JPH05261677A - Pneumatic driving type shock mechanism - Google Patents

Abstract

PURPOSE:To prevent the housing of a tool from shifting in the direction of separating from the surface of a material to be driven in, with the reaction at the time of driving a shock piston, and produce the action force for shifting the housing of a nail driving machine toward the material to be driven in, synchronously with the driving of the nail driving machine. CONSTITUTION:A reaction absorbing member 7, which fronts on the chamber above the shock piston 2 of a shock cylinder 1 and is equipped with a downward effective face larger than the effective area of the upward face of the shock piston 2 and is opposed to the topside of the shock piston 2, is arranged slidably in the axial direction of the work of the shock piston 2. When driving the shock piston 2 with compressed air pressure, the housing takes a shifting action in the driving direction of the shock piston 2 with one part of the reaction arising when driving the reaction absorbing member 7 by driving the reaction absorbing member 7 equipped with an effective face larger than the sectional area of the shock piston 2 in the opposite direction of the shock piston.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a nailing machine in which an impact piston slidably accommodated in an impact cylinder is impact-driven by compressed air pressure to drive a nail by a driver connected to the impact piston. The present invention relates to a pneumatic drive type impact mechanism used for the above.

[0002]

2. Description of the Related Art A pneumatic driven nail driving machine is known in which a piston accommodated in a cylinder is shocked by compressed air pressure and a fastener such as a nail is driven into a driven material by a driver connected to the piston. Has been. As shown in FIG. 7A, the impact mechanism of this conventional nail driver has a driver 8 in an impact cylinder 80 fixedly arranged in a tool housing.
An impact piston 81 in which the two are integrally connected is slidably accommodated, and by introducing compressed air into the cylinder above the impact piston 81, the impact piston 81 is driven downward in the figure and the driver 82 Is designed to drive nails into the material to be driven.

The compressed air introduced into the cylinder 80 drives the impact piston 81 downward in the figure, and at the same time acts on the inner wall surface of the upper end of the impact cylinder 80 which is practically closed to move the impact cylinder 80 upward. Generates a reaction force to move. At the same time as the impact piston 81 is driven by the impact, this reaction force moves the position of the shock absorbing bumper 83 installed at the lower end of the impact cylinder 80 together with the tool housing upward, so that the impact piston is located above the original stop position. It will be stopped by 83 and the driving force will be insufficient.

In order to minimize the lifting of the tool due to the above reaction, the operator needs to sufficiently press the tool against the material to be driven and drive it, and when the tool is installed on a vertical wall surface or ceiling surface or on an unstable scaffold. It takes too much effort to work in. Further, due to the variation in the pressing force, the floating amount of the tool fluctuates, resulting in variation in the driving force.

A reactionless nailing machine which can obtain a stable driving force by eliminating the recoil of the tool in the conventional impact mechanism has already been proposed as shown in, for example, Japanese Utility Model Laid-Open No. 3-29272. As shown in the outline of FIG. 7B, the impact mechanism of this nailing machine has an impact cylinder 90 accommodating an impact piston 91 slidably arranged slidably with respect to a housing 94 for piston stop. The impact bumper 93 is disposed in the housing, and the compressed air introduced into the impact cylinder 90 drives the impact piston 91 downward, and at the same time, the reaction force of the impact piston 91 generated in the impact cylinder 90. The impact cylinder 90 is moved upward with respect to the housing 93 by the
The mechanism prevents the reaction force to 0 from being transmitted to the housing 94.

As a result, the position of the bumper 93 for stopping the piston does not fluctuate with respect to the material to be driven, so that the stopping position of the impact piston 91 is always constant and a constant driving force can be maintained. However, the movable impact cylinder 9
Since the biasing force by the compression spring 95 and compressed air for returning 0 to the initial bottom dead center position is formed between the movable impact cylinder 90 and the housing 94, the movable impact cylinder 9
The movement due to the reaction of 0 is the compression spring 95 which is the above-mentioned urging means.
Is propagated to the housing 94 via the above, and does not become a complete recoilless motion. In the impact mechanism, the movable impact cylinder 90 is urged downward by utilizing the air pressure, and the urged compressed air is discharged to the atmosphere in synchronization with the drive of the impact piston 91, thereby causing no recoil. Although there has been proposed an improved technique for making the state, there is a problem that the mechanism for it becomes complicated and the cost of the tool becomes high.

