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BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates in general to sidewall inspection devices for
containers and in particular to a method and apparatus for adjusting an
inspection device for glass bottles.
2. Description of the Prior Art
The use of optical scanning devices for inspecting the sidewalls of
containers is well known. Numerous devices, such as those shown in U.S.
Pat. Nos. 3,708,680 and 3,716,136 have circuitry including means for
receiving and interpreting light passed through or directed onto an item
under inspection. Such devices incorporate either a visual display for
comparison of the item or employ a device capable of producing a
resistance proportional to the intensity of light directed thereon.
Whether the output of such a device is visual or electrical in nature, it
is eventually compared against a model to determine if the item under
inspection is suitable as to size and construction and is without flaws,
cracks, or foreign objects. Such devices are each intended to provide an
automated inspection means for checking, as in a moving column of bottles,
single or multiple objects in that moving column.
U.S. Pat. No. 2,798,605 is representative of the prior art inspection
circuits and utilizes a cathode ray tube to display the object being
inspected. A scanning generator subassembly provides a vertical sweep
circuit and a horizontal sweep circuit for the scanning element of a
cathode ray presentation tube provided in a monitor unit. An iconoscope is
provided for receiving a focused image of the bottle under inspection. The
monitor is arranged to receive the video output of a selected camera unit
and is controlled in its electrostatic deflection circuits by the same
sweep voltage waves employed in the deflection circuits of the selected
camera unit, so that is reproduces the picture image focused on the
iconoscope.
SUMMARY OF THE INVENTION
The present invention concerns a method and apparatus for performing the
setup of an inspection device for objects such as glass bottles and for
displaying an output of the inspection device. A digitized video signal
representing a point of inspection is generated by a photodiode camera.
The digitized video signal is generated to an adder and to a latch in
which is stored the digitized video signal from the previous point of
inspection. A signal representing the difference between the present
digitized signal from the adder and the previous digitized signal from the
latch is generated and compared with a stored threshold level for the
current point of inspection. If the threshold level is exceeded, the
difference signal is stored as an event signal.
When the entire bottle has been scanned, the stored information is
generated to a means for displaying the stored signals on a video screen.
The signals are displayed in a two-dimensional representation of the
surface of the inspected object, as if the object had been cut through one
side and unwrapped for display. The stored signals include the location of
each detected defect, thus enabling the display means to properly position
the defect on the video screen relative to the representation of the
unwrapped object. By utilizing the apparatus in this manner and varying
the threshold levels, the operator can determine what the proper threshold
levels should be for inspecting the particular object.
The apparatus can also be utilized to monitor the output of the inspection
device. The latch is disabled, the threshold signal is cleared to zero,
and only one vertical inspection sweep is made of the object. The data is
then transferred to a means for displaying the signals as a
two-dimensional representation of the signal magnitude on one axis and the
location of the point on the other axis. By utilizing the apparatus in
this manner, the operator can adjust the sensitivity of the inspection
device to the camera signals without using an oscilloscope or other
external device.
It is an object of the present invention to provide an apparatus having
means for decreasing the setup time and increasing the accuracy of an
inspection device for glass bottles.
It is another object of the present invention to provide an apparatus
having means for monitoring the video output of a line scan camera without
the use of an oscilloscope.
It is a further object of the present invention to provide an apparatus
having means for generating a two-dimensional visual representation of an
object under inspection.
Other objects and advantages of the invention will be apparent to those
skilled in the art from the following detailed description of the
preferred embodiment of the invention, when considered in light of the
accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block diagram of an apparatus for detecting defects in objects
according to the present invention; and
FIG. 2 is a block diagram of the inspection device interface of the
apparatus for detecting defects of FIG. 1.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring now to the drawings, there is illustrated in FIG. 1 a block
diagram of an apparatus for detecting defects in objects according to the
present invention. An object, such as a glass bottle (not shown), is
scanned by a camera 10. The camera 10 generates a plurality of signals
proportional in magnitude to the amount of light received from the glass
bottle. In the preferred embodiment of the invention, a light source (not
shown) directs a beam of light through the glass bottle under inspection
and into the camera 10. The camera 10 includes a plurality of
photosensitive devices, such as photodiodes, which are vertically arranged
in a linear array. It has been found that a linear array of two hundred
fifty-six photodiodes yields statisfactory results. The photodiode is a
variable resistance device that will pass a voltage proportional to the
amount of light falling thereon. Each photodiode receives light which has
passed through different segments or portions of the bottle under
inspection. If a flaw, crack, or foreign object is contained in the
bottle, then the light passing through that portion of the bottle will be
partially blocked or reflected and the corresponding photodiode will
register a lesser intensity of light than had no defect been present.
