Note: Descriptions are shown in the official language in which they were submitted.
R'O 96113799 PCT/US95114219
DATAFORM RFADERR ahD METHODS
This invention relates to systems and methods for
reading dataforms, such as bar codes and matrix codes,
and to such systems operating with overlapping exposure
' periods for successive lines of sensor elements of an
array and having automatic exposure control implemented
,for successive lines or subsets of lines of sensor
elements.
BACKGROUND OF TH . TnroFNmTnnr
While a variety of types of sensor array scanners
have been provided for reading more complex forms of two
dimensional bar-codes and matrix codes, these sensor
array scanners are all continuous frame scanners and
therefore suffer from high power consumption. Because
many sensor array scanners are portable and powered by
batteries, there exists a need for a portable reader
with single frame capability and therefore reduced power
consumption and correspondingly extended battery life.
There also exists a need for a portable reader with
enhanced accuracy and reliability, as well as reduced
size and light weight.
In such a portable reader it is further desirable
to provide for increased imaging accuracy by enabling
exposure control to be accomplished on the basis of
individual lines of sensor elements or successive
limited subsets of lines of sensor elements of an
imaging array.
BACKGROUND OF DATAFORMS
The application and use of bar codes and matrix
codes are well known and growing. Bar codes and matrix
codes are forms of "dataforms"
which for present
,
purposes are defined to include all arrangements whereby
data is fixed in some form of machine readable copy.
Thus, dataforms include one and two dimensional bar
codes, matrix codes and graphic codes, as well as words
and numbers and other symbols, which may be printed or
etched on paper, plastic cards and metallic and other
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R'0~96I13799 PCT/US95/14219
items. Dataforms may be printed in invisible ink,
magnetically recorded via magnetic stripes or magnetic
ink fonts, electromagnetically recorded via RF tags,
engraved, stamped, tattooed (on skin), formed by ion
doping (for semiconductor wafers) or biochemical
binding, etc.
In the utilization of dataforms, data originally
encoded is recovered for further use in a variety of
ways. For example, a printed bar code may be optically
scanned to derive reflectance values which are
digitized, stored in buffer memory and subsequently
decoded to recover the data encoded in the bar code.
Regardless of the particular type of dataform, an image
is typically acquired and stored as pixel values for
further processing. An image of a bar code or matrix
code existing as a graphic image can be acquired by use
of a CCD scanner, a laser scanner or other suitable
device which is capable of distinguishing between
different reflective values of light reflected from a
dataform. Thus, for example, a bar code typically
comprises black or dark colored bar type elements
printed on a white or light colored background area,
with white or light colored spaces between the elements
of the bar code. The spaces are typically the same
color as the background area, but may be of a different
light color in this example. In other examples the
elements of a bar code or matrix code are white or light
colored and are defined by black or darker colored
spaces and background area.
In other applications, such as laser engraving on
silicon wafers, illumination may result-in a dark on
light relationship in one orientation and a light on
dark relationship in a different orientation, In
addition to pixel values representing reflective values
of light (~~light~~ being defined as encompassing the
entire-electromagnetic spectrum for present purposes),
in other arrangements pixel values representative of
reflective values may be based upon reflection of sound
waves or other mediums from a dataform of an appropriate
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configuration. In any arrangement
in which a dataform
is arranged to be read on the
basis of reflective
values, such reflective values
may typically be stored
as pixel values in an image buffer
memory or other
storage medium in bit map or other
form which, while
representative of pixel values
for an image, may utilize
any appropriate data storage format.
EACKGROUND OF SENSOR RRAV RFpnFRS
As noted, prior arrangements for
reading dataforms
have been based upon laser or
continuous frame CCD
scanners adapted for use with
two-dimensional bar codes.
However, these approaches have
generally been subject to
one or more limitations in the
quest for a practical,
low power consumption, low cost,
light weight hand-
holdable reader providing fast
and accurate reading of
two-dimensional dataforms. For
example, a continuous
frame reader typically consumes
a full watt of power
because the continuous frame architecture
requires that
the sensor array continuously
produces a stream of image
data. When a microprocessor decodes
a bar-code, it
merely selects appropriate data
to decode from the
continuous stream of image data.
Full frame progressive scan CCD
devices, as
proposed for continuous frame
transfer video or very
high resolution still photograph
capture, are subject to
one or more of high cost, bulky
configuration, high
power consumption and slow gain
control response time.
Such factors limit applicability
to practical hand-held
dataform reading applications.
Objects of the present invention
are, therefore, to
provide new and improved dataform
readers and methods
avoiding one or more disadvantages
of prior
arrangements.
Further objects are to provide
dataform readers and
methods capable of providing one
or more of the
' following:
- image capture with overlapping
exposure periodsfor
successive lines of sensor elements;
- automatic.exposure control on
a line-by-line basis;
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- overall low power consumption;
- single frame image capture;
- rapid automatic gain control;
- automatic focus sensing and reading activation;
- light weight hand-holdable configuration; and
- single chip configuration capability.
SUMMARY OF THE INVENTION
In accordance with a first aspect of the invention, there
is provided a dataform reader comprising:
an array of sensor elements readable to provide image
signals, including a plurality of lines of sensor elements;
an array control assembly coupled to the array and arranged
to initiate exposure of a line of sensor elements by causing
sensor elements of the line to be set to a reference potential
in response to an exposure start signal, and to cause image
signals to be read from sensor elements of the line in
response to an exposure stop signal and coupled to an output
point; and
an exposure control system coupled to the output point and
successively responsive to the level of image signals read
from selected lines of sensor elements to determine an
exposure period for at least one subsequent line of sensor
elements based on the level of image signals from each
selected line, and arranged to provide the exposure start and
stop signals to the array control assembly to implement the
exposure periods in a sequence causing the exposure period for
one line of sensor elements to overlap the exposure period for
at least one subsequent line of sensor elements.
