Robot positioning of a device

Abstract

The present invention relates to robotic device positioning. By extending a robotic arm into a surgical region, a system is provided that automatically aligns an instrument using only instrument tracking feedback to follow a plan (e.g., a surgical plan). No tracking markers on the robot are required.

Description

TECHNICAL FIELD

[0001] The present invention relates to instrument positioning. In particular, the present invention relates to a system for instrument positioning, a method of controlling a system for instrument positioning, a computer program element and a computer readable medium. BACKGROUND

[0002] Robotic device positioning has become increasingly common in applications including, for example, surgical instrument guidance, manufacturing, and machine operation, such as airplanes, construction machines, for drilling, nailing, etc. Robotic solutions often rely on external tracking systems to position the robot and utilize optical markers rigidly fixed to the object of interest (e.g., a patient or an object to be drilled) to establish a robot-to-object reference frame (e.g., a patient reference frame). An example of a robotic solution can be found in US 2015 / 164607 A. However, the reference frame is susceptible to accidental movement and obstruction, thereby reducing the accuracy of object tracking and increasing the risk of registration errors.

[0003] US 2018 / 0000546 discloses a medical robotic system comprising a robot coupled with an actuator element, wherein the robot is configured for controlled movement and positioning.

[0004] US 2018 / 0185100 discloses systems and methods for surgical navigation that provide mixed reality visualization. The mixed reality visualization depicts virtual images in conjunction with real objects to provide improved visualization to a user.

[0005] WO 2019 / 204699 discloses methods and systems for controlling a robotic arm that include tracking motion of a handheld device using a motion tracking system and controlling the robotic arm to adjust at least one of a position and an orientation of an end effector of the robotic arm based on the tracked motion of the handheld device. SUMMARY

[0006] The invention is defined by the claims.

[0007] There can be a need for improving robotic device positioning.

[0008] The object of the present invention is solved by the subject matter of the independent claims, wherein further embodiments are incorporated in the dependent claims. It is pointed out that the following description aspects of the present invention also apply to the system, the method, the computer program element and the computer readable medium.

[0009] According to a first aspect of the present application, a system for instrument positioning is provided. The system comprises a robotic system having a robotic arm with four or more degrees of freedom (DOF) and a system controller having an interface unit. The robotic arm comprises an instrument interface capable of connecting with an instrument. The interface unit of the system controller is configured to provide sensor data comprising pose information of the instrument and a target position with respect to an object. The pose information of the instrument comprises a position and an orientation of the instrument. The interface unit of the system controller is further configured to provide image data at the target position. A target trajectory is planned in the image data for positioning the instrument to the target position. The system controller is configured to transfer the pose information of the instrument and the planned target trajectory into an object coordinate system. The system controller is further configured to compute a positional error between the tracked pose information of the instrument and the planned target trajectory. The system controller is further configured to transfer the positional error into a robot coordinate system of the robotic system to control the robotic arm to align the instrument with the planned target trajectory. The positional error comprises at least one of a translational error and a rotational error.

[0010] In other words, a system is provided comprising a robotic guiding arm for instrument positioning with four or more degrees of freedom, which can be used in a hybrid operating room environment with integrated surgical navigation. The system uses the pose information, i.e. the position and orientation, of the instrument to provide feedback to the robotic system in maintaining the trajectory of the instrument with respect to a target trajectory planned by a user, e.g. a surgeon. The alignment with the planned trajectory is achieved using instrument tracking as direct feedback, without the need for any manual registration. The proposed system can be based on 4-DOF or 5-DOF device position feedback without the need for additional tracking subjects on the robot.

[0011] In some examples, the proposed system can be used as a surgical instrument guiding system.

[0012] In some examples, the proposed system can be applied in manufacturing industry for alignment of parts or for machine operations like airplanes, construction machines, etc. where drilling, nailing or concentric alignment is common.

[0013] The instrument has an elongated shape. The system controller is configured to control the robotic arm during a first movement of the robotic arm at each new target selection time to move the instrument in a predetermined movement to create a coarse six degrees of freedom registration between the object coordinate system and the robot coordinate system. The predetermined movement comprises a predetermined rotational movement.

[0014] Optionally, the predetermined movement can also comprise a predetermined translational movement.

[0015] In other words, in cases where only 4-DOF or 5-DOF instrument tracking is available: either on the instrument axis inserted into the instrument interface, like a needle guide, or on the instrument interface axis attached to the robot arm, an approximate registration method is used to facilitate alignment, as the object of interest, like the patient, and the robot base are generally static relative to each other for the short duration of the treatment. The position of the instrument interface is also known relative to the robot arm. A coarse 6-DOF registration between the object coordinate frame and the robot coordinate frame is generated based on two pose information of the instrument and two pose information of the robot arm before and after movement. This will be explained below, especially with respect to the exemplary embodiments shown in Figure 3A and Figure 3B

[0016] The first movement of the robot arm automatically initiates the coarse registration process. In general, assuming that the motion of the robot system and the instrument tracking feedback can be precisely synchronized, the predetermined rotational movement for coarse registration can be arbitrary as long as it includes a large rotation, as larger angles result in more accurate registration. Arbitrary translations can also be added. This feature can be used in real-time to update or verify that the registration has not changed because of movement of the patient relative to the robot system. Thus, the system controller can automatically perform the coarse registration, thereby avoiding any input from the user or increasing the time of the operation.

[0017] According to an embodiment of the present invention, the sensor data includes real-time pose information of the instrument with respect to a target position. The system controller is configured to calculate a real-time position error between the tracked pose information of the instrument and a planned target trajectory, and to transfer the real-time position error into a robot coordinate frame of the robot system to iteratively control the robot arm to align the instrument with the planned target trajectory.

[0018] In other words, real-time instrument position feedback can be used to iteratively move the instrument mounted in the instrument interface in order to align with the target trajectory for achieving accurate alignment.

[0019] In an example, during alignment, the system controller can be configured to keep the height of the instrument interface relative to the patient, table, imaging axis, robot base, initial tool position, or other physical or virtual reference constant. This height constraint can provide safer and more intuitive robot behavior. Once aligned, the surgeon can lower the robot arm along the guide axis and, if needed, command the robot to align the target.

[0020] According to an embodiment of the present invention, the system controller is further configured to apply a coarse 6-DOF registration to control the robot arm to align the instrument with a planned target trajectory when the sensor data does not include pose information of the instrument.

