Patent Publication Number: US-11654538-B2

Title: Powered fastener driver

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to co-pending U.S. patent application Ser. No. 16/363,635 filed on Mar. 25, 2019, which claims priority to U.S. Provisional Patent Application No. 62/667,898 filed on May 7, 2018, and U.S. Provisional Patent Application No. 62/648,086 filed on Mar. 26, 2018, the entire contents of each of which are incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to a power tool, and more particularly to a powered fastener driver. 
     BACKGROUND OF THE INVENTION 
     Powered fastener drivers are used to drive fasteners (e.g., nails, tacks, staples, etc.) into a workpiece. Such fastener drivers may be powered by compressed air generated by an air compressor, for example. 
     SUMMARY OF THE INVENTION 
     The invention provides, in one aspect, a pneumatic fastener driver operable in a single sequential mode and a bump-fire mode. The pneumatic fastener driver includes a housing, a nosepiece extending from the housing from which fasteners are ejected, a trigger moveable between a default position, in which a drive cycle is inhibited from initiating, and a depressed position, in which the drive cycle is permitted to be initiated, a contact arm movable relative to the nosepiece between an extended position and a retracted position, and a timeout mechanism operable in the bump-fire mode to inhibit the drive cycle from being initiated in response to inactivity of the contact arm over a preset time interval defined by unwinding of a mainspring that is initially wound in response to the trigger being actuated from the default position to the depressed position. The pneumatic fastener driver also includes a counting assembly having a gear train driven by the mainspring and an escapement wheel that decrementally controls the unwinding of the mainspring over the preset time interval. 
     The invention provides, in another aspect, a pneumatic fastener driver operable in a single sequential mode and a bump-fire mode. The pneumatic fastener driver includes a housing, a nosepiece extending from the housing from which fasteners are ejected, a trigger moveable between a default position, in which a drive cycle is inhibited from initiating, and a depressed position, in which the drive cycle is permitted to be initiated, a contact arm movable relative to the nosepiece between an extended position and a retracted position, and a timeout mechanism operable in the bump-fire mode to inhibit the drive cycle from being initiated in response to inactivity of the contact arm over a preset time interval defined by unwinding of a mainspring that is initially wound in response to the trigger being actuated from the default position to the depressed position. The pneumatic fastener driver also includes a counting assembly having a gear train driven by the mainspring and a gas spring assembly that decrementally controls the unwinding of the mainspring over the preset time interval. 
     The invention provides, in another aspect, a pneumatic fastener driver operable in a single sequential mode and a bump-fire mode. The pneumatic fastener driver includes a housing, a nosepiece extending from the housing from which fasteners are ejected, a drive mechanism having a drive blade reciprocably driven through the nosepiece to eject fasteners, a trigger moveable between a default position, in which a drive cycle is inhibited from initiating, and a depressed position, in which the drive cycle is permitted to be initiated, a trigger valve assembly adjacent the trigger and operable to release an airflow to atmosphere when the trigger is actuated to the depressed position, causing the drive mechanism to actuate, a contact arm movable relative to the nosepiece between an extended position and a retracted position, and a timeout mechanism operable in the bump-fire mode to inhibit the airflow through the trigger valve assembly in response to inactivity of the contact arm over a preset time interval that begins once the trigger is actuated from the default position to the depressed position. 
     The invention provides, in another aspect, a pneumatic fastener driver operable in a single sequential mode and a bump-fire mode. The pneumatic fastener driver includes a housing, a nosepiece extending from the housing from which fasteners are ejected, a trigger moveable between a default position, in which a drive cycle is inhibited from initiating, and a depressed position, in which the drive cycle is permitted to be initiated, a contact arm movable relative to the nosepiece between an extended position and a retracted position, and a timeout mechanism operable in the bump-fire mode to inhibit the drive cycle from being initiated in response to inactivity of the contact arm over a preset time interval defined by unwinding of a mainspring that is initially wound in response to the trigger being actuated from the default position to the depressed position. The pneumatic fastener driver also includes a counting assembly having a female barrel pivotably coupled to a pivot shaft of the trigger and driven by the mainspring and a lockout linkage coupled to the female barrel that is capable of interfering with a portion of the trigger. 
     Other features and aspects of the invention will become apparent by consideration of the following detailed description and accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a perspective view of a powered fastener driver in accordance with an embodiment of the invention. 
         FIG.  2    is a cross-sectional view of a portion of the powered fastener driver along line  2 - 2  of  FIG.  1   , illustrating a timeout mechanism in an expired state, an activation trigger in a default position, and a contact arm in an extended position. 
         FIG.  3    is a cross-sectional view of the powered fastener driver of  FIG.  2   , illustrating the timeout mechanism in an unexpired state, the activation trigger in a depressed position, and the contact arm in the extended position. 
         FIG.  4    is a cross-sectional view of the powered fastener driver of  FIG.  2   , illustrating the timeout mechanism in the unexpired state, the activation trigger in a depressed position, and the contact arm in a retracted position. 
         FIG.  5    is a cross-sectional view of the powered fastener driver of  FIG.  2   , illustrating the timeout mechanism in the expired state, the activation trigger in a depressed position, and the contact arm in the extended position. 
         FIG.  6    is a cross-sectional view of the powered fastener driver of  FIG.  2   , illustrating the timeout mechanism disengaged from the activation trigger. 
         FIG.  7    is a cross-sectional view of a portion of a powered fastener driver in accordance with another embodiment along line  2 - 2  of  FIG.  1   , illustrating a timeout mechanism in an expired state, an activation trigger in a default position, and a contact arm in an extended position. 
         FIG.  8    is a cross-sectional view of a portion of the powered fastener driver of  FIG.  7   , illustrating the timeout mechanism in an unexpired state, the activation trigger in a depressed position, and the contact arm in the extended position. 
         FIG.  9    is a cross-sectional view of a portion of the powered fastener driver of  FIG.  7   , illustrating the timeout mechanism in the unexpired state, the activation trigger in a depressed position, and the contact arm in a retracted position. 
         FIG.  10    is a cross-sectional view of a portion of the powered fastener driver of  FIG.  7   , illustrating the timeout mechanism in the expired state, the activation trigger in a depressed position, and the contact arm in the extended position. 
         FIG.  11    is a cross-sectional view of a portion of the powered fastener driver of  FIG.  7   , illustrating the timeout mechanism disengaged from the activation trigger. 
         FIG.  12    is a cross-sectional view of a portion of a powered fastener driver in accordance with another embodiment along line  2 - 2  of  FIG.  1   , illustrating a timeout mechanism in an expired state, an activation trigger in a default position, and a contact arm in an extended position. 
         FIG.  13    is a cross-sectional view of a portion of the powered fastener driver of  FIG.  12   , illustrating the timeout mechanism in an unexpired state, the activation trigger in a depressed position, and the contact arm in the extended position. 
         FIG.  14    is a cross-sectional view of a portion of the powered fastener driver of  FIG.  12   , illustrating the timeout mechanism in the unexpired state, the activation trigger in a depressed position, and the contact arm in the extended position. 
         FIG.  15    is a cross-sectional view of a portion of the powered fastener driver of  FIG.  12   , illustrating the timeout mechanism in the unexpired state, the activation trigger in a depressed position, and the contact arm in a retracted position. 
         FIG.  16    is a cross-sectional view of a portion of the powered fastener driver of  FIG.  12   , illustrating the timeout mechanism in the expired state, the activation trigger in a depressed position, and the contact arm in the extended position. 