The signals from the photodiodes are fed along a group of parallel lines 12
to a sampler 14. Each of the photodiodes is sampled in sequential order,
producing a series of pixel signals on a line 16 which represent the
amount of light which passed through the bottle under inspection along one
vertical sequential check or sweep of the photodiodes. The sampler 14 is a
device well known in the art and forms no part of the present invention.
By rotating the bottle under inspection relative to the camera 10, a
plurality of different sweeps can be made, each sweep inspecting a
different portion of the bottle. It has been found that about three
hundred seventy-five to four hundred sweeps will sufficiently cover an
average bottle and insure an accurate inspection. Thus, the sampler 14
generates a plurality of series of pixel signals on line 16 representing
the amount of light passing through the inspected portions of the entire
bottle.
The pixel signals from the sampler 14 on line 16 are an input to an
inspection device interface 18. The interface 18 rapidly extracts
significant data from a sparse object, such as a glass bottle, in a manner
suitable for computer analysis. When a bottle is ready to be scanned, the
interface 18 is enabled to receive and store data concerning that bottle.
When no bottle is ready to be scanned, the interface 18 stores the data
concerning the last scanned bottle until a new bottle is ready to be
scanned. The operation of the interface 18 is more fully explained below.
The interface 18 is a means for generating groups of signals representing
the characteristics of the bottle under inspection. The output of the
interface 18 is fed to a control circuit for generating a reject signal
whenever a defective bottle is detected. The control circuit includes a
first control unit means 20 and a second control unit means 22, which
receive the output signals from the interface 18 over lines 24 and 26
respectively. The first control unit 20 and the second control unit 22 are
each responsive to the groups of signals representing the characteristics
of the bottles under inspection for determining whether to generate a
reject signal.
The first control unit 20 and the second control unit 22 are connected to a
master control unit means or processor 28 by lines 30 and 32 respectively.
The master processor 28 also provides inputs to the interface 18 over a
plurality of lines 34 to allow an operator to set certain tolerance
limits, as will be more fully described below. The master processor 28
alternately connects one of the first and second control units 20 and 22
to the interface 18 to receive groups of signals representing the
characteristics of a bottle while the other of the first and second
control units 20 and 22 determines whether to generate a reject signal
based upon the plurality of signals representing the characteristics of a
preceding bottle. Thus, while the first control unit 20 is reading data
from the inspection interface 18 concerning a bottle which has just been
scanned, the second control unit 22 is processing data obtained on a prior
scan to determine whether to generate a reject signal for the preceding
bottle.
The master processor 28, the first control unit 20, and the second control
unit 22 can all be microprocessors, such as a model 6800 manufactured by
Motorola which is conventional and well known in the art. The master
processor 28 has an input device 36 by which an operator can program the
system and set various tolerance parameters. The input device 36 is
connected to the master processor 28 by a line 38. The master processor 28
is also connected by a line 40 to an output device 42, such as a video
display, so as to permit an operator to monitor or calibrate the system.
Alternatively, the device 42 can be a means responsive to a reject signal
generated by the master processor 28 for rejecting a particular bottle
which has been determined to be defective. A further input to the master
processor 28 is a gauge 44. The gauge 44 is provided to generate a signal
on a line 46 when a bottle is in the proper position to be scanned.
The interface 18 can receive data so long as the gauge 44 signals that a
bottle is in the proper scanning position. When the gauge 44 ceases to
generate such a signal, as during the period when the inspected bottle is
removed and an uninspected bottle is moved in, the collected information
is stored in the interface 18. The master processor 28 prevents
interference between the first and second control units 20 and 22 by
selecting one of the units to receive the data held in the interface 18.
