Magnetic suspension gas static pressure numerical control rotary table and control method thereof

Abstract

This invention discloses a magnetically levitated gas static pressure CNC turntable and its control method, comprising: a base, on which a rotatable turntable is mounted, and a positioning shaft is installed at the center of the turntable; wherein, electromagnetic coil assemblies are distributed and installed within the base, and permanent magnet assemblies corresponding to the electromagnetic coil assemblies are arranged within the turntable; static pressure chambers are provided on the end face and side face of the base, and the base and the turntable are sealed by a high flow resistance gap in the static pressure chamber. By setting a magnetic levitation-gas static pressure hybrid support structure, with the turntable assembly as the rotor and the housing base as the stator, levitation rotation can be achieved. This structure retains the high precision characteristics of gas static pressure while introducing the active control capability of magnetic levitation, significantly improving the dynamic performance and stability of the turntable under complex working conditions.

Description

Technical Field

[0001] This invention relates to the field of technology, and in particular to a magnetically levitated gas static pressure CNC turntable and its control method. Background Technology

[0002] As ultra-precision machining technology advances towards nanometer-level accuracy, the performance requirements for CNC rotary tables are increasing. Currently, mainstream high-precision rotary tables mainly employ two technical routes: gas hydrostatic bearings and magnetic levitation bearings. Gas hydrostatic rotary tables achieve frictionless rotation by forming an air film between the rotary table and the base using compressed air. They offer advantages such as high precision and no wear, but their stiffness and damping characteristics are relatively low, and gas leakage can cause pressure fluctuations, affecting stability. Magnetic levitation rotary tables use electromagnetic force support, enabling active control and high stiffness, but the system is complex, costly, and faces challenges in power failure protection.

[0003] In existing technologies, gas static pressure turntables maintain stable pressure in the static pressure chamber by setting up gas supply and exhaust devices. However, this structure is highly dependent on the gas medium and has limited response speed under load changes or external disturbances. While magnetic levitation technology can be actively controlled, conventional magnetic levitation has a relatively low levitation height, requiring extremely high manufacturing precision. Summary of the Invention

[0004] In view of the above-mentioned defects or deficiencies, the purpose of this invention is to provide a magnetic levitation gas static pressure CNC rotary table.

[0005] To achieve the above objectives, the technical solution of the present invention is as follows: A magnetically levitated gas static pressure CNC rotary table includes: a base, on which a rotatable rotary table is disposed, and a positioning shaft is installed at the center of the rotary table; wherein, electromagnetic coil assemblies are distributed and installed inside the base, and permanent magnet assemblies corresponding to the electromagnetic coil assemblies are arranged inside the rotary table; static pressure chambers are provided on the end face and side face of the base, and the base and the rotary table are sealed by a high flow resistance gas film gap in the static pressure chamber.

[0006] The electromagnetic coil assembly includes: a magnetic levitation coil and an axial magnetic levitation coil installed in the base; the permanent magnet assembly includes: a magnetic levitation permanent magnet disposed at the center of the turntable body, wherein the magnetic levitation permanent magnet has multiple axial magnetic levitation permanent magnets arranged circumferentially, and the axial magnetic levitation permanent magnets correspond to the axial magnetic levitation coils; wherein the axial magnetic levitation coils and axial magnetic levitation permanent magnets are radially levied relative to the turntable body, and the magnetic levitation coils and magnetic levitation permanent magnets rotate relative to the turntable body.

[0007] The magnetically levitated permanent magnet is a neodymium iron boron permanent magnet.

[0008] The base is connected to a high-pressure air source and is independently equipped with a proportional valve and a high-speed switching valve.

[0009] The static pressure chamber is equipped with a pressure sensor for detecting the pressure in the static pressure chamber.

[0010] The base cavity is provided with a base spacer, which isolates the adjusting magnetic levitation coil and the axial magnetic levitation coil from the inner wall of the base.

