Patent Publication Number: US-10759029-B2

Title: Powered fastener driver and operating method thereof

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of International Patent Application No. PCT/CN2014/077551, filed on May 15, 2014, which claims priority to U.S. Provisional Patent Application No. 61/970,963, filed on Mar. 27, 2014, the entire contents of both are incorporated herein by reference. 
     FIELD OF THE INVENTION 
     The present invention relates to power tools, and more specifically to powered fastener drivers. 
     BACKGROUND OF THE INVENTION 
     There are various fastener drivers known in the art for driving fasteners (e.g., nails, tacks, staples, etc.) into a workpiece. These fastener drivers operate utilizing various means known in the art (e.g., compressed air generated by an air compressor, electrical energy, flywheel mechanisms), but often these designs are met with power, size, and cost constraints. 
     SUMMARY OF THE INVENTION 
     The invention provides, in one aspect, a powered fastener driver including a cylinder and a drive piston within the cylinder being acted on by a driving force resulting from a pressure differential. The powered fastener further includes a drive blade coupled to the drive piston and operable to drive a fastener, and an adjustable valve for selectively introducing air from ambient atmosphere into the cylinder, thereby changing the pressure differential acting on the drive piston. 
     Changing the pressure differential acting on the drive piston may change a driving depth of the fastener. 
     A larger pressure differential acting on the drive piston may increase the driving depth of the fastener. 
     The adjustable valve may include a lever that is movable to adjust the amount of air from ambient atmosphere introduced into the cylinder. 
     The lever may be rotatable to adjust the amount of air from ambient atmosphere introduced into the cylinder. 
     The adjustable valve may include an end cap secured to one end of the cylinder, wherein the end cap has an aperture therein, and a shutter movable to block at least a portion of the aperture. 
     The shutter may be movable between a first position in which the aperture is substantially unblocked and a second position in which the aperture is substantially blocked. The pressure differential acting on the drive piston when the shutter is in the first position is greater than when the shutter is in the second position. 
     The adjustable valve may include a lever that is manipulatable by a user of the fastener driver and that is coupled for co-rotation with the shutter. 
     The adjustable valve may be located above the drive piston in a top portion of the cylinder. 
     A screen may be positioned between the adjustable valve and the atmosphere. 
     The pressure differential acting on the drive piston may be defined in part by a vacuum created within the cylinder. 
     The powered fastener driver may include a reciprocating piston within the cylinder for creating the vacuum. 
     The invention provides, in another aspect, a powered fastener driver including a cylinder, a reciprocating piston within the cylinder, and a drive blade. The powered fastener driver further includes a latch holding the drive blade in position while being acted on by a driving force, and a trip member carried by the reciprocating piston for disengaging the latch from the drive blade, thereby allowing the drive blade to move under the influence of the driving force. 
     The powered fastener may further include a drive piston coupled to the drive blade. 
     The driving force may result from a pressure differential acting on the drive piston. 
     The pressure differential may be created by a vacuum developed between the drive piston and the reciprocating piston. 
     The vacuum may be developed by moving the reciprocating piston away from the drive piston. 
     The reciprocating piston may include a first side facing the drive piston and a second side opposite the first side. The trip member may be coupled to the second side. 
     The drive blade may include a notch. 
     The latch may include a pin that is receiveable in the notch. 
     The powered fastener driver may include a spring biasing the latch towards the drive blade. 
     The pressure differential may increase as the reciprocating piston approaches the latch. 
     The invention provides, in another aspect, a powered fastener driver including a cylinder, a reciprocating piston within the cylinder, and a leak path at least partially defined by the piston that selectively fluidly communicates portions of the cylinder adjacent, respectively, opposite sides of the piston. The powered fastener driver further includes a seal carried by the piston. The seal is movable relative to the piston between a first position in which the seal is engaged with the piston for blocking the leak path, and a second position in which the seal is disengaged from the piston for unblocking the leak path. 
     The powered fastener driver may include a drive piston having a drive blade that passes through the reciprocating piston. 
     The seal, when in the first position, may seal a space within the cylinder between the drive piston and the reciprocating piston. 
     The seal, when in the second position, may unseal the space within the cylinder between the drive piston and the reciprocating piston. 
     The reciprocating piston may include a recess in which the seal is received when in the first position. 
     The reciprocating piston may include a bracket that supports the seal when in the second position. 
     The seal may be moved between the first position and the second position by frictional contact between the seal and the drive blade. 
     The drive blade may pass through an aperture in the seal. 
     The seal may include a rib extending into a groove formed in the drive blade. 
     The leak path may be at least partially defined by the recess when the seal is in the second position. 
     The powered fastener driver may include a first lip seal coupled to a circumference of the reciprocating piston and extending radially outward to contact the cylinder. 
     The powered fastener driver may include a second lip seal coupled to a circumference of the drive piston and extending radially outward to contact the cylinder. 
     The powered fastener driver may include a rack coupled to the reciprocating piston. 
     The seal, when in the first position, may seal a space within the cylinder between the drive piston and the reciprocating piston. 
     The seal, when in the second position, may unseal the space within the cylinder between the drive piston and the reciprocating piston. 
     The reciprocating piston may include a recess in which the seal is received when in the first position. 
     The powered fastener driver may include a fastener connecting the rack to the reciprocating piston. The seal may be disposed around a shank of the fastener. 
     The seal may be moved between the first position and the second position in response to displacement of the rack relative to the reciprocating piston. 
     The seal may be an O-ring. 
     The leak path may be at least partially defined by the recess when the seal is in the second position. 
     The invention provides, in another aspect, a method of operating a powered fastener driver having a cylinder, a drive piston within the cylinder having a drive blade, and a reciprocating piston within the cylinder through which the drive blade is extendable. The method includes maintaining the drive piston within the cylinder at a top dead center position, and moving the reciprocating piston away from the drive piston at a first speed while the drive piston is maintained at the top dead center position. The method further includes detecting the reciprocating piston with a monitoring system prior to the reciprocating piston reaching a bottom dead center position within the cylinder, and decelerating the reciprocating piston from the first speed in response to being detected. 
