Ultra-precision hydrostatic rotary table

Abstract

The present application relates to a kind of ultra-precision hydrostatic rotary table, including shell, motor stator, water-cooled shell, mandrel, magnetic steel, rotary table top and radial-axial composite oil static pressure bearing.Motor stator includes stator winding and stator core, stator winding is installed in stator core, the inner diameter of stator core is linearly changed along the axial direction;Stator core and water-cooled shell interference fit constitute stator assembly, stator assembly clearance fit is installed in shell;Magnetic steel is fixedly connected with mandrel, rotary table top is fixedly connected with mandrel, mandrel, magnetic steel and rotary table top constitute a rotating body.Radial-axial composite oil static pressure bearing makes the rotating body suspended after being passed into liquid;The stator core of inner diameter linear variation makes the rotating body rotate after being passed into three-phase alternating current, and simultaneously generates controllable thrust upward perpendicular to rotary table top.The present application significantly enhances the bearing capacity and impact resistance of rotary table top, effectively solves the problem of insufficient axial impact load capacity of existing liquid ultra-precision hydrostatic rotary table.

Description

Technical Field

[0001] This invention relates to the field of machining equipment technology, specifically to an ultra-precision hydrostatic rotary table. Background Technology

[0002] The liquid ultra-precision hydrostatic rotary table is a high-precision rotary table that utilizes a high-pressure oil film to achieve contactless support. It is a core component of high-end CNC machine tools and precision measuring equipment. Its working principle involves forcibly injecting precision-filtered lubricating oil into the tiny gap between the rotating shaft and the base, forming a pressure-bearing oil film with a thickness of only a few micrometers to tens of micrometers. This completely "suspends" the table, eliminating mechanical friction and wear.

[0003] The axial stiffness of a liquid ultra-precision hydrostatic rotary table primarily relies on the supporting "oil film." When the rotary table is suddenly subjected to a large axial impact load, the integrity or uniformity of the oil film is disrupted, resulting in a significant weakening or destruction of the axial stiffness. This often leads to rotary table overload, oil supply failure, overheating, and wear. Currently, once a liquid rotary table is designed and manufactured, the only way to improve its axial load-bearing capacity is to increase the oil pump's supply pressure, but this method is prone to oil pump leakage. Furthermore, the instantaneous adjustment capability of the external oil supply system is very limited, and it has a relatively long feedback time, which cannot effectively counteract the axial impact load on the rotary table.

[0004] Therefore, there is an urgent need for a liquid ultra-precision hydrostatic rotary table technology that can withstand axial impact loads during operation. Summary of the Invention

[0005] The purpose of this invention is to provide an ultra-precision hydrostatic rotary table that generates a controllable thrust perpendicular to the table surface while the rotating body rotates, significantly enhancing the load-bearing capacity and impact resistance of the table surface, and effectively solving the problem of insufficient axial impact load capacity of existing liquid ultra-precision hydrostatic rotary tables.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: An ultra-precision hydrostatic rotary table includes: chassis; The motor stator includes a stator core and stator windings. The stator windings are mounted on the stator core, wherein the inner diameter of the stator core varies linearly along the axial direction. The stator core is installed with an interference fit to the water-cooled housing. The stator core, stator windings and water-cooled housing together constitute the stator assembly. The stator assembly is installed in the housing with a clearance fit. The spindle is rotatably connected to the stator core; Magnets are fixedly connected to the spindle; The turntable surface is fixedly connected to the spindle. Radial-axial composite hydrostatic bearing, with clearance fit mounted on the housing; The rotating body is composed of a spindle, a magnet, and a turntable surface. The radial-axial composite hydrostatic bearing can suspend the rotating body after liquid is introduced. The stator core, whose inner diameter changes linearly along the axial direction, rotates the suspended rotating body after three-phase alternating current is introduced, and at the same time, the rotating body generates an upward thrust perpendicular to the turntable surface.

[0007] Preferably, the minimum inner diameter of the stator core is a, the maximum inner diameter of the stator core is b, ba = tan(θ) * Ls, where θ is the angle between the inner wall of the stator core and the bottom end face of the stator core, Ls is the axial length of the stator core, and the stator slot type, slot size and slot area of ​​each stator core remain unchanged along the axial direction.

[0008] Preferably, the number of stator slots in the stator core is Ns, the number of magnet pole pairs is PN, and the relationship between Ns and PN is Ns±2=2×PN.

[0009] Preferably, the outer diameter Dr of the mandrel corresponding to the inner wall of the stator core remains unchanged.

[0010] Preferably, the angle between the outer surface of the magnet and the bottom end face of the mandrel is α; the radial thickness of the magnet in the axial direction varies linearly, the height of the magnet in the axial direction is L1, and the relationship between the thickness Hpm1 of the bottom end face 17 of the magnet and the thickness Hpm2 of the top end face 14 of the magnet is Hpm2-Hpm1=tan(α)×L1.

