Tibia resection operation virtual wall construction method based on force vector prediction

Abstract

The invention belongs to the field of osteotomy robot control, and particularly relates to a tibia resection operation virtual wall construction method based on force vector prediction, which comprises the following steps of: 1) calibrating and acquiring a multi-coordinate system transformation matrix among a mechanical arm base coordinate system, a navigator coordinate system, a sawdust placing end coordinate system and an osteotomy plane coordinate system; 2) collecting an acting force vector in real time through a six-dimensional force sensor, and mapping force information into a position increment of the tail end of the mechanical arm; (3) the position of the sawdust swinging end of the mechanical arm at the next moment is predicted according to the position increment; 4) judging whether the current position and the predicted position exceed the boundary or not; and 5) dynamically adjusting the position constraint of the swing saw dust end according to the border crossing state of the current position and the predicted position, so that the tail end of the swing saw blade is always in the virtual border. The real-time position information collection and prediction algorithm is combined, the hysteresis problem of a traditional pure vision system is solved, the virtual wall limitation can be generated in advance when the swing saw is close to the operation boundary, and quick response of the system is ensured.

Description

Technical Field

[0001] The present invention belongs to the field of controlling a bone cutting surgical robot, and particularly relates to a method for constructing a virtual wall for tibial resection surgery based on force vector prediction. Background Art

[0002] Tibial resection surgery is a common operation in orthopedic surgery for treating diseases such as osteoarthritis, tibial deformity, and other related diseases. The surgery requires high precision, and any operation deviation will have a profound impact on the patient's postoperative recovery and function. Currently, robotic assisted systems and navigation technologies have been widely applied to such surgeries. However, traditional vision-based assisted systems have problems of insufficient real-time performance and predictive ability due to high dependence on visual information.

[0003] Traditional pure vision navigation systems mainly collect the position of the saw and the intraoperative area image of the tibia through an intraoperative camera, and use image processing and calculation methods to determine whether the saw exceeds the boundary. However, this method has the following limitations:

[0004] Lag: Since the pure vision system can only respond when the saw actually exceeds the surgical boundary, there is an operation lag problem, which may lead to damage to the operative area and resection error.

[0005] Lack of predictive ability: It is difficult for the vision system to predict the risk of exceeding the boundary in advance based on the movement trajectory and speed of the saw, and it cannot actively avoid the saw from going out of the boundary, but can only respond passively.

[0006] Strong environmental dependence: Factors such as intraoperative light changes and blood occlusion are likely to affect the accuracy of visual information, further increasing the difficulty of out-of-bounds detection. Summary of the Invention

[0007] The purpose of the present invention is to provide a method for constructing a virtual wall for tibial resection surgery based on force vector prediction. In this method, the position increment of the saw end at the next moment can be obtained through the applied force vector collected by a six-dimensional force sensor. By judging whether the saw end position at the next moment is within the virtual constraint, different position commands are sent to the robotic arm servo interface to construct a virtual wall for tibial resection surgery, ensuring that the end of the saw blade does not exceed the virtual boundary during the tibial resection surgery.

[0008] The technical solution adopted by the present invention to achieve the above purpose is: A method for constructing a virtual wall for tibial resection surgery based on force vector prediction, comprising the following steps:

[0009] 1) Calibrate and obtain the multi-coordinate system transformation matrices between the robotic arm base coordinate system, the navigator coordinate system, the saw end coordinate system, and the bone cutting plane coordinate system;

[0010] 2) Collect the acting force vector in real time through a six - dimensional force sensor, and map the force information into the position increment at the end of the robotic arm;

[0011] 3) Predict the position of the end of the oscillating saw of the robotic arm at the next moment according to the position increment;

[0012] 4) Combine the pre - planned virtual boundary to judge whether the current position and the predicted position exceed the boundary;

[0013] 5) Dynamically adjust the position constraint of the end of the oscillating saw according to the out - of - boundary status of the current position and the predicted position, so that the end of the saw blade of the oscillating saw is always within the virtual boundary.

