U.S. patent number 3,917,947 [Application Number 05/470,761] was granted by the patent office on 1975-11-04 for foreign particle detector.
This patent grant is currently assigned to Borden, Inc.. Invention is credited to Marvin J. Fenton.
United States Patent |
3,917,947 |
Fenton |
November 4, 1975 |
Foreign particle detector
Abstract
This apparatus inspects products for presence of foreign
fragments while the product is in motion and includes a timing
screw driven by a synchronous motor, an X-ray source for
intermittently pulsing an X-ray beam which is in phase with the
motor in response to actuation by the product disposed at an
inspection zone, an image intensifier, monitor, photomultiplier,
conventional circuitry for defining inspection zone on the product
which also sub-divides the zone into sections whereby each section
is scanned and compared to a pre-set value and then rejected if the
pre-set value is exceeded. Sensitivity can be varied in each
section by raising or lowering the threshhold level of the pre-set
value. A number of masks are used to facilitate the inspection
process. X-ray mask is interposed in front of the X-ray source to
flatten out the X-ray beam; outline mask disposed between the
product and the image intensifier shields background radiation;
product mask disposed on the output side of the image intensifier
compensates for variations in product consistency and container
irregularities; and the edge mask at the output side of the monitor
blocks out background light from the monitor.
Inventors: |
Fenton; Marvin J. (Stamford,
CT) |
Assignee: |
Borden, Inc. (Columbus,
OH)
|
Family
ID: |
26985703 |
Appl.
No.: |
05/470,761 |
Filed: |
May 15, 1974 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
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327060 |
Jan 26, 1973 |
|
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Current U.S.
Class: |
378/57; 209/524;
209/589; 378/147; 378/98.2; 209/566; 378/95 |
Current CPC
Class: |
G01N
23/043 (20130101); B07C 5/3416 (20130101); G01V
5/0016 (20130101) |
Current International
Class: |
B07C
5/34 (20060101); G01N 23/02 (20060101); G01N
23/04 (20060101); G01V 5/00 (20060101); G01N
023/02 () |
Field of
Search: |
;250/312,322,358,360,359,510 ;209/111.5 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Borchelt; Archie R.
Attorney, Agent or Firm: Maskas; George P. Kap; George A.
Mast; Daniel D.
Parent Case Text
This is a continuation of application Ser. No. 327,060, filed Jan.
26, 1973, now abandoned.
Claims
I claim:
1. Inspection apparatus comprising X-ray source connected to an
electrical power source for delivering X-rays across a path in the
form of discrete beams, means connected to and being in phase with
said power source for continuously moving test objects along said
path, means actuated by said test objects for actuating said power
source to allow a beam of X-rays to be emitted as one of the test
objects becomes registered at an inspection station, detecting
means for receiving the X-rays, means for analyzing the X-rays
received by said detecting means and comparing them with a pre-set
value, and means for rejecting certain of the test objects in
response to actuation by said analyzing and comparing means.
2. Apparatus of claim 1 wherein said means for continuously moving
the test objects is a timing screw driven by a synchronous motor
synchronized with said power source.
3. Apparatus of claim 2 wherein said X-ray source is a
self-rectified X-ray head and said synchronous motor is a permanent
magnet synchronous motor.
4. Apparatus of claim 3 including an X-ray mask interposed between
said X-ray source and the test objects as they move past the
inspection station, said X-ray mask being provided for the purpose
of rendering the X-ray beams more uniform in intensity.
5. Apparatus of claim 4 wherein said analyzing and comparing means
includes an image intensifier with an output screen which
electrically amplifies the X-ray image of a test object and
converts it to a visible minified image on the output screen and a
TV camera where the image is converted to video signals which are
electronically inverted so that the image is dark except where
additional X-ray attenuation occurs as a result of the presence of
a foreign particle in a test object.
6. Apparatus of claim 5 including a product mask disposed on the
output side of said image intensifier for compensating variations
in the test objects.
7. Apparatus of claim 6, wherein the test objects are glass jars
containing an edible substance and wherein said product mask is a
film negative of a control test object taken on the output side of
said image intensifier and is used to compensate for variations in
density of the edible substance and various irregularities on or in
the glass jars.
