| 摘要 |
Apparatus and method for automatically injecting and/or withdrawing air from tubularly extruded film when needed, to obtain precise size control of the film. Such apparatus can include movable, opposed follower assemblies gravity operated inwardly toward the film to continuously engage opposite sides thereof, respectively, while still in the inflated condition. Any relative movement between the followers indicates a film size change, and is converted into electrical signals such as by potentiometer means or the like. Such signals energize electronic circuitry which, in turn, operates electrical valving means for inserting or withdrawing air from the film at the proper moment. The apparatus is not affected by film edge wrinkle or lateral sway of the film during measurement and, in addition, does not require drive motors or the like to operate.
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