[0014] The specific content of step 1) is as follows:

[0015] Use a navigator to calibrate the hand - eye calibration matrix, that is, the transformation matrix from the navigator coordinate system to the robotic arm base coordinate system, defined as Calibrate the transformation matrix from the coordinate system at the end of the saw blade to the Marker on the oscillating saw, defined as The transformation matrix from the Marker coordinate system on the oscillating saw to the navigator coordinate system, defined as The transformation matrix from the bone - cutting plane coordinate system to the navigator coordinate system, defined as The transformation matrix from the robotic arm flange coordinate system to the Marker coordinate system on the oscillating saw, defined as

[0016] The specific content of step 2) is as follows:

[0017] 2 - 1) According to the flange set at the end position of the robotic arm, obtain the transformation matrix from the robotic arm flange coordinate system to the robotic arm base coordinate system at the current t0 moment, defined as Calculate the pose matrix of the oscillating saw blade in the bone - cutting plane coordinate system at the current t0 moment

[0018]

[0019] 2 - 2) Obtain the applied force through the six - dimensional force sensor set on the robotic arm, and define the acting force vector as: F=(F x ,F y ,F z ,T x ,T y ,T z );

[0020] 2 - 3) Through the admittance formula, map the force vector into the position increment, that is: According to the obtained acting force vector information, calculate the acceleration as:

[0021]

[0022] And sequentially update the velocity and position of the component direction i of the force as follows:

[0023]

[0024] Where i ∈ {x, y, z}, representing the component direction of the force; e is the position vector; M is the mass, determining the response inertia; B is the damping coefficient, determining the compliance of the system; K is the stiffness coefficient; Δt is the discrete time step; scaling_factor is the displacement scaling coefficient, used to adjust the control amplitude.

[0025] The specific content of step 3) is as follows:

[0026] According to the position increment, calculate the position increment at the next moment (t1 = t0 + Δt), and then obtain the transformation matrix from the flange coordinate system of the robotic arm to the base coordinate system of the robotic arm at t1, defined as And further calculate the pose matrix of the band saw blade in the bone cutting plane coordinate system at the next moment as:

[0027]

[0028] Extract the position information from the pose matrix That is: the first three rows of the fourth column of the pose matrix are the position coordinate values.

[0029] The specific content of combining with the pre-planned virtual boundary to judge whether the current position and the predicted position exceed the boundary is as follows:

[0030] Obtain the position point coordinates according to the pose matrix of the current position and the predicted position, and calculate the sum of the angles formed by the connections between all virtual contour vertices and the position point starting from the position point;

[0031] If the position point is inside the polygon, the sum of these angles is equal to 2π, that is: 360°, then judge that the current position and the predicted position do not exceed the boundary;

[0032] If the position point is outside the polygon and the sum of the angles is 0, then judge that the current position and the predicted position exceed the boundary.

[0033] In step 5), the specific content of dynamically adjusting the position constraint of the end of the band saw according to the out-of-bounds state of the current position and the predicted position is as follows:

[0034] 5-1) If it is judged that the end of the band saw blade at the current moment does not exceed the boundary, continue to judge whether the band saw blade at the next moment exceeds the boundary. If it does not exceed the boundary, the robotic arm issues a new position command to control the band saw blade to continue moving in the direction of the force, ensuring that the cutting operation does not exceed the boundary; if it exceeds the boundary, the robotic arm maintains the current position information and does not change the end position of the band saw blade, thereby preventing further movement outside the boundary;

[0035] 5-2) If it is determined that the end of the oscillating saw blade is out of bounds at the current moment, it is further determined whether the included angle α between the position vector and the vector pointing to the center point is less than the set threshold. If the included angle is less than the threshold, the robotic arm issues a new position command to control the oscillating saw blade to continue moving in the direction of the force, ensuring that the cutting operation does not go out of bounds; otherwise, the robotic arm maintains the current position information and does not change the end position of the oscillating saw blade, thereby preventing further movement outside the boundary.

[0036] A computer-readable storage medium, on which a computer program is stored. When the computer program is executed by a processor, it implements a method for constructing a virtual wall for tibial resection surgery based on force vector prediction.

[0037] The present invention has the following beneficial effects and advantages:

[0038] 1. By combining real-time position information acquisition and prediction algorithms, the present invention overcomes the lag problem of traditional pure vision systems and can generate virtual wall restrictions in advance when the oscillating saw approaches the surgical boundary, ensuring the rapid response of the system.

