Movable arm adjusting structure and electric loader

Abstract

The movable arm adjusting structure comprises a connecting bridge, the connecting bridge is in a pincerlike shape, the connecting bridge is connected with the middle of the front end of a frame through a connecting structure, the connecting bridge comprises a top plate and a bottom plate, mounting frames are arranged on the two sides of the top plate, the top ends of the mounting frames are hinged to a movable arm of the loading machine, and the bottom plate is connected with the movable arm of the loading machine. The front end of the bottom of the mounting frame is connected with a loading vehicle drive axle through a front adjusting structure, and the rear end of the bottom of the mounting frame is connected with the bottom plate through a rear adjusting structure. By the adoption of the modular design thought, the two parts for controlling the movable arm of the loading machine and the middle part can be prefabricated and assembled separately, and the assembling difficulty of the whole machine is lowered.

Description

Technical Field

[0001] The present invention relates to the technical field of loaders, and in particular to a movable arm adjustment structure and an electric loader. Background Art

[0002] Electric loaders are a type of construction machinery powered by batteries. They utilize an electric motor to drive various operating operations. They are suitable for a wide range of working conditions, particularly in areas with stringent environmental requirements and where long-term, continuous operation is required. With the advancement of battery technology and the reduction of costs, the market outlook for electric loaders is promising, and the market is expected to expand further in the future.

[0003] The loader can be equipped with a variety of different tools as needed, such as ordinary buckets. Forks, jaws and other grippers can also be installed in lumberyards. Therefore, the working tools can be adjusted as needed under different working conditions and different needs. The loader mainly controls the working tools through the front-end control part, that is, the two booms and the components between the two booms (including rocker arms, some tie rods, etc.). In this way, the components are more fragmented during assembly of the whole machine due to the relatively scattered parts, which increases the complexity and difficulty of assembly. It is also inconvenient to make fine adjustments according to different needs and working conditions. Summary of the Invention

[0004] In order to overcome the defects of the prior art, the technical problem to be solved by the present invention is to propose a boom adjustment structure and an electric loader. By adopting a modular design concept, the two parts that control the loader boom can be prefabricated and assembled separately from the middle part, so as to reduce the tedious difficulty in assembling the whole machine.

[0005] To achieve this object, the present invention adopts the following technical solutions:

[0006] The present invention provides a boom adjustment structure, including a connecting bridge, wherein the connecting bridge is clamp-shaped, and the connecting bridge is rotatably connected to the middle part of the front end of the frame through a connecting structure, and the connecting bridge includes a top plate and a bottom plate, and mounting frames are provided on both sides of the top plate, and the top end of the mounting frame is hinged to the loader boom, the bottom front end of the mounting frame and the loader drive axle are detachably connected through a front adjustment structure, and the bottom rear end of the mounting frame and the bottom plate are connected through a rear adjustment detachable structure, and the two loader booms are assembled and adjusted through the front adjustment structure and the rear adjustment structure. In this way, the mounting frame and the loader boom part can be prefabricated and assembled in advance, and then installed on the loader through the front adjustment structure and the rear adjustment structure, and the mounting frame can be moved later to achieve adjustment of the loader boom, so as to further adjust the assembly accuracy and adapt to more tools.

[0007] According to the overall scheme described above, the front adjustment structure includes a fixing pin and a fixing block that cooperates with the fixing pin, the mounting frame is fixed with a slide that cooperates with the top of the loader drive axle, and the top of the loader drive axle is also provided with a guide rail that cooperates with the slide, the slide and the guide rail are slidably connected, and a plurality of fixing grooves that cooperate with the fixing pin are evenly opened on both sides of the loader drive axle from the middle to the wheel direction, the cross-section of the fixing groove is arc-shaped, and when fixed, at least two of the fixing pins cooperate with the fixing grooves, and the two ends of the fixing pin are locked with nuts to the loader drive axle; in this way, the mounting frame is realized The front end is moved and fixed, and the rear adjustment structure includes a fixing foot, which is fixedly connected to the mounting bracket, and a fixing hole is provided on the fixing foot. Positioning holes that match the fixing holes are evenly provided on the base plate along the spacing adjustment direction of the two mounting brackets. Locking bolts are inserted into the fixing holes and the positioning holes to fix the fixing foot and the base plate, thereby realizing the movement and fixation of the rear end of the mounting bracket. With the simultaneous cooperation of the front and rear ends, the mounting bracket moves along the direction of the driving axle of the loader, so that the assembly and subsequent adjustment of the loader boom and the mounting bracket can be conveniently performed.

