CN213075177U

CN213075177U - Folding joint and infant bed

Info

Publication number: CN213075177U
Application number: CN202022217587.5U
Authority: CN
Inventors: 谭业鹏; 戚军
Original assignee: Kunshan Aisibeier Children's Products Co ltd
Current assignee: Kunshan Aisibeier Children's Products Co ltd
Priority date: 2020-09-30
Filing date: 2020-09-30
Publication date: 2021-04-30
Anticipated expiration: 2030-09-30

Abstract

A folding joint and infant bed, the folding joint includes a first main brace, a second main brace, a first assistant brace, a second assistant brace and a synchronous rotating mechanism, the end of the folding joint is respectively arranged around a concentric shaft in a rotating way, the synchronous rotating mechanism includes a moving member, a first driving groove arranged on the first main brace, a second driving groove arranged on the second main brace, a first guide groove arranged on the first assistant brace and a second guide groove arranged on the second assistant brace, the folding joint is applied to a novel infant bed, the moving member slides in the driving groove and the guide groove in the radial direction relative to the axis of the concentric shaft in the unfolding or folding process through the synchronous rotating mechanism, thereby driving the main brace and the assistant brace to rotate synchronously, completing the unfolding and folding of the bed, the unfolding or folding operation is convenient, the folding joint has small volume and is easy to store, is convenient to carry.

Description

Folding joint and infant bed

Technical Field

The utility model relates to a folding joint and infant bed.

Background

Infant beds are widely used due to their convenience, and in particular, with the recent release of a two-child policy, there are increasing demands for infant beds, and requirements for performance of infant beds, particularly operability and size, are increasing.

In the prior art, a baby bed as shown in publication No. CN209733216U is a foldable baby bed frame, which includes side brackets at two sides, wherein each side bracket includes a first foldable upper surrounding bracket, a second foldable upper surrounding bracket, a first foot brace and a second foot brace; the first upper surrounding frame, the second upper surrounding frame, the first foot supporting frame and one end part of the second foot supporting frame on each side are rotatably connected and then provided with a side frame locking mechanism at the rotating connection position, the first upper surrounding frame on the two sides and the second upper surrounding frame on the two sides are rotatably arranged between the other end parts of the first upper surrounding frames and the other end parts of the second upper surrounding frames respectively, and the side frame locking mechanisms are arranged at the rotating arrangement positions of the two positions respectively. The infant bed cannot be unfolded or folded at once.

Disclosure of Invention

The to-be-solved technical problem of the utility model is to provide a folding joint with expand position and folding position.

In order to solve the technical problem, the utility model discloses a technical scheme is: a folding joint with an unfolding position and a folding position comprises a first main support rod, a second main support rod, a first auxiliary support rod, a second auxiliary support rod and a synchronous rotating mechanism, wherein one end part of the first main support rod, the second main support rod, the first auxiliary support rod and the second auxiliary support rod are respectively arranged around a concentric shaft in a rotating mode, the synchronous rotating mechanism comprises a moving piece, a first driving groove arranged on the first main support rod, a second driving groove arranged on the second main support rod, a first guide groove arranged on the first auxiliary support rod and a second guide groove arranged on the second auxiliary support rod, and when the folding joint is unfolded or folded, the moving piece is inserted into the first driving groove, the second driving groove, the first guide groove and the second guide groove in a sliding mode and moves along the radial direction relative to the axis of the concentric shaft, so that the first main support rod, the second main support rod and the first auxiliary support rod can move along the radial direction relative to the axis of the, The second auxiliary supporting rod rotates among the four components.

In some embodiments, the first guide groove includes a first guide groove section, a first lock groove section that turns with respect to the extending direction of the first guide groove section and communicates with one end of the first guide groove section, the second guide groove includes a second guide groove section, and a second lock groove section that turns with respect to the extending direction of the second guide groove section and communicates with one end of the second guide groove section, and when the folding joint is in the unfolded position, the moving member is located in the first lock groove section and the second lock groove section.

In some embodiments, the first locking groove section and the second locking groove section are respectively straight grooves, and when the folding joint is located in the unfolded position, a connecting line between a center line of the first locking groove section and the second locking groove section and a center of the moving member and an axis of the concentric shaft coincides.

