US 3417409 A
Description (OCR text may contain errors)
Dec. 24, 1968 J. PRAHL 3,417,409
7 cm orsnuran HYDRAULIC 1mm: JOINT FOR AN ARTIFICIAL LEG Filed Sept. 27, 1966 2 sheet -sheet 1 IFIGJ INVENTOR fo m fic r/r/ WWW Dec. 24, 1968 J. PRAHL 3,417,409
CAM OPERATED HYDRAULIC KNEE JOINT FOR AN ARTIFICIAL LEG Filed Sept- 27, 1966 2 Sheets-Sheet 2 Fuel.
INVENTOR Jan fiah/ United States 8 Claims. c1. 3-1.2
This invention relates to leg prostheses, and particularly to a knee joint for an artificial leg which is to be attached to a thigh stump of the wearer and operated automatically in response to swinging movements of the thigh stump in the hip joint, as during normal walking.
It is known to control relative angular displacement of two artificial leg portions about the connecting knee joint by means of hydraulic apparatus which includes a cylinder coaxially mounted in the portion of the artificial leg which replaces the natural shin bone, and a piston axially movable in the cylinder and connected to the thigh portion of the artificial leg. When the leg is bent and stretched or straightened, hydraulic fluid is moved outward and inward of the cylinder by the piston through throttling conduits. The resulting damping of the knee movement provides a careful wearer with some measure of control over the knee movement, but does not permit duplicating the natural knee movement. Moveover, the attention required by the known device even under favorable operating conditions, as during walking on a smooth horizontal surface, is a source of serious mental stress to the patient. It makes adjustment to the artificial leg difficult, and sometimes impossible.
The problem of duplicating a natural gait by means of an artificial leg articulated at the knee, and the solution provided by the instant invention will be better understood by reference to the attached drawing in which:
FIG. 1 diagrammatically illustrates the angular displacement of thigh and lower leg portions in a natural leg during normal walking, and also diagrammatically shows characteristics of a structural element of this invention;
FIGS. 2 and 3 illustrate two positions of a natural leg during normal walking, the views being in side elevation; and
FIG. 4 shows a knee joint of the invention in section on its pivot axis.
Referring now to the drawing in detail, and initially to FIG. 1, a fully drawn curve A shows the angular relationship between the axes of the thigh bone (femur) and of the shin bone (tibia) during normal human walking movement. The ordinate is calibrated in degrees of the angle formed between the two axes and also in radians of the angle a of deviation from a fully stretched position of the leg in which the axes coincide. The abscissa is calibrated in arbitrary units. With respect to the fully drawn curve A, each unit is second of time.
FIG. 2 shows a human leg L in the position in which the angle between the afore-mentioned axes L L is at the usual maximum value of 175 reached during walking while the leg is supported on the ground. FIG. 3 shows the leg in a position in which the minimum angle of 125 is reached While the foot is lifted from the ground.
Reverting now to FIG. 1, it is seen that the leg is initially bent slowly from the position of maximum value for about second, then more rapidly for second, and that the rate of angular displacement then diminishes until the direction of displacement is reversed after a total bending time of second. The normal stretching movement from the position of FIG. 3 to that of FIG. 2
3,417,49 Patented Dec. 24, 1968 is more rapid and is performed at practically uniform angular speed within the significantly shorter period of second. The leg is then supported on the ground while the other leg is bent and lifted in an analogous manner. While standing on the ground, leg is bent somewhat and stretched again in a manner not directly relevant to this discussion, and the bending movement preparatory to lifting from the ground begins very shortly before the other leg is fully stretched. The illustrated cycle is then repeated.
An artificial leg should perform in the same manner. If the stretching movement is delayed, the patient must make a conscious effort to control the artificial leg. The stretching movement must be performed rapidly, and must not be braked except in its terminal stage if a natural gait is to be achieved. Braking would upset the desired relationship between the length of the bending period and the length of the stretching period.
