A door ring assembly for a circular knitting machine

Abstract

The application relates to the technical field of circular weaving machines, and discloses a door ring assembly of a suspension circular weaving machine, which comprises an upper door ring and a lower door ring, a plurality of rollers are arranged between the upper door ring and the lower door ring, the roller comprises a roller shaft arranged through the upper door ring and the lower door ring, and a sleeve is rotationally arranged on the circumferential surface of the roller shaft; the two ends of the roller shaft are both threadedly connected with self-locking nuts; and the two self-locking nuts are arranged on the sides of the upper door ring and the lower door ring which are far away from each other. When the roller needs to be separately disassembled in the application, the self-locking nuts are only needed to be loosened from the roller shaft, and then the roller shaft is pulled out, so that the roller can be disassembled without separating the upper door ring and the lower door ring, the single roller is convenient to maintain, and the maintenance efficiency of the single roller is improved.

Description

Technical Field

[0001] This application relates to the technical field of circular looms, and in particular to a gate assembly for a suspended circular loom. Background Technology

[0002] The suspended circular loom is a new type of plastic weaving equipment. By adopting a suspended design, the weft shuttle is freed from the fixed track of the traditional rubber wheel during operation. Dynamic balance is achieved through the swing arm and roller system, which greatly reduces the problem of rubber wheel wear.

[0003] In related technologies, a suspended circular loom includes a gate assembly and a shuttle. The gate assembly comprises an upper gate and a lower gate, with rollers rotatably mounted between them. The rollers are connected to the upper and lower gates via a rotating shaft, and both the upper and lower gates are equipped with bushings for rotating the shaft. The shuttle moves in a circular motion within the track formed by the rollers to weave the weft yarn onto the warp yarn, while the rollers also support the upper and lower gates.

[0004] However, when the rollers of the aforementioned suspended circular loom are damaged, the upper and lower gate rings need to be completely separated from all the rollers in order to increase the distance between the upper and lower gate rings so that the rollers can be replaced. This makes it inconvenient to replace individual rollers, resulting in low efficiency in fault repair. Therefore, improvements are needed. Summary of the Invention

[0005] To improve the maintenance efficiency of rollers in a suspended circular loom, this application provides a gate assembly for a suspended circular loom.

[0006] The door ring assembly of a suspended circular loom provided in this application adopts the following technical solution:

[0007] A gate assembly for a suspended circular loom includes an upper gate and a lower gate, with a plurality of rollers disposed between the upper and lower gates. Each roller includes a roller shaft passing through the upper and lower gates and a sleeve rotatably disposed around the roller shaft. Both ends of the roller shaft are threaded with self-locking nuts, and two self-locking nuts are respectively disposed on the side of the upper and lower gates away from each other. An upper cover and a lower cover are passing through the roller shaft, and the upper and lower covers are respectively disposed on both sides of the sleeve. The upper and lower covers are both disposed between the upper and lower gates, and the sleeve is rotatably disposed on the upper and lower covers.

[0008] By adopting the above technical solution, when a single roller needs to be replaced due to damage, simply loosen the two self-locking nuts, then pull the roller out from the upper and lower door rings. The roller sleeve, upper cover, and lower cover can then be removed from between the upper and lower door rings. Next, rotate the new roller sleeve between the new upper and lower covers, then install the new upper cover, lower cover, and roller sleeve between the upper and lower door rings. Then, thread the new roller through the upper and lower door rings, ensuring it passes through the upper cover, lower cover, and roller sleeve. Finally, tighten the self-locking nuts at both ends of the roller. Replacing rollers in this way eliminates the need to completely separate the upper and lower door rings from all the rollers, allowing for the replacement of individual rollers. This simplifies the maintenance process, facilitates individual roller replacement, and improves the efficiency of roller failure repair.

[0009] Optionally, a deep groove ball bearing is provided between the roller and the sleeve, and a rotary bearing is provided at both ends of the sleeve. The two rotary bearings are partially disposed in the upper cover and the lower cover, and the other part is disposed in the sleeve.

[0010] By adopting the above technical solution, when the roller rotates, the deep groove ball bearing can reduce the friction between the sleeve and the roller, while the rotating bearing can reduce the friction between the sleeve and the upper and lower covers, making the sleeve rotate more smoothly, reducing the sleeve rotation resistance, and extending the service life of the roller. This makes the shuttle rotate more smoothly in the circumferential track formed by the roller, less prone to jamming, thereby improving the weaving quality of the circular loom.