In accordance with a second aspect of the invention, there
is provided a dataform reader comprising:
an array of sensor elements readable to provide image
signals , including a plurality of lines of sensor elements;
an array control assembly arranged to initiate exposure of
a line of sensor elements by causing sensor elements of the
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line to be set to a reference potential in response to an
exposure start signal and to cause image signals to be read
from sensor elements of the line in response to an exposure
stop signal and coupled to an output point; and
an exposure control system coupled to the output point
and successively responsive to the level of image signals read
from selected lines of sensor elements to determine an
exposure period for at least one subsequent line of sensor
elements based on the level of image signals from each
selected line, and arranged to provide the exposure start and
stop signals to the array control assembly to implement the
exposure periods for lines of sensor elements.
In accordance with a third aspect of the invention,
there provided a dataform reader, usable to read a
is dataform
in a
target
area
at a
distance
from
the
reader
comprising:
an array of sensor elements readable to provide
image
signals,including a plurality of lines of sensor elements;
at least one exposure illuminator arranged to illuminate
the target area; a focusing device positioned in front
of the
array nd arranged to focus on the array illumination
a
reflected
from
at least
a portion
of the
dataform
when
the
distanceis within a focus range;
an array control assembly coupled to the array
and
arrangedto initiate exposure of a line of sensor elements
by
causing sensor elements of the line to be set to a reference
potential in response to an exposure start signal and
to cause
image gnals to be read from sensor elements of the
si line in
responseto an exposure stop signal and coupled to an
output
point;
an exposure control system coupled to the array
control
assemblyand arranged to provide the exposure start and
stop
signals to the array control assembly to implement the
exposureperiods in a sequence causing the exposure period
for
one lineof sensor elements to overlap the exposure period
for
at leastone subsequent line of sensor elements; and
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a processing unit coupled to the output point and
arranged to process the image signals to decode the dataform.
In accordance with a fourth aspect of the invention,
there provided a method, for use with a dataform
is reader
includingan array of sensor elements, comprising the
followingsteps:
a) causing illumination of a target area including
a
dataform image to be reflected onto the array of sensor
elements;
(b) coupling a first line of sensor elements to
a
referencepotential in response to an exposure start
signal;
(c) accumulating charge on sensor elements of the
first
line in
an exposure
period;
(d) terminating the first line exposure period
by
reading mage signals from sensor elements of the first
i line
in response to an exposure stop signal;
(e) coupling the first line image signals to an
output
point;
(f) repeating steps (b) through (d) for successive
lines
of sensorelements, with step (b) for each successive
line of
sensor ements initiated during the step (c) exposure
el period
for the respective preceding line of sensor elements,
resultingin partially overlapping exposure periods;
(g) coupling image signals from successive lines
of
sensor
elements
to the
output
point
in sequence
following
image nals from the respective preceding line; and
sig
(h) terminating the reflection of illumination
onto the
array sensor elements.
of
In accordance with a fifth aspect of the invention,
there provided a method, for use with a dataform
is reader
includingX lines of sensor elements arranged in an array,
comprising the following steps:
(a) reading image signals from sensor elements
of a
selected line of sensor elements, the image signals
including
image
signals
representative
of at
least
a portion
of a
dataform;
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(b) utilizing the level of the image signals read in
step (a) to determine an exposure period;
(c) utilizing the exposure period to control a duration
of exposure to illumination reflected from a target area onto
a first subset of Y lines of sensor elements, where Y is at
least one and less than X; and
(d) repeating steps (a) through (c) substituting in step
(a) image signals from a line subsequent to the selected line,
and in step (c) utilizing the exposure period to control the
duration of exposure of a second subset of Y lines subsequent
to the first subset of Y lines.
The foregoing and other objects, advantages and features
of the present invention will become more apparent upon
reading of the following non-restrictive description of
illustrative embodiments thereof, given by way of example only
with reference to the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
In the appended drawings:
Figs. 1A, 1B and 1C are respectively front, side and top
views of a hand-held dataform reader utilizing the invention.
Fig. 2 is a block diagram of portions of the dataform
reader with a conceptual side view of optical components of
the reader.
Fig. 3 illustrates details of implementations of a
portion of the Fig. 2 system.
Fig. 4 is a conceptual side view illustrating aspects of
an automatic focus sensing system in accordance with the
invention.
Fig. 5 is a block diagram showing a second embodiment of
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CA 02179154 2006-05-10
a portion of the Fig. 2 dataform reader.
Fig. 6 is an operational flow chart useful in describing
operation of the illustrated dataform reader.
Fig. 7 is a flow chart useful in describing operation of
the second embodiment of the invention.
Fig. 8 illustrates, partially in block form, an
embodiment of a dataform reader in accordance with the
invention.
Fig. 9 is a flow chart useful in describing operation of
the Fig. 8 dataform reader.
DESCRIPTION OF THE INVENTTON
An embodiment of a dataform reader utilizing the
invention is illustrated in Figs. 1A, B and C. Fig. 1A is a
front conceptual view of the dataform reader 10 and Figs . 1B
and 1C are corresponding side and top views, respectively. A
portion of the upper casing is removed in Fig. 1B to provide a
simplified view of internal components. Before addressing
specific aspects in accordance with the invention, it can be
observed that.
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WO 96113799 PCT/US95/I4Z19
as shown, the reader includes a suitable impact-
resistant plastic case with a hand grip portion 12, a
trigger device 14 and battery compartment 16. The
dataform reader also includes an upper enclosure portion
18 which, as illustrated in simplified form in Fig. iB,
may include a sensor array assembly 20, illuminator
array 22 and illuminator lens 24, each of which will be
described in greater detail. Fig. 1B also depicts a
processor and memory unit 30 and an input/output (I/O)
unit 32, which may take the form of pluggable circuit
boards inserted into slots from the rear of the reader
10. Additional slots at 34 and 36 may be utilized to
provide additional or-extended operating capabilities by
enabling ir_sertion of PCMCIA type cards, etc. As
further depicted in Figs. 1B and 1C, the dataform reader
10 may include a data entry keyboard 40 and a display
42, represented as adjustable to different viewing
angles. These and other features may be provided by
skilled persons using known techniques and types of
components, except that features and elements
particularly relevant to implementation of the invention
are provided as will be further described.
