Abstract:
A brace hinge includes an upper and lower intermeshing gear members each having an elliptical gear intermeshed with the other and sandwiched by two very thin profile cover and support plates. The elliptical gears produce an eccentric motion which lends it self to following the natural motion of the human knee or other joints such as the elbow. The elliptical gear of one member has its radius extend toward the pivot axis of the other gear as the radius of the other elliptical gear retreats from the pivot axis of the one member. The magnitude and radial extent over which the ellipse extends can be varied. The combination of advancing and retreating radius gear members, relatively few gear teeth and sandwiched support plates eliminate any interruption to a smooth transition, provide superior load bearing ability and provide for extremely low friction.

Description:
FIELD OF THE INVENTION 
     The present invention relates to an improved, gear mechanism for controlling the motion and angular displacement of upper and lower members of a leg brace for the stabilization and control of a human knee joint of the left and or the right leg, and more particularly to a pair of intermeshing perpendicular elliptical gears, one invading and the other retreating, and including structure for limiting the angular displacement of the gear. 
     BACKGROUND OF THE INVENTION 
     The prior art describes many orthopedic devices which attempt to support and stabilize the human knee over a wide range of angular, lateral and rotational displacement of the human leg. However, in most cases high integration of a motion controlling structure produces a non-smooth operation. In U.S. Pat. No. 4,773,404 to Jeffrey H. Townsend one of the hinge members is required to snap sharply in one direction before pivoting can take place. This is also described in U.S. Pat. No. 5,330,418 to Jeffrey H. Townsend. In U.S. Pat. No. 4,940,044 to Castillo, the hinge is placed so far forward of the axis of pivot of the leg that the device does little more than tenuously accommodate a pivot connection between the upper and lower cuff members. 
     In all of these cases, a smooth control between the upper and lower cuffs of a leg brace is simply not obtainable. The use of two circular gears alone would not provide a movement which is more supportive to the leg joint throughout its angular displacement. A simple single or double circular gear cannot produce a motion which closely follows the arc of rotation of the human knee which is based upon the cam shaped condyles of the human femur. This cam shape is commonly referred to as the sagittal plane in the orthopedic profession and commonly varies only slightly from person to person. This movement path is generally described as being of a lesser radius or flatter curve at the initiation of movement and thence transitioning into an increasingly tighter, yet relatively constant radius motion. The above described hinges are clumsy attempts to provide a hinge which provides a shifting radius throughout the angular displacement of the hinge to truly track the motion of the human knee. 
     Another drawback of the hinges, such as those referred to above is the use of pins traveling in slots. These devices create additional friction through extended friction surfaces and concentrate the force in the pins sliding in the slots. 
     Another problem with currently available hinges is their width profile. Most two component hinges have overlapping members supported from one side, or have mutual support between the overlapping members. The width is bulky and the extension, even when not in flexion, is such that it must be worn with looser clothing. In flexion, the protrusion in the direction toward the front of the knee is severe and even more space and looser clothing is required. In addition, forward extension during flexion increases the probability that the brace will be caught or snagged on other objects, or as clothing is damaged from being stretched across the protruding hinge. 
     What is therefore needed is a hinge which enables guided controlled movement support of the knee, which is as friction free as possible. The needed hinge should be able to bear significant weight without binding and should produce a motion which is as close as possible to the movement of the human leg and which eliminates pin in slot structures. 
     SUMMARY OF THE INVENTION 
     The brace hinge of the present invention includes an upper and lower intermeshing gear members each having an elliptical gear intermeshed with the other and sandwiched by two very thin profile cover and support plates. The elliptical gears produce an eccentric motion which lends it self to following the natural motion of the human knee or other joints such as the elbow other motion of other joints can be mimicked as needed by varying the shape of the ellipses of the gears used in the hinges and further utilizing an ellipse which actually increases desirable forces during the motion of the hinge to increase the performance of the brace. The user&#39;s knee, or other joint, will track in a correct natural arc and will be controlled by the brace having the hinges of the invention applying controlling forces to the knee or other joint to prevent its deviation from its correct and natural path. 
     The elliptical gear of one member has its radius extend toward the pivot axis of the other gear as the radius of the other elliptical gear retreats from the pivot axis of the one member. The magnitude and radial extent over which the ellipse extends can be varied. The combination of advancing and retreating radius gear members, relatively few gear teeth and sandwiched support plates eliminate any interruption to a smooth transition, provide superior load bearing ability and provide for extremely low friction. Because of the planar and close fitting of the surfaces between the cover and support plates and the upper and lower gear supports the hinge can hold lubrication for an extended period. The hinge members can be constructed of plastic, ceramic, metal, metal matrix composite or any combination thereof. The mesh points of the gear teeth provide a constant force there between along a line drawn from one rotational or pivot center to the other. The ellipses reciprocally compensate and they gain and withdraw the mesh interface moves from one gear support pivot point to the other. 
