A method for calibrating the end effector of a robotic arm

Abstract

This invention discloses a method for calibrating the end effector of a robotic arm, comprising: identifying marker points on the end effector using an optical positioning system to obtain the pose of the end effector relative to the optical positioning system; setting a point on the end effector of the robotic arm, and setting three directions based on this point, controlling the movement of the robotic arm to cause the end effector to perform spherical motion around the point and rotational motion around the three directions as axes, obtaining the position of the marker point during the movement through the optical positioning system, and calculating the pose of the end effector relative to the optical positioning system accordingly; obtaining the pose of the end effector relative to the robotic arm system based on the robotic arm design parameters, and calculating the pose of the end effector relative to the robotic arm system accordingly. This invention can quickly calibrate the end effector of a robotic arm, enabling the "arm" and "eye" of the surgical robot to accurately know the position of the "hand," thereby achieving coordination between the "arm" and "eye."

Description

Technical Field

[0001] This invention relates to the field of robotics, and more particularly to a method for calibrating the end effector of a robotic arm. Background Technology

[0002] Surgical robots are integrated systems combining multiple modern high-tech methods and are currently used in various fields such as orthopedics, neurosurgery, and endourology. Taking surgical navigation robots as an example, they can use robotic arms to assist in the positioning of surgical instruments, helping doctors to perform visual surgical planning and surgical channel positioning, thereby improving surgical precision and reducing surgical trauma.

[0003] Currently, the main actuator in surgical assisted navigation robot systems is the robotic arm. By installing specific structural components at the end of the robotic arm as a specific "hand," it performs specific gripping or positioning functions during surgery. To ensure the accuracy of this specific "hand's" gripping or positioning, it is necessary to accurately determine the relative positional relationship between the structural components installed at the end of the robotic arm and the robotic arm's own coordinate system.

[0004] In existing technologies, a widely used method is to obtain the key reference parameters on the end effector structure by measuring them using a high-precision coordinate measuring machine (CMM). Using the robot arm coordinate system as the reference coordinate system, the pose of the CMM coordinate system is obtained, and the pose of the structural component relative to the CMM coordinate system is obtained through the CMM. Matrix transformation is then performed to obtain the pose of the structural component relative to the robot arm coordinate system. However, this method has the following drawbacks: Firstly, high-precision CMMs are expensive; secondly, because conventional CMMs are three-axis structures and use contact measurement, for complex structural components, especially those with complex curved surfaces, very complex fixtures or specially designed probes need to be designed. Furthermore, the structural component needs to be adjusted to a suitable pose before both sides can be measured, which is very inconvenient and significantly reduces calibration efficiency. Summary of the Invention

[0005] Purpose of the invention: To address the above-mentioned shortcomings, this invention proposes a calibration method for the end effector of a robotic arm, which can quickly achieve the calibration of the end effector of the robotic arm.

[0006] Technical solution:

[0007] A method for calibrating the end effector of a robotic arm, comprising:

[0008] The pose of the end-effector relative to the optical positioning system is obtained by identifying the marker points on the end-effector.

[0009] Set a point on the end effector of the robotic arm, and set three directions based on this point. Control the movement of the robotic arm so that the end effector moves spherically around the point and rotates around the three directions. Obtain the position of the marker point during the movement through the optical positioning system, and calculate the pose of the end effector relative to the optical positioning system.

[0010] The pose of the end effector relative to the robotic arm system is obtained based on the design parameters of the robotic arm, and the pose of the end effector relative to the robotic arm system is calculated accordingly.

[0011] The specific pose of the end effector of the computational robotic arm relative to the optical positioning system is as follows:

[0012] During the spherical motion, the sphere is fitted with the position of the marked point obtained by the optical positioning system, and the center of the sphere is the position of the point on the end of the robotic arm relative to the optical positioning system. Thus, the position of the end of the robotic arm relative to the optical positioning system is obtained.

[0013] During the rotational motion, the corresponding circular surfaces in each direction are fitted according to the positions of the marked points obtained by the optical positioning system, and the normals of these three directions are obtained. These three directions are the directions of the optical positioning system, and thus the posture of the robotic arm end relative to the optical positioning system is obtained.

[0014] The position and orientation of the robotic arm end relative to the optical positioning system are obtained by combining the above position and orientation.