In the illustrated embodiment, there is provided an
automatic exposure dataform reader 10 configured to read
a dataform (such as a two-dimensional bar code) existing
in a target area positioned at a distance from the
dataform reader. Thus, for example a bar code can be
printed on a label affixed to a package, component or
letter-and the dataform reader held by an operator, with
the front of the reader at a distance from the bar code.
As shown in Fig. lA, the reader 10 includes an
array of illuminators with three different functions.
Perimeter illuminators, such as shown at 50, are
positioned in a frame type configuration and arranged to
illuminate the target area with a border or frame effect
-- which indicates the field of view of the sensor array
assembly 20. Focusing illuminators, shown at 52, are
arranged in this embodiment to provide angled beams of
light which intersect ar overlap at a predetermined
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distance in front of the reader. That distance
represents a fixed-focus distance, as will be further
described. Exposure illuminators; such as shown at 54
and which typically may be included in greater numbers,
are arranged to provide a relatively uniform level of
target area illumination when turned on during an
exposure period for-the purpose of reading the dataform
(e. g., capturing an image of the dataform in the sensor
array). Each of the illuminators may be an appropriate
form of device, such as a low cost light emitting diode
(LED), arranged to provide the respective levels of
illumination determined to be appropriate in
applications of the invention. The number, types,
arrangement and utilization ofthe illuminators can be
determined as appropriate. Depending upon the
application, the perimeter illuminators 50 or focusing
illuminators-52 may be used alone or in combination to
provi.deexposure illumination during exposure periods.
The illuminator lens 24 may comprise an array
configuration including a small lens portion in front of
each of the illuminators 50, 52 and 54 in order to
provide appropriately focused beam configurations for
each of the respective functions already discussed. In
the Fig. lA view a central lens 56 is arranged to focus
upon the face of the sensor array contained in assembly
20 illumination reflected from the target area and any
included dataform, in order to enable the array to sense
the image and provide-iiSage signals.
Referring now to Fig. 2, there is--shown a
simplified block diagram of portions of the dataform
reader utilizing the invention. A conceptual cross-
sectional view of related optical elements is included.
As shown, sensor array assembly 20 projects through lens
assembly 24 and the array of illuminators 50 and 54 and
includes a sensor array 21, optical filter 26 and array
control unit 28, with associated clock device 29.
Sensor array 21 is positioned behind (to the right of,
in this side view) central lens 56 and filter 26. By
providing a filter-26 which is transmissive to
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VVO 96/13799 PCTYUS95I14219
illumination provided by the illuminators, but effective
to reduce transmission in other portions of the ambient
light spectrum, the effects produced by ambient light
during the exposure period are reduced.
As noted, sensor array assembly 20 may include a
two-dimensional array 21 of sensing cells (each
_utilizing a photodiode and responsive to incident
reflected-light). Array control unit 28 may typically
include vertical and horizontal readout circuits,
devices for sensing charge or voltage appearing at
individual sensing cells, and an output amplifier device
with adjustable gain for coupling image signals from the
sensor array assembly 20, as well as clock device 29 for
providing timing control of the reading of image signals
from selected sensor elements. While other types of
sensor array arrangements may be utilized in
implementation of the invention, an advantage in use of
the type of arrangement of the referenced patent
application is that the entire sensor array, plus some
or all of the associated gain control, focus sensing and
exposure control circuitry, may be enabled to be
implemented on a single chip using known application of
CMOS technology (or PMOS, NMOS, Bipolar, BiMOS, BiCMOS,
or other existing or newly available technology). Use
of existing CMOS technology, for example, is effective
to provide significant advantages of established
production techniques, single chip size, weight and cost
advantages and, possibly most importantly, low power
consumption (as compared to higher power requirements of
prior CCD or other arrangements whereby support
circuitry for the sensor array is located off chip).
In Fig. 2, the sensor array is focused, via lens
56, on target area 58 which is at a distance 59 from
lens 56. The filter, 26 is placed between the lens 56
and the sensor array. Filter 26 can be specified so
that it is primarily transmissive only to light in a
particular portion or band of the electromagnetic
spectrum and is effective to reduce transmission in
other portions of the ambient light spectrum (e. g.,
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WO 96113799 PCT/U595/14219
portions differing from the transmissive band or
portion). With this approach, the sensor array can be
arranged to be relatively non-responsive to ambient
light reflected from the target area.
Fig. 2 also includes an in-focus sensing device 62
responsive to image signals provided.from a plurality of
sensor elements and arranged to provide an "in-focus"
signal usable to initiate a dataform reading session. '
The in-focus signal is provided when an area of -
IO illumination provided by the focus illuminator or
illuminators is characterized by having at least one of
(a) a size within a predetermined size range, (b) a
brightness within a predetermined brightness range, and
(c) a location within a predetermined location range, as
represented by such image signals. Fig. 3 indicates two
arrangements for providing -appropriate image signals to
device 62. In Fig. 3, 56 represents an outline of the
array focusing lens and 21a represents the outline of an
array of sensing elements included in sensor array
assembly 20. At 21b is indicated a linear sensor which
may comprise one or two lines of sensor elements
provided separately from the element array 21a. Linear
array 21b is connected to point 48 of Fig. 2 underthe
control of array control unit 28 (not shown in the
simplified representation of Fig. 3).
Fig. 4 is a representation of focus illuminators 52
providing, via lens assembly 24, angled light beams 52a
and 52b as previously discussed. As shown, these beams
intersect or-cross at a distance 59 from the front of
the lens 56. At distance 59, there is represented-a
side view of the plane of focus 70 of the sensor array
of array assembly 20 in combination with focusing lens
56 (see also Fig. 2).
