Adjustable support
By combining the rack bracket and slider assembly, the instrument angle adjustment without screws is achieved, and the problems of large size, large space consumption and complex adjustment in the prior art are solved, which improves the portability of the eye-viewing instrument Sex and stability.
Patent Information
- Application Number
- CN202420930828.6
- Authority / Receiving Office
- CN · China
- Patent Type
- Utility models(China)
- Current Assignee / Owner
- Filing Date
- 2024-04-30
- Publication Date
- 2024-12-17
- Estimated Expiration
- 2034-04-30
AI Technical Summary
The existing adjustable brackets have problems such as large size, high space consumption, complex assembly and difficult to adjust quickly in the field of ophthalmic optometry, especially the lack of pitch angle adjustment ability of desktop optometry instruments.
An adjustable bracket including rack bracket, support bar, mounting base, fixing seat, adjustment assembly and connecting rod is designed. The rack structure is hierarchical adjustment and the combination of slider, snap and spring blade to achieve no screws. This can fix the pitch angle of the instrument, simplify operation and improve stability.
It realizes tight integration with eye-optical instruments, saves space, simplifies assembly, improves portability and stability, and makes the pitch angle of the instrument adjustable to meet different user needs.
Smart Images
Figure CN222186446U_ABST
Abstract
Description
Technical Field
[0001] The utility model relates to the technical field of auxiliary devices for eye optometry instruments, in particular to an adjustable bracket. Background Art
[0002] With the development of the field of ophthalmology, various ophthalmic instruments are moving towards portability and desktop. Along with this development, the height and angle adjustment of desktop ophthalmic instruments has also become a demand. The adjustable bracket is a device that meets this demand.
[0003] Adjustable brackets can adjust their own support length, angle and other parameters according to the different usage requirements of users. It mainly includes adjustment structure and support structure. First, the adjustment structure is adjusted to the desired angle or height, and then the support structure is used to maintain this state to play a supporting role. At present, adjustable brackets have been developed in the fields of photovoltaic power generation, electronic devices, etc.
[0004] However, adjustable brackets still have the following shortcomings in the field of ophthalmology, which are mainly manifested in the following aspects:
[0005] 1. The adjustable brackets in the existing market are large in size, and most of them are separated from the instruments they need to support, and need to occupy independent space, which consumes a lot of space resources and requires a large amount of assembly work;
[0006] 2. Most adjustable brackets are still screw-fixed, which makes assembly and adjustment very troublesome, and it is difficult to quickly and easily adjust the instrument to the target position to meet the needs of users;
[0007] 3. There are relatively few stands for ophthalmic optometry instruments. The existing adjustable stands are difficult to effectively adjust the pitch angles of desktop ophthalmic optometry instruments, and cannot meet the different needs of users for desktop ophthalmic optometry instruments. Utility Model Content
[0008] In view of this, the utility model aims to provide an adjustable bracket to solve the above problems.
[0009] To achieve the above-mentioned purpose, the technical solution of the utility model is implemented as follows: an adjustable bracket, including a rack bracket, a support bar, a mounting seat, a fixed seat, an adjustment component and a connecting rod, two rack brackets are provided, the right ends of the two rack brackets are connected by the support bar, the left ends of the two rack brackets are respectively rotatably connected to the fixed seat, each rack bracket is slidably connected with an adjustment component, the adjustment component is rotatably connected with a connecting rod, and the end of the connecting rod away from the adjustment component is rotatably connected to the mounting seat; when the adjustment component slides along the rack bracket, the angle between the connecting rod and the rack bracket will change.
[0010] Furthermore, the rack bracket includes a guide rail bracket, a bracket cover plate and a rack structure, the guide rail bracket and the bracket cover plate are respectively arranged on both sides of the rack structure, and the guide rail bracket, the bracket cover plate and the rack structure are detachably connected, a first limiting hole is arranged on the guide rail bracket, a second limiting hole is arranged on the bracket cover plate, the first limiting hole and the second limiting hole are arranged opposite to each other, and a serrated structure with alternating concave and convex shapes is arranged on the rack structure.
[0011] Furthermore, the first limiting hole and the second limiting hole are both long strip-shaped through hole structures.
