A low-frequency vibration isolation device based on linear magnetic negative stiffness

Abstract

The present invention discloses a low-frequency vibration isolation device based on linear magnetic negative stiffness, comprising two spring positive stiffness modules, an electromagnetic negative stiffness module and a central axis; the two spring positive stiffness modules are symmetrically arranged at the upper and lower parts of the electromagnetic negative stiffness module respectively; the upper end of the central axis is connected to the load, and the lower end of the central axis passes through the spring positive stiffness module at the upper part, the electromagnetic negative stiffness module and the spring positive stiffness module at the lower part in sequence. The beneficial effects of the present invention are as follows: the present invention has both high load-bearing capacity and low-frequency vibration isolation performance, and adopts the coupling mode of the attraction type electromagnetic negative stiffness mechanism and the repulsion type electromagnetic negative stiffness mechanism to realize the mutual offset of the nonlinear parts of the softening stiffness characteristics and the hardening stiffness characteristics, thereby improving the linearity of the negative stiffness in the high static and low dynamic stiffness vibration isolation device.

Description

Technical Field

[0001] The present invention relates to the technical field of vibration isolation, and particularly relates to a low-frequency vibration isolation device based on linear magnetic negative stiffness. Background Art

[0002] During operation, the power equipment on ships generates low-frequency vibrations. Due to its high transmissibility and low attenuation, it has always been a major factor threatening the stealth of ships. At the same time, due to the special working environment of ship equipment, the vibration isolation system is required to have certain high-static and low-dynamic stiffness characteristics. Therefore, constructing a suitable vibration reduction system to improve the stealth and survival rate of ships is the main aspect of current underwater vibration reduction research.

[0003] Passive vibration isolation devices still have a wide range of engineering application spaces due to their simple structure, high reliability, and no external energy. Traditional linear stiffness vibration isolation devices have good isolation effects on medium- and high-frequency vibrations, but the isolation effect on low-frequency vibrations is not ideal. In recent years, in order to break through the performance bottleneck of linear vibration isolation systems, researchers have proposed negative stiffness mechanisms, realizing a high-static and low-dynamic stiffness vibration isolation system with stiffness varying with the compression amount. Connecting the negative stiffness mechanism in parallel with the positive stiffness system at the equilibrium position can cancel out the positive stiffness near the equilibrium position of the system, achieving a lower dynamic stiffness, and not affecting the static load-bearing stiffness of the system at zero compression and the static displacement of the load. Thus, while not reducing the load-bearing capacity of the system, the natural frequency of the system can be reduced, and the vibration isolation frequency band can be extended.

[0004] The negative stiffness device is the key structure for realizing high-static and low-dynamic stiffness vibration isolation. So far, researchers have used various methods to achieve negative stiffness, and typical methods include: mechanical springs, magnets, rubber, cams, and bionic structures, etc. For example, utility model patents CN202021960720.X, CN201821473137.9, CN201822217954.4, invention patents CN201610423635.1, CN201510788865.3, etc. However, all of these methods have a problem: non-linear stiffness characteristics, which may cause the "jump" phenomenon in the movement of the system. According to the dynamic model of the vibration isolation system, non-linear stiffness will produce unexpected responses under large excitations, deteriorating the vibration isolation performance and restricting the application of high-static and low-dynamic stiffness vibration isolation systems in the isolation of large-amplitude vibrations. Summary of the Invention

[0005] The purpose of the present invention is to provide a low-frequency vibration isolation device based on linear magnetic negative stiffness in view of the deficiencies of the prior art.