When all of the data has been transferred to the first control unit 20,
for example, the interface 18 is free to receive new data on the next
bottle as soon as the signal from the gauge 44 is restored. The first
control unit 20 processes the data in order to determine whether to
generate a reject signal. When scanning is completed on the next bottle
and the gauge 44 ceases to generate its signal, the accumulated data is
stored in the interface 18. The master processor 28 then selects the
second control unit 22 to receive the data while the first control unit 20
continues to process the original information. Thus, each of the control
units 20 and 22 has two full cycles of the gauge 44 to process the data
concerning each bottle to determine whether or not to generate a reject
signal. By providing parallel processing paths, the control circuit
increases the speed and efficiency of the inspection apparatus.
Referring now to FIG. 2, there is illustrated a block diagram of the
details of the inspection device interface 18. The interface 18 is a means
for rapidly extracting significant data from a sparse object, such as a
glass bottle, in a manner suitable for computer analysis. The sampler 14
can generate digital signals, or analog signals to an analog-to-digital
converter, representing the magnitude of the light received by the camera
10. Line 16 presents the plurality of signals to an event detector 48
including a data latch 50 and an adder 52. The latch is a means for
storing one of the plurality of signals. In the illustrated embodiment,
the preceding pixel signal is stored in the latch 50 and is presented to
the complementary input of adder 52. Thus, the adder 52 is a means for
generating a signal which represents the difference between the magnitude
of the stored preceding pixel signal in the latch 50 and the successive
pixel signal presented on line 16. The output of the adder 52 is a signal
representing the difference in the magnitudes of adjacent pixel signals.
When the difference signal is generated by adder 52, the present pixel
signal is stored in latch 50 to be compared with the next pixel signal. A
control logic unit 54 of the interface 18 generates a command over a LATCH
NEXT PIXEL line to cause the latch 50 to store the present pixel signal
available on line 16. The contents of the latch 50 can be cleared to zero
by a command from the master processor 28 over a CLEAR L line.
The difference signal from the adder 52 can be either positive or negative,
depending upon the magnitudes of the present and previous pixel signals.
Because only the magnitude of the difference between adjacent pixel
signals is relevant in the detection of defects, it is convenient to feed
the difference signal to a means for generating the absolute magnitude of
the difference signal. As illustrated, the output from adder 52 is fed to
an absolute magnitude circuit 56. The circuit 56 can be constructed of a
plurality of exclusive OR gates, as is well known in the art. The CARRY
output of adder 52 controls the absolute magnitude circuit 56 such that
the output is always positive. Rectification of the difference signal
prevents misleading comparison readings in the event detector 48.
The event detector 48 includes a means for storing a threshold signal. In
the preferred embodiment, a threshold random access memory (RAM) 58 is
provided for storing a plurality of threshold signals. Each threshold
signal stored in the threshold RAM 58 corresponds to a specific pixel
difference signal generated by the adder 52. The means for selecting the
individual threshold signal from the threshold RAM 58 which corresponds to
the present difference signal is a diode counter 60. The diode counter 60
can be cleared to zero by a command from the control logic 54 over a CLEAR
DC line and can be incremented by a command over an INCREMENT DC line. The
diode counter 60 provides the threshold RAM 58 with the memory address of
the proper threshold signal. The desired threshold signals can be loaded
into the threshold RAM 58 from the master processor 28 over a LOAD DATA
line. The output of the diode counter 60 is also connected to an internal
data bus 62.
The signal from the threshold RAM 58 is presented to the complementary
input of an adder 64 where it is combined with the signal from the
absolute magnitude circuit 56. The adder 64 is a means for generating
event signals when the difference signal obtained from the absolute
magnitude circuit 56 exceeds the threshold signal obtained from the
threshold RAM 58. Event signals are generated, over an EVENT line to the
control logic 54, indicating the detection of a defect, and over a
MAGNITUDE line to the internal data bus 62, indicating by how much the
difference signal differed from the threshold signal.
