Abstract:
A power tool, which actuates a tool linearly in a longitudinal direction of the tool, the power tool performs a predetermined operation to a workpiece, having: a drive mechanism which actuates the tool; a rotational shaft which actuates the drive mechanism; a swing lever which swings along the longitudinal direction by a rotational motion of the rotational shaft; and a dynamic vibration reducer which alleviates vibration generated during the predetermined operation. The dynamic vibration reducer includes a weight which is linearly movable in the longitudinal direction an elastic member which biases the weight. The weight is adapted to be actuated mechanically and forcibly by a motion component with respect to the longitudinal direction of a swinging motion of the swing lever in a state that the weight is biased by the elastic member.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     The present application claims priority from Japanese Patent Application No. 2011-123303, filed on Jun. 1, 2011, the disclosure of which is incorporated herein by reference in its entirety. 
     FIELD OF THE INVENTION 
     The invention relates to a power tool which actuates a tool linearly in a longitudinal direction of the tool and performs a predetermined operation to a workpiece. 
     BACKGROUND OF THE INVENTION 
     Japanese non-examined Patent Application Publication No. 2008-307655 discloses a power tool having a dynamic vibration reducer as vibration suppression device which alleviates vibration generated when the power tool is working. The power tool described in No. 2008-307655, has a crank mechanism which is actuated by a motor and actuates a hammering mechanism. In addition a second crank mechanism is disposed at one side of the crank mechanism opposed to the motor. The second crank mechanism actuates a weight of the dynamic vibration reducer aggressively. Namely vibration generated during an operation is decreased by forcibly actuating the dynamic vibration reducer. 
     However, because the crank mechanism for hammering the tool bit and the second crank mechanism for actuating the dynamic vibration reducer are disposed to be aligned with each other in an axial direction, a construction of the power tool is complicated and irrational for the purpose of weight saving of the power tool. 
     SUMMARY OF THE INVENTION 
     Problem to be Solved by the Invention 
     An object of the invention is, in consideration of the above described problem, to provide a power tool to improve a technique with respect to a forcible actuation of a dynamic vibration reducer. 
     Means for Solving the Problem 
     Above-mentioned object is achieved by the claimed invention. According to a preferable aspect of the invention, a power tool which actuates a tool linearly in a longitudinal direction of the tool which performs a predetermined operation to a workpiece is provided. The power tool comprising: a drive mechanism which actuates the tool; a rotational shaft which actuates the drive mechanism; a swing member which swings along the longitudinal direction by a rotational motion of the rotational shaft; and a dynamic vibration reducer which alleviates vibration generated when the tool is performing the predetermined operation. The dynamic vibration reducer includes a weight which is linearly movable in the longitudinal direction and an elastic member which biases the weight. Further the weight is adapted to be actuated mechanically and forcibly by a motion component with respect to the longitudinal direction of a swinging motion of the swing member in a state that the weight is biased by the elastic member. 
     A terminology of “mechanically” in the invention is defined by a feature that the dynamic vibration reducer and the swing member is connected to each other thereby a power is transmitted between the dynamic vibration reducer and the swing member. In a state that the weight is biased by a biasing force of the elastic element, the weight is actuated and alleviates vibration passively on the basis of vibration generated during the predetermined operation. A terminology of “forcibly” in the invention is defined by a feature that the dynamic vibration reducer alleviates vibration actively to be exerted vibration force as an external force which is different from vibration generated during the predetermined operation. A predetermined operation of the invention preferably includes features that a tool performs a hammering operation to make a hammering motion with respect to a longitudinal direction of the tool to a workpiece, a tool performs a hammer drill operation to make a hammering motion with respect to a longitudinal direction of the tool and a rotational motion with respect to a circumference direction of the tool to a workpiece, and a blade performs a cutting operation to make a linear motion with respect to a longitudinal direction of the blade to a workpiece. 
     According to the aspect, the weight of the dynamic vibration reducer is driven by the swing member which is swung by the rotational shaft for driving the tool. In this way a composition of driving the weight is simplified and lightened. Namely, driving the weight is reasonably improved. Since the composition of driving the weight is simplified, a total cost of the power tool is decreased. 
