GB2633016A

GB2633016A - Wrist apparatus

Info

Publication number: GB2633016A
Application number: GB2313013.1A
Authority: GB
Inventors: James Nisbet Christopher; Joseph Donald Mackie Ferhal
Original assignee: Metacarpal Ltd
Current assignee: Metacarpal Ltd
Priority date: 2023-08-25
Filing date: 2023-08-25
Publication date: 2025-03-05
Also published as: WO2025045563A1; GB202313013D0

Abstract

A wrist apparatus 2 (Figure 1) for a prosthetic hand 3 (Figure 1) comprises a base 5 and a hand mount 7 to which a prosthetic hand is mountable. The hand mount is attached to the base and is movable relative to the base between, and releasably retainable in, at least two different positions corresponding to at least two different hand flexion configurations. The hand mount may be fixedly mounted on an axle 19, with movement of the hand mount relative to the base comprising rotation about the longitudinal axis of the axle, wherein the axle is constrained by a ball bearing or bearings 27 located within a bearing race 26A, 26B on the axle and a bearing carrier 23 moveable relative to the axle parallel to the longitudinal axis. Adjacent regions of the bearing race may be connected by V-shaped segments (Figure 6), resulting in a biasing force towards each of the flexion positions which must be overcome to move between them.

Description

WRIST APPARATUS

Field

The present disclosure concerns wrist apparatus for prosthetic hands, prosthetic apparatus comprising the wrist apparatus and a prosthetic hand, and associated methods.

Background

A prosthesis is an artificial device that replaces a body part which may be missing, for example, due to trauma, disease, amputation or a congenital disorder.

A person who is missing a hand may use a prosthetic hand or other terminal device (such as a hook) which is typically attached to a socket worn on the body (for example, supported by a harness).

Prosthetic hands or other terminal devices can be body-powered (where movement of device components is driven by movements of the user's body) or electrically powered (also known as "myoelectric", where movement of device components is driven by electric motors). Such devices may be cable-operated, where movement of device components is driven by applying tension to operating cables. Both body-powered and electrically powered devices may be cable-operated.

The human hand is typically moveable in three different modes by action of the wrist or forearm: flexion and extension; supination and pronation; and abduction and adduction. Devices have been developed which enable movement of prosthetic hands in similar modes.

However, some such known devices are excessively bulky and/or heavy. Some known devices are incompatible with body-powered and/or cable-operated prosthetic hands. Some known devices only permit movement in a single mode. Some known devices require use of a free hand to adjust the position of the prosthetic hand or to lock the hand in place. Improved prosthetic apparatuses, including wrist apparatuses, would therefore be desirable.

Summary

According to a first aspect, there is provided a wrist apparatus for a prosthetic hand, the wrist apparatus comprising: a base; and a hand mount to which a prosthetic hand is mountable; wherein the hand mount is attached to the base and is movable relative to the base between, and releasably retainable in, at least two different positions corresponding to at least two different hand flexion configurations.

The angle between the hand mount and the base may be different in the at least two different positions. For example, movement of the hand mount relative to the base may comprise pivoting the hand mount about a pivot point to vary the angle between the hand mount and the base. The at least two different hand flexion configurations may correspond to at least two different angular orientations of the hand mount relative to the base.

The hand mount may be movable relative to the base between, and releasably retainable in, at least three different positions (e.g. at least three different angular orientations of the hand mount relative to the base) corresponding to at least three different hand flexion configurations. For example, the hand mount may be movable relative to the base between, and releasably retainable in, (i.e. only) three different positions (e.g. (i.e. only) three different angular orientations of the hand mount relative to the base) corresponding to (i.e. only) three different hand flexion configurations.

It will be appreciated that the term "hand flexion configuration" refers to a configuration that the prosthetic hand would take (when mounted to the hand mount) in the flexion-extension mode of movement. Therefore, it will be appreciated that a hand flexion configuration is not necessarily a flexed configuration but may be an extended configuration or a neutral (i.e. neither flexed nor extended) configuration. Thus, the term "hand flexion configuration" could be replaced by the equivalent terms "flexion-extension configuration" or "extension configuration".

It will be appreciated that the angle between the hand mount and the base is measured in the same sense in each of the at least two different positions. For example, a position in which the hand mount is pivoted by X° away from a neutral configuration into a flexed configuration is not the same position in which the hand mount is pivoted by X° away from the neutral configuration into an extended configuration, and the angle between the hand mount and the base is different in each of the two configurations when measured in the same sense (i.e. in one of the configurations, it may be Y° and in the other it may be (Y+2X)°).

