Patent Publication Number: US-6981630-B2

Title: Cartridge strip advancing mechanism for fastener driving tool

Description:
This application is a Continuation of U.S. application Ser. No. 10/246,261, filed on Sep. 18, 2002, now abandoned which is a Continuation-In-Part of U.S. application Ser. No. 09/689,095, filed on Oct. 12, 2000, now U.S. Pat. No. 6,547,120 and this application claims priority to the Australian Provisional Application 2002951660, filed on Sep. 25, 2002 in the Australian Patent Office. 

   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention is directed to powder actuated tools, and more particularly to a powder actuated fastener driving tool having automatic powder cartridge strip indexing. 
   2. Description of the Related Art 
   Powder actuated fastener setting tools are known generally. U.S. Pat. No. 5,429,291 entitled “Compression Actuated Tool For Driving Fasteners” assigned commonly with the present application, for example, discloses a powder driven tool including a manually operated spring biased indexing lever pivotally mounted thereon for advancing a magazine strip retaining a plurality of powder cartridges therein through a magazine channel of the tool. 
   For many powder actuated tools it is desirable to have a mechanism that indexes a strip of explosive powder cartridges after the tool has been fired so that a fresh cartridge is ready for firing without the operator having to do anything. An example of an indexing mechanism is disclosed in the commonly assigned patent application having the Ser. No. 09/689,095 entitled “Powder Driven Fastener Setting Tool,” the disclosure of which is incorporated herein by reference. The above referenced application teaches the use of a reciprocating sleeve which drives an indexing lever to index a strip of cartridges along a magazine channel. The sleeve reciprocates during firing of the tool, and is returned when an operator pushes the sleeve into its original position. 
   In some applications it may be desirable to make the indexing of the cartridge strip automatic, so that the operator does not have to perform the added step of pushing the reciprocating sleeve back into its original, pre-firing position. However, the indexing of the cartridge strip still must be driven by the motion of some part of the fastener driving tool. One possible part to use to drive the indexing of the cartridge strip is to use the motion of a trigger, wherein the trigger also actuates a firing mechanism of the tool. U.S. Pat. No. 6,272,782 to Dittrich et al. discloses a cartridge advancing mechanism linked to the trigger using connected pivoting levers. 
   A problem that has occurred with tools using pivoting levers has been “dead stop” of the trigger. When the trigger and advancing mechanism are directly linked, such as with connected pivoting levers, the trigger can come to a hard, or dead, stop when the advancing mechanism comes to a stop as it engages with the cartridge strip. Dead stopping can become uncomfortable for an operator due to repetitive use of the tool. 
   Another problem that has been common with advancing mechanism for explosive powder actuated tools is complexity requiring a large number of interconnected parts and moving parts to ensure operation of the advancing mechanism. 
   What is needed is a fastener driving tool which uses the motion of the trigger to drive an automatic indexing of a strip of explosive cartridges, while requiring fewer parts and overcoming the dead stop phenomenon of the prior art. 
   BRIEF SUMMARY OF THE INVENTION 
   In accordance with the present invention, a powder driven fastening tool is provided with a novel and inventive cartridge strip advancing mechanism. The fastening tool comprises a magazine channel for feeding a strip of cartridges to a firing mechanism, a trigger for actuating the firing mechanism, the trigger being movable between a first position and a second position, an advancing lever pivotally coupled to the tool, the advancing lever having a strip engagement portion extending into the magazine channel for indexing the strip, an advance link cammingly engaged with the advancing lever and operationally associated with the trigger, the magazine engagement portion being in a first position in the magazine channel when the trigger is in the first position, and the magazine strip engagement portion being in a second position in the magazine channel when the trigger is in the second position. 
   These and other objects, features and advantages are evident from the following description of an embodiment of the present invention, with reference to the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       FIG. 1  is a partial sectional view of an exemplary powder actuated tool in a first configuration. 
       FIG. 2  is a partial sectional view of the exemplary powder actuated tool in a second configuration. 
       FIG. 3  is a top view of an exemplary magazine strip indexing lever. 
       FIG. 4  is a partial sectional view of the magazine strip indexing lever engaged with a magazine strip. 
       FIG. 5  is a perspective view of an alternative powder actuated tool. 
       FIG. 6  is a perspective view of a firing mechanism and a cartridge strip advancing mechanism of the powder actuated tool. 
       FIG. 7  is as side sectional view of the powder actuated tool. 
       FIG. 8  is a partial side sectional view of the cartridge strip advancing mechanism in a first position. 
       FIG. 9  is a partial side sectional view of the cartridge strip advancing mechanism in a second position. 
