Abstract:
A fastener driving tool including a power source having a reciprocating driver blade, a tool nose associated with the power source for receiving the driver blade for driving fasteners fed into the nose, a magazine constructed and arranged to house a supply of the fasteners and a magazine feeder mechanism associated with the magazine for sequentially feeding fasteners into the nose. The feeder mechanism operates between a retracted position and an advanced position. An electromechanical retention device is operationally associated with the feeder mechanism and is configured for retaining the feeder mechanism in the retracted position until the driver blade is positioned to allow fastener advancement into the nose.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates generally to fastener driving tools employing magazines feeding fasteners to a nosepiece for receiving a driving force; and more specifically to such tools employing a fastener feeder mechanism powered with gas pressure generated during the fastener driving process. 
     Fastener driving tools, referred to here as tools or nailers, are known in the art and are powered by combustion, compressed gas (pneumatic), powder, and electricity. Portable fastener driving tools that drive collated fasteners disposed in a coil magazine are commercially available on the market and are manufactured by ITW Buildex, Itasca, Ill. The core operating principle of the tool and the respective fastener feeding mechanism is defined in ITW U.S. Pat. Nos. 5,558,264 and 7,040,521, both of which are incorporated by reference. In U.S. Pat. No. 5,558,264, a gas conduit is placed in fluid communication with the main drive cylinder of the power source. 
     Upon ignition and combustion, as the drive piston attached to the driver blade travels down the cylinder toward the fastener or nail to be driven, a supply of combustion gas is distributed into the gas conduit and is used to operate a spring-biased feeder mechanism. The gas pressure overcomes a biasing force provided by a spring, and causes movement of a feed piston located within a feed cylinder and connected to a feeding claw. Operationally associated with a strip of collated fasteners, the burst of compressed gas causes the feed piston and a linked feeding claw to retract and engage the next fastener in the strip. Next, upon dissipation of the combustion gas, the compressed spring expands, advances the feed piston and the next fastener toward the tool nosepiece for subsequent engagement with the driver blade. 
     In the &#39;264 patent, the gas conduit is located in a wall of the drive cylinder and positioned between the drive piston&#39;s uppermost location (pre-firing position) and exhaust port openings located closer to an opposite end of the drive cylinder. The position of the conduit is such that a designated timing relationship is established during the drive cycle between the relative displacement of the drive piston and that of the feeder mechanism&#39;s feed piston. Such timing is an important design parameter for obtaining effective nail control and preventing nail jams within the nosepiece or the magazine. Optimally, the drive piston shears the nail from the collation media before the feed piston begins retraction, otherwise the nail will be driven with less control and an unsatisfactory nail drive can result. 
     Once the nail driving process is complete, a subsequent timing relationship between the return of the drive piston and advancement of the feeder mechanism is also important to obtain reliable piston return and nail feeding. The preferred timing scenario is for the drive piston to return to the pre-firing position before the feeder mechanism advances the nail into the tool nosepiece or nose (the terms are considered interchangeable). Currently, the feeder mechanism attempts to advance the nail into the nose while the drive piston and driver blade is returning to the pre-firing position. More specifically, the feed piston urges the next fastener toward the nosepiece prior to full retraction of the drive piston. This results in the nail being biased against the driver blade during the return cycle. See  FIG. 6  and its associated description for timing diagram details. Between t 2  and t 3 , the feed piston is urging the next fastener against the driver blade as the drive piston returns to its prefiring position. Only when the driver blade is fully retracted to its pre-firing position and a clear fastener passageway is provided does the fastener reach its drive position, indicated at t 3 . It should be understood that, referring to  FIG. 6 , as well as the other timing diagram in the application, that while tool state transitions are shown occurring instantaneously, there may be relative discrepancies or delays between steps. 
     The feeder mechanism includes a biasing spring that indirectly acts on the next nail to be driven, thereby exerting a transverse load component on the blade. The resulting friction prolongs the return of the driver blade, or even worse, prevents the driver blade from returning to the pre-firing position. When this occurs, the next fastener drive cycle does not result in a fastener being driven. This problem can be exacerbated by the amount of dirt, debris or collation media in the nose area of the tool. 