[0011] The electromagnetic coil assembly is equipped with a displacement sensor and a circular grating for detecting the rotation angle and speed of the turntable body.

[0012] The pressure sensor and displacement sensor are connected to a controller, and the output of the controller is connected to a device for controlling the output force of the permanent magnet assembly and the gas supply / exhaust device for the static pressure chamber.

[0013] The bases are provided with a multi-step groove structure, and the turntable is matched with the multi-step groove structure.

[0014] A control method for a magnetically levitated gas static pressure CNC rotary table, comprising: The pressure P1 in the inner radial annular static pressure chamber and the pressure P2 in the axial annular static pressure chamber at both ends are measured, as well as the actual value of the gas film thickness D1. Calculate the pressure difference ΔP = |P1 - P2| and the thickness deviation ΔD = D_set - D1; If ΔP>P threshold or ΔD>D threshold, then adjust the output force of the permanent magnet assembly F = Kp•ΔD + Kd•d(ΔD) / dt, and simultaneously control the operation of the air supply / exhaust valve. If ΔP is less than or equal to the P threshold or ΔD is less than or equal to the D threshold, the system will maintain the current control quantity unchanged and will not change the output force of the magnetic levitation array or the opening of the air supply / exhaust valve.

[0015] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention provides a magnetically levitated gas static pressure CNC turntable and its control method. By setting a magnetic levitation-gas static pressure hybrid support structure, the turntable assembly is set as the rotor, and the magnetic flux coil serves as the stator, fixed inside the base, and directly driven by magnetic coupling. This structure retains the high precision characteristics of gas static pressure while introducing the active control capability of magnetic levitation, significantly improving the dynamic performance and stability of the turntable under complex working conditions.

[0016] Furthermore, this invention offers several advantages: improved precision (rotational error ≤ 0.2 arcseconds, more than 50% better than traditional gas hydrostatic turntables); enhanced stiffness (axial stiffness ≥ 300 N / μm, 3 times better than pure gas hydrostatic structures, meeting the processing requirements of heavy workpieces); optimized dynamic performance (magnetic levitation unit response time ≤ 5 ms, controlling the vibration amplitude of the turntable within 0.1 μm at 2000 rpm); and high reliability (gas hydrostatic pressure as the main support, magnetic levitation as auxiliary control, reducing reliance on complex control and making the system more robust). Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the magnetic levitation gas static pressure CNC turntable structure of the present invention; Figure 2 This is a schematic diagram of the turntable structure of the present invention; Figure 3 This is a schematic diagram of the turntable installation structure of the present invention; Figure 4 This is a side view of the turntable installation of the present invention; Figure 5 This is a schematic diagram of the base structure of this invention; Figure 6 This is a side view of the base of the present invention; Figure 7 This is a schematic diagram of the base spacer installation structure of the present invention; Figure 8 This is a side view of the base spacer installation of the present invention.

[0019] In the figure, 1—turntable; 2—magnetic levitation assembly; 3—positioning shaft; 4—base; 6—magnetic fluid; 7—static pressure chamber; 8—base spacer; 9—displacement sensor; 10—circular grating; 11—pressure sensor; 21—magnetic levitation permanent magnet; 22—axial magnetic levitation permanent magnet; 51—magnetic levitation coil; 52—axial magnetic levitation coil; 71—inner radial annular static pressure groove; 72—axial annular static pressure groove; 101—positioning stop hole; 102—T-slot. Detailed Implementation

[0021] The present invention will now be described in detail with reference to the accompanying drawings. Obviously, the described embodiments are merely some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the protection scope of the present invention.

