Three-way variable frequency vibration absorber for suppressing time-varying chatter of robot and its design method

Abstract

The present invention belongs to the technical field related to robot processing and manufacturing, and discloses a three-way variable frequency vibration absorber for suppressing time-varying vibration of a robot and its design method, wherein the vibration absorber includes a mounting plate, a connecting plate, and a base plate arranged in parallel in sequence; an upper coil and an upper MRE assembly are respectively provided between the mounting plate and the connecting plate, and a lower coil and a lower MRE assembly are respectively provided between the connecting plate and the base plate, the upper MRE assembly and the lower MRE assembly being cylindrical and axially perpendicular to the connecting plate; a negative stiffness structure is connected to the connecting plate for applying negative stiffness to the mounting plate, and the mounting plate is connected to the connecting plate via a guide structure, which is arranged axially. The present invention utilizes MRE to achieve stiffness variability, utilizes the negative stiffness structure to generate a negative stiffness effect to reduce the natural frequency, and utilizes the shear modulus and compression modulus of the MRE assembly to achieve three-way adjustable stiffness, which can meet the robot's requirements for the time-varying frequency and time-varying direction of the vibration suppression device.

Description

Technical Field

[0001] The present invention belongs to the technical field related to robot processing and manufacturing, and more specifically, relates to a three-way variable frequency vibration absorber for suppressing time-varying vibration of a robot and a design method thereof. Background Art

[0002] Industrial robots, with their flexible structure, wide workspace, strong reconfigurability, and low cost, are playing an increasingly important role in the manufacturing of large or complex components. However, serial robots have poor rigidity, especially when the end is extended, resulting in increased chatter, which leads to reduced processing quality and, for example, reduced tool life when used in milling operations. Therefore, suppressing low-frequency chatter in milling robots is important for improving cutting volume and processing efficiency. The robot's high posture dependence causes its dynamic characteristics to continuously change during milling and other processes. The chatter mode exhibits both frequency and direction time-varying characteristics. Both time-varying characteristics should be considered when developing vibration suppression devices.

[0003] A tuned mass damper (TMD) is a dynamic vibration absorber composed of a mass, a stiffness element, and a damping element. It is used to reduce the vibration response of the target at its natural frequency and is widely used in vibration control. Prior art has developed TMDs with frequency modulation capabilities, which can achieve natural frequency variation and are used to suppress low-frequency chatter in robots. However, these TMDs typically only suppress vibration in a single direction. Passive combined TMDs have also been developed to address the forced vibration of milling in parallel robots. These can be configured to operate in multiple directions on the feed plane, but most are passively controlled, and their frequencies cannot be adjusted to the target vibration suppression frequency.

[0004] Currently, many vibration suppression devices for robots mainly focus on one of the factors, time-varying frequency or time-varying direction, which cannot adapt well to the vibration suppression needs of robots, and the vibration suppression effect needs to be improved. Summary of the Invention

[0005] In response to the above-mentioned defects or improvement needs of the prior art, the present invention provides a three-way variable frequency vibration absorber and a design method for suppressing the time-varying vibration of a robot, which is used to solve the problem that the existing vibration suppression devices for robots mainly focus on one of the factors of time-varying frequency or time-varying direction, cannot adapt well to the vibration suppression needs of the robot, and the vibration suppression effect needs to be improved.

[0006] To achieve the above objectives, according to one aspect of the present invention, a three-way variable frequency vibration absorber for suppressing time-varying chatter of a robot is provided, comprising a mounting plate, an upper coil, an upper MRE assembly, a connecting plate, a lower MRE assembly, a lower coil, a bottom plate, and a negative stiffness structure, wherein the mounting plate, the connecting plate, and the bottom plate are sequentially arranged in parallel;

[0007] The upper coil and the upper MRE assembly are respectively provided between the mounting plate and the connecting plate, and a conducting magnetic circuit can be formed between the upper coil and the upper MRE assembly. The lower coil and the lower MRE assembly are respectively provided between the connecting plate and the bottom plate, and a conducting magnetic circuit can be formed between the lower coil and the lower MRE assembly. The upper MRE assembly and the lower MRE assembly are respectively cylindrical and axially perpendicular to the connecting plate.

[0008] The negative stiffness structure is connected to the connecting plate and is used to apply a force to the mounting plate to form negative stiffness. The mounting plate is connected to the connecting plate via a guide structure, and the guide structure is arranged along the axial direction.

[0009] According to the three-way variable frequency vibration absorber for suppressing time-varying vibration of a robot provided by the present invention, the negative stiffness structure includes a cam, a side plate, a roller and a pushing structure, the cam is connected to the side of the mounting plate away from the connecting plate, the side plates are respectively provided on both sides of the cam, the side plates are connected to the connecting plate, and the pushing structure is provided on any one of the side plates, and the pushing structure is connected to the roller, and is used to apply a thrust to the roller so that the roller abuts against the cam surface, so as to apply a force to the mounting plate through the cam.

[0010] According to the three-way variable frequency vibration absorber for suppressing time-varying vibration of a robot provided by the present invention, the pushing structure includes a spring, the spring is sleeved on a guide rod, the guide rod is movably connected to the side plate in a direction perpendicular to the axial direction, the end of the guide rod facing the cam is connected to the roller and is provided with a convex edge, and the spring abuts between the convex edge and the side plate.

[0011] According to the three-way variable frequency vibration absorber for suppressing time-varying chatter of a robot provided by the present invention, the upper coil is connected to the mounting plate, and the lower coil is connected to the base plate;

[0012] And / or, the guide structure includes a guide column, which is arranged in the middle part of the mounting plate, and the guide column is movably connected to the connecting plate along the axial direction. The upper coil is sleeved on the guide column, and the mounting plate is evenly provided with a plurality of first connecting columns on the periphery of the upper coil. An upper MRE assembly is provided between any first connecting column and the connecting plate, and the mounting plate, the guide column, the first connecting column and the connecting plate are respectively magnetic conductors.

[0013] According to the three-way variable frequency vibration absorber for suppressing time-varying vibration of a robot provided by the present invention, a plurality of second connecting columns are symmetrically provided on the base plate, a lower coil is provided on the outer sleeve of any second connecting column, and a lower MRE assembly is provided between any second connecting column and the connecting plate, and the base plate and the second connecting column are respectively magnetic conductors.

[0014] According to the three-way variable frequency vibration absorber for suppressing time-varying chatter of a robot provided by the present invention, the upper MRE assembly and the lower MRE assembly respectively include an MRE layer and a support layer stacked in sequence.

