JPS5652475A - Mark reading method - Google Patents

Abstract

PURPOSE: To make it possible to cause little reading failure even in case of variation of density and also execute reading with a relatively high accuracy, by comparing with the reference level of multi-stage and obtaining normal data.

CONSTITUTION: A sensor equipped with light emitting elements S₁WS₅ and photo detecting elements f₁Wf₅ moves and starts reading. At first, when the sensor is in the mark of the first digit, the light emitting elements S₁WS₅ which have been driven by a pulse of the pulse current generator G irradiate the respective marks, read them by the photo detecting elements f₁Wf₅, convert them to electric signals, and input them to the comparator A4. On the other hand, the deciding reference level voltage V₁ of the first stage is input to other input of the comparator A4. As a result of the check by the check circuit CH, in case all the bits become "0", it is regarded as abnormal, the change-over switch S is changed by a change-over signal from the check circuit CH, and the check is executed by changing the level voltage to V2. When the check result has become normal, it is output from the check circuit CH as a normal data.

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