U.S. patent application number 09/736771 was filed with the patent office on 2001-05-03 for spatially-separated optical filtering system for a laser bar code symbol scanner.
This patent application is currently assigned to Metrologic Instruments, Inc.. Invention is credited to Amundsen, Thomas, Blake, Robert, Knowles, Carl H., Rockstein, George, Wilz, David M. SR..
Application Number | 20010000615 09/736771 |
Document ID | / |
Family ID | 26967983 |
Filed Date | 2001-05-03 |
United States Patent
Application |
20010000615 |
Kind Code |
A1 |
Amundsen, Thomas ; et
al. |
May 3, 2001 |
Spatially-separated optical filtering system for a laser bar code
symbol scanner
Abstract
A laser bar code symbol scanner employing a narrow band-pass
optical filtering system of novel construction is disclosed. A
first optical filtering element is installed in the light
transmission aperture of a bar code scanner housing. A second
optical filtering element is installed inside the scanner housing
near the light detecting element. The first and second optical
filtering elements have wavelength selective properties such that
taken together they cooperate to form a narrow wavelength bandpass
optical filtering system which allows only transmission of light at
and around a certain predetermined wavelength into the
photodetector element. The present invention also hides
aesthetically unappealing electro-optical components mounted in the
scanner housing from plain view and the optical filtering elements
of the system can be easily and inexpensively manufactured without
compromising the performance of the scanner.
Inventors: |
Amundsen, Thomas;
(Turnersville, NJ) ; Blake, Robert; (Woodbury
Heights, NJ) ; Rockstein, George; (Audobon, NJ)
; Wilz, David M. SR.; (Sewell, NJ) ; Knowles, Carl
H.; (Moorestown, NJ) |
Correspondence
Address: |
Nancy A. Smith, Esq.
Metrologic Instruments, Inc.
90 Coles Road
Blackwood
NJ
08012
US
|
Assignee: |
Metrologic Instruments,
Inc.
|
Family ID: |
26967983 |
Appl. No.: |
09/736771 |
Filed: |
December 14, 2000 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09736771 |
Dec 14, 2000 |
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09436742 |
Nov 9, 1999 |
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09436742 |
Nov 9, 1999 |
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09258005 |
Feb 26, 1999 |
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6029894 |
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09258005 |
Feb 26, 1999 |
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08850295 |
May 5, 1997 |
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08850295 |
May 5, 1997 |
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08439224 |
May 11, 1995 |
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5627359 |
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08439224 |
May 11, 1995 |
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08293491 |
Aug 19, 1994 |
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08293491 |
Aug 19, 1994 |
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07761123 |
Sep 17, 1991 |
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5340971 |
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Current U.S.
Class: |
235/472.01 |
Current CPC
Class: |
G06K 7/10564 20130101;
G06K 2207/1018 20130101; G06K 7/10594 20130101; G06K 7/1443
20130101; G06K 2207/1016 20130101; G06K 7/14 20130101; G06K
2207/1012 20130101; G06K 7/10663 20130101; G06K 7/10801 20130101;
G06K 7/10881 20130101; G06K 7/10702 20130101; G06K 2207/1017
20130101; G06K 7/10891 20130101; G06K 7/10792 20130101; G06K
7/10861 20130101; G06K 7/10693 20130101; G06K 7/10603 20130101;
G02B 26/106 20130101; G06K 17/0022 20130101; G06K 7/10851
20130101 |
Class at
Publication: |
235/472.01 |
International
Class: |
G06K 007/10 |
Claims
What is claimed is:
1. A laser symbol scanning system, cpmprising: a housing having a
light transmission aperture through which light can enter and exit
said housing; a first optical filter element disposed in said light
transmission aperture and along a laser light path extending
through said light transmission aperture, and having
wavelength-selective filtering characteristics, said first optical
filter element function as a scanning window in said housing; laser
beam producing means in said housing for producing a laser beam
characterized by a predetermined wavelength; laser beam scanning
means in said housing for projecting said laser beam through said
scanning window and scanning said laser beam across a code symbol
on an object located within at least a portion of a scan field
defined external to said housing; laser light detection means is
said housing disposed in said laser light path, for detecting the
intensity of laser light reflected off said code symbol; and a
second optical filter element in said housing, spatially separated
from said first optical filter element and disposed along said
laser light path between said first optical filter element and said
laser light detection means, and having wavelength-selective
filtering characteristics, said second optical filter element
cooperating with said first optical filter element so as to form a
band-pass optical filtering system having a narrow wavelength band
width positioned about said predetermined wavelength and passing
light reflected off said code symbol having wavelengths only within
said narrow wavelength bandwidth.
