Patent Description:
<CIT> discloses an impact tool having a vibration reducing mechanism. <CIT> discloses an impact tool having a vibration reducing mechanism, in which the structure of connecting a counter weight to a swinging member comprises a biasing spring and a protruding piece integrally formed with the counter weight and which is moved backwards by the swinging member and pushed forwards by the biasing spring. <CIT> discloses an impact tool having a vibration reducing mechanism. Japanese laid-open patent publication (<CIT> discloses a work tool which is provided with a dynamic vibration reducer having a weight disposed on a shaft and elastic members disposed on both sides of the weight.

In this work tool, the weight is forcibly driven by reciprocating movement of an end of one of the elastic members.

This work tool is effective to a certain extent for reducing vibration caused in the work tool. However, further improvement is desired in the mechanism for reducing vibration.

Accordingly, it is an object of the present teachings to provide a further rational technique relating to a work tool having a mechanism for reducing vibration.

In order to solve the above-described problem, a work tool according claim <NUM> or claim <NUM> is provided according to the present invention.

According to the invention, a work tool is provided which is configured to perform a specified operation on a workpiece by linearly driving a tool accessory. The work tool includes a driving motor, a rotary shaft member that is configured to be rotationally driven by the driving motor, a swinging member that is configured to be caused to swing by rotation of the rotary shaft member, a tool accessory driving mechanism that is configured to drive the tool accessory by swinging of the swinging member, a body that houses the driving motor, the rotary shaft member, the swinging member and the tool accessory driving mechanism, and a vibration reducing mechanism that is configured to reduce vibration caused in the body.

Examples of the work tool which is configured to linearly drive the tool accessory may include an electric hammer which is configured to perform a crushing operation on a workpiece such as concrete, and an electric reciprocating saw that is configured to perform a cutting operation on a workpiece such as wood. In this sense, the driving motor, the rotary shaft member, the swinging member and the tool accessory driving mechanism may have various structures according to the work tool to be realized.

For example, when the work tool is realized as an electric hammer, the tool accessory driving mechanism may be formed by a piston which is caused to reciprocate by swinging of the swinging member, and a striking element which is moved by reciprocating of the piston, collides with the tool accessory and drives the tool accessory. In this case, the swinging member and the tool accessory driving mechanism may be configured to rotate on a specified connecting position with respect to each other.

The rotary shaft member may include a rotary body which is provided with an outer peripheral surface having a specified inclination angle with respect to a rotation axis of the rotary shaft member. In this case, the swinging member may be formed by a swinging shaft which is disposed to be rotatable with respect to the rotary body. The swinging shaft may include an annular part that surrounds the rotary body, and a tool accessory driving mechanism connection part that is provided to the annular part. The tool accessory driving mechanism connection part may be formed by a shaft part extending from the annular part. With this structure, the annular part may move following inclination of the outer peripheral surface which changes as the rotary body rotates. Accordingly, the shaft part may be caused to swing in a direction along the rotation axis. The tool accessory driving mechanism may be then driven by a linear motion component of the swinging motion of the shaft part.

According to the invention, the vibration reducing mechanism includes a dynamic vibration reducer having an elastic member and a weight which is biased by the elastic member and which is reciprocatable, and a connecting member that connects the weight and the swinging member. The vibration reducing mechanism is configured to directly and forcibly reciprocate the weight via the connecting member by swinging of the swinging member.

In the vibration reducing mechanism, the dynamic vibration reducer can reduce vibration caused in the body by reciprocating movement of the weight which is caused by the vibration. This reciprocating weight is further reciprocated directly and forcibly by the motion of the connecting member which is caused by the swinging of the swinging member. As a result, the work tool according to the present teachings can effectively reduce vibration. Further, with the above-described structure, it can also be said that the vibration reducing mechanism according to the present teachings includes a mechanism that is configured to forcibly reciprocate the weight by the swinging of the swinging member.

