Collaborative medical robot for securing the insertion of medical instruments

Abstract

The invention relates to a medical robot (10) for assisting a practitioner in a medical procedure. The medical robot comprises a robotic arm (13) provided, at one end, with a tool guide (14) that is intended to guide a medical instrument (15) along a planned trajectory. The medical robot (10) comprises a control unit (12) that is configured to control the movement of the robotic arm (13). A "collaborative axial control" mode enables the tool guide (14) to be moved along the planned trajectory axis from an insertion position to the patient's body (20) and then back to the insertion position. This enables the medical instrument (15) to be partially inserted when the tool guide is close to the patient and then fully inserted when the tool guide is in the insertion position. This prevents the medical instrument from bending upon the insertion thereof.

Description

Collaborative medical robot to safely insert medical instruments Field of invention The present application belongs to the field of robotic devices for assisting a practitioner during a medical procedure. More particularly, the application relates to a medical robot comprising a robotic arm equipped with a tool guide for holding, guiding and releasing a medical instrument during a minimally invasive medical procedure. State of the art Minimally invasive or percutaneous medical procedures may require a practitioner to insert one or more medical instruments (e.g., a needle, probe, catheter, etc.) into a patient's body to a certain depth to reach a target point in an anatomy of interest (e.g., a tumor in the liver, lung, kidney, or bone). When the medical instrument insertion procedure is performed entirely by the practitioner, the outcome of the procedure is highly dependent on the practitioner's skill. The accuracy of the procedure can be improved with the assistance of remote-controlled medical robots. Here again, the success of the procedure remains partially dependent on the practitioner's skill and may require continuous acquisition of medical images of the patient, which involves subjecting the patient to high doses of radiation. To further improve the accuracy of the insertion gesture and limit the radiation doses to the patient, it is possible to use automatically controlled robotic arms. For example, the practitioner indicates on a pre-interventional medical image a trajectory that the medical instrument must follow from an entry point located at the patient's skin level until reaching a target point in the patient's anatomy of interest. The robotic arm can be equipped with a tool guide to guide the medical instrument along an axis corresponding to that of the planned trajectory. The robotic arm can then be controlled to automatically adopt an insertion pose (position and orientation) in which the tool guide allows the medical instrument to be guided along the planned trajectory until reaching the target point in the anatomy of interest. When the robotic arm is in the insertion position, the tool guide is generally at a significant distance (several centimeters or even more than ten centimeters) from the patient's skin. This distance depends on the length of the medical instrument and the depth to which it is to be inserted into the patient's body (the insertion depth corresponds to the distance between the entry point at the skin and the target point). It then happens that the medical instrument is deviated from the planned trajectory when it pierces the patient's skin at the entry point. The medical instrument generally has a certain flexibility, and the greater the distance between the tool guide and the entry point at the time of insertion, the greater the risk of deviation of the medical instrument from the planned trajectory. This problem of deviation (curvature) of a medical instrument is known and one of the most used solutions to resolve this problem consists of calculating a deviation from the planned trajectory (see for example paragraphs

