Precise air floating main shaft based on small hole throttling

Abstract

The invention provides a precise air floating main shaft based on small hole throttling. The precise air floating main shaft comprises a cylinder barrel, a shell, a rotating shaft, a front radial air floating bearing, a rear radial air floating bearing, a front axial thrust air floating bearing, a rear axial thrust air floating bearing, a driving motor, a broach mechanism and various sensors. A reciprocating type spiral groove is formed in the outer circle of the cylinder barrel and forms a spiral cooling water channel with the shell, and the rear end cover is integrated with an air inlet interface, an air outlet interface, a cooling water interface and an air control interface; compressed gas is throttled through an axial gas path and a small hole to form a high-rigidity gas film to support the rotating shaft, and cooling water flows in the spiral water path to take away heat; the control module is based on rotating speed, displacement, temperature and pressure signals, adopts a thermal-mechanical coupling model and a predictive control algorithm, adaptively adjusts air supply pressure and cooling water flow, and is suitable for semiconductors and ultra-precision machining equipment. Through the collaborative design of the small hole throttling air bearing, the reciprocating type spiral cooling water channel and multi-sensor intelligent control, the rigidity, the heat stability and the operation reliability of the main shaft are greatly improved, and the high-precision ultra-precision machining device is suitable for long-term high-rotating-speed and high-precision ultra-precision machining.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of ultra-precision high-speed cutting spindle, and particularly relates to a precision air-floating spindle based on small-hole throttling. BACKGROUND

[0002] In the processes of semiconductor wafer cutting, grinding, polishing and ultra-precision turning, the spindle needs to be stably operated at a speed of hundreds of thousands of revolutions per minute or even higher for a long time, and the rotation accuracy and positioning accuracy need to be maintained within the nanometer range, while the vibration is extremely low and the thermal drift is extremely small; any slight spindle vibration, thermal deformation or bearing wear will be amplified as the workpiece surface morphology error and pattern distortion, directly affecting the chip yield and the processing quality of high-end optical elements.

[0003] Disadvantages of the prior art: 1. The axial thrust air-floating bearing has insufficient carrying capacity and stability.

[0004] The axial thrust air-floating bearing of the existing air-floating spindle mostly adopts a simple plane air film structure, an annular air cavity or a porous medium throttling structure, and the throttling form and air film cavity arrangement are relatively fixed. When the spindle works at high speed and under variable load, the air film pressure distribution is easily affected by the inlet pressure, gap fluctuation and machining error, and is uneven, the axial stiffness and damping decrease significantly, and the axial jump increases or the air film is unstable. Although some schemes use small-hole throttling, the throttling holes are arranged only on one side of the thrust surface, or the throttling holes and the air groove structure are not reasonably matched, and it is still difficult to obtain sufficient carrying capacity and stiffness margin under small air film gap conditions.

[0005] 2. The radial / axial air path arrangement is unreasonable, and the gas supply utilization efficiency is low.

[0006] Many existing air-floating spindles are simplified structures, and only a plurality of radial gas supply holes are formed on the cylinder or the shell, and compressed gas is directly sent to the radial bearing and the axial thrust bearing. Since the air path arrangement is short and concentrated, the gas supply of each bearing greatly influences each other, when the gas consumption or the air film gap of a certain bearing changes, the gas supply pressure of other bearings is easily fluctuated, the radial and axial stiffness is coupled to change, and the overall stability of the spindle is affected. At the same time, the throttling and discharge process of the gas in the bearing is difficult to fine control, the gas supply utilization rate is low, and the system noise and energy consumption are high.

[0007] 3. The cooling structure is simple, and the spindle thermal stability is poor.

[0008] Traditional electric spindles mostly only set annular water jacket or several axial straight grooves outside the cylinder barrel, and the cooling water is discharged after flowing along the shortest path, so the length of flow channel is short, the heat exchange area is limited, and the temperature distribution is uneven in the circumferential and axial directions, which is easy to form obvious temperature gradient. With the increase of spindle speed, the driving motor loss, gas compression and throttling heat and cutting zone conduction heat continuously accumulate, resulting in significant thermal elongation and bending deformation of the cylinder barrel and the rotating shaft, which finally shows the increase of spindle end face axial drift and radial runout. Although some solutions introduce independent air cooling or water cooling circuit, there is lack of systematic design and collaborative control between air circuit and water circuit, which is difficult to optimize the thermal-mechanical coupling characteristics as a whole.

[0009] 4. Lack of online monitoring and closed-loop control of key operating parameters.

[0010] Most of the existing air floating spindles only manually monitor the gas supply pressure and cooling water state through simple pressure gauges, flow meters or temperature switches, and the gas supply pressure and cooling water flow are usually set by manual valves or open-loop adjustment devices, which cannot be adjusted in real time according to the spindle operating conditions. Even if some spindles are externally configured with independent temperature control devices or pressure controllers, they are mostly single-variable control, lack of collaborative use of multi-source information such as speed, axial displacement, temperature and gas supply pressure, and are difficult to compensate for the changes in gas film gap and thermal deformation in time, and cannot guarantee the dynamic stability of the spindle in the whole speed range from the system level.

[0011] Therefore, the prior art has deficiencies and needs to be further improved. SUMMARY

[0012] In view of the problems existing in the prior art, the present application provides a precision air floating spindle based on small hole throttling.

[0013] To achieve the above-mentioned purpose, the specific scheme of the present application is as follows: The present application provides a precision air floating spindle based on small hole throttling, comprising: front end cover, rear end cover, cylinder barrel, rotating shaft inserted into the cylinder barrel, front radial air floating bearing and rear radial air floating bearing supporting the rotating shaft, front axial thrust air floating bearing and rear axial thrust air floating bearing matched with the front and rear end faces of the rotating shaft thrust disc, driving motor, broach mechanism and shell; Wherein, the front end cover and the rear end cover are fixed at the front end and the rear end of the cylinder barrel respectively, the front end of the rotating shaft extends out of the cylinder barrel through the front end cover and is used for connecting the tool shank, the rear end of the rotating shaft is fixedly connected with the rotor of the driving motor through the positioning shaft shoulder, and the stator of the driving motor is fixed on the inner wall of the cylinder barrel, thereby forming a direct-connection type electric spindle structure. The front radial air floating bearing and the rear radial air floating bearing are sleeved on the middle section of the rotating shaft, and the front axial thrust air floating bearing and the rear axial thrust air floating bearing are arranged on the front end face and the rear end face of the rotating shaft thrust disc respectively, and the radial air floating bearing and the axial thrust air floating bearing jointly support the rotating shaft in the radial and axial directions; The outer periphery of the cylinder is sleeved with the shell, the outer circular surface of the cylinder is provided with a reciprocating spiral groove in the axial direction, the reciprocating spiral groove and the inner wall of the shell form a closed spiral cooling water channel, and the rear end cover is provided with a cooling water inlet and a cooling water outlet which are in communication with the spiral cooling water channel. Axial gas channels for conveying pressure gas are arranged in the front radial air floating bearing, the rear radial air floating bearing, the front axial thrust air floating bearing and the rear axial thrust air floating bearing, and radial gas channels are further arranged in the front axial thrust air floating bearing and the rear axial thrust air floating bearing, and a small hole throttling structure is used on the respective end faces to form a load-carrying air film. The puller mechanism includes a push rod arranged in the inner cavity of the rotating shaft, a piston fixedly connected with the rear end of the push rod, a disc spring sleeved on the outer periphery of the puller, and a puller matched with the front end of the rotating shaft, the piston is in communication with a gas control interface arranged on the rear end cover, so as to drive the push rod and the puller to move axially under the action of compressed gas, so as to realize the clamping and releasing of the tool handle. A sensor for detecting the working state of the main shaft is arranged on one side of the cylinder close to the rear end cover, including a rotating speed sensor for detecting the rotating speed of the tail end of the rotating shaft, a displacement sensor for detecting the axial position of the push rod, and a temperature sensor for detecting the temperature of the bearing area and the cylinder, and a pressure sensor for detecting the gas supply pressure. The air floating spindle further comprises a control module electrically connected with the above-mentioned sensors, the control module adjusts the gas supply pressure of the gas inlet on the rear end cover and the cooling water flow in the spiral cooling water channel according to the output of the rotating speed sensor, the displacement sensor, the temperature sensor and the pressure sensor, so that the axial thermal elongation and the radial runout of the spindle are kept within a preset range.

