| 摘要 |
Tape reading system wherein the tape (50) in a tape cassette (10) has color marks (133 a, b, c) on the tape (50) to be read by an optical system, part of which is in the cassette (10) and another part of which is in the tape drive (51, 18, 61, 63, 65). The part in the cassette (10) consists of an optical element (51) having mutually isolated light transmission paths. The paths carry light reflected from or transmitted through different portions of the width of the magnetic tape (50). The light is directed to optical sensors (63, 65) which are part of the tape drive (51, 18, 61, 63, 65). A lamp (61), also part of the drive (51, 18, 61, 63, 65), illuminates the tape (50) so that light shining on the tape (50) will contrast with the color marks (153, a, b, c). Changes in contrast due to the color marks (153, a, b, c), transmitted through the optical element (51), are detected by optical sensors (63, 65) and converted to electrically readable signals. A feedback circuit (144, 146, 148, 150, 156, 158, 162, 164, 166, 168) connected to the lamp (61) and to the sensors (63, 65) provides electrical feedback to the lamp (61). The level of illumination detected by the optical sensors (63, 65) is kept constant relative to slow background contrast changes, although a low pass filter (156, 158) prevents the feedback circuit (144, 146, 148, 150, 156, 158, 162, 164, 166, 168) from responding to light signals representing the color marks (153, a, b, c). |
