Special lifting appliance for prefabricated stairs

Abstract

The utility model provides a special lifting appliance for a prefabricated stair. The special lifting appliance comprises a main lifting ring, a pulley assembly and a sling, pulley assemblies are arranged on the two sides of the main hanging ring respectively. Each pulley assembly comprises a pulley support, a pulley and a locking device. When the locking device is in an open state, the pulley and the pulley bracket are rotationally connected; the pulleys of the two pulley assemblies are each in lap joint with a sling, the two ends of each sling are each provided with a lifting hook used for lifting a prefabricated stair, and the pulleys and the slings are fixed to the pulley supports through the locking devices in the locking state. The device overcomes the defect that a special lifting appliance for the prefabricated stairs in the prior art needs to prepare slings with different lengths for the prefabricated stairs with different specifications, so that the equipment adaptability is low.

Description

Technical Field

[0001] The utility model relates to the technical field of construction devices, and particularly relates to a special sling for precast stairs. Background Art

[0002] In construction, when hoisting precast stairs, generally two long and two short slings are used to lift the four corners of the stairs, so that the stairs form an inclined posture after being lifted, to meet the angle requirements for the installation position of the stairs. However, for different precast stairs, in order to make the lifted stairs reach the required angle, the length requirements for the slings will be different. In this way, it is very difficult for the existing slings to have good universality, and different lengths of slings need to be prepared for different stairs. Summary of the Invention

[0003] Therefore, the technical problem to be solved by the utility model is to overcome the defect that the special sling for precast stairs in the prior art needs to prepare slings of different lengths for different specifications of precast stairs, resulting in low adaptability of the equipment.

[0004] To solve the above technical problem, the present application provides a special sling for precast stairs, including a main lifting ring, a pulley assembly and a sling; pulley assemblies are arranged on both sides of the main lifting ring, and the pulley assembly includes a pulley bracket, a pulley and a locking device; when the locking device is in the open state, a rotational connection is formed between the pulley and the pulley bracket; a sling is lapped on each of the pulleys of the two pulley assemblies, and hooks for lifting the precast stairs are arranged at both ends of the sling, and the locking device fixes the pulley and the sling on the pulley bracket in the locked state.

[0005] Further, the sling is a steel cable, a fixed side plate is fixedly connected to one side of the pulley, the locking device includes a movable side plate, the movable side plate is slidably connected to the other side of the pulley, the outer edges of both the movable side plate and the fixed side plate protrude from the rim of the pulley, and the sling is located between the movable side plate and the fixed side plate; when the locking device is in the open state, the movable side plate does not contact the sling; when the locking device is in the locked state, the movable side plate presses towards the fixed side plate and clamps the sling between the movable side plate and the fixed side plate.

[0006] Further, a rotational connection is formed between the movable side plate and the pulley bracket; after the movable side plate presses towards the fixed side plate, the surface of the fixed side plate away from the movable side plate presses and fits with the inner wall of the pulley bracket, thereby forming a frictional force to prevent the pulley from rotating.

[0007] Further, a limiting device is arranged between the movable side plate and the pulley bracket, and the limiting device limits the rotation between the movable side plate and the pulley bracket.

[0008] Further, a sliding shaft is provided on the side of the movable side plate away from the fixed side plate. A sliding connection is formed between the sliding shaft and the pulley bracket. The limiting device is a sliding key, which is arranged on the sliding shaft, and a key groove adapted to the sliding key is arranged on the pulley bracket.

[0009] Further, a central hole is formed in the sliding shaft, and the central hole penetrates the movable side plate; a rotating shaft is arranged at the axis of the pulley, and one end of the rotating shaft is inserted into the central hole, and a rotating connection is formed between the rotating shaft and the central hole.

[0010] Further, the locking device includes a spring and a nut. A compressed spring is arranged between the movable side plate and the pulley bracket. The spring is arranged around the outside of the sliding shaft. The head end of the sliding shaft penetrates and protrudes from the pulley bracket. A nut is threadedly connected to the head end of the sliding shaft, and the nut can abut against the pulley bracket. The distance between the movable side plate and the pulley bracket can be adjusted by rotating the nut.

