Method for controlling an articulated end effector actuated by one or more actuation tendons of a surgical instrument of a robotic system for surgery, with compensation of the elastoplastic elongation of the tendons, and related robotic system

Abstract

There is described a method for controlling an articulated end effector 40 actuated by one or more actuation tendons of a surgical instrument 20 of a robotic surgical system, to be performed during an operating phase of the surgical instrument. The method is applied to a robotic surgical system comprising an articulated end effector 40 and at least one actuation tendon 31, 32, 33, 34, 35, 36, configured to actuate the articulated end effector 40, and also comprising control means 9 and at least one motorized actuator 11, 12, 13, 14, 15, 16, operatively connectable to a respective one of the aforesaid at least one actuation tendons 31, 32, 33, 34, 35, 36 to impart an action to the respective actuation tendon, controlled by the control means 9. The method comprises, during the aforesaid operating phase, when the at least one motorized actuator 11, 12, 13, 14, 15, 16 is in contact with the respective at least one actuation tendon 31, 32, 33, 34, 35, 36, the following steps: - estimating a desired target force F(ΔX) associated with an expected elastic elongation of the at least one actuation tendon 31, 32, 33, 34, 35, 36 at and / or as a function of a respective known stroke and / or known position Ax imparted by the control means 9 to the at least one motorized actuator 11, 12, 13, 14, 15, 16 with respect to a reference zero position; - detecting an actual force F exerted by at least one of the aforesaid one or more motorized actuators; - estimating and / or calculating, based on the difference between the aforesaid detected actual force F and the aforesaid desired target force F(ΔX), a length variation Δi of the aforesaid at least one actuation tendon 31, 32, 33, 34, 35, 36, due to plastic or elastoplastic elongation of the actuation tendon. The method further provides using the estimated and / or calculated length variation Δi, due to plastic or elastoplastic elongation of the actuation tendon, as a compensation input for a control of the at least one motorized actuator 11, 12, 13, 14, 15, 16. A robotic system for surgery configured to carry out and / or to be controlled by the aforesaid method is further described.

Description

[0001] “Method for controlling an articulated end effector actuated by one or more actuation tendons of a surgical instrument of a robotic system for surgery, with compensation of the elastoplastic elongation of the tendons, and related robotic system”

[0002] DESCRIPTION

[0003] TECHNOLOGICAL BACKGROUND OF THE INVENTION

[0004] Field of application.

[0005] The present invention relates to a method for controlling an articulated end effector actuated by one or more actuation tendons of a surgical instrument of a robotic system for surgery.

[0006] In particular, the invention relates to a control method which includes a compensation of the plastic or elastoplastic elongation of the actuation tendons.

[0007] Therefore, the present description more generally relates to the technical field of operational control of robotic systems for teleoperated surgery.

[0008] Description of the prior art.

[0009] Known robotic systems for medicine and / or surgery typically comprise at least one articulated terminal (or "articulated end effector" or "end effector") intended to interact with an anatomy of a patient, whether to perform surgical or microsurgical procedures such as sutures, anastomoses, incisions, or to acquire images, or diagnostic information.

[0010] The articulated end effector is typically actuated by actuation cables (tendons) which transfer a traction action to the articulated end effector.

[0011] Robotic systems for medicine and / or surgery can operate according to a masterslave control architecture, for example where the master is hand-held by a surgeon, or they can operate in autonomous mode, for example by performing a series of programmed operations.

[0012] Anthropomorphic robotic systems are also known in which the articulated end effector comprises anthropomorphic joints, such as the joints of the phalanges of a robotic hand, which are implemented by traction action applied on actuation tendons.

[0013] The robotic system motors can be placed upstream of the articulated end effectors, and the actuation tendons are operatively connected to both the motors and the articulated end effector. The pose of the articulated end effector is determined by the action of the motors of the robotic system which is transmitted by the actuation tendons.

[0014] The number of actuation tendons for the movement of a plurality of degrees of freedom can vary, but typically two antagonistic tendons are connected to the same degree of freedom of the articulated end effector to move it in opposite directions.

[0015] In addition, in the case of miniaturized articulated end effectors, the sizing and the materials of the actuation tendons becomes decisive for transferring the action of the motors to the articulated end effector. In fact, as the scale decreases, a longitudinal deformation of the tendon by a precise amount (whether recoverable or not) becomes increasingly significant.

[0016] To facilitate the miniaturization of the articulated end effector, it is possible to resort to the use of polymeric actuation tendons, as shown for example by WO- 2022 / 137052 A1 to the same Applicant.

[0017] Such types of actuation tendons allow reducing tendon friction and diameter, thus allowing very small connecting radii to be traveled.

[0018] Moreover, miniaturized articulated end effectors are typically arranged at the distal end of a positioning shaft which can be rigid or flexible or jointed and which forces the actuation tendons to extend for relatively long stretches in relation to the extent of the tendon stretch along the only articulated end effector device at the distal end of the shaft.

[0019] In operating conditions, the tendons of miniaturized articulated end effectors are stressed in traction even under very high forces so as to obtain gripping forces suitable for the clinical application despite the small radii around which such tendons wind distally.

[0020] The provision of such long, thin tendons increases the occurrence of deformability of the tendon in the longitudinal direction, when in operating conditions.

[0021] For example, in winch transmission systems, the tendons wind on a rotating spool and can intersect with each other, i.e., intertwine during such winding, locally increasing friction and potentially causing a tearing transmission of the action of the motors.

[0022] Similarly, where the tendons are intertwined, i.e., interwoven inside the extension of the shaft of a medical and / or surgical instrument, an increase in friction which would affect the transmission would occur locally.

[0023] Moreover, the surgical instruments in hand can be used to grasp or cut tissues. The force used to perform a grip is exerted by the motors by means of the actuation tendons. The force applied by the motors, and thus the force by which the tendons are stressed during gripping, is much greater with respect to the force used during normal non-gripping movement. In the particular instrument configuration as shown for example by WO2022 / 137052 A1 to the same Applicant, each tip is actuated by two different tendons, a closing one and an opening one for each tip.

[0024] Once the tips have been closed, an increase in the gripping force generated by the tips on the object will be given by the thrust of the motors acting on the two tendons used to close both tips. It is thus a direct consequence to observe much higher average force loads on the "closing" tendons.

[0025] Generally speaking, all cords (or tendons) are subject to elongation when subjected to loads.

[0026] New and / or previously unstressed cords typically have a high elastoplastic elongation when under load at least partially due to the unraveling of the fibers forming the braided cord itself. For this reason, it is common practice to subject the new cords, before assembly on a surgical instrument, to a high initial load in order to remove part of the residual plasticity of the drawing and braiding process or of the material itself.

[0027] In fact, braided cords typically have three elongation elements:

[0028] (1 ) elastic elongation deformation, which is recovered when the tensile load stops;

[0029] (2) recoverable deformation, i.e., a relatively small deformation which is gradually recovered in a certain time period; this time period is often a function of the braiding, and generally takes from a few minutes to a day before being completely recovered;

[0030] (3) permanent non-recoverable elongation deformation.

[0031] As the tendons used for closing and gripping are stressed by much higher average forces than the remaining tendons, it is understandable how these are subject to a much greater or more significant recoverable and non-recoverable elongation deformation.

[0032] During operation, the surgical instrument is thus in a situation of elongation asymmetry between closing tendons and the remaining tendons, in particular this difference between closing tendons and opening tendons can change the correspondence between actuation pistons and tip orientation.

[0033] The elongation of a transmission tendon causes the motion transmitted by the motor on the articulated end effector of the surgical instrument to be different and less effective, generating a variation in movement. In practice, an elongation causes part of the movement transmitted by the motor not to be transferred to the instrument due to the elongation of the tendons.

[0034] This inconvenience, in turn, can lead to a worsening of performance and usability. In other words, in the aforementioned cases, there would be a mismatch between the action of the motors and the movement of the articulated end effector of the surgical instrument. In order to try to mitigate such a problem, some known solutions suggest adding sensors to the articulated end effector, for example by "encoder"-type sensors arranged on the joints or by means of the integration of Bragg Fibers in the kinematic chain of the articulated end effector to monitor the pose and the taken orientation in real time.

[0035] Such a detection of information on the pose of the articulated end effector does not fully solve the aforementioned problem, because it requires providing the articulated end effector with further sensor elements, which, in addition to increasing the dimensions of the articulated end effector, can represent design challenges as they necessarily unbalance the distribution of weights and dimensions in the articulated end effector and can represent a mechanical constraint which limits the number and complexity of the positions which can actually be reached by the articulated end effector when in operating conditions.

[0036] This inconvenience represents a serious obstacle to the miniaturization of the articulated end effector.

[0037] Miniaturized articulated end effectors are desirable in the medical-surgical field, as well as in the field of anthropomorphic robots, as well as in micro-electronics, micromechanics, precision mechanics, watchmaking, jewelry and costume jewelry and more generally in automation.

