GB2588248A - A mechanical hand - Google Patents

Abstract

A support such as a wrist joint for a mechanical hand comprising a support member 300 coupled at a hinge axis to a mounting member 200 and a biasing spring arrangement, that may be a pair of spring arrangements either side of the hinge axis, to resist movement of the support member about the hinge axis. The spring arrangement comprises at least one bearing element 328, 330 that may be a ball bearing, urged by a spring element 326 such as a compression spring, against a bearing surface 336 associated with the support or mounting member. The spring arrangement may comprise a compression spring mounted between two ball bearings; the bearings may ride in a curved recess of concave bearing surface that engage the bearing during rotation of the hinge away from the neutral position. Additional leaf springs may further resist rotation of the joint away from a neutral position.

Description

Intellectual Property Office Application No. GB1916462.3 RTM Date:11 May 2020 The following terms are registered trade marks and should be read as such wherever they occur in this document: Bluetooth Wi-Fi Intellectual Property Office is an operating name of the Patent Office www.gov.uk/ipo

A MECHANICAL HAND

The present invention relates to mechanical hands such as for a robot or a prosthetic hand for a human. In particular, but not exclusively, the present invention relates to a prosthetic hand having improved functionality and operation.

A conventional prosthetic hand is typically controlled by a plurality of electrodes located on a user's residual limb which detect electrical signals generated by the user's muscles and send corresponding signals to a controller of the prosthetic hand.

The controller actuates motors in response to the received signals which in turn drive motors to move fingers of the prosthetic hand. The signals are typically mapped to open (extend) and close (flex) the fingers relative to a palm portion of the hand.

The prosthetic hand is typically connected at a wrist region thereof by suitable means to a distal end region of a socket in which the residual limb is located.

The ability for a prosthetic hand to be able to passively flex and extend is particularly desirable to allow a user to bend the wrist and orient the hand in a desired position to efficiently use an object they are gripping, whilst minimising excessive shoulder compensation. Allowing the hand to flex towards the user and lock in a desired position is also particularly desirable when moving the prosthetic hand to the user's face. However, conventional wrist assemblies do not closely replicate the range and nature of movement of a natural wrist, particularly at or close to the equilibrium position, and the limited space available has prevented the addition of a function attempting to provide one or more of the above desired benefits such that, for example, a flex wrist function is completely omitted, particularly for relatively small limbs, or it may be a flex function relying on manual positioning. This is further compounded by the fact a user with a relatively long remnant limb may not have sufficient available length to allow the fitting of a hand and a flex wrist. An additional issue is conventional locking mechanisms of available wrist assemblies can be difficult for a user to activate and deactivate.

It is an aim of certain embodiments of the present invention to provide a prosthetic hand having improved functionality and operation.

It is an aim of certain embodiments of the present invention to provide a prosthetic hand including a relatively short and compact wrist assembly which allows automatic flex functionality, such as when the hand is bent backwards on impact with an object or the like.

It is an aim of certain embodiments of the present invention to provide a prosthetic hand including a wrist assembly which provides a non-complex and compact locking/unlocking function to allow the user to efficiently lock the hand in a desired orientation with respect to the limb socket.

According to a first aspect of the present invention there is provided apparatus for supporting a mechanical hand, comprising: a support member pivotally coupled at a hinge axis to a mounting member; and at least one spring arrangement configured to resist movement of the support member about the hinge axis, wherein the at least one spring arrangement comprises at least one bearing element urged by a spring element against a bearing surface associated with the support member or the mounting member.

Optionally, the at least one bearing element comprises a ball bearing.

Optionally, the spring element comprises a compression spring.

Optionally, the compression spring is located between a pair of ball bearings to urge the same in opposed directions against respective bearing surfaces.

Optionally, the or each bearing surface comprises a curved recess for partially accommodating the bearing element when the support member is in a neutral equilibrium position with respect to the mounting member.

Optionally, the curved recess is located substantially centrally between a pair of concave bearing surfaces configured to engage the bearing element during rotational movement of the support member about the hinge axis in either direction away from the neutral equilibrium position.

Optionally, the at least one spring arrangement comprises a pair of spring arrangements axially spaced apart with respect to the hinge axis.

Optionally, each spring arrangement is mounted at a respective end region of a hinge pin defining the hinge axis.

Optionally, the apparatus comprises a further spring arrangement configured to urge the support member towards a neutral equilibrium position with respect to the mounting member.

Optionally, the further spring arrangement comprises at least one leaf spring.

Optionally, the further spring arrangement comprises a first leaf spring configured to resist movement of the support member in a first direction about the hinge axis, and a second leaf spring configured to resist movement of the support member in a second direction about the hinge axis, the second direction being opposed to the first direction.

