A compact low-frequency vibration isolation device with magnetic mixing to adjust positive and negative stiffness

Abstract

The invention discloses a compact low-frequency vibration isolation device for magnetic mixed adjustment of positive and negative stiffness, comprising an upper support platform, a base, an elastic airbag positive stiffness mechanism, a central axis, a vibration isolation box, two spring positive stiffness modules and an electromagnetic negative stiffness module installed in the vibration isolation box; the elastic airbag positive stiffness mechanism comprises an elastic airbag, the upper end of which is connected to the upper support platform, and the lower end of which is connected to the base; the base of the vibration isolation box is fixed on the base; the two spring positive stiffness modules are symmetrically arranged at the upper and lower parts of the electromagnetic negative stiffness module; the upper end of the central axis is connected to the upper support platform, and the lower end of the central axis passes through the spring positive stiffness module, the electromagnetic negative stiffness module and the spring positive stiffness module located at the upper part of the vibration isolation box in sequence. The beneficial effects of the invention are: the combination of the spring airbag and the electromagnetic negative stiffness makes the structure of the vibration isolation device simple, compact and easy to install; when the load mass or external excitation changes, the stiffness of the vibration isolation system is more easily adjusted in real time by using the airbag and the electromagnetic mechanism, and the stability is higher.

Description

Technical Field

[0001] The invention relates to the technical field of vibration isolation, and in particular to a compact low-frequency vibration isolation device capable of adjusting positive and negative stiffness by magnetic mixing. Background Art

[0002] The low-frequency line spectrum caused by ship power machinery has become the main characteristic signal for detecting, tracking and identifying targets in modern underwater acoustic confrontation, and is the main hazard to the underwater acoustic stealth performance of ships. Therefore, low-frequency line spectrum isolation is of great significance for improving the acoustic stealth performance of ships. Passive vibration isolator is a load-bearing energy-consuming element with the advantages of simple structure, low energy consumption, easy implementation and good economy. It is the main means of isolating vibration transmission.

[0003] However, at present, most of the passive vibration isolators designed based on classical vibration isolation theory have input and output frequency retention, and are powerless to change the spectrum structure of ship radiation noise; and the linear vibration isolation system has limited isolation ability for low-frequency line spectra with external excitation frequencies less than twice the root natural frequency of the system; at the same time, the contradiction between large bearing capacity and ultra-low frequency vibration isolation, ultra-low stiffness and position stability, low resonance point transmission rate and high attenuation rate in a wide frequency domain has always restricted the engineering application of passive vibration isolators.

[0004] The quasi-zero stiffness isolator, which is composed of positive and negative stiffness elements connected in parallel, has a small combined stiffness within a certain range of the static equilibrium position, and can obtain high static stiffness to support the isolated equipment and low dynamic stiffness characteristics to reduce the vibration transmission rate, which can not only ensure the low-frequency vibration isolation performance near the working point, but also improve the stability of the system. However, if the weight of the object to be isolated is not the ideal weight of the design, that is, the object to be isolated is placed on the quasi-zero stiffness isolator and cannot be stabilized in the ideal static equilibrium position, the performance of the quasi-zero stiffness isolator will be affected. In response to this problem, invention patents CN104455181A, CN203641365U, CN202132428U and CN102678804A all adjust the compression of the positive stiffness spring through the adjustment sleeve to make the system reach the static equilibrium position, but the preload adjustment amount of the spring is limited. When the weight of the object to be isolated deviates greatly from the ideal weight of the design, this method is difficult to achieve the ideal effect. Moreover, although there are several methods to achieve adjustable negative stiffness, most of them adjust the parameters of the negative stiffness mechanism by adding complex mechanical mechanisms, and the adjustment mechanism is single and not flexible enough, which is not conducive to dealing with complex environments in actual engineering. In addition, the additional mechanical adjustment mechanism not only makes the structure of the vibration isolation system complex and occupies a large space, but also causes the system to have a more obvious delay effect in negative stiffness adjustment, affecting the control effect. Summary of the invention

[0005] The purpose of the present invention is to provide a compact low-frequency vibration isolation device with simple structure and magnetic mixing to adjust positive and negative stiffness in view of the shortcomings of the prior art.

