Safety limiting device of metallurgical crane

Abstract

The invention discloses a safety limiting device of a metallurgical crane, and relates to the field of cranes. According to the safety limiting device of the metallurgical crane, the driving frame, the elastic buffering piece, the brake and the elastic damper are arranged on the track bridge, and when the crane needs to be stopped, friction between the brake and a friction strip and meshing between the brake and brake teeth serve as stress stopping measures of the crane correspondingly; in the process that the brake limits the movement of the crane, a hung weight drags the driving frame through the electric hoist to compress the elastic buffering piece and the elastic damper, gradually-increased movement restraining force is provided for the connecting rope and the electric hoist, and kinetic energy of the hung weight is converted into elastic potential energy of the elastic buffering piece and the elastic damper; and the elastic potential energy is converted into heat energy in the elastic damper to be released, so that the kinetic energy of the electric hoist and the hung weight is gradually transferred and reduced until the hung weight is static, and the hung weight is prevented from being unhooked.

Description

Technical Field

[0001] This invention relates to crane technology, and more specifically to a safety limit device for a metallurgical crane. Background Technology

[0002] Metallurgical cranes are heavy-duty lifting equipment specifically designed for the metallurgical industry. They are primarily used for lifting high-temperature, large-tonnage materials such as molten steel ladles, ingots, and continuously cast billets. Their robust structure utilizes high-temperature resistant steel, explosion-proof motors, and heat insulation devices to withstand the high-temperature, dusty, and corrosive environment of smelting workshops. To ensure safe and stable operation, cranes must be equipped with safety limit systems, including devices for lifting height, travel distance, and load limits. These limit functions are monitored in real time through mechanical or electronic sensors to prevent overloading, overstepping, or operational errors, avoiding accidents such as collisions, overturning, or component damage. This ensures personnel safety, equipment integrity, and production continuity, and is a key measure to improve operational reliability and efficiency.

[0003] Chinese invention patent CN115744642B discloses a highly stable metallurgical bridge crane, including a crossbeam. A movable platform is located above the crossbeam, and a winding component is located above the movable platform. The winding component includes a winding machine, a wire rope, and a connecting box. A lifting machine is also located above the movable platform to drive the wire rope to wind or lower. A lifting plate is located at the bottom of the connecting box, and a main hook is located at the bottom of the lifting plate. The main hook is used to lift the connecting shafts on both sides of the molten steel ladle. A clamping mechanism is located on one side of the crossbeam to reduce the swing arm length of the wire rope. In this metallurgical bridge crane, the clamping mechanism reduces the swing arm length of the wire rope. Therefore, after the operator drives the auxiliary hook to lift the bottom of the molten steel ladle, the swaying amplitude of the wire rope lifting the ladle will also be reduced, keeping the molten steel ladle in a relatively stable state during the pouring process and effectively reducing the difficulty of pouring molten steel.

[0004] When existing metallurgical bridge cranes are in use, the hook and the suspended load continue to move forward due to inertia when the crane stops and brakes. Since the crane position is fixed and the length of the hoisting rope does not change, the hook and the suspended load may undergo some circular motion under the traction of inertial force and the pull of the hoisting rope. This may cause the suspended load to detach from the hook. Therefore, it is necessary to modify the structure of the existing crane to minimize the impact of inertial force on the hook and the suspended load after the crane stops. Summary of the Invention

[0005] The purpose of this invention is to provide a safety limit device for metallurgical cranes to solve the problem in the prior art where, after a crane stops, the hook and the suspended load continue to move under the action of inertial force, resulting in a high risk of the suspended load detaching from the hook.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a safety limit device for a metallurgical crane, comprising:

[0007] A track bridge, the inner wall of which is provided with friction strips and braking teeth;

[0008] A drive frame, mounted on the track bridge, includes two sets of rotating shafts slidably connected to the track bridge. The ends of the rotating shafts are connected to mounting plates, and the bottom of the mounting plates is provided with connecting ropes. An electric hoist is connected to the connecting ropes.

[0009] An elastic buffer is provided on the drive frame, including a mounting frame sleeved on the mounting plate and a sliding plate connected to the mounting plate. The mounting frame is provided with a plurality of spring plates clamped between two sliding plates.