Optionally, each spring is configured such that both springs engage the mounting member when the support member is in the neutral equilibrium position.

Optionally, the at least one leaf spring comprises an elongate main portion coupled to the support portion and at least one elongate leg portion extending from the main portion and engageable with the mounting member to provide a reaction force when the support member is forced to move about the hinge axis.

Optionally, the leg portion defines a first angle with respect to a plane of the main portion which is around 5-85 degrees.

Optionally, the leg portion is coupled to the main portion by an intermediate portion which defines a second angle with the respect to the plane of the main portion which is greater than the first angle.

Optionally, the at least one leaf spring comprises a plurality of unconnected layers.

Optionally, the at least one leaf spring is a linear leaf spring.

Optionally, the apparatus comprises a lock arrangement to lock the support member with respect to the mounting member in a rotational position about the hinge axis.

Optionally, the lock arrangement comprises a locking button to move a locking element to the locked position from an unlocked position, and vice versa.

According to a second aspect of the present invention there is provided a mechanical hand comprising apparatus according to the first aspect of the present invention.

Description of the Drawings

Certain embodiments of the present invention will now be described with reference to the accompanying drawings in which: Figure la illustrates the back side of a prosthetic hand according to certain embodiments of the present invention; Figure lb illustrates the palm side of the hand of Figure 1a with the thumb in a non-opposed position; Figure lc illustrates the hand of Figures la and lb with the thumb in an opposed position; Figure ld illustrates a side view of the hand of Figures la to lc with the thumb in an opposed position; Figure le illustrates a side view of the hand of Figures la to ld with the thumb in an opposed position and in a flexed state; Figure if illustrates a side view of the hand of Figures la to le with the thumb in an opposed position and the fingers in a flexed state; Figure 2a illustrates a wrist assembly of the hand of Figures la to 1f; Figure 2b illustrates a side cross sectional view of the wrist assembly of Figure 2a in a flexed state; Figures 2c and 2d illustrate a lock arrangement of the wrist assembly of Figures 2a and 2b in an unlocked and locked state respectively; Figures 2e to 2i illustrate an actuation mechanism of the lock arrangement of Figures 2c and 2d; Figures 2j to 2v illustrate an alternative embodiment of the wrist assembly; Figures 3a to 3d illustrate an alternative embodiment of the wrist flex assembly; and Figure 4 illustrates the resistive torque provided by different spring arrangements according to certain embodiments of the present invention.

Detailed Description

As illustrated in Figures la to 1f, a prosthetic hand 100 according to certain embodiments of the present invention includes a plurality of finger assemblies 102 each extending from a palm region 106 and a thumb assembly 104. The hand 100 terminates at a wrist region 108 which is removably connectable to a socket (not shown) in which a residual limb of a user is received. The socket includes a plurality of sensors/electrodes arranged to engage with the skin of the user and detect electrical signals intentionally generated by the user's muscles which are then used by a controller to selectively control the finger assemblies 102 and thumb assembly 104 of the prosthetic hand 100. The connection between the wrist region and the socket may be any suitable connection, such as a bayonet connection, a threaded connection, a snap-fit connection, a frictional connection, or the like to secure the prosthetic hand to the socket and to allow electrical signals to pass from the sensors to the controller location in the hand. Alternatively, the sensors may communicate wirelessly with the controller located in the hand, e.g. via a BluetoothTM or Wi-Fi connection, or the controller may be located remotely from the hand and connected wirelessly to operate the hand.

As illustrated for example in Figure 1f, a base chassis 200 of the hand 100 on which the finger assemblies 102, the palm region 106, and the thumb assembly 104 are supported is pivotally coupled to the wrist region 108.

As illustrated in Figures 2a and 2b, the wrist region 108 of the hand according to certain embodiments of the present invention comprises an arm plate 600 coupled to the base chassis 200. The base chassis 200 supports the finger assemblies and thumb assembly and the arm plate 600 is mountable to a limb socket. The base chassis 200 is pivotally coupled to the arm plate 600 by a hinge assembly including for example a hinge pin 602 defining a hinge axis 604. A pair of spaced apart lugs 605,606, or the like, respectively extend from each of the base chassis 200 and the arm plate 600 with which the hinge pin 602 engages to thereby pivotally couple the base chassis 200 and arm plate 600 together. Other forms of hinge arrangement may be suitable, such as the arm plate lugs each having an integral pin or projection which cooperates with a corresponding hole or recess in a respective one of the base chassis lugs. The hinge axis 604 is oriented substantially perpendicular to an axis of a user's radius and ulnar, and also to the wrist axis of the device.