[0006] The technical solution adopted by the present invention is: a compact low-frequency vibration isolation device with magnetic mixed adjustment of positive and negative stiffness, comprising an upper support platform, a base, an elastic airbag positive stiffness mechanism, a central axis, a vibration isolation box, two spring positive stiffness modules and an electromagnetic negative stiffness module installed in the vibration isolation box;

[0007] The support platform and the base are arranged vertically and parallelly; the elastic airbag positive stiffness mechanism includes an elastic airbag, the upper end of the elastic airbag is connected to the upper support platform, and the lower end of the elastic airbag is connected to the base; the elastic airbag, the upper support platform and the base are enclosed to form a cavity; the base is provided with an air hole connected to the cavity; the entrance of the air hole can be connected to an external gas control unit;

[0008] The vibration isolation box is installed in the cavity, and the base of the vibration isolation box is fixed on the base; the two spring positive stiffness modules are symmetrically arranged on the upper and lower parts of the electromagnetic negative stiffness module;

[0009] The upper end of the central axis is connected to the upper support platform, and the lower end of the central axis passes through the spring positive stiffness module located at the upper part of the vibration isolation box, the electromagnetic negative stiffness module and the spring positive stiffness module located at the lower part of the vibration isolation box in sequence, and is connected to the base of the vibration isolation box.

[0010] According to the above scheme, the electromagnetic negative stiffness module includes an upper annular permanent magnet, an intermediate 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 intermediate 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;

[0011] 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.

[0012] According to the above scheme, the spring positive stiffness module includes a coil spring, a limiter and an adjusting member; the coil spring is sleeved on the central axis, one end of the coil spring is connected to the adjusting member, and the adjusting member cooperates with the central axis; the other end of the coil spring is connected to the upper end surface of the limiter; the central axis passes through the center of the limiter; the electromagnetic negative stiffness module is installed between the limiters of the two coil spring positive stiffness modules; when adjusting the adjusting members of the two spring positive stiffness modules, the compression amount of the two coil springs can be changed, and then the axial position of the central axis can be changed, 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.

[0013] According to the above scheme, 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.

[0014] According to the above scheme, three annular wires are arranged vertically and symmetrically on the same axis 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.

[0015] According to the above solution, the annular coils are all water-cooled coils.

[0016] According to the above scheme, 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.

[0017] According to the above scheme, the linear bearing is a sliding bearing with an aluminum shell and a tetrafluoroethylene resin lining.

[0018] 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.

[0019] According to the above solution, the spring airbag is made of rubber material.

[0020] The beneficial effects of the present invention are as follows: the present invention combines the positive stiffness mechanism of the airbag spring with the electromagnetic negative stiffness module, and by adjusting the control current, the electromagnetic negative stiffness can be matched with the positive stiffness of the airbag spring, and near-zero stiffness and low-frequency vibration isolation can be always achieved within a certain load range, ensuring that the system has both high load-bearing capacity and low-frequency vibration isolation performance. This vibration isolation device is mainly suitable for occasions with limited installation space, different load masses, and complex working environments. The combination of spring airbags and electromagnetic negative stiffness makes the structure of the vibration isolation device simple, compact, and easy to install; when the load mass or external excitation changes, the airbag and electromagnetic mechanism are easier to adjust the stiffness of the vibration isolation system in real time and the stability is higher. In addition, the present invention also adopts the coupling method of the attractive electromagnetic negative stiffness mechanism and the repulsive electromagnetic negative stiffness mechanism to achieve 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 quasi-zero stiffness isolator, having good anti-swaying performance, simple structure, and convenient maintenance, and is suitable for low-frequency and even ultra-low-frequency vibration isolation. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a schematic diagram of the overall structure of a specific embodiment of the present invention.

[0022] Figure 2 It is a front cross-sectional view of this embodiment.

[0023] Figure 3 Schematic diagram of the overall structure of the electromagnetic negative stiffness module in this embodiment.

[0024] Figure 4 It is a front cross-sectional view of the electromagnetic negative stiffness module in this embodiment.

[0025] Figure 5 is a side view of the electromagnetic negative stiffness module in this embodiment.

[0026] Figure 6 Schematic diagram of the installation of the annular permanent magnet and the upper and lower linear bearings in this embodiment.