[0008] During the above-mentioned mobile assembly process, the stability of the overall structure must also be considered. The mounting frame is also fixed with a stabilizing plate that cooperates with the top plate. Stabilizing holes that cooperate with the stabilizing plate are evenly opened on the top plate along the spacing adjustment direction of the two mounting frames. The stabilizing plate and the top plate are connected by stabilizing hole bolts.

[0009] In order to achieve automatic control during movement, an upper beam and a lower beam are provided between the two mounting frames, a double-headed positioning cylinder is provided in the upper beam, and piston rods at both ends of the double-headed positioning cylinder are fixedly connected to the side surfaces of the mounting frame to drive the mounting frame to move along the axial direction of the driving axle of the loader, and the lower beam is fixedly provided on the base plate, and a telescopic rod is provided in the lower beam, and both ends of the telescopic rod are fixedly connected to the mounting frame.

[0010] The connection between the connecting bridge and the frame must realize both the steering function and the connection between the working part and the frame. The connecting structure includes a connecting block and a rotating pin. The connecting block is arranged between the top plate and the bottom plate. The rotating pin is passed through the connecting block. The rotating pin is rotatably connected to the connecting bridge and the connecting block. Steering ears and steering cylinders that cooperate with the mounting frame are arranged on both sides of the connecting block. The steering ears are fixedly connected to the connecting block. One end of the piston rod of the steering cylinder is hinged to the steering ear, and one end of the cylinder barrel of the steering cylinder is hinged to the side of the mounting frame. In this way, the steering of the electric loader is realized by adjusting the steering cylinders on both sides.

[0011] The frame is provided with a rotating seat which cooperates with the connecting block, the rotating seat and the connecting bridge are rotatably connected, and the connecting bridge rotates around the axial direction of the rotating seat, and the axial direction of the rotating seat is perpendicular to the axial direction of the rotating pin; the frame also includes a limiting structure, which includes two vertical blocks and two horizontal blocks which cooperate with the two vertical blocks, the two vertical blocks are fixed on both sides of the connecting block, and the two horizontal blocks are fixed on the frame, when the connecting bridge rotates, when one of the vertical blocks abuts against the horizontal block, the rotation stops, and the rotating seat drives the connecting bridge to rotate in an angle range of 0 to 10 degrees.

[0012] The beneficial effects of the present invention are:

[0013] The present invention adopts a modular setting for the operation control part of the loader, so that the two parts that control the loader's boom can be prefabricated and assembled separately from the middle part (such as the upper beam in this case), and are connected to the loader's body using a front adjustment structure and a rear adjustment structure. This makes assembly easy to operate, and during the assembly process, the front adjustment structure and the rear adjustment structure can also be used to fine-tune the position of the mounting frame and the loader's boom in different situations. Therefore, it can be flexibly adjusted when operating in different environments, and has better adaptability and stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 It is a schematic diagram of the overall structure of the electric loader provided in a specific embodiment of the present invention;

[0015] Figure 2 is a side view of an electric loader without a cab provided in a specific embodiment of the present invention;

[0016] Figure 3 1 is a schematic diagram of the structure of the front regulating structure provided in a specific embodiment of the present invention;

[0017] Figure 4 yes Figure 3 A is an enlarged schematic diagram;

[0018] Figure 5 This is a schematic structural diagram of a connecting bridge provided in a specific embodiment of the present invention from one perspective;

[0019] Figure 6 is a schematic structural diagram of two mounting brackets provided in a specific embodiment of the present invention when viewed from the front at the beginning;

[0020] Figure 7 This is a schematic structural diagram of two mounting brackets provided in a specific embodiment of the present invention at an initial perspective;

[0021] Figure 8is a schematic structural diagram of two mounting brackets provided in a specific embodiment of the present invention at an initial state from another perspective;

[0022] Figure 9 is a schematic structural diagram of two mounting brackets provided in a specific embodiment of the present invention when viewed from the front with the two mounting brackets separated;

[0023] Figure 10 is a schematic structural diagram of two mounting brackets provided in a specific embodiment of the present invention when separated from one another;

