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BACKGROUND OF THE INVENTION
This application is related to the following co-pending U.S. patent
applications Ser. No. 08/554,042 for "HAND-HELD ELECTRONIC PRINTER" filed
on Nov. 6, 1995; and Ser. No. 08/554,043 for "HAND-HELD SWEEP ELECTRONIC
PRINTER" filed on Nov. 6, 1995; the entire disclosures of which are fully
incorporated herein by reference.
The invention relates generally to methods and apparatus for scanning or
reading an image from a portion of a document, such as lines of text and
images. More particularly, the invention relates to fully self contained
and hand-held scanning apparatus that is operated, for example, using a
sweeping motion of the apparatus across a selectable area of a document.
Hand-held scanners known heretofore have used external apparatus, such as a
personal computer, for example, to receive, store, and process image
information, and can exhibit considerable image distortion. This
distortion arises from movement of the scan head along a nonlinear path.
Additionally, in a hand controlled scanning device, it is possible to
rotate the scan head such as by a pivoting action brought about by the
natural tendency of an operator to allow the apparatus to tilt or rotate
during a sweeping movement. This pivoting action changes the orientation
of the scan head with respect to the document and thus can further result
in distortion of the scanned image. In some cases, mechanical devices have
been incorporated into the scanner to restrict or constrain movement to a
linear path and to reduce the occurrence of a pivoting or rotational
motion imparted to the apparatus. Such devices are less than desirable as
the mechanical constraints reduce the flexibility of the apparatus,
increase the apparatus size and weight, and restrict use of the scanner to
flat surfaces. Therefore, information cannot be read from a
three-dimensional object such as a book. Further, such devices typically
block ambient illumination and require a supplemental light source to be
built into the apparatus, increasing power requirements.
The objectives exist, therefore, for providing a more convenient apparatus
and methods for a hand-held and operated fully self contained scanner that
is responsive to a simple and unconstrained sweeping motion that exhibits
reduced distortion in the recorded image caused by such sweeping motion,
and that generally requires only ambient illumination.
SUMMARY OF THE INVENTION
To the accomplishment of the foregoing objectives, the present invention
contemplates, in one embodiment, a hand-held and self contained electronic
optical scanning apparatus for reading images from a document disposed
outside the apparatus comprising a housing that can be manually positioned
adjacent a surface of the document and manually swept across a selected
area of the document during a scanning sequence; a scanner disposed in the
housing and having a scan head with a plurality of light sensitive
elements for detecting image information; and electronic control means
disposed in the housing for controlling the scanner to scan an image on a
document during a scanning sequence, the control means comprising
compensation means for reducing image distortion based on detecting
position of the light sensitive elements during a scanning sequence.
These and other aspects and advantages of the present invention will be
readily understood and appreciated by those skilled in the art from the
following detailed description of the preferred embodiments with the best
mode contemplated for practicing the invention in view of the accompanying
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a simplified schematic perspective of a self-contained and hand
operated scanning apparatus according to the present invention;
FIG. 2 is an electrical schematic diagram of a control circuit suitable for
use with the scanner apparatus of FIG. 1;
FIG. 3 is a simplified schematic in elevation of a scanning apparatus
according to the invention using a full width scan head embodiment;
FIG. 4 is a side elevation of the embodiment illustrated in FIG. 3;
FIGS. 5A and 5B illustrate pivoting motion of the apparatus of FIG. 3;
FIG. 6 is a graphical representation of geometric relationships for the
light sensitive elements under pivoting motion as in FIGS. 5A and 5B;
FIG. 7 is a flow chart for a control sequence of a scanning operation in
accordance with the invention as embodied in FIGS. 3-5;
FIG. 8 is an elevation of another embodiment of the invention;
FIGS. 9 and 10 illustrate distortion compensation for scanned images in
accordance with the invention;
FIG. 11 is a flow chart for a control sequence of a scanning operation in
accordance with the invention as embodied in FIG. 8;
FIGS. 12A and 12B illustrate an additional feature of the invention
incorporating audio input and output.
