Abstract:
A prosthetic device includes an energy storing member, a lever member attached to the energy storing member, a rocking member and an energy transfer line. This line has a first end attached to a front end of the energy storing member and a second end attached to a back end of the lever member. The line has its middle portion attached to the rocking member. The energy storing member is preferably a leaf spring. This combination of elements in the prosthetic device may be a lower leg or foot for use by a below-the-knee amputee to simulate more closely the natural gait of a person while walking or running.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is related to U.S. Provisional Patent Application Ser. No. 60/105,532, filed Oct. 22, 1998, from which priority is claimed. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a prosthetic device for a lower leg or foot for use by a below-the-knee amputee. 
     2. Description of the Related Art 
     Although prosthetic devices have been in use for centuries, not until relatively recently have efforts been made to design prosthetic legs and feet to react dynamically to the cyclic loading and unloading of the foot during movement to simulate more closely natural gait. To this end, prosthetic devices typically are configured to store and release energy during normal body movements. Typical prosthetic feet include a spring plate arranged longitudinally approximately within the sole of a shoe. The spring plate is usually arranged so as to provide flexure of the foot while walking. 
     Materials undergo a certain amount of deformation when they are stressed. If a mechanical element experiences a steady deformation when acted upon by steady forces, it is exhibiting compliance which is the basic characteristic of a spring. A translational spring is a mechanical element which deforms by steady amounts when loaded by steady forces. A linear spring has a proportional relation between deformation and force. Thus, the spring stores work as energy associated with its deformation. This stored energy is called translational potential energy. Hence, the energy stored in the spring depends directly on the force transmitted to the spring. In other words, the work done by any force acting on a spring during a specified displacement is equal to the change in the kinetic energy of the spring. This statement is the basic work-energy principle of body dynamics in physics. 
     The single spring plate of the prior art may have varying thicknesses along its length to give varying compliances across the spring plate in order to simulate more closely the curling movement of a foot during a walking motion. Improvements to the spring plate have included multiple plates of different thicknesses attached or adhered to each other within the prosthetic foot in order to create different compliances along the length of the foot. However, these attempts to achieve different compliances by varying the thicknesses have not been successful because it has been found that spring plates are inherently limited in their simulation of the natural motion of a foot. In particular, as a prosthetic foot using such a spring plate is curled, as it is during a normal walking or running motion, the effort required to curl the prosthetic foot increases, thereby inhibiting the full range of motion. Therefore, it is desirable to provide a prosthetic device that provides a more natural simulation of the motion of a leg or a foot. 
     SUMMARY OF THE INVENTION 
     Accordingly, it is an object of the present invention to provide a prosthetic device which more naturally simulates the motion of a user&#39;s leg or foot. 
     According to the invention, the prosthetic device is provided with a base portion, a leaf spring attached to the base portion, a lever member hingedly attached to the leaf spring, a rocking member attached to the base portion, and a line having a first end attached to a front end of the leaf spring and having a second end attached to a back end of the lever member. The line has a middle portion, between the first and second ends, that is attached to the rocking member. The prosthetic device can convert a pivoting motion of the lever member into a deflection of the leaf spring, thereby storing energy imparted by the lever member to the leaf spring. 
     Preferably, the rocking member is an eccentric body, such as a cam-shaped wheel. The line is fixed to the eccentric body such that, as the lever member pivots, the amount of deflection caused in the leaf spring by the pulling of the line changes through the range of foot motion. Accordingly, the eccentric body can be configured such that the deflection of the leaf spring changes over the range of pivoting of the lever member. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A more complete appreciation of the invention and many of the attendant advantageous thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein: 
     FIG. 1 is a side elevational view of a first embodiment of the present invention at the beginning of a step; 
     FIG. 2 is a side elevational view of the embodiment shown in FIG. 1 at the midpoint of a step; 
     FIG. 3 is a side elevational view of the embodiment shown in FIG. 1 at the completion of a step; 
     FIG. 4 is a side elevational view of a second embodiment of the present invention in a standing position; 
     FIG. 5 is a side elevational view of the embodiment shown in FIG. 4 at the beginning of a step; 
     FIG. 6 is a side elevational view of the embodiment shown in FIG. 4 at the midpoint of a step; 
     FIG. 7 is a side elevational view of the embodiment shown in FIG. 4 at the completion of a step; and 
     FIG. 8 is a top plan view of the embodiment taken through line  8 — 8  in FIG.  4 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A prosthetic leg  10  according to the present invention is generally illustrated in FIG.  1 . It includes a prosthetic sleeve  12  attached to a base portion  14  and configured to be donned over a stump of an amputee. The base portion  14  provides a connection between the prosthetic sleeve  12  and the moving parts of the prosthetic leg  10 . The base portion  14  has an extension  15  through which a shaft  23  extends to secure a rocking member  22  thereto. An energy storing member  16  is secured to a bottom  11  of the base portion  14 . A flexible lever member  18  is attached to the energy storing member  16  at hinge  20 . The energy storing member  16  may be a leaf spring  26  or any other known energy storage means. The leaf spring  26  may be constructed of any known material appropriate for a spring, such as carbon fiber-reinforced plastic, fiberglass, urethane composites and steel. A line  24  may be made from a strap, cable, cord, rope, or other equivalent element appropriate for transferring energy to and from the leaf spring  26 . 
