Keycap press-fitting device for keyboard production

Abstract

The utility model discloses a keycap press-fitting device for keyboard production, which comprises a fixing plate, two ends of the fixing plate are rotatably provided with limiting plates in a penetrating manner through rotating shafts, and an adjusting mechanism is arranged between the two limiting plates. According to the improved keycap press-fitting device for keyboard production, when keycap press-fitting operation is carried out, the angle of the limiting plates is adjusted through the adjusting mechanism, so that the device can adapt to adsorption operation of inclined side walls of keycaps of different specifications, the application range of the device is expanded, and due to the fact that the fixed plate and the two limiting plates form an isosceles trapezoid keycap adsorption groove, the keycap adsorption efficiency is improved. The device can perform adsorption operation on key caps with different lengths, finally, the mechanical arm can continuously adsorb the key caps with different lengths to the key shaft through movement of the fixing plate and complete press-fitting operation, finally, the adsorption state of the key caps is automatically relieved through resistance generated when the key shaft is separated from the key caps, an operator does not need to perform other operation, and the operation efficiency is improved. And the labor intensity of an operator is greatly reduced.

Description

Technical Field

[0001] The utility model relates to the technical field of key cap press-fitting devices, in particular to a key cap press-fitting device for keyboard production. Background Art

[0002] A keyboard is a device for inputting instructions and data to operate computer equipment. It also refers to a group of function keys that are systematically arranged to operate a machine or device, such as a typewriter or computer keyboard. The structure of a keyboard also includes components such as keys, key switches, and circuit boards. Keys are usually made of plastic or metal, and key switches are responsible for detecting whether the keys are pressed and transmitting signals to the circuit board for processing.

[0003] For example, a device for pressing keycaps for keyboard production with publication number CN219704072U includes a processing plate, the upper end surface of the processing plate is symmetrically fixedly connected with a vertical plate, the upper ends of the two vertical plates are commonly fixedly connected with a top plate, a fixing groove is provided on the lower end surface of the top plate, a telescopic cylinder is fixedly installed in the fixing groove, the telescopic end of the telescopic cylinder is fixedly connected with a suction cup, and the lower end of the suction cup is fixedly connected with a connecting plate. The utility model, through the coordinated arrangement of the buffer plate, the telescopic rod and the buffer spring, in the process of driving the keyboard cap to move downward, the vertical column will abut against the buffer plate, driving the keyboard cap to continue to move downward for pressing and the buffer spring is compressed, and the buffer spring can buffer the downward pressure, so that the downward pressure is evenly applied to the keyboard, and the keycap can be pressed evenly, while preventing excessive pressure from damaging the keyboard.

[0004] For example, a device for pressing keycaps for keyboard production with publication number CN217182083U includes a workbench, a press machine body is provided on the inner top wall of the workbench, a mounting groove is provided on the inner bottom wall of the workbench, a mounting frame is provided inside the mounting groove, and a mounting mechanism includes a press frame, and the outer surface of the press frame is movably connected to the inner wall of the mounting frame. The utility model realizes stable installation of keycaps by setting a workbench, a press machine body, a mounting frame, a press frame, a socket, a shock absorbing rod, a suction cup and a shock absorbing spring. In actual use, the staff first installs the keyboard to be installed inside the press frame, and fixes the keyboard by tightening the screw rod, so that the top fixing strip plate fixes the keyboard. At this time, the mold for installing the keycap is stably aligned and placed on the keyboard, and the press machine body is started to drive the downward pressing positioning rod and the lower pressing plate to move downward, and the downward pressing positioning rod can be firstly fixed stably with the suction cup.

[0005] The keycaps and key shafts of a keyboard are generally assembled by press-fitting. An existing keycap press-fitting device generally arranges all the keycaps on the mounting end of the press-fitting device, and then press-fits all the keycaps together. Since the keycaps are of different sizes, the keycaps need to be arranged manually, which greatly increases the labor intensity of the operator. Utility Model Content

[0006] The purpose of the utility model is to provide a keycap press-fitting device for keyboard production, so as to solve the problems raised in the above-mentioned background technology.

[0007] To achieve the above-mentioned purpose, the utility model provides the following technical solutions: a keycap pressing device for keyboard production, comprising a fixed plate, both ends of the fixed plate are provided with limit plates through which the fixed plate is rotated by a rotating shaft, an adjustment mechanism is provided between the two limit plates, and an adsorption mechanism is provided inside the fixed plate.