Thus, with particular choices of a sensor array ,
configuration and lens, the dataform reader-will exhibit
an in-focus condition, with an image of the target area ,
and any included dataform accurately focused on the-
sensor elements of array 21, if the target area lies in
the plane 70 which is at a distance 59. Further, the
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. PCT/US95/14219
lens 56 can be specified so as to provide a reasonable
depth of focus, with the result that an image of the
target area will be acceptably focused on the sensor
elements for any separation distance within the depth of
focus range indicated at 72. Once the distance 59 has
been determined for a particular reader design, the beam
angles of illuminators 52 can be adjusted to provide
beam intersection or overlap at the distance 59, as
shown in Fig. 4. With this arrangement, linear sensor
21b of Fig. 3 will initially provide image signals
representative of target area illumination by two spots
of light located at spaced positions when the target
area lies in plane 74 at a distance 76. Then, as the
dataform reader is moved closer to the target area so
that the target area lies in plane 70 at distance 59,
the two spots of light will converge into a single
brighter spot at a central location. The image
signals from linear array 21b will thus provide
information representative of the single brighter spot
of illumination and its location, thereby providing
information indicative of the in-focus condition. By
providing a degree of tolerance on the in-focus image
signal indication, the in-focus indication can be
adjusted to accommodate the depth of focus range 72.
Upon successful distance adjustment (e. g., user movement
of a hand-held reader closer or farther from the
dataform image) to achieve an in-focus indication, in-
focus _sensing device-6Z'is arranged to provide an "in-
focus" signal usable for initiating a reading and
3o decoding cycle. It will be apparent that the
arrangement as described also enables operation in a
manual in-focus determination mode. Thus, with the
operator adjusting the position of the dataform reader
relative to the target area and observing the
convergence of the two spots of light into a single
. spot, as described, an in-focus indication can be
provided by operator activation of an appropriate key of
keyboard 40 when convergence is achieved.
With reference to Fig. 3, the dotted connection
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between sensing element array 21a of assembly 20 and
circuit point 48 indicates an alternative configuration.
As shown in Fig. 2, point 48 provides connection to in-
focus unit 62 (as well as units 60 and 64). Instead of
providing additional sensing elements necessary in order
to provide a dedicated linear sensor,2lb, it can be
arranged to make temporary use of one or more lines of
elements of array 21a for focusing purposes, '
independently of the basicimage sensing function of
array 21a. With the latter arrangement, the desired in-
focus determination can thus be made without the
requirement to provide-any separate linear sensor such
as 21b.
As shown, Fig. 2 further includes an exposure
control device 64 responsive to image signals from one
or more selected sensor elements and arranged to provide
"start" and "stop" signals usable for beginning and
terminating an exposure period. Exposure control 64
- utilizes the image signals to provide the stop signal in
response to reflection of a predetermined level or
intensity of illumination. Typically, such
predetermined level or intensity will be measured within
a period initiated by the start signal provided by the
exposure control device and may represent an accumulated
representation of the intensity of reflected light over
time. By converting image signals received in the
period to a voltage representative of accumulated image
signal levels, and comparing that voltage to a preset
threshold voltage, the stop signal can be generated when
the accumulated voltage reaches the threshold voltage,
representing a predetermined illumination exposure of
__ the target area.
In another embodiment illustrated in Fig. S, the
- . exposure control device sets the duration of the time
between the start and stop signals by responding to the
illumination intensity as measured by a preset fixed .
time period sample exposure of one or more selected
sensor elements. The image signals from such sensor -_
elements (typically, two lines of sensor elements, as
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discussed above) will thus be representative of the
level of illumination reflected from the target area
during the preset sample exposure period. By converting
the image signals to a gray level signal, an exposure
control signal representative of the appropriate
duration of the adjustable exposure period is provided.
In order to determine the actual duration of the
exposure period represented by the control signal, the
exposure control device 64a is coupled to the CPU 88.
- As shown in Fig. 5, the CPU is arranged to access a
look-up table (stored in memory unit 82a) containing
exposure period data correlated to gray level signal
values. The actual look-up table data can be derived in
advance on an empirical or other appropriate basis
utilizing the level of reflected light during the preset
initial period of predetermined duration as an
indication of the exposure time which will be required
to enable the capture of usable image data on a single
frame activation basis.
As also indicated in Fig. 2, gain control device 60
is arranged to respond to image signals provided from
one or more of the sensor elements of array assembly 20,
and more particularly to the level of reflected light
represented by such image signals, to control image
signal amplification. The gain control in this
embodiment is achieved by a gain control signal coupled
back to the above-referenced adjustable gain output
amplifier included in the sensor control unit 28. This
enables the amplitude of the image signals provided by
the sensor array to be maintained within a predetermined
range substantially independently of reflected ambient
illumination as represented by amplitude levels of
selected image signals.
As illustrated in Fig. 2, this embodiment of the
dataform reader in accordance with the invention also
comprises a processing unit 80, memory unit 82 and
input/output (I/O) module 84. Processing unit 80,.which
may include a digitizer 86, CPU 88 and power management
module 90, receives image signals from sensor array
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assembly 2o and provides image data in digitized form
for storage in memory unit 82. Unit 80 is responsive to
the start and stop signals from units 62 and 64 to
control the exposure period. As will be further
described, during the operating sequence processing unit
80 is also arranged, via power management module 90
coupled to a battery (not shown), to turn on and off the
perimeter, focus illuminators 50 and 52, and exposure
illuminators and couple power for operation of the
sensor array assembly 20. Processing unit 80 is further
arranged to implement decoding of a dataform using image
data stored in memory unit 82. Upon successful decoding
of the dataform, unit 80 also provides an end-cycle
signal effective to terminate decoding operation and
also to end the reading of sensor elements to provide
image signals, by terminating at least one of the
coupling of input power and provision of clock signals
which are both required in the reading of sensor
elements under the control of array control unit 28.