[0027] Among them: 1. Upper support platform; 2. Coil spring; 3. Upper annular coil; 4. Middle annular coil; 5. Lower annular coil; 6. Base; 7. Locking nut; 8. Fine-tuning nut; 9. Upper linear bearing; 10. Fixing ring; 11. Vibration isolation box; 12. Lower linear bearing; 13. Coarse-adjusting nut; 14. Center axis; 15. Through bolt; 16. Upper annular permanent magnet; 17. Lower annular permanent magnet; 18. Middle annular permanent magnet; 19. Middle annular coil box; 20. Upper linear spring box; 21. Lower annular coil box; 22. Lower annular coil box; 23. Upper annular coil box; 24. Elastic airbag; 25. Base; 26. Wire hole; 27. Air hole. DETAILED DESCRIPTION

[0028] In order to better understand the present invention, the present invention is further described below in conjunction with the accompanying drawings and specific embodiments.

[0029] like Figure 1-2 A compact low-frequency vibration isolation device with magnetic mixing to adjust positive and negative stiffness is shown.

[0030] It includes an upper support platform 1, a base 27, an elastic airbag positive stiffness mechanism, a central axis 14, a vibration isolation box 11, two spring positive stiffness modules and an electromagnetic negative stiffness module installed in the vibration isolation box 11;

[0031] The support platform 1 and the base 27 are arranged vertically and in parallel; the elastic airbag positive stiffness mechanism includes an elastic airbag 24, the upper end of the elastic airbag 24 is connected to the upper support platform 1, and the lower end of the elastic airbag 24 is connected to the base 25; the elastic airbag 24, the upper support platform 1 and the base 25 are enclosed to form a closed cavity; the base 25 is provided with an air hole 27 connected to the cavity; the entrance of the air hole 27 can be connected to an external gas control unit;

[0032] The vibration isolation box 11 is installed in the cavity, and the base 6 of the vibration isolation box 11 is fixed on the base 25; the two spring positive stiffness modules are symmetrically arranged on the upper and lower parts of the electromagnetic negative stiffness module;

[0033] The upper end of the central shaft 14 is connected to the upper supporting platform 1 through a locking nut 7, and the lower end of the central shaft 14 passes through the spring positive stiffness module, the electromagnetic negative stiffness module and the spring positive stiffness module located at the upper part of the vibration isolation box 11 in sequence, and is connected to the base 6 of the vibration isolation box 11; the central shaft 14 can move axially (the upper supporting platform 1 moves accordingly) to change the stiffness of the spring positive stiffness module and the electromagnetic negative stiffness module.

[0034] In the present invention, the elastic airbag 24 is located outside and fixedly connected to the upper support platform 1 and the base 25 by bolts; the entrance of the air hole 27 avoids the vibration isolation box. The entrance of the air hole 27 can be connected to an external gas control unit, which includes a gas source, a pipeline and related control valves, and can be used to control the pressure inside the elastic airbag 24 in real time to adjust the stiffness and load-bearing capacity.

[0035] Preferably, if Figures 3 to 6As shown, 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 which are sequentially arranged axially along the central axis 14, and the upper and lower annular permanent magnets are symmetrically arranged at the upper and lower parts of the intermediate annular permanent magnet 18; the outside of each annular permanent magnet is respectively configured with a coaxial annular coil (the upper annular coil 3, the intermediate annular coil 4 and the lower annular coil 5 are respectively configured), and the annular coil is fixed to the corresponding annular coil box (each annular coil corresponds to the upper annular coil box 23, the intermediate annular coil box 19 and the lower annular coil box 21); the three annular permanent magnets can move axially in the cavity inside the corresponding annular coil along the central axis 14; the axial displacement of the central axis 14 can be adjusted by 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.

[0036] Preferably, the spring positive stiffness module includes a coil spring 2, a limit piece and an adjusting piece; the coil spring 2 is sleeved on the central axis 14, one end of the coil spring 2 is connected to the adjusting piece, and the adjusting piece cooperates with the central axis 14; the other end of the coil spring 2 is connected to the upper end surface of the limit piece; the central axis 14 passes through the center of the limit piece; the electromagnetic negative stiffness module is installed between the limit pieces of the two spring positive stiffness modules; when adjusting the adjusting pieces of the two spring positive stiffness modules, the compression amount of the two coil springs 2 can be changed, and then the axial position of the central axis 14 can be changed, 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.

