Actuation mechanism

Abstract

An actuation mechanism, e.g. the end effector of a robotic surgical instrument, comprises a pair of jaws (e.g. forceps, graspers, scissors) that are directly coupled on an axis of relative rotation 20

Description

Technical Field The present disclosure relates to an actuation mechanism and, in particular, to an actuation mechanism comprising a first jaw rotatable about a first jaw axis, and a second jaw rotatable about a second jaw axis offset from the first jaw axis, wherein the first jaw is directly coupled to the second jaw on the second jaw axis. An associated surgical instrument is also disclosed. Background Surgical instruments with higher dexterity are becoming increasingly desirable in robotic surgery but are subject to grasping force limitations. Accordingly, there is a need for improvements in surgical instruments to achieve higher grasping forces while maintaining dexterity. The listing or discussion of a prior-published document or any background in this specification should not necessarily be taken as an acknowledgement that the document or background is part of the state of the art or is common general knowledge. One or more aspects / examples of the present disclosure may or may not address one or more of the background issues. Summary According to a first aspect, there is provided an actuation mechanism comprising: a first jaw rotatable about a first jaw axis; and a second jaw rotatable about a second jaw axis offset from the first jaw axis, wherein the first jaw is directly coupled to the second jaw on the second jaw axis, wherein, when a force is applied to rotate the second jaw about the second jaw axis, at least part of the applied force is transferred to the first jaw through the direct coupling between the first jaw and the second jaw. The first jaw may be directly hingedly coupled to the second jaw. The first jaw may be directly hingedly coupled to the second jaw via respective mating portions. One of the mating portions may comprise a pin or protrusion and the other mating portion may comprise a hole. The second jaw may comprise a jaw engagement portion, wherein: the first jaw is configured to be actuated at a distance rl from the first jaw axis, the jaw engagement portion is configured to be actuated at a distance L22 from the second jaw axis, and the first jaw and the second jaw are configured such that a ratio of rl to a distance Lil between the first jaw axis and a distal end of the first jaw is less than a ratio of L22 to a distance L21 between the second jaw axis and a distal end of the second jaw. The part of the applied force transferred to the first jaw may be proportional to a force applied to a pivot point P2 on the second jaw axis and rl, and inversely proportional to Lil. Each jaw may be actuated by a tendon directly or through a non-force amplification driver. The jaw engagement portion may be coupled to a force amplification driver, such that the applied force is an amplified force generated due to actuation of the force amplification driver. The second jaw may be rotatable about the first jaw axis together with the first jaw in a wrist movement. The force amplification driver may be configured to be rotatable about the first jaw axis and be actuated at a distance rd from the first jaw axis, and may be configured to engage the jaw engagement portion at a distance rp from the first jaw axis that is less than rd. The distance rd may be substantially equal to the distance rl. The first jaw and the second jaw may each be rotatable between an open position and a closed position, and wherein at least part of the applied force to the second jaw may be transferred to the first jaw when the first jaw and / or the second jaw are rotated toward their respective open or closed positions. The force amplification driver may comprise a drive engagement portion slidably engageable with the jaw engagement portion. The jaw engagement portion and the drive engagement portion may be one or more of positioned and oriented to facilitate generation of the amplified force. One of the jaw engagement portion and the drive engagement portion may be a male portion and the other may be a female portion. The female portion may comprise a slot or hole and the male portion may comprise a pin or protrusion. The slot or hole may comprise a curved portion and / or an angled portion. The second jaw axis and the jaw engagement portion of the second jaw may be provided on opposing sides of the first jaw axis. The second