TW256902B - Method for fixed focus CCD imaging - Google Patents

Abstract

Methods are provided to assist in selection of appropriate optical components for optimizing performance of the optical scanner for reading one-, two- and three-dimensional optically encoded information at a wide range of field depths and angles. The optical components are fixed in position relative to each other so that no position adjustments are required to obtain a reading at a desired distance once the optical components are optimized. Among the parameters that are considered are LEDs for emitting light within specific wavelength ranges, optical filters, lens focal lengths, magnification, etc. The fourier transform of an input square wave signal generated by light reflected from a bar code is used to generate the appropriate resolution requirements. Selection of appropriate optical components is dependent upon the intended operation of the scanner. For example, depth of field is considered, as is scan angle and density of the code to be read. The performance models are based upon the modulation transfer function (MTF) of the optical system, comprising the encoded information, the lens system and the CCD array.