The wrist apparatus may be configured to exert a returning force on the hand mount, when the hand mount is in each position of the at least two different positions (e.g. in each position of the at least three different positions), which biases the hand mount towards said position. Movement of the hand mount away from each of the said positions may require movement of the hand mount against the returning force. Therefore, when the hand mount is in any one of the at least two different positions, the wrist apparatus may resist displacement of the hand mount from said position. Moreover, when the hand mount is displaced from said position by application of an external force, the wrist apparatus may cause the hand mount to return to the said position when the external force is removed.

The wrist apparatus may be configured such that movement of the hand mount from a first position of the at least two different positions to a second position of the at least two different positions requires overcoming the returning force which biases the hand mount towards the first position. Similarly, movement of the hand mount from the second position to the first position may require overcoming the returning force which biases the hand mount towards the second position.

The wrist apparatus may be configured to exert the same returning force on the hand mount for each position of the at least two different positions. Alternatively, the wrist apparatus may be configured to exert different returning forces for some or all of the at least two different positions.

The returning force may be provided by biasing means such as one or more springs or elastically deformable media.

The hand mount may be (e.g. fixedly) mounted on an axle and movement of the hand mount relative to the base may comprise rotation of the hand mount with the axle about a longitudinal axis of the axle. The longitudinal axis of the axle may therefore function as a pivot point about which the hand mount may be pivoted. The axle may be (e.g. rotatably) attached to the base. The hand mount may be attached to the base by way of the axle.

The invention therefore extends to a wrist apparatus for a prosthetic hand, the wrist apparatus comprising: a base; a hand mount to which a prosthetic hand is mountable; and an axle on which the hand mount is (e.g. fixedly) mounted; wherein the hand mount and the axle are attached to the base, the hand mount is rotatable with the axle about a longitudinal axis thereof to vary the angle between the hand mount and the base, and the hand mount and axle are rotatable between, and releasably retainable in, at least two different positions (i.e. angular orientations) corresponding to at least two different hand flexion configurations.

Rotation of the axle may be constrained by a bearing. The bearing may define the at least two different positions between which the hand mount is movable and in which the hand mount is releasably retainable.

The bearing may comprise: a bearing race; a bearing element movable within the bearing race; and a bearing carrier for retaining the bearing element within the bearing race.

The bearing race may be located on (and thus rotatable with) the axle. The bearing race may comprise (e.g. be) one or more channels or grooves formed on the axle. The bearing race may define the at least two different positions between which the hand mount is movable and in which the hand mount is releasably retainable. For example, the shape of the bearing race may define the at least two different positions between which the hand mount is movable and in which the hand mount is releasably retainable.

The bearing element may comprise (e.g. be) one or more ball bearings. The bearing element may be movable within the bearing race by rotation of the axle.

The bearing carrier may comprise one or more pockets for holding the one or more ball bearings. The bearing carrier may be movable relative to the axle parallel to the longitudinal axis thereof. For example, the bearing carrier may be slidable relative to the axle parallel to the longitudinal axis thereof. For example, the bearing carrier may be mounted on one or more guides (e.g. one or more guide rails) which extend parallel to the longitudinal axis of the axle.

The bearing carrier may be fixed in orientation relative to the base (e.g. by the one or more guides). The axle may be rotatable relative to the bearing carrier. For example, the bearing carrier may be positioned around the axle and the axle may be rotatable within the bearing carrier.

In some embodiments, the bearing comprises: a bearing race (e.g. one or more channels or grooves) located on and rotatable with the axle; a bearing carrier positioned around the axle, such that the axle is rotatable within the bearing carrier, and mounted on one or more guides such that the bearing carrier is slidable relative to the axle parallel to the longitudinal axis thereof; and a bearing element (e.g. one or more ball bearings) retained within the bearing race by the bearing carrier (for example, positioned within one or more corresponding pockets in the bearing carrier) and movable within the bearing race by rotation of the axle.

Rotation of the axle may drive movement of the bearing carrier along the axle parallel to the longitudinal axis thereof as the bearing element moves within the bearing race.

The wrist apparatus may be configured to resist movement of the bearing carrier along the axle in one direction parallel to the longitudinal axis (i.e. in the direction in which the bearing carrier moves initially when a force is applied to the hand mount to cause rotation of the hand mount out of one of the at least two positions). For example, the wrist apparatus may be configured to exert a returning force on the bearing carrier which resists movement of the bearing carrier along the axle in the one direction parallel to the longitudinal axis. For example, the wrist apparatus may comprise biasing means (e.g. one or more springs or elastically deformable media) which resist movement of the bearing carrier along the axle in the one direction parallel to the longitudinal axis.

The bearing race may comprise at least two different regions (e.g. locations) corresponding to the at least two different positions of the hand mount. For example, it may be that when the hand mount is in any one of the at least two different positions, the bearing element is in a corresponding one of the at least two different regions (e.g. locations) of the bearing race. Movement of the hand mount between the at least two different positions may comprise movement of the bearing element between the at least two different regions (e.g. locations) of the bearing race.

