Patent Publication Number: US-2010107829-A1

Title: Torque limiting driver

Description:
RELATED APPLICATION 
     The present application claims the benefit of U.S. Provisional Patent Application Ser. No. 61/109,539, filed on Oct. 30, 2008, the entire disclosure of which is hereby incorporated by reference. 
    
    
     TECHNICAL FIELD 
     The present invention relates generally to drivers that apply up to a predetermined torque to a device, such as a screw or bolt. 
     BACKGROUND 
     There are many torque limiting devices in the marketplace today, including the medical and automotive industries. Torque limiting wrenches, for example, are used in many different applications to adjust various components including, but not limited to, bolts and fasteners to a specified torque. Such a device can be important to prevent over-torquing. 
     Torque limiting wrenches used with medical devices are designed to be used multiple times, with re-sterilization after each use. The sterilization process subjects the wrench&#39;s components to increased wear and tear. Moreover, re-sterilization causes the accuracy of the device to decrease; thus, hospitals (and other health care providers) continually send instruments to manufacturers for recalibration. 
     Therefore, there is a need for a novel torque limiting device that overcomes these issues. 
     SUMMARY 
     According to one aspect, the invention provides a torque limiting driver for applying up to a maximum torque to an associated driven member. In one embodiment, the driver includes first and second rotatable members with proximal and distal ends. A torque limiting assembly may be operatively coupling the distal end of the first rotatable member with the proximal end of the second rotatable member. The torque limiting assembly may include a plurality of torque limiting devices that are arranged to sequentially uncouple the second rotatable member from a torque load applied to the first rotatable member when the torque load exceeds the preselected maximum torque. 
     In some embodiments, the proximal end of the first rotatable member and/or the distal end of the second rotatable member includes a quick connect fastening portion. For example, the quick connect fastening portion could include an opening dimensioned to receive an external device. In some cases, an interference member could be disposed within the opening to frictionally engage the external device. Embodiments are contemplated in which the torque limiting assembly could include a frangible member that is configured to release the second rotatable member from a torque load applied to the first rotatable member when the torque load exceeds the preselected maximum torque. For example, the frangible member could be a shear pin. 
     According to another aspect, the invention provides a method for driving a device in a torque limited manner. The method includes the step of providing a torque limiting driver having a torque limiting assembly operatively coupling a first rotatable member with a second rotatable member. The torque limiting assembly could include a frangible portion that is configured to shear when a preselected maximum torque is applied to the first rotatable member. Another step could be applying a torque load to the first rotatable member. In response to the torque load on the first rotatable member exceeding the preselected maximum torque, the method includes the step of releasing the second rotatable member from the torque load applied to the first rotatable member by breaking the frangible member. 
     According to a further aspect, the invention provides a kit for use by a health care provider. In this embodiment, the kit includes at least one medical device. A single-use torque limiting driver is also provided that has an end adapted to be coupled with the medical device. Typically, the single-use torque limiting driver is capable of transferring torque to the medical device up to a preselected maximum torque. For purposes of example only, the health care provider could drive the single-use torque limiting device up to the maximum torque a certain number of times during a medical procedure and then dispose of the single-use torque limiting driver. 
     Additional features and advantages of the invention will become apparent to those skilled in the art upon consideration of the following detailed description of the illustrated embodiment exemplifying the best mode of carrying out the invention as presently perceived. It is intended that all such additional features and advantages be included within this description and be within the scope of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present disclosure will be described hereafter with reference to the attached drawings which are given as non-limiting examples only, in which: 
         FIG. 1  is an exploded view of an example torque limiting driver according to an embodiment to the invention; 
         FIG. 2  is a side view of the example torque limiting driver shown in  FIG. 1 ; 
         FIG. 3  is a side cross-sectional view of the example torque limiting driver shown in  FIG. 1  along line A-A; 
         FIG. 4  is a perspective view of an example housing for the torque limiting driver according to an embodiment of the invention; 
         FIGS. 5 and 6  are side cross-sectional views of the example housing shown in 
         FIG. 4 ; 
         FIG. 7  is a partially-exploded perspective view of the example torque limiting driver shown in  FIG. 1  showing the housing exploded; 
         FIG. 8  is a perspective view of the example torque limiting driver shown in  FIG. 1  with the housing removed and the first rotatable member separated from the second rotatable member; 
         FIG. 9  illustrates a possible step during assembly of the torque limiting driver according to an embodiment of the invention; 
         FIG. 10  is a side cross-sectional view of an example quick connection prior to coupling according to an embodiment of the invention; 
         FIG. 11  is a side cross-sectional view of the example quick connection shown in 
         FIG. 10  after coupling; 
         FIG. 12  is a front cross-sectional view of the example quick connection shown in  FIG. 11 ; and 
         FIG. 13  is a side cross-sectional view of an example quick connection according to an alternative embodiment of the invention. 
