Direct drive clamp shaft

Abstract

The utility model embodiment provides a kind of direct connection drive type clamp shaft, comprising: main shaft component, the first end of its axle rod is equipped with annular empty position, and first end extends out outer shaft sleeve;The outer shaft sleeve is sleeved in the axle rod, and the coaxiality of both is not more than 0.002mm;The second end of the axle rod is connected with the output shaft of motor by coupling. By the coaxiality design of high accuracy, cooperate direct connection drive mode, so that clamp shaft can more stably run in working process. Compared with the coaxiality problem that traditional gear transmission can be caused by assembly error and other factors, the above-mentioned direct connection drive type clamp shaft of the application can better ensure the stability of power transmission, further reduce vibration and noise, and also help to prolong the service life of equipment.

Description

Technical Field

[0001] This utility model relates to the field of electric spindle technology, and in particular to a direct-drive clamping shaft. Background Technology

[0002] With the development of technology, many devices require precision components, especially in fields such as aerospace, precision optical instruments, and high-end electronic manufacturing. High-precision machining has always been one of the bottlenecks restricting industrial development. For example, crystal oscillators used in satellites and chips used in electronic devices are manufactured using processes such as photolithography and etching on silicon wafers, and also include the polishing of optical lenses and mirrors.

[0003] Current electric spindles, especially clamping spindles, are mainly driven by gears. On the one hand, this generates significant friction and vibration between the gears during transmission, especially at high speeds, resulting in loud transmission noise and pollution, which is detrimental to the working environment. On the other hand, transmission losses also affect transmission efficiency. Therefore, this invention proposes a direct-drive clamping spindle to at least partially solve the problems that exist in the prior art. Utility Model Content

[0004] In view of the above problems, the present invention provides a direct-drive clamp shaft that overcomes or at least partially solves the above problems.

[0005] To address the aforementioned problems, this utility model discloses a direct-drive clamp shaft, comprising:

[0006] The spindle assembly has an annular clearance at the first end of its shaft, and the first end extends out of the outer bushing.

[0007] The outer bushing is fitted onto the shaft, and the coaxiality between the two is no greater than 0.002 mm;

[0008] The second end of the shaft is connected to the output shaft of the motor via a coupling.

[0009] Optionally, the spindle assembly further includes:

[0010] An inner bushing is fitted onto the middle of the shaft, and at least two bearings are provided at each end of the bushing, with the inner bushing abutting against the inner ring of the bearings;

[0011] The outer bushing is fitted over the inner bushing and the bearing, and is connected to the outer ring of the bearing.

[0012] Optionally, the second end of the shaft is provided with a collar integrally formed with the shaft, the collar having a first gap on its side, and the output shaft of the motor being nested within the collar;

[0013] The coupling is a non-closed ring, and a second gap is provided on one side; the coupling is also provided with a screw hole that passes through the second gap;

[0014] The coupling is fitted onto the outside of the collar.

[0015] Optionally, the shaft is located on one side of the clearance position, and a disc integral with the shaft is provided at the end of the outer bushing;

[0016] The disk has a protrusion on the side facing the bearing that abuts against the inner ring of the bearing;

[0017] The diameter of the disk is not less than the inner diameter of the outer bushing and not greater than the outer diameter of the outer bushing.

[0018] Optionally, a functional pressure ring is also nested and fixed inside the outer bushing, located on one side of the clearance position;

[0019] The inner side of the functional pressure ring abuts against the outer ring side of the bearing;

[0020] The outer side of the functional pressure ring is provided with an oil seal mounting position, and an oil seal concentric with the functional pressure ring is nested in the oil seal mounting position;

[0021] The protrusion is positioned inside the functional pressure ring and the oil seal, but does not contact them.

[0022] Optionally, the center of the shaft is a hollow cylinder.

[0023] Optionally, a rotating disk is also provided on one side of the shaft located in the coupling;

[0024] The rotating disk is located inside the outer bushing and remains separated from the outer bushing;

[0025] The coupling is located on the outside of the rotating disk.

[0026] Optionally, the end of the outer bushing is further provided with a connecting sleeve for connection to the motor;

[0027] The coupling is located inside the connecting sleeve, and the connecting sleeve is provided with a through hole;

[0028] In the rotational trajectory of the coupling, the screw hole and the through hole are aligned in a straight line.

