A primary active ultra-low frequency vertical vibration isolation system

Abstract

The application discloses a primary active ultra-low frequency vertical vibration isolation system, comprising a passive vibration isolation platform, a load, a vibration sensor, a driver and a control circuit, wherein the passive vibration isolation platform is internally provided with a horizontal limiting mechanism, the horizontal limiting mechanism is any mechanism capable of limiting three rotational degrees of freedom and two degrees of freedom of translation in a horizontal plane of an object, and only has a single degree of freedom of vertical translation. The system has the characteristics of low complexity and good long-term stability, the scheme for realizing horizontal limiting through mechanical design is simpler, and is helpful to improving the stability of the active vibration isolation system. Compared with the prior art, the application does not need more cost, and the efficiency is not obviously reduced.

Description

Technical Field

[0001] This invention belongs to the field of absolute gravity measurement technology, specifically relating to a single-stage active ultra-low frequency vertical vibration isolation system. Background Technology

[0002] Absolute gravity measurement, the precise measurement of the absolute value of gravitational acceleration, is of great significance and has wide applications in metrology, geophysics, resource exploration, navigation aids, military, and marine monitoring. It also provides a reference standard for relative gravity measurement. The instrument used to measure absolute gravity is called an absolute gravimeter. After more than two centuries of development, absolute gravimeters now generally calculate gravitational acceleration indirectly by measuring the trajectory of a free-falling body in a vacuum, with a measurement accuracy reaching up to microgal (μGal, 1 μGal = 1 × 10⁻⁶). -8 m·s -2 The magnitude is on the order of 10^-10^-1. Measurements of descent trajectories commonly employ laser interferometry or atomic interferometry, both requiring a stable reference mirror. In practice, ground vibration noise significantly impacts the reference mirror, severely limiting the measurement accuracy of absolute gravimeters. Currently, common methods for addressing ground vibration noise fall into two main categories: vibration isolation systems and vibration compensation methods, both of which are used in various optical and atomic gravimeters. Vibration isolation systems physically construct a low-pass filter to reduce the impact of high-frequency ground vibrations on the reference mirror.

[0003] Ultra-low frequency vertical vibration isolation systems can be classified into passive (passive) and active (active) types based on their principles. Active systems can be further divided into single-stage and two-stage active systems. A single-stage active vertical vibration isolation system can be simplified to a long-period single-spring-oscillator structure using feedback control. The system uses an accelerometer to measure the absolute acceleration of the isolated object. The feedback control circuit controls a linear motor to drive the isolated object based on the acceleration signal, keeping its acceleration constant and thus eliminating the influence of ground vibration noise. The atomic interferometer absolute gravimeter developed by Stanford University uses a vertical vibration isolation system developed by Hensley et al. In this system, an accelerometer is installed inside the oscillator, supported by a vertical spring, and performs strictly linear motion under the constraint of an air bearing. Its vibration is suppressed by the feedback force applied by the linear motor, with a period of 30 seconds. In addition to accelerometers, seismometers can also be used as sensors to measure the motion of the isolated object. Tang Biao et al. developed a single-stage active vertical vibration isolation system based on the passive vibration isolation platform of Minus K Technology, which uses this structure and has a period of 66 seconds. Zhou Minkang et al. realized a triaxial active vibration isolation system based on a similar structure, with a period of up to 100s in the vertical direction.

[0004] While ideally, the horizontal and vertical vibrations of the reference mirror in an absolute gravimeter are uncorrelated, in reality, no mechanical structure can completely eliminate the cross-coupling between horizontal and vertical vibrations. Existing primary vibration isolation techniques that construct active feedback loops in the horizontal direction to suppress horizontal vibrations increase system complexity, and improper gain selection can lead to system instability. Summary of the Invention

[0005] To address the aforementioned shortcomings of existing technologies, the present invention aims to provide a single-stage active ultra-low frequency vertical vibration isolation system. This invention solves the problems of complex horizontal limiting structures in existing single-stage active vertical vibration isolation systems, and the potential decrease in system stability when suppressing horizontal vibrations of the reference mirror.

[0006] To achieve the above-mentioned objectives, the technical solution adopted by this invention is as follows:

[0007] A primary active ultra-low frequency vertical vibration isolation system is provided, including a passive vibration isolation platform, a load, a vibration sensor, a driver, and a control circuit. The passive vibration isolation platform is equipped with a horizontal limiting mechanism, which is any mechanism capable of limiting the three rotational degrees of freedom and the two translational degrees of freedom of an object in the horizontal plane.