8. Apparatus of claim 7 wherein said analyzing and comparing means
further includes a monitor which receives the image from said
camera intensifier after the image has passed through said product
mask, and a level detector; said apparatus further including an
edge mask on the output side of said monitor for blocking out
extraneous light from said monitor, a photomultiplier detector
which converts the image from said monitor into electrical signals,
means for amplifying the electrical signals from said
photomultiplier detector and means for integrating the amplified
electrical signals from said photomultiplier detector and rejecting
the glass jar for which the integrated value exceeds certain
pre-set value.
9. Apparatus of claim 8 wherein said analyzing and comparing means
further includes means for defining a main inspection zone, means
for sub-dividing said main zone into secondary zones for processing
inspection in each of the secondary zones, means for separately
integrating each of the secondary zones, means for comparing the
integrated value with a pre-set value, and means for rejecting a
test object if the pre-set value is exceeded.
10. Apparatus of claim 9 including means for separately varying
sensitivity in each of the secondary zones.
11. Apparatus of claim 1 including a timing logic circuit for
initiating inspection of a test object by triggering said X-ray
source in phase as a test object comes into registry for inspection
at inspection station.
12. Apparatus for inspecting containers filled with a product
comprising an X-ray source for delivering at an inspection station
X-rays across a path in the form of discrete pulses; an X-ray mask
disposed in front of said X-ray source for imparting uniformity to
the X-ray pulse; conveyor means for continuously moving the
containers through the inspection station so that said X-ray mask
is interposed between said X-ray source and the containers as the
containers move through the inspection station; an outline mask
which blocks out X-rays passing beyond the outline of the
containers as the containers move through the inspection station
and allows passage of the X-rays falling within the outline of the
containers; an image intensifier with an output screen which
electrically amplifies the image formed by X-rays and converts it
to a visible image on the output screen, said image intensifier
being disposed on the output side of the said outline mask; a
product mask disposed on the output side of the said image
intensifier for compensating container and product variations; a TV
camera which receives the image through said product mask and
converts the image to video signals which are electrically inverted
so that the image is dark except where additional X-ray attenuation
occurs as a result of the presence of a foreign particle in the
container; and means for comparing light derived from the
containers and rejecting the container when a pre-set light value
is exceeded.
13. Apparatus of claim 12 wherein said X-ray source is a
self-rectified X-ray head which operates on AC power, said
apparatus further including a monitor which receives electrical
signals of the image from said TV camera and converts them to
visual images, an edge mask on the output side of said monitor for
blocking out extraneous light from said monitor, a photomultiplier
detector for converting the image from said monitor into electrical
signals, means for amplifying the electrical signals from said
photomultiplier detector and means for integrating the amplified
electrical signals from said photomultiplier detector and rejecting
the container for which the integrated value exceeds a certain
pre-set value.
14. Apparatus of claim 13 wherein said X-ray mask consists of an
aluminum backing and a layer of material selected from auto body
solder, lead and mixtures thereof, said material having a generally
convex exterior outline.
15. Apparatus of claim 13 wherein said outline mask is made of lead
and said product mask is a film negative of a control container
taken on the output side of said image intensifier.
16. Apparatus of claim 15 including means for defining a main
inspection zone, means for subdividing said zone into secondary
zones for processing inspection in each of the secondary zones,
means for separately integrating each of the secondary zones, means
for comparing the integrated value with a pre-set value, and means
for rejecting a test object if the pre-set value is exceeded.
17. Apparatus of claim 16 including means for varying sensitivity
in each of the secondary zones.
18. Apparatus of claim 17 wherein said conveyor means includes a
timing screw driven by a synchronous motor synchronized with an AC
power source, said apparatus including a timing logic circuit
connected to the AC power source for triggering said X-ray source
in phase with said synchronous motor.
19. Apparatus of claim 18 wherein said motor is a permanent magnet
synchronous motor and said edge mask is made from cardboard.
20. Automatic inspection apparatus comprising an X-ray generator
for delivering X-rays on signal across a path; means for
continuously moving test objects along said path; means for
actuating said signal by the test objects to allow a pulse of
X-rays to pass through a test object; means for detecting the X-ray
image field passing through the test objects; means for converting
the X-ray image field to a visual image field; means for converting
the visual image field to electronic values; means for processing,
analyzing and comparing the electronic values with pre-set values;
and means for automatically rejecting certain of the test objects
in response to said comparing means.
21. Apparatus of claim 20 including an X-ray mask interposed
between the test objects and said X-ray generator for rendering the
X-rays more uniform in intensity.
22. Apparatus of claim 20 wherein said means for converting X-ray
image field to visual image field is an electron optical
intensifier.
