Registers – Coded record sensors – Particular sensor structure
Reexamination Certificate
2002-09-27
2004-03-16
Frech, Karl D. (Department: 2876)
Registers
Coded record sensors
Particular sensor structure
C235S462010, C235S462320
Reexamination Certificate
active
06705525
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to the field of optical scanners such as bar code scanners. More specifically, the invention relates to the use of tunable optical components for noise reduction within optical scanners.
BACKGROUND OF THE INVENTION
Electro-optical scanners, such as bar code symbol scanners, are now quite common. Typically, a bar code symbol comprises one or more rows of light and dark regions, typically in the form of rectangles. The widths of the dark regions, i.e., the bars, and/or the widths of the light regions, i.e, the spaces between the bars, when partitioned into groups, indicate encoded information to be read.
A bar code symbol reader illuminates the symbol and senses light reflected from the coded regions to detect the widths and spacings of the coded regions and derive the encoded information. Bar code reading type data input systems improve the efficiency and accuracy of data input for a wide variety of applications. The ease of data input in such systems facilitates more frequent and detailed data input, for example to provide efficient inventories, tracking of work in progress, etc.
A variety of scanning systems are known. One particularly advantageous type of reader is an optical scanner which scans a beam of light, such as a laser beam, across the symbols. Laser scanner systems and components of the type exemplified by U.S. Pat. Nos. 4,387,297 and 4,760,248—which are owned by the assignee of the instant invention and are incorporated by reference herein—have generally been designed to read indicia having parts of different light reflectivity, i.e., bar code symbols, particularly of the Universal Product Code (UPC) type, at a certain working range or reading distance from a hand-held or stationary scanner.
FIG. 1
illustrates an example of a prior art bar code symbol reader
10
implemented as a gun shaped device, having a pistol-grip type of handle
53
. A lightweight plastic housing
55
contains a light source
46
, a detector
58
, optics
57
, signal processing circuitry
63
, a programmed microprocessor
40
, and a power source or battery
62
. An exit window
56
at the front end of the housing
55
allows an outgoing light beam
51
to exit and an incoming reflected light
52
to enter. A user aims the reader at a bar code symbol
70
from a position in which the reader
10
is spaced from the symbol, i.e., not touching the symbol or moving across the symbol.
As further depicted in
FIG. 1
, the optics may include a suitable lens
57
(or multiple lens system) to focus the scanned beam into a scanning spot at an appropriate reference plane. The light source
46
, such as a semiconductor laser diode, introduces a light beam into an optical axis of the lens
57
, and other lenses or beam shaping structures as needed. The beam is reflected from an oscillating mirror
59
which is coupled to a scanning drive motor
60
energized when a trigger
54
is manually pulled. The oscillation of the mirror
59
causes the outgoing beam
51
to scan back and forth in a desired pattern.
A variety of mirror and motor configurations can be used to move the beam in a desired scanning pattern. For example, U.S. Pat. No. 4,251,798 discloses a rotating polygon having a planar mirror at each side, each mirror tracing a scan line across the symbol. U.S. Pat. Nos. 4,387,297 and 4,409,470 both employ a planar mirror which is repetitively and reciprocally driven in alternate circumferential directions about a drive shaft on which the mirror is mounted. U.S. Pat. No. 4,816,660 discloses a multi-mirror construction composed of a generally concave mirror portion and a generally planar mirror portion. The multi-mirror construction is repetitively reciprocally driven in alternative circumferential directions about a drive shaft on which the multi-mirror construction is mounted.
The light
52
reflected back by the symbol
70
passes back through the window
56
for transmission to the detector
58
. In the exemplary reader shown in
FIG. 1
, the reflected light reflects off of mirror
59
, passes through an optical filter
47
and impinges on the light sensitive detector
58
. The filter is typically designed to have a band-pass characteristics in order to pass the reflected (return) laser light and block the light coming from other light sources. The detector
58
produces an analog signal proportional to the intensity of the reflected light
52
.
The signal processing circuitry includes a digitizer
63
mounted on a printed circuit board
61
. The digitizer processes the analog signal from detector
58
to produce a pulse signal where the widths and spacings between the pulses correspond to the widths of the bars and the spacings between the bars. The digitizer serves as an edge detector or wave shaper circuit, and a threshold value set by the digitizer determines what points of the analog signal represent bar edges. The pulse signal from the digitizer
63
is applied to a decoder, typically incorporated in the programmed microprocessor
40
which will also have associated program memory and random access data memory. The microprocessor decoder
40
first determines the pulse widths and spacings of the signal from the digitizer. The decoder then analyzes the widths and spacings to find and decode a legitimate bar code message. This includes analysis to recognize legitimate characters and sequences, as defined by the appropriate code standard. This may also include an initial recognition of the particular standard to which the scanned symbol conforms. This recognition of the standard is typically referred to as autodiscrimination.
To scan the symbol
70
, the user aims the bar code reader
10
and operates movable trigger switch
54
to activate the light source
46
, the scanning motor
60
and the signal processing circuitry. If the scanning light beam
51
is visible, the operator can see a scan pattern on the surface on which the symbol appears and adjust aiming of the reader
10
accordingly. If the light beam
51
produced by the source
46
is marginally visible, an aiming light may be included. The aiming light, if needed, produces a visible-light spot which may be fixed, or scanned just like the laser beam
51
. The user employs this visible light to aim the reader at the symbol before pulling the trigger.
The reader
10
may also function as a portable data collection terminal. If so, the reader would include a keyboard
48
and a display
49
, such as described in the previously noted U.S. Pat. No. 4,409,470.
In electro-optical scanners of the type discussed above, the laser source, the optics, the mirror structure, the drive to oscillate the mirror structure, the photodetector, and the associated signal processing and decoding circuitry can all be packaged in a “scanning module”, which in turn is placed into the scanner's, or terminal's housing.
One of the factors which can affect scanner's performance is it's signal-to-noise ratio. The signal-to-noise ratio can be separated into two components, optical and electrical. The optical signal-to-noise ratio depends upon the amount of the reflected diffused laser light detected by the sensor
58
, verses the amount of parasitic light impinging upon the sensor
58
which comes from other light sources such as an ambient light. In order to increase the optical signal-to-noise ratio, the band-pass filter is designed to transmit in the spectrum of the laser source and to block the light in other optical spectrums. A typical bandwidth of the optical filter used in bar code scanners is approximately 70 nanometers. In comparison, a typical bandwidth of a laser beam generated by a laser diode is on the order of few nanometers. The large difference between the filter bandwidth and the laser beam bandwidth is due to a number of variables.
The optical filter has to accommodate laser wavelength variations, as well as the laser wavelength changes due to temperature. In addition sufficient bandwidth must be allocated for filter variations and filter slope roll-off.
Therefore, a need exists fo
Katz Joseph
Krichever Mark
Frech Karl D.
Hess Daniel A.
Kirschstein et al.
Symbol Technologies Inc.
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