2. The laser code symbol scanning system of claim 1, wherein said
first optical filtering element prevents light having wavelengths
up to slightly below said predetermined wavelength from passing
through said first filter.
3. The laser code symbol scanning system of claim 1, wherein said
second optical filtering element transmits light having wavelengths
from slightly above said predetermined wavelength.
4. The laser code symbol scanning system of claim 1, wherein said
predetermined wavelength is about 670 nanometers.
5. The laser code symbol scanning system of claim 2, wherein said
predetermined wavelength is about 670 nanometers.
6. The laser code symbol scanning system of claim 3, wherein said
predetermined wavelength is about 670 nanometers.
7. The laser code symbol scanning system of claim 1 wherein said
laser beam producing means comprises a visible laser diode for
producing a visible laser beam.
8. The laser code symbol scanning system of claim 1 wherein said
second optical filtering element is disposed immediately adjacent
said light detecting means.
9. The laser code symbol scanning system of claim 1 wherein said
wavelength filtering characteristics of said first optical
filtering element obscures each of said means positioned in said
housing from plain view.
10. The laser code symbol scanning system of claim 1 wherein in
said housing is a compact hand-supportable housing.
11. The laser code symbol scanning system of claim 1 wherein said
housing is mounted above a countertop.
12. The laser code symbol scanning system of claim 1 wherein said
laser beam scanning means produces a single-line laser scanning
pattern.
13. The laser code symbol scanning system of claim 1 wherein said
laser beam scanning means produces an omnidirectional laser
scanning pattern.
Description
RELATED CASES
1. This Application is a Continuation of application Ser. No.
08/850,295, filed May 5, 1997, which is a Continuation of
application Ser. No. 08/439,224, filed May 11, 1995, now U.S. Pat.
No. 5,627,359, which is a Continuation-in-Part of copending
application Ser. No. 08/293,491 filed Aug. 19, 1994, now abandoned
which is a Continuation of application Ser. No. b 07/761,123 filed
Sep. 17, 1991, now U.S. Letters Pat. No. 5,340,971, incorporated
herein by reference in its entirety.
BACKGROUND OF THE INVENTION
2. 1. Field of the Invention
3. 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.
4. 2. Brief Description of the Prior Art
5. 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.
6. For example, a major problem with prior art laser scanners is
that as they become more widely used in poinr-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.
7. 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.
8. 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 or laser scanner performance. Several optical
filtering techniques commonly employed are detailed below.
9. 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.
10. 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; 4,093,863; 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.
11. 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
12. 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.
13. 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.
14. 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.
15. 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.
16. 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.
17. These and further objects of the present invention will become
apparent hereinafter and in the claims.
SUMMARY OF THE PRESENT INVENTION
18. In general, the laser scanner of the present invention provides
a simple, low cost solution to the problems described inr 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.
19. 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.
20. As a result of this novel laser scanner construction, the
wavelength selective properties of the first optical filter element
inherently render it semi-transparent, and thus hide from plain
view, otherwise aesthetically unappealing electro-optical
components mounted within the scanner housing. At the same time,
the second optical filter element can be made substantially smaller
than the size of the light transmission window over which the first
optical filter element is installed, yet still cooperate with the
first optical filter element to achieve narrow wavelength band-pass
filtering about the characteristic wavelength of the laser beam.
Whereas the optical filtering properties of the relatively large
first optical filter element render its manufacture relatively easy
and inexpensive, the optical filtering properties of the relatively
small second optical filter element render its manufacture
relatively difficult and expensive. Thus, laser scanner
construction of the present invention represents a significant
advance in the state of the art in laser scanner design and
construction.
