Patent ID: 8821365

Claim:
A rotation drive device including a housing having first and second chambers partitioned from each other by a diaphragm, a rotor rotatably provided in said first chamber along said diaphragm, and a drive unit provided in said second chamber for driving said rotor to rotate with said diaphragm interposed therebetween, said rotor comprising a plurality of first permanent magnets, the first permanent magnets having an angular spacing between each magnet, each of said first permanent magnets being magnetized in a direction orthogonal to said rotation direction of said rotor, every two adjacent ones of the first permanent magnets having magnetic polarities different from each other, said drive unit including: a plurality of first magnetic materials arranged to face said plurality of first permanent magnets, a plurality of coils wound around said plurality of first magnetic materials, respectively, for generating a rotating magnetic field; wherein a plurality of second permanent magnets is provided in said rotor and magnetically coupled to said plurality of first permanent magnets, wherein each of said second permanent magnets is provided correspondingly to a gap between every two adjacent ones of the first permanent magnets, and is magnetized in said rotation direction of said rotor, wherein each of said second permanent magnets is inserted in a corresponding gap, each of said second permanent magnets has a first magnetic polarity oriented to one of the two adjacent first permanent magnets having the first magnetic polarity oriented to the diaphragm, and each of said second permanent magnets has a second magnetic polarity oriented to the other of the two adjacent first permanent magnets having the second magnetic polarity oriented to the diaphragm; and wherein a ratio of a surface area of each of said second permanent magnets facing said diaphragm to a surface area of each of said first permanent magnets facing said diaphragm is set to be ½ or more and 2 or less.