Separately, decoded dataform information is
provided to an-output device 92, via I/O module 84. The
I/O module 84 may be arranged to operate with PCMCIA
cards in interface slots 34 and 36 discussed with
reference to Fig. iB, and may be arranged to provide
radio, infrared, wired or other signal transmission and
reception capabilities. Output device 92 may
accordingly be an output port for coupling output
signals via a conductor, an antenna or optical device
for radio or infrared transmission, or other suitable
device, with I/O unit 84 arranged to provide the decoded
datafo~m information in suitable form for use with the
particular farm of output device. Modem, speech
recognition, handwriting recognition, memory and other
types of additional capability or peripheral cards may ,
. also be inserted in the PCMCIA slots for operation in
-- -- cooperation with processing unit 80 and I/O module 84 to
provide extended and further features. Items not
specifically described can be provided by persons
skilled in the relevant technologies.
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2 1 9 4
1
With an understanding of
the dataform reader as
described, it will be apparent
that for dataform reading
and in other applications
an imaging system provided
in
accordance with the invention
may include automatic gain
control, automatic exposure,
automatic-focus sensing,
single frame image capture
and other,features as
described.
'
OPERATION
With reference now to Fig.
6 there is shown an
operational flow chart with
reference to operation
of a
dataform reader utilizing
the invention. At step
100, a
user activates trigger device
14 of dataform reader 10
shown in Fig. 1B. At step
104, perimeter illuminators
50
and focus illuminators 52
are turned on and reading
of
sensor elements is initiated.
At step 106, the user
adjusts the distance between
the dataform reader 10
and
the target area to achieve
a separation distance within
range 72 in Fig. 4, at which
point the areas of
illumination intersect and
merge into a single smaller,
brighter area or spot of
illumination having a central
location. At step 108, the
focus condition achieved
in
step 106 is monitored on
the basis of image signals
from
a linear array of sensors
indicative of whether the
area
of illumination is characterized
by at least one of (a)
a size within a predetermined
size range, (b) a
brightness within a predetermined
brightness range, and
(c) a location within a
predetermined location
range, or
any combination of the three,
as will occur as the two
illumination areas, as provided
on the target area by
beams 52a and 52b in Fig.
4, overlap and merge. For
two
round spots of illumination,
the spots will thus become
concentric when focused
and this minimum size condition
can be detected in a variety
of ways, including
detecting the relative positions
of the two spots within
the field of view. When
such illumination area
merge is
achieved as characterized,
an "in-focus" signal is
effective at step 110 to
turn on all illuminators
of the
exposure array (e.g., illuminators
50 or illuminators 50 ,_
and 52, depending upon the
particular configuration).
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As discussed, such in-focus signal can be implemented
automatically or manually based on operator observation.
Upon turning on the exposure illuminators, the
exposure control device sends a start signal to sensor
array assembly 20 which is effective to reset any
accumulated charge on the sensors to,a reference charge.
The photo sensors immediately begin accumulating a new
charge as indicated at step 112. Simultaneously the
exposure control device and the gain control device
periodically measure accumulated charge on a sample of
photodetectors at steps 113 and 114. The gain control -
device at step 113 uses sample image data to select an
appropriate amplitude gain and offset signal to apply to
the sensor array amplifier in array control unit 28. At
step 114, the exposure control device monitors the
sample image data and when the sample image data
indicates that the level o~ reflected light from the
target area, on a cumulative basis, has reached a
predetermined level, the exposure control device
generates a stop signal. In response to the stop signal
the accumulated charge on the exposed sensor is measured
and converted to a voltage signal. Known types of
sensor arrays utilizing two-dimensional arrays of
photosensitive cells are structured so that sensor
elements are grounded to a reference charge level-and
then permitted to accumulate charge during an exposure
period. Then, pursuant to a reading process, either all
or selected cells (e.g., one half of-the cells, in an
interlaced configuration, or one line in a line-by-line
readout arrangement) are sampled simultaneously to
measure accumulated charge, with data temporarily stored
and read out line-by-line sequentially using a shift
register arrangement. At step 115, if no more cells
require readout (e. g., allcells have been sampled
simultaneously) the exposure illuminators are turned
off. However, if the configuration is such that
additional cells remain to be read, in this embodiment
the system will return to steps 112 and 113. The
exposure control device will then generate a start
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signal to initiate an exposure period for the next group
of cells, which will be read out at the end of that
exposure period. After reading a complete frame, the
system will advance from step 115 to step 116 at which
point the exposure illuminators are turned off.
At step 117, processor unit 80 attempts to decode
the dataform utilizing image data consisting of image
signals from array assembly 20 which have been digitized
and stored in memory unit 82. If decoding is
successful, at step 118 the decoded dataform information
is made available for transmission out of the dataform
reader 10 and an end-cycle signal is provided to
terminate the reading cycle by turning off at least one
of input power and clock signals as utilized by the
array control unit 28. If the decoding is not
successful, at step 117 the reading cycle is reactivated
or repeated starting at step 104, as indicated in Fig.
6.
It should be noted that in step 117, if a dataform
is in fact present in the captured image of the target
area, it will typically be necessary to locate the
dataform within the image to enable decoding. Location
of the dataform image can be accomplished as described
in U.S. patent No. 5,304,787, entitled "LOCATING 2-D BAR
CODES", issued April 19, 1994, and having a common
assignee.