21. In summary, the present invention provides a simple and
inexpensive way or making 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
lighting conditions in POS environments.
BRIEF DESCRIPTION OF THE DRAWINGS
22. For a fuller understanding of the Objects of the Present
Invention, the Detailed Description of the Illustrated Embodiments
will be taken in connection with the accompanying Drawings,
wherein:
23. FIG. 1 is a perspective view of a laser bar code symbol reading
device constructed in accordance with the principles of the present
invention;
24. FIG. 2 is a cross-sectional elevated side view along the
longitudinal extent of the bar code symbol reading device of FIG.
1, showing various hardware and software components used in
realizing the illustrative embodiment;
25. FIG. 2A is a cross-sectional plan view along with longitudinal
extent of the bar code symbol reading device taken along line
2A--2A of FIG. 2, also showing the various components used in
realizing the illustrative embodiment;
26. FIG. 3 is a schematic representation of the
spectraltransmission characteristics of the first and second
optical filter elements empoloyed in the laser bar code symbol
reading device of the present invention, graphically illustrating
how the spectral transmission characteristics of these
spatially-separated optical filter elements cooperate to produce a
narrow-band optical filter system centered about the characteristic
wavelength of the visible laser scanning beam;
27. FIG. 4 is a block functional system diagram of the bar code
symbol reading device of the illustrative embodiment of the present
invention, illustrating the principal components of the device
integrated with the control system thereof;
28. FIG. 5 is a perspective view of alternative embodiment of the
laser bar code symbol reading device of the present invention;
and
29. FIG. 5A is a cross-sectional view of the laser bar code symbol
reading device of FIG. 5, taken along line 5A--5A thereof.
DETAILED DESCRIPTION OF THE ILLUSTRATIVE EMBODIMENT
30. For purposes of illustration, the present invention will be
described below with reference to the accompanying Drawings, with
like structures being indicated by like reference numbers.
31. As shown in FIG. 1, automatic bar code symbol reading system 1
of the first illustrative embodiment comprises an automatic
hand-holdable bar code symbol reading device 2 operably associated
with hand-holdable data collection device 3, described in detail in
U.S. Pat. No. 5,340,971. Operable interconnection of bar code
symbol reading device 2 and data collection device 3 is achieved by
a flexible multiwire connector cord 4 extending from bar code
symbol device 2 and plugged directly into the data-input
communications port of the data collection device 3.
32. Referring to FIGS. 1 through 2A, automatic bar code symbol
reading device 2 is shown to comprise an ultra-lightweight
hand-holdable housing 5 having a head portion 5A that continuously
extends into a contoured handle portion 5B. As illustrated in FIGS.
1 through 3A, the head portion of housing 5 has a transmission
aperture 6 formed in an upper portion of front panel 7 and covered
by plastic filter lens 69, to permit laser radiation of a
predetermined band of wavelengths, to exit and enter the housing.
In general, the lower portion of front panel 7B is optically
opaque, as are all other surfaces of the housing.
33. As illustrated in FIG. 1, bar code reading device 2 generates
two different fields external to the hand-holdable housing, in
order to carry out automatic bar code symbol reading according to
the principles of the present invention. Specifically, an object
detection field, indicated by broken and dotted lines, is provided
externally to the housing for detecting energy reflected off an
object bearing a bar code, located within the object detection
field. A scan field, on the other hand, having at least one
scanning plant of essentially planar extent, is provided external
to the housing for scanning an object present within the scan
field. Such scanning is achieved with a laser light beam so that
scan data can be collected for detecting the presence of a bar code
within the scan field, and subsequently reading (i.e., scanning and
decoding) the detected bar code symbol.
