CA2093955C

CA2093955C - Control and blower system for extruded film tubes

Info

Publication number: CA2093955C
Application number: CA002093955A
Authority: CA
Inventors: Daniel R. Joseph
Original assignee: Individual
Current assignee: Individual
Priority date: 1992-04-13
Filing date: 1993-04-13
Publication date: 1998-09-29
Anticipated expiration: 2013-04-13
Also published as: CA2093955A1

Abstract

In a blown film extrusion system in which film is extruded as a tube from an annular die and then pulled along a predetermined path, an apparatus is provided for gauging and controlling the circumference of the extruded film tube. At least one transducer, preferably ultrasonic, is mounted adjacent the extruded film tube for transmitting and receiving interrogating pulses along paths normal to the extruded film tube, and for producing a current position signal corresponding to the circumference of the extruded film tube. The current position signal is continuously compared with at least one previous position signal, preferably with a computer program resident in a controller memory. If at least one preselected condition is violated, the current position signal is disregarded in favor of an estimated position signal. The quantity of air within the extruded film tube is varied in response to either the current position signal or the estimated position signal to maintain the extruded film tube at a preselected circumference. The transducer may be mounted to an adjustable sizing cage, and is thus moveable inward, outward, upward, and downward relative to the extruded film tube as changes are made in its circumference or frostline position. A pair of controllers may be employed to establish two minimum circumference values, and two maximum circumference values. If a collapsing or overblown extruded film tube is detected, the system goes into override, and the flow of air is either accelerated or decreased to counter the alarm condition. The system of the present invention also allows for automatic startup. In a startup mode, the current position signal is continuously compared with a selected minimum circumference threshold. Once the selected minimum circumference threshold is exceeded, the system switches to an operating mode which continuously compares the current position signal with a selected setpoint value to maintain the extruded film tube at a desired circumference.

Description

~ ~ ~ 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.

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 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.

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.

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.

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.

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.

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.

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.

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.

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.

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 _ 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:

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;

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;

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;

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;

19 Figur- 8~b) is a graphic depiction of the operation of the filtering system;

22 Figure 9 is a schematic representation of the 23 automatic sizing and recovery logic (ASRL) of Figur- 6;

Figure 10 is a schematic representation of 26 the health/state logic (HSL) of Figur- 6;

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;

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;

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;

23 Figure 17 is a schematic representation of 24 the automatic sizing and recovery logic (ASRL) of Figure 1~;

27 Figure 18 is a schematic representation of 28 the health/state logic (HSL) of Figure 14;

Figure 19 is a schematic representation of 31 the loop mode control logic (LMCL) of Figure 14;

33 Figure 20 is a schematic representation of 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;

14 Figure 2~ is a graphic depiction of the normal operation of the filtering system;

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;

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;

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 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;

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;

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.

20~3955 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.

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.

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.

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.

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 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 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.

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 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.

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.

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.

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.

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.

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.

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.

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 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.

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 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 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.

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 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.

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.

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.

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:

l9 m = K*e + K/T e)dt + ms 21 In this equation:

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

- 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.

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 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.

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.

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.

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.

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.

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.

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 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.

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~ -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.

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.

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.

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.

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.

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.

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.

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.

32 When extruded film tube 81 extends in size 33 beyond the minimum threshold (C and D of Figure 7~a)), 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.

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.

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

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.

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.

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.

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.

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.

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.

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.

- ~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.

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.

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 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.

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 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.

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 -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.

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.

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.

32 With the exception of analog to digital 33 converter 1~1, digital to analog converter 1~3, and 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.

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:

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.

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, 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.

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.

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.

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 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.

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.

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 ~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.

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~ --.

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.

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.

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.

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.

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.

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 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.

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 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.

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.

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 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.

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 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.

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 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.

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.

32 In the second stage of filtering, the 33 suggested change 8C value is compared to positive and - 6~ -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.

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.

-- CS --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.

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 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.

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.

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 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.

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.

32 As stated above, in connection with Figure 22 33 and the discussion of the operation of the emergency 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.

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 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 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.

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.

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-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.

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 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.

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.

33 A number of airflow control devices li)ce -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.

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A method of gauging and controlling the circumference of an extruded film tube formed from film extruded from an annular die, comprising:

providing a transducer;

placing said transducer adjacent said extruded film tube;

transmitting an interrogating signal to, and receiving an interrogating signal from, said extruded film tube;
producing a detected position signal based on information contained in said interrogating signal;
determining if said detected position signal violates at least one preselected condition, and providing an estimated position signal in lieu of said detected position signal if said at least one preselected condition is violated; and varying a quantity of air within said extruded film tube in response to said detected and estimated position signals depending upon whether or not said at least one preselected condition is violated.

2. In a blown film extrusion system in which film is extruded as a tube from an annular die and then pulled along a predetermined path, an apparatus for gauging and controlling the circumference of said extruded film tube, comprising:

at least one transducer means adjacent said extruded film tube for transmitting interrogating pulses to, and receiving interrogating pulses from, said extruded film tube and for producing a signal corresponding to a detected position of said extruded film tube;
an airflow controller at least in-part responsive to said detected position for varying a quantity of air within said extruded film tube, including:
a housing with an inlet, outlet, and an airflow path defined therethrough;
at least one selectively-expandable flow restriction members disposed in said housing in said airflow path;
wherein said air flow controller selectively expands and reduces said at least one selectively-expandable flow restriction members to moderate airflow through said extruded film tube.

