CA2150898C

CA2150898C - Method and apparatus for cooling extruded film tubes

Info

Publication number: CA2150898C
Application number: CA002150898A
Authority: CA
Inventors: Daniel R. Joseph
Original assignee: Individual
Current assignee: Individual
Priority date: 1994-06-03
Filing date: 1995-06-02
Publication date: 1999-05-25
Anticipated expiration: 2015-06-02
Also published as: CA2150898A1

Abstract

A blown film extrusion system includes an annular die for receiving a molten material and extruding a film tube. At least one cooling air ring is positioned adjacent to the annular die for passing an air stream along a particular surface of the film tube. In particular embodiments, this cooling air ring may provide a cooling air stream for either an exterior surface of the extruded film tube, an interior surface of the extruded film tube, or for both an exterior surface and interior surface of the extruded film tube. A blower is provided for entraining and supplying cooling air or gas to the at least one cooling ring. A flow sensor is positioned in an air flow path intermediate the at least one cooling ring and the blower. The flow sensor provides an air mass flow signal which is indicative of air flow through the air flow path, and which provides a measure of air mass flow per unit time. An adjustable air flow attribute modifier is also provided in communication in the air flow path. The adjustable air flow attribute modifier is utilized for selectively modifying the air mass per unit time. A controller member is provided which is in communication with both the flow sensor and the adjustable air flow attribute modifier. The controller member receives the mass air flow signal from the flow sensor, and provides a control signal to the adjustable air flow attribute modifier, to provide a preselected value of air flow in terms of air mass flow per unit time.

Description

BACKGROUND OF THE INVENTION
Field of the Invention This invention relates generally to blown film extrusion lines, and specifically to improved cooling systems for use with blown film systems.

Description of the Prior Art:
Blown film extrusion lines are used to manufacture plastic bags and plastic sheets. A molten tube of plastic is extruded from an annular die, and then stretched and expanded to a larger diameter and a reduced radial thickness by the action of overhead nip rollers and internal air pressure.
Typically air is entrained by one or more blowers to provide a cooling medium which absorbs heat from the molten material and speeds up the change in state from a molten material back to a solid material. Additionally, blowers are used to provide air pressure which is utilized to control the size and thickness of the film tube. One type of blown film extrusion line utilizes an air flow on the exterior surface of the film tube in order to absorb heat. A different, and more modern, type of blown film extrusion line utilizes both an external flow of cooling air and an internal flow of cooling air in order to cool and size the film tube.
The cooling and sizing effect of these external and internal air flows is dependent upon the density of the air column and the rate of flow of the air column. These variables can be considered together in units of "mass air flow" which is simply the total density of the cooling air multiplied times the flow rate. The density of the cooling air or gas is complex and is dependent B

215089~
,, upon the relative humidity of the air or cooling gas, the absolute pressure of the

2 air or cooling gas, the temperature of the air or cooling gas, the saturation

3 vapor pressure of the air or cooling gas at the given temperature, the partial

4 pressure of the water vapor in the air or cooling gas at the given temperature, and the specific gravity of the air or cooling gas. The flow rate of the air or 6 cooling gas is of course more easily calculated.

8 Changes in the humidity, barometric pressure, and temperature g of the ambient atmosphere will have an impact upon the cooling and gaging influence of the air or cooling gas, and will effect the product quality and 11 production rates in a manner which is not easily calculated. The prior art 12 systems are devoid of any useful technique or apparatus for adjusting for 13 changes in ambient humidity, barometric pressure, and temperature in order to 14 maintain product uniformity and to obtain the highest production rates possible.

Page - 3 -DOCKET NO. 291 H-19705 21~0898 --SUMMARY OF TllE INVENTION

3 It is therefore one object of the present invention to provide an 4 improved blown film extrusion system which includes a flow sensor positioned in an air flow path intermediate at least one external or internal cooling ring and 6 a blower, for providing a mass air flow signal which is indicative of air flow 7 through the air flow path and which provides a measure of air rnass flow per 8 unit time, in order to obtain uniformity of product quality and high production g rates.

1 It is another object of the present invention to provide an improved 12 blown film extrusion system which includes a flow sensor which is utilized to 3 provide a measure of air mass flow per unit time to a controller member which 14 provides a control signal to an adjustable air flow attribute modifier which is communication with an air flow path within the blown film extrusion apparatus, 16 and which is utilized to selectively modify the air mass per unit time in order to 17 obtain product uniformity and high production rates.

19 It is yet another object of the present invention to provide an improved air flow control apparatus in order to obtain better control of air flows 21 utilized for either cooling a blown film tube or shaping and sizing a blown film 2 tube.

24 These and other objectives are achieved as is now described.
The present invention is directed to an improved blown film extrusion system 26 which includes a number of components which cooperate together. An annular 27 die is provided for receiving a molten material and extruding a film tube. At 28 least one cooling air ring is positioned adjacent to the annular die for passing 29 an air stream along a particular surface of the film tube. In particular embodiments, this at least one cooling air ring may provide a cooling air stream31 for either an exterior surface of the extruded filnn tube, an interior surface of the Page - 4 -DOCKET NO. 291H-19705 extruded film tube, or for both an exterior surface and interior surface of the 2 extruded film tube. A blower is provided for entraining and supplying cooling 3 air or gas to the at least one cooling ring. A flow sensor is positioned in an air 4 flow path intermediate the at least one cooling ring and the blower. The flow sensor provides an air mass flow signal which is indicative of air flow through 6 the air flow path, and which provides a measure of air mass flow per unit time.
7 An adjustable air flow attribute modifier is also provided in communication in the 8 air flow path. The adjustable air flow attribute modifier is utilized for selectively g modifying the air mass per unit time. In some embodiments, the adjustable air flow attribute modifier may comprise a cooling system which includes heat 11 exchange coils in communication with the air flow path and a circulating heat 12 exchange medium which is passed through the heat exchange coils. In other 13 embodiments, the adjustable air flow attribute modifier may comprise an air flow 14 control member, such as a valve, which is in communication with the air f!ow path. In still more particular embodiments, the air flow control member may 16 comprise an electrically-actuated valve which is utilized to moderate air flow 17 through the air flow paths. In yet other embodiments, the adjustable air flow 18 attribute modifier may comprise a fluid injection system in communication with 19 the air flow path which is utilized to modify the humidity of air passing through the air flow path. Finally, a controller member is provided which is in 21 communication with both the flow sensor and the adjustable air flow attribute 22 modifier. The controller member receives the mass air flow signal from the flow 23 sensor, and provides a control signal to the adjustable air flow attribute 24 modifier, to provide a preselected value of air flow in terms of air mass flow per unit time.

27 The above as well as additional objects, features, and advantages 28 of the present invention will become apparent in the following detailed written 2g description.

Page - 5 -DOCKET NO. 291 H-19705 BRIEF DESCRIPTION OF THE DRAWINGS

3 The novel features believed characteristic of the invention are set 4 . forth in the appended claims. The invention itself however, as well as a preferred mode of use, further objects and advantages thereof, will best be 6 understood by reference to the following detailed description of an illustrative 7 embodiment when read in conjunction with the accompanying drawings, 8 wherein:

Figure 1 is a view of a blown film extrusion line equipped with the improved control system of the present invention;

13 Figure 2 is a view of the die, sizing cage, control subassembly 14 and rotating frame of the blown film tower of Figure 1;

16 Figure 3 is a view of the acoustic transducer of the improved 17 control system of the present invention coupled to the sizing cage of the blown 18 film extrusion line tower adjacent the extruded film tube of Figures 1 and 2;

Figure 4 is a view of the acoustic transducer of Figure 3 coupled 21 to the sizing cage of the blown film tower, in two positions, one position being 22 shown in phantom;

24 Figure 5 is a schematic and block diagram view of the preferred2s control system of the present invention;

27 Figure 6 is a schematic and block diagram view of the preferred28 control system of Figure 5, with special emphasis on the supervisory control 29 'unit;

Page - 6-DOCKET NO. 291H-19705 ,.

Figure 7(a) is a schematic and block diagram view of the signals 2 generated by the ultrasonic sensor which pertain to the position of the blown 3 film layer;

Figure 7(b) is a view of the ultrasonic sensor of Figure 3 coupled 6 to the sizing cage of the blown film tower, with permissible extruded film tube 7 operating ranges indicated thereon;

g Figure 8(a) is a flow chart of the preferred filtering process applied to the current position signal generated by the acoustic transducer;

12 Figure 8(b) is a graphic depiction of the operation of the filtering 1 3 system;

Figure 9 is a schematic representation of the automatic sizing and 16 recovery logic (ASRL) of Figure 6;

18 Figure 10 is a schematic representation of the health/state logic 19 (HSL) of Figure 6;

21 Figure 11 is a schematic representation of the loop mode control 22 logic (LMCL) of Figure 6;

24 Figure 12 is a schematic representation of the volume setpoint control logic ~JSCL) of Figure 6;

27 Figure 13 is a flow chart representation of the output clamp of 28 Figure 6.

Figure 14 is a schematic and block diagram, and flowchart views 31 of the preferred alternative emergency condition control system of the present Page - 7 -DOCKET NO. 291H-19705 215089~
,, invention, which provides enhanced control capabilities for detected overblown 2 and underblown conditions, as well as when the control system determines that 3 the extruded film tube has passed out of range of the sensing transducer;

Figure 15 is a schematic and block diagram view of the signals 6 generated by the ultrasonic sensor which pertain to the position of the blown 7 film layer;

g Figure 16 is a view of the ultrasonic sensor of Figure 3 coupled to the sizing cage of the blown film tower, with permissible extruded film tube 11 operating ranges indicated thereon;

13 Figure 17 is a schematic representation of the automatic sizing14 and recovery logic (ASRL) of Figure 14;

16 Figure 18 is a schematic representation of the health/state logic 17 (HSL) of Figure 14;

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

22 Figure 20 is a schematic representation of the volume setpoint 23 control logic (VSCL) of Figure 14;

Figure 21 is a flow chart representation of the output clamp of 26 Figure 14;

28 Figure 22 is a schematic and block diagram view of emergency 29 condition control logic block of Flgure 14;

Page - 8 -DOCKET NO. 291H-19705 21~089~ ~

Figure 23 is a flowchart depiction of the preferred software filter 2 of the alternative emergency condition control system of Figure 14;

4 Figure 24 is a graphic depiction of the normal operation of the s filtering system;

7 Figure 25a is a graph which depicts the emergency condition 8 control mode of operation response to the detection of an underblown g condition, with the X-axis representing time and the Y-axis representing position of the extruded film tube;

12 Figure 25b is a graph of the binary condition of selected 13 operating blocks of the block diagram depiction of Figure 22, and can be read 14 in combination with Figure 25a, wherein the X-axis represents time, and the Y-axis represents the binary condition of selected operational blocks;

17 Figure 26a is a graph which depicts the emergency condition 18 control mode of operation response to the detection of an underblown 19 condition, with the X-axis representing time and the Y-axis representing position of the extruded film tube;

22 Figure 26b is a graph of the binary condition of selected 23 operating blocks of the block diagram depiction of Figure 22, and can be read 24 in combination with Figure 26a, wherein the X-axis represents time, and the Y-axis represents the binary condition of selected operational blocks;

27 Figure 27a is a graph which depicts the emergency condition 28 control mode of operation response to the detection of an underblown 29 condition, with the X-axis representing time and the Y-axis representing position of the extruded film tube;
3t Page- 9 -DOCKET NO. 291H-19705 Figure 27b is a graph of the binary condition of selected 2 operating blocks of the block diagram depiction of Figure 22, and can be read 3 in combination with Figure 27a, wherein the X-axis represents time, and the 4 Y-axis represents the binary condition of selected operational blocks;

6 Figure 28 is a schematic and block diagram depiction of one 7 embodiment of the improved air flow control system of the present invention;

gFigure 29 is a simplified and partial fragmentary and longitudinal 10section view of the preferred air flow control device used with the air flow 11control system of the present invention;

13Figure 30 is a schematic depiction of a IBC blown film extrusion 14line equipped with mass air flow sensors in communication with both a supply 15of cooling air and an exhaust of cooling air, which may be utilized to obtain 16uniformity in the mass air flow of the cooling air stream supply to the interior of 17the blown film tube;

19Figure 31 is a schematic depiction of an IBC blown film line 20equipped with mass air flow sensors for controlling the supply and exhaust of 21air to the interior of the blown film tube, and additionally equipped with a mass 22air flow sensor for monitoring and controlling the supply of external cooling air;

24Figures 32, 33, 34, and 35 are schematic depictions of an 25external cooling air system for a blown film extrusion line, with a mass air flow 26sensor provided to allow control over an adjustable air flow attribute modifier;
27 and 29Figure 36 is a flowchart representation of computer program 30implemented operations for achieving a feedback control loop for a blown film 31system.

PAge- 10-DOCKET NO. 291H-19705 ~ .

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT

3 In this detailed description of the invention, Figures 1 through 29, 4 and accompanying text, provide a very detailed overview of an internal-bubble-cooling blown film extrusion system which is equipped with a preferred sizing 6 control system. Figures 30 through 36, and accompanying text, provide a 7 description of the preferred method and apparatus for cooling extruded film 8 tubes of the present invention used either in combination with the preferred g sizing control apparatus, or alone.

11 Figure 1 is a view of blown film extrusion line 11, which includes 12 a number of subassemblies which cooperate to produce plastic bags and the 13 like from plastic resin. The main components include blown film tower 13, 14 which provides a rigid structure for mounting and aligning the various 1~ subassemblies, extruder subassembly 15, die subassembly 17, blower 16 subassembly 19, stack 21, sizing cage 23, collapsible frame 25, nips 27, control 17 subassembly 28 and rollers 29.

19 Plastic granules are fed into hopper 31 of extruder subassembly 15. The plastic granules are melted and fed by extruder 33 and pushed into die 21 subassembly 17, and specifically to annular die 37. The molten plastic granules 22 emerge from annular die 37 as a molten plastic tube 39, which expands from 23 the die diameter to a desired final diameter, which may vary typically between 24 two to three times the die diameter.

26 Blower subassembly 19 includes a variety of components which 27 cooperate together to provide a flow of cooling air to the interior of molten 28 ' plastic tube 39, and also along the outer periphery of molten plastic tube 39.
29 Blower subassembly includes blower 41 which pulls air into the system at intake 43, and exhausts air from the system at exhaust 45. The flow of air into molten 31 plastic tube 39 is controlled at valve 47. Air is also directed along the exterior Page- 11 -DOCKET NO. 2s1H-19705 of molten plastic tube from external air ring 49, which is concentric to annular2 die 37. Air is supplied to the interior of molten plastic tube 39 through internal 3 air diffuser 51. Air is pulled from the interior of molten plastic tube 39 by 4 exhaust stack 53.

6The streams of external and internal cooling airs serve to harden 7molten plastic tube 39 a short distance from annular die 37. The line of 8demarcation between the molten plastic tube 39 and the hardened plastic tube 955 is identified in the trade as the "frost line.H Normally, the frost line is 10substantially at or about the location at which the molten plastic tube 39 is expanded to the desired final diameter.

13Adjustable sizing cage 23 is provided directly above annular die 1438 and serves to protect and guide the plastic tube 55 as it is drawn upward 15through collapsible frame 25 by nips 27. Afterwards, plastic tube 55 is directed 16through a series of rollers 57, 59, 61, and 63 which serve to guide the tube to 17packaging or other processing equipment.

19In some systems, rotating frame 65 is provided for rotating relative 20to blown film tower 13. It is particularly useful in rotating mechanical feeler arms 21of the prior art systems around plastic tube 55 to distribute the deformations.
22Umbilicai cord 67 is provided to allow electrical conductors to be routed to 23rotating frame 65. Rotating frame 65 rotates at bearings 71, 73 relative to 24stationary frame 69.

26Control subassembly 28 is provided to monitor and control the 27extrusion process, and in particular the circumference of plastic tube 55.
28Control subassembly 28 includes supervisory control unit, and operator control29panel 77.

Page- 12-DOCKET NO. 2s1H-1s70s -Figure 2 is a more detailed view of annular die 37, sizing cage 23, 2 control subassembly 28, and rotating frame 65. As shown in ~igure 2, 3 supervisory control unit 75 is electrically coupled to operator control panel 77, 4 valve 47, and acoustic transducer 79. These components cooperate to control the volume of air contained within extruded film tube 81, and hence the 6 thickness and diameter of the extruded film tube 81. Valve 47 controls the 7 amount of air directed by blower 41 into extruded film tube 81 through internal 8 air diffuser 51.

10If more air is directed into extruded film tube 81 by internal air 11diffuser 51 than is exhausted from extruded film tube 81 by exhaust stack 43, 12the circumference of extruded film tube 81 will be increased. Conversely, if 13more air is exhausted from the interior of extruded film tube 81 by exhaust 14stack 53 than is inputted into extruded film tube 81 by internal air diffuser 51, 15the circumference of extruded film tube 81 will decrease.

17In the preferred embodiment, valve 41 is responsive to supervisory 18control unit 75 for increasing or decreasing the flow of air into extruded film 19tube 81. Operator control panel 77 serves to allow the operator to select the 20diameter of extruded film tube 81. Acoustic transducer 79 serves to generate 21a signal corresponding to the circumference of extruded film tube 81, and direct 22this signal to supervisory control unit 75 for comparison to the circumference23setting selected by the operator at operator control panel 77.