[0015] According to another aspect of the present invention, a design method for a three-way variable frequency vibration absorber for suppressing time-varying chatter of a robot is provided. Based on any of the above-mentioned three-way variable frequency vibration absorbers for suppressing time-varying chatter of a robot, the design method includes:

[0016] Constructing dynamic models for the three-way variable frequency vibration absorber in three orthogonal directions, analyzing the modal mass and natural frequency in any direction, and obtaining mass constraints that can satisfy equal modal mass in the three directions and equal stiffness and mass constraints that can satisfy equal natural frequencies in the three directions;

[0017] Based on the mass constraint condition and the stiffness mass constraint condition, design parameters of the three-way variable frequency vibration absorber are obtained.

[0018] According to the design method of the three-way variable frequency vibration absorber for suppressing time-varying chatter of a robot provided by the present invention, obtaining the design parameters of the three-way variable frequency vibration absorber specifically includes:

[0019] According to the mass constraint conditions and the modal mass of the robot to which the three-way variable frequency vibration absorber is applied, the mass parameters of each component of the three-way variable frequency vibration absorber are designed and obtained;

[0020] According to the mass parameters of the components of the three-way variable frequency vibration absorber and the stiffness-mass constraint conditions, the natural frequency in any direction of the dynamic model is set to be equal to the lowest target frequency of the applied robot, thereby obtaining the stiffness parameters in the dynamic model;

[0021] The size parameters of the upper MRE component and the lower MER component are obtained according to the stiffness parameters in the dynamic model, the preset negative stiffness information and the elastic mechanical properties of the MRE material.

[0022] According to the design method of the three-way variable frequency vibration absorber for suppressing time-varying chatter of a robot provided by the present invention, obtaining the design parameters of the three-way variable frequency vibration absorber further includes:

[0023] Determining the magnetic flux density required for the conductive magnetic circuits where the upper MRE assembly and the lower MRE assembly are located, respectively, based on the highest target frequency of the applied robot;

[0024] Performing a magnetic circuit analysis on the conductive magnetic circuit where the upper MRE component is located, and obtaining setting parameters of the upper coil according to the required magnetic flux density and the size parameters of the upper MRE component;

[0025] A magnetic circuit analysis is performed on the conductive magnetic circuit where the lower MRE component is located, and setting parameters of the lower coil are obtained according to the required magnetic flux density and the size parameters of the lower MRE component.

[0026] According to the design method of the three-way variable frequency vibration absorber for suppressing time-varying vibration of a robot provided by the present invention, the negative stiffness structure includes a cam, a side plate, a roller and a pushing structure, the cam is connected to the side of the mounting plate away from the connecting plate, the side plates are respectively provided on both sides of the cam, the side plates are connected to the connecting plate, any of the side plates is provided with the pushing structure, the pushing structure is connected to the roller, and is used to apply a thrust to the roller so that the roller abuts against the cam surface, so as to apply a force to the mounting plate through the cam; the design method also includes:

[0027] Performing force analysis on the cam to obtain mechanical equations of the cam in the axial direction and in a direction perpendicular to the axial direction;

[0028] According to the preset negative stiffness information, a force-position relationship equation is established between the force caused by the negative stiffness and the position where the negative stiffness is located;

[0029] According to the mechanical equation and the force-position relationship equation, the motion trajectory curve of the position where the negative stiffness is located, that is, the motion trajectory curve of the center of the roller, is calculated and obtained, and then the profile curve of the cam is obtained.

[0030] In general, compared with the prior art, the above technical solutions conceived by the present invention provide a three-way variable frequency vibration absorber and a design method thereof for suppressing time-varying chatter of a robot:

[0031] 1. Taking into account both time-varying frequency and direction, magnetorheological elastomers (MREs) are used to construct elastic elements to achieve variable frequency vibrations. To address the low-frequency nature of robot flutter, a negative stiffness structure is used to generate a negative stiffness effect to reduce the natural frequency, enabling the vibration absorber to meet low-frequency requirements and improve load-bearing capacity. For multi-directional adjustment, the upper and lower MRE components are connected in series, and their shear and compression moduli are utilized to achieve three-way adjustable stiffness. This allows the vibration absorber to adapt to vibrations in different directions and frequencies, meeting the robot's requirements for time-varying frequency and direction of the vibration suppression device, achieving excellent vibration suppression results.

[0032] 2. A cam-roller structure is designed to generate a negative stiffness effect. The structure is simple, compact, and easy to set up. The rollers on both sides apply force to the cam, which helps improve structural stability. The negative stiffness structure does not interfere with the MRE components when applying force, which helps ensure vibration suppression performance.

[0033] 3. A mass constraint condition is proposed, in which the modal masses in the three directions of the vibration absorber dynamic model are equal, and a stiffness-mass constraint condition is proposed, in which the natural frequencies in the three directions are equal. Based on these two constraints, the vibration absorber parameters are designed, ensuring that the vibration absorber satisfies the three-way orthogonality condition during application. The natural frequencies in the three directions can be adjusted simultaneously according to the target vibration suppression frequency, ensuring that all three directions reach the target vibration suppression frequency. This allows the three-way variable-frequency vibration absorber to simultaneously suppress modes in the three directions, better adapt to the time-varying nature of the flutter direction, and achieve a better and more stable vibration suppression effect.

[0034] 4. The overall parameter design process of the three-way variable frequency vibration absorber is provided, and different parameters are calculated according to the vibration frequency bands of different robots, including MRE parameters, effective mass, coil parameters and negative stiffness parameters. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 It is a structural schematic diagram of the three-way variable frequency vibration absorber provided by the present invention;

[0036] Figure 2 This is a schematic diagram of the magnetic field and magnetic circuit direction of the three-way variable frequency vibration absorber provided by the present invention;

[0037] Figure 3 It is a schematic diagram of the design process of the three-way variable frequency vibration absorber provided by the present invention;

[0038] Figure 4 It is a schematic diagram of the dynamic model of the three-way variable frequency vibration absorber system provided by the present invention;

[0039] Figure 5 Schematic diagram of the magnetic circuit in the three-way variable frequency vibration absorber provided by the present invention;

[0040] Figure 6 Schematic diagram of the cam-roller interaction analysis in the three-way variable frequency vibration absorber provided by the present invention;

[0041] Figure 7 Schematic diagram of the three-way frequency response of the three-way variable frequency vibration absorber provided by the present invention under different currents;

[0042] Figure 8 Schematic diagram of experimental results of applying the three-way variable frequency vibration absorber provided by the present invention to a milling robot;

[0043] Throughout the drawings, the same reference numerals are used to denote the same elements or structures, wherein:

[0044] 1-Mounting plate; 2-Upper coil; 3-Upper MRE assembly; 4-Connecting plate; 5-Lower MRE assembly; 6-Lower coil; 7-Base plate; 8-Side plate; 9-Cam; 10-Roller; 11-Spring; 12-Guide rod; 13-Guide column; 14-First connecting column. DETAILED DESCRIPTION

[0045] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely for the purpose of explaining the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.

