An axial error compensation mechanism for an air floating shaft

Abstract

An axial error compensation mechanism for an air-bearing spindle belongs to the technical field of ultra-precision machining equipment. The spindle rotor is coaxially arranged inside the inner cavity of the bearing housing, and a driving device is arranged between the spindle rotor and the bearing housing. The driving device can drive the spindle rotor to move axially. The overall structure of the present invention is relatively compact. The actual axial position of the spindle rotor is determined by the signals obtained by the axial displacement sensor and the axial velocity sensor, and is compared with the theoretical position. The electromagnetic force generated by the driving device is used to directly control the axial movement of the spindle rotor to eliminate the difference between the two, compensate for the axial error of the air-bearing spindle, and improve the machining accuracy of the machine tool. Since the axial movement of the spindle rotor can be controlled, the machining of non-rotationally symmetric surfaces can also be achieved. The air-bearing spindle of the present invention has high axial stiffness, and at the same time, the air-bearing spindle unit can replace the function of the axial slide block of the lathe, which reduces the total number of guide rails of the lathe and increases the structural ring stiffness between the workpiece and the tool.

Description

Technical Field

[0001] The present invention belongs to the technical field of ultra-precision machining equipment, and particularly relates to an axial error compensation mechanism for an air-bearing spindle. Background Art

[0002] In the field of ultra-precision machining equipment, the precision requirements for machined parts are getting higher and higher. Due to the advantages of small friction, small temperature rise, large load-bearing capacity, high precision, etc., aerostatic bearings are widely used in ultra-precision machining equipment. An aerostatic bearing uses gas as a lubricant and relies on a gas pressure source to provide a constant pressure. After the compressed gas passes through the throttle orifice, a lubricating gas film is formed at the coupling surface between the shaft and the bearing sleeve. The lubricating gas film can completely float the shaft and its load and provide support stiffness for it. Since the lubricating film has the function of error averaging, it can reduce the influence of the machining errors of bearing components on the rotational accuracy of the air-bearing. When the load on the bearing changes, the coupling surface gap between the shaft and the bearing sleeve changes. Due to the principle of gas partial pressure, the partial pressure is large at the place where the coupling surface gap between the shaft and the bearing sleeve is small, so that the shaft can always be kept at the center position of the bearing sleeve. Due to the high precision, small friction, small temperature rise, and error averaging function of the aerostatic bearing, the aerostatic bearing is widely used in the field of ultra-precision machining equipment.

[0003] Although the aerostatic bearing has so many above-mentioned advantages, with the continuous miniaturization of precision products, the tolerances of parts are constantly getting smaller. Due to the existence of the axial error of the aerostatic bearing, it is difficult for ultra-precision machine tools to meet the requirements when machining miniaturized parts, especially when machining miniaturized parts by the process of end turning. Using a spindle with a rigid coupling between the axial and radial bearing surfaces, the accuracy of the workpiece turning surface is mainly limited by the axial error motion of the spindle. This motion is caused by the alignment error of the axial bearing surfaces of the spindle and the bearing housing relative to the spindle rotation axis. The spindle makes a sine wave motion axially every revolution. The surface turned on such a spindle will have a shape deviation. Another influence of the spindle axial error motion is the excitation of the machine frame, which may cause resonance in the machine tool equipment. Summary of the Invention

[0004] In order to reduce the axial error of the aerostatic bearing, improve the axial stiffness of the aerostatic bearing and simultaneously realize the machining of non-rotationally symmetric surfaces, the present invention provides an axial error compensation mechanism for an air-bearing spindle.

[0005] The technical solution adopted by the present invention is as follows:

[0006] An axial error compensation mechanism for an air-bearing spindle, comprising a bearing housing, a spindle rotor and a driving device; the spindle rotor is coaxially arranged in the inner cavity of the bearing housing, and a driving device is arranged between the spindle rotor and the bearing housing, and the driving device can drive the spindle rotor to move axially.

[0007] The present invention has the following beneficial effects compared with the prior art:

[0008] 1. The overall structure of the present invention is relatively compact. The actual axial position of the main shaft rotor is determined by the signals obtained by the axial displacement sensor and the axial velocity sensor, and compared with the theoretical position. The electromagnetic force generated by the driving device is used to directly control the axial movement of the main shaft rotor to eliminate the difference between the two, compensating for the axial error of the air-bearing shaft. This can avoid the shape error of the machined workpiece caused by the alignment error of the axial bearing surfaces of the main shaft rotor and the bearing housing relative to the rotation axis of the main shaft rotor, improving the machining accuracy of the machine tool. Since the axial movement of the main shaft rotor can be controlled, the machining of non-rotationally symmetric surfaces can also be achieved.

[0009] 2. The electromagnetic force generated by the permanent magnet and the coil in the present invention directly acts on the main shaft rotor, resulting in a high axial stiffness of the air-bearing shaft. At the same time, the air-bearing main shaft unit can replace the function of the axial slide block of the lathe, reducing the total number of guide rails of the lathe and increasing the structural ring stiffness between the workpiece and the tool.

