GB2511336A - A dummy instrument for use in a simulator - Google Patents

Abstract

A dummy endoscope system for use in an endoscopy simulator. Angulation control knobs (105) on the control body (101) are attached to a drive mechanism which moves as the knob rotates. Each drive mechanism is attached to a piston or pistons (204) slidable in a respective cylinder (205). First and second ports in the cylinder are arranged such that increasing pressure at the first or second port exerts a force on the drive mechanism in a first or second direction respectively. Each port is connected to a flexible tube (209) extending along an umbilical (103) and being connected to an actuator cylinder (211) containing an actuator piston (213). The space between the piston and actuator piston is filled with hydraulic liquid. Each actuator piston is connected to a motor (219) controlled by the endoscopy simulator to vary the pressure on the actuator piston and hence the force felt at the control knobs in accordance with the requirements of the simulator.

Description

A DUW INSTRUMENT FOR USE IN A SIMULATOR

The present invention relates to a dummy instrument for use in a simulator. In particular, the present invention relates to a dummy endoscope for use in an endoscopy simulator.

?n endoscopy simulator is a system useful in training operators in the use of endoscopes without risking harm to patients. The system consists of a dummy endoscope which mimics, as closely as possible, the look and feel of a real endoscope. The insertion tube of the endoscope is inserted into a housing (whereas a real endoscope would be inserted into a patient body). Sensors within the housing measures the linear and rotational position of the insertion tube and sensors on the angulation controls sense the orientation of the.tip. This is then used to determine the position of the insertion tube in relation to a software model of the colon.

The software model determines a view corresponding to one that the user would see in a real endoscope procedure and displays this on the screen. In addition, the software model is able to determine the interaction between the insertion tube and the wall of a simulated colon based on the position data and calculate the resistive force that would be flt by the user in a real procedure. Within the housing is a force feedback mechanism to provide variable linear and rotational force feedback so that the user experiences realistic forces as they manipulate the insertion tube. This is important as the operator needs to learn how the endoscope will feel in practice.

An early example of an endoscopy simulator is described in GB 2 252 656.

A real endoscope is provided with an angulation control on the endoscope handle. This control takes the form of a pair of coaxial rotatable knobs one for controlling up/down angulation and the other for left/right angulation. Each knob has a cog within the endoscope handle around which a chain passes. The ends of the chain are each connected to a wire which extends to the tip of the insertion tube. Thus, turning one of the handles causes the wire to move (via the cog and chain) and, depending upon the direction of movement, the endoscope tip is caused to bend in an up/down or left/right direction. Thus, by manipulating the lb angulation controls, the user is able to steer the endoscope through the colon and to execute various other procedures.

If the tip is manipulated such that it encounters the wall of the colon, the user experiences a resistive force on the control knobs and it is important to learn to recognise this as this gives an indication that they are pressing the end of the endoscope against the colon wall. A well designed simulator needs to be able to provide realistic force feedback to the angulation controls to replicate this force.

Examples of attempts to address this problem are disclosed in Wa 2003/058583, Wa 2004/015654 and WO 2005/059866. In each case, the approach taken is to use as much as possible of the real endoscope mechanism in order to replicate this force. Thus, the angulation wires which previously extended from the endoscope handle to the tip of the insertion tube are re-routed around a pulley system in the handle and they extend down the umbilical of the endoscope. At the distal end of the umbilical, the up/down wires are connected to a wheel attached to a first motor while the left/right wires are connected to a wheel attached to.a second motor. The simulation software is provided with information concerning the linear and rotational insertion position of the endoscope as well as the up/down and left/right position of the angulation tip. This is compared with the software model of the colon to determine the amount of force feedback to be applied to the angulation controls.