     The method may include releasing the drive piston from the top dead center position once the reciprocating piston reaches the bottom dead center position. 
     The method may include moving the reciprocating piston toward the drive piston at a second speed once the drive piston has been released from the top dead center position. 
     The method may include detecting the drive piston with the monitoring system prior to the drive piston reaching the top dead center position, and decelerating the reciprocating piston from the second speed in response to being detected. 
     The method may include detecting the reciprocating piston with the monitoring system prior to the reciprocating piston reaching the top dead center position, and continuing to move the reciprocating piston toward the drive piston for a predetermined period of time. 
     The method may include detecting abnormal operation with the monitoring system. 
     The method may include moving the reciprocating piston toward the drive piston in response to detecting abnormal operation. 
     In another aspect of the present invention, a powered fastener driver includes a cylinder; a reciprocating piston within the cylinder; a driving module connected to the reciprocating piston to drive the same for moving within the cylinder; a user actuating device connected to the driving module to control activation of the driving module; a magazine adapted to store a plurality of fasteners; and a lock out mechanism connected to the magazine. The lock out mechanism further contains a lock member movable between a first position in which the lock member unlocks the user actuating device to operate and a second position in which the lock member locks the user actuating device from operation. 
     The lock out mechanism may include a fastener push mechanism adapted to urge the lock member to move from the first position to the second position. 
     The fastener push mechanism may urge the lock member to move from the first position to the second position when the fasteners in the magazine are depleted. 
     The lock member may be rotatable around a hinge; the fastener push mechanism adapted to urge the lock member to rotate from the first position to the second position. 
     The powered fastener driver may also include a contact member. When the lock member is at the first position, the contact member separated from the lock member; when the lock member is at the second position, the contract member engaging and locked by the lock member. 
     In another aspect of the present invention, a powered fastener driver contains a cylinder; a reciprocating piston within the cylinder; a motor for providing driving power; a driving module connected to the motor and the reciprocating piston such that the driving power is provided to the reciprocating piston for moving within the cylinder; wherein the driving module further comprising a rotary member, and a clutch mechanism between the motor and the rotary member; the rotary member connecting to the reciprocating piston; the clutch mechanism adapted to selectively engage the motor with the reciprocating piston. 
     The rotary member may be a ring gear. The clutch mechanism may further include at least length-variable clutching element that can be configured to change between at least a first length and a second length. 
     The clutching element may include a spring. Oone end of the spring is connected to one of the rotary member and the motor. The other end of the spring connected to a detent member which in turn connects to the other one of the rotary member and the motor. 
     The first length may be an uncompressed length of the spring, and the second length may be the minimum length of the spring after compression. 
     The detent member may be a detent ball. The other one of the rotary member and the motor facing the detent ball has a surface on which there is formed two or more protrusions. Between two the protrusions there is formed a groove. When the clutching element is at the first length, rotation of the ring gear causes the detent ball to move along the groove and bypass the protrusions, so that the motor is not driven by the rotation of the ring gear. When the clutching element is at the second length, rotation of the motor causes the detent ball to be confined in the groove and not capable of bypassing the protrusions, so that the ring gear is driven to rotate by the motor. 
     Other aspects of the invention will become apparent by consideration of the 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 partial cutaway view of the powered fastener driver of  FIG. 1  with a cylinder shown in phantom. 
         FIG. 3  is a perspective view of a drive assembly of the powered fastener driver of  FIG. 1 . 
         FIG. 4A  is a cross-sectional view of a latch in a first, engaged position of the power fastener driver of  FIG. 1 . 
         FIG. 4B  is a cross-sectional view of the latch of  FIG. 4A  in a second, released position. 
         FIG. 5A  is a cross-sectional view of a reciprocating piston of the powered fastener driver of  FIG. 1  traveling in a first direction having seals in a first, sealed position taken along line  5 A- 5 A in  FIG. 2 . 
         FIG. 5B  is a cross-sectional view of the reciprocating piston of  FIG. 5A  traveling in a second direction having seals in a second, unsealed position. 
         FIG. 5C  is a cross-sectional view of the reciprocating piston of  FIG. 5A  traveling in the first direction having seals in the first, sealed position taken along line  5 C- 5 C in  FIG. 2 . 
         FIG. 5D  is a cross-sectional view of the reciprocating piston of  FIG. 5C  traveling in the second direction having seals in the second, unsealed position. 
         FIG. 6A  is a top perspective view of a drive blade and blade seal of the powered fastener driver of  FIG. 1 . 
         FIG. 6B  is a bottom perspective view of the drive blade and blade seal of  FIG. 6A . 
         FIG. 7A  is a partial, cross-sectional view of a backup static seal in accordance with another embodiment of the invention in a first, sealed position. 
         FIG. 7B  is a partial, cross-sectional view of the backup static seal of  FIG. 7A  in a second, unsealed position. 
         FIG. 8  is a cross-sectional view of a reciprocating piston with a lip seal in accordance with another embodiment of the invention. 
         FIG. 9A  is a rear perspective view of an adjustable valve of the powered fastener driver of  FIG. 1 , in a first position with some components removed for clarity. 
         FIG. 9B  is a rear perspective view of the adjustable valve of  FIG. 9A  in a second position. 
         FIG. 9C  is an exploded view of the adjustable valve of  FIG. 9A . 
         FIG. 10A  is a cross-sectional view of the powered fastener driver of  FIG. 1  illustrating both the reciprocating piston and a drive piston in a top dead center position. 
         FIG. 10B  is a cross-sectional view of the powered fastener driver of  FIG. 10A  illustrating the reciprocating piston in a bottom dead center position and the drive piston in the top dead center position. 
