Abstract:
The retention device for retaining a fastener comprises an outer tubular shaft slidably disposed upon an inner tubular shaft. Extending from the distal end of the inner tubular shaft is a plurality of resilient gripping members, each having an arcuated portion protruding outwardly from the cylindrical axis of the inner tubular shaft. The outer tubular shaft, having a conically tapered inner bore, is longitudinally slid along the inner tubular shaft to press inwardly the arcuated portions so that the gripping members grasp a fastener at the distal ends thereof. The outer tubular shaft can be internally threaded to provide varying strength for retaining or releasing the fastener. A restraining resilient member is provided to prevent the retention device from falling off from the fastening tool by engaging an annular flange disposed upon the shank of the fastening tool. Another retention device, comprising two independent sets of gripping members for use separately in combination with two co-operating outer tubular shafts, is employed to provide multiple contact points at the head and shank of the fastener for better alignment and improved holding capability.

Description:
BACKGROUND OF INVENTION 
     The invention relates generally to fasteners and fastener drivers and particularly to those utilizing a retention device to retain the fastener in position for positive engagement into its target location. 
     It has often happened that a bolt or a screw is required to be inserted into an area that is difficult to access. A retaining device is usually needed to save time and effort to bring the bolt or screw into its target location. In medical surgery, the surgical area in which a bone screw is to be introduced is usually very narrow. It is often difficult to hold the bone screw by hand or by other tool so that the bone screw can be accurately and securely fastened into the targeted area. 
     There are many prior art screwdrivers which address the aforementioned difficulty in many different ways. These include, but not limited to a magnetized screwdriver, a gripper of different designs and a tubular shaft for guiding the screw. 
     U.S. Pat. No. 6,189,422 discloses a screwdriver having a retention device capable of retaining a bone screw before inserting the screw into a human or an animal body. The retention device includes a clamping gripper mounted at the distal end of an inner tubular shaft which surrounds the shaft of the screwdriver. An actuation device is provided on the handle of the screwdriver to longitudinally displace an outer tubular shaft so that the outer tubular shaft is moved relative to the inner tubular shaft and over the clamping gripper to close the jaws of the clamping gripper, thereby holding the screw firmly without wobbling. However, the retention device is relatively complicated in terms of the needed disassembly and assembly that is required for disinfection. 
     U.S. Pat. No. 4,016,913 discloses a holding device comprising a sleeve adapted to fit over the shank of a screwdriver. A pair of diverging arms is mounted at the distal end of the sleeve. A pair of coil springs extending between the diverging arms is adapted to grip the shank of a fastener. Use of bulky items like the coil springs and diverging arms often renders the retention device inadequate for use in a confined space where the fastener is to be located for insertion. 
     One of the disadvantages of these prior art devices utilizing a gripper is that the gripper can only assume two distinct positions while holding the screw in place in its jaws. The jaws are either open very widely or closed very tightly. The range on the sizes of the screw that can be covered by a specific retention device is limited. The holding strength for retaining or releasing the screw in its place cannot be varied. Moreover, any alignment error of the screw while being held by the gripper cannot be easily corrected. 
     The screw usually cannot be released gently from the clamping gripper in many of the prior art retention devices. 
     The retention means of some of the prior art devices for retaining a bolt or screw are quite complicated. The magnetic strength of a magnetized screwdriver is known to decay over time. Furthermore the magnetized screwdriver is often inadequate for some dedicated works, especially for a fastener which is made of a plastic material or of a non-ferromagnetic metal. 
     Other retention devices are only applicable to some specific applications of introducing a screw for insertion into a workpiece. An object of this invention is to provide a holding device that is simpler in construction, which usually translates into a lower cost of manufacture. Some of the inventive devices described hereinafter can easily be made by molding, further reducing the production cost of the retention device. 
     Another object is to have a retention device for use with a screwdriver that can be easily assembled and disassembled. A fast disassembly and assembly feature of the retention device is especially important for easy cleaning in medical surgery so that the various components of the retention device and the screwdriver can be thoroughly, readily and quickly sterilized before an operation. 