3. In a blown film extrusion system in which film is extruded as a tube from an annular die and then pulled along a predetermined path, an apparatus for gauging and controlling the position of said extruded film tube, comprising:

at least one transducer means adjacent said extruded film tube for transmitting interrogating pulses to, and receiving interrogating pulses from, said extruded film tube and for producing a signal corresponding to a detected position of said extruded film tube;

means for varying a quantity of air within said extruded film tube in response to control signals for urging said extruded film tube to a desired position;
control means for receiving said detected position signal and for providing said control signals to said means for varying; and wherein during selected extruded film tube position conditions, said control means activates said means for varying to provide at least one predetermined air flow rate.

4. An apparatus for gauging and controlling the position of said extruded film tube, according to Claim 3:
wherein said selected extruded film tube position conditions include start-up position conditions.

5. An apparatus for gauging and controlling the position of said extruded film tube, according to Claim 3:

wherein said selected extruded film tube position conditions include an underblown position condition.

6. An apparatus for gauging and controlling the position of said extruded film tube, according to Claim 3:
wherein said selected extruded film tube position conditions include an overblown position condition.

7. An apparatus for gauging and controlling the position of said extruded film tube, according to Claim 3:

wherein, during a start-up mode of operation, said control means provides a start-up control signal to said means for varying to provide at leastone predetermined airflow rate which is suitable for automatic start-up of said extruded film tube.

8. An apparatus for gauging and controlling the position of said extruded film tube, according to Claim 3:

wherein, after start-up of said extruded film tube is obtained, at least one feedback loop is established which includes said at least one transducer means, said control means, and said means for varying, to maintain said extruded film tube at a desired position.

9. In a blown film extrusion system in which film is extruded as a tube from an annular die and then pulled along a predetermined path, an apparatus for gauging and controlling the position of said extruded film tube, comprising:

at least one transducer means adjacent said extruded film tube for transmitting interrogating pulses to, and receiving interrogating pulses from, said extruded film tube and for producing (a) a position signal corresponding to a detected position of said extruded film tube and (b) a range signal which provides an indication of whether or not said extruded film tube is within rangeof said at least one transducer means;

control means for providing a selected position signal if at least one preselected condition is violated; and means for varying a quantity of air within said extruded film tube in response to said control means for urging said extruded film tube to a desired position.

10. An apparatus for gauging and controlling the position of said extruded film tube, according to Claim 9:

wherein said at least one preselected condition includes at least one of:
(a) a range signal indicative of said extruded film tube being out of range of said at least one transducer means;

(b) a position signal indicative of said extruded film tube being in an overblown condition; and (c) a position signal indicative of said extruded film tube being in an underblown condition.

11. An apparatus for gauging and controlling the position of said extruded film tube, according to Claim 10:
wherein said selected position signal is provided by said control means upon return of said extruded film tube into range of said at least one transducer means as determined by said range signal.

12. An apparatus for gauging and controlling the position of said extruded film tube, according to Claim 10:
wherein said selected position signal is provided by said control means upon cessation of said overblown condition.

13. An apparatus for gauging and controlling the position of said extruded film tube, according to Claim 10:

wherein said selected position signal is provided by said control means upon cessation of said underblown condition.

14. In a blown film extrusion system in which film is extruded as a tube from an annular die and then pulled along a predetermined path, an apparatus for gauging and controlling the position of said extruded film tube, comprising:

at least one transducer means adjacent said extruded film tube for sending and receiving interrogating pulses to and from said extruded film tube and producing at least one position signal indicative of at least one of (a) whether or not said extruded film tube is within range of said at least one transducer means, (b) whether or not said extruded film tube is in an overblown condition, and (c) whether or not said extruded film tube is in an underblown condition;
control means for providing a preselected control signal in response to said at least one position signal; and means for varying a quantity of air within said extruded film tube in response to said control means for urging said extruded film tube to a desired position.

15. A method of gauging and controlling the circumference of an extruded film tube, according to Claim 1:

wherein said at least one preselected condition includes at least one of:
(a) a start-up position condition;
(b) an underblown position condition; and (c) an overblown position condition.

16. A method of gauging and controlling the circumference of an extruded film tube, according to Claim 1, further comprising:

providing a range indicator for determining when said extruded film tube is out-of-range of said transducer; and wherein said at least one preselected condition includes said extruded film tube being out-of-range of said transducer.

17. An apparatus for gauging and controlling the circumference of said extruded film tube, according to Claim 2:

wherein said at least one selectively expandable flow restriction members include a bladder member which selectively communicates with a control fluid; and wherein application of said control fluid to said at least one selectively-expandable flow restriction members causes expansion and reduction of said at least one selectively-expandable flow restriction members.

18. An apparatus for gauging and controlling the circumference of said extruded film tube, according to Claim 2, wherein said airflow controller includes:
a plurality of housings, each having an inlet, outlet, and an airflow path defined therethrough;
a plurality of selectively-expandable flow restriction members disposed in each of said housings; and with each airflow path through said plurality of housings in at least one of (a) series and (b) parallel communication with selected others of said airflow paths.

19. An apparatus for gauging and controlling the circumference of said extruded film tube, according to Claim 2:

wherein expansion of said at least one selectively-expandable flow restriction members restricts said airflow path defined through said housing;
and wherein reduction of said at least one selectively-expandable flow restriction members expands said airflow path defined through said housing.