Patent Publication Number: US-11396094-B2

Title: Driving tool with reaction absorbing mechanism

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This is a continuation application of copending application Ser. No. 15/297,872, filed on Oct. 19, 2019, which is a continuation of copending application Ser. No. 14/722,578, filed on May 27, 2015, which issued as U.S. Pat. No. 9,505,115 on Nov. 29, 2016, which is a continuation of copending application Ser. No. 13/369,484, filed on Feb. 9, 2012, which issued as U.S. Pat. No. 9,302,381 on Apr. 5, 2016. The copending and prior application Ser. Nos. 15/297,872, 14/722,578, and 13/369,484 are incorporated by reference herein in their entireties. 
    
    
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates to a driving tool. 
     Related Art 
     As types of driving tools, for example, a type in which a tool is driven by a compressed air, and a type in which a tool is driven by a spring force are known. 
     JP-A-09-295283 discloses a spring drive type nailing machine which can sequentially drive out nails stored in a magazine using a plunger normally biased downward by a spring and a driver fixed to the plunger. 
     In the above type driving tool, in the case that a nose portion of the driving tool is separated from a driven workpiece due to a reaction on driving, a nail cannot be sufficiently driven or a driven mark caused by the driver off the nail can be left on the workpiece. 
     To prevent such reaction, the nose portion of the driving tool must be strongly pressed against the workpiece. However, when the nose portion is strongly pressed against the workpiece, the nose portion can damage the workpiece and also can cause an operator to get tired. 
     SUMMARY OF THE INVENTION 
     One or more embodiments and modifications thereof of the invention provide a driving tool having a mechanism for absorbing a reaction on driving in order to provide a sufficient driving force with a small pressing force against a workpiece. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a section view of a driving tool. 
         FIGS. 2 ( a )  and  2  ( b ) are external views of a plunger unit. 
         FIGS. 3( a ) and 3( b )  are external views of a plunger. 
         FIG. 4( a )  is a section view of the plunger unit taken along  4 A- 4 A line shown in  FIG. 4 ( b ) .  FIG. 4 ( b )  is a side view of the plunger unit. 
         FIG. 5  is a section view of the plunger unit taken along  5 - 5  line shown in  FIG. 4( b ) . 
         FIG. 6  is an explanatory view to show how the plunger is pushed up by a drive mechanism. 
         FIG. 7  is a section view of the plunger unit, showing a state where the plunger exists at its bottom dead center position. 
         FIG. 8  is a section view of the plunger unit, showing a state where the plunger exists at its top dead center position. 
         FIG. 9  is a section view of the plunger unit, showing a state where the plunger is moving from the top dead center position to the bottom dead center position. 
         FIG. 10( a )  is a partially enlarged section view of the plunger unit near to a pulley, showing a state where the plunger is moving from the top dead center position to the bottom dead center position.  FIG. 10( b )  is a (partially omitted) section view taken along the  10 B- 10 B line shown in  FIG. 10( a ) . 
         FIG. 11  is a section view of the plunger unit, showing a state just after the plunger has reached the bottom dead center position from the top dead center position. 
         FIG. 12  is an explanatory view to show the equilibrium of forces when the plunger exists at its top dead center position. 
         FIG. 13  is an explanatory view to show a reaction amount in a state where the plunger is moving from the top dead center position to the bottom dead center position. 
         FIG. 14( a )  is a section view taken along  14 A- 14 A line shown in  FIG. 14( b ) .  FIG. 14( b )  is a side view of a plunger unit including a vibration isolator, according to a first modification of the embodiment. 
         FIG. 15  shows a second modification of the embodiment, showing a driving tool with a balancer disposed outside its housing. 
         FIG. 16  shows a third modification of the embodiment. Specifically, it is a section view of a plunger unit including a tensile spring as a balancer biasing member. 
         FIG. 17  shows a fourth modification of the embodiment. Specifically, it is a section view of a plunger unit including a magnetic spring as a balancer biasing member. 
         FIG. 18  shows a fifth modification of the embodiment. Specifically, it is a section view of a plunger unit with a balancer disposed outside its pipe. 