jaw axis and the jaw engagement portion may have an angular separation of at least 90 degrees, preferably at least 135 degrees, more preferably 180 degrees. The angular separation may be with respect to the first jaw axis. The second jaw axis may be on a longitudinal centre line between the first jaw and the second jaw. Alternatively, the second jaw axis may be offset from a longitudinal centre line between the first jaw and the second jaw. The second jaw axis may be parallel to the first jaw axis. The first jaw and the second jaw may be configured as scissor blades, forceps, a dissector, or a grasper. Only the second jaw may be coupled to a force amplification driver. The actuation mechanism may comprise an axle arranged along the first axis, the first jaw and the force amplification driver may be configured to be mounted on the axle, wherein the second jaw may comprise a slot having clearance from engaging with the axle. According to a second aspect, there is provided a surgical instrument comprising an end effector wherein the end effector comprises an actuation mechanism according to the first aspect. According to a third aspect, there is provided an apparatus as substantially described herein with reference to, and as illustrated by, the accompanying drawings. The optional features described in relation to the actuation mechanism of the first aspect are also applicable to the surgical instruction of the second aspect, and / or the apparatus of the third aspect where compatible. The present disclosure includes one or more corresponding aspects, examples or features in isolation or in various combinations whether or not specifically stated (including claimed) in that combination or in isolation. Corresponding means for performing one or more of the discussed functions are also within the present disclosure. Throughout the present specification, descriptors relating to position or force such as "left", "right", "push" and "pull", as well as any adjective and adverb derivatives thereof, are used in the sense of the position or force of the apparatus or a portion(s) thereof as presented in the drawings. However, such descriptors are not intended to be in any way limiting to an intended use of the described or claimed invention. The above summary is intended to be merely exemplary and non-limiting. Brief Description of the Figures A description is now given, by way of example only, with reference to the accompanying schematic drawings, in which: Figures la-c show in plan view an actuation mechanism and portions thereof. Figure 2 shows in exploded isometric view an actuation mechanism according to an example. Figures 3a-c show in alternative exploded isometric views the actuation mechanism of Figure 2. Figures 4a-c show in plan view portions of the actuation mechanism of Figure 2. Figures 5a-c show in plan view static forces acting on portions of the actuation mechanism of Figure 2. Figures 6a-b show in plan view second jaws of an actuation mechanism according to further examples. Figure 7 shows in plan view portions of an actuation mechanism according to a further example. Figure 8 shows in plan view portions of the actuation mechanism of Figure 7. Detailed Description Figures la-c show in plan view an actuation mechanism 100 and portions thereof. The actuation mechanism 100 comprises a first jaw 102 rotatable about a first jaw axis 104, and a second jaw 106 rotatable about the first jaw axis 104. The actuation mechanism 100 may be a combined end-effector with open / close functions and positioning (two end-effector elements - the first jaw 102 and the second jaw 106 -moving in the same direction). The combined functions enable surgical instruments to have better dexterity with relatively few joints. However, with the limitations of instrument diameter and available pulling force (or tendon strength) Tl, Fpl, Fp2 - see Figures lb-c - the positioning force and grasping force are limited to the pulling force on Tl and the offset distance R from the axis of rotation 104. The inventor has determined that in circumstances when a relatively high grasping force is needed, these limitations pose a barrier to better instrument performance. One example is when the actuation mechanism holds a needle to perform suturing. The needle can slip or spin if the holding force is insufficient. Figure 2 shows in exploded isometric view an actuation mechanism 200 according to an example. Like the actuation mechanism 100 of Figure 1, the actuation mechanism 200 comprises a