AU2016250360A1 - Improved remote centre of motion mechanism - Google Patents

Abstract

An apparatus 1, for constraining a device 3 to pivot about a remote centre of motion 5. A humerus-member 7 is mounted to pivot, relative to a torso structure 9, about a shoulder axis 11. A radius-member 13 is mounted to pivot, relative to the 5 humerus-member, about an elbow axis 15. A hand-member 17 is mounted to pivot, relative to the radius-member, about a wrist axis 19 and is, or is fixable or integral to, the device. A functional four-bar linkage 21 includes a humerus constraint-member 23 mounted to pivot, relative to the humerus-member, about a humerus-constraint axis 25 spaced an elbow-offset distance from the elbow axis. 10 The linkage further includes a radius-constraint-member 27 mounted to pivot, relative to the radius-member, about a radius-constraint axis 29 spaced the elbow offset distance from the elbow axis; and mounted to pivot, relative to the humerus constraint-member, about an elbow-constraint axis 31 a constraint-offset distance from each of the humerus-constraint axis and the radius-constraint axis. A parallel 15 keeping mechanism 33 by which the humerus-constraint-member is held parallel to a notional straight line 35 fixed relative to the torso is provided. Another parallel keeping mechanism 37 by which the radius-constraint-member is held parallel to a notional straight line 39 fixed relative to the hand-member is provided. There is a guide-member 41. Also provided is a passive mechanical transmission 43 by 20 which two members 7, 13, of the functional four-bar linkage and mounted to pivot about one of the elbow axis and the elbow-constraint axis, are mutually connected, and the guide-member is constrained to move with a notional centerline 45 centered between the two members. A translation mechanism 47 connects the guide-member to, and constrains to move along the notional centerline, the other 25 of the elbow axis and the constraint axis. <NO * P5

Description

IMPROVED REMOTE CENTRE OF MOTION MECHANISM

FIELD

The invention relates to remote centre of motion mechanisms.

BACKGROUND

Remote centre of motion (RCM) mechanisms are employed to constrain an item to pivot about a point remote from the mechanism, which point is referred to as a remote centre of motion. RCM mechanisms have application in laparoscopic surgery wherein the remote centre of motion is positioned coincident with the incision point. The surgeon is thereby freed to concentrate on the actions of the surgical tool internal to the patient without fear of a potentially injurious lateral movement of the tool at the incision point. RCM devices can be placed into two broad categories: software-driven devices and mechanically-constrained devices. Software-driven devices have a robotic arm (or the like) having multiple degrees of freedom and which is constrained to move about the RCM by software. Mechanically-constrained devices do without software, and the logic arrangements to implement them, and instead have an arrangement of mechanical components inherently limited to move about the RCM. Mechanically-constrained devices are generally considered more reliable.

Many existing mechanically-constrained RCM mechanisms are based on the Da Vinci mechanism which entails a first parallelogram rising up from a base (or to adopt the language that will be subsequently used herein, rising up from a torso portion) to a second parallelogram which extends horizontally across to overlie the patient.

In the context of surgical applications, it is highly desirable for a RCM mechanism to be compact and otherwise shaped to minimise the risk of crashing with other RCM mechanisms that might be employed over the patient. A wide range of motion (i.e. a wide angle through which the carried device can pivot about the RCM) is also highly desirable.

With these goals in mind, the present inventors have previously proposed a ‘dual triangle’ RCM mechanism in the international patent application published as WO 2014/000041. A device consistent with that earlier application is illustrated in Figure 1. The vertices ACO define a first triangle, whereas the vertices CEO define a second triangle of the dual triangle mechanism. Links GH and FG are added and constrained to remain parallel to the links CE and AC, whereby notional lines mutually connecting points AF, mutually connecting points CG and mutually connecting points EH remain centred on the remote centre of motion O, as the input angle 0in is varied and the tool T subsequently pivoted about the remote centre of motion O through angle 80Ut·

To hold the link CE parallel to the link GH, the link DG is added to define a parallelogram DEHG. Likewise the link BG is added to define another parallelogram to keep the link AC parallel to the link FG.

The earlier international patent application discloses a motorised constraint arrangement by which the four-bar linkage BCDG is enabled to stably move through a fully flat configuration as 0in moves through 180°.