[0011] Optionally, a plurality of support members are provided between the upper door ring and the lower door ring, with both ends of the support members fixedly connected to the upper door ring and the lower door ring respectively, and the support members are provided on both sides of each roller.

[0012] By adopting the above technical solution, when replacing one or more rollers individually, after the rollers are removed from between the upper and lower door rings, the support members will support them between the upper and lower door rings. This prevents the upper and lower door rings from collapsing due to lack of local support after partial roller removal, thus reducing deformation and extending the service life of the door ring assembly. Furthermore, when reinstalling the rollers, the upper cover, lower cover, and roller sleeve can be placed between the two support members to create a space. The support members can limit the movement of the upper cover, lower cover, and roller sleeve, preventing misalignment or detachment from the upper and lower door rings before the rollers are inserted. This facilitates the insertion of the rollers and thus facilitates reinstallation, further improving roller maintenance efficiency.

[0013] Optionally, both the upper and lower door rings are rotatably provided with unlocking rings on their outer sides. Each unlocking ring includes a coaxially arranged mounting part and an unlocking part. The mounting part is rotatably connected to the upper and lower door rings. The unlocking part is located on the side of the two mounting parts away from each other. The unlocking part is provided with transmission teeth on the side of the upper and lower door rings. The self-locking nut is provided with a transmission gear in its circumferential direction. The transmission gear meshes with the transmission teeth. Both ends of the roller are provided with connecting posts. The roller is provided with a self-locking thread for threaded connection of the self-locking nut between the two connecting posts. The height of the transmission teeth in the vertical direction is greater than the height of the transmission gear in the axial direction.

[0014] By adopting the above technical solution, when all rollers need to be removed, the unlocking rings on the upper and lower door rings can be directly rotated to loosen all the self-locking nuts, eliminating the need to manually loosen each self-locking nut individually. This saves time in disassembling the rollers and further improves the efficiency of roller maintenance. When installing the rollers, the self-locking nuts can be first inserted onto the connecting posts at both ends of the roller, allowing the transmission gears to mesh with the transmission teeth. Then, by rotating the unlocking ring, all the self-locking nuts can be rotated to tighten, ensuring simultaneous tightening of all self-locking nuts without the need for additional tools such as screwdrivers to tighten each nut individually. If a self-locking nut becomes loose during use, it can also be tightened by directly rotating the unlocking ring, making the operation simple. This facilitates quick installation and removal of all rollers, improving efficiency. The unlocking ring is located inside the door ring, eliminating the need for operators to access the self-locking nuts in narrow areas, thus reducing maintenance difficulty.

[0015] Optionally, the mounting part and the unlocking part are detachably connected. The mounting part has a plurality of mounting slots, and the unlocking part has a plurality of mounting blocks. When the mounting part and the unlocking part are connected together, the mounting blocks and the mounting slots are interference-fitted.

[0016] By adopting the above technical solution, when a single roller needs to be disassembled or reassembled, the unlocking part of the unlocking ring can be removed from the mounting part by pulling the mounting block out of the mounting slot. This separates the transmission teeth on the unlocking part from all transmission gears, allowing each transmission gear to rotate independently. This enables the individual loosening or tightening of a single self-locking nut, thus allowing for the individual replacement of that roller. When the number of self-locking nuts is small and the unlocking ring is not required, it can also be removed, and the self-locking nuts can be tightened using ordinary methods. This makes the unlocking ring flexible in its use and suitable for various door ring assemblies. When the transmission teeth of the unlocking part wear, the unlocking part can be removed from the mounting part for individual replacement without replacing the entire mounting part, thus reducing maintenance costs.

[0017] Optionally, both the upper and lower door rings are threaded with fixing bolts, which are used to fix the unlocking ring and the upper and lower door rings. The upper and lower door rings and the mounting part are all provided with fixing screw holes for the fixing bolts to be threaded.

[0018] By adopting the above technical solution, after all the self-locking nuts are tightened, the fixing bolts can be screwed into the fixing screw holes, thereby fixing the position of the mounting part relative to the upper and lower door rings, thus fixing the position of the unlocking ring. During the circular motion of the shuttle, the unlocking ring is not easy to rotate at will, thus making the self-locking nuts not easy to loosen, improving the stability of the door ring assembly.

