OR CHARACTERISTIC

The present invention relates to methods and systems for discriminating an attribute or state or characteristic of something interacting with a medium.

Drilling processes are common in many procedures in the area of surgery, manufacturing, excavation, building, maintenance, decommissioning, mining and many others. A development was made at the University of Bristol in 1990 identifying that one could avoid breaking out of a flexible bone tissue by

discriminating the presence of a boundary prior to breaking out of the medium.

US 8,463,421 is based on a subsequent version of the technique that worked well under carefully presented conditions.

WO98/24017 discloses control means and actuators with feed-back sensors suitable for use in tele-operated systems, especially surgical tools and

endoscopes. WO 2005/005947 discloses a system and method for sensing and interpreting dynamic forces.

Aspects of the present invention seek to provide an improved method and assembly for discriminating an attribute or state or characteristic of something interacting with a medium.

According to an aspect of the invention, there is provided a method of

discriminating an attribute or state or characteristic of something interacting with a medium based on transient sensing signals from a plurality of sensors, the sensing signals being coupled by the medium. According to an aspect of the invention, there is provided a method of

discriminating an attribute or state of an object based on transient sensing signals from a plurality of sensors, the sensing signals being coupled by a medium with which the object is arranged to interact.

Coupled signals means that the attribute or state or characteristic can be discriminated by, with features which are coincident in the transients of the coupled signals in the attribute or state or characteristic having been pre-identified, detecting the coincidence of those features in the transients of the coupled signals. These features generally result from movement or a dynamic disturbance. In embodiments, most information is extracted from dynamic causes.

The sensing signals are coupled by the medium with which the thing, for example the object, is arranged to interact. In other words, the interaction of thing, for example the object, with the medium causes the sensing signals to exhibit correlated features in response to certain attributes or states or characteristics of the thing, for example of the object.

In embodiments, with different features which are coincident in the transients of the coupled signals in different attributes or states or characteristics having been pre-identified, the method includes discriminating different attributes or states or characteristics by detecting the presence of the pre-identified signal transients coupled by the interactive structure or medium. In some embodiments, different sensing signals show correlated features or transients in different attributes or states or characteristics.

The plurality of sensing signals can include a first signal relating to a first property and a second signal relating to a second property. The first and/or second properties can be kinetic properties. The plurality of sensing signals can include first and second signals relating to the same property but measured at different locations.

The sensing signals can advantageously relate to the kinetics of a moving object which can be a drill.

The plurality of sensors is in some embodiments provided on or in the object or on or in the medium. In embodiments, the method includes discriminating the attribute or state or characteristic from derivatives of the sensing signals, the derivatives being of the first order only. However, although the derivatives are of the first order only, other values can be also taken into account where those other values are not derivatives. For example, the actual value of the sensing signals can be used.

In embodiments, the attribute or state is a state in proximity to a movement event, wherein discriminating the attribute or state includes predicting the movement event, and wherein the sensing signals exhibit pre-identified coincident features in advance of the movement event.

In embodiments, the method includes discriminating the attribute or state or characteristic from derivatives of the sensing signals, and wherein for each sensing signal the derivatives include a coarse derivative and a fine derivative. δχ

The coarse derivative for variable x is— and the fine derivative for variable x is δχ

η^- and 5t _± > St ₂ . Preferably 5t _± is at least twice δΐ ₂ . δχ _± is the change in x in time

5t _t and δχ ₂ is the change in x in time 5t ₂ . In other words, the fine derivative is the average rate of change over a first (preferably very short) length of time and the coarse derivative is the average rate of change over a longer time. By utilising both coarse and fine derivatives, the imposition of noise in the discrimination process can be reduced.

Embodiments of the invention provide a smart drilling technique that is able to discriminate the presence of an interface ahead on a trajectory in order to avoid breakthrough, or to control the state of tool breakthrough to be achieved. The method is robust, in contrast with earlier approaches to solve the problem of detecting an interface, and is also able to discriminate the relative nature of an underlying medium or structure before the interface is reached. This technique has been demonstrated successfully in the differing circumstances presented in different applications and operating environments: In cochleostomies, open transnasal surgery, skull drilling, metals, composite materials and the drilling of wall structures. Embodiments can provide significant improvements as compared with the prior art, and the preferred technique is now well proven in different types of medium. It is versatile, particularly robust and is able to anticipate the next medium, able to operate under a range of conditions and environments and able to be applied to a range of tool types.

One particularly advantageous embodiment of the invention is for a dental drill. In dentistry it is important that when drilling a tooth, the drill does not penetrate into the tooth pulp as drilling into the tooth pulp can damage the tooth. Embodiments of the invention are able to discriminate the presence of tooth pulp ahead on a drilling trajectory before the tooth pulp is penetrated, thereby increasing the safety of many dental drilling procedures.

Preferred embodiments of the invention enable the discrimination of different tissues and tissue structures ahead on the drilling trajectory. For example, preferred embodiments enable the discrimination of:- Multi tissue types Wide range of planar angles to the drilling path.

Condition of the drill bit.

Underlying structure

Material type

Building materials and ceramic structures.

