CN113404762A

CN113404762A - Self-locking bolt

Info

Publication number: CN113404762A
Application number: CN202110581686.8A
Authority: CN
Inventors: 吴自明; 任育柳
Original assignee: Individual
Current assignee: Individual
Priority date: 2021-05-27
Filing date: 2021-05-27
Publication date: 2021-09-17

Abstract

The invention relates to the field of bolts, in particular to a self-locking bolt which comprises a nut, wherein the lower end of the nut is connected with a screw rod, the upper end of the nut is provided with a fixed block, two sides of the fixed block at the upper end of the nut are provided with rectangular openings, the interior of each rectangular opening is movably connected with a pulling mechanism, each pulling mechanism comprises a pulling plate, two ends of each pulling plate are connected with vertical rods, one end of each pulling plate is connected with a first spring, the lower end of each vertical rod is connected with a movable plate, the surface of each movable plate is provided with a through hole, the interior of each fixed block is movably connected with a locking mechanism, each locking mechanism comprises a stretching rod, the surface of each stretching rod is connected with a cross rod, the surface of each cross rod close to one end of the cross rod is connected with a locking rod, and the inner bottom end of each screw rod is provided with a supporting table. According to the self-locking bolt, the bolt can be prevented from continuously rotating after being screwed down, and the bolt is prevented from loosening.

Description

Self-locking bolt

Technical Field

The invention relates to the field of bolts, in particular to a self-locking bolt.

Background

The bolt is a mechanical part, a cylindrical threaded fastener matched with a nut, a fastener composed of a head part and a screw (a cylinder with an external thread) needs to be matched with the nut and is used for fastening and connecting two parts with through holes, the connection form is called bolt connection, if the nut is screwed off from the bolt, the two parts can be separated, and therefore the bolt connection belongs to detachable connection; on one hand, after the bolt is used for fastening a target object, the bolt is loosened due to vibration of the target object, so that the risk of loosening exists, on the other hand, lubricating grease is not fully filled in the bolt hole, and the bolt is difficult to be screwed out from the bolt hole after rusting.

Disclosure of Invention

The invention mainly aims to provide a self-locking bolt, which aims to solve the problems that after the bolt is used for fastening a target object, the bolt is loosened due to vibration of the target object, and on the other hand, the bolt hole is not fully filled with lubricating grease, so that the bolt is difficult to screw out from the bolt hole after rusting.

In order to achieve the purpose, the invention adopts the technical scheme that:

the utility model provides a self-locking bolt, includes the nut, the lower extreme of nut is connected with the screw rod, the upper end of nut is fixed with the fixed block, the both sides of fixed block are provided with pull mechanism, the inside locking mechanism that is provided with of screw rod.

Preferably, the both sides of fixed block are equipped with the rectangle opening on the nut, rectangle open-ended inside swing joint has pull mechanism, pull mechanism includes the pull board, the both ends of pull board are connected with the pole setting, the one end of pull board is connected with first spring, the lower extreme of pole setting is connected with the fly leaf, the through-hole has been seted up on the surface of fly leaf, the inside swing joint of fixed block has locking mechanism, locking mechanism includes tensile pole, the surface of tensile pole is connected with the horizontal pole, the surface of horizontal pole is close to one end department and is connected with the locking lever, the inside bottom of screw rod is provided with a supporting bench.

Preferably, one end of the movable plate penetrates through the surface of the screw, the movable plate and the screw are in sliding connection, the lower end of the movable plate is in sliding connection with the support platform, and the diameter of the support platform is equal to the inner diameter of the screw.

Preferably, be fixed connection between pole setting, the pull board, be fixed connection between pole setting, the fly leaf, pole setting and the open-ended size looks adaptation of rectangle, be sliding connection between pole setting, the rectangle opening.

Preferably, one end of the first spring is fixedly connected with the drawing plate, and the other end of the first spring is fixedly connected to the center of one end of the fixed block.

Preferably, a holding block is fixedly connected above a fixed block at one end of the stretching rod, two groups of the cross rod and the locking rods are symmetrically arranged relative to the stretching rod, and the two groups of the locking rods are matched with the through hole in size.

Preferably, the screw rod is of a hollow structure, the support table is fixedly connected to the bottom end of the interior of the screw rod, a circular hole is formed in the center of the surface of the support table, and the size of the stretching rod is matched with the circular hole in the surface of the support table.

