies, and the laser displacement sensor is easy to replace; compared with GPS, the sampling frequency selection is more flexible and the accuracy is more guaranteed. Attached Figure Description

[0042] Figure 1 This is a schematic diagram illustrating the design and monitoring process of the absolute displacement sensor of the present invention.

[0043] Figure 2 This is a schematic diagram of the structure of a large-range wide-frequency domain absolute displacement sensor in an embodiment of the present invention, wherein (a) is a front view and (b) is a side view.

[0044] Figure 3 This is a schematic diagram of the negative stiffness system in an embodiment of the present invention.

[0045] Figure 4 This is a schematic diagram of the structure of the positive stiffness system in an embodiment of the present invention.

[0046] Figure 5 This is a schematic diagram of the optical axis structure with ball bearings at the joint in an embodiment of the present invention.

[0047] Figure 6This is a schematic diagram of the machining of the optical axis connecting the tension spring in an embodiment of the present invention.

[0048] Figure 7 This is a schematic diagram of the flange-type linear bearing installation on the upper plate in an embodiment of the present invention.

[0049] Figure 8 This is a schematic diagram of the structure of the flange-type linear bearing in an embodiment of the present invention.

[0050] Figure 9 This is a schematic diagram of the force-displacement curve of the negative stiffness system and the force-displacement curve of the compression spring in an embodiment of the present invention.

[0051] Figure 10 This is a schematic diagram of the force-displacement curves over the entire stroke range in an embodiment of the present invention.

[0052] Figure 11 This is a schematic diagram of the stiffness-displacement curves over the entire stroke range in an embodiment of the present invention.

[0053] Figure 12 This is a schematic diagram showing the curve comparison between the relative displacement and the absolute displacement obtained by monitoring in an embodiment of the present invention.

[0054] In the diagram: 1—Diagonal rod, 2—Horizontal support rod, 3—Tension spring, 4—Optical axis seat, 5—Lower plate, 6—Upper plate, 7—Guide rod shaft, 8—Counterweight, 9—Spring seat, 10—Compression spring, 11—Laser displacement sensor, 12—Joint optical axis, 13—Flange-type linear bearing, 14—Nut hole, 15—Ball bearing, 16—Flange, 17—Spring hook groove, 18—Base plate threaded hole, 19—Spring hole, 20—Pin hole, 21—Pin bolt, 22—Ball bearing, 23—Fixed optical axis. Detailed Implementation

[0055] To describe the present invention in more detail, the technical solution of the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0056] like Figure 2 As shown, this embodiment provides a large-range, wide-frequency-domain absolute displacement sensor that does not require a reference point. It includes three main systems: a negative stiffness system, a positive stiffness system, and a displacement monitoring system, wherein:

[0057] The composition of a negative stiffness system is as follows Figure 3 As shown, it includes a diagonal rod 1, a horizontal support rod 2, a tension spring 3, a light axis seat 4, a lower plate 5, an upper plate 6, a joint light axis 12, and a fixed light axis 23. The light axis seats 4 are symmetrically fixed to the upper plate 6 and the lower plate 5, totaling 16. The fixed light axes 23 pass through the light axis seats 4 and are fixed in place. The joint light axes 12 connect the symmetrically positioned diagonal rods 1 and horizontal support rods 2. Figure 5As shown, in order to reduce friction between the joints during movement and lower the sensor's response frequency, ball bearings 22 are installed at the contact points between the inclined rod 1, the horizontal support rod 2 and the optical axis.

[0058] like Figure 3 As shown, tension springs 3 are suspended in the middle of the front and rear rod system, and are suspended in two layers. One end of the two upper tension springs 3 is attached to the fixed optical axis 23 on the inner side of the upper plate 6, and the other end is connected to the upper and lower inclined rods 1 on the outer side via the joint optical axis 12. One end of the two lower tension springs 3 is attached to the fixed optical axis 23 on the inner side of the lower plate 5, and the other end is connected to the upper and lower inclined rods on the outer side via the joint optical axis 12. To ensure that the tension springs 3 do not move during sensor operation, spring hook grooves 17 are provided on the fixed optical axis 23 and the joint optical axis 12 suspending the tension springs 3, as shown in the figure. Figure 6 As shown.

[0059] like Figure 7 As shown, the upper plate 6 of the negative stiffness system has a through hole in the middle, and a flange-type linear bearing 13 is installed on the plate concentrically with the through hole. The linear bearing is as follows: Figure 8 As shown, its inner wall is provided with multiple rows of ball bearings 15. The flange-type linear bearing 13 is fixedly connected to the upper plate 6 by bolts through the nut holes 14 on the flange 16. The outer diameter of the flange 16 is larger than the diameter of the through hole on the upper plate 6, and the diameter of the flange-type linear bearing 13 is less than or equal to the diameter of the through hole on the upper plate 6. The inner diameter of the flange-type linear bearing 13 matches the diameter of the spring guide rod shaft 7 in the positive stiffness system. This design allows the sensor to remain vertical during movement and uses rolling contact, which greatly reduces frictional damping. On the other hand, it avoids contact and collision between the guide rod shaft 7 and the upper plate 6 during sensor operation, which helps to improve the sensor's monitoring accuracy and extend its service life.