     According to a further preferable aspect of the invention, the power tool further comprises a rotational member which integrally rotates together with the rotational shaft. The swing member is adapted to be swung by a motion component with respect to a radial direction of a rotational motion of the rotational member. It is preferred that the rotational member is arranged within the range of a required length of the rotational shaft which is designed in advance for driving the drive mechanism, without extending the length of the rotational shaft for the purpose of arranging the rotational member. The rotational member of the invention is generally provided with a circular disk whose center is positioned at a position radially offset from a center of a rotational motion of the rotational shaft, namely the rotational member is provided with an eccentric cam. According to this aspect, because the swing member is arranged within the range of the length of the rotational shaft, the power tool is downsized with respect to a longitudinal direction of the rotational shaft. 
     According to a further preferable aspect of the invention, the power tool further comprises a support shaft which supports the swing member as a support point of the swinging motion of the swing member. The support shaft is arranged to be parallel to the rotational shaft. According to this aspect, a rotational motion of the rotational shaft is reasonably changed to a swinging motion of the swing member. 
     According to a further preferable aspect of the invention, a center of the rotational member is arranged at an eccentric position which is offset from a center of a rotational motion of the rotational shaft. A displacement of the weight by means of the motion component with respect to the longitudinal direction of the swinging motion of the swing member is defined by a displacement of the swing member and an offset distance of the rotational member. According to this aspect, the displacement of the weight is defined by adjusting the displacement of the swing member and/or the offset distance of the rotational member. 
     According to a further preferable aspect of the invention, the swing member includes and actuated part which is actuated by the rotational member and an actuating part which actuates the weight. A length between the support point and the actuated part is shorter than a length between the support point and the actuating part. According to this aspect, the displacement of the actuating part which actuates the weight is amplified by the displacement of the actuated part. Therefore the displacement of the swing member which drives the weight is obtained easily. 
     According to a further preferable aspect of the invention, the power tool further comprises a bearing which supports an intermediate part of the rotational shaft in a longitudinal direction of the rotational shaft being rotatable. The rotational shaft includes a tool actuating part which actuates the tool at one end of the rotational shaft in the longitudinal direction of the rotational shaft. The rotational member is arranged between the intermediate part and the tool actuating part in the longitudinal direction of the rotational shaft. According to this aspect, because the rotational member is arranged on the rotational shaft, a size with respect to the longitudinal direction of the rotational shaft is downsized. 
     According to a further preferable aspect of the invention, the power tool further comprises a rolling bearing which is arranged and intervened between the rotational member and the swing member. According to this aspect, a burning and/or a friction of contacting surfaces of the rotational member and swing member is reduced. 
     According to a further preferable aspect of the invention, the rotational member is provided with an eccentric cam which is arranged integrally with the rotational shaft. 
     According to the invention, a power tool which is effectively improved with respect to a forcible actuation of a dynamic vibration reducer is provided. 
     Other objects, features and advantages of the invention will be readily understood after reading the following detailed description together with the accompanying drawings and the claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a cross-sectional view of a total composition of an electrical hammer in accordance with an embodiment of the invention. 
         FIG. 2  shows a cross-sectional view of a dynamic vibration reducer and a surrounding area of the dynamic vibration reducer in which a motor and a gear and so on are not shown. 
         FIG. 3  shows a cross-sectional view taken from line A-A of  FIG. 2 . 
         FIG. 4  shows a cross-sectional view taken from line B-B of  FIG. 3 . 
         FIG. 5  shows a bottom view of  FIG. 2 . 
         FIG. 6  shows a cross sectional view taken from line D-D of  FIG. 5 . 
         FIG. 7  shows a perspective view of a forcible vibration exerting mechanism of the dynamic vibration reducer. 
         FIG. 8  shows a partial cross-sectional view of the forcible vibration exerting mechanism of the dynamic vibration reducer. 
         FIG. 9  shows a 90 degrees rotated partial cross-sectional view of the forcible vibration exerting mechanism of  FIG. 8 . 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Each of the additional features and method steps disclosed above and below may be utilized separately or in conjunction with other features and method steps to provide and manufacture improved power tools and method for using such the power tools and devices utilized therein. Representative examples of the invention, which examples utilized many of these additional features and method steps in conjunction, will now be described in detail with reference to the drawings. This detailed description is merely intended to teach a person skilled in the art further details for practicing preferred aspects of the present teachings and is not intended to limit the scope of the invention. Only the claims define the scope of the claimed invention. Therefore, combinations of features and steps disclosed within the following detailed description may not be necessary to practice the invention in the broadest sense, and are instead taught merely to particularly describe some representative examples of the invention, which detailed description will now be given with reference to the accompanying drawings. 
