Calibration of Incremental Position Encoder for the Precise Measurement of Low Speeds

Accurate speed measurement is mandatory for precision electric drives. These drives frequently utilize incremental position encoders for speed measurement as a derivative of the position in time. At present, the best practice is the implementation of the constant elapsed time (CET) methods, which operate with the position increment of multiples of four owing to the inaccuracies of the position encoder. The position increment defines the measurement time or the delay in the feedback, which strongly affects the performance of the speed loop. At low speeds, the position increment should be made smaller than four to keep the measurement delay within the limits of speed loop stability. However, the utilization of position increments smaller than four leads to high errors in speed estimation due to the uncompensated errors of the incremental encoder. Therefore, this study examined the errors of the incremental encoder to propose a calibration strategy for the synchronous CET speed estimation technique, which allows for accurate speed measurement at low speeds. The experimental results proved that the proposed method helps in decreasing the minimum measurable speed four times more than the original synchronous CET method with acceptable accuracy and computational complexity.