[0011] Preferably, the air gap length between the inner diameter of the stator core and the outer surface of the magnet remains constant, satisfying the following relationship: 0.5×a-(0.5×Dr+Hpm1)=0.5×b-(0.5×Dr+Hpm2), And 0.5mm < 0.5×a - (0.5×Dr + Hpm1) < 1mm.

[0012] Preferably, the formula for calculating the upward thrust F perpendicular to the turntable surface is: , , , g is the air gap length between the inner diameter of the stator core and the outer surface of the magnet. Let be the axial misalignment displacement between the mandrel and the stator core, and Rav be the equivalent average radius of the stator core. Where is the circumferential angle, H is the air gap magnetic field strength, and Bg is the air gap magnetic flux density.

[0013] Preferably, the magnitude of the thrust generated after the stator core is supplied with three-phase alternating current is adjusted by changing the direct-axis current Id of the three-phase alternating current. The influence of the quadrature-axis current Iq of the three-phase alternating current on the thrust is smaller than the influence of the direct-axis current Id of the three-phase alternating current on the thrust.

[0014] Preferably, the axial oil film clearance of the radial-axial composite hydrostatic bearing is 10 to 20 micrometers.

[0015] Preferably, it also includes a base, on which the housing is mounted.

[0016] In summary, the present invention has the following advantages: This invention employs a structural design where the inner diameter of the stator core varies linearly along the axial direction, coupled with corresponding radial thickness variations in the magnets. This allows the motor stator to generate a controllable electromagnetic thrust perpendicular to and upwards from the turntable surface when three-phase AC power is applied. This significantly enhances the load-bearing capacity and impact resistance of the turntable surface, effectively solving the problem of insufficient axial impact load capacity of existing liquid ultra-precision hydrostatic rotary tables. Simultaneously, the thrust is adjusted in real-time via the direct-axis current Id, resulting in a fast response speed and timely counteracting of axial impact loads on the turntable. Attached Figure Description

[0017] Figure 1 This is a half-section schematic diagram of an ultra-precision hydrostatic rotary table.

[0018] Figure 2 This is a cross-sectional view of the motor stator.

[0019] Figure 3 This is a partial sectional view of the motor stator.

[0020] Figure 4 This is a schematic diagram showing the relationship between the magnet and the mandrel.

[0021] Figure 5 The figure shows the axial force characteristic curve of the ultra-precision hydrostatic rotary table under the combined action of direct-axis current Id and quadrature-axis current Iq.

[0022] The reference numerals in the attached figures are explained as follows: 1—Casing; 2—Base; 3—Radial-axial composite hydrostatic bearing; 4—Motor stator; 4-1—Stator core; 4-2—Stator winding; 5—Water-cooled housing; 6—Spindle; 7—Adjusting ring; 8—Magnet; 9—Turntable surface; 10—Stator slot; 11—Inner wall of stator core; 12—Bottom end face of stator core; 13—Outer surface of magnet; 14—Top end face of magnet; 15—Inner surface of magnet; 16—Bottom end face of spindle; 17—Bottom end face of magnet. Detailed Implementation

[0023] The present invention will now be described in further detail with reference to specific embodiments.

[0024] Example 1 like Figure 1 and Figure 2 As shown, this embodiment provides an ultra-precision hydrostatic rotary table, including a housing 1, a base 2, a radial-axial composite oil hydrostatic bearing 3, a motor stator 4, a water-cooled housing 5, a spindle 6, an adjusting ring 7, a magnet 8, and a turntable surface 9. The motor stator 4 includes a stator core 4-1 and a stator winding 4-2.

[0025] The housing 1 is mounted on the base 2. The stator winding 4-2 is mounted on the stator core 4-1, and the inner diameter of the stator core 4-1 changes linearly along the axial direction. The stator core 4-1 and the water-cooled housing 5 are installed with an interference fit. The stator core 4-1, stator winding 4-2, and water-cooled housing 5 constitute the stator assembly, which is installed on the housing 1 with a clearance fit. The spindle 6 is rotatably connected to the stator core 4-1, the magnet 8 is fixedly connected to the spindle 6, the turntable surface 9 is fixedly connected to the spindle 6, and the adjusting ring 7 is fixedly connected to the spindle 6. The radial-axial composite hydrostatic bearing 3 is installed on the housing 1 with a clearance fit.

