COMPENSATION OF GRAVITY-RELATED DISPLACEMENTS OF MEDICAL CARRIER STRUCTURES

Abstract

The present application relates to a computer-implemented medical method of determining a compensation for gravity-related displacements of a medical carrier structure having at least one adjustable and selectively fixable joint which respectively connects two sections of the carrier structure. The present application further relates to a corresponding computer program and medical system.

Claims

1. A computer-implemented medical method of determining a compensation for gravity-related displacements of a medical carrier structure having at least one adjustable and selectively fixable joint which respectively connects two sections of the carrier structure, the method comprising the following steps: acquiring target position data which describes a target position for a predefined section of the carrier structure; acquiring rest position data which describes a rest position into which the predefined section of the carrier structure is displaced by gravity after being positioned at the target position with the at least one selectively fixable joint being fixed and the predefined section of the carrier structure being free of any actuator effects or support from an operator; determining deviation data based on the target position data and the rest position data, which describes a spatial deviation between the target position and the rest position; and determining prepositioning data based on the deviation data, which describes an offset position at which the predefined section of the carrier structure needs to be positioned in order for it to be displaced by gravity into the target position.

2. The method according to claim 1, wherein the target position is acquired after the at least one joint is fixed, with the predefined section of the carrier structure being held at the target position.

3. The method according to claim 1, wherein the rest position data is acquired after the predefined section has come to rest at the rest position.

4. The method according to claim 1, wherein determining prepositioning data is further based on: the rest position data, wherein the offset position is determined based on a spatial offset from the rest position, wherein the spatial offset is calculated from the spatial deviation between the target position and the rest position; or the target position data, wherein the offset position is determined based on a spatial offset from the target position, wherein the spatial offset is calculated from the spatial deviation between the target position and the rest position.

5. The method according to claim 1, further involving the step of: transmitting the prepositioning data to a graphical-user-interface-(GUI)-module adapted to output instructions to a user to manually position the predefined section at the offset position; and/or transmitting the prepositioning data to an actuator-control-module adapted to output control signals to at least one actuator to automatically position the predefined section at the offset position.

6. The method according to claim 1, wherein the target position data is acquired from a medical planning module and/or from at least one tracking system adapted to determine the spatial position of the predefined section.

7. The method according to claim 1, wherein the rest position data is acquired from at least one tracking system adapted to determine the spatial position of the predefined section.

8. The method according to claim 6, wherein at least one tracking system is selected from the group consisting of: an optical tracking system; an EM-tracking system; an ultrasound tracking system; a position sensor tracking system; a capacitive tracking system; and a permanent magnetic tracking system.

9. The method according to claim 1, wherein the carrier structure comprises a plurality of joints, wherein each one of the joints respectively connects two sections of the carrier structure; at least one joint is a pivot joint providing a rotational degree of freedom; at least one joint comprises a position sensor adapted to determine the relative position of the sections connected via the joint; the predefined section is an end section of the carrier structure; and/or the carrier structure comprises a spatially invariant base section which connects to the predefined section via the at least one joint.

10. The method according to claim 1, wherein the target position and the assigned offset position are stored in a database.

11. A computer-implemented medical method of retrieving a compensation for gravity-related displacements of a medical carrier structure having at least one adjustable and selectively fixable joint which respectively connects two sections of the carrier structure, the method comprising executing, on a processor of a computer, the steps of: acquiring target position data describing a target position for a predefined section of the carrier structure; and acquiring prepositioning data describing an offset position at which the predefined section of the carrier structure needs to be positioned in order for it to be displaced by gravity into the target position with the at least one selectively fixable joint being fixed and the predefined section of the carrier structure being free of any actuator effects or support from an operator, wherein the prepositioning data is retrieved from a database storing at least one offset position, and wherein the database is established by the method according to claim 10.

12. The method according to claim 11, wherein an offset position assigned to a new target position is calculated on the basis of at least two offset positions assigned to target positions stored in the database and proximate to the unknown target position.