[0039] 2. Based on the combination of force sensors and admittance control, the present invention can dynamically predict the position of the oscillating saw according to its movement trajectory and speed, judge the risk of going out of bounds in advance, and actively limit the movement of the oscillating saw to avoid the occurrence of out-of-bounds situations. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 is a flowchart of the method of the present invention;

[0041] Figure 2 is a schematic diagram of the coordinate systems of the robotic arm, the oscillating saw Marker, the saw blade, and the bone cutting plane in the present invention;

[0042] Figure 3 is a schematic diagram of the initial point outside the virtual wall boundary. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0043] The following further describes the present invention in detail with reference to the drawings and embodiments.

[0044] As Figure 1 shown, it is a schematic diagram of the process of the present invention. A method for constructing a virtual wall for tibial resection surgery based on force vector prediction according to the present invention is characterized by including the following steps:

[0045] 1) Calibrate and obtain the multi-coordinate transformation matrices between the base coordinate system of the robotic arm, the navigator coordinate system, the end coordinate system of the oscillating saw, and the bone cutting plane coordinate system;

[0046] 2) Real-time collect the acting force vector through a six-dimensional force sensor and map the force information into the position increment at the end of the robotic arm;

[0047] 3) Predict the position of the end of the oscillating saw of the robotic arm at the next moment according to the position increment;

[0048] 4) Combine the pre-planned virtual boundary to judge whether the current position and the predicted position exceed the boundary;

[0049] 5) Dynamically adjust the position constraint of the end of the oscillating saw according to the out-of-bounds states of the current position and the predicted position, so as to ensure that the end of the oscillating saw blade is always within the virtual boundary.

[0050] The specific steps are as follows. As Figure 2 shown, it is a schematic diagram of the coordinate systems of the robotic arm, the oscillating saw Marker, the saw blade, and the bone cutting plane in the present invention. In each step, the above-mentioned coordinate systems are used;

[0051] Step 1: Navigator calibration and determination of the coordinate system transformation matrix. Before the operation, use the navigator to calibrate the surgical system. The calibration process includes determining the following transformation matrices:

[0052] Eye-to-hand calibration matrix: Determine the transformation matrix from the navigator coordinate system to the robotic arm base coordinate system through eye-to-hand calibration

[0053] Transformation matrix between the end of the saw blade and the oscillating saw Marker: Calibrate the transformation matrix between the coordinate system of the end of the saw blade and the Marker coordinate system on the oscillating saw

[0054] Transformation matrix between the Marker and the navigator coordinate system: Determine the transformation matrix from the Marker coordinate system on the oscillating saw to the navigator coordinate system

[0055] Transformation matrix between the bone cutting plane and the navigator coordinate system: Obtain the transformation matrix from the bone cutting plane coordinate system to the navigator coordinate system through calibration

[0056] Transformation matrix between the robotic arm flange and the oscillating saw Marker: Calibrate the transformation matrix from the robotic arm flange coordinate system to the oscillating saw Marker coordinate system

[0057] Step 2: Calculate the current position of the robotic arm and the pose of the saw blade. Use the position of the end of the robotic arm at the current moment (t0), and combine the above calibration matrices to calculate the pose matrix of the oscillating saw blade in the bone cutting plane coordinate system:

[0058]

[0059] This step can accurately obtain the spatial position of the oscillating saw blade at the current moment, providing basic data for the next prediction and control.

[0060] Step 3: Obtain the applied force vector. Use a six-axis force sensor to obtain the vector of the current applied force F = (Fx, Fy, Fz, Tx, Ty, Tz), including the three-dimensional components of the force and the three-dimensional components of the torque. These data represent the force applied by the doctor's hand to the oscillating saw during the operation and are the basis for calculating the position increment at the next moment.

[0061] Step 4: Calculate the position increment through the force sensor data. According to the force vector data, calculate the acceleration, velocity, and position increment through the admittance control formula. The formula is as follows:

[0062]

[0063] And update the velocity and position in sequence:

[0064]

[0065] where i ∈ {x, y, z} represents the component direction of the force; e is the position vector; M is the mass, which determines the response inertia; B is the damping coefficient, which determines the compliance of the system; K is the stiffness coefficient; Δt is the discrete time step; and scaling_factor is the displacement scaling coefficient used to adjust the control amplitude.

