Abstract:
A screwdriver for collated screws in which a tip of the screw projects forwardly of the tool prior to initiation of the screwdriving sequence and, preferably, a forwardly directed socket carried on a retractable nose portion engages the head of the screw to be driven and urges the screw forwardly into a workpiece such that the pinching of the screw between the nose portion and the workpiece initiates retraction of the nose portion preferably leading to engagement of the screw by a rotating driver shaft.

Description:
TECHNICAL FIELD 
       [0001]    This technology relates to an autofeed screwdriving tool for driving collated screws which are joined together in a strip and, more particularly, to a power screwdriver for use in driving collated screws. 
       BACKGROUND 
       [0002]    Autofeed screwdrivers are known for driving collated screws. For example, one known autofeed screwdriver for collated screws is disclosed in U.S. Pat. No. 6,453,780 to Habermehl, issued Sep. 24, 2002, the disclosure of which is incorporated herein by reference. In this patent to Habermehl, a screwstrip comprising a plurality of screws held in spaced relation on a plastic strap are incrementally fed through a guideway into a slide body which is mounted for sliding relative to a housing carrying a rotating drive shaft with a bit for engaging a screw. The slide body has a nose portion for engagement with a work surface. A user engages the nose portion with a workpiece and urges the screwdriving tool forwardly into the workpiece to retract the slide body within the housing and drive a screw coaxially aligned with the driveshaft into a workpiece after which a user discontinues applying forwardly directed forces to the tool. In the cycle of operation of applying forces to the tool to drive each successive screw and then releasing such forces, the slide body is moved reciprocally inwardly and outwardly in the housing which relative movement advances each successive screw in the screwstrip into a position in alignment with the driver shaft for driving into the workpiece. 
         [0003]    Various different types of screwstrips are known including screwstrips as disclosed in the above-noted U.S. Pat. No. 6,453,780 and screwstrips of the type disclosed, for example, in U.S. Pat. No. 6,494,322 to Habermehl et al, issued Dec. 17, 2002 and U.S. Pat. No. 6,783,001 to Wollner, issued Oct. 31, 2004. 
         [0004]    Such screwstrips have the common features that they include a plurality of screws arranged in a generally side-by-side relation which are held together by a strap which preferably comprises a plastic material but may be formed from various other materials including paper, metal and other materials alone or in combinations. In the screwstrips disclosed in U.S. Pat. Nos. 6,453,780 and 6,494,322 which are referred to herein as “upright strap” screwstraps, these straps holding the screws are elongate not only between the screws but also in a direction parallel the axis of the screws. In contrast, in the screwstrip of the type taught by the patent to Wollner which are referred to herein as “flat tape” screwstrips, the strap is elongate between the screws and in a direction normal the axis of the screws. 
         [0005]    Various metal connectors are known for connecting of wide range of wood products with holes pre-formed in the connectors and through which screws are to be passed to secure the connectors to wood surfaces which they overlay. Such connectors are well known and include hangers for joints and rafters, joint ties, hurricane ties, framing anchors, staircase angles, deck post ties and the like. For example, U.S. Pat. No. 6,453,634 to Pryor issued Sep. 24, 2002 illustrates a strap adapted to be secured to the face of a wood member via a plurality of threaded fasteners which are to pass through suitably sized holes in the strap. 
         [0006]    The inventor of this application has appreciated a disadvantage which arises with previously known autofeed screwdrivers is that it is difficult to drive a screw into a precise point within a workpiece. For example, the applicant has appreciated that it is difficult with non-autofeed screwdrivers to drive screws accurately through the center of openings in known connection brackets which are sized to closely receive the screw. 
         [0007]    The applicant has appreciated a further disadvantage that autofeed screwdrivers do not provide a mechanism whereby a screw to be driven protrudes forwardly from the tool prior to activation of the tool in a manner which permits a bit of a screw to be driven to be placed accurately at the desired location as, for example, centered in the opening through a connection strap. 
       SUMMARY 
       [0008]    To at least partially overcome these disadvantages of the prior art, the present technology provides a screwdriver for collated screws in which a tip of the screw projects forwardly of the tool prior to initiation of the screwdriving sequence. 
         [0009]    An object of the present technology is to provide an improved screwdriver for collated screws. 
         [0010]    Another object is to provide an improved method of operating a screwdriver for collated screws. 
         [0011]    Another object is to provide an improved guideway for flat tape collated screws which facilitates holding the screw to be driven in a desired position parallel to an axis of a driver shaft. 
         [0012]    Another object is to provide a screwdriver for collated screwstrips in which in driving a screw, the tip of the screw is the first element to engage a work surface. 
         [0013]    Another object is to provide a screwdriver for collated screws in which the pinching of a screw to be driven between the workpiece and the slide body of the tool before the screw is engaged is used to retract a slide body within a housing for the tool. 
         [0014]    Accordingly, in one aspect, the present technology provides an apparatus for driving with a power driver a screwstrip comprising threaded fasteners such as screws or the like, which are joined together in a strip comprising: 
         [0015]    a housing; 
         [0016]    an elongate drive shaft for operative connection to a power driver for rotation thereby and defining a longitudinal axis; a bit at a forward end of the drive shaft for engagement with a head of a screw, 
         [0017]    a slide body coupled to the housing for displacement parallel to the axis of the drive shaft between an extended position and a retracted position; 
         [0018]    the slide body having: 
         [0019]    (a) a guide channel for said screwstrip extending through said slide body generally transverse to the axis; 
         [0020]    (b) a screw feed activation mechanism coupled between the slide body and the housing whereby displacement of the slide body relative the housing between the extended position and the retracted position advances successive screws through the guide channel to an initial screw position axially in alignment with said drive shaft for engagement in driving of each screw by a bit carried at a forward end of the drive shaft forwardly into a workpiece; 
         [0021]    (c) a socket with a forwardly directed surface to engage a rearwardly directed surface of a head of a screw axially in alignment with said drive shaft and urge the screw forwardly, and 
         [0022]    (d) a forwardly directed touch down foot to engage the workpiece; 
         [0023]    wherein with the slide body in the extended position relative the housing the screw in the initial screw position extends forwardly beyond the touch down foot for engagement of a tip of the screw with the workpiece, 
         [0024]    wherein from the extended position with the screw in the initial position with the tip of the screw engaging the workpiece, on moving the housing forwardly toward the workpiece the forwardly directed surface of the socket engages the rearwardly directed surface of the head of the screw and pinches the screw between the socket and the workpiece causes the housing to move relative the slide body towards the retracted position such that the bit engages the head of the screw rotating the screw and the screw is driven sufficiently forwardly into the workpiece that the touch down foot engages the workpiece, whereupon with continued forward movement of the housing toward the workpiece engagement of the touch down foot with the workpiece causes the housing to move relative the slide body further towards the retracted position such that the bit in continued engagement with the head of the screw drives the screw further into the workpiece. 
         [0025]    In another aspect, the present technology provides in an autofeed screwdriving tool an improved arrangement for engaging a shank of a screw including a pair of pivoting guide members disposed on opposite sides of the shank of the screw and movable from an open position to a closed position in which the guide members capture the shank therebetween, the guide members having camming portions which on movement from the open position to the closed position urge the shank of the screw to a desired position coaxial about an axis of a driver shaft to drive the screw. 
         [0026]    In another aspect, the present technology provides in an autofeed screwdriving tool an advance pawl to engage and advance a screwstrip in a first advancing direction, the pawl resiliency deflectable laterally of the screwstrip for movement in a second return direction past the screwstrip, the tool also including a pivoting guide member engaged on one lateral side of the screwstrip and movable from an open position to a closed position in which the guide member locates a shank of a screw in a desired position, wherein with the tool in a fully extended position the guide member is manually movable to the open position and on movement to the open position engages the pawl to deflect it laterally out of engagement with the screwstrip to permitting manual insertion or removal of the screwstrip. 
         [0027]    In another aspect, the present technology provides an autofeed screwdriving tool with a socket to engage the head of a screw to urge the screw forwardly, the socket having a bore extending rearwardly therefrom through which a driver shaft is extended to engage and rotate the screw head. 
