Apparatus for actuating a mechanical digit

Abstract

An apparatus (100) for actuating a mechanical digit is provided. The apparatus comprises an actuator (1) comprising an actuator output. The apparatus further comprises an output element (7), a first drive element (3) mechanically coupled to the actuator output, and a second drive element (2) mechanically coupled to the actuator output. A high speed driven element (5) is mechanically engaged with the first drive element, such that the motion of high speed driven element (5) is proportional to the motion of the first drive element. A low speed driven element (4) is mechanically engaged with the second drive element, such that the motion of said low speed driven element is proportional to the motion of the second drive element. A driven element selector (6) selectively engages the high speed driven element to the output element and disengages the low speed driven element from the output element, or engages the low speed driven element to the output element and disengages the high speed driven element from the output element. A controller (510) controls the driven element selector.

Description

[0001] APPARATUS FOR ACTUATING A MECHANICAL DIGIT

[0002] TECHNICAL FIELD

[0003] The present disclosure relates to apparatus for actuating a mechanical digit and methods for actuating a mechanical digit. In particular, but not exclusively, it relates to an apparatus for actuating a mechanical digit which forms part of a mechanical gripping apparatus, for example a mechanical or prosthetic hand, to allow such a mechanical or prosthetic hand to grip objects.

[0004] Aspects of the invention relate to apparatus for actuating a mechanical digit and a method of actuating a mechanical digit.

[0005] BACKGROUND

[0006] The ability for a prosthetic hand, for example in the form of a mechanical hand, to handle or grip objects is limited by the operation of mechanical digits on the mechanical hand. For example, a mechanical hand may comprise a plurality of mechanical digits operating as fingers and a mechanical digit operating as a thumb, such that the mechanical finger digits may flex and extend, and the mechanical thumb digit may flex and extend and also take opposed and unopposed positions in order to allow a user to grip or manipulate objects or the environment more effectively.

[0007] Conventionally, the process of handling an object comprises two movement phases for a mechanical digit, the first phase is to move the mechanical digit to the object and the second phase comprises gripping the object with the mechanical digit.

[0008] In a conventional mechanical hand, each mechanical digit is controlled by an actuator with a fixed gearing ratio, where the fixed gearing ratio limits both the maximum speed at which the mechanical digit can be actuated, and the maximum force that the mechanical digit can apply to an object. The fixed gearing ratio in a conventional mechanical hand is chosen as a compromise between a maximum unloaded mechanical digit speed and a maximum loaded mechanical digit force. It is an aim of the present invention to address at least some of the disadvantages associated with the prior art.

[0009] SUMMARY OF THE INVENTION

[0010] Aspects and embodiments of the invention provide apparatus for actuating a mechanical digit and a method of actuating a mechanical digit, as claimed in the appended claims.

[0011] According to an aspect of the invention there is provided apparatus for actuating a mechanical digit comprising: an actuator, wherein said actuator comprises an actuator output; an output element; a first drive element mechanically coupled to the actuator output; a second drive element mechanically coupled to the actuator output; a high speed driven element mechanically engaged with the first drive element, such that the motion of high speed driven element is proportional to the motion of the first drive element; a low speed driven element mechanically engaged with the second drive element, such that the motion of said low speed driven element is proportional to the motion of the second drive element; a driven element selector for selectively engaging the high speed driven element to the output element and disengaging the low speed driven element from the output element, or engaging the low speed driven element to the output element and disengaging the high speed driven element from the output element; and a controller to control the driven element selector.

[0012] An advantage of this invention is that the user has increased control of speed of operation of, and the force applied by, a mechanical digit in the movement and gripping phases of operation of the mechanical digit. Further, such an arrangement may be more easily protected from mechanical impact and water and dirt ingress.

[0013] The apparatus may comprise a sensing element configured to detect the position and / or speed of the driven element selector, wherein the controller may control the driven element selector based on signal information from the sensing element.

[0014] The driven element selector may comprise a gear selector with external engagement teeth configured to selectively engage with the low speed driven element and the high speed driven element. The low speed driven element and the high speed driven element may comprise respective internal engagement teeth configured to interface with the external engagement teeth of the gear selector.

[0015] The first drive element may comprise twenty four radially extending teeth, the high speed driven element may comprise twelve radially extending teeth, the second drive element may comprise twelve radially extending teeth, and the low speed driven element may comprise twenty four radially extending teeth.

