WO2014000041A1

WO2014000041A1 - Mechanical remote centre of motion

Info

Publication number: WO2014000041A1
Application number: PCT/AU2013/000697
Authority: WO
Inventors: Chao Chen
Original assignee: Monash University
Priority date: 2012-06-29
Filing date: 2013-06-27
Publication date: 2014-01-03

Abstract

An apparatus for constraining a device (7) to pivot about a remote centre of motion (0). The apparatus includes a first member (1). A second member (2) is pivotally connected to the first member at a first pivotal connection (1'). A third member (3) is pivotally connected to the first member at a second pivotal connection (2'). A fourth member (4) is pivotally connected to the second member at a third pivotal connection (3'). A fifth member (5) is pivotally connected to the third member at a fourth pivotal connection (4'). A sixth member 6 (a) is pivotally connected to the fourth member at a fifth pivotal connection 5', (b) is pivotally connected to the fifth member at a sixth pivotal connection 6', and (c) is, or is fixable or integral to, the device. The apparatus further includes a mechanism for in substance maintaining a notional straight line, from the first pivotal connection to the third pivotal connection, parallel to a notional straight line from the second pivotal connection to the fourth pivotal connection. The apparatus further includes a mechanism for in substance maintaining a notional straight line, from the third pivotal connection to the fifth pivotal connection, parallel to a notional straight line from the fourth pivotal connection to the sixth pivotal connection. Each pivotal connection has a respective pivot axis. The pivot axes of the first pivotal connection and the second pivotal connection in substance lie in a common plane (9). The pivot axes of the third pivotal connection and the fourth pivotal connection in substance lie in another common plane (10). The pivot axes of the fifth pivotal connection and the sixth pivotal connection in substance lie in another common plane (11). The common planes in substance intersect at the remote centre of motion.

Description

MECHANICAL REMOTE CENTRE OF MOTION FIELD OF THE INVENTION

This invention relates to apparatus for constraining devices to pivot about remote centres of motion and to uses thereof. The invention will be described in relation to surgery, although various embodiment of the invention may suit other applications.

BACKGROUND TO THE INVENTION

"Keyhole surgery" refers to surgery conducted through a very small incision. By way of example, the incision may be no bigger than is required to accommodate an 8mm diameter shaft of a surgical device. To complete the surgery the device is rotated about a centre of motion coincident with the incision point, allowing portions of the surgical device internal to the patient to be moved as required without damaging the incision point.

Keyhole surgery has significant advantages including faster healing and reduced infection rates.

During some surgeries the surgeon will simply manipulate a surgical device by hand about an approximate centre of motion. During more elaborate surgeries, some of which involve multiple keyholes, an apparatus is employed to constrain the device to move about the remote centre of motion. The existing constraint devices fall into two broad categories: "software driven" devices have mechanical components having multiple degrees of freedom which are driven electronically to move about the remote centre of motion as required; and "mechanical constraints" which are mechanically limited to a range of motion about the remote centre of motion.

Software driven devices carry the risk of injury to the patient in the event of a problem in their electronics or software, e.g. a programming error. On the other hand, existing mechanical constraints are bulky and cumbersome, and so present a risk of collision between multiple devices in the crowded work area above the patient.

It is an object of at least a preferred form of the invention to provide a reliable constraint having reduced bulk in the work area.

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 at the priority date.

SUMMARY

One aspect of the invention provides an apparatus for constraining a device to pivot about a remote centre of motion, the apparatus including a first member; a second member mounted to pivot relative to the first member about a first pivot axis; a third member mounted to pivot relative to the first member about a second pivot axis; a fourth member mounted to pivot relative to the second member about a third pivot axis; a fifth member mounted to pivot relative to the third member about a fourth pivot axis; a sixth member mounted to pivot relative to the fourth member about a fifth pivot axis, mounted to pivot relative to the fifth member about a sixth pivot axis, and being, or being fixable or integral to, the device; a mechanism for in substance maintaining a notional straight line, from the first pivot axis to the third pivot axis, parallel to a notional straight line from the second pivot axis to the fourth pivot axis; a mechanism for in substance maintaining a notional straight line, from the third pivot axis to the fifth pivot axis, parallel to a notional straight line from the fourth pivot axis to the sixth pivot axis; wherein the first pivot axis and the second pivot axis in substance lie in a common plane; the third pivot axis and the fourth pivot axis in substance lie in another common plane; the fifth pivot axis and the sixth pivot axis in substance lie in another common plane; and the common planes in substance intersect at the remote centre of motion.

