A device and method for inhibiting the conduction of non-primary vibration direction acceleration response of a vibration table

Abstract

This invention discloses a device and method for suppressing the transmission of non-primary vibration direction acceleration response of a vibration table, relating to the field of vibration testing technology. The device includes a lower ball joint system, an upper ball joint system, a guide rail system, and a vibration table base. The lower ball joint system includes a first pressure plate and a first ball joint. The first pressure plate is connected to the vibration table base and has a first ball groove. The first ball joint includes a first sphere that fits with the first ball groove with a clearance. The upper ball joint system includes a second pressure plate and a second ball joint. The second pressure plate has a second ball groove, and the second ball joint includes a second sphere that fits with the second ball groove with a clearance. The first ball joint has a screw rigidly connected to the second ball joint. The guide rail system is disposed on the vibration table base and includes a vertically sliding slider connected to the second pressure plate. This invention employs a multi-ball joint parallel + guide rail composite structure to establish a non-primary vibration direction energy conversion path, effectively suppressing the transmission of non-primary vibration direction vibration between the vibration table surface and the fixture system.

Description

Technical Field

[0001] This invention relates to the field of vibration testing technology, specifically to a device and method for suppressing the transmission of non-primary acceleration response of a vibration table. Background Technology

[0002] A uniaxial vibration table is a core piece of equipment in the field of vibration testing. Its controller can only achieve precise control of the acceleration response in the principal vibration direction (usually the vertical direction), and cannot effectively regulate the acceleration response in the non-principal vibration direction (mainly the horizontal direction) of the table surface. During the operation of the vibration table, the table surface will inevitably generate non-principal vibration direction acceleration response components, which will be directly transmitted to the fixture and specimen system through the fixed connection structure between the vibration table and the fixture.

[0003] Unexpected non-principal vibration transmission can easily excite the non-principal modal frequencies of the fixture and the specimen, thus causing resonance. In severe cases, the non-principal acceleration response value of the key points of the fixture or specimen may exceed the principal acceleration response value, resulting in overtesting, or even directly causing the specimen structure to be damaged and the test data to become invalid.

[0004] In existing technologies, the influence of non-primary vibrations is often reduced by increasing the stiffness of the connecting structure. However, such methods can only slightly reduce the vibration transmission efficiency and cannot fundamentally cut off the transmission path of non-primary vibrations, thus the suppression effect is limited.

[0005] Therefore, existing technologies need to be improved. Summary of the Invention

[0006] This invention addresses the technical deficiencies of existing single-axis vibration table systems regarding the transmission of non-primary vibration direction acceleration responses. It provides a device and method for suppressing the transmission of non-primary vibration direction acceleration responses from vibration tables. The device employs a multi-spherical hinge connection and a guide rail composite structure to establish a non-primary vibration direction energy conversion path, converting non-primary vibration direction motion into principal vibration direction motion as much as possible. This fundamentally suppresses the transmission of non-primary vibration direction acceleration responses, thereby improving the accuracy and safety of vibration tests.

[0007] This invention is achieved through the following technical solution:

[0008] In a first aspect, the present invention provides a device for suppressing the transmission of non-principal acceleration response of a vibration table, comprising a lower ball joint system, an upper ball joint system, a guide rail system, and a vibration table base.

[0009] The lower ball joint system includes a first pressure plate and a first ball joint. The first pressure plate is connected to the vibration table base. The first pressure plate is provided with a first ball groove. The first ball joint includes a first ball that fits with the first ball groove with a clearance.

[0010] The upper ball joint system includes a second pressure plate and a second ball joint. The second pressure plate is provided with a second ball groove, and the second ball joint includes a second ball that is clearance-fitted with the second ball groove.

[0011] The first ball joint is provided with a screw that is rigidly connected to the second ball joint. The guide rail system is provided on the vibration table base and the guide rail system is provided with a vertically sliding slider. The slider is connected to the second pressure plate.

[0012] Furthermore, in this invention, the guide rail system described above includes a base connected to the vibration table base, a vertical rail is provided on the side wall of the base, the slider is connected to the rail, and the rail restricts the slider from sliding up and down.