[0012] Furthermore, the adjustment assembly includes a slider, a slider cover, a buckle and a spring sheet. The slider and the slider cover are detachably connected. The buckle and the spring sheet are arranged between the slider and the slider cover, and the buckle is rotatably connected to the slider and the slider cover through a rotating shaft.
[0013] Furthermore, the slider is provided with a vertical limit structure, an upper limit structure and a lower limit structure. The vertical limit structure is arranged on the left side of the upper limit structure and the lower limit structure, and the upper limit structure is arranged directly above the lower limit structure. At the same time, there is a gap between the vertical limit structure and the upper limit structure and the lower limit structure. The left end of the slider is provided with a first connecting hole connected to the connecting rod, and the right end is provided with a second connecting hole connected to the snap fit.
[0014] Furthermore, the slider cover is provided with through holes respectively matched with the first connection hole and the second connection hole. At the same time, the slider cover is also provided with a side limit structure, and the side limit structure is matched and connected with the first limit hole.
[0015] Furthermore, both ends of the spring sheet are respectively arranged in the interval gaps between the vertical limit structure and the upper limit structure and the lower limit structure, and the arc convex part of the spring sheet is arranged between the upper limit structure and the lower limit structure.
[0016] Furthermore, a protruding structure is provided at the upper end of the buckle. When the buckle is subjected to force, the protruding structure provided at its upper end can slide along the arc protruding part of the spring sheet, sliding from the gap position between the spring sheet and the upper limit structure to the gap position between the spring sheet and the lower limit structure, or sliding from the gap position between the spring sheet and the lower limit structure to the gap position between the spring sheet and the upper limit structure. When the buckle moves on the rack structure, its lower end contacts the serrated structure of the rack structure.
[0017] Compared with the prior art, the adjustable bracket described in the utility model has the following advantages:
[0018] (1) The adjustable bracket of the utility model is integrated with the ophthalmic optometry instrument, which saves the space occupied by the adjustable bracket. At the same time, the integration also reduces the risk of missing or defective brackets;
[0019] (2) The adjustable bracket of the utility model utilizes the rack structure of the rack bracket to achieve graded adjustment, and the instrument can be fixed at a certain pitch angle without the use of screws or external devices. The operation is simple, which improves the portability and simplicity of the desktop ophthalmology instrument, and also has certain stability and reliability;
[0020] (3) The adjustable bracket described in the utility model enables the pitch angle of the ophthalmic optometry instrument to be adjusted to meet the usage requirements of different users for the instrument. BRIEF DESCRIPTION OF THE DRAWINGS
[0021] The accompanying drawings constituting a part of the present invention are used to provide a further understanding of the present invention. The illustrative embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation on the present invention. In the accompanying drawings:
[0022] Figure 1 This is a structural schematic diagram of an adjustable bracket according to an embodiment of the utility model;
[0023] Figure 2 It is a schematic diagram of the coordinated installation of the rack bracket, mounting seat, fixing seat, adjustment assembly and connecting rod;
[0024] Figure 3 This is a schematic diagram of the structure of the slider according to an embodiment of the utility model;
[0025] Figure 4 This is a schematic diagram of the structure of the slider cover according to an embodiment of the utility model;
[0026] Figure 5 A schematic diagram of the installation of the slider, buckle and spring sheet;
[0027] Figure 6 A schematic diagram of the coordination between the rack bracket and the adjustment assembly when the adjustable bracket is adjusted and fixed (the guide rail bracket and the slider cover are hidden in the figure);
[0028] Figure 7 A schematic diagram of the coordination between the rack bracket and the adjustment assembly when the adjustable bracket begins to be stored (the guide rail bracket and the slider cover are hidden in the figure);
[0029] Figure 8 A schematic diagram of the coordination between the rack bracket and the adjustment assembly when the adjustable bracket is stored (the guide rail bracket and the slider cover are hidden in the figure);
[0030] Fig. 9 Schematic diagram of the rack bracket and the adjustment assembly when the adjustable bracket is stored (the side plate and slider cover of the guide rail bracket are hidden in the figure)
[0031] Description of reference numerals:
[0032] 0. Equipment; 1. Rack bracket; 2. Support bar; 3. Mounting seat; 4. Fixed seat; 5. Adjustment assembly; 6. Connecting rod;
[0033] 11. Guide rail bracket; 111. First limiting hole; 12. Bracket cover; 121. Second limiting hole; 13. Rack structure; 131. Sawtooth structure; 132. Last level groove edge; 133. First level groove edge;
[0034] 51. Slider; 511. Vertical limiting structure; 512. Upper limiting structure; 513. Lower limiting structure; 514. First connecting hole; 515. Second connecting hole; 52. Slider cover; 521. Side limiting structure; 53. Buckle; 531. Protruding structure; 54. Spring sheet. DETAILED DESCRIPTION
[0035] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments can be combined with each other.
