U.S. patent application number 09/066622 was filed with the patent office on 2001-08-16 for technique for scanning documents using a spiral path locus.
This patent application is currently assigned to HEWLETT-PACKARD COMPANY. Invention is credited to CARIFFE, ALAN E..
Application Number | 20010013956 09/066622 |
Document ID | / |
Family ID | 22070665 |
Filed Date | 2001-08-16 |
United States Patent
Application |
20010013956 |
Kind Code |
A1 |
CARIFFE, ALAN E. |
August 16, 2001 |
TECHNIQUE FOR SCANNING DOCUMENTS USING A SPIRAL PATH LOCUS
Abstract
An optical scanning technique employs an optical sensor array
for collecting image pixel data from a flat medium during a
scanning cycle. A motion apparatus provides relative motion between
the sensor array and the medium such that a spiral locus is defined
by the sensor array relative to the media during a scanning cycle.
The spiral maximum diameter may be made equal to the diagonal
dimension of a rectangular media, thus allowing pixel data to be
collected very close to the edge of the media, and so reducing or
eliminating the area of unscannable margins on both sides and the
top and bottom of the media. The motion apparatus can include a
turntable for rotating the flat medium about a center of
coordinates, and a translatable carriage holding the sensor array.
An ink jet printhead can be mounted on the motion apparatus, to
provide a multi-function scanner/printer machine.
Inventors: |
CARIFFE, ALAN E.; (SAN
DIEGO, CA) |
Correspondence
Address: |
HEWLETT PACKARD COMPANY
P O BOX 272400, 3404 E. HARMONY ROAD
INTELLECTUAL PROPERTY ADMINISTRATION
FORT COLLINS
CO
80527-2400
US
|
Assignee: |
HEWLETT-PACKARD COMPANY
|
Family ID: |
22070665 |
Appl. No.: |
09/066622 |
Filed: |
April 24, 1998 |
Current U.S.
Class: |
358/474 |
Current CPC
Class: |
B41J 3/4071 20130101;
H04N 1/19 20130101; H04N 2201/0424 20130101 |
Class at
Publication: |
358/474 |
International
Class: |
H04N 001/04 |
Claims
What is claimed is:
1. A method for optically scanning a flat image, comprising a
sequence of the following steps; providing an optical sensor array;
supporting a flat medium to be optically scanned by the sensor
array during a scanning cycle; providing relative motion between
the sensor array and the medium such that a spiral locus is defined
by the sensor array relative to the media during an optical
scanning cycle; and collecting sensor data representing the image
during the optical scanning cycle.
2. The method of claim 1, wherein said step of providing relative
motion is accomplished without causing the sensor array to stop and
reverse its direction periodically during the scanning cycle.
3. The method of claim 1 wherein said sensor array is mounted on an
arm which radiates from a center of coordinates, and wherein said
step of providing relative motion includes moving the nozzle array
outwardly on the arm from the center of coordinates while rotating
the medium about the center of coordinates.
4. The method of claim 3 wherein the sensor array spans a first
distance in a direction extending radially from the center of
coordinates, and said step of providing relative motion includes
moving the sensor array radially at a rate such that the sensor
array is moved radially by a distance equal to the first distance
for each complete rotation of the medium about the center of
coordinates.
5. The method of claim 3 wherein the sensor array spans a first
distance in a direction extending radially from the center of
coordinates, and said step of providing relative motion includes
moving the sensor array radially at a rate such that the sensor
array is moved radially by a distance which is less than the first
distance for each complete rotation of the medium about the center
of coordinates.
6. The method of claim 3 wherein the sensor array includes a
plurality of sensor elements including an outermost sensor relative
to the center of coordinates, and the step of collecting sensor
data includes sampling the sensor elements at a constant rate, and
the step of providing relative motion includes varying the rotation
rate of the medium to achieve a substantially constant tangential
velocity of the outermost sensor element of the sensor array.
7. The method of claim 1 wherein said step of providing relative
motion between the sensor array and the medium includes moving the
sensor array radially at a rate selected to provide a partial
overlap of the sensor array relative to the medium during the
scanning cycle.
8. The method of claim 1 wherein said step of providing relative
motion between the sensor array and the medium includes moving the
sensor array radially at a rate selected to provide a partial
underlap of the sensor array relative to the medium.