[0046] See also Figure 1 and Figure 2 This embodiment provides a three-way variable frequency vibration absorber for suppressing time-varying chatter of a robot. The three-way variable frequency vibration absorber includes a mounting plate 1, an upper coil 2, an upper MRE assembly 3, a connecting plate 4, a lower MRE assembly 5, a lower coil 6, a base plate 7, and a negative stiffness structure. The mounting plate 1, the connecting plate 4, and the base plate 7 are arranged in parallel in sequence; that is, the connecting plate 4 is arranged between the mounting plate 1 and the base plate 7, and the three are arranged parallel to each other.

[0047] The upper coil 2 and the upper MRE assembly 3 are respectively provided between the mounting plate 1 and the connecting plate 4, and a conducting magnetic circuit can be formed between the upper coil 2 and the upper MRE assembly 3. The lower coil 6 and the lower MRE assembly 5 are respectively provided between the connecting plate 4 and the bottom plate 7, and a conducting magnetic circuit can be formed between the lower coil 6 and the lower MRE assembly 5. The upper MRE assembly 3 and the lower MRE assembly 5 are respectively cylindrical and axially perpendicular to the connecting plate 4; that is, the upper MRE assembly 3 is supported and arranged between the mounting plate 1 and the connecting plate 4, bearing the weight of the mounting plate 1 and the components on the mounting plate 1; the lower MRE assembly 5 is supported and arranged between the connecting plate 4 and the bottom plate 7, bearing the weight of the connecting plate 4 and the components on the connecting plate 4.

[0048] The negative stiffness structure is connected to the connecting plate 4 and is used to apply a force to the mounting plate 1 to generate negative stiffness. The mounting plate 1 is connected to the connecting plate 4 via a guide structure positioned along the axial direction. This guide structure limits the movement direction of the mounting plate 1, allowing it to move along the axial direction of the MRE while restricting movement perpendicular to the axial direction. This guide structure helps stabilize the force applied by the negative stiffness on the mounting plate 1, thereby improving the stability of the negative stiffness and the overall vibration absorption system.

[0049] The three-way variable-frequency vibration absorber for suppressing time-varying chatter of a robot provided in this embodiment uses magnetically driven intelligent materials (MREs) to construct spring elements. By varying the current in the coil, the stiffness of the corresponding MRE component is changed, achieving adjustability of the absorber's stiffness, and thus, adjustability of the natural frequency. By introducing negative stiffness in parallel with the upper MRE component 3, a negative stiffness effect is generated, which reduces the absorber's natural frequency while increasing its load-bearing capacity. Since the time-varying chatter of the robot used is typically low-frequency, the introduction of negative stiffness can reduce the natural frequency, thereby meeting the low-frequency vibration absorption requirement. The upper and lower MRE components of the structure are connected in series, and the compression modulus of the upper MRE component 3 and the lower MRE component 5, as well as the shear modulus of the lower MRE component 5, are used to impart variable stiffness to the absorber in three orthogonal directions. This allows the absorber to adapt to vibrations in different directions and frequencies, thereby meeting the robot's requirements for the time-varying frequency and direction of the vibration suppression device.

[0050] Furthermore, the negative stiffness structure is used to apply a force to the mounting plate 1 in a direction away from the connecting plate to form negative stiffness; the negative stiffness force applied by the negative stiffness structure to the mounting plate 1 can be axially and toward the side away from the connecting plate 4, thereby producing a negative stiffness effect.

[0051] In some specific embodiments, the negative stiffness structure includes a cam 9, a side plate 8, a roller 10, and a pushing structure. The cam 9 is connected to the side of the mounting plate 1 facing away from the connecting plate 4. The side plates 8 are respectively provided on both sides of the cam 9. The side plates 8 are connected to the connecting plate 4. The pushing structure is provided on any of the side plates 8. The pushing structure is connected to the roller 10 and is used to apply a thrust to the roller 10 so that the roller 10 abuts against the surface of the cam 9, thereby applying a force to the mounting plate 1 through the cam 9. The side plates 8, rollers 10, and pushing structure are provided on either side of the cam 9, so that the rollers 10 on both sides abut against the surface of the cam 9, jointly pushing the rollers 10 to form negative stiffness, and the structure is relatively stable.

[0052] Specifically, the pushing structure includes a spring 11, which is sleeved on a guide rod 12. The guide rod 12 is movably connected to the side plate 8 in a direction perpendicular to the axial direction. The end of the guide rod 12 facing the cam 9 is connected to the roller 10 and has a convex edge. The spring 11 abuts between the convex edge and the side plate 8. The guide rod 12 and the side plate 8 can be movably connected via a linear bearing. The linear bearing can be arranged in a direction perpendicular to the axial direction, thereby limiting the deviation of the spring 11 in other directions, which helps to improve the stability of the force applied by the spring 11 and the stability of the force applied by the roller 10 on the cam 9.

[0053] Furthermore, the pushing structure is a structure capable of applying pressure to the roller 10. Other structures, such as a cylinder, may also be used in other embodiments, without limitation. The negative stiffness structure may also employ other structures capable of providing a corresponding force, such as a magnetic negative stiffness mechanism, a buckling beam negative stiffness mechanism, etc., without limitation, with the goal of providing stable negative stiffness.

[0054] Furthermore, the upper coil 2 is connected to the mounting plate 1; the mounting plate 1 is supported on the upper MRE assembly 3, thereby supporting the upper coil 2 on the upper MRE assembly 3, providing effective mass in the axial direction and improving the space utilization of the device. The lower coil 6 is connected to the base plate 7; the lower coil 6 is supported on the base plate 7, rather than on the lower MRE assembly 5, resulting in a lower effective mass in the axial direction of the lower MRE assembly 5. As a result, the vibration absorber primarily suppresses vibrations in the axial direction by the upper MRE assembly 3, while in the direction perpendicular to the axial direction, the lower MRE assembly 5 primarily suppresses vibrations, facilitating the adjustment of the natural frequencies in different directions.

[0055] Furthermore, the guide structure includes a guide post 13 disposed in the middle of the mounting plate 1 and movably connected to the connecting plate 4 along the axial direction. The upper coil 2 is sleeved on the guide post 13. The mounting plate 1 is provided with a plurality of first connecting posts 14 evenly distributed around the periphery of the upper coil 2. An upper MRE assembly 3 is disposed between each first connecting post 14 and the connecting plate 4. The mounting plate 1, the guide post 13, the first connecting posts 14, and the connecting plate 4 each serve as a magnetic conductor. This facilitates magnetic conduction between the upper MRE assembly 3 and the upper coil 2 to form a conductive magnetic circuit.

[0056] The guide post 13 can be inserted into a linear bearing and connected to the connecting plate 4 via the linear bearing. The linear bearing is arranged axially, thereby restricting the movement of the mounting plate 1 relative to the connecting plate 4 to the axial direction. This helps prevent deviation of the mounting plate 1 and improves the stability of the negative stiffness force. The linear bearing can also be a magnetic conductor, facilitating magnetic conduction between the upper coil 2 and the upper MRE assembly 3 to form a circuit, thereby enabling the stiffness of the upper MRE assembly 3 to be adjusted by adjusting the coil current.