The connecting member may be rotatably connected with respect to the swinging member. In this case, it may be preferable that a region of the swinging member in which a position for connecting the swinging member and the connecting member is provided is opposed to a region of the swinging member in which a position for connecting the swinging member and the tool accessory driving mechanism is provided. In other words, in the case of the swinging member having the above-described structure, the position for connecting the swinging member and the connecting member may be arranged in a region of the annular part which is opposed to the shaft part. This region may form a connecting member connection part in the swinging member. In this structure, for example, in a state in which the tool accessory driving mechanism connection part is turned to one side of the rotation axis by swinging of the swinging member, the connecting member connection part may be turned to the other side opposite to the one side of the rotation axis. Further, in a state in which the swinging member is caused to further swing and the tool accessory driving mechanism connection part is turned to the other side of the rotation axis, the connecting member connection part may be turned to the one side of the rotation axis. In other words, the tool accessory driving mechanism connection part and the connecting member connection part may be moved in opposite phase along with the swinging of the swinging member. Thus, the tool accessory driving mechanism and the weight may be driven in opposite phase along with the swinging of the swinging member, so that vibration can be reduced more effectively.

According to the inventive work tool of claim <NUM>, the weight and the connecting member are connected to be rotatable on a pivot axis with respect to each other.

In the work tool according to the present teachings, it may be preferred that the weight is linearly reciprocated. On the other hand, the swinging of the swinging member having the above-described structure may be rotation along the rotation axis. Therefore, the connecting member may need to have a motion converting function of converting the rotation of the swinging member into linear motion of the weight. In the work tool according to this aspect of the present teachings, with the structure in which the weight and the connecting member can rotate with respect to each other, the connecting member can smoothly linearly reciprocate the weight by the rotation of the swinging member.

As another aspect of the work tool according to the present teachings, the tool accessory driving mechanism may define a driving axis, and the weight may be configured to surround the driving axis around the driving axis. In this case, the term "around the driving axis" may not refer to a perfect circle around the driving axis or a circular arc on the perfect circle, but to a "periphery of the driving axis". Further, the manner in which the weight "surrounds the driving axis" may not mean that the weight surrounds all around the driving axis in the periphery of the driving axis. For example, it may be sufficient that the weight is arranged to extend in a specified direction perpendicular to the driving axis and in a direction different from this specified direction and crossing the driving axis.

When the tool accessory driving mechanism is driven, vibration may be caused in a direction along the driving axis. In the work tool according to this aspect, the weight may reciprocate in the periphery of the driving axis, so that the vibration caused in the direction along the driving axis can be efficiently reduced.

According to the inventive work tool of claim <NUM>, he weight is disposed on a shaft extending in a direction parallel to the driving axis and is configured to slide with respect to the shaft.

In the work tool according to this aspect, the weight can efficiently perform linear reciprocating motion, and the vibration caused in the direction along the driving axis can be efficiently reduced.

As another aspect of the work tool according to the present teachings, the rotary shaft member may define a rotation axis, and the connecting member may be configured to surround the rotation axis around the rotation axis. In this case, the term "around the rotation axis" may not refer to a perfect circle around the rotation axis or a circular arc on the perfect circle, but to a "periphery of the rotation axis". In this case, the manner in which the connecting member "surrounds the rotation axis" may not require that the connecting member surrounds all around the rotation axis in the periphery of the rotation axis. For example, it may be sufficient that the connecting member is arranged to extend in a specified direction perpendicular to the rotation axis and in a direction different from this specified direction and crossing the rotation axis.

In the work tool according to this aspect, the connecting member can be efficiently arranged, so that the vibration reducing mechanism can be reduced in size.

As another aspect of the work tool according to the present teachings, the connecting member may include a pair of end regions and an intermediate region that is formed between the pair of end regions and connected to the swinging member.

In the work tool according to this aspect, the position for connecting the connecting member and the swinging member with respect to the rotation axis can be arranged on the opposite side to the tool accessory driving mechanism. Therefore, the tool accessory driving mechanism and the weight can be driven in opposite phase by the swinging member, so that the vibration reducing function can be effectively exhibited. Further, in this case, it may be preferable that the end regions of the connecting member and the weight are connected to each other.

