Patent ID: 7839030

Claim:
A linear motor which includes a stator and a movable element, comprising: an armature disposed on one of the stator and the movable element, the armature including: an iron core having three or more magnetic pole portions arranged along a moving direction of the movable element; and armature windings of three phases wound around the iron core to excite the three or more magnetic pole portions; and a plurality of permanent magnet magnetic pole rows disposed on the other of the stator and the movable element, the permanent magnet magnetic pole rows each including: a base made of a magnetic material; and a plurality of permanent magnets disposed at a given interval in a row along the moving direction on the base so that north poles and south poles may alternately be arranged, the plurality of permanent magnets facing the three or more magnetic pole portions with a given gap therebetween; wherein a plurality of the permanent magnets disposed at one side ends of the plurality of permanent magnet magnetic pole rows are different in length from one another as measured in the moving direction, and an average length of the permanent magnets disposed at the one side ends is defined as W 10 ; a plurality of the permanent magnets disposed at the other side ends of the plurality of permanent magnet magnetic pole rows are different in length from one another as measured in the moving direction, and an average length of the permanent magnets disposed at the other side ends is defined as W 20 ; the average length W 10 and the average length W 20 are less than a length W of the remaining permanent magnets as measured in the moving direction; the number of slots per pole per phase is ⅜, three-eighths; and when a pitch between centers of two adjacent magnetic pole portions of the plurality of magnetic pole portions constituting the armature is defined as τs, the length W of the permanent magnet is defined as W=τs; a ratio W 10 /W of the average length W 10 to the length W is 0.43<W 10 /W<0.49; and a ratio W 20 /W of the average length W 20 to the length W is 0.43<W 20 /W<0.49.