Variable damping-variable rigidity joint of robot grinding motorized spindle and flutter suppression method

Abstract

The invention provides a variable damping-variable rigidity joint of a robot grinding motorized spindle and a flutter suppression method. The variable damping-variable rigidity joint comprises a driving end used for driving a grinding wheel to rotate. The variable damping-variable rigidity joint is used for adjusting grinding damping and rigidity; the upper computer is used for processing signals and calculating damping-rigidity; the torque sensor is used for detecting and collecting relative rotation angle signals and rotation torque signals of the grinding wheel; the variable damping-variable stiffness joint comprises a power input shaft, a magnetorheological fluid magnetic field coil, a disc type rotor, magnetorheological fluid, a stator coil, a permanent magnet, a connecting piece, a thin flexible rod, a rotating shell and a grinding output shaft. According to the method, the optimal joint damping coefficient-rigidity coefficient parameter combination is calculated, and the currents of the magnetorheological fluid coil and the stator coil are accurately adjusted, so that the torsional damping and torsional rigidity of the joint are controlled, high-efficiency and high-quality stable grinding work of the non-circular curved surface grinding robot is achieved, and the adaptive capacity of the robot to the grinding environment is improved.

Description

Technical Field

[0001] The present invention relates to the field of robot joints, and particularly to a variable damping-variable stiffness joint for a robot grinding electric spindle and a chatter suppression method. Background Art

[0002] Grinding, as a key process for precision machining of engine crankshafts, directly determines the geometric tolerance and surface integrity of workpieces. In the high-speed grinding operation of a robot electric spindle, the non-circular contour machining characteristics lead to a significant enhancement of the inertial effect and electromechanical coupling vibration of the grinding wheel headstock, and the problem of dynamic fluctuation of grinding force caused thereby is particularly prominent. As a typical weak-rigidity complex curved surface part, the crankshaft is prone to induce machining system chatter due to the interaction between its structural characteristics and dynamic cutting force. When the chatter frequency resonates with the natural frequency of the process system, it will cause defects such as machining surface vibration marks and subsurface damage, resulting in the surface roughness index exceeding the process requirements. More seriously, continuous chatter will not only reduce the material removal efficiency but also cause systematic damages such as abnormal wear of the robot electric spindle bearings and abnormal shedding of grinding wheel grains, ultimately affecting the vibration characteristics and service reliability of the entire engine.

[0003] Therefore, a variable damping-variable stiffness joint for a robot grinding electric spindle and a chatter suppression method are needed to reduce the chatter behavior of grinding caused by frequent changes in grinding force, improve the stability of the grinding process, and avoid the generation of chatter. Summary of the Invention

[0004] In view of the deficiencies in the prior art, the present invention provides a variable damping-variable stiffness joint for a robot grinding electric spindle and a chatter suppression method. A thin flexible rod is used to transmit static torque, and the torsional damping and torsional stiffness of the joint are changed by magnetorheological fluid and electromagnetic spring respectively, solving the problems of grinding chatter, poor stability, and low quality caused by the significant enhancement of the inertial effect and electromechanical coupling vibration of the grinding wheel headstock in the current stage of grinding robots.

[0005] The present invention achieves the above technical objectives through the following technical means.

[0006] A variable damping-variable stiffness joint for a robot grinding electric spindle, comprising

[0007] A driving end for driving the grinding wheel to rotate;

[0008] A variable damping-variable stiffness joint for adjusting grinding damping and stiffness;

[0009] An upper computer for processing signals and calculating damping-stiffness;

[0010] A torque sensor for detecting and collecting the relative rotation angle signal and rotational torque signal of the grinding wheel;

[0011] The variable damping - variable stiffness joint includes a power input shaft, a magnetorheological fluid magnetic field coil, a disc rotor, magnetorheological fluid, a stator coil, a permanent magnet, a connecting piece, a thin flexible rod, a rotating housing, and a grinding output shaft;

[0012] The driving end is in transmission connection with the input shaft, and the input shaft is in transmission connection with the connecting piece; the disc rotor is installed on the input shaft, and the thin flexible rod is installed between the connecting piece and the rotating housing for flexible transmission of static torque; the rotating housing is supported on the input shaft, the disc rotor is located inside the rotating housing, and the cavity between the disc rotor and the rotating housing is filled with magnetorheological fluid; the magnetorheological fluid coil is installed inside the rotating housing for generating a magnetic field to change the viscosity of the magnetorheological fluid; the stator coil is installed in the inner cavity of the rotating housing, and the permanent magnet is fixed on the outer surface of the input shaft. By rotating the permanent magnet, the rotating housing rotates relative to the permanent magnet; the outside of the rotating housing is connected to the grinding output shaft; the grinding output shaft is connected to the grinding wheel; the driving end, the variable damping - variable stiffness joint, and the torque sensor are respectively connected to the upper computer.

