| 摘要 |
PURPOSE:To detect the rotary phase of a rotary drum by an inexpensive device, by providing small-area marks, differing in reflectivity or transmittivity, on the external surface of the rotary drum. CONSTITUTION:A cut part (a) is made at each magnetic-head fitting part so that when a magnetic head 5 and a magnetic-head base plate 4 are fitted to a rotary drum 3, the magnetic head 5 is prevented from touching the rotary drum 3. Light from a light emitting element 15 is emitted to the cut part (a) and its reflected light is photodetected by a photodetecting element 16, so that the other part of the rotary drum 3 generates hardly any output. When (n) cut parts are made, a pulse to the photodetecting element 16 appears at intervals of a 1/n turn, so the rotary phase of the rotary drum 3 is detected easily. |