         [0028]    In another aspect, the present technology provides an autofeed screw driving tool for a screwstrip, preferably a flat strap screwstrip, in which a guideway for guiding the advance of a strap of the screwstrip is symmetrical about an axis of a driver shaft to drive each successively advanced screw held in the strap such that when the strap is advanced to a location that the head of the screw is coaxial with the axis, the strap holds the screw with its shaft extending from the head substantially coaxially with the axis. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0029]    Further aspects and advantages of the present technology will become apparent from the following description taken together with the accompanying drawings in which: 
           [0030]      FIG. 1  is a pictorial view of a power screwdriver assembly including an autofeed screwdriving tool in accordance with a first embodiment of the present technology showing notably a first side of the tool; 
           [0031]      FIG. 2  is a side view of the tool shown in  FIG. 1  in a ready position; 
           [0032]      FIG. 3  is a pictorial view of a segment of the screwstrip used in the tool of  FIG. 1 ; 
           [0033]      FIG. 4  is a schematic enlarged side view of the tool in  FIG. 2  schematically illustrating a portion of the screwstrip engaged within a strap feed guideway; 
           [0034]      FIG. 5  is a pictorial view of a forwardmost portion of a slide body of the tool shown in  FIG. 2  without the screwstrip and with a first guide member in an open position to permit manual advancement or withdrawal of a screwstrip; 
           [0035]      FIG. 6  is a pictorial view of an advance lever shown as an element of the nosepiece of the tool from the side shown in  FIG. 2 ; 
           [0036]      FIG. 7  is a schematic pictorial view of a forward end of the advance lever in  FIG. 6  as seen from the first side opposite to that shown in  FIG. 6 ; 
           [0037]      FIG. 8  is a schematic pictorial view of a forward resilient portion of the advance lever of  FIG. 6  illustrating its resiliency; 
           [0038]      FIG. 9  is a schematic view looking downwardly on a screwstrip as illustrated in  FIG. 3  to schematically illustrate the manner in which the forward portion of the advance lever shown in  FIGS. 6 to 8  advances the screwstrip in a schematic sequence of operation of the tool; 
           [0039]      FIG. 10  schematically illustrates a rear portion of the housing of the tool shown in  FIG. 2  to illustrate a socket for coupling of the tool to a power driver and a strap slideway on the housing for releasably engaging the screwstrip; 
           [0040]      FIGS. 11 to 21  are schematic pictorial views of the forward portion of the slide body the same as that shown in  FIG. 5  but partially cut away and with each of the different  FIGS. 11 to 21  representing different relative positions of the various elements during normal use of the tool and, in which: 
           [0041]      FIG. 11  illustrates an arrangement with a first guide member in an open position ready for advance of a screwstrip; 
           [0042]      FIG. 12  is identical to  FIG. 11  but showing a first screw in the screwstrip in a ready position to which the screw is manually advanced; 
           [0043]      FIG. 13  schematically illustrates a screw in a ready position as shown in  FIG. 2  but with the tip of the screw merely touching without any pressure the surface of a workpiece; 
           [0044]      FIGS. 14 to 21  are pictorial views similar to that shown in  FIG. 13  but illustrating the sequential positions following the position of  FIG. 13  which the elements of the tool assume in driving of a screw into the workpiece in a cycle of operation with, as seen in  FIG. 21 , the tool returned to the ready position with a next successive screw from the screwstrip but otherwise the same as in  FIG. 13 ; 
           [0045]      FIGS. 22 to 29  illustrate the tool shown in  FIG. 1  in side views similar to that shown in  FIG. 2  but in sequential positions in the driving of a screw into a workpiece successively from the position of  FIG. 22  with the first screw in a ready position to a position of  FIG. 29  in which the first screw is fully driven into a workpiece and the next successive screw from the screwstrip is in a ready position; 
           [0046]      FIG. 30  is a schematic enlarged side view similar to  FIG. 4  but of a tool in accordance with a second embodiment of the present technology showing the screw being advanced in the tool; 
           [0047]      FIG. 31  is a view the same as shown in  FIG. 30  but with the screw advanced to a ready position; and 
           [0048]      FIG. 32  is a schematic enlarged side view the same as in  FIG. 4  but of a tool in accordance with a third embodiment of the present technology showing a screw advanced to the ready position. 
       
    
    
     DETAILED DESCRIPTION 
       [0049]    Reference is made to  FIG. 1  which shows a complete power screwdriver assembly  10  in accordance with the present invention. The assembly  10  comprises a power driver  11  to which an autofeed screwdriver tool  12  is secured. The tool  12  is shown as carrying a collated screwstrip  14  having a strap  13  carrying spaced screws  16  to be successively driven. 
         [0050]    Referring to  FIGS. 1 and 2 , the major components of the tool  12  are a housing  18  and a slide body  20 . The slide body  20  comprises a rear portion  22  and a forward nose portion  24 . 
         [0051]    As seen in  FIG. 10 , the rearmost end  26  of the housing  18  has a rearwardly directed socket  27  to receive and securely clamp the housing  18  onto a housing  30  of the power driver  11  so as to secure the housing  18  of the tool  12  to the housing  30  of the power driver  11  against relative movement. The power driver  11  in a known manner has a chuck (not shown) rotatable relative to the driver housing  30  preferably by an electric motor (not shown). The chuck releasably engages the rear end  32  of a driver shaft  34  in a known manner to couple the driver shaft  34  to the motor for rotation. 
         [0052]    The slide body  20  is slidably received in the housing  18  with the driver shaft  34  received in a bore  33  extending through the slide body  20  as seen in cross-section in  FIG. 11 . A compression spring  38  schematically shown in  FIG. 2  is disposed between the housing  18  and the rear portion  22  of the slide body  20  coaxially about the driver shaft  34  to bias the slide body  20  forwardly away from the housing  18  from a retracted position towards an extended position. In a known manner, the slide body  20  is slidably received in the housing  18  for sliding of the slide body  20  relative the housing coaxially about an axis  52  coaxial with the driver shaft  34 . In a known manner, interacting slide surfaces are provided between the housing  18  and the slide body  20  to guide the slide body  20  in sliding parallel the axis  52  relative to the housing. In a known manner, the slide body  20  is slidably engaged within the housing  18  against relative rotation. 
         [0053]    As is known, a mechanism is provided to prevent the slide body  20  from being moved forwardly out of the housing  18  past a fully extended position shown in  FIG. 2 . 
         [0054]    An advance lever  46  is pivotally mounted to the rear portion  22  of the slide body  20  by an axle-forming bolt  50  for pivoting about an axis  51  of the bolt  50  normal to the longitudinal axis  52  which passes coaxially through the driver shaft  34  and about which the driver shaft  34  is rotatable. As best seen in  FIG. 8 , the advance lever  46  has a forward arm  48  extending forwardly to its forward end  56  and a rear arm  58  extending rearwardly to its rear end  60 . A cam roller  61  is mounted to the rear arm  58  proximate its rear end  60  on a pin axle  61  for rotation about an axis  63  normal to the axis  52  of the driver shaft  34 . 
         [0055]    In a known manner, the cam roller  61  is engaged within a cam slot  64  provided in the housing  18  as shown schematically in solid lines in  FIG. 22 . The cam slot  64  has a first camming surface  65  and a second camming surface  66  spaced therefrom and presenting different profiles as schematically shown in  FIG. 22 . The cam roller  61  is received in the cam slot  64  between the first camming surface  65  and the second camming surface  66  for engagement of each under different conditions of operations in a manner as is known and is taught, for example, in the above-noted U.S. Pat. No. 6,453,780. A spring  69  about the bolt  50  disposed between the rear arm  58  and the nose portion  22  biases the lever  46  to pivot about the bolt  50  in a counter-clockwise direction as seen in  FIG. 22  and thus biases the advance lever  46  to pivot in a direction which moves its forward end  56  towards the right and biases the cam roller  61  towards the first camming surface  65 . In a known manner, with relative sliding of the slide body  20  and the housing  18  between extended and retracted positions, the cam roller  61  translates the relative movement and positioning of the slide body  20  in the housing  18  into relative pivoting and positioning of the advance lever  46  about the axis  51 . 
         [0056]    Reference is made to  FIGS. 3 and 4  which illustrate a flat tape screwstrip  14  shown in  FIG. 2  for use with the tool  12 . The screwstrip  14  comprises a retaining strip  13  and a plurality of screws  16 . In  FIG. 3 , one end of the screwstrip  14  is shown with one screw  16  shown separated from the screwstrip. The retaining strip  13  is preferably formed from a plastic material. The retaining strip  13  comprises a central web  70  of relatively uniform thickness between a rear surface  71  of the web  70  and a forward surface  72 . The web  70  carries at each of its sides, flange members  73  which extend forwardly and rearwardly a greater extent than the rear surface  71  and the forward surface  72  such that as seen in a longitudinal end view the web  70  would appear to have a generally H shape. Rectangular openings  76  extend through the web  70  transverse to a longitudinal  77  through the strap  13  with the rectangular openings  76  effectively serving to divide the web  70  into a series of segments  75 . These rectangular openings  76  are provided at each end of each segment  75  at a location where the flange members  73  are not provided on the web  70  and the rectangular openings  76  so as to enhance the ability of the strap  13  to be flexible and bend between segments  75  as along notional hinge axes  279  perpendicular to longitudinal  77  through each pair of the rectangular openings  76  to assist the strap  13  to generally adopt a curved shape as illustrated in  FIG. 4  as constrained by a guideway  82  while maintaining an axis  39  extending centrally through each of the screws  16  to be disposed in a common flat plane including the longitudinal with the axis  39  of the various screws disposed at an angle to each other. 
