WO2014132025A1

WO2014132025A1 - A force feedback device

Info

Publication number: WO2014132025A1
Application number: PCT/GB2014/050237
Authority: WO
Inventors: Mohammed AFZAL; Martin Bennison
Original assignee: Keymed (Medical & Industrial Equipment) Limited
Priority date: 2013-02-28
Filing date: 2014-01-29
Publication date: 2014-09-04
Also published as: GB2511337B; GB2511337A; GB201303597D0

Abstract

A force feedback device for applying force feedback to the insertion tube (19) of a medical instrument. The device has a duct (1) defining a path for the tube. A cylinder (40) containing a volume of liquid (41) is at the far end of the duct, and there are means (42) for pressurising the liquid in response to force feedback commands. A piston (10) in the cylinder is acted on by the liquid to urge it in a first direction. A capture mechanism (9) is arranged to receive and retain a distal end of the tube inserted in the duct and to slide within the duct. A rod (7) extends along the duct (1) to connect the capture mechanism (9) and piston (10) and is arranged to transmit a sliding motion from one to the other. Insertion of the tube (19) further into the duct (1) pushes the piston (10) via the rod (7) against the liquid (41) in a second direction opposite to the first direction.

Description

A FORCE FEEDBACK DEVICE

The present invention relates to a force feedback device for applying force feedback to the insertion tube of a medical instrument. Such force feedback devices are employed in medical simulators to replicate the resistive forces that a user feels when inserting a real instrument into the patient body. The present invention has been designed for use with an endoscope for use in simulated colonoscopy. Such endoscopes have long flexible insertion tubes. However, the same principle could also be employed in other instruments with insertion tubes such as bronchoscopes, ultrasound scopes, cystoscopes, nasalscopes, gastroscopes and rigid scopes.

Medical simulators of the type the invention is

concerned with comprise a device which receives an insertion tube. The device has sensors to measure the linear and rotational position of the insertion tube. This information is fed into simulation software. The simulation software retains a software model of the part of the body that the tube is inserted into. As the position detectors detect movement of the instrument, this is translated into a corresponding movement in the software model and the view that a user sees on a screen is adjusted accordingly to reflect the view that they would see in a real life

operation . In order to provide added realism, force feedback is provided to the insertion tube. Thus, when the software model determines from the positional information that the insertion tube has met an obstruction, it increases the force on the tube to simulate the resistance which would be felt in use of the real instrument. An early example of a simulator constructed in this way is disclosed in GB 2 252 656. This is provided with a frictional brake to provide a variable resistive force on the insertion tube. A further development of this is disclosed in WO

2003/050783. This provides two sets of rollers which surround the insertion tube and are rotatable about an axis perpendicular to the direction of insertion. Force feedback is provided against rotation of at least one of the rollers to provide linear force feedback against movement in the direction of insertion. Each set of rollers is mounted on a disc which is rotatable about the axis of rotation. Force feedback is applied to the disc which provides a force against rotational movement of the endoscope.

The system is an improvement on GB 2 252 656 in that it can provide independent linear and rotational force

feedback. However, it does suffer from a number of

drawbacks. Firstly, the insertion tube is tangential to the outer surface of the rollers which is not ideal for

resisting linear motion of the tube. In order to be able to transmit the magnitude of forces required to provide

effective force feedback for an endoscopy simulator, the force feedback unit is required to have two sets of rollers and a set of sensing rollers. Each set of rollers has a large number of components many of which have to be

precisely machined which adds to the mass and complexity of the unit. Also, the rotational force feedback is transmitted via the rollers and the disc. As a result of this, at least one of the rollers is provided with

circumferential ridges which have sharp crests in order to grip the surface of the insertion tube so as to reliably transmit the rotational force feedback force. As this interface between the rollers and the tube also transmits the linear force feedback, the wheels are biased radially inwardly to a high degree by at least one spring in order to enhance the gripping force. As a result of this, damage can occur to the surface of the insertion tube caused by these ridges and their high degree of biasing.

