A Speed Measurement Algorithm for an Incremental Encoder Based on Pulse Period Measurement Using a Digital Filter
Aleksey Anuchin, Valentina Podzorova, Yuliya KAZEMIROVA, Dmitriy Savkin, Maksim Lashkevich, Chen Xao, Galina Demidova · Vestnik MEI · 2024
Precise rotor speed measurement is a must for machine tool spindle drives and other drives that shall comply with stringent requirements for speed stabilization accuracy. These drives are commonly equipped with incremental encoders, which determine speed as a time derivative of the displacement. Currently, the best solution for speed measurement is to use a constant elapse time method, the accuracy of which is limited by the encoder accuracy and the elapse time measurement quantization. However, the constant elapse time method ignores all intermediate data on the pulses arriving from the encoder and uses only those required to measure the speed at the current moment. An analysis of the periods (time intervals) between the pulses from the encoder has shown that these periods have the properties of delta-sigma modulated signals. Thus, it was suggested to process the results of the period-based speed measurement method using a high-order digital sinc filter to obtain additional information from the incoming data. The proposed period-based method involves a third-order sinc filter as the filtration type most commonly used in measurement equipment. To demonstrate the efficiency of the proposed method, a simulation model was developed, which shows the error distribution for the suggested and classical methods considered in the study. The experimental results have been obtained both for a steady operation mode and for the drive speeding-up mode. The methods have been compared for the same input data and the same measurement time. The simulation and experimental results have shown that at high speeds the proposed period-based method with sinc3 filtering provides a much smaller r.m.s. deviation from the actual value than the other methods. The computational complexity of the proposed method was analyzed, and a conclusion can be drawn from the analysis results that it can be implemented using modern microcontrollers.