Hand held two dimensional symbol reader with a symbol illumination window

A symbol reader which projects an illumination window or field that is the same size as a field of view of a sensor used to read a symbol. The illumination window is aligned with the field of view of the sensor. The window or field can provide an area of relatively constant illumination or edges of the window or field can be at a higher illumination creating an outline or capture border. The outline alone can be projected when the ambient light level is sufficient for capture of the symbol. The window or field can be created by projecting light from various light sources.

CROSS REFERENCES TO RELATED PATENTS AND APPLICATIONS 
This application is related to U.S. Pat. No. 4,924,078 and U.S. application 
Ser. No. 07/485,832 entitled Symbol Reader by James L. Karney filed Feb. 
28, 1990 both incorporated by reference herein. 
BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention is directed to a hand held reader used for capturing 
two dimensional symbols, and, more particularly, to a system in which a 
target outline is projected by the reader allowing the user to easily 
position the targeted symbol within the outline for symbol capture. 
Description of the Related Art 
Two dimensional symbols, such as described in U.S. Pat. No. 4,924,078, can 
be captured for decoding in a number of different ways. The symbols can be 
scanned with a laser beam in much the same way that barcode symbols are 
scanned thereby capturing portions of the symbols sequentially. Such 
capture systems, if the symbol is moving relative to the capture system, 
may erroneously read the symbol. The entire symbol can also be captured at 
one time using an array of sensors such as a CCD array. Capturing all the 
symbol at the same time avoids the problems of relative symbol movement 
which occur in the scanned systems. However, positioning the sensor so 
that all of the symbol is in the field of view of the sensor can be a 
problem. What is needed is a capture system that allows the user to 
position the field of view of the sensor to cover the symbol being 
captured. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to allow a user to position a 
symbol reader field of view to cover a symbol being captured. 
It is another object of the present invention to provide a simple method of 
sensor and symbol alignment. 
It is also an object of the present invention to provide an illumination 
window the same shape as the target symbol. 
It is a further object of the present invention to provide an illumination 
window or field that encompasses the area in which a target symbol resides 
on an object. 
It is also an object of the present invention to provide illumination 
windows of various shapes. 
It is still another object of the present invention to simplify and 
automate capturing a two dimensional symbol using a portable reader that 
allows capturing the symbol at varying distances from the reader, allows 
capturing symbols of various sizes and shapes, allow capturing symbols on 
varying surfaces at various orientations when capture criteria are met. 
The above objects can be attained by a symbol reader which projects an 
illumination window which can be called a field or a frame. The window is 
preferably approximately the same size as a field of view of a sensor used 
to read a symbol. The window or field can provide an area of relatively 
constant illumination or edges of the window or field can be at a higher 
illumination creating an outline or capture border. The outline alone can 
be projected when the ambient light level is sufficient for capture of the 
symbol. The window or field can be created by projecting light from 
various light sources. 
These together with other objects and advantages which will be subsequently 
apparent, reside in the details of construction and operation as more 
fully hereinafter described and claimed, reference being had to the 
accompanying drawings forming a part hereof, wherein like numerals refer 
to like parts throughout.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
As illustrated in FIG. 1 a symbol 10 such as that described in U.S. Pat. 
No. 4,924,078 is fixed to or made a part of the surface 12 of an object. 
To ensure that the symbol is within the viewing range of the detector in a 
hand held symbol reader, in accordance with the present invention, an 
illumination window 14 is projected by the hand held reader allowing the 
user to position the window 14, such that the symbol 10 falls within the 
window, thereby falling within the capture view range of the sensor, such 
as a CCD array detector, of the hand held symbol reader. The window 14 can 
also be used by the user to align the sensor of the reader with the symbol 
10 in the most favorable capture position. Even though the symbol 
described in U.S. Pat. No. 4,924,078 can be captured from an omni 
directional, three dimensional orientation, the chance for error during 
image decoding, when is reduced when the sensor and symbol are aligned. 