[0026] Specifically, the spindle 6, adjusting ring 7, magnet 8, and turntable surface 9 constitute the rotating body. During installation, the radial-axial composite hydrostatic bearing 3 is installed with a small clearance fit to the housing 1, and then bolts are used to fix the radial-axial composite hydrostatic bearing 3 to the housing 1. The magnet 8 is fixed to the spindle 6 by adhesive bonding. The spindle 6, adjusting ring 7, and turntable surface 9 are bolted together to form the rotating body. The motor stator assembly is installed on the housing 1 with a clearance fit, and the end face of the water-cooled housing is fixed to the housing 1 by bolts.

[0027] During operation, the liquid flows from the housing 1 into the radial-axial composite hydrostatic bearing 3, causing the rotating body to achieve a high-precision and stable suspension state. Subsequently, three-phase alternating current is supplied to the stator core 4-1, whose inner diameter changes linearly along the axial direction, causing the suspended rotating body to begin stable rotation. Simultaneously, due to the special linearly changing structure of the stator core 4-1, a controllable electromagnetic thrust perpendicular to the turntable surface 9 is generated, greatly enhancing the load-bearing capacity and impact resistance of the turntable surface 9. The axial oil film clearance of the radial-axial composite hydrostatic bearing 3 is 10–20 micrometers.

[0028] Example 2 like Figure 3 As shown, this embodiment provides a detailed description of the specific structure of the stator core.

[0029] The minimum inner diameter of stator core 4-1 is a, and the maximum inner diameter is b, and ba = tan(θ) × Ls, where θ is the angle between the inner wall 11 of the stator core and the bottom end face 12 of the stator core, and Ls is the axial length of stator core 4-1. The slot shape, slot size, and slot area of ​​each stator slot 10 of stator core 4-1 remain unchanged along the axial direction.

[0030] The stator core 4-1 has Ns stator slots 10 and PN pole pairs 8. The relationship between Ns and PN is Ns ± 2 = 2 × PN. The rotating body eliminates the need for a conventional rotor core, using rectangular permanent magnets 8 directly glued to the mandrel 6. The mandrel 6 is made of a high-strength magnetically conductive material to ensure good magnetic permeability and mechanical strength.

[0031] The outer diameter Dr of the mandrel 6, which corresponds to the inner wall 11 of the stator core, remains unchanged.

[0032] like Figure 4 As shown, the inner surface 15 of the magnet is in contact with the outer surface of the mandrel 6, and the angle between the outer surface 13 of the magnet and the bottom end face 16 of the mandrel is α. The radial thickness of the magnet 8 varies linearly in the axial direction, and the height of the magnet 8 in the axial direction is L1. The relationship between the thickness Hpm1 of the bottom end face 17 of the magnet and the thickness Hpm2 of the top end face 14 of the magnet is: Hpm2-Hpm1=tan(α)×L1.

[0033] The air gap length between the inner diameter of the stator core 4-1 and the outer surface 13 of the magnet remains constant, satisfying the following relationship: 0.5×a-(0.5×Dr+Hpm1)=0.5×b-(0.5×Dr+Hpm2), And 0.5mm < 0.5×a - (0.5×Dr + Hpm1) < 1mm.

[0034] The parts not mentioned in this embodiment are the same as in Embodiment 1.

[0035] Example 3 This embodiment provides a detailed explanation of the generation principle and control method of axial thrust.

[0036] The formula for calculating the upward thrust F perpendicular to the turntable surface 9 is: , , , Where g is the air gap length between the inner diameter of the stator core and the outer surface of the magnet. Let be the axial misalignment displacement between the mandrel and the stator core, and Rav be the equivalent average radius of the stator core. Where is the circumferential angle, H is the air gap magnetic field strength, and Bg is the air gap magnetic flux density.

[0037] The magnitude of the thrust generated after three-phase alternating current is applied to the stator core 4-1 is adjusted by changing the direct-axis current Id of the three-phase alternating current. The influence of the quadrature-axis current Iq of the three-phase alternating current on the thrust is smaller than that of the direct-axis current Id of the three-phase alternating current on the thrust.

[0038] like Figure 5 As shown, under the combined action of the direct-axis current Id and the quadrature-axis current Iq, the output axial force characteristics of the ultra-precision hydrostatic rotary table are as follows: Overall, changing Id results in a larger range of axial force variation, while changing Iq does not significantly alter the axial force. The maximum axial force is 404.2 N, and the minimum is 105.6 N. Therefore, in practical applications, precise control of the axial thrust is mainly achieved by adjusting the direct-axis current Id to effectively counteract the axial impact load on the ultra-precision hydrostatic rotary table.

[0039] The parts not mentioned in this embodiment are the same as in Embodiment 1.

[0040] Example 4 This embodiment provides an application example of specific parameter selection.

