This invention relates to a joint coupling for a movable joint, and more particularly although not exclusively, to a joint coupling for a movable joint forming part of an articulated manipulator which, in turn, forms part of a master controller.

Known remote-control systems comprise a master controller, situated locally to an operator, and a slave device, situated remotely to the operator, wherein the system allows the slave device to be manipulated by the operator at a distance. Such systems may be useful if there is a barrier to direct manipulation. For example, a slave device may be used to carry out a minimally invasive surgical procedure in which direct manipulation of surgical tools by a surgeon is not possible due to restricted access to the patient’s internal tissues and organs. Other examples may include military applications such as bomb disposal, emergency service applications such as search and rescue, and scientific research activities such as carrying out tasks in inhospitable environments (e.g., vacuums or high levels of reactivity) where direct manipulation could be hazardous or impossible.

For demonstrative purposes, the field of remote-control robotic surgical systems will be the focus from here on. However, this does not exclude the invention from being applied to other fields, such as those mentioned above.

In remote robotic surgery, a master controller is needed for transferring a surgeon’s hand motion to a remote robotic instrument motion. Known master controllers comprise two articulated manipulator arms for bimanual (two-handed) control that allows the control of a robotic instrument with each hand simultaneously.

The surgeon holds a handle at the end of each manipulator arm via fingers or the whole hand and moves the handle to control the robotic instruments while he or she monitors the robotic instruments via an endoscope image, for example. The manipulator arms can be classified into two categories: active and passive. An active manipulator arm has a motor to drive each joint and these motors allow the pose of the whole manipulator arm to be maintained regardless of whether the surgeon continues to hold the handle of the manipulator arm. This means that the surgeon can let go of the manipulator arm without risk of the manipulator arm dropping under the effect of gravity and a corresponding motion being replicated by the robotic instrument with the potential of harming a patient. Hence, the risk associated with dropping a manipulator arm handle is reduced and the surgeon may readily pause control of the robotic instrument to carry out a different task.

However, known active manipulator arms are bulky due to the complex components required to drive each joint during use. The drive of the motors can also bias the motion of a surgeon's hand away from the intended motion, which can reduce the accuracy and precision achievable by the surgeon.

On the other hand, passive manipulator arms measure the position of each joint in the arm but do not actively drive each joint. This means that the manipulator arm will return to a ‘floppy’ state when the surgeon’s hand releases the handle, and the manipulator arm will drop under the effect of gravity.

To negate the fact that a passive manipulator arm returns to a floppy state when released by the operator, known passive manipulator arms are lockable. In short, the manipulator arms are configured so that each joint in the manipulator arm is locked when the handle is released and are unlocked only when an operator re-grasps the handle or otherwise triggers disengagement of the locks.

According to a first aspect of the invention there is provided a joint coupling for a movable joint, the joint coupling comprising: a first body comprising a first formation; a second body movable relative to the first body, the second body comprising a second formation slidably engageable with the first formation; a cavity formed by one or more of the first and second bodies, the cavity having a length along which at least one of the first and second formations can travel on movement of the second body relative to the first body; and first and second resiliently compressible members received within the cavity in a partially compressed configuration, the first and second resiliently compressible members separated from one another by the first and second formations thereby biasing the first and second bodies towards a balanced configuration in which the first and second formations are aligned with one another. In use, such a joint coupling may be applied to a movable joint comprising a first limb and a second limb that are movable with respect to one another and, also, lockable in a particular configuration depending on the intent of a user. More specifically, the first body of the joint coupling may be coupled to the first limb and the second body may be coupled to the second limb.

If no force is acting on the joint coupling in a direction that might cause the second body to move relative to the first body (or vice versa) then the first and second bodies will hold the balanced configuration, in which the first and second formations are aligned or, at least, substantially aligned bearing in mind manufacturing tolerances. This means the movable joint will hold its intended position.

If a force is applied to one or more of the first and second bodies in a direction that might cause the second body to move relative to the first body (or vice versa), but the force is not large enough to cause further compression of the first or the second resiliently compressible member, the first and second bodies will continue to hold the balanced configuration. This rigidity of the joint when small forces are being applied is useful because it prevents a locked movable joint from moving away from its intended position at the slightest touch or merely due to the effect of gravity, for example. The rigidity of the joint coupling also means that when the movable joint is unlocked and being operated by a user, no backlash is introduced to the movable joint by the presence of the joint coupling.

If a force is applied to one or more of the first and second bodies in a direction that might cause the second body to move relative to the first body (or vice versa), and is large enough to cause further compression of the first or the second resiliently compressible member, the movable joint will be moved accordingly.

