U.S. patent application number 10/143374 was filed with the patent office on 2002-11-28 for system and method for identifying and rejecting defective blow-molded plastic products.
Invention is credited to Pena, Victor M..
Application Number | 20020175448 10/143374 |
Document ID | / |
Family ID | 23982095 |
Filed Date | 2002-11-28 |
United States Patent
Application |
20020175448 |
Kind Code |
A1 |
Pena, Victor M. |
November 28, 2002 |
System and method for identifying and rejecting defective
blow-molded plastic products
Abstract
A system and method for detecting and rejecting defective blow
molded containers is provided. The invention includes a sound
detector system for sensing the sound level from a mold during the
blowing process, and outputting a sound level signal. If the sound
level signal exceeds a predetermined set point, thereby indicating
a discontinuous container, a kick mechanism rejects the defective
container. The kick mechanism is sequenced with the sound detector
system. A proximity switch may be employed to indicate the mold
being in position in front of the sound detector.
Inventors: |
Pena, Victor M.; (Houston,
TX) |
Correspondence
Address: |
WOODCOCK WASHBURN LLP
ONE LIBERTY PLACE, 46TH FLOOR
1650 MARKET STREET
PHILADELPHIA
PA
19103
US
|
Family ID: |
23982095 |
Appl. No.: |
10/143374 |
Filed: |
May 10, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10143374 |
May 10, 2002 |
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09498690 |
Feb 7, 2000 |
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6416308 |
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Current U.S.
Class: |
264/406 ;
264/523; 425/169; 425/215; 425/522; 425/540 |
Current CPC
Class: |
B29C 49/80 20130101;
B29L 2031/7158 20130101; B29C 49/12 20130101; B29C 49/36 20130101;
B29C 49/06 20130101; B29C 49/42 20130101 |
Class at
Publication: |
264/406 ;
425/169; 425/215; 425/522; 425/540; 264/523 |
International
Class: |
B29C 049/36; B29C
049/80; G01B 015/06 |
Claims
We claim:
1. A system for rejecting a defective discontinuous container from
a container production line, the system comprising: a blow molding
carousel comprising at least two molds, each one of the at least
two molds including an interior surface corresponding to a shape of
the container and a nozzle coupled to the carousel and disposed
proximate an opening in said mold, the carousel including a
preform-loading point and a container-unloading point, each one of
the molds receiving pressurized blow air into the mold through the
nozzle; a sound detector system that outputs a reject signal upon
sensing a blow air sound level exceeding a predetermined sound
level set point; and a kick mechanism that ejects the discontinuous
container in response to the reject signal being output from the
sound detector, whereby a preform contiguously expands within the
mold interior surface in response to the pressurized blow air to
form the container and a failure of a wall of the preform or the
container during expansion forms said discontinuous container
having a hole through which the blow air flows to form the blow air
sound level exceeding the predetermined sound level set point.
2. The system of claim 1 wherein the predetermined sound level set
point is less than a sound level of the pressurized blow air
flowing outwardly through the container hole and the mold.
3. The system of claim 1 further comprising a container transfer
wheel for transferring a plurality of the containers from the
carousel at the container-unloading point, said kick mechanism
disposed on the container transfer wheel.
4. The system of claim 1 wherein the kick mechanism includes a
reject arm that strikes the discontinuous container from the
container transfer wheel to eject the discontinuous container
therefrom.
5. The system of claim 4 wherein the reject arm is actuated based
on a signal from said sound detector after a time delay
approximately equal to the time interval between the container
moving from the sound detector to the reject arm such that the
operation of the reject arm is sequenced with the sound
detector.
6. The system of claim 4 wherein the reject arm is actuated based
on a signal from said sound detector after a preset number of
pulses from a proximity switch approximately corresponding to the
number of containers between the sound detector and the kick
mechanism such that the operation of the reject arm is sequenced
with the sound detector, the proximity switch sensing the presence
or absence of a mold at a position proximate the carousel.
7. The system of claim 4 wherein the kick mechanism includes a
controller receiving a sound level signal from the sound detector
and outputting a reject signal in response to the sound signal
exceeding the predetermined set point.
8. The system of claim 7 wherein the controller outputs the reject
signal after an interval to sequence the sound detector with the
reject arm.
