Method of velocity measurement based on Moiréfringe and nonlinear tracking differentiator

In order to realize velocity and acceleration measurement at low speed, a new type method of velocity measurement at low speed was designed which is based on the method of Moirfringe and nonlinear tracking differentiator. First of all, the electric signal of Moirfringe was analyzed. Then the electric signal from photoelectric encoder was filtered by nonlinear tracking differentiator and the phase delays were compensated. Finally, velocity and acceleration measurement was realized by using cascaded nonlinear tracking differentiators. The test proves that the stationarity and precision of velocity measurement at low speed are improved, as well as the sampling frequency. The method was applied in a system with a 21-bit encoder as the angle sensor, and velocity and acceleration could be measured. When the speed is 0.001 7()/s and sampling time is 5 ms, sampling numbers is 20 times than that of ordinary methods. The real-time performance, stationarity and precision of velocity measurement at low speed can be improved by using the method.