[0008] Preferably, the adsorption mechanism comprises a soft plate, the soft plate is fixedly mounted on the bottom side of the fixed plate, two rectangular holes are provided on the soft plate, and honeycomb-shaped holes are provided inside the soft plate.

[0009] Preferably, a plurality of fixed cylinders are fixedly inserted at positions corresponding to the rectangular holes in the fixed plate, and the bottom sides of the fixed cylinders are coplanar with the bottom sides of the fixed plate, and the spacing between two adjacent fixed cylinders is equal. A support plate in a cross shape is fixedly installed in the bottom opening of the fixed cylinder, a piston plate is provided in the fixed cylinder, and the outer peripheral wall of the piston plate is connected to the inner wall of the corresponding fixed cylinder, and the piston plate is located above the corresponding support plate.

[0010] Preferably, a first one-way valve is commonly penetrated in the support plate and the piston plate, and the first one-way valve is fixedly connected to the corresponding support plate, the first one-way valve is slidably connected to the corresponding piston plate, and the interior of the first one-way valve is communicated with the interior of the fixed cylinder, a second one-way valve is fixedly penetrated at the top end of the fixed cylinder at the position corresponding to the first one-way valve, a spring is provided between the top side of the piston plate and the corresponding inner wall of the fixed cylinder, and both ends of the spring are respectively fixedly connected to the corresponding piston plate and the inner wall of the corresponding fixed cylinder.

[0011] Preferably, a plurality of support rods are relatively fixedly installed on the bottom side of the piston plate, the bottom of the support rods passes through the notch of the corresponding support plate and the corresponding rectangular hole and extends to the bottom side of the fixed plate, and the outer peripheral wall of the support plate contacts the inner wall of the notch of the corresponding support plate.

[0012] Preferably, the adjustment mechanism includes a fixed block, which is fixedly mounted at the middle position of the top side of the fixed plate and is located between the corresponding two fixed cylinders. A threaded cylinder is rotatably penetrated in the fixed block, a bolt is threadedly penetrated at the middle position of the top side of the fixed block, and push rods are penetrated in the openings at both ends of the threaded cylinder.

[0013] Preferably, the push rod is divided into a threaded shaft and an elastic rod with a rectangular cross-sectional shape, one end of the elastic rod is inserted into the threaded barrel and fixedly connected to the corresponding threaded shaft, and the threaded shaft is threadedly connected to the inner wall of the threaded barrel, the other end of the elastic rod is fixedly connected to the corresponding limit plate, and the outer peripheral wall of the elastic rod is gap-matched with the inner wall of the threaded barrel.

[0014] Preferably, two square tubes are relatively fixedly installed at the middle position of the top side of the fixing plate, and the elastic rod passes through the corresponding square tubes and contacts with the inner walls of the corresponding square tubes.

[0015] The utility model has the following beneficial effects:

[0016] The improved device for pressing keycaps for keyboard production can adjust the angle of the limit plate through an adjusting mechanism during the keycap pressing operation, so that the device can adapt to the inclined side wall adsorption operation of keycaps of different specifications, thereby expanding the application scope of the device. In addition, since the fixed plate and the two limit plates form an isosceles trapezoidal keycap adsorption groove, the device can perform adsorption operations on keycaps of different lengths. Finally, the manipulator can continuously adsorb keycaps of different lengths onto the key shaft through the movement of the fixed plate and complete the pressing operation. Finally, the keycap is automatically released from the adsorption state through the resistance when the key shaft and the keycap are separated. The operator does not need to perform other operations, thereby greatly reducing the operator's labor intensity. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the technical solutions of the embodiments of the utility model, the drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are some embodiments of the utility model. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0018] Figure 1 It is an overall schematic diagram of the utility model;

[0019] Figure 2 It is a schematic diagram of the overall structure of the fixed plate, the limiting plate and the soft plate of the utility model;

[0020] Figure 3 For this utility model Figure 2 A schematic diagram of the enlarged structure at A in the middle;

[0021] Figure 4This is a schematic diagram of the overall structure of the soft board, the fixing tube and the support rod of the utility model;

[0022] Figure 5 This is a schematic diagram of the internal structure of the fixed cylinder of the utility model;

[0023] Figure 6 The utility model is a schematic diagram of the overall structure of the push rod.