Also with this design, once the insertion tube has passed through the force feedback device, it is fed to a duct which is external to the main device. This is because if the insertion tube of the endoscope is coiled with too tight a radius of curvature, the frictional forces on the tube become too large for the force feedback system to cope with. The radius of curvature is therefore relatively large and the duct cannot be accommodated in the main body of the device. The insertion tube of an endoscope for colonoscopy is a flexible tube which is at least one and a half metres long. As the duct in which this is accommodated is exposed on the rear of the device, it is prone to kinking, and may become caught in surrounding objects and is vulnerable to damage. Further, if it does become damaged or kinked, irregularities in the insertion tube can be felt by the user manipulating the instrument, thereby providing unreliable force feedback characteristics. A further example is disclosed in WO 99/38141. This discloses a number of concentric rings of different

diameters and the degree of inflation of each ring

determines the force feedback. This suffers from a number of drawbacks. Firstly, it cannot discriminate between rotational and linear force feedback and secondly the interface between an endoscope and an inflatable ring is a frictional interface. This is unlikely to generate the level of force required for an endoscopy simulator. Also, the rings will need to be made of a flexible material to allow them to inflate and this is likely to be vulnerable to damage .

US 2004/0048230 discloses a force feedback mechanism in which a capture mechanism is provided on a trolley which is attached to a belt. The belt is wound around a pair of pulleys, and a force feedback unit is provided to resist rotation of one of the pulleys and hence provide linear force feedback. The force feedback unit is an

electromagnetic device which is vulnerable to slippage.

Further, the capture mechanism is off-set from the belt such that linear pressure on the insertion tube will give rise to a bending moment on the trolley assembly which carries the capture mechanism. This is arranged to run on guide rails, but the generation of a bending moment will cause increased friction between the trolley and the guide rails, thereby interfering with the accurate force feedback.

Thus, to date, there is a need for a more effective force feedback mechanism for generating linear force

feedback against the insertion of an insertion tube which can generate the level of force feedback required for an endoscope used in a colonoscopy.

According to the present invention, there is provided a force feedback device for applying force feedback to the insertion tube of a medical instrument, the device having: a port to receive the tube;

a duct leading from the port at one end to an opposite end and defining a path for the tube from the one end to an opposite end;

a cylinder at the opposite end of the duct;

a cylinder containing a volume of liquid;

a means for pressurising the liquid in response to force feedback commands;

a piston in the cylinder which is acted on by the liquid to urge it in a first direction;

a capture mechanism having a receiver arranged to receive and retain a distal end of the tube inserted through the port and being slidable within the duct; and

a rod extending along the duct to connect the receiver and piston and being arranged to transmit a sliding motion from one to the other, whereby insertion of the tube further into the duct pushes the receiver and hence moves the piston via the rod against the liquid in a second direction

opposite to the first direction.

According to the present invention, the insertion tube is pushing, via the rod, against hydraulic force. Such a hydraulic system can replicate the high levels of force required for a successful colonoscopy simulator. The mechanism is simple in construction. As the insertion tube is retained within the capture mechanism, the tube can be more precisely guided through the duct. This allows the duct to have a tighter radius of curvature such that it can be accommodated in a much smaller space. This allows it to be retained in the main body of the device where it is protected from kinking and damage. This also assists with the provision of reliable force feedback.

The rod may be arranged to fill a substantial portion of the duct, such that it is effectively guided by the inner wall of the duct. However, bearing in mind that the length of the rod needs to be able to accommodate the full length travel of the insertion tube, this will make the overall the device unnecessarily heavy. Preferably, therefore, the rod is provided with a plurality of spacers which project radially outwardly from the rod and engage with the inner wall of the duct. This provides a lightweight system while still ensuring that the rod is guided reliably through the tube .

The insertion tube may be rigid in which case the duct has to be straight. However, if the insertion is flexible, then the duct is preferably curved. This means that, rather than projecting from the device for a length substantially equivalent to the length of the insertion tube, it can be coiled up into a much less obtrusive region.

Preferably, the capture mechanism comprises a set of jaws which are held in an open position in a stopper in the device against the action of a spring, the mechanism being arranged to be closed around the distal end upon insertion of the distal end of the tube which dislodges the jaws from the stopper allowing the spring to close the jaws, the stopper being arranged to catch the jaws as the tube is withdrawn and is arranged such that continued withdrawal of the tube forces the jaws open against the action of the spring thereby returning the jaws to the open position.

The invention may also then extend to a combination of force feedback device according to the present invention with a dummy medical instrument having an insertion tube with a main longitudinal axis, the insertion tube having a distal tip engageable with the capture mechanism and being rotatable about the axis of the tube. In such an

arrangement, any twisting of the insertion tube is not transmitted to the tip and therefore is not communicated to the capture mechanism and rod. As such, the feedback device is effectively isolated from the rotation of the tube and provides linear force feedback only. The force feedback device preferably further comprises an actuator to provide rotational force feedback to a portion of the insertion tube which is proximal of the rotatable distal tip portion.

