Patent ID: 6160330
Filing Date: 2000-12-12
Classification: H02K,H02P

Abstract:
A three-phase stepping motor comprising:a rotation shaft rotatably supported by a pair of bearings provided in predetermined places of a housing so as to be in opposition to each other;a permanent-magnet rotor formed in a cylindrical shape so as to have south (S) and north (N) poles magnetized alternately in the direction of rotation on an outer circumferential portion of said rotor, or an induced magnetization rotor having S and N poles disposed alternately in the direction of rotation which are formed in a manner so that permanent magnets with the same polarity are fitted or formed so as to be identical in polarity at their surfaces in grooves formed parallelly to each other at a regular pitch in a surface of a magnetic body formed to be cylindrical in parallel to said rotation shaft and said cylindrical magnetic body is subjected to induced magnetization to form said S and N poles alternately in the surface of said cylindrical magnetic body, or a hybrid rotor constituted by two magnetic disks disposed on said rotation shaft perpendicularly thereto and a permanent magnet magnetized in the direction of rotation axis and held between said two magnetic disks, each of said two magnetic disks having pole teeth formed at a predetermined pitch at edge portions thereof, said two magnetic disks being displaced from each other in the direction of rotation by 1/2 of said predetermined; anda stator disposed so as to be in opposition to a surface of one of said rotors through a gap of a predetermined size, said stator having main poles the number of which is a multiple of 3, each of said main pole having a predetermined number of pole teeth and having a stator coil mounted thereon;wherein the following conditions are satisfied:(a) the number Q of said main poles is Q=6k, and k N-poles and k S-poles are formed in 2k main poles for each phase at the time of excitation of each phase, where k is an integer not smaller than 1;(b) the number Nr.sub.6 of S and N pole pairs of said rotor is set to be Nr.sub.6 =yk(6n.+-.1), where n is an integer not smaller than 1 and y is 1/2 or 1; and(c) said stator coils are formed with three excitation feeding terminals of a star or delta connection.