[0008] Furthermore, the passive vibration isolation platform includes a base and a top platform, with the top platform horizontally positioned inside the base, and a spring connecting the base and the top platform.

[0009] Furthermore, the load includes a reference mirror, a frame, and counterweights.

[0010] Furthermore, the horizontal limiting mechanism is a limiting rod, and there are several limiting rods, some of which are distributed in a rotationally symmetrical manner in the upper horizontal plane, and the other part is distributed in a rotationally symmetrical manner in the lower horizontal plane; the two ends of each limiting rod are connected to the top plate and the base respectively.

[0011] Furthermore, the limiting rod is made of steel wire or a rod made of shape memory alloy.

[0012] Furthermore, the limiting mechanism is a linear bearing assembly, which includes an optical axis, a bearing, and a connector. The optical axis is connected to the base, the lower end of the connector is connected to the top platform, and the upper end of the connector is connected to the optical axis through the bearing.

[0013] Furthermore, the vibration sensor is a seismometer or an accelerometer.

[0014] Furthermore, the driver is a voice coil motor or other DC motor.

[0015] Furthermore, the control circuit can be an analog circuit or a digital circuit.

[0016] Furthermore, the control circuit comprises five main parts: an amplification module, a bias adjustment module, a filtering module, a PID module, and a drive module, as well as a power rectification module, a reference module, and a motor switch auxiliary circuit.

[0017] The beneficial effects of this invention are as follows:

[0018] The single-stage active ultra-low frequency vertical vibration isolation system of this invention features low complexity and good long-term stability. The horizontal limiting scheme achieved through mechanical design is simpler and helps improve the stability of the active vibration isolation system. Compared with existing technologies, this invention requires no additional cost and does not significantly reduce efficiency. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the passive vibration isolation platform provided in Embodiment 1 of the present invention; wherein, (a) vertical vibration isolation, (b) horizontal vibration isolation;

[0020] Figure 2 This is a schematic diagram of the vibration isolation system structure provided in Embodiment 1 of the present invention; wherein, (a) is the overall mechanical structure, (b) is the upper horizontal limiting mechanism, and (c) is the lower horizontal limiting mechanism;

[0021] Figure 3 This is a schematic diagram of the analog control circuit used in Embodiment 1 of the present invention;

[0022] Figure 4 This is a schematic diagram of a vibration isolation system provided in Embodiment 1 of the present invention; wherein, (a) is a physical model, and (b) is a block diagram;

[0023] Figure 5 This is a schematic diagram of the vibration isolation system structure provided in Embodiment 2 of the present invention;

[0024] Figure 6 This is a schematic diagram of the vibration isolation system structure provided in Embodiment 3 of the present invention;

[0025] Figure 7 This is a schematic diagram of the vibration isolation system structure provided in Embodiment 4 of the present invention;

[0026] Figure 8 This is a schematic diagram of the vibration isolation system structure provided in Embodiment 5 of the present invention;

[0027] Figure 9 This is a schematic diagram of the vibration isolation system structure provided in Embodiment 6 of the present invention.

[0028] The components are: 1. Base; 2. Top platform; 3. Spring; 4. Vibration sensor; 5. Driver; 6. Reference mirror; 7. Counterweight; 8. Limiting rod; 9. Bearing assembly; 10. Optical axis; 11. Bearing; 12. Connector; 13. Frame; 14. Housing; 15. Leveling platform. Detailed Implementation

[0029] The specific embodiments of the present invention are described below to enable those skilled in the art to understand the present invention. However, it should be understood that the present invention is not limited to the scope of the specific embodiments. For those skilled in the art, various changes are obvious as long as they are within the spirit and scope of the present invention as defined and determined by the appended claims. All inventions utilizing the concept of the present invention are protected.

