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Abstract

Before detecting a mechanical angular absolute position θabs of a rotating shaft (4) within one turn using a two-pole absolute value encoder (2) and a multi-pole absolute value encoder (3) having Pp (Pp: an integer of 3 or more) pole pairs, the rotating shaft (4) is rotated to measure a temporary absolute value θelt of the multi-pole absolute value encoder (3) in relation to each absolute value θt of the two-pole absolute value encoder (2), and a temporary pole-pair number (Nx) for a multi-pole magnet is assigned to each absolute value θt. In actual detecting, an absolute value θti of the two-pole absolute value encoder and an absolute value θelr of the multi-pole absolute value encoder are measured, the temporary pole-pair number (Nx) assigned to the absolute value θti is corrected on the basis of an absolute value θelti of the multi-pole absolute value encoder assigned to the absolute value θti and the measured absolute value θelr, thus calculating a pole-pair number (Nr). The absolute position θabs is calculated using an expression of (Nr×θelp+θelr)/Pp with a mechanical angle θelp corresponding to an electrical angle of one period of an output signal of the multi-pole absolute value encoder.

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