[0066] Step 5: Calculate the pose matrix of the saw blade in the bone cutting coordinate system at the next moment: According to the position increment obtained in the previous step, calculate the position increment at the next moment (t1 = t0 + Δt), and further calculate the pose matrix of the oscillating saw blade in the bone cutting plane coordinate system:

[0067]

[0068] Step 6: Judge according to the pose matrix obtained in Step 2 and in combination with the geometric relationship: If the end of the oscillating saw blade does not cross the boundary at the current moment, go to Step 7; if it crosses the boundary, go to Step 8.

[0069] Step 7: Judge whether it crosses the boundary at the next moment according to the pose matrix obtained in Step 5. If in the judgment of Step 6, the end of the oscillating saw blade does not cross the boundary at the current moment, continue to judge whether the oscillating saw blade crosses the boundary at the next moment. If it does not cross the boundary, execute Step 9; if it crosses the boundary, execute Step 10.

[0070] Step 8 judgment: If the judgment in Step 6 is negative, that is, the end of the current oscillating saw has exceeded the virtual boundary, as Figure 3 shown, then further judge whether the angle α between the position vector and the vector pointing to the center point is less than the set threshold. If the angle is less than the threshold, execute Step 9; otherwise, execute Step 10.

[0071] Step 9: Issue a position command. If the judgment in Step 7 or Step 8 is yes, and the end of the pendulum saw will be within the virtual boundary at the next moment, the robotic arm issues a new position command to control the pendulum saw blade to continue moving in the direction of the force, ensuring that the cutting operation does not cross the boundary.

[0072] Step 10: Maintain the current position. If the judgment in Step 7 or Step 8 is no, the robotic arm maintains the current position information and does not change the end position of the pendulum saw blade, thereby preventing it from continuing to move outside the boundary.

[0073] As Figure 3 shown, this is a situation where the initial point is outside the virtual wall boundary in this embodiment. The specific method for judging whether the current position and the predicted position exceed the boundary is as follows:

[0074] Among them, the virtual wall edge is a pre-planned boundary; obtain the position point coordinates according to the pose matrix of the current position and the predicted position, and calculate the sum of the angles formed by the connections between all virtual contour vertices and the position point starting from the position point;

[0075] If the position point is inside the polygon, the sum of these angles is equal to 2π, that is: 360°, then it is judged that the current position and the predicted position do not exceed the boundary; if the position point is outside the polygon and the sum of the angles is 0, it is judged that the current position and the predicted position exceed the boundary.

[0076] Based on the above embodiments, the method mentioned in this embodiment combines real-time position information acquisition and prediction algorithms to actively generate virtual wall restrictions when the pendulum saw approaches the surgical boundary, avoiding the occurrence of out-of-bounds situations. By real-time sensing the movement trajectory of the pendulum saw and dynamically predicting its position, it ensures that the surgical operation is always completed within the set boundary. Compared with the traditional pure vision system, this method significantly improves the real-time performance and pre-judgment ability of the system, can effectively reduce the risk of surgical area injury, and further improve the safety and accuracy of tibial resection surgery.

[0077] Those skilled in the art can understand that the above are only the preferred embodiments of the present invention. The features described in each embodiment and / or claim of the present disclosure can be combined or combined in various ways, even if such combinations or combinations are not explicitly recorded in the present disclosure. It is not used to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, for those skilled in the art, they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements on some of the technical features. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

[0078] Although the preferred embodiments of the present invention have been described, additional changes and modifications can be made to these embodiments by those skilled in the art once they learn the basic creative concept. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the present invention. Obviously, those skilled in the art can make various changes and variations to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalent technologies, the present invention is also intended to include these modifications and variations.

Claims

1. A method for constructing a virtual wall for tibial resection surgery based on force vector prediction, characterized in that: The following steps are involved: 1) Calibrate and obtain the multi-coordinate transformation matrix between the robot base coordinate system and the navigator coordinate system, the oscillating saw end coordinate system and the bone cutting plane coordinate system; 2) The force vector is collected in real time through a six-dimensional force sensor, and the force information is mapped into the position increment of the end of the robotic arm; 3) Based on the position increment, predict the position of the end of the swing saw of the robot arm at the next moment; 4) Combined with the pre-planned virtual boundary, determine whether the current position and the predicted position exceed the boundary; 5) Dynamically adjust the end position constraint of the swing saw according to the out-of-bounds status of the current position and the predicted position, so that the end of the swing saw blade is always within the virtual boundary.

