WO1994015314A1

WO1994015314A1 - Portable optical reader system for reading optically readable information located within a three dimensional area

Info

Publication number: WO1994015314A1
Application number: PCT/US1993/012459
Authority: WO
Inventors: William H. Ii Keehn; Dennis A. Durbin; Steven E. Koenck
Original assignee: Norand Corporation
Priority date: 1992-12-21
Filing date: 1993-12-21
Publication date: 1994-07-07
Also published as: CA2152366A1; AU5957494A

Abstract

A non-laser type scanner for reading optically readable information within a three dimensional area which utilizes a two dimensional photosensitive array associated with a plurality of lenses wherein each lens is discretely associated with a line of resolution of the array. A computer connected to the array may be programmed and operated for decoding the output of the array such that optically readable information may be decoded within a three dimensional area.

Description

PORTABLE OPTICAL READER SYSTEM FOR READING OPTICALLY READABLE INFORMATION LOCATED WITHIN A THREE DIMENSIONAL AREA Technical Field The present invention is directed to optical information readers and more particularly to portable optical reader systems for instantaneously reading optical information within a substantial area.

Background Art Many industries designate their products with optically readable information. Optically readable information often takes the form of a bar code symbol consisting of a series of lines and spaces of varying widths. Various bar code readers and laser scanning systems have been employed to decode such symbol patterns. One of the many problems encountered in the bar code reader art, wherein a photosensitive array is utilized, is to produce an optical system capable of focusing images of optically readable information where such information lies at varying distances from the reader.

Known to the art are readers which utilize mechanical means to change the focal length of an optical system. Although such mechanical means may be employed to read optical information over a substantial range of distances, such means are often somewhat cumbersome in design, temperamental, expensive, and require the expenditure of additional battery energy. Thus, in the hand-held optical information reader art, where power consumption, weight, portability, convenience, range, and depth-of-field are of great concern, means for obviating and simplifying focusing requirements have long been sought. Therefore, it is a principal object of the present invention to provide a method and apparatus for focusing an image of optical information over a substantial range of distances which requires no moving parts, is convenient, easy to use and simple in construction.

Another object of the present invention is to provide a method and apparatus for focusing an image of optical information within a substantial area and over a^' substantial range of distances.

Disclosure of the Invention

The present invention provides an apparatus capable of reading optically readable information located within a three-dimensional area. The present invention utilizes a two-dimensional photosensitive array which is operated as a plurality of linear arrays. Each linear array has a lens or series of lenses associated therewith for focusing the reflected light image of an object having a discrete set of coordainates within a three-dimensional space in front of the apparatus. In this fashion, a user of the apparatus may simply direct the apparatus at a bar code or the like located within the coordinate range of the apparatus in order to read the bar code or the like.

Brief Description of the Drawings FIG. 1 is a diagrammtic perspective view of the apparatus of the present invention illustrating the coordinate range of the apparatus;

FIG. 2 is a diagrammatic top plan of the multi-segment lens array of a preferred embodiment of the present invention;

FIG. 3 is a diagrammatic perspective view of a portion of the mult-isegment lens array of a preferred embodiment of the present invention;

FIG. 4 is a diagrammatic side-elevational view of a portion of the multi- segment lens array of a preferred embodiment of the present invention; FIGS. 5, 6, and 7 illustrate the configuration of a photosensitive array and multi-segment lens array of a preferred six target plane model of the present invention;

FIG. 8 is a diagrammatic side elevational view of a preferred six target plane model of the present invention illustrating the six target planes; and FIG. 9 is a diagrammatic perspective view of of a preferred six target plane model of the present invention illustrating the six target planes. Best Mode for Carrying Out the Invention Typical resolution on a two-dimensional CCD imaging device might be aroixnd 512 by 512 pixels and some arbitrary gray-scale levels (16 or 256). Assume the CCD device has been used to digitally capture a barcode image, for the sake of argument, a UPC code. Let us then assume that we wish to decode this barcode The Nyquist limit applied here dictates that we must be assured of havmg at least two pixels per vertical line. Since the lines on a UPC code are of varying widths, we must interpret it to mean the thinnest vertical lines

From looking at a sample UPC, the thickest lines are about 4 times the width of the thinnest lines, and there are white lines as well as black lines. After counting the vertical bands and weighing the widths, a reasonable estimate is that it would require around 200 pixels across the length of the code in order to accurately decode it. Thus, it is very important that the barcode occupy as large a portion of the sensing area as possible in order to be able to get the best resolution possible.