[0010] 3. Since a part of the magnetic circuit of the driving device is installed on the balance mass in the present invention, the mass of the rotating parts is reduced.

[0011] 4. Since the balance mass is connected to the bearing housing through the electromagnetic force generated by the coil and the permanent magnet, the reaction force of the balance mass acting on the bearing housing is reduced.

[0012] 5. Since the axial movement of the main shaft rotor is controlled by the driving device, the axial error movement of the main shaft can be offset, avoiding the resonance of the machine tool equipment caused by the axial error movement of the main shaft.

[0013] 6. Since the axial movement of the main shaft rotor is controlled by the driving device, the machining of non-rotationally symmetric surfaces can be achieved.

[0014] 7. Since the axial displacement sensor is arranged on the side close to the machined part, the influence of temperature change on the measurement accuracy is reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 is a schematic structural diagram of the present invention;

[0016] Wherein: 1, bearing housing; 2, axial velocity sensor; 3, rotational speed sensor; 4, balance mass position sensor; 5, balance mass; 6, driving device; 61, permanent magnet A; 62, coil A; 7, connecting device; 71, permanent magnet B; 72, coil B; 8, main shaft rotor; 9, axial displacement sensor; 10, pin. DETAILED DESCRIPTION OF THE INVENTION

[0017] To better understand the purpose, structure and function of the present invention, the following further describes the present invention in detail with reference to the accompanying drawings.

[0018] Referring to Figure 1 As shown, an axial error compensation mechanism for an air floating shaft of the present invention includes a bearing seat 1, a main shaft rotor 8 and a driving device 6; the main shaft rotor 8 is a cylindrical structure, the main shaft rotor 8 is coaxially arranged in the inner cavity of the bearing seat 1, and a driving device 6 is arranged between the main shaft rotor 8 and the bearing seat 1, and the driving device 6 can drive the main shaft rotor 8 to move axially.

[0019] The axial error compensation mechanism for the air floating shaft further includes a balance mass 5; the balance mass 5 is coaxially and gap - arranged between the driving device 6 and the bearing seat 1, and the driving device 6 includes a permanent magnet A61 and a coil A62; the permanent magnet A61 is fixed on the main shaft rotor 8 through its magnetic seat, the coil A62 is fixed on the balance mass 5 through its coil seat, and the driving device 6 controls the axial movement of the main shaft rotor 8 through electromagnetic force.

[0020] The coil A62 of the driving device 6 is on the balance mass 5, reducing the mass of the main shaft rotor 8. A closed magnetic circuit is formed between the permanent magnet A61 and the coil A62. When the coil A62 is energized, an axial force will be generated between the permanent magnet A61 and the coil A62 under the action of the magnetic field, so as to control the axial movement of the main shaft rotor 8. By changing the polarity of the voltage at both ends of the coil A62, the movement direction of the main shaft rotor 8 can be controlled. Since the electromagnetic force directly acts on the main shaft rotor 8, the axial stiffness of the air floating shaft is improved;

[0021] The raised parts at both ends of the inner cavity of the bearing seat 1 cooperate with the main shaft rotor 8 to form a radial bearing of the main shaft, and the middle raised part of the inner cavity of the bearing seat 1 cooperates with the balance mass 5 to form a radial bearing of the balance mass 5.

[0022] A connecting device 7 is installed between the balance mass 5 and the bearing seat 1; the connecting device 7 includes a permanent magnet B71 and a coil B72; the permanent magnet B71 is fixed on the balance mass 5 through its magnetic seat, and the coil B72 is fixed on the bearing seat 1 through its coil seat. The electromagnetic force generated by the connecting device 7 acts on the balance mass 5, and can reduce the reaction force of the balance mass 5 acting on the bearing seat 1.

[0023] The balance mass 5 is connected to the bearing seat 1 through the electromagnetic force generated by the coil and the permanent magnet. Since the balance mass 5 and the bearing seat 1 are not rigidly connected, when the balance mass 5 makes high - frequency axial reciprocating movements, the force of the balance mass 5 acting on the bearing seat 1 will be less than the force of the balance mass 5 acting on the main shaft rotor 8, reducing the reaction force of the balance mass 5 acting on the bearing seat 1.

[0024] Axial velocity sensors 2 and axial displacement sensors 9 are respectively arranged at both ends of the main shaft rotor 8 for detecting the axial velocity and displacement of the main shaft rotor 8. The axial displacement sensor 9 is a cylindrical grating sensor and is arranged on the side close to the machined part to reduce the influence of temperature change on the measurement accuracy.

[0025] A rotational speed sensor 3 is arranged in the middle of the main shaft rotor 8 for detecting the rotational speed of the main shaft rotor 8.

[0026] A balance mass position sensor 4 is arranged at one end of the balance mass 5 close to the axial velocity sensor 2.

