| 摘要 |
PURPOSE:To control a cylinder motor for VTR, by preparing the switching pulse of a rotary head by dividing in frequency the detected output of a detecting means by using a signal produced in accordance with the difference between a detected output influenced by the magnetization of a magnetic pole and that influenced by a specific non-magnetized magnetic pole as a reference. CONSTITUTION:When a driving current is supplied to a driving coil 6, driving force is produced across the coil 6 and multi-pole magnet 4 and a rotor section rotates with a rotary shaft 1 at the center. A Hall element 10 detects the change in a magnetic flux caused by the rotation of the magnet 4 and also changes in magnetic fluxes caused by the rotation of small circular magnetized parts 4a, 4b, and 4c. By using a signal produced in accordance with the difference between the output of a detecting means influenced by a demagnetized magnetic pole and the output of the detecting means influenced by a specific magnetic pole which has the same polarity as the magnetic pole has but no magnetized part as a reference, the output detected by the detecting means is divided in frequency and the divided one is used as the switching pulse of a rotary head. Therefore, a Hall element to be used for detecting the change in a magnetic flux caused by a PG magnet at the time of rotation of a motor can be omitted and, as a result, the motor can be miniaturized and cost of the motor can be reduced.
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