9. The system of claim 8 wherein the kick mechanism includes a
valve that opens in response to receiving the reject signal.
10. The system of claim 9 wherein the valve is a pneumatic valve
and the reject arm is air actuated.
11. The system of claim 1 further comprising a proximity switch
that senses a position of any one of the molds of the carousel, the
proximity sensor fixed relative to the carousel.
12. The system of claim 11 wherein the sound detector is activated
in response to any one of the molds of the carousel being disposed
at a first position relative to the proximity switch and is
deactivated in response to said any one of the molds of the
carousel being disposed at a second position relative to the
proximity switch.
13. The system of claim 12 wherein the proximity switch is
circumferentially aligned with the sound detector relative to the
carousel.
14. The system of claim 12 wherein the carousel is rotatable and
the sound detector includes a microphone that is disposed between
150 degrees and 210 degrees from the preform-loading point relative
to the carousel.
15. The system of claim 14 wherein the microphone is disposed
approximately 180 degrees from the preform-loading point relative
to the carousel
16. The system of claim 1 further comprising a preform transfer
wheel for transferring a preform to the carousel at the
preform-loading point.
17. The system of claim 1 wherein the kick mechanism ejects the
discontinuous container from the carousel between the
preform-loading point and the container-unloading point.
18. The system of claim 1 wherein the pressurized blow air is
applied substantially between the preform-loading point and the
container-unloading point.
19. The system of claim 1 wherein the sound detector system
includes a sound detector microphone housing having an inlet that
is directed to the mold.
20. The system of claim 1 further comprising an acoustical
enclosure substantially surrounding the carousel and the sound
detector.
21. The system of claim 1 wherein mold includes vents through which
blow air escapes while the mold houses the discontinuous
container.
22. A sound detection system for identifying a defective
discontinuous container from a container production line, the sound
detection system comprising: a microphone for sensing a sound level
proximate a container mold of the production line, the sound level
varying according to whether pressurized blow air flows through a
vent in the container mold; the microphone providing a sound level
signal; and a control system in communication with the microphone,
the control system receiving the sound level signal and comparing
the sound level signal to a predetermined sound level set point,
the control system outputting a reject signal in response to said
sound level signal exceeding the predetermined sound level set
point, the sound level set point being less than a sound level
signal corresponding to pressurized blow air flowing through the
container mold vent.
23. The sound detection system of claim 22 further comprising a
proximity switch for sensing the position of the mold relative to
the microphone, wherein the sound level system is activated in
response to the proximity switch indicating that the mold is within
a predetermined sensing range of the microphone and deactivated in
response to the proximity switch indicating that the mold is
outside of the predetermined sensing range.
24. The sound detection system of claim 23 further comprising a
controller that compares the sound level signal to the
predetermined set point, the controller generating a reject signal
in response to the sound level signal exceeding the predetermined
set point, the controller delaying generating the reject signal
according to a predetermined interval.
25. The sound detection system of claim 24 whereby a preform
contiguously expands within the mold in response to a pressurized
blow air to form the container, and a failure of a wall of the
preform or the container during expansion forms the discontinuous
container having a passage through which the blow air flows to form
the blow air sound level signal exceeding the predetermined sound
level set point.
26. A method for rejecting a defective discontinuous container from
a container production line comprising the steps of: (a) sensing a
sound level proximate a blow molding carousel comprising at least
two molds, each one of the at least two molds including an interior
surface corresponding to a shape of the container, each one of the
molds receiving pressurized blow air into the mold; (b) generating
a sound level signal that corresponds to the sound level; (c)
comparing the sound level signal with a predetermined sound level
set point; (d) generating a reject signal in response to the sound
signal exceeding the predetermined set point; and (e) rejecting the
discontinuous container from the production line in response to the
reject signal; whereby a preform contiguously expands within the
mold interior surface in response to the pressurized blow air to
form the container and a failure of a wall of the preform or the
container during expansion forms the discontinuous container having
a hole through which the blow air flows to form the blow air sound
level exceeding the predetermined sound level set point.
27. The method of claim 26 further comprising a deactivating step
and an activating step, the activating step including activating
the method in response to the carousel being disposed in a first
circumferential position; the deactivating step disabling at least
one of the sensing step (a), the generating step (b), the comparing
step (c), the generating step (d), and the rejecting step (e) in
response to the carousel being disposed in a second circumferential
position.