23. Apparatus of claim 20 wherein said means for converting visual
image field to electronic values is a TV camera.
Description
Detection of foreign particles in processed foods has been a
critical problem in quality control programs. Most of the companies
in the food processing, food manufacturing or food distribution
business have, at one time or another, been subjected to costly and
protracted litigation because the product they make, sell or
distribute contained a foreign particle which caused injury to the
plaintiff. Awards in such cases have been stunningly high with the
result that this and other considerations have prompted a
development of detectors or inspection devices which could detect
and reject a jar of food product containing a foreign particle.
The basic problem with such devices is one of detecting millimeter
and larger size foreign fragments within filled containers at
realistic throughput rates. Detection of foreign fragments with
X-ray equipment results from localized attenuation caused by the
fragment which, with presently available equipment, requires a
difference of attenuation of at least about 10 percent to be
detectable using an X-ray radiation imaging system.
A device has now been developed for automatically inspecting filled
containers for the presence of foreign fragments such as glass,
metal or stone. Variation in image contrast is used to generate an
electrical signal which controls a rejection mechanism. Inspection
is performed on containers which are continuously moving on a
conveyor and the rejected containers are automatically sorted from
the main stream of containers. The inspection process has no
harmful effect on the food in the containers, the container itself
or the operating personnel. Product flavor and appearance are also
unaffected by test conditions and the exposure levels are too low
to achieve any sterilizing effect. The maximum external radiation
at peak tube voltage and peak testing rate is 0.5 mR per hour. This
level occurs close to the tube shield at the edge of the opening
for the test beam. This location is impossible to reach with more
than a small portion of the human body. An installed physical guard
on the conveyor lines prevents the very low level of radiation from
reaching any part of the operator's or observer's body. Inside the
conveyor line guard, the stray radiation level is so low as to fall
under the category of "Exempt Protective Installation" promulgated
by U.S. Department of Commerce, Handbook No. 93, p. 1, item
2-1.
Sensitivity of the inspection device depends on many variables
including glass container characteristics and normal variations in
product density. Container characteristics include consistency of
wall thickness, angle between the wall and the base, consistency of
base thickness, presence of ribs or ridges or areas of increased or
decreased thickness for decoration or for other purposes,
contamination of glass itself, and the like.
The probability of detection is also influenced by particle
position in the jar relative to the X-ray field of view. A particle
at the edge of the field of view must be larger than a particle at
the center of the field of view to be detected. The field of view
subjected to inspection by the X-ray imaging process is limited by
an outline mask which excludes from inspection wall of the jar,
base and the closure. Configuration of the outline mask is matched
to a particular jar.
The invention is described below in connection with the
accompanying drawings in which:
FIG. 1 depicts structural outline of the inspection device as it
relates to inspection of a sealed glass container moving at
conveyor speed when the inspection is performed in a period of a
few one-hundredths of a second;
FIG. 2 is an electrical block diagram showing the major logic
functions of the system which senses, by a combination of
electronic and optical means, the localized attenuation caused by a
foreign particle within the container and subsequently rejects the
container.
The preferred embodiment of the invention disclosed in FIGS. 1 and
2 is adapted to electronically and optically inspect a filled glass
container for the presence of foreign particles. Glass jars 12 are
shown disposed on and moved by conveyor 14 which includes link
chain 16. Jars 12 should be spaced about one inch apart to
facilitate triggering of the photo cell when a jar enters the
inspection area and to facilitate ejection of the jars containing
foreign matter at an appropriate point. As the inspection area is
approached, the jars are impelled by spring biased guide rail 18
against timing screw 20 and cradled in the screw flights. The
timing screw can be obtained from Earnst Manufacturing. The timing
screw is driven by motor 22 through belt 24. A motor such as
permanent magnet 3600 RPM synchronous motor manufactured by McLean
under model No. 47GBH1B9, which has a 15:1 gear reducer, may be
used. The motor is hooked into the power line which also supplies
power to the electronic portion of the inspection system. By virtue
of being driven by the synchronous motor which is provided with a
15:1 gear reducer, the bottles are mechanically in phase with the
power line. Since the jars are in phase with the power line, the
inspection area is located as close as possible to the terminal
point of the timing screw so that when a jar enters the inspection
area, an in-phase pulse of X-rays shall be emitted to initiate an
inspection cycle.
