CN112571416A - Coordinate system calibration method suitable for robot system and motion capture system - Google Patents

Coordinate system calibration method suitable for robot system and motion capture system Download PDF

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CN112571416A
CN112571416A CN202011457099.XA CN202011457099A CN112571416A CN 112571416 A CN112571416 A CN 112571416A CN 202011457099 A CN202011457099 A CN 202011457099A CN 112571416 A CN112571416 A CN 112571416A
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coordinate system
rigid body
robot
motion capture
virtual
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CN112571416B (en
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贺京杰
邓双城
徐枫
刘强
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Beijing Institute of Petrochemical Technology
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B25—HAND TOOLS; PORTABLE POWER-DRIVEN TOOLS; MANIPULATORS
    • B25J—MANIPULATORS; CHAMBERS PROVIDED WITH MANIPULATION DEVICES
    • B25J9/00—Programme-controlled manipulators
    • B25J9/16—Programme controls
    • B25J9/1679—Programme controls characterised by the tasks executed
    • B25J9/1692—Calibration of manipulator

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Abstract

The invention discloses a coordinate system calibration method suitable for a robot system and a motion capture system, which comprises the steps of firstly, initializing the pose in the motion capture system aiming at any rigid body with a marker ball in the robot system, and having no limit to the pose; obtaining an expression mode of the positive direction vector of the axis X, Y, Z of the virtual rigid body coordinate system in a world coordinate system; obtaining an expression mode Q of the posture of the robot base coordinate system under a world coordinate system of a motion capture system1(ii) a Direct reading of attitude Q of virtual controller rigid body by motion capture system2(ii) a Then setting a coordinate system Q of the robot end effector3The attitude of (a); and keeping the coordinate system of the robot end effector consistent with the initial posture of the rigid body of the virtual controller or setting a determined posture conversion relation according to a chain method. The method can accurately map rigid body postures of the robot end effector and the virtual controller in the motion capture system, so that the two calibrated coordinate systems do not contain posture errors, and the calibration accuracy is improved.

