Abstract:
A tool for driving a workpiece during surgical procedures has a handle. A gear with teeth thereon is rotatably supported along an axis within the handle. Two pawls are pivotally supported by the handle adjacent the gear and are orbital about the axis upon rotation of the handle. Each pawl has teeth that engage the gear teeth to transmit torque from the handle to the workpiece. Two springs yieldingly urge the pawls into engagement the gear teeth. A cap, with an actuator thereon, is rotatable with respect to handle. The cap has a first position in which the actuator retracts the first pawl out of engagement with the gear teeth, a second position in which the actuator retracts the second pawl out of engagement with the gear teeth, and a third position in which neither the first pawl nor the second pawl is retracted by the actuator.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    Not Applicable 
       STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
       [0002]    Not Applicable 
       BACKGROUND OF THE INVENTION 
       [0003]    1. Field of the Invention 
         [0004]    The present invention relates to ratcheting surgical instruments, such as those for fastening screws or bolts, and more particularly, to such instruments which can be set to ratchet in either of two rotational directions or locked into a non-ratcheting state. 
         [0005]    2. Description of the Related Art 
         [0006]    Ratcheting drivers are commonly employed to apply fasteners, such as screws, bolts and the like. One type of ratcheting driver has a handle shaped like that of a conventional fixed blade screwdriver. However, the working end of the handle contains an actuator that maneuvers a gear and pawl assembly to selectively enable the handle to rotate the gear in either direction while allowing ratcheting in the opposite direction. A tool bit, such as a screwdriver blade or fastener socket, is attached to the gear and is driven by the handle motion. 
         [0007]    In using a ratcheting driver, torque is applied by the user&#39;s hand to the handle and then via the pawl to the gear. The torque is transferred further to the tool bit which engages a workpiece, such as a screw, nut, or bolt. It is important to have the assembly arranged for optimum transmission of the applied hand torque in a reliable and consistent manner. That achievement is dependent on the construction, mounting, and location of the pawls. 
         [0008]    Ratcheting drivers of this type are used as surgical instrument for orthopedic operations and other procedures. For example, a surgeon uses a ratcheting instrument to insert screws into bones to fasten plates to the skeleton of the patient. Surgical instruments have special requirements that common tools do not have to meet. Such instruments must be capable of withstanding high sterilizing temperatures of an autoclave. Any lubricants must be approved by the Food and Drug Administration of the United States Government if the surgical instrument is to be used in that country. Ratcheting driver also must be very durable as its failure during surgery may have serious consequences. 
       SUMMARY OF THE INVENTION 
       [0009]    A ratcheting surgical instrument has a handle to which a ratchet housing is fixedly attached. A gear is rotatably located within the housing and a tool bit is operably connected to the gear. A first pawl is pivotally disposed in the housing and selectively engages the gear to enable the handle to drive the gear and the tool bit only in a first direction. A second pawl also is pivotally disposed within the housing and selectively engages the gear to enable the handle to drive the gear and the tool bit only in a second direction. In a preferred embodiment of the surgical instrument, each pawl has a plurality of teeth that mesh with teeth of the gear to reliably transfer of torque between those components. Preferably, separate compression springs bias the first and second pawls with respect to the housing and toward engagement with the gear. 
         [0010]    An actuator selectively retracts the first pawl away from engagement with the gear and retracts the second pawl away from engagement with the gear. In a preferred embodiment, the actuator is attached to a cap that can be rotated into different positions with respect to the housing. In a first position of the cap, actuator retracts the first pawl out of engagement with the teeth of the gear, in a second position the actuator retracts the second pawl out of engagement with the teeth of the gear, and in a third position neither the first pawl nor the second pawl is retracted by the actuator. 
         [0011]    In the preferred construction of the surgical instrument, the housing is secured to a metal core and the handle is formed by a plastic, preferably an elastomer and in particular silicone rubber, that is molded around the core and the housing. In addition, the tool bit has a shaft that extends through a bore in the gear and the shaft has an end section onto which a nut is threaded. At least a portion of the bore in the gear has a non-circular cross section and the tool bit has a segment that mates with that non-circular cross section to rotationally lock the tool bit to the gear. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]      FIG. 1  is a side view of a ratcheting surgical instrument according to the present invention; 
           [0013]      FIG. 2  is a longitudinal cross sectional view along line  2 - 2  in  FIG. 1 ; 
           [0014]      FIG. 3  is an enlarged view of a drive assembly in  FIG. 2 ; 
           [0015]      FIG. 4  is an exploded view of the surgical instrument; 
           [0016]      FIG. 5  is an isometric view of a cap of the surgical instrument; 
           [0017]      FIG. 6  is a cross sectional view along line  6 - 6  in  FIG. 1 ; and 
           [0018]      FIG. 7  is a longitudinal cross sectional view along line  7 - 7  in  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0019]    With initial reference to  FIG. 1 , a ratcheting surgical instrument  10  has a handle  12  with a working end  14  to which a gear and pawl assembly  16  is attached. A tool bit  18  is inserted into the gear and pawl assembly and may comprise a socket for a nut or bolt, a blade to engage a screw, or other type of tool for engaging a workpiece. 