first jaw 202 rotatable about a first jaw axis (Axis 1) 204, and a second jaw 206. As devised by the inventor, the second jaw 206 is rotatable about a second jaw axis (Axis 2) 208 offset from the first jaw axis 204, wherein the first jaw 202 is directly coupled - shown in part by the part labelled with the reference sign 210 - to the second jaw 206 on the second jaw axis 208. When a force is applied to rotate the second jaw 206 about the second jaw axis 208, at least part of the applied force is transferred to the first jaw 202 through the direct coupling 210 between the first jaw 202 and the second jaw 206. Optionally, the second jaw 206 comprises a jaw engagement portion 212 configured to couple to a force amplification driver 214, which in this example is a disc, that comprises a drive engagement potion 216, further details of which will be discussed below. Additionally, or alternatively, the actuation mechanism 200 may also comprise an axle 218 arranged along the first axis 204, with the first jaw 202, and the force amplification driver 214 configured to be mounted on the axle 218, wherein the second jaw 206 comprises a slot 220 having clearance from engaging with the axle 218. That is, the centre line of the slot 220 substantially follows an arc whose centre is the second jaw axis 208 (i.e., the centre coincides with the direct coupling 210 between the first jaw 202 and the second jaw 206) and whose radius is equal to the distance between the first jaw axis 204 and the second jaw axis 208 so that the second jaw 206 does not collide with the axle 218 at any orientation of the second jaw's movement. The two ends of the slot 220 can be used as hard stops for the second jaw's movement. The second jaw axis 208 and the jaw engagement portion 212 of the second jaw 206 may be provided on opposing sides of the first jaw axis 204. The second jaw axis 208 may be parallel to the first jaw axis 204, as seen in Figure 2, but may adopt an alternative alignment (e.g., slanting with respect to the first axis 204 at an angle of up to several degrees or more) so long as at least part of the applied force can be transferred to the first jaw 202 through the direct coupling 210 between the first jaw 202 and the second jaw 206. When in use the actuation mechanism 200 advantageously provides an amplified grasping force over with the actuation mechanism of Figure 1 and related technologies investigated by the inventor. This advantage is achieved within the same mechanical limitations (such as instrument diameter and available tendon pulling force) as these related technologies and maintains mechanical dexterity. A non-limiting example application of the actuation mechanism 200 is as follows. An endeffector comprises two jaws 202, 206 for a surgical instrument, the first jaw 202 is rotatable about a first axis 204, the second jaw 206 is rotatable about a second axis 208 that is offset from the first axis 204. The second jaw 206 is actuated by a disk 214 that amplifies the driving force. The amplified driving force from the second jaw 206 contributes to the driving force of the first jaw 202. The end-effector may thereby function as a combined end-effector with open / close functions and positioning and with force amplification. Figures 3a-c show in alternative exploded isometric views the actuation mechanism 200 of Figure 2. Since the features and operating principles are the same, the discussion of certain features has been (or is) omitted for brevity. The first jaw 202 may use a pair of tendons (not shown) to actuate the first jaw 202 such that the first jaw 202 rotates about the first jaw axis 204 (which may be termed a centre axis). A hole 222 in the first jaw 202 - see Figure 3b - that is offset from the rotation centre (i.e., offset from the first jaw axis 204) is configured to receive a pin 210 on the second jaw 206 - see Figures 3a and c - the pin 210 located on the second jaw axis 208. The combination of the hole 222 in the first jaw 202 and the pin 210 on the second jaw 206 represents a non-limiting example of a direct coupling between the first and second jaws 202, 206 on the second jaw axis 208. The second jaw axis 208 moves with the first jaw 202 as the first jaw 202 rotates about the first jaw axis 204. The second jaw 206 is driven by a disk 214, that is, by a pin 216 (exemplary of a drive engagement portion) on the disk 214 that engages with a slot 212 (exemplary of a jaw engagement portion) in the second jaw 206. The second jaw 206 rotates about the second