Mapping disc defect detector

Claim 1

Apparatus for generating a map of detectable characteristics of a rotatable disc, comprising: a scanning signal display device; detecting means for examining a small fraction of the disc at a time, said detecting means generating a first electrical signal coupled to the intensity input of said scanning signal display device, said signal being representative of a detected characteristic of the disc in the fraction of the disc being examined; scanning means for moving the disc relative to said detecting means such that said detecting means examines the disc in a spiral pattern, said scanning means including a spindle for holding the disc, means for rotating said spindle, and means for translating said spindle relative to said detecting means; pulse generator means for generating a rotation pulse signal each complete rotation of said spindle; variable signal means for generating a translation signal which varies in accordance with the translational position of said spindle; and function generator means coupled to said pulse generator means and to said variable signal means for generating a first sinusoidal output signal and a second sinusoidal output signal, each at a frequency proportional to the frequency of said rotational pulse signal and each having an amplitude proportional to the value of said translation signal, said signals differing in phase by 90°, said first and said second sinusoidal output signals being coupled to said scanning signal display device such that the trace of said device follows a spiral pattern corresponding to the position of said detecting means relative to the disc.