[0029] Optionally, the motor is a servo motor.

[0030] Optionally, the shaft, located on both sides of the inner bushing, is fitted with at least one first bearing and / or one second bearing respectively; or, the shaft, located on both sides of the inner bushing, is fitted with at least two first bearings or two second bearings on one side, and at least one first bearing and at least one second bearing on the other side.

[0031] The first bearing is a self-aligning ball bearing, and the second bearing is a deep groove ball bearing.

[0032] Optionally, the shaft has two first bearings and one second bearing fitted at one end near the clearance position, wherein the second bearing is located between the two first bearings; or, the shaft has one first bearing and two second bearings fitted at one end near the clearance position, wherein the first bearing is located between the two second bearings.

[0033] The shaft is fitted with two first bearings or two second bearings on the side closest to the fixing groove.

[0034] The embodiments of this utility model have the following advantages:

[0035] The spindle assembly has an annular clearance at the first end of its shaft, and an outer sleeve extends from the first end. The outer sleeve is fitted onto the shaft, and the coaxiality between the two is no greater than 0.002 mm. The second end of the shaft is connected to the output shaft of the motor via a coupling. Through high-precision coaxiality design and a direct-drive method, the fixture shaft can operate more smoothly during operation. Compared to the coaxiality problems that may arise from assembly errors in traditional gear transmissions, the direct-drive fixture shaft of this application better ensures the smoothness of power transmission, further reduces vibration and noise, and also helps extend the service life of the equipment. Attached Figure Description

[0036] Figure 1 This is a schematic diagram of the structure of a direct-drive clamp shaft provided in one embodiment of the present invention;

[0037] Figure 2 This is an exploded view of a direct-drive clamp shaft provided in one embodiment of the present invention;

[0038] Figure 3 This is a cross-sectional structural diagram of a direct-drive clamp shaft provided in one embodiment of the present invention. Detailed Implementation

[0039] To make the above-mentioned objectives, features and advantages of this utility model more apparent and understandable, the utility model will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0040] Reference Figures 1 to 3 The diagram illustrates a direct-drive clamping shaft according to this invention, comprising: a spindle assembly, wherein the first end of the shaft 1 has an annular clearance 104, and an outer bushing 3 extends from the first end; the outer bushing 3 is fitted onto the shaft 1, and the coaxiality between the two is no greater than 0.002 mm; the second end of the shaft 1 is connected to the output shaft of a motor 6 via a coupling 5. The high coaxiality ensures the stability of the shaft 1 during operation. In mechanical transmission, poor coaxiality can cause eccentricity of the shaft during rotation, leading to additional vibration and wear, which is beneficial for the machining of high-precision components. Through a high-precision coaxiality design, combined with a direct-drive method, the clamping shaft can operate more smoothly during operation. Compared to the coaxiality problems that may arise from assembly errors and other factors in traditional gear transmissions, the direct-drive clamp shaft described in this application can better ensure the smoothness of power transmission, further reduce vibration and noise, and also help extend the service life of the equipment.

[0041] In this embodiment, the advantages of direct drive principle are utilized to solve the problems of high transmission noise and relatively low efficiency in traditional clamping shafts. Specifically, the second end of the aforementioned shaft 1 is connected to the output shaft of the motor 6 via coupling 5. Unlike traditional gear transmission, the direct drive of this application avoids the meshing between gears. In gear transmission, the contact and separation process between teeth generates frequent impact forces at high speeds, resulting in significant frictional vibration. Direct drive eliminates these collisions and frictions between gears, fundamentally reducing vibration sources. For example, in traditional gear transmission, when teeth mesh, they continuously collide with each other, transmitting power, and each collision generates vibration; however, this application, through direct drive, directly transmits power via linear connecting rods, eliminating these collision processes, thus significantly reducing vibration. Furthermore, regarding noise, since vibration is a major factor in noise generation, reducing vibration also reduces noise generation. During high-speed operation, vibrations generated by friction and collisions between gears propagate outwards in the form of sound waves, creating significant transmission noise. The direct drive method of this application avoids gear noise sources, effectively reduces noise, thereby improving the working environment and reducing noise pollution.