On the other hand, as a working environment of an impact tool such as a nail driving machine, for example, in a nail driving machine, when the upper material is fixed to a base material, a gap may occur between the two materials due to deformation of the upper material, It is necessary to press the nailing machine against the surface of the upper material to bring the upper material and the base material into close contact with each other. Even with the above-mentioned conventional recoilless nailing machine, it is necessary to press the nailing machine to perform construction, and work on an unstable scaffolding requires excessive labor and is also dangerous. It is a thing.

[0008]

It is possible to reliably prevent the housing of the tool from moving in the direction away from the surface of the material to be driven due to the reaction when the impact piston is driven.
(EN) Provided is an impact mechanism that can be used in a pneumatically driven nail driving machine or the like that can generate an acting force that moves a housing of the nail driving machine toward a driven material in synchronization with the driving of the nail driving machine. This is an issue.

[0009]

In order to solve the above problems, the present invention comprises an impact cylinder fixedly arranged in a housing of a tool, and an impact piston slidably accommodated in the impact cylinder. In an impact mechanism that drives the impact piston by introducing compressed air to the upper surface of the impact piston in the impact cylinder, the impact mechanism faces the upper chamber of the impact piston of the impact cylinder and has an upward effective area of the impact piston. A reaction absorbing member having a larger and downward effective surface facing the upper surface of the impact piston,
It is characterized in that it is provided so as to be slidable in the operating axis direction of the impact piston. An impact cylinder fixedly disposed in the housing of the tool and slidably accommodating the impact piston is provided, and a sub-cylinder having an inner diameter larger than the inner diameter of the impact cylinder is linearly connected to the upper end of the impact cylinder. And a weight piston having an outer diameter larger than the outer diameter of the impact piston is slidably accommodated in the sub-cylinder, and an opening for introducing compressed air is introduced into the cylinder between the pistons. It is characterized in that it is formed on the cylinder wall. Furthermore,
An impact cylinder, which accommodates the impact piston slidably and has an open upper end, is fixedly provided in the housing, and a movable sleeve having an inner diameter larger than the inner diameter of the impact cylinder is urged in the axial direction on the outer peripheral side of the impact cylinder. Arranged freely, the upper end of the movable sleeve is closed to form a downward compressed air working surface larger than the sectional area of the impact piston on the inner surface of the sleeve, and compressed air is introduced into the upper surface of the impact piston and the movable sleeve in the impact cylinder. The opening is formed in the side wall of the movable sleeve.

[0010]

According to the present invention, when the impact piston is driven by the compressed air pressure, the reaction absorbing member having an effective surface larger than the sectional area of the impact piston is driven by the same compressed air pressure in the opposite direction to the impact piston. , All the reaction force generated in relation to the drive of the impact piston can be absorbed by a part of the reaction force generated when the reaction absorbing member is driven in the opposite direction, and the upper reaction force generated by the drive of the impact piston is completely eliminated. You can prevent it from happening. Further, the residual reaction force generated by driving the reaction absorbing member is applied to the housing via the cylinder, so that the housing can be moved downward in synchronization with the driving of the impact piston.

[0011]

When the above-mentioned impact mechanism is used in a nailing machine, no reaction force is generated to lift the nailing machine body upward during nailing, so that the impact piston stops at a fixed stop position. The condition stabilizes. Also, if the diameter difference between the impact piston and the reaction absorbing member is set to be large so that a downward acting force is generated in the housing, it is not necessary to press the nailing machine strongly against the material to be nailed, and the nailing work becomes unnecessary. Can be done easily.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows an outline of an impact mechanism of a nailing machine according to the present invention. An impact cylinder 1 in which an impact piston 2 integrally connected with a driver 3 protruding toward a lower surface is fixedly arranged in a housing. It is slidably housed inside. A cylindrical nose member 4 for slidably guiding the driver 3 is formed below the housing.
A bumper 5 that buffers the impact force of the impact piston 2 and stops it is disposed on the upper end surface of the. A sub-cylinder 6 having an inner diameter larger than the inner diameter of the impact cylinder 1 is integrally formed at the upper end of the impact cylinder 1.
A weight piston 7 which is a reaction absorbing member having an outer diameter larger than that of the impact piston 2 is slidably arranged therein.
A compression spring 8 is interposed between the upper end of the weight piston 7 and the inner surface of the upper wall of the housing, and the weight piston 7 is constantly urged to the bottom dead center position by the compression spring 8. Is normally placed at the top dead center position by a piston return device (not shown).