       FIG. 10  is a sectional view of the cartridge strip advancing mechanism taken along line  10 — 10  in  FIG. 8 , wherein the advancing mechanism is in the first position. 
       FIG. 11  is a sectional view of the cartridge strip advancing mechanism wherein the advancing mechanism is moving from the first position to the second position. 
       FIG. 12  is a sectional view of the cartridge strip advancing mechanism taken along line  12 — 12  in  FIG. 9 , wherein the advancing mechanism in is the second position. 
       FIG. 13  is a sectional view of the cartridge strip advancing mechanism in the first position, wherein the advancing mechanism has indexed a cartridge strip from the second position to the first position. 
       FIG. 14  is a perspective view of the advancing mechanism shown with a breach block. 
       FIG. 15  is a perspective view of the advancing mechanism shown in an uncocked state of the tool. 
       FIG. 16  is a perspective view of the advancing mechanism shown after an advancing lever has completed its movement during firing of the tool. 
       FIGS. 17A and 17B  are perspective views showing an adjustable connection between the trigger and an advance link of the advancing mechanism in order to provide fine tuning. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Generally, a magazine strip or some other member is incrementally indexed through a channel of a fastening tool by an indexing lever actuated by a lever cam that moves between first and second positions with some other portion of the tool. 
   In the exemplary powder driven fastener setting tool  10  of  FIG. 1 , a magazine strip  11  is fed or indexed along a magazine channel  20  disposed in a pistol-type grip  12  of the tool. The magazine channel  20  extends to and through a firing chamber disposed between a barrel breech end  32  and a breech block  42  of the tool. 
   The magazine strip  11  retains a plurality of spaced apart explosive cartridges  13  that are sequentially positioned in alignment with a cartridge recess in the breech end of the barrel, for accommodation therein during detonation, as the magazine strip is indexed through the magazine channel. 
   In other embodiments, the magazine channel may be configured differently, and more generally it may be any passage, or channel, in the tool through which it is desirable to move, or index, a magazine strip or some other member. 
   In  FIG. 1 , a lever cam  50  is coupled to a compression triggering mechanism of the tool  10 , and more particularly to a spring biased sleeve  60  that reciprocates between first and second positions during operation of the tool. 
   The firing mechanism sleeve is aligned substantially axially with the barrel of the tool and reciprocates along its axis upon compression thereof against the spring bias. 
   Particularly, in  FIG. 2 , a spring  14  disposed between the breech block  42  and the sleeve  60  biases the sleeve to the first position when the spring is relatively expanded. The sleeve is movable to the second position against the spring bias, as illustrated in FIG.  1 , upon application of an axial compression force thereto as is known generally by those having ordinary skill in the art. 
   Alternative exemplary compression triggering mechanisms in powder driven fastener setting tools are known generally and the operation thereof is disclosed more fully, for example, in the referenced U.S. Pat. No. 5,429,291 entitled “Compression Actuated Tool For Driving Fasteners”, the disclosure of which is incorporated herein by reference. 
   In  FIGS. 1 and 2 , the lever cam  50  extends from an integral flange  52  that is coupled, for example by screw thread or other engagement, to the sleeve  60  and particularly to a handle portion  62  thereof. The exemplary handle portion  62  is assembled with the sleeve  60  and abuts a firing pin actuating spring within the sleeve. 
   The exemplary handle portion  62  includes an optional pole connector  64 , to which may be coupled, for example by screw thread or other engagement, an extension pole. 
   Alternatively, the handle portion  62  may be formed integrally with the sleeve  60 , or the handle portion  62  may be formed integrally with the flange  52  and the lever cam  50 . 
   In other embodiments, the handle portion  62  and flange  52  may not be required, for example in embodiments that do not include a firing pin actuating spring. In this embodiment, the lever cam  50  is an integral part of or is coupled directly to the sleeve or to some other member coupled thereto extending axially from the rear end portion of the tool. 
   In still other alternative embodiments, the lever cam  50  may be coupled to some other reciprocating portion of the tool, for example to the barrel thereof. 
   The tool also comprises an indexing lever  70  pivotally coupled thereto, for example by a pivot pin  72  or some other pivoting member or members. The indexing lever generally comprises a magazine engagement portion and a cam follower portion disposed on generally opposite sides of the pivot pin in the exemplary embodiment. 
   The cam follower portion of the indexing lever is cammingly engaged with the lever cam as the lever cam moves between first and second positions in unison with the reciprocating portion of the tool to which it is coupled, thereby pivoting the indexing lever. 
