Polyamide spinning tensile strength detection device

Abstract

The invention relates to the field of chinlon spinning detection, and discloses a chinlon spinning tensile strength detection device which comprises a detection table, a moving plate is arranged on the detection table through a moving structure, a pre-clamping structure is arranged on the moving plate, a support is fastened between the left side face and the right side face of the detection table through bolts, and the support is provided with a pulling structure. During detection, the chinlon spinning end part can be directly pulled into the pre-clamping structure for pre-clamping work, then the chinlon spinning strength can be directly detected through the pulling structure, and in the pulling detection process, the lifting structure is matched to press the lower pressing plate on the pre-clamping structure, so that the detection efficiency is improved while the detection is performed. The clamping and fixing work of chinlon spinning is automatically realized, so that the operation is more labor-saving and convenient, and the detection work efficiency is improved.

Description

Technical Field

[0001] This invention relates to the technical field of nylon spinning testing, and in particular to a device for testing the tensile strength of nylon spinning. Background Technology

[0002] Spinning, also known as chemical fiber forming, is the process of manufacturing chemical fibers. It refers to the process of forming fibers by pressing a polymer compound into a colloidal solution or melt through the fine orifices of a spinneret. The main forming methods include electrospinning and other technologies. The existing tensile strength testing device, through a slot, an extension slot, and a protective cover, works in conjunction with a mounting base, a universal joint, and a display device. When not in use, the display device can be stored in the slot by rotating and folding the universal joint. The protective cover, after fixing the slot, reduces the space occupied by the display device and protects it from being exposed to the outside and easily collided. When the display device is in normal use, it can also be adjusted at multiple angles via the universal joint for easy use by staff. During the testing process, the two ends of the nylon yarn need to be clamped manually, and then the clamped nylon yarn is pulled to test its strength. After the test, when another nylon yarn needs to be tested, it is necessary to loosen the nylon yarn from the clamping structure and replace it. This operation is quite troublesome, so there is room for improvement. Summary of the Invention

[0003] To address the problems mentioned in the background art, the present invention provides a device for testing the tensile strength of nylon spinning.

[0004] The present invention provides a nylon spinning tensile strength testing device using the following technical solution: A device for testing the tensile strength of nylon spinning includes a testing platform, a movable plate on the testing platform via a movable structure, a pre-clamping structure on the movable plate, a bracket fastened between the left and right sides of the testing platform via bolts, and a tension structure on the bracket. The pre-clamping structure includes multiple sets of transverse grooves formed on a movable plate. A slider is slidably arranged in the transverse grooves. A clamping seat is arranged on the slider. A lower pressure plate is arranged directly above the clamping seat. A fixing strip is arranged on the front of the slider. A through rod moves through the fixing strip. The top end of the through rod is connected to the lower pressure plate. A first pressing structure is arranged on one side of the lower pressure plate. A second pressing structure is arranged on the other side of the lower pressure plate. A first spring is sleeved on the through rod. The two ends of the first spring are respectively connected to the bottom block and the fixing strip. A rubber pad is arranged under the lower pressure plate. The tensioning structure includes a bidirectional screw that rotates laterally through the bracket. The left and right sections of the bidirectional screw have opposite thread directions. A motor is installed on the upper side of one side of the bracket. One end of the motor's output shaft is connected to the bidirectional screw. Two movable sleeves are fitted on the bidirectional screw. The movable sleeves have threaded grooves for the bidirectional screw to pass through. The upper part of the movable sleeves is attached to the bracket. A pressing plate is installed below the movable sleeves through a lifting structure. The pressing plate is L-shaped and the two pressing plates are symmetrically arranged.

[0005] Preferably, the lifting structure includes a fixed frame connected to the lower part of the movable sleeve, a lifting plate is movably inserted into the fixed frame, the bottom end of the lifting plate is connected to the push plate, through slots are provided on both sides of the fixed frame, a first insert rod is fixedly inserted through the lifting plate near the top, a vertical plate is connected to the middle of the rear side of the bracket, a horizontal slot is provided in the middle of the vertical plate, two first driving slots communicating with the horizontal slot are provided on both sides of the vertical plate, and the rear end of the first insert rod is movably inserted into the horizontal slot.

[0006] Preferably, the first pressing structure includes a first pressing plate connected to one side of the lower pressing plate, and the clamping seat is provided with a first pressing seat near one side of the lower pressing plate, with a pressing groove formed on the first pressing seat.

