US2784416A - Mechanical action for prosthetic joints - Google Patents

Description

March 12, 1957 w. H. GOODWIN ETAL MECHANICAL ACTION FOR PROSTHETIC JOINTS INVENTORS. Huebner, Beeh/er,

WALTER H. GOODWIN,

808 A KINDRED Worrel, 8 Herzig.

rromvsvs. By

March 12, 1957 w, oonwm ETAL 2,784,416

MECHANICAL ACTION FOR PROSTHETIC JOINTS Filed April 4, 1955 3 Sheets-Sheet 2 \J WALTER H, GOODWIN, 808 A. KINDRED,

INVENTORS.

Huebner, Beehler,

Worrel 8 Herzig.

arramvsvs.

United States Patent MECHANICAL ACTION FOR PROSTHETIC JOINTS Walter H. Goodwin, Sierra Madre, and Bob A. Kindred, Duarte, Califi, assignors to Sierra Engineering Co., Sierra Madre, Calih, a corporation of California Application April 4, 1955, Serial No. 498,906 7 Claims. (Cl. 3-12.2)

The application relates to prosthetics and has particular reference to a joint for an artificial limb wherein the joint is adapted to be locked and unlocked at will by use of a mechanical alternator. More particularly the device is an improvement on the means for locking disclosed in patent application Serial No. 436,284, filed June 14, 1954, of which this is a continuation-in-part.

In recent years great reliance has been placed upon the use of mechanically actuated aids for persons deprived in particular of an arm extremity by use of which a person so afflicted is enabled to perform a great variety of the usual tasks which are expected to be performed by a human arm. The mechanical aids have been such as to make use of whatever portion may remain of the natural arm. To make such use of the natural arm substitute joints have been provided. These joints may be either intermediate the ends of the artificial limb or adjacent one end on those occasions where the artificial limb, for example, might be attached to the stub of a natural limb. Joints which heretofore have been resorted to have to a large extent been located indiscriminately with respect to the natural jointing location of the limb. The result of these expedients has been an awkward appearing and somewhat awkwardly usable mechanical aid not sufiiciently natural to admit of the regular motion of the natural limb. Such aids frequently have been such as to attract unnecessary attention to the necessity for use of such prosthetic devices. Moreover, devices heretofore relied upon have been somewhat complicated in structure, have not been easy to adjust, and more particularly have been stiff and hard to operate to the extent that manipulation often has become a burden upon the person so afflicted. When these occasions exist the artificial limb fails in giving proper encouragement to those persons forced to rely upon such mechanical aids.

More particularly where the mechanical aid has been developed to a point where it is capable of application to jobs requiring considerable force and expertness, those joints which have been relied upon in mechanisms previously available have either tended to ratchet out of proper locked position under heavy stress or, if so designed that they cannot ratchet out of position, then the adjustment at the volition of the user to unlock the joint has been such as to need more force than the user can readily manipulate or can manipulate with sufiicient rapidity and dexterity to make full and unrestricted use of the mechanical appendage.

a considerable degree of comfort and more particularly in a perfectly natural fashion.

Still another object of the invention is to provide a new and improved joint for an artificial limb which includes an alternator mechanism adapted to operate on a relatively short throw .so that the artificial limb can be quickly and readily moved to a desired new position and there immediately fixed for manipulation, the object further including a locking device featuring with suflicient ease and operating in virtual silence without, however, in any way sacrificing the positiveness of the lock when the joint needs to be locked.

Still further among the objects of the invention is to provide a new and improved joint for an artificial limb which is simple in its construction thereby to greatly facilitate assembly as well as operation and to make possible the manufacture of these prosthetic aids at a price which. is as economical as is permissible in view of the positive operation needed, thereby to make such aids available to all who might be in such need.