[0014] Further, an air inlet cavity is arranged in the shell, the air inlet cavity is in communication with the axial gas supply channels in the cylinder through a plurality of radially distributed radial gas supply holes on the cylinder, each axial gas supply channel extends along the axial direction of the main shaft and is in communication with a plurality of circumferentially distributed axial gas holes in the front radial air floating bearing, the rear radial air floating bearing, the front axial thrust air floating bearing and the rear axial thrust air floating bearing, so that the high-pressure gas is distributed to each air floating bearing in sequence along the axial direction.

[0015] Further, the front axial thrust gas bearing and the rear axial thrust gas bearing are each formed by interference fit pressing connection of a metal annular seat and a gas-impermeable material ring, the gas-impermeable material ring is a gas-impermeable graphite material; a ring-shaped air groove is formed between the metal annular seat and the gas-impermeable material ring, the diameter of the inlet of the ring-shaped air groove is larger than the diameter of the throttle orifice on the gas-impermeable material ring, and high-pressure gas first enters the ring-shaped air groove and then is sprayed to the corresponding shaft thrust disc end face through the throttle orifices arranged on the gas-impermeable material ring, so as to form a uniform and stable axial bearing gas film.

[0016] Further, the reciprocating spiral groove is arranged as a plurality of opposite spiral segments in the axial direction of the cylinder barrel, and adjacent spiral segments are connected through a turning groove at the end of the cylinder barrel, so as to form a long-passage spiral cooling water channel in the axial length; the cross section of the reciprocating spiral groove is rectangular, trapezoidal or semicircular, and the depth and width thereof remain consistent in the axial direction, so as to ensure uniform flow of the cooling water in the circumferential direction of the cylinder barrel.

[0017] Further, the rear end cover adopts an integrated structure, and the cooling water inlet, the cooling water outlet, the main shaft air inlet, the main shaft air outlet, the motor wiring port, the sensor wiring port and the broach gas control interface are arranged on the integrally processed end cover body, the interfaces are distributed in a radial or axial array manner, and are in communication with the inside of the cylinder barrel or the inside of the driving motor through built-in flow channels or cable through holes, so as to reduce the number of external hoses and improve the compactness and assembly reliability of the whole machine.

[0018] Further, the precision gas bearing spindle has a first cooling circuit and a second cooling circuit: the first cooling circuit is a compressed gas cooling circuit, high-pressure gas enters the annular air inlet cavity through the air inlet, flows through the front radial gas bearing, the rear radial gas bearing, the front axial thrust gas bearing and the rear axial thrust gas bearing, and then enters the driving motor cavity through the exhaust passage formed by the cylinder barrel and the rear end cover after completing the support and cooling of the bearings, and is discharged after forcibly ventilating and cooling the driving motor; the second cooling circuit is a liquid cooling circuit, cooling water enters the spiral cooling water channel through the cooling water inlet, flows along the reciprocating spiral groove and is discharged through the cooling water outlet, and is used to carry away the heat generated by the cylinder barrel and the driving motor.

[0019] Further, the gas-impermeable material ring is a low-permeability material formed by sintering of graphite, ceramic or metal powder and impregnation densification treatment, has a large number of micro-pore channels or micro-defect structures inside, and each throttle orifice is in communication with the micro-pore channels or micro-defect structures or communicates to the peripheral dense layer thereof, so that the gas pressure sprayed through the throttle orifice is uniformly distributed in the circumferential and radial directions, thereby improving the static stiffness and dynamic stability of the axial thrust gas bearing.

[0020] Further, the control module adopts a gas supply pressure adaptive adjustment algorithm based on multi-sensor data fusion, the algorithm comprising: simultaneously collecting the axial displacement of the push rod measured by the displacement sensor, the gas supply pressure measured by the pressure sensor and the bearing area temperature measured by the temperature sensor at a preset sampling period, substituting the axial displacement of the push rod and the temperature into a thermal-force coupling mathematical model of the spindle shaft system to solve the current gas film gap; comparing the obtained gas film gap with a preset target gas film gap to obtain a gap deviation, calculating an inlet pressure correction amount according to the gap deviation using a proportional-integral-derivative control law, and superimposing the correction amount on the current gas supply pressure set value, so as to realize closed-loop constant control of the gas film gap of the front and rear axial thrust gas floating bearings.

[0021] Further, the control module further adopts a predictive control algorithm for cooling water flow and spindle temperature rise collaborative optimization, the algorithm comprising: slidingly sampling the speed sensor, temperature sensor and driving motor current signal at a preset time window to construct a spindle temperature rise prediction model; according to the predicted cylinder temperature and rotating shaft thermal elongation in the future multiple sampling periods, establishing a performance index function of weighted sum of temperature overrun penalty term and cooling water pump power consumption penalty term, obtaining the optimal control sequence of the cooling water flow and the gas supply pressure by solving the constrained optimization problem online, and applying the control amount at the first sampling time to the cooling water inlet and the air inlet, so as to reduce the energy consumption under the premise of ensuring the thermal stability of the spindle.

[0022] Further, the control module further has a spindle operating state evaluation and fault early warning function, the function being realized by the following steps: filtering and normalizing the original data output by the speed sensor, displacement sensor, pressure sensor and temperature sensor, calculating a multi-dimensional health feature vector containing the gas film gap, axial thermal elongation, radial vibration amplitude and temperature gradient based on a preset health reference working condition; inputting the health feature vector into a spindle health evaluation model trained by historical operation data to obtain a health score, issuing a maintenance warning when the health score is lower than a first threshold, and automatically reducing the maximum spindle speed or cutting load when the health score is lower than a second threshold, so as to avoid sudden failure caused by bearing instability or overheating.

[0023] The technical scheme of the present application has the following beneficial effects: 1. Significantly improve the axial bearing capacity and running stability.

[0024] The present application sets front axial thrust gas floating bearing 15 and rear axial thrust gas floating bearing 14 in front and back of thrust disc of rotating shaft 5 respectively, bearing end face adopts small hole throttling structure, preferably is composed of metal annular seat matched with air-tight graphite ring, and is supplied with gas through multiple throttling small holes to thrust disc end face after annular air groove.

[0025] 2. Radial support and axial support are coordinated, and overall stiffness and rotation accuracy are higher.

[0026] The front radial gas floating bearing 17 and the rear radial gas floating bearing 13 are organically connected in series with the front and rear axial thrust gas floating bearings 15 and 14 through the axial gas path in the cylinder 3 and the gas path system in the shell 4, forming multi-surface envelope support for the rotating shaft 5. The gas floating bearings are reasonably distributed along the axial direction, the axial line coaxiality is high, and the high stiffness gas film after cooperation with the small hole throttling can maintain very small radial vibration and radial runout in the full speed range, thereby improving the rotation accuracy and cutting stability of the spindle and meeting the requirements of nanometer geometric accuracy for super-precision cutting and single-point turning.