[0188] has

[0190] of US patent application 2022 / 0265355 A1 ). For example, mathematical models can be used to determine the potential bending or twisting of a medical instrument (depending on its length, diameter, material used, etc.). This solution is not ideal due to the accuracy errors in the deflection estimation. Another solution is to check, after insertion, whether the instrument has deviated from the trajectory and, if necessary, to correct the positioning of the instrument accordingly. This solution is also not ideal since it may require acquiring additional medical images (greater irradiation of the patient) and inserting the medical instrument into the patient several times (prolonging the duration of the procedure). Furthermore, in the case of percutaneous tumor ablation, this solution may also lead to an increased risk of tumor spread. International patent application WO 2022 / 195210 A1 describes a medical robot with a robotic arm equipped with a tool guide. The medical robot is configured to control the movement of the robotic arm in a collaborative mode in which the speed of movement of the tool guide is determined based on a force exerted by the practitioner on the tool guide. The movement of the tool guide can also be constrained in particular directions. However, this document does not address the problem of the deflection of the medical instrument during its insertion into the patient's body. US patent application 2016 / 242849 A9 describes a medical robot comprising a robotic arm equipped with an effector coupled to a distal end of the arm. The effector may comprise a surgical instrument. Patent application US 2019 / 282301 A1 describes a guidance system by image that allows you to define the trajectory of a needle by setting the locations of an insertion point and a target point. Statement of the invention The present application aims to remedy all or part of the drawbacks of the prior art, in particular those set out above, by proposing a solution for making the angle and depth of insertion of a medical instrument more reliable during a minimally invasive procedure. For this purpose, and according to a first aspect, a medical robot is proposed for assisting a practitioner during a minimally invasive medical intervention on an anatomy of interest of a patient. The medical robot comprises a robotic arm, a distal end of which is equipped with a tool guide intended to guide the insertion of at least part of a medical instrument into the patient's body along a planned rectilinear trajectory between an entry point located at the level of the patient's skin and a target point located in the anatomy of interest. The medical robot comprises a control unit configured to control the robotic arm in order to move the tool guide. The control unit is configured to determine and memorize an insertion pose from the planned trajectory. In an "automatic control" mode, the control unit is configured to autonomously move the tool guide to the insertion pose.In a “collaborative axial control” mode, the control unit is configured to determine, using a force sensor coupled to the tool guide, a force exerted by the practitioner on the tool guide, and to move the tool guide according to the force thus determined. In the collaborative axial control mode, the movement of the tool guide is constrained to allow only:. - a movement allowing a translation of the tool guide along the axis of the planned trajectory, or - a movement allowing a translation of the tool guide along the axis of the planned trajectory and a rotation of the tool guide around the axis of the planned trajectory. In the collaborative axial control mode, the control unit is configured to provide haptic feedback to the practitioner when the tool guide returns to the insertion pose. In this application, the term "lay" is to be understood as meaning "position and orientation". The "insertion lay" corresponds to a lay of the tool guide at which the tool guide has a guide conduit for guiding the medical instrument along the axis of the planned trajectory and at the exact depth for reach the target point. During insertion, the medical instrument is guided in translation by the guide duct until it reaches a stop position (a part of the medical instrument then comes into abutment against the tool guide and prevents further insertion). The insertion pose is defined such that when this stop position is reached, the distal end of the part of the instrument which has penetrated the patient's body is at the target point. When the part of the medical instrument intended to penetrate the patient's body has axial symmetry along the axis of the guide duct, the different poses of the tool guide obtained by rotation along this axis correspond to the same insertion pose. Collaborative axial control mode allows the tool guide to be moved from the insertion pose to a position closest to the patient's skin at the entry point, while maintaining the axis of the planned trajectory. The medical instrument can then be placed in the tool guide and partially inserted into the patient's body when the tool guide is closest to the patient's skin, to avoid inflection of the medical instrument and deviation from the planned trajectory. Collaborative axial control mode and haptic indication then allow the tool guide to be returned exactly to the insertion pose (the medical instrument is then still partially inserted). Once the tool guide is returned to the insertion pose, the insertion of the medical instrument can be completed to the stop position to reach the target point. When the tool guide is returned to the insertion pose in the collaborative axial control mode, the medical instrument is in place and the robotic arm or practitioner may potentially obstruct the line of sight of an optical navigation system used to determine the tool guide pose. Having previously recorded the insertion pose in the medical robot's frame of reference allows the medical robot to autonomously return the tool guide to the insertion pose without using an optical navigation system. Haptic feedback allows the practitioner to feel the exact moment the insertion position is reached. Haptic feedback can optionally also allow the practitioner to feel the approach to the insertion position. This allows for easy and intuitive return to the insertion position. Haptic feedback gives the user a virtual notch impression when the tool guide reaches the insertion position. In particular embodiments, the invention may further comprise one or more of the following features, taken individually or in any technically possible combination. In particular embodiments, in the collaborative axial control mode, when the distance between a current pose of the tool guide and the insertion pose is less than a first threshold, the control unit is configured to calculate a movement speed of the tool guide as a function of a gain factor applied to the force exerted by the practitioner on the tool guide, the value of the gain factor gradually decreasing as a function of the distance between the current pose and the insertion pose. Decreasing the tool guide movement speed allows the practitioner to feel the approach of the insertion position. In particular embodiments, in the collaborative axial control mode, when the distance between a current pose of the tool guide and the insertion pose is less than a second threshold, the control unit is configured to limit or maintain the speed of movement of the tool guide at a predetermined speed regardless of the force exerted by the practitioner on the tool guide. In particular embodiments, in the collaborative axial control mode, the control unit is configured to prohibit any movement of the tool guide for a predetermined duration when the insertion pose is reached. The momentary stoppage of the tool guide movement allows the practitioner to feel the exact moment when the insertion position is reached. The insertion position may in particular be determined using a navigation system (for example an optical navigation system) and a pre-interventional medical image. Thus, in particular embodiments, the tool guide comprises at least one marker detectable by a navigation system and the control unit is configured to: - receive, from said navigation system, initial information relating to a positioning of the tool guide in a reference frame of the navigation system, - receive, from said navigation system, a second piece of information relating to an insertion position, in the reference frame of the navigation system, that the tool guide must take to guide the medical instrument along the planned trajectory until reaching the target point, - determine the insertion pose, in a reference frame of the