Device for the thermal erasure of mechanically readable optical markings

Abstract

An apparatus adapted for thermally erasing or changing machine readable optical markings previously entered on a carrier of thermoplastic material which has two major sides, and wherein the optical markings cause a predetermined modification of any light rays impinging on the optical markings by either diffraction or refraction, include a erasing device adapted to be located on one major side of the carrier, for erasing or changing the markings, a reading device, operative during operation of the erasure device, and including at least two light sensors adapted to be located on the other major side of the carrier, so as to check the erasure or change of the markings effected by the erasing device. The light sensors provide output signals of respective opposite polarities following erasure or change of any one of the markings. A moving device generates a relative movement between the carrier and the erasing and reading devices, respectively, and a comparator is postcoupled to the light sensors, and includes a detector for indicating whether the output of the comparator exceeds or is below respective predetermined limits. A control device controls the operation of the erasing device of the moving device and is arranged to inhibit the operation of the erasure device when the output of the comparator exceeds or falls below the limits, respectively, so that the limits establish a uniform criterion for effecting erasure of the markings.

Dependencies are inferred from the claim text.