The sixth member may include an elongate portion for spacing an operative portion of the device from the other members, which elongate portion preferably in substance extends circumferentially about the remote centre of motion. Preferably the mechanism for in substance maintaining the notional straight line from the first pivot axis to the third pivot axis includes a further member mounted to pivot relative to the second member and the third member about respective pivot axes spaced relative to the first pivot axis and the second pivot axis to in substance define a functional parallelogram.

Optionally the mechanism for in substance maintaining the notional straight line from the first pivot axis to the third pivot axis includes another further member mounted to pivot relative to the second member and the third member at respective pivot axes spaced relative to the first pivot axis and the second pivot axis to in substance define another functional parallelogram.

Preferably the mechanism for in substance maintaining the notional straight line from the third pivot axis to the fifth pivot axis includes a further member mounted to pivot relative to the fourth member and the fifth member about respective axes spaced relative to the fifth pivot axis and the sixth pivot axis to in substance define a functional parallelogram.

Optionally the mechanism for in substance maintaining the notional straight line from the third pivot axis to the fifth pivot axis includes another further member mounted to pivot relative to the fourth member and the fifth member about respective axes spaced relative to the fifth pivot axis and the sixth pivot axis to in substance define another functional parallelogram.

Preferred forms of the apparatus are configured for the notional straight line from the first pivot axis to the third pivot axis to pivot through the common plane in which the first pivot axis and the second pivot axis in substance lie. The apparatus may further include a drive mechanism, e.g. electro-mechanical drive mechanism, for driving the device to move about the remote centre of motion. Preferably the drive mechanism acts on the first member and at least one of the second member and the third member to drive the first member relative to the at least one of the second member and the third member. The drive mechanism preferably acts on at least one of the second member and the third member; and at least one of the fourth member and the fifth member to drive the at least one of the second member and the third member relative to the at least one of the fourth member and the fifth member. Preferably the first member is mounted, and most preferably the drive mechanism is configured to drive the first member, to pivot about an axis which in substance extends radially from the remote centre of motion such that the device is constrained to pivot spherically about the remote centre of motion. Of course this mode of pivoting would also be useful without a drive mechanism so configured. Another aspect of the invention provides an apparatus for constraining a device to pivot about a remote centre of motion, the apparatus including a member including an elongate portion extending circumferentially about the remote centre of motion, wherein the member is, or is fixable or integral to, the device and is constrained to pivot about the remote centre of motion; and the elongate portion spaces an operative portion of the device from other portions of the apparatus for reduced collisions within a work area.

Also disclosed is an apparatus for constraining a device to pivot about a remote centre of motion, the apparatus including an outer arm; an inner arm between the outer arm and the remote centre of motion; wherein the arms each include a first arm member pivotally connected to a forearm member at an elbow; each first arm member is pivotally connected to a base member at respective shoulders; each forearm member is pivotally connected to a hand member at respective wrists; a mechanism for in substance holding the first arm members parallel; a mechanism for in substance holding the forearm members parallel; wherein the hand member is, or is fixable or integral to, the device; the shoulders, elbows and wrists each have a respective pivot axis; the pivot axes of the shoulders in substance lie in a common plane; the pivot axes of the elbows in substance lie in another common plane; the pivot axes of the wrists in substance lie in another common plane; and the common planes in substance intersect at the remote centre of motion. The above apparatus may be surgical apparatus. Another aspect of the invention provides an above apparatus when used in surgery. BRIEF DESCRIPTION OF DRAWINGS The figures illustrate exemplary apparatus.