[0060] like Figure 4 As shown, the positive stiffness system includes a guide rod shaft 7, a spring seat 9, and a compression spring 10. The spring seat 9 is fixed to the lower plate 5. The spring seat 9 has a spring hole 19 that matches the compression spring 10, allowing the spring to be secured within it. This structure primarily prevents direct contact between the compression spring 10 and the lower plate 5, avoiding unwanted slippage and buckling during vibration displacement monitoring. The lower plate 5 has four threaded holes 18 for fixing the sensor to the bridge surface with bolts. Considering that the actual stiffness of the spring may not match the design stiffness due to manufacturing processes and equipment conditions, pin holes 20 are machined along the guide rod shaft 7 from bottom to top. When the actual spring stiffness is found to be too low during testing, the effective working length of the spring can be changed by inserting bolts 21 into the pin holes, thereby adjusting the spring stiffness and improving testing accuracy.

[0061] The displacement measurement system is used to directly measure the relative displacement between the upper and lower plates. It consists of a laser displacement sensor 11, which is fixed to the lower or side of the upper plate 6 by nuts and brackets.

[0062] The counterweight 8 is placed on the upper plate 6 to press the upper plate 6 down to the static balance position within the corresponding quasi-zero stiffness region. The static balance position should be within the quasi-zero stiffness range, and there should be a quasi-zero stiffness stroke before and after this balance position to meet the requirements of the maximum amplitude of the monitoring, so as to ensure that this absolute displacement sensor can achieve normal monitoring function. If the required stroke is much smaller than the designed quasi-zero stiffness range of the sensor, the balance position is generally placed at the point where the stiffness of the quasi-zero stiffness segment is closest to zero; the force corresponding to the static balance position is the required weight of the counterweight 8.

[0063] like Figure 1 As shown, this embodiment also provides a design method and an absolute displacement monitoring method for this large-range wide-frequency domain absolute displacement sensor, the specific process of which is as follows:

[0064] (1) First, it is necessary to determine the vertical vibration natural frequency and maximum displacement amplitude of the target bridge. A max This provides basic information for sensor design; the displacement amplitude range is used to determine the sensor size; and the vibration frequency is used to verify whether the sensor's monitoring performance meets the requirements.

[0065] (2) Based on the maximum displacement amplitude A max The length of the diagonal brace can be preliminarily determined. and thickness and length of horizontal support rods And thickness, then calculate the rod length ratio ;in The length must meet the following conditions:

[0066]

[0067] (3) Preliminary determination of the stiffness of the tension spring Its stiffness should not be too large, as excessive spring stiffness will cause the device to be too stiff during the initial compression stage; after determining the above parameters, the full-stroke stiffness of the negative stiffness system K It can be calculated using the following formula:

[0068] ;

[0069] , ;

[0070] ;

[0071] ;

[0072] This stiffness is negative in the linear stiffness range, so the stiffness of the compression spring is selected as follows: . Figure 9 The solid line in the figure represents the force-displacement curve of the negative stiffness system over its entire stroke, while the dashed line represents the force-displacement curve of the compression spring. It can be seen that after the displacement exceeds 6 cm, the force of the negative stiffness system decreases as the displacement increases, exhibiting a long linear negative stiffness characteristic.

[0073] When the maximum displacement amplitude of the monitored target is much smaller than the designed quasi-zero stiffness stroke of the sensor, the overall stiffness of the sensor static balance position selection device is the smallest, that is, the position closest to zero stiffness. When the maximum displacement amplitude of the monitored target is large, it should be ensured that the selected static balance position has a quasi-zero stiffness stroke before and after that to meet the requirements of the maximum amplitude of monitoring, so as to ensure the quality of displacement monitoring. Thus, the weight of the counterweight block required to press the upper plate down to the static balance position is the magnitude of the force corresponding to the static balance position.

[0074] (4) Verify and analyze the determined parameters.

[0075] Under the above design, if the relative displacement range of the sensor is always within the quasi-zero stiffness range and the displacement monitoring accuracy meets the expected requirements, the design is completed. If the requirements are not met, return to step (2) to readjust the rod length ratio and repeat steps (3) and (4). For designs that meet the requirements, a sensor prototype can be manufactured and the absolute displacement monitoring test at the corresponding vibration frequency can be performed on the sensor prototype. If the test results meet the expected requirements, production and installation can be carried out. If the results do not meet the expected requirements, return to step (2) to redesign.