This force is then replicated on the two motors which provide a resistance to the movement to the wires which the user then feels on the angulation controls.

whilst this approach has met with some success, it does suffer from a problem. In a real endoscopic procedure, the endoscope is steered along a tortuous path as it travels along the colon. This often results in loops occurring in the insertion tube. Endoscopists are trained to manipulate the handle of the endoscope such that these loops are transferred from the insertion tube to the umbilical. As a result of this, however, the umbilical can often contain multiple loops which have a reasonably tight radius of curvature. This causes a problem for the above described angulation force feedback mechanism. The umbilical contains four wires that it was not designed to contain in a real endoscope. Further, these wires are required to slide relatively to one another as the angulation controls are manipulated. When the umbilical contains a number of loops, the tight radius of curvature of the umbilical increases the frictional force on the wires to such an extent that the user experiences significant resistive forces which are undesirable as they are not generated via the simulation software. The problem could be addressed by sensing the curvature of the umbilical and attempting to estimate the frictional force caused by this curvature and to subtract this from any force feedback applied to the angulation controls. However, the force is difficult to estimate, and this does not deal with the problem that the unwanted frictional force will still be applied even when little or no force feedback force is called for in the simulation.

According to the present invention there is provided a dummy endoscope system for use in an endoscopy simulator, the system comprising a dummy endoscope comprising an insertion tube and an umbilical both extending from a control body, a pair of rotatable angulation control knobs on the control body, each knob being attached to a drive mechanism which moves as the knob rotates, each drive mechanism being attached to a piston which is slidable in a cylinder or to a pair of pistons each of which is slidable in a respective cylinder first and second ports in the cylinders or cylinders arranged such that increasing pressure at the first port exerts a force on the drive mechanism in a first direction and increasing pressure at the second port exerts a force on the drive mechanism in the opposite direction, each port being connected to a flexible tube extending along the umbilical to the distal end and being connected to a hydraulic actuator comprising an actuator cylinder containing an actuator piston, the space between the piston and actuator piston being filled with hydraulic liquid, each actuator piston being connected to a motor arranged to be controlled by control signals from the endoscopy simulator to vary the pressure on the actuator piston and hence the force felt at the control knobs via the hydraulic fluid and piston in accordance with the requirements of the simulator.

Hydraulic actuators are traditionally used in very high power applications such as transmissions on hydraulic vehicles and lifting equipment. As far as we are aware, the present invention is unique in employing hydraulic transmission in such a low power environment. However, using the hydraulic transmission in this new way provides considerable berief its over the prior art system which uses wires in the umbilical. The flexible tubes which extend along the umbilical and are filled with liquid are able to accommodate the bends in the umbilical without kinking.

Further, as there is no relative sliding between adjacent solid elements as in the case of the wires, the problems with friction as set out above are eliminated. The invention also reduces the maintenance required as it eliminates the wires that have to be re-tensioned or replaced relatively frequently.

As well as providing more accurate control, the present invention also provides enhanced functionality. In a real endoscope, in use, when the user has changed the orientation of the tip using the angulation controls and subsequently lets go of the controls, the pressure exerted by the colon on the tip will cause the tip to be pushed back to the neutral position (which will not necessarily be a straight ahead position) and, in the process, will rotate the control knobs as it moves. With the hydraulic transmission, a similar effect can be achieved in the simulation as the hydraulic pressure is able to transmit relatively low levels of force even when the umbilical is curved. Such functionality is not possible with the wire based system of the prior art as such low level forces cannot be reliably transmitted to the angulation control as they tend to be insufficient to overcome the frictional forces on the wires.

Therefore, with this invention, the user experiences a more realistic feel in the controls and is able to experience certain effects which they will encounter in practise and which cannot otherwise be simulated.

The pistons in the hydraulic actuators are effectively pulled via the drive mechanism as the control knobs rotate.

They are therefore required to have a sufficient stroke to allow them to accommodate the full range of movement of the control knob. On the other hand, they are required to produce a very low (in hydraulic terms) output force.

Although a conventional hydraulic actuator could be employed, it would effectively be over-rated such that it would not operate at its optimum power range making it unresponsive. It would also require modification to the control body to incorporate it.

