Semi-active particle collision damper based on magnetic fluid suspension properties

Abstract

Based on the magnetic liquid suspension characteristics of semi-active particle collision damper, belongs to the field of vibration control. Successfully solved the existing particle collision damper cannot be applied to low frequency vibration, and the semi-active control effect is not good. The damper includes a ball (1), a magnetic liquid (2), a lower magnetic field source (3), a shell (4) and an excitation coil (5), when the external vibration, the ball (1) in the shell (4) movement and collision, produce fluid viscous damping and collision damping to absorb energy. In addition, the excitation coil (5) according to the vibration, at any time to the magnetic liquid (2) in the shell (4) to apply magnetic field excitation, change the suspension force of magnetic liquid (2), so as to change the size of the damping, achieve the semi-active control of vibration.

Description

Technical Field

[0001] This invention belongs to the field of vibration control in mechanical engineering (including machines, mechanisms and various parts). Background Technology

[0002] Particle collision dampers are dampers that dissipate vibrational energy through collisions between particles under external vibration excitation. They are applicable to high vibration frequencies and have advantages such as simple structure and long lifespan. However, existing particle collision dampers are mostly passive damping with a narrow damping bandwidth, often only effective at specific frequencies. Furthermore, due to the high friction between solid particles, they cannot solve low-to-mid-frequency vibration problems. Their damping effect is poor for vibrations below 1000Hz, and for vibrations below 100Hz or even lower frequencies, existing particle collision dampers are essentially ineffective.

[0003] To improve the collision probability between particles and the vibration reduction efficiency of particle collision dampers, methods such as injecting a suitable amount of viscous liquid into the container or combining multiple particle collision dampers are commonly used. For example, in Reference 1 (patent application CN106930425 B), the particles are designed as a nested spherical structure connected by springs, and the viscous liquid is used to increase the collision probability between particles. However, the ratio of air to particles inside the nested sphere needs to be properly adjusted to ensure the sphere's suspension, increasing the manufacturing difficulty of the particle damper. Furthermore, the use of springs limits the damper's lifespan. In addition, this design results in the equivalent density of the entire nested sphere being the same as the density of the viscous liquid, making it impossible to generate effective relative motion between the nested sphere and the viscous liquid. Finally, this design is greatly affected by gravity, which causes the particles inside the nested sphere to completely accumulate together. Vibrational energy can only generate motion by overcoming the solid friction between the particles, thus resulting in poor vibration suppression for low and mid-frequency vibrations. Reference 2 (patent application CN 114962514 B) suspends a sphere within a cavity filled with magnetic fluid and equipped with an elastic cushion under the influence of an external magnetic field. This invention can solve the problem that traditional magnetic fluid dampers cannot be applied to vibration environments above 100Hz. However, this damper contains only one sphere, and the collision damping only occurs between the copper sphere and the cushion inside the cavity, resulting in very limited damping force. As the vibration frequency increases, the damping force of this damper will be insufficient. Furthermore, the sphere in this damper is only constrained by the levitation force of the magnetic fluid, resulting in a fixed levitation height, and there is no possibility of adjustment according to the vibration conditions.

[0004] Another approach involves introducing semi-active or active control methods into the particle damper, such as in document 3 (patent application CN107339356A). This method incorporates the particle damping material into a vibration isolation device, generating a magnetic field through an external coil. Eddy currents are generated as the particles move, increasing the loss of vibrational energy. While this method introduces eddy current damping, it doesn't change the forces acting on the particles; they remain in a state of gravitational aggregation. Therefore, it cannot solve the problem of insensitivity to low- and mid-frequency vibrations caused by excessive friction between particles. Document 4 (patent application CN106402239A) adds a variable unit capable of altering stiffness to the particle damper, such as a magnetorheological elastomer or spring, and simultaneously uses an electromagnet to excite the ferromagnetic particles for damping, achieving control over both stiffness and damping. However, this method causes the particles to collide and aggregate after being attracted by the magnetic force, failing to address the problem of insensitivity to low- and mid-frequency vibrations due to excessive friction between particles.

