Analysis And Application Of Real-time Compensation For Positioning Precision Of The Turntable With Harmonic Function

The turntable can realize continuous measurement of circular angle.It is widely used in precision engineering,aerospace navigation,national defense and other fields,and plays an important role in the measurement standard device system.The accuracy of the turntable angular position is inevitably affected by factors such as component size error,circular grating installation eccentric error and deviation error,tilt angle rotation error and others.With the development of science and technology,the requirements for the accuracy of the turntable’s angular position increase highly.To obtain higher angular position accuracy without changing the structure of the turntable,the compensation of angular position error is required.Through the investigation of the compensation methods for angular position error of the turntable,the software compensation method for harmonic error has been widely used which has advantages of simple operation and remarkable compensation effect.However,the compensation process is completed offline in the upper computer,which has the problem of low real-time performance.To resolve this problem,this paper proposed a new real-time compensation method: it obtains the harmonic error function model of the turntable which based on the fitting of harmonic analysis method,and carries out the research of real-time compensation method of turntable angular position error based on the error model.The main contents include:(1)The compensation principle of angle position error is analyzed according to the periodic characteristic.Since only discrete position error compensation can be realized,the principle of using harmonic analysis to fit the turntable’s harmonic error function is illustrated,and continuous angle position error compensation can be realized according to the function.Aiming at the low real-time problem of software compensation method of harmonic error,the feasibility of the proposed real-time compensation method is expounded.(2)The key parameters of the harmonic error function in fitting process are analysed,and the feasibility of the CORDIC calculation error function principle is isillustrated.The CORDIC algorithm principle error are analysed,the accuracy quantification model in the harmonic error function calculation process are established and the calculation accuracy loss are evaluated.(3)Development of a FPGA circuit system for real-time compensation of the turntable signal reception and angular position errors,design of a four-interpolation circuit for the readhead signal and a harmonic error function calculation compensation circuit,as well as evaluation of the resource usage of the circuit system and the real-time performance of the error compensation method.(4)The calibration experiment of turntable angle position error is carried out to obtain the error data.Four numerical fitting methods are used to fit the error model respectively,and the superiority of harmonic analysis method is compared.Aiming at the fitted harmonic error function of the turntable,the correctness of the quantization model of the error function’s calculation accuracy is verified by circuit experiments.Turntable position error compensation experiments are carried out,and the accuracy of turntable angular position is improved from 29.0″to 5.3″.The effectiveness of the real-time compensation method for the turntable angle position error proposed in this paper is verified through experiments.