Patent ID: 7388308

Claim:
A built-in motor type spindle device comprising: a housing including a cooling jacket to which a cooling medium is supplied from an outside; a main shaft; a static pressure bearing for supporting the main shaft rotatably with respect to the housing by a pressure transmission medium which is supplied to a clearance between the static pressure bearing and the main shaft; and an AC servomotor comprising: two lines of magnets mounted on the main shaft so that opposite polarity poles are arranged alternately in a circumferential direction; and two pairs of coils mounted in the housing so as to face the two lines of magnets respectively, the two pairs of coils being wound around two pairs of cores respectively, wherein phase arrangements of at least one of the opposite polarity poles of the two lines of magnets and the pairs of cores are displaced from each other in a circumferential direction, and, wherein at least one of the two lines of magnets and the two pairs of cores has skews whose directions are opposite to each other wherein when both the two lines of magnets and the two pairs of cores have the skews, angles of the skews are different from each other.