[0013] Further, the thin flexible rods are symmetrically arranged on the connecting piece, and the cross - sectional shape of the thin flexible rod is circular.

[0014] Further, the magnetorheological coil is located inside the rotating housing and generates an axially distributed magnetic field; by changing the magnitude of the current in the magnetorheological coil, the magnitude of the magnetic field is changed, thereby changing the viscosity of the magnetorheological fluid, and further changing the viscous frictional force generated between the disc rotor and the magnetorheological fluid for adjusting the torsional damping.

[0015] Further, by changing the magnitude of the current flowing into the stator coil, the magnitude of the magnetic field generated by the stator coil is changed to achieve adjustable torsional stiffness of the rotating housing.

[0016] Further, a magnetic isolation ring is provided between the magnetorheological fluid coil and the stator coil of the rotating housing.

[0017] Further, the gap between the magnetorheological fluid and the input shaft is sealed by a sealing ring.

[0018] Further, the upper computer controls the magnitudes of the magnetic fields generated by the magnetorheological fluid coil and the stator coil according to the dynamic torsional angle and torque value of the grinding wheel shaft collected by the torque sensor.

[0019] A method for suppressing chatter of a variable damping - variable stiffness joint of a robot grinding electric spindle includes the following steps:

[0020] The dynamic torsional angle and torque value of the grinding wheel shaft are collected in real - time by the torque sensor and transmitted to the upper computer;

[0021] A variable-damping and variable-stiffness joint dynamic model of a robotic grinding electric spindle is established, and the model is analyzed using numerical methods to obtain the relationship between the torsional damping coefficient - torsional stiffness coefficient and the grinding wheel chatter angle and torque;

[0022] The stable region of the damping coefficient and the stable region of the stiffness coefficient in the variable-damping and variable-stiffness joint are determined. Combining the spectral characteristics of the dynamic cutting force of the grinding wheel monitored in real time by the torque sensor, the combination of the torsional damping coefficient - stiffness coefficient of the optimal joint that minimizes the chatter amplitude of the grinding wheel is calculated;

[0023] The host computer controls the magnitudes of the currents passed through the magnetorheological fluid coil and the stator coil respectively according to the combination of the optimal joint damping coefficient - stiffness coefficient, and then controls the actions of the joint torsional damping and torsional stiffness;

[0024] When the chatter motion of the grinding wheel causes relative motion between the input shaft and the rotating housing through the thin flexible rod, viscous friction torsional damping is generated between the disk rotor and the magnetorheological fluid, and electromagnetic torsional stiffness is generated between the stator coil and the permanent magnet, thereby changing the chatter frequency of the grinding wheel and absorbing the chatter energy.

[0025] Furthermore, a variable-damping and variable-stiffness joint dynamic model of a robotic grinding electric spindle is established, and the model is analyzed using numerical methods to obtain the relationship between the torsional damping coefficient - torsional stiffness coefficient and the grinding wheel chatter angle and torque. Specifically:

[0026] The variable-damping and variable-stiffness joint dynamic model of the robotic grinding electric spindle is:

[0027]

[0028] Where: J m is the moment of inertia of the permanent magnet electric spindle; J L is the moment of inertia of the grinding wheel; C is the torsional damping coefficient of the joint; K is the torsional stiffness coefficient of the joint; θ m represents the torsional vibration angle of the permanent magnet electric spindle; θ L represents the torsional vibration angle of the grinding wheel; k1, k2, and k3 respectively represent the first-order, second-order, and third-order coefficient terms of the driving torque of the permanent magnet electric spindle; T L is the amplitude of the load; Ω is the frequency of the load; is the second derivative of θ m ; is the first derivative of θ m ; is the second derivative of θ L ; is the first derivative of θ L ;