Preferred embodiments can be applied to different applications, for example:

Cochleostomy -otology

Hypophysectomy -rhinology

Cranial tissues - neuro surgery/ maxillofacial surgery

Building materials

In embodiments of the invention, hand-held drills can reduce set-up time and cost.

Embodiments of the invention can also provide other tool actions, such as:

Saws, Needles, Different drill bits, Milling (Also method to control shape of resection.) Hand-held drilling (Able to discriminate disturbances of operator and differing mediums.)

Embodiments of the invention use the coupling function between force and torq to identify the discriminating signatures of events

to discriminate types of feature on the trajectory.

US 8,463,421 emphasises a technique for drilling that detects features requiring 4 derivatives in Force and Torque to recognise an underlying membrane. The inventors of the present invention have discovered the means to detect the same and different types of medium and structure in most types of cutting process that requires the detection of only first order derivatives. Consequently, preferred embodiments of the invention are now robust to differing operating conditions and the pose of mediums relative to drilling trajectories. They also enable the device to operate when hand held, and in a wide variety of mediums.

As well as drilling, embodiments of the invention are applicable in other situations.

In some embodiments, the object includes an elongate flexible member, such as a medical device for insertion into a patient, for example a catheter.

In such embodiments, the plurality of sensors can include a plurality of strain sensors and the medium can be the medium through or into which the member is to be inserted.

The strain sensors are preferably located at different axial and/or circumferential positions on the member.

In some embodiments, the strain sensors include first, second and third strain sensors, each located a different axial position on the member, and

circumferentially spaced at intervals of 120°. Preferably, each of the strain sensors includes an elongate Bragg grating sensor.

The method can measure how many peaks in reflectivity there are, how wide the peaks are and/or how much the peaks move. Preferably, the method includes calculating for each sensing signal:

a change in wavelength of a peak in reflectivity with respect to a non- strained condition;

a change in reflectivity of the peak with respect to a non-strained condition; a change in wavelength of a first point with respect to a non-strained condition; and a change in wavelength of a second point with respect to a non-strained condition;

wherein the first point is a wavelength less than the wavelength of the peak at which the reflectivity drops below a threshold value and the second point is a wavelength greater than the wavelength of the peak at which the reflectivity drops below a threshold value.

The first point is preferably the wavelength closest to and less than the wavelength of the peak at which the reflectivity drops below a threshold value and the second point is preferably the wavelength closest to and greater than the wavelength of the peak at which the reflectivity drops below a threshold value. The threshold values for the first and second points are preferably the same.

The way in which preferred embodiments of the member use 3 strain

measurements, coupled by the continuum of the structure of the surface of the member, enables the construction of different types of meaningful information from contact with tissues. The changing shape features on the profile of spectra reflected from gratings is used to interpret, tactile conditions within the

environment of the vascular lumen. The use of long rather than point Bragg gratings accentuates features and augments processes for automatically detecting and distinguishing the features.

Preferred embodiments of the catheter provide a device that is advantageous in that it is a hand guided device that is rich in sensory information provided by the approach to sensing. It is a hand guided device as opposed to a robotically actuated steerable device as this provides a workable solution, it requires low setup time and low operator training requirements.

In some embodiments, one or more breaks or clutches are provided to vary a force provided by the operator. For example, the break or breaks can resist operator motion to avoid inadvertently puncturing tissues. Preferred embodiments of the device enable perception of the working

environment at the tip of the device for the operator. Preferred embodiments of device lower procedure time significantly and augment the skill of the operator.

Preferred embodiments of the device can identify the shape of a lumen as it progresses by using the same 3 sensing elements that are applied to interrogate branches in vessels, obstructions and other tactile features (even texture and sliding velocity). The device can also work relative to the position of tissue interfaces and therefore achieve unprecedented accuracy.

Preferred embodiments of the device are low cost to achieve the requirement of disposability in view of protecting patient safety.

Preferred embodiments of the invention provide the following advantages and features:

Hand held and actuated catheter by the operator benefitting from greater perception (sensory feedback).

A robotic sensing scheme and a catheter moved by the operator with respect to the position of features in the tissue and able to avoid inadvertent penetration of tissue structures. This can be achieved by brakes or clutches in the action mechanism.

· Detect lumen curvature in 3D.

Discrimination of the 3D direction of the tip.

Discriminate holes and other tactile features expected in the vascular lumen environment.

Follow process to detect luminal branches and insert guide wires precisely. · Detect internal curved guide wire orientation and position with respect to tissue position. (Historic scan data less accurate). Embodiments of the invention can discriminate shape, twist, contact positions, sliding velocity, lumen stiffness, texture, potential penetration and tactile features. In embodiments, the output is discriminative rather than a measurement and is information rather as a description.

According to an aspect of the invention, there is provided an elongate flexible member including a plurality of strain sensors operable to detect an attribute or state of the elongate flexible member.

According to an aspect of the invention, there is provided a method of

discriminating a state of movement based on transient sensing signals from a plurality of sensors, the plurality of sensors being in different locations and/or of different types.

In embodiments, the sensing signals are coupled.

According to an aspect of the invention, there is provided a drill assembly including a processor configured to perform the method described herein, a drill and a coupling arrangement for coupling the plurality of sensors to the processor. The drill can be a dental drill.

