Collaborative medical robot for safe instrument guidance

Abstract

The invention relates to a medical robot for assisting a practitioner during a medical procedure on a relevant part of a patient's anatomy. The medical robot comprises a robot arm equipped at one end with a tool guide designed for guiding a medical instrument. The medical robot further comprises a control unit configured to control the displacement of the robot arm. The tool guide is coupled to a force sensor. When the medical robot is used in a "cooperative manual control" mode, the control unit is configured to determine the force exerted by the practitioner on the tool guide through the force sensor and to calculate the velocity of displacement of the tool guide as a function of a gain factor applied to the force. Advantageously, the value of the gain factor is variable and calculated as a function of the determined force.

Description

TECHNICAL FIELD

[0001] The present invention belongs to the field of robotic devices assisting a practitioner during a medical or surgical procedure. More particularly, the present invention relates to a medical robot comprising a robot arm equipped with a tool guide to guide and release a medical instrument during a minimally invasive or percutaneous medical procedure. BACKGROUND

[0002] A medical procedure performed by minimally invasive or percutaneous means can require the practitioner to insert one or more medical instruments (e.g. a needle, a probe, a catheter, etc.) into the patient's body up to a given depth so as to reach a target anatomical region (e.g. a tumor in the liver, the lung, the kidney or a bone).

[0003] When the insertion movement of the medical instrument is performed entirely by the practitioner, the outcome of the procedure is highly dependent on the practitioner's skills. With the assistance of a remotely controlled medical robot, the precision of the movement can be improved. In this case, the success of the procedure still depends partly on the practitioner's skills and can require the continuous acquisition of medical images of the patient, which involves subjecting the patient to a high dose of radiation.

[0004] To further improve the precision of the insertion movement and limit the dose of radiation to the patient, an automatically controlled robot arm can be used. The robot arm can be equipped with a tool guide to guide the medical instrument. The practitioner indicates, for example on a medical image prior to the intervention, a trajectory that the medical instrument must follow so as to reach the target region of the relevant part of the patient's anatomical structure, and the robot arm automatically displaces to a position such that the tool guide can guide the medical instrument according to the planned trajectory.

[0005] Advantageously, the practitioner is able to manually move the robot arm in order to move the tool guide towards the relevant part of the patient's anatomical structure or to release the tool guide after (optionally partial) insertion of the medical instrument. When the practitioner manually moves the robot arm, and when the tool guide is relatively far from the relevant part of the patient's anatomical structure, the movement of the robot arm must be fluid and reactive. On the other hand, when the tool guide is relatively close to the relevant part of the patient's anatomical structure, the movement of the robot arm must be precisely controlled at low speed in order to accurately reach the insertion position of the medical instrument and without risk of injury to the patient using the medical instrument or the tool guide. Furthermore, it is necessary to avoid the trembling of the robot arm caused by the practitioner's trembling.

[0006] To this end, it is conceivable to carry out a frequency study of the forces exerted by the practitioner by means of an accelerometer in order to determine whether there is trembling. However, this type of solution is relatively complex to implement and requires the integration of an additional sensor (accelerometer) in the medical robot.

[0007] It is also necessary to take measures to ensure that the patient is not injured by the medical instrument during the operation, for example if, during the insertion of the medical instrument into the patient's body, the patient makes an unexpected movement while the robotic arm is guiding the medical instrument, the medical instrument is usually inserted during the patient's apnea, and it is therefore also necessary to ensure that the patient is not injured by the medical instrument if the respiratory movement is resumed before the medical instrument is released from the tool guide. SUMMARY

[0008] It is an object of the present application to eliminate some or all of the drawbacks of the prior art, in particular those summarized above.

[0009] To this end, and according to a first aspect, the present application proposes a medical robot for assisting a practitioner during a medical procedure on a relevant portion of a patient's anatomy. The medical robot comprises a robotic arm comprising at a distal end a tool guide designed for guiding a medical instrument. The medical robot further comprises a control unit configured to control the displacement of the robotic arm. The tool guide is coupled to a force sensor. When the medical robot is used in a "cooperative manual control" mode, the control unit is configured to determine, through the force sensor, the force exerted by the practitioner on the tool guide, and to calculate the speed of displacement of the tool guide according to a gain factor applied to the force thus determined. Advantageously, the value of said gain factor is variable and is calculated as a function of the force exerted by the practitioner on the tool guide. The control unit is configured to control the displacement of the robotic arm according to the speed thus calculated.

[0010] Thus, the practitioner moves the robotic arm by exerting a force by hand on the tool guide fixed at the end of the robotic arm. The force sensor allows the control unit to control the speed of displacement of the robotic arm as a function of the force exerted by the practitioner. Indeed, the speed of displacement of the tool guide is calculated by applying a gain factor to the force exerted by the practitioner on the tool guide. The force exerted by the practitioner on the tool guide is determined, for example by the control unit, based on the force and torque measured by the force sensor through a series of operations which can include filtering, noise reduction, compensation of the weight of the tool guide, change of reference point to the tool guide, etc. The greater the force exerted by the practitioner on the tool guide, the greater the speed of displacement of the tool guide calculated by the control unit. Thus, when the tool guide is relatively far from the patient and the practitioner exerts a significant force on the tool guide, the robotic arm moves quickly, fluidly and reactively. On the other hand, when the practitioner exerts a slight force on the tool guide because the tool guide is close to the patient's body, the robotic arm moves at low speed in order to guarantee precision and safety.

[0011] Moreover, as will be explained hereafter, the fact that the gain factor varies as a function of the force exerted by the practitioner on the tool guide makes it possible to avoid the chattering of the displacement of the robot arm in the event of trembling of the practitioner (the trembling corresponding to a low-amplitude force varying at high frequency).

[0012] For example, when the force varies between a minimum value F min and a maximum value F max , the gain factor varies linearly as a function of the force exerted by the practitioner on the tool guide.

[0013] In particular embodiments, the application can also comprise one or more of the following features, alone or according to all the combinations technically possible.

[0014] In particular embodiments, the gain factor corresponds to the proportional parameter of a proportional-integral-derivative corrector implemented by the control unit.

