Patent ID: 6354505
Filing Date: 2002-03-12
Classification: G02B,G06K,G07F,G07G,H01M,Y02E

Abstract:
A scan data signal processor for use in a multi-focal zone laser scanning system including(1) a laser beam scanning mechanism for (i) producing a laser beam, (ii) focusing said produced laser beam within a scanning volume having a depth of field and a plurality of predefined focal zones, (iii) scanning said focused laser beam across a bar code symbol within said depth of field, (iv) collecting a laser light signal produced by said scanned laser beam reflecting off said bar code symbol, (v) detecting said collected laser light signal, and (vi) producing, during laser scanning operation an analog scan data signal corresponding to the detected laser light intensity and having a frequency bandwidth determined by (i) the speed of the laser beam across the scanned bar code symbol and (ii) the structure of said scanned bar code symbol, and (2) a control signal generator for dynamically generating a control signal indicative of the predefined focal zone in which said scanned bar code symbol resides at any instant in time when scanned by said laser beam during said laser scanning operations; said scan data signal processor comprising: a first derivative signal generator for receiving said analog scan data signal and generating a first derivative signal representative of the first time-derivative of said analog scan data signal; a plurality of pass-band filter structures, each one of said plurality of pass-band filter structures being preassigned to one of said predefined focal zones and having frequency response characteristics for optimally filtering the first derivative signal produced when scanning said bar code symbol within said predefined focal zone; and control circuitry, responsive to the control signal generated by said control signal generator, for dynamically switching one of said plurality of pass-band filter structures into operation so that the first derivative signal produced in response to said laser beam scanning a bar code symbol within one of said predefined focal zones is optimally filtered by said dynamically-switched pass-band filter structure preassigned to said predefined focal zone.