Figure 1 is a schematic side view of an apparatus in accordance with a preferred form of the invention; Figures 2a to 2d schematically illustrate the apparatus moving through a range of motion;

Figures 3a and 3b schematically illustrate the apparatus in two positions in which its arcuate arm is extended to differing degrees; and Figure 4 is a schematic side view of an alternative exemplary apparatus;

Figures 5a to 5f are perspective views of an apparatus moving through a range of movement;

Figure 5g is a close up view of a portion of Figure 5a;

Figure 6 is a perspective of the apparatus of Figures 5a to 5g in another orientation; Figure 7 is a perspective view of a drive unit;

Figure 8 is side view of an apparatus;

Figure 9 is another side view of the apparatus of Figure 8; and

Figure 10 is a close up plan view of a portion of the apparatus of Figures 8 and 9 in a fully folded position. DETAILED DESCRIPTION OF EMBODIMENTS

The apparatus of Figure 1 includes links 1 , 2, 3, 4, 5 and 6 joined at pivotal connections 1 ', 2 ', 3', 4', 5' and 6' to move a device 7 to pivot about a remote centre of motion 0.

Link 1 is pivotally connected to link 2 at pivotal connection 1 '. The pivotal connection 1 ' (and the other pivotal connections) may take a variety of forms. By way of example, each of the links 1 , 2 may include a respective aperture, which apertures are doweled by a common pin such that each of the links 1 , 2 is mounted to pivot relative to the other about the axis of the pin. Alternatively more elaborate pivotal connections, such as virtual pivots, are also possible.

Link 1 is pivotally connected to link 3 at pivotal connection 2'. Link 2 is pivotally connected to link 4 at connection 3' such that links 2 and 4 together define an arm including a "shoulder joint" 1 ' and an "elbow" 3'. This arm is connected to the final link 6 by the connection 5' which forms a wrist.

Likewise links 3 and 5 form an arm including a shoulder 2', elbow 4' and wrist 6'. The arm 3, 5 is spaced inwardly (i.e. towards the remote centre of motion 0) from the arm 2, 4. A mechanism in the form of a link 8a is provided to mutually constrain the upper arm portions 2, 3 (i.e. the portions adjacent the shoulders 1 ', 2') to maintain the arms 2, 3 in parallel relation. The link 8a is pivotally connected to the link 3 at pivotal connection 4' (although it may be connected at any other convenient location along the link 3 as in Figure 4). The link 8a is pivotally connected to link 2 at the pivotal connection 8a'. The link 8a is of the same length as link 1 and the pivotal connection 8a is positioned at a distance along the link 2 equivalent to the length of the link 3 whereby the pivotal connections 1 ', 2', 4' and 8a' together define the vertices of a parallelogram.

There are other ways to keep the parallelism between links 2 and 3, and between links 4 and 5. For example transmissions (such as gears, belt-wheels or cable-pulleys) on joints 1 ' and 2', and joints 5' and 6 may be employed to maintain the parallelism.

As used herein, except as the context requires otherwise, "link" (or member or similar term) takes in multi-component structures, the length of a link (or member or similar term) refers to the spacing of its pivotal connections, and the direction of a link (or member or similar term) to be considered when assessing whether a link is parallel to another link is the direction of a notional straight line connecting its pivotal connections. In particular, whilst the links are illustrated in Figure 1 as simple unitary linear members extending between the connection points, in practice the links will likely have more elaborate shapes and the pivotal connections need not be mounted along the centre line of the links.

In a manner analogous to the link 8a, the link 8b is pivotally connected to the link 4 at pivotal connection 8b' and to the link 5 at pivotal connection 4' to form a mechanism to keep links 4 and 5 mutually parallel.

The pivot axes of connections 1 ', 2' lie in a common plane 9, the pivot axes of connections 3', 4' lie in a common plane 10, and pivot axes of connections 5', 6' lie in a common plane 1 1. The planes 9, 10 and 1 1 are each normal to the page and intersect at an axis normal to the page at the remote centre of motion 0. This remote centre of motion "axis" is fixed relative to the base, or "shoulder", link 1. In a surgical application the remote centre of motion 1 may pass through a trocar at the incision point and the link 1 mounted to a fixture off to the side of the operating table and fixed relative to the patient.