Such a rotational force feedback mechanism may be as disclosed in WO 2003/050783 having a plurality of rollers mounted on a rotatable disc. With such an arrangement, the rollers no longer need to be biased with such a high force in a radial direction towards the insertion tube as the linear force feedback is no longer transmitted via these rollers. This removes the need to have a high biasing force radially against the insertion tube. Further, the two force feedback motors which are required in WO 2003/050783 to provide the linear force feedback are no longer required and the force feedback and sensing can be done via the same set of rollers, thereby significantly reducing the weight of the rotary force feedback system.

The means for pressurising the liquid in response to force feedback commands may, for example, be a pump which can selectively pump the liquid from a reservoir into the cylinder to increase the pressure.

Alternatively, it may be the rack and pinion mechanism connected to a second piston adjacent to the liquid and driven by a feedback motor. The cylinder may be

supplemented with a second cylinder containing a second piston arranged such that the space between the piston and second piston is filled with hydraulic fluid, the second cylinder having a diameter greater than that of the

cylinder, the second piston being exposed to the means for pressurising the liquid. This larger diameter second cylinder reduces the length of travel and the load on the motor for the force feedback actuator.

The present invention also extends to method of

operating a force feedback device according to the first aspect of the invention, the method comprising the steps of inserting insertion tube of the medical instrument into the port; capturing the distal end of the tube in the capture mechanism; sensing the depth of insertion tube; calculating the force feedback signal to be applied to the insertion tube based on its sensed depth; and pressurising the liquid in accordance with the calculated force feedback.

Preferably, the method further includes the step of determining from the measurement of the depth of the insertion tube a value corresponding to the frictional force between the insertion tube and the duct, and reducing the level of force feedback to compensate for the calculated frictional force.

Examples of force feedback devices in accordance with the present invention will now be described with reference to the accompanying drawings, in which: Fig. 1 is a schematic cross-section of a first device;

Figs. 2A-2C are schematic cross-sections showing the interface between the device and an insertion tube in various degrees of insertion of the tube;

Fig. 3 is a second example of a device suitable for a rigid insertion tube; and

Fig. 4 is a schematic cut away side view of a force feedback unit containing the device of the present

invention . The present invention is directed to a force feedback device which is used in a medical simulator. In particular, it has been designed for a medical simulator for an

endoscope suitable for colonoscopy. However, it can be applied to any simulator with an insertion tube that

requires force feedback. General details of the simulator are provided in GB 2 252 656. The present invention relates to an improvement in the force feedback device only, and only this element of the simulator is described below. The force feedback device comprises a duct 1 in the form of a hollow tube which is fixed in place. As shown in Fig. 1, the duct 1 has a port 2 at one end. This extends via a first straight section 3 to a curved section 4 which has a substantially uniform radius of curvature and leads to a second straight section 5 which terminates at an end 6 at the opposite end of the duct from the port 2.

Within the duct 1 is a flexible rod 7. This is

supported along its length by a plurality of spacers 8 which have a disc-like configuration to enable them to slide within the duct 1. Both the spacers and the inner wall of the duct may be coated with a low coated friction, such as PTFE . At the end of the rod 7 adjacent to the port 2 is a capture mechanism 9 and on the opposite end is a piston 10. These are both described in greater detail below. The capture mechanism 9 is shown in Figs. 2A-2C. At the end of the rod is a disc 11 which may have a similar construction to the spacers 8. Mounted on the opposite side to this disc from the rod 7 is a latch mechanism 12 which comprises a set of pivotally mounted jaws 13 which define a socket 14 with an open mouth. In the present case, there are two semi-annular jaws, although there could be more segments. At the end of the socket 14 opposite to the mouth is a retractable spring-loaded pin 16, depression of which causes the jaws 13 to converge towards one another. The jaws are held on pivotal linkages 17 and are biased towards one another by spring 18.