[0011] Further, when the locking device is in the open state, a pin for restricting the displacement of the movable side plate is inserted between the sliding shaft and the pulley bracket. One end of the pin faces downward and is connected with a pulling rope. The nut is away from the pulley bracket, and the distance from the nut to the pulley bracket is not less than the displacement amount of the movable side plate for clamping the sling; when the locking device changes from the open state to the locked state, the pulling rope is pulled to make the pin disengage from between the sliding shaft and the pulley bracket.

[0012] Further, a boss is arranged on the outer side surface of the pulley bracket. The head end of the sliding shaft penetrates the boss, and the pin is inserted on the side wall of the boss; when the locking device is in the open state, the distance from the nut to the boss is not less than the displacement amount of the movable side plate for clamping the sling.

[0013] Further, when the locking device is in the open state, the end of the rotating shaft inserted into the central hole does not contact the pin, and a stop pin for restricting the displacement between the rotating shaft and the pulley bracket is arranged at the other end of the rotating shaft penetrating the pulley bracket.

[0014] By adopting the above technical solutions, the utility model has the following technical effects:

[0015] The special hoist for precast stairs provided by the present utility model passes two equal-length sling ropes through two pulley assemblies respectively. Since the pulley assemblies are provided with locking devices, when the locking devices are opened, the lengths of the sling rope sections extending from both sides of the pulley can be adjusted. In this way, during use, the same sling rope is used for lifting on each side of the high and low ends of the precast stairs. Before that, the lengths of the sling ropes on both sides of the high and low ends are calculated according to the correct posture of the precast stairs, and the lengths of the sling ropes extending from both sides of the pulley are adjusted according to the calculation results, and then the sling ropes are locked by the locking devices. In this way, when the precast stairs are lifted, the precast stairs can be in the correct posture. Since the lengths of the sling ropes extending from both sides of the pulley can be adjusted arbitrarily, there is no need to prepare sling ropes of different lengths for each specification of precast stairs, which enhances the adaptability of the equipment. In addition, since the sling ropes are locked to the pulley, it prevents the precast stairs from accidentally rotating and deviating from the predetermined posture during the lifting process, and prevents the risk of overturning caused by excessive rotation. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the specific embodiments of the present utility model or the technical solutions in the prior art, the following will briefly introduce the drawings required for use in the description of the specific embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present utility model. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0017] Figure 1 The main structural schematic view of the embodiment of the present utility model;

[0018] Figure 2 The left structural schematic view of the embodiment of the present utility model;

[0019] Figure 3 The main structural schematic view of the pulley assembly of the embodiment of the present utility model (the locking device is in the open state);

[0020] Figure 4 For Figure 3 The cross-sectional view at A-A in

[0021] Figure 5 For Figure 3 The cross-sectional view at B-B in

[0022] Description of the reference numerals:

[0023] 1 - Main lifting ring, 2 - Pulley assembly, 3 - Suspension rope, 4 - Hook, 5 - Pulling rope, 6 - Prefabricated staircase, 7 - Auxiliary lifting ring, 8 - Pulley bracket, 9 - Boss, 10 - Movable side plate, 11 - Pin, 12 - Nut, 13 - Slide shaft, 14 - Pin ring, 15 - Stop pin, 16 - Pulley, 17 - Spring, 18 - Central hole, 19 - Friction plate, 20 - Fixed side plate, 21 - Rotating shaft, 22 - Keyway, 23 - Slide key. Detailed implementation mode

[0024] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of them. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0025] It should be noted that in the description of the present invention, the coordinate system used in describing the orientation is determined by the attitude of its front view, and the viewing angle naming of the corresponding view is also based on this. Therefore, the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc. in this specification indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings. It is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation to the present invention.

[0026] In the description of the present invention, it should be noted that unless otherwise clearly specified and limited, the terms "installation", "connection", and "connection" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium, and it can be the communication inside two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific situations.