[0057] Positioning the upper coil 2 in the center and the upper MRE assembly 3 around it also improves space utilization and reduces structural footprint. The upper coil 2 is attached to the mounting plate 1, with a gap between it and the connecting plate 4 to provide compression space for the upper MRE assembly 3.

[0058] Furthermore, a plurality of second connecting posts are symmetrically provided on the base plate 7, a lower coil 6 is provided on the outside of any second connecting post, and a lower MRE assembly 5 is provided between any second connecting post and the connecting plate 4; the base plate and the second connecting post can also be magnetic conductors to facilitate conduction between the lower MRE assembly 5 and the lower coil 6 to form a magnetic circuit.

[0059] The specific arrangement structure of the upper coil 2, upper MRE assembly 3, lower coil 6 and lower MRE assembly 5 provided in this embodiment makes the overall structure of the vibration absorber compact, space utilization reasonable, and multiple MRE assemblies can provide sufficient rigidity.

[0060] The upper MRE assembly 3 and the lower MRE assembly 5 each comprise an MRE layer and a support layer, stacked sequentially. The stacked MRE structure improves the MRE's load-bearing capacity, reduces operational deformation, and ensures more stable vibration absorber performance. The support layer can be a sheet metal layer or other structural layer that provides support and magnetic conductivity, without limitation.

[0061] In some specific embodiments, you can press Figure 1As shown in the figure, a coordinate system is established. In the vertical direction (Z), i.e., the axial direction, the upper coil 2 and the cam 9 are fixed to the mounting plate 1, and together they constitute the effective mass in the Z direction. The rollers 10 arranged symmetrically on both sides are connected to the side plates 8 via springs 11 and upper linear bearings. The upper linear bearings limit the up and down swinging of the springs 11, so that it is stretched or compressed only in the horizontal direction. Driven by the springs 11, the rollers 10 roll relative to the surface of the cam 9, producing a negative stiffness effect. The compressive stiffness of the upper MRE assembly 3 provides positive stiffness in the Z direction. The upper MRE assembly 3 is made of MRE layers and iron sheets overlapped to improve the load-bearing capacity and magnetic conductivity. Four laminated MREs are arranged at the four corners of the connecting plate 4 to prevent the vibration absorber from overturning when the robot changes its posture.

[0062] In the horizontal direction (X and Y directions), the lower MRE assembly 5 is also laminated, and its shear stiffness provides horizontal stiffness. The connecting plate 4 and the various structures above it together constitute the effective mass in the horizontal direction. Four lower coils 6 are installed on the bottom plate 7. Opposite currents are passed between adjacent lower coils 6 to form a closed magnetic circuit. Figure 2 The mounting plate 1 is inserted into the lower linear bearing via the guide column 13 to limit its horizontal movement relative to the connecting plate 4.

[0063] The three-way variable frequency vibration absorber can work in the X, Y, and Z directions simultaneously. Changing the input current of the upper coil 2 and the lower coil 6 can change the external driving magnetic field received by the magnetorheological elastomer, thereby achieving the effect of variable stiffness. The direction of the upper and lower magnetic circuits of the device is as follows: Figure 2 As shown. When working, the three-way variable frequency vibration absorber is installed at the end of the robot, specifically on the end effector of the robot to suppress the vibration of the end effector of the robot, for example, it can be installed on the electric spindle at the end of the robot. Taking the milling robot as an example, a sensor such as an acceleration sensor can be set on the robot, and the sensor is used to collect the robot milling vibration signal in real time, extract the main frequency of the vibration, and control the current passed into the upper and lower coils 6 to adjust the three-way natural frequency of the three-way variable frequency vibration absorber to be close to the dominant modal frequency, thereby suppressing the time-varying frequency in different directions during milling online. The three-way variable frequency vibration absorber can also enhance the dynamic stiffness of other robots, such as grinding robots, drilling robots, etc., and the specific application is not limited.

[0064] Further, refer to Figure 3 This second embodiment provides a design method for a three-way variable frequency vibration absorber for suppressing time-varying chatter of a robot, which is used to design the three-way variable frequency vibration absorber for suppressing time-varying chatter of a robot described in any of the above embodiments. The design method includes:

[0065] Constructing dynamic models for the three-way variable frequency vibration absorber in three orthogonal directions, analyzing the modal mass and natural frequency in any direction, and obtaining mass constraints that can satisfy equal modal mass in the three directions and equal stiffness and mass constraints that can satisfy equal natural frequencies in the three directions;

[0066] Based on the mass constraint condition and the stiffness mass constraint condition, design parameters of the three-way variable frequency vibration absorber are obtained.

[0067] First, the dynamic modeling of the three-way variable frequency vibration absorber is carried out:

[0068] The three-way variable frequency vibration absorber can be equivalent to the following in the X, Y and Z directions: Figure 4 The dynamic system shown in the figure has a two-degree-of-freedom system in the Z direction, and the models in the X and Y directions are the same, both are single-degree-of-freedom systems. Figure 1 Taking the specific structure shown as an example, that is, taking the structure in which the negative stiffness structure is a cam 9-roller 10 structure, the upper coil 2 is connected to the mounting plate 1, and the lower coil 6 is connected to the base plate 7 as an example, m1 is the mass mainly composed of the connecting plate 4 and the side plate 8, m2 is the mass composed of the cam 9, the upper coil 2 and the mounting plate 1; k1 and c1 are the compression stiffness and compression damping of the lower MRE component 5, respectively; k2 and c2 are the total stiffness and total damping composed of the upper MRE component 3 and the negative stiffness, respectively; k3 and c3 are the shear stiffness and shear damping of the lower MRE component 5, respectively.

[0069] Dynamic modeling of the vertical direction Z: The Z direction is equivalent to a two-degree-of-freedom system, and the two-order natural frequencies and modal masses are solved. To simplify the expression, let The two-order natural frequencies are shown in formula (1), and the two-order modal masses are shown in formula (2).

[0070]

[0071] where f Z1 、f Z2 are the first-order natural frequency and the second-order natural frequency in the Z direction respectively.

[0072]

[0073] where m Z1 、m Z2 are the first-order modal mass and second-order modal mass in the Z direction, respectively.