     An object of this invention is to provide a means of manipulating the size of the gripping jaw&#39;s opening, thus increasing the range of sizes of bolts and screws the retention device can hold for insertion into a normally inaccessible area of a workpiece. Such a retention device also provides varying strength for holding or releasing the fastener gently. 
     A still further object is to provide multiple contact points at different parts of the fastener for better screw alignment and improved holding capability, thus further preventing the fastener from dislodging by a sideward displacement during a fastening process. Initial alignment error of the fastener can easily be corrected since the holding strength on the fastener can be varied. The improved retention device is still relatively simple to produce, operate and assemble. 
     Many of the prior art retention devices are very complicated in design, usually involving many structural components. Some of the retention systems have obvious advantages, however, are expensive to manufacture. 
     Accordingly, it is the object of the present invention to provide an improved retention device which is simpler to manufacture at a lower cost and easier to operate than the prior art retention means. 
     SUMMARY OF INVENTION 
     The retention device for retaining a fastener comprises an outer tubular shaft slidably disposed upon an inner tubular shaft. Extending from the distal end of the inner tubular shaft is a plurality of resilient gripping members, each having an arcuated section protruding radially away from the axis of the inner tubular shaft. A resilient restraining member mounted on the opposite end of the inner tubular shaft engages an annular flange disposed upon the shank of the fastening tool to prevent the inner tubular shaft from falling off from the fastening tool. 
     The outer tubular shaft, a portion of which has an inner through bore in a conical shape, is moved along the inner tubular shaft and over the arcuated sections to press in the gripping members to grasp a fastener at the distal end. In another embodiment of the invention, the inner tubular shaft is internally threaded. The holding strength for retaining or releasing the fastener at the distal ends of the gripping members can be gradually varied by rotating the outer tubular shaft with respect to the inner tubular shaft. 
     In yet another embodiment of the invention, the outer tubular shaft and the inner tubular shaft are both mounted on the handle of the fastening tool for easy handling by simply rotating the outer tubular shaft to engage the fastener for insertion into the workpiece. The fastener can be released gently in a controllable fashion. A simple retention device, comprising mainly an outer tubular shaft and a plurality of gripping members mounted on an inner tubular shaft is also discussed. The device preferably provides a resilient restraining member for engaging either an annular flange on the shank, or an annular recess embedded in the shank, to prevent the retention device from falling off from the fastening tool. 
     Another retention device, comprising two independent sets of gripping members for use separately in combination with two co-operating outer tubular shafts, is employed to provide multiple contact points at different parts of the fastener, namely at the head and shank of the fastener for better alignment and improved holding capability. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS 
     FIG. 1 is a simplified diagram of a first preferred embodiment showing an outer tubular shaft and an inner tubular shaft with a pair of gripping jaws. 
     FIG. 2 is a simplified diagram of a second preferred embodiment showing an internally threaded outer tubular shaft. 
     FIG. 3 is a simplified diagram of a third preferred embodiment having a plurality of jaws. 
     FIG. 4 is a simplified diagram of a fourth preferred embodiment showing an inner tubular shaft being mounted on the handle of the fastening tool. 
     FIG. 5 is a simplified diagram of a fifth preferred embodiment showing a plurality of hooks for engaging an annular flange mounted on the shank of the fastening tool. 
     FIG. 6 is a simplified diagram showing a plurality of hooks for engaging an annular recess in the shank of the fastening tool. 
     FIG. 7 is a simplified diagram of another preferred embodiment showing a plurality of jaws for engaging the shank and head of the fastener. 
    
    
     DETAILED DESCRIPTION 
     A more complete understanding of my invention may be obtained through a study of this description when taken together with the appended drawings, wherein like reference symbols refer to like elements of the drawings. 
     Referring now to the first preferred embodiment of the invention shown in FIG. 1, wherein a retention device  10  comprises an inner tubular shaft  20  receivable upon an elongated shank  30  of a fastening tool  40  having a handle  45 , and an outer tubular shaft  50  slidably disposed upon the inner tubular shaft  20 . 
     The fastening tool  40  can be a flat blade screwdriver, a Phillips screwdriver, a power-driven screwdriver or the like. Extended from the distal end  65  of the inner tubular shaft  20  is a clamping gripper  60 , which comprises generally a pair of resilient deformable opposing gripping members  62 . Each of the gripping members  62  has on its elongated handle  68  a curved arcuated portion  70  protruding outward from a central axis, which is the cylindrical axis  75  of the inner tubular shaft  20 . At the distal end of each gripping member  62  is a gripping jaw  78 . 