jaw axis 208. Alternative coupling configurations can include a pin on the first jaw 202 that matches a hole in the second jaw 206; a pin on the second jaw 206 that engages with a slot in the disk 214; or any combination(s) of male - female features. As such, the first jaw 202 may be directly hingedly coupled to the second jaw 206. In such examples, the first jaw 202 may be directly hingedly coupled to the second jaw 206 via respective mating portions, such as one of the mating portions comprising a pin 210 or protrusion and the other mating portion comprising a hole 222. Furthermore, the force amplification driver 214 may comprise a drive engagement portion 216 slidably engageable with the jaw engagement portion 212. The jaw engagement portion 212 and the drive engagement portion 216 may be one or more of positioned and oriented to facilitate generation of the amplified force, as discussed further below. One of the jaw engagement portion 212 and the drive engagement portion 216 may be a male portion - such as a slot or hole - and the other a female portion (e.g., a pin or protrusion). Figures 4a-c show plan views of portions of the actuation mechanism 200 of Figure 2. Figure 4a shows the disk 214 and the pin 216 thereof; Figure 4b shows the second jaw 206, the pin 210 and the slot 212 thereof; and Figure 4c shows the first jaw 202 and the hole 222 thereof. The following discussion of a non-limiting example actuation mechanism is provided to assist the reader in further understanding how the actuation mechanism 200 of Figure 2 advantageously provides an amplified grasping force. In particular, which force is present due to the combination of a force-amplified second jaw 206 and a moving first jaw 202; and how a force acting on the first jaw 202 is amplified by force actuation of the second jaw 206, are discussed. Figures 5a-c shows in plan view static forces acting on portions of the actuation mechanism 200 of Figure 2. For the sake of simplicity, the following analysis is based on static force and torque analysis but neglects inertia, mass and friction which are insignificant with regards to the forces and torques being considered here. Furthermore, the arrows in these figures represent magnitudes of the forces considered in this analysis but are not to scale. Force amplification of the second jaw 206 is achieved in two stages. In the first stage, a distance rp between the driving pin 216 on the disk 214 and the rotation centre of the disk 214 is less than a distance rd from an actuation tendon - not shown but represented by the force Fp2 - to the centre of the disk 214. In the second stage, a distance (moment arm) L22 from the driving force (amplified in the first stage) to the offset pivot (the pin 210) on the second jaw 206 is more than a distance rl from an actuation force Fpl acting on the first jaw 202 to the rotation centre on the first jaw 202. The distance rd may be substantially equal to the distance rl. Referring now to Figure 5a for the disk 214, a pulling force Fp2 is applied to the actuation tendon (not shown but represented by the force Fp2) that is wrapped around the disk 214. The disk 214 rotates about its centre, e.g., the disk 14 rotates about the first axis 204. The forces and torques are: Fp2 x rd = Fd x rp (1) Rearranging equation (1) for Fd gives: Fd = Fp2 x rd / rp (2) In equation (2) the ratio rd / rp is the force amplification ratio on the disk 214. The force Fd is the force from the pin 216 on the disk 214 that is applied to a side wall of the slot 212 of the second jaw 206. Turning now to Figure 5b for the second jaw 206, the slot 212 (or other portion that mates with a corresponding portion on the disk 214) is oriented towards the pivot point P2 (that corresponds to the location of the pin 210 on the second jaw axis) so that the force Fd from the pin 216 on the disk 214 (equivalently Fd' acting on a side wall of the slot 212) is near perpendicular to the moment arm L22 when the first and second jaws 202, 206 are at closed positions to maximize the driving efficiency. As the second jaw 206 rotates about the pivot point P2, the forces and torques are: Fd' x L22 = FJ2 x L21 (3) Rearranging equation (3) for FJ2 gives: FJ2 = Fd'x L22 / L21 (4) Because Fd' and Fd have the same magnitude, equation (4) can also be expressed as: FJ2 = Fd x L22 / L21 (5) Inserting equation (2) into equation (5) gives: FJ2 = Fp2 x rd / rp x L22 / L21 (6) Now looking at the forces applied to the second jaw 206, there is a force FJ2 (imagining the two