In the work tool according to the present teachings, the vibration reducing mechanism is configured to reciprocate the weight via the connecting member by swinging of the swinging member. Therefore, as another aspect of the work tool according to the present teachings, the vibration reducing mechanism may also serve as an assisting mechanism that is configured to shift the weight from a stationary state to a moving state, a mechanism that is configured to increase an amount of reciprocating movement of the weight, a mechanism that is configured to change a phase in reciprocating movement of the weight, or a mechanism that is configured to control an amount of reciprocating movement of the weight. Further, the connecting member may form a counter weight which is configured to be caused to reciprocate by swinging of the swinging member.

In other words, in the work tool according to this aspect, the vibration reducing mechanism that is configured to exhibit various functions can be provided to be suitable to the work tool to be realized.

According to the present teachings, a rational technique can be provided in a work tool having a mechanism that is configured to reduce vibration.

An embodiment of a work tool according to the present teachings is now described with reference to <FIG>. In the embodiment of the present teachings, a hammer drill <NUM> is explained as an example of the work tool. It is noted here, although the hammer drill <NUM> has a vibration reducing mechanism <NUM>, for the sake of explanation, particularly in <FIG> and <FIG>, the vibration reducing mechanism <NUM> is illustrated in a simple manner.

<FIG> is a sectional view for illustrating the outline of the hammer drill <NUM>. As shown in <FIG>, the hammer drill <NUM> is a hand-held work tool having a handgrip <NUM> designed to be held by a user. The hammer drill <NUM> is configured to perform hammering motion for a hammering operation on a workpiece by linearly driving a tool bit <NUM> in an axial direction of the tool bit <NUM> and to perform rotating motion for a drilling operation on the workpiece by rotationally driving the tool bit <NUM> around an axis of the tool bit <NUM>. A user can appropriately set a drive mode of the tool bit <NUM> in the hammer drill <NUM> by operating a mode change lever (not shown). The hammer drill <NUM> according to this embodiment has a hammer drill mode in which the tool bit <NUM> is caused to perform the hammering motion and the rotating motion, and a drill mode in which the tool bit <NUM> is caused to perform only the rotating motion.

A tool holder <NUM> is configured to make the tool bit <NUM> attachable and removable. The tool holder <NUM> extends in a specified longitudinal direction, and the longitudinal direction of the tool holder <NUM> defines a body longitudinal direction, which is a longitudinal direction of the hammer drill <NUM>. When the tool bit <NUM> is coupled to the hammer drill <NUM>, the axial direction of the tool bit <NUM> is parallel to the body longitudinal direction.

The hammer drill <NUM> and the tool bit <NUM> are examples that correspond to the "work tool" and the "tool accessory", respectively, according to the present teachings.

In a state of the hammer drill <NUM> shown in <FIG>, a front end side of the tool holder <NUM> in the body longitudinal direction is defined as a front side and a handgrip <NUM> side opposite to the front side is defined as a rear side. Further, in a direction crossing the body longitudinal direction, the tool holder <NUM> side is defined as an upper side and the handgrip <NUM> side is defined as a lower side. Specifically, the left, right, upper and lower sides in <FIG> correspond to the front, rear, upper and lower sides of the hammer drill <NUM>, respectively. These definitions relating to the positions according to the attitude of the hammer drill <NUM> shown in this drawing are also applied to <FIG>, <FIG>, <FIG>, <FIG>, <FIG> and <FIG>.

As shown in <FIG>, the tool holder <NUM> is provided on a front end of a body housing <NUM>, and the handgrip <NUM> designed to be held by a user is provided on a rear end of the body housing <NUM>. A trigger 109a for energizing a driving motor <NUM> is provided on a front side of the handgrip <NUM>. A power cable 109b for supplying current to the driving motor <NUM> is provided on a lower end of the handgrip <NUM>. When a user holds the handgrip <NUM> and operates the trigger 109a, current is supplied to the driving motor <NUM> through the power cable 109b and the tool bit <NUM> is driven in a specified drive mode.