Consistent with the foregoing, a method, for use
with a dataform reader including an array of sensing
elements, includes all or selected ones of the following
steps, particularly in application of the invention to
the reading of a dataform:
(a) positioning in front of the array an optical
filter transmissive to light from an exposure
illuminator (described below) and effective to reduce
transmission in other portions of the ambient light
spectrum;
(b) initiating reading of selected sensor elements
by providing input power and clock signals required for
such reading;
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(c) illuminating a target area with an area of
illumination characterized-by at least one of a size, a
brightness and location which varies with the distance
between the array and the target area;
(d) adjusting such distance to cause the area of
illumination to be characterized by at least one of a
size within a predetermined size range and a brightness
within a predetermined brightness range and a location
within a predetermined location range;
(e) providing an in-focus signal when an image
signal from at least one sensing element indicates that
the illumination is characterized as described in step
(d) ;
(f) turning on an exposure illuminator in response
to the in-focus signal;
(g) utilizing image signals from selected sensing
elements, as representative of the level of reflected
light, to provide a gain control signal to control the
amplification of image signals from the array;
(h) providing a stop signal when image signals
from at least one sensing element indicate reflection of
a predetermined level of illumination from the target
area;
(i) upon complete exposure of the sensor cells,
turning off the exposure illuminator; and
(j) processing image data, representing image
signals from the array which have been digitized and
stored in memory, to decode the dataform;
(k) upon successful-decoding of the dataform,
providing an end-cycle signal, ending sensor reading by
terminating at least one of the input power and clock
signals, and coupling decoded dataform information to an
I/O module; and
(1) if decoding is unsuccessful, repeating the ,
method from step (d).
Fig. 7 shows a flowchart corresponding to the
second embodiment. Steps 100 to 108 operate the same as
described in the previous embodiment. After determining
the in-focus condition at 108 and generating an in-focus
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signal, the exposure illuminators are turned on for a
preset sample exposure period and image data is
collected at step 122. To do this, the exposure control
devicegenerates a sample exposure start signal whereby
selected photo sensors are grounded to a reference
charge and begin accumulating a sample charge. At the
end of the preset exposure period, the exposure control
device, a portion of which could simply be a timer for
this purpose, generates a stop signal whereby the sample
accumulated charge on each selected sensor is read as
image data. At 124, in response to image data collected
during the sample exposure, the exposure control device
determines the appropriate duration of an adjustable
exposure period. As discussed, the appropriate duration
of the exposure period may be determined by
accumulating, via exposure unit 64a of Fig. 5, image
data from the selected-sensors and referring a resulting
voltage level to a look up table stored in memory 82a.
It will be appreciated that the level of reflected
illumination will be determined by, among other possible
factors, the reflectance of the target area. Such
reflectance may be substantially higher or lower than an
expected or typical value in certain conditions of
surface texture or coloration. Accordingly, it may be
desirable to control the gain of image signals from the
array, as well as the exposure period. This result can
be provided by accumulating, via gain unit 60a of Fig.
5, image data from selected sensor elements and
referring a signal representative thereof to a look-up
table in memory 82a which, for particular levels of
illumination reflected during the preset initial period,
provides values for adjustment of image signal output
gain. With an understanding of the invention, skilled
persons will be enabled to provide appropriate look-up
tables utilizing empirical or other techniques. Fig. 7
thus provides step 126 for using the sample image data
to determine an appropriate gain adjustment to apply to
the output amplifier of the sensor array assembly.
At 128 the device captures a single frame of image
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data. As discussed above, if the sensor array is
structured so that all-photosensor cells are referenced,
exposed, and sampled in parallel to generate a full
frame of data, then step 128 will consist of only one
cycle of grounding, exposing and sampling the
accumulated charge on the cells. At step 130 the
exposure illuminator is turned off.- As further
discussed, if the photosensor array is structured so
that only selected sensor elements may be read in
parallel in a single cycle, the exposure control device
will generate a plurality of start and stop signals
corresponding to the predetermined exposure time as
indicated by dashed path 128, as appropriate to complete
the reading of all cells. After collecting a full. frame
of data, at 130 the exposure illuminators are turned
off. If-the data form is successfully decoded at 132
the data transmission and termination of the reading
cycle, including termination of at least one of the
input power and clock signals utilized by the array
control device, proceed at step 134.
Simplicity and efficiency of operation are enhanced
by automatic gain control, automatic no-shutter exposure
control and automatic in-focus sensing on a hand-held,
user positioned basis. Operative advantages include
full resolution, full frame image capture on a single
frame, automatic exposure (e. g., shutter speed) basis
regardless of ambient light levels. Necessary gain
adjustment can be sensed in a period of the order of 100
microseconds. With single frame image capture,
continuous image data transfer and data processing is
avoided. In addition to hand-held applications, the
simplicity, cost and reliability advantages of -imaging
systems in accordance with the invention are readily
adapted for use in automated, fixed-position, non-
attended applications for dataform reading and other
imaging purposes. Additionally, the invention provides
the advantage that, using available CMOS or other
technology, the sensor array assembly 20 and all or
major portions of units 60, 62, 64 and 80 can be
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fabricated on a single chip enhancing small size, light
weight, ease of packaging and low power consumption
(e.g., as low as one-tenth the power consumption of
comparable CCD array components). This enables
provision of a small, lightweight, long operating period
hand-held battery operated unit suitable for reading
dataforms or other image capture applications.
7.TNT FXPpSTma ARRANGEMENTS OF FIGS 8 AND 9_
Prior sensor array scanners focus an image of a
target area onto a sensor array to simultaneously expose
all or half of the sensor elements. Thus, for example,
image capture may be accomplished by simultaneous
exposure of all alternate lines of a sensor array
followed by sequential read out on a line-by-line basis.
This interlaced exposure approach is then completed by
simultaneously exposing the remaining lines in a second
exposure period. In each step there is one exposure
period, which subjects the image capture process to a
number of potential problems or shortcomings. Non-
uniform image illumination or surface reflectivity can
result in inclusion of image areas which are overexposed
or underexposed when an exposure period is determined
for the average illumination associated with an entire
image. Also, the exposure period may be initiated at a
given time and then continue for each line until the
exposure time for that line is terminated by the image
data being read out of the line of sensor elements.
with this approach, as the lines are read out in
sequence, the exposure time for the last line is
significantly longer than for the first line. As a
result the first line may be underexposed and the last
line overexposed to the point of loss of image data.
