Note: Descriptions are shown in the official language in which they were submitted.
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FASTENER VERIFICATION SYSTEM
This invention relates to automated fastener installation systems, and
more particularly to systems for verifying that the correct fastener is ready
for
installation in a work piece, and that it is oriented correctly for
installation in the
work piece.
BACKGROUND OF THE INVENTION
High volume fastening machines used for large structures such as
airplane wings for commercial transports are designed to operate rapidly and
precisely, which is a practical necessity considering that a fastener is
inserted
about every 1.5 inches in multiple rows along the entire length of the wing,
which
in a medium sized airplane can extend about 50 feet long. The operation, even
with modern high speed equipment, is very labor intensive and time consuming.
is The necessity for speed has resulted in some time consuming and costly
production problems. If a rivet is fed to the rivet hole in a cocked or
inverted
position and the ram is not halted in time, it can damage the wing panel.
There
have been instances in which the damage was so severe that in was necessary
to scrap the"entire wing panel, an enormousiy costly event. Other problems
include a rivet of the wrong length or diameter in the rivet feeder. A wrong
size
rivet will ordinarily not damage the wing panel, but must be drilled out and
replaced with a correctly sized rivet before the wing panel can be used to
build
up the wing. The wasted time and cost of such errors demonstrates the need for
a system that can examine the orientation and size of a rivet while in the
rivet
holder before it is inserted into the rivet hole.
These same considerations apply with equal or more force to the insertion
of threaded fasteners in wing panels and other large structures that are
fastened
by automated equipment. Threaded fasteners used in the aerospace industry
include conventional helically threaded fasteners that engage a threaded nut,
and lock bolts that have circular threads gripped by a swaged collar. They are
usually high strength materials, including titanium alloys, and they are
harder
and stronger than the aluminum structures they are used in. When such a
fastener is fed by an automatic fastener insertion machine in a cocked or
inverted position, the likelihood of damage is even greater than when aluminum
rivets are used. If anything, the need for a fastener size and position sensor
is
even greater for threaded fasteners than it is for rivets.
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The problem has existed for many years and numerous attempts have
been made to solve the problem. A fastener scanning system, shown in U.S.
Patent No. 4,823,396, was developed to scan fasteners on route to the fastener
insert device to ensure that the fastener is the correct size and oriented
correctly, that is, tail first. This did not solve the problem of cocked
fasteners
held in the fastener holder being crushed at a cocked angle into the panel.
Moreover, the rivets used in some airplane wings are so called "ice box
rivets"
which must be kept at a low temperature until they are upset. The low
temperature of such ice box rivets could cause fogging or frosting of the
viewing
glass in the '396 patent and interfere with the image of the fastener.
A light-interrupt system is used on some riveting machines to confirm that
a rivet is held in the rivet holder before the machine is operated to press
the rivet
into the rivet hole to prevent damage to the panel by the ram when no rivet is
present. This light interrupt system does not detect cocked or inverted
rivets,
nor can it distinguish between correctly sized and incorrectly sized rivet.
Experienced operators can often sense when a cocked fastener is being
pressed against the panel, and can often stop the machine before extensive
damage is done. The operator perceives sound and vibration from the operation
of the machine in the feeding of a cocked rivet which tells him that the rivet
squeezing operation is not normal, so he can halt the ram motion before the
panel has been ruined. However, there is some reaction time before the
operator can act, and the operator may be distracted at the moment with some
of
the other tasks in operation of the machine, so damage occurs occasionally
even with attentive operators.
Image processing systems are know for circuit board terminal examination
and hole location checks, and other such applications. Indeed, a camera is
used on some automatic riveting machines to view the rivet after upsetting and
shaving to give the operator real time information about the process so he can
correct it if the results begin to appear unsatisfactory. However, the use of
an
image processing system in the inner mechanisms of an automatic fastener
installation machine presents special problems that have deterred those
skilled
in the art from successfully applying the image processing technology to this
application. The environment is extremely cluttered with a tangle of tubes,
wires, and moving mechanisms of many kinds, and this makes it nearly
impossible for
the image processing system to discern the fastener from the background.
Lights placed to illuminate the machine, the panel and the controls can
interfere
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with the operation of the image processing system. Lubricants and cutting
fluids
in use in the machine can become airborne as aerosols and can coat the camera
of an image processing system to blur the image it creates. The machine must
often be adjusted and a camera in the heart of the machine, especially an
existing machine into which the camera is to be retrofitted, can interfere
with
= adjustment or replacement of mechanisms in the normal course of operation.