     
    
    
     Corresponding reference characters indicate corresponding parts throughout the several views. The components in the figures are not necessarily to scale, emphasis instead being placed upon illustrating the principals of the invention. The exemplification set out herein illustrates embodiments of the invention, and such exemplification is not to be construed as limiting the scope of the invention in any manner. 
     DETAILED DESCRIPTION OF THE DRAWINGS 
     While the concepts of the present disclosure are susceptible to various modifications and alternative forms, specific exemplary embodiments thereof have been shown by way of example in the drawings and will herein be described in detail. It should be understood, however, that there is no intent to limit the concepts of the present disclosure to the particular forms disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the disclosure. 
       FIG. 1  shows a torque limiting driver, generally referred to by reference number  10 , constructed according to an embodiment of the present invention. While the torque limiting driver  10  will be discussed below in tell is of torquing medical devices, such as bone screws, it should be appreciated that the torque limiting driver  10  could be used in other contexts. The torque limiting driver  10  shown in  FIG. 1  includes an input assembly comprising an input member  12 , a plurality of shear pins  14 , a set screw  16 , and a pin retaining member  18 . The input assembly operatively couples with an output member  20 . As shown, a housing assembly comprises a first housing member  22  and a second housing member  24  surrounding a portion of the input assembly and the output member  20 . 
     In the embodiment shown, referring now to  FIGS. 1-3 , the input member  12  includes a first end  26  and a second end  28 . As shown, the first end  26  includes a fastener portion  30  adapted to releasably attach a medical instrument, such as a handle. Embodiments are contemplated in which a variety of connection types and styles could be used for the fastener portion  30 , including but not limited to a male-type fastener, a female-type fastener, a square connection, and/or an AO style connection. Typically, the fastener portion  30  would be a quick connect, including but not limited to, the embodiments shown in  FIGS. 10-13  and discussed below. An input shaft  32  extends between the fastener portion  30  and a shoulder portion  34 . As shown, the input shaft  32  is dimensioned to be received by a top opening  36  in the housing assembly. The shoulder portion  34  is dimensioned to be received within a cavity  38  defined by the housing assembly. 
     As shown, the second end  28  of the input member  12  terminates with a fastener  40  ( FIG. 3 ) for coupling the second end  28  of the input member  12  with the pin retaining member  18 . In the embodiment shown, the fastener  40  includes external threads  42  ( FIG. 3 ) that are received by internal threads  43  in the pin retaining member  18 . Although a threaded connection is shown for purposes of example, it should be appreciated that the input member  12  could be coupled with the pin retaining member  18  in other manners, such as an interference or frictional fit. 
     In the example shown, a plurality of shear pins  14  are disposed in the pin retaining member  18 . Although this example shows six shear pins  14  for purposes of example, there could be less shear pins  14  or more shear pins  14 . The number of shear pins  14  could be chosen depending on the number of times that the torque limiting driver  10  is configured to reach its maximum torque. As discussed below, a single shear pin  14  shears each time the torque limiting driver reaches the maximum torque in one embodiment. Consider a medical procedure in which six bone screws were intended to be used. In this embodiment, a shear pin  14  would shear each time a bone screw is screwed into the maximum torque. At the end of this example procedure with six bone screws, each of the shear pins  14  would have sheared. Accordingly, after each shear pin  14  has sheared, the torque limiting driver  10  could be disposed of, which would eliminate the need for re-sterilization and recalibration of the torque limiting driver  10 . Alternatively, embodiments are contemplated in which a new set of shear pins  14  could be loaded into the pin retaining member  18 . For example, pins could be loaded similar to a revolver. Rotate the revolver and load one pin, break pin, and then rotate revolver to load a new pin. Other embodiments contemplate shear pins extending radially from circumferential slots into another structure that shears the pins upon reaching the desired torque. Embodiments are also contemplated in which other devices could be used to sequentially release a torque load between the input assembly and the output member without shearing any pins, including teeth and magnets. 