25If the actual circumference of extruded film tube 81 exceeds the 26selected circumference, supervisory control unit 75 operates valve 47 to restrict 27the passage of air from blower 41 into extruded film tube 81. This results in a 28decrease in circumference of extruded film tube 81. Conversely, if the 29circumference of extruded film tube 81 is less than the selected circumference, 30supervisor,v control unit 75 operates on valve 47 to increase the flow of air into 31extruded film tube 81 and increase its circumference. Of course, extruded film Page- 13-DOCKET NO. 291 H-1 s705 2150898 ;

.

- 1 tube 81 will fluctuate in circumference, requiring constant adjustment and 2 readjustment of the inflow of air by operation of supervisory control unit 75 and 3 valve 47.

5Figure 3 is a view of ultrasonic sensor 89 of the improve control 6system of the present invention coupled to sizing cage 23 adjacent extruded 7film tube 81. In the preferred embodiment, acoustic transducer 79 comprises 8an ultrasonic measuring and control system manufactured by Massa Products gCorporation of Hingham, Massachusetts, Model Nos. M-4000, M410/21~, and 10M450, including a Massa Products ultrasonic sensor 89. It is an ultrasonic 11ranging and detection device which utilizes high frequency sound waves which 12are deflected off objects and detected. In the preferred embodiment, a pair of13ultrasonic sensors 89 are used, one to transmit sonic pulses, and another to 14receive sonic pulses. For purposes of simplifying the description only one 15ultrasonic sensor 89 is shown, and in fact a single ultrasonic sensor can be 16used, first to transmit a sonic pulse and then to receive the return in an 17alterating fashion The elapsed time between an ultrasonic pulse being 18transmitted and a significant echo being received corresponds to the distance 19between ultrasonic sensor 89 and the object being sensed. Of course, the 20distance between the ultrasonic sensor 89 and extruded film tube 81 21corresponds to the circumference of extruded film tube 81. In the present 22situation, ultrasonic sensor 89 emits an interrogating ultrasonic beam 87 23substantially normal to extruded film tube 81 and which is deflected from the 24outer surface of extruded film tube 81 and sensed by uitrasonic sensor 89.

26The Massa Products Corporation ultrasonic measurement and 27control system includes system electronics which utilize the duration of time 28between transmission and reception to produce a useable electrical output such29as a voltage or current. In the preferred embodimentl ultrasonic sensor 89 is 30coupled to sizing cage 23 at adjustable coupling 83. In the preferred 3tembodiment, ultrasonic sensor 89 is positioned within seven inches of extruded Page- 14-DOCKET NO. 291 H-19705 film tube 81 to minimize the impact of ambient noise on a control system.
2 Ultrasonic sensor 89 is positioned so that interrogating ultrasonic beam 87 3 travels through a path which is substantially normal to the outer surface of 4 extruded film tube 81l to maximize the return signal to ultrasonic sensor 89.
s 6Figure 4 is a view of ultrasonic sensor 89 of Figure 3 coupled to 7sizing cage 23 of the blown film tower 13, in two positions, one position being8shown in phantom. In the first position, ultrasonic sensor 89 is shown adjacentgextruded film tube 81 of a selected circumference. When extruded fllm tube 81 10is downsized to a tube having a smaller circumference, ultrasonic sensor 89 will 11move inward and outward relative to the central axis of the adjustable sizing 12cage, along with the adjustable sizing cage 23. The second position is shown 13in phantom with ultrasonic sensor 89' shown adjacent extruded film tube 81' of14a smaller circumference. For purposes of reference, internal air diffuser 51 and 15exhaust stack 5~ are shown in Figure 4. The sizing cage is also movable 16upward and downward, so ultrasonic sensor 89 is also movable upward and 17downward relative to the frostline of the extruded film tube 81.

19Figure 5 is a schematic and block diagram view of the preferred 20control system of the present invention. The preferred acoustic transducer 79 21of the present invention includes ultrasonic sensor 89 and temperature sensor 2291 which cooperate to produce a current position signal which is independent 23of the ambient temperature. Ultrasonic sensor 89 is electrically coupled to 24ultrasonic electronics module 95, and temperature sensor 91 is electrically 25coupled to temperature electronics module 97. Together, ultrasonic electronics26module 95 and temperature electronics module 97 comprise transducer 27electronics 93. Four signals are produced by acoustic transducer 79, including28one analog signal, and three digital signals.

30As shown in Figure 5, four conductors couple transducer 31electronics to supervisory control unit 75. Speciflcally, conductor 99 routes a Page- 15-DOCKET NO. 291H-19705 0 to 10 volts DC analog input to supervisory control unit 75. Conductors 101, 2 103, and 105 provide digital signals to supervisory control unit 75 which 3 correspond to a target present signal, maximum override, and minimum 4 override. These signals will be described below in greater detail.

6 Supervisory control unit 75 is electrically coupled to setpoint 7 display 109 through analog display output 107. An analog signal between 0 8 and 10 volts DC is provided to setpoint display 109 which displays the selected g distance between ultrasonic sensor 89 and extruded film tube 81. A distance is selected by the operator through distance selector 111. Target indicator 113,11 preferably a light, is provided to indicate that the target (extruded film tube 81) 12 iS in range. Distance selector 111 is electrically coupled to supervisory control 13 unit 75 by distance setting conductor 119. Target indicator 113 is electrically 14 coupled to supervisory control unit 75 through target present conductor 121.

16 Supervisory control unit 75 is also coupled via valve control 17 conductor 123 to proportional valve 125. In the preferred embodiment, 18 proportional valve 125 corresponds to valve 47 of Figure 1, and is a pressure 19 control component manufactured by Proportionair of McCordsville, Indiana, Model No. BB1. Proportional valve 125 translates an analog DC voltage 21 provided by supervisory control unit 75 into a corresponding pressure between 22 .5 and 1.2 bar. Proportional valve 125 acts on rotary valve 129 through cylinder 23 127. Pressurized air is provided to proportional valve 125 from pressurized air 24 supply 131 through 20 micron filter 133.

26 Figure 6 is a schematic and block diagram view of the preferred 27 control system of Figure 5, with special emphasis on the supervisory control 28 unit 75. Extruded film tube 81 is shown in cross-section with ultrasonic sensor 29 89 adjacent its outer wall. Ultrasonic sensor 89 emits interrogating pulses which are bounced off of extruded film tube and sensed by ultrasonic sensor 31 89. The time delay between transmission and reception of the interrogating Page- 16-DOCKET NO. 2s1H-1s705 215089~

pulse is processed by transducer electronics 93 to produce four outputs:
2 CURRENT POSITION signal which is provided to supervisory control unit 75 via 3 analog output conductor 99, digital TARGET PRESENT signal which is provided 4 over digital output 105, a minimum override signal (MIO signal) indicative of a collapsing or undersized bubble which is provided over digital output conductor 6 103, and maximum override signal (MAO signal) indicative of an overblown 7 extruded film tube 81 which is provided over a digital output conductor 101.

g As shown in Figure 6, the position of extruded film tube 81 relative to ultrasonic sensor 89 is analyzed and controlled with reference to a number of distance thresholds and setpoints, which are shown in greater detail in Figure 12 7(a). All set points and thresholds represent distances from reference R. The 13 control system of the present invention attempts to maintain extruded film tube 14 81 at a circumference which places the wall of extruded film tube 81 at a tangent to the line established by reference A. The distance between reference 16 R and set point A may be selected by the user through distance selector 111.
17 This allows the user to control the distance between ultrasonic sensor 89 and 18 extruded film tube 81.

The operating range of acoustic transducer 79 is configurable by 21 the user with settings made in transducer electronics 93. In the preferred 22 embodiment, using the Massa Products transducer, the range of operation of 23 acoustic transducer 79 is between 3 to 24 inches. Therefore, the user may 24 select a minimum circumference threshold C and a maximum circumference threshold B, below and above which an error signal is generated. Minimum 26 circumference threshold C may be set by the user at a distance d3 from 27 reference R. Maximum circumference threshold B may be selected by the user 28 to be a distance d2 from reference R. In the preferred embodiment, setpoint 29 A is set a distance of 7 inches from reference R. Minimum circumferencethreshold C is set a distance of 10.8125 inches from reference R. Maximum 31 circumference threshold B is set a distance of 4.1 inches from reference R.

Page- 17-DOCKET NO. 291H-19705 "_ 2150898 Transducer electronics 93 allows the user to set or adjust these distances at will 2 provided they are established within the range of operation of acoustic 3 transducer 79, which is between 3 and 24 inches.

Besides providing an analog indication of the distance between 6 ultrasonic sensors 89 and extruded film tube 81, transducer electronics 93 also 7 produces three digital signals which provide information pertaining to the 8 position of extruded film tube 81. If extruded film tube 81 is substantially normal g and within the operating range of ultrasonic sensor 89, a digital "1" is provided at digital output 105. The signal is representative of a TARGET PRESENT
11 signal. If extruded film tube 81 is not within the operating range of ultrasonic 12 sensor 89 or if a return pulse is not received due to curvature of extruded film 13 tube 81, TARGET PRESENT signal of digital output 105 is low. As discussed 14 above, digital output 103 is a minimum override signal MIO. If extruded film tube 81 is smaller in circumference than the reference established by threshold 16 C, minimum override signal MIO of digital output 103 is high. Conversely, if 17 circumference of extruded film tube 81 is greater than the reference established 18 by threshold C, the minimum override signal MIO is low.

Digital output 101 is for a maximum override signal MAO. If 21 extruded film tube 81 is greater than the reference established by threshold B, 22 the maximum override signal MAO is high. Conversely, if the circumference of 23 extruded film tube 81 is less than the reference established by threshold B, the 24 output of maximum override signal MAO is low.

26 The minimum override signal MIO will stay high as long as 27 extruded film tube 81 has a circumference less than that established by 28 threshold C. Likewise, the maximum override signal MAO will remain high for 29 as long as the circumference of extruded film tube 81 remains larger than the reference established by threshold B.

Page- 18-DOCKET NO. 291H-19705 ~ 2150898 Threshold D and threshold E are also depicted in Figure 7(a).
2 Threshold D is established at a distance d4 from reference R. Threshold E is 3 established at a distance d5 from reference R. Thresholds D and E are 4 established by supervisory control unit 75, not by acoustic transducer 79.
Threshold D represents a minimum circumference threshold for extruded film 6 tube 81 which differs from that established by transducer electronics 93.
7 Likewise, threshold E corresponds to a maximum circumference threshold 8 which differs from that established by acoustic transducer 79. Thresholds D
g and E are established in the software of supervisory control unit 75, and provide a redundancy of control, and also minimize the possibility of user error, 11 since these threshold are established in software, and cannot be easily 12 changed or accidentally changed. The coordination of all of these thresholds 13 will be discussed in greater detail below. In the preferred embodiment, 14 threshold C is established at 10.8125 inches from reference R. Threshold E is established at 3.6 inches from reference R.

17 Figure 7(b) is a side view of the ultrasonic sensor 89 coupled to 18 sizing cage 23 of the blown film tower 13, with permissible extruded film tube 19 81 operating ranges indicated thereon. Setpoint A is the desired distance between ultrasonic sensor 89 and extruded film tube 81. Thresholds D and C
21 are established at selected distances inward from ultrasonic sensor 89, and 22 represent minimum circumference thresholds for extruded film tube 81.
23 Thresholds B and E are established at selected distances from setpoint A, and 24 establish separate maximum circumference thresholds for extruded film tube 81.
As shown in Figure 7(b), extruded film tube 81 is not at setpoint A. Therefore, 26 additional air must be supplied to the interior of extruded film tube 81 to expand 27 the extruded film tube 81 to the desired circumference established by setpoint 28 A.

If extruded film tube 81 were to collapse, two separate alarm 31 conditions would be registered. One alarm condition will be established when Page- 19-DOCKET NO. 291H-19705 '_ 2150898 extruded film tube 81 falls below threshold C. A second and separate alarm 2 condition will be established when extruded film tube 81 falls below threshold 3 D. Extruded fiim tube 81 may also become overblown. In an overblown 4 condition, two separate alarm conditions are possible. When extruded film tube 81 expands beyond threshold B, an alarm condition is registered. When 6 extruded film tube 81 expands further to extend beyond threshold E, a separate 7 alarm condition is registered.

g As discussed above, thresholds C and B are subject to user adjustment through settings in transducer electronics 93. In contrast, thresholds D and E are set in computer code of supervisory control unit 75, 12 and are not easily adjusted. This redundancy in control guards against 13 accidental or intentional missetting of the threshold conditions at transducer 14 electronics 93. The system also guards against the possibility of equipment failure in transducer 79, or gradual drift in the threshold settings due to 16 deterioration, or overheating of the electronic components contained in17 transducer electronics 93.

19 Returning now to Figure 6, operator control panel 137 and supervisory control unit 75 will be described in greater detail. Operator control 21 panel 137 includes setpoint display 109, which serves to display the distance 22 d1 between reference R and setpoint A. Setpoint display 109 includes a 7 23 segment display. Distance selector 111 is used to adjust setpoint A. Holding 24 the switch to the " + " position increases the circumference of extruded film tube 81 by decreasing distance d1 between setpoint A and reference R. Holding the 26 switch to the "-" position decreases the diameter of extruded film tube 81 by 27 increasing the distance between reference R and setpoint A.

2g Target indicator 113 is a target light which displays information pertaining to whether extruded film tube 81 is within range of ultrasonic 31 transducer 89, whether an echo is received at ultrasonic transducer 89, and Page- 20-DOCKET NO. 291H-19705 - 21~ 0898 whether any alarm condition has occurred. Blower switch 139 is also provided 2 in operator control panel 137 to allow the operator to selectively disconnect the 3 blower from the control unit. As shown in Figure 6, all these components of 4 operator control panel 137 are electrically coupled to supervisory control unit 75.

7 Supervisory control unit 75 responds to the information provided 8 by acoustic transducer 79, and operator control panel 137 to actuate g proportional valve 125. Proportional valve 125 in turn acts upon pneumatic cylinder 127 to rotate rotary valve 129 to control the air flow to the interior of 11 extruded film tube 81.

13 With the exception of analog to digital converter 141, digital to 14 analog converter 143, and digital to analog converter 145 (which are hardware items~, supervisory control unit 75 is a graphic representation of computer 16 software resident in memory of supervisory control unit 75. In the preferred 17 embodiment, supervisory control unit 75 comprises an industrial controller, 18 preferably a Texas Instrument brand industrial controller Model No. PM550.
19 Therefore, supervisory control unit 75 is essentially a relatively low-powered computer which is dedicated to a particular piece of machinery for monitoring 21 and controlling. In the preferred embodiment, supervisory control unit 7522 serves to monitor many other operations of blown film extrusion line 11. The 23 gauging and control of the circumference of extruded film tube 81 through24 computer software is one additional function which is "piggybacked~ onto the industrial controller. Alternately, it is possible to provide an industrial controller 26 or microcomputer which is dedicated to the monitoring and control of the 27 extruded film tube 81. Of course, dedicating a microprocessor to this task is 28 a rather expensive alternative.

For purposes of clarity and simplification of description, the 31 operation of the computer program in supervisory control unit 75 have been P~ge- 21 -DOCKET NO. 291 H-19705 _ 2150898 segregated into operational blocks, and presented as an amalgamation of 2 digital hardware blocks. In the preferred embodiment, these software 3 subcomponents include: software filter 149, health state logic 151, automatic 4 sizing and recovery logic 153, loop mode control logic 155, volume setpoint control logic 157, and output clamp 159. These software modules interface 6 with one another, and to Pl loop program 147 of supervisory control unit 75.
7 Pl loop program is a software routine provided in the Texas Instruments' PM550 8 system. The proportional controller regulates a process by manipulating a g control element through the feedback of a controlled output. The equation for the output of a Pl controller is:
11 ~
12 m = K*e + K/T e dt + ms 14 In this equation:

16 m = controller output 17 K = controller gain 18 e = error 19 T = reset time dt = differential time 21 ~ ms = constant 22 e dt = integration of all previous errors 23 ~
24 When an error exists, it is surnmed (integrated) with all the previous errors, thereby increasing or decreasing the output of the Pl controller 26 (depending upon whether the error is positive or negative). Thus as the error 27 term accumulates in the integral term, thè output changes so as to eliminate the 28 error.

CURRENT POSITION signal is provided by acoustic transducer 31 79 via analog output 99 to analog to digital converter 141, where the analog Page- 22-DOCKET NO. 291H-19705 CURRENT POSITION signal is digitized. The digitized CURRENT POSITION
2 signal is routed through software filter 149, and then to Pl loop program 147.
3 If the circumference of extruded film tube 81 needs to be adjusted, Pl loop 4 program 147 acts through output clamp 159 upon proportional valve 125 to adjust the quantity of air provided to the interior of extruded film tube 81.

7 Figure 8(a) is a flowchart of the preferred filtering process applied 8 to CURRENT POSITION signal generated by the acoustic transducer. The g digitized CURRENT POSITION signal is provided from analog to digital converter 141 t~ software filter 149. The program reads the CURRENT
11 POSITION signal in step 161. Then, the software filter 149 sets SAMPLE (N) 12 to the position signal.