jaws 202, 206 are closed holding an object with a force) and a force Fd' from the pin 216 on the driving disk 214, such that both forces push the second jaw 206 to the left. There must be another force (labelled Fadd) applied to the pivot point P2 to stop the second jaw 206 being moved. The magnitude and direction of this force Fadd is illustrated in the inset of Figure 5b. For this analysis, only an additional force Fadd on the second jaw 206 and the reaction force Fadd' applied to the first jaw 202 are considered to demonstrate how the closing force from the first jaw 202 is amplified without calculating the exact magnitude and direction of Fadd and Fadd'. Turning now to Figure 5c for the first jaw 202, if both the first jaw 202 and the second jaw 206 had the same, non-force amplification configuration as the first jaw 202, the closing force would be: Fpl x rl = Fl x Lil (7) Rearranging equation (7) for Fl gives: Fl = Fpl x rl / Lil (8) However, with the additional force Fadd', the closing force is calculated as (see also the inset to Figure 5b): Fpl x rl + Fadd' x roff x cos(0) = FJ1 x Lil (9) Note that roff is the distance from the offset pivot point P2 to the first jaw 202 pivot point Pl. That is, the offset between the first axis 204 and the second axis 208. In a non-limiting example configuration, roff = rl, but having roff >rl further improves the force amplification effect. A larger roff results in a longer distance L22 and a shorter distance L21, and therefore larger a force amplification ratio L22 / L21. Rearranging equation (9) for FJ1 gives: FJ1 = (Fpl x rl + Fadd'x roff x cos(9)) / Lil (10) That is: FJ1 = Fpl x rl / Lil + Fadd' x roff x cos(0) I Lil (11) Comparing equations (8) and (11), the above calculations clearly show that FJ 1 is greater than Fl. In a general sense, then, the second jaw 206 may comprise a jaw engagement portion 212, the first jaw 202 may be configured to be actuated at a distance rl from the first jaw axis 204, the jaw engagement portion 212 may be configured to be actuated at a distance L22 from the second jaw axis 208, and the first jaw 202 and the second jaw 206 may be configured such that a ratio of rl to a distance Lil between the first jaw axis 204 and a distal end of the first jaw 202 is less than a ratio of L22 to a distance L21 between the second jaw axis 208 and a distal end of the second jaw 206. The part of the applied force transferred to the first jaw 202 may be proportional to a force applied to a pivot point P2 on the second jaw axis 208 and roff, and inversely proportional to Lil. In use, pulling an actuation tendon (not shown) for the first jaw 202 exerts a closing force Fl on the first jaw 202. This is the closing force without force amplification. The force Fadd' applied to the pivot hole P2 in the first jaw 202 exerts an additional closing force F2 on the first jaw 202. The combination of Fl and F2 is the closing force to balance with the closing force on FJ2 on the second jaw 206. As such, each jaw 202, 206 may be actuated by a tendon directly or through a non-force amplification driver. Alternatively, the jaw engagement portion 212 may be coupled to a force amplification driver (e.g., a disk) 214, such that the applied force is an amplified force generated due to actuation of the force amplification driver 214. In such alternative examples, only the second jaw may be coupled to a force amplification driver. An end-effector comprising the actuation mechanism 200 may be actuated by a combination of driving the first jaw 202 and the force amplification driver (disk) 214. When the first jaw 202 and the disk 214 are driven in the same direction with the same angular speed, the first and second jaws 202, 206 remain static relative to each other, corresponding to a wrist movement. Keeping the first jaw 202 static and moving the disk 214, however, will result in a jaw open / close movement. Combining the moving direction and speed of the first jaw 202 and the force amplification driver 214 results in the combination of jaw open / close and wrist movements. In other words, the second jaw 206 may be rotatable about the first jaw axis 204 together with the first jaw 202 in a wrist movement. The first jaw 202 and the second jaw 206 may each be rotatable between an open position and a closed position, with at least part of the applied force to the second jaw 206 is transferred to the first jaw 202 when the first jaw 202 and / or the second jaw 206 are rotated toward their respective open or closed positions. The