Hydraulic Pump Assembly for Artifical Hand

Abstract

A hydraulic pump assembly (72) comprises: a low-pressure hydraulic pump (74), a high-pressure hydraulic pump (76), and a drive shaft assembly (78) that passes along an axis of the pump assembly (72); wherein both hydraulic pumps (74, 76) are arranged to be rotated simultaneously by the drive shaft assembly (78); and wherein the pump assembly (72) is formed a single unit arranged to fit into a pump chamber (80).

Claims

1. A hydraulic pump assembly comprising: a low-pressure hydraulic pump, a high-pressure hydraulic pump, and a drive shaft assembly that passes along an axis of the pump assembly; wherein both hydraulic pumps are arranged to be rotated simultaneously by the drive shaft assembly; and wherein the pump assembly is formed as a single unit arranged to fit into a pump chamber.

2. A hydraulic pump assembly as claimed in claim 1, wherein the hydraulic pump assembly is for powering a hydraulic circuit in an artificial hand and the single unit may be arranged to fit into a pump chamber within a palm unit of the artificial hand.

3. A hydraulic pump assembly as claimed in claim 1 or 2, wherein the low-pressure hydraulic pump is capable of operating at pressures from 0 bar up to 10-15 bar and the high-pressure hydraulic pump is capable of operating at pressures from 0-50 bar.

4. A hydraulic pump assembly as claimed in claim 1, 2 or 3, wherein The hydraulic pump assembly includes a seal or a groove for holding a seal at one end of the hydraulic pump assembly.

5. A hydraulic pump assembly as claimed in any preceding claim, having a prismatic shape for fitting into a pump chamber of a corresponding prismatic shape.

6. A hydraulic pump assembly as claimed in any preceding claim, wherein having a cylindrical shape for fitting into a pump chamber of a corresponding cylindrical shape.

7. A hydraulic pump assembly as claimed in any preceding claim, comprising a hydraulic axle seal between the two hydraulic pumps for the drive shaft assembly, and no seals between pump plates of the hydraulic pumps.

8. A hydraulic pump assembly as claimed in any preceding claim, wherein the drive shaft assembly is arranged for connection to a single motor for rotation of the drive shaft assembly.

9. A hydraulic pump assembly as claimed in any preceding claim, wherein the drive shaft assembly includes a shaft that passes through one of the pumps in order to reach the other pump.

10. A hydraulic pump assembly as claimed in claim 9, comprising one pump at one end of the axis of the pump assembly and the other pump at an opposite end of the axis with the shaft passing parallel to the axis, for example along the centre of a cylindrically shaped pump assembly.

11. A hydraulic pump assembly as claimed in claim 9 or 10, wherein the shaft is split in two, having a low-pressure section and high-pressure section driving the respective hydraulic pump, with axial play between the two sections.

12. A hydraulic pump assembly as claimed in any preceding claim, wherein the hydraulic pumps of the pump assembly are gear pumps.

13. A hydraulic pump assembly as claimed in any preceding claim, wherein the pump assembly is assembled from a number of pump plates assembled together and held with bolts extending through the length of the pump assembly.

14. A hydraulic pump assembly as claimed in any preceding claim, wherein the pump assembly has been initially manufactured oversized and then machined down to size to fit within a pump chamber of known or nominal size.

15. A palm unit for an artificial hand including a hydraulic pump assembly as claimed in any preceding claim.

16. A palm unit as claimed in claim 15 comprising a palm unit body forming a sealed enclosure for a hydraulic circuit and the hydraulic pump assembly, thereby containing all hydraulic parts.

17. A palm unit as claimed in claim 15 or 16, comprising a variable speed and/or reversible motor for powering the hydraulic pump assembly.

18. A palm unit as claimed in claim 15, 16 or 17 comprising: a palm unit body; a motor held by the palm unit body; the hydraulic pump assembly held by the palm unit body, wherein both hydraulic pumps are powered simultaneously by the motor; and a hydraulic circuit held by the palm unit body and coupled to both hydraulic pumps, wherein the hydraulic circuit has a low-pressure configuration in which the discharge sides of both hydraulic pumps are coupled to one or more hydraulic actuator(s) for the artificial hand and a high-pressure configuration in which the discharge side of the low-pressure pump is isolated from the hydraulic actuator(s) and recirculates fluid to the suction side of the low pressure pump with the discharge side of the high-pressure pump remaining coupled to the hydraulic actuator(s), and wherein the hydraulic circuit is arranged to switch from the low-pressure configuration to the high-pressure configuration automatically during a closing grip pattern when the pressure in the system increases beyond a threshold value.

19. An artificial hand including a palm unit as claimed in any of claims 15 to 18 along with artificial fingers and a thumb.

20. An artificial hand as claimed in claim 19, wherein the fingers and thumb to have mechanical joints arranged to be actuated by hydraulic actuators within the palm unit, but not including any hydraulic elements themselves.

