Seam inspection device

A video seam inspection device includes a video imaging device, a support for a container along an optical axis of the video imaging device and independent light means for illuminating a seam on the container. The two light means include a side light source and a direct light source. The direct light source may be used to transmit light through a ring illuminator which reflects light off a mirror located along the optical axis of the video imaging device. A side light source transmits light to a light transmission means which focuses the light towards the seam of the container at an angle different from the angle of light from the ring illuminator. A can having a cut-out section of the bottom is placed on the support such that the cross-section of the can is exposed and illuminated by each of the light means. The video imaging device then transmits an image of the seam to a display device.

BACKGROUND OF THE INVENTION 
The present invention relates to a can seam inspection device and, more 
particularly to an improved optical seam inspection device which provides 
increased inspection performance due to improved illumination methods. 
The purpose of a can seam inspection device is to accurately measure the 
component parts of a double seam as is typically found around the top of a 
normal soup-type can. Traditionally, seam measurements were taken by 
tearing the seams down into their components parts and measuring them with 
a seam micrometer. This method has been used for many years and is still 
used regularly in canning plants having low product volume. Seam 
micrometers are limited, however, in that the positioning of parts therein 
may vary and thus affects readings, that part measurements vary from 
inspector to inspector due to slight and varying deformations of the part 
caused by personal differences in micrometer pressure. Seam micrometers 
are also time consuming and not practical for high volume production 
inspection. 
An improvement on the traditional method has come in the form of 
video-based can seam inspection devices which display magnified images of 
specially prepared seam cross-sections on a video screen or computer 
monitor where they are measured with video cross-hairs or cursor lines 
that have been calibrated to measurement units. A video-based can seam 
inspection device consists mainly of three groups of components: optical, 
electrical, and mechanical. The optical group comprises a video camera, a 
magnifying lens, a light source, and a mirror, and in some cases a fiber 
optic light pipe. The camera and magnifying lens are located toward the 
back of the device and point directly toward the front of the device where 
the mirror is located. The mirror is mounted vertically and is angled 45 
degrees with respect to the front of the device so that it allows the 
camera to look 90 degrees to the side of the device. The optical axis of 
the camera and magnifying lens are coincidental and also pass through the 
center of the mirror. A small light source is located near the optical 
axis such that it casts light in a direction essentially parallel to the 
optical axis and toward the mirror. In some conventional can seam 
inspection devices a fiber optic light pipe is used to convey the light 
from a light source to a point near the optical axis instead of placing 
the light itself near the axis. The electrical group comprises a power 
supply which powers the light source, and in some devices, also the 
camera. The mechanical group comprises a base, a mirror mount, a can 
platform, and an enclosure. The camera and magnifying lens are attached to 
the base toward the back of the device. The mirror mount holds the mirror 
in a fixed orientation protruding out slightly from the front of the base 
and is attached to the front of the base at a height centered about the 
optical axis of the device. The can platform is also attached to the front 
of the base in an orientation which is essentially horizontal and parallel 
to the optical axis and at a height at which a can seam sample is visible 
to the camera when a can is placed on the platform. The enclosure 
enshrouds all components except for the can platform, the mirror mount and 
mirror. It serves to protect the internal components and also shields the 
camera from stray light. In practice, to perform measurements, a prepared 
can is placed on the platform so that the seam is visible to the camera. 
The light source casts predominantly direct light on the seam via the 
mirror thus illuminating the seam. The illuminated seam reflects light 
back via the mirror to the magnifying lens and camera which picks up the 
enlarged image and transmits it to either a video screen or a computer 
monitor where it is measured with video cross-hairs or line cursors. 
The conventional video-based measurement method has clear advantages over 
traditional methods since it does not measure through contact of the part, 
so is not subject to the same problems of part positioning or measurement 
pressure with its resulting part deformation. Measurement accuracy is 
improved as is inspection efficiency. 
Although the conventional video-based can seam inspection device has clear 
advantages over traditional methods, there are several drawbacks which 
stem from the prior art's dependence on predominantly direct illumination. 
These drawbacks affect the accuracy of the device and its use over a wide 
range of materials. An ideally prepared seam is perfectly flat across its 
surface, uniformly reflective and composed of metal. Although direct 
illumination is very appropriate in this situation, it becomes less 
appropriate the further the seam departs from ideal. Due to the quality of 
the saws used in the preparation of seam samples, many prepared seams have 
rounded or nicked edges that make the seam appear smaller under direct 
illumination. Still other seams, containing regions with disparate 
reflectivities, such as plastic or composite seams, when viewed under 
direct illumination, lack enough definition to reveal key edges of the 
seam components, thus can not be measured at all. Also, in situations 
where a seam must be analyzed for attributes other than dimensional, as in 
a visual inspection, direct illumination severely limits visual cues that 
reveal surface detail and texture. 