Alignment will minimize skew and may eliminate the need for determining 
symbol image orientation. 
Various versions of the window 14 are illustrated in FIGS. 2a-2c. FIG. 2a 
illustrates a window 20 in which the entire area of the window 20 is 
illuminated with light of a substantially constant intensity. The window 
20 would typically be used when emphasis on alignment of the symbol with 
the window 20 is not desired and when different shaped symbols are to be 
captured. The window 20 should be the same size and shape as the view of 
the sensor of the reader and should be aligned with the view. However, it 
is possible for the window to be a different shape and size than that of 
view of the sensor which would be the case when a rectangular sensor is 
used with a square symbol and square window. FIG. 2b illustrates a window 
22 which includes a border 24 where the border 24 is created with light of 
a constant intensity. The interior portion 26 of the window 22 is not 
illuminated. Window 22 would typically be used when the environmental 
illumination of the symbol 50 is sufficient for image capture. The 
interior edge of border 24 should be the same size as and aligned with the 
view of the sensor of the reader. FIG. 2c depicts a window 28 which is a 
combination of the windows 20 and 22. In this window the interior portion 
30 of the window 28 is illuminated at a constant illumination while the 
border 32 is at an increased illumination. Window 28 would typically be 
used when the ambient light for illuminating the symbol is too low for 
image capture. The inner edge of border 32 should be the same size and 
aligned with the view of the sensor of the reader. 
FIGS. 3a-3d illustrate how the target window can have different shapes. 
FIG. 3a illustrates a window 40 which is rectangular. FIG. 3b illustrates 
a window 42 circular in shape. FIG. 3c illustrates a square window while 
FIG. 3d illustrates a polygonal window 46. FIG. 3e illustrates a different 
polygonal window 48 while FIG. 3f depicts an elliptical window 50. Other 
shapes of windows are possible such as triangular, freeform and a 
generalized spot. Of course, the window can be a bordered or non-bordered 
window. 
The shape and size of the window can be adjusted, depending upon the shape 
of the symbol being captured, using an adjustable aperture through which 
the illumination light is beamed, as illustrated in FIGS. 4a and 4c. The 
aperture 60 can be adjusted in size by adjusting the relative position of 
aperture plate 62-68. When the aperture plates 62 and 66 are closed as 
illustrated in FIG. 4b, the rectangular aperture 60 is converted into a 
square aperture 70 as illustrated by a comparison of FIGS. 4a and 4b. 
Additional plates 80-86 positioned at angles with respect to plates 62-68 
can be added to the adjustable aperture, so that the shape of the aperture 
can be reconfigured as illustrated by the polygonal aperture 90 of FIG. 4c. 
The aperture can be adjustable through a stepper motor control mechanism 
producing an illumination iris that can be changed in size and/or shape as 
desired. 
The window 22 with the border, as illustrated in FIG. 2b, can be created in 
a number of different ways one of which is illustrated in FIG. 5. The view 
of a sensor or detector 100 is illustrated by the view lines 102. To 
provide a border, such as border 24, that outlines the view of the sensor 
100, a light source 104 is positioned behind the detector 100. The light 
source 104 can include a parabolic mirror or another focusing device that 
produces a cone or beam of light as defined by beam projection lines 106 
and 108. Because the sensor 100 is positioned within the cone a portion of 
the light cone is blocked by the sensor 100 as indicated by the dashed 
lines 110. When an aperture 112 with the same shape as the sensor 100 is 
positioned in front of the sensor 100 and is slightly larger than the view 
range of the sensor 100, the aperture 112 and the sensor 100 will combine 
to create a lighted border 114 which can be projected around a symbol 116 
mounted on a surface 118. 
A window 20 of uniform illumination in accordance with of FIG. 2a can be 
created using an arrangement as illustrated in FIG. 6. The light source 
104 projects a cone of light onto a partially reflective mirror 130 which 
reflects the cone toward the aperture 112. The aperture 112 restricts the 
cone of light, such that the view of the sensor 100 matches the portion of 
the light cone projected toward the target 116. 