     A plurality of resilient u-shaped members  80 A and  80 B are respectively mounted at the distal end  65  in between the gripping members  62  and at the proximal end  85  of the inner tubular shaft  20 . U-shaped members  80 A and  80 B slidingly engage the shank  30  of the fastening tool  40 , so that the inner tubular shaft  20  is longitudinally slidable and rotatable about the shank  30 . 
     A pair of resilient beams  90 , each comprising an end portion  92  engaging the shank  30 , are mounted at the proximal end  85  of the inner tubular shaft  20 . 
     Beams  90  are shown to have been displaced with respect to the u-shaped members  80 B, so that a clearer view of all the components in the diagram can be presented. 
     The outer tubular shaft  50 , having an inner through bore  95 , comprises a conically tapered bore portion denoted by dashed lines  96  and a substantially uniform end bore portion  98 . Tapered bore portion  96  has an inner diameter which is decreasing with depth as measured in a direction from end  100  to the opposite end  105  of the outer tubular shaft  50 . End bore portion  98  is substantially constant in its inner diameter and is slidably disposed upon the inner tubular shaft  20 . The outer tubular shaft  50  is inserted onto the shank  30  of the fastening tool  40 , followed by a flexible annular ring or flange  110  slidably mounted and held frictionally onto the shank  30 . The inner tubular shaft  20  is inserted next and mounted along the shank  30 , with the u-shaped members  80 B and beams  90  lifted away from shank  30  so that the annular flange  110  on shank  30  is positioned between the u-shaped members  80 A and the u-shaped members  80 B. 
     The linear movement of the inner tubular shaft  20  is constrained at position  115  by the annular flange  110  on shank  30 . The annular flange  110  blocks the u-shaped members  80 B of the inner tubular shaft  20  at position  115 , preventing the inner tubular shaft  20  from coming off unless the u-shaped members  80 B and beams  90  are lifted away from shank  30 . Annular flange  110 , which can also be a ridge on the shank  30 , serves as a blocking and passive restraining means to prevent the passage of the inner tubular shaft  20 . 
     The outer tubular shaft  50  is longitudinally slid along the inner tubular shaft  20  to come into engagement with the arcuated portion  70 . The interior bore wall surface  99  of the inner tapered bore  96  presses the arcuated portion  70  of the handle  68  inwardly towards the cylindrical axis  75  of the inner tubular shaft  20 , thereby moving the opposing gripping jaws  78  of the gripping members  62  radially towards each other. Gripping jaws  78  are eventually closed from an initially open position to finally grasp a bolt  140  in a closed position. 
     With the bolt  140  being retainably held firmly in place by the clamping gripper  60 , the engaging bit in the driver head  150  of the fastening tool  40  starts the fastening process by engaging a receptacle  160  in the head of the bolt  140 . The tips at the distal ends  120  of the gripping members  62  are radially bent or spread outwardly away from the cylindrical axis  75  so that the bolt  140  can be fastened completely into a workpiece (not shown). 
     In its preferred mode of fabrication, the clamping gripper  60  may be fabricated using a resilient material such as molded plastic, fiber glass or other sufficiently strong material to provide suitable spring resiliency for the gripping jaws. 
     Referring now to the second preferred embodiment of the invention shown in FIG. 2, wherein a retention device  10  comprises an inner tubular shaft  20  enclosing an elongated shank  30  of a fastening tool  40  having a handle  45 , and an outer tubular shaft  50  slidably disposed upon the inner tubular shaft  20 . 
     Extending from the distal end  65  of the inner tubular shaft  20  is a clamping gripper  60 , which comprises a pair of resilient opposing gripping members  62 . 
     Each of the gripping members  62  has on its elongated handle  68  an arcuated portion  70  protruding radially outward from a cylindrical axis  75  of the inner tubular shaft  20 . 
