U.S. patent application number 15/678767 was filed with the patent office on 2017-11-30 for method and system for thermally monitoring process for forming plastic blow-molded containers.
The applicant listed for this patent is GRAHAM PACKAGING COMPANY, L.P.. Invention is credited to Patrick M. O'Connell, Garrett R. Pennington, Russell Varone.
Application Number | 20170343342 15/678767 |
Document ID | / |
Family ID | 44628293 |
Filed Date | 2017-11-30 |
United States Patent
Application |
20170343342 |
Kind Code |
A1 |
O'Connell; Patrick M. ; et
al. |
November 30, 2017 |
METHOD AND SYSTEM FOR THERMALLY MONITORING PROCESS FOR FORMING
PLASTIC BLOW-MOLDED CONTAINERS
Abstract
The present invention provides a method of measuring the
placement of material forming a blow-molded plastic container after
the container is released from a mold of a blow molder having a
plurality of molds, wherein each plastic container comprises a
continuous sidewall and a base, the method comprising the steps of:
detecting with an infrared camera infrared light emitted from the
container after the container is released from a mold; converting
the detected infrared light into corresponding electrical signals;
transmitting the electrical signals to a microprocessor; comparing
in the microprocessor the electrical signals with stored data
regarding desired material distribution forming the plastic
container; and producing output information regarding the placement
of material forming the container.
Inventors: |
O'Connell; Patrick M.;
(Hershey, PA) ; Pennington; Garrett R.; (Manheim,
PA) ; Varone; Russell; (Red Lion, PA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
GRAHAM PACKAGING COMPANY, L.P. |
Lancaster |
PA |
US |
|
|
Family ID: |
44628293 |
Appl. No.: |
15/678767 |
Filed: |
August 16, 2017 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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14824904 |
Aug 12, 2015 |
9778031 |
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15678767 |
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13176850 |
Jul 6, 2011 |
9146099 |
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14824904 |
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61362188 |
Jul 7, 2010 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B29C 2949/78151
20130101; B29C 2949/78563 20130101; B29C 49/28 20130101; B29C
2949/78168 20130101; B29C 2949/78605 20130101; G01B 21/085
20130101; B29C 2949/7826 20130101; B29L 2031/7158 20130101; B29C
49/78 20130101; B29C 49/04 20130101; B29C 49/36 20130101; B29C
49/42 20130101; B29C 2949/7821 20130101; B29C 2949/78512 20130101;
B29C 2949/78663 20130101; B29C 2949/78722 20130101 |
International
Class: |
G01B 21/08 20060101
G01B021/08; B29C 49/04 20060101 B29C049/04; B29C 49/78 20060101
B29C049/78; B29C 49/28 20060101 B29C049/28; B29C 49/42 20060101
B29C049/42 |
Claims
1. A method of controlling a blow molding production line based on
measuring the placement of material forming a blow-molded plastic
container produced on the production line, the method comprises the
steps of: providing an extrusion blow molding machine having a
plurality of molding stations each comprising a mold and a parison
extruding system, wherein the extrusion blow molding machine
provides an output of plastic blow-molded containers, wherein each
plastic container has a continuous sidewall and a base; measuring
the placement of material in the sidewall and base of the
containers by: detecting with an infrared camera infrared light
emitted from the container; converting the detected infrared light
into corresponding electrical signals; transmitting the electrical
signals to a microprocessor; comparing in the microprocessor the
electrical signals with stored data regarding desired material
distribution forming the plastic container; and producing output
information regarding the placement of material forming the plastic
container and, if the output information indicates that a container
has a material distribution that is a deviation from the stored
data regarding desired material distribution, performing in the
microprocessor at least one of the following steps: i. activating a
rejection chute to reject the deviant container; ii. adjusting at
least one parameter of the extrusion blow molding machine to bring
material placement within the desired material distribution; and
iii. stopping the production line.
2. The method of claim 1 wherein the measuring step further
comprises the steps of: comparing in the microprocessor the
electrical signals of the plastic blow-molded containers from each
of the stations in the blow molding machine with stored reference
data regarding desired material distribution forming the plastic
blow-molded container; and determining whether there is a
station-to-station and/or a cycle-to-cycle variation.
3. The method of claim 1 wherein the blow molder is an extrusion
blow molder.