[0074] This embodiment aims to suppress the low-frequency vibration of the robot, so the first-order mode with a lower damper frequency is selected as the vibration suppression mode, that is, the Z-direction modal mass m Z and the Z-direction natural frequency f Z is equivalent to:

[0075]

[0076]

[0077] Dynamic modeling of horizontal X and Y directions: The dynamic models of horizontal X and Y directions are the same, equivalent to a single degree of freedom system. X-direction modal mass m X and the Y-direction modal mass m Y are equal and are provided by m1 and m2, and the horizontal stiffness is provided by the shear stiffness k3 of the lower MRE component 5. Dynamic analysis of the system yields:

[0078] Horizontal modal mass:

[0079] m X =m Y =m1+m2 (5)

[0080] Horizontal natural frequency:

[0081]

[0082] where f X is the natural frequency in the X direction, f Y is the natural frequency in the Y direction.

[0083] The three-way orthogonal equivalence condition is to make the modal mass in the three directions equal to obtain the mass constraint condition and to make the natural frequency in the three directions equal to obtain the stiffness mass constraint condition:

[0084] Taking the application in milling robots as an example, during the milling process of the robot, the direction of the low-frequency vibration mode is constantly changing. In order for the three-way variable frequency vibration absorber (MRE-TMD) to suppress the modes in three directions at the same time, it is necessary to ensure that the three-way variable frequency vibration absorber has the same modal mass and adjustable natural frequency in the three directions. Specifically, when the installation direction of the vibration absorber is consistent with the vibration mode direction, the vibration suppression effect is optimal. In order to deal with the time-varying nature of the vibration direction, the vibration absorber can achieve the maximum effect without detecting the vibration direction and adjusting the installation direction after the vibration direction changes. The three-way orthogonal equivalence principle is proposed. The three-way orthogonal equivalence principle shows that when the vibration absorber meets the three-way orthogonal equivalence condition, the vibration absorber can provide the same natural frequency in three directions at the same time, which can be the target vibration suppression frequency, so that no matter what the relative direction of the robot and the vibration absorber is, the vibration of the robot will be suppressed in the appropriate direction. At this time, the vibration absorber and the vibration absorber installed in the modal direction have completely equal vibration suppression effects. The three-way orthogonal equivalence condition is:

[0085] Condition 1: m X =m Y =m Z (7)

[0086] Condition 2: f X =f Y =f Z (8)

[0087] For condition 1: The connecting plate 4 and the side plate 8 are designed as lightweight thin plates, so that m2>>m1, that is, λ>>1, and because Therefore Z ≈m1+m2=m X =m Y ; Condition 1 is satisfied. That is, the mass constraint condition is: the connecting plate 4 and the side plate 8 are lightweight thin plates, so that m2>>m1; m Z ≈m1+m2=m X =m Y

[0088] Condition 2 can be achieved by designing the relationship between the stiffness and negative stiffness provided by the upper MRE component 3 and the lower MRE component 5. Taking η>>1, so that Γ1>>Γ2>>Γ3, then formula (3) can be simplified to: Then condition 2 can be simplified to the following relationship:

[0089]

[0090] That is, the stiffness and mass constraints are: Take η>>1 and satisfy formula (9).

[0091] In some specific embodiments, obtaining the design parameters of the three-way variable frequency vibration absorber specifically includes:

[0092] According to the mass constraint conditions and the modal mass of the robot to which the three-way variable frequency vibration absorber is applied, the mass parameters of each component of the three-way variable frequency vibration absorber are designed and obtained;

[0093] According to the mass parameters of the components of the three-way variable frequency vibration absorber and the stiffness-mass constraint conditions, the natural frequency in any direction of the dynamic model is set to be equal to the lowest target frequency of the applied robot, thereby obtaining the stiffness parameters in the dynamic model;

[0094] The size parameters of the upper MRE component 3 and the lower MER component are obtained according to the stiffness parameters in the dynamic model, the preset negative stiffness information and the elastic mechanical properties of the MRE material.

[0095] Parameter calculation principle of three-way variable frequency vibration absorber:

[0096] The MRE modulus increases with increasing magnetic field, with a rate of change exceeding fourfold, covering a frequency range twice that of low-frequency chatter during robotic milling. Therefore, to effectively achieve online variable-frequency vibration suppression with a three-way variable-frequency vibration absorber, only two aspects need to be considered: first, designing the dimensional parameters so that the initial natural frequency of the three-way variable-frequency vibration absorber in zero magnetic field reaches the target minimum frequency for suppression; second, designing the excitation coil to provide the MRE with sufficient magnetic field density to drive its modulus variation to cover the frequency range of robotic milling.

[0097] First, determine the modal parameters of the target vibration suppression robot, that is, the applied robot, mainly the modal mass M that dominates the vibration and the target frequency range f of the vibration. Mmin 、f Mmax , then determine the parameters of the three-way variable frequency vibration absorber.

[0098] Mass calculation: Taking into account the vibration suppression effect and the limitation of the additional mass at the end of the robot, the effective mass of the vibration absorber should usually be 3% to 5% of the modal mass of the robot. That is, the mass parameters of the three-way variable frequency vibration absorber are: take m X =m Y =m Z =μM, where μ=3% to 5%. X =m1+m2, From condition 1, we know that λ>>1, and the larger the better. However, in actual processing, there are restrictions on the size of the object, so we take λ=4~6, and the sizes of masses m1 and m2 are as follows:

[0099]

[0100] Stiffness calculation: After obtaining the mass m1 and m2, it is necessary to calculate the magnitude of each stiffness value. According to the principle of material elasticity, the relationship between k1, k2, k3 and MRE size is as follows:

[0101]

[0102] Where d1 and h1 are the diameter and height of the MRE layer in the lower MRE component 5, respectively; d2 and h2 are the diameter and height of the MRE layer in the upper MRE component 3, respectively; E0 and G0 are the zero-field compression modulus and zero-field shear modulus of the MRE, respectively, which are related to the physical properties of the MRE material itself; k N is the magnitude of negative stiffness, which is determined by the interaction between the cam 9 and the roller 10.

[0103] From formula (11), we know Substituting into formula (6), we can get the values ​​of k1 and k3 as shown in formula (12):

[0104]

[0105] Then, according to the relational formula (9) of condition 2 derived from the three-way orthogonal equivalence condition, the value of k2 is obtained as shown in formula (13).

[0106]

[0107] In summary, the stiffness parameters k1, k2, and k3 in the dynamic model can be obtained from equations (12) and (13).

[0108] Negative stiffness k N Calculation of the specific size of MRE: The relationship between each stiffness and MRE size is known from formula (11). Now let the ratio of the diameter and thickness of the MRE layer in the MRE component 5 be In order to make the structure stable and not easy to overturn, γ needs to be as large as possible. However, in order to make the effective magnetic resistance formed by MRE as small as possible to obtain a larger magnetic field strength, γ is set to be as small as possible. Considering all factors, γ is set to be 0.7 to 3. Similarly, let the ratio of the diameter and thickness of the MRE layer in the upper MRE component 3 be κ=0.7~3. Select the appropriate negative stiffness k according to actual needs N =-40%~-20%k2, combined with formula (11), the size parameters of the MRE layer in the lower MRE component 5 are shown in formula (14), and the size parameters of the MRE layer in the upper MRE component 3 are shown in formula (15).

