A small-pore throttling air flotation main shaft based on a graphite matrix

Abstract

This invention discloses a micro-orifice throttling air-bearing spindle based on a graphite matrix, comprising a spindle with a front and rear axle sleeve respectively fitted on its front and rear journals. The spindle has a cross-shaped stepped shaft structure with a smooth cylindrical surface axially and a circular flange plate radially. Porous graphite is fixedly disposed in the inner cavity of both the front and rear axle sleeves. The porous graphite includes an axial graphite matrix and a radial graphite matrix, and multiple throttling orifices are directly formed on the porous graphite. Both the front and rear axle sleeves have sequentially connected air inlets, annular air passages, annular petal-shaped radial air chambers, and annular petal-shaped axial air chambers. High-pressure gas is depressurized and flow-limited through the throttling orifices and enters the micron-level gap between the porous graphite and the spindle, forming a stable high-pressure gas film that suspends and supports the spindle. This invention directly integrates the throttling orifices onto the graphite matrix, which can meet the high-precision rotary support requirements of fields such as ultra-precision machining, semiconductor manufacturing, and optical component processing.

Description

Technical Field

[0001] This invention relates to an air-bearing spindle, specifically a small-hole throttling air-bearing spindle based on a graphite matrix, belonging to the field of precision and ultra-precision machining equipment technology. Background Technology

[0002] In the field of ultra-precision machining, the spindle system is a core functional component that determines machining accuracy and surface quality. Traditional spindle support methods mainly fall into two categories: mechanical contact bearings (rolling bearings, sliding bearings) and gas hydrostatic bearings. However, as machining accuracy requirements advance towards the sub-micron and even nanometer levels, existing technologies have revealed a series of problems that urgently need to be addressed: For traditional mechanical bearing spindles, the rolling bearings of these spindles experience Hertzian contact stress between the steel balls and raceways. This stress generates significant frictional heat during high-speed operation, leading to thermal deformation of the spindle. Simultaneously, raceway geometric errors directly translate into rotational errors, making it difficult to achieve sub-micron level rotational accuracy. The periodic vibrations of the rolling elements, caused by frequency, are transmitted to the machined surface, producing regular machining textures and affecting surface quality. Grease lubrication suffers from splashing and degradation issues under ultra-high-speed conditions, while oil-air lubrication systems are complex and have high maintenance costs. For traditional air-bearing spindles, conventional gas static pressure spindles typically use metal (such as stainless steel or copper alloy) as the bearing base, requiring the embedding or press-fitting of independent throttling elements (such as orifice throttling elements, porous throttling elements, slit throttling elements, etc.) into the base. This configuration presents challenges due to the large number of parts, high assembly precision requirements, and difficulties in machining and debugging. Unavoidable dimensional and positional deviations in the independent throttling elements during machining and installation result in inconsistent air film stiffness and load-bearing capacity at different throttling points, affecting the overall spindle performance. Furthermore, during high-speed operation, air film shear heat is generated in the bearing clearance area, and the metal base has a high coefficient of thermal expansion (typically 10~17×10⁻⁶). -6 / ℃), which causes changes in bearing working clearance, resulting in stiffness fluctuations or even air hammer self-excited oscillation; when the air supply to the metal-based air-bearing spindle fails or is overloaded, the journal and bearing surface come into direct contact, which can easily lead to metal seizure (cold welding) and cause irreversible bearing damage.

[0003] With the development of ultra-precision hard turning and grinding composite machining, optical freeform surface machining, and other processes, higher requirements are placed on spindle systems: spindle speeds need to reach tens of thousands or even hundreds of thousands of revolutions per minute (rpm), while maintaining sub-micron level rotational accuracy and radial / axial stiffness of tens to hundreds of N / μm. This requirement poses a severe challenge to the design and manufacturing precision of the throttle, the stability of the air film, and the overall structural integration of the spindle.

[0004] In summary, there is an urgent need to develop a new type of gas hydrostatic spindle with simplified structure, high throttling accuracy, excellent thermal stability, and self-lubricating fault tolerance. Summary of the Invention

[0005] The purpose of this invention is to provide a small-hole throttling air-bearing spindle based on a graphite matrix to solve at least one of the above-mentioned technical problems. By directly machining the throttling orifice onto a high-density graphite bearing matrix, the independent throttling element is eliminated, simplifying the spindle structure. At the same time, by utilizing the self-lubricating properties, low coefficient of thermal expansion, and excellent machinability of graphite material, an integrated air-bearing spindle system with high rotational accuracy (≤70nm), high rigidity (radial ≥100N / μm), high speed (≥80000rpm) and high reliability is achieved.