The apparatus of WO 2014/000041 are a significant advance over earlier apparatus such as the Da Vinci apparatus. The link EH can carry a long slender arm such as the cantilever illustrated in Figure 1, thus minimising the bulk (and the associated obstruction and risk of collision) over the patient. The arm could be any convenient shape, e.g. the arm may be an arc concentric to the remote centre of motion. Moreover, the mechanism ACEHGF is also relatively compact.

Whilst the apparatus of WO 2014/000041 are a significant advance over what is otherwise publicly known, the present inventors have continued to improve upon that device.

It is not admitted that any of the information in this patent specification is common general knowledge, or that the person skilled in the art could be reasonably expected to ascertain or understand it, regard it as relevant or combine it in any way before the priority date.

SUMMARY

One aspect of the invention provides an apparatus, for constraining a device to pivot about a remote centre of motion, including a humerus-member mounted to pivot, relative to a torso structure, about a shoulder axis; a radius-member mounted to pivot, relative to the humerus-member, about an elbow axis; a hand-member mounted to pivot, relative to the radius-member, about a wrist axis and being, or being fixable or integral to, the device; a functional four-bar linkage including a humerus-constraint-member mounted to pivot, relative to the humerus-member, about a humerus-constraint axis spaced an elbow-offset distance from the elbow axis; a radius-constraint-member mounted to pivot, relative to the radius-member, about a radius-constraint axis spaced the elbow-offset distance from the elbow axis; and mounted to pivot, relative to the humerus-constraint-member, about an elbow-constraint axis a constraint-offset distance from each of the humerus-constraint axis and the radius-constraint axis; a parallel-keeping mechanism by which the humerus-constraint-member is held parallel to a notional straight line fixed relative to the torso structure; another parallel-keeping mechanism by which the radius-constraint-member is held parallel to a notional straight line fixed relative to the hand-member; a guide-member; a passive mechanical transmission by which two members, of the functional four-bar linkage and mounted to pivot about one of the elbow axis and the elbow-constraint axis, are mutually connected, and the guide-member is constrained to move with a notional centerline centered between the two members; and a translation mechanism connecting the guide-member to, and constraining to move along the notional centerline, the other of the elbow axis and the constraint axis.

For the avoidance of doubt, anatomical terms such as humerus, torso, shoulder, radius, elbow, hand and wrist are used herein as labels to enable the labelled components to be conveniently and uniquely identified. They do not convey any other meaning. By way of example, ‘a humerus-member mounted to pivot, relative to a torso structure, about a shoulder axis’ is not a suggestion that the member bears any similarity to a humerus, that the structure bears any similarity to a torso, and/or that the pivotal mounting bears any similarity to a shoulder. ‘Member’ is used herein in its ordinary sense to refer to an arrangement of rigidly connected matter. The term goes beyond simple integrally-formed members to take in, for example, two integrally-formed members which are rigidly connected to each other, but does not go so far as to take in two separate pieces which are pivotally connected to each other.

The person of ordinary skill in the art will appreciate that there are various approaches, by which two members may be ‘mounted to pivot relative to each other’, many of which do not entail a central pivot pin or anything akin thereto. By way of example, the quoted terminology (and similar terminology) as used herein takes in virtual pivots.

The transmission preferably includes an element mounted to pivot relative to the guide-member; a transmission portion by which the element is constrained to pivot, in relation to the guide-member, in the same direction as one of the two members; and another transmission portion by which the element is constrained to pivot, in relation to the guide-member, in the opposite direction to the other of the two members.

The transmission portion preferably includes a flexible pulling-member. Likewise, the other transmission portion preferably includes a flexible pulling-member.

The two of the members may be the humerus-member and the radius-member.

