Abstract:
A percutaneous access device implantable beneath the skin of a patient includes a turret assembly containing current limiters, electrical contacts and fluid couplings and includes a sealing device having a small screw fastener at the bottom of the turret assembly. A screwdriver is provided configured to have access through a required air inlet passage to provide rapid removal and replacement of a new turret. The screwdriver includes a shaft having an eccentric drive socket. A handle has a roller clutch bearing pressed in place to allow the handle to freely turn clockwise to tighten the screw but locks the handle to the shaft for screw extraction in the counterclockwise direction. A driver captively engages a fastener for assembling a first part having a shoulder to a mating fitting having an aperture. The driver includes a shaft having a fastener-engaging end, and a mechanism, operably engageable between the shaft and the first part, for holding the fastener in a full forward position against the shoulder of the first part during attachment of the fastener to the aperture of the mating fitting.

Description:
FIELD OF THE INVENTION 
     This invention pertains to a driver for captively holding a fastener during assembly and disassembly of two parts, and more particularly to percutaneous access devices employed to establish a connection through the skin between an organ or device implanted within the human body and an external device such as a monitor, pump or the like. More particularly, this invention pertains to means for accessing the electrical conduits as well as fluid conduits and mechanical connection features of the percutaneous access device. 
     BACKGROUND OF THE INVENTION 
     Percutaneous access devices hereinafter referred to as PAD, are employed to establish a connection projecting outward through the skin between an organ or a device implanted on a long term basis within the human body, and an external device such as a monitor, pump or the like. The PAD provides both mechanical and electrical access to the internal organs or devices and as such can be equipped with channels for conveying fluids or gases as well as electrical contacts for transmitting signals, for example, an ECG, or supplying power to devices. Such electrical contacts are usually partially exposed and could convey voltages and currents or become the grounding point for a substantial discharge of electricity generated in fabrics, carpets and the like. 
     For this reason it is necessary to install a current limiting device between the PAD contact and the organ or device, and this places the location of the limiter within the PAD (as a non-surgically renewable component). Because current limiters can fail, it is necessary that the limiters are positioned such that removal and replacement is possible without resorting to any surgery. Electrical contacts as well as fluid sealing surfaces and mechanical connection features also require periodic monitoring and maintenance since they are subject to everyday abrasion, abuse and actual breakage. The placement of electrical and/or mechanical devices in the PAD housing complicates the task of performing routine diagnostics and general troubleshooting and is limited by the permanent connection of the PAD to organs and devices requiring a carefully controlled operating or interrogating procedure. 
     A turret assembly containing the current limiters, electrical contacts and the fluid coupling and sealing device is used to render all of the components that are susceptible to breakdown and damage (except the implant body itself) to rapid removal and replacement by a fresh turret so that the PAD function is only momentarily disabled. 
     It is physiologically advantageous to use a PAD size consistent with sound implantation practices (minimal intrusion) and the ability to survive intact for long periods of time (conservative material mass). This severely limits the space and location available for a turret and requires the use of a small screw fastener at the bottom of the turret which must be accessed by a screwdriver working through the required air inlet passage which branches off just shy of the bottom. 
     It is desired to make the installation and lock down or removal of the turret as foolproof and rapid as possible, capable of accomplishment by a person of average skill. It is further desired to preclude a person from using tools or fasteners that are unsuitable. Further, it is desired to prevent a screwdriver of the wrong shape or size being applied to the screw head so that the drive slot or socket is damaged preventing removal of the turret. It is desired to prevent the fastener being overtorqued such that it is structurally compromised. It is desired to prevent the fastener prior to tightening, to shift in orientation or assume a position which makes the screwdriver engagement difficult or impossible. It is desired to prevent the wrong fastener being used which can jam into the threaded receiver of the PAD body and making turret removal very difficult. Further, it is desired to prevent excessive torque being applied to the fastener causing trauma to the PAD or skin interface. 
