Abstract:
A device for impacting a fastener in one embodiment includes a drive channel, a cylinder opening at an end portion to the drive channel, a microcellular polyurethane elastomer (MPE) bumper fixedly positioned at the end portion of the cylinder, the MPE bumper including a drive bore extending therethrough and aligned with the drive channel, and an outer wall defining a plurality of grooves extending radially about the MPE bumper, and a drive mechanism including a drive blade aligned with the drive bore.

Description:
FIELD OF THE INVENTION 
     This invention relates to the field of devices used to drive fasteners into work pieces and particularly to a device for impacting fasteners into work pieces. 
     BACKGROUND 
     Fasteners such as nails and staples are commonly used in projects ranging from crafts to building construction. While manually driving such fasteners into a work piece is effective, a user may quickly become fatigued when involved in projects requiring a large number of fasteners and/or large fasteners. Moreover, proper driving of larger fasteners into a work piece frequently requires more than a single impact from a manual tool. 
     In response to the shortcomings of manual driving tools, power-assisted devices for driving fasteners into wood and other materials have been developed. Contractors and homeowners commonly use such devices for driving fasteners ranging from brad nails used in small projects to common nails which are used in framing and other construction projects. Compressed air has been traditionally used to provide power for the power-assisted devices. Specifically, a source of compressed air is used to actuate a piston assembly which impacts a nail into the work-piece. 
     The energy stored within the piston assembly is typically more than the amount of energy required to drive a nail or other fastener into a work piece. Accordingly, as the piston assembly reaches the end of a full stroke, a substantial amount of energy remains in the moving components of the piston assembly. A bumper is commonly located at the end of the piston assembly to arrest the moving components and to absorb the energy stored therein. Nitrile rubber is commonly used to fabricate such bumpers. 
     Nitrile rubber bumpers are very effective at absorbing the kinetic energy from the piston assembly. The heavy shock loads to which the bumper is subjected, however, ultimately results in wear and eventual disintegration of the bumper. Accordingly, the bumper component is prone to frequent failure and is one of the most frequently serviced components of a pneumatic nailer. A typical service life of a nitrile rubber bumper is on the order of 150,000 to 250,000 firings. 
     What is needed is a device incorporating an element which can be used to absorb kinetic energy from a drive mechanism. What is further needed is a device incorporating an element which is simple, reliable, lightweight, and compact. A further need exists for a device that incorporates a energy absorbing element that has a long useful lifetime. 
     SUMMARY 
     In accordance with one embodiment, there is provided a device for impacting a fastener which includes a drive channel, a cylinder opening at an end portion to the drive channel, a microcellular polyurethane elastomer (MPE) bumper fixedly positioned at the end portion of the cylinder, the MPE bumper including a drive bore extending therethrough and aligned with the drive channel, and an outer wall defining a plurality of grooves extending radially about the MPE bumper, and a drive mechanism including a drive blade aligned with the drive bore. 
     In accordance with another embodiment, there is provided a device for impacting a fastener including a drive channel, a cylinder including a first end portion in communication with the drive channel, a second end portion spaced apart from the first end portion, and a cylinder wall extending between the first end portion and the second end portion, a microcellular polyurethane elastomer (MPE) bumper fixedly positioned at the first end portion of the cylinder, the MPE bumper including a drive bore extending axially therethrough and aligned with the drive channel, and an outer wall extending radially about the MPE bumper, the outer wall spaced apart from the cylinder wall about the circumference of the cylinder, and a drive mechanism including a drive blade aligned with the drive bore. 
     In accordance with a further embodiment, a device for impacting a fastener includes a drive channel, a cylinder including a first end portion in communication with the drive channel, a second end portion spaced apart from the first end portion, and a cylinder wall extending between the first end portion and the second end portion, a microcellular polyurethane elastomer (MPE) bumper fixedly positioned at the first end portion of the cylinder, a drive bore extending axially from an upper surface of the MPE bumper to a lower surface of the MPE bumper and aligned with the drive channel, a throat portion within the drive bore, a first conical portion extending upwardly and outwardly from the throat portion toward the upper surface of the MPE bumper, and a drive mechanism including a drive blade aligned with the drive bore and configured to impact the upper surface of the MPE bumper. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  depicts a front perspective view of a fastener impacting device in accordance with principles of the present invention; 
         FIG. 2  depicts a partial simplified side cross sectional view of the drive section of the fastener impacting device of  FIG. 1  with a microcellular polyurethane elastomer bumper fixed at one end of a cylinder and including an extension area spaced apart from the cylinder wall by a gap; 
         FIG. 3  depicts a top perspective view of the bumper of the device of  FIG. 2 ; 
         FIG. 4  depicts a bottom plan view of the bumper of the device of  FIG. 2 ; 
         FIG. 5  depicts a cross sectional view of the bumper of the device of  FIG. 2  showing vents, flutes and grooves formed in the bumper for cooling and controlled deformation of the bumper; 
         FIG. 6  depicts a partial simplified side cross sectional view of the drive section of the fastener impacting device of  FIG. 1  after the device has been fired and the piston has contacted the microcellular polyurethane elastomer bumper but before deformation of the bumper; and 
         FIG. 7  depicts a partial simplified side cross sectional view of the drive section of the fastener impacting device of  FIG. 1  after the microcellular polyurethane elastomer bumper has been deformed showing a gap remaining between the bumper and the cylinder wall and between the bumper and the drive mechanism. 