[0027] The rotational speed sensor 3 and the balance mass position sensor 4 are an integrated optical measurement system. The rotational speed sensor 3 consists of a ring with slits and a reading head. The balance mass position sensor 4 outputs the balance mass position by detecting the magnitude of the light source signal obtained by the reading head of the rotational speed sensor 3.

[0028] This error compensation mechanism determines the actual axial position of the main shaft rotor 8 through the signals obtained by the axial displacement sensor 9 and the axial velocity sensor 2, compares it with the theoretical position, and directly controls the axial movement of the main shaft rotor 8 by using the electromagnetic force generated by the driving device 6 to eliminate the difference between the two, compensates the axial error of the air floating shaft, and improves the machining accuracy of the machine tool.

[0029] The connecting device 7 is arranged at one end of the balance mass 5 far from the axial velocity sensor 2.

[0030] The axial length of the coil A62 of the driving device 6 is greater than the axial length of the closed magnetic circuit air gap, so that the length of the coil A62 in the magnetic circuit is constant, and the electromagnetic force acting on the main shaft rotor 8 can be controlled by controlling the magnitude of the current passing through the coil A62.

[0031] The balance mass 5 is connected to the bearing block 1 through a pin 10 to restrict its rotation without restricting its axial movement. The pin 10 is arranged along the axis of the bearing block 1. One end of the pin 10 is fixedly connected to the bearing block 1, and the other end of the pin 10 is slidably inserted into the chute arranged on the balance mass 5, so as to realize the limit of the balance mass 5. Alternatively, one end of the pin 10 is slidably connected to the chute of the bearing block 1, and the other end of the pin 10 is fixedly connected to the balance mass 5.

[0032] It will be understood that the present invention is described by way of some embodiments, and those skilled in the art will know that various changes or equivalent replacements can be made to these features and embodiments without departing from the spirit and scope of the present invention. Additionally, under the teaching of the present invention, these features and embodiments can be modified to adapt to specific circumstances and materials without departing from the spirit and scope of the present invention. Therefore, the present invention is not limited by the specific embodiments disclosed herein, and all embodiments falling within the scope of the claims of this application belong to the scope protected by the present invention.

Claims

1. An axial error compensation mechanism for an air floating shaft, characterized in that: It includes a bearing housing (1), a main shaft rotor (8) and a driving device (6); the main shaft rotor (8) is coaxially arranged in the inner cavity of the bearing housing (1), and the driving device (6) is arranged between the main shaft rotor (8) and the bearing housing (1), and the driving device (6) can drive the main shaft rotor (8) to move axially. The air floating shaft axial error compensation mechanism further includes a balance mass (5); the balance mass (5) is coaxially arranged with a gap between the driving device (6) and the bearing housing (1), and the driving device (6) includes a permanent magnet A (61) and a coil A (62); the permanent magnet A (61) is fixed on the main shaft rotor (8), the coil A (62) is fixed on the balance mass (5), and the driving device (6) controls the axial movement of the main shaft rotor (8) through electromagnetic force. A connecting device (7) is installed between the balance mass (5) and the bearing housing (1); the connecting device (7) includes a permanent magnet B (71) and a coil B (72); the permanent magnet B (71) is fixed on the balance mass (5), the coil B (72) is fixed on the bearing housing (1), and the electromagnetic force generated by the connecting device (7) acts on the balance mass (5), which can reduce the reaction force of the balance mass (5) acting on the bearing housing (1). The balance mass (5) is connected to the bearing housing (1) through a pin (10) to restrict its rotation but not its axial movement. Axial speed sensors (2) and axial displacement sensors (9) are respectively arranged at both ends of the main shaft rotor (8) to detect the axial speed and displacement of the main shaft rotor (8). The actual axial position of the main shaft rotor (8) is determined through the signals obtained by the axial displacement sensor (9) and the axial speed sensor (2), and compared with the theoretical position. The electromagnetic force generated by the driving device (6) is used to directly control the axial movement of the main shaft rotor (8) to eliminate the difference between the two, compensating for the axial error of the air floating shaft.

2. The axial error compensation mechanism of an air floating shaft according to claim 1, wherein: The raised parts at both ends of the inner cavity of the bearing housing (1) cooperate with the main shaft rotor (8) to form a radial bearing of the main shaft, and the middle raised part of the inner cavity of the bearing housing (1) cooperates with the balance mass (5) to form a radial bearing of the balance mass (5).

3. The axial error compensation mechanism of an air floating shaft according to claim 1, wherein: A speed sensor (3) is arranged in the middle of the main shaft rotor (8) to detect the speed of the main shaft rotor (8).

4. The axial error compensation mechanism of the air floating shaft according to claim 3, wherein: A balance mass position sensor (4) is arranged at one end of the balance mass (5) close to the axial speed sensor (2).

5. The axial error compensation mechanism of an air floating shaft according to claim 1, characterized in that: The axial length of the coil A (62) of the driving device (6) is greater than the axial length of the closed magnetic circuit air gap. By controlling the magnitude of the current passing through the coil A (62), the electromagnetic force acting on the main shaft rotor (8) can be controlled.

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