Another aspect of the invention provides an apparatus, for constraining a device to pivot about a remote centre of motion, including a humerus-member mounted to pivot, relative to a torso structure, about a shoulder axis; a radius-member mounted to pivot, relative to the humerus-member, about an elbow axis; a hand-member mounted to pivot, relative to the radius-member, about a wrist axis and being, or being fixable or integral to, the device; a functional four-bar linkage including a humerus-constraint-member mounted to pivot, relative to the humerus-member, about a humerus-constraint axis spaced an elbow-offset distance from the elbow axis; a radius-constraint-member mounted to pivot, relative to the radius-member, about a radius-constraint axis spaced the elbow-offset distance from the elbow axis; and mounted to pivot, relative to the humerus-constraint-member, about an elbow-constraint axis a constraint-offset distance from each of the humerus-constraint axis and the radius-constraint axis; a parallel-keeping mechanism by which the humerus-constraint-member is held parallel to a notional straight line fixed relative to the torso structure; and another parallel-keeping mechanism by which the radius-constraint-member is held parallel to a notional straight line fixed relative to the hand-member; wherein at least one of the parallel-keeping mechanism and the other parallelkeeping mechanism includes a flexible pulling-member.

The parallel-keeping mechanism preferably includes a flexible pulling-member. Likewise, the other parallel-keeping mechanism preferably includes a flexible pulling-member.

The apparatus preferably includes a driver for driving the apparatus to move the device to pivot about an axis perpendicular to the notional straight line fixed relative to the torso. The driver preferably acts between the torso-member and the humerus-member.

Another aspect of the invention provides an apparatus, for constraining a device to spherically pivot about a remote centre of motion, including a preceding apparatus mounted to pivot about an axis intersecting the remote centre of motion.

Preferably the axis intersecting the remote centre of motion is parallel to, or coincident with, the notional straight line fixed relative to the torso. Most preferably the apparatus includes a driver for driving the preceding apparatus to pivot about the axis intersecting the remote centre of motion.

Another aspect of the invention provides a preceding apparatus when used in surgery.

The preceding apparatus may be a surgical apparatus.

BRIEF DESCRIPTION OF DRAWINGS

Figure 1 schematically illustrates a prior art RCM device;

Figure 2 is a perspective view of a passive mechanical transmission;

Figure 3 is a perspective view of an RCM apparatus at three positions about its range of motion (ROM);

Figure 4 schematically illustrates key components of the RCM device;

Figure 5 schematically illustrates selected components of an RCM device at two points of its ROM;

Figure 6 schematically illustrates an RCM apparatus at two extremes of its ROM; Figure 7 schematically illustrates further detail of an RCM apparatus;

Figure 8 is a plan view of an RCM apparatus in its fully flat configuration.

Figure 9 is a close up view of the functional four bar linkage of the device of Figure 3. DESCRIPTION OF EMBODIMENTS

Figure 3 illustrates a preferred form of RCM apparatus 1. It includes a humerus-member 7 mounted to pivot, relative to torso structure 9, about shoulder axis 11. In this example, each of the torso structure 9 and the humerus-member 7 are U-shaped members. The member 7 is narrower than the member 9 so that it is dimensioned for its free ends to sit between and in register with the free ends of the torso structure 9. A respective pivot pin dowels the free ends on each side of these U-shapes.

The base of the U-shaped humerus 7 is an axle which skewers a radius-member 13. This axle portion thus defines an elbow axis 15 about which the radius 13 is mounted to rotate relative to the humerus 7. A hand-member 17 is pivotally connected to the free end of the radius 13 by a pivot pin. The hand-member 17 could take a wide variety of forms. In this example, it is a Z-shaped member formed of a straight integrally-formed member 17a bolted to an L-shaped member 17b. The hand-member 17 is configured to be fixed relative to the device 3. In this example, it is so configured by the inclusion of a through-hole directed towards the remote centre of motion 5 and through which the tool 3 is passed. The tool is held in place with a pair of fasteners 49. In other examples the tool 3 may form part of the device 1. In this example, the tool 3 intersects the remote centre of motion 5. A functional four-bar linkage 21 is associated with the elbow axis 15. ‘Functional four-bar linkage’ is a reference to the four members mounted to pivot relative to each other to function as a four-bar linkage. The term is not limited to four bars mutually connected by four pivot pins, but also takes in more elaborate arrangements including virtual pivots, etc.

In this example, the linkage 21 incorporates a humerus-constraint-member 23, a radius-constraint-member 27 and end portions of the humerus 7 and radius 13. The members 23, 27 have the same length. In this context, the length of the member is defined by the distance between the two pivot axes with which it is associated.

