Patent Publication Number: US-2023138234-A1

Title: Lifter mechanism for a powered fastener driver

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of co-pending U.S. patent application Ser. No. 17/719,855 filed on Apr. 13, 2022, which is a continuation of co-pending U.S. patent application Ser. No. 17/665,150 filed on Feb. 4, 2022, which is continuation-in-part of co-pending U.S. patent application Ser. No. 17/584,060 filed on Jan. 25, 2022, which is a continuation-in-part of co-pending U.S. patent application Ser. No. 17/154,389 filed on Jan. 21, 2021, which is a continuation of U.S. patent application Ser. No. 17/052,463 filed on Nov. 2, 2020, now U.S. Pat. No. 11,331,781, which is a national phase filing under 35 U.S.C. § 371 of International Application No. PCT/US2020/037692 filed on Jun. 15, 2020, which claims priority to U.S. Provisional Patent Application No. 62/901,973 filed on Sep. 18, 2019 and to U.S. Provisional Patent Application No. 62/861,355 filed on Jun. 14, 2019, the entire contents of all of which are incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to powered fastener drivers, and more specifically to lifter mechanisms of 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, a flywheel mechanism, etc.) to drive a driver blade from a top-dead-center position to a bottom-dead-center position. 
     SUMMARY OF THE INVENTION 
     The present invention provides, in one aspect, a powered fastener driver including a driver blade movable from a top-dead-center position to a driven or bottom-dead-center position for driving a fastener into a workpiece, a drive unit for providing torque to move the driver blade from the bottom-dead-center position toward the top-dead-center position, and a rotary lifter engageable with the driver blade. The lifter is configured to receive torque from the drive unit in a first rotational direction for returning the driver blade from the bottom-dead-center position toward the top-dead-center position. The lifter having a body and a drive pin coupled to the body. A roller is positioned on the drive pin and configured to engage with a tooth of the driver blade when moving the driver blade from the bottom-dead-center position toward the top-dead-center position. The roller includes a first engagement section configured to receive an end portion of the tooth and a second engagement section. An engagement member configured to engage the second engagement section for aligning the first engagement section of the roller with the end portion of the tooth to facilitate meshing between the end portion of the tooth and the roller. 
     The present invention provides, in another aspect, a powered fastener driver including a driver blade movable from a top-dead-center position to a driven or bottom-dead-center position for driving a fastener into a workpiece, a drive unit for providing torque to move the driver blade from the bottom-dead-center position toward the top-dead-center position, and a rotary lifter engageable with the driver blade. The lifter is configured to receive torque from the drive unit in a first rotational direction for returning the driver blade from the bottom-dead-center position toward the top-dead-center position. The lifter having a body and a drive pin coupled to the body. A roller is positioned on the drive pin and configured to engage with a tooth of the driver blade when moving the driver blade from the bottom-dead-center position toward the top-dead-center position. The roller includes a first engagement section configured to receive an end portion of the tooth and a second engagement section and a biasing member is coupled to the lifter. The biasing member configured to engage the second engagement section to position the roller in a first rotational orientation relative to the body of the rotary lifter so the end portion of the tooth aligns with the first engagement section of the roller. 
     The present invention provides, in another aspect, a powered fastener driver a driver blade movable from a top-dead-center position to a driven or bottom-dead-center position for driving a fastener into a workpiece, a drive unit for providing torque to move the driver blade from the bottom-dead-center position toward the top-dead-center position, and a rotary lifter engageable with the driver blade. The lifter is configured to receive torque from the drive unit in a first rotational direction for returning the driver blade from the bottom-dead-center position toward the top-dead-center position. The lifter having a body and a drive pin coupled to the body. A roller is positioned on the drive pin and configured to engage with a tooth of the driver blade when moving the driver blade from the bottom-dead-center position toward the top-dead-center position. The roller includes a first engagement section configured to receive an end portion of the tooth and a second engagement section. An engagement member is biased into engagement with the second engagement section and configured to position the roller in a first rotational orientation relative to the body of the rotary lifter so the end portion of the tooth aligns with the first engagement section of the roller. 
     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 perspective view of a powered fastener driver in accordance with a first embodiment of the invention. 
         FIG.  2    is another perspective view of the powered fastener driver of  FIG.  1   , with portions of a housing removed to show a drive unit and a lifter assembly of the powered fastener driver. 
         FIG.  3    is a front cross-sectional view of the lifter assembly of  FIG.  2    illustrating a driver blade of the powered fastener driver of  FIG.  1    in a TDC position, and a rotary lifter of the lifter assembly of  FIG.  2    in a first rotational position. 
         FIG.  4    is another front cross-sectional view of the lifter assembly of  FIG.  2    illustrating the rotary lifter of  FIG.  3    in an intermediate position. 
         FIG.  5    is another front cross-sectional view of the lifter assembly of  FIG.  2    illustrating the driver blade of  FIG.  3    moving from the TDC position toward a BDC position, and the rotary lifter of  FIG.  3    in a second rotational position. 
         FIG.  6    is a plan view of a portion of the rotary lifter of  FIG.  3   . 
         FIG.  7    is an exploded view of the lifter assembly of  FIG.  2   . 
         FIG.  8    is a front cross-sectional view of a lifter assembly in accordance with a second embodiment of the invention. 
         FIG.  9    is side cross-sectional view of the lifter assembly of  FIG.  8   . 
         FIG.  10    is a rear cross-sectional view of the lifter assembly of  FIG.  8   . 
         FIG.  11    is a perspective view of a lifter roller of the lifter assembly of  FIG.  8    in accordance with a first configuration and illustrating a camming portion. 
         FIG.  12    is a front cross-sectional view of the lifter assembly of  FIG.  8    illustrating a driver blade of the powered fastener driver approaching a TDC position, and the lifter roller of  FIG.  8    in a first position. 
         FIG.  13    is another front cross-sectional view of the lifter assembly of  FIG.  8    illustrating the driver blade reaching the TDC position such that a lowermost tooth of the driver blade engages the lifter roller of  FIG.  8   . 
         FIG.  14    is yet another front cross-sectional view of the lifter assembly of  FIG.  8    illustrating continued rotation of the lifter and the continued engagement of the lowermost tooth of the driver blade with the lifter roller. 
         FIG.  15    is yet still another front cross-sectional view of the lifter assembly of  FIG.  8    illustrating the lifter roller adjusted from the first position of  FIG.  12    to a second position. 
         FIG.  16    is another front cross-sectional view of the lifter assembly of  FIG.  8    illustrating continued rotation of the lifter and the continued engagement of the lowermost tooth of the driver blade with the lifter roller such that the lifter roller is maintained in the second position. 
         FIG.  17    is yet another front cross-sectional view of the lifter assembly of  FIG.  8    illustrating continued rotation of the lifter and the continued engagement of the lowermost tooth of the driver blade with the lifter roller such that the lifter roller is maintained in the second position. 
         FIG.  18    is yet still another front cross-sectional view of the lifter assembly of  FIG.  8    illustrating the driver being fired from the TDC position to a BDC position, and the lifter roller of  FIG.  8    in the second position. 
         FIG.  19    is a front cross-sectional view of the lifter assembly of  FIG.  8    illustrating a lifter roller in accordance with a second construction. 
         FIG.  20    is a front cross-sectional view of the lifter assembly of  FIG.  8    illustrating a lifter roller in accordance with a third construction. 
         FIG.  21    is a front cross-sectional view of the lifter assembly of  FIG.  8    illustrating a lifter roller in accordance with a fourth construction. 
         FIG.  22    is a front cross-sectional view of the lifter assembly of  FIG.  8    illustrating a lifter roller in accordance with a fifth construction. 
         FIG.  23    is a front cross-sectional view of the lifter assembly of  FIG.  8    illustrating a lifter roller in accordance with a sixth construction. 
         FIG.  24    is front cross-sectional view of a lifter assembly in accordance with a third embodiment of the invention. 
         FIG.  25    is a side cross-sectional view of the lifter assembly of  FIG.  24   . 
         FIG.  26    is a front view of a lifter of the lifter assembly of  FIG.  24   . 
         FIG.  27    is a perspective view of a spring of the lifter assembly of  FIG.  24   . 
         FIG.  28    is a rear cross-sectional view of another construction of the lifter assembly of  FIG.  24    illustrating a retaining mechanism. 
         FIG.  29    is a front cross-sectional view of a lifter assembly in accordance with a fourth embodiment of the invention, illustrating a driver blade of the powered fastener driver at a BDC position. 
         FIG.  30    is a side cross-sectional view of the lifter assembly of  FIG.  29    illustrating a lifter. 
         FIG.  31    is a front cross-sectional view of the lifter assembly of  FIG.  29    illustrating the driver blade nearing a TDC position, and the lifter of  FIG.  30    in a first position. 
         FIG.  32    is another front cross-sectional view of the lifter assembly of  FIG.  29    illustrating the driver blade approaching the TDC position such that a lowermost tooth of the driver blade engages a last lifter roller of the lifter of  FIG.  30   . 
         FIG.  33    is yet another front cross-sectional view of the lifter assembly of  FIG.  29    illustrating the driver blade reaching the TDC position. 
         FIG.  34    is yet still another front cross-sectional view of the lifter assembly of  FIG.  29    illustrating the lifter adjusting from the first position of  FIG.  31    toward a second position. 
         FIG.  35    is another front cross-sectional view of the lifter assembly of  FIG.  29    illustrating the continued adjustment of the lifter toward the second position and continued rotation of the lifter. 
         FIG.  36    is yet another front cross-sectional view of the lifter assembly of  FIG.  29    illustrating the continued adjustment of the lifter toward the second position and continued rotation of the lifter. 
         FIG.  37    is yet still another front cross-sectional view of the lifter assembly of  FIG.  29    illustrating the continued adjustment of the lifter toward the second position and continued rotation of the lifter. 
         FIG.  38    is another front cross-sectional view of the lifter assembly of  FIG.  29    illustrating the driver being fired from the TDC position to a BDC position, and the lifter in the second position. 
         FIG.  39    is a front cross-sectional view of a lifter assembly in accordance with a fifth embodiment of the invention, illustrating a driver blade of the powered fastener driver at a BDC position. 
         FIG.  40    is a side view of the lifter assembly of  FIG.  39    illustrating a lifter of the lifter assembly and a frame supporting the lifter assembly. 
         FIG.  41    is another side view of a portion of the lifter assembly of  FIG.  39   . 
         FIG.  42    is an exploded view of the lifter assembly of  FIG.  41   . 
         FIG.  43    is a front view of the lifter assembly of  FIG.  41   , illustrating a pivot pin assembly of the lifter of  FIG.  40    in a first position. 
         FIG.  44    is another front view of the lifter assembly of  FIG.  41   , illustrating the pivot pin assembly of  FIG.  43    adjusted into a second position. 
         FIG.  45    is a perspective view of the frame of  FIG.  40   . 
         FIG.  46    is a front cross-sectional view of the lifter assembly of  FIG.  39    illustrating the driver blade nearing a TDC position, and the pivot pin assembly of  FIG.  44    in the second position. 
         FIG.  47    is another front cross-sectional view of the lifter assembly of  FIG.  39    illustrating the driver blade approaching the TDC position such that a lowermost tooth of the driver blade engages a last lifter roller of the lifter of  FIG.  40   . 
         FIG.  48    is a side view of the lifter assembly of  FIG.  47   , illustrating an engagement portion of the frame of  FIG.  40    engaging with the pivot pin assembly of  FIG.  43   . 
         FIG.  49    is a front cross-sectional view of the lifter assembly of  FIG.  39   , illustrating the pivot pin assembly of  FIG.  43    in the first position as the driver blade reaches the TDC position. 
         FIG.  50    is another front cross-section view of the lifter assembly of  FIG.  39    illustrating the driver blade at the TDC position. 
         FIG.  51    is yet another front cross-sectional view of the lifter assembly of  FIG.  29    illustrating the pivot pin assembly of  FIG.  44    in the second position after the driver blade has reached the TDC position. 
         FIG.  52    is yet still another front cross-sectional view of the lifter assembly of  FIG.  39    illustrating the continued rotation of the lifter and the pivot pin assembly of  FIG.  44    in the second position. 
         FIG.  53    is a front cross-sectional view of a lifter assembly in accordance with a sixth embodiment of the invention, illustrating a driver blade of the powered fastener driver nearing a TDC position. 
         FIG.  54    is a perspective of a portion of the lifter assembly of  FIG.  53    illustrating a lifter of a first construction of the lifter assembly. 
         FIG.  55    is a perspective view of a portion of the lifter assembly of  FIG.  53    illustrating a lifter of a second construction of the lifter assembly. 
         FIG.  56    is a front cross-sectional view of the lifter assembly of  FIG.  53    illustrating a lowermost tooth of the driver blade of  FIG.  53    engaging a last lifter roller of the lifter of  FIG.  54   . 
         FIG.  57    is another front cross-sectional view of the lifter assembly of  FIG.  53   , illustrating the last lifter roller of  FIG.  56    in a first position relative to the lifter. 
         FIG.  58    is yet another front cross-section view of the lifter assembly of  FIG.  53    illustrating the driver blade at the TDC position. 
         FIG.  59    is a perspective cross-sectional view of a portion of a powered fastener driver illustrating a lifter assembly in accordance with another embodiment of the invention. 
         FIG.  60    is a front cross-sectional view of the lifter assembly of  FIG.  59    illustrating a means for aligning a lifter roller with a lowermost tooth of a driver blade to facilitate meshing between the lowermost tooth and the lifter roller. 
         FIG.  61 A  is another front cross-sectional view of the lifter assembly of  FIG.  59    illustrating the lifter roller rotated towards an intermediate rotational orientation, which compresses a biasing member prior to the driver blade reaching TDC position. 
         FIG.  61 B  is another front cross-sectional view of the lifter assembly of  FIG.  59    illustrating the lifter roller rotated towards a second rotational orientation, where the driver blade is released and moving towards BDC position. 
         FIG.  62    is a perspective cross-sectional view of a portion of a powered fastener driver illustrating a lifter assembly in accordance with another embodiment of the invention. 
         FIG.  63    is a front cross-sectional view of the lifter assembly of  FIG.  62    illustrating a means for aligning a lifter roller with a lowermost tooth of a driver blade to facilitate meshing between the lowermost tooth and the lifter roller according to another embodiment of the invention. 
         FIG.  64 A  is another front cross-sectional view of the lifter assembly of  FIG.  62    illustrating the lifter roller rotated towards an intermediate rotational orientation, which compresses a biasing member prior to the driver blade reaching TDC position. 
         FIG.  64 B  is another front cross-sectional view of the lifter assembly of  FIG.  62    illustrating the lifter roller rotated towards a second rotational orientation, where the driver blade is released and moving towards BDC position. 
         FIG.  65    is a perspective cross-sectional view of a portion of a powered fastener driver illustrating a lifter assembly in accordance with another construction of the invention. 
         FIG.  66    is a cross-sectional view of a lifter of the lifter assembly of  FIG.  65    illustrating a means for aligning a lifter roller with a lowermost tooth of a driver blade to facilitate meshing between the lowermost tooth and the lifter roller according to another embodiment of the invention. 
         FIG.  67    is a perspective cross-sectional view of a portion of a powered fastener driver illustrating a lifter assembly in accordance with another embodiment of the invention. 
         FIG.  68    is a cross-sectional view of a lifter of the lifter assembly of  FIG.  67    illustrating a means for aligning a pin assembly with a lowermost tooth of a driver blade to facilitate meshing between the lowermost tooth and the pin assembly according to another embodiment of the invention. 
         FIG.  69    is a partial cutaway view of a portion of the lifter assembly of  FIG.  67    illustrating the pin assembly being biased by the aligning means towards a first rotational orientation to facilitate meshing between the lowermost tooth of a driver blade the pin assembly. 
         FIG.  70 A  is another is a partial cutaway view of a portion of the lifter assembly of  FIG.  67    illustrating the pin assembly rotated towards an intermediate rotational orientation, which allows driver blade to be fired from the TDC position to the BDC position. 
         FIG.  70 B  is another is a partial cutaway view of a portion of the lifter assembly of  FIG.  67    illustrating the pin assembly rotated towards a second rotational orientation, where the driver blade is released and moving towards the BDC position. 
         FIG.  71    is a perspective cross-sectional view of a portion of a powered fastener driver illustrating a lifter assembly in accordance with another construction of the invention. 
         FIG.  72    is a side view of a lifter of the lifter assembly of  FIG.  71   . 
         FIG.  73    is a side cross-sectional view of the lifter assembly of  FIG.  71    illustrating a means for aligning a drive pin with a lowermost tooth of a driver blade to facilitate meshing between the lowermost tooth and the lifter roller according to another embodiment of the invention. 
         FIG.  74    is a front cross-sectional view of the lifter assembly of  FIG.  71    illustrating the aligning means. 
         FIG.  75    is a side view of a lifter having a drive pin in accordance with another construction of the invention. 