The arrangements of FIGS. 5 and 6 can be combined to create the window 28 
of FIG. 2c. 
FIG. 7 illustrates a still further arrangement. In this arrangement plural 
light sources 140, such as light emitting diodes, are arranged around the 
periphery of the sensor and the view of the sensor 110 is restricted by a 
tube 142. The tube 142 is the shape of the sensor 110, such as a square. 
The light sources 140 project light cones defined by projection lines 144 
and 146. A portion of each cone is blocked by the sensor 110 and tube 142. 
Another portion of each cone is blocked by aperture 112 such that a ring or 
border is created around the symbol 116. 
FIG. 8 illustrates a solid mask 150 being used to project a border type 
window 152 where the window 152 is triangular in shape. A lense 154 
focuses the light from light source 156 onto the solid mask which blocks 
all light from source 156 except the desired pattern for the window. 
FIG. 9 illustrates a still further method of creating the window with or 
without a border. In this arrangement a rotating wheel 160 includes a 
appropriately shaped mirrors 162 and 164. One or more beams 166 and 168 of 
light from an illumination source 170, such as a laser, are raster scanned 
by the rotating mirrors to produce the window. The wheel with the mirrors 
can be located behind the detector 110 as illustrated in FIG. 6 or to one 
side as illustrated in FIG. 7. An optional aperture 172 can also be 
provided to restrict the projection of the beams. The window thus created 
can be like the windows of FIGS. 2a-2c. 
Other techniques for creating the window using beams of light include 
oscillating mirrors and a mask with holes for creating a dotted border. 
FIG. 10 illustrates an example of a hand held symbol reader 200. This 
reader 200 is typically connected to conventional personal computer (not 
shown) such as an Intel 386 based PC capable of including a conventional 
video frame grabber board (not shown) such as the high resolution frame 
grabber DT2851 available from Data Translation, Inc. A conventional RS-170 
video output produced by the reader 200 is provided to the frame grabber. 
The reader 200 includes a case 202 housing the window projection apparatus 
as well as a portion of the electronics for capturing the symbol 198. The 
housing includes a glare or baffle tube 204 with light emitting diodes 206 
mounted around the exterior of the tube. The tube 204 is mounted on an 
optics unit 208 which can be used to focus the image of the symbol 198 on 
the sensor 210. The sensor 110 can be a conventional CCD array or a random 
access memory as described in the Karney application previously mentioned. 
The optics can be fixed focus, fixed image size optics providing a fixed 
depth of field sufficient for the symbol to be in focus in the preferred 
operating range of the reader (2-14 inches) or automatic focus. The optics 
can also provide automatic zoom type enlargement in combination with the 
fixed focus or autofocus optics. The tube 204 along with an aperture 212 
project the light produced by the diodes 206 to create a border type 
window 214. The electronics for image capture and illumination control can 
also be provided in the unit handle 216. A trigger 218 is used to initiate 
window projection and when further depressed image capture. The electronic 
control units 220 and 222 operations under the control of a microcomputer 
as will be discussed in greater detail later. 
FIG. 11 illustrates the optical components of the optics unit 208 in 
greater detail. The handheld symbol reader includes a capability of 
performing a conventional autofocus operation at the same time that a 
conventional zoom operation is performed. The autofocus operation focuses 
the symbol on the sensor 116, so that each of the data cells are clearly 
defined on the light sensitive elements. Any of a number of conventional 
automatic focus methods can be used. For example, the brightness of a 
central region can be used to determine focus under constant illumination 
where focus exists when brightness peaks. The techniques used in single 
lense reflex cameras which balance the brightness of adjacent sensing 
element lines of the image transmitted through a lense can also be used. 