14 In step 165, the absolute value of the difference between CURRENT
POSITION (SAMPLE (N)) and the previous sample (SAMPLE (N - 1)) is 16 compared to a first threshold. If the absolute value of the difference between 17 the current sample and the previous sample is less than first threshold T1, the 18 value of SAMPLE (N) is set to CFS, the current filtered sample, in step 167. If 19 the absolute value of the difference between the current sample and the previous sample exceeds first threshold T1, in step 169, the CURRENT
21 POSITION signal is disregarded, and the previous position signal SAMPLE (N
22 - 1) iS substituted in its place.

24 Then, in step 171, the suggested change SC is calculated, by determining the difference between the current filtered sample CFS and the best 26 position estimate BPE. In step 173, the suggested change SC which was 27 calculated in step 171 is compared to positive T2, which is the maximum limit 28 on the rate of change. If the suggested change is within the maximum limit 29 allowed, in step 177, allowed change AC is set to the suggested change SCvalue. If, however, in step 173, the suggested change exceeds the maximum Page- 23 -DOCKET NO. 291 H-19705 limit allowed on the rate of change, in step 175, the allowed change is set to 2 + LT2, a default value for allowed change.

4 In step 179, the suggested change SC is compared to the negative limit for allowable rates of change, negative T2. If the suggested 6 change SC is greater than the maximum limit on negative change, in step 181, 7 allowed change AC is set to negative -LT2, a default value for negative change.
8 However, if in step 179 it is determined that suggested change SC is within the g maximum limit allowed on negative change, in step 183, the allowed change AC
is added to the current best position estimate BPE, in step 183. Finally, in step 11 185, the newly calculated best position estimate BPE is written to the Pl loop 12 program.

14 Software filter 149 is a two stage filter which first screens the CURRENT POSITION signal by comparing the amount of change, either 16 positive or negative, to threshold T1. If the CURRENT POSITION signal, as17 compared to the preceding position signal exceeds the threshold of T1, the 18 current position signal is discarded, and the previous position signal (SAMPLE
19 (N - 1)) is used instead. At the end of the first stage, in step 171, a suggested change SC value is derived by subtracting the best position estimate BPE from 21 the current filtered sample CFS.

23 In the second stage of filtering, the suggested change SC value24 iS compared to positive and negative change thresholds (in steps 173 and 179).
If the positive or negative change thresholds are violated, the allowable change26 iS set to a preselected value, either + LT2, or -LT2. Of course, if the suggested 27 change SC is within the limits set by positive T2 and negative T2, then the 28 allowable change AC is set to the suggested change SC.

The operation of software filter 149 may also be understood with 31 reference to Figure 8(b). In the graph of Figure 8(b), the y-axis represents the Page- 2~-DOCKET NO. 291H-19705 21~0898 signal level, and the x-axis represents time. The signal as sensed by acoustic 2 transducer 79 is designated as input, and shown in the solid line. The 3 operation of the first stage of the software filter 149 is depicted by the current 4 filtered sample CFS, which is shown in the graph by cross-marks. As shown, the current filtered sample CFS operates to ignore large positive or negative 6 changes in the position signal, and will only change when the position signal 7 seems to have stabilized for a short interval. Therefore, when changes occur 8 in the current filtered sample CFS, they occur in a plateau-like manner.

In stage two of the software filter 149, the current filtered sample 11 CFS is compared to the best position estimate BPE, to derive a suggested 12 change SC value. The suggested SC is then compared to positive and 13 negative thresholds to calculate an allowable change AC which is then added 14 to the best position estimate BPE. Figure 8(b) shows that the best position estimate BPE signal only gradually changes in response to an upward drift in the POSITION SIGNAL. The software filtering system 149 of the present 17 invention renders the control apparatus relatively unaffected by random noise, 18 but capable of tracking the more "gradual" changes in bubble position.

Experimentation has revealed that the software filtering system of the 21 present invention operates best when the position of extruded film tube 81 is 22 sampled between 20 to 30 times per second. At this sampling rate, one is less 23 likely to incorrectly identify noise as a change in circumference of extruded film 24 tube 81. The preferred sampling rate accounts for the common noise signals 2s encountered in blown film extrusion liner.

27 Optional thresholds have also been derived through 28 experimentation. In the first stage of filtering, threshold T1 is established as 29 roughly one percent of the operating range of acoustic transducer 79, which in the preferred embodiment is twenty-one meters (24 inches less 3 inches). In Pag~- 25 -DOCKET NO. 291 H-19705 215089~

the second stage of filter, thresholds + LT2 and -LT2 are established as roughly 2 0.30% of the operating range of acoustic transducer 79.

4 Figure 9 is a schematic representation of the automatic sizing and recovery logic ASRL of supervisory control unit 75. As stated above, this figure6 iS a hardware representation of a software routine. ASRL 153 is provided to 7 accommodate the many momentary false indications of maximum and minimum 8 circumference violations which may be registered due to noise, such as the g noise created due to air flow between acoustic transducer 79 and extruded film tube 81. The input from maximum alarm override MAO is "ored" with high 11 alarm D, from the Pl loop program, at "or" operator 191. High alarm D is the 12 signal generated by the program in supervisory control unit 75 when the 13 circumference of extruded film tube 81 exceeds threshold D of Figure 7(a). If 14 a maximum override MAO signal exists, or if a high alarm condition D exists, the output of "or4 operator 191 goes high, and actuates delay timer 193.

17 Likewise, minimum override MIO signal is ~ored~ at "or" operator 18 195 with low alarm E. If a rninimum override signal is present, or if a low alarm 19 condition E exists, the output of "or" operator 195 goes high, and is directed to delay timer 197. Delay timers 193, 197 are provided to prevent an alarm 21 condition unless the condition is held for 800 milliseconds continuously. Every 22 time the input of delay timers 193,197 goes low, the timer resets and starts 23 from 0. This mechanism eliminates many false alarms.

If an alarm condition is held for 800 milliseconds continuously, an 26 OVERBLOWN or UNDERBLOWN signal is generated, and directed to the health 27 state logic 151. Detected overblown or underblown conditions are "ored" at "or"
28 operator 199 to provide a REQUEST MANUAL MODE signal which is directed 29 to loop mode control logic 155.

Page- 26 -DOCKET NO. 291H-19705 Figure 10 is a schematic representation of the health-state logic 2 151 of Figure 6. The purpose of this logic is to control the target indicator 113 3 of operator control panel 137. When in non-error operation, the target indicator 4 113 is on if the blower is on, and the TARGET PRESENT signal from digital output 105 is high. When an error is sensed in the maximum override MAO or 6 minimum override MIO lines, the target indicator 113 will flash on and off in one 7 half second intervals.

g In health-state logic HSL 151, the maximum override signal MAO
is inverted at inverter 205. Likewise, the minimum override signal is inverted at 11 inverter 207.

13 "And" operator 209 serves to "and" the inverted maximum override 14 signal MAO, with the OVERBLOWN signal, and high alarm signal D. A high output from "and" operator 209 indicates that something is wrong with the 16 calibration of acoustic transducer 79.

Likewise, "and" operator 213 serves to "and" the inverted minimum 19 override signal MIO, with the OVERBLOWN signal, and low alarm signal E. If the output of "and" operator 213 is high, something is wrong with the calibration 21 of acoustic transducer 79. The outputs from "and" operators 209, 213 are 22 combined in "or" operator 215 to indicate an error with either the maximum or 23 minimum override detection systems. The output of ~or" operator 215 is 24 channeled through oscillator 219, and inverted at inverter 217. UAnd'' operator 211 serves to "and" the TARGET PRESENT signal, blower signal, and inverted 26 error signal from "or" operator 215. The output of "and" operator of 211 is 27 connected to target indicator 113.

29 If acoustic transducer 79 is properly calibrated, the target is within range and normal to the sonic pulses, and the blower is on, target indicator 11331 Will be on. If the target is within range and normal to the sonic pulses, the Page- 27 -DOCKET NO. 291H-19705 blower is on, but acoustic transducer 79 is out of calibration, target indicator2 113 will be on, but will be blinking. The blinking signal indicates that acoustic 3 transducer 79, and in particular transducer electronics 93, must be recalibrated.

Figure 11 is a schematic representation of loop mode control logic 6 LMCL of Figure 6. The purpose of this software module is coordinate the 7 transition in modes of operation. Specifically, this software module coordinates 8 automatic startup of the blown film extrusion process, as well as changes in g mode between an automated "cascade" mode and a manual mode, which is the required mode of the Pl controller to enable under and overblown 11 conditions of the extruded film tube 81 circumference. The plurality of input 12 signals are provided to loop mode control logic 155, including: BLOWER ON, 13 REQUEST MANUAL MODE, Pl LOOP IN CASCADE MODE, UNDERBLOWN
14 and OVERBLOWN. Loop mode control logic LMCL 155 provides two outp~
signals: MANUAL MODE, and CASCADE MODE.

17 Figure 11 includes a plurality of digital logic blocks which are 18 representative of programming operations. "Or" operator 225 "ores" the 19 inverted BLOWER ON SIGNAL to the REQUEST MANUAL MODE SIGNAL
"And" operator 227 "ands" the inverted REQUEST MANUAL MODE SIGNAL with 21 an inverted MANUAL MODE SIGNAL, and the BLOWER ON SIGNAL. "And~
22 operator 229 "ands" the REQUEST MANUAL MODE SIGNAL to the inverted 23 CASCADE MODE SIGNAL. This prevents MANUAL MODE and CASCADE
24 MODE from both being on at the same time. "And" operator 231 "ands" the MANUAL MODE SIGNAL, the inverted UNDERBLOWN SIGNAL, and the 26 OVERBLOWN SIGNAL. "And" operator 233 "ands" the MANUAL MODE
27 SIGNAL with the UNDERBLOWN SIGNAL. This causes the overblown condition 28 to prevail in the event a malfunction causes both underblown and overblown 29 conditions to be on. Inverters 235, 237, 239, 241, and 243 are provided to invert the inputted output signals of loop mode control logic 155 were needed.
31 Software one-shot 245 is provided for providing a momentary response to a Page- 28 -DOCKET NO. 291H-19705 -~ 2150.8g8 condition. Software one-shot 245 includes ~and~ operator 247, off-deiay 249, 2 and inverter 251.

4 The software of loop mode control logic 155 operates to ensure that the system is never in MANUAL MODE, and CASCADE MODE at the same 6 time. When manual mode is requested by REQUEST MANUAL MODE, loop 7 mode control logic 155 causes MANUAL MODE to go high. When manual 8 mode is not requested, loop mode control logic 155 operates to cause g CASCADE MODE to go high. MANUAL MODE and CASCADE MODE will never be high at the same time. Loop mode control logic 155 also serves to ensure 11 that the system provides a "bumpless transfer" when mode changes occur.
12 The term "cascade mode" is understood in the automation industries as 13 referring to an automatic mode which will read an adjustable setpoint.

Loop mode control logic 155 will also allow for automatic startup 6 of the blown film extrusion process. At startup, UNDERBLOWN SIGNAL is high, Pl LOOP IN CASCADE MODE is low, BLOWER ON SIGNAL is high. These 8 inputs (and in\/erted inputs) are combined at "and" operators 231, 233. At 19 startup, "and" operator 233 actuates logic block 253 to move the maximum air flow value address to the Pl loop step 261. At startup, the MANUAL MODE
21 SIGNAL is high. For the Pl loop controller of the preferred embodiment, when 22 MANUAL MODE is high, the value contained in Pl loop output address is 23 automatically applied to proportional valve 125. This results in actuation of 24 proportional valve 125 to allow maximum air flow to start the extruded film tube 81.

27 When extruded fllm tube 81 extends in size beyond the minimum 28 threshold (C and D of Figure 7(a)), the UNDERBLOWN SIGNAL goes low, and 29 the Pl LOOP IN CASCADE MODE signal goes high. This causes software one-shot 245 to trigger, causing logic blocks 265, 267 to push an initial bias 31 value contained in a program address onto the Pl loop. Simultaneously, logic Page- 29-DOCKET NO. 291 H-19705 21~0898 ,j,_ blocks 269, 271 operate to place the selected setpoint value A onto 2 volume-setpoint control logic VSCL 157. Thereafter, volume-setpoint control 3 logic VSCL 157 alone serves to communicate changes in setpoint value A to 4 Pl loop program 147.

6 If an overblown or underblown condition is detected for a 7 sufficiently long period of time, the controller will request a manual mode by 8 causing REQUEST MANUAL MODE SIGNAL to go high. If REQUEST MANUAL
g MODE goes high, loop mode control logic LMCL 155 supervises the transfer through operation of the logic blocks.

Loop mode control logic LMCL 155 also serves to detected overblown and underblown conditions. If an overblown or underblown condition is detected by the control system, REQUEST MANUAL MODE goes high, and the appropriate OVERBLOWN or UNDERBLOWN signal goes high.
The logic operators of loop mode control logic LMCL 155 operate to override the normal operation of the control system, and cause maximum or minimum air flow by putting the maximum air flow address 261 or minimum air flow 19 address 263 to the Pl output address. As stated above, when MANUAL MODE
is high, these maximum or minimum air flow address values are outputted 21 directly to proportional valve 125. Thus, when the extruded film tube 81 is 22 overblown, loop mode control logic LMCL 155 operates to immediately cause23 proportional valve 125 to minimize air flow to extruded film tube 81. Conversely, 24 if an underblown condition is detected, loop mode control logic LMCL 155 causes proportional valve 125 to immediately maximize air flow to extruded film 26 tube 81.

28 Figure 12 depicts the operation of volume-setpoint control logic 29 VSCL 157.

Page- 30-DOCKET NO. 2g1H-19705 , Volume setpoint control logic VSCL 157 operates to increase or 2 decrease setpoint A in response to changes made by the operator at distance 3 selector 111 of operator control panel 137, when the Pl loop program 147 is in 4 cascade mode, i.e. when Pl LOOP IN CASCADE MODE signal is high. The INCREASE SETPOINT, DECREASE SETPOINT, and Pl LOOP IN CASCADE
6 MODE signals are logically combined at "and" operators 283, and 287. These 7 "and" operators act on logic blocks 285, 289 to increase or decrease the 8 setpoint contained in remote setpoint address 291. When the setpoint is either g increased or decreased, logic block 293 operates to add the offset to the remote setpoint for display, and forwards tt~e information to digital to analog converter 143, for display at setpoint display 109 of operator control panel 137.
12 The revised remote setpoint address is then read by the Pl loop program 147.

14 Figure 13 is a flowchart drawing of output clamp 159. The purpose of this software routine is to make sure that the Pl loop program 1~7 16 does not over drive the rotary valve 129 past a usable limit. Rotary valve 129 17 operates by moving a vane to selectively occlude stationary openings. If the 18 moving vane is over driven, the rotary valve will begin to open when the Pl loop 19 calls for complete closure. In step 301, the output of the Pl loop program 147 iS read. In step 303, the output of Pl loop is compared to a maximum output.
21 If it exceeds the maximum output, the Pl output is set to a predetermined 22 maximum output in step 305. If the output of Pl loop does not exceed the 23 maximum output, in step 307, the clamped Pl output is written to the 24 proportional valve 125 through digital to analog converter 145.

26 Figures 14, through 27 will be used to describe an alternative 27 emergency condition control mode of operation which provides enhanced 28 control capabilities, especially when an overblown or underblown condition is 29 detected by the control system, or when the system indicates that the extruded film tube is out of range of the position-sensing transducer. In this alternative 31 emergency condition control mode of operation, the valve of the estimated Page- 31 -DOCKET NO. 291H-19705 -- 215~89~

position is advanced to a preselected valve and a more rapid change in the 2 estimated position signal is allowed than during previously discussed operating 3 conditions, and is particularly useful when an overblown or underblown 4 condition is detected. In the event the control system indicates that the extruded film tube is out of range of the sensing transducer, the improved 6 control system supplies an estimated position which, in most situations, is a 7 realistic estimation of the position of the extruded film tube relative to the 8 sensing transducerJ thus preventing false indications of the extruded film tube g being out of range of the sensing transducer from adversely affecting the 0 estimated position of the extruded film tube, greatly enhancing operation of the control system. In the event an overblown condition is detected, the improved 2 control system supplies an estimated position which corresponds to the 3 distance boundary established for detecting an overflow condition. In the event 4 an underblown condition is detected, the improved control system supplies an estimated position which corresponds to the distance boundary established for 16 detecting an underblown condition.

8 Figures 14, through 27 are a block diagram, schematic, and 19 flowchart representation of the preferred embodiment of a control system which is equipped with the alternative emergency condition controi mode of operation.
21 Figures 25, 26, and 27 provide graphic examples of the operation of this 22 alternative emergency condition control mode of operation.

24 Figure 14 is a schematic and block diagram view of the preferred 2s alternative control system 400 of the present invention of Figure 5, with special 26 emphasis on the supervisory control unit 75, and is identical in almost all 27 respects to the supervisory control unit 75 which is depicted in Figure 6;
28 therefore, identical referenced numerals are used to identify the various 2g components of alternative control system 400 of Figure 14 as are used in the control system depicted in Figure 6.

