Registers – Coded record sensors – Particular sensor structure
Reexamination Certificate
1999-11-09
2001-04-03
Le, Thien M. (Department: 2876)
Registers
Coded record sensors
Particular sensor structure
C235S462350
Reexamination Certificate
active
06209789
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to laser scanners used in reading bar and like code symbols, and more particularly to a novel optical filtering system for use therein, which provides improved scanner performance, appearance and manufacturability at lower cost.
2. Brief Description of the Prior Art
Laser-based bar code symbol scanning systems have become increasingly popular in recent times. However, despite technical advancements in the art, such systems still suffer from numerous problems that have yet to be adequately solved.
For example, a major problem with prior art laser scanners is that as they become more widely used in point-of-sale (POS) environments, aesthetic considerations play a greater role in their purchase decisions by store managers considering their use at POS locations. The reason for this is clear. Store owners invest in a great deal of time, money and artistic effort in making their stores and display counters attractive to customers. Consequently, store owners and managers demand that laser scanning systems do not detract from the appearance of their display and check-out counter environments.
Another problem with prior art laser scanning systems is that the laser, mirrors, and other electro-optical components used in such systems are revealed to customers at POS locations through optically transparent scanning windows. Consequently, the sight of rotating mirrors and swirling laser beams behind the scanning windows of prior art laser scanners, constitutes a significant source of fear to many customers. While such fears are often based on a lack of knowledge of lasers and optics, store managers are nevertheless concerned that such fears may translate into customer anxiety and thus a decrease in sales.
Other problems of a more technical nature arise when using prior art laser scanners in POS environments. In particular, typical ambient lighting levels in store environments have the potential of adversely effecting the signal-to-noise ratio (SNR) of laser scan data signals detected within prior art laser scanners. Thus, to date, a number of different optical filtering techniques have been developed for use in combating the adverse effects of ambient lighting levels on laser scanner performance. Several optical filtering techniques commonly employed are detailed below.
One popular filtering technique involves installing before the scanner photodetector, a band-pass optical filter narrowly tuned to the laser wavelength. Typically, this wavelength lies in the visible region of the electromagnetic spectrum (i.e., about 670 nanometers). This common filtering technique is used in the prior art laser scanning systems disclosed in U.S. Pat. Nos. 5,180,904; 5,015,833; 4,816,660; 4,387,297 and 5,115,333. However, this approach is not without shortcomings and drawbacks. When using this approach, store customers are typically permitted to see the rotating or oscillating mirrors and swirling laser beams behind the scanning window. In addition to presenting a source of worry for many customers, the plain view of such electro-optical components also detracts from the overall aesthetic appearance of laser scanners employing this common filtering technique.
Another prior art approach to reducing ambient light in a post-based laser scanners involves installing a spatial filter (i.e., a slotted or aperture plate) over the scanning window of the laser scanner. Typically, the aperture or slot pattern of the aperture plate spatially corresponds to the cross-sectional geometry of projected laser scanning pattern at the plane of its scanning window. This spatial filtering technique is used in the many prior art laser scanning systems, disclosed in U.S. Pat. Nos. 4,713,532; 4,093,865; and 4,647,143. However, this approach is not without its shortcomings and drawbacks. Such spatial filters detract from the overall appearance of the laser scanners in which they are employed. In addition, such spatial filters cannot be effectively used when the laser scanning patterns are spatially complex, as in the case of the omnidirectional projection laser scanner disclosed in U.S. Pat. No. 5,216,232.
Thus, there is a great need in the art for a laser scanner which solves the above-described problems, while overcoming the shortcomings and drawbacks of prior art laser scanning apparatus and methodologies.
OBJECTS OF THE INVENTION
Accordingly, it is a primary object of the present invention to provide a laser bar code symbol scanning system that is capable of reading bar code symbols, without the shortcomings and drawbacks of prior art devices.
A further object of the present invention is to provide a laser bar code symbol scanner having a novel optical filtering system which provides improved scanner performance, appearance and manufacturability.
A further object of the present invention is to provide such a laser bar code symbol scanner, in which the wavelength-selective components of the optical filter system are strategically installed in a spatially-separated manner in order to achieve improved scanner performance, appearance and manufacturability, in a simple low-cost manner.
A further object of the present invention is to provide such a laser bar code symbol scanner in which the optical filtering system employed therein inherently hides from view, unappealing electro-optical components mounted within the laser scanner housing, while rejecting unwanted spectral noise outside the narrow spectral band of the laser scanning beam.
A further object of the present invention is to provide a laser bar code symbol scanner that satisfies the concerns of store owners and managers alike, while effectively overcoming the problems caused by high intensity ambient lighting.
These and further objects of the present invention will become apparent hereinafter and in the claims.
SUMMARY OF THE PRESENT INVENTION
In general, the laser scanner of the present invention provides a simple, low cost solution to the problems described in the Background of the Invention. This is achieved by strategically embodying a pair of discrete optical filter elements in the housing of a laser scanner in which the following system components are provided; a light transmission window; a laser source for producing a laser beam having a predetermined characteristic wavelength; a scanning mechanism for projecting the produced laser beam through the light transmission window, and scanning the produced laser beam across a scanning field defined external to the housing; a laser light focusing means for focusing laser light reflected off a scanned bar code symbol, and along a focused laser light return path within the housing; and a laser light detection means, disposed along the focused laser light return path, for detecting the intensity of focused laser light and generating an electrical signal representative thereof.
In accordance with the present invention, the first optical filter element is installed over the light transmission aperture of the scanner housing, and has wavelength selective properties which transmit only light having wavelengths from slightly below a predetermined wavelength in the visible band of the electromagnetic spectrum (e.g., slightly below 670 nanometers and greater). The second optical filter element is installed within the housing, along the focused laser return light path and between the light focusing means and the first optical filter element, and transmits only light having wavelengths from slightly above the predetermined wavelength (e.g., slightly above 670 nanometers and greater). Collectively, the first and second optical filter elements cooperate to form a narrow wavelength band-pass filtering system centered about the predetermined wavelength, thereby rejecting wavelengths outside the spectral band of the scanned laser beam and thus providing improved signal-to-noise ratio.
As a result of this novel laser scanner construction, the wavelength selective properties of the first optical filter element inherently render it semi-transparent,
Amundsen Thomas
Blake Robert
Knowles Carl H.
Rockstein George
Wilz, Sr. David M.
Le Thien M.
Metrologic Instruments Inc.
Smith, Esq. Nancy A.
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