         [0057]      FIGS. 3 and 9  show at the left-hand end of each screwstrip  14  a segment  75  in which a screw is not provided. Each segment  75  has a central opening  74  through its web  70  adapted to engage about a shank  40  of a screw  16 . The web  70  carries a sleeve  79  which extends forwardly from the forward surface  72  about the center opening  74  and sized to closely receive an upper portion  37  of the shank  40  of a screw  16 . The web  70  has four corner openings  78 . A slit  80  extends from each corner opening  78  radially towards a center of the central opening  74  with the slit preferably extending entirely between the forward surface  71  and the rear surface  72  of the web and into the sleeve  79 , however, with the slit  80  ending rearward of a forward end  81  of the sleeve  79 .  FIG. 9  shows at the right hand end a segment  75  from which a screw has been driven, schematically showing the sleeve  79  as ruptured at the forward end of one slot  80  in the upper left hand quadrant of the segment  75  in the driving of a screw forwardly through the sleeve  79 . 
         [0058]    As seen in  FIGS. 3 and 9 , each flange member  73  has a flange catch surface  110  which is disposed in a plane approximately normal to the longitudinal  77  of the strap  13  and a flange cam surface  112  disposed in a plane at an angle to the longitudinal  77 . Each flange member  73  also has a center notch  113  which is formed between a first cam shoulder  114  and a second cam shoulder  115 . The notch  113  of the flange  73  on one side of the strap  13  and the notch  113  of the flange member  73  on the other side of the strap  13  are aligned such that a plane  280  joining the two located in the apex of each notch  113  is disposed substantially to longitudinal  77  centrally through the sleeve  79 . 
         [0059]    As schematically illustrated in  FIG. 9 , the flange catch surface  110  is adapted to be engaged by a pawl  99  carried at the forward end  56  of the forward arm  48  of the advance lever  46  to advance a screwstrip  14  to the right in use of the tool and with the flange cam surface  112  as well as the first cam shoulder  114  and second cam shoulder  115  permitting the pawl  99  to slide to the left as seen in  FIG. 9  from engagement with one flange catch surface  110  of one segment  75  over the laterally outward surfaces of the flange member  73  to a position where the pawl  99  may engage the next flange catch surface  110  of the next segment  75  of the strap  13 . 
         [0060]    Reference is made to  FIGS. 5 and 11  to describe the configuration of the forward nose portion  24  of the slide body  20 . In  FIGS. 5 and 11 , the nose portion  24  is shown in a fully extended position the same as that as in  FIG. 2 , however, for ease of convenience with merely a forward portion  166  of the forward arm  48  of the advance lever  46  shown and not the remainder of the advance lever  46 . 
         [0061]    Reference is made to  FIG. 2  which illustrates a screwstrip  14  as engaged with the tool  12 . In this regard, as schematically illustrated in broken lines in  FIG. 2 , the guideway  82  is provided through the nose portion  24  through which the screwstrip  14  passes with the guideway  82  having an exit opening  87  from which the strap  13  is shown to extend as a segment  75  of the strap  13  from which its screw has been removed. 
         [0062]    The nose portion  24  defines a screw guide chamber  120  therein between a first side wall  121 , a second side wall  122  opposite the first side wall  121 , an entrance side wall  123  and an exit side wall  124  opposite the entrance side wall  121 . The screw guide chamber  120  has a rear wall  125  through which the bore  33  for the driver shaft  34  extends. The bore  33  opens into a downwardly directed generally concave screw head engaging socket  127 . The screwstrip guideway  82  has an entranceway  83  on the left-hand side of the nose portion  24  as seen in  FIGS. 2 ,  5  and  11  to permit the screwstrip  14  including both its strap  13  and its screws  16  to enter the screw guide chamber  120  but with the exit opening  87  of the guideway  82  on the left-hand side to merely permit exit of the strap  13 . The guideway  82  is schematically shown in side view in  FIG. 4  and, in a similar schematic manner, is shown in  FIG. 2 . The guideway  82  extends in a generally U-shape through the screw guide chamber  120  to guide the strap  13  from the entranceway  83  to the exit opening  87 . The guideway  82  includes a strap feed channelway  129  adapted to capture the strap  13  therein. The strap feed channelway  129  is defined between two C-shaped channel forming members  130 . Each channel facing member  130  has a pair of laterally inwardly extending rear arms  132  and forward arms  133  extending laterally inwardly from a bridging back plate  134  so as to define a bight  135  sized to closely receive the flange members  73  of the strap  13  therein. Between the rear arms  132 , a head channel  136  is provided as part of the feed strap channelway  129  sized to receive the head  17  of each screw and let the head  17  pass freely through the feed strap channelway  129 . Between the forwardmost arms  133 , a channel  137  is provided which extends forwardly through the entrance side wall  123  and towards the right as seen in  FIG. 5  and forming a forward portion of the guideway  82  that extends between the first side wall  121  and the second side wall  122  towards the exit side wall  124  but not through the exit side wall  124 . 
         [0063]    As seen in  FIGS. 2 and 5 , the first side wall  121  has a recess  138  removed therefrom open to an outer surface  138  of the first side wall  121 . The recess  138  extends inwardly through the back plate  134  and into the front arm  132  and the rear arm  133  leaving but a thin laterally inwardmost portion of each of the arms  132  and  133  to assist in guiding the strap  13  through the strap feed channelway  129 . The recess  137  provides access for the pawl  99  on the forward portion  166  of the forward arm  48  of the advance lever  46  to extend laterally into the strap feed guideway  129  to engage the strap  13  and notably the catch surfaces  110  on the flange members  73  of the strap  13  to permit the screwstrip  14  to be advanced through the guideway  82  by engagement with the pawl  99 . 
         [0064]    As seen in the partially cross-sectional view of  FIG. 11 , the second side wall  122  carries a touch down foot  140  in the form of a vertically truncated tubular member disposed to one side of the guideway  82  so as to not impede sliding of the shank  40  of each successive screw  16  along the guideway  82  to a ready position axially in line with the driver shaft  34 . 
         [0065]    As seen in  FIG. 3 , each screw  16  extends along the screw axis  39  from its head  17  to its tip  15 . The head  17  has rearwardly directed rear upper surface  42 . A recess  43  extends forwardly into the head  17  through the upper surface  42  and is shown to have a generally hexagonal shape disposed coaxially about the screw axis  39 . The recess  43  extends into the head to a blind end (not shown). The head  17  is shown to have a forwardly directed forward shoulder  142  which is disposed in a plane normal to the screw axis  39 . Each screw has the shank  40  which is threaded by threads  41  over a lower portion  36  of the shank  40  to an unthreaded upper portion  37  of the shank, which upper portion  37  is generally enlarged compared to the remainder of the shank and preferably frustoconical as shown. The upper portion  37  merges into the head  17 . 
         [0066]    The bit  35  carried on the forward end of the driver shaft  34  is sized to become engaged within the recess  43  in the head of the screw to rotate the screw and urge the screw forwardly by transfer of axially directed forces from the driver shaft  34  to the screw  16 . 
         [0067]    Reference is made to  FIG. 11  which shows in partial vertical cross-section the interior of the screw guide chamber  120  and notably the provision therein of a first guide member  142 , a second guide member  144  and a spreader member  146 . The second guide member  144  has an axle member  147  secured thereto with one end of the axle member journalled in a bore in the entrance side wall  123  and the other end of the axle member  147  journalled in the exit side wall  124  only schematically shown such that the axle member  147  may pivot relative the nose portion  24  about an axis coaxially through the axle member  147  and normal the axis  52 . The second guide member  144  is rotatable from a closed position as shown in  FIG. 11  to an open position as shown in  FIG. 17 . A coil spring  148  is disposed about the axle member  147  between the second guide member  144  and the second side wall  122  so as to bias the second guide member  144  to rotate to the closed position shown in  FIG. 11 . The second guide member  144  may be deflected to rotate with the axle member  147  against the bias of the coil spring  148 , however, with the coil spring  148  inherently biasing the second guide member  144  to return to the closed position of  FIG. 11 .  FIG. 11  shows a stop member  249  carried on the inside surface of the second side wall  122  rearward of the second guide member  174  to engage the second guide member  144  and prevent it from rotating rearwardly beyond the open position. While not shown in the drawings, another stop member is also provided on the second side wall  122  to prevent rotation of the second guide member  144  beyond the open position shown in  FIG. 17 . The second guide member  144  includes a plate portion  149  having a rear surface disposed substantially in a flat plane and from which a frustoconical half guide tube  150  extends. On the left-hand side of the half guide tube  150 , the plate portion  149  carries a screw shaft camming surface  151  which, as seen in  FIG. 11 , extends laterally outwardly towards the second side wall  122  as it extends towards the entrance side wall  123 . To the right of the half guide tube  150 , the plate portion  149  has a stop surface  152  directed laterally away from the second side wall  122 . 
         [0068]    The first guide member  142  is substantially a mirror image of the second guide member with the exception of the inclusion of a cam arm  153 . In this regard, as seen in  FIG. 11 , the first guide member  142  includes an axle member  155  extending parallel to the axle member  147 . The axle member  155  has one end journalled in a bore in the entrance side wall  123  and the other end journalled in a bore in the exit side wall  124  such that the axle member  155  may pivot relative the nose portion  24  about an axis coaxially through the axle member  155 . A coil spring  156  is disposed about the axle member  155  between the first guide member  142  and the first side wall  121  so as to bias the first guide member  142  to rotate to a closed position as, for example, illustrated in  FIG. 13 . The first guide member  142  may be pivoted with the axle member  155  from the closed position as shown in  FIG. 13  to an open position as shown in  FIG. 11  against the bias of the coil spring  156 . Suitable stop members similar to the stop member  149  are provided in respect of the first guide member  142 , while not shown, to limit rotation of the first guide member  142  between the open position and the closed position. 