Preferably, the stretching rod penetrates through the inside of the fixing block, the stretching rod and the fixing block are in sliding connection, and the lower end of the fixing block is fixedly connected to the center of the upper end of the nut.

Preferably, the locking rod and the through hole are on the same vertical line.

In another embodiment, a locking mechanism is movably connected inside the fixed block, the locking mechanism and the fixed block are sealed through a sealing ring, the locking mechanism penetrates through the screw rod and is arranged in a groove with a T-shaped section arranged at the bottom end of the screw rod, the locking mechanism comprises a stretching rod, the surface of the stretching rod is connected with a cross rod, the surface of the cross rod close to one end of the cross rod is connected with a locking rod, the stretching rod penetrates through the clamping mechanism and is positioned in a through hole in the supporting plate, and the diameter of the through hole in the supporting plate is larger than that of the stretching rod;

the fixed blocks are fixedly connected with the pull plate through air bags, one-way valves are arranged at air inlets of the air bags, air outlets of the air bags are communicated with pipelines arranged inside the bolts, the pipelines inside the bolts are provided with the one-way valves, and the pipelines inside the bolts are communicated with the grooves with the T-shaped sections;

the clamping mechanism is arranged inside the groove with the T-shaped cross section and located at the bottom end of the locking rod, the clamping mechanism comprises a first top plate, two through holes are formed in the first top plate and matched with the locking rod, two first push plates are attached to the bottom end of the first top plate and fixedly connected with each other through a tension spring, the sum of the width of the two first push plates and the initial length of the tension spring is larger than the distance between the two locking rods, steel needles are fixed to one sides of the two first push plates and can penetrate through the screw and extend to the outside of the screw, a second top plate is attached to the bottom ends of the two first push plates, and the two first push plates can slide between the first top plate and the second top plate;

the bottom of second roof is provided with the backup pad, the backup pad is with the recess interference fit of screw rod bottom, the backup pad includes the second push pedal, the second push pedal is located the recess of backup pad bottom and blocks the through-hole that has tensile pole in the backup pad, the bottom mounting of second push pedal has the second spring, the bottom of second spring is provided with the screw thread post, the screw thread post passes through threaded connection with the recess of backup pad bottom, be provided with the through-hole on the screw thread post.

Compared with the prior art, the invention has the following beneficial effects:

1. the surface of the drawing plate is pressed to drive the upright stanchion to slide in the rectangular opening, so that the positions of the upright stanchion and the movable plate can be changed, the movable plate can be pulled back into the screw from the outer surface of the screw, the hand pressing the surface of the drawing plate is released, and at the moment, the movable plate slides out from the inside of the screw to realize self-locking; the first spring provides a buffering effect, so that the movable plate can be controlled more conveniently, and one end of the locking rod is conveniently inserted into the through hole by positioning the locking rod and the through hole on the same vertical line, so that the movable plate is prevented from continuously sliding; the upper end through the fly leaf will support at the lower extreme surface of target, and the cooperation screw rod locks the target, can prevent the bolt to continue to rotate to reach the purpose of fastening, the effect of use is better for traditional mode.

2. By arranging the pull plate and the air bag, the clamping mechanism can be inflated through a pipeline in the bolt; a steel needle is fixed on one side of the first push plate, and the steel needle can penetrate through the screw rod and extend to the outside of the screw rod to be clamped with a thread groove of a plate to be fixed, so that self-locking is realized; by arranging the tension springs, the steel needles on the two first push plates can be pulled back into the screw rod when the locking mechanism is pulled up, and the self-locking state is released; the locking mechanism can lock the first push plate to realize self-locking, and the stretching rod can push the second push plate to open a channel for conveying air for extruding lubricating grease; the second push plate and the second spring can prevent air leakage before the clamping mechanism is clamped, and the threaded column is connected with the groove at the bottom end of the supporting plate through threads, so that the mounting and the dismounting are facilitated; through set up the through-hole on the screw thread post, can extrude lubricating grease with the leading-in bolt hole of the air that fills in the chucking mechanism, make lubricating grease upwards fill along the thread, guarantee that lubricating grease can lubricate the upper half of bolt hole, realized the purpose of abundant lubrication bolt hole.

