JP4663573B2 - Rotating hammer tool - Google Patents

Description

  The present invention relates to a rotary impact tool called, for example, an impact driver or an impact tool, and relates to a hand-held tool that can be firmly tightened while being intermittently impacted in the screw tightening direction (rotation direction). .

Rotating impact tools such as so-called impact drivers have a function of tightening screws firmly by giving intermittent impact in the screw tightening direction to the driver bit. A hammer is pivoted on a spindle that rotates using an electric motor as a drive source. Provided with a configuration in which the anvil is supported coaxially and independently at the tip of the spindle and a bit or socket for screw tightening is mounted on the tip of the spindle, while being able to move in the direction and relatively rotatable around a certain axis. ing. Two steel balls are usually sandwiched between the spindle and the hammer. Each steel ball is sandwiched between a spindle-side guide groove and a hammer-side guide groove that are inclined in the axial direction. For this reason, the hammer moves along the axial direction while rotating with respect to the spindle.
The hammer is spring-biased toward the spindle axial advance side. Further, the hammer and the anvil are provided with a striking portion and an engaging portion that engage with each other in the screwing direction.
When a large external torque (screw tightening resistance) is applied to the hammer via the anvil as the screw tightening progresses, the hammer moves backward along the spindle axis direction while rotating in the anti-screw tightening direction with respect to the spindle. When the hammer is retracted, the striking portion thereof is disengaged from the engaging portion of the anvil and the applied state of the external torque is released. Therefore, the hammer moves forward in the spindle axis direction while rotating in the screw tightening direction by the spring biasing force. Thus, the hammer hitting portion rotating in the screw tightening direction while moving forward is hit against the engaging portion of the anvil, whereby the hit in the screw tightening direction is applied to the anvil.
JP 2002-273666 A

In a tool equipped with such a rotary striking mechanism, the hammer retreats against the spring biasing force, and on the contrary, the operation of moving forward by the spring biasing force is repeated at a high speed, and vibration is generated. There is a problem that the operability and usability of the tool are impaired.
Therefore, an object of the present invention is to provide a rotary impact tool with less vibration than conventional ones.

For this reason, this invention was set as the rotary impact tool described in each claim of a claim.
According to the rotary impact tool of the first aspect, when the external torque such as the screw tightening resistance added to the anvil reaches a constant torque, the hammer moves backward against the spring biasing force while rotating with respect to the spindle. At this time, the balancer also moves (advances) to the opposite side of the hammer while rotating integrally with the hammer relative to the spindle.
When the hammer moves backward and the state of engagement with the anvil is released, the external torque applied state to the hammer is released, so that the hammer rotates while moving forward on the spindle by the spring biasing force, and the anvil is hit. At this time, the balancer also moves to the opposite side of the hammer while rotating integrally with the hammer with respect to the spindle.
In this way, when the balancer moves simultaneously with the hammer and in the opposite axial direction, the vibrations (inertial forces) in the opposite directions that accompany each movement cancel each other out and are absorbed. Can do well.
According to the rotary impact tool of claim 2, the steel ball interposed between the first cam groove and the groove on the hammer side restricts the axial movement and rotation of the hammer relative to the spindle, and the hammer Rotates about its axis while moving axially relative to the spindle. On the other hand, the steel ball interposed between the second cam groove and the groove on the balancer side restricts the movement and rotation of the balancer in the axial direction relative to the spindle, and the balancer moves in the axial direction relative to the spindle. While rotating around the axis with the hammer. Further, the first cam groove and the second cam groove are provided symmetrically with respect to the cross section of the spindle, and the inclination directions are reversed. For this reason, when the hammer and the balancer rotate together around the spindle axis, they move to the opposite sides along the spindle axis direction.
Thus, according to the rotary impact tool of claim 2, since the hammer and the balancer rotate at the same time and move in opposite directions, the hammer and the balancer are generated by moving in the spindle axis direction. Vibrations (inertial forces) cancel each other out and are absorbed, whereby the vibrations transmitted to the hand of the operator holding the rotary impact tool can be greatly reduced.
According to the rotary impact tool of the third aspect, the hammer and the balancer can be urged in opposite directions to each other in the axial direction with a simple configuration.