Upon receiving a signal from the gauge 44 that a bottle is ready to be
scanned, the master processor 28 generates a signal over a GAUGE line to
the control logic 54. In response to that signal, the control logic 54
generates a signal over a CLEAR SC line to a sweep counter 66. The
contents of the sweep counter 66 are thus cleared to zero before each
bottle is scanned. The output of the sweep counter 66 is connected to the
internal data bus 62.
To initiate a sweep, the master processor 28 generates a signal over a
START SWEEP line to the control logic 54. In response to that signal, the
control logic 54 increments the sweep counter 66 by generating a signal
over an INCREMENT SC line. The control logic 54 also clears the contents
of the diode counter by generating a signal over the CLEAR DC line. The
control logic 54 further generates a signal over a CLEAR EC line to clear
an event counter 68. These three initialization functions prepare the
interface 18 for the receipt of data. The output of the event counter 68
is connected to the internal data bus 62. The event counter 68 generates a
signal on an OVERFLOW line to the data bus 62 when the contents of the
register exceed its limits. The event counter 68 is incremented by the
control logic 54 over an INCREMENT EC line each time that the event
detector 48 signals that an event has occurred.
The interface 18 includes a means for storing the event signals. An
interface random access memory (RAM) 70 is provided for reading and
storing the signals available on the data bus 62. The first control unit
20 and the second control unit 22 alternatively read the accumulated data
from the interface RAM 70 through the data bus 62 and lines 24 and 26
respectively. Data is stored in the interface RAM 70 when the control
logic 54 generates a signal over a WRITE line. The interface RAM 70 also
generates a signal on an OVERFLOW line to the data bus 62 when the
contents of the register exceed its limits. A RAM counter 72 provides the
interface RAM 70 with memory address locations. The RAM counter 72 can be
cleared to zero by a command from the control logic 54 over a CLEAR RC
line and can be incremented by the control logic 54 by a command over an
INCREMENT RC line.
The interface 18 also includes a means for defining a range for extracting
data. In the illustrated embodiment, a window generator 74 is provided to
limit the number of sweeps over which data can be extracted. A lower sweep
limit is entered by an operator through the input device 36 to the master
processor 28. The instruction is sent over a LO SET line to a low sweep
comparator 76. The output of the sweep counter 66 is also an input to the
low sweep comparator 76. When the number in the sweep counter 66 equals or
exceeds the number generated over the LO SET line, the low sweep
comparator 76 generates a signal over a SET line to a flip-flop 78. The
flip-flop 78 generates a signal over an ENABLE line to the control logic
54, instructing it to process the incoming data. Signals received by the
interface 18 on sweeps taken of a bottle below the lower sweep limit are
ignored to prevent erroneous data associated with the initial sweeps from
being processed. Similarly, the operator can enter a high sweep limit
value to cause the interface 18 to stop processing data after a certain
number of sweeps. The master processor 28 sends the instruction over a HI
SET line to a high sweep comparator 80. The output of the sweep counter 66
is also an input to the high sweep comparator 80. When the number in the
sweep counter 66 equals or exceeds the number generated over the HI SET
line, the high sweep comparator 80 generates a signal over a RESET line to
the flip-flop 78. The flip-flop 78 thus ceases to generate the signal over
the ENABLE line, causing the control logic 54 to ignore all subsequent
data.
Prior to utilizing the apparatus for detecting defects, the operator will
enter the parameters under which the machine will operate through the
input device 36. The parameters include the low and high sweep limits and
the group of threshold signals. The low and high sweep limits define the
sweep window, which is the range of sweeps over which data can be accepted
by the interface 18. By selecting a particular set of threshold signals to
be loaded into the threshold RAM 58, the operator determines the
acceptable tolerances of light deviation which will cause an event to be
detected. The master processor 28 loads the appropriate data into the
interface 18.
When a bottle has been moved into a proper position for scanning, the gauge
44 generates a signal to the master processor 28. The signal is relayed
along the GAUGE line to the control logic 54, which generates signals to
clear the contents of both the sweep counter 66 and the RAM counter 72.
These tasks are performed each time a new bottle is ready to be inspected.
The interface 18 is then prepared to receive data from the camera 10.
