Optical scanner with extended depth of focus

• US 5,814,827 A
• Filed: 05/05/1997
• Issued: 09/29/1998
• Est. Priority Date: 05/19/1995
• Status: Expired due to Term

• Current Assignee: Symbol Technologies, LLC (Zebra Technologies Corporation)
• Original Assignee: Symbol Technologies, Inc. (Zebra Technologies Corporation)
• Inventors: Katz, Joseph
• Primary Examiner(s): LE, QUE TAN
• Application Number:
  US08/850,967
• Time in Patent Office: 512 Days
• Field of Search: 250/556, 250/557, 250/566, 250/235, 235/472, 235/462, 382/313, 382/316
• US Class Current: 250/556
• CPC Class Codes: G06K 7/10722 Photodetector array or CCD scanning
• CPC Class Codes: G06K 7/10811 Focalisation

Abstract

A scanner with an extended depth of focus for electro-optically reading indicia having parts of different light reflectivity, comprises a collection optical system for collecting radiation reflected from objects in the field of view along plural different optical axes and an optical detector for detecting radiation collected by the collection optical system along each of the plural different optical axes and for generating electrical output signals indicative thereof. The scanner further includes processing circuitry for processing the output signals of the optical detector by comparing the output signals of the optical detector with one another, a memory for storing the detector output signals and further processing circuitry receiving the stored output signals of the optical detector from the memory and selectively outputting one of the received signals to a decoder.

Claims

1. A bar code reading device with an extended depth of focus for reading complete lines of bar code information by optically scanning light reflected from a bar code symbol having bars and spaces of different light reflectivity, said bar code reading device comprising:

(a) a plurality of integrated circuits, each of said circuits comprising an addressable solid-state-imaging detector, each of said detectors comprising an array of individual photosensors arranged so as to receive light reflected from the entirety of said bar code symbol without requiring any movement of the bar code reading device as a whole relative to the bar code symbol;

(b) a plurality of lenses, each of said lenses having a focal length different from each other, each of said lenses associated with and focused on a corresponding one of said detectors so as to provide a plurality of lens/detector pairs, wherein each of said lens-detector pairs provides an optical axis different from and substantially parallel with each other;

(c) a processor for selecting the lens/detector pair that provides a desired optical property when said bar code symbol is placed in a field of view of at least one of said lens/detector pairs.

2. The bar code reading device of claim 1 further comprising bar code data decoder, and wherein data from the lens/detector pair selected by said processor as having a desired optical property is provided to said bar code data decoder.

3. The bar code reading device of claim 2 wherein said processor selects the lens/detector pair that provides the highest degree of focus as the desired optical property.

4. The bar code reading device of claim 3 wherein said processor comprises:

(i) a memory for storing contrast data output from each of said detectors;

(ii) a contrast comparator for measuring the relative contrast between each of said detectors and selecting the detector with the highest relative contrast measurements;

(iii) means for providing, to said bar code data decoder, data from the detector selected to have to the highest relative contrast measurements.

5. The bar code reading device of claim 4 wherein said processor is comprised on one of said integrated circuits.

6. The bar code reading device of claim 4 wherein said contrast comparator comprises:

(i) a plurality of sample and hold circuits, each of said sample and hold circuits associated with data from memory provided by each of said detectors, each of said sample and hold circuits providing an output signal indicative of the relative contrast of each of said associated detectors;

(ii) a plurality of comparison circuits for comparing each output signal from each sample and hold circuit with each other so as to provide a plurality of signals indicative of the relative contrast measurements between each detector; and

(iii) logic means for providing an output signal indicative of the detector having the highest relative contrast measurement.

7. The bar code reader of claim 6 wherein said data providing means comprises a multiplexer, said multiplexer being controlled by said output signal from said logic means indicative of the detector having the highest relative contrast measurement.

8. A method for reading a bar code at various distances using a bar code reader having a plurality of optical lense/solid-state-detector pairs, each of said pairs having its own optimum bar-code-placement zone, said method comprising the steps of:

a) placing the bar code a fixed distance away from and within a field-of-view of said bar code reader;

(b) illuminating said bar code with an illuminating sourse;

(c) extracting a detector output signal from each of said lense/detector pairs;

(d) comparing the extracted output signals;

(d) selecting a desired output signal from the extracted output signals based upon a predetermined signal criteria; and

(e) decoding the desired output signal.

9. The method of claim 8, wherein the illuminating sourse is located outside of the bar code reader.

10. The method of claim 8, wherein the illuminating sourse is located inside the bar code reader.

11. The method of claim 8, wherein the predetermined signal criteria is a relative contrast level.