     As shown, the shear pins  14  include a head portion  44  and a pin portion  46 . In this embodiment the head portion  44  is sized to be substantially tightly-fit between the second end  28  of the input member  12  and an interior surface  48  of the pin retaining member  18  (as best seen in  FIG. 3 ). Each of the pin portions  46  are received in respective holes  50  in the pin retaining member  18 . In one embodiment, the edges of the holes  50  are chamfered to aid in the shearing process. The head portions  44  are sized to prevent the shear pins from falling through the holes  50 . 
     As best seen in  FIG. 3 , the pin portions  46  extend into respective slots  52  defined in the output member  20 . As discussed below, the slots  52  are configured to sequentially shear a shear pin  14  each time the maximum torque is reached. The maximum torque could be based upon (among other things) the diameter of the pin, the distance of the pin from the central axis, and the depth of the clearance groove at the site of the pin. In the embodiment shown, the slots  52  are arcuately shaped. The length of the slots  52  are progressively longer so that only a single shear pin  14  is sheared each time the maximum torque is exceeded. Typically, the slots  52  are dimensioned to hold sheared portions of the shear pins  14 . For example, the slots could have sufficient depth to receive the sheared portion of the pin. Typically, the slots would be wide enough to prevent drag on the sides of the slots with the pins. In some cases, the slots  52  could be associated with one or more magnets to retain the pin fragments within the slots  52 . Although the slots are arranged for clockwise movement in the example shown, it should be appreciated the torque limiting driver  10  could be configured to drive in a counterclockwise direction. Embodiments are contemplated in which the pins  14  could extend approximately perpendicularly to the axis of rotation. In such an embodiment, for example, the pins could extend into slots in the circumferial wall of the pin retaining member  18 . 
     Other embodiments are contemplated for limiting the maximum torque for the torque limiting driver  10 . For example, a single pin (longer than those shown in the drawings) could be spring loaded within the input assembly. Once the housing assembly is fit together, then the input member  12  would be rotated until the pin snapped into a bottom hole in the output member  20 . The pin would be sheared, thus resulting in a pre-selected amount of torque. The input member  12  could be rotated until the pin drops into another hole and then the pin would be sheared again upon reaching the maximum torque. This procedure would be repeated using up the remainder of the pin and filling all holes with pin fragments. The breaking of the pin would be accomplished by a consistent force which would be dependent on pin geometry and diameter of rotation among other factors. 
     In another embodiment, the maximum torque could be established using the pull of magnets to determine a constant force. Breaking of magnetism would be accomplished at a consistent torque. For example, different size of magnets could be used depending on what torque needs to be accomplished. 
     In another embodiment, teeth similar to a ratchet-like device could be used to establish the maximum torque. For example, it would take a certain amount of torque to get up the incline of the teeth, thus resulting in a consistent torque. The teeth could be made in either direction and there would be no clockwise turning and then inadvertent counterclockwise turning in the process. In another embodiment, the gear teeth could be vertical with a pin backed by a spring and set screw (or all of this could be in the form of a ball plunger) to create a variable piece that engages the teeth. The torque could be adjusted by tweaking the spring via the set screw. 
     Referring again to  FIGS. 1-3 , the pin retaining member  18  includes a central hole  54  that is dimensioned to receive a finger member  56 . In the embodiment shown, the input assembly rotates about the finger member  56 . Due to the shear pins  14  extending into the slots  52 , torque is applied to a shear pin  14  until it shears when the maximum torque is reached. The opposing end of the output member  20  includes a fastening portion  58 . As shown, the fastening portion  58  is adapted to releasably attach a medical instrument. Embodiments are contemplated in which a variety of connection types and styles could be used for the fastening portion  58 , including but not limited to a male-type fastener, female-type fastener, a square connection, and/or an AO style connection. Typically, the fastening portion  58  would be a quick connect, including but not limited to the embodiments shown in  FIGS. 10-13  and discussed below. 
     In the embodiment shown, the housing assembly is a clam-shell style design. In some embodiments, the housing assembly could be formed from plastic or metal (such as stainless steel). As shown, the first housing member includes hooks  60  that are received in slots (not shown) in the second housing member  24 .  FIGS. 4-6  show an alternative embodiment for the housing assembly. In the embodiment shown, a first member  62  is received by a second member  64 . Typically, this would be a press fit arrangement. 