medical robot, from the first information and the second information. In particular embodiments, the second information corresponds to a pose, in the reference frame of the navigation system, of a patient reference intended to be placed on the patient near the anatomy of interest. patient reference comprises at least one marker detectable by the navigation system and at least one radiopaque marker. The control unit is configured to determine the insertion pose from the pose of the patient reference and from the planned trajectory. The planned trajectory is defined relative to the pose of the patient reference using a pre-interventional medical image on which the anatomy of interest of the patient and said at least one radiopaque marker of the patient reference are visible. In particular embodiments, the portion of the medical instrument intended to penetrate the patient's body has axial symmetry along an axis which, upon insertion of the medical instrument, corresponds to the axis of the planned trajectory. In the collaborative axial control mode, the movement of the tool guide is constrained to limit it to a movement allowing a translation of the tool guide along the axis of the planned trajectory and a rotation of the tool guide around the axis of the planned trajectory. With such arrangements, the part of the instrument intended to penetrate the patient's body is unchanged when it is rotated around the axis of symmetry. In this case, the collaborative axial control mode can act both in translation and in rotation around the trajectory axis. This allows the tool guide position to be changed without changing the trajectory axis (the trajectory axis is the same as the guide duct axis, and the guide duct remains identical when the tool guide is rotated around this axis). When the tool guide is brought close to the patient's skin, the rotation control mode allows the tool guide's position to be modified while keeping the guide conduit along the trajectory axis. This allows, for example, avoiding a collision of the tool guide with an obstacle (for example, the patient or a marker positioned on the patient's body). At the insertion position, the rotation control allows the tool guide's position to be modified without changing the insertion position (any rotation of the tool guide around the trajectory axis corresponds to the same insertion position because the guide conduit remains identical). This can, in particular, clear the practitioner's workspace. In particular embodiments, the tool guide comprises two jaws. Each jaw comprises a groove. The jaws can be driven between a closed position in which the grooves are adjacent and define a guide conduit for holding the medical instrument and guiding it in translation, and an open position in which the grooves are spaced apart from each other for placing or releasing the medical instrument. The guide conduit takes on an insertion position coaxial with the planned trajectory. The transition from the closed position to the open position can be caused by pressure from the practitioner on a lever formed by a bearing surface of one of the jaws. In the collaborative axial control mode, the control unit is configured to transpose the force exerted by the practitioner on the tool guide to a virtual application point positioned such that the axis of a pressure force exerted on the lever and the axis passing through an actual application point of the pressure force and the virtual application point form an angle of less than twenty degrees. When the tool guide is closest to the patient's skin, the practitioner presses the lever to open the jaws to place the medical instrument. The practitioner then releases the lever so that the tool guide holds the medical instrument, and proceeds to partially insert the medical instrument. Before raising the tool guide to the insertion position to finalize the insertion of the medical instrument, the practitioner presses the lever again to open the jaws of the tool guide. The particular position of the force application point in the control law makes it possible to avoid untimely rotation of the tool guide when the practitioner presses the lever to open the jaws of the tool guide before replacing it at the insertion position. This allows an intuitive transition from translational control to rotational control: pressure on the lever does not cause rotation of the tool guide; on the other hand, pressure exerted on another part of the tool guide can cause rotation of the tool guide. In particular embodiments, the robotic arm has at least six degrees of freedom. The use of at least six degrees of freedom advantageously makes it possible to achieve any pose for the tool guide in three-dimensional space. Presentation of figures The invention will be better understood by reading the following description, given by way of non-limiting example, and made with reference to the following figures: [Fig. 1] a schematic representation of an embodiment of a medical robot according to the invention, [Fig. 2] a schematic representation of a path to be followed by a medical instrument from an entry point at the patient's skin to a target point in or near a region to be treated in the patient's anatomy of interest, [Fig. 3] A schematic representation of the robotic arm of the medical robot shown in Figure 1, [Fig. 4] A schematic representation of the tool guide attached to a distal end of the robotic arm shown in Figure 3, [Fig. 5] a detailed representation of the tool guide shown in Figure 3, [Fig. 6] another representation of the tool guide, when the medical instrument is held by the tool guide, [Fig. 7] a schematic representation of one embodiment of a patient reference, [Fig. 8] an illustration of the collaborative axial control mode, the tool guide being positioned at the insertion pose, [Fig. 9] an illustration of the collaborative axial control mode, the tool guide having been moved in translation from the insertion pose, along the axis of the planned trajectory, to be approached at the entry point, to allow partial insertion of the medical instrument, [Fig. 10] an illustration of the collaborative axial control mode, the tool guide having been replaced at the insertion position to finalize the insertion of the medical instrument until reaching the target point, [Fig. 1 1] a schematic representation of one embodiment of the tool guide holding system, [Fig. 12] a schematic representation of a force applied to one of the jaws of the holding system of figure 11 to move it into the open position, [Fig. 13] a schematic representation of a force applied to one of the jaws of the holding system of Figure 11 to hold it in the open position, [Fig. 14] a representation, for a particular example of implementation, of the variation in the speed of movement of the tool guide as a function of the distance which separates the current position of the tool guide and the insertion position, for a constant force exerted by the practitioner on the tool guide. In these figures, identical references from one figure to another designate identical or similar elements. For reasons of clarity, the elements represented are not necessarily to the same scale, unless otherwise indicated. Detailed description of an embodiment of the invention Figure 1 schematically represents an example of an embodiment of a medical robot 10 according to the invention. The medical robot 10 is used to assist a practitioner during a minimally invasive medical intervention on an anatomy of interest of a patient 20 positioned on an intervention table 21. This type of intervention generally requires the insertion by the practitioner of one or more medical instruments 15 into the body of the patient 20 from a point input located at the patient's skin level to a certain depth to reach a target point in or near a region of the anatomy of interest to be treated. The intervention may in particular aim to perform the ablation or biopsy of a tumor in an organ or in a bone, to treat a bone pathology (for example by vertebroplasty or cementoplasty), or to stimulate a particular anatomical area. The anatomy of interest may correspond to an organ or a bone, for example the liver, a lung, a kidney, the brain, a vertebra, the tibia, the femur, the hip, the knee, the bones of the pelvis, the pelvis, etc. The medical instrument 15 may be a needle, an electrode, a probe, a drill, a trocar, a screw, etc. Figure 2 illustrates a rectilinear trajectory 41 that the medical instrument 15 must follow from an entry point 43 located at the skin of the patient 20 to a target point 44 to be reached in or near a region to be treated in the anatomy of interest 45 of the patient 20. In the example considered and illustrated in Figure 1, the