         [0020]    As shown in  FIG. 2 , the handle  12  comprises a tubular metal core  20  and an outer grip  22  of plastic, that preferably is an elastomer and in particular silicone rubber. A ratchet housing  24  also is part of the handle  12  and is threaded into an open end of the core  20  and extends partially outward from the working end  14  of the handle. The ratchet housing  24  and core  20  are assembled and placed within a mold, so that the plastic grip  22  then is over-molded around the core and housing. This secures the interior handle components within the grip  22 . The outer surface of the core  20  is not round or at least that surface has depressions into which the grip material penetrates during molding to lock the core and grip together. Therefore when torque is applied to the handle  12 , the grip  22  cannot rotate about the core  20 . 
         [0021]    The opposite end  26  of the grip  22  that is remote from the working end  14  has an aperture  28  there through that opens into the central bore  30  extending along an axis  31  through the core  20 . This aperture  28  enables a guide wire and the like to pass through the surgical instrument  10  to the work site in the patient. 
         [0022]    The remaining components are then assembled onto the molded handle  12 . With reference to  FIGS. 3 and 4 , a gear  32  is inserted through the central aperture of the housing  24  and extends into an enlarged portion of the bore  30  in the core  20 . The gear  32  is a tube with a center section having a plurality of teeth  34  that project outwardly from the exterior circumferential surface. One end of the gear  32  fits through a center aperture  36  in a cap  38 . The cap  38  is rotatably attached to the open end of the housing  24  being interlocked thereon. The cap is able to rotate on the housing partially around the smooth end portion of the gear  32 . The tool bit  18  has a shaft  40  extending into a central bore  33  in the gear  32  and projects out of the interior end of the gear. A section of the tool bit shaft  40  near its interior end has a square cross section  41  that mates with a similarly shaped cross section  37  of the bore in the gear  32  and shown in  FIG. 3 . That mating rotationally locks the gear onto the shaft  40 . A nut  42  is threaded onto the interior end of the tool bit shaft  40  and bonded thereto by a commercially available thread locking adhesive, thereby securing the tool bit  18  to the gear and pawl assembly  16 . 
         [0023]    With reference to  FIGS. 3 and 6 , the housing  24  has a blind aperture  44  within which a detent  46 , in the form of a plunger, is slideably received and biased outwardly therefrom a helical compression spring  48 . The exterior end of the detent  46  has a hemispherical surface that successively nests into three hemispherical depressions  51 ,  52  and  53  in the interior surface of the cap  38 , which depressions are shown in  FIG. 5 . As will be described, the detent  46  slides into one of these depressions  51 - 53  in each of three different rotational positions of the cap  38  about the end of the handle  12 . Such engagement releasably holds the cap in the respective rotational position which places the ratcheting gear and pawl assembly  16  into one of three operating states, as will be described. 
         [0024]    The gear and pawl assembly  16  further includes a pair of oppositely arranged pawls  54  and  55  that are received within grooves  56  and  57 , respectively, within the housing  24 . Each pawl  54  and  55  has a dog-leg shape with a rounded first end  58  that is pivotally received within the curved groove  56  or  57  in the housing. An arm  60  projects from the curved end  58  and out of the groove  56  into a cavity  62  within the housing  24 . Each pawl has a plurality of teeth  64  that selectively engage the teeth  34  of the gear  32 . The plurality of teeth  64  on each pawl  54  and  55  provide a secure engagement over a relatively large surface area between the respective pawl and the gear  32 . Each pawl has an aperture  59  in its outward facing surface within which one end of a pawl spring  66  is received. The other end of the pawl spring  66  is received within a cap-like, hemispherical plunger  68  that engages a wall of the housing cavity  62 . The pawl spring  66  biases the respective pawl  54  or  55  toward engagement with the teeth  34  of gear  32 . As seen in  FIG. 5 , a pawl actuator  70  project from the interior surface  50  of the cap  38  and into the housing cavity  62  as illustrated in  FIG. 6 . The pawl actuator  70  has a generally truncated triangular shape. 
