CN107351084B - Space manipulator system error correction method for maintenance task - Google Patents

Space manipulator system error correction method for maintenance task Download PDF

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CN107351084B
CN107351084B CN201710661192.4A CN201710661192A CN107351084B CN 107351084 B CN107351084 B CN 107351084B CN 201710661192 A CN201710661192 A CN 201710661192A CN 107351084 B CN107351084 B CN 107351084B
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mechanical arm
maintenance
coordinate system
point
camera
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CN107351084A (en
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樊春光
谢宗武
刘伊威
刘宏
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Harbin Institute of Technology
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Harbin Institute of 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
    • B25J9/1602—Programme controls characterised by the control system, structure, architecture
    • G—PHYSICS
    • G05—CONTROLLING; REGULATING
    • G05B—CONTROL OR REGULATING SYSTEMS IN GENERAL; FUNCTIONAL ELEMENTS OF SUCH SYSTEMS; MONITORING OR TESTING ARRANGEMENTS FOR SUCH SYSTEMS OR ELEMENTS
    • G05B2219/00—Program-control systems
    • G05B2219/30—Nc systems
    • G05B2219/39—Robotics, robotics to robotics hand
    • G05B2219/39214—Compensate tracking error by using model, polynomial network

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Abstract

A maintenance task-oriented space manipulator system error correction method belongs to the technical field of manned spacecraft overall design. The invention aims to solve the problem of error accumulation caused by installation error, emission vibration, gravity unloading and the like when multiple operation terminals jointly execute the same task. The method comprises the following steps: the method comprises the following steps: positioning pose information of the maintenance tool; step two: and correcting the coordinate system of the maintenance tool by using the hand-eye camera. The error correction method provided by the invention corrects the position error generated when the Tiangong No. two space manipulator system completes the on-orbit operation task by using the global camera and the hand-eye camera, and ensures that the on-orbit maintenance task is successfully completed.

Description

Space manipulator system error correction method for maintenance task
Technical Field
The invention relates to a method for correcting errors of a space manipulator system, and belongs to the technical field of general design of manned spacecrafts.
Background
With the further increase of human space activities, the on-orbit maintenance and repair operation of space equipment becomes more and more important, the previous space robot, the end effector, the operation tool and the like facing a single operation task cannot meet the requirements, and the development trend of the space robot in the future can be predicted: (1) single operation task → various operation requirements, and the operation such as simple grasping, carrying and the like is converted into the fine operation such as module replacement, filling and the like; (2) cooperative target → non-cooperative target, diversity and uncertainty of operation task and operation target require the robot to have higher compatibility, including target identification, grasping and operation method; (3) single tool → multiple operation tools, the diversity of operation tasks determines the diversity of on-orbit operation tools, and the operation method and the operation tools are matched; (4) single mechanical arm → multi-arm system, multi-arm coordination, finish lighting, vision, grasp and multiple workmanship such as the operation; (5) rigid grasping → intelligent flexible operation, a mechanical arm and a tail end operation tool, wherein the grasping and the operation of a target are realized based on the compliance control, the influence of a positioning error on the operation is overcome, and the success rate and the safety of the operation are improved; (6) basic motion perception → coexistence of multiple perceptions, and development from a position sensor which is necessary for realizing position closed-loop control to multiple perception directions such as moment, current, temperature, vision and the like, and the vision and a measurement algorithm thereof can greatly improve the working capacity of the space robot in the future; (7) pre-programming operation → telepresence teleoperation, and controlling the mechanical arm outside the cabin by a spacecraft from the inside of the cabin or a ground technician on the basis of various perception interaction, time delay correction algorithms and the like.
Disclosure of Invention
The invention aims to provide a maintenance task-oriented space manipulator system error correction method, which adopts a track correction strategy oriented to an experiment cabin internal track maintenance task to ensure that a terminal coordinate system of a manipulator system is completely consistent with a maintenance tool coordinate system.