Following this geometry the link 6 is constrained by the other links to rotate about the remote centre of motion.

The link 6 includes a base portion 6a extending between connections 5', 6' and an elongate portion 6b in the form of a curved arm 6b extending from the base portion 6a. The arm 6b carries the device 7 at its terminal end. Because the link 6 is constrained to move about the remote centre of motion it need not have any moving parts. Thus the arm 6b is desirably a simple, slender, rigid arm extending from linkages 1 to 6a into the work space above the remote centre of motion 0.

In at least preferred forms of the invention, this simple, slender arm 6b occupies significantly less space in the potentially crowded work area above the remote centre of motion 0 than various existing mechanical constraints. Of course it is also contemplated that components 6a, 6b, 7 may be integrated in a single integral piece. Desirably, the size of the linkage mechanism 1 to 6a does not vary in proportion to its distance from the desired centre of motion. In preferred forms of the invention:

• the ratio of the lengths of the upper arms,

• the ratio of the lengths of the forearms, · the ratio of the distances of connections 1 ', 2' to the remote centre of motion 0, and

• the ratio of the distances of connections 5', 6' to the remote centre of motion 0 have a common value.

Variants of the described apparatus may incorporate a drive mechanism for driving the device 7 about the remote centre of motion 0. Alternatively one or both of the apparatus and the device may be manipulate by hand to move as desired. The apparatus preferably includes various arrangements for retaining a position to which the device 7 is moved.

Preferably the drive mechanism acts between the base member 1 and one of the links 2, 3 pivotally connected thereto. By way of example, a drive mechanism may be arranged to drive the link 2 so as to vary the angle Θ.

Preferred forms of the apparatus include a mounting arrangement by which the link 1 , and the other components depending therefrom, pivot about an axis 12 radial to the remote centre of motion 0 whereby the device is constrained to pivot spherically about the remote centre of motion 0. In this embodiment the axis 12 lies in the plane 9 and in the plane of the page. A further drive mechanism may be associated with this range of motion. The drive mechanism(s) may be driven by software (or otherwise electronically driven) to suit robotic surgery.

It is also contemplated that the simple cantilevered arm 6b may be extendible, e.g. so that its reach along its arcuate path away from the links 1 to 5 may be extended as in the transition from Figures 3a to Figures 3b, to approach the remote centre of motion from a different angle. The apparatus may incorporate a sensor for determining the extent to which the arm 6b is extended. By way of example, a rotary sensor may be connected to the moving part of the arm 6b so that structure parameters can be updated online for remote surgery. Figures 2a to 2d schematically illustrate an apparatus moving through a range of motion in which the angle Θ (see Figure 1 ) varies from about 70° to about 160° and

correspondingly an output angle a varies from about 60° to about 15°.

Figures 5a to 10 illustrate apparatus having an extended range of movement. Figures 5a to 6 illustrate an apparatus incorporating a planetary bevel gear drive illustrated in Figure 7. Figures 8 to 10 illustrate a similar surgical apparatus instead incorporating a spur gear drive.

Figures 5a to 5f are perspective views of an apparatus moving though a range of motion in which the angle Θ (see Figure 1 ) varies from about 70° (in Figure 5a) to about 290° (in Figure 5f) and the output angle a correspondingly varies from about 60° to about -60°. The components of the arm of the apparatus are detailed in Figure 5g. The extended range of movement extends the range of angles at which an operative portion of a device (not shown) carried by the apparatus may approach (and pass through) the remote centre motion.

The extended range of movement requires the apparatus pass through a "fully folded" (i.e. 0=180°) position illustrated in Figure 5d; i.e. the notional straight line from the first pivotal connection 1 ' to the third pivotal connection 3' pivots through the common plane 9 in which the pivot axes of the first pivotal connection 1 ' and the second pivotal connection 2' in substance lie.

