Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
~ ~ ~ 3 g 5 ~
BACKGROUND OF THE lNV~N'1'1ON
Field of the Invention:
This invention relates generally to blown film
extrusion lines, and specifically to improved control and
blower systems for use with blown film systems.
Description of the Prior Art:
Blown film extrusion lines are used to manufacture
plastic bags and similar products. A molten tube of plastic
is extruded from an annular die and then stretched and
expanded to a larger diameter and a reduced thickness by the
action of overhead nip rollers and internal air pressure.
Typically, the annular die or the overhead nip rollers are
slowly rotated to distribute film thickness irregularities
caused by die imperfections. To control the circumference of
the finished tube, it is generally necessary to adjust the
volume of air captured inside the tube between the annular die
and the overhead nip rollers. It has been conventional to
adjust the entrapped volume of air by operating a rotary valve
which controls air flow to the annular die, although
~ 69701-65
20939~
1 some control can be obtained by adjusting the supply
2 and exhaust valve and blower systems.
4 One significant problem with rotary valve
s mechanisms is that they operate at their best only over
6 a narrow range of loading conditions. More
7 specifically, rotary valves work best when the air
8 pressure load on the rotary valve is matched to the air
9 pressure load of the annular die. When these loads are
mismatched, start up operations are difficult, and when
11 the bubble has been started it may be quite unstable,
12 and can be characterized as "shaky". Furthermore, when
13 the loads are mismatched between the rotary valve and
14 the annular die, control over the bubble is impaired;
for example, control over an extruded tube may drop
16 from plus or minus one-eighth of an inch in diameter to
17 approximately plus or minus one inch in diameter, an
18 eight fold decrease in control over the extruded tube.
19 Measurement and control of the extruded film
tube circumference is rather important. Mechanical,
21 optical, and acoustic mechanisms have been employed to
22 provide a signal corresponding to the extruded film
23 tube circumference.
24
Systems which employ mechanism feelers are
26 currently disfavored, since feelers produce
27 deformations in the film which impair the quality and
28 grade of the plastic products. In addition, with
29 mechanical feelers, tube size measurements must be made
beyond the molten region of the tube to avoid serious
31 deformations in the tube wall as a result of contact by
32 the feeler. Making the measurement away from the
33 molten region can introduce a detrimental delay into
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1 the control system, and reduce accuracy.
3 Optical and acoustic systems have been
4 provided as substitutes for the mechanical feeler arm.
These optical and acoustic systems eliminate the
6 problem of mechanically induced deformations in the
7 extruded plastic tube, but they are more susceptible to
8 false readings than the mechanical systems. Such false
9 readings can occur as a result of the constant flutter
of the extruded film tube. For acoustical systems,
11 scattered interrogating pulses, as well as ambient
12 noise, and ambient temperature changes can result in
13 inaccurate readings.
14
Consequently, most prior art systems use
16 multiple sensors, which are expensive, to reduce the
17 frequency of misreadings. A false reading can result
18 in an unnecessary overinflation or deflation of the
19 extruded film tube, and can result in an exploded or
collapsed extruded film tube.
21
22 In this worse case situation, the production
23 line is brought to a complete standstill. Such an
24 error can be expensive, since production time is
frequently valued at over one thousand dollars per
26 hour. When an extruded film tube is collapsed or
27 damaged by being overblown, a new bubble must be
28 initiated. In the prior art systems, a skilled
29 operator must take control of the system at startup to
initiate an extruded film tube.
20939S5
8~JMMARY OF THB INVENI ION
3 It is one objective with the present
4 invention to provide an improved control system for
blown film extrusion lines which employs an intelligent
6 filtering system which continuously compares a current
7 position signal corresponding to the circumference of
8 the extruded film tube to at least one previous
g position signal, and which disregards the current
position signal in favor of an estimated position
11 signal if at least one -preselected condition is
12 violated.
13
14 It is another objective of the present
invention to provide a improved control system for a
16 blown film extrusion line, which employs a single
17 acoustic sensor in combination with an intelligent
18 filtering system to gauge and control the circumference
19 of the extruded film tube.
21 It is yet another objective of the present
22 invention to provide an improved control system for
23 blown film extrusion lines in which a single ultrasonic
24 sensor is mounted to the adjustable sizing cage in
close proximity to the extruded film tube and which is
26 moveable inward and outward relative to the central
27 axis along with the adjustable sizing cage as changes
28 are made in the circumference of the extruded film
29 tube.
31 It is still another objective of the present
32 invention to provide an improved control system for
33 blown film extrusion lines which employs two controller
~9395S
1 means for separately comparing the current position
2 signal to first and second maximum and minimum
3 circumference values, in order to detect a collapsing
4 or overblown extruded film tube.
6 It is another object of the present invention
7 to provide an improved control system for blown film
8 extrusion lines which includes a controller with a
9 computer program resident in memory for continuously
comparing in a startup mode the current position signal
11 with a selected minimum circumference threshold, to
12 allow for an automatic startup of the extruded film
13 tube.
14
It is yet another objective of the present
16 invention to provide an improved control system for
17 blown film extrusion lines which includes one or more
18 pneumatically or hydraulically controlled air flow
19 valves which regulate the quantity of air within the
extruded tube, and which include a number of
21 selectively expandable air flow restriction members
22 which are pneumatically or hydraulically enlarged or
23 reduced to regulate the quantity of air within the
24 extruded tube.
These objectives are achieved as is now
26 described. In a blown film extrusion system in which
27 film is extruded as a tube from an annular die and then
28 pulled along a predetermined path, an apparatus is
29 provided for gauging and controlling the size of the
extruded film tube. At least one transducer,
31 preferably ultrasonic, is mounted adjacent the extruded
32 film tube for transmitting and receiving interrogating
33 pulses along paths normal to the extruded film tube,
20939~5
1 and for producing a current position signal
2 corresponding to the circumference of the extruded film
3 tube. The current position signal is continuously
4 compared with at least one previous position signal,
preferably with a computer program resident in a
6 controller memory. If at least one preselected
7 condition is violated, the current position signal is
8 disregarded in favor of an estimated position signal.
g The quantity of air within the extruded film tube is
varied in response to either the current position
11 signal or the estimated position signal to maintain the
12 extruded film tube at a preselected size.
13
14 In order to optimize control and stability of
the extruded film tube, an air flow control valve is
16 used which includes a housing with an inlet and an
17 outlet, an air flow path defined therethrough, and a
18 plurality of selectively-expandable flow restriction
19 members which are disposed in the air flow path within
the housing, and which are hydraulically or
21 pneumatically controlled to expand or reduce in size to
22 allow a greater or lesser quantity of air within the
23 extruded film tube.
24
The transducer may be mounted to an
26 adjustable sizing cage, and is thus moveable inward and
27 outward relative to the extruded film tube as changes
28 are made in its circumference. A pair of controllers
29 may be employed to establish two minimum circumference
values, and two maximum circumference values. If a
31 collapsing or overblown extruded film tube is detected,
32 the system goes into override, and the flow of air is
33 either accelerated or decreased to counter the alarm
2~93~55
1 condition.
3 The system of the present invention also
4 allows for automatic startup. In a startup mode, the
current position signal is continuously compared with a
6 selected minimum circumference threshold. Once the
7 selected minimum circumference threshold is exceeded,
8 the system switches to an operating mode which
g continuously compares the current position signal with
a selected setpoint value to maintain the extruded film
11 tube at a desired circumference.
12
13 An alternative emergency condition control
14 mode of operation provides enhanced control
capabilities, especially the extruded film tube is
16 determined to be either overblown or underblown, or
17 when the extruded film tube is determined to be out of
18 range of the transducer. In this emergency condition
19 control mode, the improved cOll~rOl and blower system of
the present invention allows for more rapid change in
21 the estimated position signal than during normal
22 operating conditions. In addition, when it is
23 determined that the extruded film tube is overblown,
24 underblown, or out of range of the transducer or
transducers, the control system of the present
26 invention supplies an estimated position which is the
27 equivalent of selected referenced boundaries, to
28 prevent momentary and false indications of an overblown
29 condition, an underblown condition, or the extruded
film tube being out of range of the transducer or
31 transducers from detrimentally effecting the estimated
32 position signal.
33
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1 The above as well as additional objects,
2 features, and advantages of the invention will become
3 apparent in the following detailed description.
_ 9 _
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1 BRIEF DE8CRIPTION OF TH~ DRA~ING
3 The novel features believed characteristic of
4 the invention are set forth in the appended claims.
The invention itself however, as well as a preferred
6 mode of use, further objects and advantages thereof,
7 will best be understood by reference to the following
8 detailed description of an illustrative embodiment when
9 read in conjunction with the accompanying drawings,
wherein:
11
12 Figure 1 is a view of a blown film extrusion
13 line equipped with the improved control system of the
14 present invention;
16 Figure 2 is a view of the die, sizing cage,
17 control subassembly and rotating frame of the blown
18 film tower of Figure l;
19
Figure 3 is a view of the acoustic transducer
21 of the improved control system of the present invention
22 coupled to the sizing cage of the blown film extrusion
23 line tower adjacent the extruded film tube of Figure~
24 1 and 2;
26 Figure 4 is a view of the acoustic transducer
27 of Figur- 3 coupled to the sizing cage of the blown
28 film tower, in two positions, one position being shown
29 in phantom;
31 Figure S is a schematic and block diagram
32 view of the preferred control system of the present
33 invention;
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2~)9395~
2 Figure 6 is a schematic and block diagram
3 view of the preferred control system of Yigure 5, with
4 special emphasis on the supervisory control unit;
6 Figure 7(a) is a schematic and block diagram
7 view of the signals generated by the ultrasonic sensor
8 which pertain to the position of the blown film layer;
Figure 7~b) is a view of the ultrasonic
11 sensor of Yiqure 3 coupled to the sizing cage of the
12 blown film tower, with permissible extruded film tube
13 operating ranges indicated thereon;
14
Figure 8(a) is a flow chart of the preferred
16 filtering process applied to the current position
17 signal generated by the acoustic transducer;
18
19 Figur- 8~b) is a graphic depiction of the
operation of the filtering system;
21
22 Figure 9 is a schematic representation of the
23 automatic sizing and recovery logic (ASRL) of Figur- 6;
24
Figure 10 is a schematic representation of
26 the health/state logic (HSL) of Figur- 6;
27
28 Figure 11 is a schematic representation of
29 the loop mode control logic (LMCL) of F~gure 6;
31 Figure 12 is a schematic representation of
32 the volume setpoint control logic (VSCL) of Y~gure C;
33 and
209395a
2 Figure 13 is a flow chart representation of
3 the output clamp of Figure 6.
s Figure 1~, is a schematic and block diagram,
6 and flowchart views of the preferred alternative
7 emergency condition control system of the present
8 invention, which provides enhanced control capabilities
9 for detected overblown and underblown conditions, as
well as when the control system determines that the
11 extruded film tube has passed out of range of the
12 sensing transducer;
13
14 Figure 15 is a schematic and block diagram
view of the signals generated by the ultrasonic sensor
16 which pertain to the position of the blown film layer;
17
18 Figure 16 is a view of the ultrasonic sensor
19 of Figur- 3 coupled to the sizing cage of the blown
film tower, with permissible extruded film tube
21 operating ranges indicated thereon;
22
23 Figure 17 is a schematic representation of
24 the automatic sizing and recovery logic (ASRL) of
Figure 1~;
26
27 Figure 18 is a schematic representation of
28 the health/state logic (HSL) of Figure 14;
29
Figure 19 is a schematic representation of
31 the loop mode control logic (LMCL) of Figure 14;
32
33 Figure 20 is a schematic representation of
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2093955
1 the volume setpoint control logic (VSCL) of Figur~
3 Figure 21 is a flow chart representation of
4 the output clamp of Figure 1~;
6 Figure 22 is a schematic and block diagram
7 view of emergency condition control logic block of
8 Figure 1~;
Figure 23 is a flowchart depiction of the
11 preferred software filter of the alternative emergency
12 condition control system of Figure 14;
13
14 Figure 2~ is a graphic depiction of the
normal operation of the filtering system;
16
17 Figure 25a is a graph which depicts the
18 emergency condition control mode of operation response
19 to the detection of an underblown condition, with the
X-axis representing time and the Y-axis representing
21 position of the extruded film tube;
22
23 Figure 25b is a graph of the binary condition
24 of selected operating blocks of the block diagram
depiction of Figure 22, and can be read in combination
26 with Figur- 25a, wherein the X-axis represents time,
27 and the Y-axis represents the binary condition of
28 selected operational blocks;
29
Figure 26a is a graph which depicts the
31 emergency condition control mode of operation response
32 to the detection of an underblown condition, with the
33 X-axis representing time and the Y-axis representing
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1 position of the extruded film tube;
3 Figure 26b is a graph of the binary condition
4 of selected operating blocks of the block diagram
depiction of Figure 22, and can be read in combination
6 with Figure 26~, wherein the X-axis represents time,
7 and the Y-axis represents the binary condition of
8 selected operational blocks;
Figure 27a is a graph which depicts the
11 emergency condition control mode of operation response
12 to the detection of an underblown condition, with the
13 X-axis representing time and the Y-axis representing
14 position of the extruded film tube;
16 Figure 27b is a graph of the binary condition
17 of selected operating blocks of the block diagram
18 depiction of F$gur- 22, and can be read in combination
19 with Figur- 27-, wherein the X-axis represents ti~e,
and the Y-axis represents the binary condition of
21 selected operational blocks;
22
23 Figure 28 is a schematic and block diagram
24 depiction of one embodiment of the improved air flow
control system of the present invention;
26
27 ~$gur- 29 is a simplified and partial
28 fragmentary and longitudinal section view of the
29 preferred air flow control device used with the air
flow control system of the present invention.