medical robot 10 comprises a base 11. The base 11 of the medical robot 10 is equipped with motorized wheels, which allows the medical robot 10 to move in different directions by translational and / or rotational movements. The medical robot 10 further comprises a robotic arm 13, one end of which is connected to the base 11. At the other end of the robotic arm 13 is fixed a tool guide 14 intended to guide a medical instrument 15 (for example a needle, a probe, an electrode, or a trocar). The medical robot 10 is used to assist a practitioner in positioning, holding, or guiding the medical instrument 15 during the medical procedure. The medical robot 10 then acts as a third hand for the practitioner. As illustrated in Figure 1, the medical robot 10 comprises a control unit 12 configured to control the movement of the robotic arm 13 (and therefore of the tool guide 14). The control unit 12 comprises at least one processor 122 and at least one memory 121 (magnetic hard disk, electronic memory, optical disk, etc.) in which a computer program product is stored, in the form of a set of program code instructions to be executed to implement the different steps of a method for positioning the robotic arm 13 and more particularly the tool guide 14. The robotic arm 13 is also illustrated in Figure 3. In the example considered and illustrated in Figures 1 and 3, the robotic arm 13 comprises six rotoid joints 131 to 136 conferring six degrees of freedom allowing the medical instrument 15 to be positioned and / or moved in any pose of the tri-space dimensional. Advantageously, the joints 131 to 135 of the robotic arm 13 are not aligned and have an offset relative to each other, which allows a greater number of possible configurations of the robotic arm 13. Each joint comprises at least one encoder making it possible to know its angular position in real time. A configuration of the robotic arm 13 then corresponds to a set of parameter values ​​taken by the joints 131 to 136 (for example the value of an angle of rotation for each joint). The rotoid joint 136 corresponds to a rotation around a main axis of the tool guide 14. It should be noted that, when the medical instrument 15 has axial symmetry for the part of the instrument which is intended to penetrate the patient's body, it is not essential to be able to rotate around the axis of symmetry (five degrees of freedom are in fact sufficient to guide and release the medical instrument in this case). This additional degree of freedom makes it possible to be in a situation of redundancy and to have an infinite number of possible configurations of the robotic arm 13 for a given position of the tool guide 14. This situation of redundancy is particularly useful for adapting to constraints linked to the position of the patient 20 or to the configuration of the operating room. As illustrated in Figures 3 and 4, the tool guide 14 is fixed to the robotic arm 13 by means of a flange 17. The tool guide has a main axis 145 represented in Figure 4 by a dotted line. The tool guide 14 is coupled to a force sensor 16 to allow the control unit 12 to determine a force exerted on the tool guide 14. This force can in particular be exerted by the practitioner when he manually moves the robotic arm 13. As illustrated in Figures 5 and 6, the tool guide 14 comprises a body 141 with a base 142 intended to be fixed to the flange 17 using screws 143, as well as a holding system 50 comprising two parts movable relative to each other. The holding system 50 is intended to hold the medical instrument 15 at the end of the body 141 of the tool guide 14 opposite the base 142. The two movable parts of the holding system 50 can be driven by a drive system such as a gear, a cam, a screw with reverse threads and / or a linear actuator, in order to lock or release the medical instrument 15. The tool guide 14 makes it possible, for example, to guide medical instruments of different diameters. For example, such a guide makes it possible to guide medical instruments whose diameter is between 1 1 and 21 gauges.Gauge is a unit of measurement commonly used to define the external diameter of a medical instrument such as a needle, probe or catheter (11 gauges correspond to an external diameter of 2.946 mm; 21 gauges. correspond to an external diameter of 0.812 mm). As illustrated in FIG. 1, a navigation system 30 may be used to provide the control unit 12 of the medical robot 10 with information relating to a current pose of the tool guide 14 and to an insertion pose that the tool guide must reach. The current pose and the insertion pose are for example initially defined in a reference frame of the navigation system 30 and then transformed into poses in a reference frame of the medical robot 10 by the control unit 12. The control unit 12 may then be configured to automatically move (in a so-called “automatic control” mode, without intervention by the practitioner) the robotic arm 13 so that it reaches the insertion pose. The navigation system 30 and the control unit 12 of the medical robot 10 may exchange data via communication means (wired or wireless). The insertion position corresponds to a position of the tool guide 14 in which it allows the medical instrument 15 to be guided along the axis of the planned trajectory 41 and at the exact depth to reach the target point 44 in the anatomy of interest 45. The holding system 50 of the tool guide 14 forms, for example, a guide conduit in which at least part of the medical instrument 15 is intended to slide during the insertion of the medical instrument 15 into the body of the patient 20. At the insertion position, the axis of the trajectory 41 is then merged with the axis of the guide conduit. The insertion position is defined as a function of the length of the medical instrument 15 and as a function of the insertion depth corresponding to the planned trajectory 41. During insertion, the medical instrument is guided in translation by the guide duct until it reaches a stop position (a part of the medical instrument then comes into abutment against the tool guide and prevents further insertion). The insertion position is defined such that when this stop position is reached, the distal end of the part of the instrument which has penetrated into the patient's body is at the target point. When the part of the medical instrument intended to penetrate the patient's body has axial symmetry along the guide duct (i.e. along the planned trajectory), the different poses of the tool guide obtained by rotation along this axis correspond to the same insertion pose (in other words, the insertion pose corresponds to the pose taken by the guide duct formed by the holding system 50 of the tool guide 14 when the tool guide 14 is in position to proceed with the insertion of the medical instrument 15). In the example considered, the navigation system 30 is an optical navigation system. The navigation system 30 comprises at least two sensors optics 31 corresponding for example to two sensors of a stereoscopic camera operating in the infrared radiation range or in the visible light range. As illustrated in Figures 5 and 6, the tool guide 14 comprises studs 144 intended to receive optical markers 147. Advantageously, the tool guide 14 comprises at least three optical markers 147 so that the pose of the tool guide 14 can be determined in the three spatial dimensions of the reference frame of the navigation system 30. The respective poses of the optical markers 147 of the tool guide relative to each other are known a priori by the navigation system 30 and / or by the control unit 12. Advantageously, the geometric shape of each optical marker 147 can also be known a priori. In the example illustrated in Figure 6, the optical markers 147 are spherical in shape. In the illustration of Figure 6, the tool guide 14 holds the medical instrument 15 in the holding system 50, and the medical instrument 15 is in abutment against the tool guide 14 (this corresponds to the position of the medical instrument when it reaches the target point 44). The optical markers 147 may be passive or active. Passive optical markers reflect optical radiation emitted by another element, such as the navigation system 30. Passive optical markers may correspond, for example, to reflective spheres detectable by an infrared stereoscopic camera (this is what is used, for example, in the Polaris® navigation systems manufactured by Northern Digital Inc.), or to black and white patterns visible by a stereoscopic camera (this is what is used, for example, in the Micro nTracker® navigation system from ClaroNav). Active optical markers themselves emit optical radiation, for example infrared radiation, detectable by the navigation system 30. As