         FIG.  17    is a cross-sectional view of a portion of the powered fastener driver of  FIG.  12   , illustrating the timeout mechanism in the expired state, the activation trigger in a depressed position, and the contact arm in the retracted position. 
         FIG.  18    is a cross-sectional view of a portion of the powered fastener driver of  FIG.  12   , illustrating the timeout mechanism disengaged from the activation trigger, the activation trigger in the default position, and the contact arm in the extended position. 
         FIG.  19    is a cross-sectional view of a portion of the powered fastener driver of  FIG.  12   , illustrating the timeout mechanism disengaged from the activation trigger, the activation trigger in the default position, and the contact arm in the retracted position. 
         FIG.  20    is a cross-sectional view of a portion of the powered fastener driver of  FIG.  12   , illustrating the timeout mechanism disengaged from the activation trigger, the activation trigger in the depressed position, and the contact arm in the retracted position. 
         FIG.  21    is a cross-sectional view of a portion of a powered fastener driver in accordance with another embodiment along line  2 - 2  of  FIG.  1   , illustrating a timeout mechanism in an expired state, an activation trigger in a default position, and a contact arm in an extended position. 
         FIG.  22    is a cross-sectional view of a portion of the powered fastener driver of  FIG.  21   , illustrating the timeout mechanism in an unexpired state, the activation trigger in a depressed position, and the contact arm in the extended position. 
         FIG.  23    is a cross-sectional view of a portion of the powered fastener driver of  FIG.  21   , illustrating the timeout mechanism in the unexpired state, the activation trigger in a depressed position, and the contact arm in the retracted position. 
         FIG.  24    is a cross-sectional view of a portion of the powered fastener driver of  FIG.  21   , illustrating the timeout mechanism in the unexpired state, the activation trigger in a depressed position, and the contact arm in the extended position. 
         FIG.  25    is a cross-sectional view of a portion of the powered fastener driver of  FIG.  21   , illustrating the timeout mechanism disengaged from the activation trigger, the activation trigger in the default position, and the contact arm in the extended position. 
         FIG.  26    is a cross-sectional view of a portion of a powered fastener driver in accordance with another embodiment along line  2 - 2  of  FIG.  1   , illustrating a timeout mechanism in an expired state, an activation trigger in a default position, and a contact arm in an extended position. 
         FIG.  27    is a cross-sectional view of a portion of the powered fastener driver of  FIG.  26   , illustrating the timeout mechanism in an unexpired state, the activation trigger in a depressed position, and the contact arm in the extended position. 
         FIG.  28    is a cross-sectional view of a portion of the powered fastener driver of  FIG.  26   , illustrating the timeout mechanism in the unexpired state, the activation trigger in the depressed position, and the contact arm in the extended position. 
         FIG.  29    is a cross-sectional view of a portion of the powered fastener driver of  FIG.  26   , illustrating the timeout mechanism in the unexpired state, the activation trigger in the depressed position, and the contact arm in the extended position. 
         FIG.  30    is a cross-sectional view of a portion of the powered fastener driver of  FIG.  26   , illustrating the timeout mechanism in the unexpired state, the activation trigger in the depressed position, and the contact arm in the retracted position. 
         FIG.  31    is a cross-sectional view of a portion of the powered fastener driver of  FIG.  26   , illustrating the timeout mechanism in the unexpired state, the activation trigger in the depressed position, and the contact arm in the retracted position. 
         FIG.  32    is a cross-sectional view of a portion of the powered fastener driver of  FIG.  26   , illustrating the timeout mechanism in the expired state, the activation trigger in the depressed position, and the contact arm in the extended position. 
         FIG.  33    is a cross-sectional view of a portion of the powered fastener driver of  FIG.  26   , illustrating the timeout mechanism in the expired state, the activation trigger in the depressed position, and the contact arm in the extended position. 
         FIG.  34    is a cross-sectional view of a portion of the powered fastener driver of  FIG.  26   , illustrating the timeout mechanism in the expired state, the activation trigger in the default position, and the contact arm in the extended position. 
         FIG.  35    is a cross-sectional view of a portion of the powered fastener driver of  FIG.  26   , illustrating the timeout mechanism in the expired state, the activation trigger in the default position, and the contact arm in the extended position. 
     
    
    
     Before any embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the accompanying drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. 
     DETAILED DESCRIPTION 
     With reference to  FIG.  1   , a fastener driver  10  is operable to drive fasteners (e.g., nails, tacks, staples, etc.) held within a magazine  14  into a workpiece. The fastener driver  10  includes a housing  18  with a handle portion  22 , a nosepiece  26  extending from the housing  18  from which the fasteners are ejected, and a drive blade  28  movable in a reciprocating manner within the nosepiece  26  for discharging the fasteners from the magazine  14 . The fastener driver  10  also includes a drive mechanism  29  disposed within the housing  18  for reciprocating the drive blade  28  through consecutive drive cycles. Each drive cycle discharges a single fastener from the magazine  14  at the nosepiece  26  and driven into a workpiece. In some embodiments, the drive mechanism  29  includes an on-board air compressor that generates pressurized air that applies a force to drive the drive blade  28  via a head valve (not shown). In other embodiments, the drive mechanism  29  may include a compression spring or a gas spring for applying a force on the drive blade  28 . In yet other embodiments, the drive mechanism  29  may include a remote power source (e.g., an external source of pressurized air) for applying a force on the drive blade  28 . 
     With reference to  FIGS.  1  and  2   , the fastener driver  10  further includes an activation trigger  30  disposed adjacent the handle portion  22  that is user-actuated to begin each drive cycle. Specifically, the trigger  30  is movable from a default position ( FIG.  1   ) to a depressed position ( FIG.  3   ) to initiate the drive cycle. The activation trigger  30  is biased toward the default position by a biasing element, such as a spring. In the illustrated embodiment, the trigger  30  pivots about a pivot shaft  34  ( FIG.  2   ) when moving between the default and depressed positions. An operator grasps the handle portion  22  to hold the driver  10  while using a finger to actuate the trigger  30 . The trigger  30  includes a trigger arm  38  that is supported on the trigger  30  via a pin  42 . The trigger arm  38  is supported on and pivots about the pin  42 . The trigger arm  38  includes a central portion  38   a  and a distal end portion  38   b.    
     The fastener driver  10  further includes a contact arm  46  ( FIG.  1   ) slidable relative to the nosepiece  26  in response to contacting a workpiece. The contact arm  46  is also movable between a biased, extended position in which fasteners are inhibited from being discharged from the magazine  14 , and a retracted position in which fasteners are permitted to be discharged from the magazine  14 . In the illustrated embodiment, the contact arm  46  mechanically interfaces with the activation trigger  30  to selectively permit a drive cycle to be initiated. Specifically, the contact arm  46  engages the distal end portion  38   b  of the trigger arm  38  in order for a drive cycle to be initiated, as shown in  FIG.  4   . 
     With reference to  FIG.  2   , the fastener driver  10  also includes a trigger valve assembly  50  disposed adjacent the activation trigger  30 . High air pressure is released to atmosphere (i.e., atmospheric pressure) through the trigger valve assembly  50  when the activation trigger  30  is actuated, causing the head valve (not shown) to actuate and allowing compressed air stored in the handle portion  22  to drive the drive blade  28 . The trigger valve assembly  50  is supported by the handle portion  22  adjacent the activation trigger  30 . The fastener driver  10  includes a first or air supply chamber  52 , a main air passage  56 , and a second or trigger air chamber  58  fluidly connecting the air supply chamber  52  and the main air passage  56 . At least a portion of the trigger valve assembly  50  is housed within the trigger air chamber  58  and interposed between the air supply chamber  52  and the main air passage  56 . The air supply chamber  52  receives and collects pressurized fluid from an external air compressor via a hose connect  64  ( FIG.  1   ). 