Drawings

FIG. 1 is a schematic view of the overall structure of a self-locking bolt according to the present invention;

FIG. 2 is a schematic structural view of a drawing mechanism, a locking mechanism and a supporting platform of the self-locking bolt of the present invention;

FIG. 3 is a schematic structural view of a locking mechanism of a self-locking bolt according to the present invention;

FIG. 4 is a schematic structural view of a drawing mechanism of a self-locking bolt according to the present invention;

FIG. 5 is a second schematic structural view of a pulling mechanism, a locking mechanism and a supporting platform of the self-locking bolt of the present invention;

FIG. 6 is a top view of a self-locking bolt of the present invention;

fig. 7 is an enlarged view of fig. 5 at a in the present invention.

In the figure: 1. a nut; 2. a screw; 3. a rectangular opening; 4. a drawing mechanism; 41. a drawing plate; 42. a first spring; 43. erecting a rod; 44. a movable plate; 45. a through hole; 46. an air bag; 5. a fixed block; 6. a locking mechanism; 61. a stretch rod; 62. a holding block; 63. a cross bar; 64. a locking lever; 7. a support table; 71. a threaded post; 72. a second spring; 73. a second push plate; 81. a steel needle; 82. a tension spring; 83. a first push plate; 84. a first top plate; 85. a second top panel.

Detailed Description

In order to make the technical means, the creation characteristics, the achievement purposes and the effects of the invention easy to understand, the invention is further described with the specific embodiments.

As shown in fig. 1-7, a self-locking bolt comprises a nut 1, and is characterized in that: the lower extreme of nut 1 is connected with screw rod 2, the upper end of nut 1 is fixed with fixed block 5, the both sides of fixed block 5 are provided with

pull mechanism

4, 2 inside locking mechanism 6 that are provided with of screw rod.

The utility model discloses a screw rod, including fixed block 5, nut 1, the both sides of fixed block 5 are equipped with rectangle opening 3 on the nut 1, the inside swing joint of rectangle opening 3 has pull mechanism 4, pull mechanism 4 includes pull board 41, the both ends of pull board 41 are connected with pole setting 43, the one end of pull board 41 is connected with first spring 42, the lower extreme of pole setting 43 is connected with fly leaf 44, through-hole 45 has been seted up on fly leaf 44's surface, the inside swing joint of fixed block 5 has locking mechanism 6, locking mechanism 6 includes tensile pole 61, the surface of tensile pole 61 is connected with horizontal pole 63, the surface of horizontal pole 63 is close to one end department and is connected with locking lever 64, the inside bottom of screw rod 2 is provided with brace table 7.

In this embodiment, one end of the movable plate 44 penetrates through the surface of the screw rod 2, the movable plate 44 and the screw rod 2 are connected in a sliding manner, the lower end of the movable plate 44 is connected in a sliding manner with the support platform 7, and the diameter of the support platform 7 is equal to the inner diameter of the screw rod 2.

A holding block 62 is fixedly connected above the fixed block 5 at one end of the stretching rod 61, two groups of cross rods 63 and two groups of locking rods 64 are symmetrically arranged relative to the stretching rod 61, and the sizes of the two groups of locking rods 64 are matched with the through hole 45.

Screw rod 2 is hollow structure, and brace table 7 fixed connection has seted up the round hole in the inside bottom of screw rod 2, brace table 7's surperficial center department, and the size of tensile pole 61 and the round hole looks adaptation on brace table 7 surface.

The stretching rod 61 penetrates through the fixing block 5, the stretching rod 61 and the fixing block 5 are in sliding connection, and the lower end of the fixing block 5 is fixedly connected to the center of the upper end of the nut 1.

The locking bar 64 and the through hole 45 are on the same vertical line.

Specifically, after the movable plate 44 enters the inside of the screw rod 2, the surface of the nut 1 is held at the same time, the screw rod 2 is inserted into a position to be fixed, at this time, the locking rod 64 and the through hole 45 are located on the same vertical line, the surface of the holding block 62 is held, the stretching rod 61 extends into the fixed block 5 and the inside of the screw rod 2, one end of the stretching rod 61 is inserted into the supporting table 7, at the same time, one end of the locking rod 64 on the surface of the cross rod 63 is inserted into the through hole 45, so that the movable plate 44 can be prevented from continuously sliding, at this time, the upper end of the movable plate 44 abuts against the lower end surface of the target, the target is locked in cooperation with the screw rod 2, and after the locking, the bolt cannot continuously rotate, and therefore, the situation that the bolt is loosened in the conventional method can be avoided.