For example, if such a force were applied to the second body in a direction suitable to move the second body relative to the first body, that force may be transferred from the second body to one of the first and second resiliently compressible members via the second formation and, thereby, cause further compression of the respective resiliently compressible member. The further compression of the respective resiliently compressible member allows the second formation to move away from alignment with the first formation and, hence, allows the second body to move relative to the first body. However, once the force is reduced to the extent that the respective resiliently compressible member may expand, the second formation will be moved back into alignment with the first formation and the first and second bodies will be returned to the balanced configuration.

This flexing of the joint coupling, when sufficient force is applied, greatly reduces the likelihood of a sudden impact causing a failure of the locked movable joint due to stresses building up at a fragile component of the movable joint, such as the means by which the joint is locked or example. Meanwhile, the ability for the joint coupling to return to its original (balanced) configuration, once the applied force has been sufficiently reduced, avoids the need for a user to return the movable joint to its intended configuration. This is particularly beneficial if the movable joint forms part of a manipulator used to remotely control a robot as the robot will not require recalibration to a new configuration of the manipulator.

Accordingly, by means of the invention, a movable joint may be coupled in such a way that, when locked or otherwise immobilised in a particular configuration, the movable joint remains rigid against small forces acting on it but is also resiliently flexible when larger forces are applied.

In embodiments of the invention, each of the first and second resiliently compressible members may have a predefined restoring force such that an applied force exceeding the predefined restoring force of the first or second resiliently compressible member is required to cause further compression of the respective resiliently compressible member to move the first and second bodies away from the balanced configuration.

In such embodiments of the invention, the predefined restoring force of each of the first and second resiliently compressible members may depend on the size, material and/or configuration of that resiliently compressible member. Accordingly, through selection of each resiliently compressible member, the predefined restoring force may be defined such that a suitable amount of force is required to further compress the respective resiliently compressible member. For example, the predefined restoring force may be defined to ensure that the weight of an articulated manipulator comprising the joint coupling is not sufficient to cause a force that could further compress the respective resiliently compressible member. In some embodiments of the invention, the predefined restoring force may be the same for each of the first and second resiliently compressible members in order that the joint coupling is equally resilient to movement of the second body relative to the first body (or vice versa) in either direction.

In other embodiments of the invention, the predefined restoring force may be different for each of the first and second resiliently compressible members in order that the joint coupling acts differently depending on the direction of a force applied to it. For example, it might be the case that, in use, one resiliently compressible member is always acting against gravity in order to maintain the balanced configuration while the other resiliently compressible member is always working with gravity. Accordingly, the predefined restoring force of each resiliently compressible member may be defined to substantially eliminate the effect of gravity on the movable joint.

The first and second formations may be any shape suitable to allow the first and second resiliently compressible members to exert a force against them, thereby biasing the first and second formations towards alignment with one another.

Each of the first and second formations may comprise first and second faces wherein each of the first and second resiliently compressible members may be abuttable against the respective face of each of the first and second formations. The abutment of each of the first and second resiliently compressible members against the respective face of one or both of the first and second formations may ensure that the resiliently compressible member reliably exerts a force against at least one of the first and second formations.

In such embodiments of the invention, when the first and second bodies are positioned in the balanced configuration, the first faces of the first and second formations may be aligned with one another and the second faces of the first and second formations may also be aligned with one another.

In embodiments of the invention, the first and second formations may be interlockable, each having at least one portion which overlaps at least one portion of the other formation. This may ensure that each of the first and second resiliently compressible members is abuttable against the respective face of each of the first and second formations with there being a plurality of contact points between the resiliently compressible member and the formation face.

The interlockable first and second formations may, further, be configured such that there is at least three separate contact points between each resiliently compressible member and the respective face of each formation and, optionally, such that the at least three contact points are substantially evenly spaced apart from one another. By providing a plurality of evenly spaced contact points, each resiliently compressible member may abut the respective face of each formation stably and reliably, with reduced risk of the resiliently compressible member deforming and either slipping past the face of a formation or becoming jammed within the cavity.

In some embodiments of the invention, the second body may be rotatably movable relative to the first body and the first and second formations may be configured to slide past one another tangentially.

Such embodiments of the invention may be useful for coupling rotatable joints. For example, the joint coupling may be used to couple a first limb to a second limb which pivots relative to the first limb (similarly to an elbow or a hinge). The joint coupling may also be used to couple a rotatable joint in which a first limb is axially rotatable relative to a second limb (similarly to a doorknob).