         FIG. 10C  is a cross-sectional view of the powered fastener driver of  FIG. 10A  illustrating both the reciprocating piston and the driver piston in a bottom dead center position. 
         FIG. 10D  is a cross-sectional view of the powered fastener driver of  FIG. 10A  illustrating an upward stroke of the reciprocating piston and the driver piston toward the top dead center positions for both pistons. 
         FIG. 11  is a flow chart illustrating a method of operating the powered fastener driver of  FIG. 1 . 
         FIG. 12  is a flow chart illustrating the method of operating the powered fastener driver of  FIG. 1  under abnormal conditions. 
         FIGS. 13A-13D  show various check valves used in the powered fastener driver in alternative embodiments. 
         FIGS. 14A-14G  show various blade seals used in the powered fastener driver in alternative embodiments. 
         FIG. 15  illustrates a cross-sectional view of a latch mechanism used in the powered fastener driver in alternative embodiment. 
         FIG. 16  shows a lock out mechanism used in the powered fastener driver according to one embodiment of the present invention. 
         FIG. 17  shows the pusher used in the lock out mechanism in  FIG. 16 . 
         FIG. 18  illustrates the lock plate and pusher configuration in the lock out mechanism in  FIG. 16 . 
         FIGS. 19A and 19B  show the lock out mechanism in its unlocking position and locking position respectively. 
         FIG. 20  illustrates the cross-sectional view of a clutch mechanism used in the powered fastener driver according to one embodiment of the present invention. 
         FIG. 21  shows the perspective view of the clutch mechanism in  FIG. 20 . 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 following drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  illustrates a vacuum powered fastener driver  10  operable to drive fasteners (e.g., nails, tacks, staples, etc.) held within a magazine  14  into a workpiece. The fastener driver  10  includes an outer housing  18  with a handle portion  22 , and a user-actuated trigger  26  mounted on the handle portion  22 . The fastener driver  10  does not require an external source of air pressure, but rather includes an on-board vacuum system  30  ( FIG. 2 ). The vacuum system  30  is powered by a power source (e.g., a battery pack  34 ), coupled to a battery attachment portion  38  of the outer housing  18 . In alternative embodiments, alternative power sources (i.e., an electrical cord) may provide power to the vacuum system  30 . 
     With reference to  FIGS. 2 and 3 , the fastener driver  10  includes a drive blade  42  actuated by the vacuum system  30  to drive the fasteners into a workpiece. The vacuum system  30  includes a variable-volume vacuum chamber  46  defined within a cylinder  50 , between a drive piston  54  and an elevator or a reciprocating piston  58  ( FIG. 2 ). The drive blade  42  is coupled to the drive piston  54 , and the vacuum chamber  46  creates a driving force as a result of differential pressure acting on the drive piston  54 . The reciprocating piston  58  is driven in a reciprocating manner by a drive assembly  60  ( FIG. 3 ). In the illustrated embodiment of the fastener driver  10 , the drive assembly  60  includes a motor  74 , a transmission  70  that receives torque from the motor, a pinion  66  drivably coupled to the output of the transmission  70 , and a rack  62  meshed with the pinion  66  and connected to the drive piston  54  for reciprocation therewith. With reference to  FIG. 2 , a vacuum is developed within the vacuum chamber  46  by moving the reciprocating piston  58  away from the drive piston  54 , while the position of the drive piston  54  is held or maintained. A bumper  76  is positioned in a bottom portion of the cylinder  50  and absorbs impact forces from the reciprocating piston  58  and drive piston  54 . The bumper  76  includes projections  77  that are received in corresponding recesses (not shown) formed in the reciprocating piston  58 . 
     With reference to  FIGS. 3-4B , a latch  78  is provided to engage the drive blade  42  and hold the drive piston  58  in a top dead center (TDC) position ( FIG. 10A ) until a trip member  82  extending from the reciprocating piston  58  actuates the latch  78  to disengage the drive blade  42 . In the illustrated embodiment, the reciprocating piston  58  includes a first side  86  facing the drive piston  54  and a second side  90  opposite the first side  86 , with the trip member  82  extending from the second side  90 . With reference to  FIG. 4A , the latch  78  is biased by a spring  94  to pivot the latch  78  about a pivot pin  98 , towards the drive blade  42 . The drive blade  42  includes a notch  102  in which a pin  106  on the latch  78  is received to engage the drive blade  42  and maintain the drive piston  54  in the TDC position. When the reciprocating piston  58  reaches a bottom dead center (BDC) position ( FIG. 10C ), the trip member  82  actuates the latch  78  by counteracting the biasing force of the spring  94  to pivot the pin  106  out of the notch  102 , releasing the drive blade 
       42 . Once the latch  78  has been disengaged from the drive blade  42 , the drive blade  42  is thereby allowed to move under the influence of the driving force acting on the drive piston  54 . In the illustrated embodiment, the pressure differential acting on the drive piston  54  increases as the reciprocating piston  58  approaches its BDC position. Both the drive piston  54  and the reciprocating piston  58  are movable between TDC positions ( FIG. 10A ) and BDC positions ( FIG. 10C ). 