         [0069]    The axle member  155  for the first guide member  142  is formed from a cylindrical rod which after extending outward through a journaling bore in the exit side wall  124  is bent to extend radially at an angle to an axis of the rod so as to form a radially extending axle extension lever  60  easily seen in  FIGS. 1 and 2 . The axle extension lever  60  is accessible outside of the slide body  20  for manual engagement as by a finger (not shown) of a user of the tool  12  so as to manually move the first guide member  142  to the open position as shown in  FIG. 11  and hold it in the open position for manual insertion and withdrawal of a screwstrip  14  from the tool  12 . 
         [0070]    The first guide member  142  has a plate portion  157  with a half guide tube  158 , a screw shaft camming surface  169  and a stop surface  162  which are substantially mirror images of the same elements provided on the second guide member  144 . The first guide member  142  also carries the cam arm  154  which, as seen in the closed position as in  FIG. 13 , extends forwardly in a plane at right angles to a plane of the plate portion  157  and presents an angled pawl arm camming surface  163 . As seen in  FIGS. 2 and 5 , the first side wall  121  has an opening  164  therethrough into the screw guide chamber  120  laterally in line with the cam arm  154 . On rotation of the first guide member  142  from the closed position shown in  FIGS. 2  and  13  to the open position shown in  FIGS. 5 and 11 , the cam arm  154  moves from an orientation extending forwardly from the plate portion  157  to an orientation extending laterally from the plate portion  157  and through the opening  164  as shown in  FIG. 11 . When the tool is in the fully extended position, in moving from the closed position of  FIGS. 2 and 13  to the open position of  FIGS. 5 and 11 , the camming surface  163  on the cam arm  154  engages the forward end  56  of the forward portion  166  of the forward arm  48  of the advance lever  46  deflecting the forward end  56  laterally outwardly away from the first side wall  121  sufficiently that the pawl  99  carried on the forward arm  54  is displaced laterally beyond engagement with the flange members  73  on any strap  13  received within the strap feed channelway  129  as best seen in  FIGS. 5 and 11 . 
         [0071]    Reference is made to  FIG. 6  which is a pictorial view of the advance lever  46  and showing that the rear arm  58  and a rear portion  165  of the forward arm  48  are formed from a inflexible rigid plate  266 . A forward portion  166  of the forward arm  48  comprises an elongate resilient plate  167  which is fixedly secured by two screws  268  to the rigid plate  266  and with the resilient plate  167  carrying at its end a camming paddle  168  carrying the pawl  99  and, as well, a camming surface  169  adapted for engagement with the camming surface  163  of the cam arm  164  to assist in lateral deflection of the forward end  56  of the forward arm  48 . The resilient plate  167  preferably comprises an elongate planar sheet of a resilient metal which is adapted to deflect in a direction normal to its plane and thus laterally of the slide body.  FIG. 8  schematically illustrates the inherent resiliency of the resilient plate  167  from a position which is unbiased in solid lines to a deflected position shown in dashed lines. The resilient plate  167  when deflected laterally to a deflected position has an inherent bias to return to the unbiased position. 
         [0072]    Reference is made to  FIG. 18  showing the spreader member  146  as having a general Y shape with a pair of arms  170  and  171  joined to a stop leg  172 . The arm  170  carries a stub axle  173  journalled in a bore in the first side wall  121  (not shown in  FIG. 18 ) and the second arm  171  carries a similar stub axle  174  journalled in a bore in the second side wall  122  with the stub axles  173  and  174  coaxial with each other and perpendicular to the axes of each of the axle member  147  and the axle member  155 . A coil spring  175  disposed about one stub axle  174  and between the spreader member  146  and the exit side wall  124  (not shown in  FIG. 18 ) biases the spreader member  146  clockwise about the stub axles  173  and  174  as seen in  FIG. 18 , that is, to urge the stop leg  72  to the left as seen in  FIG. 18  towards the first guide member  142  and the second guide member  144 . A release pin  176  extends laterally from the arm  170  parallel to the stub axles  173  and  174  and through a slotway  177  in the first side wall  121  to protrude laterally on the outside of the second side wall  122  as seen, for example, in  FIG. 2 . The slotway  177  is elongate having a first end closer to the entrance side wall  123  than a second end and extending from the first end towards the exit side wall  124 . The release pin  176  is received in the slotway  177  with the ends of the slotway  177  limiting movement of the spreader member  146  from an unblocking position as shown in  FIG. 11  to a blocking position as shown in  FIGS. 17 to 20 . The coil spring  175  biases the spreader member  146  to assume the blocking position shown in  FIG. 18  and to return to the blocking position if displaced from the blocking position to the unblocking position. The release pin  176  extends laterally from the first side wall  121  at a location that the release pin  176  is engaged by the paddle  168  of the forward portion  166  of the advance lever  46  at desired times during a cycle of movement of the slide body  20  relative to the housing  18  in use of the tool  12  such that, as schematically illustrated, in the paddle  168  moving from a position shown in  FIG. 20  to the position shown in  FIG. 21 , a surface  178  of the paddle  168  engages the release pin  176  to move the release pin  176  in the slotway  177  to the right and thus pivot the spreader member  146  about the stub axles  173  and  174  against the bias of the coil spring  175  to the unblocking position. As seen in  FIG. 5 , the release pin  176  extends laterally of the first side wall  121  sufficiently that when the first guide member  142  is in the open position as shown in  FIG. 5  with the cam arm  154  urging the paddle  168  laterally, the surface  178  of paddle  168  continues to engage the release pin  176  and urge the spreader member  146  to the unblocked position. 
         [0073]    As best seen in  FIG. 7 , the pawl  99  has a catch surface  180  and a camming surface  181 . Referring to  FIG. 9 , the catch surface  180  of the pawl  99  is adapted to engage the catch surface  110  on a flange member  73  of the strap  13  such that movement of the pawl  99  with the forward arm  48  of the advance lever  46  in the direction indicated by the arrows  182  in  FIG. 9  will advance the strap  13  in the strap feed channelway  129  in an advance stroke of the advance lever  46 . On a return stroke of the advance lever  46 , the pawl  99  and the forward arm  48  are moved in an opposite direction, that is, in the direction of the arrow  183 . In so doing, when the camming surface  181  of the pawl  99  engages the cam surface  112  or the first shoulders  114  of the next flange member  73 , the resilient plate  167  will become deflected laterally such that the pawl  99  will be moved laterally as seen in  FIG. 9  as schematically illustrated by arrow  184 . The pawl  99  will thus ride over the laterally outermost surface of the flange member  73  as it is further moved to the left as indicated by arrow  185 . Upon the pawl  99  becoming disposed rearward of the catch surface  110  of the next flange member  73 , the pawl  99  under the bias of the resilient plate  167  will be moved laterally inwardly as indicated by arrow  186  with the pawl  99  to become disposed in an engagement position with the catch surface  110  of the flange member  173  of the next segment  75  ready for advancing the screwstrip in a direction of the arrow  182 . 
         [0074]    In contrast with a lateral position to which the paddle  168  is biased laterally in normal cycling of the advance lever  46  to advance successive segments  75  of the strap  13 , when the first guide member  142  is in the open position as shown, for example in  FIG. 5 , the paddle  168  and the pawl  99  are biased laterally away from the strap  13  beyond the positions that are shown in  FIG. 9  such that the pawl  99  does not engage any portion of the strap  13 . 
         [0075]    The screwstrip  14  is engaged on the tool  12  by reason of passing through the guideway  82  of the slide body  20 . In addition, a strap slideway  284  is provided coupled on the outside of the housing  18  on an entrance side  285  of the housing  18  to removably slidably engage the strap  13 . As best seen in  FIG. 10 , the strap slideway  284  provides a channelway  286  extending forwardly therethrough with a pair of U-shaped arms  287  and  288  each having a respective bight  289  and  290  to receive the flange members  73  and permit the strap  13  to slide forwardly or rearwardly therethrough. Preferably, one arm  288  is pivotable laterally from a position shown in  FIG. 10  in solid lines to a position shown in dotted lines so as to facilitate ease of insertion of a screwstrip  14  into a position in sliding engagement with the strap  13  within the strap slideway  284  without having to feed, for example, either end of the strap  13  through the slideway  284 . 