The invention aims to solve the problem of error accumulation caused by installation error, emission vibration, gravity unloading and the like when multiple operation terminals jointly execute the same task. The error correction method provided by the invention corrects the position error generated when the Tiangong No. two space manipulator system completes the on-orbit operation task by using the global camera and the hand-eye camera, and ensures that the on-orbit maintenance task is successfully completed.
In order to achieve the purpose, the invention adopts the technical scheme that:
a space manipulator system error correction method facing maintenance tasks comprises the following steps:
the method comprises the following steps: positioning pose information of the maintenance tool;
in order to give pose information of the maintenance tool, firstly, defining a plurality of coordinate systems so as to solve the description of the maintenance tool in a world coordinate system;
TB-a robot arm base coordinate system
TE-the robot arm end coordinate system
TG-global camera coordinate system
TH-hand-eye camera coordinate system
TM-on-orbit calibration plate coordinate system
TT-service tool coordinate system
The coordinate systems are distributed in the experiment cabin, the global cameras are fixed on the ceiling of the experiment cabin, the two global cameras are defined as a global camera A and a global camera B respectively, the mechanical arm is installed at the tail end of the mechanical arm through a quick-change flange, the hand-eye cameras are installed on the wrist portion of the mechanical arm, the maintenance single machine is installed right below a mechanical arm system, the calibration plate is located in the center of the maintenance single machine, and two loose and non-loose screws are arranged on the maintenance single machine;
the global camera is responsible for positioning the position of the maintenance tool electric hand drill in real time, a mechanical arm arranged at the tail end of the mechanical arm grips the electric hand drill by utilizing position information provided by the global camera, the visual servo guides the mechanical arm to be right above the release screw, the mechanical arm moves downwards to press the release screw and simultaneously pulls a trigger of the electric hand drill, and then the visual servo guides the mechanical arm to return the maintenance tool to the initial position;
in order to ensure that the tail end of the mechanical arm system is fully contacted with the complex matching surface of the operated maintenance tool, firstly, a teaching mode is adopted to attach the mechanical arm to the complex matching surface of the tool, and at the moment:
TT＝Tc1·TE(1)
TC1a bias matrix between a normal virtual gripping central point of the manipulator and a gripping central point of the manipulator when the manipulator is in a complex matching surface; t isEThe terminal coordinate system of the mechanical arm is in a normal configuration;
the position and the posture of the maintenance tool need to be determined by the global camera, so the description of the maintenance tool in a global camera coordinate system needs to be determined firstly, and then the description is converted into a world coordinate system;
the four target points are pasted on the side face of the maintenance tool, so that the description of solving the maintenance tool in the world coordinate system is converted into a PNP problem, and the basic principle of the PNP problem is described simply:
simply speaking, the PNP problem is that the projection relation between N characteristic points in the world coordinate system and N image points imaged by the global camera is calculated, and finally the object pose or the global camera pose described by the characteristic points is obtained;
assume that the global camera center is at point O and the feature point is P1,P2,P3...PN；
When N is 1, there is only one feature point, and no point P is provided1At the very center of the global camera image imaging, then OP1Is the Z-axis in the global camera coordinate system, when the global camera is facing P1The point, global camera position may be P1Is the center of a sphere, OP1Is on a spherical surface with a radius, and then has infinite solutions;
when N is 2, two feature points P1,P2And the point O forms a triangle, wherein one side P of the triangle1P2Of known length, vector OP1And OP2Is known, so that OP can be calculated1、OP2Length of (1), let R1＝OP1,R2＝OP2With P1As a center of circle, R1Sphere O for making a radiusAWith P2As a center of circle, R2Sphere O for making a radiusB；
When the global camera is located on ball OAAnd ball OBThere are numerous solutions at the intersection of (A) and (B);
when N is 3, an extra P is added on the basis of N being 23Is a sphere center R3Is a sphere O of radiusCThe global camera is located at the intersection of the three spherical surfaces, and at this time, there should be four solutions, one of which is the true position of the global camera, but which solution is specific cannot be determined;