An air supply port 9 for introducing compressed air into the cylinder between the standby position of the impact piston 2 and the bottom dead center position of the weight piston 7 is formed in the wall between the cylinders 1 and 6. Compressed air is supplied between the pistons 2 and 7 by a main valve mechanism (not shown). On the other hand, the compressed air introduced into the cylinder drives the impact piston 2 in the downward direction to drive the nails previously arranged in the nose member 4 from the inside of the nose member 4 by the driver 3 coupled to the lower surface of the impact piston 2 to a predetermined object. Drive into the driving material. Further, the compressed air, on the other hand, drives the weight piston 7 in the sub-cylinder 6 upward.

The impact piston 2 receives a downward driving force F1 corresponding to the effective diameter of the piston in the impact cylinder 1 by compressed air pressure. Further, the compressed air is a shoulder portion 1'in the cylinder formed in the diameter difference portion between the impact cylinder 1 and the sub cylinder 6.
A downward acting force F2 is generated to drive the impact cylinder downward. Further, the compressed air drives the weight piston 7 in the sub-cylinder 6 upward with the driving force F3 corresponding to the effective diameter. Here, since the total effective area of the impact piston 2 and the shoulder portion 1'is equal to the effective area of the weight piston 7, the magnitude of the force acting on each member is the sum of F1 and F2 equal to F3. The reaction force when each member is driven has the same magnitude as the driving force F1, F2, F3 of each member, and the direction is generated in the opposite direction. However, the upward reaction force of F1 and F2 is the downward force of F3. There is no upward reaction force that acts on the impact cylinder 1 and the housing and is canceled by the reaction force of 1. On the other hand, the driving force F2 for driving the impact cylinder 1 downward by the compressed air acting on the shoulder portion 1'of the impact cylinder 1.
As a result, the housing is driven downward via the impact cylinder 1.

Here, a force for moving the housing upward as the weight piston 7 is driven upward acts via the compression spring 8 which generates a biasing force for moving the weight piston 7 toward the bottom dead center. However, the impact generated by the compressed air acting on the shoulder portion 1'formed by the difference in diameter between the two cylinders 1 and 6 described above, and the force for driving the cylinder 1 downward and the upward movement via the compression spring 8 described above. It is possible to completely eliminate the recoil by canceling out the operating force.
Further, by setting the above-mentioned diameter difference large and increasing the force for moving the impact cylinder downward, it is possible to generate the action of pressing the housing against the driven material in synchronization with the driving of the nail.

Next, an embodiment of a nailing machine adopting the shock absorbing mechanism of the present invention will be described with reference to FIGS. In FIG. 2, an impact cylinder 11 is fixedly arranged, which forms an outer shell of a nailing machine and also forms a main chamber 13 for storing compressed air in a grip portion 12. Inside the impact cylinder 15, the impact cylinder 11 faces downward. An impact piston 14 having a driver 16 projectingly coupled therein is slidably accommodated.
A tubular nose member 17 for slidably guiding a driver 16 coupled to the impact piston 14 is fixed to a lower portion of the housing 11, and a part of the nose member 17 is inserted into the nose member 17. Opening 18 for feeding nails
And a nail supply mechanism 1 for feeding the mutually connected nails to the nose member 17 sequentially from a magazine (not shown).
9 are arranged. On the bottom surface of the housing 11 supporting the lower end of the impact cylinder 15, the impact piston 1 is attached.
A bumper 20 is arranged to buffer the impact force of No. 4 and stop.

A sub-cylinder 21 having an inner diameter larger than the inner diameter of the impact cylinder 15 is coaxially and integrally formed at the upper end of the impact cylinder 15, and a weight piston 22 is slidably disposed in the sub-cylinder 21. ing. The weight piston 22 is constantly urged to the bottom dead center position by a compression spring 24 interposed between the weight piston 22 and a cylinder cap 23 that closes the upper portion of the housing 11. A shoulder portion 25 is formed at a joint portion between the front and rear cylinders 15 and 21 due to a difference in diameter between the front and rear cylinders 15, 21.
Piston stop 2 to stop the vehicle at the top dead center position
6 are arranged. On the lower surface side of the piston stop 26, there is formed a piston holding portion 26 'which engages with a protrusion formed on the upper surface of the impact piston 14 and holds the impact piston 14 at the top dead center position.

