Tape drive sensor

A device for sensing torque in a tape drive apparatus and indicating absence of tape at a sensing zone of the apparatus, comprising

• a driven member mounted to the apparatus for rotation about an axis,
• means for driving a tape in the apparatus, drivingly coupled to said driven member,
• a driving member for applying driving torque about said axis,
• torsionally resilient means for coupling the driving member to the driven member,
• first and second apertured opaque discs coupled to said driving and driven members respectively for rotation therewith, said discs being so arranged that, when the torque exerted by the driving member is within a normal range, apertures in the first disc are aligned opposite corresponding opaque regions of the second disc;
• and when the torque exerted by the driving member is greater than said normal range, apertures in the first and second discs are at least partially aligned opposite each other, and
• indicating means comprising a bifurcated part having first and second arms;
• a radiation emitting element mounted to the first arm;
• a radiation receiving element mounted to the second arm;
• means for mounting said part for movement between a first position in which the apertured portions of the first and second discs pass between the radiation emitting and radiation receiving elements, and a second position in which radiation from the emitting element can pass by the discs;
• means for biasing said part toward the second position;
• and means responsive to presence of tape at the sensing zone of the apparatus for holding said bifurcated part in the first position.