In other embodiments of the invention, the second body may be linearly movable relative to the first body and the first and second formations may be configured to slide past one another translationally.

Such embodiments of the invention may be useful for coupling a linearly movable joint in which a first limb moves telescopically relative to a second limb.

It is to be understood that the term “torque” may be used with respect to embodiments of the inventions that are rotatably movable and the term “force” may used with respect to embodiments of the invention that are linearly movable. Further, these terms are essentially interchangeable within the context of this invention, particularly in terms of the overall functionality.

In embodiments of the invention, each of first and second resiliently compressible members may comprise a spring or elastomeric block. Specific characteristics of the spring or elastomeric block may be selected to define the restoring force of that resiliently compressible member. For example, for a spring, characteristics such as the number of coils may be adapted to vary the spring’s resilience to compression. For an elastomeric block, the material composition may be selected to provide the desired resilience to compression. The elastomeric block may comprise one or more of the following elastomeric materials: rubber, silicone, nitrile, vinyl and neoprene.

In embodiments of the invention, the first and second bodies may comprise a plurality of first and second formations, and the joint coupling may comprise a respective plurality of cavities and first and second resiliently compressible members.

In such embodiments of the invention, the plurality of first resiliently compressible members may work in unison to bias the first and second formations towards alignment with respect to one direction of movement of the second body relative to the first body. Similarly, the plurality of second resiliently compressible members may work in unison to bias the first and second formations towards alignment with respect to an opposite direction of movement of the second body relative to the first body.

This means that, in order to move the second body relative to the first body, it may be necessary to apply a force that exceeds the cumulative predefined restoring force of the plurality of first or second resiliently compressible members.

By incorporating a plurality of first and second resiliently compressible members it is therefore possible to increase the joint coupling’s overall resilience to movement, particularly if only a small range of movement is to be allowed by the joint coupling.

In embodiments the joint coupling may further comprise a third body coupled to the first body, wherein: the first body may comprise a first gripping surface and the third body may comprise a second gripping surface; and the first and second gripping surfaces may be configured to grip a limb of a movable joint with a predefined gripping force such that an applied force exceeding the predefined gripping force is required to move the joint coupling relative to the limb of the movable joint.

In some such embodiments, the joint coupling may be linearly movable relative to the limb of the movable joint. In other such embodiments, the joint coupling may be rotatably movable relative to the limb of the movable joint. It is to be understood that the term ‘predefined gripping force’ may be used interchangeably with the term ‘predefined gripping torque’ as appropriate for the type of movement available. For example, the first and second gripping surfaces may be configured to grip a limb of a movable joint with a predefined gripping torque such that an applied torque exceeding the predefined gripping torque is required to rotate the joint coupling relative to the limb of the movable joint.

In use, a joint coupling according to such embodiments of the invention may be applied to a movable joint comprising a first limb and a second limb that are movable with respect to one another and, also, lockable in a particular configuration depending on the intent of a user. More specifically, the first body of the joint coupling may be movably coupled to the first limb by way of the first and third bodies gripping the first limb. Meanwhile, the second body may be coupled to the second limb.

In situations where no force exceeding the predefined gripping force is acting on the joint coupling in a direction that might cause the second body to move relative to the first body (or vice versa), the joint coupling will either remain rigid or flex, as described above. In such situations, the relationship between the first and second limbs essentially mirrors the relationship between the first and second bodies. In other words, the movable joint is rigid when the joint coupling is rigid but when the joint coupling flexes, so too does the movable joint.

However, if a force is applied to one or more of the first and second bodies in a direction that might cause the second body to move relative to the first body (or vice versa), and exceeds the predefined gripping force, the first and third bodies may lose traction against the first limb. Once traction is lost, the entire joint coupling is movable relative to the first limb and, therefore, the second limb is also movable relative to the first limb.

This ability for the joint coupling to ‘slip’ relative to a limb that it is gripping prevents large forces, which might fully compress one of the first and second resiliently compressible members, from causing damage to a locked movable joint. Such a force might be accidentally applied by a person attempting to move the articulated manipulator without first unlocking it, for example.

Traction between the first and third bodies and the limb may be restored once the force being applied reduces below the predefined gripping force. However, any displacement of the second limb relative to the first limb which occurred while traction had been lost may not be recovered. Therefore, if the movable joint forms part of a manipulator used to remotely control a robot, the robot may require recalibration to a new configuration of the manipulator. That being said, the surgical robot may be returned to an operable state through recalibration much more quickly than would be the case if an excessive force applied to the manipulator has caused it to break.