The constraint 23 is dowelled to the humerus 7 to rotate about axis 25 an elbow-offset distance from the elbow axis 15. The constraint 27 is dowelled to pivot, relative to the radius 13 about axis 29, the same elbow-offset distance from the elbow axis 15. In this example, the axis 25 sits on the centerline of the humerus 7 and the axis 29 sits on the centerline of the radius 13. The other ends of the constraints 23, 27 are mutually dowelled by a pivot pin to pivot about an elbow-constraint axis 31.

Given the common length of the elbow-offset distances and the common length of the constraints 23, 27, the functional four-bar linkage 21 is in elevation symmetric about the line 7, 31. Throughout most of its ROM it is elevation kite-shaped as suggested in Figures 4, 5 and 7. As suggested in Figure 6, at the extremes of the ROM the four-bar linkage takes on a triangular shape. At a mid-point of its operation the linkage 21 passes through a fully flat configuration illustrated in Figure 8. In the fully flat configuration, a distance between the axes 15, 31 is at its maximum and the axes 25, 29 are mutually coincident. A parallel-keeping mechanism 33 keeps the member 23 and notional line 35 mutually parallel. In this context, the direction of the member 23 (i.e. that which is parallel to the line 35) is defined by a notional line connecting the axes 25, 31; the external shape of the member 23 is not critical.

In this example, the parallel-keeping mechanism includes a pulley 33a coincident with the axis 25 and fixed relative to the member 23. The mechanism further includes a pulley 33b fixed relative to the torso structure 9 and coincident with the axis 11. A flexible pulling element 33c operatively connects the pulleys 33a, 33b to rotate in the same sense about the member 7 as it moves through its ROM. The flexible pulling element preferably takes the form of a continuous loop. In this example the element 33c takes the form of a toothed belt. A similar parallel-keeping mechanism 37 mutually connects the members 17, 27 to keep the member 27 parallel to a notional straight line 39 fixed relative to the hand-member 17.

Other forms of parallel-keeping mechanisms, such as the parallelograms of Figure 1, are possible.

Whilst an RCM apparatus in line with what has been described thus far could usefully operate through an ROM of 0in from about 60° to almost 180° (i.e. almost to the fully flat configuration) preferred forms of the device are configured to pass smoothly and stably through the fully flat configuration (0in = 180°) for 0in values ranging from about 60° to about 300° corresponding to an output ROM (Figure 6) of about 69°.

To enable the linkage 21 to pass through the fully flat configuration, the device 1 is equipped with a guide-member 41 and a passive mechanical transmission 43. ‘Passive mechanical transmission’ is used herein to refer to an arrangement of mechanical components for transmitting force between the components with which it co-operates. The term excludes arrangements which receive power from external sources and as such is used in contradiction to the term ‘active transmission’ to exclude servos and other motor driven devices.

In this example the guide member 41 is skewered by the axle portion of the humerus 7 and is thus mounted to pivot relative to the humerus. Also coincident with that axle portion are pulleys 43a and 43b. The pulley 43a is a portion of the humerus 7. The pulley 43b is a portion of the radius 13. The transmission 43 further includes pulleys 43c and 43d which are rigidly connected to form a transmission element including the pulleys 43c, 43d and an axle by which the pulleys 43c, 43d are pivotally connected to the member 41. The pulleys 43c, 43d are mounted to pivot about an axis 51. The member 41 controls the spacing of the axes 15, 51. A flexible pulling member in the form of a cable loop operatively connects the pulleys 43a, 43c to each other to form a transmission portion by which the element 43c, 43d is constrained to pivot in relation to the guide member in the same direction as the humerus 7. A flexible pulling element in the form of a cable loop twisted to follow a Figure 8 path operatively connects the pulleys 43b, 43d to each other whereby the member 43c, 43d is constrained to pivot in relation to the guide in the opposite direction to the radius 13.

This passive mechanical transmission, i.e. the pulleys and the cables, connects the humerus 7 to the radius 13 and also serves to constrain the guide-member 41 to follow a notional centre line 45 centered between the members 7, 13.