     Thus, there is a need for an improved fastener driver tool employing a method of establishing a preferred timing relationship between the drive piston and the advancement of the feeder mechanism during the return cycle of the drive piston. 
     BRIEF SUMMARY OF THE INVENTION 
     The above-listed needs are met or exceeded by the present feeder mechanism retention device for a fastener driving tool, which, in the preferred embodiment, features an electromechanical retention device and a control module that accommodates complete drive piston return before the feeder mechanism advances a nail into the tool nose. The present fastener driving tool uses a gas conduit that receives a supply of gas pressure from the power source, typically generated by combustion, and transmits the gas to the feed cylinder to overcome the feed piston return spring, thus retracting the feed piston, and uses an electromagnet for retaining the feed piston in the retracted position until the drive piston has returned to its pre-firing position or soon thereafter. 
     Advantages of the present tool include reduced nail or collation malfunction due to interference with the driver blade during piston return, improved piston return speed and reliability due to reduced frictional load on the drive piston assembly, and increased operational life for the drive piston and the retention device due to low wear. Also, the retention device is lightweight and operates with increased energy efficiency compared to conventional fastener feeder mechanisms. The present device is relatively uncomplicated with few parts to produce, install and maintain, and it is substantially enclosed, resulting in a dirt and debris-tolerant assembly, as opposed to prior art designs, which use small gas passages that are prone to dirt problems and complex mechanisms that can be damaged, require lubricant, are susceptible to corrosion, and can be affected by debris. In the present tool, the control module provides electronically controlled automatic operation of the retention device, and end-user input variability is avoided. Lastly, by providing a relatively simple mechanism which is operable independently of the normal tool functions, the tool actuation force required to be applied by the user prior to driving a fastener is maintained as in conventional tools and is not increased. 
     More specifically, a fastener driver tool includes a power source including a reciprocating driver blade, a tool nose associated with the power source for receiving the driver blade for driving fasteners fed into the nose, a magazine constructed and arranged to house a supply of the fasteners, a magazine feeder mechanism associated with the magazine for sequentially feeding fasteners into the nose, the feeder mechanism including a reciprocating feed piston, and an electromechanical retention device that is operationally associated with the feeder mechanism and configured for retaining the feed piston in a retracted position until the driver blade is positioned to allow fastener advancement into the nose. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         FIG. 1  is a perspective view of a fastener driving tool having a coil magazine and equipped with the present feeder mechanism retention device; 
         FIG. 2  is an enlarged fragmentary perspective elevation of the fastener driving tool of  FIG. 1 ; 
         FIG. 3  is a fragmentary vertical cross-section taken along the line  3 - 3  of  FIG. 2  and in the fully advanced position; 
         FIG. 4  is a fragmentary vertical cross-section similar to  FIG. 3  depicting a fully retracted position; 
         FIG. 5  is a fragmentary vertical cross-section similar to  FIG. 4  depicting a subsequent advancing forward position; 
         FIG. 6  is a prior art timing chart of a conventional fastener driving tool provided with combustion-derived compressed gas power for the fastener feeder; and 
         FIG. 7  is a timing chart of a tool provided with the present feeder mechanism. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to  FIGS. 1-4 , a fastener driving tool of the type suitable with the present feeder mechanism is generally designated  10  and is depicted as a combustion-powered tool. The general principles of operation of such tools are known in the art and are described in U.S. Pat. Nos. 5,197,646; 4,522,162; 4,483,473; 4,483,474 and 4,403,722, all of which are incorporated by reference. However, it is contemplated that the present feeder mechanism is applicable to fastener driver tools powered by other power sources that employ a reciprocating driver blade for driving fasteners into a workpiece. Also while it should be understood that the tool  10  is operable in a variety of orientations, directional terms such as “upper” and “lower” refer to the tool in the orientation depicted in  FIG. 1 . 