         FIG.  76    is a front cross-sectional view of the lifter assembly of  FIG.  75    illustrating a means for aligning the drive pin with a lowermost tooth of a driver blade to facilitate meshing between the lowermost tooth and the lifter roller according to another embodiment of the invention. 
         FIG.  77    is a side cross-sectional view of the lifter assembly of  FIG.  75    illustrating the engagement between the engagement member and the drive pin. 
         FIG.  78    is a cross-sectional view of a drive unit of a powered fastener driver according to another embodiment, illustrating a motor and a transmission having a carrier defining a torque input member and an output shaft and a lifter defining a torque output member for providing torque to a driver blade of the powered fastener driver. 
         FIG.  79    is a perspective view of a portion of the powered fastener driver with portions of a housing removed to illustrate the drive unit of  FIG.  78   . 
         FIG.  80 A  is a front cross-sectional view of the lifter of  FIG.  78    about the line  80 A- 80 A illustrating the driver blade of the powered fastener driver near a TDC position. 
         FIG.  80 B  is a front cross-sectional view of the drive unit of  FIG.  78    about the line  80 B- 80 B illustrating the torque output member in a first rotational position relative to the torque input member when the driver blade is in the position shown in  FIG.  80 A . 
         FIG.  81 A  is another front cross-sectional view of the lifter of  FIG.  78    about the line  80 A- 80 A illustrating the driver blade in the TDC position. 
         FIG.  81 B  is another front cross-sectional view of the drive unit of  FIG.  78    about the line  80 B- 80 B illustrating the torque output member in an intermediate rotational position relative to the torque input member when the driver blade is in the position shown in  FIG.  81 A . 
         FIG.  82 A  is another front cross-sectional view of the lifter of  FIG.  78    about the line  80 A- 80 A illustrating the driver blade moving from the TDC position toward a BDC position. 
         FIG.  82 B  is another front cross-sectional view of the drive unit of  FIG.  78    about the line  80 B- 80 B illustrating the torque output member in a second rotational position relative to the torque input member when the driver blade is in the position shown in  FIG.  82 A . 
         FIG.  83    is a cross-sectional view of a drive unit of a powered fastener driver according to another embodiment, illustrating a motor and a transmission having a driven gear and a spur gear defining a torque input member and an output shaft and a lifter defining a torque output member for providing torque to a driver blade of the powered fastener driver. 
         FIG.  84    is a perspective view of a portion of the powered fastener driver with portions of a housing removed to illustrate the drive unit of  FIG.  83   . 
         FIG.  85 A  is a front cross-sectional view of the lifter of  FIG.  83    about the line  85 A- 85 A illustrating a driver blade of the powered fastener driver near a TDC position. 
         FIG.  85 B  is a front cross-sectional view of the drive unit of  FIG.  83    about the line  85 B- 85 B illustrating the torque output member in a first rotational position relative to the torque input member when the driver blade is in the position shown in  FIG.  80 A . 
         FIG.  86 A  is another front cross-sectional view of the lifter of  FIG.  83    about the line  85 A- 85 A illustrating the driver blade in the TDC position. 
         FIG.  86 B  is another front cross-sectional view of the drive unit of  FIG.  83    about the line  85 B- 85 B illustrating the torque output member in an intermediate rotational position relative to the torque input member when the driver blade is in the position shown in  FIG.  81 A . 
         FIG.  87 A  is another front cross-sectional view of the lifter of  FIG.  83    about the line  85 A- 85 A illustrating the driver blade moving from the TDC position toward a BDC position. 
         FIG.  87 B  is another front cross-sectional view of the drive unit of  FIG.  83    about the line  85 B- 85 B illustrating the torque output member in a second rotational position relative to the torque input member when the driver blade is in the position shown in  FIG.  82 A . 
     
    
    
     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. 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  FIGS.  1  and  2   , a gas spring-powered 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 cylinder  18 . A moveable piston (not shown) is positioned within the cylinder  18 . With reference to  FIG.  3   , the fastener driver  10  further includes a driver blade  26  that is attached to the piston and moveable therewith. The fastener driver  10  does not require an external source of air pressure, but rather includes pressurized gas in the cylinder  18 . 
     With reference to  FIG.  1   , the fastener driver  10  includes a housing  30  having a cylinder housing portion  34  and a motor housing portion  38  extending therefrom. The cylinder housing portion  34  is configured to support the cylinder  18 , whereas the motor housing portion  38  is configured to support a drive unit  40  ( FIG.  2   ). In addition, the illustrated housing  30  includes a handle portion  46  extending from the cylinder housing portion  34 , and a battery attachment portion  50  coupled to an opposite end of the handle portion  46 . A battery pack  54  supplies electrical power to the drive unit  40 . The handle portion  46  supports a trigger  58 , which is depressed by a user to initiate a driving cycle of the fastener driver  10 . 
     With reference to  FIGS.  3 - 5   , the driver blade  26  defines a driving axis  62 . Further, the driver blade  26  includes a plurality of lift teeth  74  formed along an edge  78  of the driver blade  26 , which extends in the direction of the driving axis  62 . In particular, the lift teeth  74  project laterally from the edge  78  relative to the driving axis  62 . During a driving cycle, the driver blade  26  and piston are moveable along the driving axis  62  between a top-dead-center (TDC) position ( FIG.  3   ) and a bottom-dead-center (BDC) or driven position. The fastener driver  10  further includes a rotary lifter  66  that receives torque from the drive unit  40 , causing the lifter  66  to rotate and return the driver blade  26  from the BDC position toward the TDC position. 
     With reference to  FIG.  2   , the powered fastener driver  10  further includes a frame  70  positioned within the housing  30 . The frame  70  is configured to support the lifter  66  within the housing  30 . 
     With continued reference to  FIG.  2   , the drive unit  40  includes an electric motor  42  and a transmission  82  positioned downstream of the motor  42 . The transmission  82  includes an output shaft  86  ( FIG.  7   ). In one embodiment, the output shaft  86  is meshed with a last stage of a gear train (e.g., multi-stage planetary gear train; not shown) of the transmission  82 . Torque is transferred from the motor  42 , through the transmission  82 , to the output shaft  86 . The lifter  66  and the drive unit  40  may be collectively referred to as a lifter assembly  88 , as further discussed below. 
     With reference to  FIG.  7   , the output shaft  86  defines a rotational axis  90 . In addition, the output shaft  86  includes an outer peripheral surface  94  having a cylindrical portion  98  and a flat portion  102  adjacent the cylindrical portion  98 . Further, in the illustrated embodiment, the outer peripheral surface  94  includes two cylindrical portions  98  and two flat portions  102  ( FIGS.  3 - 5   ). The cylindrical portions  98  are positioned opposite one another relative to the rotational axis. Likewise, the flat portions  102  are positioned opposite one another relative to the rotational axis  90 . Each of the flat portions  102  is oriented parallel with the rotational axis  90 . In the illustrated embodiment, the output shaft  86  defines a torque input member and the lifter  66  defines a torque output member. 
     With reference to  FIGS.  2 - 7   , the lifter  66  includes an aperture  110  through which the output shaft  86  is received. With particular reference to  FIG.  7   , the lifter  66  includes a body  114  having a hub  116  through which the aperture  110  extends, a first flange  118 A radially extending from one end of the hub  116 , and a second flange  118 B radially extending from an opposite end of the hub  116  and spaced from the first flange  118 A along the axis  90 . Further, the lifter  66  includes a plurality of pins  120  extending between the flanges  118 A,  118 B and rollers  121  supported upon the pins  120 . The rollers  121  sequentially engage the lift teeth  74  formed on the driver blade  26  as the driver blade  26  is returned from the BDC position toward the TDC position. 
     As illustrated in  FIG.  6   , the aperture  110  is partly defined by two opposed curvilinear segments  122  and two opposed protrusions  124  that extend radially inward of a base circle A coinciding with the curvilinear segments  122 . Each of the protrusions  124  includes flat segments  126 ,  130  and an apex  134  between the segments  126 ,  130 . Thus, the aperture  110  is also partly defined by the protrusions  124 , in addition to the curvilinear segments  122 . As explained in further detail below, each curvilinear segment  122  is configured to engage with the respective cylindrical portion  98  of the output shaft  86 , while each protrusion  124  is configured to engage with a corresponding flat portion  102  on the outer peripheral surface  94  of the output shaft  86 . 
     With reference to  FIGS.  6  and  7   , the first and second flat segments  126 ,  130  of each protrusion  124  define an obtuse included angle B therebetween ( FIG.  6   ). In other words, the first and second flat segments  126 ,  130  and the apex  134  therebetween form a “V-shape” defining the obtuse included angle B. In some embodiments, the obtuse included angle B is between about 100 degrees and about 170 degrees. More specifically, in some embodiments, the obtuse included angle B is between about 120 degrees and about 160 degrees. In the illustrated embodiment, the obtuse included angle B is about 140 degrees. Each of the first and second flat segments  126 ,  130  of each of the protrusions  124  is configured to alternately engage with the respective flat portion  102  of the output shaft  86  ( FIG.  7   ). Accordingly, each flat segment  126 ,  130  may be considered a driven lug and each flat portion  102  may be considered a driving lug. A combination of the driven lugs  126 ,  130  and driving lugs  102  defines a kickout arrangement  136  located between the lifter  66  and the output shaft  86 . As explained in greater detail below, the driven lugs  126 ,  130  are alternately engageable with the respective driving lugs  102  of the output shaft  86 . 
     With reference to  FIGS.  3 - 5   , the lifter  66  is movable relative to the output shaft  86  between a first position ( FIG.  3   ), in which the first flat segments or driven lugs  126  of the rotary lifter  66  are engaged with the respective flat portions or driving lugs  102  of the output shaft  86 , and a second position ( FIG.  5   ), in which the lifter  66  is rotated about the output shaft  86  (i.e., about the rotational axis  90 ) such that the second flat segments or driven lugs  130  are engaged with the respective flat portions or driving lugs  102 . The lifter  66  is in the first position relative to the output shaft  86  when returning the driver blade  26  from the BDC position toward the TDC position. The lifter  66  rotates (in a counter-clockwise direction from the frame of reference of  FIG.  3   ) to the second position after the driver blade  26  reaches the TDC position. In other words, the aperture  110  is configured to selectively allow rotation of the lifter  66  relative to the output shaft  86  such that only the driving lugs  126  or only the driving lugs  130  engage the output shaft  86  at any given time. 
     More specifically, as illustrated in  FIG.  3   , as the driver blade  26  approaches the TDC position, a contact normal (i.e., arrow A 1  in  FIG.  3   ) perpendicular to a line tangent to both a last lifter roller  121 A and the surface on a lowermost tooth  74 A on the driver blade  26  with which the roller  121 A is in contact is formed. A reaction force is applied to the rotary lifter  66  along the contact normal A 1 , which is oriented along a line of action C located below the rotational axis of the lifter  66 , which is coaxial with the rotational axis  90  of the output shaft  86 , from the frame of reference of  FIG.  3   . Thus, a reaction torque (arrow T 1 ) is applied to the lifter  66  in a clockwise direction (from the frame of reference of  FIG.  3   ), thereby maintaining the lifter  66  in the first position as the driver blade  26  is moved toward the TDC position. The line of action C of the contact normal A 1  remains below the rotational axis of the lifter  66  until the lifter  66  reaches the TDC position. Thereafter, as shown in  FIG.  4   , the contact normal A 1  between the lowermost tooth  74 A and the last lifter roller  121 A changes direction such that the line of action C is located above the rotational axis of the lifter  66 . Thus, the reaction torque (arrow T 2 ) exerted on the lifter  66  by the driver blade  26  is redirected in a counter-clockwise direction (from the frame of reference of  FIG.  4   ), thereby causing the lifter  66  to rotate about the output shaft  86  from the first position shown in  FIG.  3    to the second position shown in  FIG.  5   . 
     With reference to  FIG.  5   , the last lifter roller  121 A has rotated past the lowermost tooth  74 A such that there is no contact between the last lifter roller  121 A and the driver blade  26 , and the driver blade  26  is moved toward the BDC position by the force of the compressed gas. As such, there is no longer any reaction torque imparted on the lifter  66  by the driver blade  26  and the lifter  66  remains in the second position as the driver blade  26  is moved toward the BDC position. 
     During a driving cycle in which a fastener is discharged into a workpiece, the lifter  66  returns the piston and the driver blade  26  from the BDC position toward the TDC position. As the piston and the driver blade  26  are returned toward the TDC position, the gas within the cylinder  18  above the piston is compressed. A controller of the gas-spring powered fastener driver  10  controls the drive unit  40  such that the lifter  66  stops rotation when the driver blade  26  is at an intermediate position between the BDC position and the TDC position (i.e., the ready position). In one example, the ready position may be when the piston and the driver blade  26  are near the TDC position (e.g., 80 percent of the way up the cylinder  18 ) such that the compressed air is partially compressed. The driver blade  26  (and the piston) is held in the ready position until released by user activation of the trigger  58  ( FIG.  1   ), which initiates a driving cycle. The lifter  66  continues rotation until the driver blade  26  is moved to the TDC position and the last lifter roller  121 A of the lifter  66  rotates past the lowermost tooth  74 A of the driver blade  26  to release the driver blade  26 . When released, the compressed gas above the piston within the cylinder  18  drives the piston and the driver blade  26  to the BDC position, thereby driving a fastener into a workpiece. The illustrated fastener driver  10  therefore operates on a gas spring principle utilizing the lifter  66  and the piston to compress the gas within the cylinder  18  upon being returned to the ready position for a subsequent fastener driving cycle. In other embodiments, the driver blade  26  may be held at the TDC position before a subsequent fastener driving cycle. 
     When the piston and the driver blade  26  are at the ready position, the rotary lifter  66  is in the first position ( FIG.  3   ) relative to the output shaft  86 . In particular, at this time, the reaction torque T 1  exerted on the lifter  66  by the drive blade  26  is oriented in a clockwise direction (from the frame of reference of  FIG.  3   ), maintaining the lifter  66  in the first position relative to the output shaft  86 . When the trigger  58  is actuated, the drive unit  40  is energized and the lifter  66  receives torque such that the lifter  66  engages with the driver blade  26  to move the driver blade to the TDC position. When the driver blade  26  reaches the TDC position, the orientation of the reaction torque exerted on the lifter  66  by the driver blade  26  is reversed (i.e., by the change in direction of the contact normal between the lowermost tooth  74 A and the last lifter roller  121 A to above the rotational axis of the lifter  66 ) such that the reaction torque T 2  is oriented in a counter-clockwise direction (from the frame of reference of  FIG.  4   ), thereby rotating the lifter  66  from the first position toward the second position. Thereafter, the lifter  66  no longer engages the driver blade  26 , and the piston and the driver blade  26  are thrust downward toward the BDC position by the compressed air in the cylinder  18  above the piston. As the driver blade  26  is displaced toward the BDC position, the lifter  66  remains in the second position. Therefore, due to the kickout arrangement  136 , the lifter  66  may “kick out” or move relatively quickly out of the way of the driver blade  26  after the driver blade  26  reaches the TDC position. 
     Upon a fastener being driven into a workpiece, the driver blade  26  is in the driven or BDC position. After the driver blade  26  reaches the BDC position, an uppermost tooth  74  (not shown; tooth closest to the piston) of the driver blade  26  is engaged by a first lifter roller  121 B of the lifter  66 , thereby causing the lifter  66  to momentarily stop rotation while the output shaft  86  continues to rotate. As such, the rotation of the output shaft  86  relative to the lifter  66  adjusts the lifter  66  back into the first position ( FIG.  3   ). Thereafter, the continued driving of the drive unit  40  rotates the lifter  66 , which returns the driver blade  26  and the piston toward the ready position. The controller deactivates the drive unit  40  when the driver blade  26  is in the ready position to complete the driving cycle. Therefore, the kickout arrangement  136  is configured to permit limited rotation of the lifter  66  relative to the output shaft  86  between the first position and the second position. In some embodiments, one complete rotation of the lifter  66  is necessary to return the driver blade  26  from the BDC position to the ready position. 
     In particular, when the lifter  66  is moving the driver blade  26  toward the TDC position, forces (from the gas being compressed in the cylinder  18 ) act on the drive teeth  74 . The forces are at a maximum on the lowermost tooth  74 A as the driver blade  26  approaches the TDC position such that the lowermost tooth  74 A may experience a high amount of wear by sliding contact with the last lifter roller  121 A as the last lifter roller  121 A rotates past the lowermost tooth  74 A to initiate a fastener driving operation. As the driver blade  26  reaches the TDC position, the kickout arrangement  136  permits the lifter  66  to rotate relative to the output shaft  86  from the first position to the second position, thereby allowing the lifter  66  (i.e., the last lifter roller  121 A) to be moved quickly out of the way of the drive blade  26  to release the driver blade  26  and initiate a fastener driving operation, thereby reducing wear on the lifter  66  and damage that might otherwise be caused to the drive unit  40  by a momentary reaction torque applied to the drive unit  40  as the driver blade  26  reaches the TDC position. 