[0027] 3. Double cooling circuit and reciprocating spiral cooling water path significantly improve thermal stability.

[0028] The present application sets two sets of cooling systems of compressed gas cooling circuit and liquid cooling circuit: compressed gas enters the cavity of the driving motor 12 after passing through the front and rear radial gas floating bearings and the front and rear axial thrust gas floating bearings, and the bearing area and the motor are synchronously air-cooled; the reciprocating spiral groove 22 is machined on the outer circular surface of the cylinder 3, and forms a long-path spiral cooling water path with the inner wall of the shell 4, cooling water enters from the cooling water inlet 20, and is discharged from the cooling water outlet 21 after passing through multiple reciprocating flow channels. The reciprocating spiral flow channel greatly increases the heat exchange area in a limited axial length, makes the circumferential and axial temperature field of the cylinder more uniform, effectively reduces the thermal gradient and thermal bending of the shaft system, cooperates with the air-cooled circuit to reduce the axial thermal elongation and radial thermal drift of the spindle, and improves the thermal stability of the whole machine.

[0029] 4. Multi-sensor online monitoring and gas / cooling closed-loop control improve dynamic accuracy and adaptability.

[0030] This invention arranges a speed sensor 6, a displacement sensor 8, a temperature sensor, and a pressure sensor on the cylinder 3 or the rear end cover 9. A control module collects and fuses these sensor signals, employing an adaptive air supply pressure adjustment algorithm based on a thermo-mechanical coupling model and a cooling water flow predictive control algorithm to achieve closed-loop regulation of the intake pressure and cooling water flow. The control module can calculate the air film clearance in real time based on axial displacement and temperature, perform PID correction on the intake port pressure, and combine model predictive control to predict and optimize the temperature rise over future multi-sampling cycles, ensuring that the bearing air film clearance and temperature field are always kept within a preset safe range. Compared with traditional open-loop or single-variable control spindles, this invention maintains smaller axial thermal drift and radial runout under different speeds, loads, and environmental conditions, significantly improving dynamic accuracy and adaptability to operating conditions.

[0031] 6. The broaching mechanism structure is optimized and the clamping status is monitored in real time, improving tool changing safety and machining efficiency.

[0032] The drawbar mechanism 2 of this invention adopts an integrated arrangement of push rod 11, piston 10, disc spring 16, and drawbar 1. The disc spring 16 is only located at the front end of the rotating shaft 5, and the rear end of the push rod 11 is connected to the piston 10. The piston movement is controlled by the pneumatic interface on the rear end cover 9, realizing reliable clamping and rapid release of the tool holder 19. The displacement sensor 8 can accurately detect the axial displacement of the push rod 11, thereby determining whether the clamping force is sufficient and whether the tool holder 19 is correctly positioned. Compared with existing structures that rely on mechanical limits or manual experience, the tool changing process of this invention can be monitored and protected online, avoiding tool flying accidents caused by insufficient or mis-clamping, and improving the safety and automation level of tool changing. Attached Figure Description

[0033] Figure 1 This is a cross-sectional view of the present invention; Figure 2 This is a schematic diagram of the throttling of the axial thrust bearing orifice of the present invention; Figure 3 This is a schematic diagram of the reciprocating spiral groove structure of the cooling water of the present invention; Attached image captions: 1. Cutting tool; 2. Cutting tool mechanism; 3. Cylinder; 4. Housing; 5. Shaft; 6. Speed ​​sensor; 7. Intake pipe; 8. Displacement sensor; 9. Rear end cover; 10. Piston; 11. Push rod; 12. Drive motor; 13. Rear radial air bearing; 14. Rear axial thrust air bearing; 15. Front axial thrust air bearing; 16. Disc spring; 17. Front radial air bearing; 18. Front end cover; 19. Tool holder; 20. Cooling water inlet; 21. Cooling water outlet; 22. Reciprocating spiral groove; 23. Thrust plate. Detailed Implementation

[0034] The application will be further described in detail below with reference to the accompanying drawings and embodiments; it can be understood that the specific embodiments described herein are only used to explain the application, but not to limit the application; in addition, it should be noted that, for the convenience of description, only the parts related to the application are shown in the drawings, but not all.

[0035] In combination Figures 1-3 As shown in the drawings, the application provides a precision gas floating main shaft based on small hole throttling, comprising: front end cover 18, rear end cover 9, cylinder 3, rotating shaft 5 inserted into the cylinder 3, front radial gas floating bearing 17 and rear radial gas floating bearing 13 supporting the rotating shaft 5, front axial thrust gas floating bearing 15 and rear axial thrust gas floating bearing 14 cooperating with the front and rear end surfaces of the thrust disc of the rotating shaft 5, driving motor 12, broach mechanism 2 and shell 4; Wherein, the front end cover 18 and the rear end cover 9 are respectively fixed at the front end and the rear end of the cylinder 3, the front end of the rotating shaft 5 extends out of the cylinder 3 through the front end cover 18 and is used for connecting the shank 19, the rear end of the rotating shaft 5 is fixedly connected with the rotor of the driving motor 12 through a positioning shaft shoulder, and the stator of the driving motor 12 is fixed on the inner wall of the cylinder 3, thereby forming a direct-connection type motorized spindle structure; The front radial gas floating bearing 17 and the rear radial gas floating bearing 13 are sleeved on the middle segment of the rotating shaft 5, the front axial thrust gas floating bearing 15 and the rear axial thrust gas floating bearing 14 are respectively arranged on the front end surface and the rear end surface of the thrust disc of the rotating shaft 5, and the radial gas floating bearing and the axial thrust gas floating bearing jointly support the rotating shaft 5 in the radial direction and the axial direction; The outer periphery of the cylinder 3 is sleeved with the shell 4, the outer circular surface of the cylinder 3 is provided with a reciprocating spiral groove 22 in the axial direction, the reciprocating spiral groove 22 and the inner wall of the shell 4 form a closed spiral cooling water channel, and the rear end cover 9 is provided with a cooling water inlet 20 and a cooling water outlet 21 which are in communication with the spiral cooling water channel; Axial gas channels for conveying pressure gas are arranged in the front radial gas floating bearing 17, the rear radial gas floating bearing 13, the front axial thrust gas floating bearing 15 and the rear axial thrust gas floating bearing 14, radial gas channels are further arranged in the front axial thrust gas floating bearing 15 and the rear axial thrust gas floating bearing 14, and small hole throttling structures are adopted on the respective end surfaces to form load-carrying gas films; The broach mechanism 2 comprises a push rod 11 arranged in the inner cavity of the rotating shaft 5, a piston 10 fixedly connected with the rear end of the push rod 11, a disc spring 16 sleeved on the outer periphery of the broach 1, and the broach 1 cooperating with the front end of the rotating shaft 5, the piston 10 is in communication with a gas control interface arranged on the rear end cover 9, so as to drive the push rod 11 and the broach 1 to move axially under the action of compressed gas, thereby achieving clamping and releasing of the shank 19; The inside of the cylinder 3 near the rear end cover 9 is provided with sensors for detecting the working state of the main shaft, including a rotating speed sensor 6 for detecting the rotating speed of the tail end of the rotating shaft 5, a displacement sensor 8 for detecting the axial position of the push rod 11, a temperature sensor for detecting the temperature of the bearing area and the cylinder 3, and a pressure sensor for detecting the supply gas pressure; The air floating main shaft further comprises a control module electrically connected with the above-mentioned sensors, and the control module performs closed loop regulation on the supply gas pressure of the air inlet on the rear end cover 9 and the cooling water flow in the spiral cooling water path according to the output of the rotating speed sensor 6, the displacement sensor 8, the temperature sensor and the pressure sensor, so that the axial thermal elongation and the radial runout of the main shaft are kept within a preset range.