Page- 32-DOCKET NO. 291 H-1s70s -- 21~0898 Extruded film tube 81 is shown in cross-section with ultrasonic 2sensor 89 adjacent its outer wall. Ultrasonic sensor 89 emits interrogating 3pulses which are bounced off of extruded film tube and sensed by ultrasonic 4sensor 89. The time delay between transmission and reception of the 5interrogating pulse is processed by transducer electronics 93 to produce four 6outputs: CURRENT POSITION signal which is provided to supervisory control 7unit 75 via analog output conductor 99, digital TARGET PRESENT signal which 8iS provided over digital output 105, a minimum override signal (MIO signal) gindicative of a collapsing or undersized bubble which is pro\/ided over digital10output conductor 103, and maximum override signal (MAO signal) indicative of 11an overblown extruded film tube 81 which is provided over a digital output 12conductor 101.

14As shown in Figure 14, the position of extruded film tube 81 15relative to ultrasonic sensor 89 is analyzed and controlled with reference to a 16number of distance thresholds and setpoints, which are shown in greater detail17in Figure 15. All set points and thresholds represent distances from reference18R. The control system of the present invention attempts to rnaintain extruded 19film tube 81 at a circumference which places the wall of extruded film tube 8120at a tangent to the line established by reference A. The distance between 21reference R and set point A may be selected by the user through distance 22selector 111. This allows the user to control the distance between ultrasonic 23sensor 89 and extruded film tube 81.

2~iThe operating range of acoustic transducer 79 is configurable by 26the user with settings made in transducer electronics 93. In the preferred 27embodiment, using the Massa Products transducer, the range of operation of 28acoustic transducer 79 is between 3 to 24 inches. Therefore, the user may 29select a minimum circumference threshold C and a maximum circumference 30threshold B, below and above which an error signal is generated. Minimum 31circumference threshold C may be set by the user at a distance d3 from Page- 33 -DOCKET NO. 2s1H-1s70s _ 21~0~9~

reference R. Maximum circumference threshold B may be selected by the user 2 to be a distance d2 from reference R. In the preferred embodiment, setpoint 3 A is set a distance of 7 inches from reference R. Minimum circumference 4 threshold C is set a distance of 10.8125 inches from reference R. Maximum circumference threshold B is set a distance of 4.1 inches from reference R.
6 Transducer electronics 93 allows the user to set or adjust these distances at will 7 provided they are established within the range of operation of acoustic 8 transducer 79, which is between 3 and 24 inches.
g ..
Besides providing an analog indication of the distance between ultrasonic sensors 89 and extruded film tube 81, transducer electronics 93 also 12 produces three digital signals which provide information pertaining to the 13 position of extruded film tube 81. If extruded film tube 81 is substantially normal 14 and within the operating range of ultrasonic sensor 89, a digital "1" is provided at digital output 105. The signal is representative of a TARGET PRESENT
16 signal. If extruded film tube 81 is not within the operating range of ultrasonic 17 sensor 89 or if a return pulse is not received due to curvature of extruded film 18 tube 81, TARGET PRESENT signal of digital output 105 is low. As discussed 19 above, digital output 103 is a minimum override signal MIO. If extruded film tube 81 is smaller in circumference than the reference established by threshold 21 C, minimum override signal MIO of digital output 103 is high. Conversely, if 22 circumference of extruded film tube 81 is greater than the reference established 23 by threshold C, the minimum override signal MIO is low.

Digital output 101 is for a maximum override signal MAO. If 26 extruded film tube 81 is greater than the reference established by threshold B, 27 the maximum override signal MAO is high. Conversely, if the circumference of 28 extruded film tube 81 is less than the reference established by threshold B, the 29 output of maximum override signal MAO is low.

Page- 34-DOCKET NO. 2s1H-1s70s 21~08g8 The minimum override signal MIO will stay high as long as 2 extruded film tube 81 has a circumference less than that established by 3 threshold C. Likewise, the maximum override signal MAO will remain high for 4 as long as the circumference of extruded film tube 81 remains larger than the reference established by threshold B.

7 Threshold D and threshold E are also depicted in Figure 15.
8 Threshold D is established at a distance d4 from reference R. Threshold E is g established at a distance d5 from reference R. Thresholds D and E are established by supervisory control unit 75, not by acoustic transducer 79.
11 Threshold D represents a minimum circumference threshold for extruded film12 tube 81 which differs from that established by transducer electronics 93.
13 Likewise, threshold E corresponds to a maximum circumference threshold 14 which differs from that established by acoustic transducer 79. Thresholds D
and E are established in the software of supervisory control unit 75, and 16 provide a redundancy of control, and also minimize the possibility of user error, 17 since these threshold are established in software, and cannot be easily 18 changed or accidentally changed. The coordination of all of these thresholds 19 will be discussed in greater detail below. In the preferred embodiment, threshold C is established at 10.8125 inches from reference R. Threshold E is 21 established at 3.6 inches from refe!ence R.

23 Figure 16 is a side view of the ultrasonic sensor 89 coupled to 24 sizing cage 23 of the blown film tower 13, with permissible extruded film tube 81 operating ranges indicated thereon. Setpoint A is the desired distance 26 between ultrasonic sensor 89 and extruded film tube 81. Thresholds D and C27 are established at selected distances inward from ultrasonic sensor 89, and 28 represent minimum circumference thresholds for extruded film tube 81.
29 Thresholds B and E are established at selected distances from setpoint A, and establish separate maximum circumference thresholds for extruded film tube 81.
31 As shown in Figure 16, extruded film tube 81 is not at setpoint A. Therefore Page- 35-DOCKET NO. 2s1H-1s70s . _ additional air must be supplied to the interior of extruded film tube 81 to expand 2 the extruded film tube 81 to the desired circumference established by setpoint 3 A.

s If extruded film tube 81 were to collapse, two separate alarm6 conditions would be registered. One alarm condition will be established when 7 extruded film tube 81 falls below threshold C. A second and separate alarm 8 condition will be established when extruded film tube 81 falls below threshold g D. Extruded film tube 81 may also become overblown. In an overblown condition, two separate alarm conditions are possible. When extruded film tube 11 81 expands beyond threshold B, an alarm condition is registered. When 12 extruded film tube 81 expands further to extend beyond threshold E, a separate 13 alarm condition is registered.

As discussed above, thresholds C and B are subject to user 16 adjustment through settings in transducer electronics 93. In contrast, 17 thresholds D and E are set in computer code of superviso~ control unit 75, 18 and are not easily adjusted. This redundancy in control guards against 19 accidental or intentional missetting of the threshold conditions at transducer electronics 93. The system also guards against the possibility of equipment 21 failure in transducer 79, or gradual drift in the threshold settings due to 22 deterioration, or overheating of the electronic components contained in23 transducer electronics 93.

Returning now to Figure 14, operator control panel 137 and 26 supervisory control unit 75 wîll be described in greater detail. Operator control 27 panel 137 includes setpoint display 109, which serves to display the distance 28 d1 between reference R and setpoint A. Setpoint display 109 includes a 7 2g segment display. Distance selector 111 is used to adjust setpoint A. Holding the switch to the " ~ ~ position incrcases the circumference of extruded film tube 31 81 by decreasing distance d1 between setpoint A and reference R. Holding the Page- 36 -DOCKET NO. 291 H-19705 switch to the "-" position decreases the diameter of extruded film tube 81 by 2 increasing the distance between reference R and setpoint A.

4 Target indicator 113 is a target light which displays information pertaining to whether extruded film tube 81 is within range of ultrasonic 6 transducer 89, whether an echo is received at ultrasonic transducer 89, and 7 whether any error condition has occurred. Blower switch 139 is also provided 8 in operator control panel 137 to allow the operator to selectively disconnect the g blower from the control unit. As shown in Figure 14, all these components of operator control panel 137 are electrically coupled to supervisory control unit 11 75.

13 Supervisory control unit 75 responds to the information provided 14 by acoustic transducer 79, and operator control panel 137 to actuate proportional valve 125. Proportional valve 125 in turn acts upon pneumatic 16 cylinder 127 to rotate rotary valve 129 to control the air flow to the interior of 17 extruded film tube 81.

19 With the exception of analog to digital converter 141, digital to analog converter 143, and digital to analog converter 145 (which are hardware 21 items), supervisory control unit 75 is a graphic representation of computer 22 sof~ware resident in rnemory of supervisory control unit 75. In one 23 embodiment, supervisory control unit 75 comprises an industrial controller, 24 preferably a Texas Instrument brand industrial controller Model No. PM550.
Therefore, supervisory control unit 75 is essentially a relatively low-powered 26 computer which is dedicated to a particular piece of machinery for monitoring 27 and controlling. In the preferred embodiment, supervisory control unit 7528 serves to monitor many other operations of blown film extrusion line 11. The 29 gauging and control of the circumference of extruded film tube 81 throughcomputer software is one additional function which is Upiggybacked'' onto th~
31 industrial controller. Alternately, it is possible to provide an industrial controller Page- 37 -DOCKET NO. 291H-19705 or microcomputer which is dedicated to the monitoring and control of the 2 extruded film tube 81. Of course, dedicating a microprocessor to this task is 3 a rather expensive alternative.

For purposes of clarity and simplification of description, the 6 operation of the computer program in supervisory control unit 75 have been 7 segregated into operational blocks, and presented as an amalgamation of 8 digital hardware blocks. In the preferred embodiment, these software g subcomponents include: software filter 149, emergency condition control mode logic 150, health state logic 151, automatic sizing and recovery logic 153, loop11 mode control logic 155, volume setpoint control logic 157, and output clamp 12 159. These software modules interface with one another, and to Pl loop 13 program 147 of supervisory control unit 75. Pl loop program is a software14 routine provided in the Texas Instruments' PM550 system. The proportionalcontroller regulates a process by manipulating a control element through the 16 feedback of a controlled output. The equation for the output of a Pl controller 1 7 iS:

19 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 e dt = integration of all previous errors Page- 38-DOCKET NO. 291H-19705 ,_ When an error exists, it is summed (integrated) with all the 2 previous errors, thereby increasing or decreasing the output of the Pl controller 3 (depending upon whether the error is positive or negative). Thus as the error 4 term accumulates in the integral term, the output changes so as to eliminate the error.

7 CURRENT POSITION signal is provided by acoustic transducer 8 79 via analog output 99 to analog to digital converter 141, where the analog g CURRENT POSITION signal is digitized. The digitized CURRENT POSITION
signal is routed through software filter 149, and then to Pl loop program 147.
11 If the circumference of extruded film tube 81 needs to be adjusted, Pl loop 12 program 147 acts through output clamp 159 upon proportional valve 125 to 13 adjust the quantity of air provided to the interior of extruded film tube 81.

Figure 17 is a schematic representation of the automatic sizing 16 and recovery logic ASRL of supervisory control unit 75. As stated above, this 17 figure is a hardware representation of a software routine. ASRL 153 is provided 18 to accommodate the many momentary false indications of maximum and 19 minimum circumference violations which may be registered due to noise, such as the noise created due to air flow between acoustic transducer 79 and 21 extruded film tube 81. The input from maximum alarm override MAO is "ored"
2z with high alarm D, from the Pl loop program, at"or" operator 191. High alarm 23 D is the signal generated by the program in supervisory control unit 75 when 24 the circumference of extruded film tube 81 exceeds threshold D of Figure 15.
2s If a maximum override MAO signal exists, or if a high alarm condition D exists, 2~ the output of "or" operator 191 goes high, and actuates delay timer 193.

28 Likewise, minimum override MIO signal is "ored" at"or" operator29 195 with low alarm E. If a minimum override signal is present, or if a low alarm condition E exists, the output of ~or" operator 195 goes high, and is directed to 31 delay timer 197. Delay timers 193, 197 are provided to prevent an alarm Pa~e- 39-DOCKET NO. 2tl1H-19705 condition unless the condition is held for 800 milliseconds continuously. Everv 2 time the input of delay timers 193, 197 goes low, the timer resets and starts 3 from 0. This mechanism eliminates many false alarms.

If an alarrn condition is held for 800 milliseconds continuously, an 6 OVERB~OWN or UNDERBLOWN signal is generated, and directed to the health 7 state logic 151. Detected overblown or underblown conditions are ~ored~ at ''orU
8 operator 199 to provide a REQUEST MANUAL MODE signal which is directed g to loop mode control logic 155.

11 Figure 18 is a schematic representation of the health-state logic 12 151 of Figure 14. The purpose of this logic is to control the target indicator 113 13 of operator control panel 137. When in non-error operation, the target indicator 14 113 is on if the blower is on, and the TARGET PRESENT signal from digital output 105 is high. When an error is sensed in the maximum override MAO or 16 minimum override MIO lines, the target indicator 113 will flash on and off in one 17 half second intervals.

19 In health-state logic HSL 151, the maximum override signal MAO
iS inverted at inverter 205. Likewise, the minimum override signal is inverted at 21 inverter 207.

23 "And" operator 209 serves to "and" the inverted maximum override24 signal MAO, with the OVERBLOWN signal, and high alarm signal D. A high output from "and" operator 209 indicates that something is wrong with the 26 calibration of acoustic transducer 79.

28 Likewise, "and" operator 213 serves to "andH the inverted minimum 29 override signal MIO, with the OVERBLOWN signal, and low alarm signal E. Ifthe output of "and" operator 213 is high, something is wrong with the oali~r~ion31 of acoustic transducer 79. The outputs from "and" operators 209, 213 are Page- 40-DOCKET NO. 291H-19705 combined in "or" operator 215 to indicate an error with either the maximum or 2 minimum override detection systems. The output of "or" operator 215 is 3 channeled through oscillator 219, and inverted at inverter 217. "And" operator 4 211 serves to "and" the TARGET PRESENT signal, blower signal, and inverted error signal from "or" operator 215. The output of "and" operator of 211 is 6 connected to target indicator 113.

8 If acoustic transducer 79 is properly calibrated, the target is within g range and normal to the sonic pulses, and the blower is on, target indicator 113 will be on. If the target is within range and normal to the sonic pulses, the blower is on, but acoustic transducer 79 is out of calibration, target indicator12 113 will be on, but will be blinking. The blinking signal indicates that acoustic 13 transducer 79, and in particular transducer electronics 93, must be recalibrated.

Figure 19 is a schematic representation of loop mode control logic 16 LMCL of Figure 14. The purpose of this software module is coordinate the 17 transition in modes of operation. Specifically, this software module coordinates 18 automatic startup of the blown film extrusion process, as wèll as changes in 19 mode between an autornated "cascade~ mode and a manual mode, which is the required mode of the Pl controller to enable under and overblown 21 conditions of the extruded film tube 81 circumference. The plurality of input 22 signals are provided to loop mode control logic 155, including: BLOWER ON, 23 REQUEST MANUAL MODE, Pl LOOP IN CASCADE MODE, UNDERBLOWN
24 and OVERBLOWN. Loop mode control logic LMCL 155 provides two output signals: MANUAL MODE, and CASCADE MODE.

27 Figure 19 includes a plurality of digital logic blocks which are 28 representative of programming operations. "Or" operator 225 ~ores" the 29 inverted BLOWER ON SIGNAL to the REQUEST MANUAL MODE SIGNAL
"And" operator 227 "ands" the inverted REQUEST MANUAL MODE SIGNAL with 31 an inverted MANUAL MODE SIGNAL, and the BLOWER ON SIGNAL ~And"

Page- 41 -DOCKET Na 291H-1970s 21~0898 -operator 229 "ands" the REQUEST MANUAL MODE SIGNAL to the inverted 2 CASCADE MODE SIGNAL. This prevents MANUAL MODE and CASCADE
3 MODE frorn both being on at the same time. "And" operator 231 "ands" the 4 MANUAL MODE SIGNAL, the inverted UNDERBLOWN SlGNAL, and the

5 OVERBLOWN SIGNAL. "And" operator 233 "ands" the MANUAL MODE

6 SIGNAL with the UNDERBLOWN SIGNAL. This causes the overblown condition

7 to prevail in the event a malfunction causes both underblown and overblown

8 conditions to be on. Inverters 235, 237, 239, 241, and 243 are provided to g invert the inputted output signals of loop mode control logic 155 were needed.10 Software one-shot 245 is provided for providing a momentary response to a 11 condition. Software one-shot 245 includes "and" operator 247, off-delay 249, 12 and inverter 251.

14 The software of loop mode control logic 155 operates to ensure 15 that the system is never in MANUAL MODE, and CASCADE MODE at the same 16 time. When manual mode is requested by REQUEST MANUAL MODE, loop 17 mode control logic 155 causes MANUAL MODE to go high. When manual 18 mode is not requested, loop mode control logic 155 operates to cause 19 CASCADE MODE to go high. MANUAL MODE and CASCADE MODE will never 20 be high at the same time. Loop mode control logic 155 also serves to ensure 21 that the system provides a "bumpless transfer" when mode changes occur.
22 The term "cascade mode" is understood in the automation industries as 23 referring to an automatic mode which will read an adjustable setpoint.