31
20~3955
1 DETAILED DESCRIPTION OF THE INVENTION
3 Figure 1 is a view of blown film extrusion
4 line 11, which includes a number of subassemblies which
cooperate to produce plastic bags and the like from
6 plastic resin. The main components include blown film
7 tower 13, which provides a rigid structure for mounting
8 and aligning the various subassemblies, extruder
9 subassembly 15, die subassembly 17, blower subassembly
19, stack 21, sizing cage 23, collapsible frame 25,
11 nips 27, control subassembly 28 and rollers 29.
12
13 Plastic granules are fed into hopper 31 of
14 extruder subassembly 15. The plastic granules are
melted and fed by extruder 33 and pushed into die
16 subassembly 17, and specifically to annular die 37.
17 The molten plastic granules emerge from annular die 37
18 as a molten plastic tube 39, which expands from the die
19 diameter to a desired final diameter, which may vary
typically between two to three times the die diameter.
21
22 Blower subassembly 19 includes a variety of
23 components which cooperate together to provide a flow
24 of cooling air to the interior of molten plastic tube
39, and also along the outer periphery of molten
26 plastic tube 39. Blower subassembly includes blower ~1
27 which pulls air into the system at inta~e ~3, and
28 exhausts air from the system at exhaust ~5. The flow
29 of air into molten plastic tube 39 is controlled at
valve ~7. Air is also directed along the exterior of
31 molten plastic tube from external air ring ~9, which is
32 concentric to annular die 37. Air is supplied to the
33 interior of molten plastic tube 39 through internal air
- ~5 -
20939!~5
1 diffuser 51. Air is pulled from the interior of molten
2 plastic tube 39 by exhaust stack S3.
4 The streams of external and internal cooling
airs serve to harden molten plastic tube 39 a short
6 distance from annular die 37. The line of demarcation
7 between the molten plastic tube 39 and the hardened
8 plastic tube 55 is identified in the trade as the
9 "frost line." Normally, the frost line is
substantially at or about the location at which the
11 molten plastic tube 39 is expanded to the desired final
12 diameter.
13
14 Adjustable sizing cage 23 is provided
directly above annular die 38 and serves to protect and
16 guide the plastic tube 55 as it is drawn upward through
17 collapsible frame 25 by nips 27. Afterwards, plastic
18 tube SS is directed through a series of rollers 57, S9,
19 61, and 63 which serve to guide the tube to packaging
or other processing equipment.
21
22 In some systems, rotating frame 65 is
23 provided for rotating relative to blown film tower 13.
24 It is particularly useful in rotating mechanical feeler
arms of the prior art systems around plastic tube 55 to
26 distribute the deformations. Umbilical cord 67 is
27 provided to allow electrical conductors to be routed to
28 rotating frame 65. Rotating frame 65 rotates at
29 bearings 71, 73 relative to stationary frame 69.
31 Control subassembly 28 is provided to monitor
32 and control the extrusion process, and in particular
33 the circumference of plastic tube 55. Control
- 16 -
2~939~5
1 subassembly 28 includes supervisory control unit, and
2 operator control panel 77.
4 Pigure 2 is a more detailed view of annular
die 37, sizing cage 23, control subassembly 28, and
6 rotatinq frame 65. As shown in Figure 2, supervisory
7 control unit 75 is electrically coupled to operator
8 control panel 77, valve ~7, and acoustic transducer 79.
9 These components cooperate to control the volume of air
contained within extruded film tube 81, and hence the
11 thickness and diameter of the extruded film tube 81.
12 Valve ~7 controls the amount of air directed by blower
13 ~1 into extruded film tube 81 through internal air
14 diffuser S1.
16 If more air is directed into extruded film
17 tube 81 by internal air diffuser 51 than is exhausted
18 from extruded film tube 81 by exhaust stack ~3, the
19 circumference of extruded film tube 81 will be
increased. Conversely, if more air is exhausted from
21 the interior of extruded film tube 81 by exhaust stack
22 53 than is inputted into extruded film tube 81 by
23 internal air diffuser Sl, the circumference of extruded
24 film tube 81 will decrease.
26 In the preferred embodiment, valve ~1 is
27 responsive to supervisory control unit 75 for
28 increasing or decreasing the flow of air into extruded
29 film tube 81. Operator control panel 77 serves to
allow the operator to select the diameter of extruded
31 film tube 81. Acoustic transducer 79 serves to
32 generate a signal corresponding to the circumference of
33 extruded film tube 81, and direct this signal to
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1 supervisory control unit 75 for comparison to the
2 circumference setting selected by the operator at
3 operator control panel 77.
If the actual circumference of extruded film
6 tube 81 exceeds the selected circumference, supervisory
7 control unit 75 operates valve ~7 to restrict the
8 passage of air from blower ~ into extruded film tube
9 81. This results in a decrease in circumference of
extruded film tube 81. Conversely, if the
11 circumference of extruded film tube 81 is less than the
12 selected circumference, supervisory control unit 75
13 operates on valve ~7 to increase the flow of air into
14 extruded film tube 81 and increase its circumference.
Of course, extruded film tube 81 will fluctuate in
16 circumference, requiring constant adjustment and
17 readjustment of the inflow of air by operation of
18 supervisory control unit 7S and valve ~7.
19
Figur- 3 is a view of ultrasonic sensor 89 of
21 the improve control system of the present invention
22 coupled to sizing cage 23 adjacent extruded film tube
23 81. In the preferred embodiment, acoustic transducer
24 79 comprises an ultrasonic measuring and control system
manufactured by Massa Products Corporation of Hingham,
26 Massachusetts, Model Nos. M-4000, M410/215, and M450,
27 including a Massa Products ultrasonic sensor 89. It i6
28 an ultrasonic ranging and detection device which
29 utilizes high frequency sound waves which are deflected
off objects and detected. In the preferred embodiment,
31 a pair of ultrasonic sensors 89 are used, one to
32 transmit sonic pulses, and another to receive sonic
33 pulses. For purposes of simplifying the description
- 18 -
20939~5
1 only one ultrasonic sensor 89 is shown, and in fact a
2 single ultrasonic sensor can be used, first to transmit
3 a sonic pulse and then to receive the return in an
4 alterating fashion. The elapsed time between an
ultrasonic pulse being transmitted and a significant
6 echo being received corresponds to the distance between
7 ultrasonic sensor 89 and the object being sensed. Of
8 course, the distance between the ultrasonic sensor 89
g and extruded film tube 81 corresponds to the
circumference of extruded film tube 81. In the present
11 situation, ultrasonic sensor 89 emits an interrogating
12 ultrasonic beam 87 substantially normal to extruded
13 film tube 81 and which is deflected from the outer
14 surface of extruded film tube 81 and sensed by
ultrasonic sensor 89.
16
17 The Massa Products Corporation ultrasonic
18 measurement and control system includes system
19 electronics which utilize the duration of time between
transmission and reception to produce a useable
21 electrical output such as a voltage or current. In the
22 preferred embodiment, ultrasonic sensor 89 is coupled
23 to sizing cage 23 at adjustable coupling 83. In the
24 preferred embodiment, ultrasonic sensor 89 is
positioned within seven inches of extruded film tube 81
26 to minimize the impact of ambient noise on a control
27 system. Ultrasonic sensor 89 is positioned so that
28 interrogating ultrasonic beam 87 travels through a path
29 which is substantially normal to the outer surface of
extruded film tube 81, to maximize the return signal to
31 ultrasonic sensor 89.
32
33 Figure 4 is a view of ultrasonic sensor 89 of
20Y39~5
1 Figure 3 coupled to sizing cage 23 of the blown film
2 tower 13, in two positions, one position being shown in
3 phantom. In the first position, ultrasonic sensor 89
4 is shown adjacent extruded film tube 81 of a selected
s circumference. When extruded film tube 81 is downsized
6 to a tube having a smaller circumference, ultrasonic
7 sensor 89 will move inward and outward relative to the
8 central axis of the adjustable sizing cage, along with
9 the adjustable sizing cage 23. The second position is
shown in phantom with ultrasonic sensor 89' shown
11 adjacent extruded film tube 81' of a smaller
12 circumference. For purposes of reference, internal air
13 diffuser Sl and exhaust stack 53 are shown in Figure 4.
14 The sizing cage is also movable upward and downward, so
ultrasonic sensor 89 is also movable upward and
16 downward relative to the frostline of the extruded film
17 tube 81.
18
19 Yigur- 5 is a schematic and block diagram
view of the preferred control system of the present
21 invention. The preferred acoustic transducer 79 of the
22 present invention includes ultrasonic sensor 89 and
23 temperature sensor 91 which cooperate to produce a
24 current position signal which is independent of the
ambient temperature. Ultrasonic sensor 89 is
26 electrically coupled to ultrasonic electronics module
27 95, and temperature sensor 91 is electrically coupled
28 to temperature electronics module 97. Together,
29 ultrasonic electronics module 95 and temperature
electronics module 97 comprise transducer electronics
31 93. Four signals are produced by acoustic transducer
32 79, including one analog signal, and three digital
33 signals.
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209395S
2 As shown in Figur- 5, four conductors couple
3 transducer electronics to supervisory control unit 75.
4 SpecificaIly, conductor 99 routes a 0 to 10 volts DC
analog input to supervisory control unit 75.
6 Conductors 101, 103, and 105 provide digital signals to
7 supervisory control unit 75 which correspond to a
8 target present signal, maximum override, and minimum
g override. These signals will be described below in
greater detail.
11
12 Supervisory control unit 75 is electrically
13 coupled to setpoint display 109 through analog display
14 output 107. An analog signal between 0 and 10 volts DC
is provided to setpoint display 109 which displays the
16 selected distance between ultrasonic sensor 89 and
17 extruded film tube 81. A distance is selected by the
18 operator through distance selector 111. Target
19 indicator 113, preferably a light, ic provided to
indicate that the target (extruded film tube 81) is in
21 range. Distance selector 111 is electrically coupled
22 to supervisory control unit 75 by distance setting
23 conductor 119. Target indicator 113 is electrically
24 coupled to supervisory control unit 75 through target
present conductor 121.
26
27 Supervisory control unit 75 is also coupled
28 via valve control conductor 123 to proportional valve
29 12S. In the preferred embodiment, proportional valve
125 corresponds to valve 47 of Figure 1, and is a
31 pressure control component manufactured by
32 Proportionair of McCordsville, Indiana, Model No. BB1.
33 Proportional valve 125 translates an analog DC voltage
20939~
1 provided by supervisory control unit 75 into a
2 corresponding pressure between .5 and 1.2 bar.
3 Proportional valve 125 acts on rotary valve 129 through
4 cylinder 127. Pressurized air is provided to
proportional valve 125 from pressurized air supply 131
6 through 20 micron filter 133.
8 Figure 6 is a schematic and block diagram
g view of the preferred control system of Figuro 5, with
special emphasis on the supervisory control unit 75.
11 Extruded film tube 81 is shown in cross-section with
12 ultrasonic sensor 89 adjacent its outer wall.
13 Ultrasonic sensor 89 emits interrogating pulses which
14 are bounced off of extruded film tube and sensed by
ultrasonic sensor 89. The time delay between
16 transmission and reception of the interrogating pulse
17 is processe~ by transducer electronics 93 to produce
18 four outputs: CURRFNT ~08I-lON signal which i8
19 provided to supervisory control unit 7S via analog
output conductor 99, digital ~ARGFT PRF8~N~ signal
21 which is provided over digital output 105, a minimum
22 override signal (MI0 signal) indicative of a collapsing
23 or undersized bubble which is provided over digital
24 output conductor 103, and maximum override signal (MA0
signal) indicative of an overblown extruded film tube
26 81 which is provided over a digital output conductor
27 101.
28
29 As shown in Figur- 6, the position of
extruded film tube 81 relative to ultrasonic sensor 89
31 is analyzed and controlled with reference to a number
32 of distance thresholds and setpoints, which are shown
33 in greater detail in Figure 7(a). All set points and
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20~3955
1 thresholds represent distances from reference R. The
2 control system of the present invention attempts to
3 maintain extruded film tube 81 at a circumference which
4 places the wall of extruded film tube 81 at a tangent
to the line established by reference A. The distance
6 between reference R and set point A may be selected by
7 the user through distance selector 111. This allows
8 the user to control the distance between ultrasonic
9 sensor 89 and extruded film tube 81.
