A method and device for adjusting axial force balance of double-row self-aligning roller bearings

Abstract

The present application relates to the technical field of wind turbine bearing, in particular to a method and device for adjusting axial force balance of double-row self-aligning roller bearing, the device comprises an axial force applying assembly arranged outside the bearing seat, the axial force applying assembly is composed of a ring-shaped positioning element and a plurality of groups of elastic elements arranged uniformly along the circumference in the cavity of the positioning element, the inner ring of the positioning element extends radially inward and projects to cover the outer ring of the bearing, one end of the elastic element faces the inner part of the cavity, and the other end contacts the outer ring of the bearing through a pressure equalizing ring. The present application generates a reverse additional support force under the action of axial load, actively transfers part of the load from the stressed side bearing row to the non-stressed side, solves the problem that the roller contact stress of the stressed side of the existing double-row self-aligning roller bearing is too high under the single-sided axial load working condition, and early fatigue spalling is easily caused, realizes the balanced distribution of axial force, effectively reduces the peak contact stress, and significantly prolongs the service life of the bearing.

Description

Technical Field

[0001] This invention relates to the field of wind turbine generator bearing technology, specifically to a method and apparatus for adjusting the axial force balance of a double-row self-aligning roller bearing. Background Technology

[0002] In large rotating machinery such as wind turbines, double-row self-aligning roller bearings are widely used for main shaft support due to their excellent self-aligning performance and high load-carrying capacity. In actual operation, axial loads are often transmitted through the inner ring of one bearing. In traditional designs, after passing through the inner ring, this axial force is primarily transmitted to the outer ring and bearing housing via the row of rollers directly corresponding to the load-bearing side, while the other row of rollers bears almost no axial force. This "single-row load" condition results in the contact stress on the load-bearing rollers being much higher than the design average, easily leading to early fatigue spalling and severely shortening the service life of the bearing and even the entire transmission chain.

[0003] Currently, common solutions focus on optimizing bearing clearance, improving material grades, or enhancing lubrication. However, these methods are all passive and cannot fundamentally change the unequal distribution of axial load between the two rows of rollers. Therefore, the market urgently needs a technical solution that can actively and adaptively balance the axial load distribution within double-row bearings to solve the problem of premature failure of single-row rollers caused by uneven axial load distribution. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a method and apparatus that are compact in structure, reliable in installation, and capable of actively balancing loads. This apparatus introduces a controllable elastic support on the non-directly stressed side of the bearing, dynamically adjusting the axial force distribution between the two rows of rollers, enabling the two rows of rollers to work together to bear the load, thereby significantly reducing the maximum contact stress and extending the bearing life.

[0005] The technical solution adopted in this invention is: a device for adjusting the axial force balance of a double-row self-aligning roller bearing, comprising an axial force application component disposed on the outside of the bearing and bearing housing, the axial force application component being composed of several sets of elastic elements and positioning elements, the positioning element being an annular structure disposed on the outer surface of the bearing housing, the inner ring surface of which extends inward toward the center of the bearing, the projection of the extended portion covering the outer ring of the bearing, the extended portion of the positioning element having a cavity with an opening facing the outer ring of the bearing, the several sets of elastic elements being uniformly disposed inside the cavity, one end of which faces the inside of the cavity, the other end contacting the outer ring of the bearing through a pressure equalizing ring and applying pressure to the outer ring of the bearing, the double-row self-aligning roller bearing comprising a left bearing row, a right bearing row, and an outer ring of the bearing disposed on the outside of the rotating shaft.

[0006] As a preferred embodiment, the positioning element is provided with a screw hole, and the adjusting screw passes through the screw hole to fix the positioning element to the bearing seat. One end of the adjusting screw facing the inside of the bearing is lower than the equalizing ring, and the other end is provided with a locking nut for locking the adjusting screw. The compression of the elastic element is controlled by tightening the adjusting screw diagonally in stages.

[0007] As a preferred embodiment, the elastic element is a disc spring, a cylindrical helical spring, or elastic rubber, and several sets of the elastic elements are uniformly and symmetrically arranged in the cavity of the positioning element along the circumferential direction of the bearing.