[0010] The brake, mounted on the elastic buffer and slidably connected to the track bridge, includes a housing connected to the mounting frame and slidably connected to the track bridge. A hydraulic rod is connected to the housing, a hinge rod is hinged to the end of the hydraulic rod, and a slider is hinged to the end of the hinge rod. The slider is slidably connected in the housing, and a friction plate and multiple rotating blocks are connected to the side of the slider near the track bridge.

[0011] An elastic damper is mounted on the mounting frame and connected to the mounting plate and the housing, respectively.

[0012] Preferably, a partition is sandwiched between the spring plates, and the end of the sliding plate abuts against the inner wall of the mounting frame.

[0013] Preferably, both the friction strip and the friction plate are made of compressible materials including rubber and silicone, and the slider slides towards the track bridge to achieve this.

[0014] The friction strip is deformed and adheres to the friction plate.

[0015] The rotating block engages with the brake teeth.

[0016] Preferably, the friction plate protrudes from the tip of the rotating block, and the friction strip protrudes from the tip of the brake tooth, meaning that the friction plate and friction strip contact the brake tooth before the rotating block does.

[0017] Preferably, the rotating block is hinged to the slider, and the slider is connected to a spacer located between adjacent rotating blocks. The spacer is connected to a buffer pad that abuts against the rotating block. The buffer pad is made of a compressible material.

[0018] Preferably, the elastic damper includes a sleeve connected to the mounting frame and a telescopic plate slidably connected to the end of the sleeve. The telescopic plate is connected to the mounting plate. A spring plate is provided inside the sleeve. One end of the spring plate abuts against the inner wall of the sleeve, and the other end abuts against the end of the telescopic plate. The end of the telescopic plate divides the internal space of the sleeve into two chambers for storing damping fluid. The two chambers exchange damping fluid through perforations formed on the telescopic plate.

[0019] Preferably, the spring sheet is assembled from multiple X-shaped plates, and the X-shaped plates are provided with oil holes.

[0020] Preferably, the track bridge has a slide rail, the rotating shaft is connected to a roller that is engaged in the slide rail, and a rotating drive component is connected to one of the rotating shafts, the rotating drive component being slidably connected to the track bridge.

[0021] Compared with the prior art, the present invention provides a safety limiting device for a metallurgical crane. By setting a drive frame, elastic buffer, brake, and elastic damper on the track bridge, when the crane needs to stop, the friction between the brake and the friction strip and the engagement between the brake and the brake teeth serve as force-based stopping measures for the crane. During the process of the brake restricting the movement of the crane, the suspended load is dragged by the electric hoist to compress the elastic buffer and elastic damper, providing a gradually increasing moving restraining force for the connecting rope and the electric hoist. The kinetic energy of the suspended load is converted into the elastic potential energy of the elastic buffer and elastic damper, and then the elastic potential energy is converted into heat energy in the elastic damper and released. In this way, the kinetic energy of the electric hoist and the suspended load is gradually transferred and reduced until the suspended load comes to a stop, thereby preventing the suspended load from detaching. Attached Figure Description

[0022] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in this invention. For those skilled in the art, other drawings can be obtained based on these drawings.

[0023] Figure 1 A schematic diagram of the overall structure provided for an embodiment of the present invention. Figure 1 ;

[0024] Figure 2 A schematic diagram of the overall structure provided for an embodiment of the present invention. Figure 2 ;

[0025] Figure 3 A schematic diagram of the overall structure provided for an embodiment of the present invention. Figure 3 ;

[0026] Figure 4A schematic diagram of the drive frame and elastic buffer structure provided in an embodiment of the present invention;

[0027] Figure 5 This is a schematic diagram of the cross-sectional structure of the track bridge provided in an embodiment of the present invention;

[0028] Figure 6 This is a schematic diagram of the connection structure between the rotating block and the slider provided in an embodiment of the present invention;

[0029] Figure 7 This is a schematic diagram of an elastic damper structure provided in an embodiment of the present invention.