[0006] The present invention achieves the above objectives through the following technical solution: a small-hole throttling air-bearing main shaft based on a graphite matrix, comprising a main shaft, a front shaft sleeve fitted on the front journal of the main shaft, a rear shaft sleeve fitted on the rear journal of the main shaft, and a motor coaxially connected to the rear end of the main shaft. The main shaft has a cross-shaped stepped shaft structure, with a smooth cylindrical surface in the axial direction and a circular flange plate in the radial direction. Porous graphite is fixedly arranged in the inner cavity of both the front and rear axle sleeves. The porous graphite includes an axial graphite matrix and a radial graphite matrix, and multiple throttling holes are opened on the porous graphite. An air inlet is provided on the body of the front axle sleeve, and an annular air passage is provided in its inner cavity. The air inlet is connected to the annular air passage b. An annular petal-shaped radial air cavity is provided in the radial inner cavity of the front axle sleeve, and an annular petal-shaped axial air cavity is provided in the axial inner cavity of the front axle sleeve. The annular air passage is connected to the annular petal-shaped radial air cavity and the annular petal-shaped axial air cavity, respectively. The rear axle sleeve also has an annular air passage, an annular petal-shaped radial air chamber, and an annular petal-shaped axial air chamber in its inner cavity, and its air passage connection method is the same as that of the front axle sleeve.

[0007] As a further embodiment of the present invention: the diameter of the graphite sheet corresponding to the throttling orifice opened on the axial graphite matrix in the inner cavity of the front axle sleeve is larger than the outer diameter of the circular flange plate of the main shaft; after the gas enters the annular petal-shaped axial gas cavity through the annular gas passage b, it acts evenly on both end faces of the circular flange plate through the throttling orifice.

[0008] As a further embodiment of the present invention: the fitting clearance between the radial graphite matrix provided in the inner cavity of the front axle sleeve and the cylindrical surface of the main shaft is 5μm to 20μm; after the gas enters the annular petal-shaped radial gas cavity through the annular gas channel, it acts uniformly on the cylindrical surface of the main shaft through the throttling orifice.

[0009] As a further embodiment of the present invention: the front bushing, the rear bushing, and the main shaft are coaxially mounted with a fitting clearance of 5μm to 20μm; a clearance adjustment seat is provided on the circular flange plate on the main shaft body, and the clearance between the axial graphite matrix in the front bushing and the rear bushing and the two end faces of the circular flange plate is adjusted by the clearance adjustment seat, with a clearance range of 5μm to 20μm.

[0010] As a further aspect of the present invention: the motor is a coreless torque motor, the stator of the motor is installed inside the rear shaft sleeve, the rotor of the motor is interference-fitted onto the journal of the main shaft, and the rotor of the motor is located between the front and rear radial bearings sleeved on the main shaft. An encoder is provided at the end of the main shaft, and an encoder magnet is connected between the encoder and the end of the main shaft. The rotational accuracy and axial runout of the main shaft are both less than 70nm.

[0011] As a further embodiment of the present invention: the rear bushing is installed inside the spindle seat, the end face of the front bushing is connected to the end face of the spindle seat, and a front outer sleeve is concentrically fitted on the outer side of the front bushing. Mounting holes for installing quick plugs are provided on both the spindle seat and the front outer sleeve.

[0012] As a further embodiment of the present invention: both the outer surface of the rear axle sleeve and the outer surface of the front axle sleeve are provided with annular cooling channels. Cooling water enters through one end of the quick connector and flows out through the annular cooling channels from the other end of the quick connector.

[0013] As a further embodiment of the present invention: a rear cover is installed on the other end face of the spindle seat, a muffler is installed on the rear cover, and the rear cover is provided with a wire hole and an aviation plug mounting hole for installing an aviation plug.

[0014] As a further embodiment of the present invention: the front and rear ends of the mating surface between the front axle sleeve and the front outer sleeve are respectively fitted with a first sealing ring and a second sealing ring; the front and rear ends of the mating surface between the rear axle sleeve and the main shaft seat are respectively fitted with a third sealing ring and a fourth sealing ring.