[0005] Therefore, there is an urgent need to redesign and improve the structure of particle collision damping so that it can perform efficient semi-active vibration control according to the vibration environment, achieving controllable stiffness and damping. It can be applied not only in high-frequency vibration applications, but also has very good results in low and medium frequency vibration applications. Summary of the Invention

[0006] The technical problem this invention aims to solve is that particle collision dampers are ineffective for vibrations below 1000Hz due to the high friction between solid particles, and are even less suitable for low-to-medium frequency vibrations below 100Hz. Even active or semi-active control methods cannot effectively address this issue. This invention provides a semi-active particle collision damper based on the suspension characteristics of magnetic liquids. Utilizing the levitation force generated by the magnetic liquid under a non-uniform magnetic field, multiple spheres made of non-magnetic materials are suspended inside a shell, reducing the solid friction between the spheres and making them highly sensitive to inertial forces. When vibration occurs, the spheres move and collide within the magnetic liquid, generating both liquid viscous damping and particle collision damping. This provides excellent vibration reduction performance for both low-frequency vibrations of a few hertz and high-frequency vibrations of thousands of hertz. Furthermore, when the damping or stiffness cannot meet the vibration reduction requirements, activating a coil on the outside of the shell changes the magnetic field inside the shell, thereby altering the levitation force of the magnetic liquid. When the vibration frequency is high, such as exceeding 100Hz, the direction of the magnetic field generated by the coil is opposite to the magnetization direction of the magnetic field source at the bottom of the shell. This reduces the magnetic field strength and gradient within the shell, decreases the levitation force of the magnetic liquid, lowers the suspension height of the particles, increases the packing density between the particles, and ultimately increases the damping force. When the vibration frequency is low, such as below 100Hz, the direction of the magnetic field generated by the coil is the same as the magnetization direction of the magnetic field source at the bottom of the shell. This increases the magnetic field strength and gradient within the shell, increases the levitation force of the magnetic liquid, raises the suspension height of the particles, decreases the packing density between the particles, and ultimately decreases the damping force.

[0007] The technical solution adopted by this invention to solve its technical problem is:

[0008] The damper includes: a sphere, a magnetic fluid, a lower magnetic field source, a housing, and an excitation coil.

[0009] A sphere is inserted into a shell to create particle collision damping. The shell is then filled with a magnetic fluid and sealed; the magnetic fluid must completely fill the shell. A magnetic field source is fixedly installed at the bottom of the outer shell to create a confinement magnetic field. The sphere is made of a non-magnetic metal with a density greater than that of the magnetic fluid. The sphere can be a solid or hollow non-magnetic metal. The outer diameter of the sphere is greater than or equal to 1 mm, and the volumetric filling rate within the shell is 10-90%. Depending on the external vibration conditions, the spheres can be the same or different. The number of spheres must be greater than one, i.e., at least two, to ensure that the spheres collide with each other after vibration occurs, generating particle collision damping.

[0010] The shell is made of a non-magnetic metal, such as copper or non-magnetic steel. The shell can be cylindrical, cuboid, or cube.

[0011] The lower magnetic field source is composed of permanent magnets, and neodymium iron boron or samarium cobalt permanent magnet materials can be selected depending on the temperature environment. It can be a combination of multiple permanent magnets or a single permanent magnet. The external dimensions of the lower magnetic field source must be greater than or equal to the internal cavity dimensions of the shell. The lower magnetic field source provides an initial non-uniform external magnetic field, causing a vertical gradient magnetic levitation force to be generated inside the magnetic fluid, suspending the sphere in the magnetic fluid. Due to the constraint effect of only one magnetic field source, this damper can only be applied to ground-based gravity environments. The vibration direction is parallel to the planes at the top and bottom of the shell. The magnetic pole direction of the lower magnetic field source is perpendicular to the plane of vibration and parallel to the normal direction of the top and bottom of the shell.

[0012] The excitation coil is inserted into the outer surface of the housing and fixed to form an excitation magnetic field.