It is therefore the object of the present invention to provide an improved 
video-based can seam inspection device which utilizes improved 
illumination methods that both provide increased measurement accuracy and 
add the capability of the device to effectively measure non-metallic 
seams. 
SUMMARY OF THE INVENTION 
The aforementioned objects may be achieved by a seam inspection device 
constructed in accordance with the principles of the present invention. 
The seam inspection device includes an optical display device, a means for 
supporting a container along an optical axis of the video imaging device, 
and a dual means for illuminating a seam on the container. 
The dual means for illuminating a seam on the container may include a side 
light source and a direct light source. The optical display device may 
comprise a video imaging device. A mirror may be located along the optical 
axis of the video imaging device and oriented at a forty-five degree angle 
relative to the optical axis. The means for supporting a container along 
the optical axis should allow the mirror to be placed within the can to 
allow an image of the seam to be obtained from the reflection off the 
mirror. 
The direct light source illuminates the seam of the container with light 
directed substantially ninety degrees from the seam. The side light source 
illuminates the seam of the container with light directed substantially 
oriented at a shallow angle to the seam. 
The direct light source may be oriented to transmit light to a ring 
illuminator. The ring illuminator may be coaxially positioned relative to 
the optical axis to transmit a ring of light towards the seam of the 
container. The ring of light may be reflected off the mirror towards the 
seam of the container. 
The side light source may be oriented to transmit light to a light 
transmission means capable of transmitting light from the side light 
source towards the seam of the container at an angle not normal to the 
seam. The light transmission means may include a fiber optic light 
transmitter. 
The side light source and direct light source may be controlled by a means 
for independently varying the intensity of the side light source and 
direct light source. The means for independently varying the intensity of 
the side light source and direct light source may include a power supply.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
In accordance with the present invention, the video-based can seam 
inspection device includes three groups of components: optical, 
electrical, and mechanical. The optical group comprises a video camera, a 
magnifying lens, a direct light source, a side light source, a ring 
illuminator, a light pipe, and a mirror. 
Referring to FIG. 1 and 2, the camera 1 and magnifying lens 2 may be 
located toward the rear of the device and point directly toward the front 
of the device where the mirror 7 is located. The optical axis A--A of the 
camera 1 and magnifying lens 2 are coincidental and also pass through the 
center of the mirror 7. The mirror is mounted vertically and is angled 45 
degrees with respect to optical axis A--A so that it allows the camera to 
focus its image 90 degrees from the optical axis A--A. The ring 
illuminator 5 is located toward the front of the device and is positioned 
such that its central axis is coincidental with and coaxial with the 
optical axis A--A of the camera and its radiant side directed forward 
toward the mirror essentially parallel to the optical axis. The ring 
illuminator 5 radiates a ring of light coaxial with optical axis A--A to 
mirror 7. The center of the ring illuminator 5 is hollow to allow the 
camera 1 a clear view through it to the mirror 7. A direct light source 3 
is positioned at the input end of the ring illuminator's input cable 15 
such that its light is directed into the cable. A light pipe 6 is located 
towards the front of the device with its output end located within the 
mirror mount 11 towards the object side of the mirror 7 and slightly below 
the optical axis A--A and is positioned such that its radiant axis points 
upward and away from the mirror at an inclination angle slightly off 
vertical (FIG. 3). The input end of the light pipe 6 is located some place 
within the device. The side light source 4 is positioned at the input end 
of the light pipe 6 such that its light is directed into the input end of 
the light pipe 6. 
The electrical group comprises a dual voltage power supply 8 and a computer 
interface 9. The dual voltage power supply powers the two light sources. 
The computer interface 9 is connected to the dual voltage power supply 8, 
and in operation, to a computer (not shown) in order to provide power 
commands. 
The mechanical group comprises a base 10, a mirror mount 11, a can platform 
12, and an enclosure 13. The camera 1 and magnifying lens 2 are attached 
to the base 10 toward the back of the device. The ring illuminator 5 and 
the light pipe 6 are attached to the base near the front of the device. 