11 The operating range of acoustic transducer 79
12 is configurable by the user with settings made in
13 transducer electronics 93. In the preferred
14 embodiment, using the Massa Products transducer, the
range of operation of acoustic transducer 79 is between
16 3 to 24 inches. Tberefore, the user may select a
17 minimum circumference threshold C and a maximum
18 circumference threshold ~, below and above which an
19 error signal i5 generated. Minimum circumference
threshold C may be set by the user at a distance d3
21 from reference R. Maximum circumference threshold B
22 may be selected by the user to be a distance d2 from
23 reference R. In the preferred embodiment, setpoint A
24 is set a distance of 7 inches from reference R.
Minimum circumference threshold C is set a distance of
26 10.8125 inches from reference R. Maximum circumference
27 threshold 8 is set a distance of 4.1 inches from
28 reference R. Transducer electronics 93 allows the user
29 to set or adjust these distances at will provided they
are established within the range of operation of
31 acoustic transducer 79, which is between 3 and 24
32 inches.
33
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1 Besides providing an analog indication of the
2 distance between ultrasonic sensors 89 and extruded
3 film tube 81, transducer electronics 93 also produces
4 three digital signals which provide information
pertaining to the position of extruded film tube 81.
6 If extruded film tube 81 is substantially normal and
7 within the operating range of ultrasonic sensor 89, a
8 digital "1" is provided at digital output 105. The
9 signal is representative of a TARGET PRE8ENT signal.
If extruded film tube 81 is not within the operating
11 range of ultrasonic sensor 89 or if a return pulse is
12 not received due to curvature of extruded film tube 81,
13 TARGET PRE8ENT signal of digital output lOS is low. As
14 discussed above, digital output 103 is a minimum
override signal MI0. If extruded film tube 81 is
16 smaller in circumference than the reference established
17 by threshold C, minimum override signal MI0 of digital
18 output 103 is high. Conversely, if circumference of
19 extruded film tube 81 is greater than the reference
established by threshold C, the minimum override signal
21 MI0 is low.
23 Digital output 101 is for a maximum override
24 signal NA0. If extruded film tube 81 is greater than
the reference established by threshold B, the maximum
26 override signal ~AO is high. Conversely, if the
27 circumference of extruded film tube 81 is less than the
28 reference established by threshold B, the output of
29 maximum override signal MA0 is low.
31 The minimum override signal MIO will stay
2093955
1 high as long as extruded film tube 81 has a
2 circumference less than that established by threshold
3 C. Likewise, the maximum override signal ~AO will
4 remain high for as long as the circumference of
extruded film tube 81 remains larger than the reference
6 established by threshold B.
8 Threshold D and threshold ~ are also depicted
9 in Figure 7 ~a) . Threshold D is established at a
distance d~ from reference R. Threshold E is
11 established at a distance d5 from reference R.
12 Thresholds D and ~ are established by supervisory
13 control unit 75, not by acoustic transducer 79.
14 Threshold D represents a minimum circumference
lS threshold for extruded film tube 81 which differs from
16 that established by transducer electronics 93.
17 Likewise, threshold E corresponds to a maximum
18 circumference threshold which differs from that
19 established by acoustic transducer 79. Thresholds D
and ~ are established in the software of supervisory
21 control unit 75, and provide a redundancy of control,
22 and also minimize the possibility of user error, since
23 these threshold are established in software, and cannot
24 be easily changed or accidentally changed. The
coordination of all of these thresholds will be
26 discussed in greater detail below. In the preferred
27 embodiment, threshold C is established at 10.8125
28 inches from reference R. Threshold ~ is established at
29 3.6 inches from reference a.
31 Figure 7~b) is a side view of the ultrasonic
32 sensor 89 coupled to sizing cage 23 of the blown film
33 tower 13, with permissible extruded film tube 81
- 25 -
20939~S
1 operating ranges indicated thereon. Setpoint A is the
2 desired distance between ultrasonic sensor 89 and
3 extruded film tube 81. Thresholds D and C are
4 established at selected distances inward from
S ultrasonic sensor 89, and represent minimum
6 circumference thresholds for extruded film tube 81.
7 Thresholds B and B are established at selected
8 distances from setpoint A, and establish separate
g maximum circumference thresholds for extruded film tube
81. As shown in Figure 7~b), extruded film tube 81 is
11 not at setpoint A. Therefore, additional air must be
12 supplied to the interior of extruded film tube 81 to
13 expand the extruded film tube 81 to the desired
14 circumference established by setpoint a.
16 If extruded film tube 8~ were to collapse,
17 two separate alarm conditions would be registered. One
18 alarm condition will be established when extruded film
19 tube 81 falls below threshold C. A second and separate
alarm condition will be established when extruded film
21 tube 81 falls below threshold D. Extruded film tube 81
22 may also become overblown. In an overblown condition,
23 two separate alarm conditions are possible. When
24 extruded film tube 81 expands beyond threshold B, an
2S alarm condition is registered. When extruded film tube
26 81 expands further to extend beyond threshold ~, a
27 separate alarm condition is registered.
28
29 As discussed above, thresholds C and B are
subject to user adjustment through settings in
31 transducer electronics 93. In contrast, thresholds D
32 and B are set in computer code of supervisory control
33 unit 75, and are not easily adjusted. This redundancy
- 26 -
2093955
1 in control guards against accidental or intentional
2 missetting of the threshold conditions at transducer
3 electronics 93. The system also guards against the
4 possibility of equipment failure in transducer 79, or
gradual drift in the threshold settings due to
6 deterioration, or overheating of the electronic
7 components contained in transducer electronics 93.
g Returning now to Figure 6, operator control
panel 137 and supervisory control unit 75 will be
11 described in greater detail. Operator control panel
12 137 includes setpoint display 109, which serves to
13 display the distance dl between reference R and
14 setpoint A. Setpoint display 109 includes a 7 segment
display. Distance selector 111 is used to adjust
16 setpoint A. Holding the switch to the n+n position
17 increases the circumference of extruded film tube 81 by
18 decreasing distance dl between ~etpoint A and reference
19 R. Holding the switch to the n_~ position decrease~
the diameter of extruded film tube 81 by increasing the
21 distance between reference R and setpoint A.
22
23 Target indicator 113 is a target light which
24 displays information pertaining to whether extruded
film tube 81 is within range of ultrasonic transducer
26 89, whether an echo is received at ultrasonic
27 transducer 89, and whether any alarm condition has
28 occurred. Blower switch 139 is also provided in
29 operator control panel 137 to allow the operator to
selectively disconnect the blower from the control
31 unit. As shown in Figure 6, all these components of
32 operator control panel 137 are electrically coupled to
33 supervisory control unit 75.
- 27 -
20939!~S
2 Supervisory control unit 75 responds to the
3 information provided by acoustic transducer 79, and
4 operator control panel 137 to actuate proportional
valve 125. Proportional valve 125 in turn acts upon
6 pneumatic cylinder 127 to rotate rotary valve 129 to
7 control the air flow to the interior of extruded film
8 tube 81.
With the exception of analog to digital
11 converter 1~1, digital to analog converter 1~3, and
12 digital to analog converter 1~5 (which are hardware
13 items), supervisory control unit 75 is a graphic
14 representation of computer software resident in memory
of supervisory control unit 7S. In the preferred
16 embodiment, supervisory control unit 75 comprises an
17 industrial controller, preferably a Texas Instrument
18 brand industrial controller Model No. PM550.
19 Therefore, supervisory control unit 75 is essentially a
relatively low-powered computer which is dedicated to a
21 particular piece of machinery for monitoring and
22 controlling. In the preferred embodiment, supervisory
23 control unit 75 serves to monitor many other operations
24 of blown film extrusion line 11. The gauging and
control of the circumference of extruded film tube 81
26 through computer software is one additional function
27 which is "piggybacked" onto the industrial controller.
28 Alternately, it is possible to provide an industrial
29 controller or microcomputer which is dedicated to the
monitoring and control of the extruded film tube 81.
31 Of course, dedicating a microprocessor to this task is
32 a rather expensive alternative.
33
- 28 -
20939~S
-
1 For purposes of clarity and simplification of
2 description, the operation of the computer program in
3 supervisory control unit 75 have been segregated into
4 operational blocks, and presented as an amalgamation of
digital hardware blocks. In the preferred embodiment,
6 these software subcomponents include: software filter
7 149, health state logic 151, automatic sizing and
8 recovery logic 153, loop mode control logic 155, volume
9 setpoint control logic 157, and output clamp ~59.
These software modules interface with one another, and
11 to PI loop program 147 of supervisory control unit 75.
12 PI loop program is a software routine provided in the
13 Texas Instruments' PM550 system. The proportional
14 controller regulates a process by manipulating a
lS control element through the feedback of a controlled
16 output. The equation for the output of a PI controller
17 is:
18
l9 m = K*e + K/T e)dt + ms
21 In this equation:
22
23 m = controller output
24 K = controller gain
e = error
26 T = reset time
27 dt = differential time
28 ms = constant
29 eSdt = integration of all previous errors
31 When an error exists, it is summed
32 (integrated) with all the previous errors, thereby
33 increasing or decreasing the output of the PI
- 29 -
- 20g39~5
1 controller (depending upon whether the error is
2 positive or negative). Thus as the error term
3 accumulates in the integral term, the output changes so
4 as to eliminate the error.
6 CURRENT P08ITION signal is provided by
7 acoustic transducer 79 via analog output 99 to analog
8 to digital converter 141, where the analog C~RRENT
9 PO8ITION signal is digitized. The digitized C~RRENT
P08ITION signal is routed through software filter 1~9,
11 and then to PI loop program 1~7. If the circumference
12 of extruded film tube 81 needs to be adjusted, PI loop
13 program 1~7 acts through output clamp 159 upon
14 proportional valve 125 to adjust the quantity of air
provided to the interior of extruded film tube 81.
16
17 Figure 8(a) is a flowchart of the preferred
18 filtering process applied to CURRENT PO8ITIO~ signal
19 generated by the acoustic transducer. The digitized
C~RRENT PO8ITION signal is provided from analog to
21 digital converter 141 to software filter 1~9. The
22 program reads the C~RRENT P08ITION signal in step 161.
23 Then, the software filter 1~9 sets 8AMPL~ (N) to the
24 position signal.
26 In step 165, the absolute value of the difference
27 between CURREN$ P08ITION (8AMPLE (N)) and the previous
28 sample (8A~PLB (N - 1)) is compared to a first
29 threshold. If the absolute value of the difference
between the current sample and the previous sample is
31 less than first threshold T1, the value of 8AMPLB (N)
32 is set to CF8, the current filtered sample, in step
33 167. If the absolute value of the difference between
- 30 -
20~39SS
1 the current sample and the previous sample exceeds
2 first threshold T1, in step 169, the CURRENT PO~ITION
3 signal is disregarded, and the previous position signal
4 8AHPLB (~ - 1) is substi~uted in its place.
s
6 Then, in step 171, the suggested change 8C is
7 calculated, by determining the difference between the
8 current filtered sample CF8 and the best position
9 estimate BPB. In step 173, the suggested change 8C
which was calculated in step 171 is compared to
11 positive T2, which is the maximum limit on the rate of
12 change. If the suggested change is within the maximum
13 limit allowed, in step 177, allowed change AC is set to
14 the suggested change 8C value. If, however, in step
173, the suggested change exceeds the maximum limit
16 allowed on the rate of change, in step 175, the allowed
17 change is set to +LT2, a default value for allowed
18 change.
19
In step 179, the suggested change 8C is
21 compared to the negative limit for allowable rates of
22 change, negative T2. If the suggested change 8C is
23 greater than the maximum limit on negative chanqe, in
24 step 181, allowed change AC is set to negative -LT2, a
default value for negative change. However, if in step
26 179 it is determined that suggested change 8C is within
27 the maximum limit allowed on negative change, in step
28 183, the allowed change AC is added to the current best
29 position estimate BPE, in step 183. Finally, in step
185, the newly calculated best position estimate BPB is
31 written to the PI loop program.
32
33 Software filter 1~9 is a two stage filter
20939~5
1 which first screens the C~RREN~ PO8ITION signal by
2 comparing the amount of change, either positive or
3 negative, to thres~old T1. If the cURREN~ PO8ITION
4 signal, as compared to the preceding position signal
exceeds the threshold of Tl, the current position
6 signal is discarded, and the previous position signal
7 (~AHPLE (N - 1)) is used instead. At the end of the
8 first stage, in step 171, a suggested change 8C value
9 is derived by subtracting the best position estimate
BPE from the current filtered sample CF8.