[0042] Regarding transmission efficiency, traditional gear drives suffer from transmission losses because friction between gears consumes energy. During gear transmission, friction between the gear teeth hinders power transmission, and wear further reduces efficiency over time. This application addresses this issue by using a direct-drive clamp shaft, specifically, a coupling 5 that directly transmits power from the motor 6 to the shaft 1, eliminating intermediate transmission components like gears. Without the friction loss between gears, power can be transmitted more efficiently from the motor 6 to the clamp shaft, reducing losses in intermediate stages and thus improving transmission efficiency.

[0043] In one embodiment of this application, the spindle assembly further includes: an inner sleeve 2, which is fitted onto the middle of the shaft 1, with at least two bearings 4 respectively at both ends, and the inner sleeve 2 abutting against the inner ring of the bearing 4; an outer sleeve 3 is fitted onto the outside of the inner sleeve 2 and the bearings 4, and connected to the outer ring of the bearing 4. The outer sleeve 3 and the inner sleeve 2 are kept parallel; the first end of the shaft 1 is provided with an annular clearance 104, which can be used to install workpieces, for example, in lens lens processing, a fixture can be installed to grind the lens.

[0044] The above structure solves the problem of insufficient precision in traditional clamping shafts. The clamping shaft of this application has a center runout and end runout (roundness error) of no more than 0.002 mm, and an error of no more than 1~1.5×10. 3 This precision, measured in millimeters, enables it to meet the requirements of high-precision grinding machine tools, such as the grinding of high-precision, large-diameter telephoto lenses, playing a crucial role in promoting the development of the domestic precision machining industry. The aforementioned structure employs a nested combination of shaft 1, inner bushing 2, and outer bushing 3, with at least two bearings carefully positioned on both sides of the critical inner bushing, constructing a highly stable shaft support architecture. This fundamentally limits the displacement deviation of the shaft during rotation, ensuring that the shaft always maintains a near-ideal rotation axis, thereby precisely controlling the radial runout and end runout (roundness error caused by axial movement) within an extremely small range of no more than 0.002mm. Such superior precision indicators far surpass those of traditional electric spindles, providing a solid foundation for high-precision machining tasks, effectively avoiding problems such as machining marks on the workpiece surface and affecting dimensional accuracy due to insufficient spindle precision, ensuring that the machined products achieve near-perfect surface quality and dimensional tolerance requirements.

[0045] Through the synergistic effect of the inner and outer bushings and the multi-bearing layout, the shaft is provided with comprehensive and high-strength support, improving the strength, rigidity, and stability of the aforementioned fixture shaft. Multiple bearings distribute the load, reducing the pressure on individual bearings, lowering the risk of wear, extending bearing life, and ensuring the long-term stable operation of shaft 1. Specifically, the outer bushing 3 remains parallel to the inner bushing 2, further standardizing the bearing installation space and running trajectory, effectively resisting external vibrations, impacts, and other interference factors. This allows the electric spindle to maintain high-precision operation even in complex industrial machining environments, reducing machining errors caused by environmental factors and improving the consistency and stability of machining quality.

[0046] In one embodiment of this application, the second end of the shaft 1 (the end connected to the coupling 5) is provided with a collar 101 integrally formed with the shaft 1. The collar 101 has a first gap 102 on its side. The output shaft of the motor 6 is nested and connected inside the collar 101. The coupling 5 is a non-closed ring, and a second gap 501 is provided on one side of it. The coupling 5 is also provided with a screw hole 502 that passes through the second gap 501. The coupling 5 is sleeved on the outside of the collar 101.

[0047] An integral collar 101 is provided at the second end of shaft 1, and the output shaft of motor 6 is nested within the collar 101. This nested connection provides a relatively precise positioning for the docking of the output shaft of motor 6 and shaft 1. During assembly, the operator can easily place the output shaft of motor 6 into the appropriate position based on the size and shape of the collar 101. Similar to a sleeve structure, the shape of the sleeve naturally positions and guides the shaft, allowing the two to be joined together more accurately, reducing the difficulty and error during assembly.