Next, an embodiment of the present invention will be described with reference to FIGS. FIG. 1 shows a rotary impact tool 1 according to this embodiment described below. In the present embodiment, a screw tightening machine called a so-called impact driver is illustrated as an example of the rotary impact tool.
The rotary impact tool 1 of the present example includes a tool body 2 and a handle portion 3 provided so as to protrude from the side of the tool body 2. A user of the rotary impact tool 1 grips the handle portion 3 and performs a screw tightening operation. A trigger-type switch lever 4 that is pulled by a user with a fingertip is provided at the base of the handle portion 3. When the switch lever 4 is pulled, the electric motor 10 built in the tool body 2 is activated. When the pulling operation of the switch lever 4 is stopped, the electric motor 10 is stopped.
The tool body 2 includes a cylindrical body case 11. The electric motor 10 is built in the rear part of the main body case 11. The output shaft of the electric motor 10 is connected to the spindle 13 via the planetary gear train 12. The spindle 13 is indirectly connected to the main body by a bearing 14 that rotatably supports the carrier 12 a of the planetary gear train 12 with respect to the main body case 11 and a bearing 15 that rotatably supports an anvil 20 to be described later with respect to the main body case 11. The case 11 is supported so as to be rotatable and not displaced in the axial direction. The spindle 13 is coaxially and integrally provided on the carrier 12a.

A hammer 30 and a balancer 40 are supported on the spindle 13. Each of the hammer 30 and the balancer 40 has a substantially cylindrical shape, and the spindle 13 is inserted through the inner periphery thereof. The hammer 30 and the balancer 40 are supported so as to be movable in the axial direction within a certain range with respect to the spindle 13 and rotatable about the axis. The hammer 30 and the balancer 40 have substantially the same weight.
Details of the support structure of the hammer 30 and the balancer 40 with respect to the spindle 13 are shown in FIGS. The hammer 30 is engaged with the spindle 13 through two steel balls 31 and 32 sandwiched between the hammer 13. The balancer 40 is engaged with the spindle 13 through two steel balls 41 and 42 that are also sandwiched between the balancer 40 and the spindle 13. The hammer 30 and the balancer 40 are engaged with the spindles 13 through the steel balls 31, 32, 41, and 42, respectively, so that the rotation and the movement operation in the axial direction with respect to the respective spindles 13 are restricted.
A total of four V-shaped guide grooves 33, 34, 43, 44 are formed on the peripheral surface of the spindle 13. FIG. 5 shows the spindle 13 and the four guide grooves 33, 34, 43, 44 in an unfolded state. 5, the lower side is the tool tip side on the right side in FIGS. 1 and 2, and the upper side is the left side in FIGS. 1 and 2, which is the tool rear side. In the following description, the two lower guide grooves 33 and 34 in FIG. 5 are referred to as first guide grooves 33 and 34, and the two upper guide grooves 43 and 44 in FIG. 5 are referred to as second guide grooves 43 and 44. .

In FIG. 5, two steel balls 31, 32 sandwiched between the hammer 30 are fitted in the lower two first guide grooves 33, 34. The two lower first guide grooves 33 and 34 are formed in a V-shape that is pointed toward the lower side (tool tip side). Both the first guide grooves 33 and 34 have inclined groove portions 33a, 33b, 34a, and 34b that are inclined at the same angle in opposite directions with respect to the axis J of the spindle 13, respectively. When tightening the screws, the steel balls 31, 32 roll along one of the V-shaped inclined grooves 33a, 34a. When loosening the screws, the steel balls 31, 32 roll along the other V-shaped inclined grooves 33b, 34b. Move. For this reason, the rotary impact tool 1 of the present example performs an impact operation (striking operation by the hammer 30 when the external resistance applied to the anvil reaches a certain value) both when the screw is tightened and when the screw is loosened. A reverse impact mechanism is provided.
On the other hand, in the inner peripheral hole of the hammer 30, two first engaging grooves 30a and 30b are formed corresponding to the first guide grooves 33 and 34, respectively. Both the first engagement grooves 30a and 30b are cut from the tip of the hammer 30 (the lower end in FIG. 5) at the same depth in the axial direction. Further, as shown in the drawing, the inner portions of the first engagement grooves 30a and 30b are formed in a V-shape opposite to the first guide grooves 33 and 34. In FIG. 5, a steel ball 31 is sandwiched between the first guide groove 33 on the right side and the first engagement groove 30a on the right side, and between the first guide groove 34 on the left side and the first engagement groove 30b on the left side. A steel ball 32 is sandwiched.

