| 摘要 |
<p>A method of making and of reading markers at control positions on a length of magnetic tape (50) having light-impeding coatings on opposed sides of a transparent tape substrate. Markers (86 and 104) are recorded by directing focused beams to control positions along longitudinal areas of the magnetic tape (50). The beams have an energy sufficient to ablate the coatings, but to leave the tape substrate intact. Raster scanning of the control position provides rectangular markers (86) and (104) at prescribed positions. An optical splitting element (51) is used in reading the markers (86 and 104). The element (51) is a heptagonal prism (116) which receives light from a tape drive and forms two parallel, spaced apart beams (166 and 168) which are first directed at separate elevations through the markers in the magnetic tape (164), then converged to the light sensors (132 and 134) in the drive. Preferably the optical path through the prism is a path formed by folding a hexagonal prism, with the fold being a reflective surface.</p> |