According to an aspect of the invention, there is provided a force plate assembly including a processor configured to perform the method as described herein, a force plate, and a coupling arrangement for coupling the plurality of sensors to the processor.

According to an aspect of the invention, there is provided an assembly including a processor configured to perform the method as described herein, an elongate flexible member, and a coupling arrangement for coupling the plurality of sensors to the processor.

According to an aspect of the invention, there is provided a method of discriminating a characteristic of something interacting with a medium based on transient sensing signals from a plurality of sensors, the sensing signals being coupled by the medium.

In embodiments, the thing interacting with the medium is a force or a sound, and the medium can be a force plate. The sensors can be provided on or in the force plate, preferably each at a different location of the force plate. The sensors are preferably coupled to a processor for performing the method. Where the method is for discriminating a characteristic of a sound, the sensors are preferably sound sensors.

The characteristic of the force or sound can be the magnitude of the force or it can relate to an amplitude, wavelength and/or frequency of the sound.

In some embodiments, an obstruction can be located between a source of the sound and the medium. The characteristic discriminated by the method can relate to the sound before passing through the obstruction. In this way, embodiments of the invention are able to recover an original sound despite the sound having been modified by passing through an obstruction before its detection. Such embodiments can be useful in hearing aids where the hearing aid is inserted into a person's head. In such cases, the skull of the person may provide the obstruction.

According to an aspect of the invention, there is provided a method of discriminating a magnitude of a force causing displacement of a medium based on transient sensing signals from a plurality of sensors, the sensing signals being coupled by the medium. According to an aspect of the invention, there is provided a method of discriminating different sounds interacting with a medium based on transient sensing signals from a plurality of sensors, the sensing signals being coupled by the medium.

Embodiments of the invention are described below, by way of example only, with reference to the accompanying drawings, in which:

Figures 1 and 2 are schematic part cross-sectional views of a drill drilling into a structure in accordance with an embodiment of the invention;

Figure 3 shows an arrangement of a drill in accordance with an embodiment of the invention; Figures 4 and 5 show hand-held drills in accordance with an embodiment of the invention;

Figure 6 is part of a graph showing a rise in torque on approach to a boundary in accordance with an embodiment of the invention;

Figures 7 and 8 show graphs showing the force and torque on approach to a boundary in accordance with an embodiment of the invention; Figure 7 shows typical force transients on approaching an interface from hard to softer mediums and Figure 8 shows typical force transients on approaching an interface from soft to harder mediums;

Figure 9(a) is a cross-sectional view through a sample of plasterboard;

Figure 9(b) is a schematic cross-sectional view through the sample of Figure 9(a) showing the layers more clearly; Figures 9(c) and (d) show coupled force transients: respectively, a graph of the force and torque, and a graph of the first derivative of the force and torque, of a drill drilling through the sample of Figure 9(a) in accordance with an embodiment of the invention;

Figure 10(a) shows a schematic diagram of a force plate according to an embodiment of the invention;

Figure 10(b) shows a schematic diagram of another force plate;

Figure 10(c) shows a layout of sensors on a force plate in accordance with an embodiment of the invention;

Figures 1 1 and 12 show devices from earlier developments;

Figures 13(a) and 13(b) show a catheter in accordance with embodiments of the invention; in Figure 13(a) the catheter is hand-held; in Figure 13(b) the catheter is automated; Figure 14 shows a graph showing points used in a method according to an embodiment of the invention;

Figure 15 shows a graph of a shift in peak reflectivity wavelength with increasing uniform strain in the catheter of Figures 13(a) or 13(b);

Figure 16 shows a graph of a shift and reduction in peak reflectivity wavelength with increased bending in the catheter of Figures 13(a) or 13(b);

Figure 17 shows a chair in accordance with an embodiment of the invention;

Figure 18 shows a force plate in accordance with an embodiment of the invention; Figure 19 shows a schematic of a distributive tactile sensing system and Figure 20 shows further details thereof; Figures 21 to 26 show a process of cochleostomy and graphs of results using a drilling tool according to an embodiment of the invention; and

Figures 27 to 49 provide further explanation of the background to and details and advantages of embodiments of the invention.

Figure 1 shows a drill 10 including a drill bit 12 drilling into a structure 14. The structure may include different mediums 16 or embedded structures 18. The drill 10 can include features described in US 8,463,421 , which is incorporated by reference herein in its entirety.

The drill 10 advances with a feed forward force F and rotates with a torque T. The drill 10 includes a sensor unit (not shown) configured to measure the feed forward force and the torque. The sensor unit includes a first sensor configured to measure the feed forward force and a second sensor configured to measure the torque.

Drilling Forces F and T are coupled by functions φ that are dependent on the presence of materials and structures in a flexible medium in time and space.

T = c (F, X, t)

Transient features in φ(χ) can be used to recognise these states/ disturbances/ structures.

The sensor unit is coupled to a processor 20 and configured to communicate to the processor sensing signals corresponding to measurements of the feed forward force and the torque. The processor 20 is configured to calculate first order derivatives of the feed forward force and the torque, and to detect from those derivatives states of movement of the drill. The derivatives used in detecting states of movement of the drill are first order derivatives only.

