Abstract:
A locking device for securing a prosthesis to a cylindrical part attached to a wearer. The device allows insertion of the cylindrical part, such as a pin, to be inserted into the locking mechanism at an oblique angle.

Description:
BACKGROUND OF THE INVENTION 
     The present invention refers to a locking device intended as a fastening means for prostheses, such as leg- and arm prostheses, of the kind where the prosthesis is to be fastened to a cylindrical part such as a pin, an axle, a tube or the like. It can for example be used in such cases where a silicone stocking is applied on the leg- or arm stump, said stocking having a plastic cup moulded into the bottom thereof and said cup having a pin attached thereto. The leg- and arm stump provided with a silicone stocking is passed into a prosthesis sleeve connected to the prosthesis, said prosthesis sleeve is provided with a locking device for the pin. 
     In the international patent application WO 94/04101 it is shown a fastening means intended for a prosthesis, said fastening means comprises a tilted washer, which by spring force is kept in tilted position and by this is locked to the pin. The degree of tilting of the washer can be reduced by means of an actuating means by which the locking to the pin can be released. 
     In DE-C-1,097,217 there is shown a clamping device for axles and tubes and which comprises a ring of balls arranged in a cage, which by means of spring action is pressed into a conical seat, at which the locking device is locked to the axle in axial direction, said clamping device further comprises actuating means for releasing the ring of balls from the conical seat. The actuating means comprises a fork-shaped member which grips the pin and which is provided with inclined surfaces cooperating with inclined surfaces on a holding-on ring, so that the holder-on ring and the ring of balls by wedge action is displaced along the pin. There is no indication that this clamping device would be intended to be used in connection with prostheses. Besides it is designed so that the axle only may be passed into the locking device in a completely straight position. 
     OBJECT AND MOST IMPORTANT FEATURES OF THE INVENTION 
     The object of the present invention is to provide a locking device of the kind mentioned above, which should be positionable in a stepless way, it should permit rotation around the pin also in locked position, it should be relatively insensitive to dirt and threads from textiles which easily may penetrate into it, it should permit the pin to be easily inserted into it also in a slightly oblique position and it should lock from movement out of the locking mechanism in a stepless way. 
     The locking device according to the invention is characterized by the fact that it comprises a cage with a ring of balls arranged therein, said ring of balls by means of spring action is pressed into a conical seat in the cage, at which the locking device is locked to the pin or the like in axial direction while rotational movement is admitted, said locking device further comprises actuating means for releasing the ring of balls from the conical seat, at which the cage is arranged in a housing provided with a through opening for receiving said pin or the like, said opening has a larger diameter than the pin or the like in order to admit this to be inserted also in an oblique position. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     The invention will in the following be closer described with reference to some embodiments shown in the accompanying drawings. 
     FIG. 1 shows a leg prosthesis provided with a locking device according to the invention. 
     FIG. 2 is a horizontal longitudinal section through an embodiment of the locking device. 
     FIG. 3 is a vertical longitudinal section through the locking device in connecting position. 
     FIG. 4 is a corresponding section as in FIG. 3 but in disconnecting position. 
     FIG. 5 is a corresponding section as in FIG. 3 showing the pin with a prosthesis sleeve connected thereto and inserted into the locking device in an oblique position. 
     FIG. 6 is a horizontal longitudinal section through a modified embodiment of the locking device. 
     FIG. 7 is a vertical longitudinal section through the locking device according to FIG.  6 . 
     FIG. 8 is a vertical longitudinal section through a further embodiment of the invention. 
     FIG. 9 shows the embodiment according to FIG. 8 in disconnecting position. 
    
    
     DESCRIPTION OF EMBODIMENTS 
     In FIG. 1 there is shown a silicone stocking  10  intended to be passed on an amputated leg. A plastic cup  10   a  is moulded into the bottom of the silicone stocking  10  and said plastic cup having a cylindrical pin  12  threaded into it. The amputated leg stump which is provided with the silicone stocking  11  is passed into a prosthesis sleeve  11 . The prosthesis sleeve has a locking device  13  for the pin  12  and is connected to a prosthesis, in the shown example a leg prosthesis  14 . 
     The locking device, which is shown more in detail in FIGS. 2-5, comprises a housing  15  with a through opening  16  for receiving the pin  12 . The opening  16  has a larger diameter than the pin  12 , at which this may be inserted into the opening also in a slightly oblique position, which is shown in FIG.  5 . 
     The opening  16  is provided with a widened threaded portion  17 , in which a cage  18  for a ring of balls  19  is threaded. The cage  18  is provided with a conical seat  20  for the ring of balls  19  with the more narrow portion directed towards the prosthesis sleeve  11 . A resilient washer  21 , e g a rubber washer, presses initially the ring of balls  19  into the conical seat  20 , at which the ring of balls is locked around the pin  12 . The locking effect is accomplished by wedging action between the balls and the pin. The pin  12  can with a low resistance be passed through the ring of balls  19  also in a slightly oblique position and be positioned in a stepless manner and locked in the locking device. The locking device locks immediately and without play and anywhere along the pin if one tries to withdraw it from the ring of balls. This type of locking by means of a ring of balls pressed into a conical seat is relatively insensitive to dirt and threads from textiles which easily may penetrate through the opening  16 . 