[0021] ​The resulting registration process can be sufficient to position the instrument near the intended trajectory in an open loop manner, e.g., when outside the tracking volume. Thus, as a further option, if the sensor data does not include pose information of the instrument, e.g., when outside the tracking volume, the system controller can be further configured to control the robotic arm to align the instrument with the planned target trajectory based on the coarse six degree of freedom registration. Once the device is visible in the tracking system, the system controller can use the pose information of the instrument to iteratively servo to a final, higher accuracy alignment.

[0022] According to an embodiment of the present application, the system further comprises a tracking system configured to obtain sensor data comprising pose information of the interventional instrument and target position of the object of interest. The tracking system comprises at least one of: an optical tracking system, an electromagnetic tracking system, and an acoustic tracking system.

[0023] The optical tracking system can use one or more cameras arranged inside the imaging chamber to track the pose information of the instrument. The one or more cameras are capable of detecting infrared light, visible light, and / or near-infrared light. The markers tracked by the cameras can be attached to the instrument.

[0024] Electromagnetic (EM) tracking systems are based on the principle of mutual induction, in which a magnetic field generator generates a known EM field to locate a small EM sensor placed within the tracking range. Due to its line-of-sight free, small sensor size, and ease of use, EM trackers have gained wide application. Due to its sub-millimeter size, the sensor can be easily placed inside the tip of the instrument.

[0025] Acoustic tracking devices employ high frequency (e.g., 20 kHz or higher) ultrasound waves in the form of time-of-flight transducers / sensors or phase reference systems.

[0026] As would be readily known by one skilled in the art, the tracking system can track markers on both the instrument and the object. Thus, the tracking system can establish a registration between the object coordinate system and the tracking coordinate system.

[0027] According to an embodiment of the present application, the tracking system is located on or inside the detector of the image acquisition system.

[0028] In an example, the tracking system, such as a camera, can be attached to the detector of the image acquisition system. For example, the camera can be temporarily attached to a predetermined location on or inside the detector of the image acquisition system during image acquisition, and detached from the detector after image acquisition.

[0029] In an example, the tracking system can be an integral part of the detector.

[0030] Providing the tracking system on or inside the detector of the imaging acquisition system can allow to inherently spatially register the tracking coordinate system to the image coordinate system. This can alleviate the need to independently track and register the tracking coordinate system of the external tracking system to the image coordinate system, for example.

[0031] According to an embodiment of the present application, the system further comprises an image acquisition system configured to acquire image data of the object of interest at a target position. The image acquisition system comprises at least one of: an X-ray imaging device, an ultrasound imaging device, and a magnetic resonance imaging device.

[0032] In other words, the instrument positioning system can be implemented in different imaging modalities.

[0033] According to an embodiment of the present application, the robotic arm comprises a mechanical "remote center of motion" (RCM) mechanism having at least one rotational control degree of freedom. The instrument interface is mounted on the RCM mechanism.

[0034] As used herein, the term "RCM" refers to a remote fixed point at which no mechanism or part thereof can rotate about a physical revolute joint.

[0035] The RCM can allow for robotic translation using a translational module. Inclusion of the RCM can minimize overall joint motion, resulting in an ergonomic robotic configuration and predictable motion to improve the user interface, particularly when performing Cartesian rotations. It can allow the instrument to be translated to an entry point by primarily actuating the translational module, and then be rotationally aligned using one or more distal joints (i.e. the RCM). The shape of the final link can be optimized such that the instrument interface is closer to the RCM, enabling the positioning of the instrument interface close to the object, and facilitating the use of short instruments.

[0036] According to an embodiment of the present application, the system controller is configured to control the robotic arm to align the instrument with a planned target trajectory while the instrument is translated within a safety plane for preventing a collision.

[0037] In an example, the safety plane can be a plane above and parallel to the table. For example, the safety plane can be defined by the XY plane of the robot and the position of the current robot guide. Alternatively, the position of the safety plane can be defined as: relative to the tip of the instrument, then transformed into the robot coordinate system, relative to the closest point to the target trajectory on the instrument under some reasonable constraints such that the point does not go too far from the robot guide, or relative to the entry point.

[0038] More generally, the safety plane can be any plane defined for preventing collisions of the robot, such as collisions of the robot with the object to be inspected, the robot itself and related equipment. In other words, the safety plane makes the robot move in a predictable way to prevent collisions of the robot.

[0039] According to an embodiment of the present application, the sensor data comprises pose information of the robot arm.

[0040] In other words, a hybrid feedback control can be employed, which includes both robot end effector tracking and device tracking feedback. This will allow for a coarse alignment with less accurate robot tracking (e.g. without the instrument in the guide), and once the instrument is visible in the camera and in the vicinity of the target, the system controller can use the pose information of the instrument to servo to the final, higher accuracy alignment.

[0041] According to an embodiment of the present application, the instrument comprises an interventional instrument.

[0042] According to an embodiment of the present application, the interventional instrument comprises at least one of: an injection needle, an interventional catheter and an interventional laser device.

[0043] According to a second aspect of the present application, there is provided a method for controlling a system as described above and below, comprising the steps of:

[0044] a) receiving sensor data comprising pose information of an instrument with respect to a target position relative to an object by an interface unit of a system controller of the system, wherein the pose information of the instrument comprises a position and an orientation of an interventional instrument.

[0045] b) receiving image data at the target position by the interface unit of the system controller, wherein a target trajectory is planned in the image data for positioning the instrument to the target position; and

[0046] c) transforming the pose information of the instrument and the planned target trajectory into an object coordinate system by the system controller of the system, calculating a positional error between the tracked pose information of the instrument and the planned target trajectory; and transforming the positional error into a robot coordinate system of a robot system for controlling the robot arm to align the instrument with the planned target trajectory, wherein the positional error comprises at least one of a translational error and a rotational error.

[0047] According to a third aspect of the present application, a computer program element for controlling a device, which, when being executed by a processing unit, is adapted to perform the method as described above and below.

[0048] According to a fourth aspect of the present application, a computer readable medium having stored the program element.

[0049] As used herein, the term "elongate" is used in its ordinary meaning, i.e., a length dimension greater than a width or diameter of the instrument. As an example, an elongate instrument can be a needle-like instrument.

[0050] As used herein, the term "instrument" can refer to a medical device, such as a surgical tool, a medical tool, a biomedical tool, and a diagnostic instrument. In some examples, an instrument can refer to an instrument for machine operation, such as an instrument for drilling, nailing, and concentric alignment.

