Registers – Coded record sensors – Particular sensor structure
Reexamination Certificate
1999-11-24
2003-01-07
Frech, Karl D. (Department: 2876)
Registers
Coded record sensors
Particular sensor structure
C235S462190, C235S462250
Reexamination Certificate
active
06502750
ABSTRACT:
TECHNICAL FIELD
The present invention relates generally to reading and decoding information symbols, and more specifically to a laser scanning system and method for reading information symbols such as optical mark recognition symbols.
BACKGROUND OF THE INVENTION
Machine readable information labels or codes, such as bar codes, are ubiquitous in today's world. Bar codes are utilized for myriad different purposes, being affixed to many consumer products to identify the cost of the products, and being utilized in industry to identify components during manufacture and items stored in inventory. A bar code consists of a series of bars and spaces of varying widths formed according to a set of rules to thereby encode data, as will be understood by those skilled in the art. In addition to bar codes, other types of machine readable codes are utilized in particular industries to encode machine readable data. One such code is known as Optical Mark Recognition (“OMR”) symbology, which is utilized in the document handling industry to encode data in OMR symbols that are affixed to documents. The document handling industry includes such companies as Xerox, Hewlett-Packard, and Pitney Bowes, which utilize OMR symbols to encode geographic regions or zip codes for use in sorting the corresponding documents.
FIG. 1
illustrates a conventional OMR scanning system
10
including an OMR symbol
11
and an optical sensor
38
for reading the OMR symbol, as will be explained in more detail below. The OMR symbol
11
includes a plurality of cells
12
-
26
arranged as shown, each cell
12
-
26
containing a single bit of binary data represented by either a corresponding mark or bar in the cell, or a space in the cell. In the OMR symbol
11
, the cells
12
,
16
,
20
, and
24
include bars
28
,
30
,
32
, and
34
, respectively, while cells
14
,
18
,
22
, and
26
include spaces (i.e., no bar). Typically, each of the bars in the cells
12
,
16
,
20
, and
24
represents a binary 1, and each of the spaces in the cells
14
,
18
,
22
, in
26
represents a binary 0. Although the OMR symbol
11
is shown having the eight cells
12
-
26
, the number of cells in an OMR symbol may vary, with there typically being between 8-32 cells in a symbol.
In a typical application, the OMR symbol
11
is attached to an object, such as a letter or package, and contains bars and spaces in the cells
12
-
26
to encode the desired data. The object is typically placed on a conveyor belt (not shown) and is thus moving at a velocity V
O
relative to the optical sensor
38
. The optical sensor
38
applies incident optical energy
40
to each cell
12
-
26
of the OMR symbol
11
as that cell passes by the sensor. As each cell
12
-
26
passes by the optical sensor
38
moving at the velocity V
O
, the sensor
38
senses optical energy reflected from the cell
12
-
26
to thereby detect the presence of a bar or space in each of the cells. In
FIG. 1
, the ONR symbol
11
a shown positioned with the cell
18
being illuminated by the optical energy
40
from the sensor
38
. As understood by those skilled in the art, the presence of a bar in a cell results in optical energy being absorbed when incident optical energy is applied to that cell, while a space (no bar) results in optical energy being reflected when incident optical energy is applied to the cell. Thus, in
FIG. 1
, the optical sensor
38
detects optical energy being reflected from the cell
18
, indicating that the cell
18
cell contains a space. From the detected bars and spaces in each of the cells
12
-
26
, the optical sensor
38
generates binary data corresponding to the decoded OMR symbol
11
, each bit in the binary data corresponding to one of the cells
12
-
26
in the OMR symbol.
The optical sensor
38
is typically an LED sensor or a fixed-beam laser type device, as will be understood by those skilled in the art. Such devices may have difficulties dealing with so-called “paper flutter” of the OMR symbol
11
which occurs when the document to which the OMR symbol is affixed moves towards or away from the LED sensor or fixed-beam laser. Moreover, poor contrast between bars in the OMR symbol
11
and the surface to which the symbol is affixed also presents difficulties for the LED and fixed-beam laser type devices. In addition, LED and fixed-beam laser type devices cannot read OMR symbols in “ladder” orientations. As will be understood by those skilled in the art, information symbols are typically read in either a ladder or picket fence orientation. A ladder orientation results when the lengths of the bars in the OMR symbol are parallel to the symbols direction of travel, and a “picket fence” orientation occurs when the lengths of the bars in the OMR symbol are perpendicular to the direction of travel (as depicted in FIG.
1
).
In contrast to the LED and fixed-beam laser type devices, laser scanners are less affected by poor symbol contrast or paper flutter, and can read OMR symbols in either picket fence or ladder orientations. A laser scanner directs a laser spot across a scan window containing a bar code label. As the laser spot travels across the scan window SW, the laser scanner detects reflected optical energy from a bar code label contained within the scan window and utilizes this reflected optical energy to decode the bar code label. Due to the physical construction of the laser scanner, the velocity of the laser spot, which is known as the “spot” velocity, varies as the laser spot travels across the scan window. During normal operation of a laser scanner in reading bar code labels, the varying spot velocity does not result in difficulties in reading the labels. This is true because the predictable characteristics of bar code labels that allow for compensation of the varying spot velocity during decoding, When a laser scanner is utilized to read OMR symbols moving relative to the laser scanner, however, difficulties arise in reliably reading such labels due to the varying spot velocity of the laser spot. The operation and characteristics of laser scanners will be understood by those skilled in the art, and thus a detailed description of such operation and characteristics has been omitted for the sake of brevity.
Referring to
FIG. 1
, the line
36
represents the path of a laser spot from a laser scanner during scanning of the OMR symbol
11
. The spot velocity of the laser is designated Vs, and the length of the line
36
from left to right corresponds to the scan window SW of the laser scanner. The spot velocity V
S
varies across the scan window SW due to the planar surface of the OMR symbol
11
truncating an arced path of the laser beam, as will be understood by those skilled in the art. If it was attempted to read the OMR symbol
11
with a laser scanner, the varying spot velocity V
S
and velocity V
O
of the symbol
11
result in difficulties in decoding the symbol. For example, the spot velocity V
S
is slower towards the center of the scan window SW. Thus, the slower spot velocity V
S
combined with the symbol velocity V
O
result in the laser beam illuminating the interior cells
18
and
20
for a longer duration than the cells
12
-
16
and
22
-
26
. In decoding an OMR symbol, a valid bar is typically detected by reflected optical energy for at least a predetermined time. Due to the variable spot velocity V
S
, this predetermined time will be longer for the interior cells
18
,
20
than for the exterior cells
12
-
16
and
22
-
26
, thereby making the detection and decoding of the OMR symbol
10
difficult.
The variable spot velocity V
S
in combination with the variable or “free-form” nature of OMR symbols has precluded reliable decoding of the symbols using laser scanners. OMR symbols are free-form in that only the first cell in an OMR symbol must contain a bar, known as a “gate” bar, and all other cells may contain either bars or spaces. In
FIG. 1
, the bar
28
in cell
12
may be the gate bar, and all other cells
14
-
26
may contain any combination of bars and spaces. This free-form format of OMR symbols makes
Allen Matthew E.
Barnes Danny S.
Blakely , Sokoloff, Taylor & Zafman LLP
Frech Karl D.
Microscan Systems Inc.
Nowlin April
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