     A plurality of resilient u-shaped members  80 A and  80 B are respectively mounted at the distal end  65  and at the proximal end  85  of the inner tubular shaft  20 . U-shaped members  80 A and  80 B slidingly engage the shank  30  of the fastening tool  40 , so that the inner tubular shaft  20  is slidable longitudinally and rotatable about the shank  30 . A pair of resilient beams  90  extending from the proximal end  85  of the inner tubular shaft  20  engages the shank  30  for linear movement along shank  30 . 
     The outer tubular shaft  50 , having an inner through bore  95  comprises a conically internally threaded tapered bore portion denoted by dashed lines  196  and a substantially uniform end bore portion  98 . Threaded tapered bore portion  196  has an inner diameter which is decreasing with depth as measured in a direction from end  100  to the opposite end  105  of the outer tubular shaft  50 . 
     Threaded tapered bore portion  196  is denoted by an array of alternate solid lines and dashed lines representing respectively the ridges and furrows of the interior portion of the inner threaded tapered bore  196 . End bore portion  98  is substantially constant in the inner diameter and is slidably disposed upon the inner tubular shaft  20 . 
     An annular flange  110  is provided on shank  30  and is positioned between the u-shaped members  80 A and the u-shaped members  80 B. The linear movement of the inner tubular shaft  20  is constrained at position  115  by the annular flange  110  on shank  30 . The annular flange  110  prevents the inner tubular shaft  20  from falling off from shank  30  unless the u-shaped members  80 B and beams  90  are lifted radially away from shank  30 . 
     The cylindrical wall  220  of the inner tubular shaft  20  is provided with a threaded through opening  225  through which a releasable fastener  230  may pass into engagement with the shank  30  of the fastening tool  40 . The tip of the fastener  230  engaging the shank  30  frictionally prevents the inner tubular shaft  20  from rotating with respect to shank  30  when the inner tubular shaft  20  needs to be held steady for the smooth relative rotation of the outer tubular shaft  50  and the inner tubular shaft  20 . 
     The fastener  230 , serving as a locking means, engages a longitudinal channel  240  provided on the shank  30  of the fastening tool  40 . The fastener  230  is insertable into and removable from the cylindrical wall  220  when the outer tubular shaft  50  is positioned to rotate about the inner tubular shaft  20 . 
     A segmented guiding ridge  250 , engageable with the threaded interior tapered wall  99  of the outer tubular shaft  50 , is mounted on the outer surface of the arcuated sections  70  of clamping gripper  60 . The outer tubular shaft  50  is slid along the inner tubular shaft  20  to come into engagement with the guiding ridge  250  on the arcuated portion  70  of the clamping gripper  60 . The outer tubular shaft  50  is rotated with respect to the inner tubular shaft  20  in the direction denoted by a curved arrow  255 . The interior tapered wall  99  continually presses inwardly on the arcuated portion  70  of the handle  68  towards the cylindrical axis  75 , which is now the axis of rotation of the outer tubular shaft  50 , until the gripping jaws  78  of the clamping gripper  60  is finally closed to grasp a fastener  140 . Further tightening can be done by simply rotating the outer tubular shaft  50  about the inner tubular shaft  20  in the direction  255  as shown in FIG.  2 . 
     The gripping jaws  78  comprises a gripping portion section  260 , adapted to hold the head of the fastener  140  to prevent slipping and to securely grasp the fastener  140  before insertion into a workpiece (not shown). 
     The fastener  140  can be released gently by rotating the outer tubular shaft  50  with respect to the inner tubular shaft  20  in a second direction opposite to the curved arrow shown as  255 . It is clear that the variation in the conically tapered interior wall  99  of the through bore  95  allows for use with fasteners of a wide variety of sizes. 
     Referring now to the third preferred embodiment of the invention shown in FIG. 3, wherein a retention device  10  comprises of an inner tubular shaft  20  having a plurality of resilient gripping members  62  mounted at a distal end  65  for grasping a fastener  140 . Gripping members  62  are preferably arranged circumferentially with axial symmetry about a cylindrical axis  75  of the inner tubular shaft  20 . The inner cylindrical tapered wall  99  of the outer tubular shaft  50  presses inwardly the arcuated portion  70  of the gripping members  62  towards the cylindrical axis  75  of the inner tubular shaft  20 . The jaws  78  of the gripping members  62  finally grasp a fastener  140  for insertion into a workpiece (not shown). The functions of the u-shaped members  80 A,  80 B and the annular flange  110  in the diagram are described in detail in the foregoing embodiments. 