[0024] In the figure: 1. fixing plate; 2. limiting plate; 3. adsorption mechanism; 31. soft plate; 32. rectangular hole; 33. fixing cylinder; 34. supporting plate; 35. piston plate; 36. spring; 37. first one-way valve; 38. second one-way valve; 39. supporting rod; 4. adjusting mechanism; 41. fixing block; 42. threaded cylinder; 43. push rod; 431. threaded shaft; 432. elastic rod; 44. bolt; 45. square tube. DETAILED DESCRIPTION

[0025] In order to make the purpose, technical solution and advantages of the utility model more clear, the utility model is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described here are only used to explain the utility model and are not used to limit the utility model.

[0026] The utility model provides a technical solution: Figure 1 The utility model discloses a device for pressing keycaps for keyboard production, comprising a fixing plate 1, a connecting plate in a U-shape is fixedly installed at the middle position of the top side of the fixing plate 1, and the device is fixed to an external manipulator by bolts 44, both ends of the fixing plate 1 are rotatably penetrated by limit plates 2, an adjustment mechanism 4 is provided between the two limit plates 2, and an adsorption mechanism 3 is penetrated in the fixing plate 1.

[0027] In this embodiment, when the fixing plate 1 is fitted with the keycap, if there is a certain degree of misalignment between the keycap and the fixing plate 1, the limit plate 2 and the side wall of the keycap can interfere with each other to push the keycap to move and automatically fine-tune the position of the keycap, so that the keycap and the fixing plate 1 are always fitted in a specific state, preventing the keycap and the key shaft from being misaligned and affecting the press-fitting of the keycap.

[0028] In a further preferred embodiment of the present invention, Figure 1 and Figure 4 As shown, the adsorption mechanism 3 includes a soft plate 31, which is fixedly mounted on the bottom side of the fixed plate 1, and has two rectangular holes 32, and honeycomb holes are formed inside the soft plate 31, and the outer wall of the soft plate 31 is solid, and the soft plate 31 is a rubber plate;

[0029] In this embodiment, the soft board 31 with honeycomb holes inside allows the soft board 31 to expand and contract to a greater extent, and the solid setting of the outer peripheral wall of the soft board 31 ensures that the holes inside the soft board 31 will not affect the keycap's blocking of the rectangular hole 32.

[0030] In a further preferred embodiment of the present invention, Figure 1 and Figure 5 As shown, a plurality of fixed cylinders 33 are fixedly penetrated at positions corresponding to the rectangular holes 32 in the fixed plate 1, and the bottom sides of the fixed cylinders 33 are coplanar with the bottom sides of the fixed plate 1, and the spacing between two adjacent fixed cylinders 33 is equal. A support plate 34 in a cross shape is fixedly installed in the bottom opening of the fixed cylinder 33, and a piston plate 35 is provided in the fixed cylinder 33, and the outer peripheral wall of the piston plate 35 is in contact with the inner wall of the corresponding fixed cylinder 33, and the piston plate 35 is located above the corresponding support plate 34;

[0031] In this embodiment, the cross-shaped support plate 34 does not block the bottom opening of the fixed tube 33 , thereby allowing gas exchange between the bottom opening of the fixed tube 33 and the interior of the rectangular hole 32 .

[0032] In a further preferred embodiment of the present invention, Figure 5 As shown, a first one-way valve 37 is commonly penetrated in the support plate 34 and the piston plate 35, and the first one-way valve 37 is fixedly connected to the corresponding support plate 34, the first one-way valve 37 is slidably connected to the corresponding piston plate 35, and the interior of the first one-way valve 37 is communicated with the interior of the fixed cylinder 33, a sealing ring for blocking the gap between the first one-way valve 37 and the piston plate 35 is installed on the outer peripheral side of the first one-way valve 37, a second one-way valve 38 is fixedly penetrated at the position of the first one-way valve 37 at the top of the fixed cylinder 33, a spring 36 is provided between the top side of the piston plate 35 and the corresponding inner wall of the fixed cylinder 33, and the two ends of the spring 36 are respectively fixedly connected to the corresponding piston plate 35 and the inner wall of the corresponding fixed cylinder 33;