     Because the lever member  18  is hingedly attached to the leaf spring  26 , together they simulate the motion of an ankle. The line  24  has a first end attached to a first point  27  on a front end  28  of the leaf spring  26  while the second end of the line  24  passes through an aperture  25  in the leaf spring  26  and is attached to a second point  29  on a back end  30  of the lever member  18 . The line  24  is attached at its midpoint to a tip  39  on the rocking member  22 . Note that the distance from the first point  27  to the tip  39  is the same as the distance from the second point  29  to the tip  39 . Thus, these two distances are constant and allow the line  24 , which is essentially inelastic, to transfer energy back and forth between the lever member  18  and the leaf spring  26 . The line  24  is wrapped around the rocking member  22  in a grooved rim such that, as the lever member  18  pivots about hinge  20  in a counterclockwise direction A, the rocking member  22  is also rocked in a counterclockwise direction B, as seen in FIG.  2 . Since one end of the line  24  is attached to the front end  28  of the leaf spring  26 , the pivoting motion of the lever member  18  is converted into a deflection of the leaf spring  26 , thereby storing energy in the leaf spring  26 . 
     As shown in FIG. 2, at the midportion of a step, the lever member  18  is generally straight, i.e. at a relaxed position. As the user moves through a stepping or walking motion, the lever member  18  is flexed and pivoted relative to the leaf spring  26 , similar to the pivoting of a foot about an ankle. During midstep, this pivoting motion allows a lower portion  32  of the lever member  18  to remain substantially in contact with the ground  34  while allowing the prosthetic sleeve  12  and the base portion  14  to follow the motion of the stump of a below-the-knee amputee. 
     When the user completes a stepping or walking motion, as shown in FIG. 3, the energy stored in the leaf spring  26  is returned to the lever member  18 . The rocking member  22  may be constructed in the form of either a round wheel or an eccentric body  36 , e.g. a cam-shaped wheel with a grooved rim. With the rocking member  22  constructed as the eccentric body  36 , it is preferable that the line  24  is fixed at its midpoint to the tip  39  on a lobe  38  of the eccentric body  36 . By fixing the line  24  to the tip  39 , the eccentric body  36  will be rocked back and forth by the line  24  as the lever member  18  and the leaf spring  26  are flexed and unflexed, respectively. 
     The amount of force imparted by the lever member  18  to the leaf spring  26  may be modified. For example, it may be preferable to provide more force for a certain user or for users participating in particular activities. Thus, a runner may prefer more force while a walker may prefer less force. Preferably, the line  24  is tensioned between the points  27 ,  39  and  39 ,  29  so as to keep the line  24  taut. 
     A second embodiment of the present invention is shown in FIGS. 4 through 8. As shown in FIG. 4, a prosthetic foot  48  includes a base portion  40  with a heel  41  and an energy storing member which is a leaf spring  42  secured at its back end by a fastener  43  to the heel  41 . The base portion  40  has an extension  45  through which the shaft  23  extends to secure the rocking member  22  thereto. A lever member  44  has a front end which serves as a toe portion  47  of the prosthetic foot  48 . The lever member  44  is attached to the leaf spring  42  at a hinge  46 . The leaf spring  42  is arranged substantially along a direction extending between the heel  41  and the toe portion  47  of the foot  48 . The rocking member  22  and the line  24  have the same construction as in the first embodiment. 
     In this second embodiment, the foot  48  may be provided with a rubber or plastic cover (not shown) which resembles human skin. The operation of the foot  48 , according to this second embodiment, is similar to the leg  10  in the first embodiment. For example, as a user moves through a walking motion, the foot  48  moves from the standing orientation shown in FIG. 4 sequentially to the step orientations shown at the beginning in FIG. 5, at the midpoint in FIG. 6, and then at completion in FIG.  7 . As shown in FIG. 5 through 7, and especially in the high stepping position shown in FIG. 7, as the lever member  44  pivots in a counterclockwise direction C around the hinge  46 , relative to the leaf spring  42 , the pivoting movement of the lever member  44  is converted into a deflection of the leaf spring  42 . As a user reaches the end of a walking step, the energy stored in the leaf spring  42  is returned through the line  24  to the lever member  44 . 
     As shown in FIG. 5, a first end of the line  24  extends from a first point  49  on the front end of the leaf spring  42  to the tip  39  of the lobe  38  on the eccentric body  36 . The second end of the line extends from a second point  51  on a back end  50  of the lever member  44 , through an aperture  52  in the leaf spring  42  to the tip  39  of the lobe  38  on the eccentric body  36 . 
     FIG. 8 shows a top plan view of the leaf spring  42  attached to the lever member  44  by the hinge  46 . The leaf spring  42  includes the aperture  52  that is aligned over the second point  51  on the back end  50  of the lever member  44 . This arrangement allows the line  24  to pass through the aperture  52  and to be attached to the second point  51 . The leaf spring  42  also has a cutout portion  53  for accommodating the heel  41 . 
     Obviously, numerous modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that the invention may be practiced otherwise than as specifically described herein.