Research Of Integrated Hall Magnetic Encoder

In the motor control system, the position sensor is essential in providing the rotor position for the implementation of motor position control, so the position sensor has already become an important part of motor control system. The common position sensor includes the electromagnetic induction rotary transformer, the photoelectric encoder, and the magneto resistor encoder. The position sensor is applied in many fields. With the requirement of position measure getting higher and higher, the traditional position sensor can't work in some special fields because of the drawbacks in itself. For example, in the large power motor control system, the problem of electro magnetic compatibility is so serious that the photoelectric encoder can't work. Usually the traditional rotary transformer is used, of which the size is large and the precision is low.This dissertation presents a new type of position sensor: the integrated hall magnetic encoder(IHME). In order to apply the sensor to the market, the dissertation focuses on the research of the key points, which affect the precision accuracy, stability and consistency of IHME. The magnet field optimization and circuit compensation are presented through the magnetic field calculation and analysis. IHME is designed based on DSP. Compared with the traditional rotary transformer, IHME is higher in precision but lower in size. It surpasses the photoelectric encode in the environment adaptation ; its errors of amplitude and phase are rather small. It is less sensitive to the alignment error; its mechanical structure and fabrication process are simple. IHME can output the position information in many modes, and therefore it can replace the traditional position sensor.The achievement of high quality air-gap magnetic field is the key point in the research of IHME. The air-gap magnetic field with two poles is designed first. The method of magnetism charging is analysed and the magnetic space distribution after charge is exhibited. Furthermore, the creation method of magnetic fields with multiple poles is presented. The magnet field distributions caused by different magnet shapes and materials are shown. The character curve of air-gap field is obtained through the magnet field calculation and analysis, which provides the laws for the magnet field optimization.In the manufacture process, owing to the magnetism charging and mechanical fabrication , the magnet distribution and the position of Hall component are non-ideal, which influence the final position calculation. The dissertation analyses the different errors, such as amplitude unbalance, DC component, harmonic component, orthogonal error, error caused by over-strong of magnet, from which the arithmetic expression of the position calculation error is deduced.According to the errors caused by the different sources, the dissertation presents a solution that an annular iron is placed around the magnet with the same center and then the space distribution of the magnet field is recalculated. The analysis of the changes of magnetic fields caused by the unideal position of the magnetic steels , the iron and Hall component shows that compared with non-iron magnet, the optimization method can improve the air-gap, decrease the error influence of iron disalignment and Hall asymmetric, and therefore it can decrease the amplitude and phase error indirectly.The magnetic field information is first checked by Hall component and is transformed to electric signal and then is transformed to digital variables by ADC. The transform of shft to angle is calculated form the two channels of the orthogonal digital variables. The different transformation algorithms from shaft to angle separately based on arc tangent and tracing RDC methods are presented. And the CORDIC algorithm is improved in order to apply to the decoder algorithms of IHMN.The mechanical structure of IHME is optimized, so a new magnetic field structure with double magnets and compound field is designed and its size becomes smaller.The position information is output after calculation. The requirement of output modes in different application field is quite different. In the dissertation, several output modes are implemented, including synchronous serial signal, PWM signal, incremental A B Z signal and analog signal. IHME with the double magnets and compound field can also output commutation signals for brushless DC motor. The experiments have been carried on for every output mode. The experiment results have been analysed and a lot of data and wave graphs are obtained. The application field for every mode is introduced, and the characteristics of IHME with different signal output modes are emphasized too. The application result of IHME in servo system of car antenna shows that IHME is characterized with small size, high precision, and high reliability, so it is suitable for different motor control systems.