4. The method of claim 3 wherein the extrusion blow molder
comprises a plurality of blow mold stations.
5. The method of claim 3 wherein the material comprises a plastic
selected from the group consisting of: polyethylene (PE), such as
high-density polyethylene (HDPE), medium-density polyethylene;
low-density polyethylene (LDPE), cross-linked high-density
polyethylene (XLPE), linear low-density polyethylene (LLDPE), ultra
low-density polyethylene, and very low-density polyethylene;
polycarbonate (PC); polypropylene (PP); polypropylene copolymer
(PPCO); polyallomer (PA); polymethylpentene (PMP or TPX);
polyketone (PK); polyethylene terephthalates (PET), including
polyethylene terephthalate G copolymer (PETG) and oriented PET;
polystyrene (PS); polyvinylchloride (PVC); naphthalate;
polybutylene terephthalate; thermoplastic elastomer (TPE); and
mixtures thereof.
6. The method of claim 5 wherein the material is selected from the
group consisting of: HDPE, PVC, PC, PP, LDPE, EPET, and PETG.
7. The method of claim 5 wherein the material further comprises a
colorant such that the container is substantially opaque to
light.
8. An apparatus for measuring the placement of material forming a
plastic blow-molded container, the apparatus comprising: a blow
molder having a plurality of molds used to form a plurality of
plastic containers, wherein each plastic container has a continuous
sidewall and a base; an infrared camera that detects infrared light
emitted from each of the plurality of plastic containers; and a
microprocessor that receives electrical signals from the infrared
camera and determines whether material distribution in the sidewall
and base of the containers are within desired reference limits
stored in the microprocessor.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a divisional of U.S. patent application
Ser. No. 14/824,904 filed Aug. 12, 2015 which is a divisional of
U.S. patent application Ser. No. 13/176,850 filed on Jul. 6, 2011
now U.S. Pat. No. 9,146,099 that issued on Sep. 29, 2015 which
claims the benefit of priority under 35 U.S.C. .sctn.119(e) to
earlier filed U.S. Provisional Patent Application No. 61/362,188,
filed on Jul. 7, 2010, the disclosures of which are incorporated
herein by reference in their entirety.
BACKGROUND OF THE INVENTION
[0002] The present invention provides a method and apparatus for
measuring the placement of material throughout a plastic
blow-molded containers and, more specifically, it relates to the
use of an infrared camera and a microprocessor to measure the
placement of material forming the plastic blow-molded container by
comparing the temperature profile images of a bottle selected as a
standard and the temperature profile image of a freshly blown
bottle.
[0003] Although the present invention is described primarily in
connection with an extrusion blow molding, the skilled artisan will
appreciate that the method of the present invention will also apply
to other blow molding processes such as, for example, injection and
stretch blow molding processes.
[0004] In the packaging industry there is a continuous effort to
reduce the overall weight of the package. Weight reduction
translates into a reduction of material and shipping costs. One of
the hurdles faced by packaging engineers is to ensure that lighter
weight packages have the minimum amount of material while meeting
specifications for strength and integrity. Achieving this balance
often means that there is only a very small margin for error and
better automated processes are always being sought.
[0005] One of the difficulties in blow molding plastic containers
is the problem of maintaining the proper placement of plastic in a
parison so that the blow-molded container has uniform wall
thickness and/or has the desired amounts of plastic in the desired
locations on the container. Ill-placed plastic in a container wall
may translate into defects in the containers that, in turn, may
affect the structural integrity of the container for its intended
use. Moreover, ill-placed material in a container may indicate that
there is a serious problem with the process, such as, for example,
a clogged screen or foreign objects in the process lines that
affect the flow of the plastic.
[0006] One way to measure placement of material in a plastic
blow-molded container is for an operator to manually remove
containers from an output conveyor, cut them open, and measure the
vertical wall thickness distribution. If the distribution is not
satisfactory, the measurement data can indicate how the process
needs to be adjusted. In some cases, there is a critical location
where one measurement can indicate how the process is running. For
example, if one area of the sidewall is too thick, the additional
thickness can indicate that some other area is running too
thin.
[0007] Wall thickness distribution information must be acquired as
quickly as possible. If the manufacturing process is out of
specification limits, a large quantity of scrap material can be
generated before such determination is made and the appropriate
correction implemented. The manual sectioning and measurement of
the wall thickness distribution can be tedious, time consuming, and
inaccurate. Consequently, the manufacturing process results in a
large variation in container wall thickness, rarely approaching the
optimum distribution necessary for achieving a desired minimum
weight of the final container.