9. The method of claim 3 wherein the sensor array includes a
plurality of optical sensor elements, and the step of collecting
sensor data during a scanning cycle includes sampling the sensor
elements at a varying sampling rate, and the step of providing
relative motion includes varying the rotation rate of the medium to
achieve a substantially constant tangential velocity of a given
sensor element comprising the sensor array.
10. The method of claim 1 wherein the step of providing relative
movement includes moving the sensor array radially by a distance
which is large enough to provide swept coverage of the sensor array
over the entire area of the medium.
11. An optical scanning system, comprising: an optical sensor array
comprising a plurality of sensor elements for collecting image data
during an optical scanning cycle; a flat medium positioned relative
to the sensor array to permit optical sensing of an image carried
by the flat medium during an optical scanning cycle; apparatus for
providing relative motion between the sensor array and the medium
such that a spiral locus is defined by the sensor array relative to
the media during an optical scanning cycle.
12. The scanning system of claim 11, wherein said apparatus for
providing relative motion is adapted to provide said relative
motion without causing the sensor array to stop and reverse its
direction periodically during the scanning cycle.
13. The scanning system of claim 11 wherein said apparatus for
providing relative motion between the sensor array and the medium
is adapted to move the sensor array radially at a rate which
provides a partial overlap of the sensor array relative to the
medium during the scanning cycle.
14. The scanning system of claim 11 wherein said apparatus for
providing relative motion between the sensor array and the medium
is adapted to move the sensor array radially at a rate which
provides a partial underlap of the sensor array relative to the
medium.
15. The scanning system of claim 11 further comprising: a carriage
for holding the sensor array, said carriage mounted for movement
along a carriage axis extending through an center of coordinates;
and an arm structure for supporting the carriage for said movement
along said carriage axis; and wherein said apparatus for providing
relative motion includes a carriage drive apparatus for moving the
optical sensor array outwardly on the arm from the center of
coordinates and a turntable drive for rotating the medium about the
center of coordinates.
16. The scanning system of claim 15 wherein the sensor array spans
a first distance in a direction extending radially from the center
of coordinates, and said carriage drive apparatus is adapted to
move the sensor array radially at a rate such that the sensor array
is moved radially by a distance equal to the first distance for
each complete rotation of the medium about the center of
coordinates.
17. The scanning system of claim 15 wherein the nozzle array spans
a first distance in a direction extending radially from the center
of coordinates, and said carriage drive apparatus is adapted to
move the sensor array radially at a rate such that the sensor array
is moved radially by a distance which is less than the first
distance for each complete rotation of the medium about the center
of coordinates.
18. The sensor system of claim 11 further comprising a controller
for generating sampling commands to cause said sensor array to
sample pixels from a given sensor element comprising the sensor
array at a constant rate for the scanning cycle, and the apparatus
for rotating the medium is adapted to vary the rotation rate of the
medium to achieve a substantially constant tangential velocity of
the given sensor element.
19. The scanning system of claim 11 further comprising a controller
for generating sampling commands to cause said sensor array to
sample image pixels at a varying rate for the scanning cycle.
20. The scanning system of claim 11 wherein the apparatus for
providing relative movement is adapted to move the sensor array
radially by a distance which is large enough to provide swept
coverage of the sensor array over the entire area of the
medium.
21. A multi-function scanner/printer system, comprising: an optical
sensor array comprising a plurality of sensor elements for
collecting image data during an optical scanning cycle; a flat
medium positioned relative to the sensor array to permit optical
sensing of an image carried by the flat medium during an ink jet
printing cycle; apparatus for providing relative motion between the
sensor array and the medium such that a spiral locus is defined by
the sensor array relative to the media during an optical scanning
cycle; a memory for storing image data collected by the optical
sensor array during said optical scanning cycle; an ink jet pen
having a nozzle array; apparatus for providing relative motion
between the nozzle array and the medium such that a spiral locus is
defined by the nozzle array relative to a flat print medium during
an ink jet printing cycle.
22. The system of claim 21 further comprising a controller adapted
to control said ink jet pen during a printing cycle using image
data collected during said scanning cycle to produce a copy of said
scanned image.
23. The system of claim 21, wherein said apparatus for providing
relative motion to said sensor array is adapted to provide said
relative motion without causing the sensor array to stop and
reverse its direction periodically during the scanning cycle.