force amplification driver 214 may be configured to be rotatable about the first jaw axis 202 and be actuated at a distance rd from the first jaw axis 202, and may be configured to engage the jaw engagement portion 212 at a distance rp from the first jaw axis 202 that is less than rd. With reference to the second jaw 206 shown in Figure 3c, for example, it can be appreciated that the force amplification driver 214 may comprise a drive engagement portion 216 slidably engageable with the jaw engagement portion 212. As discussed with reference to Figures 5a-b, the jaw engagement portion 212 and the drive engagement portion 216 may also be one or more of positioned and oriented to facilitate generation of the amplified force. In an analogous manner to where the first jaw 202 is directly hingedly coupled to the second jaw 206, one of the jaw engagement portion 212 and the drive engagement portion 216 may be a male portion and the other may be a female portion. For example, the female portion may comprise a slot 212 or hole and the male portion may comprise a pin 216 or protrusion. Figures 6a-b show in plan view second jaws 604 according to further examples. The discussion of features in these second jaws 604 that are identical to the second jaw 204 shown in Figure 2 is omitted for brevity. Attention is drawn in Figure 6, however, to alternative forms and / or orientations of the jaw engagement portion. That is, the jaw engagement portion 612a - see Figure 6a - may be a female portion that comprises a curved portion and / or an angled portion. The jaw engagement portion 612b - see Figure 6b - may be angled to point away from the pivot point P2 (a comparison can be made here with, in particular, the orientation of the jaw engagement portion discussed with reference to Figures 5a-b). Figures 7 and 8 show in plan view portions of an actuation mechanism 700 according to a further example. The actuation mechanism 700 functions according to the same general principles as the actuation mechanism 200 of Figure 2, and so the discussion of like features is omitted for brevity. According to this further example, the offset second axis 708 can be away from a centre line between the two jaws 702, 706, or blades in this non-limiting case for a pair of scissors. That is, the second jaw axis 708 may be on a longitudinal centre line between the first jaw and the second jaw (as seen from Figure 2, for example) or may be offset from a longitudinal centre line 724 between the first jaw 702 and the second jaw 706 (as seen from the left portion of Figure 7, for example). To amplify the driving force, the driving pin 716 of the force amplification driver 714 and the slot 712 of the second jaw 706 should be located far away from the offset second axis 708. A preferred location is around 180 degrees relative to the first jaw axis 704, but not limited to any angle. That is, the second jaw axis 708 and the jaw engagement portion 712 may have an angular separation of at least 90 degrees, preferably at least 135 degrees, more preferably 180 degrees, which may be with respect to the first jaw axis 704 as seen from Figure 8. As set out above, an actuation mechanism described with reference to Figures 2-8 enables an improved end-effector grasping force within the same mechanical constraints and available actuation elements as related technologies investigated by the inventor. In turn, this realises improved surgical instruments. The first jaw and the second jaw may be configured as scissor blades, forceps, a dissector, or a grasper, for example, and an actuation mechanism described with reference to Figures 2-8 may be comprised by an end effector that in turn is comprised by a surgical instrument. The applicant hereby discloses in isolation each individual feature described herein and 5 any combination of two or more such features, to the extent that such features or combinations are capable of being carried out based on the present specification as a whole, in the light of the common general knowledge of a person skilled in the art, irrespective of whether such features or combinations of features solve any problems disclosed herein, and without limitation to the scope of the claims. The applicant indicates 10 that the disclosed aspects / embodiments may consist of any such individual feature or combination of features. In view of the foregoing description, it will be evident to a person skilled in the art that various modifications may be made within the scope of the disclosure.

