LINEAR ACTUATOR ASSEMBLY, BIONIC DIGIT AND PROSTHETIC HAND

Abstract

A linear actuator assembly housed within a bionic digit, which comprises a base portion, an intermediate portion and an end portion; the intermediate portion pivotally connected to the base portion at one end and pivotally connected to the end portion at the opposite end. The linear actuator assembly includes a drive mechanism; a carriage mechanism having a longitudinal axis (L); a transmission member for transmitting rotational force from the drive mechanism to the carriage mechanism; and a drive member coupled to the carriage mechanism. The carriage mechanism converts the rotational force into an axial force applied to the drive member, moving the drive member along the axis as the carriage mechanism rotates. The drive member is pivotally connected to the end portion. The intermediate portion houses the linear actuator, which further includes a first thrust bearing between the carriage mechanism and the drive mechanism, and the second thrust bearing between the carriage mechanism and a seat provided within the intermediate portion, the carriage mechanism confined between the thrust bearings at each end.

Claims

1. A bionic digit comprising: a base portion; an intermediate portion and an end portion; the intermediate portion having a longitudinal axis (A), a proximal end connected to the base portion, and a distal end; the bionic digit having a central plane (CP) that includes the longitudinal axis (A) of the intermediate portion; the end portion having a proximal end connected to the distal end of the intermediate portion, and a distal end; a first connector connecting the proximal end of the intermediate portion to the base portion, including a pivotal connection for allowing the intermediate portion to pivot about a first pivot axis (P1) perpendicular to the central plane (CP); a second connector connecting the proximal end of the end portion to the distal end of the intermediate portion, including a pivotal connection for allowing the end portion to pivot relative to the intermediate portion, about a second pivot axis (P2) perpendicular to the central plane (CP); a linear actuator assembly, including a drive mechanism for generating a rotational force and having a proximal end and a distal end; a carriage mechanism having a longitudinal axis (L); a transmission member interconnected with the carriage mechanism for transmitting the rotational force from the drive mechanism to the carriage mechanism; and a drive member coupled to the carriage mechanism; the carriage mechanism converting the rotational force into an axial force applied to the drive member, moving the drive member along the longitudinal axis (L) as the carriage mechanism rotates; the carriage mechanism having a proximal end and a distal end; a third connector connecting the drive member to the proximal end of the end portion, including a pivotal connection between the drive member and the end portion, for allowing the end portion to pivot about a third pivot axis (P3) perpendicular to the central plane (CP), relative to the drive member; the intermediate portion including a housing volume, housing the linear actuator; wherein the linear actuator assembly further includes a first thrust bearing and a second thrust bearing; the transmission member being interconnected with the carriage mechanism, for allowing the drive mechanism to drive rotation of the carriage mechanism, while allowing the carriage mechanism (330) to move axially along the transmission member, as axially constrained by the first and second thrust bearings.

2. A bionic digit comprising: a base portion; an intermediate portion and an end portion; the intermediate portion having a longitudinal axis (A), a proximal end connected to the base portion, and a distal end; the bionic digit having a central plane (CP) that includes the longitudinal axis (A) of the intermediate portion; the end portion having a proximal end connected to the distal end of the intermediate portion, and a distal end; a first connector connecting the proximal end of the intermediate portion to the base portion, including a pivotal connection for allowing the intermediate portion to pivot about a first pivot axis (P1) perpendicular to the central plane (CP); a second connector connecting the proximal end of the end portion to the distal end of the intermediate portion, including a pivotal connection for allowing the end portion to pivot relative to the intermediate portion, about a second pivot axis (P2) perpendicular to the central plane (CP); a linear actuator assembly, including a drive mechanism (310) for generating a rotational force and having a proximal end and a distal end; a carriage mechanism (330) having a longitudinal axis (L); a transmission member interconnected with the carriage mechanism for transmitting the rotational force from the drive mechanism to the carriage mechanism; and a drive member coupled to the carriage mechanism; the carriage mechanism converting the rotational force into an axial force applied to the drive member, moving the drive member along the longitudinal axis (L) as the carriage mechanism rotates; the carriage mechanism (330) having a proximal end and a distal end; a third connector connecting the drive member to the proximal end of the end portion, including a pivotal connection between the drive member and the end portion, for allowing the end portion to pivot about a third pivot axis (P3) perpendicular to the central plane (CP), relative to the drive member; the intermediate portion including a housing volume, housing the linear actuator; wherein the linear actuator assembly further includes a first thrust bearing and a second thrust bearing; the first thrust bearing disposed between the proximal end of the carriage mechanism and the distal end of the drive mechanism; and the housing volume includes a seat at the distal end of the intermediate portion, for seating the second thrust bearing, the second thrust bearing disposed between the distal end of the carriage mechanism and the seat, the carriage mechanism being axially confined between the first and second thrust bearings.