when N is 4, since when N is 3, four solutions can be calculated by equation (2), and four rotation and translation matrices are obtained, where (x, y) is the image point coordinate of the spatial point P, and (f) is the image point coordinate of the spatial point Px,fy) Is the magnification factor in the X-axis and Y-axis directions, (c)x,cy) Is the coordinate of the center point of the optical axis, (r)ij,tk)i,j,k＝1,2,3Is global camera external parameter, (x, y, z) is the position of point P in world coordinate system;
Figure GDA0002342723880000031
substituting the world coordinate system of the fourth point into the formula (1) to obtain four projections of the fourth point on the image, wherein the solution with the minimum projection error is the required positive solution;
step two: correcting the coordinate system of the maintenance tool by using the hand-eye camera;
when an error occurs, the coordinate system of the maintenance tool needs to be corrected by using the hand-eye camera, a calibration plate for correcting the error is positioned near the central position of the maintenance stand-alone, and the position of the calibration plate and the initial position of the maintenance tool are determined by a constant matrix TC2And (3) conversion is carried out:
TM＝TC2·TT(3)
the combination formula (1):
TM＝TC1·TC2·TE(4)
wherein T isC2Representing a transformation matrix between the calibration plate and the initial position of the maintenance tool, and considering T as the design requirement of the maintenance unitC2Is a constant matrix;
teaching a mechanical arm on a tool complex surface when a task is executed for the first time, recording data of a joint position sensor of the mechanical arm at the moment, moving the mechanical arm to a normal position configuration, and recording pose information of a calibration plate at the moment by using a hand-eye camera; there are three cases that can cause the manipulator to fail to grab the service tool:
1. in the debugging stage, the mechanical arm and the maintenance plate need to be disassembled and assembled for many times, which brings certain installation errors;
2. the vibration in the rocket launching process can cause the relative motion between the mechanical arm body and the maintenance single machine;
3. the gravity unloading in the space environment can bring deflection change to the vertical plates of the cabin body and a maintenance single machine;
the following correction method is therefore used, which is described in detail below:
(1) under the ground environment, obtaining an ideal motion track of a mechanical arm system for task operation through kinematics teaching, and representing the ideal motion track by adopting the positions and postures of the tail end of the mechanical arm on a series of key position points;
(2) when a ground experiment and a space experiment are started, the robot is moved to the same fixed position, the hand-eye camera is used for measuring the position and the attitude of a calibration plate fixed on the maintenance stand-alone machine, and then the relative displacement of the maintenance stand-alone machine in the ground environment and the space environment is indirectly calculated;
(3) correcting a task track of the mechanical arm system to ensure that the relative position of the tail end of the mechanical arm and the operated maintenance tool is constant;
the related pose relationship is defined as follows:
Figure GDA0002342723880000041
-calibrating a displacement matrix of the plate position in the spatial experiment relative to the ground experiment;
Figure GDA0002342723880000042
the hand-eye camera measures the pose of the calibration plate in the ground experiment;
Figure GDA0002342723880000043
the hand-eye camera measures the pose of the calibration plate in the space experiment;
thus:
Figure GDA0002342723880000044
Figure GDA0002342723880000045
in the formula (6)
Figure GDA0002342723880000046
The relative movement of the maintenance tool between the space environment and the ground environment is shown, the maintenance tool and the calibration plate are both placed on the maintenance stand-alone machine, the rigidity of the maintenance stand-alone machine is higher according to the technical requirements, and the T can be considered according to the formula (3)C2The matrix does not change with gravity unloading, i.e.:
Figure GDA0002342723880000051
equation (6) can thus be written as:
Figure GDA0002342723880000052
the method aims to ensure the relative pose of the tail end of the robot and the workpiece, namely:
Figure GDA0002342723880000053
in summary, the pose of the new robot arm tip position relative to the robot arm base can be expressed as:
Figure GDA0002342723880000054
Figure GDA0002342723880000055
-obtaining a key point of a tail end position track of the mechanical arm through a ground experiment;
Figure GDA0002342723880000056
-a matrix of fine measured poses of the end of the manipulator relative to the service tool;
as shown in the formula (10), the description of the new robot arm tip position in the world coordinate system can be completely represented by the known matrix, and one part of the known matrix is calculated by the synchronous ground experiment, and the other part of the known matrix is calculated by using the calibration plate position information acquired by the hand-eye camera.