34. In general, the energy reflected off an object in the object
detection field can be optical radiation or acoustical energy,
either sensible or non-sensible by the operator, and may be either
generated by an external ambient source, or from the automatic bar
code svmbcol reading device itself. In the illustrative embodiment,
this energy is a beam of infrared light projected forwardly from
transmission aperture 6 in a spatially directed fashion, preferably
essentially parallel to the longitudinal axis 9 of the head portion
of the housing. In a preferred embodiment, the object detection
field has a three-dimensional volumetric expanse spatially
coincident with the transmitted infrared light beam. This ensures
that an object within the object detection field will be
illuminated by the infrared light beam and that infrared light
reflected therefrom will be directed generally towards the
transmission aperture of the housing where it can be detected, to
indicate that an object is within the object detection field.
35. In order to scan a bar code symbol on an object within the
object detection field, a laser light beam having a characteristic
wavelength .lambda.c is automatically generated within the head
portion of the housing and repeatedly scanned through the
transmission aperture across the scan field. As illustrated in FIG.
1, at least a portion of the scanned laser beam aligned with bar
code on the detected object, will be reflected off the bar code and
directed back towards and through the transmission aperture for
collection, detection and subsequent processing in a manner which
will be described hereinafter.
36. To more fully appreciate the mechanisms employed in providing
the object detection and scan fields of bar code symbol reading
device 2, reference is best made to the operative elements within
the hand-holdable housing.
37. As shown in FIG. 4, bar code symbol reading device of the first
illustrated embodiment comprises a number of system components,
namely, an object detection circuit 10, scanning means 11,
photoreceiving circuit 12, analog-to-digital (A/D) conversion
circuit 13, bar code presence detection module 14, bar code scan
range detection module 15, symbol decoding module 16, data format
conversion module 17, symbol character data storage unit 18, and
data transmission circuit 19. In addition, a magnetic field sensing
circuit 20 is provided for detecting a housing support stand, while
a manual switch 21 is provided for selecting long or short range
modes of object and bar code presence detection. As illustrated,
these components are operably associated with a programmable system
controller 22 which provides a great degree of versatility in
system control, capability and operation. The structure, function
and advantages of this controller will be described in detail
hereinafter.
38. In the illustrative embodiment, system controller 22, bar code
presence detection module 14, bar code scan range detection module
15, symbol decoding module 16, and data format conversion module 17
are realized using a single programmable device, such as a
microprocessor having accessible program and buffer memory, and
external timing means. It is understood, however, that any of these
elements can be realized using separate discreet components as will
be apparent to those skilled in the art.
39. The purpose of the object detection circuit is to determine
(i.e., detect) the presence of an object (e.g., product, document,
etc.) within the object detection field of bar code symbol reading
device 2, and in response thereto, automatically produce first
control activation signal A.sub.1. in turn, first control
activation signal A.sub.1 is provided as input to the system
controller which, as will be described in greater detail
hereinafter, causes the device to undergo a transition to the bar
code svmbol presence detection state.
40. As illustrated in FIG. 4, scanning means 11 comprises a light
source 47 which, in general, may be any source of intense light
suitably selected for maximizing the reflectivity from the object's
surface bearing the bar code symbol. In the illustrative
embodiment, light source 47 comprises a solid-state visible laser
diode (VLD) which is driven by a conventional driver circuit 48. In
the illustrative embodiment, the wavelength of laser light produced
from laser diode 47 is about 670 nanometers. In order to scan the
laser beam output from laser diode 47 over a scan field having a
predetermined spatial extent in front of the head portion of the
housing, a planar scanning mirror 49 can be oscillated back and
forth by a stepper motor 50 driven by a conventional driver circuit
51, as shown. However, it is understood that other conventional
laser scanning mechanisms may be used to practice the present
invention.
41. To selectively activate laser light source 47 and scanning
motor 50, the system controller provides laser diode enable signal
E.sub.L and scanning motor enable signal E.sub.M as input to driver
circuits 48 and 51, respectively. When enable signal E.sub.L is a
logical "high" level (i.e., E.sub.L=1) , a laser beam is generated,
and when E.sub.M is a logical high level the laser beam is scanned
through the transmission aperture and across the scan field.
42. When an object such as product bearing a bar code symbol is
presented within the scan field at the time of scanning, the laser
beam incident thereon will be reflected. This will produce a laser
light return signal of variable intensity which represents a
spatial variation of light reflectivity characteristic of the
spaced apart pattern of bars comprising the bar code symbol.