24. The system of claim 21 further comprising: a carriage for
holding the sensor array and said ink jet pen, said carriage
mounted for movement along a carriage axis extending through an
center of coordinates; and an arm structure for supporting the
carriage for said movement along said carriage axis; and wherein
said apparatus for providing relative motion includes a carriage
drive apparatus for moving the optical sensor array outwardly on
the arm from the center of coordinates and a turntable drive for
rotating the medium about the center of coordinates.
25. The system of claim 24 wherein the sensor array spans a first
distance in a direction extending radially from the center of
coordinates, and said carriage drive apparatus is adapted to move
the sensor array radially at a rate such that the sensor array is
moved radially by a distance equal to the first distance for each
complete rotation of the medium about the center of
coordinates.
26. The sensor system of claim 24 wherein said sensor array is
adapted to sample image pixels at a constant rate for the scanning
cycle, and the apparatus for rotating the medium is adapted to vary
the rotation rate of the medium to achieve a substantially constant
tangential velocity of the sensor array.
27. The sensor system of claim 21 further comprising a controller
adapted to control the ink jet pen and the apparatus for providing
relative motion between the nozzle array and the print medium to
provide a print mode wherein ink droplets are ejected by the pen at
predetermined pixel positions on the print medium, and said
controller is further adapted to control the sensor array and the
apparatus for providing relative motion between the sensor array
and the medium carrying the image to provide a scan mode wherein
the image data collected during an optical scanning cycle
correspond in position to said predetermined pixel positions
employed during said print mode.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application is related to co-pending application Ser.
No. ______, entitled "TECHNIQUE FOR MEDIA COVERAGE USING INK JET
WRITING TECHNOLOGY," attorney docket 10971883-1, the entire
contents of which are incorporated herein by this reference.
TECHNICAL FIELD OF THE INVENTION
[0002] This invention relates to optical scanning techniques, and
more particularly to a new method for continuous unidirectional
scanning which reduces mechanical hysteresis and reduces the area
of unscanned media to zero by scanning along a spiral locus path.
This method produces data which exactly matches the data
requirements of a spiral path locus ink-jet printer.
BACKGROUND OF THE INVENTION
[0003] Conventional optical scanners employ linear array optical
sensors, and an apparatus for providing relative motion between the
document or image to be scanned and the linear array sensor. In a
general sense, the image is scanned by producing a series of scans
of a given swath width, which are then assembled or processed by a
processor in a rectilinear, Cartesian sense to provide the scanned
data representing the image or document.
[0004] This invention improves upon the typical, rectilinear
Cartesian document scan in such a way as to produce sampled
information from printed, drawn or photographic media which exactly
matches a method of ink-jet printing along a spiral path locus.
This invention also provides a way to capture the information
present on the media all the way to the edges of the scanned media
the same as in flat-bed scanners, and results in a simpler
mechanical structure for the scanner.
[0005] In the referenced co-pending application serial number
______,entitled "TECHNIQUE FOR MEDIA COVERAGE USING INK JET WRITING
TECHNOLOGY," a method is described which improves upon an ink-jet
printing hysteresis problem, and an ink-jet printing margin
problem. In this co-pending application, it is shown that, by
printing in a uni-directional manner along a spiral path, both of
these printing problems are reduced or eliminated. However, because
document scanners typically scan information from text or
photographic media in a raster or x-y Cartesian fashion, there then
necessitates a re-sampling or conversion from rectangular
coordinates to polar coordinates to effect the printing of the
scanned data on a spiral path. It is realized that this conversion
process could produce undesirable printing artifacts under some
circumstances, and the purpose of this invention is to eliminate
these artifacts entirely. Also, in many non-flatbed scanners,
mechanical constraints do not allow the scanning sensors to view
documents all the way to the document edges; hence information may
be lost during a conventional non-flatbed scanning process. This
invention also can result in a simplification of the mechanism
required to move and house the scanner, since the scanning array
may be mounted either in place of, or radially co-linear with, an
ink-jet printing nozzle array, thus providing a printer and a
scanner, both of which share electrical and mechanical parts to a
large extent.
