CN220618345U - Arm support structure - Google Patents

Abstract

The utility model belongs to the technical field of telescopic arms, and discloses an arm support structure, which comprises a primary arm cylinder, a secondary arm cylinder … … N-level arm cylinder, a driving cylinder and a pulley mechanism, wherein the primary arm cylinder and the secondary arm cylinder are sequentially nested, the fixed end of the driving cylinder is positioned in the primary arm cylinder and connected with the primary arm cylinder, and the telescopic end is positioned in the secondary arm cylinder and connected with the secondary arm cylinder; two pulleys are arranged from the second-level arm cylinder to the N-1-level arm cylinder, one of the two pulleys positioned on the K-level arm cylinder is wound with an arm extending connecting piece, the other pulley is wound with an arm contracting connecting piece, two ends of the arm extending connecting piece extend towards one side of the first-level arm cylinder and are respectively connected with the K-1-level arm cylinder and the K+1-level arm cylinder, and two ends of the arm contracting connecting piece extend towards one side of the N-level arm cylinder and are respectively connected with the K-1-level arm cylinder and the K+1-level arm cylinder; k is a natural number, and K is more than or equal to 2 and less than or equal to N; for the secondary arm cylinder, a pulley corresponding to the arm extending connecting piece is arranged in the secondary arm cylinder and connected to the telescopic end. The arm support structure provided by the utility model has a simple structure and more reasonable space layout.

Description

Arm support structure

Technical Field

The utility model relates to the technical field of telescopic arms, in particular to a boom structure.

Background

An aerial work platform is a large-scale industrial machinery used to transport workers and work equipment to a designated height for work. The arm support structure of the aerial working platform comprises a plurality of arm cylinders which are nested in sequence, wherein the arm cylinder positioned at the most end of the chassis of the aerial working platform is connected with the chassis, and the arm cylinder positioned at the most end of the chassis is connected with the workbench.

In the prior art, some boom structures use a combination of a driving cylinder and a pulley mechanism to control telescoping. Specifically, for example, patent document CN209308712U discloses a boom extension mechanism, according to the disclosure of which, among a plurality of sequentially nested boom cylinders, extension and retraction are controlled between a first arm and an adjacent second arm, which are close to a chassis, through a driving oil cylinder, and extension and retraction are controlled between the second arm and a third arm, and between … … N-1 arm and an nth arm, which are between the third arm and a fourth arm, through a pulley mechanism. The above patent document also has some disadvantages. Specifically, the driving oil cylinder is arranged outside the first arm, so that the driving oil cylinder can be directly exposed to the external environment, the risk of damage and corrosion of the driving oil cylinder is increased, and the driving oil cylinder is not easy to protect. In addition, the pulleys are arranged at the upper side end and the lower side end of the arm support, so that the external size of the arm support structure is further increased, and the whole arm support structure is more and more complicated.

Disclosure of Invention

The utility model aims to provide a cantilever crane structure which is simple in structure, can effectively enhance the protection of a driving cylinder and reasonably optimize the arrangement structure of pulleys.

To achieve the purpose, the utility model adopts the following technical scheme:

the utility model provides a cantilever crane structure, includes the first order arm section of thick bamboo, the second grade arm section of thick bamboo … … N level arm section of thick bamboo that nest in proper order set up, N is natural number and N is greater than or equal to 3, cantilever crane structure still includes:

the driving cylinder comprises a fixed end and a telescopic end, wherein the fixed end is positioned in the primary arm cylinder and connected with the primary arm cylinder, and the telescopic end is positioned in the secondary arm cylinder and connected with the secondary arm cylinder;

the pulley mechanism comprises pulleys, an arm extending connecting piece and an arm contracting connecting piece, wherein two pulleys are arranged from the second-stage arm cylinder to the N-1-stage arm cylinder, one of the two pulleys positioned on the K-stage arm cylinder is wound on the arm extending connecting piece, the other pulley is wound on the arm contracting connecting piece, two ends of the arm extending connecting piece extend towards the retraction direction of the arm frame structure and are respectively connected with the K-1-stage arm cylinder and the K+1-stage arm cylinder, and two ends of the arm contracting connecting piece extend towards the extension direction of the arm frame structure and are respectively connected with the K-1-stage arm cylinder and the K+1-stage arm cylinder; k is a natural number, and K is more than or equal to 2 and less than or equal to N-1;

for the secondary arm cylinder, the pulley corresponding to the arm extending connecting piece is arranged in the secondary arm cylinder and connected to the telescopic end.