[0008] A method for adjusting the axial force balance of a double-row self-aligning roller bearing includes the following steps: S1. Load parameter determination: Obtain the maximum unilateral axial load under the operating conditions of the double-row self-aligning roller bearing. And the force difference between the bearing rows on the stressed side and the bearing rows on the unstressed side under the maximum axial load when the balancing device is not installed. The force difference This is equal to the additional support reaction force generated by further compression of the elastic element. ,Right now ; S2. Elastic system parameter design: Determine the allowable axial compensation displacement based on the bearing's internal clearance. Based on the difference in force With axial compensation displacement The total equivalent elastic coefficient required to calculate the elastic system is obtained by using Hooke's law. The calculation formula is: Based on the total equivalent elasticity coefficient Determine the number n of elastic elements and the elastic coefficient of a single elastic element. ,satisfy And the number of elastic elements Less than the maximum number that can be arranged along the circumference ; S3. Device installation and pre-tightening: The elastic element is pre-compressed and installed in the mounting cavity of the positioning element. The device is fixed to the outer end face of the bearing housing by the positioning element. The elastic element abuts against the non-stressed end face of the outer ring of the bearing through the pressure equalizing ring. The compression amount of the elastic element is adjusted to set the initial axial pre-tightening force. S4. Adaptive Balanced Operation: When the inner ring of the bearing is subjected to axial load, the inner ring drives the bearing row to generate axial displacement, compressing the elastic element to generate a support force opposite to the axial load, transferring part of the load from the bearing row on the stressed side to the bearing row on the unstressed side, thus achieving adaptive balanced distribution of axial force in the double-row bearings.

[0009] Furthermore, in step S2, the number of elastic elements n and the elastic coefficient k of a single elastic element must also satisfy the following constraints: a) Spatial constraint: n is not greater than the maximum number of bearing housings that can be installed along the circumference on the outer end face of the bearing housing; b) Strength constraint: The maximum load that a single elastic element can withstand. The rated load of the selected elastic element .

[0010] Furthermore, in step S2, the elastic coefficient is calculated. Make it satisfy The specific steps are as follows: First, pre-select a size based on available space and common specifications. Value, the minimum quantity required for calculation Then Select a suitable interval and verify the strength constraints. If the conditions are not met, then select again. Larger components or adjustments to design goals Continue until all conditions are met.

[0011] As a preferred option, in step S2, the elastic system adopts a graded or nonlinear stiffness design, with at least two sets of elastic elements with different elastic coefficients stacked in series along the axial direction or connected in parallel along the circumferential direction; under low load conditions, the elastic element with the smaller elastic coefficient provides the balancing force, and under high load conditions, the two sets of elastic elements work together to improve the overall stiffness of the system to match the load changes.

[0012] The beneficial effects of this invention are: To address the shortcomings of existing technologies, this invention provides a method and apparatus for adjusting the axial force balance of double-row self-aligning roller bearings. Through optimized structural design, this invention achieves the following technical advantages: Firstly, this invention sets a pre-compressed elastic element and a matching positioning structure between the outer ring end face of the non-directly stressed side of the double-row self-aligning roller bearing and the bearing housing, and precisely designs the total equivalent stiffness of the elastic system. This allows the elastic element to generate a reverse additional support force under external axial load, thereby dynamically transferring part of the load from the stressed side to the non-stressed side. This method actively intervenes and optimizes the axial load transmission path inside the bearing, realizing the adaptive balance and coordinated bearing of the axial force of the double-row rollers. It significantly reduces the peak contact stress of the rollers on the stressed side and effectively solves the problem in the prior art where axial load imbalance causes the single-row rollers to bear high contact stress too early, which easily leads to early fatigue spalling.

[0013] Secondly, this invention can design the elastic system to have graded or nonlinear stiffness characteristics. By stacking or paralleling at least two sets of elastic elements with different elastic coefficients in the axial direction, the elastic system can switch stiffness working modes in different load ranges. This design allows the balancing device to achieve sensitive load response with low stiffness under normal working conditions or small axial loads, and to provide greater additional support force with high stiffness after the load increases to a certain threshold. This ensures that the device can maintain efficient load distribution capability under a wide range of axial load changes, further expanding the applicable working conditions of the device, improving the reliability of the bearing system throughout its entire life cycle, and solving the problem that a single stiffness elastic system cannot simultaneously meet the response sensitivity of small loads and the support force requirements of large loads under a wide range of loads, resulting in a significant decrease in load sharing effect with load changes.

