EP0713566A1

EP0713566A1 - Spherical rolling ball joint device

Info

Publication number: EP0713566A1
Application number: EP94917705A
Authority: EP
Inventors: Michel Martial Revest; Thierry Leblond; Richard Zimmermann; Patrick Thiebault
Original assignee: Individual
Current assignee: Individual
Priority date: 1993-06-04
Filing date: 1994-06-02
Publication date: 1996-05-29
Also published as: FR2705883A1; AU6931994A; FR2705883B1

Abstract

Joint device comprising a concave sphere portion (14) of a first inner radius, a convex sphere portion (16) of a second outer radius, a plurality of balls (18) disposed in the space formed between both sphere portions (14 and 16), their diameter being equal to the difference between the first and second radius, and a rigid element (20) integral with the convex sphere portion (16) capable of performing angular movements by using the convex sphere portion (16) as a first ball joint. The balls (18) are captive in the space between both sphere portions (14 and 16) in a circular groove (30) in which they are no longer subjected to friction and can therefore be easily recycled. The unit is contained in a spherical cupule (12) in which the concave sphere portion (14) can move in firm frictional engagement, thereby functioning as a second ball joint. Such a dual ball joint device can be used as an articular prosthesis.

Description

Articulation device with spherical ball bearing

Technical area

The present invention relates to articulation devices of the ball joint type which can be used in particular as joint prostheses, and relates in particular to an articulation device with a spherical ball bearing.

STATE OF THE ART There are already many joint prostheses to date. Such joints generally consist of a male part consisting of a cap with a concave internal surface, and a female part intended to be inserted into this male part. In the hypothesis of a prosthesis intended to be inserted into a living organism, for example in the human body, these joints generally emit wear particles. Indeed, the sliding of the different parts on top of each other by friction, causes tears in the form of free particles. These free particles are considered by the organism as foreign agents, which attack them by producing chemicals which destroy the bone skeleton and which therefore cause the loosening of the prosthesis. This wear therefore results in a limitation of the life of the prosthesis.

Furthermore, it has been shown that the movable contact surfaces of these prostheses wear out around one tenth of a millimeter per year, and therefore that the service life associated with normal use of the prosthesis does not exceed twelve to fifteen years. The game then reaches more than a millimeter and the degradation then accelerates suddenly resulting in necessarily a new operation. Therefore, even if the interface between the bone and the prosthesis is perfect, the surgeon may have to unseal the part to replace it with a new one, which is much more traumatic than a first operation. The prostheses must be robust, resistant to the highly corrosive environment of the organism, capable of absorbing vibrations, capable of withstanding significant stresses (in the case of the hip for example), capable of angular deflection geometry greater than that of the normal anatomy and of a lifetime greater than the life expectancy of the patient under the conditions of use corresponding to those of a sports person. To date there are already joint prostheses which try to overcome these drawbacks, and therefore to limit wear particles, by using ball bearings inserted between the male part and the female part, as described for example in the document. EP-A-0.481.855. But one of the problems posed by this type of articulation is the recycling of the balls during the movements of the male part inside the female part. This recycling is necessary if one wants to avoid significant friction of the balls which oppose the movements. To do this, the device described in the above document provides a cavity located in the female part in which the balls are driven by the movements of the male part. But to reach this cavity, the balls are forced to make a trajectory break at 180 * and to go back up into the cavity where they are released from friction. Such an arrangement inevitably leads to considerable friction of the balls on the walls due to the rather "uneven" course that they have to perform to recycle.

Statement of the invention

This is why a first object of the invention is to produce an articulation device, usable in particular as a prosthesis, of the ball-and-socket type ball bearing having a means of recycling the balls avoiding any friction. Another object of the invention is to produce a hinge device with two ball joints usable in particular as a prosthesis, in which a ball bearing ball joint is included in another ball joint with solid friction.