[0008] On-line automated processes to measure wall thickness of
blow molded plastic containers have been developed to address the
foregoing concerns. For example, U.S. Pat. Nos. 6,863,860,
7,374,713, and 7,378,047 to Birckbichler et al. ("the Birckbichler
patents") disclose a method of inspecting wall thickness of
blow-molded plastic containers wherein the method involves
impinging infrared light thereon and detecting the portion of
infrared light that passes through the container and converting the
same into corresponding electrical signals that are delivered to a
microprocessor. The microprocessor compares the electrical signals
with stored information regarding desired wall thickness of the
container and emits output thickness information. In such method,
the microprocessor receives signals from sensors associated with
the blow-molder relating to the position of the molds, the identity
of the molds and the identity of the spindles in order that the
wall thickness information that is determined by inspection can be
associated with specific molds and spindles. This method, however,
suffers from at least the following three drawbacks.
[0009] First, the method disclosed in the Birckbichler patents
requires multiple IR emitters and IR detectors to determine
thickness. The emitter sends out the IR wave from one side of the
package, while the detector senses the IR wave from the other side
of the package. Such configuration is expensive, complex, and
difficult to maintain in continuous working operation.
[0010] Moreover, since the method disclosed in the Birckbichler
patents relies on radiation passing through the container, so the
containers must be clear for the method to be effective.
[0011] Finally, the method disclosed in the Birckbichler patents
takes data points only where the emitter and detectors are aimed
and, thus, is incapable of measuring wall thickness continuously
(i.e., without interruption) along the side of the container
wall.
[0012] Accordingly, there is a need in the art for an on-line,
automated method of measuring material placement in a blow-molded
plastic bottle that does not suffer from the above-identified
drawbacks.
BRIEF SUMMARY OF THE INVENTION
[0013] The present invention satisfies this need by providing a
method of measuring the placement of material forming a blow-molded
plastic container after the container is released from a mold of a
blow molder having a plurality of molds, wherein each plastic
container comprises a continuous sidewall and a base, the method
comprising the steps of: detecting with an infrared camera infrared
light emitted from the container after the container is released
from a mold; converting the detected infrared light into
corresponding electrical signals; transmitting the electrical
signals to a microprocessor; comparing in the microprocessor the
electrical signals with stored data regarding desired material
distribution forming the plastic container; and producing output
information regarding the placement of material forming the
container.
[0014] In another aspect, the present invention provides a method
of controlling a blow molding production line based on measuring
the placement of material forming a blow-molded plastic container
produced on the production line, the method comprising the steps
of: providing an extrusion blow molding machine having a plurality
of molding stations each comprising a mold and a parison extruding
system, wherein the extrusion blow molding machine provides an
output of plastic blow-molded containers, wherein each plastic
container comprises a continuous sidewall and a base; measuring the
placement of material forming the sidewall and base of the
containers by: detecting with an infrared camera infrared light
emitted from the container; converting the detected infrared light
into corresponding electrical signals; transmitting to a
microprocessor the electrical signals; comparing in the
microprocessor the electrical signals with stored data regarding
desired material distribution forming the plastic container; and
producing output information regarding the placement of material
forming the plastic container and, if the output information
indicates that a bottle has a material distribution that is a
deviation from the desired material distribution, manually
performing at least one of the following steps: adjusting at least
one parameter of the extrusion blow molding machine to bring
material placement within the desired material distribution; and
stopping the production line.
[0015] In yet another aspect, the present invention provides a
method of controlling a blow molding production line based on
measuring the placement of material forming a blow-molded plastic
container produced on the production line, the method comprises the
steps of: providing an extrusion blow molding machine having a
plurality of molding stations each comprising a mold and a parison
extruding system, wherein the extrusion blow molding machine
provides an output of plastic blow-molded containers, wherein each
plastic container has a continuous sidewall and a base; measuring
the placement of material in the sidewall and base of the
containers by: detecting with an infrared camera infrared light
emitted from the container; converting the detected infrared light
into corresponding electrical signals; transmitting the electrical
signals to a microprocessor; comparing in the microprocessor the
electrical signals with stored data regarding desired material
distribution forming the plastic container; and producing output
information regarding the placement of material forming the plastic
container and, if the output information indicates that a container
has a material distribution that is a deviation from the stored
data regarding desired material distribution, performing in the
microprocessor at least one of the following steps: activating a
rejection chute to reject the deviant container; adjusting at least
one parameter of the extrusion blow molding machine to bring
material placement within the desired material distribution; and
stopping the production line.