[0013] After being energized, the excitation coil is magnetized perpendicular to the plane of vibration and parallel to the magnetic pole direction of the lower magnetic field source. The magnetic field gradient within the shell is adjusted by changing the direction and intensity of the current flowing into the excitation coil, thereby altering the levitation height of the sphere and ultimately adjusting the damping force. For example, when the vibration sensor (displacement or acceleration sensor) detects an external vibration frequency less than 100Hz, the sphere needs to be highly sensitive to inertial forces, requiring a small damping force. Therefore, by inputting current, the magnetic field direction of the excitation coil is aligned with the magnetic pole direction of the lower magnetic field source, increasing the magnetic field strength and gradient within the shell, thus increasing the sphere's levitation height, increasing the dispersion between spheres, and reducing particle collision damping. When the vibration sensor detects a vibration frequency greater than 100Hz, a larger damping force is required. By changing the current input direction within the excitation coil, the magnetic field direction of the excitation coil is reversed compared to the magnetic pole direction of the lower magnetic field source, decreasing the magnetic field strength and gradient within the shell, thus reducing the sphere's levitation height, decreasing the dispersion between spheres, and increasing particle collision damping. The increase or decrease in the sphere's levitation height can be controlled by adjusting the current intensity in the excitation coil. The current intensity in the excitation coil is adjustable from 0 to 5A.

[0014] The advantages of this invention compared with existing technologies are as follows: (1) By utilizing the external magnetic field provided by the lower magnetic field source, all spheres are suspended in the magnetic liquid, reducing the friction between the spheres. Moreover, the spheres can be of different sizes and suspended at different heights, making the spheres more sensitive and diverse to external vibrations. This invention can be applied not only to vibrations with frequencies of several hundred or even thousands of hertz, but also to vibrations with frequencies below 100 Hz. (2) The spheres are made of non-magnetic metal, which allows them to be suspended by the magnetic liquid. By changing the size of the spheres, the suspension position of the spheres can be controlled at the beginning of the design according to the vibration mode, thereby adjusting the probability of collisions between the spheres and the magnitude of collision damping. (3) The equivalent density of the spheres is greater than the density of the magnetic liquid. When external vibrations occur, the spheres will move relative to the magnetic liquid, thereby driving the magnetic liquid to flow and generating additional magnetic liquid damping to consume vibration energy. This is very beneficial for low-frequency vibrations below 10 Hz. (4) The excitation coil is energized according to the external vibration to generate a magnetic field. When the magnetic pole direction of the excitation coil is the same as that of the lower magnetic field source after energization, the levitation force of the magnetic liquid inside the shell will increase significantly after energization, resulting in a higher levitation height of the sphere, a lower aggregation degree, a smaller particle collision damping, a lower total damping force, and greater sensitivity to inertial forces, making it more suitable for low-frequency vibration. When the magnetic pole direction of the excitation coil is opposite to that of the lower magnetic field source after energization, the levitation force of the magnetic liquid inside the shell will decrease significantly after energization, resulting in a lower levitation height of the sphere, a higher aggregation degree, a larger particle collision damping, a higher total damping force, making it more suitable for high-frequency vibration. Attached Figure Description

[0015] Figure 1 Semi-active particle collision damper based on magnetic liquid suspension properties.

[0016] Figure 2 A semi-active particle collision damper based on the magnetic liquid suspension properties when the sphere is hollow;

[0017] In the diagram: sphere 1, magnetic fluid 2, lower magnetic field source 3, shell 4, and excitation coil 5. Detailed Implementation

[0018] The present invention will be further described with reference to the accompanying drawings as specific embodiments:

[0019] Semi-active particle collision dampers based on the magnetic fluid suspension properties, such as Figure 1 and Figure 2 The damper includes: a sphere 1, a magnetic fluid 2, a lower magnetic field source 3, a housing 4, and an excitation coil 5.