       FIGS.  8 - 23    illustrate a second embodiment of a kickout arrangement  336  of a lifter assembly  288 , with like components and features as the embodiment of the lifter assembly  88  of the fastener driver  10  shown in  FIGS.  1 - 7    being labeled with like reference numerals plus “200”. The lifter assembly  288  is utilized for a fastener driver similar to the fastener driver  10  of  FIGS.  1 - 7    and, accordingly, the discussion of the fastener driver  10  above similarly applies to the kickout arrangement  336  of the lifter assembly  288  and is not re-stated. Rather, only differences between the kickout arrangement  136  and of the driver blade  26  of  FIGS.  1 - 7    and the kickout arrangement  336  and the driver blade  226  of  FIGS.  8 - 23    are specifically noted herein, such as differences in a last one of the lifter pins and the shape of the lowermost tooth of the driver blade. 
     With reference to  FIGS.  12  and  13   , the driver blade  226  includes a plurality of lift teeth  274  formed along an edge  278  of the driver blade  226 . Each one of the lift teeth  274  includes an end portion  280 . Each of the end portions  280 , except for the end portion  280 A of a lowermost tooth  274 A of the driver blade  226 , has the same shape. In particular, the end portion  280 A of the lowermost tooth  274 A has a rounded shape, as further discussed below. 
     The lifter assembly  288  includes a drive unit (e.g., drive unit  40  of  FIG.  2   ) having an output shaft  286 , and a lifter  266  coupled for co-rotation with the output shaft  286 . The output shaft  286  defines a rotational axis  290 . The lifter  266  includes a plurality of pins  320  extending between flanges  318 A,  318 B of a body  314  of the lifter  266 , and rollers  321  supported upon the pins  320 . Each roller  321  is rotatably supported on the respective pin  320 . Further, the rollers  321  sequentially engage the lift teeth  274  (i.e., the end portions  280 ) formed on the driver blade  226  as the driver blade  226  is returned from the BDC position toward the TDC position. 
     With reference to  FIGS.  8 ,  9 , and  12   , a last lifter pin  320 A of the plurality of pins  320  includes a cam roller  321 A having a camming portion  338 . In particular, the cam roller  321 A has an outer circumference, and the camming portion  338  has a first end  340  and a second end  342  ( FIG.  11   ). The camming portion  338  extends from the first end  340  radially outward relative to the outer circumference to the second end  342 . The cam roller  321 A further includes a first engagement section  344  proximate the first end  340 , and a second engagement section  346  proximate the second end  342 . Each of the first engagement section  344  and the second engagement section  346  is defined by a concave shape proximate the first and second ends  340 ,  342 , respectively. The first engagement section  344  is configured to slidably engage the end portion  280 A of the lowermost tooth  274 A during rotation of the lifter  266 . In particular, the rounded shape of the end portion  280 A of the lowermost tooth  274 A cooperates with the concave shape of the first engagement section  344 . 
     The lifter  266  includes a protrusion  348  ( FIG.  12   ) located proximate the cam roller  321 A. The protrusion  348  extends between an inner surface of each flange  318 A,  318 B. The second engagement section  346  of the camming portion  338  is configured to selectively engage the protrusion  348  such that the protrusion  348  inhibits rotation of the cam roller  321 A about the last lifter pin  320 A in a first rotational direction (e.g., in a counter-clockwise direction from the frame of reference of  FIG.  12   ). 
     The lifter  266  further includes a torsion spring  350  ( FIG.  9   ). In the illustrated embodiment, the torsion spring  350  is positioned in a cavity  352  define by the flange  318 A of the lifter  266 . One end  350 A of the torsion spring  350  is fixed to the lifter  266  (i.e., the flange  318 A,  FIG.  10   ), and an opposite, second end  350 B is attached to the cam roller  321 A. The torsion spring  350  is configured to apply a biasing force to the cam roller  321 A in the first rotational direction to bias the camming portion  338  (i.e., the second engagement section  346  at the second end  342 ) into engagement with the protrusion  348 . A combination of the camming portion  338  and the lowermost tooth  274 A of the driver blade  226  defines a kickout arrangement  336  located between the lifter  266  and the driver blade  226 . As explained in greater detail below, the cam roller  321 A is selectively rotatably about the last lifter pin  320 A in the first rotational direction and a second, opposite rotational direction. 
     With reference to  FIGS.  13 - 18   , the cam roller  321 A is rotatable relative to the last lifter pin  320 A between a first position ( FIG.  13   ), in which the second engagement section  346  of the cam roller  321 A is in engagement with the protrusion  348 , and a second position ( FIG.  15   ), in which the cam roller  321 A is rotated about the pin  320 A in the second rotational direction (e.g., clockwise from the frame of reference of  FIG.  15   ) to create a circumferential gap between the second engagement section  346  and the protrusion  348 . The cam roller  321 A is in the first position relative to the protrusion  348  when returning the driver blade  226  from the BDC position toward the TDC position. 
     As illustrated in  FIGS.  9  and  12   , the last lifter pin  320 A defines a pin axis  323  extending parallel to the rotational axis  290 . The cam roller  321 A is configured to rotate in the first rotational direction (e.g., counter-clockwise from the frame of reference of  FIG.  12   ) by the bias of the torsion spring  350  about the pin axis  323  toward the first position. The cam roller  321 A is inhibited from continued rotation about the pin  320 A by the protrusion  348 . As such, the biasing force of the torsion spring  350  and the protrusion  348  maintain the cam roller  321 A in the first position. Further, when the cam roller  321 A is in the first position, it is configured to rotate with the lifter  266  as the driver blade  226  is returned from the BDC position toward the TDC position. 
     As shown in  FIGS.  13 - 17   , as the driver blade  226  approaches the TDC position, a contact normal (i.e., arrow J 1  in  FIGS.  13 - 14   ) perpendicular to a line tangent to both the cam roller  321 A (i.e., the first engagement section  344 ) and the rounded end portion  280 A on the lowermost tooth  274 A on the driver blade  226  with which the cam roller  321 A is in contact is formed. A reaction force is applied to the cam roller  321 A along the contact normal J 1 , which is oriented along a line of action K located above the pin axis  323  of the last lifter pin  320 A, from the frame of reference of  FIG.  13   . Thus, a reaction torque (arrow T 1 B) is applied to the cam roller  321 A in a counter-clockwise direction (from the frame of reference of  FIG.  13   ), thereby maintaining the cam roller  321 A in the first position (along with the biasing force of the torsion spring  350 ) as the driver blade  226  is moved toward the TDC position. The line of action K of the contact normal J 1  remains above the pin axis  323  until the lifter  266  reaches the TDC position. Thereafter, as shown in  FIG.  15   , the contact normal J 1  between the rounded end portion  280 A of the lowermost tooth  274 A and the cam roller  321 A changes direction such that the line of action K is located below the pin axis  323  of the last lifter pin  320 A. Thus, the reaction torque (arrow T 2 B) exerted on the cam roller  321 A by the driver blade  226  is redirected in a clockwise direction (from the frame of reference of  FIG.  15   ), thereby overcoming the biasing force of the torsion spring  350  and causing the cam roller  321 A to rotate about the pin axis  323  from the first position shown in  FIGS.  13 - 14    toward the second position shown in  FIG.  15   . 
     As shown in  FIG.  18   , the cam roller  321 A has rotated past the lowermost tooth  274 A such that there is no contact between the cam roller  321 A and the driver blade  226 , and the driver blade  226  is moved toward the BDC position by the force of the compressed gas. As such, there is no longer any reaction torque imparted on the cam roller  321 A by the driver blade  226  and the cam roller  321 A is biased by the torsion spring  350  toward the first position as the driver blade  226  is moved toward the BDC position, and then from the BDC position toward the TDC position again. 
     With reference to  FIGS.  19 - 23   , in alternative embodiments, the cam roller  321 A may include one or more camming portions  338 . For example, as shown in  FIG.  19   , the cam roller  321 A includes four camming portions  338 . In another example, as shown in  FIG.  20   , the cam roller  321 A includes five camming portions  338 . In yet another example, as shown in  FIG.  21   , the cam roller  321 A includes six camming portions  338 . In yet still another example, as shown in  FIG.  22   , the cam roller  321 A includes seven camming portions  338 . In another example, as shown in  FIG.  23   , the cam roller  321 A includes eight camming portions  338 . 
     During a driving cycle in which a fastener is discharged into a workpiece, the lifter  266  returns the piston and the driver blade  226  from the BDC position toward the TDC position ( FIGS.  12 - 14   ). In particular, the cam roller  321 A is in the first position when returning the driver blade  226  from the BDC position toward the TDC position such that the cam roller  321 A rotates with the rotation of the lifter  266 . As the driver blade  226  approaches the TDC position, the lowermost tooth  274 A engages the cam roller  31 A, and the reaction torque T 1 B exerted on cam roller  321 A by the drive blade  226  is oriented in a counter-clockwise direction (from the frame of reference of  FIG.  13   ). 
     When the driver blade  226  reaches the TDC position, the orientation of the reaction torque exerted on the cam roller  321 A by the driver blade  226  is reversed (i.e., by the change in direction of the contact normal J 1  between the lowermost tooth  274 A and the cam roller  321 A to below the pin axis  323  of the last lifter pin  320 A) such that the reaction torque T 2 B is oriented in clockwise direction (from the frame of reference of  FIG.  15   ), thereby overcoming the biasing force of the torsion spring  350  and rotating the cam roller  321 A from the first position toward the second position. Thereafter, the cam roller  321 A no longer engages the driver blade  226 , and the piston and the driver blade  226  are thrust downward toward the BDC position by the compressed air (e.g., in the cylinder  18  above the piston,  FIG.  2   ). As the driver blade  226  is displaced toward the BDC position and the cam roller  321 A is released from the driver blade  226 , the torsion spring  350  rotates the cam roller  321 A in the first rotational direction (e.g., counter-clockwise from the frame of reference of  FIGS.  15 - 18   ), thereby adjusting the cam roller  321 A into the first position again. Therefore, due to the kickout arrangement  336 , the cam roller  321 A may “kick out” or move relatively quickly out of the way of the lowermost tooth  274 A of the driver blade  226  after the driver blade  226  reaches the TDC position. 
     Upon a fastener being driven into a workpiece, the driver blade  226  is in the driven or BDC position. Additionally, the torsion spring  350  has already rotated the cam roller  321 A from the second position toward the first position. Thereafter, the continued driving of the drive unit (e.g., drive unit  40 ,  FIG.  2   ) rotates the lifter  266  for returning the driver blade  226  toward the TDC position. Similar to  FIGS.  1 - 7    of the first embodiment, a controller may deactivate the drive unit when the driver blade  226  is in the ready position. The driver blade  226  (and the piston) is held in the ready position until released by user activation of a trigger (trigger  58 ,  FIG.  1   ), which initiates another driving cycle. 
     In particular, when the lifter  266  is moving the driver blade  226  toward the TDC position, forces (from the gas being compressed in the cylinder  18 ) act on the drive teeth  274 . The forces are at a maximum on the lowermost tooth  274 A as the driver blade  226  approaches the TDC position such that the lowermost tooth  274 A may experience a high amount of wear by sliding contact with the cam roller  321 A as the cam roller  321 A rotates past the lowermost tooth  274 A. The kickout arrangement  336  is configured to permit limited rotation of the cam roller  321 A relative to the lifter pin  320 A between the first position and the second position such that the cam roller  321 A is moved quickly out of the way of the drive blade  226  to release the driver blade  226  and initiate a fastener driving operation, thereby reducing wear on the lifter  266  (i.e., the cam roller  321 A) and damage that might otherwise be caused to the drive unit by a momentary reaction torque applied to the drive unit as the driver blade  226  reaches the TDC position. 
       FIGS.  24 - 28    illustrate a third embodiment of a kickout arrangement  536  of a lifter assembly  488 , with like components and features as the embodiment of the lifter assembly  88  of the fastener driver  10  shown in  FIGS.  1 - 7    being labeled with like reference numerals plus “400”. The lifter assembly  488  is utilized for a fastener driver similar to the fastener driver  10  of  FIGS.  1 - 7    and, accordingly, the discussion of the fastener driver  10  above similarly applies to the kickout arrangement  536  of the lifter assembly  488  and is not re-stated. Rather, only differences between the kickout arrangement  136  of  FIGS.  1 - 7    and the kickout arrangement  536  of  FIGS.  24 - 28    are specifically noted herein, such as differences in a configuration of the lifter and the output shaft. 
     With reference to  FIGS.  24 - 25   , the driver blade  426  includes a plurality of lift teeth  474  formed along an edge  478  of the driver blade  426 . Further, the powered fastener driver includes a frame  470  positioned within a housing (e.g., housing  30 ,  FIG.  1   ). The frame  470  is configured to support the lifter assembly  488  within the housing. 
     The lifter assembly  488  includes a drive unit (e.g., drive unit  40 ,  FIG.  2   ) having an output shaft  486 . The output shaft  486  defines a rotational axis  490 . In addition, the output shaft  486  includes an outer peripheral surface  494  having a cylindrical portion  498  and a flat portion  502  adjacent the cylindrical portion  498 . Further, in the illustrated embodiment, the outer peripheral surface  494  includes two cylindrical portions  498 A,  498 B and two flat portions  502  ( FIG.  24   ). The cylindrical portions  498 A,  498 B are positioned opposite one another relative to the rotational axis  490 . Likewise, the flat portions  502  are positioned opposite one another relative to the rotational axis  490 . Each of the flat portions  502  is oriented parallel with the rotational axis  490 . 
     With reference to  FIGS.  24 - 26   , the lifter  466  includes an aperture  510  through which the output shaft  486  is received. With particular reference to  FIG.  26   , the lifter  466  includes a body  514  having a hub  516  through which the aperture  510  extends, a first flange  518 A radially extending from one end of the hub  516 , and a second flange  518 B radially extending from an opposite end of the hub  516  and spaced from the first flange  518 A along the axis  490 . Further, the lifter  466  includes a plurality of pins  520  extending between the flanges  518 A,  518 B and rollers  521  supported upon the pins  520  ( FIG.  25   ). The rollers  521  sequentially engage the lift teeth  474  formed on the driver blade  426  as the driver blade  426  is returned from the BDC position toward the TDC position. 
     As illustrated in  FIGS.  24  and  26   , the aperture  510  is partly defined by one curvilinear segment  522 , one flat segment  525  opposed to the curvilinear segment  522 , and two opposed protrusions  524  that extend radially inward of a base circle B 1  coinciding with the curvilinear segment  522 . Alternatively, the flat segment  525 ′ may also be curvilinear, as shown in  FIG.  26   . Each of the protrusions  524  includes flat segments  526 ,  530 . The aperture  510  is partly defined by the protrusions  524 , in addition to the curvilinear segment  522  and the flat segment  525 . The curvilinear segment  522  is configured to engage with one of the cylindrical portions  498 A of the output shaft  486  ( FIG.  24   ), while each protrusion  524  is configured to engage with a corresponding flat portion  502  on the outer peripheral surface  494  of the output shaft  486 . 
     With particular reference to  FIGS.  24 - 25   , the lifter assembly  488  includes a cavity  554  defined between the other one of the cylindrical portions  498 B of the output shaft  486  and the flat segment  525  of the aperture  510 . More specifically, the aperture  510  is sized such that during assembly of the lifter assembly  488 , the flat segment  525  is spaced from the cylindrical portion  498 B to define the cavity  554 . Further, in the illustrated embodiment, the cylindrical portion  498 B of the output shaft  486  includes a cutout  556  ( FIG.  25   ) to further define the cavity  554 . The cutout  556  extends radially inward relative to the rotational axis  490  from the outer peripheral surface  494 . 
     The lifter assembly  488  includes a spring  558  ( FIG.  27   ) positioned within the cavity  554 . As shown in  FIG.  25   , each end of the spring  558  is fixedly coupled to the output shaft  486 . In the illustrated embodiment, each end is positioned within the cutout  556 . The spring  558  is configured to apply a biasing force to the lifter  466  in a first linear direction L 1  perpendicular to the rotational axis  490  (i.e., to the right from the frame of reference of  FIG.  25   ). In the illustrated embodiment, the spring  558  is a leaf spring. In other embodiments, the spring  558  may be a compression spring. Further, in other embodiments, the lifter assembly  488  may include one or more springs (e.g., two, three, four, etc.). A combination of the output shaft  486  and the lifter  466  defines a kickout arrangement  536  located between the output shaft  486  and the lifter  466 . As explained in greater detail below, the lifter  466  is selectively movable relative to the output shaft  486  in the first linear direction L 1 , and in a second, opposite linear direction L 2 . 
     With reference to  FIG.  24   , the lifter  466  is movable relative to the output shaft  486  between a first position ( FIG.  24   ), in which the spring  558  biases the lifter  466  toward the driver blade  426 , and a second position, in which the lifter  466  is moved away from the driver blade  426  relative to the output shaft  486  in the second, opposite linear direction L 2 . The flat segment  525  of the aperture  510  may contact the cylindrical portion  498 B of the output shaft  486  when the lifter  466  is in the second position relative to the output shaft  486 . The lifter  466  is in the first position when returning the driver blade  426  from the BDC position toward the TDC position. The lifter  466  moves in the second linear direction L 2  (i.e., to the left from the frame of reference of  FIG.  24   ) to the second position after the driver blade  426  reaches the TDC position. In other words, the aperture  510  is configured to selectively allow linear movement of the lifter  466  relative to the output shaft  486  in a direction that is transverse to the output shaft  486 . 
