Registers – Coded record sensors – Particular sensor structure
Reexamination Certificate
1999-12-23
2003-04-15
Le, Thien M. (Department: 2876)
Registers
Coded record sensors
Particular sensor structure
C235S462380, C235S462390, C235S462250, C235S462400
Reexamination Certificate
active
06547144
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of Invention
The present invention relates generally to holographic laser scanners of ultra-compact design capable of reading bar and other types of graphical indicia within a large scanning volume using holographic optical elements and visible laser diodes, and also a method of designing and operating the same for use in diverse applications.
2. Brief Description of the Prior Art
The use of bar code symbols for product and article identification is well known in the art. Presently, various types of bar code symbol scanners have been developed. In general, these bar code symbol readers can be classified into two distinct groups.
The first class of bar code symbol reader simultaneously illuminates all of the bars and spaces of a bar code symbol with light of a specific wavelength(s) in order to capture an image thereof for recognition/decoding purposes. Such scanners are commonly known as CCD scanners because they use CCD image detectors to detect images of the bar code symbols being read.
The second class of bar code symbol reader uses a focused light beam, typically a focused laser beam, to sequentially scan the bars and spaces of a bar code symbol to be read. This type of bar code symbol scanner is commonly called a “flying spot” scanner as the focused laser beam appears as “a spot of light that flies” across the bar code symbol being read. In general, laser bar code symbol scanners are subclassified further by the type of mechanism used to focus and scan the laser beam across bar code symbols.
The majority of laser scanners in use today employ lenses and moving (i.e. rotating or oscillating) mirrors in order to focus and scan laser beams across bar code symbols during code symbol reading operations. Examples of such laser scanners are disclosed in great detail in the Background of Invention of U.S. Pat. No. 5,216,232 to Knowles et al.; U.S. Pat. No. 5,340,973 to Knowles et al.; U.S. Pat. No. 5,340,971 to Rockstein et al.; U.S. Pat. No. 5,424,525 to Rockstein et al., which are incorporated herein by reference.
One type of laser scanner that has enjoyed great popularity in recent years is called the “polygon scanner” in that it employs a rotating polygon whose sides bear light reflective surfaces (e.g. mirrors) for scanning a laser beam over multiple paths through space above the scanning window of the scanner. In polygon-type laser scanners, the angular sweep of the outgoing laser beam and the light collection efficiency of the return laser beam are both directly related to the number and size of light reflective facets on the rotating polygon.
In contrast to laser scanners, which use lenses (i.e. light refractive elements) to shape and focus laser light beams and light reflective surfaces to scan focused laser beams, there exists another subclass of laser scanner which employs a high-speed holographic disc. In general, the holographic disc comprises an array of holographic optical elements (HOEs) called “facets” which function to focus and deflect outgoing laser beams during laser beam scanning operations, as well as focus incoming reflected laser light during light collection/detection operations. Such bar code symbol scanners are typically called holographic laser scanners or readers because holographic optical elements (HOEs) are employed. Examples of prior art holographic scanners are disclosed in U.S. Pat. Nos. 4,415,224; 4,758,058; 4,748,316; 4,591,242; 4,548,463; 5,331,445 and 5,416,505, incorporated herein by reference.
Holographic laser scanners, or readers, have many advantages over laser scanners which employ lenses and mirrors for laser beam focusing and scanning (i.e. deflection) functions.
One of the major advantages of holographic laser scanners over polygon laser scanners is the ability of holographic laser scanners to independently control (i) the angular sweep of the outgoing laser beam and (ii) the light collection efficiency for the returning laser beam.
Holographic laser scanners have other advantages over polygon-type laser scanners. In particular, in holographic laser scanners, light collection efficiency is determined by the size of the light collecting portion of each holographic facet, while the angular sweep of the outgoing laser beam is determined by the angular width of the outgoing beam portion of the holographic facet and the angles of incidence and diffraction of the outgoing laser beam.
While prior art holographic scanning systems have many advantages over mirror-based laser scanning systems, prior art holographic scanners are not without problems.
In the first holographic scanner produced by International Business Machines (IBM), the holographic facets on its holographic disc were simple sectors which did not allow for independent control over light collection and light scanning functions. Consequently, such holographic scanners had faster scanning speeds than were needed for the applications at hand. Subsequent industrial scanners designed by IBM allowed independent control of these functions. However, the holographic discs employed in prior art holographic scanners, e.g. the HOLOSCAN 2100™ holographic laser scanner designed and sold by Holoscan, Inc. of San Jose, Calif. fail to (i) maximize the use of available space on the disc for light collection purposes, and (ii) minimize the scan line speed for particular laser scanning patterns. As a result of such design limitations, prior art holographic scanners have required the use of large scanning discs which make inefficient use of the available light collecting surface area thereof. They also are incapable of producing from each holographic facet thereon, detected scan data signals having substantially the same signal level independent of the location in the scanning volume from which the corresponding optical scan data signal is produced. Consequently, this has placed great demands on the electrical signal processing circuitry required to handle the dramatic signal swings associated with such detected return signals.
While U.S. Pat. No. 4,415,224 to Applicant (Dickson) discloses a method of equalizing the light collection efficiency of each facet on the holographic scanning disc, it does not disclose, teach or suggest a method of equalizing the light collection efficiency of each facet on the holographic scanning disc, while utilizing substantially all of the light collecting surface area thereof. Thus, in general, prior art holographic laser scanners have required very large scanner housings in order to accommodate very large scanning discs using only a portion of their available light collection surface area.
In many code symbol reading applications, the volumetric extent of the holographic scanner housing must be sufficiently compact to accommodate the small volume of space provided for physical installation. However, due to limitations of conventional design principles, it has not been possible to build prior art holographic scanners having sufficient compactness required in many applications. Consequently, the huge housings required to enclose the optical apparatus of prior art holographic laser scanners have restricted their use to only a few practical applications where housing size constraints are of little concern.
While highly desirable because of their low power usage and miniature size, solid-state visible laser diodes (VLDs) cannot be used practically in prior art holographic laser scanners because of several problems which arise from inherent properties of conventional VLDs.
The first problem associated with the use of VLDs in holographic laser scanners is that the VLDs do not produce a single spectral line output in the manner of conventional He—Ne laser tubes. Rather, conventional VLDs always produce some background super-luminescence, which is a broad spectrum of radiation of the type produced by conventional light emitting diodes (LEDs). Also, VLDs often operate in more than one oscillation mode and/or exhibit mode hopping, in which the VLD jumps from one mode of oscillation to another. Both of these characteristics of VLDs result in
Amundsen Thomas
Dickson LeRoy
Groot John
Knowles Carl Harry
Le Thien M.
Le Uyen-Chau N.
Metrologic Instruments Inc.
Thomas J. Perkowski Esq., P.C.
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