Note: Descriptions are shown in the official language in which they were submitted.
CA 02355756 2006-06-16
METHOD AND APPARATUS FOR SCANNING
LUMBER AND OTHER OBJECTS
[0001] This application claims benefit of U.S. Provisional Application Ser.
No.
60/227,015 and Ser. No. 60/227,017, both filed August 23, 2000, now expired.
CROSS REFERENCES TO RELATED CO-PENDING APPLICATIONS
[0002] U.S. Ser. No. 09/931,179, entitled "High Speed and Reliable
Determination of
Lumber Quality Using the Tracheid Effect", by Metcalfe and Dashner, filed
August 17,
2001, now abandoned.
[0003] U.S. Ser. No. 09/931,181, entitled "High Speed Camera Based Sensors",
by
Metcalfe and Reuser, filed August 17, 2001, now issued as U.S. Patent No.
6,825,936.
FIELD OF THE INVENTION
[0004] The invention relates to TV Camera based and other electro-optical
sensors
and systems, providing affordable methods and apparatus for high speed
scanning of
dimensions and other features of objects.
[0005] The invention uses one or more light sources combined with TV cameras
whose output is used as input to a computer, such as a PC. This data is
analyzed to
typically provide data concerning the location or dimension of objects or
parts of
objects and/or the presence or characteristics of certain features of objects.
[0006] The invention is particularly useful for applications relating to wood
products,
including boards moving at high speed on conveyor lines in sawmills. More
specifically it is concerned with triangulation sensors for object dimension,
shape,
thickness and position determination, especially at multiple locations on
moving
boards up to 28 feet long and at 3 boards per second. Data taken with such
sensors
is used to control sophisticated sawing operations aimed at maximizing yield
from
boards of variant shape, particularly in their edge regions.
[0007] A large number of data points per piece (e.g. every 0.1 inch or
greater) is
today considered essential to obtain a high quality 3D representation of the
object
shape so as to optimally control sawing operations used to maximize the yield
of logs
sawn. The invention discloses novel methods and apparatus to achieve this
goal.
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CA 02355756 2006-06-16
BACKGROUND OF THE INVENTION
[0008] Laser triangulation sensors have found favor in industry, particularly
the
lumber industry where, for example, requirements exist to determine shape,
thickness or local contour of 28 foot long boards moving sideways on chain
conveyors at 3 boards per second, in order to control the saws used to trim
the
boards of non conforming stock. Current trends call for more and more board
sections to be taken, in order to better categorize the product and its
subsequent
sawing or other processing steps.
[0009] Over the last few years, sectional data density requirements have
steadily
progressed from one section every 6 inches of axial board length, to the
existing
state of the art of every one inch. This application seeks to improve this
ability to
every 0.1 inch or better down the length of a 16 foot board, say, while still
maintaining
the high quality of data with minimum latency needed to control actual process
operations.
[0010] In the specific area of interest of this application in the field of
wood
measurement, examples of laser triangulation based sensor units specifically
designed for this are Leong et al: U.S. Pat. No. 4,937,445, entitled Apparatus
for
determining the distances of points on a surface from a reference axis and
Cielo et
al, U.S. Pat. No. 5,056,922 entitled Method and apparatus for monitoring the
surface
profile of a moving workpiece. Both of these applications illustrate systems
which
represent the norm today for measuring moving boards, in which the direction
of
board motion is transverse to the longitudinal or long axis of the board. The
lens axis,
detector array and the longitudinal axis of the board are all basically in a
common
plane.
[0011] For the case of boards traveling in the direction of their longitudinal
axis, a
light stripe type system such as Chasson, U.S. Pat. No. 4,188,544 entitled
Method
and Apparatus for Automatically Processing a workpiece employing calibrated
scanning, can be employed. Handling boards however, in this manner at high
speed
needed to cover all the board is very difficult.
[0012] A generic reference on dimensional and positional measurement of
objects by
Electro-optical means is Pryor et al: U.S. Pat No. 5,734,172 entitled Method
and
apparatus for electro optically determining the dimension, location and
attitude of
objects. Other references disclosing
2
CA 02355756 2006-06-16
triangulation measurements with photo-detector arrays are; U.S. Pat. No.
4,891,772
Case et al. entitled Point and line range sensors; and Liptay-Wagner et al,
U.S. Pat.
No. 4,394,683 entitled New photodetector array based optical measurement
systems.