13. The method according to claim 11, wherein offset positions determined for a plurality of medical carrier structures are stored in the database.

14. A computer program comprising instructions which, when the program is executed by a computer, cause the computer to carry out a method comprising: acquiring target position data which describes a target position for a predefined section of a carrier structure having at least one adjustable and selectively fixable joint which respectively connects two sections of the carrier structure; acquiring rest position data which describes a rest position into which the predefined section of the carrier structure is displaced by gravity after being positioned at the target position with the at least one selectively fixable joint being fixed and the predefined section of the carrier structure being free of any actuator effects or support from an operator; determining deviation data based on the target position data and the rest position data, which describes a spatial deviation between the target position and the rest position; and determining prepositioning data based on the deviation data, which describes an offset position at which the predefined section of the carrier structure needs to be positioned in order for it to be displaced by gravity into the target position.

15. A medical system, comprising: a) at least one computer configured to perform a method including: acquiring target position data which describes a target position fora predefined section of a medical carrier structure having at least one adjustable and selectively fixable joint which respectively connects two sections of the carrier structure; acquiring rest position data which describes a rest position into which the predefined section of the carrier structure is displaced by gravity after being positioned at the target position with the at least one selectively fixable joint being fixed and the predefined section of the carrier structure being free of any actuator effects or support from an operator; determining deviation data based on the target position data and the rest position data, which describes a spatial deviation between the target position and the rest position; and determining prepositioning data based on the deviation data, which describes an offset position at which the predefined section of the carrier structure needs to be positioned in order for it to be displaced by gravity into the target position; b) at least one electronic data storage device storing at least the target position data; and c) the medical carrier structure having the at least one adjustable and selectively fixable joint respectively connecting two sections of the medical carrier structure, wherein the at least one computer is operably coupled to the at least one electronic data storage device for acquiring, from the at least one data storage device, at least the target position data, and the medical carrier structure for issuing a control signal to the medical carrier structure for controlling the operation of the medical carrier structure on the basis of the target position data.

16. The method according to claim 10, wherein a plurality of target positions and the assigned offset positions are stored in the database.

17. The method according to claim 12, wherein the offset position is calculated via interpolation or extrapolation.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0084] In the following, the invention is described with reference to the appended figures which give background explanations and represent specific embodiments of the invention. The scope of the invention is however not limited to the specific features disclosed in the context of the figures, wherein

[0085] FIG. 1 shows a medical carrier structure, a computer and a navigation system as used in connection with the present invention;

[0086] FIG. 2 shows the basic steps of the method according to the first aspect;

[0087] FIG. 3 is a schematic illustration of the system according to the fifth aspect.

DESCRIPTION OF EMBODIMENTS

[0088] FIG. 1 shows an articulated support arm 4 as used during robot assisted surgery, a distal, functional section 7 which is adapted to hold or guide medical instruments or devices with respect to a patient, and therefore comprises an effector. The distal, functional section 7 of the support arm 4 will be referred to in the following as “predefined section” 7. The support arm 4 further includes a base-section 14 which remains stationary with respect to the patient. The predefined section 7 is connected to the base section 14 via two intermediate sections 6, wherein the sections 6, 7, 14 are connected to each other via rotatable joints 5, each of which provides a single rotational degree of freedom. As the rotational axes of the joints are not arranged in parallel, the support arm 4 is adapted to hold the predefined section 7 at any desired spatial position.