[0006] The technical solution adopted by the present invention is as follows: A low-frequency vibration isolation device based on linear magnetic negative stiffness, which includes two spring positive stiffness modules, an electromagnetic negative stiffness module, and a central shaft; the two spring positive stiffness modules are symmetrically arranged above and below the electromagnetic negative stiffness module respectively; the upper end of the central shaft is connected to a load, and the lower end of the central shaft sequentially passes through the spring positive stiffness module located in the upper part, the electromagnetic negative stiffness module, and the spring positive stiffness module located in the lower part;

[0007] The electromagnetic negative stiffness module includes an upper annular permanent magnet, an intermediate annular permanent magnet, and a lower annular permanent magnet arranged axially along the central shaft in sequence. The upper and lower annular permanent magnets are symmetrically arranged above and below the intermediate annular permanent magnet; an annular coil coaxial with each permanent magnet is correspondingly arranged outside each permanent magnet, and the annular coil is fixed to the corresponding annular coil box; the three annular permanent magnets can move axially in the cavities inside the corresponding annular coils along with the central shaft;

[0008] The axial displacement of the central shaft can be adjusted through the two spring positive stiffness modules, thereby changing the relative positions of the annular permanent magnets and the corresponding coils, and thus adjusting the negative stiffness of the electromagnetic negative stiffness module.

[0009] According to the above solution, the spring positive stiffness module includes a helical spring, a limiting member, and an adjusting member; the helical spring is sleeved on the central shaft, one end of the helical spring is connected to the adjusting member, and the adjusting member is matched with the central shaft; the other end of the helical spring is connected to the upper end surface of the limiting member; the central shaft passes through the center of the limiting member; the electromagnetic negative stiffness module is installed between the limiting members of the two helical spring positive stiffness modules; when adjusting the adjusting members of the two spring positive stiffness modules, the compression amounts of the two helical springs can be changed, thereby changing the axial position of the central shaft, and thus adjusting the relative positions of the annular permanent magnets and the corresponding coils, and thus adjusting the negative stiffness of the electromagnetic negative stiffness module.

[0010] According to the above solution, the limiting member is a linear bearing. The linear bearings of the two spring positive stiffness modules are symmetrically arranged on the central shaft along the equilibrium position of the vibration isolation device; one end of the helical spring is connected to the end surface of the linear bearing, and the linear bearings are respectively connected to the annular coil boxes through a plurality of through bolts arranged at axial intervals.

[0011] According to the above solution, three annular coils are vertically coaxially symmetrically arranged to form an attractive electromagnetic negative stiffness mechanism; the upper and lower two annular coils are respectively symmetrically arranged at both ends of the intermediate annular coil, and the same-direction and equal-magnitude currents are passed through them.

[0012] According to the above solution, the annular coils are all water-cooled coils.

[0013] According to the above scheme, three annular permanent magnets and three annular coils are vertically arranged coaxially and symmetrically to form a repulsive electromagnetic negative stiffness mechanism; the annular permanent magnets are all fixedly connected to the central shaft through fixing rings, and the three annular coils are coaxial with the corresponding annular permanent magnets at the same height.

[0014] According to the above scheme, the annular permanent magnets are all axially magnetized.

[0015] According to the above scheme, the vertical spacing of the annular coils is 14 - 15 mm, the vertical spacing of the annular permanent magnets is 14 - 15 mm, and the lateral spacing between the annular coils and the corresponding permanent magnets is 4 - 5 mm.

[0016] According to the above scheme, the pitch of the adjusting nut of the upper spring positive stiffness module is smaller than that of the adjusting nut of the lower spring positive stiffness module.

[0017] According to the above scheme, the linear bearing selects a sliding bearing with an aluminum shell and a polytetrafluoroethylene resin lining; the annular permanent magnets are made of rare earth permanent magnetic materials; the central shaft, bolts and nuts are made of non-magnetic or weakly magnetic materials; and each box body is made of aluminum alloy materials.