     More specifically, the spring  558  is selected having a stiffness, once the spring  558  is preloaded within the cavity  554 , sufficient to apply a predetermined force necessary to maintain the lifter  466  in the first position until the driver blade  426  reaches the TDC position. In particular, as the driver blade  426  is returned from the BDC position toward the TDC position, reaction forces (from the gas being compressed in the cylinder  18 ) act on the drive teeth  474 . A resultant reaction force from these forces is applied to the rotary lifter  466  along the second linear direction L 2 , which is perpendicular to the rotational axis  490  of the output shaft  486  from the frame of reference of  FIG.  25   , by the driver blade  426 . As the lifter  466  approaches the TDC position, the forces increase toward a maximum force on a lowermost tooth  474 A such that the reaction force increases to a maximum value that is greater than the force applied to the lifter  466  by the spring  558  in the first linear direction L 1 . As such, after the lifter  466  reaches the TDC position, the resultant reaction force from the driver blade  426  on the lifter  466  exceeds the preload force applied by the spring  558  in the first linear direction L 1 , and the lifter  466  is moved from the first position to the second position (e.g., to the left from the frame of reference of  FIG.  24   ) against the bias of the spring  558 . As the driver blade  426  is driven from the TDC position to the BDC position, the driver blade  426  no longer contacts the lifter  466  to apply the reaction force, and as such the spring  558  rebounds to return the lifter  466  from the second position to the first position relative to the output shaft  486 . 
     With reference to  FIG.  28   , in some embodiments, the lifter assembly  488  includes a retaining mechanism  560  for selectively retaining the lifter  466  in the first position relative to the output shaft  486  until the driver blade  426  reaches the TDC position. As shown in  FIG.  28   , the illustrated retaining mechanism  560  includes a retaining member  562  positioned at a predetermined location on the frame  470 . The retaining member  562  is engageable with a flat member  564  defined on the hub  516  of the lifter  466 . In particular, the retaining member  562  engages the flat member  564  for a portion of the lifter rotation when returning the driver blade  426  from the BDC position to the TDC position. The flat member  564  is configured such that the retaining member  562  of the frame  470  disengages the flat member  564  when the driver blade  426  reaches the TDC position. This may allow for a relatively smaller preload force of the spring  558  necessary for maintaining the lifter  466  in the first position. Further, this may inhibit any inadvertent movement of the lifter  466  toward the second position except for when the driver blade  426  reaches the TDC position. 
     During a driving cycle in which a fastener is discharged into a workpiece, the lifter  466  returns the piston and the driver blade  426  from the BDC position toward the TDC position. In particular, the lifter  466  is in the first position when returning the driver blade  426  from the BDC position toward the TDC position. After the driver blade  426  reaches the TDC position, the reaction force reaches the maximum value, thereby exceeding the preload force applied to the lifter  466  by the spring  558 , and adjusting the lifter  466  from the first position to the second position. 
     As the lifter  466  is moved toward the second position, a last lifter roller  521 A of the lifter  466  moves away from the lowermost tooth  474 A of the driver blade  426  to release the driver blade  426 . Thereafter, the lifter  466  no longer engages the driver blade  426 , and the piston and the driver blade  426  are thrust downward toward the BDC position by the compressed air (e.g., in the cylinder  18  above the piston,  FIG.  2   ). As the driver blade  426  is displaced toward the BDC position, the driver blade  426  no longer contacts the lifter  466  to apply the reaction force, and the spring  558  rebounds to move the lifter  466  from the second position toward the first position again (e.g., to the right from the frame of reference of  FIG.  24   ). Therefore, due to the kickout arrangement  536 , the lifter  466  (i.e., the last lifter roller  521 A) may “kick out” or move relatively quickly out of the way of the driver blade  426  (i.e., lowermost tooth  474 A) after the driver blade  426  reaches the TDC position. 
     Upon a fastener being driven into a workpiece, the driver blade  426  is in the driven or BDC position. Additionally, the spring  558  applies the biasing force to move the lifter  466  from the second position toward the first position. Thereafter, the continued driving of the drive unit (e.g., drive unit  40 ,  FIG.  2   ) rotates the lifter  466  for returning the driver blade  426  toward the TDC position. Similar to  FIGS.  1 - 7    of the first embodiment, a controller may deactivate the drive unit when the driver blade  426  is in the ready position. The driver blade  426  (and the piston) is held in the ready position until released by user activation of a trigger (trigger  58 ,  FIG.  1   ), which initiates another driving cycle. 
     In particular, when the lifter  466  is moving the driver blade  426  toward the TDC position, the forces (from the gas being compressed in the cylinder  18 ) act on the lowermost tooth  474 A as the driver blade  426  approaches the TDC position such that the lowermost tooth  474 A may experience a high amount of wear by sliding contact with the last lifter roller  521 A as the last lifter roller  521 A rotates past the lowermost tooth  474 A. The kickout arrangement  536  is configured to permit limited linear movement of the lifter  466  relative to the output shaft  486  between the first position and the second position such that the last lifter roller  521 A is moved quickly out of the way of the drive blade  426  to release the driver blade  426  and initiate a fastener driving operation, thereby reducing wear on the lifter  466  (i.e., the last lifter roller  521 A) and damage that might otherwise be caused to the drive unit by a momentary reaction torque applied to the drive unit as the driver blade  426  reaches the TDC position. 
       FIGS.  29 - 38    illustrate a fourth embodiment of a kickout arrangement  736  of a lifter assembly  688 , with like components and features as the embodiment of the lifter assembly  88  of the fastener driver  10  shown in  FIGS.  1 - 7    being labeled with like reference numerals plus “600”. The lifter assembly  688  is utilized for a fastener driver similar to the fastener driver  10  of  FIGS.  1 - 7    and, accordingly, the discussion of the fastener driver  10  above similarly applies to the kickout arrangement  736  of the lifter assembly  688  and is not re-stated. Rather, only differences between the kickout arrangement  136  of  FIGS.  1 - 7    and the kickout arrangement  736  of  FIGS.  29 - 38    are specifically noted herein, such as differences in a configuration of the lifter and the output shaft. 
     With reference to  FIG.  29   , a driver blade  626  includes a plurality of lift teeth  674  formed along an edge  678  of the driver blade  626 . Further, the powered fastener driver includes a frame  670  positioned within a housing (e.g., housing  30 ,  FIG.  1   ). The frame  670  is configured to support the lifter assembly  688  within the housing. 
     With reference to  FIG.  30   , the lifter assembly  688  includes a drive unit (e.g., drive unit  40 ,  FIG.  2   ) having an output shaft  686 . The output shaft  686  defines a rotational axis  690 . In addition, the output shaft  686  includes a first drive shaft  687  and a second drive shaft  689  coupled for co-rotation with the output shaft  686 . In the illustrated embodiment, the output shaft  686  includes a first portion  691  and a second portion  692  spaced from the first portion  691  along the rotational axis  690 . The first drive shaft  687  and the second drive shaft  689  extend between the portions  691 ,  692  of the output shaft  686  parallel to the rotational axis  690 . In one embodiment, the first drive shaft  687  and the second drive shaft  689  are pressed between the first portion  691  and the second portion  692 . Further, rollers  693  are supported on each of the first drive shaft  687  and the second drive shaft  689 . 
     With reference to  FIGS.  29  and  30   , a lifter  666  of the lifter assembly  688  includes a slot  712  through which the first drive shaft  687  and the second drive shaft  689  are received. In particular, the lifter  666  includes a body  714  having a hub  716  through which the slot  712  extends, a first flange  718 A radially extending from one end of the hub  716 , and a second flange  718 B radially extending from an opposite end of the hub  716  and spaced from the first flange  718 A along the axis  690 . The first portion  691  of the output shaft  686  is adjacent the first flange  718 A and the second portion  692  is adjacent the second flange  718 B relative to the rotational axis  690 . 
     The lifter  666  further includes a plurality of pins  720  extending between the flanges  718 A,  718 B and rollers  721  supported upon the pins  720 . The rollers  721  sequentially engage the lift teeth  674  formed on the driver blade  626  as the driver blade  626  is returned from the BDC position toward the TDC position. 
     As illustrated in  FIG.  29   , the slot  712  is defined by a plurality of curvilinear segments  766 A,  766 B and rounded segments  768 A,  768 B to form a curvilinear-shaped slot  712 . More specifically, the slot  712  includes a first rounded segment  768 A and a second, opposite rounded segment  768 B. A first curvilinear segment  766 A and a second curvilinear segment  766 B extend between the first and second rounded segments  768 A,  768 B. The first rounded segment  768 A and the second rounded segment  768 B are opposite to each other relative to the rotational axis  690 . Additionally, the second curvilinear segment  766 B is spaced from and has a shape coinciding with the shape of the first curvilinear segment  766 A. Each of the segments  766 A,  766 B,  768 A,  768 B is positioned interior to an outer edge of the lifter  666  such that the curvilinear-shaped slot  712  is formed by an interior wall of the lifter  666 . The first and second rounded segments  768 A,  768 B and the first and second curvilinear segments  766 A,  766 B are configured to selectively engage with the rollers  693  of the first and second drive shafts  687 ,  689 . 
     In particular, the segments  766 A,  766 B,  768 A,  768 B of the slot  712  of the lifter  666  are configured to engage with the first and second drive shafts  687 ,  689  (i.e., the rollers  693 ) as the first and second drive shafts  687 ,  689  rotate in a rotational direction about the rotational axis  690  of the output shaft  686 . The first and second drive shafts  687 ,  689  rotate, with the rotation of the drive shaft  686 , to apply a rotational force on the lifter  666  (i.e., the curvilinear segments  768 A,  768 B) for rotation of the lifter  666  with the rotation of the output shaft  686 . A combination of the curvilinear and rounded segments  766 A,  766 B,  768 A,  768 B, and the first and second drive shafts  687 ,  689  define a kickout arrangement  736  located between the lifter  666  and the output shaft  686 . As explained in greater detail below, the lifter  666  is selectively movable relative to the output shaft  686  about the first and second drive shafts  687 ,  689  as the lifter  666  continues to rotate with the rotation of the output shaft  686 . 
     With reference to  FIGS.  32  and  38   , the lifter  666  is movable about the first drive shaft  687  and the second drive shaft  689  between a first position ( FIG.  32   ), in which the first and second drive shafts  687 ,  689  are engaged with the first and second curvilinear segments  766 A,  766 B, respectively, and closer to the first rounded segment  768 A, and a second position ( FIG.  38   ), in which the lifter  666  is moved away from the driver blade  626  relative to the output shaft  686  such that the first and second drive shafts  687 ,  689  are positioned closer to the second rounded segment  768 B. The second drive shaft  689  may engage with the second rounded segment  768 B when the lifter  666  is in the second position relative to the output shaft  686  ( FIG.  38   ). The lifter  666  is in the first position when returning the driver blade  626  from the BDC position toward the TDC position. The lifter  666  moves toward the second position after the driver blade  626  reaches the TDC position. In other words, the slot  712  is configured to selectively allow movement of the lifter  666  relative to the output shaft  686 . 
     More specifically, as illustrated in  FIGS.  29  and  31 - 33   , the slot  712  has a center which defines a pivot point X at which the lifter  666  will move or shift from the first position to the second position. Specifically, as the driver blade  626  is being returned from the BDC position to the TDC position, a contact normal (i.e., arrow D 1  in  FIGS.  29  and  31 - 33   ) perpendicular to a line tangent to both one of the lifter rollers  721  and the surface of the respective tooth  674  of the driver blade  626  with which the roller  721  is in contact is formed. A reaction force is applied to the rotary lifter  666  along the contact normal D 1  oriented along a line of action E as each roller  721  of the lifter  666  engages with each respective driver tooth  674 . The line of action E is misaligned or otherwise does not extend through the pivot point X prior to the driver blade  626  reaching the TDC position such that the reaction force of the driver blade  626  on the lifter  666  maintains the lifter  666  in the first position. Said another way, the reaction force is oriented along the line of action E that extends above the pivot point X, as shown in  FIG.  31   . 
     With particular reference to  FIGS.  32  and  33   , as the driver blade  626  approaches the TDC position, the contact normal D 1  is formed perpendicular to the line tangent to both a last lifter roller  721 A and the surface on a lowermost tooth  674 A on the driver blade  626  with which the roller  721 A is in contact ( FIG.  32   ). As illustrated in  FIG.  33   , after the driver blade  626  reaches the TDC position, the reaction force oriented along the line of action E extends through the pivot point X, thereby causing the lifter  666  to move or pivot about the first and second drive shafts  687 ,  689  from the first position shown in  FIGS.  29 ,  31 , and  32    toward the second position shown in  FIG.  38    (i.e., to the left from the frame of reference of  FIG.  33   ). 
     With reference to  FIGS.  33 - 38   , the lifter  666  continues to rotate (by the first and second drive shafts  687 ,  689 , respectively) as the lifter  666  pivots from the first position toward the second position, and the last lifter roller  721 A has rotated past the lowermost tooth  674 A such that there is no contact between the last lifter roller  721 A and the driver blade  626  ( FIGS.  34 - 37   ), and the driver blade  626  is moved toward the BDC position by the force of the compressed gas. The continued rotation of the lifter  666  by a centrifugal force from the first and second drive shafts  687 ,  689 , respectively, on the lifter  666  eventually drives the lifter  666  to move outward again relative to the first and second drive shafts  687 ,  689  (i.e., to the right from the frame of reference of  FIG.  38   , thereby moving or pivoting the lifter  666  from the second position ( FIG.  38   ) toward the first position ( FIG.  29   ). As such, as the driver blade  626  is being fired from the TDC position to the BDC position, the lifter  666  is momentarily allowed to move or shift from the first position into the second position until the centrifugal force returns the lifter  666  from the second position to the first position again. 
     During a driving cycle in which a fastener is discharged into a workpiece, the lifter  666  returns the piston and the driver blade  626  from the BDC position toward the TDC position. In particular, the lifter  666  is in the first position when returning the driver blade  626  from the BDC position toward the TDC position. After the driver blade  626  reaches the TDC position, the reaction force is oriented along the line of action E extending through the pivot point X, thereby moving or pivoting the lifter  666  from the first position toward the second position. 
     As the lifter  666  is moved toward the second position, the last lifter roller  721 A of the lifter  666  moves away from the lowermost tooth  674 A of the driver blade  626  to release the driver blade  626 . Thereafter, the lifter  666  no longer engages the driver blade  626 , and the piston and the driver blade  626  are thrust downward toward the BDC position by the compressed air (e.g., in the cylinder  18  above the piston,  FIG.  2   ). As the driver blade  626  is displaced toward the BDC position, the lifter  666  continues to rotate about the first and second drive shafts  687 ,  689 , with the centrifugal force acting on the lifter  666  returning it from the second position toward the first position again (i.e., to the right from the frame of reference of  FIG.  38   ). Therefore, due to the kickout arrangement  736 , the lifter  666  (i.e., the last lifter roller  721 A) may “kick out” or move relatively quickly out of the way of the driver blade  626  (i.e., lowermost tooth  674 A) after the driver blade  626  reaches the TDC position. 
     Upon a fastener being driven into a workpiece, the driver blade  626  is in the driven or BDC position. Additionally, the centrifugal force acting on the lifter  666  moves the lifter  666  from the second position toward the first position. Thereafter, the continued driving of the drive unit (e.g., drive unit  40 ,  FIG.  2   ) rotates the lifter  666  for returning the driver blade  626  toward the TDC position. Similar to  FIGS.  1 - 7    of the first embodiment, a controller may deactivate the drive unit when the driver blade  626  is in the ready position. The driver blade  626  (and the piston) is held in the ready position until released by user activation of a trigger (trigger  58 ,  FIG.  1   ), which initiates another driving cycle. 
     In particular, when the lifter  666  is moving the driver blade  626  toward the TDC position, the forces (from the gas being compressed in the cylinder  18 ) act on the lowermost tooth  674 A as the driver blade  626  approaches the TDC position such that the lowermost tooth  674 A may experience a high amount of wear by sliding contact with the last lifter roller  721 A as the last lifter roller  721 A rotates past the lowermost tooth  674 A. The kickout arrangement  736  is configured to permit limited movement of the lifter  666  relative to the output shaft  686  between the first position and the second position such that the last lifter roller  721 A is moved quickly out of the way of the drive blade  626  to release the driver blade  626  and initiate a fastener driving operation, thereby reducing wear on the lifter  666  (i.e., the last lifter roller  721 A) and damage that might otherwise be caused to the drive unit by a momentary reaction torque applied to the drive unit as the driver blade  626  reaches the TDC position. 
