Weakly nonlinear vibration isolation structure

Abstract

The application relates to a weak nonlinear vibration isolation structure and belongs to the technical field of low-frequency vibration isolation. The vibration isolation structure comprises a base, a load platform and a vibration isolation module arranged between the base and the load platform, the vibration isolation module comprises a positive stiffness vibration isolation unit and a negative stiffness vibration isolation unit, the negative stiffness vibration isolation unit is divided into an upper spring structure and a lower spring structure, when the load platform and the base are relatively displaced, the stiffness curve of the upper spring structure is in a 'convex' type, and the stiffness curve of the lower spring structure is in a 'concave' type. The application utilizes the principle of a classical three-spring vibration isolation structure, symmetrically arranges five springs up and down, forms two three-spring structures, realizes quasi-zero stiffness in parallel connection, and the whole is a symmetric structure, can provide a basis for system stability, the stiffness curve is gentle, the nonlinearity of the structure is obviously reduced, the vibration isolation frequency band is widened, and the resonance frequency is reduced.

Description

Technical Field

[0001] This invention belongs to the field of low-frequency vibration isolation technology, specifically relating to a weakly nonlinear vibration isolation structure. Background Technology

[0002] With the rapid development of modern industrialization, precision and ultra-precision machining, measurement, and other fields are facing increasingly higher demands. This is especially true when dealing with low-frequency vibrations, which place higher demands on the stability and accuracy of the system. Low-frequency vibrations refer to vibrations with frequencies below 20Hz. Low-frequency vibrations not only increase mechanical wear and reduce equipment lifespan but may also lead to a decline in product quality.

[0003] Traditional linear vibration isolation systems are effective at isolating mid- and high-frequency vibrations due to their relatively high resonant frequency, but their isolation effect on low-frequency vibrations is less than ideal. Quasi-zero stiffness vibration isolation technology connects positive and negative stiffness structures in parallel, reducing the system's resonant frequency while ensuring high load-bearing capacity, thus achieving effective isolation of low-frequency vibrations.

[0004] Quasi-zero stiffness vibration isolation structures exhibit nonlinear problems in engineering applications. This means that during structural loading, the system's stiffness (the relationship between deformation and force) is not linear but nonlinear. This implies that under load, the structure's stiffness changes with increasing or decreasing displacement, no longer remaining constant. Reducing nonlinearity is crucial for the application of negative stiffness structures. Lower nonlinearity indicates a more controllable and stable response to external vibrations or impacts. This is essential for enhancing the structure's vibration isolation performance, reducing vibration transmission, and protecting critical components. Therefore, a weakly nonlinear vibration isolation structure is proposed. Summary of the Invention

[0005] The purpose of this invention is to provide a weak nonlinear vibration isolation structure with quasi-zero stiffness and a wide vibration isolation frequency band in order to solve the above-mentioned problems.

[0006] The present invention achieves the above objectives through the following technical solutions:

[0007] A weakly nonlinear vibration isolation structure includes a base and a load platform, and a vibration isolation module disposed between the base and the load platform. The vibration isolation module includes a positive stiffness vibration isolation unit and a negative stiffness vibration isolation unit. The negative stiffness vibration isolation unit is divided into an upper spring structure and a lower spring structure, and the upper spring structure and the lower spring structure are positioned opposite each other between the base and the load platform. When the load platform and the base are relatively displaced, the stiffness curve of the upper spring structure is convex, and the stiffness curve of the lower spring structure is concave.

[0008] As a further optimization of the present invention, the upper spring structure includes a first V-shaped double link assembly disposed on the top of the base, and a first V-shaped double spring assembly disposed on the bottom of the load platform and connected to the first V-shaped double link assembly.

[0009] The lower spring structure includes a second V-shaped double link assembly located at the bottom of the load platform, and a second V-shaped double spring assembly located at the top of the base and connected to the second V-shaped double link assembly.

[0010] As a further optimization of the present invention, the two sides of the first V-shaped double link assembly are respectively hinged to the two sides of the second V-shaped double link assembly to form two X-shaped structures.