[0016] The first drive element may comprise twenty seven radially extending teeth, the high speed driven element may comprise nine radially extending teeth, the second drive element may comprise nine radially extending teeth, and the low speed driven element may comprise twenty seven radially extending teeth.

[0017] The first drive element may comprise forty radially extending teeth, the high speed driven element may comprise ten radially extending teeth, the second drive element may comprise ten radially extending teeth, and the low speed driven element may comprise forty radially extending teeth.

[0018] The driven element selector may comprise a shift rod mechanically coupled to the output element, the gear selector and a gear selector magnet, wherein the shift rod may be spring loaded to be mechanically biased such that the external engagement teeth of the driven element selector are mechanically biased towards one of the internal engagement teeth of the low speed driven element or the internal engagement teeth of the high speed driven element.

[0019] The apparatus may comprise a shift magnet configured to interact with the gear selector magnet in order to effect movement of the gear selector between a first position where the external engagement teeth of the driven element selector are mechanically engaged with the internal engagement teeth of the low speed driven element and a second position where the external engagement teeth of the driven element selector are mechanically engaged with the internal engagement teeth of the high speed driven element. According to an aspect of the invention there is provided a method of operating an apparatus for actuating a mechanical digit, comprising: receiving a user input at a control unit; determining the position of a driven element selector of the apparatus; engaging a digit actuator in a first mode; determining a speed and / or position of the mechanical digit; and when the speed and / or position of the mechanical digit reaches a threshold speed and / or position, engaging the digit actuator in a second mode.

[0020] An advantage of this invention is that movement of a single actuator may be used to cause the mechanical digit to rotate in two axes, thus reducing the number of actuators required leading to reduced weight and cost for a mechanical hand comprising the mechanical digit assembly.

[0021] Within the scope of this application, it is expressly intended that the various aspects, embodiments, examples and alternatives set out in the preceding paragraphs, in the claims and / or in the following description and drawings, and in particular the individual features thereof, may be taken independently or in any combination. That is, all embodiments and / or features of any embodiment can be combined in any way and / or combination, unless such features are incompatible. The applicant reserves the right to change any originally filed claim or file any new claim accordingly, including the right to amend any originally filed claim to depend from and / or incorporate any feature of any other claim although not originally claimed in that manner.

[0022] BRIEF DESCRIPTION OF THE DRAWINGS

[0023] One or more embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

[0024] Figure 1 illustrates an apparatus for driving a mechanical digit, according to an embodiment of the invention;

[0025] Figure 2 illustrates a driven element selector, according to an embodiment of the invention; Figure 3 illustrates in more detail the gear selector of the driven element selector engaging with a low speed driven element 4;

[0026] Figure 4 illustrates an example control system algorithm for driving a mechanical digit according to an embodiment of the invention; and

[0027] Figure 5 illustrates an example control system for controlling a mechanical digit according to an embodiment of the present invention.

[0028] In the drawings, like parts are denoted by like reference numerals.

[0029] DETAILED DESCRIPTION

[0030] Examples of the present disclosure relate to apparatus for actuating a mechanical digit and a method of actuating a mechanical digit. In particular, examples of the present disclosure relate to an apparatus for actuating a mechanical digit and a method of actuating a mechanical digit, wherein the mechanical digit is configured through the action of the apparatus or operation of the method to move with selectable low speed and high speed. Non-limiting examples will now be described with reference to the accompanying drawings.

[0031] In general, the figures illustrate an apparatus 100 for actuating a mechanical digit, the apparatus 100 comprising an actuator 1 , an output element 7, a first drive element 3, a second drive element 2, a low speed driven element 4, a high speed driven element 5, a driven element selector 6 and a controller 510.

[0032] Figure 1 illustrates an apparatus 100 which is configured to be controlled by a control unit or controller 510, and to be attached or operably connected to a mechanical digit to control the movement of the mechanical digit. The apparatus 100 illustrated in Figure 1 also comprises a shift spring 8, a worm wheel 9, a digit driver 10, and a shift magnet 11 , the operation of which will be described further below.

[0033] It is envisaged that the herein disclosed multiple speed actuator can be used to control a single mechanical digit or multiple mechanical digits. Figure 1 shows the output element 7 coupled to a spur differential, sharing torque between two mechanical digits.

[0034] The apparatus 100 may be mechanically mounted to, be comprised in, or form part of, a mechanical gripper, which may be in the form of a prosthetic hand or mechanical hand.