       FIGS.  39 - 52    illustrate a fifth embodiment of a kickout arrangement  936  of a lifter assembly  888 , with like components and features as the embodiment of the lifter assembly  88  of the fastener driver  10  shown in  FIGS.  1 - 7    being labeled with like reference numerals plus “800”. The lifter assembly  888  is utilized for a fastener driver similar to the fastener driver  10  of  FIGS.  1 - 7    and, accordingly, the discussion of the fastener driver  10  above similarly applies to the kickout arrangement  936  of the lifter assembly  888  and is not re-stated. Rather, only differences between the kickout arrangement  136  and of the lifter  66  of  FIGS.  1 - 7    and the kickout arrangement  936  and the lifter  866  of  FIGS.  39 - 52    are specifically noted herein, such as differences in a last one of the lifter pins. 
     With reference to  FIG.  39   , the driver blade  826  includes a plurality of lift teeth  874  formed along an edge  878  of the driver blade  826 . Further, the powered fastener driver includes a frame  870  positioned within a housing (e.g., housing  30 ,  FIG.  1   ). The frame  870  is configured to support the lifter assembly  888  within the housing. 
     With reference to  FIGS.  40 - 41   , the lifter assembly  888  includes a drive unit (e.g., drive unit  40  of  FIG.  2   ) having an output shaft  886 , and a lifter  866  coupled for co-rotation with the output shaft  886 . The output shaft  886  defines a rotational axis  890 . The lifter  866  includes a plurality of pins  920  extending between flanges  918 A,  918 B of a body  914  of the lifter  866  (except for a last lifter pin  920 A), and rollers  921  supported upon the pins  920 . Each roller  921  is rotatably supported on the respective pin  920 . Further, the rollers  921  sequentially engage the lift teeth  874  formed on the driver blade  826  as the driver blade  826  is returned from the BDC position toward the TDC position. 
     With reference to  FIGS.  39 ,  41 , and  42   , the last lifter pin  920 A forms a portion of a pivot pin assembly  910  of the lifter  866 . The pivot pin assembly  970  includes a first pivot arm  972 , a second pivot arm  974 , a rod  976 , and the last lifter pin  920 A supported on a first end  978  of each pivot arm  972 ,  974 . The illustrated first and second pivot arms  972 ,  974  are pivotably supported on the lifter  866  by the rod  976 . In particular, the flanges  918 A,  918 B define first and second holes  980 A,  980 B that are configured to align with first and second holes  982 A,  982 B of the first and second arms  972 ,  974 , respectively. The respective hole  982 A,  982 B of each arm  972 ,  974  is located intermediate the first end  978  and a second, opposite end  984  of each arm  972 ,  974 . The rod  976  is received within each hole  980 A,  980 B,  982 A,  982 B such that the rod  976  extends between the flanges  918 A,  918 B of the body  914  of the lifter  866  and the first and second arms  972 ,  974 . The rod  976  defines a pivot axis  986 , which extends parallel to the rotational axis  890  ( FIG.  41   ). The last lifter pin  920 A (and roller  921 A) is supported between each first end  978  of the arms  972 ,  974 . Accordingly, the last lifter pin  920 A is pivotable with the pivot arms  972 ,  974  about the pivot axis  986  toward or away from the rotational axis  890  (i.e., the lifter  866 ). 
     The lifter  866  further includes a detent assembly  988  positioned at the second end  984  of the first pivot arm  972  and opposite the last lifter pin  920 A ( FIGS.  41  and  42   ). The detent assembly  988  includes a first recess  990  and a second recess  992  defined by the lifter  866 , and a ball or detent  993  configured to be selectively received in each of the first and second recesses  990 ,  992 . In the illustrated embodiment, the first recess  990  and the second recess  992  are defined by an outer surface  991  of the flange  918 A. The first recess  990  is positioned radially closer to the rotational axis  890  than the second recess  992 . The detent assembly  988  further includes a spring  994  configured to bias the detent  993  into one or the other of the first and second recesses  990 ,  992 . The detent  993  and the spring  994  are positioned within a cavity  995  at the second end  984  of the first pivot arm  972 . The spring  994  is configured to bias the detent  993  away from the first pivot arm  972  toward the flange  918 A (from the frame of reference of  FIG.  41   ) relative to the rotational axis  890 . 
     With reference to  FIG.  42   , the lifter  866  includes a first stop member  996 A and a second stop member  996 B. The illustrated first stop member  996 A extends axially from the outer surface  991  of the flange  918 A relative to the rotational axis  890 . Additionally, the first stop member  996 A extends from a first end radially outward to a second, opposite end. The first stop member  996 A is configured to engage the first pivot arm  972  proximate the second end  984  of the first pivot arm  972 . The lifter  866  may further include another first stop member positioned on an outer surface of the other flange  918 B. The illustrated second stop member  996 B is defined by a side edge of each of the first and second flanges  918 A,  918 B. In particular, the second stop member  996 B is positioned radially closer to the rotational axis  890  than the pivot axis  986 . The second stop member  996 B is configured to engage the first end  978  of each of the first and second pivot arms  972 ,  974 . 
     With reference to  FIGS.  45  and  48   , the frame  870  includes an engagement member  998  extending axially inward relative to the rotational axis  890  from an inner surface of the frame  870  toward the lifter  866 . The engagement member  998  is positioned axially below the outer surface  991  of the flange  918 A and proximate the plurality of pins  920 . Furthermore, the engagement member  998  is positioned at a predetermined location on the frame  870 . The predetermined location is selected based on a position of the last lifter pin  920 A at a specific point of rotation of the lifter  866 . The specific point of rotation is the point in the lifter rotation just before the last lifter roller  921 A is configured to engage a lowermost driver tooth  874 A (i.e., when the driver blade  826  is nearing the TDC position). The engagement member  998  is configured to engage the pivot pin assembly  970  (i.e., the first and second pivot arms  972 ,  974 ) for moving or pivoting the last lifter pin  920 A/roller  921 A. A combination of the pivot pin assembly  970  and the lowermost tooth  874 A of the driver blade  826  defines a kickout arrangement  936  located between the last lifter roller  921 A and the lifter  866 . As explained in greater detail below, the last lifter pin  920 A is selectively pivotable relative to the lifter  866 . 
     With reference to  FIGS.  43  and  44   , the pivot pin assembly  970  is movable relative to the lifter  866  between a first position ( FIG.  43   ), in which the detent assembly  988  releasably couples the second end  984  of the first pivot arm  972  to the first recess  990  for maintaining the last lifter pin  920 A (and roller  921 A) in a radially outward position, and a second position ( FIG.  44   ), in which the detent assembly  988  releasably couples the second end  984  of the first pivot arm  972  to the second recess  992  for maintaining the last lifter pin  920 A (and roller  921 A) in a radially inward position. The pivot pin assembly  970  is in the second position relative to the lifter  866  when returning the driver blade  826  from the BDC position toward the TDC position. The pivot pin assembly  970  is pivoted to the first position just before the driver blade  826  reaches the TDC position. Further, the detent assembly  988  is configured to maintain the pivot pin assembly  970  in both the first and second positions. The first and second stop members  996 A,  996 B, respectively, limit the movement of the pivot pin assembly  970  between the first and second positions. 
     More specifically, as illustrated in  FIGS.  46 - 52   , the lifter  866  is in the second position when returning the driver blade  826  from the BDC position to the TDC position (e.g.,  FIG.  46   ). The engagement member  998  is configured to engage the second end  984  of the first pivot arm  972  of the pivot arm assembly  970  before the driver blade  826  reaches the TDC position ( FIGS.  47  and  48   ). The engagement member  998  is configured to apply a force to the pivot arm assembly  970  to overcome a biasing force of the detent assembly  988  for pivoting the pivot pin assembly  970  radially outward (counter-clockwise from the frame of reference of  FIG.  47   ) relative to the rotational axis  890  from the second position toward the first position. 
     With particular reference to  FIGS.  49  and  50   , as the driver blade  826  approaches the TDC position, a contact normal (i.e., arrow G 1  in  FIG.  49   ) perpendicular to a line tangent to both the last lifter roller  921 A and the surface on the lowermost tooth  874 A on the driver blade  826  with which the roller  921 A is in contact is formed. A reaction force is applied to the last lifter pin  920 A (i.e., to the first end  978  of the pivot pin assembly  970 ) along the contact normal G 1 , which is oriented along a line of action H located below the pivot axis  986  of the pivot pin assembly  970 , from the frame of reference of  FIG.  49   . Thus, a reaction torque (arrow T 1 A) is applied to the pivot pin assembly  970  in a counter-clockwise direction (from the frame of reference of  FIG.  47   ), thereby maintaining the pivot pin assembly  970  in the first position (along with the biasing force of the detent assembly  988 ) as the driver blade  826  is moved toward the TDC position. The line of action H of the contact normal G 1  remains below the pivot axis  986  of the pivot pin assembly  970  until the lifter  866  reaches the TDC position. Thereafter, as shown in  FIG.  50   , the contact normal G 1  between the lowermost tooth  874 A and the last lifter roller  921 A changes direction such that the line of action H is located above the pivot axis  986  of the pivot pin assembly  970 . Thus, the reaction torque (arrow T 2 A) exerted on the pivot pin assembly  970  by the driver blade  826  is redirected in a clockwise direction (from the frame of reference of  FIG.  50   ), thereby overcoming the biasing force of the detent assembly  988  and causing the pivot pin assembly  970  to pivot about the pivot axis  986  from the first position shown in  FIG.  48    toward the second position shown in  FIG.  52   . 
     As shown in  FIGS.  51 - 52   , the last lifter roller  921 A has rotated past the lowermost tooth  874 A such that there is no contact between the last lifter roller  921 A and the driver blade  826 , and the driver blade  826  is moved toward the BDC position by the force of the compressed gas. As such, there is no longer any reaction torque imparted on the pivot pin assembly  970  by the driver blade  826  and the pivot pin assembly  970  remains in the second position as the driver blade  826  is moved toward the BDC position, and then from the BDC position toward the TDC position again. 
     During a driving cycle in which a fastener is discharged into a workpiece, the lifter  866  returns the piston and the driver blade  826  from the BDC position toward the TDC position ( FIGS.  39  and  46 - 47   ). In particular, the pivot pin assembly  970  (and the last lifter roller  921 A) is in the second position when returning the driver blade  826  from the BDC position toward the TDC position. The detent assembly  988  releasably couples the second end  984  of the pivot arm  972  to the second recess  992 . Before the driver blade  826  reaches the TDC position, the engagement member  998  engages the second end  984  of the pivot arms  972 ,  974 , thereby causing the pivot pin assembly  970  to pivot about the pivot axis  986  from the second position toward the first position against the bias of the detent assembly  988 . The first stop member  996 A engages with the first pivot arm  972  proximate the second end  984 , thereby limiting the pivoting movement of the pivot pin assembly  970 . Subsequently, the detent assembly  988  releasably couples the second end  984  of the first pivot arm  972  to the first recess  990 , thereby maintaining the pivot pin assembly  970  into the first position. 
     As the driver blade  826  approaches the TDC position, the lowermost tooth  874 A engages the last lifter roller  921 A, and the reaction torque T 1 A exerted on the pivot pin assembly  970  by the drive blade  826  is oriented in a counter-clockwise direction (from the frame of reference of  FIG.  49   ). When the driver blade  826  reaches the TDC position, the orientation of the reaction torque exerted on the pivot pin assembly  970  by the driver blade  826  is reversed (i.e., by the change in direction of the contact normal G 1  between the lowermost tooth  874 A and the last lifter roller  921 A to above the pivot axis  986  of the pivot pin assembly  970 ) such that the reaction torque T 2 A is oriented in clockwise direction (from the frame of reference of  FIG.  50   ), thereby overcoming the biasing force of the detent assembly  988  and rotating the pivot pin assembly  970  from the first position toward the second position. Thereafter, the pivot pin assembly  970  no longer engages the driver blade  826 , and the piston and the driver blade  826  are thrust downward toward the BDC position by the compressed air (e.g., in the cylinder  18  above the piston,  FIG.  2   ). Therefore, due to the kickout arrangement  936 , the last lifter roller  921 A may “kick out” or move relatively quickly out of the way of the driver blade  826  (i.e., lowermost tooth  874 A) after the driver blade  826  reaches the TDC position. 
     Upon a fastener being driven into a workpiece, the driver blade  826  is in the driven or BDC position. Additionally, the second stop member  996 B has limited the movement of the pivot pin assembly  970  relative to the second recess  992  such that the detent assembly  988  engages the second recess  992  and maintains the pivot pin assembly  970  in the second position. Thereafter, the continued driving of the drive unit (e.g., drive unit  40 ,  FIG.  2   ) rotates the lifter  866  for returning the driver blade  826  toward the TDC position. Similar to  FIGS.  1 - 7    of the first embodiment, a controller may deactivate the drive unit when the driver blade  826  is in the ready position. The driver blade  826  (and the piston) is held in the ready position until released by user activation of a trigger (trigger  58 ,  FIG.  1   ), which initiates another driving cycle. 
     In particular, when the lifter  866  is moving the driver blade  826  toward the TDC position, forces (from the gas being compressed in the cylinder  18 ) act on the drive teeth  874 . The forces are at a maximum on the lowermost tooth  874 A as the driver blade  826  approaches the TDC position such that the lowermost tooth  874 A may experience a high amount of wear by sliding contact with the last lifter roller  921 A as the last lifter roller  921 A rotates past the lowermost tooth  874 A. The kickout arrangement  936  is configured to permit limited movement of the pivot pin assembly  970  (i.e., the last lifter pin  920 A and roller  921 A) between the first position and the second position such that the last lifter roller  921 A is moved quickly out of the way of the drive blade  826  to release the driver blade  826  and initiate a fastener driving operation, thereby reducing wear on the lifter  866  (i.e., the last lifter roller  921 A) and damage that might otherwise be caused to the drive unit by a momentary reaction torque applied to the drive unit as the driver blade  826  reaches the TDC position. 
       FIGS.  53 - 58    illustrate a sixth embodiment of a kickout arrangement  1136  of a lifter assembly  1088 , with like components and features as the embodiment of the lifter assembly  88  of the fastener driver  10  shown in  FIGS.  1 - 7    being labeled with like reference numerals plus “1000”. The lifter assembly  1088  is utilized for a fastener driver similar to the fastener driver  10  of  FIGS.  1 - 7    and, accordingly, the discussion of the fastener driver  10  above similarly applies to the kickout arrangement  1136  of the lifter assembly  1088  and is not re-stated. Rather, only differences between the kickout arrangement  136  and of the lifter  66  of  FIGS.  1 - 7    and the kickout arrangement  1136  and the lifter  1066  of  FIGS.  53 - 58    are specifically noted herein, such as differences in a last one of the lifter pins. 
     With reference to  FIG.  53   , the driver blade  1026  includes a plurality of lift teeth  1074  formed along an edge  1078  of the driver blade  1026 . Further, the powered fastener driver includes a frame  1070  positioned within a housing (e.g., housing  30 ,  FIG.  1   ). The frame  1070  is configured to support the lifter assembly  1088  within the housing. 
     With reference to  FIGS.  53 - 54   , the lifter assembly  1088  includes a drive unit (e.g., drive unit  40  of  FIG.  2   ) having an output shaft  1086 , and a lifter  1066  coupled for co-rotation with the output shaft  1086 . The output shaft  1086  defines a rotational axis  1090 . The lifter  1066  includes a hub  1116 , a plurality of pins  1120  extending between flanges  1118 A,  1118 B ( FIG.  54   ) of a body  1114  of the lifter  1066  (except for a last lifter pin  1120 A), and rollers  1121  supported upon the pins  1120 . Each roller  1121  is rotatably supported on the respective pin  1120 . Further, the rollers  1121  sequentially engage the lift teeth  1074  formed on the driver blade  1026  as the driver blade  1026  is returned from the BDC position toward the TDC position. 
     The last lifter pin  1120 A (and last lifter roller  1121 A) is cantilevered from the hub  1116 . In the illustrated embodiment, the lifter  1066  includes a first arm  1171  and a second arm  1173  extending from the first flange  1118 A and the second flange  1118 B, respectively. Each of the first arm  1171  and the second arm  1173  is a leaf spring to form a leaf spring assembly  1175 . The last lifter pin  1120 A and roller  1121 A are supported at an end  1177  of the leaf spring assembly  1175 . A cover (not shown) may fixedly couple the last lifter pin  1120 A to the end  1177  of the leaf spring assembly  1175 . 
     As shown in  FIG.  53   , the plurality of lifter pins  1120 , including the last lifter pin  1120 A, are located on a circumference Y of the lifter  1066  relative to the rotational axis  1090 . A combination of the leaf spring assembly  1175  and a lowermost tooth  1074 A of the driver blade  1026  defines a kickout arrangement  1136  located between the lifter  1066  and the driver blade  1026 . As explained in greater detail below, the last lifter pin  1120 A and roller  1121 A are movable relative to the lifter  1066  such that the last lifter pin  1120 A and roller  1121 A are no longer located on the circumference Y. 
     With reference to  FIG.  55   , in alternative embodiments, each of the first arm  1171 ′ and the second arm  1173 ′ is configured to include multiple bends to form the leaf spring assembly  1175 ′. 