     A situation akin to the PAD example above, in which a turret or insert having a slenderness ratio of approximately 3 to 1 (length to diameter) or greater, is frequently encountered in mechanical and electromechanical assemblies. Oftentimes such a component is held into a base by means of a threaded fastener because it is only a threaded fastener that will provide great holding strength while occupying the smallest possible volume that makes lockdown of the part possible. Screws are also among the most economical of fasteners, are universally understood and are easily replaceable. 
     The installation and removal of such turrets is complicated by the difficulty of positioning the fastener drive tool so that it will engage the screw slot or drive socket. Visibility is usually very limited and may even be unattainable for deep turrets with small passages that access the screw, where the driver occupies most of the passage. Furthermore, the screw may be quite short in length and have a small head and not fall into the pilot diameter or clearance hole in the bottom of the turret. The turret may be a drawn can or a part with a thin bottom and simply having a clearance hole in lieu of any pilot hole. It can then become very difficult to probe for the fastener to get it to fall into place ready for driving. All this can become substantially more challenging if time is of the essence (a medical procedure), or if one is working upside down, for example, because the base (which could be a vehicle underside) cannot be strategically placed in a comfortable working position. 
     For these reasons, devices such as captive fasteners are sometimes used where the screw is disengaged from the base by turning but which cannot fall out of the turret clearance or pilot hole. The captive fastener is not an option for many assemblies due to considerations of space, cost and strength. These captive fasteners can still misalign because they are inherently free to mutate in the clearance hole. One common variant of such fastener devices involves relieving the threads adjacent to the head so that the screw may be threaded into a tapped hole in the bottom of the turret and fall into place and be captivated when the relief diameter is reached. This fastener scheme is limiting in application because it is usually desired to push the turret into the socket or housing prepared for it in the base so that it bottoms out and in some cases keys in place for the proper orientation. To accomplish this with a relieved screw requires that the screw be able to slide up into the turret so it does not interfere with seating or that it fit into a counterbore in the housing for the same reason. Both solutions mandate more depth of material and lead to increasing the overall size of the assembly. In the case of very tiny screws, i.e. No.  1  and smaller, thread relief becomes a difficult and expensive option because most screws are produced by thread rolling and will require post machining. 
     Yet another option is to push the turret into position and screw it down by holding the screw in a locking or magnetized (ferrous screws) driver. Such drivers frequently fail to hold the fastener properly leading to cross threading and possible thread damage which goes unnoticed and can lead to product failure or make removal a daunting task. The screw can also be dropped accidentally into the turret hole and may be very hard to remove (non-magnetic materials). 
     SUMMARY OF THE INVENTION 
     It is the intent of this invention to address the aforementioned problems and concerns. The invention is a screwdriver having a special drive end with a non-tamp screw head that is frictionally preassembled into a turret already in screw head engagement. Therefore, the screw, being a mating non-tamp type, is held in its full forward position against a shoulder to prevent shifting. The turret is positioned; and the screw is then tightened and torqued up to a preadjustable torque limit. The driver is then removed. When the screwdriver is reinserted to engage and untighten the screw, the torque limiting feature is locked out to compensate for possible increases in backout torque, thereby permitting screw disengagement while the screwdriver is held axially by friction and the screw itself remains correctly captivated in the turret. 
     In its simplest form, the present invention provides a driver for captively engaging a fastener for assembling a first part having a shoulder to a mating fitting having an aperture. The driver according to the present invention includes a shaft having a fastener-engaging end, and means for holding the fastener in a full-forward position against the shoulder of the first part during attachment of the fastener to the aperture of the mating fitting. The holding means operably engages between the shaft and the first part. 
