Design Of High Performance Incremental Encoder Decoder Based On FPGA

Optical encoder is a sensor which transforms mechanical displacement of the output shaft geometry into a pulse or digital by photoelectric conversion.It has been widely used to measure the angle of the servo system and played a crucial role in control of the servo system.With the requirement on precision of the servo system is more and more high,how to improve the accuracy of angle measurement has become an urgent problem.There are two ways to improve the precision of angle measurement,the one is to use a photoelectric encoder which has a higher precision;the second is to deal with the signal through the external circuit segment,it forms a position sensor of ultra high resolution by using moderate resolution encoder and digital times subdivision circuit.Directly using high resolution encoder is not only expensive but also exist difficulties on making craft.Therefore,this article design a angle encoder calculating system based on FPGA to realize a high precision of Angle measurement.In the first place,on the base of the study of the theory,structure and classification of photoelectric encoder,this thesis makes detailed analysis of the photoelectric encoder and has defined using Incremental photoelectric encoder as the measuring device.Then the principle,advantages and disadvantages of Various subdivision algorithmare has been compared and finally used cordic to realize the arctangent calculations.The signal of the photoelectric encoder is divided into two road after dealing with the differential amplification and filtering.One signal formates square wave signal which used to counting and debate through the shaping circuit and then sent into the FPGA to form the angle of the coarse part code;another sent to the FPGA to achieve the calculation of the angle by the cordic algorithm after A/D conversion and then get the angle precision code.After these calculations,we sent the final data to dsp to control.In this paper,as the traditional cordic algorithm haslimitations in angle coverage and slow speed,we had improved the problem based on the study of traditional cordic algorithm.This paper realizated the range of(0,360°)decoding through quadrant method and improved the calculationspeed.On the basis of the hardware design,we had writed the angle calculation module and count the defense to the module with the VHDL language and verified the feasibility and accuracy of the improved algorithm through Quartus.The experimental results show that the decoding system can improve the calculating speed and precision,has a very good dynamic performance and can meet the requirements of motor control.