Next, two steel balls 41 and 42 sandwiched between the balancer 40 are fitted in the upper two second guide grooves 43 and 44 in FIG. 5. The two upper second guide grooves 43 and 44 are formed in a V-shape that is pointed toward the upper side (tool rear side) opposite to the first guide grooves 33 and 34. Both the second guide grooves 43 and 44 have inclined groove portions 43 a, 43 b, 44 a and 44 b which are inclined at the same angle with respect to the axis J of the spindle 13. In other words, the upper second guide grooves 43 and 44 are provided vertically symmetrically with respect to the lower first guide grooves 33 and 34 with respect to the cross section of the spindle 13 (surface perpendicular to the axis J). Yes.
Two second engagement grooves 40 a and 40 b are formed in the inner peripheral hole of the balancer 40 with respect to both the second guide grooves 43 and 44 of the spindle 13. Both the second engagement grooves 40a and 40b are formed by cutting at the same depth in the axial direction from the rear end (the upper end in FIG. 5) of the balancer 40. Further, the inner portions of the second engagement grooves 40a and 40b are formed in a V-shape opposite to the second guide grooves 43 and 44. That is, both the second engagement grooves 40a and 40b are provided vertically symmetrically with respect to the first engagement grooves 30a and 30b of the hammer 30 with respect to the cross section of the spindle 13 (cross section perpendicular to the axis J). . In FIG. 5, a steel ball 41 is sandwiched between the second guide groove 43 on the right side and the second engagement groove 40a on the right side, and between the second guide groove 44 on the left side and the second engagement groove 40b on the left side. A steel ball 42 is sandwiched between the two.
Since the second guide grooves 43 and 44 are formed in the same V shape as the first guide grooves 33 and 34, the balancer 40 and the hammer 30 are allowed to rotate integrally as will be described later. Accordingly, the steel balls 41 and 42 roll along the inclined groove portions 43a and 44a when the screws are tightened, and the steel balls 41 and 42 roll along the inclined groove portions 43b and 44b when the screws are loosened.

A compression spring 45 is interposed between the hammer 30 and the balancer 40 thus provided on the spindle 13. The compression spring 45 is attached to the spindle 13 with the spindle 13 inserted through the inner peripheral side thereof.
By this compression spring 45, the hammer 30 is urged toward the tool tip side (lower side in FIG. 5), and conversely, the balancer 40 is urged toward the tool rear side (upper side in FIG. 5). The hammer 30 and the balancer 40 are supported in a state of being repelled by being urged opposite to each other in the axis J direction with the compression spring 45 interposed therebetween.
In the following description, regarding the movement direction of the hammer 30 and the balancer 40 in the axis J direction, the movement in the direction in which the urging force of the compression spring 45 acts is defined as forward movement, and the movement in the opposite side is defined as backward movement. Accordingly, in FIGS. 1 and 2, the hammer 30 advances to the right side in the figure by the urging force of the compression spring 45, and retreats to the left side in the figure against the urging force of the compression spring 45. The balancer 40 advances to the left side in the figure by the urging force of the compression spring 45, and moves back to the right side in the figure against the urging force of the compression spring 45.
As shown in FIGS. 3 and 4, the hammer 30 and the balancer 40 are integrated with respect to the rotation around the axis J of the spindle 13. As shown in the drawing, on the outer peripheral surface of the hammer 30, four coupling piece portions 30 c to 30 c are provided at four equal positions in the circumferential direction. The four coupling piece portions 30c to 30c are provided parallel to each other along the axis J. The four coupling piece portions 30c to 30c are all provided with the same width from the front end to the rear end of the hammer 30.

On the other hand, the four coupling piece portions 40c to 40c are also provided on the outer peripheral surface of the balancer 40 at positions equally divided in the circumferential direction. The four coupling piece portions 40c to 40c are formed with the same width. The widths of the four coupling piece portions 40c to 40c are set such that the gaps between the coupling piece portions 30c and 30c on the hammer 30 side can be inserted without rattling.
The hammer 30 and the balancer 40 are coaxially arranged in parallel on the spindle 13, and the coupling piece 40 c on the balancer 40 side does not rattle in each gap between the coupling piece parts 30 c and 30 c on the hammer 30 side. It is inserted so as to be relatively movable in the axis J direction. Thereby, the coupling piece portions 30c to 30c on the hammer 30 side and the coupling piece portions 40c to 40c on the balancer 40 side are alternately meshed in the circumferential direction, and the hammer 30 and the balancer 40 allow relative movement in the axis J direction. On the other hand, the rotating operation is always coupled in an integrated state.
As described above, the hammer 30 is engaged with the spindle 13 via the steel balls 31 and 32, and the balancer 40 is engaged with the spindle 13 via the steel balls 41 and 42, respectively. And the rotation operation around the axis line J is restricted, and the hammer 30 and the balancer 40 move along the axis line J direction while rotating around the axis line J. From this, when the hammer 30 and the balancer 40 rotate integrally around the axis J, the inclination directions of the first guide grooves 33 and 34 and the second guide grooves 43 and 44 are opposite to each other. The balancer 40 moves in the direction opposite to the axis J direction. That is, when the hammer 30 moves backward against the compression spring 45, the balancer 40 moves backward by the same distance. When the hammer 30 moves forward, the balancer 40 moves forward by the same distance simultaneously.