[0011] As a further optimization of the present invention, the first V-shaped double link assembly includes a second link and a third link positioned opposite each other on the top of the base, and the first V-shaped double spring assembly includes a second spring and a fourth spring positioned opposite each other on the bottom of the load platform, and the ends of the second spring and the fourth spring are respectively connected to the ends of the second link and the third link.

[0012] The second V-shaped double linkage assembly includes a first linkage and a fourth linkage positioned at the bottom of the load platform, and the second V-shaped double spring assembly includes a first spring and a fifth spring positioned at the top of the base, with the ends of the first spring and the fifth spring respectively connected to the ends of the first linkage and the fourth linkage.

[0013] As a further optimization of the present invention, an upper fixed seat is fixedly provided at the bottom of the load platform, and a lower fixed seat is fixedly provided at the top of the base. The opposite ends of the second connecting rod and the third connecting rod are both hinged to the lower fixed seat. The opposite ends of the second spring and the fourth spring are both hinged to the upper fixed seat. The opposite ends of the first connecting rod and the fourth connecting rod are both hinged to the upper fixed seat. The opposite ends of the first spring and the fifth spring are both hinged to the lower fixed seat. The positive stiffness vibration isolation unit includes a third spring disposed between the upper fixed seat and the lower fixed seat.

[0014] As a further optimization of the present invention, the first link and the fourth link are hinged to the second link and the third link respectively, forming two mutually symmetrical X-shaped structures; the lengths of the first link, the second link, the third link and the fourth link are all equal.

[0015] As a further optimization of the present invention, the stiffness of the first spring and the fifth spring is greater than that of the second spring and the fourth spring.

[0016] As a further optimization of the present invention, a number of guiding modules are provided between the substrate and the load platform.

[0017] As a further optimization of the present invention, the guiding module consists of a guide cylinder fixed to the top of the base, a guide rod slidably disposed inside the guide cylinder, and a linear motion bearing disposed between the guide cylinder and the guide rod, wherein the upper end of the guide rod is fixedly connected to the load platform.

[0018] The beneficial effects of this invention are as follows:

[0019] 1) This invention utilizes the principle of a classic three-spring vibration isolation structure. Five springs are arranged symmetrically in the upper and lower parts to form two three-spring structures. The four outer springs form a negative stiffness structure in the vertical direction, while the middle spring provides positive stiffness. The two are connected in parallel to achieve quasi-zero stiffness, and the whole structure is symmetrical, which can provide a foundation for system stability.

[0020] 2) The stiffness curve of the upper spring structure in this invention is "convex" and the stiffness curve of the lower spring structure is "concave". By connecting the two in parallel, a relatively flat stiffness curve is obtained, the nonlinearity of the structure is significantly reduced, the vibration isolation frequency band is widened, and the resonant frequency is reduced.

[0021] 3) When the present invention is used for vibration isolation under a single load, the length of the connecting rod and the stiffness of the spring are fixed. If the load changes, the stiffness of the overall structure can be changed by changing the hinge point position of the two connecting rods of the X-shaped structure on the basis of the existing structure, so that the structure can achieve excellent vibration isolation capability under different load conditions.

[0022] 4) In this invention, when the connecting rod length L1 is 0.9m and the distance L2 from the connecting rod hinge point to the fixed seat is 0.6m, the working range of the structure in the QZS zone is approximately 0.9m, accounting for 75% of the total stroke. A typical QZS vibration isolator has a working range of approximately 0.48m in the QZS zone, accounting for 40% of the total stroke, and its vibration isolation frequency band is significantly smaller than that of this invention. After optimizing L2, i.e., when L2 is 0.5m, the working range of the structure in the QZS zone is approximately 1.06m, accounting for 88% of the total stroke, further improving the vibration isolation performance and stability of the vibration isolation system.