[0030] Example 1

[0031] This embodiment uses the Minus K Corporation 25-BM10 commercial passive vibration isolation platform as the elastic structure to construct a primary active ultra-low frequency vertical vibration isolation system. This vibration isolation platform simultaneously possesses vertical and horizontal vibration isolation functions, such as… Figure 1 As shown in (a), the vertical vibration isolation structure mainly consists of a load (including user load and top platform), helical springs, and a pair of symmetrically arranged horizontal bars connected by hinges. This horizontal bar assembly is called a "Negative Stiffness Mechanism" (NSM). The positive stiffness of the helical springs is k. s In its free state, the NSM has zero stiffness in the vertical direction, but is subjected to a symmetrical horizontal pressure F. h At that time, NSM has an equivalent negative stiffness k in the vertical direction. n When the system is subjected to a downward vertical load of magnitude mg (where m is the load mass), the total stiffness of the structure in the vertical direction is k = k s -k n Therefore, when the load is near the static equilibrium position, the structure can be equivalent to a simple spring-mass structure consisting of a helical spring with stiffness k and a point mass m. When the load mass is within a certain range, the horizontal pressure F applied to the NSM can be adjusted. h To change the negative stiffness k n This changes the stiffness k of the entire structure. Therefore, this vertical vibration isolation structure has adjustable dynamic stiffness, and its equivalent spring-mass structure has a variable resonant frequency of about 1 Hz.

[0032] like Figure 1 As shown in (b), the horizontal vibration isolation structure mainly consists of its load (i.e., the aforementioned vertical vibration isolation structure) and several symmetrically arranged slender rods. One end of each rod is fixed to the base, and the other end is fixed to the load. By designing the geometric and structural parameters of the rods, the load mass on them can be made close to its buckling load. At this time, the rod assembly and its load are equivalent to a spring-mass structure with relatively small positive stiffness in the horizontal direction, with a resonant frequency of about 1 Hz.

[0033] Reference Figure 2 This embodiment provides a single-stage active ultra-low frequency vertical vibration isolation system, including a passive vibration isolation platform, a load, and a control circuit. The passive vibration isolation platform includes a base 1 and a top platform 2, with the top platform 2 horizontally positioned within the base 1. A vertical spring 3 is provided between the base 1 and the top platform 2. The load includes a vibration sensor 4, a driver 5, a reference mirror 6, and a counterweight 7, all mounted on the top platform 2. The vibration sensor 4 is positioned in the center of the top platform 2 and directly above the spring 3. Two drivers 5 are symmetrically distributed on either side of the vibration sensor 4. The reference mirror 6 and the counterweight 7 are respectively positioned between the vibration sensor 4 and the drivers 5. In this embodiment, the vibration sensor 4 is a seismometer, and the drivers 5 are two voice coil motors, symmetrically distributed on either side of the vibration sensor 4.

[0034] The base 1 also includes a horizontal limiting mechanism, consisting of limiting rods 8 capable of withstanding both tensile and compressive stresses. These limiting rods 8 are made of steel wire or a shape memory alloy. There are five limiting rods 8, three of which are rotationally symmetrically distributed in the upper horizontal plane, and the other two are rotationally symmetrically distributed in the lower horizontal plane. Each limiting rod 8 is connected at both ends to the top plate 2 and the base 1, respectively. These five limiting rods restrict the other five degrees of freedom of the top plate and all its components, ensuring that it has only a single degree of freedom: vertical translation.

[0035] The control circuit comprises five main parts: an amplification module, a polarization adjustment module, a filtering module, a PID module, and a drive module, as well as a power rectification module, a reference module, and motor switching auxiliary components. Some modules of the control circuit, such as the amplification module, polarization adjustment module, filtering module, and PID module, can be converted into digital circuits to acquire the seismograph signal U. s The output current I is obtained through digital circuit processing and then output to the drive module.

[0036] Reference Figure 3 The output signal U of the seismometer s After passing through the bias adjustment module, it becomes an error signal U without a DC component. i After being amplified by the inverting amplifier circuit, and then passed through the low-pass filter circuit used to remove high-frequency circuit noise from the seismometer itself, the signal enters the PID control module, ultimately obtaining the control signal U. c Finally, the control signal U c After passing through the voltage-controlled current source module, it is converted into current for the driver to perform feedback force.

[0037] After the horizontal limiting mechanism is installed, its limiting effect can be examined using a precision level with a resolution of 20 arcseconds / 2mm divisions. The results show that when the vertical amplitude of the top platform is 1cm, its horizontal deflection angle does not exceed 1 / 4 division, or 5 arcseconds, while without the horizontal limiting mechanism, its horizontal deflection angle is 1 to 2 degrees. The comparison shows that the horizontal vibration is well suppressed, indicating that the limiting structure can meet the control requirements of the vibration isolation system.

