Calibration, Alignment, and Dynamic Tilt Maintenance Method Based on Vehicular Hybrid Measurement Unit

Aiming at the urgently required for miniaturization, low cost and high reliability in north seeking, and attitude maintenance, a six-axis MEMS inertial measurement unit (IMU) and single-axis fiber optic gyro (FOG) composite measuring device is proposed, in which the six-axis MEMS IMU is installed in a conventional orthogonal configuration; while the single-axis FOG is mounted in parallel with the MEMS horizontal X-axis approximately. Based on this new combinational inertial measurement device, there are two functions can be achieved: North-seeking function, three-axis MEMS accelerometers, and single-axis FOG are used to complete four-position north seeking and initial horizontal attitude calculation. Once the alignment is completed, the novel equipment constructs an attitude maintaining device and transfer the calculated attitude and orientation results to the six-axis MEMS-IMU. Concerning the low-speed working environment and changeable motion state of the equipment, the static state and uniform motion of the instrument can be automatically detected. The MEMS gyro error and attitude error are corrected by filter while in static and uniform-speed state, and maintain attitude tracking in other condition. A detailed calibration, alignment, and attitude maintaining method of the new measuring device is introduced in this paper. The calibration of the turntable, the multi-position alignment of the turntable, and the dynamic performance experimental results demonstrate that the novel equipment and method can effectively and feasibility achieve the user index requirements. The three-axis alignment accuracy is better than 1.5 degree (3σ), and the 15-minute tilt maintaining accuracy is better than 2 degree (3σ).