Blown film extrusion apparatus with improved collapsing frame

Abstract

An improved blown film extrusion apparatus is provided. The apparatus includes an annular die for extruding a film tube. At least one tube position transducer is provided and located adjacent to the extruded film tube. The tube position transducer transmits interrogating pulses to the extruded film tube and produces a position signal corresponding to a detected position under the extruded film tube. A bubble position control system is provided for receiving and processing the position signal. A valve is provided for varying a quantity of air within the extruded film tube in response to the bubble position control means. This urges the extruded film tube to a desired position. The apparatus further includes a collapsing frame assembly for receiving the extruded film tube and collapsing it. The collapsing frame assembly includes several frame boards. Typically, two opposing main boards and two opposing side boards are provided. A position transducer is provided for detecting the position of at least one of the frame boards. Preferably, this is a non-contact sensor. At least one board position actuator is provided for adjusting the position of at least one of the boards. Typically, the actuator is an electric motor. A board control system is provided for receiving the board position information from the board position transducer and for providing control signals to the board position actuator to maintain at least one of the boards in a predetermined position.

What is claimed is:  
     
         1 . A blown film extrusion apparatus, comprising: 
 (a) an annular die for extruding a film tube;    (b) at least one tube position transducer located adjacent said extruded film tube for transmitting interrogating pulses to said extruded film tube and for producing a position signal corresponding to a detected position of said extruded film tube;    (c) a bubble position control system for receiving and processing said position signal;    (d) means for varying a quantity of air within said extruded film tube in response to said bubble position control means for urging said extruded film tube to a desired position;    (e) a collapsing frame assembly for receiving said extruded film tube and collapsing said extruded film tube;    (f) said collapsing frame assembly including: 
 (1) a plurality of frame boards;  
 (2) at least one board position transducer for detecting the position of at least one of said plurality of frame boards;  
 (3) at least one board position actuator for adjusting the position of at least one of said plurality of frame boards;  
 (4) a board control system for receiving board position information from said at least one board position transducer and for providing control signals to said at least one board position actuator to maintain at least one of said plurality of frame boards in a predetermined position.  
   
     
     
         2 . A blown film extrusion apparatus according to claim  1 : 
 wherein said blown film extrusion apparatus includes an adjustable sizing cage which surrounds at least a portion of said extruded tube; and    wherein said at least one transducer means is coupled to said sizing cage and will move relative to said extruded tube with said adjustable sizing cage.    
     
     
         3 . A blown film extrusion apparatus according to claim  1 : 
 wherein said blown film extrusion apparatus includes a processor; and    wherein said control means included instructions which are executed by said processor.    
     
     
         4 . A blown film extrusion apparatus according to claim  1 : 
 wherein at least one transducer means comprises a signal ultrasonic transducer.    
     
     
         5 . A blown film extrusion apparatus according to claim  1 : 
 wherein said board control system maintains said collapsing frame in a position which is suitable for a particular size of extended film tube.    
     
     
         6 . A blown film extrusion apparatus according to claim  1 : 
 wherein said collapsing frame assembly includes a pair of opposed main boards which are controlled as a pair by said board control system and a pair of opposed side boards which are controlled as a pair by said board control system.    
     
     
         7 . A blown film extrusion apparatus according to claim  1 : 
 wherein said at least one board position transducer comprises at least one non-contact position sensor.    
     
     
         8 . A blown film extrusion apparatus according to claim  7 : 
 wherein said at least one non-contact position sensor comprises at least one dual switch point ultrasonic proximity sensor.