Compared with the prior art, the invention has the beneficial effects that:
1. the technical scheme of the invention considers the influence of various errors on the positioning precision of the maintenance tool, such as the installation errors of the mechanical arm and the maintenance plate; virtual position errors of a mounting flange of a mechanical arm base caused by vibration in the rocket launching process; the influence of the deflection changes of the vertical plates of the cabin body and the maintenance workbench caused by gravity unloading in the space environment on the positioning precision of the maintenance tool ensures that the accumulated errors of various errors are corrected through the multiple conversion of the coordinate system.
2. The operation method solves the problem that the mechanical arm cannot be calibrated on site through calibration equipment such as an API laser scanner and the like when the position of the base is accidentally changed during space task execution, and the influence of various errors can be quickly corrected through the method provided by the invention.
Drawings
FIG. 1 is a schematic representation of the coordinate positions of a spatial robotic arm system of the present invention;
FIG. 2 is a diagram of the coordinate system relationship transformation of the spatial manipulator system of the present invention during maintenance tasks, including both spatial and ground scenarios, where the letters in FIG. 2 correspond to the coordinate system description in step one, specifically, TH' represents a hand-eye camera coordinate system in space, TT' representing the coordinate System of the service tool in space, TM' represents a calibration plate coordinate system in space.
Detailed Description
The error correction method of the present invention will be described in detail below with reference to the accompanying drawings, but the present invention is not limited to the following embodiments.
The specific implementation mode is as follows: the embodiment discloses a space manipulator system error correction method facing a maintenance task, which comprises the following steps:
the method comprises the following steps: positioning pose information of the maintenance tool;
as shown in fig. 1, to give pose information of a maintenance tool, the following coordinate systems are first defined so as to solve the description of the maintenance tool in the world coordinate system;
TB-base coordinate system of robot arm
TE-the robot arm end coordinate system
TG-global camera coordinate system
TH-hand-eye camera coordinate system
TM-on-orbit calibration plate coordinate system
TT-service tool coordinate system
The coordinate systems are distributed in the experiment cabin, the global cameras are fixed on the ceiling of the experiment cabin, the coordinate systems are defined as a global camera A and a global camera B, the mechanical arm is arranged at the tail end of the mechanical arm through a quick-change flange (the quick-change flange refers to a specific connecting mechanism between the mechanical arm and forms a mechanical arm hand system together with the mechanical arm hand system), the hand-eye camera is arranged at the wrist part of the mechanical arm, the maintenance single machine is arranged right below the mechanical arm hand system, the calibration plate is positioned at the center of the maintenance single machine, and two non-detachable screws are arranged on the maintenance single machine (the task is to unscrew the non-detachable screws from the maintenance single machine);
the global camera is responsible for positioning the position of the maintenance tool electric hand drill in real time, a mechanical arm arranged at the tail end of the mechanical arm grips the electric hand drill by utilizing position information provided by the global camera, the visual servo guides the mechanical arm to be right above the release screw, the mechanical arm moves downwards to press the release screw and simultaneously pulls a trigger of the electric hand drill, and then the visual servo guides the mechanical arm to return the maintenance tool to the initial position;
in order to ensure that the tail end of the mechanical arm system is fully contacted with the complex matching surface of the operated maintenance tool, firstly, a teaching mode is adopted to attach the mechanical arm to the complex matching surface of the tool, and at the moment:
TT＝TC1·TE0(1)
