GB2309314A

GB2309314A - Universal joint for testing a lower limb prosthesis

Info

Publication number: GB2309314A
Application number: GB9600723A
Authority: GB
Inventors: Alan James Laidlaw
Original assignee: Vessa Ltd
Current assignee: Vessa Ltd
Priority date: 1996-01-16
Filing date: 1996-01-16
Publication date: 1997-07-23
Anticipated expiration: 2016-01-16
Also published as: GB9600723D0; GB2309314B

Description

UNIVERSAL JOINT This invention relates to a universal joint suitable for testing a lower limb prosthesis to the proposed ISO 10328 test standards to which reference should be made.

These proposed standards require the use of test configurations causing the prosthesis to bend in anterior/posterior and medial/lateral directions with a torsional component. The testing is carried out by means of a test machine having two multi-axis joints which will remain at a constant minimal friction for the duration of the test i e three million cycles under an applied load for example 1.3 KN.

It is an object of the present invention to provide a universal joint which substantially enables these requirements to be met.

In accordance with the invention a universal joint comprises a part spherical member located within a correspondingly part-spherically shaped cavity in a sleeve, a casing for receiving the sleeve, means for applying hydraulic pressure to the member and spring means for opposing the hydraulic pressure, the part-spherical member thereby being capable of free movement within the cavity.

Preferably the sleeve has a cylindrical outer surface and fits slidingly within a cylindrical cavity in the casing. A plate is preferably fixed to the sleeve and acts against the spring means, for example belville washers mounted on pillars, secured to the casing.

The means for applying hydraulic pressure may comprise an injection nipple on the casing, through which hydraulic fluid e g an oil, may be injected into a fluid retaining chamber.

One embodiment of the invention will now be described by way of example only with reference to the accompanying drawings of which: Figure 1 shows a cross-section through the universal joint in accordance with the invention, and Figure 2 shows diagrammatically a lower limb prosthesis set up in the test configuration.

The universal joint shown in Figure 1 comprises a part-spherical member 10, a sleeve 12, a casing 14, a cover plate 16 and springs 18 mounted on pillars 20 in the casing 14.

The part spherical member 10 in effect comprises an aluminium alloy sphere from which two segments have been removed. The member has two parallel flat surfaces 21,22 both arranged to lie horizontally as shown, the upper surface 22 being closer to the centre of the sphere than the lower 21.

Two grooves 23,24 are provided in the outer surface of the member 10, each lying in a horizontal plane and containing an '0' ring (not shown). The upper groove 24 lies the same distance below the upper surface 22 as the lower groove 23 lies above the lower surface 21. In the centre of the upper surface is a hemispherical recess 25 for a purpose to be described.

The part spherical member 10 is located inside a complementary shaped cavity in the sleeve 12 which for ease of assembly comprises two rings, an upper ring 30 and a lower ring 32. The outer surface 34 of the sleeve is cylindrical and the inner surface 28 is part-spherical, complementary to the outer surface of the member 10. The upper part of the upper ring 30 is formed with a frusto-conical cavity 36 and the lower part of the lower ring 32 is formed with a frusto conical cavity 38, the cavities leading from the top surface and the bottom surfaces respectively to the cavity. The outer surface of each ring is provided with a groove 40, the groove in the upper ring being parallel to the groove in the lower ring. Each ring retains an O-ring seal (not shown).

A cover plate 16 is secured to the sleeve by means of a plurality of bolts 42 the shanks of which pass through apertures in the cover plate and into the upper ring. The upper ring is connected to the lower ring by further bolts 44.

The sleeve 12 is located in a cylindrical casing 14 being closed at the bottom by a lower plate 46 bolted thereto by bolts 48 and closed at the top by the cover plate 16. Provided around the top of the casing and regularly spaced-apart is a plurality of pillars 20 each having a flange 52 at their upper extremity. The pillars 20 each pass through one of a plurality of holes formed near the edge of the cover plate 16. Mounted on each pillar between its \flange and the upper side of the cover plate is the plurality of belville washers 18 for a purpose to be described.

Attached to the top ring 30 by means of a plurality of bolts (not shown) is a wedge-shaped ring 54 having a central hole 56 and an upper surface 58 which is inclined with respect to a lower, horizontal surface 60.

The upper surface 22 of the member 10 is the same diameter as and supports the lower, horizontal surface 60 of the wedge-shaped ring 54. The central hole 56, the lower part 62 of which is part spherical having the same diameter as and lying directly above the hemispherical recess. The upper part of the hole 56 is tapered, having a frusto conical shape.

In use two universal joints are assembled in the positions shown in Figure 2, the upper joint being inverted. Two rigid beams 70 are secured to the top and bottom of the prosthesis P respectively above and below the knee joint K and each rigid beam 70 attached to the inclined surface 58 of the respective universal joint by means of a screw-threaded shaft 72 with a ball end 74. (The shaft [shown above the joint for convenience in Figure 1] has to be assembled by placing the ball end 74 in the recess 25 and then putting the wedge-shaped ring 54 on the shaft 72). The ball seats in the recess 25 and the beam 70 is held firmly against the inclined surface 58 of the wedge shaped ring at the angle required by the test by a nut 76 on the shaft. (The ring may be one of a series of rings each having a top surface inclined at a different angle. The ring is chosen as required).

Prior to commencement of a test oil is charged via a nipple (not shown) in the outer casing 14 to fill the cavity 38 between the lower ring 32, the lower plate 46 of the casing and the member 10. The oil is prevented from escaping between the sleeve and the member by the O-ring seal in the lower groove 23. The pressure of the oil causes the sleeve and the member to move upwards against the belville washers 18 which apply an opposing downwards force.

During tests a cyclic test load F is applied as shown and the member is forced downwards into the casing against the pressure of the oil but the belville washers maintain a pressure on the sleeve so relieving the wear areas of the member.

In a modification (not shown) a further wedge shaped ring may be secured above the wedge shaped ring 54 shown in Figure 1. The further wedge may be rotated to any one of a number of positions thus enabling the member 10 to be adjusted to its required horizontal position when the joint is mounted on the prosthesis P and in position ready for a test to commence.

Claims

CLAIMS:

1. A universal joint comprising a part spherical member located within a correspondingly part spherically-shaped cavity in a sleeve, a casing for receiving the sleeve, means for applying hydraulic pressure to the member and spring means for opposing the hydraulic pressure, the part spherical member thereby being capable of free movement within the cavity.

2. A universal joint according to Claim 1, wherein the sleeve has a cylindrical outer surface and fits slidingly within a cylindrical cavity in the casing.

3. A universal joint according to Claim 1 or Claim 2 comprising a plate fixed to the sleeve and acting against the spring means.

4. A universal joint according to Claim 3 wherein the spring means comprises Belville washers.

5. A universal joint according to Claim 3 wherein the spring means comprises Belville washers mounted on pillars secured to the casing.

6. A universal joint according to any one of the preceding claims wherein the means for applying hydraulic pressure comprises an injecting nipple on the casing through which hydraulic fluid may be injected into a fluid retaining chamber.

7. A universal joint according to any one of the preceding claims comprising a wedge-shaped ring attached to the part spherical member.

8. A universal joint substantially as described herein with reference to and as shown in Figure 1 of the accompanying drawings.