In some embodiments, an elastic limiting part extending outward from a part of the groove wall and forming a limiting convex point at an end is provided in the first groove section and/or the second groove section, the limiting convex point is adjacent to the other end of the first groove section or the other end of the second groove section, and the limiting convex point is partially blocked on a moving path of the moving member.

In some embodiments, a line connecting the center of the moving member and the axis of the concentric shaft forms a symmetry line, the first driving groove and the second driving groove are bilaterally symmetrical with respect to the symmetry line, and the first driving groove and the second driving groove are respectively straight grooves.

In some embodiments, the synchronous rotating mechanism further includes a slider groove disposed on the first main supporting rod or the second main supporting rod, a slider slidably disposed in the slider groove, and a slider positioning member fixed to the corresponding slider groove and the slider, the first driving groove or the second driving groove is disposed at a central portion of the corresponding slider groove, the slider positioning member is disposed with a slider positioning member groove corresponding to the first driving groove or the second driving groove, and the moving member penetrates through the slider and is inserted into the slider positioning member groove.

In some embodiments, a reinforcing iron plate is fixed to the first auxiliary stay bar and/or the second auxiliary stay bar, a reinforcing iron plate groove corresponding to the first guide groove and/or the second guide groove is formed in the reinforcing iron plate, and the moving member is also inserted into the reinforcing iron plate groove.

The utility model also aims to solve the technical problem of providing an infant bed.

In order to solve the technical problem, the utility model discloses a technical scheme is: an infant bed comprises two folding joints according to any one of the above technical solutions, the two folding joints are symmetrically arranged on two sides of the infant bed respectively, one end of a first bed surrounding rod is rotatably connected to the first auxiliary supporting rod on each side through a first surrounding rod shaft, one end of a second bed surrounding rod is rotatably connected to the second auxiliary supporting rod on each side through a second surrounding rod shaft, a first unidirectional rotation joint is arranged between the other ends of the first bed surrounding rods on two sides, a second unidirectional rotation joint is arranged between the other ends of the second bed surrounding rods on two sides, the first surrounding rod shaft is arranged in parallel with a rotating shaft on the first unidirectional rotation joint and is spatially vertical to the concentric shaft, the second surrounding rod shaft is arranged in parallel with a rotating shaft on the second unidirectional rotation joint and is also spatially vertical to the concentric shaft, and a central support frame for promoting the four main support rods to synchronously close or synchronously keep away is arranged between the first main support rod on two sides and the second main support rod on two sides.

In some embodiments, the center support frame includes a center seat located in the middle, and four sets of link mechanisms arranged around the center seat, and the four sets of link mechanisms are respectively connected between the two first main supporting rods, the two second main supporting rods and the center seat.

In some embodiments, each set of the link mechanisms includes an upper bottom bar located at the upper portion, and a lower bottom bar located below the upper bottom bar, one end of the upper bottom bar is pivotally connected to the upper portion of the central seat around a first bottom axis, the other end of the upper bottom bar is rotatably disposed with the corresponding main supporting rod through a first ball joint, one end of the lower bottom bar is pivotally connected to the lower portion of the central seat around a second bottom axis, the other end of the lower bottom bar is rotatably disposed with the corresponding main supporting rod through a second ball joint, a flattened upper limit mechanism is disposed between each upper bottom bar and the central seat, and a flattened lower limit mechanism is disposed between each lower bottom bar and the central seat.

The scope of the present invention is not limited to the technical solutions formed by specific combinations of the above technical features, and other technical solutions formed by arbitrary combinations of the above technical features or equivalent features should be covered. For example, the above features and the technical features (but not limited to) having similar functions disclosed in the present application are mutually replaced to form the technical solution.

Because of the application of the technical scheme, compared with the prior art, the utility model has the following advantages: the utility model provides a novel folding joint can be applied to novel infant's bed, through synchronous slewing mechanism for folding joint is expanding or folding in-process, and the axle center of the relative concentric shaft of moving member is at driving groove and guide way internal diameter to slide, thereby drives four parts synchronous rotations of main stay bar and supplementary stay bar, accomplishes the expansion and folding of bed, expandes or folding convenient operation, folding back small and easily deposit convenient to carry.