At the beginning of each sweep, the master processor 28 generates a signal
over the START SWEEP line to the control logic 54. The control logic 54
generates appropriate signals to clear the contents of the diode counter
60, clear the contents of the event counter 68, and increment the contents
of the sweep counter 66. These tasks are performed at the beginning of
each sweep made by the sampler 14.
The incoming pixel signals are fed to the adder 52 and the latch 50. The
latch 50 holds the previous pixel signal at its output, which is then fed
to the complementary input of the adder 52. Thus, the output of the adder
52 represents the difference between the two adjacent pixel signals. The
output of the adder 52 is fed to the absolute magnitude circuit 56, which
insures that the input to adder 64 is always a positive signal.
The threshold RAM 58 holds the programmed plurality of threshold signals,
each of which corresponds to a specific difference signal representing a
pair of pixels. Since each pixel signal represents a sampled photodiode in
the camera 10, the diode counter 60 can be incremented with each incoming
pixel signal to select the memory address of the appropriate threshold
signal stored in the threshold RAM 58. That particular threshold signal is
fed to the complementary input of adder 64 to be compared with the actual
difference signal generated by adder 52 and rectified by the absolute
magnitude circuit 56. The output of adder 64 is a plurality of event
signals which represent a comparison between the difference signal and the
threshold signal. When the magnitude of the difference signal exceeds the
threshold signal, the adder 64 will generate an event signal over the
EVENT line to the control logic 54. The magnitude of the event signal as
well as the output of the diode counter are gated onto the data bus 62 for
storage in the interface RAM 70.
When an event is detected during the sweep window, as defined by the
operator using the window generator 74, the control logic 54 generates
signals which increment the event counter 68 and increment the RAM counter
72. The control logic 54 also generates a signal over the WRITE line to
the interface RAM 70 to read and store the contents of the diode counter
60 and the magnitude of the output adder 64. This process is repeated with
each pair of adjacent pixel signals until a sweep is completed. The signal
on the START SWEEP line is removed at the end of each sweep, causing the
contents of the sweep counter 66 and the event counter 68 to be written
into the interface RAM 70 if one or more events have occurred in that
particular sweep. Thus, in each sweep where an event is detected, the
gathered data includes a series of events denoted by diode number and
event magnitude, followed by a final single entry consisting of the sweep
number and the number of events which occurred in that sweep. When the
next sweep of the same bottle begins, the contents of the diode counter 60
are cleared to zero, the contents of the event counter 68 are cleared to
zero, and the sweep counter 66 is again incremented. The scanning
continues until the window generator 74 disables the interface 18 when the
high sweep limit has been reached.
The groups of signals stored in the interface RAM 70 which represent the
characteristics of the inspected bottle are then fed to either the first
control unit 20 or the second control unit 22, as determined by the master
processor 28. The data in the interface RAM 70 is downloaded into the
selected control unit, which determines whether or not to generate a
reject signal for that particular bottle. Two checks are made before
processing begins to make sure that the interface 18 has not overflowed
because of an unusually bad bottle. These checks are indicated by status
flags on the event counter 68 and the interface RAM 70. If the contents of
either unit exceeds the capability of the register, a signal is generated
over the respective OVERFLOW lines. When either overflow signal is
present, the bottle will be immediately rejected because of a gross
defect.
As stated above, the format of the data which is read by the selected
control unit includes a series of diode numbers and associated event
magnitudes, followed by a sweep number and a number of events. The bottle
data is downloaded from the interface RAM 70 to the particular control
unit. By checking each event along a sweep to see if it can be linked to a
preceding event, the control units 20 or 22 can generate a string. A
string is defined as a collection of one or more events in proximity to
each other and having four properties which are calculated during
generation. These properties include: the beginning of the string, which
is the first diode number; the end of the string, which is the last diode
number; the magnitude of each string, which is the sum of the magnitudes
of each event comprising the string; and the number of events that formed
the string. Checking for excess string magnitude occurs during string
generation and the decision process will halt if a string magnitude
exceeds a user-adjustable threshold. In other words, the selected control
unit 20 or 22 links together events within a single sweep to determine if
the sum of the magnitudes of the events exceeds a user-specified
tolerance. If so, a reject signal is generated and the particular bottle
will be removed.