[0109]

[0110]

[0111] This size is the size parameter of the MRE layer in the MRE component. When the MRE component is set as a stacked structure, the calculated thickness parameter can be divided by the number of MRE layers in the component to obtain the thickness of each MRE layer. In addition, since formula (11) is based on Figure 1 The stiffness formula derived from the structure shown, that is, setting four upper MRE components 3 and four lower MRE components 5 at the same time, therefore, the diameter and thickness parameters of the MRE layer in the lower MRE component 5 obtained by formula (14) are the parameters of a single lower MRE component 5, and the diameter and thickness parameters of the MRE layer in the upper MRE component 3 obtained by formula (15) are the parameters of a single upper MRE component 3.

[0112] Furthermore, obtaining the design parameters of the three-way variable frequency vibration absorber also includes:

[0113] Determine the magnetic flux density required for the conductive magnetic circuits where the upper MRE component 3 and the lower MRE component 5 are located, respectively, based on the highest target frequency of the applied robot;

[0114] Performing magnetic circuit analysis on the conductive magnetic circuit where the upper MRE component 3 is located, and obtaining setting parameters of the upper coil 2 based on the required magnetic flux density and the size parameters of the upper MRE component 3;

[0115] A magnetic circuit analysis is performed on the conductive magnetic circuit where the lower MRE component 5 is located, and setting parameters of the lower coil 6 are obtained according to the required magnetic flux density and the size parameters of the lower MRE component 5.

[0116] The coil parameter calculation principle is as follows: the effective mass determined above and the size parameters of the MRE ensure that when no magnetic field is added, the frequency of each direction of the three-way variable frequency vibration absorber can reach the minimum target frequency f required for suppression. Mmin In order to achieve the function of variable frequency vibration suppression, it is necessary to provide a sufficiently large magnetic field to the MRE to drive its modulus change so that the three-way variable frequency vibration absorber can cover the highest target frequency f Mmax Typically, the magnetostrictive modulus of an MRE reaches saturation at a magnetic field of 0.7 T, so the magnetic flux density at the MRE is assumed to be B = 0.7 T. Next, a three-dimensional variable frequency vibration absorber is required to perform magnetic circuit analysis and determine coil parameters. The magnetic fields of the upper MRE assembly 3 and the lower MRE assembly 5 are formed by the upper and lower magnetic circuits, respectively.

[0117] refer to Figure 2 The conductive magnetic circuit shown in the figure, the equivalent magnetic circuit models of the lower magnetic circuit and the upper magnetic circuit are as follows Figure 5 Where R1 is the magnetic resistance of the lower MRE component 5, R2 is the magnetic resistance of the connecting plate 4, R3 is the magnetic resistance of the bottom plate 7, R4 is the magnetic resistance of the upper MRE component 3, and R5 is the magnetic resistance of the mounting plate 1. N1I1 and N2I2 are the magnetomotive forces generated by the lower coil 6 and the upper coil 2, respectively. The calculation expressions for the lower and upper magnetic circuits can be obtained as follows:

[0118]

[0119] Among them F a1 、F a2 are the total magnetomotive force of the lower and upper magnetic circuits, respectively, which are determined by the currents I1 and I2 and the number of coil turns N1 and N2; φ1 and φ2 are the total magnetic flux of the lower and upper magnetic circuits, respectively, which depend on the magnetic flux density B and the effective magnetic flux area S1 and S2; R a1 、R a2 are the total magnetic resistance of the lower magnetic circuit and the upper magnetic circuit respectively. Due to the relative magnetic flux rate μ of MRE MRE ≈2, the relative magnetic permeability of magnetic materials such as structural steel is about 8000, and the magnetic resistance of MRE is much greater than that of other parts, so Vacuum magnetic permeability μ0=4π×10 -7 T·m / A.

[0120] Substituting the previously determined MRE component dimensions, we can obtain the control current and number of turns of the lower coil 6 and upper coil 2. That is, the setting parameters of the lower coil 6 and upper coil 2 are:

[0121]

[0122] After the setting parameters of the upper coil 2 are determined, the mass parameters of the upper coil 2 can be determined, and the mass parameters of the cam 9 and the mounting plate 1 can be further specifically designed according to m2; in addition, according to condition 1, the connecting plate 4 and the side plate 8 can be set as lightweight plates, and the connecting plate 4 can be set as an aluminum plate as a magnetic conductor, and the mass of the connecting plate 4 and the side plate 8 can be specifically designed according to m1.

[0123] In some specific embodiments, the negative stiffness structure includes a cam 9, a side plate 8, a roller 10, and a pushing structure. The cam 9 is connected to the side of the mounting plate 1 facing away from the connecting plate 4. The side plates 8 are respectively provided on both sides of the cam 9. The side plates 8 are connected to the connecting plate 4. The pushing structure is provided on any of the side plates 8. The pushing structure is connected to the roller 10 and is used to apply a thrust to the roller 10 so that the roller 10 abuts against the surface of the cam 9, thereby applying a force to the mounting plate 1 through the cam 9. The design method also includes:

[0124] Performing force analysis on the cam 9 to obtain mechanical equations of the cam 9 in the axial direction and in a direction perpendicular to the axial direction;

[0125] According to the preset negative stiffness information, a force-position relationship equation is established between the force caused by the negative stiffness and the position where the negative stiffness is located;

[0126] According to the mechanical equation and the force-position relationship equation, the motion trajectory curve of the position where the negative stiffness is located is calculated, that is, the motion trajectory curve of the center of the roller 10, and then the profile curve of the cam 9 is obtained.

[0127] This embodiment uses a special design on the surface of the cam 9 to create a negative stiffness effect in the interaction between the cam 9 and the roller 10, thereby reducing the natural frequency of the vibration absorber while increasing the load-bearing capacity. The principle of calculating the cam 9 profile size is as follows: negative stiffness is generated by the interaction between the cam 9 and the roller 10. Figure 6 This is a unilateral force analysis of the interaction between the cam 9 and the roller 10. The cam 9 is subjected to the normal force F applied by the roller 10. C and rolling friction F f , the resultant force is F CS The roller 10 is subjected to the horizontal restoring force F provided by the horizontal spring 11. H and the reaction force F of cam 9 C ' S .

[0128] The force analysis on one side of the structure shows that the interaction between the roller 10 and the cam 9 is projected onto the x-axis, which is perpendicular to the axial direction, and the y-axis, which is the horizontal force F in the axial direction. H and vertical force F V The expression of the mechanical equation is as follows:

[0129]

[0130] in is the rolling friction angle, rolling friction coefficient Determined by the surface material of the cam 9 and the roller 10; δ is the pre-compression amount of the horizontal spring 11 when the center of the roller 10 is at the origin, k H is the stiffness of the unilateral horizontal spring 11, and x is the coordinate of the center of the roller 10 on the x-axis.