[0016] In yet another aspect, the present invention provides an
apparatus for measuring the placement of material forming a plastic
blow-molded container, the apparatus comprising: a blow molder
having a plurality of molds used to form a plurality of plastic
containers, wherein each plastic container has a continuous
sidewall and a base; an infrared camera that detects infrared light
emitted from each of the plurality of plastic containers; and a
microprocessor that receives electrical signals from the infrared
camera and determines whether material distribution in the sidewall
and base of the containers are within desired reference limits
stored in the microprocessor.
[0017] According to the present invention, a system for measuring
the material distribution of a plastic blow-molded container is
integrated with a multiple station production machine wherein each
of the stations is used repetitively in turn. As a result, it is
possible separately to analyze the performance of each station.
Unlike container inspection systems of the prior art, the system
and method of the present invention is less complex, can measure
all blow molded bottles regardless of bottle color or clarity, and
can measuring wall thickness continuously along the entire
container.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] The patent or application file contains at least one drawing
executed in color. Copies of this patent or patent application
publication with color drawing(s) will be provided by the Office
upon request and payment of the necessary fee.
[0019] The foregoing and other features and advantages of the
invention will be apparent from the following, more particular
description of a preferred embodiment of the invention, as
illustrated in the accompanying drawings wherein like reference
numbers generally indicate identical, functionally similar, and/or
structurally similar elements.
[0020] FIG. 1 is a schematic plan view of the apparatus according
to the present invention;
[0021] FIG. 2 is an infrared image of a plastic blow-molded
container without a defect;
[0022] FIG. 3 is an infrared image of a plastic blow-molded
container having a defect;
[0023] FIG. 4 is an infrared image of the plastic blow-molded
container of FIG. 3 with wall thickness measurements overlaid on
the image;
[0024] FIG. 5 is an infrared image of the plastic blow-molded
container of FIG. 3 with a temperature profile to illustrate an
aspect of the present invention;
[0025] FIG. 6A is the same infrared image of a plastic blow-molded
container shown in FIG. 3 for comparison with the image in FIG.
6B;
[0026] FIG. 6B is an infrared image of a plastic blow-molded
container having a defect and after operator adjustment of at least
one process parameter of an extrusion blow molding machine; and
[0027] FIG. 7 is a flow chart illustrating an embodiment of the
present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0028] As used herein, the term "containers" refers to plastic
bottles, jars, vials and other plastic containers usable for
storage of liquid and other flowable materials. Examples of the
size of containers for which the present invention is particularly
well suited are containers having a capacity of about 0.2 to 3
liters, although large volume packages such as, for example, 55
gallon drums are also contemplated by the present invention.
[0029] As used herein, the term "material placement" or "placement
of material in a blow-molded plastic container" generally refers to
the thickness characteristics of a blow-molded plastic bottle
including the thickness of the overall wall, base, and neck finish
of the container and also to particular areas of the container
wall, base, and neck that may contain too much or too little
plastic material relative to a desired amount of material for the
particular location in the container.
[0030] Blow-molded plastic containers according to the present
invention are those made from plastics such as, for example,
polyethylene (PE), such as high-density polyethylene (HDPE),
medium-density polyethylene; low-density polyethylene (LDPE),
cross-linked high-density polyethylene (XLPE), linear low-density
polyethylene (LLDPE), ultra low-density polyethylene, and very
low-density polyethylene; polycarbonate (PC); polypropylene (PP);
polypropylene copolymer (PPCO); polyallomer (PA); polymethylpentene
(PMP or TPX); polyketone (PK); polyethylene terephthalates (PET),
including polyethylene terephthalate G copolymer (PETG) and
oriented PET; EPET; polystyrene (PS); polyvinylchloride (PVC);
naphthalate; polybutylene terephthalate; thermoplastic elastomer
(TPE); mixtures thereof; and the like. Such plastics are suitable
for use in consumer food and household chemical and automotive
markets, and pharmaceutical packaging. In preferred embodiments,
the plastic material further includes a colorant such that the
plastic blow-molded container is substantially opaque to light.