It is essential for proper operation of the leg, and more particularly of the knee joint, that the rapid stretching movement be stopped quickly, yet without shock. Suddenly engaging abutments are most unsatisfactory. Abutments combined with a damping device do not satisfy the requirement for a stretching movement whose speed is practically uniform from beginning to end.
The achievement of a natural gait which does not require a conscious effort of the patient wearing an artificial leg is also to be maintained under varying conditions of static loading, while the patient descends an inclined path, the forces causing the bending movement of the knee joint are greater than in walking on a horizontal surface. Many known artificial legs are very difficult to control under these conditions.
The object of the invention is the provision of a knee joint for an artificial leg which achieves the desired gait even under difficult operating conditions without conscious attention or only with a minimum of attention on the part of the patient.
Another object is the provision of a knee joint which is compact and sturdy.
The invention resides in one of its aspects in a knee joint for an artificial leg in which the angular movements of the two leg parts connected by the joint are controlled by a hydraulic system operated by means of a cam.
FIG. 4 shows a preferred embodiment of the knee joint of the invention. It includes a cylinder 1 whose two axial ends are hollow and are respectively closed by threadedly attached caps 2, 3. A shaft 4 is coaxially journalled in the central portion of the cylinder 1 and in the two caps 2, 3. The cylinder 1 is normally attached to the thigh portion of the artificial leg, and the axial ends of the shaft 4 project from the cylinder 1 and carry fasteners 22 which normally fasten the shaft to the lower leg portion of the artificial leg in a fixed angular relationship. Only one fastener is shown in the drawing. A radial bore 27 in the central portion of the cylinder 1 is outwardly closed by a threaded plug 19. An integral nipple 15 radially project ing from the cylinder 1 about the plug 19 is normally re ceived in a conforming recess of the thigh portion of the artificial leg to prevent rotation of the cylinder 1.
The cavity of the cylinder 1 near the cap 2 is axially divided by a piston 5 which is freely slidable on the shaft 4 and is movably sealed to the shaft and to the inner wall of cylinder 1 in a conventional manner, not shown. The piston 5 divides the cavity into a pressure chamber 23 and into an outer compartment in which an annular cam 25 is secured against rotation on the shaft 4 by a key 13. The piston 5 has a radially projecting lug 14 which engages an axially elongated groove 26 in the wall of the cylinder 1 and prevents rotation of the piston relative to the cylinder. The piston 5 is held in engagement with J the cam face 29 of the cam 25 by the pressure of hydraulic fluid in the chamber 23.
The cavity of the cylinder 1 near the cap 3 is divided by a piston 6 which is slidable on the shaft 4 and urged away from the cap 3 by a strong helical compression spring 12. The piston 6 movably seals an expansion chamber 24 in an axially outward direction.
The annular central portion of the cylinder 1 in which the shaft 4 is journallecl is provided with two axial conduits of greatly different flow section which connect the chambers 23, 24 in a parallel arrangement. The narrower conduit is formed mainly by two ducts 16, 20 which connect the aforementioned radial bore 27 in the nipple 15 with the pressure chamber 23 and with the expansion chamber 24 respectively. A plunger 17 is radially slidable in the bore 27. It is formed with an axially open cavity and the open axial end of the plunger 17 is normally held in engagement with the shaft 4 by a helical compression spring 18 interposed in the bore 2'7 between the plug 19 and the plunger 17 An annular groove 30 in the outer cylinder surface of the plunger connects the two ducts 16, 26 in the illustrated axial position of the plunger 17. It communicate with the plunger cavity through bores 31 which are disconnected from the duct 20 when the plunger moves radially outward of the cylinder 1 against the restraint of the spring 18 and separates the ducts 16, 20 from each other. A throttle valve 21 is arranged in the duct 20. It is accessible from the outside and permits the effective flow section of the duct 20 to be adjusted by means of a screwdriver in the same manner as the tension of the spring 18 may be adjusted by turning the plug 19.
The wider axial conduit 28 is provided with a check valve which permits liquid flow through the conduit only in a direction from the expansion chamber 24 to the pressure chamber 23. A ball 8 is normally pressed against a valve seat on a shoulder in the conduit 28 by a spring 7 which is retained by a ring 9.