[0036] The present invention will be described in detail below with reference to the accompanying drawings and in combination with embodiments.
[0037] like Figure 1-Figure 9 As shown, the utility model is an adjustable bracket, including a rack bracket 1, a support bar 2, a mounting seat 3, a fixed seat 4, an adjustment component 5 and a connecting rod 6. The mounting seat 3 and the fixed seat 4 are both fixedly mounted on the ophthalmic optometry instrument 0. The fixed seat 4 is used to realize the connection between the device 0 and the rack bracket 1, and the mounting seat 3 is used to realize the connection between the device 0 and the connecting rod 6. Two rack brackets 1 are provided, the right ends of the two rack brackets 1 are connected by the support bar 2, and the left ends of the two rack brackets 1 are respectively rotatably connected to the fixed seat 4. An adjustment component 5 is slidably connected in each rack bracket 1, and a connecting rod 6 is rotatably connected to the adjustment component 5. The end of the connecting rod 6 away from the adjustment component 5 is rotatably connected to the mounting seat 3; the connecting rod 6 is a mechanical rod, and the so-called mechanical rod refers to a mechanical rod without a circuit board and a voltage regulator. When the adjustment component 5 slides along the rack bracket 1, the angle between the connecting rod 6 and the rack bracket 1 will change. In the description of the present invention, it should be understood that the terms "center", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present invention.
[0038] The support bar 2 is a long strip structure, which is used to connect the rack brackets 1 on both sides, so that the rack brackets 1 on both sides move synchronously during the adjustment process, ensuring that there is no height difference on both sides of the ophthalmic instrument 0. At the same time, the force bearing area of the adjustable bracket is increased during support, so that the support force is evenly distributed on the support bar 2, thereby making the support more stable.
[0039] The rack bracket 1 includes a guide rail bracket 11, a bracket cover plate 12 and a rack structure 13. The guide rail bracket 11 and the bracket cover plate 12 are respectively arranged on both sides of the rack structure 13, and the guide rail bracket 11, the bracket cover plate 12 and the rack structure 13 are detachably connected. The guide rail bracket 11 is provided with a first limiting hole 111, and the bracket cover plate 12 is provided with a second limiting hole 121. The first limiting hole 111 and the second limiting hole 121 are arranged opposite to each other, and the rack structure 13 is provided with a serrated structure 131 with alternating concave and convex shapes. Preferably, the first limiting hole 111 and the second limiting hole 121 are both long strip through hole structures. The guide rail bracket 11 and the bracket cover plate 12 have the function of protecting the internal structure. At the same time, the slider cover plate 52 and the side protrusions of the slider 51 are respectively embedded in the long strip through hole structure, which plays the role of fixing the relative positions of the slider 51 and the slider cover plate 52 and limiting the sliding track of the slider 51 and the slider cover plate 52. In the description of the present utility model, it should be understood that the terms "first", "second", etc. are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first", "second", etc. may explicitly or implicitly include one or more of the features.
[0040] The adjustment assembly 5 includes a slider 51, a slider cover 52, a buckle 53 and a spring sheet 54. The slider 51 and the slider cover 52 are detachably connected. The buckle 53 and the spring sheet 54 are arranged between the slider 51 and the slider cover 52, and the buckle 53 is rotatably connected to the slider 51 and the slider cover 52 via a rotating shaft. The spring sheet 54 is a U-shaped structure, fixed on the slider 51, and interacts with the buckle 53 to limit and adjust the position of the buckle 53.