[0131] Dividing formula (18) up and down and expanding it, we can get formula (19):

[0132]

[0133] Vertical force F of cam 9-roller 10 mechanism V is the force caused by negative stiffness, which can represent the force-position relationship of negative stiffness, that is, the relationship between the force caused by negative stiffness and the location of negative stiffness. To avoid introducing nonlinear stiffness, the negative stiffness force-position curve is designed as a piecewise linear function, that is, the force-position relationship equation is shown in Equation (20). Where C1≤y≤C2 is the effective working range, which is selected according to the working stroke of the vibration absorber. C2-C1 can be the compression deformation stroke of the upper MRE component 3; The negative stiffness brought by the negative stiffness structure is a stable value k within the axial working range of the vibration absorber. N ; b1, b2, b3, and C3 are constant coefficients of the negative stiffness force-position curve function, which do not affect the effect of negative stiffness in the section C1≤y≤C2 and can be selected and adjusted according to the actual required cam 9 profile size.

[0134]

[0135] Due to the symmetry of the cam 9-roller 10 structure, Substituting into equation (19), we get the center motion trajectory curve L(x, y) of roller 10. The actual profile curve U(x, y) of cam 9 should be the center trajectory curve of roller 10 offset by the radius r of roller 10, as shown in equation (21):

[0136] U(x,y)=L(x+rsinθ,y-rcosθ) (21)

[0137] According to the above method, the parameters of the three-way variable frequency vibration absorber suitable for online suppression of low-frequency chatter in robot milling, such as the MRE component size, cam 9 profile, and coil parameters, can be determined.

[0138] Example verification

[0139] Hammer test tests the frequency variation range of the three-way variable frequency vibration absorber: using the m+p data acquisition system (m+pAnalyzer), a PCB pulse hammer is used to excite the three-way variable frequency vibration absorber at different currents to obtain its three-way frequency response function as shown below: Figure 7 As shown in the figure, the natural frequency of the three-axis variable frequency vibration absorber changes with current from 10.7 to 24.7 Hz in the X direction; from 10.9 to 24.2 Hz in the Y direction; and from 10.2 to 23 Hz in the Z direction. Experimental results show that the frequencies in all three directions are around 10-20 Hz, which covers the range of low-frequency vibrations of the robot.

[0140] Specifically, experiments can be conducted on the upper coil 2 under different current excitations to analyze the changes in the natural frequency of the three-way variable frequency vibration absorber in the Z direction, i.e., the axial direction, under different currents, and obtain the relationship between the current excitation of the upper coil 2 and the natural frequency in the Z direction. Then, in the application stage, the excitation current of the upper coil 2 can be adjusted according to this relationship based on the target vibration suppression frequency, so that the natural frequency in the Z direction is consistent with the target vibration suppression frequency.

[0141] Experiments can also be conducted on the lower coil 6 under different current excitations to analyze the changes in the natural frequency of the three-way variable frequency vibration absorber in the horizontal direction, i.e., the direction perpendicular to the axial direction (including the X direction and the Y direction) under different currents, and obtain the relationship between the current excitation of the lower coil 6 and the horizontal natural frequency. Then, in the application stage, the excitation current of the lower coil 6 can be adjusted according to the relationship based on the target vibration suppression frequency, so that the horizontal natural frequency is consistent with the target vibration suppression frequency.

[0142] Experiment on chatter suppression in robot milling based on three-way variable frequency vibration absorber

[0143] This experiment validated this method using an ABB IRB6660 heavy-duty milling robot. A three-axis variable frequency vibration absorber was installed on the motorized spindle at the end of the milling robot. A 16mm diameter, four-tooth flat-bottom cutter was used to mill a 6061 aluminum alloy workpiece. Two tool paths were used, with the corresponding milling parameters shown in Table 1.

[0144] Table 1 Milling experiment settings

[0145]

[0146] The DYTRAN 3263A2 triaxial accelerometer is used to measure the milling vibration signal of the robot. The maximum amplitude of the signal within 10-20 Hz is extracted as the target frequency for vibration suppression, and the corresponding current is passed into the vibration absorber. Figure 8 The measurement results are shown. Under the two paths, the acceleration amplitudes of X0, Y0 and Z0 all decrease by about 70% after adding the three-way variable frequency vibration absorber, verifying the vibration suppression effectiveness of the three-way variable frequency vibration absorber.

[0147] In view of the shortcomings of the prior art in related aspects, the present invention designs a three-way variable frequency vibration absorber for suppressing time-varying chatter of a robot. Specifically: (1) Design the structure of the three-way variable frequency vibration absorber; (2) Perform dynamic modeling of the three-way variable frequency vibration absorber: Based on the magnetic variable stiffness characteristics of the MRE, a vibration model of the three-way variable frequency vibration absorber system is established, and the vibration absorber is dynamically modeled in the three orthogonal directions of X, Y, and Z to obtain the modal mass and modal frequency of the three directions. In order to enable the device to absorb multi-directional vibrations simultaneously, the conditions for the three-way modal mass and frequency to be equal are derived, and the constraint conditions for the three-way equivalent frequency modulation are obtained. This serves as the basis for subsequent design. (3) Design the parameters of the three-way variable frequency vibration absorber: Calculate the mass and stiffness based on the target vibration suppression frequency and the derived three-way equivalent conditions. Then, calculate the specific dimensions of the MRE and the profile curve of the cam 9 based on the stiffness, and then analyze the magnetic circuit that drives the MRE to calculate the coil size parameters, etc., to provide a reference for online suppression of robot milling chatter based on the three-way variable frequency vibration absorber.

[0148] Many current vibration suppression devices for robots focus primarily on either time-varying frequency or time-varying direction. This invention addresses both factors, specifically suppressing the dominant mode of milling chatter by installing a three-way variable-frequency vibration absorber at the robot's end. The three-way variable-frequency vibration absorber is parametrically designed based on the robot's modal parameters, enabling it to suppress low-frequency chatter in different directions and frequencies during milling.

[0149] In general, the three-way variable frequency vibration absorber proposed in the present invention can suppress vibrations in different directions. The device is simple and compact in structure. The coil is used as part of the effective mass, which improves the space utilization of the device. The interaction between the cam 9 and the roller introduces negative stiffness, which improves the load-bearing capacity of the device while ensuring the low-frequency working range of the device. By using two parts of MRE to provide effective stiffness in three orthogonal directions, low-frequency vibrations in different directions during robot milling can be suppressed. The provided three-way variable frequency vibration absorber has a better online frequency modulation function. The natural frequency of the three-way variable frequency vibration absorber is adjusted by adjusting the input current to drive the magnetic field to change the MRE stiffness. The response is fast and can reach millisecond level response. During robot milling, the frequency of the three-way variable frequency vibration absorber can be quickly matched to the same as the robot vibration frequency by online controlling the current based on the vibration signal collected in real time.