     
    
    
     DESCRIPTION 
     For the purposes of promoting an understanding of the principles of the invention, reference will now be made to the embodiments illustrated in the drawings and described in the following written specification. It is understood that no limitation to the scope of the invention is thereby intended. It is further understood that the present invention includes any alterations and modifications to the illustrated embodiments and includes further applications of the principles of the invention as would normally occur to one skilled in the art to which this invention pertains. 
       FIG. 1  depicts a fastener impacting device  100  including a housing  102  and a fastener cartridge  104 . The housing  102  defines a handle portion  106 , an air receptacle portion  108  and a drive section  110 . The fastener cartridge  104  in this embodiment is spring biased to force fasteners, such as nails or staples, serially one after the other, into a loaded position adjacent the drive section  110 . A trigger  112  extends outwardly from the housing  102  and controls the supply of compressed air which is provided from a source of compressed air through an air supply hose  114 . 
     Referring now to  FIG. 2 , which is a simplified depiction of the internal components of the drive section  110 , a piston  120  is located within a cylinder  122 . A drive blade  124  is located at one end of the piston  120  and aligned with a drive channel  126  into which a fastener to be driven is forced by the fastener cartridge  104 . A bumper  128  is positioned at the end portion  130  of the cylinder  122  which opens to the drive channel  126 . 
     The bumper  128 , shown in additional detail in  FIGS. 3-5 , includes a flange  140 , a number of vents  142 , and an extension area  144 . A drive bore  146  extends completely through the bumper  128 . An inner lip  150  is located between an outer passage  152  and a lower passage  154  in each of the vents  142 . Each lower passage  154  communicates with an upwardly extending flute  156  within the drive bore  146 . 
     A portion of the upwardly extending flutes  156  extend in the drive bore  146  along a cylindrical throat  158  which exhibits a uniform diameter. Above the throat  158 , an upper conically shaped portion  160  of the drive bore  146  extends outwardly and upwardly to an upper surface  162 . Below the throat  158 , a lower conically shaped portion  164  of the drive bore  146  extends outwardly and downwardly to a lower surface  166 . 
     An outer surface  170  of the extension area  144  extends between the upper surface  162  and the flange  140 . Two grooves  172  and  174  extend radially about the outer surface  170 . The groove  172  includes opposing walls  176  and  178  which are set at a right angle (90°) to each other. The groove  174  is similarly shaped. 
     The bumper  128  in this embodiment is constructed using a microcellular polyurethane elastomer (MPE). MPEs form a material with numerous randomly oriented air chambers. Some of the air chambers are closed and some are linked. Additionally, the linked air chambers have varying degrees of communication between the chambers and the orientation of the linked chambers varies. Accordingly, when the MPE structure is compressed, air in the chambers is compressed. As the air is compressed, some of the air remains within various chambers, some of the air migrates between other chambers and some of the air is expelled from the structure. One such MPE is MH 24-65, commercially available from Elastogran GmbH under the trade name CELLASTO®. 
     The manner in which the bumper  128  is deformed when subjected to an impact is a function of the particular geometry of the bumper  128 , the cylinder  122 , and the piston  120 . With respect to the cylinder  122 , the end portion  130  has a diameter that is closely matched with the diameter of the flange  140 . Accordingly, a lip  180 , shown in  FIG. 2 , which extends about the end portion  130  retains the bumper  128  within the end portion  130  of the cylinder  122 . The diameter of the extension area  144 , however, has a diameter that is less than the diameter of the cylinder  122  resulting in a gap  182  between the outer surface  170  of the bumper  128  and the cylinder  122 . 
     The relative diameters of the extension area  144  and the cylinder  122 , and thus the size of the gap  182 , is selected to reduce or eliminate contact between the extension area  144  and the cylinder  122  as the bumper  128  is compressed. Contact between the extension area  144  and the cylinder  122  can decrease the working life of the bumper  128 . Additionally, the radially formed grooves  172  and  174 , the shape of the drive bore  146 , and the vents  142  guide the manner in which the bumper  128  deforms as described below. 