    
    
     Other objects, advantages and applications of the present invention will become apparent to those skilled in the art when the following description of the best mode contemplated for practicing the invention is read in conjunction with the accompanying drawings. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The description herein makes reference to the accompanying drawings wherein like reference numerals refer to like parts throughout the several views, and wherein: 
     FIG. 1 is a schematic diagram illustrating the PAD device used in combination with an internally implanted device and an external monitoring/control device; 
     FIG. 2 is a schematic diagram illustrating a top view of the PAD with a removable turret and turret/screwdriver assembly; 
     FIG. 3 is a cross sectional view screwdriver disengaged from the turret; 
     FIG. 4 is a cross sectional view of the device taken on the lines  4 — 4  of FIG. 2 showing the screwdriver and screw assembled into the turret; 
     FIG. 5 is the turret and torque screwdriver assembly in the torque position; and 
     FIG. 6 is a schematic diagram illustrating a driver for engaging a fastener to assemble a first part with respect to a second part according to the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Looking at FIGS. 1-5, a percutaneous access device (PAD) generally comprises a housing  10  and a removable turret assembly  12 . As seen in FIG. 1, the housing  10  is implantable beneath the skin of a patient in any suitable manner. The PAD  10  provides fluid contact through the PAD  10  between an associated organ or device D and any external mechanisms or devices such as a pump P. The general type of PAD may be employed, for example, to supply a pneumatic connection and electrocardiogram lead connections to a dynamic aortic patch of the type disclosed in Kantrowitz et al, U.S. Pat. No. 4,051,840. The PAD and removable turret assembly disclosed herein is described in detail in Ser. No. 08/856,905, filed on May 15, 1997, the specification of which is incorporated by reference herein. Generally, the PAD includes a flange body  14  having a generally flat disk shape configuration and an upper wall contiguous with a neck  16  and a lower wall opposed to the upper wall and generally connected therewith. The housing  10  is implanted immediately below the dermal layer at the junction between the dermis and hypodermis. The flange body  14  defines a central interior chamber  18  including at least one fluid conveying channel which facilitates the transfer of fluids such as a gaseous or liquid material through the housing  10  and terminating in an aperture  22  which is capable of providing communication between the exterior of the flange body  14  and the fluid conveying channel in instances in which the PAD is employed with a dynamic aortic patch D. A suitable conduit  24  can be secured to the housing  10  at aperture  22  to provide communication between the corresponding fluid conveying channel in the flange body  14  and the associated device or organ D. The specific conduit  24  can convey gaseous material which controls the inflation and deflation of the associated aortic patch D. In FIG. 4, an auxiliary aperture  26  and associated channel are also provided. This auxiliary aperture  26  and channel can provide access for various electronic monitoring leads, electrical wires or the like i.e. for electrocardiogram monitoring leads, etc. Other apertures can be included in the flange body  14  as necessary. However, it is to be understood that the material conveyed through such conduits can be varied depending on the particular use desired for the PAD. Further, it is understood that the PAD is described as an illustration of a typical use for the screwdriver and turret assembly; but the invention is also beneficial for mechanical and electromechanical assemblies having similar structures. 
     The neck  16  of the housing  10  defines a hollow interior which communicates with a fluid channel defined in the flange body  14 . The hollow interior is accessible through an opening  18 . The hollow interior defined in the neck  16  is, preferably, essentially cylindrical and has a predefined internal diameter sufficient to receive the removable turret assembly  12 . 
     The removable turret assembly  12  is adapted to matingly fit within the hollow interior defined by the neck  16  of the housing  10 . The turret assembly  12  is removably fastened within the neck by suitable fastening means. The fastening means is preferably contained in the flange body  14  of the housing  10  and will be described in greater detail subsequently. 
     The turret assembly  12  includes means for providing electric communication through the housing in a manner which provides insulation of electrical current from communication and contact with body tissue surrounding the exterior of the housing  10 . The turret assembly  12  also includes means for providing fluid access in communication to the fluid conveying channel  24  in the flange body  14 . 