[0014] Third, this invention proposes a key parameter design method for elastic elements based on "balancing the force difference on both sides," which clarifies the calculation method of the total equivalent elastic coefficient and the steps for determining the elastic coefficient and quantity of a single elastic element. It also provides iterative optimization constraints for matching space, strength, and stiffness, as well as optimal strategies for engineering implementation. This design method can quickly complete the design of balancing devices adapted to different wind turbine main shaft bearings, solving the problems of existing axial force balancing technologies lacking clear parameter design guidance, being difficult to implement in engineering, and being unable to quickly adapt to bearing design requirements under different working conditions.

[0015] Fourth, this invention provides a dedicated positioning structure for radial constraint of the elastic element, and sets an equalizing ring between the elastic element and the outer ring end face of the bearing. Multiple elastic elements are evenly arranged along the circumferential direction. This structural design can ensure that the position of the elastic element is stable and does not deviate during the operation of the bearing, and can also make multiple elastic elements bear force evenly and effectively prevent point contact. This achieves uniform load transfer, significantly improves the working reliability and service life of the balancing device itself, and ensures the stability of the bearing load distribution. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 This is a schematic diagram of the structure of the present invention; Figure 2 This is a schematic diagram illustrating the principle of axial load distribution and balance. (See diagram:) -External axial load; - The bearings on the left side are under stress; The bearings on the right side are under stress; -Reaction force of elastic element; Figure 3 This is a schematic diagram of the elastic element in this invention; Figure 4 This is a graph showing the trend of deformation and force of the elastic element in this invention (F). A F B F C They are respectively Figure 3 (The corresponding forces acting on the elastic element when it deforms to points A, B, and C). Figure 5 A schematic diagram of the positioning element.

[0018] In the diagram: 1-rotating shaft; 2-left bearing row; 3-right bearing row; 4-bearing outer ring; 5-bearing housing; 6-elastic element; 7-positioning element; 8-pressure equalizing ring. Detailed Implementation

[0019] The present invention will now be described in detail through exemplary embodiments. However, it should be understood that, without further description, elements, structures, and features in one embodiment may be advantageously incorporated into other embodiments.

[0020] It should be noted that, unless otherwise defined, the technical or scientific terms used herein should have the ordinary meaning understood by one of ordinary skill in the art to which this invention pertains. The terms "a," "an," or "the," and similar words used in the specification and claims of this patent application do not express a limitation of quantity, but rather indicate the presence of at least one; terms such as "comprising" or "including" indicate that the elements or objects preceding "comprising" encompass the elements or objects listed following "comprising" or "including" and their equivalents, but do not exclude other elements or objects having the same function.

[0021] To more clearly describe the specific structural composition of the method and device used for adjusting the axial force balance of double-row self-aligning roller bearings, see attached... Figure 1 -Appendix Figure 4 This embodiment is described as follows: The following is an embodiment of a method and apparatus for adjusting the axial force balance of a double-row self-aligning roller bearing: The specific implementation of the present invention is as follows: A device for balancing the axial force of a double-row self-aligning roller bearing includes an axial force application assembly disposed on the outside of the bearing housing 5. The axial force application assembly consists of several sets of elastic elements 6 and positioning elements 7. The positioning element 7 is an annular structure disposed on the outer surface of the bearing housing 5, with its inner ring surface extending inward toward the bearing center. The projection of its extended portion covers the outer ring 4 of the bearing. The extended portion of the positioning element 7 has a cavity with an opening facing the outer ring 4 of the bearing. The several sets of elastic elements 6 are evenly disposed inside the cavity, with one end facing the inside of the cavity and the other end contacting the outer ring 4 of the bearing through a pressure equalizing ring 8. The elastic elements 6 are compressed and installed to provide a continuous initial axial preload pointing inward to the right bearing row 3. The positioning element 7 is provided with a screw hole, and an adjusting screw passes through the screw hole to fix the positioning element 7 to the bearing housing 5. One end of the adjusting screw is lower than the pressure equalizing ring 8, and the other end is provided with a locking nut for locking the adjusting screw. The compression amount of the elastic element 6 is controlled by tightening the adjusting screw step by step diagonally.