[0024] Figure 11 is a schematic structural diagram from another perspective of the two mounting brackets provided in a specific embodiment of the present invention when they are separated;

[0025] Figure 12 2. It is a schematic diagram of the rear view structure of the frame portion provided in a specific embodiment of the present invention;

[0026] Figure 13 2. It is a schematic diagram of the test viewing angle structure of the frame part provided in a specific embodiment of the present invention;

[0027] Figure 14 yes Figure 13 A magnified schematic diagram of B in the middle;

[0028] In the picture:

[0029] 1. Connecting bridge; 2. Connecting structure; 3. Vehicle frame; 11. Top plate; 12. Bottom plate; 4. Mounting frame; 5. Loading boom; 6. Loading vehicle drive axle; 7. Front adjustment structure; 8. Rear adjustment structure; 71. Fixing pin; 72. Fixing block; 41. Slide seat; 61. Guide rail; 62. Fixing slot; 81. Fixing foot; 811. Fixing hole; 121. Positioning hole; 42. Stabilizing plate; 111. Stabilizing hole; 9. Upper beam; 122. Lower beam; 91. Piston rod; 1221. Telescopic rod; 21. Connecting block; 22. Rotating pin; 23. Steering ear; 24. Steering cylinder; 31. Rotating seat; 231. Adjusting hole; 13. Limiting structure; 131. Vertical block; 132. Horizontal block; 51. Mounting part; 52. Connecting rod. DETAILED DESCRIPTION

[0030] The technical solution of the present invention will be further described below with reference to the accompanying drawings and through specific implementation methods.

[0031] As shown in the figure, the present invention provides a boom adjustment structure, including a connecting bridge 1, which is clamp-shaped. The connecting bridge 1 is rotatably connected to the middle part of the front end of the frame 3 through the connecting structure 2. Its main function is to connect the body of the loader and the working device part. The connecting bridge 1 includes a top plate 11 and a bottom plate 12. Mounting frames 4 are provided on both sides of the top plate 11. The top of the mounting frame 4 is hinged to the loader boom 5. A hydraulic system that cooperates with the loader boom 5 is provided and installed on the mounting frame 4, so that the loader boom 5 can be operated during operation. The bottom front end of the mounting frame 4 and the loader drive axle 6 are detachably connected through the front adjustment structure 7, and the bottom rear end of the mounting frame 4 and the bottom plate 12 are detachably connected through the rear adjustment structure 8. In this way, the mounting frame 4 can be pre-made. And first complete the installation of each component on the mounting frame 4 in advance, and then assemble the prefabricated mounting frame 4 with the vehicle body (the loader boom 5 can be connected to the mounting frame 4 before assembling it with the vehicle body, or it can be hinged to the top of the mounting frame 4 after assembling it with the vehicle body). Then, the front adjustment structure 7 and the rear adjustment structure 8 are moved together along the axial direction of the loader drive axle 6 to make the final position adjustment, so as to drive the mounting frame 4 to move to the position where it needs to be assembled, and then fix the mounting frame 4 to complete the assembly. Specifically, the front adjustment structure 7 includes a fixing pin 71 and a fixing block 72 that cooperates with the fixing pin 71. The mounting frame 4 is fixed with a slide 41 that cooperates with the top of the loader drive axle 6. A guide rail 61 is also provided on the top of the moving bridge 6, which cooperates with the slide 41. The slide 41 and the guide rail 61 are slidably connected. A number of fixing grooves 62 that cooperate with the fixing pins 71 are evenly opened on both sides of the loader drive axle 6 from the middle to the wheel direction. The cross-section of the fixing groove 62 is arc-shaped, which can ensure stability during operation or vehicle steering and prevent the two mounting frames 4 from shifting sideways. When fixed, at least two fixing pins 71 cooperate with the fixing grooves 62, and the two ends of the fixing pin 71 are locked with the loader drive axle 6 with nuts. At the same time, the rear adjustment structure 8 includes a fixing foot 81, which is fixedly connected to the mounting frame 4. A fixing hole 811 is opened on the fixing foot 81, and positioning holes that cooperate with the fixing holes 811 are evenly opened on the bottom plate 12 along the spacing adjustment direction of the two mounting frames 4. 121, insert locking bolts into the fixing holes 811 and the positioning holes 121 to fix the fixing feet 81 and the base plate 12; in this way, when the safety frame 4 and the loader boom 5 need to be moved during the assembly process, first loosen the fixing pin 71 and the fixing foot 81 so that the mounting frame 4 can be moved. In order to facilitate movement, an upper beam 9 and a lower beam 122 are provided between the two mounting frames 4, and a double-headed positioning cylinder (not shown in the figure) is provided in the upper beam 9. The piston rods 91 at both ends of the double-headed positioning cylinder are fixedly connected to the side surfaces of the mounting frame 4 to drive the mounting frame 4 to move along the axial direction of the loader drive axle 6. The lower beam 122 is fixed on the base plate 12, and a telescopic rod 1221 is provided in the lower beam 122. Both ends of the telescopic rod 1221 are fixedly connected to the mounting frame 4;During movement, the hydraulic system controls the piston rods 91 at both ends of the double-headed adjustment cylinder to drive the mounting frame 4 to move synchronously. The spacing between the two mounting frames 4 is adjusted according to the working conditions and assembly requirements. At the same time, the telescopic rod 1221 of the lower beam 122 also moves accordingly. Under the cooperation of the guide rail 61 of the loader drive axle 6 and the slide 41 of the mounting frame 4, it plays a guiding and limiting role, making the movement more stable and accurate. After moving to the target position, the fixing pin 71 is aligned with the fixing slot 62 at the front end and is re-locked with the loader drive axle 6 using a nut. At the rear end, the fixing foot 81 is aligned with the corresponding positioning hole 121 and is fixed and connected with bolts. After the above steps are completed, the middle rocker arm and guide rod and other components are installed on the upper beam 9. At the same time, in order to improve stability during operation, a front beam can be set between the loader boom 5 and close to the bucket (the setting method is the same as that of the upper beam 9). Then, the hydraulic system is connected to complete the assembly of the entire machine.

