| 摘要 |
PURPOSE:To eliminate effect on external equipment while making influence from an external magnetism hard to receive along with the minimization of a magnetic drum by shaping it so as to house a magnetic sensor for reading out a magnetic flux generated from a plurality of magnetic poles formed at an equi-space along the internal periphery. CONSTITUTION:As a drum turns in the direction of the arrow 8, the tip of a gear 11 is magnetized with a magnet 22, a condition which is sensed as signal with a gap 21 of a reading head 20. The number of reading signals per unit time is counted and the comparison of variation in the counts enables a measurement- based judgement of wow and flutter of the drum so that the drive system is controlled by feeding back the results to regulate the constant-speed rotation of the drum. A cup magnetic body 10 is covered with a cover 30, which is made of a highly magnetoconductive material to prevent the external leakage of a magnetic flux generated from the magnetic body 10. It also has an effect of preventing the magnetic flux from outside the drum affecting an influence to a magnetic sensor 20. |