Preferably, therefore, each cylinder has a bore of less than 10mm and a stroke of greater than 20mm. Each piston/cylinder combination preferably generates a maximum output force of less than 2N.

* Preferably, each piston that is connected to a motor is connected by a piston rod which is sealed with respect to the cylinder and is connected to a coupling element which couples the piston rod to the motor, the connecting rod and the piston rod being coaxial. This coaxial arrangement ensures that all forces transmitted to the piston are axial thereby facilitating the ability of the seal to seal against the piston rod. Preferably, also, the pistons in the control body each have a piston rod which is sealed to the cylinder at the end which is coupled to respective drive mechanism, with the drive mechanism and piston rods being coaxial.

Again, this helps to maintain the integrity of the seal.

The drive mechanism may be any suitable arrangement such as a rack and pinion. However, it is preferably a belt drive. This belt drive may be of any suitable form, such as one or more cables of a flat belt. However, preferably, the belt drive is a chain which engages with a cog attached to the control knob. This provides for a more reliable transmission of higher forces.

The cylinders may each be individually housed in separate elements. However, preferably, the first cylinders are housed in a first cylinder block and/or the second cylinders are housed in a second cylinder block.

Art example of a dummy endoscope in accordance with the present invention will now be described with reference to the accompanying drawings, in which: Fig. 1 is a schematic view of the simulator system incorporating the dummy endoscope; Fig. 2 is a schematic drawing showing the angulation force feedback system; Fig. 2A shows a detail of one of the cylinder arrangements; Figs. 3A and 3B are diagrammatic views of the hydraulic and mechanical systems showing movement in opposite directions; and Fig. 4 is a view similar to Fig. 3A showing a further examp]e.

The basic system to which the invention is applicable is shown schematically in Fig. 1. An endoscope 100 consists of a control body 101 with an insertion tube 102 and an umbilical 103 at the distal end of which is a connector 104.

The control body 101 is provided with a pair of concentric angulation control wheels 105 as found on a conventional real endoscope.

The connector 104 connects to a force feedback unit 110. The insertion tube 102 is also inserted into an orifice in the force feedback unit 110. Here, the insertion tube 102 engages with sensors (not shown) which monitor its linear and rotational position and a force feedback mechanism (not shown) to transmit linear and rotational force feedback to thS insertion tube as appropriate. A suitable sensing and force feedback arrangement is disclosed in WO 03/050783.

The system is controlled by a controller 106 which interfaces with the force feedback unit 110. The controller 106 also controls the graphical simulation which is displayed on a monitor 107 and also interfaces with a keyboard 108. It will be appreciated that other user interfaces such as a mouse, or touch-sensitive screen may alternatively be used.

It should be noted that the simulation software which calculates the graphical display and also levels of force feedback to be applied to the insertion tube and angulation controller are well known in the art and will not be S descri1ed here. The improvement provided by the present invention relates to the manner in which the angulation force feedback is to be transmitted to the control wheels and this is described below with reference to Figs. 2 and 3.

The control wheels 105 of a conventional endoscope are arranged as a co-axial pair with the outermost wheel having a smaller diameter than the innermost wheel to allow either wheel to be gripped and rotated individually. Rotation of one of the wheels causes the tip of the insertion tube 102 of the endoscope to move in an up/down direction, while the other wheel controls movement in the orthogonal direction nominally designated as the left/right direction. The two wheels are arranged on concentric shafts 200 each terminating in a cog 201 around which a chain 202 is fitted.

In a real endoscope, the ends of the chain are connected to cables which extend along the insertion tube 102 to the distal tip to allow the above mentioned movement to be transmitted to the tip. The components described to date are components of a conventional endoscope. In the present invention, the angulation cables extending to the tip of the insertion tube are replaced by the mechanism described below.

The mechanism described below is duplicated in that there is one mechanism for the up/down control wheel 105 and the same mechanism for the left/right control wheel 105.

-10 -Both mechanisms are shown in Fig 2 and Fig. 2A, but Fig. 3 only describes one such mechanism. As the mechanism is duplicated, only one will be described except.where the specification specifies that both are being referred to.