[0033] In this embodiment, the setting of the first one-way valve 37 prevents the gas at the top of the fixed cylinder 33 from flowing into the rectangular hole 32, so that when the piston plate 35 is located in the fixed cylinder 33 and moves downward, the gas in the rectangular hole 32 can be sucked into the fixed cylinder 33, and when the piston plate 35 moves upward, the gas in the fixed cylinder 33 will not be pushed into the rectangular hole 32. The setting of the second one-way valve 38 ensures that when the piston plate 35 moves upward, the gas in the fixed cylinder 33 can be discharged to the outside, and when the piston plate 35 moves downward, the outside gas will not flow into the fixed cylinder 33 through the second one-way valve 38.

[0034] In a further preferred embodiment of the present invention, Figure 1 , Figure 4 and Figure 5As shown, a plurality of support rods 39 are relatively fixedly mounted on the bottom side of the piston plate 35, the bottom of the support rod 39 passes through the corresponding notch of the support plate 34 and the corresponding rectangular hole 32 and extends to the bottom side of the fixed plate 1, and the outer peripheral wall of the support plate 34 contacts the inner wall of the notch of the corresponding support plate 34;

[0035] In this embodiment, the support rod 39 is provided so that during the bonding process between the fixing plate 1 and the key cap, as the soft plate 31 shrinks and deforms, the piston plate 35 is automatically pushed upward without the operator having to perform other operations.

[0036] In a further preferred embodiment of the present invention, Figure 1-3 As shown, the adjustment mechanism 4 includes a fixed block 41, which is fixedly mounted at the middle position of the top side of the fixed plate 1 and is located between the corresponding two fixed cylinders 33, and the connecting plate is sleeved on the outer peripheral side of the fixed block 41, and a threaded cylinder 42 is rotatably penetrated in the fixed block 41, and a bolt 44 is threadedly penetrated at the middle position of the top side of the fixed block 41, and push rods 43 are penetrated in the openings at both ends of the threaded cylinder 42;

[0037] In this embodiment, the arrangement of the fixing block 41 and the bolt 44 allows the lengths of the two push rods 43 in the threaded barrel 42 to be adjusted synchronously when the threaded barrel 42 rotates, thereby adjusting the angles of the limit plates 2 on both sides simultaneously.

[0038] In a further preferred embodiment of the present invention, Figure 1 , Figure 2 , Figure 3 and Figure 6 As shown, the push rod 43 is divided into a threaded shaft 431 and an elastic rod 432 with a rectangular cross-section. One end of the elastic rod 432 is inserted into the threaded barrel 42 and fixedly connected to the corresponding threaded shaft 431, and the threaded shaft 431 is threadedly connected to the inner wall of the threaded barrel 42. The other end of the elastic rod 432 is fixedly connected to the corresponding limit plate 2, and the outer peripheral wall of the elastic rod 432 is gap-matched with the inner wall of the threaded barrel 42. The elastic rod 432 is made of elastic materials such as spring 36 steel or elastic alloy;

[0039] In this embodiment, the push rod 43 composed of the elastic rod 432 and the threaded shaft 431 allows the push plate to bend and deform to a certain extent as required.

[0040] In a further preferred embodiment of the present invention, Figure 1 and Figure 2 As shown, two square tubes 45 are relatively fixedly installed at the middle position of the top side of the fixed plate 1, and the elastic rod 432 penetrates the corresponding square tube 45 and contacts the inner wall of the corresponding square tube 45;

[0041] In this embodiment, the setting of the square tube can constrain and limit the elastic rod 432 to a certain extent, so that the square rod will not bend or deform when it is located above the fixed plate 1, thereby preventing the square rod from bending and deforming above the fixed plate 1 and affecting the push and pull of the limit plate 2 by the push rod 43.