     With reference to  FIG. 5B , leak paths  110 ,  114  through the reciprocating piston  58 , when opened or unblocked, fluidly communicate portions of the cylinder  50  adjacent, respectively, opposite sides  86 ,  90  of the reciprocating piston  58 . The reciprocating piston  58  includes an aperture  118  through which the drive blade  42  extends, and the fastener driver  10  further includes seals  122 ,  126  carried by the reciprocating piston  58 . The seals  122 , 126  are movable relative to the reciprocating piston  58  between a first position ( FIG. 5A ) in which the seals  122 ,  126  are engaged with the reciprocating piston  58  for blocking the leak paths  110 ,  114 , and a second position ( FIG. 5B ) in which the seals  122 ,  126  are disengaged from the reciprocating piston  58  for unblocking the leak paths  110 ,  114 , respectively. In other words, the seals  122 ,  126 , when in the first position, seal the variable-volume vacuum chamber  46 , and the seals  122 ,  126 , when in the second position, unseal the vacuum chamber  46  to fluidly communicate the vacuum chamber  46  with the space within the cylinder  50  below the reciprocating piston  58 . In the illustrated embodiment, the reciprocating piston  58  includes both a blade seal  122  and a rack seal  126 , the details of which are described below. In alternative embodiments, any number of seals may be included and the seals may be positioned on either the drive piston or the reciprocating piston. 
     With reference to  FIGS. 5A-6B , the reciprocating piston  58  includes a recess  138  in which the blade seal  122  is received when in the first position, and a bracket  142  that supports the blade seal  122  when in the second position. The blade seal  122  includes a projection  146  ( FIGS. 6A and 6B ) to facilitate alignment of the blade seal  122  with the recess  138 , and an aperture  150  through which the drive blade  42  passes. The blade seal  122  is moved between the first position ( FIG. 5A ) and second position ( FIG. 5B ) by relative movement between the reciprocating piston  58  and the drive blade  42 , relying upon frictional contact between the blade seal  122  and the drive blade  42  to maintain a generally tight, sliding fit between the blade seal  122  and the drive blade  42 . The leak path  110  is at least partially defined by the recess  138  when the blade seal  122  is in the second position and the aperture  118 . In the illustrated embodiment, the drive blade  42  includes grooves  154  formed in one side of the drive blade  42 , and the blade seal  122  includes ribs  158  extending into the grooves  154  to ensure fit between the drive blade  42  and blade seal  122  ( FIGS. 6A and 6B ). 
     With reference to  FIGS. 5A and 5B , the reciprocating piston  58  includes a first recess  162  in which the rack seal  126  is received when in the first position, and a second recess  166  in which the rack  62  is received. A fastener  170  connects the rack  62  to the reciprocating piston  58 , and the rack seal  126  is disposed around a shank  174  of the fastener  170 . In the illustrated embodiment, the rack seal  126  is an O-ring. In alternative embodiments, the rack seal is a lip seal. The rack seal  126  is moved between the first position and the second position in response to relative movement between the rack  62  and the reciprocating piston  58  (i.e., when the rack  62  is driven upwards or downwards by the motor  74 ). The leak path  114  ( FIG. 5B ) is at least partially defined by the recesses  162 ,  166  and an aperture  176  communicating the recesses  162 ,  166  when the seal  126  is in the second position. In the illustrated embodiment, the leak path  144  is formed at least in part through a groove  178  formed in the rack  62 . In alternative embodiments, the leak path is formed at least in part through a groove formed in the reciprocating piston. 
     With reference to  FIGS. 5C and 5D , the reciprocating piston  58  further includes a check valve seal  177  and a leak path  179  ( FIG. 5D ) through the reciprocating piston  58  that when opened or unblocked, fluidly communicates portions of the cylinder  50  adjacent, respectively, opposite sides  86 ,  90  of the reciprocating piston  58 . The check valve seal  177  is movable relative to the reciprocating piston  58  between a first position ( FIG. 5C ) in which the seal  177  is engaged with the reciprocating piston  58  for blocking the leak path  179 , and a second position ( FIG. 5D ) in which the seal  177  is disengaged from the reciprocating piston  58  for unblocking the leak path  179 . The leak path  179  is formed at least partially through an aperture  180  formed within the reciprocating piston  58 . The check valve seal  177  is biased toward the first position by a spring  181  positioned between an end cap  183  and the check valve seal  177 . The check valve seal  177  is moved between the first position and the second position in response to pressure created between the reciprocating piston  58  and the drive piston  54 . For example, the seal  177  is moved from the first position to the second position in response to a positive pressure created between the reciprocating piston  58  and the drive piston  54 . In the illustrated embodiment, the check valve seal  177  is in addition to the blade seal  122  and the rack seal  126 . 
     However, in alternative embodiments, the blade seal  122  and the rack seal  126  can be omitted, and only the check valve seal  177  could be used in the reciprocating piston  58  for sealing and unsealing the leak path  179 . In further alternative embodiments, any number or combination of the blade seal  122 , rack seal  126 , and check valve seal  177  can be used. For example, in some embodiments, two of the three seals  122 ,  126 , and  177  could be utilized while, in other embodiments, only one of the three seals  122 ,  126 ,  177  could be utilized. 
     With reference to  FIGS. 7A and 7B , an alternative embodiment of a powered fastener driver  10 ′ is shown, with like components and features being shown with like reference numerals with a single prime (′) mark. The driver  10 ′ includes a backup static seal  182  located in a top portion  186  of the cylinder  50 ′ and is coupled to a ring  190 . The ring  190  is coupled to an end cap  194  via a stop screw  198  and is adjustable to set the distance the ring  190  is spaced from the cap  194 . A spring  202  biases the ring  190  away from the end cap  194  and toward the drive piston  54 ′. When the drive piston  54 ′ is being held in the TDC position ( FIG. 7A ), the outer periphery of the drive piston  54 ′ abuts and compresses the backup static seal  182 , displacing the ring  190  toward the end cap  194  against the bias of the spring  202 , to further seal the variable volume vacuum chamber  46 ′ from atmosphere. The backup static seal  182  works in conjunction with a dynamic piston seal (i.e., a lip seal  130 ′) positioned around the periphery of the drive piston  54 ′. When the drive piston  54 ′ is released from the TDC position ( FIG. 7B ), the backup static seal  182  is returned by the spring  202  to the extended position, which is determined by the stop screw  198 . 