[0038] Particularly in the medical-surgical field, the articulated end effector is a sterile component of the system and works in the sterile field when in operating conditions, and therefore, it is often not possible or not desirable to equip the articulated end effector with an active sensor system to allow the robotic system to detect the pose taken by the articulated end effector itself in real time.

[0039] At the same time, the push towards extreme miniaturization of the articulated end effectors is strongly felt in this field and a fine control on the position of the articulated end effector and on the action performed by the articulated end effector is necessary to ensure safety and, at the same time, usability.

[0040] In the case of a robotic system remotely operated according to a master-slave control architecture, the action of the motors is controlled based on the action imparted by the user on a master control device. The master control device can be in the form of a joystick, i.e., a mechanical appendage projecting cantilevered from a master operating console, and can comprise a motorized force feedback system which returns tactile feedback to the user, which depends on the information detected by the sensor system of the articulated end effector.

[0041] Teleoperated robotic systems are also known, in which the master control device is "ungrounded", i.e., not constrained to the ground, where it is possible to not provide a tactile feedback system.

[0042] Therefore, the need to devise a solution to ensure a more precise correspondence between the action imparted by the motors of a robotic system and the action performed by the articulated end effector is strongly felt in different areas, while avoiding the provision of sensor systems on the articulated end effector itself.

[0043] At the same time, there is a need to miniaturize articulated end effectors of robotic systems without resulting in decreased control over the articulated end effector itself.

[0044] The need to optimize the control of miniaturized articulated instruments actuated by cables subject to elastoplastic deformation during the use is also strongly felt.

[0045] SUMMARY OF THE INVENTION

[0046] It is the object of the present invention to provide a method for controlling an articulated end effector, actuated by actuation tendons of a surgical instrument of a robotic system for surgery, which allows at least partially overcoming the drawbacks complained above with reference to the prior art, and responding to the aforementioned needs particularly felt in the technical field considered. Such an object is achieved by a method according to claim 1 .

[0047] Further embodiments of such a method are defined by claims 2-30.

[0048] It is a further object of the present invention to provide a robotic system for surgery configured to carry out and / or to be controlled by the aforesaid method. Such an object is achieved by a robotic system according to claim 31 .

[0049] Further embodiments of such a robotic system are defined in claims 32-57.

[0050] Such a method and such a robotic system provide solutions to the aforementioned technical problems.

[0051] In fact, by virtue of the suggested solutions, it is possible to use a behavior model in operating conditions of an actuation tendon to create a position control method of a motor (or of a pair of motors) of a robotic manipulator aimed at actuating a miniaturized articulated end effector.

[0052] The information on the imparted force can be detected by a load cell placed on the motor at the interface with the transmission unit.

[0053] For example, the transmission unit comprises a rigid element, for example a piston, which interfaces with the motor and an actuation tendon connected to the articulated end effector and rigidly connectable to the rigid element, for example glued to the piston. Thereby, the force detected at the interface between the motor and the rigid element of the transmission unit rigidly connectable to the actuation tendon is substantially equal to the traction force applied on the actuation tendon.

[0054] Where the connection between the motor and the actuation tendon is not rigid, the method can take into account the yielding of the connection between motor and tendon.

[0055] The information on the movement of the motor is used to estimate the force generated by the elastic elongation of the actuation tendon in real time and compared with the actual force read by the sensors, by comparing these two forces it is possible to estimate the elastoplastic elongation of the tendon observed.

[0056] By virtue of the suggested solutions, it is possible to ensure the correspondence between the action of the motors and the pose taken by the articulated end effector, avoiding adding sensors to the articulated end effector, keeping the sensors for detecting useful information for the control method as much "upstream" as possible. For example, in the medical-surgical field this allows keeping the sensors out of the sterile field.

[0057] Where a teleoperated master-slave robotic system is provided, by virtue of the suggested solutions, it helps to ensure the correspondence between the action of the master device and the pose taken by the articulated end effector of the slave device, minimizing tracking delay.

[0058] Crucially, by virtue of the suggested solutions, it is allowed to compensate for an elastoplastic component of said non-correspondence between the action of the motor and the pose taken by the articulated end effector.

[0059] By virtue of the suggested solutions, it is possible to use long, thin actuation tendons in a precise and controlled manner and subject to a high elastoplastic deformation based on the force imparted by the motors.

[0060] By virtue of the suggested solutions, it is possible to accurately estimate the current pose of the articulated end effector by means of a model of the transmission action performed by the transmission unit based on the force imparted to the transmission unit, as detected.

[0061] The method according to the invention is particularly adapted but not uniquely intended to control a robotic system for surgery, not necessarily of the master-slave type.

[0062] The method according to the invention is adapted to control an anthropomorphic robotic system not necessarily comprising robotic phalanges actuated by actuation tendons.

[0063] BRIEF DESCRIPTION OF THE DRAWINGS

[0064] Further features and advantages of the method according to the invention will become apparent from the following description of preferred exemplary embodiments, given by way of non-limiting indication, with reference to the accompanying drawings, in which:

[0065] - figure 1 shows in axonometric view a robotic system for teleoperated surgery, according to an embodiment;

[0066] - figure 2 shows in axonometric view a portion of the robotic system for teleoperated surgery in figure 1 ;

[0067] - figure 3 shows in axonometric view a distal portion of a robotic manipulator, according to an embodiment;

[0068] - figure 4 shows in axonometric view a surgical instrument, according to an embodiment, in which tendons are diagrammatically shown in a dashed line;

[0069] - figure 5 diagrammatically shows a motorized actuator, a transmission element and a tendon of a surgical instrument, according to an embodiment;

[0070] - figure 6 is an axonometric view, partially sectioned for clarity, showing an articulated end effector of a surgical instrument, according to an embodiment;

[0071] - figure 7 depicts a motor-piston-tendon assembly, comprised in an embodiment of the robotic system of the invention, in which the motor and the piston are moved by a stroke Axwith respect to a zero point, in conditions of no elastoplastic elongation;

[0072] - figure 8 shows in a simplified manner the effect of an elastoplastic elongation Ai on the operation of the motor-piston-tendon assembly in figure 7;

[0073] - figure 9 depicts a pair of antagonistic motor-piston-tendon assemblies, which determine a rotation movement, in one direction and in the other, of an end of a surgical instrument comprised in an embodiment of the robotic system of the invention;

[0074] - figure 10 depicts two pairs of antagonistic tendons, which determine rotation movements of two ends of the surgical instrument, adapted to control an opening / closing degree of freedom of grip / cut of the end effector of the surgical instrument, consisting of the two ends;

[0075] - figure 1 1 shows in a simplified manner the structure and function of a part of the robotic system (motor-piston-tendon-end effector assembly of the surgical instrument) according to an embodiment of the invention;

[0076] - figure 12 shows in a simplified manner the structure and function of a part of the robotic system (antagonistic pair of motor-piston-tendon-end effector assemblies of the surgical instrument) according to an embodiment of the invention;

[0077] - figure 13 shows an embodiment of the method and system according to the present invention;

[0078] - figure 14 shows, by means of exemplary "strain-stress" curves, some illustrative details regarding the typical behavior of actuation tendons.

[0079] DETAILED DESCRIPTION

[0080] With reference to figures 1-14, a method is described for controlling an articulated end effector 40 actuated by one or more actuation tendons of a surgical instrument 20 of a robotic system for surgery.

[0081] The articulated end effector will hereinafter also be referred to as “articulated end device” or “end effector”.

[0082] The method is advantageously executable during an operating phase of the surgical instrument.

[0083] The method is applied to a surgical instrument 20 comprising an articulated end effector 40 and at least one actuation tendon 31 , 32, 33, 34, 35, 36, configured to actuate the articulated end effector 40.

[0084] The method is applied to a robotic system for surgery comprising, in addition to said surgical instrument 20, control means 9 and at least one motorized actuator 11 , 12, 13, 14, 15, 16, operatively connectable to a respective said at least one actuation tendon 31 , 32, 33, 34, 35, 36 to impart an action to the respective actuation tendon, controlled by the control means 9, so as to determine a univocal correlation between at least one movement of one or more motorized actuators 1 1 , 12, 13, 14, 15, 16 and a respective at least one movement of the articulated end effector 40.

[0085] The method comprises, during the aforesaid operating phase, when the at least one motorized actuator 11 , 12, 13, 14, 15, 16 is in contact with the respective at least one actuation tendon 31 , 32, 33, 34, 35, 36, the following steps:

[0086] - estimating a desired target force F(AX) associated with an expected elastic elongation of the at least one actuation tendon 31 , 32, 33, 34, 35, 36 at and / or as a function of a respective known stroke and / or known position Aximparted by the control means 9 to the at least one motorized actuator 1 1 , 12, 13, 14, 15, 16 with respect to a reference zero position;

[0087] - detecting an actual force F exerted by at least one of the aforesaid one or more motorized actuators 1 1 , 12, 13, 14, 15, 16 on a respective one of said at least one actuation tendons 31 , 32, 33, 34, 35, 36;

[0088] - estimating and / or calculating, based on the difference between the aforesaid detected actual force F and the aforesaid desired target force F(AX), a length variation Ai of the aforesaid at least one actuation tendon 31 , 32, 33, 34, 35, 36, due to plastic or elastoplastic elongation of the actuation tendon.