[0076] Figure 10 and Figure 11 These are the force-displacement curve and the full-stroke stiffness curve of the sensor after its design. It can be seen that the sensor has a long quasi-zero stiffness range, thus possessing great potential for monitoring the absolute displacement of bridges with large displacement amplitudes. The quasi-zero stiffness range is determined according to different monitoring accuracy requirements; however, the force change within the quasi-zero stiffness range cannot exceed 5%, i.e. The initial displacement of the upper plate when this relationship is satisfied is the starting point of the quasi-zero stiffness interval. The corresponding upper plate displacement is the end point of the quasi-zero stiffness interval (due to linear stiffness, it is usually the end point of the entire stroke).

[0077] The specific process of using the above-mentioned absolute displacement sensor for bridge vibration displacement monitoring is as follows:

[0078] (1) Install and fix the sensor to the corresponding position on the bridge deck, that is, fix the lower plate of the sensor to the bridge deck by bolts or other connection measures.

[0079] (2) such as Figure 11 As shown, the sensor in its initial installation position does not possess quasi-zero stiffness characteristics; instead, it exhibits significant positive stiffness. Therefore, the sensor needs to be initially controlled to its static equilibrium position. The sensor's static equilibrium position must be within the quasi-zero stiffness range, and it must have sufficient travel forward and backward to cover the maximum amplitude of the monitored displacement. Figure 11 The orange hexagon shown indicates the point where the designed sensor's stiffness is closest to zero (27.1 cm). Based on this, if the forward and backward quasi-zero stiffness strokes meet the maximum displacement monitoring amplitude requirement, the sensor will function normally. The balance point should then be placed at this position; the force corresponding to this position is the required weight of the counterweight. Figure 10 The required weight of the counterweight is obtained at the corresponding position, and then it can be pressed down to the corresponding position by applying the corresponding counterweight block on the upper plate.

[0080] (3) When the sensor is working, that is, when the bridge vibrates vertically, the laser displacement sensor will collect the relative displacement data between the upper and lower plates of the sensor. Due to the quasi-zero stiffness characteristic, a vibration-free point is created. Therefore, within this range, the upper plate will not displace or will only have a very small displacement. At this time, the relative displacement data collected by the laser displacement sensor is the absolute displacement of the lower plate. Since the lower plate is fixedly connected to the bridge deck and moves synchronously, the absolute displacement of the lower plate at this time is the absolute vibration displacement of the bridge.

[0081] like Figure 12 The image shows a comparison between the relative displacement data monitored by the laser displacement sensor and the absolute displacement data of the lower plate. It can be seen that the error between the two is very small, which also shows the effectiveness of the present invention for absolute displacement monitoring.

[0082] The above description of the embodiments is provided to enable those skilled in the art to understand and apply the present invention. Those skilled in the art can readily make various modifications to the above embodiments and apply the general principles described herein to other embodiments without creative effort. Therefore, the present invention is not limited to the above embodiments, and any improvements and modifications made to the present invention by those skilled in the art based on the disclosure thereof should be within the scope of protection of the present invention.