[0051] As used herein, the term "object of interest" can refer to a patient, a human subject, or an animal subject. In some examples, an object of interest can refer to an object in manufacturing and machine operation, e.g., an object to be drilled, nailed, etc.

[0052] As used herein, the term "system controller" can refer to, be a part of, or include an application specific integrated circuit (ASIC), an electronic circuit, a processor (shared, dedicated, or group) and / or memory (shared, dedicated, or group) that execute one or more software or firmware programs, a combinational logic circuit, and / or other suitable components that provide the described functionality. The system controller can include a consumer electronic device, a smartphone, a tablet personal computer, a wearable computing device, a personal digital assistant (PDA), a laptop computer, and / or any other similar physical computing device capable of providing the described functionality.

[0053] As used herein, the term "instrument interface" can refer to a mechanical component for receiving an instrument for positioning by a robotic device. For example, an instrument interface can be a needle guide. A surgical device, such as an injection needle, can be inserted and secured on the needle guide.

[0054] As used herein, the term "unit" can refer to, be a part of, or include an ASIC, an electronic circuit, a processor (shared, dedicated, or group) and / or memory (shared, dedicated, or group) that execute one or more software or firmware programs, a combinational logic circuit, and / or other suitable components that provide the described functionality.

[0055] Throughout the description, reference is made to different coordinate systems. These coordinate systems can be Cartesian coordinate systems, polar coordinate systems, spherical coordinate systems, cylindrical coordinate systems, quadrilateral coordinate systems, hexagonal coordinate systems, or any other three-dimensional (3D) coordinate systems discussed above. Definitions are now made to the coordinate systems mentioned below.

[0056] The term "object coordinate system" refers to a coordinate system in which position is defined relative to an origin that is a preselected point associated with the object and has a relative position that remains constant thereto. For example, if the object is a patient, the term "object coordinate system" can also be referred to as a patient coordinate system. For example, the object coordinate system can be a Cartesian coordinate system with orthogonal axes xyz, can be defined relative to a preselected point thereof, and can use natural language relative positioning terms, such as left, right, up, down, forward, and backward, to determine position relative to the preselected point. Alternatively, polar coordinates can be used to define position in virtual space relative to the preselected point associated with the object. Alternatively, any other 3D coordinate system can be used. Similarly, the term "robot coordinate system" refers to a coordinate system in which position is defined relative to an origin that is a preselected point associated with the robot and has a relative position that remains constant thereto. For example, the robot coordinate system can be a Cartesian coordinate system with orthogonal axes xyz, can be defined relative to a preselected point thereof, and can use natural language relative positioning terms, such as left, right, up, down, forward, and backward, to determine position relative to the preselected point. Alternatively, polar coordinates can be used to define position in virtual space relative to the preselected point associated with the robot. Additionally, any other 3D coordinate system can be used.

[0057] Similarly, the term "tracking coordinate system" refers to a coordinate system in which position is defined relative to an origin that is a preselected point associated with the tracking system and has a relative position that remains constant thereto. For example, the tracking coordinate system can be a Cartesian coordinate system with orthogonal axes xyz, can be defined relative to a preselected point thereof, and can use natural language relative positioning terms, such as left, right, up, down, forward, and backward, to determine position relative to the preselected point. Alternatively, polar coordinates can be used to define position in virtual space relative to the preselected point associated with the tracking system. Additionally, any other 3D coordinate system can be used.

[0058] These and other aspects of the application will become apparent from the embodiments described below. BRIEF DESCRIPTION OF DRAWINGS

[0059] Exemplary embodiments of the application will be described below with reference to the following drawings.

[0060] Figure 1 A perspective view of an exemplary hybrid operating room (OR) for performing minimally invasive robotic surgical procedures is shown.

[0061] Figure 2 A top view of an exemplary system for instrument positioning in the exemplary hybrid OR is shown in accordance with some embodiments of the present disclosure.

[0062] Figure 3A An example of a coordinate system in a system for instrument positioning is shown.

[0063] Figure 3B An example of an error metric for alignment is shown.

[0064] Figure 4 An example of a robotic arm is shown schematically.

[0065] Figure 5 A flowchart of a method of a control system according to some embodiments of the present disclosure is shown.

[0066] Figure 6 A flowchart of a method of a control system according to some other embodiments of the present disclosure is shown. DETAILED DESCRIPTION

[0067] In the following, embodiments are presented in the context of robotically guided pedicle screw placement surgery, but can be generalized to any robotic device positioning application that requires accurate (e.g., less than 2 mm) position guidance. Examples of robotic device positioning applications can include, but are not limited to, neurosurgical oncology, biopsy, ablation, and many other minimally invasive surgeries and percutaneous applications. Further examples of robotic device positioning applications can include applications in manufacturing and machine operation, such as airplanes, construction machinery, etc.

[0068] Spinal fusion surgery is a common surgical method to address spinal degenerative disease and spinal deformity, with approximately 450,000 procedures performed annually in the United States. In posterior spinal fusion surgery, screws are placed in the pedicles of the vertebral bodies and connected by rods to fuse the vertebral bodies. For mechanical stability, large diameter screws are desirable. However, maximizing the screw diameter relative to the size of the pedicle can increase the risk of pedicle breakage and damage to critical structures such as spinal nerves, spinal cord, or blood vessels. Therefore, accurate pedicle screw placement is of utmost importance. The current trend towards minimally invasive surgery (MIS) also emphasizes the need for accuracy. MIS is an attractive technique that is associated with shorter hospital stays, reduced postoperative pain, reduced blood loss, reduced risk of infection, and reduced costs. However, pedicle screw placement in MIS relies heavily on tools for guidance, as the small incision, similar to a perforation, provides little or no visual feedback to the surgeon. Guidance is typically provided by fluoroscopy, but this has the disadvantages of radiation exposure of the patient and staff, and providing only a 2D view of a 3D target task.

[0069] Surgical navigation systems provide a way to plan a surgical approach and translate the preoperative plan into an expected trajectory during surgery. In addition, such systems provide visual guidance to the surgeon (freehand) within the surgical field. However, surgical navigation requires the surgeon to manually keep the instrument aligned with the virtual plan displayed on a screen outside the surgical field while performing the surgical operation. Robotic assistance is naturally suited for this alignment and stabilization task, and there are many commercial and academic solutions. The use of robots results in higher accuracy of pedicle screw placement, reduced radiation exposure for the surgeon, and earlier discharge compared to freehand methods.