SUMMARY OF THE INVENTION
[0006] A method for optically scanning a flat image is provided in
accordance with one aspect of the invention. The method includes a
sequence of the following steps;
[0007] providing an optical sensor array;
[0008] supporting a flat medium to be optically scanned by the
sensor array during a scanning cycle;
[0009] providing relative motion between the sensor array and the
medium such that a spiral locus is defined by the sensor array
relative to the media during an optical scanning cycle; and
[0010] collecting sensor data representing the image during the
optical scanning cycle.
[0011] In a preferred embodiment, the step of providing relative
motion is accomplished without causing the sensor array to stop and
reverse its direction periodically during the scanning cycle.
[0012] In a further aspect of the invention, an optical scanning
system comprises an optical sensor array comprising a plurality of
sensor elements for collecting image data during an optical
scanning cycle. A flat medium is positioned relative to the sensor
array to permit optical sensing of an image carried by the flat
medium during an optical scanning cycle. A relative motion
apparatus provides relative motion between the sensor array and the
medium such that a spiral locus is defined by the sensor array
relative to the media during an optical scanning cycle.
[0013] The scanning system can further include, in a multi-function
system, an ink jet pen having a nozzle array, and apparatus for
providing relative motion between the nozzle array and the medium
such that a spiral locus is defined by the nozzle array relative to
a flat print medium during an ink jet printing cycle.
BRIEF DESCRIPTION OF THE DRAWING
[0014] These and other features and advantages of the present
invention will become more apparent from the following detailed
description of an exemplary embodiment thereof, as illustrated in
the accompanying drawings, in which:
[0015] FIG. 1 is a diagrammatic isometric view of an exemplary
embodiment of an optical scanning system embodying the present
invention.
[0016] FIG. 2 is a graphical illustration of the spiral locus path
of the relative motion between the optical sensor array and the
flat medium, in accordance with an aspect of the invention.
[0017] FIG. 3 illustrates a simplified sensor array with a
plurality of sensor elements for the sensor head of the scanning
system of FIG. 1, in two positions relative to the surface of the
flat medium.
[0018] FIG. 4 is a simplified illustration of one exemplary path of
the outermost sensor of the sensor array of FIG. 3 for a complete
rotation (2.pi. radians) of the medium, for the case of a
non-overlapped sensor array spiral.
[0019] FIG. 5 is a simplified illustration of a first alternate
path of the outermost sensor element of the sensor array of FIG. 3
for a complete rotation (2.pi. radians) of the medium, for the case
of a partially-overlapped sensor array spiral.
[0020] FIG. 6 is a simplified illustration of a second alternate
path of the outermost sensor element of the sensor array of FIG. 3
for a complete rotation (2.pi. radians) of the medium, for the case
of a partially-underlapped sensor array spiral.
[0021] FIG. 7 is a graph of the angular speed of the flat medium as
a function of radial distance for the embodiment of FIG. 2.
[0022] FIG. 8 is a simplified schematic block diagram of the
control system comprising the optical scanner system of FIG. 1.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0023] In accordance with an aspect of the invention, a technique
of optical scanning involves providing relative motion between a
flat medium bearing the image to be scanned and an array of light
sensors along a spiral path, which preferably is the exact spiral
path to be subsequently used in an ink-jet printing process. This
scanning technique eliminates the need for any coordinate
conversions whatsoever, and eliminates any printing artifacts
introduced by such conversions or resampling when used with a
printer designed for such data. Alternatively, the data produced
may be easily re-sampled into commonly used rectangular coordinates
using known techniques, such as a convolution technique.
[0024] Additionally, the spiral maximum diameter may be made equal
to the diagonal dimension of a rectangular media, thus allowing
information very close to or at the edges of the media to be
captured, and so reducing the area of non-scanned margins to zero
on both sides and the top and bottom of the media when it is
subsequently rendered. Benefits resulting from uni-directional
scanning and non start-stop motions of the scanning array will also
reduce effects of mechanical hysteresis present in some scanning
mechanisms.
[0025] What is desired is to provide relative motion between a
light sensor array and a flat media, without actually causing the
light sensor array or media to stop and reverse direction
periodically, and, according to a further aspect of the invention,
to cause the information so scanned to match, in a one-to-one
correspondence, that information subsequently required by an
ink-jet rendering process. A spiral pattern of pixels so scanned in
accordance with this aspect of this invention provides image data
pixels located at physical media coordinates which may be exactly
rendered or printed by a spiral printer whose nozzle arrays
correspond in physical location to those of the array of light
sensors comprising the light sensor array. This results from the
characteristic of sensor arrays that pixels are sampled at some
sample rate, and the sampling rate can be chosen in dependence on
the firing rate of the ink jet printer nozzles.