21. An artificial hand or a palm unit as claimed in any of claims 15 to 20 combined with a digit mechanism.

22. An artificial hand or a palm unit as claimed in claim 21, wherein the digit mechanism comprises: a lower digit arranged to be rotatably coupled to a palm unit of the artificial hand; an upper digit rotatably coupled to the lower digit; a lower digit rotation mechanism for applying a moment to the lower digit to rotate the lower digit relative to the palm unit; an upper digit rotation mechanism for applying a moment to the upper digit to rotate the upper digit relative to the lower digit; and a force balancing mechanism for mechanically adjusting the magnitude of the moment applied by the lower digit rotation mechanism and/or the upper digit rotation mechanism in accordance with the magnitude(s) of outside forces resisting rotation of the upper digit and/or the lower digit in order to preferentially apply movement to the digit experiencing lower resistance to movement; wherein the lower digit rotation mechanism and upper digit rotation mechanism are arranged to be mechanically actuated, in use, by a force applied from a single actuator at the palm unit.

23. A method of manufacture of a pump assembly, the method comprising: assembling pump plates with other components to form a low-pressure hydraulic pump, a high-pressure hydraulic pump, and a drive shaft assembly that passes along an axis of the pump assembly; wherein both hydraulic pumps are arranged to be rotated simultaneously by the drive shaft assembly; and machining the assembled pump plates to size to thereby form the pump assembly as a single unit arranged to fit into a pump chamber.

24. A method as claimed in claim 23, including securing the pump plates with bolts extending through the length of the pump assembly.

25. A method as claimed in claim 23 or 24 comprising providing the pump assembly with features as claimed in any of claims 1 to 14.

26. A pump assembly or a method of manufacturing a pump assembly substantially as hereinbefore described with reference to the accompanying drawings.

Description

[0051] Certain preferred embodiments of the invention will now be described by way of example only and with reference to the accompanying drawings in which:

[0052] FIG. 1 shows a design for a prosthetic hand in perspective view with the cosmetic glove removed and one finger shown partially transparent so that internal detail can be seen;

[0053] FIG. 2 is a partial cutaway view of the prosthetic hand of FIG. 1 showing a cross-section through the hydraulic cylinders for the middle finger and for the thumb;

[0054] FIG. 3 shows a finger mechanism in more detail illustrating a clutch system for producing adaptive movement with the finger joints;

[0055] FIG. 4 is a schematic diagram showing the basic principles of operation of the clutch system;

[0056] FIG. 5 is a perspective view of the palm unit with the outer housing shown transparent so that internal detail of the motor and hydraulic pumps can be seen;

[0057] FIG. 6 is a partial cross-section through the palm unit showing the high and low pressure hydraulic pump and equaliser adjacent to the hydraulic cylinder for the thumb;

[0058] FIG. 7 shows a similar cross-section to FIG. 6, from a different angle, with the hydraulic pump assembly removed so that the hydraulic pump pressure and suction channels can be seen;

[0059] FIG. 8 is a perspective view of a hydraulic subassembly of the palm unit with the finger joints at the upper part and the thumb joint at the lower part and also showing the location of an emergency hydraulic valve;

[0060] FIG. 9 shows the emergency valve in more detail with the outer part of the hydraulic subassembly shown transparent for clarity;

[0061] FIG. 10 is a hydraulic schematic;

[0062] FIGS. 11 and 12 show a cross-section and perspective view of a hydraulic cylinder for the index and middle fingers;

[0063] FIGS. 13 and 14 shows similar views for a hydraulic cylinder for the thumb;

[0064] FIGS. 15 and 16 show the emergency valve in cross-section and perspective view;

[0065] FIGS. 17 and 18 show more detail of an equaliser that is seen in situ in FIG. 5 and FIG. 6;

[0066] FIGS. 19 and 20 show a cross-section and perspective view for the high and low pressure hydraulic pumps, which again are already seen in situ in FIG. 5 and FIG. 6;

[0067] FIGS. 21 and 22 show a cross-section and perspective view for a pressure controlled valve that redirect the oil flow to switch from low-pressure to high pressure operation;

[0068] FIGS. 23 and 24 are a cross-section and perspective view of a design for an electromagnet controlled valve used within the hydraulic circuit;

[0069] FIG. 25 shows a 3-D printed body section for the hydraulic subassembly shown in FIG. 8; and

[0070] FIG. 26 shows a cutaway view of the body section illustrating some of the hydraulic connections.

[0071] By way of a preferred embodiment the drawings show a prosthetic hand and various features of the mechanisms used to produce finger and thumb movements for this prosthetic hand. It will however be appreciated that the same mechanisms could equally well be used in artificial hands for other purposes, for example for remote handling or in robotic applications. In addition, it will be noted that whilst there are particular advantages to the various features of the hand when taken in combination as shown in the Figures, there are also advantages that would arise when the different features of the hand are taken alone, for example the arrangement of the finger joint as described herein would provide advantages when used with alternative driving mechanisms and not just the hydraulic driving mechanism with the particular arrangement of the current palm unit, and similarly the palm unit and/or hydraulic circuit described herein would provide advantages when used with an alternative arrangement for the finger and thumb mechanisms.

