Friction damper and tower crane

Abstract

This invention discloses a friction damper and a tower crane, relating to the field of tower cranes, to reduce the probability of tower crane overturning. The friction damper includes a housing, a sleeve, a rod, and a first friction element. The housing includes a first through hole extending along its length and a first wall hole, the first wall hole being arranged circumferentially around the housing and penetrating the wall of the housing. The sleeve includes a first countersunk hole and a second wall hole; the open end of the first countersunk hole is located in the first through hole, and the closed end of the first countersunk hole is located outside the first through hole; the second wall hole is arranged circumferentially around the sleeve and penetrates the wall of the sleeve; the first wall hole and the second wall hole are interconnected. One end of the rod is inserted into the first countersunk hole, and the other end of the rod is located outside the first countersunk hole. The first friction element is installed in the second wall hole; the first friction element contacts the outer wall of the rod. The above technical solution can effectively consume the overturning moment caused by the relative motion of the components to be damped, reducing the risk of overturning.

Description

Technical Field

[0001] This invention relates to the field of tower cranes, and more specifically to a friction damper and a tower crane. Background Technology

[0002] Tower cranes, also known as tower hoists, consist of a base frame, tower body, and jib, and are widely used in housing construction, large bridges, wind power construction, and nuclear power plants. Typically, the jib of a tower crane is fixed to the top of the tower body and includes a jib and a counterweight jib. The jib is equipped with a hook and a luffing trolley for lifting heavy objects. The counterweight jib is equipped with a counterbalance.

[0003] In recent years, with the increasing trend of infrastructure projects towards larger scale and more complex construction environments, tower cranes have been required to meet performance or structural requirements such as high operating height, large upper weight, large lifting capacity, and long luffing radius. Ultra-large tower cranes are expensive and massive, and the property damage and casualties caused by accidents are staggering. In particular, when the wire rope of the hoisting mechanism breaks or the counterweight fails and falls off, the lifting torque of the boom or the balancing torque of the counterweight boom suddenly decreases. Given the characteristics of ultra-large tower cranes—high operating height, large upper weight, large lifting capacity, and long luffing radius—they are extremely prone to overturning when unbalanced on both sides, resulting in significant property damage and safety accidents.

[0004] The inventors discovered that the industry urgently needs a technical solution that can improve the performance of tower cranes and reduce the probability of accidents. Summary of the Invention

[0005] This invention proposes a friction damper and a tower crane to reduce the probability of tower crane overturning.

[0006] This invention provides a friction damper, comprising:

[0007] The housing includes a first through hole extending along its own length and a first wall hole, the first wall hole being arranged along the circumference of the housing and penetrating the wall of the housing;

[0008] A sleeve includes a first countersunk hole and a second wall hole; the open end of the first countersunk hole is located in the first through hole, and the closed end of the first countersunk hole is located outside the first through hole; the second wall hole is arranged along the circumference of the sleeve and penetrates the wall of the sleeve; the first wall hole and the second wall hole are connected.

[0009] A rod, one end of which is inserted into the first countersunk hole, and the other end of which is located outside the first countersunk hole; and

[0010] The first friction element is installed in the second wall hole; the first friction element is in contact with the outer wall of the rod.

[0011] In some embodiments, the number of the first wall holes is multiple, and the multiple first wall holes are distributed circumferentially along the housing.

[0012] In some embodiments, the number of the second wall holes is multiple, and the multiple second wall holes are distributed circumferentially along the sleeve.

[0013] In some embodiments, there are multiple first wall holes and multiple second wall holes; multiple first wall holes correspond to one second wall hole and are connected.

[0014] In some embodiments, the friction damper further includes:

[0015] A preload application component is mounted on the outside of the housing to apply a preload to the first friction element.

[0016] In some embodiments, the preload application component includes:

[0017] Preload bolts are installed in the first wall hole; and

[0018] A disc spring is located between the preload bolt and the first friction element;

[0019] The magnitude of the preload force applied by the disc spring to the first friction element is adjusted by tightening the preload bolt.

[0020] In some embodiments, each of the first wall holes is fitted with one of the preload bolts and at least one of the disc springs.

[0021] In some embodiments, at least one of the first friction elements is installed in each of the second wall holes.