Drawings

FIG. 1 is a perspective view of an infant bed in an unfolded state;

FIG. 2 is a schematic side view of the infant bed in an expanded state;

FIG. 3 is a perspective view of the infant bed in a folded state;

FIG. 4 is an enlarged exploded view taken at A of FIG. 1;

FIG. 5 is a schematic view showing the internal structure of the folded joint in the unfolded position;

FIG. 6 is a schematic diagram showing the internal structure during the folding process of the folding joint;

wherein 1, folding joints; 11. a first main stay; 12. a second main stay; 13. a first auxiliary stay bar; 14. a second auxiliary stay bar; 15. a synchronous rotation mechanism; 151. a moving member; 152. a first drive slot; 153. a second driving groove; 154. a first guide groove; 154a, a first channel section; 154b, a first keyway segment; 155. a second guide groove; 155a, a second guide groove section; 155b, a second keyway section; 156. an elastic limiting part; 156a, a limit bump; 157. a slider slot; 158. Reinforcing iron sheets; 159. a slider; 159a, a slider positioning member; 2. a first bed rail; 21. a first boom shaft; 22. a first unidirectional rotational joint; 3. a second bed rail; 31. a second boom shaft; 32. a second unidirectional rotation joint; 4. a central support frame; 41. a center seat; 411. a first bottom shaft pivot; 412. a second bottom shaft pivot; 413. flattening the upper limit mechanism; 414. flattening the lower limiting mechanism; 42. a link mechanism; 421. an upper bottom rod; 422. and a lower bottom rod.

Detailed Description

As shown in the figures, the utility model provides a folding joint 1 with an unfolding position and a folding position, which is applied to an infant bed with the folding joint 1 as shown in figure 1.

The infant bed comprises two folding joints 1 which are symmetrically arranged on two sides of the infant bed respectively, and each folding joint 1 comprises a first main supporting rod 11, a second main supporting rod 12, a first auxiliary supporting rod 13 and a second auxiliary supporting rod 14, wherein one end parts of the first main supporting rod, the second main supporting rod, the first auxiliary supporting rod and the second auxiliary supporting rod are rotatably arranged around a concentric shaft respectively.

In this embodiment, each folding joint 1 further includes a synchronous rotation mechanism 15, and the synchronous rotation mechanism 15 includes a moving member 151 using a pin, a first driving groove 152 disposed on the first main supporting rod 11, a second driving groove 153 disposed on the second main supporting rod 12, a first guiding groove 154 disposed on the first auxiliary supporting rod 13, and a second guiding groove 155 disposed on the second auxiliary supporting rod 14.

In this embodiment, as shown in fig. 2, the first guide groove 154 includes a first guide groove section 154a, a first lock groove section 154b that is turned with respect to the extending direction of the first guide groove section 154a and communicates with one end thereof, the second guide groove 155 includes a second guide groove section 155a, and a second lock groove section 155b that is turned with respect to the extending direction of the second guide groove section 155a and communicates with one end thereof, wherein the first lock groove section 154b and the second lock groove section 155b are both straight grooves, when the folding joint 1 is in the unfolded position, the moving member 151 of the pin is simultaneously located in the first lock groove section 154b and the second lock groove section 155b, and at this time, the center lines of the first lock groove section 154b and the second lock groove section 155b coincide with the line connecting the center of the moving member 151 to the center axis, the first auxiliary strut 13 and the second auxiliary strut 14 cannot slide with respect to the moving member 151, that is, the first auxiliary strut 13 and the second auxiliary strut 14 are locked in position, at this time, the first main lever 11 and the second main lever 12 are angularly spread to the extreme positions, so the position of the moving member 151 is positioned by the first driving groove 152 and the second driving groove 153, and the positions of the first auxiliary lever 13 and the second auxiliary lever 14 are fixed relative to the first main lever 11 and the second main lever 12.

As shown in fig. 4-6, the second guiding groove segment 155a has an elastic stop 156 extending outward from a part of the groove wall and forming a stop protrusion 156a at an end thereof, the stop protrusion 156a is adjacent to the other end of the second guiding groove segment 155a, and the stop protrusion 156a is partially blocked on the moving path of the moving member 151, during the folding process, the moving member 151 overcomes the stop protrusion 156a and enters the other end of the second guiding groove segment 155a, at this time, the stop protrusion 156a plays a role in damping the unfolding of the moving member 151, and the user needs to rotate the second auxiliary stay 14 upward with a slight force to unfold the infant bed, that is, the elastic stop 156 having the stop protrusion 156a plays a role in positioning the folded position of the whole infant bed.