[0072] Considering the Figures in more detail, FIG. 1 shows a perspective view for a prosthetic hand including a palm unit 12, a thumb mechanism 14, an index finger mechanism 16, a middle finger mechanism 18 and a combined ring finger/little finger mechanism 20. FIG. 2 shows a partial cutaway view with a slice taken along the line of the thumb 14 and between the index finger 16 and middle finger 18.

[0073] In this example the hand is provided with a standard quick connect Otto Bock design wrist joint 22 that allows for coupling with batteries and one or two electromyocardiographic (EMG) sensors, which would typically be mounted inside the user's underarm. It would of course be possible to adapt the hand to use an alternative wrist connection system if required. Advantageously, the coupling for the wrist joint 22 is 3-D printed. The use of a standard quick connect system 22 makes it possible for an existing electric hand prosthetic user to try this hand very easily.

[0074] The index finger mechanism 16 and the middle finger mechanism 18 are very similar and differ generally only in relation to the size of the fingers. The thumb mechanism 14 is similar to the finger mechanisms 16, 18 with the addition of a pulley/guide 24 directing the main cable 34 about an angle to allow for the thumb 14 to open at 90 to the fingers 16, 18, 20, and of course with some changes in size and dimensions so as to accurately mimic typical dimensions for a thumb. The ring finger/little finger mechanism 20 is resiliently coupled to and effectively slaved with the mechanism for the first digit of the middle finger mechanism 18. In this example a coiled spring is used, and this is advantageously fitted with a bushing allowing for a sprung movement of the little and ring fingers whilst opening, within limits, and a free movement (resisted by the spring, but without any restriction on the extent of movement) in the closing direction.

[0075] Microprocessor control electronics and software are provided to interpret the signals from the user's EMG sensors. These electronics are mounted behind the quick connect 22 inside the palm unit 12, i.e. within the right hand side of the palm unit 12 when viewed in the orientation of FIG. 2. It is important to understand that this hand design can operate with just a single sensor input if necessary, and based solely on the strength of this signal it is possible to achieve a very adaptable grip controlled by the user, as explained in more detail below. The use of a second EMG sensor is preferred since it allows for a more intuitive action of the user in releasing the grip of the device: one sensor can be used to control closing of the hand, and the other sensor will control opening of the hand. However, if necessary a single sensor can be used along with a prearranged signal for switching from closing to opening of the hand, for example a double click type movement. Further detail of the construction and operation of the thumb and finger mechanisms 14, 16, 18 will be discussed below with reference to FIG. 3 and FIG. 4 and the relevant reference numerals are not shown in FIG. 1 and FIG. 2 for the sake of clarity. In FIGS. 1 and 2 further detail of the basic parts of the palm unit 12 can be seen including the belt 28 that couples the motor 68 to the hydraulic pumps (shown in further detail in FIG. 5 and FIG. 6 amongst others); finger return springs 30, which are connected at the base of the finger joints and urge the hand toward an open configuration; finger piston couplings 32, which join the finger main cables 34 to the finger hydraulic cylinders 36; the finger hydraulic cylinder 36 for the middle finger mechanism 18 (in cross-section in FIG. 2); the thumb hydraulic cylinder 38 (again in cross-section in FIG. 2) and thumb piston coupling 40; and the thumb return spring 42. The operation and interaction of these various features will be obtained from the discussion below and from the drawings.

[0076] Turning now to FIGS. 3 and 4, which show a finger mechanism in greater detail, it should first be noted that the same basic functional parts are used for both the index finger mechanism 16 and middle finger mechanism 18, as well as also for the thumb mechanism 14, with appropriate adjustments to achieve the required difference in size for the different fingers and the thumb. Thus, in the discussion below references to the fingers and finger joints can be taken to apply equally well to the thumb and thumb joints.

[0077] In this explanation the upper digit is the digit of the finger or thumb at the distal end, i.e. closest to the fingertip, and the lower digit is the digit of the finger or thumb at the proximal end, i.e. closest to the palm, and the terms upper and lower are used in the same way to refer to other parts of the mechanism. This example uses two digits for each of the index finger and middle finger mechanisms 16, 18 and for the thumb mechanism 14. It would be possible to expand to have three digits by repeating the mechanism described below for a third joint of the finger and to thereby obtain an even more natural finger movement. However, this is considered to add additional complexity without any significant benefit in relation to usability and the grip patterns that can be achieved.

[0078] FIG. 3 shows detail of a finger joint with the outer housing shown transparent so that the internal mechanism can be understood. FIG. 4 shows a part of the mechanism in schematic form, with equivalent parts given the same reference numbers.