[0018] The beneficial effects of the present invention are as follows: The present invention adopts the coupling method of an attractive electromagnetic negative stiffness mechanism and a repulsive electromagnetic negative stiffness mechanism to realize the mutual cancellation of the non-linear parts of the softening stiffness characteristic and the hardening stiffness characteristic, improve the linearity of the negative stiffness in the low-frequency vibration isolation device, ensure that the system has both high load-bearing capacity and low-frequency vibration isolation performance, and at the same time solve the problems of "jumping" and "unexpected response under large excitation", and further improve the working stability of the vibration isolation system. The present invention adopts a coarse adjustment nut, a fine adjustment nut and an electromagnetic negative stiffness structure, can control the current in the electromagnet in real time according to the change of the load mass, and adjust the negative stiffness in real time, ensure that the vibration isolation frequency at the equilibrium position of the vibration isolation system is quasi-zero state, improve the performance stability of the vibration isolation system, and enhance the low-frequency or ultra-low-frequency vibration isolation effect of the vibration isolation system. The present invention has a very low dynamic stiffness near the static equilibrium position; through the coupling of the attractive electromagnetic negative stiffness mechanism and the repulsive electromagnetic negative stiffness mechanism, the stability of the vibration isolation system is improved, it has good anti-sway performance, simple structure, convenient maintenance, and is suitable for low-frequency and even ultra-low-frequency vibration isolation. Description of the Drawings

[0019] Figure 1 It is a schematic diagram of the overall structure of a specific embodiment of the present invention.

[0020] Figure 2 It is a front view sectional view of the overall structure of this embodiment.

[0021] Figure 3 It is a side view sectional view of the internal structure of this embodiment.

[0022] Figure 4Schematic connection diagram of the linear bearing device, the attractive electromagnetic negative stiffness adjustment device, the repulsive electromagnetic negative stiffness adjustment device, and the positive stiffness spring adjustment device in this embodiment.

[0023] Wherein: 1. Load; 2. Helical spring; 3. Upper annular coil; 4. Intermediate annular coil; 5. Lower annular coil; 6. Base; 7. Locking nut; 8. Fine adjustment nut; 9. Upper linear bearing; 10. Fixed ring; 11. Vibration isolation device housing; 12. Lower linear bearing; 13. Coarse adjustment nut; 14. Central shaft; 15. Through bolt; 16. Upper annular permanent magnet; 17. Lower annular permanent magnet; 18. Intermediate annular permanent magnet; 19. Intermediate annular coil housing; 20. Upper end linear spring housing; 21. Lower annular coil housing; 22. Lower annular coil housing; 23. Upper annular coil housing. Detailed implementation manner

[0024] To better understand the present invention, the present invention will be further described below in conjunction with the accompanying drawings and specific embodiments.

[0025] As Figures 1 to 4 shown, a low-frequency vibration isolation device based on linear magnetic negative stiffness includes two spring positive stiffness modules, an electromagnetic negative stiffness module, and a central shaft 14; the two spring positive stiffness modules are symmetrically arranged above and below the electromagnetic negative stiffness module respectively; the upper end of the central shaft 14 is connected to the load 1 (the upper end of the central shaft 14 cooperates with the locking nut 7, and the locking nut 7 is connected to the bottom of the load 1), and the lower end of the central shaft 14 sequentially passes through the spring positive stiffness module located in the upper part, the electromagnetic negative stiffness module, and the spring positive stiffness module located in the lower part;

[0026] The electromagnetic negative stiffness module includes an upper annular permanent magnet 16, an intermediate annular permanent magnet 18, and a lower annular permanent magnet 17 arranged axially along the central shaft 14 in sequence, and the upper and lower annular permanent magnets are symmetrically arranged above and below the intermediate annular permanent magnet 18; an annular coil coaxial with each annular permanent magnet is respectively arranged outside each annular permanent magnet (the upper annular coil 3, the intermediate annular coil 4, and the lower annular coil 5 are respectively arranged correspondingly), and the annular coil is fixed to the corresponding annular coil housing (each annular coil corresponds to the upper annular coil housing 23, the intermediate annular coil housing 19, and the lower annular coil housing 21 respectively); the three annular permanent magnets can move axially in the cavities inside the corresponding annular coils along with the central shaft 14;

[0027] The axial displacement of the central shaft 14 can be adjusted through the two spring positive stiffness modules (the load 1 moves synchronously with the central shaft 14), thereby changing the relative positions of the annular permanent magnets and the corresponding coils, and thus adjusting the negative stiffness of the electromagnetic negative stiffness module.