Claims

1. A large-range, wide-frequency-domain absolute displacement sensor that requires no reference point, characterized in that, This includes a negative stiffness system, a positive stiffness system, a laser displacement sensor, and a counterweight, among which: The negative stiffness system is used to provide linear negative stiffness, and the positive stiffness system is used to compensate for the linear negative stiffness generated by the negative stiffness system, thereby obtaining a large range of linear quasi-zero stiffness. It includes a compression spring, a guide rod shaft, and a spring seat. One end of the guide rod shaft is fixed at the center point of the lower plate of the negative stiffness system, and the other end passes through the upper plate of the negative stiffness system. The spring seat is fixed on the lower plate and sleeved around the guide rod shaft. The compression spring is wound around the guide rod shaft between the upper and lower plates, with one end fixed inside the spring seat and the other end fixed to the bottom of the upper plate. The laser displacement sensor is installed at the bottom of the upper plate and is used to measure the relative displacement between the upper and lower plates. The counterweight is placed on the upper plate to press the upper plate down to the static equilibrium position within the linear quasi-zero stiffness range; The negative stiffness system includes an upper plate, a lower plate, diagonal braces, horizontal support rods, tension springs, optical axis seats, fixed optical axes, and articulated optical axes. The optical axis seats are distributed and fixed on the surface of the lower plate and the bottom of the upper plate, with two pairs on the left, two pairs on the right, and four pairs on each side. Each pair of optical axis seats is used to install the corresponding fixed optical axis. The diagonal braces have through holes at both ends for the optical axes to pass through. Each fixed optical axis is connected to two diagonal braces at the front and back. The diagonal braces are divided into upper and lower layers. One end of the upper layer's diagonal brace is connected to the upper plate via a fixed optical axis, and the other end is connected to the corresponding lower plate via an articulated optical axis. One end of the diagonal bar is connected to the upper plate, and the other end of the lower diagonal bar is connected to the lower plate via a fixed optical axis; a total of 4 horizontal support rods are set in the middle of the upper and lower plates, one on the left front and one on the right front and one on the right. One end of the horizontal support rod is connected to the upper and lower diagonal bars on the inner side via a joint optical axis, and the other end is connected to the upper and lower diagonal bars on the outer side via a joint optical axis. Thus, each joint optical axis passes through the 4 upper and lower diagonal bars and the 2 horizontal support rods on the front and back; one end of the tension spring is hung on the fixed optical axis on the inner side, and the other end is hung on the joint optical axis on the outer side. The joint optical axis is connected to the inclined rod and the horizontal support rod through ball bearings, and the fixed optical axis is connected to the inclined rod through ball bearings to reduce friction; the joint optical axis is provided with retaining springs on both sides to limit the movement of the inclined rod and the horizontal support rod. The upper plate of the negative stiffness system has a through hole for the guide rod shaft to pass through. A flanged linear bearing is concentrically installed in the through hole. It consists of a linear bearing body, a flange and balls. The balls are set on the inner wall of the linear bearing body. The end of the linear bearing body is connected to the flange. The flange has a nut hole for bolts to pass through and is fixed to the upper plate by bolts. The guide rod shaft has multiple pin holes in the vertical direction for bolt insertion. By inserting bolts into the corresponding pin holes to lock the compression spring, the effective working length of the compression spring is changed, thereby adjusting the stiffness of the compression spring during operation.

2. The large-range, wide-frequency-domain absolute displacement sensor according to claim 1, characterized in that: The optical axis of the suspension tension spring is provided with a spring hook groove to fix the spring position and prevent the spring from shifting during operation; the spring seat is provided with a spring hole that mates with the compression spring to fix the compression spring in the spring hole.

3. The large-range, wide-frequency-domain absolute displacement sensor according to claim 1, characterized in that: The lower plate of the negative stiffness system has several threaded holes for fixing the lower plate to the bridge deck with bolts.

4. The design method of the large-range wide-frequency domain absolute displacement sensor as described in any one of claims 1 to 3, characterized in that, Includes the following steps: (1) Determine the natural frequency of vertical vibration and the maximum vibration displacement amplitude of the target bridge; (2) Determine the length of the diagonal rod based on the maximum vibration displacement amplitude. And thickness, and initially estimate the length of the horizontal support rod. And thickness, and calculate the rod length ratio. ; (3) Select the stiffness of the tension spring And calculate the stiffness of the compression spring used to compensate for the negative stiffness. And the mass of the counterweight required to press the upper plate down to the static balance position; (4) Perform simulation calculations to verify whether the requirements are met. If the requirements are met, the device can be installed, tested, and put into use. If the requirements are not met, return to step (2) to adjust the rod length ratio. and stiffness Then recalculate.

5. The design method according to claim 4, characterized in that: The specific implementation method of step (3) is as follows: First, determine the following relationship. K and y Relationship curve: ， in: K For the stiffness of a negative stiffness system, y This represents the downward displacement of the upper plate after applying counterweights of varying weights. A and B To simplify the parameters, and For about y Simplified function, θ The initial assembly angle is the angle between the diagonal rod and the horizontal plane when no counterweight is applied, and θ Selected as 80°; Then, the stiffness is determined based on this relationship curve. K minimum value K min and its corresponding y Value, that y The value corresponds to the static equilibrium position within the linear quasi-zero stiffness range, and this value is used to determine the mass of the counterweight; finally, the stiffness of the compression spring is calculated. .

6. A method for monitoring bridge vibration displacement, characterized in that: First, the large-range, wide-frequency absolute displacement sensor as described in any one of claims 1 to 3 is installed at the corresponding position on the bridge deck, i.e., the lower plate is fixed to the bridge deck with bolts; then, the upper plate is pressed down to the static equilibrium position within the linear quasi-zero stiffness range by applying counterweights; when the bridge experiences vertical vibration, the relative displacement between the upper and lower plates is measured using a laser displacement sensor; since the linear quasi-zero stiffness range creates a vibration-free point, the upper plate will not move within this range, and the relative displacement measured by the laser displacement sensor at this time is the absolute displacement of the lower plate. Since the lower plate is fixedly connected to the bridge deck, the absolute displacement of the lower plate at this time is the vibration displacement of the bridge.

Images