[0079] A lower digit 44 is connected to the palm unit 12 (not shown in these Figures) via a pivot along a lower axis of rotation 46. The finger return spring 30 is positioned so as to urge the lower digit 44 back towards the open position, rotating it around the lower axis of rotation 46. At the distal end of the lower digit 44 and upper digit 48 is connected and can rotate relative to the lower digit 44 via a pivot along an upper axis of rotation 50. The finger main cable 34 is attached to a lower pulley 52 placed on the lower axis of rotation 46 and tension on the finger main cable 34 will rotate the lower pulley 52 in order to rotate the finger towards a closed position, with an adaptive grip as discussed below. In the view in FIGS. 3 and 4 shown this rotation would be in an anticlockwise direction.

[0080] It is important to allow for rotation of both the upper digit 48 and the lower digit 44, and advantageously this is done in such a way so as to provide an adaptive grip that can react to pressure on either one of the digits 44, 48. This is in contrast to various prior art arrangements that have a fixed mechanical relationship between the various digits in finger joint, requiring that the upper digit rotate in proportion to rotation of the lower digit. With the current design when the finger main cable 34 is pulled by the actuating mechanism (the piston connector of the finger hydraulic cylinder in this example) then this rotates the lower pulley 52 which applies tension to a secondary cable 54 that is connected to an upper pulley 56. The upper pulley 56 is mounted on the upper axis of rotation 50 and arranged such that rotation of the upper pulley will rotate the upper digit 48, pulling it toward the closed position (again, an anticlockwise rotation in the orientation shown in the Figures).

[0081] In order to achieve the required adaptive grip the current joint design uses a brake/clutch arrangement 58 to transfer rotational forces from the lower pulley 52 to the lower joint 44 in accordance with the tension in the secondary cable 54. The brake/clutch arrangement 58 allows for a degree of slipping in the system, so that either one digit can rotate whilst the other digit has stopped moving. The strength of the forces applied via brake/clutch arrangement 58 varies dependent on the balance of forces on the digits. Thus, in situations where there is less resistance to the closing motion of the upper digit 48 then there will be a reduced force closing the lower digit 44, whereas when there is increased resistance to the closing motion of the upper digit 48 then there will be an increased force closing the lower digit 44. The brake/clutch arrangement 52 and the various pulleys are arranged so that if there is no resistance to closing motion of the upper digit 48 or lower digit 44 then both digits will pull close with a similar degree of rotational motion resulting in a pincer grip pattern. However, when any one digit meets with resistance, i.e. when it contacts an object that is to be gripped, then its movement is stopped and forces are transferred preferentially to the other digit of that finger joint, which will continue to move until it meets with a similar resistance. When all of the digits are in contact with an object then the pressure will increase and therefore the strength of grip will also increase. The mechanism hence balances torques between the upper digit 48 and lower digit 44 ensuring that each finger mechanism 16, 18 (and likewise the thumb mechanism 14) provides an intuitive adaptive grip with a great flexibility in the grip pattern that can be achieved, whilst only requiring a single actuator input in the form of tension on the main cable 34.

[0082] In this example the brake/clutch arrangement 58 is a band brake. It will, however, be apparent that this band brake could be replaced by alternative designs for a brake/clutch arrangement 58, such as a system using clutch plates. The brake/clutch arrangement 58 is coupled to a torque balancing mechanism 60 that arranged so that as the tension in the secondary cable 54 increases then the brake/clutch arrangement 58 transfers increased forces between the lower pulley 52 and the lower digit 44. In this example the torque balancing mechanism 60 comprises a lever arm 62 attached to a pivot 64 that is fixed relative to the lower axis of rotation 46 and fixed relative to the main body of the lower digit 44. This is shown schematically in FIG. 4. The end of the lever arm 62 presses against the secondary cable 54, with the secondary cable 54 going through a change in direction around a guide surface at the end of the lever arm 62, such that tension in the secondary cable 54 will generate a force pushing the end of the lever arm 62.

[0083] When the lower pulley 52 is pulled by the main cable 34 (not shown in FIG. 4) and rotates in the anticlockwise direction then tension is applied along the secondary cable 54 and the upper pulley 56 also tends to rotate in an anticlockwise direction. As noted above, with no resistance to motion then the brake/clutch arrangement 58 is set so that both the lower digit 44 and the upper digit 48 both rotate to form a pincer grip pattern. If there is resistance to motion of the upper digit 48, for example through a contact force applied with the direction A at the fingertip, then the tension in the secondary cable 54 would increase. As will be understood from FIG. 4 this increased tension will have the effect of pushing the end of the lever arm 62 with a greater force in the direction B, hence applying a moment to the lever arm 62 around its pivot 64.