DETAILED DESCRIPTION OF THE INVENTION
With reference to FIG. 1, an embodiment of the invention is illustrated in
simplified schematic form for purposes of describing the basic concepts of
the invention. In this exemplary configuration, a hand-held and operated
scanning apparatus 10 is illustrated. A significant feature of this
apparatus is that it is a completely self contained unit that can be
manually operated without an external connection. However, as will be
explained hereinafter, the apparatus 10 is equipped with interface
devices, which can be hardwired connectors or wireless links, to permit
external data output and/or control if so desired for a particular
application.
In the embodiment of FIG. 1, the apparatus 10 is shown disposed adjacent a
document, D, in this case an open book. Although the invention is
illustrated and described herein with specific reference to scanning from
a paper document, such as a book, letter, and so on, such description is
exemplary for purposes of illustration and explanation and should not be
construed in a limiting sense. Those skilled in the art will readily
appreciate that the invention can be utilized for reading indicia, images,
characters, bar codes, text and so on in virtually any color, as well as
black or white, from any medium. The scanner mechanism can be selected
from any number of commercially available units, or special made,
depending on the particular application. In the embodiments described
herein, the scanner mechanism is a charge coupled device (CCD), comprised
of a number of individual light sensitive elements disposed in a linear
array. In many applications of the invention, other scanner mechanisms
both known and later developed will also be suitable for use with the
present invention.
The apparatus 10 includes a housing 12 which for convenience may be made
from metal, plastic, composites or other suitable material. The housing 12
preferably is a rigid structure that is capable of supporting a scanning
mechanism therein along with an electronics package and an internal power
supply, such as a battery. The housing 12 should also be sturdy enough to
withstand manual forces applied to the structure to actuate the apparatus
without damage or stress. The housing 12 should also provide a stable
platform so that the apparatus 10 can be manually held and stably
positioned adjacent the document D, as illustrated in FIG. 1, for example,
and easily swept across the document. Further, the lower portion of
housing 12 may be so shaped, or made of transparent material, so as to
minimize obstruction of ambient illumination and the operator's view of
the area-being scanned.
The housing 12 holds a key pad device 14, which for convenience can be a
conventional push pad or thin membrane type key pad. The housing 12 also
holds a display device 16 such as a conventional LCD or LED display.
Internal to the housing 12 (not shown in FIG. 1) is a circuit board or
boards which hold the various electronic components and power supply
components for operating the electronic scanning apparatus 10.
Part of the control circuitry may include an interface device, such as, for
example, a conventional transceiver 18, that transmits and receives data
and/or instructions from a remote device (not shown) such as a personal
computer, for example. A suitable transceiver device 18 is an infrared
transceiver, although other communication links could be used such as RF,
microwave, acoustic and so on.
In the embodiment of FIG. 1, the apparatus 10 is supported on the document
during a scanning sequence by one or more rollers 20. These rollers 20 are
coupled to encoder devices and will be explained in greater detail
hereinafter. The rollers 20 in combination with the encoder devices
provide an enabling function for the apparatus 10 in which movement of the
apparatus across the document is sensed and a signal can be generated to
initiate the scanning of an image on the document. If so desired, a push
button enable switch (see discussion of switch 54 shown in FIG. 2) or
other mechanical release can be included for manual actuation prior to a
scanning sequence being permitted to occur.
As best illustrated in FIG. 3, a bottom end of the housing 12 includes an
aperture through which scanning is accomplished by a scanner mechanism 25
while the apparatus 10 is positioned adjacent the document.
Note in FIG. 3 that the scanner mechanism 25 includes a scan head 26 which
is supported in the housing 12. The scan head 26 in this example consists
of a linear array of CCD light sensitive elements 30 which are represented
schematically in FIG. 3 by a row of dots. Each of the elements 30 is
constrained to view a limited area of the document, representing a single
point or pixel, by use of a suitable lens as is known, or an aperture or
mask as is also known.
