A tool and method for polishing the inner surface of a hemispherical resonator based on multi-field coupling

Abstract

The present invention relates to a tool and method for polishing the inner surface of a hemispherical resonator based on multi-field coupling. The tool comprises a permanent magnet magnetorheological polishing head and a hemispherical resonator fixing fixture. The permanent magnetorheological polishing head comprises a permanent magnet polishing head and a metal clamping rod. The bottom surface of the permanent magnet polishing head is a circular arc surface that matches the curvature of the hemispherical resonator's inner surface. A groove is provided horizontally in the middle of the permanent magnet polishing head. A vertical injection hole for real-time injection of magnetorheological fluid is provided between the permanent magnet polishing head and the metal clamping rod. The hemispherical resonator fixing fixture has four built-in ultrasonic transducers on the bottom and two side surfaces. By adding horizontal and vertical acoustic fields, the transducer promotes the vibration of abrasive particles and improves processing efficiency. Compared to traditional hemispherical resonator magnetorheological polishing tools, the larger size of the tool increases the effective contact area between the magnetorheological fluid and the resonator's inner surface. Furthermore, the spherical shape and unique motion of the polishing head enable full-area processing of the resonator's inner surface, ensuring inner surface uniformity. The coupling of the acoustic and magnetic fields further improves processing efficiency.

Description

Technical Field

[0001] The present invention relates to the technical field of ultra-precision and high-efficiency polishing processing, and in particular to a tool and method for polishing the inner surface of a hemispherical resonator based on multi-field coupling. Background Art

[0002] Hemispherical resonators, the core components of hemispherical resonator gyroscopes, are widely used in military, aviation, and other fields. They are primarily made of fused quartz crystal, which boasts excellent light transmittance, high hardness, and thermal stability. However, the high hardness and complex shape of the resonator material make its machining difficult. Grinding can leave significant residual stress, a surface damage layer, and microcracks on the workpiece surface, impacting the navigation accuracy and service life of the hemispherical resonator gyroscope. Therefore, after precision grinding, hemispherical resonators require precision polishing to remove the crack layer on the surface and improve the resonator's quality.

[0003] Currently, hemispherical resonators are polished using shear rheological polishing or magnetorheological polishing. Shear rheological polishing suffers from long polishing times and difficulty ensuring consistent surface accuracy. Magnetorheological polishing, on the other hand, uses a smaller polishing head to drive magnetorheological fluid to perform a small, full-coverage machining of the resonator's inner surface. This results in low efficiency and difficulty ensuring surface uniformity. Currently, the primary method for polishing the inner surface of a hemispherical resonator is single-point machining using a small polishing head. This suffers from low efficiency, poor molding quality, and a complex process. Summary of the Invention

[0004] The purpose of the present invention is to overcome the deficiencies of the prior art and to provide a high-efficiency magnetorheological full-area polishing tool for the inner surface of a hemispherical resonator based on multi-field energy coupling.

[0005] To achieve the above object, the present invention adopts the following technical solutions:

[0006] A hemispherical resonator inner surface polishing tool based on multi-field coupling, comprising a permanent magnet magnetorheological polishing head and a hemispherical resonator fixing fixture;

[0007] The permanent magnet magnetorheological polishing head includes a permanent magnet polishing head and a metal clamping rod. The permanent magnet polishing head is fixedly connected to the lower end of the metal clamping rod by gluing. The bottom surface of the polishing head is concentric with the arc of the inner surface of the hemispherical resonator. A groove is opened in the middle horizontal direction of the permanent magnet polishing head. The groove and the arc surface adopt a rounded transition and the rounded corner section is concentric with the rounded corner section of the inner surface of the hemispherical resonator. Clamping surfaces are provided on both sides of the metal clamping rod for clamping with a wedge-shaped clamp. An injection hole for real-time injection of magnetorheological fluid is opened in the vertical direction between the permanent magnet polishing head and the metal clamping rod.