The endoscope has an insertion tube 19 with a distal tip 20 which has a bulbous end portion having a

complimentary shape to the shape of the socket 14 when the jaws 13 converge. The distal tip 20 is mounted on a bearing 21 so that it is rotatable with respect to the remainder of - li the insertion tube 19 about the main axis 22 of the

insertion tube 19. The purpose of this rotational tip is described below. The jaws 13 are retained in a stopper 23 which is mounted adjacent to the port 2 on a spring loaded mount 24. The stopper comprises two semi-annular elements. However, as with the stopper, more than two segments may be present. Within the stopper is a resilient element 25 which retains the jaws in place. The stopper 23 also has one or more rearwardly projecting fingers 26 which engage in a

complimentary circumferential recess 27 in the latch

mechanism to hold the latch mechanism in the open

configuration as shown in Fig. 2A against the action of the spring 18.

When the tip 20 of the insertion tube 19 is inserted into the socket 14, it presses on the pin 16 thereby causing the jaws 13 to be pushed into the tube 4 and to close around the tip as shown in Fig. 2B under the action of the spring 18 as the linkages 17 work to pull the recess 27 away from the fingers 26. Further pushing of the insertion tube 19 causes the latch mechanism to be released from the stopper 23 so that the insertion tube 19 may then be inserted fully into the tube 4. The spring 18 biases the jaws closed.

This and the external diameter of the latch mechanism 12 as compared to the inner diameter of the tube 14 ensure that the insertion tube is securely held in the latch mechanism. As the insertion tube is withdrawn, the latch mechanism

12 returns into the stopper 23 and the fingers 26 catch the latch mechanism 12 by the groove 27. Further pulling on the insertion tube 19 forces open the jaws 13 by virtue of the bulbous end of the distal tip pushing against the jaws thereby releasing it to the position shown in Fig. 2A in which the pin 16 and linkages 17 are reset to their original positions.

As shown in Fig. 1, at the opposite end of the rod 7 is the piston 10. This is slidably retained within a cylinder 40 which is filled, on the side of the piston opposite to the rod 7 with a liquid 41. This liquid is pressurised by a pump 42 which pumps liquid from a reservoir 43 and is controlled in accordance with signals from the simulation software. The linear position of the piston 10 is

determined by a set of magnet sensors 44 arranged along the cylinder 40.

This simulation software is known in the art and stores a software model of the area of the body into which an instrument is inserted. It also receives data containing the linear and rotational positions of the insertion tube. From this, it can calculate the interaction between the virtual instrument and the software model of the body and is able to calculate the force which would be felt on the instrument in a corresponding real life situation. The manner in which this is done is known in the art and will not be described here.

However, the value representing the linear force feedback is sent to the pump 42 which then raises or lowers the pressure of the liquid 41 in the cylinder 40

accordingly. It should be emphasised that this change in pressure is not primarily intended to move the piston. Instead, it is simply designed to vary the resistive force felt by the user on the insertion tube 19. There may, however, be certain situations to be simulated where the piston 10 is positively moved by the liquid pressure. For example, the piston may be arranged to exert a pull (or at least a reduced push) against the insertion tube to

compensate for the frictional force on the insertion tube.

In order to achieve this, the system can first be calibrated by inserting the insertion tube 19 into the duct 5 without applying any force feedback and measuring the resistance to insertion (both linear and rotational) caused by the frictional force between the spacers 11 and duct 1 and between the insertion tube 19 and the duct 1. The system already includes measurement of the depth of

insertion of the insertion tube into the duct. Using this and the values from the calibration, the software can calculate the degree of frictional force which is being felt by the user for any depth of insertion of the insertion tube. This figure can then be subtracted from the force feedback applied to the insertion tube 19 by the piston 10 such that the resultant force felt by the user matches the force which would be felt in use with greater precision than it would be if no such friction, compensation were to be applied.

Once the insertion tube 19 has been released from the stopper 23, continued insertion by the user will push it deeper into the duct 1. This pushes the flexible rod 7 further into the duct with the spacers 8 ensuring that the rod remains centrally within the duct. This has the effect of pushing the piston 10 up the cylinder 40 thereby displacing the liquid 41 into the reservoir 43. Throughout this process, a linear position detector detects the degree of insertion of the insertion tube 19 into the duct 1 and this information is used by the simulation software as described above to set the pressure of the liquid 41 by the pump 42.

The above described mechanism is for imparting linear force feedback only to the insertion tube. For certain instances, such as for an endoscope used in colonoscopy, the user will also experience resistive forces when they twist the endoscope. In order to accommodate this, a rotational force feedback mechanism 45 is provided. This may also accommodate the linear position detector. The detector may be a known system, for example, the roller based system described in WO 2003/050783 which can be implemented as it is, except that it no longer requires there to be motors present to provide force feedback to the rollers as the linear force feedback is now being provided by the above described system. One further modification required to accommodate this rotary force feedback is the presence of the bearing 21 as described above. This means that the insertion tube 19 behind the tip 20 is free to rotate despite the fact that the tip 20 is retained within the capture mechanism 12.