It is understood that each element 30 converts the average light level
within the entire area of its view to an electrical signal which is
processed as will be described. For this reason the lens, aperture, or
mask does not serve to focus an image on each element, but rather serves
merely to define the area of the document viewed by each said element 30.
The scanner apparatus 10 can be configured as desired, for example, to
operate with gray scale scanning, or more simply to operate from a single
bit per pixel to indicate whether the pixel is black or white. The width
of the scan head 26 generally defines the height of the scanning area on
the document. A suitable CCD device for use in the scan head 26 is part
no. IL-C3-1024 available from DALSA Inc., Waterloo, Ontario.
It is further understood that the apparatus 10 can function using only
ambient light, but that if supplemental illumination is required for a
particular application it may be readily provided by, for example, one or
more light emitting diodes (LEDs) disposed to illuminate the area being
scanned, as is known.
With reference next to FIG. 2, there is shown in simplified block diagram
form a control circuit 40 suitable for use with all the embodiments of the
present invention described herein. Those skilled in the art will readily
appreciate that many of the features of this control circuit 40 are
optional and can be used or omitted as desired for a particular
application. Furthermore, although the circuit 40 is described in terms of
a microprocessor based system, the invention can conveniently be practiced
with the use of a microcontroller, microcomputer, digital signal
processing, application specific integrated circuit (ASIC) and discrete
logic circuits depending on the overall complexity of the control
functions for a particular application.
In FIG. 2, a microprocessor 42 is connected to a number of peripheral
circuits, and is used to provide the overall control function for the
apparatus 10. A significant feature of the invention is that the apparatus
10 is a wholly self-contained and operational hand-held scanner that does
not require the use of external inputs and controls. Thus, all of the
circuits in FIG. 2 are fully contained within the housing 12. However,
provision is made for external connection should such a configuration be
desired for a specific application. The microprocessor 42 is programmed in
a conventional manner according to the manufacturer's instructions, as is
well-known to those skilled in the art. A suitable microprocessor is part
no. MC6800 available from Motorola Incorporated. For embodiments that
utilize additional control and processing functions, it may be desirable
to use a more powerful microprocessor such as part no. NS486SXF available
from National Semiconductor, Inc.
A system clock 44 provides timing pulses at regular intervals for the
operation of the system, including tracking current time and date
information. A replaceable or rechargeable battery type power supply 45
provides system power for the microprocessor 42 and all other circuits
within the housing 12.
The microprocessor 42 accesses program instructions and data via a memory
circuit 46 which includes a nonvolatile ROM memory 48 and a suitable
volatile temporary memory, such as a RAM memory 50. The ROM is used to
store control programs, conversion tables and the like for the
microprocessor 42. The RAM 50 is used to store system data produced during
operation such as images read, or an activity log, where the log may
include, for example, date and time of the scanning operation. The RAM can
further be used to store programs, instructions and data entered manually
by the operator through a user interface 52, or received from an external
source such as a computer through an input/output (I/O) device 60, or the
results of calculations performed by the microprocessor 42. These
calculations may include coordinate conversions, distortion compensation,
data read from bar codes, and so on. Those skilled in the art will readily
appreciate that the volatile memory 50 can also be realized in the form of
a FIFO memory, for example. The particular hardware selected for use in
realizing the various components of the control circuit 40 will depend on
the specific system requirements needed or desired.
The microprocessor 42 reads the electrical signal output of each light
sensitive element 30 and stores this information in RAM 50. Depending upon
the application of the scanner, this information may be a single bit, "1"
or "0" indicating a dark or light image point, or the information may take
the form of multiple bits of digital information to indicate shades of
gray. Further, it is recognized that three scan heads 26 may be
incorporated into a single scanner mechanism 25, with one of the scan
heads viewing the image being scanned through a red filter, another
through a green filter, and the third through a blue filter, thus
providing full color scanning of the image. Alternatively, for example, a
single scan head may be equipped with a red/blue/green striped filter to
achieve color scanning.