     With initial reference to  FIGS. 2-5 , operation of the fastener impacting device  100  begins with the fastener impacting device in the configuration of  FIG. 2 . In  FIG. 2 , the piston  120  is at the rearward portion of the cylinder  122  and a fastener (not shown) is positioned in the drive channel  126 . In this embodiment, the drive blade  124  is configured to extend into the drive bore  146 . In other embodiments, the drive blade  124  may be spaced apart, but aligned with, the drive bore  146 . Additionally, the drive bore  146  and the drive blade  124  are aligned with the drive channel  126 . 
     When the fastener impacting device  100  is positioned against a work piece, the operator manipulates the trigger  112  resulting in venting of compressed air into the cylinder  122  at a location behind the piston  120  (to the right of the piston  120  as viewed in  FIG. 2 ). The compressed air forces the piston  120  to move in the direction of the arrow  184  of  FIG. 2  toward the end portion  130  of the cylinder  122 . When the piston  120  reaches the position shown in  FIG. 6 , the fastener (not shown) has been driven by the drive blade  124  and the kinetic energy remaining in the piston  120  may be transferred to the bumper  128 . 
     In  FIG. 6 , the piston  120  is in contact with the upper surface  162  of the bumper  128 . The throat  158  has a diameter that is larger than the base  186  of the drive blade  124 . Thus, the bumper  128  does not contact the drive blade base  186 . Continued travel of the piston  120  in the direction of the end portion  130  of the cylinder  122  begins compression of the bumper  128 . Air forced out of the bumper  128  is vented through vent holes  188 . The vented air removes some of the heat that is generated by the deformation of the bumper  128 . 
     The amount of MPE to be compressed in the bumper  128  has been selected such that when the piston  120  reaches the position shown in  FIG. 7 , substantially all of the kinetic energy initially in the piston  120  has been transferred to either the driven fastener or the bumper  128 . Additionally, as shown in  FIG. 7 , the size of the throat  158  along with the taper of the upper portion  160  and lower portion  164  of the drive bore  146  has guided deformation of the bumper  128  such that the bumper  128  is not in contact with, or is only slightly in contact with, the drive blade  124  and/or the drive blade base  186 . Likewise, the gap  182  resulting from the difference in diameter of the extension area  144  and the cylinder  122 , along with the sizing and location of the grooves  172  and  174 , have guided deformation of the bumper  128  such that the extension area  144  is not in contact with, or is only slightly in contact with, the cylinder  122 . 
     Once the kinetic energy from the piston  120  has been transferred to the bumper  128 , the piston  120  is returned to the position shown in  FIG. 2 . Movement of the piston  120  away from the bumper  128  allows the resilient characteristic of the bumper  128  to reform into the shape shown in  FIG. 2 . As the bumper  128  reforms, air is provided through the vents  142  to the upwardly extending flutes and the drive bore  146 . Air also flows through the outer passages  152  toward the cylinder  122 . This air, in addition to refilling air chambers within the bumper  128 , removes additional heat from the bumper  128 . The remaining air then passes into the area of the cylinder  122  between the bumper  128  and the piston  120 . 
     One embodiment of a bumper  128  made from MH 24-65 MPE which provides desired kinetic energy transfer and deformation has an overall height of 44 millimeters and includes a flange  140  with a diameter of about 66 millimeters and an extension area  144  with a diameter of 52.6 millimeters. The outer passages  152  and the lower passages  154  have diameters of 4 millimeters and the upwardly extending flutes  156  are 4 millimeters wide, about 6.2 millimeters deep, and extend upwardly along the drive bore  140  to a height of 25 millimeters above the lower surface  166 . 
     The throat  158  has a diameter of 20.1 millimeters and the upper conically shaped portion  160  has a height of 18.1 millimeters and is formed with a cone angle of 20° about a longitudinal axis  190  (see  FIG. 5 ). The lower conically shaped portion  164  has a height of 13.1 millimeters and is formed with a cone angle of 20° about the longitudinal axis  190 . The grooves  172  and  174  in this embodiment are about 2 millimeters deep and, at their widest point, are 6.9 millimeters wide. The outer surface  170  extends between the grooves  172  and  174  for a distance of 3.2 millimeters. These dimensions may be modified for different applications or design requirements. 
     While the invention has been illustrated and described in detail in the drawings and foregoing description, the same should be considered as illustrative and not restrictive in character. It is understood that only the preferred embodiments have been presented and that all changes, modifications and further applications that come within the spirit of the invention are desired to be protected.