One or more springs 607,608 are mounted on the pin to urge the base chassis 200 towards a neutral position, when no rotational force is being applied to the base chassis in use, wherein a plane of the base chassis is substantially parallel with a plane of the arm plate. As shown best in Figure 2b, a pair of torsion springs are axially mounted on the hinge pin 602. The end region of a first leg of each spring is fixed or coupled to the hinge pin to be rotationally constrained thereto. An end region of a second leg 609 of each spring engages with the arm plate 600 on a respective side of the hinge pin. The second leg of each spring comprising the flat engagement surface is angled by around 60 degrees and has a curved ski-like end region to allow the same to slide over an upper surface of the arm plate when the spring is being compressed or uncompressed.

The second leg 609 of each spring is configured to perform like a leaf spring and the coiled portion is configured to perform like a spiral torsion spring, such that each spring is a hybrid combination of a spiral torsion spring and a leaf spring. The sum of the combined torques of the two types of spring provides a high resistive torque, but also a particularly compact size to allow the joint to be relatively compact and short and the flex axis to be closer to that of a natural wrist joint. The torsion springs are also laminated, i.e. comprising two or more unconnected layers which are allowed to slide over each other during coiling and uncoiling, to thereby reduce stress in the material which reduces fatigue during flexing and minimises/eliminates the risk of spring failure in use.

When the base chassis 200 is rotated relative to the arm plate 600 to either side about the hinge pin axis 604 when a rotational force is applied to the basis chassis, such as when the hand is unintentionally knocked in use, the underside of the base chassis 200 engages with a substantially flat engagement surface of the second leg of a respective one of the springs 607,608. Further rotation of the base chassis with respect to the arm plate causes the coiled torsion spring portion to tighten around the hinge pin and the leaf spring portion to compress. The combination of the two actions provides a resistive torque. The resistive torques of both springs equalises when the base chassis 200 and the arm plate 600 are parallel.

The base plate 200 is adapted to rotate +/-around 30 degrees about the hinge axis relative to the flat neutral plane. When the rotational force is removed from the base chassis, the compressed spring urges the base plate back to the neutral position with respect to the arm plate. Aptly, the two spiral torsion springs 607,608, e.g. clock springs, are configured such that one resists flexion and the other resists extension and are adapted such that when one spring is being compressed, the other spring decouples from the base chassis and provides no resistance to the spring being compressed. The only time both springs may be 'active' is +/-around 5 degrees to either side of the neutral plane. The clock springs 607,608 are made of a spiral wound spring steel or other suitable material. Other forms of resilient member, such as compression and/or extension springs, or a torsion bar arrangement, or the like, may also be suitable to provide such a wrist mechanism to allow the hand to flex and extend relative to a user's arm.

In addition to the passive flex mechanism described above, the wrist region 108 further includes a locking arrangement 650 which allows a user to lock the hand 100 in a number of positions relative to the arm about the hinge axis 604. This is particularly useful for eating, for example.

As illustrated in Figures 2c and 2d, the locking arrangement 650 consists of three primary components; static lock apertures 652, a spring-loaded lock bolt 654, and a is lock button 656. The lock bolt 654 is mounted on the underside of the base chassis and oriented substantially parallel with the hinge axis 604 of the wrist hinge/flex mechanism. The lock bolt 654 is slidable in an axial direction between an unlocked position (Figure 2c) and a locked position (Figure 2d). Each of the axially spaced apart lugs 606 extending from the arm plate 600 on which the hinge pin 602 is zo mounted includes a plurality of static lock apertures 652 which in the illustrated example are three spaced apart curved notches in an upper edge of each lug. Alternatively, each lock aperture may be a through hole in a corresponding one of the lugs, a slot, a square notch, or the like. Furthermore, an opposed arrangement can also be envisaged wherein the lock bolt is mounted on the arm plate and the zs static lock apertures are provided by the base chassis. The lock apertures 652 are indexed to correspond to predetermined locking angles of the wrist relative to the limb socket/arm of a user, i.e. a different rotational position of the base chassis 200 with respect to the arm plate 600 about the hinge axis 604.

The lock bolt 654 is slidable in an axis perpendicular to the array of lock apertures 652 and is generally of a shape which would lock into the apertures, preventing the base chassis 200 rotationally moving relative to the arm plate 600 about the hinge axis 604. The lock bolt 654 also has a pair of axially spaced apart gates 660,662 which allows the lugs to pass through the gates of the lock bolt 654 when the same is in the unlocked position and in turn allowing rotation between the base chassis 200 and the arm plate 600 about the hinge pin 602.

The lock bolt 654 is moved from the unlocked position to the locked position, and vice versa, by depressing the lock button 656. The lock bolt 654 is urged towards the lock button 656 but is not rigidly connected thereto. The lock button 654 is slidably coupled to the base chassis 200 and is urged away from the lock bolt 654 by a compression spring 658 towards a parked position.