Accordingly, there has long been a need in the art, and particularly in the
aircraft industry, for a fastener inspection system that could examine a
fastener,
in real time, after it is injected into a fastener holder in preparation for
insertion
into a hole to be drilled into a wing panel or other work piece, and
accurately and
reliably determine if the fastener is the correct size and is oriented
properly, that
is, held vertically centered in the holder with the head up. The system should
serve as a quality control tool to anticipate when problems in the process are
beginning to develop so that the problem can be corrected before it interferes
with quality or the production rate, and also facilitate the compilation of a
record
to demonstrate to management, to the customer, and to government authorities
that the process is functioning properly as designed.
SUMMARY OF THE INVENTION
Accordingly, it is an object of this invention to provide an improved
method of examining a fastener in an automatic fastener installation machine
to
ensure that only properly sized and oriented fasteners are being installed, so
that tipped, inverted or incorrectly sized fasteners will be rejected before
installation. Another object of this invention is to provide an improved
method
for operating an automatic fastener installation machine that incorporates a
fastener size and orientation check while allowing the installation rate to be
as
fast or faster than the rate was without the fastener checking step. Yet
another
object of this invention is to provide an image processing system for
examining
the orientation and size of a fastener held in a fastener holder of an
automatic
fastener installation machine and comparing it with the size of the fastener
designated for insertion at that location in the work piece, and for
preventing
insertion of any fastener that is the wrong size or wrongly orientation. Still
another object of this invention is to provide an image processing system, for
examining the size and orientation of a fastener in a fastener holder, that
can
= 35 operate reliably in a hostile, dirty, cluttered and visually noisy
environment
existing in the heart of an automatic fastener installation machine.
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These and other objects of the invention are attained in an image
processing system having a pair of cameras aimed at the ejector end of a
fastener feed mechanism where the feed mechanism injects a fastener into a
fastener holder. Two back lights are supported opposite the cameras on the
other side of the fastener holder and illuminate the fastener in the fastener
holder with a uniform back light through a blank white diffuser on each back
light to facilitate the generation of a clean sharp silhouette image by the
cameras.
The image is measured along a series of horizontal gauge lines and along a
vertical gauge line along the centerline of the fastener by detecting edges of
the
1o fastener, that is, where the light changes from light to dark in the course
of a few
pixels at one edge, and then back to light again at the other edge. Those
measurements, taken in the form of pixels and converted to length
measurements by the image processing system processor, are transmitted to the
system controller and compared with the dimensions of a correctly sized and
oriented fastener held in that fastener holder. If the dimensions correspond
within a certain range of tolerance, the machine is enabled to proceed with
the
machine cycle. If the dimensions do not correspond, the operator is notified
by a
message on his monitor and he can operate the appropriate control to feed a
correctly sized fastener into the holder, pushing the incorrectly sized or
oriented
fastener out.
DESCRIPTION OF THE DRAWINGS
The invention, and its many attendant objects and advantages, will
become more clear upon reading the description of the preferred embodiment in
conjunction with the following drawings, wherein:
Fig. 1 is a perspective view of a representative fastener installation
machine on which the image processing system of this invention is mounted;
Fig. 2 is a perspective view of the upper head of the fastener installation
machine shown in Fig. 1, showing the fastener injector aligned with the moving
tool shuttle, and showing the pressure foot assembly exploded away for clarity
of
illustration;
Fig. 3 is an enlarged view of the fastener holder and ram aligned with the
pressure foot in the machine shown in Fig. 1, with the fastener holder shown
without a fastener for clarity of illustration;
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Fig. 4 is a schematic plan view of the lights and camera of the invention,
shown aimed at a fastener holder of the fastener installation machine shown in
Fig. 1;
Fig. 5 is a schematic end elevation of the fastener installation machine
= s shown in Fig. 4, showing the lights of the invention aimed at the fastener
holder
of the machine, and showing the camera brackets on the opposite side of the
machine, but omitting the camera for clarity of illustration;
Fig. 6A is a schematic side elevation of the structure shown in Fig. 5;
Fig 6B is a schematic side elevation of the structure shown in Fig 5;
Fig. 7 is an exploded view of the camera ands camera mounting and
support brackets, illustrating the structure used to mount the camera in the
machine shown in Fig. 1;
Fig. 8 is an exploded view of the lights and light mounting and support
brackets, illustrating the structure used to mount the lights in the machine
shown
in Fig. 1;
Fig. 9 is an exploded view of the camera and camera support and
mounting brackets shown in Fig. 7;
Fig. 10 is an exploded view of the lights and light support and mounting
brackets shown in Fig. 8;
Fig. 11 is an elevation of the light assembly (without the mounting
brackets) shown in Fig. 10;
Fig. 12 is a plan view of the light assembly shown in Fig. 11;
Fig. 13 is a system schematic diagram of the control system for the
fastener inspection system of this invention;
Figs. 14-17 show side elevation images made by the side camera shown
in Fig. 4 of rivets in a fastener holder in various positions in which the
rivet can
be held;
Figs. 18-20 show oblique angle elevation images made by the oblique
angle camera shown in Fig. 4 of rivets in offset, cocked and straight
positions,
respectively.