3. The bionic digit as claimed in claim 2, the transmission member being interconnected with the carriage mechanism, for allowing the drive mechanism to drive rotation of the carriage mechanism, while allowing the carriage mechanism to move axially along the transmission member, as axially constrained by the first and second thrust bearings.

4. The bionic digit as claimed in claim 1, the drive mechanism including a drive motor for generating torque, and a planetary gear system for converting a torque generated by the drive motor (320) to a torque applied to the transmission member.

5. The A bionic digit as claimed in claim 1, wherein the drive member is coupled to the intermediate portion by a fourth connector; the fourth connector connecting the drive member and the intermediate portion, for allowing the drive member to move over a distance (D) along the intermediate portion, whilst preventing the drive member from rotating about the longitudinal axis (L) of the carriage mechanism, relative to the intermediate portion when the carriage mechanism rotates in use.

6. The bionic digit as claimed in claim 1, wherein the carriage mechanism comprises a threaded rod and the drive member includes a mating screw-threaded portion for interconnecting with the threaded rod, wherein the threading converts rotation of the carriage mechanism to movement of the drive member along the longitudinal axis (L) of the threaded rod.

7. The bionic digit (200) as claimed in claim 1, wherein the transmission member, and the carriage mechanism into its proximal end, receiving the drive shaft, the recess being coaxial with the longitudinal axis (L) of the carriage mechanism.

8. The bionic digit as claimed in claim 7, wherein the recess and the drive shaft have the same cross-sectional polygonal shape.

9. The bionic digit as claimed in claim 1, the intermediate portion comprising an encasement having an interior volume defining the housing volume, wherein the encasement and the drive mechanism have a complementary fastening mechanism between them.

10. The bionic digit as claimed in claim 1, one or both of the first thrust bearing and the second thrust bearing being a thrust ball bearing system, comprising ball bearings, a ball cage for supporting the ball bearings, a first race ring and a second race ring; wherein the ball bearings are supported between the first and second race rings by the ball cage.

11. The bionic digit as claimed in claim 1, at least one of the first thrust bearing and the second thrust bearing being a roller bearing system, comprising roller bearings, a roller cage for supporting the roller bearings, a first race ring and a second race ring; wherein the roller bearings are supported between the first and second race rings by the roller cage.

12. The bionic digit as claimed in claim 1, wherein the first and second thrust bearings are of the same type.

13. The bionic digit as claimed in claim 1, the bionic digit having right- and left-hand sides on laterally opposite sides of the central plane (CP); each side having respective first connectors, second connectors and third connectors; each pair of left- and right-hand connectors having the same respective pivot axis (P1, P2, P3).

14. The bionic digit as claimed in claim 1, comprising a support element having a proximal end connected to the base portion and a distal end connected to the drive member; a fifth connector connecting the proximal end of the support element to the base portion, including a pivotal connection for allowing the support element to pivot relative to the base portion, about a pivot axis (P5) perpendicular to the central plane (CP); and a sixth connector connecting the distal end of the support element to the drive member, including the pivotal connection for allowing the support element to pivot relative to the drive member, about the third pivot axis (P3) perpendicular to the central plane (CP).

15. The bionic digit as claimed in claim 14, comprising a right-hand support element and a left-hand support element, the right-hand support element connecting the base portion to the drive member on the right-hand side of the bionic digit; and the left-hand support element connecting the base portion to the drive member on the left-hand side of the bionic digit; respective fifth connectors on the right-hand side and the left-hand side, connecting the proximal ends of the respective support elements to the respective side of the base portion, and respective sixth connectors on the right-hand side and the left-hand side, connecting the distal ends of the respective support elements to the respective pivotal connections extending from the respective sides of the drive member.