[0013] Furthermore, in this invention, the lower ball joint system described above also includes a first pressure cap, which is detachably connected to the first pressure plate, and the first pressure cap is provided with a through hole through which the screw of the first ball joint passes.

[0014] Furthermore, in this invention, the first pressure cover is provided with a first clamping screw and a first adjusting screw, and the first pressure plate is provided with a first screw hole that cooperates with the first clamping screw and the first adjusting screw.

[0015] Furthermore, in this invention, the aforementioned upper ball joint system further includes a second pressure cap, which is detachably connected to the second pressure plate, and the second pressure cap is provided with a through hole for the threaded joint of the second ball joint to pass through.

[0016] Furthermore, in this invention, the second pressure cover is provided with a second clamping screw and a second adjusting screw, and the second pressure plate is provided with a second screw hole that cooperates with the second clamping screw and the second adjusting screw.

[0017] Furthermore, in this invention, the upper ball joint system and the lower ball joint system are in a one-to-one correspondence.

[0018] Furthermore, in this invention, the spherical surfaces of the first ball joint and the second ball joint are provided with a wear-resistant coating; the groove walls of the first ball groove and the second ball groove are provided with a wear-resistant coating.

[0019] Secondly, the present invention also provides a method for suppressing the transmission of non-principal acceleration response of a vibration table, comprising the aforementioned device for suppressing the transmission of non-principal acceleration response of a vibration table, and further comprising the following:

[0020] Fix the lower ball joint system to the vibration table surface, fix the upper ball joint system to the vibration fixture, and rigidly connect the lower ball joint system and the upper ball joint system in parallel. Fix the base of the guide rail system to the vibration table base; fix the slider to the upper ball joint system.

[0021] The horizontal non-principal vibration load F on the shaking table surface is transmitted from the lower ball joint system to the upper ball joint system and decomposed into a component FG along the ball joint direction and a component FC perpendicular to the ball joint direction. Utilizing the horizontal displacement constraint characteristics of the guide rail system, the decomposed load components drive the slider to move perpendicular to the principal vibration direction along the guide rail, realizing the transformation of non-principal vibration direction motion into principal vibration direction motion. Through the structural characteristics of the ball joint system, the horizontal load component transmitted to the upper ball joint system is significantly attenuated, realizing the transmission suppression of non-principal vibration direction acceleration response.

[0022] Furthermore, in this invention, the above-mentioned load decomposition relationship satisfies ,

[0023] in The angle between the direction of the upper and lower ball joints and the vertical direction. Let be the horizontal displacement of the lower ball joint system. The distance between the centers of the upper and lower ball joints;

[0024] The distance between the first pressure plate and the second pressure plate shall be no less than 70mm and no more than 300mm to ensure assembly space and vertical transmission stiffness.

[0025] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0026] This invention employs a multi-spherical hinge connection and guide rail composite structure to establish a conversion path for non-dominant vibration energy. It directly converts the non-dominant vibration motion of the vibration table surface into dominant vibration motion, fundamentally suppressing the transmission of non-dominant acceleration response to the fixture and specimen system, effectively avoiding non-dominant resonance and overtesting. Furthermore, both the lower and upper spherical hinge systems are made of high-strength alloy steel, and the spherical mating surfaces are coated with a wear-resistant coating, ensuring the structural rigidity and connection stability of the device. This allows it to adapt to complex vibration conditions with high frequency and large loads, while reducing component wear and extending service life. Attached Figure Description

[0027] The accompanying drawings, which are included to provide a further understanding of embodiments of the invention and form part of this application, do not constitute a limitation thereof. In the drawings:

[0028] Figure 1 This is a schematic diagram of the device for suppressing the transmission of non-primary vibration direction acceleration response of the vibration table according to the present invention;

[0029] Figure 2 This is a schematic diagram of the lower ball joint system of the present invention;

[0030] Figure 3 This is a schematic diagram of the first pressure plate of the present invention;

[0031] Figure 4 This is a schematic diagram of the upper ball joint system of the present invention;

[0032] Figure 5 This is a schematic diagram of the second pressure plate of the present invention;

[0033] Figure 6 This is a partial cross-sectional schematic diagram of the engagement of the lower ball joint system and the upper ball joint system of the present invention;

[0034] Figure 7 This is a schematic diagram showing the force analysis of the lower ball joint system and the upper ball joint system of the present invention.

