On velocity estimation using position measurements

Velocity measurement is often required in control system design of mechanical machines including robot manipulators. However, precise velocity measurement/estimation remains a challenging task, especially for very slow motions. Several methods have been published to estimate velocity from position measurements, typically the output of an incremental optical encoder. In the present work, a simple and efficient method is proposed to estimate velocity from an incremental encoder pulse train. Based on the physical characteristics of incremental encoders, the proposed method allows the user to select the estimation precision and to tune the time delay, and yet requires less calculation than other methods. The proposed method has been evaluated experimentally using a direct drive robot arm. An external laser dynamic calibrator is used to obtain accurate reference velocity measurements for comparison. The experimental results have confirmed the advantages of the proposed method.