This invention relates to a rotary head assembly in which a magnetic tape runs while being would helically, consisting of a fixed cylinder 21 having a fixed cylindrical part, and a rotatable rotary member 19 having a diameter approximately equal to that of said fixed cylinder 21, being disposed coaxially...http://www.google.fr/patents/US4525757?utm_source=gb-gplus-shareBrevet US4525757 - Rotary head assembly