     An embodiment of the invention will be explained with reference to  FIG. 1  to  FIG. 9 . In this embodiment, the invention will be explained by applying to an electrical hammer as one example of a power tool. As shown in  FIG. 1 , the electrical hammer  101  is mainly provided with a body  103 , a tool holder  137 , a hammer bit  119  and a hand grip  109 . The body  103  is defined as a power tool body which constitutes an outline of the electrical hammer  101 . The tool holder  137  is disposed at a front part (a left side part of  FIG. 1 ) of the body  103  in a longitudinal direction of the body  103 . The hammer bit  119  is adapted to detachably connect to the tool bit  137 . The hand grip  109  is defined as a main handle held by a user, which is disposed at an opposed part (a right side part of  FIG. 1 ) with respect to the hammer bit  119  in the longitudinal direction of the body  103 . The hammer bit  119  corresponds to a tool of the invention. The hammer bit  119  is held by the tool holder  137  so that the hammer bit  119  is reciprocally relatively movable against the tool holder  137  with respect to the longitudinal direction of the body  103  and is regulated to relatively rotate against the tool holder  137  with respect to a circumference direction of the tool holder  137 . Hereinafter, a side where the hammer bit  119  is disposed is called a front side of the electrical hammer  101  and the other side where the hand grip  109  is disposed is called a rear side of the electrical hammer  101 . 
     The body  103  is mainly provided with a main housing  105  and a barrel housing  107 . The main housing  105  houses a driving motor  111  and a motion conversion mechanism  113 . The barrel housing  107  is formed as an approximately cylindrical shape and housed a hammering element  115 . The driving motor  111  is disposed to which a rotational axis extends in a vertical direction of  FIG. 1  and crosses the longitudinal direction of the body  103 . Namely, the rotational axis of the driving motor  111  crosses the longitudinal direction of the body  103 . A rotational output of the driving motor  111  is converted to a linear motion by the motion conversion mechanism  113  and is transmitted to the hammering element  115  and thereby an impact force to the hammer bit  119  via the hammering element  115  in a longitudinal direction of the hammer bit  119  is generated. The motion conversion mechanism  113  and the hammering element  115  correspond to a drive mechanism of the invention. The barrel housing  107  is disposed at a front end of the main housing  105  and extends in the longitudinal direction of the hammer bit  119 . 
     The hand grip  109  is disposed to extend and cross the longitudinal direction of the hammer bit  119  and has connecting portions. The connecting portions which protrude toward the front side of the electrical hammer  101  are disposed at an upper end and a lower end of the hand grip  109 . The hand grip  109  is connected to the body at the upper part and the lower part, therefore the hand grip  109  is shown a substantially D-shape in a side view. A switch  131  and an operated member  133  are disposed at an upper part of the hand grip  109 . The switch  131  is movable between an ON-position and an OFF-position when a user slides the operated member  133 . The driving motor  111  is driven by a movement of the switch  131 . 
     The motion converting mechanism  113  converts a rotational motion of the driving motor  111  to a linear motion and transmits the linear motion to the hammering element  115 . The motion converting mechanism  113  is mainly provided with a crank mechanism which comprises a crank shaft  121 , an eccentric pin  123 , a connecting rod  125  and a piston  127  and so on. The crank shaft  121  is driven by the driving motor  111  via a plurality of gears and thereby the crank shaft  121  is decelerated. The eccentric pin  123  is disposed at an eccentric position which is positioned away from a rotational center of the crank shaft  121 . The connecting rod  125  is connected to the crank shaft  121  via the eccentric pin  123 . The piston  127  is linearly driven by the connecting rod  125 . The piston  127  is disposed slidably in a cylinder  141  thereby the piston  127  is moved linearly along the cylinder  144  in association with a driving of the driving motor  111 . The crank shaft  121  corresponds to a rotational shaft of the invention. 