     With reference to  FIGS.  53  and  56 - 58   , the last lifter roller  1121 A is movable relative to the hub  1116  between a first position ( FIG.  53   ), in which the last lifter roller  1121 A (and pin  1120 A) is located on the circumference Y defined by the lifter  1066 , and a second position, in which the last lifter roller  1121 A (and pin  1120 A) is deflectable (e.g., radially inward from the frame of reference of  FIG.  58   ) relative to the rotational axis  1090 . The last lifter roller  1121 A is in the first position relative to the lifter  1066  when returning the driver blade  1026  from the BDC position toward the TDC position. The last lifter roller  1121 A is deflectable from the first position into the second position after the driver blade  1026  reaches the TDC position. 
     More specifically, the leaf spring assembly  1175  is selected having a stiffness sufficient to apply a predetermined force necessary to the leaf spring assembly  1157  to maintain the last lifter pin  1120 A and roller  1121 A in the first position until the driver blade  1026  reaches the TDC position. In particular, as the driver blade  1026  is returned from the BDC position toward the TDC position, reaction forces (from gas being compressed in the cylinder  18 ) act on the driver teeth  1074 . A resultant reaction force from these forces is applied to the rotary lifter  1066  (i.e., the lifter pins  1120 ) as the lifter  1066  approaches the TDC position. As the lifter  1066  approaches the TDC position, the forces increase toward a maximum force on a lower most tooth  1074 A such that the reaction force increases to a maximum value that is greater than the predetermined force of the leaf spring assembly  1175 . As such, after the lifter  1066  reaches the TDC position, the resultant reaction force from the driver blade  1026  on the lifter  1066  (i.e., the last lifter roller  321 A) exceeds the predetermined force of the leaf spring assembly  1175 , and the last lifter roller  1121 A is moved from the first position toward the second position against the bias of the leaf spring assembly  1175 . As the driver blade  1026  is driven from the TDC position to the BDC position, the driver blade  1026  no longer contacts the lifter  1066  to apply the reaction force, and as such the leaf spring assembly  1175  rebounds to return the last lifter roller  1121 A from the second position to the first position relative to the output shaft  1086 . 
     During a driving cycle in which a fastener is discharged into a workpiece, the lifter  1066  returns the piston and the driver blade  1026  from the BDC position toward the TDC position. In particular, the last lifter roller  1121 A is in the first position when returning the driver blade  1026  from the BDC position toward the TDC position. After the driver blade  1026  reaches the TDC position, the reaction force reaches the maximum value, thereby exceeding the predetermined force of the leaf spring assembly  1175  and adjusting the last lifter roller  1121 A from the first position to the second position. 
     Subsequently, the last lifter roller  1121 A of the lifter  1066  moves away from the lowermost tooth  1074 A of the driver blade  1026  to release the driver blade  1026 . Thereafter, the lifter  1066  no longer engages the driver blade  1026 , and the piston and the driver blade  1026  are thrust downward toward the BDC position by the compressed air (e.g., in the cylinder  18  above the piston,  FIG.  2   ). As the driver blade  1026  is displaced toward the BDC position, the driver blade  1026  no longer contacts the lifter  1066  to apply the reaction force, and the leaf spring assembly  1175  rebounds to move the last lifter roller  1121 A from the second position toward the first position again (e.g., radially outward from the frame of reference of  FIG.  58   ). Therefore, due to the kickout arrangement  1136 , the last lifter roller  1121 A may “kick out” or move relatively quickly out of the way of the driver blade  1026  (i.e., lowermost tooth  1074 A) after the driver blade  1026  reaches the TDC position. 
     Upon a fastener being driven into a workpiece, the driver blade  1026  is in the driven or BDC position. Additionally, the leaf spring assembly  1175  applies the biasing force to move the last lifter pin  1120 A and roller  1121 A from the second position toward the first position. Thereafter, the continued driving of the drive unit (e.g., drive unit  40 ,  FIG.  2   ) rotates the lifter  1066  for returning the driver blade  1026  toward the TDC position. Similar to  FIGS.  1 - 7    of the first embodiment, a controller may deactivate the drive unit when the driver blade  1026  is in the ready position. The driver blade  1026  (and the piston) is held in the ready position until released by user activation of a trigger (trigger  58 ,  FIG.  1   ), which initiates another driving cycle. 
     In particular, when the lifter  1066  is moving the driver blade  1026  toward the TDC position, the forces (from the gas being compressed in the cylinder  18 ) act on the lowermost tooth  1074 A as the driver blade  1026  approaches the TDC position such that the lowermost tooth  1074 A may experience a high amount of wear by sliding contact with the last lifter roller  1121 A as the last lifter roller  1121 A rotates past the lowermost tooth  1074 A. The kickout arrangement  1136  is configured to permit limited movement of the last lifter roller  1121 A relative to the lifter  1066  between the first position and the second position such that the last lifter roller  1121 A is moved quickly out of the way of the drive blade  1026  to release the driver blade  1026  and initiate a fastener driving operation, thereby reducing wear on the lifter  1066  (i.e., the last lifter roller  1121 A) and damage that might otherwise be caused to the drive unit by a momentary reaction torque applied to the drive unit as the driver blade  1026  reaches the TDC position. 
       FIGS.  59 - 61 B  illustrate a seventh embodiment of a lifter assembly  1288 , with like components and features as the embodiment of the lifter assembly  88  of the fastener driver  10  shown in  FIGS.  1 - 7    being labeled with like reference numerals plus “1200”. The lifter assembly  1288  is utilized for a fastener driver similar to the fastener driver  10  of  FIGS.  1 - 7    and, accordingly, the discussion of the fastener driver  10  above similarly applies to the lifter assembly  1288  and is not re-stated. Rather, only differences between the lifter assembly  88  of  FIGS.  1 - 7    and the lifter  1266  of  FIGS.  59 - 61    are specifically noted herein, such as differences in a last one of the lifter pins. 
     The lifter  1266  includes a body  1314  having a hub  1316  through which an aperture  1310  extends, a first flange  1318 A radially extending from one end of the hub  1316 , and a second flange (not shown) radially extending from an opposite end of the hub  1316  and spaced from the first flange  1318 A. Further, the lifter  1266  includes a plurality of pins  1320  extending between the flanges  1318 A and at least one roller  1321 A supported upon at least one of the pins  1320 . The roller  1321 A or the pins  1320  sequentially engage the lift teeth  1274  formed on the driver blade  1226  as the driver blade  1226  is returned from the BDC position toward the TDC position. In the illustrated embodiment, the last lifter pin  1320 A of the lifter  1266  includes the roller  1321 A. In other embodiments, each pin  1320  may include a roller. 
     The roller  1321 A includes a non-cylindrical outer peripheral surface having one or more engagement sections  1309   a - d  ( FIGS.  60 ,  61 A, and  61 B ) that may be aligned and engageable with the last tooth  1274 A of the driver blade  1226  for holding the driver blade  1226  in a ready position prior to initiating a fastener driving operation. For example, the roller  1321 A includes a plurality of radial protrusions  1305  that define valleys therebetween, which form the engagement sections  1309   a - d  of the roller  1321 A. The construction of the roller  1321 A reduces stress on the driver blade tooth  1274 A and the last roller  1321 A when holding the driver blade  1226  at the ready/TDC position. In the illustrated embodiment, the roller  1321 A includes a plurality of valleys. For example, the roller  1321 A may include eight valleys. In other embodiments, the roller  1321 A may include more or fewer valleys. 
     Now with reference to  FIGS.  59 - 61 B , the lifter  1266  also includes a means for aligning one of the engagement section  1309   a - d  of the roller  1321 A with the last blade tooth  1274 A to facilitate re-meshing between the last blade tooth  1274 A and one of the engagement sections  1309   a - d  of the roller  1321 A. In the illustrated embodiment, the means for aligning the engagement section  1309   a - d  positions the roller  1321 A in a first rotational orientation (e.g., relative to the pin  1320 A,  FIG.  60   ) so a first engagement section  1309   a  of the roller  1321 A is aligned with the last blade tooth  1274 A. Further, the means for aligning includes a biasing member  1307  having a first end coupled to the hub  1316  of the lifter  1266  and a second end in engagement with a second engagement section  1309   b  of the roller  1321 A. In particular, the biasing member  1307  is a leaf spring and engages the second engagement section  1309   b , which is 180 degrees from the first engagement section  1309   a.    
     Without the means for aligning the roller  1321 A, the blade tooth  1274 A may the contact one of the protrusion  1305  of the last lifter roller  1321 A if the roller  1321 A is not in the desired rotational orientation, which may increase stress on the driver blade  1226  and/or the roller  1321 A. As shown in  FIG.  60   , the biasing member  1307  is configured to limit the rotational movement of the roller  1321 A to facilitate proper meshing between the last blade tooth  1274 A and the roller  1321 A. In other words, the biasing member  1307  biases the roller  1321 A toward a desired or first rotational orientation to ensure the last tooth  1274 A on the driver blade  1226  engages the engagement section  1309   a  between adjacent radial protrusions  1305  instead of the protrusion  1305  itself. 
     As shown in  FIGS.  60 ,  61 A, and  61 B , the biasing member  1307  may be preloaded and the force of the biasing member  1307  prevents the roller  1321 A from rotating when the driver blade tooth  1274 A is moving from the TDC position to BDC position ( FIG.  60   ). As the driver blade  1226  approaches the TDC position ( FIG.  61 A ), the roller  1321 A overcomes the force of the biasing member  1307 , which allows the roller  1321 A to move against the bias of the biasing member  1307 . 
     For example, during a driving cycle in which a fastener is discharged into a workpiece, the lifter  1266  returns the piston and the driver blade  1226  from BDC towards the TDC position. In particular, the last lifter roller  1321 A is in the first rotational orientation ( FIG.  60   ) when returning the driver blade  1226  from the BDC position towards the TDC position. As the driver blade  1226  approaches the TDC position, the reaction force reaches the maximum value, thereby exceeding the predetermined force of the biasing member  1307  and adjusting the last lifter roller  1321 A from the first rotational orientation ( FIG.  60   ) to an intermediate rotational orientation ( FIG.  61 A ), and then to a second rotational orientation ( FIG.  61 B ). In the intermediate rotational orientation, the second end of the biasing member  1307  is compressed and moves over the protrusion  1305  of the roller  1321 A. Once the driver blade  1226  reaches the TDC position, the last tooth  1274  of the blade  1226  is released ( FIG.  61 B ) so the driver blade  1226  can move towards the BDC position. Concurrently, the biasing member  1307  engages a third engagement section  1309   c , which restricts further movement of the roller  1321 A and aligns a fourth engagement section  1309   d  with the end portion of the last blade tooth  1274 A to facilitate re-meshing between the last blade tooth  1274 A and the fourth engagement section  1309   d  for a subsequent fastener driving event. In the illustrated embodiment, the third engagement section  1309   c  is positioned directly adjacent the second engagement section  1309   b  and the fourth engagement section  1309   d  is positioned directly adjacent the first engagement section  1309   a . In other embodiments, the biasing member  1307  may traverse one or more engagement sections during the fastener driving event. 
       FIG.  62 - 64    illustrate an eighth embodiment of a lifter assembly  1488 , with like components and features as the embodiment of the lifter assembly  88  of the fastener driver  10  shown in  FIGS.  1 - 7    being labeled with like reference numerals plus “1400”. The lifter assembly  1488  is utilized for a fastener driver similar to the fastener driver  10  of  FIGS.  1 - 7    and, accordingly, the discussion of the fastener driver  10  above similarly applies to the lifter assembly  1488  and is not re-stated. Rather, only differences between the lifter assembly  88  of  FIGS.  1 - 7    and the lifter  1466  of  FIGS.  62 - 64    are specifically noted herein, such as differences in a last one of the lifter pins. 
     The lifter  1466  includes a body  1514  having a hub  1516  through which an aperture  1510  extends, a first flange  1518 A radially extending from one end of the hub  1516 , and a second flange (not shown) radially extending from an opposite end of the hub  1516  and spaced from the first flange  1518 A. Further, the lifter  1466  includes a plurality of pins  1520  extending between the flanges  1518 A and at least one roller  1521 A supported upon at least one of the pins  1520 . The roller  1521 A or the pins  1520  sequentially engage the lift teeth  1474  formed on the driver blade  1426  as the driver blade  1426  is returned from the BDC position toward the TDC position. In the illustrated embodiment, the last lifter pin  1520 A of the lifter  1466  includes the roller  1521 A. In other embodiments, each pin  1520  may include a roller. 
     The roller  1521 A includes a non-cylindrical outer peripheral surface having one or more engagement sections that may be aligned and engageable with the last tooth  1474 A of the driver blade  1426  for holding the driver blade  1426  in a ready position prior to initiating a fastener driving operation. For example, the roller  1521 A includes a plurality of radial protrusions  1505  that define valleys therebetween, which forms the engagement sections  1509   a - d  of the roller  1521 A. The construction of the roller  1521 A reduces stress on the driver blade tooth  1474 A and the last roller  1521 A when holding the driver blade  1426  at the ready/TDC position. In the illustrated embodiment, the roller  1521 A includes a plurality of valleys  1509 . 
     Now with reference to  FIGS.  62 - 64 B , the lifter  1466  also includes a means for aligning one of the engagement section  1509   a - d  of the roller  1521 A with the last blade tooth  1474 A to facilitate re-meshing between the last blade tooth  1474 A and one of the engagement sections  1509   a - d  of the roller  1521 A. In the illustrated embodiment, the means for aligning the engagement section  1509   a - d  positions the roller  1521 A in a first rotational orientation (e.g. relative to the pin  1520 A,  FIG.  63   ) so a first engagement section  1509   a  of the roller  1521 A is aligned with the last blade tooth  1474 A. Further, the means for aligning includes a biasing member  1507  and an engagement member  1511  (e.g., a ball pin) supported within a recess  1513  formed in the body  1514  of the lifter  1466 . The biasing member  1507  urges the engagement member  1511  into contact with a second engagement section  1509   b  of the roller  1521 A. In particular, the biasing member  1507  is a compression spring that biasing the engagement member  1511  into engagement with the second engagement section  1509   b , which is 180 degrees from the first engagement section  1509   a.    
     As shown in  FIGS.  63 ,  64 A and  64 B , the biasing member  1507  may be preloaded and the force of the biasing member  1507  urges the engagement member  1511  into engagement with the roller  1521 A, which prevents the roller  1521 A from rotating when the driver blade tooth  1574 A is moving from the TDC position to the BDC position ( FIG.  63   ). As the driver blade  1574 A approaches the TDC position, the roller  1521 A overcomes the force of the biasing member  1507 , which allows the roller  1521 A to move against the bias of the biasing member  1507 . 
     For example, during a driving cycle in which a fastener is discharged into a workpiece, the lifter  1466  returns the piston and the driver blade  1426  from the BDC position towards the TDC position. In particular, the last lifter roller  1521 A is in the first position ( FIG.  63   ) when returning the driver blade  1426  from BDC towards TDC. As the driver blade  1426  approaches the TDC position, the reaction force reaches the maximum value, thereby exceeding the predetermined force of the biasing member  1507  and adjusting the last lifter roller  1521 A from the first rotational orientation ( FIG.  63   ) to an intermediate rotational orientation (FIG.  64 A), and to a second rotational orientation ( FIG.  64 B ). In the intermediate rotational orientation, the engagement member  1511  compresses the biasing member  1507  within the recess  1513  so the engagement member  1511  can move over the protrusion  1505  of the roller  1521 A. Once the driver blade  1226  reaches the TDC position, the last tooth  1474  of the blade  1426  is released ( FIG.  64 B ) so the driver blade  1426  can move towards the BDC position. Concurrently, the engagement member  1511  engages a third engagement section  1509   c , which restricts further movement of the roller  1521 A and positions a fourth engagement section  1509   d  in the first rotational orientation to facilitate re-meshing between the last blade tooth  1474 A and the fourth engagement section  1509   d  for a subsequent fastener driving event. In the illustrated embodiment, the third engagement section  1509   c  is positioned directly adjacent the second engagement section  1509   b  and the fourth engagement section  1509   d  is positioned directly adjacent the first engagement section  1509   a . In other embodiments, the engagement member  1511  may traverse one or more engagement sections during the fastener driving event. 
       FIGS.  65  and  66    illustrate a ninth embodiment of a lifter assembly  1688 , with like components and features as the embodiment of the lifter assembly  88  of the fastener driver  10  shown in  FIGS.  1 - 7    being labeled with like reference numerals plus “1600”. The lifter assembly  1688  is utilized for a fastener driver similar to the fastener driver  10  of  FIGS.  1 - 7    and, accordingly, the discussion of the fastener driver  10  above similarly applies to the lifter assembly  1688  and is not re-stated. Rather, only differences between the lifter assembly  88  of  FIGS.  1 - 7    and the lifter  1666  of  FIGS.  65  and  66    are specifically noted herein, such as differences in a last one of the lifter pins. 