As illustrated in Figures 2e to 2i, the lock button 656 comprises, or is coupled to, a track element 657 comprising a track 659 for engagement with an elongate and resilient member 661, e.g. a leaf spring, having a follower element 663 at a free end region thereof which follows the track of the tracked element 657. The track element 657 is slidably coupled to the lock bolt and an end region of the resilient member 661 distal the follower element 663 is fixed with respect to the base chassis 200.

The lock button 656 and track element 657 cycle between two positions corresponding to the locked and unlocked positions of the lock bolt 654 by being depressed by a user. As illustrated in Figures 6e to 6i, a position of the track element 657 is controlled by the leaf spring 661. The leaf spring 661 is allowed to flex in a direction approximately perpendicular to the axis of travel of the lock button 656. The track element 657 has two stable positions; locked and unlocked.

From the locked stable position (Fig.2e), the button is pressed, causing the follower element 663 of the leaf spring 661 to slide up an unlocking path of the track and bend off the central axis (Fig.2f). At the top of the unlocking path there is a pocket which the leaf spring springs into, as the button is released and urged away from the lock bolt by the compression spring 658, the follower element of the leaf spring is captured by a stop surface 665 of the track as the leaf spring straightens up (Fig.2g). The lock bolt 654 is now in the unlocked position and the track element 657 is in a corresponding unlocked position. If the lock button is depressed again, the follower element 663 of the leaf spring 661 engages an angled surface of the track and is urged into a further depression in the track (Fig.2h) defined by a further unlocking path of the track. When the lock button is released again, the leaf spring is urged down the further locking path of the track to return to the locked position (Fig.2i).

In the unlocked position, the lock button 656 keeps the lock bolt gates 660,662 aligned with the edge of the lugs 606 and the lock apertures 652, allowing free rotation of the hand relative to the arm about the hinge axis 602. When the lock button 656 is in the locked position, the lock bolt spring urges the locking portion of the lock bolt to interface with a pair of the lock apertures. If the lock apertures are not perfectly aligned at the point the lock button is moved to the locked position, the lock bolt is spring-loaded and will drop into the next available aperture as the wrist is flexed.

The 'push-push' locking arrangement according to certain embodiments of the present invention allows a user with one or two prosthetic hands to efficiently select/adjust and lock a rotational position of the hand relative to the residual limb and with respect to the wrist flex axis, and also to release a locked rotational position to allow for wrist flex in either direction about the wrist flex hinge axis. The locking arrangement is also configured to spring into the next available locking position if the locking bolt is not aligned with a pair of locking apertures when in the locked position meaning the hand does not need to be perfectly aligned to latch the lock.

An alternative locking arrangement may be for the lock button to be rigidly coupled to the lock bolt to slide therewith between locked and unlocked positions and urged by a spring towards the locked position. However, such an arrangement would require a user to keep the button depressed with an able hand during rotation of the prosthetic hand relative to the limb socket/arm.

An alternative embodiment of the passive flex arrangement of the wrist assembly is illustrated in Figures 2j to 2m. Aptly, a pair of leaf springs 707,708 are mounted between the base chassis 200 and the lugs 705,706. Each leaf spring comprises a substantially planar and elongate main portion 709 which engages with flat upper surfaces of the lugs such that the main portion of each spring bridges the lugs on a respective side of the pin 702. As illustrated in Figure 21, the main bridge portion of a first one of the springs is disposed on one side of the pin 702 and the main bridge portion of the second one of the springs is disposed on the other side of the pin 702. Each end region of each elongate main portion has a through hole 710 to allow a suitable fixing, e.g. a bolt, to pass through the main portion of each spring when attaching the base chassis 200 to the outer lugs 705 to thereby sandwich the main bridge portions of the springs therebetween.

An elongate leg portion 711 extends inwardly towards pin axis and downwardly from the main portion 709 of each leaf spring 707,708 such that it passes over the hinge pin 702 and a free end region 712 thereof engages with the arm plate 700 at an opposite side of the hinge pin to the main portion from which it extends. The leg portion is oriented substantially perpendicularly to the main portion. The leg portion 711 is angled downwardly by around 5-85 degrees, aptly around 15 degrees, with respect to the planar main portion 709 when the base chassis is in the neutral position, as illustrated in Figure 2k. Aptly, the leg portion 711 is coupled to the main portion 709 by an intermediate portion 713 which is angled downwardly by around 50 degrees to the planar main portion 709 such that it passes under and clears the locking element 754.

To allow the wrist assembly to flex by around at least 30 degrees to either direction, the planar main portion 709 of each spring, and a corresponding portion of the base chassis 200, comprises a notch 703 in its outer edge to accommodate the leg portion 707 of the other spring at full flex of the wrist.