11
12 In the second stage of filtering, the
13 suggested change 8C value is compared to positive and
14 negative change thresholds (in steps 173 and 179). If
the positive or negative change thresholds are
16 violated, the allowable change is set to a preselected
17 value, either +LT2, or -LT2. Of course, if the
18 suggested change 8C is within the limits set by
l9 positive T2 and negative T2, then the allowable change
AC is set to the suggested change 8C.
21
22 The operation of software filter 1~9 may also be
23 understood with reference to Figure 8~b). In the graph
24 of Figur- 8(b), the y-axis represents the signal level,
and the x-axis represents time. The signal as sensed
26 by acoustic transducer 79 is designated as input, and
27 shown in the solid line. The operation of the first
28 stage of the software filter 1~9 is depicted by the
29 current filtered sample CF8, which is shown in the
graph by cross-marks. As shown, the current filtered
31 sample CF8 operates to ignore large positive or
32 negative changes in the position signal, and will only
33 change when the position signal seems to have
209395~
.
1 stabilized for a short interval. Therefore, when
2 changes occur in the current filtered sample CF8, they
3 occur in a plateau-like manner.
In stage two of the software filter 149, the
6 current filtered sample CF8 is compared to the best
7 position estimate BP~, to derive a suggested change 8C
8 value. The suggested 8C is then compared to positive
9 and negative thresholds to calculate an allowable
change AC which is then added to the best position
11 estimate BPB. Figure 8~b) shows that the best position
12 estimate BP~ signal only gradually changes in response
13 to an upward drift in the PO8ITION 8IGNA$. The
14 software filtering system 1~9 of the present invention
renders the control apparatus relatively unaffected by
16 random noise, but capable of tracking the more
17 "gradual" changes in bubble position.
18
19 Experimentation has revealed that the software
filtering system of the present invention operates best
21 when the position of extruded film tube 81 is sampled
22 between 20 to 30 times per second. At this sampling
23 rate, one is less likely to incorrectly identify noise
24 as a change in circumference of extruded film tube 8~.
The preferred sampling rate accounts for the common
26 noise signals encountered in blown film extrusion
27 liner.
28
29 Optional thresholds have also been derived
through experimentation. In the first stage of
31 filtering, threshold T1 is established as roughly one
32 percent of the operating range of acoustic transducer
33 79, which in the preferred embodiment is twenty-one
- 33 -
2093955
1 meters (24 inches less 3 inches). In the second stage
2 of filter, thresholds +LT2 and -LT2 are established as
3 roughly 0.30% of the operating range of acoustic
4 transducer 79.
s
6 Figure 9 is a schematic representation of the
7 automatic sizing and recovery logic ASRL of supervisory
8 control unit 75. As stated above, this figure is a
9 hardware representation of a software routine. ASRL
153 is provided to accommodate the many momentary false
11 indications of maximum and minimum circumference
12 violations which may be registered due to noise, such
13 as the noise created due to air flow between acoustic
14 transducer 79 and extruded film tube 81. The input
from maximum alarm override MAO is "ored" with high
16 alarm D, from the PI loop program, at "or" operator
17 191. High alarm D is the signal generated by the
18 program in supervisory control unit 75 when the
19 circumference of extruded film tube 81 exceeds
threshold D of ~igure 7~a). If a maximum override MAO
21 signal exists, or if a high alarm condition D exists,
22 the output of "or~ operator 191 goes high, and actuates
23 delay timer 193.
24
2S Likewise, minimum override MIO signal is
26 "ored" at "or" operator 195 with low alarm ~. If a
27 minimum override signal is present, or if a low alarm
28 condition ~ exists, the output of "or" operator 195
29 goes high, and is directed to delay timer 197. Delay
timers 193, 197 are provided to prevent an alarm
31 condition unless the condition is held for 800
32 milliseconds continuously. Every time the input of
33 delay timers 193, ~97 goes low, the timer resets and
- 3~ -
2093955
starts from 0. This mechanism eliminates many false
2 alarms.
4 If an alarm condition is held for 800
milliseconds continuously, an OVERBLO~N or ~NDERBLOlIN
6 signal is generated, and directed to the health state
7 logic 151. Detected overblown or underblown conditions
8 are "ored" at "or" operator 199 to provide a REQUE8T
9 MAN~AI. HODE signal which is directed to loop mode
control logic 155.
11
12 Figure 10 is a schematic representation of
13 the health-state logic lS1 of Fi~ure C. The purpose of
14 this logic is to control the target indicator 113 of
operator control panel 137. When in non-error
16 operation, the target indicator 113 is on if the blower
17 is on, and the TARGE~ PP~E8ENT signal from digital
18 output 105 is high. When an error is sensed in the
19 maximum override l~AO or minimum override ~IIO lines, the
target indicator 113 will flash on and off in one half
21 second intervals.
22
23 In health-state logic ~I8L 151, the maximum
24 override signal M~O is inverted at inverter 205.
Likewise, the minimum override signal is inverted at
26 inverter 207.
27
28 "And" operator 209 serves to "and" the
29 inverted maximum override signal 2~0, with the
OVERBLOWN signal, and high alarm signal D. A high
31 output from "and" operator 209 indicates that something
32 is wrong with the calibration of acoustic transducer
33 79.
-- 35 --
20939~
2 Li~cewise, "and" operator 213 serves to "and"
3 the inverted minimum override signal MIO, with the
4 ov~ o~rN signal, and low alarm signal B. If the
output of "and" operator 213 is high, something is
6 wrong with the calibration of acoustic transducer 79.
7 The outputs from "and" operators 209, 213 are combined
8 in "or" operator 215 to indicate an error with either
9 the maximum or minimum override detection systems. The
output of "or" operator 215 is channeled through
11 oscillator 219, and inverted at inverter 217. "And"
12 operator 211 serves to "and" the TARGET PRE8ENl~ signal,
13 blower signal, and inverted error signal from "or"
14 operator 215. The output of "and" operator of 211 is
connected to target indicator 113.
16
17 If acoustic transducer 79 is properly
18 calibrated, the target ig within range and normal to
19 the sonic pulses, and the blower i8 on, target
indicator 113 will be on. If the target is within
21 range and normal to the sonic pulses, the blower is on,
22 but acoustic transducer 79 is out of calibration,
23 target indicator 113 will be on, but will be blinking.
24 The blinking si~nal indicates that acoustic transducer
79, and in particular transducer electronics 93, must
26 be recalibrated.
27
28 Figure 11 is a schematic representation of
29 loop mode control logic LMCL of Figure 6. The purpose
of this software module is coordinate the transition in
31 modes of operation. Specifically, this software module
32 coordinates automatic startup of the blown film
33 extrusion process, as well as changes in mode between
20939~5
-
1 an automated "cascade" mode a~d a manual mode, which is
2 the required mode of the PI controller to enable under
3 and overblown conditions of the extruded film tube 81
4 circumference. The plurality of input signal~ are
provided to loop mode control logic 15S, including:
6 BLO~ER ON, REQ~E8T MAN~A~ MODE, PI LOOP IN CA8CADE
7 MOD~, UNDERBLO~N and OVERBLO~. Loop mode control
8 logic LMCL 155 provides two output signals: MANUAL
9 MOD~, and CASCADE MODE.
11 Figure 11 includes a plurality of digital
12 logic blocks which are representative of programming
13 operations. "Or" operator 225 "ores" the inverted
14 BLOWER ON 8IGNAL to the R~Q~E8T MANUAL MODE 8IGNAL.
"And" operator 227 "ands" the inverted REQ~EST MANUAL
16 MOD~ 8IGNAL with an inverted ~ANUAL MOD~ 8IGNAL, and
17 the BLOWER ON 8IGNAL. "And" operator 229 "ands" the
18 REQUE8T ~ANUA~ MODB 8IGNAL to the inverted CA8CADB ~ODE
19 8IGNAL. This prevents MAN~AL MODE and CA8CADE MOD~
from both being on at the same time. "And" operator
21 231 "ands" the MANUAL ~ODB 8IGNAL, the inverted
2 2 UNDERBLO~N 8IGNAL, and the OVERBLO~N 8IGNAL. nAndn
23 operator 233 "ands" the NAN~AL ~ODB 8IGNAL with the
24 UNDERBLO~N 8IGNAL. This causes the overblown condition
to prevail in the event a malfunction causes both
26 underblown and overblown conditions to be on.
27 Inverters 235, 237, 239, 2~1, and 243 are provided to
28 invert the inputted output signals of loop mode control
29 logic 155 were needed. Software one-shot 2~5 is
provided for providing a momentary response to a
31 condition. Software one-shot 2~5 includes "and"
32 operator 2~7, off-delay 2~9, and inverter 251.
33
- 37 -
2~)93955
1 The software of loop mode control logic 155
2 operates to ensure that the system is never in MANUAI
3 MOD~, and CA8CAD~ MOD~ at the same time. When manual
4 mode is requested by REQUE~T MAN~AL ~ODE, loop mode
control logic 155 causes MAN~AL MODE to go high. When
6 manual mode is not requested, loop mode control logic
7 155 operates to cause CA8CADB MODE to go high. MANUAL
8 MOD~ and CA~CADE MODE will never be high at the same
9 time. Loop mode control logic 155 also serves to
ensure that the system provides a "bumpless transfer"
11 when mode changes occur. The term "cascade mode" is
12 understood in the automation industries as referring to
13 an automatic mode which will read an adjustable
14 setpoint.
16 Loop mode control logic 155 will also allow
17 for automatic startup of the blown film extrusion
18 process. At startup, UND~PR~O~N 8IGNaL is high, PI
19 LOOP IN CA8CAD~ MODE is low, B~Ol~lSR ON ~IGNAI. is high.
These inputs (and inverted inputs) are combined at
21 "and" operators 231, 233. At startup, "and" operator
22 233 actuates logic block 253 to move the maximum air
23 flow value address to the PI loop step 261. At
24 startup, the MAN~Ah MODE 8IGN~L is high. For the PI
loop controller of the preferred embodiment, when
26 MANUAL MODE is high, the value contained in PI loop
27 output address is automatically applied to proportional
28 valve 125. This results in actuation of proportional
29 valve 125 to allow maximum air flow to start the
extruded film tube 81.
31
32 When extruded film tube 81 extends in size
33 beyond the minimum threshold (C and D of Figure 7~a)),
- 38 -
2093953
1 the ~NDERBLOwN ~IGNAL goes low, and the ~I LOOP lN
2 CA8CADB MODE signal goes high. This causes software
3 one-shot 245 to trigger, causing logic blocks 26S, 267
4 to push an initial bias value contained in a program
address onto the PI loop. Simultaneously, logic blocks
6 269, 271 operate to place the selected setpoint value A
7 onto volume-setpoint control logic VSCL 157.
8 Thereafter, volume-setpoint control logic VSCL 157
g alone serves to communicate changes in setpoint value A
to PI loop program 1~7.
11
12 If an overblown or underblown condition is
13 detected for a sufficiently long period of time, the
14 controller will request a manual mode by causing
REQUE8T ~AN~AL MOD~ 8IGNAL to go high. If ~EQUE8T
16 MANUAL NOD~ goes high, loop mode control logic LMCL 155
17 supervises the transfer through operation of the logic
18 blocks.
19
Loop mode control logic LMCL 155 also serves
21 to detected overblown and underblown conditions. If an
22 overblown or underblown condition is detected by the
23 control system, REQUE8T NAN~AL NODE goes high, and the
24 appropriate OVERBLO~N or UNDERBLO~N signal goes high.
The loqic operators of loop mode control logic LMCL 155
26 operate to override the normal operation of the control
27 system, and cause maximum or minimum air flow by
28 putting the maximum air flow address 2Cl or minimum air
29 flow address 263 to the PI output address. As stated
above, when NANUA~ NODL is high, these maximum or
31 minimum air flow address values are outputted directly
32 to proportional valve 125. Thus, when the extruded
33 film tube 81 is overblown, loop mode control logic LMCL
- 39 -
2~93955
1 155 operates to immediately cause proportional valve
2 ~25 to minimize air flow to extruded film tube 81.
3 Conversely, if an underblown condition is detected,
4 loop mode control logic LMCL 155 causes proportional
valve 125 to immediately maximize air flow to extruded
6 film tube 81.
8 Figure 12 depicts the operation of volume-
9 setpoint control logic VSCL 157.
11 Volume setpoint control logic VSCL 157
12 operates to increase or decrease setpoint A in response
13 to changes made by the operator at distance selector
14 111 of operator control panel 137, when the PI loop
program 1~7 is in cascade mode, i.e. when PI LOOP IN
16 CA~CAD~ MODB signal is high. The INCREA8B 8ETPOINT,
17 DFCP~QE 8ETPOIN~, and PI LOOP IN CA8CADB MOD~ signals
18 are logically combined at "and" operators 283, and 287.
19 These "and~ operators act on logic blocks 28S, 289 to
increase or decrease the setpoint contained in remote
21 setpoint address 291. When the setpoint is either
22 increased or decreased, logic block 293 operates to add
23 the offset to the remote setpoint for display, and
24 forwards the information to digital to analog converter
143, for display at setpoint display 109 of operator
26 control panel 137. The revised remote setpoint address
27 is then read by the PI loop program 147.