     The turret assembly  12  includes a turret body  30  configured to be received within the neck  16  of the housing  10 . The turret body has a central shaft  20  defining the fluid conveying channel which extends from the aperture  19  located in the upper outwardly facing surface  17  into the central region of the turret body  30 . The central shaft  20  is preferably positioned coaxially with the central longitudinal axis of the turret body  30 . The central shaft  20  terminates at a blind inner wall  34  located proximate to a lower surface of the exterior of the turret body  30 . The shaft  20  extends through to the blind inner wall  34  to matingly receive a screw  36  sealed with a sealer or a gasket (not shown). The screw  36  extends from the blind inner wall  34  through the shaft  20  and into threading engagement with suitable means for securing the turret body  30  into the PAD housing  10 . Access to the screw  36  is provided through the aperture  19  in the outwardly facing surface  17  and the associated central shaft  20 . This provides access to remove or replace the turret assembly as necessary. 
     The turret  12  nests in the PAD housing  10  so that it bottoms out against the surface of a key and the side branch outlet  22  of the turret  12  is aligned with the side branch outlet  24  of the PAD  10 . The key includes a configuration that allows the turret assembly  12  to be placed within the PAD housing  10  in only one unique direction. The key configuration should also include means to prevent the turret assembly  12  from shifting or otherwise moving once installed in the PAD housing  10 . In FIG. 5, the key configuration is shown as legs  48  of the turret positioned in complementary grooves  50  of the PAD housing  10 . 
     The screw  36  preferably has a unique configuration that includes a major head diameter  38  and a reduced head diameter  40  eccentric to the major head diameter  38 . This creates a customized non-tamp head  42  in which locking torque is transmitted to the head  42  by the known eccentric locking concept. This is only one example of the screw head  42  which may also utilize a special slot, socket or other configuration that does not permit standard screwdrivers, socket drivers or the like to be used. The screw  36  is not held into the turret body  30  by any restraining means and would fall out or shift position with respect to the orientation of the turret at this stage of the assembly. The screw  36  length is limited by the location of the auxiliary aperture  26  for the various electronic monitoring leads. As a result, the handling and removal of the screw  36  in the deep hole within the PAD housing  10  is more difficult. 
     FIG. 3 shows a view of a tool defining a screwdriver  46  for removal of the screw  36  before engagement into the turret  12 . The turret body  30  houses contacts, a current limiter, and an inlet/outlet port  19  for the screwdriver  46  and a branch outlet port for fluid communication to the PAD body. As stated supra, the turret body  30  may be configured to have opposing legs  48  extending from its bottom portion  49  for communicating with complementary grooves  50  located at the end of the central interior chamber  18  in the PAD body  10 . The legs and complementary groove configuration form the key to provide accurate installation of the turret body  30  into the PAD body  10 . The inlet/outlet port  19  in the upper outwardly facing surface  17  of the turret body  30  forms the channel  20  that extends through the center of turret body  30  and terminates at a centrally located threaded aperture  54 . The upper surface of the turret body at the inlet/outlet port  18  incorporates a spherical sealing surface  44  for reasons to be discussed further. 
     In the Figures, the screwdriver  46  is shown having a shaft  58  that is configured to matingly fit within the channel  20 . The shaft  58  of the screwdriver  46  has an eccentric drive socket  60  at its lower end to complement and receive the head  42  of the screw  36 . The shaft  58  of the tool or screwdriver  46  has a radially recessed area  62  on its length for receiving an O-ring  64 . Spaced above the recessed area  62  on the shaft  58  is a radial flange  70 . A handle  66  is secured at the upper portion of the screwdriver shaft  58  by a threaded locking collar  68 . The handle  66  rests on the radial flange  70  located on the shaft  58 . The handle  66  has a lower shoulder  72  that is positioned such that a slip washer  74  separates the handle shoulder  72  and the radial flange  70 . The locking collar  68  compresses a conical washer  78  which in turn places an axial load on a second slip washer  80 . The second slip washer  80  is positioned on an upper ledge  73  of the shoulder  72 . Therefore, the handle shoulder  72  is compressed between the two slip washers  74  and  80 . The washers  74  and  80  may be manufactured from a Delrin AF material or other similar plastic that has a static and dynamic coefficient of friction that have similar values so that breakout torque and slip torque are reasonably close in value. A roller clutch bearing  84  is located on the screwdriver shaft  58  between the two slip washers  74  and  80 . Bearing  84  is also disposed between the shaft  58  and an inner radial surface  76  of the shoulder  72  of the handle  66 . The locking collar  68  is preadjusted to a predetermined value to provide the proper seating torque to the screw  36  so that the handle  66  slips when this predetermined value is attained. The roller clutch  84  acts as a radial bearing member capable of free axial motion on the shaft  58  to compensate for wear on the slip washer faces. 