Other more sophisticated techniques that use neural networks are also 
possible. The automatic zoom operation causes the symbol to enlarge, so 
that it covers a predetermined area of the sensor 116. Any number of 
conventional automatic zoom operations can be used. It is preferred that 
the zoom operation take advantage of the characteristics of symbol. The 
preferred symbol includes a border preferably of dark elements along the 
periphery of a matrix. When the image of this border falls on the sensing 
array the sensing elements sensing the border have a low light level 
compared to the elements sensing the illuminated area adjacent to and 
outside the symbol the border. To maximize the area of the image of the 
symbol on the sensor the zoom control enlarges or magnifies the image 
until one or more sensing elements on the periphery of the sensor sense a 
reduced light level. The zoom control then backs off the magnification 
slightly to reduce the size of the image until the one or more peripheral 
sensing elements detect the higher light level of the area outside the 
symbol border. The zoom control maintains the size such that the one or 
more sensing elements interior of the peripheral sensing elements sense 
the lower light level of the border while the peripheral elements sense 
the higher light level of the region outside the border. Since the reader 
is hand held the zoom control will continually hunt for this optimum until 
the trigger indicates symbol capture is desired. This zoom control 
technique has the capability of filling the sensor to 99% of the area of 
the sensor when the sensor is 512 by 512 elements and the sensor and 
symbol are aligned and to 40% of the area of the sensor when the symbol 
and sensor are completely misaligned. If a technique which enlarges the 
image until the peripheral sensing elements sense the low light level is 
used the sensor fill can be in the range of from 100% to 70%. The zoom 
operation preferably enlarges the symbol, so that at least 9 pixels of the 
sensor are shadowed or illuminated by each data cell of the preferred 
symbol. The optical components include a conventional variable zoom lense 
250 system including zoom lense 251 controlled as to its zoom position by 
a stepper motor 252 and linear actuator 253. An intermediate lense 254 is 
provided to collimate the view window of the sensor 116 before the image 
is provided to a conventional variable focus lense system 256 including a 
lense 257 controlled as to focus by a stepper motor 258 and a linear 
actuator 259. Other motion devices such as hydraulic actuators could be 
used. The variable zoom and variable focus systems are controlled by a 
conventional central processing unit 260 through conventional driving 
amplifiers 262 and 264. 
FIG. 12 illustrates the electronic components of the reader 202 in greater 
detail. The output of the CCD sensor 116 is provided through a 
conventional video amplifier 270 to a conventional video signal controller 
and interface 272 capable of converting the output from a CCD sensor 116 
into a conventional RS-170 video signal transmitted to the frame grabber 
273 and computer 274 by a conventional coaxial cable. The output produced 
by the video signal controller interface 272 is triggered by a trigger 
position detector 275 detecting the capture trigger position and alerting 
the CPU 260 which activates the video controller interface 272. The 
central processor 260 also controls the illumination level of the light 
emitting diodes 260 by controlling the pulse frequency and duty ratio of 
the light emitting diodes through a driver unit 276 in a conventional 
manner. The central processor 260 controls the stepper motors 252 and 256 
through a conventional stepper motor control driver unit 277. Of course it 
is possible, rather than having CPU 260 controlling the stepper motor for 
focus and zoom control to provide conventional integrated circuit units 
which automatically perform these operations when initiated by the CPU. 
The CPU also controls the output of red and green light emitting diodes 
278 and 280 which indicate whether the symbol has been captured. A buzzer 
(not shown) could also be activated to provide an audible indication. The 
program and the variable data which is used by the CPU 260 to perform the 
symbol capture operation is stored in a memory 282 which can include both 
RAM and ROM type memory. 
If illumination control is provided by the reader to attain a constant 
illumination the electronic component arrangement would result in a 
control loop as illustrated in FIG. 13. In this control loop a light 
source 280, such as the light emitting diodes, projects light to the 
target which is reflected back to the sensor 284, such as a CCD array. The 
light from the sensor 284 is conventionally analyzed by an illumination 
control unit, which can be computer 260, to determine the brightness of 
the reflected image. The illumination control unit 286 can average the 
light produced by all the sensing elements of the sensor 234 to provide an 
average illumination and then adjust the intensity of the light produced by 
source 230 to provide an average intensity above a predetermined threshold. 