         FIG. 19 ( a )  is a side section view of a plunger unit including a balancer guide having a different shape according to a sixth modification of the embodiment.  FIG. 19( b )  is a section view thereof taken along the  19 B- 19 B line shown in  FIG. 19( a ) . 
         FIGS. 20( a ) to 20( c )  shows a seventh modification of the embodiment. Specifically,  FIG. 20( a )  is a front view of a plunger unit with a plunger guide disposed only one side of a pipe.  FIG. 20( b )  is a section view thereof when viewed from above.  FIG. 20( c )  is a section view thereof when viewed from side. 
         FIG. 21  shows a fifth modification of the embodiment, where a driving tool using a flywheel is employed. 
     
    
    
     DETAILED DESCRIPTION OP THE EMBODIMENTS 
     Description will be given below of an embodiment and modifications thereof with reference to the accompanying drawings. 
     The embodiment and the modifications described herein are not intended to limit the invention but only to exemplify the invention, and all features or combinations of the features of the embodiment and the modifications are not always essential to the invention. 
     A driving tool  10  according to the embodiment is a spring drive type nailing machine for carrying out its driving operation using a spring force, while it strikes out a nail as a fastener. The driving tool  10 , as shown in  FIG. 1 , includes, within its housing  11 , a plunger unit  30  connected to a driver  31  for driving out the nail, a drive mechanism  20  for actuating the plunger unit  30 , a magazine  12  storing therein connected nails (connected staples) to be driven out by the driver  31 , and so on. 
     The magazine  12  includes a nose portion  15  formed in its front end portion, while the leading one of the connected nails stored in the magazine  12  is supplied to the nose portion  15  by a supply device (not shown). The leading nail supplied to the nose portion  15  is driven out from a nozzle  16  formed in the leading end of the nose portion  15 . The driver  31  of this embodiment is formed as part of the plunger unit  30  and, when the plunger unit  30  is operated, the driver  31  is caused to slide toward the nozzle  16  to thereby drive out the nail supplied to the nose portion  15  from the nozzle  16 . 
     The plunger unit  30  is structured in an elongated bar-like unit such that, as shown in  FIG. 2 ( a )  and  FIG. 2 ( b ) , two plunger guides  34  are fixed respectively to the two sides of a cylindrical pipe  35  functioning as a balancer guide. A plunger  32  is slidably mounted on the outer surface of the pipe  35 , while a plunger biasing member  33  for normally biasing the plunger  32  toward the nozzle  16  is also mounted on the outer surface thereof. 
     Here, the plunger guide  34  is used to guide the sliding movement of the plunger  32  and, as shown in  FIGS. 4( a )  to  5 , it has a rail portion  34   a  formed in its inside facing the pipe  35  and extending in its longitudinal direction. 
     The plunger unit  30  is fixed within the housing  11  such that the longitudinal direction of the pipe  35  can be parallel to the nail drive-out direction and the driver  31  can become most distant from the grip  13  (in other words, the pipe  35  can be situated nearer to the grip  13  than the driver  31 ). 
     The plunger  32  includes in its side portion a driver connecting portion  32   b  for connecting the driver  31  thereto. The driver  31  is connected to this driver connecting portion  32   b  and thus it is able to slide to the sliding movement of the plunger  32 . 
     The plunger  32 , as shown in  FIGS. 3( a ) and 3( b ) , has a pipe hole  32   e  which is opened up in its center and through which the pipe  35  can be penetrated. On the wall portions of both sides of the pipe hole  32   e , there are provided guide rollers  32   a . Each guide roller  32   a , as shown in  FIG. 4 ( a ) , slides within the rail portion  34   a  of the plunger guide  34 . The plunger  32 , due to provision of the pipe hole  32   e  and guide rollers  32   a , can be guided to slide along the pipe  35  and plunger guide  34 . 