The end of each chain 202 is attached to a respective piston rod 203 which is fixed to a piston 204. The piston 204 is reciprocally movable in a respective cylinder 205.

The cylinders 205 are particularly small for hydraulic cylinders (for example having an 8mm bore and a 30mm stroke). Such hydraulic cylinders are not commercially available. However, pneumatic cylinders are available with the correct dimensions and these can be used in this context. The interface between the piston rod 203 and the cylinder 205 is sealed by a seal 206. One such seal suitable for the purpose is a 3mm ID piston rod seal, for example, available from Trelleborg. The second seal 207 seals between the piston 204 and the cylinder 205.

The cylinder 205 is filled with a hydraulic fluid 210.

One example of this is QE Dynobear 22 available from Q8 oils. This is a low viscosity oil which has been found in tests to be particularly suited to this application. Other options include de-ionised water with additives and other low-viscosity hydraulic fluids.

The physical layout of the cylinders 204 is shown in Figs. 2 and 2A where the two cylinders described above are positioned together with the two cylinders for the left/right wheel in a two-by-two array which may be formed as a single cylinder block.

-11 -Each cylinder has a port 208 from which a flexible tube 209 extends. This is filled with hydraulic fluid. As shown in Fig. 2, the four tubes from the four cylinders 204 are S bundled together such that they extend along the umbilical 103. As shown in Fig. 2A, the ports 208 are physically positioned at the end of the cylinder opposite to the piston rods 203 and are then re-routed back past the cylinders through gaps between the cylinders.

The four hydraulic tubes extend all the way to the distal end 210 of the umbilical. The arrangement of cylinders, pistons and motors described below may be positioned in the connector 104 at the distal end of the umbilical 103,. or in the force feedback unit 110 as necessary.

The ends of the two cylinders 205 on the opposite side of the seals 206 of the piston 204 from the seals 206 are connected by a line 209' providing a direct hydraulic connection between the two cylinders. As an alternative, the line 209' may be omitted. In such a case1 however, any hydraulic fluid leaking past the seal 207 will be lost to the environment. With the additional line 209', the hydraulic fluid circuit is effectively closed.

Each of the tubes 209 is connected to one of a second set of cylinders 211 via a respective port 212. The cylinders 211 have pistons 213 and rods 214 with seals 213, 216 as described above in relation to the first set of cylinders. A line 209'' for hydraulic fluid directly connects the cylinders 211 on the side of the cylinder opposite to the pistons 212. The piston rod 214 is connected to a chain 217 which is wrapped around a pulley 218 connected to a motor 219. There is a second motor (not shown) for the tubes and cylinders associated with the S left/right wheel.

During operation of the simulation system, the degree of insertion of the insertion tube 102 and its orientation are sensed sensors in a manner known in the art. Sensors are also provided to detect the position of the wheels 105 which provides an indication of the position of the simulated tip of the insertion tube. This information is processed by the controller 106 which compares the detected position of the insertion tube against a stored software model of the colon and determines the forces that would be exerted by the colon on the insertion tube in use.

Fig. 3A shows the situation where the user rotates the control knob 105 in a clockwise direction. This causes the upper chain 202 and the corresponding uppermost piston 204 to move to the right, while the lowermost piston moves in the opposite direction as shown by the arrows in Fig. 3A. At this point, the fluid in the lowermost cylinder is actively displaced along the lowermost tube 209 and flows into lowermost cylinder 211 pushing the piston 213 to the left thereby generating a clockwise force on the motor 219. At the same time, the displacement of the uppermost piston 204 to the right draws fluid to the uppermost cylinder 210 which pulls the uppermost piston 213 to the right at the same time that it is also being pushed to the right by a flow through line 209''. This secondary flow in the uppermost part of the system effectively works to remove any slack from the -13 -mechanical linkages in the system so that a change in the input direction of the control knobs is quickly translated to the force feedback system.