         [0076]    The tool  12  permits manual insertion of a screwstrip  14  into the tool  12  while the slide body  20  is in a fully extended position. With the tool in the fully extended position and no screwstrip  14  in the tool, a user engages the axle extension lever  160  moving this lever  160  to pivot the first guide member  142  to the open position as seen in  FIG. 11 . In the position of  FIG. 11 , the user then feeds an end of a strap  13  of a screwstrip  14  into the strip feed channelway  129  and slides the screwstrip  14  inwardly through the entranceway  83  to the guideway  82 . The screwstrip  14  will slide within the guideway  82  with the flange members  73  engaged within the strip feed channelway  129  until the head  17  of the first screw  16  in the screwstrip  14  engages a radially inwardly stop portion  91  of the socket  127  carried on the rear wall  125  of the screw guide chamber  120 . In this regard, reference is made to  FIG. 4  which schematically illustrates in a side view in a plane including centrally through the strap feed channelway  129  and including the axis  52  of the driver shaft  34  and the axis of the screws  16 , the cross-sectional profile of the forward portion of the rear wall  125  illustrating the socket  127  as having on the right-hand side which is remote from the entranceway  83  a forwardly extending stop portion  91  of the interior surface  92  of the socket  127  which stop portion  91  is adapted to engage the head  17  of the screw  16  preferably on at least a portion of a radially directed side surface  147  (shown on  FIG. 3 ) of the head  17  of the screw which is directed radially. As seen in  FIG. 4 , the stop portion  91  extends forwardly, however, the stop portion  91  does not extend forwardly so far as to engage the web  70  of the strap  13  of a screwstrip  14  received in the strap feed channelway  129  in a manner which prevents advance of the screwstrip  14 . On the entranceway side of the screw head engaging socket  127 , the socket  127  is open rearwardly to a height above the rear upper surface  42  of the head  17  of a screw  16  permitting the head  17  to be advanced with the strap  13  towards the exitway  87  until the head  17  engages the stop portion  91  of the socket  127 . The stop portion  91  preferably extends downwardly about the socket  127  circumferentially up to about  180  degrees about the socket on the side of the socket opposite to the entranceway  83 . The engagement of the head  17  of the screw  16  in the screw head engaging socket  127  serves to locate the head  17  of the screw  16  such that the screw axis  39  at the head  17  of the screw  16  is coaxial with the axis  52  of the driver shaft  34 . The interior surface  92  of the socket  127  forms an annular surface about the bore  33  including an annular drive portion  93  of the interior surface adjacent to the bore  33 . The annular drive portion  93  is directed forwardly, that is, as seen axially forwardly and partially radially inwardly. In contrast, the stop portion  91  is shown as directed principally as seen in  FIG. 4  radially inwardly. 
         [0077]    The annular drive portion  93  is adapted when it is urged forwardly into a screw head  17  to engage the screw head  17  and transmit forwardly directed forces to the screw head  17  to move the screw  16  forwardly. In addition, the annular drive portion  93  is preferably to serve as a centering cam surface to engage the screw head  17  and by such engagement cam and guide the screw head  17  into a coaxial location centered within the socket  127  relative the axis  52 . The annular drive portion  93  is shown to extend 360 degrees about the axis and to decrease in diameter from threads  52  as it extends forwardly. The annular driver portion  93  has a profile which is concave facing forwardly and with central areas closely mirroring the rearwardly directed rear surface  42  of the screw head  17 . 
         [0078]    Referring to  FIG. 11 , with the first guide member  142  in the open position as shown, there is sufficient lateral space between the first guide member  142  in the open position and the closed second guide member  144  in the closed position that the shank  40  of the screw  16  may pass therebetween and become engaged within the one half guide tube  150  of the second guide member  144 , however, with the shaft  40  of the screw  16  being deflected to a minor extent laterally towards the first guide member  142  in order to gain access to the one half guide tube  150  of the second guide member  144  as is aided by engagement of the shank  40  on the screw shaft camming surface  151  of the second guide member  144 . With the head  17  of the screw  16  urged into the stop portion  91  of the socket  127  and the shaft  40  engaged within the half guide tube  150  of the second guide member  144 , the user releases the axle extension lever  160  and the first guide member  142  returns under the bias of its spring  156  to the closed position as seen, for example in  FIG. 13 , with the shank  40  of the screw  16  engaged within and between the half guide tube  150  of the second guide member  144  and the half guide tube  158  of the first guide member  142 . The two half guide tubes  150  and  158  together define a frustoconical screw guideway therebetween coaxially about the driver shaft axis  52 . Each of the half guide tubes  150  and  158  are frustoconical tapering forwardly to a diameter substantially equal to the outside diameter of the threads  41  on the lower portion  36  of the shank  40  of the screw  16  so as to locate the lower portion  36  of the shaft  40  which passes through the lower portion of the half guide tubes  150  and  158  such that the screw axis  39  is coaxial with the axis  52  of the driver shaft  34  where the shank  40  passes through the lower portion of the half guide tube  150  and  158 . 
         [0079]    In operation of the tool  12 , each successive screw  16  is advanced to a ready position engaged within the slide body  20  and held within the slide body with the axis of the screw  39  substantially in coaxial alignment with the axis  52  of the driver shaft  34  as seen in  FIG. 13 . 
         [0080]    The particular configuration of the strap feed channelway  129  of the guideway  82  assists in locating the screw  16  coaxially relative with the axis  52  of the driver shaft  34  as schematically illustrated in  FIG. 4 .  FIG. 4  illustrates the strap feed channelway  129  of the guideway  82  in side view showing between the dashed lines the bight  135  between the rear arm  132  and the forward arm  134  of one of the channel forming members  130  which are to receive and constrain the flange members  73  of the strap  13 . The bight  135  of the strap feed channelway  129  is shown to be symmetrical about the axis  52  such that portions on the entranceway side of the axis  52  are mirror images of portions on the exitway side of the axis  52  as seen in  FIG. 4 . With the strap  13  preferably having relative inherently consistency in resiliency along the longitudinal of the strap  13 , the uniform deflection of the strap  13  on either side of the axis  52  causes a U-shape curved deflection of the strap  13  matching the U-shape of the bight  135  in a manner such that the guideway constrains the strap  13  so that the inherent bias of the strap  13  causes it to assume a position in which the screw  16  to be advanced has its screw axis  39  substantially coaxially aligned with the driver shaft axis  52 . 
         [0081]    Each segment  75  of the strap  13  preferably is relatively rigid as enhanced by the sleeve  79  fixedly secured to the web  70  and providing a three-dimensional structure to the segment  75 . The sleeve  79  engages the upper portion  37  of the shank  40  of the screw. The upper portion  36  of the shank  40  of the screw  16  forward of the head  17  is provided with a shape which is substantially the same as interior surfaces of the sleeve  79  such that each screw  16  is securely held in each segment  75  of the strap  13  coaxially aligned within the sleeve  79 . Preferably, the forward end of the sleeve  79  is engaged on the threads  41  of the shank  40  of the screw  16  to resist axial movement of the screw  16  relative to the sleeve  79  prior to a screw  16  being rotated by the driver shaft  34  and to assist in drawing a screw when rotated forwardly relative the segment  75 . 
         [0082]    The screwstrip  14  may be provided to be of almost any length, however, a screwstrip  14  may have a length of approximately 12 to 16 inches. Each end  210  of a screwstrip  14  which is desired to be advanced into the guideway  82  preferably has at least one forwardmost segment  75  which does not contain a screw  16 . Thus, preferably, a screwstrip  14  as shown in  FIGS. 1 and 2  before use will have one segment  75  at each end which does not contain a screw. 
         [0083]    The screwstrip  14  illustrated in  FIGS. 1 and 2  is adapted for having either of its ends  210  fed into the entranceway  83  and, in this regard as seen in  FIG. 9 , if the screwstrip  14  shown in  FIG. 9  were rotated  180  degrees as though its opposite end were fed first into the entranceway  83 , then the flange members  73  and their rear catch surfaces  110  would continue to be orientated in the appropriate manner for engagement by the catch surface  180  of the pawl  99 . 
         [0084]    As seen in  FIG. 13 , the first guide member  142  and the second guide member  144  are spaced forwardly from the socket  127 . As a result, the screw shank  40  is supported and engaged by the half guide tubes  150  and  158  at a location spaced forwardly from the screw head  17 . Spacing the distance between (a) where the screw head  17  is to be engaged by the screw head engaging socket  127  and (b) where the half guide tube  150  and the half guide tube  158  engage the screw shank  40  is advantageous towards enhancing the extent to which the screw  16  has its screw axis  39  coaxially aligned with respect to the driver shaft axis  52  when engaged by the socket  127  and the half guide tubes  150  and  158 . 
         [0085]      FIGS. 1 ,  2 ,  4  and  12  illustrate the tool  12  with the slide body  20  in an extended position and the screwstrip  14  engaged within the slide body  20  in a ready position for use. As best seen in  FIGS. 4 and 13 , the head  17  of the screw  16  is spaced axially forwardly from the axially directed drive portion  93  of the socket  127 . In a first step in use in driving the screw, the tool  12  is manually moved to a first touch position as illustrated in  FIGS. 13 and 22  in which the tip  15  is of the screw  16  to be driven merely touches the upper surface  193  of a workpiece  194  into which the screw is to be driven. In this first touch position as seen in  FIG. 13 , the head  17  of the screw continues to be spaced axially forwardly from the drive portion  93  of the socket  127 . From the first touch position of  FIG. 13 , a user manually applies forces forwardly onto the power driver  11  so as to urge the housing  18  forwardly towards the workpiece  194 . In a first forward motion step with the screw tip  15  engaged on the workpiece  194 , the socket  127  on the slide body  20  moves downwardly such that the drive portion  93  engages the screw head upper surface  42  as seen in  FIG. 14  and  FIG. 23 . In this first forward motion step, the slide body  20  is not moved relative to the housing  18 . The screw  16  has become pinched between the workpiece  194  and the socket  127  by upward deflection of the strap  13  carrying the screw to be driven. This pinching serves to guide the screw head  17  to assume a coaxial position in the socket  127 . 