     The hammering element  115  is mainly provided with a striker  143  and an impact bolt  145 . The striker  143  is defined as an impacting member and is disposed in the cylinder  141  thereby the striker  143  is slidable in contact with an inner surface of the cylinder  141 . The impact bolt  145  is defined as an intermediate member which transmits a motion energy of the striker  143  to the hammer bit  119  and is disposed to be slidable against the tool holder  137 . An air room  141   a  is formed between the piston  127  and the striker  143  inside the cylinder  141 . The striker  143  is driven via an air spring of the air room  141   a  in association with a sliding movement of the piston  127  and impinges on the impact bolt  145  which is slidably disposed against the tool holder  137 . Therefore an impact power is transmitted to the hammer bit  119  via the impact bolt  145 . 
     As to the electrical hammer  101  descried above, when the driving motor  111  is driven, the piston  127  is slid linearly along the cylinder  141  via the motion conversion mechanism  113  which is mainly composed of the crank mechanism. When the piston  127  is slid, the striker  143  is moved toward the front side in the cylinder  141  by means of an effect of the air spring of the air room  141   a  of the cylinder  141 . Then the striker  143  impinges on the impact bolt  145  thereby the motion energy is transmitted to the hammer bit  119 . When a user exerts a pressing force toward the front side on the body  103  and the hammer bit  119  is pressed against a workpiece, the hammer bit  119  operates a hammering operation on the workpiece such as concrete. 
     A dynamic vibration reducer  151  which alleviates vibration on the body  103  when the electrical hammer  101  is working, and a mechanical forcible vibration exerting mechanism  161  which exerts a movement mechanically and forcibly on the dynamic vibration reducer  151  will be explained. Hereinafter, to exert the movement forcibly on the dynamic vibration reducer  151  is called a forcible vibration exertion. As shown in  FIG. 2 ,  FIG. 7  to  FIG. 9 , the dynamic vibration reducer  151  is mainly provided with a weight  153  and springs  155 F,  155 R. The weight  153  is disposed so as to circularly surround an outside surface of the cylinder  141 . The springs  155 F,  155 R are respectively disposed at a front side and a rear side of the weight  153  with respect to the longitudinal direction of the hammer bit  119 . The dynamic vibration reducer  151  is disposed at an inner space of the barrel housing  107  of the body  103  (refer to  FIG. 1 ). The springs  155 F,  155 R respectively exert an elastic force on the weight  153  from the front side and the rear side of the weight  153  when the weight  153  is moved in the longitudinal direction of the hammer bit  119 . The springs  155 F,  155 R correspond to an elastic member of the invention. 
     A gravity point of the weight  153  is disposed so as to be aligned with a longitudinal axis of the hammer bit  119 . An outside surface of the weight  153  is slidably disposed along the barrel housing  107  in a state that the outside surface of the weight  153  is in contact with an inner surface of the barrel housing  107 . Namely the inner surface of the barrel housing  107  is defined as a guide surface which guides a linear motion of the weight  153 . Similar to the weight  153 , respective gravity points of the springs  155 F,  155 R are disposed respectively so as to be aligned with the longitudinal axis of the hammer bit  119 . One end (rear end) of a spring  155 R is adapted to contact with a front surface of a flange  157   a  of the slide sleeve  157  represented as a sliding member, and the other end (front end) of the spring  155 R is adapted to contact with a rear end of the weight  153  with respect to the longitudinal direction. One end (rear end) of a spring  155 F is adapted to contact with a front end of the weight  153 , and the other end (front end) of the spring  155 F is adapted to contact with a ring-shaped spring receiving member  159  which is disposed at a front side of the cylinder  141  and is fixed on the outside surface of the cylinder  141 . 
     The slide sleeve  157  is defined as an inputting member which inputs a driving force of the forcible vibration exerting mechanism  161  to the weight  153  via the spring  155 R. The slide sleeve  157  is slidably engaged with the outside surface of the cylinder  141  with respect to the longitudinal direction of the hammer bit  119  and is slid by the forcible vibration exerting mechanism  161 . 
     As shown in  FIG. 3 , the forcible vibration exerting mechanism  161  is mainly provided with an eccentric cam  163 , a support shaft  165 , a swing lever  167  and a power transmission pin  169 . The eccentric cam  163  is disposed on the crank shaft  121  thereby the eccentric cam  163  is integrally rotated together with the crank shaft  121 . The swing lever  167  is driven by a rotational motion of the eccentric cam  163  and is swung along a front-back direction around the support shaft  165  as a swinging support point. The power transmission pin  169  transmits a motion component with respect to the longitudinal direction of the hammer bit  119  of a swinging motion of the swing lever  167  to the weight  153 . 