[0035] The attached diagram shows the markings and corresponding component names: 1. Lower ball joint system, 1-1. First pressure plate, 1-2. First ball joint, 1-3. First pressure cap, 1-4. First clamping screw, 1-5. First adjusting screw, 2. Upper ball joint system, 2-1. Second pressure plate, 2-2. Second ball joint, 2-3. Second pressure cap, 2-4. Second clamping screw, 2-5. Second adjusting screw, 3. Guide rail system, 4. Vibration table base. Detailed Implementation

[0036] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments and accompanying drawings. The illustrative embodiments and descriptions of this invention are for explanation only and are not intended to limit the invention. The following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without inventive effort are within the scope of protection of this invention.

[0037] It should be noted that similar reference numerals and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures. In the description of the embodiments of the present invention, it should also be noted that, unless otherwise explicitly specified and limited, the terms "set," "install," and "connect" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0038] Example 1

[0039] This embodiment 1 provides a device for suppressing the transmission of acceleration response in non-principal vibration directions of a vibration table, such as... Figures 1-7 As shown, the device includes a lower ball joint system 1, an upper ball joint system, a guide rail system 3, and a vibration table base 4; wherein the guide rail system 3 is provided with 8 sets, which are evenly distributed around the upper ball joint system 2.

[0040] Combination Figure 1 , Figure 2 and Figure 3 As shown, the lower ball joint system 1 is the connection end of the vibration table platform, including a first pressure plate 1-1, a first ball joint 1-2, a first pressure cap 1-3, a first clamping screw 1-4, and a first adjusting screw 1-5. Except for the first clamping screw 1-4 and the first adjusting screw 1-5, which are standard parts, all other components in the lower ball joint system 1 are made of 42CrMo high-strength alloy steel. After quenching and tempering, the hardness reaches HRC38~42, ensuring structural rigidity and fatigue resistance.

[0041] The first pressure plate 1-1 is a circular tabletop mounting plate with multiple Φ20 through holes arranged in a circular pattern on its end face for fixed connection to the vibration table surface via bolts. Its upper end face has a ball groove structure with 16 circumferentially distributed first ball grooves. These first ball grooves match the first spheres of the first ball hinge 1-2, with a spherical fit clearance of 0.02~0.05mm, achieving a small clearance fit. The ball groove structure and through holes are staggered, reserving sufficient installation space.

[0042] Combination Figure 2 and Figure 3 As shown, the first ball joint 1-2 is an integrated structure of the first ball and the screw. The first ball forms a spherical fit with the ball groove of the first pressure plate 1-1 and the first pressure cover 1-3. The screw part is M20 in size and 80mm in length. The screw surface is machined with fine threads to improve the connection stability.

[0043] Furthermore, in combination Figure 2 As shown, the first pressure cover 1-3 is a circular cover plate with a thickness of 40mm; its lower end face has a ball groove surface that matches the first ball joint 1-2, and the upper end face of the ball groove surface has a through hole for the screw part of the first ball joint 1-2 to pass through; the edge of the first pressure cover 1-3 has 12 circumferentially distributed screw holes for installing 6 first clamping screws 1-4 and 6 first adjusting screws 1-5.

[0044] It should be noted that the first clamping screw 1-4 can be an M16 socket head cap screw, and the first adjusting screw 1-5 can be an M16 socket head cap fine thread adjusting screw. After the two are tightened together, the gap between the first ball joint 1-2 and the first pressure plate 1-1 and the first pressure cover 1-3 should be eliminated as much as possible to achieve a gapless connection.

[0045] Furthermore, the spherical surface of the first ball joint 1-2, the ball groove surface of the first pressure plate 1-1 and the first pressure cover 1-3 are all coated with a molybdenum disulfide-based wear-resistant coating with a coating thickness of 0.01~0.03mm, which reduces the wear of the spherical surface under high-frequency vibration.