[0032] In the process of assembling and adjusting the distance between the two mounting frames 4, it is necessary to consider the connection problem between the body of the loader and the working device. Before and after the adjustment, the normal driving and operation of the loader should not be affected. The hydraulic system is mainly installed on the mounting frame and can be conveniently adjusted under the action of the double-headed adjustment cylinder in the upper beam 9. Therefore, the problem is concentrated on driving and steering. Therefore, the connection structure 2 includes a connecting block 21 and a rotating pin 22. The connecting block 21 is set between the top plate 11 and the bottom plate 12. The rotating pin 22 is passed through the connecting block 21. The rotating pin 22 rotates with the connecting bridge 1 and the connecting block 21. Connection; Specifically, the two ends of the rotating pin 22 are rotatably connected to the top plate 11 and the bottom plate 12 of the connecting bridge 1, and the part of the rotating pin 22 located between the top plate 11 and the bottom plate 12 is rotatably connected to the connecting block 21. Furthermore, steering ears 23 and steering cylinders 24 that cooperate with the mounting frame 4 are provided on both sides of the connecting block 21. The steering ears 23 and the connecting block 21 are fixedly connected. One end of the piston rod 91 of the steering cylinder 24 is hinged to the steering ear 23, and one end of the cylinder barrel of the steering cylinder 24 is hinged to the side of the mounting frame 4. At the same time, a rotating seat 31 that cooperates with the connecting block 21 is installed on the vehicle frame 3. The rotating seat 31 is rotatably connected to the connecting bridge 1, and the connecting bridge 1 rotates around the axis of the rotating seat 31, and the axis of the rotating seat 31 is perpendicular to the axis of the rotating pin 22. In this way, the steering can be performed by adjusting the stroke of the two steering cylinders 24 by the hydraulic system. Since one side of the connecting block 21 is connected to the rotating seat 31 on the frame 3, the connecting block 21 cannot rotate along the axis of the rotating pin 22. That is, in the process of adjusting the stroke of the two steering cylinders 24 for steering, the force of the two steering cylinders 24 will be transmitted to the corresponding mounting frame 4. Since the two mounting frames 4 and the connecting bridge 1 are fixedly connected, the connecting bridge 1 can only be driven to rotate along the rotating pin 22 to achieve steering. During this process, due to the adjustment of the spacing between the two mounting frames 4, in order to better achieve the steering function, the angles of the two steering cylinders 24 may sometimes be adjusted as needed. Therefore, the steering ear 23 is evenly provided with a plurality of adjustment holes 231 along the spacing adjustment direction of the two mounting frames 4. When adjusting the boom spacing, one end of the piston rod 91 of the steering cylinder 24 is hinged to the corresponding adjustment hole 231 to ensure the normal operation of the steering cylinder 24.That is, when the distance between the two mounting brackets 4 needs to be increased during assembly, the piston rod 91 of the steering cylinder 24 can be adjusted outwardly to the hinged position to ensure normal steering function. When not in motion, the two steering cylinders 24 can also achieve left and right swinging function. At the same time, the swivel seat 31 and the connecting block 1 are rotatably connected, so that the vehicle body can also maintain a certain stability when passing through certain rough roads. The rotation angle range of the connecting bridge 1 is 0-10°. When swinging up and down, to ensure a safe swing angle, a limiting structure is required. Therefore, it also includes a limiting structure 13. The limiting structure 13 includes two vertical blocks 131 and two transverse blocks 132 that cooperate with the two vertical blocks 131. The two vertical blocks 131 are fixed on both sides of the connecting block 21, and the two transverse blocks 132 are fixed on the vehicle frame 3. When the connecting bridge 1 rotates, when one of the vertical blocks 131 abuts against the transverse block 132, the rotation stops.