[0022] The elastic element 6 can be one or more of a disc spring, a cylindrical helical spring, or elastic rubber. When multiple elastic elements 6 are used, they are evenly arranged in the circumferential direction. When the elastic element 6 is installed between the outer ring 4 of the bearing and the bearing housing 5, the positioning structure is used to radially constrain the elastic element 6; and a pressure equalizing ring 8 is provided between the elastic element 6 and the end face of the outer ring 4 of the bearing to ensure that the multiple elastic elements 6 are subjected to uniform force and to prevent point contact.

[0023] Furthermore, as an extension of the above, the elastic support structure of the present invention is not limited to an elastic element 6 with a single stiffness. In order to better cope with a wide range of varying axial loads, the elastic system can be designed to have graded or nonlinear stiffness characteristics.

[0024] For example, multiple sets can be stacked and connected in series in the axial direction, or at least two sets of elastic elements with different elastic coefficients can be arranged in parallel along the circumferential direction. Under normal operating conditions or small axial loads, F a1 The first group of elements with smaller elastic moduli deform and provide balancing forces, resulting in low overall system stiffness and sensitive response. When the load increases to a specific threshold F... a2 When the deformation of the first group of components reaches the design stroke, it begins to work together with the second group of components with a larger elastic coefficient. The overall stiffness of the system then increases to provide a greater support reaction force to balance the high load.

[0025] This "soft-hard" combination or graded stiffness design enables the balancing device to maintain efficient load distribution capabilities across different load ranges, further broadening the applicable operating conditions of the invention and improving the reliability of the bearing system throughout its entire life cycle.

[0026] Furthermore, a method for adjusting the axial force balance of a double-row self-aligning roller bearing to ensure effective load balance is provided. This mainly includes the following steps: 1. Determination of load parameters: Assume the maximum unilateral axial load that the wind turbine is expected to withstand during operation is Without this device installed, this load is almost entirely borne by the right-side bearing row 3 (at which time the force is...). The force on bearing row 2 on the left is ( The design goal of this device is to... Under the action, the left bearing row 2 is subjected to force. Force on the right bearing row 3 Towards equilibrium, that is, to significantly reduce the force difference. .

[0027] The elastic element 6 is installed on the right side, and the additional support reaction force generated by its further compression It acts directly on the right-side bearing row 3, in the direction of the external axial load. The force transmitted to bearing row 3 on the right is in the opposite direction. This reaction force is the key force used to balance the force difference on both sides. Under the target operating condition, the approximate relationship is as follows: .

[0028] 2. Elastic system parameter design: To achieve the target load allocation, in Under operating conditions, the allowable axial displacement of the right-side bearing row 3 (together with the elastic support system) relative to the bearing housing 5 is: (This displacement must be within the allowable range of the bearing's internal clearance, typically 0.1-0.5 mm). According to Hooke's Law, the balancing force provided by an elastic system is proportional to the amount of deformation, i.e. ,in, Let be the total equivalent elastic coefficient after all 6 elastic elements are connected in parallel. Combining the above equations, we get: This formula shows that, in order to eliminate the target force difference under maximum load... The total stiffness of the required elastic system.

[0029] Number of elastic elements 6 ( ) and a single coefficient ( The determination of ) If the elastic coefficient is selected as The same elastic element If installed in parallel, then Therefore, based on the steps described above, determine... After that, the elastic modulus of a single component and quantity The product should satisfy this value. The specific choice requires iterative optimization in conjunction with the following constraints: a) Space constraints: Determine the maximum number that can be arranged along the circumference based on the dimensions of the installation location. .

[0030] b) Strength constraint: In Under operating conditions, the force borne by a single elastic element 6 The rated load of the selected elastic element 6. Must be greater than And leave a safety margin (usually ≥1.5 times).

[0031] c) Stiffness matching: the final determination and Should meet (To achieve or exceed the design balance effect), and .

[0032] In terms of engineering, one can first pre-select a model based on the available space and commonly used specifications. Value, calculate the minimum number of elastic elements required (6). Then Select a suitable interval and verify the strength constraints. If the conditions are not met, then select again. Value of the elastic element 6 or adjustment of design target Continue until all conditions are met.