16. A linear actuator assembly for a bionic digit that includes a housing for accommodating the linear actuator assembly; the linear actuator assembly comprising: a drive mechanism having a proximal end and a distal end, for generating a rotational force; a carriage mechanism having a longitudinal axis (L), a proximal end and a distal end; a transmission member for transmitting the rotational force from the drive mechanism to the carriage mechanism, the carriage mechanism being interconnected with the transmission member; and a drive member coupled to the carriage mechanism; the carriage mechanism converting the rotational force into an axial force applied to the drive member, moving the drive member along the longitudinal axis (L) as the carriage mechanism rotates; a first thrust bearing and a second thrust bearing; wherein the first thrust bearing is disposed between the proximal end of the carriage mechanism and the distal end of the drive mechanism; and the second thrust bearing can be disposed between the distal end of the carriage mechanism and a portion of the housing, the carriage mechanism being axially confined between the first and second thrust bearings.

17. The linear actuator assembly as claimed in claim 16, the transmission member being interconnected with the carriage mechanism, for allowing the drive mechanism to drive rotation of the carriage mechanism, while allowing the carriage mechanism to move axially along the transmission member, as axially constrained by the first and second thrust bearings, the transmission member not transmitting axial forces between the carriage mechanism and the drive mechanism.

18. The linear actuator assembly as claimed in claim 16, the drive mechanism including: a drive motor for generating torque, and a planetary gear system for converting a torque generated by the drive motor to a torque applied to the transmission member.

19. The linear actuator assembly as claimed in claim 16, wherein the carriage mechanism comprises a threaded rod and the drive member includes a mating screw-threaded portion for interconnecting with the threaded rod, wherein the threading converts rotation of the carriage mechanism to movement of the drive member along the longitudinal axis (L) of the threaded rod.

20. The linear actuator assembly as claimed in claim 16, wherein the transmission member comprises a drive shaft, and the carriage mechanism includes a recess into its proximal end receiving the drive shaft, the recess being coaxial with the longitudinal axis (L) of the carriage mechanism.

21. The linear actuator assembly as claimed in claim 20, wherein the recess and the drive shaft have the same cross-sectional polygonal shape.

22. The linear actuator assembly as claimed in claim 16, one or both of the first thrust bearing and the second thrust bearing being a thrust ball bearing system, comprising ball bearings, a ball cage for supporting the ball bearings, a first race ring and a second race ring; wherein the ball bearings are supported between the first and second race rings by the ball cage.

23. The linear actuator assembly as claimed in claim 16, at least one of the first thrust bearing and the second thrust bearing being a roller bearing system, comprising roller bearings, a roller cage for supporting the roller bearings, a first race ring and a second race ring; wherein the roller bearings are supported between the first and second race rings by the roller cage.

24. The linear actuator assembly as claimed in claim 16, wherein the first and second thrust bearings are of the same type.

25. The prosthetic hand comprising a bionic digit as claimed in claim 1.

Description

[0028] Non-limiting example arrangements of screw mechanisms, bionic digits and prosthetic hands will be described with reference to the accompanying drawings, of which:

[0029] FIG. 1A shows a schematic top view of an example of a partly closed prosthetic hand, showing top views of the knuckles and the intermediate portions; and

[0030] FIG. 1B shows a schematic underside view of the example prosthetic hand, showing the tops of the end portions of example bionic fingers;

[0031] FIG. 2A shows a schematic perspective view of an example bionic finger in the fully open, extended position (although the third 260, fourth 250 and sixth 290 connectors are indicated in this drawing because they share a common pivot pin that extends from the drive member, only the sixth 290 is visible); and

[0032] FIG. 2B shows a schematic perspective view of the bionic finger in the fully closed, curled-inward position;

[0033] FIG. 3 shows a schematic perspective view of an example support element for a bionic finger;

[0034] FIG. 4A shows a schematic perspective view of an example intermediate portion, showing its longitudinal axis A; and

[0035] FIG. 4B shows a schematic exploded perspective view of the example intermediate portion;

[0036] FIG. 5 shows a schematic perspective view of an example base portion for a bionic finger, including the central plane CP;

[0037] FIG. 6 shows a schematic perspective view of an example end portion for a bionic finger;

[0038] FIG. 7A shows a schematic cut-away side perspective view of an example intermediate portion, showing the linear actuator assembly, in which the drive motor is fastened to an encasement of the intermediate portion;

[0039] FIG. 7B shows a schematic cut-away side view of the example intermediate portion, showing the linear actuator assembly; and