. .Also among the objects of the invention is to provide a new and improved prosthetic joint wherein the joint i can be immovably locked in position without impairing ease of entry or exit of the locking member, the lock being as capable of adjustment to operate in both directions as to lock in' one direction and to ratchet in the other at a predetermined torque. e

. With these and other objects in view, the invention consists in the construction, arrangement and combination of the various parts of the device whereby the objects contemplated are attained, as hereinafter set 'forth,

pointed out in the appended claims and illustrated in the It is therefore among "the objects of the invention to and which is so formed that the user can wear it with accompanying drawings.

In the drawings:

Figure 1 is a perspective view of an artificial joint of the'type in which the invention herein described is employed.

Figure 2 is a longitudinal sectional view of the device on the central vertical axis.

Figure 3 is a longitudinal sectional view at right angles to the view of Figure 2 taken on the line 3-3 of Figure 2.

Figure 4 is a vertical sectional view through the vertical axis of the device taken on the line 4-4 of Figure 2. Figure 5 is a fragmentary view drawn to a larger scale and with parts removed so as to clearly illustrate the structure and action of the locking arrangement of the present invention.

Figure 6 is a fragmentary view similar to Figure 5 showing a slightly different location of pivot point for the locking bar of the invention.

Figure 7 is another fragmentary view similar to Figure 5 showing still a third possible location for the pivot point of the locking arrangement.

In the form of the invention chosen for the purpose of illustration a prosthetic elbow joint is shown adapted especially to an amputation in the upper arm at some distance above the elbow. In this form a relatively stationary member in indicated generally by the reference character 10. This is that portion adapted to be fastened to the body of the user. For that purpose a fiat plate 11 has a threaded base 12 centrally mounted thereon for securement by an appropriate fixture, not shown, to the arm stub of the user. A washer 15 may be provided at the connection to provide a resistance to rotation.

The plate 11 which may be considered as a platform serves as a means for mounting thereon a pair of spaced parallel plates 16 and 17, the plates and platform preferably constituting a single integral piece. A jacket 18 is provided to serve as a finishing cover for the stationary member. For attachment to the movable artificial member there is provided a relatively movable joint member 3 indicated generally by the reference character 19. The movable joint member is here illustrated as comprising longitudinal extensions and 21 joined by a band 22, both portions being provided with suitable apertures for attachment to the appropriate artificiallimb. The extensions 20 and 21 are attached to a pivot tube or hollow shaft 23, the extensions being non-rotatably fixed relativeto the shaft by means of splines 24. Washers 25 may be providedover the exterior ends of the shaft anchored to each other by means of screws 26 extending into a tube 27-.. Theshaft 23 is so constructed that it pivotsfreely within appropriate bearing apertures 28 and 29, respectively, in the plates 16-and'17.

Intermediate the plates 16 and 17 and non-rotatably' mounted on the shaft 23 is a positioning segment 30. The segment is non-rotatably secured to the shaft by means of aset screw 31. The positioning segment has an. arcuate perimeter 32 in which-is a series of spaced notches 33 separated by sections 34, the outer ends of the sections 7 lying in the plane of the arcuate perimeter. Shoulders 35 and 36 on opposite ends of the arcuate perimeter are provided with suitable pads 37 adapted for abutment against a stop-block 38, thereby to limit rotation of the movable member'19'relative to the stationary member 10. The'stop block is secured to and forms. apart} of the stationary member 10-.

A -catch is-provided on the stationary member 10 for engagement with the movable member 19 in. order to anchor it in-any one of its various positions of adjustment. The catch comprises in part a lever 39 pivotally jointed by means of a pin 40 to a bracket 41. The leveris therefore permitted a limited rotation about the pin- 40-. The lever is normally urged in a direction clockwise, as viewed in Figure 4, by means of a spring 42, one end 43 of which is'wound'loosely around the pin 40 and brought. into abutment against a pin 44 on the lever. The otherend of the spring presses upwardly against a portion 45 of thestationary member 10.