     The trigger valve assembly  50  further includes a valve stem  60  ( FIG.  2   ) capable of being depressed upon actuation of the activation trigger  30 . Specifically, the central portion  38   a  of the trigger arm  38  engages the valve stem  60  in order to depress the valve stem  60  when the activation trigger  30  is actuated, as shown in  FIG.  4   . The valve stem  60  is nested and reciprocates within the trigger air chamber  58 , such that the valve stem  60  selectively opens the trigger valve assembly  50  to atmosphere. The valve stem  60  is urged toward a default position ( FIGS.  2  and  3   ) by a biasing member, such as a spring. 
     With reference to  FIGS.  2 - 6   , the fastener drive  10  further includes a timeout mechanism  68  that is operable to lock the trigger  30 , and more specifically the trigger arm  38 , from being actuated in response to inactivity (i.e., lack of actuation) of the contact arm  46  over a preset time interval that begins once the trigger  30  is initially depressed, as described in further detail below. The timeout mechanism  68  is disposed within the housing  18  and includes a gear train  72 , a mainspring  70  for driving the gear train  72 , a hairspring or counting assembly  76  to control the release of energy from the mainspring  70 , and a lockout linkage  80  capable of interfacing with the distal end portion  38   b  of the trigger arm  38 . The gear train  72  includes a trigger gear  84  disposed about the pivot shaft  34  of the trigger  30 , an intermediate gear  88  intermeshed with and driven by the trigger gear  84 , a rack gear  92  selectively intermeshed with a rack  96  on the contact arm  46  and the intermediate gear  88 , and an escapement wheel  100  that interacts with the hairspring assembly  76 . The lockout linkage  80  has one end pivotably coupled to the intermediate gear  88  and an opposite free end capable of interfering with the distal end portion  38   b  of the trigger arm  38 . A support wall  104  on the housing  18  is disposed adjacent the lockout linkage  80  and prevents the lockout linkage  80  from pivoting upward beyond the orientation shown in  FIG.  2   . 
     With continued reference to  FIGS.  2 - 6   , the hairspring assembly  76  includes a hairspring  108 , a balance wheel  112  coupled to and driven by the hairspring  108 , a balance axle  116  about which the balance wheel  112  rotates, and a roller  120  offset from the balance axle  116 . The hairspring assembly  76  further includes a palette lever  124  that intermittently receives the roller  120  at one end as the balance wheel  112  oscillates, while the other end of the palette lever  124  intermittently engages with the escapement wheel  100  via a palette crossarm  126 . The hairspring assembly  76  alternately checks and releases the gear train  72  by a fixed amount and transmits a periodic impulse from the mainspring  70  to the balance wheel  112 . The hairspring assembly  76  is similar to a traditional hairspring assembly that is well-known in the watch making industry and the field of horology. 
     In operation, the fastener driver  10  is operable in two modes of operation—a first or single sequential mode ( FIG.  6   ) and a second or bump-fire mode ( FIGS.  2 - 5   ). In sequential mode, an operator first presses the contact arm  46  against a workpiece, causing it to retract, and then presses the activation trigger  30  to initiate a drive cycle for discharging a fastener from the magazine  14 . In contrast, bump-fire mode allows an operator to first actuate the activation trigger  30  from the default position to the depressed position, and thereafter, initiate a drive cycle each time the contact arm  46  is retracted coinciding with being depressed against a workpiece. In order to switch the fastener driver  10  between the two modes of operation, the fastener driver  10  is provided with a knob  66  ( FIG.  1   ) having a cammed surface that moves the trigger  30  (and therefore the trigger arm  38 ) relative to the valve stem  60 , thereby altering the spatial relationship therebetween to affect how a drive cycle is initiated. 
     While the fastener driver  10  is in bump-fire mode, the timeout mechanism  68  limits the amount of time an operator has to initiate a drive cycle (i.e., depress the contact arm  46  against a workpiece) after the trigger  30  is actuated to the depressed position. As illustrated in  FIG.  2   , the trigger gear  84  is intermeshed with the intermediate gear  88  and the lockout linkage  80  is adjacent the distal end portion  38   b  of the trigger arm  38 . At this point, the mainspring  70  is unwound, and thus the gear train  72  is in an expired state. By actuating the trigger  30  to the depressed position as illustrated in  FIG.  3   , the trigger gear  84  co-rotates with the trigger  30  in a counter-clockwise direction, which ultimately winds the mainspring  70  and places the gear train  72  in an unexpired state. Specifically, rotation of the trigger gear  84  causes the following sequence of events to simultaneously occur: (a) rotation of the intermediate gear  88  in a clockwise direction; (b) rotation of the rack gear  92  in a counter-clockwise direction; (c) rotation of the escapement wheel  100  in a counter-clockwise direction; and (d) separation of the lockout linkage  80  and the distal end portion  38   b  of the trigger arm  38  such that interference therebetween no longer exists ( FIG.  3   ). The mainspring  70  and the gear train  72  are fully wound, thereby starting the preset time interval during which the operator is permitted to initiate the drive cycle. In the event the operator depresses the contact arm  46  against a workpiece (i.e., initiates the drive cycle) as illustrated in  FIG.  4   , the contact arm  46  contacts the distal end portion  38   b  of the trigger arm  38 , causing rotation of the trigger arm  38  towards the valve stem  60  at which point the central portion  38   a  of the trigger arm  38  actuates the valve stem  60 . Subsequently, the drive mechanism  29  drives the drive blade  28  to discharge a fastener through the nosepiece  26  and into the workpiece. By doing so, the rack  96  of the contact arm  46  is displaced into mesh engagement with the rack gear  92  to again cause rotation of the rack gear  92  in the counter-clockwise direction. This time, rotation of the rack gear  92  rotates the intermediate gear  88  in the clockwise direction, thereby resetting the timeout mechanism  68  as the mainspring  70  and gear train  72  are fully rewound again. 
     Now, in the event the operator fails to depresses the contact arm  46  against a workpiece (i.e., initiates the drive cycle) within the preset time interval, the lockout linkage  80 , which itself is prevented from pivoting upward by the support wall  104 , mechanically interferes with the distal end portion  38   b  of the trigger arm  38  at which point the trigger arm  38  is no longer pivotable to actuate of the valve stem  60 , as illustrated in  FIG.  5   . The support wall  104  inhibits the contact arm  46  from pivoting both the lockout linkage  80  and the trigger arm  38  if an attempt is made to depress the contact arm  46  after expiration of the preset time interval. At the beginning of the preset time interval, the mainspring  70  and gear train  72  are fully wound and the timeout mechanism  68  is thereby set in motion. The mainspring  70  and the gear train  72  are slowly unwound over the preset time interval via the hairspring assembly  76 , which acts to count the preset time interval. In other words, the hairspring assembly  76  operates to release the stored energy of the mainspring  70  in a controlled manner. The escapement wheel  100  gradually rotates along with the gear train  72 ; however, the palette crossarm  126  checks and releases each tooth of the escapement wheel  100  causing intermittent motion of the escapement wheel  100 . The act of checking and releasing via the palette crossarm  126  causes the palette lever  124  to sway as the palette lever  124  catches and throws the roller  120  of the balance wheel  112 . The balance wheel  112  is now set in an perpetual oscillating motion as the hairspring  108  momentarily stores the energy (i.e., rotational energy) exerted on the balance wheel  112  and releases similar, almost equal energy back to the balance wheel  112  to rotate in the opposite direction. The roller  120  is caught by the palette lever  124  causing the palette lever  124  to sway back where an adjacent tooth of the escapement wheel  100  is checked and released by the palette crossarm  126 . The aforementioned sequence of events related to the hairspring assembly  76  continues until the mainspring  70  is completely unwound and no more energy is transmitted through the gear train  72 ; thus, expiring the preset time interval. 