[0026] The spiral pattern can be accomplished, in one exemplary
embodiment, by mounting the scanner array on an arm which radiates
from a center of coordinates in RHO (.rho.) THETA (.theta.)
coordinate space, where RHO is a measure of distance from a center
of coordinates, and THETA is a measure of angle, most usually in
radians. The scanner array can then be moved outward from this
center, while at the same time the media may be rotated in a circle
around the center of coordinates. Alternatively, the sensor array
can be rotated and translated instead of the media to provide a
spiral locus for the sensor elements relative to the print
medium.
[0027] FIGS. 1-8 illustrate an optical scanning system 50 which
embodies this invention. An optical sensor head 52 is supported in
a carriage 60. The sensor head includes a sensor array 54
comprising sensor elements 56A-56N, and an illumination source 52A
(FIG. 3). An exemplary optical scanning head suitable for the
purpose is described in pending application Ser. No. 08/717,921,
entitled UNDERPULSED SCANNER WITH VARIABLE SCAN SPEED, P.W.M. COLOR
BALANCE SCAN MODES AND COLUMN REVERSAL, by Haselby et al., filed
Sep. 23, 1996, the entire contents of which are incorporated herein
by this reference. The carriage 60 is adapted for movement along a
scan axis 62. A carriage drive system 70 is coupled to the carriage
to drive the carriage in a path along the axis 62. The exemplary
carriage drive system 70 includes a drive motor 72, belt drive 74,
and encoder strip 76 with encoder sensor 78 (FIG. 4) for providing
carriage position data. Other drive mechanisms can alternatively be
employed, such as leadscrew drives.
[0028] The medium 10 bearing the image to be scanned, e.g. a sheet
of a document, a drawing, or a photograph, is supported on a flat
turntable platen 80 which is in turn mounted for rotation about a
center axis 82, which at the plane of medium 10 defines the center
of coordinates 86. The turntable platen 80 is driven by a rotary
turntable drive system 90 which includes a turntable motor 92 and a
turntable encoder 94 (FIG. 8) for providing turntable position
data.
[0029] In an exemplary embodiment, an apparatus is provided for
holding the medium 10 flat against the turntable platen 80. Such
apparatus are well known in the art, e.g. a vacuum hold-down
system, an electrostatic system, or a mechanical system with a
fixture for holding the medium in place.
[0030] The carriage axis 62 intersects the linear sensor array axis
above the center of coordinates 86 (FIG. 3).
[0031] Also shown in FIG. 1 is a second device 40 held by the
carriage. This device can be an ink jet pen, so that the machine 50
is a multi-function machine capable of both optical scanning
functions and ink jet printing function, e.g. as a copy machine for
first scanning a document and then printing a copy. Motions of the
carriage and the media turntable may be used to allow both devices
to sweep over the same regions on the medium. The second device 40
is optional, and can be omitted for some applications requiring
only an optical scanning function.
[0032] FIG. 2 is a chart illustrating the relative motion path, a
spiral locus, of the sensor array in relation to the medium 10
during a scanning operation in accordance with an aspect of the
invention. LOCUS 1 is a trace of the path taken by the light sensor
element of sensor array 54 which is mounted furthest from the
center of coordinates 86, relative to the surface of the medium 10.
REGION 1 is the circular region defined by the light sensor sweep
which would occur with a stationary light sensor, when the center
of the innermost light sensor is coincident vertically with the
center of coordinates, such that the inner light sensor element is
over the center of coordinates 86, and the light sensor element
located at the position of LOCUS 1 is the furthest from this
center. REGION 2 illustrates a rectangular scanning region, of
dimensions W by H, of an exemplary rectangular image or document.
REGION 3 is bounded by a circle indicating the outer limit of
coverage for the spiral scanning process.
[0033] FIG. 3 illustrates a simplified linear sensor array 54 with
a plurality of sensor elements 56A-56N and a linear illumination
source 52A. The sensor array can provide monochromatic or color
image data; both types of sensor heads are well known in the art.
