Optical: systems and elements – Lens – Fluid
Reexamination Certificate
1998-12-17
2001-05-15
Sugarman, Scott J. (Department: 2873)
Optical: systems and elements
Lens
Fluid
Reexamination Certificate
active
06233098
ABSTRACT:
BACKGROUND OF THE INVENTION
In a beam scanner a small spot of light is swept rapidly across the target. After reflection from the target a photo electric converter such as a photo diode detects the reflected light and converts it to electronic signals representing features of the target. To successfully resolve features of the target, it is necessary that the spot size be about the size of, or smaller than, the smallest features of the target.
A bar code reader is an important commercial application for beam scanners and is referred to herein as a typical example of a specific application for the present invention.
In typical barcode scanners, optical components such as converging lenses and stop apertures are placed in front of a light source such as a laser diode causing the beam to converge to a small spot about several inches away from the source. The densest bar codes, those with the narrowest bars and spaces, are most resolvable where the beam spot has the smallest cross sectional dimensions. This narrow region is sometimes referred to as the beam waist.
The range of distance over which the most dense codes may be resolved with a fixed focus lens is quite short. For example dense bar code targets with 5 mil, (0.005 inch), wide bars and spaces may only be resolvable over a range of 1 or 2 inches when the waist is located at about 6 inches from the laser source. Such readers are perceived to have a sensitive “sweet spot” when attempting to read dense codes.
Beyond the beam waist where the beam diverges it is only possible to resolve wider bars and spaces. It is very desirable however for portable scanners to have a longer depth of operating field for the dense 5 and 7 mil bar codes.
In the U.S. patent application entitled “ELECTRO-OPTICAL SCANNING SYSTEM WITH GYRATING SCAN HEAD”, Ser. No. 07/776,663 of which the present invention is a continuation-in-part, several methods were described for extending the depth of field of a beam scanning bar code reader. One of these methods employs the use of a moving lens system which may be electrically focused and another employs a non-imaging cone shaped optical element to provide a beam which is narrow over a certain distance then diverges rapidly beyond that distance.
U.S. Pat. No. 4,816,660 describes the use of a conventional aperture stop to increase depth of field of a laser bar code reader. The aperture stop has draw backs in that it wastes a substantial portion of the laser beam power to gain increased depth of field and requires precise mounting of numerous parts including a separate blocking wall, aligned with and spaced from a separate lens, thus forming a bulky system.
For fixed focused systems, when the beam spot is not at its smallest size at a particular distance down range, a dense bar code target becomes difficult or impossible to resolve.
U.S. Pat. No. 5,438,187 describes lenses with compound surfaces, i.e., different curvatures on a single lens surface to simultaneously focus light at different points down range. This approach is difficult to implement because the production of such lenses is complicated even if they are molded from plastic. The focusing of such lenses is also complex and leads to tedious compromises. Signal processing is also impaired due to decreased signal to noise ratios associated with simultaneously apportioning light to different regions. (Light not in focus for one region may add to noise especially between foci.)
SUMMARY OF THE INVENTION
The present invention provides for increased field depth in optical systems such as beam scanners while reducing the number of parts and complexity needed as compared to prior art systems. Simplified mounting, packaging and adjustment requirements are combined in common structures thereby keeping production costs and space requirements low.
Various embodiments of these structures are combined with a novel fluidic or gel lens mechanism to effect a continuously variable focus thereby providing a minimum spot size over a wide range to significantly extend the depth of scanning range over prior art scanners with little wasted light while saving power.
The present invention effectively solves problems of increasing resolution over a long working range while providing the benefits of small size, low power and low cost, all of which are valuable features in portable equipment. Signal processing of light signals is also much more straight foreword, requiring simpler electronic signal amplification and conditioning circuits for signals from close and distant targets, respectively.
In particular, the present invention is directed to an optical system for distinguishing features of a target. A light source is located at a source position for generating a plurality of light rays emanating from the source position. A lens is positioned in front of the light source position. The lens has a first surface for receiving light rays emanating from the source position and a second surface, opposite the first surface, for outputting the received light rays. The first and second surfaces are separated by a thickness. The second surface having a first clear area for passing a first group of light rays through the lens. The second surface further includes a treated that is area separate from the first clear area.
In accordance with a further aspect, the present invention is directed to a method for treating an optical lens. A lens substrate formed of clear material is provided. The lens substrate has a first surface, a second surface opposite the first surface, and a thickness represented by a distance between the first and second surfaces. A treated area is formed on a portion of the second surface of the clear material. After the treated area is formed, the second surface includes the treated area and a separate first clear area different from the treated area.
In accordance with a still further aspect, the present invention is directed to an optical system and method for distinguishing features of a target. A light source is located at a source position for generating a plurality of light rays emanating from the source position. An aperture window is positioned in front of the light source position. The aperture window has an open hole for passing a first group of light rays though the aperture window, a clear portion formed of a clear material for passing a second group of light rays through the aperture window, and a translucent portion for scattering a third group of light rays as the third group of light rays passes through the aperture window.
In accordance with a still further aspect, the present invention is directed to a lens system for focusing a light beam. A shell has a first liquid bounding surface having a first width, a second surface having a second width, and an open hole spanning between the first liquid bounding surface and the second surface. The open hole has a third width that is smaller than the first and second widths. A cured resin material is positioned against the first liquid bounding surface and throughout the open hole. The cured resin material includes a first curved lens surface that is positioned against the first liquid bounding surface and which spans the first width.
In accordance with yet a further aspect, the present invention is directed to a method for making a lens system for focusing a light beam. A shell having a first liquid bounding surface with a first width, a second surface having a second width, and an open hole spanning between the first liquid bounding surface and the second surface is provided. The open hole has a third width that is smaller than the first and second widths. A droplet of curable liquid resin is deposited on top of the first liquid bounding surface, and a portion of the droplet is allowed to flow through the open hole. The curable liquid is cured to form a cured resin material positioned against the first liquid bounding surface and throughout the open hole. The resulting cured resin material includes a first curved lens surface that is positioned against the first liquid bounding surface and which spans the fir
Reed Smith LLP
Sugarman Scott J.
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