TC1a bias matrix between a normal virtual gripping central point of the manipulator and a gripping central point of the manipulator when the manipulator is in a complex matching surface; t isE0The robot arm is a terminal coordinate system of the robot arm in a normal configuration (the normal configuration refers to an initial configuration which is kept before the robot arm executes a task each time, and a complex matching surface is a specially-processed curved surface for ensuring stable grabbing, so that the robot arm is attached to a grabbed object as much as possible when the robot arm executes a grabbing task, and the stability of passive grabbing is ensured);
the position and the posture of the maintenance tool need to be determined by the global camera, so the description of the maintenance tool in a global camera coordinate system needs to be determined firstly, and then the description is converted into a world coordinate system;
the four target points are pasted on the side face of the maintenance tool, so that the description of solving the maintenance tool in the world coordinate system is converted into a PNP problem, and the basic principle of the PNP problem is described simply:
simply speaking, the PNP problem is that the projection relation between N characteristic points in the world coordinate system and N image points imaged by the global camera is calculated, and finally the object pose or the global camera pose described by the characteristic points is obtained;
assume that the global camera center is at point O and the feature point is P1,P2,P3...PN；
When N is 1, there is only one feature point, and no point P is provided1At the very center of the global camera image imaging, then OP1Is the Z-axis in the global camera coordinate system, when the global camera is facing P1The point, global camera position may be P1Is the center of a sphere, OP1Is on a spherical surface with a radius, and then has infinite solutions;
when N is 2, two feature points P1,P2And the point O forms a triangle, wherein one side P of the triangle1P2Of known length, vector OP1And OP2Is known, so that OP can be calculated1、OP2Length of (1), let R1＝OP1,R2＝OP2With P1As a center of circle, R1Sphere O for making a radiusAWith P2As a center of circle, R2Sphere O for making a radiusB；
When the global camera is located on ball OAAnd ball OBThere are numerous solutions at the intersection of (A) and (B);
when N is 3, an extra P is added on the basis of N being 23Is a sphere center R3Is a sphere O of radiusCThe global camera is located at the intersection of three spherical surfaces, and there should be four solutions, one of which isThe true position of the global camera, but it is not possible to determine which solution is specific;
when N is 4, since when N is 3, four solutions can be calculated by equation (2), and four rotation and translation matrices are obtained, where (x, y) is the image point coordinate of the spatial point P, and (f) is the image point coordinate of the spatial point Px,fy) Is the magnification factor in the X-axis and Y-axis directions, (c)x,cy) Is the coordinate of the center point of the optical axis, (r)ij,tk)i,j,k＝1,2,3Is global camera external parameter, (x, y, z) is the position of point P in world coordinate system;
Figure GDA0002342723880000081
substituting the world coordinate system of the fourth point into the formula (1) to obtain four projections of the fourth point on the image, wherein the solution with the minimum projection error is the required positive solution;
step two: correcting the coordinate system of the maintenance tool by using the hand-eye camera;
when an error occurs, the coordinate system of the maintenance tool needs to be corrected by using the hand-eye camera, a calibration plate for correcting the error is positioned near the central position of the maintenance stand-alone, and the position of the calibration plate and the initial position of the maintenance tool are determined by a constant matrix TC2And (3) conversion is carried out:
TM＝TC2·TT(3)
the combination formula (1):
TM＝TC1·TC2·TE(4)
wherein T isC2Representing a transformation matrix between the calibration plate and the initial position of the maintenance tool, and considering T as the design requirement of the maintenance unitC2Is a constant matrix;
when a task is executed for the first time, teaching a mechanical arm on a tool complex surface, recording data of a joint position sensor of the mechanical arm at the moment, moving the mechanical arm to a normal position configuration, and recording pose information of a calibration plate at the moment by using a hand-eye camera (the significance of the calibration mode is that the requirement of the task on position precision is higher due to rigid contact between the mechanical arm and a maintenance tool and the existence of the complex surface); there are three cases that can cause the manipulator to fail to grab the service tool:
1. in the debugging stage, the mechanical arm and the maintenance plate need to be disassembled and assembled for many times, which brings certain installation errors;
2. the vibration in the rocket launching process can cause the relative motion between the mechanical arm body and the maintenance single machine;
3. the gravity unloading in the space environment can bring deflection change to the vertical plates of the cabin body and a maintenance single machine;
(therefore, if the robot arm system is directly controlled to grasp the maintenance tool, the possibility of failure of the grasping task is increased, and the maintenance tool or the robot arm is damaged in a serious case) due to the existence of the above three cases;
the following correction method is therefore used, which is described in detail below:
(1) under the ground environment, an ideal motion track of a mechanical arm system for task operation is obtained through kinematics teaching, and the position and the posture of the tail end of the mechanical arm on a series of key position points are adopted for representation, wherein the key position points have the following meanings: in the whole task execution process, the whole task execution process is divided into a plurality of macro movements, each macro movement is divided into a plurality of micro movements, the key position points describe the starting position and the end position of each micro movement, and the end position of the previous micro movement is also the starting position of the next micro movement;
(2) when a ground experiment and a space experiment are started, the robot is moved to the same fixed position, the hand-eye camera is used for measuring the position and the attitude of a calibration plate fixed on the maintenance stand-alone machine, and then the relative displacement of the maintenance stand-alone machine in the ground environment and the space environment is indirectly calculated;
(3) correcting a task track of the mechanical arm system to ensure that the relative position of the tail end of the mechanical arm and the operated maintenance tool is constant;
as shown in fig. 2, the relative pose relationship is defined as follows:
Figure GDA0002342723880000091
-calibrating a displacement matrix of the plate position in the spatial experiment relative to the ground experiment;
Figure GDA0002342723880000092
the hand-eye camera measures the pose of the calibration plate in the ground experiment;
Figure GDA0002342723880000093
the hand-eye camera measures the pose of the calibration plate in the space experiment;
thus:
Figure GDA0002342723880000094
Figure GDA0002342723880000095
in the formula (6)
Figure GDA0002342723880000096
The relative movement of the maintenance tool between the space environment and the ground environment is shown, the maintenance tool and the calibration plate are both placed on the maintenance stand-alone machine, the rigidity of the maintenance stand-alone machine is higher according to the technical requirements, and the T can be considered according to the formula (3)C2The matrix does not change with gravity unloading, i.e.:
Figure GDA0002342723880000097
equation (6) can thus be written as:
Figure GDA0002342723880000098
the method aims to ensure the relative pose of the tail end of the robot and the workpiece, namely:
Figure GDA0002342723880000099
in summary, the pose of the new robot arm tip position relative to the robot arm base can be expressed as:
Figure GDA00023427238800000910
Figure GDA00023427238800000911
-obtaining a key point of a tail end position track of the mechanical arm through a ground experiment;
Figure GDA0002342723880000101
-a matrix of fine measured poses of the end of the manipulator relative to the service tool;
according to the formula (10), the description of the end position of the new mechanical arm in the world coordinate system can be completely represented by a known matrix, one part of the known matrix is calculated by a synchronous ground experiment, and the other part of the known matrix is calculated by using the position information of the calibration plate acquired by the hand-eye camera (the method has the characteristics of simple principle, easiness in operation and high reliability).