The processor is coupled to an output unit, such as a monitor 22, in order to output to the user details of the force and torque, their derivatives and/or detected states of movement of the drill. Preferably the output includes descriptive information relating to the state of movement.

States of movement that the processor can detect include those in which the feed forward force and the torque exhibit correlated features or transients resulting from the structure 16 coupling the force and torque. One such state of movement is as the drill approaches a boundary between one medium 16 and another, or the edge of an embedded structure 18. This can be considered as a breakthrough detection since it detects an impending breakthrough from one medium to another.

As discussed above, the breakthrough detection is achieved by monitoring the feed forward force (F) and rotation torque (T) transients. When breakthrough is occurring at the interface from a hard to a softer medium, the F will start to drop and the T will start to rise rapidly, such as shown in Figure 7. By calculating a variable F' representing the rate of change of F, and T representing the rate of change of T, impending breakthroughs can be detected and accordingly control of the degree of breakthrough can be achieved.

An example of the detection of a sharp rise in the torque is discussed with respect to Figure 6. However, the details described can be applied with appropriate modification to detecting other features of the torque or indeed other variablesof interest.

Figure 6 is an example of a graph of rising T on approach to a boundary. The value of T is sampled at five points in this example, point pO to p4.

The detection method is using two parameters (P1 and P2) as explained as follows:

P1_1 = p1 - pO, P2_1 = p3 - pO;

P1_2 = p2 - p1 ; P2_2 = p4 - p1 ;

In other words, the difference in time between the samples used to calculate P2 is greater than for P1 . P2 can be considered to be a coarse gradient, whereas P1 can be considered to be a fine gradient.

By calculating the two parameters, it is possible to make sure the rising / dropping of the transient can be detected constantly without being affected by noise or disturbances.

By using the 4 values of P1_1 , P2_1 , P1_2 and P2_2 one can determine automatically that there is a progressively curving transient and whether it is increasing or decreasing in value. Also by searching different sample points one can automatically reduce the imposition of noise in the discrimination process. By applying these trend factors to coupled transients one can assign their nature through a process of discrimination. Additionally the process can be set to expect mediums in a specific order, or may be set to search for a feature within a type of medium. A similar process is applied with respect to dynamic disturbances that need to be discriminated. Thus it is possible to apply the method to hand-held tools.

During the drilling procedure, variable feed speed is important to maintain feed force within an acceptable range with material removal occurring at the

appropriate rate for the advancing tool. Robustness of breakthrough detection

Some variables will affect the discrimination of breakthrough. Such variables include the angle of the drilling trajectory with respect to the plane of interfaces, and the presence of environmental disturbances. Studies show that embodiments of the invention using drilling technology are tolerant to the trajectory angle up to 45 degrees and environment vibration up to 100mm/s pk to pk amplitude.

Various materials drilling

When drilling through various materials with different stiffness properties, the force and coupled torque transients show different characteristics, as a signature, to discriminate a wide range of conditions and differing interfaces, and the state of tool and medium, and the nature of interaction between tool and medium. When the feed speed is constant, both force and torque show higher amplitude level during drilling through the material with higher hardness. Using such a feature, a variable feed and drilling speed control strategy can be applied. The variable speed level will also help to maintain the right level of force and torque so that detection of multiple layers structure can be achieved.

Multi layers of materials and different types of interface encountered on the drilling trajectory

As discussed above, embodiments of the invention using smart drilling technology can distinguish between different layers of material with different hardness. As the cutting tool point or drill bit 12 approaches an interface between two mediums, if drilling from a harder material to a softer material the force and torque transient show similar features as shown in Figure 7. This would be similar to a case for example when drilling say bone into a cavity.

When drilling from a softer material to a harder material, the combined coupled force and torque transients show opposite tendencies, as shown in Figure 8. When associated with pre-scan data / pre-knowledge of the structure, the control of penetration in different layers can be achieved too. Some features are short period or long duration, or intermittent but frequent. Knowledge of the application enables deduction of the nature of the medium, and different features will be relevant such that algorithms can be deployed to automatically deduce the situation through a process of discrimination. Thus for an application there is normally knowledge of the presence, or potential presence, of mediums or structures and these can be identified through a process of deduction as perhaps certain mediums/ structures can only be present in a certain order or after a certain event.

One advantageous application is for dental drilling. In dental drilling, it is important that the drill does not penetrate the tooth pulp, since penetrating the tooth pulp can cause irreparable damage to the tooth. The above techniques for discriminating approaches to a boundary between two materials can be advantageously used for a dental drill to provide warning when the drill is about to penetrate the tooth pulp. The warning can be provided as an audio, visual and/or tactile warning to the dentist and/or the processor making the discrimination can be configured to stop operation of the drill when imminent penetration into tooth pulp is discriminated. Such warnings and operation stopping can be used in other embodiments as well.

Figure 9 shows the Force and Torque transients when drilling plasterboard.

However, the same will be true of other building mediums and indeed other mediums such as in mining.