[0035] The apparatus 100 provides for selection of multiple speeds, for example two different speeds, for driving actuation of an output element 7. The driving actuation of the output element 7 causes actuation of a mechanical digit that may be operably connected to the apparatus 100. Output element 7 is operably connected to a digit driver 10 via a worm wheel 9, such that the driving of the output element 7 to cause rotation of the output element 7 around its rotation axis causes rotation of the worm wheel 9 in an axis perpendicular to the rotation axis of the output element 7. The driving of the output element 7 thereby causes a mechanical digit, which is mechanically or operably coupled to the digit driver 10, to move from a first position or condition to a second position or condition. The first position may be an open position and the second position may be a closed position.

[0036] In the apparatus 100, mechanical torque is provided via an actuator 1 , which may be an electrical actuator attached to an energy source, and may be known as a digit actuator. Two drive elements or gears are mechanically mounted or coupled to an actuator output, the actuator output being, for example, in the form of output shaft of the actuator 1. The first drive element 3 may be a first gear or first compound gear and the second drive element 2 may be a second gear or second compound gear.

[0037] Each of the first drive element 3 and the second drive element 2 mates with, or is mechanically coupled to or engaged with, a respective driven element or driven gear.

[0038] The first drive element 3 is mechanically coupled to a first driven element 5 or first driven gear, which may be called a high speed driven element 5 or high speed driven gear. The rotation or motion of the first drive element 3 is proportional to the rotation or motion of the high speed driven element 5. Such a high speed driven element 5 may also be referred to as a low torque driven element or gear. The first drive element 3 may comprise a plurality of radially extending external teeth configured to engage with a plurality of radially extending external teeth on the first driven element 5.

[0039] The second drive element 2 is mechanically coupled to a second driven element 4 or second driven gear, which may be called a low speed driven element 4 or low speed driven gear. The rotation or motion of the second drive element 2 is proportional to the rotation or motion of the low speed driven element 4. Such a low speed driven element 4 may also be referred to as a high torque driven element or gear. The second drive element 2 may comprise a plurality of radially extending external teeth configured to engage with a plurality of radially extending external teeth on the second driven element 4.

[0040] It will be understood that the terms high speed and low speed indicate speeds of the first driven element 5 and second driven element 4 respectively when considered relative to each other. Likewise, it will be understood that the terms low torque and high torque indicate torque values of the first driven element 5 and second driven element 4 respectively when considered relative to each other.

[0041] In one embodiment, the first drive element 3 comprises twenty four radially extending teeth and the second drive element 2 comprises twelve radially extending teeth, with the high speed driven element 5 comprising radially extending twelve teeth and the low speed driven element 4 comprising twenty four radially extending teeth. Such an arrangement provides a high speed ratio of 0.5:1 and a low speed ratio of 2:1.

[0042] In another embodiment, the first drive element 3 comprises twenty seven radially extending teeth and the second drive element 2 comprises nine radially extending teeth, with the high speed driven element 5 comprising nine radially extending teeth and the low speed driven element 4 comprising twenty seven radially extending teeth. Such an arrangement provides a high speed ratio of 0.333:1 and a low speed ratio of 3:1.

[0043] In yet another embodiment, the first drive element 3 comprises forty radially extending teeth and the second drive element 2 comprises ten radially extending teeth, with the high speed driven element 5 comprising ten radially extending teeth and the low speed driven element 4 comprising forty radially extending teeth. Such an arrangement provides a high speed ratio of 0.25:1 and a low speed ratio of 4:1.

[0044] Figure 2 illustrates in more detail the driven element selector 6 of the apparatus 100, according to some embodiments. The driven element selector 6 may comprise a gear selector 6a with external engagement teeth 6e, a shift rod 6b, a static mount 6c and a gear selector magnet 6d. Figure 2 illustrates the driven element selector 6 being rotationally aligned with the output element 7.

[0045] The driven element selector is configured to selectively engage the high speed driven element 5 to the output element 7 and disengage the low speed driven element 4 from the output element 7, or engage the low speed driven element 4 to the output element 7 and disengage the high speed driven element 5 from the output element 7.

[0046] The driven element selector 6 comprises a gear selector 6a with external engagement teeth 6e, a shift rod 6b, a static mount 6c and a gear selector magnet 6d. Figure 2 illustrates that the driven element selector 6 is rotationally aligned along an axis with the output element 7, which may be considered as the rotational axis of the output element 7.