[0030] Explanation of reference numerals in the attached figures:

[0031] 1. Track bridge; 11. Slide rail; 12. Friction strip; 13. Brake tooth; 2. Drive frame; 21. Rotating shaft; 22. Roller; 23. Rotary drive component; 24. Mounting plate; 25. Connecting rope; 3. Electric hoist; 4. Elastic buffer; 41. Mounting frame; 42. Slide plate; 43. Spring plate; 44. Partition plate; 5. Brake; 51. Housing; 52. Hydraulic rod; 53. Hinge rod; 54. Slider; 55. Friction plate; 56. Rotating block; 57. Spacer; 58. Buffer pad; 6. Elastic damper; 61. Sleeve; 62. Telescopic plate; 63. Spring plate; 64. Perforation. Detailed Implementation

[0032] To enable those skilled in the art to better understand the technical solution of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings.

[0033] As attached Figure 1 To be continued Figure 7 As shown:

[0034] Example 1:

[0035] This invention provides a safety limit device for a metallurgical crane, comprising:

[0036] Track bridge 1, the inner wall of which is provided with friction strips 12 and brake teeth 13;

[0037] The drive frame 2 is mounted on the track bridge 1 and includes two sets of rotating shafts 21 slidably connected to the track bridge 1. The ends of the rotating shafts 21 are connected to the mounting plates 24. The bottom of the mounting plates 24 is provided with connecting ropes 25. Electric hoists 3 are connected to the connecting ropes 25. The electric hoists 3 are provided with hooks for lifting heavy objects.

[0038] The elastic buffer 4 is disposed on the drive frame 2, including a mounting frame 41 sleeved on the mounting plate 24 and a sliding plate 42 connected to the mounting plate 24. The mounting frame 41 is provided with a plurality of spring plates 43 clamped between the two sliding plates 42.

[0039] The brake 5 is mounted on the elastic buffer 4 and slidably connected to the track bridge 1. It includes a housing 51 connected to the mounting frame 41 and slidably connected to the track bridge 1. A hydraulic rod 52 is connected to the housing 51. A hinge rod 53 is hinged to the end of the hydraulic rod 52. A slider 54 is hinged to the end of the hinge rod 53. The slider 54 is slidably connected in the housing 51. A friction plate 55 and a plurality of rotating blocks 56 are connected to the side of the slider 54 near the track bridge 1.

[0040] An elastic damper 6 is disposed on the mounting frame 41 and is connected to the mounting plate 24 and the housing 51 respectively.

[0041] As can be seen from the above, by setting a drive frame 2, an elastic buffer 4, a brake 5, and an elastic damper 6 on the track bridge 1, when the crane needs to stop, the friction between the brake 5 and the friction strip 12 and the engagement between the brake 5 and the brake tooth 13 serve as force-based stopping measures for the crane. During the process of the brake 5 restricting the movement of the crane, the suspended load is dragged by the electric hoist 3 to compress the elastic buffer 4 and the elastic damper 6, providing a gradually increasing moving restraining force for the connecting rope 25 and the electric hoist 3, converting the kinetic energy of the suspended load into the elastic potential energy of the elastic buffer 4 and the elastic damper 6, and then converting the elastic potential energy into heat energy in the elastic damper 6 for release, thereby gradually transferring and reducing the kinetic energy of the electric hoist 3 and the suspended load until the suspended load stops, thus preventing the suspended load from detaching.

[0042] Specifically, when the crane needs to brake and stop, the hydraulic rod 52 extends, causing the hinge rod 53 to rotate. The rotating hinge rod 53 pushes the slider 54 to slide within the housing 51. As the slider 54 slides towards the rail bridge 1, the friction plate 55 first contacts the friction strip 12. As the slider 54 gradually approaches the rail bridge 1, the sliding friction between the friction plate 55 and the friction strip 12 gradually increases, thus slowly stopping the brake 5 and the mounting frame 41. When the brake 5 reaches the preset stopping position, the sliding slider 54 drives the rotating block 56 to engage with the brake tooth 13, thereby forcing the brake 5 to stop at the preset position. When the brake 5 is fixed in position, the electric hoist 3 and the suspended load continue to move forward under inertia. Through the connecting rope 25, the mounting plate 24 and the sliding plate 42 slide and compress the spring plate 43 inside the mounting frame 41. At the same time, the mounting plate 24 also compresses the elastic damper 6, thereby converting the kinetic energy of the suspended load and the electric hoist 3 into the elastic potential energy of the spring plate 43 and the compressed elastic damper 6. When the spring plate 43 and the compressed elastic damper 6 reset and release the elastic potential energy, the elastic damper 6 can generate heat, converting the elastic potential energy into heat energy and releasing it. This gradual conversion reduces the kinetic energy of the electric hoist 3 and the suspended load, and eventually stops the suspended load.

