Control of tubular film size
AssigneeGloucester Engineering Co., Inc.
InventorJohn J. Mulcahy
Life of this patent
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Abstract
A blown-film system, for producing plastic tubing, in which the rate of flow of air, into or out of the tube, is made directly dependent upon the deviation in position of the tube wall and in which stability in tube size is achieved by providing a control system that feeds back both tube circumference and air valve position to drive a valve motor.
Claims11
In apparatus for maintaining a desired circumference of a longitudinally extending thin-wall expanded plastic tube being extruded from an annular die, comprising means for producing a flow of air to establish the volume of the tube, a flow control means to adjust the flow rate of said air, an actuator for said flow control means and control apparatus for said actuator, said control apparatus including at least one tube wall position sensor for producing a circumference-deviation signal dependent upon the deviation in tube circumference from a desired set point, the improvement wherein said control apparatus comprises:
- valve position sensing means responsive to changes in actual position of said flow control means for generating a valve position signal that is dependent upon said actual position;
- processing means responsive to said circumference-deviation and valve-position signals for generating an error signal dependent upon the difference between said signals;
- driving means responsive to said error signal for generating a control signal for driving said actuator,
- said sensing means, processing means, driving means, and actuator thereby defining an inner feedback loop that feeds back valve position to said processing means,
- whereby the presence of said inner loop permits said control apparatus to rapidly and stably correct deviations in the circumference of said tube.
Dependencies are inferred from the claim text.