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Abstract

The present invention aims to easily suppress noise components of aliases when measuring a velocity based on an output from an encoder. The invention comprises a step for converting in which two-phase signals indicating the movement of a spinning body, etc., are converted to a ternary pulse train signal having a positive or a negative or a zero value corresponding to the phases of the two-phase signals, a step for low pass filtering in which a low frequency component of the pulse train signal is obtained by arithmetically processing the pulse train signal and filter coefficients, and a step for output-sampling in which the signal obtained by the step for low pass filtering is sampled at a predetermined sampling period. In the step for low pass filtering, a convolution (operation for convolution) between the pulse train signal obtained by sampling the pulse train signal at a predetermined period and the filter coefficients is carried out. Sampling the pulse train signal is synchronized with and has the same phase as reading the filter coefficients for the convolution. The sampled signal by the step for output-sampling is output as a velocity signal corresponding to the velocity determined by the two-phase signal.

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