[0007] Preferably, the second clamping structure includes a second pressure plate connected to the other side of the lower pressure plate, and a second pressure seat is provided on the other side of the clamping seat, the second pressure seat being stepped.

[0008] Preferably, the movable structure includes a central groove formed in the middle of the testing platform, the movable plate being movably fitted in the central groove, two guide rods being connected to the rear side of the movable plate, one end of each guide rod being movably inserted into a hole formed in the testing platform, and a driving structure being provided between the movable plate and the support.

[0009] Preferably, the driving structure includes multiple second driving slots formed on the movable plate, multiple third driving slots formed on the movable plate, the second driving slots and the third driving slots being spaced apart from each other, and adjacent second driving slots and third driving slots being interconnected, a top slot being formed on one side of the front of the bracket, a top block being slidably arranged in the top slot, a vertical strip being connected below the top block, a second insert rod being provided at the bottom end of the vertical strip, the bottom end of the second insert rod being movably inserted into one of the second driving slots, and a push-pull structure being provided between the vertical strip and one of the fixed frames.

[0010] Preferably, the second insert rod is provided with threads, the top end of the second insert rod is rotatably inserted into the threaded groove opened at the bottom end of the vertical bar, and a rotating sleeve is fixedly sleeved on the middle of the second insert rod.

[0011] Preferably, the push-pull structure includes a protrusion disposed below the front of one of the fixed frames, a push-pull rod movably passing through the protrusion, one end of the push-pull rod being connected to a second push-pull block, the other end of the push-pull rod being connected to a first push-pull block, the second push-pull block being pressed against the vertical bar, a limiting sleeve being fixedly sleeved on the push-pull rod near one end, a fixing ring being fixedly sleeved on the push-pull rod near the other end, and a second spring being connected between the fixing ring and the protrusion.

[0012] In summary, the present invention has the following beneficial technical effects: 1. This invention, by setting up a pre-clamping structure, a pulling structure, and a lifting structure, allows the nylon filament end to be directly pulled into the pre-clamping structure for pre-clamping during testing. Then, the tensile strength of the nylon filament can be directly tested through the pulling structure. Furthermore, during the tensile testing process, the lifting structure can press down the lower plate on the pre-clamping structure, thereby automatically clamping and fixing the nylon filament while testing. This operation is more labor-saving and convenient, improving the efficiency of the testing work. 2. By setting a first pressing structure and a second pressing structure on the lower pressure plate, the nylon yarn can be pressed and fixed again on both sides of the clamping seat when the lower plate is pressed down by the lifting structure. This makes the nylon yarn clamped more firmly and reduces the problem of nylon yarn falling off during the testing process. 3. By setting up a moving structure, a driving structure, and a push-pull structure, the present invention enables the pulling structure to automatically drive the moving plate to move intermittently while pulling the nylon yarn for detection. This allows the other nylon yarn to be switched to the detection position in a timely manner after one nylon yarn has been detected, thus further improving the efficiency of the detection work. Attached Figure Description

[0013] Figure 1 This is a schematic diagram of the structure of a nylon spinning tensile strength testing device according to an embodiment of the present invention; Figure 2 This is a schematic diagram of the structure of the support in an embodiment of the present invention; Figure 3 This is an embodiment of the present invention. Figure 2 Enlarged view of the structure at point A; Figure 4 This is a schematic diagram of the structure of the moving plate in an embodiment of the present invention. Figure 5 This is a schematic diagram of the structure of the clamping seat in an embodiment of the present invention; Figure 6 This is a schematic diagram of the structure on the other side of the clamping seat in an embodiment of the present invention.

[0014] Explanation of reference numerals in the attached drawings: 1. Testing table; 2. Support; 3. Moving plate; 4. Motor; 5. Bidirectional screw; 6. Moving sleeve; 7. Push plate; 8. Horizontal groove; 9. Clamping seat; 10. Slider; 11. Lower pressure plate; 12. Through rod; 13. Base block; 14. First spring; 15. Rubber pad; 16. Fixed frame; 17. Lifting plate; 18. Through groove; 19. First insertion rod; 20. Horizontal groove; 21. First driving groove; 22. Vertical plate; 23. First pressure plate 24. First pressure seat; 25. Pressure groove; 26. Second pressure plate; 27. Second pressure seat; 28. Guide rod; 29. ​​Intermediate groove; 30. Second driving groove; 31. Third driving groove; 32. Vertical bar; 33. Second insert rod; 34. Rotating sleeve; 35. Protrusion; 36. Push-pull rod; 37. Limiting sleeve; 38. Fixing ring; 39. First push-pull block; 40. Second spring; 41. Top block; 42. Top groove; 43. Second push-pull block; 44. Fixing strip. Detailed Implementation

[0015] The following is in conjunction with the appendix Figures 1-6 The present invention will be described in further detail below.