[0031] In a typical prior art extrusion blow mold process, a hot
tube of plastic material (a "parison") is dropped from an extruder
and captured in a water cooled mold. Once the molds are closed, air
is injected through the top or the neck of the container. When the
hot plastic material is blown up and touches the walls of the mold
the material "freezes" and the material then maintains the rigid
shape of the mold.
[0032] In such process, there are a number of potential problems
that could result in poor material distribution in the blown
container. For example, dirt or other impurities can contaminate
the melted polymer and affect the polymers melt and flow
properties; the screen in the extruder screen changer can become
clogged; there can be a heating element failure; a misaligned flow
head; and there can be die pin problems that affect the die gap
which, in turn, affects the container wall thickness.
[0033] By employing the apparatus and method of the present
invention, preferably located within the blow molder near the
output portion where the containers are extracted from the molds,
the material distribution throughout the container can be readily
determined as described in more detail below.
Apparatus and Method of Measuring the Placement of Material in a
Blow-Molded Container
[0034] In one embodiment, the method of the present invention is a
method of measuring the placement of material in a blow-molded
plastic container. This method comprises providing a plastic
container blow molder having a plurality of molds and providing an
output of plastic containers, wherein each plastic container has a
continuous sidewall and a base. As used herein, the term "sidewall"
or "container sidewall" is used herein to refer to the longer walls
of a plastic blow-molded container, regardless of the container's
shape, and includes a handle portion if applicable. As used herein,
the term "base" of the container refers to the bottom of the
bottle; the surface upon which the bottle stands. Referring to FIG.
1, an embodiment of an apparatus according to the present invention
is shown, which includes and exemplary blow molding machine. The
exemplary blow molding machine of FIG. 1 is an extrusion blow
molding machine 2 having a rotary wheel 4 that includes multiple
mold stations 6. In the blow molding machine shown in FIG. 1, the
rotary wheel 4 has twelve mold stations. Parison 8 is extruded
through flow head 12 where a water-cooled mold 14 clamps and closes
on parison 8. A needle (not shown) then pierces the parison through
which air is blown thus forming a container in the shape of the
mold 14. As rotary portion 4 rotates, the mold is released and the
plastic blow-molded blown container 16 is ejected for further
processing. Although FIG. 1 depicts a rotary wheel-type blow
molding machine, one of ordinary skill in the art will appreciate
that the method of the present invention can be employed on any
type of blow molding machine, whether having a single stage/station
or multiple stages/stations.
[0035] The method of the present invention further includes the
steps of measuring the placement of material forming the sidewall
and base of the containers by detecting the infrared light
emittance with an infrared camera and converting the detected
infrared light into corresponding electrical signals which are
transmitted to a microprocessor. Still referring to FIG. 1, there
is shown an inspection station which has a plastic blow-molded
container 16 passing there through as it is released from the
rotary wheel 4 in the direction indicated by the arrows under the
influence of a suitable conveyance device (not shown). An infrared
camera 18 is in communication with microprocessor 20, which, in
turn, is connected to an output device 22 (e.g., a monitor) and
keyboard 24. A suitable infrared camera 18 for use in accordance
with the present invention is, for example, the Fluke Thermal
Imager IR Flexcam.RTM.Ti40 (Fluke Corporation, Everett, Wash.).
Output device 22 receives output information from microprocessor
20. In operation, infrared camera 18 detects infrared light and,
therefore, the amount of heat emitted from container 16 and
converts the detected infrared light into corresponding electrical
signals which are delivered to microprocessor 20 for further
processing as described in more detail below.
[0036] Infrared camera 18 operates on the principle that all
objects emit a certain amount of black body radiation as a function
of their temperatures. Generally speaking, the higher an object's
temperature is, the more infrared radiation, or "black-body"
radiation, it emits. When viewed graphically, the brightest
(warmest) parts of the image are typically colored white,
intermediate temperatures reds and yellows, and the dimmest
(coolest) parts blue. Because plastic is a good insulator, not only
do plastic blow-molded containers retain heat, but they retain heat
in different amounts throughout their profile because plastic
containers require different amounts of plastic in different
locations on the container. For example, a container's base portion
typically requires more plastic relative to the label area. With
respect to heat retention, it is known that thicker areas (areas
with more material) on a plastic container retain heat longer than,
for example, thinner areas (areas with less material). Thus,
thicker areas will typically be hotter out of the molds and will
emit more infrared radiation.