A user interface circuit 52 includes the visual display 16 and the key pad
14. The display 16 is used to view the scanned image during scanning, as
illustrated in an exemplary manner in FIG. 1. The display 16 can also be
used to communicate warnings (such as low battery or insufficient memory
available), status information or a prompt to request data entry. The key
pad 14 is used, for example, for selecting instructions to be executed
from a menu displayed by the apparatus 10, as well as for command inputs
and data entry, such as information for identifying a scanned image.
A manually actuated enable switch 54 is provided, preferably on the housing
12, that the operator operates and holds during a scanning sequence. This
prevents accidental operation of the scanning apparatus 10. Note in FIG. 2
that the enable switch 54 also provides a disable function for the keypad
14 (represented by the line between the switch 54 and the keypad 14)
during a scanning operation. This prevents accidental actuation of the
keypad 14 while the scanner is operating. Actual disable control of the
keypad 14 can be effected via the microprocessor 42 in response to
actuation of the disable switch 54 by simply having the microprocessor 42
programmed to ignore all keypad 14 commands during a scanning sequence.
A plug-in module 58 is provided so that information, instructions, images,
or programs may be transferred between the apparatus 10 and an external
apparatus such as, for example, a computer. The module can be, for
example, an industry standard PCMCIA card.
A communication link to an external apparatus is accomplished by use of an
I/O device 60 such as a serial port 62, a parallel port 64 or a wireless
link such as an RF transceiver, or the infrared transceiver 18, an
acoustic transducer or a modem. The transceiver 18 may be, for example, a
Hewlett-Packard HSDL-1000 transceiver.
The apparatus 10 further includes the scanning mechanism 25, which in the
exemplary embodiment includes a CCD scan head 26 and a scan head position
encoder 56. The encoder 56 can be, for example, Hewlett-Packard device
HEDR-8000. Those skilled in the art will readily appreciate and understand
that because the light sensitive elements 30 are fixed in the scan head
26, position data of the scan head 26 can be easily converted into
position data for each and every light sensitive element 30 on a real time
basis.
In addition to providing position and movement information for the scan
head 26, the encoder 56 is also used to indicate to the microprocessor 42
that a scanning sequence is to begin. As the operator begins to sweep the
apparatus 10 across the surface of the document, the encoder 56 begins to
produce output pulses, so that these pulses can serve as an indication to
begin scanning. As used herein, the terms "scanning sequence" and
"scanning operation" are used interchangeably to simply refer to the steps
carried out between actuation of the apparatus 10 and completion of a
scanning function on the medium.
The position encoder 56 provides pulses to the microprocessor 42 as the
scan head 26 sweeps across the selected area. These pulses can be counted
and timed and thus provide both position and velocity information about
the scan head 26, and in particular the light sensitive elements 30
disposed on the head 26. The microprocessor 42 software utilizes the light
sensitive element 30 position and velocity information to determine the
exact relative position on the document being viewed by each element 30.
The encoder 56 is operably coupled to the rollers 20 that support the
apparatus 10 against the document during a scanning sequence. It is
important to note that the encoder 56 will produce pulses caused by
relative rotation between the scan head 26 and the rollers 20. Therefore,
position pulses are produced when the apparatus 10 is swept along the
document, and also produced by pivoting motion of the apparatus 10, even
if at the time of pivoting the apparatus 10 is sweeping slowly or even
stationary. The encoder 56 will also detect backward movement of the
apparatus 10. Thus, the encoder 56 output signals can be used for not only
controlling scanning during a sweeping operation, but also to compensate
for scan head deviations or changes caused by pivoting and other
non-linear movements. The encoder 56 can be configured, for example, to
produce a pulse for each incremental change in angular displacement of the
rollers 20 relative to the scan head 26. By the convenient use of look-up
tables, calculations or approximations, the angular displacement of the
rollers 20 can easily be converted to actual position data for each
element 30. The encoder 56 produces position pulses from the moment that
rotation of the rollers 20 occurs relative to the scan head 26.