[0008] The hemispherical resonator fixing fixture is composed of two symmetrical parts. Its inner surface is a concentric arc surface that is adapted to the outer surface of the hemispherical resonator. A connecting plate is provided on the side for connecting to the machine tool processing platform, and a built-in ultrasonic transducer is used to generate ultrasonic waves, thereby promoting the vibration of abrasive particles through the coupling of the ultrasonic sound field and the magnetic field generated by the permanent magnet polishing head.

[0009] Furthermore, the width of the middle groove of the permanent magnet polishing head is greater than the inner cylinder diameter of the hemispherical resonator, the groove height is greater than the inner cylinder height of the hemispherical resonator, and the arc surface radius of the permanent magnet polishing head is smaller than the inner surface radius of the hemispherical resonator.

[0010] Furthermore, the gap between the arc surface at the bottom of the permanent magnet polishing head and the inner arc surface of the hemispherical resonator is 0.1 mm, the gap between the side of the middle groove of the permanent magnet polishing head and the inner cylindrical section of the hemispherical resonator is 0.1 mm, the gap between the end face of the groove and the inner cylindrical end face of the hemispherical resonator is 4 mm, and the gap between the transition fillet between the middle groove of the permanent magnet polishing head and the arc surface and the inner fillet section of the hemispherical resonator is 0.1 mm.

[0011] Furthermore, the permanent magnet polishing head is formed by hot pressing, bonding or laser 3D printing.

[0012] Furthermore, when the permanent magnet polishing head is formed by hot pressing, the mold used is a cube as a whole, and there is a cavity inside the mold. The curvature of the bottom surface of the cavity is the same as the curvature of the inner surface of the resonator. An intermediate baffle is provided in the middle position of the bottom of the cavity. The two sides of the intermediate baffle are left-right symmetrical parts. The intermediate baffle is used to form a groove for the permanent magnet polishing head. A cylinder is provided on the top of the intermediate baffle, which is used to form an injection hole for the permanent magnet polishing head.

[0013] Furthermore, the hot pressing method comprises the following steps:

[0014] 1) Mold fixing: clamp the mold;

[0015] 2) Raw material preparation: NdFeB magnetic powder is refined to obtain a particle size of about 3.6μm~5.2μm. One or more polymers such as polyvinyl alcohol, acrylic acid, polyurethane, etc. are used as a binder to promote the bonding of NdFeB magnetic powder.

[0016] 3) Mixing: Mix the NdFeB powder and the binder thoroughly and stir evenly, with the NdFeB powder accounting for 92% to 97% and the rest being the binder;

[0017] 4) Hot Pressing: Place the NdFeB magnetic powder mixed with a binder into a hot press molding die for the polishing head, heat it to 650°C in a vacuum environment or in a protective inert gas atmosphere, and apply a pressure of 100Mpa to 150Mpa on the top of the die for 10 to 12 minutes to obtain a hot-pressed permanent magnet polishing head blank.

[0018] 5) Sintering treatment: The permanent magnet polishing head blank obtained by hot pressing is sintered at a temperature of 800°C to 1200°C for 3h to 5h;

[0019] 6) Magnetization treatment: The sintered permanent magnet polishing head blank is placed in a 1.2T~2.0T magnetic field for axial magnetization;

[0020] 7) Machining: The cylindrical surface of the permanent magnet polishing head blank is machined to reduce the cylindrical radius and increase its movement angle.

[0021] Furthermore, the bonding molding method includes the following steps:

[0022] 1) Processing of permanent magnet layered workpieces: Laser cutting is used to pre-process permanent magnet layered workpieces of different shapes;

[0023] 2) Bonding molding: Use high-strength structural adhesive to bond each layer of the permanent magnet layered workpiece in sequence to obtain a patch-type permanent magnet polishing head blank;

[0024] 3) Grinding and polishing: Finally, the arc surface of the permanent magnet polishing head blank is ground and polished to make it a smooth overall arc, thereby obtaining the required permanent magnet polishing head. The curvature of the arc surface is consistent with the inner surface of the hemispherical resonator.