     A housing  12  of the tool  10  encloses a self-contained internal power source  14  (shown hidden) within a housing main chamber  16  (shown hidden). As in conventional combustion tools, the power source  14  is powered by internal combustion and includes a combustion chamber  18  (shown hidden) that communicates with a drive cylinder  20 . A drive piston  22  reciprocally disposed within the drive cylinder  20  is connected to the upper end of a driver blade  24  (cylinder, piston and driver blade all shown hidden). An upper limit of the reciprocal travel of the drive piston  22  is referred to as a pre-firing position, which occurs just prior to firing, or the ignition of the combustion gases that initiates the downward driving of the driver blade  24  to impact a fastener  26  to drive it into a workpiece. 
     Through depression of a trigger  28 , an operator induces combustion within the combustion chamber  18 , causing the driver blade  24  to be forcefully driven downward through a nose or nosepiece  30 . The nosepiece  30  guides the driver blade  24  to strike the forward-most fastener  26  that had been delivered into the nosepiece via a fastener magazine  32 . While a variety of magazines are contemplated as are known in the art, in the present tool  10  the magazine  32  is preferably a coil magazine in which the fasteners  26  are secured in a strip  34  using collating materials, typically metal, paper or plastic. 
     In proximity to the nosepiece  30  is a workpiece contact element  36 , which is connected, through a linkage or upper probe (not shown) to a reciprocating valve sleeve (not shown), which partially defines the combustion chamber  18 . Depression of the tool housing  12  against the workpiece (not shown) in a downward direction in relation to the depiction in  FIG. 1 , causes the workpiece contact element  36  to move from a rest position to a firing position, closing the combustion chamber  18  and preparing it for combustion. Other pre-firing functions, such as the energization of a fan in the combustion chamber  18  and/or the delivery of a dose of fuel to the combustion chamber are performed mechanically or under the control of a control circuit or program  38  embodied in a central processing unit or control module  40  (shown hidden), typically housed in a handle portion  42  ( FIG. 1 ) of the housing  12 . 
     Upon a pulling of the trigger  28 , a spark plug is energized, igniting the fuel and gas mixture in the combustion chamber  18  and sending the drive piston  22  and the driver blade  24  downward toward the waiting fastener  26  for entry into the workpiece. A conduit  44  has an inlet end  46  connected to a wall of the drive cylinder  20  via a suitable fitting  48  for diverting combusted gases at a location between the uppermost position of the drive piston  22  and the position of the driving piston when combusted gases are exhausted from the drive cylinder  20 , via exhaust ports (not shown). It will be appreciated that other locations on the power source for the inlet end  46  of the conduit  44  are contemplated, such as, but not restricted to the combustion chamber as described in U.S. Pat. No. 7,040,521 which is incorporated by reference, as well as utilization of the compressed gas generated in front of the drive piston  22 . Such gases are collectively referred to as power source gases. 
     As shown in  FIGS. 1-5 , at an opposite end from the fitting  48 , the conduit  44  is connected to a fastener feeder mechanism, generally designated  50 . An outlet end  52  of the conduit  44  is connected to a nipple-type fitting  53  in a cylindrical wall  54  of a feeder mechanism cylinder  56 , also referred to as the feed cylinder. The conduit  44  diverts power source gas, here combustion gas from the driving cylinder  20  into the feed cylinder  56  against a feed piston  58  to move the feed piston, a piston rod  60 , and a feed claw  62  from an advanced position of the feed piston ( FIG. 3 ) into a withdrawn or retracted position of the feed piston ( FIG. 4 ). Except as presently illustrated and described, the fastener-feeder mechanism  50  is similar to fastener feeder mechanisms provided with pneumatically powered fastener-driving tools available commercially from ITW Paslode. 
     More specifically, and referring to  FIGS. 1 and 2 , the feeder mechanism  50  includes the magazine  32  which is provided with a fixed portion  64  and a pivotable portion  66 . The fixed portion  64  is fixed to the housing  12  and the nosepiece  30  via an arm  68 . An arm  70  pivotably connects the pivotable portion  66  to the fixed portion  64 , and the arm  70  is hinged to the arm  68  via a hinge  72 , and is pivotable between an opened position, in which it is shown in  FIGS. 1 and 2 , and a closed position (not shown). The pivotable portion  66  is pivoted to the opened position for loading of a coiled strip  34  of fasteners  26  into the canister magazine  32  and to the closed position for operation of the tool  10  and the mechanism  50 . Also included in the mechanism  50  is a latch  74  for releasably latching the pivotable portion  66  in the closed position. The arms  68 ,  70  combine to define a fastener-feeding track. 