[0089] Finally, the method provides using the aforesaid estimated and / or calculated length variation Ai as a compensation (in particular, elastoplastic compensation) input for a control of the at least one motorized actuator 1 1 , 12, 13, 14, 15, 16.

[0090] It should be noted that the aforesaid technical effect of reducing or cancelling the error introduced by the elastic elongation can comprise or correspond to a "compensation" for such error and / or a "minimization" of such error.

[0091] The terms "elastoplastic elongation" are meant in this description as the recoverable elongation deformations (i.e., relatively small deformations which are gradually recovered over a certain time period, which can typically vary from a few minutes to a day before being completely recovered) and / or non-recoverable permanent elongation deformations (plastic deformations, strictly speaking).

[0092] Therefore, the plastic or elastoplastic deformations compensated by the present method are those deformations which are not instantly recovered when the tensile load ceases.

[0093] The aforesaid definition of "elastoplastic elongation" thus excludes, among the possible deformations, only elastic deformations (those which are instantly recovered when the tensile load ceases).

[0094] According to an embodiment of the method, the aforesaid step of detecting an actual force F comprises detecting an instantaneous actual force Ft exerted by the at least one motorized actuator 11 , 12, 13, 14, 15, 16 at an instant corresponding to the instant in which the aforesaid known stroke and / or position Axof the at least one motorized actuator 1 1 , 12, 13, 14, 15, 16 occurs and for which the aforesaid expected elastic force is estimated.

[0095] According to an implementation option of such an embodiment, the aforesaid step of estimating and / or calculating an elastoplastic length variation Ai comprises calculating the elastoplastic length variation Ai by the following formula:

[0096] F(A) - F(t) (0 = « - T -

[0097] Kpl where kptis an elastoplastic constant representative of a simplified model representative of the elongation, and a is a parameter associated with the elastoplastic compensation function.

[0098] According to a particular implementation option, kptis equal to k, i.e., the known elastic constant of the at least one tendon, and a is equal to -1 :

[0099] F( J - F(t)

[0100] 4;(t)

[0101] — k In accordance with an embodiment of the method, the aforesaid step of detecting an actual force F comprises detecting an instantaneous actual force F(t-1 ) exerted by the at least one motorized actuator 11 , 12, 13, 14, 15, 16 at an instant preceding, by a known time interval, the instant in which the aforesaid known stroke and / or position Axof the at least one actuation tendon 31 , 32, 33, 34, 35, 36 occurs and for which the aforesaid expected elastic force is estimated.

[0102] According to an embodiment of the method, the aforesaid control of the at least one motorized actuator comprises a position control of the at least one motorized actuator 1 1 , 12, 13, 14, 15, 16, which comprises imparting a movement on the at least one motorized actuator 11 , 12, 13, 14, 15, 16 taking into account the estimation of length variation Ai of the at least one actuation tendon, due to elastoplastic elongation of the actuation tendon, so as to reduce or cancel the error introduced by the aforesaid elastoplastic length variation Ai between a force F(t) exerted on the articulated end effector 40 and a desired nominal force on the articulated end effector 40.

[0103] According to an implementation option, the aforesaid position control comprises defining a compensated kinematic-zero position Po-mod by adding the estimated and / or calculated value of length variation Ai to an initial reference kinematic-zero position Po in accordance with the formula:

[0104] Po-mod ~ PQ "F I

[0105] In accordance with an embodiment, the aforesaid steps of the method are carried out iteratively, in a discrete sequence of evaluation steps, in which, in particular, the length variation Ai(t), due to plastic or elastoplastic elongation of the actuation tendon at an instant t, is calculated based on the actual force F(t-1 ) detected at the previous instant.

[0106] According to an implementation option, the step of detecting a force Fm is executed dynamically, at discrete detection instants having a predefined detection frequency and control frequency.

[0107] According to an implementation option of the aforesaid embodiment, the position of the at least one motorized actuator at an instant t is calculated as a function of the modified kinematic-zero position Po-mod, or as a function of the initial reference kinematic- zero position Po, of the sum of the length variation Ai(t) due to plastic or elastoplastic elongation of the actuation tendon and the instantaneous position Ax(t) of the motorized actuator, in accordance with the following chain of equations: io In accordance with an embodiment, in which the method is applied to a masterslave system in which the surgical instrument is a slave device controlled, according to a control mode, by a master device of the robotic system, the method, in the absence of external forces, allows minimizing in a finite time the error between the pose controlled by the master device and the pose reached by the articulated end effector 40 of the slave device.

[0108] According to an embodiment, the method is applied to a robotic system in which the surgical instrument 20 comprises a plurality of actuation tendons 31 , 32, 33, 34, 35, 36, and a respective plurality of motorized actuators 11 , 12, 13, 14, 15, 16.

[0109] According to such an embodiment, the method provides that the aforesaid step of estimating a desired target force F(AX) is carried out with reference to a plurality or with reference to all the actuation tendons 31 , 32, 33, 34, 35, 36, the aforesaid step of detecting an actual force F is carried out on a plurality or on all the motorized actuators 1 1 , 12, 13, 14, 15, 16, the aforesaid step of estimating and / or calculating a length variation Ai due to plastic or elastoplastic elongation of the actuation tendon is carried out with reference to a plurality or with reference to all the motorized actuators 1 1 , 12, 13, 14, 15, 16, and the aforesaid step of using the length variation Ai in a position control is carried out with reference to a plurality or with reference to all the motorized actuators 1 1 , 12, 13, 14, 15, 16.

[0110] According to possible implementation options, the length variation (Ai) is estimated based on a linear model, or based on more complex, even non-linear models.

[0111] In accordance with an embodiment (shown, in particular, in figures 9-12), the method is applied to a robotic system in which the master device of the robotic system is a hand-held, unconstrained master device, adapted to be moved by an operator and to be manipulated by the operator according to a degree of freedom associated with the grip opening / closing and / or cut of the surgical slave instrument.

[0112] Each of the aforesaid one or more actuation tendons 31 , 32, 33, 34, 35, 36 is operatively connected to both a respective motorized actuator of the robotic surgical system and the aforesaid articulated end effector 40, to actuate a respective degree of freedom among the one or more degrees of freedom of the articulated end effector 40.

[0113] The aforesaid actuation tendons 31 , 32, 33, 34, 35, 36 comprise one or more pairs of antagonistic tendons, for example two pairs of antagonistic tendons configured to control, respectively, degrees of freedom of a grip opening and closing and / or cut to be performed by two tips or ends or tweezers 43, 44 of the articulated end effector 40 of the surgical slave instrument.

[0114] According to such an embodiment, the method provides that the aforesaid step of using the estimated and / or calculated length variation Ai as a compensation input for a control is carried out with reference to the tendons of the aforesaid pairs of antagonistic tendons, so as to control the aforesaid degrees of freedom of grip opening and closing and / or cut.

[0115] According to an embodiment, the method is performed, during the aforesaid operating phase of the surgical instrument, only during a sub-phase of gripping of two tips or tweezers or ends 43, 44.

[0116] According to an implementation option of such an embodiment, during the operating phase of the surgical instrument, the orientation and opening / closing of the articulated end effector 40 of the surgical instrument is controlled in position, the elastoplastic compensation is activated only during the aforesaid gripping sub-phase, and the elastoplastic compensation contribution is added to the position control.

[0117] In accordance with an embodiment, the method further comprises performing an elastic compensation, calculated in real time, of the elastic elongation undergone by the at least one actuation tendon, in which either or both elastoplastic compensation and elastic compensation are carried out and applied, so that the position control determines as a whole a compensated position X(t) in which both the elastic compensation contribution Axeand the elastoplastic compensation contribution AxePare added to a nominal position Xc:

[0118] X(t1) = XC + AXe + AXep

[0119] According to an embodiment, the method includes that subsequent compensations are performed at a series of subsequent instants, during the operating phase of the surgical instrument, and the subsequent compensations are added over time, during the operating phase, and are not recoverable.

[0120] According to an implementation option, both the elastoplastic compensation and the elastic compensation are carried out and applied simultaneously.

[0121] According to another implementation option, the elastic compensation and elastoplastic compensation are used in different configurations, in which one or the other is activated or deactivated. In such a case, a compensation contribution of a momentarily deactivated (elastic or elastoplastic) compensation is frozen, maintained and then updated during the subsequent activation of the respective compensation.

[0122] According to an implementation example, when a closing force is recognized during the operating phase, the elastoplastic compensation control is activated and the elastic compensation control is instead deactivated on the actuators which cause the articulated end effector to close.

[0123] In accordance with an embodiment, the method comprises the further step of actuating the motorized actuators associated with the tendons of the aforesaid pairs of antagonistic tendons, according to respective nominal strokes Axj for which it is expected that the tips or ends of the articulated end effector 40 come into contact and lock the degree of freedom of grip and / or cut.

