Abstract:
A screwdriver of the type having a variable torque-limiting in-line drive with a handle having a cavity and a drive bit disposed in the cavity. Over-ride drive members are disposed in the cavity and a spring exerts a force on the drive members for transmitting only a maximum force to a bit in the screwdriver. Two adjustable controls are at a back end of the tool and they are used to apply a varying force to the spring and thus limit the amount of maximum torque to be transmitted.

Description:
This invention relates to a screwdriver of the type having a variable torque-limiting in-line drive. 
     BACKGROUND OF THE INVENTION 
     Screwdrivers with gear mechanisms, or the like, are commonly in use in various fields, including the medical instrument field where this invention is useful. Those screwdrivers have an elongated handle with gear-type teeth or the like within the handle and with a spring pressing on the teeth to hold the teeth in mutual engagement while the handle is being rotated to apply a torque to a work piece such as a screw. Also, in that arrangement, the gear teeth may be held together for a transmission therebetween of a maximum torque applied to the work piece. Even further, the screwdriver might have an adjustment which permits adjusting the force of the spring on the gear teeth to thereby adjust the maximum torque transmitted through the handle and to the work piece. 
     The present invention provides an adjustable control for applying selective forces on the gears or the like and doing so with a spring which forces on the gears in accord with the setting of the adjustable control. 
     Still further, the aforementioned adjustable control can have indicia thereon, such as graduation markings, so that the adjusted position of the control can be readily detected by the user and thus the control can be set in a desired position for effecting the desired spring force on the gears or those items which are transmitting the torque. 
     Also the control itself has an adjustable rotational stop for an initial setting to permit the movement of the control to be to a maximum amount and thereby have the screwdriver able to transmit up to a maximum torque from that selected initial setting. Thus, the range of the setting can be selected. 
     In that arrangement, it is desirable to have the adjustable control rotatable on the handle so that it can be set in the desired position but also have the control limited in its adjustable positioning so that it will operate exclusively within only a range of adjustment and not exceed its positioning to where it could actually become disconnected or otherwise fail in its operation. The entire arrangement is such that the operator can set the adjustable control to one of various selectable torque-limiting positions, and the operator can be assured that each time the control is set in that position that the desired maximum torque will be transmitted by the screwdriver, and the transmitted torque will be limited to that one maximum amount in accord with that one setting of the adjustable control. 
     In this invention, the screwdriver is elongated and has a handle with a rear end, and that is where the controls are located for setting the limit to the transmitted torque. Thus, the surgeon, or other user, can securely hold the handle with one hand and have access to and adjustment of the torque controls, all for accuracy of the desired settings. 
     Still further, the screwdriver is constructed to have its moving parts in relationships and positions of inter-related support and close tolerance, so the settings and the use are precise. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of a preferred embodiment of a screwdriver of this invention with a fragment of a tool bit shown thereon. 
     FIG. 2 is an enlarged longitudinal sectional view of the screwdriver of FIG.  1 . 
     FIG. 3 is an enlarged perspective view of a part shown in FIG.  2 . 
     FIG. 4 is an enlarged sectional view of a part as seen in FIG.  1 . 
     FIGS. 5,  6 ,  7 , and  8  are enlarged perspective views of parts shown in FIG.  2 . 
     FIG. 9 is a sectional and fragmentary view of the gear portion, similar to FIG.  1 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIGS. 1 and 2, show the screwdriver of this invention includes a handle, generally designated  10 , having a core or body portion  11  and a cover portion  12  which may be a silicone or like resilient cover encapsulating the core  11 . The handle  10  is shown elongated, and it has a longitudinal axis A and a longitudinal cavity which extends co-axially with the axis A in two contiguous but different diameters at cavity lengths  13  and  14 . A shaft  15  is disposed in the cavity and extends along the axis A and is snugly and rotatably disposed in the cavity portion  13 . An elongated bit  16  can be inserted into an opening  17  in the shaft  15 , and it has its own elongated axis B coaxial with the handle axis A to extend therealong as fragmentarily shown in FIG.  1 . Thus the bit  16  is at the front end of the screwdriver. 