Figure 9(a) is a cross-sectional view through a sample of plasterboard, and Figure 9(b) is a schematic cross-sectional view showing the layers more clearly. The force and torque show the expected transients in crossing an interface between harder paper 24 and then softer plaster 26, then from soft plaster 26 to harder paper 28, then paper 28 to a harder finishing plaster 30, and then harder plaster 30 to air 32. In the soft plaster 26 the disturbances are due to harder or softer particles or cavities, respectively, that are present in such materials. To the discriminating algorithms these will be quite different and able to be used to determine the type or nature of a medium. These characteristic features can be used to discriminate the subsequent medium at an interface before the interface is penetrated.

Contrasting first derivative coupled transients can also be used to further discriminate the nature of certain mediums. Figure 9(c) shows the force and torque of a drill as it passes through the sample of plasterboard, and Figure 9(d) shows the first derivatives of the force and torque.

Dynamic disturbances can be recognised and discriminated as these will produce different characteristics in the coupled transients. An operator holding the tool with hand tremor will appear quite distinct from movement of a patient/ work-piece or other induced disturbances such as external knocks and physical disturbances such as rubbing, tool misalignment, imperfections or indeed changes in cutting conditions, such as presence of debris. As well as drilling, the method of preferred embodiments of the invention can also advantageously enable utilising a minimum number of sensing elements as a tactile sensing system to retrieve information about contacting surfaces and interfaces. The applications range from surfaces where people can stand or move, steerable endoscopes and seats and catheters.

In the frame of mind of the sensing process one has to approach the task with a view of discriminating conditions rather than measurement. Also one needs to identify with some contacting/ modulating continuum, affected by the process, through which the sensing elements are coupled. Thus for a standing/ walking surface it would be a plate with sensing elements at a handful of discrete points to observe strain or deflection. For a chair it could be the structure of the chair, the seat or back of the chair. For an endoscope/ catheter it would be the exo-structure of the device which strains as it curves. For the drill or other penetrating devices, it is the cut medium through which force data transients are coupled. The concept of information, as opposed to data is applied to the coupled sensory transients where certain states attributable to the moving object/ person can be discriminated from coupled features in the data transients. Thus, as described above, in drilling it is possible to discriminate condition of tissues in surgery/ medium, condition of the drill bit, movement of the medium, penetration depth and to detect interfaces or buried structures ahead on the drilling path. The same can be applied with other cutting tools, such as mills, needles, debriders, saws. As a tactile element/ surface it is possible to discriminate characteristics/ behaviour (static and dynamic) of the object/ person, or other disturbance in close proximity to or contact with the surface/ structure. For a walking surface this can be used to recognise personnel, identify gait, balance and posture. For a seated person one can discriminate types of motion, identify a person, identify balance, types of motion and behaviour.

Figure 10 (a) is a schematic diagram of a force plate for performing tactile sensing by the distributive method over a surface area in contrast to Figure 10 (b) which shows array tactile sensing over a surface area.

An interesting point is that it is not necessary to constrain the position or orientation of the subject/ object in order to perform the task of discrimination. It just makes the algorithms easier to implement if one reduces the Order' of the problem. It is also profitable to use the method to contrast changes in people or objects.

At Bristol University the approach began with the drill and then was used in robotic grippers in tactile sensing for sensing the behaviour of dough-like materials which would deform and slide as they were gripped and moved. It was also applied to discriminate shoe size, and used as a steerable endoscope digit as a

demonstration. Publication WO98/24017 relates to this work. The approach was on static objects in contact with a surface. At Aston University the approach was on dynamic objects in contact with a surface. Here it was shown that the method could be used in golf swing and later in discriminating force transients under feet while walking. Using 3 axial strain measurements in the exo-skin of the digit, it was shown that it could be applied on a flexible digit in lumen (as a steerable endoscope) to discriminate sliding velocity relative to a tactile feature, contact forces, and multiple contact points

simultaneously, it could also estimate a single curvature. The importance toward endoscopes was clear: as only a few sensing elements were used, the sensing scheme could be manufactured to be mechanically simple and the physical volume of cables/ optical fibres would be small, thus not obstructing the critical working cross-section of the device more than absolutely necessary.

As a surface, the method was applied to discriminate gait which proved difficult utilising a virtual closed-form solution to estimate the characteristics of foot-fall. In golf swing it could be used to estimate the total stance of the person during the swing as well as to discriminate position of the head, foot separation, concentric swing, point of gripping on the golf club and an indication of respiration.

Figures 1 1 and 12 show devices from the work at Aston University. Embodiments of the present invention have enhanced the drilling, milling and sawing algorithms and have demonstrated their robustness and benefit with regard to tissue trauma. Embodiments can be used in hand-held surgical robots that are disposable. Embodiments can also be used in mining as the method has been demonstrated in building materials. Embodiments of the invention can be applied to slender, flexible surgical tools and for discriminating characteristics and behaviour in people. An embodiment of the invention, shown in Figure 13(a), includes a catheter 100, although it can be any elongate flexible member, especially a medical device. The catheter 100 includes a plurality of elongate optical Fibre Bragg Gratings (FBG) referred to herein as Bragg grating sensors 102, only one of which is visible in the figure. The Bragg grating sensors 102 are placed in different axial positions on the external exo-skin of the catheter 100 and are configured to communicate signals to a processor 104 which can detect strain through a change in the shape, shift and amplitude of reflected light spectrum. The output of the Bragg grating sensors represents the change of strains applied on the catheter tip. This change can be due to the catheter tip shape or contact conditions such as rubbing on the wall or penetrating into the tissue. The data can be interpreted into meaningful descriptions using an artificial neural network method, although algorithms other than a neural network can be used.