[0015] As a further aspect of the present invention: the throttling orifices on the porous graphite have a diameter of 0.1 mm to 0.3 mm, and the throttling orifices are evenly distributed in the circumferential direction, with 12 to 24 orifices per row, and 2 to 4 rows distributed in the axial direction.

[0016] The beneficial effects of this invention are: 1) This invention directly processes the throttling orifice on a high-density graphite matrix, eliminating the need for independent throttling elements (throttling plugs, porous throttling blocks, etc.) that must be configured in traditional air-bearing spindles, greatly simplifying the spindle structure, reducing the number of parts by more than 30%, and reducing assembly difficulty and manufacturing costs. 2) The porous graphite matrix set in this invention adopts a small-hole throttling method, combined with the principle of gas static pressure lubrication, so that the spindle can achieve full gas film suspension support. The spindle rotation accuracy and axial runout are both ≤70nm, which meets the stringent requirements of ultra-precision machining for spindle accuracy. The homogenization effect of small-hole throttling can compensate for the micron-level manufacturing tolerance of the graphite matrix. 3) By controlling the orifice diameter (0.1~0.3mm), number of orifices and spacing of the throttling orifice, the present invention can precisely regulate the distribution of air film pressure, achieving radial stiffness ≥100N / μm and axial stiffness ≥80N / μm, and can maintain extremely small radial and axial runout errors even under the condition of metal cutting grinding force; 4) Porous graphite matrix graphite materials naturally possess self-lubricating properties. Even in the event of an unexpected air supply failure or overload, the low coefficient of friction and layered slip structure of graphite prevent metal-on-metal contact (cold welding) damage when the journal contacts the graphite matrix surface, protecting the spindle journal and extending the overall machine service life. Graphite materials have an extremely low coefficient of thermal expansion (typically 2~4×10⁻⁶). -6 / ℃), which is much lower than that of metallic materials (10~17×10). -6 / ℃), under high-speed operating temperature rise environment, the size of the throttling orifice and the bearing working clearance remain highly stable, avoiding stiffness fluctuations and air hammer instability caused by thermal expansion; the graphite material has moderate hardness and no burrs, which makes it easy to directly process high-precision micro throttling orifices on its matrix, ensuring the consistency of flow rate at each throttling point and the uniformity of throttling effect, overcoming the problems of difficult and inconsistent micro-orifice processing on metal matrix; 5) The present invention has a rear cover installed on the rear end face of the spindle seat, and a muffler is configured on the rear cover to effectively reduce exhaust noise. The entire process is without mechanical contact operation, and the noise level is better than that of traditional bearing spindles. It is suitable for high-precision, high-speed rotary support applications such as ultra-precision machine tools, semiconductor manufacturing and testing equipment, and optical component processing equipment. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the overall assembly structure of the present invention; Figure 2 This is a schematic diagram of the front axle sleeve structure of the present invention; Figure 3 This is a schematic diagram of the rear axle sleeve structure of the present invention; Figure 4 This is a schematic diagram showing the layout of the graphite matrix throttling layer inside the front axle sleeve of the present invention; Figure 5 This is a schematic diagram of the main shaft structure of the present invention; In the diagram: 1. Main spindle; 2. Clearance adjustment seat; 3. Encoder magnet; 4. Encoder; 5. Motor; 6. Rear bushing; 7. Porous graphite; 8. Radial bearing; 9. Front bushing; 10. Main spindle seat; 11. Quick connector; 12. Muffler; 13. Aviation connector; 14. Front outer sleeve; 15. Rear cover; a. Air inlet; b. Annular air passage; c. Annular petal-shaped radial air chamber; d. Annular petal-shaped axial air chamber. Detailed Implementation