[0023] 5) The present invention has a simple structure, is easy to install and use. The positive stiffness vibration isolation unit and a pair of negative stiffness vibration isolation units of the vibration isolation module are integrated on a double X-shaped linkage mechanism, which has the advantages of compact structure and low space occupation ratio. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the vibration isolation structure in this invention;

[0025] Figure 2 This is a schematic diagram of the working state of the load platform when it fluctuates downwards in this invention;

[0026] Figure 3 This is a schematic diagram of the structure of the fixing base in this invention;

[0027] Figure 4 This is a schematic diagram of the linear motion bearing in this invention;

[0028] Figure 5 This is a static stiffness curve of the negative stiffness structure in this invention;

[0029] Figure 6 This is a static stiffness curve of the negative stiffness structure under different L2 values ​​in this invention;

[0030] Figure 7 This is a comparison of the static stiffness curves of the L2 optimization and the typical QZS vibration isolator before and after optimization in this invention.

[0031] In the diagram: 1. Base; 2. Guide cylinder; 3. First spring; 4. First connecting rod; 5. Second connecting rod; 6. Load platform; 7. Second spring; 8. Upper fixed seat; 9. Third spring; 10. Fourth spring; 11. Guide rod; 12. Third connecting rod; 13. Fourth connecting rod; 14. Fifth spring; 15. Linear motion bearing; 16. Lower fixed seat. Detailed Implementation

[0032] The present application will now be described in further detail with reference to the accompanying drawings. It should be noted that the following specific embodiments are only used to further illustrate the present application and should not be construed as limiting the scope of protection of the present application. Those skilled in the art can make some non-essential improvements and adjustments to the present application based on the above application content.

[0033] Example

[0034] like Figure 1-3 As shown, this embodiment relates to a weakly nonlinear vibration isolation structure. The structure includes a base 1, a load platform 6, and a guide module and a vibration isolation module located between the base 1 and the load platform 6. The vibration isolation module consists of three vibration isolation units: one positive stiffness vibration isolation unit and two mutually symmetrical negative stiffness vibration isolation units. An upper fixing seat 8 is fixedly installed at the center of the lower surface of the load platform 6, and a lower fixing seat 16 is fixedly installed at the center of the upper surface of the base 1. The two fixing seats 8 and 16 are symmetrically arranged and used to connect the positive stiffness vibration isolation unit and the negative stiffness vibration isolation unit.

[0035] Specifically, please refer to Figure 1The lower fixed base 16 has a second connecting rod 5 and a third connecting rod 12 hinged to its top. The second connecting rod 5 and the third connecting rod 12 are symmetrical to each other and form a first V-shaped double connecting rod assembly. The upper fixed base 8 has a second spring 7 and a fourth spring 10 hinged to its bottom. The second spring 7 and the fourth spring 10 are symmetrical to each other and form a first V-shaped double spring assembly. The end of the second spring 7 away from the upper fixed base 8 is hinged to the upper end of the second connecting rod 5, and the end of the fourth spring 10 away from the upper fixed base 8 is hinged to the upper end of the third connecting rod 12. The above-mentioned first V-shaped double connecting rod assembly and first V-shaped double spring assembly constitute an upper spring structure.

[0036] The bottom of the upper fixed base 8 is hinged to a first connecting rod 4 and a fourth connecting rod 13, which are symmetrical to each other and form a second V-shaped double connecting rod assembly. The top of the lower fixed base 16 is hinged to a first spring 3 and a fifth spring 14, which are symmetrical to each other and form a second V-shaped double spring assembly. The end of the first spring 3 away from the lower fixed base 16 is hinged to the lower end of the first connecting rod 4, and the end of the fifth spring 14 away from the lower fixed base 16 is hinged to the lower end of the fourth connecting rod 13. The aforementioned second V-shaped double connecting rod assembly and second V-shaped double spring assembly constitute a lower spring structure.

[0037] It should be noted that the upper and lower spring structures are two symmetrical negative stiffness vibration isolation units. A third spring 9 is provided between the two fixed seats 8 and 16, which is a positive stiffness vibration isolation unit. When the load platform 6 is relatively displaced from the base 1, the stiffness curve of the upper spring structure is convex, and the stiffness curve of the lower spring structure is concave.