Loop mode control logic 155 will also allow for automatic startup 26 of the blown film extrusion process. At startup, UNDERBLOWN SIGNAL is high, 27 Pl LOOP IN CASCADE MODE is low, BLOWER ON SIGNAL is high. These 28 inputs (and inverted inputs) are combined at "and" operators 231, 233. At 29 startup, "and" operator 233 actuates logic block 253 to move the maximum air 30 flow value address to the Pl loop step 261. At startup, the MANUAL MODE
31 SIGNAL is high. For the Pl loop controller of the preferred embodiment, when Page- 42-DOCKET NO. 291H-19705 _ MANUAL MODE is high, the value contained in Pl loop output address is 2 automatically applied to proportional valve 125. This results in actuation of 3 proportional valve 125 to allow maximum air flow to start the extruded film tube 4 81.

6 When extruded film tube 81 extends in size beyond the minimum 7 threshold (C and D of Figure 15 ), the UNDERBLOWN SIGNAL goes low, and 8 the Pl LOOP IN CASCADE MODE signal goes high. This causes software g one-shot 245 to trigger, causing logic blocks 265, 267 to push an initial bias value contained in a program address onto the Pl loop. Simultaneously, logic 11 blocks 269, 271 operate to place the selected setpoint value A onto 12 volume-setpoint control logic VSCL 157. Thereafter, volume-setpoint control 13 logic VSCL 157 alone serves to communicate changes in setpoint value A to 14 Pl loop program 147.

16 If an overblown or underblown condition is detected for a 17 sufficiently long period of time, the controller will request a manual mode by 18 causing REQUEST MANUAL MODE SlGNALto go high. If REQUEST MANUAL
19 MODE goes high, loop mode control logic LMCL 155 supervises the transfer through operation of the logic blocks.

22 Loop mode control logic LMCL 155 also serves to detected 23 overblown and underblown conditions. If an overblown or underblown 24 condition is detected by the control system, REQUEST MANUAL MODE goes high, and the appropriate OVERBLOWN or UNDERBLOWN signal goes high.
26 The logic operators of loop mode control logic LMCL 155 operate to override 27 the normal operation of the control system, and cause maximum or minimum 28 air flow by putting the maximum air flow address 261 or minimum air flow 29 address 263 to the Pl output address. As stated above, when MANUAL MODE
iS high, these maximum or minimum air flow address values are outputted 31 directly to proportional valve 125. Thus, when the extruded film tube 81 is Page- 43-DOCKET NO. 291H-19705 overblown, loop mode control logic LMCL 155 operates to immediately cause 2 proportional valve 125 to minimize air flow to extruded film tube 81. Conversely, 3 if an underblown condition is detected, loop mode control logic LMCL 155 4 causes proportional valve 125 to immediately maximize air nOw to extruded film tube 81.

7 Figure 20 depicts the operation of volume-setpoint control logic 8 VSCL 157.

Volume setpoint control logic VSCL 157 operates to increase or 11 decrease setpoint A in response to changes made by the operator at distance 12 selector 111 of operator control panel 137, when the Pl loop program 147 is in 13 cascade mode, i.e. when Pl LOOP IN CASCADE MODE signal is high. The 14 INCREASE SETPOINT, DECREASE SETPOINT, and Pl LOOP IN CASCADE
MODE signals are logically combined at "and" operators 283, and 287. These 16 "and" operators act on logic blocks 285, 289 to increase or decrease the 17 setpoint contained in remote setpoint address 291. When the setpoint is either 18 increased or decreased, logic block 293 operates to add the offset to the 19 remote setpoint for display, and forwards the information to digital to analog converter 143, for display at setpoint display 109 of operator control panel 137.
21 The revised remote setpoint address is then read by the Pl loop program 147.

23 Figure 21 is a flowchart drawing of output clamp 159. The 24 purpose of this software routine is to make sure that the Pl loop program 147 does not over drive the rotary valve 129 past a usable limit. Rotary valve 129 26 operates by moving a vane to selectively occlude stationary openings. If the 27 moving vane is over driven, the rotary valve will begin to open when the Pl loop 28 calls for complete closure. In step 301, the output of the Pl loop program 147 29 iS read. In step 303, the output of Pl loop is compared to a maximum output.
If it exceeds the maximum output, the Pl output is set to a predetermined 31 maximum output in step 305. If the output of Pl loop does not exceed the Page- 44-DOCKET NO. 291H-19705 -maximum output, in step 307, the clamped Pl output is written to the 2 proportional valve 125 through digital to analog converter 145.

4 As shown in Figure 14, emergency condition control mode logic 150 is provided in supervisory control unit 75, and is shown in detail in Figure6 22. As shown in Figure 22, emergency condition control mode logic 150 7 receives three input signals: the OVER BLOWN signal; the UNDERBLOWN
8 signal; and the TARGET filter signal. The emergency condition control modeg logic 150 provides as an output two variables to software filter 149, including:
"SPEED HOLD"; and UALIGN HOLD". The OVERBLOWN signal is directed to 11 anticipation state "or" gate 403 and to inverter 405. The UNDERBLOWN signal 12 iS directed to anticipation state "or" gate 403 and to inverter 407. The TARGET
13 signal is directed through inverter 401 to anticipation state "or" gate 403, and 14 to "and~' gate 409. The output of anticipation "or" gate 403 is the ~or"
combination of OVERBLOWN signal, and the inverted TARGET signal.
16 Anticipation state "or" gate 403 and "and" gate 419 cooperate to provide a17 locking logic loop. The output of "or" gate 403 is provided as an input to ~and"
18 gate 419. The other input to "and" gate 419 is the output of inverter 417. The 19 output of inverter 417 can be considered as a "unlocking" signal. If the OVERBLOWN signal or UNDERBLOWN signal is high, or the inverted TARGET
21 signal is high, the output of anticipation state "or" gate 403 will go high, and will 22 be fed as an input into "and" gate 419, as stated above. The output of 23 anticipation state "or" gate 403 is also provided as an input to "and" gates 413, 24 411, and 409. The other input to "and" gate 413 is the inverted OVERBLOWN
signal. The other input to "and" gate 411 is the inverted UNDERBLOWN signal.
26 The other input to "and" gate 409 is the TARGET signal. The outputs of aand"
27 gates 409, 411, and 413 are provided to "or" gate 415. The output of "or" gate 28 415 is provided to inverter 417.

In operation, the detection of an overblown or underblown 31 condition, or an indication that the extruded film tube is out of range of the Page- 45 -DOCKET NO. 291H-19705 '. ~

sensor will cause the output of anticipation state "or" gate 403 to go high. This 2 high output will be fed back through "and" gate 419 as an input to anticipation 3 state "or" gate 403. Of course, the output of "and" gate 419 will be high for so 4 long as neither input to "and" gate 419 is low. Of course, one input to aand"
gate 419 is high because a change in the state of the OVER BLOWN signal, the 6 UNDER BLOWN signall and the TARGET signal has been detected. The other 7 input to "and" gate 419 is controlled by the output of inverter 417, which is 8 controlled by the output of next-state "or~ gate 415. As stated above, the g output of next-state "or" gate 415 is controlled by the output of Hand" gates 409, 411, 413. In this conflguration, anticipation state Ror" gate 403 and "and" gate419 are locked in a logic loop until a change is detected in a binary state of one 2 of the following signals: the OVERBLOWN signal, the UNDERBLOWN signal, 3 and the TARGET signal. A change in state of one of these signals causes14 next-state "or" gate 415 to go high, which causes the output of inver~er 417 to go low, which causes the output of "and" gate 419 to go low.

7 The output of next-state ''orU gate 415 is also provided to timer 8 starter 421, the reset pin for timer starter 421, and the input of block 423.
19 When a high signal is provided to the input of timer starter 421, a three second software clock is initiated. At the beginning of the three second period, the 21 output of timer starter 421 goes from a normally high condition to a temporary 22 low condition; at the end of the three second software timer, the output of timer 23 starter 421 returns to its normally high condition. If any additional changes in 24 the state of the OVERBLOWN signal, the UNDERBLOWN signal, and the TARGET signal are detected, the software timer is reset to zero, and begins 26 running again. The particular change in the input signal of the OVERBLOWN
27 signal, the UNDERBLOWN signal, and the TARGET signal, also causes the 28 transmission of a high output from NandU gates 409, 411, and 413 to blocks 429, 29 427, and 425 respectively.

Page- 4s-DOCKET NO. 291H-19705 ,_ In operation, when the input to block 423 goes high, the numeric 2 value associated with the variable identified as "quick filter align" will be pushed 3 to a memory variable identified as "speed hold". "Quick filter align" is a filter 4 variable which is used by software filter 149 (of Figure 23, which will be discussed below), which determines the maximum allowable rate of change in 6 determining the estimated position. "Speed hold" is a holding variable which 7 holds the numeric value for the maximum allowable rate of change in 8 determining the estimated position of the blown film tube. ~Speed hold" can g hold either a value identified as "quick filter align" or a value identified as "normal filter align". "Normal ~llter align" is a variable that contains a numeric value which determines the normal maximum amount of change allowed in 12 determining the estimated position of the blown film tube relative to the 13 transducer. Blocks 423 and 431 are both coupled to block 433 which is an 14 operational block representative of a "push" operation. Essentially, block 433 represents the activity of continuously and asynchronously pushing the value 16 held in the variable "speed hold" to "LT2" in software filter 149 via data bus 402.
17 The value for ~normal filter align" is the same as that discussed herebelow in 18 connection with Figure 8a, and comprises thirteen counts, wherein counts are 19 normalized units established in terms of voltage. The preferred value for 8quick filter align~ is forty-eight counts. Therefore, when the software filter 149 is 21 provided with the quick filter align value, the control system is able to change 22 at a rate of approximately 3.7 times as fast as that during a ~normal filter align~
23 mode of operation.

Also, when a "locked" condition is obtained by anticipation state 26 "or" gate 403 and Uand'' gate 419, any additional change in state of the values 27 of any of the OVERBLOWN signal, the UNDERBLOWN signal, and the TARGEr 28 signal will cause "and" gates 409, 411, and 413 to selectively activate blocks 29 429, 427, 425. Blocks 429, 427, and 425 are coupled to block 433 which is linked by data bus 402 to software filter 149. When block 429 receives a high 31 input, the variable held in the memor,v location "target reslore count~ is moved Pa~e- 47-DOCKET NO. 2s1H-ls70s 2150g98 to a memory location identified as "align hold". When block 4Z7 receives a high 2 input signal, the value held in the memory location identified as ~underblown 3 count" is moved to a memory value identified as "align hold~'. When block 425 4 receives a high input signal, the numeric value held in a memory location identified as "overblown count" is moved to a memory location identified as 6 "align hold". As stated above, block 433 performs a continuous asynchronous 7 "push" operation, and will push any value identified to the Ualign hold" memory 8 location to the values of SAMPLE (N), SAMPLE (N-1), and BPE in the software g filter of Figure 23. In the preferred embodiment of the present invention, the value of "overblown count" is set to cor,es~ond to the distance between reference R and maximum circumference threshold B which is depicted in ~2 Figure 16, which is established distance at which the control system will 13 determine that an "overblown" condition exists. Also, in the preferred 14 embodiment of the present invention, the value of the ''underblownU count will be set to a minimum circumference threshold C, which is depicted in Figure 16, 16 and which corresponds to the detection of an underblown condition. Also, in 17 the present invention, the value of "target restore count" is preferably 18 established to correspond to the value of set point A, which is depicted in 19 Figure 16, and which corresponds generally to the distance between reference R and the imagina~ cylinder established by the position of the sizing cage with 21 respect to the blown film tube.

23 Figure 23 is a flowchart of the preferred filtering process applied 24 to CURRENT POSITION signal generated by the acoustic transducer. The digitized CURRENT POSITION signal is provided from analog to digital 26 converter 141 to software filter 149. The program reads the CURRENT
27 POSITION signal in step 161. Then, the software filter 149 sets SAMPLE (N) 28 to the position signal.
2g In step 165, the absolute value of the ~ rence between CURRENT
31 POSITION (SAMPLE (N)) and the previous sample (SAMPLE (N - 1)) is Page- 48-DOCKET NO. 2slH-1s7os 215û898 compared to a first threshoid. If the absolute value of the difference between 2 the current sample and the previous sample is less than first threshold T1, the 3 value of SAMPLE (N) is set to CFS, the current filtered sample, in step 167. If 4 the absolute value of the difference between the current sample and the previous sample exceeds first threshold T1, in step 169, the CURRENT
6 POSITION signal is disregarded, and the previous position signal SAMPLE (N
7 - 1) iS substituted in its place.

g Then, in step 171, the suggested change SC is calculated, by determining the difference between the currentfiltered sample CFS and the best l1 position estimate BPE. In step 173, the suggested change SC which was 12 calculated in step 171 is compared to positive T2, which is the maximum limit 13 on the rate of change. If the suggested change is within the maximum limit 14 allowed, in step 177, allowed change AC is set to the suggested change SC
value. If, however, in step 173, the suggested change exceeds the maximum 16 limit allowed on the rate of change, in step 175, the allowed change is set to 17 +LT2, a default value for allowed change.

19 In step 179, the suggested change SC is compared to the negative limit for allowable rates of change, negative T2. If the suggested 21 change SC is greater than the maximum limit on negative change, in step 181, 22 allowed change AC is set to negative -LT2, a default value for negative change.
23 However, if in step 179 it is determined that suggested change SC is within the 24 maximum limit allowed on negative change, in step 183, the allowed change AC
iS added to the current best position estimate BPE, in step 183. Finally, in step 26 185, the newly calculated best position estimate BPE is written to the Pl loop 27 program.

29 Software filter 149 is a two stage fllter which first screens the CURRENT POSITION signal by comparing the amount of change, either 31 positive or negative, to threshold T1. If the CURRENT POSITION signal, as Page- 49-DOCKET NO. 291H-1~705 .
compared to the preceding position signal exceeds the threshold of T1, the 2 current position signal is discarded, and the previous position signal (SAMPLE
3 (N - 1)) is used instead. At the end of the first stage, in step 171, a suggested 4 change SC value is derived by subtracting the best position estimate BPE from s the current filtered sample CFS.

7 In the second stage of filtering, the suggested change SC value8 iS compared to positive and negative change thresholds (in steps 173 and 179).
g If the positive or negative change thresholds are violated, the allowable change is set to a preselected value, either + LT2, or -LT2. Of course, if the suggested 11 change SC is within the limits set by positive T2 and negative T2, then the 12 allowable change AC is set to the suggested change SC.

14 As is shown in Figure 23, data bus 201 couples the emergency condition control logic block 150 to software filter 149. As stated above, 16 emergency condition control logic block 150 is designed to asynchronously 17 push a numeric value identified in the memory location of "speed hold~ to LT2 18 in software filter 149. Furthermore, emergency condition control logic block 150 19 will asynchronously push a numeric value in the memory location identified as "ALIGN HOLD" to SAMPLE (N), SAMPLE (N - 1), and BPE. As sta~ed above, 21 SAMPLE N corresponds to the current position signal as detected by the 22 transducer. SAMPLE (N - 1) corresponds to the previous position signal as 23 determined by the transducer. BPE corresponds to the best position estimate.

26 Since the operation of emergency condition control mode logic 27 block 150 is asynchronous, block 186 of Figure 23 should be read and 28 understood as corresponding to an asynchronous read function. Therefore, at 29 all times, as set forth in block 186, software filter 149 receives values of ~speed hold~ and "align hold" from emergency condition control mode logic block 150, 31 and immediate substitutes them into the various logic blocks found in software P~ge- s0 -- DOCKET NO. 291H-19705 filter 149. For example, SAMPLE (N) is found in logic blocks 163, 165, and 16~.
2 SAMPLE (N -1) is found in logic blocks 165, and 169. BPE is found at logic 3 block 183. The program function represented by block 186 operates to 4 asynchronously and immediately push the values of Uspeed hold" and "align hold~ to these various functional blocks, since OVERBLOWN, UNDERB-OWN, 6 and lost TARGET conditions can occur at any time.

8 The normal operation of software filter 149 may also be g understood with reference to Figure 24, and will be contrasted with examples of the emergency condition mode of operation as depicted in Figures 25, 26, 11 and 27. In the graph of Figure 24, the y~axis represents the signal level, and 12 the x-axis represents time. The signal as sensed by acoustic transducer 79 is 13 designated as input, and shown in the solid line. The operation of the first 14 stage of the software filter 149 is depicted by the current filtered sample CFS, which is shown in the graph by cross-marks. As shown, the current filtered 16 sample CFS operates to ignore large positive or negative changes in the 17 position signal, and will only change when the position signal seems to have 18 stabilized for a short interval. Therefore, when changes occur in the current 19 filtered sample CFS, they occur in a plateau-like manner.

21 In stage two of the software filter 149, the current filtered sample 22 CFS is compared to the best position estimate BPE, to derive a suggested 23 change SC value. The suggested SC is then compared to positive and 24 negative thresholds to calculate an allowable change AC which is then added to the best position estimate BPE. Figure 24 shows that the best position 26 estimate BPE signal only gradually changes in response to an upward drift in 27 the POSITION SIGNAL. The software filtering system 149 of the present 28 invention renders the control apparatus relatively unaffected by random noise, 2g but capable of tracking the more "gradual" changes in bubble position.

pa9e- 51 -DOCKET NO. 291H-19705 215~898 Experimentation has revealed that the software filtering system of the 2 present invention operates best when the position of extruded film tube 81 is 3 sampled between 20 to 30 times per second. At this sampling rate, one is less 4 likely to incorrectly identify noise as a change in circumference of extruded film s tube 81. The preferred sampling rate accounts for the common noise signals 6 encountered in blown film extrusion liner.