     When the fastener driver  10  is in the sequential mode ( FIG.  6   ), the timeout mechanism  68  is disengaged from the trigger  30  such that the operator is not required to initiate the drive cycle within the preset time interval defined by the timeout mechanism  68 . By placing the fastener driver  10  in sequential mode, the trigger  30  is displaced relative to the handle portion  22  via the cammed surface of the knob  66 . Accordingly, the trigger gear  84  is also displaced relative to the intermediate gear  88  such that the gears  84 ,  88  are no longer intermeshed. Also, the lockout linkage  80  is no longer in proximity to interfere with the trigger arm  38  of the trigger  30 . Thus, the timeout mechanism  68  is disabled when the fastener driver  10  is in the sequential mode. During operation of the fastener driver  10  in sequential mode, compressed air at high pressure is maintained within the air supply chamber  52  prior to the activation trigger  30  being actuated towards the depressed position. Air from the supply chamber  52  is guided into the trigger air chamber  58  and the main air passage  56 . Once the contact arm  46  and the activation trigger  30  (and therefore the valve stem  60 ) is actuated to the depressed position, the trigger air chamber  58  opens to atmosphere as air exits the trigger valve assembly  50 , allowing the head valve (not shown) to actuate and causing the compressed air from the air supply chamber  52  to actuate the drive mechanism  29  and the drive blade  28 . 
       FIG.  7    illustrates a fastener driver  510  in accordance with another embodiment of the invention. The fastener driver  510  includes a timeout mechanism  568  operable to inhibit a drive cycle, but is otherwise similar to the fastener driver  10  described above with reference to  FIGS.  1 - 6   , with like components being shown with like reference numerals plus  500 . Differences between the fastener drivers  10 ,  510  are described below. 
     The fastener driver  510  includes a housing  518  with a handle portion  522 , an activation trigger  530 , a contact arm  546 , and a trigger valve assembly  550 . The activation trigger  530  is disposed adjacent the handle portion  522  and is user-actuated from a default position ( FIG.  7   ) to a depressed position ( FIG.  8   ) to initiate the drive cycle to begin each drive cycle. The contact arm  546  is also movable between a biased, extended position in which fasteners are inhibited from being discharged from the magazine  14 , and a retracted position in which fasteners are permitted to be discharged from the magazine  14 . In the illustrated embodiment, the contact arm  546  mechanically interfaces with the activation trigger  530  to selectively permit a drive cycle to be initiated. The trigger valve assembly  550  is disposed adjacent the activation trigger  530 . High air pressure is released to atmosphere (i.e., atmospheric pressure) through the trigger valve assembly  550  via the valve stem  560  when the activation trigger  530  is actuated, causing the head valve (not shown) to actuate and allowing compressed air stored in the handle portion  522  to drive the drive blade  28 . 
     The timeout mechanism  568  is operable to lock the trigger  530 , and more specifically the trigger arm  538 , from being actuated in response to inactivity (i.e., lack of actuation) of the contact arm  546  over a preset time interval that begins once the trigger  530  is initially depressed, as described in further detail below. The timeout mechanism  568  is disposed within the housing  518  and includes a rack gear  592 , a mainspring  570  for driving the rack gear  592 , a gas spring or counting assembly  576  to control the release of energy from the mainspring  570 , and a lockout linkage  580  capable of interfacing with the distal end portion  538   b  of the trigger arm  538 . The timeout mechanism  568  further includes a trigger linkage  584  coupled to the pivot shaft  534  of the trigger  530  and capable of interacting with the rack gear  592 . The rack gear  592  selectively intermeshes with the rack  596  on the contact arm  546 . The lockout linkage  580  has one end pivotably coupled to the rack gear  592  and an opposite free end capable of interfering with the distal end portion  538   b  of the trigger arm  538 . A support wall  604  on the housing  518  is disposed adjacent the lockout linkage  580  and prevents the lockout linkage  580  from pivoting upward beyond the orientation shown in  FIG.  7   . 
     In operation, the fastener driver  510  is operable in two modes of operation—a first or single sequential mode ( FIG.  11   ) and a second or bump-fire mode ( FIGS.  7 - 10   ). While the fastener driver  510  is in bump-fire mode, the timeout mechanism  568  limits the amount of time an operator has to initiate a drive cycle (i.e., depress the contact arm  546  against a workpiece) after the trigger  530  is actuated to the depressed position. As illustrated in  FIG.  7   , the trigger linkage  584  is engaged with the rack gear  592  and the lockout linkage  580  is adjacent the distal end portion  538   b  of the trigger arm  538 . At this point, the mainspring  570  is unwound, and thus the rack gear  592  is in an expired state. Also, the gas spring assembly  576  is in an extended position. By actuating the trigger  530  to the depressed position as illustrated in  FIG.  8   , the trigger linkage  584  co-rotates with the trigger  530  in a counter-clockwise direction, which ultimately winds the mainspring  570  and places the rack gear  592  in an unexpired state. Specifically, rotation of the trigger linkage  584  causes the following sequence of events to simultaneously occur: (a) rotation of the rack gear  592  in a clockwise direction; (b) separation of the lockout linkage  580  and the distal end portion  538   b  of the trigger arm  538  such that interference therebetween no longer exists; and (c) actuation of the gas spring assembly  576  towards a retracted position. The mainspring  570  and the rack gear  592  are fully wound, thereby starting the preset time interval during which the operator is permitted to initiate the drive cycle. In the event the operator depresses the contact arm  546  against a workpiece (i.e., initiates the drive cycle) as illustrated in  FIG.  9   , the contact arm  546  contacts the distal end portion  538   b  of the trigger arm  538 , causing rotation of the trigger arm  538  towards the valve stem  560  at which point the central portion  538   a  of the trigger arm  538  actuates the valve stem  560 . Subsequently, the drive mechanism  29  drives the drive blade  28  to discharge a fastener through the nosepiece  526  and into the workpiece. By doing so, the rack  596  of the contact arm  546  is displaced into mesh engagement with the rack gear  592  to again cause rotation of the rack gear  592  in the clockwise direction. This time, rotation of the rack gear  592  via the rack  596  re-actuates the gas spring assembly  576  to the retracted position, thereby resetting the timeout mechanism  568  since the mainspring  570  and the rack gear  592  are fully rewound again. 