[0016] Reference Figures 1-6 This invention discloses a nylon spinning tensile strength testing device, including a testing platform 1, a movable plate 3 on the testing platform 1 via a movable structure, a pre-clamping structure on the movable plate 3, and a bracket 2 fastened between the left and right sides of the testing platform 1 by bolts, with a tension structure provided on the bracket 2. The pre-clamping structure includes multiple sets of transverse grooves 8 opened on the movable plate 3. A slider 10 is slidably arranged in the transverse grooves 8. A clamping seat 9 is arranged on the slider 10. A lower pressure plate 11 is arranged directly above the clamping seat 9. A fixing strip 44 is arranged on the front of the slider 10. A through rod 12 moves through the fixing strip 44. The top end of the through rod 12 is connected to the lower pressure plate 11. A first pressing structure is arranged on one side of the lower pressure plate 11. A second pressing structure is arranged on the other side of the lower pressure plate 11. A first spring 14 is sleeved on the through rod 12. The two ends of the first spring 14 are respectively connected to the bottom block 13 and the fixing strip 44. A rubber pad 15 is arranged under the lower pressure plate 11. The tensioning structure includes a bidirectional screw 5 that rotates laterally through the bracket 2. The two sections of the bidirectional screw 5 have opposite thread directions. A motor 4 is installed on the upper side of one side of the bracket 2. One end of the output shaft of the motor 4 is connected to the bidirectional screw 5. Two movable sleeves 6 are fitted on the bidirectional screw 5. The movable sleeves 6 have threaded grooves for the bidirectional screw 5 to pass through. The upper part of the movable sleeves 6 is attached to the bracket 2. A push plate 7 is set below the movable sleeves 6 through a lifting structure. The push plate 7 is "L" shaped and the two push plates 7 are symmetrically arranged between each other. The lifting structure includes a fixed frame 16 connected to the lower part of the movable sleeve 6. A lifting plate 17 is movably inserted into the fixed frame 16. The bottom end of the lifting plate 17 is connected to the push plate 7. Through slots 18 are provided on both sides of the fixed frame 16. A first insert rod 19 is fixedly inserted through the lifting plate 17 near the top. A vertical plate 22 is connected to the middle of the rear side of the bracket 2. A horizontal slot 20 is provided in the middle of the vertical plate 22. Two first driving slots 21 are provided on both sides of the vertical plate 22 to connect the horizontal slot 20. The rear end of the first insert rod 19 is movably inserted into the horizontal slot 20. During testing, the two ends of the nylon yarn to be tested are directly pulled into the chain of each clamping seat 9 and the lower pressure plate 11 of each group. The nylon yarn is clamped between the rubber pad 15 and the clamping seat 9. Then, the motor 4 is started to drive the bidirectional screw. As rod 5 rotates, the two movable sleeves 6 move synchronously away from each other on the rotating bidirectional screw 5. At the same time, they drive one end of the first insertion rod 19 to slide in the horizontal groove 20. When one end of the first insertion rod 19 slides into the first driving groove 21, it drives the lifting plate 17 to move horizontally. At the same time, the lifting plate 17 moves downward on the fixed frame 16. Thus, when the movable sleeve 6 drives the push plate 7 to move and press against the second pressure plate 26, as the lifting plate 17 and the push plate 7 move downward as a whole, they push the lower pressure plate 11 to move the through rod 12 up and down on the fixed strip 44 while pushing the clamping seat 9 to move. In this way, the nylon yarn can be automatically clamped and fixed at the same time as the test, making the operation more labor-saving and convenient, and improving the efficiency of the test.