If string checking does not reject the bottle, another processing stage is
entered wherein the strings are checked to see if they form blobs. A blob
is defined as collection of strings in proximity to each other. The string
diode numbers must overlap, or at most be within a user-specified range,
for the end of one string on one sweep and the beginning of another string
on a different sweep. A blob has three properties which are calculated
during formation. These properties include blob width, blob magnitude, and
the number of events in the blob. During blob formation, blob width and
blob magnitude are checked against user-specified tolerances and
processing stops if either threshold is exceeded. If a bottle is not
rejected because of blob width or blob magnitude, the number of events
contained in the blob is compared to another user-specified number. If the
number of events exceeds the specified tolerance, the bottle will also be
rejected. If the bottle has not been rejected for any of the above
reasons, it is considered a good bottle and no reject signal will be
generated.
The apparatus for detecting defects can also be utilized to generate and
display a picture of the object under inspection. A bottle is inspected
under the normal procedure described above and data is stored in the
interface RAM 70. When the bottle has been completely scanned, the master
processor 28 instructs either the first control unit 20 or the second
control unit 22 to receive the data from the inspection interface 18. The
selected control unit 20 or 22 does not process the received information
but rather transmits the data in raw form to the master processor 28. The
gathered data includes the diode number, the sweep number, and the event
magnitude for each event detected by the interface 18. The data is then
presented to the output device 42, which can include a two-dimensional
graphic module and a video screen. The graphic module and video screen are
well known in the art. The data can be displayed in a two-dimensional
graphic form, utilizing the sweep number of each event as the horizontal
component and the diode number of each event as the vertical component.
The video screen will display a dot at each sweep and diode number
location where an event was detected. The result in a two-dimensional
representation of the inspected bottle showing all of the detected
defects, as if the bottle had been cut through one side and unwrapped for
display.
The event magnitude may be used in conjunction with a synthetic threshold
level which can be varied to generate new pictures which show the effect
that different threshold levels have. Using the apparatus in this mode, an
operator is aided in determining what the appropriate threshold levels for
the particular style of bottle should be. Although the preferred
embodiment of the invention provides only a two-dimensional representation
of the object under inspection, it will be appreciated that a
three-dimensional representation could be generated on the video screen by
the use of additional circuitry. Such circuitry is also well known in the
art.
The apparatus for detecting defects can also be utilized to monitor the
video output of the line scan camera. Such a use permits an operator to
calibrate the interface 18 without requiring the use of an oscilloscope.
When the apparatus is operated in this mode, the master processor 28
continuously clears the contents of the latch 50 to zero by generating a
signal over the CLEAR L line. With the latch 50 cleared, the plurality of
pixel signals on lines 16 from the sampler 14 pass through the adder 52
unaltered. The master processor 28 also utilizes the LOAD DATA line to
load the threshold RAM 58 with all zeros. Thus, every pixel signal is
detected as an event and is stored in the second control unit 22 to
receive the data from the interface RAM 70. The data includes the diode
number and event magnitude for each pixel of the sweep.
The data is transferred from the selected control unit 20 or 22 to the
master processor 28. The master processor 28 relays the information to the
output device 42, which again can consist of a two-dimensional graphic
module and a video screen. The graphic module can utilize the diode number
as the horizontal component and the event magnitude as the vertical
component. The graph which is thus displayed on the video screen
represents the amount of light received by the photodiodes over a single
sweep. The procedure can be repeated continuously to simulate an
oscilloscope. However, unlike an oscilloscope, no sweep or gain
adjustments are necessary since the data is always properly scaled to a
specific diode number or event magnitude. Operation of the apparatus in
this mode permits an operator to make sensitivity adjustments relating to
the event magnitude voltage without requiring the use of an oscilloscope.
In accordance with the provisions of the patent statutes, the principle and
mode of operation of the invention have been explained and illustrated in
its preferred embodiment. However, it must be understood that the
invention may be practiced otherwise than as specifically illustrated and
described without departing from its spirit or scope.
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