[0037] Preferably, the adjusting member is an adjusting nut. The coil spring 2 is a linear coil spring. 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 two nut threads are different, and the pitch of the coarse-tuning nut 13 is greater than the pitch of the fine-tuning nut 8. The coarse-tuning nut 13 can be used for larger position adjustments, and the fine-tuning nut 8 can be used for fine fine-tuning. The structural design is simple, but both coarse and fine adjustments are taken into account, and the operation is convenient.

[0038] In the present invention, the upper support platform 1 is arranged on the locking nut 7, the upper end of the central axis 14 passes through the locking nut 7 and extends into the reserved slot of the upper support platform 1, and the upper support platform 1 can move axially with the central axis 14 (at this time, the shape of the elastic airbag 24 changes accordingly); a slot for the axial movement of the central axis 14 is reserved in the base 26.

[0039] Preferably, the limiter is a linear bearing, and 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 axis 14 along the equilibrium position of the vibration isolation device (the central axis 14 is adapted to the inner ring of the linear bearing); one end of the coil spring 2 is connected to the end face of the linear bearing, and the linear bearings are connected to the annular coil box through a number 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 23, and the lower linear bearing 11 of the lower spring positive stiffness module is bolted to the lower annular coil box 21; the two linear bearings are installed on the outside of the upper and lower annular coils to ensure the coaxiality of the box and the central axis 14 and reduce friction during movement. The upper surfaces of the two linear bearings are provided with spring notches, which can effectively limit the position of the coil spring 2.

[0040] In the present invention, three annular permanent magnets are mounted on the central shaft 14 through a fixing ring 10. The upper annular permanent magnet 16 is correspondingly configured with an upper annular coil 3 and an upper annular coil box 23, the middle annular permanent magnet 18 is correspondingly configured with an middle annular coil 4 and an middle annular coil box 19, and the lower annular permanent magnet 17 is correspondingly configured with a lower annular coil 5 and a lower annular coil box 21; the three annular coil boxes 19, 20, 21 are each internally provided with a retaining ring for fixing the corresponding annular coils. The vibration isolation box 11 includes a spring box at the top (such as Figures 1 to 4 The top spring box 20 in the middle, the three annular coil boxes in the middle (such as the upper annular coil box 23, the middle annular coil box 19 and the lower annular coil box 21 in the figure) and the bottom spring box (reference numeral 22) are fixedly connected by external bolts. The bottom spring box 22 is also the base box of the entire vibration isolation device, and its base 6 is provided with bolt holes for fixed connection; the coarse adjustment nut 13 of the lower spring positive stiffness module is installed on the base 6.

[0041] In the present invention, the linear bearing uses a sliding bearing with an aluminum shell and a tetrafluoroethylene resin lining to avoid the influence of ordinary steel ball linear bearings on the magnetic field; the annular permanent magnets are made of rare earth permanent magnet materials; the central shaft 14, the fixing ring 10, the bolts and nuts and other components and structures are made of non-magnetic or weakly magnetic materials, such as 304 stainless steel; and each box body is made of aluminum alloy material.

[0042] In the present invention, the components of the electromagnetic negative stiffness module can respectively constitute an attractive electromagnetic negative stiffness mechanism and a repulsive electromagnetic negative stiffness mechanism.

[0043] The three annular coils 3, 4, and 5 are arranged vertically and symmetrically on the same axis to form an attractive electromagnetic negative stiffness mechanism. Figure 3 and Figure 4As shown, the attraction-type electromagnetic negative stiffness mechanism includes two symmetrically arranged upper and lower annular coils 3 and 5 and a middle annular coil 4, each of which is wound by enameled wire. The two upper and lower identical annular coils 3 and 5 are respectively located at the two ends of the middle annular coil 4 along the central axis 14, symmetrically arranged, and currents of the same direction and equal magnitude are passed through them. The three annular coils are fixed to each other; the annular coils are all water-cooled coils, which can effectively solve the heating problem of the coils.