Although it is not a prerequisite to efficient operation of the
inspection device, the speed of the belt should be adjusted to the
linear movement imparted by the timing screw in order to avoid
motion non-uniformities and the problems associated therewith. In
the preferred embodiment, the belt speed is 90 feet per minute and
due to a 15:1 gear reduction, the inspection rate is 240 jars per
minute. At this rate, each slot in the timing screw is filled.
Although at lower rates one or more of the slots will be empty, the
inspection cycle will take place in exactly the same time and rate
independent of the input rate. It should be apparent that the rate
can be increased well beyond 240 jars per minute.
The use of the timing screw with the synchronous motor is a simple
and practical solution to a problem of registering a moving test
object with a timed burst of X-rays without having to
intermittently arrest the motion of the conveyor or the test
object.
It is the timing screw, which is in phase with the power line, that
delivers the jar to the inspection area at the instant that a pulse
of X-rays is released. As the jar leaves the timing screw, it
enters the inspection area in which it is interposed between X-ray
source 26 and image intensifier 28. The X-ray source used in the
preferred embodiment is Americana X-ray head model WX900 and image
intensifier is the Machlett dynascope 9TZ including DF2 power
supply. In this position, the jar interrupts light beam from the
trigger lamp 30 to trigger photocell 32 which causes an electrical
pulse to be generated from the power line and the inspection cycle
to begin. Since the jar is mechanically in phase with the power
line which also produces the trigger pulse, the jar will be in
registry for a shot of X-rays when the initial negative cycle of AC
line causes the X-ray pulse to be generated. Duration of the X-ray
pulse is one-half of a complete line cycle of 1/120th of a second.
The succeeding positive half cycle of the line initiates image
scanout by the closed circuit TV system 34 which continues for a
complete line cycle or 1/60th of a second. The TV camera is the
Visual Educon Dage 800 camera with separate mesh vidicon and
Concord TVL 14 close-up lense. As should be apparent, the complete
inspection cycle in terms of duration is 1/40 of a second (1/120 +
1/60).
Positioned between the X-ray source 26 and jar 12 is an X-ray mask
31 which functions to flatten out the gross non-uniformities of the
X-ray beam itself. The mask can be made with an aluminium backing
1/16 inch in thickness with a layer of solder or lead thereon
facing the X-ray source. This layer is generally convex and about
1/8 inch thick. The shape of the X-ray mask is dictated by the fact
that the X-ray beam is strongest at the center and weakens towards
the fringes. This mask produces a field which is within 30 percent
of being uniform.
If a foreign particle is present in a jar, the X-rays passing
through the jar will impinge upon the front surface of the image
intensifier and will form an image which is attenuated in the
region of the foreign particle. Since diameter of the entrance
pupil in the image intensifier is 9 inches at most, this permits
products of up to 8 inches in height to be inspected in one pass.
Larger articles can be inspected by passing them through the X-ray
field a number of times until all of it has been inspected. The
X-ray shadow in the image intensifier is amplified electrically
about 5000 times and appears as a visible minified image on
intensifier's output screen 29, which is approximately 1 inch in
diameter.
An outline mask 36 is positioned between the jar and the front face
of image intensifier 28. The outline mask can be made of lead or
any other material which can effectively absorb and thus block
X-rays. The mask has the outline of a jar which corresponds to the
jars being inspected. The outline mask is necessary to block X-rays
outside of the bottle outline from entering the image intensifier.
In absence of the outline mask, the powerful unattenuated X-rays
would diffuse into the bottle outline and blanket out any foreign
particles disposed at the edge of the jar.
Another mask is also positioned between the output screen 29 of
image intensifier 28 and TV camera 34. This is a product mask 38
which is simply a film negative of a control jar taken from the
output side of the image intensifier. This mask compensates for
difference in density of the various products and bottle
configuration such as shape of bottle, ribs or ridges on the
bottle, etc. A different mask is made and used for different
products. The non-uniformities due to the X-rays in the image on
the output side of the product mask are further reduced by the
product mask to about 3 percent.
After passing through the product mask 38, the light is detected by
the closed circuit camera 34 and converted to video signals which
are inverted, gated and applied to the TV monitor 40. TV monitor 40
is the Sony View Finder Monitor model AVF 3200. Since the image is
electronically inverted, it appears on the monitor as dark except
where additional attenuation is obtained from the foreign particle.
Therefore, when a bottle is being inspected, a bright spot is seen
when a foreign particle is present in addition to a partial outline
of the bottle.
