Calibration with a flat calibration object

Important commands

• Start iiwa

  • Either with the standard tool

    roslaunch tum_iiwa_zimmer_r840_moveit moveit_planning_execution.launch sim:=false iiwa_sensor:=hokuyo_utm30lx
    

  • Or in case of initial calibration with the calibration pin model

    roslaunch tum_iiwa_calibration_pin_moveit moveit_planning_execution.launch sim:=false
    

• Start Hokuyo Sensor

    roslaunch tum_workcell_launch hokuyo_utm_30lx_ew.launch
    roslaunch tum_workcell_launch sick_tim571_2050101.launch
  

• User confirmation (confirmation during teaching of calibration object coordinate system)

    rostopic pub -1 /user_confirmation calibration_flat/UserConfirmation "userConfirmation: true"
  

• Start Calibration Node

     roslaunch calibration_flat arm_to_laser_scanner_calibration_hokuyo.launch
     roslaunch calibration_flat arm_to_laser_scanner_calibration_sick.launch
  

• Hand Guiding Client

    rosrun actionlib axclient.py activate_hand_guiding hand_guiding/HandGuidingAction
  

• Action Client Calibration

     rosrun actionlib axclient.py arm_to_laser_scanner_calibration calibration_flat/ArmToLaserScannerCalibrationAction
  

Calibration

1. Initial Calibration

   • Robot moving to home position
   • Activate hand guiding mode
   • Move the robot arm to the calibration points p1, p2, p3 on the calibration object and confirm each point (Topic /user_confirmation)
   • Deactivate hand guiding mode
   • Calculate homogeneous transformation base frame to calibration object frame
   • Save transformation matrix in target_directory

2. Collect Scan Data

   • Move to scan position 1
   • Collect laser scan data (~200 meas.)
   • Move to scan position 2
   • Collect laser scan data
   • Process laser scan data (averaging over collected scans)

3. Extracting the significant points

   • Limitation of observed angle area (scan)
   • Transformation of measured ranges into xy-coordinates of laser scanner frame
   • Depth limitation
   • Defining line model parameters
   • RANSAC and Least Square (LS) optimization
   • Collecting of edge points p1 to p6 used for homogeneous transform calibration object frame into laser scanner frame

4. Determine the Calibration Matrix

   • Determine homogeneous transformation matrix base frame to tool frame
   • Calculate homogeneous transformation matrix laser scanner frame to calibration object frame (formulas of paper)
   • Calculate homogeneous transformation matrix tool frame to laser scanner (final result)
   • Save transformation matrix tool frame to laser scanner frame in target_directory

Parameters

• autostart
  • typ: boolean
  • description: If selected, the calibration process starts after 3 seconds after the calibration node is started.
• initial_calibration
  • typ: boolean
  • description: If selected, the initial calibration is performed. If not selected, the saved transformation matrix base to calibration object is used.
• width_calib_obj
  • typ: float
  • description: Width (in meter) of the calibration object
• angle_calib_obj
  • typ: float
  • description: Angle (in degree) of the cutout on the calibration object.
• delta_a_calib_obj
  • typ: float
  • description: Distance (in meter) between the point p1 on the calibration object and the cutout corner.
• offset_alpha_z
  • typ: double
  • description: Rotation (in degree) of end effector to scan tilted around the z-axis onto the calibration object
• offset_pre_scan
  • typ: double
  • description: Position (in meter) of end effector over scan positions in the z-axis
• near_distance
  • typ: float
  • description: Distance (in meter) during the first laser scan between the calibration object and robot arm end effector in Y axis of the calibration object.
• far_distance
  • typ: float
  • description: Distance (in meter) during the second laser scan between the calibration object and robot arm end effector in Y axis of the calibration object.
• calib_obj_offset_z
  • typ: float
  • description: Distance (in meter) during the first and second laser scan between the laser scanner center and the calibration object frame (Estimation)
• trans_ee_l
  • typ: double
  • description: Distance (in meter) between laser scanner z-axis and laser scanner center (Estimation)
• Pin length
  • typ: double
  • description: Distance (in meter) from end effector plane to pin peak
• number_of_scans
  • typ: int
  • description: Number of laser scans evaluated per shot.
• number_of_iterations_ransac_ls
  • typ: int
  • description: Number of tries for Ranscac and least squares to find optimal model paramters
• ransac_threshold
  • typ: double
  • description: Distance (in meter) of a point to the line model estimation performed by ransac
• tolerance inlier
  • typ: double
  • description: Distance (in meter) of final edge points of calibration object towards fitted model by ransac/leas squares
• home_pos_x
  • typ: float
  • description: X coordinate of the robot home position.
• home_pos_y
  • typ: float
  • description: X coordinate of the robot home position.
• home_pos_z
  • typ: float
  • description: Z coordinate of the robot home position.
• target_directory
  • typ: string
  • description: Destination folder in which the homogeneous transformation matrices are stored.