As shown in <FIG>, an outer shell of the hammer drill <NUM> is formed by the body housing <NUM>. The body housing <NUM> mainly includes a motor housing <NUM>, a gear housing <NUM> and an inner housing <NUM>. The motor housing <NUM> and the gear housing <NUM> form a main part of the outer shell of the hammer drill <NUM>. The body housing <NUM> is an example that corresponds to the "body" according to the present teachings.

As shown in <FIG>, the driving motor <NUM> has an output shaft <NUM>. The output shaft <NUM> is rotatably supported by a bearing 111a fixed to the inner housing <NUM> and a bearing 111b fixed to the motor housing <NUM>. A fan <NUM> and a pinion gear <NUM> are provided on the output shaft <NUM> and can rotate together with the output shaft <NUM>. The fan <NUM> sends air to the driving motor <NUM> by rotation of the output shaft <NUM> and cools the driving motor <NUM>. The driving motor <NUM> is an example that corresponds to the "driving motor" according to the present teachings.

A structure of a tool accessory driving mechanism that is configured to drive the tool bit <NUM> within the body housing <NUM> is now explained with reference to <FIG> and <FIG> is an enlarged sectional view for illustrating the tool accessory driving mechanism.

As shown in <FIG>, the tool accessory driving mechanism mainly includes a motion converting mechanism <NUM> and a striking mechanism <NUM> which serve to linearly drive the tool bit <NUM>, and a rotation transmitting mechanism <NUM> for rotationally driving the tool bit <NUM>. A mechanism formed by the motion converting mechanism <NUM> and the striking mechanism <NUM> is an example that corresponds to the "tool accessory driving mechanism" according to the present teachings.

As shown in <FIG>, the rotation transmitting mechanism <NUM> has an intermediate shaft <NUM> that can rotate on a rotation axis 116c. The rotation axis 116c is parallel to the output shaft <NUM> of the driving motor <NUM> and a striking axis 140a (which is described below) defined by the tool accessory driving mechanism. The intermediate shaft <NUM> and the rotation axis 116c are examples that correspond to the "rotary shaft member" and the "rotation axis", respectively, according to the present teachings.

As shown in <FIG>, front and rear end parts of the intermediate shaft <NUM> are mounted to the gear housing <NUM> via a bearing 116a and a bearing 116b, respectively. A driven gear <NUM>, which engages with the pinion gear <NUM> of the driving motor <NUM>, is provided on the rear end part of the intermediate shaft <NUM>. A first gear <NUM>, which engages with a second gear <NUM> integrally formed with a sleeve <NUM>, is provided on the front end part of the intermediate shaft <NUM>.

As shown in <FIG>, the sleeve <NUM> is integrally connected to the tool holder <NUM> via a ring spring 159a. Further, a front end part of the sleeve <NUM> is mounted to the gear housing <NUM> via a bearing 129a and a rear end part of the sleeve <NUM> is mounted to the inner housing <NUM> via a bearing 129b, so that the sleeve <NUM> is rotatably disposed within the body housing <NUM>.

With this structure, an output of the pinion gear <NUM> is transmitted to the driven gear <NUM> and the intermediate shaft <NUM> is rotated. Then the rotation of the intermediate shaft <NUM> is transmitted to the sleeve <NUM> via the first gear <NUM> and the second gear <NUM>, and the tool bit <NUM> is rotationally driven together with the tool holder <NUM>.

As shown in <FIG>, the motion converting mechanism <NUM> mainly includes a clutch cam <NUM>, a rotary body <NUM> and a swinging shaft <NUM>. The rotary body <NUM> is configured to rotate with respect to the intermediate shaft <NUM>. The clutch cam <NUM> is spline-connected to the intermediate shaft <NUM>, so that the clutch cam <NUM> can move in a direction of the rotation axis 116c and is caused to rotate by rotation of the intermediate shaft <NUM>.

More specifically, the clutch cam <NUM> is moved in a front-rear direction along with user's operation of the mode change lever. Detailed description of the mode change lever is omitted for convenience sake.