Aptly, each of the leaf springs is configured such that the free end regions 712 thereof engage the arm plate 700 when the base chassis 200 is in the neutral equilibrium position, as illustrated in Figure 2k. The free end region of the leg portion is bent downwardly to avoid sharp ends of the spring otherwise contacting and compromising the integrity of the soft glove portion surrounding the mechanics of the hand. This end portion could alternatively be bent 180 degrees (like a hair pin) for the same reason.

Aptly, the planar main portion of each leaf spring is around 38 mm long and around 6-7mm wide. The intermediate portion is around 5mm long and the leg portion is around 20mm long. The intermediate portion and leg portion are around 7.5mm wide. Each leaf spring is around 1.2mm thick.

The leaf springs are aptly laminated, i.e. they each comprise two or more unconnected layers which are allowed to slide over each other during flexion to thereby reduce stress in the material which in turn reduces fatigue during flexing and minimises/eliminates the risk of spring failure in use. The leaf springs 707,708 are aptly made of a spring steel or other suitable material. Aptly, each spring is a linear leaf spring. The leaf springs according to certain embodiments of the present invention allow the wrist assembly to be more compact (shorter) than conventional wrist assemblies which rely on coiled torsion springs for example, whilst providing sufficient torque.

The base plate 200 is adapted to rotate +/-around 30 degrees about the hinge axis relative to the flat neutral plane. When the rotational force is removed from the base chassis, the compressed spring urges the base plate back to the neutral position with respect to the arm plate. Aptly, the two linear leaf springs 707,708 are configured such that one resists flexion and the other resists extension and are adapted such that when one spring is being compressed, the other spring decouples from the base chassis and provides no resistance to the spring being compressed. The only time both springs may be 'active' is +/-around 5 degrees to either side of the neutral plane.

As illustrated in Figures 2m to 2v, an alternative form of locking arrangement 750 according to certain embodiments of the present invention includes a lock button 756 depressible by a user and a driving cam member 766 coupled thereto by an elongate portion 780 slidably mounted in an aperture of a fixed support portion 768. The driving cam member 766 may be attached by suitable means to the elongate portion which extends from the lock button or the button, elongate portion and driving cam member 766 may be integrally formed. The lock button 756 and in turn the driving cam member 766 are slidable in an axial direction with respect to an axis of the elongate portion 780 when the button is pressed by a user. The elongate portion 780 is oriented substantially parallel with the hinge axis 704. A compression spring 758, or other suitable resilient member, located between the lock button 756 and the support portion 768 urges the button, and in turn the driving cam, outwardly in the axial direction such that a user is pressing the button against a reaction force of the spring. A pair of opposed elongate rail elements 782 extend inwardly from the support portion 768 in a direction parallel to the elongate portion 780 and engage with a respective one of a pair of opposed notches/grooves 783 in the outer surface of the driving cam member 766 such that the driving cam member is slidable along the rail elements 782 when the lock button is pressed and released, whilst being rotationally constrained by the rail/notch arrangement.

The locking arrangement 750 also includes a driven cam member 767 which is coupled to an end of an elongate locking element 754 such that it is rotatable with respect to the locking element 754. The driven cam member 767 however also includes opposed notches/grooves 784 in its outer surface for sliding engagement with the rail elements 782. The locking element 754 is mounted on the underside of the base chassis 200 and oriented substantially parallel with the hinge axis 704 of the wrist hinge/flex mechanism. The locking element 754 is axially slidable along a lock axis 772 between an unlocked position (as depicted in Figure 2r) and a locked position (as depicted in Figure 2n). The locking element 754 is rotationally constrained by the base chassis 200.

As illustrated in Figures 21 and 2m, one of the lugs 706 extending from the arm plate 700 on which the hinge pin 702 is mounted includes a plurality of static lock apertures 752 which, in a similar manner as illustrated in Figure 2c, may be three spaced apart curved notches in an upper edge of the lug. Alternatively, each lock aperture may be a through hole in a corresponding one of the lugs, a slot, a square notch, or the like. Furthermore, an opposed arrangement can also be envisaged wherein the locking element 754 is mounted on the arm plate and the static lock apertures are provided by the base chassis. Aptly, the lock apertures are indexed to correspond to predetermined locking angles of the wrist relative to the limb socket/arm of a user, i.e. a different rotational position of the base chassis 200 with respect to the arm plate 700 about the hinge axis 704.

The locking element 754 is slidable along the locking axis 772 which is substantially perpendicular to the array of lock apertures 752 and is generally of a shape which would lock into the apertures, preventing the base chassis 200 rotationally moving relative to the arm plate 700 about the hinge axis 704. Aptly, the locking element 754 includes a tapered tooth element 771 or the like for engagement in a selected one of the lock apertures. The locking element 754 also has a gate 773 which allows the lugs to pass through the gate of the locking element 754 when the same is in the unlocked position and in turn allowing rotation between the base chassis 200 and the arm plate 700 about the hinge pin 702.