   In  FIGS. 1 and 2 , the lever cam  50  includes a ramped cam slot  56 , and the cam follower portion of the indexing lever  70  includes a lever pin  74  that is disposed in and follows the ramped cam slot  56  as the lever cam  50  moves with the sleeve between the first and second positions. Particularly, the lever pin  74  moves between first and second positions along the ramped cam slot  56  as the lever cam  50  moves between its first and second positions in unison with the reciprocating portion of the tool to which it is coupled. 
   Generally, the magazine engagement portion of the indexing lever extends into the magazine channel where it engages and indexes the magazine strip during movement of the indexing lever toward the firing chamber. 
     FIG. 3  illustrates the exemplary indexing lever  70  having a known ratcheting magazine engagement portion with a spring biased tooth  76  for engaging the magazine strip. In other embodiments, however, other magazine engagement configurations may be employed. 
   The reciprocating action of the lever cam  50  pivots the indexing lever  70  back and forth to locate the magazine engagement portion thereof between first and second positions in the magazine channel of the tool, alternately toward and away from the firing chamber. 
   In  FIG. 2 , when the sleeve  60  is extended by the spring  14 , the magazine strip engagement portion of the indexing lever is positioned toward the firing chamber. And in  FIG. 1 , when the sleeve is depressed or compressed against the bias of the spring  14 , the magazine strip engagement portion is positioned away from the firing chamber. 
     FIG. 4  illustrates the magazine engagement portion of the indexing lever and particularly the ratcheting tooth  76  thereof engaged with spaced apart notches  80  disposed along a side of the magazine strip  82 . 
   The magazine strip is indexed upwardly in  FIG. 4  as the indexing lever  70  moves from the position away from the firing chamber, illustrated in  FIG. 1 , to the position toward the firing chamber illustrated in  FIG. 2 . During this upward motion of the magazine engagement portion of the indexing lever, the tooth  76  thereof is spring biased into a notch of the magazine strip, notch  80  in  FIG. 4 , whereby the magazine strip is indexed upwardly. 
   As the magazine engagement portion of the indexing lever moves away from the firing chamber, from the position illustrated in  FIG. 2  to the position illustrated in  FIG. 1 , the tooth  76  is withdrawn against its spring bias from the notch without moving the magazine strip downwardly. In  FIG. 4 , as the magazine engagement portion of the indexing lever moves downwardly, the magazine engagement portion is withdrawn from the notch  80  and is moved to a lower position, where it engages a lower notch  83  on the magazine strip  82 . 
   The incremental indexing of the magazine strip thus proceeds with the reciprocation of the firing mechanism or other moving portion of the tool to which the indexing lever is coupled. 
   In the above-mentioned embodiment, the reciprocating motion of sleeve  60  is used as the driving motion behind the indexing of cartridge strip  82 . As described above, this embodiment requires an operator to push sleeve  60  back into position to return indexing lever  70  into its original, pre-firing position shown in  FIG. 1 . It is preferred that tool  10  be designed so that all parts of tool  10  return to their pre-firing position automatically, including indexing lever  70 . 
   Turning to  FIG. 5 , an embodiment of a fastener driving tool  110  includes a spring  116  to bias a muzzle  118  into an extended pre-firing position with respect to a housing  122  of tool  110 . Tool  110  includes a back end  124  and a front end  126 . 
   Turning to  FIG. 7 , a firing mechanism  130  is contained within back end  124  of housing  122  for firing explosive cartridges  113  in a firing chamber  134  to drive a piston  136  in the driving direction to drive fasteners  138 . The front end  126  includes muzzle  118 , a magazine  140  for feeding a collation strip  144  of fasteners  138  to muzzle  118 , and a clutch (not shown) for rotating muzzle  118  and magazine  140  with respect to housing  122 , allowing magazine  140  to be set in various orientations. 
   Examples of a preferred magazine and a preferred clutch are disclosed in the commonly assigned patent applications entitled “Magazine Assembly With Stabilizing Members,” having U.S. application Ser. No. 10/246,186, “Lock Out Mechanism For Powder Actuated Tool,” having U.S. application Ser. No. 10/245,942, and “Magazine Clutch Assembly,” having U.S. application Ser. No. 10/246,203, all filed on Sep. 18, 2002, the disclosures of which are incorporated herein by reference. 
   Continuing with  FIG. 7 , tool  110  includes a barrel  132  enclosed within housing  122 , and a muzzle  118  extending axially away from housing  122 . Housing  122 , barrel  132  and muzzle  118  are all generally cylindrical in shape having a common central axis  146  extending throughout the length of tool  110 . Barrel  132  encloses piston  136  which drives fasteners  138  into a substrate  148 , wherein piston  136  is also generally cylindrical in shape and is aligned coaxially with barrel  132  and muzzle  118 . Muzzle  118  includes a bore  152  for axially guiding a driving  137  of piston  136  and fasteners  138  toward substrate  148 . 