[0033] Whether driving, turning, or operating with the loader boom 5, the stability of the connection between the mounting frame 4 and the connecting bridge 1 is particularly important. Therefore, the mounting frame 4 is also fixed with a stabilizing plate 42 that cooperates with the top plate 11. Stabilizing holes 111 that cooperate with the stabilizing plate 42 are evenly opened on the top plate 11 along the direction of adjusting the spacing between the two mounting frames 4. The stabilizing plate 42 and the top plate 11 are bolted together through the stabilizing holes 111. This further strengthens the stability of the assembled mounting frame 4 and the connecting bridge 1, ensuring safety during operation.

[0034] It should be further explained that the above-mentioned rear adjustment structure 8 and the upper beam 9 are provided with a double-headed adjustment cylinder, and the stabilizing plate 42 can also be implemented with a rack structure or a worm structure. This example only uses a relatively simple implementation case. It should also be explained that in the part where the loader boom 5 is connected to the working tool (bucket, fork and jaw, etc.), since the spacing of the loader boom 5 is different when the mounting frame 4 is assembled under different working conditions, the spacing of the mounting part 51 used to connect the loader boom 5 and the working tool also needs to be adjusted synchronously, such as setting a connecting rod 52 with retractable ends between the two mounting parts 51, so that the two mounting parts 51 are also convenient for cooperating with the loader boom 5 at different spacings after assembly.

[0035] An electric loader adopts the above-mentioned boom adjustment structure; it can realize more complex environments and working tools, and is more convenient to assemble and adjust. Fixation and assembly adjustment are carried out by relatively simple mechanical means, which is convenient for operation.

[0036] The present invention is described through preferred embodiments. Those skilled in the art will appreciate that various modifications or equivalent substitutions may be made to these features and embodiments without departing from the spirit and scope of the present invention. The present invention is not limited to the specific embodiments disclosed herein; other embodiments falling within the scope of the claims of this application are intended to be protected by the present invention.

Claims

1. A boom adjustment structure, comprising a connecting bridge (1), wherein the connecting bridge (1) is in a clamp shape, and the connecting bridge (1) is rotatably connected to the middle of the front end of a frame (3) through a connecting structure (2), and is characterized in that: The connecting bridge (1) comprises a top plate (11) and a bottom plate (12), and mounting frames (4) are arranged on both sides of the top plate (11), the top end of the mounting frame (4) is hinged to the loader boom (5), the bottom front end of the mounting frame (4) and the loader drive axle (6) are detachably connected via a front adjustment structure (7), the bottom rear end of the mounting frame (4) and the bottom plate (12) are detachably connected via a rear adjustment structure (8), and the two loader booms (5) are assembled and adjusted via the front adjustment structure (7) and the rear adjustment structure (8).