Preferably, the device further comprises an adjusting block, wherein the adjusting block is hinged on the primary arm cylinder around a first direction, fixing holes are formed in two sides of the hinging position of the adjusting block, two arm extending connectors are arranged on the secondary arm cylinder, first ends of the two arm extending connectors are fixed on the tertiary arm cylinder, and second ends of the two arm extending connectors are fixedly arranged in the two fixing holes in a penetrating mode after the pulleys are wound;

the first direction is perpendicular to the telescopic direction of the arm support structure and the axial direction of the pulley.

Preferably, the adjusting block is provided with two guide cylinders coaxially communicated with the fixing hole.

Preferably, a bracket is fixedly arranged on the primary arm cylinder, and the adjusting block is hinged on the bracket through a hinge shaft.

Preferably, the inner peripheral wall of the fixing hole is provided with an internal thread, and the outer peripheral walls of the second ends of the two extension arm connecting pieces on the secondary arm cylinder are respectively provided with an external thread which is in matched connection with the internal thread.

Preferably, the device further comprises a position sensor and an alarm device, wherein the position sensor is arranged on the bracket and used for detecting the position of the regulating block, and the alarm device is suitable for alarming when the position sensor detects that the position change of the regulating block exceeds a threshold value.

Preferably, the K-stage arm cylinder is fixedly provided with a pulley pin shaft corresponding to the pulley, the pulley pin shaft comprises a primary shaft part and a secondary shaft part extending to the end part of the primary shaft part, the primary shaft part is fixed on the K-stage arm cylinder, the shaft diameter of the secondary shaft part is smaller than that of the primary shaft part, and the pulley is sleeved on the secondary shaft part.

Preferably, a baffle is arranged on one side of the secondary shaft part away from the primary shaft part, the primary shaft part is connected with the secondary shaft part through a step end surface, and the step end surface and the baffle can limit the pulley to move along the axial direction of the pulley together.

Preferably, a screw connection piece is arranged between the pulley pin shaft and the baffle, a first perforation penetrating through the primary shaft part and the secondary shaft part is formed in the pulley pin shaft, a second perforation is correspondingly formed in the baffle, an internal thread which is in matched connection with the screw connection piece is arranged in the second perforation, and the screw connection piece penetrates through the first perforation and the second perforation to be in screw connection.

Preferably, the secondary shaft portion is sleeved with a shaft sleeve, the pulley is rotatably sleeved on the shaft sleeve, wear-resistant pieces are arranged on two opposite sides of the shaft sleeve in the axial direction of the shaft sleeve, and the wear-resistant pieces are sleeved on the secondary shaft portion.

The beneficial effects are that:

according to the arm support structure provided by the utility model, the fixed end is positioned in the first-stage arm cylinder and is connected with the first-stage arm cylinder, the telescopic end is positioned in the second-stage arm cylinder and is connected with the second-stage arm cylinder, and the whole structure equivalent to the driving cylinder is positioned in the arm support structure, so that the driving cylinder can be better protected, and the damage and corrosion of the driving cylinder are avoided.

In addition, to the second grade arm section of thick bamboo, locate the second grade arm section of thick bamboo in with the pulley that stretches out and connect on flexible end, can reduce the pulley quantity of locating the cantilever crane side, under the prerequisite of guaranteeing the reliable operation of whole cantilever crane structure, further reduce the holistic external dimension of cantilever crane structure, realize the effective utilization to arm section of thick bamboo inner space, rationally optimize the arrangement structure of pulley.