         [0086]    From the position of  FIG. 14  in a second forward motion step, with the screw  16  pinched between the workpiece  194  and the slide body  20  by reason of the screw head  17  being received within the socket  127 , downward movement of the housing  18  compresses the compression spring  38  and moves the housing  18  forwardly relative the slide body  20 , that is, moving the slide body  20  from a fully extended position towards a retracted position. With such relative movement of the housing  18  relative to the slide body  20 , the rotating driver shaft  34  comes to have its bit  35  become engaged within the screw head recess  43  as shown in  FIG. 15  and  FIG. 24 . 
         [0087]    In  FIG. 15 , as is the case with each of  FIGS. 13 and 14 , the touch down foot  140  carried on the nose portion  24  remains spaced rearwardly of the upper surface  193  of the workpiece  194  enabling a user to precisely locate the screw tip  15  at a desired location on the upper surface  193  of the workpiece  194  signified, for example, in  FIG. 13  by an “X” marked as  195  in dashed lines on the upper surface  193  of the workpiece  194 . In a second forward step, in moving from the position of  FIG. 15  to the position of  FIG. 16 , the screw  16  has been rotated by the driver shaft  34  with the driver shaft bit  35  engaged on the blind end of the screw head recess  43  to apply forwardly directed forces as well as rotational forces to the screw  16  rotating the screw such that the screw is threaded forwardly into the workpiece  194  to a position as shown in  FIG. 16  in which the touch down foot  140  engages the upper surface  193  of the workpiece  194  as shown in  FIG. 16 . In moving from the position of  FIG. 15  to the position of  FIG. 16 , the compression spring  38  urges the slide body  20  forwardly relative the housing  18  and thus urges the socket  127  into the screw head  17 , albeit preferably with not substantial force given that the spring  38  is only compressed a small extent. 
         [0088]    From the position of  FIG. 16  in a third forward step, with the touch down foot  140  of the slide body  20  engaging the workpiece  194 , further forward movement of the slide body  20  is prevented such that forward movement of the housing  18  compresses the compression spring  38  with forward movement of the housing  18  relative the slide body  20  urging the screw  16  forwardly relative to the slide body  20  and thus moving the screw head  17  forwardly out of engagement with the socket  127 . The screw  16  is subsequently driven into the workpiece  194  forwardly relative to the slide body  20  with the screw head  17  moving downwardly into engagement with the first guide member  42  and the second guide member  43  such that engagement of the uppermost portion  36  of the screw shank  40  and the screw head  17  with the first guide member  142  and the second guide member  144  urges each of the first guide member  142  and the second guide member  144  to pivot to an open position as seen in  FIG. 17  in which open position there is sufficient clearance between the first guide member  142  and the second guide member  144  to permit the screw head  17  as well as the driver shaft  34  to pass forwardly therebetween. In the screw  16  moving downwardly to engage the first guide member  142  and the second guide member  144 , the frustoconical upper portion  37  of the screw shank  40  and the rear surface  142  and side surface  147  of the screw head  17  may come into engagement with plate portions  149  and  157  and an enlarged rear portion of each of the half guide tubes  150  and  158  assisting in camming the first guide member  142  and the second guide member  144  from the closed position to the open position. As seen in  FIG. 17 , with relative movement of the housing  18  relative to the slide body  20  towards a retracted position, the forward end  56  of the advance lever  46  is moved to the left out of engagement with the release pin  176  of the spreader member  146  such that the spreader member  146  under the bias of the coil spring  175  pivots towards the blocked position. As seen in  FIG. 17 , with the first guide member  142  and the second guide member  144  each in the open position, the space between the plate portions  157  and  149  is greater than the lateral width of the stop leg  172  permitting the spreader member  146  to pivot to its blocking position as shown in  FIG. 17  in which the stop leg  172  is disposed between the plate portion  157  of the first guide member  142  and the plate portion  149  of the second guide member  144  maintaining the first guide member  142  and the second guide member  144  substantially in the open position and against moving further towards their closed positions. The position of  FIG. 17  is also illustrated in  FIG. 26 . 
         [0089]    With further downward movement of the housing  18  from the position of  FIG. 17 , the housing  18  moves downwardly relative to the slide body  20  to a position as illustrated in  FIG. 18  and  FIG. 27  in which the screw  16  has been driven into the workpiece  194  fully with the screw head  17  engaging the upper surface  193  of the workpiece.  FIGS. 18 and 27  effectively represent a fully retracted position of the housing  18  and slide body  20  and in which the forward end  56  of the forward arm  48  of the advance lever  46  has moved a maximum distance to the left away from the release pin  176 .  FIG. 18  represents the end of the steps in which the housing is directed by a user forwardly into the workpiece. In the fully retracted position shown in  FIG. 18 , the pawl  99  carried on the advance lever  46  is moved to a position rearwardly of the catch surface  110  of the flange member  73  of the next segment  75  as in a manner which has been illustrated with respect to  FIG. 9  and ready to advance the screwstrip  14  on movement of the pawl  99  to the right as seen in  FIG. 9  with subsequent extension of the slide body  20  relative to the housing  18 . 
         [0090]    After reaching the fully retracted position as illustrated in  FIGS. 18 and 27 , a user will manually move the power driver  11  rearwardly away from the workpiece  194  and, in so doing, release compression forces applied to the compression spring  38 . As a result, the compression spring  38  will urge the slide body  20  and the housing  18  axially apart, that is, to move the slide body  20  from the retracted position towards an extended position relative the housing  18 . Such relative movement of the slide body  20  towards the extended position relative the housing  18  causes the forward end  56  of the forward arm  48  of the advance lever  46  with the pawl  99  carried thereon to move in an advancing direction, that is, towards the right as seen in  FIG. 18 , with such movement advancing the screwstrip  14  by reason of the pawl  99  being engaged with the rear catch surface  110  of the flange member  173  of the next segment  75 .  FIG. 19 , for ease of illustration, does not show the strap  13  and merely shows two screws  16 , the screw  16  driven into the workpiece and another screw  16  being the screw previously adjacent the screw which has been driven into the workpiece  194 .  FIG. 19  illustrates the forward end  56  of the advance lever  46  being moved to the right, the slide body  20  being moved upwardly, and the housing  18  being moved upwardly albeit with the housing  18  as symbolized by the driver shaft  34  moving upwardly a greater extent than the slide body  20 .  FIG. 28  illustrates in side view substantially the same position as illustrated in  FIG. 19 . From the position in  FIG. 19 , with further extension of the slide body  20  relative the housing  18  by the compression spring  38 , each of the forward end  56  of the advance lever  46  and the screws  16  are shown as being advanced further towards the right as in  FIG. 20 . 
         [0091]    As seen in each of  FIGS. 17 ,  18 ,  19  and  20 , the first guide member  142  and the second guide member  144  continue to be held in the open position by the spreader member  146 .  FIG. 28  illustrates a condition substantially the same as  FIG. 20 . From the position of  FIG. 20 , the tool moves to the condition shown in  FIG. 21  as also shown in  FIG. 29 . In moving from the position of  FIG. 28 , the forward end  56  of the actuating lever  46  continues to be moved towards the right, the strap  13  has been moved by the pawl  99  to the right to a position in which the head  17  of the screw  16  is engaged by the stop portion  91  of the socket  127  and in the last movement of the forward end  56  of the advance lever  46 , after the screw  16  has been moved such that its head  17  is engaged by the stop portion  91  of the socket  127 , the paddle  168  on the advance lever  46  engages the release pin  176  of the spreader member  146  moving the release pin  176  towards the right with the stop leg  172  to become disengaged from between the plate portions  157  and  159  of the first guide member  142  and the second guide member  144  after the screw  16  has been located substantially coaxially of the driver shaft axis  52 . The tool  12  in the position shown in  FIG. 29 , and corresponding  FIG. 21 , has the screw  16  to be driven in a ready position, the same position as that shown, for example, in  FIGS. 1 and 2  and a cycle of operation can thus be repeated by a user again urging the power driver  11  carrying the tool  12  forwardly into a workpiece. 
         [0092]    In operation of the tool  12 , the slide body  20  moves relative the housing  18  in a cycle of operation in which the slide body  20  moves in a retracting stroke from the extended position to the retracted position and then moves in an extending stroke from the retracted position to the extended position. Engagement between the cam roller  61  and the surfaces of the cam slot  64  will determine the relative rotational position of the advance lever  46 . The cam slot  64  is therefore selected so as to provide the desired relative position of the advance lever  46  and therefore its camming paddle  168  and pawl  99  having regard to the relative position in the stroke, that is, the relative position of the slide body  20  relative to the housing  18  and whether the slide body  20  is in a retracting stroke or an extending stroke. Configuration of the advance lever  46  and its cam roller  61  and the configuration of the cam slot  64  may be made in a known manner as, for example, in the manner disclosed by above-mentioned U.S. Pat. No. 6,453,780, the disclosure of which is incorporated herein. 
