Research Of Magneto-Inductive Electronic Compass And Calibration Method

Electronic compass by measuring the orientation of the earth magnetic field has been widely used in many fields such as aerospace, aeronautics, marine, robotics, vehicle autonomous navigation, indoor navigation, activity monitoring because of its small size, lower energy consumption, high precision, low cost, etc. Magneto-inductive sensor were chosen as the sensing element for earth magnetic field measurement because it has many advantages such as low power, little temperature, wide measurement range, etc. Moreover, the output of the magneto-inductive sensors is inherently digital and can be fed into microprocessor directly. The simplicity of circuit with lack of signal conditioning makes it easier and less expensive to use in product design. By combining magneto-inductive sensors with three-axis digital accelerometers, the electronic compass was developed. Electronic compass must be calibrated before used to eliminate the errors caused by the bias, misalignment, inconsistence in sensitivity and external magnetic interference. The work in this paper mainly focused on calibration method of electronic compass.Firstly, the working principle of electronic compass was elaborated in detail, and the formula of computing tilt angle by the measurement of gravitational vector with accelerometers was introduced. Similarly, the formula of heading calculation is also given. Then, this paper presented the overall hardware schematic of electronic compass. And, the signal acquisition and processing of magnetic sensors and the accelerometers were discussed in detail. A high-precision non-magnetic three-axis rotation platform with high-resolution optical encoder was designed and manufactured in order to implement and verify the calibration method. Moreover, the software flow diagrams were presented according to the functional needs of electronic compass, and the software development of electronic compass was completed.The errors of electronic compass can be divided into instrumentation error and magnetic deviation according to the different sources. Next, an improved least square method for ellipsoid fitting based on matrix decomposition was given which overcame the drawbacks of general non-iterative ellipsoid fitting algorithm. Aimed at the shortcomings of existent calibration methods, an error-separation calibration method based on non-magnetic three-axis rotation platform was presented, which not only can eliminate the different errors effectively, but also evaluated the individual effect on the heading error accordingly. Given to the practical requirement, a temperature compensation method for electronic compass was employed and was verified with experiment.