| 摘要 |
<p>A scanning device and method for reading bar code or other contrasting marks from a surface (2) at a variable distance from the scanning device (11, 9) operates by modulating the focal point of the optical system (9) to yield pulse responses on detected code bars while in focus, and average background response levels from the bar code surface while out of focus. Modulation of focal point of the optical system (9) is achieved in selected ways such as by positioning optical elements using piezoelectric or electromagnetic drivers or liquid-crystal elements, or by staggering the positions along an optical axis of arrays of optical sensors, or of optical fibers coupled to the sensors. The light sources and detectors may be transposed to provide an array of individual light sources that are selectably and rapidly energized at locations in the optical system which provide illumination that is substantially in focus or out of focus on the surface being scanned. The detected reflections from focussed and unfocussed devices are processed to produce output signals representative of the bar-coded data independently of scanning rate and spacing between the scanning device and the bar-coded surface being scanned.</p> |