A first object of the invention is therefore a ball bearing articulation device comprising a portion of concave sphere of a first inner radius, a portion of convex sphere of a second outer radius, a plurality of balls arranged in the space formed between the portion of concave sphere and the portion of convex sphere and whose diameter is equal to the difference between the first radius and the second radius. A rigid element secured to the portion of the convex sphere is caused to make movements relative to the portion of the concave sphere by using the portion of the convex sphere as the first ball joint. The means for recycling the balls is a circular groove formed in the portion of concave sphere on the perimeter of the opening which the latter defines and thus delimiting the space between the portion of concave sphere and the portion of convex sphere, this groove circular having a width in the radial dimension slightly greater than the diameter of the balls so that any ball brought into the groove by a movement of the rigid element is freed from any friction stress and can easily be evacuated along the groove circular so that the recycling of the balls does not create any friction opposing the movements of the rigid element. Another object of the invention is a device as described above in which the portion of concave sphere is inside a spherical cup, the outer wall of the portion of concave sphere being in contact with the wall inside the cup and being able to move angularly relative to the latter so as to act as a second ball joint for the rigid element. Brief description of the figures

The aims, objects and characteristics of the invention will be better understood on reading the following description made with reference to the drawings in which: FIG. 1 represents the articulation device according to a preferred embodiment of the invention, in a first position without rotation, FIG. 2 represents the circular groove for recycling the balls of the articulation device according to the present invention, FIG. 3 represents the articulation device illustrated in FIG. 1, having undergone a rotation of the ball joint ball bearing, FIG. 4 represents the articulation device illustrated in FIGS. 1 and 3, having further undergone a rotation of the ball joint with solid friction, and FIG. 5 represents the articulation device according to another embodiment of the invention.

Detailed description of the invention

Referring to FIG. 1, the articulation device used as a prosthesis comprises a structural or acetabular frame 10 intended to be fixed for example in the femoral cavity and having a concave internal surface in which is inserted a spherical cup 12. A portion of concave sphere or confinement shell 14 is placed in the hemispherical space delimited by the spherical cup 12. A portion of convex sphere 16 is introduced into the concavity of the concave sphere 14 while being separated from the latter by a layer of balls 18 The convex sphere 16 has a fitting hole (not shown) in the form of a standardized cone into which a stick 20 is inserted, the other end of which is intended to be installed in the framework of one of the members to be articulated. At the base of the portion of the convex sphere is a flange 22 preventing excessive rotation of the portion of the convex sphere in the portion of the concave sphere 14 as will be seen below.

The layer of balls 18 is trapped in the space between the portion of the convex sphere 16 and the portion of the concave sphere 14 by means of a cover 24 comprising a circular groove for recycling the balls. Although the circular groove is in a separate cover in the embodiment illustrated in Figure 1, it goes without saying that it could be an integral part of the portion of concave sphere 14 whose opening would then have the shape of the cover 24 shown in FIG. 1.

A magnification of the circular groove 30 located in the cover 24 is illustrated in FIG. 2. As can be seen in this figure, the balls 18 are wedged between the wall of the convex sphere 16 and the interior wall of the concave sphere 14 because their diameter is equal to the difference between the radii of these two spheres. However, the last ball 18-n is in contact with the previous ball and with the bottom of the circular groove 30, but is no longer in contact with the wall of the convex sphere portion 16 because the width of the groove is greater than the diameter of the balls.

During the rotation of the portion of the convex sphere 16 inside the portion of the concave sphere 14, if the convex sphere has an animated movement of a speed V in the direction of a meridian, the balls are animated by a rolling movement without friction of speed V / 2, also in the direction of the meridian. When the ball, for example 18-n, reaches the circular groove 30, it is no longer wedged between the walls of the convex and concave spheres and can then freely engage without friction in the circular groove (therefore along a parallel of the sphere) while being entrained by the other balls also being in the circular groove. No longer being trapped by the walls, the change of direction of the ball 18-n at 90 * therefore occurs without friction. In other words, the circular groove 30 discharge of any stress the balls which arrive at a "source of balls", and allows them to be quite naturally driven without friction in the direction of a "well of balls" from where they will be reinjected into the layer of marbles. Indeed, at the moment when the ball 18-n reaches the circular groove in its movement along the meridian of the sphere, another ball, being opposite in the circular groove, is entrained in the layer of balls by rolling without rubbing at speed V / 2 along the same meridian, between the walls of the portions of convex and concave spheres. There is therefore strictly speaking "recycling" of the balls via the circular groove.