28
29 Figure 13 is a flowchart drawing of output
clamp 159. The purpose of this software routine is to
31 make sure that the PI loop program 147 does not over
32 drive the rotary valve 129 past a usable limit. Rotary
33 valve 129 operates by moving a vane to selectively
2-~93955
1 occlude stationary openings. If the moving vane is
2 over driven, the rotary valve will begin to open when
3 the PI loop calls for complete closure. In step 301,
4 the output of the PI loop program 1~7 is read. In step
303, the output of PI loop is compared to a maximum
6 output. If it exceeds the maximum output, the PI
7 output is set to a predetermined maximum output in step
8 30S. If the output of PI loop does not exceed the
9 maximum output, in step 307, the clamped PI output is
written to the proportional valve 125 through digital
11 to analog converter l~S.
12
13 Figures 1~, through 27 will be used to
14 describe an alternative emergency condition control
mode of operation which provides enhanced control
16 capabilities, especially when an overblown or
17 underblown condition is detected by the control system,
18 or when the system indicates that the extruded film
19 tube is out of range of the position-sensing
transducer. In this alternative emergency condition
21 control mode of operation, the valve of the estimated
22 position is advanced to a preselected valve and a more
23 rapid change in the estimated position signal is
24 allowed than during previously discussed operating
conditions, and is particularly useful when an
26 overblown or underblown condition is detected. In the
27 event the control system indicates that the extruded
28 film tube is out of range of the sensing transducer,
29 the improved control system supplies an estimated
position which, in most situations, is a realistic
31 estimation of the position of the extruded film tube
32 relative to the sensing transducer, thus preventing
33 false indications of the extruded film tube being out
2~939!~5
1 of range of the sensing transducer from adversely
2 affecting the estimated position of the extruded film
3 tube, greatly enhancing operation of the control
4 system. In the event an overblown condition is
s detected, the improved control system supplies an
6 estimated position which corresponds to the distance
7 boundary established for detecting an overflow
8 condition. In the event an underblown condition is
g detected, the improved control system supplies an
estimated position which corresponds to the distance
11 boundary established for detecting an underblown
12 condition.
13
14 Figures 1~, through 27 are a block diagram,
schematic, and flowchart representation of the
16 preferred embodiment of a control system which is
17 equipped with the alternative emergency condition
18 control mode of operation. Figur-s 2S, 2~, and 27
l9 provide graphic examples of the operation of this
alternative emergency condition control mode of
21 operation.
22
23 Figur~ 1~ is a schematic and block diagram
24 view of the preferred alternative control system ~00 of
the present invention of Figur- S, with special
26 emphasis on the supervisory control unit 75, and i8
27 identical in almost all respects to the supervisory
28 control unit 75 which is depicted in Figur- 6;
29 therefore, identical referenced numerals are used to
identify the various components of alternative control
31 system ~00 of Figure 1~ as are used in the control
32 system depicted in F~gure C.
33
2ag39s~
1 Extruded film tube 81 is shown in cross-
2 section with ultrasonic sensor 89 adjacent its outer
3 wall. Ultrasonic sensor 89 emits interrogating pulses
4 which are bounced off of extruded film tube and sensed
by ultrasonic sensor 89. The time delay between
6 transmission and reception of the interrogating pulse
7 is processed by transducer electronics 93 to produce
8 four outputs: C~RRENT PO8ITION signal which is
9 provided to supervisory control unit 75 via analog
output conductor 99, digital TARGET PRERENT signal
11 which is provided over digital output 105, a minimum
12 override signal (MIO signal) indicative of a collapsing
13 or undersized bubble which is provided over digital
14 output conductor 103, and maximum override signal (~AO
signal) indicative of an overblown extruded film tube
16 81 which is provided over a digital output conductor
17 101.
18
19 As shown in Figur- 1~, the position of
extruded film tube 81 relative to ultrasonic sensor 89
21 is analyzed and controlled with reference to a number
22 of distance thresholds and setpoints, which are shown
23 in greater detail in Figur- lS. All set points and
24 thresholds represent distances from reference a. The
control system of the present invention attempts to
26 maintain extruded film tube 81 at a circumference which
27 places the wall of extruded film tube 81 at a tangent
28 to the line established by reference A. The distance
29 between reference R and set point A may be selected by
the user through distance selector lll. This allows
31 the user to control the distance between ~ltrasonic
32 sensor 89 and extruded film tube 81.
33
- ~3 -
2Q939~5
1 The operating range of acoustic transducer 79
2 is configurable by the user with settings made in
3 transducer electronics 93. In the preferred
4 embodiment, using the Massa Products transducer, the
range of operation of acoustic transducer 79 is between
6 3 to 24 inches. Therefore, the user may select a
7 minimum circumference threshold C and a maximum
8 circumference threshold ~, below and above which an
9 error signal is generated. Minimum circumference
threshold C may be set by the user at a distance d3
11 from reference R. Maximum circumference threshold B
12 may be selected by the user to be a distance d2 from
13 reference R. In the preferred embodiment, setpoint A
14 is set a distance of 7 inches from reference R.
Minimum circumference threshold C is set a distance of
16 10.8125 inches from reference R. Maximum circumference
17 threshold 8 is set a distance of 4.1 inches from
18 reference R. Transducer electronics 93 allows the user
19 to set or adjust these distances at will provided they
are established within the range of operation of
21 acoustic transducer 79, which is between 3 and 24
22 inches.
23
24 Besides providing an analog indication of the
distance between ultrasonic sensors 89 and extruded
26 film tube 81, transducer electronics 93 also produces
27 three digital signals which provide information
28 pertaining to the position of extruded film tube 81.
29 If extruded film tube 81 is substantially normal and
within the operating range of ultrasonic sensor 89, a
31 digital "1" is provided at digital output lOS. The
32 signal is representative of a TARGET PRE8ENT signal.
33 If extruded film tube 81 is not within the operating
2Q93~
1 range of ultrasonic sensor 89 or if a return pulse is
2 not received due to curvature of extruded film tube 81,
3 TARGET PRE8ENT signal of digital output 105 is low. As
4 discussed above, digital output 103 is a minimum
override signal ~IO. If extruded film tube 81 is
6 smaller in circumference than the reference established
7 by threshold C, minimum override signal MIO of digital
8 output 103 is high. Conversely, if circumference of
g extruded film tube 81 is greater than the reference
established by threshold C, the minimum override signal
11 MIO is low.
13 Digital output 101 is for a maximum override
14 signal HA0. If extruded film tube 81 is greater than
the reference established by threshold B, the maximum
16 override signal ~AO is high. Conversely, if the
17 circumference of extruded film tube 81 is less than the
18 reference established by threshold B, the output of
19 maximum override signal MAO is low.
21 The minimum override signal MIO will stay
22 high as long as extruded film tube 81 has a
23 circumference less than that established by threshold
24 C. Likewise, the maximum override signal ~AO will
remain high for as long as the circumference of
26 extruded film tube 81 remains larger than the reference
27 established by threshold B.
28
29 Threshold D and threshold ~ are also depicted
in Figure 15. Threshold D is established at a distance
31 d4 from reference R. Threshold E is established at a
- 45 -
20939~
1 distance d5 from reference R. Thresholds D and E are
2 established by supervisory control unit 75, not by
3 acoustic transducer 79. Threshold D represents a
4 minimum circumference threshold for extruded film tube
81 which differs from that established by transducer
6 electronics 93. Likewise, threshold ~ corresponds to a
7 maximum circumference threshold which differs from that
8 established by acoustic transducer 79. Thresholds D
g and ~ are established in the software of supervisory
control unit 75, and provide a redundancy of control,
11 and also minimize the possibility of user error, since
12 these threshold are established in software, and cannot
13 be easily changed or accidentally changed. The
14 coordination of all of these thresholds will be
discussed in greater detail below. In the preferred
16 embodiment, threshold C is established at 10.8125
17 inches from reference ~. Threshold F is established at
18 3.6 inches from reference R.
19
Figure 16 is a side view of the ultrasonic
21 sensor 89 coupled to sizing cage 23 of the blown film
22 tower 13, with permissible extruded film tube 81
23 operating ranges indicated thereon. Setpoint A is the
24 desired distance between ultrasonic sensor 89 and
extruded film tube 81. Thresholds D and C are
26 established at selected distances inward from
27 ultrasonic sensor 89, and represent minimum
28 circumference thresholds for extruded film tube 81.
29 Thresholds B and E are established at selected
distances from setpoint A, and establish separate
31 maximum circumference thresholds for extruded film tube
32 81. As shown in Figure 16, extruded film tube 81 is
33 not at setpoint a. Therefore, additional air must be
- 46 -
209~9~5
1 supplied to the interior of extruded film tube 81 to
2 expand the extruded film tube 81 to the desired
3 circumference established by setpoint A.
If extruded film tube 81 were to collapse,
6 two separate alarm conditions would be registered. One
7 alarm condition will be established when extruded film
8 tube 81 falls below threshold C. A second and separate
g alarm condition will be established when extruded film
tube 81 falls below threshold D. Extruded film tube 81
11 may also become overblown. In an overblown condition,
12 two separate alarm conditions are possible. When
13 extruded film tube 81 expands beyond threshold B, an
14 alarm condition is registered. When extruded film tube
81 expands further to extend beyond threshold E, a
16 separate alarm condition is registered.
17
18 As discussed above, thresholds C and B are
19 subject to user adjustment through settings in
transducer electronics 93. In contrast, thresholds D
21 and F are set in computer code of supervisory control
22 unit 75, and are not easily adjusted. This redundancy
23 in control guards against accidental or intentional
24 missetting of the threshold conditions at transducer
electronics 93. The system also guards against the
26 possibility of equipment failure in transducer 79, or
27 gradual drift in the threshold settings due to
28 deterioration, or overheating of the electronic
29 components contained in transducer electronics 93.
31 Returning now to Figure 1~, operator control
32 panel 137 and supervisory control unit 75 will be
33 described in greater detail. Operator control panel
- ~7 -
209395S
1 137 includes setpoint display 109, which serves to
2 display the distance dl between reference R and
3 setpoint A. Setpoint display 109 includes a 7 segment
4 display. Distance selector 111 is used to adjust
setpoint a. Holding the switch to the "~" position
6 increases the circumference of extruded film tube 81 by
7 decreasing distance dl between setpoint A and reference
8 R. Holding the switch to the "-" position decreases
9 the diameter of extruded film tube 81 by increasing the
distance between reference R and setpoint A.
11
12 Target indicator 113 is a target light which
13 displays information pertaining to whether extruded
14 film tube 81 is within range of ultrasonic transducer
89, whether an echo is received at ultrasonic
16 transducer 89, and whether any error condition has
17 occurred. Blower switch 139 is also provided in
18 operator control panel 137 to allow the operator to
19 selectively disconnect the blower from the control
unit. As shown in Figure 1~, all these components of
21 operator control panel 137 are electrically coupled to
22 supervisory control unit 75.
23
24 Supervisory control unit 75 responds to the
information provided by acoustic transducer 79, and
26 operator control panel 137 to actuate proportional
27 valve 125. Proportional valve 125 in turn acts upon
28 pneumatic cylinder 127 to rotate rotary valve 129 to
29 control the air flow to the interior of extruded film
tube 81.
31
32 With the exception of analog to digital
33 converter 1~1, digital to analog converter 1~3, and
- 48 -
0939!~5
1 digital to analog converter 1~5 (which are hardware
2 items), supervisory control unit 75 is a graphic
3 representation of computer software resident in memory
4 of supervisory control unit 7S. In one embodiment,
supervisory control unit 75 comprises an industrial
6 controller, preferably a Texas Instrument brand
7 industrial controller Model No. PM550. Therefore,
8 supervisory control unit 75 is essentially a relatively
9 low-powered computer which is dedicated to a particular
piece of machinery for monitoring and controlling. In
11 the preferred embodiment, supervisory control unit 75
12 serves to monitor many other operations of blown film
13 extrusion line 11. The gauging and control of the
14 circumference of extruded film tube 81 through computer
software is one additional function which is
16 "piggybacked" onto the industrial controller.
17 Alternately, it is possible to provide an industrial
18 controller or microcomputer which is dedicated to the
19 monitoring and control of the extruded film tube 81.
Of course, dedicating a microprocessor to this task is
21 a rather expensive alternative.