[0015] By means of the control loop, the control unit calculates a speed of displacement of the tool guide, which is intended to cancel out the force exerted by the practitioner. To this end, a PID corrector can be used. PID is the acronym of Proportional Integral, Derivative. It is a closed-loop control system commonly used in industry. Indeed, the present application is based on the assumption that the movement resulting from the low-amplitude force exerted by the practitioner will contain the trembling. The proposed solution therefore does not require frequent analysis to detect the trembling. With this assumption, it is possible to simplify the problem and use a PID corrector.

[0016] In particular embodiments, the control unit is also configured to prevent the displacement of the tool guide in at least one direction.

[0017] The term "direction" corresponds to a degree of freedom of the tool guide in the three-dimensional reference system (x, y, z) in which it is located. This direction can in particular be a translation along each of the x, y or z axes, or a rotation around each of these axes.

[0018] This type of arrangement makes it possible to control the displacement of the robot arm so as to, for example, prevent the tool guide from colliding with the medical instrument when the robot arm is released, after the medical instrument has been partially or totally inserted into the patient's body, and after the medical instrument has been released from the tool guide.

[0019] In particular embodiments, the control unit is also configured to limit the displacement of the tool guide in a single direction, for example corresponding to the main axis of the tool guide.

[0020] This type of arrangement makes it possible to control the displacement of the robot arm, for example so as to bring the robot arm to a position corresponding to the position in which the medical instrument has been inserted.

[0021] In particular embodiments, the value of the gain factor is defined as:

[0022] [Equation 1]

[0023]

[0024] where G(f) is the gain factor; K is a constant; |f| is the force exerted by the practitioner on the tool guide, measured by the control unit through the force sensor; F min and F max correspond to the minimum and maximum values of the force exerted by the practitioner, respectively. |f|, F min and F max correspond to the standard of the force (intensity of the force measured in Newtons). In the following of the description, unless otherwise specified, when referring to a "force" exerted by the practitioner or by the medical instrument, there is an inexactitude in that we refer to the "intensity of the force".

[0025] In particular embodiments, the control unit is configured to calculate the displacement speed of the tool guide also as a function of the distance between the current position of the tool guide and a target position that the tool guide has to reach.

[0026] In particular, this type of arrangement makes it possible to further limit the approach speed of the tool guide as it approaches its target position, in order to enhance precision and safety as the medical instrument approaches the relevant portion of the patient's anatomy.

[0027] In particular embodiments, the robotic arm is an articulated arm having at least six degrees of freedom.

[0028] The use of at least six degrees of freedom on the robotic arm makes it possible to ensure that the tool guide can reach any position in space. Moreover, if the medical instrument has axial symmetry (for example, if the medical instrument is a needle), five degrees of freedom are sufficient, since it is not necessary to perform a rotation around the axis of symmetry of the medical instrument. This additional degree of freedom makes it possible for the robotic arm to be in a situation of redundancy, and makes it possible to have an infinite number of possible configurations of the robotic arm for a given position. This provides a certain degree of flexibility, since the physician can subsequently select the optimal configuration of the robotic arm, for example as a function of the constraints inherent in the operating room (space available to the medical staff, presence of obstacles, visibility of the tool guide by any navigation system, etc.).

[0029] In particular embodiments, when the medical robot is used in the "medical instrument insertion" mode, the control unit is configured to prevent any displacement of the tool guide and to measure the force exerted on the medical instrument by means of the force sensor. The tool guide comprises means for automatically releasing the medical instrument upon command from the control unit. The control unit is configured to command the tool guide to release the medical instrument when the force exerted on the medical instrument is greater than a predetermined threshold, or when the variation of the force exerted on the medical instrument over a given period of time is greater than a predetermined threshold.

[0030] This type of arrangement makes it possible to release the medical instrument immediately at the stage of insertion of the medical instrument, i.e. when the medical instrument remains in the tool guide to guide its insertion into the patient, for example if the patient exerts an accidental force on the medical instrument due to respiratory movements, while the patient should be in apnea.

[0031] In particular embodiments, the tool guide comprises at least one marker detectable by the navigation system and the control unit is configured to:

[0032] - receive from the navigation system a first piece of information relating to the position of the tool guide in the reference of the navigation system;

[0033] - receive from the navigation system a second piece of information relating to a target position that the tool guide must reach in the reference of the navigation system;

[0034] - determine the target position of the medical robot in the reference from the second piece of information;

[0035] - move the robot arm in the "automatic control" mode, without intervention from the practitioner, so that the tool guide reaches the target position.

[0036] This type of arrangement makes it possible to move the robot arm automatically and precisely to bring the tool guide to the target position at which the medical instrument can be inserted into the patient in order to carry out a surgical operation.

[0037] In particular, the target position of the tool guide can be determined according to a trajectory that the medical instrument must follow, planned on a pre-intervention medical image. To this end, in particular embodiments, the second piece of information corresponds to the position of a patient reference in the reference of the navigation system, which is intended to be positioned in the vicinity of the relevant part of the patient's anatomy. The patient reference comprises at least one marker detectable by the navigation system and at least one radiopaque marker. The trajectory is defined by the position of the patient reference with respect to the relevant part of the patient's anatomy on a pre-intervention medical image on which the relevant part of the patient's anatomy and the radiopaque marker of the patient reference can be seen. The control unit is configured to determine the target position of the tool guide from the position of the patient reference and the planned trajectory.

[0038] In a particular embodiment, the control unit is configured to:

[0039] - store the position of the tool guide at the first instant of time with respect to the reference position of the patient;

[0040] - determine whether the difference between the position of the tool guide at the second instant of time and the reference position is lower than a predetermined threshold.

[0041] This type of arrangement is particularly advantageous in the case where the robotized arm has to be released after partial insertion of the medical instrument, for example in order to allow acquisition of a medical image to verify that the medical instrument is properly inserted, and then has to be brought to the initial position of insertion of the medical instrument, for example in order to complete the insertion of the medical instrument.