[0038] Furthermore, the two sides of the first V-shaped double-link assembly are respectively hinged to the two sides of the second V-shaped double-link assembly, forming two X-shaped structures. Specifically, the first link 4 and the fourth link 13 are respectively hinged to the second link 5 and the third link 12, forming two mutually symmetrical X-shaped structures.

[0039] The first link 4, the fourth link 13, the upper end of the third spring 9, and the near ends of the second spring 7 and the fourth spring 10 are coaxially mounted. The second link 5, the third link 12, the lower end of the third spring 9, and the near ends of the first spring 3 and the fifth spring 14 are also coaxially mounted. The second spring 7 and the fourth spring 10 have equal stiffness, and the first spring 3 and the fifth spring 14 have equal stiffness, but the stiffness of the first spring 3 and the fifth spring 14 is greater than that of the second spring 7 and the fourth spring 10. By adjusting the link length and spring stiffness, the structure can achieve excellent vibration isolation capability under different load conditions.

[0040] like Figure 1 and Figure 4As shown, the guiding module includes several guide rods 11, several linear motion bearings 15 and several guide cylinders 2 sleeved on the guide rods 11. There are two sets of guide rods 11, linear motion bearings 15 and guide cylinders 2. The linear motion bearings 15 are fixed to the inner wall of the guide cylinders 2. The upper end of the guide rods 11 is fixedly connected to the lower end of the load platform 6. The lower end of the guide cylinders 2 is fixed to the upper end of the base 1.

[0041] like Figure 2 As shown, in static equilibrium, the overall structure of the vibration isolation structure is in its initial state. When subjected to external disturbances, the static equilibrium state is broken. Assuming the direction of motion is downward, as... Figure 2 As shown by the dashed line, the load platform 6 causes the vibration isolation unit to shift downwards, thus disrupting the balance. When the vibration isolation unit shifts downwards, the second spring 7, the fourth spring 10, the first spring 3, and the fifth spring 14 are stretched, while the third spring 9 is compressed. The stretching of the second spring 7 and the fourth spring 10 generates an upward restoring force, while the stretching of the first spring 3 and the fifth spring 14 generates a downward compressive force. When the stiffness of the first spring 3 and the fifth spring 14 is greater than the stiffness of the second spring 7 and the fourth spring 10, the compressive force exceeds the restoring force, causing the vibration isolation unit to shift downwards more and more rapidly. This characteristic is known as the negative stiffness characteristic.

[0042] Since the stiffness curve of the upper spring structure is convex and that of the lower spring structure is concave, their parallel connection flattens the stiffness curve, significantly reducing the nonlinearity of the structure, widening the vibration isolation bandwidth, and lowering the resonant frequency. Because the stiffness curve after their parallel connection has a negative value near the equilibrium point, it needs to be used in conjunction with a positive stiffness structure. By connecting positive and negative stiffness structures in parallel, the system can achieve high static and low dynamic characteristics near the equilibrium position. When the third spring 9 is compressed, it generates an upward restoring force. By connecting it in parallel with the second spring 7, the fourth spring 10, the first spring 3, and the fifth spring 14, the overall stiffness of the system can be zero at the equilibrium point, achieving high static and low dynamic characteristics near the equilibrium position—that is, a quasi-zero stiffness system.

[0043] Under static equilibrium, the vertical height from fixed seat 8 to fixed seat 16 is H. The lengths of the first link 4, second link 5, third link 12, and fourth link 13 are all L1. The distances from the hinge points of the two X-shaped structures to the upper fixed seat 8 and lower fixed seat 16 are both L2. The two hinge points are the hinge points of the first link 4 and the second link 5, and the hinge points of the third link 12 and the fourth link 13, respectively. The stiffness of the second spring 7 and the fourth spring 10 is K1, and the stiffness of the first spring 3 and the fifth spring 14 is K2. The four springs 7, 10, 3, and 14 have equal lengths and the same horizontal angle. When the downward displacement is x, the expression for the force exerted by the second spring 7, the fourth spring 10, the first spring 3, and the fifth spring 14 in the vertical direction is:

[0044] F=2(K2-K1)·(L3-L)·sin(α) (1)

[0045] In the formula, L3 is the length of springs 7, 10, 3, and 14 after being stretched, L is the original length of springs 7, 10, 3, and 14, and α is the angle between springs 7, 10, 3, and 14 in the horizontal direction.