       FIG. 9  shows an embodiment in which a removable strip  66  could be used to maintain a specific gap between internal components of the torque limiting driver  10  during assembly. For example, it may be advantageous to maintain a specific gap between the housing assembly and input member or output member during assembly. Once assembled, the strip  66  could be removed. An embodiment is also contemplated in which a dissolvable member could be used to maintain a gap between internal components in the torque limiting driver  10 . In such an embodiment, the torque limiting driver  10  could be submerged in a fluid, such as alcohol, that would dissolve the dissolvable member. 
       FIGS. 10-12  show an embodiment of a quick connect mechanism  68  which could be used in the torque limiting driver  10 . It should be appreciated by one skilled in the art that the quick connect mechanism  68  could be used in devices other than the torque limiting driver  10 . The discussion of the quick connect mechanism  68  herein in regards to its application on the torque limiting driver  10  is for example purposes only. In the embodiment shown, the quick connect mechanism  68  comprises a female connection  70 , a male connection  72  and an interference device  74 . In the embodiment shown, the female member  70  includes a cavity  76  that is dimensioned to receive an extension portion  78  on the male connection  72 . A circumferential groove  80  is defined in the cavity  76  to hold the interference device  74 . The groove  80  maintains a fixed lateral position of the interference device  74  and has a depth so that at least a portion of the interference device  74  is exposed within the cavity  76 . A groove  82  is defined in the extension portion  78  to approximately correspond with the depth of the circumferential groove  80  within the cavity  76 . This allows the groove  82  to receive the exposed portion of the interference device  74 , which tends to maintain the locked position of the male connection  72  due to frictional resistance between the interference device  74  and the groove  82  on the extension portion  78 . The interference device  74  could be a spring, o-ring or other resilient member that could provide functional interference to releasably lock the members  70  and  72 . This frictional resistance can be overcome by pulling on the male connection  72  to unlock the male connection  72 . As best seen in  FIG. 11 , the depth of the circumferential groove  80  and the groove  82  could be varied to vary the amount of force needed to insert/remove the male connection  72 . Likewise, the depth could be configured to adjust the axial movement between the female connection  70  and the male connection  72 . In other words, the interference device  74  could be configured to limit rotation between the female connection  70  and the male connection  72 . For example, as seen in  FIG. 12 , the area of friction between the female connection  70  and the male connection  72  could be used to adjust the maximum torque that could be transferred between the female connection  70  and the male connection  72 . Embodiments are contemplated in which ridges could be provided on groove  82  and circumferential groove  80  to set the force needed to rotate the female connection  70  with respect to the male connection  72 . 
     An embodiment shown in  FIG. 13  includes a male connection  72  without a groove. Instead a leading portion  84  is tapered to frictionally engage a tapered portion  86  of the female member  70 . The biasing member  74  and an adjustable sleeve provide frictional areas to maintain a connection between the male member  72  and female member  70 . In this embodiment, threads  88  are provided to linearly adjust the sleeve  90 , which adjusts the amount of force that is needed to insert/withdraw the male member  72 . Likewise, this adjustable area of friction could be used to adjust the torque that could be transferred between the members  70  and  72 . 
     Consider an example operation of the torque limiting driver  10  during a surgery in which six bone screws are intended to be secured at a predetermined torque. The surgeon could receive a kit with six bone screws, along with the torque limiting driver  10  configured with a preselected torque for the bore screws to be used during the surgery. In this example with six bore screws to be attached, the torque limiting driver  10  could include six shear pins  14 . The surgeon would typically attach a medical instrument to the fastener portion  30 , such as a handle. As discussed above, this could be with the use of the quick connect mechanism described with respect to  FIGS. 10-13 . On the opposing end, the surgeon would place a bone screw. In order to attach the bone screw, the surgeon would torque the input member  12 , which would transfer torque to the output member  20 , thereby driving the bone screw. When the maximum torque has been reached, the shear pin  14  would shear in the embodiment shown, which would prevent the bone screw from being over-torqued. The surgeon would feel the resistance decrease due to the shearing of the shear pin  14  and would, therefore, know that the maximum torque had been reached for that bone screw. Additionally, the surgeon would likely hear the shearing of the shear pin  14  which would provide an audible feedback indicator that the maximum torque has been reached. The surgeon would then place another bone screw on the torque limiting driver  10 . The process would continue until the surgeon has attached all the bone screws or until each shear pin  14  has been sheared. 
     Although the present disclosure has been described with reference to particular means, materials, and embodiments, from the foregoing description, one skilled in the art can easily ascertain the essential characteristics of the invention and various changes and modifications may be made to adapt the various uses and characteristics without departing from the spirit and scope of the invention.