If one considers a similar CCD device, the portable camcorder, it may be observed that there is a lens array, with zoom and focus capabilities. The user (or perhaps the camera with the aid of fuzzy logic) centers and zooms in and focuses the subject using a small viewscreen as feedback. This approach has several problems for use in barcode detection:

♦ Speed—Camcorder focusing and zooming systems are way too slow to keep up with the changing demands of a handheld scanning device.

♦ Moving Parts— Moving parts mean more opportunity for failure, tolerance problems, need for calibration, and slowness.

♦ Effort— The user must interact too much with such a device. They need something that is as easy as point and shoot. ♦ Precision— Most people cannot aim with the accuracy required to keep a distant target centered. Again, point and shoot. Let the user do the general aiming and the device do the precision aiming.

Each smgle line of the CCD might have its own lens at a different magnification factor and focal length. A lens could be constructed that smoothly changed from one set of optical characteristics to another, as you might find in a pair of bifocals, only on a grander scale.

In this fashion you could not only could you vary focal length and magnification, but the amount of lens prism ("prism" is the magnitude and direction of linear translation (shifting) that a lens gives an image). This would allow a CCD to have a wider field of view.

Bar codes have a great deal of vertical redundancy. There are an infinite number paths across a barcode that will allow it to be decoded, yet you need only one. Imagine a digitized barcode image, let us say 256 by 256 that has been centered for proper decoding, every pixel along any horizontal line is desired, yet vertically the same image has been reproduced 255 times. For any barcode image scanned with a 2-D CCD, only 1/256 of the scanning area is really used. What if you could sacrifice some of the vertical redundancy? Obviously you would gain more sensing area. If you gave up 50% of the vertical redundancy, you could possibly have two 128 x 256 CCD arrays, each sensing different images. At the extreme, if you eliminated all redundancy, you might have 256 - 1 x 256 CCD sensing arrays.

With four 1 x 256 CCD sensing arrays, you could look for the barcode in any one of 4 distinct sectors of the device's field of vision. If the four 1 x 256 CCD sensing elements could give us 4 adjacent sectors within the barcode, that is the first element senses the first 25%, etc., in effect we then have one 1 x 1024 CCD array. We have suddenly quadrupled the resolution and by doing so, have quadrupled the range. Illumination may utilize fiber optics, holographic properties, or means to vibrate the lens in such a way that the signal may be sampled several times from slightly shifted perspectives. This invention uses a 2-dimensional imaging device which has a very large amount of redundancy in the vertical dimension. In this case, we have 700 x 500 or 350,000 or 2 orders of magnitude more pixels with redundancy. So spatially in the depth dimension you cover all the possible places that you have determined from a minimum to a maximum that you might need to be able to focus. Presumably, if you have the target somewhere in there then, one of those distances will give the best signal and that would be the one that you would then work with and the others would be degraded to the point that they don't have enough information to be recognized by the recognition digital process.