[0018] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0019] Example 1, as Figures 1 to 5 As shown, a small-hole throttling air-bearing main shaft based on a graphite matrix includes a main shaft 1, a front shaft sleeve 9 is sleeved on the front end journal of the main shaft 1, a rear shaft sleeve 6 is sleeved on the rear end journal of the main shaft 1, and a motor 5 is coaxially connected to the rear end of the main shaft 1. Main shaft 1 has a cross-shaped stepped shaft structure, with a smooth cylindrical surface in the axial direction and a circular flange plate in the radial direction; Porous graphite 7 is fixedly disposed in the inner cavity of both the front axle sleeve 9 and the rear axle sleeve 6. The porous graphite 7 includes an axial graphite matrix and a radial graphite matrix, and multiple throttling holes are opened on the porous graphite 7. The front axle sleeve 9 has an air inlet a and an annular air passage b in its inner cavity. The air inlet a is connected to the annular air passage b. The radial inner cavity of the front axle sleeve 9 has an annular petal-shaped radial air chamber c and the axial inner cavity of the front axle sleeve 9 has an annular petal-shaped axial air chamber d. The annular air passage b is connected to the annular petal-shaped radial air chamber c and the annular petal-shaped axial air chamber d, respectively. The inner cavity of the rear axle sleeve 6 is also provided with an annular air passage b, an annular petal-shaped radial air chamber c, and an annular petal-shaped axial air chamber d, and its air passage connection method is the same as that of the front axle sleeve 9.

[0020] By directly machining the throttling orifice onto the porous graphite 7, the independent throttling element is eliminated, simplifying the spindle structure. At the same time, the self-lubricating properties, low coefficient of thermal expansion, and excellent machinability of graphite material are utilized. Meanwhile, the gas is depressurized and limited through the throttling orifice to form a stable high-pressure gas film between the spindle 1 and the porous graphite 7, achieving full gas film suspension support and ensuring no mechanical contact and low friction operation.

[0021] Example 2: In addition to all the technical features in Example 1, this example also includes: the diameter of the graphite sheet corresponding to the throttling orifice on the axial graphite matrix in the inner cavity of the front axle sleeve 9 is larger than the outer diameter of the circular flange plate of the main shaft 1; after the gas enters the annular petal-shaped axial gas cavity d through the annular gas passage b, it acts evenly on both sides of the circular flange plate through the throttling orifice, so that the axial thrust surface is completely covered by the graphite sheet, ensuring that the static pressure gas is evenly distributed along the circumference of the axial graphite surface, forming a uniform and rigid axial gas film on both sides of the circular flange plate, thereby providing stable and reliable axial load-bearing capacity and axial stiffness, and ensuring the accuracy and stability of the bidirectional thrust positioning of the main shaft 1.

[0022] The fit clearance between the radial graphite matrix in the inner cavity of the front axle sleeve 9 and the cylindrical surface of the main shaft 1 is 5μm to 20μm. After the gas enters the annular petal-shaped radial gas cavity c through the annular gas channel b, it acts evenly on the cylindrical surface of the main shaft 1 through the throttling orifice, so as to achieve a uniform distribution of the radial gas film along the circumference of the cylindrical surface of the main shaft 1, forming a stable and highly rigid radial gas film support, providing high radial load-bearing capacity and radial stiffness. At the same time, the homogenization effect of the orifice throttling can compensate for the micron-level manufacturing tolerance of the porous graphite 7, ensuring that the main shaft 1 still maintains a very small radial runout error when running at high speed.

[0023] The front bushing 9, rear bushing 6, and main spindle 1 are coaxially mounted with a fit clearance of 5μm to 20μm. A clearance adjustment seat 2 is fitted on the circular flange plate on the main spindle 1 shaft body. The clearance between the axial graphite matrix in the front bushing 9 and rear bushing 6 and the two end faces of the circular flange plate is adjusted by the clearance adjustment seat 2. The clearance range is 5μm to 20μm, realizing independent adjustment of the radial fit clearance and the axial clearance. This allows for precise control of each key clearance dimension according to the actual working conditions during assembly, ensuring the consistency of the thickness of the radial air film and the axial air film, thereby ensuring rotational accuracy.

[0024] Motor 5 is a coreless torque motor. The stator of motor 5 is installed inside the rear axle sleeve 6, and the rotor of motor 5 is interference-fitted onto the journal of spindle 1. The rotor of motor 5 is located between the two radial bearings 8 sleeved on the spindle 1, realizing direct drive coupling between motor 5 and spindle 1 without transmission chain error. An encoder 4 is installed at the end of spindle 1, and an encoder magnet 3 is connected between encoder 4 and the end of spindle 1. The rotational accuracy and axial runout of spindle 1 are both less than 70nm, realizing direct drive of spindle 1 rotation by motor 5, eliminating errors and vibrations introduced by the transmission chain. The maximum speed can reach more than 80,000rpm. At the same time, encoder 4 and encoder magnet 3 provide real-time feedback on the angular position of spindle 1 to ensure the rotational accuracy of spindle 1 and meet the stringent requirements of ultra-precision machining for spindle accuracy.