Description

Coordinate system calibration method suitable for robot system and motion capture system
Technical Field
The invention relates to the technical field of robot control, in particular to a coordinate system calibration method suitable for a robot system and a motion capture system.
Background
The automatic motion control of video cameras is one of the key technologies in future movies, and various camera business-grade video camera motion control systems, such as BOLT, etc., are available at present. In recent years, motion capture systems have been developed as an emerging technology, which capture characteristic signals of a moving object by using sensors such as optics and inertia to realize a function of tracking a target position and posture in real time. In a motion capture system, the tracked objects are cursor points, and each cursor point has a position coordinate which can be tracked. If the tracked object is a rigid body, the rigid body is represented by 4 cursor points which are not mutually positioned on the same plane, and is called a virtual rigid body, and when the rigid body is regarded as a camera in a virtual space, the rigid body is called a virtual controller rigid body. It is customary in the industry that the lens direction of the virtual camera is the Z-axis direction, the top surface of the virtual camera is the Y-axis direction, and the pose of the robot end effector coordinate system should be consistent with the pose of the virtual camera. The motion capture system uses a world coordinate system calibration scale as a reference coordinate system, the robot system sets a base coordinate system near a base, and when a virtual rigid body in the motion capture system is used for controlling the motion of the end effector of the mechanical arm, the posture and the motion track of the end effector of the robot are consistent with the virtual rigid body no matter how the robot is placed, so that the coordinate systems of the two systems need to be calibrated.
The calibration scheme in the prior art is that the directions of a world coordinate system X, Y and Z of an action capture system and a base coordinate system X, Y and Z of a robot are set to be consistent, a marker ball which can be identified by an optical capture system is pasted on a desktop of the robot, the relative position and pose relationship between the marker ball and the base of the robot is measured, and the relationship is introduced into an ROS system. The mathematical expression of the calibration operation is a formula
Figure BDA0002829097790000011
Namely measuring the pose of the robot desktop relative to the world coordinate system of the optical motion capture system and then measuringMeasuring the pose of the robot base relative to the robot desktop, and obtaining the pose expression of the robot base UR relative to the world coordinate system of the optical motion capture system through a transmission rule. In the scheme, the base coordinate system of the robot is usually not located at the center of the robot base, so that the pose of the robot relative to the desktop marker point cannot be accurately determined; in addition, the robot body is heavy, fine adjustment of the posture of the robot body is difficult to achieve in reality, meanwhile, random variation errors can be caused when the system is installed every time, and in the system installation stage, the optical capture system world coordinate system, the robot desktop marker spherical coordinate system and the mechanical arm base coordinate system are required to be guaranteed to be consistent in posture, so that the robot is inconvenient to install and use.
Disclosure of Invention
The invention aims to provide a coordinate system calibration method suitable for a robot system and a motion capture system, which can accurately map rigid body postures of a robot end effector and a virtual controller in the motion capture system, so that two calibrated coordinate systems do not contain posture errors, and the calibration accuracy is improved.
The purpose of the invention is realized by the following technical scheme:
a coordinate system calibration method suitable for use in robotic systems and motion capture systems, the method comprising:
step 1, firstly, initializing the pose in an action capturing system aiming at any rigid body with a marker ball in a robot system, wherein the pose is not limited;
step 2, fixedly mounting the calibrated virtual rigid body on a robot end effector in any posture and at any position;
step 3, obtaining the origin position of the virtual rigid body coordinate system by using the motion capture system, and obtaining the expression mode of the positive direction vector of the axis X, Y, Z of the virtual rigid body coordinate system in the world coordinate system of the motion capture system;
step 4, obtaining an expression mode Q of the posture of the robot base coordinate system under the world coordinate system of the motion capture system according to the expression mode obtained in the step 31；
Step 5, taking down the virtual rigid body as a virtual controller rigid body, and directly reading the posture Q of the virtual controller rigid body through the motion capture system2；
Step 6, setting a robot end effector coordinate system Q according to the actual application situation3I.e. the pose of the robot tool coordinate system relative to the robot base coordinate system;
and 7, keeping the coordinate system of the robot end effector consistent with the initial posture of the rigid body of the virtual controller or setting a determined pose conversion relation according to a chain rule to finish the calibration of the coordinate system.
According to the technical scheme provided by the invention, the rigid body postures of the robot end effector and the virtual controller in the motion capture system can be accurately mapped, so that the two calibrated coordinate systems do not contain posture errors, and the calibration accuracy is improved.
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In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings needed to be used in the description of the embodiments are briefly introduced below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings based on the drawings without creative efforts.
Fig. 1 is a schematic flowchart of a coordinate system calibration method suitable for a robot system and a motion capture system according to an embodiment of the present invention;
fig. 2 is a schematic diagram of coordinate system calibration according to an embodiment of the present invention.
Detailed Description
The technical solutions in the embodiments of the present invention are clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments of the present invention without making any creative effort, shall fall within the protection scope of the present invention.
The embodiments of the present invention will be described in further detail with reference to the accompanying drawings, and fig. 1 is a schematic flow chart of a coordinate system calibration method suitable for a robot system and a motion capture system according to the embodiments of the present invention, where the method includes:
step 1, firstly, initializing the pose in an action capturing system aiming at any rigid body with a marker ball in a robot system, wherein the pose is not limited;
step 2, fixedly mounting the calibrated virtual rigid body on a robot end effector in any posture and at any position;
step 3, obtaining the origin position of the virtual rigid body coordinate system by using the motion capture system, and obtaining the expression mode of the positive direction vector of the axis X, Y, Z of the virtual rigid body coordinate system in the world coordinate system of the motion capture system;
in this step, the process of obtaining the expression manner of the positive direction vector of the virtual rigid body coordinate system X, Y, Z in the world coordinate system of the motion capture system specifically includes:
respectively enabling the robot to move for any long distance (more than 20cm is recommended) based on the X axis of the base coordinate system, recording the origin coordinates of the virtual rigid body coordinate system in the initial state and the final state, and respectively recording the origin coordinates as P1And P2；
Then, subtracting the initial state origin coordinate from the final state origin coordinate to obtain an expression mode of the positive direction vector of the X axis of the virtual rigid body coordinate system in the world coordinate system of the motion capture system;
Vx＝P2-P1
the expression mode of the Y-axis and the Z-axis of the virtual rigid body coordinate system in the world coordinate system of the motion capture system is obtained in the same way and is marked as VyAnd Vz。
Step 4, obtaining an expression mode Q of the posture of the robot base coordinate system under the world coordinate system of the motion capture system according to the expression mode obtained in the step 31；
In this step, Q1Expressed as:
Q1＝f(Vx,Vy,Vz)
and the f function is a standard vector passing through a coordinate axis, and an attitude quaternion is solved.
Step 5, taking down the virtual rigid body as a virtual controller rigid body, and directly reading the posture Q of the virtual controller rigid body through the motion capture system2；
Step 6, setting a robot end effector coordinate system Q according to the actual application situation3I.e. the pose of the robot tool coordinate system relative to the robot base coordinate system;
in a specific implementation, for example, the rigid body of the virtual controller requires that the positive direction of the Z axis is the lens shooting direction, the normal vector direction of the top surface of the camera is the Y axis (customary in the industry), and the posture of the end effector is set for this purpose.
And 7, keeping the coordinate system of the robot end effector consistent with the initial posture of the rigid body of the virtual controller or setting a determined pose conversion relation according to a chain rule to finish the calibration of the coordinate system.
In this step, as shown in fig. 2, which is a schematic diagram of coordinate system calibration according to the embodiment of the present invention, according to the chain rule, the following relationship exists:
Q2·Q1＝Q4·Q3；
wherein Q is4Representing the transformation of the robot tool coordinate system to the virtual rigid body controller coordinate system;
thereby obtaining Q4Is expressed as
Figure BDA0002829097790000041
In the specific implementation, after the coordinate system calibration is completed in step 7, in the motion process, the robot end effector coordinate system can correctly track the virtual controller rigid body coordinate system or track the virtual controller rigid body coordinate system in an arbitrary functional relationship, specifically:
when the rigid body of the virtual controller moves and rotates in space, the motion capture system transmits the posture of the rigid body of the virtual controller to the upper computer system and converts the posture of the rigid body of the virtual controller into a table under a robot base coordinate systemTo be, recorded as Qm；
At this time, the robot end effector coordinate system only needs to execute Q ═ Q4·Qm·Q3And dynamic tracking can be realized.
In addition, the coordinate system of the robot end effector can be aligned with the coordinate system of the mobile platform through the design of cylindrical surface mechanism matching, positioning pins and the like; when the robot base coordinate system is calibrated in the motion capture system, the mobile platform coordinate system is also calibrated together.
By the calibration method, no matter how the robot is placed, after the rigid body of the virtual controller is calibrated, the virtual lens direction set by the external handle of the virtual controller corresponds to the world coordinate system direction of the motion capture system. For example, when the virtual lens is set to the Z-axis, the virtual control direction of the virtual rigid body external grip should also be the Z-axis direction.
It is noted that those skilled in the art will recognize that embodiments of the present invention are not described in detail herein.
The above description is only for the preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present invention are included in the scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claims.