Referring now to Fig. 8, there is shown an
embodiment of a dataform reader including automatic line
exposure features usable in the Fig. 2 dataform reader
in accordance with the invention. As illustrated, the
Fig. 8 dataform reader includes an array 21c of sensor
elements, indicated typically at 140, which are readable
to provide image signals. As shown, the sensor elements
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140 are arranged in a plurality of horizontal lines and i
vertical columns.
The Fig. 8 dataform reader also includes an array
control assembly corresponding generally to array
control unit 28 of Fig. 2. As shown, the Fig. 8 array
control assembly comprises a line control shift register
142 which is coupled to successive lines of the sensor
elements 140 by way of common horizontal conductors 143
connected to flip-flop units 144-151. Vertical columns
of sensor elements 140 are also connected to common
vertical conductors 152, which connect to grounding
switches shown typically at 154 and to sample and hold
amplifiers 156-162, via sensor readout switches shown
typically at 168.- The Fig. 8 dataform reader further
includes output shift register 166 arranged to
successively activate the sensor readout switches, shown
typically at 168, individually connected to the flip-
flop units 170-176, to cause image data stored in sample
and hold amplifiers 156-162 to be successively coupled
to output point 178 for successive sensor elements 140
of a selected line of the array 21c.
As illustrated, the Fig. 8 dataform reader includes
an exposure control system 64/80, generally
corresponding to the combination of exposure control
device 64 and processing unit 80 of Fig. 2, adapted to
operate as will be described with reference to Fig. 8.
As shown in Fig. 8, exposure control system 64/80 is
arranged to control: sensor element line selection via
shift register 142; reference potential grounding of
columns of sensor elements via control of switches 164;
readout of image signals from a selected line ofsensor
elements via switches 156-162; and output of image
signals from successive sensor elements of a selected
line by control of shift register 166, to control
activation of sensor readout switches 168 to couple
image signals to output point 178. Output point 178 may ,
typically be coupled to the input of digitizer 86 of
Fig. 2, enabling the image data to be stored in memory __
82 for decoding, transmission or other use. Exposure
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control system 64/80 is also coupled to output point 178, via
conductor 180, so as to enable an averaged image signal level
to be obtained from a particular line of the sensor elements
140. Such image signal level is thus made available for use in
determining the exposure time for a subsequent line or subset
of lines of sensor elements. Basic construction and operation
of the sensor array and related portions of the Fig. 8
dataform reader can be those as currently used and familiar to
skilled persons, except to the extent of aspects unique to the
present invention, which will be described in further detail.
Operation of the Fig. 8 dataform reader can be more fully
described with reference to the Fig. 9 flow chart.
At step 200 operation is initiated by a user activated
trigger signal in order to read a dataform in the form of a
bar code printed within a target area on a surface, for
example. At 210 exposure illuminators, such as shown at 54 in
Fig. 2, are turned on to illuminate the bar code within the
target area.
At step 220A, exposure control system 64/80 of Fig. 8,
acting by way of control signals provided to shift register
142, flip-flop 144 and grounding switches 154, couples each of
the sensor elements in the first horizontal line of the
elements 140 to a reference potential (e.g., to ground) in
order to remove any accumulated charge on the first line of
elements (e. g., photo cells). In this manner, the signal from
exposure control system 64/80 which is effective to close the
grounding switches 154 acts as an exposure start signal for
the first line of sensor elements 140 which are connected to
flip-flop 144. Thus, as illumination provided at step 210 is
reflected onto the array of sensor elements, the exposure
period for the first line of elements begins immediately after
those elements are set to reference potential at step 220A and
then begin to accumulate charge representative of the level of
illumination reflected from different portions of the
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bar code in the target area.
At step 222A charge is accumulated on the sensor
elements of the first line in an exposure period. This
initial exposure period for-the first line may be
determined in any appropriate averaged, standardized or
other manner to initiate the image data readout process.
At step 224A an exposure stop signal is provided to the
readout switches 164, via conductor 163, to cause each
one of the sensor elements in the first line connected
to flip-flop unit 144 to be coupled to a respective one
of the sample and hold amplifiers 156-162. Image data
is thereby simultaneously read out of all of the sensor
elements of the first line, with the image data from
each sensor element respectively held in one of the
amplifiers 156-162. The exposure period for each. sensor
element of the first line is thus initiated by the
exposure start signal causing the elements to be
grounded and simultaneously terminated when exposure
stop signal causes the elements to be read into the
sample and hold amplifiers.
At step 226A shift register 166 is activated to
control flip-flop units 170-176 which sequentially
actuate the switches 168 to cause a signal comprising a
sequence of data representative ofthe level of image
signals read from the individual sensor elements of the
first line to be coupled to output point 178.
The same series of steps, denoted at 220B, 222B,
224B and 226B in Fig. 9, are carried out for the second
line of sensor elements. As represented in Fig. 9,
because the exposure period required to appropriately
expose a line of cells is longer than the time required
to sample the cells to read the image data and output
the data to output point 178, the controlled exposure
period for the next line of sensor elements is initiated
during the preceding exposure period. Thus, with the
passage of time represented_in a downward direction in .
Fig. 9, it will be seen that the exposure periods 222A,
222B and 222C for the first three lines of sensor
elements begin on a successive time-stepped sequence so
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that the exposure period 222B overlaps the exposure
period 222A for the preceding line of sensor elements in
this example. Fig. 9 is provided for illustrative
purposes and actual timing relationships may be
different than those shown. The timing is controlled so
that the first, second and third lines are read and the
resulting image coupled to output 178 in succession, so
' as to produce a stream of image data. In this way,
image data for each successive sensor element of the
second line follows the corresponding image data for the
first line, etc., without interference. This is
accomplished under the control of a sequence of exposure
periods determined by exposure start and stop signals
provided for each line of sensor elements, respectively
by the exposure control system 64/80. The sequence of
overlapping time controlled exposure periods for
successive lines continues until all lines have been
exposed, read and image data coupled to output point
178, as represented by corresponding steps 220N, 222N,
etc. implemented for the last, or bottom line, denoted
line N.