DESCRIPTION OF THE PREFERRED EMBODIMENT
= Tuming now to the drawings wherein like reference characters designate
identical or corresponding parts, and more particularly to Fig. 1 thereof, an
= 35 automatic fastener installation machine 30 is shown mounted on tracks 32
for
movement along an X axis of travel. Machine includes a ladder 34 by which
an operator may ascend to one or more operating positions, one of which is
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shown at 36. The machine 30 supports a large C frame 38 having an upper
head 40 and a lower head 42 projecting perpendicular to the X axis of travel
and spanning a work zone in which a work piece such as an airplane wing skin
is supported horizontally on a series of spaced supports (not shown). A s
description of the invention will use the orientation of the machine in Fig. 1
for
reference although obviously the invention could be used in other orientations
and is not dependent on the orientation shown in Fig. 1.
The upper head 40 includes a transfer head 44 mounted for swiveling
through an arc shown in Fig. I as the "A Axis .". This swivel enables the
tools
io on the transfers head 42 to be presented normal to the curved surface of
the
wing skin along the line of rivets being installed by the machine 30. A tool
shuttle 46 is mounted for linear movement along the X axis in the transfer box
44 and supports three tools shown in Fig. 2, namely a ram 48, a shaved spindle
50, and a drill spindle 52. The position of the tool shuttle 46 is controlled
by a
15 pair of pneumatic cylinders 54 and 56 by which the three tools on the tool
shuttle
46 can be positioned in order in line with the center line 58 through a
opening in
a pressure foot 60. The pressure foot is mounted on the transfer box 44 by
hydraulic cylinders 62 so that it can raise and lower the pressure foot 60 to
press
a pressure foot bushing 64 against the wing skin. Simultaneously a
20 corresponding ram on the lower head 42 ascends to press a stringer against
the
underside of a wing skin and this clamp arrangement between the upper and
lower heads 40 and 42 is maintained during operation of the tools.
A rivet injector 68 is mounted on the transfer box 44 axially lined along the
Y axis - with the ram 48. The rivet injector 68 receives rivets from a
pneumatic
25 feed system connected to a tube 70 which delivers the rivet in a head up
position to the inner end of the rivet injector 68. A pneumatic cylinder 72 on
the
rivet injector 68 operates a rivet ram (not shown) in the rivet injector 68 to
push
the rivet out of the rivet injector and in between a pair of rivet fingers 74
of a rivet
holder 76. The rivet fingers 74 are mounted in opposed slots in a cylindrical
3o anvil 78 mounted at the lower end of the ram 48. The rivet fingers 74 are
spring
bias toward one another by a spring loaded caliber (not shown) which engages
the rivet fingers 74 at opposed recesses 80 a the top of the rivet fingers 74.
When the tool shuttle 46 is in its left most position with the inner end of
the rivet injector 68 positioned to inject a rivet into the rivet fingers 74,
the drill
35 spindle 52 is aligned with the center line 58 through the pressure foot 60
and the
machine is in positioned to drill a hole for injection of the rivet. The next
step
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would be for the shuttle 46 to travel to its extreme right hand position
illustrated
in Fig. 2 and for the ram 48 to descend to push the anvil 78 against the head
of
the rivet to drive it into the hole drilled by the spindle 52. However,
occasionally
the rivet injector 68 injects a rivet so that it is caught and held by the
fingers 74
in a non vertical or inverted position, or occasionally stacked rivets may be
fed
between the fingers in the same feed operation.. In any of these events, that
is,
whenever a single rivet is not fed to the fingers 74 and held vertically
centered
between the fingers, the force exerted by the ram 48 on the anvil 78 could
force
a wrongiy position rivet against the top of the wing skin which could cause
io damage to the wing skin. The damage is occasionally severe enough that the
wing skin can not be repaired and must be scrapped, at an enormous cost.
