Tape position sensing apparatus for magnetic tape drive

摘要

The disclosed apparatus includes a hollow column for receiving a loop of magnetic tape. A slot runs along the length of this column. A rigid conductive strip lies spaced apart from and parallel to the slot; and a flexible conductive strip lies between the rigid conductive strip and the slot. The two conductive strips form the plates of a variable capacitor. A vacuum is generated in the portion of the column lying beneath the magnetic tape loop to force a corresponding portion of the flexible conductive strip against the perimeter of the slot. Further, a partial vacuum is generated at the outside of the column near the conductive strips to force the portion of the flexible conductive strip lying above the tape loop against the rigid conductive strip. Air escape passages are included in the rigid conductive strip. As the two strips are forced together, any air lying therebetween instantaneously escapes through the passages. This substantially decreases errors between tape position and instantaneous capacitance between the plates.