The wrist apparatus may be configured to exert the returning force on the bearing carrier which, when the bearing element is in any one region (e.g. location) of the at least two different regions (e.g. locations), biases the bearing element towards said region (e.g. location), such that movement of the bearing element from a first region (e.g. location) of the at least two different regions (e.g. locations) to a second region (e.g. location) of the at least two different regions (e.g. locations) by rotation of the axle requires overcoming the returning force which biases the bearing element towards the first region (e.g. location).

The bearing (e.g. the bearing race) may be configured such that rotation of the axle by greater than a threshold angle is required to overcome the returning force to move the bearing element from the first region (e.g. location) to the second region (e.g. location).

The threshold angle may be no less than about 5°, for example, no less than about 10°, or no less than about 15°, or no less than about 20°, or no less than about 30°. The threshold angle may be no more than about 60°, for example, no more than about 50°, or no more than about 40°. The threshold angle may be from about 5° to about 60°, for example, from about 10° to about 60°, or from about 15° to about 50°, or from about 20° to about 40°.

The threshold angle required to overcome the returning force to move the bearing element from the first region (e.g. location) to the second region (e.g. location) may be the same as or different from the threshold angle required to overcome the returning force to move the bearing element from the second region (e.g. location) to the first region.

The biasing means (e.g. one or more springs or elastically deformable media) may be configured to exert the returning force on the bearing carrier.

Adjacent regions (e.g. locations) of the at least two different regions (e.g. locations) of the bearing race may be connected by V-shaped bearing race segments. A V-shaped bearing race segment may comprise two bearing race arms (i.e. straight-line segments) connected to form a V-shape. Each of the at least two different regions may therefore be endpoints or vertices of a V-shaped bearing race segment. The V-shaped bearing race segment may be symmetric (e.g. the two arms may have the same lengths and/or may be inclined at the same angle with respect to the longitudinal axis of the axle) or it may be asymmetric.

The bearing race may comprise at least first, second and third regions (e.g. locations) corresponding to at least first, second and third positions of the hand mount.

The first and second regions (e.g. locations) of the bearing race may be connected by a first V-shaped bearing race segment and the second and third regions of the bearing race may be connected by a second V-shaped bearing race segment. The first, second and third regions (e.g. locations) of the bearing race may therefore be connected to one another in a W-shaped bearing race. Each of the at least two different regions may therefore be endpoints or vertices of a W-shaped bearing race segment.

It will be appreciated that the bearing race could include more than three regions (e.g. locations) between which the bearing element is movable, thus defining more than three different positions of the hand mount and thus more than three different hand flexion configurations.

The wrist apparatus may be configured to exert the returning force on the bearing carrier which, when the bearing element is in any one of the first, second or third regions, biases the bearing element towards said region, such that movement of the bearing element between the first and second regions or between the second and third regions by rotation of the axle requires overcoming the returning force.

The first position of the hand mount may correspond to an extended hand flexion configuration, the second position of the hand mount may correspond to a neutral hand flexion configuration and the third position of the hand mount may correspond to a flexed hand flexion configuration.

The bearing may comprise more than one bearing race located on and rotatable with the axle. For example, the bearing may comprise (e.g. only) two bearing races located on and rotatable with the axle, the bearing races being located on opposing sides of the axle. The bearing may comprise more than one bearing element (e.g. ball bearing), wherein at least one bearing element is retained within each bearing race by the bearing carrier and movable within said bearing race by rotation of the axle. Each bearing race may be substantially identical in shape and size.

It will be appreciated that the returning force generated by the wrist apparatus releasably retains the hand mount in any given position of the at least two positions. This enables a user to position the hand mount in a desired position (corresponding to a desired hand flexion configuration) and the hand mount will remain in the desired position, or return to the desired position following minor displacements, until the user decides to reposition the hand.

However, the wrist apparatus may further comprise a latch for locking the position of the hand mount. The latch may block rotation of the axle. For example, the latch may comprise a stop which engages with a portion (e.g. a cut-away portion) of the axle to block rotation thereof The hand mount may be a hand mounting arm. The hand mount (e.g. the hand mounting arm) may comprise a connector for attachment to the prosthetic hand. For example, the hand mount (e.g. the hand mounting arm) may comprise an aperture to which the prosthetic hand may be attached (e.g. by a bolt).

The wrist apparatus may be configured for attachment to a user's socket. For example, the base may be configured for attachment to a user's socket. Alternatively, the base may be mounted on a support and the support may be configured for attachment to the user's socket. In any case, attachment may be achieved by any means known in the art.