[0022] In some embodiments, the friction damper further includes:

[0023] A limiting component is fixed to the inner wall of the first countersunk hole;

[0024] The rod is provided with a receiving groove, and the limiting member is located in the receiving groove.

[0025] In some embodiments, the friction damper further includes:

[0026] The second friction element is disposed between the limiting element and the inner wall of the first countersunk hole.

[0027] In some embodiments, both ends of the receiving groove are closed along the length of the rod to limit the relative displacement between the limiting member and the receiving groove.

[0028] In some embodiments, a plurality of the first wall holes are arranged along the length and circumference of the housing, respectively.

[0029] In some embodiments, a plurality of second wall holes are arranged along the length and circumference of the sleeve, respectively.

[0030] This invention also provides a tower crane, comprising:

[0031] Tower body;

[0032] The boom is located at the top of the tower body; and

[0033] The friction damper provided by any technical solution of the present invention has a sleeve located outside the first through hole that is hinged to one of the tower body and the boom, and the rod located outside the first countersunk hole that is hinged to the other of the tower body and the boom.

[0034] In some embodiments, a plurality of the friction dampers are installed between the tower body and the boom.

[0035] In some embodiments, the area enclosed by the ends of each friction damper connected to the boom is A, and the area enclosed by the ends of each friction damper connected to the tower body is B, where A is less than B.

[0036] The friction damper provided by the above technical solution forms a friction pair by setting friction plates between a moving rod and a sleeve. During use, the rod is connected to one of the components to be damped, and the sleeve is connected to the other component. Whenever these two components move relative to each other, the friction pair functions to absorb the overturning moment caused by the relative movement of the components to be damped, reducing the risk of overturning. Specifically, installing the friction damper between the tower body and the boom effectively absorbs the overturning moment of the tower crane caused by the boom's upward movement, ensuring that the tower body bears a constant and less than the overturning moment, achieving moment balance on both sides of the tower body, and ultimately achieving the tower crane's overturning resistance function at its ultimate limit. Attached Figure Description

[0037] The accompanying drawings, which are included to provide a further understanding of the invention and form part of this application, illustrate exemplary embodiments of the invention and, together with their description, serve to explain the invention and do not constitute an undue limitation thereof. In the drawings:

[0038] Figure 1This is a structural schematic diagram of a tower crane provided in an embodiment of the present invention.

[0039] Figure 2 This is a schematic diagram of the boom lifting structure of a tower crane provided in an embodiment of the present invention.

[0040] Figure 3 This is a three-dimensional structural diagram of a friction damper provided in an embodiment of the present invention.

[0041] Figure 4 This is a schematic diagram of the main structure of the friction damper provided in an embodiment of the present invention.

[0042] Figure 5 This is a top view schematic diagram of the friction damper provided in an embodiment of the present invention.

[0043] Figure 6 This is a side view of the friction damper structure provided in an embodiment of the present invention.

[0044] Figure 7 This is a cross-sectional structural diagram of a friction damper provided in an embodiment of the present invention.

[0045] Figure label:

[0046] 1. Shell; 2. Sleeve; 3. Rod; 4. First friction element; 5. Preload application component; 6. Limiting element; 7. Tower body; 8. Boom; 9. Second friction element; 10. Friction damper;

[0047] 11. First through hole; 12. First wall hole;

[0048] 21. First countersunk hole; 22. Second wall hole;

[0049] 31. Receiving groove;

[0050] 51. Preload bolt; 52. Disc spring;

[0051] 61. Fastening screws. Detailed Implementation

[0052] The following is combined with Figures 1 to 7 The technical solution provided by this invention will be described in more detail below.

[0053] The inventors discovered through research that the degree of vibration experienced by a tower crane is directly proportional to the probability of a dangerous accident. If the tower crane experiences significant vibration, it is more prone to accidents; conversely, if the tower crane experiences minimal vibration, the probability of an accident is greatly reduced. Therefore, this invention provides the following technical solution to dissipate energy and reduce vibration in tower cranes, particularly the boom 8.