[0020] All spheres 1 are inserted into the shell 4 to form particle collision damping. Spheres 1 are made of non-magnetic metal with a density greater than that of the magnetic liquid 2. Spheres 1 can be solid or hollow non-magnetic metal. If hollow, the equivalent density of sphere 1 must also be greater than that of the magnetic liquid 2, and it must be weldable in a segmented manner. The outer diameter of the spheres is greater than or equal to 1 mm, the volumetric filling rate in the shell is 10-90%, and the number of spheres must be greater than one, i.e., at least two, to ensure that the spheres collide with each other after vibration, generating particle collision damping. All spheres 1 can be the same or different in size. Larger spheres 1 are more sensitive to low-frequency vibrations, while smaller spheres 1 have greater damping force for high-frequency vibrations; the selection is based on the specific vibration conditions. If the vibration frequency is relatively uniform, and the vibration frequency of the object being damped is only tens of hertz, the number of spheres 1 should be reduced, preferably to less than 10, while the size of spheres 1 should be increased. If the vibration frequency is relatively uniform and the frequency is greater than 100 Hz, the number of spheres 1 should be increased as the vibration frequency increases, while the size of spheres 1 should be decreased. If the vibration frequency range of the object being damped is large, large-sized spheres 1 and small-sized spheres 1 can be mixed in a certain proportion according to their volume fraction.

[0021] The magnetic fluid 2 must completely fill the interior cavity of the shell 4. Therefore, only the spheres 1 and the magnetic fluid 2 exist inside the shell 4; there can be no cavities. For example, if the filling rate of the spheres 1 inside the shell 4 is 20%, the filling rate of the magnetic fluid 2 inside the shell 4 must be 80%.

[0022] The shell 4 is made of a non-magnetic metal, such as copper or non-magnetic steel. The shape of the shell 4 can be cylindrical, cuboid, or cube.

[0023] The lower magnetic field source 3 is composed of permanent magnets. It can be a combination of multiple permanent magnets or a single permanent magnet. The external dimensions of the lower magnetic field source 3 must be greater than or equal to the internal cavity dimensions of the shell 4. The lower magnetic field source 3 is used to provide an initial non-uniform external magnetic field, causing a vertical gradient magnetic levitation force to be generated inside the magnetic liquid 2, suspending the sphere 1 in the magnetic liquid 2. The vibration direction is parallel to the top and bottom planes of the shell 4. The magnetic pole direction of the lower magnetic field source 3 is perpendicular to the plane of vibration and parallel to the normal direction of the top and bottom of the shell 4. The lower magnetic field source 3 can also use a magnetically conductive metal for magnetic circuit design, or generate a sufficiently strong gradient magnetic field inside the shell 4 by arranging permanent magnets with different magnetization directions.

[0024] The excitation coil 5 is fitted into the side wall of the housing and fixed, forming an excitation magnetic field. After being energized, the magnetization direction of the excitation coil 5 is perpendicular to the plane of vibration and parallel to the magnetic pole direction of the lower magnetic field source 3. By changing the direction and intensity of the current flowing into the excitation coil 5, the magnitude of the magnetic field gradient within the housing 4 is adjusted, thereby changing the suspension height of the sphere 1 and ultimately achieving the purpose of adjusting the damping force.

[0025] After vibration occurs, because the density of sphere 1 is greater than that of magnetic fluid 2, all spheres 1 will move inside magnetic fluid 2 under the influence of its viscosity and inertial force, creating a displacement difference with the shell 4, and converging in the opposite direction of vibration. During this process, all spheres 1 not only generate viscous damping force with magnetic fluid 2, but also collide with each other and even with the wall of shell 4, generating particle collision damping. The effect of the viscous damping force of magnetic fluid 2 weakens with increasing vibration frequency, while the effect of particle collision damping increases with increasing vibration frequency. Therefore, at low frequencies, such as below 10Hz, energy consumption is mainly due to the fluid friction between magnetic fluid 2 and spheres 1. At vibrations below 100Hz, some collisions will occur between spheres 1, generating particle collision damping. At this time, the energy consumption of the damper is mainly due to the fluid friction between magnetic fluid 2 and spheres 1, and some particle collision friction between spheres 1. At frequencies of several hundred or even thousands of hertz, the fluid friction between the magnetic fluid 2 and the sphere 1 is very small, but the collisions between the spheres 1 will be very frequent, and the energy consumption will mainly be due to the damping of particle collisions between the spheres 1.