In the embodiment shown in FIG. 1, the portion of concave sphere 14 can move inside the spherical cup 12 by solid friction of the walls in contact with one another. The operation of the articulation device according to the invention is therefore comparable to a double ball joint, the first ball joint being with ball bearing 18 between the portion of convex sphere 16 and the portion of concave sphere 14, and the second ball joint being in friction solid between the portion of concave sphere 14 and the spherical cup 12.

The operation of the double ball joint is illustrated in FIGS. 3 and 4. As can be seen in FIG. 3, the butt 20 has made an angular displacement X by subjecting the portion of the convex sphere 16 to maximum rotation in the portion of concave sphere 14 since the flange 22 is in abutment against the cover 24. This rotational movement called upon the only first ball joint and the rolling of the balls 18. In fact, the geometric movements which the butt 20 undergoes are of two kinds: roll type movements and site / deposit type movements. The high confinement of this first ball joint limits its use to only low angular deflections and roll. This first ball joint which has a low starting torque compared to that a solid friction ball joint (factor of 10) absorbs all the rolls as well as the sites and deposits of low amplitude which in fact represent 95% of the movements carried out by an individual. Thus, the maximum angle α is less than about 16 *.

The operation of the second ball joint, illustrated in FIG. 4, is done by solid friction between the outer wall of the concave sphere 14 and the inner wall of the cup 12. This solid friction uses a pair of materials having a low coefficient of friction solid under load, for example the metal (sphere 14) / ultra high density polyethylene (cup 12) couple. This couple is interesting for its anti-friction, anti-wear, bio-compatible properties (frequent use in the medical field). In addition, polyethylene gives the whole system anti-vibration properties allowing good impact resistance. Finally, the retained metal, preferably a hardened chrome-cobalt alloy, constitutes at this date the best compromise of resistance to compressive stress, resistance to puncture, resistance to highly corrosive atmospheres in the field of application considered (medical , aeronautics, space, cybernetics). Compared to a ceramic such as alumina or zirconia, it also has the advantage of easy machinability and especially that of excellent impact resistance, particularly at the flange when the part reaches maximum amplitude. and comes to a stop. This alloy can be the subject of an additional surface treatment intended to increase its micro-duration and therefore its resistance to solid friction on the convex side, as well as its resistance to punching on the concave side. This surface treatment can be a sputtering deposit such as ion implantation of nitrogen or amorphous hard carbon or titanium nitride, or else a plasma spray deposit such as zirconia, chromium or any other deposit intended to increase the surface hardness of the metal. It should be noted that the portion of the convex sphere is preferably made of the same metal or alloy as the portion of concave sphere serving as the second ball joint.

The balls 18 can be ceramic or metal. However, in order to avoid introducing harmful electrochemical couples between the portion of convex sphere 16 or the portion of concave sphere 14 on the one hand, and the balls 18 on the other hand, it is preferable to have balls constituted of the same metal (or alloy) as the portions of convex sphere or concave sphere. As can be seen in FIG. 4, the stock has undergone a rotation of an angle φ in addition to the first rotation α by means of the first ball joint, this second rotation, due to the starting torque of the second ball joint much more important that the starting torque of the first ball joint does not start until the end of the maximum travel α obtained by means of the first ball joint. It therefore only takes place for large angular deflections, that is to say greater than about 16 * and can extend up to an angle φ of about 34 * as illustrated in FIG. 4 when the butt 20 arrives at abutment against the cup 12. However, these large amplitude displacements, since they are between approximately 16 * and 50 *, represent only around 5% of the movements of an individual. Consequently, wear and tear, as it occurs in the devices of the prior art, is no longer a determining factor since the life of such a device is multiplied by 20.