[0033] 3. Installation and pre-tightening of the device: The elastic element 6 is pre-compressed and installed in the mounting cavity of the positioning element 7. The device is fixed to the outer end face of the bearing seat 5 by the positioning element 7. The elastic element 6 abuts against the non-stressed end face of the outer ring 4 of the bearing through the pressure equalizing ring 8. The compression amount of the elastic element 6 is adjusted to set the initial axial pre-tightening force. 4. Adaptive Balanced Operation: When the inner ring of the bearing is subjected to axial load, the inner ring drives the bearing row to generate axial displacement, and the compression elastic element 6 generates a support reaction force opposite to the axial load, transferring part of the load from the bearing row on the stressed side to the bearing row on the unstressed side, thereby realizing the adaptive balanced distribution of axial force in the double-row bearing.

[0034] Working principle: When axial load When applied to the inner ring of the bearing from the left, in the initial state, due to the preload of the elastic element 6 on the right, the left bearing row 2 already bears part of the axial force. With the axial load... As the bearing inner ring assembly increases, it tends to move to the right, thereby compressing the elastic element 6 on the right side. The support reaction force generated by the compression of the elastic element... The force acts directly on the right-side bearing row 3, and its direction is the same as... The component force acting on the right-side bearing row 3 through the inner ring is in the opposite direction. According to the principle of force balance, This effectively "offsets" some of the force that would normally be borne directly by the right-side rollers, and transfers this load through the inner ring to the left-side bearing row 2. This is achieved through precise design of the elastic system's stiffness. It can accommodate external axial loads of different sizes. The difference in axial force shared by the two rows of rollers under the action. It is controlled within a preset, small range, thereby achieving adaptive balance and load distribution.

[0035] Given a certain wind turbine main shaft bearing, the maximum unilateral axial load that may occur during its operation is F. amax =200kN. Based on actual measurements or simulation analysis, under this load, without this device installed, the load distribution is extremely uneven. Assuming the right-side bearing row 3 is under stress... kN, bearing row 2 on the left is subjected to force. kN, then the force difference on both sides kN.

[0036] The design goal of this device is to significantly reduce this force difference, and it is expected that at F amax Under operating conditions, the forces on both sides are adjusted to near equilibrium, for example, by making kN, kN. The new force difference at this point. kN.

[0037] 1. Determine the required balancing force: To achieve the above objective, the balancing force that the device needs to provide is the force difference that needs to be "canceled," i.e. kN. This is the design load that the elastic system needs to withstand.

[0038] 2. Determine the overall stiffness: Based on the bearing's internal clearance, set the allowable axial compensation displacement. The total equivalent stiffness required by the elastic system is... =80000N / 0.25mm=320000N / mm.

[0039] 3. Selection and Configuration of Elastic Element 6: Pre-select a certain model of disc spring with a single leaf stiffness of [missing information]. N / mm. To obtain the required deformation, a "two-piece series connection as a group" method is used, then the stiffness of a single group is... The value is 20000 N / mm. Theoretically, the minimum number of elements required is... Considering the limitations of installation space and load distribution, it was ultimately decided to use 24 sets of the springs, evenly arranged along the circumference.

[0040] 4. Strength verification: The actual force that each set of springs can withstand. kN, far below the spring's rated load, ensuring safety. This not only fully meets the 80kN design requirement with a margin, but also proves that this configuration can reduce the stress difference under the most unfavorable working conditions to an extremely low level, and may even achieve... and They are completely equal.

[0041] It should be noted that although the present invention has been described through the above embodiments, the present invention may have many other embodiments. Without departing from the spirit and scope of the present invention, those skilled in the art can obviously make various corresponding changes and modifications to the present invention, but all such changes and modifications should fall within the scope of protection of the appended claims and their equivalents.