[0028] Preferably, the spring positive stiffness module includes a helical spring 2, a limiting member, and an adjusting member; the helical spring 2 is sleeved on the central shaft 14, one end of the helical spring 2 is connected to the adjusting member, and the adjusting member cooperates with the central shaft 14; the other end of the helical spring 2 is connected to the upper end surface of the limiting member; the central shaft 14 passes through the center of the limiting member; the electromagnetic negative stiffness module is installed between the limiting members of the two spring positive stiffness modules; when adjusting the adjusting members of the two spring positive stiffness modules, the compression amount of the two helical springs 2 can be changed, thereby changing the axial position of the central shaft 14, so as to adjust the relative position of the annular permanent magnet and the corresponding annular coil, and thus adjust the negative stiffness of the electromagnetic negative stiffness module.

[0029] In the present invention, the load 1 is provided on the locking nut 7, the upper end of the central shaft 14 cooperates with the locking nut 7, and the load 1 can axially move along with the central shaft 14; a notch for the axial movement of the central shaft 14 is reserved in the base 6.

[0030] Preferably, the adjusting member is an adjusting nut. The helical spring is a linear helical spring 2, and an external thread adapted to the adjusting nut is provided on the outer peripheral surface of the central shaft 14. Specifically, the adjusting nut of the upper spring positive stiffness module is a fine-tuning nut 8, and the adjusting nut of the lower spring positive stiffness module is a coarse-tuning nut 13. The pitches of the threads of the two nuts are different, and the pitch of the coarse-tuning nut 13 is greater than that of the fine-tuning nut 8. The coarse-tuning nut 13 can be used for large position adjustments, and the fine-tuning nut 8 can be used for fine fine-tuning. The structural design is simple, but it takes into account both coarse and fine tuning and is convenient to operate.

[0031] Preferably, the limiting member is a linear bearing. The linear bearings of the two spring positive stiffness modules (the upper one is the upper linear bearing 9 and the lower one is the lower linear bearing 12) are symmetrically arranged on the central shaft 14 along the equilibrium position of the vibration isolation device (the central shaft 14 is adapted to the inner ring of the linear bearing); one end of the helical spring 2 is connected to the end face of the linear bearing, and the linear bearings are respectively connected to the annular coil box body through a plurality of through bolts 15 arranged at axial intervals. Specifically, the upper linear bearing 9 of the upper spring positive stiffness module is bolted to the upper annular coil box body 23, and the lower linear bearing 11 of the lower spring positive stiffness module is bolted to the lower annular coil box body 21; the two linear bearings are installed on the outside of the upper and lower annular coils, which can ensure the coaxiality of the box body and the central shaft 14 and reduce the friction during movement. Spring notches are provided on the upper surfaces of the two linear bearings, which can effectively limit the position of the helical spring 2.

[0032] In the present invention, three annular permanent magnets are mounted on the central shaft 14 through the fixing ring 10. The upper annular permanent magnet 16 is correspondingly provided with an upper annular coil 3 and an upper annular coil box body 23, the middle annular permanent magnet 18 is correspondingly provided with a middle annular coil 4 and a middle annular coil box body 19, and the lower annular permanent magnet 17 is correspondingly provided with a lower annular coil 5 and a lower annular coil box body 21; retaining rings are arranged inside the three annular coil box bodies 19, 20, 21 for fixing the corresponding annular coils. The vibration isolation box body 11 includes a spring box body at the top (such as the top spring box body 20 in Figures 1 to 4 ), three annular coil box bodies in the middle (such as the upper annular coil box body 23, the middle annular coil box body 19, and the lower annular coil box body 21 in the figure), and a spring box body at the bottom (reference numeral 22). The box bodies are fixedly connected to each other through external bolts. The spring box body 22 at the bottom is also the base box body of the entire vibration isolation device. Bolt holes are provided on its base 6 for fixed connection; the coarse adjustment nut 13 of the lower spring positive stiffness module is installed on the base 6.