The use of first moment calculations to determine a image location is
described in
U.S. Pat. No. 4,219,847 by Pinkney et al. entitled Method and apparatus of
determining the center of area or centroid of a geometrical area of an
unspecified
shape lying in a larger x-y scan field.
[0013] Further information is provided in a patent application entitled "High
Speed
Camera based Sensors", filed by our colleagues Leonard Metcalfe and Cash
Reuser
on August 17, 2001, now issued as U.S. Patent No. 6,825,936.
[0014] Further information is also provided in an application by our co-
worker,
Richard McBain, entitled High speed laser Triangulation Measurements of Shape
and
Thickness, filed May 23, 2000 claiming benefit of U.S. Provisional application
No.
60/135,680, now issued as U.S. Patent No. 6,466,305.
[0015] U.S. Pat. No. 5,717,199 by Carbone et al. discloses methods and
apparatus
by which data can be read randomly from pixels of a camera, while U.S. Pat.
No.
5,982,393 by Forchheimer et al. describes methods by which computing can be
done
directly on pixel data using processors located on the same image chip.
However,
neither reference discloses methods by which such devices can actually be used
to
make practical measurements required in industry in an apparatus such as
disclosed
herein.
[0016] Categorization of lumber defects such as knots, is discussed in our
copending
application referenced above as well as U.S. Patents such as Mathews et al.
U.S.
Pat. No. 3,976,384 and Soest, U.S. Pat. No 5,703,960.
SUMMARY OF THE INVENTION
[0017] This invention relates to a significant advance over the state of the
art as
disclosed in Leong, Cielo et al. etc, and others for measuring boards moving
transversely at the high speeds needed to provide information to real time
sawing
and other operations in lumber mills. One aspect covers a novel sensor
arrangement,
in which the camera system is oriented 90 degrees to that known heretofore,
and
uses novel signal processing methods to achieve the necessary data density,
speed
and obscuration elimination desired.
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[0018] A preferred embodiment utilizes laser triangulation with a multiplicity
of points,
or one or more lines, said points or lines extending in the direction of the
longitudinal
axis of the object and perpendicular to the transfer direction of the object.
Images of
points on the surface of the object are determined in their position by two
cameras
one on each side of point or line projection direction, which as disclosed can
eliminate problems with obscuration which otherwise would render inadequate a
device such as that of Chasson if employed in this way.
[0019] The invention in some embodiments also utilizes a knowledge of the part
itself
to control the sensing characteristics to facilitate determination of object
location or
dimension in the presence of undesirable conditions caused by the surface
condition
of the object, which may be, for example, different surfaces of a moving
board, or log,
which face in the direction of motion or away from same.
[0020] It is noted that in the following discussion, the word "laser" is meant
to connote
not only the laser device itself of whatever kind (typically a semi-conducting
diode
laser), but also any associated optics and power sources needed to assure that
reliable optical energy can be delivered to a zone on the surface of the
object to be
measured. Typically, but not necessarily, such a zone is produced by focusing
the
radiation emanating from the laser to a small zone at the mean point of object
location in the laser projection direction. In other cases cylindrical optics
are used to
create line projections. Optics may be either refractive, reflective or
diffractive/holographic in nature.
[0021] While the preferred detector array employed for board measurement to
date
has been a CCD, or charge coupled device, type array (for example a Reticon
1024C linear CCD type), this application is particularly concerned with use of
specialized matrix array types, including, but not limited to CMOS as well as
CCD
types, capable of random or quasi-random scanning of their respective pixel
outputs.
GOALS OF THE INVENTION
[0022] It is a goal of the invention to provide a triangulation device,
employing at least
one photo-detector array camera and projecting on an object multiple projected
laser
or other light zones, which overcomes reflection, obscuration and other
problems
caused by object surface shape and other discontinuities while operating at
the
highest possible operational speed, with acceptable accuracy and at reasonable
cost.
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[0023] It is a further goal of the invention to provide high density data via
a novel
sensory arrangement in which two camera devices are disposed in the direction
transverse to the object longitudinal axis for viewing light zones projected
along the
object longitudinal axis and for discerning from comparison of data obtained
from the
cameras the range data corresponding to each zone, even in the presence of
object
occlusions, obscurations, or areas of unusual reflectance.
[0024] It is a goal of the invention to provide means to economically and
accurately
measure object length as well as obtain thickness and profile related
information.