In this embodiment, the upright rod 43 and the drawing plate 41 are fixedly connected, the upright rod 43 and the movable plate 44 are fixedly connected, the upright rod 43 is matched with the rectangular opening 3 in size, and the upright rod 43 and the rectangular opening 3 are slidably connected.

One end of the first spring 42 is fixedly connected with the drawing plate 41, and the other end of the first spring 42 is fixedly connected to the center of one end of the fixed block 5.

Specifically, the hand is pressed on the surface of the drawing plate 41 and pressed towards the fixed block 5, the vertical rod 43 is driven to slide in the rectangular opening 3, the positions of the vertical rod 43 and the movable plate 44 can be changed, the movable plate 44 can be pulled back into the screw rod 2 from the outer surface of the screw rod 2, and in addition, the first spring 42 provides a buffering effect, so that the movable plate 44 can be controlled more conveniently.

As another embodiment of the present invention, a locking mechanism 6 is movably connected inside the fixed block 5, the locking mechanism 6 and the fixed block 5 are sealed by a sealing ring, the locking mechanism 6 passes through the screw rod 2 and is disposed in a groove with a T-shaped cross section, which is disposed at the bottom end of the screw rod 2, the locking mechanism 6 includes a stretching rod 61, a cross rod 63 is connected to the surface of the stretching rod 61, a locking rod 64 is connected to a position, which is close to one end, on the surface of the cross rod 63, the stretching rod 61 passes through the clamping mechanism 8 and is disposed in a through hole on the support plate 7, and the diameter of the through hole on the support plate 7 is greater than the;

the fixed blocks 5 are fixedly connected with the drawing plate 41 through air bags 46, one-way valves are arranged at air inlets of the air bags 46, air outlets of the air bags 46 are communicated with pipelines arranged inside bolts, the pipelines inside the bolts are provided with the one-way valves, and the pipelines inside the bolts are communicated with the grooves with the T-shaped cross sections;

the clamping mechanism 8 is arranged inside the groove with the T-shaped cross section, the clamping mechanism 8 is located at the bottom end of the locking rod 64, the clamping mechanism 8 comprises a first top plate 84, two through holes are formed in the first top plate 84 and matched with the locking rod 64, two first push plates 83 are attached to the bottom end of the first top plate 84, the two first push plates 83 are fixedly connected through a tension spring 82, the sum of the width of the two first push plates 83 and the initial length of the tension spring 82 is larger than the distance between the two locking rods 64, steel needles 81 are fixed to one sides of the two first push plates 83, the steel needles 81 can penetrate through the screw 2 and extend to the outside of the screw 2, a second top plate 85 is attached to the bottom ends of the two first push plates 83, and the two first push plates 83 can slide between the first top plate 84 and the second top plate 85;

the bottom of second roof 85 is provided with backup pad 7, backup pad 7 and the recess interference fit of screw rod 2 bottom, backup pad 7 includes second push plate 73, second push plate 73 is located the recess of backup pad 7 bottom and blocks the through-hole that has tensile pole 61 on the backup pad 7, the bottom mounting of second push plate 73 has second spring 72, the bottom of second spring 72 is provided with screw thread post 71, screw thread post 71 passes through threaded connection with the recess of backup pad 7 bottom, be provided with the through-hole on the screw thread post 71.

Specifically, by arranging the pull plate 41 and the air bag 46, the clamping mechanism 86 can be inflated through a pipeline inside the bolt; the steel needle 81 is fixed on one side of the first push plate 83, and the steel needle 81 can penetrate through the screw rod 2 and extend to the outside of the screw rod 2 to be clamped with a thread groove of a plate to be fixed, so that self-locking is realized; by arranging the tension spring 82, the steel needles 81 on the two first push plates 83 can be pulled back into the screw rod 2 when the locking mechanism 6 is pulled out, so that the self-locking state is released; the locking mechanism 6 can lock the first push plate 83 to realize self-locking, and the stretching rod 61 can push the second push plate 73 open a channel for conveying air for extruding lubricating grease; can prevent through setting up second push pedal 73 and second spring 72 and leak gas before the chucking at chucking mechanism 8, pass through threaded connection through the recess that sets up screw thread post 71 and backup pad 7 bottom, made things convenient for the installation to dismantle, through set up the through-hole on screw thread post 71, can extrude lubricating grease with the leading-in bolt hole of the air that fills in chucking mechanism 8, make lubricating grease upwards fill along the thread, guarantee that lubricating grease can lubricate the upper half of bolt hole, realized the purpose of abundant lubrication bolt hole.