8 Optional thresholds have also been derived through g experimentation. In the first stage of filtering, threshold T1 is established as roughly one percent of the operating range of acoustic transducer 79, which in the preferred embodiment is twenty-one meters (24 inches less 3 inches). In the second stage of filter, thresholds + LT2 and -LT2 are established as roughly0.30% of the operating range of acoustic transducer 79.

Figure 25a is a graphic depiction of the control system response - to the detection of an UNDERBLOWN condition. The X-axis of the graph of Figure 25a is representative of time in seconds, and the Y-axis of the graph of Figure 25a is representative of position in units of voltage counts. A graph of 19 the best position estimate BPE is identified by dashed line 503. A graph of the actual position of the extruded film tube with respect to the reference position21 R is indicated by solid line 501. On this graph, line 505 is indicative of the 22 boundary established for determining whether the blown film tube is in an 23 "underblown" condition. Line 507 is provided as an indication of the normal 24 position of the blown film tube. Line 509 is provided to establish a boundary for determining when a blown film tube is considered to be in an "overblown"
26 condition.

28 The activities represented in the graph of Figure 25a may be 29 coordinated with the graph of Figure 25b, which has an X-axis which is representative of time in seconds, and a Y-axis which represents the binary 31 condition of the TARGET signal, and the UNDERBLOWN signal, as well as the Page- 52-DOCKET NO. 291 H-19705 :
output of block 421 of Figure 22, which is representative of the output of the 2 time out filter realignment software clock. Now, with simultaneous reference to 3 Figures 25a and 25b, segment 511 of the best position estimate indicates that 4 for some reason the best position estimate generated by software filter 149 is lagging substantially behind the actual position of the blowrl film tube. As 6 shown in Figure 25a, both the actual and estimated position of the blown film 7 tube are in an underblown condition, which is represented in the graph of 8 ~igure 25b.

As stated above, in connection with Figure 22 and the discussion 11 of the operation of the emergency condition control logic block 150, the locking 12 software loop which is established by anticipation state "orU gate 403 and "and"
13 gate 419 will lock the output of anticipation state "or" gate 403 to a high 14 condition. Therefore, next-state "or" gate 415 is awaiting the change in condition of any of the following signals: the OVERBLOWN signal, the 16 UNDERBLOWN signal, and the TARGET signal. As shown in Figure 25a, at a 17 time of 6.5 seconds, the actual position of the blown film tube comes within the 18 boundary 505 established for the underblown condition, causing the output of 19 next-state "or" gate 415 to go high, which causes the output of inverter 417 to go low, which causes the output of "andH gate 419 to go low. This change in 21 state also starts the software timer of block 421, and causes block 427 to push 22 the value of "underblown count" to the ~align hold" variable. Also, 23 simultaneously, soft~ware block 423 pushes the value of "quick filter align~ to the 24 "speed hold" variable. The values of "speed hold" and ~underblown count" are automatically pushed to block 433. Meanwhile, the software timer of block 421 26 overrides the normal and continuous pushing of "normal filter align" to the 27 "speed hold" variable for a period three seconds. The three second period 28 expires at 9.5 seconds.

Thus, for the three second time inter~al 513, software filter 149 is 31 allowed to respond more rapidly to change than during normal operating Page- 53-DOCKET NO. 291H-19705 2l5o898 conditions. As shown in Figure 22, block 433 operates to automatically and 2 asynchronously push the value of "speed hold~ to "LT2~ in software filter 149.
3 Simultaneously, block ~33 operates to continuously, automatically, and 4 asynchronously push the value of "align hold" to SAMPLE (N), SAMPLE (N-1) and BPE in software filter 149. This overriding of the normal operation of 6 software filter 149 for a three second interval allows the software best position 7 estimate 503 to catch up with the actual position 501 of the blown film tube.
8 The jump represented by segment 515 in the best position estimate 503 of the g blown film tube is representative of the setting of SAMPLE (N), SAMPL E (N-1) and BPE to the "underblown count" which is held in the ~align hold~ variable.
11 Segment 517 of the best position estimate 503 represents the more rapid rate 12 of change allowable during the three second interval, and depicts the best 13 position estimate line 503 tracking the actual position line 501 for a brief interval.
14 At the expiration of the three second interval, software filter 149 of the control system returns to a normal mode of operation which does not allow such rapid 16 change in the best position estimate.

18 Figures 26a and 26b provide an alternative example of the 19 operation of the emergency condition control mode of operation of the present invention. In this example, the TARGET signal represented in segment 525 of 21 Figure 26b is erroneously indicating that the blown film tube is out of range of 22 the transducer. Therefore, segment 529 of dashed line 527 indicates that the 23 best position estimate according to software filter 149 is set at a default 24 constant value indicative of the blown film tube being out of range of the transducer, and is thus far from indicative of the actual position which is 26 indicated by line 531. This condition may occur when the blown film tube is 27 highly unstable so that the interrogating pulses from the transducer are 28 deflected, preventing sensing of the blown film tube by the transducer.
29 Segment 533 of Figure 26b is representative of stabilization of the blown film tube and transition of the TARGEr signal from an "off" state to an "on~ state.
31 This transition triggers initiation of the three second software timer which is P~ge- s4-DOCKET NO. 291H-19705 ,...

depicted by segment 535. The time period begins at 12.5 seconds and ends 2 at 15.5 seconds. The transition of the TARGET signal from a low to a high 3 condition triggers the pushing of the "target restore count" value to the ~align 4 hold" variable, as is graphically depicted by segment 537. During the three second interval1 the best position estimate established by software filter 149 is 6 allowed to change at a rate which is established by the "quick filter align~ value 7 which is pushed to the "speed hold" variable and bused to software fi~ter 149.
8 At the termination of the three second interval, the software filter 149 returns to g normal operation.

Figure 27a provides yet another example of the operation of the 12 emergency condition control mode. Segment 541 of Figure 27b indicates that 13 the TARGET signal is in a low condition, indicating that the blown film tube is 14 out of range of the transducer. Segment 543 indicates that the blown film tube has come into range of the transducer, and the TARGET signal goes from a low 16 to a high condition. Simultaneous with the movement of the blown film tube 17 into range of the transducer, the UNDERBLOWN signal goes from a low to a 18 high condition indicating that the blown film tube is in an underblown condition.
19 Segment 545 of Figure 27b indicates a transition from a high UNDERBLOWNsignal to a low UNDERBLOWN signal, which indicates that the blown film tube 21 iS no longer in an underblown condition. This transition initiates the three 22 second interval which allows for more rapid adjustment of the best position 23 estimate.

Figure 28 is a schematic and block diagram representation of an 26 airflow circuit for use in a blown film extrusion system. Input blower 613 is 27 provided to provide a supply of air which is routed into airflow circult 611. The 28 air is received by conduit 615 and directed to airflow control device 617 of the 29 present invention. Airflow control device 617 operates as a substitute for a conventional rotary-type airflow valve 631, which is depicted in simplified form31 also in Figure 28. The preferred airflow control device 617 of the present Page- 55-WCKET NO. 2s1H-1s70s 215089~

-invention is employed to increase and decrease the flow of air to supply 2 distributor box 619 which provides an air supply to annular die 621 from which 3 blown film tube 623 extends upward. Air is removed from the interior of blown 4 film tube 623 by exhaust distributor box 625 which routes the air to conduit 627, and eventually to exhaust blower 629.

7 The preferred airflow control device 617 is depicted in fragmentary 8 longitudinal section view in Figure 29. As is shown, airflow control device 617 g includes housing 635 which defines inlet 637 and outlet 639 and airflow pathway 641 through housing 635. A plurality of selectively expandable flow restriction 11 members 671 are provided within housing 635 in airflow pathway 641. In the 12 view of Figure 29, selectively-expandable flow restriction members 673, 675, 13 677, 679, and 681 are depicted. Other selectively-expandable flow restriction 14 members are obscured in the view of Figure 29. Manifold 6~5 is provided to route pressurized air to the interior of selectively-expandable nOw restriction 16 members 671, and includes conduit 683 which couples to a plurality of hoses, 17 such as hoses 687, 689, 691, 693, 695 which are depicted in Figure 29 (other 18 hoses are obscured in Figure 29).

Each of the plurality of selectively-expandable flow restriction 21 members includes an inner air-tight bladder constructed of an expandable 22 material such as an elastomeric material. The expandable bladder is 23 surrounded by an expandable and contractible metal assembly. Preferably, 24 each of the plurality of selective-expandable flow restriction members issubstantially oval in cross-section view (such as the view of Figure 29), and 26 traverse airflow pathway 641 across the entire width of airf!ow pathway 641. Air 27 flows over and under each of the plurality of selectively~expandable airflow 28 restriction members, and each of them operates as an choke to increase and 29 decrease the flow of air through housing 635 as they are expanded and contracted. However, the flow restriction is accomplished without creating Page- s~-DOCKET NO. 291H-19705 turbulence in the airflow, since the selectively-actuable flow restriction members are foil shaped.
Returning now to Figure 28, airflow control device 617 is coupled to proportional valve 657 which receive either a current or voltage control signal and selectively vents pressurized fluid to airflow control device 617. In the preferred embodiment, proportional valve 657 is manufactured by Proportion Air of McCordsville, Indiana. Supply 651 provides a source of pressurized air which is routed through pressure regulator 653 which maintains the pressurized air at a constant 30 pounds per square inch of pressure. The regulated air is directed through filter 655 to remove dust and other particulate matter, and then through proportional valve 657 to airflow control device 617.
In the preferred embodiment of the present invention, airflow control device 617 is manufactured by Tek-Air Systems, Inc. of Northvale, New Jersey and is identified as a "Connor Model No. PRD Pneumavalve". This valve is the subject matter of at least two U.S. patents, including U.S.
Patent No. 3,011,518, which issued in December 1961 to Day et al., and U.S. Patent No. 3,593,645, which issued on July 20, 1971, to Day et al., which was assigned to Connor Engineering Corporation of Danbury, Connecticut, and which is entitled "Terminal Outlet for Air Distribution".
Experiments have revealed that this type airflow control device provides for greater control than can be provided by rotary type valve 631 (depicted in Figure 28 for comparison purposes only), and is especially good at providing control in mismatched load situations which would ordinarily be difficult to control economically with a rotary type valve.

'ii~
A number of airflow control devices like airflow control device 617 can be easily coupled together in either series or parallel arrangement to - 57a -B

control the total volume of air provided to a blown film line or to allow 2 economical load matching. In ~igure 28, a series and a parallel coupling of 3 air~low control devices is depicted in phantom, with airflow control devices 681, 4 683, and 685 coupled together with airflow control device 617. As shown in the detail airflow control device 617 is in parallel with airflow control device 683 but 6 iS in series communication with airflow control device 685. Airflow control 7 device 685 is in parallel communication with airflow control device 681. Airflow 8 control devices 681 and 683 are in series communication.

The present invention is also directed to a method and apparatus 11 for cooling extruded film tubes, which utilizes a mass air flow sensor to provide 12 a measure of the flow of air in terms of both the air density and air flow rate.
13 The mass air flow sensor provides a numerical value which is indicative of the 14 mass air flow in an air flow path within a blown film extrusion system. A
controller is provided for receiving the measure of mass air flow from the mass 16 air flow sensor and for providing a control signal to an adjustable air flow 17 attribute modifier which serves to selectively modify the mass air flow in terms 18 of mass per unit time by typically changing one or more of the cooling air 19 temperature, the cooling air humidity, or the cooling air ~elocity. The preferred method and apparatus for cooling extrude film tubes is depicted and described 21 in detail in Figures 30 through 36, and the accompanying text.

23 The particular type of mass air flow sensor utilized in the present 24 invention makes practical the utilization of mass air flow values in blown film extrusion systems. Of course, Umass air flow" is simply the total density of the26 cooling air or gas multiplied times the flow rate of the cooling air or gas.
27 Typically, blown film extrusion lines utilize ambient air for cooling and/or sizing 28 the molten blown film tube as it emerges from the annular die. It may become 29 economically practical in the future to utilize gases other than ambient air; for purposes of clarity and simplicity, in this detailed description and the claims, the Page- 58-DOCKET NO. 291H-19705 .,_ term "air" is intended to comprehend both ambient air as well as specially 2 provided gases or gas mixtures.

4 While it is simple to state what the "mass air flow" represents, it s is far more difficult to calculate utilizing conventional techniques. This is true 6 because of the difficulty associated with calculating the density of air. Air which 7 contains water vapor requires the following information for the accurate 8 calculation of "mass air flow": the relative humidity of the air, the absolute g pressure of the air, the temperature of the air, the saturation vapor pressure for the air at the given temperature, the partial pressure of the water vapor at the11 given temperature, the specific gravity of the air, and the flow rate of the air.
12 Utilizing conventional sensors, one could easily measure relative humidity, 13 temperature of the air, absolute pressure, and the flow rate of the air. With 14 established data tables correlating the temperature of the gas and the relative humidity, the saturation vapor pressure and the partial pressure of the water 16 vapor can be calculated. For ambient air applications, the specific gravity of the 17 gas is unity so it drops out of consideration. A good overview of the complexity 18 associated with the calculation of these factors which make up the "mass air 19 ~ow" is provided in a book entitled Fan Engineering: Ar7 Engineers Handbook On FansAnd TheirApplications, edited by Robert Jorgensen, 8th edition, which 21 is published by Buffalo Forge Company of Buffalo, New York. While such 22 calculations are not particularly difficult given modern technologies for both 23 sensors and data processors, the utilization of a single sensor which provides 24 a direct indication of the "mass air flow" lessens the costs associated with implementation of the method and apparatus for cooling extruded film tubes of 26 the present invention. Such use of a mass air flow sensor also reduces the 27 complexity associated with calculating mass air flow utilizing a more 28 conventional technique. This can be seen by comparing the calculations 29 required for a system which does not utilize a mass air flow sensor, with one which does utilize a mass air flow sensor. The "mass flow rate" of air is 31 determined by equation 1.1 which is set forth here below:

Page- 59-DOCKET NO. 291H-19705 215089~

Equation 1.1 2 Mass Flow Rate = Density*Flow Rate 4 Of course, the flow rate is easy to obtain from flow rate meters, but the density of the cooling air must be determined in accordance with 6 equation 1.2 which is set forth here below:
7 Equation 1.2 Den5itY= ( ( 7543 (T+459 7) wherein P is representative of the absolute pressure of the air, Pws is representative of the saturation vapor pressure, ~ is representative of the 12 relative humidity, and ~ is representative of the ratio of the density of the water 13 vapor to the density of dry air, and T is representative of the temperature of the 14 cooling air in degrees F. Since we measure P, ~, and T directly, we only have to derive Pws and ~ . By using a saturation vapor pressures table of water, we 16 can determine the saturation vapor pressure (Pws) from the temperature of the 17 cooling air. The following equation 1.3 allows one to calculate~, which is the 18 ratio of the water vapor density to dry air density:
Equation 1.3 22 This formula is accurate to 0.1% in the range of temperatures from 32~F to 23 400~F.

Therefore, it is evident that, in addition to a velocity sensor, 26 sensors must be provided for the measurement of pressure, relative humidity, pa9e- 60-DOCKET NO. 291~1-19705 and temperature. Additionally, the saturation vapour pressure and the ratio of the density of water vapour to the density of dry air must be calculated utilizing a provided table, which in microprocessor implementations must be represented by a data array maintained in memory. A11 together, the complexity and opportunity for error presented by such an array of sensors and series of calculations and table look-up operations renders this technique difficult and expensive to implement.
In contrast, the present invention for cooling extruded tubes utilizes a single sensor which provides a direct measurement of the mass air flow. Such mass air flow sensors have found their principle application in internal combustion engines, and are described and claimed in the following issued United States Patents.
(1) U.S. Patent No. 4,366,704, to Sato et al., entitled Air Intake Apparatus For Internal Combustion Engine, which issued on January 4, 1983, and which is owned by Hitachi, LTD., of Tokyo, Japan;
(2) U.S. Patent No. 4,517,837, to Oyama et al., entitled Air Flow Rate Measuring Apparatus, which issued on May 21, 1985, and which is owned by Hitachi, LTD., of Tokyo, Japan;
(3) U.S. Patent No. 5,048,327, to Atwood, entitled Mass Air Flow Meter, which issued on September 17, 1991;
(4) U.S. Patent No. 5,179,858, to Atwood, entitled Mass Air Flow Meter, which issued on January 19, 1993.

r~

Mass air flow sensors operate generally as follows.
One or more (typically platinum) resistor elements are provided in an air flow path way. An energizing current is provided to the one or more resistor elements. Air passing over the resistor elements reduces the temperature of the resistor elements. A control circuit is provided which maintains currents at a constant amount in accordance with King's Principal.