[0046]

[0047]

[0048]

[0049] In the formula,

[0050] Differentiating F, the total stiffness produced by the forces exerted by the second spring 7, the fourth spring 10, the first spring 3, and the fifth spring 14 in the vertical direction is:

[0051]

[0052] In the formula: L5 = Hx - L4,

[0053] The structural parameters of the negative stiffness structure in the weak nonlinear vibration isolator proposed in this embodiment are L1 = 0.9m, L2 = 0.6m, H = 0.6m, K1 = 150N / m, K2 = 200N / m. Let u = Hx, where u is the displacement of the upper fixed seat 8 relative to the lower fixed seat 16. Substituting the above parameters into equation (5), the static stiffness curve of the negative stiffness structure in this invention can be obtained, as shown in the figure. Figure 5 As shown. From Figure 5 As can be seen, the stiffness curve of the upper spring structure is convex, while the stiffness curve of the lower spring structure is concave.

[0054] The length L2 at the hinge point of the connecting rod is crucial to the overall vibration isolation performance of the structure. In some other embodiments, with the connecting rod length and spring stiffness fixed, the vibration isolation performance of the overall structure can be changed by adjusting the value of L2. To obtain the optimal vibration isolation performance, while keeping other parameters constant, the value of L2 is varied, resulting in the static stiffness curves of the negative stiffness structure of this invention under different L2 values. The L2 values ​​are 0.4m, 0.45m, 0.5m, 0.55m, and 0.6m. Please refer to [link / reference]. Figure 6The convex curve corresponds to the stiffness curve when L² is 0.4m, and the straight curve corresponds to the stiffness curve when L² is 0.45m. The rectangle below the arrow is an enlarged view of the rectangle above the arrow. The three curves in the rectangle below the arrow, from top to bottom, correspond to the stiffness curves when L² is 0.5m, 0.55m, and 0.6m, respectively. Figure 6 As can be seen, when L2 is 0.4m, the stiffness curve is convex, and the overall stiffness curve has a large nonlinearity. When L2 is 0.45m, that is, when the connecting rod hinge point is 1 / 2 of the rod length, the overall structure is in a completely symmetrical state at this time. When the stiffness of the upper and lower springs is not much different, the overall stiffness value is close to 0. As the value of L2 increases again, the stiffness curve changes from convex to concave, and the degree of nonlinearity of the curve also decreases. When L2 is 0.5m, the degree of nonlinearity of the stiffness curve is the smallest. When the value of L2 continues to increase, the degree of nonlinearity of the curve will continue to increase. Therefore, under the premise of ensuring the negative stiffness effect value, the vibration isolation performance of the overall structure is best when L2 is 0.5m. It can be seen that when the ratio of L2 to L1 is greater than 1 / 2 and less than or equal to 5 / 9, the vibration isolation structure has good vibration isolation performance. The preferred ratio of L2 to L1 is 5 / 9, at which time the vibration isolation performance is optimal. Furthermore, when the value of L1 changes, the ratio of L2 to L1 is not limited to between 1 / 2 and 5 / 9. The position of the hinge point can be adjusted accordingly to find the optimal value of the ratio of L2 to L1 for different link lengths.