[0025] Furthermore, the laser 3D printing method includes the following steps:

[0026] 1) 3D modeling: Use 3D modeling software to design a three-dimensional model of permanent magnet polishing;

[0027] 2) Raw material preparation: NdFeB magnetic powder and binder are used as the molding material of the permanent magnet polishing head, and one or more organic resins such as epoxy resin, acrylic resin, polyurethane, etc. are used as binders to promote the bonding of NdFeB magnetic powder;

[0028] 3) Refining and cleaning treatment: The particles of NdFeB magnetic powder are crushed and sieved to obtain NdFeB powder with a particle size of about 2μm~5μm; the obtained NdFeB powder is washed and dried to obtain pure NdFeB magnetic powder;

[0029] 4) Mixing: Mix the NdFeB powder and the binder thoroughly and stir evenly, with the magnetic powder accounting for 80% to 85% and the rest being the binder;

[0030] 5) Adding materials: Add the mixed raw materials into the feeding box of the laser 3D printing equipment;

[0031] 6) Printing: Import the designed 3D model of the permanent magnet polishing head into the printing equipment software and print the permanent magnet polishing head model layer by layer;

[0032] 7) Sintering treatment: The printed permanent magnet polishing head model is sintered at a temperature of 800°C to 1200°C for 3h to 5h.

[0033] 8) Magnetization treatment: The sintered permanent magnet polishing head model is placed in a 1.2T to 2.0T magnetic field for axial magnetization treatment.

[0034] Furthermore, the ultrasonic transducer is arranged on the two side surfaces and the bottom surface of the hemispherical resonator fixing fixture, with a power of 60W and a frequency of 40KHz.

[0035] A polishing method for a hemispherical resonator inner surface polishing tool based on multi-field coupling, comprising the following methods:

[0036] 1) Installation of fixture: Use a swing-arm five-axis machining center for processing. Clamp the permanent magnet magnetorheological polishing head on a wedge-shaped fixture, which is then connected to the machine tool spindle. Install the hemispherical resonator fixture on the C-axis machining platform of the machine tool, and then clamp and secure the hemispherical resonator.

[0037] 2) Tool setting: Use a tool setting instrument to set the tool. After the tool setting is completed, the gap between the surface of the permanent magnet polishing head and the inner surface of the hemispherical resonator should be equal;

[0038] 3) Polishing program writing: Program the motion program of the polishing process. Through the reasonable movement of the Z and Y axes and the reasonable swing of the A axis, the permanent magnet polishing head can swing at an angle of ±35° at 60 times / min and the C axis can rotate continuously at 800r / min.

[0039] 4) Preparation and addition of magnetorheological fluid: 100ml of hydroxyl iron powder is thoroughly cleaned to remove oil and impurities, then dried. 10ml of silane coupling agent and 15ml of isopropyl alcohol are added and stirred thoroughly to ensure full contact with the hydroxyl iron powder to promote activation. After drying the activated and stirred mixture, 168ml of silicone oil and 12ml of diamond polishing powder are added, stirred thoroughly, and then ultrasonically dispersed. Finally, 8ml of silicon dioxide and 10ml of bentonite are added and stirred thoroughly. The prepared magnetorheological fluid is added through the injection port of the polishing head.

[0040] 5) Polishing: Turn on the ultrasonic transducer, run the polishing program, and polish the inner surface of the hemispherical resonator for 6 hours;

[0041] 6) Cleaning: After polishing, lift the spindle, remove the hemispherical resonator, put it in a beaker and pour in excess alcohol, then put it in an ultrasonic cleaner for 8 to 10 minutes, then rinse it in running deionized water for 2 to 3 minutes, and then put it in a dryer for drying.