It is a relatively small matter for each of those lensing elements to be tipped or tilted or swiveled if you would in space such that they cause by doing a reverse ray tracing process of all of the stack of these vertical lines to be moved out spatially, left to right, and top to bottom, as well as focus by focal length of the lens shape. A fly has a large array of discrete non-moving eyes each of which fan out and are optically disposed to read a certain or detect a certain area which would then reassemble back in the fly's brain to build it into a picture. We're suggesting a similar thing here where we have a piece of the bar code maybe detectable to one' of the optical paths and another piece detectable to another path and so on such that our minimized resolution is built back together piece-wise. Furthermore, our processing system can know what its optical paths are like so that by a fixed area it can have a pretty good idea of what it is looking at and know where the rest of it should be found and assemble these things in sort of a mapping process. We contemplate the facets being oblong in shape and rectangular so that they can be filled in solid in some material and then through some kind of a determination that we have to make, determine how the image locations both in X, Y, and Z map into a physical location on the image sensing array. The object here, is to fill the volume a truncated four-sided pyramidal volume in space- with areas that are connected to each other such that as you move from one roughly cubic volume to the next roughly cubic volume, there is continuity of image capturing capability so that if you move from one to the next you jump from the point of focus of one to the focus of the next as it moves, say left to right, you cross-over such that maybe one area might be adjacent to one beside it so that you got part of the barcode in one area and part in the next.

An alternate embodiment might utilize further optical paths that include variable magnification. And a further alternate embodiment might have certain portions of the optical paths that are used for spotting. For example, some areas might have very low magnification and are used to identify targets. And maybe even in conjunction with some additional aiming or zooming effect so it might be used as a ranging assistant.

Consider an area CCD scanner such as, for example, a black and white TV camera device of, say 768 pixels horizontal x 492 lines vertical. For bar code only applications, this area sensor could be considered as 42 individual linear sensing arrays of 768 elements each. Now, given this array of 492 individual linear arrays, consider an optical system with 492 separate optical paths to each linear array, where the target or image area may be located in a large variety of positions. (In fact, the variety of locations may vary in each of the X, Y, and Z positions and the image magnification as well.) In essence, a spatial volume may be created anywhere within which a target bar code may be located and read. For the total image sensing CCD array, only one line of 768 elements might have an acceptable sample of the bar code, while all others sense nothing, but that is sufficient. A single flashable light source may illuminate the entire imaging volume, so an "electronic picture" of the imagable volume may be captured. The multiple path optical system should be designed such that for any target location within the imaging volume, at least one yields an interpretable result.

As mentioned above, 768 horizontal pixels may not provide high enough resolution for most bar code reading purposes. It would be feasible, however, to use the multiple optical paths to project the target areas by section onto the imaging array for re-assembly of pieces of the target into the single bar code for interpretation. A basic concept upon which all of this discussion is based is immediate transfer of the signals from the imaging device to a microcomputer memory for signal processing and decoding. FIG. 1 illustrates the volume scannable region concept. The multiple discrete optical paths must be designed such that there are no "holes" big enough that a generally horizontally positioned bar code of ordinary height such as 0.5 inch cannot be captured. The X, Y and Z dimensions are determined by the implementation of the optical system including a lens or reflector of compound construction. A good conceptual example is a bifocal vision correcting lens, where multiple optical characteristics are included in a single structure and are disposed at different locations of the structure. Our compound lens structure might have rectangular regions of various optical characteristics to form the desired optical path for gathering, focusing and directing light from each of the plural potential target positions to generally linear sensing regions on the surface of the imaging device.

Consider the compound lens which forms the plural optical paths. Such a lens might be best constructed of injection molded plastic of optical quality and might have oblong rectangular "facets" as shown in FIGS. 2-7.

For practical considerations, 492 separate, single-line optical paths may not be realizable with available technology. Several dozen to say 100 paths may be practical. The larger number of discrete paths and positions, the larger the effective scanning volume. A major benefit of this concept is there are no moving parts whatsoever. Compactness and low power consumption also result.

Claims

1. A non-laser type scanner for reading optically readable information within a three dimensional area, comprising:

(a) a two dimensional photosensitive array having an output and both horizontal and vertical lines of resolution;

(b) a plurality of lenses, each of said lenses discretely associated with at least one of said horizontal and vertical lines of resolution;

(c) each of said lenses having a focal length coordinate within said three dimensional area; and (d) a computer associated with said array output for locating and decoding optically readable information located within said three dimensional area.

2. The apparatus of claim 1, further comprising a housing having an opening for facing optically readable information and for housing said array, lenses, and computer.

3. The apparatus of claim 2, further comprising data port means for integrating said housing with a hand-held data terminal.