Abstract:
A fastener driving tool capable of driving a fastener in a direction orthogonal to a surface of a workpiece. A fastener driving operation is performed upon manipulation of a trigger and pressing a push lever against a surface of the workpiece. The push lever is slidably movable along a nose, and is biased by a spring in a fastener driving direction. The spring is positioned offset from a center of a fastener driving tool. The push lever is slidable in a sliding axis inclined by an angle Δθ relative to the center of the fastener driving tool. The push lever is configured to provide an angle defined between the sliding axis and the surface of the workpiece in a range of more than 90 degrees, i.e., 90 degrees plus Δθ.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The present invention relates to a faster driving tool for driving a fastener such as a nail and a staple into a workpiece. 
         [0002]    A conventional fastener driving tool is shown in  FIG. 7 . The driving tool  101  includes a main housing  102  having a fastener injection portion  126 , and a push lever  127  protruding downwardly from the injection portion  126 . A driver blade (not shown) is reciprocally movably disposed in the main housing  102  for impactingly driving a fastener set in the injection portion  126 . Further, a trigger is provided at the main housing  102  for initiating fastener driving operation. 
         [0003]    The push lever  127  includes an upper section  127 A formed of a metal plate, a lower section  127 B and a adjuster  129  that connects the upper section  127 A to the lower section  127 B. The lower section  127 B has a recumbent U-shape configuration and is formed by bending a metal rod. The adjuster  129  is adapted for adjusting a height of the push lever  127 , i.e., a protruding length of the driver bit from the push lever in order to adjust a driving depth of the fastener. 
         [0004]    The lower section  127 B of the push lever  127  has right and left vertical wall portions  127   a ,  127   b . Right and left guide portions  102   b ,  102   c  are provided at the main housing  102  at a position adjacent to the injection portion  126 . These vertical wall portions  127   a ,  127   b  are vertically movably guided by the right and left guide portions  102   b ,  102   c , respectively. Further, the push lever  127  is urged in a faster driving direction by a spring (not shown) disposed at one lateral side (left side or at a side of the adjuster  129  in  FIG. 7 ) of the push lever  127 . 
         [0005]    Fastener driving operation will be started upon pulling the trigger and pressing the push lever  127  against the workpiece. That is, the fastener such as a nail will be driven by the driver blade into the workpiece. Such arrangement is disclosed in Japanese Patent Application Publication No. H10-286784. 
         [0006]    In such conventional fastener driving tool, a fastener may be driven into the workpiece in an inclined orientation. Therefore, defects in workmanship would be found. 
       SUMMARY 
       [0007]    This and other object of the present invention will be attained by a fastener driving tool including a main housing, a trigger, a driver blade, a push lever, and a biasing member. The main housing has a fastener injection portion. The trigger is supported to the main housing. The driver blade is movable in the main housing and is aligned with a driving center for striking against a fastener set in the fastener injection portion. The push lever is supported to the main housing and is slidably movable on a sliding axis. The push lever has a contact surface in contact with a surface of the workpiece. The biasing member biases the push lever in a faster driving direction and is positioned offset from the driving center. Fastener driving operation is performable upon operation of the trigger and pressing the push lever against the surface of the workpiece. The push lever is configured to provide an angle defined between the sliding axis and the contact surface in a range of more than 90 degrees. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]    In the drawings: 
           [0009]      FIG. 1  is a front view of a fastener driving tool according to an embodiment of the present invention; 
           [0010]      FIG. 2  is a cross-sectional view of the fastener driving tool according to the embodiment and showing a state where a cylinder is seated on a head cap and a piston is at its top dead center position; 
           [0011]      FIG. 3  is a cross-sectional view of the fastener driving tool according to the embodiment and showing a state where the cylinder is separated from the head cap and the piston is at its bottom dead center position, and a driver bit protrudes from a push lever by a length D; 
           [0012]      FIG. 4  is a cross-sectional view of the fastener driving tool according to the embodiment and showing a state where the cylinder is again seated on the head cap and the piston is returned to its top dead center position; 
           [0013]      FIG. 5  is a cross-sectional view of the fastener driving tool according to the embodiment and showing a state where the driver bit protrudes from the push lever by a length E; 
           [0014]      FIG. 6  is an enlarged front view of an essential portion of the embodiment and showing a state where the push lever is pressed against a workpiece; 
           [0015]      FIG. 7  is a front view of a conventional fastener driving tool; and 
           [0016]      FIG. 8  is an enlarged front view of an essential portion of a comparative example. 
