Registers – Coded record sensors – Particular sensor structure
Reexamination Certificate
1997-09-16
2001-05-08
Pitts, Harold I. (Department: 2876)
Registers
Coded record sensors
Particular sensor structure
C235S472010
Reexamination Certificate
active
06227450
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of Invention
The present invention relates to laser scanning systems and more particularly, to electronically-controlled damped off-resonant mechanisms for reliably scanning laser beams during bar code symbol reading operations and the like.
2. Brief Description of the Prior Art
Laser scanning bar code symbol scanners are widely used to read bar code symbols on products and packages for identification purposes. Many different techniques exist for scanning laser beams across objects.
One commonly used beam scanning technique involves driving a resonant element bearing a mirror into oscillatory motion within a plane, while a laser beam is directed incident the mirror surface. As the resonant element oscillates, so too does the mirror, causing the incident laser beam to be scanned across a scanning field of substantially planar extent, as well as a bar code symbol disposed therewithin. In general, laser light reflected from the scanned bar code symbol is collected and detected to produce an electrical signal representative of the scanned symbol. Ultimately, the electrical signal is processed in order to decode the scanned symbol and produce symbol character data representative of the decoded symbol.
In U.S. Pat. Nos. 5,168,149, 5,280,165, 5,374,148 and 5,581,067, several different scanning mechanisms are disclosed, in which strips made of Mylar™ or Kapton™ plastic material are used to realize resonant scanning elements. While such prior art scanning elements are durable, they are not without their shortcomings and drawbacks.
Such prior art laser scanning mechanisms are generally massive and large in comparison to the size of the scanning mirror supported thereby. Prior art laser scanning mechanisms are generally difficult to produce, expensive to manufacture, difficult to precisely tune, and typically require an anti-shock mechanism to protect the scanning element from damage when dropped. Consequently, there are numerous applications where such limitations prevent prior art scanning mechanisms from being used in a commercially feasible manner.
Addressing the shortcomings and drawbacks associated with the above-described scanning mechanism, Applicants hereof have attempted to construct a laser beam scanning mechanism, in which a thin strip of Kapton™ film, anchored at its base end and supporting a miniature mirror and a ferrite magnet on its free end, is driven in an off-resonant mode of operation in order to scan a laser beam incident the mirror. While laboring long and hard, Applicants have been unable to consistently manufacture in large volume and at low cost, a laser beam scanning mechanism based on such prior art design principles, without seriously sacrificing the operation and performance thereof.
Consequently, hitherto, Metrologic's ScanQuest® Laser Scanning Engine (Models 4110 and 4120), in which the above-described scanning mechanism is employed, could not be manufactured in high volume or at low cost.
Therefore, there is a great need in the art for an improved laser scanning mechanism which avoids the shortcomings and drawbacks of prior art laser beam scanning apparatus and methodologies.
OBJECTIVES AND SUMMARY OF THE INVENTION
Accordingly, it is a primary object of the present invention to provide an improved laser beam scanning apparatus that avoids the shortcomings and drawbacks of prior art technologies.
A further object of the present invention is to provide such a laser beam scanning apparatus in the form of an electronically-controlled mechanically-damped off-resonant laser beam scanning mechanism comprising an etched scanning element having a small flexible gap region of closely-controlled dimensions disposed between an anchored base portion and a laser beam deflecting portion.
Another object of the present invention is to provide such a laser beam scanning mechanism, in which the resonant frequency of oscillation of the laser beam deflecting portion relative to the anchored base portion is determined by the closely controlled dimensions of the flexible gap region set during manufacture.
A further object of the present invention is to provide such a laser beam scanning mechanism, in which the resonant frequency of oscillation of the scanning element is tuned by adjusting the thickness and width of the flexible gap region.
Another object of the present invention is to provide such a laser beam scanning mechanism, in which the physical dimensions of the flexible gap region are closely controlled by using chemical-etching techniques during manufacture.
Another object of the present invention is to provide such a laser beam scanning mechanism, in which the etched scanning element is manufactured by chemically etching a double-sided copper clad sheet consisting of a polyamide base material laminated between ultra-thin copper sheets.
Another object of the present invention is to provide such a laser beam scanning mechanism, in which a permanent magnet is mounted on the rear surface of the laser beam deflecting portion, and a laser beam deflecting element is mounted on the front surface of the laser beam deflecting portion.
Another object of the present invention is to provide such a laser beam scanning mechanism, in which the base portion is securely fixed to an optical bench and the laser beam deflecting portion is forced to oscillate substantially away from the natural resonant frequency of the scanning element, by a reversible electromagnet disposed in close proximity to a permanent magnet mounted to the rear surface of the laser beam deflecting portion.
Another object of the present invention is to provide such a laser beam scanning mechanism, in which the natural harmonic (i.e., resonant) frequency of the laser beam deflecting portion about the anchored base portion is mechanically-damped by adding a thin layer of flexible rubber material to the gap region of the scanning element during manufacture, and the laser beam deflecting portion is forcibly driven by a reversible electromagnet operated at a forcing (i.e., driving) frequency tuned substantially away (i.e., off) from the natural resonant frequency of the laser beam deflecting portion.
Another object of the present invention is to provide such a laser beam scanning mechanism, in which the steady-state frequency of oscillation of the laser beam deflecting portion is determined by the frequency of polarity reversal of the electromagnet, which is electronically controlled by the polarity of the electrical current supplied to the input terminals of the magnet coil of the reversible electromagnet.
Another object of the present invention is to provide such a laser beam scanning mechanism, in which the driving or forcing frequency of the electromagnet is selected to be at least ten percent off (i.e., greater or less than) the natural resonant frequency of the laser beam deflecting portion.
Another object of the present invention is to provide such a laser beam scanning mechanism, in which the steady-state (i.e., controlled) frequency of oscillation of the scanning element can be set at the time of manufacture to be any one of a very large range of values (e.g., 25-125 Hz) for use in both low-speed and high-speed laser scanning systems.
Another object of the present invention is to provide such a laser beam scanning mechanism having ultra-low power consumption, and a low operating current.
Another object of the present invention is to provide such a laser beam scanning mechanism, in which the angular sweep of the laser beam deflecting element is about thirty degrees (i.e., ±15° degrees) measured with respect to the point of pivot about the anchored base portion of the scanning element of the present invention.
Another object of the present invention is to provide such a laser beam scanning mechanism, in which the scanning element and electromagnet are mounted within an ultra-compact housing having integrated stops for limiting the sweep that the scanning element is permitted to undergo during operation.
Another object of the present invention is to provide such a l
Amundsen Thomas
Blake Robert E.
Carullo Thomas
Colavito Stephen J.
Knowles C. Harry
Metrologic Instruments Inc.
Perkowski Esq. P.C. Thomas J.
Pitts Harold I.
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