[0043] Example 2:

[0044] This invention provides a safety limit device for a metallurgical crane, comprising:

[0045] Track bridge 1, the inner wall of which is provided with friction strips 12 and brake teeth 13;

[0046] The drive frame 2 is mounted on the track bridge 1 and includes two sets of rotating shafts 21 slidably connected to the track bridge 1. The ends of the rotating shafts 21 are connected to the mounting plates 24. The bottom of the mounting plates 24 is provided with connecting ropes 25. Electric hoists 3 are connected to the connecting ropes 25. The electric hoists 3 are provided with hooks for lifting heavy objects.

[0047] The elastic buffer 4 is disposed on the drive frame 2, including a mounting frame 41 sleeved on the mounting plate 24 and a sliding plate 42 connected to the mounting plate 24. The mounting frame 41 is provided with a plurality of spring plates 43 clamped between the two sliding plates 42.

[0048] The brake 5 is mounted on the elastic buffer 4 and slidably connected to the track bridge 1. It includes a housing 51 connected to the mounting frame 41 and slidably connected to the track bridge 1. A hydraulic rod 52 is connected to the housing 51. A hinge rod 53 is hinged to the end of the hydraulic rod 52. A slider 54 is hinged to the end of the hinge rod 53. The slider 54 is slidably connected in the housing 51. A friction plate 55 and a plurality of rotating blocks 56 are connected to the side of the slider 54 near the track bridge 1.

[0049] An elastic damper 6 is disposed on the mounting frame 41 and is connected to the mounting plate 24 and the housing 51 respectively.

[0050] As can be seen from the above, by setting a drive frame 2, an elastic buffer 4, a brake 5, and an elastic damper 6 on the track bridge 1, when the crane needs to stop, the friction between the brake 5 and the friction strip 12 and the engagement between the brake 5 and the brake tooth 13 serve as force-based stopping measures for the crane. During the process of the brake 5 restricting the movement of the crane, the suspended load is dragged by the electric hoist 3 to compress the elastic buffer 4 and the elastic damper 6, providing a gradually increasing moving restraining force for the connecting rope 25 and the electric hoist 3, converting the kinetic energy of the suspended load into the elastic potential energy of the elastic buffer 4 and the elastic damper 6, and then converting the elastic potential energy into heat energy in the elastic damper 6 for release, thereby gradually transferring and reducing the kinetic energy of the electric hoist 3 and the suspended load until the suspended load stops, thus preventing the suspended load from detaching.

[0051] Specifically, when the crane needs to brake and stop, the hydraulic rod 52 extends, causing the hinge rod 53 to rotate. The rotating hinge rod 53 pushes the slider 54 to slide within the housing 51. As the slider 54 slides towards the rail bridge 1, the friction plate 55 first contacts the friction strip 12. As the slider 54 gradually approaches the rail bridge 1, the sliding friction between the friction plate 55 and the friction strip 12 gradually increases, thus slowly stopping the brake 5 and the mounting frame 41. When the brake 5 reaches the preset stopping position, the sliding slider 54 drives the rotating block 56 to engage with the brake tooth 13, thereby forcing the brake 5 to stop at the preset position. When the brake 5 is fixed in position, the electric hoist 3 and the suspended load continue to move forward under inertia. Through the connecting rope 25, the mounting plate 24 and the sliding plate 42 slide and compress the spring plate 43 inside the mounting frame 41. At the same time, the mounting plate 24 also compresses the elastic damper 6, thereby converting the kinetic energy of the suspended load and the electric hoist 3 into the elastic potential energy of the spring plate 43 and the compressed elastic damper 6. When the spring plate 43 and the compressed elastic damper 6 reset and release the elastic potential energy, the elastic damper 6 can generate heat, converting the elastic potential energy into heat energy and releasing it. This gradual conversion reduces the kinetic energy of the electric hoist 3 and the suspended load, and eventually stops the suspended load.

[0052] To avoid motion interference between the spring plates 43, a partition plate 44 is sandwiched between the spring plates 43. The end of the slide plate 42 abuts against the inner wall of the mounting frame 41. During the extension and retraction of the spring plates 43, the slide plate 42 moves along the inner wall of the mounting frame 41.