       
    
    
     DETAILED DESCRIPTION 
       [0017]    A fastener driving tool according to a first embodiment of the present invention will be described with reference to  FIGS. 1 through 6 . A pneumatically operated stapler  1  will be described as the fastener driving tool. 
         [0018]    The stapler  1  has a main housing  2  whose upper opening is fluid-tightly covered with an exhaust cover  3  with a plurality of bolts  4  (four bolts). As shown in  FIG. 2 , an accumulation chamber S 1  is defined in an interior of the main housing  1  for accumulating a compressed air. The main housing  2  includes a handle portion  2   a , whose free end portion is provided with an air plug (not shown) to which an air hose (not shown) extending from a compressor (not shown) is connected. 
         [0019]    A magazine  5  is attached to the main housing  2  for accommodating a plurality of staples (generally u-shaped fasteners). Further, a trigger valve  8  is provided at the main housing  2 . The trigger valve  8  includes a plunger  7  vertically movable by the trigger  6 . Incidentally, the expressions “front”, “rear”, “above” and “below” are used throughout the description to define the various parts when the exhaust cover is an uppermost component of the stapler  1 . 
         [0020]    As shown in  FIG. 2 , in the main housing  2 , a cylinder  9  vertically extends and is movable in its axial direction. A piston  10  is reciprocally slidably movably disposed within the cylinder  9 . The piston  10  divides an interior of the cylinder  9  into an upper chamber S 2  ( FIG. 3 ) and a lower chamber S 3  ( FIG. 2 ). A driver blade  11  extends in the lower chamber S 3  and has one end connected to the piston  10 . A piston bumper  12  made from an elastic material such as a rubber is disposed at a bottom end portion within the cylinder  9 . The piston bumper  12  allows the piston  10  to bump thereagainst to absorb kinetic energy of the piston  10 . 
         [0021]    Further, a cylindrical return chamber S 4  is defined by a lower outer peripheral surface of the cylinder  9  and an inner surface of the main housing  2 . A plurality of upper air vent through-holes  14  and lower air vent through-holes  15  are formed in the part of cylinder  9 , the part defining the return chamber S 4 . These through-holes  14  and  15  are arrayed in the circumferential direction of the cylinder  9 . Check-valves  16  are positioned to overlap with the upper air vent through-holes  14  for allowing compressed air to flow only from the upper chamber S 2  to the return chamber S 4 . 
         [0022]    A valve seat member  17  is supported to the exhaust cover  3  by a plurality of bolts  18 , and the valve seat member  17  has a lower outer peripheral end portion covered with a head cap  19 . An air passage  20  is defined at a radial center of the valve seat member  17  and the head cap  19 . An exhaust valve  21  is vertically movably disposed in the valve seat member  17  to selectively open the air passage  20 . An air passage  22  is formed in the valve seat member  17 , and an exhaust hole (not shown) is formed in the exhaust cover  3 . The air passage  20  is in selective fluid communication with an atmosphere through the air passage  22  and the exhaust hole. An exhaust valve chamber S 5  is defined at an upper side of the exhaust valve  21 . The exhaust valve chamber S 5  is in selective fluid communication with the trigger valve  8  through an air passage (not shown). 
         [0023]    Annular partition walls  23 ,  24  and  13  are immovably disposed between an upper outer peripheral surface of the cylinder  9  and the inner surface of the main housing  2 . The partition walls  23  and  24  define a first chamber S 6 , and the partition walls  24  and  13  define a second chamber S 7 . The cylinder  9  has an upper flange portion, and a compression spring  25  is interposed between the flange portion and the partition wall  13  in the second chamber S 7  for biasing the cylinder  9  upward. The first and second chambers S 6 , S 7  are selectively applied with compressed air pressure or atmospheric pressure in accordance with the operation of the trigger  6 . 
         [0024]    A nose  26  providing a fastener injection portion is disposed at a lower end of the main housing  2 . The nose  26  is formed with an injection opening  28  at which each staple fed in the magazine  5  is set. Further, a push lever  27  is disposed slidably movable along the nose  36 . 
         [0025]    The push lever  27  includes an upper segment  27 A made from a metal plate, and a lower segment  27 B provided by bending a metal rod into recumbent U-shape configuration. The upper segment  27 A has an upper end portion connected to a lower end of a plunger  7  of the trigger valve  8 . The lower segment  27 B is adapted to be in surface contact with the workpiece W. An adjuster  29  is disposed at a junction between the upper and lower segments  27 A and  27 B. The adjuster  29  is adapted for adjusting a height of the push lever  27 , i.e., a protruding length of the driver blade  11  from the push lever  27  in order to adjust a driving depth of the staple. More specifically,  FIG. 3  shows a maximum protruding length D of the driver blade  11  from the lower segment  27 B, and  FIG. 5  shows a minimum protruding length E. 