Claims (1)

1. A space manipulator system error correction method for maintenance tasks is characterized by comprising the following steps: the method comprises the following steps:
the method comprises the following steps: positioning pose information of the maintenance tool;
in order to give pose information of the maintenance tool, firstly, defining a plurality of coordinate systems so as to solve the description of the maintenance tool in a world coordinate system;
TB-a robot arm base coordinate system
TE-the robot arm end coordinate system
TG-global camera coordinate system
TH-hand-eye camera coordinate system
TM-on-orbit calibration plate coordinate system
TT-service tool coordinate system
The coordinate systems are distributed in the experiment cabin, the global cameras are fixed on the ceiling of the experiment cabin, the two global cameras are defined as a global camera A and a global camera B respectively, the mechanical arm is installed at the tail end of the mechanical arm through a quick-change flange, the hand-eye cameras are installed on the wrist portion of the mechanical arm, the maintenance single machine is installed right below a mechanical arm system, the calibration plate is located in the center of the maintenance single machine, and two loose and non-loose screws are arranged on the maintenance single machine;
the global camera is responsible for positioning the position of the maintenance tool electric hand drill in real time, a mechanical arm arranged at the tail end of the mechanical arm grips the electric hand drill by utilizing position information provided by the global camera, the visual servo guides the mechanical arm to be right above the release screw, the mechanical arm moves downwards to press the release screw and simultaneously pulls a trigger of the electric hand drill, and then the visual servo guides the mechanical arm to return the maintenance tool to the initial position;
in order to ensure that the tail end of the mechanical arm system is fully contacted with the complex matching surface of the operated maintenance tool, firstly, a teaching mode is adopted to attach the mechanical arm to the complex matching surface of the tool, and at the moment:
TT＝Tc1·TE(1)
TC1a bias matrix between a normal virtual gripping central point of the manipulator and a gripping central point of the manipulator when the manipulator is in a complex matching surface; t isEThe terminal coordinate system of the mechanical arm is in a normal configuration;
the position and the posture of the maintenance tool need to be determined by the global camera, so the description of the maintenance tool in a global camera coordinate system needs to be determined firstly, and then the description is converted into a world coordinate system;
the four target points are pasted on the side face of the maintenance tool, so that the description of solving the maintenance tool in the world coordinate system is converted into a PNP problem, and the basic principle of the PNP problem is described simply:
simply speaking, the PNP problem is that the projection relation between N characteristic points in the world coordinate system and N image points imaged by the global camera is calculated, and finally the object pose or the global camera pose described by the characteristic points is obtained;
assume that the global camera center is at point O and the feature point is P1,P2,P3...PN；
When N is 1, there is only one feature point, and no point P is provided1At the very center of the global camera image imaging, then OP1Is the Z-axis in the global camera coordinate system, when the global camera is facing P1The point, global camera position may be P1Is the center of a sphere, OP1Is on a spherical surface with a radius, and then has infinite solutions;
when N is 2, two feature points P1,P2And the point O forms a triangle, wherein one side P of the triangle1P2Of known length, vector OP1And OP2Is known, so that OP can be calculated1、OP2Length of (1), let R1＝OP1,R2＝OP2With P1As a center of circle, R1Sphere O for making a radiusAWith P2As a center of circle, R2Sphere O for making a radiusB；
When the global camera is located on ball OAAnd ball OBThere are numerous solutions at the intersection of (A) and (B);
when N is 3, an extra P is added on the basis of N being 23Is a sphere center R3Is a sphere O of radiusCThe global camera is located at the intersection of the three spherical surfaces, and at this time, there should be four solutions, one of which is the true position of the global camera, but which solution is specific cannot be determined;
when N is 4, since when N is 3, four solutions can be calculated by equation (2), and four rotation and translation matrices are obtained, where (x, y) is the image point coordinate of the spatial point P, and (f) is the image point coordinate of the spatial point Px,fy) Is the magnification factor in the X-axis and Y-axis directions, (c)x,cy) Is the coordinate of the center point of the optical axis, (r)ij,tk)i,j,k＝1,2,3Is global camera external parameter, (x, y, z) is the position of point P in world coordinate system;