[0053] Both the friction strip 12 and the friction plate 55 are made of compressible materials including rubber and silicone, thereby increasing the friction between the friction strip 12 and the friction plate 55. Furthermore, the friction strip 12 can deform and thin after contact with the friction plate 55, facilitating the sliding block 54 to continue pushing the rotating block 56 to engage with the brake tooth 13. The sliding block 54 slides towards the track bridge 1 to achieve the following:

[0054] The friction strip 12 is deformed and adheres to the friction plate 55;

[0055] The rotating block 56 engages with the brake tooth 13.

[0056] To prevent the rotating block 56 and the brake tooth 13 from making premature contact, the side of the friction plate 55 protrudes from the tip of the rotating block 56, and the side of the friction strip 12 protrudes from the tip of the brake tooth 13, that is, the friction plate 55 and the friction strip 12 can make contact with the brake tooth 13 before the rotating block 56.

[0057] The rotating block 56 is hinged to the slider 54, and a spacer 57 is connected to the slider 54 between adjacent rotating blocks 56. A buffer pad 58 is connected to the spacer 57 and abuts against the rotating block 56. The buffer pad 58 is made of a compressible material. When the end of the rotating block 56 contacts the brake tooth 13, the brake tooth 13 can force the rotating block 56 to rotate and compress the buffer pad 58, thereby causing the rotating block 56 and the brake tooth 13 to be misaligned. At this time, there is sliding friction between the rotating block 56 and the brake tooth 13, which can only increase the friction force on the brake 5, but cannot forcibly stop the brake 5. As the slider 54 drives the rotating block 56 to continue to approach the brake tooth 13, the rotating block 56 and the brake tooth 13 engage, forcing the brake 5 to stop moving. The braking process of the brake 5 is divided into the following three stages, which can effectively avoid the risk of the heavy object disengaging due to the sudden stop of the brake 5:

[0058] During the first braking stage, the friction strip 12 contacts the friction plate 55;

[0059] In the second stage of braking, the friction strip 12 contacts the friction plate 55, and the end of the rotating block 56 contacts the brake tooth 13 and can rotate to disengage from the contact.

[0060] In the third stage of braking, the friction strip 12 contacts the friction plate 55, and the rotating block 56 fully engages with the brake tooth 13.

[0061] The elastic damper 6 includes a sleeve 61 connected to the mounting frame 41 and a telescopic plate 62 slidably connected to the end of the sleeve 61. The telescopic plate 62 is connected to the mounting plate 24. A spring plate 63 is provided inside the sleeve 61. One end of the spring plate 63 abuts against the inner wall of the sleeve 61, and the other end abuts against the end of the telescopic plate 62. The end of the telescopic plate 62 divides the internal space of the sleeve 61 into two chambers for storing damping fluid. The two chambers exchange damping fluid through a perforation 64 opened on the telescopic plate 62.

[0062] As can be seen from the above, when the mounting plate 24 drives the telescopic plate 62 to slide, the telescopic plate 62 will retract into the sleeve 61 to compress the spring plate 63. At this time, the damping fluid in the two chambers at the ends of the telescopic plate 62 is exchanged through the perforation 64. At the same time, the kinetic energy of the telescopic plate 62 is converted into the heat energy of the damping fluid and released, thereby preventing the telescopic plate 62 from sliding. The elastic dampers 6 on both sides of the brake 5 work together to realize the conversion and release of the kinetic energy of the mounting plate 24.

[0063] The spring plate 63 is assembled from multiple X-shaped plates, which together form multiple small oil cavities. Oil holes are provided on the X-shaped plates. During the compression and deformation of the spring plate 63, the damping fluid inside the small oil cavities will also flow to other oil cavities through the oil holes, converting the elastic potential energy of the spring plate 63 into the heat energy of the damping fluid, thereby improving the conversion efficiency between kinetic energy and heat energy.

[0064] The track bridge 1 is provided with a slide rail 11. A roller 22 is connected to the rotating shaft 21 and engaged in the slide rail 11. A rotary drive component 23 is connected to one of the rotating shafts 21. The rotary drive component 23 is slidably connected to the track bridge 1. The rotary drive component 23 can be an electric motor. The rotary drive component 23 drives the rotating shaft 21 and the roller 22 to rotate, thereby driving the mounting plate 24, the elastic buffer 4, the brake 5 and the elastic damper 6 to move.