To ensure that a single rivet of the correct dimensions is held properly
oriented in the fingers 74 before operation of the ram to push the rivet into
a hole
drilled by the spindle 52, an image processing system is provided to create an
is image of the rivet held in the fingers 74, and those images are analyzed
and
compared with data corresponding to a correctly sized and positioned rivet of
that location. The image processing system includes two cameras, shown in
Fig. 4, aimed at the rivet fingers 74 of the fastener holder 76 for acquiring
images of the rivet in the rivet fingers, and a back light opposite each
camera on
20 the other side of the rivet fingers to backlight the rivet.
The cameras include a side view camera 80 and an oblique view cameras
82 mounted at 35 from the "Y" axis on an angle bracket 84 which in turn is
connected to an upright support bar 86. The support bar 86 is removably
connected to a mounting knuckle 88 by way of a cylindrical tenon 90 which fits
25 into a cylindrical opening 92 in the knuckle 88 and is held in a vertical
position
by a key slot 94 on the cylindrical tendon 90 which mates with a key 96 in the
cylindrical opening in the knuckle 88. The knuckle 88 is slit at 98 and has a
handle 100 which can be tumed to close the slit 98 to grip the cylindrical
tendon
90 tightly in the opening 92 and the knuckle 88.
30 The two cameras 80 and 82 are identical so that description of the
camera 80 will also apply to the camera 82. The camera 80, shown exploded in
Fig. 9, includes a scanning video camera 102 such as model CV-31 SH made by
Motion Analysis Company Naturally, other cameras could be used and in fact
have been used in this application. The camera 102 is held in a cylindrical
35 opening 104 and is gripped therein by squeezing closed a slit 108 through
the
edge of the angle bracket 84 with a screw 106 which tightens the opening 104
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around the camera 102. A camera support ring 110 is fastened to the face of
the
bracket 84 coaxially around the opening 104 and is connected by screws or the
like to a cylindrical housing 112 which encloses and protects a lens such as a
6
millimeter SNX 612 lens from Tamron Company The lens 114 is screwed into s the
video camera 102 in the usual manner.
A protective cover disk 120 is connected to the front end of the cylindrical
hoUsing 112 with screws extending through holes 122 in the disk 120 and
threaded into holes drilled into the edge of the cylindrical wall of the
housing
112. A fitting 124 for connection to a flexible air tube (not shown) is
screwed into
1o the side of the housing 112 adjacent the front end thereof communicating
with
the front end of the housing by way of an axial hole drilled into the edge of
the
cylindrical wall of the housing 112 that intersects the hole into which the
fitting
124 is threaded.
The disk 120 has a stepped recess 126 which extends from a rectangular
ls opening 128 through the center of the disk 120 to a necked down portion
adjacent one edge of the disk 120. A cover plate 130 is seated in the stepped
edges of the recess 126 and is supported on the center portion adjacent the
rectangular opening 128 by two ribs. A hole 132 in the necked down portion of
the cover plate 130 aligns with the axially hole in the housing 112 that
20 communicates with the fitting 124, so that air delivered to the fitting 124
passes
through the hole 132 and into the recess 126 behind the cover plate 130 to
biow
air into the opening 128. In this way, a steady stream of clean air blows
outwardly through the opening 128 to prevent ingress of airborne contaminants
such as drilled chips and lubricants.
25 A glass plate 118 is glued over the opening 128 and , together with the
disk 120 provides a sealed enclosure for the lens 114. The glass plate 118 is
made of filter glass which passes only light in the near infrared spectrum
produced by the back lights.
As shown in Fig. 10, the back lights include two back light units 146 and
30 148 mounted on a straight flange 142 and an oblique flange 144 of a
transition
bracket 140. The transition bracket 140 is connected by screws or the like to
a
vertical light bracket removabiy connected to a support knuckle 88' by a
cylindrical tenon 90', identical to the corresponding structure 88 and 90 used
to
support the cameras 80 and 82. The knuckles 88 and 88' are each connected
35 through elongated holes 136 to the transfer box. An identical pair of
support
knuckles (not shown) is attached to the transfer box in a position spaced away
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from the rivet= injector 68 to provide a convenient mount to which the lights
and
cameras may be removed when the area around the rivet injector must be
cleared for service or for changing components of the machine.