[0042] Working principle: When performing the keycap press-fitting operation, the operator rotates the bolt 44 in the opposite direction to release the conflict between the bolt 44 and the threaded barrel 42, and then rotates the threaded barrel 42 to pull the push rod 43 to move back and forth in the limit plate 2 through the conflict between the external thread of the threaded shaft 431 and the internal thread of the threaded barrel 42, thereby pulling or pushing the limit plate 2 to rotate, and adjusting the angle of the limit plate 2 according to the keycap specifications;

[0043] It should be noted that, due to the mutual interference between the inner wall of the square tube 45 and the outer wall of the elastic rod 432, when the threaded barrel 42 rotates, the push rod 43 will not be driven to rotate together due to the friction between the outer thread of the threaded shaft 431 and the inner thread of the threaded barrel 42;

[0044] After the inclination adjustment of the limit plate 2 is completed, the manipulator moves the fixed plate 1 to the top of the keycap, and moves the fixed plate 1 toward the keycap, and continues to move a specific distance toward the keycap after the soft plate 31 is attached to the keycap, so that the soft plate 31 shrinks and deforms;

[0045] It should be noted that if there is a certain degree of deviation between the position of the keycap and the fixing plate 1, during the process of fitting the fixing plate 1 and the keycap, due to the mutual interference between the limiting plate 2 and the keycap, the keycap can be pushed to the bottom of the fixing plate 1 through the mutual interference between the limiting plate 2 and the outer edge of the top side of the keycap;

[0046] During the process of the soft plate 31 shrinking and deforming, due to the mutual interference between the support rod 39 and the key cap, the support rod 39 pushes the piston plate 35 upward, so that the space on the bottom side of the piston plate 35 is expanded, and the key cap blocks the opening of the rectangular hole 32, so that a negative pressure state is formed in the rectangular hole 32, and the second one-way valve 38 prevents the gas in the fixed cylinder 33 from flowing into the rectangular hole 32, which forms a pressure difference at both ends of the first one-way valve 37, and finally causes the excess air on the top side of the piston plate 35 to flow to the outside through the first one-way valve 37, and makes the air pressure in the top space of the piston plate 35 equal to that of the outside, and then the manipulator moves up the fixed plate 1, and due to the push of the spring 36 on the piston plate 35, the piston plate 35 moves downward, at this time, the space on the top side of the piston plate 35 is expanded, and a negative pressure state is formed on the top of the fixed cylinder 33, and part of the gas in the rectangular hole 32 flows into the top of the fixed cylinder 33 due to the pressure difference at both ends of the first one-way valve 37, and finally causes the negative pressure in the rectangular hole 32 to continue to expand;

[0047] When the piston plate 35 moves downward, the keycap is pushed downward through the support rod 39, and due to the deformation and reset of the soft plate 31, the bottom side of the soft plate 31 is always in contact with the keycap, and the blocking state of the rectangular hole 32 remains unchanged. Finally, the adsorption force of the negative pressure in the rectangular hole 32 on the keycap is equal to the thrust of the spring 36 on the keycap through the piston plate 35 and the support rod 39, and the keycap is adsorbed under the fixed plate 1;

[0048] After the keycap is adsorbed, as the manipulator moves the fixing plate 1, the keycap can be directly moved above the key shaft, and then the manipulator pushes the keycap toward the key shaft to press fit the keycap and the key shaft. After the press fitting operation of the keycap and the key shaft is completed, the manipulator moves up the fixing plate 1. Due to the pulling of the keyshaft on the keycap, the balance between the adsorption force of the negative pressure in the rectangular hole 32 on the keycap and the thrust of the spring 36 on the keycap through the piston plate 35 and the support rod 39 will be broken, so that the keycap will not move up with the fixing plate 1, and finally the keycap and the soft The quality plate 31 is separated, and the blocking state of the rectangular hole 32 opening is released. Part of the external gas passes through the rectangular hole 32 opening and enters the rectangular hole 32, so that the pressure in the rectangular hole 32 is connected to the external pressure. Another part of the gas passes through the first one-way valve 37 and flows into the fixed cylinder 33, so that the pressure in the fixed cylinder 33 is the same as the external pressure. The spring 36 pushes the piston plate 35 to move down and reset until the piston plate 35 and the bracket are in conflict with each other, and the piston plate 35 and the support rod 39 are reset. The above operation is repeated continuously, and the manipulator can continue to press the keycap;

[0049] It should be noted that during the assembly process of the keycap and the key shaft, due to the mutual interference between the keycap and the key shaft, the piston plate 35 moves upward, thereby reducing the space on the top side of the piston plate 35. The negative pressure strength on the top side of the piston plate 35 is reduced, which will not affect the press-fitting operation of the keycap.