[0027] In addition, the technical features involved in different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0028] This embodiment provides a special lifting tool for prefabricated staircases. In one implementation, as Figures 1 to 5As shown in the figure, it includes a main lifting ring 1, a pulley assembly 2 and a sling 3. The main lifting ring 1 is provided with a pulley assembly 2 on each side. The pulley assembly 2 includes a pulley bracket 8, a pulley 16 and a locking device. An equal-length sling 3 is lapped on the pulley 16 of each of the two pulley assemblies 2, and hooks 4 for lifting the precast staircase 6 are provided at both ends of the sling 3. A secondary lifting ring 7 can be provided at the top of the pulley bracket 8 and connected in series with the main lifting ring 1, so that a certain angle of swing can be formed between the pulley assembly 2 and the main lifting ring 1, which is beneficial for the pulley assembly 2 to better adapt to the tensile direction of the sling 3. When the locking device is in the open state, a rotational connection is formed between the pulley 16 and the pulley bracket 8. The locking device fixes the pulley 16 and the sling 3 on the pulley bracket 8 in the locked state.

[0029] This device passes two equal-length slings 3 through the two pulley assemblies 2 respectively. Since the pulley assembly 2 is provided with a locking device, when the locking device is opened, the lengths of the sling 3 sections extending from both sides of the pulley 16 can be adjusted. In this way, when in use, the same sling 3 is used for lifting on each side of the high and low ends of the precast staircase 6. Before that, the lengths of the slings 3 on the high and low ends on both sides are calculated according to the correct posture of the precast staircase 6. After adjusting the lengths of the slings 3 extending from both sides of the pulley 16 according to this calculation result and locking the sling 3 with the locking device, the precast staircase 6 can be in the correct posture when being lifted. Since the lengths of the sling 3 extending from both sides of the pulley 16 can be adjusted arbitrarily, there is no need to prepare slings 3 of different lengths for each specification of the precast staircase 6, enhancing the adaptability of the equipment. In addition, since the sling 3 is locked with the pulley 16, it prevents the precast staircase 6 from accidentally rotating and deviating from the predetermined posture during the lifting process, and prevents the risk of overturning caused by excessive rotation.

[0030] Based on the above embodiment, in a preferred embodiment, as Figures 1 to 5 shown, the sling 3 is a steel cable. A fixed side plate 20 is fixedly connected to one side of the pulley 16. The locking device includes a movable side plate 10. The movable side plate 10 is slidably connected to the other side of the pulley 16. The outer edges of both the movable side plate 10 and the fixed side plate 20 protrude from the rim of the pulley 16. The sling 3 is located between the movable side plate 10 and the fixed side plate 20. When the locking device is in the open state, the movable side plate 10 does not contact the sling 3. When the locking device is in the locked state, the movable side plate 10 presses towards the fixed side plate 20 and clamps the sling 3 between the movable side plate 10 and the fixed side plate 20. To enhance the clamping force, friction plates 19 can be provided on both sides of the movable side plate 10 and the fixed side plate 20 that are close to each other.

[0031] When the sling 3 is a chain and the pulley 16 is set as a sprocket adapted thereto, the locking device can actually lock only the rotation of the pulley 16 to simultaneously lock the sling 3. However, in construction sites, steel cables are often used as lifting tools. Therefore, how to lock a steel cable that is prone to slipping has become a problem. In this embodiment, a fixed side plate 20 and a movable side plate 10 protruding from the rim of the pulley 16 are used to clamp the sling 3 along the axial direction of the pulley 16. Compared with the solution of using friction blocks to clamp along the radial direction of the pulley 16, in this solution, since the sling 3 will turn around the pulley 16, a relatively longer contact interval is formed between the sling 3 and the clamping plates on both axial sides of the pulley 16. Therefore, a more stable lock can be formed, the occurrence of slipping can be reduced, the wear of the clamping components can be reduced, and their service life can be extended.