Photoreceiving circuit 12 is provided for the purpose of detecting
at least a portion of laser light of variable intensity, which is
reflected off the object and bar code symbol within the scan field,
and subsequently focused along a focused laser light return path
within the housing, onto the photosensor of photo-receiving circuit
12. Upon detection of this scan data signal, photoreceiving circuit
12 produces an analog scan data signal D.sub.1 indicative of the
detected light intensity.
43. In the illustrative embodiment, photoreceiving circuit 12
generally comprises scan data collection optics 53, which focus
optical scan data signals for subsequent detection by a
photoreceiver 54 having, mounted in front of its sensor, a
wavelength-selective filter 150 which only transmits optical
radiation of wavelengths up to a small band above 670 nanometers,
as illustrated in FIG. 3. Photoreceiver 54, in turn, produces an
analog signal which is subsequently amplified by preamplifier 55 to
produce analog scan data signal D.sub.1. In combination, scanning
means 11 and photoreceiving circuit 12 cooperate to generate scan
data signals from the scan field, over time intervals specified by
the system controller. As illustrated hereinafter, these scan data
signals are used by bar code presence detection module 14, bar code
scan range detection module 15 and symbol decoding module 16.
44. As illustrated in FIG. 4, analog scan data signal D.sub.1, is
provided as input to A/D conversion circuit 13. As is well known in
the art, A/D conversion circuit 13 processes analog scan data
signal D.sub.1 to provide a digital scan data signal D.sub.2 which
resembles, in form, a pulse width modulated signal, where logical
"1" signal levels represent spaces of the scanned bar code and
logical "0" signal levels represent bars of the scanned bar code.
A/D conversion circuit 13 can be realized bv any conventional A/D
chip. Digitized scan data signal D.sub.2 is provided as input to
bar code presence detection module 14, bar code scan range
detection module 15 and symbol decoding module 16.
45. The purpose and function of bar code presence detection module
14 is to determine whether a bar code is present in or absent from
the scan field over time intervals specified by the system
controller. When a bar code symbol is detected in the scan field,
the bar code presence detection module 14 automatically generates
second control activation signal A.sub.2 (i.e., A.sub.2=1) which is
provided as input to the system controller, as shown in FIG. 4.
Preferably, bar code presence detection module 14 is realized as a
mircrocode program carried out by the microprocessor and associated
program and buffer memory, described hereinbefore. The function of
the bar code presence detection module is not to carry out a
decoding process but rather to simply and rapidly determine whether
the received scan data signals produced during bar code presence
detection, represent a bar code symbol residing within the scan
field. There are many ways in which to realize this function
through a programming implementation.
46. When a bar code symbol envelope is detected, the bar code
symbol presence detection module provides second control activation
signal A.sub.2=1 to the system controller. As will be described in
greater detail hereinafter, second control activation signal
A.sub.2 =1 causes the device to undergo a transition from the bar
code presence detection state to bar code symbol reading state.
47. The function of symbol decoding module 16 is to process, scan
line by scan line, the stream of digitized scan data D.sub.2, in an
attempt to decode a valid bar code symbol within a predetermined
time period allowed by the system controller. When the symbol
decoding module successfully decodes a bar code symbol within the
predetermined time period, symbol character data D.sub.3 (typically
in ASCIII code format) is produced corresponding to the decoded bar
code symbol. Thereupon a third control activation signal A.sub.3 is
automatically produced by the symbol decoding module and is
provided to the system controller in order to perform its system
control function.
