Device and method for measuring overturning rigidity of rolling bearing

Abstract

The invention belongs to the technical field of rolling bearing measurement, and particularly relates to a rolling bearing overturning rigidity measuring device and method, and the device comprises an upper pressing gasket, a loading device, a torque sensor, a motor, a bearing, a lower supporting gasket, a bearing supporting seat, a sensor supporting seat, a platform, a control box, a measuring meter, and a nut A; the motor, the sensor supporting seat and the bearing supporting seat are respectively fixed on the platform; the torque sensor is fixed on the sensor supporting seat, one end of the torque sensor is connected with an output shaft of the motor through a high-rigidity coupling, and the other end of the torque sensor is connected with the loading device through a flange plate and a bolt; according to the method, controllable overturning moment is accurately applied to a bearing outer ring through a high-rigidity and coaxial driving and measuring system, tiny overturning angular displacement generated by the bearing outer ring is synchronously measured, and the overturning rigidity of the bearing is obtained by calculating the slope of a moment-angular displacement relation curve.

Description

Technical Field

[0001] This invention belongs to the field of rolling bearing measurement technology, specifically relating to a device and method for measuring the overturning stiffness of rolling bearings. Background Technology

[0002] Rolling bearings are core components in the machinery industry, and their performance directly affects the precision, lifespan, and reliability of main equipment. In high-end equipment such as precision machine tool spindles, wind turbine gearboxes, industrial robot joints, and heavy machinery slewing supports, the rolling bearings used not only need high precision but also must withstand complex combined loads, such as radial, axial, and overturning moments. Under these conditions, the bearing's overturning stiffness is one of the key parameters for evaluating its performance and ensuring system stability.

[0003] Currently, there is no publicly available, unified standard method for measuring the overturning stiffness of rolling bearings in the industry, and there is a lack of dedicated measuring devices. This results in a lack of critical data support in the bearing design, manufacturing, and selection processes. Therefore, developing an accurate, reliable, and adaptable rolling bearing overturning stiffness measuring device and method is a necessary and urgent task in this field. Summary of the Invention

[0004] The purpose of this invention is to provide a device and method for measuring the overturning stiffness of rolling bearings. The method uses a high-rigidity, coaxial drive and measurement system to precisely apply a controllable overturning torque to the outer ring of the bearing and simultaneously measure the small overturning angular displacement generated therefrom. The overturning stiffness of the bearing is obtained by calculating the slope of the torque-angular displacement relationship curve.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: A device for measuring the overturning stiffness of a rolling bearing includes an upper pressure washer, a loading device, a torque sensor, a motor, a bearing, a lower support washer, a bearing support seat, a sensor support seat, a platform, a control box, a measuring instrument, and nut A. The motor, sensor support, and bearing support are fixed on the platform. The torque sensor is fixed on the sensor support, and one end of the torque sensor is connected to the output shaft of the motor through a high-rigidity coupling. The other end of the torque sensor is connected to the loading device through a flange and bolts. The inner ring of the bearing is fixed on the bearing support through a lower support washer, an upper pressure washer, and nut A. The loading device contacts the end face of the outer ring of the bearing and applies a torsional torque to the outer ring, causing the outer ring to tilt relative to the inner ring. The measuring instrument is installed on the end face of the outer ring of the bearing. The described loading device consists of a loading rod, a loading bar, nut B, and a rubber sleeve; the loading rod is overall in an "⊥" shape, with its "丨" structure connected to a torque sensor, a through slot is opened in the middle of the "—" structure to connect the loading bar, and there is a scale marked on one side, with the "0" scale in the middle; there are two loading bars, one side of the loading bar is a threaded structure and is fixed on the loading rod through nut B, and a rubber sleeve is installed on the other side of the loading bar. The two loading bars are symmetrically installed on the loading rod with the "0" scale as the center. The distance between the two loading bars is determined by the outer diameter of the bearing outer ring, ensuring that the rubber sleeve can apply force to the end face of the bearing outer ring during loading and does not interfere with the cage and the bearing inner ring.

[0006] Further, the bearing support seat is overall in a "convex" shape, and a threaded rod is provided on the upper part of the bearing support seat. The threaded rod is used to install the lower support washer, the bearing, the upper pressure washer, and nut A.