[0025] It is another goal of the invention to allow the reconstruction of
object curved
edges and other regions measured at high speed by using interpolated or
extrapolated data, for example to fill in readings obtained.
[0026] It is also a goal of the invention to provide a method for increasing
the
reliability of detection of projected zones on objects with variant
reflectance
characteristics at different portions of their surface.
[0027] It is another goal of the invention to provide a method to control
sensing
characteristics with respect to moving objects using a knowledge of their
movement
and shape.
[0028] It is a still further goal of the invention to provide a triangulation
device,
employing a pair of twin PSD (position sensing diode) array based cameras in a
novel arrangement in the direction of object motion utilizing a projection on
an object
of multiple projected laser or other light zones.
BRIEF DESCRIPTION OF THE DRAWINGS
[0029] FIG. 1 illustrates an example of the prior art, typified by the Leong
et al. and
Cielo et al. patents.
[0030] FIGS. 2a-c illustrate an obscuration problem with moving contoured
objects,
when the camera system is oriented in the plane of the direction of object
motion.
[0031] FIG. 3 is a simplified side view of a preferred two camera embodiment
of the
invention used for measuring moving boards in a sawmill, and further
incorporating
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means to control sensor characteristics such as light power, exposure or data
density
from board shape or location.
[0032] FIG. 4 illustrates an embodiment of the invention similar to FIG. 3,
employing
multiple laser sources and a single array.
[0033] FIG. 5 illustrates a pixel scan and processing embodiment useful with
the
photo-detector array versions of the invention.
[0034] FIG. 6 illustrates an embodiment of the invention similar to FIG. 4,
employing
a line laser source and a single array.
[0035] FIG. 7 illustrates an embodiment of the invention having multiple
sensor heads
and further illustrating a length measurement capability.
[0036] FIG. 8 illustrates a variation on the embodiment of FIG. 4 in which a
PSD
array is used.
PREFERRED EMBODIMENTS OF THE INVENTION
FIG. 1
[0037] FIG. 1 illustrates a typical sensor, of the type disclosed in Leong et
al. or Cielo
et al. references mentioned above, used for generation of cross sectional data
on
boards moving transverse to their longitudinal axis (x axis in the drawing of
FIG. 1).
For simplicity only 3 lasers are here shown, projecting 3 zones on a moving
board.
However sensors in the trade today have up to 24 lasers in such an
arrangement.
[0038] The lasers 101-103 typically project substantially round or elongate
zones
111-113 on the board 118, which are imaged by lens 120, to form images 131-133
on a detector array 140 typically, a linear array such as a Reticon 1024C.
This
arrangement has proven very valuable in practice as it allows measurement of
the
board and the edges thereof without obscuration, and at high speed. The board
is
moving out of the plane of the drawing at typically >3 feet per second.
[0039] However, as the density of points in the longitudinal direction "X" of
the board
increases, this arrangement becomes increasingly cumbersome. The state of the
art
today achieves points on 1 inch centers in the x direction, but has
considerable
difficulty when variant wood is observed, and some aspects and difficulties of
such
measurements are discussed in the McBain application referred to herein.
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CA 02355756 2006-06-16
[0040] It is thus desirable to have a sensor which can cover a much larger
number of
data points in the longitudinal direction (that is achieve a higher point
density in the x
direction), but at the same time operate at high measurement speeds needed to
resolve the same density of points in the "y" direction of motion--
particularly in the
region of the edges of the board where most definition is needed for sawing
operations, and at the same time avoid obscuration and other effects.
FIG. 2
[0041] At this point it is of interest to illustrate triangulation measurement
and the
obscuration problem which occurs if one views the board from another vantage
point
than that of FIG. 1 above, where the viewing direction is oriented
longitudinally.
[0042] FIG. 2 illustrates obscuration and other problems with moving contoured
objects. As shown in FIG. 2a, a laser 201 projects a zone of light 202 onto
the object
204, in this case a moving board having a shaped edges 206 and 207, being
transported on a conveyor 210.
[0043] As disclosed in the references, triangulation measurements of board
location
and shape can be made using a lens such 220 to image the zone on to a photo-
detector 230 which is processed by means 235 to give an output indicative of
the
position of the zone image 240 on the photo-detector. This arrangement is
particularly of use in profiling the shape or thickness of objects in multiple
sections
(spaced out of the plane of the drawing), such as is desirable for determining
parameters of ostensibly flat boards in sawing operations in lumber mills.