[0084] FIG. 3 shows further detail of the connections between the lever arm 62 and the brake/clutch arrangement 58, i.e. the band brake in this example. Movement of the lever arm 62 increases forces on the band brake thereby increasing transfer of forces between the lower pulley 52 and the lower digit 44, creating a tendency for the lower digit 44 to be closed in preference to closing of the upper digit 48. If there were also resistance to movement of the lower digit 44 then increasing resistance of this type would result eventually in balancing of the forces as pressure increased via the main cable 34, so that both digits will apply pressure to increase the strength of the grip when there is full contact of both digits with an object. If there is resistance to motion of the lower digit 44 with less resistance to motion of the upper digit 48 then the lower digit 44 will cease to rotate and the upper digit 48 will continue to rotate, with a high degree of slipping of the brake/clutch arrangement 58 which at this point would be transferring relatively low forces between the lower pulley 52 and the lower digit 44. The mechanism described above therefore provides the required intuitive and adaptive movement of each of the finger and thumb mechanisms 14, 16, 18.

[0085] Further adaptability of the grip pattern provided by the hand comes from the fact that the two finger hydraulic cylinders 36 and the thumb hydraulic cylinder 38 are coupled together with equal pressure, as can be seen in the cross-section drawing in FIG. 2 and the hydraulic schematic of FIG. 10, for example. As a result then as well as a resistance on individual digits affecting the pattern with which an individual finger or thumb mechanism closes, then varying resistance between the different finger and thumb mechanisms 14, 16, 18, 20 will result in the hand closing in a natural fashion around a gripped object of any shape. The first finger or thumb to meet the object (with all digits) will cease moving and the hydraulic interconnection means that fluid will continue, without an increase in hydraulic pressure, to move the digits of the other finger(s) and/or the thumb until all digits of all the finger and thumb mechanisms are meeting similar resistance, at which point the hydraulic pressure will increase and the strength of grip of the whole hand increases.

[0086] As mentioned above, movement of the fingers is controlled via one or two EMG sensors controlling a variable speed motor that drives the hydraulic pumps of the system. The hydraulic circuit and its interaction with the variable speed motor are explained in more detail below. In relation to the grip from each finger, what is important is that the user can choose when to close the hand and when to open the hand, and the digits in each finger will grip adaptively as explained above. Therefore, the user is able to stop movement in order to acquire the desired grip, and the user can also place the hand against an object or use their other hand in order to resist movement of the fingers/thumb and therefore close the hand with the fingers and thumb in a required pattern. Unlike many of the prior art systems there is no requirement for a complicated code system requiring a sequence of clicks of an EMG sensor in order to place the hand into a required grip pattern. Instead, it will adaptively grip to any object that is presented to it, and also by means of selectively resisting motion of digits as required the user can place the hand into any pattern that they require.

[0087] The speed and direction of movement of the fingers and thumb is controlled by the speed and direction of the electric motor. The pressure applied is controlled by two hydraulic pumps as discussed below, with a hydraulic circuit that switches automatically between a low pressure high-volume configuration and a high-pressure low-volume configuration. The control of the fingers by the speed and direction of the electric motor is different to normal hydraulics where the electric motor runs at a continuous speed in a single direction and multiple valves are used to control the speed and direction of the flow of hydraulic fluid. Controlling both speed and direction of the hydraulic actuators with the electric motor minimises the number of valves required. This makes the hydraulic system much simpler and results in the hydraulic circuit operating in a considerably different way to normal hydraulics. This type of system is only feasible in hydraulic systems with relatively low pressures and small fluid volumes, which works well for an artificial hand, but would not be applicable in all other fields where hydraulics are used.

[0088] Since the fingers and thumb are robustly actuated via hydraulics and are spring return then they can be pushed away from their natural position without risk of damaging the mechanism. In particular, the fingers are able to absorb knocks and other intended or inadvertent impacts by moving against the hydraulics and the springs without risk of damage to the mechanism of the hand. This is a significant advantage compared to some prior art products that use lead screws, worm gears, and so on, which are very fragile and vulnerable to damage when the fingers or thumb are knocked.

[0089] To provide the required strength and lightness whilst also achieving the complex shapes necessary then 3-D printing is used in manufacturing the device. The outer bodies for the upper and lower digits of the fingers and thumb mechanisms 14, 16, 18 are 3-D printed in titanium, as is the structural end plate 66 of the palm unit 12. The main body for the palm unit 12, which is described in more detail below, is in this example 3-D printed in plastics, but could be re-engineered to be printed in aluminium or titanium with adjustments to the design for maximum weight saving (for example, by including additional voids such as in a honeycomb type construction). The various cables are made of steel in this example.

[0090] As well as providing advantages resulting from the arrangement of the finger and thumb mechanisms 14, 16, 18 as described above, the artificial hand of FIG. 1 also has important and advantageous features in relation to the arrangement of the palm unit 12 and the internal parts thereof. FIGS. 5 to 9 illustrate additional details of these parts, which are also described below. FIG. 10 is hydraulic schematic for the palm unit 12 illustrating the arrangement of the high and low pressure hydraulic pumps and the simplicity of the hydraulic circuit (especially as compared to prior art systems which are fully hydraulic such as the Fluidhand design). FIGS. 11 to 26 show various components of the system in greater detail.