     Now, in the event the operator fails to depresses the contact arm  546  against a workpiece (i.e., initiates the drive cycle) within the preset time interval, the lockout linkage  580 , which itself is prevented from pivoting upward by the support wall  604 , mechanically interferes with the distal end portion  538   b  of the trigger arm  538 . As a result, the trigger arm  538  is no longer pivotable to actuate the valve stem  560 , as illustrated in  FIG.  10   . The support wall  604  inhibits the contact arm  546  from pivoting both the lockout linkage  580  and the trigger arm  538  if an attempt is made to depress the contact arm  546  after expiration of the preset time interval. At the beginning of the preset time interval, the mainspring  570  and rack gear  592  are fully wound and the timeout mechanism  568  is thereby set in motion. The mainspring  570  and the rack gear  592  are slowly unwound over the preset time interval via the gas spring assembly  576 . The gas spring assembly  576  includes a cylinder  608  and a piston rod  612  slidably disposed within the cylinder  608 . The gas spring assembly  576  operates as a conventional gas spring assembly, such that the gas spring assembly  576  uses compressed gas contained within the enclosed cylinder  608  sealed by the sliding piston rod  612  to pneumatically store potential energy and withstand external force applied parallel to the direction of the piston rod  612 . In other words, the gas spring assembly  576  is a viscous fluid damper that controls the unwinding (i.e., the energy release) of the mainspring  570  throughout the preset time interval. In the illustrated embodiment, the piston rod  612  is urged toward the retracted position as the rack gear  592  rotates in the clockwise direction. The piston rod  612  gradually moves toward the extended position since the piston rod  612  is biased toward the extended position. The movement of the piston rod  612  from the retracted position toward the extended position is gradual as the piston rod  612  moves slowly through the fluid (i.e., gas or liquid) contained within the cylinder  608 . Subsequently, the piston rod  612  is in the fully extended position coinciding with the mainspring  570  being completely unwound and the rack gear  592  is in the expired state. 
     When the fastener driver  510  is in the sequential mode ( FIG.  11   ), the timeout mechanism  568  is disengaged from the trigger  530  such that the operator is not required to initiate the drive cycle within the preset time interval defined by the timeout mechanism  568 . By placing the fastener driver  510  in sequential mode, the trigger  530  is displaced relative to the handle portion  522  via the cammed surface of the knob  66 . Accordingly, the trigger linkage  584  is also displaced relative to the rack gear  592  such that the trigger linkage  584  and the rack gear  592  are no longer in contact. Also, the lockout linkage  580  is no longer in proximity to interfere with the trigger arm  538  of the trigger  530 . Thus, the timeout mechanism  568  is disabled when the fastener driver  510  is in the sequential mode. During operation of the fastener driver  10  in sequential mode, compressed air at high pressure is maintained within the air supply chamber  552  prior to the activation trigger  530  being actuated towards the depressed position. Air from the supply chamber  552  is guided into the trigger air chamber  558  and the main air passage  556 . Once the contact arm  546  and the activation trigger  530  (and therefore the valve stem  560 ) are actuated to the depressed position, the trigger air chamber  558  opens to atmosphere as air exits the trigger valve assembly  550 , allowing the head valve (not shown) to actuate and causing the compressed air from the air supply chamber  552  to actuate the drive mechanism  29  and the drive blade  28 . 
       FIG.  12    illustrates a fastener driver  1010  in accordance with another embodiment of the invention. The fastener driver  1010  includes a timeout mechanism  1068  operable to inhibit a drive cycle, but is otherwise similar to the fastener driver  10  described above with reference to  FIGS.  1 - 6   , with like components being shown with like reference numerals plus  1000 . Differences between the fastener drivers  10 ,  1010  are described below. 
     The fastener driver  1010  includes a housing  1018  with a handle portion  1022 , an activation trigger  1030 , a contact arm  1046 , and a trigger valve assembly  1050 . The activation trigger  1030  is disposed adjacent the handle portion  1022  and is user-actuated from a default position ( FIG.  12   ) to a depressed position ( FIG.  13   ) to initiate the drive cycle to begin each drive cycle. The contact arm  1046  is also movable between a biased, extended position ( FIG.  14   ) in which fasteners are inhibited from being discharged from the magazine  14 , and a retracted position ( FIG.  15   ) in which fasteners are permitted to be discharged from the magazine  14 . In the illustrated embodiment, the contact arm  1046  mechanically interfaces with the activation trigger  1030  to selectively permit a drive cycle to be initiated. The trigger valve assembly  1050  is disposed adjacent the activation trigger  1030 . High air pressure is released to atmosphere (i.e., atmospheric pressure) through the trigger valve assembly  1050  via the valve stem  1060  when the activation trigger  1030  is actuated, causing the head valve (not shown) to actuate and allowing compressed air stored in the handle portion  1022  to drive the drive blade  28 . 
     In this particular embodiment, the timeout mechanism  1068  is operable to inhibit high air pressure from releasing to atmosphere by blocking the main air passage  1056 , thereby effectively disabling the valve stem  1060  in response to inactivity (i.e., lack of actuation) of the contact arm  1046  over a preset time interval that begins once the trigger  1030  is initially depressed, as described in further detail below. The timeout mechanism  1068  is disposed within the handle portion  1022  and includes a timeout air chamber or counting assembly  1076 , an air-lock pin  1080 , a sled  1086  moveable between a retracted position and an extended position within the timeout air chamber  1076 , and a spring  1088  biasing the sled  1086  toward the extended position. The air-lock pin  1080  is moveable between a first or “blocking” position (as shown in  FIG.  12   ) corresponding to the sled  1086  being in the extended position and a second “unblocking” position (as shown in  FIG.  13   ) corresponding to the sled  1086  being in the retracted position. In the blocking position, the air-lock pin  1080  substantially blocks airflow from escaping through the main air passage  1056 , whereas airflow is allowed to escape through the main air passage  1056  when the air-lock pin  1080  is in the unblocking position. The air-lock pin  1080  is pushed into the blocking position when contacted by the sled  1086  returning to the extended position shown in  FIG.  12   . Likewise, when the pin  1080  is released by the sled  1086 , compressed air in the main air passage  1056  pushes the pin  1080  from the blocking position ( FIG.  12   ) to the unblocking position ( FIG.  13   ) as a result of compressed air flooding the scallop  1078  in the pin  1080  and exerting an axial biasing force on the pin  1080  toward the unblocking position. 
     The timeout mechanism  1068  further includes a first control valve  1092 , a second control valve  1096 , a trigger linkage  1084  coupled between the trigger  1030  and the first control valve  1092 , and a trigger arm linkage  1082  coupled between the trigger arm  1038  and the second control valve  1096 . The first and second control valves  1092 ,  1096  are in fluid communication with the timeout air chamber  1076  and are capable of selectively introducing pressurized air therein. 
     In operation, the fastener driver  1010  is operable in two modes of operation—a first or single sequential mode ( FIG.  18 - 21   ) and a second or bump-fire mode ( FIGS.  12 - 17   ). While the fastener driver  1010  is in bump-fire mode, the timeout mechanism  1068  limits the amount of time an operator has to initiate a drive cycle (i.e., depress the contact arm  1046  against a workpiece) after the trigger  1030  is actuated to the depressed position. As illustrated in  FIG.  12   , the preset time interval of bump-fire mode has not started since the trigger  1030  is in the default position and the contact arm  1046  is in the extended position. Once the trigger  1030  is actuated towards the depressed position ( FIG.  13   ), pressurized air is introduced into the timeout air chamber  1076  in response to the first control valve  1092  opening (via a force exerted by the trigger linkage  1084 ), thereby actuating the sled  1086  to the retracted position. With the sled  1086  in the retracted position, the air-lock pin  1080  is urged towards the unblocking position when pressurized air within the main air passage  1056  floods the scallop  1078 . At this point, the fastener driver  1010  is ready to initiate a drive cycle upon actuation of the contact arm  1046 . In other words, the preset time interval has started during which the operator is permitted to initiate the drive cycle. 