illustrated in Figure 1, all of the markers 147 present on the tool guide 14 correspond to a robot reference 18. The use of at least three optical markers 147 makes it possible to define a plane and therefore a direct orthonormal three-dimensional reference frame with a z axis normal to the plane and x and y axes in the plane so that the reference frame is direct. This thus makes it possible to determine the pose of the reference frame formed from the optical markers 147 which represent the tool guide 14. The three axes x, y and z make it possible to define six degrees of freedom, namely a translation along each of the x, y or z axes and a rotation around each of these axes. It should be noted, however, that a single optical marker having a characteristic geometric shape in three dimensions could be used instead of the 147 spherical optical marker set. As illustrated in Figure 1, a patient reference 22 is placed on the patient 20 near the anatomy of interest. Figure 7 schematically represents the patient reference 22. The patient reference 22 comprises at least three optical markers 221, such that the pose of the patient reference 22 can be determined in the three spatial dimensions of the reference frame of the navigation system 30. The respective poses of the optical markers 221 of the patient reference 22 relative to each other are known a priori by the navigation system 30 and / or by the control unit 12. Advantageously, the geometric shape of each optical marker 221 can also be known a priori. In the example illustrated in Figure 7, the patient reference 22 comprises three optical markers 221 of spherical shape. The spherical shape makes it possible to optimize the reflection of the optical radiation.What was mentioned previously for the active or passive type of the optical markers 147 of the tool guide 14 is also true for the optical markers 221 of the patient reference 22. Here again, it would be conceivable to use a single optical marker having a characteristic geometric shape in three dimensions instead of the three spherical optical markers 221. In the remainder of the description, it is considered by way of non-limiting example that the optical sensors 31 of the navigation system 30 and the various optical markers 147, 221 are designed to operate with infrared optical radiation. It is further considered that the optical markers 147, 221 are passive markers. The optical sensors 31 of the navigation system 30 are configured to emit infrared radiation. This infrared radiation is reflected by the various optical markers 147, 221 towards the optical sensors 31. The optical sensors 31 are configured to receive this reflected infrared radiation. The navigation system 30 can then determine the distance between an optical marker 147, 221 and an optical sensor 31 by measuring the time taken by an infrared ray to make the round trip between said optical sensor 31 and said optical marker 147, 221.By knowing the distance between each optical marker 147, 221 and each optical sensor 31, and by knowing a priori the arrangement of the optical markers 147, 221 relative to each other on the tool guide 14 and on the patient reference 22, it is possible to determine the position of the tool guide 14 and of the patient reference 22 in the reference frame of the navigation system 30. The insertion position that the tool guide 14 must reach can in particular be defined from the position of the patient reference 22. For this purpose, and as illustrated in FIG. 7, the patient reference 22 also comprises radiopaque markers 222 which are visible on a medical image acquired by a medical imaging device (for example by computed tomography, magnetic resonance, ultrasound, tomography, positron emission tomography, etc.). The respective poses of the radiopaque markers 222 relative to each other are known a priori by the navigation system 30 and / or by the control unit 12. Advantageously, the geometric shape of the radiopaque markers 222 may also be known a priori. Preferably, the patient reference 22 comprises at least three radiopaque markers 222. The radiopaque markers 222 may be, for example, ceramic beads. It should be noted, however, that a single radiopaque marker having a characteristic geometric shape in three dimensions could be used instead of the three spherical radiopaque markers 222. It is thus possible to plan the medical intervention from a pre-interventional medical image 40 acquired on the patient provided with the patient reference 22 (this may in particular be a three-dimensional image). This pre-interventional medical image 40 is stored in the memory 121 of the control unit 12. It is then possible for the control unit 12, from the pre-interventional medical image 40, to define the insertion pose that the tool guide 14 must take to guide the medical instrument 15 to carry out the medical intervention. The insertion pose can then be stored by the control unit 12. The planning comprises determining, on the pre-interventional image 40, the trajectory 41 to be followed by the medical instrument 15 (e.g., a needle) between an entry point 43 located at the skin of the patient 20 and a target point 44 located in or near a region to be treated (e.g., a tumor) in the anatomy of interest 45 (e.g., the liver) of the patient 20. The patient reference 22 (more precisely, the radiopaque elements 222 of the patient reference 22) is visible on the pre-interventional image 40. The pose of the patient reference 22 can therefore be defined in the medical image. The insertion pose of the tool guide 14 for following the trajectory 41 can then be defined relative to the pose of the patient reference 22. The entry point 43, the target point 44 and the patient reference 22 can be determined on the image automatically (for example using an automatic segmentation algorithm), semi-automatically (with the help of the practitioner) or manually by the practitioner. It should be noted that the trajectory determination can also be performed on a preoperative image acquired several days before the intervention (image acquired without the patient being provided with the patient reference). The preoperative image can then be registered with the pre-interventional image 40 on which the reference patient 22 is visible, in order to obtain a relative pose of the patient reference 22 with respect to the trajectory, and therefore with respect to the insertion pose of the tool guide 14. In the example considered, the navigation system 30 is configured to provide the control unit 12 of the medical robot 10 with the current pose of the tool guide 14 (or more precisely the pose of the robot reference 18) in the reference frame of the navigation system 30. However, the control unit 12 of the medical robot 10 knows the current pose of the tool guide 14 in the reference frame of the medical robot 10 (via the encoders of the joints 131 to 136). The control unit 12 can therefore determine the transformation to be carried out to define a pose in the reference frame of the medical robot 10 from a pose in the reference frame of the navigation system 30. The navigation system 30 is also configured to provide the control unit 12 of the medical robot with the pose of the patient reference 22 in the reference frame of the navigation system 30. The control unit 10 can then define the pose of the patient reference 22 in the reference frame of the medical robot 10. Now, thanks to the pre-intervention image 40, the control unit 12 of the medical robot 10 knows the insertion pose that the tool guide 14 must reach relative to the pose of the patient reference 22. The control unit 12 can therefore determine the insertion pose, in the reference frame of the medical robot, that the tool guide 14 must reach from the information provided by the navigation system 30. The control unit 12 can then be configured to automatically move (in the so-called “automatic control” mode) the robotic arm 13 so that it reaches the insertion pose. The movements of the robotic arm 13 are for example conditioned by the selection of a control mode on a user interface of the medical robot 10 and the activation of the selected mode by a control pedal 19. The automatic control mode corresponds to a mode in which the robotic arm 13 is completely controlled by the control unit 12. The robotic arm 13 is then moved automatically, without the intervention of the practitioner. In a so-called “collaborative control” mode, the control unit 12 is configured to determine, using the force sensor 16, a force exerted by the practitioner on the tool guide 14, and to move the tool guide 14 according to the force thus determined. This corresponds to a mode in which the practitioner can manually move the robotic arm 13 