     The plunger  32  has first and second engaging portions  32   c  and  32   d  for engagement with the drive mechanism  20  which, as shown in  FIGS. 3( a ) and 3( b ) , are respectively provided on and projected from its side portion. These first and second engaging portions  32   c  and  32   d  are disposed on the opposite side (on the drive mechanism  20  side) to the side where the driver connecting portion  32   b  is disposed. Here, the first and second engaging portions  32   c  and  32   d  are disposed respectively at mutually different height positions (positions with respect to the nozzle  16 ). That is, as shown in  FIG. 3 ( b ) , the first engaging portion  32   c  is disposed at a position nearer to the nozzle  16  than the second engaging portion  32   d . Thus, the first and second engaging portions  32   c  and  32   d  are disposed alternately with respect to the sliding direction of the plunger  32 . 
     The drive mechanism  20  for pushing up the plunger  32  against the biasing force of the plunger biasing member  33 , as shown in  FIG. 6 , includes multiple gears. The multiple gears can be rotated by the driving force of a motor  17 . The motor  17  can be operated when a trigger  14  is operated and its operation will continue until a micro switch (not shown) detects that the plunger  32  has moved to a given position. 
     Here, within the driving tool  10 , there is provided a control apparatus (not shown) including a CPU, a RAM and the like, while the control apparatus controls the driving of the motor  17  according to input signals from the trigger  14  and micro switch. 
     The drive mechanism  20  rotates the gears in engagement with the plunger  32 , thereby pushing up the plunger  32 . And, when the engagement of the gears with the plunger  32  is removed, the plunger  32  is caused to move due to the biasing force of the plunger biasing member  33 , whereby the driver  31  connected to the plunger  32  is slid toward the nozzle  16  for driving out the nail. 
     Specifically, in the drive mechanism  20 , as shown in (a) of  FIG. 6 , on a torque gear plate  21  fixed to the housing  11 , there are pivotally supported first and second torque gears  22  and  23  in such a manner that they can be rotated respectively. Here, the first and second torque gears  22  and  23  are arranged side by side along the sliding direction of the plunger  32 , while the first torque gear  22  is disposed nearer to the nozzle  16  than the second torque gear  23 . Thus, the plunger  32  is engaged sequentially with the first and second torque gears  22  and  23  in this order to be thereby lifted up gradually. 
     (b) of  FIG. 6  shows a state where the plunger  32  exists at its bottom dead center position (a state where the driving-out of the nail by the driver  31  is completed). When the first and second torque gears  22  and  23  are rotated from this state, the torque roller  22   a  of the first torque gear  22  is engaged with the first engaging portion  32   c  of the plunger  32 . 
     As shown in (c) of  FIG. 6 , the plunger  32  is lifted up by the first torque gear  22  with the above engagement maintained. When the first torque gear  22  is rotated up to a position where the torque roller  22   a  comes to its upper-most position, the engagement between the torque roller  22   a  and first engaging portion  32   c  is removed. At the then time, before the engagement between the torque roller  22   a  and first engaging portion  32   c  is removed, the torque roller  23   a  of the second torque gear  23  is engaged with the second engaging portion  32   d  of the plunger  32 . 
     As shown in (d) of  FIG. 6 , with the above engagement maintained, the plunger  32  is lifted up by the second torque gear  23  and is thereby moved up to its top dead center position. 
     After then, as shown in (e) of  FIG. 6 , when the second torque gear  23  is further rotated up to a position where the torque roller  23   a  comes to its upper-most position, the engagement between the torque roller  23   a  and second engaging portion  32   d  is removed. Thus, since the plunger  32  is biased by the plunger biasing member  33 , it is moved down to its bottom dead center position shown in (b) of  FIG. 6 . Consequently, the driver  31  connected to the plunger  32  is caused to slide toward the nozzle  16  for driving out the nail. 
     Here, in this embodiment, the plunger  32  normally waits at its top dead center position shown in (d) of  FIG. 6 . When the trigger  14  is operated, the drive mechanism  20  is operated to move the plunger  32  sequentially through the states respectively shown in (e) to (b) and (b) to (c) of  FIG. 6  and, after then, the plunger  32  waits again at the top dead center position shown in (d) of  FIG. 6 . 