[0029] When the electromagnetic torque of the permanent magnet motorized spindle is in balance with the grinding load torque, the torsional vibration angle of the motorized spindle and the grinding wheel satisfies J m θ m +J L θ L = 0; Let x = θ m -θ L , and transform the torsional dynamics equation of the grinding system into a single-variable form:

[0030]

[0031] where: x = θ m -θ L , τ = ω0t,

[0032] Obtain the relationship between the joint torsional damping coefficient - torsional stiffness coefficient and the chatter angle and torque of the grinding wheel;

[0033]

[0034] where r is the amplitude value of the system chatter, γ is the chatter phase, and σ is the tuning parameter.

[0035] Furthermore, according to the instability condition of the system steady-state solution, determine the stability domain of the damping coefficient and the stability domain of the stiffness coefficient, where the expression of the instability condition of the system steady-state solution is:

[0036]

[0037] The beneficial effects of the present invention are as follows:

[0038] 1. For the variable damping - variable stiffness joint and chatter suppression method of the robot grinding motorized spindle of the present invention, a thin flexible rod is used to transmit static torque, and the joint torsional damping and torsional stiffness are changed by magnetorheological fluid and electromagnetic spring respectively, solving the problems of grinding chatter, poor stability, low quality, etc. caused by the significant enhancement of the inertia effect of the grinding wheel frame and the electromechanical coupling vibration in the current stage of grinding robots.

[0039] 2. The variable damping - variable stiffness joint and chatter suppression method of the robot grinding motorized spindle of the present invention has the characteristic of auto-disturbance rejection. By using a torque sensor to detect the dynamic torsional angle and torque value of the grinding wheel shaft in real time, and using the upper computer to calculate the optimal joint damping coefficient - stiffness coefficient parameter combination, the currents of the magnetorheological fluid coil and the stator coil are accurately adjusted to control the joint torsional damping and torsional stiffness, realizing high-efficiency and high-quality stable grinding work of the non-circular surface grinding robot, improving the adaptability of the robot to the grinding environment, and having wide practicability in the technical field. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the accompanying drawings required for the description of the embodiments or the prior art. The accompanying drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, it is obvious that other drawings can also be obtained based on these drawings.

[0041] Figure 1 This is the main sectional view of the variable damping - variable stiffness joint of the robot grinding electric spindle according to the present invention.

[0042] Figure 2 This is the left sectional view of the variable damping - variable stiffness joint of the robot grinding electric spindle according to the present invention.

[0043] Figure 3 This is the schematic diagram of the flow direction of the magnetorheological fluid and the magnetic field of the coil according to the present invention.

[0044] Figure 4 This is the rotational schematic diagram of the input shaft and the rotating housing according to the present invention.

[0045] Figure 5 This is the flow chart of the chatter suppression method according to the present invention.

[0046] In the figure:

[0047] 1 - Permanent magnet electric spindle; 2 - Variable damping - variable stiffness joint; 3 - Host computer; 4 - Torque sensor; 5 - Grinding wheel; 2 - 1 - Input shaft of the permanent magnet electric spindle; 2 - 2 - First half - key; 2 - 3 - Sealing ring; 2 - 4 - Magnetic field coil of the magnetorheological fluid; 2 - 5 - Bearing; 2 - 6 - Disk rotor; 2 - 7 - Magnetorheological fluid; 2 - 8 - Stator coil; 2 - 9 - Permanent magnet; 2 - 10 - Magnetic isolation ring; 2 - 11 - Connector; 2 - 12 - Thin flexible rod; 2 - 13 - Second half - key; 2 - 14 - Rotating housing; 2 - 15 - Grinding output shaft. Detailed implementation manners

[0048] The following will describe in detail the embodiments of the present invention. The examples of the embodiments are shown in the accompanying drawings, where the same or similar reference numerals represent the same or similar elements or elements with the same or similar functions throughout. The embodiments described by referring to the accompanying drawings are exemplary and are intended to explain the present invention, and should not be construed as a limitation to the present invention.