48. As shown in FIG. 4, system controller 22 generates and provides
enable signals E.sub.EC, E.sub.DS, E.sub.DT to data format
conversion module 17, data storage unit 18 and data transmission
circuit 19, respectively, at particular stages of its control
program. As illustrated, symbol decoding module 16 provides symbol
character data D.sub.3 to data format module 17 to convert data
D.sub.3 into two differently formatted types of symbol character
data, namely D.sub.4 and D.sub.5. Format-converted symbol character
data D.sub.4 is of the "packed data" format, particularly adapted
for efficient storage in data storage unit 18. Format-converted
symbol character data D.sub.5 is particularly adapted from data
transmission to data collection and storage device 3, or a host
device such as, a computer or electronic cash register. When symbol
character data D.sub.4 is to be converted into the format of the
user's choice (based on a selected option mode), the system
controller will generate and provide enable signal E.sub.DS to data
storage unit 18, as shown in FIG. 4. Similarly, when format
converted data D.sub.5 is to be transmitted to a host device, the
system controller will generate and provide enable signal E.sub.DT
to data transmission circuit 19. Thereupon, data transmission
circuit 19 transmits format-converted symbol character data D.sub.5
to data collection device 3, via the data transmission lines of
flexible connector cable 4.
49. It is understood that there are a variety of ways in which to
configure the above-described system components within the housing
of bar code symbol reading device 2, while successfully carrying
out the functions of the present invention. In FIGS. 2 and 2 A, one
preferred arrangement is illustrated.
50. In FIG. 2A, the optical arrangement of the system components is
shown. Specifically, visible laser diode 47 is mounted in the rear
corner of circuit board 64 installed within the head portion of the
housing. A stationary concave mirror 53 is mounted centrally at the
front end of circuit board 63, primarily for collecting laser
light. Notably, the height of concave mirror 53 is such that it
does not block light transmission aperture 6. Mounted off center
onto the surface of concave mirror 53, is very small second mirror
64 for directing the laser beam to planar mirror 49 which is
connected to the motor shaft of a scanning motor 50, for joint
oscillatory movement therewith. As shown, scanning motor 50 is
mounted centrally at the rear end of circuit board 63. In the
opposite rear corner of circuit board 63, photodetector 54 is
nounted.
51. In operation, laser diode 47 adjacent the rear of the head
portion, produces and directs a laser beam in a forward direction
to the small stationary mirror 64 and is reflected back to
oscillating mirror 49. Osc illating mirror 49 scans the laser beam
over the scan field. The returning laser light, reflected from the
bar code, is directed back to oscillating mirror 49, which also
acts as a collecting mirror. This oscillating mirror then directs
the beam to stationary concave mirror 53 at the forward end of the
housing head portion. The beam reflected from the concave mirror 53
is directed to photodetector 54 to produce an electrical signal
representative of the intensity of the reflected light.
52. In front of stationary concave mirror 53, IR LED 28 and
photodiode 31 are mounted to circuit board 63 in a slightly offset
manner from longitudinal axis 9 of the head portion of the housing.
Apertures 65 and 66 are formed in opaque portion 7B of the housing
below the transmission aperture, to permit transmission and
reception of IR type object sensing energy, as hereinbefore
described. In order to shield IR radiation from impinging on
photodiode 31 via the housing, a metallic optical tube 67 having an
aperture 68 encases ohotod iode 31. By selecting the size of
aperture, the placement of photodiode 31 within optical tube 67
and/or the radiation response characteristics of the photodiode,
desire geometric characteristics for the object detection field can
be achieved, as described hereinbefore.
53. To prevent optical radiation slightly below 670 nanometers from
entering the transmission aperture 6, and transmitting therethrough
only optical radiation from slightly below 670 nanometers, a
plastic filter lens 69 is installed over the transmission aperture
6, as shown in FIG. 1. In this way the combination of plastic
filter lens 69 installed at the transmission aperture and the
wavelength selective filter 150 mounted before photoreceiver 54, as
shown in FIG. 2A, cooperate with each other in terms of wavelength
selection characteristics, to form a narrow band-pass optical
filter system having a center wavelength .mu..sub.c=670 nanometers,
as shown in FIG. 3.
54. In the illustrative embodiment, plastic window filter lens 69
is made from acrylic-type plastic material (e.g., DuPont RD 2177)
which can be purchased in 4'.times.8'sheets. These acrylic sheets
are cut to size so as to fit over the light transmission aperture
6. The resulting plastic filter lens 69 is then installed into the
light transmission aperture in a manner well known in the art.
