CN111546277B

CN111546277B - Pneumatic screwdriver and impact mechanism

Info

Publication number: CN111546277B
Application number: CN202010402513.0A
Authority: CN
Inventors: 林学军
Original assignee: Taitian Group Co ltd
Current assignee: Taitian Group Co ltd
Priority date: 2020-05-13
Filing date: 2020-05-13
Publication date: 2022-04-19
Anticipated expiration: 2040-05-13
Also published as: CN111546277A

Abstract

The invention discloses an impact mechanism which comprises a main shaft and an impact frame, wherein the impact frame is used for being connected with and rotating along with a pneumatic motor, the impact frame is provided with an annular cavity, and the first end of the main shaft is inserted into the annular cavity; the inner wall of the annular cavity is provided with an arc bulge, and the first end of the main shaft is provided with an elastic roller assembly fixedly connected along the radial direction of the main shaft; the elastic roller component is attached to the inner wall of the annular cavity, and when the impact frame rotates to drive the arc bulge to impact the elastic roller component, the elastic roller component retracts along the radial direction of the main shaft and passes over the arc bulge to drive the main shaft to rotate. The invention also discloses a pneumatic screwdriver comprising the impact mechanism. The impact mechanism provided by the invention can effectively reduce the abrasion between the impact frame and the main shaft, improve the running stability of the impact mechanism and prolong the service life of the impact mechanism and even the service life of the pneumatic screwdriver.

Description

Pneumatic screwdriver and impact mechanism

Technical Field

The present invention relates to hand-held mechanical working tools, and more particularly to an impact mechanism. The invention also relates to a pneumatic screwdriver with the impact mechanism.

Background

The pneumatic screwdriver is a hand-held mechanical working tool which takes compressed air as power and effectively mounts and demounts a threaded connector at high speed, and is a main category of pneumatic tools. It is suitable for assembling, installing and maintaining equipment with great amount of screw thread connecting parts, and has high work efficiency. The pneumatic screwdriver inputs compressed air through the air inlet interface, drives the pneumatic motor to rotate and do work, and then drives the impact mechanism to impact and output torque for screwing and disassembling the threaded fastener. The impact mechanism converts the rotational energy of the pneumatic motor into impact energy of the metal member in the form of impact (collision), and converts the impact energy into a fastening torque, thereby tightening the threaded coupling to a certain torque of the pneumatic tool. The basic structure of the pneumatic impact mechanism generally comprises an air inlet system, a pneumatic motor and an impact mechanism. The pneumatic motor is rotationally connected with an impact frame of the impact mechanism, and the impact frame collides with the main shaft to transmit torque to the main shaft so as to drive a screwdriver head connected with the main shaft to rotate. The main shaft and the impact frame generate larger impact and heat when being impacted, so that the main shaft and the impact frame are easily abraded, and lubricating oil between the main shaft and the impact frame is lost due to the impact, so that the abrasion of an impact mechanism is further aggravated.

Therefore, how to reduce the impact wear of the impact mechanism and improve the service life and the operation stability of the impact mechanism and the pneumatic screwdriver become technical problems to be solved by the technical personnel in the field.

Disclosure of Invention

The invention aims to provide an impact mechanism which can effectively reduce the abrasion between an impact frame and a main shaft, improve the running stability of the impact mechanism and prolong the service life of the impact mechanism. It is another object of the present invention to provide a pneumatic screwdriver including the impact mechanism described above.

In order to achieve the purpose, the invention provides an impact mechanism which comprises a main shaft and an impact frame, wherein the impact frame is used for being connected with and rotating along with a pneumatic motor, the impact frame is provided with an annular cavity, and the first end of the main shaft is inserted into the annular cavity;

the inner wall of the annular cavity is provided with an arc bulge, and the first end of the main shaft is provided with an elastic roller assembly fixedly connected along the radial direction of the main shaft;

the elastic roller component is attached to the inner wall of the annular cavity, and when the impact frame rotates to drive the arc bulge to impact the elastic roller component, the elastic roller component retracts along the radial direction of the main shaft and passes over the arc bulge to drive the main shaft to rotate.

Optionally, the first end of the main shaft is hermetically connected with the annular cavity, and lubricating oil is injected into the annular cavity.