[0033] In the present invention, the linear bearing selects a sliding bearing with an aluminum shell and a polytetrafluoroethylene resin lining to avoid the influence of an ordinary steel ball linear bearing on the magnetic field; the annular permanent magnets are all made of rare earth permanent magnet materials; components and structures such as the central shaft 14, the fixing ring 10, bolts and nuts are all made of non-magnetic or weakly magnetic materials, such as 304 stainless steel; each box body is made of aluminum alloy material.

[0034] In the present invention, the components of the electromagnetic negative stiffness module can respectively form an attracting electromagnetic negative stiffness mechanism and a repulsive electromagnetic negative stiffness mechanism.

[0035] The three annular coils 3, 4, and 5 are vertically coaxially symmetrically arranged to form an attracting electromagnetic negative stiffness mechanism. As shown in Figure 3 and Figure 4 , the attracting electromagnetic negative stiffness mechanism includes two symmetrically arranged upper and lower annular coils 3 and 5 and a middle annular coil 4. Each annular coil is wound with enameled wire. The two identical upper and lower annular coils 3 and 5 are respectively located at both ends of the middle annular coil 4 along the central shaft 14, symmetrically arranged, and the same-direction and equal-sized currents are passed through. The three annular coils are fixed to each other; the annular coils are all water-cooled coils, which can effectively solve the problem of coil heating.

[0036] The three annular permanent magnets 16, 17, and 18 and the three annular coils 3, 4, and 5 are vertically coaxially symmetrically arranged to form a repulsive electromagnetic negative stiffness mechanism. As shown in Figure 3 and Figure 4As shown, the repulsive electromagnetic negative stiffness mechanism includes three pairs of paired structures composed of toroidal coils and permanent magnets (upper toroidal coil 3 and upper end toroidal permanent magnet 16, middle toroidal coil 4 and middle toroidal permanent magnet 18, lower toroidal coil 5 and lower end toroidal permanent magnet 17), and these three pairs of paired structures composed of toroidal coils and permanent magnets are symmetrically arranged along the central axis 14. Preferably, the toroidal permanent magnets in the three pairs of paired structures are fixedly connected to the central axis 14 through fixing rings 10, and the three toroidal coils 3, 4, and 5 are fixed to each other and are coaxial and at the same height with the corresponding toroidal permanent magnets 16, 17, and 18. The vertical distance between each pair of paired structures formed by the toroidal coils and the corresponding permanent magnets is 14 - 15 mm (that is, the vertical spacing between the toroidal coils is 14 - 15 mm, and the vertical spacing between the toroidal permanent magnets is 14 - 15 mm), and the lateral spacing between the toroidal coil and the corresponding toroidal permanent magnet is 4 - 5 mm. The toroidal permanent magnets in the three pairs of paired structures are axially magnetized. From the two-dimensional axial symmetry of the toroidal permanent magnet and the toroidal coil, only axial force acts on the toroidal permanent magnet, that is, only axial negative stiffness is generated.

[0037] The two spring positive stiffness adjustment mechanisms respectively adopt linear helical springs 2. As Figure 3 and Figure 4 shown, the two linear helical springs 2 are sleeved on the central axis 14 and are located outside the two linear bearings 9 and 12. One end of the linear spring 2 is pressed against the notches of the linear bearings 9 and 12, and the other end is respectively pressed against the coarse adjustment nut 13 or the fine adjustment nut 8 on the central axis 14. The design of pressing the middle electromagnetic negative stiffness module with the two helical springs 2 can ensure that the load will not break away from the springs when the vibration isolation system generates large displacements during resonance.