         [0093]      FIG. 22  schematically shows in solid lines the cam slot  64  having a front end  67 , a rear end  68  and with the first camming surface  65  extending on the left-hand side between the first end  67  and the second end  68  and the second camming surface  66  extending on the right side between the first end  67  and the second end  68 . The spring  69  biases the advance lever  46  counter-clockwise such that the cam roller  61  is inherently biased into the first camming surface  65 . In any position in the cycle of operation, whether the cam roller  61  will engage the first camming surface  65  or the second camming surface  66  will depend on a number of factors. Most significant of these factors involve resistance to movement of the forward end  56  of the advance lever  46  as compared to the strength of the spring  69  biasing the forward end  56  towards the right as seen in  FIG. 22 . Under conditions in which the bias of the spring  69  is dominant over resistance to a movement of the advance lever forward end  56 , then the bias of the spring  69  will place the cam roller  61  into engagement with the first camming surface  65  with relative movement of the advance lever  46  relative the position of the slide body  20  in the housing  18  to be dictated by the profile of the first camming surface  65 . Under conditions where the resistance to movement of the advance lever forward end  56  is greater than the force of the spring  69 , then the cam roller  61  will engage the first camming surface  65  or the second camming surface  66  depending on the direction of such resistance and whether the slide body  20  is in the retracting stroke or the extending stroke. For example, in the extension stroke, when the pawl  99  is engaging and advancing the strap  13  and the resistance offered to advance by the strap  13  is greater than the force of the spring  69 , then the cam roller  61  will engage on the second camming surface  66  with relative motion of the advance lever  46  relative the position of the slide body  20  in the housing  18  to be dictated by the profile of the second camming surface  66 . 
         [0094]    For normal operation of the tool  12  in accordance with the present invention, in a retracting stroke, the cam roller  61  moves from the front end  67  of the cam slot to the rear end  68  of the cam slot in rolling engagement with the first camming surface  65  and, in an extending stroke, the cam roller  61  moves from the second end  68  of the cam slot to the first end  67  of the cam slot in rolling engagement with the second camming surface  66 . In this manner, in identical positions of the slide body  20  and the housing  18 , the cam roller  61  engages the first camming surface  65  in the retracting stroke and the second camming surface  66  in the extending stroke such that the advance lever  46  places its forward end  56  at different positions relative the identical positions of the slide body  20  in the housing in a retracting stroke, then in an extending stroke. This arises in that, amongst other things, different portions of the first camming surface  65  and the second camming surface  67  have different profiles spaced by distances greater than the diameter of the cam roller  61 . In the embodiment illustrated, approximate each of the front end  67  of the cam slot and the rear end  68  of the cam slot, the cam slot has a width only marginally greater than the diameter of the cam roller  41  and the first camming surface  65  and the second camming surface  66  have substantially the same profiles. Over other portions of the first camming surface  65  and the second camming surface  66 , the first camming surface  65  and the second coming surface  66  have different profiles spaced by distances substantially greater than the diameter of the cam roller  61 . Engagement of the cam roller  61  in the front end  67  of the cam slot  64  preferably also serves as a mechanism to limit extension of the slide body  20  out of the housing  18  to a maximum under the bias of the compression spring  68  and representing the fully retracted position. 
         [0095]    On  FIG. 22 , two circles in dotted lines have been shown marked with the designations P 25  and P 27  as representing the relative positions of the cam roller  61  in the cam slot  65  respectively in  FIGS. 25 and 27 . 
         [0096]    Portions of each of the first camming surface  65  and the second camming surface  66  are straight and parallel to the driver shaft axis  52 . When the cam roller  61  moves over these portions of the camming surfaces which are parallel to the axis  52 , there is no relative rotation of the advance lever  46  relative to the slide body  20  and such straight portions of the camming surfaces parallel to the axis  52  in effect provide lost link motion portions where relative movement of the slide body  20  compared to the housing does not translate into relative pivoting of the advance lever  46 . In contrast, when the cam roller  61  moves over portions of the first camming surface  65  and the second camming surface  66  which are disposed at an angle to the axis  52  then with relative movement of the slide body  20  compared to the housing  18 , the advance lever  46  pivots relative to the slide body  20 . 
         [0097]    The tool  12  is preferably provided with an adjustable depth stop mechanism which can be used to adjust the fully retracted position, that is, the extent to which the slide body  20  may slide into the housing  18 . An adjustable depth stop mechanism such as illustrated in above-mentioned U.S. Pat. No. 6,453,780 may be adopted.  FIG. 27  schematically shows a depth setting cam member  196  which is secured to the housing  18  for sliding transversely of the housing as in the direction of the arrow and with a rotatable worm gear  197  for moving and fixing the depth setting cam member  196  at any particular lateral position relative to the housing  18 . The cam member  196  has a cam surface  198  disposed at an angle to the axis  52 . A portion of the cam surface  198  is axially aligned with a rearwardly directed depth stop surface  199  as schematically shown in  FIG. 22  carried on the rear portion  22  of the slide body  20 . By suitable positioning of the depth stop cam member  196  laterally relative to the housing  18 , the extent to which the slide body  20  may slide into the housing  18  may be set, that is, the slide body  20  is prevented from sliding further into the housing  18  when the depth stop surface  199  on the slide body  20  engages the depth stop cam surface  198  on the housing. The depth stop mechanism controls the extent to which screws are driven into a workpiece and, for example, can control the extent of any desired countersinking. 
         [0098]    The tool  12  in the embodiment is adapted for use with screws in which the maximum diameter of any portion of the screw  16  rearward of the first guide member  142  and the second guide member  144  is less than the spacing between the first guide member  142  and the second guide member  144  when each of these guide members are in the open position. The maximum diameter of the screw  16  rearward of the first and second guide members  142  and  144  typically is the maximum diameter of the head  17  of the screw. The tool  12  may be used with screws which have different head diameters provided the head diameters are smaller than this maximum diameter. Similarly, the tool is adapted for use with a driver shaft  34  which has a diameter less than the maximum distance the first guide member  142  and the second guide member  144  are laterally spaced when they are open. 
         [0099]    While the embodiment illustrates the recess  43  in the screw head  17  as being hexagonal, various other recesses may be provided including star shaped such as Phillips and square shape such as Robertson. The screw  16  has been illustrated as having underneath its head  17  an upper portion  37  of the shaft  40  which is frustoconical. This upper portion  37  is not necessary. The screw has been illustrated as having its shank  40  substantially threaded with a simple thread of constant pitch throughout its length other than over the upper portion  37  underneath the head  17 . This is not necessary and there is no need for the shank  40  to be continuously threaded or threaded with threads of only one diameter or pitch. 
         [0100]    The tool  12  is adapted for use with screws of different lengths. Preferably, each different screwstrip  14  will have a set of screws of the same length. Different screwstrips may be provided with screws of different lengths. The tool  12  will function in driving screws of almost any length provided that the distance from the rear surface  42  of the head  17  of the screw  16  to the tip  15  of the screw is greater than the distance from the drive portion  93  of the socket  127  to the first guide member  142  and the second guide member  144 , such that when the screw head  17  is engaged in the socket  127  the screw shank  40  is engaged between the first guide member  142  and the second guide member  144 . If, when the tool  12  is in the ready position, the screw tip  15  does not extend forwardly beyond a forward surface  202  of the touch down foot  140 , then the tool  12  will remain operative to drive the screw into the workpiece, however, there will not be the opportunity to easily locate the tip  15  of the screw  16  at a desired location on the surface of the workpiece before driving the screw. Preferably, therefore, in accordance with the present invention, when in the ready position as, for example, shown in  FIG. 2 , the screw will have a length such that with its head  17  proximate the socket  127 , the tip  15  of the screw  16  extends forwardly beyond the forward surface  202  of the touch down foot  140 . The length of screws that can be used with the tool  12  of the present technology is not limited. Insofar, for example, that screws are used in the tool  12  which are longer than the screws  16  shown in  FIG. 2 , then the screw in the ready position will necessarily space the tip  15  of the screw  16  further forwardly from the tool  12  and thus provide proportional additional room for the next screw to be disposed at an angle to the workpiece and avoid contact with the workpiece  194  as is the case, for example, in  FIG. 22 . 
         [0101]    In the first embodiment, with the screw  16  in a ready position such as shown in  FIG. 4  and  FIG. 13 , the screw  16  has been advanced held by the strap to a position in which the head  17  of the screw  16  engages the stop portion  91  of the socket  127  and the screw head  17  is disposed spaced forwardly from the annular drive portion  93  of the socket  127 . Subsequently, after the tip  15  of the screw  16  first engages the workpiece  194 , forward movement of the tool  12  moves the slide body  20  downwardly preferably with the annular drive portion  93  engages the head  17  of the screw  16  and guides the screw  16  into coaxial location centered within the socket  127  relative to the axis  52 . 