The assembly of the articulation device illustrated in FIG. 1 is done by introducing the portion of convex sphere 16 inside the portion of concave sphere 14 previously filled with an adequate quantity of balls 18. In order to be able to enter the convex sphere, it is imperative that the diameter of the latter is less than the diameter of the opening of the concave sphere. Then the balls are finished and the cover 24 ensuring the closure is mounted, either by screwing, or by mounting under nitrogen and welding by electron beam or rays laser to ensure a good seal. It should be noted that, in order not to cause discontinuity in the raceway of the balls, the connection of the cover must be made on the edge of the circulation groove, without play.

In the preferred embodiment of the invention as a joint prosthesis, in particular for the lower limbs, the portion of the convex sphere 16 has a diameter between 10 and 25 mm, the balls 18 have a diameter between 0.5 and 2.5 mm , ie between 5 and 10% of the diameter of the convex sphere, and the concave sphere 14 has an internal diameter between 11 and 27 mm. In a particularly recommended embodiment, the diameter of the convex sphere is 22.83 mm, that of the balls is 1.587 mm (1/16 inch) and the interior diameter of the concave sphere is 26.004 mm. A prosthesis produced with such dimensions makes it possible to support a load of between 1.2 tonnes and 2 tonnes depending on the materials used, therefore much greater than the weight that a prosthesis has to support. It is understood that these dimensions are given by way of example but cannot be limiting.

It will be noted that the concave sphere-cover assembly closes well beyond the equatorial plane of the convex sphere over a distance allowing the imprisonment of at least 3 rows of balls relative to the equator. This arrangement blocks the convex sphere in the device while leaving enough room for the circular groove. Although it can take all possible positions as a joint prosthesis, the articulation device shown in Figures 1, 3 and 4, is most often arranged with the stick directed vertically downwards, the balls being in the upper part , especially when it is a femur prosthesis. This has the disadvantage that the effort due to the weight of a part of the body is focused mainly on the balls situated at the top of the portion of the convex sphere, and in particular on the ball which occupies the highest position when the device has not undergone any angular displacement and the stock is vertical. This is why a solution consists in leaving the top location without a ball or, in other words, in removing the ball occupying this position when the balls are placed inside the portion of concave sphere. It is also possible to remove not the top ball, but this one and the 6 balls which surround it and which also support a greater load in the rest position. Of course, the location without balls is caused to move when the prosthesis undergoes angular displacements, but it is always found at the top of the portion of the convex sphere when the prosthesis returns to the vertical rest position because the balls are jammed. between the two walls and roll without sliding.

Another variant consists in replacing the solid friction of the second ball joint by a ball bearing identical to that described above. In this case, the cup 12 is replaced in whole or in part by a layer of balls identical to the balls 18, and also comprises a circular groove situated at the opening of the structural frame 10 (see FIG. 1) whose function is to recycling the beads of this second layer in the same way as explained above.

Although the articulation device of the invention finds mainly application in the field of prostheses, it is also possible to use it in other fields as a ball joint or double ball joint.

Indeed, the ball joints are the subject of many applications in aeronautics with among others:

- wing ball joints,

- the landing gear ball joints, - the long service life ball joints.

The wing ball joints are mounted in an inaccessible manner at various critical points such as: complex articulations of the various moving surfaces of a wing. The current service life is in the best case 50,000 cycles in difficult environmental conditions with severe pollution. Finally, a particular feature of mounting these ball joints involves a movement of the outer ring relative to the fixed inner ring, a situation opposite to that which is encountered in the vast majority of cases, that is to say the inner ring and the axis rotating by compared to the fixed outer ring.

The landing gear ball joints are repeatedly subjected to rough loads or impacts. Multiple metal / metal ball joint technologies exist to meet the requirements of this application. The maximum number of solicitations currently obtained is around 100,000.

To reduce maintenance operations, we have gradually succeeded in considerably increasing the service life of certain self-lubricating ball joints subjected to small amplitude movements such as oscillations or swivels of 1 * to 8 * maximum, movements exerted at frequencies several cycles per second. Durations of several thousand hours, or several tens of millions of cycles, are necessary under average load conditions. Obviously an infinite lifetime is strongly desired.

All the above-mentioned ball joints work on the principle of solid friction.