[0044] The three annular permanent magnets 16, 17, 18 and the three annular coils 3, 4, 5 are arranged vertically coaxially and symmetrically to form a repulsive electromagnetic negative stiffness mechanism. Figure 3 and Figure 4 As shown, the repulsive electromagnetic negative stiffness mechanism includes three pairs of matching structures composed of annular coils and permanent magnets (upper annular coil 3 and upper end annular permanent magnet 16, middle annular coil 4 and middle annular permanent magnet 18, lower annular coil 5 and lower end annular permanent magnet 17), and the matching structures composed of the three pairs of annular coils and permanent magnets are symmetrically arranged along the central axis 14. Preferably, the annular permanent magnets in the three pairs of matching structures are fixedly connected to the central axis 14 through a fixing ring 10, and the three annular coils 3, 4, and 5 are fixed to each other and are all highly coaxial with the corresponding annular permanent magnets 16, 17, and 18. The vertical distances of the matching structures formed by the three pairs of annular coils and the corresponding permanent magnets are all 14 to 15 mm (that is, the vertical spacing of the annular coils is 14 to 15 mm, and the vertical spacing of the annular permanent magnets is 14 to 15 mm), and the lateral spacing between the annular coils and the corresponding annular permanent magnets is 4 to 5 mm. The annular permanent magnets in the three pairs of matching structures are all axially magnetized. From the two-dimensional axial symmetry of the annular permanent magnets and the annular coils, it can be seen that only axial force acts on the annular permanent magnets, that is, only axial negative stiffness is generated.

[0045] The positive stiffness mechanism includes two coil springs 2 and an elastic airbag 24. Figure 1-6 As shown, the coil spring 2 is sleeved on the central shaft 14 and is located outside the two linear bearings 9 and 12. The elastic airbag 24 is located outside the vibration isolation box 11 and is fixedly connected to the upper support platform 1 and the bottom base 25 by bolts; one end of the linear spring 2 is pressed against the notch of the linear bearings 9 and 12, and the other end is respectively pressed against the coarse adjustment nut 13 and the fine adjustment nut 8 of the central shaft 14. A wire hole 26 is also opened inside the bottom base 25, and the connecting wires of each annular coil are led out through the wire hole 26.

[0046] In the present invention, the linear bearing uses a sliding bearing with an aluminum shell and a tetrafluoroethylene resin lining to avoid the influence of the magnetic field on the ordinary steel ball linear bearing; the elastic airbag 24 is made of rubber material; the annular permanent magnets 16, 17, and 18 are all made of rare earth permanent magnet materials; the upper support platform, the central axis, the fixing ring, the base, the bolts and nuts and other components and structures are all made of non-magnetic or weakly magnetic materials, such as 304 stainless steel; and the vibration isolation box is made of aluminum alloy.

[0047] The equilibrium position refers to the position when the system is in a static state; the equilibrium position in the present invention is the position where the middle annular permanent magnet is at the vertical center of the middle annular coil. According to the electromagnetic negative stiffness generation mechanism of the magnetic element configuration, the attractive electromagnetic negative stiffness mechanism produces softening negative stiffness, because the attraction between the magnets is inversely proportional to the square of their distance. The farther away from the equilibrium position, the closer to one end of the magnet, and the greater the force difference generated. The repulsive electromagnetic negative stiffness mechanism produces hardening negative stiffness, because the more it deviates from the equilibrium position, the smaller the repulsive force between the magnetic elements. Therefore, the repulsive and attractive electromagnetic negative stiffness mechanisms are coupled to achieve the mutual cancellation of the nonlinear parts of the softening stiffness characteristics and the hardening stiffness characteristics, while the linear parts are superimposed on each other, thereby improving the value of the negative stiffness while improving the linearity of the negative stiffness. Negative stiffness with softening or hardening characteristics can be generated using permanent magnets or coils. The negative stiffness generated between permanent magnets is larger, but cannot be adjusted; the coil can control the size of the magnetic field by controlling the excitation current, but the current carrying capacity is limited, and the negative stiffness generated by the electromagnetic force between the coils alone is too weak; therefore, a combined configuration of coils and permanent magnets is selected to design an electromagnetic negative stiffness mechanism to achieve adjustable negative stiffness in order to obtain a larger adjustable range.

[0048] In the present invention, the repulsive electromagnetic negative stiffness device uses three annular permanent magnets 16, 17, 18 and three annular coils 3, 4, 5. When current is passed through the annular coil, due to the magnetic effect of the current, the current-carrying ring will excite a constant magnetic field and generate an interaction force with the annular permanent magnet. The magnetic field distribution generated by magnetic elements such as permanent magnets and coils in a vacuum is relatively regular, and the electromagnetic field generated by them can be calculated to calculate the electromagnetic force.