When the hammer drill mode is selected with the mode change lever, the clutch cam <NUM> is moved rearward, and a clutch teeth 180a of the clutch cam <NUM> and a clutch teeth 123a of the rotary body <NUM> engage with each other. Therefore, in this case, the tool holder <NUM> is rotationally driven and the rotary body <NUM> is rotated, so that a piston <NUM> is driven as described below.

When the drill mode is selected with the mode change lever, the clutch cam <NUM> is moved forward and the clutch teeth 180a of the clutch cam <NUM> and the clutch teeth 123a of the rotary body <NUM> are disengaged from each other. Therefore, in this case, the tool holder <NUM> is rotationally driven, but rotation of the intermediate shaft <NUM> is not transmitted to the rotary body <NUM>, so that the piston <NUM> is not driven. <FIG> and <FIG> show the state in the drill mode.

As shown in <FIG>, the rotary body <NUM> has an outer peripheral surface 123c having a specified inclination angle with respect to the rotation axis 116c. The swinging shaft <NUM> includes: an annular part 125b which is mounted on the outer peripheral surface 123c of the rotary body <NUM> via a plurality of steel balls 123b and surrounds the rotary body <NUM>; a shaft part 125a which protrudes upward from the annular part 125b and is connected to the piston <NUM> via a joint pin <NUM>; and a projection 125c which protrudes downward from the opposite side (lower end) of the annular part 125b from the shaft part 125a and connected to a connecting member <NUM> which is described below. Further, the shaft part 125a and the joint pin <NUM> are rotatably connected with respect to each other and form a tool accessory driving mechanism connection part. Further, the projection 125c and the connecting member <NUM> are rotatably connected with respect to each other and form a connecting member connecting mechanism. The swinging shaft <NUM> is an example that corresponds to the "swinging member" according to the present teachings. With this structure, the annular part 125b moves following inclination of the outer peripheral surface 123c which changes as the rotary body <NUM> rotates. Accordingly, the shaft part 125a is caused to swing in the front-rear direction along the rotation axis 116c. The tool accessory driving mechanism is then driven as described below by a linear motion component of the swinging motion of the shaft part 125a.

Further, the shaft part 125a and the projection 125c are arranged oppositely to each other with respect to the rotation axis 116c. Therefore, the projection 125c is turned rearward when the shaft part 125a is turned forward, while the projection 125c is turned forward when the shaft part 125a is turned rearward.

As shown in <FIG>, the striking mechanism <NUM> mainly includes: the piston <NUM> that is formed by a bottomed cylindrical member and slidably disposed in a bore of the sleeve <NUM>; a striking element in the form of a striker <NUM> that is slidably disposed in a bore of the piston <NUM>; and an intermediate element in the form of an impact bolt <NUM> that is slidably disposed in a bore of the tool holder <NUM> and transmits kinetic energy of the striker <NUM> to the tool bit <NUM>.

An air chamber 127a is formed between the bottom of the piston <NUM> and the striker <NUM>, and the striker <NUM> is linearly driven by pressure fluctuations caused in the air chamber 127a when the piston <NUM> reciprocates within the sleeve <NUM>. Specifically, when the piston <NUM> moves forward and compresses air in the air chamber 127a, the striker <NUM> is pushed forward by expansion of the compressed air, collides with the impact bolt <NUM> and moves the tool bit <NUM> forward. On the other hand, when the piston moves rearward, the air in the air chamber 127a is expanded. Then the striker <NUM> is retracted rearward by negative pressure of the expanded air. Further, during a processing operation, a tip end of the tool bit <NUM> is pressed by the user, so that the impact bolt <NUM> is pushed rearward by a rear end of the tool bit <NUM>. Then, the impact bolt <NUM> that has been moved rearward is moved forward and collides with the tool bit <NUM> as described above, when the piston <NUM> moves forward. By repeating this series of operations, the tool bit <NUM> is linearly and continuously driven. The above-described operation of the striking mechanism <NUM> defines the striking axis 140a shown in <FIG>. The striking axis 140a is parallel to the rotation axis 116c. The striking axis 140a is an example that corresponds to the "driving axis" according to the present teachings.