For example, the wrist apparatus (e.g. the base or the support) may be configured to attach to any commercially available sockets, which may make use of screw thread connections, spring-loaded plug and socket connections, etc. In embodiments comprising a support, the base may be rotatably mounted on the support to enable rotation of the base relative to the support about an axis of rotation substantially orthogonal to an interface between the base and the support.

The axis of rotation may extend through the centre (e.g. the centre of mass) of the base and the centre (e.g. the centre of mass) of the support. The axis of rotation may be a central axis of the wrist apparatus.

The support may be substantially disc shaped or annular and the axis of rotation may extend through the centre of the disc or annulus, orthogonal to the plane of the disc or the annulus.

The base may be substantially disc shaped or annular and the axis of rotation may extend through the centre of the disc or annulus, orthogonal to the plane of the disc or the annulus.

The base and the support may comprise a magnetic clutch mechanism which resists or restricts rotation of the base relative to the support.

For example, at least one of the base and the support may comprise (e.g. be formed from) ferromagnetic metal (e.g. steel) and at least one other of the base and the support may comprise one or more magnets configured to exert an attractive force on the ferromagnetic metal and thereby resist or restrict rotation of the base relative to the support. For example, the base may comprise (e.g. be formed from) ferromagnetic metal and the support may comprise one or more magnets configured to exert an attractive force on the ferromagnetic metal and thereby resist or restrict rotation of the base relative to the support.

Alternatively, both the base and the support may each comprise one or more magnets configured (e.g. arranged) to exert a magnetic (e.g. attractive) force between the base and the support to thereby resist or restrict rotation of the base relative to the support.

The wrist apparatus may be for a cable-operated prosthetic hand.

The wrist apparatus may comprise a channel for guiding an operating cable of the cable-operated prosthetic hand through the wrist apparatus.

The channel may extend between a cable inlet for receiving the operating cable from a user's harness and a cable outlet for feeding the operating cable to the cable-operated prosthetic hand.

The cable outlet may be located proximate or at the centre of the wrist apparatus. The cable outlet may be located proximate the hand mount. The cable outlet may be configured such that the cable is movable relative to the base with the hand mount.

The wrist apparatus may comprise one or more pulleys for feeding the cable through the channel. For example, the support may comprise the one or more pulleys. The wrist apparatus (e.g. the support) may comprise two pulleys for feeding the cable through the channel, one of the pulleys located at the cable inlet and the other of the pulleys located at the cable outlet.

The hand mount may be movable between the at least two different positions by body power. For example, it may be that, when a prosthetic hand is mounted on the hand mount, the hand mount is movable between the at least two different positions (corresponding to the at least two different hand configurations) by applying a force to the hand by pressing the hand against the user's body or against a surface. It may be that the wrist apparatus does not comprise any motors for driving movement of the hand mount.

In embodiments in which the wrist apparatus comprises a base rotatably mounted on a support, it may be that, when a prosthetic hand is mounted on the hand mount, the base is rotatable with respect to the support by applying a torque to the prosthetic hand, for example, by another hand of the user.

It may be that the wrist apparatus does not comprise any motors for driving rotation of the base relative to the support.

The wrist apparatus may be a body-powered wrist apparatus. It may be that the wrist apparatus does not comprise any motors for driving movement of any components of the wrist apparatus.

The wrist apparatus may be for a body-powered prosthetic hand. For example, the wrist apparatus may be for a body-powered, cable-operated prosthetic hand.

Alternatively, the wrist apparatus may be for an electrically powered prosthetic hand.

According to a second aspect, there is provided a prosthetic apparatus comprising the wrist apparatus according to the first aspect and a prosthetic hand mounted on the hand mount such that the prosthetic hand is movable between, and releasably retainable in, the at least two different hand flexion configurations by movement of the hand mount between, and releasable retention of the hand mount in, the at least two different positions.

The wrist apparatus may have any of the features described hereinabove in relation to the first aspect.

The prosthetic hand may be a cable-operated prosthetic hand.

The prosthetic hand may be a body-powered prosthetic hand. For example, the prosthetic hand may be a body-powered, cable-operated prosthetic hand.

Alternatively, the prosthetic hand may be an electrically powered prosthetic hand.

According to a third aspect, there is provided a method of moving the prosthetic hand of the second aspect from a first flexion configuration to a second flexion configuration, the method comprising applying a force to the hand to cause movement of the hand mount from a first position of the at least two different positions to a second position of the at least two different positions.

The prosthetic apparatus may be worn by a user (for example, attached to a user's socket), and applying the force to the hand may comprise pressing the hand against the user's body or against a surface.

The prosthetic apparatus may have any features described hereinabove in relation to the second aspect.