The-lever 39 in the form here shown comprises parallel side elements overlying opposite faces of the positioning segment and includes alocking bar or block 46- extending between the sides in a position adapted to fall into one or-another of the notches 33. The lever is designed to be held in one of two positions, namely, in a disengaged positio'nwherein the locking bar is engaged in one of the notches 33 and a position withdrawn therefrom, per- .mitting the movable member 19 to pivot freely with respect tothestationary member 10. For holding thelever in either one of these two positions there is provided a leaf spring 47, one end 48 of which is anchored on a portion 49' of the stop block 38 by means of a pad and screw 50. A free end 51' of the spring has a hook in the form of a pin 52 attached thereon, the pin being adapted to extend beyond the edge of the spring into positions of engagement with a cam 55. The cam 55 has a tapered end 56 facing obliquely upwardly, as viewed in Figure 3, at one side of the pin 52. On'the face of the cam opposite fromthe tapered end 56 is a recess 57 located between round ends 58 and 59. A guide 60 fastened upon one side of the lever 39 as is also the cam has a tapered end extending into the recess 57 providing thereby a guideway or track within which the pin 52 is confined when it enters and leaves the'recess 57. A damping pad 61 is secured to and extends throughout a substantial portion of the length of the spring 47 in order to minimize vibration of the spring during operation and resultant noises which might be disconcerting to the user.

For manipulating the mechanism thus described, there is provided a cable 65 adapted to be attached to a conventional shoulder harness, not shown. The cable 65 is appropriately fastened to the lever 39 near its free end thereby to provide a means for moving the lever against tension of the spring 42. p

In operation when the parts have the positions ilcounter-clockwise, as viewed in Figure 4. The new posi tion is the broken line position 39 shown in Figure 3.

While that movement is taking place, the pin 52 slides down the adjacent face of the cam moving toward the right, as viewed in Figure 3, until it passes the rounded end 58, at which point the pin will be sprung back by spring action against'the guide 60 preparatory to entrance into the channel orguide-way provided between the recess 57 and the guide 60. The guide and the side of the recess opposite thereto prevent the pin 52 from being sprung past the cam at this point. When the cable 65 is then released, the spring 42 moves the lever 39 a slight distance counter-clockwise, as viewed in Figure 3, until the bottom of the recess 57 is pushed against the pin 52. The relationship of the parts is such that in this position the locking bar 46 will be clear of the perimeter 30. Consequently the movable member 19 may be rotated at will by some appropriate conventional attachment, Well known in this branch of prosthetics.

When the movable member is moved to the-desired position, the member can be anchored there by a succeeding pull upon the cable 65. When the cable is pulled upon at this time, the cam 55 is pulled away from the pin 52 which rides out of the channel adjacent the rounded end 59 and is sprung past the rounded end 59 by tension in the spring so that the pin 52 is in a position adapted to ride against the lower cam face of the cam 55.. Then when the cable 65 is released, the pin will ride along the lower cam faceuntil it passes the tapered end 56, after which itwill be sprung back to the initial position illustrated in Figures 4 and 6. In that position the lever 39 will have been sprung back against the positioning segment until the locking bar 46 enters theappropriate notch- 33. Here also should the locking bar fall against one of the sections 34 between notches 33, the weight of the forearm will be sufficient to cause the locking block to fall into the next adjacent notch. Should this additional movement be not desirable, the sections 34 may be rounded slightly so that the locking bar will automatically enter the nearest adjacent notch.

In prosthetic joints of the type herein described the importance of'a secure but easily operated lock has already been stressed. The lock moreover must beone whichcan be easily manipulated by, for example, a slight hitch or movement of the shoulder of the user whereby some form of harness is adapted to transmit the movement through the cable 65 to the alternator and the lever in order to lift it out of locking position and to again lift it to a new position wherein it can be spring-pressed into locking engagement. The locking bar must slide quickly and easilyinto the notch provided for it. There must beat relative minimum amount of clearance, thereby to improve'the ease of operation and to make the locking engagement and disengagement as silent as possible.