[0042] In a particular embodiment, the tool guide comprises means for automatic release of the medical instrument according to the commands of the control unit. The control unit is configured to command the release of the medical instrument by the tool guide when the control unit receives information from the navigation system indicative of an unexpected displacement of the patient reference.

[0043] Thus, when the patient makes an unexpected movement during the insertion of the medical instrument into the patient's body, it is possible to avoid that the medical instrument injures the patient. BRIEF DESCRIPTION OF DRAWINGS

[0044] By reading the following description, provided by way of non-limiting example and with reference to the Figures 1 to 9 The present application will be better understood by reading the following description, Figures 1 to 9 which shows:

[0045] [ Figure 1 ] is a schematic view of a medical robot according to the present application, which assists a practitioner on a relevant portion of the patient's anatomy during a medical procedure.

[0046] [ Figure 2 ] is a schematic view of a robotized arm of a medical robot.

[0047] [ Figure 3 ] is a schematic view of a tool guide designed to be fixed at the end of a robotized arm.

[0048] [ Figure 4 ] is a schematic view of a tool guide, showing the device for holding the medical instrument on the end of the tool guide.

[0049] [ Figure 5 ] is a schematic view of a tool guide, showing the positioning of the medical instrument on the tool guide, and the markers detectable by the navigation system.

[0050] [ Figure 6 ] is a schematic view of a patient reference designed to be positioned in the vicinity of the relevant portion of the patient's anatomy.

[0051] [ Figure 7 ] is a diagram illustrating the cooperation of a medical robot according to the present application with a navigation device.

[0052] [ Figure 8 ] consists of data graphs representing, in particular, the force applied by the practitioner on the tool guide, the speed and the acceleration sustained by the tool guide, in this case the speed being defined according to a constant gain factor applied to the force exerted.

[0053] [ Figure 9 ] consists of data graphs similar to those represented in Figure 8 , in this case the speed being defined according to a variable gain factor applied to the force exerted, the gain factor varying according to the force exerted.

[0054] In these figures, identical references from one figure to another designate identical or similar elements. The represented elements are not necessarily drawn to the same scale for the sake of clarity, unless otherwise stated. DETAILED DESCRIPTION

[0055] Figure 1 A medical robot 10 according to the present application is schematically represented. The medical robot 10 is intended to assist a practitioner during a medical procedure on a relevant portion of the anatomy of a patient 20 located on an operating table 21.

[0056] As a non-limiting example, this case is for a medical procedure performed in a minimally invasive or percutaneous manner. This type of procedure generally requires the practitioner to insert one or more medical instruments (e.g. a needle, a probe, a catheter, etc.) into the patient's body up to a given depth in order to reach a target anatomical area (e.g. a tumor in the liver, the lung, the kidney, etc.) of the relevant portion of the anatomy.

[0057] The medical robot 10 comprises a base 11. In the example considered, 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.

[0058] The medical robot 10 also comprises an articulated robot arm 13, one end of which is connected to the base 11. At the other end of the robot arm 13, a tool guide 14 is fixed, which is designed to guide a medical instrument 15, for example a needle, a probe, a catheter, an electrode, etc. Thus, the medical robot 10 can be used to help the practitioner to position, hold or guide the medical instrument 15 during a medical procedure. Thus, the medical robot 10 plays the role of a third hand for the practitioner.

[0059] In Figure 2In the example considered and illustrated, the robot arm 13 comprises six revolute joints 131 to 136 providing six degrees of freedom so that the medical instrument 15 can be positioned and / or moved to any position of a three-dimensional space. Advantageously, the joints 131 to 135 of the robot arm 13 are not aligned and are offset with respect to each other, which allows for more possible configurations of the robot arm 13. Each joint comprises at least one encoder so that its angular position can be determined in real time. The configuration of the robot arm 13 thus corresponds to a series of parameter values (for example the values of the angles of rotation of each joint) obtained by the joints 131 to 136. The revolute joint 136 corresponds to a rotation around the main axis of the tool guide 14. However, it should be noted that it is not necessary to rotate around a symmetry axis of the medical instrument (indeed five degrees of freedom are sufficient to guide and release the medical instrument). This additional degree of freedom makes it possible for the robot arm to be in a redundant situation and for the tool guide 14 to have an infinite possible configuration of the robot arm 13 for a given position. This redundant situation is particularly advantageous to adapt to constraints related to the position of the patient or the configuration of the operating room.

[0060] As Figure 3 illustrated, the tool guide 14 is fixed on the robot arm 13 by a flange 17. The tool guide comprises a main axis 145, which is represented by a dashed line in Figure 3 The tool guide 14 is coupled to the force sensor 16 so as to allow the control unit 12 to determine the force exerted on the tool guide 14. This force can in particular be exerted by the practitioner when he manually moves the robot arm 13. This force can also correspond to the force exerted by the body of the patient on the tool guide 14 through the medical instrument 15 (for example due to an accidental movement of the patient during the insertion of the medical instrument).

[0061] It should be noted that the force sensor can measure a total force corresponding to the resultant force and the resultant moment borne by the force sensor 16 (including not only the force exerted by the practitioner, but also the weight of the tool guide 14, the weight of the medical instrument 15, etc.). The control unit is configured to determine the force exerted by the practitioner on the tool guide 14 from the resultant force and the resultant moment borne by the force sensor 16. To do this, for example, it is necessary to subtract from the total force the force corresponding to the weight of the tool guide 14, the force corresponding to the weight of the medical instrument 15 (if the instrument is held by the tool guide 14), the torque resulting from the difference between the point of measurement and the center of mass of the tool guide, and / or any compensation related to measurement noise. It is also conceivable to filter the measurements made on the force sensor 16.