A second resilient member 770, e.g. compression spring, is provided between a second fixed support portion 769 and the end of the locking element distal to the driven cam member 767. The second spring urges the locking element towards the ends of the rail elements 782. The second spring 770 preloads the locking element 754 to the rotatable driven cam member 767 and also urges the driven cam member 767 against either the ends of the rail elements 782 (Figure 2q) or the slidable driving cam member 766 (Figure 2n) depending on the orientation of the driven cam member 767 with respect to the locking axis 772 and in turn the grooves/notches 784 of the driven cam member 767 with respect to the rail elements 782.

The first spring 758 preloads the lock button 756 and thus the driving cam member 20 766 such that the driving cam member 766 rests on the flanged face of the fixed housing portion 768. Pressing the lock button 756 allows the driving cam member 766 to move away from the flanged face along the locking axis 772.

The driving cam member 766 and the driven cam member 767 are substantially circular in cross section and each include at least one angled engagement surface such that when the engagement surface of the driving cam member engages the angled engagement surface of the driven cam member, the driven cam member is forced to rotate about the lock axis. Aptly, as illustrated, each of the cam members comprise a plurality of angled engagement surfaces, and aptly including at least one curved engagement surface. The engagement surfaces of the driving cam member 766 and the driven cam member 767 are angled in such a way to allow the linear motion of the driving cam member 766 to convert efficiently to rotation motion of the driven cam member 767 at quarter turns. Aptly, the engagement surfaces are angled by around 60 degrees.

Figure 2n shows the locking mechanism in the locked position. In this position, the lock button 756 is in a fully out position so that the driving cam member 766 is resting against the flanged face of the fixed support portion 768. This is held in place by the first spring 758. The driven cam member 767 is orientated such that the grooves/notches 784 provided therein are allowed to slide over the rail elements 782. The driven cam member 767 is resting against the driving cam member 766 and the locking element 754 is resting against the driven cam member 767 due to the action of the second spring 770. The tooth element 771 of the locking element 754 is within a selected one of the lock apertures 752 of the lug 706. This prevents the base plate 200 rotating about the hinge axis with respect to the arm plate 700.

To unlock the wrist arrangement, the user presses the lock button 756 which in turns axially moves the driving cam member 766 along the rail element 782 in a direction of the lock axis 772. The driving cam member 766 pushes the driven cam member 767 along the lock axis. The driven cam member 767 is prohibited to rotate until the grooves/notches 784 therein are clear of the rail elements 782, as illustrated in Figure 2o.

Once the grooves 784 of the driven cam member 767 are clear of the rail elements 782, the driven cam member 767 rotates until the teeth elements thereof are stopped by the correspondingly shaped teeth elements of the driving cam member 766, as illustrated in Figure 2p. The rotation is due to the angled/sloped surfaces of the engaged teeth elements of the cam members 766,767 and the urging force provided by the second spring 770.

Once the lock button 756 is released, the first spring 758 returns the lock button and the driving cam member 766 back to its resting position, as illustrated in Figure 2q. The driven cam member 767 is now allowed to rotate further until the rail elements 782 engage with the grooves 784 of the driven cam member 767 prevent any further movement, as illustrated in Figure 2r. The rotation is due to the angled/sloped surfaces of the engaged teeth elements of the cam members 766,767 and the urging force provided by the second spring 770. At this position, the tapered tooth element 771 of the locking element 754 is clear of the lock apertures 752 of the lug 706 and in turn the base chassis 200 is allowed to rotate about the hinge axis 704 with respect to the arm plate 700.

To lock the wrist, the user presses the lock button 756 which axially moves the driving cam member 766 along the rail elements 782 in a direction of the lock axis 772 until it engages with and pushes the driven cam member 767 along the lock axis. The driven cam member 767 is prohibited to rotate until the grooves 784 thereof are clear of the rail elements 782, as illustrated in Figure 2s. Once the grooves 784 are clear of the rail elements 782, the driven cam member 767 rotates until the teeth elements thereof are stopped by the teeth element/s of the driving cam 766, as illustrated in Figure 2t. The rotation is due to the angled/sloped surfaces of the engaged teeth elements of the cam members 766,767 and the urging force provided by the second spring 770.

Once the lock button 756 is released, the first spring 758 returns the lock button and the driving cam member 766 back to its resting position, as illustrated in Figure 2u. The driven cam member 767 is now allowed to rotate further, as a result of being engaged with and rotatably urged by the tapered end region of the rail elements 782, until the grooves 784 thereof align with the fixed rail elements 782. The driven cam member 767 is then slid back until it rests on the driving cam member 766 when urged by the second spring 770, as illustrated in Figure 2v. The locking element 754 is in the locked state, wherein the tooth element 771 of the locking element 754 is within a selected one of the lock apertures 752 of the lug 706 to thereby prevent the base chassis 200 rotating with respect to the arm plate 700.