[0046] In this embodiment, combined with Figure 1 , Figure 4 and Figure 5 As shown, the upper ball joint system 2 is the clamp connection end, including the second pressure plate 2-1, the second ball joint 2-2, the second pressure cover 2-3, the second clamping screw 2-4, and the second adjusting screw 2-5; its component materials and structural specifications are completely consistent with those of the lower ball joint system 1. Similarly, except for standard parts, the other components are all made of 42CrMo high-strength alloy steel, and the spherical surface and the ball groove surface are coated with a molybdenum disulfide-based wear-resistant coating.

[0047] Furthermore, in combination Figure 1 ,and Figure 5 and Figure 6 As shown, the second pressure plate 2-1 is a circular clamp mounting plate, and the bottom of the second ball joint 2-2 has a threaded joint. The internal threaded hole of the threaded joint and the screw of the lower ball joint 1-2 form a high-strength thread pair. The tightening torque is set to 250Nm. The thread mating surface is coated with Loctite 263 high-strength thread adhesive for anti-loosening treatment, which rigidly connects the first ball joint 1-2 and the second ball joint 2-2.

[0048] After connection, the net height between the first pressure plate 1-1 and the second pressure plate 2-1 is 150mm; the side wall of the second pressure plate 2-1 is evenly provided with 8 slider connecting surfaces, which are fixed to the slider of the guide rail system 3 by bolts or welding; the upper end face of the second pressure plate 2-1 is provided with multiple circumferentially distributed M20 threaded holes, which are consistent with the interface of the vibration table surface and are used for fixed connection with the vibration fixture.

[0049] The second ball joint 2-2 is an integrated structure with a spherical internal thread. The spherical part is consistent with the lower ball joint 1-2, and the internal thread hole is precisely matched with the screw of the lower ball joint 1-2. The structure of the second pressure cap 2-3, the second clamping screw 2-4, and the second adjusting screw 2-5 is completely consistent with the structure of the upper pressure cap 1-3, the lower ball joint clamping screw 1-4, and the lower ball joint adjusting screw 1-5 of the lower ball joint, so as to achieve gapless clamping and fixing.

[0050] Combination Figure 1As shown, the guide rail system 3 includes a slider, a guide rail, and a base. The slider and guide rail adopt high-precision linear guide rail components. The base is a welded steel plate structure, which is fixed to the vibration table base 4 by expansion bolts to ensure installation rigidity. The guide rail is a vertically arranged linear guide rail, which is fixed to the base by bolts. The slider slides in conjunction with the guide rail, allowing it to slide freely in the vertical direction without clearance along the guide rail, while completely constraining the horizontal displacement degree of freedom. The slider is fixedly connected to the side wall interface of the second pressure plate 2-1 to realize the displacement constraint and guidance of the upper ball joint system 2.

[0051] The vibration table base 4 serves as the fixed foundation for the single-axis vibration table and provides installation support for the guide rail system 3. It has sufficient structural rigidity to prevent deformation caused by vibration loads and ensure the working stability of the device.

[0052] Example 2

[0053] This embodiment provides a method for suppressing the transmission of non-principal acceleration response of a vibration table, using the device for suppressing the transmission of non-principal acceleration response of a vibration table in Embodiment 1.

[0054] Based on the apparatus of Embodiment 1, the method utilizes the combined action of the lower ball joint system 1, the upper ball joint system 2, and the guide rail system 3 to convert the non-principal vibration direction motion of the vibration table surface into the principal vibration direction motion, thereby achieving the transmission suppression of the non-principal vibration direction acceleration response.

[0055] Device assembly: The lower ball joint system 1 is fixedly connected to the vibration table surface via the first pressure plate 1-1, and the upper ball joint system 2 is fixedly connected to the vibration fixture via the second pressure plate 2-1. The lower ball joint system 1 and the upper ball joint system 2 are rigidly connected in parallel by the screw of the first ball joint 1-2 and the internal thread hole of the second ball joint 2-2, ensuring that the distance between them is 70mm~3100mm. The base of the guide rail system 31 is fixed to the vibration table base 42, and the slider is fixed to the second pressure plate 2-1, ensuring that the slider can slide freely vertically along the guide rail and has no displacement in the horizontal direction.