[0036] The housing 4 is provided with an air inlet cavity, the air inlet cavity is communicated with the axial air supply channels in the cylinder 3 through a plurality of radially distributed radial air supply holes on the cylinder 3, each of the axial air supply channels extends along the axial direction of the main shaft and is communicated with a plurality of circumferentially distributed axial air holes in the front radial air floating bearing 17, the rear radial air floating bearing 13, the front axial thrust air floating bearing 15 and the rear axial thrust air floating bearing 14, so that the high pressure gas is distributed to each air floating bearing along the axial direction in turn.

[0037] The front axial thrust air floating bearing 15 and the rear axial thrust air floating bearing 14 are both composed of a metal annular seat and a gas impermeable material ring by interference fit pressing connection, the gas impermeable material ring is a gas impermeable graphite material; a ring-shaped air groove is formed between the metal annular seat and the gas impermeable material ring, the diameter of the hole at the inlet of the ring-shaped air groove is larger than the diameter of the throttle small hole on the gas impermeable material ring, the high pressure gas first enters the ring-shaped air groove, and then is sprayed to the corresponding rotating shaft 5 thrust disc end surface through a plurality of throttle small holes arranged on the gas impermeable material ring, so as to form a uniform and stable axial bearing gas film.

[0038] The reciprocating spiral groove 22 is arranged as a plurality of opposite spiral segments along the axial direction of the cylinder 3, adjacent spiral segments are connected through a turning groove at the end of the cylinder 3, so as to form a spiral cooling water path with long flow channels in the axial length; the cross section of the reciprocating spiral groove 22 is rectangular, trapezoidal or semicircular, the depth and width of the reciprocating spiral groove 22 remain consistent along the axial direction, so as to ensure the uniform flow of cooling water in the circumferential direction of the cylinder 3.

[0039] The rear end cover 9 adopts an integrated structure, the cooling water inlet 20, the cooling water outlet 21, the main shaft air inlet, the main shaft air outlet, the motor wiring port, the sensor wiring port and the broach 1 gas control interface are arranged on the integrally processed end cover body, each interface is distributed in a radial or axial array manner, and is communicated with the inside of the cylinder 3 or the inside of the driving motor 12 through the built-in flow channel or the cable through hole, so as to reduce the number of external hoses, improve the compactness and assembly reliability of the whole machine.

[0040] The precision air floating spindle has a first cooling circuit and a second cooling circuit: the first cooling circuit is a compressed gas cooling circuit, high-pressure gas enters the annular air inlet cavity through the air inlet, flows through the front radial air floating bearing 17, the rear radial air floating bearing 13, and the front axial thrust air floating bearing 15 and the rear axial thrust air floating bearing 14, and then enters the driving motor 12 cavity through the exhaust passage formed by the cylinder 3 and the rear end cover 9 to cool the driving motor 12, and is then discharged after forced ventilation cooling; the second cooling circuit is a liquid cooling circuit, cooling water enters the spiral cooling water path through the cooling water inlet 20, flows along the reciprocating spiral groove 22, and is then discharged through the cooling water outlet 21 to carry away the heat generated by the cylinder 3 and the driving motor 12.

[0041] The air-tight material ring is made of low air permeability material formed by sintering graphite, ceramic or metal powder and impregnation densification treatment, and has a large number of micro-porous channels or micro-defect structures inside, each throttling small hole is communicated with the micro-porous channels or micro-defect structures or is communicated to the peripheral dense layer thereof, so that the gas pressure sprayed through the throttling small hole is uniformly distributed in the circumferential and radial directions, thereby improving the static stiffness and dynamic stability of the axial thrust air floating bearing.

[0042] The control module adopts a gas supply pressure self-adaptive adjustment algorithm based on multi-sensor data fusion, the algorithm includes: simultaneously collecting the axial displacement of the push rod 11 measured by the displacement sensor 8, the gas supply pressure measured by the pressure sensor, and the bearing area temperature measured by the temperature sensor at a preset sampling period, substituting the axial displacement of the push rod 11 and the temperature into a thermal-force coupling mathematical model of the spindle shaft system to solve the current gas film gap; comparing the solved gas film gap with a preset target gas film gap to obtain a gap deviation, calculating an air inlet pressure correction amount according to the gap deviation by using a proportional-integral-derivative control law, and superimposing the air inlet pressure correction amount on a current gas supply pressure set value, thereby realizing closed-loop constant control of the gas film gap of the front axial thrust air floating bearing 15 and the rear axial thrust air floating bearing 14.

[0043] The control module also adopts a predictive control algorithm for collaborative optimization of cooling water flow and spindle temperature rise, the algorithm includes: slidingly sampling the speed sensor 6, the temperature sensor, and the driving motor 12 current signal at a preset time window to construct a spindle temperature rise prediction model; according to the predicted cylinder 3 temperature and the rotating shaft 5 thermal elongation in the future multiple sampling periods, establishing a performance index function in which a temperature overrun penalty term and a cooling water pump power consumption penalty term are weighted and summed, obtaining an optimal control sequence of the cooling water flow and the gas supply pressure by solving an online constrained optimization problem, and applying the control amount at the first sampling time to the cooling water inlet 20 and the air inlet, thereby reducing energy consumption while ensuring the thermal stability of the spindle.

[0044] The control module also has a main shaft operation state evaluation and fault early warning function, which is realized by the following steps: filtering and normalizing the original data output by the rotation speed sensor 6, the displacement sensor 8, the pressure sensor and the temperature sensor, calculating a multi-dimensional health feature vector containing a gas film gap, an axial thermal elongation, a radial vibration amplitude and a temperature gradient based on a preset health reference working condition; inputting the health feature vector into a main shaft health evaluation model trained through historical operation data to obtain a health degree score, and issuing a maintenance warning when the health degree score is lower than a first threshold value, and automatically reducing the maximum rotation speed or cutting load of the main shaft when the health degree score is lower than a second threshold value, so that sudden failures caused by bearing instability or overheating are avoided.

[0045] Working principle: As shown in Figure 1 The present application based on small hole throttling is generally composed of a cylinder 3, a shell 4, a rotating shaft 5, a front radial air floating bearing 17, a rear radial air floating bearing 13, a front axial thrust air floating bearing 15, a rear axial thrust air floating bearing 14, a driving motor 12, a front end cover 18, a rear end cover 9, a broach mechanism 2 and various sensors and control modules. A spiral cooling waterway is formed between the cylinder 3 and the shell 4, and an air floating bearing working cavity and a driving motor 12 working cavity are formed inside the cylinder 3, and the rotating shaft 5 is supported in the radial and axial directions by the front and rear air floating bearings without contact.

[0046] 1. Air floating support and rotation driving principle Before the main shaft works, the external air compression system supplies compressed gas with stable pressure to the air inlet pipeline 7 on the rear end cover 9. The compressed gas enters the annular air inlet cavity in the shell 4 through the internal flow channel in the rear end cover 9, and then enters multiple axial gas supply channels through the radial gas supply holes uniformly distributed on the wall of the cylinder 3. Each axial channel is connected with the throttling small holes of the front radial air floating bearing 17, the rear radial air floating bearing 13, the front axial thrust air floating bearing 15 and the rear axial thrust air floating bearing 14.