Optionally, the first end of the main shaft is provided with a fixing hole formed along a radial direction of the main shaft, and the elastic roller mechanism is arranged in the fixing hole.

Optionally, an oil filler hole is formed in the annular cavity, and a sealing piece is arranged in the oil filler hole.

Optionally, the main shaft penetrates out of the annular cavity, an annular impact cover is arranged at the position where the main shaft penetrates out of the annular cavity, and sealing rings are arranged between the inner wall of the impact cover and the main shaft and between the outer wall of the impact cover and the annular cavity.

Optionally, retaining ring, fixing base, elastic component, gyro wheel mount pad and gyro wheel that elastic roller subassembly includes, the retaining ring card end in the fixed orifices, the fixing base laminating the retaining ring sets up the elastic component is located the fixing base with between the gyro wheel mount pad, the gyro wheel is in conflict under the spring action of elastic component in the inner wall of annular cavity.

Optionally, the roller mounting seat is a cylindrical housing, one end of the elastic member is clamped on an inner wall of the cylindrical housing, and an installation groove for fixing a wheel shaft of the roller is formed in one end of the cylindrical housing facing the inner wall of the annular cavity.

Optionally, the elastic roller assemblies are arranged in multiple groups, the multiple groups of elastic roller assemblies are arranged alternately along the axial direction of the main shaft and uniformly along the circumferential direction of the main shaft, and the arc protrusions are arranged in one-to-one correspondence with the elastic roller assemblies.

Optionally, the rounded protrusion is a flat arched protrusion.

The invention also provides a pneumatic screwdriver which comprises any one of the impact mechanisms, an air inlet system, a pneumatic motor and a screwdriver head connected to one end of the main shaft, which is far away from the annular cavity, wherein one end of the main shaft, which is far away from the annular cavity, is provided with a mounting hole for fixing the screwdriver head.

Compared with the prior art, the impact mechanism provided by the invention has the advantages that the impact frame is rotationally connected with the pneumatic motor, so that the impact frame is driven by the pneumatic motor to rotate; impact the frame and be equipped with annular cavity, the first end of main shaft is pegged graft in annular cavity, annular cavity's inner wall is equipped with the circular arc arch, the main shaft is pegged graft and is equipped with the elastic roller assembly along the radial setting of main shaft in annular cavity's part, under the non-impact state, the laminating of elastic roller assembly is at annular cavity's inner wall, during impact state, the elastic roller assembly is strikeed to the circular arc arch, elastic roller assembly pressurized is along the radial retraction of main shaft, elastic roller assembly crosses the circular arc arch, the circular arc arch is with torque transfer drive main shaft rotation for the main shaft. The elastic roller components are abutted against the inner wall of the annular cavity, so that stable operation in a non-impact state is ensured, and abrasion of the main shaft and the annular cavity is reduced; under the impact state, the arc bulge and the elastic roller component can form relatively stable and smooth impact, further reduce abrasion and ensure the running stability of the impact mechanism. And because the annular cavity is arranged, the loss of lubricating oil between the arc protrusions and the elastic roller wheel assembly and between the main shaft and the annular cavity can be effectively reduced, so that the abrasion of the impact mechanism is reduced, the operation stability of the impact mechanism is improved, and the service life of the impact mechanism is prolonged.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the provided drawings without creative efforts.

FIG. 1 is a cross-sectional view of an impact mechanism provided in an embodiment of the present invention;

FIG. 2 is an exploded view of FIG. 1;

FIG. 3 is a sectional view taken along line A-A of the impact frame and resilient roller assembly of FIG. 1 in an initial state;

FIG. 4 is a sectional view taken along line B-B of the impact frame and resilient roller assembly of FIG. 1 in an initial state;

FIG. 5 is a sectional view taken along line A-A of the impact frame and resilient roller assembly of FIG. 1 in a striking state;

FIG. 6 is a sectional view taken along line B-B of the striking state of the impact frame and the resilient roller assembly of FIG. 1;

FIG. 7 is a sectional view taken along line A-A of the impact frame and resilient roller assembly of FIG. 1 in a critical state;

FIG. 8 is a sectional view taken along line B-B of the impact frame and resilient roller assembly of FIG. 1 in a critical state;

fig. 9 is a schematic view of a driving screwdriver according to an embodiment of the present invention.