[0054] See Figures 1 to 3This invention provides a friction damper 10, comprising a housing 1, a sleeve 2, a rod 3, and a first friction element 4. The housing 1 includes a first through hole 11 extending along its length and a first wall hole 12, the first wall hole 12 being arranged circumferentially around the housing 1 and penetrating the wall of the housing 1. The sleeve 2 includes a first countersunk hole 21 and a second wall hole 22; the open end of the first countersunk hole 21 is located in the first through hole 11, and the closed end of the first countersunk hole 21 is located outside the first through hole 11; the second wall hole 22 is arranged circumferentially around the sleeve 2 and penetrates the wall of the sleeve 2; the first wall hole 12 and the second wall hole 22 are interconnected. One end of the rod 3 is inserted into the first countersunk hole 21, and the other end of the rod 3 is located outside the first countersunk hole 21. The first friction element 4 is installed in the second wall hole 22. The first friction element 4 contacts the outer wall of the rod 3 to increase the frictional force when the rod 3 slides relative to the sleeve 2.

[0055] See Figure 3 The housing 1 is generally rectangular. The housing 1 is provided with a first through hole 11 for the sleeve 2 to pass through. There is no relative movement between the sleeve 2 and the housing 1, so the fitting clearance between the first through hole 11 and the sleeve 2 can be set to be relatively small; or the clearance can be set to be relatively large, and the sleeve 2 and the housing 1 can be fixedly connected by bolts or other fasteners.

[0056] The housing 1 is provided with a plurality of first wall holes 12. Specifically, a matrix of multiple first wall holes 12 can be provided on two opposite sides of the housing 1. The size of the first wall holes 12 is relatively small. The first wall holes 12 are arranged in a matrix.

[0057] In some embodiments, there are multiple first wall holes 12, which are distributed around the circumference of the housing 1. This allows components installed in the first wall holes 12 to be set and adjusted from different positions around the circumference of the housing 1.

[0058] In other embodiments, multiple first wall holes 12 are arranged along the length and circumference of the housing 1. This allows components installed in the first wall holes 12 to be set and adjusted from different positions circumferentially and axially of the housing 1. Even if no components are installed in the first wall holes 12, the working status of the first friction element 4 located in the second wall hole 22 can be easily observed through the first wall holes 12, so that it can be replaced and repaired in a timely manner when necessary.

[0059] The outer contour shape of the sleeve 2 matches the shape of the first through hole 11 of the housing 1. In some embodiments, the first through hole 11 is a rectangular hole, and the outer contour of the sleeve 2 is also rectangular. See also Figures 3 to 5 ,or Figure 7The sleeve 2 includes a first countersunk hole 21 and a second wall hole 22. The central axis of the first countersunk hole 21 is along the length of the sleeve 2. The central axis of the second wall hole 22 intersects the central axis of the first countersunk hole 21, specifically, it can be perpendicular. The first countersunk hole 21 is used to install the rod 3. The closed end of the sleeve 2 is provided with a first hinge hole, which is used to realize the hinge between the friction damper 10 and the component to be damped. The depth of the first countersunk hole 21 corresponds to the maximum insertion depth of the rod 3. If the displacement of the component to be damped is large, the depth of the first countersunk hole 21 is set deeper; if the displacement of the component to be damped is small, the depth of the first countersunk hole 21 is set shallower accordingly.

[0060] See also Figure 7 The second wall hole 22 is used to install the first friction element 4. Multiple first wall holes 12 can be connected to a corresponding second wall hole 22. Each second wall hole 22 is provided with one or more first friction elements 4.

[0061] In some embodiments, there are multiple second wall holes 22, which are distributed along the circumference of the sleeve 2. This arrangement allows multiple first friction elements 4 to be installed at multiple different locations on the friction damper 10, thereby effectively adjusting the damping magnitude of the friction damper 10.

[0062] In some embodiments, a plurality of second wall holes 22 are arranged along the length and circumference of the sleeve 2. This structure allows the first friction element 4 installed in the second wall holes 22 to be adjusted and set in multiple directions along the length and circumference of the sleeve 2, so that the performance of the friction damper 10 better meets the requirements.