[0047] When the compressed gas enters the small gap between the rotating shaft 5 and the working surface of each bearing through the throttling small holes, the gas expands rapidly in the gap and forms a pressure gradient, and a stable and uniform bearing gas film is formed in the circumferential and radial directions. The radial gas films generated by the front and rear radial air floating bearings 17 and 13 provide high stiffness radial support for the rotating shaft 5, and the axial gas films generated by the front and rear axial thrust air floating bearings 15 and 14 bear the axial cutting force transmitted by the cutter and the workpiece and the weight of the rotating shaft. Since the axial gas supply channels are arranged in series between the bearings, the gas pressure is distributed step by step from the rear to the front, which not only ensures the stiffness of the rear bearing area, but also takes into account the support accuracy of the front bearing area.

[0048] The stator of the drive motor 12 is fixed to the inner wall of the cylinder 3, and the rotor is integrated with the rear end of the shaft 5 by an interference fit or a key. When the CNC system supplies power to the drive motor 12, the stator windings generate a rotating magnetic field, causing the drive motor rotor to rotate, which in turn drives the shaft 5 and the tool holder 19 and tool mounted at its front end to rotate at high speed. Thanks to the non-contact support method of the air bearing, the shaft 5 has minimal friction loss at high speeds, and the operating vibration and noise are significantly reduced.

[0049] After the gas completes its supporting function for each air bearing, it flows into the exhaust channel of the drive motor 12 and the exhaust channels at the front and rear ends of the main shaft through the exhaust grooves and gaps at the bearing ends. Part of it is used to force air exchange and cooling of the drive motor 12, and finally it is discharged from the outside of the main shaft.

[0050] 2. Spiral cooling water circuit and heat balance principle like Figure 3 As shown, the outer surface of the cylinder 3 is machined with multiple reciprocating spiral grooves 22 along the axial direction. After the cylinder 3 is assembled into the housing 4, the reciprocating spiral grooves 22 and the inner wall of the housing 4 together form a closed spiral cooling water channel. Cooling water enters through the cooling water inlet 20 on the rear end cover 9. This inlet is connected to the starting section of the reciprocating spiral grooves 22. The cooling water flows back and forth between the multiple opposite spiral sections along the outer periphery of the cylinder 3 in the direction indicated by the arrow, and finally flows out from the cooling water outlet 21.

[0051] During spindle operation, the copper and iron losses generated by the drive motor 12, the heat generated by bearing film throttling, and the heat generated by cutting are continuously conducted to the cylinder 3 and the housing 4. Cooling water flows along a long path within the reciprocating spiral groove 22, significantly increasing the contact area and contact time with the cylinder 3, resulting in a more uniform circumferential and axial temperature distribution within the cylinder 3, effectively reducing local hot spots and temperature gradients. Combined with the aforementioned forced ventilation cooling of the bearing and motor cavities by compressed gas, the spindle can achieve a relatively stable thermal equilibrium state, thereby reducing the axial thermal elongation and radial thermal bending of the shaft 5, ensuring dimensional stability and positional accuracy during machining.

[0052] 3. Clamping and releasing principle of the broaching mechanism like Figure 1 As shown, the drawbar mechanism 2 mainly consists of a push rod 11 arranged in the hollow cavity of the rotating shaft 5, a piston 10 fixed to the rear end of the push rod 11, a disc spring 16 fitted around the outer periphery of the drawbar 1, and a drawbar 1 that matches the handle 19.

[0053] Under normal clamping conditions, without air pressure, the disc spring 16 is in a compressed state, applying a backward elastic force to the push rod 11 and the puller 1, causing the puller 1 to retract and tightly pull the pull pin of the tool holder 19 into the spindle taper hole, thus achieving reliable clamping of the tool holder 19.

[0054] When automatic tool changing is needed, the CNC system sends high pressure gas to the puller pneumatic interface on the rear cover 9, the gas acts on the pressure end face of the piston 10, generating a forward thrust to overcome the elastic force of the disc spring 16, driving the push rod 11 and the puller 1 to move forward, making the puller 1 disengage or release from the pull pin of the tool holder 19, and the tool holder 19 is taken out under the action of the external robot or tool changing device; after the new tool holder is installed, the gas supply is cut off, the piston 10 is reset under the elastic force of the disc spring 16, the puller 1 is pulled again to the new tool holder 19, and the automatic tool changing is completed.

[0055] The displacement sensor 8 and the push rod 11 are connected by rigidity or magnetic coupling to realize position detection, the control module monitors the axial displacement of the push rod 11 in real time, judges the compression amount of the disc spring 16 and the clamping stroke of the puller 1, and determines whether the tool holder 19 is reliably clamped or completely loosened, so as to realize online monitoring and protection of the tool changing process.

[0056] 4. Multi-sensor closed-loop control and intelligent adjustment principle During the operation of the spindle, the actual speed signal of the rotating shaft 5 is collected in real time by the speed sensor 6, the displacement sensor 8 measures the displacement of the push rod or the end face of the rotating shaft related to the axial thermal elongation, the temperature sensors are distributed at key positions of the bearing area and the cylinder 3 for monitoring temperature changes, and the pressure sensor detects the supply pressure of the gas inlet pipeline 7. The above-mentioned transmission signals are transmitted to the control module, which synchronously collects and data fuses according to the preset sampling period.

[0057] The control module internally pre-establishes a thermal-force coupling mathematical model of the spindle shaft system. During operation, the control module calculates the current axial thermal elongation and gas film gap according to the real-time collected displacement and temperature data, compares the calculated gas film gap with the target gas film gap, and obtains the gap deviation. The control module calculates the gas inlet pressure correction amount by using proportional-integral-derivative (PID) or other adjustment methods, adjusts the pressure of the gas inlet pipeline 7 by controlling the electric proportional valve or mass flow control valve, so that the gas film gaps of the front and rear axial thrust gas-film bearings 15 and 14 are always maintained within a reasonable range, thereby maintaining stable axial stiffness and axial position under different speeds and loads.

[0058] At the same time, the control module establishes a spindle temperature rise prediction model using speed, temperature, driving motor 12 current and other signals, according to the predicted temperature change trend in the future several sampling periods, comprehensively considers the temperature overrun penalty and energy consumption penalty, and optimizes the flow setting at the cooling water inlet 20 and the gas inlet pressure setting online, to realize the collaborative control of compressed gas cooling and water cooling. Through this prediction-feedback combined control method, the spindle of the present application can make adjustments in advance for possible temperature rise and thermal drift, significantly improving thermal stability.

[0059] 5. Operation state evaluation and fault warning principle In order to ensure long-term reliable operation, the control module also integrates the main shaft health state evaluation and fault early warning function. The system filters and normalizes multiple signals such as rotation speed, axial displacement, vibration, temperature, pressure, etc. within a certain time window, constructs a multi-dimensional health feature vector reflecting the gas film gap, axial thermal elongation, radial vibration amplitude, temperature gradient, etc., and inputs it into the pre-trained health evaluation model to output the current health score.

[0060] When the health score is higher than the set threshold, the main shaft is in normal health state; when the score gradually approaches the warning threshold, the control module prompts the operator to perform maintenance inspection through the numerical control system or the upper computer interface; when the score is lower than the safety threshold, the control module automatically limits the maximum rotation speed or cutting load of the main shaft, and interlocks the machine when necessary to prevent serious failure caused by problems such as instability of the air floating bearing, blockage of the throttle small hole, abnormal gas supply or cooling failure, etc.