[0032] Based on the above embodiment, in a preferred embodiment, the movable side plate 10 and the pulley bracket 8 are rotatably connected. No specific illustration is given in this embodiment, but reference can be made to Figure 4 to understand the similar parts. Although the movable side plate 10 is rotatable, after the movable side plate 10 is pressed towards the fixed side plate 20, the side of the fixed side plate 20 away from the movable side plate 10 is pressed and fitted against the inner wall of the pulley bracket 8, thereby forming a frictional force that prevents the pulley 16 from rotating, and finally realizing the simultaneous locking of the pulley 16 and the sling 3, and reducing the occurrence of slipping. To enhance the corresponding frictional force, a friction plate 19 can be provided on the corresponding contact surface. This structure that does not limit the rotation of the movable side plate 10 has the advantages of simpler structure and more convenient manufacturing compared with the embodiment that will be mentioned below and adopts restricted rotation. However, since the locking of the pulley 16 and the sling 3 is achieved through the transmission connection of two-stage friction components, the phenomenon of slipping is relatively more likely to occur.

[0033] In another preferred embodiment, a limiting device is provided between the movable side plate 10 and the pulley bracket 8, and the limiting device restricts the rotation between the movable side plate 10 and the pulley bracket 8. In this way, since the rotation of the movable side plate 10 is strictly restricted, as a friction component on one side of the sling 3, the situation of the sling 3 slipping caused by its own rotation is avoided.

[0034] The limiting device can either adopt Figure 5 the key connection form shown, or adopt the form of providing more than two sliding pins on the wall plate of the movable side plate 10. The key connection has the advantages of more compact structure and more convenient processing and manufacturing. The following takes the limiting device as the sliding key 23 to illustrate the relevant specific structure: As Figure 5 shown, a sliding shaft 13 is provided on the side of the movable side plate 10 away from the fixed side plate 20, and a sliding connection is formed between the sliding shaft 13 and the pulley bracket 8. The sliding key 23 is provided on the sliding shaft 13, and a key groove 22 adapted to the sliding key 23 is provided on the pulley bracket 8.

[0035] Based on the above-described embodiments, in a preferred embodiment, as Figure 4 and 5 shown, a central hole 18 is formed in the sliding shaft 13, and the central hole 18 penetrates through the movable side plate 10; a rotating shaft 21 is provided at the axis center of the pulley 16, and one end of the rotating shaft 21 is inserted into the central hole 18, and the rotating shaft 21 forms a rotational connection with the central hole 18. Although the pulley 16 can form a rotational connection with the pulley bracket 8 by relying on a shaft member on one side, for example Figure 4 only connects the left end of the rotating shaft 21 to the pulley bracket 8, this will cause the pulley 16 to form a cantilever beam support structure, reducing its force-bearing upper limit. However, in this embodiment, by forming a central hole 18 in the sliding shaft 13, the sliding shaft 13 becomes a bushing-type component, and then by inserting one end of the rotating shaft 21 into the central hole 18, both sides of the pulley 16 can be effectively supported, improving the force-bearing upper limit of the pulley 16. And by transforming the sliding shaft 13 into a bushing, while providing better support for the pulley 16, the volume of the entire device is not overly increased, making the structure of the entire device very compact.

[0036] Based on the above-described embodiments, in a preferred embodiment, as Figure 4 and 5 shown, the locking device includes a spring 17 and a nut 12. A compressed spring 17 is provided between the movable side plate 10 and the pulley bracket 8. The spring 17 is disposed around the outer side of the sliding shaft 13, which can make the structure more compact. The head end of the sliding shaft 13 penetrates and protrudes from the pulley bracket 8, and a nut 12 is threadedly connected to the head end of the sliding shaft 13. The nut 12 can abut against the pulley bracket 8. By tightening the nut 12, the movable side plate 10 can be driven to move outward to loosen the sling 3; and by loosening the nut 12, under the resilience of the spring 17, the movable side plate 10 can be moved inward to clamp the sling 3. In short, by rotating the nut 12, the distance between the movable side plate 10 and the pulley bracket 8 can be adjusted, thereby realizing the opening and locking of the locking device. This structure of the locking device has the advantages of simple structure, convenient manufacturing and high reliability, and because the adjustment of the movable side plate 10 is in the form of screw drive, and the screw mechanism is a strong force-increasing structure, in this way, while ensuring that the adjustment force is of an appropriate magnitude, the elastic force of the spring 17 can be increased as much as possible, so as to provide a stronger clamping force for the clamping action and prevent the occurrence of slipping.