The major components of the apparatus of Figures 5a to 6 correspond to the

components schematically illustrated in Figure 1 and are assigned the same reference numerals. The base member 1 takes the form of a fork (or yoke) including a pair of laterally spaced arms. The spaced arms project horizontally. Outer upper arm link 2 is pivotally connected to one of the arms via an axle forming pivotal connection 1 '. A further link 2a is pivotally connected to the other arm via another axle to form pivotal connection 1 a'. The axes of the connections 1 ', 1 a' are coincident and spaced from these axes the links 2, 2a are dowelled by a common axle to pivotally connect these links to the outer forearm link 4. Thus links 2, 2a move in unison, and each of the links 2, 2a is "pivotally connected" and "mounted to pivot relative" to each and both of the arms of base link 1 as the quoted terms and similar terms are used herein.

As in Figure 1 , when the arms 2, 4 and 3, 5 are above or below the fully folded position: » the axes of pivotal connections 1 ', 2', 8a' (Figure 9), 4' define a functional

parallelogram to hold link 2 (and link 2a) parallel to link 3;

• the axes of pivotal connections 8b', 4', 5', 6' define another functional

parallelogram to hold link 4 parallel to link 5;

• there is 1 : 1 correspondence between the angle Θ and the position of the link 6 (and positions of the intervening links); and in particular

• there is a 1 :1 correspondence between the angle Θ at the shoulder and the angle at the elbow (between links 2 and 4).

A drive unit 13a (Figure 5a) acts on link 1 and link 2a to directly control the angle Θ. The drive unit includes • a motor 13a' carried by the link 1 and

• a wheel 13a" fixed relative the links 2, 2a.

The motor 13a' drives the wheel 13a" via a belt (not shown).

Given the 1 : 1 correspondences, aside from in the fully folded position, the motor 13a fully defines the position of the link 6 (and any device carried thereby) relative to the link 1.

The apparatus includes additional links 8c, 8f and a drive unit 13b to control link 6 relative to link 1 whilst the arms 2, 4 and 3, 5 pass through the fully folded position.

In the fully folded position the pivot axes of pivotal connections 1 ', 2 ', 3', 4', 5' and 6' lie in the common plane 9. In particular, the axes of the functional parallelogram 1 ', 2', 8a', 4' lie in a common plane and the axes of the functional parallelogram 8b', 4', 5', 6' lie in a common plane. But for components 8c, 8f and 13b this geometry would result in a "singularity" such that at the fully folded position: a) a change in the angle Θ at the shoulder (i.e. between 1 and 2) could cause the angle at the elbow (i.e. between 2 and 4) to vary unpredictably in one direction or the other; b) a change in the angle between links 8b and 4 could cause the angle between links 5 and 6 to vary unpredictably in one direction or the other; c) a change in the angle Θ between links 1 and 2 could cause the angle between links 3 and 8a (Figure 9) to vary unpredictably in one direction or the other.

Components 13b, 8c and 8f are additional constraints addressing potential problems a), b) and c) respectively. Drive unit 13b (Figure 7) includes an operative portion 13c and a guide portion 13d. The guide portion 13d serves to orient the operative portion 13c. The operative portion 13c includes a motor unit 13e carried by the axle of pivotal connection 3'. The motor unit 13e drives bevel gear (i.e. toothed wheel) 13f to rotate about an axis perpendicular to the axle of the pivotal connection 3', to which axle a pair of bevel gears 13g, 13h are journalled to rotate about. The bevel gears 13g, 13h mesh with so as to be driven by the gear 13f. The gears 13g, 13h thus constitute planetary gears and rotate in opposite directions in response to the motor unit 13e.

Gear 13g is fixed to link 2 and gear 13h is fixed to the link 4 whereby the drive 13b acts on the link 2 and the link 4 to directly control the angle therebetween (i.e. the elbow angle).

Shaft 13i projects from the motor unit 13e in a plane parallel and a direction

perpendicular to the axis of pivotal connection 3'. The shaft 13i projects through a slide block 13 j skewered by the axle of pivotal connection 4'. The shaft 13i slides through the slide block 13 j as the apparatus moves through its range of movement. A respective clamp ring 13k is clamped to the shaft 13i fore and aft of the slide block. The clamp rings define stops to limit the range of the movement.

With co-ordinated control of the drive unit 13a and drive unit 13b, the elbow angle can be controlled as the apparatus passes through the fully folded position. In the variant of Figures 8 to 10, the drive unit 13b is replaced with a drive unit 13b'. The drive unit 13b' incorporates spur gears in place of bevel gears.