     The elliptical advancing and retreating interface is protected and stabilized by support and stabilization plates. The specific characteristics of the elliptical gears can be custom formed by the user or technician to even more closely follow the leg angular displacement motion and knee characteristics of a given user. Although the embodiment herein illustrates a 0° to 180° angular displacement of the hinge, other displacement ranges can be provided. 
     The cover and support plates form a seemingly center link and retract through flexion relative to the farthest forward point of the knee when viewed from the side. This creates a slimmer profile for the brace at the hinge level when viewed in the horizontal plane. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention, its configuration, construction, and operation will be best further described in the following detailed description, taken in conjunction with the accompanying drawings in which: 
     FIG. 1 is a perspective view of a left leg brace including the hinges of the invention; 
     FIG. 2 is an exploded view of the outside hinge of the left leg brace seen in FIG.  1  and illustrating upper and lower gear supports having elliptical gears with an elliptical and limited progression of gear teeth; 
     FIG. 3 is a partially assembled view of the hinge of FIG. 2 in an un-flexed position; and 
     FIG. 4 is the left hinge of FIG. 3 shown in a flexed position. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     A description of the improved brace of the present invention will be best initiated with reference to FIG. 1. A brace  21  has an upper main support  23  and a lower main support  25 . This type of brace  21  upper and lower main support  23  and  25  is formable to more closely fit the leg of the user. Close interfitting enables the brace  21  to provide a more exacting degree of support and thus the operation of the hinged movement is important to maintaining control. 
     A right hinge  31  includes an outer cover  33  having a forward surface  35 . An inside plate  37  is seen supporting the heads of two rivets  39 . A left hinge  41  is also seen having similar structure. 
     Referring to FIG. 2, an exploded view of the left hinge is shown and further details of the structure is seen. An upper gear support  43  has a set of gears  45  which intermesh with a set of gears  47  of a lower gear support  49 . Note that the upper gear support  43  attaches to the inside of upper main support  23  while the lower gear support  49  attaches to the inside of the lower main support  25 . 
     Upper gear support  43  includes an upper pivot aperture  51 , and a series of upper rivet apertures  53 . The upper gear support  41  has a smooth section  55  at the end of the gears teeth  45  in order to limit the movement of the upper gear support  43  with respect to the lower gear support  49 . Similarly, the lower gear support  49  contains a smooth section  57  opposing the smooth section  55  of the upper gear support  43 . Lower gear support  49  includes a lower pivot aperture  59 . Lower gear support  49  also contains a series of lower rivet apertures  61 . 
     The lower gear support  49  contains a stop structure  63  which will be used to limit the motion of the hinge  33  if so desired, as will be shown. To the right of the upper and lower gear supports  43  &amp;  49  is a first cover and support plate  65 , and to the left of the upper and lower gear supports  49  is a second cover and support plate  67 . The hinge  31 , especially since it is riveted, could operate with only one of the first and second cover and support plates  67  and  67 , but the use of two gives greater stability. First and second gear cover and support plates  65  and  67  are preferably identical. To the left of second cover and support plate  67 , a pair of rivets  39  are seen in an orientation before bending the ends thereof. The structures on the first and second cover and support plates  65  &amp;  67  are identical. First and second cover and support plates  65  &amp;  67  include apertures  71  for securing the cover  33  onto the outermost one of the first and second cover and support plates  65  &amp;  67 , which in this case is second cover and support plate  65 . Aperture  71  can accept a screw  85  for assisting the first and second cover and support plates  65  &amp;  67  together. 
     First and second cover and support plates  65  &amp;  67  include a correspondingly opposing set of limit stop apertures  77  which act in concert with stop structure  63  to limit the extent to which the hinges  31  will angularly displace. A screw is placed in one of the apertures  77  corresponding to the extent to which angular displacement is limited. First and second cover and support plates  65  &amp;  67  &amp; each have an upper pivot rivet aperture  79  and a lower pivot rivet aperture  81 . Once the upper and lower gear supports  43  and  49  and their upper and lower pivot rivet apertures  81  are joined on the two rivets  39  extending through one of the first and second cover and support plates  65  &amp;  67 , the relative rotational position of each are locked. 