Figure FDA0002342723870000021
substituting the world coordinate system of the fourth point into the formula (1) to obtain four projections of the fourth point on the image, wherein the solution with the minimum projection error is the required positive solution;
step two: correcting the coordinate system of the maintenance tool by using the hand-eye camera;
when an error occurs, the coordinate system of the maintenance tool needs to be corrected by using the hand-eye camera, a calibration plate for correcting the error is positioned near the central position of the maintenance stand-alone, and the position of the calibration plate and the initial position of the maintenance tool are determined by a constant matrix TC2And (3) conversion is carried out:
TM＝TC2·TT(3)
the combination formula (1):
TM＝TC1·TC2·TE(4)
wherein T isC2Representing a transformation matrix between the calibration plate and the initial position of the maintenance tool, and considering T as the design requirement of the maintenance unitC2Is a constant matrix;
teaching a mechanical arm on a tool complex surface when a task is executed for the first time, recording data of a joint position sensor of the mechanical arm at the moment, moving the mechanical arm to a normal position configuration, and recording pose information of a calibration plate at the moment by using a hand-eye camera; there are three cases that can cause the manipulator to fail to grab the service tool:
1. in the debugging stage, the mechanical arm and the maintenance plate need to be disassembled and assembled for many times, which brings certain installation errors;
2. the vibration in the rocket launching process can cause the relative motion between the mechanical arm body and the maintenance single machine;
3. the gravity unloading in the space environment can bring deflection change to the vertical plates of the cabin body and a maintenance single machine;
the following correction method is therefore used, which is described in detail below:
(1) under the ground environment, obtaining an ideal motion track of a mechanical arm system for task operation through kinematics teaching, and representing the ideal motion track by adopting the positions and postures of the tail end of the mechanical arm on a series of key position points;
(2) when a ground experiment and a space experiment are started, the robot is moved to the same fixed position, the hand-eye camera is used for measuring the position and the attitude of a calibration plate fixed on the maintenance stand-alone machine, and then the relative displacement of the maintenance stand-alone machine in the ground environment and the space environment is indirectly calculated;
(3) correcting a task track of the mechanical arm system to ensure that the relative position of the tail end of the mechanical arm and the operated maintenance tool is constant;
the related pose relationship is defined as follows:
Figure FDA0002342723870000031
-calibrating a displacement matrix of the plate position in the spatial experiment relative to the ground experiment;
Figure FDA0002342723870000032
the hand-eye camera measures the pose of the calibration plate in the ground experiment;
Figure FDA0002342723870000033
the hand-eye camera measures the pose of the calibration plate in the space experiment;
thus:
Figure FDA0002342723870000034
Figure FDA0002342723870000041
in the formula (6)
Figure FDA0002342723870000042
Representing the relative movement of the maintenance tool between the space environment and the ground environment, the maintenance tool and the calibration plate are both placed on the maintenance stand-alone machine, and the rigidity of the maintenance stand-alone machine is determined according to the technical requirementsLarger, T can be considered according to equation (3)C2The matrix does not change with gravity unloading, i.e.:
Figure FDA0002342723870000043
equation (6) can thus be written as:
Figure FDA0002342723870000044
the method aims to ensure the relative pose of the tail end of the robot and the workpiece, namely:
Figure FDA0002342723870000045
in summary, the pose of the new robot arm tip position relative to the robot arm base can be expressed as:
Figure FDA0002342723870000046
Figure FDA0002342723870000047
-obtaining a key point of a tail end position track of the mechanical arm through a ground experiment;
Figure FDA0002342723870000048
-a matrix of fine measured poses of the end of the manipulator relative to the service tool;
as shown in the formula (10), the description of the new robot arm tip position in the world coordinate system can be completely represented by the known matrix, and one part of the known matrix is calculated by the synchronous ground experiment, and the other part of the known matrix is calculated by using the calibration plate position information acquired by the hand-eye camera.
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