WO2003099152A1

WO2003099152A1 - Navigator-robot for surgical procedures

Info

Publication number: WO2003099152A1
Application number: PCT/IT2003/000322
Authority: WO
Inventors: Danieli A. Guido; Fragomeni Gionata; Gatti Gianluca; Mundo Domenico
Original assignee: Calabrian High Tech S.R.L.
Priority date: 2002-05-28
Filing date: 2003-05-27
Publication date: 2003-12-04
Also published as: EP1528896A1; AU2003241154A1

Abstract

The invention is relative to a navigation system consisting in a goniometric measuring system of the relative position between its extremes, having one of the extremes fixed to the floor and the other suspended through a system of springs whose tension may be controlled by motors and measurable, to allow the links of which it is composed to rest in any configuration it may be placed into, balancing the suspended masses and transmitting its weight to the floor. The system may also, connecting front teeth, rigidly couple the various links that become active and motorized rather than be controlled manually. This may be made, for instance but not exclusively, placing a torsion spring between the two links, whose extension is adjusted by a motor, through a worm screw and mating gear. On the same links a male front teeth is placed on one side, and a bush provided with female front teeth, able to slide axially to connect the two parts upon request, locking the hinge, and making it driven by the same motor.

Description

Description Navigator - Robot for Surgical Procedures General Description of the Previous State of the Art The need to reduce ionising radiation absorption from the medical teams during orthopaedic surgeries has induced different firms to propose navigation systems allowing to visualize in Virtual Reality the instrument position with respect to the patient's body structure, on the base of radiographic or CAT initial images. These systems however, particularly suitable to the orthopaedic field, if on the one side supply the doctor a full vision of the operatory scene, eventually indicating on the screen the operations to be performed, on the other side do not supply any physical support to the doctor, that must in any event operate freely to reach the desired objectives. And this may be extremely difficult, since it is in any event necessary to position correctly the instruments, adjusting in the mean time the six degrees of freedom of an object in space. To overcome this problem operatory robots have been proposed that, on the basis of operatory preplanning, do substitute the doctor in operating the necessary resections, needed, for instance, to install a prosthesis. Now it is firm idea of the authors of this patent that the doctor should never be substituted by an equipment. One thing is to suggest, another is to perform a surgery on an human being. Only a doctor may have the experience and sensitivity to understand if a given operation, planned preoperatively on the base of images, is indeed to be performed. This originated the idea to develop a new equipment able to join the two characteristics of

Navigator and Robot, changing from one form to another on doctor's request. Practically the system is made by a six DOF self balancing gonϊometric system, whose hinges may transmit torques, through ad hoc springs whose tension may be controlled by motors, in order to exactly balance the forces acting on the links suspended to the given hinge, taking into account the position actually assumed by the system. Obviously this requires conti- nuous updating of the transmitted torques, in order to allow the operator to move without feeling the weight of the kinematical, chain supporting the operatory tools, and without having to exert big forces to move the same chain, in order to reduce to a minimum the errors caused by the physical characteristics of the goniometer. In case of shift to robot working mode, all hinges, up to that moment passive elements, are locked by frontal teeth in order to rigidly connect the two extremes of the kinematical chain, becoming active in order to correct the position, supplying the doctor the correct drilling or sawing position to accomplish the required operatory act. Obviously in this case a further degree of freedom, of translation must be placed at the end of the kinematical chain, to be unlocked when operating in robot mode, to allow for the surgical act to take place. Moreover, the system will have to be equipped, in correspondence to each encoder/hinge, also by a further motor that, through a worm screw and mating gear, drives the rotation of a front gear which, translating, blocks the hinge making it controlled directly by the motor. Possible applications in self balancing goniometer mode is the measure in space of the relative positions between its extremes, in order to reconstruct in Virtual Reality and in real time the operatory theatre, in substitution of fluoroscopy, in robot mode, upon operator's request, precise positioning of the equipment to allow for instance a precise bone resection by the doctor, that will be allowed to move the saw only in the plane defined by the robot, using a further translational degree of freedom that will be released in this situation. The doctor however will have the possibility of modify that plane, should he observe, during the surgery, that this is necessary. Differently from the robot actually used, that tend to substitute the doctor, this just works on his side, intervening, upon request, only to stabilize the operation, never to substitute the doctor, that is and must continue to be the only responsible. Description of the preferred embodiment. The preferred embodiment is made by a couple of kinematical chains, one bearing six DOF, the other seven. The first of the two presents, on the base, a first hinge aving vertical axis and whose position is monitored by an encoder, on which is mounted, through a second rigid link having horizontal axis, whose position is monitored by a further encoder, From this a third link originates, at the end of which a third hinge with encoder also with axis parallel to the second one is placed, followed by a fourth link bearing at the end still another hinge with encoder, again with axis parallel to the last two hinges To this hinge is also connected, through a fifth very short link, another hinge with encoder, whose axis should lay on a plane parallel or passing through the axis of the first encoder, followed by a last hinge with encoder, supported a sixth link, still very short, whose axis is perpendicular to the fiflh hinge, and, in extended position, also to the fourth. The presence of a possible rotating counter weight placed on the link following the first vertical hinge is also foreseen. This might also be mobile on special rails in order to balance any device configuration, since the idea is to balance the structure weight as a function of the position assumed, transmitting to the floor its entire weight.

The second kinematical chain is similar to the first, presenting, fixed to the sixth encoder a further degree of translational freedom usually locked, and that may be unlocked in robot mode.

In correspondence to each hinge there must be a device able to transmit the torque needed to exactly balance the weight of the links suspended to it, torque that must be modified as a function of the position assumed by the system.