An air supply port 27 for introducing compressed air into the cylinder or discharging compressed air inside the cylinder to the outside of the cylinder is formed in the cylinder wall between the impact cylinder 15 and the sub cylinder 21. The air supply port 27 is selectively connected to the main chamber 13 and the exhaust port 29 by an annular main valve 28 arranged in an annular space formed between the outer peripheral surface of the cylinder 21 and the inner wall surface of the cylinder cap 23. To be done. The main valve 28 is operated and controlled by the compressed air pressure in the control chamber 30 facing the upper end surface of the valve, and the control chamber 30 is manually operated by the trigger lever 3
1 and a trigger valve 33 which is operated by a safety device 32 or the like arranged at the tip of the nose member 17 so as to project.

The weight piston 22 is a driver 16
The impact piston 14 is formed of a material such as iron so as to have a sufficiently large weight with respect to the impact piston 14, and the impact piston 14 contacts the bumper 20 and is stopped on the inner wall surface of the cylinder cap 23 within a time period in which the piston is stopped. Consider not to move too much stroke so that there is no collision. Further, an elastic member 35 is arranged on the upper surface of the weight piston 22 for buffering the impact and reducing the noise when it collides with the inner wall surface of the cylinder cap 23.

Next, the operation of the nailing machine according to the above embodiment will be described. In the normal state, as shown in FIG. 2, the impact piston 14 is held at the top dead center position in the impact cylinder 15 by the piston stop 26, and the weight piston 22 is actuated by the compression spring 24 so that the upper surface of the piston stop 26. It is located at the bottom dead center position where it abuts against. In the cylinder between the pistons 14 and 22, the main valve 28 is located at the bottom dead center position by the action of the compressed air supplied into the control chamber 30 via the trigger valve 33. It is connected to the atmospheric pressure.

When the trigger valve 33 is operated by operating the safety device 32 and manually operating the trigger lever 31, the compressed air in the control chamber 30 of the main valve 28 passes from the trigger valve 28 to the atmosphere via the air passage 34. It is released, which causes the main valve 28 to move upwards due to the compressed air pressure in the main chamber 13 acting on its lower end. By moving the main valve 28 upward, the air supply port 27 is blocked from the exhaust port 29, and at the same time, it is connected to the main chamber 13 so that the compressed air in the main chamber 13 is introduced into the cylinder. The impact piston 14 and the weight piston 22 are impact-driven in opposite directions by the action of the compressed air.

When the impact piston 14 is driven downward in the impact cylinder 15, a driver 16 integral with the impact piston 14 drives a nail previously supplied into the nose member 17 from the nose member 17 to cause the nose member 17 to move. The material to be driven placed at the lower end is driven. Meanwhile weight piston 2
2 is driven upward against the compression spring 24. The reaction force generated when the impact piston 14 is driven is the impact piston 1
When the weight piston 22 having a diameter larger than 4 is moved upward, it is completely absorbed and no reaction force for moving the housing 11 upward is generated. A part of the reaction force caused by driving the weight piston 22 having a larger diameter than the impact piston 14 upward is offset by the reaction force of the impact piston 14,
A reaction force generated by a difference in diameter with the impact piston 14 is generated downward in a shoulder portion 25 formed in a difference in diameter between the impact cylinder 15 and the sub-cylinder 21, and this reaction force is generated.
It is transmitted to the housing 11 via 5 and moves the housing 11 downward.

With the upward movement of the weight piston 22, an upward force acts on the cylinder cap 23, that is, the housing 11 via the compression spring 24 interposed between the weight piston 22 and the cylinder cap 23. If the diameter difference is set so that the magnitude of the force through the compression spring 24 and the magnitude of the downward driving force generated by the shoulder portion 25 of the diameter difference portion become equal, the housing 11 is actually repulsed. There is no upward movement at all.
Further, the diameter difference is set to a larger value so that the downward reaction force generated by the diameter difference becomes larger, so that the housing 11
It is also possible to positively generate a downward actuating force.