[0025] In Example 3, in addition to all the technical features in Example 1, this example also includes: the rear bushing 6 is installed inside the spindle seat 10, the end face of the front bushing 9 is connected to the end face of the spindle seat 10, the outer side of the front bushing 9 is concentrically fitted with the front outer sleeve 14, and the spindle seat 10 and the front outer sleeve 14 are both provided with mounting holes for installing quick plugs 11, providing standardized interface installation positions for external air circuits, hydraulic circuits and electrical connections, which facilitates the assembly and maintenance of the whole machine.

[0026] Both the outer surfaces of the rear bushing 6 and the front bushing 9 are provided with annular cooling channels. Cooling water enters through one end of the quick connector 11 and flows out through the other end of the quick connector 11 after passing through the annular cooling channel, so that the cooling water circulates in the annular cooling channel, effectively removing the heat generated by the motor 5 winding and air film friction when the spindle 1 is running. The low thermal expansion coefficient of porous graphite 7, combined with active water cooling, suppresses the thermal deformation of the spindle 1 and avoids changes in bearing clearance and stiffness fluctuations caused by temperature rise.

[0027] A rear cover 15 is installed on the other end face of the spindle housing 10. A muffler 12 is installed on the rear cover 15, and the rear cover 15 has a wire hole and an aviation plug mounting hole for installing the aviation plug 13. This achieves closed protection for the tail of the spindle 1 and the area of ​​the motor 5, preventing external contaminants from entering the spindle. At the same time, the muffler 12 effectively reduces exhaust noise. The wire hole and aviation plug mounting hole facilitate the lead-out and electrical connection of the motor 5 cable and the aviation plug 13, ensuring the quiet operation of the whole machine and the reliability of the electrical connection.

[0028] The front and rear ends of the mating surfaces of the front axle sleeve 9 and the front outer sleeve 14 are respectively fitted with a first sealing ring and a second sealing ring; the front and rear ends of the mating surfaces of the rear axle sleeve 6 and the spindle seat 10 are respectively fitted with a third sealing ring and a fourth sealing ring, which realizes multiple sealing protection at both ends of the cooling water flow channel, effectively preventing cooling water from leaking from the mating surfaces and invading the interior or exterior environment of the spindle 1, protecting electrical components such as the motor 5 and encoder 4 from moisture damage, and ensuring the reliability and safety of the spindle 1 during long-term operation.

[0029] The throttling orifices on the porous graphite 7 have a diameter of 0.1 mm to 0.3 mm. The throttling orifices are evenly distributed in the circumferential direction, with 12 to 24 orifices per row, and 2 to 4 rows distributed in the axial direction. By controlling the orifice diameter, number of orifices and arrangement, the gas flow rate and gas film pressure distribution at each throttling point can be precisely controlled to ensure the consistency of the throttling effect of each throttling orifice, thereby optimizing the matching of gas film stiffness and load-bearing capacity.