[0007] Further, the outer diameter of the upper pressure washer is smaller than the outer diameter of the bearing inner ring and larger than the inner diameter of the bearing inner ring; the inner diameter of the upper pressure washer is larger than the diameter of the threaded rod of the bearing support seat and is used to press the bearing inner ring.

[0008] Further, the radius of the known outer diameter surface of the bearing is R; the measuring gauge is set at a position H away from the outer diameter on the end face of the bearing outer ring, and the connection line with the center of the bearing is perpendicular to the loading bar.

[0009] Further, the rubber sleeve is overall in a circular ring shape. The rubber sleeves are respectively installed on one side of the two loading bars and are at the same distance from the loading rod, and are used to directly contact the bearing end face; the center connection line of the two rubber sleeves intersects with the axis of the bearing, ensuring that when an inclined torque is applied to the bearing, it can directly act on the center line of the bearing, enabling the contact area during loading of the bearing outer ring to be a surface contact, accurately controlling the loading force within this area, avoiding the uncertainty of the contact point position between the loading bar and the bearing surface caused by the influence of the工装加工精度 (workpiece processing accuracy), and also avoiding damage to the bearing surface caused by the direct contact between the loading bar and the bearing surface.

[0010] Further, the lower support washer is overall a circular ring with a boss. The outer diameter of the boss is the same as the inner diameter size of the bearing, and they are in clearance fit; the overall outer diameter size of the lower support washer is smaller than the outer diameter of the bearing inner ring; the inner diameter of the lower support washer is the same as the diameter of the threaded rod on the bearing support seat, and they are in clearance fit; by adjusting the width of the lower support washer, the center of the bearing width and the center of the torque sensor are on the same horizontal plane.

[0011] Further, the control box is electrically connected to the motor and the torque sensor. The control box is used to control the start and stop of the motor, set the target torque value, collect torque data, and implement the function of automatically stopping after reaching the preset torque.

[0012] Furthermore, the smooth operation of the motor drives the torque sensor to rotate, and the torque sensor drives the loading device to act on the outer ring of the bearing, thereby generating torque. When the torque sensor reaches the specified torque, it transmits the signal to the control box, and then the control box issues a command to stop the motor. At this time, the bearing is subjected to overturning torque.

[0013] A method for operating a device for measuring the overturning stiffness of a rolling bearing includes the following steps: S1. Fix the inner ring of the bearing to the bearing support, while the outer ring of the bearing is in a free state; S2. Install a measuring instrument on the end face of the bearing outer ring to ensure that the bearing outer ring is horizontal and that the radial center of the bearing outer ring and the radial center of the bearing inner ring are in the same plane. At this time, zero the reading of the measuring instrument. S3. By using a motor-driven torque sensor, a preload torque M0 is applied to the outer ring of the bearing via a loading device to eliminate the internal clearance of the bearing and maintain this torque state. S4. Apply a series of increasing test torques Mi in sequence, where Mi>M0, and record the actual torque value Mx and the measured value Sx for each load. Calculate the overturning angle θx corresponding to each load load using the formula θx= arctan(Sx / (RH)), where R is the outer ring radius of the bearing and H is the distance from the measuring instrument contact point to the outer diameter of the bearing. Plot the curve of the relationship between torque M and overturning angle θ, select the linear region, and calculate the slope of this region as the overturning stiffness K of the bearing, K=(Mx-My) / (θx-θy), where (Mx,θx) and (My,θy) are two sets of data points within the linear region.

[0014] The beneficial effects of this invention are as follows: The rolling bearing overturning stiffness measuring device and method provided by this invention adopts closed-loop control of a motor and a high-precision torque sensor, ensuring precise torque application; the use of preload torque to eliminate gaps ensures that data is collected from the actual elastic deformation zone; by setting the zero point of the measuring instrument, the influence of bearing axial clearance on the overturning torque measurement is avoided; the spacing of the loading bars in the loading device is adjustable, adaptable to bearings with different outer diameters; a rubber sleeve at the end of the loading bar forms a surface contact with the bearing end face, protecting the bearing surface and avoiding stress concentration and positional uncertainty caused by point contact. Overall, the rolling bearing overturning stiffness measuring device and method of this invention fills the gap in the quantitative measurement of rolling bearing overturning stiffness in the industry and meets the needs of the rolling bearing industry for measuring bearing overturning stiffness. Attached Figure Description