In embodiments of the invention, the joint coupling may further comprise a tightening mechanism adjustably coupling the third body to the first body. In such embodiments of the invention, the tightening mechanism may be tightened or loosened to adjust the predefined gripping force.

The tightening mechanism may be any mechanism suitable to adjust the positioning of the third body relative to the first body and, in turn, adjust how tightly the first and third bodies grip the limb. For example, the tightening mechanism may comprise a nut and screw adjustably receivable within the nut.

In embodiments of the invention, the tightening mechanism may comprise a biasing element, such as a spring, biasing the third body towards the first body. In such embodiments of the invention, the resilience to compression of the biasing element may, at least partially, contribute to the predefined gripping force. That is, the greater the resilience to compression of the biasing element, the greater the associated predefined gripping force will be. The friction factor between the first and second gripping surfaces and the limb of the movable joint may also contribute to the predefined gripping force such that the greater the friction factor, the greater the predefined gripping force. The predefined gripping force may be considered as the effect that results from the combination of the resilience to compression of the biasing element and the friction factor between the first and second gripping surfaces and the limb. Or, more simply, the predefined gripping force may be considered as equivalent to the force required to overcome the friction caused by the biasing element and the friction factor between the first and second gripping surfaces and the limb.

In embodiments of the invention, the predefined gripping force may be greater than the predefined restoring force so that the second body may recoverably move relative to the first body before the joint coupling is irrecoverably moved relative to the limb of the movable joint. In other words, the joint coupling will only slip relative to the limb if a force being applied to it is large enough that the integrity of the movable joint is at risk despite it complying to the force which is being applied to some degree.

In embodiments of the invention, each of the first and second resiliently compressible members is still further compressible with a force greater than the predetermined gripping force. This prevents a maximum amount of possible movement between the first and second bodies being reached prior to the joint coupling being able to slip relative to the limb of the movable joint. In other words, it prevents there being an intermediate range of forces, between the predefined restoring force and the predefined gripping force, which could cause the joint to become rigid, as this would expose the joint to increased risk of failure.

According to a second aspect of the invention there is provided an articulated manipulator, the movable joint comprising: a first limb; a second limb; and a joint coupling, according to the first aspect of the invention, coupling the second limb to the first limb. The joint coupling may be configured to suit the specific characteristics of the first and second limbs which it is to couple. For example, the joint coupling may be configured to be suitable for the required mode of movement, i.e., pivotal rotation, axial rotation or linear translation. The joint coupling may also be configured to be a suitable size for the associated limbs. The predefined restoring force and/or the predefined gripping force may also be defined for the specific application in which the movable joint is to be used.

The features and advantages of the aforementioned aspects of the invention and their embodiments apply mutatis mutandis to the second aspect of the invention and its embodiments.

According to a third aspect of the invention there is provided an articulated manipulator for a surgical robot controller, the articulated manipulator comprising a movable joint according to the second aspect of the invention.

The articulated manipulator may be more robust than known articulated manipulators lacking a joint coupling that allows joints of the articulated manipulator to comply to an applied force which might otherwise cause failure of the joint.

The features and advantages of the aforementioned aspects of the invention and their embodiments apply mutatis mutandis to the third aspect of the invention and its embodiments.

The invention will now be described by way of example only with reference to the accompanying drawings in which:

Figures 1 and 2 are schematic representations of a joint coupling according to an embodiment of the first aspect of the invention;

Figures 3 and 4 show the joint coupling of Figures 1 and 2 when moved to a different configuration;

Figure 5 is a schematic representation of a master controller comprising a pair of articulated manipulators according to the third aspect of the invention;

Figure 6 is a schematic representation of a movable joint according to the second aspect of the invention; Figure 7 shows a cross-sectional view of the movable joint shown in Figure 6;

Figure 8 shows a cross-sectional view of the movable joint shown in Figure 6 when moved to a different configuration to that shown in Figure 7;

Figure 9 shows a further cross-sectional view of the movable joint shown in Figure 6;

Figure 10 shows another cross-sectional view of the movable joint shown in Figure 6;

Figure 11 is a schematic representation of a third body forming part of the movable joint shown in Figure 6;

Figure 12 is a schematic representation of a first body forming part of the movable joint shown in Figure 6;

Figure 13 is a graphical representation of the torque required to rotate the movable joint shown in Figure 6;

Figures 14 and 15 are schematic representations of a joint coupling according to another embodiment of the first aspect of the invention; and

Figures 16 and 17 show the joint coupling of Figures 14 and 15 when moved to a different configuration.