[0019] Optionally, the two ends of the roller have opposite thread directions, one of the unlocking rings has a receiving groove, a linkage rod is rotatably disposed in the receiving groove, the groove wall of the receiving groove is provided with a limiting member for limiting the linkage rod, and the other unlocking ring has a fixing groove for the linkage rod to extend into.

[0020] By adopting the above technical solution, when all rollers need to be disassembled or installed simultaneously, the limiting component can be loosened first, and then the linkage rod can be rotated until one end extends into the fixing groove, so that one end of the linkage rod abuts against the groove wall. At this time, the unlocking rings on the upper and lower door rings are connected together through the linkage rod. Then, by holding the linkage rod and pulling or pushing it in the same direction, the unlocking rings on the upper and lower door rings can be rotated synchronously in the same direction, without having to rotate the unlocking rings on the upper and lower door rings separately, further simplifying the operation steps of the unlocking rings. When the door ring assembly is in normal use, the linkage rod can also be fixed in the receiving groove by the limiting component, so that the linkage rod is not easy to rotate out of the receiving groove, thus not easily affecting the normal passage of the diameter between the upper and lower door rings.

[0021] Optionally, a limiting groove is formed on the wall of the receiving groove. The limiting component includes a limiting block slidably disposed in the limiting groove and a return spring disposed between the limiting block and the wall of the limiting groove. The return spring has a tendency to drive the limiting block into the receiving groove. The limiting block is provided with a guide slope, which is used to guide the limiting block to retract into the limiting groove.

[0022] By adopting the above technical solution, when the linkage rod needs to be rotated out of the receiving groove, the limiting block can be pushed into the limiting groove so that the limiting block no longer obstructs the linkage rod from rotating out of the receiving groove. Then, the linkage rod will automatically rotate into the fixed groove under the action of gravity, realizing the connection of the two unlocking rings. When the linkage rod needs to be locked in the receiving groove, the linkage rod can be rotated directly in the direction of entering the receiving groove, so that the side wall of the linkage rod abuts against the guide slope. Then, the limiting block will enter the limiting groove under the push of the linkage rod until the linkage rod rotates to the side of the limiting block away from the lower door ring. At this time, the limiting block will extend out of the limiting groove under the action of the return spring and block the linkage rod on the side close to the lower door ring, thus making it difficult for the linkage rod to rotate out of the receiving groove at will and ensuring the stability of the linkage rod.

[0023] In summary, this application includes at least one of the following beneficial technical effects:

[0024] 1. When a roller needs to be disassembled individually, the self-locking nut can be loosened directly, and then the roller can be pulled out. The upper cover, lower cover and roller sleeve of one roller can be removed individually, which improves the maintenance efficiency of a single roller.

[0025] 2. When it is necessary to disassemble or assemble all or most of the rollers, multiple self-locking nuts can be loosened or tightened simultaneously by rotating the unlocking ring, which further improves maintenance efficiency;

[0026] 3. The fixing bolts secure the unlocking ring to the upper and lower door rings, ensuring that the transmission teeth are always engaged with the transmission gears. This prevents the self-locking nut from loosening during the operation of the circular loom, thus improving the stability of the door ring assembly. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the overall structure of Embodiment 1 of this application.

[0028] Figure 2 yes Figure 1 Enlarged view of point A in the middle.

[0029] Figure 3 This is an exploded structural diagram of the roller in Embodiment 1 of this application.

[0030] Figure 4 This is a schematic diagram of the overall structure of the door ring assembly in Embodiment 2 of this application.

[0031] Figure 5 This is a partial exploded structural diagram of the mounting block used to illustrate Embodiment 2 of this application.

[0032] Figure 6 This is a partial structural schematic diagram of the receiving groove in Embodiment 2 of this application.

[0033] Figure 7This is a partial structural schematic diagram of the fixing groove used in Embodiment 2 of this application.