[0041] The slider 51 is a flat rectangular structure, and is provided with a vertical limiting structure 511, an upper limiting structure 512 and a lower limiting structure 513. Preferably, the upper limiting structure 512 and the lower limiting structure 513 are both block-shaped protrusion structures 531; the vertical limiting structure 511 is arranged on the left side of the upper limiting structure 512 and the lower limiting structure 513, and the upper limiting structure 512 is arranged directly above the lower limiting structure 513. At the same time, there is a gap between the vertical limiting structure 511 and the upper limiting structure 512 and the lower limiting structure 513, which is used to provide a fixed position for the U-shaped spring sheet 54. At the same time, the two block-shaped protrusions of the upper limiting structure 512 and the lower limiting structure 513 can limit the position of the buckle 53 by limiting the protrusion structure 531 at the upper end of the buckle 53. The two block-shaped protrusions are also the parts that realize the connection and fixation between the slider 51 and the slider cover plate 52. The slider 51 is placed in the rack bracket 1 , one end of which is connected to the connecting rod 6 , and the other end of which is connected to the buckle 53 .
[0042] The left end of the slider 51 is provided with a first connection hole 514 that is connected with the connecting rod 6, and the right end is provided with a second connection hole 515 that is connected with the buckle 53. The first connection hole 514 and the second connection hole 515 are provided with a rotating shaft to realize the connection between the slider 51, the connecting rod 6, and the slider cover 52, and the connection between the slider 51, the buckle 53, and the slider cover 52. A side protrusion structure 531 (not shown in the drawings of the specification) is provided on the side of the slider 51 away from the vertical limiting structure 511. The side protrusion structure 531 is connected with the second limiting hole 121, that is, the side protrusion of the slider 51 is embedded in the second limiting hole 121, which plays a role in fixing the relative position of the slider 51 and limiting the sliding track of the slider 51.
[0043] The slider cover 52 is provided with through holes that respectively cooperate with the first connecting hole 514 and the second connecting hole 515. At the same time, the slider cover 52 is also provided with a side limiting structure 521, and the side limiting structure 521 is connected with the first limiting hole 111, that is, the side protrusion of the slider cover 52 is embedded in the first limiting hole 111, which plays a role in fixing the relative position of the slider cover 52 and limiting the sliding trajectory of the slider cover 52.
[0044] Both ends of the spring sheet 54 are respectively arranged in the interval gaps between the vertical limiting structure 511 and the upper limiting structure 512 and the lower limiting structure 513 , and the arc convex part of the spring sheet 54 is arranged between the upper limiting structure 512 and the lower limiting structure 513 .
[0045] The buckle 53 is a fan-shaped structure, and a protrusion structure 531 is provided at the upper end of the buckle 53. The protrusion structure 531 at the upper end of the buckle 53 interacts with the spring sheet 54 and the two square-shaped protrusions on the slider 51 to limit the relative position of the buckle 53 itself; the lower end of the buckle 53 interacts with the rack structure 13 of the rack bracket 1 to play a role in fixing the support angle. When the buckle 53 is subjected to force, the raised structure 531 arranged at its upper end can slide along the arc raised part of the spring sheet 54, and slide from the gap position between the spring sheet 54 and the upper limit structure 512 to the gap position between the spring sheet 54 and the lower limit structure 513, or slide from the gap position between the spring sheet 54 and the lower limit structure 513 to the gap position between the spring sheet 54 and the upper limit structure 512. When the buckle 53 moves on the rack structure 13, its lower end contacts the serrated structure 131 of the rack structure 13, and part of the rack structure 13 interacts with the buckle 53, so as to adjust the support angle in stages and fix the target angle after the adjustment is completed.
