Design Of The Electronic Compass Based On Weak Magnetic Sensors And Study Of Interference Compensation Algorithm

Electronic compass as a navigation tool, with high accuracy, rapid response, small size, low power consumption, low cost, suitable for mass production, etc., has been widely used in aerospace, aviation, marine, vehicle navigation, mobile positioning, biomedical, geographic mapping and other areas. In recent years, electronic compass has been extensively studied, and a lot of research was made, but the interference from the surrounding environment reduces the accuracy of electronic compass severely, there is a certain gap between practical. In this paper, an electronic compass based on the weak magnetic sensors was designed, an analysis of the causes of interference with electronic compass and effective interference compensation algorithms were put forward.In the first place, we introduce the measurement principle of electronic compass and derive mathematical relationships between the heading angle and measurement data of the sensors based on the establishment of a mathematical model by way of pure mathematics matrix to ensure that the rigor of the derivation,and then we design an system framework of electronic compass. Then we carried out the selection of the key components of the electronic compass and design an electronic compass hardware measurement system which contains main control module, sensor module, power module and display module and data transmission module based on the system framework of electronic compass and hardware design requirements. Finally, a design of the software program supporting the hardware of electroinc compass was proposed, based on the design of the hardware supporting software program, wherein the sensor module transmit the measurement data via IIC bus to the control module, and the control module figure out the heading angles and send the heading angles to LCD or send to a computer via the USART data bus.According to the material properties of soft magnetic materials and hard magnetic materials, an mathematical model of soft magnetic interference and an mathematical model of hard magnetic interference were established, respectively, and based on the mathematical models of hard and soft magnetic interference, an trajectory expression indicating the measurement data distribution was given which is proved that the hard and soft magnetic interference makes the distribution of the magnetic sensor data from the origin to the center of a perfect circle distorted into an oval origin deviate from the origin. In this paper, analyzes on the triaxial no quadrature error, sensitivity error and zero drift error of the electronic compass and establishment of appropriate mathematical models were also given, the mathematical models proved the triaxial no quadrature error and sensitivity error interference effects of electronic compass can be equivalent to the soft magnetic interference, zero drift error can be modeled as a hard magnetic interference.Finally, an analysis of the vibration acceleration vectors for three-axis acceleration sensor influence when the electronic compass is used in vibration environments and an establishment of the corresponding mathematical models were presented. Based on the mathematical models of the vibration interference, we have proposed limiting filtering and recursive averaging method to compensate for the vibration environment of the electronic compass interference and achieve results show that this method can effectively filter the measurement data inferferenced by occasional vibration disturbance and smooth the measurement data. Based on the mathematical models of the soft and hard magnetic interference, we have proposed the ellipse minor axis compensation method and the improved least squares ellipse methods to compensate for the soft and hard magnetic interference. Ellipse minor axis method is proposed based on the geometric characteristics of the ellipse, which is fast, small computational features, especially for embedded processors with not strong computing power. The improved least squares ellipse method was based on the least squares ellipse methods, in which the hard and soft magnetic interference was compedsated for respectively. The improved least squares ellipse method has high accuracy and can make up for the great defects of the great amount of computation of the least squares ellipse method. The experiment data proves that ellipse minor axis compensation method and improved least squares ellipse method can quickly and effectively compensate for the hard and soft magnetic interfere. Through comparative analysis, the measurement accuracy of the electronic compass can be achieved within 1° after compensation, and the maximum measurement error of the electronic compass can reach 23 ° without compensation.