Automatic calibration method and device for robot vision system
According to one aspect of the present invention, disclosed is an automatic calibration method for a calibration device connected to a camera that is disposed the end effector of a robot and to a robot controller for controlling the robot. The method comprises the steps of: acquiring, from the camera and the robot controller, a robot-based coordinate system and an image of a marker marked in the work area of the robot (wherein the acquired image and robot-based coordinate system are recorded while the end effector is moved to a plurality of sample coordinates); and estimating the position of a robot coordinate system-based marker by using the acquired image and robot-based coordinate system.
1. An automatic calibration method of a calibration device connected to a camera provided in an end effector of a robot and to a robot controller controlling the robot, the method comprising:
obtaining an image of a marker marked in a work area of the robot from the camera and a robot-based coordinate system from the robot controller, the obtained image and robot-based coordinate system being recorded while moving the end effector to a plurality of sample coordinates; and
estimating a position of the robot coordinate system-based marker based on the obtained image and robot-based coordinate system.
2. The automatic calibration method of claim 1 , wherein the estimating the position of the robot coordinate system-based marker based on the obtained image and robot-based coordinate system comprises
estimating a camera-robot offset T off by setting the camera-robot offset T off as an assumed value and minimizing a coordinate error rate in converting a camera-based marker position T mj in a plurality of postures into the robot-based coordinate system by a nonlinear optimization algorithm.
3. The automatic calibration method of claim 2 , wherein the camera-robot offset T off is calculated based on a function of variables comprising x-y-z coordinates and z-y-x Euler angles.
4. The automatic calibration method of claim 3 , wherein the camera-robot offset T off represents a degree of deviation between a first sample coordinate and a second sample coordinate by an error of a rotation matrix R and an error of a position P, and is estimated by the nonlinear optimization algorithm that minimizes the error of a rotation matrix R and the error of a position P.
5. The automatic calibration method of claim 4 , wherein
the camera-robot offset T off is calculated by
arg
min
T
off
∑
j
log
(
Δ
R
j
)
F
+
γ
Δ
P
j
[
Δ
R
j
Δ
P
j
0
1
]
=
(
T
j
-
1
T
off
T
m
,
j
-
1
)
-
1
T
j
T
off
T
m
,
j
where, j is an index of sample coordinates, T j is a transformation matrix of the sample coordinates j, T mj is the camera-based marker position in the sample coordinate j, R is a variable related to the rotation matrix, and P is a variable related to the error of the position.
6. The automatic calibration method of claim 1 , wherein
the end effector is provided with a taught movable area, and
the movable area is defined by a plurality of reference points as a reference area for calibration.
7. The automatic calibration method of claim 6 , wherein the plurality of sample coordinates is disposed in an area surrounded by the plurality of reference points.
8. The automatic calibration method of claim 1 , wherein the plurality of sample coordinates is extracted by:
recording a transformation matrix from the robot-based coordinate system to a robot distal end in a plurality of reference points;
recording variables, which determines positions of the plurality of reference coordinates based on the set operation center point, and extracting a minimum value and a maximum value of the variables; and
extracting the plurality of sample coordinates through randomly weighted sums between the plurality of reference points.
9. The automatic calibration method of claim 8 , wherein the variables comprise at least two of an azimuth angle, an elevation angle, a roll and a distance from the operation center point.
10. The automatic calibration method of claim 8 , wherein the transformation matrix T j of each sample coordinate system is calculated from the variables of the plurality of extracted sample coordinates.
11. An automatic calibration method of a calibration device connected to a camera positioned as separated from a robot and to a robot controller controlling the robot, the method comprising:
obtaining an image of a marker provided in an end effector of the robot from the camera and a robot-based coordinate system from the robot controller, the obtained image and robot-based coordinate system being recorded while moving the end effector to a plurality of sample coordinates; and
estimating a robot base-based camera position from the obtained image.
12. The automatic calibration method of claim 11 , wherein the estimating the robot base-based camera position based on the obtained image and robot-based coordinate system comprises
estimating a robot end-marker offset T em by setting the robot end-marker offset T em as an assumed value and minimizing a coordinate error rate in converting a robot base-based camera position in a plurality of postures into the robot-based coordinate system by a nonlinear optimization algorithm.
13. The automatic calibration method of claim 12 , wherein the robot end-marker offset T em is calculated based on a function of variables comprising x-y-z coordinates and z-y-x Euler angles.
14. The automatic calibration method of claim 13 , wherein the robot end-marker offset T em represents a degree of deviation between a first sample coordinate and a second sample coordinate by an error of a rotation matrix and an error of a position, and is estimated by the nonlinear optimization algorithm that minimizes the error of a rotation matrix and the error of a position.
15. The automatic calibration method of claim 14 , wherein the robot end-marker offset T em is calculated by
T
ftx
=
T
1
(
arg
min
T
em
∑
j
log
(
Δ
R
j
)
F
+
γ
Δ
P
j
)
T
m
,
1
-
1
[
Δ
R
j
Δ
P
j
0
1
]
=
(
T
j
-
1
T
em
T
m
,
j
-
1
-
1
)
-
1
T
j
T
em
T
m
,
j
-
1
where, j is an index of sample coordinates, T j is a transformation matrix of the sample coordinates j, T em is an offset estimation value from a distal end of the robot to the marker, T mj is a position of the marker from the camera, R is a variable related to the rotation matrix, and P is a variable related to the error of the position.
16. A calibration device connected to a camera provided in an end effector of a robot and to a robot controller controlling the robot, the calibration device comprising:
an input unit configured to obtain an image of a marker marked in a work area of the robot from the camera and a robot-based coordinate system from the robot controller, the obtained image and robot-based coordinate system being recorded while moving the end effector to a plurality of sample coordinates; and
a processor configured to estimate a camera-based marker position based on the obtained image and robot-based coordinate system.
17. A calibration device connected to a camera positioned as separated from a robot and to a robot controller controlling the robot, the calibration device comprising:
an input unit configured to obtain an image of a marker from the camera and a robot-based coordinate system from the robot controller, the obtained image and robot-based coordinate system being recorded while moving an end effector to a plurality of sample coordinates; and
a processor configured to estimate a robot base-based camera position based on the obtained image.