An easy speed measurement for incremental rotary encoder using multi stage moving average method

Classical theoretical algorithms to calculate rotation speed from incremental encoder information, frequency counting and period counting algorithm, delivers notable measurement error which is a function of rotation speed. This error will cause failure in overall motor control algorithm, resulting in both motor and drive failure. Furthermore, the needs of FPGA as high frequency clock calculation device in period counting algorithm made the implementation cost higher. Two stages moving average method was implemented to reduce error. In addition, DSP sampling time will be used to replace high frequency clock generated by FPGA. With these proposed methods, more accurate speed measurement result can be achieved and no FPGA needed to implement the algorithm. In addition, less data samples are needed compared to classical method. Implementation result in PMSM motor control shows that these methods are able to reduce quantization error that generated when measuring speed using rotary incremental encoder, showing no observable electrical or mechanical problem.