[0048] The coupling 5 has a screw hole 502 that passes through the second gap 501. By installing screws or other connecting parts in the screw hole 502, the coupling 5 can be tightened. On the one hand, this ensures that the coupling 5 is firmly fixed to the outside of the collar 101, further enhancing the stability of the connection between the motor 6 output shaft, shaft 1, and coupling 5, ensuring that there is no relative displacement between the components under conditions such as high-speed operation and high torque transmission. On the other hand, if slight loosening is found in the connection during use, it can be adjusted in time by adjusting the tightness of the screws, ensuring the normal operation of the entire transmission system and improving the flexibility and maintainability of the equipment.

[0049] In one embodiment of this application, the shaft 1 is located on one side of the clearance position 104, and a disk 105 integral with the shaft 1 is provided at the end of the outer bushing 3; the side of the disk 105 facing the bearing 4 has a protrusion 103 that abuts against the inner ring of the bearing 4; the diameter of the disk 105 is not less than the inner diameter of the outer bushing 3 and not greater than the outer diameter of the outer bushing 3. This disk 105 prevents foreign objects from falling into the outer bushing 3, thus affecting its accuracy, and rotates together with the shaft 1 during rotation.

[0050] In one embodiment of this application, a functional pressure ring 7 (also called a threaded ring) is nested and fixed inside the outer bushing 3, located on one side of the clearance position 104, for pressing the bearing and fixing the oil seal; the inner side of the functional pressure ring 7 abuts against the outer ring side of the bearing 4; an oil seal mounting position is provided on the outer side of the functional pressure ring 7, and an oil seal 8 concentric with the functional pressure ring 7 is nested in the oil seal mounting position; the protrusion 103 passes through the functional pressure ring 7 and the oil seal 8, but does not contact them. A rotating disk 9 is also provided on one side of the coupling 5 on the shaft 1; the rotating disk 9 is located inside the outer bushing 3 and is kept separate from the outer bushing 3; the coupling 5 is located outside the rotating disk 9. The end of the outer bushing 3 has an annular groove on one side of the fixing groove 102; this allows the bearing 4 and the inner bushing 2 to be stably fixed inside the outer bushing 3, and the rotating disk 9 to rotate with the shaft, preventing the drive device, such as a gear, from contacting the edge of the outer bushing 3 when it rotates, while also providing protection for the inside of the outer bushing 3.

[0051] In one embodiment of this application, the center of the shaft 1 is a hollow cylinder. Since the shaft is generally rotated during operation, and the shaft 1 is relatively sealed inside the inner bushing 2, especially when rotating at high speed, the heat generated by the shaft 1 is difficult to be released from the surface. The hollow cylinder at the center of the shaft 1 can play a certain role in heat dissipation and can also reduce the overall weight.

[0052] In one embodiment of this application, the end of the outer bushing 3 is further provided with a connecting sleeve 302 for connection with the motor 6; the coupling 5 is located inside the connecting sleeve 302, and the connecting sleeve 302 is provided with a through hole 301; in the rotation trajectory of the coupling 5, the screw hole 502 and the through hole 301 are aligned in a straight line. When the coupling 5 rotates, the screw hole 502 is aligned with the through hole 301, which facilitates the adjustment of the screw in the screw hole 502 from the position of the through hole 502.

[0053] Furthermore, the aforementioned motor 6 is a servo motor. Because servo motors offer more precise rotational control, the directly driven fixture shaft can not only rotate unidirectionally but also reciprocate precisely via servo motor control. This servo motor drive enables programmable machining, allowing for the grinding of irregularly shaped curved glass. Specifically, for example, grinding irregularly shaped curved glass can be programmed. This may require reciprocating rotary grinding, and possibly multiple steps with combined grinding at different rotation amplitudes. By programming and controlling the servo motor in conjunction with the fixture shaft, high-precision grinding can be completed in one operation, significantly improving production efficiency and resulting in a more stable and effective improvement in product accuracy.

[0054] In one embodiment of this application, the shaft 1, located on both sides of the inner bushing 2, is fitted with at least one first bearing and / or one second bearing; wherein the first bearing is a self-aligning ball bearing and the second bearing is a deep groove ball bearing. Alternatively, the shaft 1, located on both sides of the inner bushing 2, may have at least two first bearings or two second bearings fitted on one side, and at least one first bearing and at least one second bearing fitted on the other side.