As illustrated in Figures 3a to 3d, an alternative wrist assembly 300 according to certain embodiments of the present invention includes the same or at least similar arrangement of opposed leaf springs 307,308 as the embodiment illustrated in Figures 2j to 2m to allow the hand to rotatably flex to either side of the hinge axis 304, and also the same or at least similar lock arrangement as illustrated in Figures 2n to 2v to allow the base chassis 200 of the hand 100 to be locked in a desired rotational position with respect to the arm plate 700.

Each leaf spring 307,308 of this alternative embodiment has a return-folded free end 310 such that any risk of the free ends of the leaf spring compromising the integrity of the outer cover of the hand is relatively low/eliminated. Furthermore, the wrist assembly 300 includes a second spring arrangement 320 to provide additional and improved flex stiffness in the region of around 10 degrees to either side of the equilibrium position of the base chassis with respect to the arm plate, i.e. in flexion and extension. This second spring arrangement 320 eliminates 'floppiness' at and around the centre position to make the wrist assembly feel more secure in the centre/equilibrium position and to more closely resemble a natural wrist.

As illustrated in the sectional view of Figure 3b, the hinge pin 302 of the wrist assembly 300 is split in two parts 303,305 which are coupled together by a dowel pin 323. This arrangement aids assembly of the wrist assembly. Each hinge pin part 303,305 is fixed to a respective portion of the arm plate 200 by a coiled spring pin 322, or the like, to be axially and rotationally constrained with respect to the arm plate. Each hinge pin part 303,305 has an enlarged and substantially rectangular outboard end region 324, e.g. hammerhead-like, which houses a compression spring 326 located between a pair of ball bearings.

As illustrated in Figure 3c, the ball bearings 328,330 sit in the open-end regions of the compression spring 326 which urges the ball bearings outwardly in opposed directions against a respective curved bearing surface 332,334 associated with the base chassis 700. When the base chassis 700 is in the central/equilibrium position with respect to the arm plate 200 (as shown in Figure 3c), each ball bearing 328,330 is urged into a correspondingly sized and shaped curved recess 336 defined in the respective bearing surface 332,334. This arrangement secures the base chassis 700, and in turn the hand 100, in the equilibrium position until a force is applied thereto to move the hand in flexion or extension about the wrist hinge axis.

As illustrated in Figure 3d, when a force is applied to the hand 100 to move the base chassis 700 in either flexion or extension about the hinge axis, each ball bearing 328,330 is forced to roll out of its respective curved recess 336 and follow the curved bearing surface 332,334. At the same time, the compression spring 326 is compressed to urge each ball bearing 328,330 against its respective bearing surface. This arrangement further provides a sense of additional security during the flex movement in view of the friction between the urged ball bearings and the bearing surfaces.

Aptly, each curved recess 336 is located substantially centrally along the respective curved bearing surface 332,334, and is substantially semi-circular in cross section to securely accommodate the respective and correspondingly shaped ball bearing. Aptly, each curved recess 336 may be a channel or notch having a concave cross section, e.g. a substantially semi-circular cross section, or each recess may be a substantially hemispherical cup, or the like, for receiving the respective ball bearing when the wrist assembly is in the neutral position. The edges of each curved recess are substantially curved to aid each ball bearing to efficiently roll out of its recess when the wrist assembly is flexed in use. The curved portions of each bearing surface 333,334 to each side of the respective curved recess 336 are slightly concave to allow the respective ball bearing to efficiently roll over the bearing surface during further flex of the wrist assembly and also to then return to the recess when the wrist is returned to its central position by the first spring arrangement comprising the leaf springs, and/or the second spring arrangement comprising the ball bearings.

Aptly, a pair of the second spring arrangements are provided at each end of the hinge pin but a single second spring arrangement may alternatively be used. Likewise, each second spring arrangement includes a compression spring and a pair of opposed ball bearings but alternatively a single ball bearing, or other suitable bearing element, may be used which engages with a curved bearing surface on either side of a curved recess therein depending on the rotational movement of the base chassis with respect to the arm plate, i.e. flexion or extension. Further alternatively, the flex wrist assembly according to certain embodiments of the present invention may use a spring arrangement according to the second spring arrangement only, e.g. compression spring and ball bearing/s, and exclude the leaf spring arrangement.