[0055] Because the combined spring structure has a negative value near the equilibrium point, it needs to be used in conjunction with a positive stiffness structure. The negative stiffness structure, composed of the second spring 7, the fourth spring 10, the first spring 3, and the fifth spring 14, is connected in parallel with the positive stiffness third spring 9 to form a quasi-zero stiffness vibration isolator. To more clearly compare the vibration isolation performance of the vibration isolator proposed in this embodiment with that of a typical QZS vibration isolator, an index for evaluating QZS characteristics is defined here: when the stiffness K of the element in the vertical direction is less than 5 N / m, the corresponding region [-ud, ud] is defined as the QZS region. For example... Figure 7 The figure shows a comparison of the static stiffness curves of the vibration isolator before and after L2 optimization, and that of a typical QZS vibration isolator. The typical QZS vibration isolator has an operating range of approximately 0.48m in the QZS region, representing 40% of the total stroke. For the proposed vibration isolator, the operating range before L2 optimization is approximately 0.9m in the QZS region, representing 75% of the total stroke. After L2 optimization, the operating range is approximately 1.06m in the QZS region, representing 88% of the total stroke, significantly greater than both the structure before L2 optimization and the typical QZS vibration isolator. This demonstrates that the proposed vibration isolator exhibits significantly reduced nonlinearity compared to the traditional typical QZS vibration isolator, possessing good linear characteristics and ensuring the stability of the vibration isolation system.

[0056] The embodiments described above are merely examples of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the protection scope of the present invention.

Claims

1. A weakly nonlinear vibration isolation structure, comprising a base and a load platform, and a vibration isolation module disposed between the base and the load platform, characterized in that: The vibration isolation module includes a positive stiffness vibration isolation unit and a negative stiffness vibration isolation unit; The negative stiffness vibration isolation unit is divided into an upper spring structure and a lower spring structure, and the upper spring structure and the lower spring structure are placed opposite each other between the base and the load platform. When the load platform and the base are relatively displaced, the stiffness curve of the upper spring structure is "convex" and the stiffness curve of the lower spring structure is "concave". The upper spring structure includes a first V-shaped double link assembly disposed on the top of the base, and a first V-shaped double spring assembly disposed on the bottom of the load platform and connected to the first V-shaped double link assembly; The lower spring structure includes a second V-shaped double link assembly located at the bottom of the load platform, and a second V-shaped double spring assembly located at the top of the base and connected to the second V-shaped double link assembly; The two sides of the first V-shaped double link assembly are respectively hinged to the two sides of the second V-shaped double link assembly to form two X-shaped structures; The first V-shaped double link assembly includes a second link and a third link positioned opposite each other on the top of the base, and the first V-shaped double spring assembly includes a second spring and a fourth spring positioned opposite each other on the bottom of the load platform, with the ends of the second spring and the fourth spring respectively connected to the ends of the second link and the third link; The second V-shaped double linkage assembly includes a first linkage and a fourth linkage positioned at the bottom of the load platform, and the second V-shaped double spring assembly includes a first spring and a fifth spring positioned at the top of the base, with the ends of the first spring and the fifth spring respectively connected to the ends of the first linkage and the fourth linkage.

2. The weakly nonlinear vibration isolation structure according to claim 1, characterized in that: The load platform is fixedly provided with an upper fixed seat at its bottom and a lower fixed seat is fixedly provided with a bottom fixed seat at its top. The opposite ends of the second and third connecting rods are both hinged to the lower fixed seat. The opposite ends of the second and fourth springs are both hinged to the upper fixed seat. The opposite ends of the first and fourth connecting rods are both hinged to the upper fixed seat. The opposite ends of the first and fifth springs are both hinged to the lower fixed seat. The positive stiffness vibration isolation unit includes a third spring disposed between the upper fixed seat and the lower fixed seat.

3. The weakly nonlinear vibration isolation structure according to claim 2, characterized in that: The first and fourth links are hinged to the second and third links respectively, forming two mutually symmetrical X-shaped structures; the lengths of the first, second, third, and fourth links are all equal.

4. The weakly nonlinear vibration isolation structure according to claim 1, characterized in that: The stiffness of the first spring and the fifth spring is greater than that of the second spring and the fourth spring.

5. The weakly nonlinear vibration isolation structure according to any one of claims 1-4, characterized in that: Several guide modules are provided between the base and the load platform.

6. The weak nonlinear vibration isolation structure according to claim 5, characterized in that: The guiding module consists of a guide cylinder fixed to the top of the base, a guide rod slidably disposed inside the guide cylinder, and a linear motion bearing disposed between the guide cylinder and the guide rod. The upper end of the guide rod is fixedly connected to the load platform.

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