[0040] FIG. 7C shows a schematic view of a central longitudinal cross-section through the intermediate portion, showing the linear actuator assembly, showing the central plane CP;

[0041] FIG. 8A shows a schematic exploded perspective view of an example linear actuator, with part of the encasement of the intermediate portion;

[0042] FIG. 8B shows a schematic exploded perspective view of part of the example linear actuator, showing a drive shaft projecting from the drive mechanism, and a threaded rod carriage mechanism removed from the drive shaft; and

[0043] FIG. 8C shows a schematic perspective view of part of the example linear actuator, in which the threaded rod carriage mechanism is mounted onto the drive shaft extending from the drive mechanism;

[0044] FIG. 9 shows a schematic exploded perspective view of a conical roller thrust bearing;

[0045] FIG. 10 shows a schematic partly exploded perspective view of an example of a cylindrical roller thrust bearing;

[0046] FIG. 11A shows a schematic partly exploded perspective view of an example of a ball thrust bearing;

[0047] FIG. 11B shows a schematic top view and a cross-section view through the ball thrust bearing;

[0048] FIG. 11C shows a schematic partly cut-away perspective view of an example ball thrust bearing;

[0049] FIG. 12 is a general view of the actuator assembly;

[0050] FIG. 13 is an exploded view of the drive member and thrust bearing arrangements;

[0051] FIG. 14 is an assembled view of the drive member and thrust bearing arrangements;

[0052] FIG. 15 is an exploded view of the drive member and thrust bearings shown in-line with the actuator with which they become coupled for rotational movement therewith; and

[0053] FIG. 16 is a view of the actuator and the carriage from a different angle such as to show the arrangement for the drive shaft

[0054] With reference to FIGS. 1A and 1B, an example prosthetic hand 100 comprises five example bionic fingers 200 and a bionic thumb. The prosthetic hand 100 can be fitted to a user by means of an attachment sleeve (not shown);

[0055] With reference to FIGS. 2A to 8C, an example bionic finger 200 comprises: a base portion 210, which may be considered as corresponding to a knuckle; an intermediate portion 220; an end portion 230; a linear actuator assembly 300 (shown in more detail in FIGS. 7A-7C) and a pair of support arms 240, on the right- and left-hand side of the digit, of which an example is shown in FIG. 3. As used herein, a linear actuator is a device that generates force to drive a body in a straight line. The intermediate portion 220 has a proximal end 221A connected to the base portion 210 and a distal end 221B, which is axially displaced from the proximal end 221A (as used herein unless otherwise indicated, the ‘end’ of a member or element includes an end region that is coterminous with the end). The end portion 230 is pivotally connected to the distal end 221B of the intermediate portion 220. The intermediate portion 220 has a longitudinal axis A and the bionic finger 200 has a central plane CP that includes the longitudinal axis A, defining left- and right-hand sides of the bionic digit 200, on either side of the central plane CP (viewed from the base portion 210 towards the end portion 230). The bionic digit 200 may be substantially symmetric (particularly but not exclusively having reflective symmetry) about the central plane CP.

[0056] In the illustrated example arrangement, the intermediate portion 220 comprises an encasement 223 defining a housing volume 225 within which the linear actuator 300 is housed. The encasement 223 comprises two longitudinal halves (a left-hand half and a right-hand half), as illustrated in FIG. 4B. In this example, the housing volume 225 is elongate, being open at the proximal end 221A of the intermediate portion 220 and closed at the distal end 221B.

[0057] An example linear actuator assembly 300 is illustrated in detail in FIGS. 7A-7C and comprises a drive mechanism 310, a threaded rod 330 (a specific example of a carriage mechanism), a drive shaft 324 (a specific example of a transmission member), a threaded nut 340 (a specific example of a drive member), and first and second thrust bearings 350, 360. The drive mechanism 310 comprises a motor 320 for generating torque, and a planetary gear system 322, and has a proximal end 309A and a distal end 309B. The threaded rod 330 has a proximal end 331A and a distal end 331B, an elongate recess 333 provided into the proximal end 331A for receiving the drive shaft 324. The recess 333 is coaxial with the longitudinal axis L of the threaded rod 330, and the drive shaft 324 transmits torque from the drive mechanism 310 to the threaded rod 330. The drive shaft 324 extends from the drive mechanism 310 and is inserted into the recess 333 of the threaded rod 330. The gear system 322 converts a torque generated by the motor 320 to a rotational force applied to the drive shaft 324, and consequently to the threaded rod 330. The drive mechanism 310 is coupled in a fixed relationship to the intermediate portion 220, so that that the drive mechanism 310 cannot rotate relative to the intermediate portion 220 in use. The exterior of the drive mechanism 310 includes a threaded region 311 that mates with a corresponding threaded region of the encasement 223, within the housing volume 225, so that the drive mechanism 310 is threadedly interconnected with the encasement 223.