[0037] Because of the relatively low thermal energy emitted from
the container, one of ordinary skill in the art will appreciate
that special conditions may need to be considered to optimize image
quality (which also may be a function of the quality of the camera
being employed). For example, the camera may need to be shielded
from the surrounding environment or a longer exposure time of the
camera may be needed. Also, the ordinarily skilled artisan will
appreciate that to capture the image, either the camera may have to
move with the container being measured or the conveyor may have to
temporarily stop or the container will have to be ejected onto an
imaging station.
[0038] The method of the present invention further includes the
steps of comparing in the microprocessor the electrical signals
with stored data regarding desired material distribution throughout
the plastic container and producing output information regarding
the placement of material throughout the container. An infrared
temperature profile can be input to a microprocessor as a standard
reference temperature profile for a given container whose material
placement is independently considered to meet desired material
placement requirements for that container. Thus, the apparatus of
the present invention operates to measure the placement of material
in, for example, the sidewall and base of a plastic blow-molded
container by employing infrared camera 18 to detect the infrared
light emittance as the containers are released from the molds onto,
for example, a discharge conveyor. The infrared camera 18 converts
the detected infrared light into corresponding electrical signals
which are transmitted to microprocessor 20, which compares the
electrical signals with stored reference data regarding desired
material distribution throughout the plastic blow-molded container
16. Output information is thus produced by the microprocessor which
may be shown on output device 22. Referring to FIG. 2, in one
embodiment, the output information is in the form of a visual image
showing the infrared temperature profile of a container. The
infrared image in FIG. 2 shows an infrared image of an HDPE oil
container 26 twenty seconds after it was taken out of a mold
(before flash 30 is removed). The sidewall 28 of the container
shown in the image in FIG. 2 generally has a uniform material
distribution throughout the sidewall as evidenced by the uniform
color/shade of the sidewall.
[0039] It has been found that the average wall thickness values
obtained by the method of the present invention agree very closely
with manual measurements made by carefully sectioning and physical
gauging of plastic blow-molded containers.
Method of Controlling a Blow Molding Production Line (I)
[0040] In view of the above method for measuring the placement of
material in a blow-molded plastic container, in another embodiment,
the present invention provides a method of controlling a blow
molding production line based on measuring the placement of
material forming a blow-molded plastic container produced on the
production line as described above. This embodiment includes the
steps detailed above with respect to measuring the placement of
material in a blow-molded plastic container, and further includes
the following steps based upon the output information provided by
the microprocessor 20. If the output information from
microprocessor 20 indicates that a bottle (or bottles) has a
material distribution that is a deviation from the desired material
distribution, manually performing at least one of the following
steps: (i) adjusting at least one parameter of the extrusion blow
molding machine to bring material placement within the desired
material distribution; and (ii) stopping the production line.
[0041] FIGS. 3 to 6 illustrate this embodiment of the method of the
present invention. FIG. 3 shows the visual image of an infrared
temperature profile of a blow-molded HDPE oil container 32 twenty
seconds after its release from a mold. The output information from
microprocessor 20 indicates that container 32 has a defect 34
characterized by a non-uniform material distribution in the
sidewall of the container (compare FIG. 3 with FIG. 2). As shown in
FIG. 4, defect 34 is shown as a thicker area of the sidewall in
thousandths of an inch. FIG. 5, shows a temperature profile 36 of
defect 34 relative to the surrounding portion of the sidewall. The
increase in temperature directly correspond with the thickness
measurements shown in FIG. 4. As detailed above, thicker areas
(areas with more material) on a plastic container retain heat
longer than, for example, thinner areas (areas with less material).
Thus, thicker areas will typically be hotter out of the molds and
will emit more infrared radiation.