[0091] It will be seen from the FIG. 5 that all the hydraulic elements as well as an electric motor 68 are fully contained within the palm unit 12, and they are housed in a palm unit body 70, the details of which can be seen in several of the Figures. The palm unit body 70 is shown without any other parts in FIG. 25, and without any other parts and with a cutaway section in FIG. 26. As noted above, the palm unit body 70 is 3-D printed out of plastics. In FIG. 5 the structural end plate 66 of the palm unit is removed so that the various connections can be seen in more detail, and the main body 70 is shown transparent for the same reason.

[0092] The electric motor 68 has an axis running lengthways along the palm unit 12 (from the wrist end toward the finger end) and this axis is parallel to the axis of a shaft that powers the hydraulic pump assembly 72. The electric motor 68 is coupled to the shaft of the hydraulic pump assembly 72 via a belt 28 that is located outside of the main body 70 of the palm unit 12 allowing better access for assembly and for maintenance. The electric motor 68 and the hydraulic pump assembly 72 are placed on the side of the hand opposite to the thumb. Finger piston couplings 32 and the thumb piston coupling 40 extend from the end of the palm unit body 70 from their respective hydraulic cylinders 36, 38 which extend back into the palm unit body 17 and are also parallel with the axis of the motor along the length of the palm unit 12. Also visible in FIG. 5 are the ends of two electromagnet controlled valves 90, and these are described in further detail below with reference to FIG. 10 as well as FIGS. 23 and 24.

[0093] Details of the palm unit can be seen in cross-section in FIG. 6 and FIG. 7, particular for the hydraulic pump assembly 72 and also, in part, hydraulic connection passages and the thumb hydraulic cylinder 38. The hydraulic pump assembly 72 includes both a low-pressure, high-volume, hydraulic pump 74 and a high-pressure, low-volume, hydraulic pump 76, which receive power from the same shaft 78, turned by the motor 68. The interaction of the two hydraulic pumps 74, 76 with the hydraulic circuit will be explained below in connection with FIG. 10. The shaft 78 passes through the high-pressure hydraulic pump 76 to the low-pressure hydraulic pump 74 and operates both hydraulic pumps 74, 76 simultaneously. The hydraulic pumps 74, 76 are functionally separate, but they are formed as a single assembly with a common shaft for ease of manufacture and assembly. This also saves weight and space as well as allowing the two hydraulic pumps 74, 76 to be mounted within a single chamber 80 within the palm unit body 70. Beyond the low pressure hydraulic pump 74, and in the same chamber 80 of the palm unit body 70 an equaliser 92 is installed. FIGS. 17 and 18 provide a close-up view of the equaliser 92. The equaliser 92 operates via spring and generates a positive oil pressure on the suction side of the low and high pressure hydraulic pumps 74, 76. The equaliser 92 acts to prevent cavitation in the hydraulic pumps 74, 76. The equaliser also moves to adjust the available volume of the chamber 80 to compensate for movement of the cylinder rods for the finger and thumb hydraulic cylinders 36, 38, which would otherwise result in changes in the volume of the system.

[0094] Referring again to FIGS. 25 and 26 it will be seen that as well as the hydraulic pump and equaliser chamber 80 the palm unit body 70 also includes three hydraulic chambers 36, 38 to form the hydraulic cylinders 36, 38 for the thumb and two finger mechanisms, two valve openings 82 for receiving the electromagnet controlled valves 90, a valve opening 84 for receiving a pressure controlled valve 86 (not visible in FIG. 5, discussed in more detail below with reference to FIGS. 21 and 22) and a motor chamber 88 for holding the motor 68. The partially cutaway view in FIG. 26 shows an example of how the hydraulic circuit is formed as an integral part of the palm unit body 70. All the required interconnections between the various hydraulic chambers are formed as passages between chambers in a single unit. The use of 3-D printing for the palm unit body 70 enables this complicated shape to be formed without undue expense. Since all significant forces on the palm unit body are axial than a relatively soft plastics material can be used, with relatively thin sections between the various axial components. The pressure of the hydraulic fluid within the cylinders creates radial forces, but these forces act generally symmetrically and the circular shapes used are effecting in containing these pressures even with relatively weak plastic materials. Although these thin sections would otherwise be vulnerable to flexing as there are no radial forces then this is not a particular risk for the system. This arrangement also provides the advantage that all of the hydraulic circuit is contained within a single housing 70 and can therefore easily be kept fully sealed. The proposed palm unit 12 hence presents minimal risk of hydraulic leakage with increased robustness compared to prior art designs using hydraulic actuation for artificial hands.

[0095] Both of the suction and pressure sides of the two hydraulic pumps 74, 76 are within the palm unit and connect to various channels through the palm unit body 70 that form the hydraulic circuit of FIG. 10. Oil (or another working fluid) is thus transported from the hydraulic pumps 74, 76 to the valves without passing outside of the palm unit body 70. The suction and pressure sides of the hydraulic pumps 74, 76 are separated from the outside world and all of the hydraulics using O-ring seals. As the hydraulic pumps 74, 76 are isolated from the outside world in this way then there is no need for any hydraulic seals between the hydraulic pump plates. This is because any leakage will only be internal and can to some extent be disregarded. Avoiding the use of hydraulic pump plate seals save space and enables easier faster and cheaper manufacture of the hydraulic pump assembly 72.