22
23 For purposes of clarity and simplification of
24 description, the operation of the computer program in
supervisory control unit 75 have been segregated into
26 operational blocks, and presented as an amalgamation of
27 digital hardware blocks. In the preferred embodiment,
28 these software subcomponents include: software filter
29 1~9, emergency condition control mode logic lS0, health
state logic 151, automatic sizing and recovery logic
31 153, loop mode control logic 155, volume setpoint
32 control logic 157, and output clamp 159. These
33 software modules interface with one another, and to PI
_ "9 _
209395~
1 loop program ~7 of supervisory control unit 75. PI
2 loop program is a software routine provided in the
3 Texas Instruments' PM550 system. The proportional
4 controller regulates a process by manipulating a
control element through the feedback of a controlled
6 output. The equation for the output of a PI controller
7 is:
g m = K*e + K/T e dt + ms
11 In this equation:
12
13 m = controller output
14 K = controller gain
e = error
16 T = reset time
17 dt = differential time
18 ms = constant
19 efdt = integration of all previous errors
21 When an error exists, it is summed
22 (integrated) with all the previous errors, thereby
23 increasing or decreasing the output of the PI
24 controller (depending upon whether the error is
positive or negative). Thus as the error term
26 accumulates in the integral term, the output changes 80
27 as to eliminate the error.
28
29 CURR~NT P08ITION signal is provided by
acoustic transducer 79 via analog output 99 to analog
31 to digital converter 1~1, where the analog CURRENT
32 P08ITION signal is digitized. The digitized CURRENT
33 P08IT~ON signal is routed through software filter ~9,
- 50 -
2093955
1 and then to PI loop program 147. If the circumference
2 of extruded film tube 81 needs to be adjusted, PI loop
3 program 1~7 acts through output clamp 159 upon
4 proportional valve 125 to adjust the quantity of air
provided to the interior of extruded film tube 81.
7 Figure 17 is a schematic representation of
8 the automatic sizing and recovery logic ASRL of
9 supervisory control unit 75. As stated above, this
figure is a hardware representation of a software
11 routine. ASRL 153 is provided to accommodate the many
12 momentary false indications of maximum and minimum
13 circumference violations which may be registered due to
14 noise, such as the noise created due to air flow
between acoustic transducer 79 and extruded film tube
16 81. The input from maximum alarm override MA0 is
17 "ored" with high alarm D, from the PI loop program, at
18 ~or~ operator 191. High alarm D is the signal
19 generated by the program in supervisory control unit 7S
when the circumference of extruded film tube 81 exceeds
21 threshold D of Figure 15. If a maximum override MA0
22 signal exists, or if a high alarm condition D exists,
23 the output of "or" operator 191 goes high, and actuates
24 delay timer 193.
26 Likewise, minimum override MI0 signal is
27 "ored" at "or" operator 195 with low alarm ~. If a
28 minimum override signal is present, or if a low alarm
29 condition B exists, the output of "or" operator 195
goes high, and is directed to delay timer 197. Delay
31 timers 193, 197 are provided to prevent an alarm
32 condition unless the condition is held for 800
33 milliseconds continuously. Every time the input of
20939~
1 delay timers 193, 197 goes low, the timer resets and
2 starts from 0. This mechanism eliminates many false
3 alarms.
If an alarm condition is held for 800
6 milliseconds continuously, an OVERBLOW~ or ~NDERBLO~N
7 signal is generated, and directed to the health state
8 logic 151. Detected overblown or underblown conditions
g are "ored" at "or" operator 199 to provide a REQ~E8T
MAN~AL MODE signal which is directed to loop mode
11 control logic 155.
12
13 Figure 18 is a schematic representation of
14 the health-state logic 151 of Figure 1~. The purpose
of this logic is to control the target indicator 113 of
16 operator control panel 137. When in non-error
17 operation, the target indicator 113 is on if the blower
18 is on, and the TARG~T ~R~8ENT signal from digital
19 output lOS is high. When an error is sensed in the
maximum override MAO or minimum override MIO lines, the
21 target indicator 113 will flash on and off in one half
22 second intervals.
23
24 In health-state logic R8L lSl, the maximum
override signal MAO is inverted at inverter 205.
26 Likewise, the minimum override ~ignal is inverted at
27 inverter 207.
28
29 "And" operator 209 serves to "and~ the
inverted maximum override signal MAO, with the
31 OVERBLOWN signal, and high alarm signal D. A high
32 output from ~and" operator 209 indicates that something
33 is wrong with the calibration of acoustic transducer
- 52 -
209395~
1 79.
3 Likewise, "and" operator 213 serves to "and~
4 the inverted minimum override signal ~lO, with the
OVERBLOWN signal, and low alarm signal ~. If the
6 output of "and" operator 213 is high, something is
7 wrong with the calibration of acoustic transducer 79.
8 The outputs from "and" operators 209, 213 are combined
9 in "or" operator 215 to indicate an error with either
the maximum or minimum override detection systems. The
11 output of "or" operator 215 is channeled through
12 oscillator 219, and inverted at inverter 217. "And"
13 operator 211 serves to "and" the ~ARGET PRE8ENT signal,
14 blower signal, and inverted error signal from "or"
operator 215. The output of "and" operator of 211 is
16 connected to target indicator 113.
17
18 If acoustic transducer 79 is properly
19 calibrated, the tarqet is within range and normal to
the sonic pulses, and the blower is on, target
21 indicator 113 will be on. If the target is within
22 range and normal to the sonic pulses, the blower is on,
23 but acoustic transducer 79 is out of calibration,
24 target indicator 113 will be on, but will be blinking.
2S The blinking signal indicates that acoustic transducer
26 79, and in particular transducer electronics 93, must
27 be recalibrated.
28
29 Figure 19 is a schematic representation of
loop mode control logic LMCL of Figure 14. The purpose
31 of this software module is coordinate the transition in
32 modes of operation. Specifically, this software module
33 coordinates automatic startup of the blown film
- 53 -
~09395~
1 extrusion process, as well as changes in mode between
2 an automated "cascade" mode and a manual mode, which is
3 the required mode of the PI controller to enable under
4 and overblown conditions of the extruded film tube 81
circumference. The plurality of input signals are
6 provided to loop mode control logic 155, including:
7 BLOWER ON, REQ~E8T MANUAL MOD~, PI LOOP IN CASCADE
8 MODE, UNDERBLOWN and OVERBLOWN. Loop mode control
9 logic LMCL 155 provides two output signals: MAN~AL
HODE, and CA8CADE MODE.
11
12 Figure 19 includes a plurality of digital
13 logic blocks which are representative of programming
14 operations. "Or" operator 225 "ores" the inverted
BLOWER ON 8IGNAL to the REQUE8T MAN~AL ~OD~ 8IGNAL.
16 "And" operator 227 "ands" the inverted REQUE8T ~ANUAL
17 MOD~ 8IGNA$ with an inverted MANUAL NODE 8IGN~L, and
18 the BLO~ER ON 8IGNAL. "And" operator 229 "ands~ the
l9 REQU~8T ~ANUAL MODE 8IGN~$ to the inverted C~C~n~ ~ODE
8IGNAL. This prevents MANUAL MODB and r~r~n~ MODE
21 from both being on at the same time. "And" operator
22 231 "ands" the MANUAL MODE 8IGN~L, the inverted
23 UNDERBLO~N 8IGNA~, and the OVERBLOWN 8IGNA~. "And"
24 operator 233 "ands" the MANUAL MODE 8IGN~L with the
UNDERBLOWN 8IGNAL. This causes the overblown condition
26 to prevail in the event a malfunction causes both
27 underblown and overblown conditions to be on.
28 Inverters 235, 237, 239, 2~1, and 2~3 are provided to
29 invert the inputted output signals of loop mode control
logic 155 were needed. Software one-shot 245 is
31 provided for providing a momentary response to a
32 condition. Software one-shot 24S includes "and"
33 operator 2~7, off-delay 249, and inverter 251.
-- S~ --
209395S
.
2 The software of loop mode control logic 155
3 operates to ensure that the system is never in MAN~AL
4 ~ODB, and CA8CADB MODB at the same time. When manual
mode is requested by REQUE8T MAN~A$ MODB, loop mode
6 control logic 155 causes MAN~AL MODE to go high. When
7 manual mode is not requested, loop mode control logic
8 155 operates to cause CA8CAD~ MOD~ to go high. MAN~AL
9 MODE and CASCADE MODB will never be high at the same
time. Loop mode control logic 155 also serves to
11 ensure that the system provides a "bumpless transfer"
12 when mode changes occur. The term "cascade mode" is
13 understood in the automation industries as referring to
14 an automatic mode which will read an adjustable
setpoint.
16
17 Loop mode control logic 155 will also allow
18 for automatic startup of the blown film extrusion
19 process. At startup, UND~RB~OWN 8IGNAL is high, ~I
LOOP ~N CA8CAD8 MODB is low, BLOWER ON 8IGNAL is high.
21 These inputs (and inverted inputs) are combined at
22 "andH operators 231, 233. At startup, ~and" operator
23 233 actuates logic block 253 to move the maximum air
24 flow value address to the PI loop step 261. At
startup, the MANUAL MOD~ 8IGNAL is high. For the PI
26 loop controller of the preferred embodiment, when
27 MANUAL MODB is high, the value contained in PI loop
28 output address is automatically applied to proportional
29 valve 125. This results in actuation of proportional
valve 125 to allow maximum air flow to start the
31 extruded film tube 81.
32
33 When extruded film tube 81 extends in size
_ 5s _
2~1939~5
1 beyond the minimum threshold (C and D of Figure 15 ),
2 the UNDERBLOW~ 8IGNAL goes low, and the PI LOOP IN
3 CA8CAD~ MODE signal goes high. This causes software
4 one-shot 24S to trigger, causing logic blocks 265, 267
to push an initial bias value contained in a program
6 address onto the PI loop. Simultaneously, logic blocks
7 269, 271 operate to place the selected setpoint value A
8 onto volume-setpoint control logic VSCL 157.
g Thereafter, volume-setpoint control logic VSCL lS7
alone serves to communicate changes in setpoint value A
11 to PI loop program 1~7.
12
13 If an overblown or underblown condition is
14 detected for a sufficiently long period of time, the
controller will request a manual mode by causing
16 REQUE8T MAN~AL MODE 8IGNAL to go high. If REQUE8T
17 MANUAL MODE goes high, loop mode control logic LMCL lS5
18 supervises the transfer throu~h operation of the logic
19 blocks.
21 Loop mode control logic LMCL 155 also serves
22 to detected overblown and underblown conditions. If an
23 overblown or underblown condition is detected by the
24 control system, REQ~E8T MANUAL MODg goes high, and the
appropriate OVERBLOWN or UNDERBLO~N signal goes high.
26 The logic operators of loop mode control logic LMCL lS5
27 operate to override the normal operation of the control
28 system, and cause maximum or minimum air flow by
29 putting the maximum air flow address 261 or minimum air
flow address 263 to the PI output address. As stated
31 above, when MAN~AL MODE is high, these maximum or
32 minimum air flow address values are outputted directly
33 to proportional valve 125. Thus, when the extruded
203395~
1 film tube 81 is overblown, loop mode control logic LMCL
2 155 operates to immediately cause proportional valve
3 125 to minimize air flow to extruded film tube 81.
4 Conversely, if an underblown condition is detected,
S loop mode control logic LMC1 155 causes proportional
6 valve 125 to immediately maximize air flow to extruded
7 film tube 81.
g Figure 20 depicts the operation of volume-
setpoint control logic VSCL 157.
11
12 Volume setpoint control logic VSCL 157
13 operates to increase or decrease setpoint A in response
14 to changes made by the operator at distance selector
111 of operator control panel 137, when the PI loop
16 program 147 is in cascade mode, i.e. when PI LOOP IN
17 CA8CADE MOD~ signal is high. The INCREABE 8~TPOINT,
18 D~rP~RE BBTPOINT, and PI ~OOP IN ~ nB MODB signals
19 are logically combined at ~andH operators 283, and 287.
These "and" operators act on logic blocks 285, 289 to
21 increase or decrease the setpoint contained in remote
22 setpoint address 291. When the setpoint is either
23 increased or decreased, logic block 293 operates to add
24 the offset to the remote setpoint for display, and
forwards the information to digital to analog converter
26 1~3, for display at setpoint display 109 of operator
27 control panel 137. The revised remote setpoint address
28 is then read by the PI loop program 147.
29
Figure 21 is a flowchart drawing of output
31 clamp 159. The purpose of this software routine is to
32 make sure that the PI loop program 1~7 does not over
33 drive the rotary valve 129 past a usable limit. Rotary
- 57 -
20s3sss
-
1 valve 129 operates by moving a vane to selectively
2 occlude stationary openings. If the moving vane is
3 over driven, the rotary valve will begin to open when
4 the PI loop calls for complete closure. In step 301,
s the output of the PI loop program 147 is read. ~n step
6 303, the output of PI loop is compared to a maximum
7 output. If it exceeds the maximum output, the PI
8 output is set to a predetermined maximum output in step
9 305. If the output of PI loop does not exceed the
maximum output, in step 307, the clamped PI output is
11 written to the proportional valve 125 through digital
12 to analog converter 1~5.
13
14 As shown in Figure 1~, emergency condition
control mode logic 150 is provided in supervisory
16 control unit 75, and is shown in detail in Figur- 22.