[0030] High-pressure gas enters the main shaft through the air inlet a on the front axle sleeve 9. The air inlet a is connected to the annular air passage b. The high-pressure gas first enters the annular air passage b. Since the diameter of the annular air passage b is larger than the diameter of the main shaft 1, the gas diffuses evenly in the circumferential direction in the annular air passage b, forming a circumferential envelope of the main shaft 1. Subsequently, the high-pressure gas is split into two streams within the annular gas passage b: one stream enters the front axle sleeve 9, and the other stream enters the rear axle sleeve 6 via the internal channel between the main shaft 1 and the front axle sleeve 9 and the rear axle sleeve 6. The flow paths of the two streams are completely symmetrical. Each gas path, after passing through the annular gas passage b within its respective bushing, is further divided into two paths: one path enters the annular petal-shaped axial gas cavity d, and the other path enters the annular petal-shaped radial gas cavity c. The function of the annular petal-shaped axial gas cavity d and the annular petal-shaped radial gas cavity c is to achieve uniform circumferential distribution of gas on the axial end face and radial inner surface of the porous graphite 7, respectively, eliminating local pressure unevenness. The uniformly distributed gas flows through throttling orifices opened on the axial and radial graphite matrix of the porous graphite 7. The orifice diameter is 0.1 mm to 0.3 mm. When the gas passes through the throttling orifice, a throttling effect occurs, the pressure decreases and the flow rate increases, thereby achieving precise control of gas flow rate and pressure. After being throttled and depressurized, the gas enters the micron-level gap between the porous graphite 7 and the main shaft 1, which ranges from 5μm to 20μm. Specifically: the gas flowing out through the throttling orifice of the axial graphite matrix enters the axial gap between the axial graphite matrix and the two end faces of the circular flange plate of the main shaft 1, forming a uniform and rigid axial gas film on both end faces of the circular flange plate, applying a bidirectional axial support force to the main shaft 1, thereby achieving axial suspension and bidirectional thrust positioning of the main shaft 1; the gas flowing out through the throttling orifice of the radial graphite matrix enters the radial gap between the radial graphite matrix and the cylindrical surface of the main shaft 1, forming a uniform and rigid radial gas film around the cylindrical surface of the main shaft 1, applying a radial support force to the main shaft 1, thereby achieving radial suspension and centering positioning of the main shaft 1; The overflow gas after radial throttling is discharged through the overflow hole on the clearance adjusting seat 2, and then discharged to the outside through the vent and exhaust hole of the spindle seat 10. The overflow gas after axial throttling flows axially along the spindle 1, flows through the tail of the spindle 1 and the inside of the motor 5, and is finally discharged to the external environment after being silenced by the silencer 12 installed on the rear cover 15. The entire exhaust path ensures stable air pressure inside the spindle 1 and avoids the adverse effects of back pressure on the air film stiffness; In the aforementioned air-film suspension state, motor 5 is a coreless torque motor. The stator of motor 5 is installed inside the rear shaft sleeve 6, and the rotor of motor 5 is interference-fitted onto the journal of main shaft 1. When motor 5 is energized, the rotor directly drives main shaft 1 to rotate, achieving direct drive coupling. Since there is no mechanical contact between main shaft 1 and porous graphite 7, the frictional resistance of main shaft 1 during rotation is extremely low, enabling a maximum speed of over 80,000 rpm. Meanwhile, cooling water enters through one end of the quick connector 11, circulates through the annular cooling channels opened on the outer surface of the rear bushing 6 and the outer surface of the front bushing 9, and then flows out through the other end of the quick connector 11, continuously carrying away the heat generated by the winding of the motor 5 and the heat generated by air film friction. Combined with the low thermal expansion coefficient of the porous graphite 7, it suppresses the thermal deformation of the spindle 1 and ensures that the size of the throttling orifice and the bearing working clearance remain highly stable under the high-speed operation temperature rise environment. When an unexpected air supply interruption occurs or the spindle 1 is overloaded, the high-pressure air film disappears or is insufficient to support the spindle 1, and the journal and circular flange of the spindle 1 come into contact with the surface of the porous graphite 7. At this time, the natural self-lubricating properties of the porous graphite 7 come into play. Its layered crystal structure slips under the action of frictional shear force, forming a lubricating transfer film with a low coefficient of friction, preventing the spindle 1 from seizing or being damaged by cold welding with the porous graphite 7, and protecting the journal surface of the spindle 1. After the air supply is restored, the spindle 1 can continue to work normally. The encoder 4, in conjunction with the encoder magnet 3, detects the rotation angle and position of the spindle 1 in real time and feeds the signal back to the control system to achieve closed-loop control of the spindle 1. Under the homogenization effect of the high-pressure gas film, the manufacturing error of the throttling orifice and the micron-level manufacturing tolerance of the porous graphite 7 are effectively homogenized, ultimately achieving excellent precision indicators of less than 70nm for both the rotational accuracy and axial runout of the spindle 1.

[0031] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

[0032] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider 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.

Claims

1. A small-hole throttling air-bearing main shaft based on a graphite matrix, comprising a main shaft (1), characterized in that: A front bushing (9) is fitted on the front journal of the main shaft (1), and a rear bushing (6) is fitted on the rear journal of the main shaft (1). A motor (5) is coaxially connected to the rear end of the main shaft (1). The main shaft (1) is a cross-shaped stepped shaft structure with a smooth cylindrical surface in the axial direction and a circular flange plate in the radial direction; Porous graphite (7) is fixedly disposed in the inner cavity of both the front axle sleeve (9) and the rear axle sleeve (6). The porous graphite (7) includes an axial graphite matrix and a radial graphite matrix, and multiple throttling holes are opened on the porous graphite (7). The front axle sleeve (9) has an air inlet (a) on its body and an annular air passage (b) in its inner cavity. The air inlet (a) is connected to the annular air passage (b). The radial inner cavity of the front axle sleeve (9) has an annular petal-shaped radial air chamber (c), and the axial inner cavity of the front axle sleeve (9) has an annular petal-shaped axial air chamber (d). The annular air passage (b) is connected to the annular petal-shaped radial air chamber (c) and the annular petal-shaped axial air chamber (d) respectively. The inner cavity of the rear axle sleeve (6) is also provided with an annular air passage (b), an annular petal-shaped radial air chamber (c) and an annular petal-shaped axial air chamber (d), and its air passage connection method is the same as that of the front axle sleeve (9).