   Housing  122  includes a handle  112  laterally extending away from axis  146 . Handle  112  provides a location for an operator to hold when actuating tool  110 . A trigger  160  is connected to handle  112  for actuating firing mechanism  130  and firing tool  110 . 
     FIG. 7  shows tool  110  driving fasteners  138  generally from the right to the left. However, tool  110  can be operated in several different orientations, such as to drive fasteners  138  into a vertically aligned substrate  148  so that fasteners  138  are driven horizontally from left to right, or tool  110  can be operated so that fasteners  138  are driven vertically upward or downward into substrate  148 . Therefore, for the purpose of discussion, any reference to the direction in which a fastener  138  is driven, such as toward the left in  FIG. 7 , is generally referred to as the driving direction or leading direction and any reference to the opposite direction, toward the right in  FIG. 7 , is generally referred to as the trailing direction. 
     FIG. 7  also show a cartridge strip  111  being indexed generally upward. However, as described above, tool  110  can be operated in several different orientations. Therefore, the direction in which cartridge strip  111  is indexed, such as upwardly in  FIG. 7 , is generally referred to as the indexing direction. For purposes of discussion, upwardly and above will refer generally to the indexing direction and downwardly and below will refer generally to a direction opposite the indexing direction. 
   Muzzle  118  is pushed against substrate  148  when tool  110  is to be used to drive a fastener  138  into substrate  148 . Pushing against substrate  148  overcomes the biasing force of spring  116 , so that muzzle  118  is forced in the trailing direction with respect to housing  122  into a retracted ready-to-fire position. Muzzle  118  is aligned coaxially with barrel  132  and is adjacent to barrel  132  in the driving direction. When muzzle  118  is pushed in the trailing direction by substrate  148 , muzzle  118  engages barrel  132  and biases barrel in the trailing direction as well. As barrel  132  is pushed in the trailing direction, it engages a cocking rod  162 , shown in  FIG. 6 , which enables a firing mechanism  130 , allowing tool  110  to be fired. The mechanism described above requires that an operator push muzzle  118  into the retracted position relative to housing  122  before tool  110  can be fired so that tool  110  cannot be actuated unless muzzle  118  is pushed into the retracted position. 
   Trigger  160  is connected to handle  112  so that trigger  160  can be pulled by an operator from a first pre-firing position, shown in  FIG. 8 , to a second fired position, shown in  FIG. 9 , actuating a firing mechanism  130  which fires a cartridge  113  placed within a firing chamber  134 . Trigger  160  is biased into the first, pre-firing position by a trigger spring  161 . In one embodiment, best seen in  FIG. 15 , trigger  160  is mounted for reciprocatory movement from a fixed trigger support  165  mounted to tool housing  122  against the bias of trigger spring  161 , which is interposed between trigger  160  and trigger support  165   
   Turning to  FIGS. 6 and 7 , firing mechanism  130  includes cocking rod  162 , a firing pin  164  and a firing spring  166  to bias firing pin  164  toward cartridge  113 . Cocking rod  162  is adjacent to barrel  132  and is pushed in the trailing direction when tool  110  is cocked as barrel  132  is pushed in the trailing direction by muzzle  118 , as described above. Cocking rod  162  includes a rotary seer (not shown) which engages firing pin  164  in the trailing direction so that firing spring  166  is compressed, as shown in  FIG. 7 . When trigger  160  is pulled by the operator, cocking rod  162  is rotated so that the rotary seer is rotated out of the way of firing pin  164  so that the rotary seer is no longer engaging firing pin  164 . When the rotary seer is no longer engaging firing pin  164 , firing spring  166  is free to extend and bias firing pin in the driving direction so that firing pin  164  can detonate cartridge  113 . In the cocked condition, shown in  FIG. 16 , an arm  162   a  at the forward end of cocking rod  162  has moved into alignment with a link  163  mounted in a trigger support  165 . When trigger  160  is depressed, link  163  is displaced upwardly to engage arm  162   a  and thereby rotate cocking rod  162  in order to release the rotary seer from engagement with firing pin  164 . The firing pin  164  is then released to be driven forwards to detonate the cartridge  113  in firing chamber  134  of barrel  132 . 