Drawings

FIG. 1 is a schematic view of a boom structure provided by the present utility model;

FIG. 2 is a cross-sectional view of a portion of the boom structure provided by the present utility model;

FIG. 3 is an enlarged schematic view of a portion of the present utility model at A in FIG. 2;

FIG. 4 is a schematic view of the structure of the adjusting block part provided by the utility model;

FIG. 5 is a cross-sectional view of another part of the boom structure provided by the present utility model;

fig. 6 is a schematic structural diagram of a pulley pin part provided by the utility model.

In the figure:

11. a primary arm cylinder; 12. a secondary arm cylinder; 13. a three-stage arm cylinder; 14. a four-stage arm cylinder;

2. a drive cylinder; 21. A fixed end; 22. A telescoping end;

31. a pulley; 32. An arm extension connector; 33. A telescopic arm connector;

41. an adjusting block; 411. a fixing hole; 412. a guide cylinder; 42. a bracket; 43. a hinge shaft;

5. a position sensor;

61. pulley pin shaft; 6101. a first perforation; 611. a primary shaft portion; 612. a secondary shaft portion; 613. a stepped end face; 62. a baffle; 621. a second perforation; 63. a screw connection; 64. a shaft sleeve; 65. wear resistant members.

Detailed Description

The utility model is described in further detail below with reference to the drawings and examples. It is to be understood that the specific embodiments described herein are merely illustrative of the utility model and are not limiting thereof. It should be further noted that, for convenience of description, only some, but not all of the structures related to the present utility model are shown in the drawings.

In the description of the present utility model, unless explicitly stated and limited otherwise, the terms "connected," "connected," and "fixed" are to be construed broadly, and may be, for example, fixedly connected, detachably connected, or integrally formed; can be mechanically or electrically connected; can be directly connected or indirectly connected through an intermediate medium, and can be communicated with the inside of two elements or the interaction relationship of the two elements. The specific meaning of the above terms in the present utility model will be understood in specific cases by those of ordinary skill in the art.

In the present utility model, unless expressly stated or limited otherwise, a first feature "above" or "below" a second feature may include both the first and second features being in direct contact, as well as the first and second features not being in direct contact but being in contact with each other through additional features therebetween. Moreover, a first feature being "above," "over" and "on" a second feature includes the first feature being directly above and obliquely above the second feature, or simply indicating that the first feature is higher in level than the second feature. The first feature being "under", "below" and "beneath" the second feature includes the first feature being directly under and obliquely below the second feature, or simply means that the first feature is less level than the second feature.

In the description of the present embodiment, the terms "upper", "lower", "right", etc. orientation or positional relationship are based on the orientation or positional relationship shown in the drawings, and are merely for convenience of description and simplicity of operation, and do not indicate or imply that the apparatus or elements referred to must have a specific orientation, be constructed and operated in a specific orientation, and thus should not be construed as limiting the utility model. Furthermore, the terms "first," "second," and the like, are used merely for distinguishing between descriptions and not for distinguishing between them.

The embodiment provides a boom structure. Referring to fig. 1 to 5, the arm support structure comprises a primary arm cylinder 11 and a secondary arm cylinder 12 … … N-stage arm cylinder which are nested in sequence, wherein N is a natural number and is more than or equal to 3, and the arm support structure further comprises a driving cylinder 2 and a pulley mechanism. The driving cylinder 2 comprises a fixed end 21 and a telescopic end 22, wherein the fixed end 21 is positioned in the primary arm cylinder 11 and is connected with the primary arm cylinder 11, and the telescopic end 22 is positioned in the secondary arm cylinder 12 and is connected with the secondary arm cylinder 12. The pulley mechanism comprises pulleys 31, arm extending connecting pieces 32 and arm contracting connecting pieces 33, two pulleys 31 are arranged on the two stages of arm cylinders 12 to N-1, one of the two pulleys 31 on the stage K arm cylinder is wound with the arm extending connecting pieces 32, the other one is wound with the arm contracting connecting pieces 33, two ends of the arm extending connecting pieces 32 extend towards the retracting direction of the arm frame structure and are respectively connected with the stage K-1 arm cylinder and the stage K+1 arm cylinder, two ends of the arm contracting connecting pieces 33 extend towards the extending direction of the arm frame structure and are respectively connected with the stage K-1 arm cylinder and the stage K+1 arm cylinder, K is a natural number and K is more than or equal to 2 and less than or equal to N-1. For the secondary arm cylinder 12, a pulley 31 corresponding to the boom connector 32 is disposed within the secondary arm cylinder 12 and connected to the telescoping end 22.

