Patent ID: 7786631

Claim:
A linear motor comprising: a field yoke composed of a hollow cylindrical member made of material having relative magnetic permeability m (where m is greater than 1.0 and equal to or less than 2.0) and a plurality of permanent magnets arranged in a straight row, each with either pole facing and contacting the same pole of either adjacent permanent magnet; an armature having an armature coil arranged, facing the row of magnets and spaced by a magnetic gap from the row of magnets; magnetic characteristic-fluctuating parts arranged at ends of the row of magnets or at the middle thereof and configured to abruptly change magnetic characteristic of the row of magnets; and a magnetic linear encoder using the row of magnets as magnetic scale unit, utilizing a distance between any two adjacent permanent magnets as scale pitch of the magnetic scale unit, and having a plurality of first magnetic detectors and a second magnetic detector, which are arranged in a lengthwise direction of the armature, the first magnetic detectors being so arranged to have a phase difference of 90° (corresponds to ¼ wavelength of the scale pitch) in terms of electrical degree with respect to each other, and the second magnetic detector being so arranged to have a phase difference of 180° (corresponds to ½ wavelength of the scale pitch) in terms of electrical degree with respect to the first magnetic detectors, wherein one component selected form the group consisting of the field yoke and the armature is provided at the stator, and the other component is provided as a movable member, the magnetic linear encoder has a scale head provided at the armature, and the field yoke and the armature move straight relative to each other.