28. The method of claim 27 wherein the deactivating step includes
deactivating at least one of the comparing step (d) and the
generating step (d) in a controller.
29. The method of claim 26 wherein the generating step (d) includes
delaying outputting the reject signal to sequence the rejecting
step (e) with the sensing step (a).
30. The method of claim 29 wherein the sequencing step includes
delaying the outputting of the reject signal approximately by a
time interval approximately equal to the discontinuous container
moving from a microphone that senses the sound level in step (a) to
a reject arm that rejects the discontinuous container in the
rejecting step (e).
31. The method of claim 29 wherein the sequencing step includes
delaying the outputting of the reject signal by a preset number of
pulses from a proximity switch approximately corresponding to the
number of containers between a microphone that senses the sound
level in step (a) and a reject arm that rejects the discontinuous
container in the rejecting step (e).
32. The method of claim 26 wherein the sensing step (a) includes
employing a microphone to sense the sound level and the generating
step (b) includes generating the sound level signal with the
microphone.
33. The method of claim 32 wherein the generating step (b) includes
outputting the sound level signal to a control system, the
comparing step (c) includes comparing the signal in the control
system, and the generating step (d) includes generating the reject
signal in the control system and outputting the reject signal from
the control system to a kick mechanism.
34. The method of claim 33 wherein the rejecting step (e) includes
receiving the signal in the kick mechanism and actuating a reject
arm to reject the discontinuous container in response to the sound
level exceeding the predetermined sound level set point.
35. The method of claim 26 wherein the predetermined sound level
set point is less than a sound level of the pressurized blow air
flowing outwardly through the mold.
Description
BACKGROUND
[0001] This invention relates to systems and methods for producing
blow-molded plastic articles, and more particularly, for
identifying and rejecting defective blow-molded plastic products
during the process of making blow-molded plastic products.
[0002] Blow molding of containers and other products is a
well-known process in which a heated thermoplastic preform is
loaded into a mold and filled with pressurized blow air to expand
the preform to the shape of the mold interior surface. For example,
U.S. Pat. No. 5,683,729, entitled "Apparatus for Making Containers
by Blow Moulding Plastic Parisons;" 5,863,571, entitled, "Machine
for Making Containers by Blow Moulding Plastic Parisons;"
4,427,360, entitled "Apparatus for blow Molding Plastic Articles
from a Parison;" and 4,943,228, entitled, "Blow Molding Machine,"
illustrate an injection blow molding process for containers. Each
of these patents are incorporated herein by reference in their
entireties.
[0003] The air pressure within the preform may begin at about 75
pounds per square inch ("PSI") and reach approximately 550 PSI
during the active blow stage. The molds typically have small vents
near the split lines and/or near the base to permit air to escape
from the mold as the preform expands. U.S. Pat. No. 5,792,491,
entitled, "Device for Sealing a Plastic Container Preform to a Blow
Moulding Nozzle," which is incorporated herein by reference in its
entirety, illustrates a mold for a container.
[0004] Even though the preform wall is designed to remain
continuous throughout the blowing process to form a continuous
container that holds the intended contents, holes or
discontinuities in the wall of a finished container sometimes occur
that render the container useless. Because such defective products
often are not identified during an inspection process, the
defective containers frequently may be shipped to a bottler, where
the defective container produces leaks, as well as loss of product
and production time. The trend toward decreasing weight and wall
thickness of containers exacerbates the problem of discontinuities
in the preform or container wall.
SUMMARY
[0005] A system for rejecting a defective discontinuous container
from a container production line is provided. The system includes a
blow molding carousel, a sound detector system, and a kick
mechanism. The blow molding carousel comprises at least two molds
such that each one the molds includes an interior surface
corresponding to a shape of the container and a nozzle coupled to
the carousel and disposed proximate an opening in said mold. Each
one of the molds receives pressurized blow air into the mold
through the nozzle. The carousel includes a preform-loading point
and a container-unloading point, and may also include a container
transfer wheel for transferring a plurality of the containers from
the carousel at the container-unloading point.
