A thorough calibration is performed for each individual robot by the TMR calibration team before shipping a robot. This calibration will ensure that accuracy of 1-2 cm is obtained.
If anything is changed in the setup, e.g. spray can type or GNSS receiver, then some calibration parameters might have to be adjusted.
The parameters that should be checked and might need adjustments are:
- Tool calibrate X
- Tool calibrate Y
- Position time offset start
- Position time offset stop
Doing an adjustment of the calibration is an iterative and advanced task.
Note the factory default values for the calibration parameters before adjusting them.
Why adjust the calibration parameters?
Reasons for adjusting the calibration parameters could be that points are not marked precisely when marking the same point from multiple directions. This is due to Tool calibrate X and Y. Another reason is that lines doesn’t meet up when doing figures, e.g. at corners.
Images- Left: point marked two times not matching due to Tool calibrate X and Y. Right: corners not matching up due to Position time offset start and stop
Adjusting tool calibrate X and Y
The Tool calibrate X and Y parameters minimize the influence of mechanical tolerances and misalignment of the spray tool. Two ways of adjusting the tool calibration will be presented.
This check and adjustment should be done prior to adjusting Position Time Offset start and stop.
Performing tool calibration with known intended points
1. Prepare robot for operation, i.e. mount GNSS antenna/receiver, adjust height of spray tool, and mount spray can.
Use the settings:
- Settings>Robot Behavior>Velocities>Drive velocity: 1m/s
- Settings>Robot Behavior>Point parameters>Approach distance: 0.5 m
2. Import the .csv file with the with known points and let the robot drive to the points.
3. If intended and marked points is without acceptable limit, then measure the distance from the intended point to the point marked by the robot. Perform the measurement in the driving direction (x-coordinate) and the sideways direction (y-direction).
Image: Example of tool calibration process with a known point
4. Add the measure values to the existing parameter values in:
Settings>Robot behavior>Calibration.
- Tool calibrate x
- Tool calibrate y
5. Iteratively repeat steps 3 and 4 multiple times to increase precision.
6. Start the robot from different direction to check precision further.
Perform tool calibration without known points
1. Prepare robot for operation, i.e. mount GNSS antenna/receiver, adjust height of spray tool, and mount spray can.
Use the settings:
- Settings>Robot Behavior>Velocities>Drive velocity: 1 m/s or ft/s
- Settings>Robot Behavior>Point parameters>Approach distance: 0.5 m/ft
2. Collect multiple points along a line. Use the template Geometry Points found in +New Job.
3. Let the robot drive to the points in ascending order. Tip: Drive the points multiple times to avoid GNSS errors
4. Let the robot drive to the points in descending order. Tip: Use a different color.
Image: Example of seven collected points (gray with crosses), marked in ascending (blue) and descending (green) driving direction. End points (gray) are not used for when calculating the calibration values
5. If calibration is needed, the ascending and descending points will differ significant.
6. Measure the distances along the line (driving direction) and diagonal to the line (sideways direction). Do not use the first and last point.
Image: example of measuring the X and Y error
7. Calculate the average error of your measurements in driving direction (x-coordinate) and side-ways direction (y-coordinate). Calculating the average error make the values more precise.
8. Add the measured values to the existing parameter values in Settings>Robot Behavior>Calibration.
- Tool calibrate x
- Tool calibrate y
9. Mark the points again to check if the adjustment has been successful.
Tip: Determining the sign (+/-) of the calibration values:
Image: Determining sign (+/-) of tool calibration