The illumination source can be an array of LEDs, and can include
for full color applications red, blue and green LEDs. Typically, as
is well known in the art, the illumination source is controlled by
a controller to provide light flashes timed in accordance with the
sampling of the sensor elements; however other illumination schemes
may also be used. Position 1 shows the sensor array in a start
position relative to the surface of the medium 10, with the sensor
element 56A at the platen center of coordinates 86. Position 2
shows a relative rotation (by some angle .theta.) between the
sensor array 54 and the medium 10. In this exemplary embodiment,
the carriage is stationary during the first complete rotation of
the platen 80, to provide complete coverage, i.e. to sweep out,
REGION 1. This first complete relative rotation is circular, and
the sensor element 56A remains at the center of coordinates 86,
which is illustrated in FIG. 3. On the second rotation, the
carriage is put in motion, to provide a relative path as shown in
FIG. 4.
[0034] FIG. 2 also illustrates the condition that the radial motion
of the light sensor array is constrained to linearly move one unit
of distance for each 2.pi. radians (360 degrees) rotation of the
media, where one unit of distance is equal to the maximum radial
`span` of the light sensor array. Thus, in FIG. 2, the spiral sweep
does not overlap or underlap onto itself. For the third and all
subsequent rotations of the platen 80, there will be no overlapped
coverage of the sensor array relative to earlier rotations/passes
of the sensor array.
[0035] In order to completely sample REGION 1 with potential light
sensor events, when the light sensor array is located over REGION
1, it needs to maintain this position during one full revolution of
the media, in order to completely scan this central region.
Subsequently, as the light sensor array moves outward, all the
remaining area of REGION 3 becomes the potential target of light
sensor events, an event being the sampling of the light emanating
from a particular RHO, THETA position on the media, that is, a
sample of one pixel which is to subsequently be rendered by an
ink-jet mechanism, as more particularly described in the co-pending
application referenced above. REGION 3 is circular, but most of the
common media which it is desired to scan and sample digitally is
rectangular, as indicated by REGION 2. In order to completely cover
this rectangular region, the innermost light sensor element of the
light sensor array needs to travel from the center of coordinates
outward, and the outermost sensor element must be able to just
reach the furthest corners of the media.
[0036] FIG. 4 is a simplified illustration of the path of the
outermost sensor element 56N for a second complete rotation (2.pi.
radians) of the medium 10, i.e. for the case of a given motion of
the carriage along the carriage axis 62 as the platen 80 rotates.
The path starts at position A of the sensor element 56N, at
.theta.=0, radius .rho.=1 unit (equal to the width of the sensor
array), and ends at position E of the sensor element 56N, at
.theta.=2.pi., .rho.=2 units. The sensor element 56N follows
through the path illustrated relative to the medium, with position
B occurring at .theta.=.pi./2, .rho.=1.25 unit, position C
occurring at .theta.=.pi., .rho.=1.5 unit, and position D occurring
at .theta.=3.pi./2, .rho.=1.75 units. During this second complete
rotation, i.e. the first rotation after the carriage is put into
motion, there will be overlapped coverage of sensor elements with
respect to the initial rotation within REGION 1. Preferably, the
printer controller is programmed to suppress collecting data from
the overlapped sensor elements, for this second rotation, over the
overlapped area to prevent duplicate pixel coverage. Also, the
sensed pixel elements are preferably spaced evenly along the spiral
path in accordance with standard design practices.
[0037] In many applications it may be desirable to overlap the path
to prevent spiral banding, just as is presently done to prevent
swath banding in known rectangular coordinate scanners by averaging
several samples at the same pixel (.rho.,.theta.) coordinate. In
this case, then, the sensor array will be moved less than a full
sensor array width (1 unit) for each 2.pi. radians rotation of the
medium 10. FIG. 5 illustrates an exemplary spiral locus for such an
overlapped case. In this example, the carriage moves outwardly at a
rate of 0.5 unit (sensor array width) per complete rotation of the
sensor array. Alternatively, the sensor array can be moved more
than a full sensor array width for each 2.pi. radian rotation of
the medium 10, providing gaps in the sensor coverage as the sensor
array moves outwardly. These gaps can be filled in on a reverse
spiral scan, moving the sensor array from an outside position back
to the start position shown in FIG. 3. FIG. 6 illustrates an
exemplary spiral locus for such an underlapped case. In this
example, the carriage moves outwardly at a rate of 2 units (sensor
array widths) per complete rotation of the sensor array.