himself, however with control of the movement of the robotic arm 13 by the control unit 12 (for example to limit the speed and / or the possible directions of movement of the robotic arm 13). There may be several “collaborative control” modes. For example, a "collaborative approach control" mode corresponds to a mode in which the practitioner moves the robotic arm 13 to approach the tool guide 14 to the patient so that the robotic arm 13 enters the field of view of the optical navigation system 30. In this mode, it is advantageous to control the speed of movement of the robotic arm 13 as a function of the force exerted by the practitioner on the robotic arm 13. In this mode, movement of the robotic arm 13 is generally permitted in all directions. The robotic arm can then be moved automatically (in the automatic control mode) to the insertion position. A “collaborative axial control” mode corresponds to a mode in which the practitioner can manually move the robotic arm 13, but only in such a way that the positioning of the tool guide 14 preserves the planned trajectory 41 when the medical instrument 15 slides in the tool guide 14, that is to say in such a way that the axis of the guide conduit formed by the holding system 50 of the tool guide 14 remains coincident with the axis of the planned trajectory 41. In other words, in the collaborative axial control mode, the control unit 13 is configured to prohibit any movement which would cause a modification of the position of the tool guide 14 such that the trajectory 41 would no longer be respected when the medical instrument 15 slides in the tool guide 14. In a particular embodiment, the movement of the tool guide 14 in collaborative axial control is constrained to only allow a movement allowing a translation of the tool guide 14 along the axis of the planned trajectory 41. In the collaborative axial control mode, the control unit 12 is configured to provide a haptic indication to the practitioner when the tool guide 14 returns to the insertion pose. Such arrangements allow for an easy and intuitive return to the insertion pose. Figures 8 to 10 illustrate the collaborative axial control mode with a translation of the tool guide 14 close to the body of the patient 20 to partially insert the medical instrument 15 therein before raising the tool guide 14 to the insertion position. In Figure 8, the tool guide is positioned at the insertion position. In Figure 9, the tool guide 14 has been moved in translation along the axis of the planned trajectory 41 to be brought closer to the body of the patient, as close as possible to the skin of the patient 20, at the entry point 43. As illustrated in Figure 9, the medical instrument 15 can then be placed in the tool guide 14 and partially inserted into the body of the patient 20 when the tool guide 14 is as close as possible to the skin of the patient, in order to avoid an inflection of the medical instrument 15 and a deviation from the planned trajectory 41.The collaborative axial control mode and the haptic indication then allow the tool guide 14 to be replaced exactly at the insertion position (the medical instrument is then always. partially inserted). Figure 10 illustrates the situation where the tool guide 14 is replaced at the insertion position. Once the tool guide 14 is replaced at the insertion position, the insertion of the medical instrument 15 can be finalized to reach the target point 44. It may happen that the line of sight between the navigation system 30 and a reference (patient reference 22 or robot reference 18) is obstructed, which may prevent obtaining information relating to the pose of the reference. In particular, when the tool guide 14 is replaced at the insertion pose in the collaborative axial control mode, the medical instrument 15 is in place and it could potentially obstruct the line of sight between the navigation system 30 and robot reference 18. The fact of having recorded the insertion pose (in the reference frame of the medical robot) makes it possible to replace the tool guide 14 at the insertion pose without having to use a navigation system 30. In another particular embodiment, the movement of the tool guide 14 in collaborative axial control is constrained to allow not only a movement allowing a translation of the tool guide 14 along the axis of the planned trajectory 41, but also a movement allowing a rotation of the tool guide 14 around the axis of the planned trajectory 41 (any other movement of the tool guide 14 being prohibited). Indeed, when the part of the medical instrument 15 intended to penetrate into the body of the patient 20 has an axial symmetry along the axis of the trajectory 41, it is advantageous for the collaborative axial control mode to be able to act both in translation and in rotation around the axis of the trajectory 41.Thus, when the tool guide 14 is brought close to the skin of the patient 20, the rotation control makes it possible to modify the position of the tool guide 14 while keeping the guide conduit along the axis of the trajectory 41 (the axis of the trajectory coincides with the axis of the guide conduit, and the guide conduit remains identical during a rotation of the tool guide 14 around this axis). This makes it possible, for example, to avoid a collision of the tool guide 14 with an obstacle (for example with the patient reference 22 or with the patient 20 himself). At the insertion position, the rotation control mode makes it possible to modify the position of the tool guide 14 without modifying the insertion position (any rotation of the tool guide 14 around the axis of the trajectory 41 corresponds to the same insertion position because the guide conduit remains identical). This can in particular make it possible to clear the practitioner's workspace. Haptic feedback allows the practitioner to feel the exact moment the insertion position is reached. Haptic feedback can also optionally allow the practitioner to feel the approach to the insertion position. This allows for easy and intuitive return to the insertion position. For example, in particular embodiments, the control unit 12 may be configured to decrease the speed of movement of the tool guide 14 when the tool guide 14 approaches the insertion position. Such arrangements allow the practitioner to feel the approach to the insertion position. The speed of movement of the tool guide 14 may in particular be controlled as a function of a distance between a current pose of the tool guide and the insertion pose. For example, the speed of movement of the tool guide 14 is controlled as a function of a gain factor applied to the force exerted by the practitioner on the tool guide 14, and the control unit is configured to progressively decrease the value of the gain factor as a function of the distance separating the current pose and the insertion pose. This progressive reduction of the gain factor may possibly be implemented only from the moment when the distance between the current pose and the insertion pose is less than a first threshold. Alternatively and / or additionally, when the distance between the current position of the tool guide and the insertion position is less than a second threshold, the control unit 12 can be configured to limit or maintain the speed of movement of the tool guide 14 at a predetermined speed regardless of the force exerted by the practitioner on the tool guide 14. Such arrangements give the user a virtual notch impression when the tool guide 14 reaches the insertion position. Decreasing the tool guide movement speed to a particularly low speed corresponds to a haptic indication that allows the practitioner to feel the approach of the insertion position. Alternatively and / or additionally, the control unit 12 may also be configured to prohibit any movement of the tool guide 14 for a predetermined duration when the insertion position is reached. The momentary stopping of the movement of the tool guide corresponds to a haptic indication allowing the practitioner to feel the exact moment when the insertion position is reached. Figure 14 represents, for a particular example of implementation, the variation of the speed v of movement of the tool guide 14 as a function of the distance d which separates the current pose and the insertion pose, for a constant force exerted by the practitioner on the tool guide 14. In the zones 61 and 62, the speed of movement of the tool guide 14 is determined by applying the gain factor to the force exerted by the practitioner. When the distance which separates the current pose and the insertion pose is greater than a first threshold d1, the gain factor is constant (zone 61 in the figure). When the distance is between the first threshold d1 and a