[0006] The sound detector system is an disposed proximate the
carousel and outputs a reject signal upon sensing a blow air sound
level exceeding a predetermined sound level set point (preferably
in decibels). The kick mechanism ejects the discontinuous container
in response to the reject signal being output from the sound
detector. Preferably, the kick mechanism includes a reject arm that
strikes the discontinuous container from the container transfer
wheel to eject the discontinuous container therefrom. The sound
detector system includes a device, which preferably is a proximity
switch) for ascertaining a position of the mold from which blow air
is escaping (that is, the mold that is creating the sound that
exceeds the predetermined sound level set point).
[0007] Thus, a preform contiguously expands within the mold
interior surface in response to the pressurized blow air to form
the container. A failure of a wall of the preform or the container
during expansion forms the discontinuous container having a hole
through which the blow air flows to form the blow air sound level
exceeding the predetermined sound level set point. The
predetermined sound level set point is less than a sound level of
the pressurized blow air flowing outwardly through the container
hole and the mold.
[0008] The system may include a delay that sequences the actuation
of the reject arm with a signal from said sound detector. The delay
may be any suitable delay that achieves such sequencing, such as a
time delay approximately equal to the time interval between the
container moving from the sound detector to the reject arm or a
preset number of pulses from a proximity switch approximately
corresponding to the number of containers between the sound
detector and the kick mechanism. A controller may control the
sequencing, although any logic, including that in a microphone that
senses the sound level, may be employed.
[0009] According to another aspect of the present invention, the
sound detection system for identifying a defective discontinuous
container from a container production line is provided that
includes a microphone and a control system. The microphone senses a
sound level proximate a container mold and produces a signal that
corresponds to the sound level. The sound level may varying
according to whether pressurized blow air flows through the
discontinuity and a vent in the container mold.
[0010] The control system, which is in communication with the
microphone, receives the sound level signal and compares the sound
level signal to a predetermined sound level set point. The control
system outputs a reject signal in response to the sound level
signal exceeding the predetermined sound level set point, which is
less than a sound level signal corresponding to pressurized blow
air flowing through the container mold vent.
[0011] The sound detection system may also include a proximity
switch for sensing the position of the mold relative to the
microphone, wherein the sound level system is activated in response
to the proximity switch indicating that the mold is within a
predetermined sensing range of the microphone and deactivated in
response to the proximity switch indicating that the mold is
outside of the predetermined sensing range. Further, the sound
detection system may include a controller that compares the sound
level signal to the predetermined set point. The controller
generates a reject signal in response to the sound level signal
exceeding the predetermined set point and delays generating the
reject signal according to the predetermined interval.
[0012] According to another aspect of the present invention, a
method for rejecting a defective discontinuous container from a
container production line is provided that comprises the steps of:
(a) sensing a sound level proximate a blow molding carousel
comprising at least two molds such that each one of the molds
includes an interior surface corresponding to a shape of the
container and receives pressurized blow air into the mold; (b)
generating a sound level signal that corresponds to the sound
level; (c) comparing the sound level signal with a predetermined
sound level set point; (d) generating a reject signal in response
to the sound signal exceeding the predetermined set point; and (e)
rejecting the discontinuous container from the production line in
response to the reject signal. Thus, a preform contiguously expands
within the mold interior surface in response to the pressurized
blow air to form the container and a failure of a wall of the
preform or the container during expansion forms the discontinuous
container having a hole through which the blow air flows to form
the blow air sound level exceeding the predetermined sound level
set point.
[0013] Further, the method may include a deactivating step and an
activating step. The activating step includes activating the method
in response to the carousel being disposed in a first
circumferential position. The deactivating step disables at least
one of the sensing step (a), the generating step (b), the comparing
step (c), the generating step (d), and the rejecting step (e) in
response to the carousel being disposed in a second circumferential
position. The deactivating step preferably may include deactivating
at least one of the comparing step (d) and the generating step (d)
in a controller. The generating step preferably may include
delaying outputting the reject signal to sequence the rejecting
step (e) with the sensing step (a). The sequencing step may include
delaying the outputting of the reject signal, as described above.
The generating step (b) may include may employ a controller.