[0124] Moreover, in such a case, said step of estimating the desired target force comprises estimating the desired target forces F(Ax,j) for each of the tendons of the aforesaid pairs of antagonistic tendons, at the aforesaid nominal strokes Ax,j.

[0125] The aforesaid step of detecting an actual force F comprises determining a target actual force F, based on the actual forces exerted by the aforesaid one or more operated motorized actuators.

[0126] The aforesaid step of estimating and / or calculating at least one length variation Ai due to plastic or elastoplastic elongation of the actuation tendon comprises calculating the length variations AIJ of the aforesaid tendons of the pairs of antagonistic tendons based on the respective expected elastic forces and the actual target force F determined.

[0127] The aforesaid step of position control of the at least one motorized actuator comprises controlling the motorized actuators associated with the tendons of the aforesaid pairs of antagonistic tendons so that they reach the aforesaid target actual force F.

[0128] According to an implementation option, the aforesaid step of determining a target actual force F comprises determining, as the target actual force F, an arithmetic average of the forces detected at two of the aforesaid antagonistic tendons.

[0129] According to another implementation option, the aforesaid step of determining a target actual force F comprises determining, as the target actual force F, the maximum force among the forces detected at two of the aforesaid antagonistic tendons.

[0130] According to another implementation option, the steps of the method are carried out iteratively, and the aforesaid step of determining a target actual force F comprises determining, as the target actual force F, a time average of the actual forces detected at two of the aforesaid antagonistic tendons at at least two previous instants.

[0131] According to particular implementation examples, the aforesaid step of determining a target actual target F(t- 1 ), at an instant t-1 , is carried out in accordance with one of the following formulae: where y is an index representing time instants, Fi and F2, F3and F4indicate actual forces detected at two pairs of said antagonistic tendons.

[0132] In accordance with an embodiment, the method further comprises defining a compensated kinematic-zero position Po-mod for the grip and / or cut control, based on the strokes and / or positions taken by the motorized actuators at the target actual force F.

[0133] Advantageously, this embodiment, by virtue of the compensation of the error due to the non-recoverable or very slowly recoverable elongation of the tendons, also allows delivering a constant closing / cutting force / torque with each closing / cutting of the tips or ends of the end effector of the surgical instrument, which is desirable because it makes such a closing / cutting force / torque repeatable without having to interrupt the teleoperation to recondition the tendons.

[0134] The calibration of the robotic system and surgical instrument, described above, is also useful, for example, to grasp a surgical needle always with the same force, or to make cuts (in this case the closing / cutting force / torque is the cutting force which must not exceed a threshold, otherwise the blades can slip off).

[0135] It should be noted that, as already shown above, although the value of the optimal closing / cutting force / torque delivered is not known, which in fact is not measured in real time in the end effector of the surgical instrument, this embodiment of the method ensures that the closing / cutting force / torque is maintained constant at each closing or cutting event because precisely at each closure or cut the error due to the elongation of the tendons is compensated, or, where appropriate, to the shortening of the tendons (in which case the motor retreats to compensate, decreasing the force, to the expected target force).

[0136] According to an implementation option, the method comprises the further step of estimating the elastic coefficient k(t) of one or more tendons as a function of time.

[0137] According to another implementation option, the steps of the method apply only if the target actual force F takes a value within a predefined range of values considered acceptable.

[0138] In accordance with an embodiment of the method, the aforesaid step of detecting the force exerted by a motorized actuator 11 , 12, 13, 14, 15, 16 is performed by a respective force or torque sensor operatively connected to the respective motorized actuator.

[0139] According to an embodiment, the method applies in the case the aforesaid surgical instrument 20 further comprises at least one transmission element 21 , 22, 23, 24, 25, 26 (for example, a piston) operatively connected to a respective at least one actuation tendon 31 , 32, 33, 34, 35, 36 and operatively connectable to a respective motorized actuator 1 1 , 12, 13, 14, 15, 16.

[0140] In such a case, therefore, the surgical instrument comprises a plurality of "transmission units", each comprising an actuation tendon and a piston, in which preferably the tendon is fixed to the piston, and the respective motorized actuator acts by imparting a movement on the piston of the transmission unit.

[0141] According to an implementation option, the surgical instrument comprises 6 transmission units, namely 6 tendons, 6 motorized actuators and 6 pistons.

[0142] According to an implementation option, each transmission unit (i.e., each motor- piston-tendon chain) is managed individually.

[0143] According to another implementation option, the antagonistic transmission units (and thus the antagonistic tendons) are managed in pairs.

[0144] According to an embodiment of the method, the length variation compensation parameters are determined in a controlled and variable manner depending on the pose of the articulated end effector 40 in order to take into account the different frictions related to the different poses.

[0145] In accordance with an embodiment of the method, the aforesaid actuation tendons are polymer tendons preferably formed from braided polymer fibers.

[0146] With reference again to figures 1-14, a robotic surgery system is described herein comprising a surgical instrument 20, control means 9, at least one actuation tendon 31 , 32, 33, 34, 35, 36, and at least one motorized actuator 1 1 , 12, 13, 14, 15, 16.

[0147] The surgical instrument 20 comprises an articulated end effector 40.

[0148] The at least one actuation tendon 31 , 32, 33, 34, 35, 36 is configured to actuate the articulated end effector 40.

[0149] The at least one motorized actuator 11 , 12, 13, 14, 15, 16 is operatively connectable to a respective one of said at least one actuation tendons 31 , 32, 33, 34, 35, 36, to impart to the respective actuation tendon an action, controlled by the control means 9, so as to determine a univocal correlation between at least one movement of one of the one or more motorized actuators 11 , 12, 13, 14, 15, 16 and a respective at least one movement of the articulated end effector 40.

[0150] The control means 9 of the robotic system are configured to carry out, during an operating phase of the robotic system, when the at least one motorized actuator 1 1 , 12, 13, 14, 15, 16 is in contact with the respective at least one actuation tendon 31 , 32, 33, 34, 35, 36, the following actions:

[0151] - estimating a desired target force F(AX) associated with an expected elastic elongation of the at least one actuation tendon 31 , 32, 33, 34, 35, 36 at and / or as a function of a respective known stroke and / or known position Aximparted by the control means 9 to the at least one motorized actuator 1 1 , 12, 13, 14, 15, 16 with respect to a reference zero position;

[0152] - detecting an actual force F exerted by at least one of the aforesaid one or more motorized actuators 11 , 12, 13, 14, 15, 16;

[0153] - estimating and / or calculating, based on the difference between the aforesaid detected actual force F and the aforesaid desired target force F(AX), a length variation Ai of the aforesaid at least one actuation tendon 31 , 32, 33, 34, 35, 36, due to plastic or elastoplastic elongation of the actuation tendon.

[0154] The control means 9 of the robotic system are further configured to use the aforesaid estimated and / or calculated length variation Ai as a compensation input for a control of the at least one motorized actuator 1 1 , 12, 13, 14, 15, 16, taking into account the estimation of length variation Ai.

[0155] According to an embodiment, the robotic system is a master-slave system in which the surgical instrument is a slave device controlled, according to a control mode, by a master device of the robotic system.

[0156] In such a case, the control means 9 of the robotic system are configured to control the system so that, in the absence of external forces, the error between the pose commanded by the master device and the pose reached by the articulated end effector 40 of the slave device is minimized in a finite time.

[0157] In accordance with an embodiment of the robotic system, the surgical instrument 20 comprises a plurality of actuation tendons 31 , 32, 33, 34, 35, 36, and the robotic system for surgery comprises a respective plurality of motorized actuators 11 , 12, 13, 14, 15, 16.

[0158] In such a case, according to several possible implementation options:

[0159] - the aforesaid action of estimating a desired target force F(AX) is carried out with reference to a plurality or with reference to all the actuation tendons 31 , 32, 33, 34, 35, 36;

[0160] - the aforesaid action of detecting an actual force F is carried out on a plurality or on all the motorized actuators 1 1 , 12, 13, 14, 15, 16;

[0161] - the aforesaid action of estimating and / or calculating a length variation Ai is carried out with reference to a plurality or with reference to all the motorized actuators 1 1 , 12, 13, 14, 15, 16;

[0162] - the aforesaid action of using the length variation Ai as a compensation input is carried out with reference to a plurality or with reference to all the motorized actuators 1 1 , 12, 13, 14, 15, 16.

[0163] According to an embodiment of the robotic system, the master device is a handheld, unconstrained master device adapted to be moved by an operator and manipulated by the operator according to a degree of freedom associated with the grip opening / closing and / or cut of the surgical slave instrument.

[0164] Moreover, each of the one or more actuation tendons 31 , 32, 33, 34, 35, 36 is operatively connected to both a respective motorized actuator of the robotic surgical system and the aforesaid articulated end effector 40, to actuate a respective degree of freedom among the one or more degrees of freedom of the articulated end effector 40.