The data can be interpreted into meaningful descriptions because the strains from the different sensors are coupled by the medium through which the catheter is passing, causing the strain signals to exhibit correlated features or transients in response to certain attributes or states.

Although the sensors are described as being optical fibre Bragg gratings, light intensity and/or strain gauges can be used.

The catheter typically has a cable or guide wire 106 passing within it.

The Bragg grating sensors or fibres are located predetermined distances (typically 30, 35 and 40 mm) away from the tip of the catheter respectively. Positioning the Bragg grating sensors as such provides 3-D discrimination and increasing of sensitivity.

To sense the strain on the catheter, the Bragg grating sensors or fibres can be attached to the catheter, or embedded into the catheter wall. The Bragg grating sensors are typically integrated into the outside structure of the catheter 100.

The sensing system is designed to detect shape of the catheter tip, the contact or/and penetration of the catheter tip into soft tissue. The system detects the contact and can in some embodiments stop the movement as described in more detail below. This feature can also be useful in actuation process, when the tip of the catheter hits the soft tissue of the artery.

In the depicted embodiment, there are three Bragg grating sensors 102. Although there are three in this embodiment, other numbers of sensors can alternatively be used. In the depicted embodiment of three sensors, circumferentially these are placed in 120 degree intervals, although other angular separations can be used in other embodiments, especially where different numbers of sensors are used. The inventors have discovered that using a few (typically three) sensing elements combined with non-linear time series the touch perception of a catheter can be retrieved. The embodiment provides 3-D discriminative tactile sensing.

The catheter in the depicted embodiment has a diameter of 3-5mm. The catheter is rather like a cantilever beam where strain measurement can correspond with curvature in two axes. When the fibre bends it does so according to contact with say the wall of the blood vessel, the current of blood flow and the cable which can move inside the catheter, and which may be pre-curved and turned around its axis to enable the tip of the catheter to be curved as required. The sensing system is designed to detect shape of the catheter tip, the contact or/and penetration of the catheter tip into soft tissue. The system detects the contact and can in some embodiments stop the movement as described in more detail below. This feature can also be useful in actuation process, when the tip of the catheter hits the soft tissue of the artery.

In Figure 14, exemplary readings of a sensor are depicted showing the reflectivity of different wavelengths. The reflectivity without strain applied is show in blue and the reflectivity when a strain is applied is shown in red. The peak location of both cases are labelled as A and B. The locations (wavelengths) of both peaks are measured as P _A and P _B . Also, the values of both peaks are measured as V _A and V _B . The location (wavelength) of the first and last points of both wavelengths when the values are bigger than a threshold value (for example 0.1 ) can be measured as L _A , L _B , RA, and R _B . In the next step, four parameters are calculated: P _B - PA, V _B - V _A , L _B - L _A , RB - RA- Based on the location of the sensor, and the states of the catheter tip, all the four parameters show different non-linear transient. A neural network is then applied to discrimination between different conditions of the tip according to the calculated parameters. However, again, different algorithms can be used instead of or in addition to the neural network.

Despite the challenge of sensitivity to diametric size, embodiments of the invention have enabled discrimination of single or double curvatures, texture, the placement of branches and the twist of inserted sliding curved wires. Embodiments can therefore advantageously be used in the placement of stents. This amplifies the theme of hand actuated robotic surgical tools in that the technique can provide information of state within the vascular lumen with regard to tactile information to help align the placement of stents through branches from leading vessels.

Actuation of the catheter is more conventional and intuitive than other applications using robots. As a result the system is more appropriate as a result of enabling aspects of cost, normal working diameter, reduced incidence of scanning and reduction of time of process and radiation exposure of patients/ operatives, disposability and reduced training of surgeons.

Embodiments advantageously provide:

-small diameter

- using long Bragg optical fibre gratings enable more data to be gathered and used to retrieve information on contacting conditions.

- tactile identification of the position and orientation to branches in vessels.

- discrimination of the position and twist of an inserted guide wire without separate sensing systems.

- hand actuated/ guided surgical tool that avoids unsafe use and reduced tissue trauma.

- discriminates types of obstruction through tactile means- branch - occlusion - avoids penetration.

-discriminates types of tactile surface within the lumen from texture.

Catheter operation applications

The focus is on the intra vascular lumen implantation of stents, although the applications are much more widespread in vascular work and also other investigative and treatment processes in the spine.

The long Bragg gratings optical fibre sensors are preferably 15mm (or similar length) attached to a catheter. The Bragg gratings sensors can sense ununiformed strains based on the location of the sensors. Different values and/or types of strains cause different shape and movement of the reflected spectra. Features in the spectra are used to

automatically discriminate the conditions of interest in real time which are fed back to the surgeon operator. For example, uniform strains cause shift in the peak of the wavelength as shown in Figure 15. Non-uniform strains, as found in bending, cause expansion of the wavelength peak area as well as lower the amplitude of the peak value as shown in Figure 16.