The mirror mount 11 holds the mirror in a fixed orientation protruding out 
slightly from the front of the base and is attached to the front of the 
base at a height centered about the optical axis of the device. The can 
platform 12 may also be attached to the front of the base in an 
orientation which is essentially horizontal and parallel to the optical 
axis and at a height at which a can seam sample is visible to the camera 
when a can is placed on the platform. The enclosure 13 enshrouds all 
components except for the can platform 12, mirror mount 11, mirror 7 and 
the output end of the light pipe 6. It serves to protect the internal 
components and also shields the camera 1 from stray light. In practice, to 
perform measurements, a prepared can is placed on the platform 12 so that 
the seam is visible to the camera. The two light sources 3,4 convey light 
via the ring illuminator 5 and the light pipe casting a combination of 
both direct and side light on the seam. The illuminated seam reflects 
light back via the mirror to the magnifying lens and camera which picks up 
the enlarged image and transmits it to either a video screen or a computer 
monitor where it is measured with video cross-hairs or line cursors. 
The improved video-based seam inspection device in accordance with the 
present invention contains several advantageous features. The ring 
illuminator 5 provides more uniform illumination than a single light 
source placed near the optical axis A--A because it is an area source not 
a point source of light. The side light source and its associated light 
pipe provide illumination at a shallow angle to the seam which effectively 
accentuates the detail and texture in the image. One of the advantages of 
this device in accordance with the invention, is that each light source 
3,4, i.e., the side and direct illuminator, may be independently varied. 
This independent light source variation allows for the optical 
illumination of each scene by adjusting the intensity of the side light 
source 4 and direct light source 3. The low angle light from the light 
pipe working in concert with the direct light from the ring illuminator 5 
can provide a mixed lighting situation which is superior to either alone. 
The low angle light intensity from the light pipe 6 and the direct light 
intensity from the ring illuminator 5 can be independently varied to 
provide the optimum lighting mixture for a given inspection situation. The 
low angle light intensity and the direct light intensity can be controlled 
by a computer via the computer interface 9 making it possible to store and 
instantly recall light settings appropriate for a given inspection 
situation. 
FIGS. 1 and 2 indicate an embodiment of the present invention as 
incorporated in a video-based seam inspection device. The device comprises 
a base 10, a mirror mount 11, a can platform 12, an enclosure 13, a video 
camera 1, a magnifying lens 2, a ring illuminator 5, a light pipe 6, a 
mirror 7, a direct light source 3, a side light source 4, a dual voltage 
power supply 8, and a computer interface 9. 
The base 10 runs the full length and width of the enclosed portion of the 
device and is the one part to which all other components are fastened and 
in this capacity serves its most important function as the foundation for 
the optical axis A--A. It may be composed of a metal alloy and be thick 
enough to hold all parts attached to it in a fixed alignment. The base may 
be blackened with a dull finish either through anodization or flat finish 
painting in order to reduce the possibility of any reflective glare or 
stray light entering into the video camera 1. 
The optical axis A--A may be parallel with the top of the base 10 and at 
right angles to the front and rear edges of the base. The optical axis is 
preferably established by optical centerline of the video camera 1 at the 
rear of the device and the center of the mirror 7 at the front of the 
device. 
The video camera 1 is preferably attached to the base toward the back of 
the device and points along the optical axis A--A directly toward the 
front of the device where the mirror 7 is located. The camera 1 is 
preferably a self-contained solid state device, preferably a high 
resolution CCD variety with an array of 510.times.492 picture elements or 
better and a format of 2/3" or 1/2", such as the SONY model XC-57 or the 
Cohu model 3310. The CCD variety is preferred over the tube variety for a 
number of reasons including greater accuracy, less image distortion, 
higher impact and vibration resistance, and small size. The camera 1 is 
preferably powered by either 12 Vdc or 12 Vac depending on the variety and 
should include its own internal voltage regulation. The output video 
signal may be obtained from a standard video connector located on the back 
end of the camera. The camera is also fitted with C-mount threads at its 
front to accept stock lenses or adapters such as extension tubes. 
The magnifying lens 2 may preferably be a multiple element CCTV or 
enlarging lens designed for either 2/3" or 1/2" format cameras fitted with 
C-mount threads. However, other types of lenses may be used. It should 
have an aperture adjustment ring for the final light sensitivity 
adjustment of the seam inspection device. The lens 2 is attached to either 
the video camera 1 or to the base 10 at a distance in front of the image 
plane of the camera that will achieve the desired magnification 
(approximately 50.times.). The effective magnification of the device will 
be found to be the product of two ratios: object distance/image distance 
and screen size/imager size, where the object distance is the distance 
from the object (in this case, the sample seam) to the front principle 
point of the lens, the image distance is the distance from the rear 
principle point of the lens to imager (light sensitive pickup array) of 
the camera, and where the screen size is the diagonal measure of the 
display device, and the imager size is the diagonal measure of the 
camera's imager. The magnifying lens must also be positioned so that its 
optical axis coincides with the optical axis A--A of the device. It can be 
attached to the camera using its C-mount threads or if it is to be mounted 
an appreciable distance in front of the camera, it can be mounted to a 
lens mount which is firmly attached to the base 10. 
