IMU Mounting Angle Calibration for Pipeline Surveying Apparatus

Odometer and nonholonomic constraints are crucial external aids for inertial navigation systems (INSs) to achieve desirable positioning accuracy for pipeline inspection gauges (PIGs). Exploiting the maximum potential of these constraints requires the accurate knowledge of the inevitably existing misalignment in the attitudes of the inertial measurement unit (IMU) with respect to the host vehicle (i.e., the IMU mounting angle relative to the PIG). In this paper, we address the mounting angle calibration of a PIG without using sophisticated equipment. Instead, the proposed method only requires the PIG to be placed on a simple leveled frame and rotated about its longitudinal axis. In this case, the existing IMU mounting angles will make the IMU's pitch and heading angles vary with rotation. Closed-form analytic solutions for the IMU's attitude angles are obtained under this specific condition and show that the magnitude and phase of the IMU's pitch and heading angles have a linear relation with the corresponding pitch and heading misalignment angles. Then, a method for the misalignment angle estimation is presented based on this principle. Simulations are performed to validate the proposed method and investigate the related error sources that influence the estimation accuracy. The results of the real tests indicate that the mounting angles can be accurately estimated and compensated through this simple and convenient calibration.