In this embodiment, the fixed end 21 is located in the primary arm cylinder 11 and connected with the primary arm cylinder 11, the telescopic end 22 is located in the secondary arm cylinder 12 and connected with the secondary arm cylinder 12, and the whole structure corresponding to the driving cylinder 2 is located inside the arm frame structure, so that the driving cylinder 2 can be better protected, and damage and corrosion of the driving cylinder 2 are avoided.

In addition, for the secondary arm cylinder 12, the pulley 31 corresponding to the arm extension connecting piece 32 is arranged in the secondary arm cylinder 12 and connected to the telescopic end 22, so that the number of pulleys arranged at the side end of the arm support can be reduced, the overall external size of the arm support structure is further reduced on the premise that the reliable operation of the whole arm support structure is ensured, the effective utilization of the internal space of the arm support structure is realized, and the arrangement structure of the pulley 31 is reasonably optimized.

In this embodiment, the lower end side walls of the first-stage arm cylinder 11 to the N-stage arm cylinder are all arc-shaped. By the arrangement, the bending modulus of the whole arm support structure can be further improved, and the arm support structure is better suitable for high-rise work platforms.

Specifically, the arc shape of the lower end side walls of the first-stage arm cylinder 11 to the N-stage arm cylinder may be a smooth arc or a polygonal arc, and is not limited herein.

As an alternative embodiment, the number of the arm cylinders is four in this embodiment, namely, the primary arm cylinder 11, the secondary arm cylinder 12, the tertiary arm cylinder 13, and the quaternary arm cylinder 14, and the case where the number of the arm cylinders is four is also shown in fig. 1 to 5.

Specifically, two pulleys 31 corresponding to the secondary arm cylinders 12 are provided in the secondary arm cylinders 12, one of the secondary arm cylinders 12 is connected to the telescopic end of the drive cylinder 2, and the other pulley 31 is connected to the inner wall of the secondary arm cylinder 12. Two pulleys 31 corresponding to the tertiary arm cylinder 13 are provided on the inner wall of the tertiary arm cylinder 13.

In this embodiment, the arm extension connector 32 and the arm retraction connector 33 may each be provided as a rope or a chain.

Specifically, when the boom structure is controlled to extend at the speed V1, the telescopic end 22 of the driving cylinder 2 is controlled to extend at the speed V1 relative to the fixed end 21, so that the secondary arm 12 extends relative to the primary arm 11. The arm extension connecting piece 32 of the secondary arm cylinder 12 and the wound pulley 31 form a movable pulley structure together, and the pulley 31 on the telescopic end 22 is driven by the arm extension connecting piece 32 wound to drive the tertiary arm cylinder 13 to extend at a speed V2 relative to the secondary arm cylinder 12, wherein V2 = 2V1. The arm extending connecting piece 32 of the tertiary arm cylinder 13 and the wound pulley 31 form a movable pulley structure together, and the pulley 31 on the tertiary arm cylinder 13 is driven by the arm extending connecting piece 32 wound on the tertiary arm cylinder 13 to drive the quaternary arm cylinder 14 to extend at a speed V3 relative to the tertiary arm cylinder 13, wherein V3 = 2V2. When the boom structure is required to retract at the speed V1 ', the telescopic end 22 of the driving cylinder 2 is controlled to retract at the speed V1' relative to the fixed end 21, so that the secondary arm cylinder 12 is retracted relative to the primary arm cylinder 11. The telescopic arm connecting piece 33 of the secondary arm cylinder 12 and the wound pulley 31 form a movable pulley structure, and the pulley 31 on the telescopic end 22 is driven by the telescopic arm connecting piece 33 to drive the tertiary arm cylinder 13 to retract at a speed V2 ' relative to the secondary arm cylinder 12, wherein V2 ' =2V1 '. The arm retracting connecting piece 33 of the tertiary arm cylinder 13 and the wound pulley 31 form a movable pulley structure together, and the pulley 31 on the tertiary arm cylinder 13 is driven by the arm retracting connecting piece 33 to drive the quaternary arm cylinder 14 to retract at a speed V3 ' relative to the tertiary arm cylinder, wherein V3 ' =2V2 '.