[0044] Typically such sensors employ photo-detectors which are photo-detector
arrays of either linear or matrix types, or Position sensing photodiodes
(PSDs) which
provide image position data as a voltage. Where photo-detector arrays are
used,
processing to determine zone image position can be using thresholded centroids
and
multiple centroids as described Pryor et al, derivatives as described in
Liptay-Wagner
et al, U.S. Pat. No. 4,394,683 entitled New photodetector array based optical
measurement systems, or first moment calculations as described in U.S. Pat.
No.
4,219,847 by Pinkney
7
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et al. entitled Method and apparatus of determining the center of area or
centroid of
a geometrical area of unspecified shape lying in a larger x-y scan field, or
by any
other suitable means.
[0045] FIG. 2b illustrates the case when the curved edge 206 of board 204 is
measured, as it passes under the laser beam 251 due to the motion of conveyor
255.
The distance "h" of movement in the z or range direction, of the projected
spot from
the laser beam hitting the board causes a shift 218 of spot image position 219
formed
by lens 220 on the detector array 240, for example a Reticon 1024C.
Alternatively
another spot image position sensing device such as a Position Sensing Diode,
or
"PSD" such as those made by SiTek Company of Sweden.
[0046] FIG. 2c illustrates the case of edge 207 on the opposite side of board
204 as it
passes under the sensor unit shown due to conveyor motion. As can be seen, at
a
certain location on the edge profile, data points such as 241 on board edge
207
cannot be seen by the camera 245 as the camera axis 246 is of necessity at an
angle theta to the direction of projected light incidence 251 in order to
determine
range by triangulation (which range answer can be used to compute the
dimension,
shape, thickness or other variable of the board). When used for such board
measurement, the triangulation angle theta and lens system magnification, is
typically
chosen such that the unit has a range of approximately 8 inches in the
vertical or z
direction, for any given choice of detector array size in the array y
direction.
Resolution then depends on the density of pixels in the array and the degree
of sub-
pixel precision obtainable in determining zone image location.
[0047] If theta is made too small, to avoid as much obscuration as possible,
the
accuracy of the sensor system can be rendered inadequate for the job. Thus in
practical terms, with many boards, and many sensor units, the obscuration of
the sort
depicted can occur.
[0048] In addition to this problem, it should be noted that sometimes severe
lighting
problems can occur, due to the reflection of the incident light from the part,
both due
to the angle with respect to the camera, and the sometimes discolored nature
of the
object surface.
8
CA 02355756 2001-08-23
Figure 3
[0049] Figure 3 is a simplified, partly diagrammatic side view of a preferred
two
camera embodiment of the invention, in which a single projected laser zone 300
is
directed at the object 301 by laser 302 and viewed by two cameras, 310 and
320,
angularly spaced (typically by the same angle, but not necessarily so) in the
direction of
motion of the object on opposite sides of the laser projection axis.
[0050] Use of this two camera arrangement, allows at least camera to obtain an
unobstructed view of the laser zone no matter which edge is present. And where
obstruction doesn't occur, both cameras can be used to view the zone, adding
to the
resolution and redundancy of the system. This is also useful when a depression
in the
board is present, such as a knot, which can also cause one view or the other
to be
obstructed.
[0051] A control algorithm allows one to take the average value of the
position
signal, as long as both fall with in certain parameters of image quality. When
one signal
is not of such quality, the other is used, or a weighted average is employed.
[0052] Another control algorithm usable by the invention, allows the laser
power,
camera integration, or other parameter to be controlled by a knowledge of the
position
and shape of the object. For example as the object comes into view, it is
clear that edge
361 will first be viewed, given the direction of object motion. This means
that camera
310 will be used exclusively for this measurement , and that laser power from
laser 302
will start at a high value indicated of the steep slope and often poor surface
condition
expected (both causing less light to reach the camera). By running the laser
power (or
other control of delivered energy per unit time such as pulse time or
frequency) at near
maximum levels (for a range of object information expected), one can in turn
maximize
the speed of response of the camera, for example by using higher scan rates.
Such
speed of response is desirable for maximum data density and /or production
throughput.
[0053] For a dual camera unit as shown, laser power delivered into the zone
affects
the choice of detector variables for both cameras. When higher power is needed
for the
one camera on an extreme edge of the object, the other camera exposure
variable such
as scan rate or integration time is altered to keep it with in the dynamic
range desired.