[0070] In the process of pedicle screw fixation, the main help provided by the robot is to precisely align the guide or instrument with the planned trajectory defined in the navigation software. Once the instrument (e.g., needle) is aligned with the target and held firmly in this alignment by the robot, the surgeon advances the needle or drill bit onto the bone and further into the interior of the vertebral body. After creating the hole, the surgeon places a screw into these pilot holes and secures adjacent screws with a rod to fuse multiple vertebral bodies into the intended configuration.

[0071] Robotic solutions typically rely on external tracking systems to localize the robot and utilize optical markers rigidly fixed to the patient’s spine or iliac crest to establish the robot’s (dynamic) frame of reference to the patient. These dynamic frames tend to be attached far from the target vertebrae and are susceptible to accidental movement and obstruction, thereby reducing the accuracy of patient tracking and increasing the risk of registration error. In addition to occupying a considerable amount of space in the typically crowded operating room, existing systems require a manual registration step using specialized hardware that needs to be installed on the robot or invasively on the patient.

[0072] Since the intended tool position is defined in the tracking coordinate frame, the robot needs to be tracked and / or registered in some way into the tracking coordinate frame in order to be able to convert the target position into its own coordinate frame (CF) for moving the instrument to the target trajectory. This is typically done with a large marker on the robot base, which requires a large tracking field of view and adds another conversion between the target and the instrument to be placed. There are also those who add large 6-DOF device tracking markers and compute the tracker’s position through the inverse transformation of standard kinematics, but this requires multiple calibrations and higher accuracy. Other solutions rigidly fix the robot to the patient or table and then perform a registration step. These methods require very good forward kinematics - very high quality parts, assembly, calibration, and overall rigidity of the robot and fixture.

[0073] Figure 1A perspective view of an exemplary hybrid OR 100 for performing minimally invasive robotic surgical procedures is shown, in which a robot can be used to achieve precise alignment of a guide or instrument with a planned trajectory defined in navigation software.

[0074] The exemplary hybrid OR 100 is a single room with a dedicated C-arm x-ray imaging system 102 capable of two-dimensional (2D) or three-dimensional (3D) imaging. The C-arm imaging system 102 has a support device 104 that can be translated about an object of interest 106 by an azimuth axis and an elevation axis. For example, the C-arm x-ray imaging system 102 can be supported on the ceiling of an x-ray facility. The support device holds a rotating anode x-ray source 108 and an x-ray detector 110.

[0075] The exemplary hybrid OR 100 also includes a patient support 112 to support the object of interest 106. The C-arm 102 is configured to be translated about the object of interest 106, not just in the sense of planar rotation (in the sense of a CT scanner), but also by tilting.

[0076] The exemplary hybrid OR 100 typically includes an external display 114 that allows a surgeon to view the internal surgical site to provide surgical navigation.

[0077] The C-arm x-ray imaging system 102 is controlled, for example, by a console 116 that includes, for example, a display screen 118, optionally a computer device 120 that serves as a stator control system, which can be controlled by a keyboard 122 and a mouse 124.

[0078] The hybrid OR can improve facility utilization by covering a number of procedures from endovascular to minimally invasive or open surgery; and enable exploration of new procedures that utilize intraoperative high-quality imaging and high levels of device integration. Incorporating robotic guidance into this environment can provide increased accuracy by precisely transferring a surgical plan to the patient and simplify the surgical workflow. However, this can be challenging due to existing OR equipment, geometric constraints from limited surgical space and imaging volume, and a confirmed surgical workflow.

[0079] For example, for a hybrid OR intra-spinal procedure, a robotically guided system for pedicle screw placement can need to be quickly set up, low profile, and sterile near the surgical area. In addition, it can need to provide a visual path for the surgeon as well as the optical tracking system. The robot can need to reach all trajectories planned for a given volume without adjusting its base position to minimize workflow interruptions. It can also need a quick and easy way to retract from the surgical area whenever the surgeon is done using it; and fit underneath the detector during normal cone beam computed tomography (CBCT) without causing significant image artifacts. The surgeon should not be required to manually register the reference frames for surgical planning, patient tracking, and the robot. Patient tracking should be non-invasive and robust to partial occlusions. Most importantly, the robot should transfer the navigation plan to the patient with high accuracy (<0.5 mm and <0.5 degrees of planned trajectory) to minimize vertebral body breach greater than 2 mm, which is clinically unacceptable.

[0080] Based on the above needs, a system is presented for providing fully integrated intra-operative 3D imaging and planning; and automatically aligning instruments to planned trajectories using a robot with at least four control degrees of freedom.

[0081] Figure 2 A top view of an exemplary system 10 for instrument positioning in the illustrated hybrid OR 100 is shown.

[0082] The system 10 includes a robotic system 12 having one or more robotic arms 14, such as the robotic arms 14a, 14b, and 14c in Figure 2 The robotic system 12 can be mounted on one side of the patient support 112, e.g., through a rail-mounted adapter 16, outside the surgical area. Each robotic arm 14 has four or more control degrees of freedom. The robotic arms 14 include an instrument interface, e.g., a needle guide, which can be connected with an instrument 18, such as the instruments 18a, 18b, and 18c in Figure 2 As an example, the central robotic arm 14b can support an endoscopic camera 18b. The robotic arms 14a and 14c can support interventional instruments, such as an interventional laser device, which manipulate tissue.

[0083] The instrument 18 can be any instrument or tool that can be connected to the robotic arm and manipulated thereby. Examples of the instrument 18 can include, but are not limited to, surgical tools, medical tools, biomedical tools, and diagnostic instruments. The surgical tools can include, for example, irrigation and injection needles, tips and tubes (for introducing liquids), scopes and probes (e.g., fiber optic endoscopes and haptic probes), ultrasonic tissue disruptors, drill bits, cryotomes, and cutting laser guides. The diagnostic instruments can include, for example, ultrasound instruments, computed tomography (CT) scanners, magnetic resonance imagers (MRI).

[0084] Generally, the robotic arm 14 can be divided into two modules, including a translational module and a rotational module, such as the rotational modules 20a, 20b, and 20c. Figure 4 Examples of the two modules are shown in FIG. 1. The translational module can be a 3-DOF translational module that allows the instrument 18 to be translated to an entry point and then rotated with the rotational module to be aligned.