[0096] The other hydraulic parts can similarly easily be isolated from the outside world by O-rings or similar seals. This makes the whole hydraulic system very robust and easy to assemble and maintain. Since the hydraulic cylinders 36, 38 are also formed as a part of the palm unit body 70 then they do not move or rotate with the moving parts and consequently they can receive hydraulic fluid from fixed channels within the palm unit body 70. Each hydraulic part can be individually removed and replaced for maintenance or repair work. There is also an easily isolated hydraulic subassembly formed by the palm unit body 70 enclosing the various hydraulic parts and optionally including the structural end plate 66. An orthopaedic workshop could choose to do maintenance in-house, or they could choose to remove the fingers and wrist connector along with the motor and send the hydraulic subassembly back to the manufacturer for maintenance or repairs. The hydraulic subassembly is shown in FIG. 8. As well as the various parts that have already been introduced the hydraulic subassembly also includes an emergency release valve 94, which can be seen in further detail in FIG. 9 and is shown in isolation in FIG. 15 and FIG. 16.

[0097] The emergency valve 94 is a mechanical user controlled valve that can be opened in case of any mechanical, hydraulic or electronic failure in order to release the hydraulic pressure in the system. The valve bypasses the electrically controlled valves 80 and connects the pressure sides of the thumb and fingers cylinders 36, 38 directly to the equaliser 92. Since there is a spring return then the hand will automatically move to open configuration when the emergency valve is pushed, but no hydraulic fluid is released from the system. FIGS. 15 and 16 show the emergency valve in more detail. Mounting and sealing rings 100 are fixed in place within the palm unit body 70 and the main shaft of the valve can be slid relative to these rings 100 in order to release the pressure from the system if required by the user.

[0098] FIG. 10 shows the hydraulic schematic for the system. The basic connections will have been apparent from the discussion above. The motor 68 powers the high-volume low-pressure hydraulic pump 74 and the low-volume high-pressure hydraulic pump 76. The hydraulic pumps 74, 76 provide hydraulic fluid to the index and middle finger cylinders 36 and the thumb cylinder 38. The index and middle finger cylinders 36 have pistons 96 and piston connectors 32, which are coupled to the main cables 34 for the finger joints as shown in the preceding Figures. The thumb cylinder 38 has a piston 98 and piston connector 40, which is coupled to the main cable 34 for the thumb joint, again as shown in the preceding Figures. FIGS. 11 through 14 show close-up views in cross-section and perspective for the pistons 96, 98 and piston connectors 32, 40. It will be noted that the diameter of the thumb piston 98 (and cylinder 38) is slightly larger than the diameter of the index and middle finger piston 96 (and cylinders 36). This is in order to balance the forces between the thumb and two fingers when the tips of the fingers and thumb close into a pincer grip. The cylinders are spring return so that when the hydraulic pressure is released, i.e. when there is no differential in hydraulic pressure between the two sides of the cylinder across the piston, then the system will return to an at rest configuration when the hand is open. The equaliser 92 is connected to the suction side of the hydraulic pumps 74, 76 and has the function explained above.

[0099] The arrangement of the hydraulic pump assembly 72 is shown in greater detail in FIG. 19 and FIG. 20. In this example the high-pressure hydraulic pump 76 is a gear pump using straight gears whereas the low pressure hydraulic pump 74 is a gear pump using helical gears. Helical gears dampen the sound from the hydraulic pump, which might otherwise be a problem for the low-pressure hydraulic pump 74. The high-pressure hydraulic pump 76 is assembled first, then the axle of the low-pressure hydraulic pump 74 is connected and the low-pressure hydraulic pump is assembled. The axle of the low-pressure hydraulic pump fits to the axle of the high-pressure hydraulic pump with axial play forming a single shaft 78 that powers both hydraulic pumps. The axial play is provided in order to keep the gears on each part of the hydraulic pumps' shaft axially independent of each other, ensuring that there is no interaction of the high and lower pressure parts of the hydraulic pump assembly during use.

[0100] All of the hydraulic pump plates are manufactured oversize, for example 1 mm in excess of the final size. The hydraulic pump plates are joined together by axial bolts 102 in order to form the hydraulic pump assembly 72. The hydraulic pump bolts 102 are tightened whilst the gears and shaft are being turned in order to allow for minimal tolerances between the gears and plates of the hydraulic pump and ensure that there is minimal play between gears and plates to thereby minimise the internal leakage. This allows for very little leakage despite the fact that hydraulic pump seals have been dispensed with as noted above. Once assembly is complete then the hydraulic pump assembly 72 is machined to the required final size and fitted with the required O-ring seals. This production method ensures that the hydraulic pump assembly 72 will always be the correct size for its chamber 80 in the hand palm and provides a cheap and quick way to produce the hydraulic pumps whilst guaranteeing high quality seals between the hydraulic pump and the outside world.