When the operation of the trigger lever 31 and the safety device 32 is released after the nail driving is completed and the trigger lever 31 is returned to the initial state, compressed air is supplied again into the control chamber 30 of the main valve 28 and the main valve 28 is released. 28 returns to the lower position. Both cylinders 1 by the return of the main valve 28
The inside of 5, 21 is connected to the atmosphere through the exhaust port 29, and the compressed air in the cylinder is discharged. The impact piston 14 has a return chamber 36 formed around the impact cylinder.
The locking portion 2 formed on the piston stop 26 by receiving the compressed air stored in the lower surface thereof, and ascending and returning to the top dead center
It is locked by 6'and stops. Meanwhile, the weight piston 22
Is returned to the bottom dead center where it comes into contact with the upper surface of the piston stop 26 by the action of the compression spring 24.

Next, another embodiment of the present invention will be described with reference to FIGS.
Will be explained. In this embodiment, an impact cylinder 50 having an open upper end is fixedly arranged in a housing 51, and an impact piston 53 having a driver 52 integrally connected to the lower surface is slidable in the impact cylinder 50. It is arranged. A movable sleeve 54 is arranged on the outer peripheral surface of the impact cylinder 50.
Is guided by the inner peripheral surface of the guide sleeve 55 and the outer peripheral surface of the impact cylinder 50, which are fixed to the housing 51 on the outer peripheral side thereof, and is slidable in the axial direction of the impact cylinder 50. ..

The inner diameter of the movable sleeve 54 is larger than that of the impact cylinder 50 by the thickness of the wall of the impact cylinder 50, and the upper end is closed by the sleeve cap 56 so that the inside of the movable sleeve 54 and the impact cylinder 50 are closed. The space above the impact piston 53 forms a common space. On the lower surface of the sleeve cap 56, there is provided a holding portion 57 ′ that buffers the shocking collision with the impact piston 53 and locks the protrusion formed on the upper surface of the impact piston 53 to hold the impact piston 53 at the top dead center position. The formed piston stop 57 is fixedly provided. Further, on the upper surface of the sleeve cap 56, a cushioning member 59 for cushioning the collision between the movable sleeve 54 and the cylinder cap 58 is arranged. A compression spring 60 is interposed between the sleeve cap 56 and the inner wall surface of the cylinder cap 58 to constantly urge the movable sleeve 54 toward the bottom dead center. A cushion 62 for cushioning a shocking collision between the movable sleeve 50 and the impact cylinder 50S is arranged on a step portion 61 formed on the outer peripheral portion of the impact cylinder 50 that supports the lower end of the movable sleeve 54 at the bottom dead center position. ..

An air supply port 63 is formed in the upper portion of the cylindrical wall of the movable sleeve 54, and a through hole 64 is formed in the cylindrical wall of the guide sleeve 55.
5, the inside of the common cylinder is selectively connected to the exhaust port 66 and the main chamber 67 via a main valve 65 arranged on the outer peripheral side of 5. Main valve 6
7 is disposed in an annular space formed between the outer peripheral surface of the guide sleeve 55 and the inner wall surface of the cylinder cap 58, and passes through a passage 69 into a control chamber 68 whose upper end surface faces. Operation is controlled by the air pressure supplied or discharged.

In the normal state, the movable sleeve 54 is arranged at the bottom dead center position by the compression spring 60, and the impact piston 53 is held by the holding portion 57 'of the piston stop 57 formed on the movable sleeve 54 so as to reach the top dead center position. Is held. When the main valve 65 is operated upward by operating a trigger valve (not shown), compressed air is introduced into the common cylinder. Impact piston 53 due to the action of compressed air
And the movable sleeve 54 are driven in opposite directions, and the impact piston 53 drives the nail by the driver 52, and the movable sleeve 54 moves upward against the compression spring 60 by the action of compressed air on the surface larger than the impact piston 53. To do.

The upward reaction force when driving the impact piston 53 is offset by a part of the downward reaction force that occurs when the movable sleeve 54 is driven, and the residual reaction force generated by the movable sleeve 54 becomes the impact cylinder 50. The force is generated in the diameter difference portion of the movable sleeve 54 to generate a force for moving the impact cylinder 50 downward, and is a force for operating the housing downward. When the impact piston 53 is driven, the difference in inner diameter between the impact cylinder 50 and the movable sleeve 54 is set to be equal to or more than the pushing force transmitted to the housing 51 via the compression spring 60 when the movable sleeve 54 moves upward. Can be eliminated at all, or the housing 51 can be positively moved toward the driven material when the impact piston 53 is driven.