The light from monitor 40 is passed through edge mask 42. This mask
functions to block out extraneous light outside the jar outline and
can be made of any suitable material which is not transparent.
After passing through edge mask 42, the light is converted into
electrical signals by photomultiplier 44, amplified and detected by
a level detector. The photomultiplier tube is the RCA 931 A tube.
When the light output exceeds a pre-set level, a reject pulse
occurs, a count is stored in the reject counter and in a shift
register. The shift register meters off a fixed distance on the
conveyor by sensing links in the link chain 16 by means of the
counting photo cell 46 and operates reject solenoid 48 at a fixed
distance from the inspection area. When the bottle reaches reject
station 50, it is ejected by reject solenoid 48. In the preferred
embodiment, ejection takes place 38 links past the inspection area.
Since each link is five-eighths inch, this distance is about 2
feet. If only one reject pulse is registered, only one actuation of
the reject solenoid will occur. If a series of reject pulses are
inserted, a series of reject pulses will occur, all delayed by the
pre-set distance.
The major logic functions of the system are illustrated by the
block diagram in FIG. 2.
When the leading edge of a jar interrupts the light from trigger
lamp 30, a pulse is generated by trigger photocell 32 which is sent
to the timing logic 52 which initiates the inspection cycle. Since
the energy for the X-ray pulse is directly derived from the power
line, the inspection cycle is also phased to the power line. The
power line, therefore, is also used in the timing logic. When the
line starts to go negative subsequent to the trigger, it is sensed
by the timing logic and a high power pulse is generated for the
X-ray source. Although this pulse has a duration of one-half cycle
of the line, that is 1/120th of a second, because of the nonlinear
relationship between voltage and usable X-ray energy, only a
portion of this 1/120th of a second is actually used for the
detection process. Therefore, the effective exposure time is only a
few milliseconds. From the timing logic 52, a pulse is sensed by
the zone and multi-vibrators unit 64 where, in conjunction with a
gate in the processing amplifier and gates unit 54, the monitor is
blanked only for the portion covering the edge of the jar. This is
done by triggering a multivibrator in unit 64 which closes a gate
in unit 54 for a split second that it takes to blank the edge of
the jar. The multivibrators are set separately in each zone and are
adjusted to completely blank out the monitor in the leading edge
region of the jar. After initial half cycle of the line when a
burst of X-ray energy is released, scanout takes place during the
succeeding full line cycle.
As previously described, the shadow image of the jar produced by
the X-ray source is converted to a visible minified image by image
intensifier 28, changed to a scan video signal by TV camera 34,
passed through processing amplifier and gates unit 54 to TV monitor
40. Signal from camera 34 through sync processor 74 triggers
multivibrators in unit 64 to generate zones which are scanned in
the manner described. Unit 54 is part of camera 34. The output
light from the monitor is detected by photomultiplier detector 44,
applied to gated integrator 56, the level detector 58 and reject
one shot 60, which generates a pulse when a reject is present. This
pulse is entered into the shift register 62 and after a pre-set
number of pulses are counted, which corresponds to a given conveyor
distance, the reject solenoid 48 is actuated and the jar containing
a foreign particle is ejected.
The system is completely insensitive to signals except during the
unblanking and zone periods. The unblanking and sensitivity section
is formed by quite a straight forward process. First, there is a
general rectangular zone which is sufficiently large to encompass
the entire jar. The zone is defined by zone and blanking
multivibrators in unit 64 in conjunction with processing amplifier
and gates in unit 54. This zone defines the inspection area within
the outline of a jar. In the vertical direction, four additional
zones are used. These may be set from top to bottom for any regions
of the jar desired.
Since a jar is normally not completely cylindrical or uniform in
wall thickness throughout vertical dimensions, the sensitivities
may be increased in the areas of uniformity and somewhat decreased
in the areas where the masking cannot remove all the
non-uniformities. As the camera continues to scan the image in the
horizontal direction, a sync pulse is applied to zone and blanking
multivibrators in unit 64 which triggers a blanking multivibrator
in the same unit. In each of the four zones, in addition to
multivibrators which blank out the leading edge of the jar, a
second multivibrator determines the length of the inspection
period. With the jar completely cylindrical, all of these second
set of multivibrators are set the same. In regions where the jar
has different cross sections, the multivibrators, that is the
inspection time, is correspondingly altered.