[0015] When the end of the robotic arm is in its initial pose, it performs the spherical motion and the rotational motion, respectively.

[0016] Both the spherical motion and the rotational motion are movements performed by the end component with a specific angular step size.

[0017] The specific angle step size is 10°.

[0018] The three directions are orthogonal to each other.

[0019] The range of the spherical motion is hemispherical.

[0020] The markers on the end component are at least three coplanar but non-collinear markers. If the optical positioning system obtains fewer than three markers, the position information obtained in this movement is ignored.

[0021] Beneficial effects:

[0022] 1. This invention can quickly calibrate the end effector of a robotic arm, enabling the surgical robot's "arm" and "eye" to accurately know the position of the "hand," thereby achieving coordination between the "arm" and "eye."

[0023] 2. This invention does not require a high-precision coordinate measuring machine, which greatly reduces equipment costs. It can improve the accuracy and efficiency of calibration based on multi-data fitting. Attached Figure Description

[0024] Figure 1 A schematic diagram of the end effector of a robotic arm and its end effector components;

[0025] Figure 2 This is a flowchart illustrating the calibration of the robotic arm end effector of the present invention;

[0026] Figure 3 This is a schematic diagram of the trajectory of the origin of the second coordinate system when the end component moves spherically around the origin of the first coordinate system;

[0027] Figure 4 This is a schematic diagram of the trajectory of the end component along the x-axis of the second coordinate system when it moves spherically around the origin of the first coordinate system.

[0028] In this designation, 1 represents the robotic arm, 2 represents the optical positioning system, 3 represents the end effector, and 11 represents the end effector of the robotic arm. Detailed Implementation

[0029] The present invention will be further explained below with reference to the accompanying drawings and specific embodiments.

[0030] Reference Figure 1 The device for implementing the present invention includes a robotic arm system, an end effector, and an optical positioning system;

[0031] The robotic arm system includes a robotic arm capable of multi-degree-of-freedom motion. Typically, the robotic arm includes multiple support arms connected by joints. The robotic arm is controlled by an industrial control computer, and the industrial control computer and the robotic arm can be integrated to form a robotic arm trolley. In this embodiment, the industrial control computer can realize 6-degree-of-freedom motion at the end of the robotic arm.

[0032] An end effector is mounted at the end of a robotic arm, which here refers to the free end of the last of a series of sequentially connected support arms. Taking an orthopedic surgical robot as an example, the end effector can be a mounting base fixed to the end of the robotic arm and a guide detachably mounted on the mounting base. The guide can position and hold devices such as Kirschner wire positioning sleeves. The end effector has multiple markers installed for identification and positioning by an optical positioning system. These markers can be optically detectable objects such as tracer balls or LEDs.

[0033] An optical positioning system includes an optical detector, which can identify the position of preset marker points and thus obtain the pose of the corresponding device (or the pose of a coordinate system constructed with the marker points).

[0034] The robotic arm is the execution component, equivalent to the "arm" of the surgical robot system; the end effector is equivalent to the "hand"; and the optical positioning system is equivalent to the "eye." To achieve precise positioning during surgery, the surgical robot system needs to transmit the pose information seen by the "eye" to the "arm" to control the "hand" to move precisely to the accurate position to perform the relevant operations. Therefore, the parameters (specifically, the pose) of the robotic arm's end effector need to be calibrated before surgery to enable rapid and accurate positioning of the end effector during the procedure.

[0035] Reference Figure 2 The robotic arm end effector calibration method of the present invention includes the following steps:

[0036] (1) Coordinate system configuration;

[0037] Specifically, a first basic coordinate system is configured for the robotic arm system, a second basic coordinate system is configured for the optical positioning system, a first motion coordinate system is configured for the robotic arm end effector, and a second motion coordinate system is configured for the end effector component.

[0038] Taking the configuration process of the first basic coordinate system as an example, the robot arm base of the robotic arm system can be determined as the origin of its coordinate system. The vertically upward direction passing through this origin is set as the z-axis of the first basic coordinate system, and the corresponding x-axis and y-axis are determined by the right-hand rule. The configuration methods for other coordinate systems can refer to the configuration method of the first basic coordinate system. Of course, the determination criteria for the origin and axes of each coordinate system can also be adjusted according to actual usage requirements.