     That is, when the trigger  14  is operated, on receiving this operation signal, the control apparatus starts to drive the motor  17 . Thus, when the gear is rotated to a position shown in (e) of  FIG. 6 , the nail driving operation is carried out. And, also after completion of the nail driving operation, the control apparatus drives the motor on. Consequently, when the plunger  32  moves up to the top dead center position shown in (d) of  FIG. 6 , the above-mentioned micro switch is depressed by the plunger  32 . On receiving the signal of the micro switch, the control apparatus controls the motor  17  to stop its driving operation. 
     Here, the plunger unit  30  of this embodiment includes a reaction absorbing mechanism for absorbing the reaction to be generated in the above nail driving operation. 
     The reaction absorbing mechanism, as shown in  FIG. 5 , includes a balancer  36  disposed slidably within the pipe  35  and a balancer biasing member  37  for biasing the balancer  36  in the direction away from the nozzle  16 . 
     The balancer  36  is a cylindrical metal member formed to follow the inside diameter of the pipe  35  and can slide inside the pipe  35 . Here, as described above, since the pipe  35  is disposed parallel to the nail drive-out direction, the balancer  36  to slide within this pipe  35  is formed to slide parallel to the driver  31 . 
     The balancer biasing member  37  is a spring mechanism constituted of a compression spring which is disposed within the pipe  35  and can be operated there. The balancer biasing member  37  is disposed nearer to the nozzle  16  than the balancer  36  and biases the balancer  36  in the direction away from the nozzle  16 . 
     Here, in this embodiment, the pipe  35  is formed to have a cylindrical shape with its outer surface closed. However, instead, the pipe  35  may also be formed such that it includes a slit or an opening in its outer surface, or it may be formed to have a prism shape or other shapes. 
     The balancer  36  is connected to the plunger  32  through a string-shaped wire  39  and thus, when the plunger  32  moves, it can be moved in linking with the plunger  32 . Specifically, since the direction of a force to be applied to the wire  39  by a pulley  40  provided as a direction changing portion is changed about 180°, when the plunger  32  is pushed up by the drive mechanism  20  and the driver  31  is thereby slid in the direction away from the nozzle  16 , the balancer  36  is pulled and moved by the wire  39  in the direction of the nozzle  16 . Thus, the balancer biasing member  37  is compressed to thereby store a spring force therein. 
     When the plunger  32  is released from the drive mechanism  20  and the driver  31  is thereby slid toward the nozzle  16  to carry out a nail driving operation, the pull by the wire  39  is removed. Therefore, the balancer  36  is biased and moved by the balancer biasing member  37  in the direction away from the nozzle  16 . 
     The reaction absorption in this embodiment is carried out by the reaction due to the bias of the balancer biasing member  37 . Now, description will be given below specifically of the mechanism of the reaction absorption with reference to the operation of the plunger unit  30 . 
       FIG. 7  shows the plunger unit  30  with the plunger  32  at the bottom dead center position. In this state, the plunger  32  is biased by a plunger biasing member  33  toward the nozzle  16  and is pressed against a rubber-made bumper  41 . Also, the balancer  36  is biased by the balancer biasing member  37  in the direction away from the nozzle  16  and is pressed against a rubber-made balancer stopper  38 . In this case, the wire  39  is pulled almost with no loosening. 
       FIG. 8  shows a state where the plunger  32  is pushed up by the drive mechanism  20  and exists at its top dead center position. In this state, the plunger is pushed up in the direction away from the nozzle  16  against the biasing force of the plunger biasing member  33 . Also, as the plunger  32  is pushed up, the wire  39  is pulled and the balancer  36  connected to the other end of the wire  39  is pulled toward the nozzle  16  against the biasing force of the balancer biasing member  37 . 
     In this state, as shown in  FIG. 12 , the housing  11  receives the biasing forces of the plunger biasing member  33  and balancer biasing member  37 , while the forces balance with each other. 
     In the state of  FIG. 8 , when the engagement between the plunger  32  and drive mechanism  20  is removed, as shown in  FIG. 9 , the biasing force of the plunger biasing member  33  allows the plunger  32  to start to move toward the nozzle  16 . Thus, since the wire  39  pulling the balancer  36  is loosened, the balancer  36  is free and the biasing force of the balancer biasing member  37  allows the balancer  36  to start to move in the direction away from the nozzle  16 . 