     A plurality of annular Belleville washers  18  are disposed within the cavity  14  and surround a length of the shaft  15 . As such, the washers  18  serve their usual purpose of being a spring which exerts a force along the axis A, in the customary manner. Also, coaxial with the bit  16  are a first gear member  19  and a second gear member  21 , both of which are annular and are disposed within the cavity  14 . The members  19  and  21  are the drive transmission members, and they have the well-known inter-engaged teeth or ramps  22  disposed on each for rotation drive connection between the two members  19  and  21 . FIG. 9 shows that the teeth  22  are slanted to transmit only limited clockwise rotational drive between the gears  19  and  21 , but the teeth are also cut to transmit unlimited counterclockwise rotational drive between the gears  19  and  21 . 
     In the arrangement shown, the member  21  can be in rotation drive and axial movement relationship with the handle  10 , such as by well-known means of rollers  23  drivingly disposed between the gear  21  and the handle  10 , as seen in FIG.  9 . Rollers  23  are trapped in grooves  24  in the member  21  and in slots  25  in the handle core  11 . That is, the arrangement is such that upon rotation of the handle  10  about its longitudinal axis A that rotation is transmitted to the rollers  23  and likewise to the member  21 , until the limit of transmitted torque is applied to the screwdriver. The rotation can be in either the clockwise or counter-clockwise direction about the longitudinal axis  13  and as viewed from the right end of FIG. 2, and, for purposes of further describing this invention, it is to be considered that the limited torque rotation is in the clockwise direction as viewed from the right-hand end of FIGS. 1 and 2. Also, the member  21  can move axially, and member  19  can too. 
     Rotation of the handle  10  and the consequent similar rotation of the member  21  is transmitted to the member  19  when there is engagement at the ramps or teeth  22  which exist on both the members  19  and  21 . Thus the member  19  will then also rotate clockwise to rotate the bit  16 . The bit  16  is in a rotational drive relationship with the member  19  in any suitable arrangement such as through a pin  26  engaging the gear  19  and the shaft  15 . When member  21  rotates, say clockwise, the bit  16  is not directly driven by the member  21 , and it is driven only through the gear  21  imposed onto the gear  19 . That is, the shaft  15  is not driven directly by the gear  21 . 
     Other arrangements could be employed for the rotational drive from the handle to the bit  16 . One example of another arrangement is such as that shown in my U.S. Pat. No. 6,095,020. 
     With just that portion of the aforementioned description, it will be understood by one skilled in the art that the rotation of the handle  10  will cause the same rotation of the member  21 , and, when that rotation is transmitted through the ramp surfaces  22  which exist mutually on the members  19  and  21 , then the member  19  will be rotationally driven to, in turn, rotate the bit  16 . However, when the bit  16  meets the maximum torque setting of this tool, then the inclined or angulated surfaces  22  will simply slide relative to each other, and the bit  16  will not be rotated. Thus, the maximum transmitted torque has been established, as desired. 
     FIG. 2 further shows an adjusting control screw  29  threaded into the handle core  11  by means of screw threads on the core  11  and mating screw threads on the member  29  and with those threads being at the mutual location  31  along the wall of the cavity  14 . That is, the piece  29  is threaded into the handle cavity  14  and abuts the spring washers  18  which in turn abut the gear  21  to cause the ramps or teeth  22  to be in nonsliding, or rotational drive, contact with each other up to a certain torque limit. 
     It can now be seen and understood that the position of the cylindrical piece  29  along the axis A, such as established by the screw threads at  31 , determines the force exerted on the spring  18  and thus determines the force for the limited torque transmitted between the angulated surfaces  22  of the members  19  and  21 . Particularly FIG. 3, shows that the member  29  has a cylindrical length  32  and a flat-sided length  33 , shown in the form of a hexagonal shape. Also, the end of the member  29  has internal threads at  34 . It will be understood that the member  29  is an adjustable control and it is disposed at the rear end of the screwdriver, that is, at the right end as seen in FIGS. 1 and 2. 