     The screwdriver tool  46  and turret  12  are supplied to the user for complete installation as a single unit. As a unit, the screw  36  has been bottomed out against a shoulder  86  in the blind inner wall  34  at the base of the turret assembly  12  and held in place by the engaged screwdriver shaft  58  within the turret, which is held in place by the O-ring  64 . 
     Looking at FIG. 5, during installation the screwdriver  46  and turret assembly  12  are together pushed into the interior chamber  18  of the PAD housing  10  wherein the opposing legs  48  at the base  49  of the turret engages within the complementary groove  50  of the PAD  10  for a key engagement to provide correct alignment. The complementary groove  50  of the PAD  10  forms an upwardly facing surface  88  therebetween. When the screwdriver  46  and turret assembly  12  are inserted into the body of the PAD  10 , the upwardly facing surface  88  pushes the screwdriver  46  and the screw  36  back a distance that is equal to the screw projection beyond the blind inner wall  34  in the base  49  of the turret assembly  12  so that the lower surface  90  of screw  36  portion is flush with the blind inner wall  34  of the turret keyway feature. This position of the screw  36  within the turret is shown in FIG.  5 . The screwdriver  46  and screw  36  are held in position within the turret by the friction of the O-ring  64  against the interior fluid channel  20  of the turret assembly  12 . The position of screw  36  is controlled by the drive socket  60 , the turret pilot aperture  54 , and the key surface configuration. 
     As positioned in FIG. 5, the screw  36  is ready for engagement into the PAD housing  10  by an axial thrust and clockwise rotation of the screwdriver  46 . This rotational movement and thrust on the screwdriver  46  overcomes the prevailing O-ring  64  friction so that the screw  36  may be threadingly secured to the PAD housing  10  via the threaded aperture  54 . When maximum torque is achieved, the handle  66  rotates with respect to shaft  58  by “slipping” along slip washers  74  and  80  to prevent overtorqueing. When the screw  36  is secured to the PAD housing  10 , the screwdriver  46  may then be removed from the turret  12 . 
     To later remove the turret, the screwdriver  46  enters the central bore or channel  20  of the turret assembly  12  and engages the screw  36  therein. The eccentric drive socket  60  of the screwdriver  46  encloses over the non-tamp head  42  of screw  36  so that axial thrust in a counterclockwise rotation of the screwdriver  46  unthreads the screw  36  in the turret assembly  12 . The clutch bearing  84  “locks” the handle  66  to the shaft  58  in the counterclockwise direction to permit application of torque greater than the predetermined value to remove the screw  36 . Once the screw  36  is unthreaded from threaded slot  54 , the entire screwdriver  46  and turret assembly  12  can then be removed from the PAD  10  by pulling on the spherical sealing surface  44  of the turret assembly  12 . 