As described above, it is possible to determine attributes or states of movement of the catheter based on derivatives of the peak wavelength, peak amplitude values, and/or width of the wavelength peak, of one or more of the Bragg grating sensors, where the derivatives are of the first order only.

Using the coupled information built from multiple sensors using the shifted length of wavelength, changed peak amplitude values, width of the wavelength peak range (typically three sensors) at different locations, different states or situations can be discriminated: Catheter tip shape, rubbing velocity, contact points, tactile features from texture, vessel branches, guide wire orientation and contact with sliding as opposed to tip contact building to penetration.

The best way to control the device is generally using conventional guide wires that can be used to bend the tip as required. With the sensing information feedback the clinician is able to operate the catheter with guide wires with considerable improvement over current practice.

Preferred embodiments can therefore provide a practical hand guided robotic solution for a precision guided catheter that is guided by the operator in response to real-time information feedback. This hand guided robot will enable motion when conditions are considered safe (no penetration).

In some embodiments, the catheter can be provided with a clutch or a break which the processor is configured to operate to vary a feed forward force of the catheter provided by the operator. This can prevent or minimise the chance of undesired penetration of tissue. The feed forward force can be provided entirely by a controllable motor 108 such as in the automated embodiment shown in Figure 13(b).

Advantageously, the catheter of preferred embodiments is at the normal catheter size unlike other approaches, and gives advantage over other approaches to sensing that are not mechanically simple to construct. The result is low cost on disposables, safer and require virtually no training beyond existing catheterisation techniques. Embodiments provide for micro actuation and sensing systems that will link up with synthetic biology and clinical surgical processes in fertility and bronchial disorders.

In another embodiment of the invention, as shown in Figure 17, there is provided a chair 200 to observe progressive motion of recovering stroke patients. The chair 200 includes a plurality of sensors in different locations configured to sense a plurality of variables relating to attributes or states or kinetics of movement of the patient 202. Typically, the sensing unit includes a plurality of sensors beneath a deformable surface, and can include features described in WO 2005/005947, which is incorporated herein by reference. The sensors can be strain

measurement types or deflection (displacement) types. They can be optical proximity sensors, strain sensors, or a combination of both.

Figure 10(c) shows a typical surface for use in a force plate or chair with first, second, third and fourth reflective sensors S1 , S2, S3, S4 which can be coupled to a processor (not shown) which can perform the discrimination method below. In Figure 10(c), the sensors are shown as being located at the four corners.

However, they can be at other locations, but their signals are coupled by the force plate surface. The sensing signal values obtained from the four sensors can be described as V1 , V2, V3, V4. The proportional value between the four sensors can be defined as V1/V2, V2/V3, V3/V4, although other proportions or ratios between the sensing signals can be used. The first derivatives of the sensing signals can also be determined, by calculating a coarse gradient and a fine gradient in a manner described above. The absolute values of the gradients are then calculated. These absolute gradients and proportional values can be corresponded to determine the movement state using a neural network or other suitable algorithm. Embodiments of the invention can be applied to a health monitoring seat at home or in cars, a security instrument to observe the behaviour of a seated person, recognise a previously seated person. The seat can discriminate different types of respiration. In another embodiment of the invention shown in Figure 18, for standing patients, a force plate, which can include features described in WO 2005/005947, can be used to look at posture and balance at a fraction of the cost of previous

techniques. The technique can be similar to that described above with respect to Figure 10(c).

Embodiments of the invention provide advantages in stroke recovery, in seated health monitoring, security, mechanically simple disposable cybergloves and health screening. In some embodiments of the invention, a force plate and technique similar to that described above with respect to Figure 10(c) can be used to discriminate magnitudes of a force on a force plate using the coupled sensing signal values from the force sensors for example using absolute gradients, proportional values and a neural network as described above. In many prior art systems, expense is incurred decoupling force plate force sensors. However, embodiments of the invention are able to exploit the coupling of the force sensors, by discriminating force magnitudes by identifying features which are coincident in the transients of the coupled signals, to avoid the need to decouple the sensors. This can provide a force plate that can measure a magnitude of a force at a reduced cost. Some embodiments of the invention can provide a cost-effective microphone. In a similar manner to that described above with respect to a force plate, a small force plate can be used to discriminate characteristics of incident sound waves, such as frequency, wavelength and/or amplitude, or even a general shape of the sound wave.

In some embodiments, the microphone is configured to discriminate characteristics of a first sound wave from an incident second sound wave, wherein the second sound wave is a modification of the first sound wave. For example, the first sound wave can be incident on an obstruction, the obstruction can modify the sound wave and transmit the sound as the second sound wave. This technique can advantageously be employed in providing a hearing aid. A small microphone as described above can be implanted in the skull. The propagation of sound waves through the skull will modify the sound. However, using the techniques described above, the original sound, in other words the sound before passing through the skull, can be recovered by analysing coincident features in transients in the sensing signals from the microphone sensors.