[0042] By adopting the above-mentioned technical solution, the present invention has the following beneficial effects: compared with the traditional small grinding head, the hemispherical resonator magnetorheological polishing head has a larger size, which increases the effective contact area between the magnetorheological fluid and the inner surface of the resonator. At the same time, due to the spherical shape and unique movement mode of the polishing head, the entire area of ​​the inner surface of the resonator can be processed, which improves the processing efficiency and ensures the uniformity of the inner surface; the coupling effect of the sound field generated by the hemispherical resonator fixing fixture with a built-in ultrasonic transducer and the magnetic field generated by the permanent magnet polishing head promotes the vibration of the polishing abrasive and further improves the processing efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments:

[0044] Figure 1 Schematic diagram of the permanent magnet magnetorheological polishing head of the present invention;

[0045] Figure 2 Schematic diagram of a hot pressing mold;

[0046] Figure 3 Schematic diagram of a permanent magnet polishing head blank formed by hot pressing;

[0047] Figure 4 Schematic diagram of a permanent magnet polishing head blank formed by bonding;

[0048] Figure 5 Schematic diagram of the permanent magnet polishing head blank after laser 3D printing, hot pressing and bonding molding;

[0049] Figure 6 Schematic diagram of a fixing fixture for a hemispherical resonator according to the present invention;

[0050] Figure 7 This is a schematic diagram of the assembly of the polishing tool and the hemispherical resonator;

[0051] Figure 8 A schematic diagram of processing a hemispherical resonator according to the present invention;

[0052] Figure 9 Schematic diagram of magnetic flux simulation of hot pressing and 3D printing polishing heads. DETAILED DESCRIPTION

[0053] like Figure 1 and Figure 6 As shown, the present invention provides a high-efficiency magnetorheological full-area polishing tool for the inner surface of a hemispherical resonator based on multi-field coupling, comprising: a permanent magnet magnetorheological polishing head 70 and a hemispherical resonator fixing fixture 150;

[0054] The permanent magnet magnetorheological polishing head 70 includes a permanent magnet polishing head 50 and a metal clamping rod 10. The permanent magnet polishing head 50 is fixedly connected to the lower end of the metal clamping rod 10 by gluing. The bottom surface of the permanent magnet polishing head 50 is hemispherical in shape, and the bottom arc of the permanent magnet polishing head 50 is concentric with the arc of the inner surface of the hemispherical resonator and has a smaller radius. A groove 40 is opened in the middle horizontal direction of the permanent magnet polishing head 50, with a width greater than the diameter of the inner cylinder of the hemispherical resonator and a height greater than the height of the inner cylinder of the hemispherical resonator. A fillet 60 is formed at the transition between the groove 40 and the arc surface. The groove and the arc surface adopt a fillet transition, and the fillet section is concentric with the fillet section of the hemispherical resonator. Its main function is to ensure that the gap with the inner surface of the hemispherical resonator is the same during the processing process, so that the inner surface of the hemispherical resonator can be subjected to swing processing and rotation processing without interference. The metal clamping rod 10 is made of 45-gauge steel and features clamping surfaces 20 on both sides, primarily to facilitate gripping with a wedge-shaped fixture. The metal clamping rod 10 and the permanent magnet polishing head 50 are bonded together using adhesive, ensuring coaxiality between the two. A vertical injection port 30 is provided between the permanent magnet polishing head 50 and the metal clamping rod 10 for real-time addition of magnetorheological fluid.

[0055] The hemispherical resonator fixing fixture 150 is composed of two symmetrical parts. Its inner surface 160 is a concentric arc surface that matches the outer surface of the hemispherical resonator. A connecting plate 170 is provided on the side for connecting to the machine tool processing platform. Four ultrasonic transducers 180 with a power of 60W and a frequency of 40KHz are built into the left and right side surfaces and the bottom surface for generating ultrasonic waves. By adding a sound field, the vibration of the polishing abrasive is promoted, thereby improving the polishing efficiency.

[0056] Figure 7 As shown, it is a schematic diagram of the assembly of the polishing tool and the hemispherical resonator: the hemispherical resonator fixing fixture 150 clamps and fixes the hemispherical resonator 200, and a 0.1mm gap is left between the permanent magnet polishing head 50 and the inner surface of the hemispherical resonator 200, and a 0.1mm gap is left on the side of the central cylinder to facilitate the flow of polishing liquid in the gap. A 4mm gap is left between the top surface of the permanent magnet polishing head groove and the end surface of the inner cylinder of the hemispherical resonator to avoid interference when the polishing head swings. During operation, magnetorheological polishing liquid abrasive particles and water and other media are injected into the interior through the central injection hole of the polishing head to effectively polish the inner surface of the hemispherical resonator and the surface of the central cylinder.