     In the illustrated embodiment, the fastener driver  10  further includes a first lip seal  130  coupled to a circumference of the drive piston  54  and extending radially outward to contact the cylinder  50  ( FIG. 2 ). In alternative embodiments, the fastener driver includes a second lip seal  134  coupled to a circumference of the reciprocating piston  58  and extending radially outward to contact the cylinder  50  ( FIG. 8 ). The second lip seal  134  works in combination with an O-ring seal  135 . In alternative embodiments, the O-ring seal  135  is replaced with an additional lip seal. 
     With reference to  FIGS. 9A-9C , the powered fastener  10  further includes an adjustable valve for selectively introducing air from ambient atmosphere into the cylinder  50 , thereby changing the pressure differential acting on the drive piston  54  which, in turn, changes a driving depth of the fasteners. In the illustrated embodiment of the powered fastener  10 , the adjustable valve is configured as an adjustable shutter assembly  206  including an end cap  210 , an adjustment mechanism (i.e., a lever  214 ), and a shutter  218  ( FIG. 9C ). The end cap  210  is secured to a top portion  222  of the cylinder  50  and includes apertures  226  formed therein. In the illustrated embodiment, the adjustable shutter assembly  206  is located above the drive piston  54  in the top portion  222  of the cylinder  50 . The lever  214  is manipulatable by a user of the fastener driver  10  and is integrally formed with a frame  230  that is securely attached to the shutter  218  for co-rotation therewith. The shutter  218  is rotatable to block part of ( FIG. 9A ), or none ( FIG. 9B ) of the apertures  226  formed in the end cap  210 . When the apertures  226  are unblocked by the shutter  218 , either partially or fully, the apertures  226  are exposed to atmospheric pressure. In other words, the lever  214  is rotatable to adjust the amount of air from ambient atmosphere that can be drawn into the cylinder  50  and above the drive piston  54 . In alternative embodiments, the lever  214  can by any type of adjustment member (e.g., a knob, a slide, etc.) and can be movable in any fashion (e.g., by pivoting, sliding, etc.). 
     With reference to  FIG. 9C , an exploded view of the adjustable shutter assembly  206  is illustrated. The end cap  210  includes a plurality of teeth  238  that are engageable by opposed detents  242  provided on the shutter  218  for holding the shutter  218  and lever  214  in the positions shown in  FIGS. 9A and 9B , and any intermediate position therebetween. With reference to  FIG. 9C , a screen  234  (not shown for clarity in  FIGS. 9A and 9B ) is sandwiched between the frame  230  and the shutter  218 , and prevents outside debris from entering the cylinder  50  through the apertures  226 . The frame  230  is secured to the shutter  218  for co-rotation therewith by ribs  246  formed on a hub  250  of the shutter  218  that are received in corresponding grooves  254  formed in the frame  230 . In addition, a fastener  258  secures the frame  230 , the shutter  218 , and the end cap  210  to the housing  18 . In alternative embodiments, the lever, the frame, the shutter, and the screen can be integrally formed as a single component. 
     By adjusting the lever  214 , and correspondingly the portion of each of the apertures  226  blocked by the shutter  218 , a user may adjust the force applied to the drive piston  54  and the drive blade  42 . Specifically, the shutter  218  adjusts the pressure differential acting on the drive piston  42  by providing a controlled leak through the apertures  226  to atmospheric pressure. For example, with the majority of each aperture  226  closed ( FIG. 9A ) a relatively low pressure, or even a competing vacuum, is formed in the cylinder  50  above the drive piston  54  as it descends in the cylinder  50 . This yields a relatively small pressure differential acting on the drive piston  54 , causing the drive piston  54  and the drive blade  42  to be driven with a relatively lower force. Alternatively, with the apertures  226  completely unblocked by the shutter  218  ( FIG. 9B ), the top of the drive piston  54  is exposed to substantially atmospheric pressure as it descends in the cylinder  50 . This yields a relatively large pressure differential acting on the drive piston  54 , causing the drive piston  54  and the drive blade  42  to be driven with a relatively higher force. 
     In operation, the vacuum powered fastener driver  10  undergoes a drive cycle, shown in  FIGS. 10A-10D , that is repeated to drive each successive fastener. With reference to  FIG. 10A , the drive cycle begins with both the reciprocating piston  58  and the drive piston  54  located in the TDC position. The reciprocating piston  58  is then lowered by the rack  62  to expand the vacuum chamber  46 , thereby creating a pressure differential acting on the drive piston  54 . The drive piston  54  however, is held in its TDC position by the latch  78 , as shown in  FIG. 10B . As the reciprocating piston  58  is lowered by the rack  62 , the leak paths  110 ,  114  are closed by the blade seal  122  and the rack seal  126 , as described above, to seal off the first side  86  of the reciprocating piston  58  from the second side  90 . With reference to  FIG. 10C , when the reciprocating piston  58  reaches its BDC position, the trip member  82  actuates the latch  78  to disengage the drive blade  42 , thereby releasing the drive piston  54 . At this time, the drive piston  54  is acted upon by a driving force caused by the pressure differential to accelerate the drive piston  54  toward the reciprocating piston  58  for driving a fastener with the driver blade  42 . Finally, with reference to  FIG. 10D , the reciprocating piston  58  is driven back to its TDC position by the rack  62 . The reciprocating piston  58  also pushes or lifts the drive piston  54  back to its TDC position as well. As the reciprocating piston  58  is driven back to its TDC position, the leak paths  110 ,  114  are opened by the blade seal  122  and the rack seal  126 , as described above, to fluidly communicate the first side  86  of the reciprocating piston  58  with the second side  90 . When the drive piston  54  is returned to its TDC position, the latch  78  re-engages the drive blade  42  to lock the drive piston  54  into its TDC position ( FIG. 10A ). 