   Continuing with  FIG. 7 , an exemplary cartridge strip  111  contains a plurality of explosive cartridges  113  arranged in a row. Each cartridge  113  of cartridge strip  111  contains a predetermined amount of explosive powder which is detonated by firing pin  164  during firing of tool  110 . A cartridge  113  can only be detonated once by firing pin  164 , because once the explosive powder has been detonated, it is used up and must be replaced by a second cartridge  113   b . Cartridge strip  111  allows a plurality of cartridges  113  to be fed to tool  110 , so that an operator may fire tool  110  several times without having to reload explosive powder cartridges  113 . Cartridge strip  111  is indexed by an advancing mechanism  154  through a cartridge strip channel  120 . Cartridge strip channel  120  extends in the indexing direction through handle  112  and housing so that cartridges  113  can be indexed into and out of firing chamber  134 . 
   Trigger  160  is also associated with advancing mechanism  154  for automatically indexing cartridge strip  111 . Advancing mechanism  154  is operationally associated with trigger  160  so that when trigger  160  is in its first pre-firing position, advancing mechanism  154  is in a first position, as shown in  FIG. 8 , and when trigger  160  is pulled by an operator into a second fired position, advancing mechanism  154  is moved into a second position, as shown in  FIG. 9 . 
   Turning to  FIGS. 8 and 9 , advancing mechanism  154  includes an advancing lever  170  and an advance link  150 . Advance link  150  is operationally associated with trigger  160  so that when trigger  160  is in a first pre-firing position, shown in  FIG. 8 , advance link  150  is in a first position, and when trigger  160  is pulled by an operator into a second fired position, shown in  FIG. 9 , advance link  150  is biased into a second position. Advancing lever  170  indexes cartridge strip  111  in the indexing direction and is cammingly engaged with advance link  150 , as described below, so that when advance link  150  is in a first position, advancing lever  170  is also in a first position, and when advance link  150  is biased into a second position, advancing lever  170  is pivoted into a second position, as described below. 
   Advancing lever  170  is pivotally connected to tool  110  by a pivot pin  172  so that advancing lever  170  can pivot between a first position, shown in  FIG. 8 , and a second position, shown in  FIG. 9 . In one embodiment, shown in  FIG. 6 , pivot pin  172  is connected to a firing mechanism housing  168  so that advancing lever  170  is pivotally connected to mechanism housing  168 . However, advancing lever  170  can be pivotally connected to tool housing  122  without varying from the broad scope of the present invention. A retaining clip  173  is connected to pivot pin  172  in order to prevent advancing lever  170  from becoming disengaged with pivot pin  172  during operation of tool  110 . 
   Continuing with  FIG. 8 , advancing lever  170  includes a strip engagement portion  171  for engaging and indexing cartridge strip  111 , a pivot hole for receiving pivot pin  172 , and a lever camming portion  186  for cammingly engaging with advance link  150 , described below. A retention clip  173  is also included to ensure that advancing lever  170  remains pivotally connected, via pivot pin  172 , to tool  110  during operation of tool  110 . 
   In a preferred embodiment, strip engagement portion  171  is located generally at a driving end of advancing lever  170 , pivot pin  172  is generally centered along advancing lever  170  and lever camming portion  186  is located generally at a trailing end of advancing lever  170 , wherein strip engagement portion  171  and lever camming portion  186  are on opposite sides of the pivot hole. However, advancing lever  170  is not limited to this configuration. An alternative embodiment (not shown) includes the pivot hole located generally at the trailing end and the camming portion generally centered along the advancing lever. The alternative advancing mechanism can still operate to index cartridge strip  111 , as described below. 
   Turning to  FIG. 6 , one embodiment of strip engagement portion  171  of advancing lever  170  is shown. Strip engagement portion  171  includes a pawl  176  connected to advancing lever  170  and a spring  177  for biasing pawl  176  toward cartridge strip  111 . Pawl  176  is pivotally connected to advancing lever  170  with a pin  178  so that pawl  176  can pivot in and out of notches  180  in cartridge strip  111  in a ratcheting motion, described below. In one embodiment, spring  177  is a flexible rod which has a first end  188  retained by advancing lever  170  and a second end  190  engaged with pawl  176 , wherein a boss  179  connected to advancing lever  170  bends spring  177  between first end  188  and second end  190  so that spring  177  provides a biasing force against pawl  176  to bias pawl into a notch  180  of cartridge strip  111 . When advancing lever  170  is in its first position, strip engagement portion  171  is in an upper first position, shown in  FIG. 8 , and when advancing lever  170  pivots to its second position, strip engagement portion  171  moves to a lower second position, shown in  FIG. 9 . 