- 61a -For the particular mass air flow sensor utilized in the preferred 2 embodiment of the present invention, the mass air flow of the air flowing 3 through an air pathway within a blown film extrusion system is established in 4 accordance with equation 1.4 as follows:
Equation 1.4 6 Mass Flow Rate = ~ 1.601 (sensor reading + offset)C
7 wherein the constants are attributable to the specific construction of the sensor 8 assembly.
g In accordance with the present invention, a mass air flow sensor 11 is utilized to control air flow to cool molten polymers when extruded in a thin 12 film tube. The air flow may be provided in contact with either an interior surface 13 of the thin film tube, an exterior surface of the thin film tube, or both an interior 14 surface of the thin film tube and an exterior surface of the thin film tube. The air flow amount must be consistent in order to maintain the desired cooling rate16 of the polymer. Changes in the cooling rate modify the extent to which polymer 17 chains are formed, linked, and cross-linked. Under the prior art, the cooling air 18 iS at best controlled to a constant temperature. There is no consideration in 19 prior art systems to the changes in the heat removing capacity of the air as the air gets more or less humid, or as the absolute pressure changes. Changes 21 in the barometric pressure of one inch of mercury can change the mass air flow 22 rate by 3.3%. Changes in the temperature in the air typically have the greatest 23 effect on the heat removing capacity of the cooling air: a 10% change for each 24 40~F change in temperature. The relative humidity of the cooling air likewise changes the heat removing capacity of the cooling air, with a 10% change in 26 relative humidity causing a tenth of 1% change in mass air flow rate. It is 27 estimated that utilization of the present invention in blown film extrusion lines 28 which have temperature control will add an additional accuracy in cooling up 29 to 3.5%. ~or blown film extrusion lines which do not have temperature control, the consistency in cooling can be improved by an amount estimated at 13% to Page- 62-DOCKET NO. 291H-19705 21~0898 15% provided physical limits of the attribute modifying equipment are not 2 reached.

4 Cooling efficiency of course influences the production rates which can be obtained by blown film extrusion lines. Generally speaking, it is 6 desirable to have the extruded molten material change in state from a molten 7 state to a solid state before the blown film tube travels a predetermined 8 distance from the annular die. In the industry, the location of the state change g is identified as the "frost line" in a blown fllm tube. In the prior art, when big changes occur in the temperature, humidity, or barometric pressure, the frost 11 line of the extruded film tube may move upward or downward relative to a12 desired location. This may cause the operator of the blown film line to 13 decrease production volumes in order to keep from jeopardizing product 14 quality, since product quality is in part determined by the position or location of the frost line. While utilization of the present invention improves the cooling 16 of extruded film tubes, the present invention also can be utilized to compensate 17 for changes in the mass air flow rate of the cooling gas supplied to the interior 18 of a blown film tube and the hot exhaust gas drawn from the blown film tube, 19 to provide essentially a constant frost line height, or at least a frost line height that does not move because of changes in the mass air flow rate. Of course, 21 the present invention can be utilized in combination with prior art external 22 cooling devices for blown film extrusion lines to provide the same benefit.

24 SO considered broadly, the present invention can be utilized to accomplish a number of desirable results, including:
26 (1) it can be used as a frost line leveler for blown film extrusion lines with 27 external air cooling only;
28 (2) it can be used in both the supply and exhaust systems of an internal-2~ bubble-cooling blown film extrusion system to manage and maintain a balanced air flow between the supply and exhaust, which could greatly stabilize the 31 position of the frost line insofar as changes in the ambient temperature, Page- 63-DOCKET NO. 291H-19705 humidity, and barometric pressure effect the position of the frost line; this could 2eliminate the need for prior art frost line location sensors;
3(3) the mass air flow sensor can be utilized in combination with the 4controller or computer to determine the most effective and efficient operating 5range of flow pump devices such as blowers, and fans, by allowing the 6computer to determine the mass air flow rate with relation to blower speed (and7valve position) and then systematically eliminate undesirable ranges of 8operation, which are generally found at the lowest and highest ends of the goperating range, where the flow pump or valve may perform in a non-linear 0fashion which would introduce unstable characteristics into the operation of the blown film line;
12(4) the mass air flow sensor can be utilized to provide a rather slow feed 13back signal to a supply blower in the blown film line, to compensate for 14changes in the ambient air, such as temperature, humidity, and barometric 15pressure, which effect the mass air flow rate;
16(5) the mass air flow sensor can be used to provide a feed back loop 17which enhances the operation of a flow control valve in the line, to ensure that 18the valve operation is providing a particular air flow characteristic in response 19to a particular valve activation signal.

21In the following detailed description, Figures 30 and 31 are 22directed to a blown film extrusion system which includes an internal cooling air 23flow and an external cooling air flow. In contrast, the detailed desc,i~.~io,124relating to Figures 32 through 35 are directed to a more simple blown film 25extrusion system which includes only an external cooling air flow.

27With reference first to Figure 30, there is depicted an internal-28bubble-cooling blown film extrusion line 701 in schematic form. As is shown, 29blown film tube 703 is extruded from annular die 705. An ultrasonic transducer30707 is utilized to gage the position of blown film tube 703, and provides a 31control signal to position processor 709, all of which has been discussed in Pag~ 64-DOCKET HO~ 291H-19705 21~0898 detail in this detailed description. A sizing cage 711 is provided to size and 2 stabilize the blown film tube 703. A flow of internal cooling air is supplied to the 3 interior of blown film tube 703 through supply stack 713. As is conventional, 4 exhaust stack 717 is also provided in an interior position within blown film tube 703 for removing the cooling air from the interior of blown film tube 703. A
6 cooling air is supplied to supply stack 713 through supply distributer box 715, 7 and the exhausted air is removed from blown film tube 703 through exhaust 8 distributor box 719. Additionally, an external cooling air ring 721 is provided for g directing a cooling stream of air to an exterior surface of blown film tube 703.
Cooling air ring 721 collaborates with the internal cooling air stream to changethe state of the molten material from a molten state to a solid state. Cooling air 12 ring 721 is provided with entrained ambient air from air ring blower 723 which 13 may be set to a flow rate either manually or automatically.

Supply distributor box 715 is provided with an entrained stream 16 of cooling air in the following manner. Ambient air is entrained by the operation 7 of supply blower 729. It is received at input filter 725, and passed through 18 (optional) manual damper 727. If supply blower 729 is a variable-speed-drive 19 type of supply blower, then manual damper 727 is not required. Preferably, however, supply blower 729 is a variable speed drive controller which provides 21 a selected amount of air flow in response to a command received at a control 22 input of variable-speed-drive 731. Also, preferably, variable speed drive 23 controller is optionally subject to synchronous command signals from IBC
24 controller 753 which controls the general operations of the blown film extrusion line. The entrained ambient air is routed through air flow path 755, first through 26 cooling system 733, which preferably includes a plurality of heat exchange coils 27 and heat transference medium in communication with the air flow, which 28 receives a circulating heat exchange medium (such as chilled water for 29 transferring heat), past mass air flow sensor 737, through air flow control device 739 (such as that depicted and described in connection with Figures 28 and 29 31 above), and through supply distributer box 715. Mass air flow sensor 737 Page - 65-DOCKET NO. 291tl-19705 ~ 21s0898 provides a voltage signal which is indicative of the mass air flow of the air 2 flowing through air flow path 755 in the region between cooling system 733 an~
3 air flow control device 739. Air flow control device 739 operates in response 4 to proportional valve 741 and selectively receives compressed air from compressed air supply 743. Air flow control device 739 includes a plurality of 6 members which may be expanded and contracted to enlarge or reduce the air 7 flow path way through the housing of air flow control device. This allows for the 8 matching of loads, as is discussed above in connection with Figures 28 and 29.
g Proportional valve 741 is under the control of IBC controller 753.

11 Exhaust distributer box 719 removes cooling air from blown film 12 tube 703 and routes it through damper 745, into air flow path 755. The air 13 passes through mass air flow sensor 747 which provides a voltage which is 14 indicative of the mass air flow of the exhaust from blown film tube 703. The air iS pulled from air flow path 755 by the operation of exhaust blower 749 which 16 iS responsive to an operator command, preferably through a variable speed 17 drive 751, which is also preferably under the synchronous control command of 18 IBC controller 753.

In broad overview, mass air flow sensor 737 provides an indication 21 of the mass air flow of the cooling air which is supplied through supply 22 distributor box 715 to supply stack 713. This cooling air removes heat from 23 blown film tube 703, helping H change from a molten state to a solid state.
24 Mass air flow sensor 747 is in communication with the exhaust air removed through exhaust stack 717 and exhaust distributor box 719. Mass air flow 26 sensor 747 provides a voltage which is indicative of the mass air flow of the 27 exhaust cooling air. The measurements provided by mass air flow sensors 737, 28 747 are supplied to a controller which includes a microprocessor component 29 for executing preprogrammed instructions.

Page- ~-DOCKET NO. 2s1H-1s70s ... i ,.. . .

'~_ In accordance with the present invention, IBC controller 753 2 compares the values from mass air flow sensors, 737, 747 and then provides 3 command controls to variable speed drives 731, 751 in order to effect the 4 operation of supply blower 729 and/or exhaust blower 749. Preferably, IBC
controller 753 may be utilized in response to an operator command to maintain 6 supply blower 729 and/or exhaust blower 749 at a particular level or magnitude 7 Of blower operation, or to provide a particular ratio of blower operation, so that 8 when the temperature, humidity, or barometric pressure of the ambient air g changes significantly, the blowers adjust the flow rate of the input cooling air and exhaust cooling air to blown film tube 703 to maintain a uniformity of heat absorbing capacity of the internal cooling air, notwithstanding the change in 12 temperature, humidity, and/or barometric pressure.

14 The operation of this rather simple feed back loop is set forth in flowchart form in Figure 36. The process starts at software block 771, and 16 continues at software block 773, wherein IBC controller 753 receives an17 operator command from either an operator interface 757 on IBC controller 753, 18 or an operator interface 759 on variable speed drive 731. Next, values provided 19 by mass air flow sensors 737 and 747 are recorded in memor,v, in accordance with soflware block 775. Then, in accordance with step 777, operation set 21 points are derived. For example, a particular ratio between the mass air flow 22 detected at mass air flow sensor 737 and mass air flow sensor 747 may be 23 derived. Then, in accordance with step 779, IBC controller 753 monitors24 signals from mass air flow sensors 737 and 747 for changes in mass air flow, which are principly due to changes in the ambient temperature, humidit~, and 26 barometric pressure. Once a change is detected, in accordance with step 781, 27 IBC controller 753 synchronously adjusts the variable speed drives 759, 731, 28 751 in order to affect the value of the mass air flow of ambient air which has 29 been entrained and which is flowing through air flow passage way 755 in a manner which returns operation to the set point values derived in step 777. For 31 example, variable speed drive 731, 751 may be utilized to increase or decrease Page- S7-DOCKET NO. 291H-19705 21S0~98 the volume of air entrained by supply blower 729 and/or exhausted by exhaust 2 blower 749. In accordance with step 783, this process is repeated until an 3 additional operator command is received. Such commands may include an 4 instruction to obtain a new operation set point, or to discontinue the feed back loop until instructed otherwise. A cooling coil 738 may also be provided in 6 communication with air flow path 745, and may be adjusted in response to IBC
7 controller 753 to adjust the value of mass air flow.

g Figure 31 depicts an alternative to the embodiment of Figure 30, wherein mass air flow sensors are utilized to control both the internal cooling 11 air supply to the interior of blown film tube 703 and an external cooling air 12 stream which is supplied to the exterior surface of blown film tube 703 from air 13 ring 721. The figures differ in that, in addition of having a control system for 14 internal cooling air, a control system for external cooling air is also provided with a mass air flow sensor 747 positioned in air flow path 741 between air ring16 blower 723 and cooling air ring 721. Mass air flow sensor 747 provides a 17 measurement of the mass air flow of the air flowing within air flow path 745.
18 This measurement is provided to IBC controller 753 and compared to a set 19 point value which has been either manually entered by the operator at operator interface 757 or which has been automatically obtained in response to an 21 operator command made at operator interface 757. IBC controller 753 supplies 22 a control signal to variable speed drive 744 which is utilized to adjust the 23 operating condition of air ring blower either upward or downward in order to 24 maintain the established set point. If the mass air flow sensor 747 indicates to IBC controller 753 that the total mass air flow has been diminished (perhaps 26 due to changes in temperature, humidity, and barometric pressure~, then IBC
27 controller 753 may supply a command signal to variable speed drive 744 which 2s increases the throughput of air ring blower 723 in a manner which compensates 29 for the diminishment in mass air flow as detected by mass air now sensor 747.
If mass air flow sensor 747 detects an increase in the mass air flow, IBC
31 controller 753 may provide a command signal to variable speed drive 744 which Page- s8-DOCKET NO. 2911~-19705 reduces the throughput of air ring blower 723, thus diminishing the amount of 2 mass air flow in order to make it equal to the set point maintained in memory 3 in response to an operator command. This simple feedback loop is also 4 characterized by the flowchart depiction in Figure 36. Since changes in ambient s temperature, ambient humidity, and barometric pressure are rather slow, it is 6 not necessary that this feedback loop be a very fast loop. It is sufficient that 7 every few minutes the value for the mass air flow sensor be monitored to 8 determine the numeric value of the mass air flow, that this value be compared g to a set point recorded in memory, and that an appropriate command be provided to a blower in order to adjust the mass air flow upward or downward 11 to make it equivalent to the set point value. This allows a program which 12 implements the present invention to be "piggy backed" onto the IBC controller 13 753. The calculations required to compare mass air flow values to set points 14 iS trivial, and these operations need only be performed every few minutes, so the IBC controller can spend the vast majority of its computational power of 16 controlling the blown film line, with only a de minimis portion expended to 17 occasional checking and adjusting of the mass air flow. Additionally, a cooling 18 coil 748 may be provided in communication with air flow path 745, and may be 19 adjusted in response to IBC controller 753 to adjust the value of mass air flow.

21 The present invention can also be utilized in far simpler blown film 22 extrusion systems which utilize only external cooling air to remove heat from a 23 molten blown film tube. Four particular embodiments are depicted in Figures 24 32, 33, 34, and 35. In each of these embodiments, a mass air flow sensor is positioned intermediate and external cooling air ring and a blower for entraining 26 and supplying air to the cooling ring. Additionally an adjustable air flow attribute 27 modifier is provided in the air flow path for selectively modifying the air mass 28 per unit time. This adjustable air flow attribute modifier may comprise any 29 mechanism for adjusting for modifying the mass air flow, but in particular will most probably comprise a cooling coil system which chills the cooling air, or an31 air flow control device which restricts or enlarges the quantity of air available for Page- 69-DOCKET N0. 291H-19705 21~0898 _, entrainment by the supply blower, or a fluid injection system which modifies the2 humidity of the cooling air. Each of these three principle alternative 3 embodiments will be discussed in detail herebelow in connection with Figures 4 32, 33, 34, and 35.
s 6 Turning first to Figure 32, an external cooling blown film extrusion 7 line is depicted in schematic form. Plastic pellets are loaded into resin hopper 8 791, passed through heating apparatus 793, and driven by extruder 795 through die 797 to form a molten extruded film tube 789, with a portion of the extruded film tube 789 below frost line 801 being in a molten state, and that 11 portion above frost line 801 being in a solid state. Air ring 799 is positioned 12 adjacent die 797 and adapted to route cooling air along the exterior surface of 13 blown film tube 789. Air ring 799 is supplied with cooling air which is entrained 14 by air ring blower 803, routed through cooling coils 805 of cooling system 809, and through mass air flow sensor 807. Preferably, mass air flow sensor 807 is 16 positioned in air flow path 821 intermediate cooling coils 805 and ex~ernal 17 cooling air ring 799. Cooling coils 805 are adapted to receive chilled water 813 18 from chiller system 811. Controller 815 is provided for receiving a signal from 19 mass air ~ow sensor 807 which is indicative of the mass air flow of the cooling air flowing through air flow path 821, and for providing a command signal to 21 chiller system 811 which adjusts the temperature of chilled water 813 which is 22 routed through cooling coil 805. A feed back loop is established about a set 23 point selected by the operator when a set point selection command button 817 24 iS depressed. Controller 815 will respond to the command by recording in memory the mass air flow value provided by mass air flow sensor 807, and by 26 adjusting the chiller system 811 upward or downward in temperature in order 27 to maintain the mass air flow value of cooling air flowing through air flow path 28 821 at a value established by the set point. Of course, the operator has an 29 operator interface for chiller system 811 which allows for the operator setting of the temperature of chiller system 811. This system works once the operator 31 has established that sufficient cooling has been obtained, and should provide Pa9e- 70, DOCKET NO. 291H-19705 an equivalent level of cooling from the external cooling air provided by air ring 2 799 even though the ambient air changes its density through relatively slow 3 changes in temperature, humidity, and barometric pressure. The embodiment 4 of Figure 32 is especially suited for blown film extrusion lines which have a dedicated chiller system. The embodiment of Figure 33 depicts a more 6 common scenario, wherein a single chiller system is shared by multiple blown 7 film lines. In this event, the configuration differs insofar as chiller system 811 8 iS utilized to provide chilled water 813 for delivery to multiple heat exchange g cooling coils, with a flow valve, such as flow valve 825, being provided for each set of heat exchange cooling coils to increase or decrease the flow of 11 circulating heat exchange fluid in order to alter the temperature of the cooling 12 air in air flow path 821. In the embodiment depicted in Figure 33, controller 815 13 provides an electrical command signal to an electrically-actuated flow valve 825 14 in order to increase or decrease the flow of chilled water 813 from chiller system 811 to cooling coil 805. Similar to the embodiment of Figure 32, the 16 operator instructs controller 815 to record the mass air flow value from mass 17 air flow sensor 807, and to utilize that as a set point for operation. Thereafter, 18 changes in the mass air flow property of the cooling air passing through air flow 19 path 821, such as changes caused by changes in temperature, humidity, and barometric pressure, are accommodated by increasing or diminishing the flow 21 of chilled water from chiller systern 811 to heat exchange cooling coil 805.
22 Increases in mass air flow will result in the controller 815 providing a command 23 to electrically-actuated flow valve 825 to diminish the flow of chilled water; in 24 contrast, decreases in mass air flow as detected by mass air flow sensor 807 will result in controller 815 providing a command signal to electrically-actuated 26 flow valve 825 to increase the flow of chilled water from chiller system 811 to 27 heat exchange cooling coils 805.