[0085] The system 10 also includes a system controller 22 with an interface unit 24. For example, the system controller 22 can be an example of the console 116 in Figure 1 The interface unit 24 of the system controller 22 is configured to provide sensor data, which includes pose information of the instrument and a target position with respect to the object of interest 106. The pose information of the instrument includes a position and an orientation of the interventional instrument. The sensor data can be obtained from a tracking system 26. For example, the tracking system 26 can be an optical tracking system, which includes one or more cameras or optical sensors, which can be arranged in the hybrid OR for capturing the sensor data including the pose information of the instrument. Non-invasive, disposable passive skin markers can be distributed around the target position, for example, around a surgical incision, for providing the required obstruction redundancy and robustness of tracking. By tracking these markers on the patient during image acquisition, the object coordinate system can be registered to the image coordinate system and / or the tracking coordinate system used for planning. Alternatively or additionally, the tracking system can include an electromagnetic tracking system and / or an acoustic tracking system.

[0086] For example, in optical tracking systems, markers coated with retroreflective material can be used to reflect light generated near the camera lens. The camera threshold can be adjusted so that only bright reflective markers are sampled, ignoring skin and fabric. Alternatively, reference markers can be used. The center point of the marker is estimated as its location within the captured 2D image. The grayscale value of each pixel can be used to provide subpixel accuracy by finding the center point. The position of each marker can be used to define the axes of the object coordinate system relative to the tracking coordinate system. The origin of the object coordinate system can be arbitrarily defined, and the orientation of the axes can be defined based on the position of the markers around the target location. Therefore, the tracking coordinate system can be registered to the object coordinate system based on the position of the markers (and possibly based on the orientation of the markers).

[0087] Alternatively, an electromagnetic tracking system can calculate the position and orientation of the electromagnetic tracker around a target location using the relative magnetic flux of three orthogonal coils on the transmitter and receiver. The relative strengths of the voltages or currents in the three coils allow the electromagnetic tracking system to calculate both range and orientation by meticulously mapping the tracking volume. Similarly, the tracking coordinate system can be registered to the object coordinate system based on the measured position and orientation of the markers. Other tracking systems may also be used.

[0088] Preferably, such as Figure 2 As shown, the tracking system 26 can be located on or inside the detector 110 of the image acquisition system. Positioning the tracking system on or inside the detector inherently spatially registers the tracking coordinate system to the image coordinate system. This reduces the need for, for example, independent tracking and registering the tracking coordinate system to the image coordinate system of an external tracking system. Tracking the instrument 18 in this manner provides more accurate instrument tracking compared to using, for example, a shape sensor on a robot (whose errors are compounded to the robot's fixed base).

[0089] The interface unit 24 of the system controller 22 is further configured to provide image data at the target location. The image data can be acquired through an image acquisition system, such as... Figure 1 The X-ray imaging device, ultrasound imaging device, or magnetic resonance imaging device shown. User 30, such as a surgeon, plans a target trajectory 28 in the image data, such as skin entry point and target point, to position the instrument to the target location. For example, during intraoperative CBCT acquisition, the surgeon plans a 3D instrument trajectory based on this, such as pedicle screw location.

[0090] The system controller 22 is configured to transfer the pose information of the instrument 18 and the planned target trajectory 28 into the object coordinate system. This is achieved by registering the object coordinate system to the tracking coordinate system and the image coordinate system. There are many methods that are known to those skilled in the art. One of these methods includes the use of markers on the object and instrument with a tracking system as described previously.

[0091] The system controller 22 is further configured to compute a positional error between the tracked pose information of the instrument and the planned target trajectory. The positional error includes at least one of a translational error and a rotational error. The error metric for alignment is the angle between the target and the trajectory, while the translational alignment is the length of the vector from the instrument to the target trajectory vector.

[0092] Figure 3A An example of the coordinate systems in the system 10 is shown. The target and entry point are defined in the object coordinate system. In the illustrated example, the object coordinate system can also be referred to as the patient coordinate system. The tracked pose information of the instrument can include the position (P D ) of the tip of the instrument and its principal axis The target trajectory can be defined by the skin entry point (P E ) and the target point (P Q ) inside the pedicle, corresponding to the planned screw trajectory. All of these are converted into the patient coordinate system (S). The main assumption is that the instrument axis is collinear with the robot guide axis, and that the patient reference does not move significantly with respect to the robot base during the target selection time.

[0093] Figure 3B An example of the error metric for alignment is shown. In the safety plane R pi1 defined by the XY plane of the robot and the current robot guide position, the error metric for alignment is the angle between the target and the trajectory, while the translational alignment is the length of the vector from the instrument to the target trajectory vector. Alternatively, the position of the safety plane can be defined as: relative to the tip of the instrument, then converted into the robot coordinate system, relative to the closest point on the target trajectory on the instrument with some reasonable constraints, such that the point is not too far from the robot guide, or relative to the entry point.

[0094] In Figure 3B , is the translation in the plane pi1 from the instrument axis to the target trajectory axis, is the 3-DOF rotation (axis angle) between the instrument axis and the target trajectory axis.

[0095] The system controller 22 is configured to translate the position error into the robot coordinate frame of the robotic system to control the robot arm to align the instrument with the planned target trajectory. For example, as shown in FIG. 3, the system controller 22 can direct the movement of the robot-controlled instrument 18a-18c through control lines 302 to cause the movement of the instrument to effect the alignment of the instrument with the planned target trajectory using one or more robot arms 14. Figure 2

[0096] In operation, an object of interest 106, e.g., a patient, is transported and prepared for surgery. An intraoperative CBCT acquisition is performed, upon which a user 30, e.g., a surgeon, plans 3D instrument trajectories, e.g., pedicle screw locations. The planned trajectories, including skin entry points and target points, are converted to the physical patient space and used with instrument tracking for the robotic system. The pose information of the instrument is used by the system controller 22 to automatically align to the target defined in the patient coordinate frame. Once aligned, the robot holds position and the surgeon taps the instrument into the pedicle to create a pilot hole into which a screw is placed. The surgeon can manually move the robot arm away from the surgical site by enabling a "swing arm" mode, or leave it in place for additional guidance or verification imaging.

[0097] Thus, by extending the robot arm 14 into the surgical area, the system 10 can automatically align the instrument 18 following a surgical plan using only instrument tracking feedback; no tracking markers on the robot arm 14 are needed. The proposed system can provide an accurate and workflow-friendly robotic guidance system, e.g., for creating pedicle screw pilot holes in spinal fusion surgery. The robot arm precisely aligns the instrument to the intended trajectory, and the surgeon taps or drills the instrument into the pedicle. The system controller uses a servo control method to achieve high alignment accuracy relying only on instrument tracking feedback, e.g., 4-DOF or 5-DOF, and no manual robot registration step is needed.