[0046] The specific implementation plan is as follows:
[0047] (Because the structures other than the support bar 2 are symmetrical, only one side is used as an example here)
[0048] 1. Adjustment
[0049] The adjustable bracket as a whole of the utility model is initially stored under the ophthalmic instrument equipment 0. In the initial state, the equipment 0 is placed on the desktop. When adjustment is needed, lift the end of the equipment 0 close to the support rod 2, hold the equipment 0 with one hand, and adjust the adjustable bracket with the other hand. The specific method is to pull down the support rod 2, the support rod 2 drives the rack bracket 1 to rotate around the fixed seat 4, the displacement of the rack bracket 1 forces the connecting rod 6 to rotate, and the connecting rod 6 drives the adjustment component 5 to move upward along the rack bracket 1. At this time, the protruding structure 531 at the upper end of the buckle 53 is located in the gap formed by the spring sheet 54 and the square block-shaped protrusion on the upper side of the slider 51 (the upper limit structure 512), and interacts with the spring sheet 54, but the interaction force is not enough to make the buckle 53 go over the spring sheet 54, so that the buckle 53 maintains a relatively fixed posture and moves upward along the rack bracket 1 together with the slider 51, and the bottom end of the buckle 53 gradually adjusts the pitch angle of the instrument equipment 0 upward along the rack part (the serrated structure 131 of the rack structure 13) until it reaches the angle required by the user.
[0050] 2. Fixation
[0051] After adjusting the instrument 0 angle to the angle required by the user, place the support bar 2 on the desktop. At this time, the bottom end of the buckle 53 interacts with the serrated edge of the serrated structure 131 of the rack bracket 1, and the bottom end of the buckle 53 is subjected to an upward force along the rack bracket 1 due to the action of the sawtooth. At the same time, the raised structure 531 at the upper end of the buckle 53 interacts with the square block-shaped raised protrusion (upper limit structure 512) on the upper side of the slider 51, and the raised structure 531 at the upper end of the buckle 53 is subjected to a force from the square block-shaped raised protrusion (upper limit structure 512) on the upper side of the slider 51. Since the buckle 53 is a structure that can rotate around the rotation axis, the buckle 53 is subjected to two forces, namely, an upward force along the rack bracket 1 due to the sawtooth action on the bottom end of the buckle 53, and a downward force from the upper limit structure 512 on the protruding structure 531 at the upper end of the buckle 53. These two forces are opposite to the direction of the rotation axis, limiting the rotation of the buckle 53, so that the sawtooth structure 131 balances and fixes the position of the buckle 53. At this time, the support angle of the adjustable bracket is completely fixed.
[0052] 3. Storage
[0053] Pull down the support bar 2 until the buckle 53 interacts with the last groove edge 132 of the sawtooth structure 131 of the rack bracket 1. At this time, the protruding structure 531 at the upper end of the buckle 53 interacts with the spring sheet 54, and the spring sheet 54 limits the further rotation of the buckle 53. Figure 7 Continue to pull down the support bar 2 to increase the interaction force between the buckle 53 and the last groove edge 132 of the sawtooth structure 131, thereby increasing the interaction force between the protruding structure 531 at the upper end of the buckle 53 and the spring sheet 54, until the spring sheet 54 cannot limit the protruding structure 531 at the upper end of the buckle 53, and the protruding structure 531 at the upper end of the buckle 53 passes over the spring sheet 54 to the gap formed by the spring sheet 54 and the block-shaped protrusion (lower limit structure 513) on the lower side of the slider 51. At this time, the bottom of the buckle 53 is tilted upward and no longer contacts the rack part of the sawtooth structure 131, as shown in FIG. Figure 8 As shown, due to the restriction of the spring sheet 54 on the upper protruding structure 531 of the buckle 53, the upper protruding structure 531 of the buckle 53 is restricted in the current gap, so the relative position of the buckle 53 is fixed, and the support bar 2 can be pulled up to retract the adjustable bracket.
[0054] When the bracket is about to be completely stored, the buckle 53 reaches the plane of the first-stage groove edge 133 of the rack part of the rack bracket 1, and the bottom end of the buckle 53 interacts with the plane, while the protruding structure 531 at the upper end of the buckle 53 interacts with the spring sheet 54. Fig. 9As shown. Continue to retract the support bar 2 upwards, increase the force between the upper protrusion of the buckle 53 and the spring sheet 54, until the spring sheet 54 cannot limit the position of the upper protrusion structure 531 of the buckle 53, the buckle 53 rotates, the upper protrusion structure 531 of the buckle 53 passes over the spring sheet 54 and returns to the initial position, and the lower end of the buckle 53 enters the first-level groove of the serrated structure 131. At this time, the adjustable bracket is completely stored in the instrument 0, and the adjustable bracket returns to the initial storage state. Repeat the adjustment and fixing steps to adjust the support angle of the adjustable bracket described in the utility model again.