[0057] The permanent magnet polishing head of the present invention is formed by hot pressing, bonding or laser 3D printing.

[0058] like Figure 2 As shown, when the permanent magnet polishing head is formed by hot pressing, the mold 80 used is a cube as a whole, and a cavity is provided inside the mold 80. The curvature of the bottom surface 110 of the cavity is the same as the curvature of the inner surface of the resonator. An intermediate baffle 100 is provided in the middle of the bottom of the cavity. The two sides of the intermediate baffle 100 are left-right symmetrical parts. The intermediate baffle 80 is used to form a groove for the permanent magnet polishing head. A cylinder 90 is provided on the top of the intermediate baffle 100, and the cylinder 90 is used to form a liquid injection hole for the permanent magnet polishing head.

[0059] The method of thermoforming comprises the following steps:

[0060] 1) Mold fixing: clamp the mold;

[0061] 2) Raw material preparation: NdFeB magnetic powder is refined to obtain a particle size of about 3.6μm~5.2μm. One or more polymers such as polyvinyl alcohol, acrylic acid, polyurethane, etc. are used as a binder to promote the bonding of NdFeB magnetic powder.

[0062] 3) Mixing: Mix the NdFeB powder and the binder thoroughly and stir evenly, with the NdFeB powder accounting for 92% to 97% and the rest being the binder;

[0063] 4) Hot pressing: Place the NdFeB magnetic powder mixed with the binder into the hot pressing mold of the polishing head, heat it to 650°C in a vacuum environment or protective inert gas, and apply a pressure of 100Mpa~150Mpa on the top of the mold for 10min~12min. Figure 3 As shown, a hot-pressed permanent magnet polishing head blank 120 is obtained;

[0064] 5) Sintering treatment: The permanent magnet polishing head blank 120 obtained by hot pressing is sintered at a temperature of 800° C. to 1200° C. for 3 h to 5 h.

[0065] 6) Magnetization treatment: The sintered permanent magnet polishing head blank 120 is placed in a 1.2T to 2.0T magnetic field for axial magnetization. The magnetic flux simulation diagram is shown in FIG. Figure 9 As shown;

[0066] 7) Machining: The cylindrical surface of the permanent magnet polishing head blank 120 is subjected to machining to obtain a polishing head blank 140 .

[0067] The bonding method comprises the following steps:

[0068] 1) Processing of permanent magnet layered workpieces: Laser cutting is used to pre-process permanent magnet layered workpieces of different shapes;

[0069] 2) Bonding molding: Use high-strength structural adhesive to bond each layer of permanent magnet layered workpiece in sequence, such as Figure 4 As shown, a patch-type permanent magnet polishing head blank 130 is obtained;

[0070] 3) Grinding and polishing: Finally, the arc surface of the permanent magnet polishing head blank 130 is ground and polished to form a smooth integral arc, thereby obtaining the desired permanent magnet polishing head 140. The laser 3D printing method includes the following steps:

[0071] 1) 3D modeling: Use 3D modeling software to design a three-dimensional model of permanent magnet polishing;

[0072] 2) Raw material preparation: NdFeB magnetic powder and binder are used as the molding material of the permanent magnet polishing head, and one or more organic resins such as epoxy resin, acrylic resin, polyurethane, etc. are used as binders to promote the bonding of NdFeB magnetic powder;

[0073] 3) Refining and cleaning treatment: The particles of NdFeB magnetic powder are crushed and sieved to obtain NdFeB powder with a particle size of about 2μm~5μm; the obtained NdFeB powder is washed and dried to obtain pure NdFeB magnetic powder;

[0074] 4) Mixing: Mix the NdFeB powder and the binder thoroughly and stir evenly, with the magnetic powder accounting for 80% to 85% and the rest being the binder;

[0075] 5) Adding materials: Add the mixed raw materials into the feeding box of the laser 3D printing equipment;

[0076] 6) Printing: Import the 3D model of the designed permanent magnet polishing head into the printing equipment software, such as Figure 5 As shown, the permanent magnet polishing head model 140 is printed layer by layer;

[0077] 7) Sintering: The printed permanent magnet polishing head model 140 is sintered at a temperature of 800° C. to 1200° C. for 3 to 5 hours.