Wherein:

01-pneumatic motor, 1-impact frame, 2-main shaft, 3-annular cavity, 4-arc bulge, 5-fixed hole, 6-retainer ring, 7-fixed seat, 8-elastic piece, 9-roller mounting seat, 10-roller, 11-oil injection hole, 12-sealing gasket, 13-sealing screw, 14-impact cover, 15-sealing ring and 16-mounting hole.

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

In order that those skilled in the art will better understand the disclosure, the invention will be described in further detail with reference to the accompanying drawings and specific embodiments.

Referring to fig. 1 to 9, fig. 1 is a sectional view of an impact mechanism according to an embodiment of the present invention, fig. 2 is an exploded view of fig. 1, fig. 3 is a sectional view taken along a line a-a of an initial state of an impact frame and an elastic roller assembly of fig. 1, fig. 4 is a sectional view taken along a line B-B of the initial state of the impact frame and the elastic roller assembly of fig. 1, fig. 5 is a sectional view taken along a line a-a of a striking state of the impact frame and the elastic roller assembly of fig. 1, fig. 6 is a sectional view taken along a line B-B of the striking state of the impact frame and the elastic roller assembly of fig. 1, fig. 7 is a sectional view taken along a line a-a of a critical state of the impact frame and the elastic roller assembly of fig. 1, fig. 8 is a sectional view taken along a line B-B of the critical state of the impact frame and the elastic roller assembly of fig. 1, and fig. 9 is a schematic view of a driving screwdriver according to an embodiment of the present invention. The direction of the arrow in the figure indicates the direction of rotation of the impact frame 1 by the pneumatic motor 01.

The impact mechanism provided by the invention comprises an impact frame 1 and a main shaft 2, wherein the impact frame 1 is connected with a pneumatic motor 01 and driven by the pneumatic motor 01 to rotate, one end of the main shaft 2 is connected with the impact frame 1 and used for rotating under the impact of the impact frame 1, and the other end of the main shaft 2 is used for mounting a screwdriver bit. Wherein, strike frame 1 and be equipped with annular cavity 3, the first end of main shaft 2 is pegged graft in annular cavity 3. In order to realize that the main shaft 2 rotates under the rotary impact of the impact frame 1, the inner wall of the annular cavity 3 is provided with an arc protrusion 4, and the part of the main shaft 2 inserted in the annular cavity 3 is provided with an elastic roller component which is fixedly connected along the radial direction of the main shaft 2 and is matched with the arc protrusion 4.

In a non-impact state, the elastic roller component props against the inner wall of the annular cavity 3 under the action of elasticity, and the main shaft 2 basically does not rotate under the rolling action of the elastic roller component; under impact state, also when circular arc protrusion 4 rotates to elastic roller assembly, impact elastic roller assembly through circular arc protrusion 4 and drive main shaft 2 rotatory, elastic roller assembly retracts along main shaft 2's radial this moment for circular arc protrusion 4 can cross elastic roller assembly and accomplish an impact. Because the elastic roller component is always attached to the inner wall of the annular cavity 3, the running stability of the impact mechanism is good, meanwhile, the design of the roller 10 type and the matching of the elastic roller component and the circular arc bulge 4 reduce the abrasion of the elastic roller component and the inner wall of the annular cavity 3 and the circular arc bulge 4, and the arrangement of the annular cavity 3 reduces the loss of lubricating oil between the circular arc bulge 4 and the elastic roller component and between the main shaft 2 and the impact frame 1, thereby further reducing the abrasion of the impact mechanism.

The impact mechanism provided by the present invention will be described in more detail with reference to the accompanying drawings and specific embodiments.

In a specific embodiment of the present invention, the structure of the impact mechanism is shown in fig. 1 and fig. 2, and in this embodiment, the working principle of the impact mechanism is described by taking two sets of elastic roller assemblies and two sets of round protrusions as an example. In practical implementation, the elastic roller assemblies and the arc protrusions 4 can be set into a plurality of groups in one-to-one correspondence as required.