BRIEF DESCRIPTION OF THE FIGURES
[0014] FIG. 1 is a schematic of a production line employing the
system according to the present invention;
[0015] FIG. 2 is a top view of a portion of a blow molding carousel
with aspects of the present invention shown in schematic;
[0016] FIG. 3 is perspective view of a housing for enclosing a
portion of the system according to the present invention;
[0017] FIG. 4 is a flow diagram illustrating schematically
illustrating aspects of the present invention;
[0018] FIG. 5 is an enlarged sectional view of a preform for which
the present invention may be employed;
[0019] FIG. 6 is a perspective view of a container for which the
present invention may be employed.
DESCRIPTION OF A PREFERRED EMBODIMENT
[0020] Referring to the Figures to illustrate an embodiment of the
present invention, a production system for producing containers by
blow-molding preforms is provided that rejects defective
containers. Referring to FIG. 1, the container production system
includes a blow molding carousel 12, a preform transfer wheel 14, a
container transfer wheel 16, a conveyor 18, and a preform oven 20.
The carousel 12 includes at least two molds for forming a plastic
container therein. Preferably, carousel 12 includes several molds,
such as twenty-four, that rotate with the carousel in a
predetermined circular path.
[0021] A series of preforms 5, an example of which is shown in FIG.
5 (including a hole 8a that will form a corresponding hole in the
container, thereby forming the discontinuous container), are
conveyed along a defined path through oven 20 wherein heat is
applied to the preform from a battery of heating elements, which
typically are elongated infrared bulbs. At a preform-loading point
22, fingers (not shown) grip the preform 5 by the finish area and
position the preform into an open mold, a portion of which is shown
in FIG. 5. The fingers retract, and a blow nozzle 34 is inserted
into the opening of the preform.
[0022] Upon seating, pressurized blow air 9, shown schematically in
FIG. 5, is introduced into the interior of the preform to expand
preform 5. Optionally, a stretch rod (not shown) may drive the
bottom surface of the preform until it impinges on the bottom of
the mold (not shown). Referring to FIG. 2, the pre-blowing stage
corresponds to stretching of the preform 5 by the stretch rod and
the active blow stage corresponds to further expansion of the
preform in the hoop direction. The blow air 9 preferably
pressurizes the preform such that after the active blow stage,
preform has expanded to the shape of the interior 34 of the mold.
For example, the preform 5 may take the shape of a bottle 4, shown
in FIG. 6, that is further described in U.S. Pat. No. 5,988,416,
which is incorporated herein by reference in its entirety.
[0023] As shown in FIG. 5, preform 5 may include a small hole or
wall discontinuity 8a. Referring to FIG. 6, bottle 4 has a sidewall
7 that preferably is continuous to form an acceptable container,
but may include a discontinuity 8b (shown in phantom in FIG. 6),
which may be caused by discontinuity 8a in the preform or some
other defect in the preform, such as excessive crystallization or
wall thickness or composition that is outside of the specified
range, or simply improper and unanticipated stretching or expansion
of the preform. Thus, the term "discontinuity" (and words formed
from the same root word) encompasses a hole, crack or other
aperture in any portion of the container, including the base and
sidewall, through which air may escape. The reference numeral 4
will be employed to designate an acceptable, continuous container,
while reference numeral 6 will be employed to designate a
defective, discontinuous container (that is, a container with a
sidewall having a discontinuity 8b).
[0024] Thus, at the end of the active blowing stage (that is, the
most counter-clockwise point of the area identified as "active
blow" in FIG. 2), the container 4,6 essentially has its final
shape, as shown in FIG. 6. The container 4,6 continues
counter-clockwise through a thermal stabilization stage in which
cooling water flowing through the mold cools and stabilizes the
material. Referring to FIG. 1, the containers 4,6 within the molds
30 continue moving to a container-unloading point 24, where the
molds open and the containers are transferred from the carousel 12
to the container transfer wheel 16. The containers 4,6 are then
transferred from the container transfer wheel 16 to a conveyor
18.
[0025] Referring to FIGS. 1, 2, 3, and 4, according to an aspect of
the present invention, a sound detector system 38 is provided that
includes a microphone 40 within a microphone housing 42. Microphone
40 may be any conventional microphone, including for example the
piezo-electric element type such as Model AF10 Sound Flow Sensor
supplied by Nohken, Inc. Alternatively, a microphone may be
employed that weights components of the sound level to emphasize
particular frequency ranges. The frequencies for weighting will
vary according to the particular aspects of the application, and
will depend on such factors as mold and vent design, frequency of
the ambient noise, size of the hole to be sensed, and similar
variables, as will be understood by persons familiar with
blow-molding technology and sound detecting or measuring
equipment.