[0038] The equilibrium position refers to the position of the system in a static state. In the present invention, the equilibrium position is the position where the middle toroidal permanent magnet is at the vertical center of the middle toroidal coil. According to the electromagnetic negative stiffness generation mechanism of the magnetic element configuration, the attractive electromagnetic negative stiffness mechanism generates softening negative stiffness because the attractive force between magnets is inversely proportional to the square of their distance. The farther away from the equilibrium position, the closer to one end magnet, and the greater the force difference generated. The repulsive electromagnetic negative stiffness mechanism generates hardening negative stiffness because the repulsive force between magnetic elements becomes smaller as the deviation from the equilibrium position increases. Therefore, by coupling the repulsive and attractive electromagnetic negative stiffness mechanisms, the non-linear parts of the softening stiffness characteristic and the hardening stiffness characteristic are mutually offset, while the linear parts are superposed, improving the value of the negative stiffness while enhancing the linearity of the negative stiffness. Using permanent magnets or toroidal coils can generate negative stiffness with softening or hardening characteristics. The negative stiffness generated between permanent magnets is greater, but it cannot be adjusted; the toroidal coil can control the magnitude of the magnetic field by controlling the excitation current, but its current-carrying capacity is limited, and the negative stiffness generated only by the electromagnetic force between toroidal coils is too weak. Therefore, a combined configuration of toroidal coils and toroidal permanent magnets is selected to design the electromagnetic negative stiffness module to achieve adjustable negative stiffness and obtain a larger adjustable range.

[0039] In the present invention, the repulsive electromagnetic negative stiffness mechanism includes three toroidal permanent magnets 16, 17, 18 and three toroidal coils 3, 4, 5. When a current is passed through the toroidal coil, due to the magnetic effect of the current, the current-carrying ring will excite a constant magnetic field and generate a mutual force with the toroidal permanent magnet. The magnetic field distribution generated by magnetic elements such as permanent magnets and coils in a vacuum is relatively regular, and the generated electromagnetic field can be calculated to further calculate the electromagnetic force.

[0040] According to the superposition theorem, an axially magnetized toroidal permanent magnet can be equivalent to superimposing a cylindrically magnetized permanent magnet with reverse magnetization inside a cylindrical permanent magnet. The axially magnetized toroidal magnet can be equivalent to two thin solenoids located on the inner and outer ring surfaces. The currents in the two solenoids are equal in magnitude and opposite in direction, respectively:

[0041]

[0042]

[0043] In the formula, μ 0 is the magnetic permeability in vacuum (H / m), I in is the internal equivalent solenoid current value (A), I out is the external equivalent solenoid current value (A), h is the axial height of the equivalent solenoid (m), N eq is the equivalent number of turns of the equivalent solenoid (turns), J is the equivalent polarization intensity (C / m 2 ).

[0044] In the present invention, the attractive electromagnetic negative stiffness mechanism adopts three toroidal coils 3, 4, and 5, and two identical toroidal coils are passed with currents having the same direction and equal magnitude. After passing currents through the toroidal coils, due to the magnetic effect of the currents, two current-carrying rings 1 and 2 will respectively excite a constant magnetic field and generate a mutual force.

[0045] The Biot-Savart law describes the magnetic field excited by a current element at any point in space:

[0046]

[0047] where I is the source current (A), dl is the infinitesimal line element of the source current (m), r is the distance from the current element to the point where the magnetic field is excited (m), and e r is the unit vector pointing from the current element to the point where the magnetic field is excited (A·m), B is the magnetic induction intensity (T), and μ 0 is the magnetic permeability in vacuum (H / m).