[0038] Working principle:

[0039] When a horizontal limiting mechanism is present, the original passive vibration isolation platform is equivalent to a spring-mass structure in the vertical direction. In this case, the overall physical model of the active vibration isolation system can be simplified to... Figure 4 (a). The vibration displacement input from the ground is z. in (t), the displacement of the top plate and all components placed on it is z. out (t) The total mass is M1, the equivalent stiffness of the passive vibration isolation platform is k1 (i.e., the total stiffness k mentioned above), and the equivalent damping is β1. A velocity-type seismograph (i.e., a vibration sensor) placed on the top plate measures the absolute velocity signal v of the platform relative to the inertial frame. out (t) is detected, and the output voltage signal enters the controller. The voice coil motor applies a force f(t) to the top platform according to the output of the controller, suppressing its absolute displacement z. out (t). Figure 4 (b) is a block diagram of the system, where G seis (s) is the transfer function of the seismometer itself, satisfying G seis (s)=N(s) / D(s)·K s (i.e., the sensitivity of the seismograph is K) s After normalization, the numerator and denominator of the transfer function are N(s) and D(s) respectively, H(s) is the transfer function of the controller, and K vc This is the force constant of the voice coil motor.

[0040] The equation of motion for the load is:

[0041]

[0042] Applying the Laplace transform to the above equation, we can obtain

[0043] M1s 2 Z out (s)+β1sZ out (s)+k1Z out (s)=β1sZ in (s)+k1Z in (s)+F(s).

[0044] Without applying a feedback force F, the system is equivalent to the original passive vibration isolation system, and the corresponding open-loop transfer function is:

[0045]

[0046] Choosing a PID proportional-integral-derivative (PID) controller as the control element of the system means that...

[0047]

[0048] The parameters of the proportional element, integral element, and differential element are K, respectively. P K I and K D Let K be the coefficient of the motor drive component. drive This stage converts the voltage signal output by the PID controller into the drive current of the voice coil motor. At this point, the feedback force within the system is...

[0049] F(s) = G seis (s)H(s)K drive K vc ·sZ out (s).

[0050] Substituting the above equation into equation M1s 2 Z out (s)+β1sZ out (s)+k1Z out (s)=β1sZ in (s)+k1Z in From F(s) + F(s), we can obtain the closed-loop transfer function of the system as follows:

[0051]

[0052] Substitute G seis The expression and formula of s Ultimately obtain

[0053]

[0054] Example 2

[0055] Reference Figure 5In this embodiment, the horizontal limiting mechanism is a linear bearing assembly 9 disposed on both sides of the vibration sensor 4. The linear bearing assembly 9 includes an optical axis 10, a bearing 11, and a connector 12. The optical axis 10 is connected to the base 1, the lower end of the connector 12 is connected to the top platform 2, and the upper end of the connector 12 is connected to the optical axis 10 through the bearing 11. At this time, the top plate 2 can be translated vertically along the optical axis 20 through the bearing 11. The limiting effect is examined using a precision level with a resolution of 20 arcseconds / 2mm divisions to ensure that it has only a single degree of freedom of vertical translation.

[0056] Example 3

[0057] Reference Figure 6 In this embodiment, the reflector 6 and the frame 13 are positioned directly above the vibration sensor 4. The reflector 6 is mounted on the frame 13, and the frame 13 is connected to the top of the vibration sensor 4. In practical applications, the placement of the reference mirror 6 and the frame 13 is not unique; they can be positioned directly above the vibration sensor 4 or at other suitable locations.

[0058] Example 4

[0059] Reference Figure 7 In this embodiment, the actuator 5 is placed between the passive vibration isolation platform base 1 and the top platform 2, and applies a feedback force to the top platform 2 according to the controller output. The two ends of each limiting rod 8 are connected to the top plate 2 and the base 1 extending inside the vibration isolation platform, respectively. In practical applications, the placement of the actuator 5 is not unique and can be set in other suitable locations. Furthermore, the number of actuators 5 is not unique; they only need to be symmetrically distributed on both sides of the vibration sensor 4.

[0060] Example 5

[0061] Reference Figure 8 In this embodiment, the base 1 is designed as a square, and a horizontal limiting mechanism is also provided inside the base 1. The horizontal limiting mechanism consists of limiting rods 8 that can withstand both tensile stress and compressive stress. The two ends of each limiting rod 8 are connected to the top plate 2 and the base 1, respectively.