     Referring now to  FIGS. 3-5 , the mechanism  50  includes the feed cylinder  56 , which is mounted fixedly to the arm  68  and which has the cylindrical wall  54 , an end  76 , an annular O-ring  78  fixed within the cylindrical wall  54  at an outer, apertured end  80  of the feed cylinder. The feed piston  58  is movable within the cylindrical wall  54  between a retracted position and an advanced position, and is provided with the piston rod  60 . Guided by the O-ring  78  and the apertured end  80 , the piston rod  60  moves commonly with the feed piston  58 . 
     Inside the feed cylinder  56  is provided a return spring  84  which is seated against the end  76  as will be described in greater detail below, and which biases the feed piston  58  toward the advanced position. An O-ring  86  is seated in a peripheral groove  88  of the feed piston  58  and seals against the cylindrical wall  54  as the feed piston  58  reciprocates. 
     Also included in the feeder mechanism  50  is the feed claw  62 , which is pivotably mounted to the piston rod  60  via a pivot pin  90 , to be commonly movable with the piston rod and the feed piston  58  between the retracted and advanced positions but also to be pivotable on the pivot pin between an operative position and an inoperative position. In  FIGS. 3-5 , the feed claw  62  is shown in the operative position in unbroken lines and in the inoperative position in broken lines. A torsion spring  92  is mounted on the pivot pin  90  and biases the feed claw  62  toward the operative position. 
     The feed claw  62  has notched end fingers  94 , which are configured for engaging one of the fasteners  26  of the strip  34  when the feed claw is in the operative position and to advance the strip when the feed piston  58 , the piston rod  60 , and the feed claw  62  are moved by spring pressure from the return spring  84  from the retracted position ( FIG. 4 ) to the advanced position ( FIG. 3 ). The notched end fingers  94  have a camming surface  96 , which is configured for camming over the next nail  26  in the strip  34  to cause the feed claw  62  to pivot from the operative position into the inoperative position when the feed piston  58 , the piston rod  60 , and the feed claw are moved by gas pressure from the conduit  44  from the advanced position to the retracted position. 
     Also included in the feeder mechanism  50  is a holding claw  98 , which is mounted pivotably to the arm  70  via a pivot pin  100  to be pivotable between an engaging position and a disengaging position. The holding claw  98  is shown in the engaging position in  FIGS. 3 and 4 , and in the disengaging position in  FIG. 5 . A coiled spring  102 , which has one end seated in a socket  104  in the holding claw  98  and its other end bearing against the arm  70 , biases the holding claw to the engaging position. The holding claw  98  has distal end fingers  106 , which are adapted to fit between two nails  26  of the strip  34 , to engage and hold the nail so that the strip, including the engaged nail, does not move with the feeding claw  62  when the feed piston  58 , the piston rod  60 , and the feed claw are moved to the retracted position by the combustion gases. 
     Referring again to  FIGS. 3-5 , to address the above-described problem of the next fastener  26  to be driven being urged against the driver blade  24  during the driver blade return cycle, the present feeder mechanism  50  is provided with a retention device, generally designated  110 . The retention device  110  holds the feed piston  58  in place in the retracted position ( FIG. 4 ) and prevents the unwanted side loading on the driver blade  24 , thus permitting more repeatable and rapid piston return. In the preferred embodiment, the retention device  110  uses an electromagnet  112  that is electrically connected to the control program  38  which determines its energization cycle. However, other types of electromechanical retention devices that act on the feeder mechanism are contemplated, provided they are able to prevent side loading against the driver blade  24  by the next fastener  26  through urging of the feed piston  58  during driver blade return cycle. 