[0101] FIGS. 21 and 22 show the pressure controlled valve 86 that is used to switch between high and low pressure operation as described below. Typically the switching pressure would be set at between 10 to 15 bar, and this can be adjusted by a screw 104. When the preset pressure is reached then the valve switches position and flow of hydraulic fluid from the low-pressure hydraulic pump 74 is redirected as explained below.

[0102] The other two valves of the system are electromagnet controlled valves 90 as shown in FIGS. 23 and 24. They operate as one-way valves and can be held in the open position via an electromagnet. One electromagnet controlled valve 90 is connected between the hydraulic pumps 74, 76 and the actuation cylinders 36, 38 for the fingers and the thumb and has the function of preventing hydraulic fluid from flowing out of the finger and thumb cylinders 36, 38 when the fingers are in the desired position. This valve hence acts as a finger locking valve 90 and makes sure that the motor 68 can be stopped without the risk of movement of the fingers away from the required position. Using a one-way hydraulic valve in this way saves battery life and means that there is no noise from the hand when the required finger position or grip of an object has been achieved.

[0103] The second electromagnet controlled valve 90 acts to close the channel between the high and low pressure hydraulic pumps 74, 76 when the system pressure increases over a set threshold and the pressure controlled valve 86 is opened. This valve 90 hence acts as a pressure retaining valve 90. Considering FIG. 10, it will be understood that during low-pressure operation both hydraulic pumps are connected to the cylinders 36, 38 and thus the high-volume low-pressure hydraulic pump 74 dominates leading to a fast movement of the pistons 96, 98 until there is resistance, for example as the fingers and thumb begin to grip an object. As described above the interconnection of the hydraulic cylinders and the design of the fingers to provide an adaptive grip means that the digits and fingers will move adaptively until there is resistance to motion of each part. When there is resistance to the movement of each part then the pressure in the system will begin to increase, increasing the grip strength from the hand. As the threshold value is reached then the pressure controlled valve 86 opens and the second electromagnet controlled valve 90 will close. At this time the high-pressure hydraulic pump 76 takes over and the system pressure can increase above the threshold, for example up to 50 bar, to further increase the grip strength. This combination of low and high pressure operation allows for an initial fast movement of the fingers with a low grip strength followed by the possibility of increasing the grip strength of the fingers to a significant degree using the high-pressure hydraulic pump 76. Whilst the pressure controlled valve 86 is opened the low-pressure hydraulic pump 74 continues to operate and simply re-circulates hydraulic fluid through the pressure controlled valve 86 back to the suction side of the low-pressure hydraulic pump 74.

[0104] This recirculation of hydraulic fluid from the low-pressure hydraulic pump 74 can easily be understood with reference again to FIG. 10. If the pressure controlled valve 86 is open and the lower electromagnet controlled valve 90 is closed then the low-pressure hydraulic pump 74 will recirculate fluid, without any pressure building up, around the lower loop of the system as shown in the Figure. When this is occurring then the high-pressure hydraulic pump 76 will be supplying low-volume high-pressure hydraulic fluid to the cylinders 38, 36 thereby allowing the increased strength of grip.

[0105] Also as seen in FIG. 10 the emergency valve 94 sits between the suction side of the hydraulic pumps 74, 76 and the cylinders 36, 38, and thus enables discharge of pressure from the cylinders in the event of any hydraulic or electrical failure, or other system failure.

[0106] As noted above, the motor 68 can be driven with varying speed in accordance with signals from the EMG sensor(s). In order to open the fingers the motor 68 is reversed. Thus, the user can easily control the speed of movement of the fingers both when opening and when closing the hand. Opening of the fingers will also occur naturally via the springs in the cylinders 36, 38 and the return springs 30, 70 mounted between the fingers and the palm unit 12. Since the fingers are locked in place by actuation of the electromagnetic valve 90 that forms the finger locking valve 90 then it is also necessary to have a small microprocessor routine to unlock the fingers and thereafter keep the finger locking valve 90 open so that the fingers can be opened (with the opening movement being controlled by the user as explained above). First the high-pressure hydraulic pump is operated forward in order to push the finger locking valve 90 open, and this valve can then be kept open by the electromagnet. The hydraulic pumps are stopped and then pressurised again at a lower pressure in order to allow the second electromagnet controlled valve 90, which is acting as a pressure retaining valve when in high-pressure operation, to be opened and again this is held open by the electromagnet. With both of the electromagnet controlled valves 90 being open then the hydraulic pumps can now be controlled with the motor running in reverse in order to open the hand. The unlocking action can be performed in a fraction of a second and is controlled by the microprocessor in response to a signal from the EMG sensor indicating that the user is trying to open the hand. Essentially, this process can be invisible to the user.