[0165] Moreover, the aforesaid actuation tendons 31 , 32, 33, 34, 35, 36 comprise one or more pairs of antagonistic tendons, for example two pairs of tendons configured to control, respectively, degrees of freedom of grip opening and closing and / or cut to be performed by two tips or ends or tweezers of the articulated end effector 40 of the surgical slave instrument.

[0166] In such an embodiment, the aforesaid action of using the length variation Ai as a compensation input is carried out with reference to the tendons of the aforesaid pairs of antagonistic tendons, so as to control the aforesaid degrees of freedom of grip opening and closing and / or cut.

[0167] According to an implementation option of the robotic system, the control means 9 are further configured to operate the motorized actuators associated with the tendons of the aforesaid pairs of antagonistic tendons, according to respective nominal strokes Axj for which it is expected that the tips or ends of the articulated end effector 40 come into contact and lock the degree of freedom of grip and / or cut.

[0168] Moreover, in such a case:

[0169] - the action of estimating the desired target force comprises estimating the desired target forces F(Ax,j) for each of the tendons of the aforesaid pairs of antagonistic tendons, at the aforesaid nominal strokes Axj ; - the action of detecting an actual force F comprises determining a target actual force F, based on the actual forces exerted by the aforesaid one or more motorized actuators operated;

[0170] - the action of estimating and / or calculating at least one length variation Ai comprises calculating the length variations Ai j due to plastic or elastoplastic elongation of the aforesaid tendons of the pairs of antagonistic tendons based on the respective expected elastic forces and the target actual force F determined;

[0171] - the action of position control of the at least one motorized actuator comprises controlling the motorized actuators associated with the tendons of the aforesaid pairs of antagonistic tendons so that they reach the aforesaid target actual force F.

[0172] According to an embodiment, the robotic system is a robotic system for micro- surgical teleoperation, and the surgical instrument is a micro-surgical instrument.

[0173] According to possible embodiments, the robotic system is configured to carry out and / or be controlled by a method according to any of the previously illustrated method embodiments.

[0174] With reference again to figures 1-14, further details will be provided below, by way non-limiting example, with reference to the operating principles and some particular embodiments of the method and system according to the present invention.

[0175] Suppose (as shown in figure 7) that the system includes a motor acting on a piston connected to a tendon free to slide on a pulley, blocked at the opposite end.

[0176] The motor and piston can move linearly along the same axis. A sensor (for example, a load cell) capable of measuring the contact force between the motor and the piston is mounted on the motor.

[0177] Suppose that initially the motor is in contact with the piston at position Po(which identifies an initial position of the motor in contact with the piston), exerting a null force F = 0.

[0178] Assuming to model the tendon as an ideal spring (without mass, having negligible thickness when fully compressed and in total absence of friction and other dissipative phenomena), the application of an offset of a movement applied by a motor (i.e., of a stroke) Axwould generate a change in the tensile force according to Hooke's law which expresses the elastic force exerted by a spring stressed longitudinally, in traction or in compression, along an axis x , i.e.:

[0179] F = — keAxx

[0180] Hence, the force F with which the spring reacts to the stress is directly proportional to the elongation Axof the spring (i.e., in this case, the elongation of the tendon). The constant kerepresents the longitudinal elastic constant of the spring (tendon), expressed in [N / m],

[0181] Then, considering only the elastic component of the tendon, when the motor is returned to position Po the piston will be in contact with the motor with force F = 0.

[0182] Therefore, if a tendon were modellable by Hooke's law, for any given movement generated by the motor on the piston, and thus on the tendon, the same contact force between motor and piston would result.

[0183] In reality, due to dissipative deformation effects, a repeated application of the same movement on a tendon (due to the action of the respective piston controlled by the respective motor) generates a deformation of the tendon, in particular an elongation which cannot be recovered instantly.

[0184] Due to this effect, when the motor, at an instant t, returns to the initial position Po, the piston will instead be in the different position Pi (as shown in figure 8). Elongation is therefore defined at time t:

[0185] Ai(t) = Pi - Po

[0186] If the movement of the motor did not consider this quantity, with the same movement (or stroke) Ax, the force obtained at the end of the movement would be lower with respect to that obtained before the deformation of the tendon, because part of the movement of the motor is used to cover the distance range which brings the motor into contact with the piston (as always shown in figure 8), which, ultimately, results in a lower tensile force, applied to the tendon, due to the elongation of the tendon.

[0187] If Hooke's law and the constant elastic coefficient over time are considered valid, Hooke's law can be used to estimate the elongation of the tendon, since, during the movement of the motor, the resulting force is known a priori, as long as the load cell reads a value >0, which indicates that the motor is in contact with the piston.

[0188] Consequently, it is possible to estimate the elongation of the tendon at any instant t of the movement of the motor in which the contact with the piston occurs:

[0189] According to an implementation option, already illustrated above, the method provides inserting a further displacement of the motor which compensates for the previously calculated elongation. The new zero position of the motor is thus: The elongation Ai is thus the movement of the motor that is necessary to maintain contact with the piston with zero force F = 0.

[0190] In iterative terms, the position of the motor at time t is described by the following equation, already mentioned above:

[0191] The information on the force imparted is used for the real-time estimation of the elastoplastic elongation of the actuation tendon.

[0192] In the case of using an articulated end effector, the tendons are connected not to a fixed terminal but to a rotational joint (as shown for example in fig. 9).

[0193] In such an embodiment, the system transforms a linear movement generated by the motor into a rotational movement of the terminal member.

[0194] If the piston undergoes a shift from the zero position thereof, the correspondence between linear displacement and the position of the terminal member is no longer valid. It is thus very important to be able to compensate for any elongation of the tendon which may result in a displacement of the piston from the initial position in which the piston-motor system creates a zeroing of the kinematic correspondence.

[0195] Consider now the embodiment in which the end effector of the surgical instrument consists of two tips or ends or tweezers 43, 44, as shown in figure 10.

[0196] The two tips or ends or tweezers can move on the rotational joint and are coaxial, and are actuated by two independent motor-piston-tendon assemblies, as shown in figure 12. In such a case, the two tips or ends or tweezers are free to rotate but are positioned coaxially so that they can close by lying on each other.

[0197] Assuming that the rotational frictions are zero, or in any case negligible, if a tip is free to rotate, the load cell reads a zero force and there are no tendon elongations.

[0198] When the two tips (or ends or tweezers) instead lie on each other, as in figure 10 and figure 12, it is possible to apply a closing force generated by a movement of the two motors which rotate the two tips or ends inwards.

[0199] In other words, in such a case, the movement of the motors is completely transformed into a force which one tip applies on the other; the motors transmit the force applied by means of the tendons according to Hooke's law, and reference is made to the previous case, in the sense that it is possible to introduce an elongation recovery offset using the same law set out above in the previous paragraph.

[0200] According to an implementation option, this occurs independently on the two "motor-piston-tendon-tip" assemblies.

[0201] Assuming now to model a dynamic case, in which the internal frictions of mechanics are considered, one end transmits a force to the other end by means of contact. The degrees of freedom must therefore be considered not independent of each other.

[0202] Due to the geometries present inside the surgical instrument, in this embodiment and with the aforesaid hypotheses, the movements of the motors and thus the applied forces are partially transmitted between one degree of freedom and another.

[0203] According to an implementation option, a combination of the forces applied by the different motors is considered a good approximation and a good index of the force F(t- 1 ) comprised in the formula shown above, valid for the elongation recovery of one or more tendons.

[0204] Such an index can be used as an expression proportional to the force applied between the tips.

[0205] Consider the system depicted in figure 10, in which the lower tip is actuated by the tendon 1 in "opening" and by the tendon 2 in "closing", while the upper tip is actuated by the tendon 3 in closing and by the tendon 4 in opening.

[0206] According to different implementation options, the combinations of forces which are used as force F(t-1 ) are alternatively expressed by one of the following formulas (where the subscripts of the forces refer to the exemplary numbering of the tendons reported above):

[0207] In another embodiment, the method described above is achieved as shown in figure 13. In such a case, the position control of the articulated end effector is flanked by an elastic compensation controller and by an elastoplastic compensation controller.

[0208] It should be noted that several elastic compensation controllers (which are not the main subject of this patent application) can be used.

[0209] For example, according to an implementation option of the embodiment shown in figure 13, the elastic compensation controller acts based on an elastic elongation compensation method articulated in the following steps:

[0210] - detecting the force exerted by at least one of the aforesaid one or more motorized actuators 1 1 , 12, 13, 14, 15, 16, during the operating phase of the surgical instrument;

[0211] - estimating, by a predefined mathematical model, based on the detected force Fm, a length variation of at least one of the one or more actuation tendons 31 , 32, 33, 34, 35, 36, due to elastic elongation of the actuation tendon; and then using the estimated length variation in a position control of the one or more motorized actuators 1 1 , 12, 13, 14, 15, 16.

[0212] Such a position control comprises imparting a movement on the aforesaid at least one motorized actuator 1 1 , 12, 13, 14, 15, 16, taking into account the estimated length variation of said at least one actuation tendon 31 , 32, 33, 34, 35, 36, so as to reduce or cancel the error introduced by said elastic elongation between the position reached by the articulated end effector 40 and a desired nominal position of the articulated end effector 40. Such a desired nominal position, with reference here only to elastic compensation, can for example be that which would be obtained in the absence of elastic elongation.