[0034] Explanation of reference numerals in the attached figures:

[0035] 1. Upper door ring; 11. Fixing screw hole; 12. Fixing bolt; 2. Lower door ring; 3. Roller; 31. Roller shaft; 32. Column sleeve; 33. Self-locking nut; 331. Transmission gear; 34. Upper cover; 35. Lower cover; 36. Deep groove ball bearing; 37. Rotary bearing; 38. Connecting column; 39. Self-locking thread; 4. Support component; 5. Unlocking ring; 51. Mounting part; 511. Mounting groove; 52. Unlocking part; 521. Transmission gear; 522. Mounting block; 53. Receiving groove; 531. Limiting groove; 532. Linkage rod; 533. Limiting component; 534. Limiting block; 535. Guide slope; 54. Fixing groove. Detailed Implementation

[0036] The following is in conjunction with the appendix Figure 1 - Appendix Figure 7 This application will be described in further detail.

[0037] This application discloses a gate assembly for a suspended circular loom.

[0038] Example 1

[0039] Reference Figure 1 and Figure 2 A gate assembly for a suspended circular loom includes an upper gate 1, a lower gate 2, several rollers 3, and several support members 4. The upper gate 1 and the lower gate 2 are arranged opposite each other in the vertical direction. The rollers 3 are arranged between the upper gate 1 and the lower gate 2. The two ends of the support members 4 are fixedly connected to the upper gate 1 and the lower gate 2, respectively, and the support members 4 are located on both sides of each roller 3 to further support the upper gate 1 and the lower gate 2.

[0040] Reference Figure 2 and Figure 3 The roller 3 includes a roller 31 and a sleeve 32. The roller 31 passes through the upper door ring 1 and the lower door ring 2, and the sleeve 32 is rotatably mounted on the circumference of the roller 31. The roller 31 and the sleeve 32 are typically made of high-strength metal, such as stainless steel, to ensure their strength and wear resistance. Both ends of the roller 31 are threaded with self-locking nuts 33. The two self-locking nuts 33 are respectively located on the side of the upper door ring 1 and the lower door ring 2 away from each other, and the roller 31 can be fixed to the upper door ring 1 and the lower door ring 2 by means of the self-locking nuts 33.

[0041] Reference Figure 2 and Figure 3The roller 31 is fitted with an upper cover 34 and a lower cover 35, which are respectively located on both sides of the sleeve 32. Both the upper cover 34 and the lower cover 35 are positioned between the upper door ring 1 and the lower door ring 2. The sleeve 32 is rotatably mounted on the upper cover 34 and the lower cover 35. The upper cover 34 and the lower cover 35 can be formed by stamping thin metal sheets, and their function is to axially limit the movement of the sleeve 32, ensuring its stable rotation. This design makes the installation and removal of the rollers 3 more convenient, and allows for quick individual replacement when a roller 3 is damaged, improving fault repair efficiency.

[0042] Reference Figure 3 A deep groove ball bearing 36 is provided between the roller 31 and the sleeve 32. Its function is to reduce the friction between the roller 31 and the sleeve 32 and improve the rotational flexibility of the sleeve 32. Rotary bearings 37 are provided at both ends of the sleeve 32. Part of the two rotary bearings 37 is located in the upper cover 34 and the lower cover 35, and the other part is located in the sleeve 32. The rotary bearings 37 can be angular contact ball bearings, which can better withstand axial and radial loads and ensure the stable rotation of the sleeve 32.

[0043] The implementation principle of the gate ring assembly of a suspended circular loom in this application embodiment is as follows: When it is necessary to replace a certain roller 3 individually, simply loosen the self-locking nut 33 from both ends of the roller 31, then pull the roller 31 out from the upper gate ring 1 and the lower gate ring 2, then remove the sleeve 32, the upper cover 34, and the lower cover 35 from between the upper gate ring 1 and the lower gate ring 2, then install the new roller 3 structure on the upper gate ring 1 and the lower gate ring 2 in sequence, and finally tighten the self-locking nut 33 at both ends of the roller 31. This allows the roller 3 to be replaced individually without completely separating the upper gate ring 1 and the lower gate ring 2 from all the rollers 3, thus improving the efficiency of fault repair.

[0044] Example 2

[0045] Reference Figure 4 and Figure 5 The difference between this embodiment and embodiment 1 is that: the roller 31 is provided with connecting posts 38 at both ends, the surface of the connecting posts 38 is smooth, and the roller 31 is provided with a self-locking thread 39 between the two connecting posts 38 for threaded connection of the self-locking nut 33. The self-locking thread 39 is provided on the side of the two connecting posts 38 that is close to each other.