   It will be understood that during the movement of advancing lever  170  and pawl  176  which occurs during firing of tool  110 , cartridge strip  111  is fixed in position as the operative cartridge  113  is held within firing chamber,  134  at the rear of barrel  132  with the breach block  133 , shown in  FIG. 14 , being closed. After firing, the breach is opened by forwards movement of barrel  132  and breach block  133  to release the spent cartridge  114 . The trigger  160  is also released and moves forwardly under the bias of trigger spring  161 . This forwards movement is translated into movement of the advance link  150  and, via cam pin  174 , and cam slot  156 , there results an upwards movement of the forward end of the advancing lever  170 ; due to the engagement of the pawl  176  with the adjacent notch  180  of the cartridge strip  111 , the cartridge strip  8  itself will also be indexed to present the next cartridge  113  at the operative firing position. 
   The spring  177  which biases pawl  176  and which is deflected during the advancing movement of the advancing lever  170  will result in an increased trigger force and this can also be readily controlled to ensure reliability of the action of pawl  176  without unduly increasing the trigger force needed to be applied to fire the tool. This spring biasing enables the spring force applied to pawl  176  to be adjusted simply by selection of spring wire of appropriate characteristics. 
   Returning to  FIG. 6 , one embodiment of lever camming portion  186  includes a ramped cam slot  156 , which corresponds to a cam pin  174  on advance link  150 . However, in an equivalent alternative embodiment (not shown) the cam pin is located on the advancing lever and the cam slot is in the advance link. Cam slot  156  extends generally along advancing lever  170  and is located generally at a trailing end  192  of advancing lever  170 . Cam slot  156  includes a ramped leading leg  194  and a trailing leg  196  aligned essentially parallel to advancing lever  170 , wherein cam slot  156  is oriented so that it is generally convex in the indexing direction, with an angle θ, shown in  FIG. 8 , between leading leg  194  and trailing leg  196 . In one embodiment, angle θ is between about 110° and about 150°, and preferably about 135°. 
   The length of leading leg  194  and trailing leg  196  are generally equal to each other, with each leg  194 , 196  having a length between about 0.220 inches and about 0.240 inches, with a preferred length of leading leg  194  being about 0.115 inches and a preferred length of trailing leg being about 0.115 inches. The width of cam slot  156  should be slightly larger than the diameter of cam pin  174  so that cam pin  174  fits within cam slot  156  within a close, predetermined tolerance. In one embodiment, cam pin  174  has a diameter of about 0.098 inches, and cam slot  156  has a width of about 0.104 inches. 
   It is necessary to “tune” the mechanism so that the trigger action provides a comfortable feel. To an extent this can be accomplished by appropriate shaping of the cam slot  156 , which can be determined empirically. The cam slot  156  provides a degree of lost motion towards the end of the depression stroke of the trigger  160  whereby the indexing movement of the advancing lever  170  occurs during the initial and intermediate parts of the movement of the trigger  160 . 
   Cam slot  156 , and particularly trailing leg  196 , should have a length sufficient to allow cam pin  174  to continue to slide along trailing leg  196  even after advancing lever  170  has pivoted from the first position to the second position so that strip engagement portion  171  is engaged with a lower second notch  180   b  in cartridge strip  111 . When cam pin  174  is allowed to continue to slide, it prevents “dead stop” of the trigger so that an operator does not feel a hard stop of trigger  160  when strip engagement portion  171  engages with a notch  180  in cartridge strip  111 , as described below, but rather can continue to pull trigger  160  in the trailing direction for a time after advancing mechanism  154  has moved from its first position to its second position. 
   Turning to  FIG. 8 , advance link  150  is operationally associated with trigger  160  so that when trigger  160  moves in the trailing direction from its first pre-firing position to its second fired position when an operator pulls the trigger  160 , advance link  150  also moves from a first position to a second position. Advance link  150  includes a trigger engagement portion  198  for engaging with trigger  160 , and a link cam portion  200  for cammingly engaging with advancing lever  170 . In one embodiment, trigger engagement portion  198  is located generally at a driving end  202  of advance link  150 , and link cam portion  200  is located generally at a trailing end  204  of advance link  150 . 
   In one embodiment, shown in  FIG. 6 , trigger engagement portion  198  includes a flange  206  having a slot  208 . Advance link  150  is connected to a trailing end  210  of trigger  160  with a screw  212 , shown in  FIG. 8 , that extends through slot  208  and into trigger trailing end  210 , wherein screw  212  is tightened so that flange  206  is tightly flush against trigger  160 . 