An audible alarm 66 can conveniently be provided as part of the user
interface 52. The audible alarm can serve a number of useful purposes,
including an audible tone signal such as a short beep to indicate that a
scanning sequence is completed, as indicated by release of the enable
switch 54, or a distinguishable audible tone signal that the sequence was
not completed, such as, for example, by the operator lifting the apparatus
10 up from the medium before the scanning is completed. The audible alarm
66 can be realized conveniently in the form of an amplifier and speaker
controlled by suitable signals from the microprocessor 42 to produce
different tones or combination of tones to indicate different conditions.
FIG. 3 is a simplified schematic in elevation of a scanner mechanism 25
equipped with a linear CCD array scan head 26. This scan head 26 is
equipped with a plurality of light sensitive elements 30 disposed to scan
a full line of length approximately equal to the width of the scan image.
If, for example, the scanner 25 is designed to scan a 2" wide image with a
resolution of 200 dots per inch (dpi), then the scan head 26 will comprise
400 light sensitive elements at a pitch of 0.005".
The scanner 25 is supported in use by a pair of rollers 20, 22, which are
joined by a shaft 24, such that both rollers 20, 22 in this embodiment
rotate together. Rollers 20, 22 have outer diameters composed of a
material having a high coefficient of friction with paper or other
material used for the document, D, such as soft rubber or plastic.
Movement of the scanner apparatus 10 in a straight line over the document,
on a path perpendicular to the axes of rollers 20, 22, uses significantly
less force than movement over other paths, because only rolling motion of
the rollers is required. Because of this, the motion of the scanner 25
over the document will inherently tend to track in a straight line path as
desired.
An encoder 56 is driven by either of the rollers 20, 22 or the shaft 24.
The encoder 56 may be, for example, an optical encoder such as
Hewlett-Packard model HEDR-8000, which provides two output channels in
quadrature relationship such that both direction and magnitude of rotation
are measured. Speed or velocity of rotation and movement can be determined
from timing the output pulses of the encoder 56.
FIG. 4 is a schematic end view of the scanner apparatus 10. Note than in
operation, as the scanner 25 is manually moved or swept across an image
area on the document, the rollers 20,22 and the shaft 24 rotate. The
encoder 56 produces pulses corresponding with the motion of the scan head
26 across the document. In addition, however, the apparatus 10 is free to
pivot about the rotational axis of the rollers 20,22. FIGS. 5A and 5B
illustrate the effect of such pivoting motion, which, if uncorrected,
could either compress or expand the read image, depending upon the
direction of the pivoting motion. Pivoting the scanner body 12 forward as
in FIG. 5A aims the light sensitive elements 30 backwards as represented
by the directional line 70 and decrements the encoder 56 count, simulating
backward motion of the scan head 26; while pivoting the scanner body
backward as in FIG. 5B aims the light sensitive elements 30 ahead and
advances the encoder count thus appearing to be forward motion of the
scanner. The encoder 56 count is stored in memory either in the
microprocessor 42, the RAM 50 or other memory device, and updated only
when a new count exceeds the previous count, and in this manner the
encoder count corresponding to the farthest advance of the scanning is
stored. Further scanning is enabled only when the encoder count exceeds
the previous high count stored in memory. This assures that if the scanner
is moved backwards, or pivoted forward, previously scanned information
written to RAM 50 by the microprocessor 42 will not be overwritten.
Scanning will resume when the scanning mechanism 25 is moved forward, or
pivoted backward, sufficiently such that the light sensitive elements 30
view information not previously scanned.
It will be appreciated that the change in encoder count resulting from
pivoting the apparatus body 12 about the roller 20, 22 axis of rotation
does not correspond identically to the change in encoder count produced by
a translation of the scan head 26 over the document, and this will result
in an insignificant residual error. This can best be illustrated by way of
example. Assume, for example, that the scanner rollers have a radius "r,"
and that the scanner is pivoted backward from the perpendicular by an
angle "a," resulting in an advance of the viewed line by a distance "d,"
as shown in FIG. 6. The magnitude of "d" may be calculated as follows:
d=r*tan a
The encoder count will advance by an amount corresponding to a translation
"t" of the scanner by a distance equal to that portion of the roller
circumference subtended by angle "a." If "a" is in degrees, then:
t=(a/360)*2.pi.*r
For there to be no error introduced by pivoting the scanner body, then "d"
must equal "t," but this is true only at a =0. As the angle "a" increases,
so too does the error in viewed position. Continuing with the example, and
assuming r=0.25", pivoting the scanner 45.degree. from the perpendicular
would introduce an error of 0.054".