[0047] In some embodiments the high speed driven element 5 and the low speed driven element 4 may have internal counterbores or internal engagement teeth. The internal engagement teeth are also referred to as anulus teeth. The internal engagement teeth can be selectively mated or engaged with a set of external engagement teeth 6e on a gear selector 6a of the driven element selector 6.

[0048] It is envisioned that in other embodiments the internal engagement teeth of the high speed driven element 5 and the low speed driven element 4 and the external engagement teeth 6e of the gear selector 6a may be replaced by a different means of selective axial mating.

[0049] In some embodiments, as illustrated in Figure 2, the shift rod 6b mates or is operably connected with the output element 7. As illustrated in Figure 1 and Figure 2, the output element 7 is an output worm or worm gear. The position of the shift rod 6b governs which gear is selected, that is whether the high speed driven element 5 or the low speed driven element 4 is engaged. The shift rod 6b is configured to move relative to a static mount 6c, which is positionally fixed relative to the actuator 1.

[0050] In some embodiments, the shift rod 6b is spring loaded via the means of a shift spring such that the external engagement teeth 6e of the driven element selector 6 may be mechanically biased towards internal engagement teeth 4e of the low speed driven element 4. The engagement of the internal engagement teeth 4e of the low speed driven element 4 and the external engagement teeth 6e of the driven element selector 6 is illustrated in Figure 3. In this embodiment the output element 7 is in a low speed and high torque mode.

[0051] In other embodiments, the shift rod 6b is spring loaded via the means of a shift spring such that the external engagement teeth 6e of the driven element selector 6 may be mechanically biased towards the internal engagement teeth of the high speed element 5. In this embodiment the output element 7 is in a high speed and low torque mode.

[0052] Figure 5 illustrates a control system for the apparatus 100. Digit actuator 550 includes an encoder 530, which measures the angular velocity of the digit actuator 550. The encoder 530 may also monitor the rotary position of the digit actuator 550. The encoder 530 may also monitor the speed of the mechanical digit.

[0053] A control unit 510, or controller, monitors the angular velocity of the digit actuator 550. If the angular velocity of the digit actuator 550 decreases, the control unit 510 may be programmed to activate a shift actuator 570 that changes the position of the shift rod 6b and therefore moves the external engagement teeth 6e of the driven element selector 6 towards the internal engagement teeth 4e of the low speed driven element 4. The shift actuator 570 may be in the form of a leadscrew actuator, a solenoid, or a linear actuator.

[0054] If the angular velocity of the digit actuator 550 increases, the control unit 510 may be programmed to activate a shift actuator 570 that changes the position of the shift rod 6b and therefore moves the external engagement teeth 6e of the driven element selector 6 towards the internal engagement teeth of the high speed driven element 5. In some embodiments, in order to effect the change of the position of the shift rod 6b, and therefore shift engagement of the external engagement teeth 6e of the driven element selector 6 between engagement with internal engagement teeth 4e of the low speed driven element 4 and internal engagement teeth of the high speed driven element 5, a magnet couple is used.

[0055] The magnet couple comprises a shift magnet 11 , as shown in Figure 1, and a gear selector magnet 6d, as shown more clearly in Figure 2. The magnet couple provides magnets which are orientated so the poles repel each other. It is envisaged that if the internal engagement teeth and the external engagement teeth are perfectly aligned, the magnetic forces drive the external engagement teeth 6e of the driven element selector 6 to engage with the internal engagement teeth 4e of the low speed driven element 4, thereby delivering a high force grip up to motor stall.

[0056] When the mechanical hand is opening, that is when the mechanical digit is releasing the grip, the reverse process will occur. In such circumstances, once the digit actuator motor is moving sufficiently quickly, the shift magnet 11 actuated by the shift actuator 570 the spring force of the shift spring 11 moves the driven element selector 6 towards the high speed driven element 5.

[0057] In some embodiments, the rotation of a mechanical digit may be measured using a potentiometer or an electronic sensing element. The current drawn by the digit actuator 550 is determined by a current sensor 590.

[0058] The apparatus 100 for actuating a mechanical digit may be operated to provide a variable speed operation of the mechanical digit. The operation of moving a mechanical digit may comprise two consecutive modes, a first mode and a second mode. In a first mode the mechanical digit is moved at a first speed and in a second mode the mechanical digit is moved at a second speed, different to the first speed. In a mechanical digit flexing operation, the first mode may be where the mechanical digit is moving at a higher speed than in the second mode. In a mechanical digit extension operation, the first mode may be where the mechanical digit is moving at a lower speed than in the second mode. In a first operation, where the mechanical digit is in an open condition, that is not in a closed or gripping condition, the first mode may be operable where the driven element selector 6 selectively engages the high speed driven element 5 to the output element 7 and disengages the low speed driven element 4 from the output element 7. The second mode may be operable where the driven element selector 6 selectively engages the low speed driven element 4 to the output element 7 and disengages the high speed driven element 5 from the output element 7. This first operation describes a flex or flexing operation for the mechanical digit.