[0039] It should be noted that, generally, once the position of the robotic arm system is fixed, the first basic coordinate system is also determined. Furthermore, in this case, the first basic coordinate system will not change with the movement of the robotic arm. Correspondingly, once the position of the optical positioning system is fixed, the second basic coordinate system will also remain unchanged. However, regarding the first and second motion coordinate systems, the end effector is rigidly connected to the end effector of the robotic arm. As the robotic arm moves, the pose of both the end effector and its end effector will change. This means that the first motion coordinate system, established as described above, will typically change, requiring real-time updates. Similarly, once the robotic arm or the end effector moves, the second motion coordinate system, also established as described above, will typically change, requiring real-time updates as well.

[0040] Furthermore, since the positions of the markers on the end effector are fixed, if the positions of the markers can be determined, a second motion coordinate system can be established in real time using the aforementioned configuration process. To ensure this, the number of markers must be at least three, and these three markers cannot be placed on the same fitted straight line. In this embodiment, four markers are used to maximize the probability that the markers will be recognized by the optical positioning system. This allows the optical positioning system to determine the second motion coordinate system based on three of the markers when the end effector is in different poses.

[0041] (2) Obtain the transformation relationship between the first motion coordinate system and the second base coordinate system;

[0042] (21) Obtain the translation vector of the first motion coordinate system relative to the second base coordinate system;

[0043] a. Keep the robotic arm system and optical positioning system in a fixed position, and control the movement of the robotic arm by issuing operation commands through the industrial control computer, so that the end effector of the robotic arm performs spherical motion around the origin of the first motion coordinate system with a specific angular step size, such as... Figure 3 As shown, after each movement, a certain period of time is paused for the optical positioning system to collect the position information of the marker points on the end component; if the optical positioning system does not collect the information, the position information obtained in that movement is ignored; wherein, the set pause time is determined according to the position data collection time of the optical positioning system; in this embodiment, the trajectory of the spherical motion can be planned in the negative to positive range of the x-axis and y-axis of the first motion coordinate system (i.e., a hemispherical trajectory located in the positive z-axis direction), with a specific angular step size of 10°.

[0044] b. Determine the position information of the origin of the second motion coordinate system based on the position information of the marker points collected each time, and denot it as point p. i In this case, the trajectory points of the origin of the second motion coordinate system constructed based on the marker points on the end member are as follows: Figure 2 As shown. Considering the fixed position of the optical positioning system, the movement of the end effector may cause some marker points to be obstructed, preventing the optical positioning system from fully acquiring the position information of the four marker points on the end effector. If the number of marker points that can be acquired is less than three when the end effector moves to a certain position, the position information of the origin of the second motion coordinate system corresponding to that position cannot be determined, and this position information is directly ignored. Without considering the unacquired origin position information, the number of hemispherical trajectory points can reach 18*18, and the position information of these trajectory points is marked as a point set {p}. i}, where i = 1, 2, 3, ..., n; n ≤ 18 * 18.

[0045] c. For each point p in the above point set {pi} iBy performing spherical fitting, the coordinates of the center of the fitted sphere in the second base coordinate system are obtained. This coordinate information is the coordinates of the origin of the first motion coordinate system in the second base coordinate system. Based on this coordinate information, the translation vector T of the first motion coordinate system relative to the second base coordinate system is determined. trans ;

[0046] In this invention, in this step, the position information of each marker point obtained by the optical positioning system can be used to fit a sphere with each marker point to obtain the center of several fitted spheres. The coordinate information of the origin of the first motion coordinate system in the second basic coordinate system can be obtained by averaging.

[0047] (22) Obtain the direction vector of the first motion coordinate system relative to the second base coordinate system, specifically including the direction vector R along the x-axis. x The direction vector R along the y-axis y and the direction vector R along the z-axis z The details are as follows:

[0048] a. Keep the positions of the robotic arm system and the optical positioning system fixed, and obtain the initial pose of the robotic arm end effector through the industrial control computer, thereby obtaining the transformation relationship T between the first motion coordinate system and the first base coordinate system. r1 And use it as the initial transformation relation;

[0049] b. The industrial control computer controls the robotic arm to rotate so that the x-axis of the first motion coordinate system points to the origin of the second base coordinate system, and acquires and records the change T of this rotation. x The industrial control computer controls the robotic arm to rotate the end effector around the x-axis of the first motion coordinate system, and forms several acquisition positions in specific angular steps (10 degrees in this invention), such as... Figure 4 As shown;