Two striking portions 30d and 30d are provided on the front surface of the hammer 30 (the front surface in FIGS. 3 and 4). The two striking portions 30d, 30d are provided at a circumferentially bisected position around the axis J.
A support shaft portion 13 a is coaxially provided at the front portion of the spindle 13. The support shaft portion 13a is inserted in a support hole 20b provided on the rear surface of the anvil 20 (the left end surface in FIGS. 1 and 2) so as to be relatively rotatable. Thus, the anvil 20 is supported coaxially with the axis J of the spindle 13. The anvil 20 is rotatably supported with respect to the main body case 11 via the bearing 15. Two engaging portions 20 a and 20 a are provided at the rear portion of the anvil 20. The two engaging portions 20a and 20a are provided in a state of protruding sideways from a circumferentially bisected position around the axis J. The striking portions 30d and 30d of the hammer 30 are hit against both the engaging portions 20a and 20a. This will be described later.
The tip of the anvil 20 protrudes from the front part of the main body case 11. A chuck portion 21 for mounting a tip tool (not shown) such as a driver bit or a socket bit is provided at the tip portion of the anvil 20. Therefore, the anvil 20 including the chuck portion 21 corresponds to the output shaft of the rotary impact tool 1. Since the chuck portion 21 has a conventionally known configuration, the description thereof is omitted.

According to the rotary striking tool 1 of the present embodiment configured as described above, vibrations generated by the striking operation of the hammer 30 against the anvil 20 can be significantly reduced as compared with the conventional art.
The rotational output of the electric motor 10 is transmitted to the spindle 13 through the planetary gear train 12. As the spindle 13 rotates, the hammer 30 and the balancer 40 rotate together.
As shown in FIG. 1, a state where external torque such as screw tightening resistance is not applied to the anvil 20 (idle state of the rotary impact tool 1), and a state where the applied external torque has not reached a certain value ( In the initial screw tightening state, the hammer 30 is moved to the tool tip side (right side in FIG. 1) by the urging force of the compression spring 45, and both striking portions 30d and 30d thereof are engaged with both engaging portions 20a and 20a of the anvil 20. Engage in the rotational direction. For this reason, when the hammer 30 is rotated by the rotation of the spindle 13, the anvil 20 is rotated integrally therewith.
In the state shown in FIG. 1, the hammer 30 advances to the tool tip side by the biasing force of the compression spring 45, and conversely, the balancer 40 advances to the tool rear side by the biasing force of the compression spring 45. Further, in this state, as shown in FIG. 5, the steel balls 31 and 32 on the hammer 30 side are the front end portions (V-shaped tip portions) of the first guide grooves 33 and 34 of the spindle 13 and the first of the hammer 30. It is located in the back part (V-shaped tip part) of the engaging grooves 30a and 30b. The steel balls 41 and 42 on the balancer 40 side are front end portions (V-shaped tip portions) of the second guide grooves 43 and 44, and deep portions (V-shaped portions) of the second engagement grooves 40 a and 40 b of the balancer 40. It is located at the tip.
The screw tightening resistance applied to the anvil 20 as the screw tightening proceeds in the above state is based on the relative rotational resistance force (maximum value of screw tightening torque that can be transmitted) of the hammer 30 to the spindle 13 determined by the biasing force of the compression spring 45. If it becomes larger, the hammer 30 moves against the compression spring 45 in the direction of the axis J while rotating relative to the spindle 13 in the anti-screw tightening direction. When the hammer 30 is retracted, the engagement of the striking portions 30d and 30d of the hammer 30 with respect to the both engaging portions 20a and 20a of the anvil 20 gradually becomes shallower and finally disengages.