Link 8c is a further link included in the mechanism for holding link 4 parallel to link 5 to hold these links parallel as the apparatus moves through the fully folded position. Link 8c: · is mounted to pivot relative to link 4 at pivotal connection 8e; • is mounted to pivot relative to link 5 at pivotal connection 8d; • is the same length as link 8b; and

• runs parallel to link 8b.

The axes of connections 8b', 8d, 8e, and 4' define another functional parallelogram. Pivotal connections 8d, 8e are offset from notional straight lines connecting connection 4' to connection 6' and connection 8b' to 5'. As such, the angles within parallelogram 8b', 8d, 8e, and 4' differ from the angles within parallelogram 8b', 4', 5', 6'. When

parallelogram 8b', 4', 5', 6' flattens to the fully folded position (in which axes 8b', 4', 5', 6' lie in a common plane) the parallelogram 8b', 8d, 8e, and 4' (i.e. the axes 8b', 8d, 8e, and 4' do not lie in a common plane) remains open to continue holding link 4 parallel to link 5.

Link 8f is a further link included in the mechanism for holding link 2 parallel to link 3 to hold these links parallel as the apparatus moves through the fully folded position. Link 8f:

• is mounted to pivot relative to link 2 at pivotal connection 8h; · is mounted to pivot relative to link 3 at pivotal connection 8g;

• is the same length as link 8a;

• runs parallel to link 8a; and

• functions analogously to link 8c.

Figure 10 illustrates the lateral spacing of the links 1 to 6, 8a, 8b, 8c and 8f. The links 8c, 8b are laterally spaced from each other such that they may pass each other as in the transition from Figure 5b to Figure 5c. In contrast, links 8a, 8f are laterally aligned. To avoid interference the spacing of pivot axes 8a', 8g is sufficiently longer than the link 8a to provide a longitudinal separation 15a between the links 8a, 8f as they pass each other in the fully folded position. Likewise the pivots of the forearm are suitably spaced to provide a longitudinal separation 15b between the link 6 and links 8b, 8c.

Base link 1 is mounted to rotate about axis 12 relative to fixed base 14. The fixed base 14 carries a drive unit 131 in the form of a motor configured to rotationally drive the link 1. Figure 5a shows the link 1 oriented such that the arms 2, 4 and 3, 5 extend upwards. Figure 6 shows the link 1 rotated about 135° from the position of Figure 5a so that the arms 2, 4 and 3, 5 extend downwardly at an oblique angle.

The drive units 13a, 13b and 131 together constitute a drive mechanism configured to drive the link 6 (and any device carried thereby) to move spherically about a remote center of motion.

Preferred forms of the apparatus incorporate a control arrangement for controlling the drive mechanism. This arrangement might include a user interface and could be either a centralised arrangement (e.g. as in a single unit which includes a user interface for receiving user input and which sends control signals to the units 13a, 13b and 131) or a set of distributed components (e.g. the drive unit 13b might incorporate a control unit by which it is responsive to the position of the drive unit 13a).

Claims

1. An apparatus for constraining a device to pivot about a remote centre of motion, the apparatus including a first member; a second member mounted to pivot relative to the first member about a first pivot axis; a third member mounted to pivot relative to the first member about a second pivot axis; a fourth member mounted to pivot relative to the second member about a third pivot axis; a fifth member mounted to pivot relative to the third member about a fourth pivot axis; a sixth member mounted to pivot relative to the fourth member about a fifth pivot axis, mounted to pivot relative to the fifth member about a sixth pivot axis, and being, or being fixable or integral to, the device; a mechanism for in substance maintaining a notional straight line, from the first pivot axis to the third pivot axis, parallel to a notional straight line from the second pivot axis to the fourth pivot axis; a mechanism for in substance maintaining a notional straight line, from the third pivot axis to the fifth pivot axis, parallel to a notional straight line from the fourth pivot axis to the sixth pivot axis; wherein the first pivot axis and the second pivot axis in substance lie in a common plane; the third pivot axis and the fourth pivot axis in substance lie in another common plane; the fifth pivot axis and the sixth pivot axis in substance lie in another common plane; and the common planes in substance intersect at the remote centre of motion.