The prosthetic wrist of the prosthetic apparatus may have any features described hereinabove in relation to the first aspect.

According to a fourth aspect, there is provided a wrist apparatus for a prosthetic hand, the wrist apparatus comprising: a base to which a prosthetic hand is mountable; and a support configured for attachment to a user's socket; wherein the base is rotatably mounted on the support to enable rotation of the base relative to the support about an axis of rotation substantially orthogonal to an interface between the base and the support.

The wrist apparatus may have any of the features described hereinabove in relation to the first aspect. In particular, the wrist apparatus may comprise the magnetic clutch mechanism.

According to a fifth aspect, there is provided a prosthetic apparatus comprising the wrist apparatus according to the fourth aspect and a prosthetic hand mounted on the base. The prosthetic hand may be rotatable with the base relative to the support. The prosthetic hand may be rotatable with the base relative to the support by body power.

The wrist apparatus may have any of the features described hereinabove in relation to any preceding aspect.

The prosthetic hand may be a cable-operated prosthetic hand.

The skilled person will appreciate that, except where mutually exclusive, a feature described in relation to any one of the above aspects may be applied mutatis mutandis to any other aspect. Furthermore, except where mutually exclusive, any feature described herein may be applied to any aspect and/or combined with any other feature described herein.

Figures Embodiments will now be described by way of example only, with reference to the Figures, in which: Figure 1 is a perspective view of prosthetic apparatus comprising a wrist apparatus and a prosthetic hand mounted thereon; Figure 2 is (a) a perspective view of the wrist apparatus of Figure 1 and (b) a perspective view of the wrist apparatus of Figure 1 with a cover and support removed; Figure 3 is first exploded view of the wrist apparatus of Figure 1 illustrating a wrist flexion mechanism; Figure 4 is a second exploded view of the wrist apparatus of Figure 1 illustrating a wrist rotation mechanism; Figure 5 illustrates flexion/extension of the wrist flexion/extension mechanism of Figure 3 between (a) fully flexed, (b) partially flexed, (c) neutral, (d) partially extended and (e) fully extended configurations; Figure 6 illustrates an axle of the wrist flexion/extension mechanism of Figure 3 in more detail; and Figure 7 illustrates flexion/extension of the prosthetic hand of Figure 1 between (a) extended, (b) neutral and (c) flexed configurations.

Detailed description

With reference to Figure 1, a prosthetic apparatus 1 includes a prosthetic wrist 2 to which a terminal device such as a prosthetic hand (illustrated in dashed lines as 3 in Figure 1) may be mounted. The prosthetic wrist 1 is configured to be mounted onto a user's socket.

The prosthetic wrist 2 is shown in more details in Figures 2 to 7.

The wrist 2 generally includes a support 4, a baseplate (a base) 5, a flexion mechanism 6, a hand mounting arm 7, a latch 8 and a cover 9.

The support 4 (illustrated in detail in Figure 4) includes a stator 10, a rotor plate 11 made of a ferromagnetic material (such as steel), and a shoulder plate 12. The stator 10 is substantially disc shaped and includes a raised central portion 13 known as a spigot. An underside of the stator 10 is provided with attachment means (e.g. a screw thread, a spring-loaded plug, etc.) for attaching the stator 10 to a user's socket. The rotor plate 11 is substantially annular and configured to fit over the spigot 13 of the stator 10. The shoulder plate 12 is substantially disc shaped and configured to hold the rotor plate 11 against the stator 10 when the shoulder plate 12 is fixed to the stator 10 by means of countersunk screws 14. The components of the support 4 are sized and arranged such that, when the shoulder plate 12 is fixed to the stator 10, the rotor plate 11 is rotatable between the shoulder plate 12 and the stator 10 about a central axis orthogonal to the interface between the rotor plate 11 and the stator 10. An upper portion 17 of the wrist 2 (including the flexion mechanism 6, the hand mounting arm 7 and the cover 9) is fixed to the rotor plate 11 by means of mounting screws 18, such that the upper portion 17 of the wrist 2 (and thus also any terminal device, such as prosthetic hand 3, mounted thereto), is rotatable about the central axis with the rotor plate 11.

The stator 10 includes a plurality of apertures 15 into which permanent magnets 16 are fixedly mounted. Magnetic attractive forces between the permanent magnets 16 and the ferromagnetic rotor plate 11 resist rotation of the rotor plate 11 about the central axis, thus functioning as a friction lock or magnetic clutch. In use, therefore, although a user may rotate the upper portion 17 of the wrist 2 (and thus also any terminal device, such as prosthetic hand 3, mounted thereto) about the central axis by applying sufficient torque, the support 4 resists rotation of the wrist 2 when insufficient torque is applied. A user can therefore select a desired degree of rotation for the wrist and the wrist will remain in the selected orientation until a sufficiently large torque is applied. It will be appreciated that the size, number, strength and arrangement of the permanent magnets can be selected to target a particular level of resistance. It will further be appreciated that alternative arrangements may be used to achieve a similar magnetic clutch effect. For example, both the stator 10 and the rotor plate 11 may be provided with magnets configured to interact with one another to provide the magnetic clutch effect. In the embodiment shown in Figure 4, the wrist is rotatable through 360°.

