Tape loop position detector

Apparatus for detecting the position of a tape loop in a chamber, the tape being supplied to one end of the chamber, the other end of the chamber being maintained at a fluid pressure less than the one end and being closed by the tape in the chamber, a portion of the chamber where the loop is located including a wall having a plurality of apertures forming separate fluid flow paths between the chamber and the detecting apparatus, the detecting apparatus being responsive to the location of a fluid pressure transition in the chamber resulting from the position of the loop and the fluid pressure difference on opposite sides of the loop, the detecting apparatus comprising a variable capacitor having fixed and flexible electrodes spaced from each other, the fixed electrode being spaced from the wall, the flexible electrode including a flexible strip consisting of metal, a dielectric region positioned between the electrodes, a vacuum source for applying a fluid pressure to the flexible electrode between the pressures at the one and other ends of the chamber, the vacuum source including a partition with a plurality of apertures forming separate fluid flow paths, first and second opposite ends of the flexible electrode having faces respectively positioned in first and second planes substantially parallel to the wall, the face of the flexible electrode in the second plane being on the partition, the flexible electrode and vacuum source being arranged so that the position of a transition of the flexible electrode from the wall to the partition is dependent on the position of the loop in the chamber, whereby a portion of the flexible electrode between the pressures of the one end and of the vacuum source is urged by the higher pressure of the one end against the partition and a segment of the other end and the vacuum source is urged by the higher pressure of the vacuum source against the wall.

Apparatus for detecting the position of a tape loop in a chamber, the tape being supplied to one end of the chamber, the other end of the chamber being maintained at a fluid pressure less than the one end and being closed by the tape in the chamber, a portion of the chamber where the loop is located including an electrically grounded wall for providing a fluid flow relation between the chamber and the detecting apparatus, the detecting apparatus being responsive to the location of a fluid pressure transition in the chamber resulting from the position of the loop and the fluid pressure difference on opposite sides of the loop, the detecting apparatus comprising a variable capacitor having fixed and flexible electrodes spaced from each other, the fixed electrode being spaced from the wall, a stationary solid dielectric positioned between the electrodes, a vacuum source for applying a fluid pressure to the flexible electrode between the pressures at the one and other ends of the chamber, first and second opposite ends of the flexible electrode having faces respectively positioned in first and second planes substantially parallel to the wall, the face in the second plane being on the dielectric, an electrical insulator between the first end and the wall for maintaining the flexible electrode electrically insulated from and at a different potential from the grounded wall, the flexible electrode and vacuum source being arranged so that the position of a transition of the flexible electrode from the wall to the region is dependent on the position of the loop in the chamber, whereby a portion of the flexible electrode between the pressures of the one end and of the vacuum source is urged by the higher pressure of the one end against the region and a segment of the flexible electrode between the pressures of the other end and the vacuum source is urged by the higher pressure of the vacuum source against the wall.