As shown in fig. 4, a reinforcing iron plate 158 is fixed to the first auxiliary stay 13, the reinforcing iron plate 158 has a reinforcing iron plate groove corresponding to the first guide groove 154, and the moving member 151 is inserted into the reinforcing iron plate groove, so as to enhance the pressure resistance of the entire synchronous rotation mechanism 15 and prevent the synchronous rotation mechanism 15 from being damaged when the entire infant bed is subjected to a large pressure.

In this embodiment, as shown in fig. 4, the first driving groove 152 and the second driving groove 153 are respectively straight grooves, a line connecting the centers of the moving member 151 passing through the two driving grooves and the axis of the concentric shaft forms a symmetry line, the first driving groove 152 and the second driving groove 153 are symmetrical with respect to the symmetry line, and the moving member 151 approaches to or departs from the concentric shaft along a straight line.

As shown in fig. 4, the synchronous rotating mechanism 15 further includes a slider groove 157 formed in the second main lever 12, a slider 159 slidably disposed in the slider groove 157, and a slider positioning member 159a fixed to the slider groove 157 and the slider 159, the slider groove 157 is a cross-shaped groove, the second driving groove 153 is located at the center of the corresponding slider groove 157, the slider positioning member 159a is formed with a slider positioning member groove corresponding to the second driving groove 153, and the moving member 151 penetrates the slider 159 and is inserted into the slider positioning member groove, so that the entire moving member 151 can stably slide in the driving groove when the infant bed is unfolded or folded, and the center line of the moving member 151 is not twisted.

During folding or unfolding of the infant bed, the moving member 151 slides along the first driving groove 152, the second driving groove 153, the first guide groove 154, and the second guide groove 155, and the moving member 151 gradually moves toward or away from the concentric axis in a radial direction.

The distances from one end to the other end of the first driving groove 152, from one end to the other end of the second driving groove 153, from one end to the other end of the first guide groove 154, and from one end to the other end of the second guide groove 155 to the concentric shafts gradually decrease, and intersect with the radial direction of the circle where the axes of the concentric shafts are located.

In this embodiment, as shown in FIGS. 1-3, the infant bed further includes: an end of the first bed fence rod 2 is rotatably connected to the first auxiliary strut 13 on each side through a first fence rod shaft 21, and an end of the second bed fence rod 3 is rotatably connected to the second auxiliary strut 14 on each side through a second fence rod shaft 31. A first unidirectional rotation joint 22 is arranged between the other ends of the first bed surrounding rods 2 at two sides, and a second unidirectional rotation joint 32 is arranged between the other ends of the second bed surrounding rods 3 at two sides.

The first boom shaft 21 is disposed parallel to the rotation shaft of the first unidirectional rotation joint 22 and is disposed spatially perpendicular to the concentric axis, and the second boom shaft 31 is disposed parallel to the rotation shaft of the second unidirectional rotation joint 32 and is also disposed spatially perpendicular to the concentric axis. The first unidirectional rotation joint 22 and the second unidirectional rotation joint 32 are prior art and will not be described in detail.

In this embodiment, as shown in FIGS. 1-3, the infant bed further includes: the center strut 4 is arranged between the first main strut 11 on two sides and the second main strut 12 on two sides, the center strut 4 enables the four to be synchronously close to or away from each other, the center strut 4 comprises a center seat 41 positioned in the middle and four groups of link mechanisms 42 arranged around the center seat 41, wherein the center seat 41 is a cross-shaped seat divided into an upper part and a lower part which are integrally formed, and the upper part and the lower part are respectively provided with four bottom shaft pivots which are symmetrical up and down; four sets of linkage mechanisms 42 are connected between the two first main support rods 11, the two second main support rods 12 and the center base 41, respectively.

Each set of link mechanism 42 includes an upper bottom bar 421 located at the upper portion, and a lower bottom bar 422 located below the upper bottom bar 421, one end portion of the upper bottom bar 421 is connected with the upper portion of the central base 41 around a first bottom shaft pivot 411, the other end portion of the upper bottom bar 421 is rotatably disposed with a corresponding main supporting rod through a first ball joint, one end portion of the lower bottom bar 422 is connected with the lower portion of the central base 41 around a second bottom shaft pivot 412, the other end portion of the lower bottom bar 422 is rotatably disposed with a corresponding main supporting rod through a second ball joint, a flattened upper limiting mechanism 413 is disposed between each upper bottom bar 421 and the central base 41, and a flattened lower limiting mechanism 414 is disposed between each lower bottom bar 422 and the central base 41.