[0037] Based on the above-described embodiments, in a preferred embodiment, as Figures 1 to 5As shown, when the locking device is in the open state, a pin 11 that restricts the displacement of the movable side plate 10 is inserted between the sliding shaft 13 and the pulley bracket 8. One end of the pin 11 faces downward and is connected to a pulling rope 5 through a pin ring 14. The nut 12 is away from the pulley bracket 8, and the distance from the nut 12 to the pulley bracket 8 is not less than the displacement amount of the movable side plate 10 for clamping the sling 3. When the locking device changes from the open state to the locked state, the pulling rope 5 is pulled to disengage the pin 11 from between the sliding shaft 13 and the pulley bracket 8.

[0038] This setting enables the lifting of the precast staircase 6 without specifically calculating the extension ratio at both ends of the sling 3 and then adjusting and locking it at the initial stage of lifting. When lifting is required, the pulley assembly 2 is placed at the midpoint of the sling 3. After lifting the precast staircase 6, through the free rotation of the sling 3 and the pulley 16, the lower end of the precast staircase 6 is pressed down and the other end is lifted, so that the precast staircase 6 originally in a lying posture is rotated and adjusted to the required inclined posture through rotation. When the adjustment is in place, the pulling rope 5 is pulled to disengage the pin 11, and as the spring 17 rebounds, the movable side plate 10 completes the clamping and locking. This simplifies the operation steps and improves the operation efficiency.

[0039] Based on the above-described embodiment, in a preferred embodiment, as Figure 4 and 5 shown, a boss 9 is provided on the outer side surface of the pulley bracket 8. The head end of the sliding shaft 13 penetrates through the boss 9, and the pin 11 is inserted on the side wall of the boss 9. When the locking device is in the open state, the distance from the nut 12 to the boss 9 is not less than the displacement amount of the movable side plate 10 for clamping the sling 3. After the boss 9 is provided, on the one hand, the pulling rope 5 can be kept away from components such as the pulley 16 that may rotate and the spring 17 that may hook the pulling rope 5, avoiding situations such as the pulling rope 5 being accidentally wound and hooked during the adjustment of the posture of the precast staircase 6, which may interfere with normal operation; on the other hand, setting the boss 9 can increase the contact and cooperation distance between the sliding shaft 13 and the pulley bracket 8, thereby enhancing the guiding property of the sliding connection and reducing the occurrence of sliding jamming.

[0040] Based on the above-described embodiment, in a preferred embodiment, as Figure 4 and 5 shown, when the locking device is in the open state, one end of the rotating shaft 21 inserted into the central hole 18 does not contact the pin 11, and the other end of the rotating shaft 21 penetrates through the pulley bracket 8 and a stop pin 15 that restricts the displacement between the rotating shaft 21 and the pulley bracket 8 is provided. Setting the stop pin 15 can prevent the axial movement of the rotating shaft 21. If the rotating shaft 21 can move freely, then when the movable side plate 10 moves outward to achieve the open state, it may drive the rotating shaft 21 to move outward together, and then it may cause the rotating shaft 21 to block the insertion hole of the pin 11, making it difficult to insert the pin 11 and interfering with normal operation.

[0041] Obviously, the above embodiments are merely examples given for clear illustration and are not limitations on the implementation manners. For those of ordinary skill in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all implementation manners here. And the obvious changes or modifications derived therefrom still fall within the protection scope of the creation of the present utility model.

Claims

1. A special lifting tool for precast stairs, characterized in that, It includes a main lifting ring (1), a pulley assembly (2) and a sling (3); the main lifting ring (1) is provided with a pulley assembly (2) on each side, and the pulley assembly (2) includes a pulley bracket (8), a pulley (16) and a locking device; when the locking device is in the open state, a rotational connection is formed between the pulley (16) and the pulley bracket (8); on the pulleys (16) of the two pulley assemblies (2), an equal-length sling (3) is lapped respectively, and hooks (4) for lifting a precast staircase (6) are provided at both ends of the sling (3), and the locking device fixes the pulley (16) and the sling (3) on the pulley bracket (8) in the locked state.