55. Wavelength-selective filter 150 is preferably made by coating
(i.e., depositing) a multi-layer dielectric film onto a glass
substrate. In a vacuum environment (i.e., chamber), the dielectric
film is preferably deposited onto the glass substrate by
evaporating a dielectric material with an electric beam, in a
manner well known in the art. Thereafter, the resulting substrate
with the dielectric film deposited thereon is cut into small pieces
having physical dimensions approximately the size of the
photosensor in photoreceiver 2, as shown in FIGS. 2 and 2A, thereby
providing wavelength-selective filter 150. The wavelength-selective
filter 150 is then mounted immediately in front of the photosensor,
as shown in FIGS. 2 and 2A.
56. The novel optical filter arrangement described above provides a
number of important advantages to the laser scanner in which it is
embodied.
57. Firstly, the narrow-band optical filter system of the present
invention rejects wavelengths outside the narrow-band of spectral
components comprising the laser scanning beam (i.e. associated with
ambient light noise), and this improves the signal-to-noise ratio
for detected scan data signals D.sub.1.
58. Secondly, the spectral filtering characteristics of plastic
filter lens 69 inherently appears reddish to the human vision
system by virtue of the fact that lens 69 only permits transmission
of optical radiation from slightly below 670 nanometers. Thus, the
semi-transparent nature of filter lens 69 naturally hides from
plain view, the laser, the mirror, the scanning motor, and other
electro-optical components within the housing that otherwise might
present source of fear in customers at a POS station, and/or
detract from the aesthetic appearance of the scanning system
installed at POS station.
59. Thirdly, the plastic filter lens 69 with its specified optical
properties is easy and inexpensive to manufacture using injection
molding techniques well known in the art. Thus, it may be made as
large as desired or formed (i.e., shaped) to embody beam-shaping or
beam-directing characteristics, without substantially increasing
the cost of manufacture of this optical filter element.
60. Wavelength-selective filter element 150, on the other hand, is
very expensive and difficult to manufacture, by virtue of its
specified optical properties. However, as this optical filter
element 150 is installed along the focused laser light return path,
in front of photoreceiving sensor 54 as shown in Fig. 2A, its size
can be maintained extremely small, independent of the surface area
of the light transmission aperture, and thus the plastic filter
lens 69. Consequently, conventional techniques can be used to
manufacture this small-sized optical filter element, and thus the
cost of manufacture of this optical element can be minimized.
61. Fourthly, by using spatially-separated optical filter elements
(i.e., plastic filter lens 69 and filter element 150), the use of
special optical cements and bonding techniques otherwise required
to physically bound such elements together in an integral filter
structure, are avoided altogether. This fact simplifies
significantly the manufacturability of the laser scanner of the
present invention.
62. The optical filter system described above may be embodied in
any type of laser bar code symbol scanner. An example of such an
alternative laser scanner design is shown in FIGS. 5 and 5A.
63. In FIGS. 5 and 5A, the optical filter system of the present
invention is shown embodied in the laser projection scanner
disclosed in U.S. Pat. No. 5,216,232. As disclosed in FIGS. 5 and
5A, plastic filter element 69' is functionally similar to optical
filter element 69 and covers the light transmission aperture of the
compact housing of the laser projection scanner, while wavelength
selective filter 150' is disposed in front of its photodector 110
along the focused laser light return path defined between light
focusing mirror 120 and photodector 110, as shown in FIG. 5A. By
virtue of the principles of the present invention, plastic filter
element 69' over light transmission aperture 6' can be made
substantially larger than wavelength selective filter 150', as
required in practical scanner designs, yet it provides all of the
advantages described above.
64. In alternative laser scanner designs the alternate optical
filter system disclosed herein may be embodied within laser
holographic scanners used to read code symbols in various
applications.
65. While the particular illustrative embodiments shown and
described above will be useful in many applications in code symbol
reading, further modifications to the present invention herein
disclosed will occur to persons skilled in the art. All such
modifications are deemed to be within the scope and spirit of the
present invention defined by the amended claims.
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