Method for writing and means for reading position-indicating markers on tape

In a tape cartridge of the type having a tape supply hub, a tape take-up hub and having a tape path for a tape of a specific length, all enclosed in a container having opposed top and bottom walls, side walls, a back wall and a front wall, said cartridge further having a first window means in the top wall for admitting light from a source for illuminating a segment of said tape path and having a second window means in the front wall for egress of light, the improvement comprising,

• a length of tape having opposed ends fixed to said tape supply hub and said tape take-up hub and having an intermediate portion trained to travel along said tape path, said tape having markers indicating tape position relative to length of the tape, said markers being control positions optically transparent relative to the optically darker remainder of said tape, said markers arranged within two longitudinal areas on said tape, and
• a beam splitter disposed in the cartridge and having an ingress portion and an ingress portion proximate respectively to said first and second window means of the cartridge, said tape path passing between said egress portion and said second window means, said ingress portion being a pair of input faces in a V-shaped configuration with an optical axis passing through the center of said V-shape for splitting an input beam directed at said ingress portion into a pair of beams, said beam splitter having means for orienting said pair of beams such that each beam impinges on one of said longitudinal areas on the tape substantially on the axis of maximum intensity of the beam.

A tape cartridge comprising,

• a tape container having top and bottom walls, side walls and front and back walls, said top wall having a first window for admitting light and said front wall having a second window for egress of light,
• a pair of tape hubs rotatably mounted within said tape container,
• a length of tape having opposite tape ends wound one on each hub and having an intermediate portion having transparent markers which optically contrast with the remainder of said tape, said tape having a transparent substrate and at least one light absorptive coating, said transparent markers defined by an absence of said coating to form exposed areas of said substrate, said exposed areas of the substrate each having a rectangular shape and disposed to indicate tape position relative to tape ends,
• at least one tape guide member mounted in said container at least partially defining a tape path for said intermediate length of tape, said tape path having a portion adjacent said second window, rotation of said hubs providing tape travel along said tape path, said rectangular transparent markers having an extent perpendicular to said tape travel that exceeds an extent of said markers parallel to said tape travel, and
• a beam turning transparent prism having a pair of generally symmetrical input faces with means for splitting an input beam into two beams, said prism having an egress portion having refractive means for orienting said two beams in generally parallel directions, with a reflective fold plane along the optical path between said input faces and said refractive means of said egress portion, said prism having an optical axis intercepting a point of symmetry of the input faces and the egress portion and making an approximate right angle between the input faces, the fold plane and the egress portion, said prism fixed within said container such that said input faces are proximate said first window and said optical axis intercepts said tape path portion adjacent said second window.