Abstract: A rotation detecting device for a brushless motor having: a stator core on which a coil is wound; a driving magnetic pole portion which opposes the stator core, which comprises a plurality of magnetic poles, and which is rotated; an FG magnetized portion which is rotated together with the driving magnetic pole portion and which comprises a plurality of magnetic poles; and an FG pattern which opposes the FG magnetized portion. In the device, relative positions of the stator core, the driving magnet pole portion, the FG magnetized portion, and the FG pattern in the circumferential direction are set so that the minimum point c of a torque ripple of the brushless motor does not coincide with points a and b of an output signal from the FG pattern which function as a trigger for rotation control.

Abstract: A rotary cylinder device has a stationary cylinder with a stationary shaft; a rotary cylinder rotatably mounted on the stationary shaft, the rotary cylinder having an opening on one side thereof which is opposite to the other side where the rotary cylinder confronts with the stationary cylinder; a signal recording and reproducing magnetic head provided on the periphery of the rotary cylinder; an electric motor including: a rotor member of the electric motor, which is provided in the opening of the rotary cylinder and secured to the rotary cylinder; a stator member of the electric motor, which is confronted with the rotor member; and a first magnetic shielding member arranged to cover the opening of the rotary cylinder.

Abstract: An object of this invention is to provide a circuit board low in manufacturing cost in which aimed circuit patterns having a circuit gap therebetween can be short-circuited substantially irrespective of the length of the circuit gap while being insulated from other circuit patterns which are laid in the circuit gap. In a circuit board on which a plurality of circuit patterns are arranged, a selected one of circuit patterns is cut to have a circuit gap where the selected circuit pattern is laid across the remaining circuit patterns, in such a manner that the circuit gap divides the selected circuit patterns into two parts, a conductor formed by cutting a wire to the length of the circuit gap bridges the circuit gap, to short-circuit the two parts thereby to complete the selected circuit pattern, the conductor being insulated from the remaining circuit patterns laid across the circuit gap.