     As illustrated in  FIG.  14   , the trigger linkage  1084  disengages a detent  1104  disposed on the trigger  1030  as the trigger  1030  approaches the fully depressed position, which causes the first control valve  1092  to slowly close and the timeout air chamber  1076  slowly loses pressure through the orifice  1098  over the preset time interval. As such, the spring  1088  gradually overcomes the pressure within the timeout air chamber  1076  and biases the sled  1086  toward the extended position. In the event the operator depresses the contact arm  1046  against a workpiece (i.e., initiates the drive cycle) as illustrated in  FIG.  15   , the contact arm  1046  contacts the distal end portion  1038   b  of the trigger arm  1038 , causing rotation of the trigger arm  1038  towards the valve stem  1060  at which point the central portion  1038   a  of the trigger arm  1038  actuates the valve stem  1060 . Since the main air passage  1056  is not blocked by the air-lock pin  1080 , the fastener driver  1010  initiates the drive cycle. The drive mechanism  29  drives the drive blade  28  to discharge a fastener through the nosepiece  1026  and into the workpiece. By doing so, the trigger arm linkage  1082  coupled to the trigger arm  1038  is displaced to open the second control valve  1096  to again introduce pressurized air into the timeout air chamber  1076 . The sled  1086  is re-actuated toward the retracted position, thereby resetting the timeout mechanism  1068  since the sled  1086  is fully retracted and the air-lock pin  1080  is not blocking the main air passage  1056 . 
     Now, in the event the operator fails to depress the contact arm  1046  against a workpiece (i.e., initiates the drive cycle) within the preset time interval, the air-lock pin  1080  mechanically blocks the main air passage  1056  at which point the valve stem  1060  is no longer able to release pressurized air to atmosphere, as illustrated in  FIG.  16   . Specifically, inactivity of the contact arm  1046  after depressing the trigger  1030  causes the following sequence of events to simultaneously occur: (a) leakage of pressurized air from the timeout air chamber  1076  through the orifice  1098 ; (b) actuation of the sled  1086  toward the extended position via the spring  1088 ; and (c) actuation of the air-lock pin  1080  to the blocking position in response to the sled  1086  being in the extended position. At this point, if the contact arm  1046  is depressed, pressurized air is introduced into the timeout air chamber  1076  behind the sled  1086  thus further biasing the sled  1086  to the extended position, as illustrated in  FIG.  17   . Thus, the drive cycle is inhibited from being initiated due to the air-lock pin  1080  being maintained in the blocking position even if the contact arm  1046  is depressed against a workpiece. 
     When the fastener driver  1010  is in the sequential mode ( FIGS.  18 - 21   ), the second control valve  1096  of the timeout mechanism  1068  is effectively disengaged such that the operator is not required to initiate the drive cycle within the preset time interval defined by the timeout mechanism  1068 . By placing the fastener driver  1010  in sequential mode, the trigger  1030  is displaced relative to the handle portion  1022  via the cammed surface of the knob  66 . Accordingly, the trigger arm linkage  1082  is also displaced relative to the second control valve  1096  such that actuation of the contact arm  1046  (and therefore the trigger arm linkage  1082 ) does not open the second control valve  1096 . Thus, during operation of sequential mode, the contact arm  1046  is first actuated to the depressed position to place the central portion  1038   a  of the trigger arm  1038  in contact with the valve stem  1060 . When an operator actuates the trigger  1030  to the depressed position, the first control valve  1092  opens (via the trigger linkage  1084 ) and pressurized air is introduced into the timeout air chamber  1076 . As a result, the air-lock pin  1080  is urged to the unblocking position ( FIG.  20   ) as a result of compressed air flooding the scallop  1078  in the pin  1080  and exerting an axial biasing force on the pin  1080  toward the unblocking position. Further, air from the supply chamber  1052  is guided into the trigger air chamber  1058  and the main air passage  1056 . The trigger air chamber  1058  opens to atmosphere as air exits the trigger valve assembly  1050 , allowing the head valve (not shown) to actuate and causing the compressed air from the air supply chamber  1052  to actuate the drive mechanism  29  and the drive blade  28 . 
       FIG.  21    illustrates a fastener driver  1510  in accordance with another embodiment of the invention. The fastener driver  1510  includes a timeout mechanism  1568  operable to inhibit a drive cycle, but is otherwise similar to the fastener driver  10  described above with reference to  FIGS.  1 - 6   , with like components being shown with like reference numerals plus  1500 . Differences between the fastener drivers  10 ,  1510  are described below. 
     The fastener driver  1510  includes a housing  1518  with a handle portion  1522 , an activation trigger  1530 , a contact arm  1546 , and a trigger valve assembly  1550 . The activation trigger  1530  is disposed adjacent the handle portion  1522  and is user-actuated from a default position ( FIG.  21   ) to a depressed position ( FIG.  22   ) to initiate the drive cycle to begin each drive cycle. The contact arm  1546  is also movable between a biased, extended position ( FIG.  21   ) in which fasteners are inhibited from being discharged from the magazine  14 , and a retracted position ( FIG.  23   ) in which fasteners are permitted to be discharged from the magazine  14 . In the illustrated embodiment, the contact arm  1546  mechanically interfaces with the activation trigger  1530  to selectively permit a drive cycle to be initiated. The trigger valve assembly  1550  is disposed adjacent the activation trigger  1530 . High air pressure is released to atmosphere (i.e., atmospheric pressure) through the trigger valve assembly  1550  via the valve stem  1560  when the activation trigger  1530  is actuated, causing the head valve (not shown) to actuate and allowing compressed air stored in the handle portion  1522  to drive the drive blade  28 . 
     The timeout mechanism  1568  is operable to lock the trigger  1530 , and more specifically the trigger arm  1538 , from being actuated in response to inactivity (i.e., lack of actuation) of the contact arm  1546  over a preset time interval that begins once the trigger  1530  is initially depressed, as described in further detail below. The timeout mechanism  1568  is disposed within the housing  1518  and includes a mainspring  1570  for driving the timeout mechanism  1568 , a counting assembly  1576  to control the release of energy from the mainspring  1570 , and a lockout linkage  1580  capable of interfacing with the distal end portion  1538   b  of the trigger arm  1538 . The lockout linkage  1580  is secured to a female barrel  1586  which, in turn, is pivotably coupled around the pivot shaft  1534  of the trigger  1530 . The lockout linkage  1580  rotates with the female barrel  1586  relative to the pivot shaft  1534 . The mainspring  1570  urges the lockout linkage  1580  towards the expired state (as shown in  FIG.  21   ), where the lockout linkage  1580  abuts a support wall  1604  of the housing  1518  to prevent the lockout linkage  1580  from pivoting beyond the orientation shown in FIG.  21 . The counting assembly  1576  further includes a damping grease (e.g., NyoGel® 767A, 774, 774L, lithium grease, etc.) disposed between the pivot shaft  1534  and the female barrel  1586  to effectively control the angular rate (i.e., angular velocity) at which the female barrel  1586  rotates about the pivot shaft  1534 . Specifically, the damping grease slows down the angular rate at which the female barrel  1586  rotates about the pivot shaft  1534 . The damping grease is operable to slow down the angular rate of rotation between the female barrel  1586  and the pivot shaft  1534  due to its positive viscous properties, thereby creating friction (i.e., opposing relative motion) between the surfaces of the barrel  1584  and the shaft  1534 . 