second threshold d2 less than d1, the gain factor decreases progressively with the distance (zone 62 in the figure). When the distance is less than the second threshold d2, the speed of displacement of the tool guide 14 is forced to a predetermined value (area 63 in the figure). When the distance becomes zero, the displacement speed of the tool guide 14 becomes zero for a predetermined duration. Other options could be considered for the haptic indication (as an alternative and / or in addition to the options proposed above), such as for example a vibration of the tool guide 14 when the insertion position is reached. The control unit 12 may also be configured to provide a visual indication of the distance between a current pose of the tool guide 14 and the insertion pose, or of the arrival of the tool guide 14 at the insertion pose. For example, the distance between the current pose of the tool guide 14 and the insertion pose may be displayed on a user interface (for example on a monitor-type display screen, or on a screen of an augmented reality mask) in the form of a number or a gauge. A symbol (for example a green circle) may further be displayed when the insertion pose is reached, i.e. when the distance between the current pose of the tool guide 14 and the insertion pose becomes zero. The control unit 12 may also be configured to provide an audible indication of the distance between the current pose of the tool guide 14 and the insertion pose, or of the arrival of the tool guide 14 at the insertion pose. For example, an audible signal may be repeated with a frequency that increases as the distance between the current pose of the tool guide 14 and the insertion pose decreases. The audible signal may, for example, become a continuous sound when the insertion pose is reached. Or a particular sound may be emitted when the insertion pose is reached. Thus, the control unit 12 can be configured to provide information on the distance between a current position of the tool guide 14 and the insertion position, or on the arrival of the tool guide 14 at the insertion position, or even when the tool guide 14 exceeds the insertion position, using one or more indications from among a haptic indication, a visual indication and an auditory indication. Figures 11 to 13 illustrate an exemplary embodiment of the holding system 50 of the tool guide 14. This embodiment of the holding system is similar to that described in patent application WO 2020 / 201286 A1 with reference to Figures 7 to 8 of this application. In this exemplary embodiment, the holding system 50 of the tool guide 14 comprises two jaws 51, 55. The jaws 51 and 55 can be driven between a closed position (as illustrated in Figure 12) or an open position (as illustrated in Figure 13). Each jaw has a groove 52, 56. The grooves 52, 56 extend transversely with respect to teeth 53, 57 arranged so as to interpenetrate when the holding system 50 is in the closed position (each tooth 53, 57 has a segment of a groove 52, 56). In the closed position, the grooves 52 and 56 are adjoining and define a guide duct 59 for holding the medical instrument 15 and guiding it in translation. In the open position, the grooves 52 and 56 are spaced apart from each other to place or release the medical instrument 15. The closed position therefore corresponds to a position for guiding the medical instrument, while the open position corresponds to a position for releasing the medical instrument. The guide duct 59 takes, at the insertion position, a position coaxial with the planned trajectory 41. The transition from the closed position to the open position can be caused by a pressure force from the practitioner on a lever 58 formed by a bearing surface of one of the jaws (the jaw 55 in the example illustrated in figures 11 to 13). As illustrated in Figures 12 and 13, in the collaborative axial control mode, the control unit 12 is configured to transpose the force exerted by the practitioner on the tool guide 14 to a virtual application point A' positioned such that the axis of a pressure force F exerted on the lever 58 and the axis (AA') passing through a real application point A of the pressure force F and the virtual application point A' form a particularly small angle 0, for example less than twenty degrees, or even less than ten degrees. When the tool guide is closest to the patient's skin, the practitioner presses the lever 58 to open the jaws 51, 55 to place the medical instrument 15. The practitioner then releases the lever 58 so that the tool guide holds the medical instrument 15 (while allowing it to slide along the guide duct 59). The practitioner can then proceed with the partial insertion of the medical instrument 15. Before raising the tool guide 14 to the insertion position to finalize the insertion of the medical instrument 15, the practitioner can press the lever 58 again to open the jaws 51, 55 of the tool guide. Alternatively, the practitioner does not press the lever 58 and the jaws of the tool guide are closed while the guide slides along the needle. The particular position of the virtual application point A' of the forces taken into account in the control law makes it possible to avoid untimely rotation of the tool guide 14 when the practitioner presses the lever 58 to open the jaws 51, 55 of the tool guide 14 before replacing it at the insertion position. Indeed, as the angle 0 is small, the torque of the pressure force F exerted on the lever 58 is small, and this makes it possible to avoid (or at least very strongly limit) the untimely rotation of the tool guide 14 when the practitioner presses the lever to open the jaws 51, 55 of the tool guide. This configuration allows an intuitive transition from a translation control mode to a rotation control mode: pressure on the lever 58 does not cause rotation of the tool guide 14; on the other hand, pressure exerted on another part of the tool guide 14 can cause rotation of the tool guide 14. This intuitive transition from translational control to rotational control is implemented through the combination of the design of the tool guide 14 and the definition of the virtual application point A' of the forces in the control law. In particular, the practitioner does not need to use a user interface (control pedal 19, dedicated physical button, virtual button on a control screen, or other) to transition from translational control to rotational control. The torque of the pressure force F exerted on the lever 58 depends not only on the cosine of the angle 0 but also on the distance AA' separating the virtual application point A' and the real application point A of the pressure force F. It is therefore also advantageous to position the virtual application point A' at a short distance from the support surface of the lever 58 (for example less than five centimeters). It should be noted that other embodiments of the holding system 50 of the tool guide 14 could be compatible with this idea of ​​advantageously positioning the virtual application point A' relative to the pressure force F exerted by the practitioner on the lever 58 of the holding system 50 (for example the embodiment of the holding system described in patent application WO 2020 / 201286 A1 with reference to figures 2 to 6 of this application). The above description clearly illustrates that, through its various features and their advantages, the present invention achieves the set objectives. The proposed solution in fact allows the insertion of the medical instrument 15 without deviation from the planned trajectory 41. The approach of the tool guide 14 as close as possible to the patient's skin to perform a partial insertion of the medical instrument 15, then the replacement of the tool guide 14 to the planned insertion position, are easily implemented by the practitioner thanks to the collaborative axial control mode. The haptic indication allows an easy and intuitive return to the insertion position. A particular design of the tool guide 14 combined with a particular position of the virtual application point A' taken into account in the control law also allows an intuitive transition from translational control to rotational control of the tool guide 14. It should be noted that the invention has been described using a system of optical navigation. However, nothing would prevent the use, in a variant, of an electromagnetic navigation system instead of the optical navigation system. In this case, the different “markers” detectable by the navigation system (markers present on the patient reference 22, markers present on the tool guide 14) would then correspond to electromagnetic sensors whose position can be determined by the navigation system in a generated electromagnetic field.

