Jikikirokushoshokyosochi

摘要

1513750 Erasing marks on magnetic-sensitive media SIMRAD AS 7 July 1975 [8 July 1974] 28582/75 Heading B6C Marks on a magnetic-sensitive medium that comprises magnetically orientatable particles rendering the medium reflective to light when the particles are orientated parallel to a surface of the medium are erased by orientating the particles using an electromagnet supported adjacent the medium by effecting relative movement between the electromagnet and the medium and simultaneously effecting repeated relative motion in a sense parallel to the surface of the medium, and perpendicular to the direction of the relative movement, and energising the electromagnet to produce a field which, in a transitional region of the medium between a region where the field is sufficiently strong to effect orientation of the particles, and a region where the field is not sufficiently strong to effect orientation, is parallel to the surface of the medium or has a component parallel to the surface larger than the component normal to the surface. This may be achieved by moving an electromagnet across the medium. In the embodiment of Fig. 1, electromagnet 7 is carried on a band 5 moved by rollers 3 and 4, current being supplied by slip contacts 8, 9. In the embodiment of Fig. 2, two electromagnets 15, 16 are mounted at respective ends of a rotatable arm.