In the device 1 the pulleys 43a to 43d are simple circular pulleys and are substantially identical to each other. This is not essential. By way of example if pulleys 43a, 43c were both increased in size by the same amount the device 1 would still be operative. The pulleys need not be simple circular pulleys. Other more elaborate shapes are possible.

Indeed passive mechanical transmissions without any form of flexible pulling member are possible. In the example of Figure 2 the passive transmission 43' takes the form of gear train including gears 43a', 43c' meshing with each other and also including gears 43b', 43d' operatively connected to each other by gear 43e' meshing with each of gears 43b', 43d'.

The gears 43c', 43d' are rigidly connected to each other to form a single member.

This element of the transmission is constrained to pivot relative to the guide member 41' in a direction opposite to the humerus 7' and in the same direction to the radius 13'.

Flexible pulling members are preferred over gear trains to avoid the backlash associated with such gear trains. Moreover, the inclusion of such flexible pulling members enables the stiffness of the RCM apparatus to be conveniently tuned by selecting a flexible pulling member having a suitable stiffness. 'Stiffness of the RCM apparatus’ is a reference to the apparatus’s resistance to deformation away from true remote centre of motion functionality. As such, a method of tuning the stiffness of an RCM apparatus is disclosed.

Turning to Figure 9, a slider mechanism 47 connects the guide-member 41 to the elbow-constraint axis 31 and constrains that axis to translate along a notional centre line 45 centered relative to the constraints 23, 27. Again, the constraints are relevantly characterised by the axes they constrain. The notional line 45 is centred between on the one hand a notional line mutually connecting the axes 25, 31 and on the other hand a notional line connecting the axes 29, 31; the exterior profiles of the constraints 23, 27 are not critical.

In this example the slider mechanism 47 takes the form of a member 47a skewered by an axle 31a by which the members 23, 27 are mutually connected. The member 47a has a cylindrical aperture through which a cylindrical extension 41 of the member 41 passes.

Other forms of translation mechanism are possible. The slider mechanism 47 may take other forms such as the telescopic arrangement suggested schematically in Figures 4 to 7.

The members 41,47a have mutually complementary stop formations positioned to move into abutment at each of the two extremes of the ROM suggested in Figure 6.

In this example the axes 11, 15, 19, 25, 29, 31 and 51 are mutually parallel and the apparatus 1 is configured to constrain the device 3 to pivot about an axis parallel to those axes and intercepting the remote centre of motion 5.

Preferred forms of the device incorporate a drive unit acting between the torso portion 9 and the humerus 7 to drive the device 1 through its ROM. It will be appreciated that this one input is enough to fully constrain the device. Furthermore it will be also be appreciated that the input could instead be applied at another point of the mechanism.

Preferred forms of the device 1 are also mounted to pivot about the notional line 35, which line is fixed relative to the torso portion 9 and intersects the remote centre of motion 5. Preferably the device 1 is driven by an electromechanical driver to so rotate. As such by controlling only two drivers the device 3 can be controlled to spherically pivot about the remote centre of motion 5.

It will be observed that relative to the inventors' earlier work of Figure 1 the linkages FG and GH have each been replaced by a respective cable loop. This has reduced the bulk of the device 1 not only because the links FG and GH are no longer present but also because there is no need for additional linkages to address the singularities associated with the parallelograms ABGF, DEHG passing through the fully flat configuration. This replacement also gives scope to tune the stiffness of the apparatus.

The invention is not limited to the described examples. Other variants are possible. By way of example the guide member 41, transmission 43 and slider 47 could be essentially reversed so that the pulleys 43a, 43b are mutually connected to the constraints 23, 27.

The inventors also note that the transmission 43 by which the member 41 is constrained to follow the centre line of the member 7, 13 may also find application in other contexts, potentially including contexts entirely unrelated to RCM apparatus.