     In operation, the fastener driver  1510  is operable in two modes of operation—a first or single sequential mode ( FIG.  25   ) and a second or bump-fire mode ( FIGS.  21 - 24   ). While the fastener driver  1510  is in bump-fire mode, the timeout mechanism  1568  limits the amount of time an operator has to initiate a drive cycle (i.e., depress the contact arm  1546  against a workpiece) after the trigger  1530  is actuated to the depressed position. As illustrated in  FIG.  21   , the trigger  1530  is in the default position and the lockout linkage  1580  is adjacent the distal end portion  1538   b  of the trigger arm  1538 . At this point, the mainspring  1570  is unwound, and thus the counting assembly  1576  is in the expired state. By actuating the trigger  1530  to the depressed position as illustrated in  FIG.  22   , the lockout linkage  1580  (and therefore the female barrel  1586 ) is rotated in a counter-clockwise direction away from the distal end portion  1538   b  of the trigger arm  1538 , which ultimately winds the mainspring  1570  and places the counting assembly  1576  in an unexpired state. In some instances, a mechanical advantage (e.g., gearing, camming, linkage, etc.) is provided to assist the lockout linkage  1580  in rotating through an angular range of motion that is twice as large as the angular rotation of the trigger  1530  in order to set the counting assembly  1576 . In other embodiments, a secondary trigger (e.g., thumb trigger, external wheel, or the like) may alternatively be provided to set the counting assembly  1576  so that setting the counting assembly  1576  is a separate action from actuation of the trigger  1530 . 
     At this point, the mainspring  1570  and the lockout linkage  1580  are fully wound, thereby starting the preset time interval during which the operator is permitted to initiate the drive cycle. In the event the operator depresses the contact arm  1546  against a workpiece (i.e., initiates the drive cycle) as illustrated in  FIG.  23   , the contact arm  1546  contacts the distal end portion  1538   b  of the trigger arm  1538 , causing rotation of the trigger arm  1538  towards the valve stem  1560  at which point the central portion  1538   a  of the trigger arm  1538  actuates the valve stem  1560 . Subsequently, the drive mechanism  29  drives the drive blade  28  to discharge a fastener through the nosepiece  1526  and into the workpiece. When the contact arm  1546  contacts the distal end portion  1538   b , the contact arm  1538  simultaneously pushes the distal end portion  1538   b  into contact with the lockout linkage  1580  to rotate the linkage  1580  in the counter-clockwise direction back towards the unexpired state, thereby resetting the timeout mechanism  1568  since the mainspring  1570  is fully wound again. 
     Now, in the event the operator fails to depresses the contact arm  1546  against a workpiece (i.e., initiates the drive cycle) within the preset time interval, the lockout linkage  1580  rotates in the clockwise direction until contact is made with the support wall  1604  and mechanically interferes with the distal end portion  1538   b  of the trigger arm  1538  at which point the trigger arm  1538  is no longer pivotable to actuate the valve stem  1560 , as illustrated in  FIG.  24   . At this point, the lockout linkage  1580  inhibits the contact arm  1546  from being able to pivot the trigger arm  1538  if an attempt is made to depress the contact arm  1546  after expiration of the preset time interval. At the beginning of the preset time interval, the mainspring  1570  and lockout linkage  1580  are fully wound and the timeout mechanism  1568  is thereby set in motion. The mainspring  1570  and lockout linkage  1580  are slowly unwound (in the clockwise direction) over the preset time interval via the viscous grease between the female barrel  1586  and the pivot shaft  1534 . In other words, the counting assembly  1576  is a viscous fluid damper that controls the unwinding of the mainspring  1570  throughout the preset time interval. Eventually, the mainspring  1570  becomes completely unwound and the counting assembly  1576  is in the expired state after, for example, three seconds after initially being set in motion. 
     When the fastener driver  1510  is in the sequential mode ( FIG.  25   ), the timeout mechanism  1568  is inoperable from engaging with the trigger  1530  such that the operator is not required to initiate the drive cycle within the preset time interval defined by the timeout mechanism  1568 . By placing the fastener driver  1510  in sequential mode, the trigger  1530  is displaced relative to the handle portion  1522  via the cammed surface of the knob  66 . The female barrel  1586  and the lockout linkage  1580  move with the trigger  1530 ; however, one of the ends of the lockout linkage  1580  interacts with the support wall  1604 , causing the lockout linkage  1580  to pivot towards a permanent position where the lockout linkage  1580  is inhibited from interacting with the trigger arm  1538 . Thus, the lockout linkage  1580  is no longer in range to interfere with the trigger arm  1538  of the trigger  1530 . As a result, the timeout mechanism  1568  is disabled when the fastener driver  1510  is in the sequential mode. During operation of the fastener driver  1510  in sequential mode, compressed air at high pressure is maintained within the air supply chamber  1552  prior to the activation trigger  1530  being actuated towards the depressed position. Air from the supply chamber  1552  is guided into the trigger air chamber  1558  and the main air passage  1556 . Once the contact arm  1546  and the activation trigger  1530  (and therefore the valve stem  1560 ) are actuated to the depressed position, the trigger air chamber  1558  opens to atmosphere as air exits the trigger valve assembly  1550 , allowing the head valve (not shown) to actuate and causing the compressed air from the air supply chamber  1552  to actuate the drive mechanism  29  and the drive blade  28 . 
       FIG.  26    illustrates a fastener driver  2010  in accordance with another embodiment of the invention. The fastener driver  2010  includes a timeout mechanism  2068  operable to inhibit a drive cycle, but is otherwise similar to the fastener driver  10  described above with reference to  FIGS.  1 - 6   , with like components being shown with like reference numerals plus  2000 . Differences between the fastener drivers  10 ,  2010  are described below. 
     The fastener driver  2010  includes a housing  2018  with a handle portion  2022 , an activation trigger  2030 , a contact arm  2046 , and a trigger valve assembly  2050 . The activation trigger  2030  is disposed adjacent the handle portion  2022  and is user-actuated from a default position ( FIG.  26   ) to a depressed position ( FIG.  28   ) to initiate the drive cycle to begin each drive cycle. The contact arm  2046  is also movable between a biased, extended position ( FIG.  26   ) in which fasteners are inhibited from being discharged from the magazine  14 , and a retracted position ( FIG.  31   ) in which fasteners are permitted to be discharged from the magazine  14 . In the illustrated embodiment, the contact arm  2046  mechanically interfaces with the activation trigger  2030  to selectively permit a drive cycle to be initiated. The trigger valve assembly  2050  is disposed adjacent the activation trigger  2030 . High air pressure is released to atmosphere (i.e., atmospheric pressure) through the trigger valve assembly  2050  via the valve stem  2060  when the activation trigger  2030  is actuated, causing the head valve (not shown) to actuate and allowing compressed air stored in the handle portion  2022  to drive the drive blade  28 . 