At a scanning pitch of 0.01" or less, this would appear to be a significant
position error, and it indeed would be if the operator were to hold the
scanner stationary on the document and pivot the scanner body 45.degree..
In actual usage, however, the scanner body 12 would be pivoted only as the
scanner is translated over the document to effect scanning of the selected
area. If the example of a 45.degree. pivot takes place over a translation
distance of just 1", then the error of 0.054" is spread over that
distance, and results in an insignificant 5.4% compression or expansion of
the read image.
By way of example and explanation, an image area to be scanned can be
characterized as a matrix of points laid out in a rectangular grid
(recognizing that a scanned pattern need not be rectangular at all) having
an X axis and a Y axis, with each point being described by a unique set of
X,Y coordinates. The X axis is considered the intended direction of
scanner travel, and is perpendicular to the Y axis, which is identically
the axis of the rollers 20, 22 at the start of a scanning operation. The
encoder 56 count increments as the scanner is either advanced along the X
axis or tilted backward (relative to the desired direction of travel). The
X value for each point is a relative position value along the direction of
travel starting from the zero encoder count position when the scanning
sequence begins. Each of the light sensitive elements 30 of the scan head
26 produces an output which is proportional to the light intensity
striking it, which is in turn a measure of the reflectivity of the point
on the document being viewed by said element. The microprocessor 42 stores
in the RAM 50 values corresponding to the outputs of each of the light
sensitive elements 30 whenever the line viewed by the scan head 26 has
advanced by an amount equal to at least one scan line pitch, i.e. the
distance between adjacent scan lines, as determined by the intended scan
resolution. If the scanner apparatus is intended to nave a resolution of
200 lines per inch, for example, then the scan line pitch will be 0.005".
FIG. 7 is a flow diagram for a control program suitable for use with the
embodiment of FIGS. 3-5. At step 200 the encoder 56 count is zeroed; at
step 202 the memory register for the HIGHCOUNT value is zeroed. At step
204, the program tests the status of the enable switch 54 to determine if
scanning is enabled. If not, the program loops and waits until scanning
has been enabled. If scanning is enabled, the system checks at 206 whether
the encoder 56 count has incremented such that the present count exceeds
HIGHCOUNT by at least an amount corresponding to the pitch between
successive scanning lines, indicating advancing movement of the scan head
across the document sufficient for further scanning to Lake place. If yes,
then the present count is used to update the HIGHCOUNT value at step 208
and the next line of image data is read at step 210 and stored in RAMP 50
at step 212. At step 214 the program once again tests the status of the
enable switch 54. If the scanner is still enabled, the program loops back
to step 206. If not, an audible signal is emitted at step 216 and the
program ends.
With reference to FIG. 8, another embodiment of the invention is
illustrated. In this embodiment, the scanner 25 is equipped with a full
line type scan head 74. This scan head 74 is equipped with a plurality of
light sensitive elements 30' disposed to scan a full line of length
greater than the width of the image to be scanned. If, for example, the
scanner is designed to scan a 2" wide image with a resolution of 200 dots
per inch (dpi), then the scan head 74 might comprise 500 elements at a
pitch of 0.005", and be capable of scanning a 2.5" wide swath.
The scanner 25 is supported in use by the rollers 20, 22 in a manner
similar to the embodiment of FIG. 3. However, in contrast to the
embodiment of FIG. 3, these rollers are disposed for rotation
independently of each other. The rollers 20, 22 can be mounted on a single
shaft or separate shafts, but the intent is to achieve completely
independent rotation of the rollers with respect to each other.
Each roller 20, 22 drives a respective encoder 76, 78 | | |