[0058] In this example, the cross-sections of the recess 333 and the drive shaft 324 are both hexagonal in shape, the mating hexagonal shapes providing azimuthal inter-connection between the drive shaft 324 and the threaded rod 330 via contact surfaces 325A and 325B respectively, enabling the drive shaft 324 to turn the threaded rod 330. In this example, there is no adhesive between the threaded rod 330 and the drive shaft 324, and the drive shaft 324 has uniform cross-sectional dimensions and shape along its length, thus allowing the threaded rod 330 to move substantially freely along the drive shaft 324 within the constraints of the first and second thrust bearings 350, 360. In other words, the threaded rod 330 is mechanically mounted onto the drive shaft 324, interconnected with the drive shaft 324 in a way that the threaded rod 330 is prevented from rotating relative to the drive shaft 324, but is not prevented by the drive shaft 324 from sliding axially on the drive shaft 324 along the longitudinal axis L of the threaded rod 330. Consequently, the drive shaft 324 cannot transmit an axial force between the drive mechanism 310 and the threaded rod 330. In other examples, different mechanical configurations and polygonal shapes may be used for rotationally interconnecting the drive shaft 324 and the threaded rod 330. The longitudinal axis L of the threaded rod 330 is parallel to the longitudinal axis A of the intermediate portion 220 in this example (and may be so in general). The threaded nut 340 includes a threaded through-hole 341, in which the threading of the threaded nut 340 mates with the threading of the threaded rod 330, and the threaded nut 340 is threadedly coupled to the threaded rod 330.

[0059] The bionic finger includes at least three pairs of connectors, each pair consisting of corresponding connectors on either side of the finger (i.e., on the left- and right-hand side of its central axis): [0060] a) a first connector 212 pivotally connects the proximal end 221A of the intermediate portion 220 to the base portion 210, [0061] b) a second connector 280 pivotally connects the proximal end 231A of the end portion 230 to the distal end 221B of the intermediate portion 220, and [0062] c) a third connector 260 pivotally connects the threaded nut 340 to the end portion 230.

[0063] Each of the left-hand and right-hand first connectors 212 comprises a respective pivot pin 213 defining a first pivot axis P1 (coaxial with both of the first pivot pins 213) and extending from the proximal end 221A of the intermediate portion 220 into corresponding apertures 217 on the left- and right-hand sides of the base portion 210. The pivotal connections 213 of the first connectors 212 allow the intermediate portion 220 to pivot about the first pivot axis P1 relative to the base portion 210, within the central plane CP (as shown in FIGS. 4A to 5).

[0064] Each of the second connectors 280 comprises a respective pivot pin 281 defining a second pivot axis P2 (coaxial with both of the pivot pins 281) and extending from the distal end 221B of the intermediate portion 220 into corresponding apertures 282 in the left- and right-hand sides of the proximal end 231A of the end portion 230. The pivotal connection 281 of the second connector 280 allows the end portion 230 to pivot about the second pivot axis P2, relative to the intermediate portion 220.

[0065] The threaded nut 340 threadedly coupled to the threaded rod 330 includes a pair of pivot pins 342 extending from left- and a right-hand sides thereof, defining a third pivot axis P3 (coaxial with both of the first pivot pins 342). Each third connector 260 comprises the respective pivot pin 342 extending from a respective side of the threaded nut 340 into a respective aperture 262 in the then portion 230.

[0066] The end portion 230 has a proximal end 231A and a distal end 231B, and includes a pair of flanges 232 coterminous with the proximal end 231A, on either side of the bionic digit 200. Each of the flanges 232 includes a respective first aperture 282 for receiving a respective pivot pin 281 of the intermediate portion 220 (forming the second connector 280), as well as a respective second aperture 262 for receiving the respective pivot pin 342 extending from a respective side of the threaded nut 340 (forming the third connector 260). When the threaded nut 340 moves along the threaded rod 330 in response to the threaded rod being 330 driven to rotate, the threaded nut 340 acts at the third connectors 260 to move the end portion 230, causing the end portion 230 to pivot at the second connector 280 about the second pivot axis P2. Viewing a prosthetic hand 100 as having a lower side and an upper side, in which the fingers can curl away from the upper side and towards a palm of a bionic hand on the lower side, the second connectors 280 are positioned above the third connectors 260.