     In this case, as shown in  FIG. 13 , the biasing reaction P 1  of the plunger biasing member and driving reaction P 2  generate the reaction on driving which provides a force to part the driving tool  10  away from the workpiece. 
     However, in the driving tool  10  of this embodiment, due to the biasing reaction P 3  of the balancer biasing member, there is applied a force to press the driving tool  10  against the workpiece. That is, since the balancer biasing member  37  biases the balancer  36  in the direction away from the nozzle  16 , on the opposite side to the balancer  36 , there is generated a reaction in a portion for receiving the balancer biasing member  37 . That is, there is generated a force to press the workpiece against the housing  11  of the driving tool  10 . 
     Therefore, the biasing reaction P 1  of the plunger biasing member and driving reaction P 2  cancel the biasing reaction P 3  of the balancer biasing member, thereby reducing the reaction on driving. Here, a reaction, which cannot be cancelled by the biasing reaction P 3  of the balancer biasing member, is to be cancelled by a pressing load P 4  given by an operator (a mechanical weight can also be added thereto). 
     The loosening of the wire  39  in the driving operation is provided because the moving speed of the plunger  32  is set faster than the moving speed of the balancer  36 . That is, by adjusting the difference between the biasing forces of the plunger biasing member  33  and balance biasing member  37  or the weights or sliding resistances of the plunger  32  and balancer  36 , the moving speed of the plunger  32  is set faster than the moving speed of the balancer  36 . Therefore, the wire  39  can be loosened due to the difference between these speeds. 
     The wire  39 , as shown in  FIG. 10( a ) , is loosenably looped on a pulley  40  and is guided using a space S formed by the housing  11 . Therefore, since, even when the loosened wire  39  comes off the pulley  40 , it is guided by the space S, it is prevented from being caught by other portions. 
       FIG. 11  shows a state just after the plunger  32  moves further from the state of  FIG. 9  and reaches the bumper  41  (just after the nail driving operation is ended). As shown in  FIG. 11 , just after the plunger  32  reaches the bumper  41 , the balancer  36  has not reached the balancer stopper  38  but it is caused to move on due to the biasing force of the balancer biasing member  37 . That is, since the moving speed of the plunger  32  is set faster than the moving speed of the balancer  36 , after the plunger  32  reaches the bumper  41 , the balancer  36  reaches the balancer stopper  38 . When the balancer  36  reaches the balancer stopper  38 , the plunger unit  30  returns to the state of  FIG. 7 . 
     In this embodiment, since there is set a time lag between the stop timing of the plunger  32  and the stop timing of the balancer  36  in this manner, the impact absorption by the balancer  36  and balancer biasing member  37  (generation of the biasing reaction P 3  of the balancer biasing member) is allowed to continue until the completion of the nail driving operation. Also, although a force is applied in the reaction direction due to impacts caused by the balancer  36  colliding with the balancer stopper  38 , the generating timing of this reaction is set after completion of the nail driving operation. 
     In accordance with the above embodiment, a driving tool may include: a driver  31  provided to be slidable toward a nozzle  16  formed in a leading end of the tool  10  and adapted to drive out a fastener from the nozzle  16 ; a balancer  36  provided to be slidable with respect to a housing  11  of the tool  10 ; and a balancer biasing member  37  adapted to bias the balancer  36  in a direction away from the nozzle  16 . The balancer  36  may be adapted to move in the direction away from the nozzle  16  by a biasing force of the balancer biasing member  37 , in accordance with a sliding movement of the driver  31  toward the nozzle  16 . 
     According to this structure, in the driving time, although there is applied a force to the driving tool  10  in a direction away from the workpiece, at the same time, due to the biasing reaction of the balancer biasing member  37  applied to the balancer  36 , there is applied a force in a direction to press the driving tool  10  against the workpiece. That is, “the force applied to the driving tool  10  in the direction away from the workpiece” and “the force applied in the direction to press the driving tool  10  against the workpiece” cancel each other, thereby being able to absorb the reaction on driving. Therefore, since a sufficient driving force can be obtained with a small pressing force against the workpiece, the fatigue of an operation can be reduced. Also, it is hard to raise a problem that the driver  31  can be caused to come off the nail due to the reaction and thus can damage the workpiece. 