[0062] Example 6

[0063] Reference Figure 9 In this embodiment, the vibration isolation system is placed on the leveling platform 15, and the bottom corners of the platform are adjusted to ensure that the system is placed on a level surface, eliminating the influence of uneven ground on the system. In practical applications, the placement of the vibration isolation system is not unique; it can be placed on a common base plate or leveling platform, or other structures. The vibration isolation system may also have a housing 14.

[0064] In this invention, the passive vibration isolation platform structure is not unique; any vibration isolation structure with vertical springs that can attenuate vertical vibrations can be used.

[0065] The number of limit rods 8 is not unique. Any number of limit rods can be used to restrict the other 5 degrees of freedom of the top plate 2 and all components on it, ensuring that it only has a single degree of freedom of vertical translation.

[0066] The material of the limit rod 8 is not unique; other materials that can withstand both tensile and compressive stresses can be used as replacements.

[0067] The bearing assembly can be either a linear bearing assembly or a sliding bearing assembly.

[0068] There is no single way to measure vibration signals with a seismometer; other vibration sensors such as accelerometers can be used instead.

[0069] There are multiple ways to provide feedback force for voice coil motors; voltage-driven or other drivers can be used instead.

[0070] The single-stage active ultra-low frequency vertical vibration isolation system of this invention features low complexity and good long-term stability. The horizontal limiting scheme achieved through mechanical design is simpler and helps improve the stability of the active vibration isolation system. Compared with existing technologies, this invention requires no additional cost and does not significantly reduce efficiency.

[0071] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, it is intended that all variations falling within the meaning and scope of equivalents of the claims be included within the present invention.

[0072] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A primary active ultra-low frequency vertical vibration isolation system, comprising a passive vibration isolation platform, a load, a vibration sensor (4), a driver (5), and a control circuit, characterized in that, The passive vibration isolation platform is equipped with a horizontal limiting mechanism, which is any mechanism capable of limiting the three rotational degrees of freedom and the two translational degrees of freedom of an object in the horizontal plane. The control circuit is an analog circuit or a digital circuit; the control circuit includes five main parts: an amplification module, a bias adjustment module, a filtering module, a PID module, and a drive module. The output signal of the vibration sensor (4) becomes an error signal without DC component after passing through the bias adjustment module. After being amplified by the amplification module, it is low-pass filtered by the filtering module and finally enters the PID module to obtain the control signal. It is then converted into the current of the driver (5) through the drive module to execute the feedback force. The expression for calculating the feedback force is: F(s)=G seis (s)H(s)K drive K vc ·sZ out (with) F(s) is the feedback force; G seis H(s) is the transfer function of the vibration sensor (4); H(s) is the transfer function of the PID module; K drive K is the coefficient of the driver (5) in the driving stage. vc is the force constant of the actuator (5).

2. The primary active ultra-low frequency vertical vibration isolation system according to claim 1, characterized in that, The passive vibration isolation platform includes a base (1) and a top platform (2). The top platform (2) is horizontally arranged inside the base (1), and a spring (3) is provided between the base (1) and the top platform (2).

3. The primary active ultra-low frequency vertical vibration isolation system according to claim 1, characterized in that, The load includes a reference mirror (6), a frame (13), and a counterweight (7).

4. The single-stage active ultra-low frequency vertical vibration isolation system according to claim 2, characterized in that, The horizontal limiting mechanism is a limiting rod (8), and there are several limiting rods (8), some of which are distributed in a rotationally symmetrical manner in the upper horizontal plane, and the other part is distributed in a rotationally symmetrical manner in the lower horizontal plane; the two ends of each limiting rod (8) are connected to the top plate (2) and the base (1) respectively.

5. The primary active ultra-low frequency vertical vibration isolation system according to claim 4, characterized in that, The limiting rod (8) is made of steel wire or a rod made of shape memory alloy.

6. The single-stage active ultra-low frequency vertical vibration isolation system according to claim 2, characterized in that, The limiting mechanism is a linear bearing assembly (9), which includes an optical axis (10), a bearing (11), and a connector (12). The optical axis (10) is connected to the base (1), the lower end of the connector (12) is connected to the top platform (2), and the upper end of the connector (12) is connected to the optical axis (10) through the bearing (11).

7. The single-stage active ultra-low frequency vertical vibration isolation system according to claim 1, characterized in that, The vibration sensor (4) is a seismometer or an acceleration sensor.

8. The primary active ultra-low frequency vertical vibration isolation system according to claim 1, characterized in that, The driver (5) is a voice coil motor or other DC motor.

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