[0015] Figure 1 This is an overall schematic diagram of the device and method of the present invention; Figure 2 This is a top view of the apparatus and method of the present invention; Figure 3This is a schematic diagram of the bearing installation, loading, and measuring instrument installation of the present invention; Figure 4 This is a schematic diagram of the loading mechanism of the present invention; Figure 5 This is a schematic diagram of the loading rod of the present invention; Figure 6 This is a schematic diagram of the loading rod of the present invention; Figure 7 This is a schematic diagram of the loading rod's state before loading in this invention; Figure 8 This is a schematic diagram of the state of the loading rod after loading according to the present invention; The following are the labels in the diagram: 1. Upper pressure washer, 2. Loading device, 3. Torque sensor, 4. Motor, 5. Bearing, 6. Lower support washer, 7. Bearing support seat, 8. Sensor support seat, 9. Platform, 10. Control box, 11. Measuring gauge, 12. Nut A, 21. Loading rod, 22. Loading bar, 23. Nut B, 24. Rubber sleeve. Detailed Implementation

[0016] Specific Embodiment 1: The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. It should be noted that: In the present invention, unless otherwise specified, all implementation methods and preferred implementation methods mentioned herein can be combined with each other to form new technical solutions. In the present invention, unless otherwise specified, all technical features and preferred features mentioned herein can be combined with each other to form new technical solutions. The "scope" disclosed in the present invention can be in the form of a lower limit and an upper limit, and can be one or more lower limits and one or more upper limits, respectively.

[0017] First, the basic idea of ​​this invention is to precisely apply a controllable overturning torque to the outer ring of bearing 5 using a high-rigidity, coaxial drive and measurement system, while simultaneously measuring the resulting minute overturning angular displacement. The overturning stiffness of bearing 5 is obtained by calculating the slope of the torque-angular displacement relationship curve. Specifically, the inner ring of bearing 5 is fixed, while the outer ring is in a free state. A loading system consisting of motor 4 and torque sensor 3, via a dedicated loading device 2 adaptable to different bearing 5 sizes, applies a pure torque to the end face of the outer ring of bearing 5. The displacement change of the end face of the outer ring of bearing 5 is monitored by measuring gauge 11 and converted into an overturning angle. By analyzing the relationship between the applied torque and the resulting overturning angle, the overturning stiffness is calculated.

[0018] Specifically, see the instruction manual. Figure 1 Instruction manual attached Figure 2, attached to the specification Figure 3 and attached to the specification Figure 4 As shown, a measuring device for the tilting stiffness of a rolling bearing 5 of the present invention includes an upper pressure washer 1, a loading device 2, a torque sensor 3, a motor 4, a bearing 5, a lower support washer 6, a bearing support seat 7, a sensor support seat 8, a platform 9, a control box 10, a measuring gauge 11, and a nut A 12; the motor 4, the sensor support seat 8, and the bearing support seat 7 are respectively fixed on the platform 9; the torque sensor 3 is fixed on the sensor support seat 8, and one end of the torque sensor 3 is connected to the output shaft of the motor 4 through a high-rigidity coupling, and the other end of the torque sensor 3 is connected to the loading device 2 through a flange and a bolt; the inner ring of the bearing 5 is fixed on the bearing support seat 7 through the lower support washer 6, the upper pressure washer 1, and the nut A 12; the loading device 2 contacts the end face of the outer ring of the bearing 5 and applies a torsional moment to the outer ring of the bearing 5, causing the outer ring of the bearing 5 to generate an inclination moment relative to the inner ring of the bearing 5; the measuring gauge 11 is installed on the end face of the outer ring of the bearing 5; the loading device 2 includes a loading rod 21, a loading bar 22, a nut B 23, and a rubber sleeve 24; the loading rod 21 is integrally in an "⊥" shape, its "丨" structure is connected to the torque sensor 3, a through groove is opened in the middle of the "—" structure to connect the loading bar 22, and a scale is marked on one side, with the "0" scale in the middle; two loading bars 22 are provided, one side of the loading bar 22 is a threaded structure and is fixed on the loading rod 21 through the nut B 23, and a rubber sleeve 24 is installed on the other side of the loading bar 22. The two loading bars 22 are symmetrically installed on the loading rod 21 with the "0" scale as the center, and the distance between the two loading bars 22 is determined by the diameter of the outer ring of the bearing 5, ensuring that the rubber sleeve 24 can apply force to the end face of the outer ring of the bearing 5 during loading and does not interfere with the cage and the inner ring. The rubber sleeve 24 in the present invention is integrally in a circular ring shape, and the rubber sleeve 24 is respectively installed on one side of the two loading bars 22 and at the same distance from the loading rod 21 for direct contact with the end face of the bearing 5; the center connection line of the two rubber sleeves 24 intersects with the axis of the bearing 5 to ensure that when an inclination moment is applied to the bearing 5, it can directly act on the center line of the bearing 5, enabling the contact area at the outer ring of the bearing 5 during loading to be a surface contact, accurately controlling the loading force within this area, avoiding the uncertainty of the contact point position between the loading bar 22 and the surface of the bearing 5 caused by the influence of the processing accuracy of the tooling, and at the same time avoiding damage to the surface of the bearing 5 caused by the direct contact between the loading bar 22 and the surface of the bearing 5.