[0048] The force exerted on the current element Idl on the current-carrying ring by another current-carrying ring is:

[0049] dF = Idl × B (4), Integrating the above formula can obtain the mutual force F between the two current-carrying rings:

[0050] F = ∫ l dF (5),

[0051] Since the two current-carrying rings are concentric, according to symmetry, the electromagnetic force is along the axial direction. Because the integration is complex and it is difficult to obtain an analytical solution, it can also be expressed by elliptic integrals:

[0052]

[0053] In the formula, I 1 is the current value of the current-carrying ring 1 (A), I 2 is the current value of the current-carrying ring 2 (A), r 1 is the radius of the current-carrying ring 1 (m), r 2 is the radius of the current-carrying ring 2 (m), z is the vertical distance between the two current-carrying rings (m), and k is K(k) and E(k) are the first and second complete elliptic integrals with k as the modulus respectively. The direction of the mutual force between the two current-carrying rings is determined by the direction of the exciting current. According to the Ampere's rule, when the currents in the two current-carrying rings are in the same direction, the electromagnetic force shows mutual attraction, and vice versa. So far, the electromagnetic force between the two current-carrying rings has been determined. By superimposing the forces between the current-carrying rings, the electromagnetic force between the energized coils or solenoids can be solved. Combining with the equivalent relationship between the axially magnetized permanent magnet and the solenoid, the electromagnetic force between the toroidal coil and the toroidal permanent magnet can also be obtained by superposition.

[0054] The working principle of the present invention is as follows: By adopting the coupling method of an attractive electromagnetic negative stiffness mechanism and a repulsive electromagnetic negative stiffness mechanism, the non-linear parts of the softening stiffness characteristic and the hardening stiffness characteristic are mutually cancelled, improving the linearity of the negative stiffness in the low-frequency vibration isolation device. Among them, the attractive electromagnetic negative stiffness mechanism consists of three toroidal coils 3, 4, and 5. Currents with the same direction are passed through the head and tail toroidal coils 3 and 5, and attractive forces are generated among them. The repulsive electromagnetic negative stiffness mechanism adopts three toroidal permanent magnets 16, 17, and 18 and three toroidal coils 3, 4, and 5. The permanent magnets move axially in the toroidal coils, and repulsive forces are generated between them. When the system is in the static equilibrium position, the forces among the three toroidal permanent magnets 16, 17, and 18 and the three toroidal coils 3, 4, and 5 cancel each other out, and the system is in a stable state. When the system is subjected to an external excitation force, the central axis moves vertically, causing the toroidal permanent magnets to deviate from the equilibrium position. As a result, repulsive electromagnetic forces are generated between the toroidal permanent magnets and the toroidal coils. In addition, attractive electromagnetic forces also exist among the other three toroidal coils, which not only provide negative stiffness but also can effectively cancel the non-linear part. Thus, the dynamic frequency of the system is relatively low, and the vibration caused by the excitation force can be effectively isolated. The electromagnetic force is in the same direction as the relative displacement, pushing it away from the equilibrium position, that is, the designed electromagnetic coupling structure generates negative stiffness. When the load mass changes, the coarse adjustment nut, the fine adjustment nut, and the electromagnetic negative stiffness module can be used to control the current in the electromagnet in real time according to the change of the load mass, and adjust the negative stiffness in real time, so as to ensure that the vibration isolation frequency of the vibration isolation device at the equilibrium position is in the quasi-zero state. In addition, reversing the current in the toroidal coil will generate positive stiffness, which can expand the adjustable range of stiffness and also extend the application range of the linear electromagnetic coupling structure.

[0055] The content not described in detail in this specification belongs to the prior art well-known to those skilled in the art. The above embodiments are only used to illustrate the technical concept and characteristics of the present invention, and their purpose is to enable those who are familiar with this technology to understand the content of the present invention and implement it accordingly, and cannot be used to limit the protection scope of the present invention. All equivalent changes or modifications made according to the spirit and essence of the present invention should be covered within the protection scope of the present invention.