[0067] With reference to FIGS. 2A, 2B, 4A and 4B, the example bionic finger 200 includes a pair of fourth connectors 250, each comprising a respective one of the pivot pins 342 of the threaded nut 340 extending into a respective slot 252 in the encasement 223 of the intermediate portion 220. Each slot 252 extends parallel to the longitudinal axis L of the threaded rod 330. This arrangement of the pivot pins 342 through the slots 252 on either side of the bionic digit 200 allows the threaded nut 340 to move along the longitudinal axis L of the threaded rod 330 between the ends of the slots 252 (the fourth connector 250 is indicated in FIGS. 2A and 2B because it shares the drive member pivot pin 342 with the third connector 260 and the sixth connector 290, of which only the sixth connector 290 is visible in this view). The axial movement of the threaded nut 340 is thus limited by length D of the slots 252, and the slots 252 receiving the pivot pins 342 substantially prevent the threaded nut 340 from rotating relative to the intermediate portion 220, about the axis L of the threaded rod 330.

[0068] With reference to FIGS. 7A to 7C, the linear actuator assembly 300 includes a first thrust bearing 350 and a second thrust bearing 360, the threaded rod 330 being axially confined between the first and second thrust bearings 350, 360. The encasement 223 includes a seat 224 for accommodating the second thrust bearing 360 at a distal end of the housing volume 225, adjacent the distal end 221B of the intermediate portion 220. The first thrust bearing 350 is positioned between the proximal end 331A of the threaded rod 330 and the distal end 309B of the drive mechanism 310, and the second thrust bearing 360 is positioned between the distal end 331B of the threaded rod 330 and the seat 224. Both the first and the second thrust bearings 350, 360 may be ball thrust bearing systems 400, examples of which are illustrated in FIGS. 9A-9C, although other types of thrust bearings may be used in other example arrangements.

[0069] In some examples, the threaded rod 330 may be axially unbound to the draft shaft 224 and may be capable of moving substantially freely (axially) along the drive shaft 330 to a limited extent that may be permitted by the first and second thrust bearings 350, 360. In other words, the first and second thrust bearings 350, 360 may allow the threaded rod 330 to rotate substantially freely, its rotation being determined by drive shaft 324. In some example arrangements, the axial movement of the threaded rod 330 may be constrained only by the thrust bearings 350, 360 at either end of thereof.

[0070] With reference to FIGS. 9-11C, example thrust bearings comprise a first race ring 410, 411 and a second race ring 420, 421, between which ball bearings 432 or roller bearings 433 are held within a cage 430, 431, allowing the first race ring 410, 411 and second race ring 420, 421 to rotate efficiently with respect to one another, with low or negligible frictional energy loss.

[0071] A first race ring 411, 410 of the first thrust bearing 350 may be attached to, or abut, the distal end 309B of the drive mechanism 310 in some example arrangements. An opposing second race ring 421, 420 of the first thrust bearing 350 can rotate substantially freely relative to the first race ring 411, 410. The proximal end 331A of the threaded rod 330 may abut the second race ring 421, 420 of the first thrust bearing 350; the proximal end 331A of the threaded rod 330 may or may not be attached to the second race ring 421, 420 of the first thrust bearing 350.

[0072] The encasement 223 of the intermediate portion 220 includes a seat 224 at the distal end of the housing volume 225, for seating a first race ring 410, 411 of the second thrust bearing 360. An opposing second race ring 420, 421 of the second thrust bearing 360 can rotate substantially freely relative to the first race ring 410, 411 of the second thrust bearing 360. The distal end 331B of the threaded rod 330 may abut the second race ring 420, 421 of the second thrust bearing 360; the distal end 331B of the threaded rod 330 may or may not be attached to the second race ring 420, 421 of the second thrust bearing 360. The threaded rod 330 is thus confined between the rotatable race rings of each of the first and second thrust bearings 350, 360.