[0019] The present invention will be further described below in conjunction with the specification drawings and specific embodiments: First, based on the theoretical drawings of the rolling bearing 5 under test, determine the radius R of the outer diameter surface of the outer ring of bearing 5. Install and fix the bearing support 7, sensor support 8, and motor 4 onto platform 9. Secure bearing 5 to bearing support 7 using upper pressure washer 1, lower support washer 6, and nut A12. Connect torque sensor 3 to motor 4 and fix it to sensor support 8. One side of loading rod 21 is connected to torque sensor 3, and the other side is used to install and fix two loading rods 22. Loading rods 22 are symmetrically installed onto loading rod 21 using nuts B23. Loading rods 22 are positioned above and below both ends of the outer ring of bearing 5. Install two rubber sleeves 24 onto loading rods 22, equidistant from loading rod 21. The state of loading rods 22 at this time is as shown in the attached instruction manual. Figure 7 As shown. Place the measuring gauge 11 on the outer ring end face of the bearing 5, away from the loading rod 22, at a distance H from the outer diameter of the bearing 5. Simultaneously, the contact point between the measuring gauge 11 and the bearing 5, the contact point between the loading rod 22 and the bearing 5, and the axial center of the bearing 5 should all be in the same vertical plane. The flexibility of the loading structure allows adjustment of the spacing of the loading rods 22 to accommodate bearings 5 ​​with different outer diameters. The rotation center of the motor 4, the rotation center of the torque sensor 3, and the center of the bearing 5 are coaxial. Through the design and planning of the installation and fixing of the motor 4, torque sensor 3, and bearing support 7, the rotation centers of the motor 4 and torque sensor 3 are made coaxial and in the same vertical plane as the threaded rod center of the bearing support 7. Adjust the size of the lower support washer 6 according to the inner diameter and width of the bearing 5 to make the center of the bearing 5 coaxial with the rotation centers of the motor 4 and torque sensor 3. Before measurement, the outer ring of the bearing 5 should be horizontal. Using a tool, make the radial center of the outer ring of the bearing 5 and the radial center of the inner ring of the bearing 5 in the same plane, then zero the reading of the measuring gauge 11. This action can prevent the axial clearance of bearing 5 from affecting the measurement of overturning moment.

[0020] By setting the feedback value of torque sensor 3 to M0 through control box 10, motor 4 is made to run smoothly at a speed of 1-3 rpm. Motor 4 drives torque sensor 3 to rotate, and torque sensor 3 drives loading device 2 to act on the outer ring of bearing 5, thereby generating torque. At this time, the state of loading rod 22 is as shown in the attached instruction manual. Figure 8As shown. When the torque sensor 3 reaches the specified torque M0, it transmits a signal to the control box 10. Then, the control box 10 issues a command to stop the motor 4 and lock it. M0 is the preload torque, the specific value of which needs to be determined according to the model and size of the bearing 5 being measured. It must be sufficient to eliminate clearance but avoid causing any plastic deformation. It should be noted that the control box is a common measurement and control system in this field, which is implemented by integrating an industrial standard programmable logic controller (PLC), human-machine interface (HMI), and data acquisition module. This type of system is widely used in closed-loop control and data acquisition of physical quantities such as torque and displacement, and belongs to existing technology. For example, by using a Siemens S7-1200 series PLC, a Weintek MT8102IE touch screen, and a matching analog input module, a control system with motor start / stop control, torque value setting and acquisition, and automatic shutdown function after reaching the preset value can be constructed. Therefore, this invention directly applies this existing technology to realize its control and data acquisition functions.