The impact mechanism comprises an impact frame 1 and a main shaft 2, wherein one end of the impact frame 1 is fixedly connected with an output shaft of the pneumatic motor 01, so that the impact mechanism is driven by the pneumatic motor 01 to rotate. The whole impact frame 1 is a cylindrical shell with one open end and one sealed wall, a connecting shaft used for connecting an output shaft of the pneumatic motor 01 is fixedly connected with the sealed end of the cylindrical shell, an annular cavity 3 is formed in the cylindrical shell, two sets of circular arc bulges 4 are arranged on the inner wall of the annular cavity 3, and the circular arc bulges 4 are preferably set to be flat arched bulges. Two sets of circular arc protruding 4 are alternately arranged along the axial direction of annular cavity 3, and simultaneously along the circumference of annular cavity 3 with 180 stagger arrangement.

Correspondingly, the first end of the main shaft 2 inserted in the annular cavity 3 is connected with two groups of elastic roller assemblies, and the two groups of elastic roller assemblies are arranged along the circumferential direction of the main shaft 2 and are in one-to-one correspondence with the two groups of annular cavities 3. The corresponding arrangement specifically means that the two groups of elastic roller assemblies are staggered by 180 degrees along the circumferential direction and are arranged at intervals along the axial direction of the main shaft 2, and the axial distance of the intervals is equal to the axial distance of the two groups of circular arc protrusions 4.

Therefore, when the impact frame 1 rotates to drive the arc protrusions 4 to rotate, the arc protrusions 4 can impact with the elastic roller assemblies in a one-to-one correspondence manner, and the torque is transmitted to the main shaft 2 through the elastic roller assemblies, so that the main shaft 2 is driven to rotate, and the screwdriver head fixedly connected with the main shaft 2 is further driven to rotate.

The elastic roller assembly specifically refers to a roller assembly capable of extending and retracting along the radial direction of the main shaft 2, and the elastic roller assembly is rigidly connected with the main shaft 2 in other directions, particularly in the circumferential direction, so that the elastic roller assembly is abutted against the inner wall of the annular cavity 3 in a non-impact state and retracts along the radial direction of the main shaft 2 in an impact state, and the elastic roller assembly can smoothly pass over the arc protrusion 4.

In the above embodiment provided by the present invention, the elastic roller assembly is connected to the main shaft 2 as shown in fig. 1 and 2, the main shaft 2 is provided with a fixing hole 5 extending along the radial direction of the main shaft 2, and the elastic roller assembly is disposed in the fixing hole 5. The elastic roller component comprises a retainer ring 6, a fixed seat 7, an elastic component 8, a roller mounting seat 9 and a roller 10. Retaining ring 6 sets up in the bottom of fixed orifices 5 and can end relative fixed orifices 5, and fixing base 7 sets up adjacent with retaining ring 6, and elastic component 8 then sets up between fixing base 7 and gyro wheel mount pad 9, and gyro wheel mount pad 9 salient is offered the mounting groove in fixed orifices 5 parts, and gyro wheel 10 installs in gyro wheel mount pad 9 through the cooperation of its shaft and mounting groove.

The rolling surface of the roller 10 is tangent to the inner wall of the annular cavity 3, when the impact frame 1 rotates, the roller 10 is attached to the inner wall of the annular cavity 3 to rotate, when the arc protrusion 4 impacts the roller 10, the elastic part 8 is pressed to retract, the roller 10 and the roller mounting seat 9 retract into the fixing hole 5, and the roller 10 is impacted by the arc protrusion 4 while rotating along the arc protrusion 4 to drive the main shaft 2 to rotate. Roller mount pad 9 specifically is cylindric casing, and the one end of elastic component 8 is contradicted in fixing base 7, the other end card and is ended at cylindric casing's inner wall, and cylindric casing is equipped with the mounting groove of the shaft of rotating connection gyro wheel 10 towards the one end of annular cavity 3 inner wall.

In the above embodiment, the fixing hole 5 may be a through hole, the fixing seat 7 is fixed by the retaining ring 6, and the elastic member 8 is preferably a spring embedded in the roller mounting seat 9.

As a preferred embodiment, the fixing hole 5 may also be a blind hole, that is, the fixing hole 5 does not penetrate through the radial direction of the main shaft 2, and at this time, the spring directly abuts against the bottom of the fixing hole 5, without providing the retainer ring 6 and the fixing seat 7.