[0061] Through the above structure cooperation and control strategy, the precision air floating main shaft based on small hole throttling of the present application can still maintain high stiffness, low vibration and excellent thermal stability under the condition of high rotation speed and long time operation, and realize automatic tool changing, online monitoring and intelligent early warning, thereby significantly improving the machining quality and reliability of the ultra-precision machining equipment.

[0062] Embodiment 1 As shown in Figure 1 The present embodiment provides a precision air floating main shaft based on small hole throttling, which is used for installing on a hydrostatic single-point lathe or an ultra-precision machining machine tool to provide high-speed and high-precision rotary support for a workpiece or a tool. The main shaft of the present embodiment mainly comprises: a cylinder barrel 3, a shell 4 sleeved on the outer periphery of the cylinder barrel 3, a front end cover 18 and a rear end cover 9 arranged at both ends of the cylinder barrel 3, a rotating shaft 5 sleeved in the inside of the cylinder barrel 3, a front radial air floating bearing 17 and a rear radial air floating bearing 13 arranged at the middle section of the rotating shaft 5, a front axial thrust air floating bearing 15 and a rear axial thrust air floating bearing 14 arranged at the front and rear end faces of the thrust disc of the rotating shaft 5, a driving motor 12 fixedly connected with the rear end of the rotating shaft 5, a broach mechanism 2 arranged in the hollow inner cavity of the rotating shaft 5, and a rotation speed sensor 6, a displacement sensor 8, a temperature sensor and a pressure sensor for monitoring the operating state of the main shaft.

[0063] The cylinder 3 is a hollow cylindrical structure. Its inner bore, arranged axially, contains a front radial air bearing 17, the middle section of the shaft 5, a rear radial air bearing 13, and the stator mounting section of the drive motor 12. The front end of the cylinder 3 is fixed to the front cover 18 via an interference fit and a locating shoulder, while the rear end is fixed to the rear cover 9 via screws or threads, forming a rigid, integral housing with the front cover 18, cylinder 3, and rear cover 9. The front end of the shaft 5 extends out of the cylinder 3 through the front cover 18, and its front end has a standard tapered hole or straight shank hole for mounting the tool holder 19 and cutting tools. The rear end of the shaft 5 is fixedly connected to the rotor of the drive motor 12 via a locating shoulder, thus forming a direct-drive electric spindle structure.

[0064] The front radial air bearing 17 and the rear radial air bearing 13 are fitted in the middle section of the rotating shaft 5, forming a small radial air film gap between the inner surface of the bearing and the outer circle of the rotating shaft 5. The front axial thrust air bearing 15 and the rear axial thrust air bearing 14 are respectively arranged on the front end face and rear end face of the thrust disk of the rotating shaft 5, forming an axial air film gap between them and the end face of the thrust disk. The axes of the front and rear radial air bearings 17 and 13, the front axial thrust air bearing 15, and the rear axial thrust air bearing 14 are coaxial with the rotation axis of the rotating shaft 5, providing non-contact support for the rotating shaft 5 in both the radial and axial directions.

[0065] In this embodiment, the housing 4 is coaxially sleeved on the outer periphery of the cylinder 3, and an annular gap is reserved between the housing 4 and the cylinder 3 to form an air passage chamber. The housing 4 is provided with an air intake interface connected to an external air compression system. The air intake interface is connected to multiple axial air supply channels in the cylinder 3 wall through an internal air passage. The axial air supply channels have multiple circumferentially distributed small holes at the front radial air bearing 17, the rear radial air bearing 13, the front axial thrust air bearing 15, and the rear axial thrust air bearing 14, respectively, for supplying compressed gas to the gaps between the bearings.

[0066] like Figure 2 As shown, in this embodiment, both the front axial thrust air bearing 15 and the rear axial thrust air bearing 14 are constructed by press-fitting a metal annular seat with an impermeable graphite ring. An annular air groove is formed between the metal annular seat and the impermeable graphite ring. The inlet end of the annular air groove is connected to the axial air supply channel, and its inlet gap is larger than the orifice gap on the outlet side of the impermeable graphite ring. Compressed gas first enters the annular air groove, and after being evenly distributed circumferentially within the groove, it is then sprayed through several throttling orifices arranged on the working surface of the impermeable graphite ring onto the front and rear end faces of the thrust disk of the rotating shaft 5, forming a uniformly pressure-distributed axial bearing air film between the end faces and the thrust disk. By rationally designing the orifice diameter, number, and circumferential distribution of the throttling orifices, this embodiment significantly improves axial stiffness and dynamic stability while ensuring moderate air consumption.

[0067] like Figure 3As shown, in order to effectively control the spindle temperature rise and thermal deformation, a plurality of reciprocating spiral grooves 22 are machined on the outer circumferential surface of the cylinder barrel 3 in the axial direction. After the cylinder barrel 3 is installed inside the housing 4, the reciprocating spiral grooves 22 and the inner wall of the housing 4 form a closed spiral cooling water path. Cooling water enters the spiral cooling water path through the cooling water inlet 20 on the rear end cover 9, reciprocally flows along the plurality of opposite spiral segments, and finally is discharged from the cooling water outlet 21. The cross section of the reciprocating spiral groove 22 is preferably rectangular or trapezoidal, and the width and depth of the groove are substantially uniform in the axial direction, so that the flow rate and heat exchange conditions of the cooling water on the outer periphery of the cylinder barrel 3 are uniform, thereby obtaining a uniform temperature field and reducing the thermal gradient of the cylinder barrel 3 and the rotating shaft 5.

[0068] The drawbar mechanism 2 includes a push rod 11 arranged in the hollow inner cavity of the rotating shaft 5, a piston 10 fixed at the rear end of the push rod 11, a disc spring 16 sleeved on the outer periphery of the drawbar 1, and the drawbar 1 cooperated with the shank 19. The piston 10 is located in the cylinder cavity arranged in the rear end cover 9, and the pressure end face thereof is connected with an external compressed gas source through the drawbar gas control interface on the rear end cover 9. When no compressed gas is introduced, the disc spring 16 is in a compressed state, and exerts a backward elastic force on the push rod 11 and the drawbar 1, so as to tightly clamp the shank 19 in the conical hole at the front end of the rotating shaft 5, thereby realizing reliable clamping of the shank 19. When the compressed gas is introduced, the piston 10 moves forward against the elastic force of the disc spring 16, drives the push rod 11 and the drawbar 1 to move forward, and makes the drawbar 1 and the shank 19 disengage, thereby realizing automatic unclamping and replacement of the shank 19.

[0069] In the embodiment, the rotating speed sensor 6 is preferably installed in the cylinder barrel 3 or the rear end cover 9 to non-contact measure the rotating speed of the tail end of the rotating shaft 5 or the rotating part. The displacement sensor 8 is preferably an eddy current displacement sensor or a linear grating displacement sensor, which is installed in the cylinder barrel 3 or the rear end cover 9 to measure the position of the push rod 11 or the tail end of the rotating shaft 5, so as to reflect the axial thermal elongation and clamping stroke. The temperature sensor can be arranged at the position of the outer wall of the cylinder barrel 3 or the inner wall of the housing 4 near the front and rear gas floating bearings, and the pressure sensor is arranged on the gas inlet pipeline 7 to detect the gas supply pressure.

[0070] In the embodiment, the control module can adopt a conventional industrial controller or a built-in module of a numerical control system to collect and monitor the signals of the above-mentioned sensors, and basically adjust the gas inlet pressure and the cooling water flow through proportional valves or flow valves, so as to verify the rigidity, thermal stability and dynamic response performance of the structure of the present application under typical rotating speed (for example, 30,000-60,000 r / min).

