Method and apparatus for cooling extruded film tubes

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

• providing a transducer;
• placing said transducer adjacent said extruded film tube;
• transmitting an interrogating signal to, and receiving an interrogating signal from, said extruded film tube;
• producing a detected position signal based on information contained in said interrogating signal;
• providing a filtered position signal derived from a dynamic filtering process in lieu of said detected position signal;
• and
• varying a quantity of air within said extruded film tube in response to said filtered position signal.

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

• at least one transducer means adjacent said extruded film tube for transmitting interrogating pulses to, and receiving interrogating pulses from, said extruded film tube and for producing a signal corresponding to a detected position of said extruded film tube;
• control means for substituting a filtered position signal developed from a particular one of a plurality of available filtering routines in lieu of said detected position signal;
• and
• means for varying a quantity of air within said extruded film tube in response to said control means for urging said extruded film tube to a desired position.

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

• providing a transducer;
• placing said transducer adjacent said extruded film tube;
• transmitting an interrogating signal to, and receiving an interrogating signal from, said extruded film tube;
• producing a detected position signal based on information contained in said interrogating signal;
• substituting a filtered position signal developed from a particular one of a plurality of available filtering routines in lieu of said detected position signal;
• and
• varying a quantity of air within said extruded film tube in response to said filtered position signal.

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

• at least one transducer means adjacent said extruded film tube for transmitting interrogating pulses to, and receiving interrogating pulses from, said extruded film tube and for producing a signal corresponding to a detected position of said extruded film tube;
• control means including executable instructions defining a plurality of filters including:
• a. a first filter which receives said signal corresponding to a detected position of said extruded film tube and modifies it based upon information derived from at least one previous detected position, during intervals of relatively unstable operation;
• b. a second filter which receives said signal corresponding to a detected position of said extruded film tube and modifies it by dynamic filtering it, only during intervals of relatively stable operation;
• means for varying a quantity of air within said extruded film tube in response to said control means for urging said extruded film tube to a desired position.

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

• providing at least one ultrasonic transducer;
• placing said at least one ultrasonic transducer adjacent said extruded film tube;
• transmitting and receiving sonic interrogating pulses with said at least one ultrasonic transducer to said extruded film tube;
• producing a position signal based on information contained in said interrogating pulses;
• filtering said position signal with a plurality of filters, including:
• a. a first filter which receives said position signal and modifies it based upon information derived from at least one previous position signal during intervals of relatively unstable operation;
• and
• b. a second filter which receives said position signal and modifies it by dynamic filtering only during intervals of relatively stable operation;
• varying a quantity of air within said extruded film tube in response to said position signal after filtering has occurred.