An air knife 1,50 is attached to the top of the light units 146 and 148 as
s shown in Figs. 10 and 11 to create an air curtain in front of the light
units to
militate against deposits of lubricants and debris from the machine operation,
such as drill chip fragments. The air knife structure, shown in Fig. 12, is an
angled air plenum having a series of vertical holes drilied adjacent the under
side of the front edge to direct a downwardly flowing curtain of air in front
of the
io back lights 146 and 148. The air knife has an opening 154 for attachment of
an
air hose coupling for delivery of clean air to the air knife.
The light units 146 and 148 are identical, so a description of one will
serve for both. The light unit 146 includes a housing 156 having a cable
connector 158 by which an electrical cable 160 for delivery of electrical
power at
15 12 volts to the light unit 146. A perforated board 152 is mounted in the
housing
156 and 55 light emitting diodes 164 are mounted in the perforations. A
diffuser
166 is placed over the diodes 164 and is covered with a scratch resistant
glass
plate 168.
The control system for the invention includes an Allen-Bradley PLC-5
20 programmable controller in an enclosure 170, and a personal computer and
monitor in an enclosure 172, communicating with an existing Allen-Bradley 7320
controller that controls the operation of the machine 30. The enclosure 170
also
contains suitable AC and DC power supplies, circuit breakers and appropriate
terminal blocks for~ nnection to field devices and other systems. The personal
25 computer is an IBM compatible unit communicating with the PLC-5 through an
RS-232 port. The PC includes image processing boards availabie from Cognex
Company a
In operation, the automatic fastener installation machine is triggered by
the Allen-Bradley 7320 controller to move to a new rivet location position.
While
30 the machine is moving, the 7320 controller sends a signal to the PLC-5
informing
it of the fastener to be installed at the new location. The code informs the
PLC-5
of the length and diameter of the fastener to be installed. While the machine
is
moving, the tool shuttle 46 moves to the left in Fig. 2 to position the
fingers 74 of
the rivet holder adjacent the rivet injector 68. A rivet is escaped from the
35 temporary storage mechanism and forced by compressed air through the tube
70 into the rivet injector, and the pneumatic cylinder is pressurized by a
signal
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from the 7320 controller to feed a rivet to the rivet fingers. On retraction
of the
ram in the rivet injector 68 a signal is transmitted from the 7320 controller
to the
PLC-5, and 200 milliseconds later the PLC-5 triggers the image processing
system cards in the PC to acquire an image from both the side view camera 80
and the oblique view camera 82.
The image processing system uses edge detection tools to locate the
position of the rivet fingers 74 in the image. The edge detection tools
include
reference tools to place the actual measurement tools of the image processing
system vertically and horizontally in position to locate the position of the
fastener
with respect to the rivet fingers 74. This allows some flexibility of movement
of
the fingers with respect to the camera since fingers of various sizes are used
for
placing different size rivets. The reference tools scan a horizontal line 180
positioned to intercept the left rivet finger 74L, shown in Fig. 14, and finds
the
right edge 182 of the finger 74L using grayscale values which are exaggerated
by the silhouette character of the image created by the backlite rivet fingers
74.
The image processor then counts several pixels to the right and establishes a
vertical reference line 184 which it scans down to find the lower edge of the
rivet
finger 74L. The image processor counts several more pixels down and
establishes a lower reference line 186 which is used to find the center of the
2o rivet held in the fingers 74 to establish a centerline gage 188 for
measuring the
rivet length, and for positioning a series of line gages shown in Figs. 16 and
18-20 for determining rivet diameter, whether stacked rivets are present, and
whether the rivet is held in an inverted or cocked position.
The image from the oblique view camera 82, shown in Figs. 14-17, is
processed to determine the length, diameter, status, inverted status, missing
status and held by the head status of the rivet. To determine the length, the
centerline gage 188 is placed vertically along the center line of the rivet.
The
image system examines the pixel values recorded along the center line of the
rivet and detects the top and bottom edges by changes in the grayscale value.
Because of the back lighting of the rivet, the brightest part of the image
will have
a pixel value near maximum and a pixel value of zero at the black part of the
image where the rivet is blocking the back light. There is typically a gradual
change in grade scale values and the image system performs a first derivative
looking for the place the pixel value drops from a lighter value to a darker
value.