[0062] As Figure 4 and Figure 5As shown, the tool guide 14 comprises a body 141 having a base 142 designed to be fixed by screws 143 on the flange 17, and a retaining system 146 comprising two parts movable relative to each other. The retaining system 146 is designed to retain 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 retaining system 146 can be driven by a drive system such as a gear, a cam, a screw with a reverse thread and / or a linear actuator, in order to block or release the medical instrument 15. The linear actuator can be reversible (then the retaining system 146 of the tool guide 14 can be opened manually or automatically according to a command from the control unit 12), or irreversible (only the retaining system 146 of the tool guide 14 can be opened automatically according to a command from the control unit). The tool guide 14 can for example guide medical instruments having different diameters. For example, this type of guide can guide medical instruments having a diameter between 11 and 21 gauge. Gauge is a unit of measurement commonly used to define the outer diameter of medical instruments such as needles, probes or catheters (11 gauge corresponds to an outer diameter of 2.946 mm; 21 gauge corresponds to an outer diameter of 0.812 mm).

[0063] As shown, Figure 1 The medical robot 10 comprises a control unit 12 configured to control the displacements of the robot arm 13. The control unit 12 comprises for example one or more processors 122 and a 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, the execution of which implements the different steps of the method for positioning the robot arm 13.

[0064] As shown, Figure 7 The navigation system 30 can be used to provide the control unit 12 of the medical robot 10 with information relating to the current position of the tool guide 14 and the target position that the tool guide has to reach. The current position and the target position are for example initially defined in the reference of the navigation system 30, then converted by the control unit 12 into a position in the reference of the medical robot 10. The control unit can then be configured to automatically move the robot arm 13 (in a so-called "automatic control" mode, without the intervention of a practitioner) so that it reaches the target position. The navigation system 30 and the control unit 12 of the medical robot 10 can exchange data by means of a (wired or wireless) communication.

[0065] In the present application, the term "position" corresponds to the combination of the location and the orientation of an object in a given reference, which is generally a three-dimensional coordinate system. The term "pose" is used in the Anglo-Saxon literature to denote this combination of the location and the orientation of an object in space.

[0066] In the considered example, the navigation system 30 is an optical navigation system. The navigation system 30 comprises at least two optical sensors 31, for example two sensors corresponding to stereo cameras operating in the infrared radiation field or in the visible light field.

[0067] As shown in Figure 4 and Figure 5 , the tool guide 14 comprises studs 144 designed to receive optical markers 147. Advantageously, the tool guide 14 comprises at least three optical markers 147, so that the position of the tool guide 14 can be determined in three spatial dimensions of the reference system of the positioning device 30. The navigation device 30 and / or the control unit 12 know in advance the respective positions of the optical markers 147 of the tool guide relative to each other. Advantageously, the geometry of each optical marker 147 can also be known in advance. In the example shown in Figure 5 , the optical markers 147 have a spherical shape.

[0068] The use of at least three optical markers 147 makes it possible to define a plane, thus defining a direct orthogonal three-dimensional reference in which the z axis is perpendicular to the plane and the x and y axes are on the plane, so that the reference is direct. This thus makes it possible to determine the position and the orientation of the reference formed by the optical markers 147 representative of the tool guide 14. The three axes x, y and z make it possible to define six degrees of freedom, namely translation along each of the x, y or z axes, and rotation around each of these axes.

[0069] The optical markers 147 can be passive or active. Passive optical markers reflect optical radiation emitted by another element, such as the positioning device 30. Passive optical markers can correspond, for example, to reflective spheres detectable by infrared stereo cameras, such as those used in the , or black and white patterns visible to stereo cameras, such as those used in the navigation system of the ClaroNav company in Active optical markers emit optical radiation, for example infrared radiation, by themselves, which can be detected by the positioning device 30.

[0070] Figure 7 As shown in , the assembly of markers 147 present on the tool guide 14 corresponds to the robot reference 18.

[0071] However, it should be noted that a single optical marker having a characteristic geometry in three dimensions can be used instead of the assembly of spherical optical markers 147.

[0072] The patient reference 22 is positioned in the vicinity of the relevant part of the anatomy of the patient 20. Figure 6A patient reference 22 is schematically represented. The patient reference 22 comprises at least three optical markers 23, so that the position of the patient reference 22 can be determined in the three spatial dimensions of the reference system of the positioning device 30. The positioning device 30 and / or the control unit 12 know in advance the respective positions of the optical markers 23 of the patient reference 22 relative to each other. Advantageously, the geometry of each optical marker 23 can also be known in advance. In Figure 6 In the example shown, the patient reference 22 comprises three optical markers 23 having a spherical shape. The spherical shape can optimize the reflection of the optical radiation. The description given previously for the optical markers 147 of active or passive type of the tool guide 14 can also be applied to the optical markers 23 of the patient reference 22. Also in this case, it is conceivable to use a single optical marker having a characteristic geometry in three dimensions instead of the three spherical optical markers 23.

[0073] In the following description, it is considered by way of example, but by no means limiting, to design the optical sensors 31 of the positioning device 30 and the different optical markers 147, 23 to operate with optical radiation of infrared type. It is also conceivable that the optical markers 147, 23 are passive markers. The optical sensors 31 are configured to emit infrared radiation. This infrared radiation is reflected by the different optical markers 147, 23 towards the optical sensors 31. The optical sensors 31 are configured to receive this reflected infrared radiation. The positioning device 30 can then determine the distance between the optical markers 147, 23 and the optical sensors 31 by measuring the time taken by the infrared rays to complete the outward and return distance between said optical sensors 31 and said optical markers 147, 23. By knowing the distance between each optical marker 147, 23 and each optical sensor 31, and by knowing in advance the arrangement of the optical markers 147, 23 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 system of the positioning device 30.

[0074] The target position that the tool guide 14 has to reach can in particular be defined according to the position of the patient reference 22. To this end, and as Figure 6 The patient reference 22 also comprises, as shown, radiopaque markers 24, which are visible on the medical images acquired by the medical imaging device (for example by tomography, by magnetic resonance, by ultrasound, by radiography, by position emission, etc.). The navigation device 30 and / or the control unit 12 know in advance the respective positions of the radiopaque markers 24 relative to each other. Advantageously, the geometry of the radiopaque markers 24 can also be known in advance. Preferably, the patient reference 22 comprises at least three radiopaque markers 24. The radiopaque markers 24 can for example be ceramic balls. It should however be noted that a single radiopaque marker having a characteristic geometry in three dimensions can be used instead of the three spherical radiopaque markers 24.