2. A boom adjustment structure according to claim 1, characterized in that: The front adjustment structure (7) comprises a fixing pin (71) and a fixing block (72) matched with the fixing pin (71); the mounting frame (4) is fixedly provided with a slide seat (41) matched with the top of the loader driving axle (6); the top of the loader driving axle (6) is also provided with a guide rail (61) matched with the slide seat (41); the slide seat (41) and the guide rail (61) are slidably connected; a plurality of fixing grooves (62) matched with the fixing pin (71) are evenly provided on both sides of the loader driving axle (6) from the middle to the wheel direction; the fixing grooves (62) are arc-shaped in cross section; when fixed, at least two fixing pins (71) are matched with the fixing grooves (62); and both ends of the fixing pin (71) are locked with the loader driving axle (6) by nuts.

3. A boom adjustment structure according to claim 2, characterized in that: The rear adjustment structure (8) comprises a fixing foot (81), the fixing foot (81) being fixedly connected to the mounting frame (4), a fixing hole (811) being provided on the fixing foot (81), and positioning holes (121) cooperating with the fixing holes (811) being evenly provided on the base plate (12) along the spacing adjustment direction of the two mounting frames (4), and locking bolts being inserted into the fixing holes (811) and the positioning holes (121) so as to fix the fixing foot (81) and the base plate (12).

4. The boom adjustment structure according to claim 3, characterized in that: The mounting frame (4) is also fixedly provided with a stabilizing plate (42) that cooperates with the top plate (11); stabilizing holes (111) that cooperate with the stabilizing plate (42) are evenly opened on the top plate (11) along the spacing adjustment direction of the two mounting frames (4); the stabilizing plate (42) and the top plate (11) are bolted together via the stabilizing holes (111).

5. The boom adjustment structure according to claim 3, characterized in that: An upper beam (9) and a lower beam (122) are arranged between the two mounting frames (4); a double-headed adjustment cylinder is arranged inside the upper beam (9); piston rods (91) at both ends of the double-headed adjustment cylinder are fixedly connected to the side surfaces of the mounting frames (4) to drive the mounting frames (4) to move along the axial direction of the loader driving axle (6); the lower beam (122) is fixedly arranged on the bottom plate (12); a telescopic rod (1221) is arranged inside the lower beam (122); and both ends of the telescopic rod (1221) are fixedly connected to the mounting frames (4).

6. The boom adjustment structure according to claim 5, characterized in that: The connection structure (2) comprises a connection block (21) and a rotation pin (22); the connection block (21) is arranged between the top plate (11) and the bottom plate (12); the rotation pin (22) penetrates the connection block (21); the rotation pin (22) is rotationally connected to the connection bridge (1) and the connection block (21); Steering ears (23) and steering cylinders (24) that match the mounting frame (4) are arranged on both sides of the connecting block (21); the steering ears (23) and the connecting block (21) are fixedly connected; one end of the piston rod (91) of the steering cylinder (24) is hinged to the steering ears (23); and one end of the cylinder barrel of the steering cylinder (24) is hinged to the side of the mounting frame (4); The frame (3) is provided with a rotating seat (31) matched with the connecting block (21); the rotating seat (31) is rotatably connected to the connecting bridge (1); the connecting bridge (1) rotates around the axis direction of the rotating seat (31); the axis direction of the rotating seat (31) is perpendicular to the axis direction of the rotating pin (22).

7. The boom adjustment structure according to claim 6, characterized in that: The steering lug (23) is evenly provided with a plurality of adjustment holes (231) along the spacing adjustment direction of the two mounting frames (4); when the whole machine is assembled, one end of the piston rod (91) of the steering cylinder (24) is hinged to the corresponding adjustment hole (231) to ensure the normal operation of the steering cylinder (24).

8. The boom adjustment structure according to claim 6, characterized in that: The invention also comprises a limiting structure (13), wherein the limiting structure (13) comprises two vertical blocks (131) and two horizontal blocks (132) matched with the two vertical blocks (131), wherein the two vertical blocks (131) are fixedly arranged on both sides of the connecting block (21), and the two horizontal blocks (132) are fixedly arranged on the frame (3); when the connecting bridge (1) rotates, when one of the vertical blocks (131) abuts against the horizontal block (132), the rotation stops.

9. The boom adjustment structure according to claim 8, characterized in that: The rotation angle range of the connecting bridge (1) is 0 to 10°.

10. An electric loader, characterized in that: A boom adjustment structure as described in any one of claims 1 to 9 is adopted.

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