Claims (5)

1. A coordinate system calibration method suitable for use in a robotic system and a motion capture system, the method comprising:
step 1, firstly, initializing the pose in an action capturing system aiming at any rigid body with a marker ball in a robot system, wherein the pose is not limited;
step 2, fixedly mounting the calibrated virtual rigid body on a robot end effector in any posture and at any position;
step 3, obtaining the origin position of the virtual rigid body coordinate system by using the motion capture system, and obtaining the expression mode of the positive direction vector of the axis X, Y, Z of the virtual rigid body coordinate system in the world coordinate system of the motion capture system;
step 4, obtaining an expression mode Q of the posture of the robot base coordinate system under the world coordinate system of the motion capture system according to the expression mode obtained in the step 31；
Step 5, taking down the virtual rigid body as a virtual controller rigid body, and directly reading the posture Q of the virtual controller rigid body through the motion capture system2；
Step 6, setting a robot end effector coordinate system Q according to the actual application situation3I.e. the pose of the robot tool coordinate system relative to the robot base coordinate system;
and 7, keeping the coordinate system of the robot end effector consistent with the initial posture of the rigid body of the virtual controller or setting a determined pose conversion relation according to a chain rule to finish the calibration of the coordinate system.
2. The coordinate system calibration method for a robot system and a motion capture system according to claim 1, wherein in step 3, the process of obtaining the expression of the positive axial direction vector of the virtual rigid body coordinate system X, Y, Z in the world coordinate system of the motion capture system is specifically:
respectively enabling the robot to move for any long distance based on the X axis of the base coordinate system, recording the origin coordinates of the virtual rigid body coordinate system in the initial state and the final state, and respectively recording the origin coordinates as P1And P2；
Then, subtracting the initial state origin coordinate from the final state origin coordinate to obtain an expression mode of the positive direction vector of the X axis of the virtual rigid body coordinate system in the world coordinate system of the motion capture system;
Vx＝P2-P1
and obtaining the expression mode of the Y axis and the Z axis of the virtual rigid body coordinate system in the world coordinate system of the motion capture system in the same way, and recording the expression mode as VyAnd Vz。
3. Machine according to claim 1Coordinate system calibration method for human system and motion capture system, characterized in that in step 4, Q1Expressed as:
Q1＝f(Vx,Vy,Vz)
and the f function is a standard vector passing through a coordinate axis, and an attitude quaternion is solved.
4. The coordinate system calibration method for a robot system and a motion capture system according to claim 1, wherein in step 7, according to the chain rule, the following relation exists:
Q2·Q1＝Q4·Q3；
wherein Q is4Representing the transformation of the robot tool coordinate system to the virtual rigid body controller coordinate system;
thereby obtaining Q4Is expressed as Q4＝Q2·Q1·Q3 -1。
5. The method for calibrating a coordinate system suitable for a robot system and a motion capture system according to claim 1, wherein after completing the calibration of the coordinate system in step 7, the robot end effector coordinate system can correctly track the virtual controller rigid coordinate system or track in an arbitrary functional relationship during the motion, specifically:
when the rigid body of the virtual controller moves and rotates in space, the gesture of the rigid body of the virtual controller is transmitted to the upper computer system by the motion capture system and is converted into an expression under a robot base coordinate system, and the expression is marked as Qm；
At this time, the robot end effector coordinate system only needs to execute Q ═ Q4·Qm·Q3And dynamic tracking can be realized.
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