[0063] See also Figure 7 In some embodiments, there are multiple first wall holes 12 and multiple second wall holes 22; multiple first wall holes 12 correspond to one second wall hole 22 and are connected. This connection method allows the size of the second wall hole 22 to be set larger, so as to install a larger first friction element 4. On the one hand, it simplifies the manufacturing and installation process of the first friction element 4. On the other hand, it also allows the friction damper 10 to still have multiple first friction elements 4, so that the damping magnitude of the friction damper 10 can be adjusted by adjusting the number of first friction elements 4. It also makes the size and area of ​​the first friction element 4 larger, and the energy consumption efficiency is higher under the same stroke conditions.

[0064] See also Figure 7To facilitate adjustment of the friction force of the first friction element 4 in each of the second wall holes 22, in some embodiments, the friction damper 10 further includes a preload application component 5, which is installed outside the housing 1 to apply a preload to the first friction element 4. The preload application component 5 can press the first friction element 4 against or move it away from the outer surface of the rod 3, thereby changing the friction force of the rod 3 relative to the sleeve 2 during movement, thus achieving damping adjustment; it also ensures the overall axial compressive stability of the friction damper 10, resulting in higher friction energy dissipation efficiency under the same stroke.

[0065] The preload application component 5 includes a preload bolt 51 and a disc spring 52. The preload bolt 51 is installed in the first wall hole 12; the disc spring 52 is located between the preload bolt 51 and the first friction member 4. The disc spring 52 is pressed by the preload bolt 51 onto the side of the first friction member 4 away from the rod 3. Each first friction member 4 can be provided with multiple preload bolts 51. One preload bolt 51 is installed in each first wall hole 12. Each preload bolt 51 corresponds to one disc spring 52. For each first friction member 4, the degree of compression in each area can be adjusted individually by the preload bolt 51 corresponding to that area. The magnitude of the preload force applied by the disc spring 52 to the first friction member 4 is adjusted by tightening the preload bolt 51.

[0066] Depending on the required damping, the first friction element 4 can be installed in some of the second wall holes 22, or at least one first friction element 4 can be installed in each of the second wall holes 22. The friction force between each first friction element 4 and the outer surface of the rod 3 can be adjusted by the preload application component 5.

[0067] See Figure 4 and Figure 7 In some embodiments, the friction damper 10 further includes a limiting member 6, which is fixed to the inner wall of the first countersunk hole 21, specifically by fastening screws 61. The rod 3 is provided with a receiving groove 31, and the limiting member 6 is located in the receiving groove 31. The dimensions of the limiting member 6 match the dimensions of the receiving groove 31, forming a surface-to-surface fit. The limiting member 6 can be in various structural forms such as a protrusion or a limiting strip, and it is used to limit the relative movement distance between the rod 3 and the sleeve 2 to prevent excessive relative movement distance, which could prevent the component to be damped from being effectively damped.

[0068] The length L of the receiving slot 31 is, for example, 500mm to 3000mm. The tower crane's boom 8 has a relatively long lifting stroke. This size range well meets the energy dissipation and vibration reduction requirements of the tower crane's boom 8 during lifting.

[0069] In some embodiments, the friction damper further includes a second friction element 9 disposed between the limiting member 6 and the inner wall of the first countersunk hole 21. Multiple second friction elements 9 may be disposed between the limiting member 6 and the inner wall of the first countersunk hole 21. The second friction element 9 has a relatively thin sheet-like structure and can be fixedly mounted to the limiting member 6.

[0070] In some embodiments, both ends of the receiving groove 31 are closed along the length of the rod 3 to limit the relative displacement between the limiting member 6 and the receiving groove 31. By providing the receiving groove 31 with this structure, not only is the relative movement distance between the rod 3 and the sleeve 2 kept within a set range, but the rod 3 and the sleeve 2 will also not disengage from each other regardless of which direction the rod 3 moves relative to the sleeve 2. Through this function of the friction damper 10, the degree of freedom of the component to be damped in the sliding direction of the rod 3 can be restricted, thereby increasing damping and vibration reduction while strengthening the stability of the component to be damped.