Referring initially to Figures 1 and 2, a joint coupling according to an embodiment of the invention is designated generally by the reference numeral 2. The joint coupling 2 comprises a first body 4, comprising a first formation 10, and a second body 6, comprising a second formation 12. The second body 6 is movable relative to the first body 4, and vice versa, and the second formation 12 is slidably engageable with the first formation 10 whereby movement of the first and second bodies 4, 6 relative to one another causes the first and second formations 10, 12 to slide past one another.

In this embodiment of the invention, the second body 6 is linearly movable relative to the first body 4, and vice versa, and the first and second formations 10, 12 are configured to slide past one another in a translational sense. The joint coupling 2 may therefore be used to couple a translational or telescopic style of joint, for example.

The joint coupling 2 further comprises a cavity 14. In this embodiment of the invention, the cavity is formed by a combination of the first and second bodies 4, 6 wherein the shape of the first body 4, in particular, defines a first end 15 and a second end 16 of the cavity 14. Further, the first and second formations 10, 12 each comprise a first face 22, facing towards the first end 15 of the cavity 14, and a second face 24, facing towards the second end 16.

The cavity 14 has a length that extends from the first end 15 to the second end 16. The first and second formations 10, 12 each extend into the cavity 14, transversely to the length of the cavity 14.

The joint coupling 2 also comprises first and second resiliently compressible members 18, 20, each of which is received within the cavity 14 in a partially compressed configuration. Specifically, the first resiliently compressible member 18 extends between, and abuts against, the first end 15 of the cavity 14 and the first face 22 of the first and second formations 10, 12 while the second resiliently compressible member extends between, and abuts against, the second end 16 of the cavity 14 and the second face 24 of the first and second formations 10, 12.

The fact that the first and second resiliently compressible members 18, 20 are partially compressed means that each of the resiliently compressible members 18, 20 exert a force against the first and second formations 10, 12. Therefore, although the first and second bodies 4, 6 are movable relative to one another, they are biased towards a balanced configuration in which the first and second formations 10, 12 are aligned with one another, as shown in Figures 1 and 2.

In this embodiment of the invention, each resiliently compressible member 18, 20 is a spring having a predefined restoring force. The resiliently compressible members 18, 20 are each configured such that an applied force exceeding the predefined restoring force of the respective resiliently compressible member 18, 20 is required to cause further compression of that resiliently compressible member 18, 20 from the configuration in which it is shown in Figures 1 and 2.

This means that, if a force smaller than the predefined restoring force is applied to the first body 4 and/or the second body 6, the joint coupling 2 will remain rigid, i.e., the first and second bodies 4, 6 will remain in the balanced configuration. However, if a force exceeding the predefined restoring force is applied to the first body 4 and/or the second body 6, the first and second bodies 4, 6 will be moved away from the balanced configuration.

For example, in Figures 3 and 4, a force greater than the predefined restoring force is being applied to the joint coupling 2, essentially causing the second body 6 to have moved left relative to the first body 4 (as viewed on the page). This has also caused the second formation 12 to have moved along the length of the cavity 14, towards the first end 15, and further compress the first resiliently compressible member 18. In accordance with Hooke’ s law, the force required to move the joint coupling 2 increases in proportion to the amount of displacement of the first and second bodies from the balanced configuration.

Once the force being applied to the joint coupling 2 is removed, or at least reduced below the predefined restoring force, the first resiliently compressible member 18 will exert sufficient force on the second formation 12 to move it back along the length of the cavity and into alignment with the first formation 10. The second body 6 will, therefore, be moved so that the first and second bodies 4, 6 are back in the balanced configuration shown in Figures 1 and 2.

Accordingly, the fact that the joint coupling 2 inherently restores to the balanced configuration allows a movable joint to ‘flex’ if a sufficiently large force is applied to it without permanently losing its intended configuration. Stresses associated with a force being applied to the movable joint are essentially absorbed by one of the resiliently compressible members 18, 20, thereby reducing the likelihood of breakage or failure occurring stresses accumulating within a fragile or vulnerable component.

Further, although the second body 6 is described above as moving left relative to the first body 4 from the configuration of Figure 3 to the configuration of Figure 4, the second body 6 could also move right. This is due to there being a resiliently compressible member 18, 20 positioned on both sides of the first and second formations 10, 12. In other words, the ability of the joint coupling to recoverably flex in compliance to an applied force may be considered ‘bi-directional’. Referring now to Figure 5, a master controller 60 for a remotely operated surgical robot (not shown) comprises a pair of articulated manipulators 50. Each manipulator 50 comprises a movable joint 40, specifically a rotatably movable joint. Each movable joint 40 allows rotation between a first limb 42 and a second limb 44.