[0075] The medical procedure can thus be planned from the pre-interventional medical image 40 of the patient provided with the patient reference 22. This pre-interventional medical image 40 is stored in the memory 121 of the control unit 12. The target position that the tool guide 14 has to adopt in order to guide the medical instrument 15 to perform the medical procedure can thus be defined from the pre-interventional medical image 40. This planning comprises determining on the pre-interventional image 40 a trajectory 41 that the medical instrument 15 (e.g. a needle) has to follow between an entry point at the skin of the patient 20 and a target point (e.g. a tumor) at a relevant portion of the patient 20 anatomy. Figure 7 The reference 42 in the figure represents the assembly of radiopaque markers 24 of the patient reference 22 that can be seen on the pre-interventional image 40 (hence this represents an image of the patient reference 22 on the pre-interventional image 40). The target position of the tool guide 14 can thus be defined with respect to the position of the patient reference 22 that enables to follow the trajectory 41.

[0076] It should be noted that the determination of the trajectory can also be performed on a pre-operative image acquired a few days before the operation (this image is acquired without providing the patient with a patient reference). The pre-operative image can then be repositioned with the pre-interventional image 40 on which the patient reference can be seen in order to obtain the relative position of the patient reference 22 with respect to the trajectory.

[0077] In the example at stake, the navigation system 30 is configured to provide to the control unit 12 of the medical robot 10 the current position of the tool guide 14 in the reference of the navigation system 30. However, the control unit 12 of the medical robot 10 knows the current position of the tool guide 14 in the reference system of the medical robot 10 (through the encoders of the joints 131 to 136). The control unit 12 can thus determine the transformation to be performed in order to define the position in the reference system of the medical robot 10 from the position in the reference system of the navigation device 30. The navigation system 30 is also configured to provide to the control unit 12 of the medical robot the position of the patient reference 22 in the reference of the navigation system 30. The control unit 10 can thus define the position of the patient reference 22 in the reference system of the medical robot 10. However, thanks to the pre-interventional image 40, the control unit 12 of the medical robot 10 knows the position of the target position that the tool guide 14 has to reach with respect to the position of the patient reference 22. The control unit 12 can thus determine the target position that the tool guide 14 has to reach from the information provided by the navigation system 30. The control unit 12 can thus be configured to automatically move the robot arm 13 (in a so-called "automatic control" mode without the intervention of the practitioner) so that it reaches the target position.

[0078] The displacement of the robot arm 13 depends for example on the selection of the control mode on the user interface of the medical robot 10 and on the activation of the mode selected by the control pedal 19.

[0079] The so-called "cooperative manual control" mode corresponds to a mode in which the practitioner can manually move the robot arm 13 by himself, but the displacement of the robot arm 13 is controlled by the control unit 12 (in order to limit the speed and / or the possible direction of displacement of the robot arm 13).

[0080] The so-called "automatic control" mode is a mode in which the robot arm 13 is entirely controlled by the control unit 12. The robot arm 13 is thus moved automatically, without intervention of the practitioner.

[0081] There are various "cooperative manual control" modes.

[0082] The so-called "proximity cooperative manual control" mode corresponds for example to a mode in which the practitioner moves the robot arm 13 in order to bring the guide tool 14 towards a proximity position 101 which is relatively close to the relevant part of the patient's anatomy and facilitates the entry of the robot arm 13 into the field of view of the navigation system 30. In this mode, it is advantageous to control the speed of displacement of the robot arm 13 as a function of the force exerted by the practitioner on the robot arm 13. In this mode, the displacement of the robot arm 13 is generally allowed in all directions.

[0083] The robot arm can then be moved automatically (in "automatic control" mode) from the proximity position 101 to an insertion position 102. The insertion position 102 corresponds to the target position in which the tool guide 14 must be positioned in order for the medical instrument 15 to be able to follow the planned trajectory.

[0084] The so-called "release cooperative manual control" mode corresponds for example to a mode in which, after partial insertion of the medical instrument 15 into the body of the patient 20, the medical instrument 15 can be released from the holding device 146 of the tool guide 14 and the practitioner can manually release the robot arm 13 from the insertion position 102 to a release position 103. This type of arrangement makes it possible to move the patient 20 in order to create a control medical image (for example to check that the trajectory followed by the medical instrument corresponds to the planned trajectory) after partial insertion of the medical instrument 15. In this mode, the control unit 12 is configured to control the robot arm 13 so as to prevent displacement of the tool guide 14 in at least one direction, or it can be advantageous to limit the displacement of the tool guide 14 according to a single direction corresponding to the main axis 145 of the tool guide 14 (the release direction follows the main axis 145 of the tool guide 14 in a direction from the holding device 146 towards the base 142). According to a particular embodiment, when the "release cooperative manual control" mode is activated, the control unit 12 is configured to store the current position of the tool guide 14 relative to the position of the patient reference 22 as a reference position. The reference position is thus the position of the tool guide 14 at the first instant tl at which the "release cooperative manual control" mode is activated.