29 Figure 34 is a schematic depiction of an external air blown film extrusion line, with blown film tube 789 extending upward from die 797 and 31 being cooled by an air stream in contact with an exterior surface of blown film Page- 71 -DOCKET NO. 291H-19705 -tube 789 which is provided by air flow path 821. Air flow path 821 includes 2 mass air flow sensor 807 which provides a numerical indication of the mass air 3 flow of the air passing through air flow path 821. It provides this numerical 4 indication to controller 815, which in turn supplies a command signal to either variable speed controller 831 or air flow control device 833 (such as that 6 depicted in Figures 28 & 29 above), each of which can effect the volume of air 7 which is entrained by air ring blower 803. Controller 815 includes a manual 8 control 817 which is utilized by the operator to establish a set point of g operation. Typically, the operator will get the blown film line operating in an acceptable condition, and then will actuate the set point command 817, causing 11 controller 815 to record in memory the value provided by mass air flow sensor 12 807. Thereafter, changes in the mass air flow due to changes in temperature, 13 humidity, or barometric pressure will be compensated for by variation in the 14 amount of air entrained by air ring blower 803, in order to maintain mass air flow value at or about the set point value. For example, if the mass air flow 16 value decreases, as determined by the mass air flow sensor 807, variable 17 speed controller 831 or air flow control device 833 are provided with command 18 signals from controller 815 to increase the volume of air flowing through air flow 19 path 821; however, if the mass air flow value increases, as determined by mass air flow sensor 807, controller 815 provides a command signal to either variable21 speed controller 831 or air flow control device 833 in order to decrease the 22 volume of air entrained by air ring blower 803. In this manner, controller 815 23 may intermittently check the ~/alue of the mass air flow, compare it to a set point 24 value recorded in memory, and adjust the volume of air entrained by air ring blower 803 in order to maintain a mass air flow value at or about the set point.26 In this manner, the cooling ability the air stream in contact with the exterior of 27 extruded film tube 789 is maintained at a constant level notwithstanding gradual 28 or dramatic changes in temperature, humidity, and barometric pressure.

Figure 35 depicts yet another embodiment of the invention, 31 wherein an external cooling blown film extrusion line is depicted in the Page- 72 -DOCKET N0. 291H-19705 schematic form, with extruded film tube 789 extending upward from annular die 2 797, which is cooled by an air stream provided by cooling air ring 799. Cooling 3 air ring 799 receives its cooling air from air flow path 821. Mass air flow sensor 4 807 is positioned in air flow path 821, and is adapted to provide a signal indicative of the mass air flow of air flowing through this passage way, to 6 controller 815. Controller 815 provides a command signal to water injector 835 7 which is also in communication with the air passing through air flow path 821.
8 Water injector 835 is adapted to increase the humidity of the air entrained by g blower 803 in response to a command from controller 815. In accordance with this embodiment of this invention, the operator depresses a set point control 11 817 on controller 815 in order to establish a set point of operation for controller 12 815. Controller 815 records in memory the value for mass air flow sensor 807, 13 and thereafter continuously monitors the values provided by mass air flow 14 sensor 807 in comparison to the set point. When an increase in mass air flow iS required, controller 815 provides a command signal to water injector 835 16 which provides a predetermined amount of moisture which is immediately 17 absorbed by the air entrained by air ring blower 803. When no additional 18 humidity is required, controller 815 will not provide such a command. In this 19 manner, the mass air flow value for air entrained in air flow path 821 may be moderated by operation of controller 815. Since this system easily allows an 21 increase in the mass air flow value, without allowing a corresponding decrease 22 in the mass air flow value, it is particularly useful in very hot and dry climates.

24 In all embodiments, it is advisable to provide a predetermined time interval of monitoring before the set point is recorded and established. This 2~ allows the operator to make changes in the operating condition of the various 27 blowers and other equipment in the blown film line prior to requesting that a set 28 point be established. It takes many minutes (5, 10, or 20 minutes) in order for 29 the system to reach a quiescent condition of operation. Having a predefined interval of time after request for a set point, during which the mass air flow 31 values are monitored but not recorded, allows the operator to change the Pa9e- 73-UOCKET NO. 291H-19705 215089~
,_ operating state of the blown film line, and request a set point value, at the same 2 time, without obtaining a set point value which is perhaps not stable or 3 quiescent. In yet another more particular embodiment of the present invention, 4 the controller may be programmed to monitor the rate of change of the mass air flow value for predetermined time interval in order to determine for itself that 6 a quiescent condition has been obtained. For example, a 10 or 20 minute7 interval may be provided after operator request of a set point, during which the 8 controller continuously polls the mass air flow sensor, calculates a rate of g change for a finite time interval, and records it in memory. Only when the rate of change reaches an acceptable level will the controller determine that a 11 quiescent interval has been obtained, and thereafter record the mass air flow 12 value in memory for utilization as a set point, or in the derivation of a set point, 13 about which the feedback loop is established.

Although the invention has been described with reference to a 16 specific embodiment, this description is not meant to be construed in a limiting 17 sense. Various modifications of the disclosed embodiment as well as 18 alternative embodiments of the invention will become apparent to persons 19 skilled in the art upon reference to the description of the invention. It is therefore contemplated that the appended claims will cover any such 21 modifications or embodiments that fall within the true scope of the invention.

PAge- 74-DOCKET NO. 291H-19705

Claims

CLAIMS:

What is claimed is:

1. An improved blown film extrusion apparatus, comprising:

an annular die for receiving a molten material and extruding a film tube;

at least one cooling air ring positioned adjacent said annular die for passing an air stream along a particular surface of said film tube;

a blower for entraining and supplying air to said at least one cooling ring;

a flow sensor positioned in an air flow path intermediate said at least one cooling ring and said blower for providing a mass air flow signal indicative of air flow through said air flow path which provides a measure of air mass flow per time unit;

an adjustable air flow attribute modifier in communication with said air flow path, for selectively modifying said air mass per time unit;

a controller member in communication with (a) said flow sensor and (b) said adjustable air flow attribute modifier, for receiving said mass air flow signal and for controlling said adjustable air flow attribute modifier to provide a preselected value of air flow in terms of air mass flow per time unit.

Page - 75 -

2. An improved blown film extrusion apparatus according to Claim 1, wherein said at least one cooling air ring comprises an external cooling air ring positioned adjacent said annular die for passing an air stream along an exteriorsurface of said film tube.

3. An improved blown film extrusion apparatus according to Claim 1, wherein said at least one cooling air ring comprises at least one internal cooling air ring adjacent said annular die for passing an air stream along an interior surface of said film tube.

4. An improved blown film extrusion apparatus according to Claim 1, wherein said at least one cooling air ring comprises at least one of:

(a) an external cooling air ring adjacent said annular die for passing an air stream along an exterior surface of said film tube; and (b) an internal cooling air ring adjacent said annular die for passing an air stream along an interior surface of said film tube.

Page - 76 -

5. An improved blown film extrusion apparatus according to Claim 1:
wherein said at least one cooling air ring comprises at least one of:
(a) an external cooling air ring adjacent said annular die for passing an air stream along an exterior surface of said film tube;
(b) an internal cooling air ring adjacent said annular die for passing an air stream along an interior surface of said film tube; and wherein said blown film extrusion apparatus further includes an exhaust blower for removing air from said film tube.

6. An improved blown film extrusion apparatus according to Claim 5:

wherein said controller member receives said mass air flow signal and controls said adjustable air flow attribute modifier to provide a preselected value of air flow in terms of air mass flow per unit time which is representative of an air mass flowing into and out of said film tube.

7. An improved blown film extrusion apparatus according to Claim 1, wherein said adjustable air flow attribute modifier comprises a cooling system which is communication with said air flow path for selectively modifying temperature of air passing through said air flow path in a manner which modifies said air mass per unit time measure of air flow.

Page - 77 -

8. An improved blown film extrusion apparatus according to Claim 7, wherein said cooling system comprises:

a set of heat exchange cooling coils in heat transference communication with said air flow path; and a circulating heat exchange medium which is passed through said heat exchange cooling coils.

9. An improved blown film extrusion apparatus according to Claim 8, further comprising:

a temperature adjustment member, which is responsive to commands from said controller member, for modifying a temperature of said circulating heat exchange medium.

10. An improved blown film extrusion apparatus according to Claim 8, further comprising:

a flow control member, which is responsive to commands from said controller member, for modifying a flow rate of said circulating heat exchange medium.

Page - 78 -

11. An improved blown film extrusion apparatus according to Claim 1, wherein said adjustable air flow attribute modifier comprises an air flow control member in communication with said air flow path, for selectively modifying said air mass flow in terms of air mass per unit time by modifying a passage area of said air flow path.

12. An improved blown film extrusion apparatus according to Claim 11, wherein said air flow control member comprises an electrically-actuated valve which is responsive to electrical command signals provided by said controller member for moderating air flow through said air flow path.

13. An improved blown film extrusion apparatus according to Claim 11, wherein said air flow control member is at least in-part responsive to command signals from said controller member for varying a quantity of air passing withinsaid air flow path, and which includes:

a housing with an inlet, an outlet, and an air path defined therethrough;

at least one selectively-expandable flow restriction member disposed in said housing in said air path; and wherein said air flow control member selectively expands and reduces said at least one selectively-expandable flow restriction member to moderate airflow through said air flow path.

Page - 79 -

14. An improved blown film extrusion apparatus according to Claim 13:

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

15. An improved blown film extrusion apparatus according to Claim 13, wherein said air flow control member includes:

a plurality of housings, each having an inlet, outlet, and an air flow path defined therethrough;

a plurality of selectively-expandable flow restriction members disposed in each of said housings; and with each flow path through said plurality of housings in at least one of (a) series and (b) parallel communication with said selected others of said air flow paths.

16. An improved blown film extrusion apparatus according to Claim 13:

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

Page - 80 -

17. An improved blown film extrusion apparatus according to Claim 1, wherein said adjustable air flow attribute modifier comprises a humidity modification system in communication with said air flow path for selectively modifying air flow in terms of said air mass per unit time by modifying the humidity thereof.

18. An improved blown film extrusion apparatus according to Claim 1:

wherein said controller member is operable in a plurality of modes of operation including at least a set point maintenance mode of operation wherein said controller member receives said mass flow signal from said flow sensor, and provides a command signal to said adjustable air flow attribute modifier in order to maintain a preselected value of air flow in terms of air mass flow per unit time.

19. An improved blown film extrusion apparatus according to Claim 18, wherein said controller member is additionally operable in a set point acquisition mode of operation, wherein said controller member is responsive to a command which initiates said set point acquisition mode of operation, and which thereafter obtains a value representative of air mass flow per unit time in the form of a flow signal from said flow sensor, and maintains said value in memory for a predetermined interval.

20. An improved blown film extrusion apparatus according to Claim 19, wherein said controller member is further operable in a change of state mode of operation, wherein said controller member monitors said air flow signal from said air flow sensor for a predetermined time interval to determine whether a quiescent condition of operation has been obtained.

Page - 81 -

21. A method of cooling in a blown film extrusion apparatus, comprising the method steps of:

providing an annular die for receiving a molten material and extruding a film tube;

providing at least one cooling air ring and positioning it adjacent said annular die for passing an air stream along a particular surface of said film tube;

providing a blower for entraining and supplying air to said external cooling ring;

locating a flow sensor in an air flow path intermediate said at least one cooling ring and said blower and utilizing it for providing a mass air flow signal indicative of air flow through said air flow path which provides a measure of air mass flow per time unit;

providing an adjustable air flow attribute modifier in communication with said air flow path, for selectively modifying said air mass per time unit;

utilizing a controller member, in communication with (a) said flow sensor and (b) said adjustable air flow attribute modifier, for receiving said mass airflow signal and for controlling said adjustable air flow attribute modifier to provide a preselected value of air flow in terms of air mass flow per time unit.

Page - 82 -

22. A method of cooling in a blown film extrusion apparatus, according to Claim 21, further comprising the method steps of:

utilizing at least one of the following as an adjustable air flow attribute modifier:

(a) a cooling system which is communication with said air flow path for selectively modifying temperature of air passing through said air flow path in a manner which modifies said air mass per unit time measure of air flow;

(b) an air flow control member in communication with said air flow path, for selectively modifying said air mass flow in terms of air mass per unit time by modifying a passage area of said air flow path; and (c) a fluid injection system in communication with said air flow path for selectively modifying air flow in terms of said air mass per unit time by modifying the humidity thereof.

Page - 83 -

23. A method of cooling in a blown film extrusion apparatus, according to Claim 21, further comprising the method steps of:

utilizing an air flow control member for said adjustable air flow attribute modifier which is at least in-part responsive to command signals from said controller member for varying a quantity of air passing within said air flow path, and which includes:

a housing with an inlet, an outlet, and an air path defined therethrough;

at least one selectively-expandable flow restriction member disposed in said housing in said air flow path; and wherein said air flow control member selectively expands and reduces said at least one selectively-expandable flow restriction member to moderate air flow through said air flow path.

Page - 84 -

24. A method of cooling in a blown film extrusion apparatus, according to Claim 21, further comprising the method steps of:

operating said controller member in a plurality of modes of operation including at least a set point maintenance mode of operation wherein said controller member receives said mass flow signal from said flow sensor, and provides a command signal to said adjustable air flow attribute modifier in order to maintain a preselected value of air flow in terms of air mass flow per unit time.

25. A method of cooling in a blown film extrusion apparatus, according to Claim 21, further comprising the method steps of:

operating said controller member in a set point acquisition mode of operation, wherein said controller member is responsive to a command which initiates said set point acquisition mode of operation, and which thereafter obtains a value of air mass flow per unit time in the form of a flow signal fromsaid flow sensor, and maintains said value in memory for predetermined interval.

Page - 85 -

26. An improved blown film extrusion apparatus, comprising:

an annular die for receiving a molten material and extruding a film tube;

at least one cooling air ring positioned adjacent said annular die for passing an air stream along a particular surface of said film tube;

a blower for entraining and supplying air to said external cooling ring;

an air flow path intermediate said at least one cooling ring and said blower, a controller member;

an air flow control member which is at least in-part responsive to command signals from said controller member for varying a quantity of air passing within said air flow path, and which includes:

a housing with an inlet, an outlet, and an air path defined therethrough;

at least one selectively-expandable flow restriction member disposed in said housing in said air flow path; and wherein said air flow control member selectively expands and reduces said at least one selectively-expandable flow restriction member to moderate air flow through said air flow path.

Page - 86 -

27. An improved blown film apparatus according to Claim 26:

wherein said at least one selectively-expandable flow restriction member includes 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 member causes expansion and reduction of said at least one selectively-expandable flow restriction member.

Page - 87 -

28. An improved blown film apparatus according to Claim 26, wherein said air flow control member includes:

a plurality of housings, each having an inlet, outlet, and an air flow path defined therethrough;

a plurality of selectively-expandable flow restriction members disposed in each of said housings; and with each flow path through said plurality of housings in at least one of (a) series and (b) parallel communication with said selected others of said air flow paths.

Page - 88 -

29. An improved blown film apparatus, according to Claim 26, wherein expansion of said at least one selectively-expandable flow restriction member restricts said air path defined through said housing; and wherein reduction of said at least one selectively-expandable flow restriction member expands said air path defined through said housing.

30. An improved blown film apparatus, according to Claim 26, wherein said at least one cooling air ring comprises an external cooling air ring positioned adjacent said annular die for passing an air stream along an exterior surface ofsaid film tube.

31. An improved blown film apparatus, according to Claim 26, wherein said at least one cooling air ring comprises at least one internal cooling air ring adjacent said annular die for passing an air stream along an interior surface ofsaid film tube.

32. An improved blown film apparatus, according to Claim 26, wherein said at least one cooling air ring comprises at least one of:

(a) an external cooling air ring adjacent said annular die for passing an air stream along an exterior surface of said film tube;
and (b) an internal cooling air ring adjacent said annular die for passing an air stream along an interior surface of said film tube.

Page - 89 -