Patent Document

BACKGROUND OF THE INVENTION  
         [0001]    The present invention relates to fastener-driving tools which are typically powered by combustion, pneumatics, electricity or powder. In such tools, a plurality of fasteners are sequentially arranged in a magazine and are urged by a biased follower toward a driving end of the magazine where the fasteners are each pushed into a nosepiece. Once in the nosepiece, the fasteners are driven into a workpiece by a reciprocating driver blade.  
           [0002]    A design criterion of most such tools is that the driving blade should be immobilized when the magazine is empty of fasteners. So-called “dry firing” can damage the workpiece or the tool itself. Indicator mechanisms are known in such tools to indicate to the user when the magazine is empty or almost empty, so that the magazine can be refilled prior to a dry firing condition. In some of these known mechanisms, the driver blade is locked when the magazine is empty to prevent dry firing.  
           [0003]    The issue of prevention of dry firing is particularly challenging when the fasteners are finish nails, which typically are provided in stamped strips. The problems associated with driving such fasteners are described in commonly-assigned U.S. Pat. No. 6,176,412 which is incorporated by reference. Each fastener is relatively thin, and as the fasteners become smaller, they also become thinner. This reduced thickness results in a relatively small increment of movement of the follower upon the driving of each fastener. Thus, it is difficult to design a tool to precisely monitor a fixed number of remaining fasteners to indicate when the magazine needs refilling. This problem is exacerbated by the fact that a given fastener-driving tool is often designed to accommodate a variety of fastener sizes. If, for example, the tool is designed so that a visual, audible or tactile warning is generated upon there being only ten fasteners left in the magazine, the location of the end of the particular strip of fasteners will vary with the size of the fastener. When very thin fasteners are used, such as small finish nails, the combined length of the ten fasteners may be insufficient to reliably enable a warning system to warn the user in time to prevent dry firing.  
           [0004]    Thus, it is a first object of the present invention to provide an improved lockout mechanism for a fastener-driving tool which prevents dry firing for a variety of fastener sizes.  
           [0005]    Another object of the present invention is to provide an improved lockout mechanism which triggers the lockout function through a mechanical magnification of the significance of a single fastener thickness.  
           [0006]    Still another object of the present invention is to provide an improved lockout mechanism which prevents dry firing without requiring additional parts and assembly to the existing tool.  
         BRIEF SUMMARY OF THE INVENTION  
         [0007]    The above-listed objects are met or exceeded by the present lockout mechanism, which features a bypass structure in a fixed position on the magazine near the driver end of the magazine adjacent the nosepiece. Once the number of fasteners in the magazine is reduced so that the follower reaches the bypass structure, the follower becomes disengaged from the remaining fasteners, and moves toward the nosepiece to lock the tool and prevent firing.  
           [0008]    More specifically, the present invention provides a lockout mechanism for a fastener-driving tool having a magazine for storing and sequentially urging fasteners toward a nosepiece through which a driver blade impacts and drives the fasteners into a workpiece. The lockout mechanism is configured for preventing the firing of the fastener-driving tool when the magazine is empty or nearly empty of fasteners. A fastener track is defined in the magazine for the passage of the fasteners toward the nosepiece. A biased follower urges the fasteners in the fastener track toward the nosepiece. The fastener track has a bypass portion dimensioned for receiving the follower, whereby upon reaching the bypass portion, the follower becomes disengaged from the fasteners and moves into engagement with the nosepiece for preventing operation of the tool. The bypass portion is located near a magazine driving end to indicate when the magazine is empty or nearly empty. 