[0085] The so-called "return to collaborative manual control" mode corresponds for example to a mode in which, after the control image has been generated, the practitioner manually moves the robotized arm 13 so that the tool guide 14 regains the reference position recorded when the "release of the collaborative manual control" mode was selected. This reference position corresponds to the insertion position 102 (target position to which the tool guide 14 must be brought). The "return to collaborative manual control" mode is thus used to bring the tool guide 14 from the release position 103 to the insertion position 102 so as to complete the insertion of the medical instrument 15. It is important that, in its displacement, the tool guide 14 does not go beyond the insertion position 103 (in other words, that the tool guide 14 is not brought to the correct position to complete the insertion and that a collision between the partially inserted medical instrument and the tool guide 14 does not occur). It can be advantageous to control the robotized arm 13 so as to limit the displacement of the tool guide 14 in the direction along the main axis 145 of the tool guide 14 (the return direction follows the main axis 145 of the tool guide 14 in the direction from the base 142 towards the holding device 146). Furthermore, it is advantageous to configure the control unit 12 so as to control the displacement speed of the tool guide 14 as a function of the distance between the current position of the tool guide 14 and the target position to which the tool guide 14 must be brought (corresponding to the recorded reference position). Thus, for the second time t2, the control unit 12 is configured to calculate the difference between the position of the tool guide at the second time t2 and the reference position (position of the tool guide 14 at the first time tl). The displacement speed of the tool guide 14 is controlled so that the shorter the calculated distance (i.e. the closer the tool guide 14 is to its target position), the lower the displacement speed, until a zero speed is reached when the target position is reached. The control unit 12 is configured to determine whether the difference between the position reached by the tool guide 14 and the reference position is below a predetermined threshold. If this is the case, it is considered that the target position has been reached. It should be noted that the position of the tool guide 14 is defined relative to the position of the patient reference 22. When the target position has been reached, the practitioner can complete the insertion of the medical instrument 15. The predetermined threshold is for example equal to 1 mm, or equal to one tenth of a millimeter (0.1 mm), or even equal to three hundredths of a millimeter (0.03 mm).

[0086] When the "collaborative manual control" mode is activated, the practitioner moves the robotized arm 13 by exerting a force on the tool guide 14 with his hand. However, the displacement of the robotized arm 13 is controlled by the control unit 12 which applies a force control (control of the displacement speed of the tool guide 14) and a position control (control of the direction of displacement of the tool guide 14).

[0087] The force control is constrained by an admittance control law. The displacement velocity of the tool guide 14 is controlled by the control unit 12. The displacement velocity of the tool guide 14 is calculated as a function of the force exerted by the practitioner on the tool guide 14, said force being measured by the control unit through the force sensor 16.

[0088] More specifically, the force thus measured corresponds to the input data of the control loop. The output data of this control loop is the Cartesian displacement velocity of the tool guide 14. The control loop operates for example at a frequency of 125 Hz (in this case, the displacement velocity value of the tool guide 14 is updated every 8 ms).

[0089] The control unit 12 calculates the displacement velocity of the tool guide 14 so that the force exerted by the practitioner on the tool guide can be counteracted. In other words, the difference (also called error) between the value of the force measured at the current instant (at each iteration of the control loop) and the value of the force required (zero force) is equal to the force measured. The algorithm of the control loop is designed to define a displacement velocity such that the error tends to zero. To correct this error, a PID corrector (PID is the acronym of "Proportional, Integral, Derivative", which is a closed loop control system commonly used in industry) can be used. The error (i.e. the difference between the force measured and the force required) is the input data of the PID corrector, which provides a velocity as output, so that the error tends to zero can be obtained.

[0090] In the following, for the sake of simplicity, only the "proportional" part of the PID corrector is considered. In other words, as if the "integral" and "derivative" parts were zero.

[0091] The displacement velocity of the tool guide 14 is calculated by applying a gain factor to the force measured:

[0092] [Equation 2]

[0093] |v| = G x |f|

[0094] where G is the gain factor, |f| is the force measured by the control unit (exerted by the practitioner on the tool guide 14), |v| is the displacement velocity of the tool guide 14. The gain factor G corresponds to the gain factor of the "proportional" part of the PID corrector.

[0095] In other words, the greater the force exerted by the practitioner on the tool guide 14, the greater the displacement speed of the tool guide 14 calculated by the control unit 12. Thus, when the tool guide 14 is relatively far from the patient and the practitioner exerts a considerable force on the tool guide 14, the robotic arm 13 moves quickly, fluidly and reactively. On the other hand, when the practitioner exerts a low-amplitude force on the tool guide 14 because the tool guide 14 is close to the relevant part of the patient's anatomy, the robotic arm 13 moves at low speed in order to guarantee precision and safety.

[0096] When the tool guide 14 is relatively close to the relevant part of the patient's anatomy, the movement of the tool guide 14 must be precisely controlled at low speed in order to accurately reach the insertion position 102 of the medical instrument. It is therefore necessary to avoid the trembling of the robotic arm 13 caused by the practitioner's tremor. To this end, the value of the gain factor is defined as variable according to the force exerted by the practitioner on the tool guide. For example, when this force varies between a minimum value F min and a maximum value F max , the gain factor varies linearly with this force. The value of the gain factor G(f) can be defined as follows:

[0097] [Equation 1]

[0098]

[0099] where K is a constant, |f| is the force measured by the control unit (exerted by the practitioner on the tool guide 14), and F min and F max correspond to the minimum and maximum values of the force that the practitioner can exert, respectively. If |f| is greater than F max , the gain is not defined: when |f| is greater than F max , the upper limit of the speed is set to the maximum speed V max . If |f| is less than F min , the gain is zero: if the force |f| is less than F min , the speed is zero.

[0100] The fact that the gain factor varies according to the force exerted by the practitioner on the tool guide makes it possible to avoid the trembling in the displacement of the robotic arm 13 resulting from the practitioner's tremor (the tremor corresponding to a low-amplitude force varying with a high frequency). The variability of the gain factor according to the force exerted by the practitioner on the tool guide makes it possible to guarantee the precision and safety of the displacement of the tool guide 14 when the tool guide 14 is close to the relevant part of the patient's anatomy. Furthermore, this type of definition of the gain factor allows the continuity of the displacement speed of the tool guide 14 when the force exerted by the practitioner on the tool guide varies between F min and F max .

