Research On Inertia Testing Turntable's Circular Grating Angle Module And Friction Compensation

In order to meet the needs of testing the new generation high precision inertia sensors, inertia testing turntables of higher precision have to be manufactured. This paper takes inertia testing turntable-whose angular measurement accuracy is asked to be 0.5 arc sec-as the background, and takes the single-axis prototype turntable in our lab as the experiment platform, and has mainly researched the circular grating angle measurement module's angle accuracy and friction torque compensation technology which have great influence on low-speed rate stability.Circular grating angle sensor has higher precison than inductosyn. The circular grating angle measurement module installed two opposite-in-diameter readheads, which has efficiently reduced the error introduced by scale eccentricity and distortion. In order to further reduce the angle measurement error, a discrete calibration of angle measurement error was made by a photoelectric auto-collimator and a 23-face metal polyhedron. Through harmonic anlysis of the error signal by FFT (Fast Fourier Transform), we got the harmonic coefficients. A software- based harmonic compensation was made, and the finally angle accuracy reached 0.5 arc sec.After the circular grating angle module giving high precision angle signal, turntable control system experiments were made at the single-axis prototype turntable. First, the turntable's mathematic model was made, and a series adjustment algorithm was proposed, and finally the algorithm was realized on a Digital Signal Processor (DSP). The experiments on the prototype turntable have demonstrated that in middle and high rate, the turntable works well and meet the performance requirements. Howerver, in low rate, the turntable emerged stick slip phenomenon, and the low rate stability is poor.The friction torque on the turntable's shaft is the main reason for stick slip phenomenon. The paper has investigated the way of friction compensation to improve low rate stability. In order to track the friction torque in real-time, and make precision friction torque compensation, an adaptive friction compensation algorithm based on LuGre model was proposed, and simulation experiment has illustrated the algorithm's validity.