       
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS  
       [0009]    [0009]FIG. 1 is a rear perspective elevation of a fastener tool of the type which is suitable for use with the present invention;  
         [0010]    [0010]FIG. 2 is a reverse side elevational view of the tool shown in FIG. 1 with portions omitted for clarity;  
         [0011]    [0011]FIG. 3 is an enlarged fragmentary elevational view of the tool of FIG. 1;  
         [0012]    [0012]FIG. 4 is an enlarged fragmentary elevational view of the tool of FIG. 2;  
         [0013]    [0013]FIG. 5 is a reverse perspective elevation of the follower shown in FIG. 3; and  
         [0014]    [0014]FIG. 6 is a section taken along the line  6 - 6  of FIG. 1 and in the direction indicated generally. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0015]    Referring now to FIGS. 1 and 2, a fastener-driving tool suitable for use with the present lockout mechanism is generally designated  10 . While the tool  10  is depicted as a pneumatic tool, it is contemplated that the present mechanism may be utilized with pneumatic, combustion, powder or electric-powered fastener tools. The tool  10  includes a housing  12  enclosing a fastener driving portion  14  which includes a reciprocating driver blade (not shown) traveling in a track (not shown) ending in a nosepiece  16 . As is typical in such tools, the nosepiece  16  includes a workpiece contact element  18  which reciprocates relative to the nosepiece, and moves upwards relative to the nosepiece to enable the firing of the tool. This operation is the same regardless of whether the tool  10  is pneumatic, combustion or powder activated.  
         [0016]    A magazine  20  has a feed end  22  and a driving end  24 , the latter closer to, and connected to the nosepiece  16  for feeding fasteners  26  (best seen in FIG. 2) contained within the magazine toward the driving blade track. The fasteners  26  are inserted into the magazine  20  at the opposite feed end  22  through a slot  27  as is well known in the art. A handle  28  is connected to the housing between the fastener driving portion  14  and the feed end  22  of the magazine  20 . In some embodiments, the handle  28 , the magazine  20  and the fastener driving portion  14  of the housing  12  are integrally formed. It is also contemplated to have the handle  28  and the fastener driving portion  14  integrally formed, with the magazine  20  a separate component. In the preferred embodiment, an endcap  29  is provided to assist the fastening of the handle  28  to the magazine  20 . In addition, since the tool  10  is depicted as a pneumatic tool, the endcap  29  houses an air inlet  30 .  
         [0017]    A depth of drive mechanism  31  (best seen in FIG. 2) is provided for adjusting the linear displacement of the workpiece contact element  18  to allow for fasteners of varying lengths, and also provides the capability of partially driving certain fasteners into the workpiece. A trigger  32  is mounted to an underside of the handle  28  for initiating the fastener driving process.  
         [0018]    Referring again to the magazine  20 , a fastener track  34  is defined for enabling the passage of the fasteners  26  toward the nosepiece  16 . The fastener track  34  is partially defined by each of the halves  36 ,  38  of the magazine. The first magazine half  36  is shown in FIG. 1 as the left side of the tool  10  as it is held by a right-handed user, and features an elongate follower track  40  running almost the full length of the magazine. In FIG. 2, an inside surface of the magazine half  36  is depicted. In the preferred embodiment, the follower track  40  is an elongate opening formed in one of the magazine halves  36 ,  38  and is adjacent the fastener track  34 .  
         [0019]    Referring now to FIGS.  3 - 6 , the present lockout assembly, generally designated  42 , includes a biased follower  44  for contacting and urging the fasteners  26  in the fastener track  34  toward the nosepiece  16 . The follower  44  includes a follower core  46  secured to a follower handle  48 , such as by a fastener  50 , chemical adhesives, ultrasonic welding or other known fastening technology. The follower core  46  is preferably dimensioned to slidably engage the follower track  40 .  
         [0020]    A negator spring  52  is also part of the assembly  42  and is connected to the follower  44  to provide the biasing force for urging the follower  44  along the follower track  40  toward the nosepiece  16 . As is well known in the art, one end of the negator spring  52  is connected to the magazine  20 . A gripping loop  54  is provided in the follower handle  48  for facilitating the pulling of the follower  44  toward the feed end  22 . A shoulder or step  56  is formed in the follower track  40  for holding the follower  44  in place while fasteners  26  are inserted into the fastener track  34 . Other equivalent devices known in the art are contemplated for temporarily securing the follower  44  in position in the follower track  40 .  
         [0021]    A follower blade  58  has an angled forward edge  60  oriented to engage the angled fasteners  26  in the fastener track  34 , and is pivotally mounted to the follower core  46  by a pin  62  passing through the core and opposing ears  64  on the follower blade  58 . A follower spring  66  is preferably located in the follower core  46  and is configured to bias the follower blade  58  laterally in the fastener track  34 . The biasing force provided by the follower spring  66  laterally stabilizes the follower  44  stabilized within the fastener track  34 . While the follower spring  66  is preferably a coiled compression spring, it is contemplated that other equivalent springs may be employed, as is well known in the art, so that the follower blade  58  is biased in the manner described above.  