[0078] 8) Magnetization treatment: The sintered permanent magnet polishing head model 140 is placed in a 1.2T to 2.0T magnetic field for axial magnetization treatment. The magnetic flux simulation diagram is shown in FIG. Figure 9 shown.

[0079] Specific implementation plan

[0080] like Figure 8As shown, the present invention provides a polishing method for a hemispherical resonator inner surface polishing tool based on multi-field energy coupling, including the following methods:

[0081] 1) Installation of fixtures: A swing-arm five-axis machining center is used for machining. The permanent magnet magnetorheological polishing head 70 is clamped on a wedge-shaped fixture 230 , which is then connected to the machine tool spindle 220 via the wedge-shaped fixture 230 . The hemispherical resonator fixing fixture 150 is installed on the machining platform of the machine tool C-axis 270 , and the hemispherical resonator 200 is clamped and fixed.

[0082] 2) Tool setting: Use a tool setting instrument to set the tool. After the tool setting is completed, the gap between the surface of the permanent magnet polishing head and the inner surface of the hemispherical resonator should be equal;

[0083] 3) Polishing program writing: Program the motion program of the polishing process. Through the reasonable movement of the Z and Y axes and the reasonable swing of the A axis, the permanent magnet polishing head can swing at an angle of ±35° at 60 times / min and the C axis can rotate continuously at 800r / min.

[0084] 4) Preparation and addition of magnetorheological fluid: Take 100ml of hydroxy iron powder, thoroughly clean it to remove oil and impurities, and then dry it. Add 10ml of silane coupling agent and 15ml of isopropyl alcohol and stir thoroughly to ensure full contact with the hydroxy iron powder to promote activation. Dry the mixture after activation and stirring, add 168ml of silicone oil and 12ml of diamond polishing powder, stir thoroughly, and then ultrasonically disperse it. Finally, add 8ml of silicon dioxide and 10ml of bentonite and stir thoroughly to effectively improve the viscosity and anti-settling properties of the magnetorheological polishing fluid. After the magnetorheological fluid is prepared, add it through the injection hole of the polishing head.

[0085] 5) Polishing: Turn on the ultrasonic transducer, run the polishing program, and polish the inner surface of the hemispherical resonator for 6 hours;

[0086] 6) Cleaning: After polishing, lift the spindle, remove the hemispherical resonator, put it in a beaker and pour in excess alcohol, then put it in an ultrasonic cleaner for 8 to 10 minutes, then rinse it in running deionized water for 2 to 3 minutes, and finally put it in a dryer for drying.

[0087] The above describes a specific embodiment of the present invention, but those skilled in the art should understand that this is only an example. Those skilled in the art can make various changes or modifications to this embodiment without departing from the principles and essence of the present invention, but these changes and modifications will fall within the scope of protection of the present invention.

Claims

1. A hemispherical resonator inner surface polishing tool based on multi-field coupling, characterized by: It includes a permanent magnet magnetorheological polishing head and a hemispherical resonator fixing fixture; The permanent magnet magnetorheological polishing head includes a permanent magnet polishing head and a metal clamping rod. The permanent magnet polishing head is fixedly connected to the lower end of the metal clamping rod by gluing. The bottom surface of the polishing head is concentric with the arc of the inner surface of the hemispherical resonator. A groove is horizontally opened in the middle of the permanent magnet polishing head. The groove and the arc surface adopt a rounded transition and the rounded corner section is concentric with the rounded corner section of the inner surface of the hemispherical resonator. Clamping surfaces are provided on both sides of the metal clamping rod for clamping with a wedge-shaped clamp. The permanent magnet polishing head and the metal clamping rod are vertically opened with injection holes for real-time injection of magnetorheological fluid. The hemispherical resonator fixing fixture is composed of two symmetrical parts. Its inner surface is a concentric arc surface that is adapted to the outer surface of the hemispherical resonator. A connecting plate is provided on the side for connecting to the machine tool processing platform, and a built-in ultrasonic transducer is used to generate ultrasonic waves, thereby promoting the vibration of abrasive particles through the coupling of the ultrasonic sound field and the magnetic field generated by the permanent magnet polishing head.