Claims (16)

1. An apparatus, for constraining a device to pivot about a remote centre of motion, including a humerus-member mounted to pivot, relative to a torso structure, about a shoulder axis; a radius-member mounted to pivot, relative to the humerus-member, about an elbow axis; a hand-member mounted to pivot, relative to the radius-member, about a wrist axis and being, or being fixable or integral to, the device; a functional four-bar linkage including a humerus-constraint-member mounted to pivot, relative to the humerus-member, about a humerus-constraint axis spaced an elbow-offset distance from the elbow axis; a radius-constraint-member mounted to pivot, relative to the radius-member, about a radius-constraint axis spaced the elbow-offset distance from the elbow axis; and mounted to pivot, relative to the humerus-constraint-member, about an elbow-constraint axis a constraint-offset distance from each of the humerus-constraint axis and the radius-constraint axis; a parallel-keeping mechanism by which the humerus-constraint-member is held parallel to a notional straight line fixed relative to the torso structure; another parallel-keeping mechanism by which the radius-constraint-member is held parallel to a notional straight line fixed relative to the hand-member; a guide-member; a passive mechanical transmission by which two members, of the functional four-bar linkage and mounted to pivot about one of the elbow axis and the elbow-constraint axis, are mutually connected, and the guide-member is constrained to move with a notional centerline centered between the two members; and a translation mechanism connecting the guide-member to, and constraining to move along the notional centerline, the other of the elbow axis and the constraint axis.

2. The apparatus of claim 1 wherein the transmission includes an element mounted to pivot relative to the guide-member; a transmission portion by which the element is constrained to pivot, in relation to the guide-member, in the same direction as one of the two members; and another transmission portion by which the element is constrained to pivot, in relation to the guide-member, in the opposite direction to the other of the two members.

3. The apparatus of claim 2 wherein the transmission portion includes a flexible pulling-member.

4. The apparatus of claim 2 or 3 wherein the other transmission portion includes a flexible pulling-member.

5. The apparatus of any one of claims 1 to 4 wherein the two of the members are the humerus-member and the radius-member.

6. The apparatus of any one of claims 1 to 5 wherein at least one of the parallelkeeping mechanism and the other parallel-keeping mechanism includes a flexible pulling-member.

7. An apparatus, for constraining a device to pivot about a remote centre of motion, including a humerus-member mounted to pivot, relative to a torso structure, about a shoulder axis; a radius-member mounted to pivot, relative to the humerus-member, about an elbow axis; a hand-member mounted to pivot, relative to the radius-member, about a wrist axis and being, or being fixable or integral to, the device; a functional four-bar linkage including a humerus-constraint-member mounted to pivot, relative to the humerus-member, about a humerus-constraint axis spaced an elbow-offset distance from the elbow axis; a radius-constraint-member mounted to pivot, relative to the radius-member, about a radius-constraint axis spaced the elbow-offset distance from the elbow axis; and mounted to pivot, relative to the humerus-constraint-member, about an elbow-constraint axis a constraint-offset distance from each of the humerus-constraint axis and the radius-constraint axis; a parallel-keeping mechanism by which the humerus-constraint-member is held parallel to a notional straight line fixed relative to the torso structure; and another parallel-keeping mechanism by which the radius-constraint-member is held parallel to a notional straight line fixed relative to the hand-member; wherein at least one of the parallel-keeping mechanism and the other parallelkeeping mechanism includes a flexible pulling-member.

8. The apparatus of any one of claims 1 to 7 wherein the parallel-keeping mechanism includes a flexible pulling-member.

9. The apparatus of any one of claims 1 to 8 wherein the other parallel-keeping mechanism includes a flexible pulling-member.

10. The apparatus of any one of claims 1 to 9 including a driver for driving the apparatus to move the device to pivot about an axis perpendicular to the notional straight line fixed relative to the torso.

11. The apparatus of claim 10 wherein the driver acts between the torso-member and the humerus-member.

12. An apparatus, for constraining a device to spherically pivot about a remote centre of motion, including the apparatus of any one of claims 1 to 11 mounted to pivot about an axis intersecting the remote centre of motion.

13. The apparatus of claim 12 wherein the axis intersecting the remote centre of motion is parallel to, or coincident with, the notional straight line fixed relative to the torso.

14. The apparatus of claim 12 or 13 including a driver for driving the apparatus of any one of claims 1 to 11 to pivot about the axis intersecting the remote centre of motion.

15. The apparatus of any one of claims 1 to 14 when used in surgery.

16. The apparatus of any one of claims 1 to 14 being a surgical apparatus.