         [0026]    The lower segment  27 B includes left and right walls  27   a ,  27   b  each being vertically slidably movably guided by left and right guide portions  2   b  and  2   c  of the nose  26 . A spring  30  is interposed between the lower segment  27 B and the nose  26  for biasing the push lever  27  in a fastener driving direction. The spring  30  is positioned close to the left wall  27   a , i.e., a position between the left wall  27   a  and the nose  26 . During non-operational phase of the driving tool  1 , the lower end face of the lower segment  27 B is positioned below the lower end face of the nose  26 . As shown in  FIG. 6 , a minute gap is formed between the left wall  27   a  and the guide portion  2   b , and another minute gap is formed between the right wall  27   b  and the guide portion  2   c  in order to enhance slidability of the push lever  27 . 
         [0027]    As shown in  FIG. 6 , the push lever  27  is slidably movable in a sliding axis Y 1 , and the lower segment  27 B is configured such that an angle θ defined between the sliding axis Y 1  and a contacting surface X 1  between the workpiece W and the lower segment  27 B is greater than 90 degrees (θ&gt;90°) as viewed from a front side ( FIG. 1 ). More specifically, the spring  30  is positioned in the vicinity of one of the walls of the lower segment  27 B, that is left side wall  27   a , and the left side wall  27   a  is inclined by an angle Δθ with respect to a vertical plane Y 2 . Preferably, the angle Δθ is not more than 5° and therefore, the angle θ is greater than 90° and preferably not more than 95° (90°&lt;θ≦95°) 
         [0028]    Operation of the stapler  1  will be described. The user connects the air hose (not shown) to the air plug (not shown), whereupon a compressed air is delivered from the compressed air source such as a compressor and is filled in the accumulation chamber S 1 . A part of the compressed air will be supplied to the second chamber S 7 , whereas the first chamber S 6  and the exhaust valve chamber S 5  are in communication with the atmosphere. Therefore, as shown in  FIG. 2 , the upper end of the cylinder  9  is seated on the head cap  19  by the compressed air pressure applied to the second chamber S 7  and the biasing force of the spring  25 . As a result, fluid communication between the accumulation chamber S 1  and the upper chamber S 2  in the cylinder  9  is shut off, preventing the compressed air from being flowed from the accumulation chamber S 1  into the upper chamber S 2 . Consequently, the piston  10  and the driver blade  11  are maintained in their top dead center positions. Thus, staple driving operation cannot be performed. In this instance, the exhaust valve  21  is at open phase to allow the air passage  20  to communicate with the atmosphere. 
         [0029]    Then, if the lower section  27 B of the push lever  27  is pressed against the workpiece W as shown in  FIG. 6 , and if the trigger  6  is pulled, the plunger  7  of the trigger valve  8  is moved upward to render the trigger valve  8  ON. Therefore, compressed air in the accumulation chamber S 1  will be supplied into the first chamber S 6  and the exhaust valve chamber S 5 , whereas the second chamber S 7  will be communicated with the atmosphere. Then, the cylinder  9  will be moved downward by the compressed air pressure in the first chamber S 6  against the biasing force of the spring  25  as shown in  FIG. 3 . Thus, the upper end of the cylinder  9  will be separated from the head cap  19 . Consequently, the accumulation chamber S 1  will be communicated with the upper chamber S 2 , so that the compressed air in the accumulation chamber S 1  will be introduced into the upper chamber S 2  through a gap between the upper end of the cylinder  9  and the head cap  19 . Simultaneously, the exhaust valve  21  will be moved downward within the valve seat member  17  by the compressed air pressure supplied into the exhaust valve chamber S 5  to close the air passage  20 . 
         [0030]    By the closure of the air passage  20  by the exhaust valve  21  and by the introduction of compressed air into the upper chamber S 2 , the piston  10  and the driver blade  11  are promptly moved downward toward their bottom dead center within the cylinder  9 . Thus, a staple supplied from the magazine  5  and set at the injection opening  28  of the nose  26  will be subjected to driving by the driver blade  11 . The staple is guided by the injection opening  28  and is driven into the workpiece W. If the piston  10  is moved past the upper air vent through-holes  14  during downward moving stroke, the compressed air in the upper chamber S 2  will be introduced into the return chamber S 4  through the upper air vent through-holes  14  and the check valves  16 , so that compressed air will be accumulated in the return chamber S 4 . Further, if the piston  10  reaches the bottom dead center as shown in  FIG. 3  in the downward movement thereof, the piston  10  bumps against the piston bumper  12  and, the bumper  12  will be elastically deformed. Thus, surplus energy of the piston  10  will be absorbed by the elastic deformation. 
