Patent ID: 8330629

Claim:
A rotary input device comprises: a casing; a disc-shaped rotary member rotatably supported to said casing; an equally-spaced electrode holding plate having N first equally-spaced electrodes spaced equidistantly along a first circle and N second equally-spaced electrodes spaced equidistantly along a second circle parallel to said first circle, said equally-spaced electrode holding plate being attached to said rotary member, said N being an integer equal to or greater than 1, and said first and second equally-spaced electrodes being electrically interconnected; and a phase electrode holding plate having α a-phase electrodes disposed along a third circle opposite said first circle in parallel relation thereto and electrically interconnected, β b-phase disposed along a fourth circle opposite said second circle in parallel relation thereto and electrically interconnected, and first and second lead wires electrically connected to said a-phase electrodes and said b-phase electrodes, respectively, said phase electrode holding plate being fixed to said casing, said a being an integer equal to or greater than 1 and said β being an integer equal to or greater than 1; wherein said equally-spaced electrode holding plate and said phase electrode holding plate are disposed so that the centers of said first through fourth circles all lie on the line of the center of rotation of said rotary member and that said line of the center of rotation crosses at right angles all planes defined by said first through fourth circles, respectively; wherein when said α is equal to or greater than 2, two arbitrary ones of said a-phase electrodes lie on the circumference of said second circle at positions displaced an angle of an integral multiple of 2π/N apart; wherein when said β is equal to or greater than 2, two arbitrary ones of said b-phase electrodes lie on the circumference of said second circle at positions displaced an angle of an integral multiple of 27/N apart; and wherein said a-phase electrodes and said b-phase electrodes are arranged with respect to the arrangement of said equally-spaced electrodes so that the angle from the rotational angular position of said equally-spaced electrode holding plate where said first equally-spaced electrodes and said a-phase electrodes overlap most with each other to the rotational angular position of said equally-spaced electrode holding plate where said second equally-spaced electrodes and said b-phase electrodes overlap most with each other may be an angle that is displaced from an integral multiple of π/N by a predetermined angle ω which is greater than 0 but smaller than π/N.