[0055] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.
Claims
1. An adjustable bracket, characterized in that: The invention comprises a rack bracket (1), a support bar (2), a mounting seat (3), a fixed seat (4), an adjustment component (5) and a connecting rod (6); two rack brackets (1) are provided, the right ends of the two rack brackets (1) are connected via the support bar (2), the left ends of the two rack brackets (1) are respectively rotatably connected to the fixed seat (4), each rack bracket (1) is slidably connected with an adjustment component, the adjustment component (5) is rotatably connected with a connecting rod (6), and one end of the connecting rod (6) away from the adjustment component (5) is rotatably connected to the mounting seat (3); when the adjustment component (5) slides along the rack bracket (1), the angle between the connecting rod (6) and the rack bracket (1) will change.
2. The adjustable bracket according to claim 1, characterized in that: The rack bracket (1) comprises a guide rail bracket (11), a bracket cover plate (12) and a rack structure (13); the guide rail bracket (11) and the bracket cover plate (12) are respectively arranged on both sides of the rack structure (13); the guide rail bracket (11), the bracket cover plate (12) and the rack structure (13) are detachably connected; a first limiting hole (111) is arranged on the guide rail bracket (11); a second limiting hole (121) is arranged on the bracket cover plate (12); the first limiting hole (111) and the second limiting hole (121) are arranged opposite to each other; and a sawtooth structure (131) with alternating concave and convex portions is arranged on the rack structure (13).
3. The adjustable bracket according to claim 2, characterized in that: The first limiting hole (111) and the second limiting hole (121) are both long strip-shaped through-hole structures.
4. The adjustable bracket according to claim 3, characterized in that: The adjustment assembly (5) comprises a slider (51), a slider cover plate (52), a buckle (53) and a spring sheet (54); the slider (51) and the slider cover plate (52) are detachably connected; the buckle (53) and the spring sheet (54) are arranged between the slider (51) and the slider cover plate (52); and the buckle (53) is rotatably connected to the slider (51) and the slider cover plate (52) via a rotating shaft.
5. The adjustable bracket according to claim 4, characterized in that: The slider (51) is provided with a vertical limit structure (511), an upper limit structure (512) and a lower limit structure (513); the vertical limit structure (511) is arranged on the left side of the upper limit structure (512) and the lower limit structure (513); the upper limit structure (512) is arranged directly above the lower limit structure (513); and a gap is provided between the vertical limit structure (511) and the upper limit structure (512) and the lower limit structure (513); the left end of the slider (51) is provided with a first connection hole (514) for connecting with the connecting rod (6); and the right end is provided with a second connection hole (515) for connecting with the buckle (53).
6. The adjustable bracket according to claim 5, characterized in that: The slider cover plate (52) is provided with through holes respectively matched with the first connection hole (514) and the second connection hole (515). At the same time, the slider cover plate (52) is also provided with a side limit structure (521), and the side limit structure (521) is matched and connected with the first limit hole (111).
7. The adjustable bracket according to claim 5, characterized in that: The two ends of the spring sheet (54) are respectively arranged in the interval gap between the vertical limit structure (511) and the upper limit structure (512) and the lower limit structure (513), and the arc convex part of the spring sheet (54) is arranged between the upper limit structure (512) and the lower limit structure (513).
8. The adjustable bracket according to claim 7, characterized in that: A protruding structure (531) is provided at the upper end of the buckle (53). When the buckle (53) is subjected to force, the protruding structure (531) provided at the upper end thereof can slide along the arc protruding portion of the spring sheet (54), and slide from the gap position between the spring sheet (54) and the upper limit structure (512) to the gap position between the spring sheet (54) and the lower limit structure (513), or slide from the gap position between the spring sheet (54) and the lower limit structure (513) to the gap position between the spring sheet (54) and the upper limit structure (512). When the buckle (53) moves on the rack structure (13), its lower end contacts the sawtooth structure (131) of the rack structure (13).