[0022] like Figure 1As shown, this invention provides a magnetically levitated gas static pressure CNC turntable, comprising: a base 4, on which a rotatable turntable 1 is mounted, and a positioning shaft 3 is installed at the center of the turntable 1; wherein, electromagnetic coil assemblies are distributed and installed within the base 4, and permanent magnet assemblies 2 corresponding to the electromagnetic coil assemblies are arranged within the turntable 1; static pressure chambers 7 are provided on the end faces and sides of the base 4, and the base 4 and the turntable 1 are sealed by a high flow resistance gap in the gas film gap of the static pressure chambers 7. Exemplarily, in this invention, a multi-step groove structure is provided between the base 4, and the turntable 1 is installed in accordance with the multi-step groove structure. When working, the turntable 1 and the positioning shaft 3 utilize a magnetic fluid 6, thereby achieving an end face sealing effect.

[0023] like Figure 2 As shown, the turntable body 1 is designed with a positioning stop hole 101 and a T-slot 102. The positioning stop hole 101 is used to install the positioning shaft 3, and the T-slot 102 is used for clamping and positioning the workpiece. In order to control the atmospheric pressure of the intake air, the base 4 is connected to a high-pressure air source and is independently equipped with a proportional valve and a high-speed switching valve.

[0024] Specifically, the electromagnetic coil assembly includes: a magnetic levitation coil 51 and an axial magnetic levitation coil 52 mounted within the base 4; as shown below. Figure 3 , 4 The permanent magnet assembly 2 includes: a magnetically levitated permanent magnet 21 disposed at the center of the turntable body 1; multiple axially levitated permanent magnets 22 arranged circumferentially around the magnetically levitated permanent magnet 21; the axially levitated permanent magnets 22 corresponding to the axially levitated coil 52; wherein the axially levitated coil 52 and the axially levitated permanent magnets 22 are radially levitated relative to the turntable body 1, and the magnetically levitated coil 51 and the magnetically levitated permanent magnets 21 rotate relative to the turntable body 1. This principle employs direct magnetic coupling drive, with the drive motor rotor back-connected to the turntable body and the stator fixed to the base, forming a contactless transmission. Exemplarily, the magnetically levitated permanent magnet 21 in this invention is a neodymium iron boron (NdFeB) permanent magnet, a permanent magnet material based on the intermetallic compound Nd2Fe14B. Compared to cast Al-Ni-Co permanent magnet materials and ferrite permanent magnet materials, NdFeB has extremely high magnetic energy product and coercivity, capable of lifting objects up to 640 times its own weight. The high energy density of neodymium iron boron permanent magnets has led to their widespread application in modern industry and electronics.

[0025] It should be noted that the magnetic pole surface of the permanent magnet assembly 2 is flush with or protrudes from the gas film forming surface, and the amount of protrusion is ≤0.1 mm.

[0026] like Figure 5 , 6As shown, the static pressure chamber 7 is equipped with a pressure sensor 11 for detecting the pressure in the static pressure chamber 7. The static pressure chamber 7 is connected to a high-pressure air source and is independently equipped with a proportional valve and a high-speed switching valve. Preferably, the edge of the static pressure chamber 7 is provided with a radial annular static pressure groove 71 and an axial annular static pressure groove 72, which are evenly distributed and set in the groove of the inner wall of the base housing. They utilize the micron-level air film gap to generate flow resistance, which is responsible for the suspension support and sealing of the turntable in the horizontal and vertical directions.

[0027] Preferably, such as Figure 7 , 8 As shown, the inner cavity of the base 4 is provided with a base spacer 8. In this invention, a plurality of circumferentially distributed magnetic levitation coils 51 and an axial magnetic levitation coil 52 located at the center of the magnetic levitation coils 51 are all disposed in the base spacer 8. The base spacer 8 isolates the adjusting magnetic levitation coils 51 and the axial magnetic levitation coils 52 from the inner wall of the base 4.

[0028] Furthermore, the electromagnetic coil assembly of this invention is equipped with a displacement sensor 9 and a circular grating 10 for detecting the rotation angle and speed of the turntable body 1. The pressure sensor 11 and the displacement sensor 9 are connected to a controller, and the output end of the controller is connected to a device for controlling the output force of the permanent magnet assembly and the gas supply / exhaust device for the static pressure chamber. The controller adopts a multivariable decoupling control algorithm to achieve coordinated adjustment of the air film pressure and magnetic force, with a control cycle ≤1 ms.