2. The hemispherical resonator inner surface polishing tool based on multi-field coupling according to claim 1, characterized in that: The width of the middle groove of the permanent magnet polishing head is greater than the inner cylinder diameter of the hemispherical resonator, the height of the groove is greater than the inner cylinder height of the hemispherical resonator, and the arc surface radius of the permanent magnet polishing head is smaller than the inner surface radius of the hemispherical resonator.

3. The hemispherical resonator inner surface polishing tool based on multi-field coupling according to claim 2, characterized in that: The gap between the bottom arc surface of the permanent magnet polishing head and the inner arc surface of the hemispherical resonator is 0.1mm, the gap between the side of the middle groove of the permanent magnet polishing head and the inner cylindrical section of the hemispherical resonator is 0.1mm, the gap between the top surface of the groove and the inner cylindrical end surface of the hemispherical resonator is 4mm, and the gap between the transition fillet between the middle groove of the permanent magnet polishing head and the arc surface and the inner fillet section of the hemispherical resonator is 0.1mm.

4. The hemispherical resonator inner surface polishing tool based on multi-field coupling according to claim 1, characterized in that: The permanent magnet polishing head is formed by hot pressing, bonding or laser 3D printing.

5. The hemispherical resonator inner surface polishing tool based on multi-field coupling according to claim 4, characterized in that: When the permanent magnet polishing head is formed by hot pressing, the mold used is a cube as a whole, and a cavity is provided inside the mold. The curvature of the bottom surface of the cavity is the same as the curvature of the inner surface of the resonator. An intermediate baffle is provided in the middle position of the bottom of the cavity. The two sides of the intermediate baffle are left-right symmetrical parts. The intermediate baffle is used to form a groove for the permanent magnet polishing head. A cylinder is provided on the top of the intermediate baffle, and the cylinder is used to form an injection hole for the permanent magnet polishing head.

6. The hemispherical resonator inner surface polishing tool based on multi-field coupling according to claim 4, characterized in that: The thermoforming method comprises the following steps: 1) Mold fixing: clamp the mold; 2) Raw material preparation: NdFeB magnetic powder is refined to obtain a particle size of 3.6μm~5.2μm. One or more of polyvinyl alcohol, acrylic acid, and polyurethane polymers are used as binders to promote the bonding of NdFeB magnetic powder. 3) Mixing: Mix the NdFeB powder and the binder thoroughly and stir evenly, with the NdFeB powder accounting for 92% to 97% and the rest being the binder; 4) Hot Pressing: Place the NdFeB magnetic powder mixed with a binder into a hot press molding die for the polishing head, heat it to 650°C in a vacuum environment or in a protective inert gas atmosphere, and apply a pressure of 100Mpa to 150Mpa on the top of the die for 10 to 12 minutes to obtain a hot-pressed permanent magnet polishing head blank. 5) Sintering treatment: The permanent magnet polishing head blank obtained by hot pressing is sintered at a temperature of 800°C to 1200°C for 3h to 5h; 6) Magnetization treatment: The sintered permanent magnet polishing head blank is placed in a 1.2T~2.0T magnetic field for axial magnetization; 7) Machining: The cylindrical surface of the permanent magnet polishing head blank is machined to reduce the cylindrical radius and increase its movement angle.