The main improvements made to date are essentially aimed at extending the life of these ball joints and reducing friction torques, thanks to self-lubricating coatings, and to surface treatments to increase the micro-hardness of the material and increase its resistance. to wear. Other fields such as cybernetics, the automobile or the space field also call for ball joints. For all these areas, the ball joints available on the market all work on the principle of solid friction. The improvements made to their operation always relate to the improvement of the binomial in contact in order to reduce the friction torque and to increase the greatly limited lifetime.

An example of a double ball joint according to the principles of the present invention and applicable to the fields mentioned above is illustrated in FIG. 5. The whole of the articulation is placed in an outer ring 40 (analogous to the structural reinforcement 10 in FIG. 1) and comprises a friction ring 42 (corresponding to the spherical cup 12), a portion of concave sphere 44 whose outer surface moves by friction in the friction ring 42, for example made of ultra high density polyethylene, and a portion of convex sphere 46 separated from the portion of concave sphere 44 by a layer of balls 48. This layer of balls forms a spherical ring between two parts with circular grooves, a first part with grooves 50 placed at the top of the layer of balls in the figure and a second grooved part placed at the bottom of the layer of balls in the figure.

In FIG. 5, it can be seen that the portion of the convex sphere is extended on each side by two arms 54 and 56, the junction of which with the portion of the convex sphere is made by flanges 58 and 60. The ball joint is shown in a position where it has undergone a maximum angular displacement (approximately 16 ′) since the flange 58 is in abutment with the circular grooved part 50. An additional angular displacement of the assembly of the two arms 54 and 56 would cause the concave sphere 44 to pivot by friction inside the friction ring 42 and thus play the role of the second ball joint. An angular movement can take place in the same way in a clockwise direction. it should be noted that, whatever the angular displacement of the arms 54 and 56 in the direction of the needles of a watch or in the opposite direction, the two circular grooves 50 and 52 are used simultaneously for recycling the balls.

Unlike the first embodiment of the articulation device as a joint prosthesis, the realization of the device of the invention as a double ball joint in the mechanical field is not limited in its dimensions. These will in fact depend on the loads that the device will have to bear. The combination of two ball joints according to the invention may be of additional technical interest in the sense that the centers of rotation of the 2 ball joints may not be confused. A voluntary off-center can be taken advantage of to obtain by a three-dimensional phenomenon a rocking effect by a combination of site / deposit on a ball joint and roll on the other ball joint, this phenomenon is particularly interesting when specific movements are sought and that the overall dimensions must be reduced to a minimum in a given angular direction: the case of the shoulder joint illustrates this phenomenon.

In another alternative embodiment, it can be provided that one or the other of the two ball joints does not have a spherical shape, but an ellipsoidal shape. Thus, the internal ball joint can comprise a convex portion 16 (see FIG. 1) of ellipsoidal shape inside a concave portion 14 also of ellipsoidal shape having a constant distance from the convex portion 16, said distance corresponding to the diameter of the balls 18. The ellipsoids formed by the convex 16 and concave 14 parts in all cases have an axial symmetry about the common axis which is also that of the rigid element 20. With respect to the axis, the ellipsoid is, either flattened at the top (lens type) if the load to be supported is mainly axial, or flattened on the sides (rugby ball type) if the load to be supported is mainly radial. In this type of device where the circular groove no longer has its usefulness as in the case where all the parts are spherical, the ball joint of ellipsoidal shape is used for the movements of roll whereas the ball joint of spherical shape (for example that with solid friction) is used for the sites and deposits.

The articulation device also has other advantages than those mentioned with reference to the figures. Thus, the use of a material such as ultra high density polyethylene for the spherical cup of the second ball joint makes it possible to increase the resistance of the device with respect to impact stresses, allows the absorption of vibrations at the level of the ball joint and finally makes it possible to reduce the mechanical stresses at the level of the contacts of the balls on their rolling surfaces.