[0056] The combined action of the lower ball joint system 1, the upper ball joint system 2, and the guide rail system 3 can convert the non-primary vibration direction motion of the vibration table surface into the primary vibration direction motion, thereby suppressing the transmission of the non-primary vibration direction acceleration response of the table surface.

[0057] Force analysis of lower ball joint system 1, upper ball joint system 2, and guide rail system 3 is as follows: Figure 7 As shown, when the horizontal component F of the shaking table surface is transmitted from the lower ball joint system 1 to the upper ball joint system 2, it can be decomposed into a component FG along the ball joint direction and a component FC perpendicular to the ball joint direction. The relationship between the three is shown in Equation 1. The clamps are located in the vertical direction and the direction of the upper and lower ball joints, respectively. x is the horizontal displacement of the lower ball joint system 1 and the horizontal displacement of the vibration table surface. L is the center distance between the upper and lower ball joints.

[0058]

[0059] The horizontal component F of the vibration table is transmitted to the upper ball joint system 2 through the ball joint system as follows: Combining Equation 1, the horizontal component suppression ratio can be obtained. As shown in Equation 2.

[0060]

[0061] The horizontal displacement component x of the shaking table surface is minimal relative to the center distance of the ball joint system, therefore Minimal amount, inhibition ratio Approaching 100%, significantly reducing the horizontal load borne by the guide rail base.

[0062] After the shaking table is started, the main vibration direction is vertical. The table surface generates vertical main vibration and horizontal non-main vibration. The horizontal non-main vibration load F is transmitted from the lower ball joint system 1 to the upper ball joint system 2. Under the action of the spherical contact of the ball joint system, the load F is decomposed into a component FG along the ball joint direction and a component FC perpendicular to the ball joint direction. The decomposition relationship satisfies: (where is the angle between the upper and lower ball joint directions and the vertical direction, is the horizontal displacement of the lower ball joint system 1, and is the center distance between the upper and lower ball joints).

[0063] The sliding fit between the slider and the guide rail of the guide rail system 3 completely constrains the horizontal displacement degree of freedom of the upper ball joint system 2, so that the decomposed load components FG and FC cannot drive the upper ball joint system 2 to make horizontal movements, but can only drive the slider to make vertical main vibration direction movements along the guide rail 3-2, realizing the complete transformation of the non-main vibration direction movements of the vibration table surface into the main vibration direction movements.

[0064] In this embodiment, the maximum horizontal displacement component of the vibration table surface is 0.5 mm, which is extremely small relative to the center distance of the upper and lower ball joints (150 mm). This makes the included angle approach 0, significantly attenuating the horizontal load component transmitted to the upper ball joint system 2. The suppression ratio of non-primary vibration direction acceleration response approaches 100%. Simultaneously, the horizontal load is converted into a vertical load through the ball joint system, reducing the horizontal load borne by the guide rail base 3-3 by more than 95%, thus preventing base deformation from affecting the stability of the device. The method in this embodiment 2 can effectively suppress the transmission of non-primary vibration direction acceleration response of the vibration table. Experimental verification shows that the non-primary vibration direction acceleration response value of the specimen is reduced to less than 1% of the principal vibration direction acceleration response value, completely avoiding non-primary vibration direction resonance and overtesting, and improving the accuracy and safety of vibration testing.

[0065] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A device for suppressing the transmission of non-principal acceleration response of a vibration table, characterized in that, It includes a lower ball joint system (1), an upper ball joint system (2), a guide rail system (3), and a vibration table base (4). The lower ball joint system (1) includes a first pressure plate (1-1) and a first ball joint (1-2). The first pressure plate (1-1) is connected to the vibration table base (4). The first pressure plate (1-1) is provided with a first ball groove. The first ball joint (1-2) includes a first ball that fits with the first ball groove with a clearance. The upper ball joint system (2) includes a second pressure plate (2-1) and a second ball joint (2-2). The second pressure plate (2-1) is provided with a second ball groove, and the second ball joint (2-2) includes a second ball that fits with the second ball groove with a clearance. The first ball joint (1-2) is provided with a screw that is rigidly connected to the second ball joint (2-2). The guide rail system (3) is provided on the vibration table base (4). The guide rail system (3) is provided with a vertically sliding slider. The slider is connected to the second pressure plate (2-1).