[0049] According to the superposition theorem, an axially magnetized annular permanent magnet can be equivalent to a cylindrical permanent magnet superimposed with a reversely magnetized cylindrical permanent magnet. An axially magnetized annular magnet can be equivalent to two thin solenoids located on the inner and outer annular surfaces. The currents in the two solenoids are equal in magnitude and opposite in direction, respectively:

[0050]

[0051]

[0052] Where μ0 is the magnetic permeability in vacuum (H / m), inis the internal equivalent solenoid current value (A), I out is the external equivalent solenoid current value (A), h is the equivalent solenoid axial height (m), N eq is the equivalent number of turns of the equivalent solenoid, J is the equivalent polarization intensity (C / m 2 ).

[0053] In the present invention, the attraction type electromagnetic negative stiffness structure uses three annular coils 3, 4, 5 as attraction type negative stiffness generating modules, wherein two identical annular coils are fed with currents of the same direction and magnitude. When current is fed into the annular coils, due to the magnetic effect of the current, the two current-carrying rings 1 and 2 will respectively excite a constant magnetic field and generate mutual force.

[0054] The Biot–Savart law describes the magnetic field generated by a current element at any point in space:

[0055]

[0056] Where I is the source current (A), dl is the tiny line element of the source current (m), r is the distance from the current element to the exciting magnetic field point (m), and e r is the unit vector of the current element pointing to the exciting magnetic field point (A·m), B is the magnetic induction intensity (T), and μ0 is the magnetic permeability in vacuum (H / m).

[0057] The force on the current element Idl on the current-carrying ring from another current-carrying ring is:

[0058] dF=Idl×B (4), integrating the above formula can give the interaction force between the two current-carrying rings:

[0059] F = ∫ l dF (5),

[0060] Since the two current-carrying rings are concentric, the electromagnetic force is along the axial direction according to symmetry. Because the integral is complex and difficult to find an analytical solution, we can also use elliptic integrals to get:

[0061]

[0062] Where I1 is the current value of current-carrying ring 1 (A), I2 is the current value of current-carrying ring 2 (A), r1 is the radius of current-carrying ring 1 (m), r2 is the radius of 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 complete elliptic integrals of the first and second kind with modulus k, respectively.

[0063] The direction of the interaction force between the two current-carrying rings is determined by the direction of the excitation current. According to Ampere's law, when the current directions in the two current-carrying rings are the same, the electromagnetic force manifests as mutual attraction, and vice versa. So far, the electromagnetic force between the two current-carrying rings has been determined. The electromagnetic force between the energized coils or solenoids can be solved by superimposing the forces between the current-carrying rings. Combined with the equivalent relationship between axially magnetized permanent magnets and solenoids, the electromagnetic force between the coil and the magnet can also be superimposed.

[0064] In the present invention, the electromagnetic negative stiffness module 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 quasi-zero stiffness isolator. The attraction type electromagnetic negative stiffness mechanism is three annular coils 3, 4, and 5. Currents in the same direction are passed through the annular coils 3 and 5 at the head and tail ends, and a mutual attraction force is generated between the three. The repulsion type electromagnetic negative stiffness device uses three annular permanent magnets 16, 17, and 18 and three annular coils 3, 4, and 5. The permanent magnets move axially in the annular coils, and a mutual repulsion force is generated between the two. The electromagnetic force is in the same direction as the relative displacement, which keeps it away from the equilibrium position, that is, the designed electromagnetic coupling structure produces negative stiffness.