[0038] In many scanning cases, the light sensor elements sample
pixels at a constant rate such that pixels are sampled at uniformly
equal distances one from another along an axis, although it is not
required by this invention. However, if this is a desired
operation, then since the relative velocity of a given sensor
element along the spiral will increase with radius RHO for a
constant rotational speed, the circular rotational velocity of
platen 80 can be adjusted such that if S is a tangential distance
along LOCUS 1, and [1] dS=RHO*dTHETA using `d` to indicate
"differential" as in calculus notation, then if t stands for time,
[2] dS/dt=RHO*dTHETA/dt=V, where V is the desired constant velocity
along LOCUS 1. Solving [3] dTHETA/dt=V/RHO, where RHO starts out as
one unit sensor array width, and reaches
(W.sup.2+H.sup.2).sup.1/2/2 at the point where full coverage of the
media has occurred. Because RHO is a variable which occurs in the
denominator position, this means the rotational velocity is a
nonlinear function of the position of the light sensor array, if a
constant tangential velocity of the array is desired. FIG. 7 is a
graph plotting the angular speed of the head as a function of the
radial distance from the center of coordinates. Put another way,
the maximum rotational rate of the media will be V radians per
second, when the innermost light sensor element is located over the
center of rotation, and the minimum rotational velocity will be
2V/(W.sup.2+H.sup.2).sup.1/2 radians per second for a light sensor
array of 1 unit length, or span.
[0039] By way of illustrative example, assume that it is desired to
sample, or scan, edge-to-edge on an 8.5.times.11 inch media using a
light sensor array which consists of 300 light sensors elements,
each of which is spaced equally from its neighbors by {fraction
(1/300)}th of an inch. This array then is 1.0 inches long. Suppose
further that the maximum tangential velocity that this head
supports, while sampling pixels at its maximum rate, is 10.0 inches
per second. Thus, 10*300=3000 light samples are taken per second
while the array moves over the media at this speed, and the
"swath-width" is 1.0 inch wide.
[0040] The maximum position the light sensor element furthest from
the center of rotation needs to be away from this center, for this
example, is
(W.sup.2+H.sup.2).sup.1/2/2=(8.5.sup.2+11.sup.2).sup.1/2/2=6.95
inches. When this light sensor element reaches this outer limit of
RHO its rotational velocity will be dTHETA/dt=V/RHO=10.0 inches
per-second/6.95 inches=1.44 radians per second, or about 13.75 RPM
(rotations per minute) as in FIG. 7. The tangential velocity is the
rotational velocity times the radius, which is 1.44*6.95=10 inches
per second, as expected. Now when the light sensor element furthest
from the center of rotation is at RHO=1.0 inch, the rotational
velocity is 10.0 inches-per-second/1.0 inches=10.0
radian-per-second, or about 95.5 RPM as in FIG. 7.
[0041] The total scan time can be approximated as the time it takes
to sweep out the total circular area of REGION 3 at the constant
rate of 10 square inches per second (the area swept out be the head
in one second is the length of the light sensor array times the
distance traveled in one second). The "swept out" circular area is
.pi.(RADIUS).sup.2=3.14159*(6.9- 5).sup.2=151.75 square inches. At
10 square inches per second, this is about 15.2 seconds.
[0042] FIG. 8 is a simplified schematic block diagram of the
control system for the system illustrated in FIG. 1. A controller
100 is coupled to a memory 102 for storage of image data collected
during a scan job. The controller generates the drive commands to
the carriage scanning motor 72, which comprises the carriage drive,
and receives position signals indicative of the carriage/sensor
array position from carriage scanning encoder 78. The controller
also generates turntable motor drive commands to control the
turntable motor 92 which rotates the turntable platen, and receives
encoder signals from the turntable encoder 94 to determine the
position and angular velocity of the turntable platen. The
controller thus can control the carriage drive to achieve a
non-overlapping spiral locus of the sensor array with respect to
the medium, or an overlapped spiral locus to prevent banding or
other artifacts, or an underlapped locus to provide for other
special scanning modes. Other exemplary scanning modes include
skipping scanning (collecting data) on alternate rotations forming
the spiral, and to reverse the direction of the carriage at the
end, filling in the omitted pixel data in the alternate
rotations.