[0071] Embodiment 2: The embodiment is further introduced on the basis of embodiment 1 to introduce a closed-loop control algorithm of multi-sensor data fusion and a spindle health state evaluation and fault early warning function, so as to further improve the thermal stability and operation reliability of the spindle under long-term high-speed operation conditions; the structure, component number and connection relationship thereof are the same as those of embodiment 1.

[0072] In the embodiment, the control module is realized by using an embedded industrial controller or a real-time control board card, and the sampling period of the rotation speed sensor 6, the displacement sensor 8, the temperature sensor and the pressure sensor is set to 1-5 ms. A thermal-force coupling mathematical model of the spindle shaft system is pre-established in the control module: a linear or nonlinear relationship between the bearing area temperature and the axial thermal elongation is obtained through offline calibration ΔL=f(T1,T2,…,T n ), and a relationship between the axial thermal elongation and the gas film gap is h=h0-ΔL, where h0 is the initial gas film gap under the normal temperature static state.

[0073] In the real-time control process, the control module reads the temperature T i (k) measured by each temperature sensor and the axial displacement x(k) measured by the displacement sensor 8 in each sampling period, calculates the current axial gas film gap h(k) according to the thermal-force coupling model, and compares it with the preset target gas film gap h_ref to obtain the deviation e(k)=h_ref-h(k). The control module calculates the inlet pressure correction amount ΔP(k) according to the proportional-integral-derivative control law: ΔP(k)=K_p·e(k)+K_i·∑_{j=0}^{k}e(j)·Δt+K_d·(e(k)-e(k-1)) / Δt; and adjusts the inlet pressure set value P_in(k+1)=P_in(k)+ΔP(k) through the electrical proportional valve or the mass flow control valve, so that the gas film gaps of the front axial thrust gas-film bearing 15 and the rear axial thrust gas-film bearing 14 are stabilized around the target value.

[0074] In order to further suppress the temperature drift of the spindle under long-term high-speed operation conditions, the control module of the embodiment further introduces the model predictive control idea: a sliding time window composed of N sampling periods is used as a prediction domain, and the current rotation speed n(k), the temperature T i(k) and the driving motor 12 current I(k) to build a main shaft temperature rise prediction model to predict the highest temperature T_max(k+p|k) and the axial thermal elongation AL(k+p|k) of the cylinder 3 in the next N sampling periods. On this basis, a performance index function containing temperature overrun, axial thermal elongation and energy consumption weight is established: J = å_{p=1}^{N} [w1 · max(0, T_max(k+p|k) - T_max)² + w2 · (Q_w(k+p) - Q_w)² + w3 · (P_in(k+p) - P_in)²], where T_max is the upper limit of the highest temperature allowed by the cylinder 3, Q_w(k+p) is the cooling water flow rate in the k+p sampling period, Q_w is the cooling water flow rate reference value, P_in(k+p) is the supply air pressure, P_in is the supply air pressure reference value, and w1, w2, w3 are weight coefficients. The control module solves the constrained optimization problem online in each control period to obtain the optimal cooling water flow rate and supply air pressure control sequence in the next N sampling periods, and applies the first step control quantity to the cooling water inlet 20 and the air inlet pipeline 7 to realize collaborative optimization control of the compressed air cooling and water cooling circuit.

[0075] In the health state assessment aspect, the embodiment filters and normalizes the raw data of the rotation speed, axial displacement, vibration signal (which can be obtained by the displacement sensor 8 or an additional vibration sensor), bearing area temperature and temperature gradient, supply air pressure, etc. at fixed time intervals to construct a multi-dimensional health feature vector:

[0076] where h(k) is the current gas film gap estimation value, AL(k) is the axial thermal elongation, v_r(k) is the radial vibration amplitude, T_max(k) is the highest temperature measured by the cylinder 3, is the temperature gradient, and P_in(k) is the supply air pressure. The control module inputs z(k) into the main shaft health assessment model (such as a model based on support vector machine or lightweight neural network) trained by historical life test data, and outputs the current health degree score H(k). When H(k) is lower than the warning threshold H1, a maintenance prompt is issued on the numerical control system or the upper computer interface; when H(k) is further lower than the safety threshold H2, the control module automatically reduces the highest rotation speed or cutting load allowed by the main shaft, and triggers the stop protection if necessary, so that intervention can be made at the early stage of bearing gas film deterioration, small hole blockage, abnormal supply or cooling failure, etc. to avoid serious accidents.

[0077] Through the above embodiment 2, based on the structure design of example 1, further combined with multi-sensor data fusion, adaptive gas supply pressure regulation, cooling water flow prediction control and health state evaluation and fault early warning function, the precision gas floating main shaft based on small hole throttling of the application has higher thermal stability, dynamic precision and operation reliability under high speed and long life working conditions, and is more suitable for long-term stable operation of semiconductor manufacturing and ultra-precision machining equipment.

[0078] The above only describes the preferred embodiments of the present application, and does not limit the patent scope of the present application. Any equivalent structural transformation made by using the content of the present application specification and drawings, or direct / indirect application in other related technical fields under the inventive concept of the present application is included in the protection scope of the present application.

Claims

1. A precision aerostatic spindle based on orifice restriction, characterized by, The application relates to a direct-drive motorized spindle structure, which comprises a front end cover (18), a rear end cover (9), a cylinder barrel (3), a rotating shaft (5) inserted into the cylinder barrel (3), a front radial air floating bearing (17) and a rear radial air floating bearing (13) supporting the rotating shaft (5), a front axial thrust air floating bearing (15) and a rear axial thrust air floating bearing (14) matched with the front and rear end faces of a thrust disc of the rotating shaft (5), a driving motor (12), a broach mechanism (2) and a shell (4). The front end cover (18) and the rear end cover (9) are fixed at the front end and the rear end of the cylinder barrel (3) respectively, the front end of the rotating shaft (5) extends out of the cylinder barrel (3) through the front end cover (18) and is used for connecting a tool shank (19), the rear end of the rotating shaft (5) is fixedly connected with a rotor of the driving motor (12) through a positioning shaft shoulder, and a stator of the driving motor (12) is fixed on the inner wall of the cylinder barrel (3), so as to form a direct-drive motorized spindle structure. The front radial air floating bearing (17) and the rear radial air floating bearing (13) are sleeved on the middle section of the rotating shaft (5), the front axial thrust air floating bearing (15) and the rear axial thrust air floating bearing (14) are arranged on the front end face and the rear end face of the thrust disc of the rotating shaft (5) respectively, and the radial air floating bearing and the axial thrust air floating bearing jointly support the rotating shaft (5) in the radial and axial directions. The outer periphery of the cylinder barrel (3) is sleeved with the shell (4), the outer circular surface of the cylinder barrel (3) is axially provided with a reciprocating spiral groove (22), the reciprocating spiral groove (22) and the inner wall of the shell (4) form a closed spiral cooling water channel, and the rear end cover (9) is provided with a cooling water inlet (20) and a cooling water outlet (21) which are communicated with the spiral cooling water channel. Axial air channels for conveying pressure gas are arranged in the front radial air floating bearing (17), the rear radial air floating bearing (13), the front axial thrust air floating bearing (15) and the rear axial thrust air floating bearing (14), radial air channels are further arranged in the front axial thrust air floating bearing (15) and the rear axial thrust air floating bearing (14), and small-hole throttling structures are arranged on the end faces of the front axial thrust air floating bearing (15) and the rear axial thrust air floating bearing (14) to form bearing gas films. The broach mechanism (2) comprises a push rod (11) arranged in the inner cavity of the rotating shaft (5), a piston (10) fixedly connected with the rear end of the push rod (11), a disc spring (16) sleeved on the outer periphery of a broach (1) and the broach (1) matched with the front end of the rotating shaft (5), the piston (10) is communicated with a pneumatic control interface arranged on the rear end cover (9) to drive the push rod (11) and the broach (1) to axially move under the action of compressed gas, so that the tool shank (19) is clamped and released. A sensor for detecting the working state of the motorized spindle is arranged on one side of the cylinder barrel (3) close to the rear end cover (9), and the sensor comprises a rotating speed sensor (6) for detecting the rotating speed of the tail end of the rotating shaft (5), a displacement sensor (8) for detecting the axial position of the push rod (11), a temperature sensor for detecting the temperature of the bearing area and the cylinder barrel (3) and a pressure sensor for detecting the gas supply pressure. ​ The air floating spindle further comprises a control module electrically connected with the sensors, the control module performs closed loop regulation on the air supply pressure of the air inlet on the rear end cover (9) and the cooling water flow in the spiral cooling water channel according to the output of the rotation speed sensor (6), the displacement sensor (8), the temperature sensor and the pressure sensor, so that the axial thermal elongation and the radial runout of the spindle are kept within a preset range.