As a preferred embodiment, fixed orifices 5 adopts the through-hole, and elastic roller assembly fixes in the through-hole, and elastic roller assembly protrusion all sets up gyro wheel 10 in the both ends of fixed orifices 5, and the middle part of elastic component 8 is blocked in fixed orifices 5, and the both ends of elastic component 8 all set up gyro wheel mount pad 9 and gyro wheel 10, so, to a set of elastic roller assembly, strike frame 1 and per rotation a week, main shaft 2 receives the impact of single point. For a plurality of groups of roller assemblies such as two groups of roller assemblies which are vertically arranged at intervals, the main shaft 2 can be impacted by two symmetrical impact points at the same time when the impact frame 1 rotates for one circle, so that the stability of the impact rotation of the main shaft 2 is obviously improved.

In order to optimize the above embodiment, the main shaft 2 is sealed at the position where the main shaft penetrates out of the annular cavity 3, that is, the first end of the main shaft 2 is hermetically connected with the annular cavity 3, and lubricating oil is injected into the annular cavity 3, so that impact wear is further reduced. In order to ensure the rotary sealing connection between the main shaft 2 and the annular cavity 3 of the impact frame 1, an annular impact cover 14 is arranged at the position where the main shaft 2 penetrates out of the annular cavity 3, and sealing rings 15 are arranged between the inner wall of the impact cover 14 and the main shaft 2 and between the outer wall of the impact cover 14 and the annular cavity 3.

Specifically, the inner periphery of the impact cover 14 is in a multi-step boss shape, and the outer wall of the main shaft 2 is provided with a boss structure matched with the multi-step bosses of the impact cover 14, so that rotary sealing is formed, and the sealing performance of the rotary sealing and the rotary sealing is further improved through a sealing ring 15; the impact cover 14 can be screwed with the annular cavity 3 through the outer wall, annular grooves matched with each other are arranged between the outer wall of the impact cover 14 and the inner wall of the annular cavity 3, and the sealing ring 15 is arranged in the annular grooves.

One end of the main shaft 2, which is far away from the impact frame 1, is provided with a mounting hole 16 extending along the circumferential direction of the main shaft, and the axis of the mounting hole 16 is superposed with the axis of the main shaft 2 and used for mounting a screwdriver bit. The mounting hole 16 of the main shaft 2 can be set to be a hexagonal hole according to needs, in addition, one end of the main shaft 2 far away from the impact frame can be set to be a square head, at the moment, the screwdriver adopts a sleeve shape matched with the square head, and the hexagonal mounting hole 16 or the square head is arranged, so that the screwdriver can be conveniently matched with a standard screwdriver bit without specifications. This is only for illustrating the connection of the spindle 2 to the screwdriver bit and should not be interpreted as a limitation of the spindle 2.

In a further preferred embodiment provided by the present invention, the annular cavity 3 is further provided with an oil filling hole 11, the oil filling hole 11 is specifically provided at the closed end of the cylindrical shell of the impact frame 1, the oil filling hole 11 is sealed by a sealing member, and the sealing member specifically adopts a sealing gasket 12 and a sealing screw 13. When needed, the sealing screw 13 can be unscrewed, lubricating oil is supplemented into the annular cavity 3 in time, abrasion between the main shaft 2 and the impact frame 1 caused by insufficient lubricating oil is avoided, and therefore the service life of the impact mechanism is prolonged.

The impact frame 1 mainly undergoes the following three states when the driving spindle 2 rotates: initial state-impact state-critical state, reference may be made in particular to fig. 3 to 8. In an initial state, the elasticity of the elastic part 8 acts on the roller 10, and the roller 10 props against the inner wall of the annular cavity 3; the pneumatic motor 01 drives the impact frame 1 to rotate, the arc-shaped protrusion 4 gradually adheres to the roller 10 in a striking state, and torque is transmitted to the spindle 2 through the roller 10 and the roller mounting seat 9; in a critical state, the roller 10 moves to the highest point of the arc protrusion 4, and after the critical state is passed, the roller 10 is abutted against the inner wall of the annular cavity 3 under the elastic force of the elastic member 8, returns to an initial state, and enters a cycle of a downward moving impact process.