[0050] c. The optical positioning system identifies and acquires the position information of the origin of the second motion coordinate system C2 at each acquisition location, obtaining the point set {P}. xj}, where j = 1, 2, 3...k; k ≤ 36; perform spatial circle fitting on this point set to obtain the normal vector T of the fitted circle facing the optical positioning system. vx This allows us to obtain the direction vector R of the first motion coordinate system relative to the second base coordinate system in the x-axis direction when the robotic arm is in its initial position. x =T vx *T x -1 , among which, T x -1 T represents x The inverse operation;

[0051] d. The industrial control computer controls the robotic arm to return its end effector to its initial pose, and also to the initial transformation relationship between the first motion coordinate system and the first base coordinate system. Referring to steps a to c, the direction vector R of the first motion coordinate system relative to the second base coordinate system in the y and z directions is obtained. y R z ;

[0052] (23) Based on steps (21) and (22), obtain the transformation relationship T between the first motion coordinate system and the second base coordinate system. e1 =[T trans ,R x ,R y ,R z ].

[0053] In this invention, step (2) obtains the pose of the end effector of the robotic arm in the second base coordinate system, that is, the pose transformation relationship of the end effector of the robotic arm relative to the optical positioning system. Therefore, this invention does not have to adopt the above method. It can define a point on the end effector of the robotic arm as its position, and obtain the center of several fitted spheres by fitting the position information of each marker point obtained in step (21). Based on this, the position of the point is calculated, that is, the position of the end effector of the robotic arm in the second base coordinate system. Then, three directions are set based on the point, and the direction vector of each direction relative to the second base coordinate system is obtained through step (22), that is, the posture of the end effector of the robotic arm in the second base coordinate system. Finally, the pose of the end effector of the robotic arm in the second base coordinate system is obtained.

[0054] (3) Obtain the transformation relationship T between the second motion coordinate system and the second base coordinate system. e2 ;

[0055] Keeping the positions of the robotic arm system and the optical positioning system fixed in step (2), the robotic arm is controlled to return its end effector to its initial pose. The position of each marker point on the end effector is identified and located by the optical positioning system. Based on the correspondence between each marker point and the second motion coordinate system, the transformation relationship T of the second motion coordinate system relative to the second base coordinate system is obtained. e2 .

[0056] It should be noted that this step can be performed immediately after step (21) or simultaneously with step (21) to improve efficiency.

[0057] In this invention, this step is actually to obtain the pose of the end component in the second base coordinate system, that is, the pose transformation relationship of the end component relative to the optical positioning system. Then, the position of each marker point on the end component can be calculated by identifying and locating the position of the end component through the optical positioning system.

[0058] (4) Obtain the transformation relationship T between the second motion coordinate system and the first motion coordinate system. 12 ;

[0059] The transformation relationship T between the second motion coordinate system and the first motion coordinate system is calculated based on steps (2) and (3). 12 =T e2 *T e1 -1 , among which, T e1 -1 T represents e1 Inverse operation;

[0060] In this invention, this step is actually to obtain the pose transformation relationship of the end effector relative to the end effector of the robotic arm. Then, the pose transformation relationship of the end effector of the robotic arm relative to the optical positioning system obtained in step (2) and the pose transformation relationship of the end effector relative to the optical positioning system obtained in step (3) can be calculated.

[0061] (5) Calculate the transformation relationship between the second motion coordinate system and the first base coordinate system;

[0062] The pose relationship T of the first motion coordinate system of the robotic arm end effector relative to the first base coordinate system of the robotic arm system. r1 The transformation relationship T between the second motion coordinate system and the first base coordinate system can be calculated based on the transformation relationship between the second motion coordinate system and the first motion coordinate system obtained in step (4). r2 =T r1 *T 12 .