In this embodiment of the invention, each manipulator 50 is passive and each movable joint 40 is lockable in order that the manipulators 50 may be locked in a particular configuration when not being operated by a user.

As shown in Figure 6, each movable joint 40 comprises a gear 46 coupled to the first limb 42 and a locking latch 47 coupled to the second limb 44 (not shown in Figure 6 in order to reveal the internal components). To lock the movable joint 40, the locking latch 47 may be engaged with the gear 46, thereby preventing the second limb from rotating, about a joint axis 48, relative to the first limb 42. Conversely, when a user of the master controller 60 intends to operate the manipulators 50, the locking latch 47 may be disengaged so that first and second limbs can rotate relative to one another about the joint axis 48.

The gear 46 is coupled to the first limb 42 via a joint coupling 102 similar to the joint coupling 2 shown in Figures 1 to 4 except that the second body 106 is rotatably movable relative to the first body 104 rather than linearly movable. Further, in this embodiment of the invention, the gear 46 and the second body 106 are integral.

In other embodiments of the invention, the manipulators may be active. For example, rather than comprising a locking latch, the second limb may comprise a motor-driven gear which is always in engagement with the gear of the movable joint. In order for the first limb to rotate relative to the second limb, the motor-driven gear may be rotated so that it travels around the gear of the movable joint. Despite being an active manipulator, each joint coupling may function in exactly the same way as the joint coupling 102, described in more detail below.

Referring now to Figure 7, a cavity 114 is formed by a combination of the first and second bodies 104, 106 whereby the cavity 114 extends in a tangential fashion around the joint axis 48 (shown in Figure 6), rather than in a linear fashion like the cavity 14 shown in Figures 1 to 4. The cavity 114 also differs from the cavity 14 in that it is the shape of the second body 106, rather than the first body 104, which defines a first end 115 and a second end 116 of the cavity 114. The length of the cavity 114 is therefore defined by the second body 106.

However, despite the differences between the joint coupling 102 and the joint coupling 2 shown in Figures 1 to 4, they function in a similar manner.

The joint coupling 102 also comprises first and second resiliently compressible members 118, 120 separated from one another by the first and second formations 110, 112. As with the embodiment of the invention shown in Figures 1 to 4, each of first and second resiliently compressible members 118, 120 is received within the cavity 114 in a partially compressed configuration so that the first and second bodies 104, 106 are biased towards a balanced configuration as shown in Figure 7.

The resiliently compressible members 118, 120 are also configured to each have a predefined restoring force such that an applied force exceeding the predefined restoring force of the respective resiliently compressible member 118, 120 is required to cause further compression of that resiliently compressible member 18, 20 from the configuration in which it is shown in Figure 7.

Accordingly, if a torque is applied to the first limb 42 and/or the second limb 44 (shown in Figure 5) that causes a force to be applied to one of the resiliently compressible members 118, 120 which is smaller than the predefined restoring force of that resiliently compressible member 118, 120, both the joint coupling 102 and the locked movable joint 40 will remain rigid, i.e., the first and second bodies 104, 106 will remain in the balanced configuration.

However, if a torque is applied to the first limb 42 and/or the second limb 44 that causes a force to be applied to one of the resiliently compressible members 118, 120 which exceeds the predefined restoring force of that resiliently compressible member 118, 120, the first and second bodies 4, 6 will be moved away from the balanced configuration.

For example, in Figure 8, a torque is being applied to the second limb 44 so that a force greater than the predefined restoring force is being applied to the first resiliently compressible member 118. The torque is being applied in a clockwise direction (as viewed on the page).

The torque is therefore large enough to cause the first formation 110 to travel along the length of the cavity 114, and thus, to cause the second body 106 to rotate relative to the first body 104.

Once the torque being applied to the second limb 44 is removed, or at least reduced so that the force acting on the first resiliently compressible member 118 is lower than its predefined restoring force, the first resiliently compressible member 118 will exert sufficient force on the first formation 110 to move it (relative to the second body 106) back along the length of the cavity 114 and into alignment with the second formation 112. The first and second bodies 104, 106 will, therefore, be restored to the balanced configuration shown in Figure 7.

