Linear motor
When a pitch between centers of two adjacent magnetic pole portions disposed on an armature is defined as τs, the length W of permanent magnets disposed in the middle is equal to the pitch τs (W=τs). The length of each of the two end permanent magnets respectively disposed at either end of a permanent magnet magnetic pole row is denoted by W 1 . A ratio w 1 /W of the length W 1 to the length W is defined as 0.43<W 1 /W<0.49. With this definition, cogging torque of a linear motor may sufficiently be reduced.
1. 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.
2. The linear motor according to claim 1 , wherein a spacer, which is made of a nonmagnetic material, is disposed between two adjacent permanent magnets of the plurality of permanent magnets to form a space therebetween.
3. The linear motor according to claim 2 , wherein the spacer is formed by cutting a wire material.
4. The linear motor according to claim 1 , wherein
the permanent magnet magnetic pole rows are disposed on the movable element;
the base is cylindrical or columnar in shape, and common to all the permanent magnet magnetic pole rows;
the plurality of permanent magnets are fixed onto an inner peripheral surface of the base;
the armature is disposed on the stator;
the stator is partially arranged inside the movable element;
the armature is fixed onto a base station via stator fixtures at both ends thereof in the moving direction;
a guide block is fixed to the movable element,
the guide block is slidably supported by a guide rail disposed on the base station; and
the movable element is capable of moving in the moving direction with respect to the stator as the guide block slides on the guide rail.