The apparent position of the edge transition can be determined to a high
degree
of accuracy by doing a center of mass calculation which gives a value that is
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resolved to a subpixel position or a non-quantitized decimal instead of a
whole
number. This is well within the accuracy requirements of the application in
which rivet dimensions vary by about one sixteenth inch, so the length and
diameter measurements are easily correlated to the various rivets sizes which
are used in a typical structure. If an intermediate size is detected it is
identified
as a mis-sized rivet and is rejected just as any other mis-sized rivet would
be.
Since the edge tool provides the rivet length in pixels and calibration has
established the height of the pixel in inches, it is simple multiplication to
determine the actual rivet length. The measured length is then checked against
io the expected length and, if the measure length is outside of the tolerance
limits
or rivet expected at that location, the image processor triggers a"wrong
length"
message to be issued by the PC, the machine is interrupted, and the true
length
of the rivet is provided on a display to the operator and is logged on the log
file.
To determine the diameter of the rivet, a series of edge tools is placed
horizontally across the rivet at regular intervals along the length of the
rivet.
Starting from one side, the edge tool reports its edge transition points along
the
length of the edge tool. The first two transition points are used to detect
the
diameter of the rivet body if it hangs down far enough below the fingers. This
measured diameter is compared to the expected diameter that was defined in
the rivet date provided by the 7320 controller. If the diameter exceeds
predetermined limits, the machine operation is interrupted, the operator is
notified of the "wrong diameter" and the error is logged to the log file.
To determine if two stacked rivets are present, as shown in Fig. 16, the
vertical edge tool information is checked for length. If the length of the
rivet
exceeds 1.5 times the expected length for the rivets specified in the
information
provided by the 7320 controller, the image processor generates a signal which
is
sent to the 7320 controller to interrupt the operation of the machine process,
a
"stacked rivet" notice is sent to the operators monitor, and the error is
logged to
the log file.
Inverted rivets, shown in Fig. 17, are detected by comparing the edge
data from a horizontal gauge lines above and below the gripping point of the
fingers. The diameter of the rivet, that is the diameter of the shank below
the
head, is known from the data provided by the 7320 controller, so if the edge
tools report a valid body diameter above the location at which the edge tool
reports the rivet head diameter, the image processor declares the rivet
"upside
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down", interrupts the machine cycle, notifies the operator and logs the error
to
the log file.
The image processor identifies missing rivets by the fact that none of the
horizontal or vertical tools present edge transition data where a rivet is
expected
and the results that are presented are consistent with blank rivet fingers.
The image processor identifies rivets held by the head by measuring the
distance from the top of the rivet using the vertical edge tool, to the bottom
of the
fingers identified by the location of the vertical finger reference gauge 182.
If
that distance is smaller than a predetermined limit, the rivet is declared
"held by
the head," the machine cycle is interrupted and the operator is notified.
The image created by the side view camera 80, shown in Figs. 18-20 is
used to determine the tipped status of the rivets. The image processor detects
edge transitions in a tipped rivet image by comparing a series of adjacent
edges
and adjacent horizontal edged tools and when it detects that there is a series
of
edges detected along these edged tools that are not vertically aligned, that
is,
produce values from the vertical centerline through the fingers 74, and that
the
edges do not protrude beyond the rivet fingers an equal amount on both sides,
a
tipped rivet is identified. The image processor generates an error signal that
interrupts the machine cycle and a "tipped rivet" message is displayed to the
operator on the monitor. An image of the tipped rivet in the fingers is
displayed
and recorded on the image record system.
When a rivet error is detected by the image processing system, the
machine cycle is halted and the operator is informed of the problem and can
see, in real time, the image of the rivet in the fingers both from the side
and from
oblique angle. If the operator concludes that it is an error, he can, with his
hand
controller, trigger the injection of a new rivet by the rivet injector into
the fingers
74, which displaces the rivet already held between the fingers. Assuming that
the new rivet is the right size and correctly oriented in the fingers, the
machine
cycle proceeds automatically to drill the hole, shift the tool shuttle 46 to
position
the ram and rivet holder vertically above the newly drilled hole, and inserts
the
rivet into the hole using the anvil 78 at the lower end of the rim 48 to push
the
rivet into the hole.
Obviously, numerous modifications and variations of the disclosed
embodiment will occur to those skilled in the art upon reading this
description.
Accordingly, it is expressly to be understood that these modifications and
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variations, and the equivalents thereof, may be practiced while remaining
within
the spirit and scope of the invention, wherein we claim:
13
SUBSTITUTE SHEET (RULE 26)
