초록 ▼

The effects of papers/substrate noise are significantly reduced in multi-focal zone laser scanning systems by processing analog scan data signals with a scan data signal processor having a plurality of pass-band filters and amplifiers that are automatically selected for passing only the spectral com

The effects of papers/substrate noise are significantly reduced in multi-focal zone laser scanning systems by processing analog scan data signals with a scan data signal processor having a plurality of pass-band filters and amplifiers that are automatically selected for passing only the spectral components of an analog scan data signal produced when a bar code symbol is scanned at a particular focal zone in the laser scanning system. Two or more different pass-band filter structures can be provided for use in the scan data signal processor, wherein each pass-band filter structure is tuned to the spectral band associated with a particular focal zone in the laser scanning system. When a bar code symbol is scanned by a laser beam focussed within the first focal zone or scanning range of the system, the pass-band filter structure associated with this focal zone or scanning range is automatically switched into operation using a control signal produced by determining the focal distance of the laser scanning beam producing the analog scan data signal and noise existing over this pass-band are allowed within the analog signal processor. By virtue of the present invention, first and second derivative signals can be generated and processed to produce a corresponding digital scan data signal for use in subsequent digitizing and decode processing operations, without compromising system performance due to the destructive effects of thermal and substrate noise outside the spectral pass-band of interest for the bar code symbol being scanned.

대표청구항 ▼

1. A laser scanning system comprising:a laser scanning mechanism for producing a laser scanning beam within a plurality of predefined focal zones and scanning said laser beam over a bar code symbol, and automatically producing an analog scan data signal indicative of the intensity of light reflected

1. A laser scanning system comprising:a laser scanning mechanism for producing a laser scanning beam within a plurality of predefined focal zones and scanning said laser beam over a bar code symbol, and automatically producing an analog scan data signal indicative of the intensity of light reflected from said scanned bar code symbol; and a scan data signal processor for processing said analog scan data signal, said scan data signal processor including a plurality of different pass-band filters, wherein one of said pass-band filters is dynamically switched into operation for pass-band filtering the analog scan data signal produced by said laser scanning beam scanning a bar code symbol within one of said predefined focal zones so as to filter out spectral components of paper noise residing outside the frequency spectrum of said analog scan data signal produced in response to scanning said bar code symbol within said predefined focal zone.