Decoding Research Of Sinusoidal Encoders

In high precision and high dynamic performance servo system, real-time and accurate measurement of the rotor position and speed must be required. The sinusoidal encoder is a sensor of converting the mechanical geometry displacement of the rotary shaft to digital, which provides technology solution for the measurement of the rotor position speed. The sinusoidal encoder is an optical encoder which can output quadrature sinusoidal signals, can obtain much higher precision than ordinary TTL encoder after subdivision, and costs far lower than ultra-high-precision optical encoders. Its high cost performance makes it widely used in high-precision motion control application.Firstly,the current development of the sinusoidal encoder is analyzed, and a variety of subdivision algorithms currently proposed are analyzed and compared. After analyzing the principle and signal characteristics of cosine encoders, the paper analyzes the key points of the decoding process with takeing the look-up table algorithm as an example. Afterwards, the principle and implementation process of the CORDIC algorithm and the closed-loop subdivision algorithm was described. The closed-loop subdivision is valuable in the subdivision algorithm research for its strong anti-interference ability, high precision segmentation and short computation time. Moreover, the CORDIC rotating coordinate system eliminates the process of floating-point operation, solves the problem of long computation time bringing by the long floating-point operation for the Trigonometric function. Therefore, the paper takes the closed-loop subdivision as the main subdivision algorithm with the CORDIC for achieving cosine operation as an auxiliary, which shortenes the operation time in segment maximize accuracy.Secondly,the paper established a system of hardware decoding with taking diodes rectifier and IGBT inverter circuit. The decoding circuit design is one of the main decoding system program. About the principle of circuit design and the parameter, the paper has done a detailed introduction. The decoding circuit involves two key technologies, which is the encoder signal shaping and the square wave interference. Since the output signal of the encoder does not meet the acceptable level of the DSP requirement, the sinusoidal signal needs to be filtered, raised and zoomed, which will be done by differential amplifiers. For the problem of the square wave signal interference, the paper also uses the D flip-flop design which has a strong anti-interference ability for jitter and peak interference.At last, the paper designed and experimented the decoding program of the sinusoidal encoder. The subdivision algorithm and the calculation of the angel position is accomplished in interrupt program. After completing the program design, the article verified the application characteristics of the sinusoidal encoder by experiments in permanent magnet synchronous motor. The experimental platform takes FP50R12KT3 as the main circuit, TMS320F28034 as the controlling chip, and the permanent magnet synchronous motor as drive object. The experimental result has demonstrated the feasibility of the scheme.