     A cylindrical insert member  36  is seen in FIGS. 2,  4 , and  5 , and it serves as a guide to other parts and it has threads  37  for fixedly threading into the handle  11 , and that is in the cavity  14 . The guide  36  has a cylindrical bore  38  which snugly receives and supports the control  29  at a cylindrical length  32  of the control  29  which can slide in the bore  38  for the adjustable positioning of the control  29 , as mentioned. To secure insert  36  in a fixed position on the handle  11 , thread locking material can be used. Member  36  presents a groove  39  and a circular surface  41  and an O-ring groove  42 , with all three extending therearound. 
     A cylindrical member  43 , serving as another adjustable control, has a flat-sided central opening  44  extending therein for a short axial length, as seen in FIGS. 2 and 6. The two hexagonal shapes  33  and  44  mate in a slidable but snug relationship, and control  43  is piloted on the control  29 . The relationship is such that rotation of the control  43  induces the same rotation in the other control  29 , and that causes control  29  to thread axially along the cavity  14  and thereby adjust the axial force on the spring  18  and thus determine the torque limit for the screwdriver. 
     Control  43  is restrained in its axial freedom on the control  29  by an end stop  46  threaded at  47  into the opening  34  in the control  29  to a fixed axial position relative thereto. FIG. 7 shows the stop  46  with its threads  48 . A cylindrical compression spring  49  is disposed between the control  43  and the stop  46  to urge the control  43  leftwards to the position shown in FIG.  2 . Guide  36  and control  43  have teeth  51  and  52 , respectively, and those teeth are mutually engaged in the leftward position of the control  43 . Thus, the control  43  cannot then rotate, so neither can the control  29 . In that manner, the adjusted position of the control  29  is established for producing the limit to the torque transmittable with the screwdriver. The control  43  can be pulled rightwardly against the spring  49  and away from the insert  36  and thereby release the control  43  for rotation to induce the same rotation in the control  29 . Upon release of the pull on control  43 , the spring  49  will cause the control  43  to engage insert  36  and thus lock in the selected rotated position. 
     It will also be seen that O-rings  53  surround the insert  36  and the control  43 , and an O-ring  56  surrounds the stop  46 , all for cleanliness. 
     A cylindrical sleeve  57  is snugly mounted onto insert  36  and the control  43  and their O-rings, and it has a scale  58  with numerals, in either form shown in FIG. 1 or  8 , and the scale  58  will show the amount of torque. FIG. 1 shows that the control  43  has a scale mark  59  which aligns with the scale  58 . The sleeve  57  is rotatably adjustably attached by a set screw  61  which extends through the sleeve  57  and enters the circular groove  39  on the guide  36  and abuts the guide  36 . With that arrangement, the zero identifier on the sleeve  57  can be adjustably aligned with the mark  59  on the control  43 . 
     Control  43  has three holes  62  facing the guide  36 , and a pin  63  is supportably insertable into any selected one of the three holes  62 , such as shown with the center hole  62  in FIG.  6 . Guide  36  has affixed thereto a stop  64  which aliens with the pin  63  to preclude rotation of the control  43  beyond a position of having the pin  63  pass the stop  64 . Hole  62  is selected for receiving pin  63  so there can be maximum rotation of the control  43 , and the starting point for that rotation will be at the lowest torque required. The hole selection is made in conjunction with the slipping of the control  43  onto the control  29 , and the flat-sided mating connection of  33  and  44  determines the relative rotated position therebetween. Of course that also depends on the final rotated position of the guide  36 . 
     In all, it will be understood that the controls  29  and  43  are all together and at the rear end of the screwdriver. The surgeon can conveniently and securely hold the elongated handle  10  with one hand and then adjust control  43  with the other hand. 
     While basically only one embodiment is disclosed herein, it will be apparent to one skilled in the art that changes can be made in that embodiment in the form of equivalent parts. The scope of the claims should determine the extent of the patent protection.