In this embodiment, the arm support structure further includes an adjusting block 41, the adjusting block 41 is hinged on the primary arm cylinder 11 around the first direction, two sides of the hinged position of the adjusting block 41 are provided with fixing holes 411, two arm extending connectors 32 located on the secondary arm cylinder 12 are provided, first ends of the two arm extending connectors 32 are fixed on the tertiary arm cylinder 13, and second ends are respectively fixed through the two fixing holes 411 after the pulley 31 is wound; the first direction is perpendicular to the telescopic direction of the boom structure and the axial direction of the pulley 31. Specifically, when the arm connectors 32 are pre-tensioned, if the tension forces of the two arm connectors 32 are different, the adjusting block 41 will rotate around the hinge point relative to the primary arm cylinder 11 due to the tension difference, and automatically adjust the tension forces of the arm connectors 32 until the tension forces of the two arm connectors 32 are equal.

Specifically, the adjusting block 41 is provided with two guide cylinders 412 coaxially communicating with the fixing holes 411. The guiding cylinder 412 can guide the arm connecting piece 32 penetrating through the fixing hole 411, so that the arm connecting piece 32 can be penetrated conveniently.

Specifically, a bracket 42 is fixedly provided on the primary arm cylinder 11, and the adjustment block 41 is hinged to the bracket 42 through a hinge shaft 43. Alternatively, a connection hole (not shown) is formed in the bracket 42, a hinge hole (not shown) is formed in the adjustment block 41, the hinge shaft 43 penetrates the connection hole and the hinge hole, and the hinge shaft 43 is rotatably connected to the adjustment block 41 through the hinge hole.

Specifically, the inner peripheral wall of the fixing hole 411 is provided with an internal thread, and the outer peripheral walls of the second ends of the two arm-extending connecting members 32 on the secondary arm cylinder 12 are each provided with an external thread which is in mating connection with the internal thread. The above arrangement makes the arm connecting piece 32 on the secondary arm barrel 12 pass through the corresponding fixing hole 411 to realize reliable fixing with the fixing hole 411. And by screwing the extension arm connecting piece 32, the penetrating length of the extension arm connecting piece 32 relative to the penetrating fixing hole 411 can be controlled, so that the pretightening force of the corresponding extension arm connecting piece 32 can be adjusted.

Specifically, the position sensor 5 is provided on the bracket 42 and is used for detecting the position of the adjustment block 41, and the alarm device is adapted to alarm when the position sensor 5 detects that the position change of the adjustment block 41 exceeds a threshold value. In this embodiment, the boom structure is provided with a control module, and the position sensor 5 can detect the position of the adjusting block 41 in real time and send a position signal to the control module. When the two arm connectors 32 penetrating the adjusting block 41 work normally, the adjusting block 41 may deflect slightly under the pulling force of one arm connector 32, but the deflection is still within the threshold range. When one of the two arm-extending connectors 32 breaks accidentally, the adjusting block 41 is pulled by the other arm-extending connector 32 to generate larger deflection, the position of the adjusting block 41 is changed greatly, the threshold range is exceeded, the position sensor 45 sends a signal for detecting that the adjusting block 41 exceeds the threshold to the control module, and the control module receives the signal and controls the alarm module to alarm in time, so that the signal is fed back to related operators in time, and the aerial work platform is overhauled in time.