[0050] The above shows and describes the basic principle, main features and advantages of the utility model. Those skilled in the art should understand that the utility model is not limited by the above embodiments. The above embodiments and the specification only describe the principles of the utility model. The utility model may be subject to various changes and improvements without departing from the spirit and scope of the utility model. These changes and improvements fall within the scope of the utility model to be protected. The scope of protection claimed by the utility model is defined by the attached claims and their equivalents.

Claims

1. A device for pressing keycaps for keyboard production, comprising a fixing plate (1), characterized in that: Both ends of the fixed plate (1) are rotatably provided with limit plates (2) through a rotating shaft, an adjustment mechanism (4) is provided between the two limit plates (2), and an adsorption mechanism (3) is provided inside the fixed plate (1); The adsorption mechanism (3) comprises a soft plate (31); A plurality of fixed cylinders (33) are fixedly provided at positions corresponding to the rectangular holes (32) in the fixed plate (1), and the bottom sides of the fixed cylinders (33) are coplanar with the bottom side of the fixed plate (1), and the spacing between two adjacent fixed cylinders (33) is equal. A support plate (34) in a cross shape is fixedly provided in the bottom opening of the fixed cylinder (33), and a piston plate (35) is provided in the fixed cylinder (33), and the outer peripheral wall of the piston plate (35) contacts the inner wall of the corresponding fixed cylinder (33), and the piston plate (35) is located above the corresponding support plate (34); A first one-way valve (37) is provided in both the support plate (34) and the piston plate (35), and the first one-way valve (37) is fixedly connected to the corresponding support plate (34). The first one-way valve (37) is slidably connected to the corresponding piston plate (35), and the interior of the first one-way valve (37) is communicated with the interior of the fixed cylinder (33). A second one-way valve (38) is fixedly provided at the top of the fixed cylinder (33) at a position corresponding to the first one-way valve (37). A spring (36) is provided between the top side of the piston plate (35) and the inner wall of the corresponding fixed cylinder (33), and two ends of the spring (36) are fixedly connected to the corresponding piston plate (35) and the inner wall of the corresponding fixed cylinder (33), respectively. A plurality of support rods (39) are relatively fixedly mounted on the bottom side of the piston plate (35).

2. The device for pressing keycaps for keyboard production according to claim 1, characterized in that: The soft plate (31) is fixedly mounted on the bottom side of the fixed plate (1), two rectangular holes (32) are provided on the soft plate (31), and honeycomb-shaped holes are provided inside the soft plate (31).

3. A device for pressing keycaps for keyboard production according to claim 2, characterized in that: The bottom of the support rod (39) passes through the notch of the corresponding support plate (34) and the corresponding rectangular hole (32) and extends to the bottom side of the fixed plate (1), and the outer peripheral wall of the support plate (34) contacts the inner wall of the notch of the corresponding support plate (34).

4. The device for pressing keycaps for keyboard production according to claim 3, characterized in that: The adjusting mechanism (4) comprises a fixing block (41), the fixing block (41) being fixedly mounted at a middle position on the top side of the fixing plate (1) and being located between two corresponding fixing tubes (33), a threaded tube (42) being rotatably penetrated in the fixing block (41), a bolt (44) being threadably penetrated at a middle position on the top side of the fixing block (41), and push rods (43) being penetrated in openings at both ends of the threaded tube (42).

5. The device for pressing keycaps for keyboard production according to claim 4, characterized in that: The push rod (43) is divided into a threaded shaft (431) and an elastic rod (432) having a rectangular cross-sectional shape. One end of the elastic rod (432) is inserted into the threaded barrel (42) and fixedly connected to the corresponding threaded shaft (431), and the threaded shaft (431) is threadedly connected to the inner wall of the threaded barrel (42). The other end of the elastic rod (432) is fixedly connected to the corresponding limit plate (2), and the outer peripheral wall of the elastic rod (432) is clearance-matched with the inner wall of the threaded barrel (42).

6. A device for pressing keycaps for keyboard production according to claim 5, characterized in that: Two square tubes (45) are relatively fixedly mounted at the middle position of the top side of the fixing plate (1), and the elastic rod (432) penetrates the corresponding square tubes (45) and contacts the inner wall of the corresponding square tube (45).

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