[0021] After the preload torque M0 is applied and stabilized, a series of incremental test torque target values ​​Mi are set in the control box 10, where Mi > M0, i = 1, 2, 3... For each Mi, the loading process is repeated. After the torque stabilizes, the actual torque value Mx fed back by the torque sensor 3 and the reading Sx of the measuring instrument 11 are recorded. The formula for calculating the overturning angle θx is as follows: θx=arctan(Sx / (R -H)) (1) Calculate the overturning angle θx corresponding to each loading step using the above formula, where R is the outer ring radius of bearing 5. Plot the relationship curve between torque M and overturning angle θ, the M-θ curve. Select the linear region of this curve; the slope of this region is the overturning stiffness K of bearing 5. The formula for calculating stiffness K is as follows: K=(Mx-My) / (θx-θy) (2) Where (Mx,θx) and (My,θy) are any two sets of data points within the linear region; Substituting equation (1) into equation (2), we obtain the following formula for calculating the overturning stiffness of bearing 5: K=(Mx-My) / (arctan(Sx / (RH))-arctan(Sy / (RH))) (3) In equation (3), (Mx, Sx), (My, Sy) are the readings of gauge 11, Sx and Sy, when the test torques are Mx and My, respectively. R is the outer ring radius of bearing 5, and H is the distance between gauge 11 and the outer diameter of bearing 5.

[0022] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A measuring device for the overturning stiffness of a rolling bearing, characterized in that, It includes an upper pressure washer (1), a loading device (2), a torque sensor (3), a motor (4), a bearing (5), a lower support washer (6), a bearing support seat (7), a sensor support seat (8), a platform (9), a control box (10), a measuring gauge (11), and a nut A (12); The motor (4), the sensor support seat (8), and the bearing support seat (7) are respectively fixed on the platform (9); the torque sensor (3) is fixed on the sensor support seat (8), and one end of the torque sensor (3) is connected to the output shaft of the motor (4) through a high-rigidity coupling, and the other end of the torque sensor (3) is connected to the loading device (2) through a flange and bolts; the inner ring of the bearing (5) is fixed on the bearing support seat (7) through the lower support washer (6), the upper pressure washer (1), and the nut A (12); the loading device (2) contacts the end face of the outer ring of the bearing (5) and applies a torsional moment to the outer ring of the bearing (5), causing the outer ring of the bearing (5) to generate an inclined moment relative to the inner ring of the bearing (5); the measuring gauge (11) is installed on the end face of the outer ring of the bearing (5). The loading device (2) includes a loading rod (21), a loading bar (22), a nut B (23), and a rubber sleeve (24); the loading rod (21) is integrally in an "⊥" shape, its "丨" structure is connected to the torque sensor (3), a through slot is opened in the middle of the "—" structure to connect the loading bar (22), and a scale is marked on one side, with the "0" scale in the middle; there are two loading bars (22), one side of the loading bar (22) is a threaded structure and is fixed on the loading rod (21) through the nut B (23), and a rubber sleeve (24) is installed on the other side of the loading bar (22), and the two loading bars (22) are symmetrically installed on the loading rod (21) with the "0" scale as the center, and the distance between the two loading bars (22) is determined by the outer diameter of the outer ring of the bearing (5) to ensure that the rubber sleeve (24) can apply to the end face of the outer ring of the bearing (5) during loading without interfering with the cage and the inner ring of the bearing (5).

2. The measuring device for the overturning stiffness of a rolling bearing according to claim 1, characterized in that, The bearing support seat (7) is integrally in a "convex" shape, and a threaded rod is provided on the upper part of the bearing support seat (7), and the threaded rod is used to install the lower support washer (6), the bearing (5), the upper pressure washer (1), and the nut A (12).