A structure of the vibration reducing mechanism <NUM> is now explained with reference to <FIG>. <FIG> is an explanatory drawing for illustrating a main part of the vibration reducing mechanism <NUM>. As shown in <FIG>, the vibration reducing mechanism <NUM> has a dynamic vibration reducer <NUM> and the connecting member <NUM>. The vibration reducing mechanism <NUM>, the dynamic vibration reducer <NUM> and the connecting member <NUM> are examples that correspond to the "vibration reducing mechanism", the "dynamic vibration reducer" and the "connecting member", respectively, according to the present teachings.

<FIG> is a sectional view taken along line I-I in <FIG>. As shown in <FIG>, the dynamic vibration reducer <NUM> includes: a plurality of shafts <NUM> that are arranged to extend between a front part 130a and a rear part 130b of the inner housing <NUM>; a weight <NUM> through which the shafts <NUM> are inserted; and an elastic member <NUM> for biasing the weight <NUM>. Although five such shafts <NUM> are used as shown in <FIG>, any number of the shafts <NUM> may be selected according to the structure of the dynamic vibration reducer <NUM> to be realized. Further, the shafts <NUM> are arranged to extend in parallel to the striking axis 140a. The weight <NUM> has insertion holes 230a through which the shafts <NUM> extend. The shaft <NUM>, the weight <NUM> and the elastic member <NUM> are examples that correspond to the "shaft", the "weight" and the "elastic member", respectively, according to the present teachings.

As shown in <FIG>, it is sufficient for the elastic member <NUM> to be mounted on one or some of the shafts <NUM>. In this embodiment, the elastic member <NUM> is provided on each of a pair of the shafts <NUM> which are arranged oppositely to each other with respect to the striking axis 140a. <FIG> is an explanatory drawing for illustrating the shaft <NUM> on which the elastic member <NUM> is mounted. The elastic member <NUM> includes a first elastic member <NUM> disposed between the front part 130a of the inner housing <NUM> and a front side of the weight <NUM>, and a second elastic member <NUM> disposed between the rear part 130b of the inner housing <NUM> and a rear side of the weight <NUM>. With this structure, the weight <NUM> can reciprocally slide with respect to the shaft <NUM>.

<FIG> is a sectional view taken along line II-II in <FIG>. As shown in <FIG>, the weight <NUM> is arranged to surround the striking axis 140a around the striking axis 140a. With this structure, the weight <NUM> is caused to easily reciprocate by vibration which is caused in a direction along the striking axis 140a when the striking mechanism <NUM> is driven. In other words, the dynamic vibration reducer <NUM> can effectively reduce vibration caused in the direction of the striking axis 140a. Further, the weight <NUM> has a pair of end regions <NUM> each including an end. A region of the weight <NUM> between the end regions <NUM> forms an intermediate region <NUM>.

As shown in <FIG>, the connecting member <NUM> is arranged to surround the rotation axis 116c around the rotation axis 116c. This structure enables efficient arrangement of the connecting member <NUM> around the rotation axis 116c. Further, the connecting member <NUM> has a pair of end regions <NUM> each including an end. A region of the connecting member <NUM> between the end regions <NUM> forms an intermediate region <NUM>. The end region <NUM> and the intermediate region <NUM> are examples that correspond to the "end region" and the "intermediate region", respectively, according to the present teachings.

The end regions <NUM> of the connecting member <NUM> and the end regions <NUM> of the weight <NUM> are connected to rotate on a pivot axis 260a with respect to each other. A specific structure of connecting the connecting member <NUM> and the weight <NUM> is described below. The intermediate region <NUM> of the connecting member <NUM> has an intermediate hole 252a through which the projection 125c of the swinging shaft <NUM> is inserted. With this structure, the connecting member <NUM> may be moved in the front-rear direction by rotation of the swinging shaft <NUM>.