[0065] The foregoing has only described certain exemplary embodiments of the present invention by way of illustration. Undoubtedly, those skilled in the art can modify the described embodiments in various ways without departing from the spirit and scope of the present invention. Therefore, the foregoing drawings and descriptions are illustrative in nature and should not be construed as limiting the scope of protection of the claims of the present invention.

Claims

1. A safety limit device for a metallurgical crane, characterized in that, include: The track bridge (1) has friction strips (12) and brake teeth (13) on its inner wall. The drive frame (2) is set on the track bridge (1) and includes two sets of rotating shafts (21) slidably connected to the track bridge (1). The ends of the rotating shafts (21) are connected to the mounting plates (24). The bottom of the mounting plates (24) is provided with connecting ropes (25). An electric hoist (3) is connected to the connecting ropes (25). The elastic buffer (4) is provided on the drive frame (2) and includes a mounting frame (41) sleeved on the mounting plate (24) and a sliding plate (42) connected to the mounting plate (24). The mounting frame (41) is provided with a plurality of spring plates (43) clamped between the two sliding plates (42). The brake (5) is mounted on the elastic buffer (4) and slidably connected to the track bridge (1). It includes a housing (51) connected to the mounting frame (41) and slidably connected to the track bridge (1). A hydraulic rod (52) is connected to the housing (51). A hinge rod (53) is hinged to the end of the hydraulic rod (52). A slider (54) is hinged to the end of the hinge rod (53). The slider (54) is slidably connected in the housing (51). A friction plate (55) and a plurality of rotating blocks (56) are connected to the side of the slider (54) near the track bridge (1). An elastic damper (6) is disposed on the mounting frame (41) and connected to the mounting plate (24) and the housing (51) respectively.

2. The safety limit device for a metallurgical crane according to claim 1, characterized in that, A partition (44) is sandwiched between the spring plates (43), and the end of the sliding plate (42) abuts against the inner wall of the mounting frame (41).

3. The safety limit device for a metallurgical crane according to claim 1, characterized in that, Both the friction strip (12) and the friction plate (55) are made of compressible materials including rubber and silicone. The slider (54) slides towards the track bridge (1) to achieve the following: The friction strip (12) is deformed and adhered to the friction plate (55); The rotating block (56) engages with the brake tooth (13).

4. A safety limit device for a metallurgical crane according to claim 3, characterized in that, The friction plate (55) protrudes from the tip of the rotating block (56) on its side, and the friction strip (12) protrudes from the tip of the brake tooth (13) on its side, that is, the friction plate (55) and the friction strip (12) contact the brake tooth (13) before the rotating block (56) does.

5. A safety limit device for a metallurgical crane according to claim 4, characterized in that, The rotating block (56) is hinged to the slider (54), and the slider (54) is connected to a spacer (57) located between adjacent rotating blocks (56). The spacer (57) is connected to a buffer pad (58) that abuts against the rotating block (56). The buffer pad (58) is made of a compressible material.

6. A safety limit device for a metallurgical crane according to claim 1, characterized in that, The elastic damper (6) includes a sleeve (61) connected to the mounting frame (41) and a telescopic plate (62) slidably connected to the end of the sleeve (61). The telescopic plate (62) is connected to the mounting plate (24). A spring plate (63) is provided inside the sleeve (61). One end of the spring plate (63) abuts against the inner wall of the sleeve (61), and the other end abuts against the end of the telescopic plate (62). The end of the telescopic plate (62) divides the internal space of the sleeve (61) into two chambers for storing damping fluid. The two chambers exchange damping fluid through a perforation (64) opened on the telescopic plate (62).

7. A safety limit device for a metallurgical crane according to claim 6, characterized in that, The spring sheet (63) is assembled from multiple X-shaped plates, and oil holes are provided on the X-shaped plates.

8. A safety limit device for a metallurgical crane according to claim 1, characterized in that, The track bridge (1) is provided with a slide (11), and a roller (22) is connected to the rotating shaft (21) and engaged in the slide (11). A rotating drive (23) is connected to one of the rotating shafts (21), and the rotating drive (23) is slidably connected to the track bridge (1).

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