As illustrated in the graph of Figure 4, the combination of the leaf spring arrangement and the ball bearing/spring arrangement effectively increases the resistive initial torque around +/-10 degrees to either side of the neutral position without increasing the resistive torque at the extremities of the flex/extension range of movement (around +/-30 degrees). The ball bearing/spring arrangement could be excluded and the leaf springs could be stiffened up to provide the desired effect of increasing the resistive torque around the neutral position but, due to the linear profile of the leaf springs, the resistive torque at the extremities of the flex/extension range would be particularly high and would undesirably cause the wrist to be too stiff to reach each extremity of the flex/extension range without excessive effort by the user. Whilst the ball bearing/spring arrangement could be used alone, i.e. without the leaf springs, to provide the desired increased resistive torque around the neutral position, the resistive torque towards and at the flex/extension extremities may be insufficient, unless the spring and bearing surfaces were configured to ensure the resistive torque was sufficient throughout the flex/extension range without being too stiff.

Certain embodiments of the present invention therefore provide a prosthetic hand having improved functionality and operation. The hand includes a wrist assembly which is compact, secure, and more closely resembles the movement and stiffness of a natural wrist than the wrist assembly of a conventional prosthetic hand, particularly at and around the central equilibrium position. The spring and ball bearing arrangement according to certain embodiments of the present invention desirably increase the torque required to flex/extend the wrist away from the neutral position, e.g. up to around +/-10 degrees. This in turn makes the wrist feel more stable in the neutral position when unlocked, and therefore reducing the need to lock the wrist in the neutral position every time, making the hand easier and more enjoyable to use. Whilst a prosthetic hand has been described throughout, certain embodiments of the present invention are applicable to other prosthetic terminal devices, such as a prosthetic foot, or a robotic device.

Claims (20)

1. Claims 1. Apparatus for supporting a mechanical hand, comprising: a support member pivotally coupled at a hinge axis to a mounting member; and at least one spring arrangement configured to resist movement of the support member about the hinge axis, wherein the at least one spring arrangement comprises at least one bearing element urged by a spring element against a bearing surface associated with the support member or the mounting member.
2. 2. The apparatus according to claim 1, wherein the at least one bearing element comprises a ball bearing.
3. 3. The apparatus according to claim 2, wherein the spring element comprises a compression spring.
4. 4. The apparatus according to claim 3, wherein the compression spring is located between a pair of ball bearings to urge the same in opposed directions against respective bearing surfaces.
5. 5. The apparatus according to any preceding claim, wherein the or each bearing surface comprises a curved recess for partially accommodating the bearing element when the support member is in a neutral equilibrium position with respect to the mounting member.
6. 6. The apparatus according to claim 5, wherein the curved recess is located substantially centrally between a pair of concave bearing surfaces configured to engage the bearing element during rotational movement of the support member about the hinge axis in either direction away from the neutral equilibrium position.
7. 7. The apparatus according to any preceding claim, wherein the at least one spring arrangement comprises a pair of spring arrangements axially spaced apart with respect to the hinge axis.
8. 8. The apparatus according to claim 7, wherein each spring arrangement is mounted at a respective end region of a hinge pin defining the hinge axis.
9. 9. The apparatus according to any preceding claim, comprising a further spring arrangement configured to urge the support member towards a neutral equilibrium position with respect to the mounting member.
10. 10. The apparatus according to claim 9, wherein the further spring arrangement comprises at least one leaf spring.
11. 11. The apparatus according to claim 10, wherein the further spring arrangement comprises a first leaf spring configured to resist movement of the support member in a first direction about the hinge axis, and a second leaf spring configured to resist movement of the support member in a second direction about the hinge axis, the second direction being opposed to the first direction.
12. 12. The apparatus according to claim 11, wherein each spring is configured such that both springs engage the mounting member when the support member is in the neutral equilibrium position.
13. 13. The apparatus according to any of claims 10 to 12, wherein the at least one leaf spring comprises an elongate main portion coupled to the support portion and at least one elongate leg portion extending from the main portion and engageable with the mounting member to provide a reaction force when the support member is forced to move about the hinge axis.
14. 14. The apparatus according to claim 13, wherein the leg portion defines a first angle with respect to a plane of the main portion which is around 5-85 degrees. 30
15. 15. The apparatus according to claim 14, wherein the leg portion is coupled to the main portion by an intermediate portion which defines a second angle with the respect to the plane of the main portion which is greater than the first angle.
16. 16. The apparatus according to any of claims 10 to 15, wherein the at least one leaf spring comprises a plurality of unconnected layers.
17. 17. The apparatus according to any of claims 10 to 16, wherein the at least one leaf spring is a linear leaf spring.
18. 18. The apparatus according to any preceding claim, comprising a lock arrangement to lock the support member with respect to the mounting member in a rotational position about the hinge axis.
19. 19. The apparatus according to claim 18, wherein the lock arrangement comprises a locking button to move a locking element to the locked position from an unlocked position, and vice versa.
20. 20. A mechanical hand comprising apparatus according to any preceding claim.