Inconsistent pose pairs in HAND-EYE calibration in HALCON warnings

Question

I am trying to perform hand-eye calibration using HALCON for the UR5 cobot. I am using 'hand_eye_stationarycam_calibration.hdev.But every time , I get a warning that says: 'Inconsistent pose pairenter image description here

Can anybody help me in this issue? I have tried all of the pose types as well, but the warning and fault results remain.

Answer 1

Try looking at the line of code:

check_hand_eye_calibration_input_poses (CalibDataID, 0.001, 0.005, Warnings)

There is a rotation tolerance (0.001 here) and a translation tolerance (0.005 here). Try to increase these values and see if that gets rid of the error.

Sometimes when I've had this problem in the past it was because my units were not consistent. For example, the translation units of the robot pose were all in 'mm' but my camera units were in 'm'. Double check the translation units and ensure they match.

Also I believe the UR5 robot might default to an axis-angle representation. You must ensure your camera poses and robot poses are all in the same format. See the link below for a description from Universal and how to convert between the different formats. You could either use the script from universal to convert to a roll, pitch, yaw convention or you could take the axis angle representation and convert it inside Halcon.

Here is an example of how I converted from axis-angle to 'abg' pose type in Halcon. In this case the camera returned 7 values: 3 describing a translation in X, Y, Z and 4 values describing the rotation using the angle axis convention. This is then converted to a pose type where the first rotation is performed around the Z axis followed by the new Y axis followed by the new X axis (which matched the robot I was using). The other common pose type in Halcon is 'gba' and you might need that one. In general I believe there are 12 different rotation combinations that are possible so you should verify which one is being used for both the camera and the robot.

In general I try and avoid using the terms roll, pitch, and yaw since I've seen it cause confusion in the past. If the translation units are given in X, Y, Z I prefer the rotation be given in Rx, Ry, and Rz followed by the order of rotation.

    *Pose of Object Relative to Camera
get_framegrabber_param (NxLib, '/Execute/halcon1/Result/Patterns/PatternPose/Rotation/Angle', RotationAngle)
get_framegrabber_param (NxLib, '/Execute/halcon1/Result/Patterns/PatternPose/Rotation/Axis/\\0', Axis0)
get_framegrabber_param (NxLib, '/Execute/halcon1/Result/Patterns/PatternPose/Rotation/Axis/\\1', Axis1)
get_framegrabber_param (NxLib, '/Execute/halcon1/Result/Patterns/PatternPose/Rotation/Axis/\\2', Axis2)

get_framegrabber_param (NxLib, '/Execute/halcon1/Result/Patterns/PatternPose/Translation/\\0', Txcam)
get_framegrabber_param (NxLib, '/Execute/halcon1/Result/Patterns/PatternPose/Translation/\\1', Tycam)
get_framegrabber_param (NxLib, '/Execute/halcon1/Result/Patterns/PatternPose/Translation/\\2', Tzcam)    
    
axis_angle_to_quat(Axis0, Axis1, Axis2, RotationAngle, QuatObjRelCam)
quat_to_hom_mat3d(QuatObjRelCam, MatObjRelCam)    
MatObjRelCam[3] := Txcam/1000 
MatObjRelCam[7] := Tycam/1000 
MatObjRelCam[11] := Tzcam/1000 
hom_mat3d_to_pose(MatObjRelCam, PoseObjRelCam)
convert_pose_type (PoseObjRelCam, 'Rp+T', 'abg', 'point', PoseObjRelCam)

EXPLANATION ON ROBOT ORIENTATION from Universal Robotics