         [0102]      FIG. 30  schematically illustrates in a second embodiment of the present technology an alternate arrangement.  FIG. 30  is a cross-sectional view of substantially the same as that shown in  FIG. 4 , however, notably with the profile of the rear wall  125  changed where it forms the uppermost part of the head channel  136  to receive the head  17  of the screw  16  and also the width of the strap feed channelway  129  changed. In  FIG. 30 , the screwstrip  14  is illustrated in a position in which the next screw  16  to be driven is being advanced towards the right as shown by the arrow. In this position, the head  17  of the screw  16  is shown as being engaged with a forwardly directed surface  301  of the rear wall  125 . The engagement of the hand  17  with the surface  301  results, at least in part, due to the pawl  99  advancing the screwstrip  14  and friction between the strap  13  and the feed strap channelway  129  which will tend to urge the screwstrip rearwardly.  FIG. 31  shows a cross-sectional view the same as in  FIG. 30  but in which the screw  16  has been advanced towards the right to be axially aligned with the axis  52  of the driver shaft  34 . In  FIG. 31 , due to the forces tending to urge the screwstrip rearwardly as developed due to the pawl  99  drawing the strip to the right and the inherent resiliency of the screwstrip, the head  17  of the screw  16  has become seated in the socket  127  engaged with the annular drive portion  93  without being spaced forwardly therefrom. 
         [0103]    In movement from the position of  FIG. 30  to the position of  FIG. 31 , a screw head  17  engages the stop portion  91  to stop advance and is urged rearwardly into the forwardly directed rear surface  301  of the rear wall  125  such that when the screw head  17  reaches the socket  127 , the screw head  17  moves rearwardly into engagement in the socket  127 . On such rearward movement of the screw head  17  into the socket  127 , engagement between the socket  127  and screw head  17  prevents further advance of the screwstrip  14  to the right as shown. The screw  16  is located in a position coaxial above the axis  50  in a position ready to be driven. As seen in  FIGS. 30 and 31 , as represented by the strap feed channelway  129 , the bight  135  between the rear arm  132  and the forward arm  133  is sized to have a front to rear width measured normal the longitudinal of the strap  13  proximate the entranceway  83  and proximate the exitway  87  to relatively closely receive the flange members  73  of the strap therebetween. However, as the strap feed channelway  129  becomes closer to the axis  52 , the channelway  129  increases in front to rear width so as to permit the strip to move rearwardly from the position of  FIG. 30  to the position of  FIG. 31 . 
         [0104]    The specific nature of the screwstrip  14  being advanced including the flexibility of the strap  13  will be relevant in selecting a profile for the feed strap channelway  129  which will permit operation as described in  FIGS. 30 and 31 . The engagement of the head  17  and the surface  301  of the rear wall  125  result in frictional forces which need to be overcome to advance the screwstrip and need to be considered in adopting any particular configuration for the tool. In the first embodiment, the socket  127  includes particularly the stop portion  91  for engagement with the head  17  of the screw  16  to have the screw being advanced stopped at a desired position where the screw head  17  is substantially axially aligned with the axis  52 . In the second embodiment illustrated in  FIGS. 30 and 31 , the equivalent of the stop portion  91  overlaps with the drive surface portion  93  insofar as the drive portion  93  is at least partially radially inwardly directed toward the axis  52 . Alternatively in the embodiments of  FIGS. 30 and 31 , a more pronounced forwardly extending stop portion  91  may be provided similar to that in  FIG. 4 . 
         [0105]    The particular nature of the pawl  99  and its arrangement as shown in the first embodiment can be used to accurately advance the strap  33  to a desired position in the feed strap channelway  129  at the end of each stroke preferably to locate each screw  16  with its head  17  substantially coaxially aligned with the axis  52  without the head  17  engaging the recess  127  at all. Where the pawl  99  will locate the next screw to be driven with its head  17  coaxial with the axis  52  then the configuration of a recess substantially shown in  FIG. 4  could be used with the screw head  17  advanced to assume a position spaced forwardly of the recess  127 . Such an arrangement is schematically illustrated in  FIG. 32 , effectively representing the same arrangement as in  FIG. 4  but with the socket  127  having the forwardly extending stop portion  91  shown in  FIG. 4  removed. In such an arrangement, the socket  127  preferably extends radially of the screw head  17  to some extent such that as the socket  127  is moved downwardly to engage the head  17  of the screw  16 , the concave or frustoconical surfaces of the annular drive portion  93  of the socket  127  will cam the screw head  17  into a centered position coaxially with the axis  52 . 
         [0106]    The embodiment illustrates the use of a particular screwstrip of a flat tape type and with a particular configuration using the flange members  73  for advancement by the pawl  99 . Other configurations of screwstrips including flat tape screwstrips and axial screwstrips may be used with a tool in accordance with the present invention. Various mechanisms may be provided for advance of the screwstrips through a guideway to locate successively each screw to be advanced axially in line with the driver shaft. The particular nature of the advance mechanism is not limited to lever mechanisms such as the advance lever  46  shown. Rather various rotating wheels and shuttle arrangements or other advance mechanisms may be used in accordance with the present invention. As well, various different guides and channels may be used to guide the screwstrip and its strap and screws in their advance or location within the slide body  20 . If an axial screwstrip is to be used, the strap may be disposed in an arc so as to locate the axes of the screws in a flat plane including the arc such as disclosed in above-noted U.S. Pat. No. 6,453,780 which is incorporated herein by reference. The curved arc of the axial screwstrip can assist in preventing the next screw to be driven from engaging the work surface. 
         [0107]    The particular nature of the screwstrip to be used in accordance with the present technology is not limited. For example, screwstrips may have screws carrying washers on the shaft of the screw at a location forward of the touch down foot when in the advanced position so as to permit driving of screws having similarities to those described in U.S. Pat. No. 4,930,630 to Habermehl, issued Jun. 5, 1990, the disclosure of which is incorporated herein by reference. 
         [0108]    The embodiment illustrates an arrangement with the advance lever  46  and its cam roller  61  carried on the slide body  20  and the cam slot  64  carried on the housing  18  so as to provide desired movement of the advance lever  46  with relative movement of the slide body  20  relative to the housing  18  in the extending stroke and the retracting stroke. However, many other mechanisms may be provided to translate the movement of the slide body  20  relative to the housing  18  in a cycle of operation and provide for desired timing and relative location of various mechanisms for advance of the screwstrip and driving of each screw including the manipulation of elements such as the spreader member  46 . U.S. Pat. No. 6,453,780 illustrates two different arrangements and various other motion translation mechanisms may be utilized in accordance with the present invention. 
         [0109]    The present technology has been described with reference to use of the tool as driven by a manually operated and manipulated power driver  11 . While this is a embodiment, this is not necessary and the tool  12  could be adapted for automatic or robotic use. 
         [0110]    The embodiment provides the first guide member  142  as carrying the axle extension lever  60  permitting manual movement of the first guide member  42  to an open position to permit manual insertion of the screwstrip  14 . The manual movement of the first guide member  142  to an open position is also of assistance to withdraw any screwstrip  14  from engagement with the tool  12  and can be useful, for example, in the event of a jammed situation or the like. 
         [0111]    The embodiment of the tool  12  shows merely the first guide member  142  as having the axle extension lever  60  permitting its opening. It is to be appreciated that both of the first guide member  142  and the second guide member  144  could be provided with similar manually operated axle extension levers or alternatively a separate mechanism could be provided to manually open both the first and second guide members  142  and  144  at the same time. The provision of a manual mechanism to open one of the first guide member  142  or the second guide member  144  is not necessary but advantageous. 
         [0112]    The embodiment shows that in the downward movement of a screw  16  being driven, the screw head  17  engages the first guide member  142  and the second guide member  144  to move them to the open position. Other arrangements may be provided for opening these guide members including an actuator carried on the housing  18 . 
         [0113]    The tool  12  in accordance with the present technology is adapted to drive a single screw. For example, with the screwstrip  14  removed, and the first guide member  142  in the open position, the tool  12  may be placed about a single screw with the head of the screw received in the socket  127  and the shank  40  of the screw engaged between the first guide member  142  and the second guide member  144 . This can be advantageous, for example, in using the tool to drive a separate new screw as, for example, where one particular screw of a different size or length may be desired than the screws in the screwstrip. As well, driving a single screw can be useful insofar as it is desired to complete the driving of a screw which may have only partially become engaged in a workpiece due to a jamming situation which prevented the screw from being fully driven. 
         [0114]    The technology illustrated, for example, in  FIG. 2  shows the advance lever  46  disposed on one side of the slide body  20 . Preferably, a protective shroud (not shown) may be provided attached to the nose portion  24  of the slide body  20  laterally outside of the camming paddle  68  of the advance lever  46  to protect it from damage or engagement with workpieces and the like yet without constraining the ability of the paddle  68  to be deflected laterally or otherwise move as is required for proper operation of the tool  12 . 
         [0115]    While the technology has been described with reference to various embodiments, the technology is not so limited. Many variations and modifications will now occur to persons skilled in the art. For a definition of the invention, reference is made to the appended claims.