[0041] Given a stator core 4-1 with an axial length Ls = 100 mm, an included angle θ = 5°, and a minimum inner diameter a = 150 mm, the maximum inner diameter b = 150 + tan(5°) × 100 ≈ 158.75 mm. The mandrel outer diameter Dr = 120 mm, the magnet bottom end face 17 thickness Hpm1 = 10 mm, an included angle α = 5°, and the magnet's axial height L1 = 100 mm, the magnet top end face 14 thickness Hpm2 = 10 + tan(5°) × 100 ≈ 18.75 mm.

[0042] At this point, the air gap length is 0.5×150-(0.5×120+10)=75-60-10=5mm, which satisfies the condition 0.5mm<air gap length<1mm.

[0043] Experiments have verified that, under the above parameters, when the direct-axis current Id = 5A and the quadrature-axis current Iq = -4A, the generated axial thrust is approximately 250N, which can effectively offset the axial impact load on the turntable under heavy-load cutting conditions, significantly improving the working stability and reliability of the turntable.

[0044] The parts not mentioned in this embodiment are the same as in Embodiment 1.

[0045] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. An ultra-precision hydrostatic rotary table, characterized in that, include: chassis; The motor stator includes a stator core and stator windings. The stator windings are mounted on the stator core, wherein the inner diameter of the stator core varies linearly along the axial direction. The stator core is installed with an interference fit to the water-cooled housing. The stator core, stator windings and water-cooled housing together constitute the stator assembly. The stator assembly is installed in the housing with a clearance fit. The spindle is rotatably connected to the stator core; Magnets are fixedly connected to the spindle; The turntable surface is fixedly connected to the spindle. Radial-axial composite hydrostatic bearing, with clearance fit mounted on the housing; The rotating body is composed of a spindle, a magnet, and a turntable surface. The radial-axial composite hydrostatic bearing can suspend the rotating body after liquid is introduced. The stator core, whose inner diameter changes linearly along the axial direction, rotates the suspended rotating body after three-phase alternating current is introduced, and at the same time, the rotating body generates an upward thrust perpendicular to the turntable surface.

2. The ultra-precision hydrostatic rotary table according to claim 1, characterized in that, The minimum inner diameter of the stator core is a, and the maximum inner diameter of the stator core is b. ba = tan(θ) * Ls, where θ is the angle between the inner wall of the stator core and the bottom end face of the stator core, and Ls is the axial length of the stator core. The stator slot type, slot size, and slot area of ​​each stator core remain unchanged along the axial direction.

3. The ultra-precision hydrostatic rotary table according to claim 1, characterized in that, The number of stator slots in the stator core is Ns, and the number of magnet pole pairs is PN. The relationship between Ns and PN is Ns±2=2×PN.

4. The ultra-precision hydrostatic rotary table according to claim 1, characterized in that, The outer diameter Dr of the mandrel corresponding to the inner wall of the stator core remains unchanged.

5. The ultra-precision hydrostatic rotary table according to claim 1, characterized in that, The angle between the outer surface of the magnet and the bottom end face of the mandrel is α; the radial thickness of the magnet varies linearly in the axial direction, the height of the magnet in the axial direction is L1, and the relationship between the thickness Hpm1 of the bottom end face 17 of the magnet and the thickness Hpm2 of the top end face 14 of the magnet is Hpm2-Hpm1=tan(α)×L1.

6. The ultra-precision hydrostatic rotary table according to claim 1, characterized in that, The air gap length between the inner diameter of the stator core and the outer surface of the magnet remains constant, satisfying the following relationship: 0.5×a-(0.5×Dr+Hpm1)=0.5×b-(0.5×Dr+Hpm2), And 0.5mm < 0.5×a - (0.5×Dr + Hpm1) < 1mm.

7. The ultra-precision hydrostatic rotary table according to claim 1, characterized in that, The formula for calculating the upward thrust F perpendicular to the turntable surface is: ， ， ， g is the air gap length between the inner diameter of the stator core and the outer surface of the magnet. Let be the axial misalignment displacement between the mandrel and the stator core, and Rav be the equivalent average radius of the stator core. Where is the circumferential angle, H is the air gap magnetic field strength, and Bg is the air gap magnetic flux density.

8. The ultra-precision hydrostatic rotary table according to claim 1, characterized in that, The magnitude of the thrust generated after three-phase alternating current is applied to the stator core is adjusted by changing the direct-axis current Id of the three-phase alternating current. The influence of the quadrature-axis current Iq of the three-phase alternating current on the thrust is smaller than that of the direct-axis current Id of the three-phase alternating current on the thrust.

9. The ultra-precision hydrostatic rotary table according to claim 1, characterized in that, The axial oil film clearance of the radial-axial composite hydrostatic bearing is 10 to 20 micrometers.

10. The ultra-precision hydrostatic rotary table according to claim 1, characterized in that, It also includes a base, on which the housing is mounted.

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