[0213] According to an embodiment option of the elastic controller, the aforesaid step of using the estimated length variation in a position control and the step of imparting a movement on the respective motorized actuator are carried out based on the formula:

[0214] Fm

[0215] U~ Q. Kel in which such a formula is specific for each motorized actuator and therefore such as to determine a specific control on each motorized actuator.

[0216] In the above formula, Fm is the detected force, u is the position that is controlled by the motorized actuator, Kel is the elastic constant of the actuation tendon, fl is a multiplicative parameter.

[0217] Returning to figure 13, it should be noted that the elastic position controller and the elastoplastic force controller are configured to be able to act (when activated) in parallel with respect to the position control and overcome the deformations of the tendons during an operating phase in which these are stressed.

[0218] The elastic controller and the elastoplastic controller can be used in different configurations, by activating or deactivating the operation thereof and thus the compensation contribution. During the operating phase when a controller is deactivated, the absolute contribution thereof is frozen and maintained and then updated during the next activation.

[0219] According to an implementation option, the elastoplastic controller is used in a complementary manner to the elastic controller. For example, if a closing force is recognized during the operating phase, the elastoplastic compensation control on the closing motors is activated while the elastic one is deactivated. In fact, the maintenance of the elastic compensator would work against the required force target during the closing of the tips and for this reason is deactivated. Thereby, the closing force used as a reference for the deformation calculation can be maintained (for example, according to the equations above).

[0220] The elastoplastic compensator manages to maintain a constant gripping force and to avoid positional deviations due to the elongation of the tendons in use.

[0221] Another implementation option includes acting according to the implementation option shown above, but with the difference that the elastoplastic controller is deactivated only on the closing tendons.

[0222] With reference to figure 14, some further illustrative details are provided regarding the typical behavior of the actuation tendons (and the material from which they are formed), by means of "strain-stress" curves.

[0223] In the curves shown in figure 14, the following phases are highlighted:

[0224] 1 ) elastic phase;

[0225] 2) plastic phase, in which the force no longer behaves elastically;

[0226] 3) return phase behaving in a manner approaching the elastic mode (according to the method of the present invention, such a phase already contains the position offset determined by the control described above);

[0227] 4) further movement phase, which unfolds first along the elastic curve, and then, if the control imposes greater forces / stress, continues on the part of the curve corresponding to the plastic area.

[0228] As can be seen, the objects of the present invention as previously indicated are fully achieved by the method and system described above, by virtue of the features described above in detail, and as widely disclosed in the previous section "Summary of the invention". In order to meet contingent needs, those skilled in the art may make changes and adaptations to the embodiments of the method described above or can replace elements with others which are functionally equivalent, without departing from the scope of the following claims. Each of the features described above as belonging to a possible embodiment can be implemented irrespective of the other embodiments described.

Claims

CLAIMS1. A method for controlling an articulated end effector (40) actuated by one or more actuation tendons of a surgical instrument (20) of a robotic surgical system, to be performed during an operating phase of the surgical instrument, wherein the surgical instrument (20) comprises an articulated end effector (40) and at least one actuation tendon (31 , 32, 33, 34, 35, 36), configured to actuate the articulated end effector (40), and wherein the robotic surgical system comprises, in addition to said surgical instrument (20), control means (9) and at least one motorized actuator (11 , 12, 13, 14, 15, 16), operatively connectable to a respective one of said at least one actuation tendon (31 , 32, 33, 34, 35, 36) to impart an action controlled by the control means (9) to the respective actuation tendon, so as to determine a univocal correlation between at least one movement of one of the one or more motorized actuators (1 1 , 12, 13, 14, 15, 16) and a respective at least one movement of the articulated end effector (40), wherein the method comprises, during said operating phase, when the at least one motorized actuator (1 1 , 12, 13, 14, 15, 16) is in contact with the respective at least one actuation tendon (31 , 32, 33, 34, 35, 36), the steps of:- estimating a desired target force (F(AX)) associated with an expected elastic elongation of the at least one actuation tendon (31 , 32, 33, 34, 35, 36) at and / or as a function of a respective known stroke and / or known position (Ax) imparted by the control means (9) to the at least one motorized actuator (1 1 , 12, 13, 14, 15, 16) with respect to a reference zero position;- detecting an actual force (F) exerted by at least one of said one or more motorized actuators (11 , 12, 13, 14, 15, 16) on a respective one of said at least one actuation tendons (31 , 32, 33, 34, 35, 36);- estimating and / or calculating, based on the difference between said detected actual force (F) and said desired target force (F(AX)), a length variation (Ai) of said at least one actuation tendon (31 , 32, 33, 34, 35, 36), due to plastic or elastoplastic elongation of the actuation tendon;- using said estimated and / or calculated length variation (Ai) as a compensation input for a control of the at least one motorized actuator (11 , 12, 13, 14, 15, 16).

2. A method according to claim 1 , wherein said step of detecting an actual force (F) comprises detecting an instantaneous actual force (F(t)) exerted by the at least onemotorized actuator (1 1 , 12, 13, 14, 15, 16) at an instant corresponding to the instant in which said known stroke and / or known position (Ax) of the at least one motorized actuator (11 , 12, 13, 14, 15, 16) occurs and for which said desired target force is estimated.

3. A method according to claim 2, wherein said step of estimating and / or calculating a length variation (Ai) comprises calculating the length variation (Ai), due to plastic or elastoplastic elongation of the actuation tendon, by means of the following formula:F(A) - F(t) (0 = « - r - pl where kplis an elastoplastic constant representative of a simplified model representative of the elongation, and a is a parameter associated with the elastoplastic compensation function.

4. A method according to claim 1 , wherein said step of detecting an actual force (F) comprises detecting an instantaneous actual force (F(t-1 )) exerted by the at least one motorized actuator (11 , 12, 13, 14, 15, 16) at an instant preceding, by a known time interval, the instant in which said known stroke and / or known position (Ax) of the at least one actuation tendon (31 , 32, 33, 34, 35, 36) occurs and for which said desired target force is estimated.

5. A method according to any one of the preceding claims, wherein said control of the at least one motorized actuator comprises a position control of the at least one motorized actuator (1 1 , 12, 13, 14, 15, 16) comprising:- imparting a movement on said at least one motorized actuator (11 , 12, 13, 14, 15, 16) taking into account the estimation of length variation (Ai) of the at least one actuation tendon, due to plastic or elastoplastic elongation of the actuation tendon, so as to reduce or cancel the error introduced by said length variation (Ai) between a force F(t) exerted on the articulated end effector and a desired nominal force F(Ax) on the articulated end effector.

6. A method according to claim 5, wherein said position control comprises:- defining a compensated kinematic-zero position (Po-mod) by adding the estimated and / or calculated value of length variation (Ai) to an initial reference kinematic- zero position (Po) according to the formula:Po-mod ~ PQ + ^17. A method according to claims 4-6, wherein the steps of the method are carried out iteratively, in a discrete sequence of evaluation steps, wherein in particular the length variation (A(t)) due to plastic or elastoplastic elongation of the actuation tendon at an instant t is calculated based on the actual force (F(t-1 )) detected at the previous instant.

8. A method according to claim 7, wherein the position of the at least one motorized actuator at an instant t is calculated as a function of the modified kinematic-zero position (Po-mod), or as a function of the initial reference kinematic-zero position (Po), the length variation (A(t)) due to plastic or elastoplastic elongation of the actuation tendon and the instantaneous position (Ax(t)) of the motorized actuator, in accordance with the following equations:

9. A method according to any one of the preceding claims, wherein the robotic system is a master-slave system in which the surgical instrument is a slave device controlled, according to a control mode, by a master device of the robotic system, wherein the method, in the absence of external forces, allows minimizing in a finite time the error between the pose commanded by the master device and the pose reached by the articulated end effector (40) of the slave device.

10. A method according to any one of the preceding claims, wherein the surgical instrument (20) comprises a plurality of actuation tendons (31 , 32, 33, 34, 35, 36), and the robotic surgical system comprises a respective plurality of motorized actuators (1 1 , 12, 13, 14, 15, 16), wherein said step of estimating a desired target force (F(AX)) is carried out with reference to a plurality or with reference to all of the actuation tendons (31 , 32, 33, 34, 35, 36), wherein said step of detecting an actual force (F) is carried out on a plurality or on all of the motorized actuators (1 1 , 12, 13, 14, 15, 16), wherein said step of estimating and / or calculating a length variation (Ai) due toplastic or elastoplastic elongation of the actuation tendon is carried out with reference to a plurality or with reference to all of the motorized actuators (1 1 , 12, 13, 14, 15, 16), wherein said step of using the estimated and / or calculated length variation (A) as a compensation input for a control is carried out with reference to a plurality or with reference to all of the motorized actuators (1 1 , 12, 13, 14, 15, 16).

