Rotational position detecting device which compensates for eccentricity of rotating object

Claim 1

An apparatus for detecting a rotational position of a rotating object, said apparatus comprising: a gear having teeth and mounted on the rotating object, said gear being of a magnetic permeable material; a first sensor located adjacent said gear for generating a first sine-wave signal E 1 in response to said teeth of said gear; a second sensor located adjacent said gear for generating a second sine-wave signal E 2 having a phase difference of 90° with respect to said sine-wave signal E 1 , said second signal being generated in response to said teeth of said gear; a pair of comparators for outputting two-phase pulse signals by respectively comparing said first sine-wave signal E 1 and said second sine-wave signal E 2 with a threshold; an up-down pulse counter for counting a number of said two-phase pulse signals output from said pair of comparators and for detecting a higher digit portion N of a positional information; a pair of sample-and-hold circuits for respectively detecting and outputting instantaneous values of said first sine-wave signal E 1 and said second sine-wave signal E 2 ; a pair of analog/digital converters for respectively converting said detected instantaneous values output by said pair of sample-and-hold circuits into digital values S 1 and S 2 ; and a digital computing circuit for calculating the rotational position of the rotating object using said digital values S 1 and S 2 and said higher digit portion N, wherein said digital computing circuit includes means for performing the following steps: (i) calculating a position θ at a lower digit portion of the positional information using one of equations: θ=tan -1 (S 1 /S 2 ) and θ=tan -1 (S 2 /S 1 ); (ii) calculating an amplitude V of the first sine-wave signal E 1 and the second sine-wave signal E 2 using an equation V=√S 1 2 +S 2 2 ; (iii) calculating an eccentricity error Δε caused by an eccentricity of the gear at the higher digit portion N from the amplitude V; (iv) detecting the rotational position of the rotating object using the higher digit portion N, the lower digit portion θ and the eccentricity error Δε.

Claim 2

An apparatus for detecting a rotational position of a rotating object, said apparatus comprising: a gear having teeth and mounted on the rotating object, said gear being of a magnetic permeable material; a first sensor located adjacent said gear for generating a first sine-wave signal E 1 in response to said teeth of said gear; a second sensor located adjacent said gear for generating a second sine-wave signal E 2 having a phase difference of 90° with respect to said sine-wave signal E 1 , said second signal being generated in response to said teeth of said gear; a pair of comparators for outputting two-phase pulse signals by respectively comparing said first sine-wave signal E 1 and said second sine-wave signal E 2 with a threshold; an up-down pulse counter for counting a number of said two-phase pulse signals output from said pair of comparators and for detecting a higher digit portion N of a positional information; a pair of sample-and-hold circuits for respectively detecting and outputting instantaneous values of said first sine-wave signal E 1 and said second sine-wave signal E 2 ; a pair of analog/digital converters for respectively converting said detected instantaneous values output by said pair of sample-and-hold circuits into digital values S 1 and S 2 ; and a digital computing circuit for calculating the rotational position of the rotating object using said digital values S 1 and S 2 and said higher digit portion N, wherein said digital computing circuit includes means for performing the following steps: (i) calculating a position θ at a lower digit portion of the positional information using one of equations: θ=tan -1 (S 1 /S 2 ) and θ=tan -1 (S 2 /S 1 ); (ii) calculating an amplitude V of the first sine-wave signal E 1 and the second sine-wave signal E 2 using an equation V=√S 1 2 +S 2 2 ; (iii) calculating an eccentricity error Δε caused by an eccentricity of the gear at the higher digit portion N from the amplitude V; (iv) detecting the rotational position of the rotating object using the higher digit portion N, the lower digit portion θ and the eccentricity error Δε.