Body to Vehicle Frame Rotation Calibration Routine

Kinematic alignment requires that the rotational offset between the vehicle and IMU Body frame (RBV) is known. If the angles are simple (that is, a simple rotation about one axis) the values can easily be entered manually through the SETINSROTATION RBV command. If the rotational offset is more complex (that is, rotation is about 2 or 3 axis), then the calibration routine provides a more accurate estimation of the values.

The steps for the calibration routine are:

  1. Apply power to the receiver and IMU.

  2. Configure the SPAN system including an approximate IMU Body to Vehicle frame (RBV) rotation. See SPAN Configuration.

  3. Ensure that an accurate lever arm has been entered into the system either manually or through a lever arm calibration, see Lever Arm Calibration Routine.

  4. Perform an initial system alignment using one of the methods described in System Start-Up and Alignment Techniques. Ensure the system reaches Solution Good.

  5. Enable calibration using the INSCALIBRATE command with an optional standard deviation target.

    INSCALIBRATE RBV NEW [target_stdev]

  6. To monitor the calibration, log INSCALSTATUS using the ONCHANGED trigger.

  7. Start to move the system. As with the lever arm calibration, movement of the system is required for the observation of the angular offsets.

    Drive a straight course on level ground (remember that most roads have a crown resulting in a constant roll of a few degrees). Avoid driving on a surface with a constant, non-zero, slope to prevent biases in the computed angles. Vehicle speed must be greater than 5 m/s (18 km/hr) for the calibration to complete.

  8. When the calibration is complete, either because the accuracy requirement has been met, or the calibration been stopped by user command (INSCALIBRATE command), the calibrated offset value is automatically applied can be viewed in either the INSCALSTATUS log or the INSCONFIG log.

To save a calibrated rotation for subsequent start ups, issue the SAVECONFIG command after calibration is complete. Each time the IMU is re-mounted this calibration should be performed again. See also Static Coarse Alignment and Kinematic Alignment for details on coarse and kinematic alignment.

After the INSCALIBRATE RBV ENABLE command is entered, there are no body-vehicle rotation parameters present and a kinematic alignment is NOT possible. Therefore this command should only be entered after the system has performed either a static or kinematic alignment and has a valid INS solution.

As with the SETINSROTATION command, the minimum standard deviation that will be applied is 0.25 degrees (as viewed in the INSCONFIG log), even though the INSCALSTATUS log may report lower standard deviations after a successful calibration.