Optimal higher-order encoder time-stamping

Abstract

Optical incremental encoders are used to measure the position of motion control systems. The accuracy of the position measurement is determined and bounded by the number of slits on the encoder. The position measurement is affected by quantization errors and encoder imperfections. In this paper, an extension to the time stamping method is proposed. The time stamping method uses encoder events, consisting of encoder counts and their time instants captured at a high resolution clock, to estimate accurate position, velocity and acceleration signals in real-time. The extension includes skip and delay options in order to obtain good position, velocity and acceleration estimates even for a very limited number of stored events, as desired in many embedded control applications. The time-stamping method with skip and delay options is referred to as higher order time stamping (HOTS). Real-time experiments on a motion system show that the proposed HOTS method significantly improves the position, velocity and acceleration estimates compared to the original time stamping method.