2. The apparatus of claim 1 wherein the sixth member includes an elongate portion for spacing an operative portion of the device from the other members.

3. The apparatus of claim 2 wherein the elongate portion in substance extends circumferentially about the remote centre of motion.

4. The apparatus of claim 1 , 2 or 3 wherein the mechanism for in substance maintaining the notional straight line from the first pivot axis to the third pivot axis includes a further member mounted to pivot relative to the second member and the third member about respective pivot axes spaced relative to the first pivot axis and the second pivot axis to in substance define a functional parallelogram.

5. The apparatus of claim 4 wherein the mechanism for in substance maintaining the notional straight line from the first pivot axis to the third pivot axis includes another further member mounted to pivot relative to the second member and the third member at respective pivot axes spaced relative to the first pivot axis and the second pivot axis to in substance define another functional parallelogram.

6. The apparatus of any one of claims 1 to 5 wherein the mechanism for in substance maintaining the notional straight line from the third pivot axis to the fifth pivot axis includes a further member mounted to pivot relative to the fourth member and the fifth member about respective axes spaced relative to the fifth pivot axis and the sixth pivot axis to in substance define a functional parallelogram.

7. The apparatus of claim 6 wherein the mechanism for in substance maintaining the notional straight line from the third pivot axis to the fifth pivot axis includes another further member mounted to pivot relative to the fourth member and the fifth member about respective axes spaced relative to the fifth pivot axis and the sixth pivot axis to in substance define another functional parallelogram.

8. The apparatus of any one of claims 1 to 7 configured for the notional straight line from the first pivot axis to the third pivot axis to pivot through the common plane in which the first pivot axis and the second pivot axis in substance lie.

9. The apparatus of any one of claims 1 to 8 further including a drive mechanism for driving the device to move about the remote centre of motion.

10. The apparatus of claim 8 wherein the drive mechanism is electro-mechanical.

1 1. The apparatus of claim 9 or 10 wherein the drive mechanism acts on the first member and at least one of the second member and the third member to drive the first member relative to the at least one of the second member and the third member.

12. The apparatus of claim 9, 10 or 1 1 wherein the drive mechanism acts on an or the at least one of the second member and the third member; and at least one of the fourth member and the fifth member; to drive the at least one of the second member and the third member relative to the at least one of the fourth member and the fifth member.

13. The apparatus of any one of claims 9 to 12 wherein the first member is mounted, and the drive mechanism is configured to drive the first member, to pivot about an axis which in substance extends radially from the remote centre of motion such that the device is constrained to pivot spherically about the remote centre of motion.

14. The apparatus of any one of claims 1 to 12 wherein the first member is mounted to pivot about an axis which in substance extends radially from the remote centre of motion such that the device is constrained to pivot spherically about the remote centre of motion.

15. An apparatus for constraining a device to pivot about a remote centre of motion, the apparatus including a member including an elongate portion extending

circumferentially about the remote centre of motion, wherein the member is, or is fixable or integral to, the device and is constrained to pivot about the remote centre of motion; and the elongate portion spaces an operative portion of the device from other portions of the apparatus for reduced collisions within a work area.

16. The apparatus of claim 15 further including a drive mechanism for driving the device to move about the remote centre of motion.

17. The apparatus of claim 16 wherein the drive mechanism is electro-mechanical.

18. The apparatus of any one of claims 15 to 17 wherein the first member is mounted, and the drive mechanism is configured to drive the first member, to pivot about an axis which in substance extends radially from the remote centre of motion such that the device is constrained to pivot spherically about the remote centre of motion.

19. The apparatus of any one of claims 15 to 17 wherein the first member is mounted to pivot about an axis which in substance extends radially from the remote centre of motion such that the device is constrained to pivot spherically about the remote centre of motion.

20. The apparatus of any one of claims 1 to 19 when used in surgery.

21. The apparatus of any one of claims 1 to 19 being a surgical apparatus.