17 As shown in Figure 22, emergency condition control mode
18 loqic 150 receives thrée input signals: the OV~R
19 8~0~N signal; the UNDERB~O~N signal; and t~e TARGET
filter signal. The emergency condition control mode
21 logic 150 provides as an output two variables to
22 software filter 1~9, including: n6PEED ~O~Dn; and
23 "ALIGN HOLDn. The OVERBLOWN signal is directed to
24 anticipation state "or" gate ~03 and to inverter ~05.
The ~NDERBLO~N signal is directed to anticipation state
26 "or" gate ~03 and to inverter ~07. The TARG~T signal
27 is directed throug~ inverter ~01 to anticipation state
28 "or" gate ~03, and to "and" gate ~09. The output of
29 anticipation "or" gate ~03 is the "or" combination of
30 OVERBLOWN signal, and the inverted TARGET signal.
31 Anticipation state "or" gate ~03 and "and~ gate ~l9
32 cooperate to provide a locking logic loop. The output
33 of "or" gate ~03 is provided as an input to "and" gate
- 58 -
20g39~5
1 419. The other input to "and" gate 419 is the output
2 of inverter 417. The output of inverter 417 can be
3 considered as a "unlocking" signal. If the OVERBLOW~
4 signal or UNDERBLOWN signal is high, or the inverted
TARGET signal is high, the output of anticipation state
6 "or" gate 403 will go high, and will be fed as an input
7 into "and" gate 419, as stated above. The output of
8 anticipation state "or" gate 403 is also provided as an
g input to "and" gates 413, 411, and 409. The other input
to "and" gate 413 is the inverted OVERBLO~N signal. The
11 other input to "and" gate 411 is the inverted
12 IJNDERB~OlqN siqnal. The other input to "and" gate 409
13 is the TARGET signal. The outputs of "and" gates 409,
14 411, and 413 are provided to "or" gate 415. The output
of "or" gate 415 is provided to inverter 417.
16
17 In operation, the detection of an overblown
18 or underblown condition, or an indication that the
19 extruded film tube is out of range of the sensor will
cause the output of anticipation state "or" gate 403 to
21 go high. This high output will be fed back through
22 "and" gate 419 as an input to anticipation state "or"
23 gate 403. Of course, the output of "and" gate 419 will
24 be high for so long as neither input to "and" gate 419
is low. Of course, one input to "and" gate 419 is high
26 because a change in the state of the OVER BLO~ signal,
27 the ~NDER BLO~N signal, and the TARGET signal has been
28 detected. The other input to "and" gate 419 is
29 controlled by the output of inverter 417, which is
controlled by the output of next-state Nor" gate 415.
31 As stated above, the output of next-state "or" gate 415
32 is controlled by the output of "and" gates ~09, 411,
33 413. In this configuration, anticipation state "or"
_ 59 _
20939~5
1 gate ~03 and "and" gate 419 are locked in a logic loop
2 until a change is detected in a binary state of one of
3 the following signals: the OVERBL0~ signal, the
4 UNDERBLOWN signal, and the TARGET signal. A change in
state of one of these signals causes next-state "or"
6 gate 415 to go high, which causes the output of
7 inverter ~17 to go low, which causes the output of
8 "and" gate ~19 to go low.
The output of next-state "or" gate 415 is
11 also provided to timer starter 421, the reset pin for
12 timer starter ~21, and the input of block ~23. When a
13 high signal is provided to the input of timer starter
14 ~21, a three second software clock is initiated. At
the beginning of the three second period, the output of
16 timer starter ~21 goes from a normally high condition
17 to a temporary low condition; at the end of the three
18 second software timer, the output of timer starter ~21
19 returns to its normally high condition. If any
additional changes in the state of the OVERB~OWN
21 signal, the UNDERB~OWN signal, and the ~ARGET signal
22 are detected, the software timer is reset to zero, and
23 begins running again. The particular change in the
24 input signal of the OVERBLOWN signal, the UNDERB~OWN
signal, and the TARGET signal, also causes the
26 transmission of a high output from "and" gates ~09,
27 ~11, and ~13 to blocks ~29, ~27, and ~25 respectively.
28
29 In operation, when the input to block ~23
goes high, the numeric value associated with the
31 variable identified as "quick filter align" will be
32 pushed to a memory variable identified as "speed hold".
33 "Quick filter align" is a filter variable which is used
2093955
1 by software filter 149 (of Figur- 23, which will be
2 discussed below), which determines the maximum
3 allowable rate of change in determining the estimated
4 position. "Speed hold" is a holding variable which
holds the numeric value for the maximum allowable rate
6 of change in determining the estimated position of the
7 blown film tube. "Speed hold" can hold either a value
8 identified as "quick filter align" or a value
9 identified as "normal filter alignn. "Normal filter
align" is a variable that contains a numeric value
11 which determines the normal maximum amount of change
12 allowed in determining the estimated position of the
13 blown film tube relative to the transducer. Blocks 423
14 and ~31 are both coupled to block ~33 which is an
operational block representative of a "push" operation.
16 Essentially, block ~33 represents the activity of
17 continuously and asynchronously pushing the value held
18 in the variable "speed hold" to "LT2~ in software
19 filter 1~9 via data bus ~02. The value for ~normal
filter align" is the same as that discussed herebelow
21 in connection with Figure 8~, and comprises thirteen
22 counts, wherein counts are normalized units established
23 in terms of voltage. The preferred value for ~quick
24 filter align" is forty-eight counts. Therefore, when
the software filter 1~9 is provided with the quick
26 filter align value, the control system is able to
27 change at a rate of approximately 3.7 times as fast as
28 that during a "normal filter align" mode of operation.
29
Also, when a "locked" condition is obtained
31 by anticipation state "or" gate ~03 and "and" gate 419,
32 any additional change in state of the values of any of
33 the OvERBLOWN signal, the UNDERBLO~N signal, and the
20~39~
1 TARGET signal will cause "and~ gates 409, ~11, and ~13
2 to selectively activate blocks ~29, ~27, 42S. Blocks
3 429, 427, and 425 are coupled to block ~33 which is
4 linked by data bus ~02 to software filter 149. When
block ~29 receives a high input, the variable held in
6 the memory location "target restore count" is moved to
7 a memory location identified as "align hold". When
8 block 427 receives a high input signal, the value held
g in the memory location identified as "underblown count"
is moved to a memory value identified as "align hold".
11 When block ~25 receives a high input signal, the
12 numeric value held in a memory location identified as
13 "overblown count" is moved to a memory location
14 identified as "align hold". As stated above, block ~33
performs a continuous asynchronous "push" operation,
16 and will push any value identified to the "align hold~
17 memory location to the values of SAMPLE (N), SAMPLE (N-
18 1), and BPE in the software filter of Figur- 23. In
19 the preferred embodiment of the present invention, the
value of "overblown count" is set to correspond to the
21 distance between reference R and maximum circumference
22 threshold B which is depicted in Figur- 16, which is
23 established distance at which the control system will
24 determine that an "overblown" condition exists. Also,
in the preferred embodiment of the present invention,
26 the value of the "underblown" count will be set to a
27 minimum circumference threshold C, which is depicted in
28 Figur- lC, and which corresponds to the detection of an
29 underblown condition. Also, in the present invention,
the value of "target restore count" is preferably
31 established to correspond to the value of set point A,
32 which is depicted in Figure lC, and which corresponds
33 generally to the distance between reference R and the
- C2 -
2 0 9 3 9 5 ~
1 imaginary cylinder established by the position of the
2 sizing cage with respect to the blown film tube.
4 Figure 23 is a flowchart of the preferred
filtering process applied to CURRENT PO8ITION signal
6 generated by the acoustic transducer. The digitized
7 C~RRENT POSITION signal is provided from analog to
8 digital converter 1~1 to software filter 149. The
g program reads the CURRENT PO8ITION signal in step 161.
Then, the software filter 149 sets 8AMPLE (N) to the
11 position signal.
12
13 In step 165, the absolute value of the difference
14 between C~RRENT P08ITION (8AMP~E (N) ) and the previous
sample (8AMPL~ (N - 1)) is compared to a first
16 threshold. If the absolute value of the difference
17 between the current sample and the previous sample ic
18 less than first threshold Tl, the value of 8ANPL~ ~N)
19 is set to CF8, the current filtered sample, in step
167. If the absolute value of the difference between
21 the current sample and the previous sample exceeds
22 first threshold Tl, in step 169, the CURRENT PO8ITION
23 signal is disregarded, and the previous position signal
24 8AMP~E ~N - 1) is substituted in its place.
26 Then, in step 171, the suggested change 8C is
27 calculated, by determining the difference between the
28 current filtered sample CF8 and the best position
29 estimate BP~. In step 173, the suggested change 8C
which was calculated in step 171 is compared to
31 positive T2, which is the maximum limit on the rate of
32 change. If the suggested change is within the maximum
33 limit allowed, in step 177, allowed change AC is set to
- C3 -
2~3g!ï~
1 the suggested change 8C value. If, however, in step
2 173, the suggested change exceeds the maximum limit
3 allowed on the rate of change, in step 175, the allowed
4 change is set to +LT2, a default value for allowed
change.
7 In step 179, the suggested change 8C is
8 compared to the negative limit for allowable rates of
9 change, negative T2. If the suggested change 8C is
greater than the maximum limit on negative chanqe, in
ll step 181, allowed change AC is set to negative -LT2, a
12 default value for negative change. However, if in step
13 179 it is determined that suggested change 8C is within
14 the maximum limit allowed on negative change, in step
183, the allowed change AC is added to the current best
16 position estimate BPB, in step 183. Finally, in step
17 185, the newly calculated best position estimate 8Pg is
18 written to tbe PI loop program.
19
Software filter 1~9 is a two stage filter
21 which first screens the C~RRENT P08ITION signal by
22 comparing the amount of change, either positive or
23 negative, to threshold ~1. If the CURRENT P08I$IO~
24 signal, as compared to the preceding position signal
exceeds the threshold of T1, the current position
26 signal is discarded, and the previous position signal
27 (8ANPLg (N - 1)) is used instead. At the end of the
28 first stage, in step 171, a suggested change 8C value
29 is derived by subtracting the best position estimate
BP~ from the current filtered sample CF8.
31
32 In the second stage of filtering, the
33 suggested change 8C value is compared to positive and
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2093~5
-
1 negative change thresholds (in steps 173 and 179). If
2 the positive or negative change thresholds are
3 violated, the allowable change is set to a preselected
4 value, either +LT2, or -LT2. Of course, if the
suggested change 8C is within the limits set by
6 positive T2 and negative T2, then the allowable change
7 AC is set to the suggested change 8C.
g As is shown in Figur- 23, data bus 201
couples the emergency condition control logic block 150
11 to software filter 1~9. As stated above, emergency
12 condition control logic block 150 is designed to
13 asynchronously push a numeric value identified in the
14 memory location of "speed hold" to LT2 in software
filter 1~9. Furthermore, emergency condition control
16 logic block 150 will asynchronously push a numeric
17 value in the memory location identified as "ALIGN HOLD~
18 to SAMPLE (N), SAMPLE (N - 1), and BPE. As stated
19 above, SAMPLE N corresponds to the current position-
signal as detected by the transducer. SAMPLE (N - 1)
21 corresponds to the previous position signal as
22 determined by the transducer. BPE corresponds to the
23 best position estimate.
24
Since the operation of emergency condition
26 control mode logic block lS0 is asynchronous, block 186
27 of Figure 23 should be read and understood as
28 corresponding to an asynchronous read function.
29 Therefore, at all times, as set forth in block 186,
software filter 1~9 receives values of "speed hold" and
31 "align hold" from emergency condition control mode
32 logic block 150, and immediate substitutes them into
33 the various logic blocks found in software filter 1~9.
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209395S
1 For example, SAMPLE (N) is found in logic blocks 163,
2 165, and 167. SAMPLE (N - 1) is found in logic blocks
3 165, and 169. BPE is found at logic block 183. The
4 program function represented by block 186 operates to
asynchronously and immediately push the values of
6 "speed hold" and "align hold" to these various
7 functional blocks, since OVERBLOWN, ~NDERBLO~N, and
8 lost ~ARGET conditions can occur at any time.
The normal operation of software filter 1~9
11 may also be understood with reference to Figure 2~, and
12 will be contrasted with examples of the emergency
13 condition mode of operation as depicted in Figures 25,
14 26, and 27. In the graph of Figure 2~, the y-axis
represents the signal level, and the x-axis represents
16 time. The signal as sensed by acoustic transducer 79
17 is designated as input, and shown in the solid line.
18 The operation of the first stage of the software filter
19 1~9 is depicted by the current filtered sample CF8,
which is shown in the graph by cross-marks. As shown,
21 the current filtered sample CF8 operates to ignore
22 large positive or negative changes in the position
23 signal, and will only change when the position signal
24 seems to have stabilized for a short interval.
Therefore, when changes occur in the current filtered
26 sample CF8, they occur in a plateau-like manner.