     The locking device is shown in locking position in FIG. 3 and 5. In this position the locking device is thus locked to the pin  12  in axial direction while rotational movements between the pin and the locking device are admitted. The pin  12  is locked by wedging action automatically when one tries to withdraw it, while it may freely be inserted into and positioned in an optional position in the locking device. 
     The amputated leg stump is often swollen in the morning and can therefore not be passed completely down into the prosthesis sleeve  11  but will sink down gradually during the day. The locking device according to the invention often admits this since locking is accomplished completely without play. With this is meant that every minimal movement of the pin downwards in the locking device will be taken up thereby and the locking device will lock immediately if the pin moves in opposite direction, the locking direction. This play-free locking function has the further advantage that irritating click-sounds are avoided, which otherwise occur if there is a play in the locking mechanism. 
     The housing  15  is provided with a radially towards the opening  16  directed tubular connection piece  22  provided with external threads and on which a holder- and guide member  23  for a push rod  24  is threaded. The tubular connection piece  22  also forms a part of the guide for the push rod  24 . The push rod is springloaded by means of a spring  25  which is fixed between a collar  26  on the push rod and a support surface on the connection piece  22 . The push rod  24  is by the spring  25  kept in the extended position shown in FIG. 2, and  5 , where the collar  25  is in contact with a support surface  27  on the holder- and guide member  23 . 
     A lever arm  28  is attached to the push rod  24  and the holder  18  in such a way that displacement of the push rod  24  in axial direction provides a rotation of the holder  18  in the housing  15 . When thus the push rod  24  against the action of the spring  25  pushes the push rod  24  inwards to the position shown in FIG. 4 the holder  18  is rotated upwards according to the drawing. The ring of balls  19  will then also be displaced upwards but meets a shoulder  29  in the housing  15  which prevents further displacement upwards of the ring of balls  19 . The holder  18  can however move further a small distance upwards to such an extent that the ring of balls  19  leaves the conical seat  20 , at which the locking to the pin  12  is disconnected. The prosthesis  14  can in this position be removed from the pin  12 . 
     The spring  25  besides contributes in locking position to actively draw the holder  18  downwards according to FIG. 3, at which the balls  19  are kept away from the shoulder  29  so that they are kept in the conical seat  20  and the locking around the pin is secured. 
     It should be noted that it would be possible also at strong jerks or pulling forces to accomplish rotation of the holder  18  out of locking position according to FIG. 3 to a released position according to FIG. 4 at which the prosthesis can be removed from the pin  12 . This is obtained by the relatively large pitch of threads of the holder and the housing. In normal use however the locking of the ring of balls to the pin should be secured. The force required to jerk the pin loose from the locking device can be adjusted by choosing the spring force of the spring  25 . 
     As mentioned above and which is also shown in FIG. 5 the pin  12  can be inserted into and positioned in a slightly oblique position in the locking device. The fact that the pin without problems can be inserted into, locked and released in an oblique position is a very big advantage. It is common that the soft silicone stocking  10  ends up somewhat askew when putting it on the leg stump. The pin  12  will then not end up in the centre of the stump end. Even if one manages to insert the pin  12  into the hole of a conventional locking mechanism in an oblique position, the tilting forces that remains when the pin is forced to an upright position can be so large that the pin  12  seizes in the locking device. This can in turn involve that it becomes difficult or even impossible to take the prosthesis off from the leg stump. 
     The obliqueness shown in the drawing is about 10°. Depending on the design of the conical seat  20  a larger angular adjustment of the pin may be permitted. The balls  19  will adjust themselves in order to adapt to the oblique pin  12 . 
     In FIG. 6 and 7 is shown a modified embodiment of the locking device according to which the holder  18  is provided with an external gear ring  30  intended to cooperate with a gear rack  31  connected to the push rod  24 . By pressing the push rod  24  inwards the gear rack  31  will provide a rotation of the holder  18  in the housing  15 . 
     In FIGS. 8 and 9 there is shown a further embodiment according to which the ring of balls  19  is arranged between two washers, a first washer  32  and a second washer  33 . The ring of balls  19  will be pressed into the conical seat  20  of the holder  29  by means of a compression spring  34  arranged between the holder  18  and the second washer  33 . The second washer  33  is preferably of a resilient material, so that the pressure from the spring  34  is distributed individually on each ball. The two washers  32  and  33  both have through openings  32   a  and  33   a  respectively, which have a larger diameter than the diameter of the pin  12 , in order to permit this to be inserted obliquely. 
     The actuating means for releasing the ring of balls  19  from the conical seat  20  is also in this case a push rod  24 . This is at its end provided with an inclined surface  35  intended to cooperate with the first washer  32  for pressing down the edge thereof against the action of a compression spring  34 , at which the ring of balls  19  is tilted and on one side leaves its engagement with the conical seat  20  of the holder  18 . The locking to the pin  12  by that ceases. 
     It is of course possible to modify the actuating means  24 ,  35  so that this acts by pressing down the whole first washer  32  and not only one side thereof. 
     The invention is of course not limited to the embodiments shown in the drawings and described above but can be modified within the scope of the claims.