[0026] In addition to the passive vibration suppression mentioned above, if the damper needs to be semi-actively controlled, it also requires an external vibration sensor (acceleration or displacement sensor) and a semi-active system module (including power supply, signal acquisition unit and current controller) as two external cooperating parts.

[0027] If the external vibration sensor detects displacement or acceleration signals and finds insufficient vibration suppression, the semi-active system module will be activated. For example, when the vibration sensor (displacement or acceleration sensor) detects external vibration and finds that the damper's passive vibration suppression effect is poor based on the amplitude attenuation, requiring a more sensitive inertial force and a smaller damping force, the semi-active system module will enter working mode. If the vibration frequency is less than 100Hz, the semi-active system module will input current to the excitation coil 5, making the magnetic field direction of the excitation coil 5 the same as the magnetic pole direction of the lower magnetic field source 3, increasing the magnetic field strength and magnetic field gradient within the shell, thereby increasing the suspension height of sphere 1, increasing the dispersion between spheres 1, and reducing the particle collision damping between spheres 1. If the vibration frequency is greater than 100Hz, the damping force needs to be increased. The semi-active system module will input current to the excitation coil 5, making the magnetic field direction of the excitation coil 5 opposite to the magnetic pole direction of the lower magnetic field source 3, decreasing the magnetic field strength and magnetic field gradient within the shell 4, thereby decreasing the suspension height of sphere 1, reducing the dispersion between spheres 1, and increasing the particle collision damping between spheres 1. The increase or decrease in the levitation height of sphere 1 can be controlled by adjusting the current intensity within excitation coil 5. The current intensity within excitation coil 5 is adjustable from 0 to 5A.

[0028] Magnetic fluid 2 should be selected from kerosene-based, engine oil-based, and ester-based magnetic fluids, with a viscosity not exceeding 500 mPa·s. It should not be replaced by similar magnetic fluids, such as magnetorheological fluids.

[0029] The above is merely an example of the implementation of the present invention and is not intended to limit the present invention. For those skilled in the art, the active control particle collision damper based on the magnetic liquid suspension characteristics can be modified according to the engineering situation, including but not limited to the size of the damper, the volume of the sphere, the shape of the shell, the material selection, the installation position, etc., to adapt to the corresponding engineering.

Claims

1. A semi-active particle impact damper based on the suspension properties of magnetic liquids, characterized in that: The damper comprises a ball (1), a magnetic liquid (2), a lower magnetic field source (3), a shell (4) and an exciting coil (5); The ball (1) is installed in the shell (4) to form a particle collision damping; the magnetic liquid (2) is filled in the shell (4); the lower magnetic field source (3) is fixedly installed at the bottom of the shell (4) to form a constraint magnetic field; and the exciting coil (5) is sleeved on the outer surface of the shell (4) and fixed to form an exciting magnetic field.

2. The semi-active particle impact damper based on magnetic liquid suspension characteristics according to claim 1, characterized in that: The number of the ball (1) is greater than 1, the material is a non-magnetic metal, and the density is greater than the density of the magnetic liquid (2).

3. The semi-active particle impact damper based on magnetic fluid suspension characteristics according to claim 1, wherein: The shell (4) is a non-magnetic metal, the material of the lower magnetic field source (3) is a permanent magnet, and the magnetic pole direction is perpendicular to the plane where the vibration is located and parallel to the normal direction of the top and bottom of the shell (4).

4. The semi-active particle impact damper based on magnetic fluid suspension characteristics according to claim 1, wherein: The exciting coil (5) is annular, and the shape is the same as the shape of the shell (4), and the inner ring size is the same as the outer surface size of the shell (4); after being electrified, the magnetization direction is perpendicular to the plane where the vibration is located and parallel to the magnetic pole direction of the lower magnetic field source (3).

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