[0046] Reference Figure 4 and Figure 5 Both the upper door ring 1 and the lower door ring 2 are rotatably provided with unlocking rings 5. When the unlocking rings 5 ​​rotate, they can drive the self-locking nuts 33 on the upper door ring 1 or the lower door ring 2 to rotate. The unlocking rings 5 ​​include a mounting part 51 and an unlocking part 52 arranged coaxially. The mounting part 51 is rotatably connected to the upper door ring 1 and the lower door ring 2. The unlocking part 52 is located on the side of the two mounting parts 51 that is away from each other.

[0047] Reference Figure 4 and Figure 5 The unlocking part 52 has a transmission tooth 521 on the side near the upper door ring 1 and the lower door ring 2. The self-locking nut 33 has a transmission gear 331 on its circumference. The transmission gear 331 meshes with the transmission tooth 521. The unlocking ring 5 drives the self-locking nut 33 to rotate through the meshing of the transmission tooth 521 and the transmission gear 331. The height of the transmission tooth 521 in the vertical direction is greater than the height of the transmission gear 331 in the axial direction, so that when the self-locking nut 33 passes through the connecting post 38, it can mesh with the transmission tooth 521, thereby facilitating the rotation of the self-locking nut 33 when the unlocking ring 5 rotates.

[0048] Reference Figure 5 The upper door ring 1, the lower door ring 2, and the mounting part 51 are all provided with fixing screw holes 11. The upper door ring 1 and the lower door ring 2 are all provided with fixing bolts 12. The fixing bolts 12 are threaded into the fixing screw holes 11 to fix the unlocking ring 5 and the upper door ring 1 and the lower door ring 2, thereby preventing the unlocking ring 5 from rotating freely during the operation of the circular loom, so that the self-locking nut 33 is not easy to loosen.

[0049] Reference Figure 5 and Figure 6 The mounting part 51 and the unlocking part 52 are detachably connected. The mounting part 51 has several mounting slots 511, and the unlocking part 52 has several mounting blocks 522. The mounting part 51 and the unlocking part 52 are connected together by the interference fit between the mounting blocks 522 and the mounting slots 511. This detachable connection method facilitates the individual installation and removal of the unlocking part 52, and it can be replaced individually when the transmission teeth 521 are worn.

[0050] Reference Figure 5 , Figure 6 and Figure 7 The two ends of the roller 31 have opposite thread directions. One unlocking ring 5 has a receiving groove 53, and a limiting groove 531 is formed on the groove wall of the receiving groove 53. A linkage rod 532 is rotatably arranged in the receiving groove 53. The other unlocking ring 5 has a fixing groove 54 for the linkage rod 532 to extend into. The bottom wall of the fixing groove 54 is arc-shaped along the cross section of the rotation plane of the linkage rod 532. After the linkage rod 532 extends into the fixing groove 54, it abuts against the vertical groove wall of the fixing groove 54.

[0051] Reference Figure 6The receiving groove 53 has a limiting member 533 on its groove wall for limiting the linkage rod 532. The limiting member 533 includes a limiting block 534 slidably disposed in the limiting groove 531 and a return spring (not shown in the figure) disposed between the limiting block 534 and the groove wall of the limiting groove 531. The limiting block 534 has a guide slope 535, and the return spring has a tendency to drive the limiting block 534 into the receiving groove 53. The guide slope 535 is used to guide the limiting block 534 to retract into the limiting groove 531 when the linkage rod 532 rotates into the receiving groove 53.

[0052] The implementation principle of the door ring assembly of a suspended circular loom in this application embodiment is as follows: When it is necessary to disassemble or assemble multiple or all rollers 3, the limiting block 534 can be pushed into the limiting groove 531 first. Then, the linkage rod 532 will automatically rotate out of the receiving groove 53 under the action of gravity and rotate into the fixing groove 54. Then, when the linkage rod 532 is pushed or pulled, since the threads at both ends of the roller 31 rotate in opposite directions, the self-locking nuts 33 on the upper door ring 1 and the lower door ring 2 can be disassembled or installed at the same time, which further improves the efficiency of fault repair.

[0053] The above are all preferred embodiments of this application and are not intended to limit the scope of protection of this application. Therefore, all equivalent changes made in accordance with the structure, shape and principle of this application should be covered within the scope of protection of this application.