Referring now to Figure 9, the first and second formations 110, 112 are interlockable. In other words, the first and second formations 110, 112 overlap one another with a labyrinthine structure as they fit together. This means that the first resiliently compressible member 118 may abut against the first face 122 of each of the first and second formations 110, 112 at a plurality of contact points 126. The same is true for the second resiliently compressible member 120 contacting the second face of each of the first and second formations 110, 112, although this is shown not in Figure 9.

In this embodiment of the invention, the first and second formations 110, 112 are configured to interlock in such a way that each resiliently compressible member 118, 120 contacts the respective face of each formation 110, 112 with three separate contact points 126. Further, the three contact points are substantially equally spaced apart from one another. Each resiliently compressible member 118, 120 may therefore abut against each formation 110, 112 in a balanced and stable manner, even if the formations 110, 112 are not aligned with one another.

In Figure 10, the joint coupling 102 further comprises a third body 108 coupled to the first body 104. As is shown more clearly in Figures 11 and 12, the first body 104 comprises a first gripping surface 136 and the third body 108 comprises a second gripping surface 138 wherein the first and second gripping surfaces 136, 138 are configured to grip the first limb 42 with a predefined gripping torque. The predefined gripping torque is defined by a combination of a tightness with which the first and third bodies are coupled and a friction factor between the first and second gripping surfaces 136, 138 and the first limb 42.

The joint coupling 102 further comprises a tightening mechanism 130 coupling the third body 108 to the first body 104 with an adjustable degree of tightness. In this embodiment of the invention, the tightening mechanism comprises a screw 134 and a nut 135 which may be tightened or loosened by applying a torsional force to the screw 134.

The tightening mechanism further comprises a biasing element 132, which is a spring in this embodiment of the invention, biasing the third body 108 towards the first body 108. Accordingly, the tightness of the coupling of the third and first bodies is defined by the tightness of the screw 134 and nut 135 as well as the resilience against compression of the biasing element 132.

If an applied torque (or rotational force) is applied to the first limb 42 and/or the second limb 44 (shown in Figure 5) that exceeds the predefined gripping torque, the entire joint coupling 102 will be caused to rotate relative to the first limb 42. Hence, the second limb 44, with which the joint coupling 102 is in locked engagement via the gear 46 and locking latch 47, will also rotate relative to the first limb 42 and the rotation will continue until the applied torque reduces below the predefined gripping torque.

Figure 13 shows a graph 100 representing the possible rotation of the second limb 44 relative to the first limb 42 while the second limb 44 is in locked engagement with the joint coupling 102 via the gear 46 and locking latch 47.

In this embodiment of the invention, the predefined restoring force of both resiliently compressible members is 10 N and the predefined gripping torque with which the first limb 42 is gripped by the first and second gripping surfaces 36, 38 is 20 N. If less than 10 Nm of torque is applied to the second limb 44, the joint coupling 102 maintains a ‘rigid’ state 172 in which no rotation occurs because the predefined restoring force is not exceeded and the first or second resiliently compressible member causes the first and second formations 110, 112 to stay in alignment with one another.

The rigid state 172 is useful because it prevents the movable joint 40 and, more broadly, the articulated manipulator 50 from moving away from its intended position at the slightest touch while the movable joint 40 is locked.

If the applied torque increases above 10 Nm in either sense (i.e., in the positive or negative direction), but does not exceed 30 Nm, the joint coupling 102 enters a ‘flexing’ state 174. The flexing state 174 exists because the predefined restoring force of one of the first and second resiliently compressible members is now being exceeded and so that resiliently compressible member is being compressed by virtue of the first and second formations 10, 12 being move out of alignment with one another.

The flexing state 174 usefully allows the movable joint 40 to temporarily comply if a large enough force is being applied to it. This greatly reduces the likelihood of an accidental knock causing a failure of the locked movable joint due to stresses building up at a fragile component, such as the locking latch 47 for example. Alternatively, if the movable joint were part of an active manipulator, the ability of the movable joint to flex may protect the expensive motor-driven components from excessive stresses and possible failure.

If the applied torque then increases further in the respective sense, i.e., above 30 Nm, the predefined gripping torque is exceeded and the joint coupling 102 enters a ‘slipping’ state 176. In this embodiment of the invention, the joint coupling is configured to allow a rotation of up to 20° in the flexing state 174 before the predefined gripping torque is exceeded. The amount of rotation allowed in the flexing state may be defined by the size and resilience to compression of the resiliently compressible biasing members 118, 120.