     The balancer biasing member  37  may include a spring mechanism which is adapted to accumulate the biasing force when the driver  31  moves in the direction away from the nozzle  16 . 
     According to this structure, the spring force thereof can generate the “force pressing the tool toward the workpiece”. 
     The balancer  36  may be structured to be pulled toward the nozzle  16  through a string-shaped member  39  when the driver  31  moves in the direction away from the nozzle  16 . 
     According to this structure, it is possible to physically link the balancer  36  with the driver  31  and thus operate the balancer  36  to the driving operation. 
     The balancer  36  may slide parallel to the driver  31 . 
     According to this structure, since “the force applied in the direction away from the workpiece” and “the pressing force applied toward the workpiece” are parallel and opposite in direction, the reaction on driving can be absorbed highly efficiently. 
     The driving tool may further include: a plunger  32  to which the driver  31  is connected; a plunger biasing member  33  adapted to bias the plunger  32  toward the nozzle  16 ; a drive mechanism  20  adapted to drive the plunger  32  in the direction away from the nozzle  16  against a biasing force of the plunger biasing member  33  and to release the plunger  32  located in a position away from the nozzle  16  so that the driver  31  moves toward the nozzle  16  by the biasing force of the plunger biasing member  33  and drives the fastener; a string-shaped member  39  that connects the balancer  36  and the plunger  32  to each other; and a direction changing portion  40  adapted to change a direction of a force applied to the string-shaped member  39 . The balancer  36  may be adapted to be pulled by the string-shaped member  39  and to move toward the nozzle  16  in accordance with a movement of the plunger  32  in the direction away from the nozzle  16 , and the balancer  36  may be also adapted to move in the direction away from the nozzle  16  by the biasing force of the balancer biasing member  37  in accordance with a movement of the plunger  32  toward the nozzle  16  when the plunger  32  is released. 
     According to this structure, the absorbing mechanism can absorb such reaction effectively. 
     The string-shaped member  39  (wire  39 ) may be loosenably looped on the direction changing portion  40  (pulley  40 ). 
     According to this structure, the balancer  36  will not be pulled by the plunger  32 . Therefore, due to the loosened wire  39 , the balancer  36  is released from the plunger  32  (wire  39 ) and is thereby allowed to operate independently. Thus, the balancer  36  can be biased by the biasing force of the balancer biasing member  37  without being obstructed by the plunger  32  (wire  39 ). The reaction to this biasing force generates a force to press the driving tool  10  toward the workpiece to thereby be able to absorb the reaction on driving. 
     The balancer  36  may be provided so as to be slidable within a pipe  35  (balancer guide  35 , cylindrical member  35 ) which is provided parallel to the nail drive-out direction. On both sides of the pipe  35 , there may be provided plunger guides  34  respectively for guiding the sliding movement of the plunger  32 . 
     According to this structure, since the balancer  36  can be disposed inside the pipe  35  and the plunger  32  can be disposed outside the pipe  35 , the plunger unit  30  with a reaction absorbing mechanism can be made compact, its manufacturing cost can be reduced and the size of a product can also be reduced. 
     The plunger unit  30  may be fixed within the housing  11  in such a manner that the driver  31  is most distant from the grip  13 . That is, the balancer  36  may be disposed nearer to the grip  13  than the driver  31 . 
     According to this structure, since the driver  31  can be situated as near as possible to the counter-grip- 13  side, it is not necessary to provide an extra projection on the counter-grip- 13  side. No provision of a projection on the counter-grip- 13  side makes it possible to use the nose portion  15  as near as possible to the wall surface. Therefore, for example, the plunger unit  30  can be applied to a finishing driving tool which is required to be able to drive a nail into an edge. 
     The balancer  36  may be adapted to continue its movement, even after the nail driving operation by the driver  31  is completed. 
