Design And Accuracy Analyses Of Measurement System For Photoelectric Encoder

Photoelectric encoder has been widely used in aero industry and military devices,it has merits of small size,light weight,and stable operation,is a kind of measurement device utilizing Moiré fringe generated by circular grating disk.Alongside rapid advancement of science,technology,aero industry and military cause,more requirements is proposed for the accuracy and stability of photoelectric encoder,so in the process of research and production,it is necessary to test all the encoders and have control of their error.This paper focuses on the measurement system for small photoelectric encoder;it is capable of testing the static error and dynamic error under different rotary speed with the same system,and will be great meaning for the research,manufacture and maintenance of photoelectric encoder.After comparing the merits and demerits of different rotary measurement systems,the structure of the measurement system is chosen.The reference encoder is designed with its main shaft as a whole,as well as the flexible connecting and its supporting base.2D and 3D drawing and modeling is accomplished with software UG NX,and then transformed into entity by mechanical workshop.Mechanical analyses of the flexible parts of the system are carried out by finite element software ANSYS Workbench.The influence of mechanical deformation of the flexible parts to the accuracy of the measurement results is analyzed.Modal analyses of the integrated shaft are conducted and each rank of modal frequencies and corresponding vibration type are obtained to testify the stability of the system.Motor servo theory is studied so that the motor can be control to rotate staidly with speed ranging from 1r/s to 20r/s.The motor is capable of rotating clock wisely and counter-clock wisely,and can be stopped and started at any point.Influence of installation error to the accuracy of the measurement results is analyzed.The relation between the misalignment angle between the measured encoder and the reference encoder with the measurement error added to the results are concluded.Maximum misalignment angle limit is given so that the measurement results can make sense of the error of the measured encoder.By adjusting the installation angle of the motor reasonably,the error brought in installation error of the encoder and error from the manufacture of the measurement system can be reduced,so that the accuracy of the measurement can be improved.The measurement system designed in this paper is small in size,with stable operation and high accuracy;it's independent of working conditions,and can be easily installed.It can measure encoders of its static and dynamic error,with a low speed or high speed and rotation direction clockwise and counter-clockwise,this paper will be of great meaning for the manufacture and design of photoelectric encoder.