[0098] Optionally, the sensor data includes pose information of the robot arm. This can allow for a hybrid feedback control that includes robot end-effector tracking and instrument tracking feedback. This can allow for a coarse alignment with less accurate robot tracking, even without the instrument in the guide, and once the device is visible in the tracking system and in the vicinity of the target trajectory, the proposed system can be used to servo to achieve the final high accuracy alignment.

[0099] Robotic system

[0100] Figure 4 ​An example of a robotic arm 14 is shown schematically. The robotic arm 14 can feature five active joints, and a sixth passive rotation within a single-axis instrument guide as an end effector. The example robotic arm 14 is split into two modules. A 3-DOF translational module includes a vertical linear stage (JO), a shoulder rotation joint (Jl), and a horizontal linear stage (J2). It carries a 2-DOF rotational module: a mechanical remote center of motion (RCM) mechanism. In some examples (not shown), alignment to a predetermined plane (e.g., 4-DOF) can be sufficient, so for these examples it can carry a 1-DOF rotational module. The RCM can include two spherical connections: J3 and J4, both with an angle of 65°, with J3 mounted at a position 60° from the vertical. This serial kinematics structure is chosen to meet the minimum number of degrees required to position a needle instrument within Cartesian space. Including the RCM can minimize the overall joint motion, resulting in an ergonomic robotic construction and predictable motion for improved user experience, particularly when performing Cartesian rotations. It allows the instrument to be translated to an entry point primarily by driving the first three joints, and then rotated into alignment using only the two distal (RCM) joints. The shape of the last link is optimized to bring the instrument guide closer to the RCM, enabling guide positioning closer to the skin incision for improved accuracy of the transfer trajectory to the patient, and to facilitate the use of short instruments.

[0101] The robotic system 10 can include a rail-mounted adapter 16 that can be attached to standard OR table rails, or integrated into rails in a custom board placed under the patient to provide rigidity and positional flexibility. The lengths of the links and the angles of the spherical connections provide at least 6 degrees of freedom and sufficient coverage of ±60° to cover unusual trajectory angles beyond the range of -14° to 20° in the sagittal plane for a healthy patient, and ±22° to 35° in the transverse plane. The last link allows for the mounting of variable diameter guides that can either lock the instrument in place or provide a side exit function. The robotic body prototype is machined from slotted aluminum, and 3D printed in the case of non-structural components. Common off-the-shelf electromechanical components are used for the motors and gearboxes. A 6-DOF force torque (FT) sensor can be integrated into the last link of the robot to provide FT measurements at the instrument guide. The FT is used in the admittance (hands-on positioning) control method and to monitor the load in the guide during the intervention. It provides the GUI, forward / inverse kinematics, and various control modes (force control, ARSN alignment servo, remote joystick, insertion, etc.). The joystick can be used for remote positioning input to trigger the automatic alignment and enable the hands-on positioning mode. In some embodiments, the FT interface can also be used to trigger the automatic alignment by detecting when the user is holding the instrument guide. Once the instrument guide is no longer held, the automatic alignment will stop.

[0102] System controller

[0103] The system controller 22 can be controlled by a trajectory alignment algorithm to align the instrument with the planned target trajectory 30. The goal of the trajectory alignment algorithm is to align the instrument with the planned target trajectory with as high precision as possible, while not adding any extra (registration) steps to the surgeon's workflow. For instruments with 4-DOF or 5-DOF, the instrument tracking feedback can inherently be insufficient to achieve 6-DOF Cartesian robotic positioning without precise coordinate system (CS) registration, especially since the exact position (e.g., depth) of the instrument within the instrument interface is unknown.

[0104] For instruments with elongated shapes, the proposed system controller 22, in the absence of a 6-DOF reference body on the robot, can be configured to control the robot arm during the first movement of the robot arm at each new target selection time, causing the instrument to move in a predetermined motion to produce a coarse six-DOF registration between the object coordinate system and the robot coordinate system. The predetermined motion includes predetermined rotational movements, and optionally, may also include predetermined translational movements. Generally, assuming that the motion of the robot system and the instrument tracking feedback can be precisely synchronized, the predetermined rotational movements for coarse registration can be arbitrary, as long as they include large rotations, since larger angles result in more accurate registration. Arbitrary translations can also be added. This feature can be used in real time to update or verify that the registration has not changed due to the patient's movement relative to the robot system.

[0105] For example, now refer to Figure 3B In order to produce a rough registration The tracked needle is fixed in the guide (to prevent slippage). During target selection, when commanded to align with the first target, the robot begins movement, for example, by rotating 15 degrees around its RCM in a predetermined direction (towards the opposite side of the worktable). Of course, the robot can also begin movement by rotating other degrees around its RCM in the predetermined direction, such as 5, 10, 20, 30, 40, 50, 60, 70, 80, or 90 degrees. Two robot poses are collected before and after movement. and ) and two needle positions ( S N1, S N2), and then use a temporary coordinate system (D) to calculate As a reminder, the patient coordinate system is referred to as (S), and the robot coordinate system is referred to as (R). Coarse registration. The calculation is as follows:

[0106] Translation component ( S P D () is calculated using the least squares method to determine the two line vectors representing the needle axis. S N1, S The point is determined by the nearest point between N2 and N3, which corresponds to the robot's RCM position. R P RCM = R P D ).

[0107] Rotational component It uses the standard cross product method to extract the normals of the two lines. Produced. It is also the normal from the z-axis of the robot guide. generated.

[0108] The (object) registration between the patient coordinate system and the temporary coordinate system is referred to as

[0109] The (robot) registration between the robot coordinate system and the temporary coordinate system is referred to as

[0110] The registration between the patient coordinate system and the robot coordinate system is referred to as

[0111] and are constructed from and respectively. Then is simply

[0112] The generated registration process can take a few seconds and can be sufficient to position the instrument in the vicinity of the intended trajectory in an open loop fashion, e.g. when outside the tracking volume, but can not be sufficient to achieve precise alignment due to limited registration data and small errors of the robot.

[0113] For precise alignment, real-time needle position feedback can be used to iteratively move the needle mounted in the guide so as to align with the target trajectory. Once aligned, the surgeon can lower the robot along the axis of the guide (by force control with an insert-along axis constraint) and, if needed, can command the robot to align to the target.