The flexion mechanism 6 (illustrated in detail in Figure 3) includes an axle 19 rotatably mounted at either end to axle supports 20A and 20B via plain bearings 21A and 21B.

The axle supports 20A and 20B fit within corresponding portions of an aperture in the base plate 5. The hand mounting arm 7 is fixedly attached to the axle 19 by means of screws 22 and includes attachment means 29 for attachment to a terminal device such as the prosthetic hand 3.

The flexion mechanism 6 includes a bearing system which restricts rotation of the axle 19 about its longitudinal axis. In particular, the axle 19 is mounted within a substantially annular bearing carrier 23 which is itself mounted on two guide rails 24, extending parallel to the longitudinal axis of the axle 19, via guide bushings 29. A helical bias spring 25 is provided between the axle support 20A and the bearing carrier 23. Two bearing races (i.e. grooves) 26A and 26B are formed in the surface of the axle 19 and corresponding ball bearings 27 are held within said bearing races by ball bearing pockets 28A and 28B in the bearing carrier 23.

The flexion mechanism 6 also includes a substantially annular debris barrel 30 for restricting ingress of external debris into the mechanism.

The flexion mechanism 6 is held in place by the cover 9 which is screwed onto the baseplate 5 and the rotor 11 of the support 4.

In use, the flexion mechanism 6 enables movement of the hand mounting arm 7, and thus also any terminal device (such as prosthetic hand 3) mounted thereto, between different flexion configurations by rotation (i.e. pivoting) of the hand mounting arm 7 with the axle 19 about the longitudinal axis of the axle 19 (as illustrated in Figures 5 and 6).

The extent of rotation of the hand mounting arm 7 and the axle 19 about said longitudinal axis is restricted by the bearing system and, in particular, the design of the bearing races 26A and 26B.

In particular, as shown in Figures 5 to 7, the bearing races 26A and 26B of the present embodiment are both substantially W-shaped, including two substantially V-shaped segments connected at a node A. In this embodiment, the hand mounting arm 7 is movable between three different positions (each corresponding to a different flexion configuration (a), (b) and (c) shown in Figure 7) by rotation of the axle 19.

When the hand mounting arm 7 is in a neutral flexion configuration (corresponding to configuration (c) of Figure 5 and configuration (b) of Figure 7), the axle 19 is positioned such that one ball bearing 27 is located at node A of bearing race 26A and the other ball bearing 27 is located at corresponding node A of bearing race 27A.

Rotation of the axle 19 away from the neutral flexion configuration (e.g. towards configurations (a), (b), (d) or (e) of Figure 5 or equivalently towards extended configuration (a) or towards flexed configuration (c) of Figure 7) requires movement of the ball bearings within the corresponding bearing races 26A and 26B towards inflection points B or C, and thus also movement of the bearing carrier 23 along the axle 19 towards the axle support 20A. However, movement of the ball bearings in either of these directions is resisted by the bias spring 25 which is compressed between the axle support 20A and the bearing carrier 23 as the bearing carrier 23 moves. The bias spring 23 exerts a returning force on the bearing carrier 23 which biases the bearing carrier 23, and thus also the ball bearings 27, back towards the starting node A. Accordingly, when a torque is applied to the axle 19 via the hand mounting arm 7 (for example, by applying a force to the terminal device such as the prosthetic hand 3) causing rotation of the axle 19 up to a threshold amount (e.g. such that the ball bearing does not travel beyond inflection point B or inflection point C), the action of the bias spring 23 will cause the axle 19 and the hand mounting arm 7 to return to the neutral configuration when the applied torque is released.

However, when sufficient torque is applied to cause rotation of the axle 19 beyond the threshold amount (such that the ball bearing passes inflection point B or inflection point C), the action of the bias spring 23 will not cause the axle 19 and the hand mount arm 7 to return to the neutral configuration but instead it will push the ball bearings 27 towards node D (corresponding to configuration (a) of Figure 5 or Figure 7) or node E (corresponding to configuration (e) of Figure 5 or equivalently configuration (c) of Figure 7).

Once the hand mounting arm 7 is in one of the extended or flexed configurations, the action of the bias spring 23 will similarly resist movement back towards to the neutral configuration unless sufficient torque is applied in the opposite direction to again overcome the returning force. The hand mounting arm 7 is therefore movable between, and releasably retainable in, each of the extended, neutral and flexed positions.