2. The device for suppressing the transmission of non-principal acceleration response of a vibration table according to claim 1, characterized in that, The guide rail system (3) includes a base connected to the vibration table base (4), and the side wall of the base is provided with a vertical rail. The slider is connected to the rail, and the rail restricts the slider from sliding up and down.

3. The device for suppressing the transmission of non-principal acceleration response of a vibration table according to claim 1, characterized in that, The lower ball joint system (1) further includes a first pressure cap (1-3), which is detachably connected to the first pressure plate (1-1). The first pressure cap (1-3) is provided with a through hole through which the screw of the first ball joint (1-2) passes.

4. The device for suppressing the transmission of non-principal acceleration response of a vibration table according to claim 3, characterized in that, The first pressure cap (1-3) is provided with a first clamping screw (1-4) and a first adjusting screw (1-5), and the first pressure plate (1-1) is provided with a first screw hole that cooperates with the first clamping screw (1-4) and the first adjusting screw (1-5).

5. The device for suppressing the transmission of non-principal acceleration response of a vibration table according to claim 1, characterized in that, The upper ball joint system (2) further includes a second pressure cap (2-3), which is detachably connected to the second pressure plate (2-1). The second pressure cap (2-3) is provided with a through hole through which the threaded joint of the second ball joint (2-2) passes.

6. The device for suppressing the transmission of non-principal acceleration response of a vibration table according to claim 5, characterized in that, The second pressure cap (2-3) is provided with a second clamping screw (2-4) and a second adjusting screw (2-5), and the second pressure plate (2-1) is provided with a second screw hole that cooperates with the second clamping screw (2-4) and the second adjusting screw (2-5).

7. The device for suppressing the transmission of non-principal acceleration response of a vibration table according to claim 1, characterized in that, The upper ball joint system (2) and the lower ball joint system (1) are in one-to-one correspondence.

8. The device for suppressing the transmission of non-principal acceleration response of a vibration table according to claim 1, characterized in that, The spherical surfaces of the first ball joint (1-2) and the second ball joint (2-2) are provided with wear-resistant coatings; the groove walls of the first ball groove and the second ball groove are provided with wear-resistant coatings.

9. A method for suppressing the transmission of non-principal acceleration response of a vibration table, characterized in that, The device for suppressing the transmission of non-principal acceleration response of a vibration table as described in claim 1 further includes the following: The lower ball joint system (1) is fixed to the table surface of the vibration table, the upper ball joint system (2) is fixed to the vibration fixture, the lower ball joint system (1) and the upper ball joint system (2) are rigidly connected in parallel, the base of the guide rail system (3) is fixed to the vibration table base (4), and the slider is fixed to the upper ball joint system (2). The horizontal non-principal vibration load F on the vibration table surface is transmitted from the lower ball joint system (1) to the upper ball joint system (2) and decomposed into a component FG along the ball joint direction and a component FC perpendicular to the ball joint direction. Utilizing the horizontal displacement constraint characteristics of the guide rail system (3), the decomposed load components drive the slider to move perpendicular to the principal vibration direction along the guide rail, realizing the transformation of non-principal vibration direction motion into principal vibration direction motion. Through the structural characteristics of the ball joint system, the horizontal load component transmitted to the upper ball joint system (2) is significantly attenuated, realizing the transmission suppression of non-principal vibration direction acceleration response.

10. The method for suppressing the transmission of non-principal acceleration response of a vibration table according to claim 9, wherein the load decomposition relationship satisfies , in The angle between the direction of the upper and lower ball joints and the vertical direction. Let the horizontal displacement of the lower ball joint system (1) be denoted as . The distance between the centers of the upper and lower ball joints; The distance between the first pressure plate (1-1) and the second pressure plate (2-1) is not less than 70mm and not more than 300mm to ensure assembly space and vertical transmission stiffness.

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