[0114] Optionally, the sensor data can include real-time pose information of the instrument with respect to the target position. Optionally, the height of the robot guide (i.e. the instrument interface) is kept constant during alignment. The height constraint can provide safer and more intuitive robot behavior. The system controller can be configured to compute real-time position error between the tracked pose information of the instrument and the planned target trajectory and to transfer the real-time position error into the robot coordinate system of the robot system to iteratively control the robot arm to align the instrument with the planned target trajectory.

[0115] For example, referring now to Figure 3B , for each iteration, the target position of the guide in the robot coordinate system can be computed as follows:

[0116] Consider the plane R π1 T defined by the XY plane of the robot R (0, 0, 1) R P RCM .

[0117] calculate R P Q1 Target line and R The intersection of π and 1; and R P N1 needle axis and R The intersection of π and 1.

[0118] The displacement error vector is Then the target translation because R P Q1 and R P N1 Located on the XY plane of the robot coordinate system (almost parallel to the worktable), the translation of the robot guide is limited to this plane.

[0119] Rotational error is detected by the needle axis. and the target trajectory axis The rotation between axes is calculated within the robot guide frame: The angle between them is α.

[0120] Normalize τ, then Set it to 0.0 and normalize it again.

[0121] This removes the surrounding The rotation is arbitrary because it is defined by the target and instrumentation of 4-DOF or 5-DOF, and the robot cannot perform such rotation.

[0122] The desired goal in It is an approximate rotational error. It is represented by a rotation matrix.

[0123] Rotating targets and translation targets are merged into a single homogeneous transformation. R R G , R G], and is sent to the robot position controller.

[0124] Each servo iteration can be performed after the previous robot instruction has been completed. In a typical setup, the robot requires fewer than 5 iterations to complete the task. The needle being tracked will be aligned with the target within an error tolerance of α < 0.25°.

[0125] Optionally, the robot's XY plane ( R [0, 0, 1] T ) and the current position of the robot guide R P RCM Defined safety plane RPi1may be updated at each iteration and can be defined by a mesh of triangles, where each triangle defines a plane on which the robot can translate. The mesh can be offset from the patient surface model by an offset, e.g. 5 cm, thereby constraining the motion of the robot to this offset. Such a model can be an approximation from a sticker placed on the patient.

[0126] In some examples, the system controller 22 can compute an approximate registration and interactively control the robot towards the target in two different steps. Alternatively, the system controller 22 can simultaneously drive the robot system towards the target while continuously updating / improving the object coordinate systems and the registration between the object coordinate systems.

[0127] Figure 5 A flowchart of a method 200 of controlling a system as described above and below according to some embodiments of the present disclosure is shown. The method comprises the following steps:

[0128] In step 210, i.e. step a), sensor data is received by an interface unit of a system controller of the system. For example, a tracking system, such as an optical tracking system, is provided to obtain the sensor data and to transfer the obtained sensor data to the system controller. The sensor data comprises pose information of the instrument with respect to a target position relative to the object. The pose information of the instrument comprises a position and an orientation of the interventional instrument.

[0129] In step 220, i.e. step b), image data of the target position is received by the interface unit of the system controller. A target trajectory is planned in the image data in order to position the instrument to the target position. Steps a) and b) can be performed in different orders, such as a) -> b), b) -> a), or a) and b) are performed simultaneously.

[0130] In step 230, i.e. step c), the pose information of the instrument and the planned target trajectory are transferred into the object coordinate system by the system controller of the system. A positional error between the tracked pose information of the instrument and the planned target trajectory is computed. The positional error is transferred into a robot coordinate system of a robot system for controlling a robot arm to align the instrument with the planned target trajectory. The positional error comprises at least one of a translational error and a rotational error.

[0131] Figure 6A flow chart of a method 200 according to some other embodiments of the present disclosure is shown. In the method 200, for an instrument having an elongated shape, a coarse registration step 202 can be provided before steps 210-230. In this step, the robot arm is controlled during a first movement of the robot arm at each new target selection time to move the instrument in a predetermined movement in order to create a coarse six degrees of freedom registration between the object coordinate system and the robot coordinate system. The predetermined movement comprises at least one of a predetermined translational movement and a predetermined rotational movement. The first movement of the robot arm automatically initiates the coarse registration process. Thus, the system controller can automatically perform the coarse registration, thereby avoiding any input from a user or increasing the time of the operation. The created registration process can take a few seconds and can be sufficient to position the instrument in the vicinity of the intended trajectory in an open loop manner, e.g. when outside the tracking volume, but due to limited registration data, and small errors of the robot can not be sufficient to make an accurate alignment.

[0132] In other words, with the registration process 202, the method can further comprise a step 240. In this step, the instrument is aligned with the planned target trajectory based on the coarse six degrees of freedom registration between the object coordinate system and the robot coordinate system. In other words, the coarse six degrees of freedom registration is used to position the instrument in the vicinity of the intended trajectory in an open loop manner, e.g. when outside the tracking volume. Once the instrument is detected, e.g. when inside the tracking volume, step 230 can be performed.

[0133] In another exemplary embodiment of the present application, a computer program or a computer program element is provided that is characterized by being adapted to execute the method steps of the method according to one of the preceding embodiments, on an appropriate system.

[0134] Accordingly, the computer program element might be stored on a computer unit, which might also be part of an embodiment of the present application. This computing unit can be adapted to perform or induce a performing of the steps of the method described above. Moreover, it can be adapted to operate the components of the above-described apparatus. The computing unit can be adapted to operate automatically and / or under control of a user.

[0135] This exemplary embodiment of the present application covers both a computer program that - from its very beginning - uses the application and a computer program that is brought to use as a computer program of the present application by an up-date of a previously existing computer program.

[0136] Further, the computer program element might be able to provide all the steps of a method as described above.

[0137] According to a further exemplary embodiment of the present application, a computer readable medium, such as a CD-ROM, having stored thereon the computer program of this application is presented.

[0138] A computer program can be stored and / or distributed on a suitable medium, such as an optical storage medium or a solid state storage medium supplied together with or as part of other hardware, but can also be distributed in other forms, such as via the internet or other wired or wireless telecommunication systems.

[0139] The computer program can also be presented over a network like the World Wide Web and can be downloaded into the working memory of a data processor from such a network. According to a further exemplary embodiment of the present application, a medium for making a computer program element available for downloading is provided, which computer program element may

[0140] It should be noted that the embodiments of the present application are described with reference to different specializations. In particular, some embodiments are described with reference to claims of method type, while further embodiments are described with reference to claims of device type. A skilled person, however, will gather from the above and the following description that, unless otherwise indicated, any combination of features related to different specialties is considered to be disclosed by the present application, in addition to any combination of features belonging to one type of specialty. However, all features can be combined in order to provide synergistic effects more than the simple sum of the features.