[0089] Further, the joints 5 do not only comprise a position sensor 13 adapted to sense the angle between the arm sections 6, 7, 14 connected via the corresponding joint 5, but also comprise means, for example joint brakes, to immobilize the corresponding joints 5, i.e. to fix the relative position of the adjacent arm sections 6, 7, 14. Optionally, some or all of the joints 5 may also comprise actuators 10, for example servo motors, which are adapted to change the relative angular arrangement of the corresponding arm sections 6, 7, 14, so as to position the predefined section 7 in a desired position fully automatically. In the alternative, the support arm 4 may be operated manually, wherein the predefined section 7 is grasped and moved to the desired position by a practitioner, who may, while doing so, receive assisting guidance information, e.g. on a graphical user interface of the navigation system, indicating the necessary positional adjustments so as to have the predefined section 7 positioned at the desired position.

[0090] Assuming that the distal tip (end effector) of a predefined section 7 needs to be placed at a target position A (represented by height A in FIG. 1) in order to fulfil a desired purpose, merely positioning the distal tip at position A and applying the joint brakes will most likely be followed by a vertical displacement of the distal tip into position B (represented by height B), which is caused not only by an inherent play within the joint breaks, but also by the elastic properties inherent to each one of the arm sections 6, 7, 14. The amount and direction by which the distal tip of the predefined section 7 will deflect, i.e. the deviation of position B with respect to position A depends on the direction of the gravity-vector g with respect to the support arm 4, the load attached to the support arm 4, the tare weight of the support arm 4, and the spatial configuration of the support arm 4, i.e. the current spatial orientation of the rotatable joints 5 and the current horizontal overhang of the predefined section's 7 distal tip with respect to the mounting of the base section 14 to a solid foundation.

[0091] In order to compensate for this deviation, the spatial deviation of position B from position A is determined, which is for the shown example substantially vertical. Thus, adding double the amount of the determined downward displacement to height B in an upward direction leads to an offset position C (represented by height C) which is the position/height from which the distal tip of the predefined section 7 will deflect into the desired target position A.

[0092] In order to determine the rest position B, the distal tip of the predefined section 7 is provided with a marker array adapted to be recognised by an optical navigation system 12 that includes a stereo-camera-array.

[0093] Once the offset position C has been determined in accordance with the present invention, the distal tip of the predefined section 7 can be positioned there, either automatically by controlling the actuators 10 and the joint brakes in the affected joints, or by instructing a practitioner, for example via a graphical-user-interface. For positioning the distal tip of the predefined section 7 in the offset position C, only those joints 5 are unlocked by releasing the corresponding brakes, which are necessary for the predefined section 7 to reach the offset position C. The remaining joints 5 remain locked, thereby providing guidance for repositioning the predefined section 7.

[0094] In case the current spatial arrangement of the joints 5 does not allow for such repositioning (in the shown example, this may be the case with each one of the rotatable joints 5 having a vertical axis of rotation), the rotational axis of one or more selected joint(s) 5 may be reoriented so as to allow the desired repositioning, for example by activating one or more of the remaining joint actuators 10, or by outputting corresponding instructions to the practitioner.

[0095] FIG. 1 further schematically shows a graphical-user-interface-(GUI)-module 8 adapted to output instructions to a user/practitioner, an actuator-control-module 9 adapted to output control signals to at least one actuator 10, a medical planning module which stores a treatment plan that may include position A as a desired target position, and a database 15 the offset position C assigned to the target position A can be stored on and/or retrieved from. All of these components are comprised within a computer 2 connected to the medical support arm 4 and the tracking system 12.

[0096] FIG. 2 shows the basic steps of the method according to the present invention. As a first step S1, data describing the target position A for the predefined section 7 is acquired. After the predefined section 7 has come to rest after having been placed in the target position A, data describing this rest position B is acquired. In a third step S3, the spatial deviation between these positions is determined and, in a fourth step S4, an offset position C is calculated based on the determined spatial deviation.

[0097] FIG. 3 is a schematic illustration of the medical system 1 according to the fifth aspect. The system comprises at least one computer 2, at least one data storage device 3 for retrieving at least the target position data, and the medical carrier structure 4 as shown in FIG. 1. The components of the medical system 1 have the functionalities and properties explained above with regard to the fifth aspect of this disclosure.