In the present embodiment, the position sensor 5 may be provided as a travel switch.

Alternatively, the alarm module may be configured as an alarm or the like and/or a buzzer.

In this embodiment, referring to fig. 6, a pulley pin 61 corresponding to the pulley 31 is fixedly provided on the K-stage arm cylinder, the pulley pin 61 includes a primary shaft portion 611 and a secondary shaft portion 612 extending from an end portion of the primary shaft portion 611, the primary shaft portion 611 is fixed on the K-stage arm cylinder, a shaft diameter of the secondary shaft portion 612 is smaller than a shaft diameter of the primary shaft portion 611, and the pulley 31 is sleeved on the secondary shaft portion 612. The pulley pin 61 provides a reliable assembly space for the pulley 31, and by providing the pulley pin 61, the pulley 31 can be reliably and effectively mounted to the corresponding arm cylinder.

Specifically, a baffle 62 is disposed on a side of the secondary shaft portion 612 away from the primary shaft portion 611, the primary shaft portion 611 and the secondary shaft portion 612 are connected by a stepped end surface 613, and the stepped end surface 613 and the baffle 62 can jointly limit movement of the pulley 31 in the axial direction thereof. Specifically, by the cooperation of the stepped end face 613 and the baffle 62, reliable limit stops can be performed on both ends of the pulley 31, so that the pulley 31 can be reliably and stably mounted on the pulley pin 61, and accidental falling of the pulley 31 is avoided.

Further, a screw connection piece 63 is arranged between the pulley pin shaft 61 and the baffle 62, a first through hole 6101 penetrating through the primary shaft portion 611 and the secondary shaft portion 612 is formed in the pulley pin shaft 61, a second through hole 621 is correspondingly formed in the baffle 62, an internal thread in matched connection with the screw connection piece 63 is arranged in the second through hole 621, and the screw connection piece 63 penetrates through the first through hole 6101 and the second through hole 621 in a screw connection manner, so that the pulley pin shaft 61 and the baffle 62 can be reliably fixed.

Further, the secondary shaft 612 is sleeved with a shaft sleeve 64, the pulley 31 is rotatably sleeved on the shaft sleeve 64, wear-resistant members 65 are respectively arranged on two opposite sides of the shaft sleeve 64 in the axial direction, and the wear-resistant members 65 are sleeved on the secondary shaft 612. The pulley 31 is rotatably connected to the pulley pin 61 through the sleeve 64, and the wear-resistant member 65 is provided to prevent the sleeve 64 from being damaged by frictional heat between the pulley 31 and the pulley pin 61 and between the pulley 31 and the shutter 62.

It is to be understood that the above examples of the present utility model are provided for clarity of illustration only and are not limiting of the embodiments of the present utility model. Various obvious changes, rearrangements and substitutions can be made by those skilled in the art without departing from the scope of the utility model. It is not necessary here nor is it exhaustive of all embodiments. Any modification, equivalent replacement, improvement, etc. which come within the spirit and principles of the utility model are desired to be protected by the following claims.

Claims (10)

1. The utility model provides a cantilever crane structure, includes the first order arm section of thick bamboo (11), second grade arm section of thick bamboo (12) … … N level arm section of thick bamboo that nest in proper order set up, N is natural number and N is greater than or equal to 3, its characterized in that, cantilever crane structure still includes:

the driving cylinder (2) comprises a fixed end (21) and a telescopic end (22), wherein the fixed end (21) is positioned in the primary arm cylinder (11) and is connected with the primary arm cylinder (11), and the telescopic end (22) is positioned in the secondary arm cylinder (12) and is connected with the secondary arm cylinder (12);