2. The precision air floating spindle according to claim 1, characterized in that, The shell (4) is provided with an air inlet cavity, the air inlet cavity is communicated with the axial air supply channels in the cylinder barrel (3) through a plurality of radially distributed radial air supply holes on the cylinder barrel (3), each axial air supply channel extends along the spindle axial direction and is respectively communicated with a plurality of circumferentially distributed axial air holes in the front radial air floating bearing (17), the rear radial air floating bearing (13), the front axial thrust air floating bearing (15) and the rear axial thrust air floating bearing (14), so that the high pressure gas is sequentially distributed to each air floating bearing along the axial direction.

3. The precision air floating spindle according to claim 1, characterized in that, The front axial thrust air floating bearing (15) and the rear axial thrust air floating bearing (14) are each composed of a metal annular seat and a gas impermeable material ring by interference fit press-in connection, the gas impermeable material ring is a gas impermeable graphite material; a ring-shaped air groove is formed between the metal annular seat and the gas impermeable material ring, the pore size of the inlet of the ring-shaped air groove is larger than the pore size of the throttle orifice on the gas impermeable material ring, the high pressure gas first enters the ring-shaped air groove, and then is sprayed to the corresponding shaft (5) thrust disc end face through a plurality of throttle orifices arranged on the gas impermeable material ring, so as to form a uniform and stable axial bearing air film.

4. The precision air floating spindle according to claim 1, characterized in that, The reciprocating spiral groove (22) is arranged as a plurality of opposite spiral segments along the axial direction of the cylinder barrel (3), adjacent spiral segments are connected through a turning groove at the end of the cylinder barrel (3), so as to form a spiral cooling water channel with long flow passage in the axial length; the cross section of the reciprocating spiral groove (22) is rectangular, trapezoidal or semicircular, the depth and width of which remain consistent along the axial direction, so as to ensure the uniform flow of cooling water in the circumferential direction of the cylinder barrel (3).

5. The precision air bearing spindle of claim 1 wherein, The rear end cover (9) adopts an integrated structure, the cooling water inlet (20), the cooling water outlet (21), the spindle air inlet, the spindle air outlet, the motor wiring port, the sensor wiring port and the broach (1) gas control interface are arranged on the integrally processed end cover body, each interface is distributed in a radial or axial array manner, and is communicated with the inside of the cylinder barrel (3) or the inside of the driving motor (12) through the built-in flow channel or cable through hole, so as to reduce the number of external hoses and improve the compactness and assembly reliability of the whole machine.

6. The precision air floating spindle according to claim 1, characterized in that, The precision air floating spindle has a first cooling circuit and a second cooling circuit: the first cooling circuit is a compressed gas cooling circuit, high-pressure gas enters the annular air inlet cavity through the air inlet, flows through the front radial air floating bearing (17), the rear radial air floating bearing (13), and the front axial thrust air floating bearing (15) and the rear axial thrust air floating bearing (14), and after completing the support and cooling of the bearings, enters the driving motor (12) cavity through the exhaust passage formed by the cylinder (3) and the rear end cover (9), and after forced ventilation cooling of the driving motor (12), is discharged; the second cooling circuit is a liquid cooling circuit, cooling water enters the spiral cooling water path through the cooling water inlet (20), flows along the reciprocating spiral groove (22), and is discharged through the cooling water outlet (21), for carrying away the heat generated by the cylinder (3) and the driving motor (12).

7. The precision air floating spindle according to claim 3, characterized in that, The air-tight material ring is made of low air permeability material formed by sintering graphite, ceramic or metal powder and impregnation densification treatment, and has a large number of micro-pores or micro-defect structures inside, each throttling small hole is communicated with the micro-pores or micro-defect structures or to the peripheral dense layer, so that the gas pressure ejected through the throttling small hole is uniformly distributed in the circumferential and radial directions, thereby improving the static stiffness and dynamic stability of the axial thrust air floating bearing.

8. The precision air bearing spindle of claim 1 wherein, The control module adopts a gas supply pressure self-adaptive adjustment algorithm based on multi-sensor data fusion, the algorithm includes: simultaneously collecting the axial displacement of the push rod (11) measured by the displacement sensor (8), the gas supply pressure measured by the pressure sensor, and the bearing area temperature measured by the temperature sensor at a preset sampling period, substituting the axial displacement of the push rod (11) and the temperature into a thermal-force coupling mathematical model of the spindle shaft system to solve the current gas film gap; comparing the obtained gas film gap with a preset target gas film gap to obtain a gap deviation, and calculating an air inlet pressure correction amount according to the gap deviation using a proportional-integral-derivative control law, and superimposing the air inlet pressure correction amount on the current gas supply pressure set value, thereby realizing closed-loop constant control of the gas film gap of the front axial thrust air floating bearing (15) and the rear axial thrust air floating bearing (14).

9. The precision air bearing spindle of claim 1 wherein, The control module also adopts a predictive control algorithm for the optimization of cooling water flow and spindle temperature rise, the algorithm includes: slidingly sampling the speed sensor (6), the temperature sensor, and the driving motor (12) current signal at a preset time window to construct a spindle temperature rise prediction model; according to the predicted cylinder (3) temperature and shaft (5) thermal elongation in the future multiple sampling periods, establishing a performance index function with a weighted sum of a temperature overrun penalty term and a cooling water pump power consumption penalty term, obtaining the optimal control sequence of the cooling water flow and the gas supply pressure by solving the constrained optimization problem online, and applying the control amount at the first sampling time to the cooling water inlet (20) and the air inlet, thereby reducing energy consumption while ensuring the thermal stability of the spindle.

10. The precision air bearing spindle of claim 1 wherein, The control module also has a main shaft operation state evaluation and fault early warning function, which is realized by the following steps: filtering and normalizing the original data output by the rotation speed sensor (6), the displacement sensor (8), the pressure sensor and the temperature sensor, and calculating a multi-dimensional health feature vector containing a gas film gap, an axial thermal elongation, a radial vibration amplitude and a temperature gradient based on a preset health reference working condition; The health feature vector is input into a main shaft health evaluation model trained through historical operation data to obtain a health degree score, and when the health degree score is lower than a first threshold value, a maintenance early warning is issued, and when the health degree score is lower than a second threshold value, the maximum rotation speed or cutting load of the main shaft is automatically reduced, so that sudden failures caused by bearing instability or overheating are avoided.

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