When the center seat 41 moves upward, under the action of the upper bottom bar 421 and the lower bottom bar 422, the two first main support bars 11 and the two second main support bars 12 are driven to move toward the center synchronously, that is, the adjacent first main support bars 11 and the second main support bars 12, between the two first main support bars 11, and between the two second main support bars 12 are moved toward the center respectively, so as to drive the synchronous rotating mechanism 15 to fold the whole infant bed.

When the center seat 41 moves downward, under the action of the upper bottom bar 421 and the lower bottom bar 422, the two first main support bars 11 and the two second main support bars 12 are driven to extend around synchronously, that is, the adjacent first main support bars 11 and the second main support bars 12, between the two first main support bars 11, and between the two second main support bars 12 are respectively separated from each other, so as to drive the synchronous rotating mechanism 15 to unfold the whole infant bed, and when the four groups of links are unfolded to the flattening upper limiting mechanism 413 and the flattening lower limiting mechanism 414 on the center seat 41, the four groups of links are stopped by limiting, and the adjacent first main support bars 11 and the second main support bars 12, between the two first main support bars 11, and between the two second main support bars 12 are unfolded to the limiting positions.

In the unfolding or folding process of the baby carriage, the two folding joints 1 are unfolded or folded around the concentric shaft, so that the two first bed surrounding rods 2 are driven to be unfolded or closed through the first unidirectional rotating joint 22, and the second bed surrounding rod 3 is driven to be unfolded or closed through the second unidirectional rotating joint 32.

In addition, in this embodiment, the unidirectional rotation joint between the two first bed surrounding rods 2 and the two second bed surrounding rods 3 has only one rotation shaft inside to cooperate with the unfolding or folding of the whole infant bed, and a double-rotation shaft type can also be adopted, so long as the purpose of synchronously moving up or down to fold along with the unfolding or folding of the infant bed is achieved, which all belongs to the protection scope of the present invention.

The above embodiments are only for illustrating the technical concept and features of the present invention, and the purpose of the embodiments is to enable people skilled in the art to understand the contents of the present invention and to implement the present invention, which cannot limit the protection scope of the present invention. All equivalent changes and modifications made according to the spirit of the present invention should be covered by the protection scope of the present invention.

Claims

1. A folding joint having an unfolded position and a folded position, comprising a first main supporting rod (11), a second main supporting rod (12), a first auxiliary supporting rod (13) and a second auxiliary supporting rod (14) with one end respectively rotatably arranged around a concentric axis, characterized in that: the folding joint (1) is unfolded or folded, the moving member (151) is inserted into the first driving groove (152), the second driving groove (153), the first guide groove (154) and the second guide groove (155), and the moving member (151) slides in the first driving groove (152), the second driving groove (153), the first guide groove (154) and the second guide groove (155) and moves in a radial direction relative to the axis of the concentric shaft, so that the first main strut (11), the second main strut (12), the first auxiliary strut (13) and the second auxiliary strut (155) are enabled to rotate in the radial direction, and the first driving groove (152) is arranged on the first main strut (11), the second driving groove (153) is arranged on the second main strut (12), the first guide groove (154) is arranged on the first auxiliary strut (13), and the second guide groove (155) is arranged on the second auxiliary strut (14) The second auxiliary supporting rod (14) rotates among four components.

2. The folding joint of claim 1, wherein: the first guide groove (154) comprises a first guide groove section (154 a) and a first lock groove section (154 b) which is turned relative to the extending direction of the first guide groove section (154 a) and communicated with one end of the first guide groove section, the second guide groove (155) comprises a second guide groove section (155 a) and a second lock groove section (155 b) which is turned relative to the extending direction of the second guide groove section (155 a) and communicated with one end of the second guide groove section, and when the folding joint (1) is located at the open position and unfolded position, the moving member (151) is located in the first lock groove section (154 b) and the second lock groove section (155 b).

3. The folding joint of claim 2, wherein: the first lock groove section (154 b) and the second lock groove section (155 b) are respectively straight grooves, and when the folding joint (1) is located at the unfolding position, the connecting line between the center lines of the first lock groove section (154 b) and the second lock groove section (155 b) and the center of the moving member (151) and the axis of the concentric shaft is overlapped.