If light emitting diodes are used as the source 280, the pulse frequency or 
the duty ratio of the light emitting diodes can be varied to vary the 
illumination. 
The operations performed by the processor 260 are illustrated in FIG. 14. 
When the trigger 218 on the unit 200 is partially depressed the light 
emitting diodes 206 are actuated 300 and the CCD and the variable 
parameters of the reader are reset. After the LEDs are actuated, the 
window is projected and used by the user to align the hand held reader 
with the target symbol. When the user depresses the trigger 218 further 
and the capture position is detected, the system simultaneously starts 304 
the autofocus and autozoom operation. The CPU during the autofocus and 
autozoom operation analyzes 306 the output of the CCD 116. When the image 
is in focus and the image has been enlarged sufficiently to fill a 
predetermined area of the sensor, the predetermined comparison criteria 
are satisfied 308 and the frame grabber 273 associated with the personal 
computer 274 is activated 310 followed by a transfer 312 of the captured 
data to the frame grabber. If a random access memory is used as the 
sensor, the readout techniques discussed in the Karney application can be 
used. The light emitting diode indicating successful capture is activated 
at this time. 
Once the image sensed by the sensor is captured the computer 274 enters a 
decoding loop, as illustrated in FIG. 15a, in which the orientation of the 
symbol is determined and the outside perimeter of the symbol is identified 
316. The operations described in U.S. Pat. No. 4,924,078 can be performed. 
The system then enters a loop in which the unique symbol for information 
identified by the captured symbol is determined. First the system 
identifies 318 the locations of unit data cells within in the symbol, 
determines 320 the side dimension of the symbols perimeter. The system 
then, within the defined parameter of the symbol, determines 322 whether 
certain key elements of the symbol which can be used for decoding symbol 
timing exist within the symbol. The system then determines 324 the center 
of each data cell and calculates 326 a timing sequence. The timing 
sequence is used to determine the value of each data cell within the 
symbol by sampling 328 the data cells at the determined timing. Next a 
determination is made as to whether the parity of the symbol and the 
perimeter of the symbol are valid. Steps 318-330 can be performed in 
accordance with the operations described in U.S. Pat. No. 4,924,078. An 
audio or visual signal by the computer 274 can be provided or a signal 
sent back to the reader indicating successful capture if desired. If a 
random access memory is used instead of a CCD, the decoding operations 
discussed in the Karney application can be used. If the symbol is valid 
the data is translated 332 into usable bit form and either displayed on 
the display of the computer 274 or used to access 336 a database or 
communicated 338 to another device. If displayed on a console the symbol 
is decoded as to it's representation and the information associated with 
the decoding is displayed 336. Note that because the border or window when 
used properly encloses the image of the symbol captured, the window can be 
used to limit the amount of the captured image that is processed, thereby 
increasing processing speed. 
The many features and advantages of the invention are apparent from the 
detailed specification and, thus, it is intended by the appended claims to 
cover all such features and advantages of the invention which fall within 
the true spirit and scope of the invention. Further, since numerous 
modifications and changes will readily occur to those skilled in the art, 
it is not desired to limit the invention to the exact construction and 
operation illustrated and described, and accordingly all suitable 
modifications and equivalents may be resorted to, falling within the scope 
of the invention. For example, a fixed position unit rather than a hand 
held unit could be used which would require the user to position the 
symbol on the object containing the symbol within the window. A liquid 
crystal or light emitting diode display could also be provided which could 
display the pattern of the image being seen by the CCD sensor to further 
aid alignment. The illumination and capture operations can be triggered at 
the same trigger position or the system could automatically activate when 
removed from a holder. Other symbols such as bar codes and polygonal 
symbols can be captured. A crosshair type illumination pattern or a dot in 
the center of the window could also be projected allowing centering of the 
field of view on the target symbol.