[0141] While the application has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive. The application is not limited to the disclosed embodiments. Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practising the claimed application, from a study of the drawings, the disclosure, and the appended claims.

[0142] In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite articles "a" or "an" do not exclude a plurality. A single processor or other unit can fulfil the functions of several items recited in the claims. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures can not be used to advantage. Any reference signs in the claims should not be construed as limiting the scope.

Claims

1. A system (10) for instrument positioning, comprising: a robotic system (12) having a robot arm (14) with four or more degrees of freedom (DOF); and a system controller (22) having an interface unit (24); wherein the robot arm comprises an instrument interface capable of connecting with an instrument (18); wherein the instrument has an elongated shape; wherein the interface unit of the system controller is configured to provide sensor data comprising pose information of the instrument and a target position with respect to an object of interest, wherein the pose information of the instrument comprises a position and an orientation of the instrument; wherein the interface unit of the system controller is further configured to provide image data at the target position, wherein a target trajectory is planned in the image data for positioning the instrument to the target position, and the target trajectory is defined by a skin entry point and a target point; and wherein the system controller is configured to: transfer the pose information of the instrument and the planned target trajectory into an object coordinate system; calculate a position error between the tracked pose information of the instrument and the planned target trajectory; control the robot arm during a first motion of the robot arm at each new target selection time to move the instrument in a predetermined movement to create a coarse six degrees of freedom registration between the object coordinate system and a robot coordinate system based on pose information before the movement of each of the instrument and the robot arm and pose information after the movement, wherein the predetermined movement comprises a predetermined rotational movement; and transfer the position error into the robot coordinate system of the robotic system for controlling the robot arm to align the instrument with the planned target trajectory, wherein the position error comprises at least one of a translational error and a rotational error.

2. The system of claim 1, wherein, The coarse six degrees of freedom registration between the object coordinate system and the robot coordinate system is based on: collecting two robot poses and two instrument positions before and after the predetermined movement; determining an instrument translational component based on calculating a closest point between two line vectors representing axes of the instrument from the positions of the instrument before and after rotation using a least squares method; determining an instrument rotational component from normals of the two instrument line vectors using a standard cross product method; determining an object registration between the object coordinate system and a temporary coordinate system based on the instrument translational component and the instrument rotational component, wherein the temporary coordinate system corresponds to a center of motion (RCM) of the robot; determining a robot translational component based on calculating a closest point between two line vectors representing axes of the robot from the poses of the robot before and after rotation using a least squares method; determining a robot rotational component from normals of the two robot line vectors using a standard cross product method; determining a robot registration between the robot coordinate system and the temporary coordinate system based on the robot translational component and the robot rotational component; and ​ Based on the object registration and the robot registration, a coarse six degrees of freedom registration is generated between the object coordinate system and the robot coordinate system.

3. The system of claim 1 or 2, wherein the sensor data comprises real-time pose information of the instrument with respect to the target position; and wherein the system controller is configured to compute a real-time position error between the tracked pose information of the instrument and the planned target trajectory and to transfer the real-time position error into the robot coordinate system of the robotic system to iteratively control the robot arm to align the instrument with the planned target trajectory.

4. The system of claim 1 or 2, wherein the system controller is further configured to apply the coarse six degrees of freedom registration to control the robot arm to align the instrument with the planned target trajectory when the sensor data does not comprise pose information of the instrument.

5. The system of claim 1 or 2, wherein, The system further comprises: a tracking system (26) configured to obtain sensor data comprising pose information of the instrument and a target position of the object of interest; wherein the tracking system comprises at least one of: an optical tracking system; an electromagnetic tracking system; and an acoustic tracking system.

6. The system of claim 5, wherein the tracking system is located on or inside a detector of an image acquisition system of the system.

7. The system of claim 1 or 2, wherein, The system further comprises: an image acquisition system (102) configured to acquire the image data at the target position of the object of interest; wherein the image acquisition system comprises at least one of: an X-ray imaging device; an ultrasound imaging device; and a magnetic resonance imaging device.

8. The system of claim 1 or 2, wherein the robot arm comprises a mechanical remote center of motion, RCM, mechanism having at least one rotational control degree of freedom; and wherein the instrument interface is mounted on the RCM mechanism.

9. The system of claim 1 or 2, wherein the system controller is configured to control the robot arm to align the instrument with the planned target trajectory when the instrument is translated within a safety plane for preventing a collision.

10. The system of claim 1 or 2, wherein the sensor data comprises pose information of the robot arm.

11. The system of claim 1 or 2, wherein, the instrument comprises an interventional instrument.

12. The system of claim 11, wherein, the interventional instrument comprises at least one of: an injection needle; an interventional catheter; and an interventional laser device.

13. A method (200) of controlling a system according to any one of claims 1 to 12, comprising the steps of: receiving (210), by an interface unit of a system controller of the system, sensor data comprising pose information of an interventional instrument with respect to a target position relative to an object of interest, wherein the pose information of the instrument comprises a position and an orientation of the instrument; receiving (220), by an interface unit of the system controller, image data at the target location, wherein a target trajectory is planned in the image data for positioning the instrument to the target location, and the target trajectory is defined by a skin entry point and a target point; and transforming (230), by a system controller of the system, the pose information of the instrument and the planned target trajectory into an object coordinate system, calculating a positional error between the tracked pose information of the instrument and the planned target trajectory; controlling the robotic arm to move the instrument in a predetermined movement during a first motion of the robotic arm at each new target selection time to generate a coarse six degrees of freedom registration between the object coordinate system and a robot coordinate system based on pose information before the movement of each of the instrument and the robotic arm and pose information after the movement, wherein the predetermined movement includes a predetermined rotational movement during which the instrument is not positioned in a living body; and transforming the positional error into a robot coordinate system of the robotic system for controlling the robotic arm to align the instrument with the planned target trajectory, during which the instrument is not positioned in a living body, wherein the positional error includes at least one of a translational error and a rotational error.

14. A computer program product comprising a computer program for controlling a device, which computer program, when executed by a processing unit, is adapted to perform the method according to claim 13.

15. A computer readable medium having stored a computer program for controlling a device, which computer program, when executed by a processing unit, is adapted to perform the method according to claim 13.

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