When the hammer 30 rotates relative to the spindle 13 in the anti-screw tightening direction, the balancer 40 rotates relative to the spindle 13 in the anti-screw tightening direction. When the balancer 40 rotates relative to the spindle 13 in the anti-screw tightening direction, the balancer 40 is opposite to the hammer 30 because the first guide grooves 33 and 34 and the second guide grooves 43 and 44 are inclined in opposite directions. Retreat to the tool tip side. The backward movement of the balancer 40 is also performed against the compression spring 45. Thus, when the screw tightening resistance applied to the spindle 20 becomes larger than the transmittable screw tightening torque determined by the biasing force of the compression spring 45, the hammer 30 and the balancer 40 rotate relative to the spindle 13, and Along with this, both 30 and 40 move in a direction approaching each other against the compression spring 45. For this reason, the inertial force in the axis J direction generated by the retraction of the hammer 30 is canceled by the movement of the balancer 40 in the opposite direction, thereby suppressing the occurrence of vibration.
When the hammer 30 moves backward with respect to the spindle 13 and the engagement portions 20a and 20a of the hitting portions 30d and 30d are disengaged from each other, screwing resistance is not added to the hammer 30. Advances along the axis J direction of the spindle 13 by the urging force of the compression spring 45. When the hammer 30 moves forward in the axis J direction, the first guide grooves 33 and 34 are inclined with respect to the axis J, whereby the hammer 30 rotates in the screw tightening direction. That is, the hammer 30 rotates in the screw tightening direction while moving forward with respect to the spindle 13 toward the anvil 20, so that the striking portions 30d and 30d are in the screw tightening direction with respect to the engaging portions 20a and 20a of the anvil 20, respectively. As a result, the impact in the screwing direction is impactively applied to the anvil 20 and thus the tip tool for screwing.

Thus, when the hammer 30 moves forward by the biasing force of the compression spring 45 and rotates in the screw tightening direction, the balancer 40 rotates integrally with the hammer 30 in the screw tightening direction. When the balancer 40 rotates in the screw tightening direction, the second guide grooves 43 and 44 are inclined with respect to the axis J in the direction opposite to the first guide grooves 33 and 34. Along with the urging force, it moves forward in the direction of the axis J. Thus, the balancer 40 rotates integrally with the hammer 30 in the screw tightening direction and moves (advances) to the opposite side of the hammer 30, thereby canceling the inertia force generated by the advance of the hammer 30 and suppressing the occurrence of vibration. Is done.
When the striking portions 30d and 30d of the hammer 30 are hit by the engaging portions 20a and 20a of the anvil 20 and the screw tightening resistance is increased again, the hammer 30 rotates in the anti-screw tightening direction with respect to the spindle 13 and the compression spring 45 The balancer 40 moves backward against the compression spring 45 while rotating integrally in the anti-screw tightening direction.
As described above, according to the rotary impact tool 1 of the present embodiment, the hammer 30 and the balancer 40 are arranged on the spindle 13, and both of these 30 and 40 are integrated with respect to the rotation about the axis J and in opposite directions to each other. Since the hammer 30 moves in the axis J direction, the balancer 40 moves in the direction opposite to the hammer 30 when the hammer 30 moves in the axis J direction, so that the hammer 30 moves in the axis J direction. Inertia generated by the movement is canceled by the movement of the balancer 40. From this, when the hammer 30 strikes the anvil 20 (impact operation), the vibration generated in the rotary impact tool 1 can be significantly suppressed as compared with the conventional case, and thus the operator's hand holding the handle portion 3 can be suppressed. The unpleasant vibration transmitted to can be reduced and the usability can be improved.