the pulley mechanism comprises pulleys (31), an arm extending connecting piece (32) and an arm contracting connecting piece (33), two pulleys (31) are arranged from the secondary arm cylinder (12) to the N-1 level arm cylinder, one of the two pulleys (31) positioned on the K level arm cylinder winds the arm extending connecting piece (32), the other pulley winds the arm contracting connecting piece (33), two ends of the arm extending connecting piece (32) extend towards the retraction direction of the arm frame structure and are respectively connected with the K-1 level arm cylinder and the K+1 level arm cylinder, and two ends of the arm contracting connecting piece (33) extend towards the extension direction of the arm frame structure and are respectively connected with the K-1 level arm cylinder and the K+1 level arm cylinder; k is a natural number, and K is more than or equal to 2 and less than or equal to N-1;

for the secondary arm cylinder (12), the pulley (31) corresponding to the arm extension connecting piece (32) is arranged in the secondary arm cylinder (12) and connected to the telescopic end (22).

2. The boom structure according to claim 1, further comprising an adjusting block (41), wherein the adjusting block (41) is hinged on the primary boom barrel (11) around a first direction, fixing holes (411) are formed in two sides of the hinged position of the adjusting block (41), two boom connecting pieces (32) are arranged on the secondary boom barrel (12), first ends of the two boom connecting pieces (32) are fixed on the tertiary boom barrel (13), and second ends of the two boom connecting pieces are fixedly arranged in the two fixing holes (411) in a penetrating manner after the pulley (31) is wound;

the first direction is perpendicular to the telescopic direction of the boom structure and the axial direction of the pulley (31).

3. Boom structure according to claim 2, characterized in that said adjusting block (41) is provided with two guiding barrels (412) coaxially communicating with said fixing hole (411).

4. The boom structure according to claim 2, characterized in that a bracket (42) is fixedly arranged on the primary boom barrel (11), and the adjusting block (41) is hinged on the bracket (42) through a hinge shaft (43).

5. The boom structure according to claim 2, characterized in that the inner peripheral wall of the fixing hole (411) is provided with an internal thread, and the outer peripheral walls of the second ends of the two boom connecting pieces (32) on the secondary boom barrel (12) are respectively provided with an external thread which is in matching connection with the internal thread.

6. Boom structure according to claim 4, further comprising a position sensor (5) and an alarm device, the position sensor (5) being provided on the bracket (42) and being adapted to detect the position of the adjustment block (41), the alarm device being adapted to alarm when the position sensor (5) detects that the change in position of the adjustment block (41) exceeds a threshold value.

7. The boom structure according to claim 1, wherein a pulley pin shaft (61) corresponding to the pulley (31) is fixedly arranged on the K-stage arm cylinder, the pulley pin shaft (61) comprises a primary shaft portion (611) and a secondary shaft portion (612) extending to the end portion of the primary shaft portion (611), the primary shaft portion (611) is fixed on the K-stage arm cylinder, the shaft diameter of the secondary shaft portion (612) is smaller than that of the primary shaft portion (611), and the pulley (31) is sleeved on the secondary shaft portion (612).

8. The boom structure according to claim 7, characterized in that a baffle (62) is provided on a side of the secondary shaft portion (612) away from the primary shaft portion (611), the primary shaft portion (611) and the secondary shaft portion (612) are connected by a stepped end surface (613), and the stepped end surface (613) and the baffle (62) can limit the movement of the pulley (31) in the axial direction thereof.

9. The boom structure according to claim 8, characterized in that a screw connection piece (63) is arranged between the pulley pin shaft (61) and the baffle (62), a first through hole (6101) penetrating through the primary shaft portion (611) and the secondary shaft portion (612) is formed in the pulley pin shaft (61), a second through hole (621) is correspondingly formed in the baffle (62), an internal thread which is in matched connection with the screw connection piece (63) is arranged in the second through hole (621), and the screw connection piece (63) is penetrated through the first through hole (6101) and the second through hole (621) in a screw connection mode.

10. The boom structure according to claim 8, characterized in that the secondary shaft portion (612) is sleeved with a shaft sleeve (64), the pulley (31) is rotatably sleeved on the shaft sleeve (64), wear-resistant pieces (65) are respectively arranged on two opposite sides of the shaft sleeve (64) in the axial direction, and the wear-resistant pieces (65) are sleeved on the secondary shaft portion (612).