Artificial Leg Having A Preset Automatic Friction Band Tension Control

Abstract

An artificial leg in which flexion about the knee axis is controlled in known manner by knee control mechanism of the kind having a friction band looped around a drum, the drum being connected to the shin of the leg and the friction band to the thigh. Wear in the knee control mechanism, and "bedding down" of its component parts, is compensated by a preset clock-type coil spring, which automatically adjusts tension applied to the friction band.

Description

BACKGROUND OF THE INVENTION

This invention relates to an artificial leg.

British Pat. No. 779,087 discloses a knee control mechanism which has proved successful in use for a number of years; this control mechanism gives a mechanical control of knee flexion and in particular prevents flexion, or prevents further flexion from an already flexed state, when an increased load is applied to the artificial leg. This prevents collapse of the knee caused by uncontrolled flexion, while permitting a desirable degree of flexion during normal use.

British Pat. No. 982,527 discloses a pneumatic swing phase control mechanism which in known manner controls knee flexion, but does not, and is not intended to, prevent collapse of the knee.

It is known to use both the above-described mechanism in the same artificial leg.

In the knee control mechanism referred to above, control of flexion is by a constant friction control which can be varied by the patient by manually adjusting for example a knurled wheel. This constant friction control provides for damping of the flexion. When the pneumatic swing phase control unit referred to above is also incorporated in the leg, this control unit takes over the damping function, and it has been found that manual adjustability of the constant friction control is unnecessary.

Nevertheless, in an artificial leg having both the knee control mechanism and the pneumatic swing phase control, when the feature of manual adjustability is omitted from the said control mechanism, it is found that some loss of operating efficiency occurs in the knee control mechanism. This is caused by wear in the knee control mechanism, and also by the "bedding down" or "settingling" of its parts.

It is an object of this invention to avoid as far as possible this loss of operating efficiency.

SUMMARY OF THE INVENTION

According to this invention there is provided an artificial leg in which flexion of upper and lower parts of the leg about a knee axis is controlled by knee mechanism, the knee mechanism including a drum connected to and movable with the said lower part and a friction band around the drum and connected to and movable with the said upper part, wherein a predetermined tension in the band is maintained by preset automatic compensating means.

The friction band may be looped around an adjustably movable member having a threaded bore in which is mounted a threaded rod which is rotatable by a preset clock-type spring coiled around the axis of the threaded rod. A clock-type coil spring occupies little space, and can be readily pretensioned during assembly of the knee mechanism. Also, although pretensioned the friction produced by it is very small.

Preferably the end of the threaded rod remote from the adjustably movable member is of square cross section, in which case the inner coil of the clock-type spring is also square and fits closely about the said end of the threaded rod. This provides a simple manner of connecting the spring operatively to the threaded rod.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a central vertical cross section of an artificial leg in accordance with the invention, with some parts shown in side elevation;

FIG. 2 is an enlarged central vertical cross section of part of FIG. 1; and

FIG. 3 is a schematic detail, partly in top plan and partly in horizontal cross section.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to the drawings, it should be understood that the invention is applicable to various well-known constructions of artificial leg and that accordingly only those parts strictly relevant to an understanding of the invention have been illustrated. Persons skilled in the art will readily understand how the parts described below can be embodied in an artificial leg.

A knee mechanism, indicated generally by 1, includes a frame 2 by means of which the knee mechanism 1 is fitted to the lower end of a thigh (not shown). A conventional knee enclosing "cup" is indicated at 3 and has a slot 3A. The knee axis, about which relative flexion between the thigh and shin occurs, is indicated at 4. A knee shaft 5 is fixed at its ends to the upper ends (one of which is seen at 6A) of a cradle or framework 6, the lower end of which is formed as a socket 6B. In the socket 6B is fixed the upper end of a well-known shin tube 6C. The framework 6 also includes side members (one of which is seen at 7A), a rear member 7B, and a transverse or front member 7C.

Known pneumatic swing phase control mechanism is indicated generally at 8. It has a body part 8A pivotally connected at 8B to the framework 6. It has a piston rod 8C extending through the slot 3A and pivotally connected at 8D to the knee mechanism frame 2. In known manner, as previously mentioned, the mechanism 8 controls knee flexion, that is, it controls relative movement of the shin and thigh about the knee axis 4. British Pat. No. 982527 discloses a suitable swing phase control mechanism.

Integral with the knee shaft 5 is a drum 5A around which extends a friction band 9 in known manner. The band 9 also passes around members 9A, 9B and finally round a member 10 which is adjustably movable for varying the tension in the band 9.

Referring to FIG. 2, the member 10 has a threaded bore 10A in which is received a rotatable threaded rod 11. The band 9 has an aperture 9C through which the rod 11 passes. The rod 11 is rotatably mounted in a bushing 11A in the frame 2. When the rod 11 is rotated, the member 10 is adjusted up or down, to adjust the tension in the band 9. The upper end 11B of the rod 11 (i.e. the end remote from the member 10) is of generally square cross section, see also FIG. 3. The rod 11 has a flange 11C which rests on the bushing 11A.

Coiled around the rod 11 is a clock-type spring 12, whose innermost coil 12A is generally square (see FIG. 3) and fits closely about the square upper end 11B of the rod 11. The outer end of the spring 12 is anchored to a pin 12B fixed in the frame 2. During assembly, the innermost coil 12A is fitted over the end 11B. Then the spring is preset (or pretensioned) by rotating its outer end say two or three times. Then the outer end is hooked over the pin 12B. In this condition it will be understood that the spring always exerts torque on the rod 11 and the arrangement is such that the spring always tends to turn the rod 11 in that direction which will cause the member 10 to be moved upwardly on the rod 11. In this way, any slackness or stretching which may gradually occur in the friction band 9 during use, is automatically compensated.

When the spring 12 has been fitted and pretensioned a cover plate 13 is fitted over it, the cover plate 13 being retained by a screw 13A.

The clock-type spring 12 is desirably of comparatively low rate so that the torsion exerted by it remains reasonably constant over a wide range of rotation of the rod 11. Friction in the spring is very small. By way of example, the spring can be of steel, have 18 working coils, and require three turns of its outer end to produce a torque of 0.15 pounds per inch.

Claims

I claim:

1. An artificial leg having an upper part, a lower part, and knee mechanism controlling flexion of the upper and lower parts about a knee axis, the knee mechanism including a drum connected to and movable with the lower part, and a friction band around the drum and connected to and movable with the upper part, characterized in that a predetermined substantially constant tension in the band is maintained by preset automatic compensating means responsive to slackening or stretching in the friction band.

2. An artificial leg according to claim 1 in which the friction band is looped around an adjustably movable member having a threaded bore, said compensating means comprising a rotatable, threaded rod mounted in the threaded bore and rotatable by a preset clock-type spring coiled around the axis of the threaded rod.

3. An artificial leg according to claim 2 characterized in that the end of the threaded rod remote from the adjustably movable member is of square cross section, the innermost coil of the spring being also square and fitting closely about the said end.

4. The artificial leg of claim 1, where the preset automatic compensating means is operatively connected to the friction band and includes biasing means for maintaining the tension in the friction band.