It should be noted that, the present invention is a self-locking bolt, a user presses the surface of the pulling plate 41 and presses towards the direction of the fixed block 5, the user will drive the upright rod 43 to slide in the rectangular opening 3, change the positions of the upright rod 43 and the movable plate 44, pull the movable plate 44 back to the inside of the screw rod 2 from the outer surface of the screw rod 2, after the movable plate 44 enters the inside of the screw rod 2, hold the surface of the nut 1, insert the screw rod 2 into the position to be fixed, when one end of the screw rod 2 passes through the target surface, loosen the hand pressing the surface of the pulling plate 41, at this time, the movable plate 44 will slide out from the inside of the screw rod 2, and the locking rod 64 and the through hole 45 are located on the same vertical line, hold the surface of the holding block 62, extend the pulling rod 61 into the inside of the screw rod 2, insert one end of the pulling rod 61 into the inside of the supporting table 7, at the same time, one end of the locking rod 64 will be inserted into the inside of the through hole 45, so that the movable plate 44 can be prevented from sliding continuously, and the upper end of the movable plate 44 will abut against the lower end surface of the target, and the target is locked by the screw 2.

In another mode, a user presses the surface of the pull plate 41 and presses the pull plate in the direction of the fixed block 5 to drive the air bag 46 to contract, the clamping mechanism 8 is inflated through a pipeline inside the bolt, the first push plate 83 pulls the tension spring 82 to move to one side under the action of air pressure, the steel needle 81 on the first push plate 83 penetrates through the screw rod 2 and extends to the outside of the screw rod 2 to be clamped with a thread groove of a plate to be fixed, so that self-locking is realized, meanwhile, the user inserts the locking rod 64 on the locking mechanism 6 into the through hole of the first top plate 84 to prevent the tension spring 82 from pulling the steel needle 81 on the first push plate 83 back to the inside of the screw rod 2, the stretching rod 61 pushes the second push plate 73 inside the support table 7, air enters the bolt hole through the through hole on the threaded column 71, under the continuous inflation of the user, the pressure in the bolt hole is increased, and the lubricating grease pre-filled in the bolt hole is filled upwards along the thread line, the lubricating grease can be ensured to lubricate the upper half part of the bolt hole, and the purpose of fully lubricating the bolt hole is realized; when the bolt needs to be disassembled, the locking mechanism 6 is pulled up, the tension spring 82 drives the steel needle 81 on the first push plate 83 to be pulled back into the screw rod 2, and meanwhile, the second spring 72 pushes the second push plate 73 upwards and blocks the through hole on the support plate 7, so that the bolt can be screwed out of the bolt hole.

The foregoing shows and describes the general principles and broad features of the present invention and advantages thereof. It will be understood by those skilled in the art that the present invention is not limited to the embodiments described above, which are described in the specification and illustrated only to illustrate the principle of the present invention, but that various changes and modifications may be made therein without departing from the spirit and scope of the present invention, which fall within the scope of the invention as claimed. The scope of the invention is defined by the appended claims and equivalents thereof.

Claims

1. A self-locking bolt comprises a nut (1), and is characterized in that: the lower extreme of nut (1) is connected with screw rod (2), the upper end of nut (1) is fixed with fixed block (5), the both sides of fixed block (5) are provided with pull mechanism (4), screw rod (2) inside is provided with locking mechanism (6).

2. A self-locking bolt according to claim 1 wherein: rectangular openings (3) are arranged on the screw cap (1) at two sides of the fixing block (5), the interior of the rectangular opening (3) is movably connected with a drawing mechanism (4), the drawing mechanism (4) comprises a drawing plate (41), two ends of the drawing plate (41) are connected with upright rods (43), one end of the drawing plate (41) is connected with a first spring (42), the lower end of the upright rod (43) is connected with a movable plate (44), the surface of the movable plate (44) is provided with a through hole (45), the inside of the fixed block (5) is movably connected with a locking mechanism (6), the locking mechanism (6) comprises a stretching rod (61), the surface of the stretching rod (61) is connected with a cross rod (63), one end of the surface of the cross rod (63) close to one end is connected with a locking rod (64), and the bottom end inside the screw rod (2) is provided with a supporting table (7).