[0150] It will be easily understood by those skilled in the art that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A three-way variable frequency vibration absorber for suppressing time-varying vibration of a robot, characterized in that: It includes a mounting plate, an upper coil, an upper MRE assembly, a connecting plate, a lower MRE assembly, a lower coil, a bottom plate and a negative stiffness structure, wherein the mounting plate, the connecting plate and the bottom plate are sequentially arranged in parallel; The upper coil and the upper MRE assembly are respectively provided between the mounting plate and the connecting plate, and a conducting magnetic circuit can be formed between the upper coil and the upper MRE assembly. The lower coil and the lower MRE assembly are respectively provided between the connecting plate and the bottom plate, and a conducting magnetic circuit can be formed between the lower coil and the lower MRE assembly. The upper MRE assembly and the lower MRE assembly are respectively cylindrical and axially perpendicular to the connecting plate. The negative stiffness structure is connected to the connecting plate and is used to apply a force to the mounting plate to form negative stiffness, and the mounting plate is connected to the connecting plate via a guide structure, and the guide structure is arranged along the axial direction; the compression modulus of the upper MRE component and the lower MRE component and the shear modulus of the lower MRE component are utilized to enable the three-way variable frequency vibration absorber to have variable stiffness in three orthogonal directions.

2. The three-way variable frequency vibration absorber for suppressing time-varying chatter of a robot according to claim 1, characterized in that: The negative stiffness structure includes a cam, a side plate, a roller and a pushing structure. The cam is connected to the side of the mounting plate away from the connecting plate. The side plates are respectively provided on both sides of the cam. The side plates are connected to the connecting plate. The pushing structure is provided on any one of the side plates. The pushing structure is connected to the roller and is used to apply a thrust to the roller so that the roller abuts against the cam surface, so as to apply a force to the mounting plate through the cam.

3. The three-way variable frequency vibration absorber for suppressing time-varying chatter of a robot according to claim 2, characterized in that: The pushing structure includes a spring, which is sleeved on a guide rod. The guide rod is movably connected to the side plate in a direction perpendicular to the axial direction. The end of the guide rod facing the cam is connected to the roller and is provided with a convex edge. The spring abuts between the convex edge and the side plate.

4. The three-way variable frequency vibration absorber for suppressing time-varying chatter of a robot according to claim 1, characterized in that: The upper coil is connected to the mounting plate, and the lower coil is connected to the bottom plate; And / or, the guide structure includes a guide column, which is arranged in the middle part of the mounting plate, and the guide column is movably connected to the connecting plate along the axial direction. The upper coil is sleeved on the guide column, and the mounting plate is evenly provided with a plurality of first connecting columns on the periphery of the upper coil. An upper MRE assembly is provided between any first connecting column and the connecting plate, and the mounting plate, the guide column, the first connecting column and the connecting plate are respectively magnetic conductors.

5. The three-way variable frequency vibration absorber for suppressing time-varying chatter of a robot according to any one of claims 1 to 4, characterized in that: A plurality of second connecting posts are symmetrically arranged on the bottom plate, a lower coil is provided on the outside of any second connecting post, and a lower MRE assembly is provided between any second connecting post and the connecting plate, and the bottom plate and the second connecting posts are magnetic conductors.

6. The three-way variable frequency vibration absorber for suppressing time-varying chatter of a robot according to any one of claims 1 to 4, characterized in that: The upper MRE assembly and the lower MRE assembly respectively include an MRE layer and a support layer stacked in sequence.

7. A design method for a three-way variable frequency vibration absorber for suppressing time-varying chatter of a robot, characterized in that: The design method of the three-way variable frequency vibration absorber for suppressing time-varying chatter of a robot based on any one of claims 1 to 6 includes: Constructing dynamic models for the three-way variable frequency vibration absorber in three orthogonal directions, analyzing the modal mass and natural frequency in any direction, and obtaining mass constraints that can satisfy equal modal mass in the three directions and equal stiffness and mass constraints that can satisfy equal natural frequencies in the three directions; Based on the mass constraint condition and the stiffness mass constraint condition, design parameters of the three-way variable frequency vibration absorber are obtained.

8. The design method of a three-way variable frequency vibration absorber for suppressing time-varying chatter of a robot according to claim 7, characterized in that: Obtaining the design parameters of the three-way variable frequency vibration absorber specifically includes: According to the mass constraint conditions and the modal mass of the robot to which the three-way variable frequency vibration absorber is applied, the mass parameters of each component of the three-way variable frequency vibration absorber are designed and obtained; According to the mass parameters of the components of the three-way variable frequency vibration absorber and the stiffness-mass constraint conditions, the natural frequency in any direction of the dynamic model is set to be equal to the lowest target frequency of the applied robot, thereby obtaining the stiffness parameters in the dynamic model; The size parameters of the upper MRE component and the lower MRE component are obtained according to the stiffness parameters in the dynamic model, the preset negative stiffness information and the elastic mechanical properties of the MRE material.

9. The design method of a three-way variable frequency vibration absorber for suppressing time-varying chatter of a robot according to claim 8, characterized in that: Obtaining the design parameters of the three-way variable frequency vibration absorber also includes: Determining the magnetic flux density required for the conductive magnetic circuits where the upper MRE assembly and the lower MRE assembly are located, respectively, based on the highest target frequency of the applied robot; Performing a magnetic circuit analysis on the conductive magnetic circuit where the upper MRE component is located, and obtaining setting parameters of the upper coil according to the required magnetic flux density and the size parameters of the upper MRE component; A magnetic circuit analysis is performed on the conductive magnetic circuit where the lower MRE component is located, and setting parameters of the lower coil are obtained according to the required magnetic flux density and the size parameters of the lower MRE component.

10. The design method of a three-way variable frequency vibration absorber for suppressing time-varying chatter of a robot according to claim 7, characterized in that: The negative stiffness structure includes a cam, a side plate, a roller, and a pushing structure. The cam is connected to a side of the mounting plate away from the connecting plate. The side plates are respectively provided on both sides of the cam. The side plates are connected to the connecting plate. The pushing structure is provided on any one of the side plates. The pushing structure is connected to the roller and is used to apply a thrust to the roller so that the roller abuts against the cam surface, thereby applying a force to the mounting plate through the cam. The design method further includes: Performing force analysis on the cam to obtain mechanical equations of the cam in the axial direction and in a direction perpendicular to the axial direction; According to the preset negative stiffness information, a force-position relationship equation between the force caused by the negative stiffness and the position of the negative stiffness is established; According to the mechanical equation and the force-position relationship equation, the motion trajectory curve of the position where the negative stiffness is located, that is, the motion trajectory curve of the center of the roller, is calculated and obtained, and then the profile curve of the cam is obtained.

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