A disc 10 fastened to the shaft 4 in the pressure chamber 24 by a lock nut 11 blocks the orifice of the duct 20 in the illustrated position of the device, opens the orifice upon rotation of the shaft 4.
The working portion of the cam face 29 is graphically represented in a developed view in FIG. 1 by a curve B in broken lines. As to that curve, the abscissa is calibrated in arbitrary units of axial dimensions. As is evident from FIG. 1, the cam 25 causes rapid axial movement of the piston during intial Stage of the knee bending movement through an angle of about 0.2 radian. The slope of the cam face 29 is then more shallow and uniform to an angle a of about 0.8 radian, and becomes very steep thereafter almost to the point corresponding to maximum bending of the knee. Only the last portion of the cam slope immediately preceding that point is again more shallow.
Hydraulic fluid, not explicitly shown in the drawing, normally fills the chambers 23, 24 and the connecting axial conduits. In view of the afore-described shape of the cam face 29, the knee joint operates as follows:
The bending movement of the knee joint is initiated by the patient who swings the stump of his thigh forward and upward at the hip joint. Inertia and gravity cause the lower leg portion to maintain its angular position relative to the ground. The pressure in the chamber 23 is increased by the inward movement of the piston 5 and the disc is swung away from the orifice of the duct 20. The pressure of the liquid in the chamber 23 is transmitted to the cavity of the plunger 17 through the duct 16, the groove 30, and the bore 31. If the pressure builds up faster in the chamber 23 than it can be dissipated by liquid flow into the expansion chamber 24, the plunger 17 is displaced upward and throttles the narrow conduit from the pressure chamber to the expansion chamber. The liquid being practically incompressible, the rate of angular displacement of the lower leg portion relative to the thigh portion is decreased below that available in the illustrated position of the plunger 17.
When the piston 5 travels over the shallow slope of the cam face 29, it displaces hydraulic fluid from the pressure chamber 23 into the expansion chamber 24 at a rate low enough to prevent a substantial pressure buildup in the chamber 23. The plunger 17 remains in the illustrated position, and the two leg portions angularly move relative to each other at the maximum rate determined by the effective flow section of the narrow axial conduit. This rate may be adjusted for individual requirements by the throttling valve 21, whereas the response of the plunger 17 to pressure in the chamber 23 may be varied by the choice of a suitable spring 18, and by adjusting the stress of the spring by means of the plug 19. The characteristics of the knee joint may be adjusted further by threadedly moving the cap 3 on the cylinder 1, and by therefore altering the stress of the spring 12.
When the piston 5 approaches the end of the cam face 29, its rate of axial displacement in response to angular movement of the leg portions is again increased, resulting in a throttling of the narrow axial conduit between the chambers 23,24 and increased resistance to knee movement. The resulting slowing down of the bending motion is evident from cilrve A in FIG. 1, and is readily controlled by the shape of the cam face 29 to achieve the desired deceleration without shock. The duct 20 is ultimately clocked by the disc 10, thereby securing the knee joint in the bent position.
When the movement of the thigh stump is reversed, the normal pressure in the chamber 23, which is mainly determined by the properties of the spring 12 and is substantially higher than atmospheric pressure under all conditions, drives the piston 5 toward the cap 2. The larger axial conduit 28 is opened by the resulting pressure differential between the chambers 23, 24, and the resistance offered by the flowing liquid to angular displacement of the two leg portions is very small until the piston 5 reaches the lowermost portion of the cam face 29. The latter is readily contoured to arrest the stretching or straightening movement of the lower leg in a precisely controlled manner without shock.
The minor variations in the angular position of the upper and lower leg portions While the leg stands on the ground are adequately controlled by the normal flow sections of the narrow and wide axial conduits in the central portion of the cylinder 1. They do not present any difliculties to the patient.