As described above, embodiments can provide a smart dynamic surface device using a distributive tactile sensing method, which can discriminate between different objects by type and behaviour. The distributive response of surfaces can be detected by the use of a few coupled sensors at certain points over the surface that correspond to a particular surface deformation profile. Unlike conventional devices used in gait laboratories (force plates, video captures systems), smart dynamic surfaces in embodiments of the invention can offer advantages of mechanical simplicity, relatively low cost, and minimal post-examination data processing. Embodiments are suited to information transfer technology for localised applications such as home use, diagnostic and/or monitoring tools. Embodiments can be used for discrimination between symmetrical and asymmetrical posture, normal and abnormal gait, gait abnormalities. Embodiments provide a distributive approach to tactile sensing to discriminate motion. Such embodiments are shown in Figure 19 and 20.

Other embodiments can provide robotic surgical tools for discriminating tissue interfaces and avoiding penetration. They are able to discriminate and control the state or behaviour of tissues, with the result that devices are capable of precise tissue penetration with little set-up time and cost, in contrast with their larger surgical robot counterparts, and sensing elements used. Figures 21 to 26 show a process of cochleostomy and graphs of results using a drilling tool according to an embodiment of the invention. In this procedure to help the profoundly deaf, it is necessary to prepare access for the cochlear implant electrode to be fed into the scala of the cochlea, the hearing organ of the inner ear. This is a skilful process dealing with small delicate tissue structures. The drill tip is a burr and is a standard drill bit. The sensing occurs within the body of the drill and the state of the process and tissues are inferred from the coupled force transients of feed force and torque as described above. When drilling in this procedure, the drill removes the bone tissue and leaves the underlying membrane intact by determining and avoiding imminent penetration. This preserves the fluids and delicate structures within. Protection for the patient is assured as sterility is maintained by an intact membrane where debris can be removed and sterile conditions maintained before inserting the electrode. In contrast with conventional surgical drills, when using the robotic drilling technique of embodiments of the invention, the peak to peak disturbance amplitude within the cochlea is only 1 % of that in current practice. This is an important factor to preserve residual hearing in patients.

Figures 27 to 49 provide further explanation of the background to and details and advantages of embodiments of the invention. As shown in Figure 30, minimally invasive therapies, which can use for example an endoscope or a laparoscope, are thought to have benefit for patients and health care budgets. As shown in Figure 31 , surgical robots can be large systems that claim to be versatile, single function tools or much smaller devices. As shown in Figure 32, surgeons and machines can be complementary as they are often better at different functions.

Figure 33 shows how robotic technologies are employed in surgery. There are 3 working environments. Interaction with tissue is less often yet important for absolute precision. Robots can therefore be said to enhance skill, provide a consistent outcome, be fit for purpose, be safe and reliable, not too complex, be at an appropriate cost, straight forward to apply, low on training, and low on set-up time. In embodiments of the invention, as shown in Figure 34, robots can be used for making judgments as to whether to penetrate, or not, or follow tissue interfaces. For example, as shown in Figure 35, they can discriminate tissue interfaces to prepare for precise penetration. A drill according to an embodiment of the invention is shown in Figure 36, and anatomical drawings relating to a cochleostomy are shown in Figure 37.

In operation, as shown in Figure 38, discrimination in the tissue ahead of the drill bit can be done by coupling transients between force and torque.

As shown in Figures 41 and 42, in many embodiments using a drill, tissue interfaces can be drilled and the membrane preserved.

Embodiments of the invention can also provide a tactile sensing scheme from which to discriminate information discriminating touch, such as shown in Figure 44. They can use a few coupled sensing elements which output signals. They can be mechanically simple and low cost, not fussy on position of applied object and disturbance. They can output information and be a discrimination process relating to multi sensor signals to some event or behaviour of interest. The sensing technique can be used to discriminate types of motion and behaviour of people. This is interesting as people are similar but different and exhibit a defined range of behaviour in a particular situation.

In embodiments, as described above, robotics can be used to help flexible tools entering lumens. Such flexible tools can be instruments such as endoscopes, catheters and some implants. Some endoscopes can see ahead with cameras. Embodiments provide advantages over previous techniques since many previous techniques had limited force feedback and no touch. Furthermore, in many previous techniques, perception is limited. Embodiments of the invention are mechanically simple and use the skin of the device. They can shape and discriminate the working environment.

Figure 47 provides an example for actuation and uses sensing, not at a point but all over the digit in 3D. Using 3 sensing points, it can discriminate shape, twist, contact positions, sliding velocity, lumen stiffness, texture, potential penetration and tactile features.

A description of touch can be built from discrimination of typical conditions relating to the luminal environment. This can be output as information to augment the perception of the surgeon of the tool's interaction and position with respect to tissues. Embodiments of the invention can also be applied to a glove, such as a disposable glove, and digit, such as shown in Figure 49.

Embodiments of the invention therefore enable greater machine perception of the state of tissues, tool and operator, provide precise interaction between tissues and toolpoint, and provide improved actuator and sensing technology, enabling small easy to apply single function surgical robots.

All optional and preferred features and modifications of the described

embodiments and dependent claims are usable in all aspects of the invention taught herein. Furthermore, the individual features of the dependent claims, as well as all optional and preferred features and modifications of the described embodiments are combinable and interchangeable with one another.

The disclosures in British Patent Application No. 1321261 .8, from which this application claims priority, and in the abstract accompanying this application are incorporated herein by reference.