   As part of the tuning of the indexing system, it is necessary to ensure that the movement of the advancing lever  170  during trigger depression moves the pawl  176  into the next notch  180  of cartridge strip  111  only when trigger  160  has been depressed sufficiently to fire the cartridge  113 , so as to avoid a mis-indexing situation which could otherwise arise if the trigger  160  is only partially depressed. While to an extent this is also determined by the shaping of the cam slot  156 , however manufacturing tolerances can adversely influence the required timing between trigger depression and indexing movement of lever  170 . In order to account for tolerances which can also arise during manufacture, the forward end of link  150  is connected to trigger  160  by a screw threaded adjustable mounting which can adjust the relative point of attachment of the forward end of link  150  in a fore-aft direction relative to trigger  160 . This adjustable mounting is shown in greater detail in  FIGS. 17A and 17B  and comprises a set screw  212  mounted within trigger  160 . Set screw  212  is rotatable to effect fore-aft adjustment of the mounting position of flange  206  of link  150  as can be seen from a compression between  FIGS. 17A and 17B  and is lockable in the set position by means of a lock nut  213 . As a result of this adjustment facility, at the time of assembly of the tool link  150  can be adjusted to ensure that the full indexing movement of lever  170  can only take place when trigger  160  has been depressed sufficiently to fire the tool. 
   Advance link  150  is guided by a guide (not shown) in tool  110  so that advance link  150  remains generally parallel to axis  146  when advance link  150  is moved from its first position to its second position. In one embodiment, shown in  FIGS. 5 and 8 , advance link  150  includes a bent leading portion  214  and a straight trailing portion  216 . Bent leading portion  214  is adjacent to flange  206  in the trailing direction. The shape of bent leading portion  214  is chosen to allow advance link  150  to fit in the tight space within tool housing  122  so that advancing mechanism  154  can operate in a small space. Straight trailing portion  216  remains generally parallel to axis  146  due to the guide. 
   Returning to  FIG. 8 , in one embodiment, link cam portion  200  includes a cam pin  174  located generally at trailing end  204  of advance link  150  and extending outwardly away from an outer surface  216  of advance link  150 . An alternative embodiment (not shown) includes cam pin  174  extending inwardly from an inner surface of advance link  150 . In another alternative (not shown), as described above, link cam portion  200  could instead include a cam slot that corresponds to a cam pin located on advancing lever  170 . 
   As described above, advance link  150  moves generally parallel to axis  146  so that cam pin  174  essentially moves in a straight line in the trailing direction when advance link  150  is biased from its first position to its second position by trigger  160 . Cam pin  174  slides along cam slot  156 , as described below, to cause advancing lever  170  to pivot about pivot pin  172 . 
   Continuing with  FIG. 8 , advancing mechanism  154  is designed so that an operator does not have to manually perform any set of tasks to index cartridge strip  111 . Pulling trigger  160  actuates firing mechanism  130 , as described above, as trigger  160  is moved from its first pre-firing position to its second fired position. Advancing mechanism  154  provides a link between trigger  160  and strip engagement portion  171  so that indexing of cartridge strip  111  is automatically performed by the movement of trigger  160 . 
   Continuing with  FIG. 8 , when trigger  160  is in the first position before an operator pulls trigger  160 , advance link  150  is located in the first position wherein advance link  150  is in its most forward position in the driving direction. When advance link is in the first position, cam pin  174  is generally at the driving end of leading leg  194  of cam slot  156  so that advancing lever  170  is in its first position with strip engagement portion  171  in its upward position. 
   When trigger  160  is pulled by an operator, advance link  150  is biased from the first position, shown in  FIG. 8 , in the trailing direction to the second position, shown in  FIG. 9 . Advance link  150  remains aligned essentially parallel to axis  146  so that cam pin  174  is biased essentially strait in the trailing direction. As cam pin  174  moves in the trailing direction, cam pin  174  comes into contact with and slides along an upper surface  218  of leading leg  194  of cam slot  156 . As cam pin  174  continues to move in the trailing direction, the ramped orientation of leading leg  194  of cam slot  156  forces the trailing end  192  of advancing lever  170  to pivot upwards, so that the entire advancing lever  170  pivots in a counterclockwise direction in  FIG. 9 . This rotation causes strip engagement portion  171  to be pivoted downward so that strip engagement portion  171  disengages from a first notch  180   a  in cartridge strip  111 , and engages with a lower second notch  180   b , shown in  FIGS. 10–12 . 
   As shown in  FIG. 10 , when strip engagement portion  171  is in the first upward position, pawl  176  is engaged within an upper first notch  180   a  so that an upper first cartridge  113   a  is aligned with axis  146  so that first cartridge  113   a  is within a firing chamber  134  (shown in  FIG. 7 ). When trigger  160  is pulled by an operator, first cartridge  113   a  is detonated by firing mechanism  130  so that cartridge  113   a  becomes a spent cartridge  114  shown in  FIG. 11 . At the same time trigger biases advance link  150  in the trailing direction, and advancing lever  170  is rotated from the first position to the second position, as shown in  FIG. 9  and described below. 