To provide additional security in each of the positions, the position of the hand mounting arm 7 may also be fixed by way of latch 8. Latch 8 is slidably mounted onto the baseplate 5 and is slidable to position a stop 31 against a cut-away portion of a protruding end 32 of the axle 19 to block rotation of the axle 19.

It will be appreciated that the number of positions between which the hand mounting arm 7 is movable, and in which the hand mounting arm is retainable, will depend on the design of the bearing races. For example, a bearing race which contains only one V-shaped segment will permit movement of the hand mounting arm between two different positions. A bearing race which contains two connected V-shaped segments, thus forming a W-shape, permits movement of the hand mounting arm between three different positions. Further positions can be included by adding further V-shaped segments to the bearing race. Similarly, additional compliance in any end positions can be included by adding further straight-line segments to the bearing race as appropriate.

It will also be appreciated that the angular separation (i.e. measured in a plane orthogonal to the longitudinal axis of the axle 19) between the positions in which the hand mounting arm is retainable will depend on the design of the bearing races and, in particular, on the circumferential distance between the nodes A, B, C, etc. It will also be appreciated that the angle through which the axle 19 must be rotated to overcome the returning force for a given node will depend on the design of the bearing races and, in particular, on the length and relative arrangement of each arm of each V-shaped segment. For example, in the embodiment shown in the Figures, the axle may be rotated through 30° in either direction away from the neutral configuration and returned to the neutral configuration when the applied torque is released. However, rotation of the axle through more than 30° will push the axle into either of the flexed or extended configurations (dependent on the sense of the rotation) and the axle will be self-latched in each configuration at 40° flexion or extension.

In the embodiment shown in the Figures, the returning force is provided by a helical bias spring 25 located between the bearing carrier 23 and the axle support 20A. However, it will be appreciated that the returning force could be provided by alternative biasing means, such as a spring located between the bearing carrier 23 and the axle support 20B which is stretched as the bearing carrier 23 is moved towards the axle support 20B, or by elastically deformable material (e.g. a rubber component) located between the bearing carrier 23 and the axle support 20B. It will also be appreciated that the strength of the returning force will depend on the strength of the biasing means used.

The wrist mechanism 2 described hereinabove is, in principle, suitable for use with many different types of terminal device and, in particular, many different types of prosthetic hand. The wrist mechanism may, however, be particularly suited for use with cable-operated prosthetic hands (which may be body-powered cable-operated prosthetic hands or electrically powered cable-operated prosthetic hands). For example, Figure 7 illustrates how a cable 32 for operating a prosthetic hand 3 can be fed through the wrist mechanism 2 by way of two pulleys 33 and 34 mounted in the stator 10. Pulley 33 is located on an external rim of the stator 10. Pulley 34 is located closer to the centre of the stator 10, in the region of the spigot 13, and extends through a pulley slot 35 in the shoulder 12 and a pulley slot 36 in the cover 9. The cable 32 emerges from the wrist mechanism 2 in the centre of the device, adjacent the hand mounting arm 7, and moves with the arm 7 when it is moved between extended, neutral and flexed positions. The cable 32 therefore does not get tangled as the hand 3 is extended or flexed or rotated about the wrist 2, nor does it apply excessive tension to the hand 3 as it is moved between configurations.

The components of the wrist 2 may be made of any suitable materials known in the art. For example, core load-bearing components may be made of metals such as aluminium, titanium, brass or steel (including anodized and/or nitrided steel). The spring 25 may be a steel spring. Non-load bearing components (e.g. the cover 9) may be made of metal or other materials such as plastic. The components may be manufactured by any suitable methods, including casting, machining or additive manufacturing.

It will be understood that the invention is not limited to the embodiments described above and various modifications and improvements can be made without departing from the concepts described herein. Except where mutually exclusive, any of the features may be employed separately or in combination with any other features and the disclosure extends to and includes all combinations and sub-combinations of one or more features described herein.