Finally, the articulation device according to the invention is interchangeable and compatible "downwards" by means of a standardized bore (case of the aeronautical application), or by means of a conical hole of the standardized morse type. (case of medical application). It is interchangeable and compatible "upwards" by means of a standardized sphere (diameter, surface condition, sphericity, tolerance on the diameter) fitting inside a cup made of ultra high density polyethylene (case of medical application) itself housed in a metal ring (case of mechanical application). This assembly can also be reduced to a simple standard ring with a self-lubricating coating similar to what is encountered in the case of conventional ball joints.

Claims

1. Ball-bearing articulation device (14, 44) with balls comprising a portion of concave sphere of a first internal radius, a portion of convex sphere (16, 46) of a second external radius, a plurality of balls (18, 48) arranged in the space formed between said portion of concave sphere and said portion of convex sphere and whose diameter is equal to the difference between said first radius and said second radius, a rigid element (20 or 54, 56 ) integral with said portion of convex sphere and caused to make movements relative to said portion of concave sphere by using said portion of convex sphere as a first ball joint for said rigid element, and a means of recycling the balls entrained by the movement of said convex sphere portion inside said concave sphere portion; said articulation device being characterized in that said means for recycling the balls is at least one circular groove (30 or 50, 52) formed in said portion of concave sphere on the perimeter of the opening which the latter defines and delimits thus the space between said portion of concave sphere and said portion of convex sphere, said circular groove having a width in the radial dimension slightly greater than the diameter of said balls so that any ball (18-n) brought into said groove by a movement of said rigid element is freed from any friction constraint and can easily be evacuated along said circular groove so that the recycling of said balls does not create any friction opposing the movements of said rigid element.

2. Device according to claim 1, wherein said portion of concave sphere (14, 44) is inside a spherical cup (12, 42), the outer wall of said portion of concave sphere being in contact with the inner wall of said cup and being able to move angularly relative to this the latter so as to act as a second ball joint for said rigid element (20 or 54, 56).

3. Device according to claim 2, wherein said portion of concave sphere (14, 44) is made of metal and said cup (12, 42) is made of ultra high density polyethylene.

4. Device according to claim 2 or 3, wherein said first ball joint formed by said portion of convex sphere (16, 46) and said second ball joint formed by said portion of concave sphere (14, 44) are concentric.

5. Device according to claim 2, 3 or 4, wherein said first ball joint has a much lower starting torque than the starting torque of said second ball so that all angular movements such as roll or the sites and deposits of small amplitude of said rigid element (20 or 54, 56) use only the movement of said first ball joint, only large amplitude movements calling on the movement of said second ball joint after said first ball joint has reached its maximum angular displacement.

6. Device according to one of claims 2 to 5, wherein said portion of concave sphere (14) and said cup (12) are closed sphere portions having only one opening in which said portion of convex sphere ( 16) is attached integrally to said rigid element (20).

7. Device according to claim 6, used as a joint prosthesis for a member.

8. Device according to claim 7, in which said plurality of balls comprises a zone without balls being at the top of said portion of convex sphere when the device has not undergone any angular movement, so that the entire weight of an individual having said joint prosthesis for a lower limb is not concentrated on the only beads located at the top when said individual has his lower limb in a vertical position.

9. Device according to claim 1, wherein said portion of concave sphere (14, 44) is inside a spherical cup (12, 42) the latter being separated from the outer wall of said portion of concave sphere by a layer of balls in the same way as the interior surface of said portion of concave sphere is separated from said portion of convex sphere (16, 46) so as to act as a second ball joint for said rigid element (26 or 54, 56 ).

10. Device according to one of claims 2 to 5, used as a mechanical double ball in fields such as aeronautics, wherein said portion of concave sphere (44) and said cup (42) are two-sphere rings openings in which said portion of convex sphere (46) is integrally connected to two portions of rigid elements (54 and 56) in line with one another, said plurality of balls also being arranged in a ring of sphere between two circular grooves (50 and 52) each forming said openings.

11. Device according to one of claims 1 to 5, 9 or 10, used as a double mechanical ball joint in fields such as aeronautics, in which said portions of convex sphere (16) and concave sphere (14) are replaced by portions of ellipsoid with the same axis of revolution so that said first ball joint is used for the movements of roll while said second ball joint is used for the movements of sites and deposits.