[0017] See Figure 5 and Figure 6 The first pressing structure includes a first pressing plate 23 connected to one side of the lower pressing plate 11, and a first pressing seat 24 is provided on one side of the clamping seat 9 near the lower pressing plate 11. A pressing groove 25 is provided on the first pressing seat 24. The second clamping structure includes a second pressure plate 26 connected to the other side of the lower pressure plate 11, and a second pressure seat 27 provided on the other side of the clamping seat 9. The second pressure seat 27 is stepped. As the lower pressure plate 11 moves downward, it drives the bottom end of the first pressure plate 23 to move downward into the pressure groove 25, clamping the nylon yarn between the first pressure seat 24 and the first pressure plate 23. At the same time, the lower pressure plate 11 drives the second pressure plate 26 to move downward onto the second pressure seat 27, and clamps the nylon yarn again between the second pressure seat 27 and the second pressure plate 26. This clamps the nylon yarn more firmly and avoids the problem of the nylon yarn falling off during the testing process.

[0018] See Figures 1-4 The movable structure includes a central groove 29 in the middle of the test table 1, a movable plate 3 is movably fitted in the central groove 29, two guide rods 28 are connected to the rear side of the movable plate 3, one end of the guide rod 28 is movably inserted into the insertion hole in the test table 1, and a driving structure is provided between the movable plate 3 and the bracket 2. The driving structure includes multiple second driving grooves 30 opened on the movable plate 3, multiple third driving grooves 31 opened on the movable plate 3, the second driving grooves 30 and the third driving grooves 31 are spaced apart from each other, and adjacent second driving grooves 30 and third driving grooves 31 are interconnected. A top groove 42 is opened on one side of the front of the bracket 2, a top block 41 is slidably arranged in the top groove 42, a vertical bar 32 is connected below the top block 41, a second insert rod 33 is arranged on the bottom end of the vertical bar 32, and the bottom end of the second insert rod 33 is movably inserted into one of the second driving grooves 30. A push-pull structure is provided between the vertical bar 32 and one of the fixed frames 16. The second insert rod 33 is provided with threads, and the top end of the second insert rod 33 is rotated and inserted into the threaded groove opened at the bottom end of the vertical bar 32. The rotating sleeve 34 is fixedly sleeved on the middle of the second insert rod 33. The push-pull structure includes a protrusion 35 located below the front of one of the fixed frames 16. A push-pull rod 36 moves through the protrusion 35. One end of the push-pull rod 36 is connected to a second push-pull block 43, and the other end is connected to a first push-pull block 39. The second push-pull block 43 is pressed against the vertical bar 32. A limiting sleeve 37 is fixedly fitted on the push-pull rod 36 near one end, and a fixing ring 38 is fixedly fitted on the push-pull rod 36 near the other end. A second spring 40 connects the fixing ring 38 and the protrusion 35. Two movable sleeves 6 When moving away from each other to perform nylon spinning inspection, the second push-pull block 43 at one end of the push-pull rod 36 on one of the fixed frames 16 pushes the vertical bar 32, causing the second insert rod 33 at the bottom of the vertical bar 32 to slide in the second driving groove 30. When the second insert rod 33 slides to one end of the second driving groove 30, it pushes the moving plate 3 to move in the middle groove 29, thereby pushing one of the nylon fibers to the bottom of the bracket 2. After the second insert rod 33 slides to one end of the second driving groove 30, as it moves... As sleeve 6 continues to move, the position of vertical bar 32 remains unchanged, and the second push-pull block 43 remains firmly attached to vertical bar 32. When sleeve 6 moves, it drives clamping seat 9 to continue moving, and push-pull rod 36 moves on protrusion 35, compressing the second spring 40. After clamping seat 9 moves to detect nylon yarn, motor 4 drives bidirectional screw 5 to rotate in the opposite direction. The two moving sleeves 6 move synchronously towards each other. When the first push-pull block 39 at the other end of push-pull rod 36 moves and adheres to vertical bar 32, the limiting sleeve 37, in conjunction with its limiting action, causes the moving sleeve 6 to move. Through the first push-pull block 39, vertical bar 32 and second insert rod 33 move in opposite directions. The bottom end of the second insert rod 33 slides in the third driving groove 31. By using the pressure of the second insert rod 33 on the groove wall of the third driving groove 31, the moving plate 3 moves. Thus, after one nylon yarn is detected, the next nylon yarn can be promptly conveyed to the detection position for detection, greatly improving detection efficiency and making reasonable use of working time.