Claims

1. An actuation mechanism comprising:a first jaw rotatable about a first jaw axis; anda second jaw rotatable about a second jaw axis offset from the first jaw axis, wherein the first jaw is directly coupled to the second jaw on the second jaw axis,wherein, when a force is applied to rotate the second jaw about the second jaw axis, at least part of the applied force is transferred to the first jaw through the direct coupling between the first jaw and the second jaw.

2. The actuation mechanism of claim 1, wherein the first jaw is directly hingedly coupled to the second jaw.

3. The actuation mechanism of claim 2, wherein the first jaw is directly hingedly coupled to the second jaw via respective mating portions.

4. The actuation mechanism of claim 3, wherein one of the mating portions comprises a pin or protrusion and the other mating portion comprises a hole.

5. The actuation mechanism of any preceding claim, wherein the second jaw comprises a jaw engagement portion, wherein:the first jaw is configured to be actuated at a distance rl from the first jaw axis,the jaw engagement portion is configured to be actuated at a distance L22 from the second jaw axis, andthe first jaw and the second jaw are configured such that a ratio of rl to a distance Lil between the first jaw axis and a distal end of the first jaw is less than a ratio of L22 to a distance L21 between the second jaw axis and a distal end of the second jaw.

6. The actuation mechanism of any preceding claim, wherein each jaw is actuated by a tendon directly or through a non-force amplification driver.

7. The actuation mechanism of claim 5, wherein the jaw engagement portion is coupled to a force amplification driver, such that the applied force is an amplified force generated due to actuation of the force amplification driver.

8. The actuation mechanism of claim 7, wherein the second jaw is rotatable about the first jaw axis together with the first jaw in a wrist movement.

9. The actuation mechanism of claim 7, wherein the force amplification driver is configured to be rotatable about the first jaw axis and be actuated at a distance rd from the first jaw axis, and is configured to engage the jaw engagement portion at a distance rp from the first jaw axis that is less than rd.

10. The actuation mechanism of claim 9, wherein rd is substantially equal to rl.

11. The actuation mechanism of any preceding claim, wherein the first jaw and the second jaw are each rotatable between an open position and a closed position, and wherein at least part of the applied force to the second jaw is transferred to the first jaw when the first jaw and / or the second jaw are rotated toward their respective open or closed positions.

12. The actuation mechanism of claim 11 when dependent on any one of claims 7-10, wherein the force amplification driver comprises a drive engagement portion slidably engageable with the jaw engagement portion.

13. The actuation mechanism of claim 12, wherein the jaw engagement portion and the drive engagement portion are one or more of positioned and oriented to facilitate generation of the amplified force.

14. The actuation mechanism of claim 13, wherein one of the jaw engagement portion and the drive engagement portion is a male portion and the other is a female portion.

15. The actuation mechanism of claim 14, wherein the female portion comprises a slot or hole and the male portion comprises a pin or protrusion.

16. The actuation mechanism of claim 15, wherein the slot or hole comprises a curved portion and / or an angled portion.

17. The actuation mechanism of claim 5 or any preceding claim dependent thereon, wherein the second jaw axis and the jaw engagement portion of the second jaw are provided on opposing sides of the first jaw axis.

18. The actuation mechanism of claim 17, wherein the second jaw axis and the jaw engagement portion have an angular separation of at least 90 degrees, preferably at least 135 degrees, more preferably 180 degrees.

19. The actuation mechanism of any preceding claim, wherein the second jaw axis is on a longitudinal centre line between the first jaw and the second jaw.

20. The actuation mechanism of any one of claims 1-18, wherein the second jaw axis is offset from a longitudinal centre line between the first jaw and the second jaw.

21. The actuation mechanism of any preceding claim, wherein the second jaw axis is parallel to the first jaw axis.

22. The actuation mechanism of any preceding claim, wherein the first jaw and the second jaw are configured as scissor blades, forceps, a dissector, or a grasper.

23. The actuation mechanism of claim 7 or any claim dependent thereon, wherein only the second jaw is coupled to a force amplification driver.

24. The actuation mechanism of any preceding claim, comprising an axle arranged along the first axis, the first jaw and the force amplification driver are configured to be mounted on the axle, wherein the second jaw comprises a slot having clearance from engaging with the axle.

25. A surgical instrument comprising an end effector wherein the end effector comprises an actuation mechanism according to any preceding claim.

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