This device may be made of a motor-pulley group that controls the tension of a cable connecting the two arms joined by the hinge, acting on a spring, fixed on the other end to one of the arms, in proximity of which a strain gauge may be placed. Obviously the cable alone would be sufficient to balance the tension, while the spring is used to allow moving the system in almost absence of loads about the equilibrium position. Such group motor- pulley cable and spring may be placed in correspondence to each hinge to make the entire mechanism self balanced. Note that the system is designed to work only on the side on which all links are present. Should anything be measured on the other side, it is enough to

80 rotate the whole system about the first vertical encoder. Table I shows a six DOF bearing a self balancing system such as the one here described.

In order to allow working also as a robot, the system will have to present, in correspondence to each measuring hinge, also a second motor that, through a worm screw and mating gear, controls the rotation of front teeth that may, translating, block the hinge

85 making it drivable by the motor. This is illustrated in Table 2. As an alternative to what previously described, it is possible, to use one motor only, possibly a step controlled one, to actuate both a torsion spring and, once front teeth are coupled, also the second arm. This is illustrated in Table 3 a and b. Note also that, to allow precision positioning of the instruments used by the doctor with

90 respect to the patient's body, and thus also a correct representation in augmented reality of the surgical procedure, it is necessary the device to be connected both to the patient and to the surgical instrument, not being admitted that the device should load the doctor with its weight, nor, even worse, the patient. In order to obtain this two different kinematical chains may be used such as the one described, and two different solutions were foud, each

95 presenting advantages and disadvantages.

A first idea might be to use two self balancing devices coupled on the base, and calibrated to supply the relative position between its extremes. Advantage of this method the certitude that both patient and operator hare coupled with equally self balancing device terminals. Two the disadvantages: a bigger size and a reduced precision, since the final kinematical

100 chain becomes composed by twelve (+ one) DOF, whose precision is a function of the degrees of freedom. And this is illustrated in table 4.

As a second alternative it is possible to use a system always bearing thirteen degrees of freedom (the last one being the one for instrument advancement), but placed in series rather than in parallel, so that with the first six one passes from the ground support to the patient

105 connection, and, with the residual seven (six + one) fron the patient to the surgical instrumen And this is presented in table 5

It is important to note that, even if the preferred instrument is characterized by a precise choice of the fashion the various constraints are coupled, it is believed that any disposition of the twelve + one constraints, whenever able to supply the measure in real time of the

110 position of the surgical tools with respect to the patient body to allow cutting or drilling as required by the surgical act, is in some way violating the present patent. Only using a similar device the doctor may move freely the instrument, characterized by an active self balancing system, in proximity of the cutting zone, indicated by the representation in Augmented Reality, and require the Robot intervention. This will block

115 the hinges, assume the required position, leaving the doctor only one degree of freedom to advance the instrument (the seventh degree of freedom of the second kinematical chain, unlocked only when al others are locked), and perform the required operation without urgency, being also able to order the system to modify the cutting plane by one or two millimetres, if this should be necessary, knowing that the system will take that into account

120 in all following operations, including the prosthesis component choice. The same instrument may also be used with a single six DOF kinematical chain for industrial dimensional control, possibly eliminating the front teeth, not necessary for this application. But the self balancing mechanism, one of the peculiarities of this device, which distinguish it from what currently available, would remain active being extremely useful.

Claims

Claims,

1) Automatic self balancing Navigator - Robot bearing seven or thirteen DOF, of which six or twelve axe for measuring and one operatory, made by a base mounted on wheels but fixable to the floor, by six or twelve measuring hinges, free but lockable through front teeth, so that the same hinges may be actuated by motors, being the hinges coupled by six or twelve rigid links, of which at least the initials have to be provided with springs whose tension may be varied by a motor, as a function of the spatial configuration assumed, in order to transmit from one link to the following a torque sufficient to maintain the same configuration, while on the last link is fixed a further translational degree of freedom, also lockable and having a measuring system that allows, when unlocked, being all other hinges locked, to actively operate on the patient, but in the direction and in the plane desired, being also measured, and hence represented in Augmented Reality the instrument advancement with respect to the patient body, that must be fixed to one of the system links. 2) Navigator-Robot bearing thirteen DOF, essentially made by a seven DOF goniometer as per claim 1, and by a second goniometer as per claim 1, but missing the seventh translational DOF, whose base elements are reciprocally fixed, to allow measuring the relative position between the two self balancing extremes, and lockable upon request on the twelve DOF, while unlocking the thirteenth, in order to permit operation in Robot mode, being the system able to measure the relative position between the surgical instrument in the hands of the doctor, and the patient's body, fixed to the other extreme of the kinematical chain.

3) Navigator-Robot bearing thirteen DOF, essentially made by a seven DOF goniometer as per claim 1, and by a second goniometer as per claim 1, but missing the seventh translational DOF, in which the second goniometer is one side placed on the floor with its base, being the seventh link fixed to the patient, working in the mean time as basic element for the second seven DOF goniometer (of which, the last one unlocked only in robot mode), being the system able to measure the relative position between the surgical instrument in the hands of the doctor, fixed to the last link^' of the second goniometer, and the patient's body, fixed to the base link of the same goniometer, being possible as described before locking and regulating the twelve DOF. 4) Navigator-Robot bearing seven DOF, essentially made by a six free DOF goniometer bearing a last DOF that may be unlocked, provided with a self balancing system and able to be blocked upon request as per claim 1. 5) Six DOF Measuring Navigator, essentially composed by a six DOF goniometer characterized by a self balancing system as per claim 1.