[0071] The working principle of the friction damper 10 is as follows: the tie rod, the first friction element 4, and the sleeve 2 together constitute a friction pair. The preload bolt 51 provides positive pressure to the first friction element 4, making the first friction element 4 fit tightly against the tie rod and the limiting element 6 fit tightly against the limiting groove. When the tie rod is displaced, the tie rod simultaneously undergoes sliding friction with the limiting element 6 and the first friction element 4, consuming the tension or pressure. When the tie rod reaches the end of its stroke, the limiting element 6 restricts the displacement of the tie rod, causing the tie rod to stop moving.

[0072] Back Figure 1 and Figure 2 This invention provides a tower crane, including a tower body 7, a boom 8, and a friction damper 10 provided by any of the technical solutions of this invention. The boom 8 is located at the top of the tower body 7. One end of the sleeve 2 of the friction damper 10 located outside the first through hole 11 is hinged to one of the tower body 7 and the boom 8, and the end of the rod 3 of the friction damper 10 located outside the first countersunk hole 21 is hinged to the other of the tower body 7 and the boom 8.

[0073] Boom 8 includes a lifting boom and a counterweight boom. The lifting boom is equipped with a hook and a luffing trolley for lifting heavy objects. The counterweight boom is equipped with a counterbalance.

[0074] The boom 8 in the upward state is the state in which the boom or counterweight of the boom 8 rotates bidirectionally in the vertical plane around the dual axes of the tower body 7 when the boom 8 flips over due to sudden unloading of the boom and failure of the counterweight.

[0075] When the boom 8 becomes unbalanced and tilts upwards, the tie rod of the friction damper 10 is pulled out. During the movement of the tie rod, since the first friction element 4 is installed in the second wall hole 22 of the sleeve 2, the relative movement of the rod 3 with respect to the first friction element 4 will generate friction, which will play a role in vibration reduction and energy dissipation. This will consume the overturning moment of the tower crane when the boom 8 tilts upwards, so that the tower body 7 bears a constant and less than the overturning moment of the tower crane, and achieves moment balance on both sides of the tower body 7, ultimately achieving the function of anti-overturning in the ultimate state of the tower crane.

[0076] When the boom 8 is reset relative to the tower 7, the tie rod of the friction damper 10 is compressed and retracted. In other states, the friction damper 10 is subjected to a static variable load less than the rated damping force.

[0077] When the tower crane boom 8 is not raised and rotated, the friction damper 10 is subjected to a tensile force less than the damping force.

[0078] by Figure 1 Taking the direction shown as an example, regardless of whether the boom 8 moves upward or downward relative to the tower 7, the friction damper 10 plays a role in vibration reduction and buffering.

[0079] A specific application scenario is as follows: When the wire rope of the tower crane hoisting mechanism breaks or the tower crane counterweight fails and falls off, an unbalanced moment occurs on both sides of the tower body 7. This unbalanced moment will pull up the boom 8, causing the boom 8 to rise and overturn. Figure 2 As shown, when the boom 8 tilts upwards, the tension is transmitted to the tie rod of the friction damper 10. The tie rod is pulled, and the friction pair generates sliding friction, which begins to do work to consume the tension and the overturning moment on both sides of the tower body 7. During the movement of the tie rod, this unbalanced moment will be consumed until the boom 8 stops tilting.

[0080] The robust crane provided by the above technical solution utilizes a friction damper 10, which relies on the frictional resistance of the friction pair to generate heat, thereby reducing the mechanical energy of the system. Its structure is compact and slender, with a small overall size, making it well-suited for the installation environment between the tower 7 and the boom 8. The damping force referred to in this article is a force opposite to the direction of the friction damper 10's movement speed, generated through the friction pair.

[0081] In some embodiments, Figure 1 In the X direction shown, i.e. Figure 1 In the vertical direction, the freedom of the tower body 7 and the boom 8 in the X direction is restricted by the friction damper 10. Specifically, it is restricted by the limiting member 6 of the friction damper 10 to prevent the boom 8 from displacing too much relative to the tower body 7 in the X direction, causing dangerous situations such as the boom 8 tilting and detaching. On the other hand, it also makes it unnecessary for the tower body 7 and the boom 8 to have excessive constraints in the X direction, thereby reducing the structural redundancy of the tower crane.

[0082] Due to the very large structural dimensions of tower cranes, in some embodiments, multiple friction dampers 10 are installed between the tower body 7 and the boom 8. Each friction damper 10 is arranged at an angle relative to the X direction, and each friction damper 10 operates independently without affecting each other.