[0043] The controller also receives sensor data from the optical
sensor array, and, in the event the system 50 includes a printing
function, provides firing pulses to the pen 40 in dependence on the
image to be generated and the position of the pen in relation to
the center of coordinates. The image data can be stored in the
memory 102, or transmitted to or received from a host computer
120.
[0044] The controller also provides sampling control signals to the
sensor elements 56A-56N of the array 54, and illumination source
control signals to the illumination source 52A, in dependence on
the scanning mode and the position of the sensor head 52 in
relation to the center of coordinates. The image pixel data
collected during the scanning process can be stored in the memory
102, or passed to a host computer 120. The controller can also set
the sampling rates for the various sensor elements. While in many
cases it is desirable to use a constant (maximum) sampling rate,
for other jobs or applications, the controller can control the
sampling rate to be non-constant over a particular scan job, or to
use a slower constant sampling rate. Faster or slower sampling
rates can be used to achieve higher or lower densities of pixel
data in particular regions on the medium 10.
[0045] Each sensor element in the sensor array 54 is at a different
radial distance from the center of coordinates 86 than any other
sensor element. The result of this is that sampling all sensor
elements at a constant rate produces pixel spacing differences
which will be readily apparent at small values of RHO, especially
in REGION 1 of FIG. 2. For example, in REGION 1 during the initial
rotation of the media (which is not accompanied by a radial motion
of the carriage), and for a {fraction (1/300)}.sup.th inch sensor
element spacing, the sensor element 56N (FIG. 3) at RHO furthest
from the center of rotation must sample 300 times for every inch
along the circumference. For a one inch sensor array, the
circumference is 2.pi. inches. Hence there will be 1,885 pixels
sampled at a spacing of {fraction (1/300)}.sup.th of an inch along
this circumference. At the second nozzle 56B out from the center of
coordinates, the circumference is only 2.pi./300 inches, or 0.0209
inch, and collecting 1,885 image pixels along this circular path is
incorrect because it will produce too many pixels along that
circular path. At the sensor element next to the outermost sensor
element, i.e. {fraction (1/300)} inch closer to the center of
rotation than sensor element 56N, the number of pixels sampled to
maintain 300 pixels per inch should be 2.pi.(1.0{fraction
(1/300)})(300), which is 1,879. Instead, however, 1,885 pixels
would actually be sampled if the sampling rate were to be the same
as the outermost sensor element, and the pixels thus produced would
be closer together than those produced by the outermost sensor
element. During the sweep of REGION 1, or at any other region of
the medium, pixels which have been sampled should not be
re-sampled, and logic in the controller can easily determine which
pixel is to be sampled by each sensor element, and sensor elements
closer to the center of rotation can be sampled less
frequently.
[0046] As a further example, when the sensor array has reached a
RHO value of 2.0, after the second complete rotation of the medium,
the sensor element 56A (closest to the center of rotation) is at a
RHO value of 1.0, and will need to be sampled at one-half the rate
of the outermost sensor element to maintain the same pixel spacing.
Again, logic in the controller will adjust the sampling rate to not
sample a pixel which has already been sampled once. However, it is
desired to minimize total scan time by making the sensor element
56N, i.e. the outermost sensor element, sample at the maximum
(constant) rate possible. FIG. 7 shows the relationship between the
constant (maximum) rate of this outermost sensor element, while all
other sensor elements will actually be sampled when the pixel over
which they are to sample is at least {fraction (1/300)}.sup.th of
an inch away from any adjacent pixel, and this will always be at a
lower rate of sampling than the maximum possible. These differences
in rate rapidly diminish with distance from the center of
rotation.
[0047] It is understood that the above-described embodiments are
merely illustrative of the possible specific embodiments which may
represent principles of the present invention. For example, other
arrangements can be employed to provide the desired relative motion
between the sensor head and the medium to provide a spiral path.
For example, the sensor head can located on an arm mechanism which
moves in a spiral path, with the medium located on a stationary
platen. Or conversely, the sensor head can be located in a
stationary position, and the medium located on a platen which
provides the desired spiral movement locus. Also, while the motion
of the sensor head has been described as commencing from a position
at the center of coordinates and moving radially outwardly, the
sensor head could alternatively be started at any other position,
e.g., at the outermost position and spiraled inwardly to end at the
center of coordinates. Other arrangements may readily be devised in
accordance with these principles by those skilled in the art
without departing from the scope and spirit of the invention.
* * * * *