     As shown in  FIG. 2 , the crank shaft  121  extends in a vertical direction crossing the longitudinal direction of the hammer bit  119 . One of a plurality of gears  122  (refer to  FIG. 1 ) which transmits the rotational output of the driving motor  111  to the crank shaft  121  is fixed at one side in an axis direction of the crank shaft  121 . A crank plate  124  which communicates the eccentric pin  123  and the crank shaft  121  is arranged at the other side in the axis direction of the crank shaft  121 . The crank shaft  121  is rotatably supported by the main housing  105  via two ball bearings  135  arranged between the one side and the other side of the crank shaft  121 . A part between the one side and the other side in the axis direction of the crank shaft  121  corresponds to an intermediate part of the invention. The crank plate  124  and the eccentric pin  123  correspond to a tool actuating part of the invention. 
     As shown in  FIG. 3 , the eccentric cam  163  is formed as a disk member whose center is positioned at an eccentric position which is offset from a rotational center of the crank shaft  121 . As shown in  FIG. 2 , the eccentric cam  163  is disposed between the crank plate  124  and one of the ball bearings  135  integral with the crank shaft  121 . A rolling bearing  171  is engaged with a periphery of the eccentric cam  163 . 
     As shown in  FIG. 3 , the swing lever  167  is disposed at a front of the crank shaft  121  so as to extend in a lateral direction crossing both a longitudinal direction of the crank shaft  121  and the longitudinal direction of the hammer bit  119 . One end of the swing lever  167  is swingably supported by the support shaft  165 . A front surface of a distal end of the swing lever  167  contacts with the power transmission pin  169 . And a rear surface of an intermediate part between the one end and the distal end of the swing lever  167  contacts with a periphery of the rolling bearing  171 . The swing lever  167  corresponds to a swing member of the invention. The distal end of the swing lever  167  which contacts with the power transmission pin  169  corresponds to an actuating part of the invention. The intermediate part of the swing lever  167  which contacts with the rolling bearing  171  corresponds to an actuated part of the invention. 
     The support shaft  165  is supported by bearing  166 . The swing lever  167  and the bearing  166  are assembled in advance via the support shaft  165 . As shown in  FIG. 5  and  FIG. 6 , the assembly of the swing lever  167  and the bearing  166  is arranged and fixed on the main housing  108  by fixing the bearing  166  by means of a fixing means such as a screw  166   a  and so on. 
     As shown in  FIG. 3 , the power transmission pin  169  is slidably inserted into a pin inserted hole  105   a  which is arranged at the main housing  105  so as to extend linearly in the longitudinal direction of the hammer bit  119 . One end (rear end) with respect to a longitudinal direction of the power transmission pin  169  is adapted to contact with a front surface of the distal end of the swing lever  167 , and the other end (front end) with respect to the longitudinal direction of the power transmission pin  169  is adapted to contact with a rear surface of a flange  157   a  of the slide sleeve  157 . The end part of the power transmission pin  169  is formed sphery. 
     A behavior of the electrical hammer  101  described above will be explained as below. During a hammering operation by using the electrical hammer  101 , an impactive and frequent vibration with respect to the hammer bit  119  is generated on the body  103 . The dynamic vibration reducer  151  in this embodiment passively alleviates vibration on the body  103  by the weight  153  and the springs  155 F,  155 R work coactive. Therefore vibration generated on the body  103  of the electric hammer  101  is reduced effectively. During the hammering operation, for example a user operates the hammering operation by pressing the electrical hammer  101  against the workpiece. Under such circumstances, because a large load is exerted on the hammer bit  119 , vibration which is input into the dynamic vibration reducer  151  is regulated. 
     As to an operating state described above, vibration of the body  103  is effectively reduced by the forcible vibration exertion of the dynamic vibration reducer  151 . Namely when the crank shaft  121  is rotated, the eccentric cam  163  is integrally rotated together with the crank shaft  121 . Then the swing lever  167  is swung in the front-rear direction by the eccentric cam  163 . When the swing lever  167  is swung forward, the slide sleeve  157  is pressed and moved forward via the power transmission pin  169  thereby the springs  155 F,  155 R are compressed. When the swing lever  167  is swung rearward, the slide sleeve  157  is moved rearward by a biasing force of the springs  155 F,  155 R. 