Claims

1. A gate ring assembly for a suspended circular loom, comprising an upper gate ring (1) and a lower gate ring (2), wherein a plurality of rollers (3) are provided between the upper gate ring (1) and the lower gate ring (2), characterized in that: The roller (3) includes a roller (31) passing through the upper door ring (1) and the lower door ring (2) and a sleeve (32) rotatably disposed around the roller (31). Both ends of the roller (31) are threaded with self-locking nuts (33). The two self-locking nuts (33) are respectively disposed on the side of the upper door ring (1) and the lower door ring (2) away from each other. An upper cover (34) and a lower cover (35) are passing through the roller (31). The upper cover (34) and the lower cover (35) are respectively disposed on both sides of the sleeve (32). The upper cover (34) and the lower cover (35) are both disposed between the upper door ring (1) and the lower door ring (2). The sleeve (32) is rotatably disposed on the upper cover (34) and the lower cover (35). Unlocking rings (5) are rotatably provided on the outer sides of the upper door ring (1) and the lower door ring (2). The unlocking ring (5) includes a mounting part (51) and an unlocking part (52) arranged coaxially. The mounting part (51) is rotatably connected to the upper door ring (1) and the lower door ring (2). The unlocking part (52) is located on the side of the two mounting parts (51) away from each other. The unlocking part (52) is provided with transmission teeth (521) on the side of the upper door ring (1) and the lower door ring (2) close to each other. The self-locking nut (33) is provided with a transmission gear (331) in the circumferential direction. The transmission gear (331) meshes with the transmission teeth (521). The roller (31) is provided with connecting posts (38) at both ends. The roller (31) is provided with a self-locking thread (39) for threaded connection of the self-locking nut (33) between the two connecting posts (38). The height of the transmission teeth (521) in the vertical direction is greater than the height of the transmission gear (331) in the axial direction.

2. The door ring assembly of a suspended circular loom according to claim 1, characterized in that: A deep groove ball bearing (36) is provided between the roller (31) and the sleeve (32). Both ends of the sleeve (32) are provided with rotating bearings (37). The two rotating bearings (37) are partially disposed in the upper cover (34) and the lower cover (35), and the other part is disposed in the sleeve (32).

3. The gate ring assembly of a suspended circular loom according to claim 1, characterized in that: Several support members (4) are provided between the upper door ring (1) and the lower door ring (2). The two ends of the support members (4) are fixedly connected to the upper door ring (1) and the lower door ring (2) respectively. The support members (4) are provided on both sides of each roller (3).

4. The door ring assembly of a suspended circular loom according to claim 1, characterized in that: The mounting part (51) and the unlocking part (52) are detachably connected. The mounting part (51) has a plurality of mounting slots (511), and the unlocking part (52) has a plurality of mounting blocks (522). When the mounting part (51) and the unlocking part (52) are connected together, the mounting blocks (522) and the mounting slots (511) are interference fit.

5. The gate ring assembly of a suspended circular loom according to claim 1, characterized in that: The upper door ring (1) and the lower door ring (2) are both threaded with fixing bolts (12). The fixing bolts (12) are used to fix the unlocking ring (5) and the upper door ring (1) and the lower door ring (2). The upper door ring (1), the lower door ring (2) and the mounting part (51) are all provided with fixing screw holes (11) for the fixing bolts (12) to be threaded.

6. The gate ring assembly of a suspended circular loom according to claim 1, characterized in that: The two ends of the roller (31) have opposite threads. One of the unlocking rings (5) has a receiving groove (53) and a linkage rod (532) is rotatably arranged in the receiving groove (53). The groove wall of the receiving groove (53) is provided with a limiting member (533) for limiting the linkage rod (532). The other unlocking ring (5) has a fixing groove (54) for the linkage rod (532) to extend into.

7. The gate ring assembly of a suspended circular loom according to claim 6, characterized in that: The receiving groove (53) has a limiting groove (531) on its groove wall. The limiting member (533) includes a limiting block (534) slidably disposed in the limiting groove (531) and a return spring disposed between the limiting block (534) and the groove wall of the limiting groove (531). The return spring has a tendency to drive the limiting block (534) into the receiving groove (53). The limiting block (534) is provided with a guide slope (535) for guiding the limiting block (534) to retract into the limiting groove (531).

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