[0065] The working principle of the present invention is: a quasi-zero state is generated by combining an electromagnetic negative stiffness module and an airbag spring positive stiffness mechanism. The electromagnetic negative stiffness and the airbag positive stiffness can control the current in the electromagnet and the pressure inside the elastic airbag in real time according to the change in load mass, adjust the stiffness and load capacity in real time, and quickly achieve a quasi-zero state of the natural frequency of the vibration isolation system at the equilibrium position. When the system is in a static equilibrium position, the forces between the three annular permanent magnets 16, 17, 18 and the three annular coils 3, 4, 5 offset each other, and the system is in a stable state. There is a very low dynamic stiffness near the static equilibrium position. By combining the electromagnetic negative stiffness with the airbag spring positive stiffness, the vibration isolation performance of the control system can be better adjusted, and the attraction type electromagnetic negative stiffness mechanism and the repulsion type electromagnetic negative stiffness mechanism are coupled to improve the stability of the vibration isolation system. When the system is subjected to an external excitation force, the central axis moves vertically, causing the annular permanent magnet to deviate from the equilibrium position, thereby generating a repulsive electromagnetic force between the annular permanent magnet and the annular coil, and an attractive electromagnetic force also exists between the other three annular coils, which not only provides negative stiffness, but also can effectively offset the nonlinear part. The negative stiffness during the movement offsets the positive stiffness provided by the elastic airbag 24, so that the dynamic frequency of the system is low, and the vibration caused by the excitation force can be effectively isolated. When the load mass changes, the elastic airbag 24 and the electromagnetic negative stiffness adjustment module can be used to control the internal pressure of the elastic airbag 24 and the current in the electromagnet in real time according to the change in load mass, and the negative stiffness and positive stiffness can be adjusted in real time at the same time, so as to ensure that the vibration isolation frequency of the vibration isolation device at the equilibrium position is quasi-zero.

[0066] The contents not described in detail in this specification belong to the prior art known to professional and technical personnel in this field. The above embodiments are only for illustrating the technical concept and features of the present invention, and their purpose is to enable people familiar with this technology to understand the contents of the present invention and implement them accordingly, and they cannot be used to limit the protection scope of the present invention. Any equivalent changes or modifications made according to the spirit of the present invention should be included in the protection scope of the present invention.

Claims

1. A compact low-frequency vibration isolation device with magnetic mixing to adjust positive and negative stiffness, characterized in that: It includes an upper support platform, a base, an elastic airbag positive stiffness mechanism, a central axis, a vibration isolation box, two spring positive stiffness modules and an electromagnetic negative stiffness module installed in the vibration isolation box; The support platform and the base are arranged vertically and parallelly; the elastic airbag positive stiffness mechanism includes an elastic airbag, the upper end of the elastic airbag is connected to the upper support platform, and the lower end of the elastic airbag is connected to the base; the elastic airbag, the upper support platform and the base are enclosed to form a cavity; the base is provided with an air hole connected to the cavity; the entrance of the air hole can be connected to an external gas control unit; The vibration isolation box is installed in the cavity, and the base of the vibration isolation box is fixed on the base; the two spring positive stiffness modules are symmetrically arranged on the upper and lower parts of the electromagnetic negative stiffness module; The upper end of the central shaft is connected to the upper support platform, and the lower end of the central shaft passes through the spring positive stiffness module located at the upper part of the vibration isolation box, the electromagnetic negative stiffness module and the spring positive stiffness module located at the lower part of the vibration isolation box in sequence, and is connected to the base of the vibration isolation box; 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 axially along 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 along the central axis in the cavity inside the corresponding annular coil; the axial displacement of the central axis can be adjusted by 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; The three annular wires are arranged vertically and symmetrically on the same axis to form an attracting electromagnetic negative stiffness mechanism; the upper and lower annular coils are arranged symmetrically at the two ends of the middle annular coil, and currents of the same direction and equal magnitude are passed through them; The spring positive stiffness module includes a coil spring, a limiter and an adjusting member; the coil spring is sleeved on the central axis, one end of the coil spring is connected to the adjusting member, and the adjusting member cooperates with the central axis; the other end of the coil spring is connected to the upper end surface of the limiter; the central axis passes through the center of the limiter; the electromagnetic negative stiffness module is installed between the limiters of the two coil spring positive stiffness modules; when adjusting the adjusting members 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; 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.

2. The compact low-frequency vibration isolation device according to claim 1, 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.

3. The compact low-frequency vibration isolation device according to claim 1, characterized in that: The annular coils are all water-cooled coils.

4. The compact low-frequency vibration isolation device according to claim 1, characterized in that: Linear bearings are sliding bearings with aluminum shells and polytetrafluoroethylene resin linings.

5. The compact low-frequency vibration isolation device according to claim 1, 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.

6. The compact low-frequency vibration isolation device according to claim 1, characterized in that: The elastic airbag is made of rubber material.

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