<FIG> is an explanatory drawing for showing the structure of connecting the weight <NUM> and the connecting member <NUM>. As shown in <FIG>, a circular cylindrical pivot shaft <NUM> is inserted through an end hole 231a formed in each of the end regions <NUM> of the weight <NUM> and an end hole 251a formed in each of the end regions <NUM> of the connecting member <NUM>. A recess is formed in a region of the pivot shaft <NUM> outside of the connecting member <NUM>, and a stopper ring <NUM> is mounted in the recess to prevent the connecting member <NUM> from slipping off. With this structure, the weight <NUM> and the connecting member <NUM> are configured to rotate on the pivot axis 260a with respect to each other. The pivot axis 260a is an example that corresponds to the "pivot axis" according to the present teachings.

An operation of the vibration reducing mechanism <NUM> is now explained with reference to <FIG>. <FIG> shows a state in which the shaft part 125a of the swinging shaft <NUM> is located to extend in a direction perpendicular to the rotation axis 116c. For the sake of explanation, a state of the vibration reducing mechanism <NUM> shown in <FIG> is defined as a first state. As shown in <FIG>, a center line 250a connecting a center point between the pair of pivot shafts <NUM> and a center point of the intermediate hole 252a of the connecting member <NUM> has a specified inclination angle with respect to a rotation axis orthogonal line 116d passing through the center line 250a and extending perpendicularly to the rotation axis 116c. More specifically, the pivot shafts <NUM> are arranged rearward of the intermediate hole 252a. With such an arrangement of the pivot shafts <NUM> and the intermediate hole 252a, the connecting member <NUM> has a communication region <NUM> extending over the end regions <NUM> and the intermediate region <NUM>. With such a structure of the connecting member <NUM>, the connecting member <NUM> can be efficiently arranged within a limited space, so that the hammer drill <NUM> can be reduced in size.

For the sake of explanation, the first state shown in <FIG> is defined as an initial state of the vibration reducing mechanism <NUM>. First, a case that the user selects the drill mode in this initial state is explained. In this case, when vibration is caused by driving of the rotation transmitting mechanism <NUM> or by user's operation of the hammer drill <NUM>, the weight <NUM> is reciprocated together with the connecting member <NUM> and thereby reduces the vibration. At this time, the weight <NUM> linearly reciprocates by sliding on the shaft <NUM>. Further, the pivot shafts <NUM> reciprocate when the weight <NUM> linearly reciprocates, so that the connecting member <NUM> pivots on the intermediate hole 252a.

Next, a case that the user selects the hammer drill mode is explained. As described above, in the hammer drill mode, the swinging shaft <NUM> is caused to swing by rotation of the intermediate shaft <NUM>. <FIG> shows a state in which the shaft part 125a is inclined forward by rotation of the intermediate shaft <NUM>. This state of the vibration reducing mechanism <NUM> is defined as a second state.

In the second state, the shaft part 125a moves the piston <NUM> forward and thus the tool bit <NUM> is moved forward. At this time, the projection 125c is inclined rearward, so that the weight <NUM> is moved rearward via the connecting member <NUM>. In this case, the first elastic member <NUM> biases the weight <NUM> and thereby assists rearward movement of the weight <NUM>. Further, the second elastic member <NUM> is compressed by the weight <NUM>.

As the intermediate shaft <NUM> is further rotated, the swinging shaft <NUM> is caused to swing from the second state to a state in which the shaft part 125a is inclined rearward as shown in <FIG> via the first state. This state of the vibration reducing mechanism <NUM> shown in <FIG> is defined as a third state.

In the third state, the shaft part 125a is inclined rearward and the projection 125c is inclined forward. Therefore, the shaft part 125a moves the piston <NUM> rearward, so that the air in the air chamber 127a is expanded and the striker <NUM> is moved rearward. Further, as the tool bit <NUM> is being pressed against the workpiece by the user, the tool bit <NUM> is moved rearward together with the impact bolt <NUM>.