The embodiment described above can be implemented with various modifications. For example, although the configuration in which the hammer 30 and the balancer 40 are urged in the direction of the axis J by one compression spring 45 is illustrated, a configuration in which the hammer 30 and the balancer 40 are urged by individual compression springs may be employed. In this case, for example, a similar effect can be obtained by providing a flange portion on the spindle and interposing individual compression springs between the flange portion and the hammer and between the flange portion and the balancer.
Moreover, although the coupling pieces 30c and 40c are provided in the hammer 30 and the balancer 40, and the both 30 and 40 are integrated with each other by meshing them alternately, the spline engagement with the spindle is illustrated. Thus, the hammer and the balancer may be configured to be movable in the opposite direction in the axial direction while being integrated with respect to the rotation.
Further, the first guide grooves 33, 34 and the second guide grooves 43, 44 are provided symmetrically with respect to the cross section orthogonal to the axis J, and the inclined groove portions 33a, 33b, 34a, Although the configuration in which the inclination angles of the inclined groove portions 43a, 43b, 44a, 44b of the 34b and the second guide grooves 43, 44 with respect to the axis J are illustrated as an example, the weight difference between the hammer 30 and the balancer 40 is taken into consideration. Thus, it is possible to make the movement distances in the axis J direction different by changing the inclination angle of each inclined groove portion between the first guide groove and the second guide groove.
Further, if the impact operation is performed only at the time of screw tightening and the impact operation is not performed at the time of screw loosening, the first and second guide grooves 33, 34, 43, 44 are not V-shaped but inclined groove portions 33a, 34a, 43a. 44a only.
Further, the first engagement grooves 30a, 30b on the hammer 30 side and the second engagement grooves 40a, 40b on the balancer 40 side are not wide grooves with a V-shaped tip as illustrated, but steel balls 31, 32, 41, It is good also as a groove part of the width | variety sufficient to accommodate 42 so that rolling is possible.

It is a side view which shows the internal structure of the rotary impact tool which concerns on embodiment of this invention. This figure shows a directly connected state where a large screwing resistance is not added to the output shaft and a hammer is engaged with the anvil. It is a side view which shows the internal structure of the rotary impact tool which concerns on embodiment of this invention. This figure shows a state at the moment when a large screwing resistance is added to the output shaft and the engagement state of the hammer with the anvil is released. In this figure, in order to clearly show the release state, the distance of the hammer from the anvil is exaggerated. It is an exploded perspective view of a spindle, a hammer, and a balancer concerning an embodiment of the present invention. It is a perspective view which shows the assembly | attachment state of the hammer and balancer with respect to a spindle regarding embodiment of this invention. It is an expanded view of a spindle. In the figure, it is clearly shown that the first guide groove and the second guide groove are provided symmetrically with respect to a cross section perpendicular to the axis J of the spindle.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Rotary impact tool 2 ... Tool main body 3 ... Handle part 4 ... Switch lever 10 ... Electric motor 11 ... Main body case 12 ... Planetary gear train, 12a ... Carrier 13 ... Spindle, 13a ... Supporting shaft part 14, 15 ... Bearing 20 ... Anvil, 20a ... engaging portion, 20b ... support hole 21 ... chuck portion 30 ... hammer 30a, 30b ... first engaging groove, 30c ... coupling piece portion, 30d ... striking portion 31, 32 ... steel balls 33, 34 ... first 1 guide groove, 33a, 33b, 34a, 34b ... inclined groove part 40 ... balancer 40a, 40b ... second engagement groove, 40c ... coupling piece part 41, 42 ... steel ball 43, 44 ... second guide groove, 43a, 43b , 44a, 44b ... inclined groove 45 ... compression spring J ... axis of spindle

Claims (3)

A spindle rotated by a motor, a hammer supported on the spindle so as to be relatively movable in the axial direction and rotatable around the axis, and an engagement groove on the hammer side and a guide groove on the spindle side. A steel ball that regulates relative movement of the hammer relative to the spindle in the axial direction and the rotational direction, and an anvil that is supported so as to be relatively rotatable coaxially with the spindle and receives a blow in the rotational direction by the hammer, When the external torque applied to the anvil reaches a constant torque, the hammer moves backward on the spindle against the spring biasing force, and when the external torque is released by the backward movement, The hammer is a rotary impact tool that advances while rotating by the spring biasing force and strikes the anvil in the rotational direction,
A balancer is supported on the spindle so as to be relatively movable in the axial direction and relatively rotatable around the axis, and the balancer is integrated with the hammer for rotation around the axis, while the balancer is integrated with the hammer for axial movement. A rotary impact tool configured to move in the opposite direction. 2. The rotary impact tool according to claim 1, wherein the spindle-side guide groove is a first guide groove that guides a steel ball in a direction inclined with respect to an axis of the spindle , and A second guide groove whose inclination direction is symmetric with respect to the cross section of the spindle, and relative movement of the hammer in the axial direction and the rotational direction with respect to the spindle via a steel ball that has entered the first guide groove. A rotary impact tool configured to restrict and move the steel ball that has entered the second guide groove into the engagement groove on the balancer side and move the balancer simultaneously and axially opposite to the hammer. The rotary impact tool according to claim 1, wherein the hammer and the balancer are arranged in parallel in the axial direction of the spindle, and a compression spring is interposed between the hammer and the balancer so as to be biased in directions opposite to each other in the axial direction. .

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