[0101] As an alternative to the solution described as reference equation 2, the displacement speed of the tool guide 14 can also be calculated in the following form:

[0102] [Equation 3]

[0103] |v| = G x (|f| - F min )

[0104] Figure 8 and Figure 9 This is described in more detail. Figure 8 Corresponding to a situation in which the force exerted by the practitioner on the tool guide, as determined by the control unit, varies between F min and F max , the gain factor G is constant. Figure 9 Corresponding to a situation in which the gain factor varies as a function of the determined force (G is defined in expression equation 1). Figure 8 and 9 Each of the figures contains four data graphs. Figure 8 and Figure 9 The data graphs in part a) of figures Figure 8 and Figure 9 The data graphs in part b) of figures Figure 8 and Figure 9 The data graphs in part c) of figures Figure 8 and Figure 9 The data graphs in part d) of figures

[0105] In the solution corresponding to Figure 8 , the gain factor G is constant when the determined force varies between F min and F max . When the determined force is lower than F min , the gain factor G is zero. When the determined force is greater than F max , the displacement speed of the tool guide 14 is capped at the maximum speed V max . As shown in part a) of figures Figure 8 , when |f| varies between F min and F max , |v| varies between zero and V maxThe relationship changes linearly between them. When |f| is lower than F... min When |v| is zero, then |v| is zero. For example... Figure 8 As shown in part a), when |f| is in F min and F max When the values ​​change, the acceleration |a| experienced by the tool guide 14 remains constant at a value of A. When |f| is lower than F... min or higher than F max At that time, the acceleration |a| experienced by the tool guide 14 is zero. Therefore, in Figure 8 Part d) shows that when |f| is in F min Nearby oscillations (low-amplitude forces applied by practitioners while trembling, such as...) Figure 8 (as shown in section c), then each time the force |f| exceeds F min At that moment, the acceleration |a| experienced by the tool guide 14 suddenly changes from zero to A. Conversely, the force |f| measured each time is lower than F. min At this time, the acceleration |a| experienced by the tool guide 14 suddenly changes from the value A to zero. This type of situation will cause the tool guide 14 to jitter.

[0106] In corresponding Figure 9 In the scheme, when |f| is in F min and F max When the force varies between these two values, the gain factor G changes linearly with the measured force |f|. When the measured force is below F... min When the measured force is greater than F, the gain factor G is zero. max At that time, the upper limit of the displacement velocity of the tool guide 14 is set to the maximum velocity V. max .like Figure 9 As shown in part a), when |f| is in F min and F max When |v| changes between zero and V, |v| is at zero and V max The relationship exhibits an exponential change. When |f| is lower than F... min When |v| is zero, then |v| is zero. For example... Figure 9 As shown in part a), when |f| is in F min and F max When the acceleration |a| experienced by the tool guide 14 varies between values, the acceleration at its minimum value A is... min and maximum value A max The relationship changes linearly between them. When |f| is lower than F... min or higher than F max At that time, the acceleration |a| experienced by the tool guide 14 is zero. Therefore, in Figure 9 As can be seen from part d), when |f| is in F min Nearby oscillations (low-amplitude forces applied by practitioners while trembling, such as...) Figure 9 (as shown in section c), then each time the force |f| exceeds Fmin the acceleration |a| undergone by the tool guide 14 varies from the value zero to the value A min when |f| is greater than F min |a| varies continuously with |f| and each measured force |f| is lower than F min |a| varies from the value A min to the value zero. However, the value A min is significantly lower than the value A. Figure 9 the variation of the acceleration |a| undergone by the tool guide 14 represented in d) of Figure 6 is obviously less than Figure 8 the variation represented in d) of Figure 5. Thus, the value of the force variation gain factor G according to the measured force makes it possible to avoid the chattering in the displacement of the robot arm 13 due to the tremor of the operator.

[0107] It should be noted that the definition of the gain factor G proposed by equation [formula 1] is only a non-limiting example. It should be understood that it is possible to envisage defining the gain factor G differently, while making it vary according to the measured force. The choice of a particular definition of the gain factor G is only a variant of the invention.

[0108] For position control, the PID corrector output calculated speed is multiplied by a selection matrix. This selection matrix makes it possible to select the position directions that must be controlled by applying multiplication coefficients equal to 0 in the forbidden directions and multiplication coefficients equal to 1 in the allowed directions. The speed obtained after application of the selection matrix corresponds to the displacement speed of the tool guide 14.

[0109] As mentioned previously, in the "cooperative manual control" mode, the control unit 12 is configured to control the robot arm 13 to prevent the displacement of the tool guide 14 in at least one direction, or it can be advantageous to limit the displacement of the tool guide 14 according to a single direction corresponding to the main axis 145 of the tool guide 14, in particular to release the tool guide 14 in the release position 103 ("release cooperative manual control" mode), or to bring the tool guide 14 from the release position 103 to the insertion position 102 ("return cooperative manual control" mode).

[0110] Furthermore, as mentioned previously for the "return cooperative manual control" mode, it can be advantageous for the control unit 12 to be configured to control the displacement speed of the tool guide 14 according to the distance between the current position of the tool guide 14 and the target position that the tool guide 14 must reach. The displacement speed of the tool guide 14 can in particular be controlled so that the shorter the distance (i.e. the closer the tool guide 14 is to its target position), the slower the displacement speed, until reaching a zero speed when the target position is reached.

[0111] For the "near-cooperative manual control" mode, there is no position control: the displacement of the tool guide 14 is not constrained in any direction. Only force control is applied in this mode.

[0112] The control unit 12 of the medical robot 10 can also be configured to detect situations of risk of injury caused by the medical instrument 15, for example when the patient 20 makes an unexpected movement while the medical instrument 15 is not yet released from the tool guide. In fact, situations of this type can lead to injury of the patient by the medical instrument (for example, damage to healthy tissue of a relevant part or another part of the patient's body anatomy by the medical instrument). Therefore, when a situation of this type is detected, measures can be taken to prevent the patient from being injured.

[0113] In a particular embodiment, the tool guide 14 of the medical robot 10 comprises an actuator capable of immediately releasing the medical instrument 15. The actuator is controlled by the control unit 12 of the medical robot in order to move apart the two movable parts of the holding device 146, thus releasing the medical instrument 15. The control unit 12 is configured to command the tool guide 14 to release the medical instrument 15 when a particular situation of risk of injury is detected.

[0114] According to a first example, when the control unit 12 receives information obtained from the navigation system 30, a particular situation of risk of injury is detected, indicating an unexpected displacement of the patient reference 22 (a change in the position of the patient reference 22 representing an unexpected movement of the patient 20).