         [0022]    Opposite the forward edge  60  is a release end  68  on the follower blade  58 . Also projecting in the same direction as the follower blade  58  is a lock-out pin  70  (best seen in FIGS. 3 and 5). In the preferred embodiment, the lock-out pin  70  has a length which extends substantially beyond a forward edge of the follower core  46  as well as from the forward blade edge  60 . The lockout pin  70  preferably has sufficient length and rigidity to engage the path of the workpiece contact element  18  and prevent movement of the element upon depression of the tool  10  toward the work piece as is done prior to firing.  
         [0023]    Upon insertion of the fasteners  26 , the gripping loop  54  is pulled back toward the feed end  22  to disengage the follower  44  from the step  56 , and the negator spring  52  then pulls the follower core  46  into contact with the fasteners  26 . Specifically, the forward edge  60  engages the last fastener in the row of fasteners  26 .  
         [0024]    An important feature of the present invention is a bypass portion dimensioned for receiving the follower  44 , whereby upon reaching the bypass portion, the follower becomes disengaged from the fasteners  26  and moves rapidly forward into engagement with the nosepiece  16  for preventing operation of the tool. More specifically, the bypass portion is preferably a window  72  formed in the magazine  20  and positioned far enough from the driving end  24  so that there will be a sufficient number of fasteners remaining in the fastener track  34  to prevent dry firing. While in the preferred embodiment, the window  72  is located in the magazine half  38  which is the opposite half from the location of the follower track  40 , it is contemplated that a different arrangement could be provided so that the window is on the magazine half  36 .  
         [0025]    The window  72  is dimensioned to receive the forward portion of the follower blade  58  as it is pushed laterally out of engagement with the fasteners  26  by the force of the follower spring  66 . However, the window  72  is not large enough that the follower blade  58  is pushed totally out of the magazine  20 .  
         [0026]    Once the follower blade  58  engages the window  72  and is pushed out of engagement with the fasteners  26 , the negator spring  52  pulls the follower  44  rapidly along the fastener track  40  toward the driving end  26 . The forward edge  60  of the follower blade  58  projects sufficiently forward from the follower core  46  to accommodate the remaining fasteners  26  in the magazine  20  between the core and the edge  60  (best seen in FIG. 2). This length can be adjusted depending on the application and/or the size of the fasteners  26  to be used and the design of the particular tool  10 . Thus, despite the fact that relatively thin fasteners are employed in the tool  10 , the present lockout mechanism  42  is configured so that the lockout function is triggered through a mechanical magnification of the significance of a single fastener thickness. In other words, once the follower blade  58  incrementally reaches the window  72 , the thickness of that last fastener results in the locking of the tool through the rapid forward movement of the follower  44 .  
         [0027]    The lock-out pin  70  is long enough so that once the follower  44  has reached the forward end of the follower track  40 , the lock-out pin projects into the path of the workpiece contact element  18  to prevent any upward movement of the element. With the movement of the workpiece contact element  18  thus blocked, the tool cannot be fired, as is well known in the art. In this manner, the user is alerted to the fact that fasteners need to be added to the magazine  20 .  
         [0028]    An additional feature of the present lock-out mechanism  42  is that once the follower  44  is disengaged from the fasteners  26  (best seen in FIG. 4), the presence of the follower in the window  72  provides a visual indication to the user that the tool  10  is disabled and there are a limited number of remaining fasteners such that the magazine  20  needs reloading.  
         [0029]    To reload the magazine  20 , the user presses the release end  68  of the follower blade  58 , which pivots the blade out of engagement with the window  70  and the user then pulls back on the pulling loop  54  to retract the follower  44  toward the feed end  22 . As described above, the follower  44  may be engaged on the step  56  during the loading process.  
         [0030]    While specific embodiments of the lockout mechanism for a fastener driving tool of the present invention have been shown and described, it will be appreciated by those skilled in the art that changes and modifications may be made thereto without departing from the invention in its broader aspects and as set forth in the following claims.

Technology Category: b