     Referring now to the fourth preferred embodiment of the invention shown in FIG. 4, wherein a retention device  10  comprises of an inner tubular shaft  20  surrounding an elongated shank  30  of a fastening tool  40  having a handle  45 , and an outer tubular shaft  50  slidably disposed upon the inner tubular shaft  20 . 
     Extending from the distal end  65  of the inner tubular shaft  20  is a clamping gripper  60 , which generally comprises a pair of resilient gripping members  62 . Each of the gripping members  62  has on its elongated handle  68  an arcuated portion  70  protruding radially outward from a cylindrical axis  75  of the inner tubular shaft  20 . 
     A plurality of resilient u-shaped members  80 A is mounted in between the gripping members  62  at the distal end  65  of the gripping members  62 . U-shaped members  80 A engage the shaft  30  of the fastening tool  40 , so that the inner tubular shaft  20  is longitudinally slidable and rotatable about the shank  30 . 
     Inner tubular shaft  20  comprises two inner cylindrical wall portions  310  and  320  of different diameters, which results in a shoulder portion  330 . The inner cylindrical wall portion  320 , retainably disposed upon the handle  45 , includes an oblong cutout section  340 . A resilient member  350 , having a knob  360  at a free end  365 , is mounted on a side  370  of the cutout section  340 . 
     The free end  365  of the resilient member  350  engages a flexible annular flange  410  disposed upon the handle  45  of the fastening tool  40 , so that the inner tubular shaft  20  does not fall off from the fastening tool  40 . In a disassembly process, the knob  360  is lifted in a direction away from the handle  45  to allow the inner tubular shaft  20  to move and pass over the annular flange  410 , so that the inner tubular shaft  20  is subsequently disengaged from the fastening tool  40 . If necessary, a releasable fastener  230  is provided for insertion into a threaded opening  225  in the inner cylindrical wall  320 . 
     Fastener  230  prevents the inner tubular shaft  20  from rotating about the handle  45  when the inner tubular shaft  20  needs to be held steady for the smooth relative rotation of the outer tubular shaft  50  and the inner tubular shaft  20 . The fastener  230  also engages a longitudinal channel  430  embedded in the handle  45  to secure the inner tubular shaft  20  to the handle  45 . 
     Outer tubular shaft  50  comprises two outer cylindrical wall portions  440  and  450  of unequal diameters, which results in a shoulder portion  460 . The outer tubular shaft  50  comprises an internally threaded tapered bore portion  196  and an end bore portion  98  of generally constant thickness. The outer tubular shaft  50  is slidably disposed upon the inner tubular shaft  20 . 
     A segmented annular guiding ridge  250 , on the outer surface of the arcuated sections  70  of clamping gripper  60 , engages the threaded interior tapered wall  99  of the outer tubular shaft  50 . The outer tubular shaft  50  is slid along the inner tubular shaft  20  to come into engagement with the guiding ridge  250  of the clamping gripper  60 . The outer tubular shaft  50  is rotated with respect to the inner tubular shaft  20  in a direction denoted by a curved arrow  255  until the distal ends  120  of the clamping gripper  60  are closed. The gripping jaws  78  finally grasp a fastener  140  in the closed position. 
     The distal ends  120  of the clamping gripper  60  comprises a gripping section  260 , adapted to hold the head of the fastener  140  to prevent slipping and to securely grasp the fastener  140  before insertion into a workpiece (not shown). 
     Referring now to the fifth preferred embodiment of the invention shown in FIG. 5, wherein a plurality of resilient retaining members  510 , in the form of a hook extending from the proximal end  85  of the inner tubular shaft  20 , engages an annular flange  110 . The annular flange  110  is disposed frictionally upon shank  30  of the fastening tool  40 . The free ends  520  of the retaining members  510  are lifted away from shank  30  to allow the clamping gripper  60  to fall off from the fastening tool  40  during a disassembly process. 