2. The orifice throttling air-bearing main shaft according to claim 1, characterized in that: The diameter of the graphite sheet corresponding to the throttling orifice on the axial graphite matrix provided in the inner cavity of the front axle sleeve (9) is larger than the outer diameter of the circular flange plate of the main shaft (1); after the gas enters the annular petal-shaped axial gas cavity (d) through the annular gas passage (b), it is uniformly applied to both ends of the circular flange plate through the throttling orifice.

3. The orifice throttling air-bearing main shaft according to claim 1, characterized in that: The fitting gap between the radial graphite matrix in the inner cavity of the front axle sleeve (9) and the cylindrical surface of the main shaft (1) is 5μm to 20μm; after the gas enters the annular petal-shaped radial gas cavity (c) through the annular gas passage (b), it acts evenly on the cylindrical surface of the main shaft (1) through the throttling orifice.

4. The orifice throttling air-bearing main shaft according to claim 1, characterized in that: The front bushing (9), the rear bushing (6), and the main shaft (1) are coaxially mounted with a clearance of 5μm to 20μm. A clearance adjustment seat (2) is provided on the circular flange plate on the shaft body of the main shaft (1). The clearance between the axial graphite matrix in the front bushing (9) and the rear bushing (6) and the two end faces of the circular flange plate is adjusted by the clearance adjustment seat (2), with a clearance range of 5μm to 20μm.

5. The orifice throttling air-bearing main shaft according to claim 1, characterized in that: The motor (5) is a coreless torque motor. The stator of the motor (5) is installed inside the rear shaft sleeve (6). The rotor of the motor (5) is interference-fitted onto the journal of the main shaft (1). The rotor of the motor (5) is located between the front and rear radial bearings (8) sleeved on the main shaft (1). An encoder (4) is provided at the end of the main shaft (1). An encoder magnet (3) is connected between the encoder (4) and the end of the main shaft (1). The rotational accuracy and axial runout of the main shaft (1) are both less than 70 nm.

6. The orifice throttling air-bearing main shaft according to claim 1, characterized in that: The rear bushing (6) is installed inside the spindle seat (10). The end face of the front bushing (9) is connected to the end face of the spindle seat (10). The outer side of the front bushing (9) is concentrically fitted with a front outer sleeve (14). The spindle seat (10) and the front outer sleeve (14) are both provided with mounting holes for installing quick plugs (11).

7. The orifice throttling air-bearing main shaft according to claim 6, characterized in that: Both the outer surface of the rear axle sleeve (6) and the outer surface of the front axle sleeve (9) are provided with annular cooling channels. Cooling water enters through one end of the quick plug (11) and flows out through the other end of the quick plug (11) after passing through the annular cooling channels.

8. The orifice throttling air-bearing main shaft according to claim 6, characterized in that: A rear cover (15) is installed on the other end face of the main spindle seat (10). A muffler (12) is installed on the rear cover (15), and a wire hole and an aviation plug mounting hole for installing an aviation plug (13) are provided on the rear cover (15).

9. The orifice throttling air-bearing main shaft according to claim 6, characterized in that: The front and rear ends of the mating surfaces of the front axle sleeve (9) and the front outer sleeve (14) are respectively fitted with a first sealing ring and a second sealing ring; the front and rear ends of the mating surfaces of the rear axle sleeve (6) and the main shaft seat (10) are respectively fitted with a third sealing ring and a fourth sealing ring.

10. The orifice throttling air-bearing main shaft according to claim 1, characterized in that: The throttling orifices on the porous graphite (7) have a diameter of 0.1 mm to 0.3 mm. The throttling orifices are evenly distributed in the circumferential direction, with 12 to 24 orifices per row and 2 to 4 rows distributed in the axial direction.

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