[0073] When the threaded rod 330 is driven to rotate about its axis L, the threaded nut 340 is forced to move axially within the limits permitted by the slots 252. The arrangement of the drive mechanism 310, drive shaft 324, threaded rod 330, threaded nut 340 and slots 252 thus converts a torque generated by the drive mechanism 310 into an axial force that drives the threaded nut 340 to move axially, and consequently to exert a force on the end portion 230 at the third connector 260, forcing the end portion 230 to pivot at the second connector 280 relative to the intermediate portion 220.

[0074] With reference to FIGS. 2A, 2B and 3, an example bionic digit 200 may include a pair of support arms 240, one on either side of the central plane, each having a respective proximal end 241A and a distal end 241B. Each support arm 240 connects the drive member 340 with the base portion 210, constraining the distance between the drive member 340 and the base portion 210. A fifth connector 214 pivotally connects a proximal end 241A of the support arm 240 with the base portion 210. In this example, each left and right support arm 240 includes a respective pivot projection 243 at the proximal end 241A, for insertion into an aperture 215 in the base portion 210 and defining a pivot axis P5, for allowing the support element 240 to pivot about the pivot axis P5, relative to the base portion 210. A sixth connector 290 pivotally connects a distal end 241B of the support arm 240 with the drive member 340. In this example, the sixth connector 290 includes an aperture 242 at the distal end of the support arm 240, into which the pivot pin 342 of the threaded nut 340 projects. In FIGS. 2A and 2B, the third connector 260, fourth connector 250 and sixth connector 290 are indicated as being coincident because they share the same pivot pin 342 of the drive member 340, although only the sixth connector 290 is visible in this view.

[0075] The first connector 212 (pivotal about P1) and the fifth connector 214 (pivotal about P5) are spaced apart from each other on the base portion 210, the fifth connector 214 positioned above the first connector 212 on the base portion 210. The support arms 240 and the intermediate portion 220 thus have different pivot axes about the base portion 210, and consequently, the longitudinal axis L of the threaded rod 330 has a different effective pivot axes about the base portion 210 than the support arms 240.

[0076] The support arms 240 limit the distance between the threaded nut 340 and the base portion 210, consequently limiting the arrangement of the bionic digit 200, including the position of the intermediate portion 220 relative to the base portion 210 and the position of the end portion 230 relative to the intermediate portion 220, depending on the position of the threaded nut 340 along the axis L of the threaded rod 330. With reference to FIG. 2A, the bionic digit 200 can be put into a fully extended arrangement, in which the threaded nut 340 is as far towards the distal end 221B of the intermediate portion 220 as is permitted by the slots 252 in the encasement 223. With reference to FIG. 2B, the bionic digit 200 can be put into a fully closed, or curled, arrangement, in which the threaded nut 340 is as far towards the proximal end 221A of the intermediate portion 220 as is permitted by the slots 252. The position of the bionic digit 200 may thus be controlled by the threaded nut 340 being driven to move axially in response to the drive mechanism 310 applying torque to the threaded rod 330 via the drive shaft 324, and as constrained by the support arms 240.

[0077] Reference will now be made to FIGS. 12 to 17 which more clearly illustrate the connection between the drive shaft 324 and the threaded rod 330 and also between the threaded rod 330 and the thrust bearings 350, 360. From these figures it will be appreciated that the drive shaft 324 will have an external surface 324A which, as shown, includes one or more keying surfaces thereon, as discussed in detail above. The keying surface 324A is matched with an equal but opposite keying surface 333A within the recess 333 within the threaded rod 330 such that the keying surfaces engage with one another and rotate together upon actuation of the actuator to cause rotational movement of the drive shaft 324. The threaded rod 330 is free to slide axially along the drive shaft 324 within the limits set by the thrust washers 350, 360 provided at the first and second ends 331A, 331B of the threaded rod 330. As a consequence of the above-described arrangement, any axial shock loading experienced by the drive member 340 due to the finger being impacted by an external load is first transferred to the threaded rod 330 upon which it is located but is not then transferred to the drive shaft 324 as the threaded rod 330 will simply slide axially along the driveshaft 324 itself. The axial movement of the threaded rod 330 will be arrested by one or other of the thrust washers 350, 360 disposed at opposite ends of the threaded rod and secured to the casing itself. These thrust bearings are as shown in FIGS. 9 to 11 and, effectively, arrest axial movement whilst allowing low friction rotation to be maintained.