     Instead of using an annular flange  110 , an annular recess  550  is provided in the shank  30  of the fastening tool  40 , as shown in FIG.  6 . The retaining members  510  mounted on the inner tubular shaft  20  engages the annular recess  550  to prevent the clamping gripper  60  from coming off the fastening tool  40 . 
     Inner tubular shaft  20 , having a plurality of generally elongated slots  560  through its body, supports a clamping gripper  60  for engaging a fastener  140  at the distal ends thereof. 
     Referring now to another preferred embodiment of the invention shown in FIG. 7, wherein a retention device  10  comprises of a first outer tubular shaft  50  slidably disposed upon a first inner tubular shaft  20 , and a second outer tubular shaft  750  slidably disposed upon a second inner tubular shaft  720 . The second inner tubular shaft  720  in turn, is longitudinally slidable and rotatable about the first outer tubular shaft  50 . Extending from the distal end  65  of the inner tubular shaft  20  is a first set of a plurality of gripping members  62 , which comprise a plurality of jaw members  78  for engaging the head  735  of a fastener  140 . 
     The first outer tubular shaft  50  comprises a conically tapered bore portion denoted by dashed lines  96  and a substantially uniform end bore portion  98 . 
     Similarly, the second outer tubular shaft  750  comprises a conically tapered bore portion denoted by dashed lines  796  and a substantially uniform end bore portion  798 . 
     Extending from the distal end of the second inner tubular shaft  720  is a second set of a plurality of gripping members  762  for engaging the shank  740  of the fastener  140 . Gripping members  62  and  762 , each having respectively an arcuated portion  70  and an arcuated portion  770  protruding separately outwardly from the cylindrical axis  75 , are arranged circumferentially with axial symmetry about the cylindrical axis  75  of the inner tubular shaft  20 . The first outer tubular shaft  50  is slid forward towards the gripping jaws  78 , the inner cylindrical tapered wall  99  of the first outer tubular shaft  50  comes into contact with the arcuated portion  70  and presses inwardly the arcuated portion  70  of the gripping members  62  towards the cylindrical axis  75  of the first inner tubular shaft  20  to thereby engage the head  735  of the fastener  140 . 
     Similarly, the second outer tubular shaft  750  presses inwardly the arcuated section  770  of the second inner tubular shaft  762 , thereby engaging the shank  740  of fastener  140 . Fastener  140  is held at multiple contact points by both the gripping jaws  78  and the end portions  725  of gripping members  762  for insertion into the workpiece  780 , preventing undesirable inclination of the fastener  140  to the surface of the workpiece  780 . 
     When the fastener  140  has advanced sufficiently into the workpiece  780 , the end portions  785  of the gripping members  762  come into contact with the surface of the workpiece  780 . End portions  785  of the gripping members  762  are bent and spread radially outwardly and moved away from the cylindrical axis  75  as the fastener  140  continues to advance into the workpiece  780 . At the same time, second inner tubular shaft  720 , on which the gripping members  762  are mounted, has the tendency to slide longitudinally towards the handle  45  of the fastening tool  40 , until the tips  790  of the gripping members  62  come into engagement with the inner surface  800  of the gripping members  762 . The tips  790  of the gripping members  62 , protruding outwardly from the cylindrical axis  75 , help to ensure that the end portions  785  of the gripping members  762  are subsequently disengaged by pushing the gripping members  762  away from the shank  740  of fastener  140 . 
     The functions of the retaining members  510  and the annular flange  110  in the diagram are described in detail in the foregoing embodiments. 
     Having described the invention and its preferred modes of operation insufficient detail for those of normal skill in the art to practice the same, it will be obvious to such practitioners to make certain changes and variation in the specific elements of the disclosed embodiments without departing from the scope of the invention. For example, the u-shaped members  80 A and  80 B shown in the diagram for engaging the shank  30  of the fastening tool  40  can assume many other shapes. Furthermore, they are not necessary needed in the operation and are not the essential elements for the gripping operation. They are needed only for use with various elongated shanks  30  of a variety of sizes now available in the markets. 
     It is clear that the foregoing disclosure is merely illustrative of the principles of the present invention. Numerous alternatives, modifications and additions, apparent to those skilled in the art, may be made without departing from the spirit and broader aspects of this invention as defined in the appended claims.