[0059] In a second operation, where the mechanical digit is in a closed condition, that is in a gripping condition and not in an open condition, the first mode may be operable where the driven element selector 6 selectively engages the low speed driven element 4 to the output element 7 and disengages the high speed driven element 5 from the output element 7. The second mode may be operable where the driven element selector 6 selectively engages the high speed driven element 5 to the output element 7 and disengages the low speed driven element 4 from the output element 7. This second operation describes an extending or extension operation for the mechanical digit.

[0060] The method of operation of the apparatus may comprise initially receiving a user input at a control unit 510. The user input may be, for example, to flex or close the mechanical digit, or to extend or open the mechanical digit.

[0061] The position of the driven element selector 6 of the apparatus 100 is then determined, for example by using a sensor 520 for the driven element selector 6.

[0062] Once the position of the driven element selector 6 is known, the digit actuator 550 can be engaged in a first mode. Subsequently, the speed and / or position of the mechanical digit is determined, for example by the use of an encoder 530 for the digit actuator 550. When the speed and / or position of the mechanical digit reaches a predetermined threshold speed and / or position, the digit actuator 550 may be engaged in a second mode. Thus by these operations a mechanical digit can be arranged or configured to move quickly from an open condition to a closed condition, whilst maximizing torque for gripping, and to ensure sufficient torque for gripping until the mechanical digit is at a point where it can be moved in a quicker manner to effect movement of the mechanical digit to the open condition.

[0063] Figure 4 illustrates blocks of a method 400 for actuating a mechanical digit when various user commands or user inputs are provided to the control unit 510 or controller. In some embodiments, the user input command may be, but is not limited to, a close hand control command, an open hand control command, a close digit control command or an open digit control command. Figure 4 provides an example where a user input at block 401 is a close digit control command.

[0064] Following receipt of the close digit control command, the position of the driven element selector 6 is determined at block 402. The driven element selector 6 may be in a position whereby the high speed driven element 5 is engaged with the output element 7 and the low speed driven element 4 is disengaged from the output element 7, in which case the process proceeds to block 405.

[0065] However, if the driven element selector 6 is in a position whereby the high speed driven element 5 is disengaged from the output element 7 and the low speed driven element 4 is engaged with the output element 7 then the driven element selector 6 is actuated using the shift actuator 570 at block 403 to ensure engagement of the high speed driven element 5 to the output element 7 and disengagement of the low speed driven element 4 from the output element 7. The driven element selector 6 is then stopped at block 404, and the process proceeds to block 405.

[0066] At block 405 the digit actuator may be actuated with high speed and low torque output to cause movement of the mechanical digit towards a closed digit position or condition.

[0067] At block 406 the speed and / or position of the mechanical digit may be determined. When it is determined, from the determination of the speed and / or position of the mechanical digit, that a threshold speed and / or position has been reached, the driven element selector 6 is actuated using the shift actuator 570 at block 407 to effectively reverse the position of the driven element selector 6. The driven element selector 6 is actuated using the shift actuator 570 at block 407 and then, once the position of the driven element selector 6 is determined at block 408 to be such that there is engagement of the low speed driven element 4 to the output element 7 and disengagement of the high speed driven element 5 from the output element 7 the driven element selector 6 is stopped at block 409.

[0068] At block 410 the digit actuator may be actuated with a low speed high torque output to cause movement of the mechanical digit towards a closed digit position or condition. In this way the apparatus 100 provides the user with increased control of the position of the mechanical digit with respect to a mechanical hand and increased control of the force applied by of the mechanical digit using a single apparatus.

[0069] At block 411 a user stop command is received and at block 412 the digit actuator is stopped.

[0070] The apparatus 100 provides an assembly for the operation of a mechanical digit which may have a substantial reduction in part count over conventional mechanical digit actuation arrangements, resulting in a lighter, more reliable, more robust, more durable, and more compact solution for a user. With reduced complexity over conventional arrangements, the apparatus 100 can be more easily protected from water ingress.