[0042] Once an operator has identified that information from the
microprocessor indicates that a bottle (or bottles) has a material
distribution that deviates from the desired material distribution,
the operator can adjust at least one parameter of the extrusion
blow molding machine to bring material placement within the desired
material distribution. For example, the defect may indicate a phase
mis-alignment in the parison programmer. As is well-known to the
skilled artisan, a parison programmer is used to raise or lower a
die pin to increase or decrease the die gap at the extruder head,
which directly determines a container's thickness profile. In
response, the operator can, for example, shift a pin in the parison
programmer to achieve the desired material distribution in the
blow-molded plastic container. For example, FIGS. 6A and 6B show
two blow-molded HDPE containers twenty seconds after release from
the mold. The container in FIG. 6A is the same container shown in
FIGS. 3-5. The container in FIG. 6B shows that the position of the
material distribution that formed defect 34 moved toward the base
38 of the container after an operator adjusted a pin in the parison
programmer. Thus, the method of the present invention can be
employed not only to identify and correct undesired placement of
material in a blow-molding process, but can be employed to monitor
the progress of correction efforts.
[0043] Alternatively, and depending on the extent of the deviation
from the desired material distribution, the operator can stop the
production line to make the required adjustments.
[0044] In another embodiment, microprocessor 20 also compares the
electrical signals of the plastic blow-molded containers from each
station in rotary wheel 4 of the production line with stored
reference data regarding desired material distribution throughout
the plastic blow-molded container and determines whether there is a
station-to-station and/or a cycle-to-cycle variation. If a
variation is detected, output information notifies an operator by
producing visual information and/or an audio alarm.
[0045] For example, if microprocessor output device 22 is a display
that highlights one mold station that is producing containers
having undesirable material distribution--either, for example, too
thick or too thin--the operator would adjust mold-related
parameters such as, for example, blow-pressure or blow-rate to
correct the problem; or the operator might need to stop the
blow-molder to replace or repair an air valve for that mold. It
will be appreciated that the mold station correlated feedback
provided by the microprocessor is used to localize the problem.
Method of Controlling a Blow Molding Production Line (II)
[0046] In view of the above method for measuring the placement of
material in a blow-molded plastic container, in another embodiment,
the present invention provides a method of controlling a blow
molding production line based on measuring the placement of
material in a blow-molded plastic container produced on the
production line as described above. This embodiment includes the
steps detailed above with respect to measuring the placement of
material in a blow-molded plastic container, and further includes
the following steps based upon the output information provided by
the microprocessor, which is integrated with the blow molding
production line. If the output information indicates that a bottle
has a material distribution that deviates from the stored data
regarding desired material distribution, performing in the
microprocessor at least one of the following steps: (1) activating
a rejection chute to reject the bottle; (2) adjusting at least one
parameter of the extrusion blow molding machine to bring material
placement within the desired material distribution; and (3)
stopping the production line.
[0047] Referring to FIG. 7 (with reference to the apparatus of FIG.
1), a flow diagram of the process is shown. In block 40, standard
material distribution for a given container is input to the
microprocessor as a reference. In preferred embodiments, the
standard material distribution for a given container is added to
the microprocessor 20 as a series of electrical signals from an
infrared camera in communication with the microprocessor (which may
be the same infrared camera on the production line). In block 42
and block 44 a bottle from a production line is conveyed through
infrared camera 18 and its infrared image is captured and converted
into corresponding electrical signals which are delivered to the
microprocessor 20. At block 46, microprocessor 20 compares the
electrical signals of the plastic blow-molded container from the
production line with stored reference data regarding desired
material distribution throughout the plastic blow-molded container.
If a major defect is detected, then the microprocessor activates a
reject chute and records the defect (blocks 48 and 50,
respectively). As used herein, the term "major defect" refers to a
container having an overall average temperature or localized
temperature that is more than 10.degree. F. deviated from the
target temperature (i.e., from the reference standard).
[0048] Referring now to block 52, if no major defect is detected,
microprocessor 20 compares the electrical signals of the plastic
blow-molded container from the production line with stored
reference data regarding desired material distribution throughout
the plastic blow-molded container and determines whether a defect
is present thus indicating a deviation from the stored data
regarding desired material distribution, then the microprocessor
sends a signal to the blow molding machine to adjust at least one
parameter of the machine and records the defect (blocks 54 and 56,
respectively). For example, in the embodiment described above with
reference to FIGS. 3-6, the microprocessor, which is integrated
with the blow molding machine (integration not shown in FIG. 1),
sends a signal to the parison programmer to re-align the phase
alignment of the parison program for the particular container.