[0019] The implementation principle of the nylon spinning tensile strength testing device of this invention is as follows: During testing, both ends of the nylon filament to be tested are directly pulled into the respective clamping seats 9 and the lower pressure plate 11 of each chain group. The nylon filament is clamped between the rubber pad 15 and the clamping seat 9. Then, the motor 4 is started to drive the bidirectional screw 5 to rotate. The two moving sleeves 6 move synchronously in opposite directions on the rotating bidirectional screw 5. At the same time, one end of the first insertion rod 19 slides in the horizontal groove 20. When one end of the first insertion rod 19 slides into the first driving groove 21, it drives the lifting plate 17 to move horizontally. At the same time, the lifting plate 17 moves downward in the fixed frame 16. Thus, when the moving sleeve 6 drives the pushing plate 7 to move and press against the second pressure plate 26, the lifting plate 17 moves downward as the lifting plate 17 moves horizontally. As the plate 17 and the push plate 7 move downwards as a whole, the clamping seat 9 is moved, which in turn pushes the lower pressure plate 11, causing the through rod 12 to move up and down on the fixing strip 44. This allows for automatic clamping and fixing of the nylon yarn during testing, making the operation more labor-saving and convenient, and improving testing efficiency. Furthermore, the downward movement of the lower pressure plate 11 causes the bottom end of the first pressure plate 23 to move down into the pressure groove 25, clamping the nylon yarn between the first pressure seat 24 and the first pressure plate 23. Simultaneously, the lower pressure plate 11 causes the second pressure plate 26 to move down onto the second pressure seat 27, further clamping the nylon yarn between the second pressure seat 27 and the second pressure plate 26. This provides a more secure clamping of the nylon yarn, preventing it from falling off during testing. When the two movable sleeves 6 move away from each other to perform the nylon spinning test, the second push-pull block 43 at one end of the push-pull rod 36 on one of the fixed frames 16 pushes the vertical bar 32, causing the second insert rod 33 at the bottom of the vertical bar 32 to slide in the second driving groove 30. When the second insert rod 33 slides to one end of the second driving groove 30, it pushes the movable plate 3 to move in the middle groove 29, thereby pushing one of the nylon fibers to the bottom of the bracket 2. After the second insert rod 33 slides to one end of the second driving groove 30, as the movable sleeve 6 continues to move, the position of the vertical bar 32 remains unchanged, and the second push-pull block 43 remains close to the vertical bar 32. Thus, when the movable sleeve 6 drives the clamping seat 9 to continue moving, the push-pull rod 36 moves on the protrusion 35, compressing the second spring 40. After the compression and clamping seat 9 moves to detect nylon spinning, the motor 4 drives the bidirectional screw 5 to rotate in the opposite direction. The two moving sleeves 6 move synchronously towards each other. When the first push-pull block 39 at the other end of the push-pull rod 36 moves and presses against the vertical bar 32, the limiting sleeve 37, in conjunction with the limiting action, causes the moving sleeve 6 to move. Through the first push-pull block 39, the vertical bar 32 and the second insert rod 33 move in the opposite direction as a whole. The bottom end of the second insert rod 33 slides in the third driving groove 31. By using the pressure of the second insert rod 33 on the groove wall of the third driving groove 31, the moving plate 3 moves. Thus, after one nylon spinning yarn is detected, the next nylon spinning yarn can be promptly transported to the detection position for detection, making reasonable use of working time and greatly improving the efficiency of detection work.

[0020] The above are all preferred embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Therefore, all equivalent changes made in accordance with the structure, shape and principle of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A device for testing the tensile strength of nylon spinning, comprising a testing platform (1), characterized in that: The testing platform (1) is equipped with a movable plate (3) through a movable structure. The movable plate (3) is equipped with a pre-clamping structure. The left and right sides of the testing platform (1) are fastened with bolts to the bracket (2). The bracket (2) is equipped with a tensioning structure. The pre-clamping structure includes multiple sets of transverse grooves (8) opened on the movable plate (3), a slider (10) is slidably arranged in the transverse grooves (8), a clamping seat (9) is arranged on the slider (10), a lower pressure plate (11) is arranged directly above the clamping seat (9), a fixing strip (44) is arranged on the front of the slider (10), a through rod (12) is movably passed through the fixing strip (44), the top end of the through rod (12) is connected to the lower pressure plate (11), a first pressing structure is arranged on one side of the lower pressure plate (11), a second pressing structure is arranged on the other side of the lower pressure plate (11), a first spring (14) is sleeved on the through rod (12), the two ends of the first spring (14) are respectively connected to the bottom block (13) and the fixing strip (44), and a rubber pad (15) is arranged under the lower pressure plate (11). The tensioning structure includes a bidirectional screw (5) that rotates laterally through the bracket (2). The two sections of the bidirectional screw (5) have opposite thread directions. A motor (4) is installed on the upper side of one side of the bracket (2). One end of the output shaft of the motor (4) is connected to the bidirectional screw (5). Two movable sleeves (6) are fitted on the bidirectional screw (5). The movable sleeves (6) have threaded grooves for the bidirectional screw (5) to pass through. The upper part of the movable sleeves (6) is attached to the bracket (2). A push plate (7) is set below the movable sleeves (6) through a lifting structure. The push plate (7) is L-shaped and the two push plates (7) are symmetrically arranged.