[0071] Features described in the preceding description may be used in combinations other than the combinations explicitly described.

[0072] Although functions have been described with reference to certain features, those functions may be performable by other features whether described or not.

[0073] Although features have been described with reference to certain embodiments, those features may also be present in other embodiments whether described or not.

[0074] Whilst endeavoring in the foregoing specification to draw attention to those features of the invention believed to be of particular importance it should be understood that the Applicant claims protection in respect of any patentable feature or combination of features hereinbefore referred to and / or shown in the drawings whether or not particular emphasis has been placed thereon.

Claims

CLAIMS1. Apparatus (100) for actuating a mechanical digit, comprising: an actuator (1), wherein said actuator comprises an actuator output; an output element (7); a first drive element (3) mechanically coupled to the actuator output; a second drive element (2) mechanically coupled to the actuator output; a high speed driven element (5) mechanically engaged with the first drive element (3), such that the motion of high speed driven element (5) is proportional to the motion of the first drive element (3); a low speed driven element (4) mechanically engaged with the second drive element (2), such that the motion of said low speed driven element (4) is proportional to the motion of the second drive element (2); a driven element selector (6) for selectively engaging the high speed driven element (5) to the output element (7) and disengaging the low speed driven element (4) from the output element (7), or engaging the low speed driven element (4) to the output element (7) and disengaging the high speed driven element (5) from the output element (7); and a controller (510) to control the driven element selector (6).

2. Apparatus for actuating a mechanical digit according to claim 1, comprising a sensing element (520) configured to detect the position and / or speed of the driven element selector (6), wherein the controller (510) controls the driven element selector (6) based on signal information from the sensing element (520).

3. Apparatus for actuating a mechanical digit according to claim 1 or claim 2, wherein the driven element selector (6) comprises a gear selector (6a) with external engagement teeth (6e) configured to selectively engage with the low speed driven element (4) and the high speed driven element (5).

4. Apparatus for actuating a mechanical digit according to claim 3, wherein the low speed driven element (4) and the high speed driven element (5) comprise respective internal engagement teeth configured to interface with the external engagement teeth (6e) of the gear selector.

5. Apparatus for actuating a mechanical digit according to any preceding claim, wherein the first drive element (3) comprises twenty four radially extending teeth, the high speed driven element (5) comprises twelve radially extending teeth, the second drive element (4) comprises twelve radially extending teeth, and the low speed driven element (2) comprises twenty four radially extending teeth.

6. Apparatus for actuating a mechanical digit according to any of claims 1 to 4, wherein the first drive element (3) comprises twenty seven radially extending teeth, the high speed driven element (5) comprises nine radially extending teeth, the second drive element (4) comprises nine radially extending teeth, and the low speed driven element (2) comprises twenty seven radially extending teeth.

7. Apparatus for actuating a mechanical digit according to any of claims 1 to 4, wherein the first drive element (3) comprises forty radially extending teeth, the high speed driven element (5) comprises ten radially extending teeth, the second drive element (4) comprises ten radially extending teeth, and the low speed driven element (2) comprises forty radially extending teeth.

8. Apparatus for actuating a mechanical digit according to claim 3, wherein the driven element selector (6) comprises a shift rod (6b) mechanically coupled to the output element (7), the gear selector (6a) and a gear selector magnet (6d), wherein the shift rod is spring loaded to be mechanically biased such that the external engagement teeth (6e) of the driven element selector (6) are mechanically biased towards one of the internal engagement teeth (4e) of the low speed driven element (4) or the internal engagement teeth of the high speed driven element (5).

9. Apparatus for actuating a mechanical digit according to claim 8, wherein the apparatus (100) comprises a shift magnet (11) configured to interact with the gear selector magnet (6d) in order to effect movement of the gear selector between a first position where the external engagement teeth (6e) of the driven element selector (6) are mechanically engaged with the internal engagement teeth (4e) of the low speed driven element (4) and a second position where the external engagement teeth (6e) of the driven element selector (6) are mechanically engaged with the internal engagement teeth of the high speed driven element (5).

10. A method of operating an apparatus (100) for actuating a mechanical digit, comprising: receiving a user input at a control unit (510); determining the position of a driven element selector (6) of the apparatus (100); engaging a digit actuator (550) in a first mode; determining a speed and / or position of the mechanical digit; and when the speed and / or position of the mechanical digit reaches a threshold speed and / or position, engaging the digit actuator (550) in a second mode.

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