Meanwhile, the projection 125c is inclined forward, so that the weight <NUM> is moved forward via the connecting member <NUM>. At this time, the second elastic member <NUM> biases the weight <NUM> and thereby assists forward movement of the weight <NUM>. Further, the first elastic member <NUM> is compressed by the weight <NUM>.

As described above with reference to <FIG>, the vibration reducing mechanism <NUM> is configured to directly and forcibly reciprocate the weight <NUM> between the second state and the third state via the first state by swinging of the swinging shaft <NUM>. Therefore, it can be said that the vibration reducing mechanism <NUM> includes a weight forcibly reciprocating mechanism.

Further, in the dynamic vibration reducer <NUM> formed only by the weight <NUM> and the elastic member <NUM>, the weight <NUM> can be reciprocated only by vibration caused in the body housing <NUM>. Therefore, the reciprocating distance of the weight <NUM> may depend on the magnitude of vibration caused in the body housing <NUM>.

In the vibration reducing mechanism <NUM> according to the present teachings, however, the weight <NUM> is forcibly reciprocated between the second state and the third state as described above via the connecting member <NUM>. Specifically, in a state in which the amount of reciprocating movement of the weight <NUM> is small in the dynamic vibration reducer <NUM> formed only by the weight <NUM> and the elastic member <NUM>, it can be said that the vibration reducing mechanism <NUM> forms a mechanism that is configured to increase the amount of reciprocating movement of the weight <NUM>. Further, in a state in which the amount of reciprocating movement of the weight <NUM> is large in the dynamic vibration reducer <NUM> formed only by the weight <NUM> and the elastic member <NUM>, it can also be said that the vibration reducing mechanism <NUM> forms a mechanism that is configured to control the amount of reciprocating movement of the weight <NUM>.

The connecting member <NUM> in the vibration reducing mechanism <NUM> according to the present teachings is configured to rotate with respect to both the weight <NUM> and the swinging shaft <NUM>, so that the connecting member <NUM> can linearly reciprocate the weight <NUM> by swinging of the swinging shaft <NUM>. Further, with the structure in which the connecting member <NUM> can rotate with respect to both the weight <NUM> and the swinging shaft <NUM>, it can also be said that the vibration reducing mechanism <NUM> forms a mechanism that is configured to change a phase in the reciprocating movement of the weight <NUM>.

Further, it can also be said that the connecting member <NUM> which is caused to reciprocate by swinging of the swinging shaft <NUM> forms a counter weight.

Therefore, the vibration reducing mechanism <NUM> according to the present teachings, which is configured to exhibit various functions, can be provided to be suitable to the work tool <NUM> to be realized.

Claim 1:
A work tool (<NUM>) configured to perform a specified operation on a workpiece by linearly driving a tool accessory (<NUM>), the work tool comprising
a driving motor (<NUM>),
a rotary shaft member (<NUM>) configured to be rotationally driven by the driving motor (<NUM>),
a swinging member (<NUM>) configured to be caused to swing by rotation of the rotary shaft member (<NUM>),
a tool accessory driving mechanism (<NUM>, <NUM>) configured to drive the tool accessory by swinging of the swinging member (<NUM>),
a body (<NUM>) housing the driving motor (<NUM>), the rotary shaft member (<NUM>), the swinging member (<NUM>) and the tool accessory driving mechanism, and
a vibration reducing mechanism (<NUM>) configured to reduce vibration caused in the body (<NUM>), wherein the vibration reducing mechanism includes a dynamic vibration reducer (<NUM>) having an elastic member (<NUM>) and a weight (<NUM>), the weight (<NUM>) being biased by the elastic member (<NUM>) and being reciprocatable,
wherein
the vibration reducing mechanism (<NUM>) further includes a connecting member (<NUM>) connecting the weight (<NUM>) and the swinging member (<NUM>), and
the vibration reducing mechanism (<NUM>) is configured to directly and forcibly reciprocate the weight (<NUM>) via the connecting member (<NUM>) by the swinging of the swinging member (<NUM>), and
wherein the weight (<NUM>) and the connecting member (<NUM>) are connected to be rotatable on a pivot axis (260a) with respect to each other.