     In this way, during the hammering operation the weight  153  of the dynamic vibration reducer  151  is driven actively via the springs  155 F,  155 R by the forcibly vibration exerting mechanism  161 . Accordingly the dynamic vibration reducer  151  is represented as vibration alleviation mechanism which actively drives the weight  153 . As a result, vibration with respect to the longitudinal direction of the hammer bit  119  generated during the hammering operation on the body  103  is effectively reduced. 
     According to this embodiment, the slide sleeve  157  is driven by the forcible vibration exerting mechanism  161  thereby the weight  153  is actively driven via the spring  155 R. Therefore adjusting a driven timing of the weight  153  by the forcible vibration exerting mechanism  161  to reduce the impactive vibration generated on the body  103  when the hammer bit  119  is hit via the striker  143  and the impact bolt  145 , vibration alleviation effect by the weight  153  is accomplished based on a preferable configuration. 
     Further, according to this embodiment, the forcible vibration exerting mechanism  161  is adapted to have the eccentric cam on the crank shaft  121  for hitting the hammer bit  119  thereby the weight  153  of the dynamic vibration reducer  151  is adapted to be driven by the eccentric cam  163  via the swing lever  167  and the power transmission pin  169 . Namely the forcible vibration exerting mechanism  161  is adapted and integrated with the crank mechanism for the hammering operation. Compared to the known composition which a crank mechanism for a hammering operation and a crank mechanism for a forcible vibration exerting mechanism are aligned in each other in their longitudinal direction, the forcible vibration exerting mechanism  161  is simplified and lightened. Therefore a total cost of the electrical hammer  101  is reduced. Further, because the forcible vibration exerting mechanism  161  is disposed within a range of a length of the crank shaft  121 , compared to the known composition, a size with respect to a longitudinal direction of the crank shaft is downsized. 
     Further, according to this embodiment, because the support shaft  165  which constitutes a support point of a swinging motion of the swing lever  167  is arranged to extend in parallel with the rotational axis of the eccentric cam  163 , the rotational motion of the eccentric cam  163  is reasonably changed into the swinging motion of the swing lever  167 . 
     Further, according to this embodiment, a displacement of the weight  153  is defined by adjusting a displacement of the swing lever  167  and/or an offset distance of the eccentric cam  163 . 
     Further, according to this embodiment, as shown in  FIG. 3 , the intermediate part with respect to an extending direction of the swing lever  167  is contacted with the rolling bearing  171 . Therefore a distance between a center of the support shaft  165  and a contact part  167   b  which contacts with the power transmission pin  169  is longer than a distance between the center of the support shaft  165  and a contact part  167   a  which contacts with the eccentric cam  163 . Accordingly the weight  153  of the dynamic vibration reducer  151  is driven with an amplified displacement which is amplified from the eccentric distance of the eccentric cam  163 . 
     Further, according to this embodiment, because the rolling bearing  171  is disposed at the periphery of the eccentric cam  163 , a burning and/or a friction of contacting surfaces of the swing lever  167  and the rolling bearing  171  is reduced. 
     The electrical hammer  101  was explained as a one example of the power tool in this embodiment, however it is not limited to the electrical hammer  101 . For example, the invention may be applied to a hammer drill comprising the hammer bit  119  which actuates a hammering motion and a rotational motion. In addition, the invention may be applied to a jigsaw or a reciprocal saw which operate a cutting operation by moving a blade linearly against a workpiece. 
     DESCRIPTION OF NUMERALS 
     
         
           101  electrical hammer 
           103  body 
           105  main housing 
           107  barrel housing 
           109  hand grip 
           111  driving motor 
           113  motion conversion mechanism 
           115  hammering element 
           119  hammer bit 
           121  crank shaft 
           122  gear 
           123  eccentric pin 
           125  connecting rod 
           127  piston 
           131  switch 
           133  operated member 
           135  ball bearing 
           137  tool holder 
           141  cylinder 
           143  striker 
           145  impact bolt 
           151  dynamic vibration reducer 
           153  weight 
           155 F spring 
           155 R spring 
           157  slide sleeve 
           157   a  flange 
           159  spring receiving member 
           161  forcible vibration exerting mechanism 
           163  eccentric cam 
           165  support shaft 
           166  bearing 
           166   a  screw 
           167  swing lever 
           167   a  contact part 
           167   b  contact part 
           169  power transmission pin 
           171  rolling bearing