In a form of the invention illustrated in Figure 5 the segment 30 isshown adapted to rotate about an axis 71 which is theaxis or center of rotation of the tube or shaft 23 previously referred to. The notches 33 and sections 34 are duplicated in Figure 5, spaced as previously described about the arcuate perimeter 32.

The lever 39. is' shown by use of a broken line so positioned that it is adapted to rotate about an axis 72 which is the center of thepin 40.

Each of the notches consists of opposite faces 73 and 74 which extendfrom theperimeter 32 inwardly to a point tangent to a rounded bottom wall 75. Thenotches 33 are-identical such that a description of one will suffice for all. V

In the form illustrated in Figure 5 the faces 73 and 74 are, arcuate and described in the case of; the face 73 by a radius 76 which is equal to the distancebetween the axis 72 and the center of the face 73 intermediate its outside and inside ends, indicated by the points 77 and 78, respectively.

The face 74, being arcuate as noted, is of slightly different radius in that it is an arcuate form described by a radius equal to the distance between the axis 72 and a point 81 midway between the points 79 and 80. The point 81 is separated by a distance from point 82 immediately opposite, which distance is in excess of the thickness of the locking bar 46 plus an appropriate clearance. The clearance should be no more than enough to permit the locking bar to slide freely into the notch to the position illustrated in Figure 5.

The locking bar 46 is also provided with opposite faces 83 and 84 which are arcuate and which are complementary to the respective faces 73 and 74. The curvatures of the arcuate faces 83 and 84 are again determined by a radius equal to the distance between the axis 72 and the center of the respective faces '83 and 84.

A radius 85 is indicated by the distance between the axis 71 and a point 86 which is on the line between the points 81 and 82 mid-way between outside and inside ends of the faces of the locking bar, these being points identical with mid-points between outside and inside ends of the faces 73 and 74 of the notches 33.

In the arrangement of Figure 5, which may be considered as a practical and workable arrangement, the forces and their effect upon the mechanism can be explained with reference to a vector diagram predicated upon application of force to the extensions 20 and 21, which force is transferred through the tube or shaft 23 to the segment 30. Assuming the application of this force to be in a clockwise direction, the force exerted by the segment on the locking bar and lever may be represented by a tangential vector 90. This force is resisted by the locking bar and lever and the resistance may be expressed by a radial vector 91 through the axis 72 as -a center and by a tangential vector 92. Similarly should the application of force to the segment be in a counterclockwise direction, it would result in a force expressed by the vector 94 resisted by the tangential vector 95 and the radial vector 96. It will be noted that the vectors 92 and 95 represent forces which act either to engage or disengage the locking bar. In the case shown in Figure the bar is forced into engagement by operation of a counter-clockwise loading. There is present a small force tending to disengage the bar should the loading be clockwise. This force, by reason of the fact that it is less than the force of friction between the bar and the tooth, is not sufficient to disengage the bar and hence the bar remains in engagement when the segment is loaded in this or the opposite direction.

It will be noted further that a line 97 lies tangent to the circle described by the radius 85 at the point 86 and that this in the specific instance shown shows an angle of four degrees and 20 minutes between the tangent line 97 and the radius 76 about the center 72 struck through the point 86. The point 72 which is the center of rotation of the lever 39 therefore lies in this chosen example insi deof the tangent line 97 which is drawntothe circumference struck- -by-theradius 85 at'the location of bar engagement with a notch.

With the structure already described there are some variations permissible in the location of the axis of the pin 40 with respect to the tangent line 97 already referred to. In Figure 7, for example, the axis is indicated by the reference character 72 and is made to lie upon the tangent line 97, which line is that previously described as tangent to the perimeter of an arc struck by the radius 85 at the center of engagement of the bar 46 with the engaging notch 33. This represents a theoretically ideal arrangement for equal locking in both directions of aphowever, thatwhere mechanical expediencies indicate some different arrangement to be feasible, it is not essential to maintain the theoretically perfect or ideal arrangement to secure the desired operation of the principle herein disclosed.