[0115] According to a second example, the "medical instrument insertion" mode can be selected through the user interface and activated by the control pedal 19. In this mode, the control unit 12 is configured to prevent any displacement of the tool guide 14 and the control unit 12 is configured to measure the force exerted on the medical instrument 15 by the force sensor. A particular situation of risk of injury is detected, for example, when the force exerted on the medical instrument is greater than a predetermined threshold (an unexpected movement of the patient 20 causes the exertion of a force on the force sensor 16 by the medical instrument 15). According to another example, a particular situation of risk of injury is detected when the variation of the force exerted on the medical instrument in a given period of time is greater than a predetermined threshold.

[0116] The automatic release of the medical instrument 15 can be accompanied by an automatic release of the robot arm 13 in the release direction (direction along the main shaft 145 of the tool guide 14 towards the base 11 of the medical robot).

[0117] The above description clearly illustrates the present application by its different features and advantages, achieving the proposed objects.

[0118] In particular, the fact of defining the displacement speed of the tool guide 14 on the basis of a gain factor that varies as a function of the force applied by the practitioner allows a controlled, precise and smooth displacement of the robotic arm 13 when the practitioner manually moves the tool guide 14 by applying a low-amplitude force. The displacement of the robotic arm 13 is still fluid and reactive when the practitioner applies a high-amplitude force on the tool guide 14.

[0119] The force control and the position control of the robotic arm 13 make it possible to release the tool guide 14 in a safe manner after insertion of the medical instrument 15, optionally in part. The application can also bring the tool guide 14 safely and precisely to the insertion position if necessary.

[0120] Finally, the automatic emergency release of the medical instrument 15 can avoid injuring the patient in the event of an accidental movement of the patient during the medical procedure.

[0121] It should be noted that the application has been described using an optical navigation system. However, according to a variant, nothing would prevent an electromagnetic navigation system from being used instead of an 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, the position of which can be determined by the navigation system in the electromagnetic field produced.

Claims

1. A medical robot for assisting an operator during a medical procedure on a relevant portion of a patient's anatomy, said medical robot comprising a robot arm comprising at a distal end a tool guide designed for guiding a medical instrument, and a control unit configured to control the displacement of the robot arm, said medical robot being characterized in that the tool guide is coupled to a force sensor, and in that, when the medical robot is used in a "cooperative manual control" mode, the control unit is configured to: - measure the force exerted by the operator on the tool guide by means of the force sensor; - calculate the velocity of displacement of the tool guide as a function of a gain factor applied to the force thus measured, the value of the gain factor being variable and calculated as a function of the force exerted by the operator on the tool guide; - control the displacement of the robot arm as a function of the velocity thus calculated; the value of the gain factor being defined as: K = Kp + Ki + Kd the gain factor corresponding to the proportional parameter of a "proportional, integral, derivative" corrector implemented by the control unit. the control unit being further configured to prevent the displacement of the tool guide in at least one direction. the control unit being further configured to limit the displacement of the tool guide in a single direction corresponding to the main axis of the tool guide. the control unit being configured to calculate the velocity of displacement of the tool guide also as a function of the distance between the current position of the tool guide and a target position that the tool guide has to reach. the robot arm being a jointed arm having at least six degrees of freedom. when the medical robot is used in a "medical instrument insertion" mode, the control unit being configured to prevent any displacement of the tool guide, and by means of the force sensor, the control unit being configured to measure the force exerted on the medical instrument, the tool guide comprising a means for automatically releasing the medical instrument as a function of a command from the control unit, and the control unit being configured to command the release of the medical instrument by the tool guide when the force exerted on the medical instrument is greater than a predetermined threshold, or when the variation of the force exerted on the medical instrument over a given period of time is greater than a predetermined threshold. the tool guide comprising at least one marker detectable by a navigation system, and the control unit being configured to: - receive from the navigation system a first piece of information relating to the position of the tool guide in the reference of the navigation system; - receive from the navigation system a second piece of information relating to a target position that the tool guide has to reach in the reference of the navigation system; - determine the target position of the medical robot in the reference from the second piece of information; - move the robot arm in an "automatic control" mode, without intervention by the operator, so that the tool guide reaches the target position. ​ ​ ​ wherein ​ where G(f) is a gain factor; K is a constant; |f| is the force exerted by the practitioner on the tool guide, measured by the control unit through the force sensor, F min and F max correspond respectively to the minimum and maximum values of the force exerted by the practitioner; the gain factor varies linearly with the force exerted by the practitioner on the tool guide when this force varies between the minimum value F min and the maximum value F max .

2. The medical robot of claim 1, wherein, ​ 3. The medical robot as claimed in claim 2, wherein, ​ 4. The medical robot as claimed in claim 3, wherein, ​ 5. The medical robot of claim 4, wherein, ​ 6. The medical robot according to any one of claims 1 to 5, wherein, ​ 7. The medical robot according to any one of claims 1 to 5, wherein, ​ 8. The medical robot according to any one of claims 1 to 5, wherein, ​ ​ ​ ​ ​ 9. The medical robot of claim 8, wherein, The second piece of information corresponds to the position of a patient reference in the frame of reference of the navigation system, the patient reference being designed to be positioned in the vicinity of the relevant part of the patient's anatomy, the patient reference comprising at least one marker detectable by the navigation system and at least one radiopaque marker, and the control unit being configured to determine the target position of the tool guide as a function of the position of the patient reference and of a trajectory that the medical instrument must follow in order to carry out the medical intervention, the trajectory being defined with respect to the position of the patient reference by means of a pre-intervention medical image on which the relevant part of the patient's anatomy and the at least one radiopaque marker of the patient reference are visible.

10. The medical robot of claim 9, wherein, The control unit is configured to: - store the position of the tool guide at a first time with respect to the position of the patient reference as a reference position; - determine whether the difference between the position of the tool guide at a second time and the reference position is below a predetermined threshold.

11. The medical robot of claim 9, wherein, The tool guide comprises a device for automatically releasing the medical instrument as a function of a command from the control unit, and the control unit is configured to command the tool guide to release the medical instrument when the control unit receives information from the navigation system indicating an unexpected displacement of the patient reference.

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