The measurement and error analysis of instantaneous angular speed using optical incremental encoder

Optical incremental encoders are used widely in rotating machinery to obtain the motion information, such as CNC machine tools and robotics. The motion information can be employed to investigate the dynamic properties for the rotating machinery. For example, the instantaneous angular speed (IAS) obtained via this way contains a lot of useful information related to the operating condition and health state of the machine, which can be used for condition monitoring and fault diagnosis. The measurement scheme for IAS by using optical incremental encoder is investigated. Subsequently, the relationship between estimation error of IAS and some parameters are discussed, such as the sampling frequency, the count number of encoder and the interpolation selection of the sinusoid output signal. Finally, an IAS estimation approach based on polynomial fitting is given. At the same time, the relationship between IAS estimation accuracy and the order of polynomial, the number of fitting points is also investigated. The effectiveness of this approach is verified by using some simulations and experiments on a CNC machine tool. The vibration source is determined successfully by using the proposed method.