[0029] For example, in this invention, the rotor diameter is 500 mm, the maximum load is 500 kg, and the target accuracy is 0.2 arcseconds.

[0030] Core component manufacturing and assembly: 1. Base 4 and turntable 1: Made of low-heat-deformation granite or ceramic material, with a linear expansion coefficient ≤0.5×10⁻ 6 / ℃. The surface flatness of the static pressure chamber is ≤1 μm, and the air film gap is designed to be 10-15 μm.

[0031] 2. Magnetic levitation unit: This consists of an electromagnetic coil assembly and a permanent magnet assembly. It uses a combination of neodymium iron boron permanent magnets and electromagnetic coils, with a single-point magnetic force ≥200 N, evenly distributed at 32 points. The coils are isolated from the air path to prevent heat generation from affecting the stability of the air film.

[0032] 3. Detection system: Displacement sensor 9 is a laser interferometer (resolution 0.1 nm); pressure sensor 11 has an accuracy of 0.1% FS.

[0033] Control process: Start-up phase: First, start the air source to establish the basic air film; after the pressure stabilizes, put the magnetic levitation unit in for fine-tuning.

[0034] During operation: The controller compares the set air film thickness (12μm) with the actual value in real time. When the deviation is greater than 0.5μm, magnetic compensation is triggered.

[0035] Anti-interference processing: When a sudden load change (such as cutting force) is detected, the magnetic levitation unit outputs a reverse electromagnetic force within 2 ms to suppress vibration.

[0036] Table 1: Performance test results of the example (1000 rpm) Operating conditions Radial runout (μm) Axial runout (μm) Noise (dB) Unloaded 0.02 0.015 ≤55 300 kg load 0.03 0.025 ≤58 Variable speed disturbance 0.05 0.04 ≤60 Key processes: The air film gap needs to be precisely ground to ensure consistency, with an error ≤0.5 μm.

[0037] The magnet coil is vacuum impregnated with epoxy resin to enhance heat dissipation and moisture resistance.

[0038] The system was assembled in an ultra-clean, temperature-controlled workshop (temperature 20±0.1℃, cleanliness level 100).

[0039] The test results of this embodiment show that the accuracy fluctuation of the turntable under full load is less than 50% of that of a traditional gas static pressure turntable (typically 0.1μm), and the noise is reduced by more than 15%.

[0040] In addition, the present invention provides a control method for the above-mentioned magnetic levitation gas static pressure CNC rotary table, characterized in that it includes: The pressure P1 of the inner radial annular static pressure chamber and the pressure P2 of the axial annular static pressure chamber in the static pressure chambers 7 at both ends are detected, as well as the actual value D1 of the gas film thickness. The pressure P1 of the inner radial annular static pressure chamber and the pressure P2 of the axial annular static pressure chamber are specifically the static pressure chamber pressures of the inner radial annular static pressure groove 71 and the axial annular static pressure groove 72.

[0041] Calculate the pressure difference ΔP = |P1 - P2| and the thickness deviation ΔD = D_set - D1; If ΔP>P threshold or ΔD>D threshold, then adjust the output force F = Kp•ΔD + Kd•d(ΔD) / dt of permanent magnet component 2, and simultaneously control the operation of the air supply / exhaust valve. If ΔP is less than or equal to the P threshold or ΔD is less than or equal to the D threshold, the system will maintain the current control quantity unchanged and will not change the output force of the magnetic levitation array or the opening of the air supply / exhaust valve.

[0042] It will be apparent to those skilled in the art that the above specific examples are merely preferred embodiments of the present invention. Therefore, any improvements or modifications that those skilled in the art may make to certain parts of the present invention still embody the principles of the present invention and achieve the objectives of the present invention, and all fall within the scope of protection of the present invention.