[0063] In this invention, the calibration of the end effector of the robotic arm is actually to obtain the pose of the end effector in the first base coordinate system and the second base coordinate system. Therefore, this invention may not require the establishment of the first motion coordinate system and the second motion coordinate system of the end effector, or even the configuration of the first base coordinate system and the second base coordinate system. It is only necessary to control the movement of the robotic arm in step (2) so that the end effector of the robotic arm moves spherically around a set point on the end effector of the robotic arm with a specific angular step. Then, multiple poses of the end effector are obtained through the optical positioning system, and the position of the set point on the end effector of the robotic arm relative to the optical positioning system can be obtained by spherical fitting of any point on the end effector. Thus, the position of the end effector of the robotic arm relative to the optical positioning system can be obtained. The position of the positioning system is determined, and then three directions are set based on the set point on the end of the robotic arm, that is, three directional axes are set through the point. The direction vector of each direction relative to the optical positioning system is obtained through step (22), and the pose of the end of the robotic arm relative to the optical positioning system is obtained. The position of the marked point on the end component can be directly identified in real time through the optical positioning system, and the real-time pose of the end component relative to the optical positioning system can be calculated. Based on the above and the pose of the end of the robotic arm relative to the robotic arm system provided by the industrial control computer, the pose of the end component relative to the robotic arm system can be calculated, so that the "arm" and "eye" of the mobile phone robot can accurately know the position of the "hand" and complete the calibration of the end component.

[0064] Furthermore, the spherical motion and rotational motion in step (2) are used to obtain the position and orientation of the robotic arm end relative to the optical positioning system, and the order of the two can be adjusted.

[0065] In summary, this invention enables the "arm" of a surgical robot to accurately know the position of the "hand," and through an optical positioning system, it can directly obtain the pose T of the second motion coordinate system in the second basic coordinate system by identifying marker points on the positioning end component. e2 This means that the "eye" can also obtain the precise position of the "hand," thereby achieving coordination between the "arm" and the "eye." Furthermore, this invention does not require a high-precision coordinate measuring machine, which significantly reduces equipment costs. On the other hand, it enables rapid identification and positioning of multiple marker points on the end-effector, and improves the accuracy and efficiency of end-effector calibration based on multi-data fitting.

[0066] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the specific details of the above embodiments. Within the scope of the technical concept of the present invention, various equivalent transformations (such as quantity, shape, position, etc.) can be made to the technical solution of the present invention, and these equivalent transformations all fall within the protection scope of the present invention.

Claims

1. A method for calibrating the end effector of a robotic arm, characterized in that: include: The pose of the end-effector relative to the optical positioning system is obtained by identifying the marker points on the end-effector. Set a point on the end effector of the robotic arm, and set three directions based on this point. Control the movement of the robotic arm so that the end effector moves spherically around this point and rotates around the three directions as axes. Obtain the position of the marker point during the movement through an optical positioning system. During the spherical motion, the sphere is fitted with the position of the marked point obtained by the optical positioning system, and the center of the sphere is the position of the point on the end of the robotic arm relative to the optical positioning system. Thus, the position of the end of the robotic arm relative to the optical positioning system is obtained. During the rotational motion, the corresponding circular surfaces in each direction are fitted according to the positions of the marked points obtained by the optical positioning system, and the normals of these three directions are obtained. These three directions are the directions of the optical positioning system, and thus the posture of the robotic arm end relative to the optical positioning system is obtained. The pose of the robotic arm's end effector relative to the optical positioning system is obtained by combining the above position and orientation. The pose of the end effector relative to the robotic arm system is obtained based on the design parameters of the robotic arm, and the pose of the end effector relative to the robotic arm system is calculated accordingly.

2. The method for calibrating the end effector of a robotic arm according to claim 1, characterized in that: When the end of the robotic arm is in its initial pose, it performs the spherical motion and the rotational motion, respectively.

3. The method for calibrating the end effector of a robotic arm according to claim 2, characterized in that: Both the spherical motion and the rotational motion are movements performed by the end component with a specific angular step size.

4. The method for calibrating the end effector of a robotic arm according to claim 3, characterized in that: The specific angle step size is 10°.

5. The method for calibrating the end effector of a robotic arm according to claim 1, characterized in that: The three directions are orthogonal to each other.

6. The method for calibrating the end effector of a robotic arm according to claim 1, characterized in that: The range of the spherical motion is hemispherical.

7. The method for calibrating the end effector of a robotic arm according to claim 1, characterized in that: The markers on the end component are at least three coplanar but non-collinear markers. If the optical positioning system obtains fewer than three markers, the position information obtained in this movement is ignored.

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