The integrator 56, which is used to accumulate the electrical
signals generated from the light output from the monitor 40, is
likewise dead whenever the monitor signals are blanked. This
provides double insurance against any noise spikes entering the
system and causing false rejects.
With a large, completely cylindrical jar, approximately 200
horizontal scan lines would be observed from the top to bottom of
the jar. Each of the four zones, therefore, would contain about 50
lines. At the end of each of these zones, the integrator which
accumulates light is reset. Therefore, the light from the particle
would need be larger than the accumulated light from 50 of normal
scanlines. In addition, however, within each four zones are 10-line
multivibrators 66, which dump or reset the integrator at the end of
each 10 horizontal lines. After every scan of the 10 lines,
integrator 56 is cleared by means of gate unit 68. Therefore, the
light output from the particle need be only larger than the light
output from 10 horizontal lines containing no foreign matter.
The monitor is quite dark except for some random noise and the
particle produces a bright image within the outline mask. This
light, then, generates the defect signal. The left outline or the
leading edge of the bottle is completely blanked electrically. In
those regions of the bottle where the diameter changes cross
sections throughout a single zone, the light from the right hand
side of the bottle is blanked by the outline mask. The larger the
particle or the more dense it is, the larger will be the output
signal. Zone sensitivities 70 are individually set in zone selector
72 for the particle size desired within a given zone. Selection of
the particular sensitivity or threshhold level of light in any
desired zone adds another dimension to operation of the inspection
device described herein.
The circuitry utilized in the inspection device described above is
conventional as evidenced by the Webb et al. U.S. Pat. No.
3,580,997 and especially by Tatham et al. U.S. Pat. No. 3,390,769.
These patents are hereby wholly incorporated by reference to
complete description of the circuitry as they relate to the
inspection device described herein. In fact, the bulk of the
circuitry can be purchased in a single unit from Electro Data
Concepts under designation 3047. This unit includes timing logic
52, processing amplifier and gate unit 54, sync processor 74, zone
and blanking multivibrators unit 64, 10-line multivibrators 66,
gate unit 68, integrator 56, level detector 58, reject one shot 60,
shift register 62, zone selector 72 and zone sensitivities 70.
The embodiment described and illustrated herein is the preferred
embodiment. It should be understood that modifications therein can
be made within the spirit and scope of the invention. For instance,
this invention need not necessarily be employed in connection with
any particular article. The substance inspected can be in glass,
metal or plastic containers or can be packaged in plastic or paper
bags. Definition of the term "containers" shall mean anything which
can be used to store or package articles whether it be paper or
plastic bags or jars, bottles or cans made of substantially rigid
material such as metal, glass and plastic. In some applications,
the use of the monitor, which converts electrical signals from the
camera into visual images, can be dispensed with and the signals
from the camera processed in a known manner. Under some operating
conditions, the inspection device can be successfully operated
without the edge mask which can be made of any material which does
not transmit light, such as cardboard. Although spacing of about 1
inch between test objects is recommended, this spacing can be
reduced and even entirely eliminated so that the test objects are
in contact during the inspection process. The circuits in the
inspection device are solid state, integrated circuits which should
be isolated from high power AC source, but here again, isolation
may not be required at some sites. Generally speaking, minimum
detectable size for glass containers is roughly one-half the wall
thickness of the containers but this can be still further reduced
and under certain operating conditions, it may be possible to
detect foreign particles of a size approaching the distance between
the scan lines. Since the inspection device is so adjusted that
registry of a test object at the inspection station is within
1/16th of an inch, if registration is off by more than that value,
the test object will be rejected as if it contained a foreign
fragment. The 1/16th of an inch tolerance can be adjusted to any
desired level. Although a constant potential X-ray head can be
used, a self-rectified X-ray head utilizing AC power is preferred
because it costs a great deal less and is particularly adapted to
the type of inspection performed herein. It is known that the X-ray
beam is most intense at its central point and for this reason, an
X-ray mask is interposed to flatten out the X-ray beam. With this
in mind, the exterior outline of the mask is therefore, convex
although a filler can be used to make the exterior surface of the
mask dimensionally flat and still perform the same function.
The distance between the end of the timing screw and the inspection
station is so adjusted that when a test object enters the
inspection station, it will coincide with the triggering of the
X-ray source. For this reason, the distance between the timing
screw and the inspection zone should be kept to a minimum. The
inspection station coincides with the position of a test object in
which it is in registry with the test object outline in the outline
mask.
* * * * *