Claims

1. A magnetically levitated gas static pressure CNC rotary table, characterized in that, include: A base (4) is provided with a rotatable turntable (1), and a positioning shaft (3) is installed at the center of the turntable (1); wherein, an electromagnetic coil assembly is distributed and installed inside the base (4), and a permanent magnet assembly (2) corresponding to the electromagnetic coil assembly is arranged inside the turntable (1); a static pressure chamber (7) is provided on the end face and side face of the base (4), and the base (4) and the turntable (1) are sealed by the high flow resistance of the air film gap of the static pressure chamber (7).

2. The magnetically levitated gas static pressure CNC rotary table according to claim 1, characterized in that, The electromagnetic coil assembly includes a magnetic levitation coil (51) and an axial magnetic levitation coil (52) installed in the base (4); the permanent magnet assembly (2) includes a magnetic levitation permanent magnet (21) disposed at the center of the turntable body (1), the magnetic levitation permanent magnet (21) is circumferentially arranged with a plurality of axial magnetic levitation permanent magnets (22), the axial magnetic levitation permanent magnets (22) corresponding to the axial magnetic levitation coils (52); wherein the axial magnetic levitation coils (52) and the axial magnetic levitation permanent magnets (22) are radially suspended relative to the turntable body (1), and the magnetic levitation coils (51) and the magnetic levitation permanent magnets (21) rotate relative to the turntable body (1).

3. The magnetically levitated gas static pressure CNC rotary table according to claim 2, characterized in that, The magnetically levitated permanent magnet (21) is a neodymium iron boron permanent magnet.

4. The magnetically levitated gas static pressure CNC rotary table according to claim 1, characterized in that, The base (4) is connected to a high-pressure gas source and is independently equipped with a proportional valve and a high-speed switching valve.

5. The magnetically levitated gas static pressure CNC rotary table according to claim 1, characterized in that, The static pressure chamber (7) is equipped with a pressure sensor (11) for detecting the pressure of the static pressure chamber (7).

6. The magnetically levitated gas static pressure CNC rotary table according to claim 1 or 6, characterized in that, The base (4) is provided with a base spacer (8) in its inner cavity. The base spacer (8) isolates the adjusting magnetic levitation coil (51) and the axial magnetic levitation coil (52) from the inner wall of the base (4).

7. The magnetically levitated gas static pressure CNC rotary table according to claim 6, characterized in that, The electromagnetic coil assembly is equipped with a displacement sensor (9) and a circular grating (10) for detecting the rotation angle and speed of the turntable body (1).

8. The magnetically levitated gas static pressure CNC rotary table according to claim 7, characterized in that, The pressure sensor (11) and displacement sensor (9) are connected to a controller, and the output end of the controller is connected to a device for controlling the output force of the permanent magnet assembly and the gas supply / exhaust device for the static pressure chamber.

9. The magnetically levitated gas static pressure CNC rotary table according to claim 1, characterized in that, The base (4) is provided with a multi-step groove structure, and the turntable (1) is matched with the multi-step groove structure.

10. A control method for a magnetically levitated gas static pressure CNC rotary table as described in claim 1, characterized in that, include: The pressure P1 of the inner radial annular static pressure chamber and the pressure P2 of the axial annular static pressure chamber of the two static pressure chambers (7) are measured, as well as the actual value of the gas film thickness D1. Calculate the pressure difference ΔP = |P1 - P2| and the thickness deviation ΔD = D 设定 - D1; If ΔP > P threshold or ΔD > D threshold, then adjust the output force F = Kp·ΔD + Kd·d(ΔD) / dt of the permanent magnet assembly (2), and control the operation of the air supply / exhaust valve at the same time. If ΔP is less than or equal to the P threshold or ΔD is less than or equal to the D threshold, the system will maintain the current control quantity unchanged and will not change the output force of the magnetic levitation array or the opening of the air supply / exhaust valve.

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