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CA 02355756 2001-08-23
[0054] In the middle of the board, between edges 361 and 362, less data is
needed,
as an object such as a sawn board hardly varies in shape in this area. In this
case data
may be taken relatively infrequently. This allows data interface to keep
transferring data
from the edge zone, even while the slower rate of change data is being
acquired.
[0055] Another issue concerns multiple zones, such as figure 4 below or line
type
zones such as depicted in fig 6 below, where all zones, or a continuum of
zones forming
a line are viewed by the same array. In this case laser power in each zone can
be
changed, to suit light requirements of image scanning, but the array
integration time and
scan rate is fixed the same for all zones- if standard matrix array cameras
(e.g. CCD TV
type) are used. However with pixel addressing types this situation can be
improved, as
disclosed in the referenced co-pending application, "High Speed Camera based
Sensors". Use of such is preferable, we have found.
[0056] It is noted that optionally such as system can be advantageously
combined
with sensor such as 380 as described in our co-pending referenced application
for a
lumber grain related defect detection device. Typically such as sensor would
view the
board substantially along a normal to the board as shown, though this is not
necessary
in all cases.
Figure 4
[0057] Figure 4 illustrates an embodiment of the invention similar to figure
3,
employing multiple laser sources disposed in the transverse direction to that
of a
moving object such as a board, and a single matrix photo-detector array. As
shown 3
independent laser sources 400, 401 and 402 direct zones of light, 410-412, in
this case
spot shaped, at a board 420 as shown, traveling on a chain conveyor 423 in the
Y
direction at 30 inches/second. The zones are in a line, parallel to the long
axis (x axis)
of the board, and perpendicular to the conveyor flow.
[0058] A camera 430, composed of photo-detector matrix array 435 and lens 448
is
used to scan the images 440-442 of the projected laser spot zones 410-412 on
the
array. Each zone is analyzed for its position on the array as described below
and for
example in USP 5,734,172, thus providing location data of the board with
respect to the
sensor composed of the laser/camera combination. By taking sequential scans, a
CA 02355756 2006-06-16
complete profile section for the board at each axial zone x location, can be
built up
during the rapid traverse of the board past the sensor station.
[0059] As disclosed in FIG. 3, a second camera such as 460 is often desirable
to
avoid obscuration and provide enhanced results.
[0060] Alternative to the above, and even faster is to address individual
pixels which
need be scanned, while ignoring those pixels in the camera field which carry
little or
no relevant information. This is very desirable in the instant application and
is
described further in the application High Speed Camera based Sensors referred
to
herein.
[FIG. 5
[0061] FIG. 5 illustrates a pixel scan and processing embodiment useful with
the
photo-detector array versions of the invention. For example, consider image
500 of a
spot type projected zone which is detected by photo-detector matrix array 501
which
is of a random line addressable or even random pixel addressable type, for
example
a Photon Vision Systems (Homer, N.Y.) ACS-I T"" active column imager.
[0062] In the first mode of operation, scan lines of the array are chosen
specifically to
correspond to the expected location in the x direction across the array
corresponding
to the axis of the board perpendicular to the direction of motion (and out of
the plane
of the paper in the sectional drawings above).
[0063] To detect the one zone image, one just has to scan a few lines such as
the
four lines 510-513 of the array, in order to characterize the location of the
zone in the
y direction of the array (the direction of change of zone position with change
in board
dimension). One can determine the centroid of the zone portion 500 seen on the
scan lines, and if desired, average the results to substantially improve
resolution and
eliminate errors due to surface condition, as taught in U.S. Pat. No.
4,667,231.
[0064] More zones than one can also be detected this way, and their position
determined, using a single array. For example zone image 530 can be scanned by
lines 540-543. The choice of which lines depends on the zone image location,
and
thence on the projected zone spacing on the object. Choosing to scan only
where
zone image information lies, results in a speed advantage, in direct
proportion to the
number of lines
ii
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of the array divided by the number only needed to be scanned. In this instant
example of two zone images, with 4 lines each needed or desired to find and
characterize same, this means that a 800 line array operating at 30 scans per
second, which only needed to scan 8 lines, would be able to run 3000 scans per
second. This is very useful for high speed measurements. Perhaps more optimal
would be 6 zone images per array, and 1000 scans per second.