Claims

1. A method for adjusting the axial force balance of a double-row self-aligning roller bearing, characterized in that, A device for adjusting the axial force balance of a double-row self-aligning roller bearing is provided, comprising an axial force application assembly disposed on the outside of the bearing housing (5). The axial force application assembly consists of several sets of elastic elements (6) and positioning elements (7). The positioning element (7) is a ring-shaped structure disposed on the outer surface of the bearing housing (5), with its inner ring surface extending inward toward the bearing center. The projection of its extended portion covers the outer ring (4) of the bearing. The extended portion of the positioning element (7) has a cavity with an opening facing the outer ring (4) of the bearing. The several sets of elastic elements (6) are evenly disposed inside the cavity, with one end facing into the cavity. The other end of the bearing is in contact with the outer ring (4) of the bearing through the equalizing ring (8) and applies pressure to the outer ring (4). The double-row self-aligning roller bearing includes a left bearing row (2), a right bearing row (3) and an outer ring (4) located outside the rotating shaft (1). The positioning element (7) is provided with a screw hole. The adjusting screw passes through the screw hole to fix the positioning element (7) to the bearing seat (5). One end of the adjusting screw facing the inside of the bearing is lower than the equalizing ring (8). The other end is also provided with a locking nut for locking the adjusting screw. The compression of the elastic element (6) is controlled by tightening the adjusting screw diagonally in steps. The elastic element (6) is a disc spring, a cylindrical helical spring or elastic rubber, and several sets of the elastic elements (6) are uniformly and symmetrically arranged in the cavity of the positioning element (7) along the circumferential direction of the bearing. Includes the following steps: S1. Load parameter determination: Obtain the maximum unilateral axial load under the operating conditions of the double-row self-aligning roller bearing. And the force difference between the bearing row on the stressed side and the bearing row on the unstressed side under the maximum unilateral axial load when the balancing device is not installed. The force difference This is equal to the additional support reaction force generated by the further compression of the elastic element (6). ,Right now ,in For the left bearing row (2) to be subjected to force, The bearing row (3) on the right side is subjected to force; S2. Elastic system parameter design: Determine the allowable axial compensation displacement based on the bearing's internal clearance. Based on the difference in force With axial compensation displacement The total equivalent elastic coefficient required to calculate the elastic system is obtained by using Hooke's law. The calculation formula is: Based on the total equivalent elasticity coefficient Determine the number n of elastic elements (6) and the elastic coefficient of a single elastic element (6). ,satisfy And the number of elastic elements (6) Less than the maximum number that can be arranged along the circumference ; S3. Installation and pre-tightening of the device: The elastic element (6) is pre-compressed and installed in the mounting cavity of the positioning element (7). The device is fixed to the outer end face of the bearing seat (5) by the positioning element (7). The elastic element (6) abuts against the non-forced end face of the outer ring (4) of the bearing through the equalizing ring (8). The compression amount of the elastic element (6) is adjusted to set the initial axial pre-tightening force. S4. Adaptive Balance Operation: When the inner ring of the bearing is subjected to axial load, the inner ring drives the left bearing row (2) or the right bearing row (3) to generate axial displacement, and the compression elastic element (6) generates a support reaction force opposite to the axial load, transferring part of the load from the stressed side of the left bearing row (2) or the right bearing row (3) to the unstressed side, thereby realizing the adaptive balanced distribution of axial force of the double-row bearing.

2. The method for adjusting the axial force balance of a double-row self-aligning roller bearing according to claim 1, characterized in that, In step S2, the number n of elastic elements (6) and the elastic coefficient k of a single elastic element (6) must also satisfy the following constraints: a) Spatial constraints: n is not greater than the maximum number of bearing housings (5) that can be installed along the circumference on the outer end face of the bearing housing (5); b) Strength constraint: The maximum load that a single elastic element (6) can withstand. The rated load of the selected elastic element .

3. The method for adjusting the axial force balance of a double-row self-aligning roller bearing according to claim 1, characterized in that, In step S2, the elastic coefficient is calculated. Make it satisfy The specific steps are as follows: First, pre-select a size based on available space and common specifications. Value, calculate the minimum number of elastic elements (6) required. Then Select a suitable interval and verify the strength constraints. If the conditions are not met, then select again. Larger elastic elements (6) or adjusted design objectives Continue until all conditions are met.

4. A method for adjusting the axial force balance of a double-row self-aligning roller bearing according to claim 1, characterized in that, In step S2, the elastic system adopts a graded or nonlinear stiffness design, and at least two sets of elastic elements (6) with different elastic coefficients are stacked in series along the axial direction or connected in parallel along the circumferential direction. Under low load conditions, the elastic element (6) with the smaller elastic coefficient provides the balancing force, and under high load conditions, the two sets of elastic elements (6) work together to improve the overall stiffness of the system to match the load changes.

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