FIG. 6 is a graph showing experimental data obtained by measuring the acting force acting on the housing when the above-described embodiment of the present invention and the conventional nailing machine are actually shot as the displacement amount of the housing. In the graph, the horizontal axis indicates the passage of time, and the vertical axis indicates the amount of vertical displacement of the housing along with the direction. Figure 6
FIG. 7A is a measurement result by the conventional nailer shown in FIG. 7A. In the conventional nailer, immediately after the main valve is actuated and compressed air is introduced into the cylinder, the housing is removed. It is clear that when the impact piston reaches the bottom dead center (B) after it starts to be displaced upward, it is lifted by L1 from the surface of the material to be driven. FIG. 6B shows the displacement amount of the housing when the nail driving machine in which the diameter difference portion according to the embodiment of the present invention is set to be larger than the acting force through the compression spring, is the same as that of the conventional art. On the contrary, the state in which the housing is displaced downward from the time (A) when compressed air is introduced into the cylinder is shown.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing a basic principle of a reaction absorbing action of an impact mechanism of the present invention.

FIG. 2 is a vertical cross-sectional side view showing an embodiment of a nailing machine implementing the first impact mechanism of the present invention.

FIG. 3 is a vertical cross-sectional side view of essential parts showing an operating state of the nail driver in the embodiment of FIG.

FIG. 4 is a vertical cross-sectional side view of essential parts of an embodiment in which another form of impact mechanism of the present invention is adopted in a nailing machine.

5 is a vertical cross-sectional side view of essential parts showing an operating state of the impact mechanism of the nailing machine in the embodiment of FIG.

FIG. 6 is a graph showing the results of measuring the displacement of the housing when the impact mechanism of the nailer is driven, (a) showing the measurement result of the impact mechanism of a conventional nailer, and (b) showing the present invention. It shows the measurement results by the impact mechanism.

FIG. 7 is a schematic mechanical diagram showing a state where recoil is generated by a conventional impact mechanism.

[Explanation of symbols]

 1 Impact Cylinder 2 Impact Piston 3 Driver 4 Nose Member 5 Bumper 6 Sub Cylinder 7 Reaction Absorption Member 8 Compression Spring 11 Housing 15 Impact Cylinder 14 Impact Piston 16 Driver 20 Bumper 21 Sub Cylinder 22 Weight Piston (Impact Absorption Member) 50 Impact Cylinder 51 Housing 52 Driver 53 Impact piston 54 Movable sleeve (impact absorption member) 56 Sleeve cap

Claims (3)

[Claims] 1. A shock cylinder fixedly arranged in a housing of a tool, and a shock piston slidably accommodated in the shock cylinder, wherein compressed air is introduced into an upper surface of the shock piston in the shock cylinder. In the impact mechanism for driving the impact piston, the impact mechanism is provided with a downward effective surface that faces the upper chamber of the impact piston and is larger than the upward effective area of the impact piston and that faces the upper surface of the impact piston. Rebound absorbing member,
A compressed air actuated impact mechanism, which is disposed so as to be slidable in the direction of the operation axis of the impact piston. 2. A shock cylinder fixedly arranged in a housing of a tool and slidably accommodating a shock piston, and a sub-cylinder having an inner diameter larger than the inner diameter of the shock cylinder is linearly provided at an upper end of the shock cylinder. In order to introduce the compressed air into the cylinder between the pistons, the weight pistons having the outer diameter larger than the outer diameter of the impact piston are slidably accommodated and arranged in the sub-cylinder while being formed continuously. A compressed air actuated impact mechanism, characterized in that the air supply port is formed in the cylinder wall. 3. An impact cylinder, slidably accommodating an impact piston and having an open upper end, is fixedly provided in the housing, and a movable sleeve having an inner diameter larger than the inner diameter of the impact cylinder is provided on the outer peripheral side of the impact cylinder. Is arranged so as to be impulsive in the axial direction, and the upper end of the movable sleeve is closed to form a downward compressed air acting surface larger than the cross-sectional area of the impact piston on the inner surface of the sleeve. A compressed air actuated impact mechanism characterized in that an air supply port for introducing compressed air is formed in a side wall of a movable sleeve.