3. A self-locking bolt according to claim 2 wherein: one end of the movable plate (44) penetrates through the surface of the screw rod (2), the movable plate (44) is in sliding connection with the screw rod (2), the lower end of the movable plate (44) is in sliding connection with the support platform (7), and the diameter of the support platform (7) is equal to the inner diameter of the screw rod (2).

4. A self-locking bolt according to claim 2 wherein: be fixed connection between pole setting (43), pull board (41), be fixed connection between pole setting (43) and fly leaf (44), pole setting (43) and rectangle opening (3) size looks adaptation, be sliding connection between pole setting (43) and rectangle opening (3).

5. A self-locking bolt according to claim 2 wherein: one end of the first spring (42) is fixedly connected with the drawing plate (41), and the other end of the first spring (42) is fixedly connected to the center of one end of the fixed block (5).

6. A self-locking bolt according to claim 2 wherein: a holding block (62) is fixedly connected above the fixed block (5) at one end of the stretching rod (61), two groups of the cross rod (63) and the locking rods (64) are symmetrically arranged relative to the stretching rod (61), and the sizes of the two groups of the locking rods (64) are matched with the through hole (45).

7. A self-locking bolt according to claim 2 wherein: the screw rod (2) is of a hollow structure, the support table (7) is fixedly connected to the bottom end of the interior of the screw rod (2), a round hole is formed in the center of the surface of the support table (7), and the stretching rod (61) is matched with the round hole in the surface of the support table (7) in size.

8. A self-locking bolt according to claim 2 wherein: the stretching rod (61) penetrates through the inside of the fixing block (5), the stretching rod (61) is in sliding connection with the fixing block (5), and the lower end of the fixing block (5) is fixedly connected to the center of the upper end of the nut (1).

9. A self-locking bolt according to claim 2 wherein: the locking rod (64) and the through hole (45) are on the same vertical line.

10. A self-locking bolt according to claim 1 wherein: the locking mechanism (6) is movably connected inside the fixed block (5), the locking mechanism (6) and the fixed block (5) are sealed through a sealing ring, the locking mechanism (6) penetrates through the screw rod (2) and is arranged in a groove with a T-shaped cross section formed in the bottom end of the screw rod (2), the locking mechanism (6) comprises a stretching rod (61), the surface of the stretching rod (61) is connected with a cross rod (63), the surface of the cross rod (63) close to one end is connected with a locking rod (64), the stretching rod (61) penetrates through the clamping mechanism (8) and is arranged in a through hole in the supporting plate (7), and the diameter of the through hole in the supporting plate (7) is larger than that of the stretching rod (61);

the fixed blocks (5) are fixedly connected with the drawing plate (41) through air bags (46), one-way valves are arranged at air inlets of the air bags (46), air outlets of the air bags (46) are communicated with pipelines arranged inside bolts, the pipelines inside the bolts are provided with the one-way valves, and the pipelines inside the bolts are communicated with the grooves with the T-shaped sections;

the cross-section is provided with chucking mechanism (8) for the inside of the recess of T shape, chucking mechanism (8) are located the bottom of locking lever (64), chucking mechanism (8) include first roof (84), be provided with two through-holes on first roof (84), two through-holes cooperate with locking lever (64), the bottom laminating of first roof (84) has two first push pedals (83), through extension spring (82) fixed connection between two first push pedals (83), two first push pedal (83) width and the total of the original length of extension spring (82) are greater than the distance between two locking levers (64), one side of two first push pedals (83) all is fixed with steel needle (81), steel needle (81) can pass screw rod (2) and extend to the screw rod (2) outside, the bottom laminating of first push pedal (83) has second roof (85), the two first push plates (83) can slide between the first top plate (84) and the second top plate (85);

the bottom of second roof (85) is provided with backup pad (7), backup pad (7) and the recess interference fit of screw rod (2) bottom, backup pad (7) include second push pedal (73), second push pedal (73) are located the recess of backup pad (7) bottom and block the through-hole that has tensile pole (61) on backup pad (7), the bottom mounting of second push pedal (73) has second spring (72), the bottom of second spring (72) is provided with screw thread post (71), screw thread post (71) pass through threaded connection with the recess of backup pad (7) bottom, be provided with the through-hole on screw thread post (71).