         [0031]    In the depicted embodiment, as described above, the angle θ defined between the sliding axis Y 1  and the contacting surface X 1  is greater than 90 degrees (θ&gt;90°) as viewed from the front side, and preferably, the angle θ is in a range of 90°&lt;θ≦95°. Advantage of this angle will be described with reference to a comparative example shown in  FIG. 8 . 
         [0032]    In the comparative example, the angle defined between the sliding axis Y 1  and the contacting surface X 1  is 90°. Further, similar to the above-described embodiment, the spring  30  for biasing the push lever  127  toward the staple driving direction is not aligned with a center C 1  of the driving tool, but is offset toward the left side wall  127   a  of the lower segment  127 B (toward the adjuster  129 ). With this arrangement, the present inventor has found the following result. 
         [0033]    That is, if the push lever  127  is pressed against the workpiece W and the trigger is pulled for starting driving operation, in  FIG. 8 , upward reaction force F 1  is exerted on the push lever  127  from the workpiece W at a driving center C 1  of the driving tool, whereas downward force F 2  is exerted on the push lever  127  by the spring  30 . Therefore, a moment of a couple will be exerted on the push lever  127 , since the force F 2  is offset from the driving center C 1  by a length “e”. As described above, minute gaps are provided between the push lever  127  and the guide portions  102   b ,  102   c  in order to smoothen the sliding movement of the push lever  127 . Therefore, if the moment of a couple is generated, the driving center C 1  will be included to C 1 ′ by an angle θ 1 . In other words, the line C 1 ′ is not orthogonal to the surface X 1 . Consequently, a fastener such as a staple will be driven in an inclined orientation in the direction C 1 , degrading workmanship. 
         [0034]    Taking this phenomenon into consideration, in the illustrated embodiment, the angle Δθ is set equal to the angle θ 1 . That is, the angle θ 1  due to the moment of a couple is provisionally envisioned, so that the push lever  27  is inlined by an angle Δθ in order to orient the center axis C 1  of the driving tool in a direction orthogonal to the contacting surface X 1  during staple driving operation. Thus, the staple can be driven into the workpiece in a direction orthogonal to the surface of the workpiece. 
         [0035]    Next, if the trigger  6  is released, or the push lever  27  is moved away from the workpiece W, the plunger  7  restores its original position to render the trigger vale  8  OFF. As a result, compressed air will be supplied into the second chamber S 7  whereas the first chamber S 6  and the exhaust valve chamber S 5  are brought into communication with the atmosphere. Consequently, the cylinder  9  will be moved upward as shown in  FIG. 4  by the compressed air pressure applied to the second chamber S 7  and biasing force of the spring  25 . Thus, the upper end of the cylinder  9  will be seated on the head cap  19  to shut-off fluid communication between the upper chamber S 2  and the accumulation chamber S 1 . Further, the exhaust valve  21  will be moved upward within the valve seat member  17  to open the air passage  20 , so that the air passage  20  will be brought into communication with the atmosphere. 
         [0036]    Then, the compressed air accumulated in the return chamber S 4  will be introduced into the lower chamber S 3  through the lower air vent through-hole  15 , so that the compressed air pressure will be applied to a lower surface of the piston  10  to rapidly move the piston  10  and the driver blade  11  toward their top dead center position. In accordance with this movement, air in the upper chamber S 2  will be discharged to atmosphere through the air passages  20 ,  22  and the exhaust hole (not shown) formed in the exhaust cover  3 . Thus, the piston  10  and the driver blade  11  will be returned to their original positions. 
         [0037]    The above-described operation will be repeatedly performed. Thus, the staples accommodated in the magazine  5  will be successively driven into the workpiece W. 
         [0038]    While the invention has been described in detail with reference to specific embodiment thereof, it would be apparent to those skilled in the art that various changes and modifications may be made therein without departing from the scope of the invention. That is, the present invention is available to an electrically driven fastener driving tool and combustion type fastener driving tool as well as pneumatically operated fastener driving tool. The driving system is not requisite matter. Further, the present invention is also available for other fastener driving tools such as a nail gun.