Movement in the opposite sense is shown in Fig. 3B.

This shows the opposite situation where the control wheels are rotated anticlockwise. All of the flows are reversed, but the principle of operation is essentially as described above.

It should be emphasised that the primary purpose of the hydraulic arrangement and pistons described above is not to actually move the control wheels 105 as this is done by manual rotation, but simply to provide an increased resistance to the motion. If the torque provided to a motor 219 is increased, it will be appreciated that the resistance to the rotation of the corresponding wheel 105 is proportionately increased. Under certain circumstances, however, the hydraulic force may be used to move the pistons 204, 213. If, for example, the user releases the controls and the software detects that there is a sufficient force exerted by the colon on the insertion tube that it would, in practice, cause a movement bf. the tip of the tube, this can be modelled in the present invention, which can vary the hydraulic pressure to drive the pistons 203, 204 and hence the control wheels 105 to the desired position.

A further example of a dummy endoscope system is shown in Fig 4. This shares a number of common components with the previous example and the same reference numerals have been used to designate the same components.

-14 -With this example, the pair of cylinders 205 and the connecting line 209' are replaced by one double ended cylinder 300. The pair of pistons 204 have been replaced by a double acting piston 301. with the first example, the pistons 204 were directly in line with the upper and lower chains 202. As this is not possible with the double acting piston 301, a pulley 302 is required which serves to reverse *the direction of the lowermost chain 202, to bring it into line with the double acting piston 301. Otherwise, as is apparent from a comparison of Fig. 3A and Fig. 4, clockwise rotation of a control wheel 105 will displace the hydraulic fluid in a similar manner and will experience the same force feedback from the corresponding motor 219.

In a similar manner, the cylinders 211 and pistons 215 associated with the motor may also be replaced with a double acting cylinder/piston arrangement. This may also require a further pulley if the same motor is to be retained.

Alternatively, the motor may be replaced by a pair of motors, e.g. linear motors, one for each chain 217.

Claims (7)

1. -15 - CLAIMS: - 1. A dummy endoscope system for use in an endoscopy simulator, the system comprising a dummy endoscope comprising an insertion tube and an umbilical both extending from a control body, a pair of rotatable angulation control knobs on the control body, each knob being attached to a drive mechanism which moves as the knob rotates, each drive mechanism being attached to a piston which is slidable in a cylinder or to a pair of pistons each of which is slidable in a respective cylinder, first and second ports in the cylinder or cylinders arranged such that increasing pressure at the first port exerts a force on the drive mechanism in a first direction and increasing pressure at the second port exerts a force on the drive mechanism in the opposite direction, each port being connected to a flexible tube extending along the umbilical to the distal end and being connected to a hydraulic actuator comprising an actuator cylinder containing an actuator piston, the space between the piston and actuator piston being filled with hydraulic liquid, each actuator piston being cormected to a motor arranged to be controlled by control signals from the endoscopy simulator to vary the pressure on the actuator piston and hence the force felt at the control knobs via the hydraulic fluid and piston in accordance with the requirements of the simulator.
2. 2. A system according to claim 1, wherein each cylinder has a bore of less than 10mm and a stroke of greater than 20mm.

   -16 -
3. 3. A system according to claim 1 and claim 2, wherein each piston/cylinder combination generates a maximum output force of less than 2N.
4. 4. A system according to any one of the preceding claims, wherein each actuator piston is connected by a piston rod which is sealed with respect to the cylinder and is connected to a coupling element which couples the piston rod to the motor, the connecting rod and the piston rod being coaxial.
5. 5. A system according to any one of the preceding claims, wherein the pistons in the control body each have a piston rod which is sealed to the cylinder at the end is coupled to respective drive mechanism, with the drive mechanism and piston rods being coaxial.
6. 6. A system according to any one of the preceding claims, wherein the drive mechanism is a belt drive.
7. 7. A system according to any one of the preceding claims, wherein the first cylinders are housed in a first cylinder block and/or the second cylinders are housed in a second cylinder block.