     The lifter  1666  includes a body  1714  having a hub  1716  through which an aperture  1710  extends, a first flange  1718 A radially extending from one end of the hub  1716 , and a second flange  1718 B ( FIG.  66   ) radially extending from an opposite end of the hub  1716  and spaced from the first flange  1718 A. Further, the lifter  1666  includes a plurality of pins  1720  extending between the flanges  1718 A and at least one roller  1721 A supported upon at least one of the pins  1720 . The roller  1721 A includes a non-cylindrical outer peripheral surface having one or more engagement sections  1709  that may be aligned and engageable with the last tooth  1674 A of the driver blade  1626  for holding the driver blade  1626  in a ready position prior to initiating a fastener driving operation. For example, the roller  1721 A includes a plurality of radial protrusions  1705  that define valleys therebetween, which forms the engagement sections  1709  of the roller  1721 A. The construction of the roller  1721 A reduces stress on the driver blade tooth  1674 A and the last roller  1721 A when holding the driver blade  1626  at the ready/TDC position. 
     Now with reference to  FIG.  66   , the lifter  1666  also includes a means for aligning one of the engagement sections  1709  of the roller  1721 A with the last blade tooth  1674 A to facilitate re-meshing between the last blade tooth  1674 A and one of the engagement sections  1709  of the roller  1721 A. In the illustrated embodiment, the means for aligning the engagement section  1709  positions the roller  1721 A in a first rotational orientation (e.g. relative to the pin  1720 A) so a first engagement section of the roller  1721 A is aligned with the last blade tooth  1674 A. Further, the means for aligning includes one or more friction inducing members, such as friction rings  1715 A,  1715 B positioned between the body  1714  and the roller  1721 A. The one or more friction rings  1715 A,  1715 B (e.g., an O-ring) are supported within one or more recesses  1713 A,  1713 B formed in the body  1714  of the lifter  1666 . A first friction ring  1715 A is positioned within a first recess  1713 A formed in the first flange  1718 A (e.g., on a first side of the roller  1721 A) and a second friction ring  1715 B is positioned within a second recess  1713 B formed in the second flange  1718 B (e.g., on a second side of the roller  1721 A). In other words, the first and second friction rings  1715 A,  1715 B are positioned on opposing sides of the roller  1721 A. 
     The friction rings  1715 A,  1715 B reduce the amount of free spin the roller  1721 A has after the driver blade  1626  is released, which reduces risk of random roller positioning. For example, as the driver blade  1626  approaches the TDC position, the roller  1721 A overcomes the force of the friction rings  1715 A,  1715 B, which allows the roller  1721 A to rotate towards a second rotational orientation. Once the driver blade  1626  is released, the friction rings  1715 A,  1715 B dissipate rotational energy of the roller  1721 A, so the roller  1721 A effectively stays in the second rotational orientation (e.g., the orientation the roller  1721 A last contacted the last tooth  1674 A of the driver blade  1626 ). During a subsequent fastener driving, the roller remains in the second rotational orientation where a second engagement section aligns with the end portion of the tooth of the driver blade. For example, the second engagement section may be positioned proximate the first engagement section. The use of the friction rings  1715 A,  1715 B also limits the effect of the grease quantity in roller  1721 A. 
       FIG.  67 - 70    illustrate a tenth embodiment of a lifter assembly  1888 , with like components and features as the embodiment of the lifter assembly  88  of the fastener driver  10  shown in  FIGS.  1 - 7    being labeled with like reference numerals plus “1800”. The lifter assembly  1888  is utilized for a fastener driver similar to the fastener driver  10  of  FIGS.  1 - 7    and, accordingly, the discussion of the fastener driver  10  above similarly applies to the lifter assembly  1888  and is not re-stated. Rather, only differences between the lifter assembly  88  of  FIGS.  1 - 7    and the lifter  1866  of  FIGS.  67 - 70    are specifically noted herein, such as differences in a last one of the lifter pins. 
     The lifter  1866  includes a body  1914  having a hub  1916  through which an aperture  1910  extends, a first flange  1918 A radially extending from one end of the hub  1916 , and a second flange  1918 B ( FIG.  68   ) radially extending from an opposite end of the hub  1916  and spaced from the first flange  1918 A. Further, the lifter  1866  includes a plurality of pins  1920  extending between the flanges  1918 A,  1918 B. A last pin assembly  1903  includes a last pin  1920 A and a roller  1921 A supported upon and co-rotatable with the last pin  1920 A. For example, the last pin  1920 A may be coupled to the roller  1921 A via a double-D profile or other connection feature (e.g., a key/keyway arrangement or spline, etc.). The roller  1921 A or the pins  1920  sequentially engage the lift teeth  1874  formed on the driver blade  1826  as the driver blade  1826  is returned from the BDC position toward the TDC position. 
     The roller  1921 A includes a non-cylindrical outer peripheral surface having one or more engagement sections  1909   a ,  1909   b  that may be aligned and engageable with the last tooth  1874 A of the driver blade  1826  for holding the driver blade  1826  in a ready position prior to initiating a fastener driving operation. For example, the roller  1921 A includes a plurality of radial protrusions  1905  that define valleys therebetween, which forms the engagement sections  1909   a ,  1909   b . The construction of the roller  1921 A reduces stress on the driver blade tooth  1874 A and the last roller  1921 A when holding the driver blade  1826  at the ready/TDC position. 
     Now with reference to  FIGS.  68 - 70 B , the last pin  1920 A also includes a pin head  1917  supported within a recess  1913  formed in the body  1914  of the lifter  1866 . The pin head  1917  also includes a non-cylindrical outer peripheral surface similar to the roller  1921 A. For example, pin head  1917  also includes a plurality of radial protrusions  1923  that define valleys therebetween, which form pin engagement sections  1927   a ,  1927   b . The pin engagement sections  1927   a ,  1927   b  are offset from the engagement sections  1909   a ,  1909   b  in a direction of a rotational axis  1929  of the rotary lifter  1866 . 
     The lifter  1866  also includes a means for aligning one of the engagement sections  1909   a ,  1909   b  of the roller  1921 A with the last blade tooth  1874 A to facilitate re-meshing between the last blade tooth  1874 A and one of the engagement sections  1909   a ,  1909   b  of the roller  1921 A. In the illustrated embodiment, the means for aligning the engagement section  1909   a ,  1909   b  positions the roller  1921 A in a first rotational orientation (e.g. relative to the lifter body  1914 ) so a first engagement section  1309   a  of the roller  1321 A is aligned with the last blade tooth  1274 A. In particular, the means for aligning includes a biasing member  1907  (e.g., a compression spring) and an engagement member  1911  (e.g., a ball detent) supported within a recess  1913  formed in the body  1914  of the lifter  1866 . Further, the means for aligning is supported within the second flange  1918 B of the lifter  1866 . The biasing member  1907  biases the engagement member  1911  into contact with a first pin engagement section  1927   a  of the pin head  1917 . In particular, the biasing member  1907  is a compression spring. 
     As shown in  FIGS.  69 ,  70 A and  70 B , the biasing member  1907  may be preloaded and the force of the biasing member  1907  urges the engagement member  1911  into contact with the first pin engagement section  1927   a  of the pin head  1917 , which prevents the pin assembly  1903  from rotating when the driver blade tooth  1874 A is moving from the TDC position to the BDC position ( FIG.  70 A ). As the driver blade  1874 A approaches the TDC position, the pin head  1917  overcomes the force of the biasing member  1907 , which allows the pin assembly  1903  to move against the bias of the biasing member  1907 . 
     For example, during a driving cycle in which a fastener is discharged into a workpiece, the lifter  1866  returns the piston and the driver blade  1826  from the BDC position towards the TDC position. In particular, the pin assembly  1903  is in a first rotational orientation ( FIG.  69   ) when returning the driver blade  1826  from the BDC position towards the TDC position. In the first rotational orientation, the first engagement section  1909   a  of the roller  1921 A is aligned with the last blade tooth  1874 A and the first pin engagement section  1927   a  is aligned with the engagement member  1911 , which restricts rotational movement of the pin assembly  1903 . As the driver blade  1826  approaches the TDC position, the reaction force reaches the maximum value, thereby exceeding the predetermined force of the biasing member  1907  and adjusting the pin assembly  1903  from the first rotational orientation ( FIG.  69   ) to an intermediate rotational orientation ( FIG.  70 A ), and to a second rotational orientation ( FIG.  70 B ). In the intermediate rotational orientation, the engagement member  1911  compresses the biasing member  1907  within the recess  1913  so the engagement member  1911  can move over the protrusion  1923  of the pin head  1917  as the pin assembly  1903  rotates. Once the driver blade  1826  reaches the TDC position, the last tooth  1874  of the blade  1826  is released ( FIG.  70 B ) and the driver blade  1826  moves towards the BDC position. Concurrently, the biasing member  1907  urges the engagement member  1911  into engagement with a second pin engagement section  1927   b , which restricts further movement of the pin assembly  1903  and positions a second engagement section  1909   b  in the first rotational orientation to facilitate re-meshing between the last blade tooth  1874 A and the second engagement section  1909   d  for a subsequent fastener driving event. In the illustrated embodiment, the second pin engagement section  1927   b  is positioned directly adjacent the first pin engagement section  1927   a  and the second engagement section  1909   b  is positioned directly adjacent the first engagement section  1909   a . In other embodiments, the engagement member  1911  may traverse one or more pin engagement sections  1927   a ,  1927   b  during the fastener driving event. 
       FIG.  71 - 74    illustrate an eleventh embodiment of a lifter assembly  2088 , with like components and features as the embodiment of the lifter assembly  88  of the fastener driver  10  shown in  FIGS.  1 - 7    being labeled with like reference numerals plus “2000”. The lifter assembly  2088  is utilized for a fastener driver similar to the fastener driver  10  of  FIGS.  1 - 7    and, accordingly, the discussion of the fastener driver  10  above similarly applies to the lifter assembly  2088  and is not re-stated. Rather, only differences between the lifter assembly  88  of  FIGS.  1 - 7    and the lifter  2066  of  FIGS.  71 - 74    are specifically noted herein, such as differences in a last one of the lifter pins. 
     The lifter  2066  includes a body  2114  having a hub  2116  through which an aperture  2110  extends, a first flange  2118 A radially extending from one end of the hub  2116 , and a second flange  2118 B ( FIG.  68   ) radially extending from an opposite end of the hub  2116  and spaced from the first flange  2118 A. Further, the lifter  2066  includes a plurality of pins  2120  extending between the flanges  2118 A,  2118 B. In the illustrated embodiment, the last pin  2120 A defines a roller that rotatable relative to the body  2114 . In other words, it should be appreciated that the roller may be integrally formed on the last pin  2120 A. The pins  2120  sequentially engage the lift teeth  2074  formed on the driver blade  2026  as the driver blade  2026  is returned from the BDC position toward the TDC position. 
     The last pin  2120 A includes a non-cylindrical outer peripheral surface having an engagement section  2109  that may be aligned and engageable with the last tooth  2074 A of the driver blade  2026  for holding the driver blade  2026  in a ready position prior to initiating a fastener driving operation. For example, the last pin  2120 A includes a pair of opposing flat surfaces  2101  and the engagement section  2109  defined therebetween. The last tooth  2074 A of the driver blade  2026  engages the engagement section  2109  of the last pin  2120 A, which reduces stress on the driver blade tooth  2074 A and the last roller  2121 A when holding the driver blade  2026  at the ready/TDC position. 
     Now with reference to  FIGS.  73  and  74   , the lifter  2066  also includes a means for aligning the engagement section  2109  of the last pin  2120 A with the last blade tooth  2074 A to facilitate re-meshing between the last blade tooth  2074 A the engagement section  1309  of the last pin  2120 A. In the illustrated embodiment, the means for aligning the engagement section  2109  positions the last pin  2120 A in a first rotational orientation (e.g., relative to the lifter  2066 ,  FIG.  71   ) so the engagement section  2109  is aligned with the last blade tooth  2074 A. Further, the means for aligning includes a bushing  2105  surrounding a portion of the pin  2120 A, a biasing member  2107  positioned between the bushing  2105  and the pin  2120 A, and a retaining member  2113  securing the bushing  2105  and biasing member  2107  to the body  2114  (e.g., the second flange  2118 B) of the lifter  2066 . In the illustrated embodiment, the biasing member  2107  is a torsion spring that urges the pin  2120 A desired or first rotational orientation and allows the pin  2120 A to rotate in both a clockwise (e.g., against the force of the torsion spring) and counterclockwise (e.g., from the force of the torsion spring) direction. In addition, the bushing  2105  is formed of a metallic material (e.g., steel, aluminum, etc.), which reduces wear on the pin  2120 A. 
     As the driver blade  2074 A approaches TDC, the pin  2120 A overcomes the force of the biasing member  2107 , which allows the pin  2120 A to rotate against the bias of the biasing member  2107 . For example, during a driving cycle in which a fastener is discharged into a workpiece, the lifter  2066  returns the piston and the driver blade  2026  from the BDC position toward the TDC position. In particular, the pin  2120 A is in a first rotational orientation when returning the driver blade  2026  from the BDC position toward the TDC position. After the driver blade  2026  reaches the TDC position, the reaction force reaches the maximum value, thereby exceeding the predetermined force of the biasing member  2107  and rotating the pin  2120 A from the first rotational orientation to a second rotational orientation (e.g., in a clockwise direction), which releases the driver blade  2026 . Once the blade  2026  is released, the biasing member  2107  rotates the pin  2120 A in an opposite direction (e.g., a counterclockwise direction) to return the first position or desired rotational orientation. 
       FIG.  75 - 77    illustrate a twelfth embodiment of a lifter  2266 , with like components and features as the embodiment of the lifter  66  of the fastener driver  10  shown in  FIGS.  1 - 7    being labeled with like reference numerals plus “2200”. A lifter assembly is utilized for a fastener driver similar to the fastener driver  10  of  FIGS.  1 - 7    and, accordingly, the discussion of the fastener driver  10  above similarly applies to the lifter assembly and is not re-stated. Rather, only differences between the lifter  66  of  FIGS.  1 - 7    and the lifter  2266  of  FIGS.  75 - 77    are specifically noted herein, such as differences in a last one of the lifter pins. 
     The lifter  2266  includes a body  2314  having a hub, a first flange  2318 A radially extending from one end of the hub  2316 , and a second flange  2318 B ( FIG.  75   ) radially extending from an opposite end of the hub  2316  and spaced from the first flange  2318 A. Further, the lifter  2266  includes a plurality of pins  2320  extending between the flanges  2318 A,  2318 B. In the illustrated embodiment, the last pin  2320 A defines a roller rotatable relative to the body  2314 . In other words, it should be appreciated that the roller may be integrally formed on the last pin  2320 A. The pins  2320  sequentially engage the lift teeth formed on the driver blade (not shown) as the driver blade is returned from the BDC position toward the TDC position. 
     The last pin  2320 A includes a non-cylindrical outer peripheral surface having one or more engagement sections  2309   a - d  that may be aligned and engageable with the last tooth of the driver blade for holding the driver blade in a ready position prior to initiating a fastener driving operation. For example, the last pin  2320 A includes a plurality of radial protrusions  2305  that define engagement sections  2309   a - d  therebetween. The last tooth of the driver blade engages one of the engagement sections  2309   a - d  of the last pin  2320 A, which reduces stress on the driver blade tooth and the last roller when holding the driver blade at the ready/TDC position 
     Now with reference to  FIGS.  76  and  77   , the lifter  2266  also includes a means for aligning one of the engagement sections  2309   a - d  of the last pin  2320 A with the last blade tooth to facilitate re-meshing between the last blade tooth and one of the engagement sections  2309   a - d  of the last pin  2320 A. In the illustrated embodiment, the means for aligning the engagement section  2309  positions the last pin  2320 A in a first rotational orientation (e.g. relative to the lifter body  2314 ) so a first engagement section  2309   a  is aligned with the last blade tooth. Further, the means for aligning includes a biasing member  2307  (e.g., a compression spring) and an engagement member  2311  (e.g., a ball detent) supported within a recess  2313  formed in the body  2314  of the lifter  2266 . More particularly, the means for aligning is positioned between the first and second flanges  2218 A,  2218 B. The biasing member  2307  urges the engagement member  2311  into engagement with one of the engagement sections  2309   a - d  (i.e., a second engagement section  2309   b ) of the last pin  2320 A. In particular, the biasing member  2307  is a compression spring. 
     As the driver blade approaches the TDC position, the last pin  2320 A overcomes the force of the biasing member  2307 , which allows the last pin  2320 A to move against the bias of the biasing member  2307 . For example, during a driving cycle in which a fastener is discharged into a workpiece, the lifter  2266  returns the piston and the driver blade from the BDC position towards the TDC position. In particular, the last pin  2320 A is in the first position when returning the driver blade from the BDC position toward the TDC position. As the driver blade approaches the TDC position, the reaction force reaches the maximum value, thereby exceeding the predetermined force of the biasing member  2307  and adjusting the last pin  2320 A from the first rotational orientation to an intermediate rotational orientation, and then to a second rotational orientation. In the intermediate rotational orientation, the engagement member  2311  compresses the biasing member  2307  so the engagement member  2311  can move over the protrusion  2305  of the last pin  2320 A. Once the driver blade reaches the TDC position, the last tooth of the blade is released so the driver blade can move towards the BDC position. Concurrently, the biasing member  2307  urges the engagement member  2311  into engagement a third engagement section  2309   c , which restricts further movement of the last pin  2320 A and positions a fourth engagement section  2309   d  in the first rotational orientation to facilitate re-meshing between the last blade tooth and the fourth engagement section  2309   d  for a subsequent fastener driving event. 