     The timeout mechanism  2068  is operable to lock the trigger  2030 , and more specifically the trigger arm  2038 , from being actuated in response to inactivity (i.e., lack of actuation) of the contact arm  2046  over a preset time interval that begins once the trigger  2030  is initially depressed, as described in further detail below. The timeout mechanism  2068  is disposed within the housing  2018  and includes a mainspring  2070  for driving the timeout mechanism  2068 , a counting assembly  2076  to control the release of energy from the mainspring  2070 , and a lockout linkage  2080  capable of interfacing with the distal end portion  2038   b  of the trigger arm  2038 . The lockout linkage  2080  is secured to a female barrel  2086  which, in turn, is pivotably coupled around the pivot shaft  2034  of the trigger  2030 . The lockout linkage  2080  rotates with the female barrel  2086  relative to the pivot shaft  2034 . The mainspring  2070  urges the lockout linkage  2080  towards the expired state (as shown in  FIG.  26   ), where the trigger linkage  2084  abuts a support wall  2104  of the housing  2018  to prevent the lockout linkage  2080  from pivoting beyond the orientation shown in  FIG.  26   . The counting assembly  2076  includes a damping grease (e.g., NyoGel® 767A, 774, 774L, lithium grease, etc.) disposed between the pivot shaft  2034  and the female barrel  2086  to effectively control the angular rate (i.e., angular velocity) at which the female barrel  2086  rotates about the pivot shaft  2034 . Specifically, the damping grease slows down the angular rate at which the female barrel  2086  rotates about the pivot shaft  2034 . The damping grease is operable to slow down the angular rate of rotation between the female barrel  2086  and the pivot shaft  2034  due to its positive viscous properties, thereby creating friction (i.e., opposing relative motion) between the surfaces of the barrel  2084  and the shaft  2034 . 
     The timeout mechanism  2068  further includes a 3-bar linkage system, where the trigger  2030  constitutes one of the linkages, a second linkage  2088  is pivotably coupled to the housing  2018 , and a third linkage  2092  is pivotably coupled between both the trigger  2030  and the third linkage  2088 . The trigger  2030  drives movement of the second and third linkages  2088 ,  2092 . For example, the third linkage  2092  is driven upwardly when the trigger  2030  is depressed to the depressed position, causing the second linkage  2088  to rotate in a clockwise direction. In contrast, the third linkage  2092  is driven downwardly when the trigger  2030  is released to the default position, causing the second linkage  2088  to rotate in the counter-clockwise direction. The second linkage  2088  includes a compressible tip  2096  that is selectively engageable with a projection  2100  of the female barrel  2086 . The compressible tip  2096  is slidable between a first position ( FIG.  26   ) and a second position ( FIG.  34   ). Although the compressible tip  2096  of the illustrated embodiment is slidable between the first and second positions, in other embodiments, the tip  2096  could alternatively be a deformable tip that deflects between first and second positions. 
     In operation, the fastener driver  2010  is operable in two modes of operation—a first or single sequential mode and a second or bump-fire mode ( FIGS.  26 - 35   ). While the fastener driver  2010  is in bump-fire mode, the timeout mechanism  2068  limits the amount of time an operator has to initiate a drive cycle (i.e., depress the contact arm  2046  against a workpiece) after the trigger  2030  is actuated to the depressed position. As illustrated in  FIG.  26   , the trigger  2030  is in the default position and the lockout linkage  2080  is adjacent the distal end portion  2038   b  of the trigger arm  2038 . At this point, the mainspring  2070  is unwound, and thus the counting assembly  2076  is in the expired state. By actuating the trigger  2030  to the depressed position as illustrated in  FIGS.  27  and  28   , the lockout linkage  2080  (and therefore the female barrel  2086 ) is rotated in a counter-clockwise direction away from the distal end portion  2038   b  of the trigger arm  2038 , which ultimately winds the mainspring  2070  and places the counting assembly  2076  in an unexpired state. Specifically, the lockout linkage  2080  is rotated in the counter-clockwise direction as the second linkage  2088  exerts a torsional force on the projection  2100  of the female barrel  2086  by way of the trigger  2030  and third linkage  2092  being actuated. Once the trigger  2030  is in the depressed position, the compressible tip  2096  of the second linkage  2088  no longer interferes with the projection  2100  of the female barrel  2086 ; thus activating the preset time interval ( FIG.  28   ). 
     At this point, the mainspring  2070  and the lockout linkage  2080  are fully wound, thereby starting the preset time interval during which the operator is permitted to initiate the drive cycle. In the event the operator depresses the contact arm  2046  against a workpiece (i.e., initiates the drive cycle) as illustrated in  FIGS.  30  and  31   , the contact arm  2046  contacts the distal end portion  2038   b  of the trigger arm  2038 , causing rotation of the trigger arm  2038  towards the valve stem  2060  at which point the central portion  2038   a  of the trigger arm  2038  actuates the valve stem  2060 . Subsequently, the drive mechanism  29  drives the drive blade  28  to discharge a fastener through the nosepiece  2026  and into the workpiece. When the contact arm  2046  contacts the distal end portion  2038   b , the contact arm  2038  simultaneously pushes the distal end portion  2038   b  into contact with the lockout linkage  2080  to rotate the linkage  2080  counter-clockwise back towards the unexpired state, thereby resetting the timeout mechanism  2068  since the mainspring  2070  is fully wound again. 
     Now, in the event the operator fails to depresses the contact arm  2046  against a workpiece (i.e., initiates the drive cycle) within the preset time interval, the lockout linkage  2080  rotates clockwise until contact is made with the support wall  2104  ( FIG.  32   ) and mechanically interferes with the distal end portion  2038   b  of the trigger arm  2038  at which point the trigger arm  2038  is no longer pivotable to actuate the valve stem  2060 , as illustrated in  FIG.  33   . At this point, the lockout linkage  2080  inhibits the contact arm  2046  from being able to pivot the trigger arm  2038  if an attempt is made to depress the contact arm  2046  after expiration of the preset time interval. At the beginning of the preset time interval, the mainspring  2070  and lockout linkage  2080  are fully wound and the timeout mechanism  2068  is thereby set in motion. The mainspring  2070  and lockout linkage  2080  are slowly unwound (in the clockwise direction) over the preset time interval via the viscous grease between the female barrel  2086  and the pivot shaft  2034 . In other words, the counting assembly  2076  is a viscous fluid damper that controls the unwinding of the mainspring  2070  throughout the preset time interval. Eventually, the mainspring  2070  becomes completely unwound and the counting assembly  2076  is in the expired state after, for example, three seconds after initially being set in motion. 
     When the fastener driver  2010  is in the sequential mode, the timeout mechanism  2068  is inoperable from engaging with the trigger  2030  such that the operator is not required to initiate the drive cycle within the preset time interval defined by the timeout mechanism  2068 . By placing the fastener driver  2010  in sequential mode, the trigger  2030  is displaced relative to the handle portion  2022  via the cammed surface of the knob  66 . The lockout linkage  2080  and the third linkage  2092  move with the trigger  2030 , causing the second linkage  2088  to pivot towards a permanent position where the lockout linkage  2080  is inhibited from interacting with the trigger arm  2038 . Thus, the lockout linkage  2080  is no longer in proximity to interfere with the trigger arm  2038  of the trigger  2030 . As a result, the timeout mechanism  2068  is disabled when the fastener driver  2010  is in the sequential mode. During operation of the fastener driver  2010  in sequential mode, compressed air at high pressure is maintained within the air supply chamber  2052  prior to the activation trigger  2030  being actuated towards the depressed position. Air from the supply chamber  2052  is guided into the trigger air chamber  2058  and the main air passage  2056 . Once the contact arm  2046  and the activation trigger  2030  (and therefore the valve stem  2060 ) are actuated to the depressed position, the trigger air chamber  2058  opens to atmosphere as air exits the trigger valve assembly  2050 , allowing the head valve (not shown) to actuate and causing the compressed air from the air supply chamber  2052  to actuate the drive mechanism  29  and the drive blade  28 . 
     Although the invention has been described in detail with reference to certain preferred embodiments, variations and modifications exist within the scope and spirit of one or more independent aspects of the invention as described.