The apparatus described above permits the wearer to move his legs during walking in a gait which is not readily distinguished from that of a natural leg, and to do so with a minimum of conscious effort spent at controlling the operation of the leg. If the desired gait of the patient should differ from the usual one inherent in the curve A of FIG. 1, the necessary adjustments are readily accomplished by turning the plug 19 or the cap 3. Angular adjustment of the disc 11 also may be necessary and is readily achieved.
The hydraulic circuit is entirely contained within the cylinder 1. It requires but a minimum of space and is safely protected against mechanical damage.
When the patient walks in a downwardly inclined path, the resulting greater forces which tend to swing the lower leg at a higher rate are counteracted by corresponding increased throttling of the narrow axial conduit between the chambers 23 and 24 by the plunger 17. The knee joint of the invention thus provides safe downhill walking without requiring any conscious action by the patient.
It should be understood, of course, that the foregoing disclosure relates only to a preferred embodiment of the invention, and that it is intended to cover all changes and modifications of the example of the invention herein chosen for the purpose of the disclosure which do not constitute departures from the spirit and scope of the invention set forth in the appended claims.
What is claimed is:
1. A knee joint for an artificial leg, having an elongated lower portion comprising, in combination:
(a) a cylinder member defining a cavity and an expan sion chamber therein, and being formed with conduit means;
(b) a shaft member rotatable in said cylinder member about an axis;
(0) fastening means for securing said members respectively to the thigh portion and the lower portion of an artificial leg in a position in which said axis is transverse of the direction of elongation of said lower portion;
(d) a piston axially movable in said cavity in sealing engagement with said cylinder member, said piston member dividing the cavity into a pressure chamber and a compartment, said pressure chamber being connected to said expansion chamber by said conduit means;
(e) engaging means on said piston and on one of said members for securing the piston against rotation relative to said one member;
(f) cam means secured against rotation on the other member and engaging said piston for axially moving the piston when said members move angularly relative to each other; and
(g) pressure means for maintaining a liquid in said expansion chamber under a pressure higher than atmospheric pressure.
2. A knee joint as set forth in claim 1, further comprising throttling means in said conduit means responsive to an increase in fluid pressure in said pressure chamber for throttling fluid flow from said pressure chamber to said expansion chamber.
3. A knee joint as set forth in claim 2, wherein said chambers are axially spaced in said cylinder member, and the throttling means are axially interposed between the chambers.
4. A knee joint as set forth in claim 3, further including means securing said piston to said cylinder member against rotation, and said cam means including a cam member mounted on said shaft member in said compartment and engaging said piston under the pressure of fluid in said pressure chamber.
5. A knee joint as set forth in claim 4, wherein said conduit means include two conduits arranged in parallel between said chambers, and check valve means in one of said conduits for permitting fluid flow through said one conduit only in a direction from said expansion chamber to said pressure chamber, said throttling means being arranged in the other conduit.
6. A knee joint as set forth in claim 5, wherein said throttling means include a throttling member movable in said other conduit between a first position in which the other conduit is at its maximum effective flow section and a second position in which said flow section is at a minimum, yieldably resilient biasing means urging said throttling member to move in a direction from said second toward said first position thereof, a face of said throttling member being exposed to fluid in communication with said pressure chamber in a direction to move the throttling member from said first toward said second position under the pressure of said fluid against the restraint of said resilient biasing means.
7. A knee joint as set forth in claim 6, further comprising blocking means mounted on said shaft member for movement therewith for blocking said other conduit in response to a predetermined angular position of the cylinder member and the shaft member.
8. A knee joint as set forth in claim 7, wherein said pressure means include a piston member axially movable in said expansion chamber in sealing engagement with said cylinder member, and yieldably resilient means urging said piston member to move in the expansion chamber in a direction to drive fluid from the expansion chamber through said conduit means toward said pressure chamber.
References Cited UNITED STATES PATENTS 2,533,008 12/1950 Hanson 31.2 2,859,451 11/1958 Mauch 322 3,069,692 12/1962 Regnell 31.2
DALTON L. TRULUCK, Primary Examiner. R. L. FRINKS, Assistant Examiner.
US. Cl. X.R.