The patent badge is an abbreviated version of the USPTO patent document. The patent badge does contain a link to the full patent document.
The patent badge is an abbreviated version of the USPTO patent document. The patent badge covers the following: Patent number, Date patent was issued, Date patent was filed, Title of the patent, Applicant, Inventor, Assignee, Attorney firm, Primary examiner, Assistant examiner, CPCs, and Abstract. The patent badge does contain a link to the full patent document (in Adobe Acrobat format, aka pdf). To download or print any patent click here.
Patent No.:
Date of Patent:
Jun. 06, 1978
Filed:
Oct. 22, 1976
Hitachi, Ltd., , JA;
Abstract
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.