Automatic helical scan head drum calibration and track timing generation

Abstract

This invention is a method and apparatus for the automatic calibration of the magnetic head offset angles in a helical scan rotating head drum and the generation of idealized track timing for recording and reading magnetic tape. A calibration tape is used to provide calibration marks and in conjunction with pulse generator (PG) encoder and frequency generator (FG) encoder signals, a processor calculates the offset angles. The offset is calculated from the time an FG signal edge occurs until the time of detection of a calibration feature. For a read head calibration, this provides a rough calibration of the angular location of the read head on the head drum. Using this rough calibration, data is read from the calibration tape, including the measured longitudinal position of the calibration feature. An accurate calibration of the angular location of the read head is then calculated. For the write head, tracks are written on a blank sector of the calibration tape, using the known relative angular location of the read head, an accurate calibration of the angular location of the write head (which just wrote the track) is thereby provided. The same circuitry can also generate track timing signals based on the edges of the FG signal.