[0049] In the description of the present invention, it should be understood that the orientation or positional relationships indicated by the terms "center", "longitudinal", "transverse", "length", "width", "thickness", "upper", "lower", "axial", "radial", "vertical", "horizontal", "inner", "outer", etc. are based on the orientation or positional relationships shown in the drawings. These are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation. Therefore, it should not be construed as a limitation to the present invention. In addition, the terms "first" and "second" are only used for descriptive purposes and cannot be construed as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, features defined with "first" and "second" may explicitly or implicitly include one or more of such features. In the description of the present invention, "a plurality" means two or more, unless otherwise specifically defined.

[0050] In the present invention, unless otherwise clearly specified and defined, the terms "mounted", "connected", "coupled", "fixed", etc. shall be construed in a broad sense. For example, it may be a fixed connection, a detachable connection, or an integral connection; it may be a mechanical connection or an electrical connection; it may be directly connected or indirectly connected through an intermediate medium, and it may be the communication inside two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0051] As Figure 1 and Figure 2 As shown, the variable-damping and variable-stiffness joint of the robotic grinding motorized spindle according to the present invention includes a permanent magnet motorized spindle 1, a variable-damping and variable-stiffness joint 2, a host computer 3, and a torque sensor 4; the permanent magnet motorized spindle 1 is used to drive the grinding wheel to rotate; the variable-damping and variable-stiffness joint 2 is used to adjust the grinding damping and stiffness; the host computer 3 is used to process signals and calculate the damping-stiffness; the torque sensor 4 is used to detect and collect the signals of the grinding wheel 5 with respect to the rotation angle signal and the rotational torque signal.

[0052] The variable damping - variable stiffness joint 2 includes a power input shaft 2 - 1, a magnetorheological fluid magnetic field coil 2 - 4, a disk rotor 2 - 6, magnetorheological fluid 2 - 7, a stator coil 2 - 8, a permanent magnet 2 - 9, a connecting member 2 - 11, a thin flexible rod 2 - 12, a rotating housing 2 - 14, and a grinding output shaft 2 - 15; the permanent magnet electric spindle 1 is drivingly connected to the input shaft 2 - 1 through a first half - key 2 - 2, and the input shaft 2 - 1 is drivingly connected to the connecting member 2 - 11 through a second half - key 2 - 13; the disk rotor 2 - 6 is installed on the input shaft 2 - 1, and the thin flexible rod 2 - 12 is installed between the connecting member 2 - 11 and the rotating housing 2 - 14 for flexible transmission of static torque; the rotating housing 2 - 14 is supported on the input shaft 2 - 1, the disk rotor 2 - 6 is located inside the rotating housing 2 - 14, and the cavity between the disk rotor 2 - 6 and the rotating housing 2 - 14 is filled with magnetorheological fluid 2 - 7; the magnetorheological fluid coil 2 - 4 is installed inside the rotating housing 2 - 14 for generating a magnetic field to change the viscosity of the magnetorheological fluid 2 - 7; the stator coil 2 - 8 is installed in the inner cavity of the rotating housing 2 - 14, the permanent magnet 2 - 9 is fixed on the outer surface of the input shaft 2 - 1, and by rotating the permanent magnet 2 - 9, the rotating housing 2 - 14 rotates relative to the permanent magnet 2 - 9; the outside of the rotating housing 2 - 14 is connected to the grinding output shaft 2 - 15; the grinding output shaft 2 - 15 is connected to the grinding wheel 5; the driving end, the variable damping - variable stiffness joint 2, and the torque sensor 3 are respectively connected to the upper computer.

[0053] There are 8 thin flexible rods 2 - 12, symmetrically arranged on the connecting member 2 - 11. The cross - sectional shape of the thin flexible rod 2 - 12 is circular to achieve flexible transmission of the grinding static torque. A magnetic isolation ring 2 - 10 is provided between the magnetorheological fluid coil 2 - 4 and the stator coil 2 - 8 of the rotating housing 2 - 14. The gap between the magnetorheological fluid 2 - 7 and the input shaft 2 - 1 is sealed by a sealing ring 2 - 3.