[0049] Referring now to block 58, if no defect is detected,
microprocessor 20 compares the electrical signals of the plastic
blow-molded containers from each station in rotary wheel 4 of the
production line with stored reference data regarding desired
material distribution throughout the plastic blow-molded container
and determines whether there is a station-to-station variation. If
a station-to-station variation is detected, then an operator is
notified by, for example, the sounding of an alarm and the defect
is recorded (blocks 60 and 62, respectively).
[0050] Still referring to FIG. 7, if the bottle is free of defects
in material distribution relative to the reference information, the
plastic blow-molded container is conveyed to down stream equipment
and the process is repeated on the next bottle (blocks 64 and 66,
respectively).
Method of Controlling a Blow Molding Production Line (III)
[0051] In another embodiment, the present invention provides a
method of controlling process parameters of a blow molding
production line based on measuring the infrared temperature profile
of a blow-molded plastic container produced on the production line
as described above. This embodiment includes the steps detailed
above with respect to measuring the placement of material in a
blow-molded plastic container, and further includes the following
steps based upon the output information provided by the
microprocessor, which is integrated with the blow molding
production line. If the output information indicates that a process
parameter such as, for example, material temperature, is deviated
from the stored data regarding the desired process parameter,
performing in the microprocessor at least one of the following
steps: (1) adjusting at least one parameter of the extrusion blow
molding machine to bring the process parameter within the desired
setting; and (2) stopping the production line.
[0052] Referring again to FIG. 7 (with reference to the apparatus
of FIG. 1), a flow diagram of the process is shown. This embodiment
will be explained in terms of material temperature but equally
applies to other process parameters such as pressure and material
flow. In block 40, standard temperature profile for a given freshly
blown container is input to the microprocessor as a reference. In
preferred embodiments, the standard temperature profile for a given
container is added to the microprocessor 20 as a series of
electrical signals from an infrared camera in communication with
the microprocessor (which may be the same infrared camera on the
production line). In block 42 and block 44 a bottle from a
production line is conveyed through infrared camera 18 and its
infrared image is captured and converted into corresponding
electrical signals which are delivered to the microprocessor 20. At
block 52, microprocessor 20 compares the electrical signals of the
plastic blow-molded container from the production line with stored
reference data regarding temperature profile throughout the plastic
blow-molded container, which may include the flash. If the
temperature profile is more than, for example, 10.degree. F. over
or under that for the stored reference data, then the
microprocessor sends a signal to the blow molding machine to
adjust, for example, the parison program and records the defect
(blocks 54 and 56, respectively). In another example, if the
average bottle indicates that the bottles are running hot (i.e.,
greater than 10.degree. F. over that for the stored reference
data), then the microprocessor sends a signal to the blow molder to
change the extruder screen pack, which could be an automated or
manual process. If such process is manual, then the microprocessor
sends a signal to an alarm (audio or visual) to alert the operator
that action needs to be taken. Alternatively, the microprocessor
can be programmed to stop the production line if integrated or the
operator can manually shut down the production line based on the
output data.
[0053] Referring now to block 58, if no defect is detected,
microprocessor 20 compares the electrical signals of the plastic
blow-molded containers from each station in rotary wheel 4 of the
production line with stored reference data regarding the standard
temperature profile throughout the plastic blow-molded container
and determines whether there is a station-to-station variation. If
a station-to-station variation is detected, then an operator is
notified by, for example, the sounding of an alarm and the defect
is recorded (blocks 60 and 62, respectively).
[0054] It will be appreciated that the present invention has
provided an improved system for wall thickness determination in a
plastic blow-molded container which, as a result of the cooperation
of an infrared camera and a microprocessor operatively associated
with a blow-molder, provides detailed information so as to
correlate wall thickness of a given container with the mold process
parameters and mold station at which it is made. The microprocessor
processes data regarding the thickness measurement and outputs the
same to a unit which may visually display and record thickness
readings such that an operator can adjust process parameters if a
defect is observed by the infrared camera and microprocessor.
[0055] From the foregoing description, one of ordinary skill in the
art can readily ascertain the essential characteristics of this
invention and, without departing from the spirit and scope thereof,
can make various changes and modifications to the invention to
adapt it to various usages and conditions. For example, one of
ordinary skill in the art would be able to employ the apparatus and
method of the present invention on thermoforming, injection
molding, or injection-stretch blow molding processes.
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