     The drive cycle is initiated when a user actuates the trigger  26 . Electrical power to the motor  74  is provided through the trigger  26  such that if a user releases the trigger  26  as the reciprocating piston  58  is moving away from the drive piston  54  during a fastener driving sequence, the drive cycle is stopped before the fastener is driven. However, in order to ensure proper operation, electrical power only passes through the trigger  26  for the nail driving sequence (i.e., with the drive blade  42  being driven downward), and the motor  74  can still operate to return the reciprocating piston  58  and the drive piston  54  to their TDC positions when the trigger  26  is not depressed. After the drive cycle has been stopped in response to releasing the trigger  26 , the reciprocating piston  58  is driven back toward its TDC position by the motor  74 , which is powered through an alternative electrical circuit. In other words, if the trigger  26  is released while the reciprocating piston  58  is moving down to create a vacuum in the chamber  46 , the electrical power to the motor  74  is stopped and the downward stroke of the piston  58  is halted. Then, the motor  74  is provided electrical power through the alternative circuit to return the reciprocating piston  58  back to its TDC position. 
     With reference to  FIGS. 2 and 10A-10D , the powered fastener  10  further includes a monitoring system  262  having a circuit board  266  with a plurality of sensors  270 A- 270 D (e.g., Hall-effect sensors) spaced along the cylinder  50  and operable to detect magnets  274 ,  278  positioned in the drive piston  54  and the reciprocating piston  58 , respectively. With reference to  FIGS. 10A-10D , for illustrative clarity the circuit board  266  and the corresponding sensors  270 A- 270 D have been illustrated in profile, alongside the cross-sectional view of the cylinder  50  with the corresponding magnets  274 ,  278  shown adjacent the circuit board  266 . In other words, the circuit board  266  and magnets  274 ,  278  are positioned out of the cross-sectional plane of  FIGS. 10A-10D  (see  FIG. 2 ), but are shown in profile schematically in  FIGS. 10A-10D  for illustrative purposes. In alternative embodiments, the circuit board and corresponding magnets can be in any circumferential position around the cylinder  50 . In the illustrated embodiment, there are four sensors  270 A- 270 D that are cooperatively able to determine the presence and direction of the drive piston  54  and the reciprocating piston  58 . Any two sensors  270 A- 270 D can work in combination to determine the average speed and direction the pistons  54 ,  58  are traveling. The spacing of the sensors  270 A- 270 D is illustrated as such so that the sensors  270 A and  270 B are close together and sensors  270 C and  270 D are close together when compared to the space between sensors  270 B and  270 C. The magnets  274 ,  278  are positioned within the drive piston  54  and the reciprocating piston  58 , respectively, and the magnets  274 ,  278  are oriented to be detectable by the sensors  270 A- 270 D as the pistons  54 ,  58  come into proximity with the sensors  270 A- 270 D. In alternative embodiments, the sensors can uniquely identify which of the drive piston and the reciprocating piston has passed by the sensor. The top-most sensor  270 A is positioned to identify when the drive piston  54  is being held in its TDC position. The bottom-most sensor  270 D is positioned to identify when the reciprocating piston  58  has reached its BDC position. 
     With regard to  FIG. 11 , a method  300  of operating the fastener driver  10  under normal conditions is illustrated. The method  300  begins at a ready position with the drive piston  54  and the reciprocating piston  58  in the TDC position ( FIG. 10A , Step  304 ), and the method  300  is initiated with user activation of the trigger  26  (Step  308 ). Following user activation, the method  300  includes the steps of moving the reciprocating piston  58  away from the drive piston  54  at a first speed while the drive piston  54  is maintained at the TDC position (Step  312 ). The method  300  further includes detecting the reciprocating piston  58  with the monitoring system  260  prior to the reciprocating piston  58  reaching the BDC position within the cylinder  50  (Step  316 ), and decelerating the reciprocating piston  58  from the first speed in response to being detected (Step  320 ). In other words, the reciprocating piston  58  is slowed to prevent impacting the bumper  76  with high forces after the magnet  278  is detected by the sensor  270 D ( FIG. 10B ). After the reciprocating piston  58  reaches the BDC position and the trip member  82  moves the latch  78  out of engagement with the drive blade  42 , as described above, the monitoring system  262  detects the drive piston  54  has left the TDC position ( FIG. 10C , Step  324 ) and waits for a predetermined amount of time (e.g., 2 ms) (Step  328 ) before the reciprocating piston  58  is driven toward the drive piston  54  at a second speed ( FIG. 10D , Step  332 ). The method  300  further includes detecting the drive piston  54  with the monitoring system  262  prior to the drive piston  54  reaching the TDC position (Step  336 ), and decelerating the reciprocating piston  58  from the second speed in response to being detected (Step  340 ). In other word, the magnet  274  in the drive piston  54  is detected by the sensors  270 A and the reciprocating piston  58  is slowed. In addition, the method  300  includes detecting the reciprocating piston  58  with the monitoring system  262  prior to the reciprocating piston  58  reaching the TDC position (Step  344 ), and continuing to move the reciprocating piston  58  toward the drive piston  54  for a predetermined period of time (e.g., 100 ms, 150 ms, etc.) (Step  348 ). In alternative embodiments, the predetermined periods of time can be adjusted according to power available in the battery  34 . By continuing to move the reciprocating piston  58  toward the drive piston  54  for a predetermined period of time (Step  348 ), any air that was trapped between the drive piston  54  and the reciprocating piston  58  can be driven beneath the reciprocating piston  58  through the open valves  122 ,  126 , so that the drive piston  54  and reciprocating piston  58  can be fully returned to their TDC positions to assume a ready position for the next drive cycle (Step  304 ). 