Also, each of the resiliently compressible members 118, 120 are still further compressible with a force greater than the predefined gripping torque. In other words, the resiliently compressible members 118, 120 are not at the maximum limit of their range of potential compression when the predefined gripping torque is exceeded. This ensures that Hooke’s law applies throughout the flexing state 174 so that the degree of rotation remains proportional to the torque being applied.

In the slipping state 176, the joint coupling 102 essentially slips past the first limb 42 because the first limb 42 is no longer being gripped tightly enough by the gripping surfaces 136, 138 for the joint coupling 102 to hold its position relative to the first limb 42. This allows the second limb 44 to be moved freely relative to the first limb 42.

The slipping state 176 prevents large external forces/torques, which might fully compress one of the resiliently compressible members 118, 120, from causing damage to the locked movable joint 40. Such a force/torque might be accidentally applied by a person attempting to move the articulated manipulator without knowing to first disengage the locking latch 47 or forgetting to do so on that occasion. Alternatively, the locking latch may have failed in the locked position and the operator might be unaware of the failure. If the movable joint were part of an active manipulator, the movable joint may essentially be locked when no power is supplied to the manipulator and the ability for the joint to slip would, therefore, also help to protect the movable joint of an active manipulator.

However, unlike in the flexing state 174, any additional rotation of the second limb 44 relative to the first limb which occurs in the slipping state may not be reversed by the joint coupling 102 as there is no component equivalent to the resiliently compressible members 118, 120 which biases the second limb 44 back to its starting position (the origin of the y- axis). Instead, any additional rotation that occurs in the slipping state 176 may be maintained, resulting in a displacement 178 of the second limb 44 relative to the first limb 42.

Accordingly, if the slipping state 176 is entered, the master controller 60 may require recalibration with the surgical robot it is configured to control.

In other embodiments of the invention which are similar to the joint coupling 102, except that they are movable linearly rather than rotationally, it is to be understood that the rigid, flexing and slipping states may still be observed. Torques may be replaced with forces, but the overall functionality may be equivalent. Referring now to Figures 14 and 15, a joint coupling 202 is shown which is similar to the joint coupling 102 of Figures 6 to 10, in that the second body 206 is rotatably movable relative to the first body 204.

However, the joint coupling 202 comprises two pairs of formations (each pair having first and second formations 210, 212), two cavities 214 and two pairs of resiliently compressible members (each pair having first and second resiliently compressible members 218, 220). Also, in this embodiment of the invention, each resiliently compressible member 218, 220 comprises an elastomeric block, made of a rubber material for example, rather than a spring.

Despite that the joint coupling 202 comprises two lots of each of these features, it functions in much the same way as the joint coupling 102 of Figures 6 to 10, whereby each pair of the first and second formations is biased towards alignment so that the first and second bodies 204, 206 are forced towards the balanced configuration shown in Figures 14 and 15.

As with the above-described embodiments of the invention, each of the first and second resiliently compressible members 218, 220 has a predefined restoring force. However, in this embodiment of the invention, the two first resiliently compressible members 218 work together, as do the two second resiliently compressible members 220. Therefore, in order to move the second body 206 relative to the first body 204, a torque must be applied which is great enough to apply a force that exceeds the predefined restoring force of both first resiliently compressible members 218 or of both second resiliently compressible members 220. In other words, the applied force must be about twice as large to further compress the resiliently compressible members 218, 220 when compared to the force that would be required if there was only one pair of first 218 and second 220 compressible members which have the same predefined restoring force.

Figures 16 and 17 show the joint coupling 202 if such a torque were being applied to the second body 206 in a clockwise sense (as viewed on the page). As can be seen, both of the second resiliently compressible members 220 are being further compressed in order to rotate the second body 206 relative to the first body 204.

By incorporating more resiliently compressible members into the joint coupling 202, it is possible to have greater control over the range of force or torque that is achievable within the flexing state (equivalent to the flexing state 174 shown in Figure 13), particularly for smaller ranges of rotation.

Preferences and options for a given aspect, feature or parameter of the invention should, unless the context indicates otherwise, be regarded as having been disclosed in combination with any and all preferences and options for all other aspects, features and parameters of the invention. For example, the joint couplings 2 and 102 shown in Figures 1 to 4 and 6 to 10 respectively should be regarded as having been disclosed in combination with elastomeric blocks (similar to those shown in Figures 14 to 17) in addition to being disclosed in combination with springs. Also, the joint couplings 2 and 202 shown in Figures 1 to 4 and 14 to 17 respectively should be regarded as having been disclosed in combination with a third body which functions equivalently to the third body 108 shown in Figure 10, that is, combining with the respective first body to grip a limb of a movable joint.