The ring illuminator 5 may be a cylindrically shaped assembly whose central 
axis coincides with the optical axis A--A and whose front face faces the 
mirror 7. Ring illuminator 5 may comprise a substantial number of optical 
fibers encased in a metal shell that determines their orientation and 
configuration. On the front face, the output end of the optical fibers are 
arranged to form a thin circular ring whose included fibers are 
constrained to point in a direction toward the mirror and parallel to the 
optical axis A--A. Also, the ring illuminator may comprise a ring shaped 
light such as a fluorescent light. The area of the assembly inside the 
ring is hollowed out to allow the video camera 1 a clear view through it 
to the mirror. The inside The inside surface of the hollow may be dulled 
to discourage unwanted reflections. The input end of the optical fibers 
exit through the side of the assembly as a single tightly packed group 
called the input cable 15 which for protection is encased in a rigid or 
flexible hose-like casing. Optimally, the diameter of the fiber bundle at 
the input tail should be sized to be approximately equal to the diameter 
of the input light beam it is expected to receive. The input end of the 
input cable 15 is placed so that its axis coincides with that of the 
radiant axis of the direct light source 3. The preferred material for the 
assembly's metal shell is a non-corrosive stainless steel alloy since it 
may come in contact acidic or salty foods. However, other materials may be 
used. The ring illuminator 5 is securely attached to the base between the 
magnifying lens 2 and the mirror 7 and is oriented so that its axis 
coincides with the optical axis A--A and is placed at a distance from the 
mirror that will afford the mirror the most uniform illumination. The use 
of a ring illuminator as a source of direct lighting is particularly 
advantageous, especially when viewing metallic samples. Conventional 
video-based seam inspection devices use primarily a single direct light 
source which, since it approximates a point source of light, causes 
illumination problems such as glare, "hot" spots, and dark undefined areas 
which hinder accurate inspection. A ring illuminator properly placed will 
reduce these problems since the light it casts is not point based and 
produces a wider and more evenly distributed area of light. 
The mirror 7 is preferably a front surface mirror formed of thin crown 
glass with a reflective metal coating deposited on its front surface. The 
mirror 7 may be either square or circular in shape and should have a 
minimum width of at least three times the length of the largest seam the 
device will be used to inspect. The mirror 7 may be held by the mirror 
mount 11 at the front of the device where it is oriented vertically with 
respect to the base 10, angled 45 degrees with respect to the front of the 
device in a way that allows the camera to focus on an object located 90 
degrees to the side of the device, and positioned so that the optical axis 
A--A passes through its center. The mirror is permanently attached to the 
mirror mount with adhesives and has its reflective surface facing out. 
The mirror mount 11 may be an approximately cube-shaped part with four 
solid faces, its top, front, left side, and bottom. Its rear face and 
right side have been cut away forming a diagonal inside face which rests 
at a 45 degree angle to both the rear and right side. This inside face 
forms the mounting surface for the mirror 7 where the mirror is 
permanently attached with adhesives. The mirror mount 11 may be fixedly 
attached to the front of the base so that it protrudes out from the 
enclosed portion of the device. It is mounted at a height and position 
that allows the optical axis A--A to pass through the center of the 
mirror. To facilitate easy placement of a can, the corner formed by the 
junction of the front and left side of the mirror mount can be cut away as 
shown in FIG. 2, thus leaving a sloping left side. The mirror mount may be 
preferably made of stainless steel for wear and corrosion resistance. 
The light pipe 6 is a conduit for conveying light from the side light 
source 4 to an area inside the mirror mount 11. The light pipe 7 includes 
a tightly bundled group of optical fibers encased in stainless steel 
tubing and bent to conform to the design needs. The output end of the 
light pipe 6 enters the underside of the mirror mount and points upward 
and away from the mirror at an inclination angle slightly off vertical. It 
is positioned so that it casts light at a very shallow angle on the seam. 
The input end of the light pipe 6 is mounted so that its axis coincides 
with the radiant axis of the side light source 4. 
The direct light source 3 and the side light source 4 are both preferably 
focused beam lamps of either the incandescent variety or the LED variety. 