   When advancing lever  170  is rotated, strip engagement portion  171  is rotated from its upward first position, shown in  FIG. 10 , to its downward second position, shown in  FIG. 12 . When strip engagement portion  171  begins to be biased downward, a bottom surface  222  of first notch  180   a  pushes against a sloped bottom surface  224  of pawl  176 , urging pawl  176  against the bias of spring  177 , and causing pawl  176  to pivot out of first notch  180   a  on pin  178 , as shown in  FIG. 11 . As strip engagement portion  171  continues to be biased downward from the first position to the second position, pawl  176  slides along side surface  226  of cartridge strip  111 . 
   Turning to  FIG. 12 , eventually strip engagement portion  171  is biased to its downward second position, so that pawl  176  encounters a lower second notch  180   b , wherein second notch  180   b  is located directly below first notch  180   a  on cartridge strip  111 . Second notch  180   b  corresponds to a second cartridge  113   b  located directly below first cartridge  113   a . Spring  177  biases pawl  176  into second notch  180   b  so that a side surface  228  of pawl  176  is biased against side surface  230  of second notch  180   b.    
   When trigger  160  is released, trigger spring  161  biases trigger  160  from its second position in the driving direction back towards the pre-firing first position. Advance link  150  is associated with trigger  160  so that advance link  150  is also biased from the second position in the driving direction to the first position. As cam pin  174  is moved along with advance link  150  in the driving direction, cam pin  174  slides first along trailing leg  196 , and then up sloped leading leg  194  where cam pin  174  contacts a bottom surface  220  of leading leg  194 , pushing trailing end  192  of advancing lever  170  downward and pivoting advancing lever  170  from the second position to the first position, or in a clockwise direction in  FIG. 8 . 
   As advancing lever  170  pivots from the second position in  FIG. 12  to the first position in  FIG. 13 , strip engagement portion  171  moves upwardly, causing a top surface  232  of pawl  176  to contact an upper surface  234  of second notch  180   b . As strip engagement portion  171  continues to move upward, top surface  232  of pawl  176  engages upper surface  234  of second notch  180   b  so that pawl  176  biases cartridge strip  111  upwardly, indexing the spent first cartridge  113   a  out of firing chamber  134  and indexing second cartridge  113   b  into firing chamber  134  so that tool  110  is ready to fire again. 
   The operator can now pull trigger  160  again, causing firing mechanism  130  to detonate second cartridge  113   b  and causing advancing mechanism  154  to move strip engagement portion  171  from its upward position, with pawl  176  engaged within second notch  180   b , to its downward position, with pawl  176  engaged within a third notch  180   c . The operator can then release trigger  160 , allowing advancing mechanism  154  to return strip engagement portion  171  to its first position so that pawl  176  can engage third notch  180   c  and index a third cartridge  113   c  into firing chamber  134 . This process may be repeated several times until cartridge strip  111  runs out of cartridges  113  that may still be fired. 
   It is important that the trigger is unable to be depressed until the tool is ready to be fired as depression of the trigger will result in movement of advancing mechanism  154 , resulting in mis-indexing of strip  111 . For this reason, trigger support  165  can carry a trigger lock lever  167  which normally engages a rear abutment edge of trigger  160  (see  FIG. 15 ) to prevent its depression. Trigger lock lever  167  includes an upwardly extending release arm  167   a  which is engaged by a projection at the rear of barrel  132  on cocking of tool  110  to pivot trigger lock lever  167  out of its locking position (see  FIG. 5 ) and thereby permit depression of trigger  160  which results in firing of tool  110  and also the described downward indexing movement of indexing lever  170  and associated pawl  176 . An example of a trigger lock is disclosed in Australian Provisional Application 2002951660, filed Sep. 25, 2002 in the Australian Patent Office, the disclosure of which is incorporated herein by reference. 
   The inventive fastener driving tool of the present invention provides an improved advancing mechanism for the indexing of a strip of explosive powder cartridges through a cartridge strip channel. The advancing mechanism provides automatic indexing of the cartridge strip caused by the motion of the trigger used to fire the tool so that once a cartridge is used, a fresh cartridge is moved into place so that the tool is automatically ready to fire without requiring an operator to manually advance the cartridge strip, or to manually perform tasks that advance the cartridge strip. The advancing-mechanism also prevents “dead stop” of the trigger, helping to improve operator comfort due to the repetitive task of pulling the trigger. 
   The present invention is not limited to the above-described embodiments, but should be limited solely by the following claims.