     Note that the use of apertures  79  and  81  combined with joinder by rivets  39  could be replaced by a system in which the first and second cover and support plates  65  &amp;  67  included interlocking structure, such as an annular projection or even a projection integrally formed with one of the plates  65  and  67  in order to engage upper and lower pivot apertures  51  and  59 . Alternatively, the upper and lower gear supports  43  and  49  could be fitted with a projection to engaged the apertures  79  and  81  of the first and second cover and support plates  65  &amp;  67 . All of these structures, as well as other structures, could be employed to provide a stable pivoting support of the upper and lower gear supports  43  and  49 . 
     Since each of the upper and lower gear teeth sections  45  and  47  contain a limited number of teeth, and since the gear sections are elliptical, the rotational lock is positive. It is impossible to fit the gear teeth sections  45  and  47  together in a mis-aligned fashion. Because the gear teeth section  45  of the upper gear support  43  increases it radial distance to the lower pivot aperture  59  while the gear teeth section  47  of the lower gear support  49  reduces its radial distance to the upper pivot aperture  51 , the relative position of the supports  43  and  49  is exactly fixed. The position and depth of each gear tooth and each valley is known and is an exact fit. The teeth sections  45  and  47  can never fall out of alignment. 
     It is understood that the radial elliptical starting and finishing points of the gear sections  45  and  47  can extend over a radially increased or radially decreased range to provide for greater or lesser angular displacement over the full range of the hinge  31 . For a given severity of elliptical radius change over any radial range, the complex motion of the hinge  31  can be varied. Because the upper and lower gear supports  43  and  49  are so simple in their structure as flat plates, a custom brace motion can be computed based upon individual leg size and characteristics and custom made upper and lower gear supports  43  and  49 , with individually specifiable teeth  45  and  47  elliptical characteristics can be machine formed inexpensively and in a short time. 
     To the right of FIG. 2 the cover  33  is seen in relationship with two screws  85  for securing it to the cover and support plate  65 . 
     Referring to FIG. 3, a view of upper gear support  43  and lower gear support  49  intermeshed together and shown with respect to second cover and support plate  67 . The upper gear support  43  and lower gear support  49  are in a position where they are most linear, in the un-flexed position. The structural portion extending away from the rivets  67  are not particularly straight, but the shape of such structure will be dependent upon the matching shape of an upper and lower main support  23  and  25  to which it is to be attached. The smooth sections  55  and  57  are seen in an interfering relationship preventing the upper gear support  43  and lower gear support  49  from pivoting further in the direction of the smooth sections  55  and  57 . The limit stop apertures  77  are seen in position just in front of the stop structure  63 . As can be seen, the radial extent of the gear set  47  on a line between the rivets  39 , is closer to the rivet  39  of the upper gear support  43 . 
     Referring to FIG. 4, a view taken with respect to the viewing perspective of FIG. 3 illustrates the upper gear support  43  and lower gear support  49  intermeshed together and shown in flexion. A tip end  91  of the stop structure  63  of upper gear support  43  is about to make contact with a side surface  93  of the lower gear support  49  to limit the flexion of the hinge  41 . As can be seen, the stop structure  63  is shown as having swept past all of the limit stop apertures  77 , any one of which could have contained a screw, or pin or other blocking object to engage the stop structure  63  to limit flexion. 
     Note in FIG. 4 that the radial extent of the gear set  47  on a line between the rivets  39 , is closer to the rivet  39  of the lower gear support  49 . FIGS. 4 and 5 taken together illustrate the action of the elliptical gear sets  45  and  47 . By shifting the rotation interface from a position closer to one pivot axis that the other before flexion, and in a continuous path toward the other pivot axis at the termination of flexion, a motion which is more natural to the knee or other joint is obtained. The rapidity of the transition will depend upon the severity of the ellipse upon which the gear sets  45  and  47  are based, as well as the shape of the gears and their contact during the pivot action. 
     While the present invention has been described in terms of an opposing elliptical gear set for use with leg brace, one skilled in the art will realize that the structure and techniques of the present invention can be applied to many similar structures. The present invention may be applied in any situation where the axis of movement is to be changed throughout the movement range in manner which is as smooth and frictionless as possible while deriving significant control forces from the hinge. 
     Although the invention has been derived with reference to particular illustrative embodiments thereof, many changes and modifications of the invention may become apparent to those skilled in the art without departing from the spirit and scope of the invention. Therefore, included within the patent warranted hereon are all such changes and modifications as may reasonably and properly be included within the scope of this contribution to the art.