[0054] As Figure 3 shown, the magnetorheological coil 2 - 4 is located inside the rotating housing 2 - 14, generating an axially distributed magnetic field; by changing the magnitude of the current in the magnetorheological coil 2 - 4, the magnitude of the magnetic field is changed, thereby changing the viscosity of the magnetorheological fluid, and further changing the viscous frictional force generated between the disk rotor 2 - 6 and the magnetorheological fluid 2 - 7 for adjusting the torsional damping. As Figure 4 shown, the stator coil 2 - 8 is fixed in the inner cavity of the rotating housing 2 - 14. A direct current is passed through the stator coil 2 - 8. By changing the magnitude of the current entering the stator coil 2 - 8, the magnitude of the magnetic field generated by the stator coil 2 - 8 is changed to achieve adjustable torsional stiffness of the rotating housing 2 - 14.

[0055] The host computer 3 controls the magnitudes of the magnetic fields generated by the magnetorheological fluid coil 2-4 and the stator coil 2-8 according to the dynamic torsional angle and torque value of the grinding wheel shaft collected by the torque sensor 4.

[0056] As Figure 5 shown, the chatter suppression method for the variable damping-variable stiffness joint of the robot grinding electric spindle of the present invention includes the following steps:

[0057] S1: When the variable damping-variable stiffness joint of the robot grinding electric spindle is working, the dynamic torsional angle and torque value of the grinding wheel shaft are collected in real time by the torque sensor 4 and transmitted to the host computer 3;

[0058] S2: Establish a dynamic model of the variable damping-variable stiffness joint of the robot grinding electric spindle, analyze the model by numerical method, and obtain the relationship between the torsional damping coefficient-torsional stiffness coefficient and the chatter angle and torque of the grinding wheel, specifically including:

[0059] The dynamic model of the variable damping-variable stiffness joint of the robot grinding electric spindle is:

[0060]

[0061] Where: J m is the moment of inertia of the permanent magnet electric spindle; J L is the moment of inertia of the grinding wheel; C is the torsional damping coefficient of the joint; K is the torsional stiffness coefficient of the joint; θ m represents the torsional vibration angle of the permanent magnet electric spindle; θ L represents the torsional vibration angle of the grinding wheel; k1, k2, and k3 respectively represent the first-order, second-order, and third-order coefficient terms of the driving torque of the permanent magnet electric spindle; T L is the amplitude of the load; Ω is the frequency of the load; is the second derivative of θ m ; is the first derivative of θ m ; is the second derivative of θ L ; is the first derivative of θ L ;

[0062] When the electromagnetic torque of the permanent magnet electric spindle is in balance with the grinding load torque, the torsional vibration angles of the electric spindle and the grinding wheel satisfy J m θ m + J L θ L = 0; Let x = θ m - θ L , and subtract the upper and lower equations in the dynamic model, and transform the torsional dynamic equation of the grinding system into a single-variable form:

[0063]

[0064] where: x = θ m -θ L , τ = ω0t,

[0065] Obtain the relationship between the joint torsional damping coefficient - torsional stiffness coefficient and the grinding wheel chatter angle and torque;

[0066]

[0067] where r is the system chatter amplitude value, γ is the chatter phase, and σ is the tuning parameter.

[0068] S3: The stability of the robot's motorized spindle grinding system depends on the eigenvalues of the coefficient matrix on the right side of the equation. According to the Routh–Hurwitz (Routh–Hurwitz stability criterion) stability criterion, since the system damping μ > 0, the expression for the instability condition of the system's steady-state solution can be obtained:

[0069]

[0070] According to the instability condition of the system's steady-state solution, determine the stability domain of the damping coefficient and the stability domain of the stiffness coefficient in the variable damping - variable stiffness joint 2. Combining with the spectral characteristics of the dynamic cutting force of the grinding wheel 5 monitored in real time by the torque sensor 4, calculate the combination of the torsional damping coefficient - stiffness coefficient of the optimal joint that minimizes the chatter amplitude value of the grinding wheel 5; Calculating the chatter amplitude value of the grinding wheel 5 according to the dynamic cutting force spectrum is the prior art.