       FIGS.  78 - 82 B  illustrate another embodiment drive unit  2440 , with like components and features as the embodiment of the drive unit  40  of the fastener driver  10  shown in  FIG.  2    being labeled with like reference numerals plus “2400”. The drive unit  2440  is utilized for a fastener driver similar to the fastener driver  10  of  FIGS.  1 - 7    and, accordingly, the discussion of the fastener driver  10  above similarly applies to the drive unit  2440  and is not re-stated. Rather, only differences between the drive unit  40  of  FIG.  2    and the drive unit  2440  of  FIGS.  78 - 82 B  are specifically noted herein. 
     The drive unit  2440  includes an electric motor  2442  and a transmission  2482  positioned downstream of the motor  2442 . The transmission  2482  includes an input  2475  (i.e., a motor output shaft) and includes an output shaft  2486  extending to a lifter  2500 , which is operable to move a driver blade  2426  ( FIG.  79   ) from the driven position to the ready position, as explained in greater detail below. In other words, the transmission  2482  provides torque to the lifter  2500  from the motor  2442 . The transmission  2482  is configured as a planetary transmission having three planetary stages  2477 ,  2479 ,  2483 . Each planetary stage  2477 ,  2479 ,  2483  includes a ring gear, a carrier, and multiple planet gears coupled to the carrier for relative rotation therewith. In alternative embodiments, the transmission may be a single-stage planetary transmission, or a multi-stage planetary transmission including any number of planetary stages. 
     A one-way clutch mechanism  2487  incorporated in the transmission  2482 . More specifically, the one-way clutch mechanism  2487  includes a carrier  2491 , which is also a component in the second planetary stage  2479 . The one-way clutch mechanism  2487  permits a transfer of torque to the output shaft  2486  of the transmission  2482  in a single (i.e., first) rotational direction, yet prevents the motor  2442  from being driven in a reverse direction in response to an application of torque on the output shaft  2486  of the transmission  2482  in an opposite, second rotational direction. In the illustrated embodiment, the one-way clutch mechanism  2487  is incorporated with the second planetary stage  2479  of the transmission  2482 . In alternative embodiments, the one-way clutch mechanism  2487  may be incorporated into the first planetary stage  2477 , for example. 
     The last planetary stage  2483  includes a ring gear  2495 , a carrier  2499 , and multiple planet gears  2503  coupled to the carrier  2499  for relative rotation therewith. The second planetary stage  2479  further includes an output pinion that is enmeshed with the planet gears  2503  which, in turn, are rotatably supported upon the carrier  2499  of the last planetary stage  2483  and enmeshed with a toothed interior peripheral portion  2507  of the ring gear  2495 . Unlike the ring gears of the first and second planetary stages  2477 ,  2479 , the ring gear  2495  of the third planetary stage  2483  is rotatable relative to a transmission cover  2509  adjacent a transmission housing  2511 . The carrier  2499  is coupled to the output shaft  2486  through a kickout arrangement  2536  described in more detail below. In the illustrated embodiment, the carrier  2499  is a torque input member that is configured to transmit torque to from the drive unit  2440  and the output shaft  2486  and the lifter  2500  defines a torque output member, which is in selective driving connection with and downstream of the torque input member. The torque output member configured to receive torque from the torque input member in a first rotational direction for returning the driver blade  2426  from the bottom-dead-center position toward the top-dead-center position. 
     As shown in  FIGS.  79  and  80 A , the lifter  2500  is coupled to the output shaft  2486  for relative rotation therewith. In the illustrated embodiment, the lifter  2500  has a D-shaped profile that engages the output shaft  2486  and a fastener  2515  ( FIG.  79   , e.g., a nut) is threadably coupled to an end portion of the output shaft  2486  to secure the lifter  2500  to output shaft  2486 . Further, the lifter  2500  has a unitary body defining a plurality of teeth  2520  that sequentially engage lift teeth  2474  formed on the driver blade  2426  as the driver blade  2426  is returned from the BDC position toward the TDC position. A last tooth  2520 A of the lifter  2500  includes a roller  2521 A that engages a last or lowermost tooth  2474 A of the driver blade  2426  as the driver blade  2426  reaches the TDC position. 
     Now with reference to  FIG.  80 B , the carrier  2499  includes an aperture  2510  that is partly defined by two opposed curvilinear segments  2522  and two opposed protrusions  2524  that extend radially inward of a base circle A coinciding with the curvilinear segments  2522 . Each of the protrusions  2524  includes flat segments  2526 ,  2530  and an apex  2534  between the segments  2526 ,  2530 . Thus, the aperture  2510  is also partly defined by the protrusions  2524 , in addition to the curvilinear segments  2522 . As explained in further detail below, each curvilinear segment  2522  is configured to engage with the respective cylindrical portion  2498  of the output shaft  2486 , while each protrusion  2524  is configured to engage with a corresponding flat portion  2502  on an outer peripheral surface of the output shaft  2486 . 
     Each of the first and second flat segments  2526 ,  2530  of each of the protrusions  2524  is configured to alternately engage with the respective flat portion  2502  of the output shaft  2486 . Accordingly, the first flat segments  2526  may be considered a driving lug and each flat portion  2502  may be considered a driven lug. A combination of the first flat segment  2526 , the second flat segments  2530 , and flat portion  2502  defines the kickout arrangement  2536  located between the carrier  2499  and the output shaft  2486 . 
     With reference to  FIGS.  80 B,  81 B, and  82 B , the output shaft  2486  and the lifter  2500  (e.g., the torque output member) is movable relative to the carrier  2499  (e.g., the torque input member) between a first position ( FIG.  80 B ), in which the flat portions  2502  of the output shaft  2486  are engaged with the respective first flat segments  2526  of the carrier  2499 , and a second position ( FIG.  82 B ), in which the output shaft  2486  and the lifter  2500  is rotated relative to the carrier  2499  (i.e., about a rotational axis  2490 ) such that the second flat segments  2530  are engaged with the respective flat portions  2502  when the lifter  2500  moves towards the TDC position ( FIGS.  80 A,  81 A,  82 A ). The output shaft  2486  and the lifter  2500  is in the first position relative to the carrier  2499  when returning the driver blade  2426  from the BDC position toward the TDC position. The output shaft  2486  and the lifter  2500  rotates (in a counter-clockwise direction from the frame of reference of  FIG.  80 B ) to the second position relative to the carrier  2499  after the driver blade  2426  reaches the TDC position. In other words, the aperture  2510  is configured to selectively allow rotation of the output shaft  2486  and the lifter  2500  relative to the carrier  2499 . 
     More specifically, as illustrated in  FIGS.  80 A,  80 B , as the driver blade  2426  approaches the TDC position, a contact normal (i.e., arrow A 1  in  FIG.  80 B ) perpendicular to a line tangent to both a last lifter roller  2521 A and the surface on a lowermost tooth  2474 A on the driver blade  2426  with which the roller  2521 A is in contact is formed. Since the lifter  2500  and the output shaft  2486  are coupled for co-rotation, a reaction force T 1  is applied to the output shaft  2486  along the contact normal A 1 , which is oriented along a line of action C located below the rotational axis of the lifter  2500 , which is coaxial with the rotational axis  2490  of the output shaft  2486 , from the frame of reference of  FIG.  80 B . Thus, a reaction torque (arrow T 1 ) is applied to the output shaft  2486  in a clockwise direction (from the frame of reference of  FIG.  80 B ), thereby maintaining the output shaft  2486  in the first position as the driver blade  2426  is moved toward the TDC position. The line of action C of the contact normal A 1  remains below the rotational axis of the lifter  2500  until the lifter  2500  reaches the TDC position. Thereafter, as shown in  FIG.  81 A , the contact normal A 1  between the lowermost tooth  2474 A and the last lifter roller  2521 A changes direction such that the line of action C is located above the rotational axis of the lifter  2500 . Thus, as shown in  FIG.  81 B , the reaction torque (arrow T 2 ) exerted on the output shaft  2486  by the driver blade  2426  is redirected in a counter-clockwise direction (from the frame of reference of  FIG.  80 B ), thereby causing the output shaft  2486  to rotate about the carrier  2499  from the first position shown in  FIG.  80 B  to the second position shown in  FIG.  82 B . 
       FIGS.  83 - 87 B  illustrate another embodiment drive unit  2640 , with like components and features as the embodiment of the drive unit  40  of the fastener driver  10  shown in  FIG.  2    being labeled with like reference numerals plus “2600”. The drive unit  2640  is utilized for a fastener driver similar to the fastener driver  10  of  FIGS.  1 - 7    and, accordingly, the discussion of the fastener driver  10  above similarly applies to the drive unit  2640  and is not re-stated. Rather, only differences between the drive unit  40  of  FIG.  2    and the drive unit  2640  of  FIGS.  83 - 87 B  are specifically noted herein. 
     The drive unit  2640  includes an electric motor  2642  and a transmission  2682  positioned downstream of the motor  2642 . The transmission  2682  includes an input  2675  (i.e., a motor output shaft) and includes an output shaft  2686  extending to a lifter  2700 , which is operable to move a driver blade  2626  ( FIG.  84   ) from the driven position to the ready position, as explained in greater detail below. In other words, the transmission  2682  provides torque to the lifter  2700  from the motor  2642 . The transmission  2682  is configured as a planetary transmission having two planetary stages  2677 ,  2679  and a spur gear stage  2683 . Each planetary stage  2677 ,  2679  includes a ring gear, a carrier, and multiple planet gears coupled to the carrier for relative rotation therewith. In alternative embodiments, the transmission may be a single-stage planetary transmission, or a multi-stage planetary transmission including any number of planetary stages. 
     A one-way clutch mechanism  2687  incorporated in the transmission  2682 . More specifically, the one-way clutch mechanism  2687  includes a carrier  2691 , which is also a component in the second planetary stage  2679 . The one-way clutch mechanism  2687  permits a transfer of torque to the output shaft  2686  of the transmission  2682  in a single (i.e., first) rotational direction, yet prevents the motor  2642  from being driven in a reverse direction in response to an application of torque on the output shaft  2686  of the transmission  2682  in an opposite, second rotational direction. In the illustrated embodiment, the one-way clutch mechanism  2687  is incorporated with the second planetary stage  2679  of the transmission  2682 . In alternative embodiments, the one-way clutch mechanism  2687  may be incorporated into the first planetary stage  2677 , for example. 
     The spur gear stage  2683  includes a first, drive spur gear  2695  and a second, driven spur gear  2699  meshed with the drive spur gear  2695  for relative rotation therewith. The motor  2642 , the planetary stages  2677 ,  2679 , and the drive spur gear  2695  are coaxial with a first rotational axis  2501 , which is offset from a second rotational axis  2690  that is coaxial with the driven spur gear  2699 . As such, the second rotational axis  2690  is also coaxial with the output shaft  2686  and the lifter  2500 . The construction of the transmission  2682  reduces the overall size of the fastener driver. In the illustrated embodiment, the spur gear stage  2683  has a gear ratio of 1:1. In other embodiments, spur gear stage  2683  may have an alternative gear ratio. The driven spur gear  2699  is coupled to the output shaft  2686  through a kickout arrangement  2736  ( FIG.  85 B ) described in more detail below. In the illustrated embodiment, the driven spur gear  2699  is a torque input member that is configured to transmit torque to from the drive unit  2640  and the output shaft  2686  and the lifter  2700  defines a torque output member, which is in selective driving connection with and downstream of the torque input member. The torque output member configured to receive torque from the torque input member in a first rotational direction for returning the driver blade  2626  from the bottom-dead-center position toward the top-dead-center position. 
     As shown in  FIGS.  84  and  85 A , the lifter  2700  is coupled to the output shaft  2686  for relative rotation therewith. In the illustrated embodiment, the lifter  2700  has a D-shaped profile that engages the output shaft  2686  and a fastener  2715  ( FIG.  83   , e.g., a nut) is threadably coupled to an end portion of the output shaft  2686  to secure the lifter  2700  to output shaft  2686 . Further, the lifter  2700  has a body having a plurality of pins  2720  that sequentially engage lift teeth  2674  formed on the driver blade  2626  as the driver blade  2626  is returned from the BDC position toward the TDC position. A last pin  2720 A of the lifter  2700  may be rotatably supported on the lifter  2700  and engages a last or lowermost tooth  2474 A of the driver blade  2626  as the driver blade  2626  reaches the TDC position. 
     Now with reference to  FIG.  85 B , the driven spur gear  1699  includes an aperture  2710  that is partly defined by two opposed curvilinear segments  2722  and two opposed protrusions  2724  that extend radially inward of a base circle A coinciding with the curvilinear segments  2722 . Each of the protrusions  2724  includes flat segments  2726 ,  2730  and an apex  2734  between the segments  2726 ,  2730 . Thus, the aperture  2710  is also partly defined by the protrusions  2724 , in addition to the curvilinear segments  2722 . As explained in further detail below, each curvilinear segment  2722  is configured to engage with the respective cylindrical portion  2698  of the output shaft  2686 , while each protrusion  2724  is configured to engage with a corresponding flat portion  2702  on an outer peripheral surface of the output shaft  2686 . 
     Each of the first and second flat segments  2726 ,  2730  of each of the protrusions  2724  is configured to alternately engage with the respective flat portion  2702  of the output shaft  2686 . Accordingly, the first flat segment  2726  may be considered a driving lug and each flat portion  2702  may be considered a driven lug. A combination of the first flat segment  2726 , the second flat segments  2730 , and flat portion  2702  defines the kickout arrangement  2736  located between the driven spur gear  1699  and the output shaft  2686 . 
     With reference to  FIGS.  85 B,  86 B, and  87 B , the output shaft  2686  and the lifter  2700  (e.g., the torque output member) is movable relative to the spur gear between a first position ( FIG.  85 B ), in which the flat portions  2702  of the output shaft  2686  are engaged with the respective first flat segments  2726  of the driven spur gear  1699 , and a second position ( FIG.  87 B ), in which the output shaft  2686  and the lifter  2700  is rotated relative to the driven spur gear  1699  (i.e., about a rotational axis  2490 ) such that the second flat segments  2730  are engaged with the respective flat portions  2702  when the lifter  2700  moves towards the TDC position ( FIGS.  85 A,  86 A,  87 A ). The output shaft  2686  and the lifter  2700  is in the first position relative to driven spur gear  1699  when returning the driver blade  2626  from the BDC position toward the TDC position. The output shaft  2686  and the lifter  2700  rotates (in a counter-clockwise direction from the frame of reference of  FIG.  85 B ) to the second position relative to the driven spur gear  1699  after the driver blade  2426  reaches the TDC position. In other words, the aperture  2710  is configured to selectively allow rotation of the output shaft  2686  relative to the driven spur gear  1699 . 
     More specifically, as illustrated in  FIGS.  85 A,  85 B , as the driver blade  2626  approaches the TDC position, a contact normal (i.e., arrow A 1  in  FIG.  85 B ) perpendicular to a line tangent to both a last lifter pin  2720 A and the surface on a lowermost tooth  2674 A on the driver blade  2626  with which the pin  2720 A is in contact is formed. Since the lifter  2700  and the output shaft  2686  are coupled for co-rotation, a reaction force T 1  is applied to the output shaft  2686  along the contact normal A 1 , which is oriented along a line of action C located below the rotational axis of the lifter  2700 , which is coaxial with the rotational axis  2690  of the output shaft  2686 , from the frame of reference of  FIG.  85 B . Thus, a reaction torque (arrow T 1 ) is applied to the output shaft  2686  in a clockwise direction (from the frame of reference of  FIG.  85 B ), thereby maintaining the output shaft  2686  in the first position relative to the driven spur gear  1699  as the driver blade  2626  is moved toward the TDC position. The line of action C of the contact normal A 1  remains below the rotational axis  2690  of the lifter  2700  until the lifter  2700  reaches the TDC position. Thereafter, as shown in  FIG.  86 A , the contact normal A 1  between the lowermost tooth  2674 A and the last lifter pin  2720 A changes direction such that the line of action C is located above the rotational axis  2790  of the lifter  2700 . Thus, as shown in  FIG.  86 B , the reaction torque (arrow T 2 ) exerted on the output shaft  2686  by the driver blade  2626  is redirected in a counter-clockwise direction (from the frame of reference of  FIG.  86 B ), thereby causing the output shaft  2686  to rotate about the driven spur gear  1699  from the first position shown in  FIG.  85 B  to the second position shown in  FIG.  87 B . 
     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. 
     Various features of the invention are set forth in the following claims.