     Also, it is preferred that the electromagnet  112  is disposed within the feed cylinder  56  and is secured therein by a flange  114  engaging a corresponding shoulder of the feed cylinder and fastener preferred embodiment the fastener hardware  116  is a disc  118 , with a vent hole  120 , and a spring clip  122  secured in the feed cylinder  56 . The vent hole  120  allows the escape of air from the feed cylinder  54  when the feed piston  58  is retracted. It is understood that other fastening technologies are contemplated for securing the electromagnet  112  in place, including but not limited to threaded engagement, chemical fasteners, welding and the like. The electromagnet  112  is secured in place to withstand the spring force generated by the return spring  84  when compressed, and the energization of the electromagnet is sufficient to overcome the biasing force of the return spring acting on the feed piston  58 . 
     The control program  38  controls the energization of the electromagnet  112 , which holds the feed piston  58  for a sufficient period of time, until the drive piston  22 , and the driver blade  24  are clear of the tool nose  30 . The time varies with the tool and the application, but is sufficiently long for the drive piston  24  returning to the pre-firing position. In one application, the designated energization time of the electromagnet  112  is approximately 100 msec; however other times are contemplated, depending on the tool and the situation. 
     As an alternate configuration, the drive piston  22  and or the cylinder  20  can be monitored with at least one piston position sensor  124  (shown schematically and hidden in  FIG. 1 ) to provide feedback to the control program  38  to de-energize the electromagnet  112  when the drive piston and driver blade  24  has returned to the pre-firing position. 
     Referring now to  FIG. 6 , the timing of prior art tools is depicted. At to, the tool  10  has not been fired and the drive piston  22  is in the pre-firing position at an upper end of the drive cylinder  20 . Also, the feed piston  58  is in the advanced position ( FIG. 3 ), and a fastener  26  is positioned in the nose  30 . At t 1 , upon firing, the drive piston  22  and the driver blade  24  travel down the cylinder  20 , and a portion of the power source gas, here combustion gas is diverted through the conduit  44  causing the feed piston  58  to retract. The feed piston  58  is retracted from t 1  to t 2  until the gases disburse, then the feed piston  58  returns towards the advanced position powered by the return spring  84  at t 2 . It will be seen that between t 2  and t 3 , the feed piston is not fully advanced, and is urging the next fastener  26  against the driver blade  24  until it reaches the pre-firing position. At t 3 , the driver blade  24  has cleared the fastener  24  and has reached the pre-firing position. Also at t 3  since the nose area is cleared, the feeder mechanism  50  advances the fastener  26  all the way into the nose  30 . As discussed above, the side loading of the fastener  26  against the driver blade  24  slows the return of the piston  22  to the pre-firing position. 
     Referring now to  FIG. 7 , the operational sequence of the present tool  10  equipped with the retention device  110  is depicted. The electromagnet  112  is energized by the control program  38  at t 0  with the start of the ignition cycle of the tool  10 . This causes the electromagnet  112  to be energized and ready to secure the feed piston  58  when it contacts electromagnet  112  in the retracted position ( FIG. 4 ) due to the ferrous material used to manufacture the feed piston. The control program  38  includes a timer function which maintains power to the electromagnet  112  until the timer expires at t 3 . While the ignition event preferably energizes the timer, a number of other means can be used to begin the timer, including but not limited to a switch, such as the trigger switch  28  or a chamber position switch (not shown). When ignition occurs at t 1 , combustion gases advance the drive piston  22  to the bumper position during which a fastener is driven. At that time, as occurred in  FIG. 6 , partial combustion gases are diverted to the conduit  44  and fully retract the feed piston  58  also shown at t 1 . Although the events at t 1  are not simultaneous, they are relatively short in duration and shown as a single time event. 
     However, unlike the operation of the prior art tool in  FIG. 6 , in the present tool, through the function of the electromagnet  112 , the feed piston  58  is held in the retracted position ( FIG. 4 ) by the control program  38  until t 3 , which is sufficiently after the drive piston  24  returning to the pre-firing position at t 2 . Due to the gap between t 2  and t 3 , the time period for energization of the electromagnet  112  may exceed the piston return time, depending on the tool and the application. Upon expiration of the timer, the electromagnet  112  is deenergized, and the return spring  84  forces the feed piston  58  to the advanced position ( FIG. 5 ), which causes the advancement of the next fastener  26 . 
     While a particular embodiment of the present feeder mechanism retention device for a fastener driving tool has been described herein, 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.