     With reference to  FIG. 12 , the method  300  of operating the fastener driver  10  is expanded to illustrate a method of operation  400  under abnormal conditions. The method  400  includes the steps of detecting abnormal operation with the monitoring system  262 . Abnormal operation is detected by the monitoring system  262  when the sequence of piston movement, which is tracked by the magnets  274 ,  278 , passing by the sensors  270 A- 270 D is not correct (Step  404 ). If the sequence of piston movement is not correct, the method  400  considers if the number of sequential abnormal cycles is greater than a predetermined number (e.g., 2, 3, 5, etc.) (Step  408 ). If the number of sequential abnormal cycles is greater than the predetermined number, the fastener driver is shut down and use of the fastener driver  10  is prevented until the battery  34  is removed and replaced (Step  412 ). If the number of sequential abnormal cycles is less than the predetermined number, the pistons  54 ,  58  are returned to their TDC position to reset the drive cycle (Step  416 ). Once the pistons  54 ,  58  are in their TDC positions, the powered fastener  10  is ready for a normal drive cycle (Step  304 ). 
     With reference to  FIGS. 13A-13D , alternative embodiments of the present invention include different types of check valves used in the reciprocating piston of the fastener driver. In  FIG. 13A , on the reciprocating piston  454  there are formed a plurality of leaking pore  451 . The leaking pores  451  are aligned on a circumferential direction surrounding a center aperture (not shown) through which the umbrella shaped leak  450  movably passes through. The umbrella shaped leak  450  contains an umbrella cover  453  in substantially round shape, and an umbrella pin  452  connected to the umbrella cover  453  on one side thereof. The umbrella shaped leak  450  when inserted in the center aperture is capable of moving between a first position and a second position. In the first position, the umbrella cover  453  is away from the leaking pores  451  so that leak paths created by the leaking pores  451  are opened. In the second position, the umbrella cover  453  approximates and closes the leaking pores  451  so that leak paths created by the leaking pores  451  are closed. The umbrella shaped leak  450  is moved between the first position and the second position in response to pressure created between the reciprocating piston  451  and the drive piston (not shown), similar to the work principle described in above embodiments. 
     The check valve shown in  FIG. 13B  is a variation of the check vale shown in  FIG. 13A . In addition to the umbrella cover  453  used for closing any leaking pores on the reciprocating piston, a pressure plate is superimposed on top of the umbrella cover  453  to further improve strength of the umbrella cover  453 . The pressure plate has a bottom part  455  in substantially the same shape as the umbrella cover  453 , and two side arms  456  connected to the bottom part  455 . The side arms  456  help to align the pressure plate with the umbrella cover  453  by pressing against side walls formed on the reciprocating piston. 
     In  FIG. 13C , a cancel valve is used to take the place of a movable leak to control pressure created between the reciprocating piston  451  and the drive piston (not shown). As skilled persons would understand, any type of suitable cancel valve may be used for this purpose. 
     The check valve shown in  FIG. 13D  on the other side is similar to the one shown in  FIGS. 5C and 5D . The check valve seal  470  is movable relative to the reciprocating piston  454  between a first position in which the seal  470  is engaged with the reciprocating piston  454  for blocking a leak path (not shown), and a second position in which the seal  470  is disengaged from the reciprocating piston  454  for unblocking the leak path. The check valve seal  470  is biased toward the first position by a spring  471  positioned between an end cap  472  and the check valve seal  470 . 
     The check valve seal  470  is moved between the first position and the second position in response to pressure created between the reciprocating piston  454  and the drive piston (not shown). Preferably, a small amount of grease is applied to the check valve seal  470  and/or spring  471  to reduce the frictions and aid in their sliding. 
     With reference to  FIGS. 14A-14G , alternative embodiments of the present invention illustrate different types of blade seals used in the reciprocating piston of the fastener driver. As mentioned above, the blade seal is received in a recess formed in the reciprocating piston to provide a sliding fit between the drive blade and the blade seal, and that the blade seal is adapted to move between different positions to enable/disable the sealing effect. The blade seal  480  in  FIG. 14A  is similar to the blade seal in  FIGS. 6A and 6B  in that the blade seal  480  also contains a ring shaped recess  482  around the center aperture formed in the blade seal  480 . The drive blade  481  is adapted to slide in the center aperture relative to the blade seal  480 . As shown in  FIG. 14A , the drive blade  481  has a substantially “E” shaped cross section, and it contains two grooves  483  formed in one side of the drive blade  481  to match with ribs formed on the contacting surfaces (not shown) of the blade seal  480  to ensure fit between the drive blade  481  and blade seal  480 . In  FIG. 14B , the blade seal  485  is different from that in  FIG. 14A  in that the blade seal  485  is a solid component, without any open recess as shown in  FIG. 14A . In  FIG. 14C , the blade seal  487  is similar to that in  FIG. 14B  as the blade seal  487  is solid and does not have any open recess. However, the drive blade  489  in this embodiment is in substantially “T” shape. Accordingly, the central aperture  488  formed on the blade seal  487  is also in “T” shape. The blade seal shown in  FIG. 14D  on the other side utilizes two layers of seal members, namely a first seal part  492  and a second seal part  491 . The first seal part  492  and the second seal part  491  are superimposed in the recess formed on the reciprocating piston  493 . The two layers of seal members result in increasing of area of contacting surfaces between the drive blade  494  and the reciprocating piston  493 , therefore improving the sealing performance. Lastly, in  FIG. 14E  there is shown a plurality of support ribs  495  connecting the side walls of the blade seal  496  with the central member  497  in which the central aperture for slidably receiving the drive blade (not shown) is formed. The support ribs  495  provide additional support to the central member  497  to increase strength of the central member  497 . 
     Turning now to  FIG. 15 , which shows a latch mechanism similar to the one shown in  FIGS. 3-4B . A latch  500  is provided to engage a drive blade  502  of the fastener driver. The drive blade  502  includes a notch (not shown) in which a pin  501  on the latch  500  is received to engage the drive blade  502  and maintain the drive piston in the TDC position. The latch  500  is biased by a spring (not shown) to pivot the latch  500  about a pivot pin (not shown) arranged on the drive piston. The material forming the latch  500  can be plastic or metal. Preferably, investment casting is applied to body of the latch  500  to increase its strength. 