In the theoretically ideal arrangement of Figurel7, a clockwise force applied to the segment 30 results in a force expressed by the vector 100. This force is resisted by a radial vector 1'01.and a tangential vector 102. It will be noted that under those circumstances where the force is applied inan opposite direction. to the segment 30 vectors 103, 104 and 105 are equal in value to the vectors 100, 101 and 102. This means that there will be no tendency to disengage the locking bar 46 regardless of which directionforce is applied to the extensions 20 and 21. Moreover, in this theoretically ideal arrangement the lifting 'force necessary to lift the locking bar out of engagement with the notch when that occasion requires may be slightly-greater than the lifting force required of the arrangement of Figure 5 where there is a slight tendency to disengagement in one direction. The

balance, however, in the opposite direction is contrary and hence the required lifting force when action in either direction is contemplated will be substantially the same for both arrangements. I

The arrangement of Figure 6 shows location of, the axis 72" on a line 106, which line is tangent to the radial line namely, the radial line 85 shifted to the position where it intersects the point 82. In point of fact the arrangement thus described sets the axis 72" 'at an angular distance from the tangent 97 previously referred to of three degrees. In this arrangement there is no force corresponding to the force indicated by the vector 92 of Figure 5. Consequently there is a state of equilibrium existing and a locking force indicated by the vector 107 is double that of the vector or 102 of Figure 7. This indicates that the locking bar and segment arrangement will be positively locking for centers of the pin 40 located between lines drawn tangent to the radial lines through the centers of both tooth faces 73 and 74.

It will be clear from the explanation that there is some variation possible in the location of the axis of the pin 40 but that variation will need to be within certain limits dependent upon the frictional force existing between the face of the tooth and the face of the locking bar which are in engagement depending upon the direction of rotation of the segment. When the axis of the pin is located outside of those limits, there will be a tendency of the locking bar to ratchet out of engagement in one direction of rotation for the segment and to lock with great force in the opposite direction, depending upon whether or not the pin is above or below the range indicated, as viewed in Figures 5, 6 and 7, for example. The workable range, however, has been described. Moreover, in the event of a tendency to ratchet, the tendency may be controlled by varying also the amount of spring force applied to the lever 39 and hence the locking bar in addition to the selectionof location for the axis of the pin 40.

There has accordingly been described herein a precise and effectively working structural arrangement of locking bar and tooth segment which is productive of a particularly effective and efficient lock and unlock alternating device for such use as in prosthetic joints which greatly facilitates the smoothness of their operation and enhances to a great degree the value of such joints to those persons afllicted with injuries which necessitate their use. I

While we have herein shown and described our invention in what we have conceived to be the most practical and preferred embodiment, it is recognized that departures may be made therefrom within the scope of our invention, which is not to be limited to the details disrilosedslierein'but is tozbe accorded the full scope of the claims-,so as wto ,embrace any and all equivalent devices. fHaving described ourinvention, what we claim as new and desire to secure by LettersPatent is:

"1 A mechanical action for artificial limb joints comprising arelatively stationary member and a ratchet segment rotatably mounted on the member, alever rota- ,tabl-y mounted on the member with the rotational axis adjacent to'the circumference of the ratchet segment, a locking bar on said lever'having opposite curved faces positioned generally perpendicular 'to the radius from the rotational .axis of the lever, said segment having a :series of spaced generally radiallyextending bar receiving notches with faces complementary to the respective 'faces of the bar'when in bar receiving position, said rotational axis'of the lever being' at a point adjacent a line "tangent to'an arc'about the-axis of said segment struck through the centers of the faces'of said notch.

'2. "A mechanical action for artificial limb joints comprising a relatively stationary member and a ratchet segment-rotatably mounted on themember on the axis of rotation of the joint, a lever rotatably mounted on the member with the rotational axis adjacent to and exterior of the circumference of the ratchet segment, a locking baron said lever having opposite faces positioned generally perpendicular to the radius from the rotational axis of the lever and the faces, saidsegment being subject to :a rotative load and having a series of spaced generally -radially extending bar receiving notches with faces complementary to the respective faces of the bar when in bar receiving position, said-rotational axis ofthe lever being withinan angular distance of a line tangent to an are-about the axis of said segment struck through the centers of the faces of said notch such that the component rofthe force resulting from. application of a rotative load 'tendingto disengage the bar from the notch is less than vthe'frictional force on the respective contacting faces.