The invention also provides a pneumatic screwdriver, as shown in fig. 9, which comprises the impact mechanism described in the above specific embodiment, an air inlet system, a pneumatic motor 01 and a screwdriver bit connected with a main shaft 2 of the impact mechanism; the air inlet system drives the pneumatic motor 01 to rotate through air inlet, the pneumatic motor 01 drives the impact frame 1 to rotate, the impact frame 1 drives the main shaft 2 to rotate through impact transmission torque, the main shaft 2 is far away from the tail end of the impact frame 1 and is provided with a mounting hole 16 for fixing a screwdriver bit, and the screwdriver bit is mounted in the mounting hole 16. Other parts of the pneumatic screwdriver, the air inlet system and the arrangement of the pneumatic motor 01 can be referred to the prior art, and the description is not expanded.

It is noted that, in this specification, relational terms such as first and second, and the like are used solely to distinguish one entity from another entity without necessarily requiring or implying any actual such relationship or order between such entities.

The pneumatic screwdriver and the impact mechanism provided by the invention are described in detail above. The principles and embodiments of the present invention are explained herein using specific examples, which are presented only to assist in understanding the method and its core concepts. It should be noted that, for those skilled in the art, it is possible to make various improvements and modifications to the present invention without departing from the principle of the present invention, and those improvements and modifications also fall within the scope of the claims of the present invention.

Claims

1. An impact mechanism is characterized by comprising a main shaft (2) and an impact frame (1) which is used for being connected with and rotating along with a pneumatic motor (01), wherein the impact frame (1) is provided with an annular cavity (3), and the first end of the main shaft (2) is inserted into the annular cavity (3);

the inner wall of the annular cavity (3) is provided with an arc bulge (4), and the first end of the main shaft (2) is provided with an elastic roller assembly fixedly connected along the radial direction of the main shaft (2);

the elastic roller assembly is attached to the inner wall of the annular cavity (3), and when the impact frame (1) rotates to drive the arc protrusion (4) to impact the elastic roller assembly, the elastic roller assembly retracts along the radial direction of the main shaft (2) and passes over the arc protrusion (4) to drive the main shaft (2) to rotate;

a first end of the main shaft (2) is provided with a fixing hole (5) which is arranged along the radial direction of the main shaft, and the elastic roller assembly is arranged in the fixing hole (5);

the elastic roller assemblies are arranged into a plurality of groups, the elastic roller assemblies are spaced along the axial direction of the main shaft (2) and are uniformly arranged along the circumferential direction of the main shaft (2), and the arc bulges (4) are arranged in one-to-one correspondence with the elastic roller assemblies;

elastic roller subassembly includes retaining ring (6), fixing base (7), elastic component (8), gyro wheel mount pad (9) and gyro wheel (10), retaining ring (6) stop in fixed orifices (5), fixing base (7) laminating retaining ring (6) set up elastic component (8) are located fixing base (7) with between gyro wheel mount pad (9), gyro wheel (10) are in the elastic force effect of elastic component (8) down contradict in the inner wall of annular cavity (3).

2. The impact mechanism according to claim 1, characterized in that the first end of the main shaft (2) is sealingly connected to the annular cavity (3), and that lubricating oil is injected into the annular cavity (3).

3. The impact mechanism according to claim 1, characterized in that said annular chamber (3) is provided with an oil hole (11), said oil hole (11) being provided with a seal.

4. The impact mechanism according to claim 2, wherein an annular impact cover (14) is arranged at the position where the main shaft (2) penetrates out of the annular cavity (3), and sealing rings (15) are arranged between the inner wall of the impact cover (14) and the main shaft (2) and between the outer wall of the impact cover (14) and the annular cavity (3).

5. The impact mechanism according to claim 1, wherein the roller mounting seat (9) is a cylindrical housing, one end of the elastic member (8) is clamped to an inner wall of the cylindrical housing, and an end of the cylindrical housing facing the inner wall of the annular cavity (3) is provided with a mounting groove for fixing a wheel axle of the roller (10).

6. The impact mechanism according to claim 1, characterized in that said rounded protrusion (4) is a flat arched protrusion.

7. A pneumatic screwdriver is characterized by comprising the impact mechanism of any one of claims 1 to 6, and further comprising an air inlet system, a pneumatic motor (01) and a screwdriver head connected to one end, far away from the annular cavity (3), of the main shaft (2), wherein one end, far away from the annular cavity (3), of the main shaft (2) is provided with a mounting hole (16) for fixing the screwdriver head.