     Referring now to FIG. 6, it is believed that the present invention has numerous applications in addition to the medical example described in detail above. The present invention provides a driver  100  for captively engaging a fastener  102  for assembling a first part  104 , having a shoulder  106  to a mating fitting  108 , having an aperture  110 . The driver  100  can include a shaft  112 , having a fastener engaging end  114 . The fastener-engaging end  114  of the shaft  112  can include any type of configuration complementary to the head of the fastener. By way of example and not limitation, the fastener-engaging end  114  can take the form of a flat blade screwdriver, Phillips head screwdriver, star screwdriver, Alan wrench driver, hex-head socket, or any other custom or standard configuration. The opposite end  116  of the shaft  112  from the fastener-engaging end  114  can include a handle (seen in FIGS.  4  and  5 ), or other standard handle configuration, or can include a head  118  for engagement by another manual or powered driver. If the opposite end  116  includes a head  118  for engagement by another driver, the head  118  can be in any standard or custom configuration desired for the particular application. By way of example and not limitation, the head  118  can be in the form of a flat blade screwdriver receiving head, a Philips screwdriver receiving head, an Alan wrench receiving head, a hex-head, a star tool receiving head, or any other standard or custom configuration desired. 
     Means  120  is provided for holding the fastener  102  in a full forward position against the shoulder  106  of the first part  104  during attachment of the fastener  102  to the aperture  110  of the mating fitting  108 . The holding means  120  is operably engageable between the shaft  112  and the first part  104 . Preferably, the holding means  120  captively retains the fastener  102  with respect to the first part  104  during an assembly process for connecting the first part  104  to the mating fitting  108 . After the assembly process is complete, the driver  100  can be removed from the first part  104 . If disassembly of the first part  104  from the mating fitting  108  is required, the driver  100  can be re-engaged with respect to the first part  104  to captively retain the fastener  102  with respect to the first part  104  during the disassembly process. In the preferred configuration illustrated in FIG. 6, the holding means  120  can include an O-ring  122 , frictionally engaging a wall  124  of the first part  104 . Preferably, the O-ring  122  is engaged on the shaft  112  and retained within a groove  126  formed in the shaft  112 . The O-ring  122  advantageously holds the driver  100  and fastener  102  in a predetermined relationship with one another with respect to the first part  104  and resist unintentional removal of the driver  100  and/or fastener  102  from the first part  104 . The O-ring  122  permits the driver  100  to be driven rotatably to engage and/or disengage the fastener  102  with respect to the aperture  110  of the mating fitting  108 . In addition, the O-ring  122  permits the driver  100  to move with respect to the first part  104  when removal of the driver  100  is desired, and/or to re-engage the driver  100  with the first part  104  in order to disassemble the fastener  102  with respect to the aperture  110  and the mating fitting  108 . 
     The driver  100  can include a handle connected to the shaft  112 . The handle can include means for adjusting the maximum torque transmittable from the handle to the fastener  102 . As previously illustrated and described with respect to FIGS. 4 and 5, the adjusting means can include a conical washer disposed between a threaded locking collar and a first slip washer set on a shoulder of the handle. The adjusting means can also include a roller clutch bearing disposed on the shaft, and a second slip washer engaging an annular flange on the shaft, such that the roller clutch bearing is positioned between the first and second slip washers, similar to that shown in FIGS. 4 and 5. With a handle similar to that shown in FIGS. 4 and 5, the driver according to the present invention can include means for rotating the shaft  112  with the handle up to a predetermined torque during attachment of the fastener  102  and for locking the handle with respect to the shaft  112  during reverse rotation of the shaft  112  when detaching the fastener  102 . The rotating and locking means can include a roller clutch bearing disposed between a portion of the handle and a portion of the shaft. If the shaft  112  is provided with a handle similar to that illustrated in FIGS. 4 and 5, the handle can have an inwardly facing shoulder portion with a first surface and a second surface, where a first slip washer is engageable with the first surface and a second slip washer is disposed between the second surface and a radially outwardly extending flange of the shaft, as can be seen in FIGS. 4 and 5. Preferably, the first and second slip washers are constructed of materials having similar static and dynamic coefficient of friction values. If the shaft  112  is provided with a handle similar to that illustrated in FIGS. 4 and 5, adjustable means can be provided for selectively setting a predetermined seating torque to be applied to the fastener during an assembly process. 
     While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiments but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims, which scope is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures as is permitted under the law.