At step 228 the exposure illumination is turned
off. At 230 the dataform reader checks for a successful
decoding of the bar code present in the target area in
this example. If the bar code has been successfully
decoded the decoded data is provided, at step 232, to
the Fig. 2 output port 92. If the decoding is found to
have been unsuccessful in providing the level of decoded
data desired, at step 230 the operation is returned to
step 210 and the illumination is turned on for an
iteration of the process.
With an understanding of the basic exposure and
reading process, attention is again directed to the
dataform reader as shown in Fig. 8. Assume the first
line of sensor elements has been exposed, read and the
resulting image data coupled to output point 178 for
coupling to digitizer 86 of Fig. 2 for further
processing and use. As shown, a representation of the -.
first line image data is also coupled to the exposure
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control system 64/80, via conductor 180. -By monitoring
the level of such image data representative of the first
line, an appropriate exposure period can be determined
for a subsequent line and used for determining the
exposure start and stop periods for that subsequent
line. For example, since the Fig. 9 illustration shows '
the third line exposure period 222C beginning after the
step 226A output from the first line, exposure
information derived from the first line image signal
level can be used for- controlling the exposure period
used for the third line. Alternatively, instead of
independently determining the exposure period for each
successive line individually, the exposure information
derived.from the first line image signal level can be
used for controlling the exposure period for a
subsequent subset of lines, for example the third,
fourth and fifth lines. This line subset approach
provides exposure period accuracy between that provided
by a single full image (or interleaved image) exposure
2o period and the higher accuracy possible by use of an
exposure period determined for each subsequent line
individually. Development of the exposure information
can be carried out by averaging the level of image data
for a plurality of sensor elements of a given line and
utilizing a look-up table arrangement, as discussed with
reference to Fig. 5, to determine the actual duration of
an appropriate exposure period for a subsequent line, or
subset of lines, of sensor elements. In utilizing such
an exposure period for exposure of a subset of three
lines, for example, each line can be grounded in series
and read out in series successively, using the same
exposure period as determined from the level of the
first line image data.
Addressing the operation of the Fig. 8 arrangement
more particularly, exposure control system 64/80 is
effective-to send control signalsto line control shift _
register 142 to determine which line (e.g., the
horizontal line of sensor elements coupled to flip-flop
unit 144) should have the voltage driven high and which
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lines (e. g., all remaining lines of sensor elements)
should have the voltage driven low. Under control of
the shift register 142, the respective flip-flop units
144-151 drive the sensor element line voltages
appropriately. When a line is driven high, the charge
accumulated on each sensor element in that line is
transferred to the respective one of the vertical
conductors 152 connected to that sensor element. When a
horizontal line is driven high, the exposure control
system 64/80 also sends a signal to either the grounding
switches 154 or the readout switches 164. In the first
case, the charge transferred to each respective vertical
conductor 152 is grounded. In the latter case, each
sensor element of the selected line is read by having
charge from it coupled to the respective one of the
sample and hold amplifiers 156-162, so that a
representation of image data on each sensor element is
saved in the amplifiers 156-162 as a voltage level for
later output coupling.
At the beginning of an exposure period a selected
line is driven high and the grounding switches 154 are
closed in response to an exposure start signal provided
via conductor 155, in order to initiate a line exposure
period. At the end of the exposure period, the line is
driven high and the readout switches 164 to the sample
and hold amplifiers 156-162 are closed by an exposure
stop signal provided via conductor 163.- After a line of
image data is collected in the sample and hold
amplifiers, the exposure control system 64/80 causes the
image data read from each sensor element to be
sequentially coupled to the output point 178. This is
accomplished by control signals sent to readout shift
register 166, which controls flip-flop units 170-176.
The flip-flop units each connect to one of the output
switches 168, so that the image data held in each of
amplifiers156-162 can be coupled sequentially to output
point 178. Tn this manner, with appropriate timing,
image data from each sensor element in a horizontal line
and from successive lines of elements can be coupled to
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output point 178 on a continuous sequential basis to
provide image data representative of a complete frame.
From output point 178 the image data is provided for
further processing as previously discussed and also
provided as an input to exposure control system 64/80
for use in determining exposure periods and providing
appropriate exposure start and stop signals.
Pursuant to the foregoing, a method, for use with a
dataform reader including X lines of sensor elements
arranged in an array, may desirably include the
following steps:
(a) reading image signals from sensor elements of
a selected line of sensor elements;
(b) utilizing the level of image signals read in
step (a) to determine an exposure period;
(c) utilizing such exposure period to control the
duration of exposure to illumination reflected from a
target area onto a first subset of Y lines of sensor
elements, where Y is at least one and less than X; and
(d) repeating steps (a) through (c) substituting
in step (a) image signals from a line subsequent to said
selected line, and in step (c) utilizing the exposure
period to control the duration of exposure of a second
subset of Y lines subsequent to the first-subset of Y
lines.
For example, with Y equal to three, each line of
sensor elements of a subset of three lines can be
exposed for an identical exposure period determined on
the basis of the level of image signals read from an
earlier selected line of sensor elements. Also, where Y
equals one, each subset of one line of sensor elements
can be exposed for an exposure period determined on the
basis of the level of image signals read from an earlier
selected line of sensor elements, so that the exposure ,
period for each line is-independently determined.
While there have been described the currently
preferred embodiments of the invention, those skilled in
the art will recognize that other and further
modifications mad be made without departing from the
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invention and it is intended to claim all modifications
and variations as fall within the scope of the
invention.
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