     According to this structure, since the ending timing of the reaction absorption by the balancer  36  can be set later than the completion of the nail driving operation by the driver  31 , the reaction absorbing mechanism can be positively operated up to the completion of the nail driving operation. 
     As shown in  FIG. 14 , when fixing the plunger unit  30  to the housing  11 , a vibration isolator  50  may also be interposed between the plunger unit  30  and housing  11 . The vibration isolator  50  may be made of resilient material such as rubber or urethane. 
     Specifically, as shown in  FIGS. 14( a ) and 14( b ) , the vibration isolator  50  can be provided, for example, between the plunger guides  34  and housing  11  or on a contact portion between the plunger unit  30  and the housing  11  at an opposite side of the nozzle  16 . 
     Provision of such vibration isolator  50  can restrict the vibrations of the plunger unit  30  in operation (such as the vibrations of the plunger biasing member  33  and balancer biasing member  37 , vibrations to be generated due to the sliding movements of the plunger  32  and balancer  36 , and vibrations to be generated due to the collision of the plunger  32  and bumper  41 ). Thus, noises to be generated when driving a nail can be reduced. 
     Here, in the above embodiment, although description has been given of an example using a spring drive type nailing machine to be driven by a spring force, the invention is not limited to this but it can also be applied a tool to be driven by other drive source such as compressed air, electricity or the like. 
     In the above embodiment, although the compression spring is used as the balancer biasing member  37 , this is not limitative but a tensile spring may also be used. And, other biasing means than the spring may also be used provided that it can generate a reaction. For example, an elastic member other than a spring may be used, electric or magnetic means may be used, or biasing means using hydraulic pressure or the like may be used. 
     In the above embodiment, although the balancer  36  is structured to slide parallel to the driver  31 , this is not limitative but it may also be structured to slide with a certain angle relative to the sliding direction of the driver  31 . 
     In the above embodiment, although the moving speed of the plunger  32  is set faster than the moving speed of the balancer  36 , this is not limitative. The moving speed of the plunger  32  and the moving speed of the balancer  36  may also be set equal, or the moving speed of the plunger  32  may be set slower than the moving speed of the balancer  36 . 
     In the above embodiment, although, in the driving operation, the plunger  32  and balancer  36  start to move simultaneously, this is not limitative. For example, by loosening the wire  39  in a state where the plunger  32  exists at its top dead center position, the movement of the balancer  36  can be set later than the movement of the plunger  32 . 
     In the above embodiment, although the balancer  36  and plunger  32  are connected by the wire  39 , this is not limitative. For example, the balancer  36  and plunger  32  may also be connected by a belt. 
     In the above embodiment, although the plunger unit  30  is disposed within the housing  11 , this is not limitative. For example, as shown in  FIG. 15 , the balancer  36  may also be disposed outside the housing  11 . Also, the whole plunger unit  30  may be disposed outside the housing  11 . In this case, the whole plunger unit  30  may also be covered with other case than the housing  11 . 
     In the above embodiment, although the compression spring is used as the balancer biasing member  37 , this is not limitative. For example, as shown in  FIG. 16 , a tensile spring may also be used as the balancer biasing member  37 . Also, as shown in  FIG. 17 , a magnetic spring (a member in which two mutually repelling magnets are disposed opposed to each other) may also be used as the balancer biasing member  37 . 
     In the above embodiment, although the wire  39  is used as the string-shaped member, this is not limitative. For example, a belt, a strip cloth, a string or a cord may also be used. 
     In the above embodiment, although the balancer  36  is structured to slide inside the pipe  35 , this is not limitative. For example, as shown in  FIG. 18 , the balancer  36  may also be structured to slide outside the pipe  35 . In this case, as the drive mechanism  20 , there may be provided, for example, such a plunger hoisting mechanism  42  as shown in  FIG. 18 . That is, by operating the plunger hoisting mechanism  42  using a motor, a plunger hoisting wire  43  may be hoisted to thereby push up the plunger  32  against the biasing force of the plunger as biasing member  33 . 