         [0025]    In a first rotational position of the cap  38  shown in  FIG. 6 , the pawl actuator  70  engages and pivots the first pawl  54  away from engagement with the teeth  34  of the gear  32 . In a second rotational position of the cap  38  the pawl actuator  70  pushes the second pawl  55  away from the gear teeth  34 . In a third cap position which is in between the first and second positions, the pawl actuator  70  does not engage either of the pawls  54  or  55  and therefor both pawls engage the teeth  34  of the gear  32  in response to the bias force of their respective pawl spring  66 . 
         [0026]    The user of the surgical instrument  10  selects the desired direction of ratchet motion by rotating the cap  38  about the handle  12  into one of the three detent positions. The first position at one extreme of the cap rotation shown in  FIGS. 6 and 7  is used to loosen a fastener, such as a bolt, that is held by the tool bit  18 . In this cap position, the pawl actuator  70  pushes the first pawl  54  away from engagement with the gear  32 , so that only the second pawl  55  now engages the teeth  34  of that gear. When the user applies torque to the handle  12  in the clockwise direction  FIGS. 6 and 7 , the handle provides additional force that causes the teeth  64  second pawl  55  into mesh with the gear teeth  34  and the second pawl cannot to ride out of engagement with the gear  32 . Thus application of this torque to the handle  12  rotates the gear  32  and the tool bit  18  secured thereto. However in this state, rotation of the handle in the counterclockwise direction in  FIG. 6 , allows the second pawl  55  to pivot within the housing  24  so that its teeth ride into and out of the teeth of the gear  32 . Now the pawls  54  and  55  orbit about the axis of the handle without applying torque to the gear and tool bit  18 . Thus rotation of the handle in this direction allows ratcheting of the surgical instrument  10  and the gear  32  and the tool bit  18  do not drive the fastener. 
         [0027]    The hemispherical plunger  68  enables an end of the pawl spring  66  to pivot with respect to the wall of the housing cavity  62  as the associated pawl  54  or  55  ratchets over the gear teeth  34 . This avoids the pawl spring from binding or bending during the ratcheting which could impede the operation of the surgical instrument  10 . The spring pivoting enabled by the plunger  68  also facilitates the retraction and engagement of each pawl  54  and  55  with respect to the gear  32  in response to rotation of the cap  38 . 
         [0028]    To tighten a fastener, the cap  38  placed into the second position, which is at the opposite end of the cap rotation with respect to the first position shown in  FIGS. 6 and 7 . In this position, the pawl actuator  70  retracts the second pawl  55  away from the gear  32 . At the same time, the first pawl  54  is forced into engagement with the gear  32  by its pawl spring  66 . Thus the state of the gear and pawl assembly  16  is now reversed so that the handle  12  can be rotated in a direction that tightens the fastener engaged by the tool bit  18 . In other words, when counterclockwise torque is applied to the handle  12 , the first pawl  54  transfers that torque to the gear  32  and the tool bit  18 . In this state the teeth  64  of the first pawl  54  are unable to move out of engagement with the gear teeth  34 . However, when clockwise torque is applied to the handle  12  in the orientation of components in  FIG. 6 , the first pawl  54  pivots within its housing groove  57  slipping over the teeth of gear  32  thereby allowing free rotation of the handle without producing movement of the tool bit  18 . 
         [0029]    When the cap  38  is rotated by the user into the center, or third position, the pawl actuator  70  is located between the two pawls  54  and  55  without engaging either pawl. Thus both the first and second pawls  54  and  55  are biased by their respective springs  66  into engagement with the teeth of the gear  32 . In this dual pawl engaging position, the first pawl  54  prevents the handle  12  from ratcheting when rotated in the counterclockwise direction and the second pawl  55  prevents the handle from ratcheting when rotated in the clockwise direction. Thus, the handle is now locked to the gear in both rotational directions. 
         [0030]    The foregoing description was primarily directed to a preferred embodiment of the invention. Although some attention was given to various alternatives within the scope of the invention, it is anticipated that one skilled in the art will likely realize additional alternatives that are now apparent from disclosure of embodiments of the invention. Accordingly, the scope of the invention should be determined from the following claims and not limited by the above disclosure.