2. The method for constructing a virtual wall for tibial resection surgery based on force vector prediction according to claim 1, characterized in that: The step 1) is specifically: Use the navigator to calibrate the hand-eye calibration matrix, that is, the transformation matrix from the navigator coordinate system to the robot base coordinate system, which is defined as The transformation matrix from the saw blade end coordinate system to the marker on the swing saw is calibrated and defined as The transformation matrix from the Marker coordinate system on the oscillating saw to the navigator coordinate system is defined as The transformation matrix from the bone cutting plane coordinate system to the navigator coordinate system is defined as The transformation matrix from the robot flange coordinate system to the swing saw Marker coordinate system is defined as 3. The method for constructing a virtual wall for tibial resection surgery based on force vector prediction according to claim 1, characterized in that: The step 2) is specifically: 2-1) According to the flange set at the end of the robot arm, the transformation matrix from the robot arm flange coordinate system to the robot arm base coordinate system at the current time t0 is obtained, which is defined as Calculate the position matrix of the saw blade in the bone cutting plane coordinate system at the current time t0 2-2) The applied force is obtained by the six-dimensional force sensor installed on the robot arm, and the force vector is defined as: F = (F x ,F y ,F z ,T x ,T y ,T z ); 2-3) The force vector is mapped into position increment through the admittance formula, that is, based on the obtained force vector information, the acceleration is calculated as: And update the velocity and position of the force component direction i in turn: Among them, i∈{x,y,z} represents the component direction of the force; e is the position vector; M is the mass, which determines the response inertia; B is the damping coefficient, which determines the flexibility of the system; K is the stiffness coefficient; Δt is the discrete time step; scaling_factor is the displacement scaling factor, which is used to adjust the control amplitude.

4. The method for constructing a virtual wall for tibial resection surgery based on force vector prediction according to claim 1, characterized in that: The step 3) is specifically: According to the position increment, the position increment at the next moment (t1=t0+Δt) is calculated, and then the transformation matrix from the robot flange coordinate system to the robot base coordinate system at moment t1 is obtained, which is defined as And further calculate the pose matrix of the oscillating saw blade in the bone cutting plane coordinate system at the next moment: From the pose matrix Extract the position information, that is, the first three lines of the fourth column of the pose matrix are the position coordinate values.

5. The method for constructing a virtual wall for tibial resection surgery based on force vector prediction according to claim 1, characterized in that: The combination of the pre-planned virtual boundary and determining whether the current position and the predicted position exceed the boundary is specifically as follows: Obtain the coordinates of the position point according to the pose matrix of the current position and the predicted position, and calculate the sum of the angles formed by the lines connecting all virtual contour vertices and the position point starting from the position point; If the location point is inside the polygon, the sum of these angles is equal to 2π, that is, 360°, and it is judged that the current location and the predicted location are within the boundary; If the location point is outside the polygon and the sum of the angles is 0, it is determined that the current location and the predicted location are out of bounds.

6. The method for constructing a virtual wall for tibial resection surgery based on force vector prediction according to claim 1, characterized in that: In step 5), the position constraint of the end of the swing saw is dynamically adjusted according to the out-of-bounds status of the current position and the predicted position, specifically: 5-1) If it is determined that the end of the oscillating saw blade has not crossed the boundary at the current moment, continue to determine whether the oscillating saw blade has crossed the boundary at the next moment. If it has not crossed the boundary, the robot arm sends a new position instruction to control the oscillating saw blade to continue to move in the direction of the force to ensure that the cutting operation does not cross the boundary; if it has crossed the boundary, the robot arm maintains the current position information and does not change the end position of the oscillating saw blade, thereby preventing it from continuing to move outside the boundary; 5-2) If it is determined that the end of the oscillating saw blade is out of bounds at the current moment, it is further determined whether the angle α between the position vector and the vector pointing to the center point is less than the set threshold. If the angle is less than the threshold, the robotic arm sends a new position instruction to control the oscillating saw blade to continue moving in the direction of the force to ensure that the cutting operation does not cross the boundary; otherwise, the robotic arm maintains the current position information and does not change the end position of the oscillating saw blade, thereby preventing it from continuing to move out of the boundary.

7. A computer-readable storage medium, characterized in that: The storage medium stores a computer program, and when the computer program is executed by the processor, the method for constructing a virtual wall for tibial resection surgery based on force vector prediction as described in any one of claims 1 to 6 is implemented.

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