2. The nylon spinning tensile strength testing device according to claim 1, characterized in that: The lifting structure includes a fixed frame (16) connected to the lower part of the movable sleeve (6), a lifting plate (17) is movably inserted into the fixed frame (16), the bottom end of the lifting plate (17) is connected to the push plate (7), and through slots (18) are provided on both sides of the fixed frame (16). A first insert rod (19) is fixedly inserted through the lifting plate (17) near the top. A vertical plate (22) is connected to the middle of the rear side of the bracket (2). A horizontal slot (20) is opened in the middle of the vertical plate (22). Two first driving slots (21) connecting the horizontal slot (20) are opened on both sides of the vertical plate (22). The rear end of the first insert rod (19) is movably inserted into the horizontal slot (20).

3. The nylon spinning tensile strength testing device according to claim 1, characterized in that: The first pressing structure includes a first pressing plate (23) connected to one side of the lower pressing plate (11), and a first pressing seat (24) is provided on one side of the clamping seat (9) near the lower pressing plate (11), and a pressing groove (25) is provided on the first pressing seat (24).

4. The nylon spinning tensile strength testing device according to claim 1, characterized in that: The second pressing structure includes a second pressing plate (26) connected to the other side of the lower pressing plate (11), and a second pressing seat (27) is provided on the other side of the clamping seat (9), with the second pressing seat (27) having a stepped shape.

5. The nylon spinning tensile strength testing device according to claim 1, characterized in that: The movable structure includes a central groove (29) in the middle of the testing table (1), the movable plate (3) is movably fitted in the central groove (29), two guide rods (28) are connected to the rear side of the movable plate (3), one end of the guide rod (28) is movably inserted into the insertion hole in the testing table (1), and a driving structure is provided between the movable plate (3) and the bracket (2).

6. The nylon spinning tensile strength testing device according to claim 5, characterized in that: The driving structure includes multiple second driving slots (30) opened on the movable plate (3), multiple third driving slots (31) opened on the movable plate (3), the second driving slots (30) and the third driving slots (31) are spaced apart from each other, and adjacent second driving slots (30) and third driving slots (31) are interconnected. A top slot (42) is opened on one side of the front of the bracket (2), a top block (41) is slidably arranged in the top slot (42), a vertical strip (32) is connected below the top block (41), a second insert rod (33) is arranged on the bottom end of the vertical strip (32), the bottom end of the second insert rod (33) is movably inserted into one of the second driving slots (30), and a push-pull structure is arranged between the vertical strip (32) and one of the fixed frames (16).

7. The nylon spinning tensile strength testing device according to claim 6, characterized in that: The second insert (33) is threaded, and the top end of the second insert (33) is rotated and inserted into the threaded groove at the bottom end of the vertical bar (32). A rotating sleeve (34) is fixedly fitted on the middle part of the second insert (33).

8. The nylon spinning tensile strength testing device according to claim 6, characterized in that: The push-pull structure includes a protrusion (35) disposed below the front of one of the fixed frames (16), a push-pull rod (36) moving through the protrusion (35), one end of the push-pull rod (36) being connected to a second push-pull block (43), the other end of the push-pull rod (36) being connected to a first push-pull block (39), the second push-pull block (43) being pressed against the vertical bar (32), a limiting sleeve (37) being fixedly fitted on one end of the push-pull rod (36), a fixing ring (38) being fixedly fitted on the other end of the push-pull rod (36), and a second spring (40) being connected between the fixing ring (38) and the protrusion (35).

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