2. The special hoisting device for precast stairs according to claim 1, wherein The sling (3) is a steel cable, and a fixed side plate (20) is fixedly connected to one side of the pulley (16). The locking device includes a movable side plate (10), and the movable side plate (10) is slidably connected to the other side of the pulley (16). The outer edges of both the movable side plate (10) and the fixed side plate (20) protrude beyond the rim of the pulley (16), and the sling (3) is located between the movable side plate (10) and the fixed side plate (20); when the locking device is in the open state, the movable side plate (10) does not contact the sling (3); when the locking device is in the locked state, the movable side plate (10) presses towards the fixed side plate (20) and clamps the sling (3) between the movable side plate (10) and the fixed side plate (20).

3. The special lifting device for precast stairs according to claim 2, characterized in that, A rotational connection is formed between the movable side plate (10) and the pulley bracket (8); after the movable side plate (10) presses towards the fixed side plate (20), the surface of the fixed side plate (20) away from the movable side plate (10) presses and fits against the inner wall of the pulley bracket (8), thereby forming a frictional force that prevents the pulley (16) from rotating.

4. The special lifting tool for precast stairs according to claim 2, wherein, A limiting device is provided between the movable side plate (10) and the pulley bracket (8), and the limiting device restricts the rotation between the movable side plate (10) and the pulley bracket (8).

5. The special lifting tool for precast stairs according to claim 4, characterized in that, A sliding shaft (13) is provided on the surface of the movable side plate (10) away from the fixed side plate (20), and a sliding connection is formed between the sliding shaft (13) and the pulley bracket (8). The limiting device is a sliding key (23), and the sliding key (23) is provided on the sliding shaft (13), and a key groove (22) adapted to the sliding key (23) is provided on the pulley bracket (8).

6. The special hoisting tool for precast stairs according to claim 5, characterized in that, A central hole (18) is provided in the sliding shaft (13), and the central hole (18) penetrates the movable side plate (10); a rotating shaft (21) is provided at the axis center of the pulley (16), and one end of the rotating shaft (21) is inserted into the central hole (18), and a rotational connection is formed between the rotating shaft (21) and the central hole (18).

7. The special hoist for precast stairs according to claim 6, characterized in that, The locking device includes a spring (17) and a nut (12). A compressed spring (17) is provided between the movable side plate (10) and the pulley bracket (8), and the spring (17) is wound around the outside of the sliding shaft (13). The head end of the sliding shaft (13) penetrates and protrudes beyond the pulley bracket (8), and a nut (12) is threadedly connected to the head end of the sliding shaft (13). The nut (12) can abut against the pulley bracket (8), and the distance between the movable side plate (10) and the pulley bracket (8) can be adjusted by rotating the nut (12).

8. The special lifting tool for precast stairs according to claim 7, characterized in that, When the locking device is in the open state, a pin (11) that restricts the displacement of the movable side plate (10) is inserted between the sliding shaft (13) and the pulley bracket (8). One end of the pin (11) faces downward and is connected to a pull rope (5). The nut (12) is away from the pulley bracket (8), and the distance from the nut (12) to the pulley bracket (8) is not less than the displacement amount of the movable side plate (10) when clamping the sling (3). When the locking device changes from the open state to the locked state, the pull rope (5) is pulled to disengage the pin (11) from between the sliding shaft (13) and the pulley bracket (8).

9. The special sling for precast stairs according to claim 8, characterized in that, A boss (9) is provided on the outer side surface of the pulley bracket (8). The head end of the sliding shaft (13) penetrates through the boss (9), and the pin (11) is inserted on the side wall of the boss (9). When the locking device is in the open state, the distance from the nut (12) to the boss (9) is not less than the displacement amount of the movable side plate (10) when clamping the sling (3).

10. The special lifting device for precast stairs according to claim 9, characterized in that, When the locking device is in the open state, one end of the rotating shaft (21) inserted into the central hole (18) does not contact the pin (11), and the other end of the rotating shaft (21) penetrates through the pulley bracket (8) and is provided with a stop pin (15) that restricts the displacement between the rotating shaft (21) and the pulley bracket (8).

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