A second example of a device is shown in Fig. 3. In this example, similar components have been designated with the same reference numerals.

The device is generally simplified as compared to the first example in that it is for a rigid insertion tube 19 and/or shorter insertion tubes. This means that the rod 7 and duct 1 are straight. The spacers 8 are still present to retain the rod 7 in the centre of the duct 1.

As shown in Fig. 3, the cylinder 40 is connected to a second cylinder 50 which has a larger diameter than the cylinder 40. A second piston 51 is provided in the second cylinder 50 and the cylinders are coupled together with the space between the two pistons 10, 51 being filled with the liquid 41.

A rack and pinion mechanism 52 is attached to a force feedback motor 53 arranged to provide the linear force feedback force which is transmitted to the second piston 51. As the second cylinder 50 has a greater diameter than the diameter of the cylinder 40, the length of the travel of the piston 51 can be proportionately reduced. If required, this arrangement may also be provided with the rotational force feedback provided for the first example. Fig. 4 is a schematic cut away side view of a force feedback unit containing the device as described in relation to Fig. 1. Such units represent the product as supplied to a consumer and is in the form of a workstation containing all of the items shown in Fig. 1. In the prior art design, the duct 1 which accommodates the insertion tube cannot maintain a tight radius of curvature and therefore cannot be accommodated within the workstation 60. However, in the present case, the radius of curvature of the duct 1 is such that it can readily be accommodated in this region. The coiled arrangement shown is simply one example of what can be achieved with the present invention. It is, however, possible that the duct may have a larger radius of curvature and may extend to the opposite side of the cylinder 40 such that the cylinder 40 effectively extends through the middle of the coiled duct 1. Alternatively, the duct 1 may be in the shape of a real colon.

Claims

CLAIMS : -

1. A force feedback device for applying force feedback to the insertion tube of a medical instrument, the device having:

a port to receive the tube;

a cylinder at the opposite end of the duct;

a cylinder containing a volume of liquid;

a means for pressurising the liquid in response to force feedback commands;

opposite to the first direction.

2. A device according to claim 1, wherein the duct is curved .

3. A device according to any one of the preceding clams, wherein the means for pressurising the liquid in response to force feedback commands is a pump.

4. A device according to claim 1 or claim 2, wherein the means for pressurising the liquid in response to force feedback commands is a rack and pinion mechanism.

5. A device according to any one of the preceding claims, wherein the cylinder is supplemented by a second cylinder containing a second piston arranged such that the space between the piston and second piston is filled with

hydraulic fluid, the second cylinder having a diameter greater than that of the cylinder, the second piston being exposed to the means for pressurising the liquid.

6. A device according to any one of the preceding claims, wherein the capture mechanism comprises a set of jaws which are held in an open position in a stopper in the device against the action of a spring, the mechanism being arranged to be closed around the distal end upon insertion of the distal end of the tube which dislodges the jaws from the stopper allowing the spring to close the jaws, the stopper being arranged to catch the jaws as the tube is withdrawn and is arranged such that continued withdrawal of the tube forces the jaws open against the action of the spring thereby returning the jaws to the open position.

7. A combination of force feedback device according to claim 3 with a dummy medical instrument having an insertion tube with a main longitudinal axis, the insertion tube having a distal tip engageable with the capture mechanism and being rotatable about the axis of the tube.

8. A combination according to claim 7, wherein the force feedback device further comprises an actuator to provide rotational force feedback to a portion of the insertion tube which is proximal of the rotatable distal tip portion.

9. A method of operating a force feedback device according to any one of the preceding claims, the method comprising the steps of inserting insertion tube of the medical instrument into the port;

capturing the distal end of the endoscope in the capture mechanism; sensing the depth of insertion tube;

calculating the force feedback signal to be applied to the insertion tube based on its sensed depth; and

pressurising the liquid in accordance with the

calculated force feedback.

10. A method according to claim 9, further including the step of determining from the measurement of the depth of the insertion tube a value corresponding to the frictional force between the insertion tube and the duct, and reducing the level of force feedback to compensate for the calculated frictional force.