Claims

Claims A wrist apparatus for a prosthetic hand, the wrist apparatus comprising: a base; and a hand mount to which a prosthetic hand is mountable; wherein the hand mount is attached to the base and is movable relative to the base between, and releasably retainable in, at least two different positions corresponding to at least two different hand flexion configurations.
2. The wrist apparatus according to claim 1, wherein an angle between the hand mount and the base is different in the at least two different positions.
3. The wrist apparatus according to claim 1 or claim 2, wherein the wrist apparatus is configured to exert a returning force on the hand mount, when the hand mount is in each position of the at least two different positions, which biases the hand mount towards said position.
4. The wrist apparatus according to claim 3, wherein the wrist apparatus is configured such that movement of the hand mount from a first position of the at least two different positions to a second position of the at least two different positions requires overcoming the returning force which biases the hand mount towards the first position.
5. The wrist apparatus according to any preceding claim, wherein the hand mount is fixedly mounted on an axle and movement of the hand mount relative to the base comprises rotation of the hand mount with the axle about a longitudinal axis of the axle.
The wrist apparatus according to claim 5, wherein rotation of the axle is constrained by a bearing.
The wrist apparatus according to claim 6, wherein the bearing comprises: a bearing race located on and rotatable with the axle; a bearing carrier movable relative to the axle parallel to the longitudinal axis; and a bearing element retained within the bearing race by the bearing carrier and movable within the bearing race by rotation of the axle.
8. The wrist apparatus according to claim 7, wherein: the bearing race comprises at least two different regions corresponding to the at least two different positions of the hand mount; and the wrist apparatus is configured to exert a returning force on the bearing carrier which, when the bearing element is in any one region of the at least two different regions, biases the bearing element towards said region, such that movement of the bearing element from a first region of the at least two different regions to a second region of the at least two different regions by rotation of the axle requires overcoming the returning force which biases the bearing element towards the first region.
The wrist apparatus according to claim 8, wherein the bearing is configured such that rotation of the axle by greater than a threshold angle is required to overcome the returning force to move the bearing element from the first region to the second region.
10. The wrist apparatus according to claim 8 or claim 9, wherein the wrist apparatus comprises a spring configured to exert the returning force on the bearing carrier.
11. The wrist apparatus according to any of claims 7 to 10, wherein adjacent regions of the at least two different regions of the bearing race are connected by V-shaped bearing race segments.
12. The wrist apparatus according to any of claims 7 to 11, wherein: the bearing race comprises at least first, second and third regions corresponding to at least first, second and third positions of the hand mount; the first and second regions of the bearing race are connected by a first V-shaped bearing race segment and the second and third regions of the bearing race are connected by a second V-shaped bearing race segment; and the wrist apparatus is configured to exert the returning force on the bearing carrier which, when the bearing element is in any one of the first, second or third regions, biases the bearing element towards said region, such that movement of the bearing element between the first and second regions or between the second and third regions by rotation of the axle requires overcoming the returning force.
13. The wrist apparatus according to claim 12, wherein the first position of the hand mount corresponds to an extended hand flexion configuration, the second position of the hand mount corresponds to a neutral hand flexion configuration and the third position of the hand mount corresponds to a flexed hand flexion configuration.
14. The wrist apparatus according to any preceding claim, wherein the wrist apparatus comprises a latch for locking the position of the hand mount.
15. The wrist apparatus according to any preceding claim, wherein the hand mount is a hand mounting arm comprising a connector for attachment to the prosthetic hand.
16. The wrist apparatus according to any preceding claim, wherein the wrist apparatus is configured for attachment to a user's socket.
17. The wrist apparatus according to claim 16, wherein the base is mounted on a support and the support is configured for attachment to the user's socket.
18. The wrist apparatus according to claim 17, wherein the base is rotatably mounted on the support to enable rotation of the base relative to the support about an axis of rotation substantially orthogonal to an interface between the base and the support.
19. The wrist apparatus according to claim 18, wherein the base and the support comprise a magnetic clutch mechanism which resists or restricts rotation of the base relative to the support.
20. The wrist apparatus according to any preceding claim, wherein the wrist apparatus is for a cable-operated prosthetic hand and the wrist apparatus comprises a channel for guiding an operating cable of the cable-operated prosthetic hand through the wrist apparatus.
21. The wrist apparatus according to claim 20, wherein the channel extends between a cable inlet for receiving the operating cable from a user's harness and a cable outlet for feeding the operating cable to the cable-operated prosthetic hand, wherein the cable outlet is movable relative to the base with the hand mount.
22. The wrist apparatus according to any preceding claim, wherein the hand mount is movable between the at least two different positions by body power.
23. The wrist apparatus according to any preceding claim, wherein the wrist apparatus is for a body-powered prosthetic hand.
24. A prosthetic apparatus comprising the wrist apparatus according to any preceding claim and a prosthetic hand mounted on the hand mount such that the prosthetic hand is movable between, and releasably retainable in, the at least two different hand flexion configurations by movement of the hand mount between, and releasable retention of the hand mount in, the at least two different positions.
25. A method of moving the prosthetic hand of claim 24 from a first flexion configuration to a second flexion configuration, the method comprising applying a force to the hand to cause movement of the hand mount from a first position of the at least two different positions to a second position of the at least two different positions, optionally wherein the prosthetic apparatus is worn by a user, and applying the force to the hand comprises pressing the hand against the user's body or against a surface.