3. The measuring device for the overturning stiffness of a rolling bearing according to claim 2, characterized in that, The outer diameter of the upper pressure washer (1) is smaller than the outer diameter of the inner ring of the bearing (5) and larger than the inner diameter of the inner ring of the bearing (5); the inner diameter of the upper pressure washer (1) is larger than the diameter of the threaded rod of the bearing support seat (7) and is used to compress the inner ring of the bearing (5).

4. The measuring device for the overturning stiffness of a rolling bearing according to claim 3, characterized in that, The measuring gauge (11) is set at a position H away from the outer diameter on the end face of the outer ring of the bearing (5), and the connection line with the center of the bearing (5) is perpendicular to the loading bar (22).

5. The measuring device for the overturning stiffness of a rolling bearing according to claim 1, characterized in that, The rubber sleeve (24) is generally circular. The rubber sleeve (24) is installed on one side of the two loading rods (22) and at the same distance from the loading rod (21) for direct contact with the end face of the bearing (5). The center line of the two rubber sleeves (24) intersects the axis of the bearing (5) to ensure that when the tilting torque is applied to the bearing (5), it can directly act on the center line of the bearing (5). This allows the outer ring of the bearing (5) to be in surface contact when loaded, and the loading force is precisely controlled within this area. This avoids the uncertainty of the contact point between the loading rod (22) and the bearing (5) surface caused by the tooling machining accuracy. It also avoids the loading rod (22) directly contacting the bearing (5) surface and causing damage to the bearing (5) surface.

6. The measuring device for the overturning stiffness of a rolling bearing according to claim 1, characterized in that, The lower support washer (6) is a ring with a boss. The outer diameter of the boss is the same as the inner diameter of the bearing (5), and the two are fitted with a clearance. The outer diameter of the lower support washer (6) is smaller than the outer diameter of the inner ring of the bearing (5). The inner diameter of the lower support washer (6) is the same as the diameter of the threaded rod on the bearing support seat (7), and the two are fitted with a clearance. The width of the lower support washer (6) is adjusted so that the center of the width of the bearing (5) and the center of the torque sensor (3) are on the same horizontal plane.

7. The measuring device for the overturning stiffness of a rolling bearing according to claim 1, characterized in that, The control box (10) is electrically connected to the motor (4) and the torque sensor (3). The control box (10) is used to control the start and stop of the motor (4), set the target torque value, collect torque data, and realize the function of automatically stopping after reaching the preset torque.

8. The measuring device for the overturning stiffness of a rolling bearing according to claim 7, characterized in that, The motor (4) drives the torque sensor (3) to rotate smoothly. The torque sensor (3) drives the loading device (2) to act on the outer ring of the bearing (5), thereby generating torque. When the torque sensor (3) reaches the specified torque, it transmits the signal to the control box (10). Then the control box (10) issues a command to stop the motor (4) from running. At this time, the bearing (5) bears the overturning torque.

9. The method of operating the measuring device for the overturning stiffness of a rolling bearing as described in any one of claims 1-8, characterized in that, Includes the following steps: S1. Fix the inner ring of the bearing (5) to the bearing support (7), and leave the outer ring of the bearing (5) in a free state. S2. Install a measuring instrument (11) on the end face of the outer ring of the bearing (5) to ensure that the outer ring of the bearing (5) is horizontal and that the radial center of the outer ring of the bearing (5) and the radial center of the inner ring are in the same plane. At this time, zero the reading of the measuring instrument (11). S3. The torque sensor (3) is driven by the motor (4) to apply a preload torque M0 to the outer ring of the bearing (5) via the loading device (2) to eliminate the internal clearance of the bearing (5) and maintain the torque state. S4. Apply a series of increasing test torques Mi in sequence, where Mi>M0, and record the actual torque value Mx and the reading Sx of the measuring instrument (11) each time; calculate the overturning angle θx corresponding to each loading according to the formula θx= arctan(Sx / (RH)), where R is the outer ring radius of the bearing (5) and H is the distance from the contact point of the measuring instrument (11) to the outer diameter of the bearing (5); plot the relationship curve between torque M and overturning angle θ, select the linear region, and calculate the slope of the region as the overturning stiffness K of the bearing (5), K=(Mx-My) / (θx-θy), where (Mx,θx) and (My,θy) are two sets of data points in the linear region.

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