3. A mechanical action for artificial limb joints comprising a relatively stationary member and .a ratchet :segment-rotatably mounted on the member on the axis of rotation of the joint, -a lever rotatably mounted on the member with the rotational axis adjacent to and exterior of the circumference of the ratchet segment, a locking bar on said lever having opposite arcuatefaces positioned generallyperpendicular to the radius from the rotational axis of the lever and the faces, said segment having a ,series of spaced generally radially extending bar receiving notches with arcuate faces complementary to the respective faces of the bar when at bar receiving position, said rotational axis of the lever being within an angular distance of five degreesinside of a line tangent to an are about the axis of said segment struck through the centers of the faces of said notch.

4. A mechanical action for artificial limb joints comprising a relatively stationary member and a ratchet segment rotatably mounted on the member on the axis of rotation of the joint, a lever rotatably mounted on the member with the rotational axis adjacent to and exterior of the circumference of the ratchet segment, a locking bar on said lever having opposite arcuate faces of radius of curvature determined by the distance between the .rotational axis of the leverand the respective face, said segment having a series of spaced generally radially extending bar receiving notches with arcuate ffaces comple mentarytotherespective faces of'the bar, vsaid rotational axis ,of theflever being at a ;point 'within ;an angular distance of 15 degrees 'on either side "of 'a line tangent to an are centered atthe axis of said segment'and through thevcenters ,of'thefaces of a notch i n'bar engaging position, the faces 'of said notches having positions wherein said last; faces are in engagement substantially throughout their areas'with the re spective faces of thebar when in bar'engaging position. 1'

5. A mechanical action for; artificial limbjoints comprising apair of members wherein one member is adapted for attachment to a natural limb, parallel plates on one of the members, the other ofsaid members comprising a tubular sleeve rotatably mountedon-said plates providing thereby an articulating joint for said action, a'ratchet'segment fixed;on said sleeve having a series of'spacedgeneral ly radially extending notches, alever pivotally mounted at acenter of rotation on'said one member, a locking bar fixed transversely on the lever, and an alternator connected between thevleverand ,one of said -,members adapted to releasably hold said'bar 'out'of notch engagementposition, said bar having opposite notch contacting facescurved in the same general direction and saidrnotches having opposite curved bar engaging faces complementary to and adapted to engage 'the respective faces of :the bar when in bar engaginggposition.

6. A mechanical action for artificial limb joints comprising a relativelystationary member adapted for attachment ,to a natural limb, parallel plates on said member and'a tubular 'sleeve 'rotatably mounted on said plates providing thereby an articulating joint for said action, a ratchet segment fixed on said sleeve having a series of spaced generally radially extending notches, a lever pivotally mounted'at a'center of rotationon said member, a locking bar-fixed transversely on the lever, a spring on said member normally urging said bar toward a notch engagement position, and an alternator connected between said member and the lever adapted to releasably hold said bar out of notch engagement position, said bar having opposite notch contacting faces of arcuate form and of radius determined by the-distance between the respective face and said center of rotation of the lever, said notches having opposite bar engaging faces of arcuate form complementary to and adapted to engage the respective faces of the bar when in bar engaging position.

7. A ratchet resistant mechanical action for artificial limb joints comprising a base, a ratchet segment rotatably mounted on the base and a locking bar having a pivotal mounting on said base, said locking bar having opposite segment-engaging faces curved in the same general direction about the axis of said pivotal mounting, said segment having a series of peripheral bar receiving notches with opposite faces respectively complementary to the faces on said bar.

References Cited in the file of this patent UNITED STATES PATENTS Germany Feb. 11, 1918

Images