[0026] Housing 42 may be a box or other-shape enclosure that houses
microphone 40. Housing 42 may be formed of any conventional
material, such as sheet metal, and preferably includes insulation
surrounding most of the microphone 40 to inhibit ambient noise and
vibration from reaching microphone 40. Housing 42 includes a
housing inlet 44 which is directed toward the molds 30 of the
carousel 12 to expose an inlet of the microphone 40 to the blow air
exiting the molds 30. The housing 42 and microphone 40 preferably
are mounted onto a slide 46 that enables the sound detector system
38 to moved circumferentially relative to carousel 12 to position
the system 38 to fine tune its operation, as will be understood by
persons familiar with sound detection principles.
[0027] Preferably, the microphone 40 is disposed relative to the
carousel between 150 degrees and 210 degrees from the
preform-loading point 22. Even more preferably, microphone 40 is
disposed approximately 180 degrees from the preform-loading point
22 in order to sense the sound level from the mold 30 based on a
substantially fully formed container 4,6. Preferably, an acoustical
enclosure surrounds the carousel 12 and sound detector system 38 to
diminish the ambient sound reaching microphone 40.
[0028] Referring to another aspect of the present invention, a
proximity switch 52 is provided. Preferably, switch 52 is disposed
circumferentially in-line (that is, at the same radial position
relative to carousel 12) with microphone 40. Switch 52 preferably
substantially senses the presence or absence of the mold along the
arc length of one mold such that switch senses the presence or
absence of a mold 30 in front of microphone 40. Thus, switch 52
outputs a first value upon the carousel reaching a first position
62 that corresponds to a leading edge of a mold passing in front of
microphone 40 and outputs a second value upon the carousel reaching
a second position 64 that corresponds to a trailing edge of the
mold passing in front of the microphone 40. Specifically, for
example, switch 52 may be a conventional proximity sensor that is
positioned vertically above the microphone.
[0029] Further, first and second carousel positions 62 and 64 may
be varied according to the desired span for which microphone 40
will be activated. Under particular circumstances, it may be
desirable for the microphone 40 to be activated for a very short
period relative to the mold width. For example, in circumstances in
which holes 8b are relatively large such that the sound level has a
high magnitude, the proximity switch may be set to provide an
interval within which the sound detector system 38 is activated
equal to one eighth of the width of the mold. Thus, the sound
detector system 38 may be less likely to pick up an ambient sound,
including pressurized blow air flowing from a mold 30 that is one
or more molds away from the microphone, thereby diminishing the
false identification of a continuous container 4.
[0030] The switch 52 may be in a normally open position, and switch
to a closed position upon sensing that the mold 30 is disposed
directly in front of microphone 40. Upon mold 30 moving away from
switch 52 and microphone 40, switch 52 may return to its normally
open state. Alternatively, a pair of limit switches (not shown) may
be employed in which the first limit switch indicates that the mold
leading edge is in position (that is, the first position 62) and
the second limit switch indicates that the mold trailing edge is in
position (that is, the second position 64). Specifically, a first
of the two limit switches may be disposed at first position 62 and
set to trigger upon contacting leading edge of mold 30. A second of
the two limit switches may be disposed at the second position 64
and set to trigger upon contacting the trailing edge of mold 30.
Other techniques and devices for ascertaining the position of the
mold 30 relative to microphone 40 will be apparent to persons
familiar with such techniques and devices in light of the present
specification.
[0031] According to another aspect of the present invention, a
control system 48 is provided that may be a conventional
programmable logic controller or part of a larger control system.
The control system 48 preferably is in electronic communication
with the sound detector system 38 and the proximity sensor 52. The
system also includes a conventional kick mechanism 56 that includes
a reject arm 58 that strikes a container 6 to eject it from the
production line. Preferably, the kick mechanism is a pneumatic
system that is controlled by an air valve 60. Preferably reject arm
58 is disposed on the transfer wheel 16 between the
container-unloading point and the conveyor 18. Alternatively, the
kick mechanism 56 may be disposed on the carousel 12 (this
configuration is not shown). The kick mechanism 56 may be of the
type that is supplied by the carousel manufacturer.