27
28 In stage two of the software filter 1~, the
29 current filtered sample CF8 is compared to the best
position estimate BPE, to derive a suggested change 8C
31 value. The suggested 8C is then compared to positive
32 and negative thresholds to calculate an allowable
33 change AC which is then added to the best position
2093955
1 estimate BPE. Figure 2~ shows that the best position
2 estimate BPE signal only gradually changes in response
3 to an upward drift in the PO~ITION 8IGNAL. The
4 software filtering system 1~9 of the present invention
renders the control apparatus relatively unaffected by
6 random noise, but capable of tracking the more
7 "gradual" changes in bubble position.
g Experimentation has revealed that the software
filtering system of the present invention operates best
11 when the position of extruded film tube 81 is sampled
12 between 20 to 30 times per second. At this sampling
13 rate, one is less likely to incorrectly identify noise
14 as a change in circumference of extruded film tube 81.
The preferred sampling rate accounts for the common
16 noise signals encountered in blown film extrusion
17 liner.
18
19 Optional thresholds have also been derived
through experimentation. In the first stage of
21 filtering, threshold T1 is established as roughly one
22 percent of the operating range of acoustic transducer
23 79, which in the preferred embodiment is twenty-one
24 meters (24 inches less 3 inches). In the second stage
of filter, thresholds +LT2 and -~T2 are established as
26 roughly 0.30% of the operating range of acoustic
27 transducer 79.
28
29 Figure 25a is a graphic depiction of the
control system response to the detection of an
31 UNDERBLOWN condition. The X-axis of the graph of
32 Figure 25a is representative of time in seconds, and
33 the Y-axis of the graph of Figure 25a is representative
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20939S~
1 of position in units of voltage counts. A graph of the
2 best position estimate BPE is identified by dashed line
3 503. A graph of the actual position of the extruded
4 film tube with respect to the reference position R is
indicated by solid line 501. On this graph, line 505
6 is indicative of the boundary established for
7 determining whether the blown film tube is in an
8 "underblown~ condition. Line 507 is provided as an
9 indication of the normal position of the blown film
tube. Line 509 is provided to establish a boundary for
11 determining when a blown film tube is considered to be
12 in an "overblown" condition.
13
14 The activities represented in the graph of
~igure 25a may be coordinated with the graph of Figure
16 25b, which has an X-axis which is representative of
17 time in seconds, and a Y-axis which represents the
18 binary condition of the TARGET signal, and the
19 UND~RBLOWN signal, as well as the output of block 421
of Figur- 22, which is representative of the output of
21 the time out filter realignment software clock. Now,
22 with simultaneous reference to Figures 25a and 25b,
23 segment 511 of the best position estimate indicates
24 that for some reason the best position estimate
generated by software filter 1~9 is lagging
26 substantially behind the actual position of the blown
27 film tube. As shown in Fiqure 25a, both the actual and
28 estimated position of the blown film tube are in an
29 underblown condition, which is represented in the graph
of Figure 25b.
31
32 As stated above, in connection with Figure 22
33 and the discussion of the operation of the emergency
- 68 -
2093955
1 condition control logic block 150, the locking software
2 loop which is established by anticipation state "or"
3 gate ~03 and "and" gate 419 will lock the output of
4 anticipation state "or" gate ~03 to a high condition.
Therefore, next-state "or" gate 415 is awaiting the
6 change in condition of any of the following signals:
7 the OVERB~O~N signal, the ~NDERBLOWN signal, and the
8 TARGET signal. As shown in Figure 25a, at a time of
9 6.5 seconds, the actual position of the blown film tube
comes within the boundary 505 established for the
11 underblown condition, causing the output of next-state
12 "or" gate ~15 to go high, which causes the output of
13 inverter ~17 to go low, which causes the output of
14 "and" gate ~19 to go low. This change in state also
starts the software timer of block ~21, and causes
16 block ~27 to push the value of "underblown count" to
17 the "align hold" variable. Also, simultaneously,
18 software block ~23 pushes the value of "quick filter
19 align" to the "speed hold~ variable. The values of
"speed hold" and "underblown count" are automatically
21 pushed to block ~33. Meanwhile, the software timer of
22 block ~21 overrides the normal and continuous pushing
23 of "normal filter align" to the "speed hold" variable
24 for a period three seconds. The three second period
expires at 9.5 seconds.
26
27 Thus, for the three second time interval S13,
28 software filter 1~9 is allowed to respond more rapidly
29 to change than during normal operating conditions. As
shown in Figure 22, block 433 operates to automatically
31 and asynchronously push the value of "speed hold" to
32 "LT2" in software filter 1~9. Simultaneously, block
33 ~33 operates to continuously, automatically, and
- 69 -
209~S5
asynchronously push the value of "align hold" to SA~IPLE
2 (N), SAMPLE (N-l) and BPE in software filter 149. This
3 overriding of the normal operation of software filter
4 149 for a three second interval allows the software
S best position estimate 503 to catch up with the actual
6 position 501 of the blown film tube. The jump
7 represented by segment 515 in the best position
8 estimate 503 of the blown film tube is representative
g of the setting of SAMPLE (N), SAMPLE (N-l) and BPE to
the "underblown count" which is held in the "align
11 hold" variable. Segment 517 of the best position
12 estimate 503 represents the more rapid rate of change
13 allowable during the three second interval, and depicts
14 the best position estimate line 503 tracking the actual
position line 501 for a brief interval. At the
16 expiration of the three second interval, software
17 filter 149 of the control system returns to a normal
18 mode of operation which does not allow such rapid
19 change in the best position estimate.
21 Figures 26a and 26b provide an alternative
22 example of the operation of the emergency condition
23 control mode of operation of the present invention. In
24 this example, the TARGET signal represented in segment
525 of Figure 26b is erroneously indicating that the
26 blown film tube is out of range of the transducer.
27 Therefore, segment 529 of dashed line 527 indicates
28 that the best position estimate according to software
29 filter 149 is set at a default constant value
indicative of the blown film tube being out of range of
31 the transducer, and is thus far from indicative of the
32 actual position which is indicated by line 531. This
33 condition may occur when the blown film tube is highly
-- 70 --
209395~
l unstable so that the interrogating pulses from the
2 transducer are deflected, preventing sensing of the
3 blown film tube by the transducer. Segment 533 of
4 Figure 26b is representative of stabilization of the
blown film tube and transition of the TARGET signal
6 from an "off" state to an "on" state. This transition
7 triggers initiation of the three second software timer
8 which is depicted by segment 535. The time period
9 begins at 12.5 seconds and ends at 15.5 seconds. The
transition of the TARGET signal from a low to a high
11 condition triggers the pushing of the "target restore
12 count" value to the "align hold" variable, as is
13 graphically depicted by segment 537. During the three
14 second interval, the best position estimate established
by software filter 1~9 is allowed to change at a rate
16 which is established by the "quick filter align" value
17 which is pushed to the "speed hold" variable and bused
18 to software filter 1~9. At the termination of the
19 three second interval, the software filter 1~9 returns
to normal operation.
21
22 Figure 27~ provides yet another example of
23 the operation of the emergency condition control mode.
24 Segment 5~1 of Figure 27b indicates that the TARGET
signal is in a low condition, indicating that the blown
26 film tube is out of range of the transducer. Segment
27 5~3 indicates that the blown film tube has come into
28 range of the transducer, and the TARG~T signal goes
29 form a low to a high condition. Simultaneous with the
movement of the blown film tube into range of the
31 transducer, the ~NDERBLOWN signal goes from a low to a
32 high condition indicating that the blown film tube is
33 in an underblown condition. Segment 5~5 of ~igure 27b
20939~5
1 indicates a transition from a high UNDERBLOWN signal to
2 a low ~NDERB~OWN signal, which indicates that the blown
3 film tube is no longer in an underblown condition.
4 This transition initiates the three second interval
which allows for more rapid adjustment of the best
6 position estimate.
8 Figure 28 is a schematic and block diagram
9 representation of an airflow circuit for use in a blown
film extrusion system. Input blower 613 is provided to
11 provide a supply of air which is routed into airflow
12 circuit 611. The air is received by conduit 615 and
13 directed to airflow control device 617 of the present
14 invention. Airflow control device 617 operates as a
substitute for a conventional rotary-type airflow valve
16 631, which is depicted in simplified form also in
17 Figur- 28. The preferred airflow control device 617 of
18 the present invention is employed to increase and
19 decrease the flow of air to supply distributor box 619
which provides an air supply to annular die C21 from
21 which blown film tube 623 extends upward. Air is
22 removed from the interior of blown film tube 623 by
23 exhaust distributor box C2S which routes the air to
24 conduit 627, and eventually to exhaust blower 629.
2S
26 The preferred airflow control device 617 is
27 depicted in fragmentary longitudinal section view in
28 Figur- 29. As is shown, airflow control device 617
29 includes housing 635 which defines inlet 637 and outlet
639 and airflow pathway 6~1 through housing 635. A
31 plurality of selectively expandable flow restriction
32 members 671 are provided within housing 635 in airflow
33 pathway 6~1. In the view of Figure 29, selectively-
- 72 -
- 209395S
1 expa~dable flow restriction members 673, 675, 677, 679,
2 and 681 are depicted. Other selectively-expandable
3 flow restriction members are obscured in the view of
4 Figure 29. Manifold 685 is provided to route
pressurized air to the interior of selectively-
6 expandable flow restriction members 671, and includes
7 conduit 683 which couples to a plurality of hoses, such
8 as hoses 687, 689, 691, 693, 695 which are depicted in
g Figure 29 (other hoses are obscured in Figure 29).
11 Each of the plurality of selectively-
12 expandable flow restriction members includes an inner
13 air-tight bladder constructed of an expandable material
14 such as an elastomeric material. The expandable
bladder is surrounded by an expandable and contractible
16 metal assembly. Preferably, each of the plurality of
17 selective-expandable flow restriction members is
18 substantially oval in cross-section view (~uch a~ the
19 view of Figure 29), and traverse airflow pathway 6~1
across the entire width of airflow pathway 6~1. Air
21 flows over and under each of the plurality of
22 selectively-expandable airflow restriction members, and
23 each of them operates as an choke to increase and
24 decrease the flow of air through housing 63S as they
are expanded and contracted. However, the flow
26 restriction is accomplished without creating turbulence
27 in the airflow, since the selectively-actuable flow
28 restriction members are foil shaped.
29
Returning now to Figure 28, airflow control
31 device 617 is coupled to proportional valve 657 which
32 receives either a current or voltage control signal and
33 selectively vents pressurized fluid to airflow control
- 73 -
2093955
device 617. In the preferred embodiment, proportional
2 valve 657 is manufactured by Proportion Air of
3 McCordsville, Indiana. Supply 651 provides a source of
4 pressurized air which is routed through pressure
regulator 653 which maintains the pressurized air at a
6 constant 30 pounds per square inch of pressure. The
7 regulated air is directed through filter 655 to remove
8 dust and other particulate matter, and then through
9 proportional valve 657 to airflow control device 617.
11 In the preferred embodiment of the present
12 invention, airflow control device 617 is manufactured
13 by Tek-Air Systems, Inc. of Northvale, New Jersey, and
14 is identified as a "Connor Model No. PRD Pneumavalve".
This valve is the subject matter of at least two U.S.
16 patents, including U.S. Patent No. 3,011,518, which
17 issued in December of 1961 to Day et al., and U.S.
18 Patent No. 3,593,645, which issued on July 20, 1971, to
19 Day et al., which was assigned to Connor Engineering
Corporation of Danbury, Connecticut, and which is
21 entitled "Terminal Outlet for Air Distributionn, both
22 of which are incorporated herein by reference as if
23 fully set forth.
24
Experiments have revealed that this type of
26 airflow control device provides for greater control
27 than can be provided by rotary type valve 631 (depicted
28 in Figur- 28 for comparison purposes only), and is
29 especially good at providing control in mismatched load
situations which would ordinarily be difficult to
31 control economically with a rotary type valve.
32
33 A number of airflow control devices li)ce
2093955
-
1 airflow control device 617 can be easily coupled
2 together in either series or parallel arrange~ent to
3 control the total volume of air provided to a blown
4 film line or to allow economical load matching. In
Figure 28, a series and a parallel coupling of airflow
6 control devices is depicted in phantom, with airflow
7 control devices 681, C83, and 685 coupled together with
8 airflow control device 617. As shown in the detail
9 airflow control device 617 is in parallel with airflow
control device 683 but is in series communication with
11 airflow control device C85. Airflow control device 685
12 is in parallel communication with airflow control
13 device 681. Airflow control devices 681 and 683 are in
14 series communication.
16 Although the invention has been described with
17 reference to a specific embodiment, this description is
18 not meant to be construed in a limiting sense. Various
19 modifications of the disclosed embodiment as well as
alternative embodiments of the invention will become
21 apparent to persons skilled in the art upon reference
22 to the description of the invention. It is therefore
23 contemplated that the appended claims will cover any
24 such modifications or embodiments that fall within the
true scope of the invention.
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