[0055] Furthermore, the shaft 1 has two first bearings and one second bearing fitted at its first end (the end near the clearance 104), wherein the second bearing is located between the two first bearings; or, the shaft 1 may have one first bearing and two second bearings fitted at its first end, wherein the first bearing is located between the two second bearings; the shaft 1 has two first bearings or two second bearings fitted at its second end. (Refer to...) Figure 2 and Figure 3 As shown, two first bearings and one second bearing are fitted at the first end, and two first bearings are fitted at the second end.

[0056] The aforementioned self-aligning ball bearing, serving as the primary bearing, possesses self-aligning properties, compensating for coaxiality deviations caused by factors such as shaft deflection and installation errors. During the operation of the electric spindle, wear may occur between the shaft 1 and the inner bushing 2 due to machining processes, assembly procedures, or prolonged use. In this situation, the self-aligning ball bearings located on both sides of the inner bushing play a crucial role. Through their own self-aligning structure, they dynamically adjust to ensure the shaft can still rotate smoothly, maintaining high rotational accuracy. This effectively reduces additional vibration and wear caused by shaft misalignment, extending the overall service life of the electric spindle. It is particularly suitable for precision machining scenarios with complex operating conditions and high requirements for shaft dynamic stability.

[0057] The second bearing mentioned above is a deep groove ball bearing, characterized by low friction and high limiting speed, providing smooth rotational support for the shaft. During high-speed operation of the electric spindle, its low-friction characteristics help reduce energy loss and improve energy utilization, enabling the electric spindle to operate more efficiently and meet the stringent speed requirements of high-speed cutting, grinding, and other machining processes. Simultaneously, the high limiting speed ensures that the bearing will not fail prematurely due to excessive speed when the electric spindle pursues higher machining efficiency and increased production capacity, laying the foundation for higher performance expansion of the electric spindle.

[0058] Through the aforementioned hybrid bearing configuration, specifically through various flexible bearing arrangement methods, such as installing at least one first bearing and / or one second bearing on each side, or installing at least two first bearings or two second bearings on one side and at least one first bearing and at least one second bearing on the other side, the advantages of both self-aligning ball bearings and deep groove ball bearings are fully utilized. This hybrid configuration can be tailored to specific machining task requirements, the design specifications of the electric spindle, and the expected service life. For example, for precision optical lens grinding applications requiring extremely high shaft concentricity but with relatively moderate speeds, the configuration of self-aligning ball bearings can be emphasized; while in high-speed milling of metal parts where shaft installation accuracy is guaranteed, appropriately increasing the proportion of deep groove ball bearings can ensure accuracy while achieving high-speed and high-efficiency machining, greatly enhancing the versatility and adaptability of the electric spindle.

[0059] Through multi-bearing collaborative support, regardless of the specific bearing configuration, the arrangement of multiple bearings on both sides of the inner bushing 2 of shaft 1 further strengthens the support for the shaft. Compared to configurations with a single bearing type or a small number of bearings, multiple bearings share the radial force, axial force, and overturning moment on the shaft, enabling the shaft to maintain a stable rotational state even under complex working conditions such as high speed and heavy load. This reduces problems such as shaft deformation and accelerated bearing wear caused by uneven force distribution, thereby continuously ensuring that the electric spindle's excellent heartbeat and end runout accuracy is controlled at a high level of no more than 0.002mm, providing reliable hardware support for high-precision machining. Since different machining tasks may face different working conditions, such as cutting force magnitude, speed range, and vibration environment, the diverse bearing combinations can flexibly cope with these changes. Self-aligning ball bearings ensure basic accuracy by addressing adverse factors such as installation errors and shaft deflection, while deep groove ball bearings contribute to high-speed stable operation. The two complement each other, enabling the electric spindle to accurately meet extremely precision-required tasks, such as grinding high-precision, large-diameter telephoto lenses, whether in a laboratory-level precision machining environment or in relatively noisy and variable industrial conditions. This consolidates and expands the original electric spindle's advantageous position in the field of precision machining.

[0060] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

[0061] Although preferred embodiments of the present invention have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments as well as all changes and modifications falling within the scope of the present invention.