11. A method according to claim 9 or claim 10, wherein the master device is a handheld, unconstrained master device adapted to be moved by an operator and manipulated by the operator according to a degree of freedom associated with the grip opening / closing and / or cut of the surgical slave instrument, wherein each of said one or more actuation tendons (31 , 32, 33, 34, 35, 36) is operatively connected to both a respective motorized actuator of the robotic surgical system and to said articulated end effector (40), to actuate a respective degree of freedom among the one or more degrees of freedom of the articulated end effector (40), wherein said actuation tendons (31 , 32, 33, 34, 35, 36) comprise one or more pairs of antagonistic tendons, for example two pairs of antagonistic tendons configured to control, respectively, degrees of freedom of a grip opening and closing and / or cut to be performed by two tips or tweezers or ends (43, 44) of the articulated end effector (40) of the surgical slave instrument, wherein said step of using the estimated and / or calculated length variation (A) as a compensation input for a control is carried out with reference to the tendons of said pairs of antagonistic tendons, so as to control said degrees of freedom of grip opening and closing and / or cut.

12. A method according to claim 1 1 , wherein the method is performed, during said operating phase of the surgical instrument, only during a sub-phase of gripping of two tips or tweezers or ends (43, 44).

13. A method according to claim 12, wherein, during the operating phase of the surgical instrument, the orientation and opening / closing of said articulated end effector (40) of the surgical instrument is controlled in position, wherein the elastoplastic compensation is activated only during said gripping sub-phase, and wherein the elastoplastic compensation contribution is added to the position control.

14. A method according to claim 12 or claim 13, further comprising performing anelastic compensation, calculated in real time, of the elastic elongation undergone by the at least one actuation tendon, wherein either or both elastoplastic compensation and elastic compensation are carried out and applied, so that the position control determines as a whole a compensated position X(t) in which both the elastic compensation contribution (Axe) and the elastoplastic compensation contribution (Axep) are added to a nominal position (Xc).

15. A method according to any one of claims 12-14, wherein subsequent compensations are performed at a series of subsequent instants, during said operating phase of the surgical instrument, and wherein the subsequent compensations are added over time, during said operating phase, and are not recoverable.

16. A method according to claim 14 or claim 15, wherein both the elastoplastic compensation and the elastic compensation are carried out and applied simultaneously.

17. A method according to claim 14 or claim 15, wherein both the elastic compensation and the elastoplastic compensation are used in different configurations, in which one or the other is activated or deactivated, wherein a compensation contribution of a deactivated compensation is frozen, maintained and then updated during the subsequent activation of the respective compensation.

18. A method according to claim 17, wherein, when a closing force is recognized during the operating phase, the elastoplastic compensation control is activated and the elastic compensation control is instead deactivated on the actuators which cause the articulated end effector to close.

19. A method according to any one of claims 11 -18, comprising the further steps of:- actuating the motorized actuators associated with the tendons of said pairs of antagonistic tendons, according to respective nominal strokes (Axj) for which it is expected that the tips or ends of the articulated end effector (40) come into contact and lock the degree of freedom of grip and / or cut; and wherein:- said step of estimating the desired target force comprises estimating the desired target forces (F(Ax,j)) for each of the tendons of said pairs of antagonistic tendons, at said nominal strokes (Ax,j);- said step of detecting an actual force (F) comprises determining a target actual force (F), based on the actual forces exerted by said one or more operated motorized actuators;- said step of estimating and / or calculating at least one length variation (Ai) due to plastic or elastoplastic elongation of the actuation tendon comprises calculating the length variations (AIJ) of said tendons of the pairs of antagonistic tendons based on the respective expected elastic forces and the target actual force (F) determined;- said step of controlling the position of the at least one motorized actuator comprises controlling the motorized actuators associated with the tendons of said pairs of antagonistic tendons so that they reach said target actual force (F).

20. A method according to claim 19, wherein said step of determining a target actual force (F) comprises determining, as the target actual force (F), an arithmetic average of the forces detected at two of said antagonistic tendons.

21. A method according to claim 19, wherein said step of determining a target actual force (F) comprises determining, as the target actual force (F), the maximum force among the forces detected at two of said antagonistic tendons.

22. A method according to any one of claims 11 -21 , wherein the steps of the method are carried out iteratively, and wherein said step of determining a target actual force (F) comprises determining, as the target actual force (F), a time average of the actual forces detected at two of said antagonistic tendons at at least two previous instants.

23. A method according to any one of claims 11 -21 , wherein said step of determining a target actual force (F(t-1 )), at an instant t-1 , is carried out in accordance with a formula selected from the following formulae:where y is an index representing time instants, Fi and F2, F3and F4indicate actual forces detected at two pairs of said antagonistic tendons.

24. A method according to any one of claims 1 1 -23, further comprising defining a compensated kinematic-zero position (Po-mod) for the grip and / or cut control, based on the strokes and / or positions taken by the motorized actuators at the target actual force (F).

25. A method according to any one of claims 11 -23, comprising the further step of estimating the elastic coefficient of one or more tendons as a function of time (k(t)).

26. A method according to any one of claims 11 -23, wherein the steps of the method apply only if the target actual force (F) takes a value within a predefined range of values considered acceptable.

27. A method according to any one of the preceding claims, wherein said step of detecting the force exerted by a motorized actuator (11 , 12, 13, 14, 15, 16) is performed by a respective force or torque sensor operatively connected to the respective motorized actuator.

28. A method according to any one of the preceding claims, wherein said surgical instrument (20) further comprises at least one transmission element (21 , 22, 23, 24, 25, 26) operatively connected to a respective at least one actuation tendon (31 , 32, 33, 34, 35, 36) and operatively connectable to a respective motorized actuator (11 , 12, 13, 14, 15, 16).

29. A method according to any one of the preceding claims, wherein the length variation compensation parameters are determined in a controlled and variable manner depending on the pose of the articulated end effector (40) in order to take into account the different frictions related to the different poses.

30. A method according to any one of the preceding claims, wherein said actuation tendons are polymer tendons preferably formed from intertwined polymer fibers.

31. A robotic surgical system comprising:- a surgical instrument (20) comprising an articulated end effector (40);- control means (9);- at least one actuation tendon (31 , 32, 33, 34, 35, 36), configured to actuate the articulated end effector (40);- at least one motorized actuator (11 , 12, 13, 14, 15, 16), operatively connectable to a respective one of said at least one actuation tendon (31 , 32, 33, 34, 35, 36) to impart to the respective actuation tendon an action controlled by the control means (9), so as to determine a univocal correlation between at least one movement of one of the one or more motorized actuators (1 1 , 12, 13, 14, 15, 16) and a respective at least one movement of the articulated end effector (40); wherein the control means (9) of the robotic system are configured to carry out, during an operating phase of the robotic system, when the at least one motorized actuator (11 , 12, 13, 14, 15, 16) is in contact with the respective at least one actuation tendon (31 ,32. 33, 34, 35, 36), the following actions:- estimating a desired target force (F(AX)) associated with an expected elastic elongation of the at least one actuation tendon (31 , 32, 33, 34, 35, 36) at and / or as a function of a respective known stroke and / or known position (Ax) imparted by the control means (9) to the at least one motorized actuator (1 1 , 12, 13, 14, 15, 16) with respect to a reference zero position;- detecting an actual force (F) exerted by at least one of said one or more motorized actuators (1 1 , 12, 13, 14, 15, 16);- estimating and / or calculating, based on the difference between said detected actual force (F) and said desired target force (F(AX)), a length variation (Ai) of said at least one actuation tendon (31 , 32, 33, 34, 35, 36), due to plastic or elastoplastic elongation of the actuation tendon; wherein the control means (9) of the robotic system are configured to carry out the following further action:- using said estimated and / or calculated length variation (Ai) as a compensation input for a control of the at least one motorized actuator (11 , 12, 13, 14, 15, 16).

32. A robotic system according to claim 31 , wherein said action of detecting an actual force (F) comprises detecting an instantaneous actual force (F(t)) exerted by the at least one motorized actuator (1 1 , 12, 13, 14, 15, 16) at an instant corresponding to the instant in which said known stroke and / or known position (Ax) of the at least one motorized actuator (11 , 12, 13, 14, 15, 16) occurs and for which said desired target force is estimated.

33. A robotic system according to claim 32, wherein said action of estimating and / or calculating a length variation (Ai) comprises calculating the length variation (Ai), due to plastic or elastoplastic elongation of the actuation tendon, by means of the following formula:F(4J - F(t) (t) = a - T - pl where kptis an elastoplastic constant representative of a simplified model representative of the elongation, and a is a parameter associated with the elastoplastic compensation function.

34. A robotic system according to claim 31 , wherein said action of detecting an actual force (F) comprises detecting an instantaneous actual force ( F(t- 1 )) exerted by the at least one motorized actuator (1 1 , 12, 13, 14, 15, 16) at an instant preceding, by a known time interval, the instant in which said known stroke and / or known position (Ax) of the at least one actuation tendon (31 , 32, 33, 34, 35, 36) occurs and for which said desired target force is estimated.