[0083] In some embodiments, the area enclosed by the ends of each friction damper 10 connected to the boom 8 is A, and the area enclosed by the ends of each friction damper 10 connected to the tower body 7 is B, where A is less than B. This arrangement of the friction dampers 10 allows for a more stable and reliable connection between the boom 8 and the tower body 7.

[0084] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only used to facilitate the description of this invention and to simplify the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limiting the scope of protection of this invention.

[0085] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. However, these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A friction damper, characterized by include: The housing (1) includes a first through hole (11) extending through its own length and a first wall hole (12), the first wall hole (12) being arranged along the circumference of the housing (1) and penetrating the wall of the housing (1); The sleeve (2) includes a first countersunk hole (21) and a second wall hole (22); the open end of the first countersunk hole (21) is located in the first through hole (11), and the closed end of the first countersunk hole (21) is located outside the first through hole (11); the second wall hole (22) is arranged along the circumference of the sleeve (2), and the second wall hole (22) penetrates the wall of the sleeve (2); the first wall hole (12) and the second wall hole (22) are connected; A rod (3), one end of which is inserted into the first countersunk hole (21), and the other end of which is located outside the first countersunk hole (21); The first friction element (4) is installed in the second wall hole (22); the first friction element (4) is in contact with the outer wall of the rod (3); A limiting member (6) is fixed to the inner wall of the first countersunk hole (21); wherein the rod (3) is provided with a receiving groove (31), and the limiting member (6) is located in the receiving groove (31); and The second friction element (9) is disposed between the limiting element (6) and the inner wall of the first countersunk hole (21).

2. The friction damper of claim 1, wherein, The number of the first wall holes (12) is multiple, and the multiple first wall holes (12) are distributed along the circumference of the housing (1).

3. The friction damper of claim 1, wherein, The number of the second wall holes (22) is multiple, and the multiple second wall holes (22) are distributed along the circumference of the sleeve (2).

4. The friction damper of claim 1, wherein, There are multiple first wall holes (12) and multiple second wall holes (22); multiple first wall holes (12) correspond to one second wall hole (22) and are connected.

5. The friction damper of claim 1, wherein, Also includes: A preload application component (5) is installed on the outside of the housing (1) to apply a preload to the first friction element (4).

6. The friction damper according to claim 5, characterized in that, The preload application component (5) includes: Preload bolts (51) are installed in the first wall hole (12); and Disc spring (52) is located between the preload bolt (51) and the first friction element (4); The magnitude of the preload force applied by the disc spring (52) to the first friction member (4) is adjusted by tightening the preload bolt (51).

7. The friction damper of claim 6, wherein, Each of the first wall holes (12) is fitted with a preload bolt (51) and at least one disc spring (52).

8. The friction damper of claim 6, wherein, At least one of the first friction elements (4) is installed in each of the second wall holes (22).

9. The frictional damper of claim 1, wherein, Along the length of the rod (3), both ends of the receiving groove (31) are closed to limit the relative displacement between the limiting member (6) and the receiving groove (31).

10. The friction damper of claim 1, wherein, A plurality of first wall holes (12) are arranged along the length and circumference of the housing (1).

11. The friction damper according to claim 1, characterized in that, Multiple second wall holes (22) are arranged along the length and circumference of the sleeve (2).

12. A tower crane, characterized in that include: Tower body (7); The boom (8) is located at the top of the tower body (7); as well as According to any one of claims 1 to 11, the sleeve (2) of the friction damper (10) is hinged at one end outside the first through hole (11) to either the tower body (7) or the boom (8), and the rod (3) of the friction damper (10) is hinged at the other end outside the first countersunk hole (21) to either the tower body (7) or the boom (8).

13. A tower crane according to claim 12, characterised in that Multiple friction dampers (10) are installed between the tower body (7) and the boom (8).

14. A tower crane according to claim 12, characterised in that The area of ​​the region enclosed by the ends of each of the friction dampers (10) connected to the boom (8) is A, and the area of ​​the region enclosed by the ends of each of the friction dampers (10) connected to the tower body (7) is B, where A is less than B.

Images