Claims

Claims 1. Medical robot (10) for assisting a practitioner during a minimally invasive medical intervention on an anatomy of interest (45) of a patient (20), the medical robot (10) comprises a robotic arm (13) a distal end of which is equipped with a tool guide (14) intended to guide the insertion of at least a part of a medical instrument (15) into the body of the patient (20) along a planned rectilinear trajectory (41) between an entry point (43) located at the skin of the patient and a target point (44) located in the anatomy of interest (45), the medical robot (10) comprises a control unit (12) configured to control the robotic arm (13) in order to move the tool guide (14), the control unit (12) is configured to determine and memorize an insertion pose from the planned trajectory (41),the insertion pose corresponding to a position and an orientation of the tool guide (14) to be maintained when the practitioner inserts the medical instrument to the target point, in an "automatic control" mode, the control unit (12) is configured to autonomously move the tool guide (14) to the insertion pose, in a "collaborative axial control" mode, the control unit (12) is configured to determine, using a force sensor (16) coupled to the tool guide (14), a force exerted by the practitioner on the tool guide (14), and to determine a speed of movement of the tool guide (14) as a function of the force thus determined, the movement of the tool guide (14) being constrained to authorize only:, - a movement allowing a translation of the tool guide (14) along the axis of the planned trajectory (41), or - a movement allowing a translation of the tool guide (14) along the axis of the planned trajectory (41) and a rotation of the tool guide (14) around the axis of the planned trajectory (41), in the collaborative axial control mode, the control unit (12) is configured to provide a haptic indication to the practitioner when the tool guide (14) returns to the insertion position.

2. Medical robot (10) according to claim 1 wherein, in the collaborative axial control mode, when the distance between a current pose of the tool guide and the insertion pose is less than a first threshold, the control unit (12) is configured to calculate a movement speed of the tool guide (14) as a function of a gain factor applied to the force exerted by the practitioner on the tool guide (14), the value of the gain factor gradually decreasing as a function of the distance between the current pose and the insertion pose.

3. Medical robot (10) according to any one of claims 1 to 2 wherein, in the collaborative axial control mode, when the distance between a current pose of the tool guide and the insertion pose is less than a second threshold, the control unit (12) is configured to limit or maintain the speed of movement of the tool guide (14) at a predetermined speed regardless of the force exerted by the practitioner on the tool guide (14).

4. Medical robot (10) according to any one of claims 1 to 3 wherein, in the collaborative axial control mode, the control unit (12) is configured to prohibit any movement of the tool guide (14) for a predetermined duration when the insertion position is reached.

5. Medical robot (10) according to any one of claims 1 to 4 wherein the tool guide (14) comprises at least one marker (147) detectable by a navigation system (30) and the control unit (12) is configured to: - receive, from said navigation system (30), first information relating to a positioning of the tool guide (14) in a reference frame of the navigation system (30), - receive, from said navigation system (30), a second piece of information relating to an insertion position, in the reference frame of the navigation system (30), that the tool guide (14) must take to guide the medical instrument (15) along the planned trajectory (41) until reaching the target point, - determining the insertion pose, in a reference frame of the medical robot (10), from the first information and the second information.

6. Medical robot (10) according to claim 5 wherein the second information corresponds to a pose, in the reference frame of the navigation system (30), of a patient reference (22) intended to be placed on the patient (20) close to the anatomy of interest, said patient reference (22) comprising at least one marker (221) detectable by the navigation system (30) and at least one radio- opaque (222), and the control unit (12) is configured to determine the insertion pose from the pose of the patient reference (22) and from the planned trajectory (41), said trajectory (41) being defined relative to the pose of the patient reference (22) using a pre-interventional medical image (40) on which the anatomy of interest of the patient and said at least one radiopaque marker (222) of the patient reference (22) are visible.

7. Medical robot (10) according to any one of claims 1 to 6 wherein the part of the medical instrument (15) intended to penetrate the body of the patient has an axial symmetry along an axis which, during insertion of the medical instrument (15), corresponds to the axis of the planned trajectory, and in the collaborative axial control mode, the movement of the tool guide (14) is constrained to limit it to a movement allowing a translation of the tool guide (14) along the axis of the planned trajectory (41) and a rotation of the tool guide (14) around the axis of the planned trajectory (41).

8. Medical robot (10) according to claim 7 wherein: the tool guide (14) comprises two jaws (51, 55), each jaw comprising a groove (52, 56), the jaws being able to be driven between a closed position in which the grooves (52, 56) are adjoining and define a guide conduit (59) for holding the medical instrument (15) and guiding it in translation, and an open position in which the grooves (52, 56) are spaced apart from each other for placing or releasing the medical instrument (15), the guide conduit taking at the insertion position a coaxial position with the planned trajectory, the passage from the closed position to the open position being able to be caused by pressure from the practitioner on a lever (58) formed by a bearing surface of one of the jaws (55), in the collaborative axial control mode,the control unit (12) is configured to transpose the force exerted by the practitioner on the tool guide (14) to a virtual application point (A') positioned such that the axis of a pressure force (F) exerted on the lever (58) and the axis (AA') passing through a real application point (A) of the pressure force (F) and the virtual application point (A') form an angle (0) less than twenty degrees., 9. Medical robot (10) according to any one of claims 1 to 8 wherein the robotic arm (13) has at least six degrees of freedom.

10. A medical robot (10) according to any one of claims 1 to 9 wherein the control unit (12) is configured to provide a visual indication and / or an audible indication when the tool guide (14) returns to the insertion pose or when the tool guide (14) passes the insertion pose.

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