     In the above embodiment, although the cylindrical pipe  35  is used as a balancer guide for guiding the balancer  36 , this is not limitative. For example, as shown in  FIG. 19 , there may also be used a balancer guide  35  shaped to be able to guide the balancer  36  while sandwiching it from both sides at two or more points. 
     Here, in the example of  FIG. 19 , although the balancer guide  35  has a substantially arc-like shape following the outer periphery of the balancer  36 , the range containing the sandwiching contact points may be reduced in size and thus the balancer may have a rectangular shape instead of the arc-like shape. 
     In the above embodiment, although the pulley  40  is used as the direction changing portion, this is not limitative. For example, a string-shaped member may be simply slid along the edge portion of a given member, whereby such edge portion may be used as the direction changing portion. 
     In the above embodiment, although the plunger guides  34  for guiding the sliding movement of the plunger  32  are disposed on both sides of the cylindrical portion (pipe  35 ), this is not limitative. For example, as shown in  FIG. 20 , a plunger guide  34  for guiding the sliding movement of the plunger  32  may also be disposed on only one side of the cylindrical portion (pipe  35 ). Or, as many as possible plunger guides may be provided on the periphery of the cylindrical portion (pipe  35 ) to thereby enhance the guide performance. 
     As shown in  FIG. 21 , a flywheel mechanism may also be used to absorb the reaction. That is, as shown in  FIG. 21 , there is provided a flywheel  44  which rotates in a clockwise direction in the vicinity of the central portion of the main body of the driving tool  10 . And, as shown in  FIG. 21 , when, simultaneously with the driving operation, the flywheel  44  is rotated in a direction where its front side (driver  31  side) is raised, due to the reaction thereof, the main body of the driving tool  10  receives a rotation force in the opposite direction (a direction where its front side is lowered). Therefore, this rotation force and the reaction on driving cancel the floating force of the main body of the driving tool  10 , thereby being able to reduce the reaction on driving. 
     The flywheel  44  may be adapted to rotate such that the rotational movement of the flywheel  44  is independent from the straight-going movement of the driver  31 . In contrast, the flywheel  44  may be rotated in linking with the driver  31 . For example, using a rack belt or a wire, the straight-going movement of the driver  31  may be converted to the rotational movement of the flywheel  44 , whereby the flywheel  44  may be rotated in linking with the driving operation of the driver  31 . Also, as the rotation center of the flywheel  44  becomes nearer to the center of gravity of the main body of the driving tool  10 , the flywheel rotates nearer around the center of gravity, thereby being able to absorb the reaction more effectively. Therefore, preferably, the rotation center of the flywheel  44  may be set as near as possible to the center of gravity of the main body of the driving tool  10 . 
     DESCRIPTION OF REFERENCE NUMERALS AND SIGNS 
     
         
           10 : Driving tool 
           11 : Housing 
           12 : Magazine 
           13 : Grip 
           14 : Trigger 
           15 : Nose portion 
           16 : Nozzle 
           17 : Motor 
           20 : Drive mechanism 
           21 : Torque gear plate 
           22 : First torque gear 
           22   a : Torque roller 
           23 : Second torque gear 
           23   a : Torque roller 
           30 : Plunger unit 
           31 : Driver 
           32 : Plunger 
           32   a : Guide roller 
           32   b : Driver connecting portion 
           32   c : First engaging portion 
           32   d : Second engaging portion 
           32   e : Pipe hole 
           33 : Plunger biasing member 
           34 : Plunger guide 
           34   a : Rail portion 
           35 : Pipe (balancer guide) 
           36 : Balancer 
           37 : Balancer biasing member 
           38 : Balancer stopper 
           39 : Wire (string-shaped member) 
           40 : Pulley (direction changing portion) 
           41 : Bumper 
           42 : Plunger hoisting mechanism 
           43 : Plunger hoisting wire 
           44 : Flywheel 
           50 : Vibration isolator 
         S: Space 
         P 1 : Biasing reaction of plunger biasing member 
         P 2 : Driving reaction 
         P 3 : Biasing reaction of balancer biasing member 
         P 4 : Operator&#39;s pressing load