[0062] Finally, it should be noted that in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or terminal device that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or terminal device. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or terminal device that includes said element.

[0063] The above provides a detailed description of a direct-drive clamp shaft provided by this utility model. Specific examples have been used to illustrate the principle and implementation of this utility model. The description of the above embodiments is only for the purpose of helping to understand the method and core idea of ​​this utility model. At the same time, for those skilled in the art, there will be changes in the specific implementation and application scope based on the idea of ​​this utility model. Therefore, the content of this specification should not be construed as a limitation of this utility model.

Claims

1. A direct-drive clamp shaft, characterized in that, include: The spindle assembly has an annular clearance (104) at the first end of its shaft (1), and the first end extends out of the outer bushing (3). The outer bushing (3) is sleeved on the shaft (1), and the coaxiality between the two is not greater than 0.002 mm; The second end of the shaft (1) is connected to the output shaft of the motor (6) via a coupling (5).

2. The direct-drive clamp shaft according to claim 1, characterized in that, The spindle assembly also includes: An inner bushing (2) is sleeved in the middle of the shaft (1), and at least two bearings (4) are provided at both ends of the bushing (2), and the inner bushing (2) abuts against the inner ring of the bearing (4); The outer bushing (3) is fitted around the inner bushing (2) and the bearing (4) and is connected to the outer ring of the bearing (4).

3. The direct-drive clamp shaft according to claim 2, characterized in that, The second end of the shaft (1) is provided with a collar (101) integrally formed with the shaft (1), and the side of the collar (101) is provided with a first gap (102). The output shaft of the motor is nested and connected inside the collar (101). The coupling (5) is a non-closed ring, and a second gap (501) is provided on one side; the coupling (5) is also provided with a screw hole (502) that passes through the second gap (501). The coupling (5) is sleeved on the outside of the collar (101).

4. The direct-drive clamp shaft according to claim 2, characterized in that, The shaft (1) is located on one side of the clearance position (104), and a disc (105) integral with the shaft (1) is provided at the end of the outer bushing (3). The disk (105) has a protrusion (103) on the side facing the bearing (4) that abuts against the inner ring of the bearing (4). The diameter of the disk (105) is not less than the inner diameter of the outer bushing (3) and not greater than the outer diameter of the outer bushing (3).

5. The direct-drive clamp shaft according to claim 4, characterized in that, Inside the outer bushing (3), on one side of the clearance position (104), a functional pressure ring (7) is also nested and fixed. The inner side of the functional pressure ring (7) abuts against the outer ring side of the bearing (4); The outer side of the functional pressure ring (7) is provided with an oil seal mounting position, and an oil seal (8) concentric with the functional pressure ring (7) is nested in the oil seal mounting position. The protrusion (103) is located inside the functional pressure ring (7) and the oil seal (8) but does not contact them.

6. The direct-drive clamp shaft according to claim 1, characterized in that, The center of the shaft (1) is a hollow cylinder.

7. The direct-drive clamp shaft according to claim 2, characterized in that, The shaft (1) is located on one side of the coupling (5) and is also provided with a rotating disk (9). The rotating disk (9) is located inside the outer bushing (3) and remains separated from the outer bushing (3); The coupling (5) is located on the outside of the rotating disk (9).

8. The direct-drive clamp shaft according to claim 3, characterized in that, The end of the outer bushing (3) is also provided with a connecting sleeve (302) that is connected to the motor (6). The coupling (5) is located inside the connecting sleeve (302), and the connecting sleeve (302) is provided with a through hole (301). In the rotational trajectory of the coupling (5), the screw hole (502) and the through hole (301) are aligned in a straight line.

9. The direct-drive clamp shaft according to claim 1, characterized in that, The motor (6) is a servo motor.

10. The direct-drive clamp shaft according to claim 2, characterized in that, The shaft (1) is located on both sides of the inner bushing (2), and is fitted with at least one first bearing and / or one second bearing respectively; or, the shaft (1) is located on both sides of the inner bushing (2), with at least two first bearings or two second bearings fitted on one side, and at least one first bearing and at least one second bearing fitted on the other side. The first bearing is a self-aligning ball bearing, and the second bearing is a deep groove ball bearing.

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