Patent ID: 8847585

Claim:
A magnetic absolute encoder comprising: a bipolar magnet in which a circular external peripheral surface thereof is a bipolar magnetized surface; a bipolar-side first magnetic detection element and a bipolar-side second magnetic detection element for obtaining detection signals that differ 90 degrees in phase in accompaniment with rotation of the bipolar magnet; a multipolar magnet in which a circular external peripheral surface thereof is a multipolar magnetized surface of four or more poles, the multipolar magnet being adjacently arranged in a coaxial state in relation to the bipolar magnet; a multipolar-side first magnetic detection element and a multipolar-side second magnetic detection element that are used for obtaining detection signals that differ 90 degrees in phase in accompaniment with rotation of the multipolar magnet; a flexible printed-wiring board on which the bipolar-side first magnetic detection element, the bipolar-side second magnetic detection element, the multipolar-side first magnetic detection element, and the multipolar-side second magnetic detection element are mounted; and an annular board-holding part arranged in a coaxial state in relation to the bipolar magnet, wherein the board-holding part holds the flexible printed-wiring board in a loop shape so as to surround the bipolar magnet and the multipolar magnet, and the bipolar-side first magnetic detection element and the bipolar-side second magnetic detection element face the bipolar magnetized surface of the bipolar magnet at a fixed interval, and the multipolar-side first magnetic detection element and the multipolar-side second magnetic detection element face the multipolar magnetized surface of the multipolar magnet at a fixed interval, and wherein the board-holding part is provided with an annular base plate, and first and second board-mounting bases that are arranged at predetermined angular intervals so as to be positioned on a same circle on an annular end surface of the base plate, the first and second board-mounting bases are provided with first and second board-mounting surfaces, respectively, that face a center of the same circle and that are perpendicular to the annular end surface, the reverse-side portion of the flexible printed-wiring board is secured to each of the first and second board-mounting surfaces, the bipolar-side first magnetic detection element and the multipolar-side first magnetic detection element are mounted to a surface of a portion that is secured to the first board-mounting surface of the flexible printed-wiring board, and the bipolar-side second magnetic detection element and the multipolar-side second magnetic detection element are mounted to a surface of the portion secured to the second board-mounting surface of the flexible printed-wiring board.