Claims

1. A low-frequency vibration isolation device based on linear magnetic negative stiffness, characterized in that: It comprises two spring positive stiffness modules, an electromagnetic negative stiffness module and a central axis; the two spring positive stiffness modules are symmetrically arranged at the upper and lower parts of the electromagnetic negative stiffness module respectively; the upper end of the central axis is connected to the load, and the lower end of the central axis passes through the spring positive stiffness module at the upper part, the electromagnetic negative stiffness module and the spring positive stiffness module at the lower part in sequence; The electromagnetic negative stiffness module comprises an upper annular permanent magnet, a middle annular permanent magnet and a lower annular permanent magnet which are sequentially arranged along the axial direction of the central axis, and the upper and lower annular permanent magnets are symmetrically arranged at the upper and lower parts of the middle annular permanent magnet; a coaxial annular coil is respectively arranged on the outside of each permanent magnet, and the annular coil is fixed to the corresponding annular coil box; the three annular permanent magnets can move axially in the cavity inside the corresponding annular coil along the central axis; The axial displacement of the central axis can be adjusted through two spring positive stiffness modules, thereby changing the relative position of the annular permanent magnet and the corresponding coil, thereby adjusting the negative stiffness of the electromagnetic negative stiffness module.

2. The low-frequency vibration isolation device according to claim 1, characterized in that: The spring positive stiffness module includes a coil spring, a limit piece and an adjusting piece; the coil spring is sleeved on the central axis, one end of the coil spring is connected to the adjusting piece, and the adjusting piece cooperates with the central axis; the other end of the coil spring is connected to the upper end surface of the limit piece; the central axis passes through the center of the limit piece; the electromagnetic negative stiffness module is installed between the limit pieces of the two coil spring positive stiffness modules; when adjusting the adjusting pieces of the two spring positive stiffness modules, the compression amount of the two coil springs can be changed, thereby changing the axial position of the central axis, thereby adjusting the relative position of the annular permanent magnet and the corresponding annular coil, thereby adjusting the negative stiffness of the electromagnetic negative stiffness module.

3. The low-frequency vibration isolation device according to claim 2, characterized in that: The limiter is a linear bearing, and the linear bearings of the two spring positive stiffness modules are symmetrically arranged on the central axis along the equilibrium position of the vibration isolation device; one end of the coil spring is connected to the end face of the linear bearing, and the linear bearing is connected to the annular coil box.

4. The low-frequency vibration isolation device according to claim 2, characterized in that: Three annular wires are arranged vertically and coaxially symmetrically to form an attractive electromagnetic negative stiffness mechanism; the upper and lower annular coils are symmetrically arranged at the two ends of the middle annular coil, and currents of the same direction and equal magnitude are passed through them.

5. The low-frequency vibration isolation device according to claim 4, characterized in that: The annular coils are all water-cooled coils.

6. The low-frequency vibration isolation device according to claim 1, characterized in that: Three annular permanent magnets and three annular coils are arranged vertically coaxially and symmetrically to form a repulsive electromagnetic negative stiffness mechanism; the annular permanent magnets are fixedly connected to the central axis through a fixing ring, and the three annular coils are coaxial with the corresponding annular permanent magnets at the same height.

7. The low-frequency vibration isolation device according to claim 6, characterized in that: The vertical spacing of the annular coils is 14-15 mm, the vertical spacing of the annular permanent magnets is 14-15 mm, and the lateral spacing between the annular coils and the corresponding permanent magnets is 4-5 mm.

8. The low-frequency vibration isolation device according to claim 2, characterized in that: The adjusting member is an adjusting nut, and the pitch of the adjusting nut of the upper spring positive stiffness module is smaller than the pitch of the adjusting nut of the lower spring positive stiffness module.

9. The low-frequency vibration isolation device according to claim 3, characterized in that: The linear bearing is made of sliding bearing with aluminum shell and tetrafluoroethylene resin lining; the annular permanent magnet is made of rare earth permanent magnet material; the central shaft, bolts and nuts are made of non-magnetic or weakly magnetic materials; and each box is made of aluminum alloy material.

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