[0032] The operation of the system will be described in conjunction
with a description of the method according to an aspect of the
present invention,. A method is provided for rejecting a defective
discontinuous container 6 from a production line, which is as
described above. As mold 30 passes to first position 62, proximity
switch 52 activates the sound detector system 38 such that
microphone 40 is activated. As mold 30 passes to second position
64, proximity switch deactivates the sound detector system 38.
Proximity switch 52 may be in communication with controller 48 in
order to deactivate the sound detector system 38 (that is, the
sound detector system 38 outputs a signal to the controller which
does no further processing of the signal based on the signal from
switch 52) or switch 52 may be in direct communication with
electronics in the microphone 40 (that is, if the microphone has
the logic circuit that can suppress its output based on the signal
from switch 52).
[0033] Referring particularly to FIG. 4, a sound level 70 is sensed
by the microphone 40. While the proximity switch 52 indicates the
presence of a mold 30, microphone 40 outputs a sound level signal
72 to controller 48. Controller 48 compares the sound level signal
72 to a predetermined sound level set point, which corresponds to a
sound level that is less than the sound level of pressurized blow
air escaping through a hole 8b in the container wall 7, but greater
than the sound level at normal operation of the production line.
Thus, if the sound level signal 72 is greater than the
predetermined set point (which is indicated in FIG. 4 as a decision
block), it indicates that the container is defective because of a
discontinuity therein.
[0034] As will be understood by persons familiar with blow-molding
processes, the predetermined set point may be determined
empirically according to the particular aspects of the application.
For example, a small hole (for example one-sixteenth inch diameter)
in the container 6 may provide a low sound level that is difficult
to distinguish from background noise. In contrast, a large hole
provides a high sound level such that the set point may be set well
above the ambient noise level. Setting the sound level set point at
a low magnitude to identify holes 8b that are small may falsely
identify some sound levels as indicating a defective discontinuous
container 6. Conversely, setting the sound level set point at a
relatively high magnitude to identify holes 8b that are relatively
large may not identify the sound level corresponding to relatively
small holes 8b. Thus, the set point may be set according to the
preferred trade-off between adequately identifying defective
containers or products and falsely identifying acceptable products
as defective.
[0035] Further, the disabling of the system by the proximity switch
52 diminishes the frequency of falsely identifying an acceptable
product as defective because, for example, if a short term ambient
sound level occurs that is above the predetermined set point while
the proximity switch 52 senses that there is no mold 30 in position
between first and second positions 62 and 64, then the sound
detector system/control system will not send a reject signal 76. If
the controller 48 determines that the sound level signal 72 is
greater than the predetermined set point, controller 48 generates a
reject signal 76, which for example may open valve 60 to actuate
reject arm 58 to eject the defective container 6 or product from
the transfer wheel 16 before the defective container or product
reaches the conveyor.
[0036] Because the reject arm 58 is preferably spaced apart from
microphone 40, the controller 48 preferably sequences the actuation
of reject arm 58 with the sound level signal 72 that exceeds the
predetermined set point. The sequencing may be achieved by delaying
the outputting of the reject signal 76 by a time interval
approximately equal to the time that the defective container 6
takes to move from in front of the proximity switch 52 to the
reject arm 58. Preferably, the sequencing is achieved by delaying
the outputting of the reject signal approximately by a preset
number of pulses from a proximity switch approximately
corresponding to the number of containers between the microphone
and the reject arm.
[0037] Aspects of the present invention is illustrated by employing
particular embodiments. However, the present invention is not
limited thereto, and reference should be made to the claims to
ascertain the scope of the invention. Particularly, the present
invention is not limited to the particular containers shown and
described, but may be employed with any blow-molded product.
Further, even though an injection blow molding process is used to
illustrate the invention, the present invention encompasses
extrusion blow molding and other blow molding techniques, including
a linear production line, as will be understood by persons familiar
with those techniques in light of the present disclosure. Further,
the components provided herein are for illustration purposes, and
the present invention is not limited to the particular components
or systems explicitly described herein.
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