A discrete position encoder is an inexpensive means for sensing the angular position of a rotating device. Often a system with higher performance can be achieved if the angular velocity is known in addition to the position. Typically, the output of a discrete position encoder is two square wave signals in quadrature. This paper investigates various methods for processing these signals to observe the velocity in real time. High performance observers based on Taylor series expansions, backward difference expansions, and least square curve fits are developed. The accuracy of the different observers are analyzed by simulations for systems with time measurement truncation and imperfect encoders. The least square curve fit based observers are the most tolerant observers investigated due to the inherent low pass filtering.
Ronald H. Brown,
Susan C. Schneider,
"Velocity Observations From Discrete Position Encoders", Proc. SPIE 0858, Signal Acquisition and Processing, (1 January 1987); doi: 10.1117/12.968287; https://doi.org/10.1117/12.968287