[0071] S4: The host computer 3 controls the magnitudes of the currents passed through the magnetorheological fluid coils 2-4 and the stator coils 2-8 respectively according to the combination of the optimal joint damping coefficient - stiffness coefficient, and then controls the action of the joint 2 torsional damping and torsional stiffness;

[0072] S5: When the chatter motion of the grinding wheel 5 causes relative motion between the input shaft 2-1 and the rotating housing 2-14 through the thin flexible rod 2-12, viscous frictional torsional damping is generated between the disk rotor 2-6 and the magnetorheological fluid 2-7, and electromagnetic torsional stiffness is generated between the stator coil 2-8 and the permanent magnet 2-9, thereby changing the chatter frequency of the grinding wheel 5 and absorbing the chatter energy.

[0073] It should be understood that although this specification is described according to various embodiments, not every embodiment only contains an independent technical solution. This narrative manner of the specification is only for clarity. Those skilled in the art should regard the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

[0074] The series of detailed descriptions listed above are only specific descriptions of the feasible embodiments of the present invention, and they are not intended to limit the protection scope of the present invention. Any equivalent embodiments or modifications made without departing from the technical spirit of the present invention should be included in the protection scope of the present invention.

Claims

1. A variable damping - variable stiffness joint for a robot grinding electric spindle, characterized in that, including a driving end for driving a grinding wheel to rotate; a variable damping-variable stiffness joint (2) for adjusting grinding damping and stiffness; a host computer (3) for processing signals and calculating damping-stiffness; a torque sensor (4) for detecting and collecting signals of the relative rotation angle and rotational torque of the grinding wheel (5); the variable damping-variable stiffness joint (2) includes a power input shaft (2-1), a magnetorheological fluid magnetic field coil (2-4), a disc rotor (2-6), magnetorheological fluid (2-7), a stator coil (2-8), a permanent magnet (2-9), a connecting member (2-11), a thin flexible rod (2-12), a rotating housing (2-14), and a grinding output shaft (2-15); the driving end is in transmission connection with the input shaft (2-1), and the input shaft (2-1) is in transmission connection with the connecting member (2-11); the disc rotor (2-6) is mounted on the input shaft (2-1), and the thin flexible rod (2-12) is mounted between the connecting member (2-11) and the rotating housing (2-14) for flexible transmission of static torque; the rotating housing (2-14) is supported on the input shaft (2-1), the disc rotor (2-6) is located inside the rotating housing (2-14), and the cavity between the disc rotor (2-6) and the rotating housing (2-14) is filled with magnetorheological fluid (2-7); the magnetorheological fluid coil (2-4) is mounted inside the rotating housing (2-14) for generating a magnetic field to change the viscosity of the magnetorheological fluid (2-7); the stator coil (2-8) is mounted in the inner cavity of the rotating housing (2-14), the permanent magnet (2-9) is fixed on the outer surface of the input shaft (2-1), and by rotating the permanent magnet (2-9), the rotating housing (2-14) rotates relative to the permanent magnet (2-9); the outside of the rotating housing (2-14) is connected to the grinding output shaft (2-15); the grinding output shaft (2-15) is connected to the grinding wheel (5); the driving end, the variable damping-variable stiffness joint (2), and the torque sensor (3) are respectively connected to the host computer.

2. The variable-damping and variable-stiffness joint of the robot grinding electric spindle according to claim 1, wherein the thin flexible rods (2-12) are symmetrically arranged on the connecting member (2-11), and the cross-sectional shape of the thin flexible rod (2-12) is circular.

3. The variable-damping and variable-stiffness joint of the robotic grinding electric spindle according to claim 1, wherein the magnetorheological coil (2-4) is located inside the rotating housing (2-14) and generates an axially distributed magnetic field; by changing the magnitude of the current in the magnetorheological coil (2-4), the magnitude of the magnetic field is changed, thereby changing the viscosity of the magnetorheological fluid, and further changing the viscous frictional force generated by the disc rotor (2-6) and the magnetorheological fluid (2-7) for adjusting torsional damping.

4. The variable-damping and variable-stiffness joint of the robotic grinding electric spindle according to claim 1, wherein by changing the magnitude of the current flowing into the stator coil (2-8), the magnitude of the magnetic field generated by the stator coil (2-8) is changed to achieve adjustable torsional stiffness of the rotating housing (2-14).

5. The variable damping-variable stiffness joint of the robot grinding electric spindle according to claim 1, characterized in that a magnetic isolation ring (2-10) is provided between the magnetorheological fluid coil (2-4) and the stator coil (2-8) of the rotating housing (2-14).

