Abstract: The permeance between the small teeth provided on the stator magnetic pole and the rotor magnetic pole may be varied regularly according to the rotation of the rotor. The small stator teeth provided on the tip end of each stator magnetic pole are divided into sets of two or three small stator teeth and at least one pitch of the adjacent teeth is different from the other pitch of the other adjacent teeth, so that the vector sum of the quaternary harmonics of permeance in each set is substantially zero.

Abstract: An electric rotary machine has a concentrated winding stator and a rotor facing the stator with a gap therebetween. The stator has M number of stator magnetic poles extending in the radial direction from an annular yoke, pole pieces each extending in the circumferential direction of the rotor from the tip end of each of the stator magnetic poles, and windings wound around the stator magnetic poles. The rotor having a permanent magnet with P number magnetic poles, wherein P:M=6n−2:6n, or P:M=6n+2:6n, where n is an integer not less than 2, and the figure of each of the pole pieces is so determined that a gap formed between the pole piece and the rotor is increased going toward the both ends of the pole piece.

Abstract: A motor has a stator and a rotor, the stator having cores and drive coils which generate magnetic fields for rotating the rotor. The stator also has a yoke surrounding the rotor and the rotor is positioned such that it is closer to one part of the outer periphery of the yoke than another part of the outer periphery of the yoke. Such a motor is particularly suitable for use in a disk drive unit as a spindle motor for rotating the disk. Then an actuator for moving a head may be located adjacent the part of the outer periphery of the yoke which is closest to the rotor. This permits the head to approach closely the axis of rotation of the disk without the spindle motor interferring with the movement of the head. The continuous yoke prevents magnetic flux leakage from the spindle motor interferring with the actuator. The actuator may itself have a yoke integral with the yoke of the spindle motor, and/or other components in common.

Abstract: An absolute encoder wherein tracks are arranged side-by-side on a magnetic drum in the axial direction thereof, and absolute patterns of circulatory random sequence codes are divided and recorded on the tracks, respectively. An additional track for generating sinewaves of two phases in synchronism with the reading of the absolute patterns is provided on the magnetic drum, so that an output can be obained by combining a coarse value of an absolute position obtained from the tracks and a fine value of an absolute position obtained from the additional track. The absolute patterns are detected from the two tracks recorded on the magnetic drum by magnetic resistive elements connected with each other to form circuits each having a three-terminal. Terminals of the magnetic resistive elements are connected through a common line with an electric power source in order to prevent the lines from being crossed.

Abstract: In an optical system including a transparent optical body such as a lens and a light reflecting surface disposed in the rear of the transparent optical body with a spacer of a light absorptive material being sandwiched therebertween to ensure the relative position and other optical relationship of the body and the surface. The spacer is cemented to a rear surface of the transparent body for masking the light reflecting surface and preventing light rays from entering from the front of the transparent optical body to the light reflecting surface to be reflected back by the latter. According to the present invention, the front surface of the spacer to be cemented to the rear surface of the transparent optical body is, before being cemented, polished to a degree of roughness which prevents the occurrence of fringes due to interference at a possible small gap between the transparent optical body and the spacer.