[0065] Finally it is noted that when the invention is used with wood or other
materials
having similar grain, that as an option, each of the zones projected can also
be
looked at for elongation of one or more zone image axes and rotation thereof
by the
tracheid effect in order to determine the possible presence of defects such as
knots,
as described in our co-pending referenced application entitled: "High Speed
and
Reliable Determination of Lumber Quality Using the Tracheid Effect" referred
to
herein.
FIG. 6
[0066] FIG. 6 illustrates an embodiment of the invention similar to FIG. 4,
employing
however, a line laser source and a single photodetector array. As shown laser
beam
600 from laser 601 is expanded by cylindrical optical element 605 (refractive,
reflective or diffractive, as desired) to form a line 610 disposed
longitudinally in the x
axis down the long axis of a board, 620 moving transversely in y. In the
particular
case shown the line, or "fan" of points 680 extends past one edge of the board
630
whose position can be found as now described.
[0067] A matrix array 634 of camera 635 whose axis is oriented at an angle
theta to
the projection axis 637, of laser radiation can be used to sense the image 640
formed
by lens 611 of line 610 on the board. As shown in the image, a contour of the
board
in the longitudinal direction is produced by the light section principle, and
the location
of the end 630 (which is typically sawed off) can be determined by the
location of
rapid contour fall of 650 in the image. By sequentially scanning lines of the
array, the
first location at which the line location is for example, 100 pixels less than
the
previous, can be chosen as the true end (not with standing a correction factor
for
parallax given the fan angles involved).
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[0068] Such a system is capable of generating a large number of points along
the
line very quickly--the number equal if desired to the number of pixel lines in
the array
in the x direction, assuming the data as to line centroid location at a given
x location
on the board can be achieved rapidly. This can be preferably achieved though
apriori
knowledge of line location, as disclosed in the High Speed Camera based
Sensors
application referred to herein and disclosing the processing of data using
pixel
addressable cameras to determine the location of individual points on the
projected
line.
[0069] As shown in FIGS. 3 and 4, a dual camera system can be advantageously
employed in this line zone example as well, to deal with obscurations and
light level
problems due to curved board edges in the y, or motion, direction. The line
sensor
having only one line source, has to control this power to give the best
performance at
all the sections of interest. This can be varied on a sectional basis by
choosing which
lines are used to set the power.
FIG. 7
[0070] FIG. 6 illustrates an embodiment of the invention having multiple
sensor
heads, which can be of the multiple zone, or line continuum zone type as
described
above.
[0071] We have found in practicing the invention that a preferable arrangement
is
often to have a sensor which can see line or point zones over an approximate
24
inch length in the x direction of the board or other object, and then to have
sensors,
such as 700-707 of the FIG. 6 type, for example, butted end to end whose 24
inch
sections slightly overlapped, for example in overlap region "A". Typical would
be 16
foot board 720, axially irradiated and viewed by 8 sensors top, 8 sensors
bottom (not
shown for clarity) having two foot swaths each, to allow determination of
thickness
and bow. Note that boards however, can range 10 to 28 feet in length in lines
used in
North America).
[0072] Also as pointed out in FIG. 6, the sensor can also see the end of the
board.
Thus by using data from the sensors such as 700 and 707 covering the board
ends,
780 and 781, and combining end location data obtained in a differential
manner, this
arrangement can provide a length measurement for the board.
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FIG. 8
[0073] FIG. 8 illustrates a different type of camera 801 comprising lens 802
and a
group of PSD (position sensitive diode) detectors 810-812 which detect zone
images
820-822 of zones 830-832 projected on board 840 by lasers 860-862. Readout 850
analyzes the analog outputs of the PSD detectors to determine data concerning
zone
image location and thence board location with respect to the sensor.
[0074] As disclosed above, two cameras of this type, 801 and 803 can be used
in a
device such as that of FIG. 4 to provide obscuration free measurement at high
speeds for example.
[0075] While only three such PSD detectors 810-812 are shown, it is possible
to have
an array of same, for example 128 in a row on a single substrate such as the
in 3D
device recently announced (see www.in3D.nl). This is capable of extremely high
rates as each PSD detector on the array of detectors directly provides the
answer as
to the y location of the zone image on that position of the array, and the
corresponding object location.
[0076] Use of such PSD arrays is described further in the application High
Speed
Camera based Sensors referred to herein.
14
