Craig & Antonelli
Electric motor
 An electric motor comprises a rotor constructed by a disk-shaped multi-pole magnet secured to a rotary shaft and rotatably supported, and a stator constructed by a pair of star-shaped flat drive coils arranged adjacent and opposing to the disk-shaped multi-pole magnet. Sinusoidal wave currents, the phase angles of which differ by 90.degree. from each other, are supplied to the pair of drive coils to drive the magnet. A speed detection coil having a plurality of power generating strands is arranged in a field of the magnet and a field of the drive coils to produce a signal having a frequency corresponding to a rotational speed of the magnet. A cancellation coil is also arranged in the field of the drive coils to produce a voltage which varies with the change of the drive coils, which voltage is added to an output signal from the speed detection coil to cancel out a signal developed across the speed detection coil by the change of the drive field so that a speed detection signal of a high S/N ratio is derived to enable the control of the rotation of the electric motor. 
Hitachi, Ltd.
H H
H02P H02K
inventional inventional
Toshihiko Masahiko Tsutomu
Gotoh Fujita Nakamura