4. The folding joint (1) according to claim 2, characterized in that: the first guide groove section (154 a) and/or the second guide groove section (155 a) are/is internally provided with an elastic limiting piece (156) which extends outwards from part of the groove wall and forms a limiting salient point (156 a) at the end part, the limiting salient point (156 a) is adjacent to the other end part of the first guide groove section (154 a) or the other end part of the second guide groove section (155 a), and the limiting salient point (156 a) is partially blocked on the moving path of the moving piece (151).

5. The folding joint of claim 2, wherein: the center of the moving piece (151) and the axis of the concentric shaft are connected to form a symmetry line, the first driving groove (152) and the second driving groove (153) are bilaterally symmetrical relative to the symmetry line, and the first driving groove (152) and the second driving groove (153) are respectively straight grooves.

6. The folding joint of claim 1, wherein: the synchronous rotating mechanism (15) further comprises a slider groove (157) formed in the first main supporting rod (11) or the second main supporting rod (12), a slider (159) slidably arranged in the slider groove (157), and a slider positioning piece (159 a) fixed on the corresponding slider groove (157) and the slider (159), wherein the first driving groove (152) or the second driving groove (153) is located at the central portion of the corresponding slider groove (157), a slider positioning piece groove corresponding to the first driving groove (152) or the second driving groove (153) is formed in the slider positioning piece (159 a), and the moving piece (151) penetrates through the slider (159) and is inserted into the slider positioning piece groove.

7. The folding joint of claim 1, wherein: and a reinforcing iron sheet (158) is fixed on the first auxiliary supporting rod (13) and/or the second auxiliary supporting rod (14), reinforcing iron sheet grooves corresponding to the first guide groove (154) and/or the second guide groove (155) are respectively arranged on the reinforcing iron sheet (158), and the moving member (151) is also inserted into the reinforcing iron sheet grooves.

8. An infant bed incorporating a folding joint according to any one of claims 1-7, characterized in that: the folding joint (1) is provided with two folding joints which are symmetrically arranged on two sides of a baby bed respectively, one end part of a first bed surrounding rod (2) is rotatably connected on the first auxiliary supporting rod (13) on each side through a first surrounding rod shaft (21), one end part of a second bed surrounding rod (3) is rotatably connected on the second auxiliary supporting rod (14) on each side through a second surrounding rod shaft (31), a first unidirectional rotation joint (22) is arranged between the other end parts of the first bed surrounding rods (2) on two sides, a second unidirectional rotation joint (32) is arranged between the other end parts of the second bed surrounding rods (3) on two sides, the first surrounding rod shaft (21) is arranged in parallel with a rotation shaft on the first unidirectional rotation joint (22) and is arranged in space vertical relation to the concentric shaft, the second surrounding rod shaft (31) is arranged in parallel with a rotation shaft on the second unidirectional rotation joint (32) and is also arranged in space vertical relation to the concentric shaft, and a central support frame (4) for urging the four main support rods to synchronously close or synchronously far is arranged between the first main support rod (11) at two sides and the second main support rod (12) at two sides.

9. An infant bed according to claim 8, wherein: the central support frame (4) comprises a central seat (41) positioned in the middle and four groups of link mechanisms (42) arranged around the central seat (41), and the four groups of link mechanisms (42) are respectively connected between the two first main supporting rods (11), the two second main supporting rods (12) and the central seat (41).

10. An infant bed according to claim 9, wherein: each group of link mechanisms (42) comprises an upper bottom rod (421) positioned at the upper part and a lower bottom rod (422) positioned below the upper bottom rod (421), one end part of the upper bottom rod (421) is connected with the upper part of the central seat (41) around a first bottom shaft pivot (411), the other end part of the upper bottom rod (421) is rotatably arranged with a corresponding main supporting rod through a first ball joint, one end part of the lower bottom rod (422) is connected with the lower part of the central seat (41) around a second bottom shaft pivot (412), the other end part of the lower bottom rod (422) is rotatably arranged with a corresponding main supporting rod through a second ball joint, a flattening upper limiting mechanism (413) is arranged between each upper bottom rod (421) and the central seat (41), and a flattening lower limiting mechanism (414) is arranged between each lower bottom rod (422) and the central seat (41).