35. A robotic system according to any one of claims 31 -34, wherein said control of the at least one motorized actuator comprises a position control of the at least one motorized actuator (1 1 , 12, 13, 14, 15, 16)) comprising:- imparting a movement on said at least one motorized actuator (11 , 12, 13, 14, 15, 16) taking into account the estimation of length variation (Ai) of the at least one actuation tendon, due to plastic or elastoplastic elongation of the actuation tendon, so as to reduce or cancel the error introduced by said length variation (Ai) between a force F(t) exerted on the articulated end effector and a desired nominal force F(Ax) on the articulated end effector.

36. A robotic system according to claim 35, wherein said position control comprises defining a compensated kinematic-zero position (Po-mod) by adding the estimated and / or calculated value of length variation (A) to an initial reference kinematic-zero position (Po) according to the formula:

37. A robotic system according to claims 34-36, wherein the steps of the method are carried out iteratively, in a discrete sequence of evaluation steps, wherein in particular the length variation (Ai(t)) due to plastic or elastoplastic elongation of the actuation tendon at an instant t is calculated based on the actual force (F(t-1 )) detected at the previous instant.

38. A robotic system according to claim 37, wherein the position of the at least one motorized actuator at an instant t is calculated as a function of the modified kinematic- zero position (Po-mod), or as a function of the initial reference kinematic-zero position (Po), the length variation (Ai(t)) due to plastic or elastoplastic elongation of the actuation tendon and the instantaneous position (Ax(t)) of the motorized actuator, in accordance with the following equations:

39. A robotic system according to any one of claims 31 -38, wherein the robotic system is a master-slave system in which the surgical instrument is a slave device controlled, according to a control mode, by a master device of the robotic system, wherein the control means (9) of the robotic system are configured to control the system so that, in the absence of external forces, the error between the pose commanded by the master device and the pose reached by the articulated end effector (40) of the slave device is minimized in a finite time.

40. A robotic system according to any one of claims 31 -39, wherein the surgical instrument (20) comprises a plurality of actuation tendons (31 , 32, 33, 34, 35, 36), and the robotic surgical system comprises a respective plurality of motorized actuators (1 1 , 12, 13, 14, 15, 16), wherein said action of estimating a desired target force (F(AX)) is carried out withreference to a plurality or with reference to all of the actuation tendons (31 , 32, 33, 34, 35, 36), wherein said action of detecting an actual force (F) is carried out on a plurality or on all of the motorized actuators (1 1 , 12, 13, 14, 15, 16), wherein said action of estimating and / or calculating a length variation (Ai) is carried out with reference to a plurality or with reference to all of the motorized actuators (11 , 12, 13, 14, 15, 16), wherein said action of using the length variation (Ai) as a compensation input is carried out with reference to a plurality or with reference to all of the motorized actuators (11 , 12, 13, 14, 15, 16).

41. A robotic system according to claim 39 or claim 40, wherein the master device is a hand-held, unconstrained master device adapted to be moved by an operator and manipulated by the operator according to a degree of freedom associated with the grip opening / closing and / or cut of the surgical slave instrument, wherein each of said one or more actuation tendons (31 , 32, 33, 34, 35, 36) is operatively connected to both a respective motorized actuator of the robotic surgical system and to said articulated end effector (40), to actuate a respective degree of freedom among the one or more degrees of freedom of the articulated end effector (40), wherein said actuation tendons (31 , 32, 33, 34, 35, 36) comprise one or more pairs of tendons, for example two pairs of tendons configured to control, respectively, degrees of freedom of grip opening and closing and / or cut to be performed by two tips or ends or tweezers of the articulated end effector (40) of the surgical slave instrument, wherein said action of using the length variation (Ai) as a compensation input is carried out with reference to the tendons of said pairs of antagonistic tendons, so as to control said degrees of freedom of grip opening and closing and / or cut.

42. A robotic system according to claim 41 , wherein the control means (9) of the robotic system are configured to carry out said actions according to claims 31 -41 , during said operating phase of the surgical instrument, only during a sub-phase of gripping of two tips or ends or tweezers (43, 44), wherein, during the operating phase of the surgical instrument, the orientation and opening / closing of said articulated end effector (40) of the surgical instrument is controlled in position, wherein the elastoplastic compensation is activated only during said gripping sub-phase, and wherein the elastoplastic compensation contribution is added to the position control.

43. A robotic system according to claim 42, wherein the control means (9) of the robotic system are further configured to perform an elastic compensation, calculated in real time, of the elastic elongation undergone by the at least one actuation tendon, wherein either or both elastoplastic compensation and elastic compensation are carried out and applied, so that the position control determines as a whole a compensated position X(t) in which both the elastic compensation contribution (Axe) and the elastoplastic compensation contribution (Axep) are added to a nominal position (Xc).

44. A robotic system according to any one of claims 42-43, wherein subsequent compensations are performed at a series of subsequent instants, during said operating phase of the surgical instrument, and wherein the subsequent compensations are added over time, during said operating phase, and are not recoverable.

45. A robotic system according to claim 43 or claim 44, wherein both the elastoplastic compensation and the elastic compensation are carried out and applied simultaneously, and / or wherein both the elastic compensation and the elastoplastic compensation are used in different configurations, in which one or the other is activated or deactivated, wherein a compensation contribution of a deactivated compensation is frozen, maintained and then updated during the subsequent activation of the respective compensation.

46. A robotic system according to claim 45, wherein, when a closing force is recognized during the operating phase, the elastoplastic compensation control is activated and the elastic compensation control is instead deactivated on the actuators which cause the articulated end effector to close.

47. A robotic system according to any one of claims 41 -46, wherein the control means (9) are further configured to operate the motorized actuators associated with the tendons of said pairs of antagonistic tendons, according to respective nominal strokes (Axj) for which it is expected that the tips or ends of the articulated end effector (40) come into contact and lock the degree of freedom of grip and / or cut; and wherein:- said action of estimating the desired target force comprises estimating the desired target forces (F(Ax,j)) for each of the tendons of said pairs of antagonistic tendons,at said nominal strokes (Axj);- said action of detecting an actual force (F) comprises determining a target actual force (F), based on the actual forces exerted by said one or more motorized actuators operated;- said action of estimating and / or calculating at least one length variation (Ai) comprises calculating the length variations (AIJ) due to elastoplastic elongation of said tendons of the pairs of antagonistic tendons based on the respective expected elastic forces and the target actual force (F) determined;- the action of position control of the at least one motorized actuator comprises controlling the motorized actuators associated with the tendons of said pairs of tendons so that they reach said target actual force (F).

48. A robotic system according to claim 47, wherein said action of determining a target actual force (F) comprises determining, as the target actual force (F), an arithmetic average of the forces detected at two of said antagonistic tendons, or wherein said action of determining a target actual force (F) comprises determining, as the target actual force (F), the maximum force among the forces detected at two of said antagonistic tendons.

49. A robotic system according to any one of claims 41 -48, wherein the control means (9) of the robotic system are configured to carry out said actions iteratively, and wherein said action of determining a target actual force (F) comprises determining, as the target actual force (F), a time average of the actual forces detected at two of said antagonistic tendons at at least two previous instants.

50. A robotic system according to any one of claims 41 -48, wherein said action of determining a target actual force (F(t-1)), at an instant t-1 , is carried out in accordance with a formula selected from the following formulae:where y is an index representing time instants, Fi and F2, F3and F4indicate actual forces detected at two pairs of said antagonistic tendons.

51. A robotic system according to any one of claims 41 -50, wherein the control means (9) of the robotic system are further configured for defining a compensated kinematic-zero position (Po-mod) for the grip and / or cut control, based on the strokes and / or positions taken by the motorized actuators at the target actual force (F).

52. A robotic system according to any one of claims 41 -50, wherein the control means (9) of the robotic system are configured to carry out the further action of estimating the elastic coefficient of one or more tendons as a function of time (k(t)).

53. A robotic system according to any one of claims 41 -50, wherein the control means (9) of the robotic system are configured to carry out said actions only if the target actual force (F) takes a value within a predefined range of values considered acceptable.

54. A robotic system according to any one of claims 41 -53, wherein said action of detecting the force exerted by a motorized actuator (11 , 12, 13, 14, 15, 16) is performed by a respective force or torque sensor operatively connected to the respective motorized actuator.

55. A robotic system according to any one of claims 41 -54, wherein said surgical instrument (20) further comprises at least one transmission element (21 , 22, 23, 24, 25, 26) operatively connected to a respective at least one actuation tendon (31 , 32, 33, 34, 35, 36) and operatively connectable to a respective motorized actuator (11 , 12, 13, 14, 15, 16).

56. A robotic system according to any one of claims 41 -55, wherein the length variation compensation parameters are determined in a controlled and variable mannerdepending on the pose of the articulated end effector (40) in order to take into account the different frictions related to the different poses.

57. A robotic system according to any one of claims 41 -55, wherein said actuation tendons are polymer tendons preferably formed from intertwined polymer fibers.

Images