6. The variable-damping and variable-stiffness joint of the robotic grinding electric spindle according to claim 1, wherein the gap between the magnetorheological fluid (2-7) and the input shaft (2-1) is sealed by a sealing ring (2-3).

7. The variable damping-variable stiffness joint of the robotic grinding electric spindle according to claim 1, wherein The host computer (3) controls the magnitudes of the magnetic fields generated by the magnetorheological fluid coil (2-4) and the stator coil (2-8) according to the dynamic torsional angle and torque value of the grinding wheel shaft collected by the torque sensor (4).

8. A chatter suppression method for a variable damping-variable stiffness joint of a robot grinding electric spindle according to claim 1, characterized in that, It includes the following steps: The dynamic torsional angle and torque value of the grinding wheel shaft are collected in real time by the torque sensor (4) and transmitted to the host computer (3). A variable-damping and variable-stiffness joint dynamics model of the robot grinding electric spindle is established, and the model is analyzed using the numerical method to obtain the relationship between the torsional damping coefficient - torsional stiffness coefficient and the grinding wheel chatter angle and torque. The stable regions of the damping coefficient and the stiffness coefficient in the variable-damping and variable-stiffness joint (2) are determined. Combining with the spectral characteristics of the dynamic cutting force of the grinding wheel monitored in real time by the torque sensor (4), the combination of the torsional damping coefficient - stiffness coefficient of the optimal joint that minimizes the chatter amplitude value of the grinding wheel (5) is calculated. The host computer (3) controls the magnitudes of the currents passed through the magnetorheological fluid coil (2-4) and the stator coil (2-8) respectively according to the combination of the optimal joint damping coefficient - stiffness coefficient, and then controls the functions of the torsional damping and torsional stiffness of the joint (2). When the chatter motion of the grinding wheel (5) causes relative motion between the input shaft (2-1) and the rotating housing (2-14) through the thin flexible rod (2-12), viscous friction torsional damping is generated between the disk rotor (2-6) and the magnetorheological fluid (2-7), and electromagnetic torsional stiffness is generated between the stator coil (2-8) and the permanent magnet (2-9), thereby changing the chatter frequency of the grinding wheel (5) and absorbing the chatter energy.

9. The chatter suppression method for the variable damping-variable stiffness joint of the robotic grinding electric spindle according to claim 8, characterized in that, A variable-damping and variable-stiffness joint dynamics model of the robot grinding electric spindle is established, and the model is analyzed using the numerical method to obtain the relationship between the torsional damping coefficient - torsional stiffness coefficient and the grinding wheel chatter angle and torque. Specifically: The variable-damping and variable-stiffness joint dynamics model of the robot grinding electric spindle is:[[]] Where: J m is the moment of inertia of the permanent magnet motorized spindle; J L is the moment of inertia of the grinding wheel; C is the torsional damping coefficient of the joint; K is the torsional stiffness coefficient of the joint; θ m represents the torsional vibration angle of the permanent magnet motorized spindle; θ L represents the torsional vibration angle of the grinding wheel; k1, k2, and k3 respectively represent the first, second, and third order coefficient of the driving torque of the permanent magnet motorized spindle; T L is the amplitude of the load; Ω is the frequency of the load; is the second derivative of θ m ; is the first derivative of θ m ; is the second derivative of θ L ; is the first derivative of θ L ; When the electromagnetic torque of the permanent magnet electric spindle is in balance with the grinding load torque, the torsional vibration angle of the electric spindle and the grinding wheel satisfies J m θ m +J L θ L = 0; Let x = θ m -θ L , and transform the torsional dynamics equation of the grinding system into a single-variable form: where: x = θ m -θ L , τ = ω0t, The relationship between the joint torsional damping coefficient - torsional stiffness coefficient and the grinding wheel chatter angle and torque is obtained. Among them, r is the system chatter amplitude value, γ is the chatter phase, and σ is the tuning parameter.

10. The chatter suppression method for the variable damping-variable stiffness joint of the robotic grinding electric spindle according to claim 9, characterized in that, The stable regions of the damping coefficient and the stiffness coefficient are determined according to the instability condition of the system steady-state solution. The expression of the instability condition of the system steady-state solution is:

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