Both have two power leads each, should operate in the voltage range of 0 
to 5 volts dc and draw no more than 0.5 amperes. Their brightness should 
increase with increasing voltage. The beam of each lamp should be focused 
into a narrow beam of approximately parallel rays for maximum light 
transmission efficiency. Both light sources are preferably located within 
the device and positioned to point directly into their respective fiber 
optic bundles. The radiant axis of the direct light source 3 should 
coincide with the axis of the input end of the input cable 15 of the ring 
illuminator 5. The radiant axis of the side light source 4 should coincide 
with the axis of the input end of light pipe 6. The focused beam diameters 
of both the two lamps should be sized to match the diameters of the input 
ends of their respective fiber optic bundles. 
The dual voltage power supply 8 is located on the inside of the device and 
is assembled from a variety of common electronic components including 
resistors, capacitors, diodes, integrated circuits and transformers that 
are mounted on a printed circuit board. As inputs it receives 120 Vac or 
240 Vac power from the mains and two control signals from the computer 
interface. It outputs two independently variable voltages which power the 
two lamps 3,4 and determine their brightness. The circuit portion that 
receives the control signals from the computer interface is high impedance 
so draws only a few milliamps of current from the computer or driving 
device. The output stage of the each power supply channel can supply a 
current of up to 0.5 amperes at a voltage in the range of 0 to 5 volts 
depending on an input control voltage which can vary in the range of 0 to 
10 volts. The dual voltage power supply has a total of five incoming and 
four outgoing leads. Two incoming leads are connected to AC line voltage 
via a power cord. The other three incoming leads are connected to the 
computer interface 9. Two of the outgoing leads are used to power the 
direct light source lamp 3. The other two are used to power the side light 
source lamp 4. 
The computer interface 9 is a multi-pin D-shaped connector which carries 
control signals between the device and the outside world. On one side it 
is joined directly to input circuitry of the dual voltage power supply 8, 
on the other it is joined to an external device via an appropriately wired 
mating connector. The external device can be any device, such as a 
computer, or voltage controller, which can output a selectable direct 
current voltage in the range of 0 to 10 volts. Only three of the pins in 
the interface are connected. Two pins are connected to the direct light 
control voltage line and the side light control voltage line, 
respectively, of the input circuits of the dual voltage power supply. The 
third pin connects to the power supply as the control voltage return. By 
varying the voltage on either or both these control lines, a connected 
device may control the brightness of the two light sources in the seam 
inspection device. 
The can platform 12 is a thick surface ground sheet of stainless steel for 
holding the can in position during inspections. It may be rectangular in 
shape with a notch cut out of its rear portion to make room for the mirror 
mount 11. It must be thick enough to prevent any flexing when a can is 
placed on it. It is mounted horizontally to the front of the base so that 
it is parallel to the optical axis A--A and at a height which allows a can 
seam sample to be visible to the camera when a can is placed on the 
platform. 
The enclosure 13 wraps around the base on four sides forming a box like 
metal shell around the internal components. It enshrouds all components 
except for the can platform 12, mirror mount 11, and the output end of the 
light pipe 6. It adds stiffness to the device and serves to protect the 
internal components from foreign matter and stray light. 
To operate the video-based can seam inspection device a can 14 is cut in 
two places on the end (i.e., bottom or top) of the can 14 (FIG. 1). One 
cut is made along the radius and toward the center of the can 14-- the 
other is made a slight distance to one side but substantially parallel to 
the first cut. The material between the two cuts is moved out of the way 
by pressing it in toward the inside of the can 14, thus, creating an 
opening in the bottom and side of the can revealing the cross-section of 
the double seam 16 located around the periphery of the top or bottom of 
the can. With a portion of the end and side of the can removed, the can is 
then placed cut side down on the can platform 12 so that the mirror mount 
11 enters the inside of the can via the cut away portion of the can 14. 
The operator moves the can to contact the right side of the mirror mount 
so that the seam 16 is visible and in focus on the display device. Light 
from the ring, illuminator 5 and direct light source transmits through the 
opening in the side of the can and is reflected off the mirror 7 to 
illuminate the seam. In addition, the output end of the light pipe 6 
located within the mirror mount 11 is oriented to transmit light towards 
the cross-section of the cut in the seam 16 without being reflected off 
mirror 7. If necessary, the operator then adjusts both the direct light 
source 3 and side light source 4 intensity levels via the computer 
interface for the best image of the seam on the display device. The seam 
may then be visually inspected and/or measured using video cross-hairs or 
line cursors on the display device. If a computer is interfaced with the 
seam inspection device, it can be used to automatically store the 
measurements of an inspection. In addition, optimum settings for both 
direct light source 3 and side light source 4 intensities can be stored by 
the computer and recalled instantly, thus making the video-based 
inspection of a wide variety of seams very fast and simple.