     With reference to  FIGS. 16-19B , in one embodiment of the present invention the fastener driver contains a lock out mechanism. The lock out mechanism, in addition to the commonly seen contact lock mechanism that is used to lock the trigger when a contact plate is not pressed firmly against an object, provides an another safety measure by locking the contact plate and in turn the trigger when there is no remaining fasteners (e.g. nails) to be shot in the magazine. As shown in  FIGS. 16-18 , the lock out mechanism contains a pusher  521  in a substantially sheet shape, and a lock leg  520  protruding from surface of the pusher  521 . The lock leg  520  is preferably formed in a folded “L” shape that has an end portion substantially parallel to the surface of the pusher  521 . The pusher  521  is capable of moving traversely when no fastener is left in the magazine  525  anymore. As skilled person would understand, there are many ways of configuring movement of such pusher when no fastener is left in the magazine, for example by using a fastener push mechanism utilizing a spring to provide a biasing force. On the frame of the lock out mechanism there is also a pivotable lock plate  522  connected to the frame by a hinge  523 . The lock plate  522  is further biased to a unlock position by a torsion spring  526 . The lock plate  522  can be rotated in order to lock the contact plate  524  from being pressed, which will also be described in more details later. 
     Next,  FIGS. 18, 19A, and 19B  illustrate the working principle of the lock out mechanism described above.  FIG. 18  is a brief illustration of how the lock plate  522  is rotated by the movement of pusher  521 . The pusher  521  is adapted to move along the direction shown by arrow  519  in  FIG. 18 . At its lower position (not shown), the lock leg  520  on the pusher  521  has not come into the cavity  527  formed in the lock plate  522 . However, when the pusher  521  moves from its lower position to its higher position (not shown) along the direction shown by arrow  519 , the lock leg  520  moves into the cavity  527 , and further movement of the lock leg  520  urges the lock plate  522  to rotate along the direction shown by arrow  528 . 
     The lock out mechanism used to lock the contact plate at the front end of the nailer is then described with respect to  FIGS. 19A-19B .  FIG. 19A  shows the status of the lock out mechanism in its unlocked position, i.e. when there is still at least one fastener in the magazine (not shown). In this status the pusher  521  is in its original position where the lock leg  520  has not come into contact with the lock plate  522 . As a result, there is gap formed between a rear end of the lock plate  522  and a stop member  531  fixed on a frame of the nailer. The contact plate  524  can then be pressed to pass through the gap  530  when the contact plate  524  is pressed firmly on a surface of the workpiece. However, when the last fastener in the magazine is already shot (i.e. depleted), the pusher  521  will move along the direction indicated by the arrow  529  due to a bias mechanism, for example by using a spring as mentioned above. The movement of the pusher  521  from its position in  FIG. 19A  to that in  FIG. 19B  along the direction  529 , makes the lock leg  520  come into contact with the cavity of the lock plate  522  as mentioned above, and consequently urges the lock plate  522  to rotate clockwise in  FIG. 19B . Such rotation of lock plate  522  makes its rear end  523  engage the stop member  531 . The previous gap allowed for the contact plate  524  to pass therethrough is now closed. Even if the user presses the contact plate  524  firmly onto a surface, the contact plate  524  cannot move axially as it is stopped by the lock plate  522 . Therefore, in this condition the user will not be able to press the trigger while the contact plate  524  is still locked. The lock out mechanism therefore prevents accidental actuation of the fastener driver when there is not any fastener present in the magazine of the fastener driver. 
     With reference to  FIGS. 21-22 , in another embodiment of the present invention the fastener driver further contains a clutch assembly used to allow free-wheeling of a ring gear by selectively engaging the ring gear and the motor. In the drawings, the illustrated clutch mechanism contains a plurality of detent balls  551 , and corresponding number of springs  550  each connecting a detent ball  151  on one end and a ring gear (not shown) on another end. The ring gear mechanically connects to the pinion  552  and in turn the pinion  552  drives the rack  553  to move. The springs  550  are compressible along their longitudinal direction. The detent balls  551  are circumferentially configured on an end surface of the motor rotor  554 , and on the same surface there are also circumferentially formed protrusions  555 . Between every two protrusions  555  there are grooves  556  formed. The detent balls  551  are movable relative to the surface of rotor  554 . In operation, when the clutch is switched to engage the ring gear with the motor rotor  554 , the springs  550  are compressed to their minimum length while the detent balls  551  are located within the grooves  556  on the ring gear  554 . When the motors rotor  554  rotates, the detent balls are driven by the protrusions  555  since the detent balls cannot “bypass” the protrusions  555  when the spring  550  cannot be further compressed and its length cannot be reduced anymore. However, when the clutch is switched to disengage the ring gear from the motor, the distance between the ring gear and the motor rotor  554  is increased, for example to an uncompressed length of the springs  550 , therefore restoring the springs  550 . As a result, when the ring gear keeps rotating due to remaining kinetic energy, the detent balls  551  cannot drive the motor in the reverse way since now the springs  550  are compressible again and any relatively movement of the detent balls  551  toward the protrusions  550  will lead the detent balls  551  to “bypass” the protrusions  550 . In the process of “bypassing” the corresponding spring  550  is compressed by a length substantially equal to the height of the protrusion  550  over the groove  556 . The detent ball  550  then enters another groove  556  on another side of the protrusion  550 . As such, the free-wheeling of ring gear does not drive the motor in the reverse way. In the event it is desired to successively drive additional fasteners, the remaining kinetic energy is available for the subsequent operation thereby economizing battery power and saving the drive assembly elements and/or the motor from having to absorb the impact that would otherwise occur by bringing the ring gear to a full stop immediately after the power stroke. 
     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.