7. The hemispherical resonator inner surface polishing tool based on multi-field coupling according to claim 4, characterized in that: The bonding method comprises the following steps: 1) Processing of permanent magnet layered workpieces: Laser cutting is used to pre-process permanent magnet layered workpieces of different shapes; 2) Bonding molding: Use high-strength structural adhesive to bond each layer of the permanent magnet layered workpiece in sequence to obtain a patch-type permanent magnet polishing head blank; 3) Grinding and polishing: Finally, the arc surface of the permanent magnet polishing head blank is ground and polished to make it a smooth overall arc, thereby obtaining the required permanent magnet polishing head. The curvature of the arc surface is consistent with the inner surface of the hemispherical resonator.

8. The hemispherical resonator inner surface polishing tool based on multi-field coupling according to claim 4, characterized in that: The laser 3D printing method comprises the following steps: 1) 3D modeling: Use 3D modeling software to design a three-dimensional model of permanent magnet polishing; 2) Raw material preparation: NdFeB magnetic powder and binder are used as the molding material of the permanent magnet polishing head, and one or more of epoxy resin, acrylic resin and polyurethane are used as binders to promote the bonding of NdFeB magnetic powder; 3) Refining and cleaning treatment: crushing and screening the NdFeB magnetic powder particles to obtain NdFeB powder with a particle size of 2μm~5μm; washing and drying the obtained NdFeB powder to obtain pure NdFeB magnetic powder; 4) Mixing: Mix the NdFeB powder and the binder thoroughly and stir evenly, with the magnetic powder accounting for 80% to 85% and the rest being the binder; 5) Adding materials: Add the mixed raw materials into the feeding box of the laser 3D printing equipment; 6) Printing: Import the designed 3D model of the permanent magnet polishing head into the printing equipment software and print the permanent magnet polishing head model layer by layer; 7) Sintering treatment: The printed permanent magnet polishing head model is sintered at a temperature of 800°C to 1200°C for 3h to 5h. 8) Magnetization treatment: The sintered permanent magnet polishing head model is placed in a 1.2T to 2.0T magnetic field for axial magnetization treatment.

9. The hemispherical resonator inner surface polishing tool based on multi-field coupling according to claim 1, characterized in that: The ultrasonic transducers are arranged on the two side surfaces and the bottom surface of the hemispherical resonator fixing fixture, and the transducer power is 60W and the frequency is 40KHz.

10. A polishing method for a hemispherical resonator inner surface polishing tool based on multi-field coupling according to any one of claims 1 to 9, characterized in that: The method includes the following steps: 1) Installation of fixture: Use a swing-arm five-axis machining center for processing. Clamp the permanent magnet magnetorheological polishing head on a wedge-shaped fixture, which is then connected to the machine tool spindle. Install the hemispherical resonator fixture on the C-axis machining platform of the machine tool, and then clamp and secure the hemispherical resonator. 2) Tool setting: Use a tool setting instrument to set the tool. After the tool setting is completed, the gap between the outer surface of the permanent magnet polishing head and the inner surface of the hemispherical resonator should be equal; 3) Polishing program writing: Program the motion program of the polishing process. Through the reasonable movement of the Z and Y axes and the reasonable swing of the A axis, the permanent magnet polishing head can swing at an angle of ±35° at 60 times / min and the C axis can rotate continuously at 800r / min. 4) Preparation and addition of magnetorheological fluid: 100ml of hydroxyl iron powder is thoroughly cleaned to remove oil and impurities, then dried. 10ml of silane coupling agent and 15ml of isopropyl alcohol are added and stirred thoroughly to ensure full contact with the hydroxyl iron powder to promote activation. After drying the activated and stirred mixture, 168ml of silicone oil and 12ml of diamond polishing powder are added, stirred thoroughly, and then ultrasonically dispersed. Finally, 8ml of silicon dioxide and 10ml of bentonite are added and stirred thoroughly. The prepared magnetorheological fluid is added through the injection port of the polishing head. 5) Polishing: Turn on the ultrasonic transducer, run the polishing program, and polish the inner surface of the hemispherical resonator for 6 hours; 6) Cleaning: After polishing, lift the spindle, remove the hemispherical resonator, put it in a beaker and pour in excess alcohol, then put it in an ultrasonic cleaner for 8 to 10 minutes, then rinse it in running deionized water for 2 to 3 minutes, and then put it in a dryer to dry.

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